In addition to providing free lead testing to its customers, Greenville is conducting research to discern the cause of the lead levels. The utility collected faucets and associated piping from six residences. Using a technique known as X-ray diffraction, researchers will study the pipes to determine the form of lead that is present in the plumbing and to analyze the scale that coats the pipes. The utility plans to collect faucets and piping from another six residences in the future to see whether the coating that forms on the pipes differs from the previous coating, Lasater said.
Another theory under examination by researchers holds that a change in the ratio of chloride to sulfate in the water may have caused the elevated lead levels, Lasater said. Unlike most treatment plants in North Carolina, Greenville uses polyaluminum chloride as a coagulant, instead of aluminum sulfate. “We're working on two different fronts to try to find out what the cause is,” said Lasater, and to determine if additional treatment changes should be made. “We're in new territory here,” he said.LANSING'S LEAD LINES
Unlike Greenville, the source of lead in the water provided by the Board of Water and Light (BWL) in Lansing, Mich., is clear. There is “no question” that the approximately 12,500 lead service lines connecting some homes to the BWL's water main are the most likely source of lead, said John Strickler, BWL's communications director. Although sampling results have never exceeded EPA's action level, recently they have come “uncomfortably close,” said Strickler. Test results in 2002, the most recent year in which BWL tested for lead, indicated that lead levels had reached 0.013 mg/L at the 90th percentile.
In 2004, PWL began a $36 million program to remove all of its lead service lines by 2014.
Although the source of the lead is apparent, BWL is still trying to determine why lead levels have been increasing. In 1992, lead levels were slightly more than 0.01 mg/L at the 90th percentile, prompting BWLto begin adding a proprietary orthopolyphosphate blend as a means of reducing corrosivity in the distribution system, said Bill Maier, BWL's water quality administrator.
“We had very good results,” said Maier. In 2000, BWL switched to a different vendor that used an orthopolyphosphate blend with a slightly different mix of components. Around this time, BWL began to have “deteriorating results,” Maier said. Whether that was a key change in terms of lead levels in the water, Maier said, “we're still not absolutely sure.” The utility also reduced the orthophosphate residual slightly in response to requirements set by the Michigan Department of Environmental Quality regarding minimum phosphate levels.
BWL hired the consulting engineering firm Malcolm Pirnie, headquartered in White Plains, N.Y., to review the utility's efforts to control corrosion. The firm is developing recommendations that BWL can follow to stabilize the scale that forms naturally in the lead service lines, Maier said. Recommended changes are expected to include using additional orthophosphate for corrosion control and maintaining “slightly tighter” control over such water quality parameters as pH and alkalinity.