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PUBLIC HEALTH ASSESSMENT

NEW BRIGHTON/ARDEN HILLS
(a/k/a U.S. ARMY TWIN CITIES AMMUNITION PLANT)
NEW BRIGHTON, RAMSEY COUNTY, MINNESOTA


ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS

This section of the public health assessment is a synthesis of environmental information ATSDR has used to determine human exposure to hazardous chemicals. However, this discussion is not intended to summarize in detail all the information collected from the more than 50 environmental investigations conducted at TCAAP and adjacent areas since 1978. Persons interested in detailed environmental analysis should review the administrative record (available at TCAAP), as well as the two remedial investigation reports that discuss TCAAP groundwater contamination and the TCAAP annual monitoring reports. On-TCAAP environmental investigations are summarized in a remedial investigation report prepared for the Army by Argonne National Laboratory and issued in April 1991 (2). Environmental information on groundwater contamination in areas outside of TCAAP is summarized in a remedial investigation report prepared for MPCA by Camp, Dresser, and McKee Corporation and issued in February 1991 (16). Recent environmental monitoring information is summarized and discussed in the TCAAP annual monitoring reports, such as the Fiscal Year 1992 Annual Monitoring Report (17).

The tables in this section list the contaminants of concern. Subsequent sections of this public health assessment contain evaluations of these contaminants, including information on whether exposure to them has public health significance. ATSDR selects and discusses contaminants using the following information:

  • concentration of contaminants on and off TCAAP;

  • field data quality, laboratory data quality, and sample design;

  • comparison of on-TCAAP and off-TCAAP concentrations of contaminants with ATSDR health assessment comparison values for (1) non-cancer end points and (2) cancer end points;

  • community health concerns; and

  • the spatial relationship between environmental sample location and possible human exposure points.

ATSDR health comparison values are contaminant concentrations in specific media used to select contaminants for further evaluation. The comparison values are derived from current health guidelines, such as EPA's cancer risk evaluation guides (CREGs) and child longer-term health advisories (CLHAs) for drinking water.

In the data tables titled "On-TCAAP Contamination" and "Off-TCAAP Contamination," the fact that a contaminant is listed does not mean that exposure to it will cause adverse health effects. Rather, the list indicates which contaminants will be evaluated further in this public health assessment. Please review Appendix E for more information about ATSDR comparison values.

The following discussion focuses on maximum concentrations of contaminants of concern by medium. The data tables in this section include the following abbreviations:

CREG -- Cancer Risk Evaluation Guide;

EMEG -- Environmental Media Evaluation Guide;

LTHA -- Lifetime Health Advisory;

MCL -- Maximum Contaminant Level;

PMCL -- Proposed Maximum Contaminant Level;

ppb -- parts per billion; and

Rfd -- Reference Dose.

A. ON-TCAAP CONTAMINATION

Sampling and analyses of environmental media were initiated in 1981; since then, they have continued and have been expanded. Results of environmental monitoring have confirmed that hazardous waste from industrial operations and disposal actions at TCAAP has contaminated the groundwater, soils, surface water, and sediments within TCAAP boundaries. Investigations of air and biota do not indicate contamination at levels greater than those typically found in the Minneapolis/St. Paul metropolitan area.

ON-TCAAP GROUNDWATER

PRODUCTION WELLS

The on-TCAAP groundwater contamination problem was first discovered in 1981, when high concentrations of VOCs were found in the TCAAP production wells. The TCAAP production wells supplied the housing units with water for drinking and the plants with water for industrial uses. Some of the TCAAP production wells are still used, but contaminants are removed by a comprehensive treatment system (17).

The TCAAP production wells draw water from Unit 4. All production wells supply water to a central treatment and storage system. Before installation of the current treatment system (including air stripping and GAC filters), a water softener system was the principal treatment system. Because of the blending of water and the probable dilution of contaminated water with water from the uncontaminated wells, the concentrations of contaminants at drinking water taps would not have been as great as concentrations in the individual wells. However, only very limited sampling and analysis of tap water is available for verification of such an assumption.

The TCAAP water supply system also provided water to the Minnesota Department of Transportation facilities (Arden Hills Training Center, License Center, and Department of Transportation maintenance buildings), which are located adjacent to the northwestern portion of TCAAP. In July 1981, the Minnesota Department of Health sampled and analyzed tap water from the Arden Hills Training Center; the report of the results described contamination exceeding drinking water standards and included a recommendation for an alternative water supply (16). Table 1 contains the analytical results of the July 1981 water samples.

Bottled drinking water was provided to federal and state employees and residents using the TCAAP water system until a water treatment system began operating in 1983 (17).


Table 1.

Contaminants of Concern measured in On-TCAAP Production Wells and in Arden Hills Training Center Water Taps in 1981. Concentrations reported as parts per billion (ppb)
CONTAMINANTS MAXIMUM
CONCENTRATION (ppb)
COMPARISON VALUE & SOURCE
PRODUCTION WELLS TRAINING
CENTER
TAPS
1,1-dichloroethane 130 11 NONE
1,2-dichloroethane 2 NOT ANALYZED .04 CREG
1,1-dichloroethylene 47 14 .06 CREG
trans-1,2-dichloroethylene 16 2.5 100 LTHA
1,1,1-trichloroethane 360 140 200 LTHA
trichloroethylene 720 440 3 CREG

Data source is data printout from MPCA computer database and reference 19.


GROUNDWATER MONITORING RESULTS

Since 1983, more than 200 monitoring wells have been installed within TCAAP and then sampled. The wells primarily monitor groundwater Units 1, 3, and 4, and there is limited monitoring of the confining layer of Unit 2. The monitoring wells are on and around the 14 source areas; Sites A, I, and K have the largest numbers of wells per site. The direction and extent of groundwater contamination on TCAAP appear to be adequately characterized for public health purposes.

Chlorinated organic chemicals (from past solvent use and disposal practices) make up the majority of the groundwater contaminants. In order of decreasing abundance, the chlorinated organic compounds measured in Unit 3 are TCE, 1,1,1-trichloroethane (TCA), 1,1-dichloroethane (1,1-DCA), 1,1-dichloroethylene (1,1-DCE), 1,2-dichloroethylene (1,2-DCE), tetrachloroethane, chloroethane, vinyl chloride, 1,4-dichlorobenzene, and chloromethane. For detailed information about chemical concentrations in monitoring wells and recent environmental monitoring results, review the TCAAP Fiscal Year Annual Monitoring report.

Because it was detected at high concentrations throughout TCAAP, TCE was used as a marker contaminant by environmental consultants for EPA, MPCA, and the Army to delineate the extent of groundwater contamination. VOCs have contaminated the groundwater in Units 3 and 4 in the central, western, and southwestern portions of TCAAP. Units 1 and 3 appear to be contaminated in the northwestern and north central portions of TCAAP.

Although VOCs have been the principal focus of the groundwater investigations, analyses of unfiltered groundwater samples taken in 1983 and 1984 reveal high concentrations of metals (lead, 492 ppb; chromium, 556 ppb) at Site K. Between 1984 and 1992, groundwater samples were field filtered, resulting in lower concentrations reported from analytical results. Results from field-filtered groundwater samples are not directly comparable to EPA drinking water standards, because those standards are developed using unfiltered samples. Metal contaminant concentrations measured in filtered samples may be lower (by a factor of 10 or 100) than concentrations in unfiltered samples.

In 1992, MPCA staff members collected unfiltered samples from the recovery wells at Building 103, the monitoring wells at Site A, and the removal wells of the groundwater recovery system. The samples were analyzed for 17 metals, including lead and chromium. The concentrations did not exceed any federal or state drinking water standards (20).

ON-TCAAP SOILS

As a result of past disposal practices, soils are contaminated at some of the source areas on TCAAP. However, the majority of soil sampling reported to date has been at one foot or more below the surface (2). Most of the soil data are considered to represent subsurface soil, which is unlikely to be inhaled or ingested or to come in contact with people unless it is mechanically disturbed. Therefore, the reported subsurface soil data will not be discussed in this public health assessment.

Additional investigations to identify likely areas of surface soil contamination (less than 6 inches in depth) are under way. However, the opportunity for human contact with and exposure to surface soil contaminants on TCAAP is limited. Access to TCAAP is controlled by chain-link fences and guarded gate entrances. On-TCAAP employees performing maintenance and environmental duties outdoors are the only persons near the source areas with surface soil contaminants. Any current exposure via inhalation, ingestion, or skin contact would be very limited, especially because hazardous waste safety procedures, such as the use of protective clothing, are followed in the source areas.

Because current and near-future human exposure to on-TCAAP surface soil contamination is unlikely, this public health assessment will not address surface soil contamination . Soil contaminants may be evaluated later if there are changes in current site access restrictions or land use that provide greater opportunity for human exposure.

ON-TCAAP SURFACE WATER AND SEDIMENT

Past practices have resulted in contaminant releases into at least two on-site surface water bodies, Rice Creek and Sunfish Lake, and possibly a third, Marsden Lake, as well as releases off site into Round Lake. In 1983, TCE-contaminated storm water from Building 103 (Site K) was reported to be flowing into the part of Rice Creek that lies within TCAAP (16). Additional investigations indicated that contaminated groundwater had been discharging into Rice Creek. A groundwater collection system was installed in 1985 to prevent further contamination of Rice Creek (16). That remedial action continues to date.

In 1987, surface water and sediment samples were taken from Rice Creek near Site K as part of the on-TCAAP remedial investigation. Analysis of surface water and sediment samples (SW30 & SE30) taken where Rice Creek flows off TCAAP did not identify any contaminants at levels greater than detection limits (2). Additional surface water and sediment samples were taken in 1993 and analyzed as part of the feasibility study for Operable Unit 2. The 1993 data has not been reviewed by ATSDR for this public health assessment.

From the 1940s to the early 1980s, large volumes of waste water and industrial process waters (a million or more gallons per day) were discharged into the TCAAP sewer and storm drainage system, which then discharged into Round Lake (2). Investigations as early as 1953 discovered liquid wastes leaking into floor drains and entering the storm sewer system (2). Some changes to the sewer and storm drainages were made in 1955 to eliminate the discharges into Round Lake.

In the past, surface water analysis was limited primarily to evaluations for oil and grease, although some early investigations did analyze for other contaminants, such as chromium and lead. In 1970, analysis of water samples from the sewer system revealed lead concentrations in excess of 500 ppb near Building 501 and at 4,750 ppb near Building 503 (2).

A 1978 report by the United States Army Toxic and Hazards Materials Agency included recommendations for investigation and remediation of the TCAAP sewer and storm water drainage systems (2). Site J includes the majority of the contaminated drainage systems. Investigations in 1983 revealed PCB contamination of portions of the drainage system; the maximum concentration of PCBs (5,200 ppb) was in the storm water drainage sediments. In 1984, TCE was reported at a maximum concentration of 1,920 ppb in the "I" line. Cleaning of the TCAAP sewer system, including Site J, was completed in 1986 (2).

In 1987, monitoring of surface water in Sunfish/Ryan Lake identified cyanide at 17.7 ppb in a ditch that flows into the lake. (21). A 1991 ecological assessment (21) recommended periodic monitoring of the inlet until the source of the cyanide was located or no longer a concern. Other contaminants measured in the surface water in Sunfish Lake included copper (5.8 and cadmium (.5 ppb). The same and 1,1,1-trichloroethane (1.9 ppb) from an April 1988 sample (50). The ecological assessment] report (21) recommended monitoring Marsden Lake for thallium because it was detected in that water body.

Sediment samples from Sunfish Lake were also analyzed; the results showed lead at 177 parts per million (ppm), copper at 89.6 ppm, and antimony at 476.7 ppm (21).

The volatility of the majority of the contaminants on TCAAP would tend to prevent any accumulation of volatile organic chemicals in the on-TCAAP surface waters and sediments. Residual accumulations of metals and PCBs would be expected in sediments.

ON-TCAAP AIR

Ambient air (breathing zone) monitoring in the vicinity of the TCAAP groundwater recovery system was conducted in 1987 using an organic vapor analyzer (OVA), a portable instrument capable of detecting total concentrations of VOCs (22).All ambient air measurements (both upwind and downwind of BGRS) were below the detection limit of 0.7 ppm.

More extensive ambient air monitoring using the OVA was conducted in November 1990 (23). Many locations both on and off TCAAP were measured. The highest breathing zone measurement (1.0 ppm) was outside Building 502. The majority of the measurements did not identify any concentrations above background levels.

In 1988, an evaluation of on-TCAAP air quality and TCE emission sources was prepared by environmental consultants for the Army. The evaluation relied on estimated emission rates and an air quality model to conclude that the highest theoretical concentration of TCE would be 1.905 micrograms per cubic meter (µg/m3) (24). EPA environmental consultants also evaluated on-TCAAP air quality using an air model and concluded that the theoretical highest concentration of TCE (5.5 µg/m3) was at Building 116 (23). According to the EPA risk assessment report (18), no breathing zone monitoring has been conducted to confirm modeled calculations of the specific air contaminants.

All of the air contaminant concentrations discussed in the preceding paragraphs were much lower than the concentrations for occupational exposure to TCE recommended by the American Conference of Governmental Industrial Hygienists: 50 ppm (time-weighted average) for a normal 8-hour workday and 40-hour workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect (25).

ON-TCAAP BIOTA

An ecological assessment of TCAAP biota was performed by the U.S. Army Environmental Hygiene Agency (USAEHA) in 1990 and 1991 (21). The report contained evaluations of both aquatic and terrestrial habitats, including analyses of contaminants in small mammals and a comparison with soil-sampling results for each source area. No significant correlation between small mammal body burdens and soil contamination could be made (21). Analyses of deer tissue were performed on samples obtained in 1988-89. The results showed that concentrations of metals and PCBs were either below detection limits or below background values (21).

B. OFF-TCAAP CONTAMINATION

The major focus of off-TCAAP environmental investigations has been on groundwater, followed by investigations of surface water and sediment from Rice Creek and Round Lake and of fish from Round Lake.

Information in the remedial investigation reports and other documents does not indicate that there is any possibility that soil contaminants have migrated off TCAAP at concentrations at or above levels of health concern. Therefore, off-TCAAP soil contamination is not discussed further in this report.

OFF-TCAAP GROUNDWATER

Off-TCAAP groundwater contamination was first discovered in nearby private drinking water wells in 1981. Extensive groundwater studies identified contamination in Groundwater Units 3 and 4 that resulted in contamination of private, mobile home park, industrial, and municipal water supply wells. Two major contaminant plumes, the North Plume and the South Plume (Figure 4 in Appendix A) have been delineated for Groundwater Units 3 and 4, beginning in the western and southwestern portions of TCAAP. The North Plume appears to originate on TCAAP at sites D and G and migrates southwest in both the Hillside Sand and Prairie du Chien/Jordan aquifers (1). The South Plume appears to originate on TCAAP at Site I. The North Plume and South Plume diverge immediately off TCAAP; the South Plume moves in a more southerly direction (1). As described in the Background section, the North Plume is considered Operable Unit 1 and the South Plume Operable Unit 3.

PRIVATE WELLS

Three areas of private well contamination were discovered from 1982 to 1986: private wells southwest of TCAAP (within the South Plume); private wells west of TCAAP, along Old Highway 8 (within the North Plume), and a few Unit 1 private wells in the Edgetown Subdivision of Shoreview, north and northwest of Site A. According to MPCA (48), an additional area of private well contamination has since been discovered within the North Plume but further downgradient of Highways 10 and 8. Contaminants were not detected in any of the private wells immediately south and east of TCAAP.

Sampling and analysis of private wells west and southwest of TCAAP revealed contamination of the Hillside Sand drinking water aquifer (Groundwater Unit 3). In 1982, VOCs were discovered in a number of the sampled wells; TCE was the primary contaminant. Of 137 private and commercial wells sampled in June 1982, 41 wells contained one or more VOCs (26).

Although environmental consultants have depicted broad contaminant plumes in the Hillside Sand Aquifer, analytical results indicate that some of the private wells within the plume boundaries have never been contaminated. Therefore, contaminants are not uniformly distributed throughout the Hillside Sand Aquifer.

Fluctuations of contaminant concentrations have been reported for all water supply wells sampled throughout the area. Several of the private wells originally analyzed in 1981 and 1982 have been monitored frequently (at least three times each year). Analytical results have revealed fluctuations in concentrations from hundreds of parts per billion of TCE to tens of parts per billion, then back up to hundreds of parts per billion. The concentrations of contaminants in the following tables are maximum concentrations that do not necessarily represent consistent concentrations for each sampling episode.


Table 3.

1982 MAXIMUM CONCENTRATIONS OF CONTAMINANTS IN PRIVATE WELLS WITHIN THE NORTH PLUME (all concentrations and values in parts per billion)
CONTAMINANTS Private WELL MN#234425

7/1/82

Private WELL
MN#234351

1/28/82

COMPARISON
VALUE &
REFERENCE
1,1-dichloroethane 76 92 NONE
1,1-dichloroethylene 120 86 0.06
CREG
trans-1,2-dichloroethylene NOT DETECTED 20 200
RMEG (child)
1,1,1-trichloroethane 600 720 200
LTHA
trichloroethylene 2,700 2,400 3
CREG
cis-1,2-dichloroethylene 18 NOT DETECTED 70
LTHA
1,2-dichloroethane 8.2 8 0.4
CREG
tetrachloroethene 7.4 8 0.7
CREG
1,1,2-trichloroethene 2.6 NOT DETECTED 3.0
CREG
chloroform 2.9 3.5 6.0
CREG
methylene chloride 6.2 2.2 5.0
CREG

DATA SOURCE: Analytical data sheets provided by MPCA (48).


Table 4.

1982-84 MAXIMUM CONCENTRATIONS OF CONTAMINANTS IN PRIVATE WELLS IN THE HILLSIDE SAND AQUIFER WITHIN THE SOUTH PLUME (all concentrations and values in parts per billion)
CONTAMINANTS Private WELL
MN#234396

6/9/82

Private
WELL
MN#234332

9/3/82

Private WELL
MN#234431

2/17/84

COMPARISON
VALUE &
REFERENCE
1,1-dichloroethane 2.5 2.6] 22 NONE
1,1-dichloroethylene 2.5 1.1 16] 0.06
CREG
trans-1,2-dichloroethylene NOT DETECTED NOT DETECTED NOT DETECTED 200
RMEG (child)
1,1,1-trichloroethane NOT DETECTED 1 4 200
LTHA
trichloroethylene 210 140 7000 3
CREG
cis-1,2-dichloroethylene 31 33 280 70
LTHA
toluene NOT DETECTED NOT DETECTED 0.8 1000
LTHA
1,2-dichloroethane NOT DETECTED NOT DETECTED 0.7 0.4
CREG
methylene chloride NOT DETECTED NOT DETECTED 2.0 5.0
CREG
chloroform NOT DETECTED NOT DETECTED 1.4 6.0
CREG

DATA SOURCE: Analytical data sheets provided by MPCA (48).


Sampling of private wells in the Edgetown Acres subdivision immediately north of TCAAP also revealed groundwater contamination in a few Unit 1 wells. A detailed well inventory (27) performed in Edgetown Acres in 1987 on behalf of the Army indicated that the water supply for this Shoreview subdivision is a combination of the domestic wells that tap either Groundwater Unit 1 or Unit 3 and the municipal water supply from Shoreview. Most of the homes are connected to the Shoreview municipal water system.

A detailed investigation of groundwater in Edgetown Acres was begun in 1987. Sampling and analyses of the private wells in Edgetown Acres were performed in four phases beginning with the sampling of six private wells in September 1987. Phase II sampling of 16 wells was performed in February 1988 (27). In April 1988, an additional 29 wells were sampled. In 1991, 11 wells in which contaminants had been previously identified were resampled. However, none of the concentrations of Site A contaminants measured in the private wells currently in use exceeded any state or federal drinking water standard. Additional sampling of private wells was performed in 1992 and 1993. Both the Army and MPCA are continuing to monitor groundwater in Edgetown Acres.

In the vicinity of Edgetown Acres, only one private well out of approximately 50 sampled private wells has consistently displayed groundwater contaminants. Analytical results of several samples taken during a 10-year period from a domestic well on County Road I at the entrance to the Edgetown Acres Subdivision have consistently identified 1,2-DCE and TCE in concentrations below comparison values. From the consistent measurements of contaminants in that private well, in the off-site monitoring well #01U902, and in the on-site monitoring wells, a shallow groundwater plume of 1,2-DCE and TCE has been projected to extend from Site A to a few private wells in Edgetown Acres. Some of these residences are now connected to the Shoreview municipal water supply. MPCA and the Army are monitoring the concentrations and movement of the contaminants.


Table 6.

MAXIMUM CONCENTRATIONS OF CONTAMINANTS IN EDGETOWN ACRES SUBDIVISION PRIVATE WELLS, OFF-SITE MONITORING WELL #01U902, AND ON-SITE MONITORING WELL #01U117. (All values are expressed in parts per billion)
CONTAMINANT MAXIMUM
VALUES
PRIVATE
WELLS
(1992)
MAXIMUM
VALUES
MONITORING
WELL
01U902
(MAR92)
MAXIMUM
VALUES
MONITORING
WELL
01U117
(MAR92)
COMPARISON
VALUE
& REFERENCE
chloroform (1) 0.6 NOT DETECTED NOT DETECTED 5.7 CREG
cis-1,2-dichloroethylene 3.2 53 130 70 LTHA
trans-1,2-dichloroethylene 0.9 3.2 6.7 100 LTHA
methylene chloride (2) 1.0 NOT DETECTED 9.1 600 EMEG
(child)
5 CREG
trichloroethylene 1.4 2.7 39.0 3 CREG
1,1,2-trichloroethane NOT DETECTED NOT DETECTED NOT DETECTED 0.6 CREG
1,1,1-trichloroethane NOT DETECTED 1.90 NOT DETECTED 200 LTHA
benzene NOT DETECTED .87 NOT DETECTED 1.2 CREG
tetrachloroethylene NOT DETECTED NOT DETECTED 6.80 0.7 CREG

Data sources: TCAAP Fiscal Year 1992 Annual Monitoring Report and personal communication with Barbara Gmabasik, MPCA, September 3, 1993

(1) Not a Site A contaminant. Commonly found in municipal water supplies as result of chlorination.

(2) Not a Site A contaminant. Probably result of laboratory contamination during analysis.


ARDEN MANOR MOBILE HOME PARK WELLS

Located within the boundaries of both the North and South plumes of contamination, Arden Manor Mobile Home Park is approximately 1,000 feet west of Site I. In 1981, VOCs were measured in the main water supply well (Well #2) and in an emergency back-up well (Well #1) used by approximately 750 residents (28). As indicated in Table 7, the maximum concentration of TCE in the main supply well was 55 ppb; in the emergency back-up well, it was 570 ppb. MDH issued a drinking water advisory to the mobile home park owners in 1981. Residents continued to use the two wells without treatment until a contaminant-free deeper well (Well #3) was drilled and connected to the mobile home park water supply lines in 1983.

With Well #3 serving as the main supply well, Well #1 was capped, and Well #2 served as the emergency back-up well. Well #2 was used intermittently from 1983 until 1993 as an emergency water supply when Well #3 was shut down for repairs. MDH analyzed a sample from Well #2 in 1993 and reported the presence of 13 ppb TCE 29. In April 1993, MDH notified the owners of the mobile home park to stop the use of Well #2.


Table 7.

1981 MAXIMUM CONCENTRATIONS OF CONTAMINANTS IN ARDEN MANOR MOBILE HOME PARK WELLS. (All concentrations expressed as parts per billion)
CONTAMINANTS ARDEN MANOR WELL #2

MAIN WATER
SUPPLY WELL

ARDEN MANOR WELL# 1

Backup well

COMPARISON VALUE
& REFERENCE
1,1-dichloroethane 1.3 68 NONE
1,1-dichloroethylene 2.1 56 90-EMEG (child)
0.06 CREG
trans-1,2-dichloroethylene 9.8 11 200 RMEG (child)
100 LTHA
1,1,1-trichloroethane 10 440 200 LTHA
trichloroethylene 55 560 3 CREG
cis-1,2-dichloroethylene 4.7 34 70 LTHA

DATA SOURCE: 1981 MNDH letter to MPCA-reference 49 and information provided by MPCA (48).


MUNICIPAL WELLS

In 1981, VOCs were discovered in several municipal water supply wells in the communities west and southwest of TCAAP. In July 1981, MDH notified the city of New Brighton that analyses of water samples from New Brighton wells indicated that six of the eight wells in use at the time of sampling (July 8, 13, and 15) were contaminated with a number of chlorinated hydrocarbons (28).

Following the July 1981 notification by MDH, the City of New Brighton implemented the following interim and permanent actions to reduce and eliminate the problem:

  1. Summer 1981
  2. Reactivated an uncontaminated well (Well #2),

    Resequenced wells so that operating the cleanest wells was first priority,

    Purchased water from Columbia Heights, and

    Implemented severe restrictions on water use (e.g., prohibited car- washing and lawn-watering).

  3. 1982
  4. Deepened Wells #9 and #8 into the uncontaminated Mt. Simon/Hinckley aquifer.

  5. 1983
  6. Installed and operated an interim gravity granular-activated carbon GAC filter system, and

    Installed Well #10 into the uncontaminated Mt. Simon/Hinckley aquifer.

  7. 1984
  8. Completed Wells #11 and #12 into the Mt. Simon/Hinckley aquifer

  9. 1988
  10. Installed a temporary GAC system on Wells #5 and #6.

  11. 1990
  12. Activated production at permanent GAC facility.

Table 8 indicates the maximum concentrations of contaminants discovered in New Brighton wells in 1981. Eventually, all operating New Brighton wells were contaminated with VOCs. As noted previously, contaminants are currently removed from the New Brighton water supply system through use of a permanent carbon filter system. In addition, three new uncontaminated wells have been installed to replace decommissioned, contaminated wells (10).

In 1982, maximum concentrations of 23 ppb TCE and 5 ppb TCA were detected in a Village of St. Anthony well (SAM #3). Use of this well was discontinued in 1984 because of increasing concentrations of contaminants (10). Contaminants were detected in St. Anthony wells #4 and #5 after shutdown of the number #3 well. Pumping of St. Anthony Well #3 was restarted in 1989, and a temporary carbon filter treatment was installed for Wells #3 and #4. A permanent treatment system began operating in 1991.

No VOCs were discovered in municipal wells for Mounds View and Shoreview during a 1982 investigation. Follow-up analyses have not detected any TCAAP contaminants. Fridley municipal wells have also been monitored. Analytical results from a sample taken from Fridley municipal Well #6 in 1988 indicated 9 ppb TCE. However, environmental consultants for MPCA did not link contamination of the Fridley well with TCAAP groundwater contamination (16).

All analytical results of municipal wells discussed in the preceding paragraphs are from samples taken from raw water intakes before treatment. Analyses of tap water samples were not discussed in the remedial investigation reports reviewed for this document. As in the case of the TCAAP water supply system, the concentrations of contaminants at point of use (water taps in homes and businesses) were probably much lower than the concentrations measured at the wells.

This assumption is supported by the results of tap water samples MDH took in 1982 from a water tap at a restaurant on Silver Lake Road. (Table 9). New Brighton municipal Well #3 is the probable source of the water for the restaurant. As indicated in Table 9, the concentrations at the water tap are considerably lower than the concentrations in the raw water sample at the well. Analysis of the tap water in 1983 did not find concentrations above drinking water standards.


Table 8.

1981 MAXIMUM CONCENTRATIONS OF CONTAMINANTS IN NEW BRIGHTON MUNICIPAL WELLS (identified by well # and MN Unique #; concentrations in parts per billion [ppb])
CONTAMINANT NB#2
206798
NB#3
206793
NB#4
206792
NB#5
206796
NB#6
206797
NB#7
206791
NB#8
206795
NB#9
206794
COMPARISON VALUES
1,1-dichloroethane NOT DETECTED 3 3 1.5 NOT DETECTED NOT DETECTED 5 2 NONE
1,1-dichloroethylene <1 5 5 2.5 1 1 8 3 0.058
CREG
trans-1,1-dichloroethylene NOT DETECTED 1 1 1 NOT DETECTED 1 2 0 200
RMEG
1,1,1-trichloroethane NOT DETECTED 31 30 16 2.1 <1 56 23 200
LTHA
trichloroethylene <1 110 110 63 5.4 <1 190 86 3 CREG

DATA SOURCE: Original data sheets provided by MPCA.


Table 9.

1982 COMPARISON OF TAP WATER SAMPLES AND SAMPLES FROM NEW BRIGHTON MUNICIPAL WELL #3 (all concentrations and comparison values in parts per billion [ppb])
JANUARY SAMPLES MARCH SAMPLES
CONTAMINANT restaurant
tap water
1/28/82
NB #3
1/5/82
restaurant
tap water
3/22/82
NB #3
3/24/82
Comparison
Values
1,1-dichloroethane less than 0.2 ppb 2.5 ppb 0.3 ppb 3.0 ppb none
1,1-dichloroethylene less than
0.2 ppb
3.8 ppb less than 0.2 ppb 5.3 ppb 90 EMEG
0.06 CREG
trans-1,1-dichloroethylene less than 0.2 ppb 1.2 ppb less than 0.2 ppb 0.91 ppb 200 RMEG
100 LTHA
1,1,1-trichloroethane 0.7 ppb 27.0 ppb 3.1 ppb 39.0 ppb 200 LTHA
trichloroethylene 2.5 ppb 90.0 ppb 9.6 ppb 130.0 ppb 3.0 CREG
chloroform 0.9 ppb NOT ANALYZED 1.0 ppb NOT ANALYZED 6.0 CREG
1,2-dichloroethane NOT DETECTED 0.5 ppb NOT DETECTED NOT ANALYZED 0.4 CREG]

Data Source: Analytical information provided by MPCA (48).


INDUSTRIAL/COMMERCIAL WELLS

In the vicinity of TCAAP, water from a number of industrial and commercial wells is used by local businesses for either industrial processes or drinking water or both. The wells, which were identified and monitored by MPCA and MDH beginning in 1981, may draw from either the Hillside Sand drinking water aquifer or the deeper Prairie du Chien drinking water aquifer. Table 10 shows the 1981 maximum concentration of contaminants in a commercial well west of TCAAP.


Table 10.

1981 MAXIMUM CONCENTRATIONS OF CONTAMINANTS IN A COMMERCIAL WELL WEST OF TCAAP
CONTAMINANTS LUMBER YARD WELL COMPARISON VALUE
& REFERENCE
1,1-dichloroethane 13 NONE
1,1-dichloroethylene 55 0.06 CREG
trans-1,2-dichloroethylene NOT DETECTED 200 RMEG
1,1,1-trichloroethane 450 200 LTHA
trichloroethylene 170 3.0 CREG
cis-1,2-dichloroethylene 5.9 70 LTHA
chloroform 1.2 6.0 CREG

DATA SOURCE: January 13, 1983, memorandum from Paul Hess, MPCA, concerning 1982 groundwater sample results.


MONITORING WELLS

A large number of groundwater monitoring wells have been installed west and southwest of TCAAP since 1982, mainly by the TCAAP contractors or by lessees. The wells are designed to monitor specific groundwater units and aquifers. Periodic monitoring of the wells has helped to define the nature and extent of the groundwater contamination. The analytical results from the monitoring wells are similar to those from the private, mobile home park, commercial, and municipal wells. The off-TCAAP groundwater monitoring program clearly indicates that contaminants are moving away from TCAAP. Without remediation, contaminant concentrations in the drinking water aquifers (North and South plumes) west and southwest of TCAAP will remain at or above levels of health concern for many years.

OFF-TCAAP AIR

As mentioned in the On-TCAAP Air subsection, ambient air sampling was performed in November 1990 on and off TCAAP using a portable instrument capable of detecting organic chemicals in low concentrations (0.7 ppm detection limit) (14). Sampling was conducted during a drive through the residential areas near TCAAP. No VOCs were detected above background levels.

OFF-TCAAP SURFACE WATER AND SEDIMENTS

Off-TCAAP surface water contamination was first reported in 1953; residents complained of odors and discolored water entering Valentine Lake from Round Lake. Follow-up investigations by MDH and the Federal Cartridge Company revealed that pollutants were entering Round Lake via the sewer outlet from Building 502 (2). Surface water samples were analyzed for oil and grease; concentrations ranged from 26.4 to 405 milligrams per liter (mg/L) in the Building 502 storm sewer and from 4 to 93 mg/L in Round Lake (2). Apparently, the samples were not analyzed for other potential contaminants, such as metals and organic chemicals. Round Lake received an estimated 1 million gallons of untreated waste water per day before the storm sewer system was altered in 1953 to divert industrial waste water to the sanitary sewer (21).

In 1967, some cyanide and other wastes were discharged into the storm sewers from floor drains in Building 502. Problems were still occurring as late as 1969 when a TCAAP tenant, Honeywell, noted that floor drains in Building 502 were still discharging to the storm sewer system that flowed into Round Lake (21). Emergency overflows continued to be discharged from the sanitary sewer system (Site J) and then into Round Lake until the discharge routing was changed in 1983 (21).

Surface water and sediment sampling has been performed in Round Lake by four different organizations since 1981. The U.S. Fish & Wildlife Service (USFWS) analyzed samples of surface water, sediments, and fish in 1981 (30). EPA contractors monitored surface water, sediments, and fish in 1982 (31). Federal Cartridge Company and environmental consultants for MPCA performed surface water and sediment sampling in 1987. None of the reported surface water concentrations exceeded drinking water standards. However, the detection limit for VOCs was 10 ppb in the USFWS report (30), which is greater than some of the EPA drinking water standards for some VOCs, including TCE. Therefore, a complete evaluation of chemicals exceeding comparison values cannot be performed using the USFWS data alone. The additional monitoring of surface water and sediments that was conducted will provide more information on existing conditions.

As a result of the 4 studies, approximately 13 locations at Round Lake were sampled for contaminated sediments. The highest concentrations of contaminants were measured in the sediments at or near the outfall into Round Lake, where past discharges of contaminants from TCAAP had entered. Table 11 summarizes the maximum concentrations measured in the sediments. Although the ecological assessment report (21) prepared by the Army Environmental Hygiene Agency mentioned that uranium had been detected in the sediments in concentrations below levels that naturally occur in soil, no measurements were provided. Therefore, uranium concentrations are absent from Table 11.

Initial sampling of surface water and sediments in Rice Creek, outside TCAAP boundaries, was very limited. In July and September 1982, EPA contractors sampled four points along Rice Creek (31). Only one of these sampling locations was downstream from where Rice Creek exits TCAAP. TCE was reported at 5.2 ppb at that downstream sample location (31). The on-TCAAP remedial investigation included surface water and sediment sampling and analysis at the point where Rice Creek exits TCAAP. No contaminants above detection limits (in low ppbs) were discovered.

Additional sampling of surface water and sediment of Rice Creek was performed as part of a feasibility study in 1993 (48).

In 1982, EPA contractors also sampled Long Lake and Rush Lake. TCE at a concentration of 1 ppb was identified on the south side of Long Lake; TCE was not detected in Rush Lake (31). In 1986 and 1987, MPCA sampled Long Lake swimming areas for TCE contamination (32); the maximum concentration measured was 20 ppb. MDH evaluated the TCE concentrations and concluded that they would not endanger swimmers and other recreational users of Long Lake. MPCA determined that "there was no groundwater connection between the aquifers with TCAAP contamination and Long or Rush lakes (48)." "Local sources unrelated to TCAAP were found to be the source of the volatilte organic hydrocarbon problem in Long Lake (20)."

Table 11.

MAXIMUM CONTAMINANT CONCENTRATIONS IN ROUND LAKE SEDIMENTS (concentrations expressed as parts per million [ppm])
CONTAMINANT MAXIMUM
CONCENTRATION
(ppm)
COMPARISON
VALUE [*]
(ppm)
SOURCE
Arsenic (As) 10.0 20 RMEG (child)
Cadmium (Cd) 85.0 40 Chronic EMEG
(child)
Copper (Cu) 4070.0 NONE  
Lead (Pb) 1010.0 NONE  
Mercury (Hg) 2.2 20 RMEG (child)
methyl mercury
Zinc (Zn) 2054.0 20,000 RMEG (child)
Cyanide (CN) 26.0 1000 RMEG (child) free cyanide
(DDD) 0.42 3 CREG
(DDE) 0.007 2 CREG
Aroclor 1016 1.0 4 RMEG (child)
Aroclor 1242 13.0 NONE  
Aroclor 1254 .04 NONE  
Aroclor 1260 .11 NONE  

Data source: United States Army Environmental Hygiene Agency, Ecological Assessment, Twin Cities Army Ammunition Plant, New Brighton, Minnesota, May 1991.

* Comparison values are based on the possibility of ingestion of contaminated soils or sediments.


During a July 1991 site visit, ATSDR staff members noted that a drainage ditch apparently flows from the parking lot of Building 503 and the rail line through the TCAAP Gate 4 area through a culvert under Highway 10 into a small pond within a mobile home park. The drainage ditch is part of subwatershed #2 described in the on-TCAAP remedial investigation. As a result of MPCA and ATSDR inquiries, Army environmental investigators have confirmed that there are no records of hazardous waste leaks or spills into this subwatershed. Therefore, there is no reason to suspect that any harmful concentrations of contaminants from TCAAP have entered the pond in Arden Manor Mobile Home park.

OFF-TCAAP BIOTA

The off-TCAAP consumable biota sampling is limited to fish in Round Lake. As described previously, the high waste loads dumped into Round Lake from TCAAP over 30 years or longer raised concerns about bioaccumulation of contaminants in fish. The U.S. Fish and Wildlife Service investigated Round Lake in 1981 (30). Fish (bullheads), benthic invertebrates, and sediment samples were taken and subsequently analyzed for radioactivity, PCBs, and inorganic compounds (metals). The investigators concluded that there was no indication of significant bioaccumulation of contaminants in the fish taken from Round Lake (30). Sampling and analyses were not performed on consumable fish from Valentine Lake.

DATA LIMITATIONS AND MISSING INFORMATION

Although numerous environmental investigations have been performed on and off TCAAP, the following discussion indicates the limitations of data reviewed for this report and identifies additional information and data that would permit a more thorough public health evaluation.

Most of the air data are derived from a single-point-in-time measurement by an organic vapor analyzer. A one-time measurement using such a portable instrument does not provide a complete data set for evaluation of potential air contamination. Air monitoring data for both indoor air and outdoor air in the adult breathing zone would provide actual measurements on which to base an evaluation of inhalation exposures at TCAAP.

Surface water and sediment investigations should focus on possible human exposure points (e.g., areas where children are known to play) to provide better assessment of possible human ingestion of or skin contact with contaminants. As noted and recommended in the USAEHA ecological assessment (21), thallium should be measured in any additional sampling and analyses of surface water and sediment.

The true concentrations of a few contaminants of concern in on-TCAAP monitoring wells are difficult to discern, because the reports merely list the concentrations as less than a concentration 100 times higher than a comparison value. For example, the concentration of vinyl chloride is reported as less than 380 ppb in a sample taken from Well #03U314 in September 1992. In the same well, vinyl chloride had been reported at a concentration of 16 ppb in January 1989 and of 3.5 ppb in April 1989. It is difficult to know whether those concentrations still exist when either the analytical procedures or reporting procedures focus only on concentrations above 380 ppb.

As previously discussed, the Army procedure of analyzing only field-filtered samples for metals also limits the evaluation of possible health effects from metal contaminants, because field-filtered samples do not represent the maximum concentrations that might have been available if the water had been used as a drinking water source.

C. QUALITY ASSURANCE AND QUALITY CONTROL

The information and data used in preparing this public health assessment are derived from reports that dated as far back as the 1960s. It is not feasible for the authors to examine the quality assurance and quality control measures used in each source document. Unless otherwise noted, it is assumed that the quality assurance and quality control measures used at the date of each source document were consistent with methods used by the majority of the scientific community and will provide useful and valid data for health assessment purposes.

D. PHYSICAL AND OTHER HAZARDS

No particular physical hazards were noted during the site visits. It is assumed that hazards associated with the various industrial processes on TCAAP are covered by standard safety procedures.


PATHWAYS ANALYSES

To determine whether persons living or working either on TCAAP or in the surrounding areas are or have been exposed to contaminants from TCAAP, ATSDR staff members evaluate the environmental and human components that lead to human exposure. This pathway analysis consists of five elements: a source of contamination, transport through an environmental medium, a point of exposure, a route of human exposure, and an exposed human population.

If all five elements are present, a pathway is considered complete. If one element is missing, but the possibility of a complete pathway exists or may exist sometime in the future, the pathway is considered potential. A pathway is considered eliminated if one or more elements are missing and will never be present. Pathways may have been completed in the past but may currently be eliminated because one or more elements have been removed, breaking the connection between the source of the contamination and the exposed population. The following discussion addresses past completed and potential pathways.

A. COMPLETED EXPOSURE PATHWAYS

PAST COMPLETED EXPOSURE PATHWAYS THAT NO LONGER EXIST

TCAAP Water Supply

Hazardous chemicals used in industrial processes at TCAAP were spilled, leaked, and disposed of at various locations within TCAAP. Environmental investigations have demonstrated that solvents and other chemicals migrated into at least two drinking water aquifers (Hillside Sand and Prairie du Chien/Jordan) beneath TCAAP. The TCAAP water supply wells draw water from the Prairie du Chien/Jordan drinking water aquifer.

In 1981, contaminants were detected at high concentrations in the water supply wells. Sampling and analysis of drinking water at the Minnesota State Training Center, which is connected to the TCAAP water system, revealed concentrations of TCE above EPA drinking water standards. Because the training center is at the end of the TCAAP distribution system, it is assumed that the contaminant concentrations measured in the training center tap water are the minimum concentrations in the water system at the time of sampling. Therefore, all persons using the water from the TCAAP system may have been exposed to those concentrations.


Table 12.

PAST COMPLETED EXPOSURE PATHWAYS THAT NO LONGER EXIST
PATHWAY NAME EXPOSURE PATHWAY ELEMENTS TIME
SOURCE ENVIRONMENTAL
MEDIUM
POINT OF
EXPOSURE
ROUTE OF
EXPOSURE
EXPOSED
POPULATION
TCAAP Water Supply TCAAP Groundwater On-TCAAP
water supply
Ingestion
Inhalation
Skin Contact
Military families,
TCAAP workers,
State workers
Past

ELIMINATED**
Municipal TCAAP Groundwater Home, business & school
water taps
Ingestion
Inhalation
Skin Contact
Municipal well users PAST

ELIMINATED**

** Human exposure was reduced and then eliminated through a combination of interim and permanent actions as explained in the Environmental Contamination and Other Hazards section.


The exposed population can be divided into two groups: workers at both the training center and TCAAP (approximately 2,100 people) and families occupying the 14 military housing units near the training center (approximately 58 people). Workers were adults using the TCAAP water supply for less than 10 hours per day, 5 days a week. However, families in the military housing included both children and adults who used the water for drinking, showering, and other household uses on a 24-hour-per day basis. Both populations could have included pregnant or lactating women.

The primary route of exposure for the workers would have been ingestion; inhalation and skin contact would have been limited. The primary exposure for military families may also have been ingestion, but the opportunity for exposure from inhalation and skin contact was greater because water was used for bathing and household activities (e.g., laundry).

All exposures to the contaminated TCAAP water ended when the treatment system was installed and began operating. Although there is no empirical evidence regarding when the exposures began, the high concentrations of contaminants and the hazardous waste disposal history at TCAAP indicate that it would be reasonable to estimate exposures ranging from 5 to 20 years. However, scientifically valid lengths of exposure for the two potentially exposed populations have not been established. The TCAAP water supply pathway no longer exists, because the groundwater treatment system prevents any harmful concentrations of contaminants from entering the water supply.

MUNICIPAL WELLS

The same chemicals that contaminated the TCAAP water supply wells also contaminated the municipal wells in the cities of New Brighton and St. Anthony, but at much lower concentrations. The concentrations of the contaminants within individual homes and businesses are not known, because such widespread sampling and analysis was not practicable. However, a small number of samples from tap water in a restaurant in the Silver Lake Road area were analyzed (Table 9).

Accurate estimations of the number of people exposed to harmful concentrations of contaminants cannot be made, because there is no conclusive information on concentrations of contaminants at all points of use, such as household water taps. Because the maximum number of people using the municipal water supplies in New Brighton and St. Anthony was approximately 30,000, that number is an estimate of the largest number of people who may have ingested any concentration of contaminants. Length of exposure is also difficult to determine, because there are no analytical data available to determine when human exposure began.

Exposure via the municipal water supply wells is considered to be a past completed pathway. This exposure pathway has been effectively mitigated with the operation of the current water treatment systems, which prevent harmful concentrations of contaminants from entering municipal water supplies.

PAST COMPLETED EXPOSURE PATHWAYS (Table 13)

PRIVATE WELLS IN THE NORTH AND SOUTH PLUMES

Environmental investigations conducted in the 1980s revealed that contaminants had entered the Hillside Sand and Praire du Chien/Jordan aquifers beneath TCAAP and had moved from TCAAP in two distinct groundwater plumes that migrated west (North Plume) and southwest (South Plume), with subsequent contamination of private wells. Although several private wells were contaminated with concentrations of TCE above EPA drinking water standards, not all private wells in the immediate area were contaminated.

Moving westward and then southwestward from Site I, the South Plume affects several residences. The nearest residences to Site I are in a small group of six homes located along a 100-yard stretch of access road on the western side of Highway 10 (Figure 5). A seventh home once was located on a nearby vacant lot but was demolished in the early 1990s. A total of eight drinking water wells in the Hillside Sand Aquifer serve the residences bordering Highway 10. Analyses of the eight wells from 1981 through 1984 indicated that only five of the eight wells were contaminated, and two of the contaminated wells served one residence. Therefore, four families out of seven were exposed to contaminated groundwater via ingestion, inhalation, and skin contact.

Apparently, the private well with the highest concentrations of contaminants (from the now vacant lot) was not sampled until December 1983. The residents may have been using that well in February 1984, when the maximum concentration of TCE in a sample from it was reported as 7,000 ppb.

Contaminants were also detected in another private well approximately 1,500 feet southwest of the seven residences bordering Highway 10. The contaminants were the same as in the other private wells, but at lower concentrations (150 ppb TCE).

Contaminants in the North Plume moved into an area west of TCAAP, contaminating private wells along Old Highway 8 south of the railroad crossing. Analytical results from samples of two private wells within 100 feet of each other have been consistently high (2,100 to 2,900 ppb TCE). However, contaminants have never been detected in another nearby well, which is used by a local church.

MDH and MPCA attempted to identify all contaminated private wells in the New Brighton and Arden Hills communities in 1981, 1982, and 1983. Letters recommending that they switch to alternative drinking water sources were sent to owners of contaminated wells. Eventually, all residents in the New Brighton and Arden Hills communities with known contaminated wells were offered connections to municipal water supplies. However, some families may have used the contaminated water for drinking, bathing, washing, etc., for as long as 3 years before alternative water was available.

In summary, during the early 1980s, at least seven families were exposed to contaminated drinking water from private wells tapping the contaminated portion of the Hillside Sand Aquifer. The exposed population may have included children and could have included pregnant and lactating women. How long these families were exposed to TCAAP contaminants is difficult to determine, because water samples were not taken until 1981. From what is known about the operating history and solvent disposal practices at TCAAP, 5 to 20 years would not be an unreasonable estimate of the range of lengths of exposure.

ARDEN MANOR MOBILE HOME PARK WELLS

In 1981, VOCs were discovered in the main supply well (Well #2) and an emergency back-up well (Well#1) at Arden Manor Mobile Home Park. The two wells provided domestic water supplies for approximately 750 persons residing in the mobile home park, which is across Highway 10 from TCAAP. The exposed population included children and possibly included pregnant and lactating women. Uncontaminated alternative water from a new, deeper well was supplied to the residents in early 1983. The least contaminated well (Well #2) was used until July 1993 as an emergency water supply when the deeper well was unavailable because of maintenance needs.

Well #1 was used as the main supply well for the original mobile home park, which consisted of 96 mobile home connection pads. Well #1 was replaced by Well #2 as the main supply well in 1976, when the mobile home park was expanded.

How long the mobile home park residents were ingesting water with contamination at levels of health concern is unknown. A minimum estimated length of exposure via ingestion, inhalation, and skin contact would be from the date of discovery in July 1981 until the switch to Well #3 in early 1983, approximately 18 months. An estimated range of lengths of exposure of 5 to 10 years is reasonable, but that estimate depends greatly on the operational history of the mobile home park and the length of service of the contaminated wells, as well as the date when the contaminants first entered the water supply wells.

Length of exposure for individual residents of the park depends on the length of the tenants' residence in the mobile home park. One of the mobile home park owners estimated that the average stay in the park is 5 years. The park records indicate that approximately 30 to 40 tenants arrive at or leave the park each year. Therefore, it is unlikely that the entire park population (750 people) was exposed to TCAAP contaminants for the minimum exposure period of 18 months, and it is certain that the entire population was not exposed for the estimated contamination duration range of 5 to 10 years.

Ingestion, inhalation, and dermal contact with groundwater contaminants probably occurred for short periods (ranging from 1 day to approximately 30 days) when Well #3 was out of service and the park used Well #2 as a back-up water supply. Analysis of a water sample from Well #2 in April 1993 revealed a TCE concentration of 13 ppb, which is above the state and federal drinking water standard of 5 ppb.

The use of Well #2 as a main water supply is considered a past completed pathway with some limited current exposure because of its intermittent usage since 1983. Park owners are currently evaluating alternative water supplies and treatment systems and plan to replace Well #2.

Table 13.

PAST COMPLETED EXPOSURE PATHWAYS
PATHWAY NAME EXPOSURE PATHWAY ELEMENTS TIME**
SOURCE ENVIRONMENTAL
MEDIUM
POINT OF
EXPOSURE
ROUTE OF
EXPOSURE
EXPOSED
POPULATION
Private Wells TCAAP Groundwater Domestic
water
supply
Ingestion,
Inhalation,
Skin Contact
Residents using private wells Past
**
Arden Manor Wells TCAAP Groundwater Mobile home park water supply Ingestion,
Inhalation,
Skin Contact
Mobile home park residents Past
**
Commercial & Industrial Wells TCAAP Groundwater Business water supplies Ingestion,
Inhalation,
Skin Contact
Workers Past
**
             

** These past completed pathways have been addressed by MPCA and MDH through
drinking water advisories and recommendations for alternative water supplies.
These pathways have been eliminated for residences that have been connected to
municipal water supplies. However, some wells may still be used for drinking water
supplies, and they are considered indeterminate health hazards.


COMMERCIAL/INDUSTRIAL WELLS

Several commercial and industrial wells, including a well supplying a lumberyard west of TCAAP, were discovered in 1981 and 1982 to be contaminated with TCE and other VOCs at levels exceeding EPA drinking water standards. Water from the wells was used for industrial processes and, at a few locations, for workplace drinking water supplies.

The primary route of exposure is assumed to have been ingestion; there was probably very limited opportunity for inhalation and skin contact, depending upon industrial or commercial processes. Workers are assumed to have been the exposed population, with an average exposure period of 5 days a week and less than 10 hours a day. No estimate of the number of exposed persons is available from existing reports. Use of the wells for drinking water may have halted following MDH's notification of the contamination in 1981. Although MPCA and MDH have monitored the known contaminated wells since 1981, the detailed well inventory conducted by Army environmental consultants (15) should allow regulators to identify any commercial or industrial wells currently operating within the area of groundwater contamination that were not previously identified.

The contaminated commercial/industrial wells constitute a past completed pathway. However, current and future exposure is possible, because there may be some unreported or unidentified wells still being used for drinking water.

B. POTENTIAL EXPOSURE PATHWAYS

PRIVATE WELLS IN THE EDGETOWN ACRES SUBDIVISION NORTH OF SITE A

Sampling and analysis of private wells located north and northwest of Site A indicated a sporadic pattern of low concentrations of a few VOCs. However, analytical results from one private well on County Road I, across from TCAAP, indicated persistent low concentrations of 1,2-DCE and TCE. The well is used for lawn irrigation. Drinking water for the residence is supplied by the Shoreview municipal water system. Comparison of contaminants in this private well with contaminants in Site A monitoring wells and one off-TCAAP monitoring well (#0U0902) indicates that some contaminants from Site A are migrating off TCAAP and across County Road I in groundwater .

In the case of at least the private well with the long history of contamination, the source of contaminants appears to be Site A. Although current concentrations are below levels of health concern, concentrations could increase during the next few years. The availability and use of municipal water supplies in the Edgetown Acres Subdivision severely limit the impact of future groundwater contaminant migration and potential increases in contamination. Only 5 or fewer residences still use Unit 1 groundwater for domestic water supplies.

PRIVATE WELLS WITHIN AND DOWNGRADIENT OF THE NORTH AND SOUTH PLUMES

The contaminated private wells closest to TCAAP (in both the North and South plumes) appear to draw water from the Hillside Sand Aquifer (Unit 3). However, the Hillside Sand Aquifer pinches out (is no longer present as a distinct hydrogeologic unit) west of TCAAP, and private wells further to the west and southwest of TCAAP derive their water from the Prairie du Chien/Jordan Aquifer system (Unit 4). Contamination of both the Hillside Sand Aquifer (Unit 3) and the Prairie du Chien/Jordan Aquifer system (Unit 4) is expected to persist for quite some time. Therefore, a potential pathway exists for any private well immediately downgradient of the contaminant plume, any well that may be drilled into the contaminated portion of these aquifers, or any known contaminated private well currently out of use that may be reconnected to a residence and used for water supplies.

This potential pathway is mitigated, but not completely eliminated, by the past and current efforts of MPCA and MDH to identify all drinking water wells threatened by TCAAP contaminants. The preferred remedy as proposed by the Army, MPCA, and EPA for Operable Unit 1 includes the following provisions to eliminate this potential pathway:

Provide an alternative water supply to residents with private wells within the North Plume;

Establish a special well construction area to regulate the installation of new private wells within the North Plume; and

Implement the groundwater extraction scheme for containment of the North Plume at the boundary of County Road E.

SURFACE WATER AND SEDIMENTS

The 1953 report that contamination from TCAAP was entering both Round Lake and Valentine Lake implies that recreational users of those lakes and adjacent residents were potentially exposed. Past, present, and future potential exposure pathways exist for human exposure via incidental ingestion of and skin contact with contaminated water and sediments. Children playing in any shallow water with highly contaminated sediments should be considered the most sensitive human population. However, that pathway is considered potential, because no measurements or other data indicate that anybody ingested or was exposed to contaminated surface water or sediments.

Although chronic ingestion of contaminated sediments remaining in Round Lake does not seem likely, any dredging and movement of contaminated sediments, particularly sediments near the outfall, could result in the contaminants being placed at points of human exposure, such as playgrounds or residential areas.

Additional investigations under way at Round Lake will provide a better definition of the potential problem and a better projection of any future need for remediation. There are no current plans to disturb the sediments.

ON-TCAAP SURFACE SOILS

Although surface soil contamination has not been completely characterized within TCAAP, limited information indicates that some contaminated surface soils may be present. Surface soil characterization is among additional environmental investigations under way or planned by the Army.

Because of current restrictions on human activities on TCAAP, chronic ingestion of contaminated surface soils or inhalation of windblown soils seems unlikely. However, this is still considered a potential pathway until either the new environmental investigations or remedial actions eliminate the possibility of future exposure.

SUMMARY OF POPULATIONS EXPOSED TO CONTAMINATED WATER SUPPLIES

Seven groups of people were exposed to contaminants before alternative water supplies became available. As described in the following paragraphs, a number of people may have had multiple opportunities for exposure.

The first exposed population consisted of on-TCAAP workers who ingested on-TCAAP contaminated drinking water supplies before alternative water supplies were provided. Some workers may also have been exposed to the same contaminants in the workplace through inhalation and dermal contact while using solvents in their work. Some workers may have been exposed at home via ingestion and inhalation of and skin contact with contaminants in domestic water supplies.

The second exposed population consisted of families residing in military housing and using the contaminated TCAAP water supply system for drinking water, bathing, laundry, and other domestic uses. Ingestion and inhalation of and dermal contact with contaminants may have occurred daily. As in the case of the workers described in this section, the families were exposed to two or more contaminants at concentrations above comparison values.

Employees of the Minnesota Department of Transportation who ingested contaminated groundwater from the TCAAP water system are the third exposed population. Some of the employees may also have been exposed to contaminants at home via ingestion and inhalation of and dermal contact with contaminated domestic water supplies.

Another exposed population was workers who used contaminated commercial or industrial wells in the New Brighton area for workplace drinking water supplies. Ingestion would have been the primary route of exposure; however, inhalation of and dermal contact with contaminants could have occurred during the work process or during showers taken at the workplace. Some of the workers may also have been exposed to contaminants in domestic water supplies.

A fifth exposed population consisted of residents of Arden Manor Mobile Home Park who used contaminated water supply wells before the park switched to a new, contaminant-free well in 1983. Exposure could have occurred as a result of ingestion, inhalation, and dermal contact. Some of the residents may also have been exposed to contaminants in the workplace.

Other exposed residential populations included residents of New Brighton and Arden Hills who used contaminated private wells for drinking water, bathing, laundry, and other household uses. Residents would have been exposed via ingestion, inhalation, and dermal contact. At least three families were exposed to two or more contaminants at concentrations above comparison values. Those three families were exposed to the highest reported concentrations of TCE and TCA.

Users of the contaminated municipal water supply systems in New Brighton and St. Anthony were the seventh exposed population. Because different municipal wells served different geographic areas, not all users of the water systems may have been exposed to contaminants via ingestion, inhalation, or dermal contact. Some of those exposed to contaminated municipal water may have also been exposed to contaminants in the workplace.

The human population with the potential for exposure to the highest concentrations of contaminants on a daily basis would have been TCAAP workers who used contaminants such as TCE in their daily work and who lived either in Arden Manor Mobile Home Park or in one of the residences with contaminated wells. Because of the opportunity for exposure in both the workplace and the home, this group may have received the greatest exposure to TCAAP contaminants.


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