Tap Sampling Procedures to Characterize Lead Changes Following Lead Service Line Replacement
- Roger B. Arnold PE – Hazen and Sawyer
Lead service lines remain a primary source of lead in drinking water, and full lead service line replacement (LSLR) is an important step in reducing the risk of lead exposure from drinking water. The purpose of this presentation is to present a review of information related to full LSLR effectiveness and provide best practices for lead service line (LSL) sampling procedures. These sampling techniques will be valuable for the growing number of utilities undertaking LSLR programs to evaluate potential strategies to mitigate lead exposure following LSLR such as point-of-use filters, flushing, or bottled water.
Prior field investigations indicate that lead levels can persist or even increase for a variable period of approximately 1-3 months after full LSLR. Over decades of use, LSLs can contribute to deposits of lead in corrosion scales of interior premise plumbing. Based on reports in the literature, physical disturbance of these existing corrosion scales during full LSLR can cause a short-term increase in lead release, primarily in the form of particulate lead. Thus, a re-stabilization period of up to 3 months after LSLR is sometimes necessary before the full benefits of LSLR are observed in tap sampling.
Verification of the effectiveness of full LSLR requires collection of representative samples despite many variables that can affect tap sampling results. Observed lead release in tap sampling often increases as a function of flow rate due to increased particulate release at high flows. Sampling at low flow rates could underestimate actual lead exposure at the tap. Thus, tap samples should be collected with the cold water tap fully open and the aerator on the faucet, and the sampling flow rate should be measured.
Although the current Lead and Copper Rule requires compliance monitoring with a 1 liter first-draw sample after 6 hours of stagnation, first-draw samples can underestimate actual lead exposure in homes with lead service lines and are not adequate to characterize changes in lead levels after LSLR. Use of the sequential sampling method is necessary to confirm the benefits of full LSLR, as first-draw sampling or other techniques are not expected to provide fully representative samples of actual lead exposure. At sites with LSLs, samples derived from the service line are often obtained between the fourth and the eighth sample liter depending on the plumbing system configuration. Field studies evaluating the effectiveness of LSLR have generally included 3 to 12 tap sampling events during a period of 2 to 12 months after LSLR.
Capturing particulate lead is critical for evaluating total lead exposure, especially following LSLR when lead release is expected to be primarily in the particulate form. Only a small fraction of the water collected in a one liter sample bottle is actually analyzed for lead using the ICP procedure, but lead particles are known to settle in the bottle or sorb to bottle walls. Therefore, acid digestion of the entire one liter sample in the original sampling container and shaking of the samples after acidification is necessary to fully dissolve lead particles and homogenize the sample prior to analysis. Particulate lead can be quantified by filtering an aliquot prior to acidification of the original sampling container. These sampling procedures will allow utilities with LSLR programs to accurately quantify benefits of full LSLR and to prudently select strategies to mitigate any spike in lead release following LSLR.
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