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 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.
- The dredge and cap project s 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.
For more information, please visit the Contaminated Lands webpage.