AWWA REUSE52130

Groundwater recharge with recycled wastewater is viewed as a necessity in water-short areas. In California, the coastal overdraft situation is already alarming and threatens to become worse. The purpose of groundwater recharge with recycled wastewater is to stop declining levels of groundwater, protect the coastal aquifers against saline intrusions, provide inexpensive storage and transmission of the recharged water, ameliorate problems of land subsidence, and provide additional treatment of the recycled water. This paper presents the case study of West Coast Basin, which provides about 20% of the potable water supply in the West Basin Municipal Water District (WBMWD) service area. In order to halt further seawater intrusion, the West Coast Basin Barrier Project (WCBBP) was initiated by the Los Angeles County Department of Public Works (LADPW) and involves the injection of potable water in order to maintain groundwater levels high enough to prevent further seawater intrusion. In mid- 1995, WBMWD began producing recycled wastewater, which is currently blended with potable water prior to injection. The main goal of a new R&D program, started in 1998, is to provide a technical and scientific basis to better understand the transport of recycled wastewater within the West Coast Basin. An important regulatory issue for approving the operation of indirect potable reuse projects, is the tracing and modeling of the behavior of recycled wastewater in the aquifers. Simulations using a groundwater flow, solute transport and salt water intrusion models in the West Coast Basin were carried out in 1993 to address regulatory requirements relating to injection of recycled wastewater into the WCBBP. Earlier model simulations evaluated the effectiveness of the barrier in preserving the aquifers from saline intrusion and in controlling the advancement of inland saline plumes. This paper presents the first results of the application of a new hydrodynamic and hydrodispersive geographic information system (GIS) model, taking into account the differences in density of salt water and the use of boron isotopes for recycled wastewater tracing purposes. Includes 6 references, tables, figures.