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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:
A review of scientific literature,
A field study to estimate nitrogen concentrations in soil water below selected OSWDS,
A tracer study of nitrogen isotope and pharmaceutical and personal care products
(PPCP) to confirm the presence of effluent from OSWDS,
An estimation of current and future discharge from OSWDS to groundwater,
A planning-level evaluation of basin impacts using the groundwater flow and nitrate
transport model, and
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:
Parcel density in the CVCOI violates the minimum half-acre parcel size requirement of
the Regional Board to be on a septic system.
Water produced from high nitrate wells in the area has a nitrogen isotopic signature
and contain PPCPs consistent with discharge from OSWDS.
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
