David R. Burris

Sorption of trichloroethylene and tetrachloroethylene in a batch reactive metallic iron-water system.

Sorption and reduction kinetics of trichloroethylene (TCE) and tetrachloroethylene (PCE) with metallic (zero-valent) iron were determined in a closed, well-mixed, anaerobic batch system by measuring aqueous and total system concentrations of the respective chlorinated solvent as a function of time. The reaction orders with respect to TCE and PCE total system concentrations were 2.7 and 1.3, respectively, indicating that the reaction mechanisms are complex. Both compounds exhibited nonlinear sorption behavior and could be fitted by the generalized Langmuir isotherm expression. After accounting for the mass sorbed to the iron, the reduction rates of PCE and TCE are first-order. This indicates that the bulk of sorption is to nonreactive sites. Competitive sorption was observed when both PCE and TCE were present ; however, no competition for reaction was detected. The design and study of treatment systems for chlorinated solvents using metallic iron requires consideration of sorption processes.

In situ modification of an aquifer material by a cationic surfactant to enhance retardation of organic contaminants

Abstract Sorption of hexadecyltrimethylammonium chloride (HDTMA), a cationic surfactant, on aquifer material from Columbus AFB, Mississippi, U.S.A., was examined. Transport studies using flow-through columns and a box model aquifer showed that an almost stationary zone of HDTMA-modified aquifer material could be produced in situ without a significant decrease in hydraulic conductivity. Perchloroethylene (PCE) and naphthalene sorption isotherms on the HDTMA-modified aquifer material were linear, and sorption coefficients were increased by over two orders of magnitude relative to the unmodified material. The retardation of PCE by insitu emplaced HDTMA zones within a column was examined. Agreement between batch- and column-derived sorption coefficients and breakthrough curve symmetry indicates that local equilibrium was attained. Significant retardation of a naphthalene plume by an in situ emplaced surfactant zone was demonstrated in the box model aquifer system. The experimental results indicate that it is feasible to create in situ a sorbent zone within an aquifer using cationic surfactants. In most situations, the sorbent zone concept needs to be coupled with contaminant degradation processes for sorbent emplacement to be a practical tool in the remediation of groundwater contamination sites. Sorbent zones may be of benefit in the engineering of suitable environments for microbial or abiotic degradation reactions and by providing time slow reactions to occur.

Microfabricated Gas Chromatograph for On-Site Determination of Trichloroethylene in Indoor Air Arising from Vapor Intrusion. 1. Field Evaluation

Results are presented of inaugural field tests of two identical prototype microfabricated gas chromatographs (μGC) adapted for the in situ determination of trichloroethylene (TCE) in indoor air in support of vapor intrusion (VI) investigations. Each μGC prototype has a pretrap and partially selective high-volume sampler of conventional design, a micromachined-Si focuser for injection, dual micromachined-Si columns for separation, and an integrated array of four microscale chemiresistors with functionalized gold nanoparticle interface films for multichannel detection. Scrubbed ambient air is used as the carrier gas. Field-generated calibration curves were linear for injected TCE masses of 26-414 ng (4.8-77 ppb·L; r(2) > 0.98) and the projected single-sensor detection limit was 0.052 ppb for an 8-L air sample collected and analyzed in 20 min. Consistent performance between the prototypes and good medium-term stability were shown. Above the mitigation action level (MAL) of 2.3 ppb for the field-test site, μGC TCE determinations fell within ±25% of those from the reference method for 21 of 26 measurements, in the presence of up to 37 documented background VOCs. Below the MAL, positive biases were consistently observed, which are attributable to background VOCs that were unresolvable chromatographically or by analysis of the sensor-array response patterns. Results demonstrate that this type of μGC instrument could serve the need for routine TCE determinations in VI-related assessment and mitigation efforts.

Microfabricated Gas Chromatograph for On-Site Determinations of TCE in Indoor Air Arising from Vapor Intrusion. 2. Spatial/Temporal Monitoring

We demonstrate the use of two prototype Si-microfabricated gas chromatographs (μGC) for continuous, short-term measurements of indoor trichloroethylene (TCE) vapor concentrations related to the investigation of TCE vapor intrusion (VI) in two houses. In the first house, with documented TCE VI, temporal variations in TCE air concentrations were monitored continuously for up to 48 h near the primary VI entry location under different levels of induced differential pressure (relative to the subslab). Concentrations ranged from 0.23 to 27 ppb by volume (1.2-150 μg/m(3)), and concentration trends agreed closely with those determined from concurrent reference samples. The sensitivity and temporal resolution of the measurements were sufficiently high to detect transient fluctuations in concentration resulting from short-term changes in variables affecting the extent of VI. Spatial monitoring showed a decreasing TCE concentration gradient with increasing distance from the primary VI entry location. In the second house, with no TCE VI, spatial profiles derived from the μGC prototype data revealed an intentionally hidden source of TCE within a closet, demonstrating the capability for locating non-VI sources. Concentrations measured in this house ranged from 0.51 to 56 ppb (2.7-300 μg/m(3)), in good agreement with reference method values. This first field demonstration of μGC technology for automated, near-real-time, selective VOC monitoring at low- or subppb levels augurs well for its use in short- and long-term on-site analysis of indoor air in support of VI assessments.

Solution of hydrocarbons in a hydrocarbon-water system with changing phase composition due to evaporation.

Pure water was brought into contact with a four-component liquid hydrocarbon phase comprised of methylcyclohexane, ethylbenzene, tetralin, and 1-methyl-naphthalene. The headspace above the hydrocarbon phase was continually purged with N/sub 2/ to provide a controlled evaporative loss. Hydrocarbon concentrations in the water and hydrocarbon phases changed due to dissolution and evaporation and were measured as a function of time. A surface renewal mass transfer model is congruent with the observed hydrocarbon concentrations in the aqueous phase. Hydrocarbon-phase composition and component interactions are important in determining the time dependence of the aqueous-phase composition. The results have implications concerning the fate of components of petroleum products discharged in the aquatic environment. 12 references, 4 figures, 1 table.

Fingerprinting Approach for Relating Nonaqueous Phase Liquid, Soil, and Groundwater Data

An advanced chemical fingerprinting approach, called nonaqueous phase liquid (NAPL)–groundwater (GW) finger printing, is presented for relating NAPL, soil, and groundwater data. This approach is accomplished by utilizing the “effective solubility” relationship and a hypothetical n-component NAPL to convert NAPL, soil (containing residual NAPL), and groundwater data to common frames of reference with respect to both phase and dilution. The resulting NAPL-GW fingerprints make it possible to perform detailed forensic analysis incorporating all three data types (assuming minimal confounding effects of attenuation processes and non-ideal solution behavior). Three case histories using the NAPL-GW fingerprinting approach are presented, illustrating its utility in forensic analysis when appropriately applied.