An article in some June 15 editions about changing federal standards for arsenic in well water did not make clear that a groundwater well at Clifton Elementary School in Fairfax County, which has arsenic levels considered potentially harmful, has not been connected to the school's main water system. (Published 06/16/05).

Arsenic levels in some wells serving several schools and community water systems in Northern Virginia may be too high to meet new federal drinking water standards that go into effect early next year, state officials said yesterday.

Officials with the Virginia Department of Health's Office of Drinking Water said data collected over the last several years suggest that 11 well-based water systems in Northern Virginia -- including six in Fauquier County -- that serve an estimated 9,500 people are at risk of exceeding new arsenic standards set by the Environmental Protection Agency. Those standards, which take effect Jan. 23, lower the acceptable level of arsenic in drinking water from 50 parts per billion to 10 parts per billion.

Hoping to preempt a larger problem next year, Virginia officials are reaching out to those who administer at-risk water supplies to offer arsenic sampling. They are also recommending that private well owners test their drinking water if they live in areas where elevated arsenic levels have been found in groundwater.

Possibly affected are well-water sources for Greenwich Presbyterian Preschool and Brentsville High School in Prince William County; Arcola Community Center in Loudoun County; Clifton Elementary School and the Country School House in Fairfax County; and six locations in Fauquier County: the Vint Hill Farms area, the Turnbull public water supply, the town of Remington, the Marsh Run Mobile Home Community, the Bealeton region and the CHEMetrics factory, which manufactures water analysis test kits for industrial applications.

Irene Cromer, a spokeswoman for the Prince William County school system, said yesterday that officials were aware of the new arsenic standards and are considering a variety of ways to address the issue.

"One of them is water softeners," Cromer said. "That's what we'll probably use."

The District and most of Northern Virginia draw their drinking water from the Potomac River or one of its tributaries and do not rely on wells as a source of drinking water.

In Maryland, the new arsenic rules will not affect major water-treatment plants such as those feeding Baltimore and the Washington suburbs, because the plants also draw from surface water and not from the ground, a state spokesman said.

Richard McIntire, a spokesman for the Maryland Department of the Environment, said that about 50 plants will be affected by the new rules, mainly in Southern Maryland and on the Eastern Shore. About 20 of these, serving fewer than 3,300 people each, are likely to request extensions to the deadline, he said.

Arsenic is a naturally occurring element sometimes present in soil, water, food and air. Inorganic arsenic occurs naturally in certain types of soils and rock formations. If wells are drilled where arsenic is present in the ground, drinking water can be contaminated.

Swallowing lower levels of inorganic arsenic, ranging from about 300 to 30,000 parts per billion in food and water, may cause stomach and intestinal irritation, with symptoms such as pain, nausea, vomiting and diarrhea.

Drinking water contaminated with high levels of arsenic has been associated with increased risk of cancer of the skin, lungs, bladder and kidney.

The EPA estimates that the new rule will prevent 21 to 30 deaths resulting from bladder and lung cancers in the United States each year.

Virginia officials said private well owners can order water-sampling kits from a state-certified laboratory. If arsenic levels exceed the new standard, officials suggest finding an alternative water source or purchasing a household treatment system to remove arsenic.

"If people are concerned about the potential for arsenic in their private wells, they should consider having it tested, but the state and federal regulations that we administer apply only to public water supplies," said Hugh Eggborn, engineering field office director for the state health department's Northern Virginia Office of Drinking Water.

Residents concerned about exposure to arsenic should contact their health care provider or local health department.

Staff writers David A. Fahrenthold and Carol D. Leonnig contributed to this report.