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Home My WebLink AboutGEO2017-00014 - GEO General - 2/22/2017 s Mason County Department of Community Development Submittal Checklist For a Geological Assessment 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 found to be not applicable, the report should explain the basis for the conclusion. Applicant/Owner CcQne.L^-ojp ro"sr Pezoars5 Parcel# (b1O(e Site Address 31 y 1 El-,S-r 6HAN1-,'6t- 1: "VG (1) A discussion of geologic conditions in the general vicinity of the PLANIVMG proposed development,with geologic unit designation based on referenced maps. Located on page(s) RECEIVED (2) (a)A discussion of the ground water conditions at the site, Located on page(s) 3 MAR 21 2017 (b) A discussion of the esNated depth to water 6�5 Located on page(s) W.AJd@{,S MW (c) A discussion of the qu tity of surface seepage Located on page(s) 3 (d) A discussion of the upslope geomorphology Located on page(s) J- (e) A discussion of location of upland waterbodies and wetlands. Located on page(s) d, (3) The approximate depth to hard or dense competent soil, e.g. glacial till or outwash sand. Located on page(s) — (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) o� (5) A discussion of the history of landslide activity in the vicinity, as available in the referenced maps and records Located on page(s) T (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 develop ent. Located on page(s) .01-4 (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. Page 1 of 2 Form Effective June 2008 Located on page(s) 3 , L4 (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) — (b) the boundaries of the landslide hazard area(top, both sides, and toe), Located on Map(s) — (c) the associated buffers(top, both sides, and toe) Located on Map(s) — (d) building or other setbacks(top, both sides, and toe). Located on Map(s) — (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) 'R!G I, 'PAkN A 13 i 6669-CrA* 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 2 Z y°17 and entitled C-,,(-'0TECtOle� A656,'NV6k ' t��oPoS�� SirvcrE C=aKt�/ RfiSI meets all the requirements of the Mason County Resource Ordinance, Landslide Hazard 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. (Signature and Stamp) oY wAsyi�CG, 50040 � clsrtiR `� l NAL Disclaimer: Mason County does not certify the quality of the work done in this Geological Assessment. Page 2 of 2 Form Effective June 2008 GEORESOURCES Elkh. earth science � geotechnical engineering 5007 Pacific Hwy E., Suite 16 ( Fife, WA 98424 1 253.896.1011 1 www.georesources.rocks February 22, 2017 Cedarland Forest Products, LLC Joseph T. Cedarland P.O. Box 2264 Gig Harbor, Washington 98335 (253)208-8136 Geotechnical Assessment Proposed Single Family Residences 31 &41 East Channel Drive Mason County,Washington PN: 122205400105, 122205400106 Doc ID: Cedarland.EChannelDr.AG INTRODUCTION This geotechnical assessment summarizes our site observations, literature research, and engineering analysis for the proposed single family residences to be located at 31 &41 East Channel Drive in Mason County, Washington. The sites are adjacent to one another and are currently undeveloped. The general location of the sites is shown on the attached Site Vicinity Map, Figure 1. Our understanding of the project is based on our discussions with you, our February 2, 2017 site visit, our review of publically available soils data, our past experience in the area, and our understanding of the Mason County Development Codes. We understand that you propose to construct a single-family residence on each of the adjacent parcels including paved driveways from East Channel Drive, septic systems, and associated utilities. The existing site configuration is illustrated on the attached Site& Exploration Plan, Figure 2. SCOPE The purpose of our services was to evaluate the surface and subsurface conditions at the site in order to evaluate the area mapped as a potential landslide hazard area by the County. Specifically, the scope of services for this project will include the following: 1. Reviewing existing and publically available geologic and geotechnical literature for the site area; 2. Describing surface conditions, including soil types, and depth to groundwater, as appropriate; and 3. Addressing the Mason County Resource Management Code Title 8 (MCC 8.52). Cedarland.EChannelDr.AG February 22,2017 Page 12 SITE CONDITIONS Surface Conditions The proposed single family residences are located in an area of existing residential development in the Allyn area of Mason County,Washington. According to the Mason County Assessor website, the parcels are irregular in shape, each measuring about 50 to 150 feet wide (north to south) by about 250 feet deep (east to west), and each encompassing approximately 0.58 to 0.66 acres. The parcels are currently undeveloped. The parcels are bounded by existing residential development on the north and south, by undeveloped forest land on the east, and by East Channel Drive on the west. The site area is situated on the Allyn glacial upland area, located about 1,250 feet southeast of Lake Anderson. From East Channel Drive, the site generally slopes down to the southeast at inclinations of 25 to 35 percent. The slope then flattens out in the central portion of the site to about 15 to 20 percent. Total topographic relief on the site is on the order of 50 to 55 feet based on Mason County GIS data and as observed in the field. Existing site conditions are shown on Figure 2. Vegetation across the site mainly consists of fir trees with a moderate to dense understory of salal, ferns, and evergreen huckleberries. No evidence of slope instability or soil movement was observed at the site at the time of our site visit. No evidence of standing water, seeps, or springs was observed on the site. Site Soils The USDA Natural Resource Conservation Service (NRCS) Web Soil Survey indicates that the site area is underlain by Alderwood gravelly sandy loam (Ac). The Alderwood soils are derived from glacial till and form on slopes of 15 to 30 percent. These soils have a "moderate to severe" 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 According to the draft Geologic Map of the Belfair 7.5-minute Quadrangle, Mason, Kitsap, and Pierce Counties, Washington by Michael Polenz et al (2009), the site is in an area underlain by glacial till (Qvt). These soils were generally deposited during the most recent Vashon Stade of the Fraser Glaciation, some 12,000 to 15,000 years ago. The glacial till consists of a heterogeneous mixture of clay, silt, sand and gravel that was deposited at the base of the continental ice mass and is typically encountered in a very dense condition. The till was overridden by the ice mass, and as such is considered overconsolidated and in a very dense condition, and exhibits high strength and low compressibility characteristics where undisturbed. An excerpt of the above reference geologic map is attached as Figure 3. No evidence of deep seated erosion or other active landslide activity was observed at the time of our site visit. No areas of landslide deposits or mass wasting are noted on the referenced map within the immediate vicinity of the site. A mapped landslide is shown on the referenced map about 650 feet south of the site, but at the same general elevation. 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 areas of known recent or older landslides in the immediate vicinity of the site, no does it identify the area of landslide deposit shown on the geologic map. A copy of the DOE Coastal Atlas is included as Figure 5. GEORESOURCES Cedarland.EChannelDr.AG February 22,2017 page 13 Groundwater Conditions No groundwater seepage was observed at the site at the time of our site visit. We do anticipated 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 will likely occur in response to precipitation patterns, off- site construction activities, and site utilization. ENGINEERING CONCLUSIONS AND RECOMMENDATIONS Based on our site observations and data review, it is our opinion that the proposed single family residential development is feasible from a geotechnical standpoint, provided the recommendations included herein are incorporated into the project plans. Furthermore, it is our opinion that a Geotechnical Report should not be required 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. Classification i. Areas with any indications of earth movement such as debris slides, earthflows, slumps and rockfalls; ii. Areas with artificial oversteepened or un-engineered slopes, i.e. cuts or fills; iii. Areas with slopes containing soft or potentially liquefiable soils; iv. Areas oversteepened or otherwise unstable as a result of stream incision, stream bank erosion, and undercutting by wave action; v. Slopes greater than 15% (8.5 degrees) and having the following: a. Hillsides intersecting geologic contacts with a relatively permeable sediment overlying a relatively impermeable sediment or bedrock (e.g. sand overlying clay), and b. Springs or groundwater seepage; vi. 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. B. The following information may be used as a guide by the county to indicate areas that have a higher likelihood of meeting the classification criteria above: i. The areas identified on the Mason County Soil Survey Map as having slopes greater than fifteen percent. ii. The areas identified on the Coastal Zone Atlas,Volume 9, of Mason County, as: a. Unstable-"U"; b. Unstable Old Slides -"UOS"; C. Unstable Recent Slides -"URS'; d. Intermediate Slopes-"I"; e. Modified Slopes -"M." GEORESOURCES Cedarland.EChannelDr.AG February 22,2017 page 14 iii. The areas identified as Class 2, 3, 4, or 5 of the maps: "Relative Slope Stability of the Southern Hood Canal Area, Washington," by M. Smith and R.J. Carson, Washington State Department of Natural Resources, Division of Earth Resources, 1977; 'The Geological Map of North Central Mason County, Washington," by R.J. Carson, U.S. Geologic Survey OFR 76-2; iv. Areas mapped as landslide deposits (Map Unit Qls) on the: Geologic map of the Longbranch 7.5-minute quadrangle, Thurston, Pierce, and Mason Counties, Washington, by R. L. Logan, T. J. Walsh, and Michael Polenz. one sheet, scale 1:24,000, 2003; Geologic map of the Squaxin Island 7.5-minute quadrangle, Mason and Thurston Counties, Washington, by R. L. Logan, Michael Polenz, T.J. Walsh, and H. W. Schasse. one sheet, scale 1:24,000, 2003; Geologic map of the Shelton 7.5-minute quadrangle, Mason and Thurston Counties, Washington, by H. W. Schasse, R. L. Logan, Michael Polenz, and T. J. Walsh. one sheet, scale 1:24,000, 2003; and Geologic map of the Summit Lake 7.5-minute quadrangle, Thurston and Mason Counties, Washington, by R. L. Logan and T. J. Walsh. forty-two by thirty-six in. color sheet, scale 1:24,000, 2004. 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 below East Channel Drive, at the top of the site, 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, 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. Per Title 8.52.140.(5).(A), the site meets the conditions of Category D, and a geologic assessment should be sufficient to address the MCC Title 8.52. Recommended Setback and Buffer Based on our observations at the site, we recommend that the location of the proposed residence 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 are on the order of 10 to 15 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 4 to 5 feet from the top of the slope. GEORESOURCES Ceda Hand.EChannelDr.AG February 22,2017 page 1 5 If these IBC setbacks cannot be met, the IBC allows the foundations to be deepened, resulting in a structural setback. We can provide additional recommendations for a structural setback if needed. LIMITATIONS We have prepared this report for use by Cedarland Forest Practices and other members of the design team, for use in the design of a portion of this project. The data used in preparing this report and this report should be provided to prospective contractors for their bidding or estimating purposes only. Our report, conclusions and interpretations are based on our subsurface explorations, data from others and limited site reconnaissance, and should not be construed as a warranty of the subsurface conditions. Variations in subsurface conditions are possible between the explorations and may also occur with time. A contingency for unanticipated conditions should be included in the budget and schedule. Sufficient monitoring, testing and consultation should be provided by our firm during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork and foundation installation activities comply with contract plans and specifications. The scope of our services does not include services related to environmental remediation and 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 for consideration in design. If there are any 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, we should be given the opportunity to review our recommendations and provide written modifications or verifications, as appropriate. GEORESOURCES Cedarland.EChannelDr.AG February 22,2017 page 16 We have appreciated the opportunity to be of service to you on this project. If you have any questions or comments, please do not hesitate to call at your earliest convenience. Respectfully submitted, GeoResources, LLC ;Z Jordan L. Kovash, GIT Geotechnical Staff Af F WAS C Fr gab J'`i r O C �. A eKw Geowcyst ,� 50 40 C 925 �y crsrERti �' hsed eon �SSfONAL E�G� QD1� , ?�I KEmi SCOTT S Dana C. Biggerstaff, PE Keith S. Schembs, LEG Senior Geotechnical Engineer Principal KSS:DCB/jlk DoclD:Cedarland.EChannelDr.AG Attachments: Figure 1:Site Vicinity Map Figure 2:Site Location Map Figure 3:NRCS Soils Map Figure 4:Geologic Map Figure 5:DOE Costal Atlas GEORESOURCES CEDAR ST ar !I E SKYLARK CT Devereaux Lake W ` - _ g J S a OHO LU s- Y U Q• QO LU ffi O Ito , ILA A. ti m t— ag 2 AO" 4 'iYF Au Coo aktr 2 t< ? Q p E CREST DR _ _ ly f ! E LAKELAND DR w - yez Lake on r1 Pricke.ttLake r 8 c ,, 3 m E UMRILL DR Approximate Site Location (map created from Mason County Public GIS http://mapmason.co.mason.wa.us/website/mason/viewer.htm) Not to Scale Site Vicinity Map Proposed Single Family Residences 31 &41 East Channel Drive GEORESOURCES Mason County, Washington earth science & geotechnical engineering PN: 122205400105, 122205400106 $007 Pacific Hwy E.,Suite 16 1 fife,WA 98424 1253.396.1011 1 www.geo resources.rocks Doc ID:Cedarland.KhannelDr.F February 2017 Figure 1 FQ A Y Approximate Site Location (map created from Mason County Public GIS http://mapmason.co.mason.wa.us/website/mason/viewer.htm) Not to Scale Site Location Plan Proposed Single Family Residences 31 &41 East Channel Drive GEORESOURCES Mason County, Washington ,arch science & geotechnical engineering PN: 122205400105, 122205400106 S007 Pacific Hwy E.,Suite 16 1 Fife,WA 98424 1253.896.1011 1 www.8eoresources.rocks Doc ID:Cedarland.KhannelDr.F February 2017 Figure 2 �e q I if 3� A • AVV �V � �` ,. '�°�', jam'}-► �� t"w�+�,F.fy, A, 3 ' u Approximate Site Location Map created from Web Soil Survey(http://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx) Soil Soil Name Parent Material Slopes Erosion Hazard Hydrologic Type Soils Group Ac Alderwood gravelly sandy Glacial till 15 to 30 Moderate to Severe C loam .� Not to Scale NRCS Soils Map Proposed Single Family Residences 31 &41 East Channel Drive GEORESOURCES Mason County, Washington C',It L 7 ;Cience & geo�ectini�::�a1 C2rig111l2er ing PN: 122205400105, 122205400106 5007 Pacific Hwy E.,Suite 161 Fite,WA 96424 1 153.696.1011 I www.georesources.rocks Doc ID:Cedarland.EChannelDr.F February 2017 Figure 3 Qa --, Qaf Qgt m op 9 Oaf kOpu /f opl Qgol Ob' J \ Ogas i / Qgo af Qgt !j 4 Ob . Qgo ��/ ab "Qp Qgt Qgt 1 , Qgo Qb. QO Qb ' n9t Qgol Oob i Qob Qgt Oaf °Pu Qao :gym Ob` Ob Ols Oa Qob Approximate Site Location An excerpt from the Geologic Map of the eelfair 7.5-minute Quadrangle, Mason, Kitsop, and Pierce Counties, Washington by Michael Polenz, Katelin Alldritt, Nicholas J. Hehemann, Isabelle Y. Sarikhan, and Robert L. Logan (2009) Qls Peat Qgt Vashon till Av++ Not to Scale USGS Geologic Map Proposed Single Family Residences 31 & 41 East Channel Drive GEORESOURCES Mason County, Washington earth science & geotechnical engineering PN: 122205400105, 122205400106 5007 Pacific Hwy E.,Suite 16 1 Fife,WA 98424 1253.896.1011 1 www.georesources.rocks Doc ID:Cedarland.EChannelDr.F February 20171. Figure 4 iY 1•' F f J r i - 3 , J f Ry �x Approximate Site Location (Map obtained from the DOE Coastal Atlas https://fortress.wa.gov/ecy/coastalatias/) C�o Stable *40 intermediate 40 Modified unstable IV Unstable (cod slide) Unstable (recent s)ide) Not to Scale DOE Coastal Atlas Proposed Single Family Residences 31 &41 East Channel Drive GEORESOURCES Mason County, Washington e,,.ii th �,cien(-e & �;e�_,technlc.il eiq,,meenng PN: 122205400105, 122205400106 S007 Pacific Hwy E.,Suite 16 1 Fite,WA 98424 1 253.896.1011 1 www.geore sources.rocks Doc ID:Cedarland.KhannelDr.F February 2017 Figure 5 GEO ZO) - 006)1 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 refer the case to the Planning Manager or Director. Applicant's Name: t opr a l Permit#: Id5- Parcel#'s: f'ZZ710 �06 Date(s)of the Document(s) reviewed: q Z I f" 1. A discussion of geologic conditions in the general vicinity of the proposed development, with geologic unit designation bV on referenced maps. OK? Comment: 2. (a) A discussion of the ground water conditions at the site, OK? \-/) Comment: (b) A discussionof the estimated depth to water, OK? �" / Comment: (c) A discussion of the quantity of surface seepage, OK? Comment: (d) A discussion f the upslope geomorphology, OK? Comment: (e) A discussion f location of upland waterbodies and wetlands. OK? Comment: 3. The approximate depth to hard or dense competent soil, e.g. glacial till o utwash sand. OK? Comment: h012 �� Ju ?r � i,J a Pe*-" ,T itiN n� .'T icy tW rc.�(� r 4. A discussion of any geomorphic expression of past slope instability (presenct of hummocky ground or g and cracks, terraced topography indicative of landslide block movement, bowed or arched trees indicating downslope moveme , etc.). OK? Comment: 5. A discussion of the story of landslide activity in the vicinity, as available in the referenced maps and records. OK? Comment: 6. An opinion on whet er the proposed development is within the landslide hazard area or its associated buffer or setback and the p ential for landslide activity at the site in light of the proposed development. OK? Comment: 7. A recommendation Py the preparer whether a Geotechnical Report should be required to further evaluate site conditions and th roposed 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: 6 t.h)G, SITt l'�t� (b) the boundaries of the landslide hazard area(top, both sides, and toe), OK? Comment: (c) the associated buffers (top, both sides, and toe) F(d) OK? ~� Comment: 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 signep and stamped? By wh m9 �� Q License#: �� Z License type: Geof�� FIRST REVIEW Approved ❑ Need more info. If not approved, what is the next action/recommendation for further action? Reviewed by CK=-+J :�� , on q 11 Time spent in review: 2 �YS 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