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<br />Avenue'....c'tofMajnSlreet....ilJbcgreatlyr~u<:edasrunofffromtheDorthernhalf
<br />ofthcSpringGukhba'inisintcrc"Ptedbythepropo~SYSlem.
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<br />The proposed alignment for the slorm sewer bel....een ISlh Avenue at Cambridge
<br />Drivc aoo Loomiller Park is sho....n on Drawings 16 and 17 (,ewer .egmcnt SG.C),
<br />These sew.r, arc ,Iized to can)' all 2'JlCJr runoff thai exceeds lhe capacity l)fthe
<br />""wer along Hover S,rcet [0 the exi.'ting Brickyard delCntion pond, Peak 2-ycar
<br />110..... in the ""werto loomiller Lake r~nge between 132 and 177 cfs.
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<br />I
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<br />The exi.ling configuration of Loomiller Lake provide, adoquatc del.mioncap <lCity
<br />for 2-year rcquircment' allbough improvemenl.to the 1Jl<e outlet ....ork.. will be
<br />needed. Elcvation-stcJragedata for lhe lale Were obtained from dra....ing' contained
<br />in the Loomiller $lOlm Drainage ProjcctrcPOrt (Rcferenc:e-5), [tispropo<edlhal
<br />3 new outl.t 'lrucrure with a 24' oudct pipe be con'tructed. The oormal waler
<br />surfJce .I.valioo wHl remain unchangoo at S500.5 aoo th. mJximum delcntion wat",
<br />.urface will be approximatcly 5504.6 with a flood ,wrag. volume of 22.4 acre-feel.
<br />The lake dischargeal lhe2.YeJr flood sloragt volume ....ill be 2J cf" Elevation.
<br />'to'"Be-di"hargeda1a for Loomiller Lake ar. presented in Table i,
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<br />I
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<br />,
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<br />Low 'urface slopes and numerous underground utililies po'e difficull design
<br />",n'lra"'t, for lhe sewer segment hetween loomiller lake and the Athlelie Field
<br />Delenlion (,ee ,ewer "'gment SG-B. Drawings 13 and 14). The overall ground
<br />surface slcpc between lhe Loomi!!.r Lake outlet and lhe AtbJclic Field Detention
<br />inlcl is appro.imately 0.25 pereent and through ,om. reaches th. proposed ,ewer
<br />will need to be placoo ataO.l percent slop<:. Thcproposcdsewcrsizcrangesfrom
<br />24"inch pipe to 84. pipe and r . 7' box cnlvens, 1he box culverts were
<br />recomm.nded in lieu of pi pc 10 provide the uced.d clearance 10 p"",,ovel exiiti,,&
<br />utililies. namely sallitary sew.rs. The2.yur tlo..... in lhis segmcm range from 23
<br />cfs 'I lhe Loom;ller oulleT TO 169 cfs al the AthlotK: Fieldinlct.
<br />
<br />Thc prOP<'sed ~'ading plan for the A,hlolK: Field Detemion facility i< prc'cnled in
<br />Dm....in~ ~l. The sile i, adoquJte to pro"ide the required 2-year .torage volumc or
<br />
<br />21
<br />
<br />12,7 ac::re.feel at adelCntion water ,ulfact ofappm.imatcly 4991.0. Runofffmm
<br />nuisance and small. more frequent stonn evClllS will bYPJSS Ihc detention faeility
<br />through a 2.5-fOOl high by 5-foot wide reinfon:cd concret" box culvert. Runoffin
<br />exc"" of the iow flow bypass capacily will spill out of the upstream S'Onn sower
<br />ov., J riprapped 'pillway inlo Ihc detention facility. As thi, detcm~," facilily i,
<br />designedfo'lhe2-y'earevent. il;,expccted thai lhc pond will detainwate rrelatively
<br />frequendy, and during pcr;o<.ls of inundalion use oflhe ,ite for recrcalion alpu'l'""es
<br />....m hecurtail.d. The pond facilily will be rcgulaled hy an O,irlCeplate wallow a
<br />maxunumrclea'eof47cfssuchlha1thecapaci1yoftheproposcddo....nsu<:a""ewer
<br />will not be exceeded. The outlel will also indudc a backflow prevcmor (Le, flap
<br />!\ate) wprev.nt the facility from tilling through the outlet pipe. At Ihe prcsent time
<br />it is as,umed lhat an underdmin sy'stem will he required to make Ih. mul1i-u'e
<br />a,peCt5 of the facilily morc viable. During final de,ign. lhe actual need for lhe
<br />underdrain. a! well as Ihe possibility of lowering the pond bottom. Should be further
<br />,.nalY1.edwi'hrespcclloinfonnalionohtainedlbroughfumre.ubsurfacegeolechnical
<br />iuvesligatio"s.
<br />
<br />II i~ pOOJlo,ed lhal J 48.inch sewer be conS1ruc1ed between thc Athle1ic Fi"ld
<br />Delenuon Jnd lhe system outfall at ~pring Gulch. Low available hydraulic grade
<br />will rcquirc lhal a mo<lifloo outfall structure he u><::d, Thc propo,.,.j Morm sewer lioc
<br />mvcn....illbelocatedapprox'matcly j,7 feel oclow lheSpring Gulch inverlclcvalion
<br />at the outfall localion. It is re<:ommended lhal ~ low.flow gravity bypass linc be
<br />installed f,om the outfall 10 a poin! on Spring Guloh downstream a, rc,!uired 10
<br />provid. the necc<,ary gradient (,ee Dra....ings 13), This configuration i, ,imilar 10
<br />th.1tused at the Spring Gulch/171h Avenue outfall which ha, provided "neffective
<br />OUlfall with low mainlenance rcquircmeUls,
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<br />151h AVC"UCSYS1Cm Ext.n,ion
<br />During laIC 1994 and early 1995 the Cityconslrucled ,tOnn !ewer 'mpro\lemenls
<br />"long 15th Avenue OCtw""" Colly.r and Coffman S\reel~, Thc master plan pro~'.les
<br />tOUlCOO Ihi, SYSTem wes1 alu"l( 15th Avenuc to I'ratl Streel and then nU1',h to;> I(~h
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