Nutrient Aggregation

The Loading Tool provides the user with the option of calculating aggregated loads for nitrogen-containing parameters and phosphorus-containing parameters. This page describes the nutrient aggregation methodology and is an updated version of section 3.2.3 of the Technical Users Background Document.

Nutrient aggregation approximates a Total Nitrogen and Total Phosphorus load by combining loads for various nitrogen and phosphorus species. Total nitrogen consists of organic nitrogen, ammonia, nitrate, and nitrite; or total Kjeldahl nitrogen (TKN), nitrate, and nitrite. Typically, organic nitrogen and TKN account for the majority of the total nitrogen load. As a result, if a facility is not required to report total nitrogen, TKN, or organic nitrogen; the loadings tool calculation will underestimate the aggregated nitrogen load. Phosphorus compounds may be reported as phosphorus or phosphate in ICIS-NPDES.

For nitrogen and phosphorus parameters, the Loading Tool calculates an aggregate nitrogen load and aggregate phosphorus load for each outfall and monitoring location at each facility using the following logic:

• For Total Nitrogen (as N):
  • If Total Nitrogen is reported, use that load for total nitrogen;
  • If Total Nitrogen is not reported and TKN is > 0, then Total Nitrogen = TKN + Nitrate + Nitrite;
  • If TKN is not reported and Organic Nitrogen is > 0, then Total Nitrogen = Organic Nitrogen + Ammonia + Nitrate + Nitrite; and
  • If Organic Nitrogen is not reported, then Total Nitrogen = Ammonia + Nitrate + Nitrite
• For Total Phosphorus (as P):
  • If Total Phosphorus is reported, then use that load for total phosphorus; and
  • If Total Phosphorus is not reported, then use the Phosphate load and convert to phosphorus

Table 3-10 presents the priorities that the Loading Tool uses to select nutrient parameters for inclusion in the total nitrogen calculation. Using these priorities, the Loading Tools selects one parameter to represent Total Nitrogen, TKN, Nitrate, Nitrite, Organic Nitrogen, and Ammonia.

Table 3-11 presents the priorities that the Loading Tool uses to select nutrient parameters for inclusion in the total phosphorus calculation.