Since 1983, there has been a steady improvement in sludge quality from domestic treatment works in New Jersey. This demonstrates that "biosolids" being produced by New Jersey generators are for the most part low in pollutants, rich in nutrients and organic matter, and highly suitable for recycling. Only one parameter (arsenic) has shown an increase in median concentration since 1983. However, the percent of samples arsenic has been detected in has dropped significantly since 1997 (61 percent detection to 43 percent detection). Two other parameters (selenium and zinc) have shown an increase over 1994 median concentrations. The increase in zinc concentrations is likely due to the increased use of zinc phosphate to control copper and lead leaching from plumbing. The increase in selenium concentrations is less understood and will need further investigation. Nevertheless, the median concentrations for all of these parameters remain well below the 40 CFR Part 503, Table 3, "Pollutant Concentrations."

DEP administers a regulatory program for the use and disposal of sludge generated by domestic treatment works in a manner that protects public health and the environment. Of fundamental importance is the need to control sludge quality. Specifically, N.J.S.A. 58:10A-6(f)(7) directs the DEP to issue permits to limit concentrations of heavy metals, pesticides, organic chemicals and other contaminants in sludge in conformance with land-based sludge management criteria.

The Sludge Quality Assurance Regulations (SQAR), N.J.A.C. 7:14C, were initially promulgated in October 1979. With the adoption of SQAR, the DEP embarked on a major program of monitoring the quality and quantity of sludge generated throughout the State by domestic treatment works. The SQAR have been in effect for more than 18 years, and the information submitted by domestic treatment works with regard to their sludge has been extremely useful to the DEP in evaluating management plans, and by the generators in developing appropriate management alternatives.

In reviewing the table below, it is important to understand a few assumptions that the DEP made in constructing the table. Due to the large ranges reported for some parameters, the abnormally high and low values produce a skewed distribution. This results in a considerable difference in magnitude between the mean and median values. The Department believes that the true central tendency for the concentration is better represented by the median than by the mean value. Hence, only the median value is presented in the table. In addition, for determining median concentrations, if analytical testing did not yield a pollutant concentration above the minimum detection level, the pollutant concentration was assumed to be the minimum amount of pollutant that could be measured. Equating undetected data points to their minimum detection level tends to overestimate pollutant concentrations. For each parameter, the percent of samples which had detected concentrations is indicated on the chart.

If you have any questions regarding sludge quality data, please contact Anthony Pilawski, Bureau of Pretreatment and Residuals at (609) 633-3823.