HomeMy WebLinkAbout1994.08.18 - Lynnesfield PUD Proposed Monitoring ProcessENGINEERING
LAND SURVEY]NG
DEVELOPMENT CONSULTING
August 18, 1994
Dear Mr-Hildt,
P.0 Box 2'199 .935 North Fifth Avenue
wA 98382
681-2161 . Far 693-5310
Mr. Michael Hildt, Director of Plannine
Ciry of Port Townsend
54O Water Sreet
PortTownsend, WA 98368
City of Port Townsend
RECEIVED
'AU6 2 2 lggt
Planning and Building
{t your reques! we have reviewed the stormwater dans for the Lynnesfield Ptanned Unit
Development The plan incorporates all applicable Best Management Practices (BMPs) as
defined in the SormwaterTechnical t\rlanual (current edition) ana has been designed in a
manner which will address potential regibnal stormwat€r impacts.
In respolqflqlog{ concern about water levels in the off-site wetland adjacent to the
proposed Pt{D, although we do not anticipate adverse impacts, we have outlined below a
timelineand process for monitoring the effects of sormwater detention on the proposed
project site oir the off-site wetland.-
PROPOSED MOMTORING PROCESS
Step One: Establish Base Data
The first step in a monitoring process will require ttre establishment of base data on the
hydrological conditions of the wedand. As ybu know the wetland has been severely
impacted and is currently in a degraded condition.
Prior to beginning o establish the base data, the construction on the school site and its
related stormwater facilities will need to be completed This is necessary to accurately
assess the schools impqct on water in the region. In addition, the buffer vegetation
enhancement plan designed by Sheldon and Associates will need to be implenrented
The School Dsrict_has agreed to perform 2 soil borings, minimum 20 feet deep, maximum
4O feet deep, to confirm infiltrarion capacity, and to monitor hydrologic conditions in thearea Jones and Stokes will be working with students and teachers this Fall to define
student participation in the enhancement and monioring projects and to cr€ate a scope for
the monioring projecr
We propose to review the scope of the monitoring project to ersure that it will provide the
information necessary o establish base data, specifically a "Historic Water kvel".
We recommend tbat the base daa be established oyer a three year period The three year
periodwill allow for the completion of the school construction and enhancement projects,
re-establishment of the wetland hydrological functions, establishment of an appropriate
vegetative buffer.
ENGINEERING
LAND SURVEYING
P.0. Box 2199 . 935 North Fifth Avenue
Sequim, WA 98382
WETLAND DELINEATION I
DEVELOPMENT CONSULTING
(360) 681-2161 . Fax (360) 683-5310
Toll Free (BBB) 681-2161
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ENGINEERING
LAND SURVEYING
DEVELOPMENT CONSULTING
L'fr(r.l rrLA6
P.O Box 2199.935 Noilh Fifth Avenue
Sequim, WA 98382
681-2161 . Fax 683-5310
April 1994
.CAIUPBELL ruD ET\CINEERIT.IC RHFCRt'
Prepared for:
CAI,IPBELL CTNSTRJ T ICN
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STREET SYSTEMS
The standard street section to be used for this project will consist of 20 feetof asphalt pavenent with an 8 foot graveled shoulder on one side for parking.significant arpunt of the right of way will be taken up with a single grassyswale used as a replacenent to typicat roadside ditches or storm sewers inkeeping with the current trend away frcn asphalt and pipes.
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Grassy drainage ways have been shown to be trernendously beneficial to thequality of storrnvater runoff. With the exception of culverts where streetcrossings cannot be avoided, the entire storrnrrater collection systen will alsoprovide biof i I tration.
The proposed structural section has been successfully used in other areas on theOlynpic P,eninsula and rmy be sqnewhat over designed for areas where good_granular isubgrade soils are encountered. This structural section will be usedfor the first phase of the project. If it proves to be overly thick, a reducedstructural section nay be subnitted for approval.
STORIvilTATER MAT IACEMENT
The proposed storrnvater nranagernent systen provides control of both quality andquantity. fui extensive network of giassy swales will be installed to providebiofiltration of all stornH,ater runoff before it leaves the project site.Crassy swales that are not adjacent tb streets will be constructed to the sanewidth and depth as those.alongside streets
The stornrrater collection systern will collect all runoff frqn the project siteas well as fran an estinatdd 8.3 acres above the site and convey it to anirregularly shaped, three cell detention pond as shown on the plans. Thedetention pond will collect all runoff and release it at a rate less than thatof the existing runoff.
The nngnitude of the existing runoff was determined by breaking the site intothe five basins shown on page I of the technical data. Tinres of concentrationfrqn each basin to the detention pond were calculated as shown on pages Z - Z.Hydrologic groupings of the soils for the five basins were taken frqnU. S.Soil Conservation Service tables. Copies are included as bages 8 - lO of thetechnical data. Runoff curve nur$ers were determined frqn the above noted datausing the chart shown on page ll. Total precipitation was taken frqn theisopluvial charts included as pages 12 - 14. A sunmry of the pertinent datafor determining predeveloprnent runoff is given on page 15.
This data was entered into King County Public Works Departnent's ccrputerprogran FffD for calculation of runoff hydrographs frqn each basin. Thehydrographs were calculated for 2, 25 and lO0 year events. The hydrographs frqnthe 5 basins were then csrbined into single hydrographs designated by the letterz. Printouts frqn the ccrputer run are included as pages 16 - 26 of thetechnical data. Cqrplete tabulated hydrographs for all basins and storm eventsare included as Pages 27 - 44. Page 45 is a graph of the total predevelopnrent
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runof f f r<m the project si te. Peak f lows are 0.21 cfs, 1.72 cfs, an<i 3.12 cfsIor 2 yr,25 yr and 100 yr events respectively. In keeping with currentpr;rctice, the naximrrn allowable offsite flow after developnent was taken to be0.115 cfs, 1.72 cfs and 3.12 cfs for the 2 yr,25 yr, and 100 yr events
respect i vely.
Postdeveloprnent runoff was estirmted in a similar nanner using projected
develoFrnent paraneters. Tinres of concentration were recalculated on pages t5 -50. Runoff curve nunbers reflecting the changed land uses were determineA asshown on page 51. A ccrplete listing of postdevelopnrent runoff .pararneters isincluded on page 52. Pages 53 - 63 contain printouts generated:during theccrputer run. Hydrographs of postdevelopnent flows are included as pages 64 -81. A graph of the cqrbined postdevelopnrent hydrographs is shown on page 82.l'lote that these flows are as yet undetained and greatly exceed the allowableoffsite release rates
These flows are then released into the detention pond as shown on the plans.Various orifice and weir devices are used in cqnbination to produce the desiredrelease rates for given design events. Details of the control structures areshown in the plans. A ccrplete listing of release rates, storage volunes, andother data tabulated as a function of the depth of the pond is given in thestaging table shown on pages 83 - 86. Routing of the 2 year, 25 year and 100year design events through the ponds is shown on the tables shown on pages 87 -98.
Thq greatly irregular shape of the detention pond was designed to increase thelength of shorelines to increase the biofiltration effect and for aestheticpurPoses. The pond is designed to release water over an emergency spillway whenthe depth of water in the pond exceeds 2 feet. The spillway is dlsilned toprevent the depth of water frcn reaching 2.50 feet (depth of flow over thesPillwaY = 0.50 feet).
After biofiltration, detention, settling, additional biofiltration and finally,serving as an aesthetic arnenity, the water witl be released via a 12 inch piplas shown on the plan details.
To reduce the total volune of runoff and to preserve the existing subsurfaceflow regirne to the largest extent possible, roof drains will be routed intodrywells and/or infiltration trenches wherever the soils will allow. While afinal determination will depend of the soils encountered on each buitdins site,it is believed that up to one third of the hqnes could be constructed withinf i I trat ion systerrs for roof drains .
TRA,ISPORTATICN
The prinary nnde of transportation for residents of this project will bepasseriger vehicles. while the project is designed to encturage uses of othernpdes, such as transit and bicycle, calculations of traffic inpacts are nadewith the assurrption that nearly all transportation will be viaprivate passengervehicles- This is done as a conservative measure to ensure inpacts areadequately addressed.
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NOU-14_'96 THU 13:34 ID:PT TOI^,N5END_PLG BLDG TEL NO:?.A6 3A5_429@ H3E3 P61
ci of Port Townsend
Port Towrrrcnd, Washirrgton 9EJ6E Stj.lOOO
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fax (206) 3SS {290
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Erirting Conditionr
A mapped wetland, Townseud Moadows Walsrd, lies approximately 200 ftet esst ofthe project
site (Exhibir E, Aorid Pboto). Towuscnd Meadows generally deffnes thc bottom ofthc drainage
basin and rs such ig the natrud recipicnt of all nrrfacc and srbsurfaoc lateral flows. This swGrtr
ocrc wctloniltas beenr dtered and digrutsd by recent humrn acth/hies. 'In 1990,.rll tbe
vegetrtio rnd topsoil were scrlped to r depth of six inches In 1994, thc Port Toumsend School
District begro construction ofthc Blue Heroa Middle Sohool which borders the w*bnd or two
sidcs. Approxirnrtcly 6,886 squarc feet ofwctlrnd buffer were filled druing corsrustion, A
Buftcr IVftigation Platr wss irylenented to compmsgte for the buffer loss. Using the Weshiogton
Strte Ddprrtmcnt ofEcology Wetlends Reting Sy*em (WDOE: l99l) thc wahnd wts rateA es a
Cless 3 scnrb-shnrb walaad, rcquiring r 50-foot wide butrer in rccordrnce wi& the city's
Environmcatally Sositive Areas ordinence.
A smdl wethn4 co'r'monly hown os tb€ Hsppy Volley WctLsq abuts tho projcct's nontcest
boundsry. This pond hrsbeen enlerged rnd is uscd * r daeodon basin for exising residatisl
devclopment to tho osst. Hsppy Vrlhy Wetlsrd has beeo classified rs a jruirdictiond wdrnd by
thc City of Port Tounseod and is also ratcd as a Closs 3 requiriry a S0-foot wide buffer.
No brsc data exists for historic watcr lwcls in cither ofthe rdjecent wetlards. hrsrant to thc
MDNS for lhe Blue Heron Mddle School, r monitoring rnd rcporting progrsm bas becn
irylcmmted for the Tounscad Mradows W*lsnd. The iutent ofthc moniloring progrrm fo.r the
middle sc,hool is to rpproximate the historicsl rste offlow, ensure that the hydmpaiod is not
rhcred rnd thet nrn-offis treated adequatcly prior to otedng &e wetland. Five'dee,p' boftgs
tre to bs nouitored scasonr& for * ler* firrc yerrs begiooiag.i! 1995. w r* erus 1,
Sevenl ofthe public coomeot lcttcrs ad&csscd watcr quality imfccts. Residents located ctst of
thc sae eloug 43rd Street coryleined of an existing problcm wilh sanding wster during the
wintcr months. Thcy erc cooccroc'il that the problem will bc ooocrbrted by the proposed
dwelopment. Ohcrs rre conceroed thet the project may coDtamnate gxisthg wells in ttc trca
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NOU-14-'96 THU 13:35 ID:PT TOI^INSEND-PLG BLDG TEL NO:286 3A5-4298 H3A3 PO3
Potcutial lgpacts
Potcntirl imprcts to tbe wetlends would be avoided as all dwelopmetrt is proposed outside ofthe
rdjrccnt wetletrds bufhrs flowwer. stormwster runoffwould be increa$d throue[ removd of
mtive vegetrtion and addition ofimpcrvious cufaces. Approximately 45o/o ofthe site would be
covcrcd with impcrvious srhccs. Projcct run-offmsybe contaminated with urban pollutmts
qp7ical ofresidentirl development inchrding oil from crrs, pcsicides, and fenilizen.
The proposcd stornwatcr runlsgqn€ot systeor is designod to traat rnd control excess $ormwcter
nrnoffiom rhe entire site md ro e*iuated 8.3 gcres cbove the she. Run-offwould be conve,ycd
vh grrss.lioed srrrlcs to the stonmrnter detention pond frr weter quality trertrncnt (ClErk bd
Ofrcc; Apdl 1994). After biofiltrrtion, detention, end serttling, the wder would bc relemed vi! e
t2 the
A soil rud wethtrds esses$uleot for sormweter infiltration potential was conducted by Pecific Rim
Soil & Wrtcr (1994). The report $rtesthat thc proposcd dwelopocnr would not sigdficrntly
iryrct the w$er quslity or habitat vrlue oftbe adjecent w€tlslds. As long rc the roilg rrc lot
swerely coryrcted, the weter quantity effects ere eryected to be minimel rnd more rehtcd to
riming ofwrter pulses thrn to totrl volumes. Ttc report recommeods thst the PIJD be dcsigned
1e minimizc soil coryaction, meintain rs much oftte vegaation rs possible, rnd infiltrate roof
nmoffuftere conditions allow. Whilc r fmal daermingtion will depeud on the soilg aeountered
o[ crch building dle, it is e*imated that up to ono third ofrhc houss could bc coustrustcd with
infltrrtiou systcnddry wells for roof dreins (Cl$k Land OSce; April 1994). As c preceution, thc
design ofthe storewator dctcntion pond rsstrmed thst none oftbe homes would hrve seprnte
infiltrrtion sy$cns.
fp prweut possible flooding ofthe llappy Vallry Wotland" rn cmcrgcocy ovcrflow stnrctrc
^ 1ftUA be designed to divert 0ows to the Townseod Mesdows Wethnd. This overflov systcm
$outd bc designed to hendle f,ows for the two year storm evcmt or gxetter. A fiml storuwtta
msrsgement plan, including the dcsign of thc over0owto Tounrscnd Mcrdows, Sould be
approvod by the Pubtic Works Dircctor pdor to the issrgnc€ ofthe clerring md gnding perndt.
Mrinteirrncc oftf,c stormwster rnnstcnlcnt systcnil would bc thc rcqponsibility ofthc
Homcoumcrs Association. Provisions for mrbtcaanoo rro inchrdod in thc Draft CC&Rs and
would atso bs inoludsd in thc ProperW Usc and Dwolopme,nt Agreeoent (PITDA), r contnct
bctrveothe devoloper rnd the Ciry.
Potontirl Cuoul*ivc Imprcr
Wrtcr lcvcls in thc Townscnd Meadows wctland may increaso as dwolopmeot within the
watcrshcd basin oontinucs. Tho applicant proposcs to eryport thc Pon Townscnd School
Oistrict end the Crty b monitoring hydroloeic conditious in the arcs. A proposcd monitoring
procedure brs bce,n prepered by Clerk Lmd Office (Augus 18, 1994). To coordinrte monitoring
efforts with the school the epplicant would retdn e quelified wetlssds professiond to:
NOU-14-'96 THU 13:36 TD:PT TOI^JNSEND-PLG BLDG TEL NO:286 385_4294 n3a3 P@4
Rcview the scope of ftc Blus Heron Middle School wetlands monitoring projecr to' ensure thar it will provide the information necessary to establish brsc datr,
ryecificrtly a "hisoric wltcr [evel".
Estabtisb brse dara ovsr a three year period. The three yerr period would allow
for tbe Cor4lletiol of thc school constructioo and cnhancemcnt projcots, rc-
establishment of thc waland hydrological function$, cstablishmc[t of ao
. approrpriatc vcgctrtivc buffcr.
o Approximatc hrsoric wstcr lwcls througl a syrthesos ofbaso data, weathcr
pstterus, urd sslrool site iryacts.
o - R+calculate thc irnrqctg ofthe stotuwater plan for remrining phescs ofthc
.,' Lynnes6eld PUD. Ifnecoeeary, the stormwlterplans would be revised to
tccomodste e faster or dower rats of dacotion as indicatcd by thc historis rrystcr
lwels. Tho rosults aud revised plan would bc srbmitted to the Dhcctor of Public
Workg for approval
t"Doring tho tlree year monitorhg period, the epplicaut proposes to construct up to 45 units- No':' additional units woutd bs constnrctsd ustil tho bese drtr hrd bccn znrlyzed $d the Stormweter''' Mrnsgcmmt Pbn revised accordingly.
The ftrblic Works D€partnent isworking on aloqg-tcnn stonnntcmretcrphnuftid would
rcmcdy pot€otial iuorcasos b hisoric watsr lorils withh Towlssrd Meadows. Strffplrns to
inOleqcot c snaitary scwer trunk lino rqloccmeot pro$$tt Uudcr thie prognm Oe exi*ing l&
incb scwcr ",.in scrying tle orea would be prnlleled by a new linc es s condition of dwelopment
pcrmits. Ultimatety, srwsge would be conducted by the ne$, 30-itroh nrin and the l&inoh main
could bc convcrtcd into o stotmwttor ovcrflow. Thc rpplicmt shoutd contribtrte to ttir progfun :
by cmsrucring rn overflow stnrsture &om lhppy VAby Wetl.tds to the City's cornwnd;{+ t
ltc nc*'stonmilcter over0ow syst€d, would e$ablish mrxinnrn water tevels in the ploposed
stonnwrtcr dctcntion pond rnd Hrppy Vclley Wotland(s) srd aot[rol flows to Towuscnd
Mcrdows Walrnd.
The rpplicent should prnicipete in the replecement progam by providing the hsallatipa ofthc &
l0 be} overflow srructurc which would cotrnect the Happy Vdley Wetlafil to thc stoluwatcr
Edu h 43rd Strc*. This struc$ac would be gnrbbed out to the old sGwsr tnrnk line but not tied
h. ,Once rhe Ciry is pro'parcd to mske the conversiou to the oew scwcr maiq thc conncctioo
would be made. This program would uhimrtely mitigrte the rogional probleor of seesonal hrgh
wrter in tbo brsin vioinity of the Toumsmd Mcsdows WetLnd. In the nerr tem, tbe prorposcd
storr$rttc dete,lrtim pond would odequrtely serve the site.
With implementation of an approvcd stormwrtcr nauagemcnt plan, monitoring of w.tcr lwels,
aad a co.nt"'imcnt to revise tbe ptan rs trecessery rnd contribute to regionrl solutions, tle
projcct's wrrcr quality/qunnthy irupaots would bc uitigrted to a lwcl bclow significance.
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NOU-14-'96 THU 13:3? ID:PT TOUNSEND-PLG BLDG TEL NO:286 38F'-4294 fl383 P65
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To midgare iniEsed run-otf volumes. the applicant shall submit a final stormwatcr
management plan which subshntially conforms with the preliminary ptan (Exhibit C,
Preliminary Drainage Plan) with the addirion of an emcrgency ovcrflo,ry;lq$ownsend
Merdows Wcdand. Thc cmergency overtlow shall be designcd to handlc flows from a
two year st6rm event or greater. A weir notch with a level spreader device is
rccommcndcd. Rock armor and a sccd mix should be used to securo soils. The
applicanr shalt submir rlesign desils for the overflow to Townsend M.adows along with
the final stormwarcr management plan. The Public Worls Director shall review the
plans for compliancc with thc Depanment of Ecolqy Stormwarcr Marugemcnt
Manual. The Public Works Direcror shall approve the overflow design and final
sormwarcr mansgement plan prior to issuance of clearing and grading permits.
9
t3 ro ridguLmpacts to watcr associated with possible incrcascs to thc avcrage
weter level of the Happy Vdley Wedand as a result of the proposed projeq, the
applicanr strall participate in the esnblishment of a rcgional stormwaar facility (if
propoccd by thc City for the drainage basin and included within the Ciry of Port
Townsend Sbrmwater Master Plan) on a proponionote, fsir share basis prior to the-
issuance of the a6th buildirg pcrmit or within fivc years from the darc of PUDA r
apprornl,'*triltrbver'od:urs fi nt.
Should it be detcrmined as a result of the wedand monitoring program that warcr level
increrses ro the Happy Valley Wetland are likely as a direc result of the project, no
additional building permits shall be issued until such time as a regional stormwatcr
facility and/or other appropria@ water-level management devices are insalled. The
Public Works Director shall revicw and approve all proposed improvements and/or
contributioru associared with this rnitigative measure.
Polriblc improvementr may includc, but arc not lirnied b the prorilto.p 9J,FLc.Eh[.lp
rcn bth ovcrflow st4lclps*onnecdng the Happy Valley Wetlarrd to thc lt inch-iffilt
locatdt'tiiiihiii"alrc SuiEilUr the conuolled diversion of rhe ourfall from the project's
deafui6'f,'Fdiiai ini; ali" Townsend Merdow Wctland (provided that this would be
consistcnt with the results of thc moniloring program, and thc applicant is able to
secure a drainage release from the Pon Townsend School District).
Should ir be dorermined by rhe Public Works Dircctor, based on result of the wetland
monitoring program. that addirional construction on the subject propeny would not
adversely affect the watcr levcl of the wetland, the epplicant shall not bc subject to the
aforcmcntioned requircmcnts.
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C. WATER
Existing Conditions
A mapped wetland, Toumsend Meadows Wetland, lies approximately 200 feet east of the project
site (Exhibit E, Aerial Photo). Townsend Meadows generally defines the bottom ofthe drainage
basin and as such is the natural recipient of all surface and zubsurface lateral flows. This seve,n
acre wetland has been altered and disnrbed by recent human activities. In 1990, all the
vegetation and topsoil were scraped to a depth of six inches. In 1994, the Port Townsend School
District began construction oftle Blue Heron Middle School which borders the wetland on two
sides. Approximately 6,886 square feet ofwetland buffer were fiIled during construction. A
Bufer Mitigation Plan was implemented to compensate for the buffer loss. Using the Washington
State Depaltment of Ecology Wetlands Rating Syrt.- (WDOE:1991) the wetland was raied as a
Class 3 scrub-shrub wetland, requiring a 5O-foot wide buffer in accordance witl the city's
Environmentally Sensitive Areas ordinance.
A small wetland, commonly known as the Huppy Valley Wetland, abuts the project's northeast
boundary. This pond has been enlarged and is used as a detention basin for existing residential
development to the east. Happy Valley Wetland has been classified as a jurisdictional wetland by'' the City of Port Torrrmsend and is also rated as a Class 3 requiring a 5O-foot wide buffer.
No base data exists for historic water levels in either of the adjacent wetlands. Pursuant to the
MDNS for the Blue Heron Middle School a monitoring and reporting progxamhas been
implemented for the Townsend Meadows Wetland. The intent ofthe monitoring program for the
middle school is to approximate the historical rate of flow, ensure that the hydroperiod is not
altered and that run-offis treated adequately prior to entering the wetland. Five "deep" borings
are to be monitored seasonally for at least five years beginning in 1995.
Several ofthe public comment letters addressed water quality impacts. Residents located east of
the site along 43rd Street complained of an existing problem with standing water during the
winter months. They are concemed that the problem will be exacerbated by the proposed
development. Others are concemed that the project rnay contaminate existing wells in the area.
Potential Inqpacts
potential impacts to the wetlands would be avoided as all development is proposed outside ofthe
adjacent *.il*d, buffers. However, stormwater runoffwould be increased through removal of
ooii1r. vegetation and addition of impervious zurfaces. Approximately 45%o of the site would be
covered *iUt i-p"*ious surfaces. *oject run-offmay be contaminated with urban pollutants
typical of resideitial development including oil from cars, pesticides, and fertilizers.
The proposed stormwater management system is desiSned to treat and cdntrol excess stormwater
runofffrom the entire site and an estimatld 8.3 acres above the site. Run-offwould be conveyed
via grass-lined swales to the stormwater detention pond for water quality treatment (Clark Land
Oft;ce; Apnl_ l9g4). After biofiltration, detention, and settling, the water would be released via a
12 inch prp"-to the adjacent Happy Valley Wetland. Ultimately, all water will reach the
Toumsend Meadowswetland which generally defines the bottom oftlis basin.
A soil and wetlands assessment for stormwater infltration potential was conducted by Pacific Rim
Soil & Water (1994). The report $ates that the proposed development would not significantly
impact the water qoutity or habitat value of the adjacent wetlands. As long as the soils are not
severely compacted, th! water quantrty effects are expected to be minimal and more related to
'^ ii-iog or*ui.r pulses than to total volumes. The report recommends that the PUD be designed
to minimize soil compaction, maintain as much.ofthe vegetation as possible, and infiltrate roof
nrnoffwhere conditiins allow. While a final determination will depend on the soils encountered
on each building site, it is sstimated tlat up to one third ofthe homes could be constructed with
infiltration systems/dry wells for roof drains (Clark Land Office; April 1994). As a precaution, ttre
design ofthe stormwater detention pond assumed that none of the homes would have separate
infiltration systems.
To prevent possible flooding of the Happy Valley Wetland. an emergency overflow structure
sto'tO be desipned to diveJflows to the Townsend Meadows Wetland. This overflow system
1\r' should be desifoed to handle flows for the two year storm event or greater. A final stormwater
management pI*, iotlodiog the design of the overflow to Townsend Meadows, should be
appro-ved by the public Woiks Direcior prior to the issuance ofthe clearing and grading permit.
Maintenance of the stonnwater management system would be the responsibility ofthe
Homeowners Association. Provisions for maintenance are included in the Draft CC&Rs and
would also be included in the Property Use and Development Agreement (PUDA), a contract
between the developer and the City.
potential Cumulativs Impacts
Water levels in the Tovrmsend Meadows wetland may increase as development within the
watershed basin continues. The applicant proposes to support the Port Townsend School
District and the Clty in monitoring Lydrologic conditions in the area. A proposed monitoring
procedure has beenprepared by Ciari Land office (August 18, 1994). To coordinate monitoring
"trott. with the schoolihe applicant would retain a qualified wetlands professional to:
Review the scope of the Blue Heron Middle School wetlands monitoring project to
eusure that it will provide the information necessary to establish base data.
specifically a "historic water level".
o Establish base data over a three year period. The three year period would allow
for the completion of the school construction and enhancement projects. re-
establishment ofthe wetland hydrological fi.rnctions, establishment of an
. appropriate vegetative buffer.
Approximate historic water levels tluough a qmtheses ofbase data, weather
pattems, and school site impacts.
o - Re-calculate the impacts of the stormwater plan for remaining phases of the,
. ' Lpnesfield PUD. Ifnecessary the stormwater plans would be revised to
accomodate a faster or slower rate of detention as indicated by the historic water
levels. The results and revised plan would be zubmitted to the Director ofPublic
Works for approval.
rV
, \. t fh,rring the three year monitoring period, the applicant proposes to construct up to 45 units. No
-., additional units would be constructed trntil the base data had been analyzed and the Stormwater
Management Plan revised accordingty.
The Public Works Department is working on a long-term stormwater master plan which would
remedy potential increases in historic water levels within Townsend Meadows. Staffplans to
implement a sanitary sewer trunk line replacement program. Under this program the existing 18-
inch sewer main serving the area would be paralleled by a new line as a condition of development
permits. [Jltimately, sewage would be conducted by t].e new 3O-inch main and the l8-inch main
could be converted into a stormwater overflow. The applicant should contribute to this prograp. :'
by construoting an overflow structure from Happy Valley Wetlands to the City's stormwater ryq: /
The new stormwater overflow syste4 would establish maximum water levels in the proposed
stormwater detention pond and Happy Valley Wetland(s) and control flows to Townse,nd
Meadows Wetland.
The applicant should participate in the replacement program by providing the installation of the 8-
10 inch overflow structure which would connect the Happy Valley Wetland to the stormwater
4ain in 43rd Street. This structure would be stubbed out to the old sewer trunk line but not tied
in. 'Once the City is prepared to make the conversion to the new sewer main, the connection
would be made. This programwould ultimately mitigate the regional problem of seasonal high
water in the basin vicinity ofthe Tornmsend Meadows Wetland. In the near term, the proposed
stormwater detention pond would adequately serve the site.
With implementation of an approved stormwater management plan, monitoring of water levels,
and a commitment to revise the plan as necessary and contribute to regional solutions, the
project's water quality/quantity impacts would be mitigated to a level below significance.
o
o
9
l.A r-r\G4.1-\' \)
\5J,szr)
To mirigaG inffised run-otf volumes. rhe applicant shall submit a final stormwater
management plan which substantially confbrms with the preliminary plan (Exhibit C,
Preliminary Drainage Plan) with the addition of an emergency overflow to Townsend
Meadows Wetland. The emergency overtlow shall be designed to handle flows tiom a
two year storm event or greater. A weir notch with a level spreader device is
recommended. Rock armor and a seed mix should be used to secure soils. The
applicant shall submit design details for the overflow to Townsend Meadows along with
the final stormwater management plan. The Public Works Director.shall review the
plans for compliance with the Department of Ecology Stormwater Management
Manual. The Public Works Director shall approve the overflow design and final
stormwater management plan prior to issuance of clearing and grading permits.
LA"Bf2-To mitigate poiential impacts to water associated with possible increases to the average
water level of the Happy Valley Wetland as a result of the proposed project, the
applicant shall participate in the establishment of a regional stormwater facility (if
proposed by the City for the drainage basin and included within the City of Port
Townsend Stormwater Master Plan) on a proportionate, fair share basis prior to the'
issuance of the 46th building permit or within five years from the date of PUDA '
approval, whichever occurs first.
Should it be determined as a result of the wetland monitoring program that water level
increases to the Happy Valley Wetland are likely as a direct result of the project, no
additional building permits shall be issued until such time as a regional stormwater
facility and/or other appropriate water-level management devices are installed. The
Public Works Director shall review and approve all proposed improvements and/or
contributions associated with this mitigative measure.
Possible improvements may include, but are not limited to the provision gf,an eiglt 9o ,
ten inch bverflow strucqle...gonnecting the Happy Valley Wetland to the 18 inch maih
located'iVithin 43rd Str6i: tr the conirolled diversion of the outfall from the project's
detentioii'pcindS into tiie Townsend Meadow Wetland (provided that this would be
consistent with the results of the monitoring program, and the applicant is'able to
secure a drainage release from the Port Townsend School District).
Should it be determined by the Public Works Director, based on result of the wetland
monitoring prolram, that additional construction on the subject property would not
adversely affect the water level of the wetland, the applicant shall not be subject to the
aforementioned requirements.
13
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NO,
P.LAI{
QUANinTY
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I.TEh'IDESCRFTTON
I]NIT
DOLLARS*
l0 lEA ASTM D3034 12'PVC Sewer
Gasketed End Cap
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$125
EA
$125
1l lEA AASFilIO M294 PVC 12" x 10"
Eccentric Reducer
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$50
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$50
l'3 IEA AASHTO 1,1294 PVC 10" x 8"
Eccentric Reducer
at
$s0
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$50
t4 lEA AASFIIO \n94 PVC 8" x 6"
Eccentric Reducer
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$20
EA
$20
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Ring Coupler
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$10
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$10
I6 1EA AASHTO lvI2szPVC 8" Split
Ring'Coupler
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$s
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$8
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$750
per Each.
$2,250
l8 l Each Storm Drain Inlet Structure at
$500
per Each
$500
t9 r32 C.Y.Native Backfill at
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per C.Y
$396
20 20 C.Y Select Backfill at
$20
per C.Y.
$400
2t 5 C.Y Conuolled Density Fill Backfill at
$100
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SURFACE
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