Page 93 - Beaumont Basin Watermaster - DRAFT 2016 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 object ives, 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 for 58 wells measured within and in the
vicinity of the Beaumont Basin wells during the 2012-2016 reporting period. A total of 40 wells
are located inside the basin with the remaining 18 in the Singleton Basin / Edgar Canyon and
the South Beaumont Basin areas.

The maximum TDS concentrations for domestic wells within the basin ranged from 170 to 370
mg/L and averaged 246 mg/L; this average value is 9 mg/L lower than the average maximum
TDS concentration reported in the 2008-11 Engineering Report indicating that TDS
concentrations have been fairly stable in the last 10 years.

In the Singleton Basin / Edgar Canyon area, the maximum TDS concentration ranged from
260 to 550 mg/L and averaged 330 mg/L. The average TDS concentration for all samples in
this area was 311 mg/L.

Beaumont Basin Watermaster 2016 Annual Report – DRAFT – August 2017 4-1