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Home My WebLink AboutPettygroves 2nd Block 58 Lots 2 & 3 - Geology Hazard Assessment - 2018.01.12STRATUM GROUP P.O. Box 2546, Bellingham,WA98227 Phone (360) 714-9409 .5C a-nredf e'^*,:bb *'-rJ A<*.-oLa'tt^ \ ir. Sv.^ryl6o,l-.,:. ,l.i; +.:{b&"u*ot|1 + K t'CI'Lt"dJ-DJanuary 12,2018 Diane Elliott and BradleY Brooks 4627 Crestwood Way Sacramento, CA 95822 Re Geolo gy Hazar d, Assessment Jefferson County Tax Parcel 985205802 Cherry Street Port Townsend, Washington Dear Ms. Elliott and Mr. Brooks: I visited the property in Novemb er 2017 to evaluate the slope stability of subject property. It is my understutrOittg that you are proposing building a home on the property. The purpose of the site visit was to assess ihe geologic stability of the site including the criteria set forth in City of port Townsend's Environmentally Sensitive Areas (ESA) Ordinance, PTMC 19.05. Based on my inspection of the property and vicinity, and areview of readily available geologic information on the site, it is my opinion that the subject property is not located in a geologically hazardous area. Furthefinore, development of the site with a home will not increase the risk of instability on site or on other sites in the area. GENERAL GEOLOGY The Geologic Map of the Port Townsend South and Part of the Port Townsend North 7'5 minute euadrangles, Jefferion County, Washington (Schasse and Slaughter, 2005) indicates that the subject propertyand vicinity are located in an area underlain glacial recessional outwash. The 1aliilrece^ssional outwash consists of sediment deposited by melt water streams associated with ihe melting receding glacial ice during the late stages of the last glacial period approximately 14,000 years ago. The sediment consists of unconsolidated sand and gravel. Site observations on the subject property including hand dug test pits and observations of slopes in the vicinity of the subjectproperty are generally consistent with the above-described mapping. The site is underlain by silty sand and gravel consistent with outwash; however the relative poor sorting of the sedimeni suggests that the deposit was proximal to melting glacial ice and may in part be ice contact/ice wasting deposits. SPECIFIC SITE OBSERVATIONS The subject property is accessed via a shared driveway that follows the V Street right-of-way to the nortlem pottiotr of the property. This driveway extends from Cherry Street to the to the east. January 12,2018 Parcel 985205802, Cherry Street, Port Townsend, WA Geology Hazard Assessment Homes are located on the properties to the north and south of the property. A building is located on the property to the west and the property to the east is vacant and tree and brush covered. The property slopes gently up from the north to the south. The southern portion of the property becomes slightly steeper with a slope ofjust under 20 percent. The property is covered with grass and brush with several mature trees growing around the perimeter of the property. Soils underlying the site consist of silty gavel and sand. The gravel and sand is consistent with the site being underlain by glacial outwash sediments and/or glacial ice wasting deposits. No areas of wet soil or seeps are present on the subject property or on the slopes in the vicinity at the time of my site visit in November 2017 and no plants that indicate seasonal wet areas were observed on the site. No indications of landslides are present on the slopes on the site or in the vicinity of the subject property. As per Port Townsend's Code 19.05.100 B 1 through 6 the following classification criteria were evaluated to determine if the subject property is located in a geologically hazardous area. 19.05.10081: Any area containing soil or soil complexes described or mappedwithin the United States Department of Agriculture/Soil Conservation Service Soil Surveyfor Jefferson County as having a severe to very severe erosion hazard potential. Soils under$ing the site consist of silty gravel with sand. The USDA map indicates the site is underlain by Hoypus gravelly loamy sand, 15 to 30 percent slopes. Test pits are consistent with the soil description; however, the slopes on the site are generally less than 15 percent with the exception of the southern edge of the site which is between 15 percent and20 percent. These soils are not subject to severe erosion. 19.05.10082: Areas with all three of thefollowing characteristics: a. Slopes steeper than 15 percent; b. Hiltsides intersecting geologic contacts with a relatively permeable sediment overlying a relatively impermeable sediment or bedrock; and c. Springs or ground water seepage; The slope along the south edge of the property and to the south of the property has slopes that exceed 15%. However, no intersection of geologic contacts of permeable material over impermeable sediment is present and no seeps, springs or perched water was noted anywhere on the slopes. No indications of potentially unstable slopes were observed on the site or adjoining sites on the slope. 2 Stratum Group File: I1.7.17 January 12,2018 Parcel 985205802, Cherry Street, Port Townsend, WA Geology Hazard Assessment 19.05.1008 j: Any area potentially subject to mass movement due to a combination of geologic, topographic, and hydrologicfactors, but not limited to those areos mapped or described by the Soil Conservation Service, the Washington State Department of Ecology, Department of Natural Resources or U.S. Geologic Service. These classiJications may be based on performance standards rather than mapping; No indications of mass wasting are apparent on the subject property or vicinity. The lack of perched water zones, relatively gentle slopes, and lack of convergent topography all indicate that the site and vicinity are stable. 19.05.10084: Any area potentially unstable or subject to erosion or sloughing as a result of rapid stormwater runoff, soil saturation or undercutting by wave action; The subject property is not in an erosion area of any streams and is not in a shoreline area. No evidence of surface water flow or indications of erosion were present on the site. The upper soils underlying the site are well drained and are not subject to saturation as long as stormwater is dispersed. 19.05.10085: Any slope of 40 percent or steeper that exceeds avertical height of I0feet over a 2 5 -foot horizontal run ; No slopes of 40 percent are present on the property or in near vicinity of the properly. 19.05.10086: Areas subject to severe risk of damage as a result of earthquakes, slopefailure, settlement, soil tiquefaction orfaulting. These areas are idenffied by the presence of poorly drained soils (greater than 50 percent silt and less than 35 percent coarse material), loose sand or gravel, peat, arfficialfi.ll and landslide materials, or soils with high organic content. The property is not underlain by potentially liquefrable soils as soils are coarse grained silty gravel and sand and saturated soils are not present. 3 Stratum Group File:11.7.17 January 12,2018 Parcel 985205802, Cherry Street, Port Townsend, WA Geology Hazard Assessment CONCLUSION AND RECOMMENDATIONS The subject property is not subject to landsliding or rapid erosion. Development of the site with a home will not increase the risk of landslides or erosion on or off the site. Stormwater from roof areas and driveways can be dispersed into the ground and stormwater runoff and footing drainage will not cause any slope stability problems. Stratum Group appreciates the opportunity to be of service to you. Should you have any questions .egurOittg this geology hazardassessment or recofilmendations please contact our offtce at (360) 7t4-9409. Sincerely yours, Stratum Group Dan McShane, L.E.G., M.Sc. Licensed Engineering Geologist 4 Stratum Group File: ll,7.l7 (C*it ':L)I 5 2020CiT{ CF p,,-3.i 1;:,frri'll":l\lD i.s&s&517',05171a)51m51@517165.t7tt)517'')517{Dlbp Scale: 1:667 ifp.irsed on Alan&cape (11" x 8,5)*reL-Mebrs0510?ososd)1?o180lbpFoFdbn: 1r'\bb1.4ercabr Comeroordnatss: WGS&I @p[rs: uIMZme 10ll\r\684Soil Map-Jefferson County Area, Weshington5t71l)5171fl)5171,0517150Attachment 3fi71m51718048P 7 5,rN48P 75f N517m4Fp7s,j$4S'Z5r"NRHg$Hgg51rciio=+IIF*;-- . . -;. i '' i-: JtNbfrNA'i::,/ h )it.\A/eb Soil SurveyNational Cooperative Soil Surveyvi, I i-,-:*,, '.: !i.-.;;; r.$fiP019Page 1 of3L6DAnConservation Service5171d)5171D USDA-Natural ResourcesConservation ServieeSoil Map-Jefferson County Area, WashingtonWeb Soil SurveyNational Cooperative Soil Survey3nt2019Page 2 of 3MAP LEGENDMAP INFORMATIONThe soil surveys that comprise your AOI were mapped at1:20.000.Warning: Soil Map may not be valid at this scale.Enlargement of maps beyond the scale of mapping can causemisunderstanding of the detail of mapping and accuracy of soilline placement" The maps do not show the small areas ofcontrasting soils that could have been shown at a more detailedscale.Please rely on the bar scale on each map sheet for mapmeasurements.Source of Map: Natural Resources Conservation ServiceWeb Soil Survey URL:Coordinate System: Web Mercator (EPSG:3857)Maps from the Web Soil Survey are based on the Web Mercatorprojection, which preserves direction and shape but distortsdistance and area. A projection that preserves area, such as theAlbers equal-area conic projection, should be used if moreaccurate calculations of distance or area are required.This product is generated from the USDA-NRCS certified data asof the version date(s) listed below.Soil Survey Area: Jefferson County Area, WashingtonSurveyArea Data: Version 17, Sep 12,2A18Soil map units are labeled (as space allows) for map scales1:50,000 or larger.Date(s) aerial images were photographed: Dec 31 , 2009-Sep27,2016The orthophoto or other base map on which the soil lines werecompiled and digitized probably differs from the backgroundimagery displayed on these maps. As a result, some minorshifting of map unit boundaries may be evident.Area of lnterest (AOl)g SpoilAreat! Stony Spottil} Very Stony SpotV Wet spotA Other.r- Special Line FeaturesWater FeaturesStreams and CanalsTransportation1-1-1 RailsAd lnterstate Highwaysiid::, US Routes::.-: Major RoadsLocal RoadsBackgroundI Aerial PhotographyArea of lnterest (AOl)Soils|*l Soil Map Unil Polygons#d Soil Map Unit LinesE Soil Map Unit PointsSpecial Foint Featurestg BlowoutEl Borrow Pitfii Clay SpotO Closed DepressionF$ Gravel Pit& Gravelly Spot& Landfill& Lava Flowd$E" Marsh or swampft Mine or Quarry{$ Miscellaneous \ later& Perennial \ /ater\f Rock Outcrop+ Saline Spot:"; Sandy spot€' Severely Eroded Spot+ Sinkholeh Slide or Sllp6 SodicSpot 'Soil Map-Jefierson County Area, Waehingtcl Map Unlt Legend Map Unlt Symbol Map Unit Name Acres ln AOI Percent ofAOl HUD Hoypus gravelly loamy sand, 1 5 to 30 percent slopes 1.6 Totals for Area of lnterest 1.6 100.0olo 't00.0% SB Natural Regources Conseryation Servlce Web $ollSurvey National Cooperative Soil Survey 3nnug Page 3 ofB ,Map Unit Description: Hoypus gravelly loamy Area, Washington 15 to 30 percent slopes--Jefferson County A rr^ ^l-.-- ^.-+ zl,'-r itilr.l llr l!illL i Jefferson County Area, Washington HuD-Hoypus gravelly loamy sand, 15 to 30 percent slopes Map Unit Setting National map unit symbol: 2grn Elevation: 0 to 590 feet Mean annual precipitation: 24 inches Mean annual air temperature: 48 degrees F Frost-free period: 200 to 240 days Farmland c/assificaflon: Not prime farmland Map Unit Composition Hoypus and similar solls; 100 percent Fstlmafes are based on observations, descriptions, and fransecfs of the mapunit. Description of Hoypus Setting Landform: Terraces Parent material: Glacial outwash Typical profile H1 - 0 to 2 inches: gravelly loamy sand H2 - 2 to 10 inches: gravelly loamy sand H3 - 10 to 26 inches: gravelly loamy sand H4 - 26 to 60 inches: gravelly loamy sand Properties and qualities S/ope: 15 to 30 percent Depth to restrictive feature: More than 80 inches Natural drainage c/ass; Somewhat excessively drained Capacity of the most limiting layer to transmit water (Ksat): High to very high (5,95 to 19.98 in/hr) Depth to water table: More than 80 inches Frequency of f/oodrng: None Frequency ofpondlng: None Available water storage in profile: Very low (about 1.6 inches) lnterpretive groups Land capability cl assification (i rrig atedJ ; None specified Land capability classification (nonirrigated): 4e Hydrologic Soil Group: A Forage suitability group: Droughty Soils (G002XN402WA) Hydric sol/ raftng; No Data Source lnformation Soil Survey Area: Jetferson County Area, Washington Survey Area Data: Version 17, Sep 12,2018 t!::ill Lii 't i-.,a\ USDATT Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 3nl2a19 Page 1 of 1