PUBLIC HEALTH ASSESSMENT
ROCKY MOUNTAIN ARSENAL
ADAMS COUNTY, COLORADO
The potential pathways of human exposure to RMA- and non-RMA-related contaminates are summarized below and in Table 18.
Potential Onpost Surface Soil and Sediment Pathway
A total of 178 soil contamination sites were identified in the SARs and two additional soil contamination sites were evaluated during the development and screening of alternatives for remediation (EBASCO, 1993b, v. II, p. 1-11). Those sites evaluated were the Basin F Wastepile and RMA "Surficial Soils", including areas outside the boundaries of the SARs sites (EBASCO, 1991). In the Detailed Analysis of Alternatives, a third site consisting of the soils beneath three buildings in the North Plants was added (EBASCO, 1993b, p. 1-11). Of those 181 sites evaluated, the bulk of the contamination detected in surface soil samples (0-2" depth) is located in the central sections of RMA in and around the manufacturing complexes, solid waste disposal areas, and liquid waste basins (EBASCO, 1993b, v. 1, p. 8). The location of that surficial soil contamination is shown generally in Figure 2.1-1 given in the RISR (EBASC0, 1992, p. 2-11). Specifically, the six most contaminated sections are Sections 25, 26, 35, and 36 (T2S, R67W) and Sections 1 and 2 (T3S, R67W). About half of the acreage of those central zone sections is contaminated.
For the purpose of this Assessment the data amassed for Onpost sediments has been included with the surface soil samples because the contaminants they contain are or could be available to the potential surface soil pathway. The sediments grouped with surface soils include dredged lake-bed sediments and dry or seasonally dry lake beds, streams, or ditch channel segments.
ATSDR reviewed Onpost surface soil and sediment data incorporated in the RMAED and identified the Organosulfur Compounds (OSCHs) Chlorophenylmethyl sulfide (CPMS), -sulfone (CPMSO2), and -sulfoxide (CPMSO); the Organophosphorous Compound - GB-Agent Related (OPHGBs) Isopropylmethyl phosphonic acid (IMPA); the Organophosphorous Compound - Pesticide Related (OPHP) Atrazine (ATZ); the Organochlorine Pesticides (OCPs) Aldrin (ALDRN), Chlordane (CLDRN), and Dieldrin (DLDRN); and Arsenic (AS), Beryllium (BE), Copper (CU), and Lead (PB) as contaminants of potential concern (see Tables 9 and 10). Those contaminants have been detected at the maximum concentrations listed in Tables 9 and 10 within the central six sections.
Although contamination of deeper soils (>2") is somewhat more widespread outside of the nucleus of contamination comprised by the six central sections of RMA, surface soil and sediment contamination in the following areas is largely localized as described below:
Thus, surrounding the surface soil contamination in the center of RMA a 1-2 mile wide zone of relatively uncontaminated surface soils exists. Within this external zone or rim of sections adjacent to the RMA boundary, scattered occurrences of two contaminants, dieldrin and arsenic, are detected at levels at or above levels of possible health concern. Aldrin is also detected in this rim of sections, but at levels below health based comparison values. This may be due, at least in part, to the fact that dieldrin, which has a half-life of 7 years in soils, is also a decomposition product of aldrin, which has a half-life of 4 to 5 years in soils (EBASCO, 1988). Table 16 gives the general location and concentration of those surface soil contaminants.
Conducted during the RI, the surface soil sampling shows that most of elevated concentrations of dieldrin and, to a lesser extent, aldrin and other organic contaminants, occur in areas immediately east and southeast of Basins A and F. The concentration of those contaminants diminishes rapidly to the west of the basins and more slowly in other directions. ATSDR reviewed the areal distribution of dieldrin in surface soils and found that, except for a few isolated occurrences, the concentration of dieldrin falls below levels of health concern within about 1 mile to the east, 1.5 miles to the southeast, 0.5 mile to the south, 0.25 mile to the west, and 0.5 mile to the north of the principal source areas.
Surface soil contaminants detected in the rim of sections surrounding the central 6-section core of contamination may have migrated to those nonsource areas by three principal mechanisms:
eolian (windblown) transport, surface water transport, and direct application (of pesticides).
Surface water transport has been an important process for the dissemination of contaminants in
sediments in Onpost creeks and ditches, overland runoff accounts for only localized erosion and
redeposition of surface soil contaminants and does not account for the pattern of surface soil
contamination observed in the samples collected (EBASCO, 1992, p. D1-11). Direct application
of pesticides has been restricted to specific areas and does not explain the observed distribution
of those contaminants outside of the sources areas. The observed pattern of contaminant
distribution is consistent, however, with observed wind patterns and eolian transportation.
Table 16 - Onpost surface soil contamination above comparison values (DLDRN = 0.04
ppm & AS = 0.40 ppm) in the sections near the RMA boundaries. (RMAED run of
10/15/93; EBASCO, 1992, Appendix D). See Fig. 3 for general locations.
| Location | Analyte | Maximum Detect (ppm) | Comments |
| T3S, R66W - Southeast boundary area | |||
| Sec. 5 | DLDRN | 0.0413 | Concentration of contaminants decreases towards RMA
boundary. Contaminants below levels of concern at the
RMA boundary.
DLDRN "hot spots" of contamination in the east half of Sec. 6 in the "old toxic storage yards" and rail spur (max 0.0949 ppm). |
| AS | 1.55 | ||
| Sec. 6 | DLDRN | 0.23 | |
| AS | 2.65 | ||
| Sec. 8 | DLDRN | 0.0446 | Isolated detection. |
| T3S, R67W - South boundary area | |||
| Sec. 11 | DLDRN | 0.047 | Isolated detection along Sand Creek Lateral. Concentration of contaminants decreases towards RMA boundary. |
| AS | 2.64 | ||
| T2S, R67W - West and northwest boundary areas | |||
| Sec. 34 | DLDRN | 0.0711 | Maximum concentrations measured just west of the central six sections of RMA and rapidly decline below levels of concern towards RMA boundary. |
| Sec. 27 | DLDRN | 0.0456 | |
| Sec. 23 | DLDRN | 0.60 | Max. just north Basin F. Below concern at boundary. |
| Sec. 24 | DLDRN | 0.11 | Contaminant concentrations decrease progressively from RMA center to below levels of concern at boundary areas. |
| AS | 4.28 | ||
| T2S, R66W - Northeast and east boundary areas | |||
| Sec. 19 | AS | 2.89 | Isolated "hot spots" of AS contamination. Progressive decrease of other contaminants from RMA center to boundary areas. |
| Sec. 20 | AS | 2.64 | |
| Sec. 30 | DLDRN | 0.20 | Max. values detected in west and levels decrease progressively towards RMA boundaries. |
| AS | 2.82 | ||
| Sec. 31 | DLDRN | 0.30 | Max. DLDRN value detected in west and levels decrease progressively towards boundary. Isolated "hot spots" of contamination in toxic storage yard. |
| AS | 3.51 | ||
The wind rose data presented previously in Figure 4 discloses that winds at RMA most commonly blow from the south or south-southwest at speed less than about 11.5 miles per hour (mph). Winds less commonly blow from the west and northwest, but about 50 percent of those winds exceed 11.5 mph. Many of the stronger west-northwest winds are the "chinook" winds which occur infrequently during the winter and spring when surface soils tend to be more susceptible to wind erosion and transport.
The average wind speed at RMA for the period 1975-1979 is about 9 mph. While meteorologic conditions certainly vary from year to year, examination of the Comprehensive Monitoring Program Air Quality Data Assessment Reports for successive years' data shows little variation. For example, during Fiscal Years 1989 and 1990 the mean and maximum wind speeds measured at RMA were 8.5 and 8.6 mph and 33.2 and 35.9 mph respectively. However, during those years short-term events such as wind gusts showed greater variation from 72.5 and 52.8 mph (Stollar, 1991).
Wind speeds in excess of 7 mph are necessary to erode silt-sized particles and exponentially greater wind speeds are necessary to move fine-grained and larger sand sizes (Chorley and others, 1984). Therefore, strong winds from the west-northwest and other less-common strong winds from more northerly or southerly directions may have accounted for most eolian transportation of contaminants (EBASCO, 1992, p. D1-13).
Prior to the Basin F and Basin A IRAs eolian transport appears to have been an important migration pathway for soil contaminants at RMA. The extent of past human exposure Onpost to contaminated surface soils is unknown, but incidental ingestion, dermal contact and inhalation was possible for RMA workers from 1942 to the cessation of industrial operations in 1982.
The Offpost Endangerment Assessment (HLA, 1992b, p. I-18, Figs. 16 and 17) presents evidence suggesting a low level of wind-borne OCPs (chlordane, dieldrin) may have been deposited in the 96th Avenue area, immediately north of RMA (sections 13 & 14, T2S, R67W). The most widespread and frequently detected OCP is dieldrin. Concentrations of dieldrin in Offpost Study Area surface soils range from 0.002 to 25 ppm. However, the highest concentrations of those pesticides and arsenic occur in an irregular pattern of "hot spots" that is not consistent with eolian transportation and deposition alone. Offpost pesticide use, natural variability of surface soils, and irrigation with well water appear to be major factors influencing the occurrence of those compounds in the Offpost surface soils.
Based upon the surface-soil contamination data developed for the Offpost Study Area, ATSDR concludes that the Offpost surface soils have been contaminated by a combination of sources including eolian deposition, agricultural application of pesticides, and irrigation practices. Wind-borne transport of contaminants from RMA represents an unknown percentage of the low levels of contamination detected. Dieldrin and other OCP surface-soil contamination detected in the 96th Avenue area is found at levels no greater than half of those OCP levels found in the adjacent Onpost soils. Elsewhere, the levels of Offpost Study Area surface soil contamination are generally tens or hundreds of times lower than detected Onpost (HLA, 1992b, p. I-18). While wind-borne transport of OCP contaminants to these Offpost areas may be a minor pathway of human exposure, the levels of surface soil contamination are, with isolated exceptions, well below levels of health concern and this potential pathway will not be considered further.
It is unknown what level of Onpost occupation exposure to RMA contaminants those workers may have experienced in the past but the opportunity for direct exposure to those chemicals in the workplace may have been much higher than the opportunity for Onpost environmental exposure to chemicals outside the manufacturing, storage and handling facilities. However, a retrospective follow-up study of the mortality experience of 2,384 workers at Shell's plant between 1952 and 1982 found an overall mortality rate similar to the Colorado rate and that there was no apparent widespread or potent health threat at the plant (Amoateng-Adjepong, Sathiakumar, and others, 1995).
At this time, IRAs have been implemented or completed that address the most significant sources of windblown contamination originating from dust and have contained and subsequently destroyed the volatile liquids previously contained in Basin F. Thus, since the termination of all RMA industrial activities in 1982, the areal distribution of surface soil contamination has not increased and, because of the natural attenuation of many RMA organic contaminants, the surface soil concentration of those contaminants has decreased.
Beginning in 1984 the Army initiated the remedial investigation process and since that time the population potentially exposed to RMA surface soil contaminants has been principally comprised of field- and office-oriented remediation workers and managers and, beginning in 1989, office and field personnel of the U.S. Fish and Wildlife Service staffing the RMA National Wildlife Area (to become a National Wildlife Refuge upon completion of clean-up activities and real estate transfer by and from the Army). Beginning in November 1989 and continuing to the present, the public (school-aged children and adults) have been participating in increasing numbers in USFWS staff- and volunteer-guided, vehicle-based tours in the rim-sections, largely external to the RMA core 6 sections of surface soil contamination. USFWS records show that, since November 1989, over 100,000 people have visited the Arsenal during 1- to 2-hour (bus) wildlife tours, nature walks, educational programs, and special events. Additionally, school and youth group activities brought about 14,000 students to RMA for supervised tours and other supervised field program activities in FY 91 and an average of about 3419 people visited the Eagle Watch Observation area (eastern boundary RMA, Sec. 5, T3S, R66W) during the FY 90, FY 91, and FY 92 winter season (USFWS, 1993b, p. 101-114).
The USFWS use of the RMA Onpost area is regulated by a site-specific Army policy memorandum (July 17, 1991). That policy sets forth an area-wide system of three mapped zones based upon surficial soil and other contaminant data (see Fig. 10):
In addition to the tours and events described above, the Arsenal has operated a popular catch and release fishing program at lakes Mary, Ladora, and Lower Derby. Those lakes and the USFWS Visitors Center are located in Sections 1 and 2 (T3S, R67W) just south and southeast of the South Plants. Here, within the southern end of the core of more highly contaminated sections, the surface soil samples collected near the lakes and from the fields near the USFWS Visitors center are found to contain higher levels of contaminants. Surface soil samples collected around Lower Derby Lake have found frequent detections of dieldrin (max. 0.94 ppm), less frequent detections of aldrin (max. 0.0952 ppm), and infrequent detections of chlordane (max. 0.63 ppm) and arsenic (max. 3.32 ppm; local AS background < 2.5 ppm). Around Lake Ladora, Lake Mary, and the Visitors Center surface soil samples show the frequent occurrence of dieldrin (max. 0.980 ppm) and isolated detections of arsenic (max. 3.58 ppm; local AS background < 2.5 ppm).
Pathway Summary - Onpost Surface Soils and Sediments
A potential past pathway of human exposure to the surface soil and sediment contaminants of potential concern given in Tables 9 and 10 may have existed for RMA workers from sometime after 1942 until all industrial operation ceased in 1982 and perhaps, for a lesser number of workers until 1988 when the Army placed the Arsenal in the inactive list. The North and South Plants and most sources of contamination are located within the 6 central sections of RMA as is the highest levels of surface soil contamination. The nature of the industrial activities conducted here suggests that most workers had no more than infrequent, incidental exposure to the environmental contaminant and the potential for much more frequent, but unquantified, occupational exposure to those same chemicals. This past pathway is not further analyzed in this Assessment.
A potential present and future pathway of incidental human exposure to the surface soil and sediment contaminants of potential concern listed in Tables 9 and 10 may have existed for RMA remediation workers since 1984. Although IRAs have been completed that minimize the potential for exposure to those chemicals, future remediation measures may create situations where remediation workers may be inadvertently exposed for short periods of time to disturbed surface soils, subsurface soil, dust, and volatile chemicals released from the soils.
Those potential present and, until final Onpost cleanup activities are completed, future exposures should be, at most, infrequent incidental ingestion, inhalation, and dermal exposures because such remediation work is planned and implemented to eliminate or minimize such occupational exposures. To detect possible environmental exposure to contaminants and to monitor the health of their employees and volunteers, the USFWS (1993c) has implemented a medical monitoring program. Additionally, RMA has established a Contingency Plan (RMA, 1993) designed to minimize hazards to human health and the environment from fires, explosions, or any unplanned release of hazardous substances or pollutants to air, soil, surface water, or groundwater. Similar contingency planning is part of the final cleanup activities at RMA as well.
Distinct from the potential pathway of exposure for remediation workers, a potential present and, until final Onpost cleanup is completed, future pathway of human exposure to dieldrin and arsenic (also to aldrin and chlordane, to a lesser extent) at levels of health concern may exist for USFWS RMA Wildlife Area workers and volunteers and the public that participate in wildlife tours and other activities at RMA (see Table 16). This potential pathway exists for infrequent, incidental ingestion, inhalation, and dermal exposure. USFWS employees, currently totalling about 40 of which 14 are field-going, have the greatest potential of incidental exposure. An estimated 50 percent of the field-going USFWS employee's time is actually spent in the field (EBASCO, 1993, p. B. 2-3) and thus, about 110 days per year is estimated as the maximum annual time period available for incidental exposure to contaminants. For those USFWS employees conducting intrusive soil activities in "Pink and Blue Areas", the potential for exposure is the greatest. But those employees are required to use personal protective equipment and thus the actual potential for exposure is low and not of health concern. Throughout the public health assessment process and RMA remediation, ATSDR will continue to work with the USFWS to further evaluate the potential for exposure pathways to their field personnel.
The USFWS part-time volunteers (approximately 60 in FY 93) collectively worked about 3.3 work-years (USFWS, 1993b, p. 113). Those volunteers have, by virtue of the nature of their duties at RMA, a very small opportunity for even incidental exposure to contaminants. The USFWS personnel that are largely office-bound, are unlikely , by virtue of the indoor nature of their jobs and the office and Visitors Center location, to be exposed to surface soil/sediment contaminants. This is true for the office-bound Arsenal employees as well.
And finally, of the public visiting RMA on tours and other permitted activities, the group that has the greatest potential for incidental (ingestion, inhalation, and dermal) exposure to dieldrin and other contaminants is comprised of the people fishing in the lakes in the southern part of RMA. A survey of angler use at RMA was conducted for USFWS (1993a, p. 117) found that Arsenal anglers average 12.5 days per year. The angler-day averaged 2.4 hours per visit. Thus, an interval of about 30 hours per year is the interval that RMA anglers might be subject to incidental ingestion, inhalation, or dermal exposure to RMA surface soil and sediments contaminants of potential concern. Other members of the public may make more frequent use of the open-space and wildlife opportunities that the annual use described for anglers but it is not expected that such regulated or casual use would be permitted in areas where surface soil or sediment contaminant concentrations are higher than those occurring around the lakes.
As discussed earlier in this Assessment, the Conceptual Remedy (Colorado, 1995) and the resultant Onpost ROD (Foster Wheeler, 1996) incorporates 28 specific components which will generally govern the conduct of final Onpost cleanup measures. Seventeen of those components deal directly with the excavation of contaminated soils, demolition of Onpost structures, Onpost landfilling of those soils and debris, and backfilling, capping, and grading with clean soils. Those components also incorporate provisions for protective controls to minimize emissions and odors and to ensure the protection of the public health of the nearby neighborhoods during the extended period of remediation activities. For these reasons, ATSDR concludes that there is a limited potential for off-site human exposure to RMA contaminants during the final remediation activities at RMA. Given the location of the contaminated soils and sediments at RMA and the safe-guards that will be in place during remediation, incidental, short-duration exposure(s) to low-levels of contaminants is all that can be reasonably foreseen.
The Remedial Investigation Summary Report and the 1985-mid 1993 data recorded in the RMAED document on- and off-post air quality monitoring at RMA. ATSDR has reviewed the data and determined 14 chemicals to be of potential concern. Those compounds are volatile halogenated organics (VHOs) 1,2-dichloroethane (12DCLE), carbon tetrachloride (CCL4), chlorobenzene (CHC6H5), chloroform (CHCL3), methylene chloride (CH2CL2), and tetrachloroethylene (TCLEE); the volatile aromatic organic (VAO) benzene; the organosulfur compounds - herbicide related (OSCHs) chlorophenylmethyl sulfone and sulfoxide (CPMSO2 & CPMSO); the organochlorine pesticides (OCPs) aldrin (ALDRN), chlordane (CLDAN), and dieldrin (DLDRN); and the elements arsenic (AS), mercury (HG), and cadmium (CD). Of those contaminants, only 5 compounds (12DCLE, CHCL3, C6H6, AS, and CD) have been detected in the off-post air at levels potentially of human health concern (see Table 11).
The Onpost remedial investigation data (EBASCO, 1992) reviewed by ATSDR suggests non-RMA sources may be wholly or partially responsible for the contaminants detected. The TRI (1994) database records that, in 1988, 30 facilities in close proximity to RMA reported 96 chemical releases. The compounds released included VHOs, VAOs, PAHs, and metals. The data recorded in the most-recent available 1991 inventory differs very slightly in detail from the 1988 data, with the exception that the total volume of releases to the atmosphere is reduced to about 54 percent of the 1988 emissions. The TRI chemical inventory data establishes that there are nearby, off-site sources of atmospheric contaminants which correspond to all of those chemicals noted as contaminants of potential concern in the Offpost Study Area (see Table 11), with the exception of the VHOs 12DCLE, CLC6H5, CH2CL2, and TCLEE.
Prior to the Basin F and Basin A IRAs, volatilization from surface water and soils accounted for low but detectable concentrations of volatiles and semivolatiles in air peripheral to these basins. IRAs have been instituted to mitigate these low-level releases (EBASCO, 1992, Appendix C), and they have addressed the most significant sources of windblown contamination originating from dust and have contained volatile liquids from Basin F. Although past disturbances of contaminated soils and releases of VOC soil contaminants occurred during implementation of IRAs and may occur as a result of future remedial actions, future remediation activities may result in an increased potential for volatilization, suspension, and transport of contamination away from source areas. Those effects can be controlled through the use of adequate engineering and management measures. Air monitoring, which is currently part of the CMP, will continue to assess air impacts at RMA.
Public concern about off-post air pollution was generated during the initial phases of the Basin F IRA (May 1988 - December 1988) and subsequently with the testing and March 1993 start-up of the Submerged Quench Incinerator (SQI) designed to destroy Basin F Liquids. Air monitoring for potential off-post human exposure (Irondale community) to airborne Basin F contaminants and subsequent health studies has been inconclusive. Comparison of the quantitative data gathered Onpost with largely qualitative data gathered in the Irondale and Commerce City areas yields a plausible explanation for the odors noted and physical symptoms experienced by some Irondale residents. However, the data will only support the possibility of short-term (less than 24 hour) episodes of acute exposure to organochlorine pesticides (OCPs) and lesser quantities of other VOCs (ATSDR, 1989). ATSDR-funded health studies by Colorado Department of Public Health and Environment and others were initiated following this possible Basin F exposure incident. The findings of these ongoing health studies of this potential past pathway of human exposure to airborne contaminants is discussed in the Background and Public Health Implication sections. Because health studies of this past pathway are ongoing, this pathway will not be further analyzed in this Assessment.
Pathway Summary - On- and Offpost Air
A potential pathway of human exposure to air contamination can be attributed to both RMA and non-RMA sources. In the past, chemical manufacturing activities conducted at RMA, including the storage and disposal of contaminants and the subsequent remedial measures taken to control those contaminant releases, may have resulted in levels of air contamination and consequent human exposure to those contaminants at levels that may be approximated by the levels given in Table 11. The available data presented in the Remedial Investigation reports and in the Health Consultation prepared by ATSDR (1989) strongly suggests that, aside from unknown levels of RMA occupational exposure, past short-term human exposure to airborne contaminants of concern may have occurred during the 1988-89 Basin F remediation episode. During this episode, remediation workers may have been exposed to contaminants at levels approximated by those values given in Table 11.
Offpost residents in the Irondale area may have been exposed to unquantified levels of those airborne contaminants during the Basin F remediation interval. Given the prevailing wind patterns and the available monitoring data of contaminant concentrations at the RMA northern boundary, it appears that those off-site residents may have experienced unquantified, short-term, acute exposure to organochloride pesticides (OCPs) and additional exposure to the quantified levels Offpost contaminants of concern identified in Table 11. Offpost sources of air contamination may be responsible for some the of the detected contamination.
The documented performance of the now completed SQI remediation project indicate that no pathway of Onpost or off-post human exposure to the air contaminants from SQI was created by this project. Continuous (24-hour) monitoring of SQI is was conducted at the Arsenal and remote monitors were installed at the offices of CDPHE and EPA to ensure safety and oversight of this incinerator.
A potential future pathway of human exposure to airborne contaminants may arise from the soil excavation, structure demolition, and Onpost landfilling activities to be conducted at RMA. In addition to the human health protective provisions of the RMA Contingency Plan (RMA, 1993), the final cleanup activities at RMA will be implemented with safe-guards that will prevent all but incidental exposure to contaminants at levels that would result in adverse health effects. The potentially exposed population is comprised of Onpost remediation workers, USFWS employees, and the public using the RMA National Wildlife Area. The observed patterns of soil contamination at RMA strongly suggest that air-borne contaminants accidently released during final site cleanup activities are not likely to result in offsite contamination of nearby neighborhoods at levels that could result in harmful health effects.
Both the Onpost and Offpost RODs (Foster Wheeler, 1996; HLA, 1995) incorporate requirements for environmental monitoring and requirements to protect public health in nearby neighborhoods during remediation.
Game and Fish
Contamination of resident game species on RMA is documented in many sources including the Biota RI (ESE, 1989b) and the Integrated Endangerment Assessment/Risk Characterization (EBASCO, 1994). Investigation of Offpost Study Area biota contamination detected low levels of contamination in both wildlife and farm animals sampled (see Table 12A).
The movement of game species of wildlife from RMA into off post areas comprises a potential pathway of migration for the higher-levels of biota contamination found on RMA into the off post environment. Off post hunting of pheasants is documented north of RMA, hunting of mourning doves southeast of RMA, and movement of deer across the north, and east boundaries of RMA is also recorded. Generally, the quality of the wildlife habitat is better Onpost than in nearby areas beyond the RMA boundary fence (ESE, 1988; HLA, 1992a; EBASCO, 1993). Thus, species that do not range far may have little incentive to leave the confines of RMA.
Information on the home range size (land area occupied by an individual animal or group of those animals that has the habitat components necessary to sustain the animal) of pheasants and cottontail rabbits was determined. Although the sample sizes were small (14 pheasants and 16 cottontails) and the duration of the radio transmitter monitoring study was only about one year, the data obtained on the home ranges size observed for RMA pheasants (11 to 278 ac.) and cottontails (2.3 to 12.6 ac.) is within the range of the home range sizes reported from studies conducted elsewhere in the nation (ESE, 1988, p. 7-1 - 7-10).
Pheasants were occasionally observed flying to and from RMA along the northern boundary, and hunters were observed along the northern boundary in November, 1985. No seasonal pattern was apparent upon examination of the fall and winter telemetry data. The greatest distance traveled by monitored pheasants was 1.4 miles but the average distance traveled seemed to increase with increasing numbers of observations. For pheasants with more that 20 observations the average distance traveled was 0.86 miles. However, a local hunter did return a RMA pheasant leg band which he claimed was from a pheasant he'd killed about 7.5 miles northeast of RMA (sec. 13, T66W, R1S). It was concluded that the pheasant home range size determined probably represents the minimum home range size (ESE, 1988). The home range size and distance traveled is large enough to permit pheasants exposed to known sites of Onpost contamination to move into off-post areas where they could be hunted. If the true home range size is relatively small (about 1.5 miles across) then RMA-resident pheasants found in off-post areas must reside in the outermost, least contaminated rim of section, just inside the RMA boundary. Alternatively, if local area pheasants occupy a large home range (about 7.5 miles across), the individual birds could access the most contaminated sites at RMA, but may spend less time in the contaminated portion of their larger habitat.
None of the cottontail rabbits that were equipped with radio transmitters during the Offpost RI study were observed in the off-post areas even though the rabbits selected for study were all located within 0.75 miles of the north RMA boundary. The small home range size determined (ave. 6.5 ac) and the short distance traveled (ave. 0.17 mi) suggest that only individuals inhabiting the least-contaminated border area of RMA might move into the off-post areas.
Of the 27 mule deer and 10 white-tailed deer collected by April 1991 for sampling on RMA, the only detectable levels of any of the contaminants for which analyses were conducted was dieldrin (ESE, 1988; EBASCO, 1993). Three detections of dieldrin in mule deer liver are reported (0.101 - 0.281 ppm) in the results amassed in the Offpost RI (ESE, 1988), the Offpost RI Addendum (HLA, 1992a), and the Onpost Integrated Endangerment/Risk Characterization (EBASCO, 1994). Those reported levels are below the 0.3 ppm FDA Action Level. The mule deer with the highest concentration of dieldrin in the liver tissue was collected between Basin A and the South Plants near the center, and most contaminated portion of the Onpost area (ESE, 1988, p. 7-11).
The USFWS conducted a deer-health/contaminant study in 1993 and published their findings in the 1994 Annual Progress Report (USFWS, 1995). Eighteen radio-collared deer were collected based upon their home ranges. Although dieldrin was detected in fat (organ fat), liver, and brain tissue, no dieldrin was reported in muscle tissue, even from deer that frequented the South Plant and Basin A areas.
RMA has had an active fishing program since the 1960s. Currently fishing permits are sold on a random lottery (prior to 1993, on a first-come, first-serve) basis for 500 anglers. Spouses and family members under the age of 18 are able to fish on one permit. Because contaminants have been detected in RMA fish (see Table 12A), fishing is catch and release only and that regulation is strictly enforced. Fishing season dates are set yearly and depend upon the bald eagle usage of the Arsenal lakes, but generally run from early April through late September or early October. Additional permits are issued to military and Arsenal personnel, senior citizens, and physically-challenged individuals (eg. 143 permits in 1991). During FY 91, about 2012 people fished at RMA (USFWS, 1993). Despite this active sport-fishing program, no pathway of human exposure is likely because the catch and release fishing program (no consumption) is effectively implemented and aggressively enforced .
Tri-County Health Department personnel conducted a survey wild game hunting and hunter-success in the one-mile-wide belt of private lands surrounding the Arsenal on the northwest, north, and east boundaries (TCHD, 1994). Those surveys were conducted during the Fall of 1988 and the Winter of 1989 disclosed that pheasant hunting to the northeast of RMA resulted in only 7 birds taken for a success ratio of about 1 bird per 21 hunters. To the east of RMA the success ratio was of about 1 bird per 10 hunters. However, one hunter was identified that frequented this area and had harvested about 12 pheasants per season. He was also responsible for taking over 100 doves, one deer, and one antelope. This individual and his family had the greatest potential for consumption of any RMA foodchain contaminants that may be present in these off-post sites.
The data given in Table 12A indicates that edible tissue of water fowl and mourning doves has, in the past, carried elevated levels of the pesticides aldrin, dieldrin, and endrin. The results of the 1994 Biomonitoring Program (USFWS, 1995) are given in Table 12B. Those data indicate that in 1994 the edible-tissue body burden of those pesticides was within FDA Action Levels. Therefore, human consumption of those species with those contaminant levels should not result in adverse health effects. The USFWS is continuing this monitoring program in their continuing effort to monitor the general health of the RMA Refuge ecosystem.
Vegetable Produce
ATSDR initially disclosed in the public comment draft of this public health assessment (ATSDR, 1995, p. 145) that a potential pathway of human exposure to vegetables grown in contaminated surface soils and irrigated by contaminated groundwater may have existed in the past and may exist again in the future on certain lands within the Offpost Study Area. Of the lands originally thought to have the highest future potential were the Offpost lands bounded by the Burlington Ditch/O'Brian Canal and the north RMA boundary in the First Creek area. Those lands are characterized by the combination of both higher levels of surface soil and groundwater contamination. Acquisition of those rural, residential properties by Shell Oil Company in 1989-90 and the conversion of those lands to non-residential uses ended the possibility of human exposure to vegetable produce grown on those lands and potentially intention to manage those lands so as to preclude any potential future residential use of those land was affirmed in a September 10, 1991 letter (Shell, 1995). The subject properties were previously served by Arapahoe Aquifer wells and thus, groundwater was never a factor in past potential foodchain contamination on these lands.
Elsewhere in the Offpost Study Area surface soils are generally uncontaminated but, Alluvial Aquifer wells are used for garden irrigation, non-food crop irrigation, or livestock watering. A summary of Offpost irrigation well samples which, as of April 1994, had elevated contaminant levels is given in Table 17. Data has been presented previously in this Assessment that shows declining trends for many groundwater contaminants.
In October and November 1995 samples were collected of vegetables grown in the Offpost
Study Area of potential concern and irrigated with well water produced from the Alluvial
Aquifer. Those vegetables were analyzed for their DIMP content to evaluate the potential
uptake of that contaminant in area vegetables and to provide data to compare with the
contaminant levels predicted in the endangerment assessment prepared for the Offpost Operable
Unit (HLA, 1992a). The samples were collected from the garden of private residence north of
RMA on October 12, 1995 and from two large vegetable farms on
Table 17 - Detections of irrigation well contaminants at levels of potential concern:
Alluvial/Unknown Aquifer, Offpost Study Area, as of April 1994 (a).
> CV (b) (ppb) |
(yr/day)(c) |
(GI, NFI, L)(d) | |
| Volatile Halogenated Organics - (VHOs) | |||
| 1,2-Dichloroethane (12DCLE) (CV = 0.4 ppb CREG; 5 ppb MCL) | |||
| 1068A | 4.58 | 93273 | GI, L |
| Tetrachloroethylene (TCLEE) (CV = 0.7 ppb CREG; 5 ppb MCL) | |||
| 1068A | 14.0 | 93723 | GI, L |
| 1189A | 14.7 | 92122 | GI, NFI |
| Organochlorine Pesticides (OCPs) | |||
| Dieldrin (DLDRN) (CV = 0.002 ppb CREG) | |||
| 1189A | 0.062 | 92122 | GI, NFI |
| ICP Metals / Anions & Cations | |||
| Arsenic (AS) (CV = 0.02 ppb CREG; 50 ppb MCL; Natural Background Level <2.5 ppb) | |||
| 1380E | 2.51 | 92196 | GI |
| Nitrate (NIT) (CV = 10,000 ppb MCL) | |||
| 986A | 12,000 | 91289 | GI, NFI |
(b) > CV = greater than or equal to the Comparison Value for drinking water (see the Environmental Contaminants and Other Concerns section of this Assessment for further discussion).
(c) yr/day = the year followed by the chronologic, numerical date (eg. "94109" is April 19, 1994).
(d) The uses of wells in the RMA Offpost Study Area were inventoried by the Tri-County Health Dept. and incorporated in their database of Offpost wells. The symbols used are "GI" for garden irrigation, "NFI" for non-food irrigation, and "L" for livestock watering.
November 10, 1995. The private garden was selected by the Army because it is irrigated only with water from well 1178B which has higher concentrations of DIMP remaining than any other Offpost area well. The concentration of DIMP in that well have ranged from about 150 to 950 ppb. The commercial farms were selected because they utilize a combination of groundwater (DIMP <20 ppb) and surface water (uncontaminated by DIMP).
The vegetables were analyzed using a recently developed method to determine DIMP concentrations in vegetables (detection limit = 20 ppb). The concentrations of DIMP detected in the private garden cucumbers ranged from 340 to 920 ppb and the tomatoes from that garden contained DIMP at an unquantifiable level below the detection limit. The vegetable samples (corn, onion, chile pepper) taken from the large vegetable farms contained no detectable DIMP.
Comparison of this 1995 garden vegetable data with the calculation of potential risk given in the Offpost Endangerment Assessment (HLA, 1992b) indicates that even under a "worst-case " exposure scenario, the consumption of vegetables irrigated with DIMP-contaminated groundwater is not expected to result in adverse health effects. This conclusion is based upon the estimation of the potential DIMP concentration in lettuce. Lettuce was selected to evaluate the potential risk associated with consumption of Offpost-grown vegetables because studies have shown that plant leaves have the highest potential to accumulate DIMP. Other "worst-case" assumption included in this evaluation were a 900 ppb concentration of DIMP in groundwater, a high ingestion rate 0.125 kg/day), and daily ingestion for 30 years. Based upon these conservative assumptions the calculated associated risk, expressed as a hazard quotient, is 0.2 (level of concern is 1.0).
The provisions of the Conceptual Agreement (Colorado, 1995) and Offpost and Onpost RODs (HLA, 1995; Foster Wheeler, 1996) specify that the existing drinking water wells in the Offpost Study Area within the "DIMP footprint area" (DIMP >0.392 ppb) will be replace by municipal water system or a suitable alternative. Thus, the use of small irrigation wells may also be greatly reduced or eliminated. Moreover, the continued functioning of the BCSs and the groundwater intercept and treatment system north of RMA will continue to lower contaminant levels in the Offpost Study Area groundwater. In addition, institutional controls will be utilized to prevent domestic use of Offpost contaminated groundwater and to discourage the development of new domestic wells in areas of contaminated groundwater.
The provisions of the RODs coupled with the low-levels of DIMP found in the vegetable samples analyzed in 1995 eliminate a present or possible future vegetable produce pathway from further consideration.
Pathway Summary - On- and Offpost Foodchain
A potential pathway of off post human exposure exists for the consumption of pheasants hunted in the nearby off post areas to the north and east of RMA. Pheasant in those areas are known to frequent or inhabit RMA. Dieldrin has been detected in pheasant tissue (0.02 - 5.95 ppm). The FDA Action Level for dieldrin is 0.3 ppm. Although dieldrin has not been detected in pheasant samples collected in the Offpost Study Area, the size of the pheasant's home range is sufficient to permit pheasants to be exposed to RMA sources of contamination and to travel to off post areas where they may be legally hunted and consumed. The home range data gathered suggests that pheasants frequenting the off post areas adjacent to RMA may also be those pheasants that inhabited the outer rim of least-contaminated sections at RMA. Thus, while a potential pathway exists for the consumption of dieldrin-contaminated pheasant tissue, it is likely that if dieldrin is present in the tissue of some unknown percentage of pheasants hunted near RMA, it is present at the lower end of the observed range of values detected thus far. The study conducted for the Offpost RI concluded that both waterfowl (eg. mallard ducks) and mourning doves migrated widely and thus, even if those species were contaminated by RMA sources, their number would be so diluted by the greater number of birds not frequenting RMA, that the potential for multiple exposure by consumption would be small (ESE, 1988, p. 2-30).
Historically, dieldrin is detected in mallard tissue in the range of 0.01 to 4.53 ppm, which exceeds the 0.3 ppm FDA Action Level. However, sampling conducted by USFWS in 1994 found a maximum of only 0.068 ppm dieldrin in the edible muscle tissue of the duck and Canada goose samples analyzed (see Table 12B; USFWS, 1995). Qualitative data presented in the Offpost RI reports suggests that the local area duck population may be large enough that it is likely that a hunter would only take an occasional RMA bird and thus, consumption of waterfowl does not appear to be a significant off post pathway of human exposure to RMA contaminants.
Samples of off post mourning dove have not been collected but those samples collected Onpost indicate the doves are frequently burdened with high levels of a number of pesticides and mercury. As shown in Table 12A, mourning doves sampled have been found to contain mercury (0.05-0.40 ppm), aldrin (0.0227-1.3 ppm), dieldrin (7.8-32.0 ppm), endrin (0.14-1.3 ppm), DDT (0.04-0.308 ppm), DDE (0.04-0.942 ppm), CPMS (0.3-1.46 ppm), and CPMSO2 (0.22-2.53 ppm). Of those detections, the ranges of values reported for the organochlorine pesticides (OCPs) aldrin, dieldrin, and endrin all exceed the respective FDA Action Level of 0.3 ppm for each pesticide. In order to more fully evaluate contaminant uptake in mourning doves and the potential health and ecosystem risk that uptake might pose, the USFWS collected additional contaminant accumulation data on this species during 1994 (USFWS, 1995, p. 1-91). A total of 12 birds were collected and samples of brain, liver, and muscle tissue analyzed for OCPs, chlordane, DDE, AS, and HG. There were no detections of aldrin, endrin, isodrin, chlordanes, or arsenic. The results of the other tests are summarized in Table 12B.
Dieldrin was detected in 6 of 12 doves tested, but of those positive contaminant detections only one sample of liver tissue at 0.533 ppm dieldrin was above the FDA Action levels. Edible muscle tissue of those dove tested did not contain contaminant concentration above FDA Action Levels and the indication is, based on the 1994 data, that human consumption of mourning doves taken in the off post areas is not likely to pose a health risk.
The nearby Denver International Airport opened in 1995 and increasing levels of urban and commercial development are already beginning in the areas north, east, and southeast of RMA. As these areas develop, it is likely that off post habitat quality for species such as pheasants may begin to decline, as will hunting pressure. On this basis, it is likely that a potential present or future pathway for the hunting and consumption of contaminated pheasants will not be a viable pathway for long.
Potential Groundwater Pathways
Potential Irondale/Western Plume Group Pathway
Potential Nitrate Contamination
In addition to the contaminants of potential concern identified in Table 7, ATSDR considers nitrate (NIT) to be a contaminant of potential concern in the Irondale/Western Plume Group pathway. The results of routine inorganic water quality sampling of SACWSD wells showed a higher than expected level of nitrate concentration in District Wells Nos. 2, 3, 5, and 17. Because nitrate was detected as high as 9.7 ppm (10 ppm is the EPA MCL for this compound) in those samples, SACWSD initiated a study to evaluate the possible source(s) and concentration of nitrate in the upgradient plume of groundwater flowing towards the system in the Irondale/Western paleochannel. In a report prepared by HRS Water Consultants (HRS, 1993) a complex plume of nitrate contamination was delineated that flowed onto RMA from the south. Nitrate concentrations at the boundary between RMA and the former Stapleton International Airport exceed 30 ppm and concentrations in the range of 15-20 ppm are interpreted in the main paleochannel and within 1 mile of the of the affected municipal wells.
ATSDR reviewed a compilation of nitrate analyses conducted by the Klein Water Treatment Facility between January 4, 1993 and August 22, 1994. That summary forwarded to ATSDR by RMA personnel (Kilgannon, 1996, personal communication) documents that during the specified time interval, nitrate levels in wells numbered 2, 3, 5, 14, 16-18, 21, and 47 fluctuated between 4.83 to 12.9 ppm.
Evaluation of the alternative measures to ensure that water supplied to the SACWSD municipal system remains below the EPA drinking water standard of 10 ppm is underway.
Thus, a potential pathway of human exposure to groundwater contamination in excess of the federal drinking water standards exists for the users of the SACWSD municipal water system supplied by water finished by the Klein Water Treatment Plant. This pathway will become complete for the more than 30,000 users of this municipal water system if the levels of nitrate in groundwater in the Irondale/Western Plume Group continue to increase and the operators of the treatment facility cannot maintain the level of nitrate below the EPA MCL of 10 ppm.
Potential VHO contamination
A potential present and future pathway of human exposure to the contaminants of potential concern listed in Table 7 may exist for the people at the 10 or fewer residences or businesses in the Commerce City "EPA Study Area" south of 88th Avenue that continue to use private Alluvial Aquifer wells for domestic, tap water uses and for persons at residences that continue to use the Alluvial Aquifer wells for garden and lawn irrigation. Because current usage of those Alluvial Aquifer drinking water wells in the EPA Study Area is not verified, current exposure to contaminants cannot be verified and this pathway is relegated to a potential pathway of human exposure. The concentration of contaminants to which those people may be exposed is less than or equal to the maximum concentrations expressed in Table 8. The total duration of exposure for those people is unknown but may have begun as soon as occupancy was established in the area and may continue to the present time.
Because most, if not all, groundwater contamination found south of 88th Avenue is not from RMA sources this potential pathway will not be analyzed further in this Assessment.
Potential Denver Formation Aquifer Pathway
Contaminants have been identified in the confined aquifer zones of the Denver Formation, although contaminant plumes have not been delineated. The contaminants have been identified in Denver Formation monitoring wells drilled the area overlain by the Northern and First Creek paleochannels of the Northern Plume Group. Unlike the unconfined flow system, pathways in the confined flow system in this aquifer are difficult to identify and generally consist of fine-grained, highly-discontinuous sand lenses and lignites separated by fine-grained siltstones and claystones. Permeability and corresponding groundwater flow rates are significantly less than in the alluvium of the unconfined flow system (EBASCO, 1992, p. 2-30). Both upward and downward groundwater flow have been detected in monitoring wells penetrating the Denver Formation in the Offpost area immediately north of the NBCS and the RMA boundary (ESE, 1988, p. 3-45). This indicates that, at least locally, contaminants in the Alluvial Aquifer can migrate into the more permeable beds of the Denver Formation. The dominant horizontal groundwater flow direction in the Denver Aquifer is to the north-northwest (ESE, 1988, p. 3-35).
The compilation of previously collected data from 16 Denver Formation wells summarized in the RISR (EBASCO, 1992) indicates that the Denver Formation detections do not appear to be spatially related. However, confined flow system detections generally correspond spatially with plumes in the overlying unconfined flow system. These data suggest that, locally, contaminants migrate from the unconfined flow system to the confined flow system. The presence of detections at varying depths in the Denver Formation indicate that vertical migration of contaminants does occur within this aquifer. Although contamination has migrated from the unconfined flow system to the confined flow system within the Denver Formation, the degree and extent of confined flow system contamination, and its rate of migration, generally are substantially less than in the unconfined flow system. In isolated locations, however, contaminant concentrations in the confined flow system may approach or exceed those in the overlying unconfined flow system.
It was speculated (EBASCO, 1993, p. 2-31) that some organic compounds such as benzene could be naturally occurring compounds that have migrated from coal or hydrocarbon deposits located elsewhere in the Denver Formation.
Fourteen Offpost monitoring wells located north of the NBCS in section 13 and 14 (T2S, R67W) were sampled for the CMP during the Fall 1989 and Spring 1991 sampling rounds (see HLA, 1992b, Fig. 15). The organic compounds detected were benzene, chlorobenzene, chloroform, DIMP, DBCP, phenol, and 111TCE. The most frequently detected organics were DIMP (0.443-46.0 ppb; 26 % of samples collected), chloroform (0.631-1.30 ppb; less than 10 % of samples collected), and chlorobenzene (1.10-51.5 ppb; less than 10% of samples collected).
Pathway Summary - Denver Formation Confined Aquifer
Based upon the available data, contaminants, at levels of potential concern, have not been detected in Offpost Study Area, Denver Formation domestic wells. The geologic data compiled during the preparation of the Offpost RI (ESE, 1988, p. 3 - 34-48) infers that a very limited area of the Offpost Study Area, largely in the area surrounding the Offpost groundwater intercept and treatment facility (IRA-A) is potentially suitable for the development of a Denver Aquifer well. If any new wells are drilled in this area, it is likely that they would be drilled to the Arapahoe Aquifer to assure adequate water volumes for domestic use. Thus, no future Denver Aquifer wells are foreseen for the area.
A significant percentage of this area is currently owned by Shell Oil Company and subject to
their controls and the institutional control provisions of the Offpost ROD (HLA, 1995). Those
controls include the provision that will prevent the use of groundwater with contaminant levels
greater than the remediation goals adopted in the ROD. On this basis, no pathway of human
exposure is identified and it is very unlikely that a pathway of human exposure to groundwater
contaminants in the Denver Formation will be created in the future.
| Pathway Name | Compounds | Exposure Pathway Elements | Time | ||||
| Source | Media | Point of Exposure |
Route of Exposure |
Potentially Exposed Population |
|||
| ONPOST SURFACE SOILS AND SEDIMENTS |
Analyte Groups: * Onpost: Core - OSCHs, OPHGBs, OPHPs, OCPs, AS, BE, CU, PB * Onpost: Outer sections - OCPs, AS |
Onpost soils in the vicinity of: - South Plants - North Plants - Basins - Ditches, etc. |
Onpost
surface
soils & sediments |
Surface soils in the "Pink Zone" (see Fig. 10) |
Incidental ingestion, inhalation, and dermal exposure |
* Workers: - USFWS (~40 people) & Remediation workers * People recreating at RMA Refuge |
Present(?)
Future(?) |
| GROUNDWATER * Confined Denver Aquifer pathway * Irondale/Western |
* Denver Aquifer - VHOs - OPHGBs * Irondale/Western - VHOs - NIT |
* Offpost
groundwater in
Denver Fm. * Largely non-RMA sources |
Ground- water |
* unknown
wells * Pvt. wells in EPA SA & poss. Klein Plant |
Ingestion, inhalation, and dermal exposure | * Unknown
* <10 pvt. wells & poss. municipal water; ~30,000 people |
Present(?) Future(?) |
| AMBIENT AIR/ SOIL/DUST |
Analyte Groups: - VHOs - VAOs - OSCHs - OCPs - Anions/metals AS, CD, HG |
Windblown dust and volatiles generated during remediation measures | Air (?) | Unknown | Inhalation, Ingestion,& Dermal contact(?) |
*Workers: Onpost - USFWS & Remediation * People visiting Refuge |
Unknown |
| FOOD CHAIN | Analyte Groups: * Hunting - OCPs |
* Offpost hunting |
* Fish/ Wildlife -doves(?) |
* Hunting on nearby offpost areas | Ingestion | Unknown | Unknown |
Next Section Table of Contents
