Oronoco Outfall Remediation Project
The City of Alexandria recently installed Non-Aqueous Phase Liquid (NAPL) recovery wells along Oronoco Street between North Lee and North Union Streets beginning March 2, 2021 and completed on April 30, 2021.
For more information, see the Recent Construction section below.
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.
ATG – Oronoco Site History
- 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.
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.
- 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.
- 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 was completed in Winter 2018.
- The dredge and cap project was completed in April 2018.
- In September 2019, the City cleaned and repaired a stormwater pipe in the 100 block of Oronoco Street to clear the residual coal tar from the pipeline floor and grout it.
- From March 2021 through April 2021, the City installed Non-Aqueous Phase Liquid (NAPL) recovery wells along Oronoco Street between North Lee and North Union Streets.
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 and continues to work on a long term plan to meet remediation goals.
The City of Alexandria contracted with Cardno Inc. to install Non-Aqueous Phase Liquid (NAPL) recovery wells along Oronoco Street between North Lee and North Union Streets. The purpose of this installation is to enhance the recovery of coal tar from beneath the street.
The project occurred in two phases:
PHASE I (INITIAL INVESTIGATION / TESTING):
- Start Date: March 2, 2021
- Completed: March 4, 2021
PHASE II (NAPL RECOVERY WELL INSTALLATION):
- Start Date: April 27, 2021
- Completed: April 30, 2021
- Monday – Friday, 7 AM to 6 PM
- Saturday, 9 AM to 6 PM
STREET AND SIDEWALK CLOSURES:
- Access to all businesses and private parking lots will be maintained during construction.
- Some equipment for use during the project will be placed temporarily along the south curb of Oronoco Street.
- Access to street parking will be impacted and portions of Oronoco Street will be blocked for the duration of the work.
- Oronoco Outfall Remediation Action Plan
- Oronoco Outfall Dredge and Cap Project
- City of Alexandria Takes Additional Steps Regarding Former Gas Plant
For more information, please visit the Contaminated Lands webpage.
Tafesse Gyes, P.E., CCM
Division Chief, Construction
Department of Project Implementation