Air Sparging Pilot Testing Including In-Well Temperature Measurement

Air sparging was pilot tested at a site where a groundwater plume containing cis-1,2-dichloroethene (cis-DCE), vinyl chloride (VC) and arsenic resulted from landfill operations. In addition to the commonly used methods for estimating air sparging zone of influence (ZOI), in-well temperature was monitored using sensitive thermocouples and data loggers at several monitoring wells of various screened intervals during the test. Following 42 days of pilot testing, the downgradient monitoring well samples were below maximum contaminant levels (MCLs)for all contaminants of concern, VC and dissolved arsenic were below detection limits (0.5 and 10 milligrams per liter [μg/L], respectively) in all of the downgradient monitoring wells. The ZOI monitoring results indicated that at some locations use of mounding data may overestimate the ZOI when the temperature data suggest that no sparged air was entering the well screen. Therefore, monitoring in-well temperature may provide additional useful information for estimating air sparging ZOI and is more indicative of air pathways than other monitoring methods. In addition, the temperature data were valuable for selecting a pulse frequency and duration to optimize groundwater mixing.     

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.     

ART in‐well technology proves effective in treating 1,4‐dioxane contamination

A common industrial solvent additive is 1,4‐dioxane. Contamination of dissolved 1,4‐dioxane in groundwater has been found to be recalcitrant to removal by conventional, low‐cost remedial technologies. Only costly labor and energy‐intensive pump‐and‐treat remedial options have been shown to be effective remedies. However, the capital and extended operation and maintenance costs render pump‐and‐treat technologies economically unfeasible at many sites. Furthermore, pump‐and‐treat approaches at remediation sites have frequently been proven over time to merely achieve containment rather than site closure. A major manufacturer in North Carolina was faced with the challenge of cleaning up 1,4‐dioxane and volatile organic compound–impacted soil and groundwater at its site. Significant costs associated with the application of conventional approaches to treating 1,4‐dioxane in groundwater led to an alternative analysis of emerging technologies. As a result of the success of the Accelerated Remediation Technologies, LLC (ART) In‐Well Technology at other sites impacted with recalcitrant compounds such as methyl tertiarybutyl ether, and the demonstrated success of efficient mass removal, an ART pilot test was conducted. The ART Technology combines in situ air stripping, air sparging, soil vapor extraction, enhanced bioremediation/oxidation, and dynamic subsurface groundwater circulation. Monitoring results from the pilot test show that 1,4‐dioxane concentrations were reduced by up to 90 percent in monitoring wells within 90 days. The removal rate of chlorinated compounds from one ART well exceeded the removal achieved by the multipoint soil vapor extraction/air sparging system by more than 80 times. © 2005 Wiley Periodicals, Inc.     

Performance of conventional remedial technology for treatment of MTBE and benzene at UST sites in Kansas

Groundwater at most underground storage tank (UST) spills sites in Kansas contains both methyl tertiary butyl ethylene (MTBE) and benzene, and both contaminants must be effectively treated to close the sites. Soil vacuum extraction, air sparging, and excavation are the most common treatment technologies in Kansas. To compare the relative performance of these conventional remedial technologies for treating MTBE as compared to benzene, 66 sites in the Kansas UST Trust Fund were identified that had initial concentrations of both MTBE and benzene above the reporting limit of 1 μg/L, and that had at least two rounds of analytical data. Sites were excluded from the comparison if the monitoring wells had free product. Of the 66 sites, 15 had met the clean‐up goal for benzene, and 50 had met the goal for MTBE. The extent of treatment for MTBE and benzene was calculated as the ratio of the highest concentration in any well at the site in the most recent round of sampling to the maximum concentration in any well at the site in the previous rounds of sampling. The extent of treatment was greater for MTBE (statistically significant at p = 0.032). The geometric mean of the extent of treatment in the 66 sites was 0.057 for MTBE, compared to 0.14 for benzene. In Kansas, conventional technologies removed MTBE from the source areas of groundwater plumes at least as effectively as they removed benzene. © 2003 Wiley Periodicals, Inc.     

Landfill leachate assessment by hydrological and geophysical data: case study NamSon,Hanoi, Vietnam

The main objective of this study was to assess the impact of the NamSon landfill on subsurface geological structure and hydrological environment by geophysical techniques and hydrochemical analysis of surface and groundwater. The electrical resistivity tomography (ERT), self-potential (SP) and very low frequency (VLF) methods were used for the investigation of geological structure near the landfill. Three profiles (900 m long in total) of the two-dimensional ERT, VLF density sections and 180 SP data points scattered throughout the study area near the disposal site constituted the basis of the data used in analysis. Additionally, surface water and groundwater samples were collected from six sites in the area for the chemical analysis. Interpretations of geophysical data show a low resistivity zone (< 15 Ωm), which appears to be a fully saturated zone with leachate from landfill. The results of the geophysical investigations are not always fully confirmed by the results of hydrochemical analysis. The quality of water in the vicinity of the landfill dramatically decreased over the year (2015–2016) and actions should be taken to inverse this negative trend.

     

In Situ solidification—A case study at a former manufactured gas plant in Macon,Georgia

In situ solidification (ISS) is a reliable, EPA‐recognized technology for the treatment of industrial and waste sites. ISS was employed at a former manufactured gas plant (MGP) site in Macon, Georgia, for the treatment of approximately 33,000 cubic yards of coal tar residues in the saturated zone soil. The site is regulated by the Georgia Environmental Protection Division (EPD) under the Hazardous Site Rehabilitation Act (HSRA) and is located approximately four blocks from downtown Macon. This article will review the technical and regulatory basis for the successful use of this technology, provide an overview of the treatability and pilot testing used to develop the design and implementation of the treatment process, and present the results of the application of ISS to an MGP site. The results of groundwater monitoring, pre and postremediation, will also be discussed. © 2004 Wiley Periodicals, Inc.     

In-situ sparging: Mass transfer mechanisms

In-situ sparging has been accepted as a method to rapidly remediate groundwater at considerably lower costs compared to remedies based on groundwater recovery alone. The success of in-situ sparging depends on effective mass transfer between air and contaminated media in the subsurface. Factors affecting mass transfer include advective airflow, diffusive transport, interphase chemical partitioning, and chemical and biological reaction rates between sparged gases and subsurface contaminants, minerals, and naturally occurring organic compounds. Understanding these factors can increase the design efficiency of in-situ sparging and assist in developing sparging systems that use gases other than air (i.e., oxygen, ozone, and methane).     

Removing gasoline from soil and groundwater through air sparging

Although a soil vapor extraction system (SVES) had effectively remediated the vadose zone soils at a gasoline spill site in Pawtucket, Rhode Island, gasoline remained in the soils below the water table. The state Department of Environmental Management (DEM) closure criteria of 10,000 parts per billion (ppb) were still not met after five years. This article describes how an air sparging system was added to the effort for $57,000, and how after three weeks, closure criteria were achieved.     

Using pneumatic fracturing extraction to achieve regulatory compliance and enhance voc removal from low-permeability formations

The New Jersey Department of Environmental Protection and Energy (NJDEPE) has been developing cleanup regulations that focus on remediation, rather than extended delineation, and on integrating regulatory requirements with technological developments. To this end, the NJDEPE, under the regulatory aegis of the Environmental Cleanup and Responsibility Act (ECRA), is monitoring an innovative treatment technology pilot test at a TCE-contaminated ECRA site in Hillsborough, New Jersey. The purpose of the study is to determine the applicability of pneumatic fracturing extraction (PFE) as a source-removal technique for extracting volatile organic compounds (VOCs) trapped informations with low permeability. The technology being pilot tested is pneumatic fracturing extraction, a process for enhancing permeability to promote in-situ removal and treatment of VOCs. The patented process uses high-pressure air injected into an isolated subsurface zone at controlled rates and pressures. At a critical point, the geologic material ruptures, and fractures are created that radiate outward from the fracture location. At the pilot test site, formation air flow was increased from 400 percent to 700 percent. PFE is a key component of the overall remediation strategy at the Hillsborough site. Consistent with proposed NJDEPE regulations, a ground-water pump-and-treat system will be installed for plume migration control. Once the pump-and-treat system has been established and shown to be effective, a more aggressive source removal program will be implemented using PFE. This program will include construction of a vadose zone PFE system and evaluation of the use of pneumatic fracturing to remove saturated zone residual dense nonaqueous phase liquids (DNAPL). Preliminary calculations suggest that if source zone concentrations can be reduced to 10 ppm of TCE, then TCE groundwater concentrations may be reduced to background levels at the property boundary compliance points.     

Toxicity Evaluation with the Microtox Test to Assess the Impact of In Situ Oiled Shoreline Treatment Options: Natural Attenuation and Sediment Relocation

Changes in the toxicity levels of beach sediment, nearshore water, and bottom sediment samples were monitored with the Microtox^® Test to evaluate the two in situ oil spill treatment options of natural attenuation (natural recovery--no treatment) and sediment relocation (surf washing). During a series of field trials, IF-30 fuel oil was intentionally sprayed onto the surface of three mixed sediment (pebble and sand) beaches on the island of Spitsbergen, Svalbard, Norway (78°56^′ N, 16°45^′ E). At a low wave-energy site (Site 1 with a 3-km wind fetch), where oil was stranded within the zone of normal wave action, residual oil concentrations and beach sediment toxicity levels were significantly reduced by both options in less than five days. At Site 3, a higher wave-energy site with a 40-km wind fetch, oil was intentionally stranded on the beach face in the upper intertidal/supratidal zones, above the level of normal wave activity. At this site under these experimental conditions, sediment relocation was effective in accelerating the removal of the oil from the sediments and reducing the Microtox^® Test toxicity response to background levels. In the untreated (natural attenuation) plot at this site, the fraction of residual oil remaining within the beach sediments after one year (70%) continued to generate a toxic response. Chemical and toxicological analyses of nearshore sediment and sediment-trap samples at both sites confirmed that oil and suspended mineral fines were effectively dispersed into the surrounding environment by the in situ treatments. In terms of secondary potential detrimental effects from the release of stranded oil from the beaches, the toxicity level (Microtox^® Test) of adjacent nearshore sediment samples did not exceed the Canadian regulatory limit for dredged spoils destined for ocean disposal.     

Examining the economics of remediation by fluid injection with vacuum extraction

Enhanced methods of in-situ remediation based on patented technology involving fluid injection with vacuum extraction have been used successfully at the Sand Creek Superfund Site in Commerce City, Colorado. Approximately 177,000 pounds of volatile organic compounds (VOCs) were removed from the subsurface in six months, two months ahead of schedule. Remediation goals were achieved on this thermally enhanced soil vapor extraction project by using vertical and horizontal wells interchangeably in vacuum or pressure service for vapor extraction, dual vacuum extraction, heated vapor reinjection, and air sparging. Although VOCs consisted of mixed chlorinated and petroleum hydrocarbons, the petroleum hydrocarbons, some in the form of nonaqueous phase liquids, had not been fully characterized. This article examines the evolution of the remedial design from that conceptualized in the Record of Decision (ROD) of the U.S. EPA, presents the rationale for the selection of alternative system components, and provides a cost analysis of the selected remedial technology, with comparisons to that of alternatives considered for use at Sand Creek.     

Biogeochemical gradients as a framework for understanding waste‐site evolution

The migration of biogeochemical gradients is a useful framework for understanding the evolution of biogeochemical conditions in groundwater at waste sites contaminated with metals and radionuclides. This understanding is critical to selecting sustainable remedies and evaluating sites for monitored natural attenuation, because most attenuation mechanisms are sensitive to geochemical conditions, such as pH and redox potential. Knowledge of how gradients in these parameters evolve provides insights into the behavior of contaminants with time and guides characterization, remedy selection, and monitoring efforts. An example is a seepage basin site at the Savannah River Site in South Carolina where low‐level acidic waste has seeped into groundwater. The remediation of this site relies, in part, on restoring the natural pH of the aquifer by injecting alkaline solutions. The remediation will continue until the pH upflow of the treatment zone increases to an acceptable value. The time required to achieve this objective depends on the time it takes the trailing pH gradient, the gradient separating the plume from influxing natural groundwater, to reach the treatment zone. Predictions of this length of time will strongly influence long‐term remedial decisions. © 2008 Wiley Periodicals, Inc.     

Remedial Process Optimization and Ozone Sparging for Petroleum Hydrocarbon‐Impacted Groundwater

A former natural gas processing station is impacted with total petroleum hydrocarbons (TPH) and benzene. Remedial process optimization (RPO) was conducted to evaluate the effectiveness of the historical air sparging/soil vapor extraction (AS/SVE) system and the current groundwater extraction and treatment system. The RPO indicated that both remedial activities offered no further benefit in meeting remediation goals. Instead, an in situ chemical oxidation (ISCO) system was recommended. Ozone was selected, and the results of a bench test indicated that the ozone demand was 8 to 12 mg ozone/mg TPH and that secondary by‐products would include hexavalent chromium and bromate. A capture zone analysis was conducted through groundwater flow modeling (MODFLOW) to ensure containment of the injected oxidant using the existing groundwater extraction system. Results of a pilot study indicated that the optimum frequency of ozone sparging is 60 minutes in order to reach a maximum radius of influence of 20 feet. TPH concentrations within the treatment zone decreased by 97 percent over two months of ozone sparging. Concentrations of hexavalent chromium and bromate increased from nondetect to 44 and 110 mg/L, respectively, during the ozone sparging but attenuated to nondetectable concentrations within three months of system shut down. ©2016 Wiley Periodicals, Inc.     

ART in‐well air stripping—An innovative technology succeeds where other technologies have failed

Accelerated Remediation Technologies LLC (ART) developed a proprietary (patent‐pending) effective remediation technology that is based on verified and established concepts. The ART technology combines in‐situ air stripping, air sparging, soil vapor extraction, enhanced bioremediation/oxidation, and Dynamic Subsurface Circulation^TM in an innovative wellhead system. The system is designed to accommodate a 4‐inch well and is cost‐effective when compared with other remediation technologies. The air‐sparging component results in lifting the water table. This lifting of the water in the well causes a net reduction in head at the well location. Vacuum pressure (the vapor‐extraction component) is applied on top of the well point to extract vapor from the subsurface. The negative pressure from the vacuum extraction results in water suction that creates additional water lifting (mounding). A submersible pump is placed at the bottom of the well to recirculate water to the top for downward discharge through a spray head. The water cascades down the interior of the well similar to what occurs in an air‐stripping tower. Enhanced stripping via air sparging near the bottom of the well occurs simultaneously. In essence, the well acts as a subsurface air‐stripping tower. The pumped‐and‐stripped, highly oxygenated water flows down well annulus and over the “mounded” water back in to the aquifer, which creates a circulation zone around the well to further enhance cleanup. The ART technology has been implemented at several sites nationwide, including industrial laundry facilities, manufacturing plants, and service stations, and has achieved significant reductions in contaminant concentrations. Specifically, a concentration of tetrachloroethene (PCE) decreased from 2,700 to 240 μg/l, in 13 days. In less than three months, the concentrations dropped further to 79 μg/l, which is within the range of background levels. Other sites utilizing the technology have exhibited similar reduction trends in complex subsurface environments. © 2002 Wiley Periodicals, Inc.     

Phytoremediation of dissolved phase organic compounds: Optimal site considerations relative to field case studies

The United States Environmental Protection Agency/Environmental Response Team (EPA/ERT) has been supporting and implementing the use of phytoremediation to remediate dissolved phase organic compounds at Superfund sites since March 1996. Since then, ERT has applied phytoremediation field plots, both pilot and full scale, to a variety of field conditions. These active sites vary considerably as to depth to groundwater, groundwater transmissivity, contaminant concentrations, contaminant hydrophobicity, climate, planting design, plant selection, planting technique, and type of monitoring. Here we compare the literature and discuss lessons learned at five Superfund sites. Current maintenance and monitoring techniques at these sites are also discussed with recommendations for the maintenance and monitoring of similar sites in the future. © 2003 Wiley Periodicals, Inc.     

Taproot™ technology: Tree coring for fast,noninvasive plume delineations

In efforts to evaluate the use of plants as a forensic tool for delineating contaminated soil and groundwater, a laboratory experiment and a field sampling effort were undertaken. Site assessments are often costly and inaccurate, requiring multiple mobilizations to hone in on source areas and getting accurate estimates of contaminant extent and distribution. As these extensive site delineations take place, valuable time and resources are lost. The findings of this study show that plants can be used as a tool to evaluate a variety of subsurface contaminants, either in the vadose zone or in the saturated zone. In the first field application of Taproot? Technology, a large, heavily forested site was sampled in one day and the contamination on‐site was more accurately delineated than had been generated at the site in over a decade, with more than 26 wells installed. New source zones were detected on the site, and the presence of new waste depositions was uncovered for the first time showing the great value of tree coring as a contaminant detection tool. © 2009 Wiley Periodicals, Inc.     

Developing Life‐Cycle Environmental Response Costs for Leaking Underground Storage Systems at Service Station Sites

Leaking underground storage tank systems at service stations have resulted in tens of thousands of petroleum releases and associated groundwater chemical plumes often extending hundreds of feet off‐site. Technical and engineering approaches to assess and clean up releases from underground tanks, product lines, and dispensers using technologies such as soil vapor extraction, air sparging, biostimulation, and monitored natural attenuation are well understood and widely published throughout the literature. This article summarizes life‐cycle environmental response costs typically encountered using site‐specific cost estimation or metric‐based cost categories considering the overall complexity of site conditions: (1) simple sites where response actions require smaller scale assessments and/or remediation and have limited or no off‐site impacts; (2) average sites where response actions require larger scale assessments and/or remediation typical of petroleum releases; (3) complex sites where response actions require greater on‐site and/or off‐site remediation efforts; and (4) mega sites where petroleum plumes have impacted public or private water supplies or where petroleum vapors have migrated into occupied buildings. Associated cleanup cost estimates rely upon appropriate combinations of individual work elements and the duration of operation, maintenance, and monitoring activities. These cost estimates can be offset by state reimbursement funds, coverage in purchase agreements, and insurance policies. A case study involving a large service station site portfolio illustrates the range of site complexity and life‐cycle environmental response costs. © 2014 Wiley Periodicals, Inc.     

Evidence for biodegradation and volatilisation of dissolved petroleum hydrocarbons during in situ air sparging in large laboratory columns

Laboratory column experiments run for up to 13 days compared air sparging of groundwater contaminated by dissolved petroleum hydrocarbons in sterile and non-sterile aquifer sediments as well as uncontaminated sediments and groundwater. Loss of dissolved BTEX compounds in the contaminated columns was very rapid, occurring through volatilisation. The majority of the dissolved total organic carbon (TOC) persisted for much longer periods however. A direct comparison between losses from sterile and non-sterile columns suggested a negligible contribution of biodegradation to the removal of TOC. This was difficult to confirm through examination of O₂ utilisation because oxidation of a small amount of reduced sulphur in the aquifer materials was the dominant sink for O₂. Despite this, it was possible to conclude that less than 22% of the removal of TOC was through biodegradation during the first three days of air sparging.     

Augmenting in-situ remediation by soil vapor extraction with six-phase soil heating

The use and performance of soil vapor extraction (SVE) as an in-situ remedial technology has been limited at numerous sites because of both geologic and chemical factors. SVE systems are not well suited to sites containing low permeability soils or sites contaminated with recalcitrant compounds. Six-phase soil heating (SPSH) has been developed by the Battelle Pacific Northwest Laboratories (Battelle) to enhance SVE systems. The technology utilizes resistive soil heating to increase the vapor pressure of subsurface contaminants and to generate an in-situ source of steam. The steam strips contaminants sorbed onto soil surfaces and acts as a carrier gas, providing an enhanced mechanism by which the contaminants can reach an extraction well. Full-scale applications of SPSH have been performed at the U.S. Department of Energy's Savannah River Site in Aiken, South Carolina; at a former fire training site in Niagara Falls, New York; and at Fort Richardson near Anchorage, Alaska. At each site, chlorinated solvents were present in low permeability soils and SPSH was applied in conjunction with SVE. The results of the three applications showed that SPSH is a cost-effective technology that can reduce the time required to remediate a site using only conventional SVE.     

Public preferences for environmental management practices at DOE's nuclear waste sites

Residents who lived within 50 miles of one of six major US Department of Energy nuclear waste sites were asked in 2005 and again in 2010 to rate environmental management options. Respondents expressed strong preference for continuously sampling the air and water, monitoring worker health, and providing training and equipment to local responders. They strongly supported some site restrictions, such as making sure that the federal government owns the site until no more hazards are present, keeping visitors and recreational users off the site, and requiring government officials to report information to community representatives. The public was much more equivocal about other options, such as restricting new nuclear‐related activities and requiring site managers to live near sites. The authors summarize factors that lead to these public preferences and discuss five population types encountered at these and perhaps other waste management sites. © 2011 Wiley Periodicals, Inc.