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APPROVED BLD GEOTECH REPORT BLD2019-0951Gary A. Flowers, PLLC Geological & Geotechnical Consulting 5205 23rd Avenue W June 8, 2019 Project No. 18019 Constantin Korovkin Principal Rnk Eastside, LLC 2603 78th Ave NE Medina, WA 98039 Subject: Geotechnical Services Report — Edmonds Apartments 23830 Edmonds Way Edmonds, Washington Everett, WA 98203 PLAN REVIEW ACCEPTANCE FOR COMPLIANCE WITH THE APPLICABLE CONSTRUCTION CODES IDENTIFIED BELOW. ® BUILDING ® STRUCTURAL ® MECHANICAL ® PLUMBING ❑ ELECTRICAL ® ENERGY ® ACCESSIBILITY ❑ FIRE PLAN REVIEW ACCEPTANCE OF DOCUMENTS DOES NOT AUTHORIZE CONSTRUCTION TO PROCEED IN VIOLATION OF ANY FEDERAL, STATE, OR LOCAL REGULATIONS. BY: o.-Tw-d..-' DATE: 07/29/2020 WEST COAS CODE CONSULTANTS, INC. This report summarizes the results of our geological and geotechnical evaluation of the property located at the above noted address in Edmonds, WA. It is our understanding that the existing structures on the property will be demolished and a new 10-unit apartment building will be constructed on the site. EXISTING CONDITIONS The property is currently developed with 3 single family residences. Two of the residences are located on the lower, western portion, of the site. The third structure is located on an upper bench level, about 6 feet higher in elevation than the other two structures. Egress to all the existing residences is off of Edmonds Way. Single family residences are present to the west, southwest and south, an automotive repair business is located to the east/southeast and Edmonds Way borders the property to the north. The upper portion of the property is located on the north end of a slight north -south trending ridge that terminates at the north end of the property. The area around the residence on the upper portion is generally flat lying at an approximate elevation of 404 feet. The property slopes gently down to the north and northeast to approximate elevation 400 feet. The lower, western, portion of the property is generally flat lying at an approximate elevation of 396 feet. The western descending slope between the upper and lower portion of the property is on the order of 5 to 6 feet tall and is relatively steep. Gary A. Flowers, PLLC. 5205 23rd Avenue W Everett, Washington 98203 206-819-4304 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington At the time of our field study there was no evidence of standing or flowing water on the property. Vegetation consists primarily of landscape bushes and grass, several small deciduous trees and multiple large evergreen trees. Subsurface Exploration In order to confirm subsurface conditions on the property a series of 5 exploration pits were excavated on the property on October 8, 2018. Logs of the exploration pits are attached with this report. Generally, very dense glacial till was observed on the western and northeastern portions of the site (EP-1 and EP-2. Significant quantities of fill soils were observed in all of the exploration pits on the upper portion of the site. The fill extended to a maximum depth of 5 feet and was underlain by loose recessional outwash sediments. Significant organics and ash was observed within some of the fill soils. In the northwest corner (EP-2) large gravels up to 4 inches in diameter were encountered. Ground water seepage was not observed in any of the exploration pits. Moderate caving conditions was observed within the loose fill soils. Mappings According to the Draft Composite Geologic Map of the Sno-King Area, Central Puget Lowland, Washington, by Booth, Cox, Troost and Shimel, January 5, 2004, the site is mapped as Vashon age glacial till. Our explorations are in agreement with the published geology map of the area. Seismic Hazards 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 nearest known fault zone is the South Whidbey Island fault that is located several miles north of the property. No surficial faulting has been noted anywhere near this area and the potential for surficial ground rupture during the lifespan of the residences is considered to be low. Due to the lack of significant slopes near the site the potential for seismically induced landslides is considered to be very low. The underlying glacial till soils are not subject to liquefaction. Based on the encountered site conditions, seismic design criteria should follow 2015 International Building Code recommendations for Site Class C soils. Gary A. Flowers, PLLC. 5205 23" Avenue W Everett, Washington 98203 206-819-4304 2 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington CONCLUSIONS AND RECOMMENDATIONS Based on the results of our site reconnaissance, subsurface investigation and literature review it is our opinion that the site is suitable for the planned development. Planned finish floor elevation for the new structures will be 399.5 which will require removal of much of the encountered fill soils on the upper portion of the site. In areas where the existing fill is not fully removed it will be necessary to further excavate to extend the foundations to suitable bearing soils. It should also be noted that loose recessional outwash sediments were observed underlying the fill soil. These loose soils are also not suitable for foundation support and must either be recompacted to a medium dense or better condition or removed down to the underlying glacial till sediments. Grading of the site will expose loose fill soil or loose native sediments along the south property line. In order to not adversely impact the adjacent properties to the south it may be necessary to provide temporary shoring to support the slope until the buildings are constructed and the foundation walls fully backfilled. We anticipate that ecology blocks or Ultrablocks can be used for this purpose, but sloughing soils could mandate other shoring methods as well. Excavation along the south property line will also likely impact a large evergreen tree that is located very near the south property line. An arborist should be consulted to determine whether or not this tree will be considered a hazard tree or how the excavation can proceed without damaging the tree. The observed fill soils are generally granular in nature and where organics are not present can generally be re -used as structural or nonstructural fill around the site. Excavation safety is incumbent on the contractor as they are on site on a continual basis. However, for planning purposes we do not recommend that temporary excavations in the loose fill or loose native sediments should be planned any steeper than 1H:1V. Even at this inclination some sloughing could occur and the slopes should be protected from storm water. Foundations Based on our field explorations suitable bearing soils will be encountered at a relatively shallow depth after the site is final graded. The foundation should be designed for an allowable soil bearing of 2,000 psf. An increase of one-third will be appropriate for short term wind or seismic loading conditions. The planned wall along the west property line will be constructed atop fill soils utilized for detention vault wall backfill. The backfill must be placed and compacted as structural fill. Lateral resistance will be provided be soil pressure against the footings and foundation walls and/or by friction between building elements and the soil. We recommend a passive resistance value of 200 pcf and a soil friction value of 0.30 for this site. These values are allowable and have a minimum factor of safety of 1.5. Gary A. Flowers, PLLC. 5205 23rd Avenue W Everett, Washington 98203 206-819-4304 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington Bearing soils will be easily disturbed and must be protected from disturbance during grading. No footing should be placed on existing fill soil. Any loose native soil that is naturally loose or has been disturbed during grading operations must either be removed or suitably recompacted to a medium dense or better and unyielding condition. Overexcavation or re -compaction of the soils must extend outward from the footing line a distance equal to the depth of excavation on each side of the footing. In other words, if a 2-foot overexcavation is required to reach suitable bearing, and the excavation will be backfilled with structural fill to footing subgrade elevation, or can be recompacted to a suitable density, the overexcavated trench or area of re -compaction must extend 2 feet outward from each side of the footing. Due to the variability of the onsite soils and depth to bearing soils all footing subgrade soils must be approved by a representative of this office prior to concrete placement. Floor Support Recommendations The observed native sediments, or granular fills soils, will provide suitable support for slab -on -grade floors provided that they are re -compacted to a medium dense or better and unyielding condition. Compaction should be attained with a hoe-pac, walk behind vibratory compactor, jumping jack or large sled compactor. Small sled compactors used for surficial leveling and compaction are not suitable for this purpose. Suitable compaction should be verified by the geotechnical professional prior to concrete placement. If any unsuitable soils are observed during excavation and/or compaction they should be removed and replaced with appropriate structural fill material. Following compaction and approval of the slab bearing soils, a capillary break layer consisting of a minimum of 4 inches of washed pea gravel, washed crushed rock or clean, coarse grained, granular soils and a heavy duty (minimum 10 mil), polyethylene plastic vapor barrier should be provided under any floor slabs where moisture intrusion is a concern. If the vapor barrier becomes compromised in any way during construction it should be replaced or an additional layer added. Penetrations through the vapor barrier should be wrapped and taped. All seams should be overlapped a minimum of 2 feet. Retaining Walls Foundation or basement retaining walls that are free to rotate at least .001 percent of their height should be designed for an active equivalent fluid pressure of 35 pcf. Wall that are not free to rotate should be designed for an at rest pressure of 50 pcf equivalent fluid pressure. These pressures are for a condition of level backflll and suitable wall drainage to eliminate hydrostatic pressure. Drainage Storm water from impermeable surfaces should be collected and discharged into a city approved storm water drainage system. Footing drains should be installed around the exterior footings with discharge to a catch basin and ultimately into the storm drain system. The footing drains should Gary A. Flowers, PLLC. 5205 23rd Avenue W Everett, Washington 98203 206-819-4304 4 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington consist of 4-inch diameter, perforated pvc pipe, bedded in washed drain rock and covered entirely with washed drain rock that is wrapped in geotextile filter cloth. The drains should be placed at the bottom of the footings and sloped to gravity drain to the catch basin. Appropriate cleanouts should be installed to allow for periodic maintenance of the drainpipes. Foundation walls taller than 3 feet should be provided a wall drain to reduce the potential for hydrostatic pressure buildup against the wall. The wall drain should consist of either a minimum of 12 inches of washed drain rock, wall backfill containing less than 3% fines or a geotextile drainage mat such as MiraDrain or DeltaDrain. The wall drains must hydraulically connect to the footing drain system. All drainage material should extend to within 18 inches of ground surface before being capped in order to prevent surface water from entering the wall drain. Infiltration of Storm Water We understand that infiltration of storm water may be considered for the project. We further understand that an infiltration facility, if feasible, would be located on the western portion of the site. During our subsurface exploration we encountered very dense glacial till soils at shallow depth on the western portion of the site and in the northeast corner of the site and they most likely underlie the entire site. The presence of shallow glacial till soils means that infiltration is not a feasible alternative for the site. Erosion Control Suitable best management practice (BMP) erosion control measures should be implemented for the project. The site will be graded nearly level which will aid in reducing the amount of potential sediment laden runoff from the parcel. A silt fence should be installed as per city of Edmonds requirements along the lower portions of the site. Soil stockpiles should be covered with plastic sheeting to contain in -situ moisture and prevent storm water runoff. Areas of disturbance should be limited to necessary construction areas. A rocked construction should be provided in order to reduce sediment impacts to the adjacent streets. The exposed soils should be covered with geotextile filter fabric prior to rock placement. The construction entrance will likely require maintenance and additional rock depending upon local weather conditions. Detention Vault A large detention vault is planned for the western portion of the site. Bottom elevation of the vault floor is planned at 385 feet, Footing excavation will be on the order of 1 foot deeper for a total excavation to approximate elevation 384 feet. Ground surface elevation ranges from 396 to 398 feet in this area. This will require an excavation on the order of 14 feet deep. The excavation will be located approximately 5 feet from the west property line. Our subsurface excavation in this area only extended to approximate elevation 391 feet due to utilizing smaller limited access equipment to access the site. Dense glacially consolidated soils Gary A. Flowers, PLLC. 5205 23rd Avenue W Everett, Washington 98203 206-819-4304 5 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington were observed in exploration pit EP-1. These sediments are typically capable of standing in temporary vertical excavations when ground water is not present. For planning purposes it is likely that an 8 foot or taller vertical cut can be established and then slope to the property line. However, it will be necessary to obtain additional subsurface information in order to verify subsurface soil and ground water conditions. We recommend that, at the time of demolition, when larger equipment will be on site, that several additional exploration pits be excavated at least to elevation 384 feet. If soils or ground water conditions are encountered at that time that are not suitable for the required vertical excavation, it will be necessary to provide temporary shoring to support the cut face. A design for a soldier pile wall would then be required. Temporary Shoring — South Property Line The required cut slopes along the south property line will encounter loose fill and/or native soils that will require temporary shoring unless a temporary construction easement is obtained from the adjacent property owner(s). We strongly recommend trying to obtain the temporary construction easement as the loose nature of the soils in this area are problematic. Also, the large evergreen tree along the south property line as discussed above will likely have multiple large roots that must be cut to make room for the block wall. The cut in this area will only be about 5 feet tall. Should temporary shoring be necessary, it is our opinion that either ecology blocks or Ultrablocks may be utilized for the temporary shoring. The face of the cut should be as far away from the property line as is feasible to allow space for the blocks and workers who will be forming the footings and foundation walls. The face of the cut slope should be continually densified with the bucket of the trackhoe as the excavation proceeds. The blocks should be installed with a small batter on the order of 5 degrees. The larger Ultrablocks (2.5'x2.5' x5') could support the cut with only 2 blocks while ecology blocks (2'x2'x6')will require 3 blocks. The bottom block must be embedded a minimum of 6 inches into bearing soils. The blocks must be staggered such that each block sits atop the two lower blocks. A minimum 4- inch-thick, crushed rock leveling pad must be placed and graded prior to block placement to establish level and batter. Any annular space behind the blocks must be immediately filled with pea gravel, sand or crushed rock in order to provide continuous contact between the back of the blocks and the excavation cut surface. The excavation should not be cut until the blocks are on site and available for use. The excavation should be staged such that no more than 10 feet is open at a time without being shored. A representative of this firm should monitor the excavation and wall building activities and periodically monitor the wall until such time as the permanent building walls are constructed and backfilled. This temporary shoring wall will be sacrificial and remain in place after the building walls are constructed and backfilled. During initial grading operations several exploratory excavations should be made near the south property line to further evaluate whether or not the loose soils will stand temporarily while the Gary A. Flowers, PLLC. 5205 23rd Avenue W Everett, Washington 98203 206-819-4304 0 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington temporary shoring is installed. Should the caving be excessive, and if no temporary construction easement can be attained, it may be necessary to redesign the temporary shoring system to avoid adversely impacting the adjacent property. Alternative methodology would likely involve some type of pile supported temporary wall. SUMMARY The conclusions and recommendations presented in this report are based on our interpretation and evaluation of soil conditions on this site based on visual observation, literature research and subsurface exploration. If changed conditions are observed during construction, we should be immediately contacted to further evaluate the changes and make suitable recommendations. Our findings and recommendations provided in this report were prepared in accordance with generally accepted principles of engineering geology and geotechnical engineering as practiced in the Puget Sound area at the time this report was submitted. We make no other warranty, either express or implied. Thank you for the opportunity to be of service. Should you have any questions please do not hesitate to contact our office. Respectfully submitted, �eoE Wash;' y� �I prr�ring Gedopfq �. '�P 105fi �'•`' qs�d Geo�o Gary A. Flowers Gary A. Flowers, P.G., P.E.G. Principal Engineering Geologist Attachments: Exploration Pit Logs Site & Exploration Plan Robert M. Pride, P.E. Geotechnical Engineer Gary A. Flowers, PLLC. 5205 23" Avenue W Everett, Washington 98203 206-819-4304 7 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington EXPLORATION PIT LOGS 23830 Edmonds Way Edmonds, WA EP-1 Approximate elevation 396 feet. 0.0' — 0.3' Forest duff and highly organic topsoil 0.3' — 2.3' Dense, moist, brownish -gray, silty SAND with occasional gravel — highly oxidized (weathered glacial till) 2.3' — 5.0' Very dense, moist, gray, silty SAND with gravel (unweathered glacial till) Bottom of pit at 5.0 feet on 10/8/2018. No ground water. No caving. EP-2 Approximate elevation 403 feet. 0.0' — 3.5' Loose, moist, gray and brown, silty SAND with large gravel to 4" diameter — 2 old drainpipes with large diameter drain rock on NW side of pit (fill) 3.5' — 4.5' Dense, moist, gray, silty SAND with gravel (glacial till) Bottom of pit at 4.5 feet on 10/8/2018. No ground water. No caving. EP-3 Approximate elevation 403 feet. 0.0' — 0.3' Grass sod and organic topsoil 0.3' — 5.0' Very loose, dry, brown, silty SAND with gravel and probable ash (fill) 5.0'— 7.0' Loose, moist, brown, silty SAND (fill or recessional outwash) Bottom of pit at 7.0 feet on 10/8/2018. No ground water. Moderate caving throughout pit. Surrounding ground loose and very spongy with many fine organics to a depth of 3 feet. EP-4 Approximate elevation 403 feet. 0.0' 2.0' Very loose, dry, brown, silty SAND with occasional gravel (fill) 2.0' — 3.0' Loose, dry, brown, gravelly SAND with silt (recessional outwash) Bottom of pit at 3 feet on 10/8/2018. No ground water. Moderate caving. Gary A. Flowers, PLLC. 5205 23" Avenue W Everett, Washington 98203 206-819-4304 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington EP-5 Approximate elevation 402 feet. Off— 3.0' Very loose, dry, brown, silty SAND with occasional gravel and ash (fill) 3.0' — 6.0' Loose, dry, brown, fine to medium SAND with gravel, trace silt (recessional outwash) Bottom of pit at 6 feet on 10/8/2018. No ground water. Moderate caving. Gary A. Flowers, PLLC. 5205 23" Avenue W Everett, Washington 98203 206-819-4304 9 THE NW 1/4 OF THE SW 1/4 OF SEC. 31, T 27 N., R 4E. 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' 9.5' \N89'\'S2"E \ 6 �, 255.96' �\ 3.5' W, 0.6' N -� � ,— � -� � \ � \ � \ — — \ o I boo o`� \� o� \ I I Legend EP-1 Approximate L�Ocation of Exploration Pity � I Reference: SDA Associates, Sheet 1.2 Existing Conditions Gary A Flowers, PLLC Geologic and Geotechnical Consulti g Project No. 18-019 � SITE I 16,957 sq.ft.± 0.38 Acr± I 20' 0 20' 40' 1 "= 20' Scale Feet APPROVED FOR CONSTRUCTION CITY OF EDMONDS DATE: .� C a� U z Y � W O Z oc � w rn Y � M Z Z a0 W � z Q � _ � o ° z_ U M � � � w � N � i H Z W H Q Q 0 Z O 0 w �_ Z 0 c� Z W C1.2 R:\Projects\410 (LZG Construction)\002-18 (Edmonds Apt)\Dwg\sheets\EW-ex01.dwg 36x24 Know what's be�OW. C111 before you dig. I� CITY ENGINEERING DIVISION