Background.Traveler's diarrhea in Thailand is frequently caused by Campylobacter jejuni. Rates of fluoroquinolone (FQ) resistance in Campylobacter organisms have exceeded 85% in recent years, and reduced fluoroquinolone efficacy has been observed.
Abstract A series of quantitative decision frameworks were developed to aid in the evaluation of Monitored Natural Attenuation (MNA) as a remedy for 1,4‐dioxane, chlorinated ethanes, and chlorinated ethenes. The end product is an updated version of BioPIC, a successful, existing decision framework for MNA of chlorinated ethenes. In evaluating MNA, the goal is to follow existing protocols but also incorporate more recent insights that have increased the potential viability of this technology for a wider number of contaminants. This includes data supporting the first line of evidence for MNA (decreasing concentration trends over time at appropriate sampling locations), as well as data that will serve as secondary and tertiary lines of evidence for MNA. For the BioPIC update, a similar lines of evidence approach was developed, using information from literature and project‐specific data to identify the relevant lines of evidence. As part of the update, a model for predicting contaminant trends over time and distance, including a method to estimate site‐specific biodegradation rate constants for chlorinated ethenes, chlorinated ethanes, and 1,4‐dioxane, has been included within BioPIC. The quantitative software tool provides step‐by‐step technical guidance for collecting and evaluating other lines of evidence, including data associated with targeted 14 C assays, isotope fractionation, biomarkers for degradation, geochemical parameters, and co‐contaminant concentrations, to improve the MNA evaluation process.
Abstract In situ biotransformation of BTEX (benzene, toluene, ethylbenzene, o ‐, m ‐, and p ‐xylenes) was investigated for a gasoline spill at Seal Beach Naval Weapons Station ( Schroeder 1991 ) under methanogenic conditions in three controlled‐release push‐pull experiments. To create methanogenic conditions, anaerobic ground water (710 to 1365 L) was extracted from the anaerobic test zone, treated by deionization to remove nitrate and sulfate, and helium‐purged to remove any traces of oxygen. Prior to release through the multiport injection/extraction well, the injection water was amended with BTEX compounds (160 to 367 μg/L) and bromide tracer. Contaminant transformation was observed in three consecutive experiments by withdrawing samples at regular intervals for periods of 73 to 159 d. BTEX removal rates were rapid for toluene and o ‐ and m ‐xylenes (<30 d), and slow for benzene, ethylbenzene, and p ‐xylene degrading (50% removal in 60 to 90 d). Methane was formed in all cases, and the levels of soluble iron, sulfate, and nitrate were too low to account for the levels of BTEX transformation observed. The data confirm that the presence of electron acceptors (oxygen, nitrate, iron, sulfate) is not a precondition for natural attenuation to occur.
The distribution of natural organic carbon was investigated at a chloroethene-contaminated site where complete reductive dechlorination of tetrachloroethene (PCE) to vinyl chloride and ethene was observed. In this study, operationally defined potentially bioavailable organic carbon (PBOC) was measured in surficial aquifer sediment samples collected at varying depths and locations in the vicinity of a dense nonaqueous phase liquid (DNAPL) source and aqueous phase plume. The relationship between chloroethene concentrations and PBOC levels was examined by comparing differences in extractable organic carbon in aquifer sediments with minimal chloroethene exposure relative to samples collected in the source zone. Using performance-monitoring data, direct correlations with PBOC were also developed with chloroethene concentrations in groundwater. Results show a logarithm-normal distribution for PBOC in aquifer sediments with a mean concentration of 187 mg/kg. PBOC levels in sediments obtained from the underlying confining unit were generally greater when compared to sediments collected in the sandy surficial aquifer. Results demonstrated a statistically significant inverse correlation (p=0.007) between PBOC levels in aquifer sediments and chloroethene concentrations for selected monitoring wells in which chloroethene exposure was the highest. Results from laboratory exposure assays also demonstrated that sediment samples exhibited a reduction in PBOC levels of 35% and 73%, respectively, after a 72-h exposure period to PCE (20,000 μg/L). These results support the notion that PBOC depletion in sediments may be expected in chloroethene-contaminated aquifers, which has potential implications for the long-term sustainability of monitored natural attenuation.
Abstract : The Strategic Environmental Research and Development Program (SERDP) and the Environmental Security Technology Certification Program (ESTCP) are the Department of Defense's (DoD) environmental research programs (herein referred to as The Programs ), harnessing the latest science and technology to improve DoD s environmental performance, reduce costs, and enhance and sustain mission capabilities. The Programs fund basic and applied research as well as field demonstration and validation efforts. For additional information, refer to www.serdp-estcp.org. This workshop focused on the research needed to more efficiently deal with the long term management and lengthy restoration of complex sites, with overall objectives to (1) review the current status of complex sites, expectations for restoration, and how they are managed, (2) identify options for achieving restoration goals more efficiently over longer periods of time, (3) prioritize the research and demonstrations needed to show that restoration goals can be achieved more efficiently over longer periods of time, and to develop the new technologies needed to support that paradigm, and (4) promote cooperation with other federal agencies to fund the needed work most efficiently. Approximately 60 invited personnel representing DoD remedial program managers (RPMs), federal and state regulators, engineers, researchers, industry representatives, and consultants were in attendance. Two breakout sessions, each with four working groups, facilitated discussions of the current state of the science and ranking of research, demonstration and technology transfer needs for four areas: enhanced attenuation, long term monitoring, predictive modeling, and emerging contaminants. The research, demonstration and technology transfer needs were prioritized in each work group (Table E-1).
