Fate and origin of 1,2-dichlorapropane in an unconfined shallow aquifer

A shallow aquifer with different redox zones overlain by intensive agricult ural activity was monitored for the occurrence of 1,2-dichloropropane (DCP) to assess the fate and origin of this pollutant. DCP was detected more fre quently in groundwater samples collected in aerobic and nitrate-reducing zo nes than those collected from iron-reducing zones. Simulated DCP concentrat ions for groundwater entering an iron-reducing zone were calculated from a fate and transport model that included dispersion, sorption, and hydrolysis but not degradation. Simulated concentrations were well in excess of measu red values, suggesting that microbial degradation occurred in the iron-redu cing zone. Microcosm experiments were conducted using aquifer samples colle cted from iron-reducing and aerobic zones to evaluate the potential for mic robial degradation of DCP and to explain field observations. Hydrogenolysis of DCP and production of monochlorinated propanes in microcosm experiments occurred only with aquifer materials collected from the iron-reducing zone , and no dechlorination was observed in microcosms established with aquifer materials collected from the aerobic zones. Careful analyses of the DCP/1, 2,2-trichloropropane ratios in groundwater indicated that older fumigant fo rmulations were responsible for the high levels of DCP present in this aqui fer.