Why don more domestic wells in the area have high nitrate levels?
Ground water moves slowly through the shallow aquifer. Because ground water moves slowly, it takes a long time for nitrate to appear in well water. For example, the severity of nitrate contamination in the La Pine core area did not become evident until 1979, nearly 70 years after development of that area began. Away from the core area, most wells currently provide drinking water that percolated to the water table decades ago, when there were very few homes and septic systems. Nitrate plumes, however, are beginning to affect a significant number of drinking-water wells. Of nearly 200 well samples collected by ODEQ in 2000, over 10 percent had nitrate concentrations above 4 ppm, indicating contamination from septic systems. Much of the nitrate in the aquifer currently is confined to plumes less than about 30 feet below the water table, so not all supply wells are drawing water from affected areas of the aquifer (fig. 3). As development proceeds and the nitrate plumes expand and move deep
