Page 76 - Beaumont Basin Watermaster - 2015 Annual Report
P. 76
1A.- Do areas with septic systems have different chemistry than areas with sewers?
The report indicates that there are statistically significant differences between groundwater in
areas with septic systems and groundwater where sewer service is available. The
concentrations of PPCPs, TDS, Nitrate-N, the sum of base cations, Boron, and Isotopes of
Nitrate were all significantly higher in areas with septic systems than in areas with sewer
service.
1B.- Do areas where groundwater recharge with water from the State Water Project or
wastewater treatment plant effluent have different chemistry from other areas?
Strong evidence of nitrate deriving from human waste was detected in Zone 1 as well as
strong biological attenuation of nitrate transported in groundwater.
2.- What sources contribute nitrate to groundwater of the BMZ?
The report indicates that in Zone 1 the isotopes of nitrate values overlap those expected for
human or animal waste. Similarly, in Zone 3 the isotopic composition of water suggest a high
probability of inputs of nitrate from human or animal waste. The presence of PPCPs in most
samples indicates the possibility that septic systems are contaminating groundwater within the
central part of Cherry Valley.
3.- How much nitrate from human waste is making its way into the groundwater of the BMZ?
The report documents the following findings:
Mixing models suggest that between 18 to 30 percent of the nitrate in central Cherry
Valley groundwater is derived from septic systems.
If septic systems were completely phased out, nitrate concentrations in central Cherry
Valley groundwater could decline by 30 percent once a steady state condition is
achieved. The time to reach a steady state is anticipated to be shorter than in other
portions of the BMZ due to relatively high rates of recharge in Zone 3.
Mass balance calculations show that nitrate-nitrogen inputs from septic systems is one
of the largest inputs of nitrogen to groundwater in the BMZ.
If the waste from septic tanks were to be conveyed to the City of Beaumont WWTP,
about 30 percent of the current input of nitrate from human waste to groundwater
would be removed.
4.2 Comparison with Federal and State Drinking Water
Standards
The California Department of Health Services (CDPH) maintains an active water quality
database of all public and private drinking water wells throughout the state. This database,
available at CDPH’s website, was assessed for the 2011-2015 reporting period for 21
domestic production wells in the Beaumont Basin. The objective of this analysis was to
determine whether any of these potable wells had exceeded the Primary or Secondary
Federal and State standards or the notification levels set by the state. Federal standards are
set by the United States Environmental Protection Agency (USEPA) while state standards in
California are set by CDPH. Primary standards at the federal and state level are enforceable
Beaumont Basin Watermaster 2015 Annual Report – Final – December 2016 4-5
