On-site analytical support: A cost-effective alternative to fixed laboratory services

Two recent projects involving soils remediation at Superfund sites in southern New Jersey and northeastern Pennsylvania exemplify the power of “real time” field analytical support in reducing time and expense during a project's remedial phase. The remediation efforts at both of these CERCLA sites were supported by ERM-FAST on-site analytical facilities which, in a “real-time” scenario, achieved all data quality objectives (DQOs), met all regulatory agency requirements, and satisfied the client's needs. Both of these sites offer illustrations of the effectiveness of field analysis for vastly differing site contaminants. The client benefited from substantial savings on analytical cost as well as the savings realized through efficient and effective process and schedule management.     

Field Performance of Point Velocity Probes at a Tidally Influenced Site

Conventional methods to estimate groundwater velocity that rely on Darcy's Law and average hydrogeologic parameter values are insensitive to local‐scale heterogeneities and anisotropy that control advective flow velocity and direction. Furthermore, at sites that are tidally influenced or have extraction wells with variable pumping schedules, infrequent water‐level measurements may not adequately characterize the range and significance of transient hydraulic conditions. The point velocity probe (PVP) is a recently developed instrument capable of directly measuring local‐scale groundwater flow velocity and direction. In particular, PVPs may offer distinct advantages for sites with complex groundwater–surface water interactions and/or with spatially and temporally variable groundwater flow conditions. The PVP utilizes a small volume of saline tracer and inexpensive sensors to directly measure groundwater flow direction and velocity in situ at the centimeter‐scale and discrete times. The probes are installed in conventional direct‐push borings, rather than in wells, thus minimizing the changes and biases in the local flow field caused by well installation and construction. Six PVPs were installed at a tidally influenced site in North Carolina to evaluate their implementability, performance, and potential value as a new site characterization tool. For this study, a new PVP prototype was developed using a rapid prototyping machine (i.e., a “three‐dimensional printer'') and included both horizontally and vertically oriented tracer detectors. A site‐specific testing protocol was developed to account for the spatially and temporally variable hydraulic conditions and groundwater salinity. The PVPs were tested multiple times, and the results were compared to the results of several different groundwater flux and velocity estimation tools and methods, including a heat‐pulse flowmeter, passive flux meters, single‐well tracer tests, and high‐resolution hydraulic gradient analysis. Overall, the results confirmed that the PVP concept is valid and demonstrated that reliable estimates of groundwater velocity and direction can be obtained in simple settings. Also, PVPs can be successfully installed by conventional methods at sites where the formation consists primarily of noncohesive soils and the water table is relatively shallow. Although some PVP tests yielded consistent and reliable results, several tests did not. This is likely due to the highly transient flow conditions and limitations associated with the PVP design and testing procedures. PVPs offer particular advantages over, and can effectively complement, other groundwater flow characterization techniques for certain conditions, and objectives may be useful for characterizing complex flow patterns under steady conditions; however, this study suggests that PVPs are best suited for conditions where the flow hydraulics are not highly transient. For sites where the hydraulic conditions are highly transient, the most reliable approach for understanding groundwater flow behavior and groundwater–surface water interactions would generally involve both a high‐resolution hydraulic gradient analysis and another local‐scale method, such as tracer testing. This study also highlighted some aspects of the current PVP design and testing protocol that can be improved upon, including a more robust connection between the PVP and injection line and further assessment of tracer solution density effects on vertical flow. © 2013 Wiley Periodicals, Inc.     

Directionally drilled horizontal wells offer cost savings and technical advantages over alternative soil and groundwater remediation systems

Directionally drilled horizontal wells offer the opportunity for significant cost savings and technical advantages over alternative trenched well and vertical well soil and groundwater remediation systems in many cases. The magnitude of the cost savings is a function of the remediation technology deployed and the values placed on the reduction of site impacts, dramatic reduction in the time required to achieve site remediation goals and requirements, the ability of horizontal well remediation to easily treat normally recalcitrant contaminants such as MTBE, and the ability to drill under paved areas, operating plants, residential areas, landfills, lagoons, waterways, ponds, basins, and other areas that are normally difficult or impossible to access with conventional drilling or trenching methods. In addition to improvements in site access capabilities, horizontal wells have been found capable of addressing contaminants that vertical wells do not readily treat, even with the same remediation technology deployed, especially if air‐based remediation technologies are deployed. With biosparging, for example, greater treatment capabilities of horizontal wells over vertical wells are attributed to greater oxygen flux over a broader area, a larger treatment zone, and extremely prolonged residence of groundwater contaminants in the aerobic treatment area, typically months or years. This article describes the use of directionally drilled horizontal wells for application of a variety of treatment technologies and includes costs of various options with a detailed comparison of biosparging options. © 2002 Wiley Periodicals, Inc.     

New paradigms for hazardous waste engineering

Today's hazardous waste engineering practice is based on the premise that the current technologies for conducting hazardous waste remediation are sufficient to solve most problems. The premise is false: Except for simple sites, the current practice cannot deliver answers with the required accuracy and precision. This article describes the huge uncertainties present in complex hazardous waste remediation efforts. It also discusses the “observational” method, which originated in the geotechnical engineering field, as a means of coping with these uncertainties during site characterization and remediation. The article includes case-study examples illustrating the use of the observational method at hazardous waste sites.     

New perspectives in the use of horizontal wells for assessment and remediation

Remediation technologies can sometimes be established, but are not prevalent, for a variety of reasons; however, they can be subject to the forces of change. In some cases, creative economics promotes new uses, but also process improvements can drive new applications and levels of acceptance. This is what is happening with the deployment of horizontal wells for site assessment and remediation. In essence, decreasing costs and a strategic shift, which can be characterized as “greater flexibility,” are two factors that have brought about a resurgence of horizontal well systems. The latter is specifically tied to moving from monolithic single well systems to segmented well systems and this article explains how this is a next‐generation advancement in site assessment and remediation. As one example, nested, discrete horizontal profiling brings additional accuracy to assessment at sites, especially those challenged by access issues and also provides more directed treatment operations with a unique flexibility in dynamic groundwater systems. Also, with horizontal nested well systems, conceptual site models can be significantly enhanced with new perspectives and, depending on the situation, may provide significant economic advantages in deployment. Finally, this technological advancement creates a new paradigm in contrast, or rather as an adjunct, to vertical profiling and high‐resolution site characterization. In fact, it opens up a new strategic approach that can be called high‐resolution contaminant distribution, because flexible horizontal segmented well systems can be used to navigate “up the spine of the plume” providing discretized data sets that illuminate contaminant distribution in new ways.     

How much heterogeneity? Flow versus area from a big data perspective

Over the past 10 years, there has been an increased recognition that matrix diffusion processes are a significant factor controlling the success of groundwater remediation. New field techniques and modeling tools have, consequently, been developed to understand how contaminants diffuse into and then out of low‐permeability (“low‐k”) zones and assess the resulting impact on groundwater quality. Matrix diffusion, in turn, is driven by one key factor: geologic heterogeneity. The importance of heterogeneity is being emphasized in the groundwater field by general rules of thumb such as “90% of the mass flux occurs in 10%‐20% of the cross‐sectional area” and conceptual models that show most of the groundwater flow occurs through the aquifer's “mobile porosity” which just a small fraction of commonly used effective porosity values (between 0.02 and 0.10 for mobile porosity vs. 0.25 for effective porosity). For this study, 141 boring logs from 43 groundwater remediation sites were evaluated to develop an empirically based estimate of the groundwater flow versus aquifer cross‐sectional area to confirm or reject the general flow versus area rules of thumb. This study indicated that at these 43 sites, an average of 30% of the cross‐sectional area carried 90% of the groundwater flow. Our flow‐only analysis does provide moderate (but not confirmatory) support for the “mobile porosity” concept with an estimated representative mobile porosity value of about 0.11 at the 43 sites.     

Cost-effective contaminant plume delineation using multilevel drive point samplers

Over the past several years, environmental professionals have sought new and innovative field techniques to allow on-site plume delineation and in-field location of monitoring wells. One technique adopted for site characterization is the multilevel drive point sampler (MLDPS). This technology allows sampling of soil gas and groundwater and measurement of aquifer permeability. MLDPSs offer a cost-effective solution to the high cost of plume delineation by providing in-field data for decisions on monitoring well location and depth. MLDPS technologies can increase the effectiveness of monitoring well installation programs, decrease the cost of site characterization, and accelerate the time between initial site assessment and implementation of a remediation program. MLDPS technologies offer distinct advantages over other field techniques, and a cost comparison is offered. A case study describing application of the MLDPS to the delineation of a TCE-contaminated plume is described.     

Automated continuous monitoring and response to toxic subsurface vapors entering overlying buildings—Selected observations,implications and considerations

Vapor intrusion characterization and response efforts must consider four key interactive factors: background indoor air constituents, preferential vapor migration pathways, complex patterns of vapor distribution within buildings, and temporal concentration variability caused by pressure differentials within and exterior to structures. An additional challenge is found at sites contaminated by trichloroethylene (TCE), which in the United States has very low indoor air screening levels due to acute risk over short exposure durations for sensitive populations. Timely and accurate characterization of vapor intrusion has been constrained by traditional passive time‐averaging sampling methods. This article presents three case studies of a robust new methodology for vapor intrusion characterization particularly suited for sites where there is a critical need for rapid response to exposure exceedances to minimize health risks and liabilities. The new methodology comprises low‐detection‐level field analytical instrumentation with grab sample and continuous monitoring capabilities for key volatile constituents integrated with pressure differential measurements and web‐based reporting. The system also provides automated triggered alerts to project teams and capability for integration with engineered systems for vapor intrusion control. The three case studies illustrate key findings and lessons learned during system deployment at two sites undergoing characterization studies and one site undergoing thermal remediation of volatile contaminants.     

Performance of water cut-off and remediation promotion techniques at coastal waste landfill sites

This paper proposes the construction of steel pipe sheet pile (SPSP) cutoff walls for promoting remediation of water-soluble toxic substances and containment of water-soluble toxic substances at landfill sites in order to maintain and ensure the environmental safety of waste landfill sites over time. It investigates environmental safety at coastal waste landfill sites by applying water cut-off and remediation promotion techniques to the joint sections of SPSP water cut-off walls that provide shore protection for waste landfills. Results from the research herein show that the construction of SPSP water cut-off walls with features such as the containment of water-soluble toxic substances and remediation promotion is possible by applying water cut-off and remediation techniques to H–H joints, which are structural joint components of SPSP walls. In addition, they show that the performance of remediation in H–H joints can be controlled by adjusting the water cut-off efficiency of the H–H joint flange.     

Multiphase extraction radius of influence: Evaluation of design and operational parameters

A common remedial technology for properties with subsurface soil and groundwater contamination is multiphase extraction (MPE). MPE involves the extraction of contaminated groundwater, free‐floating product, and contaminated soil vapor from the subsurface. A network of recovery wells conveys fluids to a vacuum pump and to the treatment system for the contaminated groundwater and soil vapor. This article describes a study of MPE operational data from nine similar remediation projects to determine the most important design parameters. Design equations from guidance manuals were used to estimate the expected radius of influence (ROI) based on measured field data. ROIs were calculated for the vapor flow rate through the subsurface and for the groundwater drawdown caused by the MPE remediation activities. The calculated ROIs were compared to the measured ROIs to corroborate the assumptions made in the calculations. Once it was established that the calculated and field‐measured ROIs were comparable, a sensitivity analysis determined ranges of different design and operational parameters that most affected the ROIs. © 2012 Wiley Periodicals, Inc.     

Geophysical and Hydrologic Monitoring of Air Sparging Flow Behavior: Comparison of Two Extreme Sites

The distribution of air around injection wells is an important determinant of the effectiveness, design, and cost of air sparging remediation systems. High-level air sparging field tests were conducted at two sites for the purpose of determining the pattern of airflow under widely different subsurface conditions. One site consisted of relatively homogeneous dune sand (Site A). The other consisted of highly heterogeneous glacial till (Site B). At both sites, cross-borehole electrical resistance tomography (ERT) was used to image the principal region of airflow in the saturated zone. The response of conventional monitoring data was compared with the ERT results. At Site A, the principal region of airflow was approximately symmetric about the sparge well and only 2.4 m in radius. At Site B, the pattern of airflow was much more complex and had a major horizontal component. In both site studies, conventional monitoring data provided a much more ambiguous indication of the region of airflow in the saturated zone than did ERT. The investigations at these two sites demonstrate that, while the exact distribution of injected air is not readily discernible by conventional monitoring, the character of the airflow pattern can be recognized when appropriate physical response data are collected. Such response data can be used to evaluate site suitability for air sparging and to improve the system design and operation.     

In situ bioremediation of an aniline spill in an industrial setting

In situ remediation of aniline from soils and groundwater using biological and physical treatments was conducted at the BASF Corporation facility in Geismar, Louisiana. To mitigate the migration of aniline, remediate contaminated soil and groundwater, and determine concentrations, 24 immobilized microbe bioreactors were fixed in the subsoil, and a horizontal recovery well and 7 monitoring wells were installed. Soil and monitoring wells were sampled quarterly to assess bioplug impact on the aniline concentrations. The recovery well was sampled monthly to estimate the pounds of aniline removed from groundwater. Soil pH, composition, and microbial counts were used to estimate the fate and transport. Aniline levels were lowered significantly after remediation and total cancer risk was below levels for industrial sites, as established by State of Louisiana Risk Evaluation/Corrective Action Program guidelines. © 2010 Wiley Periodicals, Inc.     

An evaluation of permeable reactive barrier projects in California

Permeable reactive barriers made of zero‐valent iron (ZVI PRBs) have become a prominent remediation technology in addressing groundwater contamination by chlorinated solvents. Many ZVI PRBs have been installed across the United States, some as research projects, some at the pilot scale, and many at full scale. As a passive and in situ remediation technology, ZVI PRBs have many attractive features and advantages over other approaches to groundwater remediation. Ten ZVI PRBs installed in California were evaluated for their performance. Of those ten, three are discussed in greater detail to illustrate the complexities that arise when quantifying the performance of ZVI PRBs, and to provide comment on the national debate concerning the downgradient effects of source‐zone removal or treatment on plumes of contaminated groundwater. © 2009 Wiley Periodicals, Inc.     

Comparison of Microscopic and Macroscopic Modeling Approaches for Subsurface Contaminant Transport

The practice of contaminant transport and remediation has shown significant progress in recent years. However, despite the significant progress made, remediation efforts are often delayed by extremely long breakthrough curve tails that render efforts to bring the level of contaminants below the regulatory standards inefficient. One hypothesis is that these long tails are due to the reservoir-like slow diffusive processes in soil micropore zones. This study compares the effects of micropores at macroscopic and microscopic levels and establishes a link between these approaches for validation and calibration purposes. The link between macroscopic and microscopic levels is established through comparisons and testing of the two models while incorporating appropriate scale and boundary effects. Despite the differences in conceptual approaches and simulation time, the two approaches rendered meaningful results. The link helps forecast the effects of micropore zone transport processes in the subsurface efficiently and thus allows development of numerical tools that could contribute towards more efficient remediation design.     

Evolution and Innovation of Hydraulic Capture Analysis Methodology

An efficient program for assessing groundwater extraction system capture zones has been developed that can be run on any digitized potentiometric surface. The program was developed in response to the need to simulate particle capture by multiple remediation system elements (i.e., extraction wells, hydraulic barrier, etc.) at a hydrogeologically complex site in California (the Site). The method uses MODPATH software but does not otherwise require a groundwater model. The program called “CapZone FileBuilder” (Capture Zone File Builder) Version 1.0 was created to import digitized potentiometric surfaces and use them to create MODFLOW output files (using native USGS MODFLOW‐2005 codes). CapZone FileBuilder was created using the C# programming language with Visual Studio 2013 as the integrated development environment. The model was applied to a site that has a regulatory requirement for capture analysis as part of an annual remedy‐effectiveness evaluation for groundwater contamination. Previously, capture analysis was highly labor intensive and time consuming, performed using manual flow net analysis or calibration of highly discretized MODFLOW groundwater models. CapZone FileBuilder is now used to perform the capture analysis for this site and is universally applicable to any site with a groundwater potentiometric map. ©2017 Wiley Periodicals, Inc.     

Managing contaminated sites and the role of domestic and international forums

Domestic and international cooperation in the field of contaminated‐site management has increased dramatically in the past decade. The expected benefits of this cooperation include the reduction of duplication in remediation efforts, the coordination of contaminated‐site research, improved synergy between various stakeholders, enhanced policy development, and better information dissemination and technology transfer. This article identifies and briefly discusses key domestic and international collaborations, partnerships, and networks relating to contaminated‐site management and remediation. Also provided is information on how the forums can be accessed. Common themes identified across the forums discussed in this article include (1) the development and demonstration of innovative technologies, (2) the use of risk assessment, (3) the use of toxicology, bioavailability, and ecotoxicity testing, and (4) the increasing need to find holistic approaches for managing contaminated sites, such as guaranteed remediation programs and transfer of environment liability, and the need for understanding implications of remediation financing mechanisms. © 2001 John Wiley & Sons, Inc.     

Stratigraphic flux—A method for determining preferential pathways for complex sites

Experience with groundwater remediation over several decades has demonstrated that successful outcomes depend on quantitative conceptual site models (CSMs). Over the last 30 years, we have progressed from groundwater pump‐and‐treat remedies, which were largely designed based on a water supply perspective, to in situ and combined remedy strategies, which are only beginning to benefit from understanding the aquifer architecture and distribution of contaminant mass to assess plume maturity, mass flux, and more reliable means of fate and transport assessment. The U.S. Air Force funded the development of the Stratigraphic Flux approach to provide a framework for understanding contaminant transport pathways at its complex sites and enable more reliable and cost‐effective remediation. Stratigraphic Flux enables the development of quantitative, flux‐based CSMs that are founded in sequence stratigraphy, and high‐resolution hydraulic conductivity and contaminant distribution measurements. The result is a three‐dimensional graphical mapping of relative contaminant flux and classification of transport potential that is easy for all stakeholders to understand. The Stratigraphic Flux graphical model is based on a hydrofacies classification system that describes transport potential in three segments of the aquifer: transport zones—where the majority of groundwater flow occurs and transport rates are measured in feet per day; slow advection zones—where transport rates are measured in feet per year; and storage zones—where typically less than 1% of flow occurs, and diffusion dominates contaminant transport. The hydrofacies architectures are based on stratigraphy and transport potential is defined by grouping facies by orders of magnitude classes in hydraulic conductivity. By combining the hydrofacies architecture with contaminant concentration distributions, one can map relative contaminant flux to define and target the complex pathways that control contaminant transport and cleanup behavior. In this article, we describe the Stratigraphic Flux framework, focusing on the key information needed and the methods of analysis. We illustrate the results of its application to evaluate migration pathways for trichlorethylene and chromium at a former chrome pit at Air Force Plant 4 in Fort Worth, Texas. A comprehensive guidance document that describes the approach with a broad spectrum of tools and several site examples can be requested from the authors.     

Advances in photocatalytic remediation technology

The cost of remediation at hazardous waste sites is estimated at billions of dollars annually. It is imperative that more cost‐effective remediation technologies be developed, particularly to address the more complex megasites. Chlorinated hydrocarbons represent the major contaminants at many such sites. It has long been recognized that chlorinated hydrocarbons can be destroyed by photocatalytic oxidation. Traditional photocatalysts, however, have often shown inadequate destruction activity, a loss of activity over time, and poor selectivity, thereby producing substantial amounts of phosgene and chloroform by‐products. This article presents results obtained using novel photocatalyst compositions. The results demonstrate the ability to achieve high photocatalytic destruction activity for chlorinated hydrocarbons with full retention of activity over extended time periods and with complete elimination of phosgene and chloroform by‐products. © 2006 Wiley Periodicals, Inc.