FDEP Groundwater Assessment and Cleanup Using Horizontal Wells
   Florida

Overview
Water & Air was selected to provide technical services to address contamination caused by long-term releases from a fuel storage tank. During assessment work, both soils and shallow groundwater were evaluated. Impacts to shallow groundwater were documented and after follow-on testing, limits of the contamination were delineated. The contaminant plume was found to stretch several hundred feet beneath a federal highway and toward a residential area.

Various engineering and institutional controls were considered during design of a remediation system. Ultimately, an array of three horizontal wells was designed to address the contaminated area. Use of horizontal wells allowed needed access to the contamination beneath the roadway. Each well included approximately 220 feet of well screen plus risers at both ends.

The horizontal wells were designed based on aquifer performance testing using conventional vertical monitoring wells. Aquifer testing results were fed into a U.S. Geological Survey (USGS) model to derive estimates of three-dimensional hydraulic conductivities. The model was then used to estimate drawdown versus flowrate. The model was coupled with a numerical estimating and iteration program that optimized data fit while varying aquifer parameters. Finally, modeling results for a single well were superimposed to evaluate well spacing options.

The cleanup technology chosen was dual phase extraction, wherein the shallow groundwater table is lowered to allow vapors to be extracted from the newly dewatered soil matrix. The design flowrates of the system was 50 gallons per minute of water and approximately 1,000 cubic feet per minute of vapor.

Large vacuum blowers were selected to extract water and vapor. Water was treated by air stripping, and both water and vapors were routed through activated carbon as a final treatment step. Design of the system provided for a change in technology should it be needed in latter stages of cleanup.

Details

• Innovative Cleanup Technologies
• Groundwater and Soil Assessment
• Groundwater Modeling
• Remedial design
• Construction specifications and management
• Regulatory agency coordination
• NPDES Testing
• Permitting

Results
Based on the innovative and aggressive cleanup design and implementation, petroleum impacted groundwater and soil media were remediated to Florida Department of Environmental Protection (FDEP) Cleanup Standards in less than two year instead of the originally projected three year clean up goal. This saved the client tens of thousands of dollars in cleanup costs and restored the subject property to clean conditions.