ABSTRACT
The Orange County Water District (OCWD) manages the Orange County Groundwater Basin located at the southern end of the Los Angeles Coastal Plain. The Basin provides 75% of the water demands for about 2.2 million residents. To date, the district has recharged more than 7,000 million m3 of imported and native waters. The first artificial recharge facilities constructed in the 1950s used the natural channel of the Santa Ana River. Later, the district began purchasing land and constructing conveyance systems for the development of the deep basins near the river. By the early 1990s, the district had developed more than 4 km2 of land into shallow spreading facilities and deep recharge basins. In total, the system, when clean, can percolate about 14 m3/s (0.3m/d).
The ordinary flow of the Santa Ana River began increasing in the early 1970s due to the expansion of wastewater treatment plants discharging tertiary treated effluent into the river upstream. The nutrient content of these waters, subsequent microbial growth and the accumulation of naturally occurring silt, cause a continued reduction in the percolation rate of the recharge system. The district has developed and tested many remedial procedures to counter the ‘clogging’ phenomenon. The paper describes these remedial measures and identifies those procedures that were successful in restoring recharge rates as well as those which were not effective.
Additionally, the lowering of groundwater levels along the coast in response to increased pumping required the construction of a seawater intrusion control project in the mid-1970s. The waters, injected to form a pressure mound along the intruded area, are treated sewage; processed by an advanced waste water treatment (AWT) system (Water Factory 21), that meets all drinking water standards. To date, more than 150 Mm3 of highly treated wastewaters have been injected into the basin. The district is in the process of replacing and expanding the existing system with an 3–6 m3/s (310 ML/d) AWT system.
