Pollutant Limits

The first of the three parameters that must be assessed to determine the overall quality of biosolids is the level of pollutants (metals), the other two being two levels of quality with respect to pathogen densities (classes A and B), and vector attraction reduction. To allow land application of biosolids of variable quality, Part 503 provides four sets of pollutant limits: pollutant ceiling concentration limits, pollutant concentration limits, cumulative pollutant loading rates, and annual pollutant loading rates. These pollutant limits are listed in Table 10.1. All limits in the table are on a dry weight basis.

The ceiling concentration limits have to be met by all biosolids that are land applied and by both bulk biosolids and biosolids sold or given away in a bag or other container. These limits are absolute values, which means that all samples of biosolids have to meet the limits.

Biosolids meeting the pollutant concentration limits (also known as exceptional quality pollutant concentration limits) achieve one of the three levels of quality necessary for exceptional quality biosolids status, hence can be sold or given away in bags or other containers. These limits must also be met when bulk biosolids are land applied.

The cumulative pollutant loading rates apply to bulk biosolids that meet ceiling concentration limits but do not meet pollutant concentration limits. These rates limit the amount of a pollutant that can be applied to an area of land in bulk biosolids for the life of the application site.

The annual pollutant loading rates apply to biosolids that meet ceiling concentration limits but do not meet pollutant concentration limits and are to be sold or given away in a bag or other container—commonly, to homeowners.

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