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22-102749-UP-Geotechnical Report-06-15-2022-V1South Sound Geotechnical Consulting P.O. Box 39500, Lakewood, WA 98496 (253) 973-0515 June 18, 2021 35000 Pacific Hwy South, LLC 3106 Sumner Tapps Hwy East, Suite A Lake Tapps, WA 98391 Attention: Mr. Eric Corliss Subject: Geotechnical Engineering Report – Infiltration Assessment Plant 2 Relocation 35000 and 35050 Pacific Hwy South Federal Way, WA SSGC Project No. 21041 Mr. Corliss, South Sound Geotechnical Consulting (SSGC) has completed an infiltration assessment for the Plant 2 Relocation at the above addressed property in Federal Way, Washington in support of design of stormwater facilities. Our services have been completed in general conformance with our proposal P21052 (dated May 10, 2021) and authorized per signature of our agreement for services. Our scope of services included completion of one pilot infiltration test and one test pit, laboratory testing, engineering analyses, and preparation of this report. PROJECT INFORMATION The site is on the east side of Pacific Highway South and encompasses four parcels. A new concrete plant is planned on the lots. Preliminary plans have stormwater control facilities in the southwest portion of the site (on the 35050 lot). Infiltration facilities are planned to assist in stormwater control. SITE CONDITIONS The proposed stormwater facility area is currently used as an access drive into the property and parking area for trailers. A short retaining wall (on the order of 2 to 3 feet) is along the sidewalk that borders the western boundary and Pacific Highway South. The access drive rises from street level to the overall generally level property elevation. SUBSURFACE CONDITIONS Subsurface conditions were characterized by completing one infiltration test and one test pit on May 27, 2021. Test holes were advanced to final depths between 7 and 11 feet below existing ground surface. Approximate locations of the explorations are shown on Figure 1, Exploration Plan. A summary description of observed subgrade conditions is provided below. Logs of t he test holes are provided in Appendix A. Infiltration Assessment SSGC Plant 2 Relocation Federal Way, Washington SSGC Project No. 21041 June 18, 2021 2 Soil Conditions Fill was observed below the surface in the test holes and extended to depths between 1.5 to 2.5 feet. Fill consisted of mixed silt, sand, and gravel with variable debris. Native soil below the fill consisted of silty sand with gravel and occasional cobbles. This soil was in a dense condition closer to the surface, grading to medium dense with depth. It extended to the base of the test holes. Groundwater Conditions Groundwater was not observed in the test holes at the time of excavation. No visual evidence of perched seasonal groundwater (such as mottling) was observed. Groundwater levels will vary throughout the year based on seasonal precipitation and on- and off-site drainage patterns. Geologic Setting Native soils on the property are mapped as Vashon recessional outwash per the USGS “Geologic Map of the Poverty Bay 7.5’ Quadrangle, King and Pierce Counties, Washington”. These soils reportedly formed in recessional glacial outwash. However, native soils were not characteristic of recessional outwash and appeared to represent sandy drift or till. INFILTRATION CHARACTERISTICS One small-scale Pilot Infiltration Test (PIT) were completed in general conformance with the 2016 King County Surface Water Design Manual to assess infiltration potential in the native soils. Results of the infiltration test is presented in Table 1. Table 1. Infiltration Test Results Infiltration Test No. Depth of Test from Surface (feet) Soil Type Field Infiltration Rate (in/hr) Corrected Infiltration Rate (in/hr) Correction Factors* (Fg/Ft/Fp) PIT-1 8 Silty SAND with gravel 4.5 2.0 (1.0/0.5/0.9) *Correction Factors from the 2016 KCSWDM. The infiltration test was completed at a depth of 8 feet as we are unaware of planned finish grades of the proposed concrete plant, and to ensure the test was completed below the base of the retaining wall along the Pacific Hwy South sidewalk. Based on field results, we recommend a design rate of 2 inches per hour (in/hr) for the soil at the tested depth. Native soils in the test pit in the north side of the proposed stormwater facility appeared similar. Groundwater was not observed in the test holes to a depth of 11 feet below existing grades. Evidence of seasonal perched groundwater (such as mottling) was not observed in the test holes. Groundwater is not Infiltration Assessment SSGC Plant 2 Relocation Federal Way, Washington SSGC Project No. 21041 June 18, 2021 3 anticipated to affect stormwater facilities in this area of the site. In addition, following completion of the infiltration test, the test hole was advanced to a depth of 11 feet with no evidence of ponded water introduced during the test. Cation Exchange Capacity (CEC) and organic content tests were completed on a soil sample from the base of the infiltration test elevation in the test holes. Test results are summarized in Table 2. Table 2. CEC and Organic Content Results Test Location CEC Results (milliequivalents) CEC Required* (milliequivalents) Organic Content Results (%) Organic Content Required* (%) PIT-1 5.3 ≥ 5 1.02 ≥1.0 * Per the 2016 KCSWDM. CEC and organic content of the tested sample satisfy county requirements. REPORT CONDITIONS This report has been prepared for the exclusive use of 3500 Pacific Hwy South, LLC and their agents for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices in the area. No warranties, either express or i mplied, are intended or made. The analysis and recommendations presented in this report are based on observed soil conditions and test results at the indicated locations, and from other geologic information discussed. This report does not reflect variations that may occur across the project limits, or due to the modifying effects of drainage patterns or weather. This report was prepared for the planned type of development of the site as discussed herein. It is not valid for third party entities or alternate types of development on the site without the express wr itten consent of SSGC. If development plans change, we should be notified to review those changes and modify our recommendations, as necessary. The scope of services for this project does not include any environmental or biological assessment of the site including identification or prevention of pollutants, hazardous materials, or conditions. Other studies should be completed if the owner is concerned about the potential for contamination or pollution. N South Sound Geotechnical Consulting P.O. Box 39500 Lakewood, WA 98496 (253) 973-0515 Figure 1 – Exploration Plan Plant 2 Relocation Federal Way, WA SSGC Project #21041 Approximate Test Pit Location PIT - 1 TP - 1 PIT - 1 Approximate Infiltration Test Location Scale: NTS Base map from drawing titled “Site Plan – Plant 2 Relocation”, by Apex Engineering, dated 2-1-21. Legend PIT-1 TP-1 Infiltration Assessment SSGC Plant 2 Relocation Federal Way, Washington SSGC Project No. 21041 June 18, 2021 5 Appendix A Field Exploration Procedures Infiltration Assessment SSGC Plant 2 Relocation Federal Way, Washington SSGC Project No. 21041 June 18, 2021 6 Field Exploration Procedures Our field exploration for this project included one small-scale Pilot Infiltration Test (PIT) and one test pit completed on May 27, 2021. Approximate locations of the explorations are shown on Figure 1, Exploration Plan. The exploration locations were determined by pacing from site features. Ground surface elevations referenced on the logs were inferred from topography from Google Earth satellite imagery. Exploration locations and elevations should be considered accurate only to the degree implied by the means and methods used. A private excavating contractor subcontracted to SSGC dug the infiltration test holes. Select soil samples were collected and stored in moisture tight for further assessment and laboratory testing. Explorations were backfilled with excavated soils and tamped when completed. Please note that backfill in the explorations will likely settle with time. Backfill located in building or pavement areas should be re- excavated and recompacted, or replaced with structural fill. The following logs indicate the observed lithology of soils and other materials observed in the explorations at the time of excavation. Where a soil contact was observed to be gradational, our log indicates the average contact depth. Our logs also indicate the approximate depth to groundwater (where observed at the time of excavation), along with sample numbers and approximate sample depths. Soil descriptions on the logs are based on the Unified Soil Classification System. Project: Plant 2 Relocation SSGC Job # 21041 EXPLORATION LOGS PAGE 1 OF 1 Location: 35050 Pacific Hwy S., Federal Way, WA EXPLORATION LOGS FIGURE A-1 South Sound Geotechnical Consulting PIT-1, TP-1 Logged by: THR Infiltration Test PIT-1 Depth (feet) Material Description 0 – 2.5 2.5 – 11 Fill: Silt, sand, gravel with some debris (asphalt, brick, plastic sheeting): Loose to medium dense, moist, brown. Silty SAND with gravel and occasional cobble: Dense grading medium dense, moist, gray grading brown at 4 feet. (SM) (Sample S-1 @ 8 feet) Test hole completed at approximately 11 feet on 5/27/21. Infiltration test run at 8 feet. Groundwater not observed at time of excavation. Piezometer set in test hole. Approximate surface elevation: 252 feet Test Pit TP-1 Depth (feet) Material Description 0 – 1.5 1.5 – 7 Fill: Silt, sand, and gravel: Loose to medium dense, moist, brown. Silty SAND with gravel and occasional cobble: Dense grading medium dense, moist, gray grading brown at 3 feet. (SM) Test pit completed at approximately 7 feet on 5/27/21. Groundwater not observed at time of excavation. Approximate surface elevation: 252 feet Infiltration Assessment SSGC Plant 2 Relocation Federal Way, Washington SSGC Project No. 21041 June 18, 2021 7 Appendix B Laboratory Testing and Results Infiltration Assessment SSGC Plant 2 Relocation Federal Way, Washington SSGC Project No. 21041 June 18, 2021 8 Laboratory Testing Organic content and cation exchange capacity (CEC) testing on a sample from the base of the PIT test hole was completed by Northwest Agricultural Consultants of Kennewick, Washington. Results of the laboratory testing are included in this appendix. 2545 W Falls Avenue Kennewick, WA 99336 509.783.7450 www.nwag.com lab@nwag.com Sample ID Organic Matter Cation Exchange Capacity Pit-1, S-1 1.02% 5.3 meq/100g Method ASTM D2974 EPA 9081 South Sound Geotechnical Consulting PO Box 39500 Lakewood, WA 98496 Report: 55334-1-1 Date: June 3, 2021 Project No: 21041 Project Name: Corliss Plant UNIFIED SOIL CLASSIFICATION SYSTEM Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification Group Symbol Group NameB Coarse Grained Soils More than 50% retained on No. 200 sieve Gravels More than 50% of coarse fraction retained on No. 4 sieve Clean Gravels Less than 5% finesC Cu  4 and 1  Cc  3E GW Well-graded gravelF Cu  4 and/or 1  Cc  3E GP Poorly graded gravelF Gravels with Fines More than 12% finesC Fines classify as ML or MH GM Silty gravelF,G, H Fines classify as CL or CH GC Clayey gravelF,G,H Sands 50% or more of coarse fraction passes No. 4 sieve Clean Sands Less than 5% finesD Cu  6 and 1  Cc  3E SW Well-graded sandI Cu  6 and/or 1  Cc  3E SP Poorly graded sandI Sands with Fines More than 12% finesD Fines classify as ML or MH SM Silty sandG,H,I Fines Classify as CL or CH SC Clayey sandG,H,I Fine-Grained Soils 50% or more passes the No. 200 sieve Silts and Clays Liquid limit less than 50 inorganic PI  7 and plots on or above “A” lineJ CL Lean clayK,L,M PI  4 or plots below “A” lineJ ML SiltK,L,M organic Liquid limit - oven dried  0.75 OL Organic clayK,L,M,N Liquid limit - not dried Organic siltK,L,M,O Silts and Clays Liquid limit 50 or more inorganic PI plots on or above “A” line CH Fat clayK,L,M PI plots below “A” line MH Elastic SiltK,L,M organic Liquid limit - oven dried  0.75 OH Organic clayK,L,M,P Liquid limit - not dried Organic siltK,L,M,Q Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat A Based on the material passing the 3-in. (75-mm) sieve B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name. C Gravels with 5 to 12% fines require dual symbols: GW -GM well-graded gravel with silt, GW -GC well-graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay. D Sands with 5 to 12% fines require dual symbols: SW -SM well-graded sand with silt, SW -SC well-graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay E Cu = D60/D10 Cc = 6010 2 30 DxD )(D F If soil contains  15% sand, add “with sand” to group name. G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM. HIf fines are organic, add “with organic fines” to group name. I If soil contains  15% gravel, add “with gravel” to group name. J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay. K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel,” whichever is predominant. L If soil contains  30% plus No. 200 predominantly sand, add “sandy” to group name. M If soil contains  30% plus No. 200, predominantly gravel, add “gravelly” to group name. N PI  4 and plots on or above “A” line. O PI  4 or plots below “A” line. P PI plots on or above “A” line. Q PI plots below “A” line.