Reclaimed Water Aquifer Storage and Recovery: Potential Changes in Water Quality
Aquifer storage recovery (ASR) operations recharge and recover water through the same well or wells, creating a “bubble” of stored water that typically mixes minimally with ambient groundwater once the storage zone has been developed. Because ASR recharge water does not flow through a vadose zone and is not drawn through an aquifer to a distant point of withdrawal, changes in water quality that occur in surficial aquifer recharge may not apply in ASR operations. Nevertheless, significant water quality changes have been observed during ASR operation, which is of special interest when reclaimed water is stored and recovered. A two-year study was conducted to observe water quality changes in reclaimed water ASR operations at four test sites over differing recharge and recovery periods. The 97 constituents measured at each site included conventional wastewater analytes as well as other constituents of concern, e.g. arsenic, estrone, and carbamazepine. Storage periods ranged from two weeks to eleven months. Where possible, samples were collected from both the ASR well and nearby monitoring wells to assess lateral variations in water quality. Total coliform and heterotrophic plate counts, combined with a reduction in total organic carbon (TOC), nutrients, and dissolved oxygen (DO), suggested microbial activity near the ASR well at most sites. Total trihalomethanes (TTHMs) and haloacetic acids (HAAs) were found to decrease in concentration at three of the four study sites. Pathogens were rarely detected. Microcontaminants exhibited high variability, largely attributed to assumed recharge water variability. Of the trace organics measured, only atrazine showed consisted reduction at all sites detected.