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APR-20-2000 THU 04 50 PM <br />RMC <br />Ms. Lori Potter <br />April 20, 2000 <br />Page 2 <br />FAX N~ <br />• ID~3D36656959 A 20'00 <br />P. 09 <br />16 31 No .010 P.03 <br />Inc <br />have migrated out of the pit, and we would be repeating the current situation. We feel tfiat the <br />program should pro-aaively detect contamination near the source, both in the pit itself and at the <br />"curtain wells." Finally, TR-028 does nor include a surface water point of compliance. This is not <br />acceptable given the relative travel times in the surface water and alluvium; contamination would <br />detrimentally impact the Rito Seco long before it triggered action at the proposed alluvial point of <br />compliance well, which is located some 2,000 feet downstream of the West Pit window. <br />i. Sscfion 2. i, ogee 4. first ~raerauh, last sentence <br />Concerning the statement that the "observedchanges in...groundwatertevels in the vicinity of the <br />West Pit have supported the conceptual hydrologic...model(sJ as contemplated in TR-026 ," TR-028 <br />should provide an analysis to support this conclusion. For example, the West Pit water management <br />system proposed in TR-026 (page 66) assumed an average extrattion rate of 150 gpm for 750 days. <br />Consequently, the removal of 100 atte-feet (33 million gallons) of water was envisioned to lower the <br />groundwater level in the West Pit by 15 feet. In practice, the West Pit extraction system has used eight <br />wells pumping at variable rates for a period of approximately 220 days to lower the West Pit <br />groundwater level 13 feet. How much groundwater was arxually pumped from the West Pft between <br />July 4, 1999 and February 9, 2000 and at what rateP Are these values consistent with the origins! <br />pt»jectionsi Absent this and other information, the conclusion that the hydrogeologlc model <br />proposed in TR-02b is still appropriate can not be substantiated. <br />2. Section 2.1.l.1, pale ~ first oar graph, fourth sentence <br />While the text states that the West Pit groundwater level has declined 13 feet, the data prbvided (see <br />Figure 2-t) only documents a 6.5-fool decline. TR•028 must supply the data to suppoA the text. <br />3. Section 2.1-1.2, page S, fird earieranR. second sentence <br />With the exception of well M-20, the "curtain" extracion wells indicate an increase in groundwater <br />levels during the last one to two months shown. This trend must be explained. <br />;, version 2. L2.2s„naee 5 first par er+lph, and p~gg 6, find aanaraob <br />Table 2.1 indicates that the interim water treatment system was commissioned on October 13, 1999. <br />We assume that treated effluent was discharged to the Rita Seco upstream of both RS2 and RS-5. <br />Assuming that the effluent discharge rate was approximately 400 gpm (0.9 cfsl, the relative percentage <br />of treated effluent in the Rito Seco under base flow conditions Is likely rather high. Therefore, at least <br />some, and perhaps a significant proportion, of the apparent Improvement attributed to the tR-026 <br />water management system is due to simple dilution. <br />$, Section 2.1.2,2, nape 6, oar~eranh ?, last sentence <br />We disagree with the use of well M-26 data to represent groundwater quality from "unaffected" <br />portions of the Rito Seco alluvial aquifer. On page 7 (see first complete paragraph), BMRI <br />acknowledges that well M-t t R, located at least 1,000 feet downgradient of the West Pit "window," has <br />