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CANOD.pdfCity of Edinonds Critical Area Notice of Decision Applicant: Property Owner: cl " ol Critical Area File Permit Number. 6� Site Location: 4�1 "7 I Number: Parcel 00-16fe, ("xx)e Project Description-, All E] Conditional Waiver. No critical area report is required for the project described above. There will be no alteration of a Critical Area or its required buffer. The proposal is an allowed activity pursuant to ECDC 23,40,220, 23,50.220, and/or 23.80.040. The proposal is exempt pursuant to ECDC 23.40.230. Erosion Hazard. Project is within erosion hazard area. Applicant must prepare an erosion and sediment control plan in compliance with ECDC 18.30. Critical Area Report Required. The proposed project is within a critical area and/or a critical area buffer and a critical area report is required. A critical area report has been submitted and evaluated for compliance with the following criteria pursuant to ECDC 23.40.160: 1 The proposal minimizes the impact oil critical areas in accordance with ECDC 23 A0,120, Mitigation sequencing; I The proposal does not pose an unreasonable threat to the public health, safety, or welfare on or off the development proposal site; 3. The proposal is consistent with the general purposes of this title and the public interest; 4. X_ Any alterations permitted to the critical area are mitigated in accordance with ECDC 23,40.110, Mitigation requirements. 5. The proposal protects the critical area functions and values consistent with the best available science and results in no net loss of critical functions and values; and 6. _Z The proposal is consistent with other applicable regulations and standards. Unfavorable Critical Area Decision. The proposed project is not exempt or does not adequately mitigate its impacts on critical areas and/or does not comply with the criteria in ECDC 23.40.1.60 and the provisions of the City of Edmonds critical area regulations. See attached findings of noncompliance, Favorable Critical Area Decision. The proposed project as described above and as shown on the attached site plan meets or is exempt from the criteria in ECDC 23.40,160, Review Criteria, and complies with the applicable provisions of the City of Edmonds critical area regulations. Any subsequent changes to the proposal shall void this decision pending re -review of the proposal. Conditions. Critical Area specific condition(s) have been applied to the permit number referenced above. See referenced permit number for specific condition(s). &Lt(z Reviewer, /7 Signature A -C4 Date Appeals: Any decision to approve, condition, or deny a developrnent proposal or other activity based oil the requirements of critical area regulations may be appealed according to, and as pail of, the appeal procedure, if ally, for the permit or approval involved. Revised 12/1612010 GEOTECHNICAL ENGINEERING STUDY �NV 0� �N�� Proposed NevvResidence '`~` - ^ �~^^ 73OQ-1G4`"Place Southwest OEVE��pyNENT3�QV/�E� Edmonds, Washington CQ0�7ER This report presents the findings and recommendations ofour geotechnical engineering study for the site of the proposed new Denson residence to be constructed in Edmonds. Based on the preliminary plans provided, we expect that the vacant lot will be developed with a new one-story residence situated centrally on the pnnporh/ The attached two -car garage will he located onthe southeastern corner ofthe house. Adeck orpatio iaexpected toextend off the northeastern side of the structure. No significant retaining m/eUs are anticipated for the site development. K the scope of the project oh8Dg83 from vvko[ we have described above, we should be provided with revised plans in order to determine if modifications to the recommendations and conclusions of this report are warranted. SITE GONDITIONS MMERM The Vicinity Map, Plate 1' illustrates the general location of the site. The subject property is a vacant, irregularly-shaped |o| located on the north side of the cul-de-sac that forms -the Vvonte'''end O[1O4"'Place Southwest. The lot was overgrown with blackberry vines and other brush atthe time ofour August 1. 2014 site visit. There were no significant trees on the lot, with the exception ofan unhealthy -looking madrona tree in the northwestern corner of the property. The ground surface over the majority of the |cd in relatively flat. There is a slight grade down toward the northvvest. Based on our observations, there are no cieeper-thon-40-peroeDtslope areas on the site, The topography on the Cr&Ga/Aroa Mao from City of Edmonds does not accurately depict this. At the north property line is 8 short older rockery where the grade drops approximately haet Below this rockery, in the right-of-way for 164m Street Southwest, the ground slopes steeply - downward over a vertical elevation change of approximately 4 feet. Below this short slope in a tall, newer rockery that was placed in front of an 8' to 1O4bot cut that was made to nnaatn the access road to two homes located to the northwest. We observed no indications ofinstability in thea~ manmade slope elements. We expect that the |�tallrockery and the short cut slope above it were made under the guidance of a geotechnical engineer when the access road was cut into the sloping � Other than the newer houses to the northwest of the site, the neighboring lots to the west and east have been previously developed with older homes. The site is located outside of the North Edmonds Earth Subsidence and Landslide Hazard Area. --- GEOITCH CONSULTANTS, INC. Ron Denson August 29, 2014 SUBSURFACE JN 14315 Page 2 The subsurface conditions were explored by excavating four test pits at the approximate locations shown on the Site Exploration Plan, Plate 2. Our exploration program was based on the proposed construction, anticipated subsurface conditions and those encountered during exploration, and the scope of work outlined in our proposal. The test pits were excavated on August 1, 2014 with a rubber -tracked backhoe. A geotechnical engineer from our staff observed the excavation process, logged the test pits, and obtained representative samples of the soil encountered. "Grab" samples of selected subsurface soil were collected from the backhoe bucket. The Test Pit Logs are attached to this report as Plate 3. Soil Conditions Test Pits 1 and 2 were conducted along the northern side of the lot, within 5 to 15 feet of north property line. These explorations revealed a thin layer of topsoil overlying dense to very dense, gravelly, silty sand. This soil has been glacially compressed, and is referred to as glacial till. The till was less than 2 feet thick, with dense, slightly gravelly sand beneath it. This glacially -compressed sand extended to the maximum 9 -foot depth of the test pits. Test Pits 3 and 4 were excavated further from the north property line. These explorations found thin topsoil over the dense, gravelly sand that we observed in Test Pits 1 and 2. Although our explorations did not encounter cobbles or boulders, they are often found scattered through soils that have been deposited by glaciers or fast-moving water. Groundwater Conditions No groundwater or wet conditions were noted in the test pits. Even though the explorations were conducted following summer, when groundwater levels are lowest, our observations indicate that the seasonal high groundwater level is below the bottom of the test pits. The stratification lines on the logs represent the approximate boundaries between soil types at the exploration locations. The actual transition between soil types may be gradual, and subsurface conditions can vary between exploration locations. The logs provide specific subsurface information only at the locations tested. The relative densities and moisture descriptions indicated on the test pit logs are interpretive descriptions based on the conditions observed during excavation. The compaction of backfill was not in the scope of our services. Loose soil will therefore be found in the area of the test pits. If this presents a problem, the backfill will need to be removed and replaced with structural fill during construction. GEOTECH CONSULTANTS, INC. Ron Denson August 29, 2014 CONCLUSIONS AND RECOMMENDATIONS GENERAL JN 14315 Page 3 THIS SECTION CONTAINS A SUMMARY OF OUR STUDY AND FINDINGS FOR THE PURPOSES OF A GENERAL OVERVIEW ONLY. MORE SPECIFIC RECOMMENDATIONS AND CONCLUSIONS ARE CONTAINED IN THE REMAINDER OF THIS REPORT. ANY PARTY RELYING ON THIS REPORT SHOULD READ THE ENTIRE DOCUMENT. The test pits conducted for this study encountered dense to very dense glacial till or sand within a few feet of the ground surface. These competent soils are acceptable to support the new house using conventional foundations. It will be important that the footing excavations be cleaned of all soil that is loosened during the excavation process. It is not acceptable to recompact any disturbed soil, it should be scraped or shoveled out of the footing areas before concrete is poured. As discussed below, at least a portion of the northern footings for the deck and residence will likely have to be extended into the dense to very dense soil. Under Edmonds City Code (ECC) section 23.80.020, the subject site would be designated as a geologically hazardous area. The steep slope and rockery immediately to the north of the site are over 10 feet in height, so would meet the definition of a landslide hazard area. It is important to note that this slope and rockery were created by previous legal grading for the neighboring access road and do not exhibit indications of instability. The recommendations of this report are intended to prevent the planned development from adversely impacting the stability of the landslide hazard area, and to protect the planned structure from damage in the event of any foreseeable future slope movement. Our setback and foundation recommendations will provide a slope stability safety factor for the residence in excess of 1.5 and 1.2 for static and seismic conditions. Considering the density of the native soils, it is our opinion that no buffer is needed to protect the landslide hazard area, provided: ® The short rockery located on the north property line, and the slope and tall rockery to the north of it, remain undisturbed; ® A wire -backed silt fence is erected immediately behind the short rockery to avoid soil (and/or debris) from being inadvertently placed on the steep slope below; and, ® No fill is placed above existing grade within 10 feet of the short rockery. We recommend that the foundations for the residence be located no closer than 15 feet to the short rockery along the northern property line. The deck foundations should be at least 10 feet from this short rockery. Additionally, any footings, including those for the northern deck, that are located within 25 feet of this rockery should be extended to a minimum of 3 feet of embedment into the dense to very dense soils. Runoff from impervious surfaces must not be discharged on, or within 25 feet of, the west, north, or east property lines. The glacial till on the northern portion of the site is relatively impervious. While the sand soils underlying the glacial till have a low silt content, their density also gives them a relatively low permeability. If limited on-site infiltration is attempted in the cleaner sand, a long-term design infiltration rate of no more than 0.5 inches/hour should be used, and all infiltration elements should be located at least 25 feet from property lines. The performance of any infiltration facilities will naturally degrade over time as the soil becomes clogged from silt and debris carried in with the GEOTECH CONSULTANTS. INC. Ron Denson JN 14315 August 29, 2014 Page 4 collected runoff. The effective life of infiltration systems can be extended by frequent cleaning of gutters and drainage elements that carry water into the system. It is prudent to provide emergency overflows for infiltration systems, in the event they fail or are overwhelmed by heavy storm flows. If the recommendations of this report are followed, the planned development: 1. Will not increase the threat of the geological hazard to adjacent properties beyond predevelopment conditions; 2. Will not adversely impact other critical areas; 3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal to or less than predevelopment conditions; and, 4. Will be safe under anticipated conditions. If the madrona tree in the northwestern corner of the property is dying, it would be more appropriate from a geotechnical standpoint to cut it down before it can topple over and pull up the root ball. The site soils are not susceptible to seismic liquefaction. The erosion control measures needed during the site development will depend heavily on the weather conditions that are encountered. While site clearing will expose a large area of bare soil, the erosion potential on the site is relatively low due to the gentle slope of the ground in the work area. Clearing should be limited to areas that will be immediately worked, particularly in wet weather. We anticipate that a silt fence will be needed around the downslope sides of any cleared areas, and should be set back at least 2 feet from the short rockery. Rocked construction access roads and staging/laydown areas should be extended into the site to reduce the amount of soil or mud carried off the property by trucks and equipment. Wherever possible, these roads should follow the alignment of planned pavements, and trucks should not be allowed to drive off of the rock -covered areas. Cut slopes and soil stockpiles should be covered with plastic during wet weather. Following rough grading, it may be necessary to mulch or hydroseed bare areas that will not be immediately covered with landscaping or an impervious surface. The drainage and/or waterproofing recommendations presented in this report are intended only to prevent active seepage from flowing through concrete walls or slabs. Even in the absence of active seepage into and beneath structures, water vapor can migrate through walls, slabs, and floors from the surrounding soil, and can even be transmitted from slabs and foundation walls due to the concrete curing process. Water vapor also results from occupant uses, such as cooking and bathing. Excessive water vapor trapped within structures can result in a variety of undesirable conditions, including, but not limited to, moisture problems with flooring systems, excessively moist air within occupied areas, and the growth of molds, fungi, and other biological organisms that may be harmful to the health of the occupants. The designer or architect must consider the potential vapor sources and likely occupant uses, and provide sufficient ventilation, either passive or mechanical, to prevent a build up of excessive water vapor within the planned structure. Geotech Consultants, Inc. should be allowed to review the final development plans to verify that the recommendations presented in this report are adequately addressed in the design. Such a plan review would be additional work beyond the current scope of work for this study, and it may include revisions to our recommendations to accommodate site, development, and geotechnical constraints that become more evident during the review process. GEOTECH CONSULTANTS, INC. Ron Denson August 29, 2014 JN 14315 Page 5 We recommend including this report, in its entirety, in the project contract documents. This report should also be provided to any future property owners so they will be aware of our findings and recommendations. SEISMIC CONSIDERATIONS In accordance with the International Building Code (IBC), the site class within 100 feet of the ground surface is best represented by Site Class Type C (Very Dense Soil and Soft Rock). The on-site soils are not susceptible to seismic liquefaction because of their dense to very dense composition. CONVENTIONAL FOUNDATIONS We recommend that continuous and individual spread footings have minimum widths of 16 and 24 inches, respectively. Exterior footings should also be bottomed at least 18 inches below the lowest adjacent finish ground surface for protection against frost and erosion. The local building codes should be reviewed to determine if different footing widths or embedment depths are required. Footing subgrades must be cleaned of loose or disturbed soil prior to pouring concrete. Depending upon site and equipment constraints, this may require removing the disturbed soil by hand. As discussed in the General section, the footings along the north side of the house and deck should be extended at least 3 feet into the dense to very dense soils. An allowable bearing pressure of 3,000 pounds per square foot (psf) is appropriate for footings supported on competent native soil. A one-third increase in this design bearing pressure can be used when considering short-term wind or seismic loads. For the above design criteria, it is anticipated that the total post -construction settlement of footings founded on competent native soil, will be less than one inch, with differential settlements on the order of one-quarter inch in a distance of 25 feet along a continuous footing with a uniform load. Lateral loads due to wind or seismic forces may be resisted by friction between the foundation and the bearing soil, or by passive earth pressure acting on the vertical, embedded portions of the foundation, For the latter condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded by level, well -compacted fill. We recommend using the following ultimate values for the foundation's resistance to lateral loading: I fficient of Friction 0.45 ive Earth Pressure 350 pcf vvnere: pct is Pounds per Cubic Foot, and Passive Earth Pressure is computed using the equivalent fluid density. If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. We recommend maintaining a safety factor of at least 1.5 for the foundation's resistance to lateral loading, when using the above ultimate values. GEOTECH CONSULTANTS, INC. Ron Denson August 29, 2014 PERMANENT FOUNDATION AND RETAINING WALLS JN 14315 Page 6 Retaining walls backfilled on only one side should be designed to resist the lateral earth pressures imposed by the soil they retain. The following recommended parameters are for walls that restrain level backfill: Active Earth Pressure * 35 pcf 7130 Passive Earth Pressure 350 pcf Coefficient of Friction 0.45 Soil Unit Weight pcf Where: pcf is Pounds per Cubic Foot, and Active and Passive Earth Pressures are computed using the equivalent fluid pressures. * For a restrained wall that cannot deflect at least 0.002 times its height, a uniform lateral pressure equal to 10 psf times the height of the wall should be added to the above active equivalent fluid pressure. The values given above are to be used to design only permanent foundation and retaining walls that are to be backfilled, such as conventional walls constructed of reinforced concrete or masonry. It is not appropriate to use the above earth pressures and soil unit weight to back -calculate soil strength parameters for design of other types of retaining walls, such as soldier pile, reinforced earth, modular or soil nail walls. We can assist with design of these types of walls, if desired. The passive pressure given is appropriate only for a shear key poured directly against undisturbed native soil, or for the depth of level, well -compacted fill placed in front of a retaining or foundation wall. The values for friction and passive resistance are ultimate values and do not include a safety factor. We recommend a safety factor of at least 1.5 for overturning and sliding, when using the above values to design the walls. Restrained wall soil parameters should be utilized for a distance of 1.5 times the wall height from corners or bends in the walls. This is intended to reduce the amount of cracking that can occur where a wall is restrained by a corner. The design values given above do not include the effects of any hydrostatic pressures behind the walls and assume that no surcharges, such as those caused by slopes, vehicles, or adjacent foundations will be exerted on the walls. If these conditions exist, those pressures should be added to the above lateral soil pressures. Where sloping backfill is desired behind the walls, we will need to be given the wall dimensions and the slope of the backfill in order to provide the appropriate design earth pressures. The surcharge due to traffic loads behind a wall can typically be accounted for by adding a uniform pressure equal to 2 feet multiplied by the above active fluid density. Heavy construction equipment should not be operated behind retaining and foundation walls within a distance equal to the height of a wall, unless the walls are designed for the additional lateral pressures resulting from the equipment. Wall Pressures Due to Seismic Forces The surcharge wall loads that could be imposed by the design earthquake can be modeled by adding a uniform lateral pressure to the above -recommended active pressure. The recommended surcharge pressure is 7H pounds per square foot (psf), where H is the design retention height of the wall. Using this increased pressure, the safety factor against sliding and overturning can be reduced to 1.2 for the seismic analysis. GEOTECH CONSULTANTS, INC. Ron Denson JN 14315 August 29, 2014 Page 7 Retaining Wall Backfill and Waterproofing Backfill placed behind retaining or foundation walls should be coarse, free -draining structural fill containing no organics. This backfill should contain no more than 5 percent silt or clay particles and have no gravel greater than 4 inches in diameter. The percentage of particles passing the No. 4 sieve should be between 25 and 70 percent. If the native sands are used as backfill, a minimum 12 -inch width of free -draining gravel should be placed against the backfilled retaining walls. The purpose of these backfill requirements is to ensure that the design criteria for a retaining wall are not exceeded because of a build-up of hydrostatic pressure behind the wall. The top 12 to 18 inches of the backfill should consist of a compacted, relatively impermeable soil or topsoil, or the surface should be paved. The ground surface must also slope away from backfilled walls to reduce the potential for surface water to percolate into the backfill. Similarly, it is important that the subgrade soils for an pervious surfaces, such as pavers or permeable pavement, be sloped to drain away from walls and foundations. It is critical that the wall backfill be placed in lifts and be properly compacted, in order for the above -recommended design earth pressures to be appropriate. The wall design criteria assume that the backfill will be well -compacted in lifts no thicker than 12 inches. The compaction of backfill near the walls should be accomplished with hand -operated equipment to prevent the walls from being overloaded by the higher soil forces that occur during compaction. The section entitled General Earthwork and Structural Fill contains additional recommendations regarding the placement and compaction of structural fill behind retaining and foundation walls. The above recommendations are not intended to waterproof below -grade walls, or to prevent the formation of mold, mildew or fungi in interior spaces. Over time, the performance of subsurface drainage systems can degrade, subsurface groundwater flow patterns can change, and utilities can break or develop leaks. Therefore, waterproofing should be provided where future seepage through the walls is not acceptable. This typically includes limiting cold -joints and wall penetrations, and using bentonite panels or membranes on the outside of the walls. There are a variety of different waterproofing materials and systems, which should be installed by an experienced contractor familiar with the anticipated construction and subsurface conditions. Applying a thin coat of asphalt emulsion to the outside face of a wall is not considered waterproofing, and will only help to reduce moisture generated from water vapor or capillary action from seeping through the concrete. As with any project, adequate ventilation of basement and crawl space areas is important to prevent a build up of water vapor that is commonly transmitted through concrete walls from the surrounding soil, even when seepage is not present. This is appropriate even when waterproofing is applied to the outside of foundation and retaining walls. We recommend that you contact a specialty consultant if detailed recommendations or specifications related to waterproofing design, or minimizing the potential for infestations of mold and mildew are desired. GEOTECH CONSULTANTS, INC. Ron Denson JN 14315 August 29, 2014 Page 8 SLABS -ON -GRADE Even where the exposed soils appear dry, water vapor will tend to naturally migrate upward through the soil to the new constructed space above it. This can affect moisture -sensitive flooring, cause imperfections or damage to the slab, or simply allow excessive water vapor into the space above the slab. All interior slabs -on -grade should be underlain by a capillary break or drainage layer consisting of a minimum 4 -inch thickness of gravel or crushed rock that has a fines content (percent passing the No. 200 sieve) of less than 3 percent and a sand content (percent passing the No. 4 sieve) of no more than 10 percent. As noted by the American Concrete Institute (ACI) in the Guides for Concrete Floor and Slab Structures, proper moisture protection is desirable immediately below any on -grade slab that will be covered by tile, wood, carpet, impermeable floor coverings, or any moisture -sensitive equipment or products. ACI also notes that vapor retarders, such as 6 -mil plastic sheeting, have been used in the past, but are now recommending a minimum 10 -mil thickness. A vapor retarder is defined as a material with a permeance of less than 0.3 perms, as determined by ASTM E 96. It is possible that concrete admixtures may meet this specification, although the manufacturers of the admixtures should be consulted. Where vapor retarders are used under slabs, their edges should overlap by at least 6 inches and be sealed with adhesive tape. The sheeting should extend to the foundation walls for maximum vapor protection. If no potential for vapor passage through the slab is desired, a vapor barrier should be used. A vapor barrier, as defined by ACI, is a product with a water transmission rate of 0.01 perms when tested in accordance with ASTM E 96. Reinforced membranes having sealed overlaps can meet this requirement. EXCAVATIONS AND SLOPES Excavation slopes should not exceed the limits specified in local, state, and national government safety regulations. Temporary cuts to a depth of about 4 feet may be attempted vertically in unsaturated soil, if there are no indications of slope instability. However, vertical cuts should not be made near property boundaries, or existing utilities and structures. Based upon Washington Administrative Code (WAC) 296, Part N, the soil at the subject site would generally be classified as Type B. We recommend that temporary cut slopes greater than 4 feet in height should not be excavated at an inclination steeper than 1:1 (Horizontal:Vertical), extending continuously between the top and the bottom of a cut. The above -recommended temporary slope inclination is based on the conditions exposed in our explorations, and on what has been successful at other sites with similar soil conditions. It is possible that variations in soil and groundwater conditions will require modifications to the inclination at which temporary slopes can stand. Temporary cuts are those that will remain unsupported for a relatively short duration to allow for the construction of foundations, retaining walls, or utilities. Temporary cut slopes should be protected with plastic sheeting during wet weather. It is also important that surface water be directed away from temporary slope cuts. The cut slopes should also be backfilled or retained as soon as possible to reduce the potential for instability. Please note that loose soil can cave suddenly and without warning. Excavation, GEOTECH CONSULTANTS, INC. Ron Denson JN 14315 August 29, 2014 Page 9 foundation, and utility contractors should be made especially aware of this potential danger. These recommendations may need to be modified if the area near the potential cuts has been disturbed in the past by utility installation, or if settlement -sensitive utilities are located nearby. All permanent cuts into native soil should be inclined no steeper than 2.5:1 (H:V). Fill slopes should not be constructed with an inclination greater than 2.5:1 (H:V). To reduce the potential for shallow sloughing, fill must be compacted to the face of these slopes. This can be accomplished by overbuilding the compacted fill and then trimming it back to its final inclination. Adequate compaction of the slope face is important for long-term stability and is necessary to prevent excessive settlement of patios, slabs, foundations, or other improvements that may be placed near the edge of the slope. Water should not be allowed to flow uncontrolled over the top of any temporary or permanent slope. All permanently exposed slopes should be seeded with an appropriate species of vegetation to reduce erosion and improve the stability of the surficial layer of soil. DRAINAGE CONSIDERATIONS Foundation drains should be used where (1) crawl spaces or basements will be below a structure, (2) a slab is below the outside grade, or (3) the outside grade does not slope downward from a building. Drains should also be placed at the base of all earth -retaining walls. These drains should be surrounded by at least 6 inches of 1 -inch -minus, washed rock and then wrapped in non -woven, geotextile filter fabric (Mirafi 140N, Supac 4NP, or similar material). At its highest point, a perforated pipe invert should be at least 6 inches below the bottom of a slab floor or the level of a crawl space, and it should be sloped for drainage. All roof and surface water drains must be kept separate from the foundation drain system. A typical drain detail is attached to this report as Plate 4. For the best long-term performance, perforated PVC pipe is recommended for all subsurface drains. Drainage inside the house's footprint should also be provided where (1) a crawl space will slope or be lower than the surrounding ground surface, (2) an excavation encounters significant seepage, or (3) an excavation for a building will be close to the expected high groundwater elevations. We can provide recommendations for interior drains, should they become necessary, during excavation and foundation construction. As a minimum, a vapor retarder, as defined in the Slabs -On -Grade section, should be provided in any crawl space area to limit the transmission of water vapor from the underlying soils. Also, an outlet drain is recommended for all crawl spaces to prevent a build up of any water that may bypass the footing drains. Providing even a thin layer of gravel under the vapor retarder is prudent to allow any water in the crawl space to flow rapidly to the outlet drain. Groundwater was not observed during our field work. If seepage is encountered in an excavation, it should be drained from the site by directing it through drainage ditches, perforated pipe, or French drains, or by pumping it from sumps interconnected by shallow connector trenches at the bottom of the excavation. GEOTECH CONSULTANTS, INC. Ron Denson JN 14315 August 29, 2014 Page 10 The excavation and site should be graded so that surface water is directed off the site and away from the tops of slopes. Water should not be allowed to stand in any area where foundations, slabs, or pavements are to be constructed. Final site grading in areas adjacent to buildings and walls should slope away at least 2 percent, except where the area is paved. It is also important to slope the subgrade soils of pervious surfaces, such as pavers and permeable pavements, to drain away from foundations and walls. Surface drains should be provided where necessary to prevent ponding of water behind foundation or retaining walls. Water from roof, storm water, and foundation drains should not be discharged onto slopes; it should be tightlined to a suitable outfall located away from any slopes. GENERAL EARTHWORK AND STRUCTURAL FILL All building and pavement areas should be stripped of surface vegetation, topsoil, organic soil, and other deleterious material. The stripped or removed materials should not be mixed with any materials to be used as structural fill, but they could be used in non-structural areas, such as landscape beds. Structural fill is defined as any fill, including utility backfill, placed under, or close to, a building, behind permanent retaining or foundation walls, or in other areas where the underlying soil needs to support loads. All structural fill should be placed in horizontal lifts with a moisture content at, or near, the optimum moisture content. The optimum moisture content is that moisture content that results in the greatest compacted dry density. The moisture content of fill is very important and must be closely controlled during the filling and compaction process. The allowable thickness of the fill lift will depend on the material type selected, the compaction equipment used, and the number of passes made to compact the lift. The loose lift thickness should not exceed 12 inches. We recommend testing the fill as it is placed. If the fill is not sufficiently compacted, it can be recompacted before another lift is placed. This eliminates the need to remove the fill to achieve the required compaction. The following table presents recommended relative compactions for structural fill: Where: Minimum Relative Compaction is the ratio, expressed in percentages, of the compacted dry density to the maximum dry density, as determined in accordance with ASTM Test Designation D 1557-91 (Modified Proctor). GEOTECH CONSULTANTS, INC. Beneath slabs or walkways 95% Filled slopes and behind retaining walls 90% Beneath pavements 95% for upper 12 inches of subgrade; 90% below that level Where: Minimum Relative Compaction is the ratio, expressed in percentages, of the compacted dry density to the maximum dry density, as determined in accordance with ASTM Test Designation D 1557-91 (Modified Proctor). GEOTECH CONSULTANTS, INC. Ron Denson JN 14315 August 29, 2014 Page 11 Structural fill that will be placed in wet weather should consist of a coarse, granular soil with a silt or clay content of no more than 5 percent. The percentage of particles passing the No. 200 sieve should be measured from that portion of soil passing the three -quarter -inch sieve. LIMITATIONS The conclusions and recommendations contained in this report are based on site conditions as they existed at the time of our exploration and assume that the soil and groundwater conditions encountered in the test pits are representative of subsurface conditions on the site_ If the subsurface conditions encountered during construction are significantly different from those observed in our explorations, we should be advised at once so that we can review these conditions and reconsider our recommendations where necessary. Unanticipated conditions are commonly encountered on construction sites and cannot be fully anticipated by merely taking samples in test pits. Subsurface conditions can also vary between exploration locations. Such unexpected conditions frequently require making additional expenditures to attain a properly constructed project. It is recommended that the owner consider providing a contingency fund to accommodate such potential extra costs and risks. This is a standard recommendation for all projects. The recommendations presented in this report are directed toward the protection of only the proposed structure from damage due to slope movement. Predicting the future behavior of steep slopes and the potential effects of development on their stability is an inexact and imperfect science that is currently based mostly on the past behavior of slopes with similar characteristics. Landslides and soil movement can occur on steep slopes before, during, or after the development of property. The owner of a property like this must ultimately accept the possibility that some slope movement could occur, resulting in possible loss of ground or damage to the facilities around the proposed residence. This report has been prepared for the exclusive use of Ron Denson and his representatives, for specific application to this project and site. Our conclusions and recommendations are professional opinions derived in accordance with current standards of practice within the scope of our services and within budget and time constraints. No warranty is expressed or implied. The scope of our services does not include services related to construction safety precautions, and our recommendations are not intended to direct the contractor's methods, techniques, sequences, or GEOTECH CONSULTANTS, INC. Ron Denson August 29, 2014 JN 14315 Page 12 procedures, except as specifically described in our report for consideration in design. Our services also do not include assessing or minimizing the potential for biological hazards, such as mold, bacteria, mildew and fungi in either the existing or proposed site development. ADDITIONAL SERVICES Geotech Consultants, Inc. should be retained to provide geotechnical consultation, testing, and observation services during construction. This is to confirm that subsurface conditions are consistent with those indicated by our exploration, to evaluate whether earthwork and foundation construction activities comply with the general intent of the recommendations presented in this report, and to provide suggestions for design changes in the event subsurface conditions differ from those anticipated prior to the start of construction. However, our work would not include the supervision or direction of the actual work of the contractor and its employees or agents. Also, job and site safety, and dimensional measurements, will be the responsibility of the contractor. During the construction phase, we will provide geotechnical observation and testing services when requested by you or your representatives. Please be aware that we can only document site work we actually observe. It is still the responsibility of your contractor or on-site construction team to verify that our recommendations are being followed, whether we are present at the site or not. The following plates are attached to complete this report: Plate 1 Vicinity Map Plate 2 Site Exploration Plan Plate 3 Test Pit Logs Plate 4 Typical Footing Drain Detail We appreciate the opportunity to be of service on this project. If you have any questions, or if we may be of further service, please do not hesitate to contact us. MRM: at Respectfully submitted, GEOTECH CONSULTANTS, INC. WASS �0 n �. 27845 CISTE��� Marc c is, P. E. Principal GEOTECH CONSULTANTS, INC. G T E C CONSULTANTS, INC. (Source: Microsoft MapPoint, 2013) VICINITY NIA.P 7309 - 164th Place S.W. Edmonds, Washington Job No: Date: Plate: 14315 Aim.2014 Existing Residence #7317 Legend: TP -1 Test Pit Location r Tall 164th Avenue S.W. GEOTECH CONSULTANTS, INC. 1014 U1 riace 0. vv. (cul-de-sac) Existing Residence #7302 TEST PIT 1 De yth feet�t �....�a-... ti SorE Descrtptron.� r s�^.. t. Y '1. i ... b. .....,.�..,:r-.—,.w�.._.«.... ... _.. 'iA. � 1 c .. v,x.:.....w..-ry✓:.�...r�i...-.. c 0-0.5 To soil 0.5-2.0 Gray, gravelly, silty SAND, fine-grained, moist, dense to very dense Glacial Till 2.0-9.0 Gray, slightly gravelly SAND, medium- to fine-grained, moist, dense Test Pit was terminated at a depth of 9.0 feet on August 1, 2014. No groundwater seepage was observed in the test pit. TEST PIT 2 Test Pit was terminated at a depth of 6.0 feet on August 1, 2014. No groundwater seepage was observed in the test pit. I NAMNOM .from'--;-�� 0 - 0.5 Topsoil 0.5-2,0 Gray, gravelly, silty SAND, fine-grained, moist, dense to very dense Glacial Till) 2.0-6.0 Gray, slightly gravelly SAND, medium- to fine-grained, moist, dense Test Pit was terminated at a depth of 6.0 feet on August 1, 2014. No groundwater seepage was observed in the test pit. I NAMNOM Test Pit was terminated at a depth of 6.0 feet on August 1, 2014. No groundwater seepage was observed in the test pit. - -, v 0-0.5_ Topsoil 0.5-6.0 Gray, slightly gravelly SAND, medium- to fine-grained, moist, dense 1 est r1L was terminates at a depth of 6.0 teet on August 1, 2014. No groundwater seepage was observed in the test pit. GEOTECH CONSULTAN'T'S, INC. TEST PIT LOGS 7309 - 164th Place S.W. Edmonds, Washington Job No: .from'--;-�� 0 — 0.5 Topsoil 0.5 — 6.0 Gray, slightly gravelly SAND, medium- to fine-grained, moist, dense Test Pit was terminated at a depth of 6.0 feet on August 1, 2014. No groundwater seepage was observed in the test pit. - -, v 0-0.5_ Topsoil 0.5-6.0 Gray, slightly gravelly SAND, medium- to fine-grained, moist, dense 1 est r1L was terminates at a depth of 6.0 teet on August 1, 2014. No groundwater seepage was observed in the test pit. GEOTECH CONSULTAN'T'S, INC. TEST PIT LOGS 7309 - 164th Place S.W. Edmonds, Washington Job No: Dafe: Plate: 14315LJ Aug. 2014 3 Slope backfill away from foundation. Provide surface drains where necessary. Backfill (See text for requirements) Nonwoven Geotextile Washed Rock Filter Fabric (7/8" min. size) Jo 0 0 0 vL�v0 vLo, J'OC °� '0O' 4" min Tightline Roof Drain (Do not connect to footing drain) Possible Slab 4" Perforated Hard PVC Pipe (Invert at least 6 inches below slab or crawl space. Slope to drain to appropriate outfall. Place holes downward.) OJ O Oo•�00 O o 0 c•JOC \'`'00. 00 •° ° J 0�• J. ° :0 0 J :OOOu':0�0•J o;�oa 0'°ea`,JC6Ouo00 Vapor Retarder/Barrier and Capillary Break/Drainage Layer (Refer to Report text) NOTES: (1) In crawl spaces, provide an outlet drain to prevent buildup of water that bypasses the perimeter footing drains. (2) Refer to report text for additional drainage, waterproofing, and slab considerations. GE TES CONSU ,TNNTS, rNC. FOOTING DRAIN DETAIL 7309 - 164th Place S.W. Edmonds, Washington Job No. Date: Plate: 14315 Au .2014 4 a k=v .3_ ' &