Addition of nitrification inhibitor: Samples that may require nitrification inhibition' include, but are not limited to, biologically treated effluents, samples seeded with biologically treated effluents, and river waters. Note the use of nitrogen inhibition and the chemical used when reporting results. (NoTE: TCMP is the preferred nitrification inhibitor but requires handling and transfer in a solid form. Allylthiourea is not always effective in inhibiting nitrification within the 5-d incubation period and con centrations above 2 mg/L may cause increases in carbonaceous BOD measurements. ATU concentrations above 2 mg/L also can adversely affect the azide modification of the iodometric meth od). Seed all samples to which nitrification inhibitor has been added. The amount of seed should be consistent with that re- quired to achieve GGA test results in the range of 198 t 30.5 g/L (16b)