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Potomac River Generating Station, Alexandria - PC 2013-3154


construction PRGS

Potomac River Generating Station as it is being built in 1932.


DEQ has created this webpage to provide access to the technical reports and technical correspondence for the petroleum release from two 25,000 gallon underground heating oil storage tanks at the Potomac River Generating Station (PRGS) in the City of Alexandria. DEQ staff will typically post reports or technical correspondence on this webpage within 30 days of receipt, after staff has reviewed the information and confirmed that it is complete.

Links to documents


The remediation system approved in March 2015 was completed and switched on in March 2016. It operated from March 2016 to March 2018 when a trial shut down was approved by DEQ. Rebound in petroleum concentrations in groundwater led to the system being started up again in August 2018 and the system operated from August 2018 to September 2019, when it was again agreed that a second trial shut down could start as the corrective action objectives were being met. Monitoring will continue for at least two more years. If during that time petroleum concentrations rise above the corrective action objectives further remediation will be requested.

Case History

On March 21, 2013, NRG, the owners of PRGS at the time, reported that two 25,000 gallon underground heating oil tanks, installed in the 1940s and 1950s, were closed in place by backfilling with flowable fill (in accordance with Alexandria City building and fire department permits). After closure, NRG’s consultants collected soil and groundwater samples which were found to contain reportable concentrations of petroleum hydrocarbons. NRG reported a petroleum release to DEQ and DEQ requested that the release be investigated in accordance with state regulatory requirements.

The investigation work completed by NRG between March 2013 and December 2014 indicated free phase hydrocarbons are present in the subsurface consistent with a release of heating oil from the two 25,000 gallon heating oil underground storage tanks (USTs) at PRGS before they were abandoned in place. These free phase hydrocarbons are found in gravel layers at elevations of broadly eight to fourteen feet approximately “above sea level” (asl), and at zero to five feet asl., The lower gravel layer is broadly at the same elevation as groundwater that is likely to be in hydraulic continuity with the Potomac River. The affected area is approximately 12,000 square feet and fifty feet wide and extends broadly from the PRGS basement to the National Park Service (NPS) land adjacent to the Potomac River (the Mt Vernon bike path). A sample of a groundwater seep from the retaining wall along the Potomac, near the estimated edge of the free phase hydrocarbons, contained detectable concentrations of petroleum contaminants consistent with heating oil.

These results indicate that petroleum hydrocarbons are present beneath PRGS that pose a risk of ongoing releases of petroleum contaminants to the Potomac River. In accordance with the Virginia DEQ Storage Tank Program Technical Manual, the Virginia DEQ asked NRG to provide a corrective action plan. NRG submitted their corrective action plan on December 29, 2014.

NRG submitted the corrective action plan for this site on December 29, 2014. The CAP was public noticed from January 1, 2015 and public comment invited until February 13, 2015.  DEQ held a public meeting at Alexandria City Hall on February 3, 2015 to invite public comment. At the meeting DEQ outlined the corrective action process. NRG and their consultants described their corrective action plan. A copy of DEQ’s presentation can be accessed from this webpage.

NRG’s Corrective Action Plan was approved by DEQ on March 17, 2015 and throughout 2015, NRG’s consultants worked to verify the extent of petroleum contamination, install remediation wells, and construct the remediation equipment. This work broadly confirmed the extent of contamination identified in the corrective action plan. By February 2016, the required wells and the remediation systems had been installed and tested and the system was ready to go into operation once final permits were received for a discharge of treated water to the sanitary system. The remediation system started up in March 2016 and has been operating effectively since then.

NRG also extended the remediation system onto the bike path on National Park Service land. Monitoring data indicated the petroleum affected groundwater is being contained and recovered by the remediation system. After sustained reductions in dissolved phase petroleum concentrations and with no free phase petroleum having been detected, a trial system shut down started in March 2018. By August 2018 there was evidence of some rebound in dissolved phase petroleum concentrations in the affected area and the systems were turned back on. System modifications were carried out over the last year to maximize the system effectiveness. The air sparging component of the system is currently not being used. Available evidence suggests that that natural degradation is occurring and the air sparge system is not necessary at this time. By August 2019 continued reductions in dissolved phase concentrations and low rates of contaminant recovery by the remediation system again indicated that a trial shut down was warranted, which started in September 2019.

The corrective action plan is designed to recover petroleum to the point where any potential discharges to the Potomac River meet DEQ standards for discharge to surface water (protect the beneficial use of that surface water) and allow the reuse of the property for its current commercial use. NRG anticipates their corrective action will last four to five years and involve multiple technologies. DEQ will monitor the performance of NRG’s corrective action. DEQ will provide ongoing corrective action implementation reports to the public on this website. If the corrective action plan needs to be significantly changed based on new information or new conditions (for example, a significant change in use) DEQ may require a corrective action plan addendum, and would invite further public comment.

DEQ continues to communicate with the DC Department of the Environment, the National Parks Service, and the City of Alexandria to ensure that the work completed by NRG in relation to this petroleum release meets appropriate regulatory requirements and is protective of human health and the environment.

Links to other information on the PRGS petroleum release

Please email the DEQ Case Manager, Alex Wardle, at with any questions or comments. You may also telephone Alex Wardle at 703-583-3822 to discus the case. 

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Virginia Department of
Environmental Quality
P.O. Box 1105
Richmond, VA 23218
(804) 698-4000

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