One of the greatest impacts of the 1991 Lead and Copper Rule on utilities across the United States has been the wholesale removal of lead service lines (LSL) from distribution systems. While the removal of LSLs is expected to reduce the lead exposure to consumers, there is considerable debate on the relative improvement in lead levels and the contribution of various lead sources on lead levels in the first liter sample. As part of an AwwaRF study, "Contribution of Service Line and Plumbing Fixtures to Lead and Copper Rule Compliance Issues", an in-depth analysis of multiple LSL replacements is being conducted at Madison Water Utility in Madison, Wisconsin and in the Boston water supply area by the Boston Water and Sewer Commission (BWSC) in concert with their regional water supplier, the Massachusetts Water Resources Authority (MWRA). The objectives of the field-testing program are to: conduct sequential sampling of stagnant water samples from kitchen faucets to identify sources of lead in service and premise plumbing and assess the contribution of these sources to lead levels at the tap prior to and several weeks after LSL replacement, (sometimes referred to as profiling); and, evaluate immediate and long-term differences in lead levels after LSL replacement. Four residential homes with lead service lines were chosen for lead service line replacement (LSLR) and associated monitoring at both BWSC and Madison. Premise piping surveys were conducted at each site prior to sampling to determine the length, diameter and type of piping between the kitchen faucet and the end of the lead service line. This data was used to calculate the water volume that must pass through the kitchen faucet in order to determine how many sequential samples would need to be collected in order to reach water that had been in contact with the lead service during the stagnation period. Water sampling was conducted at the kitchen faucet using the cold water portion of the faucet, and was conducted in three stages: Stage 1 - prior to LSLR to identify lead contributions from premise plumbing and the LSL and to establish baseline conditions for LSLR impact; Stage 2 - immediately before and after LSLR, and also for three consecutive days following the replacement to quantify short-term impacts; and, Stage 3 - monthly for 2 months following LSLR to determine long-term impacts. An initial flushed sample was collected, after which the water was allowed to stagnate for a minimum of six, and not more than 8, hours. Flushed samples were collected by allowing the water to run long enough to ensure that freshwater from the water main was flowing through the faucet. Multiple sequential stagnant water samples were collected at the end of the stagnation period. On the day of LSLR an initial flushed sample was collected prior to replacement, and another flushed sample was collected after the replacement was completed. For all samples, any aerator on the kitchen faucet was left attached during sampling. Samples were analyzed for total and dissolved lead, with samples filtered for dissolved lead analyses as soon as possible after collection. Selected samples were also analyzed for temperature, pH, conductivity, free and total chlorine, HPC, alkalinity, copper, zinc, and calcium. At Madison, results indicate that lead occurrence is defined by the random release of lead particulate matter that forms when a lead service line is or has been in a plumbing system, along with the presence of iron and manganese scale layers. Specifically: particulate lead was the significant fraction of the total lead found in the water; in flowing samples, particulate lead was below the Action Level of 15 µg/L before the lead service line was replaced, and increased immediately after replacement, and within one day of lead service line replacement, the total and particulate lead levels fell to at or near the Limit of Detection at 1 µg/L; for stagnation samples, most of the lead captured i