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<br />C'OLOILIDO DEPARTMENT OF PUBLIC HEALTH AND ENV/RONMEM ; Water Quality Control Division <br />,9mendment No. 1, Rationale -Page 2. Permit No. CO-0042161 <br />,{~V, PurF~ose and Discussion of Amendment <br />In a letter dated Apri15, 2000, the permittee requested a variance from the upper pH limitation of 9.0 s. u. for outfall <br />001. They stated that when flows reach the maximum level of 1, 200 gpm, the pond pH may approach 10.0 s. u. due to <br />algae growth. Meeting the effluent limit would necessitate addition of acid to the pond. <br />The i~ermittee believes that even if the pond pH is at 10.0 s. u. the insh~eam pH in Fish Creek, the receiving water, would <br />not exceed the water quality standards. They submitted a monitoring :summary that included 77 dates during the period <br />from March 1998 through September 1999. Included in the summary .are pH and flow data for instream monitoring <br />locations upstream and downstream of outfall 001 as well as outfal1001 itself. The record is not complete--most data <br />points for the various dates are missing one or more monitoring locations and none represent periods when the effluent <br />flow was at or near 1, 200 gpm (or 2.67 cfs). The highest effluent flox~ represented is 1.0 cjs. Additionally, the highest <br />efllu~>nt pH is 9.0 s. u. jor one data point. The carrespondirig instrennt points for that one date are missing from the <br />sumnwry. The highest effluent pH was 8.8 s.u. where upstream and downstream data were also included. This <br />occurred on two separate dates. On one date, downstream pH was 0.2 s. u. higher than downstream_~H. On the other <br />date, downstream pH was 0.2 s. u. lower than downstream pH. On none of the dates was inrtream pH, either upstream <br />or downstream, ar or above the upper standard of 9.0 s. u. <br />Additionally, when the current permit was wriaen in 1994, the acute low flow in Fish Creek was determined to be 0.7 <br />cfs, ttnd the chronic low flow was 1.4 cjs. Thus, dilution would always be available. <br />The Division concludes after review of these data that the receiving water pH would likely not be significantly affected by <br />efflu~rnt pH. However, there are insufficient data to make a solid dete,rntination. On this basis, the permiaee's request <br />will be conditionally granted. The upper pH [imitation jor outfal! 001 will be raised to 10.0 s. u., but the permit will <br />include instream pH monitoring (both upstream and downstream--at points away from any influence from other sources) <br />to ascertain that this higlter effluent pH limitation does not cause exceedences of the instream water quality standard. <br />/f this monitoring shows that the higher pH limitation causes an instre~vn exceedence of the pH water quality standard, <br />the permit will 6e reopened to lower the pH limitation to bring the statulard back into compliance and the permittee may <br />be required to adjust effluent pH at tha! time. <br />V. Chmtges to Permi[ <br />Par! LA.1. (a) of the permit on page iii amended to reflex the change in the upper pH [imitation for outfa11001. Pan <br />/.B.1. (a) on page v will be amended to add instream monitoring. <br />Jon Kubic <br />June 28, 2000 <br />