Arequa Gulch Use-Attainability Analysis (UAA)

Cripple Creek and Victor Mining Company (CC&V) had been unable to meet the required water quality “table value standards” in Arequa Gulch. GEI was retained to perform a Use Attainability Analysis (UAA) and site-specific standards. Our study has become the benchmark for subsequent UAAs and site-specific standards in Colorado, providing stability in water quality regulations in support of site operations.

As a result of flows from a spring naturally high in metals and low pH, CC&V had trouble meeting “table value standards” in Arequa Gulch. Without some adjustment, CC&V would be required to construct and operate a treatment plant or capture and pumpback all flow in perpetuity.

GEI’s ecological staff developed a workplan for UAA; conducted seasonal sampling of Arequa Gulch and the receiving stream; sampled for fish populations, benthic invertebrates, zooplankton; and assessed habitat quality and stream flows.

The staff then reviewed CC&V water quality data and compared it to Colorado water quality standards. These data were used to refine the aquatic life use classification for Arequa Gulch and develop site-specific standards for zinc, manganese, aluminum and pH.

Our ecological staff prepared a detailed technical report summarizing the findings of the UAA, along with a supplemental UAA specific to pH. We presented the findings to the Colorado Water Quality Control Division and EPA Region 8.

We testified before the Colorado Water Quality Control Commission twice and prepared appropriate prehearing statements, rebuttal statements and other response documents. By re-defining the aquatic life use through a UAA, we could support derivation of site-specific standards, be protective of the environment, but preclude the need for treatment.

The study resulted in a number of “firsts” for Colorado including:

• First UAA of its kind conducted in Colorado
• First Colorado stream to have “approved” refined use classification with “no fish”
• First Colorado stream with “approved” site-specific standards for zinc, aluminum, and manganese based on “no fish” and “no zooplankton”
• First Colorado stream with site-specific pH standard.