BTEX Remediation under Challenging Site Conditions Using In-Situ Ozone Injection and Soil Vapor Extraction Technologies: A Case Study

Remediation was successfully completed in a petroleum-contaminated site using ozone sparging combined with soil vapor extraction technologies. The site contained high levels of BTEX contamination in dissolved, adsorbed, and free phases. The presence of fine-grained soil, smear zone contamination, and shallow groundwater posed challenging site conditions for this remediation. Active remediation was performed for approximately 18 months followed by one year of post-remediation monitoring. Application of soil vapor extraction technology effectively removed free phase contamination. Biodegradation during active and post-remediation periods also played a role in bringing down the contaminant levels and achieving closure of the release. The cost of this remediation approach was estimated to be $2.04 per cubic foot ($72.08 per cubic meter) and found to be cost-effective. Timely completion of the project prevented the spreading of contaminants towards the down-gradient residential and school properties.     

SoilCAM: soil contamination: advanced integrated characterisation and time-lapse monitoring

The SoilCAM project is aimed at improving current methods for monitoring contaminant distribution and biodegradation in the subsurface. Currently proven methods, based on invasive sampling of soil, soil water and gaseous phase, are unable to provide sufficiently accurate data with high enough resolution, resulting in inability to assess bioremediation progress and quantification of the processes involved in such bioremediation at field sites. Consequently, present assessment strategies to decide on optimal remediation approach, including design of monitoring systems, and evaluation of degradation progress, are severely flawed by uncertainty. Geophysical time-lapse measurements in combination with novel ground truthing methods give the possibility to determine contamination levels and their spatial spreading in a heterogeneous environment. Geophysical methods of data acquisition alone are presently unable to provide absolute levels of biodegradable contamination concentrations. We aim to test and develop fundamental constitutive relations between soil physical and degradation activity parameters and geophysically measurable parameters. Despite current improvements, there is a strong need to test these theories in practical field situations. The SoilCAM project is dedicated to improving both site contamination assessment and the monitoring of bioremediation processes, and changes in soil environmental conditions. We suggest combining improved conventional soil monitoring techniques with state-of-the-art geophysical approaches and modelling. Two European sites with mobile contaminants in a highly permeable subsurface are central in the project. Focus on practical field situations and strong communication with stake-holders and SMEs will ensure high relevance for society. This article is a research project funded under FP7 .     

Defining TCE Plume Source Areas Using the Membrane Interface Probe (MIP)

A variety of traditional characterization methods, such as soil gas surveys, soil and groundwater sampling, and fixed laboratory analysis, is commonly used to define the magnitude and extent of soil and groundwater contamination in volatile organic compound source areas. One significant limitation of these methods is that they require multi-media sample collection to define the full unsaturated and saturated vertical profile in any given location. In addition, attaining higher resolution by increasing sample frequency increases costs substantially. A relatively new technology, the Membrane Interface Probe (MIP), was used to define trichloroethene plume source areas at F.E. Warren Air Force Base in Cheyenne, Wyoming, and at a confidential security products manufacturer in Tennessee. The MIP offered significant advantages over traditional drilling and direct-push methods and yielded data critical to a fuller understanding of subsurface conditions. The near-continuous MIP profile minimized the number of soil and groundwater samples required to fully delineate the extent of the plume-head source areas. In addition, the MIP is also able to collect data in the vadose and saturated zones, providing detailed vertical contaminant profiling information and geologic conditions based on soil conductivity that aided in the development of the site conceptual model. The MIP was not without its disadvantages; principal among these the relatively high detection limit (approximately 100 ppb in soil and groundwater), making the method useful for source characterization but limited for delineating lower levels of contamination. The data obtained from the MIP are considered screening-level data and need to be supplemented with analytical soil or groundwater data to fully support risk or remediation decisions. In summary, the vertical profiling obtained using the MIP aided in the interpretation of the complex relationship between the presence of gross contamination in soil and groundwater and the geologic conditions controlling contaminant distribution.     

Methodology for using contaminated soil leachability testing to determine soil cleanup levels at contaminated petroleum underground storage tank (UST) sites

The costs of environmental remediation at leaking petroleum underground storage tank (UST) sites are influenced significantly by soil cleanup levels. The use of conservative generic soil cleanup levels may be inappropriate at some sites contaminated by leaking petroleum USTs. At many contaminated sites, a primary objective of site remediation is long‐term protection of water resources (e.g., groundwater) from pollution. Leaching of pollutants from residual soil contamination to groundwater is a primary consideration in establishing site‐specific soil cleanup levels at fuel‐contaminated sites. The use of laboratory soil leachability testing methods may be useful in objectively evaluating the leaching potential of contaminants from residual soil contamination and estimating potential groundwater impacts. Developing soil cleanup levels that are protective of water resources must include a technically sound integration of site‐specific soil leachability data and contaminant attenuation factors. Evaluation of the leaching potentials of soil contaminants may also provide essential supplementary information for other site characterization methods that may be used to evaluate risks to human health. Contaminant leachability testing of soils may provide a cost‐effective and technically based method for determining soil cleanup levels that are protective of groundwater resources at contaminated petroleum UST sites.     

Uncertainty-based dynamic multimedia human health risk assessment for polycyclic aromatic hydrocarbons (PAHs) in a land oil exploitation area

With the increasing development of the petrochemical industry and the growing demand for oil, polycyclic aromatic hydrocarbons (PAHs) pollutions in the environment, especially in petroleum exploitation areas, are caused by the discharge of waste from the petroleum extraction process into an environmental system. This study aims to develop a new health risk assessment approach based on interval dynamic multimedia fugacity (IDMF) model and uncertainty analysis that could analyze the human exposure risk level for PAH contamination. The developed IDM health risk assessment (IDMHRA) approach is applied to assess previous, current, and future risks at a case study site in Daqing, Heilongjiang, China, from 1985 to 2020 for model validation. The human health risk assessment results show that 11 PAHs (NAP, ANT, FLA, PYR, BaA, CHR, BbF, BkF, BaP, IPY, and DBA) in the study site require further remediation efforts in terms of their unacceptable non-carcinogenic and carcinogenic risk. The results of risk source analysis reveal that soil media is the main risk pathway as compared with other exposure pathways. It can be seen that remediation process for soil contamination in the study site is urgently demanded. The assessment results demonstrate that the developed IDMHRA approach provides an effective tool for decision-makers and environmental managers to make remediation decisions in contaminated sites.     

Utilization of Multi-Tasking Non-Edible Plants for Phytoremediation and Bioenergy Source-A Review

Heavy metal contamination of land and freshwater resources is a serious concern worldwide. It adversely affects the health of animals, plants and humans. Therefore, remediation of toxic heavy metals must be highly considered. Unlike other techniques, phytoremediation is a holistic technology and can be used in large scale for soil remediation as it is costless, novel, environmentally-safe and solar-driven technology. Utilization of non-edible plants in phytoremediation is an ingenious technique as they are used to generate new bioenergy resources along with the remediation of contaminated soils. Some nonfood bioenergy crops such as Salix species, Miscanthus species, Populus species, Eucalyptus species, and Ricinus communis exhibit high capability to accumulate various metals and to grow in contaminated lands. However, there are still sustainable challenges facing coupling phytoremediation with bioenergy production from polluted lands. Therefore, there has long been a need for developing different strategies to resolve such challenges. In this article review, we will discuss the phytoremediation mechanism, the technique of phytoremediation coupling with bioenergy production, sustainable problems facing linking phytoremediation with energy production as well as possible strategies to enhance the efficiency of bioenergy plants for soil decontamination by improving their characteristics such as metal uptake, transport, accumulation, and tolerance.     

Significance of organic chemical adsorption in soil and groundwater remediation

Adsorption of organic chemicals onto soils is affected by a number of factors related to the soil properties, chemical type, and environment. Organic chemical adsorption has significant impact on soil and groundwater cleanup criteria and on the time required for remediation using in situ vapor extraction, bioventing, and biosparging methods. Phase equilibrium relationships will permit specifying the contaminant concentration levels in soil that would prevent groundwater contamination beyond the limits prescribed by provincial regulations. Computer programs that neglect the adsorption effects will significantly underestimate the time required for soil remediation by vapor extraction.     

LCA of Ex-Situ Bioremediation of Diesel-Contaminated Soil (11 pp)

- DOI: http://dx.doi.org/10.1065/lca2004.09.180.12 Goal and Scope Primary and secondary environmental impacts associated with bioremediation of diesel-contaminated sites were assessed using a retrospective life cycle assessment (LCA) as a function of the duration of treatment and the achievement of regulatory criteria. The case study was the remediation with biopiles of 8000 m3 of subsurface soil impacted with an average of 6145 mg of diesel fuel/kg soil during a two-year period. Methods Two scenarios were compared; the construction of a single-use treatment facility on site or the use of a permanent treatment center that can accept 25000 m3 soil/year. Moreover, since bioremediation is never 100% efficient, different efficiency scenarios, including the transportation of partially treated soil to landfill were analyzed. The primary impact of residual soil contamination was determined by developing a specific characterization factor (ecotoxicity and human toxicity categories in the EDIP method) based on the toxic components of diesel. Secondary impacts were assessed with an LCA software. Results and Discussion One major observation was the fact that the soil itself is responsible for an important fraction of the system's total impact, suggesting that it is beneficial to reach the highest level of remediation. The reutilization of the treatment facility is also an important issue in the overall environmental performance of the system. In the case of a single-use treatment center, the analysis showed that site preparation and site closure were the major contributing stages to the overall impact, mainly due to the asphalt paving and landfilling processes. Results indicated that off-site transport and the biotreatment process did not contribute notably to the level of environmental impact. The use of a permanent treatment center is preferred since it allows a significant decrease of the secondary impact. However, when soil had to be transported for a distance greater than 200 km from the site, global impacts increased significantly. Conclusion – Results from this study allowed identifying several process optimizations in order to improve the environmental performance of the biopile technology including: the achievement of low level of residual contaminants, the minimization of asphalt or the use of a permanent treatment center. Recommendation and Outlook LCA was found to be an efficient tool to manage contaminated soil in a sustainable way. However, because of the major contribution of residual soil contamination, additional spatial and temporal data should be collected and integrated in the substance characterization models.     

A decision framework for selecting remediation technologies at hydrocarbon‐contaminated sites

A variety of remediation technologies are available to address hydrocarbon contamination, including free product recovery, soil venting, air sparging, groundwater recovery and treatment, and in situ bioremediation. These technologies address hydrocarbon contamination distributed between free, adsorbed, and dissolved phases in both the vadose and saturated zones. Selection of appropriate technologies is dependent on a number of factors, including contaminants, site‐specific characteristics, clean‐up goals, technology feasibility, cost, and regulatory and time requirements. This article describes a decision framework for selecting appropriate remediation technologies at hydrocarbon‐contaminated sites in a structured and tiered manner. Decision modules include (1) site characterization and product recovery; (2) vadosezone treatment: soil venting, bioremediation, and excavation; (3) saturated zone treatment: sparging, bioremediation, groundwater recovery, and excavation; and (4) groundwater treatment: carbon, air stripping, advanced oxidation, and bioreactors. Selection criteria for treatment technologies that address vadose‐ and saturated‐zone soils, as well as recovered groundwater, are described. The decision framework provides a systematic process to formulate solutions to complex problems and documents the rationale for selecting remediation systems designed to achieve closure at hydrocarbon‐contaminated sites.     

Microbial characterization of a JP-4 fuel-contaminated site using a combined lipid biomarker/polymerase chain reaction--denaturing gradient gel electrophoresis (PCR-DGGE)-based approach

The impact of pollution on soil microbial communities and subsequent bioremediation can be measured quantitatively in situ using direct, non-culture- dependent techniques. Such techniques have advantages over culture-based methods, which often account for less than 1% of the extant microbial community. In 1988, a JP-4 fuel spill contaminated the glacio-fluvial aquifer at Wurtsmith Air Force Base, Michigan, USA. In this study, lipid biomarker characterization of the bacterial and eukaryotic communities was combined with polymerase chain reaction– denaturing gradient gel electrophoresis (PCR–DGGE) analysis of the eubacterial community to evaluate correlation between contaminant (JP-4 fuel) concentration and community structure shifts. Vadose, capillary fringe and saturated zone samples were taken from cores within and up- and down-gradient from the contaminant plume. Lipid biomarker analysis indicated that samples from within the plume contained increased biomass, with large proportions of typically Gram-negative bacteria. Outside the plume, lipid profiles indicated low-biomass microbial communities compared with those within the initial spill site. 16S rDNA sequences derived from DGGE profiles from within the initial spill site suggested dominance of the eubacterial community by a limited number of phylogenetically diverse organisms. Used in tandem with pollutant quantification, these molecular techniques should facilitate significant improvements over current assessment procedures for the determination of remediation end-points.     

污染场地土壤生态风险评估研究进展

随着我国快速城市化以及产业结构的调整,遗留下了大量的污染场地,发展和实施污染场地土壤生态风险评估是进行大规模污染场地修复行动的必要条件。本文围绕污染场地土壤生态风险评估的科学原理、框架构建及技术方法等方面的关键问题: 1)评估框架的场地实际针对性;2)概念模型的不确定性;3)土壤复合污染毒性机制;4)评估终点筛选;5)评估方法和框架构建等展开讨论,指出土壤复合污染的制毒机制,即污染物生物有效性和联合效应是污染场地土壤生态风险评估的关键科学问题。耦合美国环保局四步法和欧盟层级法的“证据-权重法”评估框架适用于野外复杂环境条件下的土壤污染生态风险评估。建议今后重点开展以下5个方面的工作: 1)污染场地土壤生态风险评估技术框架与风险管控技术框架之间的联合;2)概念模型研究;3)基于过程的场地土壤污染物反应运移模型研究;4)场地土壤复合污染生态毒理学机制研究;5)生态系统高水平生态风险评估终点研究。旨在为形成我国本土污染场地土壤生态风险评估技术指南提供理论基础和构架。     

2020污染土壤的生物修复专刊序言

生物修复技术,作为可持续发展的重要方向,因其环境友好、高效且无二次污染并能从根本上解决土壤污染问题而受到关注,已经在土壤污染治理中得到了广泛的应用。为了梳理和凝练生物修复技术的发展状况,本专刊收录了该研究领域的16篇论文,分别从植物修复、微生物修复、联合修复、重金属吸收积累的相关分子机制、资源化再利用等方面,详细阐述生物修复技术的发展动态,展望未来的发展趋势,为促进生物修复技术的发展提供参考。     

Assessing the applicability of phytoremediation of soils with mixed organic and heavy metal contaminants

Soil pollution is a major environmental problem and many contaminated sites are tainted with a mixture of organic and heavy metal contaminants. Compared to other remedial strategies, phytoremediation is a low cost, environmentally-friendly, sustainable means of remediating the contamination. This review first provides an overview of phytoremediation studies where the soil is contaminated with just one type of pollutant (heavy metals or organics) and then critically evaluates the applicability of phytotechnologies for the remediation of contaminated sites where the soil is polluted by a mixture of organic and heavy metal contaminants. In most of the earlier research studies, mixed contamination was held to be detrimental to plant growth, yet there were instances where plant growth was more successful in soil with mixed contamination than in the soil with only individual contaminants. New effective phytoremediation strategies can be designed for remediation of co-contaminated sites using: (a) plants species especially adapted to grow in the contaminated site (hyperacumulators, local plants, transgenic plants); (b) endophytic bacteria to enhance the degradation in the rizhosphere; (c) soil amendments to increase the contaminants bioavailability [chelating agents and (bio)surfactants]; (d) soil fertilization to enhance the plant growth and microbial activity in the soil; and (e) coupling phytoremediation with other remediation technologies such as electrokinetic remediation or enhanced biodegradation in the rhizosphere.     

Physicochemical and Mineralogical Characterization of Uranium-Contaminated Soils

Physicochemical and mineralogical properties of the contaminants should be taken into account to decide a remediation strategy for a given radionuclide because development and optimization of soil remedial technologies are based on physicochemical and mineralogical separation techniques. The objectives of this study are to (1) demonstrate how a priori physicochemical and mineralogical characterization of soil contaminants can direct the development of remediation strategies and their performance evaluation for soil treatments and (2) understand the nature of uranium contamination and its association with the soil matrix by chemical extractions. This study examined two U-contaminated sites (K311 and K1300) at the DOE K-25 site, presently located at East Tennessee Technology Park, Oak Ridge, Tennessee. Uranium concentrations of the soils ranged from 1499 to 216,413 Bq kg^?1 at both sites. Scanning electron microscopy with backscattered electron spectroscopy and X-ray diffraction analysis showed that the dominant U phases are U oxides (schoepite), U-Ca-silicate (uranophane) and U silicate (coffinite) from the K311 site soils, whereas U-Ca-oxide and U-Ca-phosphate dominate in the K1300 site soils. Sodium carbonate/bicarbonate leaching was effective on the K1300 site soils, whereas citric acid leaching is effective on the K311 site soils. Sequential leaching showed that the majority of the uranium in the contaminated soils was contained in carbonate minerals (45%) and iron oxides (40%). Conventional leaching showed that citric acid treatment was most effective on the K311 site soils, whereas the sodium carbonate/ bicarbonate treatment was most effective on the K1300 site soils.     

Selection of a remediation scenario for a diesel-contaminated site using LCA

Goal and Scope A comparison of in situ and ex situ treatment scenarios for a diesel-contaminated site was performed using an evolutive LCA. Treatment time along with primary (residual contamination left in soil or groundwater after treatment) and secondary (impacts due to remediation) environmental impacts were considered. The site under study had a light Non Aqueous Phase Liquid (LNAPL) thickness of up to 1 m, a diesel soil concentration of 10,500 mg/kg and a residual contamination in groundwater. Methods Four treatment scenarios to remove LNAPL and to treat soil and groundwater were compared: 1) pump and treat 2) bioslurping, bioventing and biosparging 3) bioslurping, bioventing and chemical oxidation and 4) ex situ treatment using biopiles. The technologies’ design was performed using simulation tools and analytical equations. The LCA was evaluated for each year of treatment. Environmental impacts were assessed using the U.S. EPA Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) method. Results and Discussion The biological in situ scenario (2) showed the least primary and secondary impacts but its treatment time was more than 4 times longer than that obtained for the ex situ scenario (4). The ex situ scenario showed the best treatment time but its secondary impacts were significantly higher than those found for the biological in situ scenario due to the pavement of the treatment area. The combined biological and chemical in situ scenario (3) was the worst in terms of secondary impacts while the pump and treat scenario (1) was the worst in terms of primary impacts. Two scenarios were selected: one based upon low environmental impacts and the other on the fastest treatment time. Conclusions Even without excavation, an in situ treatment can generate more secondary impacts than an ex situ treatment. Low environmental impact scenarios require time while rapid treatment scenarios generate high environmental impacts. The selection of the best remediation scenario will depend on the site owner’s priority. Recommendations Better characterization factors for aggregated substances are required. This paper is openly accessible!     

A new program for biomonitoring status and trends in the environment

Environmental contaminants threaten the biological integrity of aquatic and semi-aquatic communities both inside and outside of U.S. National Wildlife Refuges (Refuges). The U.S. Fish and Wildlife Service (FWS) and the U.S. National Biological Survey are developing a new biomonitoring program, the Biomonitoring of Environmental Status and Trends (BEST) Program. The BEST Program is being designed to respond to the effects of contemporary environmental contaminant problems associated with fish and wildlife and their habitats. When fully operational, BEST will evaluate the effects of contaminants on fish and wildlife resources; identify and prioritize national, regional, and local contaminant issues for decision makers; monitor national trends of the presence and effects of contaminants; and provide baseline information to support various contaminant investigation activities. The BEST Program will use an integrated network to evaluate contaminant impacts at the tissue, organism, population, community, and ecosystem levels. The sampling approach will be designed around two major components, trust resources on FWS lands (primarily Refuges) and trust species and their habitats outside of FWS lands. The BEST Program is adopting bioassessment techniques from four broad categories including ecological surveys, biomarkers, bioassays and toxicity tests, and residue analysis. Pilot and demonstration projects will be conducted through fiscal year 1997.     

MINOTAURUS: microorganism and enzyme immobilization: novel techniques and approaches for upgraded remediation of underground-, wastewater and soil

The European project MINOTAURUS aims to deliver innovative bio-processes to eliminate emerging and classic organic pollutants. These bio-processes are all based on the concept of immobilization of biocatalysts (microorganisms and enzymes) and encompass bioaugmentation, enzyme technology, rhizoremediation with halophytes, and a bioelectrochemical remediation process. The immobilization-based technologies are applied to engineered ex situ and natural systems in situ for the bioremediation of groundwater, wastewater and soil. The selection and application of modern physico-chemical, biological and ecotoxicological monitoring tools combined with a rational understanding of engineering, enzymology and microbial physiology is a pertinent approach to open the black-box of the selected technologies. Reliable process-monitoring constitutes the basis for developing and refining biodegradation kinetics models, which in turn will improve the predictability of performances to be achieved with our technologies. A key strength of MINOTAURUS is the possibility of direct implementation of our technologies at five European reference sites that are confronted with pollutants (two technologies will be tested on-site starting from the first year). We will deliver not only a set of tools, techniques, and processes, which will enhance the ability of our communities to respond to the challenges of organic pollutants but also frameworks for structuring and making evidence-based decisions for the most sustainable and appropriate bioremediation measures. The MINOTAURUS consortium includes fifteen partners from eight European countries. Eight research & education institutions, five SMEs covering the whole chain of our bioremediation approaches (production, and monitoring of biocatalysts, bioremediation and engineering), one large end-user operating wastewater treatment plants and one environmental agency work together with the support of an advisory board mainly consisting of environmental decision-makers.     

Social acceptability of phytoremediation: The role of risk and values

A former gas production site that was converted to a public park was chosen as the research location for the present study. Some of the contaminants at the site have been remediated; however, much of the soil is still contaminated with polycyclic aromatic hydrocarbons (PAHs). PAHs are toxic pollutants that have been shown to have numerous negative health effects. The primary form of remediation at the site has been capping, which is usually considered a temporary remediation strategy since it does not remove contaminants from the site but simply covers them, and this requires repeated re-capping efforts. Endophyte-assisted phytoremediation using willow shrubs is an alternative remediation strategy that could improve soil quality and permanently reduce contaminant levels in the soil. The goal of the present study was to explore the social acceptability of utilizing phytoremediation strategies. Surveys were used to explore public perceptions of the park and of using phytoremediation to clean up existing contamination. Results indicated a high level of social acceptability of phytoremediation at the park. Additionally, ecocentrism was shown to be a significant predictor of phytoremediation acceptability. Risk and anthropocentrism were not significant predictors of acceptability. Results suggest that messages intended to encourage the use and acceptability of phytoremediation should focus on the environmental benefits of phytoremediation.     

土壤复合污染的联合修复技术研究进展

复合污染是土壤污染的主要存在形式,其中重金属、有机污染物等是主要的污染源。例如,共存于土壤中铅和镉会发生交互作用,从而增强了镉的迁移能力。此前单一的物理、化学、生物等修复手段对复合污染的修复效果并不明显。联合修复技术的使用可以在一定程度上克服使用单一的修复手段存在的缺点,提高修复效率、降低修复成本。最近有研究表明,综合利用化学氧化和超声波方法可以在很短的时间内将土壤中的甲苯和二甲苯完全氧化为CO和CO2。介绍了综合利用物理、化学、生物等方法对土壤复合污染修复的进展,并对研究中需要注意的问题及未来的发展趋势说明。     

Nitrogen Cycling and Nitric Oxide Emissions in Oil-Impacted Prairie Soils

A remote site in the Tallgrass Prairie Preserve of Oklahoma (The Nature Conservancy) was contaminated with crude oil from a pipeline break and is being bioremediated using landfarming techniques. Landfarming is designed to stimulate microbial-based catabolism of petroleum through combined dilution/mixing and fertilization-based effects. To evaluate nitrogen-based effects during remediation, the site was sectioned and treated with urea, ammonium sulfate, or ammonium nitrate. Samples were obtained from prairie soil without chemical nitrogen addition and with or without hydrocarbon contamination. Nitrogen cycling dynamics were followed by measuring ammonium, nitrite, nitrate, and volatile nitric oxide (NO_x) levels. Nitrifying and denitrifying bacterial numbers were estimated and compared to soil oxygen, carbon dioxide, and methane levels as well as to overall total petroleum hydrocarbon (TPH) reduction. For a prairie ecosystem of this type, a high level of fertilization, particularly with nitrogen, can have ecological effects almost as profound as the petroleum contamination itself. Fertilization of the oil-contaminated soil with the reduced and/or oxidized forms of nitrogen quickly resulted in elevated steady-state levels of both ammonium and nitrate, and exceptionally high levels of NO_x released from soil. Although nitrogen fertilization increased microbial nitrogen metabolism and nitrogen cycling, it had minimal effects on the overall remediation efficiency.