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Appendix D, Comments jrom Rocky Mountain Consultants, Inc., Hydrokinetics, /nr., & Hydrodynamics,Inc. (Cont.) Page 10 The suggestion by the reviewers that BMR! install a reactive barrier/wall is an inadequate technical solution because of the nature of the chemical changes that x~ould have to occur in order to alter the concentrations of the key constituents (i. e., sulfate and manganese). A reduction in the concentration of sulfate (and TDS) can only occur tlrrouglr a c/emical transformation that includes: (/) precipitation of a solid phase (e.g., gypsum) or (2) a redaz trarujonnation coupled to the precipitation of a solid phase (e.g., elemental sulfur or a metal sulfide). /rr contrast, manganese removal would require an oxidizing environment idealty coupled with a state of elevated pH. 71rus, the ideal chemical score of a reactive barrier for treatment of sulfate is antithetical to the optimum conditions for trearrnent of manganese. SPEC/FIC COMMENTS Comment: 1. Section //.F, yaee 1 second paragraph. last sentence Discharge Point 002 is not shown on either Figures / or 2 of the pennit. As noted above, Discharge Point 002 actually consists of at least five separate and discrete disc/rarges: 002, the window, and 003 through 006, the jour separate seeps along the Rito Seca. Response: Revised language for 002 has been included in the pennit and rationale, and is identified in figure 2 of the permit. Also, see the response to the first comment under the heading GENERAL COMMENTS. Comment: 2. Section /l.G. oaee 2 77re duration of the "initial "and "(titer" rune periods for Discharge Point 001 must be defined. It is implied drat the discharge rates jrom Discharge Point 001 rill progressively decrease (i. e., 400 gprn to 250 gpm to 1 /0 gpm). This progression roust be specifieA. Ij there is cause to seven back to a higher pumping rate, it would indicate that the "water management plan " /ras failed, and the rationale for the pennit should be re-erarnined of that time. There are no rnarimum discharge rate lirnitatians listed for Discharge Point 002, the location of which is never given. Assuming that it is the seepage front, note that Item 3 on page 1 /10 in the August 30, 1999 document CDPS Permit Application: Minimal Discharge Industrial Wastewater submitted by BMR/, states that pumping of the system at a capacity of 400 gpm will reverse the gradient away from the Rito Seco, thereby eliminating the seepage front. However, jrom a location along the County Road, Castilla County Conservancy District (CCCD) ofj4cials observed flow from one of the seeps on the bank of the Rim Seco on April 30, 2000 (M. McGowan, CCCD, electronic commun.). /n subsequent sections, the permit states tlut! BMP's are to be used in association xdth Discharge Point 002, but again does not address the discharge rates jrom either the window or the springs. We believe that quantification of these flows is important. The applicant estimates West Pit outflows in Section 3.1.4.4 of TR-26. Through monitoring ojthe water levels in the alluvium, arsd the utilization oJthe penneabilities determined from aquifer testing, the applicant should be able to reasonably quantify groundwater flow through the restricted "window". If successful, the BMP's should terminate Jlaw through the xdndow during active pumping. Quantification of flows through the xdndow should assist !n assessing the degree ojsuccess achieved by the BMP's daring active remediation, and will assist in evalua[ing the system in the passive treatment period until contamination is no longer a problem. Response: At the time of subrniltal of the pennit application, initial and later time periods for the discharge flow rates were indicated; but at this point, these periods are no longer applicable. The tiered-discharge approach for Discharge Point 001 provides the fieribiliry necessary to reasonably represent the probable range of flows tha! are e_cpected to occur during t/re extraction of groundwater jrom the West Pit. For the purposes of the CDPS pennit, BMR/ will pump the backfilled West Pit as necessary, up to a maximum Jlaw rate oJ400 gprn (30 day average), to maintain a state of reversed /rydraulic gradient. See also the previous discussion on page 24 of the rationale.