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Ms. Darcy O'Connor October 27, 1999 Page 2 West Pit Again on page 2, the enhanced evaporation system covers a total of 9.7 acres with approximately 2.5 acres comprising the holding pond. In the following sentence, reference is made to the operation of the enhanced evaporation system. In the original design, groundwater was to be pumped from the backfill wells BF-3, BF-4, and BF-5 into the holding pond at a total rate of approximately 350 gallons per minute (gpm). Water from the holding pond would teen be ptunped, using the two-stage pumping system, to the five evaporators, potentially at a m~ucimum rate of 500 gpm. Additional sources of water pumped to the holding pond include alluvial aquifer monitoring wells (M-18, M-19, M-20, M-28, and M-29) and the seep collection system. Therefore, water is not pumped directly from the welts or seep collection system to the evaporators as stated in the narrative section of the inspection report. Seep Areas on the Bank of Rito Seco Creek According to the EPA inspection report in the second pazagraph of this section, wale r was observed "flowing from behind the corrugated metal fence to the Rito Seco Creek." At the time of the inspection, the pylon that was placed to contain the seepage flow consisted of inu:rlocking metal pylons. The joints where individual pieces of metal pylon interlock do not provide ~Natertight seals and, therefore,.the potential may have existed for some.leakage at these locations. This potential ..leakage has been addressed by the placement of watertight,.interlocking I-IDPE pylon that has been installed adjacent to the metal pylon. In addition, to the best of our knowledge, the' ]SPA inspection '~ teant.did not collect any samples of any direct surface .water flow from the seepage containment :structures (pylon) to the Rito Seco. In the third paragraph of this section of the inspection report reference is made to "reddish-orange discoloration" and "dead trees" in the azea of the "second seep", which is located just upstream of i the original seep. The reddish-orange discoloration identified by the EPA inspection team is corrunon throughout the incised reach of the Rito Seco (roughly from just east of the West Pit to ~ downstream of RS-5) on both the north and south bank of the stream channel. The preceding ~ conclusion is su orted b the results of a re-tttinin see /s ran surve conducted b consultants PP Y P g P P g Y, Y to Respondents, in which similar reddish-orange discoloration was observed at a seep along the Rito ;; Seco (Attachment A). In addition, the arroyo sidewalls of the Rito Seco are also rec!dish-orange in color, which is indicative of the iron-rich nature of the sediments comprising the Rito Seco alluvium. Thus, the reference to "reddish-orange discolorntion" in the vicinity of the seep area along the Rito Seco is ambiguous at best, makes no distinction with respect to naturally occurring sources ofiron-staining and has no bearing or relationship to the flow of groundwater from the West Pit. Similazly, reference to "dead trees" is simply an observation that could be made at most locations along the Rito Seco. There is no basis for any implication that the dead tre~;s were related to seepage flows. The seep referred to in the fourth paragraph of this section constituted a restricted bog area with no observable water movement. Thus, to our knowledge, there has been, no observabl: flow and the term "seep" overstates the nature of the surface/groundwater regime at that location. Nevertheless,