Testing of private water supplies near a sampling of Long Island composting facilities found high levels of manganese, a state Department of Environmental Conservation report shows.
The investigation initially focused on contamination near Long Island Compost in Yaphank and expanded into an examination of the impact of composting on groundwater.
Near Long Island Compost's site on Horseblock Road, tests found manganese levels of up to 31,600 parts per billion, according to the report released late Tuesday. The state drinking water standard is 300 parts per billion.
Manganese exists naturally and is a normal part of the human diet. Long-term inhalation of high levels of the element can damage the nervous system, but no definitive impacts on human health from drinking water contamination have been established.
The report also compared tests from two off-site farms used by the firm, plus composting facilities run by the towns of Islip and East Hampton. In Islip, manganese levels reached 8,840 parts per billion.
"Data . . . suggest that these types of facilities cause elevated concentrations of manganese in groundwater," the report said.
The data also suggest that composting facilities are raising levels of radioactive materials, such as radium, in water, but those levels are considered low, according to the report.
The DEC said in a release that the public is not at risk because "no pathway exists for humans to become exposed to the contaminants."
Based on the report, investigations of groundwater quality at other sites that manage vegetative waste will continue by the DEC, state Department of Health and Suffolk County Department of Health Services.
The DEC is also considering revisions to its regulations governing composting facilities. "The study pointed out a number of steps that can be taken to reduce potential groundwater impacts," DEC regional director Peter Scully said.
Long Island Compost chief executive Charles Vigliotti said, "We won't have a comment until we've had an opportunity to fully digest the report."
Last month, Vigliotti announced a $50 million plan to modernize the 62-acre facility, which includes moving most operations indoors. In 2011, the DEC revoked an operating permit for the facility after receiving odor and noise complaints.
Adrienne Esposito, executive director of Citizens Campaign for the Environment, urged action. "They need blanket regulations for these facilities," she said.