The Hydraulic Profiling Tool (HPT) has become one of the most widely accepted approaches for obtaining vertical profiles of hydraulic conductivity (K) in environmental site investigations. The current tool, however, is limited to use in moderately permeable settings with a measurable K range of 0.03 to 25 m/d. In this work, we added a low‐flow injection system to standard HPT and modified the field profiling procedure so that it could be used more effectively in lower‐K settings. The modified lower‐K HPT was tested and evaluated against direct‐push slug tests at a field site in the Kansas River floodplain. Results indicated that when the injection rate was reduced, injection pressure decreased, which reduced the potential of injection‐induced formation alteration. A particular challenge of applying HPT in lower‐K zones is the large pressure generated by probe advancement; this can significantly affect the pressure signal measured at the injection screen. Our results showed that the impacts of advancement‐generated pressure could be mitigated by reducing the speed of probe advancement. Compared to K estimates by slug tests, the vertical variability in HPT K was much lower. The reduced variability in HPT K was likely due to formation alteration during probe advancement, as well as pressure interference from injections at previous depths and probe advancement at the bottom. Additional work, such as the use of a smaller‐diameter probe, is needed to further improve the performance of HPT in lower permeability zones.
水力剖面工具（HPT）已成为在环境现场调查中获取水力传导性（K）垂直剖面图的最广为接受的方法之一。然而，目前的工具仅限于在中等渗透性环境中使用，可测量的 K 值范围为 0.03 到 25 m/d。在这项工作中，我们在标准 HPT 中添加了一个低流量注入系统，并修改了现场剖析程序，使其能够更有效地用于 K 值较低的环境。在堪萨斯河洪泛区的一个野外地点，我们对改进后的低 K 值 HPT 进行了测试，并与直接推动弹头测试进行了对比评估。结果表明，当注入速度降低时，注入压力也随之降低，从而降低了注入引起地层变化的可能性。在低 K 区应用 HPT 的一个特殊挑战是探头推进产生的巨大压力；这会严重影响在注入滤网处测得的压力信号。我们的研究结果表明，降低探头推进速度可以减轻推进产生的压力的影响。与泥浆测试估计的 K 值相比，HPT K 值的垂直变化要小得多。HPT K 值的变异性降低可能是由于在探头推进过程中地层发生了变化，以及前一深度的注入和探头在底部的推进产生了压力干扰。要进一步提高 HPT 在低渗透区的性能，还需要开展更多的工作，例如使用直径更小的探头。
{"title":"Assessment of the Hydraulic Profiling Tool for Lower Permeability Characterization","authors":"Gaisheng Liu, Steven Knobbe","doi":"10.1111/gwmr.12685","DOIUrl":"https://doi.org/10.1111/gwmr.12685","url":null,"abstract":"The Hydraulic Profiling Tool (HPT) has become one of the most widely accepted approaches for obtaining vertical profiles of hydraulic conductivity (K) in environmental site investigations. The current tool, however, is limited to use in moderately permeable settings with a measurable K range of 0.03 to 25 m/d. In this work, we added a low‐flow injection system to standard HPT and modified the field profiling procedure so that it could be used more effectively in lower‐K settings. The modified lower‐K HPT was tested and evaluated against direct‐push slug tests at a field site in the Kansas River floodplain. Results indicated that when the injection rate was reduced, injection pressure decreased, which reduced the potential of injection‐induced formation alteration. A particular challenge of applying HPT in lower‐K zones is the large pressure generated by probe advancement; this can significantly affect the pressure signal measured at the injection screen. Our results showed that the impacts of advancement‐generated pressure could be mitigated by reducing the speed of probe advancement. Compared to K estimates by slug tests, the vertical variability in HPT K was much lower. The reduced variability in HPT K was likely due to formation alteration during probe advancement, as well as pressure interference from injections at previous depths and probe advancement at the bottom. Additional work, such as the use of a smaller‐diameter probe, is needed to further improve the performance of HPT in lower permeability zones.","PeriodicalId":501449,"journal":{"name":"Groundwater Monitoring & Remediation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142225049","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Three new programs have been developed to perform parameter estimation to assist in the calibration of analytical contaminant transport models. The Domenico equation was chosen as an example analytical model for each of the three programs rather than a model with the exact solution, because the former is a closed‐form expression involving significantly less processing time. One of the programs studied is a quasi‐exhaustive search method and the second is a successive parameter variation method. The third program is based on Box's Complex nonlinear, direct‐search optimization method. The three programs and an already available calibration tool (PEST) were compared in tests using data from two different sites in southeastern Pennsylvania. These tests demonstrated the validity of the three programs as examples to assist the calibration of groundwater analytical transport models. The final estimates for the parameter values for the three methods and PEST applied to the data from each of the two sites compared quite closely and, with two exceptions were well within an order of magnitude of each other. The three newly available programs individually should serve as calibrating tools indispensable for field hydrogeologists, environmental project managers, and others who have been asked to run analytical transport models. The results from the runs performed on the two sites indicate the Complex method to be the best option as a calibration tool, with the quasi‐exhaustive method and the successive parameter estimation method being acceptable alternatives.
我们开发了三个新程序来进行参数估计，以帮助校准污染物迁移分析模型。这三个程序都选择了多梅尼科方程作为分析模型的示例，而不是精确解的模型，因为前者是闭式表达，处理时间大大减少。所研究的程序之一是准穷举搜索法，第二个是连续参数变化法。第三个程序基于 Box 的复杂非线性直接搜索优化方法。在使用宾夕法尼亚州东南部两个不同地点的数据进行的测试中，对这三个程序和已有的校准工具（PEST）进行了比较。这些测试证明了这三个程序作为协助校准地下水分析传输模型的示例的有效性。这三种方法和 PEST 应用于两个地点数据的参数值的最终估计值非常接近，除两个例外情况外，彼此都在一个数量级之内。对于现场水文地质学家、环境项目经理和其他被要求运行分析迁移模型的人来说，这三个新推出的程序都是不可或缺的校准工具。在两个地点进行的运行结果表明，复合方法是校准工具的最佳选择，而准穷举法和连续参数估计法是可以接受的替代方法。
{"title":"Studies in Parameter Estimation for Analytical Transport Equations","authors":"Andrew Mills","doi":"10.1111/gwmr.12684","DOIUrl":"https://doi.org/10.1111/gwmr.12684","url":null,"abstract":"Three new programs have been developed to perform parameter estimation to assist in the calibration of analytical contaminant transport models. The Domenico equation was chosen as an example analytical model for each of the three programs rather than a model with the exact solution, because the former is a closed‐form expression involving significantly less processing time. One of the programs studied is a quasi‐exhaustive search method and the second is a successive parameter variation method. The third program is based on Box's Complex nonlinear, direct‐search optimization method. The three programs and an already available calibration tool (PEST) were compared in tests using data from two different sites in southeastern Pennsylvania. These tests demonstrated the validity of the three programs as examples to assist the calibration of groundwater analytical transport models. The final estimates for the parameter values for the three methods and PEST applied to the data from each of the two sites compared quite closely and, with two exceptions were well within an order of magnitude of each other. The three newly available programs individually should serve as calibrating tools indispensable for field hydrogeologists, environmental project managers, and others who have been asked to run analytical transport models. The results from the runs performed on the two sites indicate the Complex method to be the best option as a calibration tool, with the quasi‐exhaustive method and the successive parameter estimation method being acceptable alternatives.","PeriodicalId":501449,"journal":{"name":"Groundwater Monitoring & Remediation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142195399","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The concentrations and transport of volatile organic compounds (VOCs) and other vapors in the vadose zone may exhibit some degree of temporal variability due to the effect of various climatic factors, including (1) Air temperature; (2) Barometric pressure; (3) Surface winds; and (4) Soil moisture, including the effects of any water infiltration and/or changes in groundwater level. These variables may directly affect the rates of gas transport through the vadose zone or may indirectly affect transport by changing the soil‐gas concentrations at a given location and depth. To understand the potential effect of these factors due to climate change, it is first necessary to understand their effect over typical time periods of one to several days, seasonally, and annually. In this paper, the effects of the above variables over various time periods are presented and the long‐term effects due to climate change are discussed. Standard approaches for soil‐gas measurement attempt to account for these variables, either to negate their potential influence or to capture data under reasonably worst‐case conditions. The appropriateness and adequacy of typical soil vapor measurement approaches are discussed.
{"title":"Climatic Effects on Vapor Flow and Behavior in the Vadose Zone","authors":"Bart Eklund","doi":"10.1111/gwmr.12682","DOIUrl":"https://doi.org/10.1111/gwmr.12682","url":null,"abstract":"The concentrations and transport of volatile organic compounds (VOCs) and other vapors in the vadose zone may exhibit some degree of temporal variability due to the effect of various climatic factors, including (1) Air temperature; (2) Barometric pressure; (3) Surface winds; and (4) Soil moisture, including the effects of any water infiltration and/or changes in groundwater level. These variables may directly affect the rates of gas transport through the vadose zone or may indirectly affect transport by changing the soil‐gas concentrations at a given location and depth. To understand the potential effect of these factors due to climate change, it is first necessary to understand their effect over typical time periods of one to several days, seasonally, and annually. In this paper, the effects of the above variables over various time periods are presented and the long‐term effects due to climate change are discussed. Standard approaches for soil‐gas measurement attempt to account for these variables, either to negate their potential influence or to capture data under reasonably worst‐case conditions. The appropriateness and adequacy of typical soil vapor measurement approaches are discussed.","PeriodicalId":501449,"journal":{"name":"Groundwater Monitoring & Remediation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142195400","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Henry C.G. Nicholls, H. Emma Mallinson, Steven F. Thornton, Markus Hjort, Stephen A. Rolfe
A limited number of microorganisms have been identified with the capability to degrade ethyl tert‐butyl ether (ETBE) in the environment. Knowledge of the identity and distribution of ETBE‐degrading microorganisms is important for the implementation of management measures such as natural attenuation and bioremediation at ETBE‐release sites. In this study, DNA‐stable isotope probing (SIP) was used to identify microorganisms able to aerobically degrade 13C‐labeled ETBE in laboratory microcosms constructed with groundwater and aquifer material from an ETBE‐release site. Microorganisms in the Class γ‐proteobacteria, Order β‐proteobacteriales, Family Burkholderiaceae, and classified as Methylibium and Leptothrix, respectively, were identified as primary ETBE degraders. Comparisons with ETBE‐responsive microorganisms (those which increased in abundance after the addition of ETBE), identified by high‐throughput sequencing of microcosms established from the same site, showed that only a small proportion of the ETBE‐responsive organisms were primary degraders as determined by SIP. ETBE degraders were taxonomically related to microorganisms able to degrade other gasoline components, but not ETBE, implying that this functionality results from acquisition of the eth gene cluster by these organisms. These ETBE degraders could also be identified at ETBE‐release sites, but at low relative abundance and generally only in those locations from which the microcosms had been established. Therefore, we recommend that molecular investigations of ETBE‐contaminated sites focus on functional genes (i.e., the eth gene cluster) rather than specific taxa.
{"title":"Identification of Aerobic ETBE‐Degrading Microorganisms in Groundwater Using Stable Isotope Probing","authors":"Henry C.G. Nicholls, H. Emma Mallinson, Steven F. Thornton, Markus Hjort, Stephen A. Rolfe","doi":"10.1111/gwmr.12679","DOIUrl":"https://doi.org/10.1111/gwmr.12679","url":null,"abstract":"A limited number of microorganisms have been identified with the capability to degrade ethyl <jats:italic>tert</jats:italic>‐butyl ether (ETBE) in the environment. Knowledge of the identity and distribution of ETBE‐degrading microorganisms is important for the implementation of management measures such as natural attenuation and bioremediation at ETBE‐release sites. In this study, DNA‐stable isotope probing (SIP) was used to identify microorganisms able to aerobically degrade <jats:sup>13</jats:sup>C‐labeled ETBE in laboratory microcosms constructed with groundwater and aquifer material from an ETBE‐release site. Microorganisms in the Class γ‐proteobacteria, Order β‐proteobacteriales, Family Burkholderiaceae, and classified as <jats:italic>Methylibium</jats:italic> and <jats:italic>Leptothrix</jats:italic>, respectively, were identified as primary ETBE degraders. Comparisons with ETBE‐responsive microorganisms (those which increased in abundance after the addition of ETBE), identified by high‐throughput sequencing of microcosms established from the same site, showed that only a small proportion of the ETBE‐responsive organisms were primary degraders as determined by SIP. ETBE degraders were taxonomically related to microorganisms able to degrade other gasoline components, but not ETBE, implying that this functionality results from acquisition of the <jats:italic>eth</jats:italic> gene cluster by these organisms. These ETBE degraders could also be identified at ETBE‐release sites, but at low relative abundance and generally only in those locations from which the microcosms had been established. Therefore, we recommend that molecular investigations of ETBE‐contaminated sites focus on functional genes (i.e., the <jats:italic>eth</jats:italic> gene cluster) rather than specific taxa.","PeriodicalId":501449,"journal":{"name":"Groundwater Monitoring & Remediation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141745284","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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