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COLORADO DEPARTMENT OF PUB. IIEALTN AND ENVIRONMENT, Water Qu / Comro! Division <br />Rationale -Page 8, Permit No. CO-0O4216I <br />• Qt <br />Qt <br />0.7 cfs <br />1.22 cfs <br />I.4 cfs <br />1.22 cfs <br />_ Qi 1.92 cfs 2.62 cfs <br />Values jor Mt and Mt vary depending on the background stream quality data (MrJ and the applicable water <br />quality standard (M~. These values art also shown in Table V/-4 along with the oaleu/ated e.QTuem Umittuions <br />(M~• <br />Table Vl~ -Summary of Mass Balance Calculations <br />Paia~iteter::::::::':.:::;-'. ;.:.:::S~tram Stnndard,.(M3),;:::>Effluent:Conterttiatlair;.:(hf2)~;:;;.' <br />:.:.:.:..::.....:::.:.::.:: cult rontc cute. rontc.;:.::;::;:::::::::.:.:.:::.:':'::;..: <br />Arsenic, mg/P 0.05/0.05 0.079/0.107 <br />Cadmium, mg/l 0.03/0.012 0.048/0.026 <br />Chromium, mg/P (hex) 0.016/0.011 0.025/0.023 <br />Copper (PDJ, mg/P 0.045/0.028 0.071/0.058 <br />/ton (/RJ, mg/P -/I.0 -/1.57 <br />Lead (PDJ, mg/P 0.48.0.016 0.75.0.034 <br />Manganese (TR), mg/P -/!.0 -/2.1 <br />Mercury (PD), mg/P -/0.0000/ -/0.00002 <br />• Nidtel (PDJ, mg/[ 1.97/0.104 3.1/0.44 <br />Selenium (PD), mg/P 0.01/- 0.016/- <br />Silver (PO), mg/P 0.011/00004 0.018/0.001 <br />PD meant the parentiatty drudted fractlan, at defined In the Basic Srmtdardt and Methodabeta far Surface Water (3.1.0). <br />Metals effluent limitations were calculated using a design flow ojO.792 MGD, the metals standards listed in <br />section /ILA.3. of this rationale, the annual chronic and acute low flows listed in Table 1/1-1 and upstrean <br />concemrations listed in Table Ill-2. Note most metals values in Table 171-2 are jor total rraoverabk, not <br />dissolved. In this case, Zero was used as the upstream connemrtuian for dissolved standards. <br />For metals with dissolvrd standards, rorrespanding efjluem limitations are based upon the potentially dissolved <br />method of analysis, except for hesavalem chromium, which must be analyzed jor using the dissolved method. <br />For standards based upon the total recoverable muhods of analysis, the limitations are based upon the same <br />method as the standard, except for arsenic and selenium. Far these two metals, the total rerovierabk analyses <br />must be performed using a graphite furnace. This method may produce erroneous results and may not be <br />available to the permittee. Thtrcfore, the total method of analysis will be speri, fled instead of the total <br />recoverable method. Table VI-4. lists the effluent limitations that were calculated. <br />The limitations listed in Table VF4. were evairtated jor inclusion in the permit. The likelihood of metals <br />concentrations being found in the effluent to levels approaching the calculated limitation and the measured <br />concentrations listed in section V.A. were factors considered in this evaluation. No ejj'luent limitations are <br />required based on these calculations. <br />• df Antide¢radntion: The Basic Standards and Methodologies for Surface Waters, 3.1.0, set out the antidegradation <br />process. The purpose ojthe review is to make a daermination on whether degradation is necessary to <br />accommodate importam economic or social development in an area. Part 3.1.8(d) of this regulation outlines <br />what is needed for this determination. The review can be avnrded tf a determination is made that the discharge <br />does not significantly degrade the stream, as outlined in pars 3.1.8(c). <br />:. ilcule (l E3) ..:.: Chronic (30E3) ::: <br />