Our client, a chemical production company, operated a 40,000 square foot commercial warehouse in a mixed-use area. Chlorinated volatile organic compounds (CVOCs) groundwater plume extending off-site to the adjacent facility. Expanded soil vapor investigations conducted in and around the off-site groundwater plume indicated soil vapor results exceeding 33x the Intrusion Screening Values (ISVs).
Additional soil vapor assessment discovered concentrations of TCE in soil vapor more than 33x the ISVs on the client property, and PCE greater than 33x the residential ISVs on an adjacent property currently utilized as a daycare. The extent of these elevated CVOCs in soil vapor appeared to be limited to these two building receptors.
Additional soil vapor monitoring points were installed around and between the client’s facility and the daycare. Twenty-seven (27) soil vapor collection points were installed and sampled, 21 of which were permanent, nested at shallow, intermediate, and deep intervals.
Elevated TCE and PCE concentrations (>33x the respective ISVs) were identified in the intermediate and deep sampling locations between the buildings and in shallow samples near the buildings.
Paired sub-slab soil gas and indoor air sampling was conducted at the client’s building and at the daycare building along with ambient outdoor air sampling. The building sub-slab samples exhibited TCE and PCE concentrations >33x the industrial ISV. PCE was not detected in the daycare facility indoor air samples.
Sub-slab depressurization systems were installed at the client building and at the daycare building.
Antea Group developed property summary reports including operation and maintenance manuals for each building to document the assessments and solutions provided. Evaluation of the results of the effectiveness of the sub-slab depressurization systems indicated both buildings were successfully mitigated.
Antea Group provided a report to the state’s pollution control agency summarizing the assessment of the soil vapor and groundwater impacts and detailing the vapor intrusion assessment, mitigation, operation, and monitoring plans. The report positions the site for closure of the soil vapor pathway, as a critical component necessary for closure of the entire project.