Final report on isotope tracer investigations in the Forebay of the Orange County groundwater basin.
California is currently faced with some critical decisions about water resource infrastructure development in highly urbanized regions, whose outcome will dictate the future long-term viability of plentiful water. Among these is developing and safely implementing the reuse of advanced treated waste water. One of the most reliable strategies for this water resource is its indirect reuse via groundwater recharge and storage, with particular emphasis on supplementing annual water demand or during drought relief. The Orange County Water District (District) is currently implementing the first phase of a large-scale water reuse project that will advance-treat up to 60 million gallons per day of waste water and recharge it into existing percolation basins in the Forebay region of the Orange County groundwater basin. In order for the District to protect public health, the fate and potability of this recharged waste water needs to be understood. In particular, the direction and rates of flow into underlying aquifers need to be characterized so that changes in water quality can be quantified between the recharge basins and points of production. Furthermore, to ensure compliance to California Department of Health Services (DHS) draft regulations, the direction and rate of recharged waste water from these basins need to be understood to sufficient detail that small mixtures can be delineated in monitoring and production wells. Under proposed DHS guidelines, consumptive use of recycled water is permissive only if its residence time in an aquifer exceeds a specified six-month time-frame. DHS guidelines also limit the percentage of recycled water at production wells. However, attaining such detail using current hydrogeological and computer-assisted modeling tools is either cost-prohibitive or results in uncertainties too large to achieve regulatory confidence. To overcome this technical barrier, the District funded Lawrence Livermore National Laboratory (LLNL) from 1995-2001 to directly measure groundwater ages and perform two artificial tracer studies using isotope methods to quantify flowpath directions, groundwater residence times, and the rate and extent of recharge water and groundwater mixing. In addition, Jordan Clark at University of California, Santa Barbara also performed an artificial tracer experiment using sulfur-hexafluoride, whose results have been integrated into the LLNL findings.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15013774
- Report Number(s):
- UCRL-TR-201735; TRN: US200803%%777
- Country of Publication:
- United States
- Language:
- English
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