It is important to point out that many trace elements of concern in biosolids are also present in conventional fertilizers and manure. There, too, those substances are nontoxic at the small concentrations and low rates at which they are applied. When applied according to DEP regulations and good farming practices, biosolids pose little or no potential risk to groundwater quality. As with any fertilizer product, however, the user must be careful not to over apply. Like other types of fertilizer, the greatest concern for groundwater from over-application is nitrate contamination.
Regulations strictly limit the amount of nitrogen applied through biosolid application.
Unlike commercial fertilizers, about 95 percent of the nitrogen in biosolids is present in the slow-release organic form, making biosolids less likely to cause groundwater pollution from nitrogen. Federal and state regulations limit the application of biosolids on agricultural land to agronomic loading rates. This means the amount of nitrogen applied is limited to that needed by the particular crop to be grown, thus minimizing the amount that passes beyond the root zone. In addition to nitrogen being managed through proper site restrictions and process, when biosolids are applied to land with the adequate soil pH, the solubility of metals is controlled such that these metals cannot move into the groundwater. DEP regulations require that the soil pH be maintained at 6.0 or higher, ensuring that metals do not contaminate the soil and ground water.