Radiotracer experiments in the Mohawk River, New York, to study sewage path and dilution

Sewage from the Knolls Atomic Power Laboratory near Schenectady, N. Y., was dosed with 4.53 curies of P prior to discharge into the Mohawk River. Its pattern of diffusion was measured in the river with immersible GM‐tubes and by sampling. The initial path of sewage was strongly influenced by differences in density between sewage and river due to temperature. During warm months relatively cold sewage moved on the river bottom perpendicularly to river current. For at least the first 800 ft of travel the maximum sewage concentration decreased logarithmically with distance from outfall. The term ‘half‐distance’ (here about 110 ft) is proposed to describe the concentration change. During cold months sewage rose to the river surface and at times was moved upstream by wind. However, when the river temperature was near freezing, the sewage first rose and then sank as the temperature of the sewage‐river mixture approached 39° F.