HomeMy WebLinkAboutPettygrove's 1st Block 25 - Geotechnical Report 2005.02.22q;+ f/" -tul
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GEOTECHNICAL REPORT
Prepared For Daryl Gillette
February 22,2005
For the property Described As
Tax # 984902501
Section 2, Township 30 North, Range 1 West, W.M
Jefferson County, Washington
Prepared by
NORTHWESTERN TERRITORIES, INC.
717 S. peabody Str:eet
Port Angeles, Washington 9g362
Phone 3604s2-8491 pai goo+s2-8498
Web Site www.nti4u.com
E-mail info@nti4u.com
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0fcrry PORI
8CD
NTI
JLS GROUP,
ING.
February 22,zOOs
Daryl Gillette
479 N. Jacob Milter Rd
Port Townsend, WA 98368
Site Description
NORTHWESTERN TERRITORIES, INC.
A JLS GROUP COMPANY
717 SOUTH PEABODY STREET, PORT ANGELES, WA 98362tr Engineerc a Land Surveyors n Geologr.ststr Construction lnspection a Materiats Testing
(360) 452-8491 FAX 452-849g www.nti4u.com E-Mait: info@nti4u.com
Geotechnical Report for
Tax # 984902501
Subject: Geotechnicall-"pgrt fgr,theProp-erty Des-cribed as Tax # 9g4902s01, Located inSection 2, T3ON, R1W, W.M., Jbtteison County, WA
Dear Mr. Gillette:
Background
l!,y9ur.reguest, Bill Paytot^Elq,l"9llg.9:"J:9lrlt *itf Norrhwestern Territories, rnc. (NTt)conducted a geotechnical inspe-ction of ine aooie-rheniioneo-propoiv on-F"6tr"rv 1, 2005. Theq_{qose of pi9 inspection was to examine the subject propertf, ov visirairn"*. and makele-cglnmendations regarding the developmelt of ttie plop6rtv in ;";ord;;i,itn section19.05.100 of the Port Townsend Municiirat Code (pT[/Ci. -:' --'
The subject property is located on the west side of Morgan Hillin port Townsend (Figures 1 and2). The propertv is bounded on the north by unop"n"o'tr-btr""i, on t".ouii'oy unopened Lstreet, on the east by Mapre street and onine r,riest bt;;.-idfiti.r prtJ.,itr "'
The plqperty is.well^v.e-gel3t?d with young to mature trees and brush. Some of the trees havecurved trunks, indicatingrlltllql g"wnislope cie"pot tt," shaltow;rrf"; soit is occurring insofg areas. No springs or seeps were obse*"0 onin" propertv and no evidence of slideactivity was observed
r.n" pfqP"rty slopes wegtwgrd predominaltty at a.slope of 337q, increasing to 36% at the southside of the propefi. There is ohe area in thri souihea'ii
"orner of the prgperty roughly 50, x s0,with.a slope ot..!s(- The slope ?lgles were meisu6; wiih a hand held clinometer. Theseangles are well below the tyfical "dngle of reposJ'-wnlcn G defined ;th; ,f,u*ffi; .ilft o,.
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ang
and
le at which loose, cohesionless material remains stable. lt commonly ranges between 33
37 degrees (65% and75%) on natural slopes".
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Geologic Conditions
The subject property is in an area mapped by the SCS Soil Survey of Jefferson County as the
Dick loamy sand, 0 to 15 percent slopes (DcC). This soil formed in glacial outwash on plains
and terraces. Permeability of this soil is listed as rapid, runoff is listed as slow and the hazard of
water erosion as slight. The'Soil Survey maps the soil to a depth of five feet.
The Washington Department of Ecglogy's "Geologic Map of Eastern Jefferson County''maps
the soil at the subject property as lodgement till (Qv't) of the Fraser Glaciation. The ioil is
described as a compact unsorted mixture of boulders, cobbles and pebbles in a matrix of sand,
silt and clay. Generally overlain by a few feet of recessional drift or Holocene sediments.
The CoastalZone Atlas of Washington describes the sqil in the area of the subject property as
thd Vashon lodgement till (Qvt1), a compact mixture of boulders, cobbles, pebbles, sand, silt
and clay, generally overlain by 1-5 feet of ablation till. The Atlas also describes this soil as being
excellent for foundation stability and good for seismic stability. The Atlas maps the slope stability
of the west slope of Morgan Hill as lntermediate (l). The Atlas states that this soil stands in
steep natural and cut slopes for long periods. For comparison purposes, the vertical bluffs
downtown along Water Street are mapped as this same soiltype.
Visual observations made at the site and in the area were consistent with the above mentioned
soit descriptions. Two shallow hand-dug test pits,were excavated on the property to a maximum
depth of three feet, one at the north end and one at the south end. The surface layer down to
about 1.5' is dark brown topsoil. Belowthe topsoil, the material is brown silty sarid with gravel
becoming lighter in color and dense at about 3'. No groundwater was encountered. This lower
material is interpreted as being glacialtill and appeared to be the same material as is exposed
in a road-cut on.Maple St near the subject property.
Conclusions and Recommendations
The subject property appears grossly stable and the development of the proper.ty seems
feasible from a geotechnical perspective. The property is wellvegetated and no apparent slide
activity was noticed. The slope angle is well below the angle of repose. No springs or seeps
were noticed on the property and the toe of the slope is not being actively undercut as is
common with a marine bluff.
Based upon our investigation, which included soiltest pits, a review of available literature and
conducting a field visit, it is our opinion that geological ESA's aqd/or their buffers do not exist
on-site as defined by Sections 19.05.020 and 19.05.100(B) of the'Port Townsend Municipal
Code exoept for the area in the southeast corner of the.property where the slope is greater than
40%. This area is roughly 50'square with a slope o145"/".
The following recommendations should be considered with regards to development of the
subject property:
1. Due to the presence of the ESA in the southeast corner, we recommend that the
property bb OiviOed in such a way as to avoid development within the ESA. This might
be accomplished with four, three or tw-o lots, and/or varying the lot dimensions. We
further recommend that the standard 25' buffer.from the ESA be reduced to 10'.
' 2. Based upon our investigation, we conclude that it is not feasible to put parklng on the
lots and recommend off'street parking from Maple Street utilizing engineered retaining
walls with backfill or some other type of engineered parking structure. There are many
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benefits to this approach. Access from L or M Street would require opening the ROWand new road construction up.slope with cons.iderable fill necedsary to tie irito tvtaptest,which is not.preferable..Creating an access drive onto the property from Maple Sireet '
would greatly increase the amount of impdrvious surface area as ivell as inirease theamount of vegetation disturbance, Temporary construction access to the property will benecessary, but should be restored after eonstruction.
3. F.ootings shouldbe founded in the native undisturbed compact glacialthat underlies the: site at a depth.of approximately three feet below the grounb suiiace. Footings should bea minimum of three feet below the ground surface. -
4. Silt fences or othef.sediment control devices will be needed during constrUction suchthat sedimentation to adjacent. properties does not exceed predev:elopment conditions.Please see the enclosed City of Port Townsend "Erosion &'sediment Control practices"
handout for further information and requirements regarding this issue.
5. Clearing of .vegetation that i: ng99::3ry for construction, excavations and earthwork
should be done during the dry season.
6. Footing drains should be utilized for the houses and any retaining walls.
7. Surface runoff from hard surfaces such,as roofs, parking areas, walkways and patios
3nd drainag.e from footing drains should be contidlleo aio rout6d to the'cityrCio'im sewerif available (preferable) or to a drainage control system such that surface water
disch.arge to_adjacent properties does not signifiiantly exceed predevelopment
conditions. Footing'drgins- should not be conhected to other driins- All drainage controldevices should be. maintained in good.worfilg order and inspected ai teasi oEcJ; y;;;An engineered drainage control plan.should b=e developed fcjr this property to addrdsithis issue. NTf can perform this task if requested.'
8. We understand that as a condition of this proposal, Maple Street willbe paved in front ofthe propertY. I drainage ditch or other fcirm of drainagd collection shoul<i be constructed'along Maple Street to intercept off-site water and prevent it from tlowing onto theproperty.
9.. After construction, disturbed areas should be revegetated. Native deep-rooted
vegetation that requites little or no irrigation wouldbe the most beneficial. Any bare
. areas that develop should be revegbtated. Lawn debris, brush, etc. should ncit be piled
up on the property.
10. Vegetation outside the construction area should be left in as natural a state as possible.
lf an enhanced view is.desired, trees should be pruned rather than topped such tfrai tnetrees are not damaged.
11. Heavy irrigation or other activities that would contribute large quantities of water to the
Soil should be avoided. One cause of slope instability is the prisence of excessive
, groundwater.
Based on the findings,.recommendations and limitations of this report, the proposal should poseno unreasonable threat to persons or property nor decrease slopd stabitity.
For further information please review the three qncloged publications published by theWashington State Department of Ecology (DOE) entitled: "Slope Stab'ilization and ErosionControlUsing..Vegetation", 'Vegetation Mahagement: A Guide'for Puget Sound Bluff property
Owners" and "Surface Water and Groundwater on Coastal Bluffs". Thise publications arb no*out of print but can also be viewed on the DOE website at:
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highly recommended.
Limitations
This report has been prepared for the exclusive use of our client in.conjunclion with the above
referenbed project; The report has not been prepared lor: use by others or for other locations.
Others may us-e it only with the expressed written permission of the Engineer.
Within the limits of scope, schedule and budget, this report was prepared in general.accordance
with dccepted professi6nal engineering and geological principles and practices in this or similar
localities bt tnei time the report was prepared, No other warranty, expressed or implied, is made
as to the conqlusions and professional advice included in this report.
The observations, conclusioris and recommendations presented in this report were ba$ed on
our visual observations of the subject property at the time of our site visit; no laboratory tests
were performed. Soil and geologic conditions can vary significantly across a p_roject site. lf there
is a substantial lapse of time, conditions at the site have changed or appear -different than those
described in this iepoit, we should be contacted and retained to evaluate the changed
conditions and make modifications to our report if
under the 1993 and 1994 year heading. The DOE website
regarding slope stability and site development and isSOmoren
necessary
Sincerely,
NORTHWESTERN TERRITORIES, INC.
Robert A. Leach, P.E., MBA
Frincipal Engineer
/) a-['3ttf
Bill Payton, L.E.G.
Engineering Geologist
G:\Gen\Bill\Reports\GLTD0501.slope stability.2(30-1).Morgan Hill.PT.doc
EXPIRES 12t30t2004
Expires 1 1/06/05
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EROSTON & SEDIMENT CONTROL PRACTICES
MINIM(.IM REQUIREMENTS foT
CLEARING, GRADING, FILLING, AND DRAINAGE FACILITIES
Land alteration and land disturbing activitics such as clcaring, grading, cutting, fitling, and consurjction can creatc erosion andscdimentation which adverscly affcct thc qualiry of our locaistr""ms,-*"ttar,dr, po.t lor"nscnd Bay, and thc Strait of Juan dcFuca' Thc goal of the following MIMMTIM srosion control practi""s is to see that no scdimcnt leaves thc construction sitc.These minimum practices are to bc followcd for gll land disruibing acrivirics whcthcr a separarc pcrmit or crosion and sedimentcontrol plan is rcquired or nor.
(l) coNsTRUcTIoN SITE ACCESS: Provide a clean hard surface for vchicles cntering thc consrruction site to eliminatetrachng of soil onto the street. This access should be limited to one routc, whercvcr porribl". surfacc materials may includcquarry spalls, cnrshed rock, river rock, or othcr non-soil or non-sand materials.
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.'rd, t'OU^nRY SP^|-!S
Maintarance:PR@|O€ FUU_ *rotH oFD€n€ss/EcA€ss ^nFrThc cntrance shall be mdintained in a condition which wilt prcvcnt tracking or flow of mud onto pubtic riglts-of-way. This mayrcquire pcriodic top dressing with 2-inch storic or othcr appioved material as conditions dcmand, and rc,pair and/or cleanout ofany structures uscd to trap scdiment. AII matsrials spillcd, .dropped,.washcd or trackcd Fom vehiclcs onto ,o"a.,""yi * in,ostorm drains must bc rernovcd immediatcly.
(2) GRADING: Thc follorving are the minimum standards for grading activitics:l' Grading shall not contributc to or crcatc tandslidcs, accclcratla soil crecp, or scttlerncnt of soils.2' ' Natural land and water fcaturcs, vegctation, drainage and other natural f""trrrs of the sitc shall be reasonable prcscrved.3' ' Grading shall not creatc or contributc to flooding Jrosion, increascd turbidity, or siltation of a watcrcoursc.4. Groundcover and trcc dist.rbancc shall bc minimizcd. --r ' -' -' - "-rvtwvsD.'
5' Grading opcrations shall bcconductcd so 8s to cxposc thc smallcst practical area to crosion for the least possiblc timc.6. Grading shall not'divsrt cxisting watcrcordcs o, irain"g"*"y,
(3) ct TS AND Frr r s Thc foltowing arc thc minimum stsrdards for cutting and filling:l' cut slopcs shall bc no stceper than is safc for thc intcndcd usc. cut slopo goit", th- fivc (5) fcct in hcight shall bc no. :!::P* tttan two (2) horizontal to 6ne (l) vcdicsl, cxccpt whcre approvtd rctaining walls are to bc instailcd.' 2' F'illing should only occur wherc the gmund snrfacc hasbcqn pr.p'o"a by rcmoval-of vcgctation -altt o *it"ur"matsrials orprcparation ofsteps wherc nahrral slopes ae stecpcrthan fivc to one (5 to rj. Fill slopcs ,t JJ i"i t"constucted on nahrat slopcs grcatcr than nro. to onc (2 to l).
3 ' Fill slopcs shall bc no stecpcr- than is safe for thc intcndcd usc. Fill slopcs grcatcr than five (i) fcct in hcight shall be nostccpcr than trvo (2) horizontal to onc (l) vcrticat, cxccpt whcre "ppro""d.a"ining wall are cnginccrcd and installcd-1- ltccpl cut/fills may b,c pcrmittcd if supportcd by an approvcd soils/gcologrca rcp-ort.
l' lut utd fill slopcs shalt not cncroach upon adjoining prop"rty without r,.riien appro,rat of thc adjaccnt owncf,.6' Cut and fill slopcs shall bc providcd with subsurfacc rna strrft"" drainagc pmvisions to appmvcd dischargclocations asnccessary to retain the slopc.7' Thq faccs ofslopcs shall bc prcparcd urd maintaincd to control opd^*.- chcck dams, rip,rap, plantings, tctrraccs,divcrsion ditchcs, ldimcntation pon&, staw batcs, othcr mcthods shall bc cn ptoy"i*ircrc ncc6sary to controlcTosion and providc safcty. The crosion control mc&surc! shall bc initiated or ins;tallcd ss soon as possiblc and shall bcmaintained by thc owncr-8' Fill matcrials uscd as a strustural fitl shall bc corqiactcd in accordancc'rvith thc requiremsnts applicablcto thc funncrxtc.'
practicc for thc ritc, which cut rodi vcgaation, plartlc covcrlng, mulching, ctc.
All oxposcd rnd unworkcd roils shall bc stabillzcd using tho bcst managemcll
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(4)
(j) CLEAN-LP: pcrsons and/or firms "ngageiin clcaring, grading, and filling or drainagc activitics shall bc rcsponsiblc for thc
."int"n*". of work areas frec of dcbris or other matcrial that may causc damag€ to or siltation of cxisting or ncw facilitics or
have thc potcntial ofcrcating a safcty hazard.
(6) CONTROL OF SITE RIJNOFF: Adjaccnt propcrtics shall bc protcctcd from scdimcnt by installation o.f (a) a silt banicr
ao,unrr""nt of thc work using a silt fcncc and/or hay balcs; (b) a surnp or basin with a filtering systsm to aicommodatc thc
directcd runoffprior to dischargc to thc cxisting drainage hcilitics'
STRAW BALES:
l. Sccure balcs with 2 stakcs or rcbar driven through each balc-
2. -Ends of adjagcnt.bglcs shall tightly abut ong 449ther.
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Maintcnance:
ioqtt a !xr4 ae t€{tr il^r ac{r a
Straw bale barries shall be inspccted immcdiately aftcr each runoFproducing rainfall and at least daily during prolongcd
rainfall.c Close attealdon shall be paid to the rcpair of damagcd bales, cnd runq and undercutting bcneath balcs.
o Scdiment deposia should be rcmoved after each runoff-producing rainfall.
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l. Thc riraterial used in a filter fatric fenee must have sufficrant stcngth to withstand various s8ess conditions and it alsc
must havc thc ability to allow passagc of watcr whilc retaining soil particlcs, The ability to pass flow through must be
balanccd wittr the matsrial's ability to trap scdimcnts
2. Monofilamsnt and non-wovcn gcotextilcs shall have an A.O.S. of 70.
3. Slit film fabrics shall havc an A.O.S. of40 to 60.
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. :.:t .j ,. .,. ..:4. Inspcct inncdiarcly alq 6ach r-atlltl, ana * lfast aaity-drlg prolongcd raiDfsll. Rcpair as ncccssary.
5. Scdimcqt uust bc removcd whco it reachcs rp'prolinately ono third thc hcight of thc fcnce, cspccialty if hcavy
ninrarsoqrccad.: .. .,
6. Any scdimcot.dcposits rqraiaUg inplacc after thc,,filtcr
with:thc,ocistlng gradc;.prc,prdis1d:sig{sd"1:,.:;.
fcucc is no longcrreqpircdplaf! bc dressed to confomi