Manufactured Gas Plant (MGP) Site Assessment


Ameren Services


Quincy, IL

CEC Services

  • QAPP & HASP Preparation
  • Risk Assessment
  • Remedial Action Design
  • Ambient Air Monitoring
  • Remediation Oversights

Owner Objective

Ameren Services needed to investigate (MGP) contamination at a site in downtown Quincy, currently operated by a landscape supply business as warehousing space. From 1854 until 1934, the site had been the location of the Quincy MGP. MGP process residuals were initially identified in site soil during a preliminary site investigation completed by Ameren in 1986.

CEC Approach

CEC began a focused site investigation for MGP contamination in site soil and groundwater in 2005 in accordance with the Illinois EPA Site Remediation Program. The site is located in a mixed commercial/multi-family residence area in the downtown commercial area of Quincy.

The focused investigations of soil and groundwater identified contamination across most of the site, as well as below adjoining streets and beneath adjacent properties. Impacted soil has been identified several hundred feet down-gradient from the site and contaminated groundwater extended nearly a full city block down-gradient from the site. CEC determined that many MGP process building foundations, process tanks, and piping remained in-place beneath the site. A complicating aspect to the site investigation was the presence of the current property owner’s 30,000 square foot warehouse covering approximately one-third of the site. Many MGP structure foundations and process equipment remain beneath the warehouse. CEC completed subsurface soil sampling beneath the warehouse using direct-push sampling techniques through the warehouse floor, while minimizing disruption to the owner’s business.

CEC completed a risk assessment for the site evaluating the MGP contaminated soil and groundwater according to Illinois EPA risk-based guidelines for establishing soil and groundwater remediation standards.

CEC completed a Feasibility Study to remove or treat contaminated soil, non-aqueous phase liquids, and groundwater at the site. Soil contamination and gas manufacture process residuals extended to bedrock 20 to 25-feet below the ground surface over most of the site. CEC recommended the use of a secant pile earth retention system to support the excavation necessary from property line to property line to the bedrock surface. A large combined sewer crossed the site within the remediation area required replacement and the right-of-way remediated. CEC’s civil engineers completed the design for the replacement sewer, supervised the construction, and worked with the City of Quincy for the design approval and inspections.

Because the Site was located in downtown Quincy and the project included the replacement of the combined sewer crossing the Site coordination with city government and public service departments were important during the project. As the project engineers, CEC coordinated the sewer design with the Quincy Public Works Department. A project traffic control and safety plan prepared by CEC was approved by the city. CEC provided regular updates during meetings with city officials. Ameren coordinated public information releases for the local media and the community, and hosted an Open House onsite before the remediation began to explain the details of the project to the community; CEC prepared materials for the information releases and the Open House and participated in the Open House.

Most of the soil remediation activities were completed within an enclosed clear span temporary structure to control emissions from the project. More than 2 million gallons of groundwater were recovered, treated, and discharged to the local P.O.T.W. during project execution. Water treatment has included the removal of free oils and tars, solids, dissolved phase volatile and semi-volatile organics and cyanide. CEC directed the design of the treatment system as well as the operation of this system. During the remediation CEC directed various contractors completing demolition, shoring, excavation, non-aqueous phase liquid recovery system installations, sewer replacement, and site restoration activities.

CEC was also responsible for conducting perimeter ambient air monitoring during the MGP remediation activities. CEC developed a comprehensive Ambient Air Monitoring Plan (AAMP) and a Quality Assurance Project Plan (QAPP). During the development of the AAMP CEC developed site-specific, risk-based ambient air quality standards based on the project’s expected duration and human health risks from specific contaminants of potential concern (CPCs). The CPCs for this project included (PM10) benzene, naphthalene and benzo(a)pyrene. CEC was responsible for the design, installation, operation, calibration, and maintenance of the air monitoring equipment. The real-time air monitoring included monitoring for volatile organic compounds (VOCs), including benzene-specific analysis using on-site gas chromatography (GC) and a portable dust monitor to measure concentrations of PM10.

CEC established six time-integrated air monitoring stations along the perimeter of the site. Each station was equipped with sampling equipment designed to collect integrated ambient air samples for VOCs, polynuclear aromatic hydrocarbons (PAHs) and PM10 over 72-hour sampling periods. CEC also installed and operated the site meteorological station, which was equipped with wind speed, wind direction, barometric pressure, ambient temperature, relative humidity and precipitation sensors. CEC was responsible for providing daily air monitoring reports to the remediation contractor and weekly briefings during project meetings. CEC was also responsible for preparing and submitting the results of the air monitoring activities in a final project air monitoring report.