HYDRO28488

• Permit No: C1981041
• IBM Index Class Name: Hydrology
• Doc Date: 9/15/2004
• Doc Name: Amendment No. 1 to CDPS Permit No. CO-0027146
• Permit Index Doc Type: NPDES
• Media Type: D
• Archive: No

Snowcap Coal Co. Inc WWTF Water Quality Assessment CO-0027146
Table A-7
Acute Assimilative Ca acities for Metals
P.:hi•'¢m et r ,dF a ~ ~''
..~srr~; ,.sa ....__`a:„. ~~jc't s"j'~"
,a«,~ k~ «Q ~cjs'~ ~
.. ~ ¢ //c` s
S+f .r'; itif~?~ a"~
~.......li,-s + ~' M~'
~,~ :h~:. ~ b1s'~s
t~. Y~...w x~?^fx ~elr$te"s''~
..u~v!-rvrkt
As, Trec (u /1 50 0.91 50.91 0 50 2,797 1
Cd, Dis u /1 50 0.91 50.91 0.39 12 650 1
Cr`}, Trec (ug/q 50 0.91 50.91 0 50 1,797 2
Cu, Dis u /1 50 0.91 50.91 9.1 33 1,3415 I
Pb, Dis u /I 50 0.91 50.91 4.8 177 9,639 1
Mn, Dis u /1 50 0.91 50.91 15 4089 127,935
Ni, Dis u (1) 50 0.91 50.91 0 1041 58,239 2
Se, Dis (u /I) 50 0.91 50.91 1.0 18 951
A ,Dis (u /1 50 0.91 50.91 0 10 559
Zn, Dis u /1) 50 0.91 50.91 85 261 9,931 1
Note t: Only limited ambient background data w ailable for total re<a verable arsenic, dissolved cadmium, dissolved copper, total
recoverable iron, dissolved lead and dissolved zine~ However, almost 50 samples (or these metals in total form were available. In order to use a
broader base ofdata and provide a conservative level of evalu atioo, the total metals data were used in this evaluation for the aforementioned
parameters.
Nose is No cumnt data were available For dissolved nickel or total recoverable trivalent chromium. Findings of com pan ble studies suggest
chat pollutants consistently found •t less to an detection levels in-stream are deleted as pollutants of concern for a weer body and are uc longer
analyzed when in-stream sampling is performed. Thus, it has been assumed Mat dissolved nickel and fatal recoverable trivalent ch ram ium have
been eliminated as pollutants of eon cero in the receiving stream. Hated on this assumption, a background con ceo tration of zero was used for
dissolved nickel and total recoverable trivalent chram iu m.
V. Antidegradation Review
As set out in The Basic Standards and Methodologies of Surface Water, Section 31.8(2)(6), an
antidegradation analysis is required except in cases where the receiving water is designated as "Use
Protected." Note that "Use Protected" waters aze waters "that the Commission has determined do
not warrant the special protection provided by the outstanding waters designation or the
antidegradation review process" as set out in Section 31.8(2)(6). The antidegradation section of the
regulation became effective in December 2000, and therefore antidegradation considerations aze
applicable to this WQA development.
According to the Classifications and Numeric Standards for Lower Colorado River Basin, stream
segment COLCLC02 is Undesignated. Thus, an antidegradation review maybe conducted for this
segment if new or increased impacts are found to occur. However, the ratio of the flow of the
Colorado River to the Snowcap WWTF design flow is 258:1 at low flows. Section 31.8 (3)(c)
specifies that the dischazge ofpollutants should not be considered to result in significant degradation
of the reviewable waters if the flow rate is greater than 100:1 dilution at low flow. Thus, condition
31.8(3)(c) of the regulations is met and no further antidegradation evaluation is necessary.
VI. References
Colorado Total Maximum Daily Load and Wasteload Allocation Guidance, CDPHE, WQCD,
November 1991.
Classifications and Numeric Standards for Lower Colorado River Basin, Regulation No. 37,
CDPHE, WQCC, Effective August 30, 2002.
Appendix A Page 11 of 12 Last Revised 9/15/2003