M -l

30B915

GLOBE PLANT C •"• f ; r

i T In pv 1-1, o

n

 -^

- - -- - . I.. I i"i i/. . /; ij

October 6, 1995 c;

- . . *'-'•'•— • ••'• ? *

; 3

''«* *

Ms. Rebecca Thomas Remedial Project Manager

E PA Region VIII

999 18th Street, Suite 500 Denver, CO 80202-2405

R E: ASARCO'S RESPONSES TO COMMENTS : HYDROGEOLOGIC AND

SURFACE WATER , REMEDIAL INVESTIGATION REPORTS, CALIFORNIA GULCH SITE, LEADVILLE , COLORADO

Rebecca:

The enclosed document includes responses to comments received from the U.S . Environmental Protection Agency (EPA). The EPA letter, dated August 1, 1995 (EPA Ref: 8HWM-SR) ,

presented comments from a review of the Hydrogeologic Remedial Investigation (RI) report

and the Surface Water RI report for the California Gulch Site, both dated May 1995. Responses to the comments are presented in Attachment 1 (Hydrogeologic RI) and Attachment

2 (Surface Water RI).

The RI reports will be finalized with your approval of the responses or with your further

recommendations relative to editing the reports. We anticipate that additional comments may

be received from the State of Colorado. The State's comments also will be incorporated into

the final reports. We appreciate your help on this project and look forward to completing the

two RI reports.

If you have any questions, please contact me at 296-5104.

Sincerely,

Margaret (Poppy) Staub Environmental Project Manager

(4 copies sent)

cc: Russ Alien, CDPHE Gerald Almquist, Weston

ASARC O Incorporated . 495 East 51st Avenue . Denver. Colorad o 80216-2098 Phon e (303 ) 296-5900 FAX (303 ) 296-0508
California Gulch NPL Site Hydrogeologic Remedial Investigation Report Comments and Responses

Comment Number Comment/Response

E PA COMMENTS WITH ASARCO RESPONSES MAY 1995 HYDROGEOLOGIC RI REPORT

(1) Comment 7: Response to EPA comment is adequate; however, the information

identified for inclusion in the text of the RI Report was not found in the text. The

statement in the text should provide clarification on the groundwater discharge

fluctuations.

Response: The followin g was added to the text: "The range of values appear to

reflect seasonal and local variations in groundwater discharge rates."

(2) Comment 14: Site Map included as Figure 1.3-2 should identify the boundaries of the

study area.

Response: Boundaries of the study area, as identified in Asarco's Work Area Management Plan, have been identified on Figure 1.3-2.

(3) Comment 15: Response to EPA comment is adequate; however, the information

identified for inclusion in the text was not found in the text.

Response: The followin g text was added to Section 1.3.1.

The statement referenced in the RI refers to the Yak Tunnel as having been the primary

source of California Gulch surface water contamination. The statement is based on

results presented in the EPA Phase I Remedial Investigation Report; mass-loading

analysis determined that pre-treatment Yak Tunnel discharge contributed over 75

percent of the zinc, cadmium and sulfate in surface water. The Record of Decision for

the Yak Tunnel also acknowledges this point.

(4) Comment 16: Response to EPA comment is adequate. Minor changes should be made

to the text to clarify locations and meaning of a the followin g statements.

*• Page 1-16, 2nd Paragraph, Turk and Taylor. Water quality for which "tunnel,"

Yak or Leadville drain?
October 6, 1995______________________2__________________________243-2819

* Page 1-16, 3rd Paragraph, EPA 1983. No mention of lead in the water from Yak Tunnel discharge; true or an oversight?

* Previous text included a reference to "ASARCO. 1984. Hydrogeologic Evaluation

of the Yak Tunnel and California Gulch. Prepared by HRS Water Consultants. Unpublished Report." Thi s reference was not included in this version of the

document, and should be reinserted for consistency.

Response: Recommended changes have been included in the text. The "tunnel"

referred to in the firs t bullet is the Leadville Drainage tunnel. The text was edited to

describe "...minor concentrations of lead," in response to the second bullet. The

reference to Asarco, 1984 was added to the text in response to the third bullet.

(5) Comment 18: Response to EPA comment is adequate; however, response and text

indicate the inclusion of a Table 2.1-3a for "Spring and Tunnel Portal Flow Measurement Methods." Thi s Table 2.1-3a was not found in the RI Report.

Response: Table 2.1-3a was added to the text.

TABLE2.1-3a

SPRING AND TUNNEL DISCHARG E FLOW MEASUREMENT METHOD

Spring/Tunnel ID Recon. Date Flow Measurement Method SPR-1 9/24/91 F SPR-2 9/24/91 V SPR-3 1 SPR-4 9/25/91 F SPR-5 9/25/91 NF

SPR-6 9/25/91 NF

SPR-7 9/25/91 E SPR-8 9/25/91 V SPR-9 1 SPR-10 9/25/91 NF

SPR-11 9/25/91 NF

SPR-12 9/25/91 E SPR-13 9/26/91 E SPR-14 9/26/91 NF

SPR-15 9/26/91 NF

SPR-16 9/26/91 V SPR-17 9/26/91 V TP-1 9/26/91 F TP-2 9/26/91 V TP-31

 N/A M
October 6, 1995 243-2819

1. NF-No Flow

2. V. - Volumetric

3. F - 2 inch flume

4. E - R Visual Estimate

5. M - Flow Meter - X-section

(6) Comment (page. 2-4): The third line of the firs t paragraph makes reference to

"water quality sample analysis results are listed in Table 2.1-6." Table 2.1-6 does not

include results, but rather a list of analytical parameters. The text should be corrected

to read "water quality analytical parameters for which surface water was analyzed are

listed in Table 2.1-6."

Response: Text was changed to indicate "...analytical parameters for which surface

water was analyzed..." rather than "...sample analysis results..."

(7) Comment (page 2-8): The second sentence of the first paragraph makes reference to Figure 2.1-2 showing bedrock monitoring wells. Reference should include Figure 2.1-

3, which also includes "BMW" well locations.

Response: Text has been modified to include reference to Figure 2.1-3.

(8) Comment (Table 2.3-5): The table should indicate when measurements were collected

(e.g., prior to or after purging, at sample collection). For static water levels, the text

on page 2-17 indicates these were measured prior to purging and that the field

parameters were measured after purging at the time of water quality sampling. Text

and table need to be consistent.

Response: Note added to the table. The standard practice of measuring water levels

prior to well purging was used during the RI.

( 9) Comment (page 2-17): The last sentence of the third paragraph references Table 2.3-

7, which is incorrect (mini-piezometers). The correct reference should be Table 2.3-3

f or the Yak Tunnel Monitoring Well s (BBW).

Response: The reference has been corrected.

(10) Comment (Table 2.1-1):The location for SPR-17 is identified as "900 feet east..."

which is contradictory to the field reconnaissance form in Appendix G that indicates the

location as "about 400 feet east..." Thi s discrepancy needs to be resolved and the text

corrected as appropriate. Additionally , Table 2.1-1 identifies location TP-3; however,

no field reconnaissance form is included in Appendix G for this location. If the form is

available it should be included in Appendix G.

Response: The reference in Appendix G "400 feet east" has been corrected and a

note added to Table 2.1-1. TP-3 was not included in the initial field reconnaissance;

therefor, no form was prepared.
October 6, 1995_____________________4_________________________243-2819

(11) Comment Appendix A, page A-l: The last sentence of the second paragraph makes

reference to "Table 2.1-3a in the text" identifying site-specific flow measurements

methods. No Table 2.1-3a was identified in the text, nor do any tables in Section 2

identify the site-specific measurement method conducted at a location. Table 2.1-3a

should be included as indicated (see Comment 5).

Response: Table 2. l-3a has been added to the text.

(12) Comment 31: Response to EPA comment is adequate. Response indicates the

inclusion of two letters discussing deviation of methods employed to measure head

difference. These letters were not found in Appendix D and should be included as

indicated in the response.

Response: A Copy of one letter has been added to Appendix D but the second letter

has not been located.

(13) Comment Appendix A: Wel l Log Summaries BMW-1 and BMW-2 are missing. These logs need to be included in Appendix A.

Response: Wel l summaries for BMW-1 and BMW-2 have been added to Appendix A.

(14) Comment (page 2-20, Section 2.4.2): Discussion should reference Appendix C

for measurement method discussion.

Response: A reference to Appendix C has been added to the text.

Slug tests were performed at mini-piezometer locations P12, P24, P31A, each of which

varies between gaining and losing conditions. The predominant mini-piezometer slug

testing was done at gaining reaches of California Gulch to obtain data needed in

estimation of metals loading into surface water from groundwater. Ground water

flowin g into the surface water in gaining stream reaches and spring flow are

particularly important in water balance calculations discussed in Section 3.2.6.2.

(15) Comment (page 3-4): The last sentence makes an incorrect reference to 1993 ASARCO documents. The reference date needs to be corrected to refer to 1994 for

consistency with Section 8, References.

Response: The reference has been corrected.

(16) Comment (page 3-12): The fourth paragraph refers to "Periodic reworking of aquifer

materials." Clarification of aquifer materials needs to be made to indicate that

reworking is representative of alluvial aquifer materials.

Response: ".. .alluvial..." has been added to the text.
October6, 1995_____________________5_________________________243-2819

(17) Comment (page 3-4, 3-11, 3-17, 3-19): Reference to Figures 3.1-7a through 3.1-7d

is incorrect. The correct reference is Figures 3.1-5a through 3.1-5d.

Response: The reference has been corrected.

(18) Comment (page 3-17): The last sentence refers to the Surface Water RI Report

(ASARCO, 1995). Thi s reference needs to be included in Section 8. Refer to Comment 48.

Response: The reference has been added to Section 8.

(19) Comment (page 3-18): Reference is made to Section 4.2.3 for chemical loading

discussion; however, Section 4.2.3 does not include such a discussion. The discussion

needs to be reincorporated into Section 4. Refer to Comment 44.

Response: The chemical loading discussion has been added as Section 4.4 and the

reference in Section 3.2.6 has been clarified as follows:

Mini-piezometer locations were sampled at gaining stream reaches on a quarterly basis

beginning in June 1992 to assess groundwater quality conditions at these locations,

surface water quality also was sampled at monitoring location CG-3, CG-4, CG-5, and CG-6 on a monthly basis during the period July 1992 through October 1992. Sprin g

and runnel portal samples were collected in September 1992. Groundwater,

spring/tunnel portal, surface water quality results, and discharge and water balance data

were used to estimate potential chemical loading from groundwater to lower California Gulch. Results of the groundwater-surface water chemical quality comparisons are

discussed in Section 4.2.3 and in the Surface Water R.I. The results of the

comparative water level and field parameter monitoring, and the surface water

gain/los s calculations are discussed in the followin g sections.

4.4. Mass Loading

Groundwater in the California Gulch area contains metals as both dissolved and

total concentrations. The chemical load contained in groundwater is transported to

surface water when groundwater flow s into the surface water system. Seasonal

variations in the flux of groundwater moving into the surface water result in

corresponding variations in the rate of which metals are added to the surface water. The rate at which chemicals are added to the surface water from groundwater is

referred to as mass loading.

Mass loading rates can be estimated based on chemical concentrations (C) in the

groundwater times the rate of volumetric discharge (Q) of groundwater flowin g into

the surface water system. As Q changes due to seasonal variations, mass loading

rates change accordingly. Variations in groundwater chemical composition (Tables

4.2-8a through 4.2-8c, 4.2-9a through 4.2-9c) also affec t mass loading rates, but
October 6, 1995______________________6__________________________243-2819

the magnitude of chemical composition changes is relatively small compared to

changes in values of Q. Estimated seasonal mass loading rates from several

groundwater sources are listed in Tables 4.2-10a, 4.2-1 Ob, 4.2-11, and 4.2-12.

(20) Comment (page 3-18): The end of the second paragraph refers to Figure 4.2-8,

which is not relevant to this discussion. An appropriate figure needs to be created or

referenced to support the discussion on gaining stream reaches. The statement also

indicates that the figure will show the "relationship of the gaining stream reaches with

each of the factors listed." Can such a figure be created to support this statement? Refer to Comment 49.

Response: The figure reference has been corrected. Gaining/losin g stream reaches

have been added to Figure 3.2-2.

(21) Comment (page 3-22): Section 3.2.6.2 is incomplete. Text to support discussion of Table 3.1-5a through f, pertaining to alluvial aquifer discharge to gaining reaches of California Gulch, and Table 3.1-6 pertaining to spring discharge to California Gulch

appears to be missing.

Response: The text has been expanded as follow s to include response discussion.

3.2.6.2 Estimation of Groundwater Influen t Rates to California Gulch

Measurement points along the stream are critical in the calculations. Extrapolation of

the data represents a significant source of water balance calculation error.

Estimated water volumes entering gaining stream reaches from groundwater sources

are listed in Tables 3.1-5a through 3.1-5g (Comment refers to only 3.1-5a through

3.1-5f) . A more detailed water balance is presented in the Surface Water RI (Asarco,

1995). Data and calculations on water balance are presented in Tables 3.1-7a through

3.1-7d. Water balance calculations presented in Tables 3.1-7a through 3.1-7d are a

measure of water losses and gains along the California Gulch stream. Surface water

gains occur where groundwater discharging from alluvial and bedrock aquifers enter

the surface water system and surface water flow decreases where water enters the

groundwater system along losing stream reaches. Gains to surface water flo w also

occur where surface water flow s into California Gulch from tributary sources.

(21a) Comment Section 3: The section no longer includes a discussion on water balance to

support data and calculations presented in Tables 3.1-7a through 3.1-7d. This

discussion needs to be reincorporated on the RI Report.

Response: The water balance discussion has been added to the text. See response

to (21).
October 6, 1995______________________7__________________________243-2819

(22) Comment 49: Response to EPA comment is adequate; however, the third paragraph of

the response was not integrated into Section 3 and should be.

Response: The followin g discussion has been added to text in Section 3.

f\ fj The relatively low hydraulic conductivity value (about 3 x 10" to 3.1 x 10" feet per

day) calculated for the slug test data at mini-piezometer P-12 is similar to values

calculated for PZ-9 (about 6 x 10"2 to 7.2 x 10"2 feet per day). The values are also

similar to ABW-3, ABW-4, PZ-5, and PZ-10 that have calculated values of about 6.3 x

10"1 to 1 foot per day. The low values may be a result of fine-grained sediments at

each of these locations.

(23) Comment 59 through 64: Responses are adequate. Integration of responses into the RI report was not found within Section 3. It appears that some portions of Section 3

were omitted in the transition from the WWC RI Report to this RI Report, thereby

making it incomplete.

Response: The referenced discussions has been added to the text in Section 3 as

follows .

The followin g equation was used to estimate the conductance or discharge between

these two potential surfaces: QR

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

where: K is a representative hydraulic conductivity for the region between the two

equipotential surfaces; L is the length of the influent stream reach of concern; W is the top width of the stream surface (usually an adequate approximation for the

wetted perimeter);

e is the representative saturated thickness of the aquifer for the immediate area; A is a distance at which the equipotential surface is essentially vertical (assumed to be

the distance from the centerline of the stream to the mini-piezometer;

h is the groundwater surface elevation (potential) at distance A;

y is the elevation of the stream surface (potential);

Parameter e was estimated to be approximately 20 feet for the flux calculations. The

thickness applied to each piezometer for hydraulic conductivity calculations for

partially-penetrating solutions was based on estimated thickness at each minipiezometer location.

The distance from the mini-piezometers to the stream centerline is less than the

minimum 5 stream-width (5W) distance required for the application of the Morel- Seytoux and Zhang method for flux estimation. An alternate method of flux calculation

was applied to these data. When the flux estimates are recalculated, the resulting

seasonal trends in aquifer discharge to California Gulch will be re-evaluated to
October 6, 1995______________________8__________________________243-2819

determine whether groundwater discharge to the stream changes significantly over

time.

Morel-Seytoux and Zhang indicated that theoretical and experimental studies have

shown that A can be approximated by 5W, where W is the width of the stream surface. The equation can be re-written as:

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

Using this equation, the volumetric inflow rates to surface water were estimated for

each gaining stream reach from May through November 1992 and summed to provide

an estimation of total groundwater discharge into lower California Gulch (Tables 3.1-

7a through 3.l-7d).

Review of the head differential s for both influent and effluen t mini-piezometer locations

throughout the monitoring period indicates that head differential s between groundwater

and surface water generally increase from May to November for losing reaches, while

these differential s tend to remain more stable for gaining reaches. Thi s trend is

probably attributable to the followin g factors:

*• During the recharge period (ice-free through freeze-up), groundwater and

surface water levels are both higher, resulting in smaller head differential s along

gaining and losing reaches and therefore a lower potential exchange rate.

*• Followin g the recharge period when surface runoff (and recharge to

groundwater) has diminished substantially, surface water levels appear to

stabilize and are probably sustained by discharge from the Yak Tunnel and Leadville Sewage Treatment Plant, while groundwater levels continue to

decrease in response to decreased recharge. Thi s results in increasing head

differential s later in the year, especially along losing reaches of the gulch.

*• In combination with the factors above, differences in hydraulic conductivities in

the aquifer along lower California Gulch may produce variable head

differentials . For regions with low hydraulic conductivities, head differential s

could be expected to be greater than regions with high hydraulic conductivities.

(24) Comment 66: Response to EPA comment is adequate. No modifications to the RI Report were found as presented in the response. Seismic information should be

included in the RI Report or reference should be made to another report if the

information is documented elsewhere. The seismic data may be helpful in the

quantification of values for the piezometers by providing information on saturated

thickness.
October 6, 1995______________________9__________________________243-2819

Response: The discussion on geophysical surveys has been added to Section 3, as

follows:

Original seismic data records, seismic survey line location information and

downhole geophysical records are retained in the project files . Interpretations of

the seismic refraction data were used to identify the sediment/bedrock interface and

to map bedrock discontinuities. The data provided insufficient information to

distinguish lithologic characteristics, assist in interpretation of slug test results, or

to characterize the hydrologic setting. The geophysical data were used in selection

of background bedrock monitoring well locations and in design of the wells.

(25) Comment 132: Response is adequate; however, the response is not integrated into

the RI Report and should be integrated into Section 3.2.3, page 3-7, last paragraph.

Response: The discussion has been added to text in Section 3 as follows:

The available information is insufficient to determine whether the regional water table

in the vicinity of Hamm's Mill impoundment and mine waste piles have been affected

by drainage to the Leadville Drainage Tunnel. However, groundwater flow

directions in the alluvial aquifer in the Hamm's Mill tailings area may be affected by

aquifer drainage toward the Leadville Drainage Tunnel. Flow may be influenced

locally by specific hydrogeologic characteristics of unconsolidated deposits bounded

by bedrock outcrops or the existence of a "highly permeable network" such as

structural-preferential groundwater flow controls along fractures or faults. Four

monitoring wells were installed in the vicinity of the tailings. Well HM1TMW2 ,

located within the tailings, was dry. Downgradient well HM1TMW3 was also dry at

the alluvium/bedrock contact. Water levels in the remaining tailings monitoring wells

and other monitoring wells hi the area suggested a northwesterly groundwater flow in

the alluvial aquifer. No upgradient well was installed in the vicinity of the Hamm's Mill tailings. Monitoring well HM1TMW 4 is located generally downgradient of the

tailings. Monitoring well HM1TMW5, which was intended to be a downgradient

well, is located on the western margin of the area and may be downgradient of the

tailings.

(26) Comment (page 4-1): The first paragraph, fourth sentence should indicate that

detailed descriptions "used to characterize background...in text and appendices...

groundwater quality are presented...."

Response: The referenced phrase has been added to text.

(27) Comment (page 4-2 and 4-6): The second paragraph, last sentence references

"(ASARCO 1993 a, b)." Thi s reference should be corrected to "(ASARCO 1994a,

b)," to be consistent with Section 8, References.

Response: The reference has been corrected.
October 6, 1995_____________________10_________________________243-2819

(28) Comment 75: Comment (page 4-5): Response to EPA comment is adequate;

however, the information on statistical methods referenced as included in Appendix F

is not presented in Appendix F. Thi s discussion needs to be added to Appendix F.

(Refer to WCC RI Report pages 4-6 to 4-8.)

Response: The referenced discussion has been added to Appendix F. Appendix F.2 Discussion of Statistical Methods

The analysis of variance and test of proportions methods compare background well

data to detection well data directly, while the tolerance limit and prediction interval

methods define intervals from background well data for comparison with the

detection well data. The tolerance limit method was proposed by Asarco to define

the upper limits of the expected range of background groundwater quality. The

tolerance limits established from the followin g statistical analysis were used as the

basis against which detection well or spring data were compared to evaluate water

quality impacts.

A tolerance interval (or limit) is defined as a concentration range that is constructed

to contain a specified proportion (p%) of the population with a specified confidence

coefficient , a. The proportion of the population included, p% is referred to as the

coverage. The probability with which the tolerance interval includes the proportion

p% of the population is referred to as the tolerance coefficient .

EPA guidance (EPA, 1989d) recommended that a coverage of 95 percent and a

tolerance coefficient of 95 percent be used. Thi s means that there is a confidence

level of 95 percent that the upper tolerance limit (UTL) will contain at least 95

percent of the distribution of observations from background well data. An upper

tolerance limit with 95 percent coverage gives an upper bound below which 95

percent of the random observations of the distribution should fall . With the

exception of pH, if observations from detection wells exceed the upper tolerance

limit, this indicates that the detection well data are not from the same distribution as

from the background well data, but rather from a distribution with higher

concentration. Theoretically this can be interpreted as statistically significant

evidence of contamination.

The objective of using other statistical procedures was to establish tolerance limits

which could not be obtained by applyin g the methods outlined in the EPA guidance. One of those statistical methods is the robust probability plottin g (RPP) method

which is widely used in engineering practices. The RPP method has been well

documented and proven to be very powerful in statistical analysis, especially in

cases where multiple detection limits are reported (Helsel , 1990; Helsel and Cohn,

1988; Hirsch and Stedinger, 1987). The probability plottin g method was used to

calculate UTLs for those analytes noted in the "Prob. plotting" column of the

detailed statistical tables included in Appendix F.
October 6, 1995______________________H__________________________243-2819

Tolerance limits are constructed using the summary statistics of a sample population

(mean, standard deviation, etc.), assuming that the data fit a certain type of

distribution (normal, log-normal, etc.). It is also possible to construct nonparametric tolerance limits using only the assumption that the data are either

normally or log-normally distributed. Therefore, the tolerance limits established

are based on normally or log-normally distributed populations.

The three statistical methods used to estimate summary statistics of data that include

non-detects (Nds) in this study include: simple substitution (1/2 detection limit),

distribution method (e.g., Cohen's adjustment method) and robust method (robust

probability plotting). The purpose of all these methods is to give best estimators

(unbiased) of summary statistics. Cohen's method is explained in the EPA

statistical guidance document (Section 8.1.3) and the robust probability plottin g method is summarized on the followin g pages.

In general, the UTL is applicable when the percentage of Nds is less than 50

percent of the total population. The UTLs were reported after followin g the

procedures depicted in Figure 4.2-1. For cases where UTLs could not be

established, the UTLs were reported as not applicable (NA). When Nds are more

than 50 percent of the total population, EPA recommended the test of proportions

for well comparison. However, the test of proportions generally requires such a

large number of observations from both background wells and compliance wells to

provide a reasonable test that it is unpractical in this application. Therefore, the RPP method was applied, when appropriate, to some cases in this study when the

percentage of Nds was more than 50 percent. If the RPP method was not able to

extrapolate Nds to estimate summary statistics, the UTL was reported as NA.

(29) Comment 76: Comment (page 4-7): Response to EPA comment is adequate;

however, text references Appendix F as containing tables and notes on cation-anion

balances. Appendix F includes tables, but no discussion on cation-anion as presented

in the WWC RI Report (Reference pages 4-10 to 4-11). Thi s discussion needs to be

incorporated for completeness.

Response: The reference has been added to the text and the discussion has been

added to Appendix F. Appendix F.3 Discussion of Cation-Anion Balances

Cation-anion balances were calculated for each alluvial background groundwater

analysis. Detailed tables of cation-anion balances reported for alluvial and bedrock

background groundwater samples are included in the followin g pages, along with

notes on cation-anion balances. In the calculation of the cation-anion balance, the

reported weights (mg/L ) of major ions were converted to the equivalent charge

represented by mg/L of that ion (i.e., milliequivalents per liter, or meq/L). The

cation-anion balance measures how well the total meq/L of positively charged ions
October 6, 1995_____________________12_________________________243-2819

(cations) compares with the total meq/L of negatively charged ions (anions), using

t he followin g formula:

Cation-anion balance (percent) =

(meq/L cations - meq/L anions)/(meq/L cations + mgq/L anions) X 100

For purposes of this review, a cation-anion balance of ± 10 percent or less was

judged to indicate agreement such that the analysis could be plotted on a water

quality diagram (Piper diagram) with sufficient accuracy. Analyses shown greater

than ±10 percent imbalance were not plotted on the Piper diagram.

The alkalinity value reported by the laboratory and entered into the database

represents the sum of separately determined bicarbonate plus carbonate alkalinity

values, so the values of bicarbonate/carbonate used to check the cation-anion

balance were estimated based on the reported laboratory pH. In the pH range of

most samples, the alkalinity reported in the database represents bicarbonate

alkalinity, as an equivalent weight of calcium carbonate.

In calculating cation-anion balances, nondetects were entered into the balance using

one-half the reported detection limit. In most cases, non detected analytes were

reported at levels of 5 mg/L or less, and adding in one-half this value had minimal

impact on the location of points on the Piper diagram. The special case of analytes

reported at elevated reporting limits (for the ABW wells, sulfate was the only

analyte affected) is discussed below. If results for any major ion or alkalinity were

rejected in data validation, the cation-anion balance was not calculated and the

analysis was not plotted on the Piper diagram.

Although the criteria of cation-anion balance within +10 percent is useful in

screening analyses, which can be plotted with reasonable certainty on the Piper

diagram, the fact that an analysis fail s the ± 10 percent balance criteria does not

indicate unacceptable quality data. Based on the data validation guidelines specified

by the EPA (EPA, 1988b) and in the QAPP for this project (Res-Asarco, 1991d),

recoveries for QC samples are allowed ± 20 percent (must be within 80 to 120

percent of true) bias. If, for example, cations in a water quality analysis were

biased high (but within acceptable limits) and anions biased low, the cation-anion

balance could exceed 10 percent, while the individual results would still exhibit

acceptable accuracy.

A further check was performed on analyses that showed a cation-anion balance

exceeding the ± 10 percent cutoff limit and major ions reported as undetected at

elevated values (i.e., greater than two times the CRDL or reporting limit stated in

the Work Plan). Results of this check for alluvial background analyses indicated

that, even though the exact sulfate value was unknown, some value within the

interval from 0 to the elevated reporting limit would bring the analysis into a
October 6, 1995______________________13__________________________243-2819

balance of ± 10 percent or better. Although the decision was made not to plot such

analyses on the Piper diagram because of the considerable uncertainty of the

location of the sulfate percentage on the trilinear Piper plot , these analyses may

exhibit acceptable analytical accuracy for other ions.

A discussion of the water types represented by the analyses, as they plot on a Piper

diagram, is given in Tables 4.3-1 and 4.3-2.

(30) Comment (page 4-11): The discussion in the last paragraph needs clarification of the

location of APITMW9 "in tailings" and APITMW7 "upgradient." Thi s clarification

needs to be incorporated throughout this section to provide clarification of which wells

are representative of upgradient conditions, downgradient conditions, and tailings

material, respectively.

Response: The text has been clarified with added discussion as follows:

The assumption that groundwater monitored in shallow tailings at AP1TMW 9 is hi a

perched zone is confirmed by several facts. Upgradient well AP1TMW 7 has a water

level elevation at about 10083 MSL, ten feet lower than the water level of about elevation

10093 hi AP1TMW9. Alluvium was encountered beneath the tailings during drilling of

well AP1TMW9. The borehole was backfilled to the top of the alluvium and a bentonite

seal was installed to isolate the perched water from alluvium encountered below the

tailings. The seal was placed adjacent to a fine-grained layer of medium to high plasticity

tailings identified during drilling of the well. The well was completed with the screened

interval installed above the seal (Tailings Disposal Area RI).

Well NW3 was completed in alluvium beneath the tailings and has a water level elevation

of about 10057 MSL respectively. These wells encountered no tailings and appear to be

screened in relatively coarse-grained alluvium with no significant, fine-grained layers to

the total depth of drilling.

An indirect hydraulic connection may exist between the perched zone and deeper

aquifers. However, it seems unlikely that groundwater (in the perched zone) is a

mounding phenomenon of unconfirmed groundwater in the deep aquifer below the

tailings.

Water quality results indicate that upgradient well AP1TMW7 and downgradient wells AP1TMW 2 and AP1TMW 3 appear to be completed in the alluvial aquifer. Water

quality results indicate a significant difference between AP1TMW 9 and AP1TMW7. Dissolved iron in well AP1TMW 9 is present at levels of at least an order of magnitude

greater than hi AP1TMW7. Manganese is present in well AP1TMW 9 at two orders of magnitude greater levels than in well AP1TMW7. Specific conductance and sulfates are

an order of magnitude higher in well AP1TMW 9 than in well AP1TMW7.
October 6, 1995_____________________14_________________________243-2819

Water quality differences vary between well AP1TMW 9 and downgradient wells AP1TMW 1 and AP1TMW2. This also indicates that the perched zone at well AP1TMW 9 is not continuous to the downgradient wells. The screen in well AP1TMW 1

was installed nearer the water table than were the screens in wells AP1TMW 2 and AP1TMW3. However, this seems to have little relevance since all three wells are

screened in coarse-grained alluvium with no evidence of significant aquitards. The area

along California Gulch at the Apache Tailings Impoundment is a losing stream reach

(influent groundwater) as stated in Section 3, not a gaining reach (effluen t groundwater). Therefore, surface water flows out of the stream into the groundwater. Surface water

may impact groundwater, or at least allow mixing in shallow perched groundwater zone

with deeper groundwater, beyond the downstream edge of the perched zone.

Water quality data from AP1TMW 1 indicate groundwater is significantly differen t than

adjacent AP1TMW2, the Starr Ditch, or surface water at CG-4. The pH value in AP1TMW 1 water is significantly lower than in either AP1TMW 2 or AP1TMW3. The

lower pH may, in part, account for higher metals concentrations in AP1TMW1 .

(31) Comment 79: Response to EPA comment is adequate. The discussion presented in the

response pertaining to the perched zone associated with the Apache Tailings should be

full y incorporated into the text pages 4-11 to 4-13.

Response: The text has been expanded to include discussion of perched zones in the Oregon Gulch area, as follows:

The water level in well OG1TMW8 is at about elevation 10,162, which is 62 feet

higher than the water level elevation in well OG1TMW1. The water level in well OG1TMW3 is about 25 feet lower elevation than in upgradient well OG1TMW1 but

87 feet higher elevation than in upgradient well OG1TMW8. Well OG1TMW3 is

laterally nearer well OG1TMW8 than well OG1TMW1. This indicates that

groundwater near OG1TMW8 is either mounded or represents a perched zone above

the alluvial aquifer.

Well s OG1TMW3, OG1TMW4, OG1TMW5, OG1TMW6A an d OG1TMW8 appear

to have similar groundwater quality. However, OG1TMW3 appears to be in a

perched groundwater zone because the data do not clearly indicate that well OG1TMW3 is in the alluvial aquifer.

The Oregon Gulch monitoring well OG1TMW5 is located within the tailings

impoundment and wells OG1TMW 3 and OG1TMW8 are downgradient from the

tailings, and are completed within the shallow perched groundwater zone. Well OG1TMW1 is located downgradient from the Oregon Gulch tailings. Water quality

results in OG1TMW1 indicate that the well is completed in the alluvial aquifer where

water quality is similar to background alluvial aquifer groundwater. This is in

contrast to other Oregon Gulch wells which had constituent concentrations one to four

orders of magnitude higher. Analytical results for the Oregon Gulch Tailings
October 6, 1995______________________15_________________________243-2819

Impoundment monitoring wells are presented in Table 4.2-3. The analytical results

also are presented in Figures 4.2-1, 4.2-2, and 4.2-3.

The text was expanded to include discussion of perched groundwater zones in the Apache Tailings as follows:

Apache Tailings Impoundments

Water quality results indicate a significant difference between well AP1TMW9 ,

completed in the tailings, and upgradient well AP1TMW7. Dissolved iron in well AP1TMW 9 was present at levels of at least an order of magnitude greater than in AP1TMW7. Manganese was present in well AP1TMW 9 at two orders of magnitude

greater levels than in well AP1TMW7. Specific conductance and sulfates were an

order of magnitude higher in tailings well AP1TMW 9 and downgradient wells AP1TMW1 and AP1TMW2. This may indicate that the perched zone within the

tailings at well AP1TMW 9 is not continuous to the downgradient wells.

The assumption that groundwater monitored in shallow well AP1TMW 9 is in a

perched zone is confirmed by several facts. Upgradient well AP1TMW7 has a water

level elevation at about 10083 MSL , ten feet lower than the water level of about

elevation 10093 hi AP1TMW9. Alluvium was encountered beneath the tailings

during drilling of well AP1TMW9. The borehole was backfilled to the top of the

alluvium and a bentonite seal was installed to isolate the perched water from alluvium

encountered below the tailings. The seal was placed adjacent to a fine-grained layer

of medium to high plasticity tailings identified during drilling of the well. The well

was completed with the screened interval installed above the seal (Tailings Disposal Area El).

Well NW3 was completed hi alluvium beneath the tailings and has a water level

elevation of about 10057 MSL . The water level elevation in well NWS is 36 feet

lower than the water level in well AP1TMW9.

Downgradient wells AP1TMW 1 and AP1MW2 have water levels at elevation 10032

and 10038 MSL , respectively. These wells encountered no tailings and appear to be

screened in relatively coarse-grained alluvium with no significant, fine-grained layers

to the total depth of drilling. An indirect hydraulic connection may exist between the perched zone and deeper

aquifers. However, it seems unlikely that groundwater (in the perched zone) is a

mounding phenomenon of unconfined groundwater in the alluvial aquifer below the

tailings.

Water quality results indicate that upgradient well AP1TMW7 and downgradient

wells A1TMW 2 and AP1TMW3 appear to be completed in the alluvial aquifer.
October 6, 1995_____________________16_________________________243-2819

Water quality differences vary between well APITMW9 and downgradient wells AP1TMW1 and AP1TMW2. This also indicates that the perched zone at well AP1TMW 9 is not continuous with the downgradient wells. Water quality results

indicate a significant difference between AP1TMW 9 and AP1TMW7. Dissolved iron

in well AP1TMW 7 is present at levels of at least an order of magnitude grater than in AP1TMW7. Manganese is present in well AP1TMW 9 at two orders of magnitude

greater than in well AP1TMW7. Specific conductance and sulfates are an order of

magnitude higher in well AP1TMW 9 than if well AP1TMW7.

The screen in well AP1TMW1 was installed nearer the water table than were screens

in wells AP1TMW 2 and AP1TMW3. However, this seems to have little relevance

since all wells are screened in coarse-grained alluvium with no evidence of significant

aquitards. The area along California Gulch at the Apache Tailings impoundment is a

losing stream reach (influent groundwater) as stated in Section 3, not a gaining reach

(effluen t groundwater). Therefore, surface water flow s out of the stream into the

groundwater. Surface water may impact groundwater, or at least allow mixing of

shallow perched groundwater zone with deeper groundwater, beyond the downstream

edge of the perched zone.

(32) Comment 81: Response to EPA comment is adequate; however, the response was not

full y incorporated into the RI as it should be to clarify the discussion of the Apache Tailings groundwater/surface water interaction.

Response: The text has been expanded to clarify groundwater/surface water

interaction. See response to (30).

(33) Comment 82: Response to EPA comment is adequate; however, the response should be

incorporated into the text for clarification and support for the Oregon Gulch tailings

"perched aquifer" discussion.

Response: The response has been added to clarify text. See response to (31)

(34) Comment 83: The response indicates that OG1TMW 3 is not in the perched

groundwater zone, but the RI text page 4-14, last paragraph indicates OG1TMW 3 is in

the perched zone. This discrepancy needs to be resolved.

Response: The text has been clarified with the addition of response. See response

to (31).

(35) Comment (page 4-14): The second paragraph needs to be rewritten to specify which

wells are within the tailings impoundment and which are downgradient of the

impoundment. A discussion on OG1TMW 2 needs to be incorporated, as appropriate.
October 6, 1995______________________17_________________________243-2819

Response: The second paragraph has been rewritten to clarify the text. See

response to (31). Wel l OGITMW2 was not included in the discussion because OGITMW2 was dry.

(36) Comment 84: Response to EPA comment is complete and needs to be incorporated into

the RI text page 4-15, second paragraph, to provide interpretation and clarification on

the extent of the perched aquifer.

Response: Discussion has been added to the text for clarification. See response to

(31).

(37) Comment (page 4-16): The last paragraph, third sentence should be corrected to read

"CZ1TMW1" not "CA1TMW1."

Response: The well designation has been corrected.

(38) Comment (page 4-18): In the last paragraph, a reference needs to be included for the Tailings Area RI Report (ASARCO, 1994a).

Response: The reference has been added to the text.

(39) Comment (page 4-20): An introductory paragraph to the mini-piezometer section

should be incorporated to identify overall area of installation and purpose for the minipiezometers, as well as a reference to Section 3.2.6, which identifies gaining/losin g

reaches of California Gulch.

Response: An introductory paragraph has been added to the text, as follows:

Thirty-five mini-piezometers were installed along California Gulch at the locations

shown on Figure 2.1-1. Groundwater samples were collected on a seasonal basis

from the mini-piezometers for comparison with surface water quality samples

collected concurrently from adjacent surface water sample locations.

Chemical analysis results for key indicator parameters are plotted on Figures 4.2-4,

4.2-5, and 4.2-6. Samples from mini-piezometers were analyzed for both dissolved

and total metals concentrations. The parameters chosen for comparison with alluvial

background values included: 1) dissolved arsenic, cadmium, lead, and zinc; 2)

dissolved aluminum, iron, and manganese; and 3) other water quality parameters

including field specific conductance, sulfate, TDS, and field pH.

Chemical analysis results are presented in Tables 4.2-8a through 4.2-8c for 6 of the

37 piezometers. All of the mini-piezometers sampled are located in reaches of California Gulch that fluctuate between gaining and losing conditions, where

groundwater periodically discharges to the stream. Figure 3.1-2 shows the

gaining/losing reaches of California Gulch, and a discussion of groundwater/surface

water interactions is presented in Section 3.2.6.1. Compared to alluvial background
October 6, 1995______________________U5_________________________243-2819

UTLs and range for pH, results for these mini-piezometers showed higher

concentrations of common ions, lower pHs , and higher concentrations of the metals. The values varied with location along California Gulch. Based on the indicator

chemical parameters plotted on Figures 4.2-4, 4.2-5, and 4.2-6, the highest values

were present at mini-piezometers P-31A and P-30 below the Apache Tailings Impoundments and the confluence of Oregon Gulch with California Gulch. Contemporaneous surface water quality results are presented in Section 6.0 of the Surface Water RI.

(40) Comment (page 4-23): The first paragraph makes reference to Tables 4.2-10a

through 4.2-10c; this should be corrected to read Tables 4.2-9a through 4.2-9c.

To aid the reader, the first paragraph should also include specific reference to springs

(SPR8, SPR7) downstream of the Apache Tailings impoundment and SPR3 below the

confluence of Oregon and California Gulches. T he firs t paragraph should also indicate which dissolved metals exhibited higher

concentrations (e.g., manganese, lead, iron, cadmium, aluminum, and zinc) as

compared to what, alluvial background?

Response: The table reference has been corrected. Reference to SPR7 and SPR8

have also been added to the text. Discussion has been added to clarify the reference to

metals being present at high concentrations, compared to UTLs , as follows:

At spring SPR-9, located upstream of the three springs discussed above, and at springs SPR-2, SPR-1, SPR-4, and SPR-5, located downstream, pH values were higher than

typical background alluvial aquifer groundwater, and concentrations of water quality

parameters were lower than at SPR3, SPR-7 and SPR-8. SPR-4 is located downgradient

of the La Plata Slag Pile. Concentrations of water quality parameters in the samples from SPR-4 are only slightly higher than alluvial background UTLs . The pH values are

somewhat lower than the range for alluvial background pH values. Metals concentrations

in the SPR-4 samples were the lowest and SPR-7 the highest reported for the springs

sampled in lower California Gulch.

Water quality results indicate that iron and zinc exceed background alluvial aquifer levels

and are present in SPR-7 and SPR-8 at concentrations an order of magnitude higher than

in samples from SPR-3. However, SPR-3 has an order of magnitude more lead and

about twice as much nickel as samples from either SPR-7 and SPR-8. Both lead and

nickel concentrations exceed background alluvial aquifer levels.

(41) Comment (page 4-23): The second paragraph, end of the first sentence, needs text

added to clarify what "lower" is in reference to. Is lower in reference to Springs 8, 7

and 3, since water quality parameters are indicated in Table 4.2-9a as higher than

alluvial background.
October 6, 1995______________________1_9_________________________243-2819

Response: The text has been edited to clarify the term "lower" refers to "...lower

then SPR-3, SPR-7 and SPR-8."

(42) Comment (page 4-23): The discussion on water quality results from alluvial spring

sampling in Lower California Gulch should be expanded to include metals analyses, not

just water quality parameters.

Response: The text has been edited to include metals concentrations as follows:

Chemical analysis results for samples from springs in lower California Gulch are

summarized in Figure 4.2-4, 4.2-5, and 4.2-6 and Tables 4.2-9a through 4.2-9b The

chemical analysis results are compared to alluvial background UTL s (and ranges for

pH). Results for the three springs SPR7 and SPR8 (located just downstream of the Apache Tailings Impoundments) and SPR3 (at the confluence of Oregon Gulch with California Gulch) showed lower pHs and higher concentrations of both water quality

parameters and dissolved metals. Concentrations of field specific conductance, sulfate,

and TDS exceeded alluvial background UTLs , while pH values were below the alluvial

background range.

Water quality results indicate that iron and zinc exceed background alluvial aquifer

levels and are present in SPR7 and SPR8 at concentrations an order of magnitude

higher than in samples from SPR3. However, SPR3 has an order of magnitude more

lead and about twice as much nickel as samples from either SPR7 or SPR8. Both lead

and nickel concentrations exceed background alluvial aquifer levels. Springs SPR-9, SPR-2, SPR-1, and SPR-5 had water quality and metals concentrations intermediate

between spring discharges from SPR-8, SPR-7, and SPR-3 and spring discharge from SPR-4.

(43) Comment (page 4-23): The fourth paragraph, fourth sentence on TDS values of

spring discharge between the Yak Tunnel area and the Lower California Gulch area

needs to be expanded to present the significance of the statement. What impact does

the TDS value have on water quality?

Response: The text has been edited to clarify TDS values discussion as follows:

The chemistry of spring and tunnel discharges sampled in the area around the Yak Tunnel (Figures 4.2-7, 4.2-8, and 4.2-9) suggested a wide variety of water types. Several springs show pH values below background levels and detectable concentrations

of heavy metals. Both dissolved and total metals concentrations were analyzed for in

these spring samples. However, the TDS values in the spring discharges in this area

were less than the TDS values reported for spring discharges hi lower California Gulch. High TDS values indicate the presence of dissolved constituents at levels above UTLs on background water quality. The water chemistry of the spring and tunnel

discharges did not appear to resemble either alluvial or bedrock background chemistry.

Chemical results are listed in Tables 4.2-9a through 4.2-9c. Results for samples from
October 6, 1995_____________________20_________________________243-2819

the Canterbury Tunnel (TP-3) are included in the table for purposes of comparisons but

are not discussed in the text. Canterbury Tunnel provides part of the Leadville

domestic water supply .

(44) Comment Section 4: The discussion pertaining to mass loading was not found in Section 4 to support Table 4.2-10a through 4.2-12. This resulted in an inability to

evaluate completeness of the RI report and responses to EPA comments 93 through 97. Thi s discussion needs to be reincorporated into the text (see WWC RI document pages

4-33 through 4-38). Refer to Comment 19.

Response: The mass loading discussion in Section 4.4 has been added to text. See

response to (19).

(45) Comment (page 5-1): The second paragraph refers to "ASARCO, 1993c," which

was not found in Section 8, References. Thi s should be corrected to read "ASARCO,

1993" to be consistent with Section 8, References.

Response: The reference has been corrected to Section 8.

(46) Comment (page 5-2): The last paragraph refers to "ASARCO, 19943b," this

reference should be corrected to read "ASARCO, 1994b."

Response: The reference has been corrected.

(47) Comment (page 5-5): The first paragraph refers to the Section 5.2 discussion on the University of Cincinnati demographic survey. However, Section 5.2 no longer

contains the discussion on groundwater receptors as included in the WWC RI Report

pages 5-10 through 5-12. This "Identification of Potential Receptors" discussion needs

to be reincorporated into the RI Report.

Response: Potential Receptors are listed in tables included in Appendix H.

(48) Comment (page 5-10): Reference is made to ASARCO, 1994c. Thi s document,

presumed to be "Surface Water Remedial Investigation Report," is not in Section 8, References and needs to be added. See Comments 18 and 50. Thi s same document

also appears to be referenced with a date of 1995.

Response: Reference to Appendix H has been added to Section 5 of the text.

(49) Comment Section 5: The inclusion of a map depicting gaining/losing reaches along California Gulch would assist in the interpretation of potential receptors and an

understanding of the location of these identified segments along the gulch. Refer to Comment 20.

Response: Figure 3.2-2 has been added to show gaining/losin g stream reaches.
October 6, 1995______________________21__________________________243-2819

(50) Comment (page 5-14): The last paragraph, last sentence refers to the Surface Water RI Report. The specific reference for the Surface Water RI Report needs to be

included.

Response: The reference has been added.

(51) Comment 109: Comment - Section 6.0: Thi s section should be deleted as it is out of

scope of the RI process and inclusive with the site-wide risk assessment for California Gulch, which should be referenced as appropriate.

Response: The section remains in the report, per the required scope of the project

defined in the Work Plan.

(52) Comment 111: Response to EPA comment is adequate. The response should be

included as a note to provide clarification in the RI that the calculated hydraulic

conductivities fall within the typical range of values for that type of aquifer lithology.

Response: Text added to clarify range of typical values for hydraulic conductivity.

(53) Comment 112: Response to EPA comment is adequate; however, inclusion of the

identified text was not found Section 7, page 7-2. Thi s text needs to be included in the

report.

Response: The referenced information has been added to the text.

(54) Comment 113: Response is complete. To satisfy the responsiveness in the text, the

reference to Section 3.2.1 for discussion of secondary porosity/permeability should be

added to the first "bullet" on page 7-3.

Response: The reference has been added to Section 7 of the text. Discussion of

secondary porosity and permeability also has been included in Section 3.1.2 is as

follows:

A portion of the bedrock hydrogeologic unit has secondary porosity and permeability

which provides access for groundwater. Fault s restrict groundwater flow although

fracture zones along the fault boundaries, cracks and joint s in fault blocks, and mine

workings provide interconnected pathways allowing groundwater flow . Zones of low

permeability cause confined groundwater conditions within the bedrock hydrogeologic

unit. The saturated portions of the bedrock hydrologic unit with sufficien t

interconnected permeability to allow groundwater to flow is referred to as the bedrock

aquifer in this RI report.

(55) Comment (page 7-5): The first bullet presents discussion on alluvial background

water quality "type," which was omitted in Section 4. Thi s discussion needs to be

added to Section 4 to support the conclusions drawn in Section 7.
October 6, 1995______________________22_________________________243-2819

Response: The discussion of water quality has been included in Appendix F. The

discussion on water type was not included in Section 4 because it reflects basic

information on water quality, rather than information collected during the RI. See

response to (29).

(56) Comment (page 7-5): In the table comparing alluvial to bedrock background, the

bedrock background UTL values require the followin g corrections to be consistent with Table4.3-3a:

Magnesium is 26 not 23 (j.g/1 Field SC is 561 not 551 |amhos/cm Field pH is 8.5 not 7.7

Response: The values in the table have been corrected.
California Gulch NPL Site Surface Water Remedial Investigation Report Comments and Responses

Comment Number Comment/Response

E PA COMMENTS WITH ASARCO RESPONSES MAY 1995 SURFACE WATER RI REPORT

(1) Comment (Section 3): The response to EPA Comment 5 included: a narrative for the

technical approach to identify how the evaluation was performed for better

understanding of how data were used; the assumptions made in characterization of

contaminant areas; and the rationale for the location of sampling locations relative to

known potential sources at contamination in the RI Study area. Thi s response needs to

be revised and incorporated in the introductory paragraph in Section 3 to address EPA Comment 5 (second paragraph).

Response: The discussion has been revised and included in the introductory text, as

follows:

A description of sampling stations and an overview of the field activities is

presented in this section. Data were collected according to the Surface Water, Bed Material and Aquatic Ecosystem Data Collection Program Workplan. Soi l and

surface water samples were collected from locations up- and down-gradient from

known metals sources and at locations throughout the study area. The samples

were analyzed for several physical parameters, for metals known to exist in the ore

body, and for constituents commonly affected by mining activities. Results of the

analyses are shown in Tables 5-1 through 5-8 and 5-9 through 5-12, and are

discussed in the followin g sections.

Analytical results were used to characterize surface water within the California Gulch drainage basin, confirm expected metals source areas, and identify

unanticipated sources of metals concentrations. Interaction between surface water

and groundwater was evaluated to calculate the drainage basin water balance, assist

in understanding the nature and extent of metals distribution, and assess fate and

transport of metals through the environment. Results of the evaluations also were

used to calculate possible human health risks.

(2) Comment (Page 4-1 to 4-2): The last sentence on 4-1 (to 4-2) is inconsistent with Figure 4-1, which indicates point B upstream of point A, whereas the text discusses

point A upstream of point B. Thi s inconsistency needs to be resolved and corrected as

appropriate.
October 6, 1995______________________2__________________________243-2819

Response: The text has been edited to be consistent with Figure 4-1.

(3) Comment (Page 4-1): In the formula, "i" needs to be defined.

Response: Definition of "i" has been added to Figure 4-1.

( 4) Comment (Page 5-3): The last sentence of the first paragraph states: "Dissolved

total metal ratios in the Arkansas River do not appear to show seasonal variation." The

basis and appropriate reference for the statement needs to be presented (e.g., existing

studies referenced, or results of this study.)

Response: References have been added to the text for clarification.

(5) Comment (Page 5-3): The second paragraph identified metals of concern, which

does not include manganese. In reviewing Tables 5-13 through 5-16, manganese

exceeds the established CRDLs; therefore, manganese should be added to the list of

contaminants of concern and incorporated in Section 5, as appropriate.

Response: Arsenic has been added to the list. Manganese was not added to the list

of metals of concern because there are no aquatic biota standards for manganese.

(6) Comment (Page 5-3): The third paragraph, second sentence needs to be clarified by

adding "Arkansas River."

Response: "Arkansas River" has been added to the text.

(7) Comment (Page 5-3): The second paragraph needs clarification that the metals of

concern are for surface water in California Gulch and its tributaries. Discussion should

be added to indicate that in the Arkansas River and Arkansas River tributaries

aluminum, iron, lead, manganese, and zinc exhibited concentrations above the CRDL.

Response: The text has been edited to include the additional metals, as follows:

Metals of concern in surface water from California Gulch and its tributaries were

determined by the frequency of occurrence (percentage detections), the relative level

of concentrations, and the toxicity of the metals. Based on analysis of the laboratory

test results, aluminum, arsenic, cadmium, copper, iron, lead, manganese, and zinc are

considered the primary metals of concern. Metals concentrations exceeding the CRDL

are shown in Table 5-15 as a percentage of total samples tested and the concentration

values are shown in Table 5-16. Except for silver, all metals were found at levels

exceeding the CRDL in the Arkansas River and its tributaries.

(8) Comment (Page 5-9): The last paragraph indicates Figures 6-2 and 6-3 as depicting

the 13 reaches divided along the California Gulch. Thi s reference appears incorrect as

appropriate figures were not identified. Figures need to be provided and/or

appropriately referenced.
October 6, 1995______________________3__________________________243-2819

Response: The reference to Figure 6-2 and 6-3 has been deleted. Figure 3.2-2 was

added to show gaining/losing reaches and replaces the two figures.

(9) Comment (Page 5-10): The first sentence of the second paragraph indicates "Table 5-

18" as representing sediment transport, the actual reference should be "Table 5-19."

Thi s reference needs to be corrected.

Response: The reference has been corrected.

(10) Comment (Section 5.3): Thi s section needs to integrate data and observations of total

metal concentrations in sediment, as it relates to concentrations and loading in surface

water. Data are presented in Figures 5-3 through 5-8 and need to be interpreted and

integrated into this section.

Response: Text has been added to Section 5.3 as follows:

Figures 5-9 through 5-14 are schematic depictions of total metal concentrations for

aluminum, cadmium, copper, iron, lead and zinc. Tables 5-1 through 5-8

summarize total metal concentrations for differen t sampling events. Figure 5-2

presents discharge, pH, and TSS for California Gulch. Figures 5-3 through 5-8

present total metal concentrations in surface water and sediment, and total metal

loads of the metals of concern in California Gulch.

Concentrations of total and dissolved metals in surface water and sediments

generally varied throughout the year at Stations CG-1, CG-2, CG-3 and CG-6. However, concentrations of aluminum, cadmium, copper, iron, and lead in surface

water at Station CG-4 increased by an order of magnitude during the ice-off

sampling event (Figures 5-3 through 5-8). The increase occurred in both total and

dissolved concentrations (except for dissolved aluminum) for these metals in water

compared to average concentrations measured at the same station during other times

of the year. The increase was not apparent in the sediments at Station CG-4 during

the ice-off sampling event. Total suspended solids in surface water also increased

by an order of magnitude at CG-4 during the ice-off sampling event, compared to

average values measured during other times of the year (Figure 5-2).

A similar increase in total and dissolved concentrations in the surface water

occurred for aluminum, copper, iron, and lead at CG-5 during the summer

sampling event. A peak in concentration of cadmium was not apparent at CG-5

during the summer sampling event, although the concentration level increased at CG-5, it remained high downstream to Station CG-6 and did not return to the lowaverage levels measured in CG-1, CG-2, and CG-3. Samples measured during the

summer event at CG-5 had concentrations for the four metals that were 1.3 to 5

times greater than values measured during the ice-off event. Total suspended solids

at CG-5 also were three tunes greater during the summer sampling event than total

suspended solids values measured during the ice-off sampling event (Figure 5-2).
Octobers, 1995______________________4__________________________243-2819

Other trends in concentration values are not apparent in the data presented in Figures 5-3 through 5-8. A more detailed discussion of the metals concentration

variations is presented in the followin g sections.

Seasonal changes in surface water metals concentrations may result from reintroduction of metals from temporarily suspended sediments during periods of high

flow. The ice-off (April/May) and summer (July) flow rates reflect peak flow

periods in California Gulch (Figure 5-2). Another factor influencing higher

concentrations may be a slight decrease in pH at Station CG-4 during the ice-off

sampling event and increased pH at Station CG-5 (Figure 5-2). The pH also

decreased slightly at Station CG-4 during the summer sampling event (compared to

the upstream CG-3 station). However, the pH at CG-5 was slightly lower than the

pH at Station CG-4 during the summer sampling event.

Figures 5-9 through 5-14 present schematic diagrams of metals concentrations for

samples from California Gulch and its tributaries and the Arkansas River and its

tributaries, including Tennessee Creek, Halfmoo n Creek, Iowa Gulch, and Empire Gulch. Data presented in the schematic diagrams indicate that tributaries to California Gulch contain metals concentrations at significantly higher levels than

tributaries to the Arkansas River. However, Stray Horse, Oregon, Georgia, Pawnee, Airport, and Malta Gulch (California Gulch tributaries) periodically go

dry, during which time they contribute nothing to the metals load in California Gulch. Flow from the California Gulch tributaries is generally minor, compared to

the surface stream in California Gulch, and several tributaries to the Arkansas River, other than California Gulch, go dry during portions of the year. A

discussion of metals loads in California Gulch and the Arkansas River is presented

in the followin g sections.

A slight increase in discharge occurred between Stations CG-5 and CG-6 during all

seasonal sampling events. A similar increase in pH occurred between Stations CG5 and CG-6, except for the ice-off sampling event (Figure 5-2). A corresponding

order of magnitude increase in aluminum, cadmium, copper, and zinc

concentrations in sediments occurred between Stations CG-5 and CG-6 during the

ice-off sampling event. Iron and lead sediment concentrations also increased

significantly between Stations CG-5 and CG-6 during the ice-off sampling event.

(11) Comment (Page 5-10): Figure 5-9 through 5-14 present data for more than just California Gulch. A summary of this data for tributaries to California Gulch and the Arkansas River needs to be reincorporated into the RI Report.

Response: Discussion has been added to the text for clarification. See response to

(10).
October 6, 1995______________________5__________________________243-2819

(12) Comment (Page 5-11): Figure 5-4 indicates that cadmium also has a peak of total

metal concentrations at CG-4 during the ice off . Thi s observation needs to be included

in the report.

Response: The cadmium reference has been added to text.

(13) Comment (Page 5-11): The discussion on the spring sampling event should be

corrected to indicate that the metal loads and concentration increase at CG-3 relates to a

corresponding increase in discharge (See Figure 5-2). The discussion needs to be

corrected to reflect the slight increase in pH as shown in Figure 5-2.

Response: Text has been added to indicate the increased discharge and pH, as

follows:.

An increase in zinc, copper and cadmium loads and concentrations were noted

between CG-2 and CG-3 during the Sprin g sampling event. Total suspended solids

did not increase but pH did increase slightly with the increase in metals at CG-3. Discharge also increased at CG-3, which appears to be a factor accounting for

increased metals loads. A possible source for the increase between these two

locations is the Apache Tailings impoundment. Another possible source for these

metals is groundwater moving in the vicinity of Starr Ditch. The confluence of

both Starr Ditch and the Yak Tunnel surge pond discharge with California Gulch

are in close proximity to CG-3. Although Starr Ditch discharges into California Gulch below CG-3, groundwater in the vicinity of the ditch may intersect California Gulch above CG-3. Metals loading during the spring sampling event show a sharp increase at CG-3 for

zinc and cadmium and a subsequent downstream decrease and leveling off . A

decrease in metals loads is indicative of a loss of metals, either to the sediment via

precipitation or adsorption, or as a loss to groundwater.

(14) Comment (Section 5.3): Nothing is presented pertaining to the typical increase in

discharge and field pH between stations CG-5 and CG-6 as reflected in Figure 5-2. There is also generally a corresponding slight increase in Cd and Zn concentrations in

sediment between CG-5 and CG-6 (refer to Figures 5-4 and 5-8). What is the

significance of the slight increase in loading between CG-5 and CG-6 for Al, Cu, Fe, Pb? These observations and explanation needs to be included in the report.

Response: Text has been added to clarify this issue. See response to (10).

(15) Comment (Page 5-13): Location AR-3A is identified as a sampling point for storm

events, but Figures 5-15 through 5-19 do not show any sample results for this location. Thi s discrepancy needs to be corrected.

Response: The text has been edited to correct the reference, as follows:
October 6, 1995______________________6__________________________243-2819

As discussed in Section 3, surface water samples were taken during three summer

storm events. Samples were taken at stations AR-2, AR-3E, and CG-6 only. Analysis indicates that runoff from California Gulch greatly influences metals

concentrations and loading rates in the Arkansas River. Figures 5-15 through 5-19

present Summer Storm loading hydrographs for cadmium, copper, iron, lead and

zinc. Aluminum was not sampled during the Summer Storm events. A slight

increase in cadmium and zinc load in California Gulch during the August 30 storm

is seen in Figures 5-15 and 5-19. Thi s may result from a gradual increase in inflow

of relatively low pH rain water and increasing discharge during the storm, prior to

the peak discharge at 20:09. Section 5.4.2 presents analysis of the contribution of California Gulch to Arkansas River metals loading.

Also added to the text for clarification is the followin g in Section 5.4:

Evaluation of the data presented in Figures 5-15 through 5-19 indicates that total loads

of cadmium, copper, iron, lead, and zinc are generally higher at the AR-3E sampling

station than at Station CG-6 during peak summer storm events. Thi s is because the AR-3E load includes both the load in the Arkansas River above the confluence with California Gulch (AR-2 plus the load contributed from California (CG-6).

(16) Comment (Page 5-13): In evaluating Figures 5-15 through 5-19, there is a trend of a

higher load at AR-3E than CG-6 for cadmium, iron, and zinc. Thi s should be added to

the discussion and an explanation of this trend provided. Thi s trend is present for the August 24 and August 30 storm events. (This comment also applies to page 5-17

discussion on storm loadings.)

Figures 5-15 and 5-19 indicate an overall increase in cadmium and zinc loading

throughout the August 30 storm event. Thi s observation needs to be included in the

discussion.

The beginning statement for the September 11 storm event is incorrect. Lead peak

concentration does exceed ranges reported for all other recorded sampling events. The

text needs to be corrected to correspond with data presented in Figure 5-18. Thi s

storm event discussion also does not address the corresponding increase in iron (see Page 5-14).

Response: The text has been added and edited for clarification. See response to

(15)

(17) Comment (Page 5-16): Clarification needs to be provided for Table 5-20 as

representative of total metal concentrations in water, and Table 5-21 as calculated loads

in surface water.

Response: The text has been edited to indicate that Table 5-20 shows total metals

concentrations in ug/1 and that Table 5-21 shows total metals loads in Ibs/day .
October 6, 1995______________________7__________________________243-2819

(18) Comment (Page 5-16): The second paragraph lists manganese as a contributor to

loads in the Arkansas River. Is there a reason why it was not included as a metal of

concern in the report and included in the specific event discussion, as it should be? Also refer to Comment 4.

Response: Manganese was not included in the metals of concern discussions

because there are neither drinking water standards (California Gulch is not a drinking

water source) nor are there any standards for aquatic biota in the Federal Water Quality Criteria.

(19) Comment (Section 5-5): The discussion on Acid Mine Drainage (AMD) is well

presented. However, the relation to AMD-characteristic pH to pH found in California Gulch should be expanded upon using surface water data along California Gulch.

Response: Discussion has been added as follow s to clarify AMD relative to California Gulch water quality.

The pH values measured in California Gulch at Stations CG-1 through CG-6 varied

seasonally, typically between about 5 and 8, with the lowest values generally occurring

during the Sprin g (Figure 5-2). A minimum seasonal pH value of 3.5 occurred during

the Sprin g sampling event at Station CG-4. The minimum pH value measured in California Gulch surface water during the RI was 2.8 at Station CG-6. Thi s value was

measured at the peak of a Summer storm event on September 11, 1991. During the

storm, pH values in California Gulch dropped from 7.1 to 2.8 over a period of 27

minutes (Appendix D). The rapid drop in pH appears to have occurred as storm runoff

flowed into the California Gulch surface stream. As the storm peak receded, pH values

increased at CG-6 to 3.7 during less than 11/2 hours.

(20) Comment (Page 6-12): Reference is made to a Table 6-2, but no Table 6-2 was found

in the report. The table needs to appropriately identified and/or created.

Response: Table 6-1 has been appropriately renumbered to 6-2 and a "new" Table

6-1 has been added to the report.
October 6, 1995 243-2819

TABLE 6-1

SUMMAR Y OF PREVIOUS WORK

Author

USGS 1979

Hydrometrics, Inc. 1987

Hydrometrics, Inc. 1987

Runnells, 1988

Woodward-Clyde SWRI 1993

USGS 1994

(Miller and McHugh) Colorado Geol. Survey

(Kirkham et al, 1995)

Approach

Analytical

Analytical and Analog Analog

Analog

Direct

Result (Dzn)

13mg/L

lOmg/ L

67 mg/L

1 to 70 mg/L

0.1 5 to 1.35 mg/L

> 1.0 mg/L

1% Dzn in Alamosa River

is Mining Related about Wightmon Fork

Location

Leadville Area Carbonate Ore

Leadville Area Carbonate Ore Leadvil l Area Sulfid e Ore California Gulch

California Gulch

Summitville Area

Summitville Area

(21) Comment (Section 8): On evaluation of Table 5-16, manganese, arsenic, and copper

are frequently detected in sediments in the study area. These metals need to be

incorporated in the conclusions. Section 8 and supported by discussion in Section 5 of

the report.

Response: Section 8 text has been expanded to include metals. Metals discussion

has also been added to the conclusions text. See response to (10).

(22) Comment (Appendix G): No reference to Appendix G was found in the report.

Response: The reference has been added to Section 5.