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20-102998-Drainage Technical Information Report-08-10-2020-V1 PRELIMINARY TECHNICAL INFORMATION REPORT Proposed Redondo Heights Senior Living Apartments 27400 Pacific Highway South Federal Way, WA 98003 Prepared for: Morgan Design Group LLC 11207 Fremont Ave N Seattle, WA 98133 August 10, 2020 Our Job No. 17157 8/10/2020 17157-TIR.doc TABLE OF CONTENTS 1.0 PROJECT OVERVIEW Figure 1 – Technical Information Report (TIR) Worksheet Figure 2 – Site Location Figure 3 – Drainage Basins, Subbasins, and Site Characteristics Figure 4 – Soils Map 2.0 CONDITIONS AND REQUIREMENTS SUMMARY 2.1 Analysis of the Nine Core Requirements 2.2 Analysis of the Five Special Requirements 3.0 OFF-SITE ANALYSIS 4.0 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN A. Existing Site Hydrology B. Developed Site Hydrology C. Performance Standards D. Flow Control System E. Water Quality System 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN 6.0 SPECIAL REPORTS AND STUDIES 7.0 OTHER PERMITS 8.0 ESC ANALYSIS AND DESIGN 9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT 10.0 OPERATIONS AND MAINTENANCE MANUAL 1.0 PROJECT OVERVIEW 17157-TIR.doc 1.0 PROJECT OVERVIEW This project is located on a 2.52-acre parcel within a portion of the Northwest quarter of Section 33, Township 22 North, Range 4 East, Willamette Meridian, City of Federal Way, King County, Washington. More particularly, the site is located at 27400 Pacific Highway South, Federal Way, WA 98003 on APN 872992-0040. A portion of this project site was previously cleared and graded as part of an overall development including the three parcels directly west of this site (APN: 872992-0010, -0020, and -0030).The four parcels combined total approximately 5.24 acres. This parcel was left undeveloped with the exception of the permanent detention pond that was constructed on the southern section of the site serving the development of all four parcels. The existing site has flat to moderate slopes with a combination of open areas, detention pond, and dense vegetation. The site slopes downward in the eastern direction falling approximately 13 feet across the site. This project proposes to construct three apartment buildings for senior housing. The buildings will each have an underground basement level to provide parking, and a portion of the basement level will daylight to accommodate the changing grade on site. The existing detention pond to the south will be regraded to increase pond capacity based on new flow control sizing standards described in more detail within this report. The developed site will be approximately 1.54 ac (61%) hard surfaces, 0.39 ac (16%) pond area, and 0.58 ac (23%) vegetated areas. The existing detention pond was sized to provide what is now considered Level 1 flow control under the current King County Surface Water Design Manual (2016 SWDM). As the project was previously constructed this was adequate storage for the area at the time, however the site now is required to provide Level 3 Flow Control for new developments. During a pre-application meeting with the City of Federal Way, the sizing for the new site will be as follows: “There is no direct (1:1) correlation between the old and new pond sizing criteria; however, based on city staff consultation with King County SWDM engineers, the following has been determined to be the appropriate approach in determining if the existing detention pond can meet the current standard: a. Analyze the project utilizing the Level 1 Flow Control standard, and determine the required pond volume under that standard; b. Analyze the project utilizing the Level 3 Flow Control standard, and determine the required pond volume under that standard; and c. The difference in volume between the Level 1 and Level 3 Flow Control Standards is the volume that the new project needs to provide, either on-site, OR, the existing pond can be modified to provide the required volume, OR, the existing pond can remain un- altered, if the analysis described above shows that that it has adequate capacity as constructed.” The existing pond will be modified to provide the calculated new volume of 1.607 acre-feet or 70,000 cubic feet of storage. Please see section 4.0 of this report for further information on how that sizing was achieved. For water quality, as this is a commercial site, Enhanced Basic water quality is required for all pollution generating surfaces in order to protect groundwater and the adjacent stream and 17157-TIR.doc wetland. Treatment will be provided by a Stormwater Treatment Wetland constructed in the bottom of the detention pond using plants to remove pollutants. This treatment option qualifies for Enhanced Basic water quality treatment per the 2016 King County SWDM. FIGURE 1 TECHNICAL INFORMATION REPORT (TIR) WORKSHEET SHAG c/o Bryan Park Redondo Senior Housing 27400 Pacific Hwy S Federal Way, WA 98003 33 4 E 22 N Dan Balmelli, PE Barghausen Consulting Engineers, Inc. (425) 251-6222 27400 Pacific Hwy S Federal Way, WA 98003 N/A 8/10/20 8/10/20 Lower Puget Sound Level 3 Flow Control (modified), Enhanced Basic WQ Menu Alderwood gravelly sandy loam 8-15% N/A N/A N/A TBD N/A TBD 1 Redondo Heights - total site Commercial Ponds Stormwater Wetland 08/07/2020 FIGURE 2 SITE LOCATION barg h au senCONSUL T ING EN G I N E E R S ,INC.Horizontal: Scale: Vertical: For: Title: VICINITY MAP Job Number 18215 72ND AVENUE SOUTH KENT, WA 98032 (425) 251-6222 (425) 251-8782 CIVIL ENGINEERING, LAND PLANNING, SURVEYING, ENVIRONMENTAL SERVICES N.T.S.N/A 17157 DATE: 04/06/15 Redondo Heights Senior Housing Federal Way, Washington P:\17000s\17157\exhibit\graphics\17157 vmap.cdr REFERENCE: Google Maps (2015) SITE FIGURE 3 DRAINAGE BASINS, SUBBASINS, AND SITE CHARACTERISTICS SHEET TITLE:08/10/2020SHEET #REVISIONDATESCALE:DATEDRAWN:DESIGN:JOB:COPYRIGHT: USE OF THIS DRAWING © 2020 MORGAN DESIGN GROUPWITHOUT AUTHORIZATION OF MORGANWITHOUT THEIR WRITTEN CONSENTDESIGN GROUP IS PROHIBITED MASTER LAND USE PERMIT MORGANDESIGNGROUPLLC11207 Fremont Ave NSeattle, WA 98133Tel: 206-375-3397Fax: 866-847-6420www.morgan-design.netArchitecture & BuildingEnvelope ConsultingCorporate Member of A.I.A.REDONDO HEIGHTS SENIOR LIVING APARTMENTS 27400 PACIFIC HIGHWAY SOUTH FEDERAL WAY, WAMLUP SUBMISSIONKnow what'sbelow.before you dig.CallRWEDASDKB08/10/20202020003APPROVED:1 of 1PRELIMINARYBASINMAP1"=30' FIGURE 4 SOILS MAP barg h au senCONSUL T ING EN G I N E E R S ,INC.Horizontal: Scale: Vertical: For: Title: SOIL SURVEY MAP Job Number 18215 72ND AVENUE SOUTH KENT, WA 98032 (425) 251-6222 (425) 251-8782 CIVIL ENGINEERING, LAND PLANNING, SURVEYING, ENVIRONMENTAL SERVICES N.T.S.N/A 17157 DATE: 04/06/15 Redondo Heights Senior Housing Federal Way, Washington P:\17000s\17157\exhibit\graphics\17157 soil.cdr REFERENCE: USDA, Natural Resources Conservation Service LEGEND: AgC = Alderwood gravelly sandy loam, 8-15% slopes SITE 2.0 CONDITIONS AND REQUIREMENTS SUMMARY 17157-TIR.doc 2.0 CONDITIONS AND REQUIREMENTS SUMMARY 2.1 Analysis of the Eight Core Requirements Core Requirement No. 1: Discharge at the Natural Location. Response: This site currently drains to a detention pond that was previously constructed. The pond discharges east through the Club Palisade apartment complex before ultimately draining north in South Star Lake Road, before going east in S. 272nd Street into a larger wetland. This discharge location will remain with this development. Core Requirement No. 2: Off-Site Analysis. Response: A Level 1 Downstream Analysis is included within this Technical Information Report, as required by King County. Core Requirement No. 3: Flow Control. Response: Flow control on this project will be provided for in the form of a detention pond. As discussed in Section 1.0 the level of detention provided will be the required storage to meet Level 3 Flow Control, minus the required storage to meet Level 1 Flow Control. Core Requirement No. 4: Conveyance System. Response: As this development is less than 10 acres in size, the conveyance system is sized based on the Modified Rational Method utilizing a 100-year precipitation event and a Manning's 'n' value of 0.012 for the pipes. Conveyance calculations will be provided in the Final TIR. Core Requirement No. 5: Erosion and Sediment Control. Response: During construction site runoff will be routed to the existing detention pond to settle out sediment prior to discharge. There will be a silt fence around the entire perimeter of the site, along with a construction entrance installed off the private access. The clearing limits will be the property boundary to the north, south, and east with the west limits being the proposed saw-cut line approximately 2 feet off the edge of existing curb line. For further information please see the attached SWPPP and TESC plan. Core Requirement No. 6: Maintenance and Operations. Response: An Operations and Maintenance Manual will be included with the Final TIR. The party responsible for maintenance of the stormwater facilities will be determined in the final TIR. Core Requirement No. 7: Financial Guarantees and Liability. Response: This project will conform to all financial guarantee and liability requirements that King County and Federal Way require for projects of this nature. Core Requirement No. 8: Water Quality. Response: The Water Quality Menu followed in accordance with the King County Surface Water Design Manual requires Enhanced Basic water quality treatment for this commercial development. A stormwater treatment wetland will be installed at the bottom 17157-TIR.doc of pond to meet the level of treatment required. Additional plantings will be planted for pollutant removal in accordance with the KCWSDM. Core Requirement No. 9: Flow Control BMPs. Response: Small Lot BMP Requirements 1. Full Dispersion - Full dispersion is infeasible because there is not enough native vegetated surface area that could be used for full dispersion. 2. Full Infiltration of Roof Runoff – The site is not conducive to infiltration and therefore any infiltration is infeasible on this project site. 3. One of following a. Full infiltration - The site is not conducive to infiltration and therefore any infiltration is infeasible on this project site. b. Limited infiltration - The site is not conducive to infiltration and therefore any infiltration is infeasible on this project site. c. Bioretention - Due to limited area on the project site, bioretention is infeasible. d. Permeable pavement - The site is not conducive to infiltration and therefore any infiltration is infeasible on this project site. 4. Basic Dispersion – Basic dispersion of landscape areas on the east side of the project site will be used. Additional dispersion of hard surfaces will not be feasible to prevent downstream erosion issues which were previously noted and described in the Level 1 Downstream Analysis. 5. One of following a. Reduced impervious surface credit - The listed techniques for reduced impervious surface credit do not apply to this project. b. Native growth retention credit – Native growth retention area cannot be credited 6. Soil Amendment - Lawn and landscaped areas will apply KCC 16.82.100(F). 7. Perforated Pipe Connection - Perforated pipe is infeasible due to steep slopes. 2.2 Analysis of the Five Special Requirement Special Requirement No. 1: Other Adopted Area-Specific Requirements. Response: This project is located within the Hylebos Creek and Lower Puget Sound Basin Plan area. The site requires Level 3 flow control due to downstream flooding issues and enhanced basic water quality treatment. Special Requirement No. 2: Flood Hazard Area Delineation. Response: Per FEMA map panel 53033C1235 F, this project in located outside the 500- year floodplain. There is no flood hazard area delineation required for this project site. Special Requirement No. 3: Flood Protection Facilities. Response: This project does not meet the threshold for this requirement. Special Requirement No. 4: Source Control. Response: This project will provide source controls in accordance with City of Federal Way requirements. Special Requirement No. 5: Oil Control. 17157-TIR.doc Response: The proposed development is not designated as a high-use site and does not required oil control. 3.0 OFF-SITE ANALYSIS LEVEL 1 OFF-SITE ANALYSIS Proposed Redondo Heights Senior Living Apartments 27400 Pacific Highway South Federal Way, Washington Prepared for: Senior Housing Assistance Group c/o Bryan Park August 10, 2020 Our Job No. 17157 CIVIL ENGINEERING, LAND PLANNING, SURVEYING 18215 72ND AVENUE SOUTH KENT, WA 98032 (425) 251-6222 (425) 251-8782 FAX BRANCH OFFICES ¨ TUMWATER, WA ¨ LONG BEACH, CA ¨ ROSEVILLE, CA ¨ SAN DIEGO, CA www.barghausen.com 17157-Level 1.doc TABLE OF CONTENTS TASK 1 STUDY AREA DEFINITION AND MAPS EXHIBIT A Vicinity Map EXHIBIT B Downstream Drainage Map EXHIBIT C Upstream Basin Map TASK 2 RESOURCE REVIEW EXHIBIT D FEMA Map EXHIBIT E Sensitive Areas Folios EXHIBIT F SCS Soils Map EXHIBIT G Assessor’s Map EXHIBIT H Wetland Inventory Map TASK 3 FIELD INSPECTION EXHIBIT I Off-Site Analysis Drainage System Table 3.1 Conveyance System Nuisance Problems (Type 1) 3.2 Severe Erosion Problems (Type 2) 3.3 Severe Flooding Problems (Type 3) TASK 4 DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS TASK 5 MITIGATION OF EXISTING OR POTENTIAL PROBLEMS TASK 1 STUDY AREA DEFINITION AND MAPS 17157-Level 1.doc TASK 1 STUDY AREA DEFINITION AND MAPS The proposed Redondo Heights Senior Living Facility will be located on an approximately 2.52-acre lot located within a portion of the Northwest quarter of the Northwest quarter of Section 33, Township 22 North, Range 4 East, Willamette Meridian, City of Federal Way, King County, Washington. More particularly, this site is located at 27400 Pacific Highway South behind existing developments already constructed on that site and has been provided its own lot with access from the south and the north, the south being a park and ride facility and the north being South 272nd Street. The project site lies at the easterly side of the overall development and is located on the west side of Club Palisade apartment complex. There is an existing detention pond on the project site sized for Level 3 Flow Control and the overall development was constructed at that site address. This remaining lot was not constructed; however, the pond was sized to include this site with development on it. The Redondo Heights Senior Living Facility will have 0.47 acre of more impervious surface that what the original pond was sized for. Runoff drains into this detention pond from the overall development exclusive of the gas station at the southeast corner of Pacific Highway South and South 272nd Street. Prior to the construction of the on-site detention pond runoff used to sheet flow onto the Club Palisade apartments westerly drive aisle and erosion was occurring on their property. Construction of the pond alleviated all erosion from occurring on that property any more, and runoff from the pond drains through a 12-inch-diameter pipe to the south to a manhole where it then courses due easterly through the Club Palisade apartment complex in varying size pipes, ultimately draining north in South Star Lake Road and then east in South 272nd Street and then to the north into a large wetland. Please refer to the Off-Site Analysis Drainage System Table located in the later sections of this report. UPSTREAM DRAINAGE ANALYSIS Based on the site visit and analysis of the upstream basin, the only upstream basin contributing flow to this project site is from the overall development covering 5.401 acres, which also includes the 2.52 acres of this proposed site located in to the southeast corner of Pacific Highway South and South 272nd Street. The detention pond was sized to include runoff from this area which will continue to drain to the detention pond after development of the Redondo Heights Senior Living Facility. EXHIBIT A Vicinity Map EXHIBIT B Downstream Drainage Map SHEET TITLE:08/10/2020SHEET #REVISIONDATESCALE:DATEDRAWN:DESIGN:JOB:COPYRIGHT: USE OF THIS DRAWING © 2020 MORGAN DESIGN GROUPWITHOUT AUTHORIZATION OF MORGANWITHOUT THEIR WRITTEN CONSENTDESIGN GROUP IS PROHIBITED MASTER LAND USE PERMIT MORGANDESIGNGROUPLLC11207 Fremont Ave NSeattle, WA 98133Tel: 206-375-3397Fax: 866-847-6420www.morgan-design.netArchitecture & BuildingEnvelope ConsultingCorporate Member of A.I.A.REDONDO HEIGHTS SENIOR LIVING APARTMENTS 27400 PACIFIC HIGHWAY SOUTH FEDERAL WAY, WAMLUP SUBMISSIONKnow what'sbelow.before you dig.CallRWEDASDKB08/10/20202020003APPROVED:C3 of 6PRELIMINARY GRADINGAND STORMDRAINAGE PLAN1"=30' EXHIBIT C Upstream Basin Map SHEET TITLE:08/10/2020SHEET #REVISIONDATESCALE:DATEDRAWN:DESIGN:JOB:COPYRIGHT: USE OF THIS DRAWING © 2020 MORGAN DESIGN GROUPWITHOUT AUTHORIZATION OF MORGANWITHOUT THEIR WRITTEN CONSENTDESIGN GROUP IS PROHIBITED MASTER LAND USE PERMIT MORGANDESIGNGROUPLLC11207 Fremont Ave NSeattle, WA 98133Tel: 206-375-3397Fax: 866-847-6420www.morgan-design.netArchitecture & BuildingEnvelope ConsultingCorporate Member of A.I.A.REDONDO HEIGHTS SENIOR LIVING APARTMENTS 27400 PACIFIC HIGHWAY SOUTH FEDERAL WAY, WAMLUP SUBMISSIONKnow what'sbelow.before you dig.CallRWEDASDKB08/10/20202020003APPROVED:1 of 1PRELIMINARYBASINMAP1"=30' TASK 2 RESOURCE REVIEW 17157-Level 1.doc TASK 2 RESOURCE REVIEW · Adopted Basin Plans: There are no available adopted basin plans for this portion of the City of Federal Way; however, King County in the 2009 King County Surface Water Design Manual and subsequent findings in the downstream drainage course have indicated at the request of the City of Federal Way that Level 3 Flow Control be provided for this project site. In addition to that, stormwater treatment wetlands for Enhanced Water Quality will also be constructed in the pond. · Floodplain and Floodway FEMA Maps: Please see the enclosed exhibit FEMA Map Panel No. 530033C1235 F dated May 1995 which indicates the project site is not located within a floodway or a floodplain of a stream or river. Please refer to that exhibit for the exact location of the project site. · Other Off-Site Analysis Reports: There is a prior approved Off-Site Analysis Report for this overall development is included with the Technical Information Report accompanying this Level 1 Off-Site Drainage Analysis. Please refer to Section 6.0 of the Technical Information Report for that prior prepared report. · Sensitive Areas Folios: The King County Sensitive Areas Folios were reviewed for this site and per their mapping there are no sensitive areas on the project site; however the site does drain to a sensitive area wetland approximately one-quarter mile downstream from the project site. · Road Drainage Problems: This is not applicable. · United States Department of Agriculture King County Soils Survey: Based on the Soils Survey for this portion of King County, the entire project site lies within Alderwood gravelly sandy loam, 8 to 15 percent slopes soil type area, which is a Type C soil. · Wetland Inventory Map: Please see the Wetland Inventory Map located in the later sections of this report for delineation of the wetland in the downstream drainage course. · Migrating River Studies: This is not applicable. EXHIBIT D FEMA Map EXHIBIT E Sensitive Areas Folios EXHIBIT F SCS Soils Map EXHIBIT G Assessor's Map EXHIBIT H Wetland Inventory Map TASK 3 FIELD INSPECTION EXHIBIT I Off-Site Analysis Drainage System Table 17157.002.doc OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLE Surface Water Design Manual, Core Requirement #2 Basin: Lower Puget Sound Subbasin Name: South Star Lake Road Subbasin Number: Symbol Drainage Component Type, Name, and Size Drainage Component Description Slope Distance from Site Discharge Existing Problems Potential Problems Observations of Field Inspector, Resource Reviewer, or Resident See Map Type: sheet flow, swale, stream, channel, pipe, pond; size, diameter, surface area Drainage basin, vegetation, cover, depth, type of sensitive area, volume % Ft. Constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosion Tributary area, likelihood of problem, overflow pathways, potential impacts 1 12-inch PVC Discharge from pond to off-site manhole on park and ride lot 3.9% 0'-30' None Noted None Noted 2 12-inch CPEP Flows east into apartment complex 1.3% 30'-113' None Noted None Noted 3 12-inch CPEP Flows southeast into catch basin ± 1.3% 113'-118' None Noted None Noted 4 12-inch RCP Flows east into catch basin ± 3.4% 118'-289' None Noted None Noted 5 12-inch RCP Flows east into manhole 3.4% 289'-481' None Noted None Noted 6 15-inch CPEP Flows east into manhole 0.46% 481'-630' None Noted None Noted 7 15-inch CPEP Flows east into manhole 0.54% 630'-750' None Noted None Noted 8 30-inch CPEP Flows northeast into manhole ? 750'-990' None Noted None Noted 9 36-inch CMP Flows northwest to grassy area near apartment complex entrance ? 990'-1,060' None Noted None Noted 10 60-inch Culvert Flows north in center of South Star Lake Road ? 1,060'-1,390' None Noted None Noted 11 60-inch Culvert Flows northeast into 272nd ? 1,390'-1,440' None Noted None Noted 12 Large Culvert Flows east in 272nd ? 1,440-1,590' None Noted None Noted 13 Large Culvert Flows north across 272nd ? 1,590'-1,630' None Noted None Noted 14 Large Culvert Flows west in 272nd ? 1,630'-1,650' None Noted None Noted 15 Large Arch CMP Outfalls north into wetland ? 1,650'-1,680' None Noted None Noted 17157-Level 1.doc TASK 3 FIELD INSPECTION There were no problems reported during the resource review and the field reconnaissance did not find any potential constrictions or lack of capacity in the existing drainage system downstream from the project site. 3.1 Conveyance System Nuisance Problems (Type 1) Conveyance system nuisance problems are minor but chronic flooding or erosion problems that result from the overflow of a constructed conveyance system that is substandard or has become too small as a result of upstream development. Such problems warrant additional attention because of their chronic nature and because they result from the failure of a conveyance system to provide a minimum acceptable level of protection. Based on the resource review and site visit, there is little evidence of past conveyance system nuisance problems occurring. 3.2 Severe Erosion Problems (Type 2) Severe erosion problems can be caused by conveyance system overflows or the concentration of runoff into erosion-sensitive open drainage features. Severe erosion problems warrant additional attention because they pose a significant threat either to health and safety or to public or private property. Per the resource review and our site visit there was no erosion occurring in any of the downstream drainage courses, partly because all of the downstream drainage flows through a pipe conveyance system which prevents erosion from occurring. There was no overtopping evident anywhere along the downstream drainage course. 3.3 Severe Flooding Problems (Type 3) Severe flooding problems, i.e., a severe building flooding problem or severe roadway flooding problem can be caused by conveyance system overflows or the elevated water surfaces of ponds, lakes, wetlands, or closed depressions. Severe flooding problems warrant additional attention because they pose a significant threat either to health and safety or to public or private property. This project is aware there is a flooding problem in the downstream drainage course from this project site. Therefore, the City has indicated that Level 3 Flow Control will be a requirement for this project site. This project is providing Level 3 Flow Control for the new development area, which is in excess of what was initially designed for on the project site. Level 1 Flow Control was originally provided on the previous development and pond construction. Increasing the pond size with this development will help alleviate any flooding problems from occurring in the downstream drainage course. The pre-developed condition for the new impervious surface proposed for the Redondo Heights Senior Living Facility is considered till forest. At the time of our field inspection, which was on April 30, 2015, the sky was clear and sunny and the temperature was approximately 65 degrees. TASK 4 DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS 17157-Level 1.doc TASK 4 DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS Runoff from the project site will continue to drain to a modified Level 3 Flow Control detention pond located in the southeast corner of the overall development. This pond will drain and currently does drain to the south into the park and ride facility where it is collected in the outfall manhole from the detention vault for the on-site park and ride. This manhole discharges due easterly through the Club Palisade apartment complex and into the South Star Lake Road conveyance system, which is a large diameter culvert approximately 60 inches in size. This runoff courses in a northerly direction to the right-of-way of South 272nd Street where it is then routed down the south side of South 272nd Street in an easterly direction to the bottom of a low area in the road where it is then routed across the street and into a large wetland that courses due north for several thousand feet. PROBLEM DESCRIPTIONS As mentioned by the City of Federal Way, there are flooding problems in the downstream drainage course which require the application of Level 3 Flow Control; therefore, this project is providing Level 3 Flow Control for this new development. TASK 5 MITIGATION OF EXISTING OR POTENTIAL PROBLEMS 17157-Level 1.doc TASK 5 MITIGATION OF EXISTING OR POTENTIAL PROBLEMS This project will not exacerbate nor create a further worsening of water quality problems or flow control problems in the downstream drainage course. Level 3 Flow Control is being provided for this project site and the 100-year peak will actually be less than it was under the existing conditions. In addition, Enhanced Water Quality will now be provided for the entire project site in the form of a stormwater treatment wetland located within the detention pond. Therefore, this project site will mitigate any problems that could be coming from this overall development. 4.0 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN 17157-TIR.doc 4.0 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN A. Existing Site Hydrology Stormwater runoff from the existing site is routed to the detention pond previously constructed. The site a moderately sloping from west to east on the project site with vegetation and shrubs covering a majority of the site. B. Developed Site Hydrology Under the developed conditions the site will be approximately 77 percent impervious surfaces. The developed site area is approximately 2.52 acres for this parcel with the entire are draining to the detention pond 5.24 acres. The existing detention pond will be modified and regrading to provide additional storage volume to meet the flow control requirements for this project site. Water quality will be provided for all areas in the form of a Stormwater Treatment Wetland located at the bottom of the detention pond to provide the necessary level of pollutant removal required for this project. C. Performance Standards A modified Level 3 flow control is required for this site. To quantify this amount, the City of Federal Way has set forth the requirements of providing the difference of the entire site modeled to provide Level 3 Flow Control, minus the entire site volume modeled to provide Level 1 Flow Control. Additional narrative from the pre-application meeting with Federal Way is providing in Section 1.0. Enhanced Basic Water quality treatment is also required for this project site. The Modified Rational Method utilizing the 100-year storm event is used for pipe conveyance, as the site is less than 10 acres. D. Flow Control System Flow control is provided for this project site in the form of a detention pond. To model the area required the following steps were utilized: a. Analyze the project utilizing the Level 1 Flow Control standard, and determine the required pond volume under that standard; b. Analyze the project utilizing the Level 3 Flow Control standard, and determine the required pond volume under that standard; and c. The difference in volume between the Level 1 and Level 3 Flow Control Standards is the volume that the new project needs to provide, either on-site, OR, the existing pond can be modified to provide the required volume, OR, the existing pond can remain un-altered, if the analysis described above shows that that it has adequate capacity as constructed.” Calculations for Level 1 and Level 3 flow control have been calculated. The difference in the storage volume was calculated to be 70,000 cubic feet of storage, which is being provided with this development. Discharge from the detention pond will flow to the existing discharge point of the pond. E. Water Quality System Enhanced Basic water quality treatment is required for this project site. Along with re- grading of the pond area to provide adequate storage for the new development, additional plantings will be planted at the bottom of the detention pond to meet the 17157-TIR.doc requirements of a Stormwater Wetland per the KCSWDM. These plantings will treat for Enhanced Basic treatment and provide the required level of pollutant removal for the project site. Flow Control and Water Quality Sizing Criteria 17157-TIR.doc FLOW CONTROL AND WATER QUALITY SIZING CRITERIA On-Site Areas Impervious = 1.58 ac Pervious = 0.58 ac Pond = 0.36 ac Total On-site Area = 2.52 ac Total Flow Control Areas Impervious = 2.23 ac Rooftop = 1.63 ac Landscape = 1.02 ac Pond = 0.36 ac Total Area to Pond = 5.24 ac Level 1 Flow Control Calculations WWHM2012 PROJECT REPORT Redondo Heights Apartments Level 1 Flow Control Calculations BCE#17157 08/10/2020 17157-Level 1 7/28/2020 1:24:07 PM Page 2 General Model Information Project Name:17157-Level 1 Site Name:Redondo Heights Site Address: City:Federal Way Report Date:7/28/2020 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2018/10/10 Version:4.2.16 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year 17157-Level 1 7/28/2020 1:24:07 PM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 5.24 Pervious Total 5.24 Impervious Land Use acre Impervious Total 0 Basin Total 5.24 Element Flows To: Surface Interflow Groundwater 17157-Level 1 7/28/2020 1:24:07 PM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 1.02 Pervious Total 1.02 Impervious Land Use acre ROADS FLAT 2.23 ROOF TOPS FLAT 1.63 POND 0.36 Impervious Total 4.22 Basin Total 5.24 Element Flows To: Surface Interflow Groundwater Trapezoidal Pond 1 Trapezoidal Pond 1 17157-Level 1 7/28/2020 1:24:07 PM Page 6 Mitigated Routing Trapezoidal Pond 1 Bottom Length:100.00 ft. Bottom Width:100.00 ft. Depth:6 ft. Volume at riser head:1.5266 acre-feet. Side slope 1:3 To 1 Side slope 2:3 To 1 Side slope 3:3 To 1 Side slope 4:3 To 1 Discharge Structure Riser Height:5 ft. Riser Diameter:18 in. Orifice 1 Diameter:1.5 in.Elevation:0 ft. Orifice 2 Diameter:1.4375 in.Elevation:1.95 ft. Element Flows To: Outlet 1 Outlet 2 Pond Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.229 0.000 0.000 0.000 0.0667 0.231 0.015 0.015 0.000 0.1333 0.233 0.030 0.022 0.000 0.2000 0.235 0.046 0.027 0.000 0.2667 0.237 0.062 0.031 0.000 0.3333 0.238 0.078 0.035 0.000 0.4000 0.240 0.094 0.038 0.000 0.4667 0.242 0.110 0.041 0.000 0.5333 0.244 0.126 0.044 0.000 0.6000 0.246 0.142 0.047 0.000 0.6667 0.248 0.159 0.049 0.000 0.7333 0.250 0.175 0.052 0.000 0.8000 0.252 0.192 0.054 0.000 0.8667 0.254 0.209 0.056 0.000 0.9333 0.256 0.226 0.059 0.000 1.0000 0.257 0.243 0.061 0.000 1.0667 0.259 0.260 0.063 0.000 1.1333 0.261 0.278 0.065 0.000 1.2000 0.263 0.295 0.066 0.000 1.2667 0.265 0.313 0.068 0.000 1.3333 0.267 0.331 0.070 0.000 1.4000 0.269 0.349 0.072 0.000 1.4667 0.271 0.367 0.073 0.000 1.5333 0.273 0.385 0.075 0.000 1.6000 0.275 0.403 0.077 0.000 1.6667 0.277 0.422 0.078 0.000 1.7333 0.279 0.440 0.080 0.000 1.8000 0.281 0.459 0.081 0.000 1.8667 0.283 0.478 0.083 0.000 1.9333 0.285 0.497 0.084 0.000 2.0000 0.288 0.516 0.098 0.000 2.0667 0.290 0.535 0.106 0.000 2.1333 0.292 0.555 0.113 0.000 2.2000 0.294 0.574 0.118 0.000 17157-Level 1 7/28/2020 1:24:07 PM Page 7 2.2667 0.296 0.594 0.123 0.000 2.3333 0.298 0.614 0.128 0.000 2.4000 0.300 0.634 0.132 0.000 2.4667 0.302 0.654 0.136 0.000 2.5333 0.304 0.674 0.140 0.000 2.6000 0.306 0.694 0.143 0.000 2.6667 0.308 0.715 0.147 0.000 2.7333 0.311 0.736 0.150 0.000 2.8000 0.313 0.756 0.153 0.000 2.8667 0.315 0.777 0.157 0.000 2.9333 0.317 0.798 0.160 0.000 3.0000 0.319 0.820 0.163 0.000 3.0667 0.321 0.841 0.166 0.000 3.1333 0.324 0.863 0.169 0.000 3.2000 0.326 0.884 0.171 0.000 3.2667 0.328 0.906 0.174 0.000 3.3333 0.330 0.928 0.177 0.000 3.4000 0.332 0.950 0.180 0.000 3.4667 0.335 0.972 0.182 0.000 3.5333 0.337 0.995 0.185 0.000 3.6000 0.339 1.017 0.187 0.000 3.6667 0.341 1.040 0.190 0.000 3.7333 0.343 1.063 0.192 0.000 3.8000 0.346 1.086 0.195 0.000 3.8667 0.348 1.109 0.197 0.000 3.9333 0.350 1.132 0.200 0.000 4.0000 0.353 1.156 0.202 0.000 4.0667 0.355 1.179 0.204 0.000 4.1333 0.357 1.203 0.207 0.000 4.2000 0.359 1.227 0.209 0.000 4.2667 0.362 1.251 0.211 0.000 4.3333 0.364 1.275 0.213 0.000 4.4000 0.366 1.300 0.215 0.000 4.4667 0.369 1.324 0.218 0.000 4.5333 0.371 1.349 0.220 0.000 4.6000 0.373 1.374 0.222 0.000 4.6667 0.376 1.399 0.224 0.000 4.7333 0.378 1.424 0.226 0.000 4.8000 0.380 1.449 0.228 0.000 4.8667 0.383 1.475 0.230 0.000 4.9333 0.385 1.500 0.232 0.000 5.0000 0.388 1.526 0.234 0.000 5.0667 0.390 1.552 0.510 0.000 5.1333 0.392 1.578 1.009 0.000 5.2000 0.395 1.604 1.644 0.000 5.2667 0.397 1.631 2.366 0.000 5.3333 0.400 1.658 3.126 0.000 5.4000 0.402 1.684 3.878 0.000 5.4667 0.404 1.711 4.573 0.000 5.5333 0.407 1.738 5.174 0.000 5.6000 0.409 1.765 5.652 0.000 5.6667 0.412 1.793 6.007 0.000 5.7333 0.414 1.820 6.269 0.000 5.8000 0.417 1.848 6.595 0.000 5.8667 0.419 1.876 6.856 0.000 5.9333 0.422 1.904 7.107 0.000 6.0000 0.424 1.932 7.349 0.000 6.0667 0.427 1.961 7.583 0.000 17157-Level 1 7/28/2020 1:24:07 PM Page 9 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:5.24 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:1.02 Total Impervious Area:4.22 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.15406 5 year 0.241958 10 year 0.291771 25 year 0.344543 50 year 0.377199 100 year 0.404974 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.152457 5 year 0.224423 10 year 0.284156 25 year 0.375397 50 year 0.456224 100 year 0.549341 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.151 0.120 1950 0.189 0.157 1951 0.339 0.230 1952 0.107 0.081 1953 0.086 0.132 1954 0.133 0.153 1955 0.212 0.161 1956 0.168 0.169 1957 0.136 0.144 1958 0.153 0.158 17157-Level 1 7/28/2020 1:24:37 PM Page 10 1959 0.131 0.138 1960 0.229 0.222 1961 0.129 0.154 1962 0.081 0.079 1963 0.111 0.145 1964 0.146 0.141 1965 0.104 0.164 1966 0.100 0.136 1967 0.209 0.163 1968 0.131 0.136 1969 0.128 0.127 1970 0.105 0.130 1971 0.113 0.159 1972 0.253 0.190 1973 0.115 0.159 1974 0.125 0.150 1975 0.169 0.156 1976 0.122 0.154 1977 0.015 0.127 1978 0.107 0.150 1979 0.065 0.081 1980 0.239 0.208 1981 0.096 0.126 1982 0.184 0.207 1983 0.165 0.161 1984 0.102 0.108 1985 0.060 0.131 1986 0.267 0.196 1987 0.236 0.213 1988 0.093 0.115 1989 0.061 0.125 1990 0.494 0.220 1991 0.297 0.217 1992 0.115 0.142 1993 0.119 0.121 1994 0.040 0.079 1995 0.171 0.166 1996 0.361 0.231 1997 0.302 0.228 1998 0.068 0.133 1999 0.283 0.206 2000 0.119 0.171 2001 0.021 0.083 2002 0.131 0.202 2003 0.167 0.137 2004 0.216 0.537 2005 0.155 0.153 2006 0.182 0.156 2007 0.367 1.014 2008 0.473 0.534 2009 0.232 0.194 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.4938 1.0141 2 0.4729 0.5374 3 0.3666 0.5339 17157-Level 1 7/28/2020 1:24:37 PM Page 11 4 0.3610 0.2307 5 0.3393 0.2305 6 0.3018 0.2279 7 0.2974 0.2216 8 0.2830 0.2200 9 0.2670 0.2168 10 0.2526 0.2133 11 0.2394 0.2082 12 0.2362 0.2071 13 0.2322 0.2060 14 0.2294 0.2024 15 0.2156 0.1957 16 0.2117 0.1936 17 0.2095 0.1896 18 0.1887 0.1707 19 0.1840 0.1687 20 0.1824 0.1660 21 0.1713 0.1643 22 0.1688 0.1627 23 0.1685 0.1615 24 0.1665 0.1611 25 0.1650 0.1587 26 0.1547 0.1587 27 0.1532 0.1584 28 0.1513 0.1569 29 0.1455 0.1564 30 0.1360 0.1556 31 0.1328 0.1541 32 0.1314 0.1540 33 0.1307 0.1535 34 0.1305 0.1526 35 0.1294 0.1498 36 0.1278 0.1497 37 0.1246 0.1455 38 0.1220 0.1443 39 0.1195 0.1422 40 0.1191 0.1412 41 0.1148 0.1381 42 0.1147 0.1374 43 0.1127 0.1365 44 0.1105 0.1356 45 0.1071 0.1330 46 0.1069 0.1320 47 0.1054 0.1315 48 0.1042 0.1304 49 0.1019 0.1274 50 0.1002 0.1270 51 0.0957 0.1258 52 0.0932 0.1255 53 0.0865 0.1213 54 0.0805 0.1199 55 0.0683 0.1146 56 0.0647 0.1085 57 0.0608 0.0828 58 0.0604 0.0814 59 0.0401 0.0809 60 0.0214 0.0789 61 0.0145 0.0788 17157-Level 1 7/28/2020 1:24:46 PM Page 17 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. 17157-Level 1 7/28/2020 1:24:46 PM Page 18 Appendix Predeveloped Schematic 17157-Level 1 7/28/2020 1:24:46 PM Page 19 Mitigated Schematic 17157-Level 1 7/28/2020 1:24:47 PM Page 32 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2020; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com Level 3 Flow Control Calculations WWHM2012 PROJECT REPORT Redondo Heights Apartments Level 3 Flow Control Calculations BCE#17157 08/10/2020 17157-Level 3 7/28/2020 9:48:33 AM Page 2 General Model Information Project Name:17157-Level 3 Site Name:Redondo Heights Site Address: City:Federal Way Report Date:7/28/2020 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2018/10/10 Version:4.2.16 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year 17157-Level 3 7/28/2020 9:48:33 AM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 5.24 Pervious Total 5.24 Impervious Land Use acre Impervious Total 0 Basin Total 5.24 Element Flows To: Surface Interflow Groundwater 17157-Level 3 7/28/2020 9:48:33 AM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 1.02 Pervious Total 1.02 Impervious Land Use acre ROADS FLAT 2.23 ROOF TOPS FLAT 1.63 POND 0.36 Impervious Total 4.22 Basin Total 5.24 Element Flows To: Surface Interflow Groundwater Trapezoidal Pond 1 Trapezoidal Pond 1 17157-Level 3 7/28/2020 9:48:33 AM Page 6 Mitigated Routing Trapezoidal Pond 1 Bottom Length:150.00 ft. Bottom Width:150.00 ft. Depth:6 ft. Volume at riser head:3.1336 acre-feet. Side slope 1:3 To 1 Side slope 2:3 To 1 Side slope 3:3 To 1 Side slope 4:3 To 1 Discharge Structure Riser Height:5 ft. Riser Diameter:18 in. Orifice 1 Diameter:1.4125 in.Elevation:0 ft. Orifice 2 Diameter:2.1875 in.Elevation:2.27 ft. Orifice 3 Diameter:3.25 in.Elevation:3.35 ft. Element Flows To: Outlet 1 Outlet 2 Pond Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.516 0.000 0.000 0.000 0.0667 0.519 0.034 0.014 0.000 0.1333 0.522 0.069 0.019 0.000 0.2000 0.524 0.104 0.024 0.000 0.2667 0.527 0.139 0.028 0.000 0.3333 0.530 0.174 0.031 0.000 0.4000 0.533 0.209 0.034 0.000 0.4667 0.536 0.245 0.037 0.000 0.5333 0.538 0.281 0.039 0.000 0.6000 0.541 0.317 0.041 0.000 0.6667 0.544 0.353 0.044 0.000 0.7333 0.547 0.390 0.046 0.000 0.8000 0.550 0.426 0.048 0.000 0.8667 0.553 0.463 0.050 0.000 0.9333 0.555 0.500 0.052 0.000 1.0000 0.558 0.537 0.054 0.000 1.0667 0.561 0.574 0.055 0.000 1.1333 0.564 0.612 0.057 0.000 1.2000 0.567 0.650 0.059 0.000 1.2667 0.570 0.688 0.060 0.000 1.3333 0.573 0.726 0.062 0.000 1.4000 0.576 0.764 0.064 0.000 1.4667 0.578 0.802 0.065 0.000 1.5333 0.581 0.841 0.067 0.000 1.6000 0.584 0.880 0.068 0.000 1.6667 0.587 0.919 0.069 0.000 1.7333 0.590 0.958 0.071 0.000 1.8000 0.593 0.998 0.072 0.000 1.8667 0.596 1.038 0.074 0.000 1.9333 0.599 1.077 0.075 0.000 2.0000 0.602 1.117 0.076 0.000 2.0667 0.605 1.158 0.077 0.000 2.1333 0.608 1.198 0.079 0.000 Level 3 - Level 1 = volume req. 3.1336 - 1.5266 = 1.607 ac-ft Volume req. = 70,000 cf 17157-Level 3 7/28/2020 9:48:33 AM Page 7 2.2000 0.611 1.239 0.080 0.000 2.2667 0.614 1.280 0.081 0.000 2.3333 0.617 1.321 0.115 0.000 2.4000 0.620 1.362 0.130 0.000 2.4667 0.623 1.404 0.142 0.000 2.5333 0.626 1.445 0.152 0.000 2.6000 0.629 1.487 0.161 0.000 2.6667 0.632 1.529 0.170 0.000 2.7333 0.635 1.571 0.177 0.000 2.8000 0.638 1.614 0.185 0.000 2.8667 0.641 1.657 0.192 0.000 2.9333 0.644 1.699 0.198 0.000 3.0000 0.647 1.743 0.204 0.000 3.0667 0.651 1.786 0.210 0.000 3.1333 0.654 1.829 0.216 0.000 3.2000 0.657 1.873 0.222 0.000 3.2667 0.660 1.917 0.227 0.000 3.3333 0.663 1.961 0.232 0.000 3.4000 0.666 2.005 0.302 0.000 3.4667 0.669 2.050 0.340 0.000 3.5333 0.672 2.095 0.370 0.000 3.6000 0.676 2.140 0.395 0.000 3.6667 0.679 2.185 0.418 0.000 3.7333 0.682 2.230 0.439 0.000 3.8000 0.685 2.276 0.458 0.000 3.8667 0.688 2.322 0.476 0.000 3.9333 0.691 2.368 0.493 0.000 4.0000 0.695 2.414 0.510 0.000 4.0667 0.698 2.460 0.525 0.000 4.1333 0.701 2.507 0.541 0.000 4.2000 0.704 2.554 0.555 0.000 4.2667 0.707 2.601 0.569 0.000 4.3333 0.711 2.648 0.583 0.000 4.4000 0.714 2.696 0.596 0.000 4.4667 0.717 2.743 0.609 0.000 4.5333 0.720 2.791 0.622 0.000 4.6000 0.724 2.840 0.634 0.000 4.6667 0.727 2.888 0.646 0.000 4.7333 0.730 2.937 0.658 0.000 4.8000 0.733 2.985 0.670 0.000 4.8667 0.737 3.034 0.681 0.000 4.9333 0.740 3.084 0.692 0.000 5.0000 0.743 3.133 0.703 0.000 5.0667 0.747 3.183 0.988 0.000 5.1333 0.750 3.233 1.496 0.000 5.2000 0.753 3.283 2.140 0.000 5.2667 0.757 3.333 2.869 0.000 5.3333 0.760 3.384 3.638 0.000 5.4000 0.763 3.435 4.398 0.000 5.4667 0.767 3.486 5.101 0.000 5.5333 0.770 3.537 5.709 0.000 5.6000 0.773 3.588 6.196 0.000 5.6667 0.777 3.640 6.559 0.000 5.7333 0.780 3.692 6.827 0.000 5.8000 0.784 3.744 7.161 0.000 5.8667 0.787 3.797 7.429 0.000 5.9333 0.790 3.849 7.687 0.000 6.0000 0.794 3.902 7.936 0.000 17157-Level 3 7/28/2020 9:48:33 AM Page 8 6.0667 0.797 3.955 8.177 0.000 17157-Level 3 7/28/2020 9:48:33 AM Page 9 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:5.24 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:1.02 Total Impervious Area:4.22 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.15406 5 year 0.241958 10 year 0.291771 25 year 0.344543 50 year 0.377199 100 year 0.404974 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.093143 5 year 0.142857 10 year 0.183743 25 year 0.245669 50 year 0.300059 100 year 0.362241 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.151 0.067 1950 0.189 0.080 1951 0.339 0.217 1952 0.107 0.061 1953 0.086 0.078 1954 0.133 0.072 1955 0.212 0.070 1956 0.168 0.163 1957 0.136 0.072 1958 0.153 0.077 17157-Level 3 7/28/2020 9:49:02 AM Page 10 1959 0.131 0.068 1960 0.229 0.189 1961 0.129 0.111 1962 0.081 0.061 1963 0.111 0.076 1964 0.146 0.081 1965 0.104 0.142 1966 0.100 0.073 1967 0.209 0.080 1968 0.131 0.073 1969 0.128 0.072 1970 0.105 0.077 1971 0.113 0.076 1972 0.253 0.194 1973 0.115 0.133 1974 0.125 0.075 1975 0.169 0.069 1976 0.122 0.073 1977 0.015 0.064 1978 0.107 0.079 1979 0.065 0.057 1980 0.239 0.200 1981 0.096 0.074 1982 0.184 0.166 1983 0.165 0.075 1984 0.102 0.062 1985 0.060 0.066 1986 0.267 0.081 1987 0.236 0.177 1988 0.093 0.069 1989 0.061 0.065 1990 0.494 0.190 1991 0.297 0.189 1992 0.115 0.080 1993 0.119 0.062 1994 0.040 0.056 1995 0.171 0.107 1996 0.361 0.211 1997 0.302 0.216 1998 0.068 0.062 1999 0.283 0.191 2000 0.119 0.080 2001 0.021 0.053 2002 0.131 0.117 2003 0.167 0.072 2004 0.216 0.218 2005 0.155 0.072 2006 0.182 0.158 2007 0.367 0.350 2008 0.473 0.203 2009 0.232 0.137 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.4938 0.3503 2 0.4729 0.2178 3 0.3666 0.2171 17157-Level 3 7/28/2020 9:49:02 AM Page 11 4 0.3610 0.2157 5 0.3393 0.2106 6 0.3018 0.2028 7 0.2974 0.1999 8 0.2830 0.1943 9 0.2670 0.1914 10 0.2526 0.1902 11 0.2394 0.1887 12 0.2362 0.1885 13 0.2322 0.1773 14 0.2294 0.1655 15 0.2156 0.1630 16 0.2117 0.1576 17 0.2095 0.1416 18 0.1887 0.1365 19 0.1840 0.1329 20 0.1824 0.1174 21 0.1713 0.1115 22 0.1688 0.1070 23 0.1685 0.0814 24 0.1665 0.0808 25 0.1650 0.0799 26 0.1547 0.0797 27 0.1532 0.0796 28 0.1513 0.0796 29 0.1455 0.0792 30 0.1360 0.0781 31 0.1328 0.0770 32 0.1314 0.0769 33 0.1307 0.0760 34 0.1305 0.0758 35 0.1294 0.0751 36 0.1278 0.0746 37 0.1246 0.0744 38 0.1220 0.0734 39 0.1195 0.0733 40 0.1191 0.0732 41 0.1148 0.0722 42 0.1147 0.0719 43 0.1127 0.0719 44 0.1105 0.0718 45 0.1071 0.0716 46 0.1069 0.0702 47 0.1054 0.0695 48 0.1042 0.0690 49 0.1019 0.0680 50 0.1002 0.0672 51 0.0957 0.0657 52 0.0932 0.0651 53 0.0865 0.0640 54 0.0805 0.0624 55 0.0683 0.0622 56 0.0647 0.0618 57 0.0608 0.0615 58 0.0604 0.0609 59 0.0401 0.0572 60 0.0214 0.0559 61 0.0145 0.0532 17157-Level 3 7/28/2020 9:49:02 AM Page 13 Duration Flows The Facility PASSED Flow(cfs)Predev Mit Percentage Pass/Fail 0.0770 17569 14938 85 Pass 0.0801 16191 9005 55 Pass 0.0831 14994 6778 45 Pass 0.0861 13892 6611 47 Pass 0.0892 12857 6453 50 Pass 0.0922 11875 6278 52 Pass 0.0952 10951 6098 55 Pass 0.0983 10168 5940 58 Pass 0.1013 9447 5775 61 Pass 0.1043 8804 5627 63 Pass 0.1074 8215 5484 66 Pass 0.1104 7659 5358 69 Pass 0.1134 7122 5230 73 Pass 0.1164 6650 5071 76 Pass 0.1195 6213 4836 77 Pass 0.1225 5833 4637 79 Pass 0.1255 5495 4440 80 Pass 0.1286 5161 4235 82 Pass 0.1316 4866 4062 83 Pass 0.1346 4584 3859 84 Pass 0.1377 4312 3625 84 Pass 0.1407 4066 3441 84 Pass 0.1437 3844 3307 86 Pass 0.1468 3595 3163 87 Pass 0.1498 3388 3031 89 Pass 0.1528 3187 2881 90 Pass 0.1559 2999 2699 89 Pass 0.1589 2834 2541 89 Pass 0.1619 2654 2357 88 Pass 0.1650 2494 2167 86 Pass 0.1680 2351 2014 85 Pass 0.1710 2162 1836 84 Pass 0.1741 2027 1706 84 Pass 0.1771 1902 1540 80 Pass 0.1801 1790 1396 77 Pass 0.1832 1695 1259 74 Pass 0.1862 1595 1090 68 Pass 0.1892 1488 921 61 Pass 0.1922 1387 800 57 Pass 0.1953 1299 699 53 Pass 0.1983 1226 602 49 Pass 0.2013 1160 482 41 Pass 0.2044 1104 384 34 Pass 0.2074 1056 335 31 Pass 0.2104 1004 287 28 Pass 0.2135 941 238 25 Pass 0.2165 890 171 19 Pass 0.2195 844 135 15 Pass 0.2226 796 128 16 Pass 0.2256 747 121 16 Pass 0.2286 720 113 15 Pass 0.2317 679 104 15 Pass 0.2347 640 65 10 Pass 17157-Level 3 7/28/2020 9:49:02 AM Page 14 0.2377 603 63 10 Pass 0.2408 575 62 10 Pass 0.2438 544 60 11 Pass 0.2468 508 59 11 Pass 0.2499 478 58 12 Pass 0.2529 446 56 12 Pass 0.2559 411 55 13 Pass 0.2590 379 54 14 Pass 0.2620 353 53 15 Pass 0.2650 323 51 15 Pass 0.2680 296 50 16 Pass 0.2711 273 49 17 Pass 0.2741 256 48 18 Pass 0.2771 235 47 20 Pass 0.2802 218 46 21 Pass 0.2832 198 45 22 Pass 0.2862 181 45 24 Pass 0.2893 158 44 27 Pass 0.2923 146 42 28 Pass 0.2953 131 42 32 Pass 0.2984 119 41 34 Pass 0.3014 110 40 36 Pass 0.3044 97 40 41 Pass 0.3075 93 39 41 Pass 0.3105 85 37 43 Pass 0.3135 78 36 46 Pass 0.3166 69 35 50 Pass 0.3196 63 34 53 Pass 0.3226 56 33 58 Pass 0.3257 48 31 64 Pass 0.3287 43 30 69 Pass 0.3317 38 28 73 Pass 0.3348 34 20 58 Pass 0.3378 29 19 65 Pass 0.3408 24 17 70 Pass 0.3438 21 16 76 Pass 0.3469 20 12 60 Pass 0.3499 19 6 31 Pass 0.3529 18 0 0 Pass 0.3560 14 0 0 Pass 0.3590 12 0 0 Pass 0.3620 9 0 0 Pass 0.3651 4 0 0 Pass 0.3681 3 0 0 Pass 0.3711 3 0 0 Pass 0.3742 3 0 0 Pass 0.3772 3 0 0 Pass 17157-Level 3 7/28/2020 9:49:02 AM Page 15 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0.5498 acre-feet On-line facility target flow:0.678 cfs. Adjusted for 15 min:0.678 cfs. Off-line facility target flow:0.382 cfs. Adjusted for 15 min:0.382 cfs. 17157-Level 3 7/28/2020 9:49:11 AM Page 17 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. 17157-Level 3 7/28/2020 9:49:11 AM Page 18 Appendix Predeveloped Schematic 17157-Level 3 7/28/2020 9:49:11 AM Page 19 Mitigated Schematic 17157-Level 3 7/28/2020 9:49:12 AM Page 33 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2020; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN 17157-TIR.doc 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN The conveyance system sizing utilizes the Modified Rational Method with a 6.3 minute initial time of concentration, Manning's 'n' value of 0.012 calculations routing the 100-year storm event of 4 inches. Please see final TIR for conveyance sizing. 6.0 SPECIAL REPORTS AND STUDIES 17157-TIR.doc 6.0 SPECIAL REPORTS AND STUDIES Special reports for this project include: · Geotechnical Report prepared by Associated Earth Sciences, Inc. - September 9, 2014 SUBSURFACE EXPLORATION, GEOLOGIC HAZARDS, AND GEOTECHNICAL ENGINEERING REPORT FEDERAL WAY SENIOR LIVING Federal Way, Washington Prepared for: Pacific Northern Construction Company 201 27th Avenue SE, Building A, Suite 300 Puyallup, Washington Prepared by: Associated Earth Sciences, Inc. 911 5th Avenue Kirkland, Washington 98033 425-827-7701 Fax: 425-827-5424 September 9, 2014 Project No. KE140420A Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Project and Site Conditions I. PROJECT AND SITE CONDITIONS 1.0 INTRODUCTION This report presents the results of our subsurface exploration, geologic hazards, and geotechnical engineering studies for the proposed Federal Way Senior Living project. The site location is shown on the “Vicinity Map,” Figure 1. The approximate locations of the exploration pits completed for this study are shown on the “Site and Exploration Plan,” Figure 2. Logs of the subsurface explorations completed for this study are included in the Appendix. 1.1 Purpose and Scope The purpose of this study was to provide geotechnical engineering design recommendations to be utilized in the design of the project. This study included a review of selected available geologic literature, completing seven exploration pits, and performing geologic studies to assess the type, thickness, distribution, and physical properties of the subsurface sediments and shallow ground water. Geotechnical engineering studies were completed to establish recommendations for the type of suitable foundations, allowable foundation soil bearing pressure, anticipated foundation settlement, erosion control, infiltration considerations, and drainage considerations. This report summarizes our fieldwork and offers recommendations based on our present understanding of the project. We recommend that we be allowed to review the recommendations presented in this report and revise them, if needed, when a project design has been finalized. 1.2 Authorization Our study was accomplished in general accordance with our initial scope of work letter dated July 17, 2014. This report has been prepared for the exclusive use of Pacific Northern Construction Company, and their agents, for specific application to this project. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering and engineering geology practices in effect in this area at the time our report was prepared. No other warranty, express or implied, is made. Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the owner. September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 1 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Project and Site Conditions 2.0 PROJECT AND SITE DESCRIPTION The site is an irregularly shaped parcel (Parcel #872992-0040) located to the east of the intersection of South 272nd Street and Pacific Highway South in Federal Way, Washington. It is currently undeveloped and comprises about 2.5 acres. The parcel is bounded to the north by South 272nd Street, to the south by a King County Park and Ride lot, to the west by existing retail development including a gas station, and to the east by existing residential development. The site is moderately vegetated with sparse trees and brush. An existing L-shaped detention pond is located at the south end of the property. The topography is relatively level over the western portion of the site and gently slopes down to the east in the northeastern area of the site. A 4- to 5-foot-high slope, trending north-south through the north-central portion of the parcel, appears to be the result of previous grading activities which leveled out the western portion of the property. We understand that a new senior living facility will be constructed on the site. The planned development will include a six-story building on the northern side of the parcel. The northern half of the building will contain a below-grade parking level, which will be close to existing grade along the eastern side of building and will require cuts up to 10 feet at the northwestern corner of the proposed building. 3.0 SUBSURFACE EXPLORATION Our subsurface exploration completed for this project included completing seven exploration pits. The conclusions and recommendations presented in this report are based on the explorations completed for this study. The locations and depths of the explorations were completed within site and budget constraints. 3.1 Exploration Pits Associated Earth Sciences, Inc. (AESI) observed excavation of seven exploration pits at the site on August 20, 2014. The approximate locations of the pits are shown on the “Site and Exploration Plan,” Figure 2. Exploration pits were excavated with a track-mounted mini excavator. The pits permitted direct, visual observation of subsurface conditions. Materials encountered in the exploration pits were studied and classified in the field by an engineering geologist from our firm. Disturbed soil samples were selected from the pits, placed in moisture- tight containers, and transported to our laboratory for further visual classification and testing, as necessary. Testing was limited to visual-manual classification of the collected samples and grain-size analyses in general accordance with American Society for Testing and Materials (ASTM) standard practices. After logging the exposed soils all exploration pits were backfilled with the excavated soil and lightly tamped with the excavator bucket. Detailed descriptions of September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 2 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Project and Site Conditions the sediments encountered in each exploration pit are provided on the exploration logs included in the Appendix. Results of grain-size and moisture content testing are also included in the Appendix. 4.0 SUBSURFACE CONDITIONS Subsurface conditions at the project site were inferred from the field explorations accomplished for this study, visual reconnaissance of the site, and review of selected applicable geologic literature. Because of the nature of exploratory work below ground, interpolation of subsurface conditions between field explorations is necessary. It should be noted that differing subsurface conditions may sometimes be present due to the random nature of deposition and the alteration of topography by past grading and/or filling. The nature and extent of any variations between the field explorations may not become fully evident until construction. 4.1 Stratigraphy Fill Fill soils (soils not naturally placed) were encountered in all exploration pits up to 7 feet in depth except at the locations of pits EP-3 and EP-5. This fill generally consisted of loose to medium dense silty sand with gravel with occasional organics and was generally similar in gradation to the underlying native lodgement till. The encountered fill likely resulted from past grading activities, including the leveling of grades along the western side of the site and construction of the existing pond. Fill thicknesses can vary over short distances and may be deeper than observed in our explorations. The fill was thickest near the top of the slope that separates the northwestern and northeastern portions of the site, at the location of EP-4. This slope appears to be the result of previous grading activities. Due to their variable density and content, the existing fill soils are not suitable for foundation support. Excavated fill material may suitable for use in structural fill applications if suitable moisture conditions are achieved and all deleterious materials are removed. At the time of exploration, we estimate that most of the fill soils that we observed were near or above optimum moisture content for compaction purposes, and therefore may require drying during favorable weather prior to compaction in structural fill applications. September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 3 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Project and Site Conditions Vashon Lodgement Till Sediments encountered below the existing fill consisted of a medium dense to very dense, poorly sorted mixture of clay, silt, sand, and gravel. We interpret these sediments to be representative of Vashon lodgement till. The till was deposited directly from basal, debris- laden glacial ice during the Vashon Stade of the Fraser Glaciation approximately 12,500 to 15,000 years ago. The high relative density of the unweathered till is due to its consolidation by the massive weight of the glacial ice from which it was deposited. The till extended to the bottom of all completed pits. Undisturbed medium dense to very dense lodgement till sediments are suitable for foundation and paving support. Due to the high percentage of fine-grained material present in these sediments, they are susceptible to disturbance when wet. Careful management of moisture- sensitive soils will be needed to reduce the potential for disturbance of wet till and costs associated with repairing disturbed sediments. Excavated lodgement till material is suitable for use in structural fill applications if suitable moisture conditions are achieved. At the time of exploration, we estimate that most of the lodgement till soils that we observed were near or above optimum moisture content for compaction purposes, and therefore may require drying during favorable weather prior to compaction in structural fill applications. Lodgement till generally has a low potential for infiltration due to its high density and high content of fine-grained sediments. 4.2 Geologic Mapping Review of the regional geologic map (Booth, D.B., Waldron, H.H., and Troost, K.G., 2004, Geologic Map of the Poverty Bay 7.5' Quadrangle, King and Pierce Counties, Washington: U.S. Geological Survey (USGS), Scientific Investigations Map SIM-2854, scale 1:24,000) indicates that the area of the subject site is underlain by Vashon lodgement till. Our interpretation of the sediments encountered in our explorations is in general agreement with the regional geologic map. 4.3 Hydrology No seepages were observed in any of the pits at the time of exploration. A mottled coloration was observed at the location of EP-6 at a depth of 9 feet, which may be indicative of seasonal or intermittent ground water at this depth. We anticipate that perched ground water may occur seasonally at the site. Perched water occurs when surface water infiltrates down through relatively permeable soils (such as the existing fill or weathered till) and becomes trapped or “perched” atop a comparatively impermeable barrier, such as unweathered lodgement till. The perched water will generally flow “downhill” over the top of the unweathered till surface at September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 4 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Project and Site Conditions depth. The duration and quantity of seepage will largely depend on the soil grain-size distribution, topography, seasonal precipitation, on- and off-site land usage, and other factors. 4.4 Infiltration Considerations We understand that infiltration into the on-site soils is being considered for the management of storm water runoff generated on-site. As discussed above, near-surface site soils consist of existing fill over glacial till. We do not recommend attempting to infiltrate into exiting fill due to its highly variable condition. The on-site native sediments consist of lodgement till which is generally composed of a very dense, unsorted matrix of silty fine to medium sand with variable percentages of clay, gravel, cobbles, and boulders. Due to its very high relative density and high content of fine-grained material, till typically has a very low permeability and is not considered a suitable receptor for infiltrating storm water runoff. September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 5 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Geologic Hazards and Mitigations II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic, slope, and ground and surface water conditions, as observed and discussed herein. 5.0 SEISMIC HAZARDS AND MITIGATIONS Earthquakes occur regularly in the Puget Lowland. The majority of these events are small and are usually not felt by people. However, large earthquakes do occur, as evidenced by the 1949, 7.2-magnitude event; the 2001, 6.8-magnitude event; and the 1965, 6.5-magnitude event. The 1949 earthquake appears to have been the largest in this region during recorded history and was centered in the Olympia area. Evaluation of earthquake return rates indicates that an earthquake of the magnitude between 5.5 and 6.0 is likely within a given 20-year period. Generally, there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture, 2) seismically induced landslides, 3) liquefaction, and 4) ground motion. The potential for each of these hazards to adversely impact the proposed project is discussed below. 5.1 Surficial Ground Rupture Generally, the largest earthquakes that have occurred in the Puget Sound area are sub-crustal events with epicenters ranging from 50 to 70 kilometers in depth. Earthquakes that are generated at such depths usually do not result in fault rupture at the ground surface. Limited and sporadic surficial faulting or earth rupture as a result of deep seismic activity has been documented to date in the region. Current research indicates that surficial ground rupture is possible in the Seattle and Tacoma Fault Zones. The Seattle and Tacoma Fault Zones are areas of active research. Our current understanding of these fault zones is poor, and actively evolving. The site is located south of the currently mapped limits of the Seattle Fault Zone. Preliminary maps of the Tacoma Fault Zone depict possible fault splays mapped west of the site and projecting generally toward the site area, but mapped fault splays fall short of the project site. If the currently mapped fault splays are projected, the nearest fault splay projects within 1 mile north of the subject site. The recurrence interval of movement along these fault systems is still unknown, although it is hypothesized to be in excess of several thousand years. Due to the suspected long recurrence interval, the potential for surficial ground rupture is considered to be low during the expected September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 6 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Geologic Hazards and Mitigations life of the structure, and no mitigation efforts beyond complying with the current (2012) International Building Code (IBC) are recommended. 5.2 Seismically Induced Landslides It is our opinion that the potential risk of damage to the proposed improvements by seismically induced slope failures is low due to the lack of steep slopes in the project area. 5.3 Liquefaction Liquefaction is a process through which unconsolidated soil loses strength as a result of vibrations, such as those which occur during a seismic event. During normal conditions, the weight of the soil is supported by both grain-to-grain contacts and by the fluid pressure within the pore spaces of the soil below the water table. Extreme vibratory shaking can disrupt the grain-to-grain contact, increase the pore pressure, and result in a temporary decrease in soil shear strength. The soil is said to be liquefied when nearly all of the weight of the soil is supported by pore pressure alone. Liquefaction can result in deformation of the sediment and settlement of overlying structures. Areas most susceptible to liquefaction include those areas underlain by non-cohesive silt and sand with low relative densities, accompanied by a shallow water table. The subsurface conditions encountered at the site pose little risk of liquefaction due to relatively high density of glacial soils encountered. No detailed liquefaction analysis was completed as part of this study, and none is warranted, in our opinion. 5.4 Ground Motion Structural design of the building should follow 2012 IBC standards using Site Class “C” as defined in Table 20.3-1 of American Society of Civil Engineers (ASCE) 7 – Minimum Design Loads for Buildings and Other Structures. 6.0 EROSION HAZARDS AND MITIGATIONS The following discussion addresses Washington State Department of Ecology (Ecology) erosion control regulations that will be applicable to the project. The on-site conditions do not meet the City of Federal Way definition for Erosion Hazard Areas. In addition, there are no erosion hazards shown in the immediate project vicinity on the Critical Areas map produced by the City. In our opinion, implementation of the following recommendations should be adequate to address the Ecology and City of Federal Way requirements for management of erosion hazards. September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 7 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Geologic Hazards and Mitigations The Ecology Construction Storm Water General Permit (also known as the National Pollutant Discharge Elimination System [NPDES] permit) requires weekly Temporary Erosion and Sedimentation Control (TESC) inspections, turbidity monitoring and pH monitoring for all sites 1 or more acres in size that discharge storm water to surface waters of the state. Because we anticipate that the proposed project will require disturbance of more than 1 acre, we anticipate that these inspection and reporting requirements will be triggered. The following recommendations are related to general erosion potential and mitigation. Project planning and construction should follow local standards of practice with respect to temporary erosion and sedimentation control. Best management practices (BMPs) should include but not be limited to: 1. Construction activity should be scheduled or phased as much as possible to reduce the amount of earthwork activity that is performed during the winter months. 2. The winter performance of a site is dependent on a well-conceived plan for control of site erosion and storm water runoff. The site plan should include ground-cover measures, access roads, and staging areas. The contractor should be prepared to implement and maintain the required measures to reduce the amount of exposed ground. 3. TESC measures for a given area to be graded or otherwise worked should be installed soon after ground clearing. The recommended sequence of construction within a given area after clearing would be to install TESC elements and perimeter flow control prior to starting grading. 4. During the wetter months of the year, or when large storm events are predicted during the summer months, each work area should be stabilized so that if showers occur, the work area can receive the rainfall without excessive erosion or sediment transport. The required measures for an area to be “buttoned-up” will depend on the time of year and the duration the area will be left un-worked. During the winter months, areas that are to be left un-worked for more than 2 days should be mulched or covered with plastic. During the summer months, stabilization will usually consist of seal-rolling the subgrade. Such measures will aid in the contractor’s ability to get back into a work area after a storm event. The stabilization process also includes establishing temporary storm water conveyance channels through work areas to route runoff to the approved treatment/discharge facilities. September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 8 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Geologic Hazards and Mitigations 5. All disturbed areas should be revegetated as soon as possible. If it is outside of the growing season, the disturbed areas should be covered with mulch, as recommended in the erosion control plan. Straw mulch provides a cost-effective cover measure and can be made wind-resistant with the application of a tackifier after it is placed. 6. Surface runoff and discharge should be controlled during and following development. Uncontrolled discharge may promote erosion and sediment transport. Under no circumstances should concentrated discharges be allowed to flow over the top of steep slopes. 7. Soils that are to be reused around the site should be stored in such a manner as to reduce erosion from the stockpile. Protective measures may include, but are not limited to, covering with plastic sheeting, the use of low stockpiles in flat areas, or the use of silt fences around pile perimeters. It is our opinion that with the proper implementation of the TESC plans and by field-adjusting appropriate mitigation elements (best management practices) during construction, the potential adverse impacts from erosion hazards on the project may be mitigated. September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 9 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations III. PRELIMINARY DESIGN RECOMMENDATIONS 7.0 INTRODUCTION Our exploration indicates that, from a geotechnical standpoint, the property is suitable for the proposed improvements provided the recommendations contained herein are properly followed. The subject site is underlain in places by a layer of existing fill that is variable in thickness and density. Existing fill or loose soils are not suitable for support of new foundations, and warrant remedial preparation where occurring below paving. Fill soils should be removed from below foundation areas and replaced with structural fill. Medium dense to very dense native deposits or structural fill placed over medium dense to very dense native deposits are suitable for support of shallow foundations with proper preparation. 8.0 SITE PREPARATION Erosion and surface water control should be established around the clearing limits to satisfy local requirements. Existing buried utilities, vegetation, topsoil, and any other deleterious materials should be removed where they are located below planned construction areas. All disturbed soils should be removed to expose underlying, undisturbed, native sediments and replaced with structural fill, as needed. All excavations below final grade made for clearing and grubbing activities should be backfilled, as needed, with structural fill, as discussed under the “Structural Fill” section of this report. Once clearing and grubbing activities have been completed, existing fill, where encountered, should be addressed. We recommend that existing fill be removed from below areas of planned foundations to expose underlying, undisturbed native sediments, followed by restoration of the planned foundation grade with structural fill. Removal of existing fill should extend laterally beyond the building footprint by a distance equal to the depth of overexcavation. For example, if existing fill is removed to a depth of 2 feet below a planned footing area, the excavation should also extend laterally 2 feet beyond the building footprint in that area. Where existing fill is removed and replaced with structural fill, conventional shallow foundations may be used for building support. The required depth of removal should be determined in the field based on actual conditions encountered during excavation. 8.1 Site Drainage and Surface Water Control The site should be graded to prevent water from ponding in construction areas and/or flowing into excavations. Exposed grades should be crowned, sloped, and smooth drum-rolled at the end of each day to facilitate drainage. Accumulated water must be removed from subgrades and work areas immediately prior to performing further work in the area. Equipment access September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 10 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations may be limited, and the amount of soil rendered unfit for use as structural fill may be greatly increased if drainage efforts are not accomplished in a timely sequence. If an effective drainage system is not utilized, project delays and increased costs could be incurred due to the greater quantities of wet and unsuitable fill, or poor access and unstable conditions. Although we did not encounter ground water at the time of our explorations (late summer), we anticipate that perched ground water may be encountered over the unweathered till during the wet season at the site. We do not anticipate the need for extensive dewatering in advance of excavations. However, the contractor should be prepared to intercept any ground water seepage entering the excavations and route it to a suitable discharge location. Final exterior grades should promote free and positive drainage away from the building at all times. Water must not be allowed to pond or to collect adjacent to foundations or within the immediate building area. We recommend that a gradient of at least 3 percent for a minimum distance of 10 feet from the building perimeters be provided, except in paved locations. In paved locations, a minimum gradient of 1 percent should be provided, unless provisions are included for collection and disposal of surface water adjacent to the structure. 8.2 Subgrade Protection If building construction will proceed during the winter, we recommend the use of a working surface of sand and gravel, crushed rock, or quarry spalls to protect exposed soils, particularly in areas supporting concentrated equipment traffic. In winter construction staging areas and areas that will be subjected to repeated heavy loads, such as those that occur during construction of masonry walls, a minimum thickness of 12 inches of quarry spalls or 18 inches of pit run sand and gravel is recommended. If subgrade conditions are soft and silty, a geotextile separation fabric, such as Mirafi 500X or approved equivalent, should be used between the subgrade and the new fill. For building pads where floor slabs and foundation construction will be completed in the winter, a similar working surface should be used, composed of at least 6 inches of pit run sand and gravel or crushed rock. Construction of working surfaces from advancing fill pads could be used to avoid directly exposing the subgrade soils to vehicular traffic. Foundation subgrades may require protection from foot and equipment traffic and ponding of runoff during wet weather conditions. Typically, compacted crushed rock or a lean-mix concrete mat placed over a properly prepared subgrade provides adequate subgrade protection. Foundation concrete should be placed and excavations backfilled as soon as possible to protect the bearing surface. September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 11 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations 8.3 Proof-Rolling and Subgrade Compaction Following the recommended clearing, site stripping, and planned excavation, the stripped subgrade within the building areas should be proof-rolled with heavy, rubber-tired construction equipment, such as a fully loaded, tandem-axle dump truck. Proof-rolling should be performed prior to structural fill placement or foundation excavation. The proof-roll should be monitored by the geotechnical engineer so that any soft or yielding subgrade soils can be identified. Any soft/loose, yielding soils should be removed to a stable subgrade. The subgrade should then be scarified, adjusted in moisture content, and recompacted to the required density. Proof-rolling should only be attempted if soil moisture contents are at or near optimum moisture content. Proof-rolling of wet subgrades could result in further degradation. Low areas and excavations may then be raised to the planned finished grade with compacted structural fill. Subgrade preparation and selection, placement, and compaction of structural fill should be performed under engineering-controlled conditions in accordance with the project specifications. 8.4 Overexcavation/Stabilization Construction during extended wet weather periods could create the need to overexcavate exposed soils if they become disturbed and cannot be recompacted due to elevated moisture content and/or weather conditions. Even during dry weather periods, soft/wet soils, which may need to be overexcavated, may be encountered in some portions of the site. If overexcavation is necessary, it should be confirmed through continuous observation and testing by AESI. Soils that have become unstable may require remedial measures in the form of one or more of the following: 1. Drying and recompaction. Selective drying may be accomplished by scarifying or windrowing surficial material during extended periods of dry and warm weather. 2. Removal of affected soils to expose a suitable bearing subgrade and replacement with compacted structural fill. 3. Mechanical stabilization with a coarse crushed aggregate compacted into the subgrade, possibly in conjunction with a geotextile. 4. Soil/cement admixture stabilization. 8.5 Wet Weather Conditions If construction proceeds during an extended wet weather construction period and the moisture-sensitive site soils become wet, they will become unstable. Therefore, the bids for site grading operations should be based upon the time of year that construction will proceed. It is expected that in wet conditions additional soils may need to be removed and/or other September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 12 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations stabilization methods used, such as a coarse crushed rock working mat to develop a stable condition if silty subgrade soils are disturbed in the presence of excess moisture. The severity of construction disturbance will be dependent, in part, on the precautions that are taken by the contractor to protect the moisture- and disturbance-sensitive site soils. If overexcavation is necessary, it should be confirmed through continuous observation and testing by a representative of our firm. 8.6 Temporary and Permanent Cut Slopes In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction. For estimating purposes, however, we anticipate that temporary, unsupported cut slopes in the existing fill or loose to medium dense native deposits can be made at a maximum slope of 1.5H:1V (Horizontal:Vertical) or flatter. Temporary slopes in dense to very dense till sediments may be planned at 1H:1V. As is typical with earthwork operations, some sloughing and raveling may occur, and cut slopes may have to be adjusted in the field. If ground water seepage is encountered in cut slopes, or if surface water is not routed away from temporary cut slope faces, flatter slopes will be required. In addition, WISHA/OSHA regulations should be followed at all times. Permanent cut and structural fill slopes that are not intended to be exposed to surface water should be designed at inclinations of 2H:1V or flatter. All permanent cut or fill slopes should be compacted to at least 95 percent of the modified Proctor maximum dry density, as determined by ASTM:D 1557, and the slopes should be protected from erosion by sheet plastic until vegetation cover can be established during favorable weather. 8.7 Frozen Subgrades If earthwork takes place during freezing conditions, all exposed subgrades should be allowed to thaw and then be recompacted prior to placing subsequent lifts of structural fill or foundation components. Alternatively, the frozen material could be stripped from the subgrade to reveal unfrozen soil prior to placing subsequent lifts of fill or foundation components. The frozen soil should not be reused as structural fill until allowed to thaw and adjusted to the proper moisture content, which may not be possible during winter months. 9.0 STRUCTURAL FILL All references to structural fill in this report refer to subgrade preparation, fill type and placement, and compaction of materials, as discussed in this section. If a percentage of compaction is specified under another section of this report, the value given in that section should be used. September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 13 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations After stripping, planned excavation, and any required overexcavation have been performed to the satisfaction of the geotechnical engineer, the upper 12 inches of exposed ground in areas to receive fill should be recompacted to a firm and unyielding condition as determined by the geotechnical engineer. If the subgrade contains silty soils and too much moisture, adequate recompaction may be difficult or impossible to obtain and should probably not be attempted. In lieu of recompaction, the area to receive fill should be blanketed with washed rock or quarry spalls to act as a capillary break between the new fill and the wet subgrade. Where the exposed ground remains soft and further overexcavation is impractical, placement of an engineering stabilization fabric may be necessary to prevent contamination of the free-draining layer by silt migration from below. After recompaction of the exposed ground is tested and approved, or a free-draining rock course is laid, structural fill may be placed to attain desired grades. Structural fill is defined as non-organic soil, acceptable to the geotechnical engineer, placed in maximum 8-inch loose lifts, with each lift being compacted to 95 percent of the modified Proctor maximum density using ASTM:D 1557 as the standard. For on-site utility trench backfill, including the backfill resulting from the removal of existing utility lines below the planned structure, we recommend the structural fill standard described above. In the case of roadway and utility trench filling within City rights-of-way, the backfill should be placed and compacted in accordance with current City of Federal Way codes and standards. The top of the compacted fill should extend horizontally outward a minimum distance of 3 feet beyond the locations of the roadway edges before sloping down at an angle of 2H:1V. The contractor should note that any proposed fill soils must be evaluated by AESI prior to their use in fills. This would require that we have a sample of the material 72 hours in advance to perform a Proctor test and determine its field compaction standard. Soils in which the amount of fine-grained material (smaller than the No. 200 sieve) is greater than approximately 5 percent (measured on the minus No. 4 sieve size) should be considered moisture-sensitive. Use of moisture-sensitive soil in structural fills should be limited to favorable dry weather conditions. The native and existing fill soils present on-site contained variably high amounts of silt and are considered moisture-sensitive. Therefore, we anticipate that the use of on-site soils as structural fill may require moisture-conditioning to achieve proper compaction. For non- structural applications, the on-site material is generally considered suitable, as long as it is free of vegetation, topsoil, and any other deleterious materials. In addition, construction equipment traversing the site when the soils are wet can cause considerable disturbance. If fill is placed during wet weather or if proper compaction cannot be obtained, a select import material consisting of a clean, free-draining gravel and/or sand should be used. Free-draining fill consists of non-organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction with at least 25 percent retained on the No. 4 sieve. September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 14 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations A representative from our firm should inspect the stripped subgrade and be present during placement of structural fill to observe the work and perform a representative number of in-place density tests. In this way, the adequacy of the earthwork may be evaluated as filling progresses, and any problem areas may be corrected at that time. It is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a fill. As such, we are available to aid in developing a suitable monitoring and testing program. 10.0 FOUNDATIONS We expect the depth to bearing soil to vary across the building footprint relative to the foundation subgrade elevation of the planned building. The existing fill was thickest (about 7 feet in depth) in the northwestern portion of the site, in the vicinity of EP-4, near the top of a north-south trending slope. This slope appears to have been constructed during previous grading activities. Based on the provided site plans, a significant portion of this fill will be removed as part of the cuts necessary for the below-level parking. Cuts up to 10 feet are anticipated at the northwestern corner of the building. Where present, existing fill should be removed below all foundations, exposing medium dense to very dense native till sediments. Spread footings may be used for building support when founded directly on undisturbed native sediments, on structural fill placed over suitable native sediments. If foundations will be supported by a combination of very dense native sediments and new structural fill, we recommend that an allowable bearing pressure of 3,000 pounds per square foot (psf) be used for design purposes, including both dead and live loads. If foundations will be supported entirely by very dense native sediments, an allowable foundation soil bearing pressure of 5,000 psf may be used for design. An increase of one-third may be used for short-term wind or seismic loading. Perimeter footings should be buried at least 18 inches into the surrounding soil for frost protection. However, all footings must penetrate to the prescribed bearing stratum, and no footing should be founded in or above organic or loose soils. It should be noted that the area bound by lines extending downward at 1H:1V from any footing must not intersect another footing or intersect a filled area that has not been compacted to at least 95 percent of ASTM:D 1557. In addition, a 1.5H:1V line extending down from any footing must not daylight because sloughing or raveling may eventually undermine the footing. Thus, footings should not be placed near the edge of steps or cuts in the bearing soils. Anticipated settlement of footings founded as described above should be on the order of ¾ inch or less. However, disturbed soil not removed from footing excavations prior to footing September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 15 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations placement and footings placed above loose soils could result in increased settlements. All footing areas should be inspected by AESI prior to placing concrete to verify that the design bearing capacity of the soils has been attained and that construction conforms to the recommendations contained in this report. Such inspections may be required by the governing municipality. Perimeter footing drains should be provided, as discussed under the “Drainage Considerations” Section 13.0 of this report. 11.0 FLOOR SUPPORT If crawl-space floors are used, an impervious moisture barrier should be provided above the soil surface within the crawl space. Slab-on-grade floors may be used over medium dense to very dense native soils, or over structural fill placed as recommended in the “Site Preparation” and “Structural Fill” sections of this report. Slab-on-grade floors should be cast atop a minimum of 4 inches of washed pea gravel or washed crushed “chip” rock with less than 3 percent passing the U.S. No. 200 sieve to act as a capillary break. The floors should also be protected from dampness by covering the capillary break layer with an impervious moisture barrier at least 10 mils in thickness. 12.0 FOUNDATION WALLS All backfill behind foundation walls or around foundation units should be placed as per our recommendations for structural fill and as described in this section of the report. Horizontally backfilled walls, which are free to yield laterally at least 0.1 percent of their height, may be designed using an equivalent fluid equal to 35 pounds per cubic foot (pcf). Fully restrained, horizontally backfilled, rigid walls that cannot yield should be designed for an equivalent fluid of 50 pcf. Walls with sloping backfill up to a maximum gradient of 2H:1V should be designed using an equivalent fluid of 55 pcf for yielding conditions or 75 pcf for fully restrained conditions. If parking areas are adjacent to walls, a surcharge equivalent to 2 feet of soil should be added to the wall height in determining lateral design forces. As required by the 2012 IBC, retaining wall design should include a seismic surcharge pressure in addition to the equivalent fluid pressures presented above. Considering the site soils and the recommended wall backfill materials, we recommend a seismic surcharge pressure of 5H and 10H psf, where H is the wall height in feet for the “active” and “at-rest” loading conditions, respectively. The seismic surcharge should be modeled as a rectangular distribution with the resultant applied at the mid-point of the walls. The lateral pressures presented above are based on the conditions of a uniform backfill consisting of excavated on-site soils, or imported structural fill compacted to 90 percent of September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 16 Subsurface Exploration, Geologic Hazards, Federal Way Senior Living and Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations ASTM:D 1557. A higher degree of compaction is not recommended, as this will increase the pressure acting on the walls. A lower compaction may result in settlement of the slab-on-grade or other structures supported above the walls. Thus, the compaction level is critical and must be tested by our firm during placement. Surcharges from adjacent footings or heavy construction equipment must be added to the above values. Perimeter footing drains should be provided for all retaining walls, as discussed under the “Drainage Considerations” section of this report. It is imperative that proper drainage be provided so that hydrostatic pressures do not develop against the walls. This would involve installation of a minimum, 1-foot-wide blanket drain to within 1 foot of finish grade for the full wall height using imported, washed gravel against the walls. A prefabricated drainage mat is not a suitable substitute for the gravel blanket drain unless all backfill against the wall is free-draining. 12.1 Passive Resistance and Friction Factors Lateral loads can be resisted by friction between the foundation and the natural glacial soils or supporting structural fill soils, and by passive earth pressure acting on the buried portions of the foundations. The foundations must be backfilled with structural fill and compacted to at least 95 percent of the maximum dry density to achieve the passive resistance provided below. We recommend the following allowable design parameters: • Passive equivalent fluid = 300 pcf • Coefficient of friction = 0.35 13.0 DRAINAGE CONSIDERATIONS All retaining and perimeter foundation walls should be provided with a drain at the base of the footing elevation. Drains should consist of rigid, perforated, PVC pipe surrounded by washed pea gravel. The level of the perforations in the pipe should be set at or slightly below the bottom of the footing grade beam, and the drains should be constructed with sufficient gradient to allow gravity discharge away from the building. In addition, all retaining walls should be lined with a minimum, 12-inch-thick, washed gravel blanket that extends to within 1 foot of the surface and is continuous with the foundation drain. Roof and surface runoff should not discharge into the foundation drain system, but should be handled by a separate, rigid, tightline drain. In planning, exterior grades adjacent to walls should be sloped downward away from the structure to achieve surface drainage. September 9, 2014 ASSOCIATED EARTH SCIENCES, INC. LDM/ld – KE140420A2 – Projects\20140420\KE\WP Page 17 D e s M o i n e s F e d e r a l W a y K e n t Copyright:© 2013 National Geographic Society, i-cubed REFERENCE: USGS, KING CO VICINITY MAPFEDERAL WAY S ENIO R LIVINGFEDERAL WAY, WASHINGTON FIGURE 1 DATE 8/14 PROJ. NO. KE140420A 0 20001000 FEETNOTE: BL ACK AND WHITE REPROD UCTION OF THIS C OLOR ORIGINAL MAYREDUCE IT S EFFECTIVENES S A ND L EAD TO IN CORRECT INTE RPRETATION.Document Path: H:\GIS_Projects\aTemplates\aVM_Template\ProjectVicinity_King.mxd± S 272nd St SR 99S I T E !(9 9 ¥5 S 2 7 2 N D S T NOTE: BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAYREDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION.a s s o c i a t e de a r t h s c i e n c e si n c o r p o r a t e dFEET25 500NREFERENCE: BARGHAUSENFIGURE 2DATE 08/14PROJ. NO. KE140420AProjects 140420 Federal Way Senior Living \ 140420 Site and Exploration Plan.cdrSITE AND EXPLORATION PLANFEDERAL WAY SENIOR LIVINGFEDERAL WAY, WASHINGTONEP-5EP-3EP-2EP-4EP-7EP-1EP-6APPROXIMATE LOCATIONOF EXPLORATION BORINGTYPAPPROXIMATE LOCATIONOF EXPLORATION BORINGTYP 7.0 OTHER PERMITS 17157-TIR.doc 7.0 OTHER PERMITS Other permits required for this development include: · SEPA Determination · NPDES Permit from the Department of Ecology · Site Development Permit from the City of Federal W ay · Building Permit from the City of Federal Way · Water connection permit from Highline Water District · Sewer connection permit from Midway Sewer District 8.0 ESC ANALYSIS AND DESIGN 17157-TIR.doc 8.0 ESC ANALYSIS AND DESIGN The existing detention pond will be used for the erosion control pond during construction to capture sediment laden runoff. Stormwater runoff will be conveyed to this sediment pond via v- ditches with rock check dams to further control onsite sediment before discharging to the existing storm system. A construction entrance will be constructed off the paved private access on-site. A silt fence will be installed around the south, east, and north property lines of the site to prevent any sediment from leaving the site and protect adjacent properties. Please see the following pages of this report for the SWPPP prepared for the project site for further information. 9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATIONS OF COVENANT 17157-TIR.doc 9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT Appropriate bond quantity worksheets and facility summary forms will be included within the final TIR. 10.0 OPERATIONS AND MAINTENANCE MANUAL 17157-TIR.doc 10.0 OPERATIONS AND MAINTENANCE MANUAL Maintenance checklists for the various stormwater facilities around the project site will be included in the final TIR. Please use these pages as guidance when performing maintenance around the site which should occur at a minimum every fall and spring, as well as after every storm event exceeding 1 inch of precipitation in 24 hours.