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## Explanatio n o f

Significan tDifference s Residential Populate d Areas , Operabl e Uni t9 Californi a Gulc

h Superfund Site Lak e County , C O
Septembe r 200 9

# Explanatio n of SigniHcan

tDifference s Residentia l an d Commercia l Populate d Areas , Operabl e Uni t9 Californi a Gulc h Superfun d Site , Lak e County , C O

Septembe r

200 9 1 . Introductio n Thi s Explanatio n o f

Significan t

Difference s (ESD ) present s th e detail s o f a n additio n t o th e remedy selecte di n th e Septembe r 2 , 199 9 Recor do f

Decisio n (ROD ) fo

r Residentia l Populate d Areas , Operabl e Unit

9 (0U9) , ofth e Californi aGulc h Superfun dSite (Site ) i n Lak e County , CO . Operabl e Uni t

9 include s thos e portion s ofth e Sit e wher e th e lan dus e i s residentia l o r tha t are currentl y zone da s residential/populate darea s an da s low-densit y residentia l areas . Futur e lan d us e o f 0U 9 i s expecte dt o continu e t o b e residential . Thi s ESD , prepare din accordanc e with Sectio n 117(c ) ofth e Comprehensiv e Environmenta l Response , Compensation , an dLiability Ac t (CERCLA ) an dwit

h Par t 300 , Sectio n 435(c)(2)(i ) o f Titl e 4 0 ofth e Cod e o f

Federa l Regulations , 4 0 CF R300.435(c)(2)(i) , document s significan t difference s t o th e ROD . Thi s ES D document s th e decisio n to requir e institutiona l control s fo r 1 7 min e wast e pile s withi n 0U9 . Thes e min e wast e pile s hav e soil s a t th e surfac e that

ar e under th e 350 0 mg/K g lea dresidentia l actio n leve l bu t ma y hav e leadcontaminatio n a t dept h that exceed s th e residentia l lea dactio n level . Thi s ES D doe s not chang e or

alte r any elemen t

ofth e Lake Count y Community Health Program(LCCHP) . The U.S. Environmental

Protection Agency (EPA) is the lead agency for

this ESD. The State of Colorado, through the Colorado Department of Public Health and

the Environment

(CDPHE) is the support

agency for

this ESD. -^ 2 . Sit e History , Contamination , an d Selecte d Remed y Th e Sit e i s locate d100 mile s southwes t o f Denve r i n Lake County , Colorado . Th e Sit e cover s 1 8 squar e mile s an dinclude s th e Cit y o f Leadville , variou s part s ofth e Leadvill e Histori c Minin g Distric t an dStringtown . Th e Sit e als o include s asectio n ofth e Arkansa s Rive r fromth e confluenc e o f

Californi aGulc h t o th e confluenc e o f Two-Bi t Gulch . Th e Sit e wa s place do n th e Nationa l Prioritie s Lis t

du e t o concern s abou t

th e impac t

o f min e drainag e o n surfac e water s i n Californi aGulc h an dth e impac t o f heav y metal s loadin g i n th e Arkansa s River . Pursuan t t o a199 4 Consen t

Decree , EP A divide dth e Site into th e 1 2 Operabl e Unit s (OUs) . OU s 1 throug h 1 1 wer e designate dt o facilitat e sourc e remediatio n an dcorrespon dwith area s o f responsibility . OUl2 , whic h cover s th e entir e Site , wa s designate dto addres s Site-wid e Surfac e an dGroundwater .0U 9 Residentia l Populate dAreas , ofth e Californi aGulc h sit e include s portion s ofth e Sit e

wher e th e lan dus e i s residentia l o r tha t ar e currentl y zone da s residential-populate darea s an da s low-density residentia l areas . Potentiall y impacte darea s withi n 0U 9 include dresidentia l yards , vacan t lots , parks , schoo l yards , playgrounds , an dcommunity us e areas , includin g unpave d street s an dalleys . I n addition , 3 8 min e wast e pile s wer e identifie dwithi n 0U9 . Th e primary contaminan t o f concern for

0U 9 i s lea di n soil , dust , paint , an dwater . Th e ris k assessmen t

determine dth e followin g actio n level s for th e medi ao f

concern . Soi l - . 3,50 0 mg/K g Dus t - 2,00 0 mg/K g Pain t - 6 mg/cm^ Ta p Wate r - 1 5 micrograms/ 1 A n Engineerin g Evaluation/Cos t Analysi s was prepare din 199 5 t o evaluat e removal actio n alternative s fo

r th e 3 8 min e wast e pile s identifie di n th e populate darea s withi n 0U9 . Durin g th e Min e Remedia l Investigation , 8 ofth e 3 8 pile s wer e foun dt o b e stockpile s o f constructio n material s o r

t o no t pos e athrea t

t o huma n health o r

th e environment . However , on e pil e representin g thi s grou p wa s evaluate dwith th e remainin g 3 0 pile s a s acontro l t o confir mth e EE/CA' s findings . A n Actio n Memorandu missue db y th e EP A i n Augus t 199 6 selecte danon time-critica l remova l actio n requirin g th e remova l o f 1 4 pile s wit

h surfac e lea dconcentration s greate r tha n 3,50 0 mg/Kg . Implementatio n o f thi s remova l actio n began i n 199 7 wit h th e remova l o f fou r min e wast e piles . Th e remova l ofth e remainin g te n min e wast e pile s wa s complete di n 1999 . Th e materia l excavate dfromth e min e wast e pile s wa s take n t o arepository fo r disposal an dth e excavate dare arevegetated . Th e 0U 9 ROD , signe do n Septembe r 2 , 1999 , wa s primaril y focuse do n describin g th e Lake - Count y Community Health Progra m(LCCHP) , th e selecte dremedy fo r Operabl e Uni t

9 . Th e LCCH P di dno t

addres s th e min e wast e pile s i n 0U 9 becaus e th e RO D foun dthat th e selecte d remova l action s fo

r th e 3 8 min e wast e pile s wer e consisten t wit h th e performanc e ofth e final remedia l actio n selecte dfor 0U9 . Additionally , thes e remova l action s wer e considere dth e final remedie s for

min e wast e pile s withi n 0U9 . 3 . Basi s fo r an d Descriptio n o f Significan tDifference s I n on e instanc e sinc e th e ROD , residentia l developmen t occurre do n on e property wher e amin e wast e pil e (#207 ) wa s lef

t i n plac e i n 0U9 . Th e property owne r contacte dEP A before workin g o n thi s min e wast e pile . Prio r samplin g o f

thi s materia l showe dsubsurfac e leadlevel s nea r or exceedin g th e 350 0 mg/K g soi l actio n leve l for 0U 9 ir i thi s property owner' s min e wast e pile . Thi s alerte dEP A an dCDPH E that subsurfac e leadlevel s withi n th e remainin g 1 7 min e wast e pile s may b e abov e th e 350 0 mg/K g actio n leve l an dtha t excavatio n o r

movemen t

o f thes e pile s coul dpresen t

a n unacceptabl e risk . A s lon g a s th e pile s wer e lef t undisturbed , th e surfac e soil s wit h lea dlevel s les s tha n th e 350 0 mg/K g leve l ac t a s a n effectiv e cap .EP A an dCDPH E hav e determine dtha t institutiona l control s ar

e neede dfo

r th e min e wast e pile s that wer e lef t i n plac e withi n 0U 9 t o protec t human health andth e environment . Th e objective s o f th e institutiona l control s ar e a s follows : 1 . Preven t constructio n o f

any typ e o f

residentia l dwellin g or

facilit y fo r human occupanc y o n th e min e wast e pile s unles s appropriat e plan s ar e approve dby EPA o r CDPHE ; an d 2 . Maintai n th e integrity o f curren t o r futur e remedies . Th e specifi c min e wast e pile s wher e institutiona l control s wil l b e necessar y ar e show n o n th e ma p i n Appendi x A , outline di n gree n (lea dconcentration s (Pb ) < 200 0 mg/Kg ) an dyello w (Pb > 2000-350 0 mg/Kg) . Min e wast e pile s shov mi n gree n (P b < 200 0 mg/Kg ) includ e piles ; 12 , 23 , 31 , 34 , 36 , 331 , an d339 . Min e wast e pile s show n i n yello w (P b < 2000-350 0 mg/Kg ) includ e piles : 13 , 18 , 20 , 27 , 32 , 33 , 35 , 207 , an d340 . (Note : wast e pil e 32 9 (show n i n green ) i s th e contro l pil e tha t

contain s constructio n materials. ) Lake County recentl y amende dit s Lan dUs e Cod e t o provid e specifi c protection s fo r remedy element s i n OU s 3 & 8 tha t EP A an dCDPH E hav e identifie da s engineere dremedies . Lake Count y ha s offere dt o exten dthos e protection s to 0U9 . Sinc e th e to p si x inche s ofth e min e wast e pile s wer e foun dt o b e belo w th e residentia l actio n level , eac h pile' s surfac e soi l i s actin g in th e manne r

o f a n engineere dca

p an ddoe s no t

represen t asourc e o f

lea dexposure . Fo r purpose s ofth e Lak e Count y Lan dUs e Code , thes e 1 7 min e wast e pile s wil l b e designate da s engineere dremedies . Extendin g th e Lak e Count y Lan dUs e Cod e provision s t o 0U 9 woul dmee t th e I C objective s se t

ou t above . 4 . Suppor tAgenc y Comment s CDPH E support s th e EPA' s decisio n t o modif y th e remedy fo

r th e Californi aGulc h 0U9 . 5 . Statutor y Determination s Unde r CERCL A Sectio n 121 , EP A mus t selec t aremed y tha

t i s protectiv e o f

human healt

h an d th e environmen t

tha t complie s wit

h Applicabl e o r

Relevan t an dAppropriat e Requirement s (ARARS) , an di s cos t

effective . EP A believe s tha t th e modificatio n t o th e RO D fo r th e min e wast e pile s i n 0U 9 i s appropriat e an dth e remed y wil l remai n protectiv e o f huma n healt

h an dth e environment . Th e selecte dremed y wil l continu e t o compl y wit h federa l an dstat e requirement s that ar e applicabl e an drelevan t an dappropriat e t o th e remedia l action . Thi s ES D doe s no t fundamentall y alte r

th e remed y selecte di n th e RO D wit h respec t t o scope , performanc e or cost . Sectio n 12 1 als o state s tha t EP A mus t

selec t aremedy that

use s permanen t

solutions , alternativ e treatmen t technologies , o r

resourc e recovery technologie s t o th e maximu mexten t practicable . I n addition , CERCL A prefer s remedie s tha t includ e treatmen t

that permanentl y an dsignificantl y reduce s th e volume , toxicity , o r mobility o f

hazardou s waste s a s aprincipa l elemen t ofth e remedy . Fo r

site s wher e hazardou s substances , pollutant s or contaminatio n remai n on-site , EP A mus t conduc t five-year review s consisten t

with th e CERCL A an dth e NCP . Th e purpos e ofth e five-year revie w i s t o determin e whethe r th e remedy bein g implemente da t asit e i s protectiv e o f 4human health an dth e environment .

6 . Publi c Participatio n Complianc e EP A wil l publis h anotic e i n th e Heral dDemocrat newspape r

that describe s th e ES D an dit s availability fo

r revie w (unde r

Sectio n 117(c ) o f

CERCLA , 4 2 U.S.C . Sectio n 9617) . A forma l publi c commen t

perio di s no t

require dwhe n issuin g an ESD . Thi s ES D an dal l document s that support th e change s an dclarification s are containe di n th e Administrativ e Recor dofth e Californi aGulc h Superftin dSit e (unde r CF R40 , Sectio n 300.435(c)(2)(i)) . EPA wil l publis h anotic e o f availability an dabrie f

descriptio n ofth e ES D i n th e Leadvill e Heral dDemocrat . Thi s ES D an dsupportin g document s wil l becom e apart ofth e Californi a Gulc h Administrativ e Recor dfile an dinformatio n repository . Comprehensiv e informatio n o n th e Sit e i s availabl e at the : U.S . EPA , Regio n 8 , Superfim dRecord s Cente r 159 5 Wynkoo p Stree t Denver , C O 80202-112 0 303.312.647 3 o r

tol l fre e 800.227.891 7 Viewin g hours : 8:0 0 a.m . t o 4:3 0 p.m. , M-F , excludin g holiday s an d Lake County Publi c Library 111 5 Harriso n Avenu e Leadville , C O 8046 1 (719)486-056 9 7 . Reference s 1987 . Californi aGulc h Remedia l Investigation , Leadville , Colorado , CH2 M Hill , May . 1992 . Soi l Inventory an dMap , Californi aGulc h Study Area , Leadville , Colorado , Wals h an d Associates, May . 1993 . Fina l Smelte r

Remedia l Investigatio n Report , Californi aGulc h Site , Leadville , Colorado , Wals h an dAssociates , April . 1994 . Fina l Soil s Investigafio n Dat aReport , Californi aGulc h CERCLA Site , Leadville , Colorado , Volum e 1 , Text , Camp , Dresse r an dMcKee , Inc . July . 1994 , Consent

Decre e betwee n th e Unite dStates , Stat e o f Colorado , ASARC O an dResurrection , Lodge di n U.S . Distric t

Court i n Denver , May 17,1994 .ASARCO , 1994 . Wor k Managemen t

Pla n for ASARC O Inc . at

th e Californi aGulc h NP L Site , Leadvill e CO . Prepare db y Woodwar dClyde . Appendi x B to th e Consen t Decree . ASARCO , Incorporated , 1994 . Engineerin g Evaluation/Cos t Analysi s fo

r Park s an dPlaygroun d Areas , Operabl e Uni t

9 , Californi aGulch , Leadville , Colorado . Prepare dby Woodwar dClyd e Consultants , November . ASARCO , Incorporated , 1995 . Engineerin g Evaluation/Cos t Analysi s fo

r Min e Wast e Piles , Operabl e Uni t

9 , Californi aGulc h Superfun dSite , Leadville , Colorado . Prepare db y Golder Associates . December . ASARCO , Incorporated , 2001 . Remova l Actio n Completio n Report , Operabl e Uni t 9 , Californi a Gulc h Superfun dSite , Leadville , Colorado . Prepare dby MFG , Inc . July . Environmenta l Protectio n Agenc y (EPA) . 1''993 . Fina l Screenin g Feasibilit y Study fo

r Remediatio n Alternative s at th e Californi aGulc h NP L Site , Leadville , Colorado . September . Environmenta l Protectio n Agenc y (EPA) . 1999 . Recor do f Decisio n Residentia l Populate dArea s Operabl e Uni t

9 Californi aGulc h Superfun dSite , Leadville , Colorado . September .

naro l L . Camnbel l ^ Dat e / Caro l L . Campbel l Dat e Assistan t Regiona l Administrato r Offic e o f Ecosystem s Protectio n an dRemediatio n U.S . EPA , Regio n 8 Gary w! Baughman \J

Date ^ Divisio n Directo r Hazardou s Material s an dWast e Managemen t Divisio n Colorad o Departmen t

o f Publi c Health an dEnvironmen t 

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