Awards and Client Recognition

Presented To: Aponowich, Driscoll & Associates, Inc. with Sevenson Environmental Services, Inc. (Contractor/Operator)
Presented By: American Academy of Environmental Engineers Scientists

ADA and Sevenson Environmental Services (contractor) have been working on the NW Natural Gas site in Portland Oregon since 2008 on an extensive remediation project, removing pollutants from the site being discharged into the Willamette River via groundwater.

In 2020 and 2021, it was determined that the groundwater flow patterns had changed over 8 years of operation. Additional measures were necessary to prevent this groundwater source from reaching the river. This groundwater showed much higher pollutant levels than existing flows. A new pretreatment system was required to collect and treat the so-called “Interceptor Trench” groundwater. The new system would then be tied into the existing Pretreatment Plant and ultimately pumped to the Main Treatment Plant for further treatment and final discharge.

Key Takeaways from the project are:

• Alternative air stripping methods were not deemed to be feasible due to the iron fouling which would occur.
• While diffused-air type air strippers are relatively rare and their performance not extensively documented, the Interceptor Trench unit has shown that, properly designed, a diffused air system can produce remarkable organics removal results, even with high solids in the wastewater.
• The iron in the groundwater was oxidized effectively and used as a no-cost method of removing heavy metals.
• The higher-than predicted removal of semi-volatile PAHs in the diffused-air unit has doubled the life of the liquid phase activated carbon system downstream.
• Since the Interceptor Trench project was commissioned, it has intercepted and successfully treated over 150 million gallons of polluted groundwater.
• The plant discharge to the Willamette River has continually met the NPDES standards, many of which are below drinking water standards.

In 2024, Sevenson was awarded PG&E’s Environmental Remediation Safety Council’s ACE Award for our work at the Former Napa Manufactured Gas Plant Site in Napa, California.

Sevenson’s scope of work included the demolition and removal of subsurface structures and excavation of the top 4-ft. of soil across the entire area; deep excavation to 18-ft. BGS in additional areas; transportation and disposal of excavated soil from OU1 in a temporary fabric structure under negative air and equipped with an air treatment system; and in-situ stabilization (ISS) to 60-ft. BGS.

Sevenson also performed remediation of the backyards of five townhomes and an open area of the townhome complex. Sevenson completed over 50,000 work hours without a lost time incident.

Presented To: Aponowich, Driscoll & Associates, Inc. with Sevenson Environmental Services, Inc. (Contractor/Operator)
Presented By: American Academy of Environmental Engineers Scientists

ADA and Sevenson Environmental Services (contractor) have been working on the NW Natural Gas site in Portland Oregon since 2008 on an extensive remediation project, removing pollutants from the site being discharged into the Willamette River via groundwater.

In 2020 and 2021, it was determined that the groundwater flow patterns had changed over 8 years of operation. Additional measures were necessary to prevent this groundwater source from reaching the river. This groundwater showed much higher pollutant levels than existing flows. A new pretreatment system was required to collect and treat the so-called “Interceptor Trench” groundwater. The new system would then be tied into the existing Pretreatment Plant and ultimately pumped to the Main Treatment Plant for further treatment and final discharge.

Key Takeaways from the project are:

• Alternative air stripping methods were not deemed to be feasible due to the iron fouling which would occur.
• While diffused-air type air strippers are relatively rare and their performance not extensively documented, the Interceptor Trench unit has shown that, properly designed, a diffused air system can produce remarkable organics removal results, even with high solids in the wastewater.
• The iron in the groundwater was oxidized effectively and used as a no-cost method of removing heavy metals.
• The higher-than predicted removal of semi-volatile PAHs in the diffused-air unit has doubled the life of the liquid phase activated carbon system downstream.
• Since the Interceptor Trench project was commissioned, it has intercepted and successfully treated over 150 million gallons of polluted groundwater.
• The plant discharge to the Willamette River has continually met the NPDES standards, many of which are below drinking water standards. The NPDES permit limits are summarized in a following section.

Sevenson Environmental Services Inc. has been a SAME Philadelphia Post Sustaining Member since 1993 and is honored to be the recipient of the post’s 2024 Sustaining Member Firm of the Year Award.

For more than 40 years Sevenson’s Federal Program has successfully worked with the USEPA, USACE, NAVFAC, and DOE. Working closely together, Sevenson and our partners in the SAME Network have collaborated to address difficult design and construction issues at several of the most sensitive and complex Superfund sites in the United States, many of which fall under USACE Philadelphia’s purview.

Sevenson has proudly supported the Philadelphia Post throughout its 30+ years of membership. It has been the “Tournament Sponsor” for the Annual SAME Philadelphia Post Liberty Golf Classic for many years and has even won the tournament a time or two. Sevenson has also been an active supporter of the DCHWS Conference that the Philadelphia Post hosts since its inception.

Sevenson Environmental Services, Inc. has been awarded a Top Workplaces 2024 honor by The Buffalo News Top Workplaces. This list is based solely on employee feedback gathered through a third-party survey administered by employee engagement technology partner Energage, LLC. The confidential survey uniquely measures the employee experience and its component themes, including employees feeling Respected & Supported, Enabled to Grow, and Empowered to Execute, to name a few.