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Stormwater Infiltration Report - 806 Cary Rd - Edmonds - 1-23-20 - Krazan 09219016STORMWATER INFILTRATION STUDY PROPOSED KENTNER SFR 806 CARY ROAD EDMONDS, WASHINGTON 98020 Project No. 092-19016 JANUARY 23, 2020 Prepared for: DANIEL AND TRESSA KENTNER 806 CARY ROAD EDMONDS, WA 98020 Prepared by: KRAZAN & ASSOCIATES, INC. GEOTECHNICAL ENGINEERING DIVISION 4303 — 198t' St SW Lynnwood, Washington 98036 (425) 485-5519 �Irazan & ASSOCIATES,INC. GEOTECHNICAL ENGINEERING • ENVIRONMENTAL ENGINEERING CONSTRUCTION TESTING & INSPECTION January 23, 2020 Daniel and Tressa Kentner 806 Cary Road Edmonds, WA 98020 Reference: Stormwater Infiltration Study Proposed Kentner SFR 806 Cary Road Edmonds, WA 98020 Greetings, Krazan File Number 092-19016 Email: daniel.kentner@yahoo.com tressakentner@ymail.com Phone: 626-388-6602 In accordance with your request, we have completed a Stormwater Infiltration Study for the referenced site. The results of our investigation are presented in the attached report. If you have any questions, or if we can be of further assistance, please do not hesitate to contact our office. Respectfully submitted, KRAZAN & ASSOCIATES, INC. Michael D. Rundquist, P.E. Senior Project Manager JGL/MDR Offices Serving The Western United States 4303 — 1981 St SW • Lynnwood, Washington 98036 • (425) 485-5519 • Fax: (425) 485-6837 I'(raZ;an & ASSOCIATEs,INC. GEOTECHNICAL ENGINEERING • ENVIRONMENTAL ENGINEERING CONSTRUCTION TESTING & INSPECTION TABLE OF CONTENTS INTRODUCTION.............................................................................................................................................1 PROJECTDESCRIPTION.............................................................................................................................. I PURPOSE AND SCOPE..................................................................................................................................1 GEOLOGICSETTING.................................................................................................................................... 2 FIELD INVESTIGATION............................................................................................................................... 2 STORMWATER INFILTRATION RATE - "PIT" METHOD...................................................................3 CONCLUSIONS AND RECOMMENDATIONS.......................................................................................... 4 TESTINGAND INSPECTION........................................................................................................................ 5 LIMITATIONS................................................................................................................................................. 5 VICINITYMAP....................................................................................................................................Figure 1 SITEPLAN............................................................................................................................................Figure 2 FIELD INVESTIGATION AND LABORATORY TESTING .................................................. Appendix A Offices Serving The Western United States 4303 —198"' St SW • Lynnwood, Washington 98036 • (425) 485-5519 • Fax: (425) 485-6837 �1ra7_ an & ASSOCIATES,INC. GEOTECHNICAL ENGINEERING • ENVIRONMENTAL ENGINEERING CONSTRUCTION TESTING & INSPECTION January 23, 2020 STORMWATER INFILTRATION STUDY PROPOSED KENTNER SFR 806 CARY ROAD EDMONDS, WASHINGTON 98020 INTRODUCTION KA Project No. 092-19016 This report presents the results of our stormwater Pilot Infiltration Test (PIT) study for the residential project located at 806 Cary Road in Edmonds, Washington, as shown on the Vicinity Map in Figure 1. The scope of this stormwater infiltration study was outlined in our proposal (Krazan proposal number G19979WAL), dated December 6, 2019. We have been requested to conduct stormwater infiltration testing to aid in project design. The scope of work for geotechnical engineering services includes the exploration and evaluation of subsurface soil and groundwater conditions at the project site, with geotechnical conclusions and recommendations regarding stormwater infiltration presented in a written report. PROJECT DESCRIPTION It is our understanding that the project will include the demolition of the existing house and the construction of a new, multi -story single family residence (SFR). The project site is located in a residential neighborhood, with a relatively level to gently sloping ground surface. We have been provided with a survey drawing prepared by West Alliance Professional Land Surveyors titled, "Final Short Plat for Mike & Sabina Norton," dated December 1, 2018. Project plans for the new residence have not been provided at this time. PURPOSE AND SCOPE We have been requested to conduct a geotechnical investigation for stormwater infiltration testing to aid in project design. It is our understanding that the City of Edmonds refers to the Washington State Department of Ecology (DOE) "Stormwater Management Manual for Western Washington," (2012, updated 2014) for stormwater management on development projects. The Washington DOE stormwater manual indicates that a stormwater Pilot Infiltration Test (PIT) should be used to determine the stormwater infiltration rate for a project site. Offices Serving The Western United States 4303 - 1981 St SW • Lynnwood, Washington 98036 • (425) 485-5519 • Fax: (425) 485-6837 KRAZAN & ASSOCIATES, INC. GEOLOGIC SETTING KA No. 092-19016 Stormwater Infiltration Study Proposed Kentner SFR 806 Cary Road Edmonds, WA January 23, 2020 Page No. 2 The "Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles, Washington," compiled by James P. Minard (USGS, 1983) indicates that the property is underlain by the Quaternary Whidbey Formation (Qw). The Whidbey Formation includes sediment from an ancient interglacial period of time. The map unit description indicates that the interglacial sediments generally consist of compact, bedded sand. Layers of compact peat and organic -rich sand are also present within the formation at some locations. FIELD EXPLORATION We visited the site on January 3, 2020 to explore the subsurface soil and groundwater conditions and preform a small-scale pilot infiltration test (PIT) in the eastern portion of the site as shown on the Site Plan in Figure 2. The two soil excavations (INF-1 and TP-1) were both excavated to a depth of approximately 6.0 feet below current grade. Geotechnical representatives from Krazan and Associates were present during the stormwater testing, examined the subsurface soil conditions encountered, obtained samples of the subsurface soils, and maintained logs of the explorations. Subsurface Conditions: Two (2) soil excavations were conducted for the subsurface investigation. The following paragraphs include soil descriptions for each pit location. Infiltration Pit 1 (INF-1) was located in the eastern portion of the property. INF-1 encountered approximately 0.5 foot of sod and topsoil. Underlying the sod and topsoil, INF-1 exposed brown silty sand with gravel and organics to a depth of about 2.0 feet below the ground surface. We interpreted this material to be undocumented fill. Underlying the fill material, INF-1 exposed medium dense, rusty brown silty sand with gravel, trace cobbles and trace organics to a depth of approximately 5.0 feet below grade. We interpreted the medium dense, rusty brown silty sand to be native weathered soil. Below the weathered soil, INF-1 exposed dense to very dense, gray silty sand with gravel to the depth explored of about 6.0 feet below grade. We interpreted the dense to very dense, silty sand with gravel to be native glacial till. Test Pit 1 (TP-1) was located in the southeast portion of the property. TP-1 encountered approximately 0.5 foot of sod and topsoil. Underlying the sod and topsoil, TP-1 exposed brown silty sand with gravel and organics to a depth of about 2.0 feet below the ground surface. We interpreted this material to be undocumented fill. Underlying the fill material, the test pit exposed medium dense, rusty brown to gray silty sand with gravel, trace cobbles and trace organics to a depth of approximately 4.0 feet below grade. We interpreted the medium dense, rusty brown to gray silty sand to be native weathered soil. Below the Krazan & Associates, Inc. Offices Serving The Western United States KRAZAN & ASSOCIATES, INC. KA No. 092-19016 Stormwater Infiltration Study Proposed Kentner SFR 806 Cary Road Edmonds, WA January 23, 2020 Page No. 3 weathered soil, the test pit exposed dense to very dense, gray silty sand with gravel to the depth explored of about 6.0 feet below the ground surface. We interpreted the dense to very dense soil to be native glacial till. Groundwater: The test pits were checked for the presence of groundwater. Soil conditions were moist to wet, however we did not observe groundwater seepage in the explorations at the time of our site visit. Perched groundwater can occur when surface water infiltrates through less dense, more permeable soils and accumulates on top of a relatively low permeability soil layer. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount of perched water to decrease during drier times of the year and increase during wetter periods. It should be recognized that groundwater elevations may fluctuate with time. The groundwater level will be dependent upon seasonal precipitation, irrigation, as well as other factors. Therefore, groundwater levels at the time of the field investigation may be different from those encountered during the construction phase of the project. The evaluation of such factors is beyond the scope of this report. STORMWATER INFILTRATION RATE — "PIT" METHOD The "Addendum to Edmonds Community Development Code Chapter 18.30" (Edmonds Stormwater Addendum) indicates that stormwater infiltration rates can be determined using methods described in Appendix B — "Methods for Determining Design Infiltration Rates". Section B.1.1 "Methods" indicates that the small-scale PIT is an acceptable method for determining infiltration rates. Appendix B refers to the Washington State Department of Ecology (DOE) "Stormwater Management Manual for Western Washington," (SWMMWW) (2012, updated 2014) for Small -Scale PIT procedures. Infiltration testing for this project was based on procedures outlined in Volume III of the SWMMWW. One small-scale stormwater Pilot Infiltration Test was performed in the eastern (backyard) portion of the property to evaluate the design stormwater infiltration rate, if feasible. The PIT method for evaluating the stormwater infiltration rate of the site soils generally includes a small-scale excavation in the area of the proposed infiltration system. The stormwater PIT at the project site was performed at a depth of approximately 4.0 feet below the current ground elevation. The bottom of the excavation for the small-scale PIT had a surface area of approximately 12 square feet. The soils encountered at a depth of approximately 5.0 feet in INF-1 and at about 4.0 feet in TP-1 generally consisted of dense to very dense, gray silty sand with gravel to the depth explored. We Krazan & Associates, Inc. Offices Serving The Western United States KRAZAN & ASSOCIATES, INC. KA No. 092-19016 Stormwater Infiltration Study Proposed Kentner SFR 806 Cary Road Edmonds, WA January 23, 2020 Page No. 4 interpreted the soils to be native glacial till. During the excavation, some of the soil was removed from the test pits in concrete -like "chunks" due to the density of the material. Water was added to the bottom of INF-1 for an initial soaking period. After the soaking period, the water source was turned off and we initiated timed measurements of the water drawdown, also known as the falling head infiltration test. Water in the stormwater PIT did not significantly change in elevation during the approximately one hour long test, indicating very slow to almost insignificant water infiltration into the soils. CONCLUSIONS AND RECOMMENDATIONS In our opinion, stormwater infiltration is not feasible at this property due to the very low permeability of the underlying concrete -like, glacial till soils. We recommend that other possibilities for stormwater runoff management be considered for this residential project. • On -Site Stormwater Dispersion: Edmonds City code indicates that stormwater dispersion might be utilized where infiltration is not feasible. A dispersion system typically consists of a perforated pipe at the bottom of a rock -filled trench with a level spreader. The level spreader is typically made of wood or concrete and is intended to disperse water evenly when the rock trench overflows. The rock would be exposed at the surface to allow water to filter out of the trench and over the vegetated landscape nearby, such as a grass lawn. Downspout splash blocks are another method for stormwater dispersion. However, downspout splash blocks might not be allowed for this project, because 50 feet of vegetated ground surface is required for the water flow path within the property. However, it may be prudent to consult with the City to determine if an exemption might be allowed for this prof ect. • Off -Site Stormwater Outfall: It might be prudent to consider stormwater outfall in the vicinity of Shell Creek or the creek buffer located beyond the east side of the property via an easement. A drainage easement through the neighbor's property, with the owner's approval as well as approval from the City, would be required. The outfall might include a dispersion trench or similar feature to spread out the stormwater runoff to minimize the impact to wetland or creek areas. Krazan & Associates, Inc. Offices Serving The Western United States KRAZAN & ASSOCIATES, INC. KA No. 092-19016 Stormwater Infiltration Study Proposed Kentner SFR 806 Cary Road Edmonds, WA January 23, 2020 Page No. 5 • Connect to the City Storm System in Caspers Street: According to City Geographic Information System (GIS) maps, the closest existing storm system catch basins are located in Caspers Street near the intersection with Hanna Park Road. Additional catch basins are located near the intersection of Caspers Street and 3' Avenue N. This approach might be a feasible, although costly, option for stormwater management. It may be worthwhile to consult with the City of Edmonds to discuss this approach. Furthermore, it may be worthwhile to consult with neighboring property owners in regards to the installation of a new stormwater line in Cary Road. This may spread out the cost of the project. The City of Edmonds, project architect and a civil engineer should be consulted to aid in determining the most cost-effective approach regarding stormwater management for this project. TESTING AND INSPECTION We recommend that Krazan be retained to evaluate the soil conditions during construction of the stormwater management system to confirm that the soil conditions are consistent with those encountered in our explorations. This activity is an integral part of our services as acceptance of earthwork construction is dependent upon observation of the consistency of the soil and groundwater conditions, and making appropriate adjustments could be warranted if conditions vary from those indicated by our explorations. LIMITATIONS Geotechnical engineering is one of the newest divisions of Civil Engineering. This branch of Civil Engineering is constantly improving as new technologies and understanding of earth sciences improves. Although your site was analyzed using the most appropriate current techniques and methods, undoubtedly there will be substantial future improvements in this branch of engineering. In addition to improvements in the field of geotechnical engineering, physical changes in the site either due to excavation or fill placement, new agency regulations or possible changes in the proposed project after the time of completion of the geotechnical report may require the geotechnical report to be professionally reviewed. In light of this, the Owner should be aware that there is a practical limit to the usefulness of this report without critical review. Although the time limit for this review is strictly arbitrary, it is suggested that two years be considered a reasonable time for the usefulness of this report. The recommendations made in this report are based on the assumption that soil and groundwater conditions do not vary significantly from those disclosed during our field investigation. If any Krazan & Associates, Inc. Offices Serving The Western United States KRAZAN & ASSOCIATES, INC. KA No. 092-19016 Stormwater Infiltration Study Proposed Kentner SFR 806 Cary Road Edmonds, WA January 23, 2020 Page No. 6 variations or undesirable conditions are encountered during construction, the geotechnical engineer should be notified so that supplemental recommendations can be made. The conclusions of this report are based on the information provided regarding any proposed construction. If construction is relocated or redesigned, the conclusions in this report may not be valid. The geotechnical engineer should be notified of any changes so that the recommendations can be reviewed and re-evaluated. The scope of our services did not include any environmental site assessment for the presence or absence of hazardous and/or toxic materials in the soil, groundwater or atmosphere, or the presence of wetlands. Any statements, or absence of statements, in this report or on any exploration log, regarding odors, unusual or suspicious items, or conditions observed are strictly for descriptive purposes and are not intended to convey engineering judgment regarding potential hazardous and/or toxic assessments. The information presented herein is based upon professional interpretation utilizing standard engineering practices and a degree of conservatism deemed proper for this project. It is not warranted that such information and interpretation cannot be superseded by future developments. We emphasize that this report is valid for this project as outlined above, and should not be used for any other site. Krazan & Associates, Inc. Offices Serving The Western United States KRAZAN & ASSOCIATES, INC. CLOSURE KA No. 092-19016 Stormwater Infiltration Study Proposed Kentner SFR 806 Cary Road Edmonds, WA January 23, 2020 Page No. 7 If you have any questions, or if we may be of further assistance, please do not hesitate to contact our office at (425) 485-5519. Respectfully submitted, KRAZAN & ASSOCIATES, INC. 01/23/20 Michael D. Rundquist, P.E. Senior Project Manager JGL/MDR wasIli �� fo 2862 $� used Geota Jaffrey G. League Jeffrey G. League, L.G. Project Geologist Krazan & Associates, Inc. Offices Serving The Western United States Vicinity Map N (Not to Scale) Approximate v Site Area OIND ST SW 7921Y0 PL Sx, EDMQ ; DS 193RO STsw jDIIG 24 I' A ST SW L. z MA W. x �— � k zn2N W— r �� DALEY ST r a i aEL C S F MAW!, ST Heights nAYroN sr MAPLE 5T �p - Marx sr sw 3 ALDER Sr wCFMRST 21215T SW x _ � BpIN r X SIN � h"AY S'v1 r•' z ; ^ P� PWNE 5T Pd 2 2 W6TH Sr $w m� r- w EIR ST 27arf1 Sr sw � I �s _ t� 210T1157 S W —Ch Se—JL < 3 Lake m a J tz4 rN Sr SW Wood ay ; ; 4' n 4 a I26TH ST 5w ; sperance 226TN PL SW 3 229TN sr IN < ; 229TN'ST•SW v & U 230TH ST SW iO4 a 806 Cary Rd, Edmonds, WA Reference: The Vicinity Map is based on a USGS topographic map titled, "Edmond East Quadrangle - Washington", dated 2017. =� K �ZZ & ASSOCIATES,INC. Kentner SFR - Infiltration - Edmonds, WA Date: January 2020 Project Number: 092-19016 Drawn By: NG Figure 1 Not to scale Site Plan N (Not to Scale) Approximate Site Boundary — — — — — — — — — — — Driveway INF-1 806 Cary Rd Residence TP-1 ---------------- LEGENDReference: The site plan is based on the PDS Map Portal Snohomish County Planning and Development Services. INF4 Number and Approximate Location of Pilot Infiltration TestZ & A S S O C I A T E S, I N C. —Kraz;at Tf Number and Approximate Kentner SFR - Infiltration - Edmonds, WA Location of Test Pit Exploration ll Note: Site plan features are approximate. APPENDIX A FIELD INVESTIGATION AND LABORATORY TESTING Field Investigation The field investigation consisted of a surface reconnaissance and a subsurface exploration program. Two (2) pit explorations were excavated by a Krazan subcontractor, and the soils were sampled for the subsurface exploration at this site. The soil explorations were conducted on January 3, 2020, and both excavations were advanced to a depth of about 6.0 feet below the existing ground surface. Approximate exploration locations are shown on the Site Plan (Figure 2). The depths shown on the attached soil logs are from the existing ground surface at the time of our exploration. The soils encountered were logged in the field during the subsurface exploration and, with supplementary laboratory test data, are described in accordance with the Unified Soil Classification System (USCS). All samples from the explorations were returned to our laboratory for evaluation. The logs of the soil explorations along with the laboratory test results are presented in this appendix. Laboratory Testing The laboratory testing program was developed primarily to determine the index properties of the soils. Test results were used for soil classification and as criteria for determining the engineering characteristics of the subsurface materials encountered. Soil Classification USCS Soil Classification Major Division Group Description Coarse- Grained Soils Gravel and Gravelly Soils < 50% coarse fraction passes #4 sieve Gravel (with little or no fines) GW Well -Graded Gravel GP Poorly Graded Gravel Gravel (with > 12% fines) GM Silty Gravel GC Clayey Gravel < 50% passes #200 sieve Sand and Sandy Soils > 50% coarse fraction passes #4 sieve Sand (with little or no fines) SW Well -Graded Sand PoorlyGraded Sand Silty Sand SP Sand (with > 12% fines) SM SC Clayey Sand Fine- Grained Soils Silt and Clay Liquid Limit < 50 ML Silt CL Lean Clay OL Organic Silt and Clay (Low Plasticity) > 50% passes #200 sieve Silt and Clay Liquid Limit > 50 MH Inorganic Silt CH Inorganic Clay OH Organic Clay and Silt (Med. to High Plasticity) Highly Organic Soils PT Peat Relative Density with Respect to SPT N-Value Coarse -Grained Soils Fine -Grained Soils Density N-Value (Blows/Ft) Density N-Value (Blows/Ft) Very Loose 0-4 Very Soft 0-1 Loose Medium Dense 5 -10 Soft Medium Stiff 2-4 11 - 30 5-8 Dense 31 -50 Stiff 9 - 15 Very Dense > 50 Very Stiff 16 - 30 Hard > 30 LOG OF EXPLORATORY TEST PIT INF-1 KRAZAN AND ASSOCIATES, INC. PROJECT: Kentner SFR - Infiltration DATE: 1/3/20 PROJECT NO.: 096-19016 PAGE: 1 of 1 CONTRACTOR: NW Exc. and Trucking SURFACE ELEV.: Approx. 42' SAMPLE METHOD: Grab LOCATION: Edmonds, WA Natural Moisture Content and Atterberg Limits J ca J W J MATERIAL DESCRIPTION z° W a. Plastic Moisture Liquid = y w W a W Limit Content Limit a. o ? � Cl) y 10 30 50 70 Sod and Topsoil - - - ------------------------------------------------------------------------------------------------ Brown Silty Sand with Gravel and Organics (Loose, Moist) (Fill) 1 2 --------------------------------------------------------------------------------------------------------------- Rusty Brown, Silty Sand with Gravel, Trace Cobbles and Trace Organics (SM)(Loose to Medium Dense, Moist)(Weathered Soils) 1 3 4 2 G 5 '' -------------------------------------------------------------- Gray Silty Sand with Gravel (SM)(Dense to Very Dense, Moist)(Glacial Till) 3 6 End of Exploratory Test Pit 7 8 9 10 Water Level Initial: 0 Final: T Water Observations: Groundwater seepage was not observed at the time of the soil exploration. Notes: -- LOG OF EXPLORATORY TEST PIT TP-1 KRAZAN AND ASSOCIATES, INC. PROJECT: Kentner SFR - Infiltration DATE: 1/3/20 PROJECT NO.: 096-19016 PAGE: 1 of 1 CONTRACTOR: NW Exc. and Trucking SURFACE ELEV.: Approx. 42' SAMPLE METHOD: Grab LOCATION: Edmonds, WA Natural Moisture Content and Atterberg Limits J ca J W J MATERIAL DESCRIPTION z° W a. Plastic Moisture Liquid = y w W a W Limit Content Limit a. o ? � Cl) y 10 30 50 70 Sod and Topsoil - - - ------------------------------------------------------------------------------------------------ Brown Silty Sand with Gravel and Organics (Loose, Moist) (Fill) 1 2 Rusty Brown to Gray, Silty Sand with Gravel, Trace Cobbles 1 G and Trace Organics (SM)(Loose to Medium Dense, Moist)(Weathered Soils) 3 2 G 4 ------ -------- ------- -------- -------- -------- Gray, Silty Sand with Gravel (SM)(Dense to Very Dense, Moist)(Glacial Till) 5 3 End of Exploratory Test Pit 7 8 9 10 Water Level Initial: 0 Final: T Water Observations: Groundwater seepage was not observed at the time of the soil exploration. Notes: -- 0-1 W Z V_ Z W U 0_ W 0- 100 90 80 70 60 50 40 30 20 10 Krazan & Associates Sieve Analysis 000 N I I i 100 10 1 0.1 0.01 0.001 GRAIN SIZE - mm. %+3„ % Gravel % Sand % Fines Coarse I Fine Coarse I Medium Fine Silt Clay 0.0 3.2 13.4 7.7 16.0 34.9 24.8 Test Results (ASTM C-136 & ASTM C-117) Opening Percent Spec." Pass? Size Finer (Percent) (X=Fail) 1.25 100.0 1 96.8 .75 96.8 .5 93.8 .375 91.2 .25 86.7 #4 83.4 #10 75.7 #20 68.6 #40 59.7 #60 49.1 #100 39.9 #200 24.8 Material Description Brown silty sand with gravel. Atterberg Limits (ASTM D 4318) PL= NP LL= NV PI= NP Classification USCS (D 2487)= SM AASHTO (M 145)= A-2-4(0) Coefficients D90= 8.4815 D85= 5.4978 D60= 0.4327 D50= 0.2617 D30= 0.0941 D15= D10= Cu= Cc= Remarks Natural Moisture Content (ASTM D-2216): 12.4% Date Received: 1/6/2020 Date Tested: 1/8/2020 Tested By: Cole Demas Checked By: Corbett Mercer Title: Lab Manager (no specification provided) Location: Test Pit 1 @ 5.5' Sample Number: 69245 Depth: 5.5' Client: Dan & Tressa Kentner Project: Kentner SFR Date Sampled: 1/6/2020