Kensington Gold Project Final Supplemental Environmental Impact ...

Receiving Water
Hardness
Table 3. (continued)
A-7
Kensington Gold Project Final SEIS
Appendix A
Water Quality-based Effluent
Limitations
(WQBELs)
Parameter
(mg/L CaCO3) Units MDL AML
200 µg/L 13 6.7
Zinc 25 µg/L 37 18
50 µg/L 67 33
100 µg/L 120 60
200 µg/L 216 108
TDS and Sulfate
The Alaska Water Quality Standards at 18 AAC 70 contain water quality criteria for TDS not to
exceed 500 mg/L and sulfate not to exceed 250 mg/L. At 18 AAC 70.235, ADEC has established
site-specific criteria for Sherman Creek of TDS not to exceed 1,000 mg/L and sulfates not to
exceed 200 mg/L. The site-specific sulfate criteria apply only to sulfate associated with sodium
and magnesium. Consistent with the state’s draft 401 certification, the draft NPDES permit
contains identical limitations for the average monthly limit and the maximum daily limits based
on the “not to exceed” provision of the standards.
Turbidity
The Alaska Water Quality Standards prohibit an increase of greater than 5 NTUs in receiving
waters above natural conditions, when the natural turbidity is 50 NTUs or less. Because natural
turbidity levels in both the Sherman Creek and East Fork Slate Creek drainages are well below
50 NTUs, the draft permit requires that turbidity in the discharges be no greater than 5 NTUs
above background.
Ammonia
The Alaska Water Quality Standards contain acute and chronic water quality standards for the
protection of aquatic life. The criteria upon which the standards are based are contained in the
Alaska Water Quality Criteria Manual for Toxic and Other Deleterious Organic and Inorganic
Substances (2003). These criteria are dependent on the pH and temperature of the receiving
waters, and whether the receiving waters support salmonids and early life stages of fish. Based on
water quality monitoring performed by the Permittee, USEPA has used a pH range of 6.0 to 8.0
for lower Sherman Creek, a pH range of 7.1 to 8.1 for East Fork Slate Creek, and temperature
ranges not to exceed 14 °C for both Sherman Creek and East Fork Slate Creek. Both creeks
support early life stages of fish, salmonids in particular. Although 14 °C may be a higher
temperature than what actually occurs in the creeks, water quality criteria are not temperature
sensitive until temperatures exceed 14 °C.
Based on the applicable water quality standard for ammonia and using the statistical methodology
presented in the TSD, USEPA is proposing the limitations in Table 3 for discharges to Sherman
Creek and East Fork Slate Creek through outfalls 001 and 002.
pH
At 40 CFR 440, NSPS require pH of discharges from outfalls 001 and 002 to be within the range
of 6.0 and 9.0 s.u. The Alaska Water Quality Standards limit receiving waters to the pH range of