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Soil Washing Treatability Study for SWMU B-20
Section 5 - Conclusion
Nine criteria are typically used in evaluating remediation technologies, such as soil washing. These evaluation criteria are as follows:
Attainment of Cleanup Standards. The ability to attain media cleanup standards set by state or federal regulations.
Protection of Human Health and Environment. Protection of human health and environment is assessed based on the overall effectiveness of the alternative to block pathways for human exposure to the contamination.
Control the Sources of Releases. The ability to stop further environmental degradation by controlling or eliminating further releases that may pose a threat to human health and/or the environment is used to define the ability to control the source of release.
Short-Term Impacts. Risk of short-term pollution exposure, physical injury and damage to site workers, community residents, community structures, and the greater environment during implementation is considered for the remediation technology.
Long-Term Impacts. The ability to protect human health and the environment over the long term. Assessment of long-term effectiveness and permanence includes the durability of actions to block pollutant pathways and the minimization of monitoring requirements.
Implementability. Site conditions, project time requirements, and service availability that effect remedial design. The complexity of land use restrictions, administrative responsibilities, regulatory approval, and long-term monitoring obligations are also considered.
Reduction of Toxicity, Mobility and Volume. The evaluation of toxicity, mobility, and volume was based on the degree to which the metals and explosive contaminants were contained, treated, or removed from the site.
Cost. Cost estimations are based upon published cost estimation guides and engineering experience.
Compliance with Waste Management Standards. A discussion of specific waste management activities required for the remedial technology is included.
The conclusions drawn from the benchscale study are discussed in detail in this section. Generally, benchscale results support the following conclusions for physical treatment techniques for SWMU B-20 soils.
The soils at B-20 contained burn residues and ash from burning activities at SWMU B-20.
An average total lead concentration in the projectile-contaminated sand was measured at 364,989 mg/kg. A 71 percent reduction in lead was achieved, resulting in a total lead concentration of 143,041 mg/kg and a total leachable lead concentration of 21.5 mg/l.
An average total lead concentration in the sifted soil was measured at 2,123 mg/kg. A 50 percent reduction in lead was achieved, resulting in a total lead concentration of 1,069 mg/kg and a TCLP lead concentration of 0.2 mg/l.
While the particulate lead found in the larger soil fractions were significantly reduced in both the projectile-sand and sifted soil samples, particulate lead in the smaller soil fractions actually increased.
The moderately alkaline soil pH (7.7) indicates a soil system highly buffered with respect to carbonates. Because of the high levels of lead associated with the carbonate fraction, acidification treatments to chemically treat the soil were not conducted.
The ineffectiveness of soil washing as a sole remediation technique precludes use of soil washing except in use in combination with another remediation method.
Conclusions based on the nine evaluating criteria discussed in section 5.1 are presented below.
5.2.1 Attainment of Cleanup Standards
The benchscale study demonstrates that density treatment is most effective for soils with contaminants in the larger soil fractions, 0.07 mm or larger. For both soil types analyzed in this study, removal rates from the first two soil fractions (sieves # 4 and #10) achieved at least 90 percent. However, removal rates for the third soil fraction (sieve #40) dropped to 70 percent for the projectile-contaminated sand and 11 percent for the sifted samples.
Results from density treatment of the sifted soils indicated that 50 percent of the lead consisted of recoverable particulate metal. At this removal rate, the total particulate lead still exceeded cleanup criteria. Soil washing of projectile-contaminated sand achieved a 61 percent removal rate of lead; however, this removal rate is not sufficient for adequate cleanup of the site. While the TCLP results for the sifted soils were favorable at 0.2 mg/l, TCLP results for the projectile-contaminated sand samples did not achieve acceptable concentrations. Therefore, it appears unlikely that soil washing alone is sufficient to remediate B-20 soils to acceptable cleanup concentrations.
Soil washing depends on the combined use of physical and chemical separation techniques for contaminant removal rates. Had the B-20 soils been suitable for chemical leaching, the process would have been more effective. It is clear that the density treatment was successful at removing contaminants from the larger soil fractions. However, because chemical leaching is not suitable for CSSA soil types, other technologies are necessary, either in conjunction with soil washing or other suitable technologies, to meet project goals.
5.2.2 Protection of Human Health and Environment
Soil washing techniques performed at B-20 indicate that the treatment technique does not result in meeting cleanup criteria. The first step of soil washing, physical treatment, may be an appropriate first step for another remediation technique such as phytoremediation. However, the second step, chemical separation, is not technically appropriate for the alkaline soils. Therefore, an additional treatment method is required to meet the protection standards specified by federal and state regulations.
5.2.3 Control the Sources of Releases
Prior to returning treated soils to B-20, analysis will be performed and only soils that meet the cleanup criteria will be placed back at the site. With the removal of contaminants from the site, and contaminant leaching at acceptable levels, further releases of lead from the site are unlikely.
5.2.4 Short-Term Effectiveness
Soil washing is a one-time operation that achieves immediate results. Clean soils are returned to the excavated area of the site, while contaminants and contaminated soils are disposed of.
Aside from restoration activities, site conditions are not expected to change following the completion of soil washing. Subsequently, long-term effectiveness is equivalent to short-term effectiveness.
Soil washing is performed ex-situ, which means it requires excavation. Following excavation, physical separation techniques are implemented and followed by chemical treatment. In the case of B-20 soils, the soil washing process will only consist of one removal process, density treatment. With the recovery of large particulate metal, such as lead slugs, copper-jacketed bullets and other munitions, a significant portion of the contaminant may be recycled. Use of other treatment technologies, e.g., phytoextraction, in conjunction with the physical treatment may result in soils meeting cleanup criteria. Since native soil loss is expected, a small amount of backfill will be needed.
Because the process occurs ex-situ, it does not require site monitoring during remediation. Monitoring of soils returned to the site is not anticipated as these soils would achieve acceptable cleanup criteria before being returned to the site.
Transportation and disposal of contaminants will require administrative support. Other administrative requirements are considered minimal.
5.2.7 Reduction of Toxicity, Mobility, and Volume
Soil washing reduces the toxicity, mobility and volume of contaminated soil at the site. With the removal of contaminants from the site, the overall toxicity and volume of particulate lead will be reduced.
It is estimated that soil washing will cost $140 per ton. Costs included in this cost estimate include excavation, treatment, backfill, waste stabilization, transportation, disposal, and other auxiliary costs. Appendix B provides the cost details estimated for use of the soil washing treatment technology at CSSA.
5.2.9 Compliance with Waste Management Standards
All waste transportation and disposal will be performed in compliance with Department of Transportation (DOT) and RCRA guidelines. A Corrective Action Management Unit (CAMU) may be required in order to effectively treat soils from B-20 and/or other sites.