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<br />., ..- <br />/-' <br />C.0 <br />01 <br /> <br />c <br /> <br />NPDES:Petmit No. CO-0042161 <br />Salinity IControl Study <br /> <br />TwentymiIe Coal Comp~ny <br /> <br />4.1.2 qptiim 2: RO Treatment <br /> <br />Option 2! involves RO treatment of up to 1 cfs prior to discharge, to 300 mglL IDS, and <br />bypass o~ flow in excess of 1 cfs. Three quarters of influent is discharged as treated water, <br />and the r~ject 25% is disposed of in a deep well. The .estimated discharge flow, salt loading <br />and conc~ntration and impacts on Fish Creek are given in Table 4, ' <br /> <br />Option 2: would reduce average salt loading for the 1990-1994 record by 1.53 tons/day,' <br />comparedjto 1.83 tons/day for complete elimination of the salt loading (Option I). As with <br />Option I, Ithis does not substantially reduce thetotal salt load in Fish Creekdownstr!llUDofthe ' <br />discharge,j An average reduction in salt load of 1.53 tons/day would reduce the average daily <br />salt load c(ownstream of the outfall by 12 to 16 percent for the, 1990-1994 record. <br /> <br />Option 2 \fould reduce IDS concentrations in Fish Creek downstream of the discharge to those , <br />measured' ppstream of the discharge most of the time. This option would not be as effective <br />when disc~arge rates exceeded the treatment system capacity, as during the summer of 1993. <br />Estimated troS concentrations downstream of the outfall with Option 2 are sometimes lower <br />than upstr4am station because the treated water often has lower IDS concentrations than the <br />receiving 4tream, especially during low flow periods. Table 4 indicates that average IDS <br />concentratiPns downstream of the mixing zone for the discharge outfall would decline 'from <br />781 ppm ~ 464 ppm. Since the average IDS concentrations .in Fish Creek at downstrealn <br />Station 30~ is 685 mgn for the 1990-1994, Option 2 would reduce IDS concentrations in Fish ' <br />Creek by 30 to 40, percent which is approximately the same as for Option 1. ' . <br /> <br />AHA P'tlename: 14$;u.cNl.OOC <br /> <br />Page 20 <br /> <br />11,59 AM 09129/95 <br /> <br />, <br /> <br />... . ,-of( .~~ <br /> <br /> <br /> <br />~~; <br />"", "':>l.",,~ <br />