Elevated levels of lead in Washington, D.C.'s drinking water became national news in 2004, reviving interest in a public health issue that had largely faded from the media spotlight since the U.S. Environmental Protection Agency finalized the Lead and Copper Rule (LCR) in 1991. Although most utilities continue to comply with the lead regulations without too much difficulty, others are discovering that changes made to comply with other regulatory requirements can affect lead levels in unforeseen ways.
The LCR is unique because it requires water providers to address contamination that often results from factors beyond their direct control. For example, lead is rarely present in water supplies, and drinking water usually contains little lead following treatment. However, lead in service lines, household plumbing fixtures, and solder can leach into drinking water under certain conditions. Because the corrosivity of water often plays a key role in this process, the LCR requires that utilities take steps to reduce corrosion within their distribution systems.
Drinking water providers are required to collect samples periodically from a certain number of residences or buildings considered at high risk of contamination. The LCR establishes a so-called action level of 0.015 mg/L of lead based on the 90th percentile level of tap water samples. If the results of its sampling exceed the action level, a utility may be required to conduct a host of measures, including additional monitoring, treatment to control corrosion, public education, and replacement of lead service lines.
Overall, the LCR has been a success, said Jim Taft, executive director of the Association of State Drinking Water Administrators in Washington, D.C. Lead levels present in drinking water have declined significantly compared to levels present before 1991, he said. However, he acknowledged that the LCR is “not a straightforward regulation.” Because lead in drinking water tends to leach from the distribution system, Taft said, adjustments made by a drinking water provider to comply with another regulation can inadvertently make the water more corrosive and cause more leaching to occur.UNWELCOME SURPRISE
For more than a decade since Greenville Utilities in Greenville, N.C., began testing in 1992, its lead levels never came to close to exceeding the EPA's action level. However, that changed abruptly in 2004. “We were surprised,” said Barrett Lasater, Greenville's water plant manager, when the results of testing conducted that year indicated that 22% of samples contained lead in concentrations above the action level. Follow-up testing in May and June 2005 found that 27% of samples surpassed the action level.
Because none of the 565 miles of pipeline that comprise the utility's distribution system contains lead, Greenville is certain that the contaminant is leaching from faucets containing lead and lead-based solder used to connect pipes in the homes of its customers. Although the utility is still trying to determine why lead levels spiked in 2004, the presumption is that changes to the disinfection process at the utility's water treatment plant likely reduced the effectiveness of the corrosion inhibitor used to prevent lead from leaching from customers' faucets and pipes.
Between the time it tested for lead in 2001 and its subsequent testing three years later, Greenville made a series of changes to its drinking water treatment plant to comply with EPA's regulations regarding disinfection byproducts (DBPs). Considered by the EPA to be a potential health threat, DBPs form when organic matter in drinking water comes in contact with chlorine. In December 2002, Greenville began using chloramines, rather than free chlorine, to provide secondary disinfection, because chloramines do not create DBPs. Then in August 2003, the facility switched from chlorine to ozonation as its method of primary disinfection before filtration.
Pilot testing conducted by the utility before making the changes did not indicate that they might make the treated water more corrosive, Lasater said. “We had not anticipated any problems from the treatment changes,” he said. Other treatment plants in North Carolina had made similar changes without experiencing elevated lead levels. However, Greenville was using a polyphosphate corrosion inhibitor, while the other plants employed an orthophosphate inhibitor.
Greenville hired AH Environmental Consultants Inc., Newport News, Va., to study its corrosion control approach within its distribution system. Although the testing found that the water was not more corrosive than it had been before the changes to its disinfection system, the study determined that orthophosphate likely would provide the most effective corrosion control. Based on these findings, Greenville switched from polyphosphate to orthophosphate in 2004.
The most recent round of testing, conducted in November and December 2005, would appear to indicate that the change is having a positive effect, with only 16% of samples exceeding the action level. “We're encouraged that we're starting to see some improvement,” said Lasater. “But obviously we're not meeting EPA's requirements yet.”