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GLOB E PLAN T C •" • f

; r i T I n p v 1-1

, o

n - ^

- - -- - . I.. I i" i i/.

. / ; i j Octobe r 6

, 1995

c ;

- . . *'-'•'•— • ••'• ? * ; 3 ''«* * Ms

. Rebecc a Thoma s Remedial Projec t Manage r E P A Regio n VII I 99 9 18t h Street

, Suit e 50 0 Denver

, C O 80202-240 5 R E : ASARCO' S RESPONSES T O COMMENTS : HYDROGEOLOGI

C AN D SURFACE WATER

, REMEDIA L INVESTIGATIO N

REPORTS

, CALIFORNI A GULC H SITE

, LEADVILLE

, COLORAD O Rebecca : Th e enclose d documen t include s response s t o comment s received fro m th e U.S

. Environmenta l Protectio n Agenc y (EPA)

. Th e EP A letter

, date d Augus t 1

, 1995 (EP A Ref : 8HWM-SR)

, presente d comment s fro m a revie w o f th e Hydrogeologi c Remedial Investigatio n (RI ) repor t

an d th e Surfac e Wate r R I repor t fo r th e Californi a Gulc h Site

, bot h date d Ma y 1995

. Response s t o th e comment s ar e presente d i n Attachmen t 1 (Hydrogeologi c RI ) and Attachmen t 2 (Surfac e Wate r RI)

. The R I report s wil l b e finalize d wit h you r approva l o f the response s or wit h you r furthe r recommendation s relativ e t o editin g th e reports

. W e anticipat e tha t additiona l comment s ma y b e receive d fro m th e Stat e o f Colorado

. Th e State' s comment s als o wil l b e incorporate d int o th e fina l reports

. W e appreciat e you r hel p o n thi s projec t an d loo k forwar d t o completin g th e tw o R I reports

. I f yo u hav e an y questions

, pleas e contac t m e a t 296-5104

. Sincerely

,

Margare t (Poppy ) Stau b Environmenta l Projec t Manage r ( 4 copie s sent )

cc : Rus s Alien

, CDPH E Geral d Almquist

, Westo n

ASARC O Incorporated

. 49 5 Eas t 51s t Avenue

. Denver

. Colorad o 80216-209 8 Phon e (303 ) 296-590 0 FA X (303 ) 296-050 8Californi a Gulch NP L Sit e Hydrogeologi c Remedia l Investigatio n Repor t Comment s an d Responses 

### Commen t Numbe r Comment/Respons e E P A COMMENT S WIT H ASARC O RESPONSE S MA Y 199 5 HYDROGEOLOGI

C RI REPOR T
(1 ) Commen t 7 : Respons e t o EP A commen t i s adequate ; however

, th e informatio n identifie d for inclusio n i n th e tex t o f th e RI Repor t wa s no t foun d i n th e text

. Th e statemen t i n the tex t shoul d provid e clarificatio n o n the groundwate r discharg e fluctuations

. Response : Th e followin g wa s adde d t o th e text : "Th e rang e o f value s appea r t o reflec t seasona l an d loca l variation s i n groundwate r discharg e rates. " (2 ) Commen t 14 : Sit e Ma p include d a s Figur e 1.3- 2 shoul d identif y th e boundarie s o f th e stud y area

. Response : Boundarie s o f th e stud y area , as identifie d i n Asarco' s Wor k Are a Managemen t Plan

, hav e bee n identifie d o n Figur e 1.3-2

. (3 ) Commen t 15 : Respons e t o EP A commen t i s adequate ; however

, th e informatio n identifie d for inclusio n i n th e tex t wa s no t foun d i n th e text

. Response : Th e followin g tex t wa s adde d t o Sectio n 1.3.1

. Th e statemen t reference d i n th e RI refer s t o th e Ya k Tunne l a s havin g bee n th e primar y sourc e o f Californi a Gulch surfac e wate r contamination

. The statement i s based o n result s presente d i n th e EP A Phas e I Remedia l Investigatio n Report ; mass-loadin g 

### analysi s determine d tha t pre-treatmen t Ya k Tunne l discharg e contribute d ove r 7 5 percent o f th e zinc

, cadmium an d sulfat e i n surfac e water

. Th e Recor d o f Decisio n fo r th e Ya k Tunne l als o acknowledge s thi s point

. (4 ) Commen t 16 : Respons e t o EP A commen t i s adequate

. Mino r change s shoul d b e mad e t o the tex t t o clarif y location s an d meanin g o f a the followin g statements

.

* • Pag e 1-16

, 2nd Paragraph

, Tur k and Taylor

. Wate r qualit y for whic h "tunnel, " Ya k o r Leadvill e drain ?Octobe r

6

, 1995______________________2__________________________243-281 9

* Pag e 1-16

, 3r d Paragraph

, EP A 1983

. N o mentio n o f lea d i n the wate r fro m Ya k Tunne l discharge ; tru e o r a n oversight ?
* Previou s tex t include d a referenc e t o "ASARCO

. 1984

. Hydrogeologi c Evaluatio n

o f th e Ya k Tunne l an d Californi a Gulch

. Prepare d b y HR S Wate r Consultants

. Unpublishe d Report. " Thi s referenc e wa s no t include d i n thi s versio n o f th e document

, and shoul d b e reinserte d fo r consistency

. Response : Recommende d

change s hav e bee n include d i n the text

. The "tunnel " referre d t o i n th e firs t bulle t i s th e Leadvill e Drainag e tunnel

. Th e tex t wa s edite d t o describ e "...mino r concentration s o f lead, " i n respons e t o th e secon d bullet

. Th e referenc e t o Asarco

, 198 4 wa s adde d t o th e tex t i n respons e t o th e thir d bullet

. (5 ) Commen t 18 : Respons e t o EP A commen t i s adequate ; however

, respons e an d tex t indicat e th e inclusio n o f a Tabl e 2.1-3 a fo r "Sprin g an d Tunne l Porta l Flo w Measurement Methods. " Thi s Tabl e 2.1-3 a wa s no t foun d i n th e R I Report

. Response : Tabl e 2.1-3 a wa s adde d t o th e text

. TABLE2.1-3 a SPRIN G AN D TUNNE L DISCHARG E FLO W MEASUREMEN

T METHO D Spring/Tunne l I D Recon

.

Dat e Flo w Measuremen t Metho d SPR- 1 9/24/9 1

F SPR- 2 9/24/9 1

V SPR- 3 1 SPR- 4 9/25/9 1

F SPR- 5 9/25/9 1

N

F SPR- 6 9/25/9 1

N

F SPR- 7 9/25/9 1

E SPR- 8 9/25/9 1

V SPR- 9 1 SPR-1 0 9/25/9 1

N

F SPR-1 1 9/25/9 1

N

F SPR-1 2 9/25/9 1

E SPR-1 3 9/26/9 1

E SPR-1 4 9/26/9 1

N

F SPR-1 5 9/26/9 1

N

F SPR-1 6 9/26/9 1

V SPR-1 7 9/26/9 1

V TP- 1 9/26/9 1

F TP- 2 9/26/9 1

V TP-3 1 N/

A MOctobe r

6

, 199 5 243-281 9

1

. NF-N o Flo w 2

. V

. - Volumetric 3

. F

- 2 inc h flum e 4

.

E

- R Visua l Estimat e 5

. M

- Flo w Mete r - X-sectio n (6 ) Commen t (page

. 2-4) : Th e thir d lin e o f th e firs t paragrap h make s referenc e t o "wate r qualit y sampl e analysi s result s ar e liste d i n Tabl e 2.1-6. " Tabl e 2.1- 6 does no t includ e results

, bu t rathe r a lis t o f analytica l parameters

. Th e tex t shoul d b e correcte d t o rea d "wate r qualit y analytica l parameter s fo r whic h surfac e wate r wa s analyze d ar e liste d i n Tabl e 2.1-6. " Response : Tex t wa s changed t o indicat e "...analytica l parameter s fo r whic h surfac e wate r wa s analyzed... " rathe r tha n "...sampl e analysi s results... " (7 ) Commen t (pag e 2-8) : Th e secon d sentence o f th e firs t paragrap h make s referenc e t o Figur e 2.1- 2 showin g bedroc k monitorin g wells

. Referenc e shoul d includ e Figur e 2.1- 3

, whic h als o include s "BMW " wel l locations

. Response : Tex t ha s bee n modifie d t o includ e referenc e t o Figur e 2.1-3

. (8 ) Commen t (Tabl e 2.3-5) : Th e tabl e shoul d indicat e whe n measurement s wer e collecte d (e.g.

, prio r t o o r afte r purging

, a t sampl e collection)

. Fo r stati c wate r levels

, th e tex t

on pag e 2-1 7 indicate s thes e wer e measure d prio r t o purgin g an d tha t th e fiel d parameters wer e measure d afte r purgin g a t th e tim e o f wate r qualit y sampling

. Tex t

an d tabl e nee d t o b e consistent

. Response : Not e adde d t o th e table

. Th e standar d practic e o f measurin g wate r level s prio r t o wel l purgin g wa s use d durin g the RI

. 

### ( 9 ) Commen t (pag e 2-17) : Th e las t sentenc e o f th e thir d paragrap h reference s Tabl e 2.3

- 7

, whic h i s incorrec t (mini-piezometers)

.

Th e correc t referenc e shoul d b e Tabl e 2.3- 3 f o r th e Ya k Tunne l Monitorin g Well s (BBW)

. Response : Th e referenc e ha s bee n corrected

. (10 ) Commen t (Tabl e 2.1-1):Th e locatio n fo r SPR-1 7 i s identifie d a s "90 0 fee t east... " whic h i s contradictor y t o th e fiel d reconnaissanc e for m i n Appendi x G tha t indicate s th e locatio n a s "abou t 40 0 fee t east... " Thi s discrepanc y need s t o b e resolve d an d th e tex t correcte d a s appropriate

. Additionally

, Tabl e 2.1- 1 identifie s locatio n TP-3 ; however

, n o fiel d reconnaissanc e for m i s include d i n Appendi x G fo r thi s location

. I f th e for m i s availabl e i t shoul d b e include d i n Appendi x G

. Response : Th e referenc e i n Appendi x G "40 0 fee t east " ha s bee n correcte d an d a not e adde d t o Tabl e 2.1-1

. TP- 3 wa s no t include d i n th e initia l fiel d reconnaissance ; therefor

, no for m wa s prepared

.Octobe r

6

, 1995_____________________4_________________________243-281 9 (11 ) Commen t Appendi x A

, pag e A-l : Th e las t sentenc e o f th e secon d paragrap h make s referenc e t o "Tabl e 2.1-3 a i n th e text " identifyin g site-specifi c flo w measurement s methods

. N o Tabl e 2.1-3 a wa s identifie d i n the text

, no r d o an y table s i n Sectio n 2 identif y th e site-specifi c measuremen t metho d conducte d a t a location

. Tabl e 2.1-3 a shoul d b e include d a s indicate d (see Commen t 5)

. Response : Tabl e 2

. l-3a ha s bee n adde d t o th e text

. (12 ) Commen t 31 : Respons e t o EP A commen t i s adequate

. Respons e indicate s th e inclusio n o f tw o letter s discussin g deviatio n o f method s employe d t o measur e hea d difference

. Thes e letter s wer e no t foun d i n Appendi x D an d shoul d b e include d a s indicate d i n th e response

. Response : A Cop y o f one lette r ha s bee n adde d t o Appendi x D bu t th e secon d lette r 

### ha s no t bee n located

. (13 ) Commen t Appendi x A : Wel l Lo g Summarie s BMW- 1 an d BMW- 2 ar e missing

. Thes e log s nee d t o b e include d i n Appendi x A

. Response : Wel l summarie s fo r BMW- 1 an d BMW- 2 hav e bee n adde d t o Appendi x A

. (14 ) Commen t (pag e 2-20

, Sectio n 2.4.2) : Discussio n shoul d referenc e Appendi x C fo r measuremen t metho d discussion

. Response : A referenc e t o Appendi x C ha s bee n adde d t o the text

. Slu g test s wer e performe d a t mini-piezomete r location s P12

, P24

, P31A

, eac h o f whic h varie s betwee n gainin g an d losin g conditions

. Th e predominan t mini-piezomete r slu g testin g wa s don e a t gainin g reache s o f Californi a Gulc h t o obtai n dat a neede d i n estimatio n o f metal s loadin g int o surfac e wate r fro m groundwater

. Groun d wate r flowin g int o the surfac e water i n gainin g strea m reache s an d sprin g flo w ar e particularl y importan t i n wate r balanc e calculation s discusse d i n Sectio n 3.2.6.2

. (15 ) Commen t (pag e 3-4) : Th e las t sentenc e make s an incorrect referenc e t o 1993 ASARC O documents

. Th e referenc e dat e need s t o b e correcte d t o refe r t o 199 4 fo r consistenc y wit h Sectio n 8

, References

. Response : Th e referenc e ha s bee n corrected

. (16 ) Commen t (pag e 3-12) : Th e fourt h paragraph refer s t o "Periodi c reworkin g o f aquife r materials. " Clarificatio n o f aquife r material s need s t o b e mad e t o indicat e that reworkin g i s representativ e o f alluvia l aquife r materials

. Response : ".

. .alluvial... " ha s bee n adde d t o th e text

.October6

, 1995 _____________________5_________________________243-281 9 (17 ) Commen t (pag e 3-4

, 3-11

, 3-17

, 3-19) : Referenc e t o Figure s 3.1-7 a throug h 3.1-7 d i s incorrect

. Th e correc t referenc e i s Figure s 3.1-5 a throug h 3.1-5d

. Response : Th e referenc e ha s bee n corrected

. (18 ) Commen t (pag e 3-17) : Th e las t sentenc e refer s t o th e Surfac e Wate r R I Repor t (ASARCO

, 1995)

. Thi s referenc e need s t o b e include d i n Sectio n 8

. Refe r t o Commen t 48

. Response : Th e referenc e ha s bee n adde d t o Sectio n 8

. (19 ) Commen t (pag e 3-18) : Referenc e i s mad e t o Sectio n 4.2. 3 fo r chemica l loadin g discussion ; however

, Sectio n 4.2. 3 doe s no t includ e suc h a discussion

. Th e discussio n need s t o b e reincorporate d int o Sectio n 4

. Refe r t o Comment 44

. Response : Th e chemica l loadin g discussio n ha s bee n adde d a s Sectio n 4. 4 an d th e referenc e i n Sectio n 3.2. 6 ha s bee n clarifie d a s follows : Mini-piezomete r location s wer e sample d a t gainin g stream reache s o n a quarterl y basi s beginnin g i n Jun e 199 2 t o asses s groundwate r qualit y condition s at thes e locations

, surfac e wate r qualit y als o wa s sample d a t monitorin g locatio n CG-3

, CG-4

, CG-5

, an d CG- 6 o n a monthl y basi s durin g th e perio d Jul y 199 2 throug h Octobe r 1992

. Sprin g

an d runne l porta l sample s wer e collecte d i n Septembe r 1992

. Groundwater

, spring/tunne l portal

, surfac e water qualit y results

, an d discharg e an d wate r balanc e dat a

wer e use d t o estimat e potentia l chemica l loadin g fro m groundwate r t o lowe r Californi a Gulch

. Result s o f th e groundwater-surfac e

wate r chemica l qualit y comparison s ar e discusse d i n Sectio n 4.2. 3 an d i n th e Surfac e Wate r R.I

. Th e result s o f th e comparativ e wate r leve l an d fiel d paramete r monitoring

, an d th e surfac e wate r gain/los s calculation s ar e discusse d i n th e followin g sections

. 4.4

. Mas s Loadin g Groundwate r i n the Californi a Gulc h are a contain s metal s a s bot h dissolve d and tota l concentrations

. The chemica l loa d containe d i n groundwate r i s transporte d t o surfac e wate r whe n groundwate r flow s int o th e surfac e water system

. Seasona l variation s i n the flu x o f groundwate r movin g int o the surfac e wate r resul t i n correspondin g variation s i n th e rat e o f whic h metal s ar e adde d t o th e surfac e water

. Th e rat e a t whic h chemical s are adde d t o th e surfac e wate r fro m groundwate r i s referre d t o a s mas s loading

. Mas s loadin g rate s ca n b e estimate d base d o n chemica l concentration s (C ) i n th e groundwate r time s th e rat e o f volumetri c discharg e (Q ) o f groundwate r flowin g int o the surfac e wate r system

. A s Q change s du e t o seasonal variations

, mas s loadin g rate s change accordingly

. Variation s i n groundwate r chemica l compositio n (Table s 4.2-8 a throug h 4.2-8c

, 4.2-9 a throug h 4.2-9c ) als o affec t mas s loadin g rates

, butOctobe r

6

, 1995______________________6__________________________243-281 9 th e magnitud e o f chemica l compositio n change s i s relativel y smal l compare d t o change s i n value s o f Q

. Estimate d seasona l mas s loadin g rate s fro m severa l groundwate r source s ar e liste d i n Table s 4.2-10a

, 4.2- 1 Ob

, 4.2-11

, an d 4.2-12

. (20 ) Commen t (pag e 3-18) : Th e en d o f th e secon d paragrap h refer s t o Figur e 4.2-8

, whic h i s no t relevant t o thi s discussion

. A n appropriat e figur e need s t o b e created o r reference d t o suppor t th e discussio n o n gainin g strea m reaches

. Th e statemen t als o indicate s tha t th e figur e wil l sho w th e "relationshi p o f th e gainin g strea m reache s wit h

eac h o f the factor s listed. " Ca n suc h a figur e b e created t o suppor t thi s statement ? Refe r t o Commen t 49

. Response : Th e figur e referenc e ha s bee n corrected

. Gaining/losin g stream reache s hav e bee n adde d t o Figur e 3.2-2

. (21 ) Commen t (pag e 3-22) : Sectio n 3.2.6. 2 i s incomplete

. Tex t t o suppor t discussio n o f Tabl e 3.1-5 a throug h f

, pertainin g t o alluvia l aquife r discharg e t o gainin g reache s o f Californi a Gulch

, an d Tabl e 3.1- 6 pertainin g t o sprin g discharg e t o Californi a Gulc h appear s t o b e missing

. Response : Th e tex t ha s bee n expande d a s follow s t o includ e respons e discussion

. 3.2.6. 2 Estimatio n o f Groundwate r Influen t Rate s t o Californi a Gulc h Measurement point s alon g the strea m ar e critica l i n the calculations

. Extrapolatio n o f th e dat a represent s a significan t sourc e o f wate r balanc e calculatio n error

. Estimate d wate r volume s enterin g gainin g stream reache s fro m groundwate r source s

ar e liste d i n Table s 3.1-5 a throug h 3.1-5 g (Comment refer s t o onl y 3.1-5 a throug h 3.1-5f)

. A mor e detaile d wate r balanc e i s presente d i n th e Surfac e Wate r R I (Asarco

, 1995)

. Dat a an d calculation s o n water balanc e are presente d i n Table s 3.1-7 a throug h 3.1-7d

. Wate r balanc e calculation s presente d i n Table s 3.1-7 a throug h 3.1-7 d ar e a 

### measur e o f wate r losse s an d gain s alon g th e Californi a Gulc h stream

. Surfac e wate r gain s occu r wher e groundwate r dischargin g fro m alluvia l an d bedroc k aquifer s ente r th e surfac e wate r syste m an d surfac e wate r flo w decrease s wher e wate r enter s th e groundwate r syste m alon g losin g stream reaches

. Gain s t o surfac e wate r flo w als o

occu r wher e surfac e wate r flow s int o Californi a Gulc h fro m tributar y sources

. (21a ) Commen t Sectio n 3 : Th e sectio n n o longe r include s a discussio n o n water balanc e t o suppor t dat a an d calculation s presente d i n Table s 3.1-7 a throug h 3.1-7d

. Thi s discussio n need s t o b e reincorporate d o n th e R I Report

. Response : Th e wate r balanc e discussio n ha s bee n adde d t o th e text

. Se e respons e t o (21)

.Octobe r

6

, 1995______________________7__________________________243-281 9 (22 ) Commen t 49 : Respons e t o EP A commen t i s adequate ; however

, th e thir d paragrap h o f th e respons e wa s no t integrate d int o Sectio n 3 an d shoul d be

. Response : The followin g discussio n ha s bee n adde d t o tex t i n Sectio n 3

. f\ fj Th e relativel y lo w hydrauli c conductivit y value (abou t 3 x 10 " t o 3. 1 x 10 " fee t pe r day ) calculate d fo r th e slu g tes t dat a at mini-piezomete r P-1 2 i s simila r t o value s calculate d for PZ- 9 (abou t 6 x 10" 2 t o 7. 2 x 10" 2 fee t per day)

. Th e value s are als o simila r t o ABW-3

, ABW-4

, PZ-5

, an d PZ-1 0 tha t hav e calculate d value s o f abou t 6. 3 x 10" 1 t o 1 foo t per day

. Th e lo w values ma y b e a resul t o f fine-graine d sediment s a t

eac h o f thes e locations

. 

### (23 ) Commen t 5 9 throug h 64 : Response s are adequate

. Integratio n o f response s int o th e RI repor t wa s no t foun d withi n Sectio n 3

. I t appear s tha t som e portion s o f Sectio n 3

wer e omitte d i n th e transitio n fro m th e WW C RI Repor t t o thi s RI Report

, thereb y makin g i t incomplete

. Response : Th e reference d discussion s ha s bee n adde d t o th e tex t i n Sectio n 3 a s follows

. The followin g equatio n wa s use d t o estimat e th e conductanc e o r discharg e betwee n thes e tw o potentia l surfaces : Q R - K L {( W + 2e ) / ( e + 2A) } ( h

- y )
where : K i s a representativ e hydrauli c conductivit y fo r the regio n betwee n the tw o equipotentia l surfaces ; L i s th e lengt h o f th e influen t stream reac h o f concern ; W i s th e to p widt h o f th e strea m surfac e (usuall y a n adequat e approximatio n fo r th e wette d perimeter) ;
e i s th e representativ e saturate d thicknes s o f th e aquife r fo r th e immediat e area ; A i s a distanc e a t whic h th e equipotentia l surfac e i s essentiall y vertical (assume d t o b e the distanc e fro m the centerlin e o f the strea m t o the mini-piezometer ; h i s th e groundwate r surfac e elevatio n (potential ) a t distanc e A ; y i s the elevatio n o f the strea m surfac e (potential) ; 

### Paramete r e wa s estimate d t o b e approximatel y 2 0 fee t fo r th e flu x calculations

. Th e thicknes s applie d t o eac h piezomete r fo r hydrauli c conductivit y calculation s fo r partially-penetratin g solution s wa s based o n estimate d thickness a t eac h mini

piezomete r location

. Th e distanc e fro m th e mini-piezometers t o th e strea m centerlin e i s les s tha n th e minimu m 5 stream-widt h (5W ) distanc e required fo r th e applicatio n o f th e Morel

- Seytou x an d Zhan g metho d fo r flu x estimation

. A n alternat e metho d o f flu x calculatio n


### wa s applie d t o thes e data

. Whe n the flu x estimate s ar e recalculated

, the resultin g
seasona l trend s i n aquife r discharg e t o Californi a Gulc h wil l b e re-evaluate d t oOctobe r

6

, 1995______________________8__________________________243-281 9 

### determin e whethe r groundwate r discharg e t o th e strea m change s significantl y ove r time

. Morel-Seytou x an d Zhan g indicate d tha t theoretica l an d experimenta l studie s hav e show n tha t A ca n b e approximate d b y 5W

, wher e W i s th e widt h o f th e strea m surface

. Th e equatio n ca n b e re-writte n as : Q R

- K L {( W + 2e ) / ( e + 10W) } ( h

- y ) Usin g thi s equation

, th e volumetri c inflo w rate s t o surfac e wate r wer e estimate d fo r

eac h gainin g stream reac h fro m Ma y throug h Novembe r 199 2 an d summe d t o provid e

a n estimatio n o f tota l groundwate r discharg e int o lowe r Californi a Gulc h (Table s 3.1

- 7 a throug h 3.l-7d)

. Revie w o f th e hea d differential s fo r bot h influen t an d effluen t mini-piezomete r

location s throughou t th e monitorin g perio d indicate s tha t hea d differential s betwee n groundwate r

an d surfac e water generall y increase fro m Ma y t o Novembe r fo r losin g reaches

, whil e thes e differential s ten d t o remai n mor e stabl e fo r gainin g reaches

. Thi s tren d i s probabl y attributabl e t o th e followin g factors :

* • Durin g th e recharg e perio d (ice-fre e throug h freeze-up)

, groundwate r an d surfac e wate r level s ar e bot h higher

, resultin g i n smalle r hea d differential s alon g 

### gainin g an d losin g reache s an d therefor e a lowe r potentia l exchang e rate

.

* • Followin g th e recharg e perio d whe n surfac e runof f (an d recharge t o groundwater ) ha s diminishe d substantially

, surfac e wate r level s appea r t o stabiliz e an d ar e probabl y sustaine d b y discharg e fro m the Ya k Tunne l an d Leadvill e Sewag e Treatmen t Plant

, whil e groundwate r level s continue t o decreas e i n respons e t o decrease d recharge

. Thi s result s i n increasin g hea d differential s late r i n th e year, especiall y alon g losin g reache s o f th e gulch

.

* • I n combinatio n wit h th e factor s above

, difference s i n hydrauli c conductivitie s i n th e aquife r alon g lowe r Californi a Gulch ma y produc e variabl e hea d differentials

. Fo r region s wit h lo w hydrauli c conductivities

, hea d differential s coul d b e expecte d t o b e greate r tha n region s wit h hig h hydrauli c conductivities

. 

### (24 ) Commen t 66 : Respons e t o EP A commen t i s adequate

. N o modification s t o th e R I Repor t wer e foun d a s presente d i n th e response

. Seismi c informatio n shoul d b e include d i n th e R I Report o r referenc e shoul d b e mad e t o another repor t i f th e informatio n i s documente d elsewhere

. The seismi c dat a ma y b e helpfu l i n the quantificatio n o f value s fo r th e piezometer s b y providin g informatio n o n saturate d thickness

.Octobe r

6

, 1995______________________9__________________________243-281 9 Response : Th e discussio n on geophysica l survey s ha s bee n adde d t o Sectio n 3

, a s follows : 

### Origina l seismi c dat a records

, seismi c surve y lin e locatio n informatio n an d downhol e geophysica l record s ar e retaine d i n th e projec t files

. Interpretation s o f th e seismi c refractio n dat a wer e use d t o identif y th e sediment/bedroc k interfac e an d t o ma p bedroc k discontinuities

. Th e dat a provide d insufficien t informatio n t o distinguis h lithologi c characteristics

, assis t i n interpretatio n o f slu g tes t results

, o r t o characteriz e th e hydrologi c setting

. Th e geophysica l dat a wer e use d i n selectio n

o f background bedroc k monitorin g wel l location s an d i n desig n o f th e wells

. (25 ) Commen t 132 : Respons e i s adequate ; however

, th e respons e i s no t integrate d int o th e RI Repor t an d shoul d b e integrate d int o Sectio n 3.2.3

, pag e 3-7

, las t paragraph

. Response : The discussio n ha s bee n adde d t o tex t i n Sectio n 3 a s follows : Th e availabl e informatio n i s insufficien t t o determin e whether th e regional wate r tabl e i n th e vicinit y o f Hamm' s Mil l impoundmen t an d min e wast e pile s hav e bee n affecte d b y drainag e t o th e Leadvill e Drainag e Tunnel

. However

, groundwate r flo w direction s i n th e alluvia l aquife r i n th e Hamm' s Mil l tailing s are a ma y b e affecte d b y aquife r drainag e towar d th e Leadvill e Drainage Tunnel

. Flo w ma y b e influence d locall y b y specifi c hydrogeologi c characteristics o f unconsolidate d deposit s bounde d b y bedroc k outcrop s o r th e existenc e o f a "highl y permeabl e network " suc h a s structural-preferentia l groundwate r flo w control s alon g fracture s o r faults

. Fou r monitorin g well s wer e installe d i n th e vicinit y o f th e tailings

. Wel l HM1TMW2

, locate d withi n th e tailings

, wa s dry

. Downgradien t wel l HM1TMW 3 wa s als o dr y a t th e alluvium/bedroc k contact

. Wate r level s i n th e remainin g tailing s monitorin g well s

an d othe r monitorin g well s h i th e are a suggeste d a northwesterl y groundwate r flo w i n th e alluvia l aquifer

. N o upgradien t wel l wa s installe d i n th e vicinit y o f th e Hamm' s Mil l tailings

. Monitorin g wel l HM1TMW 4 i s locate d generall y downgradien t o f th e tailings

. Monitorin g wel l HM1TMW5

, whic h wa s intende d t o b e a downgradien t well

, i s locate d o n th e wester n margi n o f th e are a an d ma y b e downgradien t o f th e tailings

. (26 ) Commen t (pag e 4-1) : Th e firs t paragraph

, fourt h sentenc e shoul d indicat e tha t detaile d description s "use d t o characteriz e background...i n tex t an d appendices..

. groundwate r qualit y ar e presented.... " Response : Th e reference d phras e ha s bee n adde d t o text

. (27 ) Commen t (pag e 4- 2 an d 4-6) : Th e secon d paragraph

, las t sentenc e reference s "(ASARC O 1993 a , b). " Thi s referenc e shoul d b e correcte d t o "(ASARC O 1994a

, b), " t o b e consisten t wit h Sectio n 8

, References

. Response : Th e referenc e ha s bee n corrected

.Octobe r

6

, 1995_____________________10_________________________243-281 9 (28 ) Commen t 75 : Commen t (pag e 4-5) : Respons e t o EP A commen t i s adequate ; however

, the informatio n o n statistica l method s reference d a s include d i n Appendi x F i s no t presente d i n Appendi x F

. Thi s discussio n need s t o be adde d t o Appendi x F

. (Refe r t o WC C R I Repor t page s 4- 6 t o 4-8. ) 

### Response : Th e reference d discussio n ha s bee n adde d t o Appendi x F

. Appendi x F.2 Discussio n o f Statistica l Method s Th e analysi s o f variance an d tes t o f proportion s method s compar e backgroun d wel l dat a t o detectio n wel l dat a directly

, whil e th e toleranc e limi t an d predictio n interval method s defin e interval s fro m backgroun d wel l dat a fo r compariso n wit h th e detectio n wel l data

. Th e toleranc e limi t metho d wa s propose d b y Asarc o t o defin e th e uppe r limit s o f th e expecte d rang e o f background groundwate r quality

. Th e toleranc e limit s establishe d fro m th e followin g statistica l analysi s wer e use d a s th e basi s agains t whic h detectio n wel l o r sprin g dat a wer e compare d t o evaluat e wate r qualit y impacts

. A toleranc e interval (o r limit ) i s define d a s a concentratio n rang e tha t i s constructe d t o contai n a specifie d proportio n (p% ) o f th e populatio n wit h a specifie d confidenc e coefficient

, a

. Th e proportio n o f th e populatio n included

, p % i s referre d t o a s th e coverage

. Th e probabilit y wit h whic h th e toleranc e interva l include s th e proportio n p % o f the populatio n i s referre d t o a s the toleranc e coefficient

. EP A guidanc e (EPA

, 1989d ) recommende d tha t a coverag e o f 9 5 percen t an d a toleranc e coefficien t o f 9 5 percen t b e used

. Thi s mean s tha t there i s a confidenc e leve l o f 9 5 percent tha t the uppe r toleranc e limi t (UTL ) wil l contai n at leas t 9 5 percen t o f th e distributio n o f observation s fro m backgroun d wel l data

. A n uppe r 

### toleranc e limi t wit h 9 5 percent coverag e give s a n uppe r boun d belo w whic h 9 5 percent o f th e rando m observation s o f th e distributio n shoul d fall

. Wit h th e exceptio n o f pH

, i f observation s fro m detectio n well s excee d th e uppe r toleranc e limit

, thi s indicate s tha t the detectio n wel l dat a ar e not fro m the sam e distributio n a s fro m th e background wel l data

, bu t rather fro m a distributio n wit h highe r concentration

. Theoreticall y thi s ca n b e interprete d a s statisticall y significan t evidenc e o f contamination

. Th e objectiv e o f usin g othe r statistica l procedure s wa s t o establis h toleranc e limit s whic h coul d no t b e obtaine d b y applyin g th e method s outline d i n th e EP A guidance

. On e o f thos e statistica l method s i s th e robus t probabilit y plottin g (RPP ) metho d whic h i s widel y use d i n engineerin g practices

. Th e RP P metho d ha s bee n wel l documente d and prove n t o b e ver y powerfu l i n statistica l analysis

, especiall y i n case s wher e multipl e detectio n limit s ar e reporte d (Helsel

, 1990 ; Helse l an d Cohn

, 1988 ; Hirsc h an d Stedinger

, 1987)

. Th e probabilit y plottin g metho d wa s use d t o 

### calculat e UTL s fo r thos e analytes note d i n th e "Prob

. plotting " colum n o f th e detaile d statistica l table s include d i n Appendi x F

.Octobe

r 6

, 1995______________________H__________________________243-281 9 Toleranc e limit s ar e constructe d usin g th e summar y statistic s o f a sampl e populatio n (mean

, standar d deviation

, etc.)

, assumin g tha t th e dat a fi t a certai n typ e o f distributio n (normal

, log-normal

, etc.)

. I t i s als o possibl e t o construct non

parametri c toleranc e limit s usin g onl y th e assumptio n tha t th e dat a ar e eithe r 

### normall y o r log-normall y distributed

. Therefore

, th e toleranc e limit s establishe d

ar e base d o n normall y o r log-normall y distribute d populations

. Th e thre e statistica l method s use d t o estimat e summar y statistic s o f dat a tha t includ e non-detect s (Nds ) i n thi s stud y include : simpl e substitutio n (1/ 2 detectio n limit)

, distributio n metho d (e.g.

, Cohen' s adjustmen t method ) an d robus t method (robus t probabilit y plotting)

. Th e purpos e o f al l thes e method s i s t o give bes t estimator s (unbiased ) o f summar y statistics

. Cohen' s metho d i s explaine d i n th e EP A statistica l guidanc e documen t (Sectio n 8.1.3 ) an d th e robus t probabilit y plottin g metho d i s summarize d o n the followin g pages

. I n general

, th e UT L i s applicabl e whe n th e percentag e o f Nd s i s les s tha n 5 0 percent o f th e tota l population

. Th e UTL s wer e reporte d afte r followin g th e procedure s depicte d i n Figur e 4.2-1

. Fo r case s wher e UTL s coul d no t b e established

, th e UTL s wer e reporte d as no t applicabl e (NA)

. Whe n Nd s ar e mor e tha n 5 0 percent o f the tota l population

, EP A recommende d the tes t o f proportion s fo r wel l comparison

. However

, th e tes t o f proportion s generall y require s suc h a larg e numbe r o f observation s fro m bot h background well s an d complianc e well s t o provid e a reasonabl e tes t tha t i t i s unpractica l i n thi s application

. Therefore

, th e RP P metho d wa s applied

, whe n appropriate

, t o som e case s i n thi s stud y whe n th e 

### percentag e o f Nd s wa s mor e tha n 5 0 percent

. I f the RP P metho d wa s not abl e t o extrapolat e Nd s t o estimat e summar y statistics

, th e UT L wa s reporte d a s NA

. (29 ) Commen t 76 : Commen t (pag e 4-7) : Respons e t o EP A commen t i s adequate ; however

, tex t reference s Appendi x F a s containin g table s an d note s o n cation-anio n balances

. Appendi x F include s tables

, bu t n o discussio n o n cation-anio n a s presente d i n th e WW C RI Repor t (Referenc e page s 4-1 0 t o 4-11)

. Thi s discussio n need s t o b e incorporate d fo r completeness

. Response : Th e referenc e ha s bee n adde d t o th e tex t an d th e discussio n ha s bee n adde d t o Appendi x F

. Appendi x F. 3 Discussio n o f Cation-Anio n Balance s Cation-anio n balance s wer e calculate d fo r eac h alluvia l backgroun d groundwate r analysis

. Detaile d table s o f cation-anio n balances reporte d fo r alluvia l an d bedroc k backgroun d groundwate r sample s ar e include d i n th e following pages

, alon g wit h note s o n cation-anion balances

. I n the calculatio n o f the cation-anio n balance

, the reporte d weight s (mg/L ) o f majo r ion s wer e converte d t o th e equivalen t charge represente d b y mg/ L o f tha t io n (i.e.

, milliequivalent s pe r liter

, o r meq/L)

. Th e cation-anio n balanc e measure s ho w wel l th e tota l meq/ L o f positivel y charge d ion sOctobe r

6

, 1995_____________________12_________________________243-281 9 (cations ) compare s wit h th e tota l meq/ L o f negativel y charge d ion s (anions)

, usin g t h e followin g formula : Cation-anio n

balanc e (percent )

= (meq/ L cation s - meq/ L anions)/(meq/ L cation s + mgq/ L anions ) X 10 0 

### Fo r purpose s o f thi s review

, a cation-anio n balanc e o f ± 1 0 percen t o r les s wa s judge d t o indicat e agreemen t suc h tha t th e analysi s coul d b e plotte d o n a water 

### qualit y diagra m (Pipe r diagram ) wit h sufficien t accuracy

. Analyse s show n greate r than ±1 0 percent imbalanc e wer e no t plotte d o n th e Pipe r diagram

. The alkalinit y valu e reporte d b y the laborator y an d entered int o the databas e 

### represent s th e su m o f separatel y determine d bicarbonat e plu s carbonat e alkalinit y values

, so th e values o f bicarbonate/carbonat

e use d t o chec k th e cation-anio n balanc e wer e estimate d based o n th e reporte d laborator y pH

. I n th e p H rang e o f

mos t samples

, th e alkalinit y reporte d i n th e databas e represent s bicarbonat e alkalinity

, a s a n equivalen t weigh t o f calciu m carbonate

. I n calculatin g cation-anion balances

, nondetect s wer e entere d int o th e balanc e usin g one-hal f the reporte d detectio n limit

. I n mos t cases , no n detecte d analyte s wer e reporte d a t level s o f 5 mg/ L o r less

, an d addin g i n one-hal f thi s value ha d minima l impac t o n the locatio n o f point s o n the Pipe r diagram

. The specia l cas e o f analyte s reporte d a t elevate d reportin g limit s (fo r th e AB W wells

, sulfat e wa s th e onl y analyt e affected ) i s discusse d below

. I f result s fo r an y majo r io n o r alkalinit y wer e rejecte d i n dat a validation

, th e cation-anion balanc e wa s no t calculate d an d th e analysi s wa s no t plotte d o n th e Pipe r diagram

. 

### Althoug h th e criteri a o f cation-anio n balanc e withi n +1 0 percent i s usefu l i n screenin g analyses

, whic h ca n b e plotte d wit h reasonabl e certaint y o n th e Pipe r diagram

, th e fac t tha t a n analysi s fail s th e ± 1 0 percent balanc e criteri a does no t indicat e unacceptabl e qualit y data

. Base d o n th e dat a validatio n guideline s specifie d b y th e EP A (EPA

, 1988b ) an d i n th e QAP P fo r thi s projec t (Res-Asarco

, 1991d)

, recoverie s for QC sample s are allowe d ± 20 percent (mus t be withi n 80 to 120 percen t o f true ) bias

. If

, fo r example

, cation s i n a wate r qualit y analysi s wer e biase d hig h (bu t withi n acceptabl e limits ) an d anion s biase d low

, the cation-anio n balanc e coul d excee d 1 0 percent

, whil e the individua l result s woul d stil l exhibi t acceptabl e accuracy

. A furthe r chec k wa s performe d o n analyses tha t showe d a cation-anion balanc e exceedin g th e ± 1 0 percen t cutof f limi t an d majo r ion s reporte d a s undetecte d a t elevate d values (i.e.

, greate r tha n tw o time s th e CRD L or reportin g limi t state d i n th e Wor k Plan)

. Result s o f thi s chec k fo r alluvia l background analyse s indicate d 

### that

, eve n thoug h th e exac t sulfat e valu e wa s unknown

, som e valu e withi n th e interval fro m 0 t o th e elevate d reportin g limi t woul d brin g th e analysi s int o aOctobe r

6

, 1995______________________13__________________________243-281 9 balanc e o f ± 1 0 percent o r better

. Althoug h th e decisio n wa s mad e no t t o plo t suc h analyse s o n the Pipe r diagra m because o f the considerabl e uncertaint y o f the locatio n o f th e sulfat e percentag e o n th e trilinea r Pipe r plot

, thes e analyse s ma y exhibi t acceptabl e analytica l accurac y fo r other ions

. A discussio n o f th e wate r type s represente d b y th e analyses

, a s the y plo t on a Pipe r diagram

, i s give n i n Table s 4.3- 1 an d 4.3-2

. (30 ) Commen t (pag e 4-11) : Th e discussio n i n th e las t paragrap h need s clarificatio n o f th e locatio n o f APITMW 9 "i n tailings " an d APITMW 7 "upgradient. " Thi s clarificatio n need s t o b e incorporate d throughou t thi s sectio n t o provid e clarificatio n o f whic h well s



### ar e representativ e o f upgradien t conditions

, downgradien t conditions

, an d tailing s material

, respectively

. Response : Th e tex t ha s bee n clarifie d wit h adde d discussio n a s follows : Th e assumptio n tha t groundwate r monitore d i n shallo w tailing s a t AP1TMW 9 i s h i a perche d zon e i s confirme d b y severa l facts

. Upgradien t wel l AP1TMW 7 ha s a wate r leve l elevatio n a t about 1008 3 MSL

, ten fee t lowe r tha n th e wate r leve l o f abou t elevatio n 1009 3 h i AP1TMW9

. Alluviu m wa s encountere d beneat h th e tailing s durin g drillin g o f wel l AP1TMW9

. Th e borehol e wa s backfille d t o th e to p o f th e alluviu m an d a bentonit e sea l wa s installe d t o isolat e th e perche d wate r fro m alluviu m encountere d belo w th e tailings

. Th e sea l wa s place d adjacen t t o a fine-graine d laye r o f mediu m t o hig h plasticit y tailing s identifie d durin g drillin g o f th e well

. Th e wel l wa s complete d wit h th e screene d interva l installe d abov e th e sea l (Tailing s Disposa l Area RI)

. Wel l NW 3 wa s complete d i n alluviu m beneat h the tailing s and ha s a wate r level elevatio n

o f abou t 1005 7 MS L respectively

. Thes e well s encountere d n o tailing s an d appea r t o b e screene d i n relativel y coarse-graine d alluviu m wit h n o significant

, fine-graine d layers t o th e tota l dept h o f drilling

. A n indirec t hydrauli c connectio n ma y exis t between th e perche d zon e an d deepe r aquifers

. However

, i t seem s unlikel y tha t groundwate r (i n th e perche d zone ) i s a moundin g phenomeno n o f unconfirme d groundwate r i n the dee p aquife r belo w the tailings

. 

### Wate r qualit y result s indicat e tha t upgradien t wel l AP1TMW 7 an d downgradien t well s AP1TMW 2 an d AP1TMW 3 appea r t o b e complete d i n th e alluvia l aquifer

. Wate r qualit y result s indicat e a significan t differenc e between AP1TMW 9 an d AP1TMW7

. Dissolve d iro n i n wel l AP1TMW 9 i s presen t a t level s o f a t leas t a n order o f magnitud e greate r tha n h i AP1TMW7

. Manganes e i s presen t i n wel l AP1TMW 9 a t tw o order s o f magnitud e greate r level s tha n i n wel l AP1TMW7

. Specifi c conductanc e an d sulfate s ar e

a n orde r o f magnitud e highe r i n wel l AP1TMW 9 tha n i n wel l AP1TMW7

.Octobe r

6

, 1995_____________________14_________________________243-281 9 Wate r qualit y difference s var y between wel l AP1TMW 9 an d downgradien t well s AP1TMW 1 an d AP1TMW2

. Thi s als o indicate s tha t the perche d zon e at wel l AP1TMW 9 i s no t continuou s t o th e downgradien t wells

. Th e scree n i n wel l AP1TMW 1

wa s installe d neare r th e wate r tabl e tha n wer e th e screen s i n well s AP1TMW 2 an d AP1TMW3

. However

, thi s seem s t o hav e littl e relevanc e sinc e al l thre e well s ar e screene d i n coarse-grained alluviu m wit h n o evidenc e o f significan t aquitards

. Th e are a alon g Californi a Gulc h at th e Apach e Tailing s Impoundmen t i s a losin g strea m reac h (influen t groundwater ) a s state d i n Sectio n 3

, no t a gainin g reac h (effluen t groundwater)

. Therefore

, surfac e wate r flow s ou t o f th e strea m int o th e groundwater

. Surfac e wate r

ma y impac t groundwater

, o r a t leas t allo w mixin g i n shallo w perche d groundwate r zon e wit h deepe r groundwater

, beyon d the downstrea m edg e o f the perche d zone

. Wate r qualit y dat a fro m AP1TMW 1 indicat e groundwate r i s significantl y differen t tha n adjacen t AP1TMW2

, the Star r Ditch

, o r surfac e wate r at CG-4

. The p H valu e i n AP1TMW 1 water i s significantl y lowe r tha n i n eithe r AP1TMW 2 o r AP1TMW3

. Th e lowe r p H may , i n part

, accoun t fo r higher metal s concentration s i n AP1TMW1

. 

### (31 ) Commen t 79 : Respons e t o EP A commen t i s adequate

. Th e discussio n presente d i n th e respons e pertainin g t o the perche d zon e associate d wit h the Apach e Tailing s shoul d b e full y incorporate d int o th e tex t page s 4-1 1 t o 4-13

. Response : The tex t ha s bee n expande d t o includ e discussio n o f perche d zone s i n the Orego n Gulch area , a s follows : 

### Th e wate r leve l i n wel l OG1TMW 8 i s a t abou t elevatio n 10,162

, whic h i s 6 2 fee t highe r than the wate r leve l elevatio n i n wel l OG1TMW1

. The wate r leve l i n wel l OG1TMW 3 i s abou t 2 5 fee t lowe r elevatio n tha n i n upgradien t wel l OG1TMW 1 but 8 7 fee t higher elevatio n tha n i n upgradien t wel l OG1TMW8

. Wel l OG1TMW 3 i s laterall y neare r wel l OG1TMW 8 tha n wel l OG1TMW1

. Thi s indicates tha t groundwate r nea r OG1TMW 8 i s eithe r mounde d o r represent s a perche d zon e abov e th e alluvia l aquifer

. Well s OG1TMW3

, OG1TMW4

, OG1TMW5

, OG1TMW6 A an d OG1TMW 8 appea r t o hav e simila r groundwate r quality

. However

, OG1TMW 3 appear s t o b e i n a perche d groundwate r zon e becaus e th e dat a d o no t clearl y indicat e tha t wel l OG1TMW 3 i s i n the alluvia l aquifer

. Th e Orego n Gulc h monitorin g wel l OG1TMW 5 i s locate d withi n th e tailing s impoundmen t an d well s OG1TMW 3 an d OG1TMW 8 ar e downgradien t fro m th e tailings

, and ar e complete d withi n the shallo w perche d groundwate r zone

. Wel l 

### OG1TMW 1 i s locate d downgradien t fro m th e Orego n Gulch tailings

. Wate r qualit y result s i n OG1TMW 1 indicat e tha t th e wel l i s complete d i n th e alluvia l aquife r wher e wate r qualit y i s simila r t o backgroun d alluvia l aquife r groundwater

. Thi s i s i n 

### contrast t o othe r Orego n Gulc h well s whic h ha d constituent concentration s on e t o fou r order s o f magnitud e higher

. Analytica l result s fo r th e Orego n Gulch Tailing sOctobe r

6

, 1995______________________15_________________________243-281 9 Impoundmen t monitorin g well s ar e presente d i n Tabl e 4.2-3

. The analytica l result s als o ar e presente d i n Figure s 4.2-1

, 4.2-2

, an d 4.2-3

. Th e tex t wa s expande d t o includ e discussio n o f perche d groundwate r zone s i n th e Apach e Tailing s a s follows : Apach e Tailing s Impoundment s Wate r qualit y result s indicat e a significan t differenc e betwee n wel l AP1TMW9

, complete d i n the tailings

, and upgradien t wel l AP1TMW7

. Dissolve d iro n i n wel l AP1TMW 9 wa s presen t a t level s o f a t leas t a n order o f magnitud e greate r tha n i n AP1TMW7

. Manganes e wa s present i n wel l AP1TMW 9 a t two order s o f magnitud e greate r level s tha n i n wel l AP1TMW7

. Specifi c conductanc e and sulfate s wer e a n orde r o f magnitud e highe r i n tailing s wel l AP1TMW 9 an d downgradien t well s AP1TMW 1 an d AP1TMW2

. This ma y indicat e tha t th e perched zon e withi n th e tailing s a t wel l AP1TMW 9 i s not continuou s t o the downgradien t wells

. The assumptio n tha t groundwate r monitore d i n shallo w wel l AP1TMW 9 i s i n a perche d zon e i s confirme d b y severa l facts

. Upgradien t wel l AP1TMW 7 ha s a wate r 

### leve l elevatio n a t abou t 1008 3 MSL

, te n fee t lowe r tha n th e wate r leve l o f abou t elevatio n 1009 3 h i AP1TMW9

. Alluviu m wa s encountere d beneat h th e tailing s durin g drillin g o f wel l AP1TMW9

. Th e borehol e wa s backfille d t o th e to p o f th e alluviu m an d a bentonit e sea l wa s installe d t o isolat e th e perche d water fro m alluviu m encountered belo w th e tailings

. The sea l wa s place d adjacen t t o a fine-graine d laye r

o f mediu m t o hig h plasticit y tailing s identifie d durin g drillin g o f th e well

. Th e wel l

wa s complete d wit h th e screene d interva l installe d abov e th e sea l (Tailing s Disposa l Are a El). Wel l NW 3 wa s complete d hi alluviu m beneat h the tailing s and ha s a wate r leve l elevatio n o f abou t 1005 7 MSL

. The wate r leve l elevatio n i n wel l NW S i s 3 6 fee t lowe r tha n the wate r leve l i n wel l AP1TMW9

. Downgradien t well s AP1TMW 1 an d AP1MW 2 hav e wate r level s a t elevatio n 1003 2

an d 1003 8 MSL

, respectively

. Thes e well s encountere d n o tailing s an d appea r t o b e screene d i n relativel y coarse-graine d alluviu m wit h n o significant

, fine-graine d layer s t o th e tota l dept h o f drilling

. 

### A n indirec t hydraulic connection ma y exis t between th e perche d zon e an d deepe r aquifers

. However

, i t seem s unlikel y tha t groundwate r (i n th e perched zone ) i s a moundin g phenomeno n o f unconfine d groundwate r i n th e alluvia l aquife r belo w th e tailings

. Wate r qualit y result s indicat e tha t upgradien t wel l AP1TMW 7 an d downgradien t well s A1TMW 2 an d AP1TMW 3 appea r t o b e complete d i n th e alluvia l aquifer

.Octobe r

6

, 1995_____________________16_________________________243-281 9 

### Wate r qualit y difference s var y betwee n wel l APITMW 9 an d downgradien t well s AP1TMW 1 an d AP1TMW2

. This als o indicate s tha t the perche d zon e at wel l AP1TMW 9 i s no t continuou s wit h th e downgradien t wells

. Wate r qualit y result s indicat e a significan t differenc e between AP1TMW 9 an d AP1TMW7

. Dissolve d iro n i n wel l AP1TMW 7 i s presen t a t level s o f a t leas t a n orde r o f magnitud e grate r tha n i n AP1TMW7

. Manganes e i s presen t i n wel l AP1TMW 9 a t two order s o f magnitud e greate r tha n i n wel l AP1TMW7

. Specifi c conductanc e and sulfate s ar e a n order o f magnitud e highe r i n wel l AP1TMW 9 tha n i f wel l AP1TMW7

. 

### Th e scree n i n wel l AP1TMW 1 wa s installe d neare r th e wate r tabl e tha n wer e screen s i n well s AP1TMW 2 an d AP1TMW3

. However

, thi s seem s t o hav e littl e relevanc e sinc e al l well s ar e screene d i n coarse-graine d alluviu m wit h n o evidenc e o f significan t aquitards

. The are a alon g Californi a Gulc h at the Apach e Tailing s impoundmen t i s a losin g strea m reac h (influen t groundwater ) a s state d i n Sectio n 3

, no t a gainin g reac h (effluen t groundwater)

. Therefore

, surfac e wate r flow s ou t o f th e strea m int o th e 

### groundwater

. Surfac e wate r ma y impact groundwater

, o r a t leas t allo w mixin g o f shallo w perche d groundwate r zon e wit h deepe r groundwater

, beyon d th e downstrea m edg e o f th e perche d zone

. (32 ) Commen t 81 : Respons e t o EP A commen t i s adequate ; however

, th e respons e wa s no t full y incorporate d int o th e R I a s i t shoul d b e t o clarif y th e discussio n o f th e Apach e Tailing s groundwater/surfac e

wate r interaction

. Response : Th e tex t ha s bee n expande d t o clarif y groundwater/surfac e

wate r interaction

. Se e respons e t o (30)

. 

### (33 ) Commen t 82 : Respons e t o EP A commen t i s adequate ; however

, th e respons e shoul d b e incorporate d int o th e tex t fo r clarificatio n an d suppor t fo r th e Orego n Gulc h tailing s "perche d aquifer " discussion

. 

### Response : Th e respons e ha s bee n adde d t o clarif y text

. Se e respons e t o (31 ) (34 ) Commen t 83 : Th e respons e indicate s tha t OG1TMW 3 i s no t i n th e perche d groundwate r zone , bu t th e RI tex t pag e 4-14

, las t paragrap h indicate s OG1TMW 3 i s i n the perche d zone

. Thi s discrepanc y need s t o b e resolved

. Response : Th e tex t ha s bee n clarifie d wit h th e additio n o f response

. Se e respons e t o (31)

. (35 ) Commen t (pag e 4-14) : Th e secon d paragrap h need s t o b e rewritte n t o specif y whic h well s are withi n th e tailing s impoundmen t and whic h are downgradien t o f th e impoundment

. A discussio n o n OG1TMW 2 need s t o b e incorporated

, a s appropriate

.Octobe r

6

, 1995______________________17_________________________243-281 9 Response : Th e secon d paragrap h ha s bee n rewritte n t o clarif y th e text

. Se e respons e t o (31)

. Wel l OGITMW 2 wa s no t include d i n th e discussio n becaus e OGITMW 2 wa s dry

. (36 ) Commen t 84 : Respons e t o EP A commen t i s complet e an d need s t o b e incorporate d int o th e RI tex t pag e 4-15

, secon d paragraph

, t o provid e interpretatio n an d clarificatio n on th e exten t o f th e perche d aquifer

. Response : Discussio n ha s bee n adde d t o th e tex t fo r clarification

. Se e respons e t o (31)

. (37 ) Commen t (pag e 4-16) : The las t paragraph

, thir d sentence shoul d b e correcte d t o rea d "CZ1TMW1 " no t "CA1TMW1. " 

### Response : Th e wel l designatio n ha s bee n corrected

. (38 ) Commen t (pag e 4-18) : I n th e las t paragraph

, a referenc e need s t o b e include d fo r th e Tailing s Are a R I Repor t (ASARCO

, 1994a)

. Response : Th e referenc e ha s bee n adde d t o th e text

. (39 ) Commen t (pag e 4-20) : A n introductor y paragrap h t o th e mini-piezomete r sectio n shoul d b e incorporate d t o identif y overal l are a o f installatio n an d purpos e fo r th e mini

piezometers

, a s wel l a s a referenc e t o Sectio n 3.2.6

, whic h identifie s gaining/losin g reache s o f Californi a Gulch

. Response : A n introductor y paragrap h ha s bee n adde d t o th e text

, a s follows : Thirty-fiv e mini-piezometer

s wer e installe d alon g Californi a Gulc h a t th e location s show n o n Figur e 2.1-1

. Groundwate r sample s wer e collecte d o n a seasonal basi s fro m th e mini-piezometer s fo r compariso n wit h surfac e wate r qualit y sample s collecte d concurrentl y fro m adjacen t surfac e wate r sampl e locations

. Chemica l analysi s result s fo r ke y indicato r parameter s ar e plotte d o n Figure s 4.2-4

, 4.2-5

, an d 4.2-6

. Sample s fro m mini-piezometer s wer e analyze d fo r bot h dissolve d

an d total metal s concentrations

. Th e parameter s chose n fo r compariso n wit h alluvia l background value s included: 1 ) dissolve d arsenic

, cadmium

, lead

, and zinc; 2 ) dissolve d aluminum

, iron

, an d manganese ; an d 3 ) othe r wate r qualit y parameters includin g fiel d specifi c conductance

, sulfate

, TDS

, an d fiel d pH

. Chemica l analysi s result s are presente d i n Table s 4.2-8 a throug h 4.2-8 c for 6 o f th e 

### 3 7 piezometers

. Al l o f th e mini-piezometer s sample d ar e locate d i n reache s o f Californi a Gulc h tha t fluctuat e betwee n gainin g an d losin g conditions

, wher e groundwate r periodicall y discharge s t o the stream

. Figur e 3.1- 2 show s the 

### gaining/losin g reache s o f Californi a Gulch

, an d a discussio n o f groundwater/surfac e wate r interaction s i s presente d i n Sectio n 3.2.6.1

. Compare d t o alluvia l backgroun dOctobe r

6

, 1995______________________U5_________________________243-281 9 UTL s an d rang e fo r pH

, result s fo r thes e mini-piezometer s showe d highe r concentration s o f commo n ions

, lowe r pHs

, an d highe r concentration s o f th e metals

. The value s varie d wit h locatio n alon g Californi a Gulch

. Base d o n th e indicato r chemica l parameter s plotte d o n Figure s 4.2-4

, 4.2-5

, an d 4.2-6

, th e highes t value s

wer e present a t mini-piezometer s P-31 A an d P-3 0 belo w th e Apach e Tailing s Impoundment s an d th e confluenc e o f Orego n Gulch wit h Californi a Gulch

. 

### Contemporaneou s surfac e wate r qualit y result s ar e presente d i n Sectio n 6. 0 o f th e Surfac e Wate r RI

. (40 ) Commen t (pag e 4-23) : Th e firs t paragrap h make s referenc e t o Table s 4.2-10 a throug h 4.2-10c ; thi s shoul d b e correcte d t o rea d Table s 4.2-9 a throug h 4.2-9c

. 

### T o ai d th e reader

, th e firs t paragrap h shoul d als o includ e specifi c referenc e t o spring s (SPR8

, SPR7 ) downstrea m o f th e Apach e Tailing s impoundmen t an d SPR 3 belo w th e confluenc e o f Orego n an d Californi a Gulches

. T h e firs t paragrap h shoul d als o indicat e whic h dissolve d metal s exhibite d highe r concentration s (e.g.

, manganese , lead

, iron

, cadmium

, aluminum

, and zinc ) a s compare d t o what

, alluvia l background ? Response : The tabl e referenc e ha s bee n corrected

. Referenc e t o SPR 7 an d SPR 8 hav e als o bee n adde d t o the text

. Discussio n ha s bee n adde d t o clarif y the referenc e t o metal s bein g presen t a t hig h concentrations

, compare d t o UTLs

, a s follows : A t sprin g SPR-9

, locate d upstrea m o f the three spring s discusse d above

, and a t spring s SPR-2

, SPR-1

, SPR-4

, an d SPR-5

, locate d downstream

, p H value s wer e highe r tha n typica l backgroun d alluvia l aquife r groundwater

, an d concentration s o f wate r qualit y parameter s wer e lowe r tha n a t SPR3

, SPR- 7 an d SPR-8

. SPR- 4 i s locate d downgradien t

o f th e L a Plat a Sla g Pile

. Concentration s o f wate r qualit y parameter s i n th e sample s fro m SPR- 4 ar e onl y slightl y highe r tha n alluvia l backgroun d UTLs

. Th e p H value s ar e somewha t lowe r tha n th e rang e fo r alluvia l backgroun d p H values

. Metal s concentration s i n th e SPR- 4 sample s wer e th e lowes t an d SPR- 7 th e highes t reporte d fo r th e spring s sample d i n lowe r Californi a Gulch

. Wate r qualit y result s indicat e tha t iro n an d zin c excee d backgroun d alluvia l aquife r level s

an d ar e presen t i n SPR- 7 an d SPR- 8 a t concentration s a n order o f magnitud e highe r tha n i n sample s fro m SPR-3

. However

, SPR- 3 ha s a n orde r o f magnitud e mor e lead an d abou t twice a s muc h nicke l a s sample s fro m eithe r SPR- 7 an d SPR-8

. Bot h lea d an d nicke l concentration s excee d backgroun d alluvia l aquife r levels

. (41 ) Commen t (pag e 4-23) : Th e secon d paragraph

, en d o f th e firs t sentence

, need s tex t adde d t o clarif y wha t "lower " i s i n referenc e to

. I s lowe r i n referenc e t o Spring s 8

, 7

an d 3

, sinc e water qualit y parameters ar e indicate d i n Tabl e 4.2-9 a a s highe r tha n alluvia l background

.Octobe r

6

, 1995______________________1_9_________________________243-281 9 Response : The tex t ha s bee n edite d t o clarif y th e ter m "lower " refer s t o "...lower the n SPR-3

, SPR- 7 and SPR-8. " (42 ) Commen t (pag e 4-23) : Th e discussio n o n wate r qualit y result s fro m alluvia l sprin g samplin g i n Lowe r Californi a Gulc h shoul d b e expande d t o includ e metal s analyses

, no t jus t wate r qualit y parameters

. Response : Th e tex t ha s bee n edite d t o includ e metal s concentration s a s follows : Chemica l analysi s result s fo r sample s fro m spring s i n lowe r Californi a Gulch ar e summarize d i n Figur e 4.2-4

, 4.2-5

, an d 4.2- 6 an d Table s 4.2-9 a throug h 4.2-9 b Th e chemica l analysi s result s ar e compare d t o alluvia l background UTL s (an d range s fo r pH)

. Result s fo r th e thre e spring s SPR 7 an d SPR 8 (locate d jus t downstrea m o f th e Apach e Tailing s Impoundments ) an d SPR 3 (a t th e confluenc e o f Orego n Gulc h wit h Californi a Gulch ) showed lowe r pH s an d highe r concentration s o f bot h wate r qualit y parameter s an d dissolve d metals

. Concentrations o f fiel d specifi c conductance

, sulfate

, an d TD S exceede d alluvia l background UTLs

, whil e p H values wer e belo w th e alluvia l backgroun d range

. Wate r qualit y result s indicat e tha t iro n an d zin c excee d backgroun d alluvia l aquife r level s an d ar e presen t i n SPR 7 an d SPR 8 a t concentration s a n orde r o f magnitud e highe r tha n i n sample s fro m SPR3

. However

, SPR 3 ha s a n order o f magnitud e mor e 

### lea d an d abou t twic e a s muc h nicke l a s sample s fro m eithe r SPR 7 o r SPR8

. Bot h lea d

an d nicke l concentration s excee d backgroun d alluvia l aquife r levels

. Spring s SPR-9

, SPR-2

, SPR-1

, and SPR- 5 ha d wate r qualit y and metal s concentration s intermediat e betwee n sprin g discharge s fro m SPR-8

, SPR-7

, an d SPR- 3 an d sprin g discharg e fro m SPR-4

. 

### (43 ) Commen t (pag e 4-23) : Th e fourt h paragraph

, fourt h sentence o n TD S value s o f sprin g discharg e betwee n th e Ya k Tunne l are a an d th e Lowe r Californi a Gulc h are a need s t o b e expande d t o presen t th e significanc e o f th e statement

. Wha t impac t doe s th e TD S valu e hav e on water quality ? 

### Response : Th e tex t has bee n edite d t o clarif y TD S value s discussio n as follows : Th e chemistr y o f sprin g and tunne l discharge s sample d i n th e are a aroun d th e Ya k Tunne l (Figure s 4.2-7

, 4.2-8

, and 4.2-9 ) suggeste d a wid e variet y o f water types

. Severa l spring s sho w p H value s belo w background level s an d detectabl e concentration s

o f heav y metals

. Bot h dissolve d and tota l metal s concentration s wer e analyze d fo r i n thes e sprin g samples

. However

, th e TD S value s i n th e sprin g discharge s i n thi s are a

wer e les s tha n th e TD S value s reporte d fo r sprin g discharge s h i lowe r Californi a Gulch

. Hig h TD S value s indicat e th e presenc e o f dissolve d constituent s a t level s abov e UTL s o n backgroun d wate r quality

. Th e water chemistr y o f th e sprin g an d tunne l discharge s di d no t appea r t o resembl e eithe r alluvia l o r bedroc k backgroun d chemistry

. Chemica l result s ar e liste d i n Table s 4.2-9 a throug h 4.2-9c

. Result s fo r sample s fro mOctobe r

6

, 1995_____________________20_________________________243-281 9 th e Canterbur y Tunne l (TP-3 ) ar e include d i n th e tabl e fo r purpose s o f comparisons bu t

ar e not discusse d i n the text

. Canterbur y Tunne l provide s par t o f the Leadvill e domesti c wate r supply

. (44 ) Commen t Sectio n 4 : Th e discussio n pertainin g t o mas s loadin g wa s no t foun d i n Sectio n 4 t o suppor t Tabl e 4.2-10 a throug h 4.2-12

. Thi s resulte d i n an inabilit y t o evaluat e completenes s o f th e R I report an d response s t o EP A comment s 93 throug h 97

. 

### Thi s discussio n need s t o b e reincorporate d int o the tex t (see WW C R I documen t page s 4-3 3 throug h 4-38)

. Refe r t o Commen t 19

. Response : The mas s loadin g discussio n i n Sectio n 4. 4 ha s bee n adde d t o text

. Se e respons e t o (19)

. (45 ) Commen t (pag e 5-1) : Th e secon d paragrap h refer s t o "ASARCO

, 1993c, " whic h

wa s no t foun d i n Sectio n 8

, References

. Thi s shoul d b e correcte d t o rea d "ASARCO

, 1993 " t o b e consisten t wit h Sectio n 8

, References

. Response : Th e referenc e ha s bee n correcte d t o Sectio n 8

. 

### (46 ) Commen t (pag e 5-2) : Th e las t paragrap h refer s t o "ASARCO

, 19943b, " thi s referenc e shoul d b e correcte d t o rea d "ASARCO

, 1994b. " Response : Th e referenc e ha s bee n corrected

. (47 ) Commen t (pag e 5-5) : Th e firs t paragrap h refer s t o th e Sectio n 5. 2 discussio n o n th e Universit y o f Cincinnat i demographi c survey

. However

, Sectio n 5. 2 n o longe r contain s th e discussio n o n groundwate r receptor s a s include d i n th e WW C R I Repor t page s 5-1 0 throug h 5-12

. Thi s "Identificatio n o f Potentia l Receptors " discussio n need s t o b e reincorporate d int o th e R I Report

. Response : Potentia l Receptor s ar e liste d i n table s include d i n Appendi x H

. (48 ) Commen t (pag e 5-10) : Referenc e i s mad e t o ASARCO

, 1994c

. Thi s document

, presume d t o b e "Surfac e Wate r Remedial Investigatio n Report, " i s no t i n Sectio n 8

, Reference s an d need s t o b e added

. Se e Comment s 1 8 an d 50

. Thi s sam e documen t als o appear s t o b e reference d wit h a dat e o f 1995

. Response : Referenc e t o Appendi x H ha s bee n adde d t o Sectio n 5 o f th e text

. (49 ) Commen t Sectio n 5 : Th e inclusio n o f a ma p depictin g gaining/losin g reache s alon g Californi a Gulch woul d assis t i n the interpretatio n o f potentia l receptor s an d a n understandin g o f th e locatio n o f thes e identifie d segment s alon g th e gulch

. Refe r t o Commen t 20

. Response : Figur e 3.2- 2 ha s bee n adde d t o sho w gaining/losin g stream reaches

.Octobe r

6

, 1995______________________21__________________________243-281 9 (50 ) Commen t (pag e 5-14) : Th e las t paragraph

, las t sentenc e refer s t o th e Surfac e Wate r R I Report

. The specifi c referenc e fo r the Surfac e Wate r R I Repor t need s t o b e included

. 

### Response : Th e referenc e ha s bee n added

. (51 ) Commen t 109 : Commen t - Sectio n 6.0 : Thi s sectio n shoul d b e delete d a s i t i s ou t o f scop e o f th e R I proces s an d inclusiv e wit h th e site-wid e ris k assessmen t fo r Californi a Gulch

, whic h shoul d b e reference d a s appropriate

. Response : Th e sectio n remain s i n th e report

, pe r th e require d scop e o f th e projec t define d i n the Wor k Plan

. (52 ) Commen t 111 : Respons e t o EP A commen t i s adequate

. Th e respons e shoul d b e include d a s a not e t o provid e clarificatio n i n th e R I that th e calculate d hydrauli c conductivitie s fal l withi n th e typica l rang e o f value s fo r tha t typ e o f aquife r lithology

. Response : Tex t adde d t o clarif y rang e o f typica l values fo r hydrauli c conductivity

. (53 ) Commen t 112 : Respons e t o EP A commen t i s adequate ; however

, inclusio n o f th e identifie d tex t wa s no t foun d Sectio n 7

, pag e 7-2

. Thi s tex t need s t o b e include d i n th e report

. Response : Th e reference d informatio n ha s bee n adde d t o th e text

. (54 ) Commen t 113 : Respons e i s complete

. T o satisf y th e responsivenes s i n th e text

, th e referenc e t o Sectio n 3.2. 1 fo r discussio n o f secondar y porosity/permeabilit

y shoul d b e adde d t o th e firs t "bullet " on pag e 7-3

. Response : Th e referenc e ha s bee n adde d t o Sectio n 7 o f th e text

. Discussio n o f secondar y porosit y an d permeabilit y als o ha s bee n include d i n Sectio n 3.1. 2 i s a s follows : A portio n o f the bedroc k hydrogeologi c uni t ha s secondar y porosit y and permeabilit y whic h provide s acces s fo r groundwater

. Fault s restric t groundwate r flo w although fractur e zone s alon g th e faul t boundaries

, crack s an d joint s i n faul t blocks

, an d min e working s provid e interconnecte d pathway s allowin g groundwate r flow

. Zone s o f lo w permeabilit y caus e confine d groundwate r condition s withi n th e bedroc k hydrogeologi c unit

. Th e saturate d portion s o f th e bedroc k hydrologi c uni t wit h sufficien t interconnecte d permeabilit y t o allo w groundwate r t o flo w i s referre d t o a s the bedroc k aquife r i n thi s R I report

. (55 ) Commen t (pag e 7-5) : Th e firs t bulle t present s discussio n o n alluvia l backgroun d wate r qualit y "type, " whic h wa s omitte d i n Sectio n 4

. Thi s discussio n need s t o b e 

### adde d t o Sectio n 4 t o suppor t th e conclusion s draw n i n Sectio n 7

.Octobe r

6

, 1995 ______________________22_________________________243-281 9 Response : Th e discussio n o f wate r qualit y has bee n include d i n Appendi x F

. Th e discussio n o n wate r typ e wa s no t include d i n Sectio n 4 because i t reflect s basi c informatio n o n wate r quality

, rather than informatio n collecte d durin g th e RI

. Se e respons e t o (29)

. (56 ) Commen t (pag e 7-5) : I n the tabl e comparin g alluvia l t o bedroc k background

, the bedroc k backgroun d UT L value s requir e th e followin g correction s t o b e consisten t wit h 

### Table4.3-3a : Magnesiu m

i s 2 6 no t 2 3 (j.g/ 1 Fiel d S C i s 56 1 not 55 1 |amhos/c m Fiel d p H i s 8. 5 no t 7. 7 Response : The value s i n the tabl e hav e bee n corrected

.

### Californi a Gulc h NP L Sit e 

### Surfac e Wate r Remedial Investigatio n Report Comment s an d Response s 

### Commen t Numbe r Comment/Respons e E P A COMMENT S WIT H ASARC O RESPONSES MA Y 199 5 SURFAC E WATE R R I REPOR T
(1 ) Commen t (Sectio n 3) : Th e respons e t o EP A Commen t 5 included: a narrativ e fo r th e technica l approach t o identif y ho w th e evaluatio n wa s performe d fo r bette r understandin g o f how dat a wer e used ; th e assumption s mad e i n characterizatio n o f contaminan t areas ; an d th e rational e fo r th e locatio n o f samplin g location s relativ e t o know n potentia l source s a t contaminatio n i n th e RI Stud y area

. Thi s respons e need s t o b e revised an d incorporate d i n th e introductor y paragrap h i n Sectio n 3 t o addres s EP A Commen t 5 (secon d paragraph)

. Response : Th e discussio n ha s bee n revise d an d include d i n th e introductor y text

, a s follows : A descriptio n o f samplin g station s and an overvie w o f the fiel d activitie s i s presente d i n thi s section

. Dat a wer e collecte d accordin g t o the Surfac e Water

, Be d Materia l an d Aquatic Ecosyste m Dat a Collectio n Progra m Workplan

. Soi l an d surfac e wate r sample s wer e collecte d fro m location s up

- an d down-gradien t fro m know n metal s source s an d a t location s throughou t th e stud y area

. Th e sample s

wer e analyze d fo r severa l physica l parameters

, fo r metal s know n t o exis t i n th e or e body

, an d fo r constituent s commonl y affecte d b y minin g activities

. Result s o f th e analyse s ar e show n i n Table s 5- 1 throug h 5- 8 an d 5- 9 throug h 5-12

, an d ar e discusse d i n th e followin g sections

. Analytica l result s wer e use d t o characteriz e surfac e wate r withi n th e Californi a Gulc h drainag e basin

, confir m expecte d metal s sourc e areas , an d identif y unanticipate d source s o f metal s concentrations

. Interactio n betwee n surfac e wate r

and groundwate r wa s evaluate d t o calculat e the drainag e basi n wate r balance

, assis t i n understandin g th e natur e an d exten t o f metal s distribution

, an d assess fat e an d transpor t o f metal s throug h th e environment

. Result s o f th e evaluation s als o wer e 

### use d t o calculat e possibl e huma n healt h risks

. (2 ) Commen t (Pag e 4- 1 t o 4-2) : Th e las t sentence o n 4- 1 (t o 4-2 ) i s inconsisten t wit h Figur e 4-1

, whic h indicate s poin t B upstrea m o f poin t A

, wherea s th e tex t discusse s poin t A upstrea m o f poin t B

. Thi s inconsistenc y need s t o b e resolve d an d correcte d a s 

### appropriate

.October

6

, 1995______________________2__________________________243-281 9 Response : Th e tex t ha s bee n edite d t o b e consisten t wit h Figur e 4-1

. (3 ) Commen t (Pag e 4-1) : I n th e formula

, "i " need s t o b e defined

. Response : Definitio n o f "i " ha s bee n adde d t o Figur e 4-1

. 

### ( 4 ) Commen t (Pag e 5-3) : Th e las t sentenc e o f th e firs t paragrap h states : "Dissolve d tota l meta l ratio s i n th e Arkansa s Rive r d o no t appea r t o sho w seasona l variation. " Th e basi s an d appropriat e referenc e fo r th e statement need s t o b e presente d (e.g.

, existin g studie s referenced

, o r result s o f thi s study. ) Response : Reference s hav e bee n adde d t o th e tex t fo r clarification

. (5 ) Commen t (Pag e 5-3) : Th e secon d paragrap h identifie d metal s o f concern , whic h does no t includ e manganese

. I n reviewin g Table s 5-1 3 throug h 5-16

, manganes e exceed s th e establishe d CRDLs ; therefore

, manganes e shoul d b e adde d t o th e lis t o f 

### contaminant s o f concer n an d incorporate d i n Sectio n 5

, a s appropriate

. Response : Arseni c ha s bee n adde d t o th e list

. Manganes e wa s no t adde d t o th e lis t

o f metal s o f concer n becaus e ther e ar e n o aquati c biot a standard s for manganese

. (6 ) Commen t (Pag e 5-3) : Th e thir d paragraph

, secon d sentenc e need s t o b e clarifie d b y addin g "Arkansa s River. " Response : "Arkansa s River " ha s bee n adde d t o th e text

. (7 ) Commen t (Pag e 5-3) : Th e secon d paragrap h need s clarificatio n tha t th e metal s o f

concer n ar e fo r surfac e wate r i n Californi a Gulch an d it s tributaries

. Discussio n shoul d b e adde d t o indicat e tha t i n th e Arkansas Rive r an d Arkansa s Rive r tributarie s aluminum

, iron

, lead

, manganese , and zin c exhibite d concentration s abov e th e CRDL

. Response : Th e tex t ha s bee n edite d t o includ e th e additiona l metals

, a s follows : Metal s o f concer n i n surfac e water fro m Californi a Gulc h an d it s tributarie s wer e determine d b y th e frequenc y o f occurrenc e (percentag e detections)

, th e relativ e leve l

o f concentrations

, an d th e toxicit y o f th e metals

. Base d on analysi s o f th e laborator y tes t results

, aluminum

, arsenic

, cadmium

, copper

, iron

, lead

, manganese , and zin c ar e 

### considere d th e primar y metal s o f concern

. Metal s concentration s exceedin g th e CRD L

ar e show n i n Tabl e 5-1 5 a s a percentag e o f tota l sample s teste d an d th e concentratio n value s ar e show n i n Tabl e 5-16

. Excep t fo r silver

, al l metal s wer e foun d at level s exceedin g th e CRD L i n th e Arkansas Rive r an d it s tributaries

. (8 ) Commen t (Pag e 5-9) : Th e las t paragrap h indicate s Figure s 6- 2 and 6- 3 a s depictin g th e 1 3 reache s divide d alon g th e Californi a Gulch

. Thi s referenc e appear s incorrec t a s 

### appropriat e figure s wer e no t identified

. Figure s nee d t o b e provide d and/o r appropriatel y referenced

.Octobe r

6

, 1995______________________3__________________________243-281 9 

### Response : Th e referenc e t o Figur e 6- 2 an d 6- 3 ha s bee n deleted

. Figur e 3.2- 2 wa s adde d t o sho w gaining/losin g reache s and replace s the tw o figures

. (9 ) Commen t (Pag e 5-10) : Th e firs t sentence o f th e secon d paragrap h indicate s "Tabl e 5

- 18 " a s representin g sedimen t transport

, th e actua l referenc e shoul d b e "Tabl e 5-19. " Thi s referenc e need s t o b e corrected

. Response : Th e referenc e ha s bee n corrected

. 

### (10 ) Commen t (Sectio n 5.3) : Thi s sectio n need s t o integrat e dat a an d observation s o f tota l meta l concentration s i n sediment

, a s i t relate s t o concentration s an d loadin g i n surfac e water

. Dat a ar e presente d i n Figure s 5- 3 throug h 5- 8 an d nee d t o b e interprete d an d integrate d int o thi s section

. Response : Tex t ha s bee n adde d t o Sectio n 5. 3 a s follows : Figure s 5- 9 throug h 5-14 ar e schemati c depiction s o f tota l meta l concentration s fo r aluminum

, cadmium

, copper

, iron

, lead an d zinc

. Table s 5- 1 throug h 5- 8 summariz e tota l meta l concentration s fo r differen t samplin g events

. Figur e 5- 2 present s discharge

, pH

, an d TS S fo r Californi a Gulch

. Figure s 5- 3 throug h 5- 8 presen t tota l meta l concentration s i n surfac e wate r an d sediment

, an d tota l meta l load s o f th e metal s o f concer n i n Californi a Gulch

. Concentration s o f tota l and dissolve d metal s i n surfac e wate r and sediment s generall y varie d throughou t the yea r at Station s CG-1

, CG-2

, CG- 3 an d CG-6

. However

, concentration s o f aluminum

, cadmium

, copper

, iron

, an d lea d i n surfac e wate r a t Statio n CG- 4 increase d b y an orde r o f magnitud e durin g th e ice-of f samplin g even t (Figure s 5- 3 throug h 5-8)

. The increase occurre d i n bot h tota l and dissolve d concentration s (excep t fo r dissolve d aluminum ) fo r thes e metal s i n water compare d t o average concentration s measure d a t th e sam e statio n durin g other time s

o f th e year

. Th e increase wa s no t apparen t i n th e sediment s a t Statio n CG- 4 durin g th e ice-of f samplin g event

. Tota l suspende d solid s i n surfac e water als o increase d b y a n order o f magnitud e a t CG- 4 durin g th e ice-of f samplin g event

, compare d t o averag e value s measure d durin g other time s o f the yea r (Figur e 5-2)

. A simila r increase i n tota l an d dissolve d concentration s i n th e surfac e wate r

occurre d for aluminum

, copper

, iron

, an d lea d a t CG- 5 durin g th e summe r samplin g event

. A pea k i n concentratio n o f cadmiu m wa s no t apparen t a t CG- 5 durin g th e summe r samplin g event

, althoug h th e concentratio n leve l increase d a t CG-5

, i t remaine d hig h downstrea m t o Statio n CG- 6 an d di d no t retur n t o th e low

averag e level s measure d i n CG-1

, CG-2

, an d CG-3

. Sample s measure d durin g th e summe r even t a t CG- 5 ha d concentration s fo r th e fou r metal s tha t wer e 1. 3 t o 5 time s greate r than value s measure d durin g th e ice-of f event

. Tota l suspende d solid s

a t CG- 5 als o wer e thre e tune s greate r durin g th e summe r samplin g even t tha n tota l suspende d solid s value s measure d durin g th e ice-of f samplin g even t (Figur e 5-2)

.Octobers

,

1995______________________4__________________________243-281 9 Othe r trend s i n concentratio n value s ar e no t apparen t i n th e dat a presente d i n Figure s 5- 3 throug h 5-8

. A mor e detaile d discussio n o f the metal s concentratio n variation s i s presente d i n the followin g sections

. Seasona l change s i n surfac e wate r metal s concentration s ma y resul t fro m re

introductio n o f metal s fro m temporaril y suspende d sediment s durin g period s o f hig h flow

. Th e ice-of f (April/May ) an d summe r (July ) flo w rate s reflec t pea k flo w period s i n Californi a Gulc h (Figur e 5-2)

. Anothe r facto r influencin g highe r concentration s ma y b e a sligh t decreas e i n pH a t Statio n CG- 4 durin g th e ice-of f samplin g even t an d increase d p H a t Statio n CG- 5 (Figur e 5-2)

. Th e p H als o 

### decrease d slightl y a t Statio n CG- 4 durin g the summe r samplin g even t (compare d t o the upstrea m CG- 3 station)

. However

, the p H at CG- 5 wa s slightl y lowe r tha n the pH a t Statio n CG- 4 durin g th e summe r samplin g event

. Figure s 5- 9 throug h 5-1 4 presen t schemati c diagrams o f metal s concentration s fo r sample s fro m Californi a Gulc h an d it s tributaries an d the Arkansa s Rive r an d it s tributaries

, includin g Tennesse e Creek

, Halfmoo n Creek

, Iow a Gulch

, an d Empir e Gulch

. Dat a presente d i n the schemati c diagram s indicat e tha t tributarie s t o Californi a Gulc h contai n metal s concentration s a t significantl y highe r level s tha n tributarie s t o th e Arkansas River

. However

, Stray Horse

, Oregon

, Georgia

, Pawnee

, Airport

, an d Malt a Gulc h (Californi a Gulc h tributaries ) periodicall y g o dry

, durin g whic h tim e the y contribut e nothin g t o th e metal s loa d i n Californi a Gulch

. Flo w fro m th e Californi a Gulc h tributarie s i s generall y minor

, compare d t o the surfac e strea m i n Californi a Gulch

, and severa l tributarie s t o the Arkansa s River

, othe r tha n Californi a Gulch

, go dr y durin g portion s o f the year

. A discussio n o f metal s load s i n Californi a Gulch and the Arkansas Rive r i s presente d i n th e followin g sections

. A sligh t increase i n discharg e occurre d betwee n Station s CG- 5 and CG- 6 durin g al l

seasonal samplin g events

. A simila r increas e i n p H occurre d betwee n Station s CG

5 an d CG-6

, excep t fo r th e ice-of f samplin g even t (Figur e 5-2)

. A correspondin g orde r o f magnitud e increas e i n aluminum

, cadmium

, copper

, an d zin c concentration s i n sediment s occurre d betwee n Station s CG- 5 an d CG- 6 durin g th e 

### ice-of f samplin g event

. Iro n an d lead sediment concentration s als o increased significantl y betwee n Station s CG- 5 an d CG- 6 durin g th e ice-of f samplin g event

. (11 ) Commen t (Pag e 5-10) : Figur e 5- 9 throug h 5-1 4 presen t dat a fo r mor e tha n jus t Californi a Gulch

. A summar y o f thi s dat a fo r tributarie s t o Californi a Gulc h an d th e 

### Arkansas Rive r need s t o b e reincorporate d int o th e R I Report

. Response : Discussio n ha s bee n adde d t o th e tex t fo r clarification

. Se e respons e t o (10)

.Octobe r

6

, 1995______________________5__________________________243-281 9 (12 ) Commen t (Pag e 5-11) : Figur e 5- 4 indicate s tha t cadmium als o ha s a pea k o f tota l meta l concentration s at CG- 4 durin g th e ic e off

. Thi s observatio n need s t o b e include d i n th e report

. Response : Th e cadmium referenc e ha s bee n adde d t o text

. (13 ) Commen t (Pag e 5-11) : The discussio n o n the sprin g samplin g even t shoul d b e correcte d t o indicat e tha t th e meta l load s an d concentratio n increas e a t CG- 3 relate s t o a correspondin g increas e i n discharg e (Se e Figur e 5-2)

. Th e discussio n need s t o b e correcte d t o reflec t th e sligh t increase i n p H a s show n i n Figur e 5-2

. Response : Tex t ha s bee n adde d t o indicat e th e increase d discharg e an d pH

, a s follows:

. A n increas e i n zinc

, coppe r an d cadmiu m load s an d concentration s wer e note d betwee n CG- 2 an d CG- 3 durin g th e Sprin g samplin g event

. Tota l suspende d solid s di d no t increas e bu t pH di d increase slightl y wit h th e increase i n metal s a t CG-3

. 

### Discharg e als o increased at CG-3

, whic h appear s t o b e a facto r accountin g fo r increase d metal s loads

. A possibl e sourc e fo r th e increas e betwee n thes e tw o location s i s th e Apach e Tailing s impoundment

. Anothe r possibl e sourc e fo r thes e 

### metal s i s groundwate r movin g i n th e vicinit y o f Star r Ditch

. Th e confluenc e o f bot h Star r Ditc h an d th e Ya k Tunne l surg e pon d discharg e wit h Californi a Gulc h

ar e i n clos e proximit y t o CG-3

. Althoug h Star r Ditc h discharge s int o Californi a Gulch belo w CG-3

, groundwate r i n th e vicinit y o f th e ditc h ma y intersec t Californi a 

### Gulch abov e CG-3

. Metal s loadin g durin g th e sprin g samplin g even t sho w a shar p increas e a t CG- 3 fo r zin c an d cadmium an d a subsequen t downstrea m decreas e an d levelin g off

. A decreas e i n metal s load s i s indicativ e o f a los s o f metals

, eithe r t o the sedimen t vi a precipitatio n o r adsorption

, o r a s a los s t o groundwater

. (14 ) Commen t (Sectio n 5.3) : Nothin g i s presente d pertainin g t o th e typica l increase i n discharg e and fiel d pH betwee n station s CG- 5 and CG- 6 a s reflecte d i n Figur e 5-2

. Ther e i s als o generall y a correspondin g sligh t increas e i n C d an d Z n concentration s i n sediment betwee n CG- 5 an d CG- 6 (refe r t o Figure s 5- 4 an d 5-8)

. Wha t i s th e significanc e o f th e sligh t increas e i n loadin g betwee n CG- 5 an d CG- 6 fo r Al

, Cu

, Fe

, Pb ? Thes e observation s an d explanatio n need s t o b e include d i n th e report

. Response : Tex t ha s bee n adde d t o clarif y thi s issue

. Se e respons e t o (10)

. 

### (15 ) Commen t (Pag e 5-13) : Locatio n AR-3 A i s identifie d a s a samplin g poin t fo r stor m events

, but Figure s 5-1 5 throug h 5-1 9 d o not sho w an y sampl e result s fo r thi s location

. Thi s discrepanc y need s t o b e corrected

. Response : Th e tex t ha s bee n edite d t o correc t th e reference

, a s follows :Octobe r

6

, 1995______________________6__________________________243-281 9 A s discusse d i n Sectio n 3

, surfac e wate r sample s wer e take n durin g thre e summe r stor m events

. Sample s wer e taken a t station s AR-2

, AR-3E

, an d CG- 6 only

. 

### Analysi s indicate s tha t runof f fro m Californi a Gulc h greatl y influence s metal s concentration s an d loadin g rate s i n th e Arkansas River

. Figure s 5-1 5 throug h 5-1 9 presen t Summe r Stor m loadin g hydrograph s fo r cadmium

, copper

, iron

, lea d an d zinc

. Aluminu m wa s not sample d durin g the Summe r Stor m events

. A sligh t increase i n cadmium an d zin c loa d i n Californi a Gulch durin g th e Augus t 3 0 storm i s see n i n Figure s 5-1 5 an d 5-19

. Thi s ma y resul t fro m a gradua l increase i n inflo w

o f relativel y lo w p H rai n water an d increasin g discharg e durin g the storm

, prio r t o the pea k discharg e at 20:09

. Sectio n 5.4. 2 present s analysi s o f the contributio n o f Californi a Gulch t o Arkansa s Rive r metal s loading

. Als o adde d t o th e tex t fo r clarificatio n i s th e followin g i n Sectio n 5.4 : Evaluatio n o f th e dat a presente d i n Figure s 5-1 5 throug h 5-1 9 indicate s tha t tota l load s

o f cadmium

, copper

, iron

, lead

, an d zin c are generall y highe r a t th e AR-3 E samplin g statio n tha n at Statio n CG- 6 durin g pea k summe r stor m events

. Thi s i s becaus e the AR-3 E loa d include s bot h th e loa d i n th e Arkansa s Rive r abov e th e confluenc e wit h Californi a Gulch (AR- 2 plu s th e loa d contribute d fro m Californi a (CG-6)

. (16 ) Commen t (Pag e 5-13) : I n evaluatin g Figure s 5-1 5 throug h 5-19

, ther e i s a tren d o f a highe r loa d a t AR-3 E than CG- 6 for cadmium

, iron

, and zinc

. Thi s shoul d b e adde d t o th e discussio n an d a n explanatio n o f thi s tren d provided

. Thi s tren d i s presen t fo r th e Augus t 2 4 an d Augus t 3 0 stor m events

. (Thi s commen t als o applie s t o pag e 5-1 7 discussio n on stor m loadings.) Figure s 5-15 an d 5-1 9 indicat e a n overal l increas e i n cadmiu m an d zin c loadin g throughou t th e Augus t 3 0 stor m event

. Thi s observatio n need s t o b e include d i n th e discussion

. The beginnin g statement fo r th e Septembe r 1 1 stor m even t i s incorrect

. Lea d pea k concentratio n doe s excee d range s reporte d fo r al l other recorde d samplin g events

. Th e tex t need s t o b e correcte d t o correspon d wit h dat a presente d i n Figur e 5-18

. Thi s storm even t discussio n als o does no t addres s th e correspondin g increas e i n iro n (see Pag e 5-14)

. Response : Th e tex t ha s bee n adde d an d edite d fo r clarification

. Se e respons e t o (15 ) (17 ) Commen t (Pag e 5-16) : Clarificatio n need s t o b e provide d fo r Tabl e 5-2 0 a s 

### representativ e o f tota l meta l concentration s i n water

, and Tabl e 5-2 1 a s calculate d load s i n surfac e water

. 

### Response : Th e tex t ha s bee n edite d t o indicat e tha t Tabl e 5-2 0 show s total metal s concentration s i n ug/ 1 an d tha t Tabl e 5-2 1 show s tota l metal s load s i n Ibs/day

.Octobe r

6

, 1995______________________7__________________________243-281 9 

### (18 ) Commen t (Pag e 5-16) : Th e secon d paragrap h list s manganes e a s a contributo r t o load s i n th e Arkansas River

. I s ther e a reaso n wh y i t wa s no t include d a s a meta l o f

concer n i n th e repor t an d include d i n th e specifi c even t discussion

, a s i t shoul d be ? 

### Als o refe r t o Commen t 4

. Response : Manganes e wa s no t include d i n th e metal s o f concer n discussion s because ther e ar e neithe r drinkin g water standard s (Californi a Gulc h i s no t a drinkin g wate r source ) no r ar e ther e an y standard s fo r aquati c biot a i n the Federa l Wate r Qualit y Criteria

. (19 ) Commen t (Sectio n 5-5) : Th e discussio n o n Acid Min e Drainag e (AMD ) i s wel l presented

. However

, th e relatio n t o AMD-characteristi c

p H t o p H foun d i n Californi a Gulch shoul d be expande d upo n usin g surfac e wate r dat a alon g Californi a Gulch

. Response : Discussio n ha s bee n adde d a s follow s t o clarif y AM D relativ e t o Californi a Gulc h wate r quality

. Th e p H value s measure d i n Californi a Gulc h a t Station s CG- 1 throug h CG- 6 varie d seasonally

, typicall y betwee n abou t 5 and 8

, wit h th e lowes t value s generall y occurrin g durin g the Sprin g (Figur e 5-2)

. A minimu m seasonal p H value o f 3. 5 occurre d durin g the Sprin g samplin g even t at Statio n CG-4

. The minimu m p H valu e measure d i n Californi a Gulc h surfac e water durin g th e R I wa s 2. 8 a t Statio n CG-6

. Thi s valu e wa s
measure d a t th e pea k o f a Summe r stor m even t o n Septembe r 11

, 1991

. Durin g th e 

### storm

, p H value s i n Californi a Gulch droppe d fro m 7. 1 t o 2. 8 ove r a perio d o f 2 7 minute s (Appendi x D)

. Th e rapi d dro p i n p H appear s t o hav e occurre d a s storm runof f flowe d int o th e Californi a Gulc h surfac e stream

. A s th e stor m pea k receded

, p H value s increased a t CG- 6 t o 3. 7 durin g les s tha n 11/ 2 hours

. (20 ) Commen t (Pag e 6-12) : Referenc e i s mad e t o a Tabl e 6-2

, bu t n o Tabl e 6- 2 wa s foun d i n th e report

. Th e tabl e need s t o appropriatel y identifie d and/o r created

. Response : Tabl e 6- 1 ha s bee n appropriatel y renumbere d t o 6- 2 an d a "new " Tabl e 6- 1 ha s bee n adde d t o th e report

.Octobe r

6

, 199 5 243-281 9

TABLE 6- 1 SUMMAR Y O F PREVIOU S WOR K
Autho r USG S 197 9 Hydrometrics

, Inc

. 198 7 Hydrometrics

, Inc

. 198 7 Runnells

, 198 8 Woodward-Clyd e SWR I 199 3 USG S 199 4 (Mille r an d McHugh ) Colorad o Geol

. Survey (Kirkha m e t al

, 1995 ) Approac h Analytica l

Analytica l an d Analo g Analo g Analo g Direc t Resul

t (Dzn ) 13mg/ L lOmg/ L

6 7 mg/ L

1 t o 7 0 mg/ L

0. 1 5 t o 1.3 5 mg/ L

> 1. 0 mg/ L

1 % Dz n i n Alamos a Rive r i s Minin g Relate d abou t Wightmo n For k Locatio n

Leadvill e Are a Carbonat e Or e Leadvill e Are a Carbonat e Or e Leadvil l Are a Sulfid e Or e Californi a Gulc h Californi a Gulc h Summitvill e Are a Summitvill e Are a

(21 ) Commen t (Sectio n 8) : O n evaluatio n o f Tabl e 5-16

, manganese , arsenic

, an d coppe r

ar e frequentl y detecte d i n sediment s i n th e stud y area

. Thes e metal s nee d t o b e incorporate d i n th e conclusions

. Sectio n 8 an d supporte d b y discussio n i n Sectio n 5 o f the report

. Response : Sectio n 8 tex t ha s bee n expande d t o includ e metals

. Metal s discussio n ha s als o bee n adde d t o th e conclusion s text

. Se e respons e t o (10)

. (22 ) Commen t (Appendi x G) : N o referenc e t o Appendi x G wa s foun d i n th e report

. Response : The referenc e ha s bee n adde d t o Sectio n 5

.