Nitrogen Case Study
Nitrate Reduction in Drinking Water, Waynesville, Ohio
(2/23/05 version)

Until 1996, the drinking water source (ground water) for the village of Waynesville was seasonally contaminated with nitrates above 5.0 mg/l. When nitrate levels exceed 5.0 mg/l, drinking water providers are required by Ohio EPA to increase monitoring, because the public drinking water supply is considered "at risk" of exceeding safe drinking water standards. Nitrates at or above the safe drinking water standard of 10 mg/l cause acute toxicity in infants.

The source of the nitrate contamination appeared to be local agricultural practices. Because methods to remove nitrates from the drinking water during the water treatment process are very costly, Waynesville officials partnered with local county extension agents to encourage farmers located up-gradient from the main wellfield to implement agricultural management practices (MPs). Waynesville also initiated a tree- planting program along the riparian corridor and purchased land to provide a buffer north of the wellfield. Because the well field is adjacent to the river, surface water makes up a portion of the ground water supply. The tree planting is intended to reduce nitrogen run-off into the stream.

A 1995 ground water monitoring project, funded in part through a Clean Water Act Section 319 grant, enabled the village of Waynesville to document improvements in drinking water quality. Nitrate levels in the treated drinking water are decreasing, after climbing steadily for several years (Figure 1). The improvements can be linked to agricultural MP implementation, riparian corridor tree planting, and land purchase.

Analytical results from monitoring well (specifically MW-4) samples also indicate that nitrate levels in the ground water north of the main wellfield may also be declining (Table 1). This suggests that the previous high levels of nitrates were related to agricultural activities on the property before it was sold to the Village for a new wellfield. If this trend continues, it will provide evidence that the MPs put in place have been effective. At the very least, it indicates that the Village made a good decision to keep the acreage directly north of the wellfield uncultivated.

Table 1. Nitrate levels (in mg/l) in ground water samples from Waynesville monitoring wells.
Sampling Date MW-1 MW-2 MW-3 MW-4 MW-6 MW-7
May 5, 1997 0.02 11.2 1.74 4.52 0.64 0.08
October 28, 1997 0.02 5.6 3.4 3.3 0.52 0.20
June 15, 1998 ND not sampled 1.24 2.75 0.63 0.12
ND = non-detect