Maximizing Recycled Water Recharge in the Chino Groundwater Basin, California

The Chino Basin Groundwater Recharge Project is a comprehensive water supply project that includes maximizing recycled water recharge. This paper focuses on critical components, challenges, and successes of the start-up process of recycled water recharge operations that are enabling Inland Empire Utilities Agency (IEUA) to maximize recharge recycled water. It will also present results of the start-up procedures of one program recharge basin (Banana Basin).IEUA is currently permitted by the California Department of Health Services (DHS) and the Regional Water Quality Control Board to recharge recycled water at five recharge basin sites (Phase I). IEUA will be adding six more recharge sites to the program (Phase II) resulting in approximately 23,700 AF/year of recycled water recharge. IEUA's groundwater recharge permit outlines compliance demonstration, limits, and reporting requirements, including the completion of start-up protocols. IEUA's start-up protocols utilize lysimeter based monitoring during a start-up period to determine the effectiveness of site specific soil-aquifer treatment (SAT) on recycled water quality. Results of the start-up period impact the relative volumes of recycled water that can be recharged at each site. At Banana Basin, recycled water total organic carbon (TOC) concentrations ranging from 6 to 10 mg/L are generally reduced to about 2 mg/L by SAT by the time recharged water percolates to the 25-foot deep lysimeter and may continue at greater depths. Although a TOC of 2 mg/L in the compliance point lysimeter would allow a Recycled Water Contribution (RWC) of 25 percent using a water quality based formula, the current limit on RWC for Banana Basin is 20 percent until formal approval by California DHS is received.Challenges faced by IEUA in the start-up of recycled water recharge include developing a new recharge program within the historical recharge constraints of California DHS's draft groundwater recharge regulations, implementing a meaningful start-up period of continuous recharge in the shadow of a permitted maximum RWC, developing compliance monitoring programs for basins that are impacted by periodic high TOC storm water runoff, and sample location selection in a widely distributed basin network having multiple recycled water sources.The recycled water provided by IEUA is of excellent quality and is a reliable source water for groundwater recharge. The start-up protocols developed by IEUA demonstrated that SAT is an effective means of further polishing recycled water quality by reducing TOC and TN. Recharge using recycled water is an important step towards sustaining growth, maximizing recharge, and providing drought tolerance within the Chino Basin.