HYDRO29057 - Laserfiche WebLink

Home Browse Search

Appendix D, Coutment Letters and Public Meeting: (Cont.): Page 8 C Comment Lener jrom Rocky Mountain Consulants, /nc., Hydrokinetics, /nc., and Hydrodynamics, Inc.: Responses ro comments provided by Rochi• Mormmin Consultants, Inc. and others me presented in the jolloxdng section. The comments and responses are indexed according to the jormnt ojthe original document. GENERAL COMAfENTS Comment: ]. Short-term West Pit Groundwater Dischar a l2 slues The permit correctly points out on page 7 that the statute, 25-8-501(/), CRS provides that: "No person shall discharge any pollutants into any state water from a point source xdthout first Itavittg obtained a permit jrom the division jot such discharge. " Note that "State inter" is defined in 25-8-103(9) to include "any and al[ surface and subsurface waters which are contained in or fiox~ in or through this state.... " Clearh~ discharge to subsurface waters, or groundwater, is regulated through the statue. The Technical Suppon Document jot the CDPS Permit Application, dated 30 Aug. /999, indicates on page 3.• "GroundwaterJloxdng through the West Pit exits the pit through a restricted zone where the backJill rnatenal contacts [he Rito Seco Alluvium (the "window"). Groundwater from the west pit Uten co-mingles with Rim Seco alluvial groundwater oral a portion of the mued groundwater emanates as surface seeps adjacent to the Rito Seco in the immediate vicinity of the xdndow. " This confirms tlrar only a potion of [he groundwater flowing from t/re west pit emanates as surface seepage, the remainder continuing to migrate through the Rifo Seco alluvia( aquifer systems withou[ definition of quantity, quality, or fate. The permit rationale indicates in the second full paragraph on page 12 that: "The heterogeneity of the alluvium and the variability of t/te groundwater flow in the alluvium and the Rito Seco are such that there are no discrete locations at which a numeric effluent [imitation can be measured. /n addition, the system is characterized by a diffuse aad dispersed seepage front. Tlrus, it is technically infeasible !o establish numeric eJj'luent limitations for the seepage front. " W/tile we agree the alluvium is heterogeneous, we disagree with the conclusion that the seepage front is so diffuse and dispersed drat the CDPHE cannot identify discrete locations for compliance. TJre applicant in both TR-26 atd in the August 30, 1999 Technical Support Document, carefully points ou! !trot the contamination from the West Pit is floxdng through a "restricted zone" where the backf~ll contacts t/re alluvium (see quote jrom page 3 of t/re Technical Suppon Dorumemt above). The lateral extent of this restricted mne or "xdndow" is carefully mapped in Figure 3-4 of TR-26. The heterogeneity of the aquifer dictates that a single monitor well is insufficient to clr(lracleriZe flow through the window, as is proposed in TR-028. However, the window is narrow enough that a series of wells in the xdndow should be able to characterize the flow. This multiple well monitoring approach is consistent xdth the monitoring program proposed in Section 6.4.2./ ojTR-26. We recommend that the West Pit discharge through the xdndow be regulated under the pernrir, and be designated as Discharge Poirtt 002. ~ Threshold level (compliance level) for specific parameters in the groundwater should be established and monitored in the existing TR-26 wells in and adjacent to the "xdndow". Paragraph 25 ojthe August 20, /999 NOV/CDO makes reference !o "...the seeps into the Rito Seco, as described in paragraphs /3 and 14 above.... " Paragraph l3 ojthe NOV/CDO refers to one specifte seep, K•hile paragraph l4 oJ11te NOV/CDO refers to three other seeps. We recommnend that these specific seeps be designated im the permit as Discharge Points 003 through 006. Monitoring ojthese seeps would be via the french drain/sump systems installed by BMRI last year. Response: Issues regarding the flow ojgroundwater from the West Pit into the Rito Seco alluvia[ aquifer fall under t/te jurisdiction of the Colorado Division of Minerals and Geology (DMG) and /rave been addressed with the submission (March 22, 1999) and approval (May 23, 20100) ojTechnical Revision (7R) 26. The defined area associated wit/r outfall 002 /ras been revised in both the permit and rationale, and this area is now identified in figure 2 of the permit. The reviewers suggest that "a series of welts in [he xdndow" would be adequate to characterize the flow ojgroundwater from [/re West Pit. 71re suggestion /ras not considered the current conditions wherein t/te flow ojgroundx~ater through dre "window" has been reversed as a result of the implementation of the pumping acrd treating of groundwaters (water management plan) required in Amendment NI to the NOV/CDO, as well as in TR-26. Thus, during this period ,the groundwater quality at the "series ojwells"would not represent the status ojthe groundwater system in the West Pit, but would, rather, measure the condition of x~ater quality in the Rito Seco alluvial aquifer adjacent to the "window. " The reversal of the lrydrau[ic gradient xdll continue throughout the period of time the CDPS permit is in effect.