Tracing waste-water in river and ground water of Orange County using boron isotopes and general geochemistry

摘要

Surface water runoff within the Santa Ana River (SAR) watershed is generated from a variety of sources, including a mountain snowmelt, urban waste-water discharge, and dairy feedlots. During summer baseflow periods, the persistent flow of approximately 200 cubic feet per second (cfs) consists almost entirely of tertiary-treated waste-water from upstream urban discharge. The Orange County Water District (OCWD) artificially recharges the majority of flow from the SAR during high and low flow periods into the Forebay region to augment groundwater pumping demands. Proposed regulations for reclaimed water recharge into portable use aquifers have direct impact on how OCWD manages groundwater recharge from the SAR. Knowledge of how much treated waste-water recharges into the Forebay area of the Orange County Groundwater Basin has direct benefit to future management and regulatory activities. This project attempted to trace the inorganic components of waste-water dissolved in the SAR and local groundwater in the Forebay by applying geochemical and boron isotopic systematics. The objectives were to characterize the chemical and boron isotropic compositions of recharged surface water and groundwater, to delineate typical mixing end-members, and to examine if recharge water from the SAR has a different isotopic signature relative to non-anthropogenically-influenced groundwater. The overall goal is to test whether a combination of boron isotopes and water chemistry will provide an accurate means to quantifiably distinguish waste-water from non-waste water sources in surface and groundwater of the Forebay.