(AP press)..Three public interest groups are threatening to sue some big Yakima Valley farms over massive groundwater contamination in that agricultural region.

The three groups say they will sue the farms unless in the next 90 days the farms stop contaminating local drinking water supplies with runoff from their operations.

The U. S. Environmental Protection Agency last month issued a long-awaited study that found that several dairies and farms in the valley are the "likely" sources of nitrates that are contaminating private drinking water wells. The report said it could take years to reduce nitrate levels in the drinking water wells.

Public justice, which represents the center for food safety and the community association for restoration of the environment, has issued 90-day notice of intent to sue letters to the farms.