The general decision rule for soil excavations involving chemical agents of interest (including chemical agents and agent breakdown products) is: if the concentration of any of the chemical agents of interest exceeds the comparison value, then further vertical or lateral excavation is warranted. If those comparison values are not exceeded, the excavation is considered complete and may be backfilled.
The general decision rule for hazardous waste constituents in soil or water is: If the concentration of any hazardous waste analyte exceeds the comparison value (RBCs or HBESLs), then one of several actions may be taken. These may include further vertical or lateral excavation and further sampling to determine extent of contamination. Or, a more formal risk assessment may be conducted to evaluate potential future risk if soils remain in place.
2.3.1. ADDITIONAL SOIL SAMPLING AND CLEANUP
A plan was developed to conduct arsenic sampling on 61 private residences and the southern portion of American University. These areas are near the site of the disposal pits.
Arsenic sampling was completed at 42 of the 61 properties. Eleven property owners would not grant permission and attempts to reach eight others were unsuccessful. Based on the results of this sampling, nine properties and several lots on the American University campus were recommended for further detailed sampling. This sampling was completed in January 2001.
One of these locations involved the area around the American University Child Development Center. Given the sensitivity of this area, soil sampling around the center was expedited and the results were provided to the university. The results identified arsenic levels higher than acceptable for a residential area. University officials relocated the Child Development Center to another area of the campus. Removal of the contaminated soil began in the summer of 2001. New soil was placed on the site, and restoration activities completed.
Following the discovery of elevated arsenic at the Child Development Center, the D.C. Health Department, EPA, and the ATSDR conducted an exposure study of the children attending the center. Study results did not indicate a health risk to the children.
At a public meeting in February 2001, the community turned out in large numbers to urge soil testing of the entire Spring Valley neighborhood. The Corps, in consultation with EPA and the DDOE, responded with a comprehensive soil sampling plan that proposed the sampling for arsenic on every property in Spring Valley (1,200 residential properties and 400 non-residential lots), with more intensive sampling in select areas. Sampling under this plan began May 31, 2001.
EPA proposed a soil cleanup/clearance goal of 20 ppm for arsenic contaminated soils. The level of 20 ppm arsenic falls within the levels associated with EPA’s cancer risk range of 10-6 to 10-4 (0.43 ppm to 43 ppm, respectively), and is protective of potential long-term risks for noncancer effects. In addition, it exceeds the site-specific average background range of 5 ppm–18 ppm arsenic. The protective cleanup/clearance goal of 20 ppm for arsenic was agreed upon by the Corps, EPA and DDOE, and approved by both the Mayor’s Scientific Advisory Panel and the Spring Valley Restoration Advisory Board.
More than 1,500 properties were sampled for arsenic. If a particular property was determined to have an elevated level of arsenic, then a more detailed grid sampling procedure was done. One hundred-fifty properties were identified with one or more grids above 20 ppm of arsenic.
2.3.2. BURIAL PUT 3 AT 4825 GLENBROOK ROAD
A number of test pit investigations have been carried out in and around Glenbrook Road due to the confirmed presence of a number of burial pits containing ordnance-related items: acids and other chemicals including various volatile organic chemicals; semi-volatile organic chemicals; and metals (most notably arsenic). In addition, HD, L, and agent breakdown products have been detected in soils.
During investigation of the burial pits, characterization samples were collected from the center of the floor of each pit and from the midpoint of each pit outer sidewall, halfway between ground level and the pit floor (on the outer boundary of the proposed excavation area) or near the elevation of scrap or any containers that were encountered. These samples were collected and analyzed and evaluated according to the Site Investigation/Remediation Decision Rules.
If it was determined that further excavation was required based on the results of the pit characterization sampling for agent and agent breakdown products, over-excavation of the pit was performed. If further excavation was required at the pit floor, the excavation proceeded one foot deeper, or until bedrock, saprolite or native soil was reached. If further excavation was required for a sidewall, the excavation was taken one foot farther.
Following the over-excavation of the pit, additional pit characterization samples were collected and the process was repeated until the pit was determined to be clear (according to Site Investigation/Remediation Decision Rules) for chemical agent or agent breakdown product, or until saprolite or native soil had been reached.
Due to the high probability of chemical munitions present in Burial Pit 3, investigations were conducted inside a negative pressure Engineering Control System (ECS) with air monitoring for chemical agent and blast/fragmentation suppression. The ECS was designed to contain metal fragments and attenuate blast in the case of an explosive release, and to minimize exposure of on-site personnel and the nearby public in the event of a release of a chemical agent. The ECS selected for the investigation of the pit included a Vapor Containment Cover placed over a metal structure designed to contain fragments and attenuate the blast from a 75 mm Mk II chemical projectile with an explosive burster, combined with a Chemical Agent Filtration System (CAFS). A Vapor Containment Cover is an impermeable fabric cover designed to prevent the release of vapors outside of the ECS. In addition, the ECS operates under negative pressure to contain a potential chemical release. The CAFS is specifically designed to monitor and remove chemical agent vapors and particulates. Workers within the ECS were monitored for exposure to chemical agents at the level of Worker Population Limits (WPLs) and STELs.
- WPLs are developed by the CDC for the DOD and are used to monitor identified areas where workers may be exposed to chemical warfare agents. The WPL is the maximum allowable 8-hour concentration that an unprotected chemical worker could be exposed for an 8-hour workday and 40- hour week for 30 years without adverse effect.
- STELs are developed by NIOSH and OSHA. The STEL is a 15-minute TWA exposure that must not be exceeded at any time during a workday. The STEL is the concentration to which it is believed that workers can be exposed continuously for a short period of time without suffering from: (1) irritation, (2) chronic or irreversible tissue damage, (3) dose-rate-dependent toxic effects, or (4) narcosis of sufficient degree to increase the likelihood of accidental injury, impaired self-rescue, or materially reduced work efficiency.
A Site-Specific Public Protection Plan was developed to educate the public in the vicinity of Burial Pit 3 on how to minimize their potential exposure in the event of a chemical release. The plan was designed to be implemented during intrusive activities associated with the investigations conducted within the ECS. The plan stated that, in the unlikely event of a chemical release, the Corps would implement a voluntary Shelter-In-Place program for individuals and organizations who reside, work, or routinely operate within the potentially impacted area surrounding Burial Pit 3 located at 4825 Glenbrook Road. Shelter-In-Place consists of staying indoors, closing all doors and windows, and shutting off central or window heat or air conditioning units. The public should remain indoors until notified by the Corps that it is “All Clear” to end Shelter-In-Place and to resume normal activities. The plan stated that the “All Clear” signal would not be given until project personnel confirmed that no chemical agent remained in the vicinity at a level that could cause harm to an individual.
- An “AEGL-2 Distance” of 742 feet was used to define the area surrounding Burial Pit 3 that may be impacted by an uncontrolled release of Arsine.
An AEGL-2 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.
Thus, the “AEGL-2 distance” defined the potentially impacted area where an exposed population may experience irreversible or other serious long-lasting health effects, or an impaired ability to escape associated with the unlikely event of a chemical release. Individuals within the “AEGL-2 Distance” would be advised to take active steps to protect themselves from exposure by sheltering-in-place. The predicted “AEGL-2 Distance” was calculated based on local meteorological conditions, and the type and quantity of suspect recovered chemical warfare materiel. Although the “AEGL-2 Distance” for Burial Pit 3 without engineering controls was estimated to be 742 feet, investigation of the pit utilized several engineering controls, including the ECS combined with a CAFS, to reduce the area potentially impacted at AEGL-2 levels outside of the ECS to zero.
It should be noted that an AEGL-2 was selected due to the lack of an AEGL-1. Although the inter-agency working group would have preferred a level of exposure consistent with reversible, non-disabling effects for the shelter-in-place decision in the event of an uncontrolled release, it was necessary to default to the AEGL-2 exposure level. The continuum of arsine-induced toxicity does not appear to include effects consistent with the AEGL-1 definition. The available human and animal data affirm that there is a very narrow margin between exposures that result in little or no signs or symptoms of toxicity and those that result in lethality.
2.3.3. OTHER SITE WORK
ATSDR Health Consultation
The ATSDR published a Health Consultation for Spring Valley in September 2005. ATSDR concluded that excluding burial pits/disposal areas, the soil pathway at the American University/Spring Valley site does not represent a public health hazard. As such, exposure to the levels of chemical warfare agents or their breakdown products detected in soil is not expected to cause the health conditions reported by residents. Precautionary measures are being taken by the Corps, however, to remove soils with elevated arsenic levels.
Burial areas discovered within Spring Valley have been or are in the process of being remediated. ATSDR acknowledged that any remaining chemical warfare materials (e.g., other chemicals, explosives) in disposal areas (burial pits and surface disposal areas) could pose a chemical or physical hazard if disturbed. Of particular concern would be munitions or containerized materials that might still contain chemical warfare agent. The ATSDR recommendations included:
- Additional, but targeted, environmental sampling, most of which is already ongoing. ATSDR also recommended continued promotion of community awareness and interaction. The Public Health Evaluation should be consulted for their recommendations in their entirety.
- Additional surface soil analyses be conducted for residential properties. Specifically, ATSDR recommended surface soil analyses for AUES-related contaminants including explosives and their transformation products, CWAs and degradation products, and metals such as lead and mercury.
- Soil gas samples be taken at disposal areas, preferably prior to excavation, to evaluate the potential for exposure by a soil gas migration pathway. This could include existing disposal areas such as the Glenbrook Road area, where some WW I remnants remain in a burial pit (Pit 23) and in a surface disposal area at Lot 18.
- The Corps continues with its plan to conduct groundwater sampling, particularly in the area of the burial pits. This sampling will provide data regarding the possible nature and extent of groundwater contamination near burial pits and other disposal areas.
In 2010, exposure scenarios for workers and residents were evaluated after finding additional munitions and contaminated items and soil. The data were limited due to the length of time between exposure and sample collection and because no indoor air samples could be collected. In 2016, a final analysis relied on the evaluation of worker transcripts to evaluate exposure.137
Groundwater Investigation
The Corps installed 45 monitoring wells between 2005 and 2010 in locations agreed upon by the Corps, EPA, and the DDOE to help determine whether there is contamination in the groundwater and where the groundwater is flowing. Sampling results identified elevated levels of perchlorate as high as 146 parts per billion (ppb) in the project area.
For perchlorate, analytical results are being compared to EPA’s Interim Drinking Water Health Advisory of 15 ppb.
4825 Glenbrook Road - Remedial Investigation/Feasibility Study
In 2010, the Corps found low-level agent (predominantly L) in soil at the Glenbrook property where WW I disposal had occurred. At about the same time there was a release of arsenic trichloride in the ECS over the work area. Investigative work at the site was halted in 2010. The Corps conducted a risk assessment and remedial investigation/feasibility study (RI/FS) to determine what to do with the property. The RI/FS is being assembled with data gathered during the site investigation and removal actions. As part of the RI/FS, a human health risk assessment is also being completed.
The RI/FS process considered the exposure scenario (residential), toxicity of the contaminants of concern, impacted groundwater, the potential for vapor intrusion and Applicable or Relevant and Appropriate Requirements, and concluded with the development of site-specific cleanup/clearance goals.