Soil Vapor Extraction Research Articles

Remediation in Situ of Hydrocarbons by Combined Treatment in a Contaminated Alluvial Soil due to an Accidental Spill of LNAPL

Soil contamination represents an environmental issue which has become extremely important in the last decades due to the diffusion of industrial activities. Accidents during transport of dangerous materials and fuels may cause severe pollution. The present paper describes the criteria of the actions which were operated to remediate the potential risk and observed negative effects on groundwater and soil originating from an accidental spill of diesel fuel from a tank truck. With the aim to evaluate the quality of the involved environmental matrices in the “emergency” phase, in the following “safety” operation and during the remediation action, a specific survey on hydrocarbons, light and heavy, was carried out in the sand deposits soil. Elaboration of collected data allows us to observe the movement of pollutants in the unsaturated soil. The remediation action was finalized to improve the groundwater and soil quality. The former was treated by a so called “pump and treat” system coupled with air sparging. A train of three different technologies was applied to the unsaturated soil in a sequential process: soil vapour extraction, bioventing and enhanced bioremediation. Results showed that the application of sequential remediation treatments allowed us to obtain a state of quality in unsaturated soil and groundwater as required by Italian law.

The radius of influence of a combined method of in situ air sparging and soil vapor extraction in the intertidal sediments of Gomso Bay on the west coast of South Korea.

BackgroundIn situ air sparging (IAS) was undertaken at sites in the tidal flats of Mandol and Hajeon, on the west coast of South Korea, to estimate variations in the radius of influence (ROI).ResultsThe Mandol core sample consisted of sand and muddy sand 1.6–3.4 Phi (average 2.3 Phi) and contained water (average 15.10 %). The Hajeon core sample consisted of muddy sand, sandy silt, and muddy sandy gravel 1.31–4.44 Phi (average 3.11 Phi) and contained water (average 19.77 %). These sites differ in their sedimentary and geochemical characteristics. At the Mandol site, no H2S or combustible gas was detected during a 48-h sampling period, except for some volatile organic compounds (0.1–2.0 ppm) at the monitoring well during the initial 30 min. At the soil vapor extraction wells, CO2 and O2 varied by 850 ppm (690–1540 ppm) and 0.5 % (20.4–20.9 %), respectively. At the Hajeon site, CO2 and O2 varied from 580 to 1250 ppm and 20.6 to 20.9 %, respectively, during the 48-h sampling period.ConclusionsAt the Mandol site, an oxygen concentration of 20.6 % was assumed as the effective concentration, and the ROI was estimated to be 128.0 cm. However, at the Hajeon site the ROI was estimated to be 85.7 cm. The smaller effective ROI at the Hajeon site was likely caused by the thin aquifer and thin screens of the sparing well. This estimated ROI show that the remediation effectiveness varies greatly as a heterogeneities and anisotropies in the porous sediments. Besides, injection pressure, flow rate, pulsing or continuous mode, and the range of intrinsic permeability for most important characteristic of sediment (soil) type impacted the ROI. Therefore, the IAS method is more effective at a pervasive air flow sediments such as Mandol, which consists of sand and muddy sand than at a channelized site such as Hajeon.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-016-3026-3) contains supplementary material, which is available to authorized users.

Estimating initial contaminant mass based on fitting mass-depletion functions to contaminant mass discharge data: Testing method efficacy with SVE operations data

The mass of contaminant present at a site, particularly in the source zones, is one of the key parameters for assessing the risk posed by contaminated sites, and for setting and evaluating remediation goals and objectives. This quantity is rarely known and is challenging to estimate accurately. This work investigated the efficacy of fitting mass-depletion functions to temporal contaminant mass discharge (CMD) data as a means of estimating initial mass. Two common mass-depletion functions, exponential and power functions, were applied to historic soil vapor extraction (SVE) CMD data collected from 11 contaminated sites for which the SVE operations are considered to be at or close to essentially complete mass removal. The functions were applied to the entire available data set for each site, as well as to the early-time data (the initial 1/3 of the data available). Additionally, a complete differential-time analysis was conducted. The latter two analyses were conducted to investigate the impact of limited data on method performance, given that the primary mode of application would be to use the method during the early stages of a remediation effort. The estimated initial masses were compared to the total masses removed for the SVE operations. The mass estimates obtained from application to the full data sets were reasonably similar to the measured masses removed for both functions (13 and 15% mean error). The use of the early-time data resulted in a minimally higher variation for the exponential function (17%) but a much higher error (51%) for the power function. These results suggest that the method can produce reasonable estimates of initial mass useful for planning and assessing remediation efforts.

Validity of the Use of the Mass Transfer Parameters Obtained with 1D Column in 3D Systems during Soil Vapor Extraction

AbstractThe efficiency of soil vapor extraction (SVE) depends primarily on mass transfer parameters. The objective of this work was to determine whether mass transfer parameters obtained from calibrating a model against unidirectional column experiments could be used for three-dimensional (3D) applications. A 3D experimental setup was designed and constructed to simulate a decontamination system at the bench scale. A mathematical model simulating multiphase flow and multicomponent transport of contaminants in the subsurface under nonequilibrium transient mass transfer conditions was developed and used. Results showed that the mass transfer parameters obtained from unidirectional column assays were several orders of magnitude greater than those obtained with the 3D trials. Quantitative analyses of the experimental data showed that mass transfer limitations occurred in 3D. Mass transfer coefficients are related to the distribution of air velocity in the 3D reactor. Consequently, unlike the 1D column, mass t...

Theoretical Application of Decision Support System in Petroleum Contaminated Ogoniland in South-Southern Nigeria

Land is an indispensable natural resource made up of soil and groundwater, both of which have many functions for which we depend on, support of agricultural activities, engineering structures, portable water for domestic and industrial use as well as sustenance of flora and fauna in order to maintain favorable ecosystem. Contaminants in land pose a number of threats to public health and the environment; other natural resources; and have detrimental effects on property such as buildings, crops and live stocks. The most effective method of dealing with these contaminants is to cleaning up and returning the sites to beneficial use. The cleanup process involves making a choice from amongst competing remediation methods, where the wrong choice may have disastrous social, economic and environmental impact. This work presents the development of a Decision Support System via thorough literature survey. The Developed DSS was applied to petroleum contaminated site in Ogoniland South-East Nigeria. Finally, Air sparging, phyto-remediation and soil vapour extraction methods were systematically recommended.

The Emperor's Old Clothes: An Inconvenient Truth About Currently Accepted Vapor Intrusion Assessment Methods

The Emperor's Old Clothes: An Inconvenient Truth About Currently Accepted Vapor Intrusion Assessment Methods

A soil-column gas chromatography (SCGC) approach to explore the thermal desorption behavior of hydrocarbons from soils.

A soil-column gas chromatography approach was developed to simulate the mass transfer process of hydrocarbons between gas and soil during thermally enhanced soil vapor extraction (T-SVE). Four kinds of hydrocarbons-methylbenzene, n-hexane, n-decane, and n-tetradecane-were flowed by nitrogen gas. The retention factor k' and the tailing factor T f were calculated to reflect the desorption velocities of fast and slow desorption fractions, respectively. The results clearly indicated two different mechanisms on the thermal desorption behaviors of fast and slow desorption fractions. The desorption velocity of fast desorption fraction was an exponential function of the reciprocal of soil absolute temperature and inversely correlated with hydrocarbon's boiling point, whereas the desorption velocity of slow desorption fraction was an inverse proportional function of soil absolute temperature, and inversely proportional to the log K OW value of the hydrocarbons. The higher activation energy of adsorption was found on loamy soil with higher organic content. The increase of carrier gas flow rate led to a reduction in the apparent activation energy of adsorption of slow desorption fraction, and thus desorption efficiency was significantly enhanced. The obtained results are of practical interest for the design of high-efficiency T-SVE system and may be used to predict the remediation time.

The vapor-phase multi-stage CMD test for characterizing contaminant mass discharge associated with VOC sources in the vadose zone: Application to three sites in different lifecycle stages of SVE operations

Vapor-phase multi-stage contaminant mass discharge (CMD) tests were conducted at three field sites to measure mass discharge associated with contaminant sources located in the vadose zone. The three sites represent the three primary stages of the soil vapor extraction (SVE) operations lifecycle—pre/initial-SVE, mid-lifecycle, and near-closure. A CMD of 32g/d was obtained for a site at which soil vapor SVE has been in operation for approximately 6years, and for which mass removal is currently in the asymptotic stage. The contaminant removal behavior exhibited for the vapor extractions conducted at this site suggests that there is unlikely to be a significant mass of non-vapor-phase contaminant (e.g., DNAPL, sorbed phase) remaining in the advective domains, and that most remaining mass is likely located in poorly accessible domains. Given the conditions for this site, this remaining mass is hypothesized to be associated with the low-permeability (and higher water saturation) region in the vicinity of the saturated zone and capillary fringe. A CMD of 25g/d was obtained for a site wherein SVE has been in operation for several years but concentrations and mass-removal rates are still relatively high. A CMD of 270g/d was obtained for a site for which there were no prior SVE operations. The behavior exhibited for the vapor extractions conducted at this site suggest that non-vapor-phase contaminant mass (e.g., DNAPL) may be present in the advective domains. Hence, the asymptotic conditions observed for this site most likely derive from a combination of rate-limited mass transfer from DNAPL (and sorbed) phases present in the advective domain as well as mass residing in lower-permeability (“non-advective”) regions. The CMD values obtained from the tests were used in conjunction with a recently developed vapor-discharge tool to evaluate the impact of the measured CMDs on groundwater quality.

Using vapor phase tomography to measure the spatial distribution of vapor concentrations and flux for vadose-zone VOC sources

A test was conducted at a chlorinated-solvent contaminated site in Tucson, AZ, to evaluate the effectiveness of vapor-phase tomography (VPT) for characterizing the distribution of volatile organic contaminants (VOC) in the vadose zone. A soil vapor extraction (SVE) system has been in operation at the site since 2007. Vapor concentration and vacuum pressure were measured at four different depths in each of the four monitoring wells surrounding the extraction well. The test provided a 3D characterization of local vapor concentrations under induced-gradient conditions. Permeability data obtained from analysis of borehole logs were used along with pressure and the vapor-concentration data to determine VOC mass flux within the test domain. A region of higher mass flux was identified in the deepest interval of the S–SW section of the domain, indicating the possible location of a zone with greater contaminant mass. These results are consistent with the TCE-concentration distribution obtained from sediment coring conducted at the site. In contrast, the results of a standard soil gas survey did not indicate the presence of a zone with greater contaminant mass. These results indicate that the VPT test provided a robust characterization of VOC concentration and flux distribution at the site.

유류로 오염된 철로지역의 지중정화를 위한 영향반경 산정과 공기주입법/토양증기추출법의 적용성 평가

The objectives of this study were to calculate the radius of influence (ROI) of well for an air-sparging (AS)/soil vapor extraction (SVE) system and to evaluate the applicability of the system applied for the remediation of the petroleum contaminated rail site. For air permeability test, three monitoring wells were installed at a location of 1.3 m, 2.3 m, 3.0 m from the extraction well. And the pressure of each monitoring well was measured by extracting air from the extraction well with the pressure and flow of (�)2,600 mmH2O and 1.58 m 3 /min. The ROI for an extraction well was calculated as 4.31 m. Air was injected into the injection well with the pressure and flow of 3,500 mmH2O and 0.6 m 3 /min to estimate the radius of influence for oxygen transfer. Oxygen concentrations of air from three monitoring wells were measured. The ROI of an injection well for oxygen transfer was calculated as 3.46 m. The 28 extraction wells and 19 injection wells were installed according to the ROI calculated. The AS/SVE system was operated eight hours a day for five months. The rail site was contaminated with the petroleum and concentrations of benzene, toluene, and xylene were over the 'Worrisome Standard' of the 'Soil Environment Conservation Act'. The contaminated area was estimated as 732 m 2 and contaminants were dispersed up to (�)3 m from the ground. During the operation period, soil samples were collected from 5 points and analyzed periodically. With the AS/SVE system operation, concentrations of benzene, toluene, and xylene were decreased from 7.5 mg/kg to 2.0 mg/kg, from 32.0 mg/kg to 23.0 mg/kg, from 35.5 mg/kg to 23.0 mg/kg, respectively. The combined AS/SVE system applied to the rail site contaminated with volatile organic compounds (VOCs) exhibited a high applicability. But the concentration of contaminants in soil were fluctuated due to the heterogeneous of soil condition. Also the effect of the remediation mechanisms was not clearly identified.

Characterization and Source History Modeling Using Low-k Zone Profiles at Two Source Areas

Like tree rings, high-resolution soil sampling of low-permeability (low-k) zones can be used to evaluate the style of source history at contaminated sites (i.e., historical pattern of concentration and composition vs. time since releases occurred at the interface with the low-k zone). This is valuable for the development of conceptual site model (CSM) and can serve as an important line of evidence supporting monitored natural attenuation (MNA) as a long-term remedy. Source histories were successfully reconstructed at two sites at Naval Air Station Jacksonville using a simple one-dimensional (1D) model. The plume arrival time and historical composition were reconstructed from the time initial releases that were suspected to occur decades earlier. At the first site (Building 106), the source reconstructions showed relatively constant source concentrations, but significant attenuation over time in the downgradient plume in the transmissive zone, suggesting MNA may not be an appropriate remedy if source control is a requirement, but attenuation processes are clearly helping to maintain plume stability and reduce risk. At the second site (Building 780), source concentrations in the transmissive zone showed an approximately a one order of magnitude over time, but apparently less attenuation in the downgradient plume. The source reconstruction method appeared to reflect site remediation efforts (excavation, soil vapor extraction) implemented in the 1990s. Finally, a detailed analysis using molecular biological tools, carbon isotopes, and by-products suggests that most degradation activity is associated with high-k zones but not with low-k zones at these source areas. Overall, the source reconstruction methodology provided insight into historical concentration trends not obtainable otherwise given the limited long-term monitoring data.

군기지 오염토양의 정화 방법에 대한 연구

Handling of the large quantity of oil, generation of heavy metals at the military blasting range and outworn facilities could cause the environmental accidents. Pollution levels of the former five U.S military bases located in Uijeongbu, Gyeonggi-do were measured. Soil contamination by TPH (Total Petroleum Hydrocarbons), BTEX (Benzene, Toluene, Ethylbenzene, Xylene), and heavy metals and groundwater contamination were detected. In order to purify contaminated soil, a variety of technologies including soil vapor extraction, slurping, landfarming and soil washing were applied. Contaminated soils of five target bases were purified and the results were suitable for the legal standards.

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.

Degradation of off-gas toluene in continuous pyrite Fenton system

Degradation of off-gas toluene from a toluene reservoir and a soil vapor extraction (SVE) process was investigated in a continuous pyrite Fenton system. The removal of off-gas toluene from the toluene reservoir was >95% by 8h in the pyrite Fenton system, while it was ∼97% by 3h in classic Fenton system and then rapidly decreased to initial level by 8h. Continuous consumption of low Fe(II) concentration dissolved from pyrite surface (0.05–0.11mM) was observed in the pyrite Fenton system, which can lead to the effective and successful removal of the gas-phase toluene due to stable production of OH radical (OH). Inhibitor and spectroscopic test results showed that OH was a dominant radical that degraded gas-phase toluene during the reaction. Off-gas toluene from the SVE process was removed by 96% in the pyrite Fenton system, and remnant toluene from rebounding effect was treated by 99%. Main transformation products from toluene oxidation were benzoic acid (31.4%) and CO2 (38.8%) at 4h, while traces of benzyl alcohol (1.3%) and benzaldehyde (0.7%) were observed. Maximum operation time of continuous pyrite Fenton system was estimated to be 56–61d and its optimal operation time achieving emission standard was 28.9d.

Multiple Linear Regression and Artificial Neural Networks to Predict Time and Efficiency of Soil Vapor Extraction

The prediction of the time and the efficiency of the remediation of contaminated soils using soil vapor extraction remain a difficult challenge to the scientific community and consultants. This work reports the development of multiple linear regression and artificial neural network models to predict the remediation time and efficiency of soil vapor extractions performed in soils contaminated separately with benzene, toluene, ethylbenzene, xylene, trichloroethylene, and perchloroethylene. The results demonstrated that the artificial neural network approach presents better performances when compared with multiple linear regression models. The artificial neural network model allowed an accurate prediction of remediation time and efficiency based on only soil and pollutants characteristics, and consequently allowing a simple and quick previous evaluation of the process viability.

Temperature as a Tool to Evaluate Aerobic Biodegradation in Hydrocarbon Contaminated Soil

AbstractThis study evaluates the theory, and some practical aspects of using temperature measurements to assess aerobic biodegradation in hydrocarbon contaminated soil. The method provides an easily applicable alternative for quantifying the rate of biodegradation and/or evaluating the performance of in situ remediation systems. The method involves two nonintrusive procedures for measuring vertical temperature profiles down existing monitoring wells; one using a thermistor on a cable for one‐time measurements and the other using compact temperature data loggers deployed for 3‐month to 1‐year period. These vertical temperature profile measurements are used to identify the depth and lateral extent of biodegradation as well as to monitor seasonal temperature changes throughout the year. The basic theory for using temperature measurements to estimate the minimum rate of biodegradation will be developed, and used to evaluate field measurements from sites in California where biodegradation of spilled petroleum hydrocarbons is due to natural processes. Following, temperature data will be used to evaluate the relative rates of biodegradation due to natural processes and soil vapor extraction (SVE) at a former refinery site in the North‐Central United States. The results from this study show that the temperature method can be a simple, cost effective tool for assessing biodegradation in the soil, and optimizing remediation systems at a wide variety of hydrocarbon spill sites.

Estimating the Impact of Vadose Zone Sources on Groundwater to Support Performance Assessment of Soil Vapor Extraction

Soil vapor extraction (SVE) is a prevalent remediation remedy for volatile organic compound (VOC) contaminants in the vadose zone. To support selection of an appropriate condition at which SVE may be terminated for site closure or for transition to another remedy, an evaluation is needed to determine whether vadose zone VOC contamination has been diminished sufficiently to keep groundwater concentrations below threshold values. A conceptual model for this evaluation was developed for VOC fate and transport from a vadose zone source to groundwater when vapor-phase diffusive transport is the dominant transport process. A numerical analysis showed that, for these conditions, the groundwater concentration is controlled by a limited set of parameters, including site-specific dimensions, vadose zone properties, and source characteristics. On the basis of these findings, a procedure was then developed for estimating groundwater concentrations using results from the three-dimensional multiphase transport simulations for a matrix of parameter value combinations and covering a range of potential site conditions. Interpolation and scaling processes are applied to estimate groundwater concentrations at compliance (monitoring) wells for specific site conditions of interest using the data from the simulation results. The interpolation and scaling methodology using these simulation results provides a far less computationally intensive alternative to site-specific three-dimensional multiphase site modeling, while still allowing for parameter sensitivity and uncertainty analyses. With iterative application, the approach can be used to consider the effect of a diminishing vadose zone source over time on future groundwater concentrations. This novel approach and related simulation results have been incorporated into a user-friendly Microsoft® Excel®-based spreadsheet tool entitled SVEET (Soil Vapor Extraction Endstate Tool), which has been made available to the public.

Recent Proportionate Treatment Methods for Crude Oil Contamination Evaluation of the Tehran Refinery Site Soil

Background: Crude oil contamination is one of the major concerns for the human health and environment. Objectives: The aim of this study was to find the optimal biological methods to remove crude oil contaminants, especially polycyclic aromatic hydrocarbons (PAHs), from the soil of the lands around the Tehran Refinery site. Materials and Methods: In this study, soil sampling was conducted from five points of the west side of the refinery area through a zigzag sampling method. The soil characteristics were identified in the soil laboratory where PAH contamination was also examined. Advantages and disadvantages of biological, physical, and thermochemical methods of soil treatment were retrieved from the literature. The biological methods were confirmed as the optimum treatment methods which had been more extensively evaluated according to the soil texture, remediated compounds, cost, and timing. Results: The soil was largely composed of silt and clay (silt:41 - 42%, clay: 40 - 43%, sand: 15 - 18%). The average moisture content of the saturated soil was 12.96%,; average electricity conductivity was 18.64 DSm-1; average pH of the paste was 8.36; and average percentage of organic carbon was 0.19%. Result of the laboratory analysis reported the average content of total nitrogen as 0.026%, phosphorus as 14.3 mg/kg-1 and potassium content as 3.4 mg/kg-1. Content of the crude oil derivatives was less than 0.5 %. Conclusions: An efficient method for treating the current low level soil contamination around the Tehran Refinery site is phytoremediation, a cost effective method that helps to create beautiful landscapes around the refinery site. Soil vapor extraction (SVE) should be used in large PAH levels (higher than the current rate). Soil washing is the most time-effective method, which is suitable for cases of emergency soil contamination with petroleum.

General well function for soil vapor extraction

This paper develops a well function applicable to extraction of groundwater or soil vapor from a well under the most common field test conditions. The general well function (Perina and Lee, 2006) [12] is adapted to soil vapor extraction and constant head boundary at the top. For groundwater flow, the general well function now applies to an extraction well of finite diameter with uniform drawdown along the screen, finite-thickness skin, and partially penetrating an unconfined, confined, and leaky aquifer, or an aquifer underneath a reservoir. With a change of arguments, the model applies to soil vapor extraction from a vadose zone with no cover or with leaky cover at the ground surface. The extraction well can operate in specified drawdown (pressure for soil vapor) or specified flowrate mode. Frictional well loss is computed as flow-only dependent component of the drawdown inside the extraction well. In general case, the calculated flow distribution is not proportional to screen length for a multiscreen well.

Toluene Removal from Sandy Soils via In Situ Technologies with an Emphasis on Factors Influencing Soil Vapor Extraction

The integration of bioventing (BV) and soil vapor extraction (SVE) appears to be an effective combination method for soil decontamination. This paper serves two main purposes: it evaluates the effects of soil water content (SWC) and air flow rate on SVE and it investigates the transition regime between BV and SVE for toluene removal from sandy soils. 96 hours after air injection, more than 97% removal efficiency was achieved in all five experiments (carried out for SVE) including 5, 10, and 15% for SWC and 250 and 500 mL/min for air flow rate on SVE. The highest removal efficiency (>99.5%) of toluene was obtained by the combination of BV and SVE (AIBV: Air Injection Bioventing) after 96 h of air injection at a constant flow rate of 250 mL/min. It was found that AIBV has the highest efficiency for toluene removal from sandy soils and can remediate the vadose zone effectively to meet the soil guideline values for protection of groundwater.