Covering 220 square miles, the Chino Basin is one of the largest groundwater basins in Southern California. It is the water source for the Chino Basin Desalter Authority (CDA), which serves more than a million people. The CDA purifies brackish groundwater extracted from the lower Chino Basin and distributes the drinking water to its member agencies. The desalter plants serve the dual purpose of providing a reliable water supply and managing groundwater quantity and quality in the region.
Most CDA member agencies purchase potable water from the Metropolitan Water District of Southern California (MWD). The purified water produced by the CDA reduces the amount of water that member agencies must buy from MWD.
In 1978, the safe yield of the Chino Basin was established as 140,000 acre-feet per year (afy), but it proved insufficient for the needs of the population, which required reliance on expensive imported or purchased water to make up the difference.
By producing their own potable water supply through wells, the CDA could significantly reduce the cost of potable water for the clients while simultaneously mitigating the historical effects of agriculture and industry activity in the basin. The margin would also provide a reliable source of water during drought or other water shortages, such as reduction in delivery volumes or missed shipments from water wholesalers. In addition, the basin was the site of the South Archibald TCE plume, a toxic contamination in the groundwater first detected in the mid-1980s, which the CDA, as stewards of the basin, have taken on the task of mitigating.
Having worked with Geoscience for well design in the past, the CDA turned to Geoscience to provide design-build services for three groundwater extraction wells in the southern portion of the Chino Basin, where complex water-bearing zones consisting of interlayered sands, gravels, silts, and clays comprise the aquifer system.
Geoscience provided technical specifications and design for the drilling, construction, development, and testing of all three groundwater extraction wells, which provided feed water to the desalter plants. One of the wells also served as a mitigation measure for the cleanup of the TCE plume. This work required additional effort that included identifying a site, developing a design, and constructing the monitoring wells that would track the cleanup process, all in coordination with the Santa Ana Regional Water Quality Control Board, the agency that is overseeing the cleanup.
Once the design was completed, Geoscience provided construction management and field supervision during drilling and construction of all three wells. The wells were drilled using the fluid reverse circulation rotary drilling method. The construction phase included pilot borehole drilling, isolated aquifer zone testing, borehole reaming, well construction, well development, and pump testing.
One well was specifically sited to extract groundwater contaminated with TCE. It was designed to extract groundwater from the complete length of the aquifer but was later modified to extract groundwater only from the contaminated portion. This design allows for future extraction from lower aquifer units once the TCE plume has been mitigated, providing maximum production for CDA. Once the contaminant plume is mitigated, the CDA can easily remove the backfill material to use the well to produce potable water like the other two wells.
All three wells exceeded expectations.
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