Page 72 - Beaumont Basin Watermaster - 2015 Annual Report

Section 4

Water Quality Conditions

The purpose of this section is to document the water quality conditions in the Beaumont Basin
during the 2011-2015 reporting period. TDS and nitrate concentrations in the basin are
compared against groundwater quality objectives for anti-degradation and maximum benefit as
established by the Regional Board for TDS and nitrate-nitrogen in the Beaumont Management
Zone (BMZ). In addition, water quality concentrations for a number of compounds are
compared against Federal and State Drinking Water Standards. Figure 4-1 depicts all the
wells that have groundwater quality data for the reporting period.

4.1 Comparison with Management Zone Objectives
Groundwater quality objectives for anti-degradation and maximum benefit have been
established by the Regional Board for TDS and nitrate-nitrogen in the BMZ, which
encompasses portions of the Beaumont Basin, the Singleton and South Beaumont basins, and
limited portions of Edgar Canyon above the Banning Fault as illustrated in Figure 4-1. The
anti-degradation objectives are based on the historic ambient TDS and nitrate-nitrogen
concentration of 230 mg/L and 1.5 mg/L respectively.

The maximum benefit objectives were adopted by the Regional Board in 2004 at the request
of STWMA and Beaumont to allow for recharge of imported water and the reuse of recycled
water. The maximum benefit objectives, set to 330 mg/L for TDS and 5.0 mg/L for Nitrate-N,
are relatively low compared to other basins and are protective of the beneficial uses of the
Basin groundwater. According to the Basin Plan, salt mitigation will be required once the
ambient TDS and nitrate-nitrogen concentration exceeds the BMZ maximum benefit
objectives.

4.1.1 Total Dissolved Solids

Figure 4-2 shows the maximum TDS concentrations measured at Basin wells during the 2011-
2015 reporting period for 65 wells including 29 domestic wells owned by Appropriators or by
Overlying Parties. The maximum TDS concentrations for domestic wells ranged from 190 to
415 mg/L and averaged 277 mg/L; this average value is 22 mg/L higher than the average
maximum TDS concentration reported in the 2008-11 Engineering Report indicating that TDS
concentrations are on a slight uptrend in the last seven years. Of the 29 potable wells, four
wells had a maximum concentration below the anti-degradation objective of 230 mg/L, 23
wells were between the anti-degradation and maximum benefit objective of 330 mg/L, and
three exceeded the maximum benefit objective for the BMZ. None of the production wells
samples exceeded the secondary federal or state drinking water standard for TDS (500 mg/L).
BCVWD wells along Edgar Canyon were not included in this analysis.

Maximum TDS concentrations for the non-domestic wells had a much wider range from 203 to
1,100 mg/L and averaged 435 mg/L just below the maximum benefit objectives. Average
concentrations were approximately 110 mg/L higher than those previously reported in the

Beaumont Basin Watermaster 2015 Annual Report – Final – December 2016 4-1