Fate of organochlorine compounds during aquifer storage and recovery: the Las Vegas experience

Two water quality concerns with aquifer storage and recovery (ASR) operations are (1) the fate of organochlorine compounds, such as trihalomethanes (THMS), in the treated recharge source, and (2) the formation of organochlorine compounds from precursor materials following the chlorination of recovered water. The fate of chloroorganic compounds in chlorinated Colorado River water was studied during a 1989 recharge/recovery operation conducted by the Las Vegas Valley Water District (LVVWD). Water samples were obtained from two dual-purpose wells during the pumping cycle for THMs and other indicators of organochlorine precursors. The percentage recovery of THMs was approximately the same as the percentage recovery of Colorado River water. This suggests that the removal of organochlorine compounds (e.g., by sorption) did not appreciably occur in the aquifer materials at the two well sites. Recovery of source water was incomplete. Accordingly, dissolved organic carbon (DOC), representing precursor material, remained in the aquifer at the end of the pumping cycle. The Las Vegas experience suggests that prolonged recharge and storage of Colorado River water in similar hydrogeologic basins (e.g., the Tucson basin) could result in problems with THM compliance at the well head. This will be a problem if THM standards are reduced during the interval that water is stored