Hello fellow swmmers

I am running the runoff model in swmm with a rating curve to produce pollutant washoff. Within the curve I am using rcoeff = desired concentration and washpo = 1 to give constant concentrations.

At the minute the model gives unbelievably high concentrations (eg ss = 0.8*10^16) however the washoff curve is the only mechanism for generating pollutants and in the summary it seems to give reasonable results eg 50 kg of total Nitrogen over one year

Has any-one else had problems with the program generating unbelievably high concentrations who might provide me with some clues as to the reason.