Oronoco Outfall Remediation Project

Page updated on Feb 10, 2017 at 10:48 AM


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City of Alexandria Takes Additional Steps Regarding Former Gas Plant

For Immediate Release: February 10, 2017

The City of Alexandria has announced additional steps to address environmental issues related to a former manufactured gas plant in Old Town.  The next step will involve storm sewer pipe cleanup and inspection work the week of February 13, from 7 a.m. to 6 p.m., near the unit block of Oronoco Street.  Some parking and sidewalk access will be limited in the area during this work, and there may be minor traffic disruptions.

The Alexandria Town Gas plant at the corner of Lee and Oronoco Streets operated from 1851 to 1946, and was owned by the City for most of that time.  In the 1970s, the site was developed into an office and townhome complex and an outfall pipe was installed to direct stormwater into the nearby Potomac River.  Over time, residue from the plant site has been identified in the area intermittently, resulting in part from ground contamination from the plant’s operation and in part from contaminants that have entered the stormwater pipe and traveled to the river.

The site has been entered into the Virginia Voluntary Remediation Program, which allows the City to work closely with the Virginia Department of Environmental Quality.  The City has taken many measures, in a multi-year, phased plan, to prevent further discharges related to the plant.  

Potomac Riverkeeper (PRK), a nonprofit organization focused on preventing pollution along the Potomac River, has shared data samples and concerns about the spread of contaminants.  The City appreciates PRK's input and technical contributions, and City and PRK staff are working together to develop solutions. On the basis of PRK's initial data, the City conducted a video inspection of the stormwater pipe between N. Union and N. Fairfax Streets and has done additional sediment sampling to identify areas requiring further work.

Next, City contractors will conduct a thorough inspection and cleanout of the outfall pipe.  The work will begin on February 13 and should take approximately one week, weather permitting.  The report on this work will include recommendations on further remedial actions to prevent contaminants from entering the pipe.

As the next phase of this project, the City has planned and budgeted for 2017 to dredge and remove contaminated sediment from around the outfall.  A special mat will be installed to “cap” the remaining sediment and prevent contaminants from moving into groundwater and seeping into the river.  The City and its environmental consultants will also continue to perform soil sampling in the area of the former plant to identify any areas where residue may remain beneath the ground.

Work involving the former gas plant site is unrelated to the City’s accelerated efforts to address its aging combined sewer outfall (CSO) system.  The outfall impacted by the former gas plant is part of the City’s dedicated storm sewer system and only conveys stormwater to the Potomac River; it is not a combined sewer outfall.

For media inquiries, contact Craig T. Fifer, Director of Communications and Public Information, at craig.fifer@alexandriava.gov or 703.746.3965.

Background on Oronoco Outfall – Alexandria Town Gas Site

  • The City of Alexandria continues to address environmental concerns associated with the Alexandria Town Gas – Oronoco site (ATG-Oronoco). Since entering the site into Virginia’s Voluntary Remediation Program (VRP) in 2000, the City has made considerable progress towards remediating this site.
  • Alexandria operated a manufactured gas plant (MGP) near the corner of North Lee and Oronoco Streets between 1851 and 1946.   The plant produced a coal-derived gas to provide energy for residents and businesses in the City. From the late 1800's to the mid 1900's, thousands of manufactured gas plants across the United States supplied homes and industry with this manufactured gas for heating, cooking, and lighting. 
  • The production of manufactured gas created wastes, some of which remain at former MGP sites, long after the MGPs ceased operating.  Over the decades during which many of these MGPs operated, coal tar leaked from storage and processing facilities and contaminated surface soils, subsurface soils, and groundwater.  Today, municipalities across the country, like Alexandria, are working to remediate sites contaminated by MGPs.
  • The City is committed to addressing issues associated with the site by pursuing cleanup under the Virginia’s VRP.  The Virginia Department of Environmental Quality (VDEQ) oversees the program to ensure that the cleanups achieve a satisfactory level of protection for human health and the environment and is actively involved in monitoring the progress of the ATG-Oronoco site remediation. The City has been pro-active in satisfying all requirements of the VRP to date. 

Corrective Actions to Date

  • Installation and operation of the floating oil containment boom around the outfall discharge area with additional oil absorbent booms installed and replaced periodically on the interior to collect contaminants.
  • The City has installed and is currently operating a free product removal system that includes recovery wells installed in the source area. The removal of free product from the subsurface will make future remedial efforts more efficient.
  • The City successfully completed the relining of the Oronoco Street storm sewer in 2006. The relining has reduced the amount of oily substances infiltrating into the pipe and subsequently reduced the amount of impacted material being discharged to the Potomac River. 
  • In 2008, the City’s environmental consultant experimented with a treatment scheme that uses air and nutrients to breakdown oily substances near the outfall site, resulting in a significant reduction in contamination levels.  Subsequent sampling has confirmed the continuing success of this biodegradation technique.
  • Based on the above successful biodegradation technique, in 2013, the City installed a groundwater treatment system beneath Oronoco Street. The system removes coal tar from groundwater before it discharges into the Potomac River. After nearly four years of operation, quarterly groundwater monitoring of wells located downgradient from the system, indicate that the system is functioning properly.  
  • With VDEQ approval, the City began planning additional remedial actions to address the contaminated sediments located below the Oronoco Street storm sewer outfall to the Potomac River. In 2015, VDEQ approved the City's Remedial Action Plan (RAP) to dredge and cap the residual coal tar-impacted sediments within the Potomac  River.   The bulk of affected sediments will be removed and a reactive cap installed over the remaining sediments will eliminate future seepage of coal tar into the river and cut off potential exposure pathways to human and ecological populations. Once in place the cap will not be visible above the waterline. The City awarded a contract to perform this work in late 2016. 

What's Next? 

  • Before proceeding with the sediment dredge and cap project at the foot of Oronoco Street, the City is conducting cleaning and inspection work inside the main storm water pipe along Oronoco Street between North Union and North Fairfax Streets. This work is to identify and repair where necessary, pipe sections to ensure pipe integrity and prevent intrusion of contaminants into the pipe. This work is scheduled for mid February 2017.
  • The City intends to proceed with the dredge and cap project as soon as the issue with the intrusion of contaminants into the pipe is resolved.
  • VDEQ also requires the City proceed with an upland investigation.  The investigation is intended to build upon data collected in previous years and is aimed at delineating the  extent of below ground contaminant spread through the soil and groundwater. The collected data will be modeled to determine if further remedial actions are necessary. The upland investigation plan was submitted and approved by VDEQ in 2016, and is currently scheduled for Spring 2017. 

For more information, please visit the Contaminated Lands webpage.

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