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Ground Water Contamination (ground + water_contamination)
Selected AbstractsSorption and leaching behaviour of polar aromatic acids in agricultural soils by batch and column leaching testsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2005R. Celis Summary Aromatic acids can reach the soil from direct anthropogenic activities or, indirectly, from the degradation of many aromatic compounds, such as pesticides or polycyclic aromatic hydrocarbons. Because of the anionic character of aromatic acids at the pH of most soil and sediment environments, they are expected to move rapidly through the soil profile and to pose a great risk of ground water contamination. We designed batch and column leaching tests to characterize the behaviour of three aromatic acids differing in their chemical structures, picloram (4-amino-3,5,6-trichloropicolinic acid), phthalic acid (2,2-benzenedicarboxylic acid), and salicylic acid (2-hydroxybenzoic acid), in four European soils with different physicochemical characteristics. Batch experiments revealed that the persistence of the three acids in soil:water suspensions decreased in the order: picloram , phthalic acid > salicylic acid, and their dissipation curves were relatively independent of soil type. Sorption by the soils, their clay-size fractions and model sorbents indicated much greater affinity of soil constituents for salicylic acid than for picloram or phthalic acid, most likely due to the ability of salicylic acid to form bidentate complexes with positively charged soil components. The extent of leaching of the aromatic acids in hand-packed soil columns decreased in the order: picloram (90,96%) > phthalic acid (25,90%) > salicylic acid (0,37%), which was consistent with the sorption and persistence results of the batch tests. The organic C content, the amount of small-size pores, and the initial concentration of aromatic acid in soil appeared to be important factors influencing the leaching patterns of phthalic acid and salicylic acid in the soils studied, but did not greatly influence the leaching pattern of picloram. Sorption and leaching of polar aromatic acids in soil can therefore vary considerably depending on the structural characteristics of the aromatic acid or soil type. [source] Validation of Numerical Ground Water Models Used to Guide Decision MakingGROUND WATER, Issue 2 2004Ahmed E. Hassan Many sites of ground water contamination rely heavily on complex numerical models of flow and transport to develop closure plans. This complexity has created a need for tools and approaches that can build confidence in model predictions and provide evidence that these predictions are sufficient for decision making. Confidence building is a long-term, iterative process and the author believes that this process should be termed model validation. Model validation is a process, not an end result. That is, the process of model validation cannot ensure acceptable prediction or quality of the model. Rather, it provides an important safeguard against faulty models or inadequately developed and tested models. If model results become the basis for decision making, then the validation process provides evidence that the model is valid for making decisions (not necessarily a true representation of reality). Validation, verification, and confirmation are concepts associated with ground water numerical models that not only do not represent established and generally accepted practices, but there is not even widespread agreement on the meaning of the terms as applied to models. This paper presents a review of model validation studies that pertain to ground water flow and transport modeling. Definitions, literature debates, previously proposed validation strategies, and conferences and symposia that focused on subsurface model validation are reviewed and discussed. The review is general and focuses on site-specific, predictive ground water models used for making decisions regarding remediation activities and site closure. The aim is to provide a reasonable starting point for hydrogeologists facing model validation for ground water systems, thus saving a significant amount of time, effort, and cost. This review is also aimed at reviving the issue of model validation in the hydrogeologic community and stimulating the thinking of researchers and practitioners to develop practical and efficient tools for evaluating and refining ground water predictive models. [source] Ground Water Chlorinated Ethenes in Tree Trunks: Case Studies, Influence of Recharge, and Potential Degradation MechanismGROUND WATER MONITORING & REMEDIATION, Issue 3 2004Don A. Vroblesky Trichloroethene (TCE) was detected in cores of trees growing above TCE-contaminated ground at three sites: the Carswell Golf Course in Texas, Air Force Plant PJKS in Colorado, and Naval Weapons Station Charleston in South Carolina. This was true even when the depth to water was 7.9 m or when the contaminated aquifer was confined beneath ,3 m of clay. Additional ground water contaminants detected in the tree cores were cis,1,2-dichloroethene at two sites and tetrachloroethene at one site. Thus, tree coring can be a rapid and effective means of locating shallow subsurface chlorinated ethenes and possibly identifying zones of active TCE dechlorination. Tree cores collected over time were useful in identifying the onset of ground water contamination. Several factors affecting chlorinated ethene concentrations in tree cores were identified in this investigation. The factors include ground water chlorinated ethene concentrations and depth to ground water contamination. In addition, differing TCE concentrations around the trunk of some trees appear to be related to the roots deriving water from differing areas. Opportunistic uptake of infiltrating rainfall can dilute prerain TCE concentrations in the trunk. TCE concentrations in core headspace may differ among some tree species. In some trees, infestation of bacteria in decaying heartwood may provide a TCE dechlorination mechanism within the trunk. [source] Used Motor Oil as a Source of MTBE, TAME, and BTEX to Ground WaterGROUND WATER MONITORING & REMEDIATION, Issue 4 2002Ronald J. Baker Methyl tert-butyl ether (MTBE), the widely used gasoline oxygenate, has been identified as a common ground water contaminant, and BTEX compounds (benzene, toluene, ethylbenzene, and xylenes) have long been associated with gasoline spills. Because not all instances of ground water contamination by MTBE and BTEX can be attributed to spills or leaking storage tanks, other potential sources need to be considered. In this study, used motor oil was investigated as a potential source of these contaminants. MTBE in oil was measured directly by methanol extraction and gas chromatography using a flame ionization detector (GC/FID). Water was equilibrated with oil samples and analyzed for MTBE, BTEX, and the oxygenate tert-amyl methyl ether (TAME) by purge- and-trap concentration followed by GC/FID analysis. Raoult's law was used to calculate oil-phase concentrations of MTBE, BTEX, and TAME from aqueous-phase concentrations. MTBE, TAME, and BTEX were not detected in any of five new motor oil samples, whereas these compounds were found at significant concentrations in all six samples of the used motor oil tested for MTBE and all four samples tested for TAME and BTEX. MTBE concentrations in used motor oil were on the order of 100 mg/L. TAME concentrations ranged from 2.2 to 87 mg/L. Concentrations of benzene were 29 to 66 mg/L, but those of other BTEX compounds were higher, typically 500 to 2000 mg/L. 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