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STATE OF COLOi~~DO <br />DtViS1pN OF.++:NlRnLS nVC GFOLOCY <br />LIWARKr c' ~:': r:; R~faM <br />Carvte, ,o a:a_::U__i <br />r..e:;:0.. ieE ;;c: <br />•nx ~~:~ta;z:gas <br /> <br />~f: Ric.: `:l:Zc <br />olv~srax a= <br />!vIIVERA'..5 <br />GEOLOGY <br />Rti-LAM A~1'Jti <br />r,N~~c~s,.ar• <br />d.': 0~ <br />Cawb • <br />L A][ed SuCCS LAV1rGnntea[ai ~rn[eCLUa nYtnC ~' ~,..!!. w•kh:. <br />Region 8 c...~•;.. o~•..:~ <br />999 lRi, 5ucat- Sui:e 500 '"""''s ~•°': <br />o."vur o:r.n:, <br />Denver CO 30202-2466 <br />Ra: Response :o EPA's Recommendations fcr Gto;:adwater 11er~torr.; in the San Luis Arai <br />Repot. Sar. Luis Project. M-dd-:'.? <br />Dear VIr. ~fuza: <br />Thank ypc For p.-:vid•.n~ the D'.1dG vita a ~cpy o; EPA's Iaaua-;~ ] 8, 2000 :rct reg-azdiag "the <br />poteatiai for itr:pacts to :he town's pt:blic water supply wets item po[eotiai rontatninaa: soaves <br />as protir:zed'oy dre locals." The DMG's review is based t:poa our ltnow:cdgc of the sig. <br />Appaserly,'rls. Kathleen Reil!y, WQCD, asked that the EPA:eview the eroundaakr Iluw <br />sysretz: in :hc vrcialry' of tlx-. Town of Saa Luis. The Division offers our heio by way of <br />commenting oa the EPA repen and tecoamead yaa contact dir. lames Dil!ie, DhfG, if <br />addiunnal data arz: racesaary to ,zrse the .pets conc:ISiune o: to di<.cu~s tcc reponc findings. <br />Ths: repays description of tae ragioaal hydrogeology and local gromdwater usage implies that <br />the Rico Seco alluvial aquifer is a sepazate groundwater pnhway that passes under the town of <br />Saa Luis; after which it joins with the Culebra Czek drunago system. Hoaroves, we did not find <br />e•~idence is the report to su6stansate :~~ t:pntiastioa that t_r' is st..arate groundwater pathway dots. <br />in fact, exiat The report saes this Theory to prcjet*. the time it will ta:'ce far a contaminant plume <br />to teach _'te town's puhlic water supply welt on rite north side of tae conm;:tliry. <br />Or. page 3 of :he report, raider recomcteadsGnns; it is sszted that ~TI:ete u a distance o[ <br />approximately 2.8 miles tmtn the southwestern earner of the permit bauadary to L'te town's <br />closext water supply well "This is as acct•tate statemee~ Howem, the data 3 the permit file <br />indicates thu an alluvial aquifer dots not axis: in this poi ion of the Ecrnut area. The shallowest <br />aquifer is the S ants Fe :ormatioa and the current groundwater levei is approximately 160 fcer <br />from surface. The average measured hydraulic coadut:dviry in his portion of the Santa Fe <br />formation :s 1.04 fcct/day, the hydraulic ; adient !dh/di? is .OS it/f: and the ave.-age porosity is <br />25, su the seerage veioClry is 0.208 ft/day or i5 03 ft/y7. If a ccntataiaant plume existed in this <br />portion of :hc permit area and a prefereltial pathway allowed the groundwater to :law towarl <br />tfie town's water supply well, it rtught, theoretically, take 195 years to reach the water supply <br />well, I-Icwever, aceorting to DMG files, a cunramiraat pl'_rne has not been :erected in she Santa <br />