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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
OSWDS is estimated between 1,700 and 3,100 ac-ft/yr. representing 13 to 21 percent
of total recharge to the BMZ.
At 4,900 lots, the contributions from OSWDS will significantly impact water quality to
the point that well head treatment will be required at certain well locations in order to
meet drinking water standards. At 8,800 lots, the contributions from OSWDS will
rendered the entire BMZ non-potable.
Left unmitigated, OSWDS discharges will contribute enough nitrate to exceed the
Basin Plan objectives for the BMZ.
There is sufficient evidence of groundwater contamination by OSWDS to warrant the
Regional Board to issue a prohibition on new OSWDS in the CVCOI.
According to WEI, as a result of this investigation, the County of Riverside issued a
moratorium, followed by a permanent prohibition on the installation of septic systems in Cherry
Valley unless the septic system is designed to remove at least 50 percent of the nitrogen in the
wastewater. In 2009, the County passed a new ordinance that removed the prohibition on
conventional OSWDS. WEI further indicates that the Regional Board initiated a process in
2009 that may lead to amending the Basin Plan prohibiting conventional OSWDS and
regulating the discharges to meet antidegradation objectives.
Summary of University of California, Riverside Study
This study is titled: “Water Quality Assessment of the Beaumont Management Zone: Identifying
Sources of Groundwater Contamination Using Chemical and Isotopic Tracers” (UCR, 2012).
The study divides the BMZ into four distinct zones; their location is depicted in Figure 2 of the
UCR report (not included here). A brief description of the zones is as follows:
Zone 1 – Region Influenced by Wastewater Treatment Plant Effluent. This zone occupies the
southernmost area of the BMZ. Water quality in this zone is influenced by effluent from the
City of Beaumont wastewater treatment plant.
Beaumont Basin Watermaster 2017 Annual Report – DRAFT – February 2018 4-5
