Page 96 - Beaumont Basin Watermaster - DRAFT 2016 Annual Report
P. 96

maximum objectives. Table 4-1 presents the average and maximum TDS and Nitrate (as N)
                 concentration for all the wells in the Beaumont Basin and surrounding areas.


                 4.1.3  Nitrate Studies in the Beaumont Management Zone
                 Rising nitrate concentrations observed in 2005 along the northern portion of the Basin
                 prompted STWMA to launch an investigation in 2006 to determine the potential impact on
                 groundwater quality from on-site waste disposal systems (OSWDS) commonly used in the
                 Cherry Valley Community of Interest (CVCOI).  STWMA retained the services of Wildermuth
                 Environmental Inc. (WEI) to conduct this study.


                 The results of this study were disputed by the Beaumont Board of Supervisors’ Groundwater
                 Quality Evaluation Committee (Committee) as they identified potential shortcomings in
                 sampling design and project execution.  The Committee recommended that an independent
                 assessment be conducted.  They recommended that the second study should expand the
                 study area, consider reasonable build-out projections and other sources of groundwater
                 contamination.  This independent study was conducted by scientist at the University of
                 California, Riverside and funded as a Supplemental Environmental Project by the State Water
                 Resources Control Board.  The results of this study were published in early 2012. A brief
                 summary and their findings is presented below for information purposes only.

                 Summary of Wildermuth Environmental Inc. Study
                 This study is titled: “Water Quality Impacts from On-Site Waste Disposal Systems in the
                 Cherry Valley Community of Interest” (WEI, 2007). The bases for this study include the
                 following:

                    ƒ  A review of scientific literature,

                    ƒ  A field study to estimate nitrogen concentrations in soil water below selected OSWDS,
                    ƒ  A tracer study of nitrogen isotope and pharmaceutical and personal care products
                        (PPCP) to confirm the presence of effluent from OSWDS,
                    ƒ  An estimation of current and future discharge from OSWDS to groundwater,

                    ƒ  A planning-level evaluation of basin impacts using the groundwater flow and nitrate
                        transport model, and
                    ƒ  A review of the threshold used in California to compel sewering when OSWDS
                        contaminate or threaten to contaminate groundwater

                 The results of the investigation are summarized as follows:

                    ƒ  Parcel density in the CVCOI violates the minimum half-acre parcel size requirement of
                        the Regional Board to be on a septic system.

                    ƒ  Water produced from high nitrate wells in the area has a nitrogen isotopic signature
                        and contain PPCPs consistent with discharge from OSWDS.

                    ƒ  Present contribution of OSWDS discharges is estimated at 665 ac-ft/yr.; this represents
                        about five percent of total recharge to the BMZ.  At ultimate buildout, there will be
                        between 4,900 to 8,800 OSWDS in the CVCOI.  Discharge contribution from these



                  Beaumont Basin Watermaster 2016 Annual Report – DRAFT – August 2017                    4-4
   91   92   93   94   95   96   97   98   99   100   101