Biosolids contain organic and inorganic nitrogen and can be applied to dramatically improve plant growth. However, the addition of too much nitrogen, whether from biosolids, animal manures or from commercial fertilizers, can leach into groundwater or run off into waterways.

In Virginia, each application of biosolids must meet the specific nutrient needs of the soil and the proposed crop, as documented by a Nutrient Management Plan written by a certified nutrient management planner trained by the Virginia Department of Conservation and Recreation (DCR). This reduces the potential for excess nitrogen levels to be applied to the soil that could leach into ground water or move off the farm site as runoff.

Biosolids nitrogen is released slowly as soil microbes convert organic nitrogen into plant available inorganic nitrogen. This process, along with adherence to setbacks required by the DEQ, helps protect the Chesapeake Bay from nutrient runoff. In contrast, setbacks are not required for chemical fertilizers, which are highly soluble and can easily run off into receiving waters.