A federal study prompted in 2008 by a series of newspaper articles says Lower Yakima Valley dairies and several farms are "likely" sources of nitrates contaminating private drinking water wells. However, federal officials said the EPA study was limited and doesn't prove a larger trend of nitrate contamination across the entire 576-square-mile area southeast of Yakima, Washington. Nor does it blame the region's entire nitrate problem on the dairies.

According to an EPA summary :

"Our research found that livestock operations are the largest potential source of nitrogen in the Lower Yakima Valley and that most of the livestock operations in the valley are dairies. The second largest potential source is from fertilizer application – either synthetic fertilizer, manure or both – to irrigated crop fields.

"To a much smaller degree, septic systems, biosolids from municipal wastewater treatment plants, and atmospheric deposition also are sources of nitrogen."

The report singles out five dairies, including several whose lagoons it estimates have leaked millions of gallons of manure into the underlying soil each year.

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"The dairies that we sampled are the only ones we could draw this conclusion about because we didn't look at all the dairies," said Mike Cox, an EPA scientist who managed the report, in an article in The Oregonian .

The EPA does not plan to levy fines.

The agency says it is working with the dairies on next steps to provide safe drinking water to affected residents where necessary, conduct source control measures to reduce nitrate levels in groundwater and residential drinking water wells in the vicinity of their dairies, and to conduct long-term monitoring.

The EPA is accepting written public input on the study until Nov. 30, 2012.

Spurred by the results of the study, environmental organizations like CARE and the Center For Food Safety are threatening to sue the dairies involved.

The Washington Dairy Federation told KNDO-TV that it's unfair to point fingers at only a few families when everyone who grows food or uses fertilizer in the valley is contributing to the nitrate problem. PD

—Compiled from Oregonian and KNDO articles and EPA news release