CTO – Gasoline Release Response | Emergency Response Services CT

Site Investigation, Emergency Response, and Remediation Services | LEP Services and Monitoring Program Oversight

Why GeoInsight

We were retained by a regional emergency response contractor to provide a wide range of environmental services to respond to a significant release of gasoline at a gasoline retail station in Bridgewater, CT.  An estimated release of 1,100 gallons of gasoline occurred over a five week period from a defective valve on their underground storage tank system.  GeoInsight’s extensive experience with emergency response activities and Connecticut’s spill remediation program were key assets in helping the client manage this significant release.  The work was conducted under the direction of a Connecticut Licensed Environmental Professional (LEP).


SUCCESSFULLY COORDINATED RESPONSE WITH CTDEEP, USEPA, CTDOT, AND LOCAL AUTHORITIES – We worked with the client, CTDEEP, USEPA, and Town of Bridgewater to respond to the significant release.  This included responding to the rapidly changing project needs and quickly evaluating changing environmental conditions.

DETAILED RECEPTOR EVALUATIONS – Immediately following the identification of the release, we conducted a detailed evaluation of potential drinking water and ecological receptors and developed a sampling program to help address local and regulatory concerns.

REMEDIAL OVERSIGHT AND COORDINATION – GeoInsight quickly developed an investigation plan to evaluate soil, groundwater, and surface water quality.  The information was used to develop a remedial plan that was immediately implemented to help prevent migration of the gasoline impacts.

MONITORING PROGRAM DEVELOPMENT AND REGULATORY CLOSURE – We helped the client to develop a long-term groundwater and drinking water monitoring program to help ensure that nearby receptors were not impacted by the release.  The goal of the monitoring program will be to close the release with the CTDEEP.

Client: Gasoline Service Station and Insurance Client
Location: Bridgewater, CT

Scope of Services

  • Emergency Response and Field Investigation Activities
  • Identification of Potential Receptors
  • Remediation Oversight and Regulatory Communications
  • Groundwater Plume Delineation and Monitoring Program Development
  • Regulatory Program Compliance and Closure Monitoring

Project Details

EMERGENCY RESPONSE AND FIELD INVESTIGATION ACTIVITIES – GeoInsight performed comprehensive and immediate assessments to evaluate the release mechanism and migration path for 1,100 gallons of gasoline, the possible impact of the release to groundwater and surface water in the area of the site, and the extent of the impacts to soil.  The assessments included the drilling of soil borings and installation of monitoring wells at the site, on the adjacent State highway, and at properties hydraulically downgradient from the release.  GeoInsight coordinated access to these properties with the CTDEEP, Connecticut Department of Transportation (DOT), Town of Bridgewater, and neighboring property owners.  In addition, we assisted the remedial contractor with the setup and monitoring of a groundwater treatment system that discharged to the storm sewer system.

IDENTIFICATION OF POTENTIAL RECEPTORS – GeoInsight performed a comprehensive receptor survey to identify drinking water and ecological receptors in the area of the site.  We identified 30 properties with drinking water supply wells within 500 feet of the site.  Given the proximity of the release to the nearby drinking water wells, the site was subject to the Significant Environmental Hazard Notification (SEHN) regulations.  GeoInsight coordinated and implemented monitoring program for each of the 30 properties to evaluate whether they were impacted by the release.  Gasoline-related constituents have not been detected in the supply wells since the monitoring program began.  Ecological receptors were not identified.

REMEDIATION OVERSIGHT AND REGULATORY COMMUNICATIONS – Following delineation of the gasoline impacts at the site, beneath the State highway, and on the neighboring properties, GeoInsight prepared a detailed remedial action plan (RAP) for approval by the CTDEEP.  In addition, we prepared an application for the closure and excavation of the state highway with the CTDOT.  The application included a detailed reconstruction of the State highway to CTDOT specifications.  The remediation included the excavation and off-site disposal of 4,386 tons of gasoline-impacted soil and pumping, treatment, and discharge of 36,000 gallons of impacted groundwater.  The presence of shallow bedrock helped to limit the vertical migration of the release.  The excavation extended vertically to the bedrock surface at the site and beneath the State highway.  During the remediation process, GeoInsight conducted a comprehensive post-remediation soil sampling program, consisting of 33 samples, in accordance with the RAP.  Following the remediation, the excavated areas were restored to previous conditions, including the reconstruction of the State highway.  GeoInsight prepared a detailed remediation summary report for submittal to the CTDEEP.  The report documented the remediation activities and provided a groundwater monitoring program to help achieve regulatory closure of the SEHN.

GROUNDWATER EVALUATION AND MONITORING PROGRAM DEVELOPMENT – During the field investigation activities, we installed an overburden and bedrock monitoring well network across the site and on neighboring properties to evaluate the vertical and horizontal components of groundwater flow, delineate the extent of the dissolved gasoline impacts, and evaluate potential impacts to downgradient and nearby groundwater receptors, including the drinking water supplies.  These activities were required under Connecticut Regulations.  Monitoring was conducted on a quarterly schedule and results indicated that the dissolved gasoline impacts decreased over the course of the monitoring program to non-detectable concentrations.  Downgradient receptors and drinking water supplies were not affected by the gasoline release.

REGULATORY PROGRAM COMPLIANCE AND CLOSURE – During the course of the project, GeoInsight prepared detailed investigation and remediation summary reports and monitoring program proposals, as required.  Following the completion of the groundwater and drinking water compliance monitoring program, GeoInsight Licensed Environmental Professional (LEP) will file an SEHN closure request with the CTDEEP.