Contiguous U.S. surface water availability and short-term trends of wastewater effluent flows in San Antonio, TX.

Surface water is a vital and sometimes stressed resource in the U.S. The quantity of this resource is threatened by population shifts and growth concurrently with climate change intensification. Additionally, growing population centers can impact water quality by discharging treated wastewater effluent, which is typically of lower quality than its receiving surface waters. Depending on baseflow and environmental factors, this could decrease water quality. From a previous model prepared in our lab, this study can improve the understanding of water resource quality and quantity, surface water availability for the contiguous U.S. was estimated for each USGS Hydrologic Unit Code (HUC) during 2015. The Mississippi River generally served as a dividing line for surface water availability, with five of the six regions with very low water availability (<24,000 LD-1Km-2) residing in the west. These same areas also experience more drought as well as more severe droughts than regions in the east. In regions with lower surface water flows, their water quality is more susceptible to the influence of wastewater effluent discharges, especially near large and growing population centers like San Antonio, Texas. A prediction model was established for this city, which found that from 2009 to 2017 wastewater effluent increased by 1.8%. As cities grow, especially in the Southwest and Western U.S. together with intensified climate change, surface water quantity and quality become more crucial to sustainability. This study shows where surface water availability is already an issue and provides a model to estimate, as well as project, wastewater effluent flows into surface water bodies.

An analysis of U.S. wastewater treatment plant effluent dilution ratio: Implications for water quality and aquaculture.

Wastewater discharge and surface flow data from 2007 to 2017 was used to calculate wastewater dilution factors (WWDF) for U.S. Geological Society hydrologic unit codes (HUC) in the contiguous U.S. HUC 10-year average WWDF values generally increased from the east coast (HUC 1-3: WWDF range 125-466) as you move west to the Mississippi River (HUC 7, 8, 10: 1435-1813) before further declining moving west (HUC 13-18: 7-908), particularly in the California (HUC 18: 9) and southwestern states (HUC 13-16: 7-351). Within HUCs, watersheds with higher population centers had lower WWDF values. This population effect on WWDF was greater in drier regions (e.g. Southwestern U.S.) or during drought. This is particularly pronounced in the regions of the Southwest and West where populations are growing in an already water limited region. Moderate WWDF improvement was observed and projected through 2022 in these regions. A few areas of the country where surface water is used for aquaculture overlap with areas of low (<2) WWDF, but it is not widespread for the period examined. With continued population growth and the intensification of climate change, the proportion of treated wastewater effluent in surface waters may grow and potentially influence users of that water, but over the 10-year period examined WWDF values were relatively stable or improving for most regions of the contiguous U.S.