Sanders, E. C. AND Y. YUAN. Fecal Coliform and E. coli Concentrations in Effluent-Dominated Streams of the Upper Santa Cruz Watershed . PATHOGENS. MDPI AG, Basel, Switzerland, 5:243-261, (2013).
Balancing water quality and water quantity concerns is an ongoing challenge for communities in the semi-arid southwest. Over pumping of groundwater aquifers and limited surface water resources have created effluent-dominated sections of watersheds. As rapid urbanization increases, the demand for potable water will also increase placing additional stress on the limited water resources. This study assesses the water resource management activities in the Upper Santa Cruz Watershed in southern Arizona in terms of pathogen concentrations discharged as effluent and from nonpoint sources into the Santa Cruz River and surrounding tributaries. Assessment of the available wastewater water treatment plant (WWTP) effluent data indicated that 14 to 29 percent of discharge monitoring report (DMR) periods contained values exceeding the water quality criteria established for fecal coliform and E.Coli. Analysis of available in-stream grab samples resulted in 16 to 34 percent of sample concentrations exceeding the 400 colony forming units (cfu) per 100ml sample maximum for fecal coliforms and 34 to 75 percent of samples exceeding the full body contact (FBC) standard of 235 cfu/100ml established for E Coli. The use of wastewater for municipal supplies and groundwater recharge may maintain water supplies; however, the impact to human and ecosystem health is not clearly understood or captured by current regulatory standards. The lack of available data limits the robustness of this assessment and thus demonstrates the need for more data collection and additional investigation into potential risks associated with effluent-dominated rivers on public health and ecosystem services.
In the semi-arid southwest, rapid urbanization and population growth has lead to increased use of wastewater. Many river sections are effluent-dominated in order to maintain perennial flow and ecosystem services due to low annual precipitation. Effluent discharge into stream channels helps to recharge the groundwater aquifers and supports riparian habitation. For example, the Arizona Department of Water Resources (ADWR) Active Management Area (AMA) along the Santa Cruz River implemented groundwater recharge sites using effluent from municipal wastewater treatment plants with the specific purpose of maintaining groundwater levels in the watershed . In addition to artificially maintaining perennial flow and recharging groundwater aquifers in the semi-arid regions, wastewater effluents are also used for agricultural or other irrigation purposes (e.g. golf courses or landscaping). Reusing wastewater effluent for agricultural or other irrigation purposes may benefit stream quality by reducing nutrient and contaminant loading to surface water bodies; however, the impacts of this practice in terms of risks to public health, soil quality, and crop health are not fully understood . In semi-arid regions where water quantity is of concern, reliance on reclaimed effluent for perennial streamflow potentially endangers human health through recreational exposure and contamination of potable water supplies by increasing microbial pathogen concentrations in surface waters and ground waters [2-4].