PUBLIC HEALTH ASSESSMENT
U.S. AIR FORCE TWIN CITIES RESERVE SMALL ARMS RANGE
(a/k/a MINNEAPOLIS ST. PAUL INTERNATIONAL AIRPORT AIR RESERVE STATION)
MINNEAPOLIS, HENNEPIN COUNTY, MINNESOTA
MDH identifies pathways by which people have been, are, or could be exposed to contaminants at a site, and determines if those exposures pose a public health concern. Based on observations made during an April 1997, site tour and review of environmental data reports, MDH has determined, based on lack of complete exposure pathways, that environmental contamination at MSP IAP ARS does not pose a current public health hazard. However, because contamination above health-based guidelines remains on MSP IAP ARS, an evaluation of potential pathways at each of the IRP Sites is presented below.
Efforts by MSP IAP ARS personnel have contained, lowered and/or mitigated the migration of contaminants on the base. Currently, all but 4 of the 17 sites have been designated as "no further action required" by the MPCA. A brief summary of these sites is provided in Appendix A. Most of the contamination found at MSP IAP ARS is a complex mixture of individual constituents found in fuels (JP-4, MOGAS, AVGAS and heating oils), lubricants and solvents. Most of these individual constituents do not have health based guidelines. Typically, an individual constituent like benzene, commonly found in fuels, will be used as a surrogate health based guideline for a complex mixture.
Health based guidelines include MDH Health Risk Limits (HRLs) and MPCA Soil Reference Values (SRVs), ATSDR Minimal Risk Levels (MRL) or EPA Action Levels (a contaminant concentration above a certain level in soil, air or water at which a remedial action is required).
An HRL is the concentration of a groundwater contaminant, or a mixture of contaminants, that can be safely consumed daily for a lifetime.
SRVs are concentrations of contaminants in soil considered safe for use in a residential setting. SRVs take into account exposure to contaminants in soils through inhalation of soil vapors/particles, incidental ingestion of soil particles, dermal contact with soil and ingestion of food contaminated by transfer from soil to plants and/or animals.
MRLs are exposure doses at which non-cancerous adverse health effects are not expected to occur in humans. MRLs are specific for route and duration of exposure.
Human health effects resulting from long term ingestion, inhalation or dermal contact with fuels, oils and lubricants have not been adequately characterized. Should exposure occur in the future, animal model data and any human data will be used to evaluate the potential health risk associated with exposure to contamination at MSP IAP ARS.
Closed IRP Sites do not pose a current public health hazard because access to the individual sites is restricted or limited, migration of contaminants to areas where exposures might occur is not expected, and/or the sites have been remediated. In addition, some IRP sites were found not to be contaminated. A summary of the closed IRP Sites and an evaluation of why they are not a public health concern is in Appendix A. The chart lists each of the IRP Sites that, based on data provided to MDH, do not pose an apparent public health hazard. The table contains information on the following topics for each IRP Site: a brief site description, waste disposal history, remedial action, pathway information and status of investigation. Decisions for each of the sites were based on data in the Final Remedial Investigation Report For Five Sites (4,5,8,9 and P-4) and findings in the MPCA document titled Minnesota Decision Document, Sites 2, 3, 6, 8, 9, P-1, Former Indoor Firing Range Site, and the Museum Site, Twin Cities Air Force Reserves Base and other documents (see references).
A closed site can have contamination remaining in groundwater and/or soil above HRLs and SRVs or other health criteria. The MPCA can close a site with contamination still present as long as the site does not pose a current health hazard. If any information becomes available pertaining to these closed sites that is not consistent with past trends or land uses, potential public health concerns will need to be re-evaluated.
Groundwater data at the following sites have exceeded HRLs for several contaminants and the EPA Action Limit for lead. The following sections evaluate groundwater contamination at each of these sites in terms of current and potential future exposure pathways.
Groundwater samples at SARL have exceeded HRLs for several contaminants. However, groundwater contaminant concentrations do not pose a current health hazard for the following reasons: there are no drinking water wells on site; SARL is in the hundred year flood plain of the Minnesota River, precluding the site from future residential development; and groundwater flow is directly into the river where contaminant levels are immediately and strongly diluted. The site has been fenced and capped (one foot of native soils) thereby limiting physical contact. Trees are not allowed to grow on the cap to reduce water infiltration. It should be noted that as a part of the removal from the NPL, SARL will be subject to EPA's 5 Year Reviews. The purpose of these reviews is to ensure that contamination remaining on site does not pose a threat to human or environmental health.
Air: Air is not an exposure pathway, because the site contains capped heavy metal contamination that is not likely to migrate off site in air or to become entrained on particulate matter.
Soil: This is not a pathway of concern because the landfill cap prevents direct contact with and off site migration of contaminated soils. Dermal contact is further restricted by fencing.
Groundwater: SARL groundwater contaminants discharge to the river. Groundwater at SARL does not pose a current public health concern because there are no drinking water wells on site and contaminant concentrations will be diluted below the HRLs upon entering the river.
Potential Future Pathways
The possibility of a completed exposure pathway occurring at SARL in the future is remote. However, should erosion of the landfill cap by the nearby river or weathering occur, exposure to contaminants of concern (COC) may occur via inhalation of soil particulate and/or dermal contact. Potential receptors include individuals who trespass on SARL property.
Site 4/5 has exceeded HRLs in groundwater for TCE and benzene and vinyl chloride. Tables in Appendix B list these findings. The remedial response for this site is natural attenuation which allows contaminants to degrade naturally (chemical dispersion, biological degradation and sorption).
Air (outdoor): Air is not likely to be an exposure pathway because most of the site is covered with pavement or buildings. In addition, should soil vapor gas reach the surface, it would be diluted with ambient air below levels of health concern.
Air (indoor): Under current conditions indoor exposure via soil vapor migration is not known to be occurring.
Soil: Soil is not likely to be an exposure pathway because most of the site is covered with pavement or buildings and small grassy areas. Dermal contact is not likely to occur on site under present conditions.
Groundwater: This does not pose a health risk under current conditions. There are no known drinking water wells on base or down gradient before groundwater discharges to the river (5).
Potential Future Pathways
If future land use at MSP IAP ARS includes excavation activities within the contaminant plume at Site 4/5 exposures may occur via inhalation of soil gases and/or dermal contact. Another future exposure scenario is the volatilization of soil gases into nearby buildings and this pathway is currently being investigated by the Air Force. Use of contaminated groundwater prior to treatment may result in ingestion, inhalation and/or dermal exposure that could pose a public health hazard.
Tables in Appendix B list exceedances of HRL for benzene and EPA Action Limit for lead in wells at Site 7. A groundwater remediation system (Air Stripper) was installed at Site 7 in October 1991, and was still in operation in April 1997. The system has removed approximately 5,129 gallons of volatile contaminants from the groundwater since October 1991 (13). Lead is not removed. Treated effluent is discharged to the sewer system under a Metropolitan Council Environmental Services discharge permit. Calculated contaminant mass removal efficiency of the air stripper ranges from 90-98 percent (5).
Air (outdoor): Outdoor air is not likely to be an exposure pathway because most of the site is covered with pavement or buildings. In addition, the pump and treat system is removing source contamination in the groundwater and soil. Air emission samples from the treatment system have been two orders of magnitude below screening emission rates established by the MPCA Division of Air Quality to evaluate the potential for ambient air concentrations of health concern(13).
Air (indoor): Indoor exposure via soil vapor migration is currently being evaluated by the Air Force. However, this pathway is not likely to exist because the pump and treat system on site includes a soil vapor extraction system that removes soil vapors.
Soil: This is not likely to be a pathway because most of the site is covered with pavement or buildings and small grassy areas. Dermal contact is not likely to occur on site under current conditions.
Groundwater: This is not a health hazard under current conditions. There are no drinking water wells on base and groundwater most likely flows southeast to the river away from known drinking water wells before discharging into the river (5). However, the Groundwater Receptor Evaluation Report may not include all potential wells (operating and abandoned) because its reference (the Minnesota Geological Survey County Well Index (CWI)) is not a complete data base. New wells were not required to be reported to the State until 1974. Therefore, any wells installed prior to that time may not be listed in the report. Current estimates suggest that the CWI contains between 25 and 50% of the wells state wide. Local reporting levels have been as low as 10% in some locations. Nevertheless, the current pumping of groundwater at the site prevents plume migration off base. For a technical description of geological conditions at site 7, refer to Appendix C.
Potential Future Pathways
If future land use at MSP IAP ARS includes excavation activities within the contaminant plume at Site 7, exposures may occur via inhalation of soil gases and/or dermal absorption. Another plausible future exposure scenario is the volatilization of gases into nearby buildings after the pump and treat system is turned off. This pathway is currently being investigated by the Air Force. Use of contaminated groundwater, prior to treatment, may result in ingestion, inhalation and dermal exposures.
Tables in Appendix B list exceedances of HRLs for benzene, ethylbenzene and toluene in groundwater at the JP-4 Spill Site. An Air Sparging/Soil Vapor Extraction remediation system was in operation from 1994-1996. The system removed an estimated 1048 gallons of contaminant as of April 3, 1996. Contamination remains in the soil and groundwater at the site in both the surficial and Platteville aquifers. The farthest north soil boring from the JP4 Spill Site is soil boring ST-1. It was drilled approximately 50 yds from a nearby residential community and monitoring wells MW-1D and MW-1 at the JP-4 Spill Site to monitor plume migration north (Figure C-7 (Appendix C)). The boring did not end in visible groundwater; the boring ended in clay material which may have interfered with the detection of groundwater contaminants (14). No contaminants were detected in ST-1.
Air (outdoor): Outdoor air is not likely to be a exposure pathway because the dilution factor is large enough to make surface concentrations below levels of health concern.
Air (indoor): Indoor exposure via soil vapor migration is currently being evaluated by the Air Force.
Soil: Soil is not likely to be a pathway because most of the site is covered with grass and dermal contact is not likely to occur on site under current conditions.
Groundwater: Groundwater is not a health risk under current conditions because no one is exposed to it. The surficial groundwater plume remains on base and flows southwest under the influence of Site 7 pump-out system as shown in Figure C-7. There are no drinking water wells on base. Although groundwater in the Platteville aquifer appears to flow northwest (Figure C-2) towards a small residential neighborhood where private wells might be in use, it is apparently influenced by the pumping activities at Site 7 (Figure C-3) and is likely captured by the pump-out system before moving off base. There are no private wells in the residential community north of the Site, and south of highway 62 based on a comprehensive groundwater receptor survey conducted by the Air Force. Appendix D lists the addresses of the homes that were included in the detailed survey and what homes received letters inquiring if they had wells. A copy of the letter sent to residents inquiring about wells, and is also included in the appendix.
Potential Future Pathways
Should future development at MSP IAP ARS include excavation activities within the contaminant plume at the JP-4 Site, exposure may occur via inhalation of soil gases and dermal contact. Another plausible future exposure scenario is the volatilization of soil gases into nearby buildings. This pathway is currently being investigated by the Air Force. Use of contaminated groundwater prior to pretreatment may result in ingestion, inhalation and dermal exposure.