WSP06151

• File Number: 8274.400
• Description: Colorado River Basin Salinity Control - General Basinwide Salinity Issues - NPDES
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 9/1/1995
• Author: Applied Hydrology
• Title: Salinity Control Study - NPDES Permit No. CO - 0042161 - Prepared for Twentymile Coal Company
• Water Supply Pro - Doc Type: Report/Study

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NPDES Permit No. CO-0042161
SalinitYl Control Study

Twentymile Coal Company

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4.0

.Evaluation of Options

This eva\uation of salinity control options includes an analysis of the potential changes in~a1t
loading, flows, and IDS concentrations in Fish Creek resulting from the various options,and
an assessjnent of the feasibility and costs of the treatment technology options considered in this
evaluation.

4.1 Sillt Loading

Estimated: salt loading and concentrations below the mixing zone of the discharge outfall are
given in !I'ables 3 - 5 for the three options described in Section 3. These estimations are
adapted !'tom the baseline salt loading spread sheets in Table I and 2. These 'analyses are
performe<{ on the monthly average flows and IDS concentration in the records from April
1990 through September 1994. '

4.1.1 Option 1: Complete Injection

Under the ifirst option, wherein all discharge is disposed of in deep wells, the average monthly
flows and ~altloads, in Table 3 for Fish Creek upstream of the discharge points (Station ,16) lire
also the estimated monthly flows and salt loads downstream of the discharge outfall. ,

This optiol1 results in the greatest possible reduction in salt loading. The average daily salt
load detenp.ined from measurements at thedischarge outfall is estimated to be 1.83 tons/d~y
for the 1990-1994 record. The average daily salt load in Fish Creek downstream of the
discharge ~utf!lll for the 1990-1994 record is estimated to be 9.35 tons/day, compared tb
12.9 tons/d,ay determined from measurements at Station 302' downstream of the discharge
outfall for ~is'period. Complete elimination of discharge would thus reduce the salt load in
Fish Creek iby 14 to 20 percent.

Complete slllt elimination would also reduce TDS concentrations in Fish Creek downstream of
the discharte, although the reductions would be apparent primarily during low flow periods.
Table 3 in4icates that average IDS concentrations downstream of the mixing zone for the
discharge o~tfall would decline from 781 ppm to 463 ppm with complete salt elimination. The
average ID~ concentration in Fish Creek measured at Station 302 downstream of the discharge
outfall is 6~5 mg/I for the 1990-1994 record, Complete elimination of discharge would thus
reduce ID~ concentrations in Fish Creek by 30 to 40 percent (most of the reduction occurs
during low flow periods). ~

AHA Ftlename: I4SALCNl.OOC

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