Challenging Hydrocarbon Remediation in an Urban Setting

By Tomas Will, Sr. Environmental Scientist

 

At a site in the southeastern US, petroleum release incidents from leaking gasoline underground storage tanks (USTs) created a very challenging hydrocarbon remediation in an urban setting. The UST leaks had resulted in contamination of both groundwater and surface water. There had been two known release incidents at the site, one recent and one in the early 1990s. The older release incident had been remediated using vertical air sparge wells. The newer release was discovered when a freephase gasoline product and a heavy petroleum sheen were observed at a nearby stream.

During site characterization, it was discovered that the initial release had not been fully remediated and that the present-day groundwater contaminant plume covered a large area. With a large area to remediate, several businesses impacted, sensitive receptors in the area, and a renewed regulatory interest in assuring that the contamination issues be resolved for good, here’s how one of our clients teamed up with Directional Technologies to implement their remedial strategy incorporating horizontal air sparge and SVE wells.

 

The Site Presented Many Unique Challenges

Due to the location of the gas station and USTs, the site presented many unique challenges. First, the USTs were located upgradient of several businesses and a tributary stream. The project site area had significant topographic relief, with an elevation difference of over 35 feet between the source area and the nearby stream. It was observed that the free product was entering the stream through an apparent seep at the toe of a slope leading down to the surface water. The site is underlain by Proterozoic-aged schist deposits that are part of the Lynchburg Formation. Lithology primarily consisted of fine-grained silty clay. The contaminant plume was located beneath several businesses including the gas station, a steakhouse, a motel, and a large commercial building with several tenants and offices. Parking lot areas associated with the affected businesses were frequently in use and limited in size, therefore typically quite full.

 

The site presented several challenges.

• The plume covered a relatively large area and would have required many vertical wells in an attempt to remediate.
• Potential work areas at the site were limited. Traditional remedial construction methods would have required blocking off the majority of the parking lots for several business and blocking ingress/egress to the gas station resulting in lost revenue for those commercial operations.
• The only available location for an equipment shed to run the remediation system was located a long distance from the farthest edge of the contaminant plume and trenching conveyance lines to the various wellheads would have been difficult due to the topographic relief, existing buildings, and existing shallow utilities.
• Due to the significant topographic relief, certain areas of the site could not accommodate a drill rig.
• The ongoing contamination of the nearby stream called for a remediation approach that would show quick results.
• For the consultant, the remediation project was high-stakes, with significant regulatory attention and a low margin for error.

 

Solution

In search of alternative remediation options, the resourceful project managers contacted Directional Technologies to evaluate the potential to use horizontal remediation technology. A combination of air sparge and SVE wells were suggested to implement a remedy that could provide the best likelihood of achieving remediation goals over an expedited timeline. Directional Technologies’ proposed system design incorporated four air sparge wells set at depths ranging from 20-30 feet below the ground surface and two shallow SVE wells to control vapor intrusion concerns within the interior spaces of buildings at the surface. Ultimately, the consultants agreed with Directional Technologies’ design and the project moved forward with implementation.

The various wells were installed beneath the buildings, parking lots, existing utilities, and steeply sloping areas. The horizontal remediation wells contained over 800 feet of screen in direct contact with the plume. Each well was 3-inch diameter HDPE with custom-designed well screens tailored to site-specific conditions. The wells were drilled from a single entry point located in a grassy area away from the parking lot and the conveyance pipe for the six wellheads was directionally drilled to connect to an equipment shed area located over 300 feet away.

 

Conclusion

Using horizontal wells the client was able to:

• Significantly reduce the overall number of wells required for the project.
• Allow business operations to continue without significant disruptions.
• Place remediation wells in otherwise inaccessible areas of the plume.
• Ensure that their remedial action would provide the greatest chance of success, including rapid initial results.

 

Related Case Study

Click Here for a related case study regarding controlling plume migration.

 

Do you have remediation sites in developed areas where traditional remediation techniques may be difficult to implement successfully? Call our horizontal remediation well experts at 1-877-788-4479 to discuss your current project needs.