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

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Se (85th Percentile µg/L)

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Fish Density (number/acre) Se Concentration (85th percentile µg/L)

Fish Populations Protected

- Positive relationship between fish density and selenium concentrations

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Consistent with other Regional Selenium Standards

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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.”

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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.

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