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Home My WebLink AboutDundee Place Block 20 - Geologic Hazard Assessment - 2020.12.12Srmrun GnouP FOBox2546,Beflinghan'Washinglon 982n Phone:(360) 71,4-9409 This geologic hazardassessment was conducted to assess the potential landslide ard erosion hazard risk to the *i:""'n[p*y po tn"Zrry of Port Tou'nsind's Environmentally Smsitive Areas (ESA) Ormrrfiii, FfUC ii.Os.lt is our unaerstanaing that you are planning to construct December 12,2020 Michael Gesinger C/O PeterBates Good Homes Constnrction Goodhomes0 I @gmail'com Re: GeotogicHazardAssessment 1192 fimatilla Ave' Port Toumsend' Washingfon Jefferson Count5r Parcel 94 800200? DearMr. Gesinger: anewhome on the ProPertY' GENrcRAL GEOLOGY Based on our geologc hazrdassessmerrt" the slopes on$e ybject properly md vicinity do not meet the criteria for "geologi"tny n""oi,I ut"ul; n"t fott Torn'nsend Municipal code and are not at risk of lmdslirlis oi J-rioo- Furthermore' the proposed home will not increase the risk of lmdslides or erosion on or offthe site- This geologic hazard assessment included a field inspectiol of the zubject property and vicinity incruding "lt stop"s. oo, *utoutioo ursoL"ioa"dr"ii"* of availabre geologicm4ping' lidar (lrght detecting and rangiry) t-ug"va-*d o*-oot" "ot"s and observations we have made in the vicinity of the ,it *a ;-r#dons oitn ri-ito geologio conditions- The propertY isunderlainbY 7 (Schasse and Slaugfuter,2005)indicates the subject Vashontill with areas to the southwest across Umatilla Avenuefromthe zubjectProPertY mapped as Vashon ablationtill (Figure l)' I StratrmCrorP File:11.10.20 December l2,2O2O Jefferson Count5r Parcel 94BOOZOO7 Gcologic Hezerd Asscssmcnt Qgt i I r : ;'. 1i I Ii i I ,t*# R,i -i i I -.t, : Qgta \ I' .{- : r;' -*qr l..rt r Su E NP I SU t,{- \L 'a t,-t .' {'t!t 1r, \ ); t\.-4u .lr '.a.tt' ;- .- ,,'{\'r .. '.'rL|. );. *:-:,ffi9))r it $uta E r}5 qFigure f. Clipped and annotatd geologicmap@ (schasse and Slaughter, 2005) showing the subject propertyloaation, Qgt: Vashon till, QCL : Vashon ablation till. Qml :modfied land. Schasse and Slaughter (2005) describe Vashon till as a vory poorly sortedmix of clay, silt, sand,and gravel with scattered cobbles and boulders. The unit is highlycompacted to the poi"t ofresembling concrste and commonly forms steep, nearly vertical io"*t"t Urrm* along puget Soundand the Strait of Juan de Fuca. Vashon till was deposited directly by overlying glacial icebetween l8'000 and 14,000 years ago. The maximum ice thicknlssin the ur.i"lias u"enestimated to be approximately 4,000 feet thick during the last mqjor regional glaciation (Schassemrd Slaughter, 2005; Thorsen" l9S l). Vashon ablation till was deposited aireclvbv rhin, wasting glacial ice during the late stages ofthe last glacial period approximately 14"000 yoars ago. v"sh; ablation till is very similar incomposition to the above described Vashon till andionsists of a very poorly sorted mix of lediments ranging from clay through troulders. However" ablation tiit i* t"** dense and compactthan Vashon till due to being deposited underneath much thinner and less massive glacial ice. Geologic observations made on the subject property are generally consistent with the abovedescribed [rapping. Moderately compact, poorly .o.t"d silt and sand with lesser clay and gravelwith scattered cobbles and boulders consistent with Vashon ablation till were observed in handdug test pits on the site @igure 2). The discrepancy between the above described mapping andour observations is likely due to mapping scale iszues that do not allow for all areas to beprecisely mapped- As noted above" Vashon ablation till is mapped in close proximity to thesubject property. g Stratum Group File: ll.l0.?O Deoember l\2O2O Jetretson Coumy kroel 943002002 Gcologic Hurrd Asscrsmrp( trigurcZ Sandyablation till on the subject fop€rty. SITE SPECrrrC OBSERVATIONS The 0-27-aorc subject propert5r is located on an inland slope on the northeast side of UmatillaAvenueinPort Toumsend. The siteis currently dwelopedwi& a septic sytem ma mall shedoo ry norfteastffn pofq of the propert5r Cig"* 3). ih" proposedhomesite and surroundingmea have been clered md graded in prepmation roiconstuction (Figure 4). the site topography is chaacterized by gefile plmr slopes (Figure 4). The site has an averageslope mgle of 1l degrees (19 percmt) with measured stop" a"gfes betwee,n 5 md 16 degreeslgmrd29 percenQ. Remeining vegetation on the site includes soattered lodgepole pine, Douglas fir, westem redcedar, andmadrone trees with brusy areas that incluOe saH, s*"o.d f"t", O.g* grape, ogeanspxay, snouiberr5r, Fnglish iv5r, Himalayan blaclberry, holly, and grass. 3 StrafirmGrorry File: 11.10.20 December l\zL?n Jeffcrsm Couagr krcel 943002007 Gcologic Errrr:d Asscssmcnt figurcS SepticFnts srnell shed on the site. View is to lhe &rrc 4. The souhturest portion of the property includipg lhe prqmod hm€sic mrrked with vruoden stid<s. ViewisOftesoult- PORT TO\ilNSEN{I} GEOLOGICALLY IIAZI\RINUS AREAS EVALUATION Daigdion of S?erW Gulogically Hazsrdous Arqs As per Porr Townsend's Code 19.05.100 C 1 througfo 4, the followiag classffication sriteria were ermluafed to determine if the subject property or vicinity ue located in a 'leologically hazardous area". 4 SlratmGtorp File:11.10.2O December l2,2O2O Ieffeson Coud5r Parcel 94.8002fi)Z Gcologic l{lz-rd Asscssmcnt BTd on our geologic hazardassessmenl the subject property and vicinity do not meet thecriteria for a "geologicalry hazmdous area" per pJrt T;v;end Municipaltode. 19'05 ' na'C' I : Erosion Hazard Areas.- Areas Any area containing soil or soil complexes(scnbed or moppedwithin the United States oipanment ofAg;cltfurelSoil Consemationsemice soil SurveyforJeferson Cwnty as havig o sseere to very severe erosion hamrdTntential. Soils underlyng the p,roperty are mqpped as Ho5pus gravelly loamy sand with a small area ofclallam gravelly sandy lom mappedit the *ooil*.i"orner of the property. Ho5pus gravellyloamy sand is classified a* so-eufrat excessivd drained and does not iave a severe to verysevere erosion hazard potential. Ctallam gravelly sandy loam is classified as well drained anddoes not have a severs to very sevsre ".osioo n**a pot""tiur. Observed soils on the site meconsistsnt with the USDA Soil Survey mapping. I9'05'ru0'C'2'a: I^andslifu HazardAreas. Areas of historicfailures, such as: i. Those areasdehneated by the USDA's Natural Resources Conservation Service as having a ,,severe,, limitationfor building site development; ii. Those arec$ mapped by Ecologf(Coastal zoneAtlas) or washington Delnrtment of Natural,Resources f*b*l $lope stabitity mapping) ast*tstable ({I or Class 3), mstable old slides (roS or Class 4), or *rtott" receit slides ((}RS orClass 5); iii- Areas designated as landslides on maps trrublished by the USGS or WDNR; oriv' Areas mapped in the Liquefaction Susceptibitt$ Iiap of Jeffeison Ccrunty pubtkhed by theVashington Department of Natural Resources; P" rytjot properry is not designated or mapped as an unstable areq landslide haz.md,area, orliquefaction hazard,'rea on my of the above riferenced maps. 19'05' 100'C'2-b: I'andslide Hazard Areas. Areas with all three of thefolknting chmacteristics:a' Slopes steeper than 15 percent; b- Hillsifus intersecting geoligrc iontactsitn " relativelypermeable sediment overlying a relatively impermeabt" iii^*i or bedrock; and c. Springs orgromdwater seepage; Portionsof the zubjectpropcrty are steqler than 15 percent- Howeveq no intersections ofperm-eabl9 over imPermeable sediment are present and no se€ps, springs or perched water werenoted on the slope. The soils underlying thi slqe are well-&ained. I9'05'100'C'2'c: I'andslide Hazard Areas. Any area potentially subject to mass movement dueto a combination of geologic, tolngraphic, *a hyaibgt"factors, but not limited to those areasmapped or described by the Soil Conservation Service, t*h"-W*hngtoo Snte iepanment ofEcologt, Dqportment ofNatural Resources o1U-S Geologic Senice. These classiJications maybe based on performance standards rather than mappingi 5 StratrmGrorry Filq 11.10.20 Decenber l\20m Jefferson Coud5r Parcel 9{80020O7 Gcologic Hrzerd Asscssmcnt The genfle slopes on the subject property and vicinity are not zubject to mass movcment. We didnot obscrve any evidence of previous, ongoing, or incipient slope failure on the site- We also didnot observe any conditions that indicate the potential for slope failure on the site- I9-05-100.C-2-d: Inndslifu HazordAreas. Any area Tntentially unstable or subject to erosion orsloughingas a result of mpid stormwater rmffi soil saturation orunfurattting bywave action; There are no areas on the subject propert5r zubject to erosion or sloughing as a result ofrapid stormwater runoff, soil safuration or undercutting by wave action. I9-05-lA0-C-2.e: I'urdslide HazmdAreas- Any slope of 40 percmt or steeryr thd qceeds avertical height of l0feet over a 25-foot horizontal rtm; There are no slopes on the subjet property that ue 40 percent or steeper that exceed a vertical height of l0 feet over a 25-foot horizontal run. 19-05-lM.C-3: Earthquake HazardAreas- Areas subject to severe risk of domage as o result of earthqunlces, slopefailure, settlement, soil liquefadion orfmrlting- These areasire idennfied iy the presence ofpoorly drained soils (greater thmt 50 percent silt and less than j5 perceni "ooir*material) loose sand or gravel, peal artificialrtU and londstide materials or soils with a high otganic content. Soils onthe site ane well drained moderately compacl and are not zusceptible to earthquake induced mass movemenl liquefaction, or faulting. I9-05J00-C.zl: Tswtami HazardAreas Tsanami hazard oreas are coastal areas and large lake meos susceptible toflooding and inmdation as the result of excessive wave action dertvedfrom seismic or other geologic events. These areas hwe been mapped by WDNR The subject propert5r is over one mile away from any shoreline area and has elevations rangingfromlZ2 feetto 166 feet above sea level. The site's locdion is well away from and above myinundation or flood hazad rea and is not at risk of tsunmis- 6 $rratumCroup File:11.10.20 December l?-2O2O Jeffetsm Count5r Parcel 948fi)2fi)ZGcdogicHzildAssaesmmt Dan McShane" L.E-G," M-Sc. Licensed Fn gineering Geologist CONCLUSIONS AhID RECOMMENDATIONS BT"9 on our geologic hazud assessment, fhe subject property and vicinity do not meet the "lFB f:l 'leologically hazardous aneas" per Poi ro*"s""i n'r""i"rpa cooe and me not at riskof lmdslides or erosion- Furthermore, the proposed developmeirt will not increase the risk oflmdslides or erosion on or offthe site. Strafum Group appreciates the opporhrnity to be of service to you" Should you have anyquestions this assesmentplease contact our office at (360) 714-i40g- Sincerdyours, Sfratum Group Geoff Malick, L.G_, M.Sc. Licensed Geologist I DANIEL McSHANE StratrmGhoW File:11.10.20