_REVISION - M1980244 ‎(31)‎

• Permit No: M1980244
• IBM Index Class Name: Revision
• Doc Name: Adequacy Response
• From: Cripple Creek & Victor Gold
• To: DMG
• Type & Sequence: AM8
• Media Type: D
• Archive: No

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19
discussion seeks to establish that a N1VP of zero is a reasonable cutoff between samples with and
wiihouF;ARD risk (not the aforementioned Q.B% total sulfur discussed eazlier). Then in the middle of
the last~paragraph of the section, it is slated:
~="Based on these average characteristics, along with the Car-tnn Mill telling material at
. ~ '=an NNP of +38 T CaCO~/kT, the AGOSA can be expected to generate circum-neutral
(' leachates.'•
The interpretation of s[adc and humidity cell data did no[ contend that overburden placed 1n AGOSA
would not become locally acidic, It was inferred only that any imerstitial solutions that may migrate out
of the AGOSA (whether acidic or not) would interact with the underlying Carbon Mill tailing material
that has an average NNP of+38 t/l,gl)Ot, The resulting leachaies, after contacting the acid-neutralizing
mill tailing, will have a circum-neutral pH. Statements in this section of the report recapitulate the
geochemical assessment of the AGOSA that was approver! as part of Amendment Na 7. Our
clarification of Figures q-2a and 4.2bfollows in our response to the next question.
(b) Please explain the possible discrepancies between Figures 4.2a and 4-2b or
submit corrected figures.
Response: It i§'important here to emphasize that SMI used humidity cell data only to identify a reasonable
criterion that would indicate what NNP level constitutes an ARD risk at CC&V. In order to develop a
representative estimate of facility-wide average NNP values. the more extensive LECO sulfur and
carbon data and static test data were used.
Figures 4.2a and 4.2b are correct as shown They were meant to illustrate that samples with NNf values
below~zero had a risk of becoming acidic after weathering, and that samples with NNP values above
zero generally would not bccamc acidic. The reason that fewer sample points are plotted In Pigure 4.2b
is because the data were not available for ANP and AGP values, although the NNP values were
available: Consequently, ttte A1vP/AGP ratio could not be calculated for these samples.
t;
4:. . =Page 25-26; Yol, Il, Figure 4.4: page 36-37.
Yj
The discussion about the relation between paste pH, NNP, depth, and sources of acidity is not
everywhere supported
(a) i Paste pH, which is dominantly a soil rest, can provide t>Eformatlon on hydrogen ion aetivtry that
"''itvould result immediately by saturation of a previously unsaturated media That a paste pH
.. . ': measurement of unoxidized or slightly oxidized rock is an appropriate utilityfor predictions of
r i ;Jong-term ARD potential is not unambiguous.
,.. ,
Response: We igree that it is inappropriate to predict ARD risk of utwxidized samples solely on the basis of
paste pal values. Much of the more strrf~cial portion of the deposit is strongly oxidized. Therefore, paste
pH determinations provide a meaningful indication of ARp risk for the more aurficial potion of the
deposittr We recognize that the paste pH tneasttred oa samples collected below the zone of oxidation
would tie expected to be stream-neutral even if the sample was potattially acid generating.
Consequently, the paste pH of deep samples would not provide a raeattingful indication of ARD risk
Our reliance on paste pH, however, was confined to the upper, oxidized diatreme. Again, we stress (as
has the`OMLR review) that of greater import is the fate of any additional acid and in the case of the
Ciesson deposit, any additional zinc, that may be generated. Thus, the focus must be on the capabilities
of the diaueme to neutralize the acid and remove the zinc that might be generated. This capacity is