Measurement of electrical properties of contaminated soil1

We present the measured dielectric constant and conductivity of soil samples contaminated by diesel oil. Measurements of the electrical properties of contaminated soil were carried out using a guarded-electrode sample holder and a parallel-plate sample holder in the frequency range 2–250 MHz. Two different soil samples were measured. Both the dielectric constant and the conductivity of the contaminated soils and uncontaminated soils are compared. The measurement results show that the change in the dielectric constant of soils before and after diesel oil contamination is small but significant. These results provide a basis for using ground-penetrating radar or other high-frequency electromagnetic sensors in the detection of soil contamination.     

PAH concentrations in Coquina (Donax spp.) on a sandy beach shoreline impacted by a marine oil spill

The BP MC252 well failure in the Gulf of Mexico, April 2010 caused concern for crude oil and polycyclic aromatic hydrocarbon (PAHs) exposure along the sandy beaches of the Florida Panhandle. We began collections of Coquina clams (Donax spp.) from the surf zone of Florida Panhandle beaches to monitor PAH contamination to compliment analysis of surf zone sand samples. These clams had higher levels of PAHs relative to ambient sand, and this allowed us to continue to monitor PAH levels after sand concentrations fell below limits of detection. PAH levels in the Coquina tissues were highly variable, perhaps indicative of the heterogeneous distribution of oil and tar on the beaches and exposure to tar particles. Overall, PAH levels decreased continuously in both sand and Coquina tissues, reaching limits of detection within one and two years respectively after oil landed on Florida Panhandle beaches. Our work suggests these surf zone molluscs may be used to monitor pollutant exposure along high energy sandy beach shorelines.     

Estimation of clay content in soil based on resistivity modelling and laboratory measurements

The determination of clay content in near‐surface formations is crucial for geotechnical, hydrogeological and oil‐contamination studies. We have developed a technique for estimating clay content that consists of the minimization of the difference between the theoretically calculated and measured soil resistivities as a function of water salinity. To calculate the resistivity, we used a model that takes into account the electrochemical processes in the clay micropores. The experimental measurements of soil resistivity were performed on soil samples, completely saturated by brines at different concentrations of NaCl salt in the range 0.6–100 g/l, to obtain the resistivity versus salinity curve. The parameters obtained with this curve inversion are the clay content, the total porosity and the cation exchange capacity. To verify the new technique, we determined clay concentrations of artificial mixtures of calibrated sand and clay. The relative mean error in the clay content does not exceed 20% for a 5% fitting error of the resistivity versus salinity curves. Such evaluations allow the correct separation of the main lithological groups (sand, sandy loam, loam, and light, medium and heavy clay). We applied this technique to estimate the petrophysical parameters of soils (clay content, porosity and cation exchange capacity) at various sites in Mexico. The results improved the interpretation of the vertical electrical soundings, the lithological soil characterization and the delineation of oil‐contaminated areas.     

Characterization of field scale soil variability using remotely and proximally sensed data and response surface method

Soil salinization of the reclaimed tidelands is problematic. Therefore, there is a need to characterize the spatial variability of soil salinity associated with soil moisture and other soil properties across the reclaimed tidelands. One approach is the use of easily-acquired ancillary data as surrogates for the arduous conventional soil sampling. In a reclaimed coastal tideland in the south of Hangzhou Gulf, backscattering coefficient (σ⁰) from remotely sensed ALOS/PALSAR radar imagery (HH polarization mode) and apparent soil electrical conductivity (ECa) from a proximally sensed EM38 were used to indicate the spatial distribution of soil moisture and salinity, respectively. After that, response surface methodology (RSM) was employed to determine an optimal set of 12 soil samples using spatially referenced σ⁰ and ECa data. Spatial distributions of three soil chemical properties [i.e. soil organic matter (SOM), available nitrogen (AN), and available potassium (AK)] were predicted using inverse distance weighted method based on the 12 samples and were then compared with the predictions generated using 42 samples obtained from a conventional grid sampling scheme. It was concluded that combination of radar imagery and EM induction data can delineate the spatial variability of two key soil properties (i.e. moisture and salinity) across the study area. Besides, RSM-based sampling using radar imagery and EM induction data was highly effective in characterizing the spatial variability of SOM, AN and AK, compared with the conventional grid sampling. This new approach may be used to assist site specific management in precision agriculture.     

轻非水相液体污染过程的高密度电阻率成像法室内监测

为探讨高密度电阻率成像法监测多孔介质中轻非水相液体迁移过程的有效性,本文通过三维砂槽进行了非饱和带中轻非水相液体的污染试验,并利用高密度电阻率成像法进行了同步的动态监测.试验之后,将砂槽层层挖开,通过数码成像,获取了污染区域的实际范围与形状.结果表明,由高密度电阻率成像法圈定的污染区域在范围与形状上都与实际的结果比较接近,并可通过三维电阻率相对值的时间变化明显的看出轻非水相液体的污染过程.这说明利用高密度电阻率成像法对非饱和多孔介质中轻非水相液体的空间分布范围进行圈定并监测其迁移过程是完全可行的.     

Occurrence of MTBE in Heating Oil and Diesel Fuel in Connecticut

The objective of this study was to confirm if MTBE, which is not intentionally added to fuels other than gasoline, is a contaminant in heating oil and diesel fuel. The study entailed conducting a statewide sampling program of heating oil and diesel fuel in Connecticut. An analytical method was developed to conduct analyses of heating oil and diesel fuel for MTBE in the milligram per liter (mg/L) range. The method involved equilibrating product with water to extract MTBE followed by static head-space analysis on aliquots of the water. Analyses were conducted using a gas chromatograph with a MTBE specific column. The statewide sampling program confirmed the widespread occurrence of MTBE in heating oil and diesel fuel. MTBE was detected in all samples collected during our sampling program at concentrations ranging from 9.7 to 906 mg/L in heating oil (26 samples), and from 74 to 120 mg/L in diesel fuel (five samples). Based on these ranges. MTBE concentrations in ground water in the vicinity of heating oil and diesel fuel releases could exceed thousands of micrograms per liter. Our analysis would suggest that the levels of heating oil and diesel fuel contamination observed could result from the commingling of only a few parts gasoline with thousands of parts of these fuels. The extent to which MTBE occurs in heating oil and diesel fuel nationwide is not known, but our data suggests that it may be widespread.     

地质雷达在乌拉山山前断裂探测中的应用

地质雷达是利用电磁波对地下不同电性介质进行探测的地球物理仪器，其探测速率快、分辨率高，可弥补探槽和其他地球物理方法存在探测盲区的缺陷，正在越来越多地应用于活动断层探测领域。本文以乌拉山山前断裂为例开展地质雷达探测工作，使用无人机正射影像技术对测线进行地形校正，获得断层浅部地质雷达图像。研究结果表明，本文研究方法能有效反映探槽揭露的地层单元和断层分布。本次探测中，雷达波形图像特征为:浅地表的土壤层反射波总体较弱；粗粒沉积为主的砾石层反射波总体较强，同相轴连续性好；细粒沉积为主的砂层反射波弱于砾石层，波形以中、高频为主，同相轴具有弱连续性；对于洪冲积地区，地质雷达能分辨具有一定特征的地层单元，这为剖面图像的断层识别提供了标志；通过无人机正射影像技术对地质雷达测线进行地形校正，有利于获得更为准确的探测结果。     

中尺度模拟土壤油污染区探地雷达探测效果分析

为使物理模拟实验效果与实际探测情形更为接近,在室外自然条件下建立中尺度土壤石油污染实验模型,油污染区扩展深度超过1 m,采用实地探测中常用的500 MHz雷达天线进行长期定时探测.通过实测雷达图像特征、土壤含水量含油量分析,并对比前人开展的小尺度室内模拟试验结果,综合评价探地雷达对油污染区的探测效果.研究表明探地雷达探测图像异常特征与污染区扩散阶段密切相关:包气带内油污染区会引起振幅增强;毛细带的油污染区则表现为水位面反射轴附近清晰可辨的高幅异常区,且水位面反射轴呈下凹状;随扩散过程持续进行,异常区下移与水位面反射轴相交,并产生水平扩张.当污染土含油饱和度大于20%时,可通过雷达图像异常区圈定污染范围;当污染土含油饱和度大于15%时,可通过频谱图出现低频响应的位置圈定污染区水平范围.中尺度实验结果与室内小尺度模拟结果具有一致性,可作为油污染区雷达图像异常的解译依据.     

Measurement of Carbon Dioxide in Soil Gases for Indication of Subsurface Hydrocarbon Contamination

A preliminary field evaluation of a new application of soil-gas measurement for delineation of subsurface organic contamination is described. The method measures carbon dioxide concentrations in soil gases and is based on the hypothesis that carbon dioxide concentrations from subsurface oxidation of organic compounds will be porportional to the extent of organic contamination. A correlation coefficient (r) of 0.81 (n=6) was observed between ground water dissolved organic carbon ground water concentrations and carbon dioxide concentrations in the overlying soil gases at one site. Soil-gas carbon dioxide concentrations measured ranged from 0.09 percent to 0.45 percent.     

城市活断层探测中钻孔岩心光释光样品的采集

钻孔岩心测年样品具有较一般地质样品更为复杂的影响因素,样品特征对年龄可靠性有非常重要的影响,且主要受钻进方法和采样过程的制约。采用回转钻进取全心的方法,对光释光测年带来的不确定性影响因素主要有扰动导致软弱土层、砂层的混染;泥浆渗入对样品的污染;挤压和摩擦生热对释光信号的可能影响等。除样品特征外,含水量的变化及放射性平衡状况等对钻孔岩心样品的年龄可能存在影响。释光测年样品的基本要求、测试技术和方法是野外正确采样的依据,针对城市活断层探测工作中钻探任务的一般要求,文中提出了岩心光释光样品采集的建议,并对年代测试时需要考虑的不确定性因素进行了讨论     

A New Soil Sampling Design in Coastal Saline Region Using EM38 and VQT Method

Spatial sampling design based on the variability and distribution of soil properties is an important issue with the progress in precision agriculture and soil ecology. Electromagnetic induction (type EM38) and variance quad‐tree (VQT) method were both applied to optimize the sampling scheme of soil salinity in a coastal reclamation field in north Jiangsu Province, China. Apparent soil electrical conductivity (EC_a) measured with EM38 was used as an ancillary variable and the spatial distribution of EC_a was used as priori information. The process and result of VQT algorithm analysis was illustrated and the obtained sampling strategy was validated using observed soil salinity. Then the spatial precision and sampling efficiency were evaluated. The result indicated that the spatial distribution of soil salinity produced with the VQT scheme was quite similar to that produced with total sampling sites, while sampling quantity of the former was reduced to approximately 1/2 of the latter. The spatial precision of VQT scheme was considerably higher than that of traditional grid method with respect to the same sampling number, and fewer samples were required for VQT scheme to obtain the same precision level. A 17.3% increase in sampling efficiency was achieved by VQT over grid method at the precision level of 90%. The VQT method was proved to be more efficient and economical because it can sample intensively or sparsely according to variation status in local areas. The associated application of EM38 and VQT method provides efficient tools and theoretical basis for saving sampling cost and improving sampling efficiency in coastal saline region and enriching soil ecology.     

Innovative Techniques for Measuring the Oil Content of Oil-Contaminated Porous Media

The oil content of oil-contaminated porous media is an important parameter for the assessment and remediation of oil pollution in soil and groundwater. However, an accurate measurement method is not available. In this study, we propose a new equation to calculate the oil content of water-bearing media based on traditional extraction–ultraviolet spectroscopy. Further, an improved experimental method was developed. The results indicate that the pure solid weight and oil content of oil-contaminated media can be accurately determined by introducing the oil drying loss coefficient (γ). The average relative errors of the improved method range from −0.14% to −0.96%. They are much smaller than errors of −4.49% to −10.97% of the original methods, indicating that the accuracy of measured oil content is enhanced. In addition, the accuracy of the new method does not depend on oil volatility and oil content.     

GPR study of pore water content and salinity in sand

High‐resolution studies of hydrological problems of the near‐surface zone can be better accomplished by applying ground‐probing radar (GPR) and geoelectrical techniques. We report on GPR measurements (500 and 900 MHz antennae) which were carried out on a sorted, clean sand, both in the laboratory and at outdoor experimental sites. The outdoor sites include a full‐scale model measuring 5 × 3 × 2.4 m³ and a salinity site measuring 7.0 × 1.0 × 0.9 m³ with three buried sand bodies saturated with water of various salinities. Our studies investigate the capability of GPR to determine the pore water content and to estimate the salinity. These parameters are important for quantifying and evaluating the water quality of vadose zones and aquifers. The radar technique is increasingly applied in quantifying soil moisture but is still rarely used in studying the problems of water salinity and quality. The reflection coefficient at interfaces is obtained from the amplitude spectrum in the frequency and time domains and is confirmed by 1D wavelet modelling. In addition, the GPR velocity to a target at a known depth is determined using techniques of two‐way traveltime, CMP semblance analysis and fitting an asymptotic diffraction curve. The results demonstrate that the reflection coefficient increases with increasing salinity of the moisture. These results may open up a new approach for applications in environmental problems and groundwater prospecting, e.g. mapping and monitoring of contamination and evaluating of aquifer salinity, especially in coastal areas with a time‐varying fresh‐water lens. In addition, the relationship between GPR velocity and water content is established for the sand. Using this relationship, a subsurface velocity distribution for a full‐scale model of this sand is deduced and applied for migrated radargrams. Well‐focused diffractions separate single small targets (diameter of 2–3 cm, at a depth of 20–180 cm and a vertical interval of 20 cm). The results underscore the high potential of GPR for determining moisture content and its variation, flow processes and water quality, and even very small bodies inside the sand or soil.     

基于开口同轴法的岩矿石样品介电常数测试

火成岩及变质岩找矿是金属探矿的重要组成部分,围岩与矿体之间存在的电性差别是区分二者的重要标志;另外探地雷达以高频电磁波传播为基础,决定电磁波场波速的主要因素是介电常数,因此以介电常数及电导率为内容的电性参数测试就显得尤为必要.传统岩矿石介电常数测试主要使用同轴传输/反射法,而开口同轴法在岩矿石电性测试方面的工作开展较少...     

基于压缩感知和宽带俞式低通整形滤波器的地震低频信息特征分析与补偿

碳酸盐岩储集层已成为世界石油新发现储量的重要组成部分,识别该类储层对地震数据的信噪比、分辨率以及成像精度提出了更高的要求.本文从地震低频信号缺失的问题出发,首先研究了低频信号缺失对子波、合成地震记录和波阻抗反演的影响,其次分析了深层碳酸盐岩裂缝储层中弱信号低频缺失的特征.针对低频信号缺失问题,本文利用压缩感知理论,并结合反射系数的稀疏特性,提出了自适应计算L1范数权重因子的方法,同时构建了改进的宽带俞式低通整形滤波器,在不影响地震高频信号的同时对地震弱信号进行低频补偿.结果表明,缺失低频信号,会使子波旁瓣变大,合成记录出现假同相轴,厚层波阻抗反演畸变,深层碳酸盐岩裂缝储层弱信号难以识别;而本文方法有效地补偿了深层碳酸盐岩裂缝储层弱信号10Hz以下的频率成分,使得波组反射特征更加清晰,深层弱信号成像质量得到改善,为进一步有效识别深层碳酸盐岩裂缝储层建立了基础.     

Application of Electromagnetic Logging to Contamination Investigations in Glacial Sand-and-Gravel Aquifers

Electromagnetic (EM) logging provides an efficient method for high-resolution, vertical delineation of electrically conductive contamination in glacial sand-and-gravel aquifers. LM. gamma, and lithologic logs and specific conductance data from sand-and-gravel aquifers at five sites in the northeastern United States were analyzed to define the relation of KM conductivity to aquifer lithology and water quality. Municipal waste disposal, septic waste discharge, or highway deicing salt application at these sites has caused contaminant plumes in which the dissolved solids concentration and specific conductance of ground water exceed background levels by as much as 10 to 20 limes.
The major hydrogeologic factors that affected KM log response at the five sites were the dissolved solids concentration of the ground water and the silt and clay content in the aquifer. KM conductivity of sand and gravel with uncontaminated water ranged from less than 5 to about 10 millisiemens per meter (mS/m); that of silt and clay zones ranged from about 15 to 45 mS/m: and that of the more highly contaminated zones in sand and gravel ranged from about 10 to more than 80 mS/m. Specific conductance of water samples from screened intervals in sand and gravel at selected monitoring well installations was significantly correlated with KM conductivity.
CM logging can be used in glacial sand-and-gravel aquifer investigations to (1) determine optimum depths for the placement of monitoring well screens: (2) provide a nearly continuous vertical profile of specific conductance to complement depth-specific water quality samples; and (3) identify temporal changes in water quality through sequential logging. Detailed lithologic or gamma logs, preferably both, need to be collected along with the F.M logs to define zones in which elevated EM conductivity is caused by the presence of sill and clay beds rather than contamination.     

北部湾软土吹填场地不同地下水位动力响应研究

为了探究不同地下水位的场地条件下对吹砂填海场地动力响应的影响,以广西北部湾吹砂填海场地为研究对象,基于FLAC3D软件结合前期室内试验结果建立了场地模型,进行了数值模拟分析。在此研究中着重分析地下水位的变化对场地加速度放大系数、加速度反应谱和地震液化效应的影响,为减轻吹砂填海建设场地的震害程度提供参考依据。结果表明:随着地下水位埋深的增加,地表加速度放大系数呈现出逐渐减小的趋势,地震放大作用主要集中在短周期,卓越周期也在短周期处取得;随着地下水位埋深的减小,地震波高频成分被过滤,低频成分被放大,场地特征周期与卓越周期均有增大趋势;地下水位变化对吹填沙土层液化的产生和发展具有显著的影响,随着地下水位的上升,砂土表现出更强的液化效应,并且液化现象随着地震峰值加速度的增大逐渐沿土层深部发展。     

用传播矩阵法研究层状正交各向异性地层中多分量感应测井响应

本文采用传播矩阵技术研究并建立了层状正交各向异性地层中多分量感应测井响应的有效算法.首先通过Fourier变换将频率空间域中的Maxwell方程组求解问题转化为频率波数域中关于电磁场水平分量常微分方程组的定解问题.利用该方程组系数矩阵的本征值和归一化本征向量将电磁场分解成上行波和下行波模式的组合,推导出均匀正交各向异性介质中由任意方向磁偶极子产生的电磁波模式解析表达式;在此基础上,利用叠加原理和边界条件研究了电磁波在层状正交各向异性地层中的反射和透射,给出各个界面上的广义反射系数和不同地层中电磁波振幅的递推公式,进而得到电磁波模式的解析解.为了有效确定频率空间域中的电磁场,采用二维Patterson自适应求积算法结合有限连分式展开技术计算傅氏逆变换.最后通过数值模拟结果证明了该算法的有效性,考察了不同各向异性系数、不同井眼倾角以及仪器长度和工作频率变化等情况下的多分量感应测井响应特征.     

A physical study of low-frequency dispersion of rock conductivity in time-domain electromagnetics

Most rocks display conductivity dispersion in the low-frequency range, when the usual displacement currents are neglected. The strong influence this low-frequency dispersion (LFD), including the response sign reversals, was revealed by field experiments with the coincident-loop configuration widely used in transient electromagnetics (EM). Mathematical modelling of LFD has been the subject of numerous studies. However, confirmation of the role of LFD or induced polarization (IP) by comparing mathematical modelling and field data is rather poor, because knowledge of the properties of rocks in the area of the field measurements is usually insufficient. For this reason physical modelling of LFD has been carried out at Moscow State Geological-prospecting Academy (Russia) in 1994-95. In order to observe criteria of similarity for both induction and polarization transients, a ring-shaped model was chosen and was represented by an electric circuit, consisting of lumped elements (real rock samples included). Qualitatively different transients for dispersive models and their non-dispersive ohmic equivalents were observed.     

CONTAMINATION INDICATIONS DERIVED FROM ELECTRICAL PROPERTIES IN THE LOW FREQUENCY RANGE1

Electrical measurements are an important and integrated component of geophysical investigations connected with environmental problems. As a result of an analysis of the electrical conductivity, basic experiments on sandstones at frequencies below 10 kHz show that the complex behaviour of conductivity is caused exclusively by a complex interface conductivity. Its value is determined mainly by the internal rock interface to porosity ratio, the composition of the pore fluid and connected matrix-water interactions resulting in a specific microstructure of the interface. Therefore, it can be expected that the interface region of a soil or rock material is very sensitive to changes in composition caused by contamination. Contaminated sandstone and clay samples were investigated using a low-frequency measurement system. The investigations are directed at the influence of different contaminants and their concentration. Results show that the complex electrical conductivity (real and imaginary parts) is influenced by properties of the pore-filling contaminant. This influence results in a change of the level of both parts and the shape of their frequency dependence. The imaginary part in particular seems to provide important secondary information; in some cases this part alone allows a differentiation of the various contaminants. The different behaviour of various rock types shows that the effects observed are the result of interactions between pore fluid properties and the internal pore surface structure.