Aquatic Life Selenium Standards Cottonwood Creek DrainageCherry 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

10/1/2

013

10/17/2

013

11/2/2

013

11/18/2

013

12/4/2

013

12/20/2

013

1/5/2

014

1/21/2

014

2/6/2

014

2/22/2

014

3/10/2

014

3/26/2

014

4/11/2

014

4/27/2

014

5/13/2

014

5/29/2

014

6/14/2

014

6/30/2

014

7/16/2

014

8/1/2

014

8/17/2

014

9/2/2

014

9/18/2

014

10/4/2

014

10/20/2

014

11/5/2

014

11/21/2

014

12/7/2

014

12/23/2

014

1/8/2

015

1/24/2

015

2/9/2

015

2/25/2

015

3/13/2

015

3/29/2

015

4/14/2

0150

5

10

15

20

25

30

35

40

45

CT-InCT-ECT-P1CT-P2CT-1CT-2

Se co

ncen

trati

on (µ

g/L)

Cottonwood Creek Selenium concentrations

Chronic standard

Acute standard

CT-2CT-P2

10/1/2

013

10/20/2

013

11/8/2

013

11/27/2

013

12/16/2

013

1/4/2

014

1/23/2

014

2/11/2

014

3/2/2

014

3/21/2

014

4/9/2

014

4/28/2

014

5/17/2

014

6/5/2

014

6/24/2

014

7/13/2

014

8/1/2

014

8/20/2

014

9/8/2

014

9/27/2

014

10/16/2

014

11/4/2

014

11/23/2

014

12/12/2

014

12/31/2

014

1/19/2

015

2/7/2

015

2/26/2

015

3/17/2

015

4/5/2

0150

5

10

15

20

25

30

35

40

45

LTC-1

LTC-2

LTC-U.S. Outfall

LTC-3

LTC-4Se co

ncen

trati

on (µ

g/L)

Acute standard

Lone Tree Creek Selenium concentrations

LTC-1

Chronic standard

LTC-2

LTC-3

10/1/2

013

10/17/2

013

11/2/2

013

11/18/2

013

12/4/2

013

12/20/2

013

1/5/2

014

1/21/2

014

2/6/2

014

2/22/2

014

3/10/2

014

3/26/2

014

4/11/2

014

4/27/2

014

5/13/2

014

5/29/2

014

6/14/2

014

6/30/2

014

7/16/2

014

8/1/2

014

8/17/2

014

9/2/2

014

9/18/2

014

10/4/2

014

10/20/2

014

11/5/2

014

11/21/2

014

12/7/2

014

12/23/2

014

1/8/2

015

1/24/2

015

2/9/2

015

2/25/2

015

3/13/2

015

3/29/2

015

4/14/2

015

4/30/2

0150

5

10

15

20

25

30

35

40

45

WC-1WC-BPWC-up tribWC-down tribWC-BHWC-2

Se co

ncen

trati

on (µ

g/L)

Chronic standard

Windmill CreekSelenium concentrations

6

Acute standard

WC-2WC-BP

Cottonwood Creek Geology

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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

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High Se sites

Length MM

20 40 60 80 100 120 140 160 180 200 220N

um

ber C

olle

cted0

20

40

60

80

100

Fathead MinnowCreek ChubWhite SuckerBrook Stickleback

Low Se sites

Length MM

20 40 60 80 100 120 140 160 180 200 220

Nu

mbe

r Co

llected

0

10

20

30

40

50

60

Fathead MinnowBrook SticklebackWhite Sucker

Fish Populations Protected

Strong evidence for multiple age classes, indicating no reproductive effects tied to deformities or selenium concentrations

WQCDAlternative 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.

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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.

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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

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Upper Lone Tree

Upper CottonwoodLower

CottonwoodMiddle Windmill

Summer Winter Summer Winter Summer Winter Summer Winter

Chronic 85th %ile

19.0 37.2 7.1 14.0 TVS 5.1 8.4 15.1

Acute 95th %ile

19.3 41.0 TVS TVS TVS TVS TVS TVS