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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). RMAwas established in 1942 and was used for the manufacture of chemical munitions. From the late1940s to the early 1980s, some of the facilities were leased to private companies for themanufacture of industrial chemicals, primarily pesticides and herbicides. All productionactivities at RMA ceased in 1982 and now the Army's sole mission at RMA is to remediatecontamination.

Industrial and waste disposal practices typical for the time were used by both the Army andlessees. Those practices resulted in contamination of soil, surface water, sediment, andgroundwater. Groundwater monitoring conducted by the Army detected the presence of organicand 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 environmentalcleanup, 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 coveringabout 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 newDenver 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 southwestof the site. Rural residential and agricultural lands are located to the north and east of theArsenal. The Montbello residential area and light industrial areas are located to the south. Thesmall community of Henderson lies four miles north of RMA.

Of the more than 750 different chemicals handled or generated at the Arsenal, more than 90were chosen as target analytes for the remedialinvestigations, Onpost and Offpost. Onpost, thecontamination is dispersed in structures, surficial soils, sediments, groundwater, surface water,and biota. Based upon soil contamination, a total of 181 contaminated sites have been identifiedOnpost. Generally, the highest detected concentrations of contaminants weremeasured insamples collected from soils, surface water, and groundwater in the central portion of RMA. The most concentrated plumes of contaminatedgroundwater occur in the Alluvial Aquiferbeneath contaminated soils and former liquid waste disposal basins in the central, and to a lesserdegree, in the western part of RMA. Contamination concentrations generally decrease as thegroundwater plumes migrate toward the western, northwestern, and northern Arsenalboundaries. Groundwater contaminated with numerous volatile and semivolatile chemicalcompounds including organochlorine pesticides and organophosphorus compounds related to themanufacture 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 elevatednear the RMA boundaries, especially at monitoring stations near population centers reflectingthe influence of off-post contaminant sources. Groundwater and surface water data gatherednear the southern and western boundaries also indicate that off-post sources have contributed tothe surface water and groundwater contamination observed in those locations. Additionally, thedata gathered on soil, groundwater, and air indicate that the areas south and east of RMA are notcontaminated with RMA-related chemicals.

Beginning in 1978, the Army and Shell Oil Company began construction of a series ofgroundwater 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 andOffpost, have greatly minimized, and are eliminating Offpost groundwater contamination. Inaddition, a total of 14 Interim Response Actions (IRAs - comprised of more than 26 separateactions have been undertaken to control, reduce, prevent, or eliminate the potential forcontaminant releases from the most important sources on the facility and to reduce or eliminatefurther contaminant migration and the potential for human exposure.

Beginning in September 1990, the Colorado Department of Public Health &Environment, inresponse to documented groundwater contamination in the Offpost Study area, began offeringbottled water to any drinking water well user in the Offpost Study Area that was affected bydiisopropylmethyl phosphonate (DIMP), an RMA-sourced groundwater contaminant. Thatbottled water program is ongoing and serves to minimize ingestion exposure toseveral RMAand non-RMA groundwater contaminants. As part of the final remedy, the Army and Shell OilCompany 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: theU.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 sitealterations 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 andfurther restricted and defined many of the current and future uses delineated in the FFA. Thestatute sets aside the majority of the Arsenal acreage as a unit of the National Wildlife RefugeSystem; mandates maximum fish and wildlife oriented public use; and imposes perpetualprohibitions on the use of the Arsenal for residential or industrial uses, the use of thegroundwater under and surface water on the Arsenal as a source of potable water, the use of theArsenal 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 thenorth, northwest, east, south, and west are based on a review of past and present environmentaldata to identify present and future exposure pathways. In addition, community health concernsand healthoutcome data, including completed health studies and HealthInvestigations, were alsoreviewed in conjunction with established exposure pathways. Thus, exposure pathways thatATSDR has determined are of public health significance are identified in this assessment.

The Onpost land use controls and visitor restrictions provide mitigation or public healthprotection in addition to the IRAs and groundwater containment and treatment systems. Thisdetailed mosaic of mitigation has eliminated many possible Onpost and Offpost pathways ofhuman exposure to RMA contaminants. Surface soil data reviewed to date, show that no harmwill come to those visitors who go on the guided tours or who do not stray off designated tourroutes 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 isconsidered to be a No Apparent Public Health Hazard. Existing institutionalcontrols andregulations are in place to assure that planned future remediation activities will be carried out insuch a fashion so as to eliminate exposures of public health concern.

Because people residing in the Offpost Study Area to the north and northwest experiencedpastexposures to RMA contaminants via groundwater and air, the area may be considered aPublicHealth hazard in thepast. However, the frequency, magnitude, and duration of those pastexposures is unknown. If chronic ingestion occurredto the known levels of groundwatercontaminants, adverse health effects were, or could be, possible. Many health studies andactivities have been conducted because of past exposures from RMA. None of the health studiesconducted thus far have shown an association between exposure to RMA contaminants andharmful health effects.

What remains, until completion of the planned final remediation measures, is a completedOffpost pathway of human exposure to non-RMA groundwater contaminantsin private wells. In August 1996, there were eight Alluvial Aquifer wells and one Arapahoe Aquifer wells in theOffpost 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 thatcontained levels of nitrate that were of health concern. However, the measured levels of nitratein those drinking water wells continues to decline and data compiled August 1996 does not showelevated levels of nitrates in any drinking water wells in the Offpost Study Area.

RMA is not the source of those contaminants. The occurrence of nitratesis widespread in thearea's groundwater, both upgradient and downgradient from RMA. The nitrate could be tracedto many sources such as agricultural fertilizers, animal wastes, or private on-site sewage disposalsystems. The lead in the water could be from several sources such as naturally occurring lead inthe groundwater or lead contamination from plumbing.

The decision has been made to supply municipal water or an alternative water supply to thedrinking 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 wellwith lead contamination apparently does not qualify for connection to a replacement watersupplies. If the lead contamination level remain elevated in this well, continued use of this wellfor drinking (including infant formula) and/or cooking may result in non-cancerous healtheffects in infants, children, adults, and pregnant women and their fetuses. That wellcontaminated by lead and any drinking water wells located outside the DIMP footprint areawhich any future monitoring may show sustained high levels of nitrate contamination areconsidered to be a present and potential future Public HealthHazard.

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 HealthHazard. A past and present pathway of human exposure to trichlorethylene (TCE) and other volatilehalogenated organic compounds exists for individuals who work or reside in the EPA StudyArea who have refused to be connected to the South Adams County Water and SanitationDistrict municipal water supply system and have continued to use their private wells. RMA isnot the only source of groundwater contaminants in this pathway. In the past RMA contributedlow-levels of TCE contamination to some municipal wells in the area but several other sourcesof contamination have also been identified. Data on those wells were collected in 1987 and1989.

Five potential pathways of human exposure involving on- and off-site soils and air, off-sitefoodchain contamination, and groundwater in the Commerce City area were identified andevaluated. Data gathered, information compiled, and final remediation decisions made duringthe course of this assessment have resulted or will result in the partial or total elimination of fourof those potential pathways.

Specific public health recommendations have been made to address the potential andcompletedpathways of exposure. Recommendations are made to eliminate exposure to groundwatercontaminants in certain private drinking water wells; to gather more information on potentiallyaffected drinking water wells; and to ensure that certain activities that may result in the creationof future pathways are precluded. In addition, a Public HealthAction Plan has been developedwhich includes community and health professional health educationfocused on concerns relatingto Offpost groundwater contamination, potential off-site air contamination during the final sitecleanup, and assistance, as needed, to the ongoing U.S. Fish and Wildlife Service public useprograms, including the wildlife bus tours.

Public health concerns were identified during ATSDR public availability meetings incommunities surrounding RMA. Those concerns include: whether Offpost health effects wouldresult from Onpost remediation; whether the Submerged Quench Incinerator would be used fornon-RMA hazardous wastes; whether an excess of cancer exists for the Montbello area south ofRMA; whether there were excesses of specific cancers (such as stomach cancer and breastcancer, for example) and if they could be associated with exposure to RMA contaminants; andwhether diseases or health conditions such as lupus, diabetes, multiple chemical sensitivity, andlearning disabilities are in excess and if they could be associated with exposure to RMAcontaminants. For some of those specific concerns, the public health data bases are inadequateor 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, pastexposure to RMA contaminants has not been directly associated with the types of cancers orhealth concerns in question. The environmental data do not show that residents of the Montbellocommunity have been exposed to RMA contaminants at levels that may result in adverse healtheffects. To date, none of the health studies conducted for off-site populations to the north andnorthwest of RMA have indicated that a relationship exists between environmental exposure toRMA contaminants and harmful health effects.

In summary, this Assessment represents an analysis of environmental and health informationrelating to RMA and surrounding areas. Included are recommendations for public health actionsand a Public Health Action Plan for carrying them out.


The Agency for Toxic Substances and Disease Registry(ATSDR) has evaluated the publichealth significance of this site. More specifically, ATSDR has determined whether health effectsare 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 HumanServices and is authorized by the Comprehensive Environmental Response, Compensation, andLiability Act of 1980 (CERCLA) to conductpublic health assessments at hazardous waste sites.

As the result of the detection of chemical contaminants possibly related to Rocky MountainArsenal (RMA) in off-post lands north and northwest of the Arsenal, the Army initiated ahydrogeologic surveillance program of more than 100 on- and off-post wells and surface waterstations in 1974. That program has since expanded to include, in 1994, annual or biannualmonitoring of more that 100 off-post domestic wells and more than 800 on- and off-postmonitoring wells. Extensive environmental investigations were also implemented to evaluatepossible 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 compiledthat documents the investigations of on- and off-post contamination, the decisions made tominimize or to eliminate human exposure to those contaminants, and actions implemented tocleanup RMA.

Because of the extensive, 20-year history of investigation and cleanup efforts at RMA, theBackground section of this public health Assessment will summarize not only the historical andenvironmental 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 tocontaminants. The Pathways Analysis section of this Assessment will then focus upon thepossible present and future pathways of human exposure to contaminants. In so doing, ATSDR'sassessment of the public health implications of RMA contaminants is then similarly focusedupon the possible present and future health effects that may arise from existing and foreseeablefuture human uses of the facility and the adjacent off-post lands. The Health Outcome Datasection will discuss the purpose, conclusion, and status of numerous site-specific health activitiesand investigations that have been completed or are still in progress.

Also incorporated in this Assessment is a discussion of off-site contamination arising fromothernearby sites including other CERCLA sites. This information is included because, for manyyears, RMA was mistakenly thought to be the sole source of contamination found west of theArsenal, and because some public health concerns relating to this off-site contamination areincorrectly attributed to the Arsenal.

Site Description andHistory


The Rocky Mountain Arsenal (RMA) is a 27-square-mile (sq mi) U.S. Army facility situatednine miles northeast of Denver, Colorado, that was formerly used for the production ofmunitions, chemical warfare agents, industrial chemicals, and agricultural chemicals (Figure 1). RMA in its entirety has been listed (Cerclis Number CO5210020769, 1987) on the NationalPriorities List (NPL) of hazardous waste sites designated for long-term remedial evaluation andresponse. 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 OUlies 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 thedocumented contamination of RMA. Subsequent paragraphs summarize the military operations,industrial operations, and waste disposal operations that have occurred at RMA. For furtherinformation, the reader is referred to the Remedial Investigation Summary Report (EBASCO,1992) for a summary of almost two decades of environmental investigations, remediation, andcleanup efforts in the Onpost area.


The U.S. Army established RMA in 1942 to manufacture chemical warfare agents andagent-filled munitions and to produce incendiary munitions for use in World War II. Initial facilitybuilding activities included: construction of the South Plants manufacturing complex; extensionof 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 3and 4; modifications to preexisting irrigation reservoirs (Lake Ladora, Lower Derby Lake) andconstruction of a new reservoir (Upper Derby Lake) to supply the South Plants complex withprocess cooling water; and construction of three seepage ponds in a large earthen depression inSection 36 (which eventually overflowed to form Basin A for the disposal of liquid industrialwastes). 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 complexwere leased to private industry for the production of industrial chemicals, primarily pesticidesand herbicides. The conversion to pesticide production was a logical step in the transition to apeace-time economy because the organic insecticides as a group were discovered during theWorld War II era and some (e.g., organophosphate insecticides - OPHPs) were discovered in thechemical warfare laboratories of World War II. Records have been located of nine companiesthat conducted manufacturing or processing operations in the South Plants (see Fig. 3) between1946 and 1982, when all manufacturing operations in the South Plants ceased. The first majorlessee of facilities in the South Plants was Julius Hyman and Company (1947-1954). Thesecond major lessee, Shell Chemical Corporation, a division of Shell Oil Company, purchasedthe stock of Hyman and in 1954 Hyman was merged into Shell. Shell continued to produceagricultural 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 weredeveloped and modified along with the various military and industrial operations. Wastes froma variety of chemical manufacturing, munitions production, testing, and demilitarizationactivities, off-post sources, shipping and handling procedures, and associated operations weregenerated and disposed in various manners. In addition to normal waste disposal, wastes,feedstock, and product chemicals have been inadvertently discharged into the RMA environmentvia accidental spills, which have occurred throughout RMA history. Spills have been associatedwith 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 activitiesassociated 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 conductedby the Army have reported the presence of organic and inorganic chemicals in samples of off-sitegroundwater.


The Rocky Mountain Arsenal (RMA), added to the National Priorities List (NPL) in 1987, iscomprised of two Operable Units (OUs): Onpost and Offpost. The Offpost OU is defined as themedia requiring remediation within the RMA Offpost Study Area (EPA, 1989). Theenvironmental setting of those OUs, the Offpost Study Area, and other areas adjacent to RMA isgiven 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 milesnortheast of downtown Denver (see Figure 1). The Arsenal is located at the western edge of theColorado high plains, near the foothills of the Rocky Mountains. It occupies an area of rollingterrain characterized by grasslands, shrublands, wetlands, aquatic habitats, and extensivedisturbed and weedy areas. These habitats supports a variety of plants and wildlife species. Theelevation above mean sea level ranges from 5,330 feet (ft) at the southeastern boundary of RMAto approximately 5,110 ft at the northwestern boundary. Maximum local relief on the Arsenal isabout 200 ft.

The topography of the RMA Offpost Study Area (also covering about 27 sq mi) is similar toRMA and consists of stream-valley lowlands separated by gently rolling uplands. The elevationwithin the Offpost Study Area ranges from 5,110 ft along the RMA northwestern boundary to5,030 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-flowingSouth Platte River. The valley of the South Platte river lies along the northwest boundary of theOffpost Study Area and parallel to the northwest boundary of RMA. Surface waters originatingsouth 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 smallerirrigation 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 thecanal intercepts First Creek. Burlington Ditch may also receive surface water infrequently fromthe First Creek. For more information on the drainage and landform features of the RMA areathe reader is directed to EBASCO (1992, p. A1-1).

Meteorology and climatology

Climatic data from the former Stapleton International Airport which adjoins RMA on thesouthwestern 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 relativehumidity, abundant sunshine, relatively low precipitation (averages 15 inches annually),moderate to high wind speed, and a wide daily range in temperature. Fluctuations of 20° to35°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. Thelengthof the bars indicates the percent of time that the wind blows from each of the indicated directionsand the patterned segments along each bar indicate the relative frequency of each wind speedclass. The figure shows that the prevailing winds blow from the south and the south-southwestto 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 aregenerally from the northwest quadrant and are the downslope "chinook" winds. The highestwindspeed recorded as a one-minute average was 65 mph from the west.

Geology and Soils

Surficial Soils

The soils of RMA were originally mapped by the U. S. Department of Agriculture, SoilConservation Service. Additional mapping and textural characterization was then completed aspart of the remedial investigation. Those investigations delineated clay-rich soils locatedgenerally 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 themajor Arsenal facilities. For additional information on the soils of RMA, the reader is referredto 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 reachthicknesses of up to 130 ft (EBASCO, 1992, p. A1-6). The older alluvial deposits tend to becoarser-grained than the younger (topographically lower and usually closer to stream/riverchannel) terrace deposits. Those older surficial deposits also generally coarsen westward. Bytheir nature, these alluvial and eolian deposits are varied and heterogenous in character anddisplay little lateral continuity. The base of these alluvial and eolian deposits lies on theirregular 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 isirregular but distinct. The coarser sandy and gravelly alluvium contrasts sharply with the muchfiner grained sandstones, siltstones, and claystones of the Denver Formation. The bedrocksurface is locally weathered and varies from granular material to more lithified, compactmaterial that is fractured and jointed over a depth interval of less than 5 ft. The contact isirregular because deep paleochannels were incised in the bedrock surface and subsequentlyinfilled with coarse-grained alluvium (ESE, 1988; EBASCO, 1992, p. A1-6). Those north tonorthwest-trending paleochannels facilitate groundwater migration and largely control thedirection and rate of movement of groundwater contaminant plumes at RMA and in the OffpostStudy 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 Formationbedsof more permeable sandstone and lignite collectively comprise what is termed the Denveraquifer. These beds are locally confined above and below by relatively impermeable shales orclaystones. The Denver Formation is separated from the underlying Arapahoe Formation by a30- 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 StudyArea, the Denver formation is locally absent and the alluvial deposits lie directly on theArapahoe Formation (ESE, 1988, p. 3-46).

Surface Waterand Groundwater Hydrology

Surface Water

The local slope of the land surface is to the northwest and the streams draining the Arsenalandthe adjacent off-post areas flow generally in that direction until they become tributary to theSouth Fork of the Platte River. The South Platte follows a northeasterly course and numerousirrigation canals, ditches, and laterals have been dug subparalleling the course of the river. Afew of those northeast flowing diversion or irrigation structures cross the Arsenal and severalmore 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 RMAandinclude the First Creek, Irondale Gulch, South Platte River, Sand Creek, and Second CreekDrainage Basins, and the Basin A, Basin F, and Sand Creek Lateral subcatchments. Locatedwithin 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 tothe southern boundary of RMA are three small ponds that receive surface runoff from theHavana Street area.

Streamflow at RMA is highly variable. Seasonal variations in stream discharge are usuallygreater than average variations between years and are strongly affected by the amount of urbanrunoff, released or diverted flows, and precipitation duration and intensity. Streams on RMA aregenerally intermittent and the highest flows usually occur during spring runoff and during majorstorms (EBASCO, 1992, p. A1-10).

Until completion of the new zero-discharge Sewage Treatment Plant in March 1994, effluentfrom the original RMA Sewage Treatment Plant entered First Creek in Section 24 (Stollar, 1990).


The two principal water-bearing units underlying the Arsenal and the adjacent off-post areasthathave been, to varying degrees, affected by contaminants originating at RMA are theunconsolidated alluvial and eolian deposits and the underlying Denver Formation. Isolatedoccurrences of a few contaminants in wells drilled to the deeper Arapahoe Formation probablyrepresent localized leakage of contaminants to that aquifer (HLA, 1992b, p. I-4). The hydraulicproperties of the alluvial aquifer are distinct from the deeper aquifers in the Denver andArapahoe Formations.

Groundwater flow occurring within the alluvium and uppermost, weathered part of theDenverFormation has been designated the "unconfined flow system" in the remedial investigationsreports prepared for RMA (EBASCO, 1992, p. A1-8; HLA, 1992a). Within the DenverFormation, the series of strata that comprise the Denver aquifer have, for the purposes of theremedial investigations, been designated the "confined flow system" (EBASCO, 1992, p. A1-8). Depending on site-specific hydrologic characteristics, varying degrees of hydraulic interchangeare possible between surface water and the unconfined flow system and between the unconfinedand confined flow systems. The available data indicates that local areas of contaminant leakageinto the Denver and Arapahoe confined aquifers are due to damaged wells or poor wellconstruction.

The presence of paleochannels in the Denver Formation surface has an impact on thegroundwater flow in the unconfined flow system. Coarse, unconsolidated sands and gravelscommonly found in those channels provide for preferential groundwater flow within the alluvialaquifer. The identified groundwater contaminant plumes that have migrated across RMAboundaries to off-site localities are generally confined to those paleochannels. Two suchpaleochannels, the First Creek and Northern paleochannels, are intercepted by and continuenorth of the RMA North Boundary Containment System. Before groundwater flow in thosepaleochannels passes beneath the O'Brian Canal and the nearby Burlington Ditch, thegroundwater is again intercepted and treated by the treatment system constructed north of RMA.

An additional paleochannel, the Northwest paleochannel, is intercepted by and continues westof the RMA Northwest Boundary Containment System (HLA, 1992b, p. I-3). A complex systemof north and northwest-flowing paleochannels underlying the western portion of RMA collectgroundwater flow from industrial and commercial areas lying south of RMA and from thewestern and southern portions of RMA. Although the areal extent and thickness of the saturatedalluvium is greater in the western portion of RMA than in the northern paleochannels, the flowof the identified groundwater plumes arising from the interior of RMA are intercepted by theIrondale Boundary Containment System (and to a lesser extent the North and NorthwestBoundary Containment Systems) where water is pumped, treated, and reinjected before flowcontinues northwestward to the South Platte River. Data collected from monitoring wellsinstalled 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 occurat the base of the unconfined flow system, except near the South Platte River where theweathered 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 0ft to a maximum of approximately 70 ft (EBASCO, 1992, Figure A1.5-4). Horizontal hydraulicconductivity 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 ofaverage linear flow rates for groundwater range from 1.5 to 10 ft/day. Near the NorthwestBoundary Containment System the estimated average linear flow rates for groundwater are from5.5 to 22.5 ft/day (ESE, 1988, p. 3-31).

Seasonal water table fluctuations at RMA generally average 1 to 3 ft. Fluctuations in thewatertable elevations are artificially induced by the Irondale, Northwest Boundary, North Boundary,and Offpost Groundwater Intercept and Treatment facilities and near the western RMAboundary, where the water table drops about 11 ft during the summer due to withdrawal of waterfrom nearby Adams County wells.

Maps showing the elevation of the water table (potentiometric maps) disclose that thegroundwater 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 lakesin the southern part of RMA. The South Platte River is interpreted as the regional dischargepoint for the unconfined flow system in this area.

Recharge to the unconfined flow system occurs as infiltration of precipitation, seepage fromlakes, reservoirs, streams, canals, and buried pipelines, and flow from the underlying confinedaquifer system. Locally, groundwater may also leak between the unconfined and confined flowsystems when: 1) the permeable sands of the Denver or Arapahoe are in contact with theAlluvial Aquifer (beneath and north of RMA); 2) poorly constructed wells allow water tomigrate along the annulus between the casing and the well bore; or 3) the well casing has beenperforated both in the unconfined and the confined flow systems.

Mass balance calculations have been used to estimate the rates of surface water - groundwaterinterchange between the lakes and basins and the unconfined flow system. Results indicate thatLower Derby Lake, Havana Pond, and Basin C are areas of groundwater recharge, whereas LakeLadora, Lake Mary, and Basin A receive groundwater in upgradient areas and lose it indowngradient areas. Recharge - discharge relationships at Upper Derby Lake are dependantupon lake level, and all streams, canals, ditches, laterals and interceptors lose water togroundwater during the course of the year. Actual recharge or discharge rates vary substantiallyin 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 andadjacent areas, including the Offpost Study Area, the unconfined flow system is consideredthe 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 westand north of RMA. Contamination of RMA and other non-RMA sources has affected many ofthose wells but the combined effects of groundwater intercept and treatment systems, drillingreplacement wells, and supplying bottled water has eliminated the use of individual domesticwells for drinking water supplies in the most contaminated areas.(1)There are, however, manysmall domestic irrigation wells and high-yield commercial irrigation wells that continue toproduce 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 CountyWaterand Sanitation District (SACWSD) - Klein Water Treatment plant are developed in the alluvialdeposits and are contaminated by Trichloroethene which has emanated from source areas inwestern RMA and off-site sources to the south and southwest of RMA. Other contaminantsdetected 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 thestate-of-the-art Klein Water Treatment Plant was specifically designed to remove thiscontamination (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 referredtoas the Denver aquifer, where water-bearing sandstones, siltstones, and lignite horizons areinterbedded 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 theDenver aquifer from uplands south and east of RMA produces artesian conditions in much of theaquifer beneath RMA and nearby areas. The individual sandy layers are commonly lense-shapedand range in thickness from a few inches to as much as 50 ft. Adjacent sand zones within theconfined flow system may be interconnected and linear flow rates of 0.03 to 4 ft/day have beenmeasured (EBASCO, 1992, p. A1-14).

The lower portion of the Arapahoe Formation is comprised of more permeable, water-bearingsandstones and conglomerate beds that are separated from the overlying Denver Formation by arelatively impermeable claystone and clay shale "buffer zone" reported to range from 30 to 100feet in thickness. Water-level data collected from three Arapahoe Formation wells indicate thatthe formation is also a confined aquifer.

Data collected for the off-post Remedial Investigation indicate that groundwater migration intheDenver 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 theArapahoe aquifer moves west beneath RMA and then north or south in response to the hydraulicgradients induced by pumping (ESE, 1988, p. 3-47).

EnvironmentalInvestigations and Controls


In 1974, the Army established a Contamination Control Program at RMA to ensurecompliancewith federal environmental laws, including the National Environmental Policy Act of 1969 andthe Federal Executive Order 11507 of February 1970, which directed federal installations torefrain from polluting the groundwater through the discharge of wastes, and further directedthese 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 ofcontamination and characterized/evaluated pathways by which contaminants could migrate intothe environment Onpost and Offpost of RMA.

Onpost Operable Unit

The Remedial Investigation (RI) at RMA was initiated in October 1984 to develop a databaseand formulate conclusions regarding the nature and extent of contamination at RMA sufficient toassess the human health and environmental effects of contaminant exposure and to aid inevaluating remedial alternatives (EBASCO, 1992, p. 1-1, 2-1). Numerous studies have beenconducted and reports prepared for the Onpost RI. Generally, those reports are organized andreported by the Study Areas.

The results of the Onpost RI have been published previously in 124 ContaminationAssessmentReports (CARs), 2 Data Presentation Reports, and 90 Phase II Data Addendum Reports preparedfor each potential hazardous waste site and for each nonsource area (the balance of eachsquare-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 foreach geographical study area at RMA (Southern Study Area, Eastern Study Area, South PlantsStudy Area, North Plants Study Area, Central Study Area, North Central Study Area, andWestern 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 (seeEbasco, 1992, Fig. 1.2-3) because of the size, geographic diversity, and varied land use historyof 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 investigativeeffort, he following numbers of samples, as of 1994, had been collected:

MediumSampling LocationsNumber of Samples
Surface Water
4,015 bores, 39 nonbore
27 locations
619 wells
110 locations
13 stations
96 locations

Samples were analyzed for as many as 90 target analytes and were screened for thousands ofnontarget organic analytes. Volatile and semivolatile organics were analyzed using gaschromatography and gas chromatography/mass spectrometry (GC/MS) techniques, metals byatomic absorptiontechniques, Army chemical warfare agents by specialized instruments andtechniques, 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 ofcontaminated sites, boundaries of groundwater contaminant plumes, the identity of thecontaminants found in these locations, and contaminant concentrations. The results obtained aregenerally consistent with those of earlier studies and tend to validate previous understandings ofthe general location of plumes and sites, the identification of major contaminants, and themagnitude 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 atconcentrations up to a few parts per hundred (or thousands of parts per million - ppm), toisolated 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, generallylow-level organochlorine pesticide (OCP) contamination (0.002 to ~ 4 ppm outside designatedsites)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 byInterim Response Actions (IRAs)(2) and other contaminantmitigation measures such as Boundary Containment Systems (BCSs)(3) . Those actions are discussed in greater detail insubsequent portions of this section of the Assessment.

Table 1 gives a generalized summary of the 178 soil-contamination sites by site type/locationand identifies what IRAs or BCSs have been implemented, if any, to mitigate or eliminatethreats to the environment while remaining consistent with the long-term, comprehensivecleanup goals at the Arsenal. It should be emphasized that the distribution of contaminants insurface and subsurface soils is typically irregular because of variations in the behavior of thechemicals 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. Soiland alluvial aquifer materials in the central and northern portions of RMA contain mostof the contaminant sources. Less extensive or less concentrated sources occur onlysporadically within the relatively uncontaminated buffer zone along the eastern, southern, andwestern boundaries. The most highly-contaminated sites (highest concentrations and/or greatestvariety of contaminants) are concentrated in the central manufacturing, transport, and wastedisposal areas. The greatest contaminant concentrations and distributions tend to occur in theupper 5 feet of the soil column, although exceptions are noted, particularly in the case of wasteburial trenches and leaks from subsurface structures. In general, contaminant distribution isinfluenced 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 weredetected over widespread areas at low to high concentrations (EBASCO, 1992, p. 2-12).


Table 1.

Contaminated Sites and Interim Response Actions(after EBASCO, 1992)
SitetypesSite description A Potentially affectedmedia BIRA or Boundary Control System (BCS) to mitigateor control(see Table 3 for further definition)
Basins & LagoonsA total of 14 sites located in the SP and NCStudy Areas and ranging from relatively smallsites of limited contamination to the largedisposal basins A, B, C, D, E, & F usedvariously 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, &PondsA 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 StreetPonds, Sand Creek Lateral, North Bog,miscellaneous drainage ditches known orinferred 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 SitesA total of 12 sites located in the E & C StudyAreas. Sites include: surface burns and burnpits; disposal trenches; detonation, impact, &test sites, buildings used for testing sites ; and anincinerator used to destroy mines.SS, SW, GW, & A - IRA L
Solid Waste Burial SitesA total of 18 sites located in the S, E, SP, C, NP,& W Study Areas. Sites include: dredged andburied lake sediments; sanitary landfills & trashpits, disposal pits & trenches for pesticides,chemical wastes, & munitions. SS, GW, & A - IRA L
Storage Sites, Buildings,& EquipmentA total of 25 sites located in the S, E, SP, NP, C,& W Study Areas. Sites include: storage yardsfor incendiary and agent filled bombs; trashdumps; 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 SitesA total of 14 sites located in the E, NP, NC, &W Study Areas. Sites include: a rail loadingarea, drum storage areas, isolated surface andsubsurface chemical and fuel spills, and asanitary sewer overflow area.SS & GW - North, Irondale, & Northwest BCSs
- IRAs A & L
Sewer SystemsA total of 10 sites located along sewer lineslocated in the SP, NP, C, NC, & W Study Areas. Sites are: sanitary & chemical sewers; processwater lines; and a deep disposal well.SS & GW- IRA J
WindblownContamination ofSurface SoilsA total of 11 areas of contaminated surface soilsadjacent to other contaminant sources in the SP,C, & NC Study Areas. Locations are known orinferred contamination sites attributed to windand/or surface water transportation. SS, SW, GW, A, &B - IRA I
Isolated ContaminationA total of 38 isolated detections of contaminantsin soils located in the S, E, NP, NC, & W StudyAreas. Sites consist of isolated detections ofusually one contaminant. SS- None Conducted Nor Planned

A- The location codes given in the Site Description columnrefer to the 7 Study Areas established at RMA (see Fig. 4). Those Study Areas are: S - SouthernStudy Area, E -Eastern Study Area, SP - South Plants Study Area, NP - North Plants Study Area, C - CentralStudy 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; therelativeimportance; the character of contaminants; and the environmental media possibly affected bythosecontaminants given in EBASCO (1992, pp. 2-12 - 2-23). The existent or possible avenues ofmigrationof those contaminants are also described.

Interim Response Actions(IRAs)

Throughout the course of the RMA cleanup program, the Army, Shell, and EPA have taken aproactive approach to mitigation of conditions that may result in a serious health threat. Amongthe first actions taken were the installation of the three boundary groundwater containment andtreatment systems. The boundary containment systems (BCSs) have been supplemented, to date,with 14 Interim Response Actions (IRAs, comprised of 26 separate actions) initiated to mitigateconditions of contamination which pose an immediate threat to human health and theenvironment. The purpose of the IRAs is to proceed with actions, based on the findings of theRI or other investigations, considered "necessary and appropriate" for implementation prior tothe final remedial decisions. These actions are designed to control, reduce, prevent, or eliminatethe potential for contaminant releases from the most important sources on the facility, andreduce or eliminate further contaminant migration and the potential for human exposure, both onand off the installation. Actions requiring removal of material are designed to be in accordancewith CERCLA regulations and are to be consistent with and contribute to the efficientperformance of the final response actions for the Onpost and Offpost OUs. Table 2 presents acomplete 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 publicattentionthan any of the others is the Basin F IRA. This IRA was designed to remediate one of the mosthighly-contaminated sites at RMA. This IRA was initiated in 1988, and the removal andcontainment phase of the action was completed in 1989. About 10.5 million gallons of highlycontaminated 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 wastepile. Leachate control systems were part of these new structures and comprehensive air qualitymonitoring 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 QuenchIncinerator (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), theNorthBoundary Containment System (NBCS), and the Northwest Boundary Containment System(NWBCS), have been installed at the RMA boundaries to control the migration of contaminantsto offpost areas (see Table 2). All three of the systems are currently in operation to intercept andtreat contaminated groundwater in the alluvial aquifer (unconfined flow system) and to rechargethe treated water. In addition to the boundary control systems, a groundwater intercept andtreatment 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 ofcontaminants 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 BCSswere 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(seeFig. 3 and Table 2) and consists of a groundwater intercept system and a carbon treatmentsystem to remove DBCP and TCE. Constructed by Shell Oil Company, the ICS becameoperational in 1981. The ICS is supplemented by additional extraction wells of the MotorPool/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 CommerceCity study area to the west and northwest of RMA, although the majority of the downgradientarea is within the confines of the RMA Offpost Study Area. A review of monitoring datadowngradient of the ICS shows contaminant concentrations to be low and attributable to thesources of contamination within the EPA off-post study area and RMA. Details of the EPAoff-post study area are given later in this section.

Although not part of the ICS, the actions taken by the Army to remove trichloroethene(TRCLEor TCE) from the water supplies of nearby Commerce City residents, including construction ofthe Klein Water Treatment Plant in 1989 were actions taken to eliminate human exposure togroundwater 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. 3and Table 2). The NBCS consists of a system of dewatering wells with contaminatedgroundwater from the unconfined flow system, a soil-bentonite barrier to separate contaminatedand treated groundwater and to impede offpost migration of contaminated groundwater, acarbon-adsorption treatment system to remove organic contaminants, and a system of rechargewells 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)
1. North Boundary Containment System(NBCS)
(also incorporates actions under IRA-B)
Implemented to intercept and treat northerly migrating groundwater.Organic contaminants are removedand 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 contaminatedgroundwater 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 fromgroundwater. Treated water rechargesalluvial aquifer in the Offpost area northwest of RMA.
- Short-term improvements to NWBCS
- Long-term improvements to NWBCS
Completed 1984

Completed 1991
Completed 1993

4. Groundwater Intercept and Treatment System North ofthe Arsenal (IRA-A)Implemented to eliminate much of the potential for any future exposurefrom contaminated groundwaterplumes in the Offpost area north of RMA.Completed 1993
5. Groundwater Intercept and Treatment System North ofBasin F
Intercept and treat contaminated alluvial groundwater north of Basin F area,to make the boundarysystems more efficient.Completed 1990
6. Closure of abandoned wells
Identify, locate, examine, and properly close old or unused wells on RMA toprevent vertical migration ofcontamination 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 GroundwaterIntercept
Intercept and treat contaminated groundwater to enhance the effectivenessof the boundary containmentsystem.
- Motor Pool vapor extraction system
Completed 1991

Completed 1992

8. Groundwater Intercept and Treatment System in theBasin A
Neck Area (IRA-E)
Intercept and treat contaminated groundwater in the alluvial aquifer betweenBasins A and F, to make theboundary systems more efficient.Completed 1990
9. Basin F Liquids, Sludges, and Soil Remediation
Mitigate any potential for infiltration of contaminants to the groundwater,preclude potential for volatileemissions, eliminate any potential impact of Basin F on wildlife, and final remediation of Basin Fliquids.
- Removal and containment of liquids (10.5 million gallons) and sludges (564,000 cubicyards)
- Basin F and Hydrazine liquid incineration (Submerged Quench Incinerator [SQI]).
Completed 1989
Completed 1995
10. Fugitive Dust Control
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
Mitigate any threat of release of wastewater stored at this facility andremediate the above-groundstructures.Completed 1992
12. Sewer Remediation
Eliminate the RMA sanitary sewers as a potential conduit for contaminantflow.Completed 1992
13. South Tank Farm Plume Stabilization
Raise level of Lake Ladora to alter groundwater flow directions and stopthe migration of a groundwaterplume containing organic contaminants. Monitor lake levels and contaminant concentration toensurestabilization is maintained.Completed 1994
14. Army Disposal Trenches Containment
Monitor groundwater contaminants to ensure that migration is notoccurring.Completed 1994
15. Shell Disposal Trenches Containment
Install impermeable barrier around trenches to contain spread ofcontaminants and construct a cap toprevent infiltration of precipitation.Completed 1991
16. M-1 Ponds Mitigation
Cap and surround basins to contain contaminants.Terminated 1993; deferred to ROD
17. Lime Settling Basins Mitigation
Cap basin to contain contaminants.Completed 1993
18. Building 1727 Sump Cleanup and Maintenance
Remediate contaminated liquid in the Building 1727 sump to mitigate anyremaining threat of release ofliquids from this sump.Completed 1989 with maintenancethrough 1993
19. Asbestos Removal
Survey of friable asbestos in structures and the prompt removal and disposalof any asbestos thatrepresents a potential threat for human exposure; routine removal of asbestos.In progress
20. Chemical Process-Related EquipmentRemovalSurvey, identify, decontaminate, and disassemble equipment and plumbingexposed to- or containingagent or related chemical contaminants.In progress
21. Non-Agent Areas Equipment RemovalIdentify other contaminated equipment, decontaminate or otherwisemitigate, remove, and dispose.In progress
22. Free Standing TanksDecontaminate, disassemble, remove, and dispose.In progress
23. Underground Storage TanksRemove, decontaminate, disassemble, and remove.In progress
24. One Ton ContainersDecontaminate 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 toremove and destroy orotherwise mitigate and render affected areas safe.Pending
26. Wastewater Treatment Facility
Treatment of wastewater resulting from Assessment and implementation ofIRAs at RMA.Completed 1993

C - The letters assigned to the IRAs are those given in the Federal FacilityAgreement (FFA) for RMA (USEPA, 1989, p. 37-38).

The NBCS was constructed in two phases during 1978 and 1981. Initially a pilot system wasinstalled and became operational in 1978. The pilot system was expanded approximately 1400feet to the west and 3840 feet to the east in 1981. Recharge trenches were added to the west endof the system in 1988. Additional recharge trenches were added to the east end of the system in1990 as a part of IRA-B. Currently, the soil-bentonite barrier is 6740 feet long andapproximately 3 feet wide, with a designed hydraulic conductivity of 1 x 10-7centimeters persecond (cm/sec) or less. The barrier depth varies from 20 feet at the western end to over 40 feetalong the eastern extension. The barrier is anchored in the Denver Formation which underliesthe 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 250gallons 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 ishavinga significant effect on the distribution of organic compounds in the Offpost OU and the StudyArea, although EPA suggests that decades of treatment will be required to flush the whole of theOffpost Study Area groundwater. The NBCS treatment plant is effectively removing the organiccontaminants for which it was designed. Concentrations of organic contaminants above certifiedreporting limits (CRLs; i.e. analytical detection limits) have not generally been detected in thesystem effluent. Inorganic contaminants such as chloride and fluoride currently meet drinkingwater 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 ofSection 22 (see Fig. 3 and Table 2). Construction of the NWBCS began in 1983, and the systembecame operational in 1984. The purpose of this system is to intercept and remove organiccompounds from onpost contaminated groundwater (HLA, 1992b, p. I-23).

The system consists of a line of 15 upgradient dewatering wells, a soil bentonite barrier, onthenorthern side, extending approximately two-thirds of the length of the dewatering system, 21downgradient recharge wells, and a carbon-adsorption treatment facility. Groundwater ispumped from the dewatering wells on the upgradient side of the barrier, treated by carbonadsorption, 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 wasincreased 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 NWBCSImprovements IRA B was divided into two phases: NWBCS Short-Term Improvements IRAand NWBCS Long-Term Improvements IRA. The long-term improvements involve a morethorough 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 interceptsystemwas extended both to the southwest and northeast. The soil-bentonite wall was extended acrossthe alluvial channel found northeast of the system to prevent contaminant bypass. Additionalextraction wells were added to the existing system to intercept and treat the water in thischannel. The northeast extension was completed in July 1990, and recharge rates at thenortheast end of the system were reduced. New extraction wells and recharge wells were addedto 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 primarycontaminant pathways within the alluvial aquifer, defined by the First Creek and Northernpaleochannels. The system has been designed to intercept and extract contaminated groundwaterfrom the alluvial aquifer in each paleochannel, upgradient of the O'Brian Canal/BurlingtonDitch, treat the organic fraction of the groundwater, and recharge treated water to the alluvialaquifer. Groundwater extraction is being achieved by installing and operating well systems. Water is being treated using a granular activated carbon adsorption system and is beingrecharged 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 theOffpost OU. Compatibility with the final remedy could be achieved by modifying the system toinclude the addition of new wells, treatment processes, or additional treatment capacity ifnecessary. Construction of IRA A began in November 1991, treatment of groundwater began in1992, 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 720gpmand an average initial flow of 480 gpm; however, the facilities will be able to accommodateflows less than the average, with a minimum flow of 200 gpm (HLA, 1992b, p. I-24).

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