Application of Transient Transit Time Distribution Theory to Study Salts in Freshwater Reservoirs

Salinization of freshwater has long been considered an environmental problem, which has intensified over the recent years into a nationwide crisis corresponding to increasing salts in drinking water sources. This in particular, is a problem in highly managed reservoirs acting as sources of drinking water, that receive salt from non-point sources (eg. road salt) as well as point sources (eg. indirect potable reuse of wastewater) and hence, building-up of salts in such reservoirs may pose a direct challenge to the increasing reliance on recycled wastewater as a 'new' water resource. With the aim of modeling salt concentrations in the reservoir, we utilized an extensive and a fairly comprehensive historical data set of sodium measurements at the inflow and outflow of a reservoir that is used as a primary source of drinking water for a bedroom community outside of Washington D.C. This study illustrates the development and testing of a transient transit time distribution (transient-TTD) theory, to complement the ongoing sodium management efforts in the reservoir, for predicting sodium concentrations at a drinking water intake location within the reservoir. The theory accounts for a myriad of flow paths possible through the reservoir, resulting in multiple transit times ranging from hours to years and their effects on the fate of sodium. This study also explores the utility of transient-TTD theory as a novel, data-driven approach for modeling reservoirs and to predict sodium transport through a surface water reservoir, including applications for now-casting and potentially forecasting sodium levels in the reservoir and assessing the time required to clear the reservoir of salt, if all point and non-point sources were completely eliminated today.