David, May I comment that in this case using concentrations is rather simplistic, and will lead to miscalculations. Most of the material disposed on the surface will stay there until a storm event (some of it is carried away by winds). Thus, when having lower annual precipitation rate, you could expect about the same load (and higher concentrations). Regards, Eran Friedler -- ==================================================================== Juanico & Friedler Mediterranean Ltd. (Israel) Juanico & Friedler Latinamerica S.A. (Uruguay) * Sewage Treatment and Storage - Process Design Consulting * Catchment Basin Management & Monitoring for Water Quality -------------------------------------------------------------------- Kibbutz Dalia, 19239 Israel Phone:+972-4-9897038 Fax:+972-4-9897037 -------------------------------------------------------------------- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%