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__,_.._.... _.__-r. Blue Mountain Energy, Inc. WWTP Water Quality Assessment CO-0038024 Ambient Water Ouality The W QCD evaluates ambient water quality based on a variety of statistical methods as prescribed in Section 31.8(2)(a)(i) and 31.8(2)(b)(i)(B) of the Colorado Department of Public Health and Environment Water Quality Control Commission Regulation No. 31. The ambient water quality was not assessed for the utmamed tributaries to Red Wash and Scullion Gulch because the backgound in-stream low flow condition is zero, and because no ambient water quality data are available for the unnamed tributaries to Red Wash and Scullion Gulch upstream of the Blue Mountain Energy, Inc. WWTP discharge. Ambient qualitydata were available for the White River. To conduct an assessment of the ambient water quality of the White River upstream of the Blue Mountain Energy, Inc. WWTP, data were gathered from USGS station 09306290 located on the White River below Boise Creek, approximately 7 miles upstream of the confluence of Red Wash and Scullion Gulch with Kenney Reservoir. These data were available for a period of record from 1990 to 1999. Data from this source were used to reflect upstream waterquality in the White River. These data aze summarized in Table A-5. III. Water Quantity The Colorado Regulations specify the use of low flow conditions when establishing water quality . based effluent limitations, specifically the acute and chronic low flows. The acute low flow, referred to as 1 E3, represents the one-day low flow recurring in athree-yeaz interval. The chronic low flow, 30E3, represents the 30-day average low flow recurring in a three-yeaz interval. Low Flow Analysis Although there is periodic flow in the unnamed tributaries [o Red Wash and Scullion Gulch upstream of the Blue Mountain Energy, Inc. WWTP, the 1 E3 and 30E3 monthly low flows are set at zero based on information provided by the local Water Commissioner. Law flows in the unnamed tributaries to Red Wash and Scullion Gulch aze summarized in Table A-6. To determine the low flows available to the Blue Mountain Energy, Inc. W WTP in the White River, USGS gage station 09306290 (White Riverbelow Boise Creek) was used. This flow gage provides a conservative measurement of the upstream flow because, although smaller waters may enter the White River between the gage station and the points where Red Wash and Scullion Gulch enter Kenney Reservoir, there aze no significant diversions or confluences between the flow gage and the reservoir. A conservative analysis is adequate for this WQA because the process required to add the confluences to reflect the actual low flow available to the facility would be resource intensive and would not change the outcome of this analysis. Appendix A Page 7 of 15