Freshwater salinization syndrome is a rising threat globally which results in increased ion concentrations in inland freshwaters. This syndrome threatens healthy aquatic ecosystems and can alter the perception of the potability of finished drinking water. The Occoquan Reservoir, located in Northern Virginia, is a freshwater system that is facing rising salinization. Stakeholders for the reservoir have been convened to address these rising salinization concerns. Among these stakeholders, there are a variety of viewpoints on the significance of the salinization, which is preventing a high level of convergence around this threat. To assist in contextualizing this system, empirical cumulative distribution functions were generated from data gathered from various governmental sources and compared the reservoir's watershed and finished drinking water ion concentrations. These analyses show that the watershed and finished drinking water have some of the highest concentrations of sodium and chloride statewide. Additional investigations determined the trend of sodium increases in finished drinking water since the 1980s. Monte Carlo simulations were ran to determined whether there would be risks to human from ingesting this water should this trend continued. Results from these analyses greatly varied due to the wide range in drinking water ingestion rates. The purpose of these analyses is to assist with stakeholder convergence around the level of threat salinization poses to the reservoir and to initiate discussions of what an acceptable threshold for management could be. / Master of Science / Freshwater salinization syndrome is a rising threat globally which results in increased ion concentrations in inland freshwaters. This syndrome threatens healthy aquatic ecosystems and can alter the perception of the potability of finished drinking water. The Occoquan Reservoir, located in Northern Virginia, is a freshwater that is facing rising salinization. Stakeholders for the reservoir have been convened to address these concerns. Among the stakeholders, there are a variety of viewpoints on the significance of salinization. Various analyses were done to compare the sodium and chloride concentrations in the reservoir's watershed and in the finished drinking water with respective statewide levels. These analyses show that the watershed and finished drinking water have some of the highest concentrations of sodium and chloride statewide. Additional investigations were conducted to determine if there was a human health risk to consuming the finished drinking water. Results from this analysis were highly dependent on how much water an individual consumed. The purpose of these analyses is to assist with stakeholder convergence around the level of threat salinization poses to the reservoir and to initiate discussions of what an acceptable threshold for management could be.

Motorboat activity can adversely effect the water quality of a reservoir. The potential impacts of motorboat activity on the Occoquan Reservoir's water and sediments were evaluated. Thirty-one sites, both marina and nonmarina, along the reservoir were selected. Sediment and water samples were collected in 1990, during peak boating activity, and in October, during low boating activity. The objectives of this research were to determine the concentrations of polyaromatic hydrocarbons (PAHs) in water and sediment samples and to determine if their presence was related to boating activity. The presence of other non-PAH organics was also determined. Contours of total PAH concentrations, boxplots and ANOVA analyses between marina and nonmarina sites were generated from gathered data in order to meet these objectives. PAHs were present in the water during peak boating activity and not detected during low boating activity, while PAHS were detected in the sediments during both sampling periods. The aqueous and sediment PAH concentrations were at or below the method detection limits. The PAH ratios of unalkylated PAHs confirmed PAH contamination to be of a combustion source. Boating was shown to be a PAH source to the water column, during peak boating activity, throughout the entire Occoquan Reservoir. An ANOVA between marina and nonmarina sites for the aqueous total PAH concentrations did not show a significant difference in June. This implied that boating did not cause any localized impacts to the water column and that there was another PAH source. There was a significant difference for total PAH concentrations between the marina and nonmarina sites for the sediment samples in June, showing localized impacts at marina areas due to boating activity. PAH profiles showed urban runoff as another major contributor to the PAH concentration in the water and sediments. The urbanization of Hooes Run and the hydrology of the reservoir caused urban runoff to impact localized areas. Finally, atmospheric deposition was also a source of PAHs to the sediments throughout the entire reservoir. Non-PAH organics found in a few of the water and sediment samples were the pesticides atrazine and p,p'-DDD, alkyl phosphates, alcohols and C₈ to C₁₂ hydrocarbons. / Master of Science

Environmental management has increasingly become a participatory process. In recent times, emphasis has been placed on watershed-based solutions to remediate the problems of diffuse source pollution and to engage stakeholders in designing solutions. Water quality models are an integral part of this process; such models are often inaccessible to lay stakeholders. A review of the literature suggests that properly applied partnerships have several benefits that go beyond decision-making. Stakeholder education and enhancements to the eventual outcome from stakeholder insight and support are two such benefits. To aid engineers and scientists, who often do not interact directly with other stakeholders, several best practices were identified that may be applied to develop, manage, and evaluate stakeholder partnerships. Environmental Decision Support Systems (EDSSs) have been shown to be an effective way to promote stakeholder partnerships in environmental decision-making. Many current EDSSs were designed to be used by experts, thus limiting their effectiveness for stakeholder engagement. Often, these EDSSs, if designed for lay stakeholders, were not coupled with water quality models. To demonstrate that complex water quality models may be made accessible to stakeholders, without any significant changes to the modeling scheme, a web-based EDSS was developed for the Occoquan Reservoir, located in northern Virginia, U.S.A., and its tributary watershed. The developed EDSS may also be readily extended to other watersheds and their modeling programs. The current implementation of the EDSS enables users to modify land use and analyze simulated changes to water quality due to these modifications. A local-network server cluster, based on the Locally Distributed Simultaneous Model Execution (LDSME) framework, was also developed and served as a backend to the EDSS. The server cluster can support simultaneous execution of multiple water quality models or any other software on disparate computers. This system was employed to study pre-development and other land use modification scenarios in the Occoquan Watershed. The pre-development scenario offers an easy-to-understand and universally-applicable baseline for measuring waterbody and watershed restoration progress. It enabled computation of a measure called the "developed-excess," which is independent of local conditions and may be used for comparisons among various watershed sub-divisions or between watersheds. / Ph. D.

Increased salinization of inland freshwater resources is present on a global scale, but is pro- gressing rapidly in the densely populated Mid-Atlantic United States. This phenomenon threatens aquatic health, ecosystem services and functionality, and can alter the percep- tion of potable drinking water. The Occoquan watershed, located in Northern Virginia has experienced rapid urbanization across recent decades and is now confronted with rising salinization. Various stakeholders in the area have focused efforts to quantify the drivers of salinization in order to take corrective action to preserve this resource. To aid these efforts, urbanization's relationship with in-stream salinity was analyzed, where its exerted influence was found to be dependent upon overland hydrologic flowpaths which connect urban areas to stream networks. The analysis was then broadened to Multiple Linear Regression models of urban and climatological drivers to statistically quantify each driver's relative influence on in-stream salinity. The models demonstrated that urbanization is the primary driver, where rainfall and roadway deicer application were also found to be significant. The model was then used to predict the magnitude of salinization in the Occoquan watershed to a time horizon of 2040 based on expected population growth as well as two anticipated climate scenarios. Finally, the analytical framework produced in this research was generated with scalability in mind, such that it can potentially be utilized as a watershed-scale screening tool accross the Mid-Atlantic, to inform proactive, regionally appropriate management decisions. / Master of Science / Increased salinization of inland freshwater resources is present on a global scale, but is progressing rapidly in the densely populated Mid-Atlantic United States. Driven by the engineered systems that define our modern world, this phenomenon threatens aquatic health, ecosystem services and functionality, and can alter the perception of potable drinking water. The Occoquan watershed, located in Northern Virginia has experienced rapid urbanization across recent decades and is now confronted with rising salinization. Various stakeholders in the area have focused efforts to quantify the drivers of salinization in order to take corrective action to preserve this resource. The analyses completed in this body of work act to model and statistically analyze the drivers which foster salinization in the Occoquan. The analyses demonstrated that while climatological factors drive salinity in the Occoquan, urbanization is the primary driver, where its exerted influence is dependent upon overland hydrologic flowpaths which connect urban areas to stream networks. Further analyses were completed to project salinization to a time horizon of 2040 based on expected population growth as well as two anticipated climate scenarios to predict the magnitude of salinization in the Occoquan watershed in decades to come. These results indicated that anticipated levels of in-stream salinity will increase across most sampling stations in coming years. Finally, the analytical framework produced in this research was generated with scalability in mind, such that it can potentially be utilized as a watershed-scale screening tool accross the Mid-Atlantic, to inform proactive, regionally appropriate management decisions.

This project reviewed the ability of hydrilla to release THM-precursors should this plant become established in the Occoquan Reservoir. It was found that the Occoquan Reservoir could support hydrilla. Three sources of THM-precursors were found to result from hydrilla. These included: 1) extracellular products (ECP) from hydrilla itself; 2) ECP from periphyton that colonized the hydrilla; and 3) decay products from hydrilla. This study projected aa potential increase in THMFP of 23 ug/L should hydrilla become established in the Occoquan. The current level of THMFP in the H reservoir is approximately l,OOO ug/L. / Master of Science

The phytoplankton data from Occoquan Reservoir surface samples collected during 1970-1988 were entered into a database. The data were analyzed to determine the relationships between changes in phytoplankton succession patterns and the various physical and chemical water-quality variables. The investigation considered the variations in both the phytoplankton and the water-quality variables with respect to sampling station location along the length of the reservoir. The variables included rainfall, season, pH, alkalinity, nitrogen, phosphorus, copper sulfate, odor intensity and type, and chlorophyll-a. The discharge from the Upper Occoquan Sewage Authority advanced wastewater treatment plant (UOSA AWT) had a noticeable influence on both the phytoplankton division dominance and the genera occurrence. Before the AWT plant was built, Chlorophycota was usually dominant; afterwards, Bacillariophycota dominance increased. The dominant genera were a subset of the genera that occurred frequently. Of the original 72 genera, an analysis of 9 prevalent genera would have provided virtually the same information. Neither the intensity nor type of odors observed were predictable on the basis of the phytoplankton genera present in the reservoir. No statistically valid conclusion could be reached about the impact that copper sulfate applications had on reservoir algae. / Master of Science

The Occoquan Reservoir is part of the largest indirect potable reuse systems in the United States. It in an important water supply source for the Northern Virginia area, as well as, an ecological and recreational area. Furthermore, the Occoquan Reservoir protects the water quality of the Chesapeake Bay because it acts as a trap for sediments and pollutants. Continuous water quality monitoring and evaluation is critical to preserve this important water resource. Reservoir water quality can be affected by the delivery of pollutants from point and nonpoint sources, potentially causing problems such as eutrophication, excess salinization, presence of compounds that affect human and aquatic health. Different management strategies have been implemented at the Occoquan Reservoir to nutrient loading into the reservoir and address eutrophication issues, including nitrate addition to hypolimnetic waters and installation of a hypolimnetic oxygenation system. The goal of this study is to assess how current management strategies implemented in the Occoquan Reservoir have affected the water quality from 1973 to 2019, with particular emphasis on the data since 2003. This analysis of the Occoquan Reservoir and its tributary watershed includes the evaluation of hydrometeorological data and morphometric characteristics; establishment of long-term trends for water quality constituents; and determination of the trophic state of the reservoir. Data from water samples from four different stations located at the Occoquan Reservoir and four stations located throughout the Occoquan tributary watershed were analyzed for nutrients, principal ions and metals, synthetic organic compounds (SOCs), and other water quality parameters. Long-term water quality trends were determined using Mann-Kendall test and relationship between constituents was evaluated using Principal Component Analysis (PCA). Trophic state of the reservoir was assessed using Carlson's Trophic State Index (TSI), Vollenweider Model, and Rast, Jones, and Lee's Model. Results indicate the Occoquan Reservoir is a eutrophic waterbody. However, the nitrate management strategy and the installation of the hypolimnetic system have improved reservoir water quality, reducing concentrations of nutrients and metals. / Master of Science / The Occoquan Reservoir is part of the largest indirect potable reuse systems in the United States. Indirect potable reuse refers to the planned discharge of reclaimed water into a water supply source, such as a reservoir or lake. The Occoquan Reservoir also serves as an ecological and recreational area, and serves to protects the water quality of the Chesapeake Bay because it acts as a trap for sediments and pollutants. To protect the different ecosystem services that the reservoir provides, it is critical to continuously monitoring and evaluate its water quality. Reservoir water quality can be affected by the delivery of pollutants from industrial and municipal waste discharges (point sources), as well as, from urban and agricultural runoff (nonpoint sources). Contaminants include nutrients (such as nitrogen and phosphorus), ions, metals, and synthetic organic compounds (SOCs) that can affect human and aquatic health. Different management strategies have been implemented at the Occoquan Reservoir to reduce load of pollutants into the reservoir, particularly to reduce concentrations of nutrients, as excessive nutrients can degrade water quality. Two strategies implemented are the addition of nitrogen, in the form of nitrate, and the installation of an oxygenation system at the reservoir bottom waters. The goal of this study is to assess how current management strategies implemented in the Occoquan Reservoir have affected the water quality from 1973 to 2019, with particular emphasis on the data since 2003. This analysis of the Occoquan Reservoir and its tributary watershed includes the evaluation of the hydrological, meteorological, and morphometric characteristics of the Occoquan Reservoir and Watershed; establishment of long-term trends for water quality constituents; and determination of the productivity (trophic state) of the reservoir. Data from water samples from four different stations located at the reservoir and four stations located throughout the watershed were analyzed for nutrients, principal ions and metals, SOCs, and other water parameters indicative of water quality. Statistical analyses were employed to determine long-term water quality trends (Mann-Kendall test) and relationship between constituents (Principal Component Analysis - PCA). The trophic state of the reservoir was assessed using three methods: Carlson's Trophic State Index (TSI), Vollenweider Model, and Rast, Jones, and Lee's Model. Results indicate the Occoquan Reservoir is eutrophic, or highly enriched with nutrients and productive. However, management strategies employed have improved the water quality and the reservoir continues to improve, though at a slow rate.

The Occoquan Reservoir is a public water supply in northern Virginia. The Occoquan Watershed has developed over the years from rural land uses to metropolitan suburbs within easy commuting distance from Washington, DC. Due to this urbanization, the Occoquan Reservoir is especially vulnerable to hypereutrophication, which results in problems such as algal blooms (including cyanobacteria), periodic fish kills, and taste and odor problems. In the 1970's, a new management plan for the Occoquan Reservoir called for the construction of the Upper Occoquan Sewage Authority (UOSA), an advanced wastewater treatment plant that would take extraordinary measures for highly reliable and highly efficient removal of particulates, organics, nutrients, and pathogens. Eliminating most of the water quality problems associated with point source discharges in the watershed, this state-of-the-art treatment is the foundation for the successful indirect surface water reuse system in the Occoquan Reservoir today. A limnological analysis of thirty years of water quality monitoring data from the reservoir and its two primary tributaries shows that the majority of the nutrient and sediment load to the reservoir comes from nonpoint sources, which are closely tied to hydrometeorologic conditions. Reservoir water quality trends are very similar to trends in stream water quality, and the tributary in the most urbanized part of the watershed, Bull Run, has been identified as the main contributor of sediment and nutrients to the reservoir. Despite significant achievements in maintaining the reservoir as a source of high quality drinking water, the reservoir remains a phosphorus-limited eutrophic waterbody. / Master of Science

Increased salinity in freshwater systems – also called the Freshwater Salinization Syndrome (FSS) – can have far-ranging implications for the natural and built environment, agriculture, and public health at large. Such risks are clearly on display in the Occoquan Reservoir – a drinking water source for roughly one million people in the northern Virginia/ National Capital Region. Sodium concentrations in the Occoquan Reservoir are approaching levels that can affect taste and health. The Reservoir is also noteworthy as a flagship example of indirect potable reuse, which further adds complexity to understanding the sources of rising levels of sodium and other types of salinity. To help understand the role residential discharges might play in salinization of the Occoquan Reservoir, a suite of laundry detergent products was identified based upon survey data collected in the northern Virginia region. The ionic compositions of these products were then characterized using ion chromatography and inductively coupled plasma-mass spectrometry to quantify select ionic and elemental analytes. Sodium, chloride, and sulfate were consistently found in appreciable amounts. To comparatively characterize the laundry detergents, principal component analysis was employed to identify clusters of similar products. The physical formulation of the products was identified as a marker for their content, with dry formulations (free-flowing and encapsulated powders) being more enriched in sodium and sulfate. This result was corroborated by comparing nonparametric bootstrap intervals for individual analytes. The study's findings suggest an opportunity wherein consumer choice can play a role in mediating residential salt inputs in receiving bodies such as the Occoquan Reservoir. / Master of Science / Many streams, rivers, and other freshwater systems have become increasingly salty in recent decades. A rise in salinity can be problematic, stressing aquatic life, corroding pipes, and even enhancing the release of more pollutants into the water. This phenomenon, called Freshwater Salinization Syndrome, can threaten such systems' ability to serve as sources of drinking water, as is the case for the Occoquan Reservoir in northern Virginia. Serving roughly one million people, the Reservoir is notable for being one of the first in the country to purposely incorporate highly treated wastewater upstream of a drinking water supply. Despite the Reservoir's prominence, the reasons behind its rising salt levels are not well understood. This study sought to understand the role that individual residences could play when household products travel down the drain and are ultimately discharged into the watershed. Laundry detergents are potentially high-salt products. A survey of northern Virginian's laundry habits was conducted to understand local tastes and preferences. Informed by the survey, a suite of laundry detergents was chemically characterized to measure salt and element concentrations. The detergents were found to have notable amounts of sodium, chloride, and sulfate in particular, with sodium being the most abundant analyte in every detergent. However, not all detergents were equally salty; statistical tools revealed that dry formulations (such as powdered and powder-filled pak detergents) contributed more sodium and sulfate, among other things. This study's findings suggest that laundry detergents could be contributing to Freshwater Salinization Syndrome in the Occoquan Reservoir, and that local consumers' choice of detergents could make a difference.