Aerial view of the Exelon West Medway II project

Exelon West Medway II

At a Glance Client

Project Size
200 MW


Epsilon performed a leading role in the environmental planning, permitting, and commissioning efforts for Exelon Generation’s major expansion of the existing West Medway power generating station.


Exelon Generation developed a new 200 MW electric generating facility in Medway, Massachusetts (adjacent to the existing Exelon West Medway Station). This facility provides additional capacity for the Southeastern Massachusetts and Rhode Island (SEMA/RI) load zone in ISO-New England. This was done to help meet energy demands during peak times and to provide quick-starting backup for intermittent renewable energy sources such as wind and solar energy. Designated West Medway II, the new facility consists of two simple-cycle gas turbines rated at 100 MW each, with the capability to fire either natural gas or distillate fuel oil. Ancillary equipment includes two emergency diesel generators and various storage tanks. Exelon secured its major approvals in 2016 and commenced commercial operation in 2019.


Epsilon worked closely with Exelon and project stakeholders during the development process to apply for and obtain the required environmental approvals, including:

  • Final Approval, Massachusetts Energy Facilities Siting Board (EFSB)
  • Massachusetts Department of Environmental Protection (MassDEP) Air Plan Approval, Prevention of Significant Deterioration (PSD) Approval, Environmental Results Program (ERP) emergency engine certifications, and CO2 Budget Trading Program Approval
  • Massachusetts Environmental Policy Act (MEPA) Certificate, per Draft Environmental Impact Report (DEIR) and Final Environmental Impact Report (FEIR)
  • Wetlands Order of Conditions, Town of Medway Conservation Commission
  • Site Plan Decision, Town of Medway Planning Board
  • U.S. EPA Acid Rain Program Permit

Epsilon conducted a variety of extensive technical analyses in support of these approvals, including a site selection study, air emissions estimations and air dispersion modeling, background noise measurements and extensive noise modeling, wetlands delineation, and development of an on-site process water well. Epsilon scientists and engineers also contributed expert testimony in response to public comments and agency reviews.

Epsilon remained engaged with the project’s construction and initial commissioning process, through the following activities:

  • General supervision of environmental tasks and milestones, including regular status meetings, maintenance of a compliance matrix, and as-needed communications to MassDEP / U.S. EPA
  • Initial noise compliance testing (including the deployment of field crews and early troubleshooting)
  • Supervision of initial air emissions compliance testing
  • Support for as-required Notices of Project Change to the Massachusetts EFSB
  • Continuous Emissions Monitoring System (CEM) and Data Acquisition System (DAS) configuration planning, including participation in Factory Acceptance Test, development of QA/QC and Monitoring Plans as required by 40 CFR 60 and 40 CFR 75, initial CEM certification applications, and receipt of site-specific Alternative Monitoring Approval from MassDEP to synchronize ongoing CEM QA/QC requirements
  • Development of Facility Response Plan (FRP) for oil and chemical spill prevention

Epsilon maintained a regular on-site presence after project construction to ensure ongoing compliance with all environmental aspects, including:

  • Routine air permit compliance (monitoring, recordkeeping, and reporting)
  • Air emissions inventory development and reporting (“Source Registration,” Greenhouse Gas)
  • “Tier 2” hazardous material reporting
  • Regular review of Continuous Emissions Monitoring system data and QA/QC activities, including preparation of quarterly Electronic Data Reports (“EDRs”) to U.S. EPA
  • Hazardous waste and waste oil management compliance
  • Aboveground storage tank (AST) compliance
  • Preparation of documentation under the Risk Management Plan (RMP) General Duty Clause, regarding the storage of aqueous ammonia


This new facility provides a reliable, clean energy source for the area. Its high-efficiency turbines paired with advanced pollution-control technology make it one of the cleanest peaker power plants of its kind.

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