Cottonwood Water & Sanitation District Rebuttal Testimony

Fish deformities?  1709 fish sampled at four upper Cottonwood sites with elevated Se (spring and fall)  Only 3 potential selenium-related deformities (0.18%) 2 white sucker (only 1.8% of all WHS sampled) 1 brook stickleback (only 3% of all BST sampled)  “Why not include fin erosion?” Not selenium-related – caused by bacterial infection 2

Fish Populations Protected - Positive relationship between fish density and selenium concentrations 3

Consistent with other Regional Selenium Standards 4

Pattern of decreased Se concentrations in lower reaches?  This is actually not new to the Commission  Similar situation in Sand Creek (Segment 16i – Upper South Platte) Upper - Se (ac/ch) = 45.1/38.2 Lower – Se (ac/ch) = TVS/9.0 Statement of basis and purpose language: “Two assessment locations are appropriate since the selenium concentrations consistently decline along Sand Creek, probably due to influx of lower concentration groundwater, however the mechanism has not been identified.” 5

Selenium reduction strategies  Convert to treatment blend of 50% RO and 50% ultrafiltration.  Relocated wells will draw from lower Se alluvial sources.  Currently investigating Se removal through chemical and biological processes.  Blend with Lone Tree WWTP effluent. 6

Ongoing fish tissue sampling  Relationship between water column and fish tissue concentrations – complicated.  Current tissue levels in Cherry Creek Reservoir are well below draft EPA criterion with little variation.  Cherry Creek Reservoir was sampled by WQCD and CPW this spring.  More fish occur in areas with highest selenium concentrations. 7