Arizona Water Resource Volume 11 Number 4

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4 Arizona Water Resource May - June 2003 Recharging Treated Water May Alter Groundwater Quality Arecent U.S Geological Survey study found that recharging an aquifer with treat- ed surface water may affect groundwater quality. The study sounds a warning to offi- cials who are considering injecting and stor- ing treated water underground to improve water supply and availability. The process may affect the future usability of the water. The study found that when treated surface water recharges an aquifer, the by- products of the water disinfection pro- cess accumulate in the aquifer. Included among the by- products are trihalomethanes (THMs), formed when chlorine reacts with organic matter in an aquifer. Further, extracted water still contained measurable concentrations of THMs long after a great- er volume of water had been pumped than injected. THMs are carcinogenic compounds, and their con- centrations in drinking water are regulated by the U.S. Envi- ronmental Protection Agency. The mean total concentration of THMs in the aquifer was estimated to be 58 micro- grams per liter. The EPA's stated maximum level for THMs is an annual average of 0.08mg /1. According to the study THMs continued to form in the aquifer until the residual disinfectant (chlorine) in the injected surface water is used up, and that bacteria in the aquifer does not consume significant amounts of THMs. THM concentrations in the water extracted from the aquifer decreased over time History repeats itself. In 1934, Arizona Governor B.B. Moeur sent a contingent of National Guardsmen to prevent the building of a dam on the Colorado Riven In pursuit of is battle objectives it requisitioned a ferryboat, and newspapers gleefully dubbed the contingent the Arizona Navy. "Above is a leaner, meanerAri .Zona navy, with the `Gov. B.B Moeur" submarine gliding under London Bridge in Lake Havasu, The digitally composed photo was used by Herb Guenther in a pomerpointpresentation at the Water Resources Research Cen- ter Prescott conference. California take note. (Photo: Arizona Department of Dater Resources) as the injected water mixed with the native groundwater in the aquifer. The re- searchers say THMs formed in the aquifer are very dif- ficult to remove completely. In the course of the study, only 67 percent of the chloride and THMs injected into the aquifer system were recovered after 132 percent of the volume of the injected water had been extracted. With 250 percent of the volume of injected water removed from the aquifer 80 percent of the injected THMs had been recovered. Miranda Fram, lead author of the study, says the accumulation of THMs could be minimized by removing the re- sidual chlorine in the water before injection or by modifying the extraction program. The USGS report, "Processes Affect- ing the Trihalomethane Concentrations As- sociated with the Third Injection, Storage, and Recovery Test at Lancaster, Antelope Valley, California, March 1998 through April 1999" by Miranda S. Fram, Brian A. Ber- gamaschi, Kelly D. Goodwin, Roger Fujii, and Jordan E Clark can be found at: http: //water.usgs.gov/pubs/wri/wri034062/. New ASU Center Studies Urban Environment Arizona State University's newly estab- lished Consortium for the Study of Rapidly Urbanizing Areas will have a 486 - square mile laboratory as it focuses on the City of Phoenix. One of the fastest growing urban regions in the country, the Phoenix area is suited for the role, its rapid urbanization raising demographic, environmental and other issues. Water resources will be one of the areas to be studied.