EFFECTS OF LAND DISPOSAL OF MUNICIPAL SEWAGE-SLUDGE ON FATE OF NITRATES IN SOIL, STREAMBED SEDIMENT, AND WATER-QUALITY

This study was undertaken to determine the effects of sewage-sludge di sposal at the Lowry sewage-sludge-disposal area, near Denver, Colorado , on ground- and surface-water quality, to determine the fate of nitra tes from sludge leachate, and to determine the source areas of leachat e and the potential for additional leaching from the disposal area. Se wage-sludge disposal began in 1969. Two methods were used to apply the sludge: burial and plowing. Also, the sludge was applied both in liqu id and cake forms. Data in this report represent the chemical composit ion of soil and streambed sediment from seven soil- and four streambed -sampling sites in 1986, chemical and bacterial composition of ground water from 28 wells from 1981 to 1987, and surface-water runoff from s even water-sampling sites from 1984 to 1987. Ground water samples were obtained from alluvial and bedrock aquifers. Samples of soil, streamb ed sediment, ground water and surface water were obtained for onsite m easurement and chemical analysis. Measurements included determination of nitrogen compounds and major cations and anions, fecal-coliform and -streptococcus bacteria, specific conductance, and pH. Thirteen wells in the alluvial aquifer in Region 3 of the study area contain water t hat was probably affected by sewage-sludge leachate. The plots of conc entration of nitrate with time show seasonal trends and trends caused by precipitation. In addition to yearly fluctuation, there were notice able increases in ground-water concentrations of nitrate that coincide d with increased precipitation. After 3 years of annual ground-water-q uality monitoring and 4 years of a quarterly sampling program, it has been determined that leachate from the sewage-sludge-disposal area cau sed increased nitrite plus nitrate (as nitrogen) concentration in the alluvial ground water at the site. Soil analyses from the disposal are a indicate that organic nitrogen was the dominant form of nitrogen in the soil. As a result of investigations at the research site, it has b een determined that a potentially large source of contamination exists in the soils of the study area owing to increased concentrations of n itrogen, sodium, calcium, magnesium, sulfate, bicarbonate, and chlorid e because of sewage disposal. Continued monitoring of surface and grou nd water for nitrogen and the other ions previously mentioned is requi red to assess long-term effects of municipal sludge disposal on water quality.