Modeling Soluble and Particulate Lead Release into Drinking Water from Full and Partially Replaced Lead Service Lines

Abstract

Partial replacement of lead service lines (LSLs) often results in the excessive long-term release of lead particulates due to the disturbance of pipe scale and galvanic corrosion. In this study, a modeling approach to simulate the release and transport of particulate and dissolved lead from full and partially replaced LSLs is developed. A mass-transfer model is coupled with a stochastic residential water demand generator to investigate the effect of normal household usage flow patterns on lead exposure. The model is calibrated by comparing simulation results against experimental measurements from pilot-scale setups where lead release under different flow rates and water chemistry scenarios was reported. Applying the model within a Monte Carlo simulation framework, partial replacement of the LSL was predicted to result in releasing spikes with significantly high concentrations of particulate lead (1011.9 ± 290.3 μg/L) that were five times higher than those released from the simulated full LSL. Sensitivity analysis revealed that the intensity of flow demands significantly affects particulate lead release, while dissolved lead levels are more dependent on the lengths of the stagnation periods. Preflushing of the LSL prior to regulatory sampling was found to underestimate the maximum monthly exposure to dissolved lead by 19%, while sampling at low flow rates (<5.2 LPM) was found to consistently suppress the high spikes induced by particulate lead mobilization.

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“…Lead can be classified as either dissolved or particulate. Particulate lead can be very challenging to model due to the random characteristics of dislodgement, and the existing limited understanding of transport phenomena such as coagulation, convection, diffusion, and deposition (Abokifa & Biswas, 2017). The concentrations of lead and other heavy metals are also impacted by the water chemistry, especially water pH, temperature, hardness, corrosion inhibitors, dissolved oxygen, and disinfectants of various types and concentrations, etc., which demonstrates the complexity involved.…”

Full Lead Service Line Replacement: A Case Study of Equity in Environmental Remediation

“…Partial replacement is not a second-best alternative to full replacement and may be worse than doing nothing. In some cases, partial replacements have been shown to accelerate lead release due to galvanic corrosion and/or disturbance of pipe coatings that normally protect against lead leaching [25,26]. Dissolved and particulate lead may spike to very high levels following a partial replacement, and higher lead levels may persist in the drinking water for months [27][28][29].…”