DERR-2024-007718

NRD Trustee – Comment Response Summary – Response to Common Comment No. 5 5-1
SOUTHWEST JORDAN VALLEY GROUNDWATER CLEANUP PROJECT
STATE OF UTAH NATURAL RESOURCE DAMAGE TRUSTEE

COMMENT RESPONSE SUMMARY
AUGUST 31, 2004

Response to Common Comment No. 5 – Zone A Acid Plume Treatment

A number of comments expressed concerns over treatment of the acid contamination in Zone A.
Kennecott’s treatment plan for the acid plume is part of its CERCLA remedial response and was
approved by EPA and DEQ in a December 2000 Record of Decision and an April 2003
Explanation of Significant Differences (see Section 2.2 of the Joint Proposal). The Trustee has
reviewed the Joint Proposal to assure that it satisfies the requirements of the Consent Decree and
complements the CERCLA remedial response. The Trustee is not making any decision at this
time regarding the treatment method for the acid plume.

Under the terms of Section V.B of the Consent Decree, Kennecott is required to extract a
minimum of 400 acre-feet of acid plume water per year on a five-year rolling average. Kennecott
has been meeting this requirement for several years. As reflected in the Joint Proposal, Kennecott
intends to extract acid water at a rate of 2000 acre-feet per year, a rate five times the Consent
Decree requirement. This extraction will be monitored and reviewed by the Technical Review
Committee (TRC), including EPA and DEQ.

Although the Trustee’s action on the Joint Proposal does not include evaluation of the treatment
method for the acid water, the Trustee recognizes that the decision to neutralize the acidic
groundwater in the Tailings Pipeline is based on years of studies as documented in Appendices A
and C of the South Facilities Final Remedial Design. This decision was reached following review
by DEQ, EPA, and the TRC. Through full-scale testing, Kennecott has demonstrated that the
acid plume water can be neutralized in the Tailings Pipeline, relying on excess neutralization
potential in the tailings and/or lime amendments. The majority of metals are precipitated out of
the water and deposited in stable solid form in the Tailings Impoundment and the decant water is
clean enough to reuse in Kennecott’s milling process or discharge in the Great Salt Lake under
Kennecott’s discharge permits.

Several comments expressed concerns that heavy metals from the acid plume would be deposited
in the Tailings Impoundment. Again, the acidic portion of the Zone A Plume is being managed in
the tailings circuit in accordance with the CERCLA response, and is not being evaluated by the
Trustee as part of the Joint Proposal. However, the deposition of heavy metals precipitated from
the acid plume has been thoroughly addressed by Kennecott, EPA, DEQ, and the TRC, and no
environmental concerns have been identified.