Modeling Nicotine-Induced Chlorine Loss in Drinking Water Using Updated EPANET-MSX.

Multispecies water quality modeling is critical for simulating complex chemical reactions in drinking water distribution systems. An updated EPANET 2.2-compatible version of EPANET multi-species eXtension (EPANET-MSX) was used, which included dispersion and improved mass balance reporting, to simulate an experimental study. The use of EPANET-MSX was supplemented by an automated Python script to process experimental data, handle model execution, and analyze results. Nicotine-associated chlorine loss in drinking water-initially investigated from a drinking water security perspective-modeled with EPANET-MSX was compared with bottle test and test injection data. Two reaction models were tested (with and without a reactive intermediate), and the model that included a reactive intermediate nicotine species using dispersion was found to produce the best model agreement with experimental data. These results provide a demonstration of the new features within EPANETMSX in the context of the nicotine-chlorine reaction.

Modeling PFAS Removal Using Granular Activated Carbon for Full-Scale System Design.

Per- and polyfluoroalkyl substances (PFAS) are increasingly of interest to drinking water utilities due to state regulations, the release of federal and state health advisories, and public concern. Pilot-scale data were fitted for 16 PFAS species and five commercial-activated carbons using an open-source pore and surface diffusion model that includes an automated parameter-fitting tool. The estimated model parameters are presented, and an uncertainty analysis was evaluated considering the expected temporal variability of influent concentrations. Expected treatment performance differed between two seasons in the pilot phase for the same carbon, which was not captured by modeled uncertainty. However, modeling results can support a utility's decision to choose activated carbon, and make design and operational decisions that can address changing water production rates and treatment goals. For the utility that undertook this pilot study and their desired treatment goals, granular activated carbon (GAC) was found to be an effective treatment technology for PFAS removal.

Understanding the Impact of Mesh on Tank Overflow System Capacity.

A 2016 incident that resulted in damage to a water storage tank's roof motivated pilot-scale experiments to be conducted to determine the impact of mesh on tank overflow capacity. A clean mesh installed near the outlet of an overflow system did not reduce the capacity during the weir dominated flow regime. The impact of a mesh was found to be a reduction in the area available to flow, which was found to lower the achievable capacity through the system. Considering only the head loss or pressure drop associated with the mesh and not area reduction resulted in an overestimation of achievable capacity, which could lead to an undersized overflow system. The results and formulas presented will help water utilities ensure overflow systems with mesh are appropriately sized.

Modeling Fate and Transport of Arsenic in a Chlorinated Distribution System.

Experimental and modeling studies were conducted to understand the fate and transport properties of arsenic in drinking water distribution systems. Pilot scale experiments were performed in a distribution system simulator by injecting arsenic and measuring both adsorption onto iron pipe material and the oxidation of arsenite by hypochlorite in tap water to form arsenate. A mathematical model describing these processes was developed and simulated using EPANET-MSX, a hydraulic and multi-species water quality software for pipe networks. Model parameters were derived from the pilot-scale experiments. The model was applied to both the distribution system simulator and EPANET example network #3, a real-world model of a drinking water system serving approximately 78,000 customers. The model can be applied to systems-level studies of arsenic fate and transport in drinking water resulting from natural occurrences, accidental spills, or intentional introduction into water.

Random Walk Particle Tracking to Model Dispersion in Steady Laminar and Turbulent Pipe Flow.

To accurately model a two-dimensional solute transport in drinking water pipes and determine the effective dispersion coefficients for one-dimensional water quality models of water distribution systems, a random walk particle tracking approach was developed to analyze the advection and dispersion processes in circular pipes. The approach considers a solute particle's two-dimensional random movement caused by molecular or turbulent diffusion and associated velocity profile, and can simulate any mixing time and accurately model the longitudinal distribution of the solute concentration. For long mixing times, the simulation results agreed with a previous analytically derived solution. For turbulent flow conditions, simulations showed that the longitudinal dispersion of the solute is very sensitive to the utilized cross-sectional velocity profiles. This approach is easy to implement programmatically and unconditionally stable. It can predict the mixing characteristics of a pipe under various initial and boundary conditions.

Pressure dependent analysis in premise plumbing system modeling.

Modeling premise plumbing systems requires accurate treatment of fixture-specific pressure and flow rate relationships. Each fixture in a building may experience different flow rates based on variable service pressure, its unique pressure-flow behavior, and demands throughout the building. Unique experimentally derived pressure-flow parameters for four faucets, a shower/tub fixture, and toilet were developed. The Water Network Tool for Resilience (WNTR) was also used to explore the impact of premise plumbing systems on water distribution systems through two simple skeletonization cases. Minimum pressures for nodes in water distribution system models that represent demand aggregated premise plumbing systems will likely be non-zero and must capture additional pressure drop or elevation differences at the building scale and associated components, such as water meters or backflow preventers. Results showed that flow rates are impacted by pressure in these systems in complex ways, and usage and system characteristics must be considered to be modeled accurately.

Relative Water Age in Premise Plumbing Systems Using an Agent-Based Modeling Framework.

Tools used to predict hydraulics and water quality within premise plumbing systems have gained recent interest. An open-source Python-based tool-PPMtools-for modeling and analyzing premise plumbing systems with WNTR or EPANET is presented. A relative water age-the time water has spent in a home-study using three real-world single-family homes was used to demonstrate PPMtools. Results showed that increased use-more people or higher flow fixtures-led to a general decrease in relative water ages. However, even with more use, one user could still experience water for a drinking activity with a relative water age equal to, or longer than, the duration of the longest stagnant period (sleeping or absence from home). Simulations also showed that the general relative water ages increased if the homes were plumbed with larger diameter piping [19.1 mm (3/4 in.) versus 12.7 mm (1/2 in.)]. Hot water heaters were found to have the largest impact on relative water age. Smaller volume uses generally had more variability in relative water ages, while larger volume uses (e.g., showering) resulted in generally low relative water ages with less variability because larger uses fully replaced water in the home with water from the main. This study highlights the potential for using PPMtools to explore more complex water quality modeling within premise plumbing systems.

Polanyi adsorption potential theory for estimating PFAS treatment with granular activated carbon.

Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals that have gained interest because some PFAS have been shown to have negative health effects and prolonged environmental and biological persistence. Chemicals classified as PFAS have a wide range of chemical moieties that impart widely variable properties, leading to a range of water treatment process efficacies. The Polanyi Potential Adsorption Theory was used to estimate Freundlich isotherm parameters to predict the efficacy of granular activated carbon (GAC) treatment for 428 PFAS chemicals for which the vast majority had no previously published treatment data. This method accounts for the physical/chemical characteristics of the individual PFAS beyond molecular weight or chain length that have previously been employed. From a statistical analysis of available data and model results, many of the 428 PFAS were predicted to be effectively treatable by GAC. Although not directly applicable to full-scale design, the approach demonstrates a systematic method for predicting the effectiveness of GAC where isotherm or column data are not available. This then can be used to prioritize future research.

Impact of phosphate addition on PFAS treatment performance for drinking water.

Adding new unit operations to drinking water treatment systems requires consideration of not only efficacy for its design purpose but also costs, water quality characteristics, impact on overall regulatory compliance, and impact of other treatment unit operations. Here, pilot study results for ion exchange (IX) and granular activated carbon (GAC) are presented for a utility with both per- and polyfluoroalkyl substances (PFAS) and volatile organic contaminant removal needs. Specifically, the impact of upstream air stripping and phosphate addition on PFAS treatment performance was evaluated. Modeling was used to fit the IX and GAC pilot data and predict performance under different scenarios. GAC performance was generally consistent for treating water before or after the air stripper, but the addition of phosphate prior to air-stripping resulted in a loss of 15%-25% capacity for some PFAS on IX media, demonstrating the need to consider the entire treatment train before implementing PFAS removal unit operations.

Near real-time event detection for watershed monitoring with CANARY.

Illicit discharges in surface waters are a major concern in urban environments and can impact ecosystem and human health by introducing pollutants (e.g., petroleum-based chemicals, metals, nutrients) into natural water bodies. Early detection of pollutants, especially those with regulatory limits, could aid in timely management of sources or other responses. Various monitoring techniques (e.g., sensor-based, automated sampling) could help alert decision makers about illicit discharges. In this study, a multi-parameter sensor-driven environmental monitoring effort to detect or identify suspected illicit spills or dumping events in an urban watershed was supported with a real-time event detection software, CANARY. CANARY was selected because it is able to automatically analyze data and detect events from a range of sensors and sensor types. The objective of the monitoring project was to detect illicit events in baseline flow. CANARY was compared to a manual illicit event identification method, where CANARY found > 90% of the manually identified illicit events but also found additional unidentified events that matched manual event identification criteria. Rainfall events were automatically filtered out to reduce false alarms. Further, CANARY results were used to trigger an automatic sampler for more thorough analyses. CANARY was found to reduce the burden of manually monitoring these watersheds and offer near real-time event detection data that could support automated sampling, making it a valuable component of the monitoring effort.

Lagrangian Method to Model Advection-Dispersion-Reaction Transport in Drinking Water Pipe Networks.

A Lagrangian method to simulate the advection, dispersion, and reaction of a single chemical, biological, or physical constituent within drinking water pipe networks is presented. This Lagrangian approach removes the need for fixed computational grids typically required in Eulerian and Eulerian-Lagrangian methods and allows for nonuniform computational segments. This makes the method fully compatible with the advection-reaction water quality engine currently used in EPANET. An operator splitting approach is used, in which the advection-reaction process is modeled before the dispersion process for each water quality step. The dispersion equation is discretized using a segment-centered finite-difference scheme, and flux continuity boundary conditions are applied at network junctions. A staged approach is implemented to solve the dispersion equation for interconnected pipe networks. First, a linear relationship between the boundary and internal concentrations is established for every pipe. Second, a symmetric and positive definite linear system of equations is constructed to calculate the concentrations at network junctions. Last, pipe internal concentrations are updated based on the junction concentrations. The solution generates exact results when the analytical solutions are available and leads to more accurate water quality simulations than advection-reaction-only water quality models, especially in the areas where dispersion dominates advection.

Evaluating Manual Sampling Locations for Regulatory and Emergency Response.

Drinking water systems commonly use manual or grab sampling to monitor water quality, identify or confirm issues, and verify that corrective or emergency response actions have been effective. In this paper, the effectiveness of regulatory sampling locations for emergency response is explored. An optimization formulation based on the literature was used to identify manual sampling locations to maximize overall nodal coverage of the system. Results showed that sampling locations could be effective in confirming incidents for which they were not designed. When evaluating sampling locations optimized for emergency response against regulatory scenarios, the average performance was reduced by 3%-4%, while using optimized regulatory sampling locations for emergency response reduced performance by 7%-10%. Secondary constraints were also included in the formulation to ensure geographical and water age diversity with minimal impact on the performance. This work highlighted that regulatory sampling locations provide value in responding to an emergency for these networks.

Framework for Modeling Lead in Premise Plumbing Systems Using EPANET.

The lead contamination of drinking water in homes and buildings remains an important public health concern. In order to assess strategies to measure and reduce exposure to lead from drinking water, models are needed that incorporate the multiple factors affecting lead concentrations in premise plumbing systems (PPS). In this study, the use of EPANET, a commonly used hydraulic and water quality model for water distribution systems, was assessed for its ability to predict lead concentrations in PPS. The model was calibrated and validated against data collected from multiple experiments in the EPA's Home Plumbing Simulator that contained a lead service line and other lead sources. The EPANET's first-order saturation kinetics model was used to simulate the dissolution of lead in the lead service line. A version of EPANET was developed to include one-dimensional mass dispersion. Modeling results were compared to experimental data, and recommendations were made to improve the EPANET-based modeling framework for predicting lead concentrations in PPS.