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Geotech Report.pdfPanGEG)C O R P O R A T E D Geotecnnlcal & tartnquake Engineering Consultants January 22, 2019 File No. 19-010 Mr. Robert Reichler 21827 76th Avenue W Edmonds, WA 98026 Subject: Infiltration Assessment Reichler Building — Daycare Tenant Improvements 21827 761" Avenue West, Edmonds, Washington Dear Mr. Reichler: As requested, PanGEO, Inc. completed an infiltration assessment of the site soils to assist the project team with the drainage design at the above referenced property. Our service consisted of excavating two test pits, performing two Small Pilot Infiltration Tests (PIT), and preparing this summary report. The intent of this report is to provide a design infiltration rate for the design of the proposed permeable pavement to be constructed at the site. PROJECT BACKGROUND The project site is located at 21827 761h Avenue West in Edmonds, Washington (see Figure 1, Vicinity Map). The subject property is an approximate half -acre lot. It is bordered by a condominium to the north, 76th Avenue West to the west, 2191h Street SW to south, and a parking area to the east. The site is currently occupied by a two-story commercial medical building and basement with parking areas to the north and east of the site. We understand the landscaped areas at the southeast portion of the site will be partially removed to extend the current parking area with permeable pavement. Furthermore, we understand it is planned to infiltrate surface water from the proposed improvements into the site soils, if feasible. The approximate layout of the site is shown on the attached Figure 2, Site and Exploration Plan. 3213 Eastlake Ave E, Ste B Seattle, WA 98102 Tel (206) 262-0370 Fax (206) 262-0374 Infiltration Assessment Reichler Building — Daycare Tenant Improvements January 22, 2019 SITE GEOLOGY AND SUBSURFACE CONDITIONS GEOLOGY Based on our review of the Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles, Washington (Minard, 1983), the site is underlain by Vashon till (geologic map unit Qvt). Vashon advance outwash (Qva) and Vashon recessional outwash (Qvr) are also mapped in the site vicinity. Vashon till (Qvt) consists of an unsorted mixture of clay, silt, sand, and gravel that is directly deposited below a glacier. This soil unit has been glacially overridden; as such it is typically dense to very dense. Till typically exhibits very low infiltration capability. Advance outwash (Qva) generally consists of sand and gravel deposited by meltwater streams emerging from advancing glaciers; it has also been glacially overridden and is typically dense to very dense. Advance outwash generally has moderate infiltration capability. Recessional Outwash (Qvr) typically consists of stratified sand and gravel, and less commonly silty sand and silt, deposited in outwash channels that carried south -draining meltwater during ice retreat away from the ice margin. Recessional outwash has not been glacially overridden and is typically loose to dense. Recessional outwash typically exhibits moderate to high infiltration capability. SOIL CONDITIONS Subsurface exploration for our infiltration assessment included logging the soils of the two test pits (PIT-1 and PIT-2) excavated on January 18, 2019. The approximate locations of these explorations are shown on the attached Figure 2, and summary test pit logs are included in Appendix A. In general, the soils encountered at the site consist of fill overlying sand with gravel that appears to be consistent with recessional outwash (Qvr). At PIT-1 we observed a surficial landscaping and fill layer to a depth of about 6 inches. Below the fill at PIT-1 we observed dense silty sand with large gravels and cobbles (Qvr) to the bottom of exploration at 2 feet below ground surface. A hand auger was used to progress to 3 feet, but large cobbles prevented any further explorations. At PIT-2, we observed fill to an approximate depth of 3 feet below ground surface. This fill consisted of bricks, wood 19-010 21827 76th Avenue W - Infiltration 2 PanGEO, Inc. Infiltration Assessment Reichler Building — Daycare Tenant Improvements January 22, 2019 debris, concrete rubble, and abundant roots. A hand auger was used to progress the pit an addition 2 feet, to 5 feet in total depth. In PIT-2, from 3 feet to 5 feet, a medium dense silty sand was observed (Qvr). GROUNDWATER Groundwater was not encountered in our test pits at the time of our exploration. It should be noted that groundwater levels will fluctuate depending on the season, amount of rainfall, surface water runoff, tides, and other factors. Generally, the water level is higher and seepage rates are greater in the wetter, winter months (typically October through May). INFILTRATION TESTING The field infiltration tests were conducted in general accordance with the procedure for Small -Scale Pilot Infiltration Test (PIT) as outlined in section B.3.2 of the June 2017 — Edmonds Stormwater Addendum. In general, the test consisted of the following procedure: • A test pit was excavated to the approximate design bottom of the proposed infiltration facilities with a minimum bottom area of 12 square feet. • The test pit was pre-soaked by maintaining a water level of at least 12 inches above the bottom of the pit. • At the end of pre-soak period, a flow meter was used to monitor the amount of water needed to maintain a constant head of 12 inches for at least one hour and until at least a point at which a constant volume of water per time unit was achieved. • At the end of the constant head test, we measured the falling head infiltration rate by shutting off the water flow and recording the drop in water level over regular time intervals for one hour or until all of the water was infiltrated. The field infiltration rate was then calculated based on the final measured volume per time unit, and the surface area of the hole. The results of our test are summarized in Table 1, below. 19-010 21827 76th Avenue W - Infiltration 3 PanGEO, Inc. Infiltration Assessment Reichler Building — Daycare Tenant Improvements January 22, 2019 Table 1 - Infiltration Test Results Test Pre- Soak Test Test Field Test Location/Depth Duration Stage Duration (hours) Result (inches/hour) Soils (hours) Constant 1 18.7 silty SAND with Head PIT-1 at 2 feet 6 gravel and cobble Falling (Recessional Head .75 11.0 Outwash) Constant 1 12.8 silty SAND with Head fill material (Fill PIT2 3 - at feet 6 Falling 75 10.0 and Recessional Head Outwash) DESIGN INFILTRATION RATE The infiltration test results measured in the field are considered short term rates. The short-term rate needs to be reduced through correction factors to generate a design infiltration rate. The corrections factors account for site variability and the number of locations tested, test method, and the degree of long-term maintenance and influent control to prevent siltation and bio-buildup. The correction factor to be used with in -situ infiltration measurements is recommended in Appendix B.2 of the June 2017 — Edmonds Stormwater Addendum. This correction factor should be 0.5 unless a lower value is warranted by site conditions, and the correction factor should be no less than 0.2. Based on the test pits excavated at the site and the subsurface conditions in the vicinity of the permeable pavement, in our opinion, a correction factor of 0.5 is appropriate for the proposed permeable pavement. Based on the test results outlined in Table 1, it is our opinion that an uncorrected test result of 10 inches per hour is appropriate. The design infiltration rate should then be 5 inches per hour, with the 0.5 correction factor. 19-010 21827 76th Avenue W - Infiltration 4 PanGEO, Inc. Infiltration Assessment Reichler Building — Daycare Tenant Improvements January 22, 2019 CONSTRUCTION CONSIDERATIONS Infiltration facilities are post -construction facilities which are designed to improve the quality and manage the volume of stormwater runoff by encouraging natural infiltration on -site. In order to protect the infiltration receptor soils from becoming clogged with sediment and/or compacted during construction, we recommend the following measures be implemented during construction: • The infiltration facilities should be constructed as late in the schedule as feasible and should not be constructed until after the upstream areas are stabilized. • Heavy equipment traffic on prepared subgrades should be limited, especially during wet weather. • If fine grained sediment is deposited or tracked onto the infiltration system subgrade, it should be removed using an excavator with a grade plate, small dozer or vacuum truck. • The subgrade should be scarified prior to placing fill to prevent sealing of the receptor soils. • Structural fill and aggregate base materials should be end -dumped at the edge of the fill area and the material pushed out over the subgrade. • Grading of the permeable pavement should be accomplished using low -impact earth -moving equipment to prevent compaction of the underlying soils. Compacting the soils to a dense to very dense conditions could significantly reduce its infiltration rates. Wide tracked vehicles such as back hoes, small dozers and bobcats are suggested. PanGEO should be retained during construction to observe excavations of infiltration facilities to confirm the infiltration facilities are constructed in the intended soil unit. LIMITATIONS We have prepared this report for use by Robert Reichler and the project team. Recommendations contained in this report are based on a site reconnaissance, a 19-010 21827 76th Avenue W - Infiltration 5 PanGEO, Inc. Infiltration Assessment Reichler Building — Daycare Tenant Improvements January 22, 2019 subsurface exploration program, review of pertinent subsurface information, and our understanding of the project. The study was performed using a mutually agreed -upon scope of work. This report may be used only by the client and for the purposes stated, within a reasonable time from its issuance. Land use, site conditions (both off and on -site), or other factors including advances in our understanding of applied science, may change over time and could materially affect our findings. Therefore, this report should not be relied upon after 24 months from its issuance. PanGEO should be notified if the project is delayed by more than 24 months from the date of this report so that we may review the applicability of our conclusions considering the time lapse. Within the limitation of scope, schedule and budget, PanGEO engages in the practice of geotechnical engineering and endeavors to perform its services in accordance with generally accepted professional principles and practices at the time the Report or its contents were prepared. No warranty, express or implied, is made. We trust that the information outlined in this report meets your need at this time. Please call if you have any questions. Sincerely, Spenser P. Scott, L.G. Staff Geologist Enclosures: Figure 1 Figure 2 Appendix A Figure A -I Figure A-2 Figure A-3 LAN r W S,y q% u 0 � o 30342 �FGIs �U AL EN Siew L. Tan, P.E. Principal Geotechnical Engineer Vicinity Map Site and Exploration Plan Summary Test Pit Logs Terms and Symbols for Boring and Test Pit Logs Log of Test Pit PIT-1 Log of Test Pit PIT-2 19-010 21827 76th Avenue W - Infiltration 6 PanGEO, Inc. Infiltration Assessment Reichler Building — Daycare Tenant Improvements January 22, 2019 REFERENCES City of Edmonds, 2017, Appendix B, Edmonds Stormwater Addendum. Minard, J.P., 1983, Geologic map of the Edmonds East and part of the Edmonds West Quadrangles, Washington: U.S. Geological Survey Miscellaneous Field Studies Map MF-1541, scale 1:24000. 19-010 21827 76th Avenue W - Infiltration 7 PanGEO, Inc. Edmonds ir me r Community College �ngsion Q wo y l Booth - ' - =a Edmonds �M.In I 11' _ ..�wsnst DHylon St - I � �302 h 2121St SW r 99 Edmonds , � 212th:,- ''• City Park •� N 22M St Sw 22Qh St SW (t0a Project Site , -'t Woodway 99 Ranch Market © > .00 , Esperance 229th St SW 22ffth St SW • -` 0 _ I ID4 i IF I. • -. 1 9a Costco Wholesale Q ;. • N 2001h St 'y - I• - — W Base Ma Goo le Terrain P� 9 - NORTH WASHINOTON Not to Scale o � PmGE(D Infiltration Assessment VICINITY MAP 21827 76th Avenue W I N C O R P O R A T E D Edmonds, Washington 19-010 I inure No 1 FM / z I wY-Janes • � II \ 11" fyP.JM.FF'(5) -i � — _ — - __..I ', 9 1 ♦ �� PUEI ti EAN1i r ,. �'� � •• RQN - .mmrNl. amn ,� ,. �� f Sow» I �•� JO"Cwr.JN I (N) Uk.NFAL' Mt.— \ F'Pyt•y ln'If l euIIUMC elSfYMI ., COwc S. - .. �.:-'—� I : PAiWB-. m I b. Q 7 "W' � ML :•6n IA PARCEL C . III IEABLE CONCRETE FOR I I I kUSE'PERMEABLE ASPHALT fCR CONC CURB (EXTRUDED). kW/REPLACED ONSITE Tw FOR ON -SITE C,AREAS, TW Aw-Jn vs ! I .wr-,H97>PIA l f F `41'�7M a • su r, x i °4t IT-1 j :;' _S �.� i - - =--�-- - -- �— LrAMENDEO SOILS. SEE r 4A INIFGRA23. 5 tIM_ 1 J':' 1 ,(a t, wEpOE CU 15. Q ! : LANDSCAPE PLANS. TYP 9955s !, �� J •p SS .T �: Q•RQi� �! 1 .--�=III$— ��-- — 1: . ' � � , I X �s✓ r J Approx. Scale 5e- 219th Street SW 1"=20' V Z k Legend: Base map modified from Site Improvement Plan by LD Engineering. LLC dated January 7. 2019 ® Approx. Test Pit Locations PanGEO, Inc., January 2019 Infiltration Assessment 17 SITE AND EXPLORATION PLAN APPENDIX A SUMMARY TEST PIT LOGS 3213 Eastlake Ave E, Ste B Seattle, WA 98102 Tel (206) 262-0370 Fax (206) 262-0374 RELATIVE DENSITY / CONSISTENCY SAND / GRAVEL SILT / CLAY SPT Approx. Relative SPT Approx. Undrained Shear Density N-values Density (/o) Consistency N-values Strength (psf) Very Loose <4 <15 Very Soft <2 <250 Loose 4 to 10 15 - 35 Soft 2 to 4 250 - 500 Med. Dense 10 to 30 35 - 65 Med. Stiff 4 to 8 500 -1000 Dense 30 to 50 65 - 85 Stiff 8 to 15 1000 - 2000 Very Dense >50 85 -100 Very Stiff 15 to 30 2000 - 4000 Hard >30 >4000 UNIFIED SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS GROUP DESCRIPTIONS •�' .. GW: Well -graded GRAVEL Gravel GRAVEL (<5% fines) .....: ...................................................... 50% or more of the coarse GP : Poorly -graded GRAVEL fraction retained on the #4 sieve. Use dual symbols (eg. o D .....: GM: ...................................................... Silty GRAVEL GP -GM) for 5% to 12% fines. GRAVEL (>12% fines) •• GC : ...................................................... Clayey GRAVEL .......................................................... .............................................................. SW: Well -graded SAND Sand SAND (<5 /o fines) 50% or more of the coarse '' % SP : Poor/ raded SAND Poorly -graded fraction passing the #4 sieve. Use dual symbols (eg. SP-SM) ..............................:....>.. " " ' ......................................................... SM : Silty SAND for 5% to 12% fines. SAND (>12% fines) ............................................................ SC : Clayey SAND ............................... ............................. ............................................................ ML : : SILT Liquid Limit < 50 CL : ............................................................ ...................................................... Lean CLAY Silt and Clay == _ OL : Organic SILT or CLAY 50%or more passing #200 sieve :.................................. MH : ...................................................... Elastic SILT Liquid Limit> 50 CH Fat CLAY OH Organic SILT or CLAY .......................... ...................................... HighlyOrganic Soils u ............................................................. PT : . PEAT Notes: 1. Soil exploration to s contain material descriptions based on visual observation and field tests using a system modified from the Uniform Soil Classification System (USCS). Where necessary laboratory tests have been conducted (as noted in the "Other Tests" column), unit descriptions may include a classification. Please refer to the discussions in the report text for a more complete description of the subsurface conditions. 2. The graphic symbols given above are not inclusive of all symbols that may appear on the borehole togs. Other symbols may be used where field observations indicated mixed soil constituents or dual constituent materials. DESCRIPTIONS OF SOIL STRUCTURES Layered: Units of material distinguished by color and/or Fissured: Breaks along defined planes composition from material units above and below Slickensided: Fracture planes that are polished or glossy Laminated: Layers of soil typically 0.05 to 1 mm thick, max.1 cm Blocky: Angular soil lumps that resist breakdown Lens: Layer of soil that pinches out laterally Disrupted: Soil that is broken and mixed Interlayered: Alternating layers of differing soil material Scattered: Less than one per foot Pocket: Erratic, discontinuous deposit of limited extent Numerous: More than one per foot Homogeneous: Soil with uniform color and composition throughout BCN: Angle between bedding plane and a plane normal to core axis COMPONENT DEFINITIONS COMPONENT SIZE / SIEVE RANGE COMPONENT SIZE / SIEVE RANGE Boulder: > 12 inches Sand Cobbles: 3 to 12 inches Coarse Sand: #4 to #10 sieve (4.5 to 2.0 mm) Gravel Medium Sand: #10 to #40 sieve (2.0 to 0.42 mm) Coarse Gravel: 3 to 3/4 inches Fine Sand: #40 to #200 sieve (0.42 to 0.074 mm) Fine Gravel: 3/4 inches to #4 sieve Silt 0.074 to 0.002 mm Clay <0.002 mm TEST SYMBOLS for In Situ and Laboratory Tests listed in "Other Tests" column. ATT Atterberg Limit Test Comp Compaction Tests Con Consolidation DID Dry Density DS Direct Shear %F Fines Content GS Grain Size Perm Permeability PP Pocket Penetrometer R R-value SG Specific Gravity TV Torvane TXC Triaxial Compression UCC Unconfined Compression Sample/In Situ test types and intervals 2-inch OD Split Spoon, SPT (140-lb. hammer, 30" drop) OD Spilt Spoon H3.25-inch (300-lb hammer, 30" drop) Non-standard penetration test (see boring log for details) Thin wall (Shelby) tube Grab Rock core ® Vane Shear MONITORING WELL SZ Groundwater Level at time of drilling (ATD) 1 Static Groundwater Level Cement / Concrete Seal Bentonite grout / seal Silica sand backfill Slotted tip Slough Bottom of Boring MOISTURE CONTENT Dry Dusty, dry to the touch Moist Damp but no visible water Wet Visible free water PanGE@) Terms and Symbols for I N C O R P O R A T E D Boring and Test Pit Logs Figure A-1 Phone: 206.262.0370 Test Pit No. PIT-1 Approximate ground surface elevation: 376 feet Coordinates (WGS84): 47.800678,-122.335056 Depth ft USCS Material Description 0 _ / Loose, moist, dark brown, silty SAND with pea gravel; shrubs, SM organics, rootlets [Topsoil and Landscaping] Dense, moist, light brown to grey, silty medium to coarse — 3 SM SAND with gravel and cobble; trace rootlets [Qvr - Vashon Recessional Outwash] Photos PIT-1: Test Pit PIT- 1 to approximately 2 feet in depth (below); Sample from bottom of exploration at 3 feet (left) a• ;t PIT-1 was hand augured to approximately 3 feet below ground surface. No groundwater was observed at the time of excavation. Date of Test Pit Observation: January 18, 2019 Test Pit Logged by: S. Scott Figure A-2 PanGEO, Inc. Test Pit No. PIT-2 Approximate ground surface elevation: 378 feet Coordinates (WGS84): 47.800778,-122.335097 Depth ft USCS Material Description Loose, moist, dark brown to brown, silty SAND; trace gravel 0-3 SM and cobble, wood debris, bricks, concrete rubble, rootlets [Fill] 3-5 Medium dense, moist, grey, silty medium to coarse SAND; SM trace rootlets [Qvr - Vashon Recessional Outwash] Photos PIT-2: Test Pit PIT- 2 to approximately 3 feet j in depth (below); Sample .V/�. from bottom of exploration at 5 feet (left) C... ; " ' e\ice below ground surface. No groundwater was PIT-2 was hand augured to approximately 5 feet observed at the time of excavation. Date of Test Pit Observation: January 18, 2019 Test Pit Logged by: S. Scott Figure A-3 PanGEO, Inc.