Oronoco Outfall Remediation Project

Page updated on May 8, 2019 at 3:11 PM

What's New

City Street and Utility Work on the 100 block of Oronoco St. January 9-10, 2019

The City of Alexandria will be working on the 100 block of Oronoco St. January 9-10, 2019.  This work will supplement the ongoing remediation activities for the former Alexandria Town Gas plant and repairs to the storm water pipe located below the street on this block.  The work will require street parking restrictions on both days.

On Thursday, the work will require the use of some heavy equipment and trucks. Work crews will begin staging equipment that morning and continue into that afternoon.   Elevated sound levels will be associated with this work for approximately 3 hours on Thursday afternoon and all efforts to minimize this sound will be employed.

Khoa Tran
Environmental Program Manager, Office of Environmental Quality
Department of Transportation & Environmental Services

About the Alexandria Town Gas – Oronoco Outfall (ATG – Oronoco) Voluntary Remediation Project

The City of Alexandria continues to address environmental concerns associated with ATG – Oronoco. Since entering the site into Virginia’s Voluntary Remediation Program (VRP) in 2000, the City has made considerable progress towards securing this site.

Background on the ATG – Oronoco Site

  • From the late 1800s to the mid 1900s, thousands of communities across the United States relied on manufactured gas plants (MGP) for heating, cooking, and lighting fuel. Alexandria operated an MGP near the corner of North Lee and Oronoco Streets between 1851 and 1946. This plant produced a coal-derived gas for residents and businesses in the City.  
  • The production of manufactured gas created wastes, some of which remain at former MGP sites long after they cease operations. Over the decades many MGPs operated, a process byproduct called coal tar leaked from storage and processing facilities into 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 MGP site issues by pursuing cleanup under Virginia’s VRP.  The Virginia Department of Environmental Quality (VDEQ) oversees the program to ensure that cleanups achieve a satisfactory level of protection for human health and the environment. In this role, VDEQ actively monitors the progress of the ATG-Oronoco site remediation. The City has been pro-active in meeting all requirements of the VRP to date. 

Corrective Actions Taken 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 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  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 five 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. This work is scheduled to begin in January 2018. 
  • In  February 2017, the City cleaned and inspected the main storm water pipe along Oronoco Street between North Union and North Fairfax Streets. Follow-up work  identified and repaired  pipe sections to ensure pipe integrity and prevent intrusion of contaminants into the pipe. 

What's Next? 

  • The  dredge and cap project is scheduled to begin in January 2018.
  • 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 will take place in two phases.  The first phase was completed in June 2017, the second phase is  scheduled for Winter 2018. 

Project Resources

For more information, please visit the Contaminated Lands webpage or the Department of Project Implementation's Oronoco Dredging and Capping project page.