1. WQCD Response: Selenium/Misc. 1

2. Reverse Osmosis Treatment Colorado currently has 42 RO treatment plants. Attractive for communities with lower source water quality RO can concentrate ambient pollutants 4-6x in waste brine If source water pollutants are elevated and the plant is located on low- dilution stream, RO brine is at risk of compliance problems

3. Cottonwood Proposal RO facility not discharging since 2011 Unable to consistently meet effluent limits from beginning of operations. Currently operating as a micro-filtration plant with effluent piped to ACCWA WWTF UAA characterized the biological and chemical conditions in 3 adjacent creeks in support of ambient Se standards

5. Summary Cottonwood UAA Upper reaches of Cottonwood, Lone Tree and Windmill Creeks drain selenium bearing shales. No evidence of point sources Chemistry: Sampling over 17 months with generally good spatial coverage. (given the challenges of flow) Biology: MMI scores and fish community composition generally indicative of urbanized, flow limited systems. Aquatic biota (fish and bugs) have elevated tissue concentrations ranging from 10-24ug/g at most sites. 3 of 1700 fish found with Se related deformities. Highest Attainable Use= Elevated Se in tissues with a low rate of fish deformities.

6. Underlying Geology A mbient Se TVS LEGEND

8. Cottonwood 4b Standards Ambient based standards for the upper portions of these systems and TVS* in lower Summer and Winter standards (due to 2x greater winter concentrations) Assessment locations capture the spatial variability well The Division recommends the proposal as stated in WQCD Exhibits 38-26 and 27

9. Milliken Overview History of compliance violations due to selenium DMR delinquency etc New personnel and technical consulting evaluating new treatment technologies and source water Proposal seeking continuation of the Se temporary modification on Little Thompson River.

14. Temporary Modification The Division withdrew our initial proposal for a “current conditions” temporary modification due to several concerns about Milliken’s facility. “Current Conditions” equals no discharge in this case. Uncertainty about the consistent and worsening trend in effluent quality. A numeric temporary modification does not build in assimilative capacity.

15. Other Proposals Clear Creek Segment 2c: The Division supports CCCSD’s proposal for new and revised temporary modifications. Big Dry Creek Segment 1: The Division supports BDCWA’s proposal to move one of the assessment locations and correct typos. Regulation 38.7: The Division supports the inclusion of language specifying that Marston Forebay is not Waters of the State.

16. Questions? Se (ppm) USGS National Geochemical Map for selenium. Map was compiled by Andrew Grosz and Jeffrey Grossman, 2006.