Recent developments in cleanup technologies

Traditional environmental investigations are expensive and time-consuming, involving heavy drilling equipment, several intermediate processes, and analyses at off-site commercial laboratories. New, relatively inexpensive in situ sampling surveys can now quickly generate preliminary data in the field, helping to analyze soil gas and soil and groundwater forvolatile organic compounds (VOCs). Many of the companies that do them now also provide their own mobile laboratories for delineating contaminant plumes more quickly and at less cost than the traditional methods and guiding the placement of groundwater monitoring wells and soil borings. This column describes the main in situ sampling surveys available today, calculates their costs per sample, explores their advantages and disadvantages for remedial investigations, and offers advice on how to carry them out.     

Rotary drum soil blending for source zone remediation: Various application scenarios

Mechanical blending of contaminated soil with amendments has recently reemerged as an important treatment technology. From its original application using large‐diameter augers in the early 1990s to the current use of rotary drum blenders, soil blending is being used as an alternative to other remediation technologies like amendment injection and soil vapor and groundwater extraction. Shallow (approximately 10 m below ground surface [bgs] or less) soil blending also offers an alternative to excavation and disposal. Soil blending has been used to remediate a site with various contaminants including, but not limited to, chlorinated solvents, petroleum, and metals. The types of soils susceptible to soil blending vary from sands and gravels to silts and clays to fractured rock and combinations of all of these. The types of amendments blended include oxidants, reducing agents, biological enhancements, and stabilizing amendments. Soil blending systems deliver the power to the mixing head to adequately mix the soil and amendment to enhance remediation effectiveness. Since long‐term contamination is often a result of heterogeneously distributed residual contaminant in localized source zones that are difficult to access, the typical aim of soil blending is to homogenize the soil while effectively distributing amendment to these zones made accessible by blending. By effectively homogenizing the soil, however, soil blending will increase the void ratio and disrupt the shear strength and bearing capacity of the soil so an important component of a soil blending technology is proper recovery of these geotechnical parameters. This can be achieved by using well‐known soil improvement techniques such as amending all or a portion of the blended area with Portland cement or lime. Several case studies of soil blending treatments of different contaminants and amendments in various soil types are provided.     

Re‐evaluation of treatment approach for a site contaminated with Freon‐113 and 1,1,1‐trichloroethane

This study demonstrates a remedial approach for completing the remediation of an aquifer contaminated with 1,1,2‐trichlorotrifluoroethane (Freon‐113) and 1,1,1‐trichloroethane (TCA). In 1987, approximately 13,000 pounds of Freon‐113 were spilled from a tank at an industrial facility located in the state of New York. The groundwater remediation program consisted of an extraction system coupled with airstripping followed by natural attenuation of residual contaminants. In the first phase, five recovery wells and an airstripping tower were operational from April 1993 to August 1999. During this time period over 10,000 pounds of CFC‐13 and 200 pounds of TCA were removed from the groundwater and the contaminant concentrations decreased by several orders of magnitude. However, the efficiency of the remediation system to recover residual Freon and/or TCA reduced significantly. This was evidenced by: (1) low levels (< 10 ppb) of Freon and TCA captured in the extraction wells and (2) a slight increase of Freon and/or TCA in off‐site monitoring wells. A detailed study was conducted to evaluate the alternative for the second‐phase remediation. Results of a two‐year groundwater monitoring program indicated the contaminant plume to be stable with no significant increase or decrease in contaminant concentrations. Monitored geochemical parameters suggest that biodegradation does not influence the fate and transport of these contaminants, but other mechanisms of natural attenuation (primarily sorption and dilution) appear to control the fate and transport of these contaminants. The contaminants appear to be bound to the soil matrix (silty and clay units) with limited desorption as indicated by the solid phase analyses of contaminant concentrations. Results of fate and transport modeling indicated that contaminant concentrations would not exceed the action levels in the wells that showed a slight increase in contaminant concentrations and in the downgradient wells (sentinel) during the modeled timeframe of 30 years. This feasibility study for natural attenuation led to the termination of the extraction system and a transaction of the property, resulting in a significant financial benefit for the original site owner. © 2003 Wiley Periodicals, Inc.     

Organic contaminants in canadian municipal sludges

A comparison of several extraction methodologies for the analysis of base-neutral and acid organic contaminants (EPA priority pollutants) in municipal sludge was conducted. Sludge was spiked with selected contaminants and extracted wet and following air-drying by a variety of techniques such as dilution, centrifuge extraction, Soxhlet extraction and high speed mixing (Polytron^R, Waring^R and ultrasonic probe). All of the techniques produced variable rdsults. Recoveries of spiked compounds ranged from 0 to > 100% and, in general, the relative standard deviations ranged from 20 to 50%. Extraction of wet sludge using high speed mixing was considered to be the most satisfactory technique. Based on analyses of 15 municipal sludges derived mainly from industrial centres, it is suggested that agricultural utilization of Canadian sludges probably does not represent a significant organic contaminant hazard to the food chain. Organic contaminant concentrations in the sludges generally were < 10 mg kg⁻¹ dw. Phthalate esters in several sludges and polynuclear aromatic hydrocarbons (PAHs) in Hamilton sludge exceeded 10 mg kg⁻¹ dw; however, phthalate esters are readily degraded in soil and the Hamilton sludge is incinerated. “Acceptable” organic contaminant concentrations in sludges for use on pasture and arable lands are suggested. However, it is recommended that further analytical research be undertaken to develop more accurate and precise methods for measuring organic contaminants in municipal sludge and that an expanded program of sampling and analysis be undertaken to provide more reliable information concerning organic contaminant concentrations in Canadian sludges.     

Smart Characterization—An Integrated Approach for Evaluating a Complex 1,4‐Dioxane Site

Smart characterization approaches apply the latest high‐resolution site characterization methods to find the contaminant mass flux, by integrating relative permeability mapping, classical hydrostratigraphy interpretation, and high‐density groundwater and saturated soil sampling. The key factor that makes Smart characterization different is the application of quantitative saturated soil sampling in less permeable slow advection and storage zones to diagnose plume maturity and understand its implications for remedy selection and performance. Because direct sensing tools like the membrane interface probe are capable of providing screening‐level assessments for hydrocarbons and chlorinated solvents in storage zones, but not 1,4‐dioxane, the recommended Smart approach involves application of specialized high‐capacity mobile laboratories or rapid turn‐around using fixed commercial labs. In addition to the benefit of rapidly characterizing sites, Smart characterization facilitates a flux‐based conceptual site model, which allows stakeholders to focus remedies on the mobile portion of the contaminant mass or, in effect, the mass that matters. Through systematic planning and implementation, predesign characterization can be completed to optimize source and plume remedy strategies, balancing investment in Smart characterization with reductions in total life‐cycle costs to ensure that an appropriate return on investigation is obtained.  © 2016 Wiley Periodicals, Inc.     

Remediation of groundwater contamination through conjunctive use of landfill gas management and soil vapor extraction

The recently completed performance testing of a conjunctive-use operation has demonstrated the applicability of combined landfill gas and Volatile Organic Compound (VOC) removal with overall contaminant migration management. The extraction of landfill gas (with subsequent control of off-site gas migration) and the removal of VOCs from the landfill gas/soil air environment will minimize VOC solubilization in the underlying groundwater. This, in turn, will permit cost efficient management of contaminant migration at the site.     

Successfully applying sparging technologies

Air sparging is an innovative methodology for remediating organic compounds present in contaminated, saturated soil zones. In the application of the technology, sparging (injection) wells are used to inject a hydrocarbon-free gaseous medium (typically air) into the saturated zone below or within the areas of contamination. Two major mechanisms of remediation are engaged/enhanced due to the sparging process. First, volatile organic compounds are dissolved in the groundwater and sorbed on the soil partition into the advective air phase, effectively simulating an in-situ air stripping system. The stripped contaminants are transported in the air phase to the vadose zone, generally within the radius of influence of a standard vapor extraction and vapor treatment system. Second, with optimal environmental conditions, volatile and semivolatile organic compounds may be biodegraded by utilizing the sparging process to oxygenate the groundwater, thereby enhancing the growth and activity of the indigenous bacterial community. Air sparging is a complex multifluid phase process which has been applied successfully in Europe since the mid-1980s. Major design considerations include site geology, contaminant type, gas injection pressures and flow rates, injection interval (areal and vertical), and site-specific biofeasibility parameters. Site-specific geology and biofeasibility are the dominant design parameters. Pilot testing and full-scale design considerations should also be addressed. Mathematical models have been developed to simulate the air flow field during the sparging process and to examine the limitations imposed by site geology. Correct design and operation of this technology have been demonstrated to achieve groundwater cleanup to low part-per-billion contaminant levels. Incorrect design and operation can introduce significant pollution liability through undesirable contaminant migration in both the dissolved and vapor phases.     

Remediation of heavy metal contaminated soils via integrated electrochemical processes

The thrust of this study is to develop an in-situ method/technique capable of modifying the contaminated soil environment and maximizing contaminant extraction. Contaminated soils were compacted in electrokinetic cells to densities similar to natural field conditions. Conditioning fluids were used during the application of a direct current to solubilize the precipitated forms of heavy metals. Mobilization of contaminants as a function of time was quantified by analysing metal ion concentrations in the extracted effluents at both the anode and cathode and in the compacted specimens. For each conditioning fluid used, the removal efficiencies were evaluated based on both effluent and soil concentrations.     

Integrated bioremediation of soil and groundwater at a superfund site

The soil and two aquifers under an active lumber mill in Libby, Montana, had been contaminated from 1946 to 1969 by uncontrolled releases of creosote and pentachlorophenol (PCP). In 1983, because the contaminated surface soil and the shallower aquifer posed immediate risks to human health and the natural environment, the U.S. Environmental Protection Agency placed the site on its National Priorities List. Feasibility studies in 1987 and 1988 determined that in situ bioremediation would help clean up this aquifer and that biological treatment would help clean up the contaminated soils. This article outlines the studies that led to a 1988 EPA record of decision and details the EPA-approved remedial plan implemented starting in 1989; EPA estimates a total cost of about $15 million (in 1988 dollars). The plan involves extensive excavation and biological treatment of shallow contaminated soils in two lined and bermed land treatment units, extraction of heavily contaminated groundwater, an aboveground bioreactor treatment system, and injection of oxygenated water to the contaminant source area, as well as to other on-site areas affected by the shallower aquifer's contaminant plume.     

Soil washing treatability tests for pesticide-contaminated soil

The 1987 Sand Creek Operable Unit 5 record of decision (ROD) identified soil washing as the selected technology to remediate soils contaminated with high levels of organochlorine pesticides, herbicides, and metals. Initial treatability tests conducted to assess the applicability of soil washing technology did not effectively evaluate the removal of the elevated contaminant concentrations that were found. To further evaluate the applicability of soil washing at this industrial site, a second more comprehensive pilot-scale treatability test was conducted. Twenty-three test runs were conducted over a two-week period in late September 1992, using a pilot-scale soil washing device called the volume reduction unit (VRU). The experimental design evaluated the effects of two wash temperatures, two pH levels, three surfactants, four surfactant concentrations, and two liquid-to-soil ratios on the contaminant removal efficiency of the soil washing process. Site soils from layers at three different depths were used in the study. Results from the pilot-scale treatability test indicated that the VRU could achieve contaminant reduction efficiencies of 97 percent for heptachlor and greater than 91 percent for dieldrin in the uppermost contaminated soils (surface to 1-ft. depth). Residual concentrations of heptachlor and dieldrin in the treated soil ranged from 50 ppm to less than 1.6 ppm, and 6.8 ppm to less than 1.6 ppm, respectively. However, the analytical method detection limit of 1.6 ppm was not low enough to provide residual concentration data at the risk-based action levels of 0.55 ppm for heptachlor and 0.15 ppm for dieldrin.     

Treatment technology for remediation of wood preserving sites: Overview

This is the first in a series of five articles describing the applicability, performance, and cost of technologies for the remediation of contaminated soil and water at wood preserving sites. Site‐specific treatability studies conducted under the supervision of the United States Environmental Protection Agency (US EPA), National Risk Management Research Laboratory (NRMRL), from 1995 through 1997 constitute much of the basis for the evaluations presented, although data from other treatability studies, literature sources, and actual site remediations have also been included to provide a more comprehensive evaluation of remediation technologies. This article provides an overview of the wood preserving sites studied, including contaminant levels, and a summary of the performance of the technologies evaluated. The subsequent articles discuss the performance of each technology in more detail. Three articles discuss technologies for the treatment of soils, including solidification/stabilization, biological treatment, solvent extraction and soil washing. One article discusses technologies for the treatment of liquids, water and nonaqueous phase liquids (NAPLS), including biological treatment, carbon adsorption, photolytic oxidation, and hydraulic containment. The reader should be aware that other technologies including, but not limited to, incineration, thermal desorption, and base catalyzed dehalogenation, also have application for treating contaminants on wood preserving sites. They are not discussed in these five articles since the focus was to evaluate lesser known and hopefully lower cost approaches. However, the reader should include consideration of these other technologies as part of any evaluation or screening of technologies applicable to remediation of wood preserving sites.     

Performing contaminant mass balances for remedy assessments

Contaminant mass‐balance assessments are useful tools to help quantify various mass transport and removal mechanisms that may be active in a remedial system setting. This article presents the basics of performing a mass balance and illustrates the utility of using the information derived to support project management decisions. It is important to understand the partitioning of contaminant mass into various environmental media and physical forms, as well as the relationships among the partitions. Contaminant partitioning tends toward an equilibrium state, so natural or engineered mass transfer into or out of one partition will affect the others. Mass balances are exercises that quantify, to the extent possible, the contaminant mass in the various environmental partitions and the transfer and transformation processes that affect contaminant distribution. Understanding mass partitioning and transfer mechanisms helps remediation practitioners to engineer and optimize those mechanisms that contribute to risk reduction at a contaminated site. Such knowledge can inform risk managers when natural mechanisms may dominate engineered approaches and help identify uncertainties in contaminant fate and transport. © 2009 Wiley Periodicals, Inc.     

Simple Modeling Tool for Reconstructing Source History Using High Resolution Contaminant Profiles From Low‐k Zones

An innovative but simple analytical modeling tool for reconstructing contaminant concentration versus time trends (i.e., “source history”) for a site using high‐resolution contaminant profiles from low permeability (low‐k) zones was developed and tested. Migration of contaminants into low‐k zones via diffusion (and possibly slow advection) produce concentration versus depth profiles that can be used to understand temporal concentration trends at the interface with overlying transmissive zones, including evidence of attenuation over time due to source decay. A simple transport‐based spreadsheet tool for generating source history estimates fit to the profiles was developed and applied to published soil concentration versus depth data from five distinct areas of four different sites contaminated with chlorinated ethenes. Using the root mean square error as an optimization metric, strong fits between measured and model‐predicted soil data were obtained in the majority of cases using site‐specific values for input parameters. In general, significant improvements could not be obtained by varying these parameters. As a result, the source history estimates generated by the tool were similar to those that had already been generated using more intensive analytical or numerical inverse modeling approaches. This included confirmation of constant source histories at locations where dense nonaqueous‐phase liquid was present (or suspected to be present), and declining source histories for locations where source isolation and/or attenuation had occurred. The advantage of the modeling tool described here is that it provides a simpler yet more dynamic method for understanding source behavior over time than existing approaches. ©2015 Wiley Periodicals, Inc.     

Cost‐Effective Rapid and Long‐Term Screening of Chemical Vapor Intrusion (CVI) Potential: Across Both Space and Time

Reviews including the latest “data‐rich” chemical vapor intrusion‐radon (CVI‐Rn) studies indicate buildings/times can be “screened‐in” as having Rn‐evident‐susceptibility/priority for soil gas intrusion, and elevated‐potential for CVI concerns, or not. These screening methods can supplement conventional indoor‐air chemical sampling, under naturally varying conditions, by prioritizing buildings and times based on indoor Rn levels. Rn is a widespread, naturally occurring component of soil gas and a tracer of soil gas intrusion into the indoor air of overlying buildings. Rn is also an indicator for generally similar behavior of other components of near‐building soil gas, possibly including chemical contaminant vapors. Indoor Rn is easily measured at a low cost, allowing continuous observations from essentially all buildings with the potential for CVI across time. This presents cost savings and other benefits for all CVI stakeholders.     

Insufficient source area remediation results in the rebound of TCE breakdown products in groundwater

In the early 1990s, a soil removal action was completed at a former disposal pit site located in southern Michigan. This action removed waste oil, cutting oil, and chlorinated solvents from the unsaturated zone. To contain groundwater contaminant migration at the site, a groundwater pump‐and‐treat system comprised of two extraction wells operating at a combined flow of 50 gallons per minute, carbon treatment, and a permitted effluent discharge was designed, installed, and operated for over 10 years. Groundwater monitoring for natural attenuation parameters and contaminant attenuation modeling demonstrated natural attenuation of the contaminant plume was adequate to attain site closure. As a result of incomplete contaminant source removal, a rebound of contaminants above the levels established in the remedial action plan (RAP) has occurred in the years following system shutdown and site closure. Groundwater concentrations have raised concerns regarding potential indoor air quality at adjacent residential properties constructed in the past 9 to 10 years. The only remedial option available in the original RAP is to resume groundwater pump‐and‐treat. To remediate the source area, an alternate remediation strategy using an ozone sparge system was developed. The ozone sparge remediation strategy addresses the residual saturated zone contaminants beneath the former disposal pit and reestablishes site closure requirements without resumption of the pump‐and‐treat system. A pilot study was completed successfully; and the final system design was subsequently approved by the Michigan Department of Environmental Quality. The system was installed and began operations in July 2010. As of the January 2011 monitoring event, the system has shown dramatic improvement in site contaminant concentrations. The system will continue to operate until monitoring results indicate that complete treatment has been obtained. The site will have achieved the RAP objectives when the system has been shut down and meets groundwater residential criteria for four consecutive quarters. © 2011 Wiley Periodicals, Inc.     

Characterizing soils contaminated with heavy metals: A uranium contamination case study

To stem rising remediation costs for soils contaminated with hazardous metals, increased emphasis is being placed on the development of in-situ and ex-situ treatment technologies. Often, a lack of basic information on the chemical and physical characteristics of the soil and contaminants hampers treatability studies used to design these technologies. This article proposes and demonstrates a characterization program to meet these information needs, employing standard analytical techniques coupled with advanced spectroscopy and microscopy techniques. To support treatments involving physical separation strategies, the program uses standard analytical techniques to characterize the soil and the association of contaminants with different soil fractions (e.g., size and density fractions). Where chemical treatments are required, spectroscopy and microscopy methods are employed to yield quantitative information on the oxidation state and speciation of the contaminant. Examples demonstrate the use of measured soil and contaminant characteristics in the screening of alternative treatment technologies and in the selection of soils for use in treatability studies. Also demonstrated is the use of these characterization tools in the design and optimization of treatment strategies and in support of risk assessment determinations.     

Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments--a review

The spread of contaminants in soil can be hindered by the soil stabilization technique. Contaminant immobilizing amendments decrease trace element leaching and their bioavailability by inducing various sorption processes: adsorption to mineral surfaces, formation of stable complexes with organic ligands, surface precipitation and ion exchange. Precipitation as salts and co-precipitation can also contribute to reducing contaminant mobility. The technique can be used in in situ and ex situ applications to reclaim and re-vegetate industrially devastated areas and mine-spoils, improve soil quality and reduce contaminant mobility by stabilizing agents and a beneficial use of industrial by-products. This study is an overview of data published during the last five years on the immobilization of one metalloid, As, and four heavy metals, Cr, Cu, Pb and Zn, in soils. The most extensively studied amendments for As immobilization are Fe containing materials. The immobilization of As occurs through adsorption on Fe oxides by replacing the surface hydroxyl groups with the As ions, as well as by the formation of amorphous Fe(III) arsenates and/or insoluble secondary oxidation minerals. Cr stabilization mainly deals with Cr reduction from its toxic and mobile hexavalent form Cr(VI) to stable in natural environments Cr(III). The reduction is accelerated in soil by the presence of organic matter and divalent iron. Clays, carbonates, phosphates and Fe oxides were the common amendments tested for Cu immobilization. The suggested mechanisms of Cu retention were precipitation of Cu carbonates and oxy-hydroxides, ion exchange and formation of ternary cation-anion complexes on the surface of Fe and Al oxy-hydroxides. Most of the studies on Pb stabilization were performed using various phosphorus-containing amendments, which reduce the Pb mobility by ionic exchange and precipitation of pyromorphite-type minerals. Zn can be successfully immobilized in soil by phosphorus amendments and clays.     

An Improved Technique for Determining Abundance of Polycyclic Aromatic Hydrocarbon Degrading Microbial Populations

The current study describes an improved method for estimating the abundance of polycyclic aramatic hydrocarbon (PAH) degraders in contaminated soil and groundwater. Since the method is a simple incremental improvement to a commonly used approach, it can be easily introduced into the remediation practitioner's testing protocols by simply changing growth indicator dyes. The procedure described is relatively easy to conduct and provides an important addition to laboratories that are using conventional, nonmolecular techniques for microbial enumeration in their bioremediation programs. © 1999 John Wiley & Sons, Inc.     

Low‐Capacity Well Pairs for Treating Contaminated Groundwater in Homogeneous and Heterogeneous Aquifers

Groundwater remediation alternatives were simulated for homogeneous and heterogeneous aquifers with a numerical mass transport model. Low‐energy alternatives involved an injection–extraction well pair positioned along a downgradient linear transect. This transect was located 5 m from the contaminant plume and oriented perpendicular to the regional hydraulic gradient. Through numerous trials, for one homogeneous and three heterogeneous settings, the model identified an optimal spacing and minimum pumping rate for a well pair: (1) centered on the downgradient tip of the plume (best centered), and (2) anywhere along the downgradient transect (best overall). Results suggest that low‐energy well pairs are an effective means for containing and removing some contaminant plumes, and best‐performing configurations are generally not centered on the downgradient tip of the initial contaminant plume. ©2015 Wiley Periodicals, Inc.