Ng G-H Crystal, Bekins Barbara A, Cozzarelli Isabelle M, Baedecker Mary Jo, Bennett Philip C, Amos Richard T
U.S. Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025, United States.
U.S. Geological Survey, 12201 Sunrise Valley Dr, Reston, VA 20192, United States.
J Contam Hydrol. 2014 Aug;164:1-15. doi: 10.1016/j.jconhyd.2014.04.006. Epub 2014 May 9.
Secondary water quality impacts can result from a broad range of coupled reactions triggered by primary groundwater contaminants. Data from a crude-oil spill research site near Bemidji, MN provide an ideal test case for investigating the complex interactions controlling secondary impacts, including depleted dissolved oxygen and elevated organic carbon, inorganic carbon, CH4, Mn, Fe, and other dissolved ions. To better understand these secondary impacts, this study began with an extensive data compilation of various data types, comprising aqueous, sediment, gas, and oil phases, covering a 260m cross-sectional domain over 30years. Mass balance calculations are used to quantify pathways that control secondary components, by using the data to constrain the sources and sinks for the important redox processes. The results show that oil constituents other than BTEX (benzene, toluene, ethylbenzene, o-, m- and p-xylenes), including n-alkanes and other aromatic compounds, play significant roles in plume evolution and secondary water quality impacts. The analysis underscores previous results on the importance of non-aqueous phases. Over 99.9% of the Fe(2+) plume is attenuated by immobilization on sediments as Fe(II) and 85-95% of the carbon biodegradation products are outgassed. Gaps identified in carbon and Fe mass balances and in pH buffering mechanisms are used to formulate a new conceptual model. This new model includes direct out-gassing of CH4 and CO2 from organic carbon biodegradation, dissolution of directly produced CO2, and sorption with H(+) exchange to improve pH buffering. The identification of these mechanisms extends understanding of natural attenuation of potential secondary impacts at enhanced reductive dechlorination sites, particularly for reduced Fe plumes, produced CH4, and pH perturbations.
二次水质影响可能源于由主要地下水污染物引发的一系列耦合反应。来自明尼苏达州贝米吉附近一个原油泄漏研究地点的数据，为研究控制二次影响的复杂相互作用提供了一个理想的测试案例，这些影响包括溶解氧耗尽以及有机碳、无机碳、甲烷、锰、铁和其他溶解离子含量升高。为了更好地理解这些二次影响，本研究首先广泛收集了各种数据类型，包括水相、沉积物、气相和油相，涵盖了一个260米的横截面区域，时间跨度为30年。通过使用这些数据来约束重要氧化还原过程的源和汇，质量平衡计算被用于量化控制二次成分的途径。结果表明，除了BTEX（苯、甲苯、乙苯、邻二甲苯、间二甲苯和对二甲苯）之外的油类成分，包括正构烷烃和其他芳香族化合物，在羽流演化和二次水质影响中发挥着重要作用。该分析强调了先前关于非水相重要性的研究结果。超过99.9%的亚铁羽流通过以亚铁形式固定在沉积物上而被衰减，85 - 95%的碳生物降解产物通过排气而去除。在碳和铁质量平衡以及pH缓冲机制中发现的差距被用于构建一个新的概念模型。这个新模型包括有机碳生物降解产生的甲烷和二氧化碳的直接排气、直接产生的二氧化碳的溶解以及通过氢离子交换吸附以改善pH缓冲。这些机制的确定扩展了对强化还原脱氯场地潜在二次影响自然衰减的理解，特别是对于还原铁羽流、产生的甲烷和pH扰动。
