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18-102763 and 18-102761CITY OF �. Federal Way Centered on Opportunity July 26, 2018 Bob Rawlings Twin Lakes Golf & Country Club 3583 SW 320t' Street Federal Way, WA 98023 robertrawlings@comcast.net RE: File #18-102761-00-AD and 18-102763-00-AD; RESPONSE TO INQUIRY Twin Lakes Golf & Country Club Lot 1 & 337, Federal Way Dear Mr. Rawlings: CITY HALL 33325 8th Avenue South Federal Way, WA 98003-6325 (253) 835-7000 www. cityoffederalway.. com Jim Ferrell, Mayor The City of Federal Way's Community Development Department has received your request for an Administrative Decision (AD) critical area letter. The request is to allow construction of a single family house within a Geologically Hazardous Area (GHA) on lots 1 and 337 of Twin Lakes #5 subdivision, parcel #s 873198-0010 and 873198-3370. The proposed properties are located within a GHA, landslide hazard area, as depicted on the City's Critical Areas Map. Per Federal Way Revised Code (FWRC) 19.145.220, the Director of Community Development may permit development activities within 50 feet of the GHA if the development will not be at risk of damage due to the geologic hazard and will not lead to or create any increased slide, seismic or erosion hazard. Based on the Geotechnical Engineering Report for Lot 1 and Lot 337, prepared by The Riley Group, Inc. (RGI), dated May 10, 2018, both sites are suitable for the proposed construction of a single family house from a geotechnical standpoint. The City concurs with this determination. No construction plans or house designs were provided with this AD request. The City may require review of an updated geotechnical report specific to the proposed building plans, meeting requirements per FWRC 19.145.250, when a building permit application is submitted for each house. At that time, a complete site assessment of all impacts to the GHA, if any, will be conducted. If you have any questions regarding this letter, please feel free to contact me at 253-835-2641 or becky.chapin@cityoffederalway.com. Sincerely, Becky Chapin Senior Planner Doc. I.D. 78076 7/16/2018 Planning Find Parcel Find Address Print O 31953 873198 3320 7; 31561 3 3598 333Ci -3198 31967 873t98 33.40 31973 873�9$ 3W5C', 0 up o " 40 ea 2mtz r'�VSE cfwgisweb/Planning Map Set/Default.aspx CFW Inti anet N ---w mom =P=f= http://cfwgisweb/Planning%20Map%2OSet/Default.aspx 1 /1 7/16/2018 31979 36th Ave SW - Google Maps j apS 31979 36th Ave SW Federal Way, Washington Google, Inc. Street View - Sep 2015 Image capture: Sep 2015 @ 2018 Google https://www.google.com/maps/@47.3141265,-122.3780822, 3a,75y,230.95h,91.47ttdata=!3m6! 1 e1 !3m4! 1 sJHMiDUphQUpNy4XoTHpCww!2e0!7i 1331... 1 /1 7/16/2018 31979 36th Ave SW 31979 36th Ave SW - Google Maps 1 / 1 1 V Federal Way, Washington P Google, Inc. Street View - Sep 2015 GZ;5 rf, � win j aktn.c rnlf , Image capture: Sep 2015 @ 2018 Google https://www.google.com/maps/@47.3142997,-122.3781446,3a,75y,80.54h,91.7tldata=!3m6!l el!3m4!l s2Gkdwcz7DJkzy7vYfXjpRA!2eO!7il3312!8i6656 1 /1 E � QUEST FOR ADMINISTRATIVE DECISION CITY OF _ COMMUNITY DEVELOPMENT DEPARTMENT 33325 8`h Avenue South Federal Way Federal Way, WA 9800 253-835-2607;Fax 253-835-2609 www.ciL%Loffederalway.com FELE NUMBER I V - I O ` Date / v Applicant NAME PRIMA" PHoSE ALTERNATE PROBE 7 0 1 -i 8nf Mi/ORGAMUnOA 'rr 1 N s e0VM MtnjBG ADDRESS r �` E-MAIL C1TY ✓+/ STATE b"I 4 ZIP FAX f Property Address/Location— �J f C /-J 7 a7-1 r Description of Request_ SLr fl �Z r List/Describe Attachments is GS avr i6 1► For Staff Use Code Interpretation/Clarification - No Fee Critical Areas Letter/Analysis/Peer Review - No Fee (Actual Cost if Applicable) Request for Extension (Land Use/Plat Approval) - Check Current Fee Schedule Revisions to Approved Permit - Check Current Fee Schedule Tree Removal Zoning Compliance Letter - No Fee - Check Current Fee Schedule as ,NCt Bulletin #079 — January 4, 2016 Page 1 of 1 k:�Handouts\Request for Administrative Decision W G O G f0 Un O G 3 / / / / / etback — 1000 SideCar a ed print � �0 rairwc ��° lire Road Seib ► setbac � 1 1 � ` ` 1t t � l 1 i 1 1 � i Il = Test pit by RGI, 5/1/18 = Site boundary RECEIVED JUN 2 2 20% CITY OF FEDEM WAY COMMUNITY DEVELOPMENT Approximate Scale: 1"=20' _ ■ 0 10 20 40 N I.- Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Twin Lakes Residences Figure 2 RGI Project Number 2018-112 j V'U �� DateEDrawn.,:' 05 RILE"GROUP Fax:4Phone.415.05.0551 CiUR r Fax:425.415.0311 Address: 3198X 36th Avenue Southwest, Federal Way, Washington 98023 TWIN LAKES N0. 5 SECTIONS 11 & 14,TWP 21 N, R 3 E,WM. KING COUNTY , WASHINGTON q 14 A lk. SHEET 4 OF 5 SHEETS CITY OF FEDERAL WAY GOMMUNrTY DEVELOPMEN71 TWIN LAKES NO.5 SECTIONS 11 & 14,TWP 21 N, R 3E,WM. KING COUNTY, WASHINGTON T TW jll.= loo. SCALE SHEET 5 OF 5 SHEETS TWIN LAKES N0.5 SECTIONS II a 14 ,TWP. 21 N , R.3E ,W.M. KING COUNTY, WASHINGTON 30 G3G4270 DESCRIPTION RECORDING CERTIFICATE ; Tr:S solo; if TWIN LAKES NO. 5 emGraces a pc-tim of the SE.': or Secuan li and a portion of the IN of ?rlml !ir -=rd at trm rMool at tet Board of County Commn ssn Dllers 'o.re_"day Section 4 ALL :n Ta�r:s^.iC 7: vol Range u Ezs: of 'h':d :r. king Colin ly IYastiing[on. oria parucularly t—,lf.� pl puiK pbil-4£:3o d 11 an,i :enrded 'n •NIis,7e 4Sro' iPa;s ;ap.:' j' •7j. �3s Uescriued as fa Runs al Kr p!¢mn It f :17Y+nllan $ilrnrn l6i[reas: pi riper it str7 Secixap irL mi�e5 1•LirAB' [ sIMg-s. _f�.lrn. of uld �'�/M..`+', ir:rx IsSER :�I x trt:e+see[ me a: Merl qe IA pr S.i P Smlel are�[ I 6+ ' 4! Id rrgv�, _ al d W.et � ! "{•tee !FtM ,rlrb 11e kit:r � la � It •� I:• F i'�.' WON lu; � at�l '>AtptL'r]Y — — � — — — — 31 Slid s[Ise:_yr iR 3N el said Wtr! m the rr,p rip a C✓Rtr of as la aT fg 5T'0.1 st•ai: KingCounty N+dt for King �tY:y alri tar ]•f = of lu c T ! fa 3 m of ;ar��C7' tltel:s N �13ET, Flli !� {9 Ne'�grmlrte 4'K Ca some IIl V1.d r raer u3 df 336 ii :'-ii Illy �L'[iS[IN it(11r3y�y !'qgR; rpl itrty! a{ 91I RIT- sa ate ar 3[a,L! ]I 9Y3 8 feel to ! PPrrt! of JI�Cy: fp{nCd can;: nJ to b� al i Lt r. pyna k d,' -1,j' ! $.Fj +� lei::Q OrS eels I rn! Qf {as weak ] rd p, rani ra Fro, a ll'! 0i''le:tivA it - q'[•SYZi• F !i sacs us: }-Mi rem sop 'ee:: 7im S sra9. n- E l8. 9s fem. Vltrru N .a0'M, II lie- INF ca v Pr= 7a F 9t A rut: xe . N 3i°m'm• L tpo Aso rat: Ihrna DEDICATION A➢ .eat: I[xiee Y 51r1S'3i' E 4c % reel. orltte S fS7•:'dd• [ �g j5 I�1, yIvIC.� 02117• E IBfl OB Sepia- Ifleler !I ra•: i'.e• E ifl rrt. 'snce 5 $' f IpM1 CO Sal. rtmee �l.'RT^J►*,�g j24 34 IQ'AW ALL 7181 BY THESE PRESENTS tta; we Vte un]erstgne,i arAersn lee s,'ylt of the land aerear Platted (se: iA A6 epP:, :rGe of Sao '•aLT S!6'1 ' E 7:m ad norm ti 1. 119 IS fsfY� b 9! hereby declare :his pla: aid Ja Cate to the Use of the nuSy.c tore... d!1 treets al&,as a„d ease, hits aft IraeaF saA0. gr„z li {Newce E I'i7'ffi 1 If send ees; Irw{ IL ift m the poirt[ dl' ,y1 rn::g :��'f `C tsKraaf ion a1 a��yfei rl {5 1y' rAf:rv?al:i 0lattrI Rf n, r8ul lr ir, i9' 4 Fife 4a: slw"n thereon old the use [herein for zll public purposes •no? �nccnsi sisn[ si ;h -ne use, hteraaf 'ci pch; is 4i . Will e;d ;7FAm am r7 q{g "Ol;l 0 unused ;reek by tnst'Imeel; farrpE{IOa�•�plc'iq hngm h rerpa ses'. al sa Me r: ITt io �azke al I necessz�j'�g; epesr far .u;s om1 Ii Its upor .the Ip:s and blacks Anditar s Fire ra shown hereon IN FITNESS {HEREOF we have Set oi;r !rands and ie! : RESTRICTIONS��4 %1 'r L9 , p: at'roll be dieided ac •I6LC pr =sal? o"r. oMta.-Snip amargdC I. SNEAxIDO OEVEtOR1B1T ell ;:red n!e: ec- :he ow'.er9tip a' a:i, Ccr U:an a! :nos P'ii shall to ess Than the area me�rred_lo• 'na o•mi� . $eCre�Lrf INVESTORS INSURANCE AGENCY INC LAND SURVEYORS CERTIFICATE Ill lduaily an as Trustee mr ss'm±i � Shernood DereloDnt Co. olim" [u::1, U: s' ! TWIN l l 4 i _ .. r : irC:i rif!ia ¢! •� ;n::ter IF .-ar a ov t :... 1, rxn, hereon bat »'J R!'_1Ni It:NS hen- .r" I the [ai n_ Loa ,y raiil :r><e:'-\ .. �'.L ir¢A y'e :ILiL I jaYe a 'et , m prlsa .rn ]x,..:'• ¢t'he :lrttitiMOP eeglri¢os 7ii 3 S l rasre •t 70f'• - LiNCOLNFIRST FEDERAL S8446S �. ••t� r �, • - LOAN OAN ASSCCIATI ON :nl vale' eioiy n. �P� TREASURER'S •CERTI.FICATE ti�re}y wee:.:J :sit Tr• atmo-ef.:mell, i•e-Ja•1 to]: :h1:G.:'P lti Noll :�Itnt Z= a• 1yf03L,Nii + SS $A :dt ea a+_ru =ssss,resi :ea:"'raaioxe's dtrix Fa• ACKN 0W LE bGME NTS rEl re.;p. s• an IVaf. tee a�`�oit ,'��': ' 'NI to is ss reif5_r I ty3 ' ar Jr 91ner 301 ': on « STATE OF s'ASIINGMN st, ire Pa•: •' •'. 1`Is1L d;r - r _ / COUNTY OF KING TI L Is to y4::r lr Ini•'nn ;ire lL�mx c' 11sdAf�r' _ 5� nr'¢- a rx Ore •n7e•I, Ire: i frnlf:t 1'i ?J'rr " .;: r xIcy `Run ti 7t4•t <e¢icee!b III pl:ilcril r, ae'p}jrtG Zx E IM, ip Bpi ifLLAZ Frsremt V4 5x'aw, 'ri7ia:t-•ity of 9IEAL00koyaR [@R "yC.. 7 7u71rrR[po xiCdlit,e! To x prom �2 {x lM r{13rriaas -to oim Ied Ff ." a: thin oadxwUer••'at! oCLvxl Ya >e Ct, ?et : jr tQ ad (life: t'r! ,we m ve,t ra+urters a" m: APPROVALS o +r4truLie e t = n taKa a -s mt moo Ele urn ,i u n+ >; ,I o; °xlr:u lllle?S5' 'Itl3 ae:r, si Ship N •�pp r.: aid: IV XQ,5 rri:[tr * wpm `• z'•"• - - Tao ; p•a; _+! rarti m. : e Nl ei'.IN if ilim l 4!1 i}' ,? 'IN a Caa-�ssic. 71 s"'• ., _-tom Sr f0 . w_�Jl 9 YN - �— No is, fpalIt • '+u arti: f a•t Sla:r st Asr.7,u ._ Aeryri elm . <ais¢,i J r ..•,•S °�:r,a a ,a=., i,_..rc app❑Ye. :.. _� _ say ar _ _IBEB•' • n Ea=rd a' Ca:aT Dunn ss; one•' OeP�;r CLri go —'or Co.�:y iacr�I ssnor.e STATE OFH�INGTON "_ss o;iv .ep-_. z.: ;,:>� 4"'-:_6�L.'—_:SE3 Ttiis E: 'o cery,ly that:.Ln Net 3_e:y orma-s __1969 betore ne. :',t^ :t:°rst a:e,: a Natoli ?.a!,;. D—Fal ij Appeared S •PHELPS and ! R. JENIINGS President and Secretary of iINESTORS iNSL'R- - — ANCE AGENCY INC a xashmg[on corpora❑on to me kwah to be the irdindaal5 who axacured the wn mtn Ca �n?y En;knee 9ediciirm m7 arhnpnN etlietl to me that [hey Si�eu and sealed Me sate as t[ei: +a L:n?ary act and 7aed 'm na'aua,a+d Wrppse [hereln mentioned. and or, oath states that they .re authcl :e execute sa,d { : strfteff'irC'that the seal affixed is the corporate seal of sa-d ColE:3�i tie fT ,yW�TG ['*11L�dzy ]I_(fy1/�•,r—ii5B r' NIT{iESS•o, hand and othctal seal M02y awd ppfiar ftey5{ whore .r r:; Ira •..y tf ys•--^;Y — 'T•ri C.C4a!f �ulA is swr•. — rwxt klbila 1. J: [rrC it2:i a' ilfa.I •-j;Sr' ftil of MI it EASEMENT PROVISIONS tr>:=■ A': zasemn:•'s tipr.py ralarrea :.err II'al to ?acr :.rmrmas[ Bel I TelePNINne Co Mkt Fil l *d Parer.rltl L' rt a1. iryd IfriIf im$CH= and assigns ,ndei aid UW the extensor 5 feet or Iron[ apd'`ear boundary' _:nay a•G ulw,�r''-Fa My [13 iftanor 2 5 feet or side Lomrdary iines of all lots to �Nrd to STATE OF lASHINGTON SS mnii uc: fst'31F );Imill wind �azn Mein untlergrWrC sendul [s onle5 and wi reS with "Kes- ❑1IMY' OF KING •Leith b atmll eodLoi l: for the purpose at serrua iltSmhtli el Ilan atd other proper�r •i tC -L iecirY"Z't7 tl: �a9r]i fltasa L*WN ei T the ngq to esl!s all [lie labs It al! tIm tar Skit our ibis Ito cer[i ly ma! on them day T: � +�e_I%d Jefore ae [he undorsiynad a Notary Puhi is poses mafEd, Alta mtm LrmW % tom: i,�t to use the sT:am for the sma purpase personally appzarel HELEN BERGLUND Assistant Secretary of LI NOILB FIRST FEDERAL SAVINGS L LOAN ASSOCIATION, a U, S corporaPpc. to me known to be the indi'.idaal eta executed tee within e'I aarrv�ars: utigr rys >I Sni ! oe ucce•grouhtl exclusvzly deli cation and acknowledged to me IDa! ste st gied and sealed me sane as her •rap un lary act and oeeC _ far he uses and purpo sus therein nent',ccad; and on oafh stated Chat Utz was authil to Ue Le saill instrW,alt .1 that the seal alfued is the corporMt seal of said wrpor ation _i=3nlT, ty' S:ctil �Tc5 Ct'p; 20 ::sue of coil t':t WITNESS nY nand and affici al Rmii day 1'C�rW Ir rst above win tter. Votary Flbine aner for the Stale of 'Washington - Resntling atIrF�16•�$=------ Wry�� r��s SHEET I OF 5SHEETS TWIN LAKES NO. 5 SECTIONS 11 & 14, TWP 21 N , R. 3 E, W.M. KING COUNTY , WASHINGTON n SCALE I"- loo, fI 7,9ACT 4� 25- i,04 J 17 Al kl, Z. elm Zee fo Z-47 266 zvs zoz SHEET OF 5 SHEETS TWIN LACES N0.5 SECTIONS I I & 14 ,TWP. 21 N , R.3 E ,W.M. KING COUNTY , WASHINGTON l36 L •T Y 4 .ti i 3 a SHEET 3 OF 5 SHEETS in SCALE: 1"% 100' .P .Pus.%n fis/rri Pio land Sd vvyvi ff l,v**v - Nv 2e77 RECEIVEREQUEST FOR ADMINISTRATIVE DECISION COMMUNITY DEVELOPMENT DEPARTMENT CETY OF JUN 2 2 2018 33325 8'" Avenue South Way ay Federal Way, WA 9800 CITY OF FEDERAL WAY ' 253-835-2607; Fax 253-835-2609 WMMUNfTY DEVELOPIulENr www.cityoffederalway.com FILE NUMBER ` - ( 0 2 � � Date (" 2r 43 Applicant NAME PR31ARY PHONE P ��v M-> P"i ZS`:k-974-�-�� HusiNzes/OROANPLATION ALTERNATE PHONE T i N XbL-G3-7 6q-4 rl IS. MAILING ADDRESS fir ' r-v.n �b�r-�r�tw�aH S e a� rC1r&D9-2'e TY STATE ZIP FAX lL' bid 4 9 0 Property Address[Location q ,4�-27 /�/f Description of Request f 1161 List/Describe Attachments t�t'.o S L For Staff Use Code Interpretation/Clarification - No Fee Critical Areas Letter/Analysis/Peer Review - No Fee (Actual Cost if Applicable) Request for Extension (Land Use/Plat Approval) - Check Current Fee Schedule Revisions to Approved Permit - Check Current Fee Schedule Tree Removal Zoning Compliance Letter - No Fee - Check Current Fee Schedule Bulletin #079 — January 4, 2016 Page I of 1 k:\Handouts\Request for Administrative Decision het 000 0000 -dip —1 �)Oqe , oot�Clrt \� 41ne , , , , , , , , , 1 , 1 1 � 1 �000 L� = Test pit by RGI, 5/1/18 = Site boundary Approximate Scale: V=20' ■ 0 10 20 40 N . Corporate Office Twin Lakes Residences Figure 2 17522 Bothell Way Northeast .-Bothell,Washington 98011 RGI Project Number 2018-112 , " Date Drawn: 05/2018 Phone: 425.415.0551 RILEYGROUP Fax: 425,415.0311 Address: 3198X 36th Avenue Southwest, Federal Way, Washington 98023 TWIN LAKES NO.5 SECTIONS 11 & 14 ,TWP. 21 N , R 3 E NIVI. KING COUNTY , WASHINGTON sI ;}•.,.�k f"�o SHEET-3 r } an C" � d� n �y.� �• •r �s. 4 �d7d yl � a �ti � � � k44 � IpI $ ad �'S . � • +b-iay;d T.fiJCT 6.. y5 ��ld A [ y.. '• .rRr.'+ysN ¢� T.P JCTD • 6y ' lw 11 Alp 6 a fi • �l4d � i¢ �f ..� ,� Y +ors'• -� � .a,�� .' •arm' ,r �� „ �• o-�> ~�,� .'� : w y: '�a � Oyu 'yY�- t#ar +� ;i. a � �..�. � per _.�t!ry +�ryt Y r P3 a +•�•- e.• AO t - t ? L .r,. 3f •�� k It • ^`�,mso y rr�,�az+ _!�' � '�� • 2! • .is •�. ,� � Y +��y�# �a<•� ,{. .4. . � —� _ �— � ��ai ._� � i �" �i�ri " w �. - ��- ' cry xx +' . E � w � ( 4F • 33 X 1l ...�V 4 iy -6• �� .vsnRm� W — &AR dlYh z awv' e}q ;w' S yifd .y az� h "' a r - :8'r -� e ��,� s� ' I .;. k' 331 372. '� `cy'ni: � ° !z y'g .�+•S -.4 yA'?� FS c 2 s r`'rr.+arx § J2 A _ xrr `ba-• - �, -. '°-r � i6 29 ��• p'f •�.uav � -�.iy Is .� �_ . - ••cv , •r ��a. ✓�S ;y��•e ��". .d. ��. �' .vim � �' 'Q Q ,29- F'�� { - '�x.�' .�29 7s a• '� v r. �� -- _- " - •T,P.fFI a - - � �— �.�, �s�: .a .r _ ."--` _ - •--• --- - ,e i3 .; �c Jr � _• 333�,tl• 3 n - y'� 7ti� 33d icy 6y Y It ..- �� .• rs �2•Q ; LAa G SCALE k'P100, \` ! a ~�P .9us.Fin fishes Pa La d Sdi✓eyo � �� Ceitl,�Iea/e Na 1677 �R SHEET4 OF5 SHEETS TWIN LAKES NO-5 SECTIONS 11 & 14,TWP 21 N, R 3E,WM. KING COUNTY , WASHINGTON 1 2 1 \ A v Al 7 SCALE: 100'FPuskn Fisher Po Lod Sum✓<yoi t --- -- -,- — 4ft-30VFr AlVe 2077 'a '0C* d SHEET 5 OF 5 SHEETS TWIN LAKES N0.5 SECTIONS II & 14 ,TWP. 21 N , R.3E NIVI. KING COUNTY, WASHINGTON 5 364 27❑ DESCRIPTION RECORDING C£RTIFICATf Ik:s pp!e] ar F1i�I 14{[$'p- '} s�! r •M, An 91 rnr S%of $w.m 1[ >ad Jr Pat M dt ia! i [tr red !or rlmrp OR ire ftedISt )1 :A[ eb ua a n:o ca—, if IAir I rii_S1A-417 o:—��E —1 Fuld. NL :ry Idnl7ld 71 fp r71 A^• 3 Fis: 9r i(a glnj sLOn!y L+Nia[M =It P3r:Ipy;,?, 1 t��7� ilfdltes dAi _IP: 00 � y n! •ems+ddd :n *al se-0=P:Njl ;aE;T [ts:a:0at a[ falrpaJ or Sin kuntF :tgrnetam *:N6rillptllryj ai Gn aOtVlbs! rprn![ ar Stl7 S� 14 ta_ Mel= 1•ag'J6• f al10 to -at-I lee dt Lud , 115 '� •'Cri JG [tILF WK Me '�Iffier]Y'ardl n jf S i �ul tritet 7res�Ily ll pp 'la p; rrt a1C.h, � R ai s.Pdlgl iM a ^y [t! IMF' �IICt tRe :=I!!r 1 ^5 Y li '1@' I:' fff d10 .3A 9e j i�Fetalt. 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I ` f7 Yr - ` :� III .W '.'AH:4N "Y. � ••/ �'r � j s r J"If � s 4 ar � ..`�� we • �' � � y z Vr` r re • +ram BA y �rti �• per"" �� $f'�4 � Ai�6 t R � . � :} $� 43 , e - ' • .P.Qus.Gin Fistrri Pio Land Sui✓ryoi SHEET 3OF5 SHEETS No ID%% mom I LW RILEYGROUP GEOTECHNICAL ENGINEERING REPORT PREPARED BY: THE RILEY GROUP, INC. 17522 BOTHELL WAY NORTHEAST BOTHELL, WASHINGTON 98011 PREPARED FOR: POWELL CUSTOM HOMES AND RENOVATIONS 22211 MARINE VIEW DRIVE SOUTHWEST DES MOINES, WASHINGTON 98198 RGI PROJECT No. 2018-112 RECEIVED JUN 22 2018 CITY OF FEDERAL WAY COMMUNf3Y DEVELOPMENT GEOTECHNICAL ENGINEERING REPORT TWIN LAKES RESIDENCE 3198X 36TH AVENUE SOUTHWEST(LOT 337) FEDERAL WAY, WASHINGTON MAY 10, 2018 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone 425.415.0551 + Fax 425.415.0311 www.riley-group.com mom I LU RILEYGROUP May 10, 2018 Todd Powell Powell Custom Homes and Renovations 22211 Marine View Drive Southwest Des Moines, Washington 98198 Subject: Geotechnical Engineering Report Twin Lakes residence 3198X 36th Avenue Southwest Federal Way, Washington RGI Project No. 2018-112 Dear Mr. Powell: As requested, The Riley Group, Inc. (RGI) has performed a Geotechnical Engineering Report (GER) for the Twin Lakes residence located at 3198X 36th Avenue Southwest, Federal Way, Washington. Our services were completed in accordance with our proposal PRP2018-148 dated April 23, 2018 and authorized by you on May 1, 2018. The information in this GER is based on our understanding of the proposed construction, and the soil and groundwater conditions encountered in the test pits completed by RGI at the site on May 1, 2018. RGI recommends that you submit the project plans and specifications to RGI for a general review so that we may confirm that the recommendations in this GER are interpreted and implemented properly in the construction documents. RGI also recommends that a representative of our firm be present on site during portions of the project construction to confirm that the soil and groundwater conditions are consistent with those that form the basis for the engineering recommendations in this GER. If you have any questions or require additional information, please contact us. Respectfully submitted, THE RILEY GROUP, INC. 44:�� Collin McCracken, GIT Project Geologist Kristina M. Weller, PE S�s�rg Principal Geotechnical Engineer Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone 425.415.0551 * Fax 425.415.0311 www.riley-group.com Geotechnical Engineering Report Twin Lakes residence, Federal Way, Washington May 10, 2018 RGI Project No. 2018-112 TABLE OF CONTENTS 1.0 INTRODUCTION...............................................................................................................................1 2.0 PROJECT DESCRIPTION...............................................................................................................1 3.0 FIELD EXPLORATION AND LABORATORY TESTING ..........................................................1 3.1 FIELD EXPLORATION...................................................................................................................................1 3.2 LABORATORY TESTING................................................................................................................................2 4.0 SITE CONDITIONS...........................................................................................................................2 4.1 SURFACE..................................................................................................................................................2 4.2 GEOLOGY.................................................................................................................................................2 4.3 SOILS.......................................................................................................................................................2 4.4 GROUNDWATER........................................................................................................................................2 4.5 SEISMIC CONSIDERATIONS...........................................................................................................................3 4.6 GEOLOGIC HAZARD AREAS.................................................................................................................... 3 5.0 DISCUSSION AND RECOMMENDATIONS................................................................................. 4 5.1 GEOTECHNICAL CONSIDERATIONS.................................................................................................................4 5.2 EARTHWORK.............................................................................................................................................4 5.2.1 Erosion and Sediment Control.....................................................................................................4 5.2.2 Stripping and Subgrade Preparation............................................................................................5 5.2.3 Excavations...................................................................................................................................5 5.2.4 Structural Fill................................................................................................................................6 5.2.5 Wet Weather Construction Considerations ........................ :...... .......................................... .... ....7 5.3 FOUNDATIONS...........................................................................................................................................8 5.4 RETAINING WALLS.....................................................................................................................................9 5.5 SLAB -ON -GRADE CONSTRUCTION.................................................................................................................9 5.6 DRAINAGE..............................................................................................................................................10 5.6.1 Surface........................................................................................................................................10 5.6.2 Subsurface..................................................................................................................................10 5.6.3 Infiltration..................................................................................................................................10 5.7 UTILITIES................................................................................................................................................10 6.0 ADDITIONAL SERVICES..............................................................................................................11 7.0 LIMITATIONS.................................................................................................................................11 LIST OF FIGURES AND APPENDICES Figure1..................................................................................................................... Site Vicinity Map Figure 2................................................................................................Geotechnical Exploration Plan Figure 3............................................................................................... Retaining Wall Drainage Detail Figure 4....................................................................................................Typical Footing Drain Detail Appendix A......................................................................... Field Exploration and Laboratory Testing ■ow I ■W RILEYGROUP Geotechnical Engineering Report ii May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 Executive Summary This Executive Summary should be used in conjunction with the entire Geotechnical Engineering Report (GER) for design and/or construction purposes. It should be recognized that specific details were not included or fully developed in this section, and the GER must be read in its entirety for a comprehensive understanding of the items contained herein. Section 7.0 should be read for an understanding of limitations. RGI's geotechnical scope of work included the advancement of 2 test pits to approximate depths of 7 feet below existing site grades. Based on the information obtained from our subsurface exploration, the site is suitable for development of the proposed project. The following geotechnical considerations were identified: Soil Conditions: The soils encountered during field exploration include medium dense to dense sandy gravel with trace silt. Groundwater: No groundwater seepage was encountered during our subsurface exploration. Foundations: Foundations for the proposed building may be supported on conventional spread footings bearing on medium dense to dense native soil or structural fill. Slab -on -grade: Slab -on -grade floors and slabs for the proposed building can be supported on medium dense to dense native soil or structural fill. mom 1 LW RILEYGROUP Geotechnical Engineering Report 1 Twin Lakes residence, Federal Way, Washington May 10, 2018 RGI Project No. 2018-112 1.0 Introduction This Geotechnical Engineering Report (GER) presents the results of the geotechnical engineering services provided for the Twin Lakes residence in Federal Way, Washington. The purpose of this evaluation is to assess subsurface conditions and provide geotechnical recommendations for the construction of a single family residence. Our scope of services included field explorations, laboratory testing, engineering analyses, and preparation of this GER. The recommendations in the following sections of this GER are based upon our current understanding of the proposed site development as outlined below. If actual features vary or changes are made, RGI should review them in order to modify our recommendations as required. In addition, RGI requests to review the site grading plan, final design drawings and specifications when available to verify that our project understanding is correct and that our recommendations have been properly interpreted and incorporated into the project design and construction. M Project description The project site is located at 3198X 36th Avenue Southwest in Federal Way, Washington. The approximate location of the site is shown on Figure 1. The site is currently heavily vegetated unoccupied land. RGI understands that a single family residence will be constructed on the site. At the time of preparing this GER, building plans were not available for our review. Based on our experience with similar construction, RGI anticipates that the proposed building will be supported on perimeter walls with bearing loads of two to six kips per linear foot, and a series of columns with a maximum load up to 30 kips. Slab -on -grade floor loading of 250 pounds per square foot (psf) are expected. 3.0 Field Exploration and Laboratory Testing 3.1 FIELD EXPLORATION On May 1, 2018, RGI observed the excavation of 2 test pits. The approximate exploration locations are shown on Figure 2. Field logs of each exploration were prepared by the geologist that continuously observed the excavation. These logs included visual classifications of the materials encountered during excavation as well as our interpretation of the subsurface conditions between samples. The test pits logs included in Appendix A represent an interpretation of the field logs and include modifications based on laboratory observation and analysis of the samples. LW RILEYGROUP Geotechnical Engineering Report 2 Twin Lakes residence, Federal Way, Washington May 10, 2018 RGI Project No. 2018-112 3.2 LABORATORY TESTING During the field exploration, a representative portion of each recovered sample was sealed in containers and transported to our laboratory for further visual and laboratory examination. Selected samples retrieved from the test pits were tested for moisture content and grain size analysis to aid in soil classification and provide input for the recommendations provided in this GER. The results and descriptions of the laboratory tests are enclosed in Appendix A. 4.0 Site Conditions 4.1 SURFACE The subject site is a rectangular -shaped parcel of land approximately 0.19 acres in size. The site is bound to the north by residential property, to the east by 36th Avenue Southwest, and to the south and west by a golf course and pathways. The existing site is vacant land covered by trees and other vegetation. The site is relatively flat with an overall elevation difference of approximately 5 feet. 4.2 GEOLOGY Review of the Geologic Map of Washington — Northwest Quadrant, by J.D. Dragovich, etc. (2002) indicates that the soil in the project vicinity is mapped as undifferentiated outwash (Qgo), which is recessional outwash deposited during glacial retreat consisting of sands, gravels, cobbles and silt. These descriptions are generally similar to the findings in our field explorations. 4.3 SOILS The soils encountered during field exploration include medium dense to dense sandy gravel with trace silt. More detailed descriptions of the subsurface conditions encountered are presented in the test pits included in Appendix A. Sieve analysis was performed on two selected soil samples. Grain size distribution curves are included in Appendix A. 4.4 GROUNDWATER No groundwater seepage was encountered during our subsurface exploration. It should be recognized that fluctuations of the groundwater table will occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the explorations were performed. In addition, perched water can develop within seams and layers contained in fill soils or higher permeability soils overlying less permeable soils following periods of heavy or prolonged precipitation. Therefore, groundwater levels now I ■W RILEYGROUP Geotechnical Engineering Report 3 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 during construction or at other times in the future may be higher or lower than the levels indicated on the logs. Groundwater level fluctuations should be considered when developing the design and construction plans for the project. j 4.5 SEISMIC CONSIDERATIONS Based on the 2012/2015 International Building Code (IBC), RGI recommends the follow seismic parameters for design. Table 1 2012/2015 IBC Parameter — Value — Site Soil Class' D2 1 Site Latitude 47.314220 N Site Longitude 122.377891) W IShort Period Spectral Response Acceleration, Ss (g) 1.311 1-Second Period Spectral Response Acceleration, Sl (g) 0.505 fi Adjusted Short Period Spectral Response Acceleration, Sms (g) 1.311 - f Adjusted 1-Second Period Spectral Response Acceleration, Smi (g) 0.758 ] 1. Note: In general accordance with Chapter 20 of ASCE 7-10. The Site Class is based on the average characteristics of the upper 100 feet 111 ofthe subsurface profile. 2. Note: The 2012/2015 IBC and ASCE 7-10 require a site soil profile determination extending to a depth of 100 feet for seismic site classification. The current scope of our services does not include the required 100 foot soil profile determination. Test pits extended to a maximum depth of 8 feet, and this seismic site class definition considers that similar soil continues below the maximum depth of the subsurface exploration. Additional exploration to deeper depths would be required to confirm the conditions below the current depth l� of exploration. Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength I due to an increase in water pressure induced by vibrations from a seismic event. - Liquefaction mainly affects geologically recent deposits of fine-grained sands that are below the groundwater table. Soils of this nature derive their strength from intergranular I friction. The generated water pressure or pore pressure essentially separates the soil grains and eliminates this intergranular friction, thus reducing or eliminating the soil's strength. RGI reviewed the results of the field and laboratory testing and assessed the potential for liquefaction of the site's soil during an earthquake. Since the site is underlain by dense sandy gravel and lacks a shallow groundwater table, RGI considers that the possibility of liquefaction during an earthquake is minimal. 4.6 GEOLOGIC HAZARD AREAS Regulated geologically hazardous areas include erosion, landslide, earthquake, or other geological hazards. Based on the 1990 King County Sensitive Areas Ordinance, the site is - J 1 -a RILEYGROUP Geotechnical Engineering Report 4 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 mapped as containing a landslide hazard area buffer. Based on our observations and explorations, the development of this lot with a single family residence will not have an adverse effect on the slope area located offsite to the southeast. 5.0 Discussion and Recommendations 5.1 GEOTECHNICAL CONSIDERATIONS Based on our study, the site is suitable for the proposed construction from a geotechnical standpoint. Foundations for the proposed building can be supported on conventional spread footings bearing on medium dense to dense native soil or structural fill. Slab -on - grade floors can be similarly supported. Detailed recommendations regarding the above issues and other geotechnical design considerations are provided in the following sections. These recommendations should be incorporated into the final design drawings and construction specifications. 5.2 EARTHWORK The earthwork is expected to include excavating and backfilling the building foundations and preparing slab subgrades. 5.2.1 EROSION AND SEDIMENT CONTROL Potential sources or causes of erosion and sedimentation depend on construction methods, slope length and gradient, amount of soil exposed and/or disturbed, soil type, construction sequencing and weather. The impacts on erosion -prone areas can be reduced by implementing an erosion and sedimentation control plan. The plan should be designed in accordance with applicable city and/or county standards. RGI recommends the following erosion control Best Management Practices (BMPs): ➢ Scheduling site preparation and grading for the drier summer and early fall months and undertaking activities that expose soil during periods of little or no rainfall ➢ Retaining existing vegetation whenever feasible ➢ Establishing a quarry spall construction entrance ➢ Installing siltation control fencing or anchored straw or coir wattles on the downhill side of work areas ➢ Covering soil stockpiles with anchored plastic sheeting ➢ Revegetating or mulching exposed soils with a minimum 3-inch thickness of straw if surfaces will be left undisturbed for more than one day during wet weather or one week in dry weather ➢ Directing runoff away from exposed soils and slopes now I ■m RILEYGROUP Geotechnical Engineering Report 5 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 ➢ Minimizing the length and steepness of slopes with exposed soils and cover excavation surfaces with anchored plastic sheeting ➢ Decreasing runoff velocities with check dams, straw bales or coir wattles ➢ Confining sediment to the project site ➢ Inspecting and maintaining erosion and sediment control measures frequently (The contractor should be aware that inspection and maintenance of erosion control BMPs is critical toward their satisfactory performance. Repair and/or replacement of dysfunctional erosion control elements should be anticipated.) Permanent erosion protection should be provided by reestablishing vegetation using hydroseeding and/or landscape planting. Until the permanent erosion protection is established, site monitoring should be performed by qualified personnel to evaluate the effectiveness of the erosion control measures. Provisions for modifications to the erosion control system based on monitoring observations should be included in the erosion and sedimentation control plan. 5.2.2 STRIPPING AND SUBGRADE PREPARATION Stripping efforts should include removal of pavements, vegetation, organic materials, and deleterious debris from areas slated for building, pavement, and utility construction. The test pits encountered up to 12 inches of topsoil and rootmass. Deeper areas of stripping may be required in forested or heavily vegetated areas of the site. Subgrade soils that become disturbed due to elevated moisture conditions should be overexcavated to reveal firm, non -yielding, non -organic soils and backfilled with compacted structural fill. In order to maximize utilization of site soils as structural fill, RGI recommends that the earthwork portion of this project be completed during extended periods of warm and dry weather if possible. If earthwork is completed during the wet season (typically November through May) it will be necessary to take extra precautionary measures to protect subgrade soils. Wet season earthwork will require additional mitigative measures beyond that which would be expected during the drier summer and fall months. 5.2.3 EXCAVATIONS All temporary cut slopes associated with the site and utility excavations should be adequately inclined to prevent sloughing and collapse. The site soils consist of medium dense to dense sandy gravel with trace silt. Accordingly, for excavations more than 4 feet but less than 20 feet in depth, the temporary side slopes should be laid back with a minimum slope inclination of 1.5H:1V (Horizontal:Vertical). If there is insufficient room to complete the excavations in this manner, or excavations greater than 20 feet in depth are planned, using temporary shoring RILEYGROUP Geotechnical Engineering Report 6 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 to support the excavations should be considered. For open cuts at the site, RGI recommends: ➢ No traffic, construction equipment, stockpiles or building supplies are allowed at the top of cut slopes within a distance of at least five feet from the top of the cut ➢ Exposed soil along the slope is protected from surface erosion using waterproof tarps and/or plastic sheeting ➢ Construction activities are scheduled so that the length of time the temporary cut is left open is minimized ➢ Surface water is diverted away from the excavation ➢ The general condition of slopes should be observed periodically by a geotechnical engineer to confirm adequate stability and erosion control measures In all cases, however, appropriate inclinations will depend on the actual soil and groundwater conditions encountered during earthwork. Ultimately, the site contractor must be responsible for maintaining safe excavation slopes that comply with applicable OSHA or WISHA guidelines. 5.2.4 STRUCTURAL FILL RGI recommends fill below the foundation and floor slab, behind retaining walls, and below pavement and hardscape surfaces be placed in accordance with the following recommendations for structural fill. The structural fill should be placed after completion of site preparation procedures as described above. The suitability of excavated site soils and import soils for compacted structural fill use will depend on the gradation and moisture content of the soil when it is placed. As the amount of fines (that portion passing the U.S. No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult or impossible to achieve. Soils containing more than about 5 percent fines cannot be consistently compacted to a dense, non -yielding condition when the moisture content is more than 2 percent above or below optimum. Optimum moisture content is that moisture that results in the greatest compacted dry density with a specified compactive effort. Non -organic site soils are only considered suitable for structural fill provided that their moisture content is within abouttwo percent of the optimum moisture level as determined by ASTM D1557. Excavated site soils may not be suitable for re -use as structural fill depending on the moisture content and weather conditions at the time of construction. If soils are stockpiled for future reuse and wet weather is anticipated, the stockpile should be protected with plastic sheeting that is securely anchored. Even during dry weather, moisture conditioning (such as, windrowing and drying) of site soils to be reused as structural fill may be required. mom I ■M RILEYGROUP Geotechnicol Engineering Report 7 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 The site soils are moderately moisture sensitive and may require moisture conditioning prior to use as structural fill. If on -site soils are or become unusable, it may become necessary to import clean, granular soils to complete site work that meet the grading requirements listed in Table 2 to be used as structural fill. Table 2 Structural Fill Gradation U.S. Sieve Size Percent Passing 4 inches No. 4 sieve No. 200 sieve *Based on minus 3/4 inch fraction. 100 22 to 100 0 to 5* Prior to use, an RGI representative should observe and test all materials imported to the site for use as structural fill. Structural fill materials should be placed in uniform loose layers not exceeding 12 inches and compacted as specified in Table 3. The soil's maximum density and optimum moisture should be determined by ASTM D1557. Location Table 3 Structural Fill Compaction ASTM D1557 Material Type Minimum Compaction Percentage Foundations On -site granular or approved 95 imported fill soils: On site granular or approved Retaining Wall Backfill imported fill soils: 92 On -site granular or approved Slab -on -grade ; imported fill soils: 95 General Fill (non- On -site soils or approved 90 structural areas) imported fill soils: Moisture Content Range Placement and compaction of structural fill should be observed by RGI. A representative number of in -place density tests should be performed as the fill is being placed to confirm that the recommended level of compaction is achieved. 5.2.5 WET WEATHER CONSTRUCTION CONSIDERATIONS RGI recommends that preparation for site grading and construction include procedures intended to drain ponded water, control surface water runoff, and to collect shallow subsurface seepage zones in excavations where encountered. It will not be possible to successfully compact the subgrade or utilize on -site soils as structural fill if accumulated � 1 � RILEYGROUP Geotechnical Engineering Report 8 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 water is not drained prior to grading or if drainage is not controlled during construction. Attempting to grade the site without adequate drainage control measures will reduce the amount of on -site soil effectively available for use, increase the amount of select import fill materials required, and ultimately increase the cost of the earthwork phases of the project. Free water should not be allowed to pond on the subgrade soils. RGI anticipates that the use of berms and shallow drainage ditches, with sumps and pumps in utility trenches, will be required for surface water control during wet weather and/or wet site conditions. 5.3 FOUNDATIONS Following site preparation and grading, the proposed building foundation can be supported on conventional spread footings bearing on dense native soil or structural fill. Loose, organic, or other unsuitable soils may be encountered in the proposed building footprint. If unsuitable soils are encountered, they should be overexcavated and backfilled with structural fill. Perimeter foundations exposed to weather should be at a minimum depth of 18 inches below final exterior grades. Interior foundations can be constructed at any convenient depth below the floor slab. Finished grade is defined as the lowest adjacent grade within 5 feet of the foundation for perimeter (or exterior) footings and finished floor level for interior footings. Table 4 Foundation Design Design Parameter Allowable Bearing Capacity Friction Coefficient Passive pressure (equivalent fluid pressure) 1. psf = pounds per square foot 2. pcf = pounds per cubic foot Value 2,000 psfl 0.30 250 pcf2 Columns: 24 inches Minimum foundation dimensions Walls: 16 inches The allowable foundation bearing pressures apply to dead loads plus design live load conditions. For short-term loads, such as wind and seismic, a 1/3 increase in this allowable capacity may be used. At perimeter locations, RGI recommends not including the upper 12 inches of soil in the computation of passive pressures because they can be affected by weather or disturbed by future grading activity. The passive pressure value assumes the foundation will be constructed neat against competent soil or backfilled with structural fill as described in Section 5.2.4. The recommended base friction and passive resistance value includes a safety factor of about 1.5. mom 1 L- RILEYGROUP Geotechnical Engineering Report 9 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 With spread footing foundations designed in accordance with the recommendations in this section, maximum total and differential post -construction settlements of 1 inch and 1/2 inch, respectively, should be expected. 5.4 RETAINING WALLS If retaining walls are needed in the building area, RGI recommends cast -in -place concrete walls be used. The magnitude of earth pressure development on retaining walls will partly depend on the quality of the wall backfill. RGI recommends placing and compacting wall backfill as structural fill. Wall drainage will be needed behind the wall face. A typical retaining wall drainage detail is shown in Figure 3. With wall backfill placed and compacted as recommended, and drainage properly installed, RGI recommends using the values in the following table for design. Table 5 Retaining Wall Design Design Parameter Value Allowable Bearing Capacity 2,000 psf Active Earth Pressure (unrestrained walls) 35 pcf At -rest Earth Pressure (restrained walls) ` 50 pcf For seismic design, an additional uniform load of 7 times the wall height (H) for unrestrained walls and 14H in psf for restrained walls should be applied to the wall surface. Friction at the base of foundations and passive earth pressure will provide resistance to these lateral loads. Values for these parameters are provided in Section 5.3. 5.5 SLAB -ON -GRADE CONSTRUCTION Once site preparation has been completed as described in Section 5.2, suitable support for slab -on -grade construction should be provided. RGI recommends that the concrete slab be placed on top of medium dense native soil or structural fill. Immediately below the floor slab, RGI recommends placing a four -inch thick capillary break layer of clean, free -draining sand or gravel that has less than five percent passing the U.S. No. 200 sieve. This material will reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting of the floor slab. Where moisture by vapor transmission is undesirable, an 8- to 10-millimeter thick plastic membrane should be placed on a 4-inch thick layer of clean gravel. For the anticipated floor slab loading, we estimate post -construction floor settlements of 1/4- to 1/2-inch. now I ■W RILEYGROUP Geotechnical Engineering Report 10 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 5.6 DRAINAGE 5.6.1 SURFACE Final exterior grades should promote free and positive drainage away from the building area. Water must not be allowed to pond or collect adjacent to foundations or within the immediate building area. For non -pavement locations, RGI recommends providing a minimum drainage gradient of 3 percent for a minimum distance of 10 feet from the building perimeter. In paved locations, a minimum gradient of 1 percent should be provided unless provisions are included for collection and disposal of surface water adjacent to the structure. 5.6.2 SUBSURFACE RGI recommends installing perimeter foundation drains. A typical footing drain detail is shown on Figure 4. The foundation drains and roof downspouts should be tightlined separately to an approved discharge facility. Subsurface drains must be laid with a gradient sufficient to promote positive flow to a controlled point of approved discharge. 5.6.3 INFILTRATION Based on the soils at the Site being comprised of sandy gravel, infiltration or dispersion is feasible on the lot. Per City of Federal Way guidelines full infiltration appears feasible on the lot based criteria in the 2016 King County Surface Water Design Manual (KCSDM). Full infiltration is feasible if the site soils consist of coarse sand, cobble, or medium sands per Appendix C, Section C.2.2.2 KCSWDM. Site soils consist of sandy gravel, meeting the soil criteria for full infiltration. The sandy gravel soils were present to the depth of our explorations, 8 feet below existing grade. No groundwater or signs of seasonal high groundwater were observed in our subsurface explorations. The site soils do not meet the requirements to provide water quality treatment for pollution generating surfaces (driveways) and therefore infiltration of any pollution generating surfaces will need to have some level of water quality treatment before being infiltrated. Non -pollution generating surfaces (roofs, patios, etc) can be infiltrated directly, without treatment. Full infiltration on single-family lots is typically facilitated using gravel filled trenches or dry wells. Sizing criteria for gravel filled trenches and drywells, based on square footage of impervious area is provided in the KCSWDM Appendix C Sections C.2.2.3 (gravel filled trenches) and C.2.2.4 (drywells). The sizing criteria for coarse sand or cobbles should be used for sizing the trench or drywells based on the site soils. 5.7 UTILITIES Utility pipes should be bedded and backfilled in accordance with American Public Works Association (APWA) specifications. For site utilities located within the right-of-ways, ■0M I ■W RILEYGROUP Geotechnical Engineering Report 11 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 bedding and backfill should be completed in accordance with City of Federal Way specifications. At a minimum, trench backfill should be placed and compacted as structural fill, as described in Section 5.2.4. Where utilities occur below unimproved areas, the degree of compaction can be reduced to a minimum of 90 percent of the soil's maximum density as determined by the referenced ASTM D1557. As noted, soils excavated on site may not be suitable for use as backfill material. Imported structural fill meeting the gradation provided in Table 2 should be used for trench backfill. 6.0 Additional Services RGI is available to provide further geotechnical consultation throughout the design phase of the project. RGI should review the final design and specifications in order to verify that earthwork and foundation recommendations have been properly interpreted and incorporated into project design and construction. RGI is also available to provide geotechnical engineering and construction monitoring services during construction. The integrity of the earthwork and construction depends on proper site preparation and procedures. In addition, engineering decisions may arise in the field in the event that variations in subsurface conditions become apparent. Construction monitoring services are not part of this scope of work. If these services are desired, please let us know and we will prepare a cost proposal. 7.0 Limitations This GER is the property of RGI, Powell Custom Homes and Renovations, and its designated agents. Within the limits of the scope and budget, this GER was prepared in accordance with generally accepted geotechnical engineering practices in the area at the time this GER was issued. This GER is intended for specific application to the Twin Lakes residence project in Federal Way, Washington, and for the exclusive use of Powell Custom Homes and Renovations and its authorized representatives. No other warranty, expressed or implied, is made. Site safety, excavation support, and dewatering requirements are the responsibility of others. The scope of services for this project does not include either specifically or by implication any environmental or biological (for example, mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, we can provide a proposal for these services. The analyses and recommendations presented in this GER are based upon data obtained from the explorations performed on site. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear ®I= I ®7 RILEYGROUP Geotechnical Engineering Report 12 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 evident, RGI should be requested to reevaluate the recommendations in this GER prior to proceeding with construction. It is the client's responsibility to see that all parties to the project, including the designers, contractors, subcontractors, are made aware of this GER in its entirety. The use of information contained in this GER for bidding purposes should be done at the contractor's option and risk. ■ow LM RILEYGROUP USGS, 2017, Tacoma North, Washington Approximate Scale: 1"=1000' USGS, 2014, Poverty Bay, Washington FM A 7.5-Minute Quadrangle 0 500 1000 2000 N -Corporate Office 17522 Bothell Way Northeast . - Bothell, Washington 98011 Phone: 425.415.0551 RILEYGROUP Fax:425.415.0311 Twin Lakes Residences Figure 1 RGI Project Number Date Drawn: Site Vicinity Map 2018-05/2018 112 � Address: 3198X 36th Avenue Southwest, Federal Way, Washington 98023 w a• S q t4 G UM 0 G look .W-O back OTP-201 \ \ 1 dashed IV 1 ZO �airWa'i 1�Fo e 1 Road Setback \ �� 11 Setback 1 \ I \ 1 1 l V \ \ 1 l 1 1 1 1 1 \ l \ 1 I\ TP-20 I Approximate Scale: 1"=20' p = Test pit by RGI, 5/1/18 A = Site boundary 0 10 20 40 N -Corporate office Twin Lakes Residences Figure 2 17522 Bothell Way Northeast RGI Project Number Date Drawn: . - Bothell, Washington 98011 Geotechnical Exploration Plan 05/2018 Phone: 425.415.05 51 2 018 -112 RILEYGRGUR Fax; 425.415.0311 Address: 3198X 36th Avenue Southwest, Federal Way, Washington 98023 12" Minimum Wide i Free -Draining Gravel Slope to Drain I' ° e o ape ... •• - too Filter Fabric Material Excavated Slope (See Report for 04 ' Appropriate ° Incliniations) do I- Compacted Structural Backfill (Native or Import) •oe X. 0 Od4DaOCe °o pa6aa❑° O e I - -- 6e ova°oo o°np°v oSna nOo _ i,� h 77N � L 12" Over the Pipe 4" Diameter PVC 3" Below the Pipe Perforated Pipe Not to Scale . - Corporate Office Twin Lakes Residences Figure 3 17522 Bothell Way Northeast RGI Project Number Date Drawn: I .- Bothell, Washington 93011 2018-112F Retaining Wall Drainage Detail 05/2018 n p Phone: 425.415.0551 RILEYGROUP Fax: 425.415.0311 Address: 3198X 36th Avenue Southwest, Federal Way, Washington 98023 Building Slab }-fix• � a �, ` � 4" Perforated Pipe 3/4" Washed Rock or Pea Gravel Not to Scale Filter Fabric -Corporate Office Twin Lakes Residences Figure 4 17522 Bothell Way Northeast RGI Project Number Date Drawn: .-Bothell, Washington 98011 Typical Footing Drain Detail 05/2018 Phone: 425.415,0551 2018-112 RILEYGROUP Fax: 425.415.0311 Address: 3198X 36th Avenue Southwest, Federal Way, Washington 98023 Geotechnical Engineering Report May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING On May 1, 2018, RGI performed field explorations using a rubber tired backhoe. We explored subsurface soil conditions at the site by observing the excavation of two test pits to a maximum depth of 8 feet below existing grade. The test pits locations are shown on Figure 2. The test pits locations were approximately determined by measurements from existing property lines and paved roads. A geologist from our office conducted the field exploration and classified the soil conditions encountered, maintained a log of each test exploration, obtained representative soil samples, and observed pertinent site features. All soil samples were visually classified in accordance with the Unified Soil Classification System (USCS). Representative soil samples obtained from the explorations were placed in closed containers and taken to our laboratory for further examination and testing. As a part of the laboratory testing program, the soil samples were classified in our in house laboratory based on visual observation, texture, plasticity, and the limited laboratory testing described below. Moisture Content Determinations Moisture content determinations were performed in accordance with ASTM D2216-10 Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass (ASTM D2216) on representative samples obtained from the exploration in order to aid in identification and correlation of soil types. The moisture content of typical sample was measured and is reported on the test pits logs. Grain Size Analysis A grain size analysis indicates the range in diameter of soil particles included in a particular sample. Grain size analyses was determined using D6913-04(2009) Standard Test Methods for Particle -Size Distribution (Gradation) of Soils Using Sieve Analysis (ASTM D6913) on one of the samples. mom 1 LW RILEYGROUP Project Name: Twin Lakes Residences I WTest Pit No.: TP-201 Project Number: 2018-112 1 ■� Sheet 1 of 1 Client: Powell Custom Homes and Renovations RILEYGROUP Date(s) Excavated: 5/1118 Logged By CM Surface Conditions: Grass Excavation Method: Backhoe Bucket Size: 18" Total Depth of Excavation: 6 feet Excavator Type: Backhoe Excavating Contractor: Kelly's Excavating Approximate Surface Elevation Not surveyed Groundwater Level Not encountered and Date Measured Sampling Grab Method(s) Compaction Method Bucket tamp Test Pit Backfill: Cuttings Location 3198X & 3198X 36th Avenue Southwest Federal Way. Washington 98023 CDJ —a)to L c. a) CD CX H N E `m a E Z N a E <n o �, U, U E) U_ t m 6 MATERIAL DESCRIPTION REMARKS AND OTHER TESTS 0 5 p284 P20t.' Tpsi 12" Topsoil and rootmass 5% Moisture 5% Moisture GP e d `os i°a v ap 0 ry aSD _ G' 0 i�q d�� en . Brown to gray sandy GRAVEL with trace silt, moist, medium dense —Becomes gray, very dense, slight iron oxidation Test pit terminated at 6 feet bgs. The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name: Twin Lakes Residences I MTest Pit No.: TP-202 Project Number: 2018-112 1 M -Sheet 1 of 1 Client: Powell Custom Homes and Renovations RILEYGROUP Date(s) Excavated: 5/1/18 Logged By CM Surface Conditions: Grass Excavation Method: Backhoe Bucket Size: 18" Total Depth of Excavation: 7 feet Excavator T e: Backhoe yP Excavating Contractor: Kelly's Excavating Approximate Not surveyed Surface Elevation Groundwater Level Not encountered and Date Measured Sampling Grab Method(s) Compaction Method Bucket tamp Test Pit Backfill: Cuttings Location 3198X & 3198X 36th Avenue Southwest Federal Way, Washington 98023 _ID~ L n 0 n CD E U3 a� E Z a) a E U) o U) ai U � 0 J U_ � m � MATERIAL DESCRIPTION REMARKS AND OTHER TESTS 0 5 10 P2p2_ Fxv2_, Tpsl 4" Topsoil and rootmass 5% Moisture o 7/a Moisture sP 4Brown M.•; Hj{= wlt�i to gray SAND with some silt and gravel, moist, _ medium dense GP ti v 0 6 lop 0 �9D Gray sandy GRAVEL with trace silt, damp, very dense, —slight iron oxidation Test pit terminated at 7 feet logs. The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 J J Project Name: Twin Lakes Residences Key to Logs Project Number: 2018-112 Sheet 1 of 1 Client: Powell Custom Homes and Renovations RILEYGROUP .-. a E ' o E rn d a)fn J U . . — Q U L a �` °' W °' 0 `0 co `6 (n U) D 0 MATERIAL DESCRIPTION REMARKS AND OTHER TESTS COLUMN DESCRIPTIONS 1Elevation (feet): Elevation (MSL, feet). 2 Depth (feet): Depth in feet below the ground surface. L3J Sample Type: Type of soil sample collected at the depth interval shown. ® Sample Number: Sample identification number. FIELD AND LABORATORY TEST ABBBIEVIATIONS CHEM: Chemical tests to assess corrosivity COMP: Compaction test CONS: One-dimensional consolidation test LL: Liquid Limit, percent MATERIAL GRAPHIC SYMBOLS RIFI.- Poorly graded GRAVEL (GP) TYPICAL SAMPLER GRAPHIC S'C1tE_3QLS Auger sampler Continuous Bulk Sample Grab Sample California w/ ' 2.5-inch-OD Modified M3-inch-OD brass rings California w/ brass liners CME Sampler Pitcher Sample GENERAL NOTES 5 USCS Symbol: USCS symbol of the subsurface material. 5 Graphic Log: Graphic depiction of the subsurface material encountered. 0 MATERIAL DESCRIPTION: Description of material encountered. May include consistency, moisture, color, and other descriptive text. ® REMARKS AND OTHER TESTS: Comments and observations regarding drilling or sampling made by driller or field personnel. Pi: Plasticity Index, percent SA: Sieve analysis (percent passing No. 200 Sieve) UC: Unconfined compressive strength test, Qu, in ksf WA: Wash sieve (percent passing No. 200 Sieve) y Poorly graded SAND (SP) Topsoil 2-inch-OD unlined split spoon (SPT) Shelby Tube (Thin -walled, fixed head) OTHER GRAPHIC�YMBOLS — Water level (at time of drilling, ATD) v Water level (after waiting) Minor change in material properties within a stratum — Inferred/gradational contact between strata —v— Queried contact between strata 1: Soil classifications are based on the Unified Soil Classification System. Descriptions and stratum lines are interpretive, and actual lithologic changes may be gradual. Field descriptions may have been modified to reflect results of lab tests. 2: Descriptions on these logs apply only at the specific boring locations and at the time the borings were advanced. They are not warranted to be representative of subsurface conditions at other locations or times. The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415-0551 FAX: (425)415-0311 GRAIN SIZE ANALYSIS ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Twin Lakes Residence - Lot 337 PROJECT NO. 2018-112 TECH/TEST DATE CM 5/2/2018 WAT R CONTENT f 7eliiered Moisture) Wt Wet Soil & Tare (gm) (w1) 1334.8 Wt Dry Soil & Tare (gm) (w2) 1243.9 Weight of Tare (gm) (w3) 16.0 Weight of Water (gm) (w4=w1-w2) 90.9 Weight of Dry Soil (gm) (w5=w2-w3) 1227.9 Moisture Content (%) (w4/w5)'100 7 % COBBLES % C GRAVEL % F GRAVEL % C SAND % M SAND % F SAND % FINES % TOTAL D10 (mm) D30 (mm) D60 (mm) Cu Cc 12.0' 3.0' 2.5' 2.0' 1.5' 1.0' 0.75' 0.50' 0.375' #Z #1C #2C #4( #6( 0.0 32.0 30.0 7.9 17.7 10.1 2.4 100.0 0.3 2 15 50.0 0.9 o� P A S S I N G 100 90 80 70 60 50 40 30 20 10 0 #10( #20C PAN �..�srrr�eir�ir� SAMPLE ID/TYPE TP-202 SAMPLE DEPTH 5' DATE RECEIVED 5/2/2018 tal Weight Of Sampie Used For Sieve Corrected For Hygroscopic Mo Weight Of Sample (gm) 1243.9 Tare Weight (gm) 16.0 (W6) Total Dry Weight (gm) 1227.9 SIEVE ANALYSIS Cumulative Wt Ret Wt-Tare €%Retained % PASS +Tara 11wirerlw5l•1003 f100-%retl 16.0 0.00 0.00 100.00 16.0 0.00 0.00 100.00 217.2 201.20 16.39 83.61 408.4 392.40 31.96 68.04 657.8 641.80 52.27 47.73 776.8 760.80 61.96 38.04 873.2 857.20 69.81 30.19 1090.1 1074.10 87.47 12.53 1201.5 1185.50 96.55 3.45 1213.9 1197.90 97.56 2.44 1243.9 1227.90 100.00 0.00 1000 100 10 1 Grain size in millimeters DESCRIPTION Sandy GRAVEL with trace silt USCS GP Prepared For: Pwell Custom Homes and Renovations Reviewed By: KMW :obbles :oarse gravel :oarse gravel :oarse gravel =oarse gravel :oarse gravel fine gravel fine gravel fine gravel zoarse sand medium sand medium sand Fine sand fine sand fine sand fines silt/clay 0.1 0.01 0.001 RILEYGROLIP now I LW RILEYGROUP GEOTECHNICAL ENGINEERING REPORT PREPARED BY: THE RILEY GROUP, INC. 17522 BOTHELL WAY NORTHEAST BOTHELL, WASHINGTON 98011 PREPARED FOR: POWELL CUSTOM HOMES AND RENOVATIONS 22211 MARINE VIEW DRIVE SOUTHWEST DES MOINES, WASHINGTON 98198 RGI PROJECT No. 2018-112 GEOTECHNICAL ENGINEERING REPORT TWIN LAKES RESIDENCE 3198X 36TH AVENUE SOUTHWEST(LOT 1) FEDERAL WAY, WASHINGTON MAY 10,2018 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone 425.415.0551 • Fax 425.415.0311 www.riley-group.com mom I LW RILEYGROUP May 10, 2018 Todd Powell Powell Custom Homes and Renovations 22211 Marine View Drive Southwest Des Moines, Washington 98198 Subject: Geotechnical Engineering Report Twin Lakes Residence 3198X 36th Avenue Southwest Federal Way, Washington RGI Project No. 2018-112 Dear Mr. Powell: As requested, The Riley Group, Inc. (RGI) has performed a Geotechnical Engineering Report (GER) for the Twin Lakes Residence located at 3198X 36th Avenue Southwest, Federal Way, Washington. Our services were completed in accordance with our proposal PRP2018-148 dated April 23, 2018 and authorized by you on May 1, 2018. The information in this GER is based on our understanding of the proposed construction, and the soil and groundwater conditions encountered in the test pits completed by RGI at the site on May 1, 2018. RGI recommends that you submit the project plans and specifications to RGI for a general review so that we may confirm that the recommendations in this GER are interpreted and implemented properly in the construction documents. RGI also recommends that a representative of our firm be present on site during portions of the project construction to confirm that the soil and groundwater conditions are consistent with those that form the basis for the engineering recommendations in this GER. If you have any questions or require additional information, please contact us. Respectfully submitted, THE RILEY GROUP, INC. Collin McCracken, GIT Project Geologist Kristina M. Weller, PE S16/l8 Principal Geotechnical Engineer Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone 425.415.0551 + Fax 425.415.0311 www.riley-group.com Geotechnical Engineering Report May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 TABLE OF CONTENTS 1.0 INTRODUCTION...............................................................................................................................1 2.0 PROJECT DESCRIPTION...............................................................................................................1 3.0 FIELD EXPLORATION AND LABORATORY TESTING..........................................................1 3.1 FIELD EXPLORATION...................................................................................................................................1 3.2 LABORATORY TESTING................................................................................................................................2 4.0 SITE CONDITIONS...........................................................................................................................2 4.1 SURFACE..................................................................................................................................................2 4.2 GEOLOGY ..................................... --- ............................. ........................................................... .......... 2 4.3 SOILS.......................................................................................................................................................2 4.4 GROUNDWATER........................................................................................................................................2 4.5 SEISMIC CONSIDERATIONS...........................................................................................................................3 4.6 GEOLOGIC HAZARD AREAS...........................................................................................................................3 5.0 DISCUSSION AND RECOMMENDATIONS................................................................................. 4 5.1 GEOTECHNICAL CONSIDERATIONS.................................................................................................................4 5.2 EARTHWORK.............................................................................................................................................4 5.2.1 Erosion and Sediment Control.....................................................................................................4 5.2.2 Stripping and Subgrade Preparation.......................................................................................... ..5 5.2.3 Excavations...................................................................................................................................5 5.2.4 Structural Fill................................................................................................................................6 5.2.5 Wet Weather Construction Considerations.................................................................................7 5.3 FOUNDATIONS...........................................................................................................................................8 5.4 RETAINING WALLS.....................................................................................................................................9 5.5 SLAB -ON -GRADE CONSTRUCTION.................................................................................................................9 5.6 DRAINAGE..............................................................................................................................................10 5.6.1 Surface........................................................................................................................................10 5.6.2 Subsurface....... .......................... .................................. ................................ ............................ 10 5.6.3 Infiltration..................................................................................................................................10 5.7 UTILITIES................................................................................................................................................11 6.0 ADDITIONAL SERVICES..............................................................................................................11 7.0 LIMITATIONS.................................................................................................................................11 LIST OF FIGURES AND APPENDICES Figure1..................................................................................................................... Site Vicinity Map Figure 2................................................................................................Geotechnical Exploration Plan Figure 3............................................................................................... Retaining Wall Drainage Detail Figure 4....................................................................................................Typical Footing Drain Detail Appendix A......................................................................... Field Exploration and Laboratory Testing mom I ■W RILEYGROUP Geotechnical Engineering Report Twin Lakes residence, Federal Way, Washington May 10, 2018 RGI Project No. 2018-112 Executive Summary This Executive Summary should be used in conjunction with the entire Geotechnical Engineering Report (GER) for design and/or construction purposes. It should be recognized that specific details were not included or fully developed in this section, and the GER must be read in its entirety for a comprehensive understanding of the items contained herein. Section 7.0 should be read for an understanding of limitations. RGI's geotechnical scope of work included the advancement of 2 test pits to approximate depths of 8 feet below existing site grades. Based on the information obtained from our subsurface exploration, the site is suitable for development of the proposed project. The following geotechnical considerations were identified: Soil Conditions: The soils encountered during field exploration include medium dense to dense sandy gravel with trace silt. Groundwater: No groundwater seepage was encountered during our subsurface exploration. Foundations: Foundations for the proposed building may be supported on conventional spread footings bearing on medium dense to dense native soil or structural fill. Slab -on -grade: Slab -on -grade floors and slabs for the proposed building can be supported on medium dense to dense native soil or structural fill. RILEYGROUP Geotechnical Engineering Report 1 Twin Lakes residence, Federal Way, Washington May 10, 2018 RGI Project No. 2018-112 1.0 Introduction This Geotechnical Engineering Report (GER) presents the results of the geotechnical engineering services provided for the Twin Lakes Residence in Federal Way, Washington. The purpose of this evaluation is to assess subsurface conditions and provide geotechnical recommendations for the construction of a single family residence. Our scope of services included field explorations, laboratory testing, engineering analyses, and preparation of this GER. The recommendations in the following sections of this GER are based upon our current understanding of the proposed site development as outlined below. If actual features vary or changes are made, RGI should review them in order to modify our recommendations as required. In addition, RGI requests to review the site grading plan, final design drawings and specifications when available to verify that our project understanding is correct and that our recommendations have been properly interpreted and incorporated into the project design and construction. 2.0 Project description The project site is located at 3198X 36th Avenue Southwest in Federal Way, Washington. The approximate location of the site is shown on Figure I. The site is currently unoccupied land with some vegetation. RGI understands that a single family residence will be constructed on the site. At the time of preparing this GER, building plans were not available for our review. Based on our experience with similar construction, RGI anticipates that the proposed building will be supported on perimeter walls with bearing loads of two to six kips per linear foot, and a series of columns with a maximum load up to 30 kips. Slab -on -grade floor loading of 250 pounds per square foot (psf) are expected. 3.0 Field Exploration and Laboratory Testing 3.1 FIELD EXPLORATION On May 1, 2018, RGI observed the excavation of 2 test pits. The approximate exploration locations are shown on Figure 2. Field logs of each exploration were prepared by the geologist that continuously observed the excavation. These logs included visual classifications of the materials encountered during excavation as well as our interpretation of the subsurface conditions between samples. The test pits logs included in Appendix A represent an interpretation of the field logs and include modifications based on laboratory observation and analysis of the samples. mom LM RILEYGROUP Geotechnical Engineering Report 2 Twin Lakes residence, Federal Way, Washington May 10, 2018 RGI Project No. 2018-112 3.2 LABORATORY TESTING During the field exploration, a representative portion of each recovered sample was sealed in containers and transported to our laboratory for further visual and laboratory examination. Selected samples retrieved from the test pits were tested for moisture content and grain size analysis to aid in soil classification and provide input for the recommendations provided in this GER. The results and descriptions of the laboratory tests are enclosed in Appendix A. 4.0 Site Conditions 4.1 SURFACE The subject site is a rectangular -shaped parcel of land approximately 0.20 acres in size. The site is bound to the north by residential property, to the east by a golf course fairway, to the south by unoccupied vacant land, and to the west by 36th Avenue Southwest. The existing site is vacant land covered by trees and other vegetation. The site is flat with an overall elevation difference of approximately 2 feet. 4.2 GEOLOGY Review of the Geologic Map of Washington — Northwest Quadrant, by J.D. Dragovich, etc. (2002) indicates that the soil in the project vicinity is mapped as undifferentiated outwash (Qgo), which is recessional outwash deposited during glacial retreat consisting of sands, gravels, cobbles and silt. These descriptions are generally similar to the findings in our field explorations. 4.3 SOILS The soils encountered during field exploration include medium dense to dense sandy gravel with trace silt. More detailed descriptions of the subsurface conditions encountered are presented in the test pits included in Appendix A. Sieve analysis was performed on two selected soil samples. Grain size distribution curves are included in Appendix A. 4.4 GROUNDWATER No groundwater seepage was encountered during our subsurface exploration. It should be recognized that fluctuations of the groundwater table will occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the explorations were performed. In addition, perched water can develop within seams and layers contained in fill soils or higher permeability soils overlying less permeable soils following periods of heavy or prolonged precipitation. Therefore, groundwater levels IBM I ■W RILEYGROUP Geotechnical Engineering Report 3 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 during construction or at other times in the future may be higher or lower than the levels indicated on the logs. Groundwater level fluctuations should be considered when developing the design and construction plans for the project. 4.5 SEISMIC CONSIDERATIONS Based on the 2012/2015 International Building Code (IBC), RGI recommends the follow seismic parameters for design. Table 12012/2015 IBC Parameter Value Site Soil Class' Dz ISite Latitude T� 47.314000 N Site Longitude 122.378190 W Short Period Spectral Response Acceleration, Ss (g) 1.310 1-Second Period Spectral Response Acceleration, S1(g) 0.505 Adjusted Short Period Spectral Response Acceleration, Sens (g) 1.310 Adjusted 1-Second Period Spectral Response Acceleration, Snn1(g) 0.758 1. Note: In general accordance with Chapter 20 of ASCE 7-10. The Site Class is based on the average characteristics of the upper 100 feet of the subsurface profile. 2. Note: The 2012/2015 IBC and ASCE 7-10 require a site soil profile determination extending to a depth of 100 feet for seismic site classification. The current scope of our services does not include the required 100 foot soil profile determination. Test pits extended to a maximum depth of 8 feet, and this seismic site class definition considers that similar soil continues below the maximum depth of the subsurface exploration. Additional exploration to deeper depths would be required to confirm the conditions below the current depth of exploration. Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength due to an increase in water pressure induced by vibrations from a seismic event. Liquefaction mainly affects geologically recent deposits of fine-grained sands that are below the groundwater table. Soils of this nature derive their strength from intergranular friction. The generated water pressure or pore pressure essentially separates the soil grains and eliminates this intergranular friction, thus reducing or eliminating the soil's strength. RGI reviewed the results of the field and laboratory testing and assessed the potential for liquefaction of the site's soil during an earthquake. Since the site is underlain by dense sandy gravel and shallow groundwater was not observed, RGI considers that the possibility of liquefaction during an earthquake is minimal. 4.6 GEOLOGIC HAZARD AREAS Regulated geologically hazardous areas include erosion, landslide, earthquake, or other geological hazards. Based on the 1990 King County Sensitive Areas Ordinance, the site is 1 LW RILEYGROUP Geotechnical Engineering Report 4 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 mapped as containing a landslide hazard area buffer. Based on our observations and explorations, the development of this lot with a single family residence will not have an adverse effect on the slope area located offsite to the southeast. 5.0 Discussion and Recommendations 5.1 GEOTECHNICAL CONSIDERATIONS Based on our study, the site is suitable for the proposed construction from a geotechnical standpoint. Foundations for the proposed building can be supported on conventional spread footings bearing on medium dense to dense native soil or structural fill. Slab -on - grade floors can be similarly supported. Detailed recommendations regarding the above issues and other geotechnical design considerations are provided in the following sections. These recommendations should be incorporated into the final design drawings and construction specifications. 5.2 EARTHWORK The earthwork is expected to include excavating and backfilling the building foundations and preparing slab subgrades. 5.2.1 EROSION AND SEDIMENT CONTROL Potential sources or causes of erosion and sedimentation depend on construction methods, slope length and gradient, amount of soil exposed and/or disturbed, soil type, construction sequencing and weather. The impacts on erosion -prone areas can be reduced by implementing an erosion and sedimentation control plan. The plan should be designed in accordance with applicable city and/or county standards. RGI recommends the following erosion control Best Management Practices (BMPs): ➢ Scheduling site preparation and grading for the drier summer and early fall months and undertaking activities that expose soil during periods of little or no rainfall ➢ Retaining existing vegetation whenever feasible ➢ Establishing a quarry spall construction entrance ➢ Installing siltation control fencing or anchored straw or coir wattles on the downhill side of work areas ➢ Covering soil stockpiles with anchored plastic sheeting ➢ Revegetating or mulching exposed soils with a minimum 3-inch thickness of straw if surfaces will be left undisturbed for more than one day during wet weather or one week in dry weather ➢ Directing runoff away from exposed soils and slopes now I ■U RILEYGRQIIP Geotechnical Engineering Report 5 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 ➢ Minimizing the length and steepness of slopes with exposed soils and cover excavation surfaces with anchored plastic sheeting ➢ Decreasing runoff velocities with check dams, straw bales or coir wattles ➢ Confining sediment to the project site ➢ Inspecting and maintaining erosion and sediment control measures frequently (The contractor should be aware that inspection and maintenance of erosion control BMPs is critical toward their satisfactory performance. Repair and/or replacement of dysfunctional erosion control elements should be anticipated.) Permanent erosion protection should be provided by reestablishing vegetation using hydroseeding and/or landscape planting. Until the permanent erosion protection is established, site monitoring should be performed by qualified personnel to evaluate the effectiveness of the erosion control measures. Provisions for modifications to the erosion control system based on monitoring observations should be included in the erosion and sedimentation control plan. 5.2.2 STRIPPING AND SUBGRADE PREPARATION Stripping efforts should include removal of pavements, vegetation, organic materials, and deleterious debris from areas slated for building, pavement, and utility construction. The test pits encountered up to 24 inches of topsoil and rootmass. Deeper areas of stripping may be required in forested or heavily vegetated areas of the site. A large (greater than 3 feet by 6 feet) concrete slab was discovered at 6 to S inches below grade in the northeast corner of the lot. Edges of the slab and slab thickness could not be determined during test pit excavation. Subgrade soils that become disturbed due to elevated moisture conditions should be overexcavated to reveal firm, non -yielding, non -organic soils and backfilled with compacted structural fill. In order to maximize utilization of site soils as structural fill, RGI recommends that the earthwork portion of this project be completed during extended periods of warm and dry weather if possible. If earthwork is completed during the wet season (typically November through May) it will be necessary to take extra precautionary measures to protect subgrade soils. Wet season earthwork will require additional mitigative measures beyond that which would be expected during the drier summer and fall months. 5.2.3 EXCAVATIONS All temporary cut slopes associated with the site and utility excavations should be adequately inclined to prevent sloughing and collapse. The site soils consist of medium dense to dense sandy gravel with trace silt. Accordingly, for excavations more than 4 feet but less than 20 feet in depth, the temporary side slopes should be laid back with a minimum slope inclination of 1.5H:1V mom I ■M RILEYGROUP Geotechnical Engineering Report 6 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 (Horizontal:Vertical). If there is insufficient room to complete the excavations in this manner, or excavations greater than 20 feet in depth are planned, using temporary shoring to support the excavations should be considered. For open cuts at the site, RGI recommends: ➢ No traffic, construction equipment, stockpiles or building supplies are allowed at the top of cut slopes within a distance of at least five feet from the top of the cut ➢ Exposed soil along the slope is protected from surface erosion using waterproof tarps and/or plastic sheeting ➢ Construction activities are scheduled so that the length of time the temporary cut is left open is minimized ➢ Surface water is diverted away from the excavation ➢ The general condition of slopes should be observed periodically by a geotechnical engineer to confirm adequate stability and erosion control measures In all cases, however, appropriate inclinations will depend on the actual soil and groundwater conditions encountered during earthwork. Ultimately, the site contractor must be responsible for maintaining safe excavation slopes that comply with applicable OSHA or WISHA guidelines. 5.2.4 STRUCTURAL FILL RGI recommends fill below the foundation and floor slab, behind retaining walls, and below pavement and hardscape surfaces be placed in accordance with the following recommendations for structural fill. The structural fill should be placed after completion of site preparation procedures as described above. The suitability of excavated site soils and import soils for compacted structural fill use will depend on the gradation and moisture content of the soil when it is placed. As the amount of fines (that portion passing the U.S. No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult or impossible to achieve. Soils containing more than about 5 percent fines cannot be consistently compacted to a dense, non -yielding condition when the moisture content is more than 2 percent above or below optimum. Optimum moisture content is that moisture that results in the greatest compacted dry density with a specified compactive effort. Non -organic site soils are only considered suitable for structural fill provided that their moisture content is within about two percent of the optimum moisture level as determined by ASTM D1557. Excavated site soils may not be suitable for re -use as structural fill depending on the moisture content and weather conditions at the time of construction. If soils are stockpiled for future reuse and wet weather is anticipated, the stockpile should be protected with plastic sheeting that is securely anchored. Even during dry weather, I ®W RILEYGROUP Geotechnical Engineering Report 7 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 moisture conditioning (such as, windrowing and drying) of site soils to be reused as structural fill may be required. The site soils are moderately moisture sensitive and may require moisture conditioning prior to use as structural fill. If on -site soils are or become unusable, it may become necessary to import clean, granular soils to complete site work that meet the grading requirements listed in Table 2 to be used as structural fill. Table 2 Structural Fill Gradation U.S. Sieve Size Percent Passing 4 inches 100 No. 4 sieve 22 to 100 No. 200 sieve 0 to 5* *Based on minus 3/4 inch fraction Prior to use, an RGI representative should observe and test all materials imported to the site for use as structural fill. Structural fill materials should be placed in uniform loose layers not exceeding 12 inches and compacted as specified in Table 3. The soil's maximum density and optimum moisture should be determined by ASTM D1557. Location Table 3 Structural Fill Compaction ASTM D1557 Material Type Foundations On -site granular or approved imported fill soils: On -site granular or approved Retaining Wall Backfill i imported fill soils: On -site granular or approved Slab -on -grade imported fill soils: General Fill (non- On -site soils or approved structural areas) imported fill soils: Minimum Moisture Content Compaction Range Percentage Placement and compaction of structural fill should be observed by RGI. A representative number of in -place density tests should be performed as the fill is being placed to confirm that the recommended level of compaction is achieved. 5.2.5 WET WEATHER CONSTRUCTION CONSIDERATIONS RGI recommends that preparation for site grading and construction include procedures intended to drain ponded water, control surface water runoff, and to collect shallow now LW RILEYGROUP Geotechnical Engineering Report 8 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 subsurface seepage zones in excavations where encountered. It will not be possible to successfully compact the subgrade or utilize on -site soils as structural fill if accumulated water is not drained prior to grading or if drainage is not controlled during construction. Attempting to grade the site without adequate drainage control measures will reduce the amount of on -site soil effectively available for use, increase the amount of select import fill materials required, and ultimately increase the cost of the earthwork phases of the project. Free water should not be allowed to pond on the subgrade soils. RGI anticipates that the use of berms and shallow drainage ditches, with sumps and pumps in utility trenches, will be required for surface water control during wet weather and/or wet site conditions. 5.3 FOUNDATIONS Following site preparation and grading, the proposed building foundation can be supported on conventional spread footings bearing on dense native soil or structural fill. Loose, organic, or other unsuitable soils may be encountered in the proposed building footprint. If unsuitable soils are encountered, they should be overexcavated and backfilled with structural fill. Perimeter foundations exposed to weather should be at a minimum depth of 18 inches below final exterior grades. Interior foundations can be constructed at any convenient depth below the floor slab. Finished grade is defined as the lowest adjacent grade within 5 feet of the foundation for perimeter (or exterior) footings and finished floor level for interior footings. Table 4 Foundation Design Design Parameter Value Allowable Bearing Capacity 2,000 psf1 — Friction Coefficient 0.30 Passive pressure (equivalent fluid pressure) 250 pcf2 i— Columns: 24 inches Minimum foundation dimensions Walls: 16 inches 1. psf = pounds per square foot 2. pcf = pounds per cubic foot The allowable foundation bearing pressures apply to dead loads plus design live load conditions. For short-term loads, such as wind and seismic, a 1/3 increase in this allowable capacity may be used. At perimeter locations, RGI recommends not including the upper 12 inches of soil in the computation of passive pressures because they can be affected by weather or disturbed by future grading activity. The passive pressure value assumes the foundation will be constructed neat against competent soil or backfilled with structural fill now I ■W RILEYGROUP Geotechnical Engineering Report 9 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 as described in Section 5.2.4. The recommended base friction and passive resistance value includes a safety factor of about 1.5. With spread footing foundations designed in accordance with the recommendations in this section, maximum total and differential post -construction settlements of 1 inch and 1/2 inch, respectively, should be expected. 5.4 RETAINING WALLS If retaining walls are needed in the building area, RGI recommends cast -in -place concrete walls be used. The magnitude of earth pressure development on retaining walls will partly depend on the quality of the wall backfill. RGI recommends placing and compacting wall backfill as structural fill. Wall drainage will be needed behind the wall face. A typical retaining wall drainage detail is shown in Figure 3. With wall backfill placed and compacted as recommended, and drainage properly installed, RGI recommends using the values in the following table for design. Table 5 Retaining Wall Design Design Parameter Value Allowable Bearing Capacity ` 2,000 psf Active Earth Pressure (unrestrained walls) 35 pcf At -rest Earth Pressure (restrained walls) 50 pcf For seismic design, an additional uniform load of 7 times the wall height (H) for unrestrained walls and 14H in psf for restrained walls should be applied to the wall surface. Friction at the base of foundations and passive earth pressure will provide resistance to these lateral loads. Values for these parameters are provided in Section 5.3. 5.5 SLAB -ON -GRADE CONSTRUCTION Once site preparation has been completed as described in Section 5.2, suitable support for slab -on -grade construction should be provided. RGI recommends that the concrete slab be placed on top of medium dense native soil or structural fill. Immediately below the floor slab, RGI recommends placing a four -inch thick capillary break layer of clean, free -draining sand or gravel that has less than five percent passing the U.S. No. 200 sieve. This material will reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting of the floor slab. Where moisture by vapor transmission is undesirable, an 8- to 10-millimeter thick plastic membrane should be placed on a 4-inch thick layer of clean gravel. ■om LW RILEYGROUP Geotechnical Engineering Report 10 May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 For the anticipated floor slab loading, we estimate post -construction floor settlements of 1/4- to 1/2-inch. 5.6 DRAINAGE 5.6.1 SURFACE Final exterior grades should promote free and positive drainage away from the building area. Water must not be allowed to pond or collect adjacent to foundations or within the immediate building area. For non -pavement locations, RGI recommends providing a minimum drainage gradient of 3 percent for a minimum distance of 10 feet from the building perimeter. In paved locations, a minimum gradient of 1 percent should be provided unless provisions are included for collection and disposal of surface water adjacent to the structure. 5.6.2 SUBSURFACE RGI recommends installing perimeter foundation drains. A typical footing drain detail is shown on Figure 4. The foundation drains and roof downspouts should be tightlined separately to an approved discharge facility. Subsurface drains must be laid with a gradient sufficient to promote positive flow to a controlled point of approved discharge. 5.6.3 INFILTRATION Based on the soils at the Site being comprised of sandy gravel, infiltration or dispersion is feasible on the lot. Per City of Federal Way guidelines full infiltration appears feasible on the lot based criteria in the 2016 King County Surface Water Design Manual (KCSDM). Full infiltration is feasible if the site soils consist of coarse sand, cobble, or medium sands per Appendix C, Section C.2.2.2 KCSWDM. Site soils consist of sandy gravel, meeting the soil criteria for full infiltration. The sandy gravel soils were present to the depth of our explorations, 8 feet below existing grade. No groundwater or signs of seasonal high groundwater were observed in our subsurface explorations. The site soils do not meet the requirements to provide water quality treatment for pollution generating surfaces (driveways) and therefore infiltration of any pollution generating surfaces will need to have some level of water quality treatment before being infiltrated. Non -pollution generating surfaces (roofs, patios, etc) can be infiltrated directly, without treatment. Full infiltration on single-family lots is typically facilitated using gravel filled trenches or dry wells. Sizing criteria for gravel filled trenches and drywells, based on square footage of impervious area is provided in the KCSWDM Appendix C Sections C.2.2.3 (gravel filled trenches) and C.2.2.4 (drywells). The sizing criteria for coarse sand or cobbles should be used for sizing the trench or drywells based on the site soils. mom ■M RILEYGROUP Geotechnical Engineering Report 11 Twin Lakes residence, Federal Way, Washington May 10, 2018 RGI Project No. 2018-112 5.7 UTILITIES Utility pipes should be bedded and backfilled in accordance with American Public Works Association (APWA) specifications. For site utilities located within the right-of-ways, bedding and backfill should be completed in accordance with City of Federal Way specifications. At a minimum, trench backfill should be placed and compacted as structural fill, as described in Section 5.2.4. Where utilities occur below unimproved areas, the degree of compaction can be reduced to a minimum of 90 percent of the soil's maximum density as determined by the referenced ASTM D1557. As noted, soils excavated on site may not be suitable for use as backfill material. Imported structural fill meeting the gradation provided in Table 2 should be used for trench backfill. 6.0 Additional Services RGI is available to provide further geotechnical consultation throughout the design phase of the project. RGI should review the final design and specifications in order to verify that earthwork and foundation recommendations have been properly interpreted and incorporated into project design and construction. RGI is also available to provide geotechnical engineering and construction monitoring services during construction. The integrity of the earthwork and construction depends on proper site preparation and procedures. In addition, engineering decisions may arise in the field in the event that variations in subsurface conditions become apparent. Construction monitoring services are not part of this scope of work. If these services are desired, please let us know and we will prepare a cost proposal. 7.0 Limitations This GER is the property of RGI, Powell Custom Homes and Renovations, and its designated agents. Within the limits of the scope and budget, this GER was prepared in accordance with generally accepted geotechnical engineering practices in the area at the time this GER was issued. This GER is intended for specific application to the Twin Lakes residence project in Federal Way, Washington, and for the exclusive use of Powell Custom Homes and Renovations and its authorized representatives. No other warranty, expressed or implied, is made. Site safety, excavation support, and dewatering requirements are the responsibility of others. The scope of services for this project does not include either specifically or by implication any environmental or biological (for example, mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, we can provide a proposal for these services. LW RILEYGROUP Geotechnical Engineering Report 12 Twin Lakes residence, Federal Way, Washington May 10, 2018 RGI Project No. 2018-112 The analyses and recommendations presented in this GER are based upon data obtained from the explorations performed on site. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear evident, RGI should be requested to reevaluate the recommendations in this GER prior to proceeding with construction. It is the client's responsibility to see that all parties to the project, including the designers, contractors, subcontractors, are made aware of this GER in its entirety. The use of information contained in this GER for bidding purposes should be done at the contractor's option and risk. now ■W RILEYGROUP USGS, 2017, Tacoma North, Washington Approximate Scale: 1"=1000' USGS, 2014, Poverty Bay, Washington 7.5-Minute Quadrangle 0 500 1000 2000 N Corporate Office 17522 Bothell Way Northeast -Bothell, Washington 98011 Phone: 425.415.0551 RILEYGROUP Fax:425.415.0311 Twin Lakes Residences Figure 1 RGI Project Number Date Drawn: Site Vicinity Map 05/2018 2018-112 Address: 3198X 36th Avenue Southwest, Federal Way, Washington 98023 = Test pit by RGI, 5/1/18 = Site boundary Approximate Scale: V=20RM ' 0 10 20 40 N Corporate office Twin Lakes Residences Figure 2 17522 Bothell Way Northeast RGI Project Number [tO5/201:8 e Dran: - Bothell, Washington 98011 Geotechnical Exploration Plan �+ {� Phone:4 Washington 2018-112 RILEYGR"UP Fax: 425.415.0311 Address: 3198X 36th Avenue Southwest, Federal Way, Washington 98023 12" Minimum Wide F Free -Draining Gravel Slope to Drain T_ 12" min. • ° .. - .- . • . _. _ .. . � _ I Filter Fabric Material 00 PLO •_ Excavated Slope (See Report for Appropriate Incliniations) Compacted Structural Backfill (Native or Import) i.......... _ ' � 12" Over the Pipe 4" Diameter PVC 3" Below the Pipe Perforated Pipe Not to Scale . - corporate office Twin Lakes Residences Figure 3 17522 Bothell Way Northeast RGI Project Number Date Drawn: .-Bothell, Washington 98011 Retaining Wall Drainage Detail 05/2018 Phone: 425.415.0551 2018-112 RILEYGROUP Fax: 425.415.0311 Address: 3198X 36th Avenue Southwest, Federal Way, Washington 98023 J Building Slab 44 " IrV acted ruomp... �.. • _ Structural _ Backflll \ .4 Filter Fabric / e . i D ❑ 4- ,-4FF D * a j .. rJ a •J 4" Perforated Pipe 3/4" Washed Rock or Pea Gravel Not to Scale Corporate Office Twin Lakes Residences Figure 4 17522 Bothell Way Northeast RGI Project Number Date Drawn: .-Bothell, Washington 98011 Typical Footing Drain Detail 05/2018 Phone: 425.415.0551 2018-112 RILEYGROUP Fax:425.415.0311 Address: 3198X 36th Avenue Southwest, Federal Way, Washington 98023 Geotechnical Engineering Report May 10, 2018 Twin Lakes residence, Federal Way, Washington RGI Project No. 2018-112 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING On May 1, 2018, RGI performed field explorations using a rubber tired backhoe. We explored subsurface soil conditions at the site by observing the excavation of two test pits to a maximum depth of 7 feet below existing grade. The test pits locations are shown on Figure 2. The test pits locations were approximately determined by measurements from existing property lines and paved roads. A geologist from our office conducted the field exploration and classified the soil conditions encountered, maintained a log of each test exploration, obtained representative soil samples, and observed pertinent site features. All soil samples were visually classified in accordance with the Unified Soil Classification System (USCS). Representative soil samples obtained from the explorations were placed in closed containers and taken to our laboratory for further examination and testing. As a part of the laboratory testing program, the soil samples were classified in our in house laboratory based on visual observation, texture, plasticity, and the limited laboratory testing described below. Moisture Content Determinations Moisture content determinations were performed in accordance with ASTM D2216-10 Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass (ASTM D2216) on representative samples obtained from the exploration in order to aid in identification and correlation of soil types. The moisture content of typical sample was measured and is reported on the test pits logs. Grain Size Analysis A grain size analysis indicates the range in diameter of soil particles included in a particular sample. Grain size analyses was determined using D6913-04(2009) Standard Test Methods for Particle -Size Distribution (Gradation) of Soils Using Sieve Analysis (ASTM D6913) on one of the samples. ■I= I iIN RILEYGROUP Project Name: Twin Lakes Residences Test Pit No.: TP-101 Project Number: 2018-112 1 ■W Sheet 1 of 1 Client: Powell Custom Homes and Renovations RILEYGRQUP Date(s) Excavated: 511118 Logged By CM Surface Conditions: Grass Excavation Method: Backhoe Bucket Size: 18" Total Depth of Excavation: 8 feet Excavator Type: Backhoe Excavating Contractor: Kelly's Excavating Approximate Not surveyed Surface Elevation Groundwater Level Not encountered and Date Measured Sampling Grab Method(s) Compaction Method Bucket tamp Test Pit Backfill: Cuttings Location 3198X & 3198X 36th Avenue Southwest Federal Way. Washin ton 98023 maQ. . a� E o E o U U N rn U > n E E U a m w in MATERIAL DESCRIPTION REMARKS AND OTHER TESTS p cn Tpsl 24" Topsoil and rootmass P101- 6% Moisture GP ©a Brown to gray sandy GRAVEL with trace silt, moist, _ medium dense, slight iron oxidation �o �oe �Ia® lo Sol o. 69P o. 0 f? o i —Becomes very dense 5% Moisture boo o. o a. Test pit terminated at 8 feet bgs. 10 — The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name: Twin Lakes Residences Test Pit No.: TP-102 Project Number: 2018-112 ■� Sheet 1 of 1 Client: Powell Custom Homes and Renovations RILEYGROUP Date(s) Excavated: 5/1118 Logged By CM Surface Conditions: Grass Excavation Method: Backhoe Bucket Size: 18" Total Depth of Excavation: 6 feet Excavator Type: Backhoe Excavating Contractor: Kelly's Excavating Approximate Not surveyed Surface Elevation Groundwater Level Not encountered and Date Measured Sampling Grab Method(s) Compaction Method Bucket tamp Test Pit Backfill: Cuttings Location 3198X & 3198X 36th Avenue Southwest Federal Way. Washington 98023 n a) � a> E a`) � Z (D E o T (n U J U m MATERIAL DESCRIPTION REMARKS AND OTHER TESTS Tpsl 6" Topsoil and rootmass GP a o Brown to gray sandy GRAVEL with trace silt, moist, PTQ2_ 0 o e v medium dense, slight iron oxidation 4% Moisture op—Becomes a• a°v p. e°a gray p. as o. a�P vo—Becomes 04 very dense P Q Q 6%Moisture 10 e6v o. Test pit terminated at 6 feet bgs The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name: Twin Lakes Residences Key to Logs Project Number: 2018-112 Sheet 1 of 1 Client: Powell Custom Homes and Renovations RILEYGROUP O °' N E N 0 U) o U N U W t N (0 U) Q f0 U) U) U) D o U MATERIAL DESCRIPTION I REMARKS AND OTHER TESTS COLUMN DESCRIPTIONS 1 Elevation (feet): Elevation (MSL, feet). 2 Depth (feet): Depth in feet below the ground surface. L3J Sample Type: Type of soil sample collected at the depth interval shown. ® Sample Number: Sample identification number. FIELD AND LABORATORY TEST ABBREVIATIONS CHEM: Chemical tests to assess corrosivity COMP: Compaction test CONS: One-dimensional consolidation test LL: Liquid Limit, percent MATERIAL GRAPHIC SYMBOLS R v Poorly graded GRAVEL (GP) TYPICAL SAMPLER GRAPHIC Auger sampler mSYMBOLS Continuous Bulk Sample Grab Sample 3-inch-OD California w/ ' 2.5-inch-OD Modified brass rings California w/ brass liners CME Sampler Pitcher Sample GENERAL NOTES e5 USCS Symbol: USCS symbol of the subsurface material. B Graphic Log: Graphic depiction of the subsurface material encountered. �7 MATERIAL DESCRIPTION: Description of material encountered. May include consistency, moisture, color, and other descriptive text. ® REMARKS AND OTHER TESTS: Comments and observations regarding drilling or sampling made by driller or field personnel. PI: Plasticity Index, percent SA: Sieve analysis (percent passing No. 200 Sieve) UC: Unconfined compressive strength test, Qu, in ksf WA: Wash sieve (percent passing No. 200 Sieve) 2-inch-OD unlined split spoon (SPT) Shelby Tube (Thin -walled, fixed head) OTHER GRAPHIC SYMBOLS Y Water level (at time of drilling, ATD) Water level (after waiting) Minor change in material properties within a stratum — — Inferred/gradational contact between strata — 7 — Queried contact between strata 1: Soil classifications are based on the Unified Soil Classification System, Descriptions and stratum lines are interpretive, and actual lithologic changes may be gradual. Field descriptions may have been modified to reflect results of lab tests. 2: Descriptions on these logs apply only at the specific boring locations and at the time the borings were advanced. They are not warranted to be representative of subsurface conditions at other locations or times. The Riley Group, Inc, 17522 Bothell Way NE, Bothell, WA 98011 PHONE: (425) 415-0551 FAX: (425)415-0311 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 GRAIN SIZE ANALYSIS ASTM D421, D422, D1144, D2487, D6913 PROJECT TITLE Twin Lakes Residence - Lot 1 PROJECT NO. 2018-112 TECH/TEST DATE CM WATER CONTENT (Delivered Moisture) Wt Wet Soil & Tare (gm) (w1) Wt Dry Soil & Tare (gm) (w2) Weight of Tare (gm) (w3) Weight of Water (gm) (w4=w1-w2) Weight of Dry Soil (gm) (w5=w2-w3) Moisture Content (%y (w4/w5)*100 SAMPLE ID/TYPE TP-102 SAMPLE DEPTH t' 5/2/2018 DATE RECEIVED 5/2po18 Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture 1182.3 Weight Of Sample (gm) 1137.1 1137.1 Tare Weight (gm) 15.8 15.8 (w6) Total Dry Weight (gm) 1121.3 45.2 SIEVE 1121.3 Cumulative 4 Wt Re t Wt-Tare CNBetained) % PASS 4-Tara Irwr rvrlw6i-iom 1100-%ret) % COBBLES % C GRAVEL % F GRAVEL % C SAND % M SAND % F SAND % FINES % TOTAL D10 (mm) D30 (mm) D60 (mm) Cu Cc 0.0 12.0' 3.0' 2.5' 2.0' 1.5' 1.0' 0.75' 0.50' 0.375' #4 #1C #2C #4C #6C 50.3 14.2 5.6 17.2 9.8 2.8 100.0 0.3 2 35 116.7 0.4 o� P A S S I N G #10C #20C PAN 15.8 0.00 0.00 100.00 15.8 0.00 0.00 100.00 450.2 434.40 38.74 61.26 579.8 564.00 50.30 49.70 674.6 658.80 58.75 41.25 739.2 723.40 64.51 35.49 802.2 786.40 70.13 29.87 995.2 979.40 87.35 12.65 1093.8 1078.00 96.14 3.86 1105.6 1089.80 97.19 2.81 1137.1 1121.30 100.00 0.00 12" 3" 2" 1".75' .375" #4 #10 #20 #40 #60 #100 #200 100 90 80 70 60 50 40 30 20 10 0 :obbles :oarse gravel :oarse gravel .oarse gravel :oarse gravel :oarse gravel fine gravel fine gravel fine gravel -oarse sand medium sand medium sand `ine sand fine sand fine sand Fines silt/clay 1000 100 10 1 0.1 0.01 0.001 Grain size in millimeters DESCRIPTION Sandy GRAVEL with some silt USCS GP Prepared For: Pwell Custom Homes and Renovations Reviewed By: KMW RILEYGROLIP