Monitoring of a Municipal Sludge Entrenchment Site
1982
Sikora, L. J. | Burge, W. D. | Jones, J. E.
Raw, highly limed, filter-cake sludge (22% solid) was entrenched 18 ha of well-drained, silt loam soil of the Manor (Typic Dystrochrept) and Glenelg (Typic Hapludalf) soil series in 1975 at a rate 2,200 wet metric tons/ha. As part of the overall evaluation of the environmental effects of sludge entrenchment, the USDA-ARS, in cooperation with the Maryland Environmental Service, began to monitor the site in 1977 to determine the mineralization and movement of N, movement of heavy metals, and die-off rate and movement of salmonellae, ascaris ova, and fecal indicators in the entrenched sludge and soil profile. Total N₁ NH₄-N, and Cl levels decreased in the entrenched sludge with time, and leached through the soil profile past the lowest sampling point, which was 100 cm below the trench bottom. Nitrate-N was formed and migrated to the deepest sampling point, and direct evidence that denitrification occurred was lacking. Heavy metal losses from the entrenched sludge were negligible probably because the pH of the sludge after 45 months was above 7.0. A predictive equation based on decreases in sludge total N was developed for use as a tool for determining the age when the entrenched sludge was stablized. Fecal coliform concentrations were very low. Ascaris ova were not detected in the sludge prior to entrenchment or in samples taken during the monitoring period which, in part, may have been due to analytical limitations. Pathogen hazard associated with the entrenched, limed sludge appeared to be minimal. The major environmental effect of sludge entrenchment is possible contamination of ground water by N leached from the sludge.
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