Environmental Site Characterization Research Articles

Review of Applications of Ground Penetrating Radar as an NDT Tool

Ground-penetrating radar (also referred to as GPR, ground probing radar, or georadar) is a near-surface geophysical tool with a wide range of applications. Over the past 30 years, GPR has been used successfully to aid in constraining problems in diverse fields such as archaeology, environmental site characterization, glaciology, hydrology, land mine/unexploded ordinance detection, sedimentology, and structural geology. In many cases, however, GPR surveys have been planned or executed with little or no understanding of the physical basis by which GPR operates and is constrained. As a result, many unsuccessful GPR studies have also been presented or published over the past 30 years. The objectives of this primer are to (1) provide an introduction to the important variables pertinent to GPR and (2) explain the relevant aspects of these variables in GPR acquisition, in an attempt to provide fundamental knowledge for improving GPR usage in the future.

Adaptive observation-based subsurface conceptual site modeling framework combining interdisciplinary methodologies: a case study on advancing the understanding of a groundwater nitrate plume occurrence.

Traditional site characterization and laboratory testing methods are insufficient to quantify and conceptualize subsurface contaminant source-pathway-receptor heterogeneity issues, as they hamper groundwater risk assessment and water resource management using mathematical modeling. To address these issues, we propose an adaptive observation-based conceptual site modeling framework, which emphasizes the need for the iterative testing of hypotheses centered on specific questions with clearly defined objectives using interdisciplinary tools (including, but not limited to, geology, microbiology, hydrogeology, geophysics, and the chemistry of solute fate and transport). Under this framework, we present a case study aimed at a goal-oriented investigation of the source and occurrence of a groundwater nitrate plume previously identified using chemical concentration data from sparsely distributed, conventional, and regional groundwater monitoring wells. These investigations occurred in stages, with the first comprehensive outcome of cost-efficient, non-invasive surface geophysical surveys localizing subsurface heterogeneities laying the groundwork for collaborative, minimally invasive, direct push-based investigations followed by groundwater chemical and stable isotope analyses for source fingerprinting and bioprocess evaluation. Despite the obvious need for further refinement of the conceptual site model as new data become available, we illustrate that the step-by-step integrative framework was useful for systematic maximization of the strengths of different investigation methodologies. Such frameworks and approaches should be encouraged for successful environmental site characterization, monitoring, and modeling.

The use of resistivity and seismic cone penetration tests for site characterization

The use of resistivity and seismic cone penetration tests for site characterization The use of resistivity and seismic cone penetration tests for site characterization. Recent application of cone penetration tests to geotechnical and environmental site characterization has generated a wide collection of new sensors. This paper presents methods of interpreting geotechnical in situ investigations carried out by electrical resistivity (RCPT) and seismic (SCPT) cones. It contains some fundamental equations and the description of in situ electrical resistivity and shear wave velocity measurements and presents the results of SCPT and RCPT investigations at the experimental Stegny site in Warsaw. The aim of the paper is to present the approach to determination of shear wave velocity and porosity of clayey soils. According to the test results obtained, it can be concluded that both applied techniques are very useful to estimate the distribution of clay deposits and some of their geotechnical parameters.

What in the Reservoir is Geostatistics Good For?

Abstract Geostatistics provokes strong reactions. There are champions who believe the application of geostatistics adds value in almost any reservoir modelling situation. There are skeptics who do not think that a geostatistical model will have a meaningful impact on reservoir management decisions. The majority of engineers and geoscientists, however, are seeing an increasing use of geostatistics and are not sure when geostatistics should be used and how the results affect reservoir decisions. There are three specific cases where geostatistics can provide valuable support for decision-making:calculating maps of uncertainty over large areas to support resource calculations and well placement;reconciling well and seismic data into high resolution reservoir models; and,constructing representative models of heterogeneity to provide input to flow simulation and support reservoir forecasting. These three cases are developed without excessive theoretical detail. Realistic examples are presented without getting lost in the details of a particular reservoir. Limitations and pitfalls are discussed. Framework of Geostatistics Geostatistics refers to the theory of regionalized variables and the related techniques that are used to predict variables such as rock properties at unsampled locations. Matheron formalized this theory in the early 1960s(1). Geostatistics was not developed as a theory in search of practical problems. On the contrary, development was driven by engineers and geologists faced with real problems. They were searching for a consistent set of numerical tools that would help them address real problems such as ore reserve estimation, reservoir performance forecasting, and environmental site characterization. Reasons for seeking such comprehensive technology included:an increasing number of data to deal with;a greater diversity of available data at different scales and levels of precision;a need to address problems with consistent and reproducible methods;a belief that improved numerical models should be possible by exploiting computational and mathematical developments in related scientific disciplines; and,a belief that more responsible decisions would be made with improved numerical models. These reasons explain the continued expansion of the theory and practice of geostatistics. Problems in mining, such as unbiased estimation of recoverable reserves, initially drove the development of geostatistics. Problems in petroleum, such as realistic heterogeneity models for unbiased flow predictions, were dominant from the mid 1980s through the late 1990s. More recently, the problems of realistic geologic modelling and reliable uncertainty quantification are driving development. The main focus of geostatistics is constructing high-resolution 3D models of categorical variables, such as facies, and continuous variables, such as porosity and permeability. It is necessary to have hard truth measurements at some volumetric scale. All other data types including geophysical data are considered soft data and must be calibrated to the hard data. It is neither possible nor optimal to construct models at the resolution of the hard data. Models are generated at some intermediate geological modelling scale, and then scaled to an even coarser resolution for resource calculation or flow simulation.

Fuzzy Tessellation Approach for Environmental Site Characterization

Environmental site investigations are carried out prior to the reclamation of industrially contaminated sites. It is required to take samples and analyze the laboratory reports to find out the distribution of contaminants over the site. In this study, an algorithm based on fuzzy assessment and overlapped partitioning is proposed to identify the topology of polluted areas in a given industrial site. The primary objective is to locate contaminated zones accurately with sparse data in a preliminary investigation and the second is to reduce the size of the area that is resubjected to expensive sampling methods (such as deep drilling) in the detailed phase of the investigation. If these objectives are achieved, a considerable cost reduction occurs in the process of site characterization.

Role of Laboratory Sampling Devices and Laboratory Subsampling Methods in Representative Sampling Strategies

Sampling is the act of selecting items from a specified population in order to estimate the parameters of that population (e.g., selecting soil samples to characterize the properties at an environmental site). Sampling occurs at various levels and times throughout an environmental site characterization process. Typically, initial (primary) sampling occurs in the field while subsequent stages of sample size reduction (subsampling) occur until the final laboratory analysis stage. At each step in the measurement process, from planning, site selection, sample collection, sample preparation, through sample analysis, errors can occur that propagate, leading to uncertainty associated with the final result upon which decisions will ultimately be made. The goal of all sampling efforts should be to select samples that are representative of the population (i.e., site) in question. General guidelines, with supporting background and theory, for obtaining representative subsamples for the laboratory analysis of particulate materials using “correct” sampling practices and “correct” sampling devices are presented (“correct” as defined by Gy sampling theory; see Pitard, 1993). Considerations are given to: the constitution and the degree of heterogeneity of the material being sampled, the methods used for sample collection (including what proper tools to use), what it is that the sample is supposed to represent, the mass of the sample needed to be representative, and the bounds of what “representative” actually means.

Integrating expert knowledge in environmental site characterization

The site characterization issue is the most essential task to be undertaken prior to the reclamation of a potentially contaminated site and it is composed of sampling, laboratory analysis, and data evaluation phases. We are primarily concerned with the data evaluation phase and we utilize a recently developed adaptive areal partitioning algorithm to characterize the site. Here, we enhance this approach by integrating expert knowledge (expert belief) into the fuzzy areal assessment scheme which derives information from sample data. We propose to allocate an adaptive weight to expert belief during the assessment. We compare the belief-integrated approach with the nonintegrated one on synthetically generated sites where both uniform and biased sampling have been applied independently. In biased sampling, the zones claimed to be highly contaminated (by the expert) are allocated a higher sampling density. We demonstrate that the belief-integrated approach outperforms the nonintegrated one both when the expert is correct or mistaken in his/her judgment irrespective of the sampling methodology.

A comparison of spatial interpolation methods and a fuzzy areal evaluation scheme in environmental site characterization

This study aims to evaluate various well-known spatial interpolation methods used in identifying hot-spots during site investigations on brownfields. Before any reclamation is carried out zones within a site with contaminant levels above the threshold limits should be identified correctly with minimum reclamation costs. The latter implies that all contaminated areas are to be determined while minimizing the space claimed for reclamation. In other words, clean areas should not be declared as contaminated. This issue is crucial both with respect to minimizing health hazards in human use after reclamation and also with respect to minimizing reclamation costs. Here, we conduct a numerical survey on the performance of spatial interpolation techniques on 360 hypothetical sites which are generated according to a given experimental design. The effects of the number of non-overlapping hot-spots in a site, the percentage of the area contaminated, and the effects of the sampling pattern are observed during the experimentation. Furthermore, as an alternative site evaluation scheme, we propose a new fuzzy areal site assessment scheme (FASA) which is independent of the assumptions implied by spatial statistics and compare its performance with those of spatial interpolation methods.

Environmental Site Characterization and Risk-Based Evaluation of a Site Contaminated with Tetrachloroethene (PCE) and Trichloroethene (TCE)

A healthcare company purchased property in eastern Iowa for a facility expansion. Before the purchase, a Phase I environmental site assessment (ESA) revealed that the property was the site of a former dry cleaning business. Phase II sampling and testing indicated that tetrachloroethene (PCE) and trichloroethene (TCE) had affected site soil and groundwater. Maximum concentrations of PCE and TCE in groundwater were 538 and 209 μg/L, respectively, and 105 and 1.51 mg/kg in soil. Additional sampling delineated the vertical and horizontal extent of contamination in the soil. The concentrations of the chlorinated solvents in both the soil and groundwater were below levels of regulatory concern. However, the company was concerned that the Iowa statewide standard for PCE in soil (780 mg/kg) might not provide adequate protection for several exposure pathways and wanted to assess the risk to the public from the contamination at the site. The results of a receptor survey were used to develop site-specific target levels (SSTLs) for contamination, using accepted human health exposure factors, models, and chemical-specific toxicity values. The recommended remedial options allowed the company to minimize the human health risks posed by contamination at the site. ABSTRACT

Innovative Use of the Cone Penetrometer Test for Highway Environmental Site Characterization and Monitoring

The cone penetrometer test (CPT) is an important tool for use in geotechnical and environmental site characterization for the transportation sector. Its role as both a primary investigation technique and as a component in an overall exploration strategy are explained. The types of sensors currently used with the CPT are discussed. Among the most promising new CPT technologies are a soil moisture probe and a fluorescence detection system. Laboratory and field results using a soil moisture probe jointly developed by Ohio University and Applied Research Associates for use with the CPT are presented. Also, application of the fuel fluorescence detector (FFD) for locating hydrocarbon contamination is presented, and typical data obtained with the FFD are illustrated and discussed.

THE USE OF INVERSE THEORY ON AN ILL-POSED ENVIRONMENTAL COMPOSITE SAMPLING PROBLEM

As an alternative to retesting, the use of inverse theory techniques is proposed to resolve the lack of information inherent in composite sampling methods. This paper evaluates the feasibility of combining composite sampling with the inverse theory technique of linear regularization on an environmental site characterization investigation. Federal legislation has mandated the cleanup of hazardous waste sites, creating the need to characterize these sites for various chemical constituents. An abundance of samples, high measurement costs, and limited budgets create the appeal of compositing samples. We propose that the number of costly laboratory analyses can be reduced by combining composite sampling and inverse theory techniques. The goal of the paper is to estimate the constituent concentration for the sample units used to construct the composite .

A Test of the In Situ Permeable Flow Sensor at Savannah River, SC

AbstractA test of the In Situ Permeable Flow Sensor was conducted in which ground‐water flow velocity measurements made by the flow sensors were directly compared to velocity estimates obtained using standard hydrologic techniques. Two flow sensors were deployed in a confined aquifer in close proximity to a well which was screened over the entire vertical extent of the aquifer. When the well was pumped at four different pumping rates, the horizontal component of the flow velocity measured by the flow sensors was directed toward the pumping well, within the uncertainty in the measurements, and the magnitude of the horizontal component of the velocity increased linearly with pumping rate, as predicted by theoretical considerations. The measured magnitudes differed from predicted values, calculated with the assumption that the hydraulic properties of the aquifer were homogeneous and isotropic, by less than a factor of two. Vertical components of ground‐water flow observed with the flow sensors are qualitatively consistent with the vertical distribution of hydraulic conductivity estimated from grain‐size analysis but are significantly larger in magnitude than predicted. This is likely due to the creation of a vertical conduit of increased hydraulic conductivity during emplacement of the probes. The results suggest that while the flow sensors measured the local ground‐water flow velocity vector during the test quite accurately, care must be exercised to disturb the formation as little as possible during emplacement. The technology has many potential uses, particularly in the area of environmental site characterization and remediation process monitoring.

Engineering and environmental geophysics get top billing at SAGEEP

Some say that, by the turn of the century, environmental and engineering geophysics will overtake oil and mineral exploration geophysics in total dollars spent for services. Ours is indeed an evolving science that every year encompasses more—from regional environmental assessments to road and bridge studies—promising to deliver many of the solutions to tomorrow’s problems. For those of us interested in the new applications of geophysics, Sageep ’92, which took place 27–29 April in Oak Brook, Illinois, was hugely rewarding. The sponsoring Society of Engineering and Mineral Exploration Geophysicists (Semeg) is to be commended for this, their fourth conference devoted to noninvasive technology for engineering and environmental site characterization.