LNAPL Remediation

Comprehensive Environmental Services for Bus Maintenance and Fueling Facility where LNAPL was Detected

Weston & Sampson conducted comprehensive environmental services for a large bus maintenance, storage, and fueling facility in South Boston, Massachusetts where several feet of floating light non-aqueous phase liquid (LNAPL) was detected. The sources of the widespread LNAPL plume and groundwater contamination were several large leaking underground storage tanks (USTs). Also, several utilities are within the LNAPL plume, which allowed migration of LNAPL farther away from the property.  The Massachusetts Turnpike Authority (MassPike) officials observed LNAPL entering their South Boston Haul Road stormwater pump station, requiring immediate response action to eliminate imminent hazard.

Weston & Sampson conducted comprehensive environmental engineering and construction services to assess and remediate the extent of LNAPL and contaminated groundwater plumes. This project included the following professional services which are described in further detail below:

  • Site Assessment and Remedial Planning
  • Federal, State, and Local Permitting
  • Subsurface utility evaluation
  • Pilot-scale remedial studies
  • Remedial alternatives feasibility study
  • Full-scale remediation design
  • Design/build/operate remediation facility
  • Public bidding assistance
  • Construction phase services including submittal/RFI processing
  • Management/observation of Operation and Maintenance (O&M) activities
  • Remedial monitoring of groundwater, utilities, and subsurface vapors
  • Regulatory reporting

The site assessment phase included investigation activities to assess the extent of the LNAPL and contaminated groundwater plumes.  We also reviewed information on the complex system of underground utilities at and around the facility and MassPike’s pump station to evaluate potential LNAPL migration pathways.  Results of the Phase II investigation indicated that LNAPL (thickness of up to six feet) was likely migrating to the pump station via the bedding materials of a large stormwater drain line.

Weston & Sampson’s Remediation Feasibility study identified dual phase extraction (DPE), LNAPL recovery, and enhanced bioremediation as the most technically feasible and cost-effective cleanup strategy for the site.  We completed the design of a dual phase extraction phase system consisting of 26 extraction wells, liquid and vapor phase carbon adsorption, metals precipitation, and injection of an oxygen/nutrient mix to stimulate bioremediation.

During the full-scale system design and construction phases, Weston & Sampson designed, built, and are currently operating/monitoring an interim product recovery system with pneumatic product-only skimming pumps, double wall piping, and explosion-proof electrical supply/controls. Weston & Sampson provided bidding assistance for the full-scale DPE system including addenda preparation, contractor inquiry response, and evaluation of the received bids. We provided construction phase services, managed the O&M activities completed by the contractor, and performed site-wide monitoring of groundwater, soil gas, and LNAPL recovery.

During the first six months of operation, this remediation system has recovered 12,000 gallons of fuel oil that has been recycled.


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