The Department of Defense (DOD) is the third-largest landowner in the country and is responsible for the management of tens of millions of acres of land, many with historical and ongoing soil and groundwater contamination problems. With such vast landholdings and a history of contaminated sites, DOD facilities offer significant opportunities for the application of new and improved remediation technologies.

In 2001, the Environmental Business Journal reported that the entire U.S. site remediation market was valued at 6.3 billion dollars with the DOD representing 14 percent of the market at 904 million dollars. Further, when considering the DOE market at 30 percent, or almost 2 billion dollars, these two entities combined generate almost half of the current U.S. remediation market.

Comprised of the Army, Navy, Air Force and Marines, the DOD has been involved in the environmental cleanup of its own facilities since the 1980s when the military was brought under the same environmental regulations as the rest of the country. In terms of remediation, the DOD's Office of Environmental Cleanup is responsible for overseeing and developing policy related to the Defense Environmental Restoration Program (DERP). This program focuses on environmental compliance, risk assessment and reduction at active, formerly used and decommissioned military bases.

A cleaner world

At the Interstate Technology Regulation Corporation (ITRC) Fall Conference, held in November of 2001, Kurt Kratz, the acting assistant deputy undersecretary of defense for environmental cleanup, noted that 66 percent of the problem sites under DERP were resolved, leaving an estimated $25 billion in remaining restoration to be undertaken. Kratz went on to state that use of in-situ, cost-effective technologies over capital and management intensive ex-situ techniques such as pump and treat may provide significant performance and economic benefits.

These facts bring to awareness the progress forged by DOD in environmental management and elucidates those areas that would benefit from innovative technology applications. They also unveil the magnitude of the opportunities can receive the benefits of evolving methodologies.

It should be noted that the DOD, through its environmental research and development group known as the Strategic Environmental Research and Development Program (SERDP), has taken integral steps to increase the efficiency and practicality of site remediation at its facilities. In August of 2001, a SERDP workshop focused on several key themes related to the reduction in the use of active remediation systems: 1) an emphasis on source zone treatment/reduction, 2) assessment tool improvements and 3) a focus on existing innovative technologies, particularly thermal and bioremediation technologies. Considering these three agendas and their implementation, significant cost savings may be realized as innovative technologies replace existing and proposed active systems.

One of the many new approaches that can play a role in this new direction toward efficiency is the use of bioremediation to accelerate natural attenuation. Natural attenuation references the fact that most contaminants will eventually degrade under natural conditions. Accelerated natural attenuation teaches that it is possible to enhance this process by providing useful chemical and microbiological "drivers" into the system.

Accelerated natural attenuation with electron donors

Hydrogen release compound is one approach to accelerating the conversion of harmful pollutants into less-toxic and non-toxic compounds. HRC, manufactured by Regenisis, of San Clemente, Calif., is specifically formulated to accelerate the inherently slow natural attenuation process, hence the term accelerated natural attenuation. Upon injection into groundwater HRC , a viscous honey-like substance releases lactic acid. This organic acid is then utilized by microbes yielding hydrogen as a by-product. The dissolved hydrogen is then used by a second set of microbes to strip chlorine atoms or nitro groups from contaminant molecules. Essentially, the hydrogen serves as a source of electrons that are necessary to chemically "reduce " the compounds of concern. It should be noted that for this reason HRC can be referred to as an electron donor. This is particularly important for the remediation of a wide variety of chlorinated hydrocarbons and nitroaromatic explosives. Bioremediation, stimulated by the release of lactic acid from HRC, can last for up to 18 months given the right conditions and the proper dosing of HRC.

Rocky Mountain Arsenal in Denver and the Army Chemical Depot in Pueblo, Colo., are two fairly high-profile sites, both in different stages of treatment with HRC, that are demonstrating the merits of this technology as a cost-effective cleanup protocol.

Rocky Mountain Arsenal

Note: These rates are not for extrapolation to field conditions due to the nature of the microcosm. The data should be used as confirmation that a given compound can degrade anaerobically and to some extent be used to form a "relative order" of expected degradation. In this case both PCE and DIMP would be expected to degrade anaerobically with PCE degrading about four times faster than DIMP.

According to the Department of Defense's Web site, "Rocky Mountain Arsenal (RMA) occupies approximately 27 square miles of prairie in southern Adams County, Colo. RMA was established in 1942 as a chemical weapons manufacturing site. After the war, the Army leased parts of the Arsenal to private industry. In 1946, Colorado Fuel and Iron leased part of the site to produce chemicals. Julius Hyman and Company began manufacturing pesticides at the site in 1947.

"In 1951, Shell Chemical Co. assumed the Hyman firm's lease. Shell Chemical made pesticides and herbicides at the Arsenal until 1982. The Army also produced nerve agent at the site from 1953 to 1957. Weapons operations continued at the Arsenal until 1969. The Army and private chemical manufacturers disposed of liquid wastes in numerous unlined waste-disposal basins and trenches, which contaminated groundwater. By 1955, nearby residents noticed crop damage and voiced concern. As a result, a lined basin (Basin F), was built in 1956 to contain future wastes. However, the liner failed and wastes from the basin continued to reach the groundwater. EPA added the Arsenal to its National Priorities List in July 1987."

Several organic compounds of concern were found on the Rocky Mountain Arsenal site including tetrachloroethene (PCE), trichloroethene (TCE), carbon tetrachloride, chloroform, methylene chloride, dieldrin (a pesticide), dibromocyclopropane, diisopropylmethylphosphonate (DIMP), chlorophenylmethylsulfide and chlorophenylmethylsulfone. Based on a 60-day bench-scale study completed in March 2000, HRC was shown to be effective in reducing the entire range of contaminants. Essentially, all of these compounds were either known from the literature, or considered to be remediable under anaerobic conditions. The latter statement references the fact that unusual compounds such as DIMP were not degrading readily under natural oxic conditions. Consequently, a microcosm study amended with the individual compounds, site water and HRC, was performed to assess potential for degradation using HRC. The results of the study are shown in Table 1-1.

This success prompted the Rocky Mountain Arsenal Water Team to consider using HRC on a larger scale and to arrange a field pilot test at the site. The field pilot study, undertaken in May of 2001, was also designed to treat the "North of Basin F plume." The recently installed field pilot consists of a permeable reactive barrier utilizing 41 HRC injection points at depths of 42 feet to 54 feet below the ground surface. Direct-push technology and high-pressure injection techniques were used to apply HRC into the subsurface. Groundwater flow in the aquifer is to the north-northeast at a velocity of approximately 0.5 ft/day.

A recent review of the progress after seven months at RMA shows that HRC has driven the aquifer into reducing conditions quite readily. The all-important redox measurements that signify this are where they need to be for reductive dechlorination to take place. Also, secondary confirmatory geochemical indicators such as reduced sulfate levels are also present.

Consequently, there are some clear trends in the reduction of several of the more easily degradable contaminants, and the other more recalcitrant compounds are expected to show some clear downward trends in the near future. In essence, the results at this point are highly consistent with the microcosm results in their rank order and the effective degradation of all the compounds is expected in the next six to twelve months. This is in line with the projected longevity of HRC and the reducing conditions it has generated. Further, site data presented clear evidence that HRC was breaking down to release the electron-donating organic acids and that they have permeated the aquifer effectively.

Army Chemical Depot

From the 1940s until 1974, the Army Chemical Depot, located in Pueblo, Colo., served as an ammunition storage and reprocessing facility for the United States Army. In December 1988, the BRAC Commission recommended realignment of the Pueblo Depot Activity, primarily due to chemical demilitarization activities scheduled for fiscal year 1995. The Base Realignment and Closure (BRAC) Commission recommended relocating the supply mission to Tooele Army Depot in Utah, and relocating the ammunition mission to Red River Army Depot in Texas.

Investigations at the Army Chemical Depot identified various types of sites, some with serious nitroaromatic soil and groundwater contamination. These sites include: a landfill; open burning and detonation grounds; an ordnance and explosive waste area; lagoons; former building sites; oil-water separators; a TNT washout facility and discharge system; and current and former hazardous waste storage units. Heavy metals and VOCs from those sites are the primary contaminants affecting groundwater and soil at the installation.

During operations at the TNT washout facility, wash water contaminated with nitroaromatic explosives was discharged into an unlined trench and leach bed. These activities resulted in the contamination of the upper aquifer with TNT, RDX and their breakdown products. The total inventory of contaminants include: 2,4,6-trinitrotoluene (2,4,6-TNT), 2,4-dinitrotoluene (2,4-DNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 1,3,5-trinitrobenzene (1,3,5-TNB), and nitrate. Most of the TNT had naturally degraded, leaving the by-products behind and in need of further remediation.

To treat this contamination with traditional, active remediation methods like pump and treat, or excavation would have burdened the cleanup effort with great expense. Thus, innovative technologies were sought with the goal of degrading explosives residues in place while minimizing the costs of cleanup. Accelerated natural attenuation using HRC was chosen to treat a small section of the site for a pilot study. This study involved the injection of HRC at 30 locations and monitoring was performed on a regular basis using 15 wells placed around the injection area.

Nitroaromatic compounds, such as TNT and RDX, and their by-products can be degraded using HRC because of its “electron donating” nature. The nitro groups of the nitroaromatics are electrophiles, which as the name implies, like to receive electrons. This makes them susceptible to chemical attack and remediation and is the basis for the efficacy of HRC in this project. Note that 2,4 – DNT and 1,3,5 TNB are sequential by-products of TNT. Nitrate levels in the aquifer may be partially explained by the reductive degradation process and are also subject to further degradation to other more benign forms of nitrogen.

Table 1-2 represents the average initial concentrations of contaminants prior to the HRC injection and the percent reduction 105 days later.

Thus, the use of HRC facilitates the low-cost, passive destruction of 2,4 DNT, 1,3,5 TNB, RDX, and nitrates over a relatively short period of time and showed excellent performance at a site impacted with a variety of contaminants.

In conclusion, the use of cost-effective remediation technologies is quickly becoming an important part of the DOD cleanup agenda. These steps forward offer a range of benefits, from significant cost savings, shorter remediation timelines and improved performance. Effective innovative technologies such as HRC are helping prove that accelerated natural attenuation can be used cost effectively at DOD sites on a wide range of contaminants. PE