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HomeMy WebLinkAboutFPA2007-00022 GEO Tech Report - FPA Reports - 3/15/2007 �6°N C06 MASON COUNTY �. ap Shelton (360) 427-9670 DEPARTMENT OF COMMUNITY DEVELOPMENT Belfair (360) 275-4467 Planning Mason County Bldg. 1 411 N. 5th Elma (360) 482-5269 P.O. Box 279 Shelton,WA 98584 --f Don Atkins 1540 Kirkland Ave Kirkland,WA 98033 May 27,2009 Re: 32235-75-90130&90120 Dear Mr. Atkins, This letter is follow up the meeting we had in November 2007 concerning your above referenced parcels in Mason County.At that meeting we discussed the status of a MEP 2007-00031 (regarding unpermitted logging in 2006)FPA 2007-00022(for additional logging)as well as process for getting a waiver from the six-year development moratorium that resulted from the unpermitted logging. Attending that meeting on 11/29/07 were Joe Staley,(WTM)Ryan Crater(former Code Enforcement Officer)and Bob Fink(former Planning Manager).According to my notes, at the conclusion of that meeting you agreed to have an existing geotechnical report revised to cover the FPA plus the MEP and a Moratorium Waiver and Joe Staley was going to revise the site plan for more detail.Mason County has heard nothing from you since then. I am enclosing copies of the letters that I have written to you on 11/13/07 and 11/29/07.Per Mason County Code,I need you to provide me with the material that I asked for in these letters with in 180-days of today's date, in order to avoid having to close your FPA case. Should your FPA case(for work to be done in the future)be closed,you will still need to do satisfy Code Enforcement regarding the unpermitted logging that occurred in 2006(MEP 2007-00031). Since our meeting in 2007,we have a new Code Enforcement Officer,Christine Clark at ext. 577. Regarding the problems with your existing geotechnical report,Mason County has since revised the way that these documents are reviewed and you could ask to re initiate the review of you report,but this would involve some additional fees and paper work. If you have any questions,I can be reached at ext. 571 or by e-mail at mms@co.mason.wa.us.Thank you. Sincerely, N) 4j Michael MacSems FPA Reviewer cc: Christine Clark Barbara Adkins Joe Staley II. The approximate location of any structures. III. The location of all existing and proposed streets,rights-of-way, easements, skid roads, and landings within the proposal. IV. The location of future land development including stormwater management facilities and vegetation to be retained for site landscaping, open space, wildlife habitat, screening and/or buffers. V. Site topography at contour intervals of 40 feet. VI. Critical areas and critical area buffers pursuant the Critical Areas Ordinance. VII. Drainage ways and culverts. VIII. Site area targeted for further harvest including proposed timing. IX. North arrow and scale shall be shown on all site plans. The scale shall be no smaller than one inch to 200 feet. (I have enclosed a base contour map of approx. 1"to 100' for your use). Related to item VII,but possibly not fully captured by it, your site plan will be forwarded to Mason County Public Works to be reviewed for consistency with the 1992 WSDOE Stormwater Manual. I have forwarded your geo-technical report to an outside contract engineer for review(an additional charge will be applied for this work), and I have visited the site. Beyond that, there is nothing more that I can do with your application until a complete site plan is received, as well as a general clarification regarding the scope of your proposal. It is possible that additional information could be required once the review begins. In order to keep this case open,please respond within 180-days. If you have any questions regarding the FPA or the development.moratorium,please contact me at extension 571 or by e-mail at mms@co.mason.wa.us. Please note that approval of this permit does not lift the exiting development moratorium. Sincerely, I � Michael MacSems FPA Reviewer cc: Ryan Crater(Code Enforcement) Joe Staley(WTM) Bob Fink(DCD Manager) John Sliva(Public Works) P6oN caa� MASON COUNTY Shelton (360) 427-9670 DEPARTMENT OF COMMUNITY DEVELOPMENT Belfair (360) 275-4467 Planning Mason County Bldg.1 411 N.5th Elma (360) 482-5269 P.O.Box 279 Shelton,WA 98584 185f ' Don Atkins 1540 Kirkland Ave Kirkland, WA 98033 November 13, 2007 Re: 32235-75-90130 & 90120 Dear Mr. Atkins, I am in receipt of your application for a forest practices permit for the above referenced parcels, near Union, Washington. I visited the site last week and was surprised to see that the site had already been logged, stumped and graded. When I returned to the office, I investigated the history of this parcel. In the process I learned that the property was logged without a permit in the summer of 2006. I also saw that an enforcement investigation was done by the County, leading up to an application for an after-the-fact Mason Environmental Permit(MEP2007-00031). From what I can tell, this permit has not been approved my Mason County. A geo-technical report was forwarded to Public Works for review in March,but has not been approved. Beyond that, the status of your MEP is.unclear, as I was unable to find a copy of your actual MEP application/file. For the record, I did notice that the MEP application was submitted with the standard review fee,'.when triple fees are required. If you have additional questions on the status of your MEP,please contact our code enforcement staff,Ryan Crater, at ext. 577. I am also concerned that you may not realize that,per state law, the portions of your property subject to the unpermitted harvest are automatically subject to a six year development moratorium from the date of discovery. I have recorded a Notice of Moratorium on your property(copy enclosed),but this is just a notice—the actual moratorium dates back to.July 26, 2006. Going forward, I am happy to review your current application, once you or your agent clarifies what you wish to do. Taken at face value, your site plan(which doesn't meet the County's criteria because it contains no contour information) suggests that you plan to harvest every tree above Timber Tides Drive. However your SEPA checklist states that the objective is only to cut trees that might pose a potential hazard to an eventual home site. I am enclosing a copy of the site plan as submitted along with some topographic information. Please have the map upgraded to meet all of the following criteria and returned to my attention. I. Harvest boundaries and tree retention areas. 6oN coa MASON COUNTY Shelton (360) 427-9670 DEPARTMENT OF COMMUNITY DEVELOPMENT Belfair (360) 275-4467 Planning .Mason County Bldg.1 411 N.5th Elma (360) 482-5269 _ P.O.Box 279 Shelton,WA 98584 85f Don Atkins 1�40 Kirkland Ave Kirkland, WA 98033 November 29, 2007 Re: 32235-75-90130&90120 Dear Mr. Atkins, This letter concerns the Geo-Technical Report for your FPA proposal on Timber Tides Drive E. I recently received comments back from contract reviewer Edward Wiltsie(of J.W. Morrissette &Associates) that the report that you submitted with your FPA .application is not sufficient for approval. It will be necessary for you to have E3RA revise the report for consistency with Mr. Wiltsie's concerns. Please find enclosed the geo-technical report and the letter from Edward Wiltsie describing the additional information that he needs to see in order to recommend approval. You will need to have E3RA amend the reports as specified. The amended . report should be delivered to my attention and I will have it forwarded to Mr. Wiltsie. Any technical question that E3RA may have should be directed to Mr. Wiltsie. My role in this process is to pass documents between the parties and log the activities into the case record. Thank you. Sincerely, i Michael MacSems FPA Reviewer i March 15, 2007 ORA, Inc. T06379/Atkins Mason County Report TEST PIT LOGS Depth(feet) Material Description Test Pit TP-1 Location: Upland,near building area Approximate ground surface elevation:About 475 feet 0.0— 1.5 Loose,moist,light brown,sandy GRAVEL with some silt(Glacial Outwash or Ablation Till)(GP-GM). 1.5—2.0 Very dense,light gray-brown,sandy GRAVEL with some silt and cobbles,cemented(Glacial Till)(GP- GM). Test pit terminated at approximately 2 feet due to refusal on hard soils No caving observed No groundwater encountered Test Pit TP-2 Location: Upland,near building area Approximate ground surface elevation:About 475 feet 0.0—1.5 Loose,moist,light brown,sandy GRAVEL with some silt(Glacial Outwash or Ablation Till)(GP-GM). 1.5—2.0 Very dense,light gray-brown,sandy GRAVEL with some silt and cobbles,cemented(Glacial Till)(GP- GM). Test pit terminated at approximately 2 feet due to refusal on hard soils No caving observed No groundwater encountered Logged by: FER on 1/3/07 526 CL530 532 534 5 3 C- 538 540 590 592 594 --,-----5 9 8-�. - --- __ QQ 16 TIMBER TIDES DR , E3RAInc. PROJECT: Atkins Proposed Home P.O.BOX 44890 TITLE: Site and Exploration Plan TACOMA, WA 98444 253-537-9400 off 253-537-9401 fax DESIGNER: CRL FIGURE 2 DRAWN BY: CRL SCALE- V=50' www.e3ra.com CHECKED BY: JEB SHEET: 1 DATE: 1/28/07 FILE:T06379 TGPO! map printed on 03/15/07 from "UnMed,tpo" 123002,000' W 123001.000' W WGS84 123000,000' W aSrierS Points IWO H � �' J• r' r r , i rq 'f !147 r / alo 123002.000' W 123001.000' W WGS84123000,000' W TN MN 0 5 1 MILE 18, 1000 FEET 0 500 ti000 METERS Map created with TOPO!®@2003 Nand Geogtaphic(wwwztiom*eogmphic.comltopo) E3RA, Inc. ATKINS PROPOSED RESIDENCE TOPOGRAPHIC AND LOCATION MAP FIGURE P.O Box 44890 Tacoma, WA 98444 UNION, WASHINGTON March 15, 2007 E3RA, Inc. T06379/Atkins Mason County Report geotechnical personnel should be considered an integral part of the construction process. Consequently,we recommend that E3RA 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 addressing relevant review comments(if required by Mason County); • Check all completed subgrades for footings and slab-on-grade floors before concrete is poured,in order to verify their bearing capacity;and • Prepare a post-construction letter summarizing all field observations, inspections, and test results(if required by Mason County). 6.0 CLOSURE The conclusions and recommendations presented in this report are based,in part,on the explorations that we observed 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. E3RA is available to provide geotechnical monitoring of soils 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 to contact our office. Sincerely, E3RA, Inc. ` • ;-� ,y � , Was r N.71 ix O� G'�A1. �Sed Gso�o EXPIRFS WJO/o` Fred Ernest Rennebaum Fred E.Rennebaum,L.E.G. James E.Brigham,P.E. Senior Geologist Principal Engineer FER/JEB TACOMOB FR ES12006 JOB FILESM6379 AWw Geotech1T06379A*insMasonCtyRpt_doc Enclosures: Figure 1 -Location Map Figure 2- Site&Exploration Plan Figure 3 -Cross Section A-A' Test Pit Logs TP-1 and TP-2 Four copies submitted 11 March 15. 2007 ORA, Inc. T06379/Atkins Mason County Report Wall Settlements: We estimate that the settlement of the wall footings constructed as recommended 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. 4.6 Structural Fill The term "structural fill' refers to any placed under foundations, retaining walls, slab-on-grade floors, sidewalks,pavements,and other structures. Our comments,conclusions,and recommendations concerning structural fill are presented in the following paragraphs. Materials: Typical structural fill materials include clean sand, gravel,pea gravel,washed rock,crushed rock, 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. Soils used for structural fill should not contain any organic matter or debris,nor any individual particles greater than about 6 inches in diameter. The glacial outwash on site should provide a good source of structural fill. Fill Placement: 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. Compaction Criteria: Using the Modified Proctor test per ASTM D-1557 as a standard,we recommend that structural fill used for various onsite applications be compacted to the following minimum densities: Fill Application Minimum Compaction Footing subgrade and bearing pad 95 percent Foundation and subgrade wall backfill 90 percent Slab-on-grade floor subgrade and subbase 95 percent 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 ofthis report. The condition of all subgrades should be observed by geotechnical personnel before filling 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. 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 2 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. 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 10 March 15, 2007 E3RA. Inc. T06379/Atkins Mason County Report Runoff Water: Roof-runoff and surface-runoff water should not discharge into the perimeter drain system. Instead,these sources should discharge into separate tightline pipes and be routed away from the building to a splash blocks, storm drain or other appropriate location. Grading and Carping: Final site grades should slope downward away from the buildings so that runoff water will flow by gravity to suitable collection points, rather than ponding near the building. Ideally, the area surrounding the building would be capped with concrete,asphalt,or low-permeability(silty)soils to minimize or preclude surface-water infiltration. 4.5 Subgrade Walls We offer these recommendations if a daylight basement becomes part of the building design: 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 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 �' g 1� ( P g ) zone should be at least 24 inches wide(measured horizontally)and extend from the base of the wall to within 1 foot of the finished grade behind the wall. 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 Soil: Ideally,all retaining wall backfill placed behind the curtain drain would consist of clean,free- draining, granular material, such as "Gravel Backfill for Walls" per WSDOT Standard Specification 9- 03.12(2). Alternatively,onsite granular soils could be used as backfill if they are placed at a moisture content near optimum. In the event that silty soils are used as backfill, a geotextile should be placed between the drainage zone and the backfill soil to prevent drain clogging. 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 per ASTM D-1 557;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. 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. 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 cantilever walls supporting slopes inclined at 2H:1 V or flatter be designed to resist an active pressure(triangular distribution) of 55 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. 9 March 15, 2007 ORA, Inc. T06379 /Atkins Mason County Report 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 for comparably loaded elements may approach one-half of the actual total settlement over horizontal distances of approximately 50 feet. Footing Backfill: To provide erosion protection and lateral load resistance,we recommend that all footing excavations be backfilled on both sides of the footings and stemwalls after the concrete has cured. Either imported structural fill or non-organic onsite 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. 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 280 pcf in and an allowable base friction coefficient of 0.35 for site soils. 4.3 Slab-On-Grade Floors In our opinion, soil-supported slab-on-grade floors can be used in the proposed structures, if desired, if the subgrades are properly prepared. . We offer the following comments and recommendations concerning these two types of slab-on-grade floors. Floor Subbase: Structural fill subbases do not appear to be needed under soil-supported slab-on-grade floors at the site. However, if a subbase is needed, all subbase fill should be compacted to a density of at least 95 percent per ASTM D-1557). Capillary Break and Vapor Barrier: To retard the upward wicking of groundwater beneath the floor slab,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 Washington State Department of Transportation(WSDOT)Standard Specification 9-03.12(4),but clean angular gravel can be used if it adequately prevents capillary wicking. In addition, a layer of plastic sheeting (such as Crosstuff, Visqueen, or Moistop) should be placed over the capillary break to serve as a vapor barrier. During subsequent casting of the concrete slab,the contractor should exercise care to avoid puncturing this vapor barrier. 4.4 Drainage Systems In our opinion,the proposed structure 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. Perimeter Drains: We recommend that the building be encircled with a perimeter drain system to collect seepage water. This drain should consist of a 4-inch-diameter perforated pipe within an envelope of pea gravel or washed rock,extending at least 6 inches on all sides of the pipe,and the gravel envelope should be wrapped with filter fabric to reduce the migration of fines from the surrounding soils. Ideally,the drain invert would be installed no more than 8 inches above the base of the perimeter footings. Subfloor Drains: Based on the groundwater conditions observed in our site explorations,we do not infer a need for subfloor drains. Discharge Considerations: If possible,all perimeter drains should discharge to a suitable location by gravity flow. Check valves should be installed along any drainpipes that discharge to a sewer system,to prevent sewage backflow into the drain system. 8 March 15, 2007 ORA Inc T06379/Atkins Mason County Report soil should be compacted to a uniform density of at least 95 percent based on American Society for Testing and Materials(ASTM)D-1557. Onsite Soils: We offer the following evaluation of these onsite soils in relation to potential use as structural fill: • SuTicial Organic Soils: Surficial organic soils can be used only for non-structural purposes, such as in landscaping areas. • Gravelly Glacial Outwash/Ablation Till: The loose,gravelly soil that mantles the building area to depths of less than 2 feet is relatively insensitive to moisture content variations,and can be reused during most weather conditions. • Glacial Till: The gravelly glacial till that underlies the site is moderately sensitive to moisture content variation,and may be difficult to reuse during wet weather. All particles larger than 6 inches should be removed before reuse. Permanent Slopes: All permanent cut slopes and fill slopes should be adequately inclined to reduce long-term raveling,sloughing,and erosion. We generally recommend that no permanent slopes be steeper than 2H:I V. For all soil types, the use of flatter slopes (such as 2Y2H:IV) would further reduce long-term erosion and facilitate revegetation. Sloe Protection: We recommend that a permanent berm swale or curb be constructed alongthe to edge of P P g all permanent slopes to intercept surface flow. Also,a hardy vegetative groundcover should be established as soon as feasible,to further protect the slopes from runoff water erosion. Alternatively,permanent slopes could be armored with quarry spalls or a geosynthetic erosion mat. 4.2 Spread Footings In our opinion, conventional spread footings will provide adequate support for proposed residence if the subgrades are properly prepared. FootingD ths and Widths: For frost and erosion protection,the base of all exterior footings should bear at eP P g least 18 inches below adjacent outside grades,whereas the base of interior footings need bear only 12 inches below the surrounding slab surface level. To reduce post-construction settlements, continuous (wall) and isolated(column)footings should be at least 18 and 24 inches wide,respectively. Bearing Subgrades: Footings should bear on medium dense or denser,undisturbed native soils or on properly compacted structural fill which bears on undisturbed native soils which have been stripped of surficial organic soils. In general, before footing concrete is placed, any localized zones of loose soils exposed across the footing subgrades should be compacted to a firm, unyielding condition, and any localized zones of soft, organic,or debris-laden soils should be overexcavated and replaced with suitable structural fill. Subgrade Observation: All footing subgrades should consist of firm,unyielding,native soils or structural fill materials compacted to a density of at least 95 percent per ASTM D-1557. Footings should never be cast atop loose,soft,or frozen soil,slough,debris,existing uncontrolled fill,or surfaces covered by standing water. Bearing Pressures: In our opinion,for static loading,footings that bear on properly prepared subgrades can be designed for a maximum allowable soil bearing pressure of 2,000 pounds per square foot(psf). A one-third increase in allowable soil bearing capacity may be used for short-term loads created by seismic or wind related activities. 7 March 15, 2007 ORA, Inc. T06379/Atkins Mason County Report 4.1 Site Preparation Preparation of the project site will involve erosion control,temporary drainage, clearing,stripping,cutting, filling,excavations,and subgrade compaction. Erosion Control: Before new construction begins,an appropriate erosion control system should be installed. This system should collect and filter all surface run offthrough either silt fencing or a series of properly placed and secured straw bales. We anticipate a system of berms, drainage ditches, and silt fencing/straw bales between the construction area and the steep slope will provide an adequate collection system. If silt fencing is selected as a filter, this fencing fabric should meet the requirements of WSDOT Standard Specification 9-33.2 Table 3. In addition,silt fencing should embed a minimum of 6 inches below existing grade. If straw baling is used as a filter,bales should be secured to the ground so that they will not shift under the weight of retained water. Regardless of the silt filter selected,an erosion control system requires occasional observation and maintenance. Specifically, holes in the.filter and areas where the filter has shifted above ground surface should be replaced or repaired as soon as they are identified. Tempo , Drainage: We recommend intercepting and diverting any potential sources of surface or near-surface water within the construction zones before stripping begins. Because the selection of an appropriate drainage system will depend on the water quantity, season, weather conditions, construction sequence,and contractor's methods,final decisions regarding drainage systems are best made in the field at the time of construction. Based on our current understanding of the construction plans,surface and subsurface conditions,we anticipate that curbs,berms,or ditches placed around the work areas will adequately intercept surface water runoff. Site Excavations: Based on our explorations, we expect that excavations will encounter very dense soils, which will need powerful excavation equipment,possible with special teeth of rippers,if excavations extend more than several feet deep. Dewatering: We did not encounter groundwater in our subsurface explorations on the site, and we do not anticipate that groundwater will be encountered during site excavations. However, if groundwater is encountered, we anticipate that an internal system of ditches, sumpholes, and pumps will be adequate to temporarily dewater excavations. Temporary Cut Slopes: All temporary soil slopes associated with site cutting or excavations should be adequately inclined to prevent sloughing and collapse. Temporary cut slopes in site soils should be no steeper than 1'/<H:1 V(horizontal to vertical),and should conform to WISHA regulations. Subgrade Compaction: Exposed subgrades for footings, slabs, and floors should be compacted to a firm, unyielding state before new concrete or fill soils are placed. Any localized zones of looser granular soils observed within a subgrade should be compacted to a density commensurate with the surrounding soils. In contrast,any organic,soft,or pumping soils observed within a subgrade should be overexcavated and replaced with a suitable structural fill material. Site Filling: Our conclusions regarding the reuse of onsite soils and our comments regarding wet-weather filling are presented subsequently. Regardless of soil type,all fill should be placed and compacted according to our recommendations presented in the Structural Fill section of this report. Specifically,building pad fill 6 March 15,2007 O RA, Inc. T06379/Atkins Mason County Report 4.0 CONCLUSIONS AND RECOMNI ENDATIONS Development plans call for the construction of a single family residence near the top of a steep slope.We offer the following general geotechnical conclusions and recommendations concerning this project. • Feasibility: Based on our field explorations,research,and analyses,the proposed construction appears feasible from a geotechnical standpoint, provided that the recommendations in Section 4 are followed. • Landslide Hazards: Our site reconnaissance did not reveal recent or ancient slide activity on site,no landslide indicators were observed on site or on nearby off site. Our slope stability analysis indicates that an adequate factor of safety exists for the planned development, provided that a building setback of 25 feet is maintained. In our opinion,the site does not currently present a landslide hazard and will not present a landslide hazard due to site development,provided our recommendations are followed. • Setbacks and Buffers: As mentioned,a building setback of 25 feet is recommended. We also recommend preserving the steep slope as a vegetative buffer,but removal of trees to provide and maintain a view corridor and replacing of non-native plants with native plants should be permitted. • Erosion Hazards: During construction, we recommend that standard erosion control measures,consisting of properly placed silt fences or straw bales and interceptor ditches,as described in Section 4.1,be implemented in the construction area. Areas of bare soils should be re-vegetated as soon as possible to permanently control site erosion. • Drainage S sy tems: Roof runoff should be directed away from the house and infiltrated on site or directed to splash blocks that are at least 40 feet from the top of the 50 percent slope. Storm water should not be allowed to flow freely over the top of the 50 percent slope. • Development Impact: Based on our slope analysis and site observations, the proposed development should not have significant detrimental impact on site or off site if our recommendations are followed- Foundation Options: Foundations should bear on subgrades consisting of organic-free, medium dense or denser native soils, found at shallow depths below existing grades. Recommendations for spread footings are provided in Section 4. • Clearing; and Grading_ Most of the clearing and grading for the site has been completed. Generally, additional clearing and grading on the upland portion of the site, outside of the construction area,should occur only during the dry season and cleared areas should be seeded or planted before the wet season begins. As mentioned,the steeper portion of the site should be preserved as a vegetative buffer, although larger trees can be felled or limbed for view purposes. Stumps and under story brush should be left in place on steeper portions of the site in areas where view corridors have been created. General grading recommendations are included in the Site Preparation section. The following text sections of this report present our specific geotechnical conclusions and recommendations concerning site preparation, spread footings, slab-on-grade floors, drainage, and structural fill. The Washington State Department of Transportation(WSDOT)Standard Specifications and Standard Plans cited herein refer to WSDOT publications M41-10, Standard Specifications for Road, Bridge, and Municipal Construction,and M21-01,Standard Plans for Road,Bridge, and Municipal Construction,respectively. 5 J March 15, 2007 ORA, Inc. T06379/Atkins Mason County Report 3.4 Seismic Conditions Based on our analysis of subsurface exploration logs and our review of published geologic maps,we interpret the onsite soil conditions to correspond with a seismic site class Sc,as defined by Table 1615.1.5 of the 2003 International Building Code(IBC).According to the IBC,the site is Seismic Region 3. 3.5 Liquefaction Potential Liquefaction is a sudden increase in pore water pressure and a sudden loss of soil shear strength caused by shear strains,as could result from an earthquake. Research has shown that saturated,loose sands with a fines (silt and clay)content less than about 20 percent are most susceptible to liquefaction. Our onsite subsurface explorations did not reveal saturated(or potentially saturated), loose,silty sand layers or lenses. 3.6 Slone Stability Analysis In order to establish an appropriate building setback from the slope at the project site,we analyzed the slope stability under selected conditions. The following section describes our method of analysis and presents our results. 3.7 Method of Analysis Slope stability analyses typically involve five basic slope parameters: (1)location and shape of the potential failure surface,(2)internal friction angle of the various soils,(3)cohesion of the various soils,(4)density of the various soils,and(5)location of the piezometric groundwater surface.Once all five parameters have been estimated,the critical slip surface and associated safety factor of a given slope can be calculated. A critical slip surface is defined as the most likely surface along which a soil mass will slide,and a safety factor is defined as the ratio of the sum of all moments resisting slope movement versus the sum of all moments tending to cause slope movement. Consequently,a slope that possesses a safety factor of 1 is on the verge of sliding,whereas a slope with a safety factor greater than 1 has some resistance to sliding. According to standard geotechnical engineering practice,a static safety factor of 1.5 and a seismic safety factor of 1.1 are considered the desirable minimum values for most slopes,but 1.25 and 1.01,respectively,are often regarded as acceptable values. Slope stability conditions for the project site were analyzed by means of Bishop Circular Analysis. All calculations were performed by means of the computer program WINSTABLE. Our conservatively estimated values of internal friction angle,cohesion, and density for each soil layer are listed in Table 2. To model the foundation load applied by a future house, located 25 feet from the top of slope,we applied a vertical force of 1500 pounds per lineal foot. Our analysis yielded a Seismic Factor of Safety of 1.2 and a Static Factor of Safetv of 1.6. TABLE 2 ESTIMATED PROPERTIES OF ONSITE SOILS FOR STABILITY ANALYSIS Soil Type Density Cohesion Internal Friction (PC') (PSI) Angle (deg ) Sandy,Gravelly Glacial Till and Glacial Drift 135 500 36 4 March 15, 2007 ORA. Inc. T06379/Atkins Mason County Report Grades beyond the north boundary vary and average 50 to 60 percent. Grades south of the site are gentle,and grades off site to the east and west are similar to those on site in that they are comprised of both level to gently sloping upland and steep slopes that grade down toward Hood Canal. A bulldozed trail extends from Timber Tides Drive on the south boundary,across the upland,to the top of the 50 percent slope. An area has been cleared and tree stumps removed on the upland near the top of the 50 percent slope. Trees have been felled, but stumps and brush left in place, on the topmost 50 feet of the 50 percent slope, in order to provide a view corridor. The site is forested with 12 to 16 inch fir and scattered cedar, pine, and madrona. Under story vegetation consists of dense salal and evergreen huckleberries. Several septic test-pits were observed on an adjacent parcel on upland near the southwest comer of the site. Soils there were comprised of a few feet of loose glacial outwash or ablation till overlying very dense,gravelly, glacial till. No indications of recent or past land sliding, such as tension cracks, scarps, or hummocky terrain, or other features,were observed on site or nearby off site. No signs of surface hydrology,such as stream beds,ponds,etc.were observed during our reconnaissance. No seeps,springs,or other surface expressions of subsurface hydrology were observed on the site or nearby off site. The Coastal Zone Atlas maps the upland as S, Stable. The same source maps the 50 percent slope,which comprises the north portion of the site,and the steeper grades to the north as I,Intermediate. Intermediate slopes are slopes greater than 15 percent that occur on stable,competent material,and have no known failures. 3.2 Soil Conditions Our test pit observations,observations of excavations nearby off site,and observations of road cuts along the Timber Tides Drive alignment as it ascends to the upland area from the shore of Hood Canal,indicate that soils on site and nearby off site consist of very dense glacial till and glacial drift,overlain by a thin mantle of loose glacial outwash or ablation till. Out two test pits were excavated in the vicinity of the planned residence. There, we observed 1% feet of outwash/ablation till, consisting of loose sandy gravel with some silt overlying glacial till consisting of cemented sandy gravel with some silt and scattered cobbles. The excavation equipment used for our explorations could not effectively penetrate the glacial till layer. The enclosed exploration logs provide a detailed description of the soil strata encountered in our subsurface explorations. 3.3 Groundwater Conditions At the time of our site reconnaissance and explorations on January 3,2007,we did not observe groundwater in our subsurface explorations, nor did we observe seeps or springs on site or nearby off site. We do not anticipate that groundwater will be encountered during site excavation. 3 March 15, 2007 E3RA, Inc. T06379/Atkins Mason County Report Table 1 summarizes the approximate functional locations and termination depths of our subsurface explorations,and Figure 2 depicts their approximate relative locations. TABLE 1 APPROXIMATE LOCATIONS AND DEPTHS OF EXPLORATIONS USED FRO THIS REPORT Termination Depth Exploration Functional Location (feet) TP-1 Near planned building site,60 feet from top of steep slope 2 TP- 1 Near planned building site,60 feet from top of steep slope 2 Elevation datum:Unavailable We estimated the relative location of each exploration. 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. It should be realized that the explorations observed for this evaluation reveal subsurface conditions only at discrete locations across the project site and that actual conditions in other areas could vary. Furthermore,the nature and extent of any such variations would not become evident until additional explorations are performed or until construction activities have begun. If significant variations are observed at that time,we may need to modify our 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 rubber-tired backhoe by an owner-operator under contract to the client. A geologist from our firm observed the test pit excavations and logged the subsurface conditions. The enclosed Test Pit Logs indicate the vertical sequence of soils and materials encountered in each test pit, based on our field classifications. Where a soil contact was observed to be gradational or undulating,our logs indicate the average contact depth. 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. 3.0 SITE CONDITIONS The following sections of text present our observations,measurements,findings,and interpretations regarding, surface,soil,groundwater, seismic,and liquefaction conditions. 3.1 Surface Conditions The project site is comprised oftwo topographic areas. The first an upland that comprises the south portion of the site and slopes down to the north from Timber Tides Drive East at grades that range from 0 to 15 percent. The second is the north half of the site,which slopes down to the north toward Hood Canal at grades of about 50 percent. The north portion of the site terminates in the vicinity of Timber Tides Drive, which has a convoluted alignment as it winds back and forth and climbs from Hood Canal to the upland area. 2 PO Box 44890 Tacoma, WA 98444 253-537-9400 253-537-9401 fax E3RA March 15,2007 T06379 Don Atkins 1540 Kirkland Avenue Kirkland,Washington 98033 (206)769-5158 Subject: Geotechnical Report Parcel#32235-75-90130 12xx East Timber Tides Drive Union, Washington Dear Don: E3 RA is pleased to submit this report describing the results of our geotechnical engineering evaluation for your vacant parcel east of Union in Mason County,Washington. The purpose of our evaluation is to address the Mason County Critical Areas Ordinances as they relate to landslide and erosion hazards at the site and to provide geotechnical conclusions and recommendations concerning residential development at the site. As outlined in our proposal letter dated September 28,2006,our scope of work comprised site reconnaissance, geotechnical research,and geotechnical engineering analysis. This report has been prepared for the exclusive use of Don Atkins and his consultants, for specific application to this project, in accordance with generally accepted geotechnical engineering practice. 1.0 SITE AND PROJECT DESCRIPTION The project site is located east of Union and south of the south shore of Hood Canal in Mason County Washington,as shown on the enclosed Location Map(Figure 1). The site is a rectangular parcel that measures about 160 feet east to west and 660 feet north to south.It is bordered on the south by Timber Tides Drive East and extends north to again abut Timber Tides Drive,which circuitously climbs up a steep hillside from Hood Canal. The site is in an area of rural residential parcels. Plans call for the construction of a single-family residence on upland near the top of a steep slope on the central portion of the site. 2.0 EXPLORATORY METHODS We explored surface and subsurface conditions at the project site on January 3, 2007. Our exploration program comprised the following elements: • A surface reconnaissance of the site,nearby areas,and the geology of nearby road cuts; • Two test pits designated TP-1 and TP-2;and • = A review of published geologic and seismologic maps and literature. GEOTECHNICAL REPORT PROPOSED ATKINS RESIDENCE PARCEL NO. 32235-75-90130 UNION, WASHINGTON Submitted to: Don Atkins 1540 Kirkland Avenue Kirkland, Washington 98033 Submitted by: E3RA\,,Inc. PO Box 44890 Tacoma, WA 98444 March 15, 2007 T06379 F. �. MASON COUNTY PLANNING GEO TECH WORK ORDER CONSULTANT JEROME W. MORRISSETTE& ASSOC. INC. 1700 COOPER POINT RD. SW, #B-2 OLYMPIA WA 98502 PERMIT # E F A 2-0C`7 — G)0 0—? D- APPLICANT DATE MAILED i I 0-7 PLANNER AC— 5a- S AMOUNT BILLED ADDITIONAL COMMENTS "Please fill out the cost of the review and return this form and the report to us with your recommendations.