Acquisition of Representative Ground Water Quality Samples for Metals

R.S. Kerr Environmental Research Laboratory (RSKERL) personnel have evaluated sampling procedures for the collection of representative, accurate, and reproducible ground water quality samples for metals for the past four years. Intensive sampling research at three different field sites has shown that the method by which samples are collected has a greater impact on sample quality, accuracy, and reproducibility than whether the samples are filtered or not. In particular, sample collection practices that induce artificially high levels of turbidity have been shown to have the greatest negative impacts on sample quality. Results indicated the ineffectiveness of bailers for collection of representative metal samples. Inconsistent operator usage together with excessive purging generally resulted in excessive turbidity (>100 NTUs) and large differences in filtered and unfiltered metal samples. The use of low flow rate purging and sampling consistently produced filtered and unfiltered samples that showed no significant differences in concentrations. Turbidity levels were generally less than 5 NTUs, even in fine-textured glacial till. We recommend the use of low flow rates, during both purging and sampling, placement of the sampling intake at the desired sampling point, minimal disturbance of the stagnant water column above the screened interval, monitoring of water quality indicators during purging, minimization of atmospheric contact with samples, and collection of unfiltered samples for metal analyses to estimate total contaminant loading in the system. While additional time is spent due to use of low flow rates, this is compensated for by eliminating the need for filtration, decreased volume of contaminated purge water, and less resampling to address inconsistent data results.     

三层BP神经网络地震灾害人员伤亡预测模型

选择地震发生时刻、震级、震中烈度、建筑物倒塌和严重破坏率、抗震设防水准、人口密度、地震预报等7个评价指标,以20次严重地震灾害为示例（其中,17个作训练样本,3个作验证样本）,建立了三层BP神经网络地震灾害人员伤亡预测模型。基于MATLAB6,5BP神经网络训练,得出的预测结果与各个示例的实际数值比较吻合。验证样本的训练结果表明,该模型适用于地震灾害人员伤亡评估。通过对评价指标的权重计算,确认人口密度、建筑物倒塌与严重破坏率、震中烈度是影响地震灾害人员伤亡的主要因素,地震预报、抗震设防水准、地震发生时刻和震级次之。作为人为可控预测指标,减少人口密度特别是城市人口密度,提高建（构）筑物抗震能力及预测预报水平,对于减少地震灾害人员伤亡起更重要的作用。     

3D multi-fractal analysis of porous media using 3D digital images: considerations for heterogeneity evaluation

Pore structure heterogeneity is a critical parameter controlling mechanical, electrical and flow transport behaviour of rock. Multi-fractal analysis method was used for a heterogeneity comparison of three-dimensional rock samples with different lithology. Six real digital samples, containing three sandstones and three carbonates, were used. Based on the mercury injection capillary pressure test on these samples, we found that the carbonate samples are more heterogeneous than sandstones, but primary results of multi-fractal behaviours for all samples were similar. We show that if multi-fractal is used to evaluate and compare heterogeneity of different samples, one needs to follow some considerations such as (1) all samples must have the same size in pixel, (2) samples volume must be bigger than representative volume element, (3) multi-fractal dimensions should be firstly normalized to a determined porosity value and (4) multi-fractal results should be interpreted based on resolution of the imaging tool (effects of fine scale sub-resolution pores are missed). Results revealed that using normalized fractal dimensions, the real samples were divided to less and high heterogeneous groups. Moreover, the study of scale effect also showed that porous structures of these samples are scale invariant in a wide range of scales (from one to eight times bigger).     

Comparison of analytical methods for the determination of silica in geothermal waters

The silica concentration of 26 Guatemalan geothermal waters were analyzed colorimetrically (spectrophotometrically) and by atomic absorption. Results by the atomic absorption method were less affected by polymerization and precipitation of silica from supersaturated solutions.Shaking the samples prior to analysis improves the accuracy of the atomic absorption results.The advantages of colorimetric analysis over atomic absorption are better sensitivity and precision. However, for accurate colorimetric results, geothermal samples must be sufficiently diluted in the field, which ensures that no further polymerization occurs and that amorphous silica that may be present will redissolve. If the samples are not diluted in the field they should be diluted in the laboratory and left standing for at least a month to allow the silica to redissolve. If analyzed immediately the diluted samples should be made alkaline and heated overnight in a 90° oven.     

Quality Assessment of Southeast Nile Delta Groundwater for Irrigation

The Nile Delta aquifer has deteriorated in the quality of the groundwater due to domestic, agricultural and industrial activities. In order to examine this, a dataset of thirty-one shallow groundwater samples and four surface water samples were collected in May 2014. The objective of our study is to investigate the hydrochemical characteristics of the groundwater at El-Khanka region in El-Qalubia governorate, southern Nile Delta to discuss the possibility of groundwater use for agricultural purpose. Groundwater types were defined, and the suitability for use in irrigation was evaluated. The factor analysis was conducted to investigate the relationship between the thirteen variables for exploring the loading of them in the model. Then, the principal component analysis was performed to identify the linear combination of variables that account for the greatest amount of common variance. Results showed that groundwater samples are mainly alkaline with an average pH value of 8.60. The total dissolved solids (TDS) range from 350 to 1456 mg/L. The highest concentrations of the anions and cations are sulfate (\(\rm{SO}_4^{2-}\)) and sodium (Na⁺) respectively. The residual sodium carbonate (RSC) is less than 1.25 meq/L. Also, all groundwater samples are located in good and permissible salinity with TDS < 1500 mg/L. In addition, all samples are located in the low sodium hazard zone where sodium adsorption ratio (SAR) is less than 10. Therefore, it is concluded that, the groundwater is suitable for irrigation use in El-Qalubia Governorate. Four factors with Eigenvalues above 1.0 which correlated to each other contributed to the model with 81% of the total variance and governed the spatial variability of the aquifer.     

Cryogenic Core Collection and Preservation of Subsurface Samples for Biomolecular Analysis

A cryogenic coring system for the collection and preservation of biomolecules in unconsolidated subsurface solid samples is presented here. The sampler is based on existing direct‐push coring technology, with the addition of a cryogenic step to freeze the sample in situ. Once brought to the surface, the frozen cores can be packed in dry ice and shipped to the laboratory for further processing and analysis. The approach prevents redistribution of fluids during sample recovery and shipping, and because the cores are frozen in situ there is little loss of solid material during retrieval to ground surface. To evaluate the performance of the approach, DNA analyses of samples collected by cryogenic coring in a very large physical model are compared with results from water samples and horizontal core samples taken in close proximity. The data indicate that the vertical distribution of DNA within the cryogenic core can be measured at the centimeter scale, providing unprecedented characterization of subsurface biogeochemical interfaces.     

Equipment for the studies of the acoustic properties of hydrate-containing samples in laboratory conditions

Equipment for simulation in laboratory conditions of hydrate-containing artificial samples and measuring their acoustic properties (wave velocities, absorption and attenuation) at different temperature and pressures is designed and constructed. The plant consists of a high-pressure chamber (up to 45 MPa), a measuring system intended for the excitation and reception of acoustic waves, systems for temperature and pressure control (axial and lateral) and for gas/liquid delivery into the sample. The measurements are performed on cylindrical samples with a 30-mm diameter and height of 10–50 mm. A set of successful test experiments was performed, including measurements of acoustic velocities of consolidated (plexiglas, sandstone, and frozen sand) and unconsolidated (dry and wet quartz sand) samples and formation of methane-hydrate bearing samples.     

Comparison of Methods for Sampling Dissolved Nitrogen in a Fractured Carbonate-Rock Aquifer

As part of an agricultural non-point-source study in the Conestoga River head waters area in Pennsylvania, different methods for collecting ground water samples from a fractured carbonate-rock aquifer were compared. Samples were collected from seven wells that had been cased to bedrock and drilled as open holes to the first significant water-bearing zone. All samples were analyzed for specific conductance, dissolved oxygen, and dissolved-nitrogen species. Water samples collected by a point sampler without pumping the well were compared to samples collected by a submersible pump and by a point sampler after pumping the well. Samples collected by using a point sampler, adjacent to major water-bearing zones in an open borehole without pumping the well, were not statistically different from samples collected from the pump discharge or from point samples collected adjacent to major water-bearing zones after pumping the well. Samples collected by using a point sampler without pumping the well at depths other than those adjacent to the water-bearing zones did not give the same results as the other methods, especially when the water samples were collected from within the well casings. It was concluded that, for the wells at this site, sampling adjacent to major water-bearing zones by using a point sampler without pumping the well provides samples that are as representative of aquifer conditions as samples collected from the pump discharge after reaching constant temperature and specific conductance, and by using a point sampler after pumping the well.     

An Evaluation of Some Systems for Sampling Gas-Charged Ground Water for Volatile Organic Analysis

Loss of volatile organics during sampling is a well-recognized source of bias in ground water monitoring; sampling protocols attempt to minimize such loss. Such bias could be enhanced for ground water highly charged with dissolved gases such as methane. Such ground water was the object of this study. A positive-displacement bladder pump, a momentum-lift pump and a suction-lift, peristaltic pump were employed in sampling both methane-charged ground water for volatile aromatic hydrocarbons and a CO₂-charged reservoir water for volatile chlorinated hydrocarbons. In both cases, the suction-lift pump produced samples with a significant negative bias (9 to 33 percent) relative to the other methods. Little difference between samples produced by the other pump Systems was noted at the field site, but in sampling the reservoir, the bladder pump produced samples that were 13 to 19 percent lower in halocarbon concentration than were samples from the momentum-lift pump.
These negative biases are tentatively interpreted as losses due to volatilization during sampling. Slightly greater negative biases occur for compounds of higher volatility as estimated from their Henry's law constants. Additional studies appear to be warranted in order to adequately establish the scientific basis for recommending protocols for sampling ground water in which degassing could enhance the loss of volatile organics during sampling.     

Observed advantage for negative binomial over Poisson distribution in partial duration series

The goodness of fit of the negative binomial and the Poisson distributions to partial duration series of runoff events is tested. The data have been recorded by eight hydrometric stations located on ephemeral rivers in Isreal. For each station, a number of threshold discharges are considered, by that series of nested subsamples are formed. Owing to size limitations, a Chi-square test is conducted on samples associated with low to moderate threshold discharges. Positive results, at a 5% significance level, are obtained in 30 out of the 53 tests of the Poisson distribution, and in 22 out of the 28 tests of the negative binomial distribution. The fit of the Poisson distribution to samples of conventionally recommended sizes (of 2 to 3 events per year) is found positive for five rivers and negative for the three other rivers The fit of the negative binomial distribution to these samples is found positive for six rivers, inconclusive for one river and short of data for the eighth river. Mixed results are obtained as the threshold level is raised. Therefore, no direct extrapolation is possible to samples associated with high thresholds.An indirect extrapolation is drawn through a comparison of the actual properties of the samples with those expected under a perfect fit of the distribution functions. Ranges of such properties are defined with respect to the properties of the tested samples and to the test results. The actual properties of nine of the eleven samples associated with high thresholds (i.e. mean number of events <-0.1year ^–1) are found within these ranges. This provides a hint for a probable good fit of either distribution, and particularly the negative binomial, to the occurrence frequency of high events.     

Observed advantage for negative binomial over Poisson distribution in partial duration series

The goodness of fit of the negative binomial and the Poisson distributions to partial duration series of runoff events is tested. The data have been recorded by eight hydrometric stations located on ephemeral rivers in Isreal. For each station, a number of threshold discharges are considered, by that series of nested subsamples are formed. Owing to size limitations, a Chi-square test is conducted on samples associated with low to moderate threshold discharges. Positive results, at a 5% significance level, are obtained in 30 out of the 53 tests of the Poisson distribution, and in 22 out of the 28 tests of the negative binomial distribution. The fit of the Poisson distribution to samples of conventionally recommended sizes (of 2 to 3 events per year) is found positive for five rivers and negative for the three other rivers The fit of the negative binomial distribution to these samples is found positive for six rivers, inconclusive for one river and short of data for the eighth river. Mixed results are obtained as the threshold level is raised. Therefore, no direct extrapolation is possible to samples associated with high thresholds.An indirect extrapolation is drawn through a comparison of the actual properties of the samples with those expected under a perfect fit of the distribution functions. Ranges of such properties are defined with respect to the properties of the tested samples and to the test results. The actual properties of nine of the eleven samples associated with high thresholds (i.e. mean number of events <-0.1year ^–1) are found within these ranges. This provides a hint for a probable good fit of either distribution, and particularly the negative binomial, to the occurrence frequency of high events.     

Laboratory technique for measurement of spectral induced polarization response of soil sampies1

Laboratory measurements of soil samples are necessary to assess the effect of mineralogy, grain size distribution, moisture content, and electrolyte composition on the resistivity spectrum of soil material. Laboratory results are also required for the interpretation of field data. Induced polarization phenomena in glacial soils are poorly understood and so far no convenient laboratory techniques are available for its measurement. Coarse grain size and the need to measure unsaturated samples and to monitor the homogeneity of the sample require a sample holder–electrode construction that differs from those presented in Clay mineral Studies. This study presents a spectral induced polarization laboratory system that is suitable for measuring fine- and coarse-grained and both saturated and unsaturated soil samples. The noise caused by the electrode–electrolyte interface is studied in detail. It is shown that easy-to-use platinum or acid-free steel potential electrodes are convenient over a broad frequency band ranging from 0.016Hz up to more than 1000 Hz. The laboratory experiments and comparisons between laboratory and field results also indicate that sampling and sample packing procedures have only a minor influence on the phase spectrum of glacial soils.     

A laboratory instrumental complex for studying the physics of the destruction of rocks

An up-to-date laboratory investigation complex for testing rock samples under controlled uniaxial and triaxial compression is designed. A wide range of loading modes of samples allows one to simulate various natural seismic regimes. The complex is equipped with systems intended for measuring and recording service and physical parameters, namely, axial, uniform, and pore pressure, axial and radial deformation, velocities of longitudinal waves along 16 travel paths, and waveforms of separate acoustic events, recorded by 16 sensors. The system ensures the continuous recording of the acoustic emission stream. Data of all measuring systems are synchronized with time. The rock samples are tested in the automatic mode, which can be optionally corrected during experiments. The experimental results are stored in a single database, which contains both raw and processed data (loading history, catalogs and bulletins of acoustic events, 3D graphic visualizations of pressure-wave velocity distributions in the sample volume, etc.). The application of the complex for the laboratory modeling of the seismic regime is illustrated by a number of practical examples.     

Kernel bandwidth selection for a first order nonparametric streamflow simulation model

A new approach for streamflow simulation using nonparametric methods was described in a recent publication (Sharma et al. 1997). Use of nonparametric methods has the advantage that they avoid the issue of selecting a probability distribution and can represent nonlinear features, such as asymmetry and bimodality that hitherto were difficult to represent, in the probability structure of hydrologic variables such as streamflow and precipitation. The nonparametric method used was kernel density estimation, which requires the selection of bandwidth (smoothing) parameters. This study documents some of the tests that were conduced to evaluate the performance of bandwidth estimation methods for kernel density estimation. Issues related to selection of optimal smoothing parameters for kernel density estimation with small samples (200 or fewer data points) are examined. Both reference to a Gaussian density and data based specifications are applied to estimate bandwidths for samples from bivariate normal mixture densities. The three data based methods studied are Maximum Likelihood Cross Validation (MLCV), Least Square Cross Validation (LSCV) and Biased Cross Validation (BCV2). Modifications for estimating optimal local bandwidths using MLCV and LSCV are also examined. We found that the use of local bandwidths does not necessarily improve the density estimate with small samples. Of the global bandwidth estimators compared, we found that MLCV and LSCV are better because they show lower variability and higher accuracy while Biased Cross Validation suffers from multiple optimal bandwidths for samples from strongly bimodal densities. These results, of particular interest in stochastic hydrology where small samples are common, may have importance in other applications of nonparametric density estimation methods with similar sample sizes and distribution shapes. Received: November 12, 1997     

多因素影响的建筑物群体震害预测方法研究

为了简化震害预测工作,提出了一种多因素影响的建筑物群体震害预测方法。首先,将已有数据库中的资料按不同相似度进行分类,从中选取所需要的样本数据。然后将所选取的样本数据按不同影响因素分类,分别求出考虑各影响因子下的震害矩阵,再由房屋普查资料得出预测区考虑各影响因素时各影响因子下的房屋的建筑面积,并将建筑面积比例作为各影响因子的权重,最终得出预测区某种结构类型整体的震害矩阵。利用文中方法建立了厦门市多层砌体结构的震害矩阵,与厦门市采用单体抽样法得出的震害矩阵相比较,其平均震害指数最大差值不大于0.041,验证了此方法的可行性。     

Kernel bandwidth selection for a first order nonparametric streamflow simulation model

A new approach for streamflow simulation using nonparametric methods was described in a recent publication (Sharma et al. 1997). Use of nonparametric methods has the advantage that they avoid the issue of selecting a probability distribution and can represent nonlinear features, such as asymmetry and bimodality that hitherto were difficult to represent, in the probability structure of hydrologic variables such as streamflow and precipitation. The nonparametric method used was kernel density estimation, which requires the selection of bandwidth (smoothing) parameters. This study documents some of the tests that were conduced to evaluate the performance of bandwidth estimation methods for kernel density estimation. Issues related to selection of optimal smoothing parameters for kernel density estimation with small samples (200 or fewer data points) are examined. Both reference to a Gaussian density and data based specifications are applied to estimate bandwidths for samples from bivariate normal mixture densities. The three data based methods studied are Maximum Likelihood Cross Validation (MLCV), Least Square Cross Validation (LSCV) and Biased Cross Validation (BCV2). Modifications for estimating optimal local bandwidths using MLCV and LSCV are also examined. We found that the use of local bandwidths does not necessarily improve the density estimate with small samples. Of the global bandwidth estimators compared, we found that MLCV and LSCV are better because they show lower variability and higher accuracy while Biased Cross Validation suffers from multiple optimal bandwidths for samples from strongly bimodal densities. These results, of particular interest in stochastic hydrology where small samples are common, may have importance in other applications of nonparametric density estimation methods with similar sample sizes and distribution shapes. Received: November 12, 1997     

Estimation of confidence interval for hydrological design value for some continuous distributions under complete and censored samples

The quantile of a probability distribution, known as return period or hydrological design value of a hydrological variable is the value corresponding to fixed non-exceedence probability and is very important notion in hydrology. In hydraulic engineering design and water resources management, confidence interval (CI) estimation for a population quantile is of primary interest and among other applications, is used to assess the pollution level of a contaminant in water, air etc. The accuracy on such estimation directly influences the engineering investments and safety. The two parameter Weibull, Pareto, Lognormal, Inverse Gaussian, Gamma are some commonly used probability models in such applications. In spite of its practical importance, the problem of CI estimation of a quantile of these widely applicable distributions has been less attended in the literature. In this paper, a new method is proposed to obtain a CI for a quantile of any distribution for which [or the probability distribution of any one-to-one function of the underlying random variable (RV)] generalized pivotal quantities (GPQs) exist for its parameters. The proposed method is elucidated by constructing CIs for quantiles of Weibull, Pareto, Lognormal, Extreme value distribution of type-I for minimum, Exponential and Normal distributions for complete as well as type II singly right censored samples. The empirical performance evaluation of the proposed method evinced that the proposed method has exact well concentrated coverage probabilities near the nominal level even for small uncensored samples as small as 5 and for censored samples as long as the proportion of censored observations is up to 0.70. The existing methods for Weibull distribution have poor or dispersed coverage probabilities with respect to the nominal level for complete samples. Applications of the proposed method in ground water monitoring and in the assessment of air pollution are illustrated for practitioners.     

Testing unbaited stygofauna traps for sampling performance

Unbaited phreatic traps are a promising new method for sampling subterranean limnofauna. The aim of this study is to evaluate whether such trap systems are suitable to gather representative samples of the physico-chemical parameters and the invertebrate fauna of the aquifer. Fifteen traps, installed in five groundwater bores, and four traps located in the hyporheic zone, were sampled twice monthly over a 1 year period (June 2003–June 2004). Water samples were removed in three separated fractions (hose, trap and aquifer water), analysed for physico-chemical and faunal characteristics and compared with one another. The study was carried out in the Nakdong River floodplain, Korea. Physico-chemical characteristics of trap and aquifer were similar, but differed greatly from the hose samples. Abundances of fauna inside the traps were higher than in the aquifer, whereas there were no differences in taxonomic composition of the trap and aquifer samples. Biases of abundances suspected due to the use of traps were negligible in the groundwater, though it is recommended that comparisons between groundwater and hyporheic abundances ascertained by traps be handled cautiously.     

南迦巴瓦峰第四纪隆升期次划分的热年代学证据

喜马拉雅东构造结南迦巴瓦峰核心区附近一个高程剖面上的8个片麻岩样品裂变径迹中值年龄介于0.71~2.07Ma之间,平均封闭径迹长度在14.51~15.87μm之间,标准偏差都小于0.84μm;其冷却年龄和径迹长度所作"香蕉图"显示出三期快速的抬升期,分别发生在距今0.71 Ma、1.23 Ma、2.05 Ma.结合已有磷灰石裂变径迹冷却年龄等值线图显示出南迦巴瓦峰核心区呈复式背斜状快速隆升,而外围拉萨地体和冈底斯构造单元隆升速率慢的空间分布特征等,分析认为这种差异隆升主要受构造作用主导,气候变化造成的均衡抬升起次要作用.