AWWA WQTC63991

Unintentional, indirect wastewater reuse is occurring as upstream wastewater treatment plant discharges impact downstream drinking water treatment plants. The anticonvulsant pharmaceutical primidone was measured because it is considered to be a conservative tracer of wastewater influences in drinking-water supplies (i.e., stable in the environment and not naturally occurring). Primidone in the wastewater treatment plant effluents, whose plants did not use reverse osmosis membranes, was typically present at ~100-200 ng/L levels. At the reverse osmosis plants, primidone was not detected. Based on primidone and/or flow data, drinking-water supplies that had >50-percent wastewater contributions were classified as effluent-dominated. For drinking-water supplies that had 10-50 or <10-percent wastewater, they were classified as effluent-impacted or low impact, respectively. During low-flow conditions in the rivers studied, wastewater effluents had a larger impact. However, primidone was not detected at drinking water treatment plant influents that were on very large lakes or rivers in which the primidone from upstream wastewater treatment plants was diluted below the minimum reporting level (i.e., 8 ng/L). At monitoring wells in basins recharged with treated wastewater, soil aquifer treatment removed a significant portion of the dissolved organic carbon in the wastewater treatment plant effluent, whereas the concentration of primidone was relatively conservative. The concentration of primidone was found to be a good indicator of wastewater contributions to river flow or groundwater recharge. Includes 10 references, tables, figures.