THE MAIN STREET WELL FIELD (MSWF) IN ELKHART, INDIANA SUPPLIES APPROX.80% OF THE CITY'S DRINKING WATER NEEDS. IN 1981, MSWF WAS SAMPLED ASPART OF USEPA'S NATIONAL GROUND WATER SUPPLY SURVEY. THE SAMPLINGRESULTS INDICATED THAT THE EASTERN SIDE OF THE WELL FIELD WASCONTAMINATED WITH TRICHLOROETHENE (TCE), 1,2,-DICHLOROETHENE (1,2,-DCE),1,1,1,TRICHLOROETHANE (TCA), 1,1-DICHLOROETHENE (DCA). USEPA RESPONDEDBY PROPOSING MSWF FOR INCLUSION ON THE NATIONAL PRIORITIES LIST TO WHICHIT WAS ADDED IN 9/83. - THE CITY OF ELKHART RESPONDED BY SHUTTING DOWN THE EASTERN PRODUCTIONWELLS AND INSTALLING INTERCEPTOR WELLS TO BLOCK FURTHER MIGRATION OF THECONTAMINANT PLUME INTO THE WELL FIELD. AS A RESULT, TCE LEVELS DROPPEDSUBSTANTIALLY. HOWEVER, FROM 1983 TO 1985, TCE LEVELS ON THE WESTERNSIDE OF THE WELL FIELD BEGAN TO INCREASE. USEPA THEN