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Soil and Groundwater Remediation

Comprehensive environmental consulting and corrective action services reduce human health risks.
  • Soil and Groundwater Remediation Effort Improves Health, Safety-Gannett Fleming

    Performing a membrane interface probe investigation to detect subsurface contamination.


Prince George's County, Maryland, and Washington, D.C.

Our Role
Environmental Consulting, Permitting, Risk Assessment, Soil and Groundwater Investigation and Remediation, Vapor Intrusion Study.

30 acres
  • Customized GIS application effectively shared information with stakeholders 
  • Multi-phase extraction remediation system to treat groundwater 
  • An angle-drilled well under a four-lane road
  • Zero emissions groundwater pump and treatment system.

A long-term, $10 million project helped to improve the environmental health and safety of a service station site. When Gannett Fleming began the project, the service station already had a history of environment concerns. Investigations of the site dated back to 1989 when a gasoline release was reported to regulators. 

Gannett Fleming assumed management of the remediation site in 2000. The following year,  liquid-phase hydrocarbons (LPH) were discovered in the down gradient monitoring well, triggering a soil and groundwater investigation in a residential area across the street from the station. The scope and complexity of the investigation grew quickly, as it became apparent that the migration distance of LPH and size of the resulting groundwater plume were larger than anticipated. Corrective action was needed.  

What We Did

Following extensive soil and groundwater investigations covering 30 acres, Gannett Fleming designed a multi-phase extraction (MPE) remediation system capable of treating approximately 50,000 gallons of groundwater a day for the source area. Gannett Fleming operated the system with no permit exceedances.

More recently, Gannett Fleming served as general contractor and constructed three remediation systems that comprise the final U.S. EPA-approved remedy for the site. We expanded the MPE system to include an angle drilled well under a four-lane road, installed two recirculation wells, and installed an oxygen reactive zone. Gannett Fleming obtained all permits and designed the systems, still in operation today. 

In addition to the purely technical challenges, this project involved complex administrative issues. Although the service station is in Maryland, the dissolved hydrocarbon plume was mostly in Washington, D.C. Because of the multi-jurisdictional location of the site, the U.S. EPA was the lead regulatory agency, with the District of Columbia’s Department of the Environment and the Maryland Department of the Environment as secondary agencies. Gannett Fleming concurrently worked with all agencies, securing all permits and approvals to make this soil and groundwater remediation project a success.

Key Features

  • More than 3,000 soil, groundwater, soil vapor, sub-slab vapor, indoor air and ambient air samples in a residential area covering approximately 30 acres 
  • Multiyear residential vapor intrusion study
  • Expedited site investigation, including vertical groundwater delineation
  • Resource Conservation and Recovery Act corrective measures study, site investigation report, corrective measures design reports, and corrective measures implementation reports
  • Carbon stable isotope analysis of benzene and methyl tertiary-butyl ether 
  • Development of a MODFLOW groundwater model
  • Design and construction of an oxygen reactive zone located in a residential alley
  • Air emissions, public space, occupancy, building, and General National Pollutant Discharge Elimination System permits.

Sustainability Features & Outcomes

  • Detailed design and construction of an innovative, zero-emissions groundwater pump and treatment system installed 100 percent below grade in a residential alley with no air emissions during operations
  • Baseline human health risk assessment.

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