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2004 - Sensitive Area Covenant and Hold Harmless Agreement - March MacDonald Inc - 20040715002118
Return to: City Clerk City of Tukwila 6200 Southcenter Boulevard Tukwila, WA 98188 20040715002118 4272 South 160th Street MARCH MACDONALD PRGE001 OF 034 NOSA 32.00 07/15/2004 14:36 KING COUNTY, WA Above this line reserved for Recorder's use SENSITIVE AREA COVENANT AND HOLD HARMLESS AGREEMENT Grantor /Borrower: March MacDonald, Inc. Grantee /Beneficiary: CITY OF TUKWILA, a municipal corporation of King County, Washington Document Reference Number(s): 20040225900003 L01 -019 Short Plat; 20030801000738 Sensitive Area Covenant and Hold Harmless; Release Sensitive Area Covenant and Hold Harmless; Section /Township /Range: SE22- T23N -R4E, W.M. Assessor's Tax Parcel Number(s): 8108600505 Property Legal Description (abbreviated): Lot 4 of City of Tukwila Plat Number L01 -019 recorded under King County recording #20040225900003, in King County, Washington. COVENANT AND HOLD HARMLESS AGREEMENT Sensitive Area 0 Page f_ of t0 SENSITIVE AREA COVENANT AND HOLD HARMLESS AGREEMENT This covenant and hold harmless agreement is entered into between March MacDonald, a Washington corporation, "Grantor), and the City of Tukwila, a Washington municipal corporation "Grantee RECITALS WHEREAS, Grantor owns and has applied for necessary permits to develop certain real property (the "Property legally described in Exhibit A, which is attached and incorporated by reference. WHEREAS, a portion of the Property contains sensitive areas of potential geologic instability (potential slide areas) as depicted in Exhibit B and described Exhibit C, Exhibit D, and Exhibit E, which are attached and incorporated by reference. WHEREAS, as a condition of the issuance of subdivision plat approval, land use permits, and /or construction permits for the Property, the Grantee required the Grantor to execute and record this "Sensitive Area Covenant and Hold Harmless Agreement" to hold the City of Tukwila harmless from all loss incurred as a result of any landslide or seismic activity, or soil disturbance. WHEREAS, Grantor assumed this obligation in order to obtain said subdivision plat approval, land use permits, and /or construction permits for the Property. WHEREAS, the parties agree that this agreement constitutes an arms length, bargained -for agreement, which includes a waiver of liability that runs with the land for risks created by the proposed use of property because of the shape, composition, location or other characteristic unique to the Property sought to be developed. NOW, THEREFORE, the parties agree as follows: AGREEMENT 1. In consideration of Grantee issuing subdivision plat approval and /or other development permits, which constitutes good and valuable consideration, the receipt of which and the sufficiency of which the Grantor hereby acknowledges, the Grantor shall defend, indemnify, and hold the Grantee, its officers, officials, employees, agents, and assigns harmless from any and all claims, injuries, damages, losses, or suits, whether brought by grantor or third parties, including all legal costs and reasonable attorney fees, arising out of or in connection with any injuries or damages to persons or property caused in whole or in part by any landslide or seismic activity or soil disturbance on the Property, legally described in Exhibit A, which is attached and incorporated by reference. COVENANT AND HOLD HARMLESS AGREEMENT Sensitive Area Page of 40 2. Grantor on its own behalf and on behalf of its heirs, successors and assigns hereby waives any right to assert any claim against the Grantee, its officers, officials, employees, agents, and assigns for any loss, or damage to people or property either on or off the site resulting from any landslide or seismic activity or soil disturbance on said Property by reason of or arising out of the issuance of the permit(s) by the City for development on said Property except only for such losses that may directly result from the sole negligence of the City. 3. Grantor will inform its successors and assigns of said Property that the Property is in an area of potential geologic instability (potential slide area), of the risks associated with development thereon, of any conditions or prohibitions on development imposed by the City of Tukwila, and of any features in this design which will require maintenance or modification to address anticipated soils changes. 4. Grantor will maintain continuous insurance coverage as required by the permit authorizing the development. 5. Grantee's inspection or acceptance of any of the Grantor's construction or other work either during construction or when completed shall not be grounds to avoid any of these covenants of indemnification. 6. This covenant and hold harmless agreement shall be a covenant running with the land and the rights and obligations contained herein shall run with and burden the Property, including each parcel comprising the Property and shall inure to the benefit of and be binding upon the Grantor and Grantee, their successors and assigns. COVENANT AND HOLD HARMLESS AGREEMENT Sensitive Area Page 3, of 40 DATED this 1 5 day of 3-3' `1 200 4 GRANTOR: March- Mar bon ttJ, I w a IA )tl3tn\ r<3# t Ct corporation By: DC\o—NS--- Print Name: (\A (`\A c Ds—se, k Its: is C. e ta S STATE OF WASHINGTON COUNTY OF KING (sed On this 15111 day of TA Q 20(4 before me a Notary Public in and for the State of Washingt.n, personally appeared ►I ]it 1 e. to me known to be the n tcc- Pfest t" of V 1 t arck- 1'YkAC1 bn vvxldi Inc. a )a,st -.i corporation that executed the foregoing instrument, and acknowledge to be the free and voluntary act of said corporation, for the uses and purposes mentioned in this instrument, and on oath stated that he /she was authorized to execute said instrument. IN WITNESS WHEREOF, I have h- reunto set _hand and official seal the day and year first above written. Notary Public Stall of Washington N MICHELLE R. SANTIAGO My Appointment Expires Feb 1S 2006 bTARY PUBLIC, in and for the State of shington, residing at Y commission expires: COVENANT AND HOLD HARMLESS AGREEMENT Sensitive Area Pagel of 40 DATED this 6 day of GRANTEE: CITY OF TUKWILA Steve Mullet, Mayor AT.i =ST: County of King J. Cantu, City Clerk STATE OF WASHINGTON ss. 2004. On this /A th day of 20 C, before me, the undersigned, a Notary Public in nd for the State of Washington, duly commissioned and sworn, personally appeared &t.L1/0 M ll�>'lP,LP and lone, F0 no fn to known to me to be the Mayor and City Clerk, respectively, of CITY OF TUKWILA, the municipal corporation that executed the foregoing instrument, and acknowledged it to be the free and voluntary act of said municipal corporation, for the uses and purposes mentioned in this instrument, and on oath stated that he /she was authorized to execute said instrument. WITNESS my hand and official seal hereto affixed the day and year above written. lt* H. ht) Ie COVENANT AND HOLD HARMLESS AGREEMENT Sensitive Area NOTARY PUBLIC in and for the State of Washington, residing at ,r,o -uputy 5.9 Page =Cot 40 EXHIBIT A LEGAL DESCRIPTION OF PROPERTY THAT PORTION OF TRACT 60, SUNNYDALE GARDENS DIVISION No. 1, ACCORDING TO THE PLAT THEREOF RECORDED IN VOLUME 25 OF PLATS, PAGE 50, IN KING COUNTY, WASHINGTON, EXCEPT THE EAST 75 FEET THEREOF, DESCRIBED AS FOLLOWS: BEGINNING AT THE NORTHWEST CORNER OF THE SOUTH 275 FEET OF SAID LOT 60; THENCE NORTH 00° 0830" EAST, ALONG SAID WEST LINE 357.23 FEET TO THE NORTH LINE OF SAID LOT 60; THENCE SOUTH 89° 35'31" EAST ALONG SAID NORTH LINE 89.43 FEET TO THE WEST LINE OF THE EAST 75.00 FEET, THEREOF; THENCE SOUTH 00° 08'17" WEST ALONG SAID WEST LINE 326.97 FEET; THENCE SOUTH 66° 51"56" WEST 75.60 FEET; THENCE NORTH 89° 45'23" WEST 20.00 FEET TO THE WEST LINE OF SAID LOT 60 AND THE POINT OF BEGINNING. Parcel Number Address Zipcode Taxpayer 8108600505 MARCH MAC DONALD ,41 COVENANT AND HOLD HARMLESS AGREEMENT Sensitive Area Page to of 40 EXHIBIT B GEOTECHNICAL REPORT FEBRUARY 22, 2002 COVENANT AND HOLD HARMLESS AGREEMENT Sensitive Area Pagel of GEOTECHNICAL REPORT SUNNYVALE GARDENS 4404 -160 STREET TUKWILA, WASHINGTON Submitted to: Mark MacDonald c/o March MacDonald Inc. 1488 127 PI. NE Bellevue, Washington 98005 -2213 Submitted by: AMEC Earth Environmental, Inc. 115 S. 8" Street Tacoma, Washington 98402 February 22, 2002 1 -93M- 00359 -0 8 O F `0 February 22, 2002 1 -93M- 00359 -0 March MacDonald Inc. 1488 127 PI. NE Bellevue, Washington 98005 -2213 ATTN: Mr. Mark MacDonald Subject: Geotechnical Report Sunnyvale Gardens 4404 160 Street Tukwila, Washington Dear Mr. MacDonald, AMEC Earth Environmental, Inc. (AMEC) is pleased to submit this report presenting our geotechnical evaluation for the above referenced project. The purpose of our evaluation is to derive conclusions and recommendations concerning site preparation, foundations, bearing pressure, liquefaction, lateral earth pressures, slab -on -grade floors, slope stability, and drainage characteristics for the proposed four -lot plat in Tukwila, Washington. As outlined in our proposal letter dated December 10, 2001 (T- 2193 -0), our scope of work consists of field exploration, geotechnical research, engineering analysis, limited laboratory analysis, and report preparation. We received your written authorization for our evaluation on December 12, 2001. As requested, we reviewed the initial geotechnical evaluation prepared by Bruce MacVeigh P.E. dated August 6, 2002 and began this portion of the study on January 23, 2002. This report has been prepared for the exclusive use of you and your consultants, for specific application to this project, in accordance with generally accepted geotechnical engineering practice. 1.0 SITE AND PROJECT DESCRIPTION The project site consists of an existing single family home with associated parking and a currently undeveloped portion of the subject property north of the existing home. The project site is located at 4404 160' Street, Tukwila, Washington as shown in the attached Location Map (Figure 1). Proposed Lots 1, 2, 3 slope downward to the north with an approximate inclination of about 5 to 7 percent (measured in field) and proposed Lot 4 gradually steepens its downward slope to the northwest and develops a maximum inclination of about 45 percent (measured in field) throughout the northernmost portion of the property. Site boundaries are generally delineated by a slope to the north, residential property to the east and west, and by 160 Street to the south. The enclosed Site Exploration Plan (Figure 2) illustrates these site boundaries, adjacent existing features, and proposed home locations. AMEC Earth 8 Environmental, Inc. 115 South Eighth Street Tacoma. Washington 98402 Tel: (253) 5724975 Fax: (253) 572 -3096 www.amec.com amee O 40 \Server\d Reports \00000s \00359 Sunnyvale Gardens Short Plat \00359 Sunnyvale.rptdoc TABLE 1 APPROXIMATE LOCATIONS AND DEPTHS OF EXPLORATIONS Exploration Functional Location Termination Depth (feet) TP -1 TP -2 TP -3 West of proposed home on Lot 2 South of proposed home on Lot 3 Southeast corner of proposed home on Lot 4 11.0 10.5 5.0 Sunnyvale Gardens 1- 93M- 00359 -0 February 22, 2002 Page 2 A visual surface reconnaissance of the site; amee We understand that development plans call for subdividing the existing lot into four smaller residential lots. Lot 1 is to contain the existing home and new single family residential structures are to be constructed on lots 2, 3, and 4. The home currently proposed for Lot 4 is to be located along the southern portion of the proposed lot, and upslope of the steep grade of the lot. The area surrounding the homes will be paved for parking and vehicle access or landscaped. 2.0 EXPLORATORY METHODS During our initial involvement with this project AMEC observed the surface conditions of the project on November 9, 2001. We then explored surface and subsurface conditions at the project site on January 24, 2002. Our exploration and testing program comprised the following elements: Three Test Pits (designated TP -1 through TP -3), advanced at strategic locations across the site; A review of published geologic and seismologic maps and literature. Table 1 summarizes the approximate functional locations, and termination depths of our subsurface explorations, and Figure 2 depicts their approximate relative locations. The following text section describes our procedures used for test pits. The specific number, locations, and depths of our explorations were selected in relation to the proposed site features, under the constraints of surface access and budget considerations. We estimated the relative location of each exploration by measuring from existing features and scaling these measurements onto a layout plan supplied to us by you. Consequently, the data listed in Table 1 and the locations depicted on Figure 2 should be considered accurate only to the degree permitted by our data sources and implied by our measuring methods. These field measurements are intended to provide the general relationship of on -site features and should not be considered a field survey of any type. ‘Dot-` AMEC \Server\d \Reports \000003 \00 Sunnyvale Gardens Short Plat\00359 Sunnyvale.rpt.doc Sunnyvale Gardens 1- 93M- 00359 -0 February 22, 2002 Page 3 ame0 It should be realized that the explorations performed for this evaluation reveal subsurface conditions only at discrete locations across the project site and that actual geologic conditions in other areas may vary. Furthermore, the nature and extent of any such variations would not become evident until additional explorations are performed or until construction activities have exposed them. If significant variations are observed at that time, AMEC may need to modify the conclusions and recommendations contained in this report to reflect the actual site conditions. 2.1 Test Pit Procedures Our exploratory test pits were excavated with a tire- mounted backhoe operated by an independent firm working under subcontract to AMEC. A geotechnical engineer from our firm continuously observed the test pit excavations and logged the subsurface conditions. After describing each test pit, the backhoe operator backfilled each test pit with excavated soils and tamped the surface. In our opinion, exploration soil pits are the preferred method of subsurface exploration for this project. Test pits, which are 8 to 12 feet in length, provide a continuous, broad, and more detailed exposure of near surface soil conditions than typically provided by 2- inch- diameter split spoon samplers, which provide samples at 2 to 5 -foot intervals and are extremely narrow in range. This is particularly important in landslide areas, where narrow slip planes can often go undetected by auger borings. The enclosed Test Pit Logs indicate the vertical sequence of soils and materials encountered in each test pit. Where a soil contact was observed to be gradational or undulating, our logs indicate the average contact depth. Our representatives continuously monitored the explorations; visually classified the soils encountered, and maintained logs of the subsurface conditions. The soils were classified in the field in general accordance with the system described on Figure 7. We estimated the relative density and consistency of the in -situ soils by means of the excavation characteristics and the stability of the test pit sidewalls. Our logs also indicate the approximate depths of any sidewall caving or groundwater seepage observed in the test pits, as well as all sample numbers and sampling locations. 3.0 SITE CONDITIONS The following sections of text present our observations, measurements, findings, and interpretations regarding surface, soil, groundwater, and seismic conditions at the project site. 3.1 Surface Conditions The project site consists of an existing single family home with associated parking and a currently undeveloped portion of the subject property north of the existing home. We understand that current development plans call for subdividing the existing lot into four smaller residential lots. Proposed Lot #1 provides vehicle access to proposed lots 2, 3, and 4, it also contains the existing home. Proposed lots 1, 2, 3 slope downward to the north with an approximate inclination of about 5 to 7 percent (measured in field) and 0F 4° A M E 0 \\Servend \Reports \00000sW Sunnyvale Gardens Short Plat\00359 Sunnyvale.rpt.doc Sunnyvale Gardens 1 -93M- 00359 -0 February 22, 2002 Page 4 3.2 Soil Conditions ameco proposed lot 4 gradually steepens its downward slope to the northwest and develops a maximum inclination of about 45 percent (measured in field) throughout the northemmost portion of the property. The project site is vegetated by cut grass, mature Douglas Fir, Alder, and Maple trees. In areas that are not currently landscaped the under -story consists of moderately thick groundcover including laurel and berry vines or bushes. No indication of past slope instability, seeps, springs, or geologic contacts were observed within or adjacent to the subject property. 3.2.1 'Published Geology According to published geologic maps, the site is located within the Puget Lowland. Quatemary sediments consisting of various glacial, fluvial, lake and marsh deposits dominate the region These sediments were deposited from the Puget Lobe of the Cordilleran continental ice sheet during the Vashon Stade of the Fraser Glaciation. The geologic map entitled "Geology of the Des Moines Quadrangle, Washington" prepared by Howard H. Waldron, Figure 3 (Geologic Mapping), classifies the soils in the vicinity of the project site as ground moraine (Qgt), which are characterized as mainly compacted unoxidized glacial till. The "Slope Map of Part of West Central King County, Washington" prepared by the U.S. Geological Survey 1975, Figure 4 (Slope Map), indicates that the slopes in the vicinity of the project site are gentle to moderate with a maximum inclination of about 15 percent. The "Map Showing Relative Slope Stability in Part of West Central King County, Washington" prepared by Robert D. Miller, Figure 5 (Slope Stability Map), classifies the slopes in the vicinity of the project site as Class 1 These slopes are generally stable even where modified by man. Sections of the proposed property may extend into a region classified as Class 2. Class 2 slopes are normally stable but may become unstable due to man's activities. It is our understanding that although the property may contain Class 2 slopes, no development is planned in these areas. The "Map Showing Relative Compressibility of Earth Materials in Part of West Central King County, Washington" prepared by Robert D. Miller, Figure 6 (Soil Compressibility Map), classifies the soil in the vicinity of the project site as Class Ila. Class Ila soils are virtually non compressible to slightly compressible consisting of course to fine- grained, dense materials. 3.2.2 Observed Soil Conditions Our explorations revealed sandy soils of varying density, and generally diverged fro the published geological mapping. Specifically, our on -site explorations revealed approximately 6 inches of loose organic soil overlying about 2 feet of loose, moist, silty sand with roots. Beneath the silty sand, we encountered about 2Y to 7%: feet of sand a o'4 A M E C \Serverd Reports \00000s \00359 Sunnyvale Gardens Short Plal\00359 Sunnyvale.rpl.doc Sunnyvale Gardens 1 -93M -00359 -0 February 22, 2002 Page 5 amee with trace silt and gravel. The sand continued to the termination of our test pits. In test pit TP -2, we encountered a 1 -foot layer of medium dense, moist, silty, gravelly sand beneath the silty sand before encountering the sand. A previous geotechnical evaluation, prepared by Bruce S. MacVeigh, P.E. indicates, "a clay loam layer was found at a depth of 31/2-feet in only one hole and appears to be an anomaly." This soil layer was not encountered during our subsurface exploration program. 3.3 Groundwater Conditions At the time of our excavations (January 24, 2002), groundwater was not encountered within the depths of our test pits. Because our explorations were performed during a period of wet weather, and during a period experiencing near normal precipitation patterns, these observed groundwater conditions may closely represent the yearly average levels. At all times of the year, groundwater levels would likely fluctuate in response to precipitation patterns, off -site construction activities, and site utilization. 3.4 Seismic Conditions Based on our analysis of the subsurface explorations and our review of published geologic maps, we interpret the on -site soil conditions to correspond to a seismic soil profile type S as defined by Table 16 -J of the 1997 Uniform Building Code. Current (1996) National Seismic Hazard Maps prepared by the U.S. Geological Survey indicate that a bedrock site acceleration coefficient of about 0.31 is appropriate for an earthquake having a 10- percent probability of exceedance in 50 years (corresponding to a retum interval of 475 years). According to Figure 16 -2 of the 1997 Uniform Building Code, the site lies within seismic risk zone 3. 1304 A M E C \Servend\ Reports \00000s \00359 Sunnyvale Gardens Short Plat \00359 Sunnyvale.rpt.doc Sunnyvale Gardens 1.93M- 00359 -0 February 22, 2002 Page 6 ame Design Parameter Value Acceleration Coefficient (USGS) 0.30 Risk Zone (UBC) 3 Soil Profile Type (UBC) So 4.0 CONCLUSIONS AND RECOMMENDATIONS Development plans call for sub dividing the existing lot into 4 smaller residential lots. We offer the following general geotechnical conclusions and recommendations concerning this project. Feasibility: Based on our field explorations, research, and analyses, the proposed development appears feasible from a geotechnical standpoint, contingent on proper design and construction. Foundation Options: In our opinion, conventional spread footings will provide adequate support for the proposed homes if the subgrades are properly prepared. Due to the inclination of the currently proposed Lot 4, a daylight basement with conventional spread footings will also provide adequate support for the proposed structure if subgrade walls are properly deigned and constructed and the subgrades are properly prepared. Floor Options: In our opinion, slab -on -grade floors can be used in the proposed structures contingent upon proper subgrade preparation. Slope Stability: In our opinion, all of the proposed building areas are grossly stable with respect to deep- seated failure. No geologic contacts, seeps, springs, or other indicators of potential slope instability were observed during our surface and subsurface reconnaissance of the site. In our opinion, no further slope analysis will be required if the homes are placed in the locations depicted in figure 2 (Site and Exploration Plan). Buffers and Setbacks: In our opinion no buffer or set back from the slope on lot 4 is required to mitigate potential slope instability. However, the City of Tukwila as well as King County may require setbacks for other purposes such as stormwater infiltration and sanitary septic drain fields. Seismic Considerations: Based on our literature review and subsurface interpretations, we recommend that the project structural engineer use the following seismic parameters for design of buildings, retaining walls, and other site structures: Hi 00o A M E C \Servend\Reports \00000s \00359 Sunnyvale Gardens Short Piat100359 Sunnyvale.rpt.doc Sunnyvale Gardens 1- 93M- 00359 -0 February 22, 2002 Page 7 amee On -Site Soil Reuse: The surficial sod, duff, topsoil, and organic -rich soils mantling most of the project site are not suitable for use as structural fill under any circumstances, due to their high organic content. The underlying soils consisting of silty sand (SM) appear to be suitable for use as structural fill in their current moisture condition. The following text sections of this report present our specific geotechnical conclusions and recommendations concerning site preparation, foundation design, slab -on -grade floor, pavement design and structural fill. 4.1 Slope Stability Analysis Based on visual observations, field- testing, empirical correlations, and experience with similar soil types, it is our opinion that all of the proposed building areas are grossly stable with respect to deep- seated failure. In our opinion, no further slope analysis will be required if the homes are placed in the locations depicted in figure 2 (Site and Exploration Plan). 4.2 Buffer and Setbacks In our opinion, no buffer or setback from the slope located on lot 4 is required to mitigate potential slope instability. However, the city of Tukwila, as well as King County, may require setbacks for other purposes such as stormwater infiltration and sanitary septic drain fields. Nonetheless, surface water runoff should be controlled and prevented from flowing onto or over the slope. The surface vegetation should be maintained by the homeowner to prevent erosion of the surface soil. 4.3 Site Preparation Preparation of the project site should involve clearing, stripping, and subgrade compaction. The paragraphs below discuss our geotechnical comments and recommendations concerning site preparation. Erosion Control: Before construction begins an appropriate erosion control system should be installed. This system should collect and filter all surface run off through either silt fencing or a series of properly placed and secured straw bales. We anticipate a system of berms and drainage ditches will provide an adequate collection system. If silt fencing is selected as the silt filter the fencing fabric should meet the requirements of WSDOT Standard Specification 9 -33.2 Table 3. The silt fence should be buried so that sediment cannot pass beneath it. If straw bails are used as the silt filter, the bales should be secured to the ground such that they will not shift under the weight of any water retained. Regardless of the sediment filter selected, it should be inspected and maintained during the time that the site soils are exposed, on a periodic basis and after any major rainstorm event. Specifically, holes in the filter and areas where the filter has shifted above ground surface should be repaired as soon as they are identified. 6 0,4D A M E C \Server\d \Reports \00000s 00359 Sunnyvate Gardens Short Plat\00359 Sunnyvale.rptdoc Sunnyvale Gardens 1 -93M- 00359 -0 February 22, 2002 Page 8 ame Because stripped surfaces and soil stockpiles are typically a source of runoff sediments, they should be given particular attention. If earthwork occurs during wet weather, we recommend that all stripped surfaces be covered with straw to reduce the runoff erosion. Similarly soil stockpiles and cut slopes should be covered with plastic sheeting for erosion protection Clearing and Stripping: The construction areas should be cleared and stripped of all grass, sod, topsoil, trees, wood, miscellaneous debris, and fill. Our explorations indicate that an average thickness of about 6 inches of soft organic soil will be encountered across most of the site, but slight variations in thickness may be encountered when excavation begins. Filling: Any holes created by the stripping operation should be filled with properly compacted structural fill, such as "pit run" or "gravel borrow." Regardless of soil type, all fill should be placed and compacted according to our recommendations presented in the Structural Fill section of this report. Temporary Cut Slopes: All temporary soil cuts associated with site regrading or excavations should be adequately back sloped to prevent sloughing and collapse. Based on our explorations, silty sand soils will likely be exposed in on -site cuts. Based on this we recommend that temporary slopes be constructed at 1 %zH:1V. However, flatter slopes may be necessary if the actual soil conditions exposed in the cuts require it. Nonetheless, the contractor should assess the conditions of the excavation before a final determination of the appropriate slope inclination has been made. Subarade Compaction: We recommend that exposed subgrades for footings, floors, pavements, and other structures be proof rolled or compacted to a dense' condition. Any localized zones of loose granular soils observed within a subgrade should be compacted to a density commensurate with the surrounding soils. Any organic, soft, or pumping soils observed within a subgrade should be overexcavated and replaced with structural fill Wet- Weather Considerations: Most of the on -site soils are expected to be relatively resistant to minor variations in moisture content and may be suitable for reuse as structural fill during wet weather. However, undisturbed native soils that are exposed to excessive moisture water for an extended period of time may become unsuitable for use as structural support. In our opinion, the project specifications should include provisions for using imported; clean, granular fill in case the on -site soils become too wet and filling must proceed during wet weather. To reduce the potential need for importing clean granular fill, we recommend scheduling construction for periods of extended dry weather, as may occur during the summer months. Project specifications should also include provisions for using quarry spells to protect high traffic areas as deemed appropriate by the contractor. A M E C \Servend \Reports \00000s \003 Sunnyvale Gardens Short Plat\00359 Sunnyvale.rpt.doc Sunnyvale Gardens 1 -93M- 00359 -0 February 22, 2002 Page 9 amee 4.4 Foundations In our opinion, conventional spread footings will provide adequate support for the proposed structures if the subgrades are properly prepared. Due to the inclination of the currently proposed Lot 4 a daylight basement with conventional spread footings will also provide adequate support for the proposed structure if subgrade walls are properly deigned and constructed and the subgrades are properly prepared. We offer the following comments and recommendations for purposes of footing design and construction. Footing Subarades: In order to provide adequate bearing conditions for spread footings, all subgrades for the buildings should consist of a minimum of 12 inches of firm and unyielding native soil or compacted structural fill per the Structural Fill section of this report. Any existing organic -rich soils should be overexcavated to expose the underlying silty sand. Subarade Observation: All footing subgrades should consist of firm, unyielding, native soils or structural fill materials. Footings should never be cast atop loose, soft, frozen soil, sloughed soils, debris, existing uncontrolled fill, or surfaces covered by standing water. We recommend that an AMEC representative observe the condition of all subgrades before any concrete is placed. Footing Backfill: To provide erosion protection and lateral load resistance, we recommend that all footing excavations be backfilled on both sides of the footings after the concrete has cured. Either imported structural fill or non- organic on -site soils can be used for this purpose, contingent on suitable moisture content at the time of placement. Regardless of soil type, all footing backfill soil should be compacted to a density of at least 90 percent (based on ASTM D- 1557). Spread Footings: In our opinion, footings that bear on properly prepared subgrades can be designed for a maximum allowable soil bearing pressure 2,000 pounds per square foot (psf) for compacted structural fill or native soils. This bearing pressure applies to all long term live and dead loads exclusive of the weight of the footing and any overlying backfill, and may be increased by one -third to include short -term loads such as wind or seismic influence. If larger bearing capacities are required, please contact our office for more information. For frost and erosion protection, the base of all exterior footings should bear at least 18 inches below adjacent outside grades, whereas the base of interior footings need bear only 12 inches below the surrounding slab surface level. Continuous (wall) and isolated (column) footings should be at least 18 and 24 inches wide, respectively. We recommend that any disturbed soils in the footing excavations be removed or, if practical, recompacted prior to concrete placement. To ensure the adequacy of bearing surfaces, all footing excavations should be observed by an AMEC representative prior to placing concrete. AMEC \Server\d \Reports \OOOOOS \00359 Sunnyvale Gardens Short PIah00359 Sunnyvale.rpt.doc Sunnyvale Gardens 1.93M -00359 -0 February 22, 2002 Page 10 amee Lateral Resistance: Footings that have been properly backfilled as recommended above will resist lateral movements by means of passive earth pressure and base friction. We recommend using an allowable passive earth pressure of 250 pcf (equivalent fluid weight) and an allowable base friction coefficient of 0.35. Footing Settlements: We estimate that total post construction settlements of properly designed footings bearing on properly prepared subgrades will not exceed 1 inch. Differential settlements should not exceed one -half of the actual total settlement between adjacent, equally loaded, foundation elements. These settlements would be reduced if the actual design bearing pressures are lower than our recommended maximum pressures. 4.5 Slab -on -Grade Floors In our opinion, soil supported slab -on -grade floors can be used in the proposed buildings if the subgrades are properly prepared. We offer the following comments and recommendations. Subgrade Conditions and Observation: All soil- supported slab -on -grade floors should bear on firm, unyielding native soils or on suitable structural fill soils. We recommend that an AMEC representative observe the condition of all slab- supporting soils before any fill or concrete is placed. Capillary Break: To retard the upward wicking of groundwater beneath the floor slabs, we recommend that a capillary break be placed over the subgrade. Ideally, this capillary break would consist of a 4- inch -thick layer of pea gravel or other clean, uniform, well rounded gravel, such as "Gravel Backfill for Drains" per WSDOT Standard Specification 9- 03.12(4). Altematively, angular gravel or crushed rock can be used if it is sufficiently clean and uniform to prevent capillary wicking. Vapor Barrier: We recommend that a layer of durable plastic sheeting (such as Crosstuff, Moistop, or Visqueen) be placed directly between the capillary break and the floor slab to prevent ground moisture vapors from migrating upward through the slab. During subsequent casting of the concrete slab, the contractor should exercise care to avoid puncturing this vapor barrier. Curing Course: A "curing course" is a thin layer (typically 2 inches thick) of clean sand that is sometimes placed over the vapor barrier to facilitate uniform curing of the overlying concrete slab. Recent studies, however, have indicated that this course is not necessary when moderately strong concrete is used for the slab. Consequently, we recommend that the project structural engineer be allowed to decide whether a curing course should be used. I ZS 00 -0 AMEC \Server\d Reports \00000s \00359 Sunnyvale Gardens Short Plat \00359 Sunnyvale.rpldoc Sunnyvale Gardens 1 -93M- 00359-0 February 22, 2002 Page 11 amee Vertical Deflections: Soil- supported slab -on -grade floors can deflect downward when vertical loads are applied, due to elastic compression of the subgrade. In our opinion, a subgrade reaction modulus of 250 pounds per cubic inch can be used to estimate such deflections. 4.6 Subqrade Walls: The required strength of a subgrade wall depends on the nature, density, and configuration of the soil behind the wall and the amount of lateral wall movement which can occur after construction has been completed. Subgrade walls are also significantly effected by the buildup of water behind a retaining wall, thus we recommend all walls be backfilled and drained as discussed below. Applied Soil Pressure: Walls that are designed to move 0.1 percent of the wall height during and after construction are usually referred to as unrestrained walls. We recommend that unrestrained subgrade walls supporting natural slopes inclined at 2H:1V or flatter be designed to resist an active pressure (triangular distribution) of 35 pounds per cubic foot (pcf). The recommended pressure does not include the effects of surcharges from surface loads hydrostatic pressures, or structural loads. If such surcharges are to apply, they should be added to the above design lateral pressures. Wall Foundations: Subgrade walls can be supported on shallow footings bearing on suitable soils as described in the Spread Footings section of this report. Footings should be designed using the recommended allowable bearing pressures and lateral resistance values presented for building foundations when the adjacent downhill slope is 3H:1V (horizontal: vertical) or flatter. Wall Drainage: Groundwater drainage should be provided behind concrete walls by placing a zone of sand and gravel containing less than 3 percent fines (material passing No. 200 sieve) against the wall. This drainage zone should be at least 24 inches thick (measured horizontally) and extend from the base of the wall to within 1 foot of the finished grade behind the wall, and capped as recommended below. Smooth- walled perforated PVC drainpipe having a minimum diameter of 4 inches should be embedded within the sand and gravel at the base of the wall along its entire length. This drainpipe should discharge into a tightline leading to an appropriate collection and disposal system. Backfill Compaction: Because soil compactors place significant lateral pressures on subgrade walls, we recommend that only small, hand operated compaction equipment be used within 2 feet of a backfilled wall. Also, all backfill should be compacted to a density as close as possible to 90 percent of the maximum dry density (based on ASTM:D- 1557); a greater degree of compaction closely behind the wall would increase the lateral earth pressure, whereas a lesser degree of compaction might lead to excessive post construction settlements. oc- A M E C \Server \Reports \00000s \0 0359 Sunnyvale Gardens Short Platt00359 Sunnyvale.rpt.doc Sunnyvale Gardens 1 -93M- 00359 -0 February 22, 2002 Page 12 amee Grading and Capping: To retard the infiltration of surface water into the backfill soils, we recommend that the backfill surface of exterior walls be adequately sloped to drain away from the wall. Ideally, the backfill surface directly behind the wall would be capped with asphalt, concrete, or 12 inches of low permeability (silty) soils to minimize or preclude surface water infiltration. If low permeability (silty) soils are selected, as the capping material a geotextile should be paced over the drainage material; typical silt fencing is appropriate of this purpose. Wall Settlements: We estimate that the settlement of the wall footings will be on the order of 1 inch or less. Most of this settlement is expected to occur as soon as the loads are applied. Differential settlement along the walls is expected to be 1 inch or less over a 50 -foot span. 4.7 Drainage Systems In our opinion, the building should be provided with permanent drainage systems to reduce the risk of future moisture problems. We offer the following recommendations and comments for drainage design and construction purposes. Runoff Water: Roof -runoff and surface -runoff water should not be discharged on the slope. Instead, runoff water should discharge into separate tightline pipes and be routed away from the building to a storm drain or other appropriate location approved by the City of Tukwila and /or King County. Grading and Capping: Final site grades should slope downward away from the building and the slope on proposed Lot 4 so that runoff water will flow by gravity to suitable collection points, rather than ponding near the building, or sheet flowing over the face of the slope. Ideally, the area surrounding the building would be capped with concrete, asphalt, or low permeability (silty) soils to reduce or preclude surface -water infiltration. 4.8 Structural Fill The term "structural fill' refers to any materials placed under foundations, retaining walls, slab -on -grade floors, sidewalks, pavements, and other structures. Our comments, conclusions, and recommendations conceming structural fill are presented in the following paragraphs. Materials: Typical structural fill materials include clean sand, gravel, pea gravel, washed rock, crushed rock, quarry spells, controlled density fill (CDF), lean -mix concrete (LMC), well graded mixtures of sand and gravel (commonly called "gravel borrow" or "pit run and miscellaneous mixtures of silt, sand, and gravel. Recycled asphalt, concrete, and glass, which are derived from pulverizing the parent materials, are also potentially useful as structural fill in certain applications, however the contractor should contact the local regulatory authority for environmental restrictions should recycled materials be utilized on the project site. Soils used for structural fill should not contain any organic matter or debris, or any individual particles greater than about 4 inches in diameter. of4v A M E C \Server\d Reports \00000s \00359 Sunnyvale Gardens Short Plat \00359 Sunnyvale.rpt.eoc Sunnyvale Gardens 1 -93M -00359 -0 February 22, 2002 Page 13 ame0 On -Site Soils: Because moderate cuts are planned for the project, we expect that moderate quantities of on -site soils will be generated during earthwork activities. Therefore, we offer the following evaluation of these on -site soils in relation to potential use as structural fill. Surficial Organic Soils: The sod, duff, topsoil, and organic -rich soils mantling portions of the site are not suitable for use as structural fill under any circumstances, due to their high organic content. Consequently, these materials can be used only for non structural purposes, such as in landscaping areas. Clay Loam: No specific information about the "clay loam layer" reported in the geotechnical evaluation prepared by Bruce S. MacVeigh was available at the time of our study. Nonetheless, based on our experience with fine grained soils we recommend that "clay loam" soils not be utilized as structural fill unless approved by an AMEC representative. Sands: The silty sands underlying the surficial organic soils appear suitable for reuse as structural fill at their present moisture contents. These soils will provide a favorable source of fill soils that can be used in a broad range of weather conditions, although aeration or sprinkling might be needed to achieve an optimum moisture content during especially wet or dry conditions, respectively. Fill Placement: Generally, pea gravel, washed rock, quarry spalls, CDF, and LMC do not require special placement and compaction procedures. In contrast, clean sand, gravel, crushed rock, soil mixtures, and recycled materials should be placed in horizontal lifts not exceeding 8 inches in loose thickness, and each lift should be thoroughly compacted with a mechanical compactor. Subgrade Observation and Compaction Testing: Regardless of material or location, all structural fill should be placed over firm, unyielding subgrades prepared in accordance with the Site Preparation section of this report. An AMEC representative before should observe the condition of all subgrades before filling and /or construction begins. Also, fill soil compaction should be verified by means of in -place density tests performed during fill placement so that adequacy of soil compaction efforts may be evaluated as earthwork progresses. Compaction Criteria: Using the Modified Proctor test (ASTM:D-1 557) as a standard, we recommend that structural fill used for various on -site applications be compacted to the following minimum densities: t 000 AMEC \Server\d Reports \00000s \00359 Sunnyvale Gardens Short Plat \00359 Sunnyvale.rpt.doc Sunnyvale Gardens 1 -93M- 00359 -0 February 22, 2002 Page 14 ame Minimum FILL APPLICATION Compaction Footing subgrade and bearing pad 95 percent Slab -on -grade floor subgrade and subbase 95 percent Utility Trenches (upper 2 feet) 95 percent Utility Trenches (below 2 feet) 90 percent Foundation backfill 90 percent Retaining wall subgrade 95 percent Retaining wall backfill 90 percent Soil Moisture Considerations: The suitability of soils used for structural fill depends primarily on their grain -size distribution and moisture content when they are placed. As the "fines" content (that soil fraction passing the U.S. No. 200 Sieve) increases, soils become more sensitive to small changes in moisture content. Soils containing more than about 5 percent fines (by weight) cannot be consistently compacted to a firm, unyielding condition when the moisture content is more than two percentage points above or below optimum. For fill placement during wet- weather site work, we recommend using "clean" fill, which refers to soils that have a fines content of 5 percent or less (by weight) based on the soil fraction passing the U.S. No. 4 Sieve. CDF Strength Considerations: CDF is normally specified in terms of its compressive strength, which typically ranges from 50 to 200 psi. CDF having a strength of 50 psi (7,200 psf) provides adequate support for most structural applications and can be readily excavated with hand shovels. A strength of 100 psi (14,400 psf) provides additional support for special applications but greatly increases the difficulty of hand excavation. CDF having a strength greater than about 100 psi requires power equipment to excavate and, as such, should not be used where future hand excavation might be needed. A M E C \\Server\d \Reports \00000s \003 Sunnyvale Gardens Short Plat \00359 Sunnyvale.rpt.doc Sunnyvale Gardens 1- 93M- 00359 -0 February 22, 2002 Page 15 ame& 5.0 RECOMMENDED ADDITIONAL SERVICES Because the future performance and integrity of the structural elements will depend largely on proper site preparation, drainage fill placement, and construction procedures; monitoring and testing by experienced geotechnical personnel should be considered an integral part of the construction process. Consequently, we recommend that AMEC be retained to provide the following post -report services: Review all construction plans and specifications to verify that our design criteria presented in this report have been properly integrated into the design; Prepare a letter summarizing geotechnical aspects of review comments Of required by the City of Tukwila and /or King County); Observe all exposed subgrades after completion of stripping and overexcavation to confirm that suitable soil conditions have been reached and to determine appropriate subgrade compaction methods; Monitor the placement of all structural fill and test the compaction of structural fill soils to observe their conformance with the construction specifications; Probe all completed subgrades for footings and slab -on -grade floors before concrete is poured, in order to verify their bearing capacity; Prepare a post- construction letter summarizing all field observations, inspections, and test results Of required by the City of Tukwila and /or King County); 40 AMEC \Serveria \Reports \00000s \0 0359 Sunnyvale Gardens Short Piat\00359 Sunnyvale.rpt.doc Mark A. Rohrbach Staff Engineer MAR/JEB /vc Sincerely, AMEC Earth and Environmental, Inc. Enclosures: Figure 1— Location Map Figure 2 —Site Exploration Plan Figure 3— Geologic Mapping Figure 4 —Slope Map Figure 5 —Slope Stability Map Figure 6 —Soil Compressibility Map) Figure 7 —Soil Classification System Test Pit logs TP -1 through TP -3 amai° Sunnyvale Gardens 1 -93M- 00359 -0 February 22, 2002 Page 16 6.0 CLOSURE The conclusions and recommendations presented in this report are based, in part, on the explorations that we performed for this study; therefore, if variations in the subgrade conditions are observed at a later time, we may need to modify this report to reflect those changes. Also, because the future performance and integrity of the project elements depend largely on proper initial site preparation, drainage, and construction procedures, monitoring and testing by experienced geotechnical personnel should be considered an integral part of the construction process. AMEC is available to provide geotechnical observation, soils and concrete testing, steel and masonry inspection, and other services throughout construction. We appreciate the opportunity to be of service on this project. If you have any questions regarding this report or any aspects of the project, please feel free o tact our office. Jame `L nghom, f.C. Associate AMEC \Serves d\Reports \00000s \00359 Sunnyvale Gardens Short PIan00359 Sunnyvale.rpt.dOc SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS GROUP SYMBOL GROUP NAME COARSE GRAINED SOILS More than 50% Retined on No. 200 Sieve GRAVEL More than 50% of Coarse Fraction Retained on No. 4 Sieve CLEAN GRAVEL GW WELL-GRADED GRAVEL, FINE TO COARSE GRAVEL GP POORLY GRADED SOIL GRAVEL WITH FINES GM SILTY GRAVEL GC CLAYEY GRAVEL SAND More than 50% of Coarse Fraction Passes No. 4 Sieve CLEAN SAND SW WELL GRADED SAND, FINE TO COARSE SAND SP POORLY GRADED SAND SAND WITH FINES SM SILTY SAND SC CLAYEY SAND FINE GRAINED SOILS More than 50% Passes No. 200 Sieve SILT AND CLAY Liquid Limit Less Than 50 INORGANIC ML SILT CL CLAY ORGANIC OL ORGANIC SILT. ORGANIC CLAY SILT AND CLAY Liquid Limit 50 or More INORGANIC MH SILT OF HIGH PLASTICITY, ELASTIC SILT CH CLAY OF HIGH PLASTICITY, FAT CLAY ORGANIC OH ORGANIC CLAY, ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT NOTES: 1. Field classification is based on visual examination of soil in general accordance with ASTM D2488-90. 2. Soil classification using laboratory tests is based on ASTM D- 2487-90. 3. Description of soil density or consistency are based on interrelation of blow count data, visual appearance of soils, and/or test data. SOIL MOISTURE MODIFIERS: 12,a- contains no moisture. Damp contains a slight amount of moisture; more than about 2 percentage points below optimum moisture content. Moist- contains a moderate amount of moisture; generally within about 2 percentage points of the r optimum moisture content for a modified Proctor test; readily compacts when squeezed. Wet contains a relatively large amount of porewater; more than about 2 percentage points abouve optimum moisture content. Saturated- contains an excessive amount of porewater; soil has zero air voids. Q f''� SOIL CLASSIFICATION SYSTEM FIGURE 7 ok, OF TEST PIT LOGS 1 -93M- 00359 -0 Depth (feet) OBSERVED SOIL CONDITION Test Pit #1 0.0 0.5 Sod, Topsoil 0.5 2.5 Moist, loose, reddish brown, silty SAND w /roots. (SM) 2.5 11.0 Medium dense, moist, tan SAND, trace silt. (SP) No caving observed. No groundwater seepage observed. Test pit terminated at 11 feet. Test Pit #2 0.0 0.5 Sod, Topsoil 0.5 2.5 Loose, moist, reddish brown, silty SAND, trace gravel. (SM) 2.5 -3.5 Loose to medium dense, moist, gray, silty gravelly SAND. (SM) 3.5 10.5 Medium dense, tan SAND, trace gravel and silt (SP) No caving observed. No groundwater seepage observed Test pit terminated at 10.5 feet. Test Pit #3 0.0 0.5 Sod, Topsoil 0.5 2.5 Loose, moist, reddish brown, silty SAND. (SM) 2.5 5.0 Loose to medium dense, moist, tan SAND, trace gravel, trace silt. (SP) No caving observed. No groundwater seepage observed Test pit terminated at 5.0 feet. 3 D.©F4 A M E C \Server\d \Reports \00000s 00359 Sunnyvale Gardens Short Plat \00359 Sunnyvale.rpt.doc EXHIBIT C GEOTECHNICAL PEER REVIEW APRIL 1, 2002 COVENANT AND HOLD HARMLESS AGREEMENT Sensitive Area Pageof HI SHANNON &WILSON, INC April 1, 2002 Ms. Jill Mosqueda, Development Engineer City of Tukwila Department of Public Works 6300 Southcenter Boulevard Tukwila, WA 98188 -2544 RE: GEOTECHNICAL PEER REVIEW, HOSKIN SHORT PLAT, 4404 SOUTH 160 STREET, TUKWILA, WASHINGTON Dear Ms. Mosqueda: This letter presents the results of our review of a geotechnical engineering report for the proposed Hoskin Short Plat project. The project site will be located north of the existing residence at 4404 South 160 Street, Tukwila, Washington. The purpose of our work is to offer an opinion as to the appropriateness and adequacy of the geotechnical engineering report submitted with the permit application. The geotechnical report for this project was prepared by Amec Earth Environmental, Inc. (AMEC) and dated February 22, 2002. The report presents the results of three test pit explorations and geotechnical recommendations for site development. The test pit explorations extended to depths of 5 to 11 feet and encountered loose to medium dense sand. The report provided descriptions of the site geology and subsurface soil and groundwater conditions. It provided opinions and recommendations regarding site development, foundations and earth pressures, slope stability, buffers and setbacks, and other general geotechnical design issues. Lots 1, 2, and 3 of the proposed short plat appear to be Class 1 areas of potential geologic instability, while Lot 4 meets the criteria for a Class 3 area because it contains slopes steeper than 40 percent. Our review of site conditions on proposed Lot 4 indicates that a minimum setback distance would not be required if the structure is located as shown in the AMEC report. Based on our review of the AMEC report and our observations of current site conditions, we generally concur with the opinions and recommendations provided. It is our opinion that the report meets generally accepted geotechnical principles and practice in this area. It is not clear from the documents we reviewed whether or not the proposed short plat development will include use of infiltration facilities to dispose of storm water. Guidelines for 400 NORTH 34TH STREET SUITE 100 P.O. BOX 300303 SEATTLE, WASHINGTON 98103 206632.8020 FAX 206.695.6 TOD: 1.800.833.6388 21-1-09678-001 J J bF'gtU Ms. Jill Mosqueda City of Tukwila Department of Public Works April 1, 2002 Page 2 determining soil infiltration rates are presented in the King County, Washington Surface Water Design Manual (September 1998), Section 5.4.1. While the AMEC report does not address infiltration rates of on -site soils, it appears that this will be necessary if the project is to involve use of on -site infiltration. In our opinion, the geotechnical report prepared for this project meets the generally accepted standards of practice in this area and meets the minimum standards of Tukwila Municipal Code 18.45.080 E. If necessary, the geotechnical engineer should review the current development plans with regard to handling of storm water and provide a supplemental letter to address infiltration rates. We appreciate the opportunity to be of service. If you have any questions I am available at (206) 695 -6875. Sincerely, SHANNON WILSON, INC. Martin W. Page, P.E. Senior Principal Engineer MWP:TMG /mwp 21 -1- 09678 -001 -L I W P/L KD SUMMARY SHANNON &WILSON. INC. 21 -1- 09678 -001 3S EXHIBIT D GEOTECHICAL REPORT ADDENDUM JUNE 25, 2004 COVENANT AND HOLD HARMLESS AGREEMENT Sensitive Area Page. f 40 June 25, 2004 1 -93M- 00359 -0 Match MacDonald P.O. Box 737 Renton, Washington 98057 Attention: Mr. Mark MacDonald Dear Mark: PROJECT DESCRIPTION AMEC Earth Environmental, Inc. 5007 Pacific Highway East, #5 Office Tacoma, Washington USA 98424 Tel (253) 896 -0132 Fax (253) 896 -0771 www.amec.com JUL 132004 TLaSVV ILA PUBLIC WORKS Subject: Geotechnical Supplement No. 1: Critical Areas Designation Sunnyvale Gardens Lots 1,2, and 3 4404 —160 Street Tukwila, Washington amee AMEC Earth Environmental, Inc. (AMEC) is pleased to submit this letter presenting our supplementary geotechnical conclusions and recommendations concerning the critical areas designations of lots 1, 2, and 3 for the above referenced short plat development. AMEC previously completed a geotechnical engineering evaluation of the project site and submitted a Geotechnical Engineering Report (1 -93M- 00359 -0) dated February 22, 2002 and an Infiltration Test Report (1 -93M- 00359 -A) was prepared on June 3, 2002. As outlined in our proposal memorandum dated June 25, 2004, our scope of work was limited to geotechnical research and letter preparation. We received your verbal authorization for our supplementary services on June 25, 2004. This letter has been prepared for the exclusive use of Match MacDonald and their consultants, for specific application to this project, in accordance with generally accepted geotechnical engineering practice. The project site consists of an existing single family home with associated parking and a currently undeveloped portion of the subject property north of the existing home that is being short platted into four lots. The existing residence (located on Lot 1) is located at 4404 160 Street, Tukwila, Washington. Lots 1, 2, 3 slope downward to the north with an approximate inclination of about 5 to 7 percent (measured in field), while proposed Lot 4 gradually steepens its downward slope to the northwest and develops a maximum inclination of about 45 percent �-O 40 SServer\D\Prcjects \00000s \00359 Sunnyvale Gardens Shod Flat \Geosup lv dot Match MacDonald June 29. 2004 (measured in field) throughout the northernmost portion of the property. Site boundaries are generally delineated by a slope to the north, residential property to the east and west, and by 160'" Street to the south. At the time of our recent site reconnaissance, June 25, 2004, the new driveway and utilities to Lots 2, 3, and 4 had been installed. SITE CONDITIONS amee 1 -93M- 00539 -0 Page 2 Lot 1 is currently occupied by an existing single family home with associated parking. Lots 2 3 have been cleared and stripped as the new driveway and utilities have been installed. The two lots slope gently downward to the north. Lot 4 is mostly vegetated by cut grass, mature douglas fir, alder, and maple trees. In areas that are not currently landscaped the under -story consists of moderately thick groundcover including laurel and berry vines or bushes. Lot 4 gradually steepens its downward slope to the northwest and develops a maximum inclination of about 45 percent (measured in field) throughout the northernmost portion of the property. No indication of past slope instability, seeps, springs, or geologic contacts were observed within or adjacent to the subject property were observed during our initial site work in 2002 or at the time of our recent reconnaissance in 2004. According to published geologic maps, the site is located within the Puget Lowland. Quaternary sediments consisting of various glacial, fluvial, lake and marsh deposits dominate the region. These sediments were deposited from the Puget Lobe of the Cordilleran continental ice sheet during the Vashon Stade of the Fraser Glaciation. The geologic map entitled "Geology of the Des Moines Quadrangle, Washington classifies the soils in the vicinity of the project site as ground moraine (Qgt), which are characterized as mainly compacted unoxidized glacial till. Our previously excavated test pit explorations encountered sandy soils of varying density, and generally diverged fro the published geological mapping. Specifically, our on -site explorations revealed approximately 6 inches of loose organic soil overlying about 2 feet of loose, moist, silty sand with roots. Beneath the silty sand, we encountered about 21/2 to 71/2 feet of sand with trace silt and gravel. The sand continued to the termination of our test pits. In test pit TP -2, we encountered a 1 -foot layer of medium dense, moist, silty, gravelly sand beneath the silty sand before encountering the sand. CONCLUSIONS AND RECOMMENDATIONS In our opinion, based on our previous site explorations and recent review of site conditions, we offer the following geotechnical recommendations concerning the critical areas designations of the Lots 1, 2, and 3. Slope Stability: The "Map Showing Relative Slope Stability in Part of West Central King County, Washington" prepared by Robert D. Miller, classifies the OF 4b \\ServeAO\Projects \00000s \00359 Sunnyvale Gardens Short Plal\Geosup (Arent Match MacDonald June 29, 2004 CLOSURE amee 1 -93M- 00539 -0 Page 3 slopes in the vicinity of the project site as Class 1. These slopes are generally stable even where modified by man. Sections of the proposed property may extend into a region classified as Class 2. Class 2 slopes are normally stable but may become unstable due to man's activities. It is our interpretation that only northern portion of lot 4 is mapped to contain Class 2 slopes, no development is planned in this area. Topography: Lots 1, 2, and 3 are generally flat to very gently sloping downward to the north. The maximum observed slope inclination at the time of our initial site work and recent reconnaissance was on the order of 5 to 7 percent. Lot 4 was the only lot on which slopes in excess of 7 percent, and extending up to 45 percent were observed. Evidence of Slope Instability: We did not observe any evidence of past slope instability during our 2002 or 2004 site work Critical Areas Designation: Based on the conclusions and recommendations in our February 22, 2002 Geotechnical Engineering Report and our June 3, 2002 Infiltration Test Report, it is our opinion that the critical areas designation of potential geologic instability be removed from Lots 1, 2, and 3 of the Sunnyvale Gardens short plat. The conclusions and recommendations presented in this letter are based, in part, on our previous subsurface explorations; therefore, if variations in the subsurface conditions are observed at a later time, we may need to modify this report to reflect those changes. AMEC is available to provide geotechnical monitoring, soils testing, and other services throughout construction. 39 or 4D \\ServenD \Projects \00000s \00959 Sunnyvale Gardens Shon PlanGeosup wdoc Match MacDonald June 29. 2004 Sincerely, Keith S. Schembs, L.E.G. Senior Project Geologist kss /mh We appreciate the opportunity to be of continued service on this project. If you have any questions regarding this letter or any aspects of the project, please feel free to contact our office. AMEC Earth Environmental, Inc. Marlea Haugen, P.E. Senior Engineer Distribution: Match MacDonald (1) Attn: Mr. Mark MacDonald amee 1 -93M- 00539 -0 Page 4 6 O 0 S 43 nServen0WrojecISW00005 ■00359 Sunnyvale Gardens Short PlanGeosup Llr.doc