APP Hearings Geochemistry and APP Hearings Geochemistry and - - PowerPoint PPT Presentation

APP Hearings – Geochemistry and Seepage Related Issues APP Hearings – Geochemistry and Seepage Related Issues

By Amy L Hudson, REM By Amy L Hudson, REM

ROSEMONT-11 A. Hudson Power Point Presentation

WITNESS ISSUES AND TESTIMONY WITNESS ISSUES AND TESTIMONY

Pima County claims that the Flow-Through Drains are inconsistent with the “objective expressed in the BADCT document to keep Stormwater run-on

• ut of waste storage facilities.”

Run-on is defined as run-off that infiltrates the ground as it flows and the portion of runoff that infiltrates. By this definition, the Flow-Through Drains due meet the

• bjectives of BADCT, in that this prevents water from

enter the facility in an uncontrolled manor and potentially contacting reactive materials. The Flow-Through Drain would only use Non-PAG/inert rock in drain construction, so no impact from drain rock itself, and it would prevent upgradient runoff from flowing across/through waste rock and becoming run-on. The seepage from the tailings has been shown to be of good quality and meets AWQS, so it would not add an impact; plus the addition of storm water would provide dilution to any seepage water that reaches the drains.

WITNESS ISSUES AND TESTIMONY WITNESS ISSUES AND TESTIMONY

Pima County contends that the Flow-Through Drain System design will mix non-contact stormwater with contact stormwater and the resulting mixture will be passed into the underdrains. The seepage from the waster rock and tailings has been shown to be of good quality and meets AWQS, so it would not add an impact. The addition of storm water would provide dilution to any seepage water that reaches the drains, further lowering concentrations. Same issue as listed four rows above. The Flow- Through Drain is a stormwater management system that falls within the footprint of a permitted discharging facility. As the County states in their Issue No. 13 (C. Infiltration Modeling and Pollutant Mobilization), “most of the water entering the underdrain will infiltrate into the groundwater beneath the facility”. Which is a permitted discharging facility, with POCs downgradient. Valid argument. Could discuss pit capture zone, but facilities extend beyond modeled zone, so we are not predicting complete capture. Could discuss dewatering wells that would extend capture zone – no work done on this.

WITNESS ISSUES AND TESTIMONY WITNESS ISSUES AND TESTIMONY

From Technical Memorandum Titled, “Alternate Materials for Use in Flow- Through Drains, Revision 1” dated 03/08/2011

WITNESS ISSUES AND TESTIMONY WITNESS ISSUES AND TESTIMONY

From Technical Memorandum Titled, “Alternate Materials for Use in Flow-Through Drains, Revision 1” dated 03/08/2011

WITNESS ISSUES AND TESTIMONY WITNESS ISSUES AND TESTIMONY

Infiltration modeling for the DSTF and the Waste Rock Storage Area has demonstrated that seepage from those facilities resulting from meteoric precipitation is unlikely. The seepage from the waster rock and tailings has been shown to be of good quality and meets AWQS, so it would not add an impact. Modeling was completed using an average one year climate file, a ten year actual daily measurement climate file, and a 50 year actual daily climate file, and under all of these conditions, it was shown the graded surfaces of the facility would promote runoff from the facility, evaporation would dry the upper surface making future infiltration more difficult, and the addition of soil cover adds further protection during

• closure. Modeling of storm events also supports this

conclusion.

WITNESS ISSUES AND TESTIMONY WITNESS ISSUES AND TESTIMONY

Water Balance for Reclaimed Waste Rock Storage Area– Daily Climate Conditions (50 year period)