Comparison of coupon and pipe rack studies for selecting corrosion control treatment

Abstract

This study directly compared the data obtained from coupon studies and flow‐through pipe rack studies from two sources in the Denver Water system. The pipe rack study was completed over multiple years using harvested lead service lines. The coupon studies were completed in about 2 months using pure lead coupons. Orthophosphate at 2 mg/L was found to reduce lead concentrations by about 81% in the pipe racks, whereas 74%–81% was observed in the coupons. At an orthophosphate dose of 1 mg/L lead concentrations were reduced by 62%–65% in the pipe loop and by 55%–75% in the coupons, pH at 8.8 reduced lead by 45%–60% in the pipe racks and by 27%–48% in the coupons. The pipe racks were able to give insights into the transition from one condition to another, which is time‐based and dependent on existing pipe scales. Both types of demonstration studies produced similar conclusions about treatment options. The pipe rack was more representative of conditions in the distribution system while the coupon studies were performed in a fraction of the time.

A literature review of bench top and pilot lead corrosion assessment studies

“…While most peer-reviewed literature focused on either bench top or pilot studies, Masters et al (2022) reported both coupon and pipe rack studies to examine the effects of pH adjustment and orthophosphate addition on lead leaching for two water sources in Denver, CO. Although the water chemistries were the same for both study types, the plumbing materials, stagnation time, sampling, and duration were different (Tables 2 and 5).…”

“…Use of a smaller water volume allowed for observation of minor changes in lead leaching, but limited the number of analyses that could be performed as a larger volume of water was needed to run certain analyses (Lytle et al, 1992). Some studies took composite samples at the end of each week (Bradley, 2018; CDPHE, 2019; Masters et al, 2022; Nguyen et al, 2010; Tang et al, 2018), which provided a greater volume of water to be analyzed and presumably simplified the study.…”

“…Some rigs were composed of excavated lead pipes (Cartier et al, 2013; Masters et al, 2022; Williams et al, 2018), while others used new lead pipes (Figure 5b) (Cartier et al, 2012; Churchill et al, 2000; MacQuarrie et al, 1997; Parks et al, 2014). Some pipe rig setups also used new copper pipes with lead solder (Cantor et al, 2000; Churchill et al, 2000; Parks et al, 2014; Treweek et al, 1985), as well as leaded brass plumbing fixtures (Figure 5c) (Churchill et al, 2000; MacQuarrie et al, 1997; Parks et al, 2014).…”

“…These once‐through pipe rig studies tried to mimic real world situations with stagnation times typically ranging from 5–16 h per day (Cartier et al, 2012, 2013; Churchill et al, 2000; Masters et al, 2022; Parks et al, 2014; Williams et al, 2018). However, some studies had longer stagnation periods of 23 h (Cantor, 2017), or 72 h over the weekend (Cartier et al, 2013).…”

“…While new plumbing materials may reduce variability in results, they are not representative of an aged plumbing system and may not produce realistic results (Eisnor & Gagnon, 2003; Roth et al, 2021). Numerous studies have highlighted the importance of having at least triplicate tests for each water condition to give a representative picture of the inherent variability of lead release from plumbing materials (Nguyen et al, 2010; Parks et al, 2014; Masters et al, 2016, 2022).…”