Chapter 10
Nitroaromatic And Nitroamine Compounds
POLLUTION BY DNAPL [DENSE NONAQUEOUS PHASE LIQUID]
The Components Clean Facility (CCF) site at the National Aeronautics and Space Administration’s (NASA’s) Kennedy Space Center near Titusville, Florida was selected for this study. The CCF site encompasses nearly 17 acres and has been used since the early 1960’s for cleaning and refurbishing of predominantly stainless steel hardware in support of space exploration operations. Cleaning operations typically included pre-cleaning of parts in ultrasonic vats and vats of cleaning agents (predominantly chlorinated solvents). The most prevalent solvents used at this facility have been 1,1,2 trichloro 1,2,2 trifluoroethane (Freon 113), as well as other freon products, and trichloroethene (TCE).
Obtaining direct evidence of DNAPL is difficult in the field. A field study was recently performed comparing several approaches to DNAPL characterization at a site where indirect and limited direct evidence of DNAPL exists.
The techniques evaluated included:a three-dimensional (3-D) high-resolution seismic survey, field screening of soil cores with a flame ionization detector (FID)/organic vapor analyzer (OVA), hydrophobic dye(Sudan IV)-impregnated reactive Flexible Liner Underground Technologies (Flute_)membrane used in combination with Rotasonic drill cores, centrifuged soil with Sudan IV dye, ultraviolet light (UV) fluorescence, a Geoprobe Membrane Interface Probe (MIP_), and phase equilibrium partitioning evaluations based on laboratory analysis of soil samples.
Sonic drilling provided continuous cores from which minor soil structures could be evaluated and the OVA provided reliable preliminary data for identifying likely DNAPL zones within the cores. The Flute_membrane provided direct evidence for the presence of DNAPL. The MIP_ probe provided rapid identification of probable DNAPL areas as well as soil conductivity data .
The 3-D seismic survey was of minimal benefit to this study and the centrifuging of samples with Sudan IV dye and the use of UV fluorescence provided no benefit. Results of phase equilibrium partitioning calculations to infer the presence of DNAPL were in good agreement with the site screening data.
CHLORINATED SOLVENT AND HEAVY METALS SOURCE
Site Description. The subject site is a former metal plating facility located within the boundaries of the South Mesa Water Quality Assurance Revolving Fund (Arizona State Superfund) Registry Site (SMWRS). In 1983, PCE was detected in an irrigation well located approximately 500 ft (152 m) downgradient of the site. This well was immediately taken off-line, though it was periodically sampled. This well was also operated as a containment pump-and treat well from 1994 to 1997, after which time the well was permanently taken off-line. In 1985, a sample collected from the irrigation well contained 780 mg/L of PCE. A second irrigation well, located approximately 1.5 mi (2.4 km) downgradient of the site, was also detected with PCE. Preliminary investigation, involving sampling of production wells and the installation of 10 monitoring wells,identified an approximate 1.5 mi long (2.4 km) by 0.5 mi (0.8 km) wide PCE groundwater plume apparently originating from the subject site site plan of the former metal plating facility. PCE and metal wastes were discharged to an on-site injection well from approximately 1979-1988. Other possible on-site sources of contamination were a septic system and leakage from processing equipment. While the metal plating facility was in operation, groundwater was as deep as 200 ft (61 m) bgs. However, due to decreased groundwater usage in the Effective source characterization is an important component in remedial alternative evaluation and selection. Arizona has unique hydrogeological conditions (deep groundwater, very dense and coarse sediments) that often result in dense non-aqueous phase liquids (DNAPL) released at source areas migrating several hundred feet vertically before they encounter a finer-grained interval that may impede or retard further migration. These conditions can make source characterization challenging and potentially costly. Characterization costs are a factor of drilling depth, number of samples collected and analyzed, and the number of monitoring wells installed. Therefore, the consultant must utilize innovative tools to reduce the number of borings that are drilled, the number of samples that are collected, and the number of wells that are installed while still collecting enough data to evaluate risks and remedial alternatives.Law Engineering and Environmental Services, Inc (LAW) is currently characterizing a deeply impacted chlorinated solvent and heavy metals source area and has utilized an innovative source characterization approach to minimize the number of borings and samples and thus costs. Data will be used to evaluate risks, determine achievable cleanup goals, and select/design potential future remedies.
REMEDIATION OF A DNAPL SOURCE ZONE AT CAPE CANAVERAL
To meet the objectives of this study, it is sufficient to estimate the overall mean TCE concentration across an entire test plot, rather than estimating TCE concentrations at various spatial locations within a test plot. In geostatistical terms, this is known as global estimation. One approach, and in fact the simplest approach, for calculating a global mean estimate is to calculate the simple arithmetic average (i.e., the equally weighted average) across all available TCE concentrations measured within the plot. However, this approach is appropriate only in cases where no correlation is present in the measured data. Unfortunately, this is a rare situation in the environmental sciences.
A second approach, and the approach taken in this analysis, is to use a spatial statistical procedure called kriging to take account of spatial correlation when calculating the global average. Kriging is a statistical interpolation method for analyzing spatiallyvarying data. It is used to estimate TCE concentrations (or any other important parameter) on a dense grid of spatial locations covering the region of interest, or as a global average across the entire region. At each location, two values are calculated with the kriging procedure: the estimate of TCE concentration (mg/kg), and the standard error of the estimate (also in mg/kg). The standard error can be used to calculate confidence intervals or confidence bounds for the estimates. It should be noted that this calculation of confidence intervals and bounds also requires a serious distributional assumption, such as a normality assumption, which is typically more reasonable for global estimates than for local estimates.
The kriging approach includes two primary analysis steps:
1. Estimate and model spatial correlations in the available monitoring data using a semivariogram analysis.
2. Use the resulting semivariogram model and the available monitoring data to interpolate (i.e., estimate) TCE values at unsampled locations; calculate the statistical standard error associated with each estimated value. This paper presents the results of a statistical analysis of data collected before and after remediation of trichloroethylene (TCE) in subsurface soil at Cape Canaveral, Florida. The primary objective of this analysis was to determine whether different remediation alternatives were effective at significantly reducing TCE in soil.
The geostatistical analysis approach was to utilize kriging, a statistical spatial interpolation procedure, to estimate the overall average TCE concentration in soil before and after remediation, and then determine if those concentrations were significantly different.approach
THE ROLE OF MICROORGANISMS ON DNAPL INTERFACIAL PROPERTIES AND TRANSPORT
PCE (tetrachloroethene) is a chlorinated solvent and suspected carcinogen, and is also a contaminant frequently present in groundwater. As a dense nonaqueous phase liquid(DNAPL), PCE migrates with relative ease through regions of high conductivity in the subsurface. However, regions of lower conductivity (smaller pore spaces) inhibit migration of PCE. It has also been observed that once regions of low conductivity are occupied by PCE, it becomes very difficult to extract from these smaller pore spaces.The overall distribution and migration of DNAPLs in a natural system is affected by a number of variables. The most critical of these variables include the complexities of the porous matrix, and the corresponding interfacial properties of this matrix. These proper-ties affect the capillary forces that define fluid and solid phase interactions, and ulti-mately the DNAPL migration.
Microorganisms have been observed to affect such interfacial properties in aero-bic systems through the production of biosurfactants (Dohse and Lion, 1994). The goal of this research is to define the role of anaerobic microorganisms on PCE migration and interfacial properties in the subsurface. Research has shown that anaerobic microorgan-isms can survive in PCE-contaminated environments, and furthermore have the ability to reductively dechlorinate tetrachloroethene completely to ethene. Such organisms have the ability to derive energy directly from PCE dechlorination, using it as a respiratory electron acceptor (Gossett et al., 1997). These organisms were chosen for their obvious ability to survive and even thrive at PCE concentrations toxic to most organisms.
Research has shown that a number of organisms have the ability to an-aerobically dechlorinate PCE and other chlorinated solvents However, the extent to which the presence of these organisms affects the interfacial properties and mobility of the DNAPL is largely unknown. Conversely, aerobic organisms have been studied and observed to change their adhesion properties, and to also produce extracellular compounds, or biosurfactants, under stressed conditions . The environmental conditions of anaerobic PCE-degrading cultures have been varied in an attempt to either stimulate similar changes in adhesion properties, or stimulate biosurfactant production. Either of these mechanisms may significantly impact the interfacial properties of PCE, thereby increasing its effective mobility in the subsurface. To date, research has shown that culture media ionic strength, nitrogen concentrations, and varying carbon sources have little effect on these mechanisms. However, it has been observed that extremely high concentrations of PCE, as well as the presence of low concentrations of DO, may have a significant impact on the properties of the organisms, thereby affecting the interfacial properties of the DNAPL, and its mobility.
REFERENCES
Dnapl site characterization—a comparison of field techniques Terry W. Griffin and Kenneth W. Watson (HSW Engineering, Inc.) Proceedings of the Third International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey, CA; May 2002). ISBN 1-57477-132-9, published by Battelle Press, Columbus, OH, www.battelle.org/bookstore.
Paper 1E-03, in: A.R. Gavaskar and A.S.C. Chen (Eds.), Remediation of Chlorinated and Recalcitrant Compounds— 2002.
Proceedings of the Third International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey, CA; May 2002). ISBN 1-57477-132-9, published by Battelle Press, Columbus, OH, www.battelle.org/bookstore.