A Review of Bench Top and Pilot Lead Corrosion Assessment Studies
Citation:
Devine, C. AND S. Triantafyllidou. A Review of Bench Top and Pilot Lead Corrosion Assessment Studies. AWWA 2023 Contaminants of Concern Virtual Symposium, Cincinnati, OH, March 14 - 16, 2023.
Impact/Purpose:
Bench top and pilot lead corrosion studies are gaining more interest, considering revisions and upcoming improvements to the Lead and Copper Rule. This presentation will review studies ranging from simpler month(s)-long bench top dump-and-fill stagnant water tests to more complicated year(s)-long intermittent flow pilot studies. With increasing complexity in design and operation, studies more closely approximated real plumbing conditions at increased cost, footprint, and duration. Comparison of bench top and pilot designs (in terms of lead test piece age/dimensions/ configuration/replicates, study duration, sample collection, and other factors) can assist in the selection of a design that matches the needs and constraints of the study.
Description:
Lead corrosion assessment tools (i.e., desktop studies, bench top studies, pilot studies, diagnostic drinking water sampling for metals and pipe scale analysis) are used for fundamental or applied research by academic groups, as well as for voluntary operational improvements or for mandatory compliance with policy requirements by drinking water utilities and their consultants. While all tools are important and can each provide complementary information, this presentation will focus on bench top and pilot studies which are gaining more interest, due to revisions and upcoming improvements to the Lead and Copper Rule (LCR). Such studies were compiled from journal articles, reports, and conference proceedings before the 1991 LCR (termed historical) to 1991-2021 (termed modern). Their critical review classified modern bench top studies into two general categories (stagnant coupon tests and stagnant pipe tests). It also identified two general categories of pilot studies (recirculating pipe loops and once-through pipe rigs). Between and within these general categories, there are many different designs (in terms of lead test piece age/dimensions/ configuration/replicates, water flow/stagnation regime, study duration, sample collection, and other factors). Comparison of bench top and pilot designs can assist drinking water utilities, consultants, academics, and others to select a design that matches their needs and constraints. Due to their relatively low cost, small footprint and simpler set up, bench top studies of submerged coupons or short pipe segments (typically new) can be used to test multiple conditions in stagnant water (typically 2-3 days of stagnation at a time, over a period of weeks to months). Pilot studies typically use harvested (i.e., aged) pipes and employ cycles of flow followed by stagnation periods of 6-16 hours for months to years. This can allow the metal release behavior of pre-existing scales on actual distribution system materials under typical hydraulic conditions to be observed. Pilot studies more closely approximate real-world complexities, but they also increase costs, take longer to start up and operate, and create greater variability within the study due to the complex nature of pre-existing scale. Generally, increasing the complexity of the study will produce more realistic lead release results but will also increase the time, resources, and the space needed. Bench top stagnant coupon tests are the easiest and simplest tests to conduct, whereas once-through pipe rigs offer the most complex and realistic study conditions if resources are available. Recirculating pipe loops could be considered a reasonable middle ground overall. Recirculating pipe loops can simulate the intermittent flows but are not as complex as once-through pipe rigs and require much less water and potentially less space. Whatever the choice, any selected surrogate test system cannot replace an actual system’s water sampling program.