Chlorinated solvents were detected in an industrial well open to a regional drinking water aquifer, located at a former dry-cleaning facility.
A downhole video survey indicated that groundwater contamination was likely a result of impact within a shallower hydrogeologic zone. To investigate the extent and source of the compounds, innovative characterization activities were performed within shallow unconsolidated materials and shallow bedrock, which contains a cave, solution conduits, and various fracture features below the water table.
Characterization activities performed include the following:
- Completion of passive soil gas survey, including 44 monitoring points over an approximately 75,000 ft2 area
- Advancement of 19 borings and seven temporary monitoring wells, targeted to areas of solvent impact as indicated by the soil gas survey
- Completion of a specialized geophysical resistivity survey to identify potential areas of impact, preferential migration pathways, fracture zones, and/or important lithologic features
- Installation of 8 shallow bedrock monitoring wells by sonic drilling to evaluate anomalies identified by the geophysical survey and the dissolved-phase plume at the site
Downhole videography to evaluate karst features
Due to the high profile nature of the site (high-traffic public park), the activities outlined above were completed within an aggressive six-month period that required meticulous care for minimal damage to park grounds. Data collected from characterization activities were utilized to develop an initial site conceptual model as part of the Missouri Risk Based Corrective Action (MRBCA) process.
EWI personnel and equipment were utilized to perform soil gas survey, install borings and temporary wells, and downhole videography. EWI geologists and scientists worked with the geophysical survey subcontractor in evaluating geophysical results and determining appropriate bedrock monitoring well locations, and performed sonic drilling oversight and detailed logging of continuous core samples. Planned activities for this ongoing project include closure of the industrial well, modification of a monitoring well intersecting a large cave, installation of additional bedrock monitoring wells, sampling, and dye tracing studies.