Comparative and empirical assessment, the professional judgment of ministry staff and a review of odour regulations and standards in other jurisdictions were used to determine where NASM of different types generally fit within the NASM odour categories. The odour categorizations assigned in accordance with the NASM Odour Category Table, Table 3 of the document titled Nutrient Management Tables, corresponds to the level of odour generally emitted by each NASM type.

Given the variability in NASM and their odours, some NASM have been assigned to OC3 even though individual examples of that NASM may fit within OC2 or OC1.

NASM that does not fit within the NASM odour category generally applicable to that NASM must be categorized using one of the other methods described in this guide.

When mixing different types of NASM together, the mixture is assumed to have the odour category of the most odorous material in the mixture. For example, if an OC2 material is mixed with OC3 material, the resulting mixture is assumed to be OC3.

Section 6.0 of this guide discusses the procedure for classifying NASM that is not listed in Table 3 of the Nutrient Management Tables and NASM that does not fit within the NASM odour category generally applicable to that NASM.