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COLORADO DEPART?SENT OF I~al.TB - Water Quality Control Division ' • Rationale - ?age 15 Perait Ao.: CO-0038776 D. Ammonia An evaluation was made far ammonia, making use of the Following mass balance equation: SF PC ~ SC ~ ( )BC SF*PF PF SF+PF where PC ~ allowable effluent concentration of total ammonia for the sewage treatment plant SC ~ instream concentration of total ammonia, derived from the mean annual pH value (7.8) and the maximum reported temperature value (66• F.,,or 19° C) value which results in an iaseream unionized ammonia concentration of 0.0 2 mg/1 as N, from Willingham (see references) ~ 0.905 mg/1 as N SF ~ the annual Q7_10 low floe value 21.3 MCD PF ~ the design floe capacity of the sewage treatment plant (0.01 MGD) • BC ~ the annual mean value for [fie background iascream total ammonia concentration ~ 0.15 mg/1 as N 21.3 PC ~ 0.905 - (21.31 )(0.15) ~ 1609 mg/1 as N total ammonia 0.01 21.31 The above mass balance evaluation indicates that there will be no problem is achieving the 0.02 mg/1 as N proposed stream standard for unionized ammonia, since, typically secondary domestic wastewater treatment discharges contain total aamonia concentrations of 15 co 25 mg/1 as N. Thus, Che secondary treatment provided for this facility is adequate. There is no need to have a permit effluent limitation for ammonia, and also no need to require ammonia monitoring. E. Salinity Monitoring far salinity as either 'IDS ar electrical conductivity will be required for discharge point 007. Please refer to the previous discussion of salinity in the Rationale far further information regarding salinity requirements. F. Other Parameters The other parameters which were Listed as proposed numeric standards for Segment 2 of the :forth Fork of the Gunnison Rivez in Table w were • evaluated in mass balance equations for the domestic G'GTP discharge (007). These evaluations indicated that there is no significant impact from the domestic WWTP discharge for the other parameters, therefore no monitoring or limitations for these ocher parameters are applicable at this time for the domestic discharge.