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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  wastewater treatment plant that remained from the manufacturing operations.  Mercury and any other contaminants were removed, and treated water was discharged in accordance with the 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:

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  • 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

  • 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 Maine DEP to install four additional extraction wells  in the Landfill 1 area to capture additional groundwater at the site. The plan was approved by Maine 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 Maine DEP approved this request in May 2016.


Because some of these extraction wells would need to be abandoned during the Landfill 1 remediation, one new well was added to the system in 2017 outside the Landfill 1 excavation areas.​​​

Mallinckrodt and the Maine DEP agreed that the long-term groundwater extraction system (GWES) at the Site would include extraction wells in two locations - former Landfill 1 area and around Landfills 3,4,and 5.  Once the remediation of the Landfill 1 area was complete, the design for the final Landfill 1 GWES, consisting of eight extraction wells and piping to the GWTP,  was submitted to the Maine DEP in 2018.  The design was approved and construction and startup of the Final GWES occurred in 2019. While Landfill 1 is located relatively near the GWTP, Landfills 3-5 are in the far northern end of the Site and a force main (a pressurized pipeline that uses pumps to move water from one location to another) was required to move the groundwater from extraction wells in this area to the GWTP. Because this force main could not be constructed until certain sections of the Plant Area were remediated, the Landfill 3-5 GWES design was submitted to the Maine DEP in 2021. The design was approved, and the system started operation that same year.  The controls for both extraction systems were recently upgraded with remote monitoring capabilities, allowing the Site’s groundwater consultants to continually check the system even when not on site. A backup generator is also in place so that even with a power outage, the extraction wells will continue to pump groundwater for treatment.

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The MEPDES permits are effective for five years and the 2014 permit was renewed in May 2019. An application to renew the 2019 permit was submitted to the Maine DEP in early 2024 and approval is expected shortly.  (As long as renewal applications are submitted prior to the end date of the current permit, operations are allowed to continue until Maine DEP issues the new permit.)  As part of the permit conditions, the treated water is sampled before discharge and monthly reports are submitted to the Maine DEP with flow and sampling results. GWTP operations are also periodically inspected by Maine DEP in person and the August 2018 inspection report from DEP noted that [the GWTP Operator] "is doing a great job running this treatment system!" Since the current GWTP began operations in 2012, over 2,570 samples have been collected (as of July 2024) and no violations or corrective actions have been noted during the agency inspections.​

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