Percolation of contaminants from the controlled land application of domestic anaerobic digested liquid sludge has affected the quality of ground water in the highly permeable unconfined Miocene Cohansey Sand aquifer at Colliers Mills and Webbs Mill areas of the Pine Barrens region in Ocean County, New Jersey.

The sludge, containing five percent solids, was applied to three soil types, the Downer, Lakewood, and Woodmansie series, at rates of 10, 20, and 40 tons per acre (22.4, 44.8, and 89.6 metric tons per hectare) per year for the growing seasons 1973-75. Contaminant concentration reached a peak at the water table in a cyclic pattern in response to peak recharge from precipitation during the cool months from November to April. The nature and occurrence of the contaminated ground water, which is moving at estimated rates of 1.1 to 1.6 feet (0.33 to 0.48 m) per day at Colliers Mills and 0.62 to 0.69 feet (0.19 to 0.21 m) per day at Webbs Mill, has been identified by comparing changes in concentration and distribution, above background levels, of specific conductance, nitrate-nitrogen, and chloride.

Contamination of ground water has occurred under all plots receiving sludge application and the degree of contamination is generally directly related to the application rates. At the 40 ton per acre per year (89.6 metric ton per hectare per year) application rate the nitrate-nitrogen concentration increased from a background level of 2.4 milligrams per liter to a peak of 93.3 milligrams per liter at the Downer soil site, from 2.0 milligrams per liter to a peak of 98 milligrams per liter at the Lakewood soil site, and from 5.0 milligrams per liter to a peak of 54 milligrams per liter at the Woodmansie soil site. At the minimum application rate of 10 ton per acre per year (22.4 metric ton per hectare per year) the nitrate-nitrogen concentration increased from a background level of 2.4 milligrams per liter to 11.6 milligrams per liter at the Downer soil site, from 2.0 milligrams per liter to 10 milligrams per liter at the Lakewood soil sites and from 5.0 milligrams per liter to 38 milligrams per liter at the Woodmansie soil site.

Under continuous sludge application at these soil sites, the contaminant concentration in ground water is expected to increase in relative proportion to loading rates. Contamination will also continue after the cessation of sludge application as long as the residual layer contains excess quantities of soluble sludge constituents.