Aquatic Life Selenium Standards Cottonwood Creek Drainage Cherry Creek Segment 4b Regulation 38 June 9, 2015

New Segment 4b and Sample Sites 2

3  Use-attainability analysis (UAA) was conducted by GEI for the Cottonwood Creek drainage Including Windmill, Lone Tree and Cottonwood Creeks  Monthly water quality sampling October 2013 – April 2015 (ongoing)  Selenium, pH, conductivity, dissolved oxygen, temperature  Spring and fall biological sampling in 2014 Fish and invertebrate populations Selenium in fish and invertebrate tissues  Including fish tissue sampling in Cherry Creek Reservoir in coordination with Colorado Parks and Wildlife UAA Sampling Efforts

Cottonwood Creek Selenium concentrations Chronic standard Acute standard CT-2 CT-P2

Lone Tree Creek Selenium concentrations LTC-1 Chronic standard LTC-2 LTC-3

Windmill Creek Selenium concentrations 6 Acute standard WC-2 WC-BP

Cottonwood Creek Geology 7  Denver Formation Contains marine shales Likely source of selenium

Protection of Aquatic Life Uses  Benthic invertebrates Populations not affected by selenium  Fish Fish populations limited by habitat and flows; not selenium  Fish and invertebrate tissue selenium Fish tissue concentrations similar in spring and fall No direct correlation between water column and fish/bug tissue  Cherry Creek Reservoir Currently meets TVS Fish tissue values were low  ≤ 5.0 mg/kg selenium  EPA draft criteria 8.1 mg/kg

9 Fish Populations Protected  Strong evidence for multiple age classes, indicating no reproductive effects tied to deformities or selenium concentrations

WQCD Alternative Proposal  Cottonwood supports the WQCD alternative proposal.  Windmill Creek standards use Se data from Winter 2014 and Spring 2015 that Cottonwood submitted with UAA and Rebuttal.  Data from Lone Tree and Cottonwood Creeks support seasonal ambient-based standards for Windmill Creek.  Pattern of selenium concentrations is consistent with the underlying geology.  Assessment locations appropriately consider spatial variability. 10

JWPP Discharge  JWPP is critical for use of local, renewable water sources to replace NTGW, an unsustainable supply.  R/O treatment is necessary to meet safety goals, treat for CECs, and reduce TDS and hardness.  JWPP plan for discharge is being developed and will greatly reduce previous selenium concentration/load.  Permitting process is where the Division will consider whether a specific proposal for discharge can protect downstream water quality standards, and is where the many of the comments received will be addressed. 11

Summary of Proposal  Resegmentation Cottonwood Creek & tributaries new Segment 4b  Retain existing aquatic life/recreational/agricultural uses and standards except selenium  Seasonal site-specific selenium standards Based on naturally elevated selenium concentrations resulting from underlying geology 12 Upper Lone Tree Upper Cottonwood Lower Cottonwood Middle Windmill SummerWinterSummerWinterSummerWinterSummerWinter Chronic 85 th %ile TVS Acute 95 th %ile TVS