Corrective Action and LNAPL Plume Remediation at a Retail Gas Station

Geosyntec worked with our client to develop and implement corrective actions at this retail gas station that were vital to preparing it for resale. Geosyntec worked with our client to develop and implement corrective actions at this retail gas station that were vital to preparing it for resale.

A group of off-site property owners successfully sued Coastal Mart, Inc. (CMI), a retail convenience store/gas station chain owned by El Paso Corporation Oil & Gas, for contamination from a store in McAllen, Texas. Post-trial negotiations resulted in remediation of the now-closed store property and related contamination beneath nearly four acres of adjacent commercial and residential properties. Geosyntec was retained to provide corrective action services with the objective of cleaning up a phase-separated hydrocarbon (PSH) plume and groundwater.

Geosyntec's Scope of Services

Geosyntec prepared a health risk evaluation; multi-phase recovery modeling; remediation system design; Corrective Action Plan implementation; construction oversight; remediation system operation and maintenance; site monitoring; and site closure activities. Recovery technology included the installation of 63 multi-function wells involving nearly 16,000 feet of underground piping. The wells could be operated independently, in combination as soil vapor extraction (SVE) and groundwater pumping wells, or independently as air injection wells. Treatment technology included the innovative use of an air-water heat exchanger installed on the thermal oxidation vapor treatment unit stack. The process equipment included: a 200 HP variable frequency drive operating a five-stage SVE blower; a 2,500 SCFM thermal treatment unit equipped with an air-water heat exchanger to heat recovered water following oil water separation to improve the stripping efficiency of MTBE using a 200 gpm water treatment system, and an air injection system rated at 500 icfm at 10 psi. Geosyntec performed a Monitored Natural Attenuation (MNA) evaluation prior to system start-up and two quarterly MNA events after remediation system shut-down in March 2005.

Notable Accomplishments

During nearly two years of system operation, the remediation system recovered and treated approximately 50 million gallons of contaminated water and removed approximately 214,000 pounds of hydrocarbons. The system achieved Texas Commission on Environmental Quality (TCEQ) cleanup criteria while maintaining hydraulic control of the recovery system so that it did not influence an adjacent product plume located approximately 300 feet from the CMI plume.

The property has achieved no further action status, and there are plans to resell the remediated property for unrestricted re-use.

Project Overview

  • Location: McAllen, Texas, USA
  • Client: Coastal Mart, Inc.
  • Project Practice Areas: Contaminated Sites
  • Type of Facility: Retail Gas Station
  • Services Provided: Corrective Action Services; Multi-Phase Remediation System Design & Implementation; Monitoring Natural attenuation
  • Type of Work: Corrective Action
  • Company: Geosyntec Consultants
  • Governing Regulation: Texas Commission on Environmental Quality (TCEQ) Voluntary Program
Geosyntec Consultants
Geosyntec is a consulting and engineering firm that works with private and public sector clients to address new ventures and complex problems involving our environment, natural resources, and civil infrastructure.

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