Evaluating sentinel pipe racks for monitoring lead release and optimizing corrosion control

Orthophosphate can limit lead contamination of tap water, but its benefits are difficult to quantify since lead concentrations are so site-specific. Sentinel homes serviced by lead pipe are ideal for monitoring orthophosphate treatment, but best practices dictate the removal of lead once identified. The best sentinel homes, then, are often short-lived. Here we explore an alternative: recovered lead pipe racks supplied with distributed drinking water at locations throughout a water system. We also propose a strategy for analyzing the data based on the generalized additive model, which approximates time series as sums of smooth functions. Geometric mean lead release from pipe racks exhibited a pronounced dose-response, falling by 54% after an increase from 1 to 2 mg PO4 L-1, and then climbing by 55% after a decrease to 1.5 mg PO4 L-1. Data from nine sentinel homes were consistent with those from pipe racks: geometric mean lead at the high orthophosphate dose was 60% of that at the low dose. Our results demonstrate sentinel pipe racks as a viable alternative to at-the-tap sampling for non-regulatory corrosion control monitoring. They also provide a Bayesian framework for quantifying changes in lead release that can incorporate information from multiple sources.