Natural atteiiiiutioma holds great promise as a cost-effective means of retiaegyii ig groii ndwater coiitmi iliation at petroleti 11.7 spill sites; this is particular(y trite at sites wit?2 sujficzent backgroutid concentrutioiis qf altemzate electron acceptors (riitrate aiid/or su@e). The stzidy reported in this al-ticle cokripayed the reszdts of a new Eirvirotimeutal Protection Agetacjl (EPA) mmericnl model (BIOPLUME III1 with an iLpdated EPA am~lytical wodel (BIOSCREEN Versiou 1.41 used to predict natural atteiiziatiomz at ail ziizdergroii7id~ firelspillsite iii Oklahoma High backgroiiiidsiivate coticeiztratiom iiieresIwion to result in unrealzstzcpi~edictiorzsfi.or7.2 both BIOSCREEN apLd BIOPLUME 111 BIOSCREEN cotrld be easily trsed with a data set izot sign ficaiztly ednrged from that used iii a roiltilie leaking jiiel tank iizuestigatioii BIOPLUME 111 was nziich more difficult to use mid did not yield reliable re.wlts Resiilts oj' this studjj indicate that the additional complexity ofthe BIOPLUMEIII model is Izotjzrstfied forszmplesites. 0 2000 John Wilev & Sons, I x .