U N I T E D S T A T E S E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y _ » . , A . .F i l b P L A NR E G i o N v . i l999 1 8th STREET - SUITE 500

DENVER, COLORADO 80202-2405

A D M I N I S T R A T I V E R E C O R DRECORD O F D E C I S I O N

C L E A R C R E E K / C E N T R A L C I T Y S U P E R F U N D S I T EC L E A R CREEK A N D G I L P I N C O U N T I E S , C O L O R A D O

O P E R A B L E U N I T N O . T W OT A I L I N G S A N D W A S T E ROCK R E M E D I A T I O N

M A R C H 3 1 , 1988

D E C L A R A T I O NF O R T H ERECORD OF D E C I S I O N

S I T E N A M E A N D L O C A T I O NC l e a r C r e e k / C e n t r a l C i t y S u p e r f u n d S i t eC l e a r Creek a n d G i l p i n C o u n t i e s , C o l o r a d oO p e r a b l e U n i t N o . T w oT a i l i n g s a n d W a s t e Rock R e m e d i a t i o n

S T A T E M E N T O F P U R P O S ET h i s d e c i s i o n document r e p r e s e n t s t h e s e l e c t e d r emedia laction f o r Operab l e Unit N o . T w o ( T a i l i n g s a n d W a s t e RockR e m e d i a t i o n ) o f t h e C l e a r C r e e k / C e n t r a l C i t y S u p e r f u n d S i t ed e v e l o p e d in accordance with the C o m p r e h e n s i v e EnvironmentalR e s p o n s e , C o m p e n s a t i o n a n d L i a b i l i t y A c t o f 1980 ( C E R C L A ) , a samended by the S u p e r f u n d A m e n d m e n t s and R e a u t h o r i z a t i o n Act o f1986 ( S A R A ) , a n d t h e N a t i o n a l C o n t i n g e n c y P l a n ( 4 0 C F R Part 3 0 0 ) .The S t a t e o f C o l o r a d o has been con su l t ed on the Propo s edP l a n and has i n d i c a t e d that it w i l l concur on the s e l e c t e d remedyf o r O p e r a b l e U n i t N o . T w o .

S T A T E M E N T O F B A S I ST h i s d e c i s i on i s based upon the A d m i n i s t r a t i v e Record f orO p e r a b l e U n i t N o . T w o o f t h e C l e a r C r e e k / C e n t r a l C i t y S u p e r f u n dS i t e . T h e a t t a c h e d index i d e n t i f i e s t h e i tems which c o m p r i s e t h ea d m i n i s t r a t i v e record upon which the s e l e c t i o n of the remedialac t i on was based.

D E S C R I P T I O N O F S E L E C T E D R E M E D YT h e C l e a r C r e e k / C e n t r a l C i t y S u p e r f u n d S i t e i s l o c a t e da p p r o x i m a t e l y 30 m i l e s west o f Denver, C o l o r a d o and p r i m a r i l yc on s i s t s of acid mine d i s c h a r g e s and m i l l i n g and m i n i n g was t e sf r o m f i v e m i n e s / t u n n e l s i n t h e C l e a r Creek a n d N o r t h C l e a r Creekdra inage s . T h e s e are the Argo T u n n e l and Big F i v e T u n n e l in theC l e a r Cre ek d r a i n a g e ; a n d t h e G r e g o r y I n c l i n e , N a t i o n a l T u n n e l ,a n d t h e Quar t z H i l l T u n n e l i n t h e N o r t h C l e a r Creek d r a i n a g e .C o n d i t i o n s a t the f i v e t u n n e l s and t a i l i n g s and waste rock p i l el o c a t i o n s po s e p o t e n t i a l i m p a c t s to human h e a l t h and theenvironment.

More s p e c i f i c a l l y , p o t e n t i a l i m p a c t s t o human h e a l t h and th eenvironment r e s u l t i n g f r o m the acid mine d i s c h a r g e s i n c l u d e :- d e g r a d a t i o n o f downs t r eam s u r f a c e water q u a l i t y r e s u l t i n gf r o m d i s s o l v e d and s u s p e n d e d m e t a l s in the d i s c h a r g e s andr e s u s p e n d e d metal l a d e n s e d i m e n t s b e low the d i s c h a r g e s ; and

r e d u c t i o n in aquatic hab i ta t q u a l i t y or p r o d u c t i v i t y inC l e a r Creek a n d N o r t h C l e a r Creek r e s u l t i n g f r o mcon tamina t ed s u r f a c e water.T h e s e i m p a c t s were a d d r e s s e d in the S e p t e m b e r 30, 1987 Record o fDecis ion for the Discharge T r e a t m e n t Operab l e U n i t or O p e r a b l eU n i t N o . O n e f o r t h e s i te.

O p e r a b l e U n i t N o . T w o f o r t h e s i t e , t h e T a i l i n g s a n d W a s t eRock Remed ia t i on Operab l e U n i t , cons ider s p o t e n t i a l i m p a c t s t ohuman h e a l t h and the environment r e s u l t i n g f r o m :d e g r a d a t i o n o f d o w n s t r e a m s u r f a c e water q u a l i t y du e t oc o l l a p s e o f t h e p i l e s into e i ther C l e a r Cre ek o r N o r t h C l e a rC r e e k ;d e g r a d a t i o n o f d owns t r eam s u r f a c e water q u a l i t y due t o runonand r u n o f f f r o m th e t a i l i n g s and was te rock p i l e s ; and

- human u p t a k e o f m e t a l s f r o m the i n h a l a t i o n o f du s t ori n g e s t i o n o f m a t e r i a l f r o m th e t a i l i n g s and was te rockp i l e s .T h e s e i m p a c t s are a d d r e s s e d in t h i s Record o f Dec i s i on .

E P A i s u n d e r t a k i n g a n a d d i t i o n a l f e a s i b i l i t y s t u d y , O p e r a b l eUnit No. T h r e e o r th e B l o w o u t / D i s c h a r g e C o n t r o l Operab l e U n i t , t oe v a l u a t e r emed ia l ac t i on a l t e r n a t i v e s f o r r e m e d i a t i n g i m p a c t s t ohuman h e a l t h and the environment r e s u l t i n g f r o m a p o t e n t i a lb lowout o f t h e A r g o T u n n e l . I n a d d i t i o n , t h e S t a t e o f C o l o r a d ohas submitted an a p p l i c a t i o n to EPA for monies to f u n d ani n v e s t i g a t i o n t o i d e n t i f y other areas w i t h i n t h e m i n i n g d i s t r i c twhich may be s i g n i f i c a n t l y i m p a c t i n g N o r t h C l e a r Creek and C l e a rC r e e k . T h e S t a t e w i l l a l s o i n v e s t i g a t e t h e q u a l i t y o fgroundwat er in the area. D e p e n d i n g upon the r e s u l t s of the S t a t es t u d y , E P A m a y c on s id er a d d i t i o n a l o p e r a b l e u n i t s .T h e s e l e c t e d remedy f o r O p e r a b l e U n i t N o . T w o c o n s i s t s o fs l o p e s t a b i l i z a t i o n a t t h e Big F i v e T u n n e l and G r e g o r y I n c l i n eand runon con tro l a t a l l f i v e t a i l i n g s and waste rock p i l e s . Noact ion w i l l be taken at t h i s t ime to a d d r e s s p o t e n t i a l i m p a c t sf r o m i n h a l a t i o n a n d i n g e s t i o n o f m a t e r i a l f r o m t h e p i l e s .

The u n s t a b l e s l o p e s a t t h e Big F i v e T u n n e l and G r e g o r yI n c l i n e could c o l l a p s e into C l e a r Creek a n d N o r t h C l e a r C r e e k ,r e s p e c t i v e l y , and the r e s u l t i n g m e t a l s l o a d i n g into th e creekswould a d v e r s e l y a f f e c t t h e water q u a l i t y o f t h e creeks. S l o p es t a b i l i z a t i o n a t t h e B i g F i v e T u n n e l w i l l c ons i s t o f r e g r a d i n gp o r t i o n s o f t h e p i l e s t o a s t a b l e c o n f i g u r a t i o n and p l a c i n g l a r g eb o u l d e r s at the base to minimize erosion. The current gabionw a l l a t the G r e g o r y I n c l i n e w i l l b e m a i n t a i n e d un t i l m o n i t o r i n gi n d i c a t e s r e m e d i a t i o n is necessary or u n t i l the t a i l i n g s areremoved for r e p r o c e s s i n g . At that t i m e , a p ermanent s o l u t i o nw i l l be i m p l e m e n t e d .Runon control w i l l reduce th e m e t a l s l o a d i n g t o C l e a r Creekand N o r t h C l e a r C r e e k r e s u l t i n g in an improvement o f s tream waterq u a l i t y . Runon con tro l a t a l l f i v e l o c a t i o n s w i l l c ons i s t o fi n s t a l l i n g d i v e r s i o n d i t c h e s on th e u p g r a d i e n t s i d e s o f t h ep i l e s .No ac t i on w i l l be taken at t h i s t ime to a d d r e s s p o t e n t i a li m p a c t s f r o m i n h a l a t i o n a n d i n g e s t i o n o f m a t e r i a l f r o m t h e p i l e sbecause t h e P u b l i c H e a l t h E v a l u a t i o n f o r t h e s i t e i n d i c a t e d tha tcurrent or e p i s o d i c human h e a l t h and environmental ri sksr e s u l t i n g f r o m th e s e e x p o s u r e p a t h w a y s were minor. Curren t u s ec o n s i s t s o f p e r i o d i c v i s i t s to the s i t e s by l o ca l r e s i d e n t s andv i s i t o r s . T h e P u b l i c H e a l t h E v a l u a t i o n i n d i c a t e d , however, thatf o r a p o t e n t i a l f u t u r e r e s i d e n t i a l s c enario , r i sk s r e s u l t i n g f r o mthe i n h a l a t i o n and inge s t i on expo sure p a t h w a y s are of someconcern. T h e r e f o r e , E P A w i l l e v a l u a t e t h i s N o A c t i o n d e c i s i o nwhen th e f i n a l remedy i s s e l e c t e d f o r t h e s i t e . EPA, inc o o r d i n a t i o n w i t h t h e S t a t e o f C o l o r a d o a n d l o c a l o f f i c i a l s , w i l le v a l u a t e the u s e o f i n s t i t u t i o n a l measures which would c on tro lany human h e a l t h or environmental threat that could be created byf u t u r e d e v e l o p m e n t upon the s e t a i l i n g s and was t e rock p i l e s anda n y o ther p i l e s which t h e S t a t e i d e n t i f i e s i n i t s s t udy . I na d d i t i o n , p u r s u a n t t o S A R A S e c t i o n 1 2 1 ( c ) , E P A w i l l review n ol e s s than every f i v e years a l l p r o p e r t i e s where h a z a r d o u ssubstances continue to remain onsite and, i f nece s sary, w i l lr e cons ider t h i s N o A c t i o n d e c i s i o n .E s t i m a t e d cos t s f o r s l o p e s t a b i l i z a t i o n a t t h e Big F i v eT u n n e l and G r e g o r y I n c l i n e and runon contro l at a l l f i v e s i t e s i sa p p r o x i m a t e l y $ 1 . 0 m i l l i o n .T h e s e l e c t e d remedy f o r O p e r a b l e U n i t N o . T w o h a s beenchosen t o m i t i g a t e a n d minimize p o t e n t i a l i m p a c t s r e s u l t i n g f r o mthe t a i l i n g s and waste rock p i l e s and to p r o t e c t human h e a l t h andt h e environment. T h e s e l ec t ed remedy f o r O p e r a b l e U n i t N o . T w ois an i n t e r i m remedy because the net b e n e f i c i a l impac t to C l e a rCreek and N o r t h C l e a r Creek w i l l not be r e a l i z e d u n t i l thec o m p l e t i o n o f remedial ac t ions f o r t h e o ther o p e r a b l e uni t s . T h es e l e c t e d remedy t h e r e f o r e requires t h e exerci se o f t h e " in t e r imremedy" waiver ( S A R A S e c t i o n 1 2 1 ( d ) ( 4 ) ( A ) ) f r o m contaminant-

s p e c i f i c A R A R s l i s t e d i n t h e F e a s i b i l i t y S t u d y . T h e in t e r imremedy waiver a l l o w s f or th e s e l e c t i o n o f a r e m e d i a l ac t ion thatdoes not a t t a i n A R A R s if "the remedial action s e l e c t ed is on lypar t of a t o t a l r e m e d i a t i o n ac t ion that w i l l a t t a i n such l e v e l ors t a n d a r d o f control when c o m p l e t e d . " The i n t e r i m remedy i sc ons i s t en t w i t h the f i n a l s i t e remedy. L o c a t i o n - and ac t ion-s p e c i f i c A R A R s w i l l b e met.

D E C L A R A T I O NT h e s e l e c t e d remedy f o r O p e r a b l e U n i t N o . T w o o f t h e C l e a rC r e e k / C e n t r a l C i t y S u p e r f u n d S i t e i s a c o s t - e f f e c t i v e remedywhich i s p r o t e c t i v e o f human h e a l t h and the environment . Thes e l e c t e d remedy is an i n t e r i m remedy which doe s not a t t a i nF e d e r a l a n d S t a t e p u b l i c h e a l t h a n d e n v i r o n m e n t a l r equ ir ement sthat are a p p l i c a b l e or re l evant and a p p r o p r i a t e and t h e r e f o r e theS A R A S e c t i o n 1 2 1 ( d ) ( 4 ) ( A ) ) in t er im remedy waiver i s r equired.T h e s t a t u t o r y p r e f e r e n c e f o r t r e a t m e n t i s n o t s a t i s f i e dbecause t r ea tment was f o u n d to be i m p r a c t i c a b l e at t h i s t ime.H o w e v e r , E P A leaves open t h e o p p o r t u n i t y f o r a n y f u t u r e t r ea tmen tor r e p r o c e s s i n g which can be shown to be p r o t e c t i v e of humanh e a l t h and the environment and which a t t a i n s F e d e r a l and S t a t ep u b l i c h e a l t h and env ironmenta l r equirement s that ar e a p p l i c a b l eor r e l evant and a p p r o p r i a t e .

0 ______J a m e s ^ / S c h e r e f r DateR e g i o n a l A d m i n i s t r a t o rE n v i r o n m e n t a l P r o t e c t i o n A g e n c yRegion V I I I

S U M M A R YF O R T H E

RECORD OF D E C I S I O N

S I T E N A M E A N D L O C A T I O NC l e a r C r e e k / C e n t r a l C i t y S u p e r f u n d S i t eC l e a r Cre ek a n d G i l p i n C o u n t i e s , C o l o r a d oO p e r a b l e U n i t N o . T w oT a i l i n g s a n d W a s t e Rock R e m e d i a t i o n

S I T E D E S C R I P T I O NT h e C l e a r C r e e k / C e n t r a l C i t y S u p e r f u n d s i t e i s l o c a t e da p p r o x i m a t e l y 30 m i l e s vest of Denver, C o l o r a d o , and p r i m a r i l yc o n s i s t s o f acid mine d r a i n a g e s and m i l l i n g and m i n i n g wa s t e sf r o m f i v e m i n e s / t u n n e l s in th e C l e a r Creek and N o r t h C l e a r Creekd r a i n a g e s . T h e s i t e en compa s s e s t h e n o r t h e a s t e r n p o r t i o n o fC l e a r C r e e k C o u n t y a n d s ou th ea s t e rn p o r t i o n o f G i l p i n C o u n t y .S p e c i f i c a l l y , t h e f o c u s o f t h e R e m e d i a l I n v e s t i g a t i o n w a sf i v e abandoned m i n e s / t u n n e l s p r o x i m a l t o t h e c i t i e s o f I d a h oS p r i n g s , Black H a w k , a n d C e n t r a l C i t y ( F i g u r e 1 ) . T h e t u n n e l sare the A r g o T u n n e l and Big F i v e T u n n e l in the C l e a r Creekd r a i n a g e a n d t h e N a t i o n a l T u n n e l , G r e g o r y I n c l i n e , a n d t h e Q u a r t zH i l l T u n n e l i n t h e N o r t h C l e a r Creek d r a i n a g e . T h e A r g o p o r t a li s w i t h i n t h e c i t y l i m i t s o f I d a h o S p r i n g s . T h e B i g F i v e p o r t a lborders t h e I d a h o S p r i n g s c i ty l i m i t s . T h e G r e g o r y I n c l i n e i sw i t h i n t h e Black H a w k c i ty l i m i t s . T h e N a t i o n a l T u n n e l i s w i t h i na m i l e o f t h e C i t y o f Black H a w k . T h e Quar t z H i l l T u n n e l i sw i t h i n a mi l e o f the C i t y o f C e n t r a l C i t y .T h e waste r o c k / t a i l i n g s p i l e s c on s id er ed i n t h i s O p e r a b l eU n i t were s e l e c t e d based on t h e i r l o c a t i o n c l o s e to the acid mined i s c h a r g e s . C u r r e n t l y , t h e m a j o r i m p a c t s on th e water q u a l i t y o fC l e a r Creek are the Big F i v e and A r g o mine tunne l d i s c h a r g e s .T h e water q u a l i t y o f N o r t h C l e a r Creek i s a f f e c t e d b y t h eN a t i o n a l T u n n e l d i s c h a r g e a n d s e epage f r o m t h e G r e g o r y I n c l i n ea n d t h e Q u a r t z H i l l T u n n e l . T h e d i s c h a r g e s f r o m t h e f i v e s i t e swere a d d r e s s e d in O p e r a b l e U n i t No. One.I n a d d i t i o n t o d i r e c t d i s c h a r g e f r o m t h e mine t u n n e l s ,c o n t a m i n a t e d water may enter the creeks d u r i n g over land sheetf l o w . Over land r u n o f f occurs d u r i n g r a p i d snow mel t a n dt h u n d e r s t o r m s . T h e r e s u l t i n g s u r f a c e f l o w across t h e t a i l i n g sand waste rock p i l e s d i s s o l v e s s o l u b l e m i n e r a l s and t r a n s p o r t sp a r t i c u l a t e t a i l i n g s and waste rock ma t e r ia l into the creeks.T h e s e mechani sms r e s u l t in e l eva t ed creek a c i d i t y and metall o a d s . The i n t r o d u c t i o n o f t a i l i n g s and waste rock in to th e

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CAM* OM>S*CH • M c H C f I N C .

creeks c ou ld a l s o occur due t o c a t a s t r o p h i c c o l l a p s e o f t a i l i n g sand waste rock p i l e s d u r i n g a f l a s h f l o o d or as a r e su l t ofu n d e r c u t t i n g o f t h e base o f t h e p i l e under any f l o w regime.

S I T E H I S T O R YT h e C l e a r C r e e k / C e n t r a l C i t y hard rock m i n i n g d i s t r i c t i sh i s t o r i c a l l y one of the most mined areas in C o l o r a d o . At onet i m e , g o l d m i n i n g accounted f o r 85 percent o f t h e a c t i v i t y /s i l v e r f o r 1 0 perc en t a n d other m i n e r a l s , ( e . g . , c o p p e r , l e a d ,and z i n c ) the r e m a i n i n g 5 perc ent . The area i n c l u d e s over 800abandoned mine work ing s and t u n n e l s . Recent d a t a i n d i c a t e tha tup to t w e n t y - f i v e mines and s ix m i l l i n g o p e r a t i o n s are c u r r e n t l yo p e r a t i n g i n G i l p i n a n d C l e a r Creek c o u n t i e s . T h e i n t e n s i t y o fmin ing o p e r a t i o n s has varied in recent year s , due l a r g e l y tof l u c t u a t i n g market p r i c e s f o r p r e c i o u s m e t a l s .M i n i n g a c t i v i t y i n t h e C e n t r a l C i t y / B l a c k H a w k areacommenced in 1 8 5 9 . P l a c e r g o l d was f o u n d at the mouth of C h i c a g oC r e e k , near I d a h o S p r i n g s , i n J a n u a r y o f 1 8 5 9 and , i n M a y o f t h esame year, the f i r s t l o d e d i s c o v e r y in the Rocki e s was made inG r e g o r y G u l c h between C e n t r a l C i t y a n d B l a c k H a w k . I n i t i a l l y ,m i n i n g was c onc en tra t ed in the G r e g o r y G u l c h area, i n c l u d i n g theG r e g o r y I n c l i n e . E x p l o r a t i o n v i a a d i t s a n d s h a f t s r a p i d l ye x p a n d e d to the s ou th and west o f C e n t r a l C i t y . E x c a v a t i o n o ft h e Q u a r t z H i l l T u n n e l w a s begun i n 1 8 6 0 , l a r g e l y f o r t h e p u r p o s eo f t r a n s p o r t i n g o r e f r o m t h e o v e r l y i n g s u r f a c e G l o r y H o l e M i n e t om i l l s in C e n t r a l C i t y . The tunnel i s over a m i l e l o n g . N a t i o n a lT u n n e l c o n s t r u c t i o n was i n i t i a t e d in 1 9 0 5 and cont inued to 1 9 3 7 .The t unne l i s b e l i ev ed to be over 3 , 1 0 0 f e e t in l e n g t h .T h e A r g o T u n n e l w a s c on s t ruc t ed f r o m 1 8 9 3 t o 1904. T h etunne l was b u i l t for the dual p u r p o s e o f mine d r a i n a g e and oret r a n s p o r t . T h e t o t a l tunnel l e n g t h i s 4 .16 m i l e s , e x t e n d i n g f r o mthe p o r t a l in I d a h o S p r i n g s in a northward d i r e c t i o n to beneatht h e h e a d w a t e r s o f G r e g o r y G u l c h , west o f C e n t r a l C i t y .I n J u l y , 1 9 8 2 , t h e C l e a r C r e e k / C e n t r a l C i t y s i t e w a s rankeda s S i t e N o . 1 7 4 o n t h e I n t e r i m P r i o r i t i e s L i s t o f 4 0 0 s i t e s . T h es i t e w a s added t o t h e f i n a l N a t i o n a l P r i o r i t i e s L i s t ( N P L ) i nS e p t e m b e r , 1 9 8 3 . E P A began t h e R e m e d i a l I n v e s t i g a t i o n ( R I ) o ft h e s i t e in J u l y , 1 9 8 5 . The RI Repor t wa s i s sued in J u n e , 1 9 8 7a n d r e p o r t e d r e s u l t s f r o m t h e s t u d y p er i od o f J u l y , 1 9 8 5 t h r o u g hDecember, 1 9 8 6 . An a d d e n d u m to the RI was i s sued in J a n u a r y ,1988 t o report r e s u l t s f r o m a d d i t i o n a l s t u d i e s c onduc t ed i n A p r i land M a y , 1 9 8 7 .A removal ac t i on w a s c onduc t ed b y E P A ' s Emergency R e s p o n s eBranch at the G r e g o r y I n c l i n e in M a r c h , 1987 to p r o t e c t humanh e a l t h and th e environment f r o m h a z a r d s a s s o c ia t ed w i t h th ec o l l a p s e o f a r e t a i n i n g crib w a l l . A c o l l a p s e would have a l l o w e d

the t a i l i n g s t o s l i d e into N o r t h C l e a r Creek and EPA wasconcerned that a large load of m e t a l s - l a d e n t a i l i n g s would washd o w n s t r e a m into C l e a r Creek and con taminat e the m u n i c i p a l waters u p p l y o f t h e C i t y o f G o l d e n , C o l o r a d o . E P A removed a n o l dd e t e r i o r a t e d crib r e t a i n i n g w a l l and d e c r ea s ed the s l o p e o f thet a i l i n g s p i l e t o s t a b i l i z e i t . EPA then c o n s t r u c t e d a gabion-basket r e t a i n i n g w a l l .

S C O P E A N D ROLE O F T H E O P E R A B L E U N I TDuring the course of the RI, EPA de t e rmined , in accordancewi th 4 0 C F R S e c t i o n 3 0 0 . 6 8 ( c ) , that t h e F e a s i b i l i t y S t u d y ( F S )s h o u l d be d i v i d e d into O p e r a b l e U n i t s in order to r e m e d i a t e s i t e-s p e c i f i c p r o b l e m s .

T h e O p e r a b l e U n i t s in c lude:O p e r a b l e U n i t N o . O n e - M i n e T u n n e l D i s c h a r g e T r e a t m e n t( R e c o r d o f Dec i s i on s igned i n S e p t e m b e r , 1 9 8 7 )O p e r a b l e U n i t N o . T w o - T a i l i n g s a n d W a s t e Rock R e m e d i a t i o nO p e r a b l e Unit N o . T h r e e - B l o w o u t / D i s c h a r g e C o n t r o lI n a d d i t i o n , t h e S t a t e o f C o l o r a d o h a s submi t t ed a na p p l i c a t i o n t o EPA for monies t o f u n d an i n v e s t i g a t i o n toi d e n t i f y o ther areas w i t h i n the m i n i n g d i s t r i c t which may bes i g n i f i c a n t l y i m p a c t i n g N o r t h C l e a r Creek a n d C l e a r Creek. T h eS t a t e w i l l a l s o i n v e s t i g a t e t h e q u a l i t y o f t h e g r o u n d w a t e r i n t h earea. D e p e n d i n g upon th e r e s u l t s o f t h e S t a t e s t u d y , EPA mayc on s id e r a d d i t i o n a l o p e r a b l e u n i t s .

S I T E C H A R A C T E R I S T I C SA p u b l i c h e a l t h e v a l u a t i o n wa s c o n d u c t e d t o i d e n t i f yc o m p o u n d s which could po se a s i g n i f i c a n t threat to human h e a l t hand the environment. Based on s a m p l i n g of environmental mediaand c o n s i d e r a t i o n o f t o x i c i t y , t w e l v e c o n t a m i n a n t s o f concernwere i d e n t i f i e d and p o t e n t i a l e x p o s u r e p a t h w a y s were a n a l y z e d .I m p a c t s on human h e a l t h and the environment were as s e s s ed fore x p o s u r e s due t o i n h a l a t i o n and i n g e s t i o n o f m a t e r i a l f r o m th ep i l e s and due t o r u n o f f f r o m th e p i l e s and c a t a s t r o p h i c s l o p ef a i l u r e o f t h e p i l e s into t h e s t r eams.A s s t a t e d , t w e l v e c on taminant s were i d e n t i f i e d d u r i n g t h ep u b l i c h e a l t h e v a l u a t i o n a s c o n t a m i n a n t s o f concern in the C l e a rC r e e k / C e n t r a l C i t y s tudy area. C o n t a m i n a n t s o f concern werechosen s e p a r a t e l y f or human r e c e p t o r s and aquat i c o r g a n i s m s .A r s e n i c , chromium ( V I ) , a n d n i ck e l a r e pr e s en t i n r e l a t i v e l y h i g hc o n c e n t r a t i o n s in the t a i l i n g s and waste rock and have been ratedby EPA as G r o u p A human car c inogen s by the i n h a l a t i o n p a t h w a y .C a d m i u m is a G r o u p B1 carcinogen by i n h a l a t i o n and is a p o t e n t

k i d n e y toxin when i n g e s t e d . Lead and s i lv er are toxicn o n c a r c i n o g e n s and are pre sent in r e l a t i v e l y h i g h c o n c e n t r a t i o n sin the t a i l i n g s and waste rock.C o n t a m i n a n t s o f concern f o r aquat i c l i f e were chosen basedon t h e i r c onc en tra t i on in water, p u b l i s h e d c r i t e r i a v a l u e s ( e . g . ,A m b i e n t W a t e r Q u a l i t y C r i t e r i a ( A W Q C ) ) , a n d s u p p l e m e n t a l d a t a f o rc h e m i c a l s that la cked c r i t e r ia . C o n t a m i n a n t s i n c l u d e a l u m i n u m ,ar s en i c , c a d m i u m , chromium, c o p p e r , f l u o r i d e , l e a d , mangane s e ,n i c k e l , s i l v e r , and zinc.E x p o s u r e to m e t a l s in t a i l i n g s or waste rock can p o t e n t i a l l yoccur t h r o u g h i n h a l a t i o n of dust by p e o p l e at or near the s i t e s .Two mechanisms for dust generat ion were cons idered in thee v a l u a t i o n : ( 1 ) dus t r e s u l t i n g f r o m wind entra inment o f t a i l i n g so r soil p a r t i c l e s ; a n d ( 2 ) dust g enera t ed f r o m human a c t i v i t i e s( i n p a r t i c u l a r , r i d i n g o f d ir t bikes o n t h e t a i l i n g s p i l e s ) . T h eG r e g o r y t a i l i n g s p i l e i s r e a d i l y a c c e s s i b l e and in some areas i squite c ompac t ed or has a s u r f a c e crust . Dirt-b ike r i d i n g isknown t o occur a t t h e G r e g o r y t a i l i n g s p i l e . T h e A r g o t a i l i n g sare a l s o r e a d i l y a c c e s s i b l e and are l e s s compacted and moref r i a b l e than t h e G r e g o r y t a i l i n g s . T h e A r g o t a i l i n g s a r e n o tused e x t e n s i v e l y by d ir t -b ike r iders due to the ir s t e epne s s .C u r r e n t l y , however, was te rock at A r g o i s be ing removed for usei n c o n s t r u c t i n g roads . T h i s a c t i v i t y , which i n v o l v e s o p e r a t i o no f d u m p t ru ck s and f r o n t - e n d l o a d e r s , increase s dust emi s s i on sf r o m t h i s area.In a d d i t i o n to i n h a l a t i o n , e x p o s u r e to m e t a l s in soil ort a i l i n g s can a l s o occur by in c id en ta l i n g e s t i o n . T o u r i s t sv i s i t i n g th e mines may contact th e t a i l i n g s , a l t h o u g h th ep o t e n t i a l f o r s i g n i f i c a n t exposure i s low. Older c h i l d r e n l i v i n gin the area, p a r t i c u l a r l y tho s e f r o m ages 6 to 16 who have l e s sp a r e n t a l s u p e r v i s i o n than younger c h i l d r e n , may p l a y or r ide d ir tbikes a t th e t a i l i n g s p i l e s e s p e c i a l l y d u r i n g th e summer month swhen school is out.F u t u r e u s e o f t h e s i t e s may i n c l u d e r e s i d e n t i a l d e v e l o p m e n t .U n d e r t h i s scenario, p o t e n t i a l exposure p a t h w a y s would i n c l u d ei n c i d e n t a l i n g e s t i o n o f c ontaminat ed m a t e r i a l by the r e s i d e n t sover the ir l i f e t ime. T h i s p o t e n t i a l f u t u r e u s e r e s i d e n t i a le x p o s u r e scenario was a l s o e v a l u a t e d .In summary, th e m a j o r p o t e n t i a l i m p a c t s a t th e s i t e due t ot a i l i n g s and was t e rock are:

o D e g r a d a t i o n o f s u r f a c e water q u a l i t y caused b y r u n o f f f r o mt h e p i l e s ;

o D e g r a d a t i o n o f s u r f a c e water q u a l i t y caused by c o l l a p s e o ft h e p i l e s into t h e creeks; a n d ,o H u m a n u p t a k e o f m e t a l s t h r o u g h i n h a l a t i o n or i n g e s t i o n .

E x p o s u r e to humansU n d e r both current land u s e c o n d i t i o n s and p o t e n t i a l f u t u r euse s c enar io s , the p r i n c i p a l p o t e n t i a l p a t h w a y s by which humanr e c e p t o r s cou ld be expo s ed to s i t e c o n t a m i n a n t s f r o m the t a i l i n g sand waste rock p i l e s is t hrough i n h a l a t i o n or inge s t i on ofm a t e r i a l f r o m t h e p i l e s . I m p a c t s r e s u l t i n g f r o m i n g e s t i o n o fs u r f a c e water were eva lua t ed a s part o f O p e r a b l e U n i t No. One.E x p o s u r e s cenarios f or average and maximum p l a u s i b l e caseswere d e v e l o p e d f o r both t h e i n h a l a t i o n and i n g e s t i o n p o t e n t i a le xpo sur e p a t h w a y s . Based on e s t i m a t e s of e x p o s u r e and aq u a n t i t a t i v e d e s c r i p t i o n o f each c o n t a m i n a n t ' s t o x i c i t y , humanh e a l t h ri sks were then as s e s s ed. The m a j o r c onc lu s i on s o f t h i sa s s e s sment are p r e s e n t e d in T a b l e 1 and can be summarized asf o l l o w s :

o I n h a l a t i o n o f w ind-en tra ined du s t f r o m t h e G r e g o r y T a i l i n g sp i l e r e s u l t s i n u p p e r b o u n d l i f e t i m e excess cancer r i sk s o f7 x 1 0 and 3 x 1 0 for the average and maximum p l a u s i b l eca s e s , r e s p e c t i v e l y , p r i m a r i l y f r o m e x p o s u r e t o arsenic.I n h a l a t i o n o f wind-entrained dust f r o m t h e A r g o T a i l i n g p i l er e s u l t s i n u p p e r b o u n d l i f e t i m e excess cancer r i sk s o f 2 x 1 0and 3 x 1 0 , for the average and maximum p l a u s i b l e ca s e s ,r e s p e c t i v e l y . G e n e r a t i o n of dust by dir t bikes r idden att h e G g e g o r y T a i l i n g s p i l e s r e s u l t s i n u p p e r b o u n d r i s k s o f5 x 1 0 and 1 x 1 0 , f or the average and maximum p l a u s i b l ecase s , r e s p e c t i v e l y . Risk s f r o m i n h a l a t i o n o f du s t f r o m t h eo ther t a i l i n g s and waste rock p i l e s are s i m i l a r .o I n g e s t i o n o f a r s e n i c - c o n t a m i n a t e d m a t e r i a l f r o m t h e t a i l i n g sand was t e rock p i l e s under current use, or the e p i s o d i cexposure scenario, po s e s an upperbound l i f e t i m e excesscancer r i sk of 2x10~^ f O r the average case and 1x10~4 undermaximum p l a u s i b l e c o n d i t i o n s .o I n g e s t i o n o f ar s eni c-contaminated m a t e r i a l f r o m t h e t a i l i n g sand waste rock p i l e s under the p o t e n t i a l f u t u r e user e s i d e n t i a l scenario po s e s an u p p e r b o u n d l i f e t i m e exce s scancer r i sk of 1x10"^ under average c o n d i t i o n s and 9x10~^under maximum p l a u s i b l e c o n d i t i o n s .

The r i s k s for i n d i v i d u a l s i t e s are p r o v i d e d in T a b l e 1 and amore d e t a i l e d d i s c u s s i o n o f the s e e x p o s u r e p a t h w a y s and ther e s u l t i n g r i sk s can b e f o u n d in th e P u b l i c H e a l t h E v a l u a t i o n ,

TABLE 1S U M M A R Y O F R I S K A S S E S S M E N T R E S U L T S F O R H U M A N E X P O S U R ET O C O N T A M I N A N T S A T T H E C L E A R C R E E K / C E N T R A L C I T Y S I T E

T o t a l Exce s s U p p e r - B o u n dL i f e t i m e Cancer Risk

E x p o s u r e P a t h w a yA v e r a g e M a x i m u m P l a u s i b l e

Case Case

I n h a l a t i o n o f Dust E n t r a i n e dby W i n dG r e g o r yA r g oI n h a l a t i o n o f Dust G e n e r a t e dby M o t o r c y c l e sG r e g o r yI n c i d e n t a l I n g e s t i o n o f S o i la n d T a i l i n g sE p i s o d i c E x p o s u r eG r e g o r yA r g o

B i g F i v eN a t i o n a lQ u a r t z H i l lI n c i d e n t a l I n g e s t i o n o f S o i la n d T a i l i n g sR e s i d e n t i a l E x p o s u r eG r e g o r y

A r g oB i g F i v eN a t i o n a lQ u a r t z H i l l

7x102x10-6-5

5x10 -6

2x102x101x102x102x10

-5-5-5-5

1x101x108x101x101x10

-4-4-5-4-4

3x103x10-5-5

1x10 -4

1x101x108x101x101x10

-4-4-5-4-4

6x106x104x106x106x10

-4-4-4-4-4

S e c t i o n 10 o f t h e Remedia l I n v e s t i g a t i o n R e p o r t . I m p a c t s onaquatic l i f e d u e t o c a t a s t r o p h i c s l o p e f a i l u r e a n d r u n o f f d u r i n gs torm event s are d i s c u s s e d in the f o l l o w i n g p a r a g r a p h s .E x p o s u r e s t o A q u a t i c L i f e

T h e e xpo sur e o f aquatic l i f e i n C l e a r Creek a n d N o r t h C l e a rCre ek were c o n s i d e r e d . T h e p r i n c i p a l p o t e n t i a l p a t h w a y s b y whicht h e t a i l i n g s a n d waste rock p i l e s impac t aquat i c l i f e are:o D e g r a d a t i o n o f s u r f a c e water q u a l i t y caused by c o l l a p s e o fthe p i l e s into the creeks; ando D e g r a d a t i o n o f s u r f a c e water q u a l i t y caused by r u n o f f f r o mt h e p i l e s .

C a t a s t r o p h i c S l o p e F a i l u r e :The f a i l u r e o f a s l o p e r e s u l t s in movement o f a mass o fwas t e rock a n d / o r t a i l i n g s into t h e a d j a c e n t creek. I f t h e s em a t e r i a l s are r eac t ive or t o x i c and are i n t r o d u c e d into a wateror air s tream, where exposure to environmental or human r e c ep t or sc a n occur, then a hazard e x i s t s . T h e p o t e n t i a l f o r c a t a s t r o p h i cs l o p e f a i l u r e w a s a s s e s s ed f o r each s i t e .

A r g o T u n n e l : A g e o t e c h n i c a l e v a l u a t i o n was p e r f o r m e d on thewaste r o c k / t a i l i n g s p i l e a t t h e A r g o T u n n e l a n d M i l l . T h ee v a l u a t i o n c o n c l u d e d that th e t o e o f th e s l o p e behind thecommerc ial b u i l d i n g s had been cut away and the s l o p e wasm a r g i n a l l y s t a b l e a n d increased weakness c ou ld r e s u l t f r o mf u r t h e r a c t i v i t i e s o r d i s t u r b a n c e . A s l o p e f a i l u r e wou ld impac tthe b u i l d i n g s but m a t e r i a l s would p r o b a b l y not reach C l e a r Creek .The vo lume o f such a f a i l u r e was e s t i m a t e d a t 1 1 , 2 0 0 cubic y a r d s( c y ) .B i g F i v e T u n n e l : A g e o t e c h n i c a l e n g i n e e r i n g e v a l u a t i o n w a sconducted on two mine waste rock p i l e s (one on the north s ide ofC l e a r Creek and one on the south s i d e ) created f r o m m a t e r i a lexcavated f r o m t h e B i g F i v e T u n n e l . T h e c o n c l u s i o n s o f t h e s ee v a l u a t i o n s i n c l u d e d :

o The eas tern por t i on of the waste rock p i l e on the north s ideof C l e a r Cre ek and the wes t ern p o r t i o n o f the was t e rockp i l e on th e s ou th s ide o f C l e a r C r e e k ar e m a r g i n a l l y s t a b l et o u n s t a b l e ;o A 100-year f l o o d could erode the toe of e x i s t i n g s l o p e s backseven to ten f e e t and d e cr ea s e s l o p e s t a b i l i t y . A 500-yearf l o o d c ou ld erode t h e s l o p e back a n a d d i t i o n a l t w o f e e t ;a n d ,o A l l s l o p e s a r e s u b j e c t t o erosion i f l e f t e x p o s e d .

8

Based on the r e s u l t s of the g e o t e c h n i c a l i n v e s t i g a t i o n s ,vo lumes o f m a r g i n a l l y s t a b l e and u n s t a b l e mine was te rock havebeen c a l c u l a t e d to be 2000 and 6200 cy for the north and s ou thbank s , r e s p e c t i v e l y . I n a d d i t i o n , t h e v o l u m e s o f waste rockwhich could become m a r g i n a l l y s t a b l e or u n s t a b l e a f t e r seven tot e n f e e t eros ion back f r o m t h e t o e o f t h e e x i s t i n g was t e p i l e sdue to a 100-year f l o o d were a l s o d e t e r m i n e d . The vo lume wasc a l c u l a t e d to be 7200 and 7900 cy for the north and south banks,r e s p e c t i v e l y .Q u a r t z H i l l a n d N a t i o n a l T u n n e l : T h e waste rock p i l e a d j a c e n t t ot h e N a t i o n a l T u n n e l i s c on s idered s t a b l e . S o m e s l o p e s near t h eQuartz H i l l T u n n e l are m a r g i n a l l y s t a b l e and some minorr e c o n t o u r i n g is r e commended.G r e g o r y I n c l i n e : I n 1 9 8 7 , t h e t a i l i n g s p i l e a t t h e GregoryI n c l i n e wa s recontoured t o a 2:1 ( h o r i z o n t a l t o v e r t i c a l ) s l o p eand a gabion-baske t r e t a i n i n g w a l l was c o n s t r u c t e d . The gabion-basket w a l l is p a r t i a l l y immersed in creek water and is e x p o s e dto acid d r a i n a g e . W i t h o u t m a i n t e n a n c e , the w a l l has an e s t i m a t e dl i f e o f f i v e years. T h e wal l i s s u p p o r t i n g a n e s t imat ed 1 , 1 0 0cubic y a r d s o f t a i l i n g s which would o th erwi s e c o l l a p s e in to N o r t hC l e a r C r e e k .

M o r e d e t a i l s on the g e o t e c h n i c a l e v a l u a t i o n s c onduc t ed att h e C l e a r C r e e k / C e n t r a l C i t y S u p e r f u n d S i t e c a n b e f o u n d i nS e c t i o n 8 o f the Remed ia l I n v e s t i g a t i o n Repor t and S e c t i o n 5 o ft h e A d d e n d u m t o t h e Remedia l I n v e s t i g a t i o n R e p o r t .E s t i m a t e d I m p a c t D u e t o C a t a s t r o p h i c C o l l a p s e :

A computer model was used to p r ed i c t water q u a l i t y in C l e a rC r e e k and N o r t h C l e a r Creek in the as se s sment o f human h e a l t h ande n v i r o n m e n t a l i m p a c t s r e s u l t i n g f r o m t h e c a t a s t r o p h i c f a i l u r e o ft h e B i g F i v e T u n n e l a n d G r e g o r y I n c l i n e was te rock a n d t a i l i n g sp i l e s . T h e c o l l a p s e o f t h e B i g F i v e was te rock p i l e s w a s m o d e l e dunder r e a l i s t i c , worst case c o n d i t i o n s . In p a r t i c u l a r , a t o t a lo f 8 , 2 0 0 cubic y a r d s o f mat er ia l ( b o t h nor th and south banksc o l l a p s e ) w a s i n s t a n t a n e o u s l y i n t r o d u c e d in to C l e a r Creek d u r i n gnormal l o w f l o w ( 4 0 cubic f e e t p e r second ( c f s ) ) . T h e 8 ,200cubic yard s i s the q u a n t i t y o f ma t e r ia l c u r r e n t l y u n s t a b l e andwhich cou ld c o l l a p s e in to C l e a r Creek a t any t i m e , i n c l u d i n gd u r i n g l ow f l o w c o n d i t i o n s . Z i n c and a l u m i n u m were s e l e c t e d t or e p r e s e n t t h e v a r i e t y o f g eo chemica l behavior e x p e c t e d f r o m t h et w e l v e i d e n t i f i e d c o n t a m i n a n t s o f concern. A r s e n i c wa s no tm o d e l e d because measured c onc en tra t i on s in the s t r eams andl e a c h a t e s were be low d e t e c t i o n l i m i t s . Lead and c o p p e r were notmode l ed because l eacha t e concentrat ions were low.A c o l l a p s e o f t h e B i g F i v e p i l e into C l e a r C r e e k wou ldr e s u l t in a peak d i s s o l v e d c o n c e n t r a t i o n o f 1 , 0 0 0 u g / L o fa l u m i n u m a t t h e po in t o f c o l l a p s e . A f t e r o n e d a y , t h e

c o n t a m i n a t i o n wou ld reach G o l d e n where a maximum c o n c e n t r a t i o n o f730 u g / L o f a l u m i n u m i s p r e d i c t e d . The a luminum concentra t i on atG o l d e n under ambient c o n d i t i o n s i s 200 u g / L . A c o l l a p s e o f t h eBig F i v e p i l e would re sul t in a maximum d i s s o l v e d concentrat iono f 1 , 1 0 0 u g / L o f zinc a t t h e c o l l a p s e p o i n t , a n increase f r o m400 u g / L o f zinc under ambient c ondi t i on s . T h i s t r a n s l a t e s intoa maximum c o n c e n t r a t i o n o f 960 u g / L o f z inc a t G o l d e n a f t e r twod a y s which would g r a d u a l l y decrease t o 400 u g / L a f t e r e ight days .The zinc c o n c e n t r a t i o n at G o l d e n under ambient c o n d i t i o n s i sabout 300 u g / L . The m o d e l i n g r e s u l t s ind i ca t e that maximumc o n c e n t r a t i o n s of a l u m i n u m and zinc would exceed AWQC in al lstream s egment s down to G o l d e n . At G o l d e n , the AWQC would beexc e eded by a f a c t o r of 24 and 89, r e s p e c t i v e l y for a l u m i n u m andzinc. Based on the m o d e l i n g of zinc and a luminum, it ise s t i m a t e d that c o n c e n t r a t i o n s o f s e l e c t e d p a r a m e t e r s in C l e a rCreek at G o l d e n would a l s o exceed maximum contaminant l e v e l s( M C L s ) e s t a b l i s h e d under t h e S a f e D r i n k i n g W a t e r A c t . T h er e s u l t s of the model c l e a r l y indi ca t e an adverse impact on C l e a rC r e e k due t o c o l l a p s e o f the was te rock p i l e s a t the Big F i v eT u n n e l .S i m i l a r a n a l y s e s o f c o l l a p s e o f t h e G r e g o r y T a i l i n g s intoN o r t h C l e a r Cre ek have been p e r f o r m e d . R e s u l t s f r o m t h i s e f f o r tind i ca t e that both AWQC and MCL value s would be exceeded in C l e a rC r e e k at G o l d e n as a r e s u l t of a c o l l a p s e .

I m p a c t D u e t o R u n o f f :I n a d d i t i o n t o c o l l a p s e o f t h e t a i l i n g s a n d was t e rockp i l e s , m a t e r i a l s w i l l a l s o enter t h e stream d u e t o r u n o f f f r o mt h e p i l e s d u r i n g snow melt and s torm event s . The r e s u l t s o f t h ea n a l y s e s o f s a m p l e s taken on C l e a r Creek and N o r t h C l e a r Creekd u r i n g s torm events i n d i c a t e that the average t o t a l a l u m i n u m andzinc concentra t ions exceeded AWQC values by f a c t o r s of 69 and 15t i m e s , r e s p e c t i v e l y . T h e r e s u l t s i n d i c a t e p o t e n t i a l impac t o naquatic l i f e due to r u n o f f dur ing storm events. I m p a c t s on humanh e a l t h due t o r u n o f f f r o m the s i t e s are minimal because the s tormevents are of l i m i t e d durat ion.

Summary o f Expo sure s t o A q u a t i c L i f e :The m a j o r c onc lu s i on s o f the assessment o f expo sure toaquat i c l i f e c an b e summarized a s f o l l o w s :

o S e v e r a l of the c h e m i c a l s of concern are at c o n c e n t r a t i o n sthat exceed the ambient water q u a l i t y cr i t er ia for thep r o t e c t i o n o f f r e s h w a t e r aquat i c l i f e ( A W Q C ) . I np a r t i c u l a r , c oncen tra t i on s o f z inc , c o p p e r , and a l u m i n u mc o n s i s t e n t l y exceed t h e acute a n d chronic A W Q C . I na d d i t i o n , c onc en t ra t i on s of manganese in the water exceedth e l owe s t observed e f f e c t l eve l in rainbow trou t . Becauseaquatic organi sms are exposed to a mix tur e and not10

i n d i v i d u a l c h e m i c a l s , t ox i c e f f e c t s may be even gr ea t e r thani n d i c a t e d by c ompar i s on t o th e AWQC. A l t h o u g h some f i s h mayt o l e r a t e the c h e m i c a l s in the creeks , i t i s h i g h l y u n l i k e l ythat t h e p o p u l a t i o n s o f f i s h f o u n d i n the s e creeks a r e f r e eo f t o x i c e f f e c t s .A more d e t a i l e d d i s c u s s i o n of th e s e e x p o s u r e p a t h w a y s andthe r e s u l t i n g r i s k s can b e f o u n d in th e P u b l i c H e a l t h E v a l u a t i o n ,S e c t i o n 1 0 o f t h e Remed ia l I n v e s t i g a t i o n R e p o r t . I t i s c l eartha t a r e l e a s e or s u b s t a n t i a l thr ea t of r e l e a s e of a h a z a r d o u ssubstance or p o l l u t a n t or contaminant into the environment hasoccurred a t t h e C l e a r C r e e k / C e n t r a l C i t y S u p e r f u n d s i t e and thatremedial act ion i s j u s t i f i e d .

C O M M U N I T Y P A R T I C I P A T I O NOn October 26, 27, and 28, 1 9 8 7 , announc emen t s for thep u b l i c comment per iod and the p u b l i c mee t ing to be h e ldconcerning t h e O p e r a b l e U n i t N o . T w o F e a s i b i l i t y S t u d y ( F S ) werep u b l i s h e d i n t h e W e e k l y Regi s t e r C a l l , t h e G o l d e n T r a n s c r i p t , a n dt h e C l e a r Cre ek C o u r a n t . The ad s announced th e N o v e m b e r 9t h r o u g h December 8, 1987 p u b l i c comment p er i od and the N o v e m b e r24 p u b l i c m e e t i n g , gave a b r i e f d e s c r i p t i o n o f the r emed ia lac t i on a l t e r n a t i v e s , a n d s t a t e d t h e r a t i o n a l e f o r t h e P r o p o s e dP l a n . T h e p r e s s r e l e a s e , a l o n g w i th t h e P r o p o s e d P l a n , w a sm a i l e d to the a p p r o x i m a t e l y 300 names on the E P A - c o m p i l e d C l e a rC r e e k / C e n t r a l C i t y S u p e r f u n d S i t e m a i l i n g l i s t .T h e p r e s s r e l e a s e n o t i f i e d t h e p u b l i c o f t h e a v a i l a b i l i t y o ft h e A d m i n i s t r a t i v e Record f o r t h e s i t e and i n f o r m e d them o fl o c a t i o n o f th e i n f o r m a t i o n r e p o s i t o r i e s which had p r e v i o u s l ybeen e s t a b l i s h e d f o r t h e s i t e . T h o s e i n f o r m a t i o n r e p o s i t o r i e sare l o ca t ed at the EPA l ibrary in Denver, the G i l p i n C o u n t y CourtH o u s e i n C e n t r a l C i t y , t h e I d a h o S p r i n g s P u b l i c L i b r a r y a n d t h eI d a h o S p r i n g s C i t y H a l l i n I d a h o S p r i n g s , a n d t h e G o l d e n P u b l i cL i b r a r y i n G o l d e n , C o l o r a d o . T h e A d m i n i s t r a t i v e Record i sl o ca t ed at the G i l p i n C o u n t y Cour thou s e and the EPA Library. Anindex of the A d m i n i s t r a t i v e Record is l o ca t ed at each i n f o r m a t i o nr e p o s i t o r y and is a l s o at tached to th i s Record of Decis ion.On November 24, 1 9 8 7 , EPA he ld a p u b l i c mee t ing concerningt h e O p e r a b l e U n i t N o . T w o F S a n d t h e P r o p o s e d P l a n .A p p r o x i m a t e l y 5 0 p e o p l e a t t e n d e d . M a j o r concerns rai sed were h o wE P A ' s pr e s enc e i n t h e area w a s a f f e c t i n g t h e economy o f t h e area,the p er c e iv ed l a r g e amount s of money which EPA is s p e n d i n g ons t u d y i n g the s i t e , and whe ther r e m e d i a l a c t i on at the s i t e i sw a r r a n t e d . At the request o f several who a t t e n d e d the p u b l i cm e e t i n g , EPA e x t e n d e d the p u b l i c comment p e r i o d on the O p e r a b l eU n i t N o . T w o F S t o December 1 8 , 1987 a n d as sured concernedi n d i v i d u a l s that l a t e comments would be a c c e p t e d up u n t i l thed e c i s i o n w a s made ( l a t e M a r c h ) .

1 1

T h e O p e r a b l e U n i t N o . T w o R e s p o n s i v e n e s s S u m m a r y c o n t a i n sthe o f f i c i a l t r a n s c r i p t o f the p u b l i c m e e t i n g , de s cr ibe s in mored e t a i l th e nature and l eve l o f th e c o m m u n i t y ' s concern, andi n c l u d e s E P A ' s r e s p o n s e s t o a l l comments received d u r i n g t h ep u b l i c review o f t h e O p e r a b l e U n i t N o . T w o F S .

E N F O R C E M E N TA r e s p o n s i b l e p a r t y search f o r t h e C l e a r C r e e k / C e n t r a l C i t yS u p e r f u n d S i t e ha s been i n i t i a t e d . The search ha s revealedi n f o r m a t i o n on o w n e r s h i p of the mine t a i l i n g s and waste rockp i l e s . At t h i s t ime , however, t h i s search has not beenc o m p l e t e d . EPA does not f e e l tha t r e s p o n s e a c t i on s s h o u l d bed e l a y e d p e n d i n g f i n a l i z a t i o n o f t h e r e s p o n s i b l e p a r t y search.U p o n f i n a l i z a t i o n o f t h e s earch, t h e s t a t u s o f r e s p o n s i b l ep a r t i e s w i l l b e d e t e r m i n e d and e v a l u a t e d a n d , i f a p p r o p r i a t e , EPAw i l l f o r m a l l y n o t i f y them o f t h e s e l e c t ed remedy f o r O p e r a b l eU n i t N o . T w o a n d w i l l i n i t i a t e n e g o t i a t i o n s f o r t h e i m p l e m e n -t a t i o n o f t h e remedy. I f t h e p o t e n t i a l l y r e s p o n s i b l e p a r t i e s d onot f o r m a l l y commit to p e r f o r m i n g the remedy in a t i m e l y manner,or i f no p o t e n t i a l l y r e s p o n s i b l e p a r t i e s are f o u n d , EPA w i l lproc e ed w i t h a F u n d - f i n a n c e d r emed ia l d e s i g n and remedia l ac t i ona n d w i l l a t t e m p t t o recover E P A ' s r e s pon s e c o s t s f r o m t h er e s p o n s i b l e p a r t i e s .

I D E N T I F I C A T I O N A N D S C R E E N I N G O F A L T E R N A T I V E ST h e E P A e v a l u a t e d p o t e n t i a l r emed ia l ac t ion a l t e r n a t i v e s t oabate the threat posed by contaminat ion f r o m the f i v e minet a i l i n g and waste rock p i l e s by p r o g r e s s i n g t h r o u g h the s erie s o fa n a l y s e s which ar e o u t l i n e d in th e N a t i o n a l C o n t i n g e n c y P l a n( N C P ) , i n p a r t i c u l a r , 4 0 C F R S e c t i o n 3 0 0 . 6 8 , t h e I n t e r i m G u i d a n c eo n S u p e r f u n d S e l e c t i o n o f Remedy, December 2 4 , 1 9 8 6 , ( O S W E RD i r e c t i v e N o . 9 3 5 5 . 0 - 1 9 ) a n d t h e A d d i t i o n a l I n t e r i m G u i d a n c e f o rF Y ' 8 7 Records o f D e c i s i o n , J u l y 2 4 , 1 9 8 7 , ( O S W E R D i r e c t i v e N o .9 3 5 5 . 0 - 2 1 ) . T h i s p ro c e s s , in p a r t , enable s th e EPA to addre s st h e S A R A S e c t i o n 1 2 1 r equ ir ement s o f s e l e c t i n g a r emed ia l a c t i onthat is p r o t e c t i v e of human h e a l t h and the environment, that isc o s t - e f f e c t i v e , that a t t a i n s F e d e r a l a n d S t a t e r equ ir ement s thatare a p p l i c a b l e or r e l evant and a p p r o p r i a t e , and that u t i l i z e sp ermanent s o l u t i o n s and a l t e r n a t i v e t r e a t m e n t t e c h n o l o g i e s orresource recovery t e c h n o l o g i e s t o the maximum ex tent p r a c t i c a b l e .A d d i t i o n a l l y , S A R A S e c t i o n 1 2 1 a n d t h e g u i d a n c e d o c u m e n t sr e f e r e n c e d above require tha t EPA give p r e f e r e n c e t o r emed i e swhich e m p l o y t r ea tmen t which p e r m a n e n t l y a n d s i g n i f i c a n t l yreduce s the m o b i l i t y , t o x i c i t y , or vo lume o f h a z a r d o u s s u b s t a n c e sas the ir p r i n c i p a l e l ement .

12

T h e s e l e c t i o n o f remedy p r o c e s s b eg in s b y i d e n t i f y i n gc e r t a i n s i t e - s p e c i f i c i n f o r m a t i o n to be a s s e s s ed in d e t e r m i n i n gthe t y p e s o f re sponse act ions that w i l l be considered for thes i t e . A general l i s t o f s i t e - s p e c i f i c i n f o r m a t i o n i s c on ta inedi n S e c t i o n 3 0 0 . 6 8 ( e ) ( 2 ) o f t h e N C P . T h i s l i s t w a s used t oi d e n t i f y s p e c i f i c s i te a n d waste c hara c t e r i s t i c s f o r O p e r a b l eU n i t N o . T w o o f t h e C l e a r C r e e k / C e n t r a l C i t y s i t e . Based uponth e s e s i t e and was te c h a r a c t e r i s t i c s , the EPA was ab l e to r educ e ,f r o m the universe of many p o s s i b l e r e spon s e a c t i on s , a set ofr e s p o n s e a c t i o n s and a s s o c ia t ed t e c h n o l o g i e s to be c o n s i d e r e d forO p e r a b l e U n i t N o . T w o .S e c t i o n 1 2 l ( b ) ( ! ) o f S A R A requires that a n as s e s sment o fp e r m a n e n t s o l u t i o n s and a l t e r n a t i v e t r ea tmen t t e c h n o l o g i e s orresource recovery t e c h n o l o g i e s t h a t , in who l e or in p a r t , w i l lr e s u l t in a p ermanen t and s i g n i f i c a n t d e cr ea s e in the t o x i c i t y ,m o b i l i t y , or vo lume o f the h a z a r d o u s s u b s t a n c e , p o l l u t a n t , orcon taminant be c o n d u c t e d . The a l t e r n a t i v e t r ea tment and resourcerecovery t e c h n o l o g i e s cons idered i n c l u d e d chemical f i x a t i o n andr e p r o c e s s i n g .The next s t e p o f th e s e l e c t i o n o f remedy p r o c e s s i sa s s e m b l i n g t h e t e c h n o l o g i e s a n d / o r d i s p o s a l o p t i o n s into remediala c t i on a l t e r n a t i v e s . P u r s u a n t t o O S W E R D i r e c t i v e N o . 9 3 5 5 . 0 - 1 9 ," I n t e r i m G u i d a n c e o n S u p e r f u n d S e l e c t i o n o f R e m e d y " , r emed ia lact ion a l t e r n a t i v e s were considered ranging f r o m tho s e that woulde l i m i n a t e t h e need f o r l o n g - t e r m management ( i n c l u d i n gm o n i t o r i n g ) a t the s i t e t o a l t e r n a t i v e s i n v o l v i n g t r e a t m e n t thatwould reduce m o b i l i t y , t o x i c i t y , or volume as th e ir p r i n c i p a le l emen t . R e m e d i a l ac t ion a l t e r n a t i v e s d e v e l o p e d in t h i s way w i l lvary m a i n l y in the degree to which t h e y r e l y on l o n g - t e r m s i t emanagement. F u r t h e r , a no action a l t e r n a t i v e was d e v e l o p e d asrequired b y S e c t i o n 3 0 0 . 6 8 ( f ) ( 1 ) ( v ) o f t h e N C P .The r emed ia l ac t ion a l t e r n a t i v e s d e v e l o p e d in th eF e a s i b i l i t y S t u d y f o r O p e r a b l e U n i t N o . T w o f o r t h e C l e a rC r e e k / C e n t r a l C i t y s i t e are:N o A c t i o nS l o p e S t a b i l i z a t i o n a n d Runon C o n t r o lC a p p i n gO f f - s i t e D i s p o s a lC h e m i c a l F i x a t i o nR e p r o c e s s i n gA l t e r n a t i v e s were s u b j e c t e d to an i n i t i a l s creening tonarrow t h e l i s t o f p o t e n t i a l r emed ia l a c t i o n s f o r f u r t h e rd e t a i l e d a n a l y s e s u s i n g t h e c r i t e r i a o f c o s t , e f f e c t i v e n e s s , a n di m p l e m e n t a b i l i t y ( a c c e p t a b l e eng ine er ing p r a c t i c e s ) a s d i r e c t edb y 4 0 C F R S e c t i o n 3 0 0 . 6 8 ( g ) . A d e s c r i p t i o n o f each a l t e r n a t i v ef o l l o w s a l o n g w i t h t h e r e s u l t s o f t h e i n i t i a l s c r e en ing a n a l y s i s .

13

N o A c t i o n A l t e r n a t i v eU n d e r the No A c t i o n A l t e r n a t i v e , there would be nom o n i t o r i n g a c t i v i t i e s and no new barriers would be c on s t ru c t ed tore s tr i c t access to the t a i l i n g s and was te rock p i l e s . Thea n a l y s i s o f t h e N o A c t i o n A l t e r n a t i v e w a s summarized e a r l i e r i nt h i s document in the sec t ion e n t i t l e d " S i t e C h a r a c t e r i s t i c s " .T h e e v a l u a t i o n i n d i c a t e d that p o t e n t i a l human h e a l t h a n de n v i r o n m e n t a l impac t could r e s u l t f r o m th e t a i l i n g s and was terock p i l e s . I n p a r t i c u l a r , c a t a s t r o p h i c f a i l u r e a n d r u n o f f c ou lda f f e c t aquatic l i f e a n d downs tream water users. I n a d d i t i o n ,i n g e s t i o n of t a i l i n g s or waste rock may have some e f f e c t s onhuman h e a l t h under t h e f u t u r e r e s i d e n t i a l u s e scenario. T h e N oA c t i o n A l t e r n a t i v e serves as a b a s e l i n e and was r e ta ined forf u r t h e r a n a l y s i s and cons iderat ion as required by S e c t i o n3 0 0 . 6 8 ( f ) ( 1 ) ( v ) o f t h e N C P .

S l o p e S t a b i l i z a t i o n a n d Runon C o n t r o l A l t e r n a t i v eS l o p e s t a b i l i z a t i o n measures e l i m i n a t e o r reducec o n t a m i n a t i o n o f s u r f a c e water r e s u l t i n g f r o m c o l l a p s e o ft a i l i n g s a n d was te rock p i l e s in to t h e s tream. S l o p es t a b i l i z a t i o n measures can i n c l u d e excavat ion, g r o u t i n g andc o n s t r u c t i o n o f r e t a i n i n g w a l l s . I n a d d i t i o n , c o n t a m i n a t i o n o fs u r f a c e water r e s u l t i n g f r o m sheet f l o w over th e p i l e s can b ereduced by p r o v i d i n g runon control to the p i l e s . Runon controlcan i n c l u d e d iv e r s i on d i t c h e s around the p i l e s or c u l v e r t st h r o u g h t h e p i l e s .I n i t i a l a s s e s s m e n t s i n d i c a t e d tha t s l o p e s t a b i l i z a t i o n a n drunon c o n t r o l s are e f f e c t i v e and can be i m p l e m e n t e d . T h e r e f o r e ,the s e a l t e r n a t i v e s were c on s id er ed f u r t h e r in th e d e t a i l e ds c r e en ing o f r emedia l a c t i on a l t e r n a t i v e s . T h e i n i t i a l s cr e eningo f s t a b i l i z a t i o n a l t e r n a t i v e s i d e n t i f i e d t h e f o l l o w i n ga l t e r n a t i v e s b y si te f o r f u r t h e r s t udy:G r e g o r y I n c l i n e

o Concre t e Crib W a l lo T i m b e r C r i b W a l lo Box C u l v e r to Runon C o n t r o lB i g F i v e

o Excava t i on and S l o p e Laybacko Erosion P r o t e c t i o n at Toeo Runon C o n t r o lN a t i o n a l , A r g o , a n d Quar tz H i l l

o Runon C o n t r o l14

T h e i n i t i a l s c r e en ing e v a l u a t i o n i n d i c a t e d tha t g r o u t i n g a n dr e t a i n i n g w a l l s at the Big F i v e were not t e c h n i c a l l y f e a s i b l e .T h e s e a l t e r n a t i v e s were e l i m i n a t e d and not c on s id e r ed in thed e t a i l e d screening.C a p p i n g A l t e r n a t i v e

S u r f a c e control measures w i l l e l i m i n a t e contaminat ion o fs u r f a c e water due t o r u n o f f f r o m th e mine t a i l i n g s and waste rocks i t e s and prevent human exposure t h r o u g h i n h a l a t i o n andi n g e s t i o n . S u c h measures cou ld i n c l u d e r e g r a d i n g th e s i t e t os t a b i l i z e e x i s t i n g s l o p e s a n d control s u r f a c e water r u n o f f ,p r o v i d i n g a c o n t a i n i n g cap over the t a i l i n g s and was t e rockm a t e r i a l , or r evege ta t i on of the site.Six t y p e s o f cap s were eva lua t ed f o r each s i te i n c l u d i n gs y n t h e t i c l i n e r s , b i t u m i n o u s p a v e m e n t , so i l cement l a y e r s , soilcover, c l a y b a r r i e r / s o i l cover, and a m o d i f i e d ResourceC o n s e r v a t i o n and Recovery Act (RCRA) cap - a f r o s t - r e s i s t a n t c l a yb a r r i e r / s o i l c over).The c a p p i n g a n a l y s i s ind i ca t ed that containment i se f f e c t i v e , t e c h n i c a l l y f e a s i b l e and can b e i m p l e m e n t e d .T h e r e f o r e , the se a l t e r n a t i v e s were considered f u r t h e r in thed e t a i l e d s c r e en ing o f r emedia l a c t i on a l t e r n a t i v e s . T h e i n i t i a lscreening r e s u l t e d i n t h e f o l l o w i n g c a p p i n g a l t e r n a t i v e s f o rf u r t h e r e v a l u a t i o n :N a t i o n a l T u n n e l

o S y n t h e t i c l in ero S o i l cement coverA r g o T u n n e l

o S y n t h e t i c l i n e ro S o i l cement coverG r e g o r y I n c l i n e

o S y n t h e t i c l i n e r or soil cement coverQ u a r t z H i l l T u n n e l

o Pavement o f p a r k i n g l o t so S y n t h e t i c l i n e r or soil cement cover

15

B i g F i v e T u n n e lo S o u t h S i d e o f C l e a r Cre ek - Remove t o nor th s id e o fcreek o r o f f - s i t e d i s p o s a l ,o N o r t h S i d e o f C l e a r Creek - S y n t h e t i c l i n e r or soilcement cover.

V a r i o u s c a p s were e l i m i n a t e d d u r i n g th e i n i t i a l s cr e ening.T h o s e c a p s screened ou t i n c l u d e d soil cover, c l a y b a r r i e r / s o i lcover, b i t uminou s cover and m o d i f i e d RCRA cap . M o s t o f t h e s ecovers could not be i m p l e m e n t e d on the s t e e p s l o p e s . Mored e t a i l s c onc ern ing the s creening e v a l u a t i o n can be f o u n d inS e c t i o n 2 o f t h e F e a s i b i l i t y S t u d y R e p o r t .O f f - S i t e D i s p o s a l A l t e r n a t i v e

T h e o f f - s i t e d i s p o s a l a l t e r n a t i v e c o n s i d e r s t h e o p t i o n o ft r a n s p o r t i n g the mine t a i l i n g s and waste rock material to e i thera l o c a l m u n i c i p a l l a n d f i l l o r t o a RCRA p e r m i t t e d l a n d f i l l .T h e most l i k e l y m u n i c i p a l l a n d f i l l wou ld b e a f a c i l i t yo p e r a t e d b y Browning F e r r i s I n c o r p o r a t e d ( B F I ) near 8 8 t h a n dT o w e r Road northeas t of Denver. T h i s is a r e l a t i v e l y newf a c i l i t y which r e p l a c e s a B F I f a c i l i t y a l o n g C o l o r a d o S t a t eH i g h w a y 93 between G o l d e n and B o u l d e r , which has now been c l o s e d .The p r i m a r y concern wi th t h i s a l t e r n a t i v e , however, wou ld b ewhe th er or not the a p p r o p r i a t e r e g u l a t o r y ag enc i e s or theo p e r a t o r would a l l o w d i s p o s a l o f m a t e r i a l s f r o m a C E R C L A s i t e a ta m u n i c i p a l l a n d f i l l even if i t was not a RCRA c h a r a c t e r i s t i cwaste. A second concern would be the impact of such a l a r g evo lume o f m a t e r i a l o n a l a n d f i l l d e s i g n e d p r i m a r i l y f o r m u n i c i p a luse.T h e second a l t e r n a t i v e f o r d i s p o s a l o f t h e m a t e r i a l i sl a n d f i l l a t a p e r m i t t e d RCRA l a n d f i l l . T h r e e s i t e s werei n v e s t i g a t e d , i n c l u d i n g th e new Last C h a n c e s i t e , o p e r a t e d by BFInear L i m o n , C o l o r a d o ; t h e U . S . E c o l o g y d i s p o s a l site near Beat ty ,N e v a d a ; a n d t h e U S P C I d i s p o s a l s i t e a t G r a s s y M o u n t a i n , U t a h .C o n s t r u c t i o n o f the BFI s i t e has no t ye t b egun, bu t w i l l p r o b a b l ycommence w i t h i n the next year. The BFI s i t e i s s c h e d u l e d t op r o v i d e c e l l s o f a p p r o x i m a t e l y 1 5 8 , 0 0 0 cubic yard c a p a c i t y .S e v e r a l o f the s e c e l l s could be d e d i c a t e d to d i s p o s a l o f theC l e a r C r e e k m i n i n g was te . T h e U . S . E c o l o g y a n d U S P C I s i t e s a r ep r e s e n t l y in o p e r a t i o n .T h e o f f - s i t e d i s p o s a l a n a l y s i s i n d i c a t e d that o f f - s i t ed i s p o s a l i s a t e c h n i c a l l y f e a s i b l e a l t e r n a t i v e that i s e f f e c t i v eand can be i m p l e m e n t e d . T h e r e f o r e , t h i s a l t e r n a t i v e wasconsidered f u r t h e r in the d e t a i l e d a n a l y s i s o f remedial act iona l t e r n a t i v e s .

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Chemical F i x a t i o n A l t e r n a t i v e sM o d i f y i n g t h e chemical environment w i t h i n t h e C l e a rC r e e k / C e n t r a l C i t y t a i l i n g s and waste rock p i l e s i s a means o fr e d u c i n g the m o b i l i t y o f m e t a l s in the p i l e s . By c h a n g i n g thechemical environment o f t h e t a i l i n g s t h r o u g h t h e a d d i t i o n o fn e u t r a l i z i n g m a t e r i a l s , the g e n e r a t i o n o f acid and the subsequentd i s s o l u t i o n o f m e t a l s can be e l i m i n a t e d . S u c h change s a l s o wouldl i m i t du s t g e n e r a t i o n and cou ld p o t e n t i a l l y reduce th e impact o fdirec t i n g e s t i o n .S e v e r a l me thod s exist f o r t h e m o d i f i c a t i o n o f t h e chemicalenvironment i n t h e p i l e s . T h e e f f e c t s o n t h e m e t a l - s p e c i f i cs p e c i e s p r e s e n t w i l l vary a c c o r d i n g t o t h e t e chn ique chosen f orm o d i f i c a t i o n . T h e a d d i t i o n o f m a t e r i a l s w i t h l a r g en e u t r a l i z a t i o n ( b a s i c ) c a p a c i t y , such a s k i l n d u s t , i s a commonmethod a v a i l a b l e f or r a i s i n g the pH o f an ac id i c m a t e r i a l w i tht h e a c c o m p a n y i n g " f i x a t i o n " o f m e t a l s a s m e t a l l i c h y d r o x i d e s .T h i s i s a c o s t - e f f e c t i v e op t i on but i t s t o t a l e f f e c t i v e n e s s i sl i m i t e d by the f a c t that some m e t a l s may remain s l i g h t l yl e a c h a b l e by t h i s method.A n o t h e r a p p r o a c h i s f i x a t i o n o f c on taminant m e t a l s bychemical b i n d i n g wi th an a c c o m p a n y i n g p h y s i c a l e n c a p s u l a t i o n .T h i s i s a c c o m p l i s h e d by th e a d d i t i o n o f f i x a t i o n ands o l i d i f i c a t i o n a g e n t s that make t h e c o n t a m i n a n t s u n a v a i l a b l e t oo x i d a t i o n and l e a c h i n g . M e t a l s that cannot be f i x e d by s i m p l e pHa d j u s t m e n t r e spond to t h i s technique. P o z z o l a n s and cementsc o n s t i t u t e t h e m a j o r p o r t i o n o f the s e f i x a t i o n a g e n t s . T h e i ra d d i t i o n to an ac id i c material a l s o causes an increase in pH.A p p r o x i m a t e l y t h i r t y d i f f e r e n t f i x a t i o n agen t s weree v a l u a t e d d u r i n g t h e s c r e en ing pro c e s s . T h e s e m a t e r i a l s werescreened for e f f e c t i v e n e s s a s shown by ac tual l ea ch r e s u l t s ,i m p l e m e n t a b i l i t y and cost p er unit n e u t r a l i z a t i o n c a p a c i t y . Thed e t a i l s o f t h i s e v a l u a t i o n are p r o v i d e d in S e c t i o n 2 o f th eF e a s i b i l i t y S t u d y . Based on t h e s c r e ening e v a l u a t i o n , f i x a t i o na p p e a r s to be a t e c h n i c a l l y f e a s i b l e c onta inment o p t i o n and was,t h e r e f o r e , f u r t h e r i n v e s t i g a t e d i n t h e d e t a i l e d a n a l y s i s o fr e m e d i a l a c t i on a l t e r n a t i v e s . I n p a r t i c u l a r , t h e f o l l o w i n gt e c h n i q u e s / f i x a t i o n agen t s were c on s id er ed:

o K i l n du s to T h r e e p r o p r i e t a r y f i x a t i o n a g e n t s

Each of these f i x a t i o n ag en t s were s u b j e c t to bench scalet e s t s . T h e r e s u l t i n g f i x e d m a t e r i a l s were a l s o t e s t e d f o re f f e c t i v e n e s s by using l e a c h i n g t e s t s . The r e s u l t s o f theset e s t s ar e summarized in th e D e t a i l e d A n a l y s i s S e c t i o n .

17

R e p r o c e s s i n g A l t e r n a t i v e sT h e r e are many p r o c e s s e s that have been d e v e l o p e d to removem e t a l s f r o m ores and th e s e pro c e s s e s c ou ld p o t e n t i a l l y b e a p p l i e dt o remove toxic m e t a l s f r o m th e f i v e waste p i l e s . The proce s se sf a l l in to t w o c a t e g o r i e s : p y r o m e t a l l u r g i c a l - p r o c e s s e s u s i n ghea t; and h y d r o m e t a l l u r g i c a l - proce s s e s u s ing water s o l u t i o n s .F a c i l i t i e s u s ing the s e p r o c e s s e s ex i s t in several p a r t s o f t h ecountry and could p o t e n t i a l l y reproces s m a t e r i a l s f r o m th e C l e a rC r e e k / C e n t r a l C i t y s i t e . T h e s e p ro c e s s e s c ou ld a l s o p o t e n t i a l l ybe used at a f a c i l i t y constructed in the C l e a r C r e e k / C e n t r a l C i t ys i t e area.T h e s cr e ening o f t e c h n o l o g i e s f o r r e p r o c e s s i n g o f t a i l i n g sand was t e rock p i l e s i n d i c a t e d that f l o t a t i o n as a r e p r o c e s s i n ga l t e r n a t i v e i s t e c h n i c a l l y f e a s i b l e and can be i m p l e m e n t e d . Ina d d i t i o n , r e p r o c e s s i n g o f G r e g o r y T a i l i n g s b y g r a v i t y s e p a r a t i o nt o recover p y r i t e i s t e c h n i c a l l y f e a s i b l e . T o d e t e r m i n e t h ee f f e c t i v e n e s s and cost o f r e p r o c e s s i n g , l a b o r a t o r y bench s ca l es t u d i e s were conduc t ed . The r e s u l t s are summarized in thed e t a i l e d a n a l y s i s o f r emedia l a c t i on a l t e r n a t i v e s .

S u m m a r y o f I n i t i a l S c r e e n i n gT h e f o l l o w i n g a l t e r n a t i v e s were c on s id er ed f o r r e m e d i a t i o nof the t a i l i n g s and waste rock p i l e s :

o N o A c t i o no S l o p e S t a b i l i z a t i o n and Runon C o n t r o lo C a p p i n g ( w i t h soil cement or s y n t h e t i c l i n e r s )o O f f - s i t e d i s p o s a lo C h e m i c a l F i x a t i o n ( w i t h k i l n dus t a n d three p r o p r i e t a r ya g e n t s )o Reproc e s s ing ( f l o t a t i o n or g r a v i t y c o n c e n t r a t i o n )

V a r i o u s o p t i o n s under each a l t e r n a t i v e were eva lua t ed fore f f e c t i v e n e s s , i m p l e m e n t a b i l i t y and cost. Based on t h i ss c r e en ing e v a l u a t i o n , o p t i o n s were s e l e c t e d f o r d e t a i l e da n a l y s e s . T h e r e s u l t s o f t h e d e t a i l e d a n a l y s e s a r e p r o v i d e d i nthe next s e c t i on.

D E T A I L E D A N A L Y S I S O F R E M E D I A L A C T I O N A L T E R N A T I V E SC o n s i s t e n t w i th S e c t i o n 3 0 0 . 6 8 ( h ) o f t h e N C P , t h e O f f i c e o fS o l i d W a s t e a n d Emergency Respons e ( O S W E R ) D i r e c t i v e N o . 9 3 5 5 . 0 -19 , and O S W E R Direc t ive No. 9 3 5 5 . 0 - 2 1 , t h e remedial act ion

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a l t e r n a t i v e s r emaining a f t e r i n i t i a l s c r e en ing were f u r t h e rr e f i n e d a n d then s u b j e c t e d t o d e t a i l e d a n a l y s i s . D e t a i l e da n a l y s i s o f each r emed ia l ac t ion a l t e r n a t i v e e n t a i l e d e v a l u a t i o nbased on th e c r i t e r ia derived f r o m th e NCP and SARA. T h e s ec r i t e r i a r e l a t e d i r e c t l y t o f a c t o r s m a n d a t e d by SARA in S e c t i o n1 2 1 , i n p a r t i c u l a r S e c t i o n 1 2 1 ( b ) ( 1 ) ( A - G ) . T h e cr i t er ia f o l l o w :o P r o t e c t i o n of human h e a l t h and the environmento C o m p l i a n c e w i t h l e g a l l y a p p l i c a b l e a n d / o r r e l e v a n t a n da p p r o p r i a t e requirementso Reduc t i on of m o b i l i t y , t o x i c i t y , or volumeo S h o r t - t e r m e f f e c t i v e n e s so L o n g - t e r m e f f e c t i v e n e s s and permanenceo I m p l e m e n t a b i l i t yo Cos to C o m m u n i t y a c c e p t a n c eo S t a t e a c c ep tanc e

T h e e v a l u a t i o n o f a l t e r n a t i v e s r e f l e c t s t h e m a n d a t e t ou t i l i z e permanent s o l u t i o n s a n d a l t e r n a t i v e t r e a t m e n tt e c h n o l o g i e s to the maximum extent p r a c t i c a b l e , as s p e c i f i e d inS e c t i o n 1 2 1 o f S A R A .

D e s c r i p t i o n o f A l t e r n a t i v e sN o A c t i o n A l t e r n a t i v e : T h e N o A c t i o n a l t e r n a t i v e assumes thatthere w i l l be no r emedia t ion of t a i l i n g s and waste rock p i l e s .The p o t e n t i a l i m p a c t s on human h e a l t h and the environmenti n c l u d e :

o C o l l a p s e o f t a i l i n g s a n d was te rock p i l e s in to C l e a r C r e e ka n d N o r t h C l e a r C r e e k ;o R u n o f f f r o m th e waste rock and t a i l i n g s p i l e s c o n t a m i n a t i n gC l e a r Cre ek a n d N o r t h C l e a r C r e e k ; a n do I n h a l a t i o n o r i n g e s t i o n o f m a t e r i a l f r o m t h e p i l e s .

T h e impac t d u e t o p o t e n t i a l c o l l a p s e o f t h e B i g F i v e a n dG r e g o r y I n c l i n e waste r o c k / t a i l i n g s p i l e s were evaluat ed in thes e c t i on e n t i t l e d " S i t e C h a r a c t e r i s t i c s " . A s d i s c u s s e d i n that19

s e c t i on, both AWQC and M C L s would be exceeded in C l e a r Creek andN o r t h C l e a r Cre ek .T h e S i t e C h a r a c t e r i s t i c s s e c t ion a l s o summarized t h e e f f e c t so f r u n o f f d u r i n g s torm event s . A c t u a l d a t a i n d i c a t e tha t A W Q Care exceeded in C l e a r Creek and N o r t h C l e a r Cre ek .I n a d d i t i o n t o p o t e n t i a l i m p a c t s d u e t o r u n o f f a n d c o l l a p s e ,t h e adver s e e f f e c t s o f i n h a l a t i o n o f i n g e s t i o n o f m a t e r i a l f r o mthe p i l e s were evaluated and summarized in the S i t eC h a r a c t e r i s t i c s s e c t i on ( T a b l e 1 ) . U n d e r current ( e p i s o d i ce x p o s u r e K w o r s t case c o n d i t i o n s , t h e ri sk f o r i n g e s t i o n o f soilwas 1 x 1 0 ( o n e excess cancer d e a t h in 1 0 , 0 0 0 p e o p l e over al i f e t i m e ) . U n d e r average c o n d i t i o n s , t h e r i sk w a s 2 x 1 0I n h a l a t i o n o f d u s t 4 u n d e r average and worst cases ind i ca t ed r i sk sof 5 x 1 0 t o 1 x 1 0 . U n d e r a p o t e n t i a l f u t u r e u s e r e s i d e n t i a lscenario, the risk of inge s t i on under average c o n d i t i o n s rangedf r o m 8 X 1 0 ~ 5 t o 1x10~ 4 . U n d e r maximum p l a u s i b l e e x p o s u r ec o n d i t i o n s the risk ranged f r o m 4x10~4 to 9x10~4.

S l o p e S t a b i l i z a t i o n and Runon C o n t r o l A l t e r n a t i v e : Based on th ed e t a i l e d e v a l u a t i o n o f c r i t e r ia ci ted p r e v i o u s l y , s l o p es t a b i l i z a t i o n at the Big F i v e waste rock p i l e s wou ld bea c c o m p l i s h e d by excavat ion, s l o p e cutback and toe r i p - r a p toprevent erosion and t a i l i n g s c o l l a p s e in to C l e a r C r e e k . Based ond e t a i l e d e v a l u a t i o n at the Gregory I n c l i n e , the current gabionw a l l would b e m a i n t a i n e d u n t i l m o n i t o r i n g i n d i c a t e s r e m e d i a t i o ni s nec e s sary or u n t i l the t a i l i n g s are removed for r e p r o c e s s i n g .At that t i m e , a permanent s o l u t i o n w i l l be i m p l e m e n t e d . Runonc o n t r o l s such as d i v e r s i o n d i t c h e s or c u l v e r t s would be p l a c e d onth e u p g r a d i e n t s ide o f a l l s i tes.S l o p e s t a b i l i z a t i o n would be a permanent s o l u t i o n thate l i m i n a t e s c o l l a p s e o f t h e t a i l i n g s a n d was te rock p i l e s . T h ep o t e n t i a l f o r c a t a s t r o p h i c c on taminat i on o f C l e a r Creek a n d N o r t hC l e a r Cre ek would b e e l i m i n a t e d . T h e r u n o f f w o u l d a l s o b ereduced by e l i m i n a t i n g runon at the u p g r a d i e n t s i d e s of thep i l e s . No r e d u c t i o n in impact due to dust or i n g e s t i o n would beach i ev ed .

C a p p i n g A l t e r n a t i v e s : R e s u l t s o f t h e s c r e en ing a n a l y s i si n d i c a t e d that because o f the s t e e p s l o p e s on ly two t e c h n i c a l l yf e a s i b l e c a p p i n g a l t e r n a t i v e s exis t f o r was t e p i l e s a t t h eN a t i o n a l T u n n e l a n d A r g o T u n n e l : s y n t h e t i c l i n e r s o r soi l cementcovers. Because of the s t e e p s l o p e s at both s i t e s , a so i l coverw o u l d not remain on a s y n t h e t i c l i n e r . A bare l i n e r w o u l d bee x t r e m e l y s u s c e p t i b l e t o damage a n d / o r v a n d a l i s m wi th f r e q u e n tr e p l a c e m e n t required. The soil cement cover r e t a i n s the n a t u r a lcolor of the t a i l i n g s and waste rock mater ia l and is p r o b a b l yp r e f e r r e d b y t h e C o l o r a d o H i s t o r i c a l S o c i e t y a n d l o c a l r e s i d e n t sover a l in er . T h u s , a soil cement cover is the p r e f e r a b l e

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c a p p i n g a l t e r n a t i v e which could be i m p l e m e n t e d a t the N a t i o n a lT u n n e l a n d A r g o T u n n e l waste p i l e s .B e f o r e t h e G r e g o r y I n c l i n e can b e c a p p e d , t h e t e m p o r a r ygabion w a l l would be r e p l a c e d . A t imber crib w a l l is p r i c e dc o m p a r a b l y w i th o ther a l t e r n a t i v e s and wou ld p r o b a b l y bep r e f e r r e d b y t h e C o l o r a d o H i s t o r i c a l S o c i e t y . A l t e r n a t i v e se v a l u a t e d for c a p p i n g were a s y n t h e t i c l i n e r and soil cementcover. The soil cement cover is a p ermanent cover and isp r o b a b l y p r e f e r r e d b y t h e C o l o r a d o H i s t o r i c a l S o c i e t y over o therc a p p i n g a l t e r n a t i v e s .T h e B i g F i v e waste rock p i l e p r o v i d e s a t e c h n i c a l c h a l l e n g ef o r c a p p i n g a n d p r o t e c t i o n aga in s t f l o o d eros ion. P h y s i c a lc o n s t r a i n t s impo s ed by the o r i g i n a l t o p o g r a p h y and the l o c a t i o no f C l e a r C r e e k a l o n g o n e s ide o f t h e p i l e s d i c t a t e that p i l e sw o u l d be r egraded and r i p - r a p would be p l a c e d for f l o o dp r o t e c t i o n . The r egraded p i l e s would then be covered by a soilcement cap . A s y n t h e t i c l i n e r could be p l a c e d , but no soi l coverc ou ld be put on the l i n e r .C a p p i n g o f t h e Quar tz H i l l waste rock p i l e w a s e v a l u a t e d f o rthree areas: p a r k i n g l o t s with a d j o i n i n g s ide s l o p e s , an areanear the tunne l en trance , and al l r e m a i n i n g areas f r o m thep a r k i n g l o t s t o t h e tunnel p o r t a l . T h e s c r e en ing a n a l y s i si n d i c a t e d that soil cement covers were more f e a s i b l e thans y n t h e t i c l i n e r s f o r non-auto t r a f f i c areas. S e l e c t i o n o f soi lcement covers would a l s o p r o b a b l y be p r e f e r r e d by the C o l o r a d oH i s t o r i c a l S o c i e t y over a l iner . T h e most f e a s i b l e c a p p i n ga l t e r n a t i v e f o r t h e p a r k i n g l o t s i s p a v i n g .I n a l l cases d i s c u s s e d above, runon a n d r u n o f f control wou ldb e p r o v i d e d . T h i s wou ld cons i s t o f d i t c h e s u p g r a d i e n t o f t h ec a p p e d area to d iver t water and d i t c h e s or c u l v e r t s b e low thes i t e s t o d ivert r u n o f f . C a p p i n g o f t h e t a i l i n g s and waste rockp i l e s would be a permanent s o l u t i o n that removes e x p o s u r e tohuman h e a l t h and the environment.

O f f - S i t e D i s p o s a l ; U n d e r t h e o f f - s i t e d i s p o s a l a l t e r n a t i v e ,t a i l i n g s and waste rock p i l e s would be excavated and t r a n s p o r t e df o r d i s p o s a l a t a m u n i c i p a l l a n d f i l l s i t e such a s t h e l a n d f i l lo p e r a t e d by BFI at 88 th and T o w e r Road nor thwe s t of Denver.L e a c h a t e t e s t s i n d i c a t e that the t a i l i n g s and was te rock are notRCRA c h a r a c t e r i s t i c was te and t h e r e f o r e do not have to be sent toa RCRA l a n d f i l l .

Removal of the t a i l i n g s and waste rock p i l e s i s a permanents o l u t i o n that removes e x p o s u r e to human h e a l t h and theenvironment . Dust contro l measures must be i m p l e m e n t e d d u r i n gex cava t i on and t r u c k s would have to be l i n e d and covered d u r i n gt r a n s p o r t a t i o n .

C h e m i c a l F i x a t i o n ; I n t h e i n i t i a l s c r e ening pro c e s s , k i l n dustand three p r o p r i e t a r y m a t e r i a l s were s e l e c t ed for d e t a i l e de v a l u a t i o n . W a s t e r o c k / t a i l i n g s f r o m G r e g o r y a n d A r g o weretreated with each o f t h e f o u r s e l e c t ed f i x a t i o n agent s . Ther e s u l t a n t f i x e d m a t e r i a l s were then s u b j e c t e d to a series o fl e a c h i n g t e s t s t o document the e f f e c t i v e n e s s o f th e t r e a t m e n t .I n a l l case s , t h e f i x a t i o n ag en t s t e s t ed were e f f e c t i v e i nr educ ing l ea cha t e concentrat ions . In some cases, l e a c h a t ec o n c e n t r a t i o n s were below AWQC for zinc. H o w e v e r , in one case,th e l eachate contained ex tremely h igh values f or a luminum( 2 7 , 7 0 0 u g / L ) . Because o f t h i s r e s u l t , t h i s f i x a t i o n agent w a se l i m i n a t e d f r o m eva lua t i on . K i l n dust and two p r o p r i e t a r y agent swere all c on s ider ed f u r t h e r . Based on cost and l e a c h a t e q u a l i t y ,k i l n dust i s the most c o s t - e f f e c t i v e . K i l n dust would be a p p l i e dat an a p p l i c a t i o n rate of a p p r o x i m a t e l y 0.58 tons per cubic yardof a v a i l a b l e t a i l i n g s and waste rock m a t e r i a l . A p p r o x i m a t e l y 9inche s of k i l n dus t would be mixed in w i t h the top 9 inche s oft a i l i n g s and waste rock material and then c o m p a c t e d .F i x a t i o n of the t a i l i n g s and waste rock p i l e s i s a permanents o l u t i o n that removes e xpo sure to human h e a l t h and theenv ironment .

R e p r o c e s s i n g A l t e r n a t i v e : T h e r e p r o c e s s i n g a l t e r n a t i v e c o n s i d e r sthe t a i l i n g s and waste rock p i l e s as an economic resource andrecovers the inherent monetary value w h i l e g e n e r a t i n g a was t ewhich may not be d e t r i m e n t a l to the env ironment . In order toe v a l u a t e t h i s o p t i o n , a t h r e e - p h a s e c h a r a c t e r i z a t i o n t a s k wasu n d e r t a k e n :o E v a l u a t i n g the p a r a m e t e r s nec e s sary to p r o c e s s the waster o c k / t a i l i n g s ;o D e t e r m i n i n g if the r e s u l t a n t waste is a h a z a r d o u s wa s t e ; ando P e r f o r m i n g a cost a n a l y s i s o f a l l o p t i o n s .

The r e p r o c e s s i n g s t u d i e s were c onduc t ed on a bench s c a l el eve l b y I n t e r n a t i o n a l Proce s s Research C o r p o r a t i o n o f G o l d e n ,C o l o r a d o . T w o o p t i o n s were e v a l u a t e d , n a m e l y :o R e p r o c e s s i n g o f a l l m a t e r i a l s ; ando R e p r o c e s s i n g o f a l l m a t e r i a l s l e s s t h a n two inche s w i t hd i s p o s a l of coarse f r a c t i o n as a was t e rock.

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T h e r e s u l t s o f th e s e t y p e s o f t e s t s were e v a l u a t e d t od e t e r m i n e i f the t a i l i n g s and was te rock cou ld be r e p r o c e s s e d .T h e s e t e s t s i n c l u d e d :o T e s t s on c h a r a c t e r i z i n g the was te rock wi th r e sp e c t top a r t i c l e s ize d i s t r i b u t i o n and s e l e c t ed contaminantc o n c e n t r a t i o n s ( c o p p e r , z inc , l e a d , chromium, a n d a r s e n i c ) ,t o t a l s u l f u r , a n d pr e c i ou s m e t a l s ( s i l v e r a n d g o l d ) i nd i f f e r e n t size f r a c t i o n s ;o F r o t h f l o t a t i o n t e s t s f o r recovery o f a n economic p r o d u c t ;ando L e a c h i n g t e s t s on waste rock and new t a i l i n g s to d e t e r m i n ep o t e n t i a l env i ronmen ta l i m p a c t s .

R e s u l t s o f t h e t e s t s i n d i c a t e that t h e q u a n t i t i e s o fc o n t a m i n a n t s r e m a i n i n g in the new waste t a i l i n g s weres i g n i f i c a n t l y r educ ed . H o w e v e r , l e a c h a t e c o n c e n t r a t i o n s weregrea t er than AWQC for s e l e c t e d c o n t a m i n a n t s such a s zinc.R e p r o c e s s i n g would be a p ermanent s o l u t i o n that e l i m i n a t e dc o l l a p s e of the t a i l i n g s and waste rock p i l e s . A new wastet a i l i n g s i s p r o d u c e d . L e a c h i n g t e s t s show that t h e new t a i l i n g scan be d i s p o s e d in a m u n i c i p a l l a n d f i l l .

C o m p a r i s o n o f A l t e r n a t i v e sL i s t e d in T a b l e 2, in matrix f o r m a t , are the key cr i t er iac o n s i d e r e d in e v a l u a t i n g and c o m p a r i n g a l t e r n a t i v e s . T h e s ec r i t e r i a a r e s p e c i f i e d i n J . W i n s t o n P o r t e r ' s memorandum" A d d i t i o n a l I n t e r i m Guidanc e f o r F Y ' 8 7 Records o f Deci s ion,"d a t e d J u l y 2 1 , 1 9 8 7 a n d i n c l u d e :

o P r o t e c t i o n of human h e a l t h and the environmento C o m p l i a n c e wi th l e g a l l y a p p l i c a b l e a n d / o r r e l e v a n t a n da p p r o p r i a t e r equirement so R e d u c t i o n of m o b i l i t y , t o x i c i t y or volumeo S h o r t - t e r m e f f e c t i v e n e s so L o n g - t e r m e f f e c t i v e n e s s and permanenceo I m p l e m e n t a b i l i t yo C o s to C o m m u n i t y a c c ep tanc eo S t a t e acc ep tance

23

T a b l e 2 summarize s th e d a t a d e v e l o p e d in the D e t a i l e dA n a l y s i s o f Remed ia l A c t i o n A l t e r n a t i v e s a n d p r o v i d e s ac o m p a r i s o n f o r s e l e c t i n g a p r e f e r r e d a l t e r n a t i v e f o r eachl o c a t i o n . T h e f o l l o w i n g p a r a g r a p h s summarize t h e e v a l u a t i o nc r i t e r i a f o r a l l s i t e s .No A c t i o n ; As p r e v i o u s l y i n d i c a t e d , c o l l a p s e would re su l t ind e g r a d a t i o n o f s tream q u a l i t y be low A W Q C a n d M C L s . R u n o f f a l s odoes not meet AWQC. No action would not reduce the m o b i l i t y ,t o x i c i t y or vo lume of the c on taminant s .S t a b i l i z a t i o n a n d Runon C o n t r o l s ; D e g r a d a t i o n o f s tream q u a l i t ydue to c o l l a p s e w i l l be e l i m i n a t e d . R u n o f f q u a l i t y w i l l not meetAWQC; however, th e volume o f r u n o f f w i l l b e reduced a s a r e s u l tof runon c o n t r o l . As a r e s u l t , c on tamina t i on to the s tream w i l lbe r educ ed . O v e r a l l m o b i l i t y of c o n t a m i n a n t s are r educed .R e l a t i v e t o other a l t e r n a t i v e s ( e x c e p t no a c t i o n ) , t h i s o p t i o nhas the l owe s t cost. The r e m e d i a t i o n is not a p ermanent s o l u t i o nfor a l l c o n t a m i n a t i o n and does no t e l i m i n a t e a l l r i sk s to humanh e a l t h and the environment.C a p p i n g : R u n o f f q u a l i t y w i l l meet A W Q C . C a p p i n g reducesm o b i l i t y o f c o n t a m i n a n t s . Ri sk s to human h e a l t h due toi n h a l a t i o n of dust and inge s t i on of m a t e r i a l s are e l i m i n a t e d .C a p p i n g i s a permanent r e m e d i a t i o n that removes e x p o s u r e to humanh e a l t h and the environment.O f f - S i t e D i s p o s a l ; O f f - s i t e d i s p o s a l reduces t h e m o b i l i t y a n dt o x i c i t y of c o n t a m i n a n t s on the s i te . H o w e v e r , the m a t e r i a l s arep l a c e d in another l o ca t i on and the u l t i m a t e volume and t o x i c i t yis not r educed . E x i s t i n g r i sk s to human h e a l t h and theenvironment are e l i m i n a t e d . O f f - s i t e d i s p o s a l i s a permanentremedy. T h e cost f o r o f f - s i t e d i s p o s a l i s t h e second h i g h e s t o fthe s i x a l t e r n a t i v e s e v a l u a t e d .C h e m i c a l F i x a t i o n ; R u n o f f q u a l i t y w i l l meet A W Q C f o r mostp a r a m e t e r s . F i x a t i o n reduces m o b i l i t y a n d p o s s i b l y t o x i c i t y o ft h e c o n t a m i n a n t s . H o w e v e r , t h e volume o f c on taminat ed mat er ia lis increased. F i x a t i o n is a permanent remedy and e l i m i n a t e se x i s t i n g r i sk s to human h e a l t h and s u b s t a n t i a l l y reduces r i sk tothe environment .R e p r o c e s s i n g ; R e p r o c e s s i n g w i l l re sul t in new t a i l i n g s that aren o t R C R A waste s . H o w e v e r , p o t e n t i a l l e a c h a t e s f r o m t h e wastew i l l exceed AWQC. Reproc e s s ing reduces m o b i l i t y , t o x i c i t y andvolume o f t h e c o n t a m i n a n t s . T h i s a l t e r n a t i v e i s t h e o n l y o p t i o nthat reduces volume. Reproc e s s ing reduces e x i s t i n g risk to humanh e a l t h and the environment. T h i s o p t i o n i s th e most e x p e n s i v e o fthe s ix a l t e r n a t i v e s evaluated even c o n s i d e r i n g the value of them i n e r a l s e x t ra c t ed ( S e e T a b l e 2 ) . O v e r a l l , r e p r o c e s s i n g i s apermanent s o l u t i o n that reduces e xpo sur e to human h e a l t h and theenvironment .

24

TABU 2COMPARISON OF ALTERNATIVES

Criteria

Argo Tunnel1. Compliance with

ARARs

No Action

R u n o f f does not aA H Q C . Col lap s e

S t a b i l i z a t i o n /Runon Control Capping

*et R u n o f f will not meet R u n o f f will meetA W Q C . A W Q C ' s .

O f f - S i t e Disposal

Risks are removed.Disposal will meet

Chemical Fixation

R u n o f f will meetmost AWQCs.

Reprocessing

Risks are removed.Reprocessed tailings

2. Reduction ofmob i l i ty ,t ox i c i ty orvolume

would result indegradation belowMCLs and AHQC.No reduction ofM , T , V .

Reduces mobi l i ty Reduces mobi l i ty ofcontaminants ofconcern.

RCRA.

Reduces mobil i ty andtoxici ty on-sitematerials are placedin another location.

Reduces mobi l i ty ofcontaminants ofconcern.

are not RCRA wastes.Leachates willexceed AHQCs.Reduces M,T and V.

3. Short TernE f f e c t i v e n e s s

K3Ln

4. Long TermE f f e c t i v e n e s s

6 . cost ( $ )- Capi ta l- Present W o r t h

10%

No reduction ofex i s t ing risks f r o mcatas trophicc o l l a p s e of p i l e sand f r o m runo f f oringestion.

Does not present apermanent solutionto remediating risksf r o m the ta i l ing sand waste rockp i l e s .

5. Impl emen tab i l i ty —

Eliminates somecontamination tostream. Can becomple t ed in 6 mo.

Does not present apermanent solutionto all risks.

Constructed withavailable equipment

40,00080,000

Eliminate s e x i s t ingrisk to human healthand the environment.Capping can becompleted in 12-18months.

Capping is apermanent remedythat eliminates theneed for long termsite management.

Constructed withavai lab l econstructionequipment.

1,969,8001,969,800

Existing risk tohuman health and theenvironment areeliminated.O f f - s i t e disposalcan be completed intwo years.O f f - s i t e d i sposal isa permanent remedythat eliminates theneed for long termsite management.

Constructed withavailableconstructionequipment.

7,347,8007,347,800

Eliminates ex i s t ingrisk to human healthand the environment.F i x a t i o n can becompleted in 12-18months.

Fixat i on is apermanent remedythat eliminates theneed for long termsite management.

Constructed withavailableconstructionequipment.

1,461,8001,461,800

Eliminates existingrisk to human healthand the environment.Reprocessing can becompleted in 5 to 9years.

Reprocessing is apermanent remedythat eliminates theneed for long termsite management.

Local mil l s can beused but arecurrentlyinoperable.

8.5-12,126,0008,5-12,126,000

7. CommunityAcceptance

No Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

8. S t a t e Acceptance No action isacceptable as aninterim solutiononly.

S t a t e ' s p r e f e r r e dalternative. C a p p i n g should be

considered in f u t u r estudies.

Costs are the m a j o rconcern.

Hay be considered inf u t u r e studies. S t a t e wouldencouragereprocessing ifeconomicallyf e a s i b l e .

9. OverallProtec t i on ofHuman H e a l t h andthe Environment

May result inadverse e f f e c t s dueto r u n o f f and directcontact with p i l e s .

Runon controleliminates some ofthe risk to theenvironment.

C a p p i n g is apermanent so lut ionthat removesexposure to humanhealth and theenvironment.

O f f - s i t e d i sposal isa permanent solutionthat removesexposure to humanhealth and theenvironment.

F i x a t i o n is apermanent solutionthat reducesexposure to humanhea l th and theenvironment.

Reprocessing is apermanent solutionthat reducesexposure to humanhealth and theenvironment.

TABLE 2 ( C o n t )COMPARISON OP ALTERNATIVES

Criter ia Ho ActionS t a b i l i z a t i o n /Runon Control capping O f f - S i t e Disposal Chemical F i x a t i o n Reprocessing

Big F i v e Tunnel1. Compliance with

ARARs

2. Reduction ofnobi l i ty,toxic i ty orvolume

3. Short TermE f f e c t i v e n e s s

4. Long TermE f f e c t i v e n e s s

Runof f does not meetA W Q C . C o l l a p s ewould result indegradation belowH C L s and ANQC.Ho reduction ofM . T . V .

Ho reduction ofexist ing risks f r o mcatastrophicc o l l a p s e o f p i l e sand f r o m r u n o f f oringestion.

Does not present apermanent solutionto remediating risksfrom the ta i l ing sand waste rockpi l e s .

5. I n p l e r a e n t a b i l i t y —

6 . Cost ( $ )- C a p i t a l- Present Worth

10%

Runof f will not meetA N Q C .

Reduces mobi l i ty andvolume (i freproces sed).

Eliminates c o l l a p s epotent ial and mostcotaminants in thestream; can becompleted in 6 no.

Provides a permanentsolution toc o l l a p s e ; eliminatesmost of long termsite management.

Constructed withavailable equipment.

562,100641,100

Runoff will meetA H Q C ' S .

Reduces mobi l i ty ofcontaminants ofconcern.

Eliminates existingrisk to human healthand the environment.Capp ing can becomple ted in 12-18months.

Capping is apermanent remedythat eliminates theneed for long termsite management.

Constructed withavailableconstructionequipment.

825,700825,700

Risks are removed.Disposal will meetRCRA.

Reduces mobility andtoxic i ty on-sitematerial s are placedin another location.Exis t ing risk tohuman health and theenvironment areeliminated.O f f - s i t e disposalcan be completed intwo years.O f f - s i t e disposal isa permanent remedythat eliminates theneed for long termsite management.

Constructed withavailableconstructionequipment.

5,654,0005,654,000

Runof f will meetmost AHQCs.

Reduces mobili ty ofcontaminants ofconcern.

Eliminates exi s t ingrisk to human healthand the environment.Fixat i on can becompleted in 12-18months.

Fixat i on is apermanent remedythat eliminates theneed for long termsite management.

Constructed withavailableconstructionequipment.

693,800693,800

Risks are removed.Reprocessed ta i l ingsare not RCRA wastes.Leachates willexceed A H Q C s .Reduces H,T and 7.

Eliminates existingrisk to human healthand the environment.Reprocessing can becompleted in S to 9years.

Reprocessing is apermanent remedythat eliminates theneed for long termsite management.

Local m i l l s can beused but arecurrentlyinoperable.

4,2-6,855,0004,2-6,855,000

7. CommunityAcceptance No Action isp r e f e r r e dal t ernat ive .No Action isp r e f e r r e dalternative.

Ho Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

8. S t a t e Acceptance No Action isacceptable as aninterim solutiononly.

S t a t e ' s p r e f e r r e dalternative. Capping should be

considered in fu tures tudies.Cost s are the m a j o rconcern.

Hay be considered inf u tur e s tudies.

S t a t e wouldencouragereprocessing ifeconomicallyf ea s i b l e .

9. OverallProtection ofHuman H e a l t h andthe Environment

May result inadverse e f f e c t s dueto r u n o f f andc o l l a p s e of waster o c k / t a i l i n g s p i l e sand direct contactwith p i l e s .

Stabi l i za t ion is apermanent solutionthat eliminatesc o l l ap s e and reducedpotent ial human andenvironmentalexposure.

Capping is apermanent solutionthat removesexposure to humanheal th and thisenvironment.

O f f - s i t e disposal isa permanent solutionthat removesexposure to humanhealth and theenvironment.

Fixation is apermanent solutionthat reducesexposure to humanheal th and theenvironment.

Reprocessing is apermanent solutionthat reducesexposure to humanhealth and theenvironment.

TABLE 2 ( C o n t )COMPARISON OF ALTERNATIVES

Criteria Ho Action Stab i l i za t i on /Runon Control Capping O f f - S i t e Disposal Chemical F i x a t i o n Reprocessing

Gregory Incl ine1. Compl iance with

ARABS

2. Reduction ofmob i l i ty ,t ox i c i ty orvolume

3. Short TermE f f e c t i v e n e s s

4. Long TermE f f e c t i v e n e s s

7. CommunityAcceptance

8. S t a t e Acceptance

9. OverallProtec t ion ofHuman H e a l t h andthe Environment

R u n o f f does not meetA W Q C . C o l l a p s ewould result indegradat ion belowMCLs and A W Q C .No reduction ofM , T , V .

No reduction ofexi s t ing risks f r o mcatastrophicc o l l a p s e o f p i l e sand f r o m r u n o f f oringestion.

Does not present apermanent solutionto remediating risksf r o m the t a i l i n g sand waste rockp i l e s .

5. I m p l e m e n t a b i l i t y —

6 . Cost ( $ )- C a p i t a l- Present W o r t h

10%No Act ion isp r e f e r r e dal t ernat ive .No Action isacceptab l e as aninterim so lu t iononly.

May result inadverse e f f e c t s dueto runo f f andc o l l a p s e of waster o c k / t a i l i n g s p i l e sand direct contactwith p i l e s .

R u n o f f will not meetA W Q C .

Reduces mobi l i ty

Eliminates c o l l a p s epotent ial and mostcontaminants in thestream; can becomple t ed in 6 mo.( p r o c e s s i n g in 2yr).Provides a permanentsolution toc o l l a p s e ; eliminatesmost of long termsite management

Constructed withavailable equipment.

32,50050,700

No Act ion isp r e f e r r e dal t ernat ive .S t a t e ' s p r e f e r r e da l t e rna t iv e .

S t a b i l i z a t i o n is apermanent so lu t ionthat eliminatesc o l l a p s e and reducespo t en t ia l human andenvironmentalexposure.

R u n o f f will meetA W Q C ' s .

Reduces nob i l i ty ofcontaminants ofconcern.

Eliminates ex i s t ingrisk to hunan h ea l thand the environment.C a p p i n g can becompleted in 12-18months.

C a p p i n g is apermanent remedythat eliminates theneed for long termsite management.

Constructed withavai lableconstructionequipment.

498,300498,300

No Action isp r e f e r r e dal t ernat ive .Capping should beconsidered in f u t u r es tudie s .

C a p p i n g is apermanent solutionthat removesexposure to humanheal th and thisenvironment.

Risks are removed.Disposal will meetRCRA.

Reduces mob i l i ty andtoxic i ty on-sitemater ia l s are placedin another location.Exis t ing risk tohunan heal th and theenvironment areeliminated.O f f — s i t e d i spo sa lcan be completed inTwo years.O f f - s i t e d i sposal isa permanent remedythat eliminates theneed for long termsite management.

Constructed withavailableconstructionequipment.

876,400876,400

No Action isp r e f e r r e dal t ernat ive .Costs are the m a j o rconcern.

O f f - s i t e d i spo sa l i sa permanent so lut ionthat removesexposure to humanheal th and theenvironment.

R u n o f f will meetmost A W Q C s .

Reduces mobi l i ty ofcontaminants ofconcern.

Eliminates ex i s t ingrisk to human healthand the environment.Fixat i on can becompleted in 12-18months.

Fixa t i on is apermanent remedythat eliminates theneed for long termsite management.

Constructed withavailableconstructionequipment.

395,800395,800

No Action isp r e f e r r e dal t ernat ive .May be considered inf u t u r e s tudies .

F i x a t i o n is apermanent solutionthat reducesexposure to humanhealth and theenvironment.

Risks are removed.Reprocessed ta i l ingsare not RCRA wastes.Leachates willexceedReduces M,T and V.

Eliminates exi s t ingrisk to human healthand the environment.Reproces s ing can becompleted in 5 to 9years.

Reprocessing is apermanent remedythat eliminates theneed for long termsite management.

Local m i l l s can beused but arecurrentlyinoperable.

3-3,480,0003-3,480,000

No Action isp r e f e r r e dal t ernat ive .S t a t e wouldencouragereproce s s ing i feconomicallyf ea s i b l e .Reprocessing is apermanent so lut ionthat reducesexposure to humanhealth and theenvironment.

•CABLE 2 ( C o n t )COMPARISON OP ALTERNATIVESC r i t e r i a Ho Action

S t a b i l i z a t i o n /Runon Control Capping O f f - S i t e Disposal Chenical Fixa t i on Reprocessing

national Tunnel1. Compliance with

ARARS

2. Reduction ofn o b i l i t y ,tox i c i ty orvolume

Runof f does not meetA H Q C . C o l l a p s ewould result indegradation belowH C L s and A W Q C .No reduction ofM . T . V .

R u n o f f wi l l not meetA H Q C .

Reduced nobil i ty.

Runof f willA W Q C ' S .

Reduces nob i l i ty ofcontaminants ofconcern.

Risks are removed.Disposal will neetRCRA.

Reduces nobility andt ox i c i ty on-sitenaterials are placedin another location.

R u n o f f will «eetnost A H Q C s .

Reduces nobil i ty ofcontaminants ofconcern.

Risks are removed.Reprocessed ta i l ing sare not RCRA wastes.Leachates willexceed AWQCs.Reduces M,T and V.

3. Short TermE f f e c t i v e n e s s

4. Long TernE f f e c t i v e n e s s

oo 5. I m p l e m e n t a b i l i t y

6 . Cost ( $ )- C a p i t a l- Present W o r t h

10%

Ho reduction ofexisting risks f roncatas trophicco l laps e o f p i l e sand f r o n r u n o f f oringestion.

Does not present apermanent solutionto remediating risksf r on the ta i l ingsand waste rockpi l e s .

Eliminates somecontamination tostream; can becomple ted in 6 no.

Does not present apermanent solutionto all risks.

Constructed withavailableequipmnent.

25,20043,400

Eliminate* ex i s t ingrisk to human healthand the environment.Capping can becompleted in 12-18months.

Capping is apermanent remedythat eliminates theneed for long termsite management.

Constructed withavailableconstructionequipment.

275,100275,100

Exist ing risk tohuman health and theenvironment areeliminated.O f f - s i t e di sposalcan be completed intwo years.O f f - s i t e disposal isa permanent remedythat eliminates theneed for long ternsite management.

Constructed withavailableconstructionequipment.

1,809,3001,809,300

Eliminates existingrisk to human healthand the environment.Fixat ion can becompleted in 12-18months.

Fixat ion is apermanent remedythat eliminates theneed for long termsite management.

Constructed withavailableconstructionequipment.

230,400230,400

Eliminates exis t ingrisk to human healthand the environment.Reprocessing can becompleted in 5 to 9years.

Reprocessing is apermanent remedythat eliminates theneed for long ternsite management.

Local mi l l s can beused but arecurrentlyinoperable.

1,9-3,190,0001,9-3,190,000

7. CommunityAcceptance

NO Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dal t ernat ive .

Do Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

Ho Action isp r e f e r r e dalternative.

8. S t a t e Acceptance

9. OverallProtec t ion ofHuman H e a l t h andthe Environment

No Action isacceptable as aninterim solutiononly.

Hay result inadverse e f f e c t s dueto r u n o f f and directcontact with p i l e s .

S t a t e ' s p r e f e r r e dalternative.

Reunon controleliminates some ofthe risk to theenvironment.

Capping should beconsidered in f u t u r estudies.

Capping is apermanent solutionthat removesexposure to humanheal th and thisenvironment.

Cost s are the m a j o rconcern.

O f f - s i t e di sposal isa permanent solutionthat removesexposure to humanhealth and theenvironment.

May be considered inf u t u r e studies.

F i x a t i o n is apermanent solutionthat reducesexposure to humanhealth and theenvironment.

S t a t e wouldencouragereprocessing ifeconomicallyf e a s i b l e .Reprocessing is apermanent solutionthat reducesexposure to humanhealth and theenvironment.

TABLE 2 ( C o n t )COMPARISON OF ALTERNATIVES

Criteria Mo ActionStab i l i za t i on/Runon Control C a p p i n g O f f - S i t e Disposal Chemical Fixation Reprocessing

Quartz H i l l Tunnel1. Compliance with

ARABS

2. Reduction ofnob i l i ty ,t ox i c i ty orvolume

R u n o f f does not BeetA H Q C . C o l l a p s ewould result indegradation belowMCLs and AHQC.No reduction ofM , T , V .

R u n o f f will not meetA H Q C .

Reduces nobil i ty.

R u n o f f will BeetA H Q C ' s .

Reduces M o b i l i t y ofcontaminants ofconcern.

Risks are removed.Disposal will »eetRCRA.

Reduces mobi l i ty andt ox i c i ty on-sitematerials are placedin another location.

R u n o f f willBost A W Q C s .

Reduces nobility ofcontaminants ofconcern.

Risks are removed.Reprocessed ta i l ing sare not RCRA wastes.Leachates willexceed A H Q C s .Reduces H,T and V.

3. Short TermE f f e c t i v e n e s s

4. Long TernE f f e c t i v e n e s s

5. I m p l e m e n t a b i l i t y

6 . Cost ( S )- C a p i t a l- Present W o r t h

10%

No reduction ofex i s t ing risks f r o ncatastrophicc o l l a p s e o f p i l e sand f r o m r u n o f f oringestion.

Does not present apermanent solutionto remediating risksf r o m the t a i l ing sand waste rockpi l e s .

Eliminates somecontamination tostream; can becompleted in 6 mo.

Does not present apermanent solutionto all risks.

Constructed withavailable equipment.

197,500219,000

Eliminates exis t ingrisk to human heal thand the environment.C a p p i n g can becomple ted in 12-18months.

Capping is apermanent remedythat eliminates theneed for long termsite management.

Constructed withavailableconstructionequipment.

665,900882,300

Exis t ing risk tohuman health and theenvironment areeliminated.O f f - s i t e disposalcan be completed intwo years.O f f - s i t e disposal isa permanent remedythat eliminates theneed for long termsite management.

Constructed withavailableconstructionequipment.

565,400565,400

Eliminates existingrisk to human healthand the environment.F i x a t i o n can becompleted in 12-18months.

Fixat ion is apermanent remedythat eliminates theneed for long term,site management.

Constructed withavailableconstructionequipment.

305,000521,400

Eliminates exist ingrisk to human healthand the environment.Reprocessing can becompleted in 5 to 9years.

Reprocessing is apermanent remedythat eliminates theneed for long termsite management.

Local mi l l s can beused but arecurrentlyinoperable.

857,000 - 1,379,000857,000 - 1,379,000

7. CommunityAcceptance

Ho Action isp r e f e r r e dalternat ive .

No Action isp r e f e r r e dal t ernat ive .

No Action isp r e f e r r e dal ternat ive .

No Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

No Action isp r e f e r r e dalternative.

8. S t a t e Acceptance No Action isacceptable as aninterim solutiononly.

S t a t e ' s p r e f e rr edalternative.

Capping should beconsidered in f u t u r estudies.

Costs are the majorconcern.

May be considered infu ture studies.

State wouldencouragereprocessing ifeconomicallyfeas ible .

9. OverallProtec t ion ofHuman H e a l t h andthe Environment

May result inadverse e f f e c t s dueto r u n o f f and directcontact with p i l e s .

Runon controle l iminates some ofthe risk to theenvironment.

Capp ing is apermanent solutionthat removesexposure to humanheal th and thisenvironment.

O f f - s i t e d i sposal i sa permanent solutionthat removesexposure to humanhealth and theenvironment.

F i x a t i o n is apermanent solutionthat reducesexposure to humanhealth and theenvironment.

Reprocessing is apermanent solutionthat reducesexposure to humanhealth and theenvironment.

S E L E C T E D R E M E D YD e s c r i p t i o n o f S e l e c t e d Remedy

T h e s e l e c t e d remedy f o r O p e r a b l e U n i t T w o o f t h e C l e a rC r e e k / C e n t r a l C i t y s i t e cons i s t s o f s l o p e s t a b i l i z a t i o n a n d runonc o n t r o l .T h e Remed ia l I n v e s t i g a t i o n i d e n t i f i e d f o u r p o t e n t i a le x p o s u r e p a t h w a y s by which the t a i l i n g s and was te rock p i l e scould impact human h e a l t h and the environment. T h e s e p o t e n t i a lp a t h w a y s are:

o C o l l a p s e o f t a i l i n g s and was te rock p i l e s into s t r e a m s ;o R u n o f f f r o m t a i l i n g s a n d waste rock p i l e s in to s t r e a m s ;o I n h a l a t i o n o f dus t f r o m t h e p i l e s ; a n do I n g e s t i o n o f mat er ia l f r o m t h e p i l e s .

Two s i t e s were i d e n t i f i e d that had t a i l i n g s and was t e rockp i l e s tha t had the p o t e n t i a l t o c o l l a p s e into C l e a r Cre ek orN o r t h C l e a r Cre ek because o f u n s t a b l e s l o p e s . T h e t w o s i t e s a r et h e B i g F i v e T u n n e l a n d t h e G r e g o r y I n c l i n e . T h e A r g o T u n n e lt a i l i n g s and was t e rock p i l e was a l s o i d e n t i f i e d a s b e ingu n s t a b l e because o f b e ing undercu t . I f t h e A r g o was te rock p i l ef a i l s , t h e s t r u c t u r e s be low i t would b e a f f e c t e d , however, t h ewaste rock would not reach C l e a r C r e e k . Based on the e f f e c t s onhuman h e a l t h and the environment f r o m the p o t e n t i a l c o l l a p s e o fthe Big F i v e was te rock p i l e in to C l e a r C r e e k , i t i s recommendedthat the s l o p e s on both s id e s of the creek be r egraded ands t a b i l i z e d and that rock r i p - r a p be p l a c e d on the toe to p r o t e c tthe s l o p e f r o m eroding and c o l l a p s i n g into C l e a r Creek. Based onthe e f f e c t s on human h e a l t h and the environment f r o m thep o t e n t i a l c o l l a p s e of the t a i l i n g s and waste rock p i l e at theG r e g o r y I n c l i n e , i t i s recommended that the gabion-basket w a l l bemaintained unt i l moni tor ing ind i ca t e s r emedia t ion is necessary oru n t i l the t a i l i n g s are removed for r e p r o c e s s i n g . At that t ime , apermanent s o l u t i o n w i l l b e i m p l e m e n t e d . S p e c i f i c d e t a i l sc onc ern ing the s t a b i l i z a t i o n r emed ia l a c t i on s w i l l b e d e v e l o p e dd u r i n g Remedial Des ign . The cost o f t h i s r emed ia t i on i s prov id edin T a b l e 3.The second expo sure p a t h w a y i s c o n t a m i n a t e d water f r o m bothr u n o f f and runon over th e t a i l i n g s and was te rock p i l e s . R u n o f fcan be c o n t r o l l e d by a l t e r n a t i v e s such as: c a p p i n g , chemicalf i x a t i o n , r e p r o c e s s i n g , a n d o f f - s i t e d i s p o s a l . Because o f t h eh i g h cost t o contro l r u n o f f and th e f a c t that th e q u a n t i t y o fr u n o f f , a s o p p o s e d t o runon, f r o m t h e f i v e s i t e s i s s m a l l whencompared t o t h e t o t a l r u n o f f f r o m t h e m i n i n g d i s t r i c t ( l e s s t h a n0.01 perc ent o f th e t o t a l d u r i n g s torm e v e n t s ) , no l a r g e - s c a l e

30

T A B L E 3S U M M A R Y O F C O S T F O R P R E F E R R E D O P T I O N

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C A P I T A LG r e g o r y I n c l i n eN a t i o n a l T u n n e lQ u a r t z H i l lA r g o T u n n e lB i g F i v e

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$ 58,200$266,000

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A n n u a l T o t a l( i n c l u d i n g 2 0 % c o n t i n g e n c y )F i v e Y e a r R e c u r r i n g T o t a l( i n c l u d i n g 20% c o n t i n g e n c y )

10,800

12,000P R E S E N T W O R T H C O S T

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31

remed ia t i on to e l i m i n a t e r u n o f f i s p r o p o s e d . H o w e v e r , runonc o n t r o l s ( u p g r a d i e n t d i t c h e s ) have been i n c o r p o r a t e d into t h ep r o p o s e d r e m e d i a t i o n . T h e c o s t s f o r runon contro l a r e shown f o ra l l f i v e s i t e s i n T a b l e 3 . Runon c o n t r o l s w i l l s u b s t a n t i a l l yreduce the q u a n t i t y o f water f l o w i n g over the was t e rock andt a i l i n g s p i l e s . A d e t a i l e d e v a l u a t i o n o f t h e s e q u a n t i t i e s i sp r o v i d e d i n t h e O p e r a b l e U n i t N o . T w o F S ( A p p e n d i x J ) . Based o nthe b e n e f i t achieved by p r o v i d i n g runon control and ther e l a t i v e l y s m a l l cost o f the s e measure s , runon c o n t r o l s arerecommended.W h e n f i n a l d e s i g n s ar e c o m p l e t e d t o treat acid mine d r a i n a g eunder O p e r a b l e U n i t N o . One, c o l l e c t i o n a n d t r ea tment o f r u n o f ff r o m t a i l i n g s and was t e rock p i l e s a t t h e t r e a t m e n t f a c i l i t i e sw i l l be e v a l u a t e d .The t h i r d and f o u r t h e xpo sur e p a t h w a y s o f concern ar ei n g e s t i o n a n d dus t i n h a l a t i o n . A s p r e v i o u s l y d i s c u s s e d ,a c c e p t a b l e r i sk s are pre s en t f or t o u r i s t s and the occas ional s i t ev i s i t o r s ( e p i s o d i c e x p o s u r e ) , t h e r e f o r e , no remedial ac t ions arec u r r e n t l y recommended t o a l l e v i a t e i n g e s t i o n and dus t i n h a l a t i o n .H o w e v e r , t h e P u b l i c H e a l t h E v a l u a t i o n f o r t h e s i te ind i ca t edt h a t , f o r a r e s i d e n t i a l s c enario , r i sk s r e s u l t i n g f r o m t h ei n h a l a t i o n and i n g e s t i o n e x p o s u r e p a t h w a y s are of some concern.T h e r e f o r e , E P A w i l l e v a l u a t e t h i s N o A c t i o n d e c i s i o n when t h ef i n a l r emedy i s s e l e c t e d f o r t h e s i t e . E P A , i n c o o r d i n a t i o n w i t ht h e S t a t e o f C o l o r a d o a n d local o f f i c i a l s , w i l l e v a l u a t e t h e u s eof i n s t i t u t i o n a l measure s which would c on tro l any human h e a l t h ore n v i r o n m e n t a l threat that c ou ld be created by f u t u r e d e v e l o p m e n tupon the s e t a i l i n g s and waste rock p i l e s and any other p i l e swhich t h e S t a t e i d e n t i f i e s i n i t s s t u d y . I n a d d i t i o n , p u r s u a n tt o S A R A S e c t i o n 1 2 1 ( c ) , E P A w i l l review n o l e s s than every f i v eyears a l l p r o p e r t i e s where h a z a r d o u s s u b s t anc e s c on t inue t oremain ons i t e and, i f nece s sary, w i l l recons ider t h i s No A c t i o nd e c i s i o n .

D o c u m e n t a t i o n o f S i g n i f i c a n t C h a n g e sE P A i d e n t i f i e d t h e S l o p e S t a b i l i z a t i o n a n d Runon C o n t r o lA l t e r n a t i v e a s t h e p r e f e r r e d a l t e r n a t i v e i n t h e P r o p o s e d P l a nwhich was r e l ea s ed to the p u b l i c on November 9, 1987. The keye l e m e n t s o f t h i s a l t e r n a t i v e a s s t a t e d in the P r o p o s e d P l a n wererunon con tro l on a l l f i v e t a i l i n g s and was te rock p i l e s and s l o p es t a b i l i z a t i o n o f t h e B i g F i v e a n d t h e G r e g o r y I n c l i n e .At the t ime of the r e l ea s e of the P r o p o s e d P l a n , EPA wasp r o p o s i n g to remove the gab ion-ba ske t w a l l a t the G r e g o r y I n c l i n eand r e p l a c e it wi th a crib w a l l . EPA in t ended to take thep r o p e r t y o w n e r ' s d e s i r e t o r eproc e s s t a i l i n g s a t t h e G r e g o r yI n c l i n e in to account when r e p l a c i n g t h e gab ion-ba ske t w a l l . S i n c etha t t i m e , EPA has received e x t en s iv e comment on t h i s p o r t i o n ofthe P r o p o s e d P l a n and ha s m o d i f i e d th e s e l e c t e d remedy t o a d d r e s s

32

th e s e concerns. T h e p r i m a r y d i f f e r e n c e between t h e p r e f e r r e dremedy as p r e s e n t e d in the P r o p o s e d P l a n and the s e l e c t e d remedyas pr e s en t ed in t h i s Record of Deci s ion is that EPA no l ongerp l a n s t o i m m e d i a t e l y r e p l a c e t h e gab ion-baske t w a l l , b u t w i l linstead m a i n t a i n the wal l un t i l moni tor ing i n d i c a t e s that thew a l l needs to be r e p l a c e d or u n t i l the t a i l i n g s are removed forr epro c e s s ing . T h e E P A w i l l s t i l l take t h e o w n e r ' s r e p r o c e s s i n gconcerns into account w h i l e m o n i t o r i n g and m a i n t a i n i n g the w a l l .The s e l e c t e d remedy i s a l o g i c a l o u t g r o w t h o f the remedyi d e n t i f i e d in th e P r o p o s e d P l a n and other a l t e r n a t i v e s d e v e l o p e da n d e v a l u a t e d i n t h e O p e r a b l e U n i t N o . T w o F S . T h e c o m p o n e n t s o fthe s e l e c t e d remedy were c o n c e p t u a l l y e v a l u a t e d in the FS and thes e l e c t e d remedy i s w e l l w i th in the range of a l t e r n a t i v e s thep u b l i c c ou ld have r ea sonab ly a n t i c i p a t e d EPA to be c o n s i d e r i n g .

S T A T U T O R Y D E T E R M I N A T I O N SProt e c t i v ene s s :

T h e P u b l i c H e a l t h E v a l u a t i o n f o r t h e C l e a r C r e e k / C e n t r a lC i t y S u p e r f u n d S i t e c l e a r l y shows that C l e a r Creek a n d N o r t hC l e a r Cre ek are being i m p a c t e d by the acid mine d i s c h a r g e s andthe t a i l i n g s and waste rock p i l e s which are a s s o c i a t e d w i t h thes i t e . T h e s e i m p a c t s i n c l u d e :d e g r a d a t i o n o f d owns t r eam s u r f a c e water q u a l i t y r e s u l t i n gf r o m d i s s o l v e d and su spended m e t a l s in the d i s c h a r g e s andr e s u s p e n d e d metal l a d e n s e d i m e n t s b e low t h e d i s c h a r g e s ;d e g r a d a t i o n o f d o w n s t r e a m s u r f a c e water q u a l i t y d u e t op o t e n t i a l c o l l a p s e o f the t a i l i n g s and waste rock p i l e s intoe i t h e r C l e a r Cre ek or N o r t h C l e a r C r e e k ; andd e g r a d a t i o n o f downs t r eam s u r f a c e water q u a l i t y due t o runonand r u n o f f f r o m th e t a i l i n g s and waste rock p i l e s .

T h e s e i m p a c t s po s e no immed ia t e danger t o p u b l i c h e a l t h becauset h e c i t i e s o f I d a h o S p r i n g s , B l a c k h a w k , C e n t r a l C i t y , a n d G o l d e nhave m u n i c i p a l water s u p p l y sy s t ems that meet M C L s . H o w e v e r ,th e s e i m p a c t s r e s u l t i n s evere ly d e g r a d e d water q u a l i t y a f f e c t i n gaqua t i c l i f e and p r o d u c t i v i t y and reduced or d e s t r o y e d aquat i chabi ta t in C l e a r Creek and N o r t h C l e a r Creek .The f i r s t impact mentioned above i s a s s o c ia t ed wi th the acidmine d i s c h a r g e s and was a d d r e s s e d under O p e r a b l e U n i t No. One.The other two impac t s are a s soc ia ted wi th the t a i l i n g s and wasterock p i l e s and are a d d r e s s e d in t h i s O p e r a b l e U n i t .T h e s e l e c t e d remedy f o r t h i s O p e r a b l e U n i t i n c l u d e s s l o p es t a b i l i z a t i o n which w i l l reduce t h e p o t e n t i a l f o r a c o l l a p s e o f

33

u n s t a b l e t a i l i n g s and waste rock p i l e s into the creeks and runoncon tro l measures which w i l l d iver t water around th e p i l e s t h e r e b ye l i m i n a t i n g the impact due to runon. T h i s p o r t i o n of thes e l e c t e d remedy is t h e r e f o r e p r o t e c t i v e and w i l l r e s u l t in animprovement o f t h e water q u a l i t y in C l e a r C r e e k and N o r t h C l e a rCreek .T h e P u b l i c H e a l t h E v a l u a t i o n a l s o cons idered i m p a c t s t ohuman h e a l t h r e s u l t i n g f r o m i n h a l a t i o n or i n g e s t i o n o f mat er ia lf r o m th e t a i l i n g s and waste rock p i l e s . H o w e v e r , a s d i s c u s s e de a r l i e r in th i s document and as shown in T a b l e 1, there are nocurrent i m p a c t s t o human h e a l t h f r o m th e s e e x p o s u r e p a t h w a y s .F o r t h i s reason, t h e s e l e c t ed remedy f o r t h i s p o r t i o n o f t h eOperab l e U n i t , No A c t i o n , i s p r o t e c t i v e o f human h e a l t h .U n d e r t h e p o t e n t i a l f u t u r e r e s i d e n t i a l u s e s cenario t h e r i skf r o m ing e s t i on o f soil i s o f some concern. For t h i s reason, E P A ,when s e l e c t i n g t h e f i n a l remedy, w i l l c on s id er i n s t i t u t i o n a lmeasures t o control f u t u r e d e v e l o p m e n t upon t h e t a i l i n g s p i l e s .

C o n s i s t e n c y W i t h Other L a w s :Pursuant t o S A R A S e c t i o n 1 2 1 ( d ) , remedial ac t ions s h a l la t t a i n a d egr e e o f c l e a n u p o f h a z a r d o u s s u b s t a n c e s , p o l l u t a n t s ,and c o n t a m i n a n t s r e l ea s ed into the environment and contro l off u r t h e r re l ease which at a minimum assures p r o t e c t i o n of humanh e a l t h a n d t h e env ironment . I n a d d i t i o n , r emedia l a c t i on s s h a l l ,upon the ir c o m p l e t i o n , reach a l eve l or s t andard o f control forsuch hazardous sub s tance s , p o l l u t a n t s , or contaminant s which atl e a s t a t t a i n s l e g a l l y a p p l i c a b l e o r re l evant a n d a p p r o p r i a t eF e d e r a l s t a n d a r d s , r equ i r emen t s , c r i t e r i a , or l i m i t a t i o n s , or anyp r o m u l g a t e d s t a n d a r d s , r equ i r emen t s , c r i t e r i a , o r l i m i t a t i o n sunder a S t a t e e n v i r o n m e n t a l or f a c i l i t y s i t i n g law tha t i s mores t r ingen t than a n y F e d e r a l s tandard ( A R A R s ) .On December 23, 1986 EPA reque s t ed that the S t a t e o fC o l o r a d o prov id e a l i s t o f a p p l i c a b l e or re l evant S t a t er e q u i r e m e n t s , s t a n d a r d s , c r i t e r ia a n d l i m i t a t i o n s f o r t h e C l e a rC r e e k / C e n t r a l C i t y S i t e . T h e S t a t e r e s p o n d e d o n M a y 1 4 , 1987with a l i s t o f requirements p e r t a i n i n g to O p e r a b l e U n i t No. One.T h e S t a t e d i d n o t f o r m a l l y submit a l i s t o f r equirement s f o rO p e r a b l e U n i t N o . T w o . S u b s e q u e n t l y , however, p r o b a b l e S t a t erequirement s were i d e n t i f i e d by S t a t e and EPA s t a f f t h r o u g hi n f o r m a l d i s c u s s i o n s . T h e s e i n f o r m a l l y i d e n t i f i e d r equ i r emen t swere taken into account d u r i n g the d e v e l o p m e n t o f a l t e r n a t i v e sfor t a i l i n g s and waste rock r e m e d i a t i o n .E P A c l a s s i f i e d a l l F e d e r a l a n d S t a t e p u b l i c h e a l t h a n de n v i r o n m e n t a l r equ ir ement s a p p l i c a b l e or r e l e v a n t and a p p r o p r i a t eto the t a i l i n g s and was t e rock r e m e d i a t i o n into three c a t e g o r i e s :c o n t a m i n a n t - s p e c i f i c A R A R s , a c t i o n - s p e c i f i c A R A R s , a n d l o ca t i on-s p e c i f i c A R A R s . A d e s c r i p t i o n o f each o f the s e c a t e g o r i e s i s

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p r o v i d e d i n S e c t i o n 2 o f t h e O p e r a b l e U n i t N o . T w o F S . T a b l e s2-1 and 2-2 in the FS contain a br i e f d e s c r i p t i o n of eachp o t e n t i a l F e d e r a l a n d S t a t e p u b l i c h e a l t h a n d e n v i r o n m e n t a lrequirement i d e n t i f i e d a n d E P A ' s a n a l y s i s o f each r e q u i r e m e n t ' sa p p l i c a b i l i t y or r e l evance and a p p r o p r i a t e n e s s to the o p e r a b l euni t .E P A h a s d e t e r m i n e d that t h e c o n t a m i n a n t - s p e c i f i c A R A R s f o rO p e r a b l e U n i t N o . T w o a r e t h e M a x i m u m C o n t a m i n a n t L e v e l s ( M C L s )e s t a b l i s h e d under t h e S a f e D r i n k i n g W a t e r A c t , Ambient W a t e rQ u a l i t y C r i t e r i a ( A W Q C s ) e s t a b l i s h e d under t h e C l e a n W a t e r A c ta n d S t a t e W a t e r Q u a l i t y S t a n d a r d s . T h e r e a r e c u r r e n t l y n oi d e n t i f i e d c o n t a m i n a n t - s p e c i f i c A R A R s f o r m e t a l s i n s o i l s s o E P Ar e l i e d on a c t i o n - l e v e l s e s t a b l i s h e d t h r o u g h the r i sk a s s e s s m e n t .T h e s e a c t i on l e v e l s are c on ta ined in T a b l e 2-3 o f the O p e r a b l e

U n i t N o . T w o F S .T h e s e l e c t e d remedy f o r O p e r a b l e U n i t N o . T w o i s a n i n t e r i mremedy which i s c o n s i s t e n t w i th the f i n a l remedy and w h i c h ,p u r s u a n t t o S A R A S e c t i o n 1 2 1 ( d ) ( 4 ) ( A ) , require s t h e exerci se o ft h e " interim remedy" waiver f r o m th e c o n t a m i n a n t - s p e c i f i c A R A R sment ioned in the p r e v i o u s p a r a g r a p h , that i s , the s e l e c t e d remedyi s o n l y part o f a t o t a l r e m e d i a t i o n tha t w i l l a t t a i n such a l eve lor s t a n d a r d of c on tro l when c o m p l e t e d . L o c a t i o n - and ac t ion-s p e c i f i c A R A R s w i l l b e met.I n accordance w i t h S A R A S e c t i o n 1 2 1 ( d ) ( 2 ) ( A ) ( i i ) , E P Ai n t e n d s that the f i n a l remedy w i l l a t l eas t a t t a i n water q u a l i t yc r i t e r i a e s t a b l i s h e d under t h e A c t s ment i oned above. H o w e v e r ,a d d i t i o n a l d a t a c o l l e c t i o n and u s e a t t a i n a b i l i t y a n a l y s e s ar enece s sary f o r E P A t o d e t e r m i n e i f such c r i t e r i a a r e a p p r o p r i a t eunder the c ircumstance s of the r e l ea s e or whether s i t e - s p e c i f i cm o d i f i c a t i o n t o t h e c r i t e r i a wou ld more a p p r o p r i a t e l y e s t a b l i s hc l e a n - u p g o a l s f o r t h e s i t e . E P A w i l l make t h i s d e t e r m i n a t i o n a spart o f t h e f i n a l remedy s e l e c t i o n .

C o s t - e f f e c t i v e n e s s a n d U t i l i z a t i o n o f Permanent S o l u t i o n s a n dA l t e r n a t i v e T r e a t m e n t T e c h n o l o g i e s or Resource RecoveryT e c h n o l o g i e s t o t h e M a x i m u m Ex t en t P r a c t i c a b l e :T h e S l o p e S t a b i l i z a t i o n a n d Runon C o n t r o l A l t e r n a t i v e i s ac o s t - e f f e c t i v e r emed ia l ac t ion a l t e r n a t i v e which e f f e c t i v e l ym i t i g a t e s and min imiz e s t hr ea t s to and p r o v i d e s adequatep r o t e c t i o n o f p u b l i c h e a l t h and th e env ironment . Other t han th eN o A c t i o n A l t e r n a t i v e , t h i s i s t h e l ea s t e x p e n s i v e a l t e r n a t i v e o ft h o s e c o n s i d e r e d . ( S e e T a b l e 2 . ) T h e e s t i m a t e d t o t a l cost f o rthe s e l e c t e d remedy i s a n t i c i p a t e d to be $ 1 , 0 4 9 , 6 0 0 . T h i s costi n c l u d e s o p e r a t i o n and main t enance a c t i v i t i e s and the cost o f thef i v e - y e a r e v a l u a t i o n .

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T h e s e l e c t e d remedy does n o t s a t i s f y t h e s t a t u t o r yp r e f e r e n c e f o r t r e a t m e n t a s a p r i n c i p a l e l ement because t r e a t m e n twas f o u n d to be i m p r a c t i c a b l e at t h i s t ime. H o w e v e r , EPA leavesopen t h e o p p o r t u n i t y f o r any f u t u r e t r e a t m e n t o r r e p r o c e s s i n gwhich can be shown to be p r o t e c t i v e of human h e a l t h and theenvironment and which a t t a i n s F e d e r a l and S t a t e p u b l i c h e a l t h ande n v i r o n m e n t a l r e q u i r e m e n t s that are a p p l i c a b l e or r e l evant anda p p r o p r i a t e .

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