Page 77 - Beaumont Basin Watermaster

Section 4

Water Quality Conditions

The purpose of this section is to document the water quality conditions in the Beaumont Basin
during the 2009-2013 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 antidegradation 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
antidegradation 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-
nitrogen, 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 2009-
2013 reporting period for 42 wells including 21 potable wells. The maximum TDS
concentrations for potable wells ranged from 199 to 415 mg/L and averaged 282 mg/L; this
average value is 27 mg/L higher than the average maximum TDS concentration reported in
the 2008-11 Engineering Report. Of the 21 potable wells, only one well (Ban C-3) had a
maximum concentration below the antidegradation objective, 17 wells were between the
antidegradation and maximum benefit objectives, and 3 wells 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).

Maximum TDS concentrations for the non-potable wells had a much wider range from 100 to
768 mg/L and averaged 319 mg/L just below the maximum benefit objectives. Average
concentrations were slightly below those previously reported in the 2008-11 Engineering
Report. Of the 21 non-potable wells, 3 had a maximum TDS concentration below the
antidegradation objective, 13 wells were between the antidegradation and maximum benefit

Beaumont Basin Watermaster Engineer’s Report No. 3 – 2008-11 (FINAL DRAFT) 4-1