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Groundwater Treatment Plant

The Groundwater Extraction and Treatment System

One of the earliest remedial actions at the Orrington site was to capture and extract groundwater and treat it to remove the mercury. A groundwater extraction well (MW-601) was installed in the area of Landfill 1 in 2005 and an extraction trench was also installed south of the manufacturing area. Groundwater captured by these two systems was pumped to the existing wastewater treatment plant where mercury was removed and treated water discharged in accordance with the site’s existing Maine Pollutant Discharge Elimination System (MEPDES) permit.

In 2011, the engineering firm Woodard & Curran of Port­land, Maine was retained to design and construct a new state-of-the-art groundwater treatment plant (GWTP). The design objectives were to provide a new treatment system that would:

  • Maintain compliance with the discharge permit

  • Replace the existing system with no interruption in service

  • Handle increased groundwater flows during implementation of the site remedy

  • Operate in the long-term with minimal maintenance


The treatment processes in the existing plant (solids coagulation and filtration followed by granular activated carbon (GAC) and Mersorb to remove mercury and other contaminants) still represented the best available treatment technology, however the design modifications to improve efficiency included:

  • A new, energy efficient building

  • All new process equipment to ensure long-term reliability

  • An improved filtration system which requires fewer chemicals

  • Two, new 15,000 gallon insulated effluent storage tanks

  • A new remote monitoring and alarm system was added

  • Additional discharge monitoring points inside the treatment building to improve safety and winter access ability.


The new GWTP began treating extracted groundwater in August 2012 and in July 2013 the Maine DEP issued a revised MEPDES Permit and Waste Discharge License. The new GWTP is designed to handle 60 gallons per minute (gpm) on an ongoing basis with additional capacity to handle increased flows during remediation or severe storms. The treated groundwater (effluent) is tested to ensure compliance with the MEPDES permit and reports are submitted to Maine DEP as required by the permit.


In 2014, Mallinckrodt US LLC (Mallinckrodt) submitted a plan to DEP to install four additional extraction wells (EW-1 through EW-4) in the Landfill 1 area to capture additional groundwater at the site.

The plan was approved by DEP in September 2014 and construction of the additional extraction wells and associated piping was completed by Sevee & Maher Engineers in February 2015. A minor modification to the permit to increase the flow was requested in April 2016 and DEP approved this request in May 2016.

Because some of these extraction wells would need to be abandoned during the Landfill 1 remediation in 2018, one new well (EW-5) was added to the system in 2017 outside the Landfill 1 excavation areas. The location of the final, long-term groundwater extraction system (Final GWES) is in the area of Landfill 1, and once the remedial design for this area was approved, the design for the Final GWES system could be developed. The piping design was submitted to DEP in August and the design for the final extraction wells was submitted to DEP in September 2018. These designs were approved in October 2018 and construction and startup of the Final GWES occurred in August 2019.

An application to renew the current Maine DEP Discharge Permit was submitted to DEP in May 2018. As long as the renewal application was submitted prior to the end date of the current permit, operations were allowed to continue under the existing permit until DEP issues the new permit. The DEP issued a new Discharge Permit dated May 3, 2019.

The GWTP operations were inspected by DEP in August 2018 and no violations or corrective actions were noted. The inspection report from DEP noted that [the GWTP Operator] "is doing a great job running this treatment system!"

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