Environmental

Site 21

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Site 21 - Industrial Area

Background: Site 21 is an industrial area in the southcentral portion of SJCA. Buildings at Site 21 were historically used as machine, vehicle, and locomotive maintenance shops; electrical shops; and munitions loading facilities. A fuel service station was also located in the vicinity. Outdoor areas were used for equipment and chemical storage. Several of these buildings and/or their surrounding areas were former IRP sites. Many of the older buildings at the site have been demolished. The existing buildings and the Site 21 area are currently used primarily for storage and maintenance activities. An active warehouse currently used by Fleet and Industrial Supply Center, Norfolk Integrated Logistics Support was constructed in 1992. A storm sewer system runs through the site and drains south to a storm water detention basin which outfalls to St. Juliens Creek.

Remedial Investigation (RI) activities identified potential risks to human health from exposure to chlorinated solvents (trichloroethene [TCE] and its breakdown products) in the shallow aquifer groundwater. Potential risk associated with vapor intrusion into onsite buildings was also identified. An Interim Proposed Plan identified in situ chemical reduction (ISCR) and enhanced reductive dechlorination (ERD) as the preferred remedial alternative for addressing potential risk from potable use of shallow groundwater and the Interim Record of Decision (ROD) documenting the interim response action has been signed. The Proposed Plan and ROD were “interim” because they did not address the potential risk to current and future building occupants from vapor intrusion through inhalation of indoor air, which was still being evaluated. The response action selected in the Interim ROD was selected as an interim action in order to reduce constituent of concern (COC) concentrations while the vapor intrusion pathway was investigated. An interim remedial design was developed for implementation of the interim action.

An investigation was conducted to further evaluate the potential vapor intrusion pathway. The results were documented in an RI and Feasibility Study (FS) Addendum Report, which recommended additional vapor intrusion monitoring and land use controls (LUCs) to maintain the current industrial building use and prevent activities that would compromise the integrity of the building envelopes throughout the Interim remedial action; and discontinuation of the monitoring and LUCs upon completion of the remedial action for groundwater.

Because no risk from vapor intrusion was identified in the RI and FS Addendum, the interim remedial action will not change and will serve as the final remedial action and a final RD will not be necessary. A LUC Remedial Design (RD) has been completed. A Proposed Plan identified ISCR and ERD as the final site preferred alternative and the ROD documenting the final response action has been signed. The remedial action was initiated in 2011 and the construction phase of the remedial action has been completed.

Site 21 Remedial Action

Specific components of the remedial action include the following:
  • Implementation of ISCR through direct injection of zero valent iron (ZVI) into the accessible portions of the high-concentration chlorinated solvents zone of the shallow aquifer groundwater
  • Implementation of ERD through injection of EVO into the accessible portions of the low-concentration chlorinated solvents zone of the shallow aquifer groundwater
  • Performance monitoring following the ZVI and ERD injections to confirm COC concentrations in the groundwater continue to decrease

What is ISCR and how is it being implemented?

  • ISCR is a process that causes a chemical reaction to break down chlorinated solvents TCE and its daughter products to nontoxic products
    • ZVI powder mixed with water was injected with pressure using nitrogen gas to help push it into the shallow aquifer groundwater
    • Results are relatively fast (can be seen within 3 to 4 weeks to 3 to 4 months) and can remain active for many years (up to 8 years)
    • As TCE and its daughter products breakdown and concentrations decrease, any additional treatment determined to be necessary at the site is not expected to require ISCR and all treatment will transition to ERD

What is ERD and how is it being implemented?

  • ERD is a process where naturally occurring microbes in the subsurface are stimulated to break down TCE to nontoxic products
    • Vegetable oil mixed with water is injected into the shallow aquifer groundwater in a similar method as the ZVI injections to create conditions favorable for microbes to flourish
    • Results are not as quick (can be seen within months to years) and do not last as long (1.5 to 3 years) as ZVI

 

Because hazardous substances, pollutants, or contaminants remain on site, a five-year review was conducted in 2020 to determine if the selected remedy remains protective of human health and the environment. The Third Five-Year Review for SJCA review indicated that the remedy at Site 21 is in place, functioning as designed, and is protective of human health and the environment. Exposure pathways that could result in unacceptable risk have been addressed by previous remedial action activities and continue to be controlled by LUCs, and RA-O maintenance and monitoring is ongoing.

CERCLA Status: The remedial action is currently in the operation phase. Remedial action-operation includes groundwater monitoring to evaluate remedy effectiveness, vapor intrusion monitoring to evaluate whether the remedial action or building deterioration have resulted in potential unacceptable inhalation risks or explosive hazards, and additional emulsified vegetable oil injections as needed. LUCs are in place to prevent unacceptable exposure to COCs in shallow aquifer groundwater.

Next Steps: Remedial action-operation, implementation and maintenance of the LUCs, and five-year reviews will continue until remedial action objectives are achieved.

 

Site 21

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