- © 2013 Association of Environmental & Engineering Geologists
In 2008, Lake Havasu City, Arizona, began a treated wastewater subsurface recharge program at its North Regional Wastewater Treatment Plant (NRP) to store treated wastewater, which is planned to be seasonally recovered for irrigation during the summer months. As a proactive measure, the city decided to monitor a suite of pharmaceuticals and other emerging contaminants (PECs) along with required regulatory constituents, e.g., nitrate. Potential contributing sources of PECs throughout the water system were identified, resulting in only six constituents detected in the untreated drinking water and treated drinking water, all at concentrations less than 50 ng/L. Thirty-three of 40 PECs analyzed were identified in the city's treated wastewater streams, with concentrations ranging from just above the detection level to 9000 ng/L (pseudoephedrine), clearly showing the dominating local urban use of these compounds. NRP treated wastewater is recharged via vadose zone injection wells. It migrates through alluvial fans sediments, some containing interstitial clays, forming a water mound and blending with groundwater of the Colorado River Aquifer. Sixteen of 33 PECs present in the NRP treated wastewater have concentrations above detection limits (>10 ng/L) within 150 m (492 ft) of the injection wells. Six PECs (sulfamethoxazole, carbamazepine, primidone, phenytoin, N,N-diethyl-meta-toluamide [DEET], and meprobamate) remained above their respective detection limit in monitoring wells that penetrate sediments largely free of clay more than 560 m (1,840 ft) away from the injection wells.