PUBLIC HEALTH ASSESSMENT
ROCKY MOUNTAIN ARSENAL
ADAMS COUNTY, COLORADO
SUMMARY
The Rocky Mountain Arsenal (RMA) occupies 27 square miles in southern Adams County, Colorado, and lies approximately nine miles northeast of downtown Denver (Figure 1). RMA was established in 1942 and was used for the manufacture of chemical munitions. From the late 1940s to the early 1980s, some of the facilities were leased to private companies for the manufacture of industrial chemicals, primarily pesticides and herbicides. All production activities at RMA ceased in 1982 and now the Army's sole mission at RMA is to remediate contamination.
Industrial and waste disposal practices typical for the time were used by both the Army and lessees. Those practices resulted in contamination of soil, surface water, sediment, and groundwater. Groundwater monitoring conducted by the Army detected the presence of organic and inorganic chemicals in samples of off-site groundwater. As a result of that contamination, RMA was added to the National Priorities List (NPL), a list of sites requiring environmental cleanup, in 1987. The site is comprised of two Operable Units (OUs): Onpost and Offpost (Figure 2). The Offpost OU is defined as the media (groundwater in the Alluvial Aquifer) requiring remediation within the Offpost Study Area. The Offpost Study Area, also covering about 27 square miles, is defined as the area southeast of the Platte River, north of 80th Avenue, southwest of Second Creek, and north of the north and northwest boundaries of RMA.
The former Stapleton International Airport abuts the southwest corner of the site and the new Denver International Airport was developed on lands 3 to 9 miles to the east of RMA. Residential and commercial properties of Commerce City are located to the west and southwest of the site. Rural residential and agricultural lands are located to the north and east of the Arsenal. The Montbello residential area and light industrial areas are located to the south. The small community of Henderson lies four miles north of RMA.
Of the more than 750 different chemicals handled or generated at the Arsenal, more than 90 were chosen as target analytes for the remedial investigations, Onpost and Offpost. Onpost, the contamination is dispersed in structures, surficial soils, sediments, groundwater, surface water, and biota. Based upon soil contamination, a total of 181 contaminated sites have been identified Onpost. Generally, the highest detected concentrations of contaminants were measured in samples collected from soils, surface water, and groundwater in the central portion of RMA. The most concentrated plumes of contaminated groundwater occur in the Alluvial Aquifer beneath contaminated soils and former liquid waste disposal basins in the central, and to a lesser degree, in the western part of RMA. Contamination concentrations generally decrease as the groundwater plumes migrate toward the western, northwestern, and northern Arsenal boundaries. Groundwater contaminated with numerous volatile and semivolatile chemical compounds including organochlorine pesticides and organophosphorus compounds related to the manufacture of Army GB nerve agent, has migrated beyond the north and northwest boundaries, and has affected private drinking water wells.
Air quality measurements for a variety of contaminants have been performed since 1985. Contaminant detections in the air are generally lower in the Arsenal interior and are elevated near the RMA boundaries, especially at monitoring stations near population centers reflecting the influence of off-post contaminant sources. Groundwater and surface water data gathered near the southern and western boundaries also indicate that off-post sources have contributed to the surface water and groundwater contamination observed in those locations. Additionally, the data gathered on soil, groundwater, and air indicate that the areas south and east of RMA are not contaminated with RMA-related chemicals.
Beginning in 1978, the Army and Shell Oil Company began construction of a series of groundwater intercept and treatment facilities along the north and northwest RMA boundaries. Three of those facilities, the Irondale, Northwest, and North Boundary Containment Systems (BCSs), supplemented by additional, more recently constructed intercept systems Onpost and Offpost, have greatly minimized, and are eliminating Offpost groundwater contamination. In addition, a total of 14 Interim Response Actions (IRAs - comprised of more than 26 separate actions have been undertaken to control, reduce, prevent, or eliminate the potential for contaminant releases from the most important sources on the facility and to reduce or eliminate further contaminant migration and the potential for human exposure.
Beginning in September 1990, the Colorado Department of Public Health & Environment, in response to documented groundwater contamination in the Offpost Study area, began offering bottled water to any drinking water well user in the Offpost Study Area that was affected by diisopropylmethyl phosphonate (DIMP), an RMA-sourced groundwater contaminant. That bottled water program is ongoing and serves to minimize ingestion exposure to several RMA and non-RMA groundwater contaminants. As part of the final remedy, the Army and Shell Oil Company have agreed to continue the bottled water program within the DIMP footprint area (DIMP >0.392 ppb) until an alternate water supply is provided.
Provisions of the legally binding Federal Facility Agreement (FFA) for RMA require that: the U.S government would retain title to the Arsenal; residential development would be prohibited; wildlife habitat would be preserved and managed to protect endangered species; major site alterations would be prohibited; and consumption of fish and groundwater would be prohibited. The passage of the Rocky Mountain Arsenal National Wildlife Refuge Act of 1992 codified and further restricted and defined many of the current and future uses delineated in the FFA. The statute sets aside the majority of the Arsenal acreage as a unit of the National Wildlife Refuge System; mandates maximum fish and wildlife oriented public use; and imposes perpetual prohibitions on the use of the Arsenal for residential or industrial uses, the use of the groundwater under and surface water on the Arsenal as a source of potable water, the use of the Arsenal for fishing or hunting consumption, and the use of the Arsenal for agricultural purposes.
ATSDR's public health findings for RMA and communities surrounding the Arsenal to the north, northwest, east, south, and west are based on a review of past and present environmental data to identify present and future exposure pathways. In addition, community health concerns and health outcome data, including completed health studies and Health Investigations, were also reviewed in conjunction with established exposure pathways. Thus, exposure pathways that ATSDR has determined are of public health significance are identified in this assessment.
The Onpost land use controls and visitor restrictions provide mitigation or public health protection in addition to the IRAs and groundwater containment and treatment systems. This detailed mosaic of mitigation has eliminated many possible Onpost and Offpost pathways of human exposure to RMA contaminants. Surface soil data reviewed to date, show that no harm will come to those visitors who go on the guided tours or who do not stray off designated tour routes or out of the areas deemed safe for RMA visitors (referred to as "the white areas"). Therefore, given the existing level of Onpost controls and remediation, Onpost RMA is considered to be a No Apparent Public Health Hazard. Existing institutional controls and regulations are in place to assure that planned future remediation activities will be carried out in such a fashion so as to eliminate exposures of public health concern.
Because people residing in the Offpost Study Area to the north and northwest experienced past exposures to RMA contaminants via groundwater and air, the area may be considered a Public Health hazard in the past. However, the frequency, magnitude, and duration of those past exposures is unknown. If chronic ingestion occurred to the known levels of groundwater contaminants, adverse health effects were, or could be, possible. Many health studies and activities have been conducted because of past exposures from RMA. None of the health studies conducted thus far have shown an association between exposure to RMA contaminants and harmful health effects.
What remains, until completion of the planned final remediation measures, is a completed Offpost pathway of human exposure to non-RMA groundwater contaminants in private wells. In August 1996, there were eight Alluvial Aquifer wells and one Arapahoe Aquifer wells in the Offpost Study Area contain levels of lead that were of health concern. Earlier, in April 1994, there were an additional 14 Alluvial Aquifer drinking water wells in the Offpost Study area that contained levels of nitrate that were of health concern. However, the measured levels of nitrate in those drinking water wells continues to decline and data compiled August 1996 does not show elevated levels of nitrates in any drinking water wells in the Offpost Study Area.
RMA is not the source of those contaminants. The occurrence of nitrates is widespread in the area's groundwater, both upgradient and downgradient from RMA. The nitrate could be traced to many sources such as agricultural fertilizers, animal wastes, or private on-site sewage disposal systems. The lead in the water could be from several sources such as naturally occurring lead in the groundwater or lead contamination from plumbing.
The decision has been made to supply municipal water or an alternative water supply to the drinking water well owners within the DIMP "footprint area" (DIMP > 0.392 ppb). Consequently, of the wells of potential health concern due to lead contamination, only one well with lead contamination apparently does not qualify for connection to a replacement water supplies. If the lead contamination level remain elevated in this well, continued use of this well for drinking (including infant formula) and/or cooking may result in non-cancerous health effects in infants, children, adults, and pregnant women and their fetuses. That well contaminated by lead and any drinking water wells located outside the DIMP footprint area which any future monitoring may show sustained high levels of nitrate contamination are considered to be a present and potential future Public Health Hazard.
Off-post private wells to the west of RMA in the EPA Study Area (OU2) of Commerce City, including wells used by businesses, are considered to be an Indeterminate Public Health Hazard. A past and present pathway of human exposure to trichlorethylene (TCE) and other volatile halogenated organic compounds exists for individuals who work or reside in the EPA Study Area who have refused to be connected to the South Adams County Water and Sanitation District municipal water supply system and have continued to use their private wells. RMA is not the only source of groundwater contaminants in this pathway. In the past RMA contributed low-levels of TCE contamination to some municipal wells in the area but several other sources of contamination have also been identified. Data on those wells were collected in 1987 and 1989.
Five potential pathways of human exposure involving on- and off-site soils and air, off-site foodchain contamination, and groundwater in the Commerce City area were identified and evaluated. Data gathered, information compiled, and final remediation decisions made during the course of this assessment have resulted or will result in the partial or total elimination of four of those potential pathways.
Specific public health recommendations have been made to address the potential and completed pathways of exposure. Recommendations are made to eliminate exposure to groundwater contaminants in certain private drinking water wells; to gather more information on potentially affected drinking water wells; and to ensure that certain activities that may result in the creation of future pathways are precluded. In addition, a Public Health Action Plan has been developed which includes community and health professional health education focused on concerns relating to Offpost groundwater contamination, potential off-site air contamination during the final site cleanup, and assistance, as needed, to the ongoing U.S. Fish and Wildlife Service public use programs, including the wildlife bus tours.
Public health concerns were identified during ATSDR public availability meetings in communities surrounding RMA. Those concerns include: whether Offpost health effects would result from Onpost remediation; whether the Submerged Quench Incinerator would be used for non-RMA hazardous wastes; whether an excess of cancer exists for the Montbello area south of RMA; whether there were excesses of specific cancers (such as stomach cancer and breast cancer, for example) and if they could be associated with exposure to RMA contaminants; and whether diseases or health conditions such as lupus, diabetes, multiple chemical sensitivity, and learning disabilities are in excess and if they could be associated with exposure to RMA contaminants. For some of those specific concerns, the public health data bases are inadequate or do not exist to address the concern. For some of the health concerns, causes are not known, or other health concerns share some of the same risk or susceptible factors. However, considering the known risk factors for the health concerns expressed by local residents, past exposure to RMA contaminants has not been directly associated with the types of cancers or health concerns in question. The environmental data do not show that residents of the Montbello community have been exposed to RMA contaminants at levels that may result in adverse health effects. To date, none of the health studies conducted for off-site populations to the north and northwest of RMA have indicated that a relationship exists between environmental exposure to RMA contaminants and harmful health effects.
In summary, this Assessment represents an analysis of environmental and health information
relating to RMA and surrounding areas. Included are recommendations for public health actions
and a Public Health Action Plan for carrying them out.
BACKGROUND
The Agency for Toxic Substances and Disease Registry (ATSDR) has evaluated the public health significance of this site. More specifically, ATSDR has determined whether health effects are possible and has recommended actions to reduce or prevent possible health effects. ATSDR, in Atlanta, Georgia, is a federal agency within the U.S. Department of Health and Human Services and is authorized by the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) to conduct public health assessments at hazardous waste sites.
As the result of the detection of chemical contaminants possibly related to Rocky Mountain Arsenal (RMA) in off-post lands north and northwest of the Arsenal, the Army initiated a hydrogeologic surveillance program of more than 100 on- and off-post wells and surface water stations in 1974. That program has since expanded to include, in 1994, annual or biannual monitoring of more that 100 off-post domestic wells and more than 800 on- and off-post monitoring wells. Extensive environmental investigations were also implemented to evaluate possible contamination of other environmental media such as surface water, soil, air, sediments, and biota. An administrative record containing more that 1.5 million pages has been compiled that documents the investigations of on- and off-post contamination, the decisions made to minimize or to eliminate human exposure to those contaminants, and actions implemented to cleanup RMA.
Because of the extensive, 20-year history of investigation and cleanup efforts at RMA, the Background section of this public health Assessment will summarize not only the historical and environmental setting, but also the rationale and results of previous Interim Response Actions (IRAs) taken to minimize or eliminate potential or completed pathways of human exposure to contaminants. The Pathways Analysis section of this Assessment will then focus upon the possible present and future pathways of human exposure to contaminants. In so doing, ATSDR's assessment of the public health implications of RMA contaminants is then similarly focused upon the possible present and future health effects that may arise from existing and foreseeable future human uses of the facility and the adjacent off-post lands. The Health Outcome Data section will discuss the purpose, conclusion, and status of numerous site-specific health activities and investigations that have been completed or are still in progress.
Also incorporated in this Assessment is a discussion of off-site contamination arising from other nearby sites including other CERCLA sites. This information is included because, for many years, RMA was mistakenly thought to be the sole source of contamination found west of the Arsenal, and because some public health concerns relating to this off-site contamination are incorrectly attributed to the Arsenal.
Location
The Rocky Mountain Arsenal (RMA) is a 27-square-mile (sq mi) U.S. Army facility situated nine miles northeast of Denver, Colorado, that was formerly used for the production of munitions, chemical warfare agents, industrial chemicals, and agricultural chemicals (Figure 1). RMA in its entirety has been listed (Cerclis Number CO5210020769, 1987) on the National Priorities List (NPL) of hazardous waste sites designated for long-term remedial evaluation and response. RMA is comprised of two Operable Units (OUs): Onpost and Offpost (Figure 2). The Onpost OU encompasses the entire area within the RMA boundaries and the Offpost OU lies within the Offpost Study Area and is comprised of the lands shaded in Figure 2.
RMA history is summarized here to explain activities and events that contributed to the documented contamination of RMA. Subsequent paragraphs summarize the military operations, industrial operations, and waste disposal operations that have occurred at RMA. For further information, the reader is referred to the Remedial Investigation Summary Report (EBASCO, 1992) for a summary of almost two decades of environmental investigations, remediation, and cleanup efforts in the Onpost area.
History
The U.S. Army established RMA in 1942 to manufacture chemical warfare agents and agent-filled munitions and to produce incendiary munitions for use in World War II. Initial facility building activities included: construction of the South Plants manufacturing complex; extension of what are now known as the Union Pacific and Burlington railway systems onto RMA; construction of a railway classification yard and service and maintenance facilities in Sections 3 and 4; modifications to preexisting irrigation reservoirs (Lake Ladora, Lower Derby Lake) and construction of a new reservoir (Upper Derby Lake) to supply the South Plants complex with process cooling water; and construction of three seepage ponds in a large earthen depression in Section 36 (which eventually overflowed to form Basin A for the disposal of liquid industrial wastes). Prior to this date, the area was largely undeveloped ranch and farm land (EBASCO, 1992, p. 1-20). A map illustrating the Onpost OU features and facilities of RMA is given in Figure 3.
From the late 1940s to the early 1980s, portions of the South Plants manufacturing complex were leased to private industry for the production of industrial chemicals, primarily pesticides and herbicides. The conversion to pesticide production was a logical step in the transition to a peace-time economy because the organic insecticides as a group were discovered during the World War II era and some (e.g., organophosphate insecticides - OPHPs) were discovered in the chemical warfare laboratories of World War II. Records have been located of nine companies that conducted manufacturing or processing operations in the South Plants (see Fig. 3) between 1946 and 1982, when all manufacturing operations in the South Plants ceased. The first major lessee of facilities in the South Plants was Julius Hyman and Company (1947-1954). The second major lessee, Shell Chemical Corporation, a division of Shell Oil Company, purchased the stock of Hyman and in 1954 Hyman was merged into Shell. Shell continued to produce agricultural chemical at the Arsenal until 1982 (EBASCO, 1992, p 1-25; Shell, 1995).
During the history of RMA, both solid and liquid waste stream handling procedures were developed and modified along with the various military and industrial operations. Wastes from a variety of chemical manufacturing, munitions production, testing, and demilitarization activities, off-post sources, shipping and handling procedures, and associated operations were generated and disposed in various manners. In addition to normal waste disposal, wastes, feedstock, and product chemicals have been inadvertently discharged into the RMA environment via accidental spills, which have occurred throughout RMA history. Spills have been associated with both military and industrial activities, and have occurred particularly in the South Plants, North Plants, railyard, motor pool, and toxic storage yard areas (EBASCO, 1992, p. 1-32). Some of these wastes, their residues and byproducts, and wastes from ancillary activities associated with the operation and maintenance of RMA ultimately found their way into the soils, water, air, and biota (EBASCO, 1992, p. 1-28). Groundwater monitoring programs conducted by the Army have reported the presence of organic and inorganic chemicals in samples of off-site groundwater.
The Rocky Mountain Arsenal (RMA), added to the National Priorities List (NPL) in 1987, is comprised of two Operable Units (OUs): Onpost and Offpost. The Offpost OU is defined as the media requiring remediation within the RMA Offpost Study Area (EPA, 1989). The environmental setting of those OUs, the Offpost Study Area, and other areas adjacent to RMA is given in detail in the Remedial Investigation Summary Report (EBASCO, 1992, Appendix A) and the Offpost Operable Unit Endangerment Assessment/Feasibility Study (HLA, 1992b, p. 1-2 - 1-5) and is summarized in this section.
Site topography and drainage
The RMA Onpost OU covers 27 sq mi in western Adams County, CO, approximately 9 miles northeast of downtown Denver (see Figure 1). The Arsenal is located at the western edge of the Colorado high plains, near the foothills of the Rocky Mountains. It occupies an area of rolling terrain characterized by grasslands, shrublands, wetlands, aquatic habitats, and extensive disturbed and weedy areas. These habitats supports a variety of plants and wildlife species. The elevation above mean sea level ranges from 5,330 feet (ft) at the southeastern boundary of RMA to approximately 5,110 ft at the northwestern boundary. Maximum local relief on the Arsenal is about 200 ft.
The topography of the RMA Offpost Study Area (also covering about 27 sq mi) is similar to RMA and consists of stream-valley lowlands separated by gently rolling uplands. The elevation within the Offpost Study Area ranges from 5,110 ft along the RMA northwestern boundary to 5,030 ft at the South Platte River. The maximum topographic relief of the area is about 300 ft.
Regional surface drainage of the uplands is towards the northwest into the northeast-flowing South Platte River. The valley of the South Platte river lies along the northwest boundary of the Offpost Study Area and parallel to the northwest boundary of RMA. Surface waters originating south of RMA, on RMA, or in the Offpost Study Area flows towards the South Platte River. Two major canals (see Figure 2), O'Brian Canal and Burlington Ditch, and several smaller irrigation ditches flow from southwest to northeast between RMA and the South Platte River. O'Brian Canal receives some surface water drainage from the Offpost OU and RMA where the canal intercepts First Creek. Burlington Ditch may also receive surface water infrequently from the First Creek. For more information on the drainage and landform features of the RMA area the reader is directed to EBASCO (1992, p. A1-1).
Meteorology and climatology
Climatic data from the former Stapleton International Airport which adjoins RMA on the southwestern corner are used to describe the meteorologic characteristics of RMA (EBASCO, 1992, p. A1-2). The area is generally classified as semi-arid and is characterized by low relative humidity, abundant sunshine, relatively low precipitation (averages 15 inches annually), moderate to high wind speed, and a wide daily range in temperature. Fluctuations of 20° to 35°F may occur in just a few hours during the winter due to warm, high-intensity "chinook" winds caused by air masses descending along the front of the Rocky Mountains.
RMA wind data for 1975-1979 is presented in the form of a "wind rose" in Figure 4. The length of the bars indicates the percent of time that the wind blows from each of the indicated directions and the patterned segments along each bar indicate the relative frequency of each wind speed class. The figure shows that the prevailing winds blow from the south and the south-southwest to the north and north-northeast. Mean wind speed is 9 miles per hour (mph). In the summer, the strongest winds are associated with thunderstorms. In other seasons, the strongest winds are generally from the northwest quadrant and are the downslope "chinook" winds. The highest windspeed recorded as a one-minute average was 65 mph from the west.
Surficial Soils
The soils of RMA were originally mapped by the U. S. Department of Agriculture, Soil Conservation Service. Additional mapping and textural characterization was then completed as part of the remedial investigation. Those investigations delineated clay-rich soils located generally in the northeast third of RMA and in lowlands along stream channels and sandy, clay-poor soils in the southwestern two-thirds portion of RMA in areas generally surrounding the major Arsenal facilities. For additional information on the soils of RMA, the reader is referred to EBASCO (1992, p. A1-4).
Alluvium and Eolian Deposits
The land surface of nearly all of RMA and adjacent areas is mantled by eolian (wind blown) deposits and unconsolidated Quaternary alluvium (transported by water) that may locally reach thicknesses of up to 130 ft (EBASCO, 1992, p. A1-6). The older alluvial deposits tend to be coarser-grained than the younger (topographically lower and usually closer to stream/river channel) terrace deposits. Those older surficial deposits also generally coarsen westward. By their nature, these alluvial and eolian deposits are varied and heterogenous in character and display little lateral continuity. The base of these alluvial and eolian deposits lies on the irregular erosional surface of the underlying bedrock formation, the Denver Formation.
Alluvium - Bedrock Contact
The contact between the alluvial deposits and the underlying Denver Formation bedrock is irregular but distinct. The coarser sandy and gravelly alluvium contrasts sharply with the much finer grained sandstones, siltstones, and claystones of the Denver Formation. The bedrock surface is locally weathered and varies from granular material to more lithified, compact material that is fractured and jointed over a depth interval of less than 5 ft. The contact is irregular because deep paleochannels were incised in the bedrock surface and subsequently infilled with coarse-grained alluvium (ESE, 1988; EBASCO, 1992, p. A1-6). Those north to northwest-trending paleochannels facilitate groundwater migration and largely control the direction and rate of movement of groundwater contaminant plumes at RMA and in the Offpost Study Area (EBASCO, 1992, p. A1-7).
Denver and Arapahoe Formations
The Denver Formation consists of 250 to 500 ft of interbedded sandstone, siltstone, claystone, and lignite that dip or are inclined ½ to 1° to the southeast. Within the Denver Formation beds of more permeable sandstone and lignite collectively comprise what is termed the Denver aquifer. These beds are locally confined above and below by relatively impermeable shales or claystones. The Denver Formation is separated from the underlying Arapahoe Formation by a 30- to 50-ft-thick, relatively impermeable claystone interval known locally as the "buffer zone" (EBASCO, 1992, p. A1-7). North of RMA near the South Platte River in the Offpost Study Area, the Denver formation is locally absent and the alluvial deposits lie directly on the Arapahoe Formation (ESE, 1988, p. 3-46).
Surface Water and Groundwater Hydrology
Surface Water
The local slope of the land surface is to the northwest and the streams draining the Arsenal and the adjacent off-post areas flow generally in that direction until they become tributary to the South Fork of the Platte River. The South Platte follows a northeasterly course and numerous irrigation canals, ditches, and laterals have been dug subparalleling the course of the river. A few of those northeast flowing diversion or irrigation structures cross the Arsenal and several more cross the off-post lands to the northwest and north of the Arsenal (see EBASCO, 1992, Fig. A1.5-1).
Five principal drainage basins and three smaller subcatchments are recognized within RMA and include the First Creek, Irondale Gulch, South Platte River, Sand Creek, and Second Creek Drainage Basins, and the Basin A, Basin F, and Sand Creek Lateral subcatchments. Located within the southern half of the Arsenal, on the southern edge of the South Plants, are five lakes: Lake Mary, Ladore Lake, Rod & Gun Club Pond, and Upper and Lower Derby Lakes. Closer to the southern boundary of RMA are three small ponds that receive surface runoff from the Havana Street area.
Streamflow at RMA is highly variable. Seasonal variations in stream discharge are usually greater than average variations between years and are strongly affected by the amount of urban runoff, released or diverted flows, and precipitation duration and intensity. Streams on RMA are generally intermittent and the highest flows usually occur during spring runoff and during major storms (EBASCO, 1992, p. A1-10).
Until completion of the new zero-discharge Sewage Treatment Plant in March 1994, effluent from the original RMA Sewage Treatment Plant entered First Creek in Section 24 (Stollar, 1990).
Groundwater
The two principal water-bearing units underlying the Arsenal and the adjacent off-post areas that have been, to varying degrees, affected by contaminants originating at RMA are the unconsolidated alluvial and eolian deposits and the underlying Denver Formation. Isolated occurrences of a few contaminants in wells drilled to the deeper Arapahoe Formation probably represent localized leakage of contaminants to that aquifer (HLA, 1992b, p. I-4). The hydraulic properties of the alluvial aquifer are distinct from the deeper aquifers in the Denver and Arapahoe Formations.
Groundwater flow occurring within the alluvium and uppermost, weathered part of the Denver Formation has been designated the "unconfined flow system" in the remedial investigations reports prepared for RMA (EBASCO, 1992, p. A1-8; HLA, 1992a). Within the Denver Formation, the series of strata that comprise the Denver aquifer have, for the purposes of the remedial investigations, been designated the "confined flow system" (EBASCO, 1992, p. A1-8). Depending on site-specific hydrologic characteristics, varying degrees of hydraulic interchange are possible between surface water and the unconfined flow system and between the unconfined and confined flow systems. The available data indicates that local areas of contaminant leakage into the Denver and Arapahoe confined aquifers are due to damaged wells or poor well construction.
The presence of paleochannels in the Denver Formation surface has an impact on the groundwater flow in the unconfined flow system. Coarse, unconsolidated sands and gravels commonly found in those channels provide for preferential groundwater flow within the alluvial aquifer. The identified groundwater contaminant plumes that have migrated across RMA boundaries to off-site localities are generally confined to those paleochannels. Two such paleochannels, the First Creek and Northern paleochannels, are intercepted by and continue north of the RMA North Boundary Containment System. Before groundwater flow in those paleochannels passes beneath the O'Brian Canal and the nearby Burlington Ditch, the groundwater is again intercepted and treated by the treatment system constructed north of RMA.
An additional paleochannel, the Northwest paleochannel, is intercepted by and continues west of the RMA Northwest Boundary Containment System (HLA, 1992b, p. I-3). A complex system of north and northwest-flowing paleochannels underlying the western portion of RMA collect groundwater flow from industrial and commercial areas lying south of RMA and from the western and southern portions of RMA. Although the areal extent and thickness of the saturated alluvium is greater in the western portion of RMA than in the northern paleochannels, the flow of the identified groundwater plumes arising from the interior of RMA are intercepted by the Irondale Boundary Containment System (and to a lesser extent the North and Northwest Boundary Containment Systems) where water is pumped, treated, and reinjected before flow continues northwestward to the South Platte River. Data collected from monitoring wells installed in the western portion of RMA support this conclusion (Shell, 1993).
Unconfined Flow System
The unconfined flow system includes saturated alluvium, eolian deposits, and the permeable, weathered alluvium - bedrock contact. Impermeable clay zones in the Denver Formation occur at the base of the unconfined flow system, except near the South Platte River where the weathered upper portion of the Arapahoe Formation directly underlies the alluvial deposits (HLA, 1992b, p. I-4). The saturated thickness of the unconfined alluvial aquifer ranges from 0 ft to a maximum of approximately 70 ft (EBASCO, 1992, Figure A1.5-4). Horizontal hydraulic conductivity estimates from aquifer tests range from 0.3 ft/day in the weathered bedrock - alluvium contact zone to greater than 900 ft/day in alluvial terrace gravels (EBASCO, 1992, p. A1-12). In the Offpost Study Area near the North Boundary Containment System, estimates of average linear flow rates for groundwater range from 1.5 to 10 ft/day. Near the Northwest Boundary Containment System the estimated average linear flow rates for groundwater are from 5.5 to 22.5 ft/day (ESE, 1988, p. 3-31).
Seasonal water table fluctuations at RMA generally average 1 to 3 ft. Fluctuations in the water table elevations are artificially induced by the Irondale, Northwest Boundary, North Boundary, and Offpost Groundwater Intercept and Treatment facilities and near the western RMA boundary, where the water table drops about 11 ft during the summer due to withdrawal of water from nearby Adams County wells.
Maps showing the elevation of the water table (potentiometric maps) disclose that the groundwater beneath RMA and adjacent areas is flowing north and northwest (EBASCO, 1992, p. A1-12; HLA, 1992b, p. I-4). Local exceptions to this general flow pattern exist near the lakes in the southern part of RMA. The South Platte River is interpreted as the regional discharge point for the unconfined flow system in this area.
Recharge to the unconfined flow system occurs as infiltration of precipitation, seepage from lakes, reservoirs, streams, canals, and buried pipelines, and flow from the underlying confined aquifer system. Locally, groundwater may also leak between the unconfined and confined flow systems when: 1) the permeable sands of the Denver or Arapahoe are in contact with the Alluvial Aquifer (beneath and north of RMA); 2) poorly constructed wells allow water to migrate along the annulus between the casing and the well bore; or 3) the well casing has been perforated both in the unconfined and the confined flow systems.
Mass balance calculations have been used to estimate the rates of surface water - groundwater interchange between the lakes and basins and the unconfined flow system. Results indicate that Lower Derby Lake, Havana Pond, and Basin C are areas of groundwater recharge, whereas Lake Ladora, Lake Mary, and Basin A receive groundwater in upgradient areas and lose it in downgradient areas. Recharge - discharge relationships at Upper Derby Lake are dependant upon lake level, and all streams, canals, ditches, laterals and interceptors lose water to groundwater during the course of the year. Actual recharge or discharge rates vary substantially in response to stream stage and aquifer head (HLA, 1992b, p. I-4; EBASCO, 1992, p. A1-13).
On the basis of an evaluation of the distribution of contaminant plumes at RMA and adjacent areas, including the Offpost Study Area, the unconfined flow system is considered the principal migration route for groundwater contaminants to off-post areas (HLA, 1992b, p. I-4).
Many shallow water wells have been developed in the alluvial deposits underlying areas west and north of RMA. Contamination of RMA and other non-RMA sources has affected many of those wells but the combined effects of groundwater intercept and treatment systems, drilling replacement wells, and supplying bottled water has eliminated the use of individual domestic wells for drinking water supplies in the most contaminated areas.(1) There are, however, many small domestic irrigation wells and high-yield commercial irrigation wells that continue to produce water from the alluvium. Some of those wells are affected by contamination.
Many of the Commerce City water wells which supply water to the South Adams County Water and Sanitation District (SACWSD) - Klein Water Treatment plant are developed in the alluvial deposits and are contaminated by Trichloroethene which has emanated from source areas in western RMA and off-site sources to the south and southwest of RMA. Other contaminants detected in the alluvial aquifer, upgradient to the SACWSD wells include 1,1-Dichloroethene, 1,1-Dichloroethane, cis-1,2-Dichloroethene, 1,1,1-Trichloroethane, Tetrachloroethene, Dibromochloromethane, Trichlorofluromethane, Vinyl Chloride, and Chloroethane), but the state-of-the-art Klein Water Treatment Plant was specifically designed to remove this contamination (James D. Jones, SACWSD, 1993, personal communication).
Off-post groundwater contamination is discussed in greater detail later in this Assessment.
Confined Flow System
The confined flow system within the Denver Formation consists of strata collectively referred to as the Denver aquifer, where water-bearing sandstones, siltstones, and lignite horizons are interbedded and confined from above and below by relatively impermeable shales or claystones. The confining effect of the impermeable beds and the upgradient, off-post recharge of the Denver aquifer from uplands south and east of RMA produces artesian conditions in much of the aquifer beneath RMA and nearby areas. The individual sandy layers are commonly lense-shaped and range in thickness from a few inches to as much as 50 ft. Adjacent sand zones within the confined flow system may be interconnected and linear flow rates of 0.03 to 4 ft/day have been measured (EBASCO, 1992, p. A1-14).
The lower portion of the Arapahoe Formation is comprised of more permeable, water-bearing sandstones and conglomerate beds that are separated from the overlying Denver Formation by a relatively impermeable claystone and clay shale "buffer zone" reported to range from 30 to 100 feet in thickness. Water-level data collected from three Arapahoe Formation wells indicate that the formation is also a confined aquifer.
Data collected for the off-post Remedial Investigation indicate that groundwater migration in the Denver aquifer has a northerly to northwesterly regional groundwater flow direction (HLA, 1992b, p. I-5; ESE, 1988, p. 3-35). Based upon limited data it appears that locally, water in the Arapahoe aquifer moves west beneath RMA and then north or south in response to the hydraulic gradients induced by pumping (ESE, 1988, p. 3-47).
Environmental Investigations and Controls
General
In 1974, the Army established a Contamination Control Program at RMA to ensure compliance with federal environmental laws, including the National Environmental Policy Act of 1969 and the Federal Executive Order 11507 of February 1970, which directed federal installations to refrain from polluting the groundwater through the discharge of wastes, and further directed these installations to prepare air and water pollution abatement projects (EBASCO, 1992, p. 1-33-34). Since that time, numerous investigations have identified potential and actual sites of contamination and characterized/evaluated pathways by which contaminants could migrate into the environment Onpost and Offpost of RMA.
Onpost Operable Unit
The Remedial Investigation (RI) at RMA was initiated in October 1984 to develop a database and formulate conclusions regarding the nature and extent of contamination at RMA sufficient to assess the human health and environmental effects of contaminant exposure and to aid in evaluating remedial alternatives (EBASCO, 1992, p. 1-1, 2-1). Numerous studies have been conducted and reports prepared for the Onpost RI. Generally, those reports are organized and reported by the Study Areas.
The results of the Onpost RI have been published previously in 124 Contamination Assessment Reports (CARs), 2 Data Presentation Reports, and 90 Phase II Data Addendum Reports prepared for each potential hazardous waste site and for each nonsource area (the balance of each square-mile section on post not considered likely to contain contaminant sites); 4 media reports, prepared for the water, structures, air, and biota; and 7 Study Area Reports (SARs), prepared for each geographical study area at RMA (Southern Study Area, Eastern Study Area, South Plants Study Area, North Plants Study Area, Central Study Area, North Central Study Area, and Western Study Area) with primary emphasis on the soils/sewers environmental media (EBASCO, 1992, p. 1-1). The Onpost OU was subdivided into seven separate study areas (see Ebasco, 1992, Fig. 1.2-3) because of the size, geographic diversity, and varied land use history of RMA. Each SAR was compiled from RI media reports and pertinent CARs (EBASCO, 1992, p. 1-18).
During the course of the on-site RI, which represents more than 15 years of investigative
effort, he following numbers of samples, as of 1994, had been collected:
| Medium | Sampling Locations | Number of Samples |
| Soils Surface Water Groundwater Structures Air Biota |
4,015 bores, 39 nonbore 27 locations 619 wells 110 locations 13 stations 96 locations |
9,692 297 1,982 151 886 494 |
Samples were analyzed for as many as 90 target analytes and were screened for thousands of nontarget organic analytes. Volatile and semivolatile organics were analyzed using gas chromatography and gas chromatography/mass spectrometry (GC/MS) techniques, metals by atomic absorption techniques, Army chemical warfare agents by specialized instruments and techniques, and rocket fuels and breakdown products by high pressure liquid chromatography, GC/MS, and spectrophotometry techniques (EBASCO, 1992, p. xxxv, xxxvi).
A vast amount of new information was obtained during the RI regarding the location of contaminated sites, boundaries of groundwater contaminant plumes, the identity of the contaminants found in these locations, and contaminant concentrations. The results obtained are generally consistent with those of earlier studies and tend to validate previous understandings of the general location of plumes and sites, the identification of major contaminants, and the magnitude of contamination.
The identification of 178 designated sites of soil contamination (see EBASCO, 1992, Fig. 2.1-1; not reproduced here because of map scale and complexity) is a major result of the Onpost RI. Those sites range from areas of several hundred acres with multiple contaminant occurrences at concentrations up to a few parts per hundred (or thousands of parts per million - ppm), to isolated occurrences of single analytes at a few parts per billion (ppb; EBASCO, 1992, p. 2-1). As a result of special investigations conducted after the SARs were completed, generally low-level organochlorine pesticide (OCP) contamination (0.002 to ~ 4 ppm outside designated sites) was identified in the surficial soils (0- to 2-inch depth interval) throughout most of RMA.
Contaminated Sites and Interim Response Actions
Several high-priority areas have been identified and have been or are now being addressed by Interim Response Actions (IRAs)(2) and other contaminant mitigation measures such as Boundary Containment Systems (BCSs)(3) . Those actions are discussed in greater detail in subsequent portions of this section of the Assessment.
Table 1 gives a generalized summary of the 178 soil-contamination sites by site type/location and identifies what IRAs or BCSs have been implemented, if any, to mitigate or eliminate threats to the environment while remaining consistent with the long-term, comprehensive cleanup goals at the Arsenal. It should be emphasized that the distribution of contaminants in surface and subsurface soils is typically irregular because of variations in the behavior of the chemicals in the pore space and heterogenous nature of the soil matrix (EBASCO, 1992, p. 2-3, 2-10).
Contamination was detected in soils, ditches, stream and lakebed sediments, sewers, groundwater, surface water, biota, structures, and, although to a much lesser extent, air. Soil and alluvial aquifer materials in the central and northern portions of RMA contain most of the contaminant sources. Less extensive or less concentrated sources occur only sporadically within the relatively uncontaminated buffer zone along the eastern, southern, and western boundaries. The most highly-contaminated sites (highest concentrations and/or greatest variety of contaminants) are concentrated in the central manufacturing, transport, and waste disposal areas. The greatest contaminant concentrations and distributions tend to occur in the upper 5 feet of the soil column, although exceptions are noted, particularly in the case of waste burial trenches and leaks from subsurface structures. In general, contaminant distribution is influenced primarily by the physical and chemical properties governing contaminant behavior, by soil type, and by former manufacturing and disposal practices (EBASCO, 1992, p. 2-10).
It was concluded in the RI that the principal contaminants at RMA are pesticides, metals, Army nerve-agent degradation products, and chlorinated or aromatic solvents. Contamination in soils and groundwater is dominated by relatively mobile volatile compounds (volatile halogenated organics, volatile hydrocarbon compounds, and volatile aromatic organics) and less mobile contaminants, principally organochlorine pesticides and arsenic, which were detected over widespread areas at low to high concentrations (EBASCO, 1992, p. 2-12).
Table 1 - Contaminated Sites and Interim Response Actions
(after EBASCO, 1992)(4).
| Site types | Site description A | Potentially affected media B | IRA or Boundary Control System (BCS) to mitigate or control (see Table 3 for further definition) |
| Basins & Lagoons | A total of 14 sites located in the SP and NC Study Areas and ranging from relatively small sites of limited contamination to the large disposal basins A, B, C, D, E, & F used variously from 1943-81. | SS, SW, GW, A, & B | - North and Northwest BCSs -IRAs A, B, C, E, F, H, I, J, K, & L |
| Ditches, Lakes, & Ponds | A total of 36 sites located in the S, E, SP, NP, NC, & W Study Areas. Sites include: Upper & Lower Derby Lakes, Rod & Gun Club Pond, Lake Ladora, Lake Mary, Havana/Peoria Street Ponds, Sand Creek Lateral, North Bog, miscellaneous drainage ditches known or inferred to contain process water of runoff, ditches between or draining contaminant basins, and the sewage treatment plant area. | SS, SD, SW, GW, A, & B | - North, Irondale, & Northwest BCSs - IRAs A, B, C, E, H, & I Additional actions taken include: - Dredging and burial of lakebed sediments - Termination of South Plants manufacturing processes - Discontinued use of the ditch system |
| Ordnance Testing & Disposal Sites | A total of 12 sites located in the E & C Study Areas. Sites include: surface burns and burn pits; disposal trenches; detonation, impact, & test sites, buildings used for testing sites ; and an incinerator used to destroy mines. | SS, SW, GW, & A | - IRA L |
| Solid Waste Burial Sites | A total of 18 sites located in the S, E, SP, C, NP, & W Study Areas. Sites include: dredged and buried lake sediments; sanitary landfills & trash pits, disposal pits & trenches for pesticides, chemical wastes, & munitions. | SS, GW, & A | - IRA L |
| Storage Sites, Buildings, & Equipment | A total of 25 sites located in the S, E, SP, NP, C, & W Study Areas. Sites include: storage yards for incendiary and agent filled bombs; trash dumps; processing and demilitarization areas; areas around tank farms and storage tanks; salvage yards; and a septic tank system. | SS, SW, & GW | - IRAs G, K, & L |
| Spill Sites | A total of 14 sites located in the E, NP, NC, & W Study Areas. Sites include: a rail loading area, drum storage areas, isolated surface and subsurface chemical and fuel spills, and a sanitary sewer overflow area. | SS & GW | - North, Irondale, & Northwest BCSs - IRAs A & L |
| Sewer Systems | A total of 10 sites located along sewer lines located in the SP, NP, C, NC, & W Study Areas. Sites are: sanitary & chemical sewers; process water lines; and a deep disposal well. | SS & GW | - IRA J |
| Windblown Contamination of Surface Soils | A total of 11 areas of contaminated surface soils adjacent to other contaminant sources in the SP, C, & NC Study Areas. Locations are known or inferred contamination sites attributed to wind and/or surface water transportation. | SS, SW, GW, A, & B | - IRA I |
| Isolated Contamination | A total of 38 isolated detections of contaminants in soils located in the S, E, NP, NC, & W Study Areas. Sites consist of isolated detections of usually one contaminant. | SS | - None Conducted Nor Planned |
A- The location codes given in the Site Description column refer to the 7 Study Areas established at RMA (see Fig. 4). Those Study Areas are: S - Southern Study Area, E - Eastern Study Area, SP - South Plants Study Area, NP - North Plants Study Area, C - Central Study Area, NC - North Central Study Area, and W - Western Study Area.
B - Media codes used in this column are: SS - Surface Soil, SD
- Sediment, SW - Surface Water, GW - Groundwater, A - Air, and B - Biota.
The reader will find detailed descriptions, by site type of the extent, thickness, or volume; the relative importance; the character of contaminants; and the environmental media possibly affected by those contaminants given in EBASCO (1992, pp. 2-12 - 2-23). The existent or possible avenues of migration of those contaminants are also described.
Interim Response Actions (IRAs)
Throughout the course of the RMA cleanup program, the Army, Shell, and EPA have taken a proactive approach to mitigation of conditions that may result in a serious health threat. Among the first actions taken were the installation of the three boundary groundwater containment and treatment systems. The boundary containment systems (BCSs) have been supplemented, to date, with 14 Interim Response Actions (IRAs, comprised of 26 separate actions) initiated to mitigate conditions of contamination which pose an immediate threat to human health and the environment. The purpose of the IRAs is to proceed with actions, based on the findings of the RI or other investigations, considered "necessary and appropriate" for implementation prior to the final remedial decisions. These actions are designed to control, reduce, prevent, or eliminate the potential for contaminant releases from the most important sources on the facility, and reduce or eliminate further contaminant migration and the potential for human exposure, both on and off the installation. Actions requiring removal of material are designed to be in accordance with CERCLA regulations and are to be consistent with and contribute to the efficient performance of the final response actions for the Onpost and Offpost OUs. Table 2 presents a complete list of the IRAs and related actions, their objectives, and status (RMA, 1991, p. 23; EPA, 1992a).
Of the IRAs completed or undertaken, the one that has perhaps attracted more public attention than any of the others is the Basin F IRA. This IRA was designed to remediate one of the most highly-contaminated sites at RMA. This IRA was initiated in 1988, and the removal and containment phase of the action was completed in 1989. About 10.5 million gallons of highly contaminated liquid and 564,000 cubic yards of sludges and contaminated soils were removed, stabilized, and contained in tanks, double-lined ponds, and a double-lined and clay-capped waste pile. Leachate control systems were part of these new structures and comprehensive air quality monitoring was conducted during and following completion of this phase of the action (RMA, 1991, p. 23). This IRA and the destruction of the Basin F liquids in the Submerged Quench Incinerator (SQI) will be discussed in greater detail in subsequent sections of this Assessment.
Groundwater Treatment Systems That Affect Offpost Areas
Three major containment/treatment systems, the Irondale Containment System (ICS), the North Boundary Containment System (NBCS), and the Northwest Boundary Containment System (NWBCS), have been installed at the RMA boundaries to control the migration of contaminants to offpost areas (see Table 2). All three of the systems are currently in operation to intercept and treat contaminated groundwater in the alluvial aquifer (unconfined flow system) and to recharge the treated water. In addition to the boundary control systems, a groundwater intercept and treatment system north of RMA (Groundwater Intercept and Treatment System North of RMA (IRA-A) was completed in 1993 to provide remediation of the highest concentrations of contaminants in the alluvial groundwater in the Offpost Study Area (HLA, 1992b, p. I-21). Additional groundwater intercept systems installed to increase the effectiveness of the BCSs were the Motor Pool/Railyard system, the Basin F system, and Basin A Neck system.
Irondale Containment System (ICS)
The ICS is located at the southern end of the RMA northwest boundary within Section 33 (see Fig. 3 and Table 2) and consists of a groundwater intercept system and a carbon treatment system to remove DBCP and TCE. Constructed by Shell Oil Company, the ICS became operational in 1981. The ICS is supplemented by additional extraction wells of the Motor Pool/Railyard Intercept System constructed in the western portion of RMA (sec. 3, T2S, R67W). A portion of the area downgradient of the ICS is contained within the EPA Commerce City study area to the west and northwest of RMA, although the majority of the downgradient area is within the confines of the RMA Offpost Study Area. A review of monitoring data downgradient of the ICS shows contaminant concentrations to be low and attributable to the sources of contamination within the EPA off-post study area and RMA. Details of the EPA off-post study area are given later in this section.
Although not part of the ICS, the actions taken by the Army to remove trichloroethene (TRCLE or TCE) from the water supplies of nearby Commerce City residents, including construction of the Klein Water Treatment Plant in 1989 were actions taken to eliminate human exposure to groundwater contaminants west of RMA regardless of the source.
North Boundary Containment System (NBCS)
The NBCS is located just south of the RMA north boundary in Sections 23 and 24 (see Fig. 3
and Table 2). The NBCS consists of a system of dewatering wells with contaminated
groundwater from the unconfined flow system, a soil-bentonite barrier to separate contaminated
and treated groundwater and to impede offpost migration of contaminated groundwater, a
carbon-adsorption treatment system to remove organic contaminants, and a system of recharge
wells and trenches to return treated groundwater to the alluvial aquifer (HLA, 1992b, p. I-22).
Table 2 - Interim Response Actions (IRAs) and Boundary
Containment Systems (BCSs).
| IRAsC & Boundary Containment Systems (BCSs) | ||
| ACTIONS TAKEN TO CLEAN GROUNDWATER | ||
| 1. North Boundary Containment System
(NBCS) (also incorporates actions under IRA-B) |
Implemented to intercept and treat northerly migrating groundwater.
Organic contaminants are removed
and treated groundwater recharges the Alluvial Aquifer north of the Arsenal. - Improvements to the NBCS - Improvements to the treatment plant |
Completed 1979-82 Completed 1990 Completed 1991 |
| 2. Irondale Containment System
(ICS) (also incorporates actions under IRA-B & L; Motor Pool/Railyard Intercept System) |
Implemented to intercept and treat DBCP & TCE contaminated groundwater from RMA and other off-post contamination sources. | Completed 1981 |
| 3. Northwest Boundary Containment System
(NWBCS) (also incorporates actions under IRA-B) |
Implemented to intercept and remove organic contaminants from
groundwater. Treated water recharges
alluvial aquifer in the Offpost area northwest of RMA. - Short-term improvements to NWBCS - Long-term improvements to NWBCS |
Completed 1984
Completed 1991 |
| 4. Groundwater Intercept and Treatment System North of the Arsenal (IRA-A) | Implemented to eliminate much of the potential for any future exposure from contaminated groundwater plumes in the Offpost area north of RMA. | Completed 1993 |
| 5. Groundwater Intercept and Treatment System North of
Basin F (IRA-C) |
Intercept and treat contaminated alluvial groundwater north of Basin F area, to make the boundary systems more efficient. | Completed 1990 |
| 6. Closure of abandoned wells (IRA-D) |
Identify, locate, examine, and properly close old or unused wells on RMA to
prevent vertical migration of
contamination between aquifers. - Closure of 353 abandoned Onpost wells - Additional well plugging (including Offpost wells) |
Completed 1990 As needed |
| 7. Rail Classification Yard and Motor Pool Groundwater
Intercept (IRA-L) |
Intercept and treat contaminated groundwater to enhance the effectiveness
of the boundary containment
system. - Motor Pool vapor extraction system |
Completed 1991
Completed 1992 |
| 8. Groundwater Intercept and Treatment System in the
Basin A Neck Area (IRA-E) |
Intercept and treat contaminated groundwater in the alluvial aquifer between Basins A and F, to make the boundary systems more efficient. | Completed 1990 |
| ACTIONS TAKEN TO CLEAN LIQUIDS, SOILS, SEDIMENTS, AND SLUDGES | ||
| 9. Basin F Liquids, Sludges, and Soil Remediation (IRA-F) |
Mitigate any potential for infiltration of contaminants to the groundwater,
preclude potential for volatile
emissions, eliminate any potential impact of Basin F on wildlife, and final remediation of Basin F
liquids. - Removal and containment of liquids (10.5 million gallons) and sludges (564,000 cubic yards) - Basin F and Hydrazine liquid incineration (Submerged Quench Incinerator [SQI]). |
Completed 1989 Completed 1995 |
| 10. Fugitive Dust Control (IRA-I) |
Mitigate any threat of the release of wind-blown contaminated dust. - Application of palliative to Basin A. - Reapplication, Basin A. - Reapplication, Basin A. - Reapplication, Basin A. |
Completed 1988-89 Completed 1991 Completed 1993 Completed 1994, annually as needed |
| 11. Closure of the Hydrazine Facility (IRA-H) |
Mitigate any threat of release of wastewater stored at this facility and remediate the above-ground structures. | Completed 1992 |
| 12. Sewer Remediation (IRA-J) |
Eliminate the RMA sanitary sewers as a potential conduit for contaminant flow. | Completed 1992 |
| ACTIONS TAKEN TO CLEAN OTHER CONTAMINATION SOURCES | ||
| 13. South Tank Farm Plume Stabilization (IRA-L) |
Raise level of Lake Ladora to alter groundwater flow directions and stop the migration of a groundwater plume containing organic contaminants. Monitor lake levels and contaminant concentration to ensure stabilization is maintained. | Completed 1994 |
| 14. Army Disposal Trenches Containment (IRA-L) |
Monitor groundwater contaminants to ensure that migration is not occurring. | Completed 1994 |
| 15. Shell Disposal Trenches Containment (IRA-L) |
Install impermeable barrier around trenches to contain spread of contaminants and construct a cap to prevent infiltration of precipitation. | Completed 1991 |
| 16. M-1 Ponds Mitigation (IRA-L) |
Cap and surround basins to contain contaminants. | Terminated 1993; deferred to ROD |
| 17. Lime Settling Basins Mitigation (IRA-L) |
Cap basin to contain contaminants. | Completed 1993 |
| ACTIONS TAKEN TO REMOVE AND DISPOSE OF CONTAMINATED FACILITIES AND EQUIPMENT | ||
| 18. Building 1727 Sump Cleanup and Maintenance (IRA-G) |
Remediate contaminated liquid in the Building 1727 sump to mitigate any remaining threat of release of liquids from this sump. | Completed 1989 with maintenance through 1993 |
| 19. Asbestos Removal (IRA-K) |
Survey of friable asbestos in structures and the prompt removal and disposal of any asbestos that represents a potential threat for human exposure; routine removal of asbestos. | In progress |
| 20. Chemical Process-Related Equipment Removal | Survey, identify, decontaminate, and disassemble equipment and plumbing exposed to- or containing agent or related chemical contaminants. | In progress |
| 21. Non-Agent Areas Equipment Removal | Identify other contaminated equipment, decontaminate or otherwise mitigate, remove, and dispose. | In progress |
| 22. Free Standing Tanks | Decontaminate, disassemble, remove, and dispose. | In progress |
| 23. Underground Storage Tanks | Remove, decontaminate, disassemble, and remove. | In progress |
| 24. One Ton Containers | Decontaminate agent containers, remove, and destroy. | In progress |
| 25. Unexploded ordnance clearance and removal (UXO) | Locate all agent and conventional munitions UXO areas and devise plan to remove and destroy or otherwise mitigate and render affected areas safe. | Pending |
| 26. Wastewater Treatment Facility (IRA-M) |
Treatment of wastewater resulting from Assessment and implementation of IRAs at RMA. | Completed 1993 |
C - The letters assigned to the IRAs are those given in the Federal Facility Agreement (FFA) for RMA (USEPA, 1989, p. 37-38).
The NBCS was constructed in two phases during 1978 and 1981. Initially a pilot system was installed and became operational in 1978. The pilot system was expanded approximately 1400 feet to the west and 3840 feet to the east in 1981. Recharge trenches were added to the west end of the system in 1988. Additional recharge trenches were added to the east end of the system in 1990 as a part of IRA-B. Currently, the soil-bentonite barrier is 6740 feet long and approximately 3 feet wide, with a designed hydraulic conductivity of 1 x 10-7 centimeters per second (cm/sec) or less. The barrier depth varies from 20 feet at the western end to over 40 feet along the eastern extension. The barrier is anchored in the Denver Formation which underlies the sand and gravels of the alluvial aquifer (HLA, 1992b, p. I-22).
Currently, the average flow through the NBCS treatment system is approximately 240 to 250 gallons per minute (GPM) according to the Final Implementation Document for IRA A (HLA, 1991b). All water is treated and recharged to the alluvial portion of the unconfined flow system (HLA, 1992b, p. I-22).
Examination of groundwater contaminant distribution patterns indicates that the NBCS is having a significant effect on the distribution of organic compounds in the Offpost OU and the Study Area, although EPA suggests that decades of treatment will be required to flush the whole of the Offpost Study Area groundwater. The NBCS treatment plant is effectively removing the organic contaminants for which it was designed. Concentrations of organic contaminants above certified reporting limits (CRLs; i.e. analytical detection limits) have not generally been detected in the system effluent. Inorganic contaminants such as chloride and fluoride currently meet drinking water standards and are not being treated (HLA, 1992b, p. I-22).
Northwest Boundary Containment System (NWBCS)
The NWBCS is located along the northwest boundary of RMA in the southeast quarter of Section 22 (see Fig. 3 and Table 2). Construction of the NWBCS began in 1983, and the system became operational in 1984. The purpose of this system is to intercept and remove organic compounds from onpost contaminated groundwater (HLA, 1992b, p. I-23).
The system consists of a line of 15 upgradient dewatering wells, a soil bentonite barrier, on the northern side, extending approximately two-thirds of the length of the dewatering system, 21 downgradient recharge wells, and a carbon-adsorption treatment facility. Groundwater is pumped from the dewatering wells on the upgradient side of the barrier, treated by carbon adsorption, and returned to the aquifer through recharge wells near the RMA boundary (HLA, 1992b, p. I-23).
Contaminant bypass was observed at the northeast end of the system in 1988. Recharge was increased at the northeast end in December 1988 to prevent continued contaminant bypass.
An IRA to improve the NWBCS was initiated in 1989. In April 1990, the NWBCS Improvements IRA B was divided into two phases: NWBCS Short-Term Improvements IRA and NWBCS Long-Term Improvements IRA. The long-term improvements involve a more thorough Assessment of the NWBCS than have the short-term improvements (HLA, 1992b, p. I-23).
Under the NWBCS Short-Term Improvements IRA, the existing groundwater intercept system was extended both to the southwest and northeast. The soil-bentonite wall was extended across the alluvial channel found northeast of the system to prevent contaminant bypass. Additional extraction wells were added to the existing system to intercept and treat the water in this channel. The northeast extension was completed in July 1990, and recharge rates at the northeast end of the system were reduced. New extraction wells and recharge wells were added to the southwest end of the system and became operational in August 1991 (HLA, 1992b, p. I-23).
Groundwater Intercept & Treatment System North of RMA (IRA A)
IRA A addresses remediation of contaminants migrating north of RMA along two primary contaminant pathways within the alluvial aquifer, defined by the First Creek and Northern paleochannels. The system has been designed to intercept and extract contaminated groundwater from the alluvial aquifer in each paleochannel, upgradient of the O'Brian Canal/Burlington Ditch, treat the organic fraction of the groundwater, and recharge treated water to the alluvial aquifer. Groundwater extraction is being achieved by installing and operating well systems. Water is being treated using a granular activated carbon adsorption system and is being recharged to the alluvial aquifer using a combination of wells and trenches (HLA, 1992b, p. I-23, I-24).
The IRA was designed to be flexible and compatible with the final remedy selected for the Offpost OU. Compatibility with the final remedy could be achieved by modifying the system to include the addition of new wells, treatment processes, or additional treatment capacity if necessary. Construction of IRA A began in November 1991, treatment of groundwater began in 1992, and the system was fully operational in June 1993 (HLA, 1992b, p. I-24).
The groundwater treatment system for IRA A is designed to treat a maximum flow of 720 gpm and an average initial flow of 480 gpm; however, the facilities will be able to accommodate flows less than the average, with a minimum flow of 200 gpm (HLA, 1992b, p. I-24).
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