Windy Gap Firming Project Draft Environmental Impact Statement August 2008

• Description: Windy Gap Firming Project Draft Environmental Impact Statement August 2008 Reclamation Managing Water in the West
• State: CO
• Date: 8/1/2008
• Title: Windy Gap Firming Project Draft Environmental Impact Statement August 2008
• Water Supply Pro - Doc Type: Publication

EXECUTIVE SUMMARY
WINDY GAP FIRMING PROJECT DRAFT ENVIRONMENTAL IMPACT STATEMENT
change in water clarity as measured by the Secchi -disk depth for any of the alternatives.
• All alternatives would increase phosphorus concentrations in Shadow Mountain Reservoir; total
nitrogen would increase in Alternatives 1 to 3 and decrease in Alternatives 4 and 5 (Table ES -5).
Chlorophyll a concentrations would increase in Alternatives 1 to 3. Water clarity would not change
in any alternative. Dissolved oxygen would decrease under the Proposed Action and not change in
other alternatives.
Table ES -5. Shadow Mountain Reservoir predicted water quality changes by alternative compared to
existing conditions.
- a
Parameter
Alternative 1
No Action
Alternative 2
Proposed Action
Alternative 3
Alternative 4
Alternative 5
Total phosphorus (gg/L)
+5.6%
+11.3%
+8.1%
+4.8%
+3.2%
Total nitrogen (gg/L)
+1.1%
+1.8%
+0.4%
-0.7%
-0.8%
Chlorophyll a (gg/L)
+1.8%
+1.8%
+1.8%
No Change
No Change
Peak chlorophyll a (gg/L)
+3.4%
+6.8%
+1.1%
No Change
-1.1%
Secchi -disk depth (m)
No Change
No Change
No Change
No Change
No Change
Trophic state
No Change
No Change
No Change
No Change
No Change
Minimum DO (mg/L)
No Change
-1.4%
No Change
No Change
No Change
TS S (mg/L)
+5.0%
+5.0%
+5.0%
+5.0%
+5.0%
• In Grand Lake, total phosphorus concentrations are expected to increase under all alternatives (Table
ES -6). Total nitrogen is expected to increase under the No Action and Proposed Action alternatives.
Chlorophyll a concentrations would increase under all alternatives and Secchi -disk depth would
decrease under all alternatives, except Alternative 5. Dissolved oxygen concentrations would
decrease under all alternatives.
Table ES -6. Grand Lake predicted water quality changes by alternative compared to existing
rnnditinns_
Parameter
Alternative 1
No Action
Alternative 2
Proposed Action
Alternative 3
Alternative 4
Alternative 5
Total phosphorus (gg/L)
+6.0%
+12.0%
+6.0%
+6.0%
+4.8%
Total nitrogen (gg/L)
+0.4%
+1.6%
-0.4%
-0.4%
-0.8%
Chlorophyll a (gg/L)
+4.2%
+6.1%
+4.2%
+2.0%
+2.0%
Peak chlorophyll a (gg/L)
+4.1%
+5.4%
+14%
+1.4%
No Change
Secchi -disk depth (m)
-3.8%
-3.8%
-3.8%
-3.8%
No Change
Trophic state
No Change
No Change
No Change
No Change
No Change
Minimum DO (mg/L)
- 11.1%
-7.4%
-5.6%
-5.6%
-5.6%
TSS (mg /L)
No Change
+5.6%
+5.6%
+5.6%
No Change
• No additional water quality standards would be exceeded at the Three Lakes, but temperature and DO
concentrations would continue to exceed state standards in Granby Reservoir. Lower DO levels
would contribute to continued exceedance of the manganese standard in the Three Lakes.
ES -13