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Snowcap Coal Co. Inc WWTF Water Quality Assessment CO-0027146 <br />Colorado River near Cameo, CO, was added to the daily flow at USGS gage number 09105000, <br />Plateau Creek neaz Cameo, CO. <br /> <br />There aze no daily flow records available for diversions to the Government Highline Canal and <br />therefore the local water commissioner was consulted. The water commissioner indicated that a <br />maximum of 2,000 cfs is withdrawn from the Colorado River to the Government Highline Canal <br />during the months of March through September. Because no more specific data were available, the <br />value of 2,000 cfs was subtracted from the daily results oftheabove-described calculations for each <br />day in the months of Mazch through September. These daily flows were used to detemune the 1 E3 <br />and 30E3 low flows using U.S. EPA DFLOW softwaze. The output from DFLOW provides <br />calculated acute and chronic low flows for each month. <br />Flow data from October 1, 1991 through September 30, 2001, were available from both gage <br />stations. The gage stations, diversions, and time frames were deemed the most accurate and <br />representative of current flows and were therefore used in this analysis. <br />Based on the low flow analysis described previously, the upstream low flows available to the <br />Snowcap WWTF were calculated and aze presented in Table A-5. <br />Table A-5 <br />Low Flows for the Colorado River at the Snowca WWTF <br /> <br />'~ -~„ ~~ <br />`uj , ~ <br />' : 4 < ~ <br />" is a~ ~ . ~ ~-~~ ~~ ~, <br /> <br />~x <br />~ naa a <br />~ ~ ~,,~ar r <br />~ QY~ <br />~ Jun Jrr Arfg <br />~ epx <br />~ .Qet~ ovm et <br />~~~" <br />, . ! t~ r : g? ,. ems. ° ~ ._.~~ ` "~ ., <br />lE3 <br />Acute 50 1241 1267 1389 1578 1037 345 120 123 50 238 1559 1248 <br />30E3 <br />CLronic 235 1398 1398 1459 1589 1837 345 235 235 235 238 1566 1471 <br />During the months of June and October, the acute low flow calculated by DFLOW exceeded the <br />chronic low flow. In accordance with WQCD standazd procedures, the acute low flow was thus set <br />equal to the chronic low flow for these months. <br />N. Technical Analysis <br />In-stream background data and low flows evaluated in Sections II and III aze ultimately used to <br />determine the assimilative capacity ofthe Colorado River neaz the Snowcap W WTF for pollutants of <br />concern. For all parameters except ammonia, it is the WQCD's approach to conduct a technical <br />analysis of stream assimilation capacity using the lowest of the monthly low flows (referred to as the <br />annual low flow) as calculated in the low flow analysis. For ammonia, it is the standazd procedure of <br />the WQCD to determine assimilative capacities for each month using the monthly low flows <br />calculated in the low flow analysis, as the regulations allow the use of seasonal flows when <br />l establishing assimilative capacities. <br />l <br />Appendix A Page 7 of 12 Last Revised 9/15/2003 <br />