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• changes are noted in Table 79. Standards for certain trace metals and ammonia now involve <br />the use of a "Table Value Standard" (TVs) which involves [he use of a logarthmie equation <br />that uses hardness values (for trace metals) or temperature and px (for ammonia). <br />Regardless, the standards that existed prior to the implementation of the TVS's are used <br />to evaluate water quality of discharges into the Fish Creek Basin. <br />For Segment 138 of the Yampa River, the CDOH has established a standard of 0.02 mg/l for <br />un-ionized ammonia (as nitrogen). Analyses performed by Peabody's contract laboratory for <br />ammonia as nitrogen resulted in reported values consisting of the sum of both the ammonium <br />ion (ionized) and ammonia (un-ionized). Because of this, it was necessary to convert <br />Peabody's reported ammonia concentrations to un-ionized ammonia concentrations in order to <br />compere them against the stream standard. The table presented on Page 773 of "Standard <br />Methods for the Examination of Water and Wastewater" (APHA, 7985) presents percent <br />correction factors used to calculate un-ionized portions of ammonia in distilled water. <br />Since percent correction factors for solutions with higher TDS are unavailable in the <br />literature, percent correction factors for distilled water were applied to the ammonia <br />values for comparison purposes. It should be noted that the percent un-ionized ammonia <br />. decreases with increasing TDS, and resultant values calculated for un-ionized ammonia are <br />probably higher than the true value. <br />Similarly, the CDOH has established a chronic standard of 0.002 mg/L for un-ionized <br />sulfide as hydrogen sulfide (H25). It should be noted that the water quality analyses in <br />the appendices of-this AHR report the sum of ionized and un-ionized sulfide as sulfide. <br />To compare Peabody's reported sulfide concentrations against the stream standard, it is <br />necessary to convert the reported concentration to un-ionized sulfide as hydrogen sulfide. <br />This is accomplished in two steps. Sulfide values are converted to sulfide as hydrogen <br />sulfide by multiplying by 7.06. To express the sulfide as hydrogen sulfide values in <br />terms of un-ionized sulfide, the procedure on Page G77 of "Standard Methods for the <br />Evaluation of Water and Wastewater" (APHA, 1985) was used. The procedure consists of <br />multiplying the sulfide as hydrogen sulfide values by an un-ionized sulfide correction <br />factor. Since any sulfides in surface water should be rapidly oxidized to sulfates, it is <br />likely that any sulfides. del acted in surface water are the result of sulfides existing in <br />the suspended solids, or are the result of interferences with the sulfide analyses. <br />• Table 20 presents the results of comparing surface water quality data from ell surface <br />water and NPDES sites within the Fish Creek Basin collected during 1993 against CDOH <br />17 <br />