Chlorinated vapor intrusion indicators,tracers, and surrogates (ITS): Supplemental measurements for minimizing the number of chemical indoor air samples—Part 1: Vapor intrusion driving forces and related environmental factors

Vapor intrusion (VI) assessment is complicated by spatial and temporal variability, largely due to compounded interactions among the many individual factors that influence the vapor migration pathway from subsurface sources to indoor air. Past research on highly variable indoor air datasets demonstrates that conventional sampling schemes can result in false negative determinations of potential risk corresponding to reasonable maximum exposures (RME). While high‐frequency chemical analysis of individual chlorinated volatile organic compounds (CVOCs) in indoor air is conceptually appealing, it remains largely impractical when numerous buildings are involved and particularly for long‐term monitoring. As more is learned about the challenges with indoor air sampling for VI assessment, it has become clear that alternative approaches are needed to help guide discrete sampling efforts and reduce sampling requirements while maintaining acceptable confidence in exposure characterization. Indicators, tracers, and surrogates (ITS), which include a collection of quantifiable metrics and tools, have been suggested as a potential solution for making VI pathway assessment and long‐term monitoring more informative, efficient, and cost‐effective. This review, compilation, and evaluation of ITS demonstrates how even low numbers of indoor air CVOC samples can provide high levels of confidence for representing the RME levels (e.g., 95th percentile) often sought by regulatory agencies for less than chronic effects. A two‐part compilation of available evidence for select low‐cost ITS is presented, with Part 1 focused on introducing the concepts of ITS, meteorologically based ITS, and the evidence from data‐rich studies to support lower cost CVOC VI assessments. Part 1 includes the results of quantitative analyses on two robust residential building VI datasets, where numerous supplemental metrics were collected concurrently with indoor air concentration data. These are supplemented with additional less‐intensive studies in different circumstances. These analyses show that certain ITS metrics and tools, including differential temperature, differential pressure, and radon (in Part 2), can provide benefits to VI assessment and long‐term monitoring. This includes indicators that narrow the assessment period needed to capture RME conditions, tracers that enhance understanding of the conceptual site model, and aid in the identification of preferential pathways and surrogates that support or substitute for CVOC sampling results. The results of this review provide insight into the scientifically supportable uses of ITS.     

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.     

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.     

Residential vapor‐intrusion evaluation: Long‐duration passive sampling vs. short‐duration active sampling

Sampling indoor air for potential vapor‐intrusion impacts using current standard 24‐hour sample collection methods may not adequately account for temporal variability and detect contamination best represented by long‐term sampling periods. Henry Schuver of the U.S. Environmental Protection Agency Office of Solid Waste stated at the September 2007 Air & Waste Management Association vapor‐intrusion conference that the US EPA may consider recommending longer‐term vapor sampling to achieve more accurate time‐weighted‐average detections. In November 2007, indoor air at four residences was sampled to measure trichloroethene (TCE) concentrations over short‐ and long‐duration intervals. A carefully designed investigation was conducted consisting of triplicate samplers for three different investigatory methods: dedicated 6‐liter Summa canisters (US EPA Method TO‐15), pump/sorbent tubes (US EPA Method TO‐17), and passive diffusion samplers (MDHS 80). The first two methods collected samples simultaneously for a 24‐hour period, and the third method collected samples for two weeks. Data collected using Methods TO‐15 (canisters) and TO‐17 (tubes) provided reliable short‐duration TCE concentrations that agree with prior 24‐hour sampling events in each of the residences; however, the passive diffusion samplers may provide a more representative time‐weighted measurement. The ratio of measured TCE concentrations between the canisters and tubes are consistent with previous results and as much as 28.0 μg/m³ were measured. A comparison of the sampling procedures, and findings of the three methods used in this study will be presented. © 2008 Wiley Periodicals, Inc.     

Dynamic subsurface explosive vapor concentrations: Observations and implications

Conventional vapor intrusion characterization efforts can be challenging due to background indoor air constituents, preferential subsurface migration pathways, sampling access, and collection method limitations. While it has been recognized that indoor air concentrations are dynamic, until recently it was assumed by many practitioners that subsurface concentrations did not vary widely over time. Newly developed continuous monitoring platforms have been deployed to monitor subsurface concentrations of methane, carbon dioxide, oxygen, hydrogen sulfide, total volatile organic constituents, and atmospheric pressure. These systems have been integrated with telemetry, geographical information systems, and geostatistical algorithms for automatically generating two‐ and three‐dimensional contour images and time‐stamped renderings and playback loops of sensor attributes, and multivariate analyses through a cloud‐based project management platform. The objectives at several selected sites included continuous monitoring of vapor concentrations and related physical parameters to understand explosion risks over space and time and to then design a long‐term risk reduction strategy. High‐frequency data collection, processing, and automated visualization have resulted in greater understanding of natural processes, such as dynamic contaminant vapor intrusion risk conditions potentially influenced by localized barometric pumping. For instance, contemporaneous changes in methane, oxygen, and atmospheric pressure values suggest there is interplay and that vapor intrusion risk may not be constant. As a result, conventional single‐event and composite assessment technologies may not be capable of determining worst‐case risk scenarios in all cases, possibly leading to misrepresentation of receptor and explosion risks. While dynamic risk levels have been observed in several initial continuous monitoring applications, questions remain regarding whether these situations represent special cases and how best to determine when continuous monitoring should be required. Results from a selected case study are presented and implications derived. © 2011 Wiley Periodicals, Inc.     

Building pressure control test to examine if VOC contamination in indoor air is caused by an interior source or by a subslab source

When determining whether or not remediation of subslab contamination is warranted, it is often important to know if the presence of volatile organic compounds (VOCs) in indoor air is caused primarily by interior sources, or primarily by subslab contamination. With a Building Pressure Control test, the pressure differential across the building envelope and, thereby, also the pressure differential across the slab, can be controlled by a blower. By measuring the indoor air concentrations of VOCs under depressurization (upward pressure gradient over the slab) and under pressurization (downward pressure gradient over the slab), it can be determined if the subslab contamination contributes significantly to the VOC concentrations in indoor air. This technique has been applied at several sites in the Central Denmark Region, and the results show that a Building Pressure Control test is a quick and effective method to examine if VOC contamination in indoor air is caused primarily by interior sources or primarily by subslab sources. With numerous measurement points in the indoor air, at some sites this test method has identified the area where the subslab contamination is located. A pressure differential at ?5/+5 Pa across the building envelope was sufficient at all the test sites to control the pressure gradient across the slab to be uniquely upward/downward.     

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.     

The ART In‐Well Technology test at a chlorinated solvent site in central Iowa

An Accelerated Remediation Technologies (ART) In‐Well Technology pilot test was performed to evaluate the removal of chlorinated volatile organic compounds (VOCs) from groundwater. The ART In‐Well Technology was installed in one well located in the source area where dense nonaqueous‐phase liquid has been identified and VOC concentrations exceed 140,000 μg/L. Monitoring wells at the site were positioned between 10 and 170 feet from the ART test well. Overall, VOC concentrations from samples collected from the groundwater monitoring wells and in the vapors extracted for discharge from the ART treatment well were analyzed over the testing period. Monitoring results showed that concentrations of perchloroethylene were reduced in the closest monitoring well to nondetectable concentrations within 90 days. The cumulative removal of chlorinated VOCs from the ART test well over the six‐month pilot test period exceeded 9,500 pounds based on air monitoring data. The ART technology proved effective and cost‐efficient in reducing contaminant concentrations and removing a large mass of contamination from the subsurface in a short period of time. The radius of influence of the ART technology at the site was estimated to range between 65 and 170 feet. © 2007 Wiley Periodicals, Inc.     

Characterization and determination of the odorous charge in the indoor air of a waste treatment facility through the evaluation of volatile organic compounds (VOCs) using TD–GC/MS

Municipal solid waste treatment facilities are generally faced with odorous nuisance problems. Characterizing and determining the odorous charge of indoor air through odour units (OU) is an advantageous approach to evaluate indoor air quality and discomfort. The assessment of the OU can be done through the determination of volatile organic compounds (VOCs) concentrations and the knowledge of their odour thresholds. The evaluation of the presented methodology was done in a mechanical–biological waste treatment plant with a processing capacity of 245.000 tons year^?1 of municipal residues. The sampling was carried out in five indoor selected locations of the plant (Platform of Rotating Biostabilizers, Shipping warehouse, Composting tunnels, Digest centrifugals, and Humid pre-treatment) during the month of July 2011. VOC and volatile sulphur compounds (VSCs) were sampled using multi-sorbent bed (Carbotrap, Carbopack X, Carboxen 569) and Tenax TA tubes, respectively, with SKC AirCheck 2000 pumps. The analysis was performed by automatic thermal desorption (ATD) coupled with a capillary gas chromatography (GC)/mass spectrometry detector (MSD). One hundred and thirty chemical compounds were determined qualitatively in all the studied points (mainly alkanes, aromatic hydrocarbons, alcohols, aldehydes, esters, and terpenes), from which 86 were quantified due to their odorous characteristics as well as their potentiality of having negative health effects. The application of the present methodology in a municipal solid waste treatment facility has proven to be useful in order to determine which type of VOC contribute substantially to the indoor air odorous charge, and thus it can be a helpful method to prevent the generation of these compounds during the treatment process, as well as to find a solution in order to suppress them.     

Laboratory validation study of new vapor‐phase‐based approach for groundwater monitoring

Recent improvements in field‐portable analytical equipment allow accurate on‐site measurement of VOCs present in air at concentrations of less than 0.1 parts per million volume (ppmv). The objective of this project is to determine if the use of these instruments for vapor‐phase measurements of headspace in a monitoring well can serve as a reliable and accurate method for monitoring volatile organic compound (VOC) concentrations in groundwater under equilibrium conditions. As part of a comprehensive research project investigating the utility of this proposed monitoring method, the authors have completed a laboratory validation study to identify instruments and sample‐collection methods that will provide accurate measurement of VOC concentrations in groundwater. This laboratory validation study identified two field‐portable instruments (a gas chromatograph and a photoionization detector) with sufficient sensitivity to measure VOCs in groundwater at concentrations below typical monitoring standards (i.e., 1 to 5 μg/L). The accuracy and precision of these field instruments was sufficient to satisfy typical data‐quality objectives for laboratory‐based analysis. In addition, two sample‐collection methods were identified that yield vapor‐phase samples in equilibrium with water: direct headspace sampling and passive diffusion samplers. These sample‐collection methods allow the field instruments (which measure VOC concentrations in vapor‐phase samples) to be used to measure VOC concentrations in water. After further validation of these sample‐collection methods in the field, this monitoring method will provide a simple way to obtain accurate real‐time measurements of VOC concentrations in groundwater using inexpensive field‐portable analytical instruments. © 2009 Wiley Periodicals, Inc.     

n-Hexane Biodegradation in Trickle Bed Air Biofilters

While hydrophilic compounds are degraded easily in Trickling bed air biofilters (TBABs), hydrophobic compounds are retarded until biological cultures produce a sufficient RNA or enzyme/protein to utilize this compound. Hydrophobic compounds are not readily bio-available which makes them reluctant to biodegradation as mass transfer between the gas and liquid phases is a rate limiting step. To enhance the destruction of hydrophobic compounds in TBABs, the utilization of surfactant was introduced to increase the solubility which helps overcoming the rate limiting step. The surfactant was used as well to limit the growth of excess biomass ensuring smooth flow through the biofilter bed and preventing short circuits. Two different non-ionic non-toxic surfactants were used in this study: Triton X-100 and Tomadol® 25-7. Two lab-scale controlled TBABs were operated for investigating the performance difference for n-Hexane as an example of hydrophobic volatile organic compound (VOC) with and without the addition of surfactant. Operating conditions in both TBABs were as follows: nutrient feed rate (2L/day), air flowrate (1.4L/min), bed depth (60cm), empty bed retention time (120s), bed material (diatomaceous earth pellets) and room-temperature. The inlet concentration was changed from 50 to 100ppmv. Acclimation period, removal profile along biofilter depth, nitrogen consumption, and CO₂ production were compared under continuous loading operation condition. The optimum concentration of surfactant in the nutrient feed was determined by a batch experiment. The effect of different surfactant concentrations on VOC water solubility with time was studied by considering different VOC concentration sets within the TBAB loading rate range.     

Sources and Variability of Indoor and Outdoor Gaseous Aerosol Precursors (O3, NOx and VOCs)

Measurements of indoor and outdoor aerosol concentrations and their gaseous precursors (O₃, NO and NO₂) as well as volatile organic compounds (VOCs) concentrations were performed at two houses in the Oslo metropolitan area. The variability of the concentration of gaseous compounds was studied in respect to their sources in the indoor and outdoor environments. Domestic heating during the winter and photochemical production during the summer were the main sources for outdoor NOx and O₃. In the indoor environment infiltration of outdoor air, candle burning, smoking and indoor chemical reactions were the main sources affecting their concentrations. The concentrations of VOCs outdoors were enhanced during the summer due to biogenic emissions whereas in the indoor environment their values were affected mostly by emissions from materials used during the recent refurbishing of the houses (>0.4 mg/m³).     

High‐Frequency Continuous Monitoring to Track Vapor Intrusion Resulting From Naturally Occurring Pressure Dynamics

Vapor intrusion characterization efforts can be challenging due to complexities associated with background indoor air constituents, preferential subsurface migration pathways, and response time and representativeness limitations associated with conventional low‐frequency monitoring methods. For sites experiencing trichloroethylene (TCE) vapor intrusion, the potential for acute risks poses additional challenges, as the need for rapid response to exposure exceedances becomes critical in order to minimize health risks and associated liabilities. Continuous monitoring platforms have been deployed to monitor indoor and subsurface concentrations of key volatile constituents, atmospheric pressure, and pressure differential conditions that can result in advective transport. These systems can be comprised of multiplexed laboratory‐grade analytical components integrated with telemetry and geographical information systems for automatically generating time‐stamped renderings of observations and time‐weighted averages through a cloud‐based data management platform. Integrated automatic alerting and responses can also be engaged within one minute of risk exceedance detection. The objectives at a site selected for testing included continuous monitoring of vapor concentrations and related surface and subsurface physical parameters to understand exposure risks over space and time and to evaluate potential mechanisms controlling risk dynamics which could then be used to design a long‐term risk reduction strategy. High‐frequency data collection, processing, and automated visualization efforts have resulted in greater understanding of natural processes such as dynamic contaminant vapor intrusion risk conditions potentially influenced by localized barometric pumping induced by temperature changes. For the selected site, temporal correlation was observed between dynamic indoor TCE vapor concentration, barometric pressure, and pressure differential. This correlation was observed with a predictable daily frequency even for very slight diurnal changes in barometric pressure and associated pressure differentials measured between subslab and indoor regimes and suggests that advective vapor transport and intrusion can result in elevated indoor TCE concentrations well above risk levels even with low‐to‐modest pressure differentials. This indicates that vapor intrusion can occur in response to diurnal pressure dynamics in coastal regions and suggests that similar natural phenomenon may control vapor intrusion dynamics in other regions, exhibiting similar pressure, geochemical, hydrogeologic, and climatic conditions. While dynamic indoor TCE concentrations have been observed in this coastal environment, questions remain regarding whether this hydrogeologic and climatic setting represent a special case, and how best to determine when continuous monitoring should be required to most appropriately minimize exposure durations as early as possible. ©2017 Wiley Periodicals, Inc.     

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.

     

PM10, O3, CO Concentrations and Elemental Analysis of Airborne Particles in a School Building

Measurements of indoor and outdoor PM10, as well as indoor O₃ and CO concentrations were conducted and are presented here. These measurements were carried out at an institute building, located in a suburban industrial area in Greece. Both indoor and outdoor PM10 samples were also collected and their elemental composition was identified by ED-XRF analysis. Twenty seven major, minor and trace elements were identified. The measurements took place generally in different periods of institute operation, from June 2004 to February 2005. The indoor PM10 concentrations which were measured during the normal operation period of the institute were found to be many times higher than the respective outdoor PM10 concentrations of the same periods. On the contrary, the indoor PM10 concentrations which were measured during the holiday period were found to be lower than their corresponding outdoor values. Indoor O₃ and CO concentrations were found to be in low level. Indoor PM10 concentrations were found to be in a relative good correlation with O₃ (r = 0.45) and in high correlation (r = 0.98) with CO concentrations. On average, total elements concentrations were much higher indoors relative to outdoors. Based on above findings we attempted to determine the pollution sources of the indoor environment and to investigate some parameters or chemical processes that affect indoor pollutants’ levels.     

Characterization and pilot‐scale studies for chemical oxidation remediation of fractured shale

The distribution of volatile organic compounds (VOCs) in fractured shale overlain by thin (< 10 feet) overburden at the Watervliet Arsenal near Albany, New York, was initially determined by sampling water from the fracture network using packer systems in boreholes and also using conventional monitoring wells. Furthermore, short‐term pumping and injection tests were conducted and the boreholes were logged using a variety of geophysical and hydrophysical tools. Tetrachloroethene is the dominant VOC in the groundwater, with lesser concentrations of trichloroethene and degradation products (cis‐1,2‐dichloroethene, trans‐1,2‐dichloroethene, and vinyl chloride). The vertical VOC distributions in the rock matrix were obtained from continuous‐cored holes from which small rock samples, collected at many depths between 18 and 150 feet below ground surface, were analyzed. The rock core VOC concentrations were determined by methanol extraction of crushed rock followed by direct methanol injection onto a gas chromatograph and subsequent estimation of rock porewater VOC concentrations. The rock core data support the concept that diffusion‐driven mass transfer has caused nearly all the VOC mass initially present in the fractures to now reside in the rock matrix, which has a porosity three or four orders of magnitude larger than the bulk fracture porosity. The results of the site characterization indicate that an effective site investigation strategy in fractured shale must include characterization of both the fracture and matrix contaminant distribution. These results also indicate that the most favorable remediation technologies for this fractured shale are those that will destroy VOCs in the rock matrix, particularly contaminants in the sorbed phase, and also destroy the VOC mass in the fractures including both dissolved and immiscible phases. The site characterization resulted in the selection of potassium permanganate for an in situ chemical oxidation pilot study. © 2004 Wiley Periodicals, Inc.     

An evaluation of the performance of multiple passive diffusion devices for indoor air sampling of VOCs

The United States Environmental Protection Agency is considering recommending longer‐term sampling to achieve more accurate time‐weighted‐average detections for indoor air monitoring of volatile organic chemicals. The purpose of the research presented herein was to compare longer sampling times using passive diffusion samplers to the results from shorter‐term testing periods using sorbent tubes and low‐flow pumps (US EPA Method TO‐17) at great frequency for trichloroethene (TCE) in indoor air. A controlled release of TCE in a large room allowed for over two‐orders‐of‐magnitude daily concentration variability over the course of the two‐week monitoring event. The daily concentration measurements by US EPA Method TO‐17 and the passive diffusion samplers were performed in triplicate and had excellent reproducibility. The results of daily tests were averaged and compared with four passive diffusion devices exposed to indoor air for three, seven, ten, and fourteen days in accordance with ASTM D6196‐02. A specific uptake rate for each of the passive devices at the four different time intervals and the statistical significance of the time‐varying uptake rates were evaluated. The performance of each passive diffusion device was determined using a statistical performance criterion. The average concentration for all of the exposure periods could be reliably predicted using the established uptake rates for two of the four passive devices. © 2009 Wiley Periodicals, Inc.     

Biofiltration treatment of odors from municipal solid waste treatment plants

An in situ compost biofilter was established for the treatment of odors from biostabilization processing of municipal solid waste. The concentrations of total volatile organic compounds (VOCs) in odors and their components were measured. Biofilter media was characterized in terms of total carbon (TC), total nitrogen (TN), total phosphorus (TP), organic matter (OM), pH value and determination of bacterial colony structure. Gas chromatography–mass spectrometry (GC–MS) analysis showed that the main components of the produced gas were benzene, toluene, ethylbenzene and xylene (BTEX) along with other alkanes, alkenes, terpenes, and sulphur compounds. The compost biofilter had remarkable removal ability for alkylated benzenes (>80%), but poor removal for terpenes (～30%). Total VOC concentrations in odors during the biostabilization process period ranged from 0.7 to 87 ppmv, and the VOC removal efficiency of the biofilter varied from 20% to 95%. After about 140 days operation, TN, TC, TP and OM in compost were kept almost stable, but the dissolved N, NH₄–N and NO₃–N experienced an increase of 44.5%, 56.2% and 76.3%, respectively. Dissolved P decreased by 27.3%. The pH value experienced an increase in the early period and finally varied from 7.38 to 8.08. Results of bacterial colony in packing material indicated that bacteria and mold colony counts increased, but yeasts and actinomyces decreased along with biofilter operation, which were respectively, 3.7, 3.4, 0.04 and 0.07 times of their initial values.     

Addressing soil gas vapor intrusion using sustainable building solutions

Soil gas vapor intrusion (VI) emerged in the 1990s as one of the most important problems in the investigation and cleanup of thousands of sites across the United States. A common practice for sites where VI has been determined to be a significant pathway is to implement interim building engineering controls to mitigate exposure of building occupants to VI while the source of contamination in underlying soil and groundwater is assessed and remediated. Engineering controls may include passive barriers, passive or active venting, subslab depressurization, building pressurization, and sealing the building envelope. Another recent trend is the emphasis on “green” building practices, which coincidentally incorporate some of these same engineering controls, as well as other measures such as increased ventilation and building commissioning for energy conservation and indoor air quality. These green building practices can also be used as components of VI solutions. This article evaluates the sustainability of engineering controls in solving VI problems, both in terms of long‐term effectiveness and “green” attributes. Long‐term effectiveness is inferred from extensive experience using similar engineering controls to mitigate intrusion of radon, moisture, mold, and methane into structures. Studies are needed to confirm that engineering controls to prevent VI can have similar long‐term effectiveness. This article demonstrates that using engineering controls to prevent VI is “green” in accelerating redevelopment of contaminated sites, improving indoor air quality, and minimizing material use, energy consumption, greenhouse gas emissions, and waste generation. It is anticipated that engineering controls can be used successfully as sustainable solutions to VI problems at some sites, such as those deemed technically impracticable to clean up, where remediation of underlying soil or groundwater contamination will not be completed in the foreseeable future. Furthermore, green buildings to be developed in areas of potential soil or groundwater contamination may be designed to incorporate engineering controls to prevent VI. © 2009 Wiley Periodicals, Inc.     

Overview of state approaches to vapor intrusion

A large number of states have issued guidance addressing the vapor intrusion pathway making it difficult to keep up with various policies and requirements. We have compiled and reviewed guidance from 35 states, half of which have issued documents within the last three years. A comparison of policies among states shows reasonable consistency in some areas—for example, 20 of 23 states that provide an exclusion distance for subsurface sources of chlorinated volatile organic compounds (VOCs) use a distance of 100 feet. However, more commonly, the policy decisions vary widely. Among states, indoor air screening concentrations for the same VOC vary by more than 2,000 times and subsurface screening concentrations vary by more than 2,000,000 times. These wide discrepancies suggest a need for communication and consensus building in order to increase consistency in the management of the vapor intrusion pathway. © 2012 Wiley Periodicals, Inc.