International Journal of Soil: Volume 1, Issue 2
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Factor Analysis Reveals Effects of Reducing Conditions on the Fate and Transport of RDX in Groundwater
Morris, Michael W.
Groundwater investigations conducted at the Massachusetts Military Reservation (MMR) show the impact of historic activities on the development of groundwater contaminant plumes emanating from military ranges. Several of the plumes, located on the southeastern side of the reservation, contain elevated concentrations of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). In most cases, these plumes show continuity from the source to the leading edge, indicating that very little attenuation of RDX is occurring in the aquifer. Interesting exceptions to this trend are locations where plumes consisting of RDX and perchlorate intercept part of the aquifer that was previously impacted by a fuel spill; reducing conditions due to biological activity resulted from this spill. RDX concentrations show a significant positive correlation with both dissolved oxygen and oxidation-reduction potential, and a significant negative correlation with specific conductivity. The distribution of RDX is more consistent upgradient from the oxygen depleted zone and implies that RDX is degrading in the aquifer near the fuel spill. A factor analysis yielded two geochemical (44 percent variability explained) and two contaminant (30 percent variability explained) factors. This suggests that the geochemical nature of the aquifer is the primary source of groundwater parameter variability determined by this investigation.
Polycyclic Aromatic Hydrocarbons (PAHs) in Urban Soil: A Florida Risk Assessment Perspective
Teaf, Christopher M
Over the past decade, polycyclic aromatic hydrocarbons (PAHs) have steadily climbed in importance on the CERCLA list of hazardous substances. Though the listing does not necessarily imply that these chemicals exhibit the greatest degree of toxicity, such recognition by ATSDR and USEPA is predicated at least in part on their demonstrated ubiquity, coupled with toxicity considerations. Regulatory agencies increasingly are under pressure to define and interpret data describing urban background levels, and to appropriately determine the relative importance of waste-producing activities and concentrations resulting from typical natural and/or human activity. Three case studies from Florida are presented that confirm the ubiquity of the PAHs at low levels, and that demonstrate the need for more sophisticated and transparent treatment by regulatory agencies. We discuss assessment and risk assessment activities related to two urban redevelopment projects, as well as one property transaction project. In each case, considerable sampling of surficial soils and sediment identified total benzo(a)pyrene-equivalent (BAPE) concentrations in the range of less than 1 ppm to about 5 ppm. Although those concentrations frequently exceeded the default Florida cleanup target level for both residential and commercial/industrial land use by a wide margin, it was concluded that they are completely consistent with levels reported in a great many urban settings. There is an ongoing need to consider the development of a default urban background level for PAHs in areas characterized by busy roadways or multiple industrial facilities, in much the same way that geological or anthropogenic background levels are established for some inorganics.
Experimental and Biogeochemcial Modeling Studies on Arsenic Release in Soil Under Anaerobic Condition
Halim, Md. Abdul; Jinno, Kenji; Razzak, Abdur; Oda, Keita; Hiroshiro, Yoshinari
The identification of release mechanism of arsenic may assist in designing safe and effective remediation strategies, due to its severe toxicity effect for the human body. In this regards, investigations were carried out to observe the release of As from soil into water. It was found that As concentration increased with decreasing oxidation reduction potential. Arsenic concentrations demonstrated negative covariation with the concentrations of NO3&#; but strongly correlated with DOC and Fe concentrations. Batch leaching tests at different pH conditions showed a strong pH dependence on arsenic and iron leaching. A numerical simulation of arsenic transport model, coupled with microbially mediated biogeochemical processes was developed for describing the release of As in soil under reducing environment. The simulation concentrations of Mn, Fe and As were well matched those found experimentally. The results of this study suggested that the microbially mediated degradation of organic matter and reductive dissolution of Fe-oxyhydroxide are considered to be the dominant processes to release As in aquifers.
Mercury and Cyanide Used as Indicators of Sediment Transport in Ephemeral Washes at the Techatticup Mine and Mill Site, Nelson, Nevada (USA)
Sims, Douglas Brian; Francis, Anthony
Mercury (Hg) and cyanide (CN-) are used as indicators of aquatic transport down gradient in ephemeral washes. The pattern of transport for Hg and CN- should mimic other metals (As, Cu, Cr, Pb, Ni, Ba) found in the soils. Hg and CN- were chosen to illustrate transport in surface soils because Hg and CN- are utilized in the milling process and Hg is available from the local geology. Stamp mills that utilize Hg and CN- flotation concentrate naturally occurring metals as byproducts. Soil samples collected from a wash system bisecting the mine waste site contained metal concentrations significantly above background levels. Mercury and cyanide concentrations showed dissimilar distribution patterns throughout the wash system with Hg and CN- 30- and 95- times greater than background concentrations. Concentrations of various heavy metals corresponded well with the concentrations of mercury and cyanide throughout the wash system validating the use of specific analytes as tracers of transport of contaminated soils.
Construction of Biologically Productive Artificial Tidal Flats with Solidified Sea Bottom Sediments
Imai, Daizo; Kaneco, Satoshi; Dabwan, Ahmed H.A.; Katsumata, Hideyuki; Suzuki, Tohru; Kato, Tadaya; Ohta, Kiyohisa
Ago Bay is a typical enclosed coastal sea that is connected to the Pacific Ocean via a very narrow and shallow entrance. The bay has been organically contaminated by the practice of culturing pearls, which has been ongoing for the past 110 years. To address this problem, a new technology — the Hi-Biah-System (HBS) —, which dewaters muddy dredged sediments and changes the muddy sediments for raw materials of tidal flat, was introduced in 2005. The solidified product from the sediments with the HBS was used to construct the tidal flat. The purpose of this study was to evaluate the environmental conditions of the constructed tidal flat 2 years after its construction. We monitored the physico-chemical (oxidation−reduction potential, acid volatile sulphide, loss on ignition, water content, total organic carbon, total nitrogen, chlorophyll a, and particle size) and biological characteristics of a constructed tidal flat (five sections) and a natural tidal flat (six points). At the same tidal level, the physico-chemical parameters were similar among the constructed and the natural tidal flats. However, the biomass and macrobenthic population were higher in the constructed flat compared to the natural one. According to the findings of this study it can be concluded that the solidified products from the sediments with the HBS could provide useful materials for constructing the tidal coastal environment.