Forensic Modeling in Arizona

Chlorinated solvents were discovered in the groundwater and soil vapor beneath a site in Arizona. As part of the investigation, Leppert Associates was commissioned to determine the probable source of the contamination. A facility approximately one half mile up gradient of the site has historically been known to use these solvents, and spills have been documented there.

Leppert Associates collected geologic information from over 100 bore holes and coupled it with other sources of geologic information such as data from past numerical models conducted by the division of water resources. Pumping from agricultural supply wells was incorporated into the model, along with typical surface recharge amounts. The model was calibrated to observed water levels, and then contaminant was placed in the model at the up gradient facility.

The model results were characteristic of what was observed in local sampling wells, indicating that the up gradient facility was the source of the contamination at the site. The up gradient facility had undergone previous remedial activities that targeted contaminant removal at the facility, but did not consider or address the contamination that had already flowed down-gradient. The contamination at the site appeared to be part of that residual tail.