Corrective Action for Diesel Release into Wetlands

Remediation of stormwater management system
Site work to reconstruct stormwater management system

Client Challenge

Nearly 13,000 gallons of fuel oil were released from an aboveground storage tank (AST) at an active military base directly upgradient of a stormwater retention pond with an engineered submersed gravel wetland. The retention pond was designed to store up to 580,000 gallons of stormwater, which then flows into a creek and directly into the Chesapeake Bay one mile downstream. The stormwater feature was engineered on top of a non-permeable clay with a relatively high-permeable sand lens lying directly above, allowing for lateral migration of light non-aqueous phase liquid (LNAPL) following the release.

GES Solution

GES directed the containment, assessment, permitting, remedy design, and reconstruction of the stormwater pond, including management of the active Maryland Department of the Environment (MDE) case under the Oil Control Program and Stormwater Management Program, to advance the case towards closure. Daily work activities were coordinated with various government and military agencies, including weekly site meetings with MDE personnel.

The initial abatement phase consisted of plugging the outfall with a pressurized “plug” to contain all LNAPL. After containment was complete, dewatering activities began by pumping all liquids from the pond through a weir, frac tank, and a carbon treatment system before discharging into the stormwater system via temporary permit obtained by GES. Remediation of the soil occurred via direct excavation and disposal of impacted soils at a waste-recycling facility. Unexploded ordnance (UXO) sweeps were required during all excavation work at the active military facility.

Real time data, such as photoionization detector data and lab analytical data, were used to guide soil excavation with surgical precision. Lateral migration of LNAPL was noted throughout a sand lens along the side wall of the stormwater pond, six feet below ground surface (bgs) and within the groundwater table. Infrastructure limited excavation to the northeast, so a geosynthetic clay liner was installed along the entire length of the northeast side wall to create a barrier to stop LNAPL from migrating back into the reconstructed pond. To recover LNAPL on the northeast side of the barrier, a passive recovery trench will be installed to allow for accumulation and removal of LNAPL that could not be recovered due to high-risk subsurface infrastructure in this area. An Interim Corrective Action Plan was submitted to MDE and approved for implementation.

Client Benefits

The pond was ultimately restored to its original condition along with redesign and installation of the engineered submersed gravel wetland designed to reduce nutrient loading to the adjacent creek, which flows directly to Chesapeake Bay. The client realized significant cost savings due to the real-time data guiding excavation activities, as various parts of the existing stormwater pond remained intact throughout the project, including the center berm running the length of the BMP. The low cost and easy installation of the geosynthetic clay liner barrier was an ideal remedial strategy, while the passive recovery trench will allow for the removal of LNAPL. Currently, the site is being monitored on a quarterly schedule prior to receiving regulatory closure.