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19-101253a =Al� PERMIT #: ADDRESS: PROJ ECT: DATE: GEOTECHNICAL REPORT Tilt 384 1019 South 351 st Street Federal Way, Washington Project No. T-7844 Terra Associates, Inc. Prepared for: Panattoni Development Company Renton, Washington 19-101253-00-CO ! 1019 S 351 st Street Retaining Walls R FEDERAL WAY TILT 3/19/19 December 19, 2018 RECEIVED MAR 19 2019 CITY OF FEDERAL WAY COMMUNITY DEVELOPMENT TERRA ASSOCIATES, Inc. Consultants in Geotechnical Engineering, Geology and Environmental Earth Sciences December 19, 2018 Project No. T-7844 Mr. Brian Mattson Panattoni Development Company 900 SW 16th Street, Suite 330 Renton, Washington 98057 Subject: Geotechnical Report Tilt 384 1019 South 351st Street Federal Way, Washington Dear Mr. Mattson: As requested, we conducted a geotechnical engineering study for the subject project. The attached report presents our findings and recommendations for the geotechnical aspects of project design and construction. Our study indicates the site is generally underlain by 2 to 12 inches of organics overlying 3 to 5 feet of medium dense silty sand with gravel over dense to very dense sand with varying amounts of silt and gravel to the termination of the test pits. There were two exceptions to this general condition. In Test Pit TP-1, we observed an approximately 1.5-foot layer of clean gravel between the upper silty sand with gravel and lower silty sand with gravel. In Test Pit TP-7, we observed approximately eight feet of silt overlying the medium dense sand with silt and gravel. Minor to moderate groundwater seepage was observed in Test Pit TP-7 at approximately five and nine feet below current site grades. In our opinion, there are no geotechnical conditions that would preclude the planned site development. The buildings can be supported on conventional spread footings bearing on competent native soils or on structural fill placed on competent native soils. Floor slabs and pavements can be similarly supported. Detailed recommendations addressing these issues and other geotechnical design considerations are presented in the attached report. We trust the information presented is sufficient for your current needs. If you have any questions or requieional information, please call. Sincerely Project 12220 113th Avenue NE, Ste. 130, Kirkland, Washington 98034 Phone (425) 821;7777 a Fax (425) 821-4334 TABLE OF CONTENTS Paaze No. 1.0 Project Description...........................................................................................................1 2.0 Scope of Work.................................................................................................................1 3.0 Site Conditions.................................................................................................................2 3.1 Surface................................................................................................................2 3.2 Soils.— .............................. .................................................................................2 3.3 Groundwater ................... ..................................................... ............................... 3 3.4 Seismic................................................................................................................3 4.0 Discussion and Recommendations.................................................................................. 3 4.1 General................................................................................................................3 4.2 Site Preparation and Grading.............................................................................4 4.3 Excavations.........................................................................................................5 4.4 Foundations........................................................................................................5 4.5 Slab -on -Grade Floors..........................................................................................6 4.6 Infiltration Facility..............................................................................................6 4.7 Lateral Earth Pressures....................................................................................... 7 4.8 Drainage..............................................................................................................7 4.9 Utilities................................................................................................................8 4.10 Pavements...........................................................---.............................................8 5.0 Additional Services........................................................................................................10 6.0 Limitations.....................................................................................................................10 Fieures VicinityMap.........................................................................................................................Figure 1 ExplorationLocation Plan.....................................................................................................Figure 2 Typical Wall Drainage Detail............................................................................................... Figure 3 Appendices Field Exploration and Laboratory Testing.......................................................................Appendix A InfiltrationTest Results....................................................................................................Appendix B Geotechnical Report Tilt 384 1019 South 351 st Street Federal Way, Washington 1.0 PROJECT DESCRIPTION The project consists of developing the approximately 4.66 acres of the site with an approximately 79,000 square - foot industrial building along with a stormwater infiltration gallery and associated infrastructure improvements. Based on the grading plans prepared by Barghausen Consulting Engineers, Inc., dated November 15, 2018, the building will be located in the eastern portion of the site with parking on the north and south sides of the building and dock high loading on the west side. Access to the site will be provided by a driveway entrance off Pacific Highway South. The building will have a finish floor elevation of 250 feet with the dock high loading at elevation 245 feet. Grading to achieve building lot and access elevations will be moderate with cuts and fills from 1 to 20 feet. 1 Site stormwater will be collected and directed to a stormwater facility located in the southern portion of the project. J The proposed infiltration gallery is approximately 100 feet by 74 feet with a bottom of stone elevation of 236 feet. This elevation is approximately two to six feet above existing site grades in the proposed location. Excavations between two and eight feet are expected in this area to reach the suitable infiltration soils. The building's floor slab will be constructed at grade with dock high loading on the west side of the structure. We 1 expect the building will be constructed using precast concrete tilt -up wall panels with interior isolated columns supporting the roof framing. Foundation loads for this type of structure should be relatively light, in the range of 4 to 6 kips per foot for continuous bearing walls and 100 to 150 kips for isolated columns. The recommendations contained in the following sections of this report are based on our understanding of the above design features. We should review design drawings as they become available to verify that our recommendations have been properly interpreted and incorporated into project design and to amend or supplement our recommendations, if required. 1 2.0 SCOPE OF WORK J Our work was completed in accordance with our authorized proposal, dated January 5, 2018. Accordingly, on January 30, 2018, we explored subsurface conditions at the site by excavating 7 test pits to a maximum depth of 16 feet below existing surface grades using a track -mounted excavator in the eastern 4.66 acres of the site. Based on the results of our field study, laboratory testing, and analyses, we developed geotechnical recommendations for project design and construction. Specifically, this report addresses the following: ■ Soil and groundwater conditions Seismic design parameters per the 2015 International Building Code (IBC) ■ Site preparation and grading J. Excavations • Foundations • Slab -on -grade floors i December 19, 2018 Project No. T-7844 • Lateral earth pressures for below -grade walls ■ Infiltration facility • Subsurface drainage • Utilities • Pavements It should be noted that recommendations outlined in this report regarding drainage are associated with soil strength, design earth pressures, erosion, and stability. Design and performance issues with respect to moisture as it relates to the structure environment is beyond Terra Associates' purview. A building envelope specialist or contractor should be consulted to address these issues, as needed. 3.0 SITE CONDITIONS 3.1 Surface The project site consists of an approximately 15.8-acre parcel of land located at 1019 South 351st Street in Federal Way, Washington. The approximate location of the site is shown on Figure 1. As we understand, only the eastern approximately 4.66 acres of the site are buildable due to a wetland and stream. The eastern portion of the site is currently undeveloped and covered with a moderate forest, very light understory, and a significant amount of trash. Site topography consists of a slight to moderate slope that descends from the northeast to the southwest with an overall relief of approximately 40 feet over the project area. 3.2 Soils In general, the soil conditions at the site consist of approximately 2 to 12 inches of organics overlying 3 to 5 feet of medium dense silty sand with gravel over dense to very dense sand with varying amounts of silt and gravel to the termination of the test pits. There were two exceptions to this general condition_ In Test Pit TP-1, we observed an approximately 1.5-foot layer of clean gravel between the upper silty sand with gravel and lower silty sand with gravel. In Test Pit TP-7, we observed approximately eight feet of silt overlying the medium dense sand with silt and gravel. The Geologic Map of the Poverty Bay 7.5' Quadrangle, King and Pierce Counties, Washington, by D.B. Booth, H.H. Waldon, and K.G. Troost (2004) shows the site underlain by Recessional Outwash (Qvr) with Till (Qvt) mapped directly south and east of the site. The soils we observed in our test pits were consistent with both mapped soil descriptions. The preceding discussion is intended to be a brief review of the soil conditions observed at the site. More detailed descriptions are presented on the Test Pit Logs attached in Appendix A. Page No. 2 December 19, 2018 Project No. T-7844 3.3 Groundwater - We observed minor to moderate groundwater seepage in Test Pit TP-7 at approximately five and nine feet below current site grades. This groundwater appeared to be perched within sandier layers within the silt formation. We would expect this water to be present .year round but dissipate when exposed by excavation. We did not observe evidence of groundwater in any other test pit. 3.4 Seismic Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength due to an increase in water pressure induced by vibrations. Liquefaction mainly affects geologically recent deposits of loose, fine grained sands underlying the groundwater table. Due to the dense and gravelly nature of the site soils, the risk of soil liquefaction resulting from ground shaking at the site is negligible. Therefore, in our opinion, unusual seismic hazard areas do not exist at the site, and design in accordance with local building codes for determining seismic forces would adequately mitigate impacts associated with ground shaking. Based on the site soil conditions and our knowledge of the area geology, per the 2015 International Building Code (IBC), site class "C" should be used in structural design. Based on this site class, in accordance with the 2015 IBC, the following parameters should be used in computing seismic forces: Seismic Design Parameters (IBC 2015) Spectral response acceleration Short Period), Sms 1.282 Spectral response acceleration (1 — Second Period), SMi 0.645 Five percent damped .2 second period, Sp, 0.855 Five -oercent damped 1.0 second period, SDI 0.430 The above values were determined using the latitude/longitude coordinates 47.28733/-122.32181 and the United States Geological Survey (USGS) ground motion parameter calculator accessed on February 20, 2018 at the website, https:Hearthquake.usgs.gov/designmaps/us/application.php. 4.0 DISCUSSION AND RECOMMENDATIONS 4.1 General Based on our study, there are no geotechnical conditions that would preclude the planned development. In general, the building can be supported on conventional spread footings bearing on competent native soils, or on structural fill placed on the competent native soils. Floor slabs and pavements can be similarly supported. Page No. 3 December 19, 2018 Project No. T-7844 The silty native soils contain a sufficient amount of soil fines and will be difficult to compact as structural fill when too wet. The ability to use these silty soils from site excavations as structural fill will depend on its moisture content and the prevailing weather conditions at the time of construction. The cleaner sands observed in our test pits have a relatively low percentage of soil fines and should be suitable for use as structural fill in most weather conditions. Depending on how the site is graded and the available volume of cleaner sands, the contractor should be prepared to import free -draining granular material for use as structural fill and backfill during the wet season. Detailed recommendations regarding these issues and other geotechnical design considerations are provided in the following sections of this report. These recommendations should be incorporated into the final design drawings and construction specifications. 4.2 Site Preparation and Grading To prepare the site for construction, all vegetation and organic soils should be stripped and removed from the site. Surface stripping depths of 4 to 12 inches should be expected to remove the upper vegetation mat and organic soils. Stripped vegetation and debris should be removed from the site. Organic soils will not be suitable for use as structural fill, but may be used for limited depths in nonstructural areas or for landscaping purposes. Once clearing and stripping operations are complete, cut and fill operations can be initiated to establish desired grades. Prior to placing fill, all exposed bearing surfaces should be observed by a representative of Terra Associates, Inc. to verify soil conditions are as expected and suitable for support of new fill. Our representative may request a proofroll using heavy rubber -tired equipment to determine if any isolated soft and yielding areas are present. If excessively yielding areas are observed, and they cannot be stabilized in place by compaction, the affected soils should be excavated and removed to firm bearing and grade restored with new structural fill. Beneath embankment fills or roadway subgrade, if the depth of excavation to remove unstable soils is excessive, the use of geotextile fabrics, such as Mirafi 500X or an equivalent fabric, can be used in conjunction with clean granular structural fill. Our experience has shown that, in general, a minimum of 18 inches of a clean, granular structural fill placed and compacted over the geotextile fabric should establish a stable bearing surface. As discussed above, the silty soils at the site contain a sufficient percentage of fines (silt and clay size particles) that will make them difficult to compact as structural fill if they are too wet or too dry. Accordingly, the ability to use these soils as structural fill will depend on their moisture content and the prevailing weather conditions when site grading activities take place. Soils that are too wet to properly compact could be dried by aeration during dry weather conditions, or mixed with an additive such as cement or lime to stabilize the soil and facilitate compaction. If an additive is used, additional Best Management Practices (BMPs) for its use will need to be incorporated into the Temporary Erosion and Sedimentation Control (TESC) plan for the project. Soils that are dry of optimum should be moisture conditioned by controlled addition of water and blending prior to material placement. The cleaner outwash sands containing relatively low percentages of fines should be suitable to reuse as structural fill in most weather conditions. We recommend removing cobbles larger than six inches and boulders from the fill prior to placement and compaction. Page No. 4 December 19, 2018 Project No. T-7844 If grading activities are planned during the wet winter months, or if they are initiated during the summer and extend into fall and winter, the owner should be prepared to import wet weather structural fill. For this purpose, we recommend importing a granular soil that meets the following grading requirements: U.S. Sieve Size Percent Passing 6 inches 100 No. 4 75 maximum No. 200 5 maximum* *Based on the 3/4-inch fraction. Prior to use, Terra Associates, Inc. should examine and test all materials imported to the site for use as structural fill. Structural fill should be placed in uniform loose layers not exceeding 12 inches and compacted to a minimum of 95 percent of the soil's maximum dry density, as determined by American Society for Testing and Materials (ASTM) Test Designation D-698 (Standard Proctor). The moisture content of the soil at the time of compaction should be within two percent of its optimum, as determined by this ASTM standard. In nonstructural areas, the degree of compaction can be reduced to 90 percent. 4.3 Excavations All excavations at the site associated with confined spaces, such as lower building level retaining walls and utility trenches, must be completed in accordance with local, state, and federal requirements. Based on the cohesionless nature of the site soils and Washington Industrial Safety and Health Administration (WISHA) regulations, the soils observed would be classified as Type C soils. Accordingly, for temporary excavations of more than 4 feet and less than 20 feet in depth, the side slopes in Type C soils should be laid back at a slope inclination of 1.5:1 (Horizontal:Vertical) or flatter. If there is insufficient lateral distance to complete the excavations in the manners discussed above, or if excavations greater than 20 feet deep are planned, you may need to use temporary shoring to support the excavations. The above information is provided solely for the benefit of the owner and other design consultants, and should not be construed to imply that Terra Associates, Inc. assumes responsibility for job site safety. It is understood that job site safety is the sole responsibility of the project contractor. 4.4 Foundations The proposed building may be supported on conventional spread footing foundations bearing on competent native soils or on structural fill placed above the native soils. Foundation subgrades should be prepared as recommended in Section 4.2 of this report. Perimeter foundations exposed to the weather should bear at a minimum depth of 1.5 feet below final exterior grades for frost protection. Interior foundations can be constructed at any convenient depth below the floor slab. Page No. 5 December 19, 2018 Project No. T-7844 We recommend designing foundations being on competent soils for a net allowable bearing capacity of 3,000 pounds per square foot (psf). For short-term loads, such as wind and seismic, a one-third increase in this allowable capacity can be used in design. With the anticipated loads and this bearing stress applied, building settlements should be less than one-half inch total and one-fourth inch differential. For designing foundations to resist lateral loads, a base friction coefficient of 0.35 can be used. Passive earth pressure acting on the sides of the footings may also be considered. We recommend calculating this lateral resistance using an equivalent fluid weight of 300 pounds per cubic foot (pcf). We recommend not including the upper 12 inches of soil in this computation because they can be affected by weather or disturbed by future grading activity. This value assumes the foundations will be constructed neat against competent native soil or the excavations are backfilled with structural fill, as described in Section 4.2 of this report. The recommended passive and friction values include a safety factor of 1.5. 4.5 Slats -on -Grade Floors Slab -on -grade floors may be supported on a subgrade prepared as recommended in Section 4.2 of this report. Immediately below the floor slab, we recommend placing a four -inch thick capillary break layer composed of clean, coarse sand or fine gravel that has less than three percent passing the No. 200 sieve. This material will reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting of the floor slab. Installation of a capillary break layer will not be necessary where the floor subgrade consists of clean native outwash or structural fill constructed using the clean outwash soils. A representative of Terra Associates, Inc. should observe the subgrade at the time of construction to verify this condition and determine if an imported capillary break layer is required. The capillary break layer will not prevent moisture intrusion through the slab caused by water vapor transmission. Where moisture by vapor transmission is undesirable, such as covered floor areas, a common practice is to place a durable plastic membrane on the capillary break layer and then cover the membrane with a layer of clean sand or fine gravel to protect it from damage during construction, and aid in uniform curing of the concrete slab. It should be noted that if the sand or gravel layer overlying the membrane is saturated prior to pouring the slab, it will be ineffective in assisting uniform curing of the slab, and can actually serve as a water supply for moisture transmission through the slab that can subsequently affect floor coverings. Therefore, in our opinion, covering the membrane with a layer of sand or gravel should be avoided if floor slab construction occurs during the wet winter months and the layer cannot be effectively drained. We recommend floor designers and contractors refer to the current American Concrete Institute (ACI) Manual of Concrete Practice for further information regarding vapor barrier installation below slab -on -grade floors. 4.6 Infiltration Facility As discussed above, site stormwater will be collected and directed to a stormwater infiltration gallery in the s%LQL ern f portion of the site. The gallery is approximately 100 feet by 74 feet with a bottom of stone elevation of 236 feet This is approximately two to six feet above existing site grades. The soils suitable for infiltration are approximately two to eight feet below existing site grades. Therefore, the area will need to be over excavated and the material that is unsuitable for infiltration replaced with a free draining material that matches the infiltration rate for the facility. Page No. 6 December 19, 2018 Project No. T-7844 On December 10, 2018, we completed a large scale infiltration test in accordance with the 2016 King County Surface Water Design Manual in the approximate center of the proposed infiltration facility. The results of the test showed the facility could be designed for a long-term infiltration rate of four inches per hour. The infiltration letter is attached in Appendix B. For water quality considerations, the native outwash will likely exhibit a low cation exchange capacity (CEC) and organic content. Therefore, pretreatment to remove pollutants as required by the design manual will need to be considered. The permeability of the native outwash soils will be significantly impacted by the intrusion of soil fines (silt- and clay -sized particles). Even a relatively minor amount of soil fines can reduce the permeability of the formation by a factor of ten. The greatest exposure to soil fines contamination will occur during mass grading and construction. Therefore, we recommend that the Temporary Erosion and Sedimentation Control (TESC) plans route construction stormwater to locations other than the permanent infiltration facilities. 4.7 Lateral Earth Pressures The magnitude of earth pressure development on engineered retaining walls will partly depend on the quality of the wall backfill. We recommend placing and compacting wall backfill as structural fill as described in Section 4.2 of this report. To guard against hydrostatic pressure development, wall drainage must also be installed. A typical recommended wall drainage detail is shown on Figure 3. With wall backfill placed and compacted as recommended, and drainage properly installed, we recommend designing unrestrained walls that support level grades for an active earth pressure equivalent to a fluid weighing 35 pounds per cubic foot (pcf). We recommend designing unrestrained walls that support a 2:1 (Horizontal:Vertical) backslope for an active earth pressure equivalent to a fluid weighing 50 pcf. For restrained walls, an additional uniform load of 100 psf should be added to the above values. For evaluation of wall performance under seismic loading, a uniform pressure equivalent to 8H psf, where H is the height of the below -grade portion of the wall should be applied in addition to the static lateral earth pressure. Friction at the base of foundations and passive earth pressure will provide resistance to these lateral loads. Values for these parameters are provided in Section 4.4 of this report. 4.8 Draina e Surface Final exterior grades should promote free and positive drainage away from the site at all times. Water must not be allowed to pond or collect adjacent to foundations or within the immediate building areas. We recommend providing a positive drainage gradient away from the building perimeters. If this gradient cannot be provided, surface water should be collected adjacent to the structures and disposed to appropriate storm facilities. Page No. 7 December 19, 2018 Project No. T-7844 Subsurface In our opinion, with the area immediately adjacent to the structure paved, and positive surface drainage maintained, perimeter foundation drains would not be necessary. If the grade is not positively drained away from the structure or is landscaped, perimeter foundation drains should be installed. Where foundation drains are installed, the drains should be laid to grade at an invert elevation equivalent to the bottom of footing grade. The drains can consist of four -inch diameter perforated PVC pipe that is enveloped in washed pea gravel -sized drainage aggregate. The aggregate should extend six inches above and to the sides of the pipe. Roof and foundation drains should be tightlined separately to the storm drains. All drains should be provided with cleanouts at easily accessible locations. 4.9 Utilities Utility pipes should be bedded and backflled in accordance with American Public Works Association (APWA) or City of Federal Way requirements. At minimum, trench backfill should be placed and compacted as structural fill as described in Section 4.2 of this report. Soils excavated on -site should generally be suitable for use as backfill material. However, there are silty soils which are fine grained and moisture sensitive; therefore, moisture conditioning may be necessary to facilitate proper compaction. If utility construction takes place during the winter, it may be necessary to import suitable wet weather fill for utility trench backfilling. 4.10 Pavements Pavement subgrades should be prepared as described in Section 4.2 of this report. Regardless of the degree of relative compaction achieved, the subgrade must be firm and relatively unyielding before paving. The subgrade should be proofrolled with heavy rubber -tired construction equipment such as a loaded 10-yard dump truck to verify this condition. The pavement design section is dependent upon the supporting capability of the subgrade soils and the traffic conditions to which it will be subjected. New pavements for the project will consist of drive aisles accessing parking spaces and loading dock areas. Accordingly, we expect traffic will consist of cars and light trucks, along with heavy J traffic in the form of tractor -trailer rigs. For design considerations, we have assumed traffic in parking and in car/light truck access pavement areas can be represented by an 18-kip Equivalent Single Axle Loading (ESAL) of 50,000 over a 20-year design life. For heavy traffic pavement areas, we have assumed an ESAL of 300,000 would be representative of the expected loading. These ESALs represent loading approximately equivalent to 3 and 18, loaded (80,000-pound GVW) tractor -trailer rigs traversing the pavement daily in each area, respectively. With a stable subgrade prepared as recommended, we recommend the following options for pavement sections: JLight Traffic and Parking: Two inches of hot mix asphalt (HMA) over four inches of crushed rock base (CRB) Full depth HMA — 3 '/z inches Page No. 8 December 19, 2018 Project No. T-7844 Heavy Traffic: e Three inches of HMA over 6 inches of CRB • Full depth HMA — 5 inches For exterior Portland cement concrete (PCC) pavement, we recommend the following: • 6 inches of PCC over two inches of CRB o 28-day compressive strength — 4,000 psi o Control joints spaced at a maximum of 15 feet The paving materials used should conform to the Washington State Department of Transportation (WSDOT) specifications for 1/2-inch class HMA, PCC, and CRB. Long-term pavement performance will depend on surface drainage. A poorly -drained pavement section will be subject to premature failure resulting from surface water infiltrating the subgrade soils and reducing their supporting capability. For optimum performance, we recommend surface drainage gradients of at least two percent. Some degree of longitudinal and transverse cracking of the pavement surface should be expected over time. Regular maintenance should be planned to seal cracks as they occur. 5.0 ADDITIONAL SERVICES Terra Associates, Inc. should review the final designs and specifications in order to verify that earthwork and foundation recommendations have been properly interpreted and implemented in project design. We should also provide geotechnical services during construction in order to observe compliance with our design concepts, specifications, and recommendations. This will allow for design changes if subsurface conditions differ from those janticipated prior to the start of construction. _J 6.0 LIMITATIONS We prepared this report in accordance with generally accepted geotechnical engineering practices. This report is the copyrighted property of Terra Associates, Inc. and is intended for specific application to the Tilt 384 project in Federal Way, Washington. This report is for the exclusive use of Panattoni Development Company and their ' authorized representatives. No other warranty, expressed or implied, is made. The analyses and recommendations presented in this report are based on data obtained from the subsurface explorations completed on -site. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear evident, Terra Associates, Inc. should be requested to reevaluate the recommendations in this report prior to proceeding with construction. IJ Page No. 9 -n+ s 74 5 3h 5t " In -340th fit . - ' Kips Comet ii- 5 ?•�1st_�:' -358th St SY %53RGY i�OS�rfdi _ _� H 5-�AatFr S# a _ Z _ -I MO .5 3fts 91 1900 2000 APAROXIMAYE SCALE IN FEET REFERENCE: https://www.bing.com/maps Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and Environmental Earth Sciences 343.rd 5t 1 a ` 34#L'st Vl N I �i'G 7 f' s 3471h +D Y SUM .5 f s� a•Q Sk� ; { Lei a II� _— 5,359thSt 5 3t�t7th St' 5 Y7 .yt 4 } e 42018 k Corporation 0 2018 HERE w ACCESSED 2/21/18 VICINITY MAP TILT 384 FEDERAL WAY, WASHINGTON Proj.No. T-7844 I Date: DEC 20181 Figure 1 FOUND YXY CONC, MONUMENT W/ NAIL IN LEAD, 1.2' BELOW 71PH 20MS-S02fL-'- GRAPE (0. 5 E. & 1. 6' S.) P-PROPOSED 0WONF, 'OF 10' -'E'-'-DR ESV� RETAINING WALL F 2. - - - .ir PROPOSED - - - - - - PROPOSED - 'S RETAINING 4Q EAST EDGE 01 STREA.-W A- A TP-6 01 p it �'tf. i. j t FOUND 4"X4" CONC. 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I q-\ /—H OE z' I I E, 1771 20121 VJ4- T04 VTI'-'�c upi CONCRETE EXTRUDED (NOT A PARI)ej g E C ISTING ROAD TO BE REGRAZIM DURING CONSTRUCTION X (TYP,) PER DETAIL s1w ACCESS TO BE PRESERVEI) AU1WI LIIII,1411S "WMMV TRASHENCLOSURE' k-7 NOT A HAH1 `"Kftir Ups um GUna TP-3 C3 STD ORATE ow k TP- - -.A -A "K RE FRI IRATM GAUUIEW APPR07WkA3CLV 100'x74' TOP OF STONE =243.0 1 -&g IN TOP OF CHAMBER=242.0 J 4 BOTTOM OF CHAMBER=237.0 BOTTOM OF STONE=236.0 VOLUME REQUIRED: 31,600 CF /VOLUME PRONGED: 31.700 CF -- --- -- A= 13 95' AREA REDIiIIIRID: 7,240 SF AREA PROVIDM 7.250 SF TW.242. A= 10.33' 41, r04 EXISTIN DRIVEWAY FAu/,l ,D' WITLAND BUFFERt Okl""• ACCESS TO BE PRESERVED TO - '% N%' I , d' EXISTING RESIDENTIAL HOME DI NOTE: LEGEND: THIS SITE PLAN IS SCHEMATIC. ALL LOCATIONS AND APPROXIMATE TEST PIT LOCATION DIMENSIONS ARE APPROXIMATE. IT IS INTENDED FOR REFERENCE ONLY AND SHOULD NOT BE USED FOR DESIGN OR CONSTRUCTION PURPOSES. REFERENCE:SITE PLAN PROVIDED BY BARGHAUSEN CONSULTING ENGINEERS. 0 80 160 APPROXIMATE SCALE IN FEET REMOVABLE BOULMS FOR FIRE DEPAAWDIT ACCESS I STD GRATE CB STD GRATE RIM=255,81 CB STD GRATE RIM=254.06 C8 STD GRATE RIM=252.23 Terra EXPLORATION LOCATION PLAN TILT 384 Associates, Inc. FEDERAL WAY, WASHINGTON go Consultants in Geotechnical Engineering Geology and Figure 2 Environmental Earth Sciences Proj.No. T-7844 I Date: DEC 2018 1 12" MINIMUM 3/4" MINUS WASHED GRAVEL 12" SEE NOTE r 6"(MIN.) III SLOPE TO DRAIN COMPACTED STRUCTURAL FILL EXCAVATED SLOPE (SEE REPORT TEXT FOR APPROPRIATE INCLINATIONS) 12" OVER PIPE 111 3" BELOW PIPE 4" DIAMETER PERFORATED PVC PIPE NOT TO SCALE NOTE: MIRADRAIN G100N PREFABRICATED DRAINAGE PANELS OR SIMILAR PRODUCT CAN BE SUBSTITUTED FOR THE 12-INCH WIDE GRAVEL DRAIN BEHIND WALL. DRAINAGE PANELS SHOULD EXTEND A MINIMUM OF SIX INCHES INTO 12-INCH THICK DRAINAGE GRAVEL LAYER OVER PERFORATED DRAIN PIPE. o Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and Environmental Earth Sciences TYPICAL WALL DRAINAGE DETAIL TILT 384 FEDERAL WAY, WASHINGTON Proj.No. T-7844 I Date: DEC 2018 Figure 3 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING Tilt 384 Pierce County, Washington On January 30, 2018, we investigated subsurface conditions at the site by excavating 8 test pits to a maximum depth of 16 feet below existing surface grades using a trackhoe. The test pit locations were approximately determined in the field by sighting and pacing from existing surface features. The approximate test pit locations are shown on Figure 2. The Test Pit Logs are presented on Figures A-2 through A-9. A geotechnical engineer from our office maintained a log of each test pit as it was excavated, classified the soil conditions encountered, and obtained representative soil samples. All soil samples were visually classified in the field in accordance with the Unified Soil Classification System. A copy of this classification is presented as Figure A-1. Representative soil samples obtained from the test pits were placed in closed containers and taken to our laboratory for further examination and testing. The moisture content of each sample was measured and is reported on the individual Test Pit Logs. Grain size analyses were performed on selected samples. The results of the grain size analyses are shown on Figures A-10 through A-13. Project No. T-7844 MAJOR DIVISIONS LETTER SYMBOL TYPICAL DESCRIPTION Clean GW Well -graded gravels, gravel -sand mixtures, little or no fines. Gravels (less GRAVELS than 5% U More than 50% fines) GP Poorly -graded gravels, gravel -sand mixtures, little or no fines. m N of coarse fraction Nm is larger than No. GM Silty gravels, gravel -sand -silt mixtures, non -plastic fines. = CD � 4 sieve Gravels with GC Clayey gravels, gravel -sand -clay mixtures, plastic fines. Zm •0 I` fines C� L7 o � Ln a Clean Sands SW Well -graded sands, sands with gravel, little or no fines. N z SANDS (less than u a More than 50% 5% fines) SP Poorly -graded sands, sands with gravel, little or no fines. coarse fraction vof is smaller than SM Silty sands, sand -silt mixtures, non -plastic fines. No. 4 sieve Sands with fines SC Clayey sands, sand -clay mixtures, plastic fines. ML Inorganic silts, rock flour, clayey silts with slight plasticity. C .N SILTS AND CLAYS CL Inorganic clays of low to medium plasticity. (Lean clay) p m Liquid Limit is less than 50% OL Organic silts and organic clays of low plasticity. p m w Eo z o N MH Inorganic silts, elastic. S o CH Inorganic clays of high plasticity. (Fat clay) Z SILTS AND CLAYS Z C L ° Liquid Limit is greater than 50 /o OH Organic clays of high plasticity. o HIGHLY ORGANIC SOILS PT Peat. DEFINITION OF TERMS AND SYMBOLS t/) Standard Penetration 2" OUTSIDE DIAMETER SPILT SPOON SAMPLER W Density Resistance in Blows/Foot J 2.4" INSIDE DIAMETER RING SAMPLER OR p Very Loose 0-4 SHELBY TUBE SAMPLER to Loose 4-10 = Medium Dense 10-30 �r WATER LEVEL (Date) O Dense 30-50 v Very Dense >50 Tr TORVANE READINGS, tsf Pp PENETROMETER READING, tsf Standard Penetration > Consistancy Resistance in Blows/Foot DD DRY DENSITY, pounds per cubic foot 2 Very Soft Soft 2-4 LL LIQUID LIMIT, percent VMedium Stiff 4-8 Stiff 8-16 PI PLASTIC INDEX Very Stiff 16-32 Hard >32 N STANDARD PENETRATION, blows per foot Terra UNIFIED SOIL CLASSIFICATION SYSTEM TILT 384 Associates, Inc. FEDERAL WAY, WASHINGTON Consultants in Geotechnical Engineering Geology and Environmental Earth Sciences Pro .No. T-7844 Date: DEC 2018 Figure A-1 � PROJECT NAME: Tilt 384 LOG OF TEST PIT NO. TP-1 PROJ. NO: T-7844 LOGGED BY:MX LOCATION: Federal Way, Wash in tq on SURFACE CONDITIONS: Brush DATE LOGGED: ;kR4@t r K. 2018 DEPTH TO GROUNDWATER: N/A Description FIGURE A-2 APPROX. ELEV: N/A DEPTH TO CAVING: N/A o Consistency/ v Relative Density (6 inches ORGANICS) 1 Red -brown silty SAND with gravel, fine to medium sand, fine to coarse gravel, moist, scattered 2 1 organics, scattered cobbles. (SM) (Weathered till) Medium Dense 3 i 2...---------------------------------------------------------- ---- - 4 Gray to light brown GRAVEL, fine to coarse sand, fine to coarse gravel, moist, some cobbles, scattered organics, some sand. (GP) 5 3 ..._.. ----- -----------------------...--------- ------ - -- — Gray silty SAND with gravel, fine to coarse sand, fine to coarse gravel, moist, some cobbles, occasional boulder. (SM) (Till) 7 8 w0 ■ 10 11 12- 13 14 15 *Slight cementation at 9 feet. *Silt content increases at 9 feet. Test pit terminated at approximately 10 feet. No groundwater seepage observed. Dense to Very Dense 19.2 3.6 6.4 8.5 f Terra NOTE: This subsurface information pertains only to this test pit location and should not be .` Associates Inc. interpreted as being indicative of other locations at the site. _�/ Consultants in Geotechnical I!ngineering Geology and Environmental Earth Sciences LOG OF TEST PIT NO. TP-2 PROJECT NAME: Tilt 384 PROJ. NO: T-7844 LOCATION: Federal Way, Washington SURFACE CONDITIONS: Brush FIGURE A-3 LOGGED BY:MX APPROX. ELEV: N/A DATE LOGGED:January 30 2018 DEPTH TO GROUNDWATER: N/A DEPTH TO CAVING: N/A 0 i Z `. 2 t a a E a� m 0 � 0 7 2 1 7 8 -1;21 i© Description (6 inches ORGANICS) Light brown silty GRAVEL with sand to GRAVEL with silt and sand, fine to medium sand, fine to coarse gravel, moist, scattered organics, some cobbles. (GM/GP-GM) -------------------------------------------------------- Gray silty SAND with gravel, fine to medium sand, fine to coarse gravel, moist, some cobbles, occasional boulder. (SM) (Till) 10 Test pit terminated at approximately 10 feet. 11 No groundwater seepage observed. 12- 13 14 15� NOTE: This subsurface information pertains only to this test pit location and should not be interpreted as being indicative of other locations at the site. Consistency/ o Relative Density Medium Dense Dense 10.4 6.1 6.: Terra oiPAssociates Inc. - Consultants in Geotechnical ngineering Geology and Environmental Earth Sciences 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 LOG OF TEST PIT NO. TP-3 FIGURE A-4 PROJECT NAME: Tilt 384 PROJ. NO: T-7844 LOGGED BY: MX. LOCATION: Federal Way, Washington SURFACE CONDITIONS: Brush APPROX. ELEV: N/A DATE LOGGED:January 30 2018 DEPTH TO GROUNDWATER: N/A Description (6 inches ORGANICS) DEPTH TO CAVING: N/A Red -brown silty SAND with gravel, fine to medium sand, fine to coarse gravel, moist, scattered organics, some cobbles. (SM) (Weathered till) Gray SAND with silt and gravel, fine to coarse sand, fine to coarse gravel, moist, some cobbles, some cementation. (SP-SM) (Sandy till) Test pit terminated at approximately 10 feet. No groundwater seepage observed. NOTE: This subsurface information pertains only to this test pit location and should not be interpreted as being indicative of other locations at the site. Consistency/ o Relative Density Medium Dense 14.0 Dense to Very Dense 6.1 10.8 Terra - Associates Inc. _ _ Consultants in Geotechnical engineering Geology and Environmental Earth Sciences PROJECT NAME: Tilt 384 LOG OF TEST PIT NO. TPA PROJ. NO: T-7844 LOGGED BY:MX LOCATION: Federal Way. Washington SURFACE CONDITIONS: Brush DATE LOGGED: January 30. 2018 DEPTH TO GROUNDWATER: N/A Description u I FIGURE A-5 APPROX. ELEV: N/A DEPTH TO CAVING: N/A (6 inches ORGANICS) 1 1 Red -brown silty SAND with gravel, fine to medium sand, fine to coarse gravel, moist, scattered organics, scattered cobbles. (SM) (Weathered till) 2 ----------------------------------------------------------------------- Gray SAND with gravel to GRAVEL with sand, medium to coarse sand, fine gravel, moist, numerous cobbles, occasional boulder, trace organics. (SP/GP) 7 10 11 !� 12 13 14 15 21 3 Gray silty SAND with gravel, fine to medium sand, fine gravel, moist, some cobbles, slight cementation. (SM) (Till) Test pit terminated at approximately 10 feet. No groundwater seepage observed. Consistency/ Relative Density 13.4 Medium Dense 1 5.2 Dense 10.5 Terra mul NOTE: This subsurface information pertains only to this test pit location and should not be \ Associates Inc. interpreted as being indicative of other locations at the site. Consultants in Geatechnical Ingineering Geology and Environmental Earth Sciences LOG OF TEST PIT NO. TP-5 FIGUREA-6 PROJECT NAME: Tilt 384 PROJ. NO: T-7844 LOGGED BY:MX LOCATION: Federal Wa Washin ton SURFACE CONDITIONS: Brush APPROX. ELEV: N/A DATE LOGGED: January 30, 2018 DEPTH TO GROUNDWATER: N/A DEPTH TO CAVING: N/A i Z Consistency/ o d Description t a, Relative Density 3 a E m m ❑ (A 0 __ f (4 inches ORGANICS) 1 I 1 13.1 Red -brown to light brown silty SAND with gravel, fine to medium sand, fine gravel, moist, scattered 2 organics, scattered cobbles. (SM) (Weathered till) Medium Dense 0" 3 7— ` 8 _I 9 10 11 1 12 13 j 14 15 ----------------------------------- Gray silty SAND with gravel to SAND with silt and gravel, fine to medium sand, fine gravel, moist, some cobbles. (SM/SP-SM) (Sandy till) *Pocket of light brown sandy SILT observed at 10 feet. Test pit terminated at approximately 10 feet. No groundwater seepage observed. Dense 8.7 9.4 Terra Associates Inc. NOTE: This subsurface information pertains only to this test pit location and should not be interpreted as being indicative of other locations at the site. ' • Consultants in Geotechnical engineering Geology and Environmental Earth Sciences LOG OF TEST PIT NO. TP-6 FIGURE A-7 PROJECT NAME: Tilt 384 PROJ. NO: T-7844 —LOGGED BY: MX LOCATION: Federal Way. Washington SURFACE CONDITIONS: Brush APPROX. ELEV: N/A DATE LOGGED: January 30 2018 DEPTH TO GROUNDWATER: N/A DEPTH TO CAVING: N/A 0 z IV Description L Q Q E d N !� to 0 (2 inches ORGANICS) 1-- Red-brown silty SAND with gravel, fine to medium sand, fine to coarse gravel, moist, scattered 2— organics, scattered cobbles. (SM) (Weathered till) 1 2 1 5 FA — 8 3 9 10 11 i 12 13 1 14 15 Gray silty SAND with gravel, fine to coarse sand, fine to coarse gravel, moist, some cobbles. (SM) (Sandy till) Test pit terminated at approximately 10 feet. No groundwater seepage observed. NOTE: This subsurface information pertains only to this test pit location and should not be interpreted as being indicative of other locations at the site. Consistency/ o Relative Density ?> Medium Dense I Dense 12.1 10.6 7.7 . Terra M IV Associates Inc. Consultants in Geotechnical engineering Geology and Environmental Earth Sciences PROJECT NAME: Tilt 384 LOG OF TEST PIT NO. TP-7 PROJ. NO: T-7844 LOCATION:Federa4a Way; Washin tq on SURFACE CONDITIONS: Brush FIGURE A-8 LOGGED BY: MX APPROX. ELEV: N/A DATE LOGGED: January 30, 2018 DEPTH TO GROUNDWATER: 5 & 9 Feet DEPTH TO CAVING: N/A 0 1 2— 1 Description (8 inches ORGANICS) Brown to light brown SILT with interbedded layers of silty SAND to sandy SILT, fine sand, moist to wet. (ML) 4 T-5 2 6 7-- 3 8 - Gray SAND with silt and gravel, fine to coarse sand, fine to coarse gravel, wet. (SP-SM) �s g 10 j 11 4 12 13 14 15 5-----------•----------------------------------- -------------------- Dark brown to black SAND with gravel, fine to medium sand, wet. (SP) 16 6 _. Test pit terminated at approximately 16 feet. 17 Light groundwater seepage observed at approximately 5 and 9 feet. 18 19 20 Consistency/ o_ Relative Density I 3: Medium Dense 17.7 26.1 29.2 10.7 12.4 15.5 Terra 1 NOTE: This subsurface information pertains only to this test pit location and should not be40,F11 Associates Inc. interpreted as being indicative of other locations at the site. / Consultants in Geotechnical engineering Geology and Environmental Earth Scienoes LOG OF TEST PIT NO. TP-8 FIGUREA-9 PROJECT NAME: Tilt 384 PROJ. NO: T-7844 LOGGED BY: MX LOCATION: Federal Way, Washinciton SURFACE CONDITIONS: Brush APPROX. ELEV: N/A DATE LOGGED: January 30, 2018 DEPTH TO GROUNDWATER: N/A DEPTH TO CAVING: N/A 6 z A L d a E m co 0 (n 0 1- 1 2 (12 inches ORGANICS) Brown to light brown SAND with silt, fine cementation. (SP-SM) Brown to gray SAND with silt and gravel occasional boulder. (SP-SM) 6- 7- 8— 3 `Slight to moderate cementation from 81 9 10 11 12 13 14 4 15 Test pit terminated at approximately 151 16 No groundwater seepage observed. 17 18 19 20 NOTE: This subsurface information pertains only to thi; interpreted as being indicative of other locations at the 1 Description Consistency/ iF Relative Density 3: Particle Size Distribution Report _ao_o tp M n f7 it it it 100 I I I I I I I I 1 1 1 11N,11lil 90 I I i I l I I I I I I I 11 f I I I I I I I I I I I 'I " $o I U I I I I I f I I I I I I I I I I I I I! I I I I I I I 1 I I I 70 ! 1 I I I I I I I I I I I i il i � so f I I I I I I I I I I ii I I I I I I I I I I F I 1 1 I l 1 1 1 l I I I I I 50LU I 1 a 40 I I I I I I I I f T I I l I f I I I I I I I f i 30 E I I I I I I I l I I I I 20 I I I! I I I f I I I I I I I I I I I I I l l l l 10 I I I I I I l I 0 I I I I I I I ! I I 100 10 0.1 0.01 GRAIN SIZE - mm. % Gravel % Sand % Fines +3" Coarse Fine Coarse Medium Fine Silt Clay 2.6 ,0 0.0 55.7 30.2 4.3 3.3 3.9 i❑ 0.0 10.5 18.7 8.9 14.9 23.1 23.9 4, 0.0 8.9 37.1 T9 I 12.3 15.8 18.0 LL PL DgS 50.7887 J D6p DSO Din D15 Din Cn C 0 27.3778 21.7241 13.4621 6.3542 2.0957 3.16 13.06 ❑ 14.4725 1.5973 0.5429 0.1406 0 15.7656 7.3307 3.1862 0.2834 Material Description USCS AASHTO GP 0 Poorly graded GRAVEL ❑ Silty SAND with gravel SM 6 Silty SAND with gravel SM Project No. T-7844 Client: Panattoni Development Company, Inc. Remarks: Project: Tilt 384 OTested on 2/1/2018 Federal Way, Washington ❑Tested on 2/1/2018 O Location: Test Pit TP-1 Depth: -3.5 feet Sample Number: 2 ATested on 2/1/2018 Location: Test Pit TP-1 Depth: -9 feet Sample Number: 4 e Location: Test Pit TP-2 Depth: -5 feet Sample Number: 2 Terra Associates, Inc. Kirkland, WA Figure A-10 Tested By: FQ Particle Size Distribution Report C C v v v C C C `n .0 C � pp O_ (O(yy �O�ll O [O[pp O 7 100 I I i I I I i 1 I I I I I I I I I I [ I I l l f I so i I I I I I I I I i l f I I I I I I I I 1 !€ I 80 I I i I i i l I I I I I I I I I# I I I I I I 1 1 I I I ! I 11 1 �0 w I I I V I 1 so i I I I I I I I I I I I I I I I I I I I I I I! I l Z I I I I I I! I I ! I I! 50 I I! I 1 1 wIX I I I I I I! I I 1 1 1 I l I ! I I I LU a 40 30 I I I I I I I I I I I I I I I I I I I I I I I I 20 10 I I l l f l ! I I I 0 I I 1 1 1 I I I I I I 100 10 1 0.1 0.01 0.001 GRAIN SIZE - mm. % Gravel % Sand % Fines o �+�„ Coarse' Medium Fine Silt Clay Coarse Fine 0 0.0 14.1 j 39.0 16.2 13.1 j 8.2 9.4 13 0.0 8.4 32.9 20.4 28.3 8.1 1.9 0 0.0 1 0.0 29.9 9.3 16.6 j 21.6 22.6 LL PL Dgg Drn Dsp D20 D DIp C C 0 18.4026 7.9324 5.4121 1.8974 0.2723 0.0953 4.76 83.20 i❑ 14.1890 5.0297 3.2825 1.3654 0.6046 0.4250 0.87 11.83 0 11.6098 1.8407 0.6761 0.1590 Material Description USCS AASHTO ,o Poorly graded GRAVEL with silt and sand GP -GM ❑ Poorly graded SAND with gravel SP o Silty SAND with gravel SM Project No. T-7844 Client: Panattoni Development Company, Inc. Remarks: Project: Tilt 384 oTested on 2/1/2018 Federal Way, Washington ❑Tested on 2/1/2018 o Location: Test Pit TP-3 Depth: -10 feet Sample Number: 3 oTested on 2/1/2018 ❑ Location: Test Pit TP-4 Depth: -4 feet Sample Number: 2 a Location: Test Pit TP-6 Depth: -8 feet Sample Number: 3 Terra Associates, Inc. Kirkland WA Figure A-I1 Tested By: FQ Particle Size Distribution Report c S o ( a(., o Inp o a c I7 iD 100TNI 1 I I I I I I I I I 1 I I I I I I I I I I so I I I I[ I I I I ! I I I! 80 I I 11 l i I I 1 I 1 l 1 1 i l 1 l I I I l l I I I 70 I I I I I I I I I I I I I I I 1 ! ! II V I I I I I I I I 1 1 I I I I I I I I 1 1 I 1 w so Z I ! I I I 1 1 I I l f l l I I I 1 1 I I I I I I I I Z 50 wLU I I I l l I I I I I I I I a 40 I I l l i l I I I l l I l I I1 PHI so I i 20 10 I I 1 1 1 I I k I I 0 I I 11! I I f I I I 100 10 1 0.1 0.01 0 001 GRAIN SIZE - mm. DID *3„ % Gravel Coarse Fine 'A Sand Coarse. Medium Fine %, Fines Silt clay 0 0.0 0.0 13.3 10.2 54.6 15.5 6.4 ❑ 5.6 C 6.9 ` 0.0 4.8 G 62.9 16.6 3.2 1 I LL PL DgS Dan Dsn Dan DIO C C 10 4.0377 0.9868 0.7738 0.5147 0.3367 0.2477 1.08 3.98 ❑ 2.4669 0.9201 0.7550 0.5267 0.3721 0.3063 0.98 3.00 Material Description USCS AASHTO ,o Poorly graded SAND with silt and gravel SP-SM ❑ Poorly graded SAND with gravel SP Project No. T-7844 Client: Panattoni Development Company, Inc. Remarks: Project: Tilt 384 oTested on 2/1/2018 Federal Way, Washington ❑Tested on 2/1/2018 c Location: Test Pit TP-7 Depth: -15 feet Sample Number: 4 �-1 Location: Test Pit TP-7 Depth: -16 feet Sample Number: 5 Terra Associates, Inc. Kirkland, WA 1=igure A-12 Tested By: FQ J a _J J J Particle Size Distribution Report c c o o g C C C� p N M pp O 1D M N w \ @! ii Q a W 100 I I I II I! I I i I I I I l i I I II I I I ! I I I I I[ 90 I i t l I 1 1 1 1 1 I I I I I I ! I ! I 1 1 1 1 1 so I I I I I I I I I I I I I I I I I I I I [ I f I l l 70 I I I I I I I l I f l l f w60 I I I 1 1 f 1 1 1 1 I I I I I I ! I I I I I I I I I I I f I I I I I I I I I I Z Z50 I I I I I I I I I I I w I I 1 I I W 40 a I I I I I ! I I I I I I I I I I I I I I I I I I 1 1 I 30 I I I I l I l ! I I I I I I I I I I I I I I I l l l l 20 I I I I I I I l 1 1 I I I I I I I I I I I i t I I 10 I I ! 0 I I I I I I I 1 I I I I I 100 10 1 0.1 0.01 OMI GRAIN SIZE - mm. % Gravel % Sand % Fines +3" %Coarse Fine _ Coarse Medium Fine Silt Clay 0 0.0 13.3 j 32.8 13.9 16.0 I 13.6 10.4 I❑ 0.0 16.6 23.1 10.1 28.2 j 16.0 6.0 I LL PL Dig rDrn D-sa Din DIS Din C C I0 17.8271 6.7069 3.8066 0.6887 0.1799 I❑ 20.5104 4.6502 1.9483 0.5553 0.3224 0.2402 0.28 19.36 Material Description USCS AASHTO 0 Poorly graded SAND with silt and gravel SP-SM ❑ Poorly graded SAND with silt and gravel SP-SM Project No. T-7844 Client: Panattoni Development Company, Inc. Remarks: Project: Tilt 384 oTested on 2/1/2018 Federal Way, Washington ❑Tested on 2/1/2018 a Location: Test Pit TP-8 Depth: -5 feet Sample Number: 2 0 Location: Test Pit TP-8 Depth: -14 feet Sample Number: 4 Terra Associates, Inc. Kirkland, WA Figure A-13 Tested By: FQ APPENDIX B INFILTRATION TEST RESULTS December 14, 2018 Project No. T-7844 Mr. Brian Mattson Panattoni Development Company 900 SW 16th Street, Suite 330 Renton, Washington 98057 Subject: Infiltration Testing Tilt 384 1019 South 351st Street Federal Way, Washington Dear Mr. Mattson: As requested, we have completed infiltration testing at the subject property. Our infiltration testing consisted of a large-scale Pilot Infiltration Test (PIT) conducted in general conformance with the procedures outlined in Section 5.2.1 (General Requirements for infiltration Facilities) of the 2016 King County Surface Water Design Manual. The test was performed near the center of the proposed Infiltration Facility. The location was based on sighting from existing structures and GPS coordinates from Google Earth. The approximate location is shown on attached Figure 1. The test results are summarized below: Estimated Design Approx. Infiltration Rate Test Steady State Measured Infiltration Correction (Isat design = Isat initial x Test Elevation Flow Rate Rate (Teat initial) Factor FT) No. (ft) (in/hr) CFT' (in/hr)_ _ 19.64 4.00 PIT-1 _ _ 227.5 _(gpm) 1 21.43 0.21 ft Feet based on available topography gpm Gallons per minute in/hr Inches per hour 1 Equation 5-11 2016 King County Surface Water Design Manual Based on the results of our test, it is our opinion that the native soils at this location and depth are suitable for support of the proposed infiltration facility. Further excavation of the test location showed outwash continued to a depth of approximately 15 feet below -grade (elevation 217 feet). The raw pilot infiltration test data has been included as Figure 2. Mr. Brian Mattson December 14, 2018 We trust the information presented is sufficient for your current needs. If you have any questions or require additional information, please call. Sincerely" �{ 1� S. Carol S? ecic. ywp Project r 47016 � cS' I/STO�� Encl:@[ALP ion Map Fig ilot Infiltration Test Data Project No. T-7844 Page No. ii I Figure 2 - Raw Pilot Infiltration Test Data Test Number: PITA Project Name: Tilt 384 Project Number: 7844 Test Date: 12/10/2018 hole dimensions 10.5' x 10' x 4.5' Hole area 105 square feet initial meter reading 1947 gal time (minutes) cum vol (gal) flow rate (gpm) Head (feet) 15 2308 20.81 1 30 2610 20.46 1 45 2927 20.08 1 60 3243 21.48 1 75 3592 22.73 1 Falling head test time (minute) HEAD (Inches) 0 12 1 11.16 measured infiltration rate using 2 11 steady state data 3 10.44 5 10.2 measured infiltration rate using 7 9.6 falling head data 10 9 15 7.68 30 4.8 40 50 60 0 70 80 90 use mean flow rate of last half hour of test as steady state infiltration rate 21.43 gpm 2.86 cfm infiltration rate=steady sate flow divided by area of pit 0.03 feet per minute 0.33 inches per minute 19.64 inches per hour 96.00 inches per hour Figure 2 - Raw Pilot Infiltration Test Data Correction factors F-testing 0.3 F geometry 1 F-frequency 1 F-plugging 1 0.7 factors were otained from the 2016 King County Surface Water Design Manual corrected steady state infiltration rate 4.13 inches per hour corrected falling head infiltration rate 20.16 inches per hour LAKEHAVEN UTILITY DISTRICT WELLHEAD PROTECTION AREA DEFINITION 011 PtiGEf SO JUNE 1996 Robinson &Noble, Inc. 5915 Orchard St. W -' Tacoma, WA 98467 Mi ROBINSON & NOBLE, INC. GROUND WATER 6 ENVIRONMENTAL GEOLOGISTS 5915 ORCHARD STREET WEST TACOMA. WASHINGTON 99467 FAX 472-5946 LAKE HAVEN UTILITY DISTRICT WELLHEAD PROTECTION AREA DEFINITION June 1996 by Joseph E. Becker LAKEHAVEN UTILITY DISTRICT WHPA DEFINITION TABLE OF CONTENTS Executive Summary . . . . . . . . . . . . . . . . . . . . . . . iv Section 1. Introduction .... . ..... .... . . . ....... . ....... 1-1 Section 2. Physical Definition of the Hydrogeologic System Layer 1, Vashon Till . . . . ... . . . . . . . . . . . . . . . . . . . . . . 2-2 Layer 2, Vashon Advance Aquifer System . . . . . . . . . . . . . . . . 2-3 Layer 3, Lower Confining Unit . . . . . . . . . . . . . . . . . . . . . . . 2-3 Layer 4, Intermediate Aquifer System . . . . . . . . . . . . . . . . . . 2-3 Layer 5, Deep Confining Unit. . . . . . . . . . . . . . - 2-4 Layer 6, Deep Aquifer Unit. - - - • . . . • • . 2-4 Hydrogeology at Wells 27M and 29T . . . . . . . . . . . . . . . . . . 2-4 Section 3. Water Quality Iron. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 Manganese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 Nitrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 Chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3 Specific Conductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4 Water Quality Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4 Section 4. Modeling Methodology MODFLOW.................................4-1 MODPATH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 Section 5. General Ground Water Flow Ground Water Paths. . . . . . . . . . . . . . • . • . . . 5-1 Travel Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 Table of Contents Section 6. Capture Zone Delineation Three -Dimensional Aspects of Capture Zones . . . . . . . . . . . . . 6-1 Capture Zone and Wellhead Protection Area. Definitions . . . . . . . . . 6-2 Relationship of "Real World" Zones to Modeled Zones . . . . . . . . . . 6-2 One -Year Capture Zones . . . . . . . . . . . . . . . . . . . . . . . 6-3 Five -Year Capture Zones . . . . . . . . . . . . . . . . . . . . . . 6-4 Ten -Year Capture Zones . . . . . . . . . . . . . . . . . . . . . . . . . 6-6 One -Hundred Year Capture Zones . . . . . . . . . . . . . _ . . . . . . 6-7 Modifications Due to Changing Stress Conditions . . . . . . . . . . . . . 6-8 Section 7. Conclusions and Recommendations ..... .. . . .. . .... 7-1 References . ....... ............ ......... ... 7-5 Tables 1. Layer/Unit Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . 2-1 2. Minimum Predicted Travel Times to RMC Wells . . . . . . . . . . . . . 2-2 3. Nitrate Concentration Trends in LUD Wells . . . . . . . . . . . . . . . . 3-3 4. Average Chloride Concentrations by Aquifer . . . . . . . . . . . . . . . . 3-4 S. Summary of Selected Parameters by Aquifer . . . . . . . . . . . . . . . . 3-5 6. Assigned Porosity Values . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 7. Amounts of Horizontal & Vertical Movement on Sample Ground Water FlowPaths . . . .. . . . . . .... . . . . . . . . . . . . . ... 5-2 8. Travel Times and Velocities for Sample Ground Water Particles . . . . . 5-3 9. One -Year Capture Zone Details . 6-4 10. Five -Year Capture Zone Details . . . . . . . . . . . . . . . . . . . . . . 6-5 11. Ten -Year Capture Zone Details . . . . . . . . . . . . . . . . . . . . . . . 6-6 12. Lakes Which Potential Recharge LUD Wells . . . . . . . . . . . . . . . 6-7 13. One Hundred -Year Capture Zone Details 6-8 Figures 1. Iron Concentrations, 1990-1995 2. Manganese Concentrations, 1990-1995 3. Nitrate Concentrations, 1990-1995 4. Chloride Concentrations, 1990-1995 5. Specific Conductance Values, 1990-1995 6. Average Nitrate Concentration vs. Chloride Concentration vs. Specific Conductance Value for the Federal Way Upland Aquifers, 1990-1995 7. Ground Water Production, Lakehaven Utility District, 1990-1995 ii Table of Contents 8. Modeled Potentiometric Surface, Vashon Advance Aquifer System, Layer 2, 1991 9. Modeled Potentiometric Surface, Intermediate Aquifer System, Layer 4, 1991 10. Modeled Potentiometric Surface, Deep Aquifer System, Layer 6, 1991 11a. Sample of Modeled Ground Water Paths to Three Wells, Map View 11b. Sample of Modeled Ground Water Paths to Three Wells, Cross Section View 12. Vertical Discretion of 100-Year Capture Zone, Well 23 13. 100-Year Capture Zone, Well 23 14. Effect of Placing Defining Particle Locations at Edge of Model Cell Instead of at Exact Well Position 15. 1-Year Capture Zones, Well 16 and Redondo -Milton Channel Aquifer Wells, Layer 2 16. 1-Year Capture Zones, Wells 10C, 22/22A, and Mirror Lake Aquifer Wells, Layer 4 17. 1-Year Capture Zones, Federal Way Deep Aquifer Wells, Layer 6 18. 5-Year Capture Zones, Well 16 and Redondo -Milton Channel Aquifer Wells, Layer 2 19. 5-Year Capture Zones, Wells 10C, 22/22A, and Mirror Lake Aquifer Wells, Layer 4 20. 5-Year Capture Zones, Federal Way Deep Aquifer Wells, Layer 6 21. 10-Year Capture Zones, Well 16 and Redondo -Milton Channel Aquifer Wells, Layer 2 22. 10-Year Capture Zones, Wells 10C, 22/22A, and Mirror Lake Aquifer Wells, Layer 4 23. 10-Year Capture Zones, Federal Way Deep Aquifer Wells, Layer 6 24. 100-Year Capture Zones, Well 16 and Redondo -Milton Channel Aquifer Wells, Layer 2 25. 100-Year Capture Zones, Wells 10C, 22/22A, and Mirror Lake Aquifer Wells, Layer 4 26. 100-Year Capture Zones, Federal Way Deep Aquifer Wells, Layer 6 27. Production Sensitivity, Change in 10-Year Capture Zone in South RMC 28. Recharge Sensitivity Deficit, Change in 10-Year Capture Zones, Well 10/10A 29. Recharge Sensitivity Excess, Change in lOYear Captures Zones, Well 10/10A 30. Wellhead Protection Areas for Wells in the Qva Aquifer System, Layer 2 31. Wellhead Protection Areas for Wells in the Intermediate Aquifer System, Layer 4 32. Wellhead Protection Areas for Wells in the Deep Aquifer System, Layer 6 Table of Contents iii LAKEHAVEN UTILITY DISTRICT WHPA DEFINITION EXECUTIVE SUMMARY Lakehaven Utility District is mandated under federal and state laws to implement a wellhead protection program. The general purpose of the program will be to protect the ground waters used by the District. The first major step in creating a wellhead protection plan is defining the management area for which the plan will be in effect. This management area is called a wellhead protection area. This report defines the wellhead protection areas for the District. The state Department of Health recommends that wellhead protection areas be based upon the areas for which water travels to a well within one, five, and ten years. These areas which contribute water to a well are called capture zones. There are several methods of delineating capture zones, the most accurate of which is generally considered to be numerical modeling. In 1992, a numerical ground water model of the Federal Way upland was constructed for the District as a ground water resource management tool. This model has been employed to delineate the capture zones for the District wells. Prior to using the model to define the zones, reviews were made of the upland's hydrogeology and water quality. The review of the water quality data focused on five parameters: iron, manganese, chloride, nitrate, and specific conductance. Generally, the current water quality is good, with the exception of high manganese concentrations at some wells. While the water quality is still good, there are indications that development on the upland over the years has impacted the water quality somewhat, especially that of the upper aquifers. These impacts, seen in the nitrate, chloride and specific conductance data, is not problematic and should not affect the potability of the ground water. Several numerical model runs were made using average recharge rates and average production rates for District wells. Results from these model runs were used to delineate the one-, five-, ten-, and 100-year capture zones for all District production wells. These model runs also allowed the general routing of water through the ground water system, from recharge points to production wells, to be investigated. It was found that ground water moves primarily vertically through confining layers and primarily horizontally through aquifers. Water can move up to hundreds of feet per year through aquifers, but is as slow as several feet per year through the confining layers. The project finished by defining wellhead protection areas for each production well and each aquifer system. Definition of the areas was based upon the interpretation of the delineated capture zones, tempered by knowledge of the limitations of the numerical model and knowledge of the hydrogeology and general response of ground water system of the upland. Executive Summary iv SECTION LAKEHAVEN UTILITY DISTRICT WHPA DEFINITION INTRODUCTION Lakehaven Utility District (LUD), a Group -A public water system which uses ground water as a source, is mandated under federal and state law to implement a wellhead protection program. The overall goal of the mandating laws is to create an awareness of the areas contributing water to wells supplying the system, and to prevent the contamination of ground water used by Group A public water systems. This is to be accomplished through a protection plan which provides management zones around public wells, detects existing ground water contamination sources in the management zones, and manages potential contamination sources within the zones. Washington State requires that a wellhead protection plan (WHPP) shall, at a minimum, include the following: • a completed susceptibility assessment • a delineated wellhead protection area • an inventory of potential contaminant sources • a distribution of findings to required entities • contingency plans for alternative water sources • appropriate spill/incident response measures Lakehaven Utility District has the primary responsibility for developing and implementing the WHPP to protect its ground water resource. Since the District serves a community of 100,000 and relies on ground water for more than 90 percent of its supply, the task of developing and implementing a WHPP is formidable. The task is further complicated by the fact that LUD relies on wells in four major aquifers: the Redondo -Milton Channel (RMC), the Mirror Lake Aquifer (MLA), the Eastern Upland Aquifers (EUA), and the Federal Way Deep Aquifer (FWDA). The first major step in developing a WHPP is defining the management zones around the protected wells. These zones are called wellhead protection areas (WHPA). This report describes the process by which the delineation of the WHPAs was accomplished for LUD, and presents the WHPAs as defined by that process. Wellhead protection areas can be defined by technical or non -technical methods, although technical methods are preferred so that the WHPP better protects the areas of the aquifer that actually contribute water to a well, known as capture zones. In general, there are four methods Introduction I - I for delineating capture zones. They are, from generally least to generally most accurate: the calculated fixed radius method (a non -technical method), analytical modeling, hydrogeologic mapping, and numerical modeling. Several steps are necessary to accurately delineate areas which contribute water to a well. First, geologic and hydrogeologic data for the general region must be collected and analyzed. Secondly, a conceptual model of the hydrogeologic system which encompasses the well or wells needs to be developed from the data analysis. Third, by using the data analysis and conceptual model, a capture zone delineation method can be chosen and the zones defined. Finally, using the defined capture zones as a base, the WHPAs can be delineated. The state Department of Health (DOH) requires that each well have three designated WHPAs, labeled Zone 1, Zone 2, and Zone 3, based upon the one-, five-, and ten-year captures zones. They also recommend wells have an additional WHPA outside of Zone 3, termed the Buffer Zone, which may protect additional aquifer or recharge areas. Based on the methodology used and the level of uncertainty involved, the designated WHPAs may generally encompass or greatly resemble the defined capture zones. In this case, the first two steps of this process had previously been completed and are reviewed in Section 2 of this report. Section 3 of the report adds to the basic data analysis by examining the typical water chemistry of the LUD aquifers. The remainder of the report deals with the delineation method and the actual definition of the capture zones and WHPAs for the LUD wells. The previous work completed for LUD to facilitate resource management included the development of a very sophisticated, three- dimensional, numerical model of the Federal Way Upland. Therefore, the numerical modeling methodology was chosen for the capture zone delineation method. The method is described in Section 4. Results and definition of the WHPAs are presented in the last several sections. 1-2 Introduction SECTION 2 LAKEHAVEN UTILITY DISTRICT WHPA DEFINITION PHYSICAL DEFINITION OF THE HYDROGEOLOGIC SYSTEM Prior to delineating the capture zones for the LUD wells, the hydrogeology of the Federal Way Upland was reviewed. A complete description of the hydrogeology is given in our previous report entitled, HydrogeologicAnalysis of the Federal Way Area, Washington (Becker, 1992). The discussion presented below summarizes that work and adds new insights derived from the drilling of Wells 27M and 29T. The 1995 report by the USGS, entitled Occurrence and Quality of Ground Water in Southwestern King County, Washington, was also reviewed for this effort. However, the USGS report fundamentally misidentified many of the unconsolidated units in the Federal Way area and, therefore, discussion of the report is not included in this review. In the 1992 report, the hydrogeology is described by model layer, with each model layer representing a different hydrostratigraphic layer. The nomenclature used is shown on Table 1. In total, there are six major hydrostratigraphic units delineated on the Federal Way upland reaching to 700 feet below sea level. Beneath these are hundreds of feet of additional unconsolidated sediments which have not been differentiated. Table 1: Layer/Unit Nomenclature Model Layer Hvdrostrati ra hic Unit I Notes 1 Vashon Till Also contains, at some locations, a thin recessional outwash at top- 2 Vashon Advance Aquifer System Contains the RMC, Auburn West Hill Springs, and Well 16 Aquifers. 3 Lower Confining Layer Confining layer beneath the RMC, above the MLA. 4 Intermediate Aquifer System Contains the Mirror Lake, Eastern Upland, and North Shore Aquifers. 5 Deep Confining Layer Confining layer beneath the MLA, above the deep aquifer. 6 Deep Aquifer System Contains the Federal Wav Deep Aquifer. Physical Definition of the Hydrogeologic System 2-1 Layer 1, Vashon Till Layer 1 includes the Vashon till and Vashon recessional deposits which overlie the till in some areas. The unit is generally less than 150 feet thick and covers most of the upland. However, it is thin to absent in some areas, particularly in the Hylebos wetland area and in Jovita and Peasley Canyons. The recessional deposits are typically coarse sand and gravel and may supply perched water in some areas. The till is a compact mixture of sand and gravel in a silt and clay matrix. The till has a low permeability, which retards ground water flow through it. Because of the low permeability, water movement through the till will be primarily vertical. Travel times through the till will vary widely depending upon the vertical gradient, the thickness of the till, and the till's porosity and vertical permeability. Using typical values for these parameters, projected travel times through the till in the RMC area between the Hylebos wetlands and Mirror Lake range from 300 to 2,000 days. However, where the till is thin, absent, or fractured, travel times can be substantially reduced. Indeed, the model -predicted travel times for RMC wells through the till were as short as 123 days (Table 2)'. Table 2: Minimum Predicted Travel Times to RMC Wells Well Minimum Predicted Travel Time (days)' 1-Year Analysis 5-Year Analysis 10-Year Analysis 10/10A >365 272 228 15/15A 137 123 123 17/17A >365 247 241 18 288 202 202 20A >365 601 534 21 358 192 185 23A2 46 38 38 Minimum backwards (discharge cell to recharge point) travel times for 1-, 5-, and 10-year MODPATH runs. Predicted travel times decrease with length of modeling analysis due to the declining RMC water table predicted by MODFLOW (see page 4-2). Short travel times for Well 23A result from particles recharging from the bottom of a constant -head cell and may, therefore, be artificially shortened. The shortest travel time for any RMC well was 38 days at Well 23A. However, this travel time represents water originating from a constant head cell (representing Mirror Lake) and, therefore, was not considered. 2-2 Physical Definition of the Hydrogeologic System Layer 2, Vashon Advance Aquifer System Over much of the upland, Vashon advance outwash deposits exist beneath the Vashon till. These deposits form the Vashon advance aquifer system, with distinct aquifers formed in the higher permeability portions of the unit. The major aquifers in the unit on the upland are the Redondo -Milton Channel, the Auburn West Hill Springs Aquifer, and the Well 16 aquifer. The outwash deposits which make up the unit are varied, ranging from silty sand to very clean, sandy gravel. The unit's thickness varies from absent to more than 200 feet at the thickest portion of the RMC. Because of the variation in the unit, its horizontal and vertical permeabilities vary widely. Therefore, water movement through the layer can be strongly horizontal, primarily vertical, or a combination thereof. Layer 3, Lower Confining Unit Layer 3 is herein labeled the lower confining unit. It represents the aquitard between the Vashon advance aquifer system and the intermediate aquifer system. It is formed by a thick sequence of silt and clay -rich sediments, including the Lawton Clay member of the Vashon Drift and, in places, a till. At many locations, the unit is predominantly silt and clay; at other locations, it is primarily a mixture of sand and gravel with silt and clay. The unit varies widely in thickness. Where the RMC reaches its maximum thickness, layer 3 ed 300 feet thick. Generally, it is thickest on the is very thin to absent. Elsewhere, it can exce eastern upland. Because of the wide variations in thickness and vertical gradients for the unit, travel times through the unit should range from less than 100 days to many years. For example, Well 25 travel time results were examined and showed that, through layer 3, particle travel times ranged from less than 200 days to more than 100 years. Water movement through the layer is, at most locations, primarily in a vertical direction. Layer 4, Intermediate Aquifer System The intermediate aquifer system is a mixture of isolated aquifers and low permeability sediments between the aquifers. The most significant aquifer in the unit is the Mirror Lake Aquifer. The aquifer system also includes smaller, isolated aquifers on both sides of the upland, collectively referred to as the Eastern Upland Aquifers and the North Shore Aquifers. The unit has upper and lower aquifer zones within it. This zonation is particularly evident in the Eastern Upland Aquifers. A good example is at Well 29T where aquifer zones were found at depths of 450-480 feet and 525-620 feet. Both of these zones are included in the current intermediate aquifer system definition. Physical Definition of the Hydrogeologic System 2-3 The materials within the unit probably have more variation in permeabilities than any other unit on the upland. The materials between the aquifers may be as impermeable as the confining layers, while the aquifer materials can be highly permeable, especially in the MLA. The layer is absent beneath the south and south-central portions of the RMC. Elsewhere, its thickness generally varies from 50 to more than 150 feet. Because of the large amount of low permeability material in the unit, water movement in the unit outside the aquifers may be primarily in a vertical direction. In the aquifers, there may be a substantial horizontal component to water movement, especially if there is significant well production in the aquifer. Layer 5, Deep Confining Unit Layer 5, herein labeled the deep confining unit, is the aquitard between the intermediate aquifer system and the deep aquifer system. It is the most substantial confining layer on the upland. It is found throughout the upland and is 200 to 400 feet thick at most locations. It consists largely of low permeability materials ranging from clay to silty, fine sand. Water movement through the unit is primarily vertical. Travel times through the unit are very long due to the layer's thickness and low vertical permeability. For example, model -predicted travel times for particles through layer 5 to Well 19 ranged from 20 to more than 100 years. Layer 6, Deep Aquifer Unit Little is known about the deep aquifer system, which contains the Federal Way Deep Aquifer (FWDA) and is in probable continuity with the deep aquifers in the Puyallup Valley. The unit includes the fine -to -medium sand deposits of the Federal Way Deep Aquifer, as well as lower permeability sediments found elsewhere on the upland where the FWDA is missing. Because the unit is probably in direct continuity with Puget Sound, much of the water movement through the layer should be horizontally directed toward the Sound. Hydrogeology at Wells 27M and 29T Wells 27M and 29T were drilled after the 1992 hydrogeology study was completed. Both wells were drilled to depths greater than 1,000 feet and provide new insights into the upland's hydrogeology. Well 27M encountered all six layers and is completed in the Federal Way Deep Aquifer. It also helped define the northwestern edge of the MLA. The MLA at the site is quite deep, 150 to 230 feet below sea level, and is formed by 15 feet of coarse sand and gravel topping 65 feet of silty, fine sand and, gravel. This aquifer configuration fits well with the interpretation of the 2-4 Physical Definition of the Hydrogeologic System MLA as a deltaic formation. Previously, it was not known that the MLA extended this far to the north and west. The other layers at the well are very similar to elsewhere in the northern RMC area. Well 29T is located on the northern part of the eastern upland. The Vashon till is thin at the site; less than 25 feet thick. Layer 2 at the well incorporates a silty sand and gravel which is believed to be part of the Auburn West Hill Springs Aquifer. Layer 3 is fairly thick, 315 feet, but otherwise is similar to elsewhere on the upland. The intermediate aquifer system, layer 4, is also fairly thick at the site and contains upper and lower aquifers. Layer 5, the lower confining layer, is distinctly different than elsewhere on the upland. The upper portion of it is very gravelly, although it still has a low permeability. The lower portion is fine-grained silt and clay. Layer 6 is either absent from the site or is similar to the lower portion of Layer 5. The Federal Way Deep Aquifer is missing from the site. Physical Definition of the Hydrogeologic System 2-5 SECTION 3 LAKEHAVEN UTILITY DISTRICT WHPA DEFINITION WATER QUALITY To provide a baseline for future comparisons of water quality within the designated WHPA, the inorganic water quality results for the LUD wells from 1990 through 1995 were examined. During that time period, many parameters were not found above their detection limits. Many of those parameters detected low concentrations with little variation. After examining the complete data set for the 1990-1995 time period, five parameters were selected for more detailed study. These parameters are: iron, manganese, nitrate, chloride, and specific conductance. Iron Overall, there is little problem with iron; only one sample collected between 1990-1995, collected at Well 19A in 1993, had an iron concentration above the maximum allowed contaminant level (MCL) at 0.3 mg/l (Figure 1). The observed concentrations indicate that waters in the Federal Way aquifers are generally similar to other south King County ground water in terms of iron. Woodward, et al. (1995) found the median iron concentration of southwestern King County wells to be 0.035 mg/l, the 1990-1995 LUD samples have a median concentration of 0.05 mg/l. There are no distinct trends in the iron data with time, except that wells that exhibit high concentrations continue to have high concentrations with time.' Spatially, wells with higher iron concentrations are scattered throughout the upland. Consistent, higher -than -average concentrations were found at Wells 7 and 19A in the RMC, and at Wells 10C, 22, and 22A in the EUA system. Manganese High manganese concentrations are a larger problem than iron in Federal Way ground waters, with many wells exhibiting concentrations above the MCL of 0.05 mg/1 (Figure 2). The median manganese concentration for southwestern King County is 0.04 mg/1(Woodward, et al., 1995). The median for the LUD samples is 0.067 mg/l. Fifteen of the twenty-three production wells had at least one water sample with a manganese concentration above the MCL during the 1990-1995 time period. ' There are possible decreasing trends in the FWDA for both iron and manganese. Water Quality 3-1 There are no clear trends with time in the manganese data.' Spatially, high manganese concentrations are scattered across each aquifer, except for the Well 16 aquifer. In the RMC, manganese concentrations are lower in the south than in the north. Woodward, et al. (1995) reports that manganese concentrations often show an increasing trend with aquifer depth. Nitrate Nitrate concentrations are often used as an indicator of contamination from septic systems and fertilizer. While none of the LUD samples are approaching the MCL for nitrate (10 mg/1) (Figure 3), there are indications of rising trends in the nitrates. The median nitrate (as nitrogen) value for southwestern King County is less than 0.1 mg/l (Woodward, et al., 1995). The median value of the LUD data set was essentially the same, at less than 0.2 mg/l.' These median values represent the natural background value for nitrate. Therefore, any concentration greater than 0.2 mg/l typically represents non -pristine water. Approximately half the LUD production wells have nitrate concentrations above 0.2 mg/l. Combining the present data set with the results of a previous study (Robinson & Noble, 1991) shows that there are only three Federal Way aquifers without any current nitrate contamination: the FWDA (Wells 17B and 19), the Wells 22 and 22A aquifer, and the Well 10C aquifer. Only one RMC well, Well 21, and one MLA well, Well 23, failed to show any sign of nitrate above the detection limit. The remainder of the wells fall into three categories (Table 3): low levels of nitrate (less than 0.5 mg/1) with no visible trends, higher levels of nitrates (0.5 - 2.0 mg/1) with no visible trends, and higher levels of nitrates with an increasing trend. No consistent decreasing trends were found. 1 There arc possible decreasing trends in the FWDA for both iron and manganese. 2 0.2 mg/l is the standard detection limit for nitrate and was used for the LUD samples. Woodward used a detection limit of 0.1 mg/I. 3_2 Water Quality Table 3: Nitrate Concentration Trends in LUD Wells Nitrate Concentration (mg/l) Well / Aquifer System No contamination <0.2 21, RMC 10C, EUA 22/22A, EUA 17B, FWDA 19, FWDA 23. MLA Minor contamination No visible trend <0.5 7, RMC 10A. RMC Medium contamination No visible trend 0.5 - 2.0 17/17A, RMC 20A, RMC 23A, RMC 20, MLA Medium contamination Increasing trend 0.5 - 2.0 10, RMC 15/15A, RMC 18, RMC 16, EUA (Shallow) 25, MLA Chloride Like nitrate, chloride can be an indicator of septic system contamination. It can also be an indicator of salt water intrusion. The MCL for chloride is Z50 mg/l; none of the LUD samples had concentrations above 10 mg/l (Figure 4). The LUD samples have a median concentration of 4 mg/l, slightly higher than the south King County median of 2.9 mg/l. The chloride data shows no indication of salt water intrusion. Values are slightly higher in the shallow aquifers (the RMC and Well 16 aquifer) and in the MLA than in the deeper aquifers (Table 4). Water Quality 3-3 Tahle 4- Average C:hlnride ( :'nncentratinns by Anuifer Aquifer Average Concentration (m 1) Number Data Points RMC 5 22 Well 16 6 2 MLA 5.5 6 Well 10C 2 2 Wells 22/22A 2.8 4 FWDA 2.3 4 Specific Conductance Specific conductance can be used as an approximation of the dissolved solids concentration within ground water. In southwestern King County, Woodward, et al. (1995) found that approximately 65 percent of the specific conductance value (in }mhos/cm) is due to the dissolved solid concentration (in mg/1). They found a median specific conductance of 174 pmhos/cm, slightly less than the median value of the LUD data set at 186 pmhos/cm (Figure 5). There are spatial and temporal variations or trends in the LUD conductance data. While there does not appear to be any correlation with depth, the northern RMC wells generally have higher specific conductance values than the southern RMC wells, with medians of 206 and 181 Nmhos/cm, respectively. Temporally, specific conductance is increasing with time. If the data set is split into two subsets, 1990-1992 and 1993-1995, the trend is evident. In the earlier set, the median value was 178 pmhos/cm, a value very close to the average for southwest King County. In the later data set, the median is 192 pmhos/cm. The trend can also be seen by comparing values at individual wells. There are 18 wells in the complete 1990-1995 data set that have two or more measurements. Of these wells, two had values that were unchanged between the measurement dates, two had values decline with time, and 13 had specific conductance values increase with time. Water Quality Summary Generally, the ground water quality of the Federal Way upland is very good, except for high concentrations of manganese. There are also indications of nitrate contamination, although current concentrations are well below the MCL and are not problematic. The observed nitrates 3-4 Water Quality may arise from septic system return flow from the unsewered areas of the upland and fertilizer use throughout the upland. Higher than average chloride concentrations in the shallow aquifers may also be due to septic return flow. Each aquifer has different chemistries, although there seems to be general groupings for shallow and deep aquifers (Table 5, Figure 6), with the MLA falling in the shallow type chemistry group. In fact, the MLA chemistry, at least for the five parameters examined, appears more like the RMC than the deep aquifers. In general, the deeper aquifers have lower nitrates, chlorides and specific conductances than the shallower aquifers. There also appears to be general differences between the northern and southern RMC.' Manganese is lower in the south RMC than in the north, as is specific conductance and, to a lesser extent, chloride. Table 5: Summary of Selected Parameters by Aquifer Aquifer RMC (whole) North RMC South RMC EUA (shallow) MLA EUA (deep) FWDA Iron Manganese' Nitrate' Chloride' Specific Conductances generally low generally high high, 3 high high, increasing generally low high high, 1 high high, increasing generally low low high, 2 high low, increasing low low high, 1 high high, steady low mixed high, 1 high high, increasing high high low low low, increasing generally low mixed low low mixed, steady 1 low <0.1 mg/l, high = >0.1 mg/1 2 low <0.05 mg/I, high = >0.05 mg/l, mixed contains both low and high values 3 relative concentration and number of wells with increasing concentration trends with time; low <0.2 mg/l, high = >0.2 mg/l ' low <3 mg/l, high = >3 mg/l s relative specific conductance and temporal trend direction; low <180 pmhos/cm, high = >180 pmhos/cm, mixed contains both low and high values 3 North defined to include Wells 7, 17, 17A, 18, 20A, and 23A. South defined to include 10, 10A, 15, 15A, 19A, and 21. Water Quality 3-5 SECTION 4 LAKEHAVEN UTILITY DISTRICT WHPA DEFINITION MODELING METHODOLOGY Numerical modeling techniques were chosen to delineate the LUD capture zones. By using the previously constructed, three-dimensional MODFLOW numerical model of the Federal Way upland (Becker, 1992), the capture zone analysis was a two-step process. First, the model was run to generate sets of head and flux distributions for the modeled area. These model - generated data sets were input into a particle tracking program to trace water paths from recharge sources to discharge points. In this case, the particle tracker MODPATH, Version 3 (Pollack, 1994), was used. Where the hydrogeologic system is well defined, as it is in the Federal Way area, the numerical modeling methodology can "provide a very high degree of accuracy" (DOH, 1995) in capture zone delineation. The methodology works by dividing the area into a three-dimensional grid and assigning aquifer (or confining layer) property values to each grid cell. First, in this case through MODFLOW, the head at every cell is computed. A detailed description of how MODFLOW computes head values is given by McDonald and Harbaugh (1988). The same aquifer parameter data set is then used to track the paths and travel times of specific water particles through the model grid. Capture zones are delineated by determining which sets of ground water particles enter a modeled well while it is pumped. This is most efficiently accomplished by particle backtracking; that is, starting particles at the well and running the model backwards through time. With this method, particles start at their discharge point (a well) and travel through the model to their recharge point, typically a point on the uppermost water table surface in the model or a constant -head model cell (typically used to simulate lakes and other bodies of water). MODFLOW The first step in capture zone delineation is the production of a head distribution array for the modeled area, which is done with MODFLOW. Prior to running the model to produce the head distribution, the set of stress conditions for the run had to be established. In particular, two conditions had to be defined: the amount of recharge and the amount of well production. Both of these factors are affected by seasonality. Therefore, prior to setting these conditions, the seasonality of LUD production was examined. Modeling Methodology 4-1 Data from LUD wells for the six -year period 1990-1995 was analyzed for total production and production by aquifer. Overall, total average daily production of the time period has been fairly constant at 9.9 mgd. However, the total ground water production data shows large, distinct summer production peaks, generally lasting from June through September (Figure 7). The summer production peaks for the individual aquifers are not so distinct. The RMC and EUA productions have summer peaks in four out of six years. The MLA has summer peaks in five out of six years, but these peaks are not always aligned with June through September. The FWDA production has summer peaks for the last three years of the data set. Based upon this data, each year in the model runs was divided into two stress periods: a June -September period representing summer peaking, and an October -May period representing non -peak times. Precipitation data was also examined. The average annual effective' precipitation at SeaTac between 1945 and 1994 was 23.5 inches. Monthly data shows that, on average, there is no effective precipitation in the months of May through September. Consequently, the stress periods chosen based on the production data, June -September and October -May, also approximate the seasonality of precipitation. Data inputs were prepared for two transient MODFLOW runs, one simulating ten years, and one simulating 100 years. The ten-year period was divided into twenty stress periods representing the annual peaking and non -peaking periods. Average well productions and average estimated recharge values were used as shown in Appendix 1. For the 100-year run, the seasonality was ignored and average production and recharge values were used in a single, 100-year long stress period. The MODFLOW results of these two runs can be reviewed at the Robinson & Noble offices. Both runs were started with 1991 simulated water levels developed during the 1992 modeling project (Becker, 1992). Results from both runs showed larger -than -expected water level declines in the RMC, but were deemed suitable for the project's requirements. These larger -than -expected declines are due to modeling error. The model was constructed so that the RMC is always confined. Yet in the real world, as water levels have fallen with time, portions of the RMC have become unconfined. When these areas become unconfined, the storage coefficient of the aquifer increases, and water level changes become less severe. So, while this change in conditions has happened in the real world, it is prevented from occurring in the model and, therefore, the model over -predicts the declining water level. For this project, the model was not adjusted to correct for this error. This is because: 1) if corrected, a lengthy model re -calibration would be required, and 2) capture zone size and shape is relatively insensitive to storage coefficient. Because capture zone size and shape is insensitive to storage coefficient, these MODFLOW results can be safely used to delineate capture zones. 1 Total precipitation minus estimated evapotranspiration. 4-2 Modeling Methodology MODPATH Prior to running the particle tracking program MODPATH, porosity values had to be entered for all model cells. Assigned porosities were based upon tables of measured porosities for various unconsolidated materials (Driscoll, 1986, Fetter, 1980) and upon the hydraulic conductivity values assigned to model cells as shown on Table 6. rV-td. A. A ooiri Yl i'+rl PAYACIft1 V Jiu-c Material Represented Hydraulic Conductivi (ft/d) Porosi Till (Layer 1) 2 15% Sand, sand and gravel >100 20% Fine sand, silty sands 5 - 100 25% Silt, clayey silts 0.1 - 5 30% Clays <0.1 40916 After porosities were entered, appropriate MODPATH data files were created and starting particle locations were selected so that the capture zones could be defined by backtracking. MODFLOW and MODPATH assume wells to be centered in their respective model cells and to be fully penetrating in those cells. It was assumed, for the purposes of this study, that water along the sides and top of a model cell containing a well enters the well shortly after production begins. 125 particles were chosen to define each well's capture zone. These particles were placed equally along the four sides and top of the cell containing a particular well, 25 particles per side. Using these starting particle locations and the results from the first MODFLOW run (10 years, 20 stress periods), the one-, five- and ten-year capture zones were defined for each well. The results of the second MODFLOW run (100 years, 1 stress period) with identical starting particle locations were used to define the 100-year capture zones for each well. Uncertainty Every method of capture zone delineation involves a certain amount of uncertainty. While the numerical modeling methods used here are considered to be highly accurate, there is a certain amount of uncertainty involved, especially in areas of the model that are poorly defined. In this case areas of poor model definition, due largely to lack of data, occur around the edges of the model. In particular, these areas include the eastern -most portion, the southwest portion, and the western portion of the upland. The deep aquifer system, layer 6, is also relatively poorly Modeling Methodology 4-3 defined. We also now know, due to Well 27M, that the MLA is undersized (on the west) in the model. These model uncertainties lead to capture zone uncertainties in these areas. However, the model is well defined in the central portion of the upland, where most the capture zones exist and, in general, is very well suited to the definition of capture zones. Another potential problem exists in areas that have gone dry in the model. The model was originally constructed for a MODFLOW code which did not allow re -wetting of model cells that went dry during a simulation. Once dry, cells remain dry throughout a run and essentially become "dead space' in the model, thereby not allowing particles to track through them. This situation presents potential uncertainties in three major areas of the model: much of layer 1, the southwest portion of the upland in layer 2, and portions of the eastern upland in layer 2. Uncertainties in capture zones due to drying in layer 2 will be discussed in the sections on the individual well capture zones. Drying of layer 1, which represents the Vashon till, has little effect on capture zone shape because the travel direction through the till is slightly horizontal to mostly vertical (see next section). Therefore, if layer 1 had not been dry, particle paths would only be slightly different in map view than they are where the layer is dry. Travel times are slightly shortened in the model compared to the "real world" where layer 1 is dry. This is because the MODFLOW/MODPATH method does not account for travel time through the vadose zone (the dry area above the water table). However, in the model, it makes little difference if a layer 1 cell is completely dry or slightly saturated (cells that should be highly saturated are not likely to go dry). This limitation of MODFLOW/MODPATH does mean that time -related capture zones are somewhat larger than they would be if vadose zone travel was included! This is equally true for all areas in layer 1, not just those that have gone dry during simulations. As explained earlier, capture zones are delineated by backtracking water particles from near the well to the points where they enter the water table. The size and shape of capture zones are partially dependent on the number of, and starting positions used, for these defining particles. The fewer particles used, the more uncertainty in the defined zone. The more concentrated the starting locations, the greater the uncertainty in the zone. By using 125 particles to define each capture zone and spreading these particles widely over the model cell containing a well, this particular uncertainty was minimized. Another uncertainty built into the model involves well. placement. The MODFLOW code requires that wells be placed at the center of model cells while, in reality, a well may occur anywhere within a cell. This modeling limitation can cause differences between simulated and 2 Travel times through the vadose zone are dependent on the thickness of the zone, the amount of recharge involved, the soil moisture content, the specific moisture capacity, and the unsaturated hydraulic conductivity. Typical times for materials on the Federal Way upland could range from days (for unsaturated recessional gravels) to possibly years (for thick sequences of dry till). 4-4 Modeling Methodology "real world" capture zones, especially for the one-year time frame. This uncertainty is explained in greater detail in the next section. The capture zones defined by the numerical methodology are predicated upon the stress conditions, chiefly production rate and recharge rate, that are applied to the model. In other words, if these stress conditions are changed, the defined capture zones can change. By inputting these conditions into the model, the modeler assumes future conditions. In this case, average well productions and average recharge conditions were input. If, in the future, production rates are changed or long periods of drought or surplus precipitation occur, the "real world" capture zones may be different than the predicted ones. Therefore, the uncertainty in future stress conditions must be kept in mind when using model results. Even with the various uncertainties involved in the capture zone delineation, the general shape and size of the capture zones are believed to be as accurate as possible with the existing methodology and level of subsurface definition. This is especially true of the wells in the central portion of the upland, which represents the preponderance of the WHPA areas defined. Modeling Methodology 4-5 SECTION 5 LAKEHAVEN UTILITY DISTRICT WHPA DEFINITION GENERAL GROUND WATER FLOW Ground Water Paths At a sufficient distance from boundary conditions (wells, springs, surface water features, ground water divides, etc.), ground water flow is primarily vertical in low conductivity materials, such as confining layers, and primarily horizontal in high conductivity materials, such as aquifers. This allows general flow directions to be estimated for aquifer systems by examining head, or potentiometric, maps. Potentiometric maps, representing 1991 water levels in the three Federal Way aquifer systems, drawn from the 1992 numerical model results (Becker, 1992), are presented as Figures 8, 9, and 10. Flow in the Vashon advance aquifer system is generally from the eastern and western portions of the upland towards the RMC which serves as a north -south trending line sink for the system (Figure 8). Once in the RMC, flow is mostly southerly. Flow in the RMC itself is primarily horizontal, as can be seen on particle path A in Figures 1la and 11b. In the less permeable sections of the aquifer system, represented on Figure 8 where the ground water gradient is steep (i.e., contour lines are close together), flow becomes more vertical. This can be seen on particle path C, Figure 11b, which steepens at its western -most point in the layer 2 sediments (the Vashon advance system). Because the intermediate aquifer system is dominated by relatively large areas of moderate to low hydraulic conductivity with pockets of higher conductivity aquifer materials, the flow patterns through the system vary laterally. At some locations, ground water flow has a large vertical component, such as on path A in Figures 11a and llb (also see Table 7); at other locations horizontal flow dominates (see path Q. The general directions of the horizontal flow components in the aquifer system are shown on Figure 9. Flow in much of the north -central portion of the upland is toward the MLA. Elsewhere, flow is toward the Auburn valley or Puget Sound. General Ground Water Flow 5-1 Table 7: Amounts of Horizontal & Vertical Movement on Sample Ground Water Flow Paths Path Laver Horizontal Vector Component (ft) Vertical Vector Component (ft) Horizontal/Vertical Ratio A 1 480 20 24 2 14720 90 164 3 150 170 0.9 4 310 40 8 5 280 310 0.9 6 3930 130 30 B 1 80 30 3 2 4340 40 109 C 2 8580 150 57 3 560 75 7 L-4 3560 160 22 Little is known about the deep aquifer system, so the potentiometric surface represented on Figure 10 is estimated. However, the existence of the FWDA in the north -central portion of the upland is confirmed. In the FWDA, flow is northwesterly toward Puget Sound. The lack of good, deep aquifers in much of the northeastern portion of the upland is also confirmed; therefore, there is probably horizontal flow (with a large vertical component) from the northeast toward the FWDA as indicated on Figure 10. Conditions southwest of the FWDA have not been confirmed and, except for the Puyallup Valley, flow patterns in this area are speculative. Flow through the confining layers is primarily vertical (Table 7, Figure 11b), especially where the confining layers are primarily silt and clay, which have very low hydraulic conductivities. In the Vashon till, layer 1, which has a higher hydraulic conductivity than silt and clay, a bit more horizontal movement can be expected and was reflected in the modeling results. Travel Times Obviously, ground water travel time from a recharge point at the surface to an aquifer increases as the depth of the aquifer increases. In general, modeled travel times for particles to reach the RMC wells were from less than a year to approximately thirty years. Travel times to the MLA wells range from ten years to more than 100 years. Ground water particles traveling from the surface to the FWDA wells can take more than 1,000 years. 5-2 General Ground Water Flow Generally, water moves faster through the aquifers than it does through the confining layers, as shown on Table 8 for the three sample paths on Figures 1la and 11b. Ground water velocity is a function of porosity, gradient and hydraulic conductivity. While porosities and gradients differ between aquifers and confining layers, the values in aquifers and confining layers are generally within an order of magnitude difference of each other. Hydraulic conductivities, however, can be several orders of magnitude higher in aquifers, thus leading to appreciably faster velocities within aquifer materials. Table 8: Travel Times and Velocities for Swii le Ground Water Particles Path Laver Travel Time Through Layer ( Ls)_ Average Velocity (fr/vr) A 1 4.5 107 2 31 475 3 37 6 4 10 31 5 122 3 6 120 33 B 1 0.6 142 2 14 310 C ji 2 32 268 3 9 63 4 9 396 General Ground Water Flow 5-3 SECTION 6 LAKEHAVEN UTILITY DISTRICT WHPA DEFINITION CAPTURE ZONE DELINEATION Three -Dimensional Aspects of Capture Zones Using the three-dimensional, numerical modeling method of capture zone delineation, ground water particles can be traced from their recharge source at the surface, through any overlying layers, into the subject aquifer, and eventually into the subject well. By defining numerous such paths for a well, the three-dimensional zone that contributes water to a well may be outlined. The ground water travel paths which define a capture zone exhibit different shapes and directions in each layer they pass through depending on the parameters of the layer and the stresses to which the layer is subjected. Obviously, the resultant capture zone, when examined layer by layer, may have a differing appearance and geometry depending on which layer is examined. To demonstrate how a particular capture zone may change with each layer, the 100-year capture zone for Well 23 was "sliced" into three map -view sections in Figure 12. Figure 12a shows the capture zone at the top of the MLA, the production aquifer for Well 23. This zone represents the area from which water in the aquifer travels to the well. Figure 12b shows the capture zone at the top of confining layer (layer 3) above the MLA (and, consequently, also represents the bottom of the RMC). This zone presents the area through which water travels through the confining layer to the production aquifer capture zone (shown on Figure 12a). Not surprisingly, it has basically the same size and shape as the production aquifer capture zone because water primarily moves vertically through the confining layer. Figure 12c shows the Well 23 capture zone at the top of the water table surface in layers 1 and 2. In other words, the areas shown in Figure 12c are the actual recharge areas for Well 23. Essentially, recharge to the areas in Figure 12c enters the top of the RMC (or associated Vashon advance sediments) and moves through the aquifer (largely horizontally) under differing gradients and stresses until it reaches the bottom of the aquifer, where the same particles have coalesced to the shape of Figure 12b. There the water enters layer 3, the confining layer, and moves (mostly vertically) downward to layer 4, the MLA, where the particles have the shape of Figure 12a. Once in the MLA, the water particles move vertically and horizontally to the well. As. can be seen from the above example, capture zone shape can be expected to increase in complexity for each confining layer and aquifer through which water must move to reach the well. Capture Zone Delineation 6-1 Capture Zone and Wellhead Protection Area Definitions A capture zone is defined as the region surrounding a well which contributes flow to a well. Capture zones can be limited by time, such that a time -related capture zone is the region surrounding a well that contributes flow to the well within a specified time. Capture zones represent three-dimensional volumes that are usually projected onto a two-dimensional surface (a map). Capture zones are not easy to map and, therefore, are typically estimated by various mathematical -based methods, such as numerical modeling. In Washington State, wellhead protection areas, by DOH guidelines, are based upon estimated one-, five-, and ten-year travel paths for water moving through an aquifer to a well (DOH, 1995). The vertical path and time, from the surface to the aquifer, is typically not considered. For this reason, the 103-page Wellhead Protection Program Guidance Document written by DOH (1995) purposely does not mention capture zones. Thus, by ignoring vertical components, WHPAs typically resemble the capture zone in Figure 12a, a capture zone delineated solely in the geometric plane of the aquifer (i.e., a two-dimensional capture zone). For deep wells, the actual surface area which contributes recharge to a well may not resemble the two-dimensional representation of a well's capture zone within its production aquifer, as was shown in Figure 12. However, if the three-dimensional capture zone is delineated and projected to a two-dimensional area, this area will always include both the surface recharge area and the production aquifer "two-dimensional' capture zone (Figure 13). By using the two- dimensional representation of a three-dimensional capture zone as the WHPA, the entire area which contributes water to a well within the stipulated time frame is protected. By using this method for definition of a wellhead protection area, the area defined is more accurate, and yet, because it includes additional areas influenced by overlying aquifers, it is more conservative than the definition method proposed under DOH guidelines. Relationship of "Real World" Zones to Modeled Zones When a well is simulated in a MODFLOW model, the program places the simulated well at the center of the model cell and makes the simulated well fully penetrating through the cell. In reality, the well may be located anywhere within the cell boundaries and have any degree of penetration (Figure 14a). Because of these differences, model capture zones will be somewhat different from "real world" capture zones, particularly for near well response predictions. The differences in defined capture zones result from both non-specific well locations within the cell and from particle "starting points" on the cell perimeter rather than at the specific well location. Because the accuracy of well locations within the model is necessarily limited to the cell size (660 feet for most model cells, 1,320 feet for other model cells), the differences in capture zones will be greatest when particle paths used to define the zones are approximately 6-2 Capture Zone Delineation (or less than) the same as the cell length. Placing the starting locations for the defining particles along the edges of the cell (as was done for this project) instead of at the modeled well location, causes the model -defined capture zone to be larger than the "real world" zone. It will, however, always include the "real world" zone (Figure 14a). As the length of the defining path grows longer, the percentage of difference arising because of imprecise positioning of the simulated well decreases. Because MODFLOW simulates wells at the center of model cells, cells that contain two production wells were simulated as having a single well with the combined production of both wells. This was done for Wells 10 and 10A, 15 and 15A, 17 and 17A, and 22 and 22A. In the "real world" case for two wells near each other, two separate capture zones will be formed. In the model, a single zone will be simulated. The simulated zone will, however, closely approximate the shape of the combined zones in the "real world" case (Figure 14b). One -Year Capture Zones The model was run to produce capture zones for LUD production wells for time periods of one, five, ten, and one -hundred years as discussed earlier. The locations of the layers 2, 4, and 6 aquifer systems' one-year capture zones are shown on Figures 15, 16, and 17, respectively. In all the one-year capture zones, the uncertainty due to cell -centered well locations in the model is significant. Defining path lengths were generally less than one cell length for all wells except for Wells 10 and 10A. Path length was especially short compared to cell size for Wells 10C, 21, and 22/22A where larger cell sizes were employed in the model. Consequently, all the one-year capture zones are conservatively larger than would be expected in the "real world" case. Even so, they are generally quite small and, in most cases, water from the surface takes longer than one year to reach the wells (Table 9). In all cases, water reaching the wells within a one-year period has come from the aquifer in which that well is completed or the confining layer above the source aquifer (Table 9). Capture Zone Delineation 6-3 Table 9: One -Year Capture Zone Details Well Aquifer, Layer Water From Surface Reaches Well, Minimum Time (days) Layers Water Started Time Period In 10/10A RMC, 2 No 2,1 10C EUA, 4 No 4,3 15/15A RMC, 2 Yes, 137 2,1 16 EUA (Shallow), 2 Yes, 140 2,1 17117A RMC, 2 No 2,1 17B FWDA, 6 No 6,5 18 RMC, 2 Yes, 219 2,1 19 FWDA, 6 No 6,5 20A RMC, 2 No 2,1 20 MLA, 4 No 4,3 21 RMC, 2 Yes, 358 2,1 22/22A EUA, 4 No 4,3 23A RMC, 2 Yes, 46 2,1 23 MLA, 4 No 4,3 25 MLA. 4 No 4.3 Five -Year Capture Zones The five-year capture zones for Iayers 2, 4, and 6 are presented on Figures 18, 19, and 20, respectively. They are sufficiently large that the uncertainty due to cell -centered well placement is minimal with the exceptions of Wells 10C, 21, and 22/22A. For these three wells, the defined five-year capture zones are only slightly larger than the one-year zones, and the capture zone radius is still close to the length of the model cell. For the other wells, the five- year zones are considerably larger than the one-year zones and the model cells. Most of the five-year zones take their shapes from the prevailing gradients of the aquifers in the regions of their respective wells. Zones for the RMC wells generally extend north of the wells (Figure 18). In the MLA, the zones for Wells 20 and 25 extend to the east and north. Some of the five-year zones are impinging on each other, especially the zones for Wells 10/10A and 15/15A and those for Wells 20 and 23. In essence, these zones are "deformed" by the production from the neighboring well, and the zone shape would be different had the neighboring well not been producing. Therefore, for these wells, it should be remembered that 6-4 Capture Zone Delineation capture zone shapes are dependent on the pumping pattern being employed by the District and may change if the neighboring wells are taken off-line for long periods of time, or are decommissioned. Re-evaluation using the model to simulate the change in pattern could be accomplished fairly easily, but should not be necessary unless significant changes in production patterns are implemented. While the five-year capture zones are considerably larger than the one-year zones, most of the water reaching the wells within the five-year period, like the one-year zones, started the five- year period in the production aquifer or the confining layer above the production aquifer (Table 10). In the deeper wells of layers 4 and 6, only Well 25 had water from above its confining layer reach the well within the five years. In all of the Qva aquifer system wells (RMC wells and Well 16), some component of the water reaching the wells within five years started at the surface. This was not the case in any of the wells in layers 4 and 6. TahlP 1 n- Five -Year C:no-tire Zone Details Well Aauifer. Laver Water From Surface Reaches Well, Minimum Time (years) TLayers Water Started Timc Period In 10/10A RMC, 2 Yes, <1 2,1 10C EUA, 4 No 4,3 15/15A RMC, 2 Yes, <1 2,1 16 EUA (Shallow), 2 Yes, <1 2,1 17/17A RMC, 2 - Yes, <1 2,1 17B FWDA, 6 No 6,5 18 RMC, 2 Yes, <1 2,1 19 FWDA, 6 No 6,5 20A RMC, 2 Yes, 1.6 2,1 20 MLA, 4 No 4,3 21 RMC, 2 Yes, <1 2,1 22/22A EUA, 4 No 4,3 23A RMC, 2 Yes, <1 2,1 23 MLA, 4 No 4,3 25 MLA, 4 No 4, 3, 2 Capture Zone Delineation 6-5 Ten -Year Capture Zones The ten-year capture zones for each of the three production systems are presented on Figures 21, 22, and 23. Uncertainty due to cell -centered well placement within the model is probably only a factor for Wells 10C and 22/22A. The zone for Well 16 encountered several dry model cells which caused the simulated capture zone to be conservatively larger than it would be if these areas are not truly dry. After 10 years of production, all of the defined capture zones in the RMC and the MLA are influenced by not only the prevailing gradients, but also by the production of other wells in the aquifers. In particular, in the RMC aquifer, the zone for Wells 10/10A is influenced by production at Wells 15/15A and 18; the zone for Well 23A is influenced by production at Wells 17/17A and 20A; and the zone for Well 20 in the MLA is influenced by production from Wells 23 and 25. Within the ten-year period, several of the intermediate aquifer wells draw water from above their confining layer. Well 25 is predicted to draw water from the surface within the 10-year period (Table 11). Table 11: Ten -Year Capture Zone Details Well Aquifer, Laver Water From Surface Reaches Well, Minimum Time (years) Layers Water Started Time Period In 10/1 OA RMC, 2 Yes, <1 2,1 lOC EUA, 4 No 4,3 15/15A RMC, 2 Yes, <1 2,1 16 EUA (Shallow), 2 Yes, <1 2,1 17/17A RMC, 2 Yes, <1 2, 1 17B FWDA, 6 No 6,5 18 RMC, 2 Yes, <1 2,1 19 FWDA, 6 No 6,5 20A RMC, 2 Yes, 1.5 2,1 20 MLA, 4 No 4, 3, 2 21 RMC, 2 Yes, <1 2,1 22/22A EUA, 4 No 4,3 23A RMC, 2 Yes, <1 2,1 23 MLA, 4 No 4,3 25 MLA, 4 Yes, 5.0 4, 3, 2, 1 6-6 Capture Zone Delineation One -Hundred Year Capture Zones The one -hundred year capture zones for aquifer layers 2, 4, and 6 are presented on Figures 24, 25, and 26, respectively. They are all sufficiently large that uncertainty due to imprecise well placement in the model is not a factor. Uncertainty due to model cell drying is again a factor for Well 16, leading to a conservatively large zone, as explained previously. Drying of modeled cells also affected the western -most portion of the Well 15/15A and Well 21 zones, the southwestern corner of the Well 10/10A zone, and the eastern -most edge of the Well 15/15A zone. In all of these cases, the uncertainty due to drying is believed to be minor. Had the cells not been dry, these zones would still be approximately the same size and shape. All the capture zones, except those for Wells 17B, 19, and 22/22A, are influencing each other. Essentially, the entire north -central portion of the upland becomes a single management zone. The simulation indicates that many of the wells may be potentially recharged from the lakes on the upland (Table 12). All of the wells are intercepting water from the surface within the 100-year time period, except for Wells 10C, 17B, and 19 (Table 13). Average travel times from land surface to the wells range from five to more than 100 years. It should be noted, however, that no consideration has been given to the transfer of water through the non -saturated material of the upland. Were the non -saturated materials included in the travel time calculations, the travel times would be expected to be slightly longer. Table 12: Lakes Which Potentially Recharge LUD Wells Lake Wells Possibly Rechar e Mirror Lake 20, 20A, 23, 23A Fischer Bog 17/17A, 18, 23 Twin Lakes 10/10A Steel Lake 20, 20A, 23 North Lake 10/10A Lake Geneva 16 Capture Zone Delineation 6-7 One -Hundred Year Capture Zones The one -hundred year capture zones for aquifer layers 2, 4, and 6 are presented on Figures 24, 25, and 26, respectively. They are all sufficiently large that uncertainty due to imprecise well placement in the model is not a factor. Uncertainty due to model cell drying is again a factor for Well 16, leading to a conservatively large zone, as explained previously. Drying of modeled cells also affected the western -most portion of the Well 15/15A and Well 21 zones, the southwestern corner of the Well 10/10A zone, and the eastern -most edge of the Well 15/15A zone. In all of these cases, the uncertainty due to drying is believed to be minor. Had the cells not been dry, these zones would still be approximately the same size and shape. All the capture zones, except those for Wells 17B, 19, and 22/22A, are influencing each other. Essentially, the entire north -central portion of the upland becomes a single management zone. The simulation indicates that many of the wells may be potentially recharged from the lakes on the upland (Table 12). All of the wells are intercepting water from the surface within the 100-year time period, except for Wells 10C, 17B, and 19 (Table 13). Average travel times from land surface to the wells range from five to more than 100 years. It should be noted, however, that no consideration has been given to the transfer of water through the non -saturated material of the upland. Were the non -saturated materials included in the travel time calculations, the travel times would be expected to be slightly longer. Table 12: Lakes Which Potentially Recharge LUD Wells Lake Wells Possiblv Rechar e Mirror Lake 20, 20A, 23, 23A Fischer Bog 17/17A, 18, 23 Twin Lakes 10/10A Steel Lake 20, 20A, 23 North Lake 10/10A Lake Geneva 16 Capture Zone Delineation 6-7 For the first set of conditions, the production at Wells 10 and 10A were set at the stated pumping capacities for the wells. In essence, the run simulated turning both wells on nonstop for ten years. The production rate changed from 414,706 cfd (3.1 mgd) to 860,602 cfd (6.4 mgd), an increase of nearly 108 percent. The results for the run are presented on Figure 27. The figure shows that, under maximum production conditions, the capture zone for Wells 10 and 10A approximately doubles in area. This change also affects the capture zones for other nearby wells in the RMC, as Wells 10 and 10A, under this scenario, intercept water that was destined for Wells 15/15A, 18, and 21; these wells are forced to draw water from another direction. As can be seen by comparing Figures 21 and 27, under maximum production from Wells 10 and 10A, the capture zone for Well 15/15A loses its western lobe and is forced to expand to the east, the capture zone for Well 18 shifts north and east to draw its required water, and the capture zone for Well 21 is forced southward. Obviously, production rate can have a significant effect on the size and shape of capture zones of both the well for which production is changed and its neighboring wells. The system, however, seems much less sensitive to changes in recharge rate. In order to test the implications of drought, the 90th worst 10-year recharge period between 1892 and 1991 was used as the recharge condition.' Over that ten-year period, the recharge averaged 14.08 inches per year, or nearly 2 inches less than the 16 inches defined as the average recharge for the upland. This constitutes a deficiency of 12 percent each year of the drought period. The results are shown on Figure 28. The capture zone under the drought scenario is approximately the same size and general shape as for average recharge conditions, but is shifted slightly south. The shape is slightly different, with the lobe in the northwest corner of the zone not as well developed in the drought case as in the higher recharge case. Capture zone size, at least in the RMC, is apparently not affected significantly by increased recharge. The run with above -average recharge showed minor response similar in scope to the below -average recharge scenario response. For the above -average run, the 90th best 10-year precipitation period between 1892 and 1991 was used as the recharge condition. This corresponded to the 1952-1961 period when the average recharge was calculated to be 21.67 inches per year, or 5.67 inches more than the presumed average condition, an excess of 35 percent. The results are shown on Figure 29. The capture zone for the above -average recharge condition is slightly smaller than the average condition and is very similar to the shape of the below -average condition, again with the northwestern lobe not as well defined. 1 This same recharge data set was used previously. See our letter of August 31, 1992, to John Bowman. Capture Zone Delineation 6-9 SECTION 7 LAKEHAVEN UTILITY DISTRICT WHPA DEFINITION CONCLUSIONS AND RECOMMENDATIONS As discussed in the introduction, there are four basic steps in delineating a WHPA: 1) study the hydrogeologic data, 2) develop a conceptual model, 3) define the capture zones, and based on the previous three steps, 4) delineate the WHPA. The first two steps and a portion of the third step were completed in our 1992 hydrogeologic analysis of the upland (Becker, 1992). This work was reviewed at the beginning of this report. New data for Wells 27M and 29T, which was not available when the 1992 report was written, was also examined. The data from the new wells is generally consistent with the interpretations within the conceptual model developed for the 1992 report. The 1992 numerical model, however, could be modified in the future to better represent the areal extent of aquifers indicated by the new well data, particularly for the MLA. Well 27M provides information to better define the northwestern edge of the MLA and the northern extent of the FWDA. The numerical model, as currently built, adequately represents the knowledge gained for the FWDA, but it simulates the MLA as being smaller than it is now known to be. It was not within the scope of the present project to revise the numerical model and, therefore, the capture zones delineated by using the model were interpreted with recognition of the knowledge that zones extending into and northwest of the MLA may not be accurately modeled. However, none of the capture zones extended into the questionable area and, therefore, the model, without modification, is believed to be adequate for the intended purposes of this project. In addition to reviewing previous work and examining new insights from Wells 27M and 29T, the water quality of the Federal Way aquifers was briefly examined. Because of the large number of water quality parameters normally tested, and the typical results of "not detected" for many of these parameters, five parameters with detectable results were chosen for a more detailed study. These were: iron, manganese, chloride, nitrate, and specific conductance. Results of the study indicate that ground water in the Federal Way area is generally of high quality, except for high concentrations of manganese. The data does indicate that, in a general sense, development of the upland has affected the ground water quality to some degree. While the water is generally of high quality, there are signs that nitrate and specific conductance are increasing with time. The data also shows that each of the aquifers have slightly different chemistries, and generally can be differentiated, based on chemistry, into shallow and deep groups. The RMC and the Well 16 aquifers are generally similar, and are distinct from the chemical signatures of the FWDA and the deeper EUA aquifers. The MLA is unusual in that it fits more with the shallow aquifer chemistry than that of the deeper aquifers. This may be Conclusions and Recommendations 7-1 because the MLA itself is relatively shallow at its northeastern end though relatively deep at its southwestern end; it could also be because it is recharged primarily by leakage out of the RMC. Following the water quality review, preparation was made to define the capture zones. Defining capture zones using the selected numerical modeling approach is a two-step process. First, the model is run to establish and record the predicted water level surfaces for the stress conditions of the intended run. These model results are then input to a particle tracking program which determines the pathways and travel times of ground water particles implied by those surfaces. The model was run with MODFLOW to generate head values; the particle tracking program used was MODPATH. Two sets of stress conditions were used for the MODFLOW runs. The first involved a time period of ten years over which there was a simulated 16 inches of precipitation recharge each winter, and no precipitation recharge in the summer. In this simulation, each well was assumed to produce year-round at its average production rate. Results of this run were used to delineate the one-, five-, and ten-year capture zones for each well. The second run also used average production values and 16 inches of natural recharge per year, except the run was for 100 years and the recharge was not divided into summer and winter periods. This run was used to delineate 100-year capture zones. In addition to delineating capture zones, the results of the MODPATH particle tracking were used to generally describe how water moves through the regional ground water system. Aquifer and confining layer properties greatly affect the direction and speed of water movement through the system. In clay -rich confining layers, water moves generally in a downward, vertical direction at speeds as low as several feet per year. However, through till layers, water can move more than 100 feet per year and move hundreds of feet horizontally as it travels downward through the till. In aquifers, water can move thousands of feet horizontally at speeds of hundreds of feet per year. One-, five-, ten-, and one hundred -year capture zones were delineated for each LUD production well. These zones, as depicted on Figures 15-26, represent the two-dimensional expressions of the three-dimensional volumes that supply water to the wells within the stated time periods. They are the best technical representations of the areas that contribute water to each of the wells. However, even with the high degree of technical analysis involved, they should not merely be accepted at face value as equivalent to the WHPAs due to uncertainties inherent in the model. Uncertainties that must be considered when using the delineated capture zones to define wellhead protection areas include: • modeling error due to portions of the model being less reliably defined ■ inaccuracies due to model response to cell drying ■ incomplete travel time calculations due to the fact that MODPATH does not include travel through the vadose (nonsaturated) zone 7-2 Conclusions and Recommendations • error introduced by simulating well placement at the center of the model cells in which they occur • uncertainty in the assumption that the stress conditions (pumping and recharge) used in the model were actually represent future, "real world" stresses • variability in capture zone shape resulting from defining particle starting locations How these uncertainties affect the definition of capture zones is demonstrated by the three supplemental model runs that were made following the initial capture zone delineation. Long- term changes in production rates can greatly affect capture zones for both the well in which the production is changed and for its neighboring wells. As compared to production changes, captures zones appear to be relatively insensitive to recharge changes (within the expected range of possible recharge rates). Even so, the differences seen for the various recharge rates in the supplemental runs show that even relatively insensitive factors can affect the outer edges of predicted capture zones. While the wellhead protection areas are necessarily based upon the capture zones, other factors need to be considered when defining the WHPA boundaries. The capture zones are based on a numerical model which was built from a well -substantiated conceptual model and an extensive hydrogeologic data study. In the effort of defining the WHPA, compensation was made for the uncertainty in the capture zones by invoking the understanding of hydrogeologic response gained from the conceptual model and from data analysis. Therefore, the areas recommended for wellhead protection management, as presented on Figures 30, 31, and 32, are based on an interpretation of the capture zones, recognizing where model confidence is high or low, and by compensating where appropriate by applying our hydrogeologic knowledge of the upland and our insight for the responses of the ground water system in the area. However, if current production patterns are significantly altered on a long- term basis, changes that may result cannot be factored into the current WHPA definition. Should significant changes occur, re-evaluation of the affected capture zones and WHPAs should be accomplished. Production changes that may require WHPA re -calculation include long-term increases or decreases in average production rates at any well or related set of wells, decommissioning of any well, or the addition of any major production well in the aquifers currently used for production. The wellhead protection areas for the three major aquifer systems are shown on Figures 30, 31, and 32, and are also available on computer disk in an AUTOCAD-compatible format. The WHPAs are designated, using the DOH -recommended terminology, as: Zone 1, Zone 2, Zone 3, and Buffer Zone. Zone 1 is based upon the defined one-year capture zones. Zone 2 is based upon the defined five-year capture zones. Zone 3 is based upon the defined ten-year capture zones. The Buffer Zone is based upon the 100-year capture zones. Separate zones are presented for each aquifer system because it is likely that the final WHPP may wish to afford Conclusions and Recommendations 7-3 different levels of protection and different types of management to zones within the different aquifers. For example, RMC wells will need a greater degree of protection than FWDA wells. The WHPP will need to give special consideration to the lakes within the WHPAs. While none of the lakes are believed to be in direct continuity with the aquifers, they definitely contribute water to the aquifers. Consequently, if the surface drainage areas for the lakes are not already in the WHPAs, the WHPP should consider adding the draining areas to the appropriate Buffer Zone. 7_4 Conclusions and Recommendations LAKEHAVEN UTILITY DISTRICT WHPA DEFINITION REFERENCES Becker, J.E., 1992, Hydrogeologic analysis of the Federal Way area, Washington: prepared for Federal Way Water and Sewer District by Robinson & Noble, Inc., Volume 1, 122p. Driscoll, F. G., 1986, Groundwater and wells: St. Paul, Johnson Division, 1089 p. Fetter, C.W., Jr., 1980, Appliedl ydrogeolog: Columbus, Charles E. Merrill Publishing Company, 488 p. Krautkramer, F.M., 1993, Federal Way Water and SewerDistrict construction report for monitor well 27M.• prepared for Federal Way Water and Sewer District by Robinson & Noble, Inc., 9 p., figures, attachments. McDonald, M.G., and Harbaugh, A.W., 1988, A modularthtre-dimensional finite-differea;ceground- waterflow model. U.S. Geological Survey Techniques of Water -Resources Investigations Book 6, Chapter Al, 586 p. Pollack, D.W., 1994, User's guideforMODPATH/MODPATH--PLOT, version 3: a particle tracking post processingpaekage forMODFLOW, the U.S. Geological Survey finite-differeveeground water flow model. U.S. Geological Survey Open File Report 94-464, 6 sections, appendices. Robinson & Noble, Inc., 1991, letter to Steve Weinke from F. Michael Krautkramer concerning septic tank issues, 3 p., figures. Robinson & Noble, Inc., 1993, Report of construction andfindings, Federal Way Water and Sewer District exploration We1129T.- prepared for Federal Way Water and Sewer District, 12 p., figures, appendix. Washington State Department of Health, 1995, Washington State wellhead protection program guidance document: Washington State Department of Health, 78 p., appendices. Woodward, D. G., et al., 1995, Occurrence and quality of ground water in southwestern King County, Washington: U.S. Geological Survey Water -Resources Investigations Report 92-4098, 60 p., plates. References 7-5 Figure I 30 28 All Wells Iron Concentrations 26 1990-1995 24 v 22 I j Q 20 Measured iron concentration from 18 routine water quality sampling. N 14 The MCL for iron is 0.3 mg/I. The 1 p median concentration for south- L 12 ! western King County is 0.035 mg/ -p I (Woodward, et. al., 1995). E 10 z 8 I I 6 1 4 I I 2 i I 0 I i 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 i Concentration (mg/1) 18 - RMC Wells 18 MLA Wells 1 16 I I 16 I 1 v 14 I CU v 14 I 'I E 12 � � 12 ") 10 ILn 10 I v 8 !Iv 8- 1 6 1 i� 6 - I � 1 z 4 I Iz 4 I 1 2 j� 2 I 0 Ij I 0 ! - 1 1 0 O 0 0 0 0 0 0 0 o - N W -P V 0o I 1 1 o 0 0 0 0 0 0 0 0 f O - fV W -A U9 b, V 07 1 Concentration (mg/I)18 I Concentration (mg/1) 18 EUA Wells I - FWDA Wells j 1 16 I l6 v 14 I v 14 I I 12 Q 12 I ! '^ 10 ru �� 10 i I v 8 0 `v 8 E 6 E 6 I ! z 4 1 'z 4 ! 2 �� 2 i 0 I 0 O 0 o N W U9 O, V 00 i 1 I 0 0 0 0 0 0 0 0 0 p - N W A U1 O� V OD 1 Concentration (mg/1) Concentration (mg/1) J Figure 2 - 10 I All Wells 8 ;v 1 � 1M 6 sV) 1`-- O I� �� 4 :z I Z 1 I I 0 I Manganese Concentrations 1990-1995 Measured manganese concentrations from routine water quality sampling. The MCL for manganese is 0.05 mg/I. The median con- centration for southwestern King County is 0.04 mg/I (Woodward, et. al., 1995). o 0 0 0 0 0 0 0 0 0 0 0 0 f N fv fV tj W O fV U1 V O N U1 V O N U1 V O O Ln O ul O U1 O Ln O Ul O Ul O Concentration (m /1)I 10 r 10 RMC Wells 1 MLA Wells 8 8 ' 2 7 i' E 7 6 �u 6 0 5 I:0 5 I 4 -- ! 1� 4 I Z) 3 ! �E 3 1 I z I 2 I Iz 2 I I 0 it 1` 1 0 i I oOOOOOOOoOoOo O o O OoOOOOooO O CD O O O— —— OOOO — —— — N N N N W Ln o .n L" o Lnto o Ln o o I NJ 14 NJ Ki I o Ln o Ln o Ln o Ln un o Ln o oo I Concentration (mg/1) I Concentration (mg/1) t 10 EUA Wells I r 10 FWDA Wells 1 [I 9 8 a 7 'Q 7 1 i I � 6 I� 6 0 5 I; 0 5 4 4 i 3 I I� 3 I z 2 Iz 2 �o ° �f F C rF1T17T_F1 I o O O o 0 0 o O o 0 o O o II o o O o 0 0 0 0 0 0 0 0 o " 0 0 0 0 -• -- --• N NJ Ili IliW N N N N W O N In V O N Vl V O N In -40 I O N In V O N Vl V CD N In V O ' O Ln O kn O cn o u1 O u1 O to O O ut O In O u7 O In O Ln O u7 O I Concentration (mg/1) f 1 Concentration (mg/1) Figure 3 i 24 I 22 ' 20 �v 18 I Nitrate Concentrations 1990-1995 C- 16 Measured nitrate (as nitrogen) con- �n 14 centrations from routine water quality sampling. The MCL for 0 12 nitrate is 10 mg/, however, the median for southwestern King County is less 1 ) 10 i than 0.1 mg/I (Woodward, et. al., E 8 [ 1995). Iz 6 I I 4 i 2 f . I I 0 t I O o O O - — ►J j O N Ul �J O N 111 _Il O i O In O Ln O Ln O Ul O i I Concentration (mg/1) r 12 RMC Wells 1 r 12 MLA Wells 1 10 N 10 I v I v I 8 1 1E 8 I ti :Iti i I 0 6 i0 6 v 1 E 4 1 E 4 i z ! 2 1 2 I 1 0 I 0 I ' � 1 O O O O — — -- — N I O O O CDN I 1 O N In V O N In V O 1 1 O N In V O N lJ I V O I O In O In O In O In CD O In O In O In O In O 1 Concentration (mg/1) Concentration (mg/1) 12 EUA Wells r 12 FWDA Wells 1 10 1 10 CL 1 ;= 8 11E 8 I 0 6 1 ;0 6 I E 4 I 4 j Iz I�z 2 I .2 n f�� 0 f 0 l l i l l l O — -- -- -- N O O O O f j I O IliLn V O ry In V O 1 O N In V O N In V O O In O Ul O In O In O O Ln O In O In O Ln O ; Concentration (mg/1) j I. Concentration (mg/1) Figure 4 j 14 Al Wells Chloride Concentrations 12 1990-1995 1 v 10 I i Measured chloride concentrations 8 I from routine water quality sampling. I L&- I The MCL for chloride is 250 mg/I; o however, the median for south- v 6 i western King County is 2.9 mg/I I Q I (Woodward, et. al., 1995). 4 i z 2 I 1 I 0 I I I I 0 1 2 3 4 5 6 7 8 9 10 Concentration (mg/1) r 12 RMC Wells I r 12 MLA Wells 1 1 1 10 1 10 — I i a 8 l i E 8 ! V) ) � I � 0 6 1 0 6 v v ! 4 i l E 4 I Z I Z 1 I 2 I 2 • 1 ; 0 l i 0 T 0 1 2 3 4 5 6 7 8 910 1 i 0 1 2 3 4 5 6 7 8 910 I 1 Concentration (mg/1) Concentration (mg/1) / J 12 EUA Wells i r 12 FWDA Wells 1 10 : ] 10 v Iv ! E 8 I I 8 ,n 1 0 6` 0 6 i Q) cu I 1_ 4 1 E 4 . I 7 Z Z I 2 2 i 0 i t 0 i 0 1 2 3 4 5 6 7 8 910 0 1 2 3 4 5 6 7 8 910 r Concentration (mg/11 I Concentration (mg/1) J J Figure 5 2 All Wells I Specific Conductance 'v'Nues 10 1990-1995 v Measured conductance values from 8 routine water quality sampling. The N MCL for conductivity is 700 umhos/cm; O6 however, the median southwestern King County value is 174 umhos/cm L ! a i (Woodward, et. al., 1995). �E 4 �z I 2 I I � -- -- -- — NJIV O N l!7 v O fV O M O In O M IV IV In --j O Ln W O O W N In Concentration (umhos/cm) r 1 RMC Wells 12 MLA Wells i I 10 l 10 v 8 I I v IE 8 1 V) 1� 0 6 ! 0 6i I 4 4 z 1 Z3 iz [ I 2 2 I I 0 I 0 I I —� NJ IV NJ N W O Ul -O Ln O Un O Ul O W I Qn I I I —. � -r —. N tV N N W W O Ul O Ul O Ln O Ul O Ul Concentration (umhos/cm) I Concentration (umhos/cm) 12 EUA Wells I 12 FWDA Wells v 10 — I �. 10 — I � 8 i a 8 � I ) 0 6 I � ) `0 • 6 I a L I� I 4 i I 4 z I z I ! Z 71 Z 0 �1 0 I [ : —� II J N NJ N W O N Ul -Il O N U1 V O O Ln O Ul O kn O UI O W I N Vl I I I -- -- N N IlitV W W O N U9 V O IN VI V O IV O Ul O Ul O Ul O Ul O Ul Concentration (umhos/cm) I Concentration (umhos/cm) J � Figure 6 E s Average nitrate (as nitrogen) concentration versus chloride concentration versus specific conductance value for the Federal Way upland aquifers, 1990-1995 LUD data set. North RMC includes Wells 7, 17, 17A, 18, 20A, and 23A. South RMC includes Wells 10, 1 OA, 15, 15A, 19A, and 21. EUA (shallow) represents Well 16. EUA (deep) includes Wells 1 OC, 22, and 22A. FWDA includes Wells 17B and 19. Figure 7 Ground Water Production, Lakehaven Utility District, 1990 - 1995 20 All Wells 15 10 5 0 1990 10 5 rn E c 0 0 1990 0 L QU 1-J 5 0 0 0 'Ln V 1990 10 ----- 5 ----- 0 1990 10 ----- 5 0 1990 1991 1992 1993 1994 1995 1996 RMC Wells 1991 1992 1993 1994 1995 1996 MLA Wells 1991 1992 1993 i } i 1991 1992 1993 i 1991 1994 1995 1996 EUA Wells ---------------- ----- ----------------- 1994 1995 1996 F\ /DA Wells i s --------------- 1992 1993 1994 1995 Em 11 N d B T21N T20N . .. i APPROMATE GROUND WATER DIVIDE T22N T21N T 21 N T20N w w FIGURE 8 w w Modeled Potentiometr.ic Surface, Vashon Advance Aquifer System, Layer 2, 1991 LAKEHAVEN UTILITY DISTRICT ROBINSON & NOBLE. //VC. 0014" B� T21N T20N %. i APPROXIMATE GROUND WATER DIVIDE W W Modeled Intermediate Aquife T 22N T21N T 21 N T 20 N FIGURE 9 r Potentiometric Surface, System, Layer 4, 1991 LAKEHAVEN UTILITY DISTRICT R09INSON & NOBLE. INC. CIa*'O�41- 4-1 T 21 N T20N ' ��/"" APPROXIMATE GROUND WATER DIVIDE l W W M T22N T21N T 21 N T20N FIGURE 10 Modeled Potentiometric Surface, Deep Aquifer System, Layer 6, 1991 LAKEHAVEN UTILITY DISTRICT a R0.6iNSON & NOBLE. INC. n8*.-2L 'ON 8Or `9661 l6dV r r Q Ln n O L �r �v cV N O Q J CD 1- F ��r ^, 4/nt � f �L �0 G 0 Q) Lo J J ?tb L N _ W U L v, m L K TACF Q o_ Z J dwLir0 Q Q� �Q L .j c c� o Q Lr) Hlbd-odv\o -i\so 1imv8G 300, 200' 100' 0' —100, —200' —300' —400' _300' —600' —700' I WELLS WELL 17/17A 20 --� 17B �— C NO TES, 1) ✓'c W IS INTENDED TO S OW GROUND 01A TER PA THS ONL )" NIEL L SCREEN L OCA TIONS,, LAND SUP, FA C_F; 01A T FR TABL F, Ai ID L A YER, CONTA C TS AP,F APPROX,IA/rA TE 2) PFEDIC TED T RA VEL T/AI S FOR THE G,ROUN5 VIA TER PA THS ARE GIVEN ON TABL F & D cc i 00 r- 0 z m 0 MILE FIGURE 11b 1/2 Sample of Modeled Ground Water Paths to hree Wells, sc Cross Section View LAKEHAVEN UTILITY DISTRICT a R09INSON & NOSLE, INC. T27N t i t i wlw pM� PUCE s 5 q T21N 3 STEEL LAKE' A/ff' LQFF n Li 23 LAKE a OIfE7�' LA >s K XA VE n NORTH L LAKE u T7?N w M 000 5� pU�E w 6 � 5 q T 21 N 3 SIE'EL LAKE AKC 11(JO[1mF �u} n e 9 14 10 V ELL 23 LAKE pREnB LA is 14 XA 17 is [AVRm 15 � KE T22N wf w T21N pM "g S000 , fl 5 q 3 PUCE AKE aLOFF r L a a 1D 10 V ELL 23 LAKEAR d pRElVF L a ,s 14 XA dE ,a n [AVRrNKE 1s MLE 1/2 , SCALE CAPTURE ZONE AT TOP OF MIRROR LAKE AQUIFER. 12a. CAPTURE ZONE AT TOP OF CONFINING LAYER (LAYER 3) AND BOTTOM OF RMC. 12b. CAPTURE ZONE AT WATER TABLE SURFACE (WITHIN LAYER 1 AND 2, VASHON TILL AND RMC). FIGURE 12 Vertical Discretion of 100—Year Capture Zone, Well 23 LAKEHAVEN UTILITY DISTRICT ° ROBINSON & NOEL E. INC. T22-N t i wlw D SOON P� G E 6 66 5 T 21 N 3 AKE ott � LAKE LAKE it 8 B 10 D n N ELL 23 LAKE o �� a C ,s x I!'A n L4��H 15 n, �c T 22 ,jN "► l J l• j r ■' + J ■ WE 1 0 1/2 1 SCALE TWO—DIMENSIONAL CAPTURE ZONE FOR WELL 23 WITHIN THE MIRROR LAKE AQUIFER. 13a. SURFACE AREAS WHICH CONTRIBUTE RECHARGE TO WELL 23. 13b. TWO—DIMENSIONAL REPRESENTATION OF THE THREE—DIMENSIONAL, 100— YEAR CAPTURE ZONE FOR WELL 23. NOTE THE AREA ENCOMPASSES BOTH THE ABOVE AREAS. 13c. 1 S cc is FIGURE 13 100—Year Capture Zone, Well 23 LAKEHAVEN UTILITY DISTRICT < ROONSON & NOBLE. INC. nS4-SL 'ON 80r 966L 11W w W Z 0= 0Li F- in W >- 0 Z Z CLQ O Q H Q �,- H ~ ui Q J Z J W a J U Li L- 3?0 K -,099� T (D ,-- W i cif/ i . r � Z O f- Q U O J U Z �QLki a� CLCf) J J Q M U U O W I- F- r W w 0 dZ W Q Q QO d d UN c /'i 0 v O z O Z �- W a U OJW Jj Z > w Z 3 �s 0 O Uj j co I.,.l p w a U QN Q Q W J 0 J p Jp J O W W �xl N J �i0� L41 p Z O = In Or rnp �C Q I L O CL H OLd Z V�z W U W LJa i v a W W Q U J U Z � J W J J p JJ L,.I LLJ m :�: U K—,099—�I �1 IH1a'ViaVn�l \ 777 T O - � co I 1 \ T nez - i K—,099—�I K--33ediat A--M of �fi C W • � J O p -O rna •V � a � CL —_ O U U N W 0 N W N Q Q w ci vi aw Z N O W N Z O W N M W H MCL I-- U CL Q 0 U J p w (xO Om 3Z W J = F- Q F- z�3 I n ME 0 ,/2 1 SCALE Well 16 and Redondo —Milton Channel FIGURE 15 1—Year Capture Zones, Aquifer Wells, Layer 2 LAKEHAVEN UTILITY DISTRICT a a r C C U a a 0 0 ROBIN5O11 & NOBLE, INC n MIS M.E o i Of 0 1/2 1 SCALE FIGURE 171 1—Year Capture Zones, Federal Way Deep Aquifer Wells, Layer 6 LAKEHAVEN UTILITY DISTRICT oc a r c 2 a c ROOIN50N & NOBLE, INC. n r I FIGURE 18 1i2 5—Year Capture Zones, s Well 16 and Redondo —Milton Channel Aquifer Wells, Layer 2 I LAKEHAVEN UTILITY DISTRICT R03INS0111 & NOBLE, INC. n MLE � 1 of 16 o 1/2 1—Year Capture Zones, SCALE Wells 10C, 22/22A and Mirror Lake Aquifer Wells, Layer 4 LAKEHAVEN UTILITY DISTRICT ROBINSON & NOBLE, INC. n FIGURE 20 MLE x rK o 1/2 1 5—Year Capture Zones, ` SCALE Federal Way Deep Aquifer Wells, Layer 6 LAKEHAVEN UTILITY DISTRICT I L 1 G ROBINSON & NOBLE, INC. i Dc a r c a c a 0 0 0 1?OBINSON & NOBLE, INC. 11 FIGURE 19 ME 12 5—Year Capture Zones, , S� Wells 10C, 22/22A and Mirror Lake Aquifer Wells, Layer 4 LAKEHAVEN UTILITY DISTRICT ROBINSON & NOBLE, INC. fl E I FIGURE 23 ML 112 , 10—Year Capture Zones, ' Federal Way Deep Aquifer Wells, Layer 6 SC&E LAKEHAVEN UTILITY DISTRICT ROBINSON & NOBLE, INC. 1-I ME 1/2 1 SCALE ' w cr FIGURE 22 10—Year Capture Zones, Wells 10C, 22/22A and Mirror Lake Aquifer Wells, Layer 4 LAKEHAVEN UTILITY DISTRICT `. ROBINSON & NOBLE, INC. c r I � x I ofFIGURE 24 o ,/2 100—Year Capture Zones, SCALE Well 16 and Redondo —Milton Channel Aquif er Wells, Layer 2 LAKEHAVEN UTILITY DISTRICT ROBINSON & NOBLE, INC. F-1 ME C � FIGURE 25 q 1/2 1 100—Year Capture Zones, SC;LE Wells 10C, 22/22A and Mirror Lake Aquifer Wells, Layer 4 LAKEHAVEN UTILITY DISTRICT ROBINSON & NOBLE, INC. kc Cr a M �+ FIGURE 26 MLE Of x 1/2 , 100—Year Capture Zones, Federal Way Deep Aquifer Wells, Layer 6 SME LAKEHAVEN UTILITY DISTRICT ROBINSON & NOBLE, INC. LEGEND WELL 10/10A CAPTURE ZONE WITH AVERAGE PRODUCTION WELL 10/10A CAPTURE ZONE WITH MAXPdIM PRODUCTION OTHER CAPTURE ZONES AFFECTED BY WELL 10/10A PRODUCTION CHANGE Li I Li � MILE � � FIGURE 27 0 1/2 Production Sensitivity, 5C Change in 10—Year Capture Zone in South RMC LAKEHAVEN UTILITY DISTRICT a I a r C a c 6 O 0 a ROBINSON & NOBLE, INC. 11 LEGEND MLE I af FIGURE 28 o 1/2 Recharge Sensitivity, Deficit, SCALE t Change in 10—Year Capture Zone, Well 10/10A LAKEHAVEN UTILITY DISTRICT 0 ROBINSON & NOBLE, 11VC. A LEGEND WE w w FIGURE 29 o 1/2 Recharge Sensitivity, Excess, SCALE Change in 10—Year Capture Zone, Well 10/10A LAKEHAVEN UTILITY DISTRICT a d i a r C C Q a a a ROBINSON & NOBLE, INC. 1 - LEGEND - j ZONE 1 ZONE 2 N2 33 34 ZONE j BUFFER ZONE 1 6 5 4 3 _- ......... ... .. _ — -..... NJELL 23A f WELL 24A mo t 1„ , 7. 111LL 8 , 9 10 f 10 11 i .: A. 15 14 13 WIELL 18 S7 10 15 17/17 ti VVELLIa WEM 1 O/1 OA 22 23 24 14 21 22 ' t d --.. 27 • 26 WELL 21 15/15A j o5 30 28 VVELL 16 27 34 RCi 31 �. 32 .33 34 T21N T 20 N 3 2 1 6 5 4 3 35 T22N. T21N I 2 11 14 23 26 35 T 21, N T20N 2 FIGURE 30 MU 0 1/2 Wellhead Protection Areas for Wells in the Qva Aquifer System, Layer 2 SCALB ROBINSON&NOBLE, INC. LEGEND ZONE 1--- - - - - - N ZONE 2 2 33 34 ZONE 3 BUFFER ZONE 3 5 S 4 3 r 2,1 r - 11 r10 WELL 2-3 u.: 35 T 22 T 21 2 m • � WELL 20 WELL i 15 j 14 l,3 18 17 16 15 14 22 �l 23 24 19 � 20 21 22 23 27 26 25 29 28 27 26 \- 30 34 ` 95 36 31 32 '33 34 35 T21 N �. N T 20 N WELL 22/22A T 20 N 1 ' 3 2 • 6 5 4 3 2 FIGURE 31 0 1/2 I Wellhead Protection Areas for Wells in the Intermediate Aquifer System, Layer 4 LAnHAVEN UTILITY DISTRICT ROBINSON $NOBLF, MC. j LEGEND E ZONE I CI ZONE 2 r ZONE 3 0 BUFFER ZONE , 1 'OU a y 15 F l4 2 I 16 34 35 3 T 2I N T 20 Iv 2 7 o � SCALE FIGURE 32 Wellhead Protection Areas for Wells in the Deep Aquifer System, Layer 6 LAKEHAVEN UTII_M DISTRICT ROBIAWN & NOBIF- INC.