Mishandled and illegally disposed 1,1,1-trichloroethane caused contamination at this warehouse facility that threatened domestic water-supply wells and a stream. The underlying geology at this site was complex and Mid-Atlantic utilized a variety of sampling, assessment and geophysical techniques to develop a site conceptual model using various software programs. In situ chemical oxidation by sodium persulfate and steam injection, augmented with an existing air sparging and soil vapor extraction, was conducted over a 12-week period using a 66-well injection field. Mid-Atlantic injected over 50,000 lbs of sodium persulfate and one billion BTUs of energy (steam) into the source area. Our assessment and corrective action resulted in post-treatment concentrations over three times lower than the target cleanup levels, which has shortened the time for the on-going processes of natural attenuation for remaining contaminants. This site is currently under the jurisdiction of the Inactive Hazardous Sites Branch and was entered the Registered Environmental Consultant Program in December 2009. A vapor intrusion (VI) assessment conducted at the site showed an incomplete VI exposure pathway.