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HomeMy WebLinkAboutGEO2019-00063 - GEO Geological Review - 3/9/2018 GEO 6�b 6� Mason County Review Checklist For a Geological Assessment Instructions: This checklist is intended to assist Staff in the review of a Geological Assessment. The Assessment is reviewed for completeness with respect to the Resource Ordinance. If an item is found to be not applicable, the report should explain the basis for the conclusion. The Assessment is also reviewed for clarity and consistency. If the drawings, discussion, or recommendations are not understandable, they should be clarified. If they do not appear internally consistent or consistent with the application or observations on site, this needs to be corrected or explained. If resolution is not achieved with the author, staff should referthe case to the Planning Manager or Director. Applicant's Name: ( dQ�� an01 7 Permit#: 6 U)p Zb I D00 I Parcel#'s: Date(s)of the Document(s) reviewed: OWI&4U�^' 3� Ion 1. A discussion of geologic conditions in the general vicinity of the proposed development, with geologic unit designation based on referenced maps. OK? Comment: 2. (a) A discussion of the ground water conditions at the site, OK? --- Comment: (b) A discussion of the estimated depth to water, OK? Comment: (c) A discussion of the quantity of surface seepage, OK? Comment: (d) A discussion of the upslope geomorphology, OK? Comment: (e) A discussion of location of upland waterbodies and wetlands. OK? — Comment: 3. The approximate depth to hard or dense competent soil, e.g. glacial till or outwash sand. OK? Comment: 4. A discussion of any geomorphic expression of past slope instability(presence of hummocky ground or ground cracks, terraced topography indicative of landslide block movement, bowed or arched trees indicating downslope movement, etc.). OK? Comment: 5. A discussion of the history of landslide activity in the vicinity, as available in the referenced maps and records. OK? Comment: 6. An opinion on whether the proposed development is within the landslide hazard area or its associated buffer or setback and the potential for landslide activity at the site in light of the proposed development. OK? Comment: 7. A recommendation by the preparer whether a Geotechnical Report should be required to further evaluate site conditions and the proposed development of the subject property. OK? Comment: 8. If the presence of a hazard is determined within 300 feet of the proposed development, then the following are delineated on a geologic map/site map: Page 1 of 2 Form Effective June 2008 (a) the area of the proposed development, OK? Comment: (b) the boundaries of the landslide hazard area(top, both sides, and toe), OK? Comment: (c) the associated buffers(top, both sides, and toe) OK? Comment: (d) building or other setbacks(top, both sides, and toe). OK? Comment: 9. A site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of existing and proposed development on the site. OK? —� Comment: Are the Documents signed and stamped? By whom? C hYisK K i a License#: License type: FIRST REVIEW Approved ❑ Need more info. If not approved, what is the next action/recommendation for further action? Reviewed by on 1 . Time spent in review: S ►�i�ti SECOND REVIEW/UPDATE ❑ Approved ❑ Need more info. If not approved, what is the next action/recommendation for further action? Reviewed by on .Time spent in second review: THIRD REVIEW/UPDATE ❑ Approved ❑ Need more info. If not approved, what is the next action/recommendation for further action? Reviewed by , on . Time spent in third review: Disclaimer. Mason County does not certify the quality of the work done in this Geological Assessment Page 2 of 2 Form Effective June 2008 Ai, 'rr.(L "adlrl 6,66 ■�- GEORESOURCES earth science & geotechnical engineering �`S 5007 Pacific Hwy E., Suite 16 Fife, WA 98424 1 253.896.1011 1 www.geo resources.rocks March 9,2018 Revised July 3,2019 Cedarland Forest Products, LLC Joseph T. Cedarland P.O. Box 2264 Gig Harbor,Washington 98335 (253)} 8C EI\/ED �'[[�C V Geologic Assessment JUL 11 2019 Proposed Single Family Residences xxx East State Route 3 615 W. Alder Street Mason County,Washington PN: 1 221 742001 30 Doc ID: Cedarland.SR3.GA.rev02 INTRODUCTION This revised geologic assessment presents the results of our recent site visit, subsurface explorations, literature research, and engineering analysis for the proposed short subdivision to be constructed at xxx East State Route 3 in the Allyn area of Mason County,Washington.The location of the site is shown in the attached Site Location Map, Figure 1. Revisions from our initial revised assessment are bolded and italicized for ease of review. We have added an addendum to the original assessment to provide additional recommendations for earthwork construction as requested by Mason County. Our understanding of the project is based on our discussions with you, our site visits on September 21, 2016 and June 11, 2019, our review of the provided site plan, our review of publicly available soils data, our past experience in the project vicinity, and our understanding of the Mason County Development Codes. We understand that you propose to develop the site with 4 duplexes, one single family residence, a shared access road from Highway 3, open space tracts, and associated utilities. We further understand that you propose to install a single-family septic system in the southeast portion of the site and a community septic system in the eastern portion of the site, above State Highway No. 3. We anticipate that the residences will be one- or two-story wood- framed structures supported by conventional shallow footings. A copy of the proposed development is included as the Site and Exploration Plan, Figure 2. SCOPE The purpose of our services was to evaluate the surface and subsurface conditions at the site to evaluate the area mapped as a landslide hazard by the county.Additionally, we have been asked to provide construction recommendations related to construction of the buildings and drainage system on moderate slopes. Specifically,our scope of services for the project included the following: 1. Reviewing existing and publically available geological and geotechnical literature for the site area; 2. Exploring surface and subsurface conditions by monitoring the excavation of 3 test pits at select locations across the site, 3. Describing surface conditions, including soil types, and depth to groundwater, as appropriate;aad 4. Addressing the Mason County Critical Area ordinances;and Cedarlan d.S R3.GA.rev02 March 9,2018 Revised July 3,2019 Page 2 5. Providing construction recommendations related to construction of the buildings and drainage system on moderate slopes in Appendix A and B. SITE CONDITIONS Surface Conditions The subject parcel is located off of East State Route 3 in the Allyn area of Mason County, Washington. The site is a single tax parcel that is rectangular in shape, measures approximately 190 feet wide (north to south) by about 550 feet deep (east to west), and encompasses approximately 6.77 acres. The site is bounded by an undeveloped large lot to the south, existing residential development on the west and north,and by East State Route 3 on the east. The site sits above and west of East State Route 3 on about a 5 to 10-foot steep road cut with inclinations of about 40 percent. From the western boundary of the site, the site slopes down to the east at inclinations of about 15 to 30 percent towards East State Route 3.The total topographic relief across the site is on the order of approximately 130 feet. The existing topography and proposed development layout is shown on the Site and Exploration Plan, Figure 2. Vegetation across the site consists of coniferous and deciduous trees with a dense understory of evergreen huckleberries, salal, ferns, ivy, and other native and invasive shrubs. No evidence of seepage was observed on the site or the slope below the site at the time of our site visit. No evidence of erosion, soil movement, landslide activity or deep-seated slope instability was observed at the site or the adjacent areas at the time of our site visit. Site Soils The USDA Natural Resource Conservation Service (NRCS) Web Soil Survey maps the soils in the site area as Alderwood gravelly sandy loam (Ab and Ac). The Alderwood soils are derived from glacial till and form on slopes of 8 to 15 percent (Ab) and 15 to 30 percent (Ac) slopes. These soils have a "moderate"(Ab)to"moderate to severe"(Ac) erosion hazard when exposed and are included in hydrologic soils group C. A copy of the NRCS Soil Conservation Survey map for the site vicinity is attached as Figure 3. We observed no evidence of surficial erosion at the site during our reconnaissance. Site Geology The Geologic Map of the Belfair 7.5-Minute Quadrangle, Mason, Kitsop, and Pierce Counties, Washington by Michael Polenz et al (2009) indicates the site as being underlain by Vashon till (Qgt) and Vashon advance outwash (Qga). These soils were deposited during the Vashon Stade of the Fraser Glaciation, approximately 12,000 to 15,000 years ago. The advance outwash consists of poorly sorted, lightly stratified mixture of sand and gravel that may contain localized deposits of clay and silt that were deposited by meltwater streams emanating from the advancing ice mass. The glacial till soils consist of a heterogeneous mixture of gravel, sand, silt, and clay that was overridden by the prehistoric continental ice mass. Glacial till is considered indurate(cemented)soil that does not support infiltration. Both the advance outwash and till were overridden by the continental ice mass, as such, they are considered to be overconsolidated and to provide high strength and low compressibility characteristics where undisturbed. No areas of landslides or landslide debris are mapped on, or within the vicinity of the site area. An excerpt of the above referenced map is included as Figure 4. The Department of Ecology(DOE) Coastal Atlas indicates the slope stability on the site is "S" for stable. The Coastal Atlas does not map any area of known recent or older landslides in the immediate vicinity of the site.A copy of the DOE Coastal Atlas is included as Figure 5. SUBSURFACE EXPLORATIONS On June 11, 2019, a representative from GeoResources LLC (GeoResources) visited the site and monitored the excavation of three test pits to depths of 5 to 6 feet below the existing ground C e darlan d.SR3.GA.rev02 March 9,2018 Revised July 3,2019 Page 3 surface. The test pits were excavated by a small track-mounted excavator operated by a licensed earthwork contractor working for you. The specific number, locations, and depths of our explorations were selected based on conversations with you and the proposed configuration of the commercial development and were adjusted in the field based on site access limitations. Our representative continuously monitored the explorations, maintained logs of the subsurface conditions encountered, obtained representative soil samples, and observed pertinent site features. Soil densities presented on the logs were based on the difficulty of excavation and our experience. Representative soil samples obtained from the explorations were placed in sealed plastic bags and taken to a laboratory for further examination and testing as deemed necessary. Each test pit was then backfilled and tamped with the bucket, but otherwise not recompacted. The subsurface explorations excavated as part of this evaluation indicate the subsurface conditions at specific locations only, as actual subsurface conditions can vary across the site. Furthermore, the nature and extent of such variation would not become evident until additional explorations are performed or until construction activities have begun. The number and approximate locations of our explorations are shown on the Site and Exploration Plan, Figure 2. The soils encountered were visually classified in accordance with the Unified Soil Classification System (USCS) and ASTM D:2488. The USCS is included as Figure 6, while the descriptive logs of our test pits are included as Figure 7. SUBSURFACE CONDITIONS Our subsurface explorations encountered relatively uniform subsurface conditions that were generally consistent with the geologic mapping for the site vicinity. Our test pits encountered about 1 to 1.5 feet of brown silty sand with gravel that appeared to be in a loose, moist condition. These upper soils are consistent with topsoil and forest duff and were underlain by light brown to grey sand and gravel with cobbles that appeared to be in a dense to very dense, moist condition that was encountered to the full depth explored. The underlying soils in the TP-2 appeared to be more cemented and denser than those observed in TP-1. We interpret the soils encountered in TP-1 to be consistent with advance outwash, while the soils observed in the lower, TP-2 appeared to be consistent with pre-Fraser sand and gravel. Both units have been glacially consolidated and have relatively high strength and low compressibility characteristics. We did observe soils consistent with glacial till in a cut in the upper portion of the site near the well. This also matches the mapped stratigraphy but to our knowledge no other construction is proposed in this area. LABORATORY TESTING Geotechnical laboratory tests were performed on select samples retrieved from the test pits to determine soil index and engineering properties encountered. Laboratory testing included visual soil classification per ASTM D:2488, moisture content determinations per ASTM D:2216, and grain size analyses per ASTM D:422 standard procedures. The results of the laboratory tests are included as Figure 8. Groundwater Conditions No groundwater seepage was observed at the site nor in our subsurface explorations at the time of our site visits. We do anticipate that perched groundwater may develop at some depth below the site, based on the mapped stratigraphy. Perched groundwater develops when the vertical infiltration rate of precipitation through a more permeable soil is slowed at depth by a deeper, less permeable soil type. We anticipate fluctuations in the local groundwater levels that likely will occur in response to precipitation patterns, off-site construction activities, and site utilization. CONCLUSIONS Based on our site observations and data review, it is our opinion that the proposed Cedarland.SR3.GA.rev02 March 9,2018 Revised July 3,2019 Page 4 residential development is feasible from a geotechnical standpoint, provided the recommendations included herein are incorporated into the project plans. The proposed septic systems are located at the bottom of the site, in an area that slopes down to the east at approximately 15 to 25 percent. Based on the inclination of the slopes in this portion of the site, it is our opinion that the slopes should not be adversely affected by the proposed septic systems. Furthermore, it is our opinion that a Geotechnical Report should not be required. Recommendations for earthwork and pond construction are provided in the attached Appendices. Landslide Hazard Areas- Mason County Resource Ordinance 8.52.140 Mason County Resource Ordinance chapter 8 states that the following shall be classified as a Landslide Hazard Area: a. Areas with any indications of earth movement such as debris slides, earthflows, slumps and rock falls; b. Areas with artificial oversteepened or unengineered slopes, i.e. cuts or fills; c. Areas with slopes containing soft or potentially liquefiable soils; d. Areas oversteepened or otherwise unstable as a result of stream incision, stream bank erosion,and undercutting by wave action; e. Slopes greater than 15%(8.5 degrees)and having the following: i. Hillsides intersecting geologic contacts with a relatively permeable sediment overlying a relatively impermeable sediment or bedrock(e.g. sand overlying clay), and ii. Springs or groundwater seepage; f. Any area with a slope of forty percent or steeper and with a vertical relief of ten or more feet except areas composed of consolidated rock. A slope is delineated by establishing its toe and top and measured by averaging the inclination over at least ten feet of vertical relief. Mason County uses the above referenced checklist to define a Landslide Hazard Area. Based on our observations of the site and review of published information,we offer the following comments. No areas with indications of earth movement were observed at the time of our site visit.The road cut above Highway 3 is a constructed slope, but we assume that the slope was engineered as it was cut for road construction.The mapped stratigraphy indicates that the site is underlain by glacial till and advance outwash, soils that are not prone to liquefaction. No areas of over-steepening and instability due to stream erosion and wave action were observed at the time of our site visit. There are slopes greater than 15 percent, but no adverse geologic contacts or seeps or springs were observed at the time of our site visit. We did not observe slopes greater than 40 percent with 10 feet or more of vertical relief. Based on the above,the site does not have any of the above 6 landslide hazard indicators, and it does not appear that there is an active landslide hazard on or within 300 feet of the site. Recommended Setback Based on our observations at the site, we recommend that the location of the proposed residences meet steep slope setback requirements, as indicated in the 2015 International Building Code (2015 IBC) Section 1808.7. As stated, the vertical height of the steep slopes in the western portion of the site is on the order of 5 to 10 feet. The 2015 IBC Section 1808.7 requires a building setback from slopes steeper than 3H:1V (Horizontal:Vertical). The setback distance is calculated based on the vertical height of the slope. The typical IBC setback from the top of the slope equals one third the height of the slope, while the typical setback from the toe of a slope equals half the vertical height of the slope. The IBC setback from the top of the steep slope in the eastern portion of the site is approximately 3 feet from the top of the slope. We were provided with a conceptual site layout drawing. Based on this drawing, the duplexes and residence will be located at least 100 feet away from the top of the bank. Based on this conceptual site layout, it appears that the proposed structures should be setback from the slope far enough to meet the top of slope setback requirements. Ce darlan d.S R3.GA.rev02 March 9,2018 Revised July 3,2019 Page 5 Where these IBC setbacks cannot be met, the IBC allows the foundations to be deepened, resulting in a structural setback. Deep foundations, such as pin piles or dilled piers, may be used to meet this setback. Provided the foundations for the addition are supported on firm and unyielding native soils, no additional setback should be required. LIMITATIONS We have prepared this report for Cedarland Forest Products and other members of the design team for use in evaluating a portion of this project. The data used in preparing this report and this report should be provided to prospective contractors. Our report analyses, conclusions and interpretations are based on data from others and the limited site reconnaissance and should not be construed as a warranty of the subsurface conditions. Variations in subsurface conditions from the mapped stratigraphy are possible and may occur with time. The scope of our services does not include services related to environmental evaluations or construction safety precautions. Our recommendations are not intended to direct the contractor's methods,techniques,sequences or procedures,except as specifically described in our report. If there are changes in the loads, grades, locations, configurations or type of facilities to be constructed, the conclusions and recommendations presented in this report may not be fully applicable. If such changes are made or site conditions change,we should be given the opportunity to review our recommendations and provide written modifications or verifications,as appropriate. Cedarlan d.SR3.GA.rev02 March 9.2018 Revised July 3,2019 Page 6 We trust this is sufficient for your current needs. Should you have any questions, or require additional information, please contact us at your earliest convenience. Respectfully submitted, GeoResources, LLC Jordan L. Kovash, GIT Geotechnical Staff c �FCI� �Rti � >4nse 1pRz EtyG 712�Ol9 E—K WILLIAM HEELER Dana C. Biggerstaff, PE Eric W. Heller, PE, LG Senior Geotechnical Engineer Senior Geotechnical Engineer JLK:DCB:EWH/jlk Doc ID:Cedorland.SR3.GA.rev02 Attachments: Figure 1:Site Location Map Figure 2:Site and Exploration Plan Figure 3:NRCS SCS Soils Map Figure 4:USGS Geologic Map Figure 5:Coastal Zone Atlas Figure 6:Unified Soil Classification System Figure 7:Test Pit Logs Figure 8:Laboratory Test Results Appendix A:Design Criteria Appendix B:Earthwork Recommendations ?a s� III 3 Approximate Site Location (map created from Google Earth, 02016) r` Not to Scale GeoResources, LLC Site Location Map 5007 Pacific Highway East, Suite 16 Proposed Single Family Residence Fife, Washington 98424 xxx East State Route 3 Phone: 253-896-1011 Mason County, Washington Fax: 253-896-2633 Doc ID: Ceciarland.SR35.rev02 July 2019 Figure 1 t, t ow., tnspoc#teM kpc t;'anmmn R E Pr( fl i r i i s �4 6 . \\� TP-3 t f L All] Approximate Site Layout (Site Plan provided by Tahja Engineering, Inc, dated January 23, 2019) Approximate Test Pit Location- TP-1 J Not to Scale GeoResources, LLC Site and Exploration Plan 5007 Pacific Highway East, Suite 16 Proposed Single Family Residence Fife, Washington 98424 xxx East State Route 3 Phone: 253-896-1011 Mason County, Washington Fax: 253-896-2633 Doc ID: Cedarland.SRIF.rev02 July 2019 Figure 2 i, 1 Approximate Site Location (map created from the USDA Natural Resource Conservation Service Web Soil Survey) Soil Soil Name Parent Material Slopes Erosion Hazard Hydrologic Type Soils Group Ab Alderwood gravelly sandy Glacial Till 8 to 15 Moderate C loam Ac Alderwood gravelly sandy Glacial Till 15 to 30 Moderate to Severe C loam �1 ti Not to Scale NRCS SCS Soils Map GeoResources, LLC Proposed Single Family Residence 5007 Pacific Highway East, Suite 16 xxx East State Route 3 Phone: 253-896-101011 Fife, Washington M C Washington Mason County, as9 Fax: 253-896-2633 Doc ID: Cedadand.SR3.F.rev02 July 2019 Figure 3 T F' S.__/ Qb 1 ? r. Qa r / I"Qgo Qgt of am Qa ` ago' Qi � - /Qb Qgic y QPil as � Qa f gic ` Qgol a .- Oat > Qb 0af Q ?a Qec! u r,{ Oa i f C) Approximate Site Location Excerpt from the Geologic Map of the Belfair 7.5-minute Quadrangle, Mason, Kitsap and Pierce Counties, Washington by Michael Polenz, et al, (2009) Qgol Vashon recessional lake-marginal outwash Qgt Vashon till Qga Vashon advance outwash Not to Scale GeoResources, LLC USGS Geologic Map 5007 Pacific Highway East, Suite 16 Proposed Single Family Residence Fife, Washington 98424 xxx East State Route 3 Phone: 253-896-1011 Mason County, Washington Fax: 253-896-2633 Doc ID: Cedarland.SRIF.rev02 July 2019 Figure 4 y a 3G3 Approximate Site Location (Map obtained from the DOE Coastal Atlas https://fortress.wa.gov/ecy/coastalatlas/) Slope stability Q C-'l Stable Intermediate V Modified Unstable Unstable (old slide) IV Unstable (recent slide) Not to Scale GeoResources, LLC DOE Coastal Atlas 5007 Pacific Highway East, Suite 16 Proposed Single Family Residence Fife, Washington 98424 xxx East State Route 3 Phone: 253-896-1011 Mason County, Washington Fax: 253-896-2633 Doc ID:Cedadand.SR3.F.rev02 July 2019 Figure 5 SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS GROUP GROUP NAME SYMBOL GRAVEL CLEAN GW WELL-GRADED GRAVEL,FINE TO COARSE GRAVEL GRAVEL GP POORLY-GRADED GRAVEL COARSE GRAINED More than 50% GRAVEL GM SILTY GRAVEL SOILS Of Coarse Fraction WITH FINES Retained on GC CLAYEY GRAVEL No.4 Sieve SAND CLEAN SAND SW WELL-GRADED SAND,FINE TO COARSE SAND More than 50% SP POORLY-GRADED SAND Retained on No.200 Sieve More than 50% SAND SM SILTY SAND Of Coarse Fraction WITH FINES Passes SC CLAYEYSAND No.4 Sieve SILT AND CLAY INORGANIC ML SILT FINE CL CLAY GRAINED SOILS Liquid Limit ORGANIC OL ORGANIC SILT,ORGANIC CLAY Less than 50 SILT AND CLAY INORGANIC MH SILT OF HIGH PLASTICITY,ELASTIC SILT More than 50% CH CLAY OF HIGH PLASTICITY,FAT CLAY Passes No.200 Sieve Liquid Limit ORGANIC OH ORGANIC CLAY,ORGANIC SILT 50 or more HIGHLY ORGANIC SOILS PT PEAT NOTES: SOIL MOISTURE MODIFIERS: 1. Field classification is based on visual examination of soil Dry- Absence of moisture,dry to the touch in general accordance with ASTM D2488-90. Moist- Damp,but no visible water 2. Soil classification using laboratory tests is based on ASTM D2487-90. Wet- Visible free water or saturated,usually soil is obtained from below water table 3. Description of soil density or consistency are based on interpretation of blow count data,visual appearance of soils,and or test data. i� - Unified Soils Classification System Proposed Single Family Residences GEORESOURCES xxx East State Route 3 Mason County, Washington earth science & geotechnical engineering 5007 Pacific Hwy E.,Suite 16 1 Fite,WA 98424 1253.896.1011 1 wwwporesources.rocks Doc ID:Cedarland.SR3.F.rev02 July 2019 Figure 6 Test Pit TP-1 Location:West Central portion of parcel Depth (ft) Soil Type Soil Description 0 - 1.0 - Dark brown topsoil and forest duff(loose, moist) 1.0 - 2.5 SP Brown gravelly SAND,with silt and cobbles(medium dense, moist)(weathered advance sand) 2.5 - 5.5 SP Grey gravelly SAND with trace silt(dense to very dense, moist)(advance sand) Terminated at 5.5 feet below ground surface. No caving observed at the time of excavation. No groundwater seepage observed. Test Pit TP-2 Location: South central portion of parcel Depth (ft) Soil Type Soil Description 0 - 1.0 - Dark brown topsoil and forest duff(loose, moist) 1.0 - 2.5 SP Brown gravelly SAND,with silt and cobbles(medium dense, moist)(weathered advance sand) 2.5 - 6.0 SP Grey gravelly SAND with trace silt(dense to very dense, moist)(advance sand) Terminated at 6.0 feet below ground surface. No caving observed at the time of excavation. No groundwater seepage observed. Test Pit TP-3 Location:Southeast portion of parcel Depth (ft) Soil Type Soil Description 0 - 1.5 - Dark brown topsoil and forest duff(loose, moist) 1.5 - 2.0 SP Brown gravelly SAND,with silt and cobbles(medium dense, moist)(weathered pre- Fraser) 2.0 - 6.5 SP Grey gravelly SAND with trace silt(very dense, moist)(cemented, pre-Fraser sand and gravel) Terminated at 6.5 feet below ground surface. No caving observed at the time of excavation. No groundwater seepage observed. Logged by: DCB Logged on:June 11,2019 Test Pit Logs Proposed Single Family Residences Gxxx East State Route 3 E O R E S O U R C E S Mason County, Washington earth science & geotechnical engineering 5007 Pacific Hwy E.,Suite 16 1 fife.WA 98424 12S3.896.1011 I www.georesources.rocks Doc ID:Cedafland.SR3.F.revO2 July 2019 F19Ure 7 Particle Size Distribution Report C C C N Qo fpy 8 {� 100 I I I I I I I I I I I I I I I I I I I I I I 1 I I I 90 I I I I I I I I I I I I I I I I I I I I I I I I I I I I 80 I I I I I I I I I 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 70 1 I I I I I I I I I I I I I I I I I I I I I I w I I I I I I I I I I 1 I I I Z 60 1 I I I I I I LL I I I I I I I I I I I I I I I I I I 1 Z I 50 I I I I I I I I I I IL 1 I I I U I I I I I of .40 Ll1 I I I 1 I I I I I I I I I I I 30 I I I I I I I I I I I I I I I 1 1 I I I I I I I I I I I 1 I I I I I I I I I I 20 I I 1 I I I I 1 I I I I I I I I I I I I I I I I I 1 I 10 I 1 1 I I I I I I I I I I I I I 1 I I I I I I I I I I I I I I I I I I I I I 1 I 0 I I I I I I I I I I I I I I 100 10 1 0.1 0.01 0.001 vi GRAIN SIZE-mm. �+ o %Gravel %Sand %Fines E h+3 Coarse Fine Coarse Medium Fine Silt Clay 0 0.0 0.0 26.4 14.4 28.1 22.5 8.6 m m Test Results ASTM D 422& ASTM D 1140 •� � ( ) Material Description 0 'D Opening Percent Spec.` Pass? Brown poorly graded SAND with silt and gravel(SP-SM) Size Finer (Percent) (X=Fail) 3 m 3.0 100.0 > M 2.5 100.0 Atterberg Limits(ASTM D 4318) sa 2.0 100.0 PL= NP LL= PI= f6 1.5 100.0 0 0 1.25 100.0 Classification 3 > 1 100.0 USCS(D 2487)= SP-SM AASHTO(M 145)= o .0 .75 100.0 Coefficients 0 5 94.0 D90= 9.0050 D85= 7.0308 D60= 2.0936 • .3125 88.5 D50= 1.0686 D30= 0.4064 D15= 0.1883 #4 73.6 1310= 0.0979 Cu= 21.38 Cc= 0.81 �0. m #10 59,2 Remarks as #20 46.6 NM:6.4% 0 v #40 31.1 r0n Co #60 18.4 3 a #100 12.3 U) #200 8.6 Date Received: 6/11/2019 Date Tested: 6/17/2019 0 W Tested By:JLK aXi - m E Checked By:DCB ` 0 Title:PM 0 a) N w (no specification provided) as o Location:TP-3 S-1 A - Sample Number:097610 De the 3-6' Date Sampled: 6/11/2019 GeoResources, LLC Client: Cedarland Forest Products a) Project: Proposed Residential Development 0 � m Fife WA Project No: Cedarland-SR3 Ficiure 8 Tested By: Checked By: APPENDIX A- DESIGN CRITERIA Foundation Support Based on the subsurface soil conditions encountered across the site and our understanding of the preliminary plans, we recommend that spread footings be founded on the medium dense to dense native soils or on structural fill that extends to suitable native soils. The soil at the base of the excavations should be disturbed as little as possible. All loose, soft or unsuitable material should be removed or recompacted, as appropriate. A representative from our firm should observe the foundation excavations to determine if suitable bearing surfaces have been prepared. We recommend a minimum width of 24 inches for isolated footings and at least 18 inches for continuous wall footings. All footing elements should be embedded at least 18 inches below grade for frost protection. Footings founded as described above on the dense sand and gravel or on imported clean "Structural Fill" may be designed with a maximum allowable bearing pressure of 2,000 psf(pounds per square foot). The weight of the footing and any overlying backfill may be neglected. The allowable bearing value may be increased by one-third for transient loads such as those induced by seismic events or wind loads. Lateral loads may be resisted by friction on the base of footings and floor slabs and as passive pressure on the sides of footings. We recommend that an allowable coefficient of friction of 0.35 be used to calculate friction between the concrete and the underlying soil. Passive pressure may be determined using an allowable equivalent fluid density of 300 pcf(pounds per cubic foot). Factors of safety have been applied to these values. We estimate that settlements of footings designed and constructed as recommended will be less than 1 inch, for the anticipated load conditions, with differential settlements between comparably loaded footings of Yz inch or less. Most of the settlements should occur essentially as loads are being applied; however, disturbance of the foundation subgrade during construction could result in larger settlements than predicted. We recommend that all foundations be provided with footing drains. Floor Slab Support Slab-on-grade floors, where constructed, should be supported on the medium dense native outwash soils or on structural fill prepared as described above. Any areas of old fill material should be evaluated during grading activity for suitability of structural support. Areas of significant organic debris should be removed. We recommend that floor slabs be directly underlain by a minimum 6-inch thick capillary break material, such as pea gravel or washed 5/8-inch clean crushed rock. This layer should be placed and compacted to an unyielding condition and should contain less than 2 percent fines. A synthetic vapor retarder is recommended to control moisture migration through the slabs. This is of particular importance where moisture migration through the slab is an issue,such as where adhesives are used to anchor carpet or tile to the slab. A subgrade modulus of 230 pounds per cubic inch may be used for floor slab design. We estimate that settlement of the floor slabs designed and constructed as recommended will be Yi- inch or less over a span of 50 feet. Subgrade/Basement Walls The lateral pressures acting on subgrade vault or basement walls will depend upon the nature and density of the soil behind the walls. It is also dependent upon the presence or absence of hydrostatic pressure. If the walls are backfilled with granular well-drained soil, the design active pressure may be taken as 35 pounds per cubic foot (pcf) (equivalent fluid density) and at rest pressures of 55 pcf. This design value assumes a level backslope and drained conditions as described below. If required, a seismic surcharge of 10H should be applied in accordance with applicable building codes. Adequate drainage behind retaining structures is imperative. Positive drainage which controls the development of hydrostatic pressure can be accomplished by placing a zone of drainage behind the walls. Granular drainage material should contain less than 2 percent fines and at least 30% greater than the #4 sieve. A geocomposite drain mat may also be used instead of free draining soils, provided it is installed in accordance with the manufacturer's instructions. A soil drainage zone should extend horizontally at least 18 inches from the back of the wall. The drainage zone should also extend from the base of the wall to within 1 foot of the top of the wall. The soil drainage zone should be compacted to approximately 90 percent of the MDD. Over- compaction should be avoided as this can lead to excessive lateral pressures. A minimum 4-inch diameter perforated, or slotted PVC pipe should be placed in the drainage zone along the base and behind the wall to provide an outlet for accumulated water and direct accumulated water to an appropriate discharge location. We recommend that a nonwoven geotextile filter fabric be placed between the soil drainage material and the remaining wall backfill to reduce silt migration into the drainage zone. The infiltration of silt into the drainage zone can, with time, reduce the permeability of the granular material. The filter fabric should be placed such that it fully separates the drainage material and the backfill and should be extended over the top of the drainage zone. Lateral loads may be resisted by friction on the base of footings and as passive pressure on the sides of footings and the buried portion of the wall, as described in the "Foundation Support" section. We recommend that an allowable coefficient of friction of 0.35 be used to calculate friction between the concrete and the underlying soil. Passive pressure may be determined using an allowable equivalent fluid density of 300 pcf(pounds per cubic foot). Factors of safety have been applied to these values. Temporary Excavations All job site safety issues and precautions are the responsibility of the contractor providing services/work. The following cut/fill slope guidelines are provided for planning purposes only. Temporary cut slopes will likely be necessary during grading operations or utility installation. All excavations at the site associated with confined spaces, such as utility trenches and retaining walls, must be completed in accordance with local,state, or federal requirements. Based on current Washington Industrial Safety and Health Act (WISHA, WAC 296-155) regulations, the dense outwash soils on the site would be classified as Type B soils. According to WISHA, for temporary excavations of less than 20 feet in depth, the side slopes in Type B soils should be sloped at a maximum inclination of 1 H:1 V or flatter from the toe to top of the slope. All exposed slope faces should be covered with a durable reinforced plastic membrane during construction to prevent slope raveling and rutting during periods of precipitation. These guidelines assume that all surface loads are kept at a minimum distance of at least one half the depth of the cut away from the top of the slope and that significant seepage is not present on the slope face. Flatter cut slopes will be necessary where significant raveling or seepage occurs, or if construction materials will be stockpiled along the slope crest. Where it is not feasible to slope the site soils back at these inclinations, a retaining structure should be considered. Where retaining structures are greater than 4-feet in height (bottom of footing to top of structure) or have slopes of greater than 15 percent above them,they should be engineered per Washington Administrative Code (WAC 51-16-080 item 5). This information is provided solely for the benefit of the owner and other design consultants, and r G•-ESOURCE`' should not be construed to imply that GeoResources assumes responsibility for job site safety. It is understood thatjob site safety is the sole responsibility of the project contractor. Site Drainage All ground surfaces, pavements and sidewalks at the site should be sloped away from the structures. The site should be graded to ensure positive drainage away from all structures and property lines. Surface water runoff from the roof areas, driveways, perimeter footing drains, and wall drains should be collected, tightlined, and conveyed to an appropriate discharge point. We recommend that footing drains are installed for the structures in accordance with IBC 1805.4.2. Precipitation water from roof downspouts should be collected into tightlines and routed away from the buildings. Downspout water should not be introduced into the foundation backfill. Surface water should be collected in catch basins and tightlined with the downspout water to an approved discharge point. Stormwater Infiltration We understand the proposed development may include stormwater management facilities. Based on our subsurface explorations at the site, the site grades and our understanding of the proposed site development, it appears that the infiltration of stormwater runoff is not feasible. As currently proposed,all water will be conveyed to stormwater detention ponds in the lower portion of the site. Infiltration of site stormwater is not recommended because of the proximity of the slopes to the ponds. The site soils are dense glacially consolidated sand and gravel and as such are not able to infiltrate water. Because of this we recommend the ponds be lined with either low permeability soils compacted to 95 percent of the dry density in an above optimum moisture content condition or a geosynthetic liner. Pond Slope Configurations Because infiltration is not feasible, we understand that stormwater detention ponds will be constructed in the lower, central and southern portions of the site. We recommend that the fill portions of the pond embankments, if necessary, have a keyway that extends at least 2 feet into the dense native soils. Fill placed on slopes that are steeper than 5H:1V (20 percent) should be keyed into the undisturbed native soils by cutting a series of horizontal benches in accordance with Appendix J of the 2015 IBC. Pond interiors should be constructed of low permeability soils that contain at least 30 percent fines or lined with a geosynthetic (PVC or HDPE) liner. For detention, the entire pond interior should be lined either with low permeability structural fill or a geosynthetic liner. Excavated pond slopes should be sloped back at inclinations of 3H:1V(Horizontal:Vertical) or as allowed by the County. However, slopes steeper than 3H:1V can be prone to shallow sloughing and slumps until the vegetation is fully established and will likely require more frequent maintenance if not lined with a geosynthetic liner. GEORESOURCES APPENDIX B - EARTHWORK RECOMMENDATIONS Site Preparation All structural areas on the site to be graded should be stripped of vegetation, organic surface soils, and other deleterious materials. Organic topsoil is not suitable for use as structural fill, but may be used for limited depths in non-structural areas. Stripping depths ranging from 6 to 12 inches should be expected to remove these unsuitable soils. Areas of thicker topsoil or organic debris may be encountered in areas of heavy vegetation or depressions; stripping depths of up to and greater than 24 inches may occur in these areas. Where placement of fill material is required, the stripped/exposed subgrade areas should be compacted to a firm and unyielding surface prior to placement of any fill. Excavations for debris removal should be backfilled with structural fill compacted to the densities described in the "Structural Fill"section of this report. We recommend that a member of our staff evaluate the exposed subgrade conditions after removal of vegetation and topsoil stripping is completed and prior to placement of structural fill. The exposed subgrade soil should be proof-rolled with heavy rubber-tired equipment during dry weather or probed with a /z-inch-diameter steel T-probe during wet weather conditions. Soft, loose or otherwise unsuitable areas delineated during proofrolling or probing should be recompacted, if practical, or over-excavated and replaced with structural fill. The depth and extent of overexcavation should be evaluated by our field representative at the time of construction. The areas of old fill material should be evaluated during grading operations to determine if they need mitigation; recompaction or removal. Structural Fill All material placed as fill associated with mass grading, as utility trench backfill, under building areas, or under roadways should be placed as structural fill. The structural fill should be placed in horizontal lifts of appropriate thickness to allow adequate and uniform compaction of each lift. Structural fill should be compacted to at least 95 percent of MDD (maximum dry density),as determined in accordance with ASTM D: 1557. The appropriate lift thickness will depend on the structural fill characteristics and compaction equipment used. We recommend that the appropriate lift thickness be evaluated by our field representative during construction. We recommend that our representative be present during site grading activities to observe the work and perform field density tests. The suitability of material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines (material passing US No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult to achieve. During wet weather, we recommend use of well- graded sand and gravel with less than 5 percent(by weight) passing the US No. 200 sieve based on that fraction passing the 3/4-inch sieve, such as "Gravel Backfill for Walls"per the 2016 Washington State Department of Transportation (WSDOT) Standard Specifications for Road, Bridge, and Municipal Construction Specification 9-03.12(2)). If prolonged dry weather prevails during the earthwork and foundation installation phase of construction, higher fines content (up to 10 to 12 percent)may be acceptable. Material placed for structural fill should be free of debris, organic matter, trash, and cobbles greater than 6-inches in diameter. The moisture content of the fill material should be adjusted as necessary for proper compaction. Suitability of On-Site Materials as Fill During dry weather construction, any non-organic on-site soil may be considered for use as structural fill, provided it meets the criteria described above in the "Structural Fill" section of GEORESOURCES� this report and can be compacted as recommended. If the soil material is over optimum moisture content at the time of excavation, it will be necessary to aerate or dry the soil prior to placement as structural fill. The soils observed in our explorations generally were moist. The shallow surficial soils underlying the topsoil generally consist of a mixture of silt, sand, and gravel with variable cobble and boulder content. These soils are generally comparable to "gravel borrow" and "common borrow" materials and should be suitable for use as structural fill provided the moisture content is maintained within 2 percent of the optimum moisture level. Silty soils are moisture sensitive and could be difficult, if not impossible, to compact during extended periods of wet weather or where seepage occurs. We recommend that completed graded areas be restricted from traffic or protected prior to wet weather conditions. The graded areas may be protected by paving, placing asphalt treated base, a layer of free draining material, such as pit run sand and gravel or clean crushed rock material containing less than 5 percent fines, or some combination of the above. Native soils could suitable for this use depending on the amount of silt in the native soils in the area being protected. Erosion Control Weathering, erosion and the resulting surficial sloughing and shallow land sliding are natural processes. As noted, no evidence of surficial raveling or sloughing was observed at the site. To manage and reduce the potential for these natural processes, we recommend erosion protection measures will been to be in place prior to the start of grading activity on the site. GEORESOURCES MASON COUNTY Submittal Checklist COMMUNITY SERVICES Geological Assessment Building.Planning,Environmental Health,Community Health Instructions: This checklist must be submitted with a Geological Assessment and completed, signed, and stamped by the licensed professional(s)who prepared the Geological Assessment for review by Mason County pursuant to the Mason County Resource Ordinance. If an item is found not applicable,the report should explain the basis for the conclusion. Note:Unless specifically documented, this report does not provide compliance to the International Residential Code Sections R403.1.7 for foundations on or adjacent to slopes, Section R403.1.8 for expansive soils or section 1808.7.1 of the International Building Code Section �for Foundations on or adjacent to slopes. / Applicant/Owner (�QG1Crf)U v,d a�,mt4t PrjadyA Parcel# r-Pa 14 '2,C) Site Address (1) A discussion of geologic conditions in the general vicinity of the proposed development,with geologic unit designation based on referenced maps. Located on page(s) 9 (2) (a)A discussion of the ground water conditions at the site, Located on page(s)�_3 (b) A discussion of the estimated depth to water, Located on page(s)_ —S (c) A discussion of the quantity of surface seepage, Located on page(s) N A (d) A discussion of the upslope geomorphology, Located on page(s) oll- (e) A discussion of location of upland waterbodies and wetlands. Located on page(s) NA (3) The approximate depth to hard or dense competent soil,e.g. glacial till or outwash sand. Located on page(s) A (4) A discussion of any geomorphic expression of past slope instability(presence of hummocky ground or ground cracks,terraced topography indicative of landslide block movement, bowed or arched trees indicating downslope movement, etc.). Located on page(s) . T (5) A discussion of the history of landslide activity in the vicinity, as available in the referenced maps and records. Located on page(s) (6) An opinion on whether the proposed development is within the landslide hazard area or its associated buffer or setback and the potential for landslide activity at the site in light of the proposed development. Located on page(s) :� I —I (7) A recommendation by the preparer whether a Geotechnical Report should be required to further evaluate site conditions and the proposed development of the subject property. Rev. February 2018 Located on page(s) (8) If the presence of a hazard is determined within 300 feet of the proposed development,then the following are delineated on a geologic map/site map: (a) the area of the proposed development, Located on Map(s) pA (b) the boundaries of the landslide hazard area (top, both sides, and toe), Located on Map(s) b,J (c) the associated buffers(top, both sides, and toe), Located on Map(s) KI A (d) building or other setbacks(top, both sides, and toe). Located on Map(s) N A (9) A site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of existing and proposed development on the site. Located on Map(s) of A I, )VyA. 9?&C-erL91MfJ ' hereby certify under penalty of perjury that I am a civil engineer licensed in the State of Washington with specialized knowledge of geotechnical/geological engineering or a geologist or engineering geologist licensed in the State of Washington with special knowledge of the local conditions. I also certify that the Geological Assessment, dated Suo4 3) 20 t Z and entitled GC-Ot-O61ck_ ASSESS MEN-- ; ?e-0P05O3eb SW&4c- 'r=r,,µILV '?-=IDENGES meets all the requirements of the Mason County Resource Ordinance, Geologically Hazardous Areas Section, is complete and true, that the assessment demonstrates conclusively that the risks posed by the landslide hazard can be mitigated through the included geotechnical design recommendations, and that all hazards are mitigated in such a manner as to prevent harm to property and public health and safety. S�pPHER 8lG �0 Uj 7 5004 �G ISCER�� '� SIGNAL Al �119 (Signature and Stamp) Page 2 of 2 Disclaimer. Mason County does not certify the quality of the work done in this Geological Assessment.