EXPLANATIO N O F SIGNIFICAN T DIFFERENCE S RECOR D O F DECISIO N (ROD )

- CAUFORNI

A GULCH/YA K TUNNEL
DECLARATION S Considerin g th e ne w Informatio n tha t ha s bee n develope d an d th e change s tha t hav e bee n mad e t o th e selecte d remed y chose n i n th e origina l RO D o f Marc h 29
, 198 8 a s modifie d o n Marc h 23
, 1989
, EP A ha s determine d tha t th e remed y remain s protectiv e o f huma n healt h an d th e environment
, complie s wit h Federa l

an d Stat e requirement s tha t ar e applicabl e o r relevan t an d appropriat e fo r thi s initia l remedial action
, excep t thos e fo r whic h a n interi m actio n waive r wa s invoke d i n th e origina l ROD

, an d i s cost-effective

. I n addition

, the revise d remed y utilize s permanen t solution s and alternativ e treatment technologie s t o the maximu m exten t practicabl e fo r thi s Site

. 

# ADMINISTRATIV E RECOR D 

# FIL E PLA N

ame s J

. Schere r Regional Administrato r 

## 0.433.4 1

Dat e 

# /FINA L

CLEANU P OF DISCHARG E FRO M TH E
Y A K TUNNE L OPERABL E UNI T
CALIFORNI A GULCH SIT E

LEADVILLE

, LAK E COUNTY

, COLORAD O
EXPLANATIO N O F SIGNIFICAN T DIFFERENCE S

OCTOBE R 199 1OVERVIE W

Thi s i s th e fina l Explanatio n o f Significan t Difference s (ESD ) whic h explain s th e U.S

. Environmenta l Protectio n Agency' s propose d change s i n th e clean-u p pla n fo r th e Ya k Tunne l Operabl e Unit o f th e Californi a Gulc h Superfun d site

. Thi s documen t explain s th e significan t difference s betwee n 

### th e remed y outline d i n th e 198 8 Recor d o f Decisio n (ROD)

, whic h wa s modifie d i n March o f 1989
, an d th e remed y propose d herein

. Publi c Involvemen t Opportunitie s
T h e Administrativ e Record

, whic h contain s th e complet e documentatio n fo r th e sit e an d additiona l copies o f th e 198 8 ROD

, a s wel l a s th e 198 9 an d 199 1 ESDs

, i s availabl e fo r publi c revie w a t th e followin g location : Lak e Count y Librar y 

### 11 5 Harriso n Avenu e 

### Leadville

, Colorad o 8046 1 (719 ) 486-056 9 

### Colorad o Mountai n Colleg e Librar y Colorad o Mountai n Colleg e Timberlin e Campu s Leadville

, Colorad o 8046 1 (719 ) 486-201 5 

### EP

A Superfun d Record s Roo m 99 9 18t h Street

, 5t h Floo r 

### Denver

, Colorad o 80202-240 5 (303 ) 293-180 7

Y a K Tunne l Operabl e Uni t Explanatio n o f Significan t Difference * Documen t Contro l Numbe r 4800-01-080 0 arcs\reports\*sdrev-2

. Revisio n 2 Octobe r 199 1 Page lINTRODUCTIO N

T h e Californi a Gulc h Superfun d sit e i s locate d i n Leadville

, Lak e County

, Colorad o (se e Figur e 1)

. Th e stud y are a fo r th e sit e include s th e Californi a Gulc h watershe d an d th e are a draine d b y th e Ya k Tunnel

. I n orde r t o mak e th e sit e mor e manageabl e i t ha s bee n divide d Int o two operabl e units

. Th e firs t Operabl e Uni t addresse d b y ERA

, an d th e subjec t o f thi s ESD

, i s th e Ya k Tunnel

. Th e remainde r o f th e sit e i s currentl y unde r investigatio n and ma y resul t i n the definitio n o f additiona l operabl e units

. Th e Ya k Tunne l extend s approximatel y 3. 5 t o 4 mile s beneat h th e mountain s southeas t o f Leadville

, Lak e County

, Colorado

, an d dewater s numerou s mines

. Th e discharg e fro m th e Ya k Tunne l i s contaminate d
wit h aci d min e drainag e containin g hig h concentration s o f heav y metals

, includin g cadmium

, copper , lea d an d
zinc

. Thes e concentration s ar e affectin g aquati c lif e i n the Arkansa s River

, and pos e a potentia l ris k t o huma n healt h an d th e environment

. Consequently

, th e sit e wa s place d o n th e Environmenta l Protectio n Agency' s (EPA ) Nationa l Prioritie s List (NPL ) fo r cleanu p unde r th e Comprehensiv e Environmenta l Response

, Compensation

, an d Liabilit y Ac t (bette r know n a s CERCL A o r Superfund)

. Unde r th e Superfun d law

, EP A i s charged wit h th e responsibilit y o f developin g an d implementin g dean-u p remedie s that protec t huma n healt h

an d th e environment

. Afte r stud y and evaluatio n o f the firs t operabl e unit
, EP A issue d a Recor d o f Decisio n (ROD ) i n Marc h
198 8 describin g th e remed y chose n t o dean u p th e Ya k Tunne l discharge

. Th e remed y selecte d wa s subsequentl y modifie d becaus e additiona l Informatio n cause d EPAt o questio n th e initia l clean-u p plan

. Thes e change s wer e containe d i n EPA' s Marc h 198 9 Recor d o f Decisio n Modification

, whic h describe d th e difference s between th e remed y propose d I n th e RO D an d th e remed y t o b e implemente d a t th e site

. Th e RO D Modificatio n provide d greate r protectio n o f huma n healt h an d th e environmen t through collectio n o f contaminate d wate r between th e porta l plu g an d secon d plug

. Dat a indicate d tha t contaminate d
wate r fro m th e Ya k wa s seepin g int o th e groun d wate r syste m nea r th e mout h o f th e tunnel

. Th e interi m

Ya k Tunne l Operabl e Uni t RevWon 2 Octobe r 189 1 Explanatio n o f Significan t Difference s Pag e 2 Documen t Contro l Numbe r 4800-01-080 0 arci\reports\esdrev-2

.Iufquoit * III * < 0

I 0 I 2 J SCAL E O F MILE S

I* 

### FIGUR E 1 LOCATIO N MA P 

## 8 " 

## S T »treatmen t

syste m wa s change d t o a permanen t treatmen t syste m t o trea t flo w collecte d fro m th e tunne l (betwee n th e flo w throug h porta l an d secon d plugs)

. I n Augus t 1988
, EP A issue d a n Administrativ e Orde r t o severa l Potentiall y Responsibl e Partie s (PRPs ) requirin g thes e partie s t o implemen t a n interi m remedy

, includin g constructio n o f th e Surg e Pon d an d a filtratio n plant

. Th e PRP s bega n constructio n i n 198 8 an d complete d mos t o f th e constructio n associate d wit h thi s interi m remed y durin g th e 198 9 constructio n season

. Th e filtratio n plan t wa s commissione d durin g December 198 9 an d i s currentl y treatin g th e discharg e fro m th e Ya k Tunnel

. I n Marc h 1989
, EP A issue d a n Administrativ e Order (AO ) t o severa l PRP s requirin g thes e partie s t o implemen t th e modifie d remedy

. Durin g preparatio n o f plan s t o implemen t th e remedy

, th e PRP s expresse d

concer n wit h the modifie d remedy

, primaril y wit h the ris k o f uncontrolle d an d undetecte d migratio n o f
contaminant s i n groun d wate r du e t o tunne l flooding

. Thereafter

, th e PRP s submitte d t o EP A a n alternativ e proposa l fo r sit e cleanup

, entitle d Selecte d Remed y Componen t Chang e Proposa l (Res-ASARCO Join t Venture

, Marc h 1990)

. Afte r revie w o f thes e additiona l considerations

, EP A propose s t o mak e furthe r revision s t o th e remedy

. Followin g ar e th e basi c component s t o th e propose d revision : (1 ) constructio n o f a surg e pond ; (2 ) installatio n o f a wate r treatmen t plant ; (3 ) constructio n o f a flo w contro l bulkhea d withi n th e tunnel ; (4 ) sealin g

o f inflo w int o th e tunnel ; (5 ) installatio n o f weir s I n th e tunnel ; (6 ) periodi c inspectio n o f th e Ya k Tunnel ; (7 ) installatio n o f a surfac e an d groun d wate r monitorin g network; (8 ) developmen t o f a contingenc y plan ; an d (9 ) operatio n an d maintenanc e o f th e remedy

. The propose d change s t o th e remed y wil l bette r contro l ground

wate r flo w an d minimiz e movemen t o f contaminate d ground wate r awa y fro m th e Ya k Tunne l throug h continue d

us e o f th e Ya k Tunne l a s a drai n fo r th e min e working s an d surroundin g area

. Unde r Sectio n 11 7 o f CERCLA

, a s amende d b y the Superfun d Amendment s an d Reauthorizatio n Ac t

o f 198 6 (SARA)

, EP A i s require d t o develo p an d publis h a RO D modificatio n o r a n explanatio n o f Significan t Differenc e whe n change s t o the RO D ar e proposed

. A RO D modificatio n I s require d whe n fundamenta l change s ar e propose d t o the selecte d remedy

. EP A I s require d t o publis h an ES D whe n significant

, bu t not

Ya k Tunne l Operabl e Uni t Revisio n 2 Octobe r 199 1 Explanatio n o f Significan t Difference * Pag e 4 Documen t Contro l Numbe r 4800-01-080 0 arci\reportt\«sdrev-2

.fundamental

, change s ar e propose d t o th e previousl y selecte d remedy

. Th e propose d change s reflec t th e rational e presente d i n th e origina l propose d pla n develope d prio r t o th e ROD

, an d therefore

, d o no t constitut e

a fundamenta l chang e t o th e remedy

. I n addition

, significan t publi c participatio n in th e pas t ha s full y supporte d th e propose d change s t o th e remedy

. Th e propose d remed y i s presente d a s a n ES D becaus e th e scop e o f th e remed y i s no t significantl y changed : the remediatio n goal s wil l remai n the sam e a s wil l the physica l are a o f the response ; the treatmen t method s an d th e contingenc y remain s th e same

. Th e propose d remed y woul d Increas e protectivenes s o f huma n healt h an d th e environmen t through reducin g th e potentia l fo r migratio n o f contaminate d ground wate r

awa y fro m th e Ya k Tunnel

. Thi s protectivenes s i s obtaine d b y allowin g fre e flo w throug h th e Ya k Tunne l (remova l o f th e plug s excep t fo r th e flo w contro l bulkhea d a t th e portal)

, an d permanen t treatment o f th e Ya k Tunne l flo w Int o perpetuity

. Th e purpos e o f thi s document I s t o describ e th e remedia l actio n t o b e undertake n fo r thi s operabl e uni t

an d explai n th e significan t way s I n whic h thi s proposa l differ s fro m th e remed y selecte d b y EP A i n 198 8 an d subsequentl y modifie d I n 1989

. Thi s documen t als o provide s a brie f histor y o f th e site

. Thi s ES D present s onl y a synopsi s o f Informatio n o n th e site

. Fo r mor e Informatio n o n th e sit e o r th e previou s RO D Modificatio n issue d i n 1989
, th e reader ma y wis h t o refe r t o th e Informatio n repositorie s a t th e Lak e Count y Library

, Colorad o Mountain Colleg e Library

, Timberiin e Campus

, an d th e EP A office s i n Denver

.

Y»JcTunne l Operabl e Uni t Revision s Octobe r 199 1 Explanatio n o f Significan t Differenc e Pag e 5 Documen t Control Numbe r 480041480 0 arc*\i*ports\esdr*v-2

.SUMMAR Y

O F SIT E HISTOR Y AN D CONTAMINATIO N

PROBLEM S

Sit e Histor y
T h e Californi a Gulc h sit e i s locate d i n Lak e County

, Colorado

. Th e stud y are a include s th e Californi a Gulc h watershe d an d th e are a draine d b y th e Ya k Tunnel

. Th e sit e I s within th e histori c Leadvill e Minin g Distric t wher e significan t quantitie s o f gold

, silver

, lead

, zinc
, manganese , an d coppe r hav e bee n mine d since the 1860s

. Hundred s o f mines
, man y mills

, mor e tha n 4 0 smelter s an d severa l place r operations nav e bee n activ e i n the area

. A s a result

, numerou s sla g piles

, tailing s pond s an d abandone d mine
, mill

, an d smelte r site s ar e foun d within th e stud y area

. Minin g activities i n th e Leadvill e are a began wit h place r minin g o f gold-bearin g deposit s alon g Californi a Gulc h I n 1859

. Th e place r deposit s wer e quickl y exhauste d an d undergroun d minin g o f lod e vein s i n th e uppe r Californi a Gulc h are a began

. Silver-lade n lead carbonat e or e wa s discovere d I n the area , and silve r minin g bega n i n 1875

. A numbe r o f mill s an d smelter s wer e buil t t o proces s th e mine d ore s an d th e tow n expande d considerably

. Undergroun d minin g wa s extensiv e an d min e drainag e tunnel s wer e buil t a s a wa y t o dewate r thes e workings

. Constructio n o f th e Ya k Tunne l bega n i n 188 9 an d I t wa s extende d a numbe r o f times t o th e presen t lengt h o f betwee n 3. 5 an d 4 miles

. Nea r th e turn o f th e centur y lead an d zin c minin g an d or e processin g als o bega n i n th e area

. Minin g

o f al l o f thes e metal s ha s followe d a cycli c patter n since
, wit h extensiv e activit y whe n metal s price s wer e hig h

an d ver y littl e minin g whe n th e metal s price s di d no t Justif y th e minin g costs

. Current minin g activitie s i n th e

are a ar e limite d t o th e Blac k Clou d Min e I n Iow a Gulc h an d severa l othe r smal l minin g ventures

. Total meta l productio n fro m th e Leadvill e Distric t fro m 185 9 throug h 196 6 totale d abou t 2 4 millio n tons

. Th e principa l metal s wer e silver

, zinc
, lead

, gold

, an d copper

.

Ya k Tunne l Operabl e Uni t Revisio n 2 Octobe r 199 1 Explanatio n o f Significan t Difference * Pag e 6 Documen t Contro l Numbe r 4800-01-060 0 aro\reports\esdrev-2

.I

n 198 2 an d 1983
, EP A conducte d a preliminar y evaluatio n o f th e site
, consistin g o f a sit e inspectio n

an d revie w o f existin g data

. Th e sit e wa s place d o n th e NP L i n 198 3 fo r cleanu p unde r th e Superfun d program

. Th e Superfun d la w require s EP A t o identif y thos e who hav e eithe r contribute d t o th e contaminatio n at th e sit e

o r who ow n contaminate d property

. Thes e person s o r companies
, calle d Potentiall y Responsibl e Partie s (PRPs ) ma y b e responsibl e fo r conductin g dean-u p activities an d payin g clean-u p costs

. Seve n partie s wer e identifie d a s PRP s for th e sit e contaminatio n base d on ownershi p or operatio n o f minin g or minera l processin g operation s i n th e area

. Thes e companie s wer e notifie d i n th e sprin g an d summe r o f 198 3 tha t the y wer e considere d potentiall y responsibl e fo r th e releas e o f hazardou s substances

, pollutants

, an d contaminant s a t th e site

. The y wer e al l offere d opportunit y t o participat e voluntaril y i n a respons e action

. T h e Phas e I Remedia l Investigatio n (Rl ) o f th e site
, includin g Californi a Gulc h an d th e Ya k Tunnel

, bega n i n 1984

. Th e Phas e i R l report wa s released i n Ma y 198 7 (EPA

, 1987a)

. I n th e sprin g o f 1986
, whil e th e R l wa s I n progress , EP A Identifie d an d notifie d si x additiona l partie s that the y wer e considere d PRPs

. A Feasibilit y Stud y (FS ) report wa s release d b y EP A i n Jun e 1987
, and i n Augus t 1987
, a propose d Remedia l Actio n Pla n fo r th e Ya k Tunne l Operabl e Uni t wa s released

. EP A hel d a 90-da y publi c commen t perio d an d a publi c meetin g t o provid e an opportunit y for th e publi c t o revie w an d commen t on thes e plans

. A ROD

, date d Marc h 1988
, wa s Issue d detailin g th e selecte d remed y fo r th e Ya k Tunne l Operabl e Unit

. Th e RO D specifie d th e components
, procedure s an d goal s fo r cleanu p o f th e Ya k Tunne l discharg e i n thi s operabl e unit

. Futur e ROD s wil l specif y components
, procedure s an d goat s fo r cleanu p o f othe r operabl e unit s withi n th e site
, possibl y Includin g soils

, groun d water
, an d surfac e water

. I n Augus t 1988
, EP A issue d a n A O t o ASARC O Inc.

, Res-ASARC O Join t Venture

, an d Resurrectio n Minin g Compan y requirin g thes e partie s t o construc t th e surg e pond portio n o f th e Ya k Tunne l remedy

. Th e surge pon d constructio n i s essentiall y complet e a t th e tim e o f th e writin g o f thi s draf t ESD

. I n Marc h 1989
, EP A modifie d th e RO D an d issued a secon d A O t o ASARC O Inc.

, Newmorr t Minin g Corporation

, Res-ASARCO Joint

Ya k Tunne l Operabl e Uni t Revisio n 2 October 199 1 Explanatio n o f Significan t Difference ! Pag e 7 Documen t Control Numbe r 480041-080 0 arci\reports\esdrev-2

.Venture

,

an d Resurrectio n Minin g Compan y fo r implementatio n o f th e remed y se t fort h i n th e RO D Modification

. Thi s remed y i s unde r way , an d I s th e subjec t o f thi s ESD

. Summar y o f Contaminatio n Problem s ER A studie s indicat e tha t th e Californi a Gulc h sit e i s contaminate d wit h heav y metals

, includin g cadmium

, copper , lead

, an d zinc
, comin g fro m bot h activ e an d abandone d minin g an d mineral s processin g facilities

. Th e Ya k Tunne l i s th e majo r contributo r t o sit e contamination

. Th e tunne l wa s designe d t o provid e drainage

, facilitat e exploration

, an d provid e transportatio n route s fo r removin g or e fro m mine s i n th e Leadvill e Minin g Distric t I t collect s ground wate r fro m th e mine s an d the n discharge s thi s wate r int o Californi a Gulch

. I n a n averag e yea r the tunne l discharge s a combine d total o f approximatel y 21 0 ton s o f cadmium

, copper , lead

, zin c an d othe r metal s int o Califomi a Gulch

. Californi a Gulch

, i n turn
, flow s int o th e Arkansa s River

. Th e tunne l contribute s 7 5 t o 8 0 percen t o f th e meta l contaminant s release d int o th e Arkansa s Rive r b y Califomi a Gulch

. Metal s fro m th e Ya k Tunne l hav e bee n show n t o mov e throug h soils

, surfac e water
, ground water
, an d ai r a t th e site

. Cadmium

, copper , lead

, and zin c ar e ke y metal s o f concer n i n the Ya k Tunne l discharge

. The heav y metal s ca n b e harmfu l t o aquati c an d terrestria l plant s an d animals

, includin g humans

. Aquati c organism s ca n absor b metals

. Plant s ca n tak e u p metal s fro m wate r an d soil s throug h their roo t systems

. Domesti c animal s

an d wildlif e ca n drin k contaminate d wate r o r eat plant s (o r othe r animals ) tha t hav e taken u p metals

. I n turn
, human s ca n b e expose d throug h Inhalatio n o f airborn e contaminants
, o r ingestio n o f contaminate d water
, sediments

, o r food

.

Ya k Tunrw l Operabl e Uni t Revisio n 2 Octobe r 189 1 Explanatio n o f Significan t Difference s Pag e 8 Documen t Contro l Numbe r 4800-01-080 0 «rcs\reports\esdrev-2

.Th e

metal s o f concer n ca n b e harmfu l t o animals

, aquati c lif e an d humans

. • Chroni c exposur e t o cadmiu m ma y resul t i n hypertensio n an d kidne y an d live r damag e i n humans

. I n lo w concentrations
, i t i s toxi c t o freshwate r fish

. Terrestria l plant s ca n accumulat e cadmiu m i n leaf y tissu e t o concentration s whic h ar e dangerou s t o animals

, includin g humans

, withou t inhibitin g th e plan t growth

. • Coppe r i s no t acutel y toxi c t o humans

, bu t I s one o f th e mos t harmfu l metal s t o fis h and othe r aquati c life

. • Long-ter m huma n exposures t o lead can caus e anemia
, Intestina l cramps , fatigue

, an d neurologica l damage

. Eve n a t ver y low levels

, lea d exposur e ca n caus e harmfu l effect s t o th e nervou s system s o f children

. Studie s on laborator y animal s hav e show n tha t exposur e t o lead

ca n caus e cance r an d a n increas e I n reproductiv e complications

. Lea d i s als o toxi c t o aquati c life

. • Fish

, suc h a s rainbo w an d broo k trout
, ar e adversel y affecte d b y exposur e t o zinc

. Zin c i s rarel y damagin g t o huma n healt h o r terrestria l anima l health ; however

, whe n human s ar e expose d t o zin c i n combinatio n wit h othe r metals

, th e result s ma y b e harmful

. Arsenic

, iron
, manganese , and othe r heav y metal s ar e als o presen t i n th e Ya k Tunne l discharge ; however

, fo r thi s operabl e uni t i n particular

, zin c i s th e meta l o f greates t concer n a t th e concentration s o f metal s know n t o b e i n th e Ya k Tunne l discharge

. Studie s o f th e Arkansa s Rive r belo w th e confluenc e wit h Californi a Gulc h sho w tha t metal s contaminatio n ha s reduce d the capacit y o f the rive r t o suppor t wel l balance d aquati c populations

. Bot h the quantit y an d variet y o f fis h ar e reduce d i n thi s portio n o f th e rive r du e t o contaminatio n fro m Californi a Gulch

. DESCRIPTION O F TH E REMEDIE S
Summar y o f th e 198 8 Recor d o f Decisio n
I n Marc h 1988
, EP A signe d a RO D outlinin g a dean-u p pla n fo r th e Ya k Tunne l portio n o f th e Californi a Gulc h site

. The remed y wa s designe d t o minimiz e th e flo w o f wate r out o f th e Ya k Tunne l an d t o preven t th e uncontrolle d releas e o f tunne l drainag e t o th e environment

. Row fro m th e tunne l woul d b e minimize d throug h

Ya k Tunne l Operabl e Uni t Revisio n 2 Octobe r 189 1 Explanatio n o f Significan t Difference s Pag e 9 Documen t Control Numbe r 4800-01-080 0 arct\reports\esdrev-2

.plugging

th e tunne l an d treatin g th e wate r whic h ma y escap e fro m behin d th e plugs

. Th e remed y consiste d

o f severa l elements : Constructio n o f surge pond s t o captur e drainag e fro m th e tunne l an d t o minimiz e th e impac t
o f surge s o n Californi a Gulc h and the Arkansa s River

. Installatio n o f a n interi m wate r treatmen t syste m t o trea t wate r fro m th e Ya k Tunne l befor e discharg e I n Californi a Gulch

. Hoodin g th e tunne l woul d hav e raise d th e wate r level depletin g th e availabl e oxygen , thu s improvin g th e groun d wate r quality

. Treatmen t woul d onl y b e necessar y unti l wate r qualit y improved

. Constructio n o f plug s at thre e location s withi n th e tunne l t o sto p uncontrolle d discharg e o f tunne l drainag e int o Californi a Gulc h an d t o preven t surges

. Sealin g o f shafts

, dril l holes an d fracture d roc k an d diversio n o f surfac e wate r fro m tunne l recharg e area s t o reduce th e amoun t o f wate r enterin g th e Ya k Tunne l system

. Groutin g o f fracture d rock

, caved-i n areas , an d dril l holes t o preven t seepag e o f contaminate d wate r t o the lan d surface

. Establishmen t o f a surfac e and ground-wate r monitorin g syste m t o detec t an y leakage

, seep s or migratio n o f contaminate d groun d wate r whic h ma y resul t fro m installatio n o f th e tunnel plugs

. Installatio n o f a pumpin g syste m t o contro l wate r level s behind th e porta l plug

, i f necessary , t o preven t uncontrolle d seepage

. The pumpe d wate r woul d b e route d t o the interi m treatmen t syste m t o remov e contaminant s befor e discharg e int o Californi a Gulch

. Developmen t an d implementation

, a s necessary , o f a contingenc y pla n t o addres s an y advers e effect s o n surfac e o r ground wate r resultin g fro m tunne l plugging

. Operatio n an d maintenanc e o f th e remedy

.

Summar y o f the 198 9 RO D Modificatio n 

### Th e RO D wa s modifie d I n 198 9 becaus e o f ne w information

, specificall y seepag e enterin g th e ground

wate r syste m nea r th e porta l plug

. Therefore

, th e porta l plu g was change d t o a flo w throug h plug

. Also

, th e interi m wate r treatmen t syste m wa s change d t o a permanen t syste m t o trea t th e wate r fro m th e flo w through porta l plu g i n perpetuity

.

Ya k Tunne l Operabl e Uni t Revisio n 2 Octobe r 199 1 Explanatio n o f Significan t Difference s Pag * 1 0 Documen t Control Numbe r 4300-01-080 0 arc»\reports\esdrev-2

.T h e

element s o f th e remed y a s modifie d i n 198 9 ar e liste d below

. Th e change s fro m th e initiall y selecte d remed y ar e note d b y highlighting

, an d ar e discusse d withi n bracket s ( [ ])

. Constructio n o f a surg e pon d o r pond s t o captur e drainag e fro m the tunne l and t o minimiz e th e impac t o f surge s o n Californi a Gulc h an d th e Arkansa s River

. [Th e multipl e surg e pond s initiall y selecte d wer e replace d wit h th e possibilit y o f a singl e surg e pond. ] Installatio n o f a permanen t wate r treatmen t syste m t o trea t wate r fro m th e Ya k Tunne l befor e discharg e i n Californi a Gulch

. [Th e interi m treatmen t facilit y fro m th e Initiall y selecte d 

### remed y wa s replace d wit h a permanen t treatmen t system. ] Constructio n o f plug s at thre e location s withi n th e tunne l t o sto p uncontrolle d discharg e o f min e drainag e int o Californi a Gulc h an d t o preven t surges

. 

### Implementatio n o f wate r contro l measure s t o reduc e surfac e water inflo w int o th e tunne l syste m an d t o minimiz e uncontrolle d ground-wate r outflo w fro m th e tunne l syste m followin g plugging

, a s necessary, fo r prope r performanc e o f th e remedy

. [Reductio n o f 

### seepag e an d recharg e wa s mad e optiona l i n th e modifie d remedy

, contingen t upo n th e abilit y o f th e wate r treatmen t syste m t o successfull y trea t seepag e an d recharge

. Groutin g 

### o f fracture d rock

, caved-i n areas , an d dril l holes t o prevent seepag e o f contaminate d wate r t o th e lan d surfac e wa s delete d fro m th e modifie d remedy. ] Establishmen t o f a surfac e and ground-wate r monitorin g syste m t o detec t an y leakage

, seep s or migratio n o f contaminate d groun d wate r whic h ma y resul t fro m Installatio n o f th e tunnel plugs

. Installatio n o f a pumpin g o r drainag e mechanis m t o contro l wate r level s behin d th e porta l plug

. 

### Th e pumpe d wate r woul d b e route d t o th e treatment syste m t o remov e contaminant s befor e discharg e Int o Californi a Gulch

. [Th e porta l plu g becam e a flo w throug h plug

, rathe r tha n 

### a solid plug

. Thi s flo w throug h plu g wa s intende d t o prevent surge s fro m affectin g th e treatmen t system
, no t t o floo d th e tunnel. ] Developmen t an d Implementatio n a s necessar y o f a contingenc y pla n t o addres s an y advers e effect s o n surfac e o r groun d wate r resultin g fro m tunne l plugging

. Operatio n an d maintenanc e o f th e remedy

. Thes e change s wer e discusse d i n detai l i n th e 198 9 RO D Modification

. Th e reader ma y wis h t o refe r t o th e 198 8 RO D an d th e 198 9 RO D Modificatio n fo r a mor e detaile d discussio n o f th e remed y selecte d i n 198 8

an d modifie d i n 1989

. Thes e document s ar e availabl e at the Lak e Count y Library

, Colorad o Mountai n Colleg e Library

, Timberlin e Campus

, an d th e EP A office s i n Denver

.

Y«kTunne l Operabl e Uni t Revision s Octobe r 199 1 Explanatio n o f Significan t Difference s Pag e 1 1 Documen t Contro l Numbe r 4800-01-080 0 arcj\reports\esdrev-2

.

### Summar

y o f the Propose d 199 1 Remed y
Bot h th e 198 8 RO D and th e 198 9 RO D Modificatio n wil l b e furthe r altere d b y th e remed y propose d I n thi s Draf t ES D upo n approva l b y EPA

. Man y o f th e element s hav e no t changed

, or hav e change d i n numbe r

o r location

, bu t remai n fundamentall y th e sam e a s th e element s describe d i n th e RO D an d RO D Modification

. Thes e element s ar e discusse d belo w i n greate r detai l tha n th e foregoin g summarie s o f th e previou s remedie s t o hel p th e reader understan d wha t th e propose d remed y includes

. Refe r t o th e sectio n "Basi s fo r Modifyin g th e Remedy " i n thi s ES D fo r a n explanatio n o f th e basi s fo r th e changes

. I n th e discussio n below

, th e component s whic h hav e change d fro m previou s remedie s wil l b e note d b y highlighting

, an d discusse d a t th e

en d o f th e paragrap h withi n bracket s ( [ ])

. Th e propose d remedy

, designe d t o allo w fre e flo w fro m th e tunnel

, through eliminatio n o f tw o o f th e plug s an d replacemen t o f th e porta l plu g wit h a flo w contro l bulkhead

. Th e propose d remed y consist s of :

• Constructio n o f a surg e pon d t o captur e drainag e fro m the Ya k Tunne l an d t o minimiz e the Impac t o f surge s fro m th e tunne l on Californi a Gulc h an d th e Arkansa s River

. Th e surg e pon d I s propose d t o b e a permanen t part o f th e remedy

. (Constructio n o f thi s surg e pon d i s essentiall y complet e a t th e time o f th e writin g o f thi s draf t ESD. )

• Installatio n o f a permanen t wate r treatment syste m t o trea t wate r fro m th e Ya k Tunne l befor e discharg e int o Californi a Gulch

. • Constructio n o f a flo w contro l bulkhea d withi n th e tunne l t o preven t surges

. [Tw o o f th e thre e 

### plug s ar e propose d t o b e eliminate d fro m th e remedy

, leavin g th e porta l plu g a s a flo w 

### contro l bulkhea d t o prevent surge s (redundan t t o th e surg e pond)

, an d t o allo w fo r operationa l flexibilit y withi n th e wate r treatment facility

. Th e flo w contro l bulkhea d i s propose d t o b e constructe d i n competen t rock

, approximatel y 2,00 0 fee t int o th e tunnel

. Th e tunne l wil l b e rehabilitate d t o th e exten t required fo r bulkhea d placemen t (construction ) and long-ter m stabilit y o f the tunne l discharg e outlet. ]

• Sealin g o f shaft s and diversio n o f surfac e wate r fro m tunne l recharg e area s t o reduc e the amoun t o f wate r enterin g th e Ya k Tunne l system
, a s necessary , fo r prope r performanc e o f th e remedy

. • Establishmen t o f a surfac e and ground-wate r monitorin g syste m t o detec t seeps , ground-wate r qualit y an d flo w direction

, an d potentia l gradien t reversa l resultin g i n migratio n o f contaminate d groun d wate r awa y fro m th e tunnel

. Th e gradien t reversa l ma y resul t fro m a 

### rockfal l o r cave-i n withi n th e tunnel

. Thi s monitorin g syste m i s propose d t o includ e a minimu m o f seve n ground-wate r monitorin g wells

. [Bot h th e RO D an d th e 198 9 RO D Modificatio n require d establishmen t o f a minimu m o f 2 3 monitorin g wells

. Sinc e th e remed y propose d i n thi s ES D eliminate s floodin g o f th e min e workings

, th e potentia l fo r

Yal e Tunne l Operabl e Uni t Revblon 2 Octobe r 199 1 Explanatio n o f Significan t Difference s Pag e 1 2 Documen t Contro l Numbe r 4800-01-OSO O arci\reports\«sdrev-2

.

### migratio n

o f contaminant s i s greatl y reduced

. Thi s reduce s th e numbe r an d location s o f th e monitorin g well s neede d t o detec t movemen t o f contaminants. ]



### • Placemen t o f si x o r mor e weirs
, o r othe r flo w measurin g devices

, a t ke y location s i n th e Y a k Tunnel

. Th e wei r location s wil l be selecte d durin g a n initia l Inspectio n o f th e tunnel

. • Periodi c inspectio n o f th e Ya k Tunnel

. Qualifie d minin g crew s wil l ente r th e tunne l 

### annuall y t o inspec t and maintai n weir s and othe r structures i n the tunnel

. Crew s wil l als o ente r the tunne l t o determin e the caus e o f unexpecte d increase s o r decrease s i n flo w withi n th e Yak Tunnel

. • Developmen t an d implementation

, a s necessary , o f a contingenc y pla n t o addres s an y advers e 

### effect s o n surfac e o r ground wate r resultin g fro m tunne l blockage

. [Implementatio n o f th e 

### contingenc y pla n wil l be base d upon : 1 ) decreas e I n flo w fro m th e Ya k Tunnel ; 2 ) ris e i n water level s i n monitorin g well s locate d outsid e th e min e workings ; 3 ) indicatio n o f 

### gradien t reversa l (flo w awa y fro m th e tunnel) ; an d 4 ) degradatio n o f wate r qualit y a s 

### detecte d b y th e monitorin g network

. A baselin e fo r Ya k Tunne l flow

, wate r levels

, 

### hydrauli c gradient

, an d water qualit y wil l be establishe d fo r compariso n wit h futur e data

. T h e remed y wil l als o b e monitore d fo r seep s b y periodi c sit e reconnaissanc e lookin g fo r surfac e seeps. ]



### • Operatio n an d maintenanc e o f th e remedy

. Explanatio n o f Significan t Difference s
Th e 198 8 remedy

, a s modifie d b y th e 198 9 remedy

, an d th e propose d 199 1 remed y remai n fundamentall y th e same

. Th e sam e wate r treatment processe s wil l b e employed

. I n addition

, a flo w contro l bulkhea d and a monitorin g networ k wil l b e constructed

. The difference s between the 198 9 RO D Modificatio n

an d th e 199 1 propose d remed y are :

1

. Remova l o f two o f th e thre e plug s t o allo w fre e flo w fro m th e tunnel

, an d placemen t o f a flo w through bulkhea d a t th e porta l fo r surge protection ; 2

. Reductio n i n th e propose d ground-wate r monitorin g syste m du e t o th e greatl y reduce d chanc e o f contaminate d wate r movemen t int o th e groun d wate r system; 3

. Continue d us e o f th e Ya k Tunne l a s a drai n fo r contaminate d water ; an d
4

. Treatmen t o f al l Ya k Tunne l water
, no t jus t wate r between th e porta l and secon d plug

.

Ya k Tunne l Operabl e Unt t Revisio n 2 Octobe r 189 1 Explanatio n o f Significan t Difference s Pag e 1 3 Documen t Control Numbe r 4600-01-080 0 arc<\reports\esdrev-2

.Th e

majo r difference s betwee n th e 198 8 remedy

, whic h wa s modifie d b y th e 198 9 RO D Modification

,

an d th e propose d 199 1 remed y include :

1

. Th e natur e an d desig n o f th e plug s t o b e installe d i n th e Ya k Tunnel

. A flo w contro l bulkhea d wil l b e installe d approximatel y 2,00 0 fee t Int o th e tunnel

. Th e bulkhea d wil l contro l flo w fro m th e tunne l t o optimiz e wate r treatmen t facilit y operatio n an d provid e surg e protection

. Th e tw o remainin g plug s wil l no t b e installe d allowin g fo r fre e flo w fro m th e tunnel

. Th e decisio n t o no t instal l th e tw o plug s wa s base d upo n th e reductio n o f exposur e t o industria l (miner ) safet y hazard s durin g rehabilitatio n o f th e tunne l an d th e unknow n wate r qualit y impact s 

### tha t pluggin g th e tunne l ma y hav e caused

. 2

. Th e installatio n o f weirs
, o r other flo w measurin g devices

, I n th e Ya k Tunnel

. Thes e weir s wil l allo w for monitorin g o f th e flo w i n variou s reache s o f th e tunnel

. Th e exac t location s an d number s o f weir s wil l b e base d upo n a n investigatio n o f th e conditio n o f th e Ya k Tunne l an d it s mai n laterals

. Thi s investigatio n wil l determin e th e relativ e wate r contributio n t o th e tunne l fro m eac h mai n lateral

. Th e investigatio n wil l als o determin e th e conditio n o f faul t zone s whic h Intersec t th e Ya k Tunne l an d it s mai n laterals

. Weirs wil l b e locate d t o determin e baselin e flo w an d t o provid e immediat e warnin g o f sudde n Increase s o r decrease s i n flo w withi n th e Ya k Tunne l o r it s laterals

. The weir s wil l serv e two purposes : • Th e weir s wil l measur e baselin e flo w i n th e tunnel

. Th e seasona l variatio n o f flo w fro m th e mai n lateral s ma y assis t i n determinin g source s o f surfac e wate r Inflo w int o th e tunne l system

. Significan t source s o f inflo w ma y the n requir e remedia l action s t o reduc e th e volum e o f wate r flowin g t o th e treatmen t plant

. • Th e weir s wil l provid e informatio n o n rapi d change s I n flo w i n th e tunnel

. I n th e cas e o f rapi d increas e i n flow

, flo w measuremen t wil l assis t th e treatment plan t operato r i n protectin g th e plan t fro m surges

. I n th e cas e o f rapi d decreas e i n flow

, flo w measuremen t wil l trigge r implementatio n o f contingenc y plans

, includin g relnspectio n o f th e Ya k Tunnel

. I f

, durin g th e investigatio n o f th e Ya k Tunnel

, EP A determine s tha t conditions i n th e tunne l wil l

not allo w Installatio n and maintenanc e o f the weirs
, EP A wil l develo p a n alternat e metho d fo r monitorin g th e tunnel

. Thi s alternat e metho d wil l b e presente d t o th e publi c prio r t o implementation

, eithe r I n a Fac t Shee t o r another ESD

. 3

. Th e modificatio n o f th e monitorin g networ k reflect s th e us e o f weir s fo r directl y monitorin g th e change s I n wate r flo w rat e withi n th e tunnel

. I n addition

, monitorin g well s constructe d within selecte d faul t zone s outsid e o f know n min e working s wil l b e use d t o monito r wate r level

, wate r qualit y an d flo w directio n t o o r fro m th e tunnel

. This monitorin g system wil l determin e potentia l contaminan t movemen t awa y fro m th e tunnel

. Thi s chang e als o reflect s th e chang e I n th e floodin g componen t o f the remedy

, wit h a greatl y reduce d chanc e o f movemen t o f contaminate d wate r int o th e groun d wate r system

.

Ya k Tunne l Operabl e Uni t Revisio n 2 Octobe r 199 1 Explanatio n o f Significan t Difference s Pag e 1 4 Documen t Contro l Numbe r 4800-01480 0 •rcs\reports\esdrev-2

.Basi

s fo r Modifyin g th e Remed y
Previou s investigation s a t th e sit e indicate d that th e geologica l settin g o f th e Leadvill e Minin g Distric t

wa s complex

. However

, thes e investigation s wer e no t abl e t o full y conside r th e difficultie s associate d wit h
monitorin g an d detectin g migratio n o f contaminate d ground wate r i n th e minin g district

, includin g th e Ya k Tunnel

. Ne w Informatio n ha s becom e availabl e t o EP A followin g remedia l action s at th e Eagl e Min e nea r Mlnturn

, Eagl e County

, Colorado

. A t tha t site
, afte r pluggin g severa l adits

, min e wate r began seepin g fro m adjacen t bedroc k fractur e zone s (ver y littl e wate r seep s fro m th e adit s themselves)

. Thi s surface

, an d subsurface

, seepag e ha s Increase d th e concentration s o f heav y metal s I n th e Eagl e Rive r belo w th e min e working s an d I n Roc k Creek

. EP A ha s focuse d on th e observe d short-ter m effect s o f min e pluggin g a t th e Eagl e sit e i n formin g it s decisio n regardin g th e Ya k Tunnel

. Althoug h i t i s no t know n whethe r thes e effect s wil l
continu e ove r th e lon g term
, EP A recognize s tha t sourc e contro l remediatio n measure s whic h hav e bee n implemente d ma y wel l prov e t o b e effectiv e a t Eagle

. EP A ha s als o gaine d additiona l informatio n abou t th e difficultie s o f installin g a n "accurate " monitorin g networ k i n highl y faulte d areas , suc h a s th e Leadvill e Minin g District

. Durin g th e constructio n o f th e Surg e Pon d i n 1989
, th e presenc e o f a geologi c faul t Immediatel y downgradien t o f th e Surg e Pon d mad e installatio n

o f a ground-wate r monitorin g networ k extremel y difficult

. Th e faul t ha d originall y bee n though t t o b e locate d

severa l hundre d fee t dow n gradien t o f the surg e pond

, not Immediatel y dow n gradien t o f the surg e pond

. Du e t o th e fault

, th e bedroc k an d th e unconsolidate d sediment s abov e th e bedroc k ar e differen t upgradien t an d downgradien t o f th e Surg e Pond

. Th e bedroc k an d unconsolldate d sediment s upgradien t o f th e pon d consis t

o f porphyr y o r weathered porphyry ; the bedroc k and unconsolidate d sediment s downgradien t o f the pon d
consis t o f dolomit e o r weathered dolomite

. Sinc e th e chemistr y o f th e geologica l deposit s i s different

, interpretatio n o f chemica l analyse s o n groun d wate r woul d b e extremel y difficult

. I n addition

, th e comple x ste p faul t appear s t o b e actin g a s eithe r a da m o r a sink

, sinc e alluvia l groun d wate r i s onl y presen t o n on e sid e

Ya k Tunne l Operabl e Uni t Revisio n 2 Octobe r 109 1 Explanatio n o f Significan t Difference * Pag e 1 5 Documen t Control Numbe r 4800-01-060 0 ara\reports\esdrev-2

.o f the fault

. Thes e condition s ar e not expecte d t o b e uniqu e t o the vicinit y o f the Surg e Pond ; ther e ma y b e othe r comple x fault s whic h Intersec t th e Ya k Tunnel

. Thi s additiona l informatio n I s presente d I n Hydrologi c Investigatio n o f Surg e Pon d Are a (Res-ASARC O Join t Venture

, Marc h 1990) ; supplementa l Informatio n i s presente d i n Appendi x A

. Selecte d Remed y Componen t Chang e Proposa l (Res-ASARC O Join t Venture

, Marc h 1990)

. Thes e technica l document s ar e availabl e a t th e informatio n repositorie s a t th e Lak e Count y Library

, Colorad o Mountai n Colleg e Library

, Timberlln e Campus

, an d th e EP A office s i n Denver

. E P A ha s worke d extensivel y wit h th e PRPs

, Includin g ASARCO

, Newmon t Mining

, Resurrectio n Mining

,

an d th e Res-ASARC O Join t Venture

, I n developin g thi s ESD

. Man y component s o f thi s remed y hav e bee n propose d b y th e PRPs

. T h e Nationa l Contingenc y Pla n (NCP)

, th e regulation s develope d b y EP A t o implemen t th e Superfun d law

, require s EP A t o use nin e criteri a t o evaluat e propose d remedie s a t Superfun d sites

. Thes e nin e criteri a

wer e establishe d t o provid e fo r consistent evaluatio n o f propose d remedie s throughou t th e country

. Th e followin g paragraph s presen t a brie f evaluatio n o f th e propose d remed y usin g th e nin e criteria

.

1

. Overal l Protectio n o f Huma n Healt h an d th e Environment : Partia l tunne l rehabilitation

, collection

, an d treatmen t o f th e min e drainag e wil l adequatel y protec t huma n healt h and th e environmen t fro m unacceptabl e risk s pose d b y th e hazardou s substance s I n bot h the shor t ter m and the lon g term

. The propose d remed y reduce s o r eliminate s impact s on surfac e and groun d water
, through collectio n and treatmen t o f th e Ya k Tunne l discharge

. 2

. Complianc e wit h Applicabl e or Relevan t and Appropriat e Requirement s (ARARs) : Th e treatment facilit y wil l attai n complianc e wit h al l applicabl e o r relevan t an d appropriat e 

### Federa l an d Stat e requirements
, excep t fo r requirement s pertainin g t o instream wate r quality

. Mos t o f th e are a fro m whic h th e contaminate d discharge s t o th e Arkansa s originat e ha s no t ye t 

### bee n adequatel y characterized

. Thus

, i t i s no t ye t possibl e t o perfor m a wasteloa d allocatio n t o determin e the exten t t o whic h the Ya k Tunne l discharg e and eac h o f the othe r discharge s mus t b e treate d I n orde r fo r the Arkansa s Rive r t o mee t instrea m wate r qualit y requirements

. Wate r quality-base d effluen t limitation s an d standard s fo r th e uppe r Arkansa s Rive r hav e therefor e bee n interi m waved

. Technology-base d treatmen t requirements
, however

, represent th e minimu m level o f contro l tha t ha s no t bee n waived

. Initiall y upo n start-u p o f th e wate r treatmen t plant

, Ne w Sourc e Performanc e Standard s (NSPS ) mus t b e met

. B y th e en d o f th e secon d yea r o f operation
, the wate r treatment plan t effluen t mus t mee t bes t availabl e technolog y requirement s base d upo n acut e toxicit y testing

. Thes e requirement s ca n b e translate d int o
Ya k Tunne l Operabl e Uni t Revisio n 2 Octobe r 199 1 Explanatio n o f Significan t Difference s Pag e 1 6 Documen t Control Numbe r 4800-01-060 0 afc$\reports\esdrev2

.interi

m numeri c standard s a s a desig n basi s and complianc e threshold

. Whe n th e are a ha s bee n studied

, th e wasteloa d allocatio n wil l b e performed

, wate r quality-base d treatmen t requirement s fo r th e Ya k Tunne l an d othe r discharge s wil l b e determined

, an d th e Arkansas Rive r wil l mee t Instrea m wate r qualit y standards

. 3

. Long-Ter m Effectivenes s an d Permanence : Th e propose d remed y provide s fo r lon g ter m maintenanc e o f th e collectio n syste m an d th e treatmen t facilit y thu s reducin g o r eliminatin g residua l ris k remainin g fro m untreate d waste

. Operatio n an d maintenanc e procedure s an d monitorin g wil l b e require d t o ensur e th e effectivenes s o f th e propose d remed y i n perpetuity

. Futur e treatmen t technologie s wil l b e evaluate d whe n th e treatmen t facilit y require s updating

. Tunne l blockag e I n th e for m o f natura l rockfall s ma y eventuall y occur , causin g a reversa l i n ground-wate r gradien t whic h ma y adversel y impac t th e local o r regiona l ground-wate r system

. However

, th e contingenc y pla n wil l mitigat e thi s impac t an d wil l allo w respons e time t o asses s the impac t an d develo p alternatives fo r effectivel y collectin g contaminate d groun d wate r an d containin g source s o f aci d min e drainage

. 4

. Reductio n o f Toxicity

, Mobility

, or Volum e through Treatment : Th e principa l threat s pose d b y th e sit e includ e min e drainag e whic h i s contaminate d wit h hig h concentration s o f metal s an d lo w pH

. Th e treatment facilit y wil l remov e th e metal s fro m th e tunne l discharg e an d increase th e p H t o acceptabl e levels

. Th e sludg e produce d b y th e treatment proces s wil l contai n meta l hydroxide s whic h hav e lo w mobilit y unde r nonacidl c conditions

. I n addition

, th e sludg e wil l recove r sufficien t zin c t o allo w recycling

. 5

. Short-Ter m Effectiveness : N o short-term risk s posed t o the communit y durin g implementatio n ar e anticipated

. Potentia l Impact s o n worker s durin g implementatio n includ e manageabl e undergroun d constructio n safet y hazard s durin g tunne l rehabilitatio n whic h wil l b e conducte d b y personne l familia r wit h th e safet y hazard s sometime s encountere d i n undergroun d work

. The probabilit y o f occurrenc e o f safet y hazard s ha s bee n reduce d fro m th e origina l propose d pla n becaus e o f th e reduce d duratio n o f exposur e i n tha t shorte r lengt h o f tunne l requirin g rehabilitation

. N o potentia l environmenta l impact s ar e anticipate d durin g Implementation

. 6

. Implementability : Th e tunne l rehabilitatio n an d th e treatmen t facilit y bot h utiliz e know n technologie s whic h ar e technicall y feasible

, reliable

, an d implementable

. Monitorin g o f th e collectio n syste m b y wa y o f monitorin g well s an d periodi c tunne l inspections wil l b e conducted

. Th e effectivenes s o f th e treatment facilit y wO l b e verifie d b y wa y o f effluen t testing

. Th e treatment proces s ma y b e upse t b y changin g conditions o f influen t resultin g i n less tha n desire d effluen t qualit y fo r shor t period s o f time

. Goo d design

, maintenance
, an d operationa l practice s ar e require d t o mee t performanc e standards

. Th e remed y include s a contingenc y pla n t o reliev e wate r accumulations occurrin g behin d tunne l blockages

. 7

. Cost: EP A i s unabl e t o determin e a significan t differenc e I n cos t betwee n th e 198 9 RO D Modificatio n an d th e 199 1 Propose d Remedy

. Th e 199 1 Propose d Remed y provide s greate r reliabilit y fo r th e collectio n o f contaminate d groun d water

.

Ya k Tunne l Operabl e Uni t Revisio n 2 Octobe r 199 1 Explanatio n o f Significan t Difference * Pag e 1 7 Documen t Contro l Numbe r 4800-01-060 0 arc*\reports\esdrev-2

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### 8

.

Stat e Acceptance : T h e Stat e o f Colorad o acknowledge d th e validit y o f th e additiona l informatio n evaluate d i n reconsiderin g a pluggin g remedy

. Th e Stat e ha s determine d tha t th e propose d change s ar e appropriat e fo r th e Ya k Tunne l situation
, bu t a t th e sam e time
, maintain s tha t min e plugging remedia l alternatives ma y b e effectiv e i n othe r situations

. 9

. Communit y Acceptance : 

### EP A ha s worke d extensivel y wit h th e communit y t o understan d th e residents concern

s regardin g th e previousl y selecte d remedies

. EP A believe s tha t th e propose d remed y wil l receiv e bette r suppor t fro m th e communit y tha n th e previou s remedies

. Thi s i s becaus e th e propose d remed y wil l allo w continue d minin g i n area s whic h woul d hav e bee n floode d unde r the previou s remedies

. I n addition

, th e propose d remed y remove s man y o f th e uncertaintie s associate d wit h pluggin g an d floodin g th e min e workings

. Informa l publi c meetings hav e bee n conducte d an d th e ora l an d writte n comment s receive d hav e bee n generall y supportiv e o f thi s propose d chang e t o th e remedy

. EP A wil l continu e t o wor k wit h th e communit y an d wil l attemp t t o addres s th e community' s comment s regardin g thi s fina l ESD

.

Ya k Tunne l Operabl e Uni t Revisio n 2 Octobe r 199 1 Explanatio n o f Significan t Difference s Pag e 1 8 Documen t Control Numbe r 480041-080 0

arc t \reports\esdrev-2

.SUPPORTIN

G AGENC Y COMMENT S

T h e Colorad o Departmen t o f Healt h has substantivel y participate d i n th e 199 1 ES D development

, EP A responde d t o th e State' s concern s an d incorporate d thei r comment s int o thi s ESD

. Th e Colorad o Departmen t

o f Healt h concur s wit h EP A i n th e propose d modification s t o th e remedy

. STATUTOR Y DETERMINATION

S
EP A ha s determine d tha t th e remedy

, a s modified

, remain s protectiv e o f huma n healt h an d th e environment
, an d I s cos t effective

. I n addition

, th e modifie d remed y utilize s permanent solution s an d innovativ e treatment o r resourc e recover y technologie s t o th e maximu m exten t practicable

. A s mentione d above

, whe n th e are a ha s bee n adequatel y studied

, a wasteloa d allocatio n wil l b e performed

, an d wate r quality-base d requirement s fo r th e Ya k Tunne l an d othe r discharge s t o th e Arkansa s Rive r wil l b e determined

. A t tha t time
, Instrea m wate r qualit y requirement s fo r the Arkansa s Rive r wil l b e achieved

. SCHEDUL E FO R TH E PROPOSE D REMED Y

Th e schedul e fo r desig n an d constructio n o f th e Ya k Tunne l remed y i s presente d i n Figur e 2

. Th e constructio n o f th e wate r treatmen t plan t i s schedule d t o b e complete d durin g th e 199 1 constructio n season ; sit e developmen t wor k bega n durin g 199 0 t o allo w fo r constructio n o f the plan t i n 1991

.

Ya k Tunne l Operabl e Uni t Revisio n 2 Octobe r 199 1 Explanatio n o f Significan t Drfference t Pag e 1 9 Documen t Contro l Numbe r 4800-01-080 0 arci\report»\esdrev-2

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• FIGUR E 2

. YA K TUNNE L PROJEC T SCHEDUL EPUBLI

C PARTICIPATIO N

Person s desirin g furthe r informatio n o n thi s Draf t Explanatio n o f Significan t Difference s an d thos e intereste d i n procedure s fo r providin g comment s t o EP A ma y contact : Jame s Hanle y Eleano r

Dwigh t Y a k Tunne l Remedia l Projec t Manage r Communit

y Involvemen t Coordinato r Phon e # : (303 ) 293-164 9 Phon e

# : (303 ) 294-113 0 Toll-fre e Number : 1 800-759-437 2 (i n Colorado )Mailin

g Lis t Addition s
I f yo u di d no t receiv e thi s ES D b y mail

, an d yo u woul d lik e t o b e adde d t o EPA' s mailin g lis t fo r th e Californi a Gulc h site
, pleas e sen d th e followin g informatio n to : Eleano r Dwigh t Communit y Involvemen t Coordinato r U.S

. EPA

, Regio n VIII

, 80E A
99 9 18t h Street

, Suit e 50 0 Denver

, Colorad o 80202-240 5
Name : Address : City/State:

. .Zip:

. Company

, organization
, o r governmenta l entity:

.

Ya k Tunne l Operabl e Uni t Explanatio n o f Significan t Difference * Documen t Contro l Numbe r 480001480 0 arc*\repon>\esdrev-2

. Revisio n 2 Octobe r 199 1 Pag e 2 1GLOSSAR Y Adi t - A n almos t horizonta l entranc e t o a mine

. Administrativ e Orde r - Se e Orde r below

. Cadmiu m - A heav y meta l foun d i n the ore s i n the Leadvill e Minin g District

. Exposur e t o cadmiu m ma y resul t i n hypertensio n an d kidne y an d live r damag e i n humans

. Cadmiu m i s use d i n meta l plating

, pigments
, an d chemica l production

. CERCL A

- The Comprehensiv e Environmenta l Response

, Compensation

, an d Liabilit y Ac t o f 198 0 - A federa l la w passe d i n 198 0 an d modifie d i n 198 6 b y SAR A (se e below)

. Th e Act s create d a specia l ta x tha t goe s int o a trus t fund

, commonl y know n a s Superfund

, t o investigat e and dean u p abandone d o r uncontrolle d hazardou s wast e sites

. Unde r th e legislation

, EP A ca n either : • Pa y for sit e clean-u p whe n partie s responsibl e for th e contaminatio n canno t b e locate d or are unwillin g o r unabl e t o perfor m th e work ; o r
• Tak e lega l actio n t o forc e responsibl e partie s fo r sit e contaminatio n t o dean u p th e sit e o r pa y bac k th e Federa l governmen t fo r th e cos t o f th e dean-up

. Contaminant s - An y chemica l tha t pose s a threa t t o publi c healt h and/o r th e environment

. Contaminant s ma y b e toxic
, ignitable

, explosive

, o r chemicall y reactive

. I n th e Leadvill e Minin g District

, th e principa l contaminant s ar e toxi c heav y metals

. Coppe r - A heav y meta l foun d i n ore s I n th e Leadvill e Minin g District

. Coppe r i s no t acutel y toxi c t o humans

, bu t i s one o f th e mos t harmfu l metal s t o fis h and othe r aquati c life

. Coppe r i s a semiprecious meta l use d I n electrica l an d electroni c equipment
, coins
, meta l plating

, an d meta l alloying

. Dolomit e - A for m o f limeston e whic h i s ric h i n magnesium

. Explanatio n o f Significan t Difference s (ESD )

- A document whic h EP A I s require d t o prepar e whe n change s ar e propose d I n th e remed y fo r a Superfun d site

. A n ES D i s issue d i f th e chang e I n th e remed y i s significant

, bu t no t fundamental

. Th e RO D mus t b e modifie d o r amende d i f th e chang e i s fundamental

. Facto r o f Safet y • Factor s o f safet y ar e use d t o incorporat e the uncertainties i n the design

, and t o reduc e the probabilit y o f failur e o f th e design

. I n engineerin g design

, th e rati o o f th e desig n propert y t o th e require d property

. Fo r example

, a pum p statio n designe d t o stor e an d pum p 15 0 gp m i n a portio n o f th e tunne l I n whic h th e averag e flo w rat e i s 10 0 gp m woul d hav e a facto r o f safet y o f 1.5

. A facto r o f safet y o f 1. 5 I s commo n i n man y engineerin g designs

. Feasibilit y Stud y - Se e Remedia l Investigation/Feasibilit

y Stud y below

. Gol d • A preciou s heav y meta l foun d I n ore s i n th e Leadvill e Minin g District

. Gra y porphyry - Se e porphyr y below

. 

### Hazardou s Substance s - Synonymou s wit h Contaminants

. Hea d
- Th e pressur e exerte d b y liqui d o r gas

. I n th e Ya k Tunnel

, hea d i s equa l t o th e dept h o f wate r standin g I n th e tunnel

, a s lon g a s th e tunne l I s no t flooded

. Hydrauli c Gradien t - Th e potentia l fo r ground wate r t o mov e i n a give n directio n du e t o th e differenc e I n pressur e betwee n tw o point s i n the aquifer

.
V« k Tunrw l Operabl e Uni t Revisio n 2 Octobe r 199 1 Explanatio n o f Significan t Difference s Pag e 2 2 Documen t Control Numbe r 4800-01-080 0 arc*\r«ports\«sdrev-2

.Lea d
- A heav y meta l foun d i n ore s i n th e Leadvill e Minin g District

. Exposur e t o lead ma y resul t i n damag e t o th e centra l nervou s syste m i n humans ; i n addition

, exposur e t o lea d ma y caus e cancer

. Lea d i s use d i n batteries

, foil

, solder

, pigments
, an d constructio n equipment
, an d a s a n additiv e i n gasoline

. Magnesiu m - A nonmeta l foun d i n limeston e an d or e bodies I n th e Leadvill e Minin g District

. Magnesiu m i s no t a contaminant i n environmenta l medi a i n th e Leadvill e area

. Manganes e - A heav y meta l foun d i n ore s i n th e Leadvill e Minin g District

. Manganes e can b e toxi c t o plant s i n acidi c soils

. Nationa l Prioritie s Lis t (NPL )

- EPA' s lis t o f th e mos t seriou s uncontrolle d o r abandone d hazardou s wast e site s identifie d fo r long-ter m remedia l respons e usin g mone y fro m th e Superfund

. Operabl e Unit - A n actio n take n a s on e part o f a n overal l sit e clean-up

. A number o f operabl e unit s ca n b e use d i n th e cours e o f a sit e dean-up

. Orde r - A lega l document whic h describe s th e action s whic h PRP s are required t o perfor m a t a Superfun d site

. Severa l type s o f Order s ma y b e used

, Including : • A Unilatera l Administrativ e Orde r (UAO ) whic h i s a document prepare d b y EP A withou t forma l

concurrenc e b y th e PRPs ; • A n Administrativ e Order on Consen t (AOC ) whic h I s a lega l agreemen t betwee n EP A and th e PRP s whereb y the PRP s agree t o perfor m o r pa y the cos t o f Superfun d sit e clean-up ; o r
• A Consen t Decre e (CD ) whic h i s a lega l agreemen t (essentiall y a n AOC)

, approve d an d issue d b y a judge

, betwee n EP A an d th e PRP s whereb y th e PRP s agre e t o perfor m al l o r part o f a Superfun d sit e dean-up

. A l l order s issue d t o PRP s fo r th e Ya k Tunne l Operabl e Unit hav e bee n Unilatera l Administrativ e Orders

. pH

- Scientifi c measur e o f th e relativ e acidit y o f a wate r solutio n on a logarithmi c scal e fro m 1 t o 14 ; lo w pH number s i n the 3 t o 5 rang e ar e typica l fo r strongl y acidi c minewate r drainin g int o the Californi a Gulc h area

. Porphyr y - Roc k havin g relativel y larg e conspicuou s crystal s I n a fine-graine d igneou s matrix

. Thi s typ e o f

roc k pushe d u p throug h th e surroundin g sedimentar y rock s an d wa s forme d afte r rapi d coolin g fro m th e molte n state

. Potentiall y Responsibl e Part y (PRP )

- A n individuals ) o r company(s ) (suc h a s owners , operators
, transporters
, o r generators ) potentiall y responsibl e for

, o r contributin g to
, the contaminatio n problem s a t a Superfun d site

. Wheneve r possible

, EP A require s PRPs

, throug h administrativ e o r lega l actions
, t o dea n u p hazardou s wast e site s the y hav e contaminated

. Unde r SARA

, som e curren t landowner s ar e exemp t I f the y di d

no t kno w abou t th e hazardou s substance s o n thei r propert y an d exercise d du e car e i n acquirin g th e property

. Recor d o f Decisio n (ROD )

- A publi c document tha t explain s whic h clean-u p alternative(s ) wil l b e use d a t N P L sites

. Th e RO D I s base d upo n informatio n an d technica l analysi s generate d durin g th e RI/F S an d consideratio n o f publi c comment s and communit y concerns

. Remedia l Actio n - Th e actua l constructio n o r implementatio n phas e tha t follow s remedia l desig n o f th e selecte d clean-u p alternatives a t a sit e on th e NP L Remedia l Desig n - A n engineerin g phas e tha t follow s th e ROD

, I n whic h technica l drawing s an d specification s ar e develope d fo r the subsequen t remedia l actio n at a sit e o n the NP L

Ya k Tunne l Operabl e Unt t Revision ! Octobe r 199 1 Explanatio n o f Significan t Difference s Pag e 2 3 Documen t Contro l Numbe r 4800-01-080 0 arcs\raports\esdrev-2

.Remedia l

Investigation/Feasibilit

y Stud y (RI/FS )

- Investigativ e an d analytica l studie s usuall y performe d

at the sam e tim e i n a n interactive
, iterativ e process , an d togethe r referre d t o a s the RI/FS

. The y ar e intende d to :
• Gathe r dat a necessar y t o determin e the typ e and exten t o f contaminatio n a t a Superfun d site ; • Establis h criteri a fo r cleanin g u p a site ; • Identif y an d scree n clean-u p alternative s fo r remedia l action ; an d

• Analyz e i n detai l th e technolog y an d cost s o f th e alternatives

. SAR A • Th e Superfun d Amendment s an d Reauthorizatio n Ac t o f 1986

. Thi s la w amende d CERCL A Silve r - A precious heav y meta l foun d i n ore s i n th e Leadvill e Minin g District

. Superfun d
- Th e commo n nam e fo r CERCL A Unconsolidate d sediment s - Th e geologi c materia l abov e bedrock

. Weathere d Dolomit e - Physicall y altere d dolomite

. Th e ter m "weathered " mean s tha t th e bedroc k ha s begun t o brea k dow n int o soli

. Zin c - A heav y meta l foun d i n ore s i n th e Leadvill e Minin g District

. Zin c i s rarel y damagin g t o huma n health ; however

, whe n human s ar e expose d t o zin c I n combinatio n wit h othe r metals

, th e result s ma y b e harmful

. A t hig h concentrations
, zin c can b e harmfu l t o fish

. Zin c i s use d i n batteries

, fuses

, pigments
, meta l platin g an d meta l alloying

.

Ya k Tunne l Operabl e Uni t Revisio n 2 Octobe r 199 1 Explanatio n o f Significan t Difference * Pag e 2 4 Documen t Contro l Numbe r 4800-01-080 0 are»\i»ports\esdrev-2

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