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<br />Mr. Bruce Humphries <br />January 3, 2000 <br />Page 4 <br />The additional input of water to the TR-026 water management system will require an <br />adjustment of the steady-state pumping rate required to maintain the proper water level elevation <br />in the West Pit backfill. In TR-026, the steady-state pumping rate for the West Pit backfill was <br />estimated to be 110 gpm. Therefore, the steady-state pumping rate, adjusted as necessary to <br />account for the additional input of ~va[er to the West Pit backfill, would be approximately 180 <br />gPm. <br />3.0 MONITORING PLAN <br />The monitoring plan consists of: (1) identifying the point(s) of compliance, (2) establishing <br />permit condition values for the point(s) of compliance, and (3) specifying the method used to <br />assess the effectiveness of the Pla~i. These issues will be addressed in the followirtg subsections. <br />3.1 Point(s) of Compliance <br />BMRI proposes to retain monitoring well M-I lR as the point of compliance in the Rito Seco <br />alluvial aquifer for two reasons. First, the constituents currently out of compliance at M-1 1 R are <br />sulfate and total dissolved solids (TDS). Sulfate is expected to behave essentially conservatively <br />iu the groundwater system such that [he only changes in the concentration of sulfate would [hen <br />be due [o the effect of dispersion during dov`mgradient migration of affected groundwater. After <br />water-level control is established within the West Pit backfill, there will no longer be a source of <br />groundwater [o the Rito Seco alluvium with elevatc~l concentrations of sulfate. Therefore, the <br />portion of the Rito Seco alluvial aquifer containing elevated concentrations of sulfate is expected <br />to flush efficiently and sufficiently to achieve the existing permit condition value for sulfate that <br />was established for M-11 R in TR-015. <br />Total dissolved solids would also be expected to respond conservatively to flushing (i.e., <br />decrease in concentration) after water level control is established in the West Pi[ backfill because <br />the primary constituent causing TDS to exceed the permit condition value at M-11R has been <br />sulfate. Therefore, as sulfate decreases in concentration, TDS would also Ipe expected to <br />decrease in concentration. <br />