HYDRO29526

• Permit No: M1988112
• IBM Index Class Name: Hydrology
• Doc Date: 8/25/1999
• Doc Name: TECHNICAL SUPPORT DOCUMENT FOR THE CDPS PERMIT APPLICATION
• Media Type: D
• Archive: No

Technical Support
' Document for the
ARCADIS GERAGHTY&MILLER CDPS Permit
Application
A seepage survey was conducted under pre-mining conditions (Appendix C) and described the presence
of a seep in the general location of the existing seeps. The survey also identified iron staining at the
location that is consistent with the mineralogy of the alluvium.
' Additionally, iron-stained areas along the banks of the Rito Seco occur both at locations of the seeps
and at locations where no seepage is related to the West Pit (i.e. on the south bank of the river). Iron-
, staining is visible in exposures of the Rito Seco alluvium at locations that are clearly not associated with
mining (i.e., three feet deep in a dry exposure six feet high).
' Naturally-occurring sediments of the Rito Seco alluvium contain iron and manganese as demonstrated
bench scale testing described in Section 4.4.3.5 of TR-26. In addition, elevated concentrations of
manganese and iron are observed in groundwater samples collected from alluvial monitoring well M-30
' located on the east side (i.e. upgradien[) of the West Pit. Comparing water quality standards with the
water quality data available for in-stream locations, shows that the standards are exceeded in-stream
during low Flow periods for iron and manganese. However, as discussed previously, data presented in
' TR-26 also indicate that the Rito Seco in the segment between RS-2 and RS-5 was impacted historically
prior to discovery of the seeps (Section 1.3.1 of TR-26). The dischazge from the industrial wastewater
treatment facility will positively affect the instream water quality, because we anticipate the treatment
' to achieve effluent limits at the low flow value. With respect to the groundwater, and the seeps, it is
likely that the hydrology will change significantly as the pit is dewatered to reverse the gradient as
contemplated in TR-26. A comprehensive surface water and groundwater monitoring program
proposed in section 6.4.2 of TR-26 is designed to monitor the performance and effectiveness of the
' response to the occurrence of the seeps.
16) Bath House/Dry and Sanitary Waste. Not applicable, no waste streams.
' 17) Chemical treatment: BMRI conducted a pilot treatment test on the backfill water to determine the
efficiency of nanofiltration on the sulfate, manganese, and fluoride concentrations. The pilot study test
' results are included in TR-26, Appendix C. In July 1999, BMRI invited 12 vendors to provide a
contract bid proposal and services to provide treatment systems capable of treating 400 gpm of the
backfill water to standards in the range of the Rito Seco segment 28 standards with a delivery date of
approximately 6 to 8 weeks. Those bids were submitted to BMRI on August 13, 1999. Although the
long-term water management plan described in TR-26 identified nanofiltration as the likely treatment
option, the vendors were not limited to bidding on nanofiltration.
' The information provided for this permit application assumes that a membrane filtration process, such
as a nanofiltration unit, will be selected. In the Request for Proposal, BMR] requested MSDS sheets on
' any chemicals used in the treatment process. Those sheets will be submitted when made available to
BMRI. However, we do not expect that the vendors will propose any chemicals for use in the system
that would affect the parameters associated with the stream water quality.
' I8) Used or manufactured toxics: Not applicable.

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