Remediation techniques for mitigating vapor intrusion from sewer systems to indoor air

Investigations at former dry cleaning sites in Denmark show that sewer systems often are a major vapor intrusion pathway for chlorinated solvents to indoor air. In more than 20 percent of the contaminated drycleaner sites in Central Denmark Region, sewer systems were determined to be a major vapor intrusion pathway. Sewer systems can be a major intrusion pathway if contaminated groundwater intrudes into the sewer and contamination is transported within the sewer pipe by water flow in either free phase or dissolved states. Additionally, the contamination can volatilize from the water phase or soil gas can intrude the sewer system directly. In the sewer, the gas phase can migrate in any direction by convective transport or diffusion. Indications of the sewer as a major intrusion pathway are:

• higher concentrations in the upper floors in buildings,
• higher concentrations in indoor air than expected from soil gas measurements,
• higher concentrations in bathrooms/kitchen than in living rooms,
• chlorinated solvents in the sewer system, and
• a pressure gradient from the sewer system to indoor air.

Measurements to detect whether or not the sewer system is an intrusion pathway are simple. In Central Denmark Region, the concentrations of contaminants are routinely measured in the indoor air at all floors, the outdoor air, behind the water traps in the building, and in the manholes close to the building. The indoor and outdoor air concentration, as well as concentrations in manholes, are measured by passive sampling on sorbent samplers over a 14‐day period, and the measurements inside the sewer system are carried out by active sampling using carbon tubes (sorbent samplers). Furthermore, the pressure gradient over the building slab and between the indoor air and the sewer system are also measured. A simple test is depressurization of the sewer system. Using this technique, the pressure gradient between the sewer system and the indoor air is altered toward the sewer system—the contamination cannot enter the indoor air through the sewer system. If the sewer system is a major intrusion pathway, the effect of the test can be observed immediately in the indoor air. Remediation of a sewer transported contamination can be:

• prevention of the contaminants from intruding into the sewer system or
• prevention of the contaminated gas in the sewer system from intruding into the indoor air.

Remediation techniques include the following:

• lining of the sewer piping to prevent the contamination from intruding into the sewer;
• sealing the sewer system in the building to prevent the contamination from the sewer system to intrude the indoor air;
• venting of manholes; and
• depressurizing the sewer system.

     

In-situ application of colloidal activated carbon for PFAS-contaminated soil and groundwater: A Swedish case study

Soil and groundwater contamination by per- and polyfluoroalkyl substances (PFAS) has been a significant concern to human health and environmental quality. Remediation of contaminated sites is crucial to prevent plume expansion but can prove challenging due to the persistent nature of PFAS combined with their high aqueous mobility. In this case study, we investigated the potential of colloidal activated carbon (CAC) for soil stabilization at the pilot scale, aiming to entrap PFAS and prevent their leaching from soil into groundwater. Monitoring of the site revealed the presence of two potential sources of PFAS contamination at concentrations up to 23 μg L⁻¹ for ∑₁₁PFAS in groundwater. After CAC application, initial results indicated a 76% reduction of ∑₁₁PFAS and high removal rates for long-chain PFAS, such as perfluorooctane sulfonic acid and perfluorooctanoic acid. A spike in concentrations was noticed 6 months after injection of CAC, showing a rebound of the plume and a reduction of treatment effectiveness. Based on long-term monitoring data, the treatment effectiveness for ∑₁₁PFAS dropped to 52%. The rebound of concentrations was attributed to the plume bypass of the barrier due to the presence of high conductivity zones, which likely occurred because of seasonal changes in groundwater flow directions or the CAC application at the site. This demonstrates the need for a detailed and accurate hydrogeological understanding of contaminated sites before designing and applying stabilization techniques, especially at sites with high geologic and hydrologic complexity. The results herein can serve as a guideline for treating similar sites and help avoid potential pitfalls of remedial efforts.     

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.     

Pollutant source identification and allocation: Advances in hydrocarbon fingerprinting

Often liability for environmental damage and cleanup of contaminated sites is made difficult, especially with chemically complex environments containing different pollutants, by the inability to differentiate potential sources (or “owners”) of pollutants from each other. As a result, unnecessary costs may be associated with having to assume financial responsibility for alleged contamination of a site. This article reviews the advances in chemical fingerprinting as a tool in identifying and differentiating sources of hydrocarbon pollutants in chemically complex environments. Appropriate hydrocarbon target analytes and required analytical methods for hydrocarbon fingerprinting are discussed, and new interpretative tools are presented that may be applied to contaminated soil, sediment, and groundwater environmental situations. With these analytical and interpretative techniques, an appropriate allocation of chemical contamination and costs at a site can be made.     

Management Systems Approach to Building Vapor Intrusion: A Facility Manager's Guide

Vapor intrusion (VI) has the potential to affect over 100,000 developed and undeveloped sites in the United States. Vapor intrusion occurs when the migration of volatile chemicals from the subsurface enters overlying buildings. A myriad of adverse health effects have been documented based on the inhalation of volatile chemicals from VI. At a time when most state and federal agencies have yet to set firm standards, the burden of responsibility is often placed on the facility manager to decide how to protect building occupants from volatile organic compounds potentially seeping into buildings. This article outlines a detailed step‐by‐step process for facility managers on how to begin a VI assessment and, when warranted, establish a site‐specific vapor intrusion management system for building occupant protection. This document should be used concurrently with current federal and state guidelines as it pertains to VI. © 2014 Wiley Periodicals, Inc.     

Institutional controls for future land use at active installation restoration program (IRP) sites

One of the strategies now in vogue in hazardous waste cleanup is basing remedial strategies on future land use. The initial thrust of CERCLA for permanent and complete remedies has given way, pushed by concepts like “brownfields” and base closure and reuse, to strategies often based on “institutional controls” that attempt to stabilize future land uses at a site based on residual risk. The heart of this concept is that instead of removing all wastes from a site, some wastes can safely remain so long as in the future the site is not used in such a way that the residual contamination poses an unacceptable risk to human health and the environment. “Institutional controls” is a term for land use management strategies that do not rely on engineering approaches to reduce risk, but rather seek to ensure that the site is not used in an inappropriate way in the future. This article cautions that such a strategy has inherent residual risks that must be understood by those involved in implementing hazardous waste cleanups and those responsible for future uses of contaminated property. Simply put, institutional controls are only as good as the processes that are in place to ensure they are respected in the future. This presents particular problems for active duty installations because most of the protections commonly available to private sector sites are not useful at active installations. This article discusses an initiative by the Air Combat Command to develop a handbook on instituting and maintaining land restrictions. It will also discuss that effort in light of the April 21 EPA Region IV guidance on assuring Land Use Controls at Federal Facilities. This article is based on a paper and presentations given at the 1998 ACC Environmental Training Symposium.     

Evaluation of a vertical frozen soil barrier at oak ridge national laboratory

Arctic Foundations, Inc. (AFI), of Anchorage, Alaska, has developed a freeze barrier system designed to hydraulically isolate a contaminant source area. The system can be used for long‐term or temporary containment of groundwater until appropriate remediation techniques can be applied. The technology was evaluated under the United States Environmental Protection Agency's (EPA's) Superfund Innovative Technology Evaluation (SITE) program at the United States Department of Energy's (DOE's) Oak Ridge National Laboratory (ORNL) facility in Oak Ridge, Tennessee. For the demonstration, an array of freeze pipes called “thermoprobes” was installed to a depth of 30 feet below ground surface around a former waste collection pond and keyed into bedrock. The system was used to establish an impermeable frozen soil barrier to hydraulically isolate the pond. Demonstration personnel collected independent data to evaluate the technology's performance. A variety of evaluation tools were used—including a groundwater dye tracing investigation, groundwater elevation measurements, and subsurface soil temperature data—to determine the effectiveness of the freeze barrier system in preventing horizontal groundwater flow beyond the limits of the frozen soil barrier. Data collected during the demonstration provided evidence that the frozen soil barrier was effective in hydraulically isolating the pond.     

Superfund site remediation by landfilling—overview of landfill design,operation, closure,and postclosure issues

This article discusses the appropriateness of using landfills as part of remediating hazardous chemical and Superfund sites, with particular emphasis on providing for true long‐term public health and environmental protection from the wastes and contaminated soils that are placed in the landfills. On‐site landfilling or capping of existing wastes is typically the least expensive approach for gaining some remediation of existing hazardous chemical/Superfund sites. The issues of the deficiencies in US EPA and state landfilling approaches discussed herein are also applicable to the landfilling of municipal and industrial solid “nonhazardous” wastes. These deficiencies were presented in part as “Problems with Landfills for Superfund Site Remediation” at the US EPA National Superfund Technical Assistance Grant Workshop held in Albuquerque, New Mexico, in February 2003. They are based on the author's experience in investigating the properties of landfill liners and the characteristics of today's landfills, relative to their ability to prevent groundwater pollution and to cause other environmental impacts. Discussed are issues related to both solid and hazardous waste landfills and approaches for improving the ability of landfills to contain wastes and monitor for leachate escape from the landfill for as long as the wastes in the landfill will be a threat. © 2004 Wiley Periodicals, Inc.     

Utilisation of Supernatants of Pure Cultures of Streptomyces thermocarboxydus NH50 to Reduce Chromium Toxicity and Mobility in Contaminated Soils

Chromium is a heavy metal used in various industrial sectors. Improper handling and storage of chromium-laden effluents or wastes can lead to the pollution of the environment. The most toxic form is the more mobile one: hexavalent chromium Cr(VI). The reduction of Cr(VI) results in the immobilisation of chromium into its less toxic trivalent form Cr(III). This phenomenon may prevent the contamination of groundwater when the soil in the vadose zone is contaminated. Many bacteria have been isolated from contaminated soils and described to reduce Cr(VI) into Cr(III). A new Cr(VI)-reducing strain, identified as a Streptomyces thermocarboxydus,has been isolated and studied in our laboratories for its ability to reduce Cr(VI). This aerobic bacterium, in contrast to other genera described which mediate reduction via enzymes, produces reducing agents into the culture supernatants. Cr(VI) reduction by these substances is accelerated by the presence of small concentration of cupric ions (Cu²⁺). The reducing agent(s) can be easily recovered from the bacterial cultures and used as cell-free solution to treat contaminated soils by an in situ or ex situ processes.     

Conceptual Site Model Development and Phased Remedy Implementation to Achieve Vapor Screening Goals at a Former Dry Cleaner

Tetrachloroethene (PCE) releases at a former dry cleaner resulted in impacts to soil and shallow groundwater beneath and adjacent to the building. Subsurface impacts led to vapor intrusion with PCE concentrations between 900 and 1,200 micrograms per cubic meter (μg/m³) in indoor air. The migration pathways of impacted soil vapor were evaluated through implementation of a helium tracer test and vapor sampling of an exterior concrete block wall. Results confirmed that the concrete block wall acted as a conduit for vapor intrusion into the building. A combination of remediation efforts focused on mass reduction in the source area as well as mitigation efforts to inhibit vapor migration into the building. Excavation of soils beneath the floor slab and installation of a spray‐applied vapor barrier resulted in PCE concentrations in indoor air decreasing by over 97.9 percent. Operation of an active ventilation system installed under the floor slab and groundwater remediation via injections of nano‐scale zero valent iron (nZVI) further reduced PCE concentrations in indoor air by over 99.8 percent compared to baseline conditions. While significant reductions of PCE concentrations in groundwater were observed within two months after injection, maximum reductions to PCE concentrations in indoor air were not observed for an additional 12 months. © 2014 Wiley Periodicals, Inc.     

Optimizing remediation strategies for a former dry‐cleaner site

Residual tetrachloroethene (PCE) contamination at the former Springvilla Dry Cleaners site in Springfield, Oregon, posed a potential risk through the vapor intrusion, direct contact, and off‐site beneficial groundwater uses. The Oregon Department of Environmental Quality utilized the State Dry Cleaner Program funds to help mitigate the risks posed by residual contamination. After delineation activities were complete, the source‐area soils were excavated and treated on‐site with ex situ vapor extraction to reduce disposal costs. Residual source‐area contamination was then chemically oxidized using sodium permanganate. Dissolved‐phase contamination was subsequently addressed with in situ enhanced reductive dechlorination (ERD). ERD achieved treatment goals across more than 4 million gallons of aquifer impacted with PCE concentrations up to 7,800 micrograms per liter prior to remedial activities. The ERD remedy introduced electron donors and nutrient amendments through groundwater recirculation and slug injection across two aquifers over the course of 24 months. Adaptive and mass‐targeted strategies reduced total remedy costs to approximately $18 per ton within the treatment areas. © 2010 Wiley Periodicals, Inc.     

Demonstration of MicroBlower™ technology for sustainable soil vapor extraction: Case studies at the Savannah River Site,South Carolina

The MicroBlower Sustainable Soil Vapor Extraction System is a cost‐effective device specifically designed for remediation of organic compounds in the vadose zone. The system is applicable for remediating sites with low levels of contamination and for transitioning sites from active source technologies such as active soil vapor extraction to natural attenuation. It can also be a better choice for remediating small source zones that are often found in “tight zones” that are controlled by diffusion rate. The MicroBlower was developed by the Savannah River National Laboratory at the US Department of Energy's Savannah River Site to address residual volatile organic compound (VOC) contamination after shutdown of active soil vapor extraction systems. In addition, the system has been deployed to control recalcitrant sources that are controlled by diffusion rates. © 2012 Wiley Periodicals, Inc.     

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.     

Sampling strategies in the assessment of long‐term exposures to toxic substances in air

The decision to mitigate exposures from vapor intrusion (VI) is typically based on limited data from 24‐hour air samples. It is well documented that these data do not accurately represent long‐term average exposures linked to adverse health effects. Limited decision guidance is currently available to determine the most appropriate sampling strategy, considering the cost of sampling alternatives along with the economic consequences of exposure‐related health effects. We present a decision model that introduces economic and statistical considerations in evaluating alternative VI sampling methods. The model characterizes the best sampling method by factoring economic and health consequences of exposure, the variability of exposure, the cost of sampling and mitigation, and the likelihood of false‐negatives and false‐positives. Decision‐makers can use results to select the sample size that maximizes net benefit. Conceptual and mathematical models are presented linking biological, statistical, and economic considerations to assess the cost and effectiveness of different sampling strategies. The model relates an average exposure concentration, determined statistically, to abatement costs and to the monetary value of health deterioration. The value of the information provided by different strategies is calculated and used to select the optimum sampling method. Simulations show that longer‐term sampling methods tend to be more accurate and cost‐effective than short‐term samples. The ideal sampling strategy shows significant seasonal variation (it is typically optimal to use longer samples in the winter) and also varies significantly with the stringency of regulatory standards. Longer‐term sample collection provides a more accurate representation of average VI exposure and reduces the likelihood of type I and type II errors. This reduces expected costs of mitigation and exposure (e.g., health consequences, legal and regulatory penalties), which in some cases can be quite significant. The model herein shows how these savings are balanced against the additional costs of longer‐term sampling.     

When the Going Gets Tough,Communities Believe It's Time to Optimize and Adapt

The people who live in the communities where complex groundwater sites are located are as diverse as the country itself, but those who fight for the cleanup of our groundwater recognize that total cleanup may be difficult, if not impossible, in our lifetimes. Still, as explained in a December 2013 joint letter to US EPA, we want those who are responsible for environmental protection, be they polluters, developers, or regulatory agencies, to try harder before admitting defeat. In Mountain View, California, community activists have developed criteria for the adaptive cleanup of the Moffett‐MEW Regional Plume of TCE groundwater contamination that emphasizes areas with high contaminant mass, source areas, locations that reduce the need for long‐term vapor intrusion mitigation, properties where the detectable plume encroaches on residential areas, schools, and other sensitive uses, and areas planned for reuse. In many other communities, trust is the key to developing community support for remedial strategies. Communities that are listened to tend to feel more empowered. Empowered communities tend to offer more constructive advice. Decision makers tend to listen to communities that offer constructive advice. In summary, when the cleanup going gets tough, empowered communities believe that it is time to optimize and adapt, not to give up. © 2014 Wiley Periodicals, Inc.     

Vapor intrusion mitigation challenges posed by a classic urban setting

AECOM's Environmental Remediation Services Group, under a Pennsylvania Department of Environmental Protection (PADEP) remediation contract, was tasked with assessing potential vapor intrusion risks and mitigating identified risks at an active commercial property affected by a former adjacent laundry and dry cleaning operation. The former dry cleaning operation was positioned in the center of row‐buildings containing various commercial businesses. The neighboring active commercial property is an antiquated building that operates as a coffee shop. The coffee shop building contains a service area, a kitchen, and a rear conference room on the first floor, a storage area on the second floor, and a partial basement. The basement has been observed to periodically flood. Adjacent to the coffee shop building is an operating hair and nail salon that formerly functioned as one of the dry cleaning operations buildings with known soil, groundwater, and soil gas impacts. Due to the disposition of the coffee shop building, a methodical approach was implemented to characterize the potential vapor intrusion risk and included a diagnostic building inspection that identified required management of basement apertures and abatement of periodic flooding prior to vapor intrusion mitigation system design and installation.     

Optimum Dose Of Lime And Fly Ash For Treatment Of Hexavalent Chromium–Contaminated Soil

The presence of hexavalent chromium, Cr(VI), in soil is an environmental concern due to its effect on human health. The concern arises from the leaching and the seepage of Cr(VI) from soil to groundwater. In this paper, a stabilization technology to prevent this problem was simulated on an artificial soil contaminated with hexavalent chromium. The process is a physico-chemical treatment in which the toxic pollutant is physically entrapped within a solid matrix formed by the pozzolanic reactions of lime and fly ash to reduce its leachability and, therefore, its toxicity. This paper presents the optimum ratio of fly ash and lime in order to stabilize artificial soils contaminated with 0.4 wt.% of Cr (VI) in a brief term process. The degree of chromium released from the soil was evaluated using a modified Toxicity Characteristic Leaching Procedure (TCLP) by US Environmental Protection Agency (EPA). Overall, experimental results showed reduced leachability of total and hexavalent chromium from soils treated with both fly ash and quicklime, and that leachability reduction was more effective with increasing amount of fly ash and quicklime. Stabilization percentages between 97.3% and 99.7% of the initial chromium content were achieved, with Cr(VI) concentration in the TCLP leachates below the US EPA limit for chromium of 5 mg/l. Adequate treatment was obtained after 1 day of curing with just 25% fly ash and 10% quicklime.     

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.     

Actuarial Risk Analysis to Promote National Contingency Plan (NCP)‐Consistent Remediation

This article provides a case study of how green and sustainable remediation (GSR) concepts (including, but not limited to, worker risk) can be incorporated into the existing National Contingency Plan (NCP)/Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) remedy selection framework. The occupational risks of worker fatalities and injuries associated with two site remediation alternatives were calculated and compared. The results demonstrated that the increased worker risks associated with one of the remedy alternatives rendered it inferior based on the NCP “Balancing Criteria” of short‐term effectiveness. This type of approach is implementable at many sites by leveraging readily available information at the remedy selection stage using published methods and data sources. © 2014 Wiley Periodicals, Inc.     

The Use of Oxygen Release Compound for the Accelerated Bioremediation of Aerobically Degradable Contaminants: The Advent of Time-Release Electron Acceptors

Oxygen Release Compound (ORC®) is a patented formulation of intercalated magnesium peroxide that releases oxygen slowly when hydrated. ORC treatment represents a “low intensity” approach to site remediation. It provides a simple, passive, low-cost and long-term acceleration of aerobic natural attenuation and has been shown to cost-effectively reduce time to site closure. ORC is now a proven technology as evidenced by its five years of use on over 5,000 sites in 50 states and 11 countries, and the existence of a full body of independent, peer reviewed literature on its performance. The first applications of ORC were for the treatment of benzene, toulene, ethylbenzene, and xylene (BTEX) and other light petroleum hydrocarbon fractions. Use has now expanded to the treatment of heavier fractions such as heating oil and some of the Polycyclic aromatic hydrocarbons (PAHs). More recently. ORC has been used to bioremediate the highly mobile and problematic gasoline oxygenate methyl tertiary butyl ether (MTBE) and has been applied to sites impacted with nitroaromatics, chloroaromatics, and some of the lower-order chlorinated hydrocarbons that can be treated aerobically—most notably vinyl chloride. Since ORC is an insoluble powder, it can be packaged in material composed of a specially designed filter fabric. These “filter socks” are then contacted with contaminated groundwater via an array of wells or trenches. ORC can also be mixed directly with water to form a slurry for permanent injection applications in the saturated zone or dispersed in powdered form for the in-situ or ex-situ treatment of soil. A broad array of treatment points, in which ORC slurry is backfilled or injected, can be implemented with low-cost, small-bore push-point technologies to directly treat dissolved phase plumes and moderate levels of sorbed contaminants. Powder or slurry is traditionally used in the remediation of residual contamination at the bottom of contaminated soil excavations. © 1999 John Wiley & Sons, Inc.