[T]he Salinas Valley, one of the nation’s most productive farm areas, is just one of many towns in California plagued by nitrate contamination of drinking water. For decades, high levels have contaminated groundwater basins throughout the state — especially in disadvantaged farm communities in the San Joaquin and Salinas valleys — as well as much of the world. … Now this year’s heavy rains may worsen this widespread contamination as fertilizer from crops and orchards and manure from ranches and dairy farms are flushed into underground water supplies. In agricultural regions, decades’ worth of fertilizers applied to orchards and row crops, and tons of cow manure stored in ponds, releases nitrogen into the ground. As much as 40% of nitrogen in fertilizer may eventually enter groundwater supplies.

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