Suchergebnisse

AbstractAn established body of research over many decades has identified the importance of both bulk‐water and pipe scale surface microenvironment buffering to meet distribution system pH targets and reduce corrosivity toward metallic piping and components. Buffer intensity quantifies the ability of water to resist pH changes, and the greater the buffer intensity, the more resistant the water is to pH changes. To provide a practical tool for exploring buffer intensity, a buffer intensity simulator (BIS) was implemented in open‐source R code, incorporating typical chemical species (e.g., carbonate and orthophosphate) that contribute to drinking water buffer intensity along with temperature and ionic strength impacts. The BIS was verified against a parallel spreadsheet implementation and is publicly available at https://github.com/USEPA/BIS. Simulations were conducted to illustrate impacts related to buffer intensity using three practical scenarios: carbonate buffering in drinking waters, temperature impacts, and free ammonia presence from chloramine use and/or source water presence.

The conventional wisdom of lead‐scale solubility has been built over the years by geochemical solubility models, experimental studies, and field sampling using multiple protocols. Rarely have the mineral phases from scales formed in real‐world drinking water lead service lines (LSLs) been compared with theoretical predictions. In this study, model predictions are compared with LSL scales from 22 drinking water distribution systems. The results show that only 9 of the 22 systems had LSL scales that followed model predictions. The remaining systems had unpredictable scales, some with unknown lead release characteristics, demonstrating that predicting scale formation and lead release solely by models cannot be relied on in all cases to protect human health. Therefore, for many systems with LSLs, pilot studies with existing LSL scales will be necessary to evaluate and optimize corrosion control, and correspondingly, appropriate residential water sampling will be needed to demonstrate consistent and optimal system corrosion control.

AbstractA theoretical equilibrium lead(II) (Pb(II)) solubility model coded in Fortran (LEADSOL) was updated and implemented in open source R code, verified against LEADSOL output, and used to simulate theoretical equilibrium total soluble Pb(II) (TOTSOLPb) concentrations under a variety of practical scenarios. The developed R code file (app.R) is publicly available for download at GitHub (https://github.com/USEPA/TELSS) along with instructions to run the R code locally, allowing the user to explore Pb(II) solubility by selecting desired simulation conditions (e.g., water quality, equilibrium constants, and Pb(II) solids to consider). In addition, the R code serves as a reproducible baseline for alternative model development and future model improvements, allowing users to update, modify, and share the R code to meet their needs. Using the R code, several solubility diagrams were generated to highlight practical relationships related to TOTSOLPb concentrations, including the impact of pH and dissolved inorganic carbon, orthophosphate, sulfate, and chloride concentrations.

AbstractMany water systems are challenged with uncertainty regarding service line material type. This work investigated using a simple drinking water flushed sampling approach and a more complicated and invasive sequential profile sampling approach to predict whether homes had an existing lead service line (LSL). Homes that never had an LSL (control groups) and homes with LSLs (study groups) in two communities having different degrees of corrosion control were sampled. Using control groups' results, community‐specific "threshold" lead levels were determined and compared to results from study groups. The flushed sampling maximum lead concentration (FMC) of lead accurately predicted 100% and 60% of LSL sites for the community with poor and good corrosion control, respectively. The weighted average sequential profile lead concentration (WASLC) increased the 40% not identified as LSL sites by fully flushed samples to 100%. The WASLC closely followed by the maximum sequential profile lead concentration were most reliable in identifying LSLs.

AbstractWith lead service lines (LSLs) remaining for decades to come, scale analyses are critical to helping limit lead exposure from drinking water. This laboratory has used an integrated suite of analytical techniques to characterize the elemental composition, mineral identification, and physical features of scales, helping the water industry to evaluate, predict, and reduce lead corrosion. The methods used in this laboratory to prepare and analyze the LSL scale, and guidance to achieving reliable and meaningful results, are described. Primary methods include the following: optical microscopy, powder X‐ray diffraction, inductively coupled plasma spectroscopy, X‐ray fluorescence, scanning electron microscopy with energy dispersive spectroscopy, combustion and coulometric analyses of C and S, and X‐ray absorption spectroscopy. Examples of associated pitfalls and ways to avoid them are provided, including pipe excavation/transport, sample preparation, analysis, and data interpretation. Illustrative examples are presented of practical scale analysis questions that could be answered by combinations of pipe scale analyses.