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by SGC's treatment of Cement Creek would report as dissolved zinc at the reference point. The <br /> original and recalculated results are presented in the following table. <br /> Reported N(i) Recalculated N(i) <br /> June 1998 -0.71 -0.64 <br /> July 1998 -0.83 -0.78 <br /> August 1998 -0.76 -0.65 <br /> September 1998 -0.59 -0.40 <br /> This table shows that treatment of Cement Creek was not necessary in 1998 to mitigate impacts <br /> from A list project construction or Sunnyside Mine bulkheading to maintain water quality at the <br /> reference point. Since negative impacts from construction activity was not seen in 1998, future <br /> negative impacts are unlikely. <br /> SGC monitors water quality of Cement Creek(before treatment) for the facility MLR permit. A <br /> plot of dissolved zinc concentration from this data is attached. There is no indication that <br /> bulkheading of the Sunnyside Mine has had any impact on Cement Creek water quality. <br /> Using Consent Decree monitoring results from the reference point (A-72), Cement Creek flow <br /> diverted for treatment (CC-lB) and Cement Creek gaging station at Silverton(C-48)- including <br /> Bureau of Reclamation data for C-48, estimates were made of Cement Creek treatment's <br /> maximum impact on dissolved zinc concentrations at A-72 and C-48 (table attached). Future <br /> monitoring without treatment will be compared to this table to determine if the full benefit of <br /> treatment is realized downstream. Knowing this will aid SGC in the decision to resume or not <br /> resume treatment in October. <br /> SGC will continue to treat lower American Tunnel flows and maintain the capability to divert <br /> and treat Cement Creek in the event that monitoring results show an impact to water quality at <br /> the reference point from bulkheading of the Sunnyside Mine or the A list projects. No negative <br /> impact is expected from SGC's planned B list activity in the 1999 construction season, since <br /> those projects are strictly water diversion projects. Causes for water quality variation in the <br /> Upper Animas have been difficult to isolate or identify, SGC will continue to monitor and <br /> evaluate the data as before. <br /> Please contact me if you have any questions. <br /> Sincerely, <br /> Larry Perino <br /> Reclamation Manager <br /> cc: EPA—Melanie Pallman <br /> EPA Region 8 (8ENF-T) <br /> DMG—Wally Erickson, <br /> Allen Sorenson <br />