The Issue
A retail gasoline station in Tallahassee Florida with leaking underground storage tanks sits atop a local groundwater divide, causing petroleum hydrocarbon plumes to migrate in opposite directions from the site. In one direction, the plume has migrated under a residential neighborhood on downward sloping terrain, and in the opposite direction, the plume has migrated under a major intersection of two 6-lane US highways and under a fast-food restaurant building and its parking lot and drive-through lanes.
The site is being remediated under a Florida state petroleum cleanup program. The preferred remedy selected under the state program was air sparging accompanied by soil vapor extraction (SVE), but the implementation proved to be difficult or impossible using vertical wells, due to the lack of available ground locations for wellheads and piping.
The Solution
Directional Technologies, Inc. was retained to design and install four horizontal air sparge wells and four horizontal soil vapor extraction wells to remediate the multidirectional petroleum hydrocarbon plume. Horizontal air sparge wells and horizontal SVE wells were installed in pairs, with the horizontal SVE wells extracting air at double the flow rate of the companion horizontal air sparge wells, per the state of Florida’s requirements. Two such pairs were installed in each of the two opposing plumes.
A horizontal well installation program was developed to meet a number of logistical challenges, including:
- A dense network of subsurface utilities, tanks and monitoring wells at the gasoline retail station that required narrow tolerance along the planned wellbore paths
- Drilling and locating through a high-density neighborhood, with many homes and fenced yards
- Drilling and locating across multiple highway lanes, with traffic and strong subsurface interference to the locating system
- Drilling and locating under the gasoline retail facility and fast-food restaurant with drive-through lanes, with zero interruption of the flow of business at either location.
The Technology
The horizontal wells were 600 to over 900 feet long, with 200 to 440 feet of slotted, 4-inch SDR-11 high density polyethylene (HDPE) well screen. Horizontal air sparge screen depths range from 45 to 50 feet below ground surface (bgs), and horizontal SVE screen depths range from 35 to 40 feet bgs. The changes in screen depth reflect both changes in topography and water table elevation. Over 6,100 feet of horizontal well casing, including almost 2,600 feet of screen, were installed and developed in less than 6 weeks. The well development program was designed to take advantage of the elevation relief between entrance and exit points of the horizontal wells.
The companies’ experience in the oil field, environmental remediation industry and utility industry allows us to complete projects that were previously considered unfeasible. The company personnel have been directional drilling horizontal wells since 1984! Please give us a call to further discuss the key elements of successful horizontal remediation systems.
For additional information, contact
Directional Technologies, Inc.
877-788-4HRW
drilling@directionaltech.com