PUBLIC HEALTH ASSESSMENT
MEMPHIS DEFENSE DEPOT (DEFENSE LOGISTICS AGENCY)
(a/k/a USA DEFENSE DEPOT MEMPHIS)
MEMPHIS, SHELBY COUNTY, TENNESSEE
DDMT was a fenced and guarded military supply, storage, and maintenance facility on the south side of Memphis from 1942 to 1997. The population within a mile of the site is nearly all African-American.
The Agency for Toxic Substances and Disease Registry (ATSDR) determines that no known exposures to DDMT contaminants exist off-site or have existed since 1989 that could result in health effects. ATSDR was unable to determine whether exposures to contaminants from DDMT prior to 1989 could have resulted in health effects because of a lack of environmental data.
Surface water and sediment, and ground water are the principal ways DDMT contaminants can move, are moving, or have moved off the site. For surface water and sediment, human contact with water from DDMT is almost entirely restricted to 3 surface-water drainages. These drainages are the Tarrent Branch that flows off the west side of the Main Facility, the ditches that flow from Dunn Field into or by the Rozelle neighborhood, and the drainage that flows south from the southeast corner of the Main Facility. Between 500 and 3,000 individuals could potentially have contact with water in these 3 drainages. The current levels of the site-contaminants in those drainages do not represent a public health hazard. Data are lacking on whether DDMT contaminants in these 3 drainages could have been a past public health hazard. For ground water, movement of site contaminants off site is primarily restricted to the northwest corner of Dunn Field. No one drinks this contaminated ground water.
Short-term exposure to air-borne contaminants from DDMT has occurred at least once. There is little indication in the data available to ATSDR that long-term exposure of all or most of the residents around DDMT to air-borne site contaminants occurred.
Food chain (e.g., rabbits, squirrels, fish, plants) and offsite soil do not appear to be viable exposure pathways.
This document fulfills ATSDR's commitment to DDMT area residents to reevaluate the 1995 DDMT Public Health Assessment (PHA). ATSDR has also fulfilled commitments to review cancer data for the DDMT area and establish the Greater Memphis Environmental Justice Work Group. Enhancement of the environmental medicine capabilities of DDMT area health care providers or clinics, another ATSDR commitment, is currently being planned. A specific health education program will be designed once this PHA is released.
This public health assessment (PHA) was written to evaluate new sampling data for the Defense Depot - Memphis, Tennessee (DDMT) National Priorities List (NPL) site, review existing data on the Dunn Field portion of DDMT, and respond to health issues and concerns raised by residents living near the site. This PHA is the fulfilment of a commitment made in 1997 by the Agency for Toxic Substances and Disease Registry (ATSDR) to review and update the DDMT PHA issued in 1995 (1,2).
In developing this public health assessment, ATSDR solicited and received many comments, concerns, or clarifications from the various stakeholders with DDMT. These stakeholders included area residents; and the various local, state, and federal agencies and elected officials involved with DDMT. However, no individual or organization outside of ATSDR approved this document before its release.
As indicated on Figure 1, the Defense Depot Memphis Tennessee is located on the south side of Memphis on land that was originally a cotton field (3). It was a fenced and guarded military supply, storage, and maintenance facility from 1942 to 1997. Commodities distributed from DDMT included food, clothing, medical supplies, electronic equipment, petroleum products, construction materials, and industrial chemicals.
Most depot operations occurred on the Main Facility (Figure 2) (3). Food, clothing, medical supplies, and similar items were stored in 28 large brick buildings called utilities. Construction materials, drums of chemicals, tires, wooden pallets, repair parts, and other supplies were kept in open-sided metal sheds. A variety of vehicles, trailers, and drums of chemicals were stored in open areas. Facilities were also available for painting, sand blasting, vehicle maintenance, disposal of medical items, plus a cafeteria, base exchange, medical clinic, gas station, and an administrative building. In addition, there were a swimming pool, nine-hole golf course, two ponds, and eight units of base housing. Most of the 26 miles of railroad tracks and 28 miles of hard surfaced roads, were or are on the Main Facility (4). The rail tracks ran north onto Dunn Field where they merged into one track, then joined the main rail line (3).
Chemical warfare-related materials were stored at DDMT from 1942 to 1961 (5). From 1942 - 1945, two of the warehouses and two sections of another plus 85,000 square feet of shed space were used to store chemical warfare-related hazardous materials. Most of this storage took place in the buildings near the northwest corner of the Depot (Figure 2).
These hazardous materials include non-persistent agents like tear gas, phosphorus grenades, and incendiary bombs; and flammable, corrosive, or toxic liquids and solids. Inert (non-hazardous) materials like gas masks, respirators, decontamination apparatus, and related materials were also stored. Persistent chemical warfare agents (e.g., mustard agent, nerve gas) were not stored at DDMT.
The amount of chemical warfare-related hazardous materials dropped rapidly after World War II (5). The main mission of the Chemical Section at DDMT became the servicing of gas masks; testing of flame throwers; and storage of decontamination materials, Chemical Agent Identification Sets (CAIS), and gas mask parts.
Ordnance such as explosive bombs, chemical warfare weapons, biological warfare weapons, and nuclear weapons was never stored or distributed from the site (5). The only exception to this is the small arms munitions used by the facility security force.
The Dunn Field portion of DDMT was used for many years to dispose of chemical and solid wastes from depot operations [Figure 3] (3). It was also used to store national stockpiles of bauxite and fluorspar, and was the location for a firing range used by the security staff.
While mustard agent was not stored at DDMT, there is one reported incident of it being disposed of at DDMT. In 1946, German mustard bombs, being transported by rail through the Memphis area, were found to be leaking (5). The train was brought to the DDMT Main Facility where the leaking bombs were unloaded and the train decontaminated. Locations where this was done are identified on Figure 2. The bombs were taken to Dunn Field where an attempt to detoxify the mustard agent was made by shooting holes in the bombs, then draining the agent into a pit of bleach which was then covered with soil. The bomb casings were buried in a separate pit on Dunn Field (Figure 3).
Burial of chemicals on Dunn Field was done without the impermeable (i.e, liquids can't flow through) liners and caps now required (3). This, along with chemicals from other non-federal sources, resulted in extensive contamination of the fluvial aquifer, both on and off the northwest corner of Dunn Field, with 1,1,2,2-tetrachloroethane, trichloroethylene, tetrachloroethylene, and related compounds. The fluvial aquifer starts about 60-80 feet below the surface and continues down another 10-20 feet. Flow of the contaminated groundwater is towards the Allen Well Field, which is used by the City of Memphis as a primary source of drinking water.
This proximity of contaminated ground water to drinking water wells was a major reason why the U.S. Environmental Protection Agency (EPA) placed DDMT on the National Priorities List (NPL) in 1992 (6). It was also placed on the NPL because of a surface water migration pathway. This pathway included a lake on the facility (Lake Danielson) which had fish and sediment contaminated with chlordane, DDT, and polychlorinated biphenyls (PCBs).
The process to clean up hazardous materials spilled, leaked, or disposed of at DDMT began in 1980 under the Department of Defense's Installation Restoration Program [IRP] (7). However, reports on the handling and impact of hazardous materials at DDMT go back to the 1960s (3).
These reports include industrial hygiene (workplace) and environmental investigations of chemical and radioactive substances. In addition to the IRP, environmental investigations address NPL-related issues, the closure of DDMT, and its restoration as a site for light industry, recreation, and other activities (8-10). These environmental investigations will be described in the next section of this PHA (Current Conditions of Site).
Recent remediation activities at the Depot include installation of a groundwater treatment on Dunn Field in 1998, removal of dieldrin-contaminated soil around the base housing units in 1998, removal of mustard agent and other chemical warfare-related materials from Dunn Field in 2000, and removal of lead-contaminated soil from the Old Paint Shop area in the Southwest corner of the Main Facility in 2000 (11-15). In addition, deed restrictions will be placed on several areas on the Main Facility to prevent their use for residences and day-care facilities (16).
The demographic characteristics of the population within a mile of DDMT are displayed on Figure 4. Nearly 97% of residents in this area are African-American.(1) About 12.5% of this population is 65 years or older which is the same percentage as for the United States, but is greater than the 8.1% for African-Americans in Shelby County. About 12% of the people living within a mile of DDMT are six years old or younger, while for African-Americans in Shelby County this age group is about 13.5% of the population. Women of child-bearing age (15-44 years old) make up 24% of both the population within a mile of DDMT and of African-Americans in Shelby County.
The demographics of area around DDMT has changed since DDMT opened in 1942. In 1950, the area west and south of DDMT had about equal numbers of African-Americans and Whites (17). By 1970, the racial distribution in the area had become similar to what was observed in the 1990 census.
The possible impact of DDMT on groundwater and the process to clean up the site became public information through a series of newspaper articles, public meetings, the Restoration Advisory Board (RAB), and regular mail-outs of information (18-41). Memphis residents were made aware, through a 1991 newspaper article, that one of the city well fields was contaminated and that DDMT was a possible source (18). Two articles in 1992 revealed that the shallow groundwater under Dunn Field was contaminated (19,20). The listing of DDMT on the National Priorities List (NPL) was also described in a 1992 article (21). Eight articles in 1993 - 1995 covered clean-up activities and public meetings (22-29). Extensive sampling of DDMT, concerns of the DDMT-Concerned Citizens Committee (CCC), a 1998 incident with some vials, the 1999 public comment release of this public health assessment, and the cleanup of the mustard agent were among the topics of the articles from 1996 to 2000 (30-14).
Since the site went on the NPL list in 1992, DDMT has made efforts to communicate with people around the facility through public meetings, establishment of a RAB, and informational mailings to the community (23,40). For example, health concerns were identified in May 1993 at a meeting with about 150 residents of the Orchid Homes community, and at an August 1993 meeting with about 60 area residents.
At Department of Defense sites, local citizens and elected officials; facility staff; and local, state and federal environmental agency staff participate in Restoration Advisory Boards (RAB). The DDMT RAB was formed in July 1994 and holds monthly meetings (41). The RAB receives briefings on and discusses activities related to site cleanup and restoration.
DDMT regularly distributes a newsletter, notices of meetings, and similar information to about 5,000 individuals.(2) They also announce activities through press releases.
Persons living around DDMT have high levels of concern about this site as indicated in a survey conducted recently by the Memphis-Shelby County Health Department (42). Results of this survey revealed that over 90% of survey respondents desired more information on the potential for exposure to and health effects from DDMT contaminants, the results of environmental sampling of DDMT, and how the Depot would be cleaned up and restored. A similar percentage of survey participants indicated that additional off-site environmental sampling should be done.
ATSDR's first major activity at DDMT was in 1992 when a preliminary evaluation was made to identify whether immediate action was needed at the site to protect public health (43). It was concluded that no immediate action was necessary.
In 1995, ATSDR evaluated the possible public health impact of the site in the DDMT Public Health Assessment (1). The soil, groundwater, surface water, air, and food chain exposure pathways were analyzed using information on site activities, the geology around DDMT, and limited environmental sampling. All these environmental pathways were classified as "no apparent public health hazard". In a 1996 letter to a concerned citizen, ATSDR indicated that this meant that, "Contamination at the depot does not pose a health concern to people living on or near the depot, and it did not pose a health hazard in the past." (44).
In 1996, ATSDR evaluated sediment sampling that was conducted after the release of the 1995 PHA (45). Of the 18 samples taken from the drainage ditches that emanate from the facility, nine were taken in or near the Rozelle area west of Dunn Field. They were analyzed for a wide variety of chemicals including volatile and semi-volatile chemicals, metals, pesticides, polychlorinated biphenyls (PCBs), and dioxins. Low levels of contaminants were found at most locations. The conclusion of the evaluation was that, "Although numerous contaminants were detected, they were not of the type and amounts that would pose a public health hazard..." (45). Results of this sediment sampling will be discussed in more detail on page 17.
In 1996, a group of area residents (DDMT-Concerned Citizens Committee [CCC]) contacted ATSDR with their concerns about the site and the 1995 DDMT PHA (46). This led to a commitment by ATSDR in 1997 to: 1) update the 1995 public health assessment, 2) review cancer incidence data gathered by the State of Tennessee in 1996, 3) review a plan for ongoing medical surveillance of residents, and 4) work with the DDMT-CCC, the Health and Human Services (HHS) Region IV Office, Memphis Health Center, the Congress of National Black Churches, local affiliates, and Shelby County/State of Tennessee to pursue the provision of primary care services with an environmental health focus(2).
Since these commitments were made, ATSDR personnel have made numerous trips to Memphis (47-59). During these trips, staff identified additional community health concerns; toured the site; represented ATSDR at the monthly RAB meeting; identified possible sampling locations; and met with DDMT-area residents and staff from DDMT, EPA, Tennessee Department of Environmental Conservation (TDEC), the Memphis-Shelby County Health Department (MSCHD), and Meharry Medical College.
ATSDR helped organize the Greater Memphis Environmental Justice Work Group. This group has met on February 27 and October 17, 1998. The working group is addressing environmental and health concerns of Memphis area residents with a focus on African-Americans and the DDMT area (52).
Objectives of the Greater Memphis Environmental Justice Work Group are being met through the activities of several sub-groups (52). Members of these subgroups include area residents and representatives of MSCHD, TDEC, ATSDR, EPA and DDMT. The health education and promotion sub-group is identifying the specific health messages that will be communicated to Memphis Depot area residents. The health concerns sub-group has reviewed and commented on the cancer incidence study being done by ATSDR and the Tennessee Department of Health. The health care sub-group is insuring that appropriate health care is provided to area residents possibly affected by environmental contaminants. In the October 1998 meeting of the Greater Memphis Environmental Justice Work Group, the site characterization sub-group described how contamination at the Memphis Depot has and is being identified. There were also subgroups for other environmental hazards and the public health assessment.
ATSDR has had considerable interaction with DDMT-area residents besides the Greater Memphis Environmental Justice Work Group, including 3 public availability sessions and 2 public meetings to identify community health concerns and solicit input from area residents on ATSDR activities (47,48,55,60,61). ATSDR staff have made 4 tours of the DDMT area with members of DDMT-CCC or other area residents to identify possible exposure pathways and gain general knowledge about DDMT and the surrounding community (47,50,51). All the activities described in this paragraph were done with the cooperation and foreknowledge of DDMT-CCC.
DDMT-area residents and staff from ATSDR, EPA, and MSCHD meet regularly as the health education and promotion sub-group of the Greater Memphis Environmental Justice Work Group to identify the specific health messages for DDMT-area residents (62-65). Members of this group receive detailed briefings of ATSDR activities and make comments and suggestions.
Available environmental data for the site are evaluated in this section of the PHA. Emphasis will be on what the results mean as far as the potential for exposure of area residents to site contaminants.
Environmental Data Evaluated
There are 4 major sources of environmental data on DDMT (3,8-10). The first was a 1990 remedial investigation done under the Installation Restoration Program (IRP) of the Department of Defense (3). Based on historical data, the investigation focused on possible sources of contamination. Samples of ground water were obtained from 9 monitoring wells on Dunn Field, 3 wells just west of Dunn Field, and 15 wells located on the DDMT Main Facility. Surface soil samples were taken from 45 locations on the Main Facility and 5 on Dunn Field. Samples of subsurface soil were taken at 3-4 different depths at 4 locations on the Main Facility and 4 on Dunn Field. Samples were taken of surface water from ditches draining the site at 13 locations on the Main Facility and 3 on Dunn Field. Sediment samples were taken at five locations on the DDMT Main Facility. No sampling of sediment was done on Dunn Field. About 130 chemicals were tested for in soil, groundwater, surface water, and sediment including volatile organic compounds (VOCs), semi-volatile organic compounds, pesticides and PCBs, and metals.
In 1995 - 1999, samples were taken from about 450 locations on the Main Facility, over 70 Dunn Field locations, and 22 locations in the area around DDMT during 4 related sampling programs (Screening Sites, Remedial Investigation, Base Realignment and Closure [BRAC], and DDMT area) (8-10,66).(3) The media tested were air from inside six of the warehouses, surface and subsurface soil, surface water, ground water, and sediment. About 200 parameters were analyzed in the Screening Sites program, 60 in the Remedial Investigation program, 120 in the BRAC program, and 170 in the background sampling. The specific parameters tested in these four sampling efforts are listed in Appendix A starting on page 61.
Results of these 4 sampling programs (except for the air, subsurface soil, and ground water data) were provided as electronic files to ATSDR by the U.S. Army Corps of Engineers' contractor, CH2MHILL, in September 1998, March 1999, and December1999. The Corps of Engineers is the agency responsible for conducting environmental sampling at federal facilities like DDMT. Data on the geographic locations where samples were taken were included in the information that ATSDR received.
Results from the sampling of the air inside six of the 28 warehouse or typical buildings, subsurface soil, or ground water is reported in the Final Memphis Depot Main Installation Remedial Investigation Report issued in January 2000 (11). No one is, was, or will be exposed to contaminants in subsurface soil and ground water so data from these media need not be evaluated in a public health assessment (67). ATSDR did not become aware of the sampling of the air inside the six warehouses until a copy of Main Installation RI was received in June 2000. These data are briefly mentioned in a discussion of worker issues on page 43.
How Data Were Evaluated
The process by which ATSDR evaluates the possible health impact of contaminants is summarized here and described in more detail in Appendix B starting on page 66. ATSDR uses comparison values to determine which chemicals to examine more closely (Appendix C). Comparison values are health-based thresholds below which no known or anticipated adverse human health effects occur. Exceeding a comparison value does not mean that health effects will occur, just that more evaluation is needed.
Further evaluation focuses on identifying which chemicals and exposure situations could be a health hazard. The first step is the calculation of child and adult exposure doses, as described in Appendix D. These are then compared to an appropriate health guideline for a chemical. The results of these calculations are presented in Tables D1 and D2 starting on page 71. Any exposure situation, in which the exposure dose is lower than a health guideline, is eliminated from further evaluation.
The next step is the revision of the exposure dose to better match probable rather than worst-case exposure scenarios. Lastly, these revised exposure doses are compared to known toxicologic values for the chemical of concern. This is mainly the no observed and lowest observed adverse health effects levels (NOAEL & LOAEL) identified in ATSDR Toxicological Profiles. If the chemical of concern is a carcinogen, the cancer risk is recalculated using the revised exposure dose. These comparisons are the basis for stating whether the exposure is a health hazard.
The comparison values and health guidelines that ATSDR uses in its evaluation are based on the lowest valid health-based thresholds available for a contaminant. This results in conclusions where there is much more certainty that health effects will not occur than that they will occur.
No contaminants were found in the extensive sampling of Dunn Field that represented a health hazard either because concentrations were too low or because opportunity was not sufficient for exposure to result in health effects.
Results of Environmental Sampling
There was limited sampling of Dunn Field surface soil in 1989 and extensive sampling in 1998 and 1999 (3)(4). The locations on Dunn Field where hazardous and other materials were probably buried has been determined and are displayed on Figure 3 (5).
ATSDR's review of the data for Dunn Field indicates that 85 of the approximately 240 chemicals tested for in surface soil were actually detected at least one sampling location. As displayed in Table 1, 11 chemicals had at least one concentration above its comparison value (CV). These 11 were alpha-chlordane, arsenic, benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, dibenz(a,h)anthracene, dieldrin, indeno(1,2,3-c,d)pyrene, iron, and lead.
|Contaminant||Range in Soil in mg/kg1||Samples > DL2||Samples > CV3||CV||CV Source4|
|Alpha-chlordane||ND - 1.5||18/72||1/05||0.5/36||CREG7/EMEG8|
|Arsenic||ND - 43.7||82/83||82/75||0.5/206||CREG7/EMEG8|
|Benzo(a)anthracene||ND - 81||24/66||8||0.9||EPA SSL9|
|Benzo(a)pyrene||ND - 68||24/66||20||0.1||CREG7|
|Benzo(b)fluoranthene||ND - 68||23/66||11||0.9||EPA SSL9|
|Benzo(k)fluoranthene||ND - 28||18/66||1||9||EPA SSL9|
|Dibenz(a,h)anthracene||ND - 26||16/66||8||0.09||EPA SSL9|
|Dieldrin||ND - 4.8||46/72||24/15||0.04/36||CREG7/EMEG8|
|Indeno(1,2,3-c,d)pyrene||ND - 44||24/66||7||0.9||EPA SSL9|
|Iron||6,360 - 36,400||27/27||12||23,000||RBC10|
|Lead||2 -2,100||83/83||4||400||EPA SSL9|
* The sources for these data are the 1990
Remedial Investigation and electronic files of the 1998-99 sampling program
provided to ATSDR by CH2MHILL in December 1999.
1 - mg/kg = milligrams of chemical per kilogram of soil. mg/kg = parts per million.
2 - DL = detection limit
3 - CV = comparison value
4 - These comparison values are described in Appendix C starting on page 68.
5 - The first number is the samples above the CREG and the second is samples above the EMEG or RMEG.
6 - The first number is the CREG and the second is the EMEG or RMEG.
7 - CREG = cancer risk evaluation guide
8 - EMEG = environmental media evaluation guide
9 - SSL = soil screening level
10 - RBC = EPA Region III's risk-based concentration. For iron, this is based on non-carcinogenic health effects for a 15 kilogram child ingesting 200 micrograms of soil a day.
In sediment, 81 chemicals were detected among the 16 locations sampled on or near Dunn Field (3,66).4 Among the chemicals detected were arsenic, dieldrin, lead, and several members of the dioxin and polycyclic aromatic hydrocarbon (PAH) groups. As displayed on Table E1 on page 74, only eight of the 81 had at least one concentration above a comparison value. These six were arsenic, beryllium, benzo(a)anthracene, benzo(b)fluoranthene, benzo(a)pyrene, dibenz(a,h)anthracene, dieldrin, and indeno(1,2,3-c,d)pyrene.
In surface water, 23 chemicals were detected in the seven Dunn Field surface water samples taken (3)4. As indicated in Table E2 on page 74, only one, arsenic, of the 23 substances detected exceeded a comparison value.
Possible Health Consequences of Chemicals found on Dunn Field
When a sample concentration exceeded a CV, the maximum level of that chemical was used to calculate an exposure dose, which is then compared to an appropriate health guideline. The results of these evaluations are summarized here and described in more detail in Appendix F on page 79.
As discussed starting on page 79, health effects due to exposure to any of the 11 contaminants found in Dunn Field surface soil above a comparison value are not likely to occur because the maximum concentrations are not high enough when compared to the known toxicity levels. More importantly, opportunities for exposure were limited for adults because no one regularly worked on Dunn Field, and nearly nonexistent for children because the facility has always been fenced (68).(5)
As discussed in more detail on page 81, health effects due to the contaminants in Dunn Field sediment are very unlikely, even with daily exposure. Daily exposure to contaminated sediment appears unlikely. As indicated on Table E2, the average levels of arsenic, beryllium, and PAHs from the 16 locations are similar to the means identified in the background sampling of the DDMT area. In addition, the PAH concentrations are within the levels of 0.2 - 61 ppm typically found in urban soil (69). While the mean concentration of dieldrin found in Dunn Field sediment samples is greater than mean in samples from the DDMT area, health effects are unlikely to occur because the concentrations found are not high enough when compared to the known toxicity levels.
Surface Water Contaminants
Health effects due to arsenic in Dunn Field surface water are unlikely. The maximum concentration of 0.01 milligrams of arsenic per liter of water is 30 times lower than the noncarcinogenic comparison value. The risk of cancer from daily exposure to the maximum level is not significant (5 in 1,000,000). Daily exposure is not plausible because no one regularly worked on Dunn Field, and nearly nonexistent for children because the facility has always been fenced (68).6
Very extensive sampling has been done of the soil, sediment, and surface water from the DDMT Main Facility. About 100 different chemicals were found among these three media. However, only polycyclic aromatic hydrocarbons (PAHs) in soil were found at concentrations that might have been harmful if an individual contacted PAH contaminated soil at a few specific locations on the Main Facility on a daily basis. However, it appears very unlikely that this occurred and thus this exposure situation is not a health risk.
Results of Environmental Sampling
The BRAC, Screening Sites, and 2000, 1997and 1990 Remedial Investigation data were evaluated together (3,8-10,11).
Thirty-one of the 114 chemicals identified in surface soil had at least one concentration above a comparison value (CV) as displayed in Table E3 on page 75. The 10 contaminants with the most concentrations above a CV are on Table 2 on page 21. Further evaluation will focus on those 10 chemicals. The locations where arsenic, benzo(a)pyrene, dieldrin, DDT, lead, and PAHs were sampled for are displayed on Figures G1 - G6 beginning on page 87.
Fifteen of the 95 chemicals identified in sediment had at least one concentration above a CV as displayed in Table E4 on page 76. Further evaluation will focus on those 15 chemicals. The locations where the contaminant levels for arsenic and benzo(a)pyrene exceeded their CVs are displayed on Figures G7 and G8 beginning on page 93.
Two of the 40 chemicals identified in surface water had at least one concentration above a CV as displayed in Table E5 on page 76. Further evaluation will be of these 2 chemicals. The locations where the contaminant levels for arsenic and dieldrin exceeded their CVs are displayed on Figures G9 and G10 beginning on page 95.
Possible Health Consequences of Chemicals found on DDMT Main Facility
When a sample concentration exceeded a CV, the maximum level of that chemical was used to calculate an exposure dose, which was then compared to an appropriate health guideline. Results of these evaluations are summarized here and described in more detail in Appendix F starting on page 82.
Of the 10 chemicals present on Table 2, it is unlikely that health effects could occur from exposure to any of them. These were arsenic, benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, dibenz(a,h)anthracene, dieldrin, DDT, indeno(1,2,3-c,d)pyrene, iron, and lead. For these chemicals, contaminant concentrations were too low to result in health effects given the amount of exposure that could have occurred or is occurring. There is a chemical-by-chemical evaluation of the possibility of health consequences from exposure to these 10 chemicals beginning on page 82.
In the public comment release of this public health assessment, it was concluded that there was a risk of cancer to workers with daily exposure to soil contaminated with benzo(a)pyrene, dibenz(a,h)anthracene, and other PAHs at certain locations. The rationale for changing this conclusion is described starting on page 84.
Chemicals in sediment with concentrations above a CV (Table E4), do not represent public health hazards. The 15 chemicals above their CVs are arsenic, antimony, benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, beryllium, cadmium, chromium, dibenz(a,h)anthracene, DDT, gamma-chlordane, iron, lead, and total polycyclic aromatic hydrocarbons (PAHs). Regular exposure to sediment from any of the sampling locations with concentrations above a CV does not appear to be plausible for anyone. This is because no facility operations appear to have been conducted at these locations so worker contact would have been minimal (50). More information on the possibility of health consequences from exposure to chemicals in on-site sediment is on page 85.
Chemicals in surface water with concentrations above CVs (Table E5), do not present public health hazards. Arsenic and dieldrin were the chemicals above CVs. The maximum levels of arsenic and dieldrin are well below the noncarcinogenic health effects comparison values. The additional lifetime cancer risk from exposure to them is not significant (2 in 1,000,000 to 4 in 100,000). This conclusion is based on the great difference between the average lifetime risk of cancer in the United States of 3 cancers per 10 individuals, and the 2 in 1,000,000 to 4 in 100,000 additional risk for exposure to these contaminants.
|Contaminant||Range in Soil in mg/kg1||Mean2 in mg/kg1||Samples > DL3||Samples > CV4||CV in mg/kg1||CV Source5|
|Arsenic||ND - 101||14.3||352/361||351/706||0.5/207||CREG8/EMEG9|
|Benzo(a)pyrene||ND - 450||5.5||164/349||121||0.1||CREG8|
|Dieldrin||ND - 10||0.4||180/324||125/96||0.04/37||CREG8/EMEG9|
|Benzo(b)fluoranthene||ND - 540||5.7||174/359||59||0.9||EPA SSL10|
|Lead||ND - 17,500||300.6||371/372||42||400||EPA SSL10|
|Benzo(a)anthracene||ND - 970||7.1||167/352||59||0.9||EPA SSL10|
|Indeno(1,2,3-c,d)pyrene||ND - 310||5||132/302||48||0.9||EPA SSL10|
|Iron||1,360 - 242,000||23,409||108/108||18||23,000||HEAST11|
|Dibenz(a,h)anthracene||ND - 160||0.7||21/334||15||0.09||EPA SSL10|
|DDT||ND - 59||0.6||205/334||15/16||2/307||CREG8/RMEG12|
|1 - mg/kg = milligrams of chemical per kilogram
of soil. mg/kg = parts per million (ppm)
2 - Non-detected chemicals were accounted for by calculating the mean using ½ of the detection limit as the value for the non-detected chemical.
3 - DL = detection limit
4 - CV = comparison value
5 - These comparison values are described in Appendix B starting on page 66.
6 - The samples above a CREG are the first number and those above a EMEG or RMEG is the second.
7 - The first number is a CREG and the second is an EMEG or RMEG.
8 - CREG = cancer risk evaluation guide
9 - EMEG = environmental media evaluation guide
10 - SSL = soil screening level
11 - HEAST = Health Effects Assessment Summary Table
* These data come from ATSDR's evaluations of files identifying sampling results and other pertinent information for each sampling location that were provided directly to ATSDR by DDMT.
With the possible exception of the Rozelle neighborhood west of Dunn Field, contaminants from DDMT do not currently represent public health hazards (i.e., either exposure is nonexistent or not enough to cause harm) and have not since at least 1989. This conclusion is based on an evaluation of the possible ways that residents in the area around DDMT might be exposed to site contaminants, and a review of available contaminant data. Included in these data are the results of sampling of surface soil, sediment, and surface water from locations around DDMT. Exposure pathways analyses indicate that limited exposure to site contaminants may have occurred through the water-borne transport to two areas other than the Rozelle neighborhood. These areas are 1) south of the southeast corner of the Main Facility, and 2) the yards on either side of Tarrent Branch which flows from the west edge of the Main Facility. The number of individuals in the residential areas around DDMT that could have been exposed is between 500 and 3,000.
Determining whether site-related health effects could have occurred from exposures since the opening of DDMT in 1942 until 1989 is not possible.
The basis for these two conclusions will be described in the following paragraphs.
Analysis of Environmental Exposure Pathways
Surface water and sediment, and ground water are the principal ways DDMT contaminants can move, are moving, or have moved off the site. Short-term exposure to airborne contaminants from DDMT has occurred. Long-term air exposures may have occurred but appear to have been limited to the area near the southwest corner of the Main Facility. Food chain and soil do not appear to be viable pathways for long-term exposure.
For surface water and sediment, current human contact with contaminants in water from DDMT is almost entirely restricted to 3 surface water drainages. An estimated 500 - 3,000 persons could potentially have regular contact with water in these drainages. This contact would be limited to chemicals in surface water or sediment, or soil contaminated by surface water. Contact with contaminants that become airborne from the surface water probably does not occur because the contaminant levels are too low for this to happen.
The contaminant levels in those drainages since at least 1989 were not and are not a public health hazard to individuals living around DDMT. Sampling data are insufficient before 1989 to estimate what the contaminant levels in those drainages might have been.
For ground water, movement of site contaminants off-site is primarily restricted to the northwest corner of Dunn Field. No one drinks this contaminated groundwater.
Surface Water and Sediment
Movement of surface water and sediment off DDMT is focused at specific locations around the Main Facility and Dunn Field as seen on Figure 5 (page 25) and discussed in Appendix H (page 97) (3). Contact would have been to contaminants in surface water or sediment, or soil contaminated by site surface water, but would not have included chemicals that become airborne after leaving the site in water. Contaminant concentrations are too low to move into the air (70-72).
Where Exposure to DDMT Contaminants in Surface Water could be occurring
Current and past exposure to site contaminants carried off DDMT in water and sediment could occur and could have occurred in the following areas.
(1) In or near the un- and concrete-lined ditches that pass through or by the Rozelle neighborhood just west of Dunn Field. This exposure is ongoing and could have occurred in the past. Little or no opportunity for exposure exists once the water has passed through the Rozelle neighborhood because the ditches join, then this ditch flows into a pipe at the Illinois Central Railroad tracks (Figure 5). In the Rozelle neighborhood, exposure to site contaminants would be daily for individuals contacting soil contaminated by surface water or sediment from Dunn Field. The areas where soil contamination appears possible are yards at the southern end of Rozelle Street, and to either side of the shallow ditch that runs through the middle of the neighborhood.
However, although daily contact with site surface water or sediments may occur, health effects from that contact are unlikely. The concentrations of chemicals in sediment and surface water on Dunn Field and in sediment from the ditches in the Rozelle neighborhood are too low. As discussed on pages 16 - 18, these levels do not present health risks. In addition, sediment levels from western Dunn Field and the Rozelle neighborhood are similar to the levels for 22 samples taken off-site in the DDMT area.
Soil, now present in the Rozelle area, may have been contaminated in the past through the overflowing of ditches in this neighborhood. No sampling has been done of the soil around these ditches.
(2) In or near Tarrent Branch. As indicated on Figure 5, Tarrent Branch drains the western third of the DDMT Main Facility, which is the area where most of the hazardous materials storage took place (3,5,7). This intermittent stream runs through the neighborhood west of DDMT and eventually flows into Nonconnah Creek. Tarrent Branch was a natural stream but is now a concrete-lined and fenced ditch. Therefore, exposure is currently unlikely because regularly contacting water and sediment from this ditch would be difficult.
Even if contact with surface water and sediment from DDMT were ongoing, it would not result in health effects. As indicated on pages 19 - 20, the contaminants identified in sediment and surface water on the Main Facility do not represent health risks. This includes the sampling points on the western edge of DDMT.
Regular exposure to the water and sediment could have occurred before the ditch (Tarrent Branch) was fenced. A long-time resident indicates that she and others used to play in Tarrent Branch as children.(6) Another resident related in a recent meeting that her yard flooded on a regular basis before Tarrent Branch was lined.(7)
It is not possible to determine whether exposures prior to the fencing and lining of Tarrent Branch could have resulted in health effects. There are insufficient environmental data prior to 1989 to estimate contaminant levels which are needed to evaluate the possibility of health effects.
(3) In or near the 4 ditches that flow south from the southeast corner of the DDMT Main Facility (Figure 5). These 4 ditches drain the southeast corner of the Main Facility where a golf course, clubhouse, swimming pool, Lake Danielson, a pond, and the base housing units are located (3,5,7). These ditches join south of the DDMT boundary and then flow into Nonconnah Creek. At least some portions of these ditches are shallow and unlined which means that more opportunity exists for contamination of the soil around the ditch with site contaminants. Thus, exposure to site contaminants could occur to individuals who had daily or nearly daily contact with sediment or surface water from the ditches or the soil immediately around the ditches. These exposures could occur now and in the past. One of the 4 ditches passes along Mullen Street between Ball and Ketchum Roads. ATSDR staff recently observed children playing in this ditch (57).
Health effects due to regular current contact with surface water and sediment from these 4 ditches in the southeast corner of DDMT are unlikely. As described on pages 19 - 20, the contaminant levels in sediment and surface water identified on the Main Facility, including sampling points on the southern side of DDMT, do not represent a health risk.
It is not possible to determine whether site contaminants levels in this drainage were great enough prior to 1989 to result in health effects. There are insufficient environmental data prior to 1989 to estimate contaminant levels which are needed to evaluate the possibility of health effects.
Where Exposure to DDMT Contaminants in Surface Water is not occurring
Regular exposure to site contaminants carried off DDMT in water and sediment does not occur in the following areas. As will be described, exposure to site contaminants may have occurred in some of these drainages in the past. (For additional explanation of the rationale for these conclusions see Appendix H on page 97.)
(1) The area north of the DDMT Main Facility and east of Dunn Field. This area is bordered by Hayes Road on the west, Airways Boulevard on the east, Person Avenue on the north, and Dunn Road on the south. As indicated on Figure 5, water from the site flows north and northwest through an industrial park in pipes or lined ditches and eventually discharges into Cane Creek. The ditches or pipes carrying water away from the northeast side of the DDMT Main Facility do not run through the residential portion of this area (56). Thus, individuals in this area would not have opportunity to contact surface water and sediment from DDMT either currently or in the past.
Please note that there are two drainage ditches that carry water from the residential area just east of Hayes Road into the northeast corner of Dunn Field near the corner of Hayes and Boyle. These two ditches join on Dunn Field and this ditch is the northeast most discharge point indicated on Figure 5.
(2) The area east of the DDMT Main Facility. This area is bordered by Airways Boulevard on the west, the St. Louis-San Francisco Railroad tracks on the east and north, and Nonconnah Creek on the south. The only flow of surface water from DDMT through this area occurs presently in Memphis storm sewer pipes. The opportunity for exposure does not currently exist and likely has not existed since at least 1953 (56,73). This conclusion is based on a 1953 Drainage Plan for DDMT that identified the storm sewer drainage points as existing then (73).
(3) Most of the area on the south side of the Main Facility. This area is bordered by Orchard Street on the east, Ball Street on the north, Perry Street on the West, and Nonconnah Creek on the south. This area is identified as the Alcy neighborhood by many area residents after Alcy Boulevard which runs east to west through the area. The drainage at the southeast corner of the Main Facility is not included in this area. The opportunity for contact with site surface water is currently non-existent because no open drainage ditches exist (3). In the past, 2 discharge points existed midway between the east and west ends of the Main Facility (3,5). Ditches from these 2 points joined shortly after crossing Ball Road, and this single ditch then flowed south into Nonconnah Creek. It is assumed that this ditch was unlined and therefore it was likely that water from the DDMT could have overflowed into the area around this ditch.
(4) The area west of the DDMT Main Facility with the exception of homes near Tarrent Branch. This is the area bordered by Perry Road on the east, Elvis Presley Boulevard on the west, Dunn Road on the north, and Alcy Road on the south. The only current opportunity for contact with site surface water is restricted to the area around Tarrent Branch (56). In the past, a second open ditch existed west of DDMT and between Dunn Road and Tarrent Branch as shown on maps of the DDMT area from 1982, 1960, and 1953 (7,73,74). The maps we examined did not identify the course of this ditch.
(5) The area northwest of the Main Facility and Dunn Field. The Illinois Central Railroad tracks on the east, Person Avenue on the north, and Elvis Presley Boulevard on the west are the borders of this area. This includes the area around and south of Hamilton High. The only drainage in this area where water from DDMT might flow is Cane Creek (56). However, DDMT is only one of many areas providing water to Cane Creek (75). The opportunity for contact with water in Cane Creek is limited because the creek is concrete-lined and fenced from the Ragan Street Bridge to the Elvis Presley Boulevard Bridge.
As indicated in Appendix H, sources for water from DDMT in Cane Creek upstream of Hamilton High are the northeast corner of the DDMT Main Facility and a small portion of Dunn Field. The contribution of water from DDMT to the overall flow of Cane Creek appears to be small. This would further dilute the already low levels of contaminants coming from DDMT.
However, the opportunity for exposure probably was greater in the past because water from the Dunn Field area used to flow through the area between the western side of Dunn Field and Hamilton High School in an open ditch rather than in the pipe in which it currently flows.(8)
Estimate of Number of Persons in Surface Water Exposure Pathways
ATSDR estimates that about 500 - 3,000 persons could have had at least occasional contact with surface water from DDMT. This represents about 2 -10 % of the 30,720 persons living within a mile of DDMT. This estimate was made by determining the number of people living within 100 feet and within 500 feet of the five drainage areas identified on Figure 5. One hundred feet from a ditch is a health protective estimate (i.e., trending towards an overestimate to be protective of health) of the extent of contamination that might occur during flooding. Five hundred feet from a ditch is an estimate of the maximum distance that a small child might reasonably be able to travel to have regular contact with contaminated sediment, surface water, or soil.(9)
Contaminants from DDMT have moved off site in ground water at the northeast corner of Dunn Field, the southwest corner of the DDMT Main Facility, and a small area near the corner of Ball and Ketchum Road which is in the southeast part of the DDMT Main Facility (3,56,11). In the Dunn Field area about 8-10 contaminants were found in offsite groundwater above an EPA maximum contaminant level (MCL) or risk-based concentration (RBC) in sampling conducted in October of 1998 (56). About half of these chemicals (all volatile organic compounds [VOCs]) were clearly site-related. The rest were considered to be background or natural levels. The principal contaminant found in the groundwater in the two areas off the Main Facility is tetrachloroethylene (PCE) (11). A detailed discussion of the groundwater pathway including an evaluation of groundwater flow patterns can be found in sections 32 - 35 of Volume II of the Final Memphis Depot Main Installation Remedial Investigation Report (11).
Available data indicate that contaminants from DDMT have not moved into the Allen Well Field which lies 1.5 to 2 miles west of Dunn Field and the Main Facility (3,56,11). This well field is one of several used to supply drinking water to Memphis area residents. Concern exists that site contaminants may eventually pollute this well field, so a system of wells was recently installed at the edge of Dunn Field to stop or reduce flow of groundwater contaminants off Dunn Field. It appears very unlikely that the groundwater contamination in the Main Facility area could reach the Allen Well Field because contaminants do not appear to be able to move down into the Memphis Sand Aquifer from which this well field draws water (11).
Exposure to site contaminants in drinking water does not appear to have been possible. This is because the likely sources of contaminants in groundwater were not buried in Dunn Field until 1955 (50). All residences around the site were connected to the Memphis public water supply by 1953 (6).
Short-term exposure to airborne contaminants from DDMT probably has occurred at least once (76). In 1988, the cover of a hazardous materials storage building called a Span Dome collapsed during a severe thunderstorm (76). This collapse resulted in release to the air of 327 - 2,000 gallons of the 250,000 gallons of the hazardous materials stored in this building (76,77).(10) The chemicals stored were acetone, isopropyl alcohol, methyl ethyl ketone, methyl isobutyl ketone, toluene, and xylene, which are all commonly-used solvents (78).
The Memphis Fire Department's (MFD) report indicates that, during the first hours of this incident, the leaking materials were detected at high levels at the northern perimeter of the DDMT Main Facility (76). This location is about 1,300 feet north of the collapsed Span Dome (79). The Span Dome was located near the western boundary of the Main Facility and north of the corner of Perry and Elliston Roads. Thus, some exposure could have occurred in the area west and northwest of the Span Dome. A more detailed description of this incident starts on page 40.
Long-term residents have indicated that several other air releases from DDMT have occurred (49,52). DDMT operated for 55 years and stored large amounts of hazardous substances, so some likelihood exists that accidental releases could have taken place (7). However, ATSDR could not evaluate these reports further because there were no data on what and how much was released.
Although short-term exposures to airborne DDMT chemicals may have occurred occasionally, there is little in the data available that indicates to ATSDR that long-term exposure to site contaminants of all or most residents around DDMT occurred via the air (3,5,7). Only one operation, spray painting of vehicles and equipment, appears to have existed on DDMT that could have resulted in regular release of contaminants to the air. As indicated on Figure 2, three or four paint spray booths existed at various times on the Main Facility. The stacks from these booths appear to have been relatively short which would result in contaminants being carried only short distances.
This is confirmed by soil sampling data for the areas around the booths. The soil near these paint booths does have elevated levels of lead, PAHs, and other chemicals. However, levels of these chemicals are not elevated in samples taken at the DDMT perimeter. This indicates that very little of the chemicals, emitted from the paint booths, actually moved off-site.
Exposure to site contaminants through food is unlikely. The known contaminant concentrations in surface water appear to be too low to result in significant contamination of crops, fish, or wild or domestic animals from the DDMT area.
The nearest location available for DDMT area residents to catch and eat fish is and was Nonconnah Creek. The ditches draining DDMT are often dry and thus could not sustain a fish population. Nonconnah Creek, which eventually receives all the water draining from DDMT, has been posted as a no fish consumption area since 1982 This is primarily because of chlordane contamination from a nearby pesticide production facility and chlordane's use around homes (80).
Individuals catching and eating fish from the bodies of water on DDMT, Lake Danielson and the golf course pond, may have had some exposure to chlordane, DDT, and PCBs because these chemicals were found in fish, sediment, and water from this lake and pond (3,6,8-10). There are no longer any fish in these bodies of water. Former workers indicated to John Crellin that people did catch fish from the lake and pond.
No systematic evaluation has been done of surface soil from any specific off-site area. Indirect evidence suggests that any contamination of soil off-site with DDMT materials would be limited. Off-site soil could have been contaminated through the overflow of ditches that drain DDMT and the deposition of chemicals carried in this surface water and sediment. However, as discussed earlier, only a limited number of places exist where this could occur. ATSDR is recommending that at least some of these areas be sampled.
Soil could also have been contaminated by the deposition of airborne materials from the site. As discussed earlier, only the paint spray booths could have been such a source, and soil sampling data do not indicate that a significant amount of the materials moved off site.
Evaluation of Sampling Data from the Area around DDMT
Low concentrations of chemicals are in soil, sediment, and surface water from the area around DDMT. Available data indicate that DDMT is not a major source for these chemicals.
Surface soil, surface water, and sediment samples from the area around DDMT were analyzed for about 170 parameters.(11) Soil samples were taken from 11 locations just off DDMT and 11 locations away from DDMT including four schools (Alcy, Charjean, and Dunn Elementary Schools; and Airways Middle School), Alcy West Park, and Pine Hills Golf Course. Surface water and sediment were sampled at 22 locations including Nonconnah and Cane Creeks; and lakes in Medal of Honor and Audubon Parks, and Botanical and Chickasaw Gardens.
The best indication that no widespread contamination of the area occurred around DDMT by chemicals from the site can be found in Table 3. In this table, the average concentrations of the most common contaminants found in DDMT soil are compared with averages for the same chemicals from soil sampling locations around DDMT. With the exception of arsenic and iron, on-site levels are considerably higher than those off-site. In addition, little difference was found in concentration between the soil samples taken at the perimeter of DDMT and those taken further away (Table 4).
Most surface water and sediment sampling locations from the area around DDMT receive little or no water from DDMT. Thus, chemicals found in this sampling program come from sources other than DDMT. Recent sampling indicates that polluted surface water is found throughout Memphis (81).
|Contaminant||BRAC/RI Mean in mg/kg**||SS Mean in mg/kg**||DDMT Area Mean in mg/kg**|
|* Non-detected chemicals
were accounted for by calculating the mean using ½ of the detection limit
as the value for the non-detected chemical.
** mg/kg = milligrams of chemical per kilogram of soil
1 - BRAC = base realignment and closure
2 - RI = remedial investigation
3 - SS = screening sites
|Contaminant||Perimeter Mean in Mg/kg**||Off Site Mean in Mg/kg**|
|* Non-detected chemicals were accounted for
by calculating the mean using ½ of the detection limit as the value for
the non-detected chemical.
** mg/kg = milligrams of chemical per kilogram of soil
Tables E6 and E7 on page 77 identify the 13 chemicals found in sediment and one in surface water with at least one concentration above a comparison value. Although comparison values were exceeded, further analysis identified no significant health risk. Even daily exposure to the highest concentrations represents insignificant cancer risk (maximum risk of 1 in 100,000).
The Superfund law requires that health outcome (i.e., mortality and morbidity) data (HOD) be considered in a public health assessment (82). This consideration is done using specific guidance in ATSDR's Public Health Assessment Guidance Manual and a 1996 revision to that guidance (67,83). The main requirements for evaluating HOD are presence of a completed human exposure pathway, great enough contaminant levels to result in measurable health effects, sufficient persons in the completed pathway for health effects to be measured, and a health outcome database in which disease rates for population of concern can be identified (83).
This site does not meet the requirements for including an evaluation of HOD in this public health assessment. Although completed human exposure pathways exist at this site, neither the contaminant levels nor the exposed population are great enough to permit meaningful measurements of possible site-related health effects as identified in existing HOD.
However, although using HOD to identify health effects possibly related to DDMT is not possible, evaluating HOD to determine whether the community's assertions of excess disease can be confirmed is good public health practice. Two preliminary evaluations of cancer mortality have already been done by the Tennessee Department of Health (TDH) and ATSDR to evaluate these assertions (84,85).
In the most recent report, TDH and ATSDR investigated the age- and race-adjusted cancer rates within 1-1½ miles of DDMT for 1990 - 1996 by evaluating 23 types of cancer for men and women.(85). Overall, the cancer rates for the area around DDMT were near or below the rates expected from Shelby County and the State of Tennessee.
Although this investigation did not identify overall excesses of cancer, the rates for other diseases or health conditions might be excessive. In addition, the results of this investigation only reflect cancer incidence for a relatively short period and do not mean that cancer rates could not have been excessive in the past. ATSDR is recommending that these other diseases be investigated, if possible, and is working with DDMT area residents and the Tennessee Department of Health to identify data on the past occurrence of cancer (85).
The following issues were identified in conversations and meetings with DDMT area residents and former workers, and in ATSDR's review of the data for the site.
- Were people exposed to ANY depot chemicals and radiation (49)? -- please give a direct answer, not an indirect one as in 1995 public health assessment.
- Depot had uncontrolled access until the 1960s or 70s and children played on-site (49).
- Residents around DDMT were exposed to contaminants through surface water flowing off-site in 21 open drainage ditches (49). Exposure was not only to contaminants in surface water, but also to site contaminants in the air and in the food chain (e.g., fish, rabbits, plants) (52).
- Individuals living in the Bunker Hill area and students at Hamilton High School were exposed to contaminants through surface water run-off in drainage ditches (49).
- One resident was concerned about possible health effects from playing in the drainage ditches in the Rozelle area in 1945 (53). This same individual indicated that he and his family drank water from a private well at that time. His father's fruit trees either didn't grow or didn't produce fruit. Another individual asserted that children played in drainage ditches, immediately off-site, and found many items including gas mask canisters (49). When this occurred was not indicated.
- Exposure took place to liquid toxic substances from the Depot that drained near Perry Avenue (49). Drainage of these toxic substances occurred on a regular basis because DDMT workers disposed of large quantities of toxic substances such as DDT and expired medicines in the facility drains as instructed by their bosses (60).(13)
- Outbreaks of rashes occurred because of contact with soil in the Freemont and Cascade areas (49).
- Did exposure to site contaminants in drinking water occur from private wells used before 1950 (49)?
- Have contaminants from the Depot affected the aquifer near site (52)?
- Fumes released from the Depot in the evenings and nights of 1968 caused people to have reoccurring skin rashes and burning eyes, and caused animals to die (49).
- People were exposed in the evenings of 1978 to air releases from Dunn Field near the corner of Person and Hayes (49). These releases had a foul odor, and those who inhaled it experienced nausea and sleepless nights.
- Persons across the street from the mounds on Dunn Field were exposed to dust blowing off them (49).
- The mustard bomb casings are in publicly accessible areas near Dunn and Perry Roads (49).
- Depot-related exposures caused various illnesses such as cancer, breast cancer, prostate cancer, strokes, heart attacks, hypertension, thyroid diseases, miscarriages, birth defects, liver disease, numbness (hands, feet, or face), ear-nose-throat problems (49,52,55).This was asserted to have been confirmed in state reports (52).
- Toxicity data for a chemical come from studies of Caucasian males and the results might not apply to African-American communities (49).
- In 1970s or 1980s, people wearing protective clothing and masks tested the west side of Depot, removed contaminated soil, and replaced it with new soil and gravel (49).
- German prisoners of war, who were housed in a camp on the southwest portion of the Main Facility, may have contaminated the environment during World War II (49).
- The Depot is similar to Love Canal where chemicals were buried in a dump, and health effects appeared 27 years later (49).
- Fallen and damaged trees were observed on Dunn Field in 1997 (49). Were any tests performed to determine why this occurred, and if they were, what were the results?
- In March 1998, two residents found two dead birds just off-site of the west boundary of Dunn Field.(16) They were concerned that the birds' deaths were due to site contaminants possibly released from nearby location on Dunn Field. A few days before, small vials had been uncovered at that location during the installation of a utility line.
- A resident wondered whether students at Dunn School had been medically evaluated after the chemical warfare building blew up in 1988. Another resident asked why Norris Elementary School wasn't closed during this incident, if Dunn School, which is about the same distance from DDMT, was closed.(18)
- Could the cleanup of the dieldrin-contaminated soil near the base housing units on the Airways Boulevard side of DDMT have polluted the soil in the apartment complex just across the fence from where the cleanup was done?
- Could the combined effect of the mixture of chemicals found at DDMT have caused cancer or other health effects, even though the concentration of each chemical may not be harmful by itself?(19) (20)
- Do any data exist that indicate that DDMT workers were exposed to site contaminants at concentrations great enough to cause health effects?(22)
- The following is a summary of concerns expressed by former DDMT workers at a meeting conducted by ATSDR on July 27, 1998 in Memphis (60).
Response: The answer is yes for depot chemicals based on the discussion in the previous section. Some residents may have had infrequent, short-term exposure to depot chemicals in air due to accidental releases, or in surface water or sediment due to accidental leaks or spills or intentional discharges. However, daily or nearly daily long-term exposure of area residents to depot chemicals is not very likely. If it did occur, it could have taken place in 3 surface water drainages and to an estimated 500 - 3,000 people. In the past, two additional surface water drainages appear to have existed.
The answer is no for radiation. No DDMT area resident was likely to have been exposed to site-related radiation (radioactive materials) because only small amounts were stored on-site. This storage appears to have been properly done so very little chance of releases to the environment existed.(12)
Response: The DDMT Main Facility and Dunn Field have been fenced and guarded since the facility opened in 1942 according to DDMT staff and the literature available to ATSDR (68).
Response: Transportation of contaminants off-site could have occurred whenever sufficient rain created water flow in the ditches draining the site. Exposure to site contaminants could have been through ingestion or having skin contact with surface water, or soil or sediments contaminated by chemicals in the surface water. These ditches could have been polluted by leaks, spills, or intentional discharges of DDMT chemicals.
ATSDR confirmed that 14 points do or did exist where water discharges from DDMT into open ditches (Figure 5). Eleven of these currently exist and 3 existed in the past. One of these 3 ditches was located between Tarrent Branch and Dunn Road on the westside of the Main Facility and the other 2 on the southside of the Main Facility about midway between the east and west ends.
ATSDR identified seven other points where water is and was discharged off site through storm sewers. These discharges into storm sewers appear to have been occurring since 1953 (73). Before 1953, we were unable to determine whether water flowed off-site at these 7 locations in storm sewers or in open ditches. Therefore, there may have been 21 open drainage ditches coming off DDMT before 1953.
As indicated earlier (page 22), about 500 - 3,000 residents may be at risk of exposure to small amounts of site contaminants transported off-site in surface water. The chance of exposure appears to have been the greatest in the Rozelle neighborhood just west of Dunn Field. The current chance of exposure in that neighborhood could be more accurately evaluated by determining levels of site contaminants in residential soil. ATSDR is planning to conduct sampling to do this.
However, any exposure to site contaminants through air or food is and was very unlikely. The known contaminant concentrations in surface water appear to be too low to result in releases of site contaminants to the air. Levels also appear to be too low to result in substantial contamination of crops grown in the area, or in fish, or wild or domestic animals.
Exposure of individuals off-site through ingestion of contaminated fish from the ditches draining DDMT does not appear to be possible because the ditches draining the site are often dry. Thus these ditches would not sustain a fish population. The nearest location from which DDMT area residents could have eaten fish is Nonconnah Creek which does have a viable fish population and which eventually receives all the water draining from DDMT. This creek has been posted as a no fish consumption area since 1982 largely because of chlordane from a nearby pesticide production facility and its use around homes (80).
Response: As described starting on page 27, residents of the Bunker Hill area or students at Hamilton High School are very unlikely to currently be exposed to site contaminants transported off-site by surface water. Water from the western side of Dunn Field does go through the residential areas between Dunn Field and Hamilton High, but, except for the Rozelle area, currently does so entirely in pipes.
Currently, direct contact with water-borne site contaminants is very unlikely in the area around Hamilton High. Cane Creek, which runs under Hamilton High, has been fenced and concrete-lined between the Ragan Street and Elvis Presley Boulevard bridges since the early 1970s. In addition, the concentration of site contaminants in the water going under Hamilton High would be much lower than levels at the site boundaries because DDMT contributes only a small portion of the water that flows under the school. See section (5) on page 27 and Appendix H on page 97 for more details.
However, direct contact with contaminants could have occurred before Cane Creek was fenced and lined in the 1970s, and when water from Dunn Field flowed through the Bunker Hill area in an open ditch.
Indirect contact of Hamilton High students and staff with DDMT contaminants moving from water in Cane Creek into the air appears extremely unlikely. The known surface water concentrations at the DDMT boundary are too low to result in release of contaminants to the air (70-72).
Response: Very little information exists about the operation of the Depot for 1942 - 1945 so we are unable to provide a specific response to the concerns about playing in the ditches and about the fruit trees (5). Exposure to site contaminants in drinking water from private wells before 1950 does not appear possible. This is because the likely sources of contaminants in groundwater were not buried in Dunn Field until 1955 (6,50).
Response: Contaminants from DDMT could have gotten into on-site drains and ditches from intentional disposal, leaks or accidental spills. This is indicated by the marginal management of toxic substances and contamination identified in a 1982 report (7). However, this apparently did not result in substantial exposure off-site, at least in the recent past. This conclusion is based on the fact that known contaminant levels in soil, surface water and sediment on DDMT are low. An example of this is DDT whose on-site levels are depicted on Figure G3 on page 89. Known contaminant levels in surface water and sediment are also low as described starting on page 22.
The disposal of toxic substances down facility drains could not have led to contamination of the drainage ditches and surrounding areas on- and off-site if most, if not all, of this disposal was in the drains inside DDMT buildings. This is because drains inside DDMT buildings were and are connected to the sanitary sewer system (3,7). Thus, no opportunity would exist for off-site exposure because the sanitary sewer system is entirely closed with no open drainage.
In addition, disposal of substantial amounts of substances such as DDT and related compounds would have been difficult because they are insoluble in water (59). It would have taken large amounts of water to wash them down the drains.
Response: Although people may have experienced these rashes, DDMT contaminants are not likely to have been the cause. ATSDR did not identify a mechanism by which DDMT contaminants could have been transported to the surface soil in the Freemont/Cascade area. A ditch from DDMT exists to the east of Freemont (Figure 5). However, materials from this ditch are unlikely to have contaminated Freemont area surface soil because the ditch appears to be at an elevation lower than Freemont.(14) See page 26 and Appendix H (page 97) for more discussion of drainage in this area.
Response: Exposure to site contaminants in drinking water from private wells before 1950 does not appear possible. This is because the likely sources of contaminants in groundwater were not buried in Dunn Field until 1955 (6,50). All residences around the site were connected to the Memphis public water supply by 1953.
Response: Contaminants buried on Dunn Field have polluted the Fluvial (shallow) aquifer under and to the west of the northern tip of Dunn Field. Contamination also occurred to a small portion of the shallow aquifer under the Main Facility (3). Three aquifers are under DDMT: the Fluvial, Memphis Sand, and Fort Pillow Sand with the Fluvial the shallowest and Fort Pillow the deepest. Contaminants from Dunn Field or the Main Facility have not moved down to the Memphis Sand Aquifer. This aquifer provides 95% of the drinking water in Memphis. However, a clear potential exists for the contaminants to move down to the Memphis Sand some time in the future. Currently, there is an extensive program underway at Dunn Field to prevent further migration of the contaminants (11).
Response: We were unable to identify any information about this issue.
Response: We are unable to provide a definitive answer to this concern. ATSDR did not identify any information about air releases from DDMT in 1978. This location is the northeast corner of Dunn Field. Available data do indicate that this area of Dunn Field appears to have been used as a burial area for impregnite in the 1940s (50). This substance was used to make clothes and shoes resistant to chemical agents. This material is unlikely to have produced the reported air releases in 1978 because it is solid. ATSDR did not find any other indication in the documents reviewed that other materials were buried in this area.
Response: Exposure to dust from these mounds probably has not resulted in any health effects. The mounds are national stockpiles of bauxite and fluorspar. These substances are not very toxic (i.e., it takes a lot to cause harm). In recent times, these mounds were covered most of the time thus eliminating or greatly reducing the amount of dust blowing into the neighborhood east of the mounds (Figure 3). However, several citizens have reported that considerable amounts did blow off these mounds before they were covered.(15)
Response: As displayed on Figure 3, the information available to ATSDR indicates that the mustard bomb casings were buried on Dunn Field (3,5). Public access is unlikely because Dunn Field reportedly has always been fenced.
Response: ATSDR found 3 reports that focus on or mention disease or death in the DDMT area (84-86). None of them identify any diseases that are attributed to exposure to DDMT contaminants.
Reviews of cancer data have taken place, one by the Tennessee Department of Health (TDH), and the other by TDH and ATSDR (84,85). In the most recent report, TDH and ATSDR investigated the age- and race-adjusted cancer incidence rates within 1-1½ miles of DDMT for 1990 - 1996 (85). Twenty-three types of cancer were evaluated for men and women. Overall, the cancer rates for the area around DDMT were near or below the rates expected from Shelby County and Tennessee. The only cancer with an elevated rate was Endometrial (corpus uteri) cancer in women. Six cancers had rates lower than expected - esophageal and lung cancer in men; and lung, breast, pancreatic, and bladder cancer in women. As described starting on page 22, off site exposures were probably too infrequent and at concentrations too low to cause any health effects from long-term exposures. The one cancer that was elevated, Endometrial, is not known to be caused by any of chemicals found on DDMT (87).
The third report was a 1998 article in the Memphis Commercial Appeal in which the Memphis-Shelby County Health Department (MSCHD) reported the number of deaths in Shelby County for 1993 - 1997 (86). The deaths were broken down by census tracts. The census tracts with the highest numbers of deaths were in the South Memphis area including a tract close to DDMT. This higher number of deaths was attributed to there being proportionally greater number of elderly people in these census tracts compared with the other census tracts. As described in the Demographics section on page 11, a larger portion of the population within a mile of DDMT is 65 or older compared to the rest of Shelby County. This report had no information on the causes of death.
Response: The toxicity data used in this public health assessment come from animal studies and epidemiologic investigations of actual human exposures. They did not come from studies of Caucasian males. The toxicity data used in this document are applicable for African-Americans and all other racial groups.
ATSDR prefers to use data from investigations of human exposures to a chemical. However, most of the data used come from studies of laboratory mice and rats, or other animals such as dogs and monkeys because valid human data are lacking for many chemicals (67).
In this document, human toxicity data were used for arsenic, cadmium, and lead (88-90). For arsenic, the main study used to identify toxicity was of non-Caucasians (residents of Tawain) who had drunk arsenic-contaminated water for years (88). For cadmium, the main study is of Japanese (89). For lead, toxicity data come mostly from studies of children exposed to lead in urban areas (90). The children evaluated included African-Americans, Caucasians, and other racial or ethnic groups.
Response: This was probably the removal of the pentachlorophenol (PCP) dipping vat and contaminated soil in 1985 (91). The location of this vat is identified on Figure 2. The vat was used regularly to treat wood with the preservative PCP from about 1952 to 1971 and infrequently after that until it was removed in 1985. The emptying and repacking of PCP in the vat would require workers to wear protective clothing and masks.
Response: ATSDR was unable to identify any information on this issue. However, even if these prisoners of war contaminated the environment, the environmental data reviewed in this document indicate that the current amount of contamination on-site is relatively low.
Response: At Love Canal, many homes were built on top of areas where hazardous waste was dumped (92). At DDMT, all available data indicate that homes were not built on top of hazardous waste disposal sites.
Response: The two arborists (tree doctors) who evaluated the dead or damaged trees for DDMT, indicated that this problem was due to natural causes such as wind damage and the trees reaching the end of their lifespan (93).
Response: It appears unlikely that these birds died because of this incident because the descriptions of what happened do not indicate that anything was released. The materials uncovered in this incident were metal canisters with small glass vials packed in them (35,94,95).(17) The burial site for these vials was not identified in the records of materials disposal at Dunn Field. However, the crew doing the remedial work was checking for buried materials before they disturbed the soil and had indications that something was there. What they found were metals canisters with small glass vials inside. These canisters were similar to those in which 35MM film is packaged. Some of the vials contained small amounts of liquid. The materials uncovered at this location (whole and damaged canisters and glass vials, and the soil around them) were certified as non-toxic by the Tennessee Department of Environmental Conservation (TDEC). These materials were disposed of at a Shelby County landfill.
Response: Dunn Elementary School was closed during a hazardous materials incident in 1988, but no medical evaluations of the students from this school were performed (76). This incident had nothing to do with chemical warfare materials because the large scale storage of them ended in 1947 and all were gone by 1961 (5).
In the January 19 - 21, 1988, hazardous material incident, the cover of a hazardous materials storage building called a Span Dome, as identified on Figure 2, collapsed during a severe thunderstorm (76). This building was located about 1,400 feet south of the corner of Perry and Dunn Avenues and about 500 feet from Perry Avenue (79). The collapse resulted in the release to the environment of about 327 - 2,000 gallons of the 250,000 gallons of the hazardous materials stored in this building and an identical building right beside it (76). The chemicals stored were acetone, isopropyl alcohol, methyl ethyl ketone, methyl isobutyl ketone, toluene, and xylene. All these are commonly-used solvents (78).
The Memphis Fire Department's (MFD) report indicates that, during the first hours of this incident, "The odors of the products and gas trac readings of flammability were very high at the north perimeter of the Depot (Dunn Street), indicating much leakage. These readings and odors were surprising at this distance considering the first four to five hours of the incident occurred while heavy thunderstorms were crossing the Memphis area" (76). [Note: As indicated on Figure 2, Dunn Avenue is about 1,300 feet north of the building (79).] MFD took measures to prevent or greatly reduce air releases. However, short-term exposures to these hazardous materials could have occurred before these measures were taken.
On January 20, Dunn School was closed as a precautionary measure while the collapsed structure was being cleared away and the spilled chemicals cleaned up (76). A shut-in was also evacuated from his or her house on the 20th.
As indicated on Figure 1, Norris Elementary School is near the southwest corner of DDMT and Dunn School is near the northwest corner. Both are about the same distance from the Span Dome. Decisions to close or evacuate schools or residential areas during hazardous materials incidents are largely based on wind direction. It appears that MFD assumed that the wind was blowing to the north (i.e., towards Dunn School) on the day the structure was cleared away. Thus, they closed Dunn School but left Norris School open.
Response: This cleanup probably did not result in contamination of apartment complex soil with dieldrin. DDMT staff indicated in presentations to the DDMT Restoration Advisory Board (RAB) that the cleanup was done using procedures that would prevent this from happening (12,13). This included monitoring the air during the removal in which dieldrin was not detected. In addition, dieldrin levels in soil represented a risk for cancer if someone was exposed to them for a long time, but not a risk for other health effects.
ATSDR is recommending that soil from this complex be sampled because it is not known whether past use of dieldrin and other chemicals in the base housing area could have led to contamination of the soil across the DDMT boundary fence.
Response: The answer to this question is no, based on the information available to ATSDR on the health effects of mixtures and the actual concentrations of chemicals found on DDMT. ATSDR has sponsored research for many years on the mixtures issue because of its importance in evaluating the possible health impact of a site and because it is often a community concern. A common finding of the ATSDR-sponsored and other investigations of this issue is that adverse effects are unlikely when the chemicals in a mixture are present at concentrations well below the toxicologic thresholds(21) for that chemical (96-99). ATSDR identified the toxicologic thresholds for the site contaminants and found that the maximum contaminant levels result in doses many times (100s to 1,000s) lower than the thresholds. This suggests that exposures to combinations of DDMT contaminants are unlikely to result in adverse effects.
Further analysis of exposure to a mixture of DDMT contaminants was done by identifying the possible interactions among the chemicals contributing most of the potential risk. For soil and sediment, 4 metals (lead, iron, chromium, and arsenic) contribute more than 95% of the total noncarcinogenic hazard. The chemical interactions that would increase risk appear to be counterbalanced by those that reduce risk. For example, cadmium may enhance the noncarcinogenic toxicity of arsenic but chromium reduces it (88,89,100).
Response: Concentrations of benzo(a)pyrene, dibenz(a,h)anthracene, or all polycyclic aromatic hydrocarbons (PAHs) together were elevated in the soil at several locations at DDMT. However, a detailed evaluation of this exposure situation and the carcinogenicity of PAHs indicate that it is unlikely that anyone was harmed by exposure to PAHs at DDMT. A more detailed discussion of those possible exposures is on page 83.
Besides these possible exposures in areas around specific buildings, former workers reportedly could have been exposed to toxic substances because of work practices inside the DDMT buildings that resulted in contact with chemicals (60). Evaluation of these situations is not within the scope and purpose of a public health assessment. As indicated in the response to the next concern, ATSDR's Office of Urban Affairs is conducting a medical records review.
As referenced in the 1990 remedial investigation, there are some industrial hygiene reports that may provide information on this issue (3). Also possibly relevant to this issue are data from the sampling of the air from six of the 28 warehouses in 1998 for some of the pesticides stored or used in those warehouses (11). The pesticides tested for included heptachlor, heptachlor epoxide, beta-benzene hexachloride (BHC), dieldrin, DDD, DDE, DDT, endrin ketone, chlordane, and methoxychlor. DDT, DDE, heptachlor, and chlordane were detected in most of the buildings but at levels well-below the health-based criteria for workers.
- Ten individuals indicated that their exposure to chemicals at DDMT had caused health effects including Hodgkin Disease; other cancers; problems with the skin, kidneys, respiratory tract, eyes, or female reproductive system; miscarriages; or headaches. One individual identified that the main exposure that she received was to DDT being used to treat around the warehouses. She also stated that the DDT killed many squirrels and other rodents on DDMT. The other workers did not know what chemical(s) they were exposed.
- Three individuals expressed concern that exposure to asbestos in the office they had worked resulted in respiratory tract problems or asthma.
- Three individuals indicated that the water coming from the taps in DDMT buildings was often brown colored and of poor quality. Mr. John DeBack of DDMT was at this meeting and indicated that this problem was ongoing.
- One former DDMT worker reported that her father, also a former worker, had brought dust home on his clothes which he thought was harmful so would not allow his children to touch him until he had removed the dusty clothes. She indicated that her father was now sick.
- One former worker indicated that she had disposed of expired medicines by putting them down the drains within the building that she worked.
Response: At this meeting in 1998, Dr. Rueben Warren, the ATSDR Associate Administrator for Urban Affairs indicated that Dr. Jewell Crawford who is a physician in his office was developing activities to assist workers. This will include an evaluation of the medical records of former workers.
Response: Anyone knowing of locations where DDMT materials were dumped or buried off-site should report this to Mr. Jim Morrison (901-368-7953) at the Memphis Office of the Tennessee Department of Environmental Conservation, or Mr. Turpin Ballard (404-562-8553) at EPA/Atlanta. These agencies have the responsibility to investigate reports of buried hazardous materials.
1. The information in this section is based on comparison of the data displayed on Figure 4 to 1990 U.S. Census data for Shelby County.
2. Based on several discussions with DDMT staff.
3. Sampling of the area around DDMT was done in late 1995. Sampling locations were selected by staff from DDMT and its contractors, EPA, TDEC, and ATSDR; and a local environmental activist. This last individual was at the time a co-chair of the DDMT RAB. DDMT titled this sampling as "background" (11). Because there is often confusion about the meaning of this term, ATSDR has chosen to identify this sampling as "area sampling." Background can be defined as being what is typical for an area without any human influence (natural) or without any influence of site contaminants. This later definition is what was used by DDMT because lay people often use the first definition and equate background with natural. See footnote 4 for documentation of the 1998-1999 sampling data for Dunn Field.
4. The results of the 1998-99 sampling of Dunn Field surface soil, sediment, and surface water were supplied to ATSDR in December 1999 as an electronic file by CH2MHILL, the contractor for the Corps of Engineers.
5. A former worker indicated to John Crellin on September 9, 1999, that some workers performed cleanup and other tasks on Dunn Field periodically. They would work on Dunn Field 8 hours a day for several days in a row.
6. Conversation with DDMT-CCC member in November 1998.
7. This was described during a meeting in Memphis on February 24, 2000 and is recorded on page 105 in the public comments section.
8. Conversation with a member of DDMT-CCC during a site visit in June 1997.
9. These population estimates were made by John Crellin using geographic information systems (GIS) techniques. After creating 100- and 500-foot zones around the five drainage ditches, population numbers for these 2 zones were then identified using 1990 census data for Shelby County.
10. The Memphis Fire Department estimated immediately after the incident that 1,500 - 2,000 gallons were released (76). After the incident, the Depot estimated that only 327 gallons had been released and that this was diluted by 37,000 gallons of rainwater (77).
11. These data were provided to ATSDR in September 1998 as an electronic file. The actual sampling of these locations was done in late 1995. Sampling locations were selected by staff from DDMT and its contractors, EPA, the Tennessee Department of Environmental Conservation, and ATSDR; and a local environmental activist. This last individual was at the time a co-chair of the DDMT RAB.
12. Discussion with Michael Grayson, Health Physicist, Federal Facilities Branch/DHAC/ATSDR.
13. Conversation among a DDMT-CCC member, John Crellin, Rueben Warren, Sandee Coulberson, and others on September 9, 1999.
14. This is based on an evaluation of the ground elevations found on the USGS topographic map for the DDMT area and my (John Crellin) observations of the area.
15. See page 131 for a description of the problem given by a resident during a meeting on February 24, 2000.
16. Phone call to John Crellin from a DDMT-CCC member on March 24, 1998.
17. John Crellin had several conversations concerning this issue: conversations with a DDMT-CCC member in March and April 1998, with Ben Moore (ATSDR) in March 1998, with Glen Kaden (DDMT) in March 1998, and with Shawn Phillips (DDMT) in August 1999.
18. This is based on a discussion with a DDMT-CCC member on January 21, 1999. This individual drove me (John Crellin) by Norris and Dunn Elementary. I agreed that these two schools are about the same distances from the western boundary of DDMT.
19. This concern was expressed to John Crellin on October 17, 1998 by a DDMT-CCC member.
20. This response was developed with the guidance of Allan Susten, Ph.D., DABT. He is the Assistant Director of Science in ATSDR's Division of Health Assessment and Consultation.
21. These toxicologic thresholds would be the no or lowest observed adverse effects levels (NOAELs and LOAELs) for the chemical of interest.
22. This has been expressed by former workers on several occasions including the January, March, and April 1999 Restoration Advisory Board (RAB) meetings.