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Investigating Soil Remediation Techniques for Military Explosive and Weapons Contaminated Sites

 

CURRENT MILITARY SITE REMEDIATION PROCESSES

 

 With a comprehensive background of the current state of excitable compound contamination within various military facilities, our focus turns towards remediation processes. Current remediation will be investigated first, followed by more promising in-situ processes that are currently in the experimental phase of implementation.

 

Since soil remediation for military facilities began, there have been three main remediation processes that have been utilized: incineration, composting, and soil slurry.  While these methods prove effective in remediating energetic compound-contaminated soils, there are several large drawbacks to these methods (namely cost and feasibility).  Such drawbacks call the need for improved remediation processes, such as lime treatment and land farming. However it is necessary to investigate current remediation practices in order to appreciate the need for improvements.

 

 INCINERATION

 

 Incineration of military-contaminated soils has been one of the most effective and most common remediation techniques [1].  The process offers a high level of accuracy and quality control [5].   However, this method requires excavating the contaminated soil, transporting it to an incinerator, and the physical incineration - all of which can be very expensive and inefficient for large scale contamination sites [1].  In the United States alone, the average cost of incineration is $30-40/ton, with some areas, such as Detroit, experiencing rates as high as $150/ton [17].  With over 1.2 million tons of explosive-contaminated US military soil, high incineration costs are a driving determent to large scale remediation. Additionally, by incinerating the contaminated soil, more negative environmental effects (aside from the transportation of the soil to the incinerator) are incurred when the soil is incinerated, which can release harmful substances into the air if not properly performed and monitored.  Lastly, after the soil is incinerated, the ashes of the soil need to be properly disposed of in a landfill - a process with a set of its own environmental factors.  Reuse of the contaminated soil is impossible in this method, meaning additional resources are needed to resupply a military site with soil, which would begin the costly remediation process once again.

 

 COMPOSTING

 

According to Lewis et al., 2003, composting “was the first biological treatment process to be tested, approved, and selected for use in remediating military sites.”  Composting as a form of remediation involves mixing the contaminated soil with organic materials such as straw, wood chips, manure, or vegetable waste, as well as potentially a bulking agent for aeration [1,5].  Composting increases the amount of bacterial activity within the soil, allowing for both aerobic and anaerobic processes to occur [1,5].  These processes increase the degradation rates of energetic compounds in the soil.  Similar to incineration, the contaminated soil used in the composting remediation method is transported off site.  Once the soil is transported to an appropriate composting facility, it typically undergoes either static pile or windrow composting [5].  Static pile, as the name implies, combines all the contaminated soil and organic additives into a large pile that remains untempered save for a motorized blower used for ventilation [5].  Figures 4 and 5 depict a typical static pile composting system.

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Figure 4. A schematic of static pile composting (fao.org)

 

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Figure 5. A static pile in use, complete with ventilation system (o2compost.com)

 

 Alternatively, windrow composting involves creating elongated piles of a soil-organic matter mixture that are periodically turned and hydrated.  Windrow composting is a cheaper method than traditional static piles since a mechanized ventilation is not required for windrow.  Figure 6 shows a typical field of windrows, while Figure 7 shows typical equipment used to turn the windrows.

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Figure 6. Typical windrow field (labroots.com)

 

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Figure 7. Typial windrow-turning equipment (dirtmaker.com)

 

 While effective at minimizing levels of TNT, RDX, and HMX within various types of contaminated soils, composting as a form of remediation can be a slow process, difficult to use on large-scale remediation projects, as well as requiring large amounts of organic material per pile [1,5].  However, unlike incineration, soil treated via composting can be reused.  Remediation composting is a cheaper alternative to incineration, but only in larger quantities; Lewis et al., 2003 notes that “Costs have been estimated at $206-$766 per ton for windrow composting, an estimated 40 to 50 percent savings over incineration at the 1,200-30,000 ton scale.”

 

SOIL SLURRY

 

 The final of the three common remediation practices for military-contaminated soil is creating a soil slurry.  The bioslurry process is “designed to optimize mass transfer of nutrients and electron acceptors by using mechanical mixing and aeration” [1].  It involves mixing the contaminated soil with water and organic materials to form a watery slurry that is contained within an constructed lagoon pool.  The pool is initially mixed, and then it is

 

“[I]ncubated to allow anaerobic conditions to develop through metabolism of the organic amendment by the indigenous microorganisms. The highly reducing environment is intended to promote the complete reduction of TNT” [2].

 

 

Figure 8 depicts a lagoon pool with an agitator for the slurry.

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Figure 8. A typical agitator in a slurry lagoon pool [5]

 

 As with both incineration and composting, using slurry as a form of remediation requires the soil to be removed from its original location and treated.  Original to the slurry method though, there are significant overhead costs for constructing the lagoon and installing the agitator equipment [5].  According to Lewis et al., 2003, “Costs for treating 5000 cubic yards of soil [via the slurry method] have been estimated at $147 per cubic yard ($200-$600 per ton)” which is quite evenly comparable to the compost method.  The slurry method is also very sensitive to the temperature fluctuations during the incubator process [5].  However the time required for remediation through the slurry process is much lower than the composting method.  Lastly, remediated soil via the slurry method is often not reused and instead either dumped into ditches or properly disposed of according to regulations [5].

 

 A NOTE ABOUT CURRENT REMEDIATION PROCESSES

 

While the three aforementioned soil remediation practices have a range of benefits and drawbacks, the largest issues with all three methods are that (1) the contaminated soil must be transported away from the military facility to be treated (and in some cases, no longer usable) and (2) the unrealistic use of these practices on large scale remediation practices.  In regards to the latter, our earlier discussions both in terms of the history of military facilities and the health impacts of energetic compounds point to the fact that remediation of these facilities must be undertaken on a large-scale immediately.  The call for such needs have been answered in the more recently-discovered in-situ remediation techniques discussed in the following sections.  While these new practices are not without their own flaws, they are certainly a step towards a more effective remediation process.

 

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