ABSTRACT Vapor intrusion (VI) investigations involve the performance of environmental assessments for the potential presence of vapor‐forming chemicals in groundwater, soil, exterior and interior (sub‐slab) soil vapor, and indoor air. VI‐decision‐making is generally guided by simple comparisons of detected concentrations to media‐specific screening levels. Such investigations are often conducted in an iterative manner, wherein VI studies may proceed from groundwater to soil vapor to indoor air, depending on data reduction outcomes. This study considers seven “problematic” compounds that can often confound VI investigations. For these compounds, screening level exceedances may not necessarily be reflective of a complete VI pathway. The rationale varies, with two compounds (1,3‐butadiene and acrolein) sometimes reported in soil vapor potentially due to sampling and analytical false positives, vinyl chloride removed from shallow soil vapor via aerobic biodegradation, carbon tetrachloride present in indoor air due to outdoor sources, and three compounds (chloroform, 1,4‐dichlorobenzene, and 1,2‐dichloroethane) potentially present in indoor air due to indoor air emission sources. Accordingly, strategies and considerations are provided for VI practitioners to understand and address when these compounds are reported in VI studies.
ABSTRACT Per‐ and polyfluoroalkyl substances (PFAS), due to their pervasiveness, mobility, and recalcitrance in natural environments, pose challenges at a time when current remediation technologies are often ineffective in mitigating their environmental risks. A full‐scale colloidal activated carbon (CAC) barrier was implemented at a contaminated site with levels of PFAS over 100,000 ng/L to evaluate the technology's effectiveness in limiting PFAS migration within a natural groundwater system. A 70 m long barrier was implemented in 2023 and comprehensively monitored with 2 years of monthly groundwater sampling from more than 50 groundwater observation wells. The results of the monitoring program show that within the barrier, more than a 99.9% reduction of ∑ 32 PFAS was achieved, and concentrations in many groundwater observation wells dropped below 4 ng/L. Downstream concentrations in nearly all observation points were expected to be influenced by the barrier decrease by more than 99.9%. Evidence of at least partial retention of ultrashort PFAS within the barrier was demonstrated during the monitoring period, as well as retention of non‐target precursors. The results of this study demonstrate that a CAC barrier is an effective method for mitigating the spread of PFAS in groundwater systems and that a careful characterization of hydrogeological and other site‐specific conditions is of great importance when designing a CAC barrier. These results provide strong evidence and demonstrated a methodology for full‐scale CAC barrier remediation that can effectively limit the spread of PFAS in natural groundwater systems.
In-situ solidification (ISS) has emerged as a cost-effective and versatile technology for sediment remediation, particularly for addressing contamination at greater sediment depths. This paper evaluates ISS in the context of conventional sediment remediation approaches, highlighting its advantages, design and implementation considerations, and effectiveness through case studies. ISS involves solidifying sediments in place with cementitious grout, thereby reducing contaminant mobility by lowering hydraulic conductivity and minimizing leaching to groundwater and surface water. The technique also enhances the geotechnical properties of treated sediments, reducing the need for excavation and minimizing impacts on adjacent infrastructure. Sub-aqueous ISS offers potential cost savings over traditional methods by mitigating transportation and disposal costs and addressing challenges associated with emerging contaminants. However, the altered sediment conditions post-ISS may not support benthic communities, necessitating the use of restoration caps for ecological recovery. ISS is particularly beneficial for sediments located more than five feet below the surface, near sensitive infrastructure, or in large volumes exceeding 10,000 cubic yards. Compared to dredging, ISS can reduce environmental disturbance, improve seismic stability, limit vapor and odor emissions, and require a smaller operational footprint, making it suitable for urban environments. The design and execution of ISS demand comprehensive site characterization, regulatory coordination, and careful planning of site preparation, water quality management, and mixing methods. Quality control measures such as GPS monitoring and appropriate grout dosing are critical for success, and long-term monitoring is essential to ensure remedy stability and effectiveness. Overall, ISS represents a valuable addition to the sediment remediation toolkit, complementing other methods to address complex site conditions.
ABSTRACT Arsenic contamination in soils is an environmental and health problem due to the high toxicity and persistence of this metalloid. This study evaluated the effect of different amendment strategies based on biochar derived from cocoa husks and agricultural lime on arsenic bioavailability during phytoremediation processes with Lolium multiflorum . The biochar was produced by pyrolysis at 500°C and subsequently enriched with phosphorus. Treatments with different ratios of biochar and lime (10:90LB, 25:75LB, 50:50LB, biochar and lime), as well as a contaminated control without amendment, were established during a 45‐day bioassay. During the experiment, soil physicochemical parameters were monitored, including pH, electrical conductivity, cation exchange capacity, total organic carbon, organic matter, and total Kjeldahl nitrogen, as well as arsenic bioavailability by determining its exchangeable fraction. Given that Lolium multiflorum is not a hyperaccumulator, the experimental framework is consistent with a phytostabilization strategy, in which reducing As mobility in the soil and its transfer to plant tissues (rather than As extraction) is the primary objective. The accumulation of arsenic in the roots and shoots of L. multiflorum and the resulting plant growth was also evaluated. The results showed that the amendments significantly reduced arsenic bioavailability compared to the control, achieving reductions between 67% and 76% at the end of the bioassay. The 50:50LB treatment exhibited the best overall performance, combining decreased arsenic bioavailability, improved soil physicochemical properties, lower concentrations of the metalloid in plant tissues, and adequate plant growth.
This study evaluates the effectiveness of sugarcane bagasse biochar (SBB) in mitigating chromium (Cr)-induced oxidative stress in Cymbopogon flexuosus (lemongrass) grown on overburden soil (OBS) collected from a chromite mining site. The aim is to determine how SBB improves soil properties, reduces Cr toxicity, and enhances plant physiological and antioxidant responses for sustainable mine soil remediation. A greenhouse experiment was conducted with five treatments: T1 (garden soil), T2 (OBS), and T3-T5 (OBS with 5%, 10%, and 15% SBB). Soil physicochemical parameters (pH, organic carbon, cation exchange capacity (CEC), electrical conductivity), plant stress indicators (relative water content, electrolyte leakage), and reactive oxygen species (superoxide radicals (O-2 center dot(-)), hydrogen peroxide (H2O2), malondialdehyde (MDA)) were quantified. Antioxidant enzyme activities ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), non-enzymatic antioxidants (AsA, GSH), and soil enzyme activities were measured to assess biological responses. OBS showed poor fertility and elevated Cr levels. SBB amendments significantly improved soil quality by increasing pH, organic carbon, CEC, and soil enzyme activities. Cr accumulation in shoots and roots was lowest under 10% SBB treatment, indicating more effective restriction of Cr uptake at this dose. However, 15% SBB showed improvement in soil physicochemical properties, antioxidant activity, relative water content, and reduction of oxidative stress markers, suggesting superior overall stress mitigation despite slightly higher Cr accumulation than 10% SBB. Antioxidant defense mechanisms were strongly enhanced, reflected in increased APX, GR, MDHAR, AsA, GSH, and improved redox ratios. SBB effectively ameliorates Cr-contaminated OBS, reduces the Cr accumulation, enhances plant physiological resilience, and strengthens antioxidant systems. The findings demonstrate that SBB is a promising, eco-friendly, and cost-effective amendment for restoring Cr-polluted mine soils and promoting sustainable cultivation of aromatic grasses on degraded lands.
Heavy metal pollution of soil is an emerging environmental and public health concern resulting from mining, industrial discharge, wastewater irrigation, and intensive agriculture. The contaminants persist in the environment, degrading soil quality, undermining food security, and contaminating water sources. Phytoremediation, a green plant-based technology, is an economical and environmentally sustainable way of countering such pollution by taking advantage of the intrinsic ability of certain plant species to accumulate, stabilize, degrade, or volatilize heavy metals. This review systematically evaluates key phytoremediation strategies, including phytoextraction, phytostabilization, phytovolatilization, phytofiltration, and phytodegradation. Strategy-wise synthesis is emphasized, where comparative tables provide data on plant species, contaminant type, bioaccumulation and translocation factors, and total recovery efficiency, thereby providing practical recommendations for context-based application. Although plant-based mechanisms such as root uptake, translocation, chelation, and antioxidant responses contribute to detoxification, the operational success of phytoremediation hinges on selecting the right strategy for the right condition. Despite certain limitations such as long remediation durations and disposal challenges of biomass, advances in microbial synergy, genetic manipulation, and field-based studies are enhancing the efficacy and scalability of these technologies. The review concludes by advocating evidence-based selection frameworks and interdisciplinary research, making phytoremediation part of sustainable soil management and pollution control measures.
The increasing demand for bio-based fibers as substitutes for synthetic materials raises concerns about land use competition with food production. One proposed solution is the cultivation of non-food fiber crops on marginal or brownfield land. This study evaluates the sustainability of cultivating stinging nettle (Urtica dioica L.) for fiber production under poplar (Populus spp.) as a multifunctional land management strategy on brownfield and industrially impacted sites. Three qualitative sustainability assessments were conducted at case study sites in France (Saint-Symphorien-sur-Sa & ocirc;ne), Italy (Tavazzano), and Germany (Bernburg), comparing nettle-poplar systems with alternative land management scenarios, including ecological succession ("no change"), conventional agriculture, and photovoltaic (PV) energy production. The assessments were undertaken ex ante between 2020 and 2022 in accordance with ISO 18504:2017 on sustainable remediation and applied the Sustainable Remediation Forum-UK (SuRF-UK) Tier 1 qualitative framework. Environmental, economic, and social indicators were selected and scoped on a site-specific basis using the SuRF-UK indicator checklist, followed by comparative ranking of options supported by documented lines of evidence. Stakeholder engagement, involving site owners, technical experts, regulators, local authorities, and community representatives, was integrated into the assessment process and used to refine indicator selection and rankings. Across all three sites, nettle cultivation beneath poplar consistently achieved the most balanced sustainability performance overall, ranking highest for the environmental dimension in each case. Key environmental benefits included improved soil functionality, reduced erosion risk, enhanced ecological value, and productive reuse of marginal land. Economic performance of the nettle-poplar option was competitive but context dependent, generally ranking equal to or below PV-based options for direct financial returns, while outperforming alternatives in employment, innovation potential, and wider induced benefits. Social outcomes varied by site, with ecological succession often favored where recreational or cultural values dominated, and novel bio-based systems scoring lower on uncertainty due to limited operational track records. The results demonstrate that nettle-poplar systems represent a robust, nature-based, and multifunctional option for the sustainable management of brownfield land, offering strong environmental performance and acceptable economic and social outcomes. The study highlights the value of qualitative, stakeholder-informed sustainability assessment in supporting land-use decision-making where quantitative data are limited or highly site-specific.
Petroleum sludge poses significant environmental challenges due to its complex composition of hydrocarbons and heavy metals. Due to the high costs and limitations of physical and chemical remediation methods, bioremediation is recognized as a cost-effective and efficient approach for decontaminating hydrocarbon-polluted soils. This study investigates the enhanced phytoremediation of petroleum sludge-contaminated soil using the halophyte Salicornia sinus-persica and assesses the synergistic effects of biochar and vermicompost as soil amendments. A 6-month greenhouse experiment was conducted using soil contaminated with petroleum sludge concentrations ranging from 0% to 8% (w/w). Treatments included unamended soil, biochar amendment, vermicompost amendment, and a combined biochar-vermicompost amendment, with setups for planted, unplanted, and sterile unplanted conditions. Results demonstrated that petroleum sludge concentrations above 4% significantly inhibited seed germination, but amendments mitigated these effects. The presence of S. sinus-persica combined with amendments significantly enhanced total petroleum hydrocarbon (TPHs) removal in the soil. The highest TPH removal efficiency (54.1%) was achieved in the 0.2% sludge treatment with combined amendments and plants. However, at higher contamination levels (4%-8% sludge), removal efficiencies were considerably lower (ranging from 19% to 37%), and plant growth was severely inhibited at 8% sludge. These results indicate that S. sinus-persica with biochar and vermicompost amendments is effective for low to moderate petroleum sludge contamination but has limited applicability at high contamination levels without additional pretreatment or dilution.
The excessive usage and improper disposal of pharmaceuticals and personal care products (PPCPs) in Pakistan have led to elevated levels of these pollutants in the sediments. This study comprehensively evaluates the occurrence, spatial variability, and ecological risk of 49 PPCPs in sediments collected from the wastewater-contaminated Hudiara Drain and the receiving River Ravi, Lahore, Pakistan. Antibiotics were the predominant class of PPCPs detected in sediments. The highest concentration was observed for ofloxacin, with a median concentration of 216 & micro;g/kg in the Hudiara Drain and 108 & micro;g/kg in the River Ravi, followed by ciprofloxacin, with a median concentration of 85.8 & micro;g/kg in the River Ravi, and norfloxacin (210 & micro;g/kg) in the Hudiara Drain. The concentration was notably higher in wastewater sediments compared to river water sediments. Spatial variation analysis revealed that local sources, environmental conditions, and PPCP mobility significantly affect their concentrations at a particular site. An ecological risk assessment was conducted by calculating the risk quotient (RQ), which indicates that the presence of these PPCPs poses considerable damage to aquatic communities. To mitigate potential risks, there is a critical need to integrate advancements in wastewater treatment and to implement monitoring programs to track the presence and levels of these pollutants in aquatic environments.
The present study investigates the field-scale application of a soil vapor extraction (SVE) system operated under intermittent conditions for the remediation of an industrial site contaminated with ethylbenzene and xylenes. The contamination, originating from a release from an underground storage tank, affected the entire thickness of the unsaturated zone down to approximately 24 m below ground surface. Following groundwater containment through a pump-and-treat system, an SVE system consisting of four extraction wells was installed, with operational configurations varying over time. The system was monitored over a 3-year period, and the collected data were used to evaluate vapor phase concentration trends, mass removal rates, and cumulative extracted mass. The results show a progressive decrease in volatile organic compound concentrations, with a total extracted mass of approximately 12,700 kg. By the end of the study period, concentrations had decreased to approximately 0.1% of their initial values, indicating the likely presence of residual contamination that could be further addressed by transitioning to alternative technologies, such as bioventing.
In situ chemical oxidation (ISCO), a remediation technology for soil and groundwater contamination, utilizes oxidants that can impact the soil environment and indirectly influence soil CO2 emissions. Understanding these emissions may support more sustainable ISCO applications by enabling adjustments to treatment conditions that limit unnecessary CO2 release. This study assessed the effects of ISCO on soil CO2 emission rates and total bacterial counts by evaluating three common ISCO oxidants: hydrogen peroxide (HP), sodium persulfate (SPS), and potassium permanganate (PM), also in combination with various activation methods. CO2 emission rates from the soil slurry system were measured using a closed static chamber method and expressed in nanograms of CO2 per gram of dry soil per hour (ng CO2 gds -1 h(-1)). Under stable conditions, soil CO2 emission rates were ranked as follows: SPS groups (2.0 similar to 4.0) > PM group (1.9-3.1) > HP groups (0.6-1.8) approximate to original soil (0.4-1.0), while total soil bacterial counts (CFU gds(-1)) ranked as: PM group (similar to 10(7)) > HP groups (similar to 10(6)) > original soil (similar to 5.0 x 10(6)) > SPS groups (similar to 10(4)-10(6)). Most oxidant activation treatments led to higher CO2 emission rates and soil bacterial counts, except under alkaline activation. These findings demonstrate the influence of different ISCO processes on soil CO2 emissions and offer a baseline for emission rates during ISCO remediation.
The decontamination of thousands of pipes in fire suppression systems, for example, aircraft hangars and firetrucks exposed to aqueous film forming foam (AFFF), may generate large volumes of PFAS-laden water requiring treatment. This study investigated the use of powdered activated carbon (PAC) to remove PFAS from washwater used to rinse pipes from aircraft hangar pipe contaminated with AFFF. The untreated washwater contained 249 & micro;g/L of total PFAS. The concentrations were highest for 6:2 FTS (178 & micro;g/L), PFHxA (48 & micro;g/L), PFOA (9.5 & micro;g/L), and PFPeA (6.2 & micro;g/L). PFAS was removed from washwater during 24-h adsorption experiments conducted over a range of adsorbent masses. Temporal increases were observed between the 2- and 4-h total PFAS concentrations during most of the experiments, corresponding to some PFAS species being displaced during complex competitive adsorption mechanisms. After 24 h in the presence of 0.23 g of PAC per liter of solution, removals of 6:2 FTS and PFHxA, two of the short-chain PFAS, were 95% and 86%, respectively. For long-chain PFAS, PFOA and PFOS were removed to below their quantitation limits (i.e., 1 and 0.01 & micro;g/L, respectively) in most cases. However, removal of 8:2 FTS was only 52% in the presence of 0.0575 grams of PAC, despite having a relatively high Log K ow and dipole moment values, also pointing to the complexity of PAC adsorption mechanisms in AFFF contaminated water. To the authors' knowledge, this is the first study to report the use of PAC to treat AFFF washwater, a niche but important matrix.
Benzothiazoles (BTs), which are a class of toxic heterocyclic micropollutants, have been frequently detected in groundwater recently. Persulfate-based in situ chemical oxidation (ISCO) is considered a promising remediation method for organic-contaminated groundwater. In this study, batch experiments and 2-dimensional tank experiments were performed to investigate the in situ oxidation of a BTs-contaminated aquifer using a persulfate/iron-bearing minerals system. The impact of three different minerals (pyrite, hematite, and magnetite) and the mass loading on the degradation of 2-mercaptobenzothiazole (MBT), benzothiazole (BTH), and 2-hydroxybenzothiazole (OBT) were evaluated. The temporal-spatial distribution of contaminants, injected persulfate, Fe2+, and geochemical parameters in an aquifer during the 100-day remediation experiment are discussed in detail. The results indicate that MBT, BTH, and OBT can be effectively degraded in the presence of both persulfate and pyrite, all reaching removals of over 85% in 8 h. The removal of BTs benefits from increasing pyrite mass loading. & centerdot;SO4 - and & centerdot;OH are the dominant reactive species involved in BTs degradation. In situ injection of persulfate into the lab-scale aquifer led to 99%, 42%, and 20% reductions of total MBT, BTH, and OBT, respectively, during the tank experiment. The migration of BTs was intercepted, and their distribution area decreased significantly over time, confirming the long-term effectiveness of the persulfate/pyrite in situ reactive zone for the treatment of BTs. The increase of ORP indicates the formation of an oxidizing condition in the subsurface. No significant disturbance to dissolved oxygen in groundwater occurred during the ISCO remediation. The outcomes of this study provide a basis for practical engineering remediation for groundwater contaminated with BTs.
Per- and polyfluoroalkyl substances (PFAS) challenge wastewater treatment facilities (WWTFs) not as conventional contaminants moving linearly from influent to effluent, but as a distributed mass that partitions, transforms, and recirculates across solids, liquids, foam, aerosols, and off-gas. Drawing on recent full-scale monitoring studies, fluorine mass-balance analyses, and statistical evaluation of nationwide data sets, this perspective demonstrates that treatment processes compress influent PFAS variability into narrow effluent and biosolids distributions, erasing source fingerprints while redistributing rather than removing mass. These observations motivate a management approach centered on PFAS mass balance rather than end-of-pipe concentration control. We propose a practical, eight-step decision framework that integrates three tiers of action: (1) source identification, classification of "low-strength," "medium-strength," and "high-strength" influent streams, and deployment of high-leverage pre-treatment; (2) targeted in-plant controls focused on enrichment points such as foam, aerosols, and sidestreams, with polishing reserved for clean matrices where media exhaustion and residuals can be managed; and (3) residuals strategies that address PFAS in biosolids, concentrated liquids, and air-pollution-control byproducts through destruction (e.g., supercritical water oxidation, pyrolysis, mechanochemical destruction, wet oxidation), or stabilization. The framework embeds conceptual PFAS flux diagrams, explicit consideration of regulatory and permitting constraints, and iterative triple bottom line evaluation to compare treatment trains on the basis of net mass reduction, cross-media trade-offs, life-cycle cost, and community acceptability. This integrated model provides utilities with a structured pathway from diagnosis to implementation, helping avoid stranded investments in low-leverage technologies and supporting PFAS management strategies that are technically defensible, regulatorily viable, and aligned with long-term environmental and public health protection.
This paper reports on a US project-based treatability study that describes the baseline geo-environmental characterization and pH buffering of soil surrogates containing 20 (S2X) or 40 (S4X) percent acid tar by volume (where X denotes testing phase) and various stabilization/solidification (S/S) mix designs using powdered ladle slag (PLS), a 60/40 (w/w) blend of Type IL Portland Cement (PC) and Grade 120 NewCem (NC) slag cement, and bentonite (B) for some mixes. The soil surrogates reflected the expected in situ S/S (ISS) profile comprising an ISS rig working platform, residual tar, bottom lagoon liner materials, and shallow subsurface soils after the bulk tars are excavated for incineration. The total benzene content of the S41, S42, and S22 soil surrogates averaged 16,300, 24,000, and 10,568 mg/kg, respectively, with corresponding sulfur contents of 28,350, 93,500, and 43,500 mg/kg and pH values typically less than 0.5. EPA 1313 testing on the S41/S42 soil surrogates tracked the leaching of EPA target analyte list (TAL) metals over a range of pH and also indicated that it took about three equivalents of base addition to maintain pH conditions above 8 to ensure the long-term stability of the ISS mixes. EPA 1316 M leaching of volatile organic compounds indicated that the S41, S42, and S22 media were characterized by benzene effective concentrations of 497, 406, and 318 mg/L, respectively. The S41 and S42 surrogates were extremely challenging to solidify, requiring 5 wt% PLS + 35 wt% PC/NC to exceed the relatively modest unconfined compressive strength (UCS) target of 276 kPa (40 lb/in2). Regardless of UCS, most ISS mixes met the permeability criterion of less than 1 & times; 10-6 cm/s. The minimum ISS reagent dose satisfying the UCS, K, and residual pH buffer capacity (3 meq/g) targets for 28-day cured mix designs for the S22 soil surrogate was 5 wt% PLS + 30 wt% PC/NC + 0.5 wt% B. This was the minimum reagent dose proposed for long-term leaching and field pilot testing.
This review synthesizes current research on the phytoremediation potential of industrial hemp (Cannabis sativa L.) for heavy metals, including arsenic, aluminium, mercury, copper, lead, cadmium, nickel, and zinc, as well as per- and polyfluoroalkyl substances (PFAS), commonly referred to as "forever chemicals." A structured and transparent review of interdisciplinary studies was conducted across greenhouse, field, hydroponic, and amendment-based experiments. Findings indicate that hemp exhibits strong tolerance and accumulation capacity for cadmium, lead, and arsenic, with metal uptake primarily concentrated in roots. Cultivar differences significantly influence both uptake efficiency and biomass yield. PFAS uptake is selective, with higher bioconcentration observed for short-chain and carboxylic acid compounds, although overall soil PFAS removal remains low to moderate. Remediation efficacy is modulated by soil properties, biosolid amendments, and microbial symbioses, which enhance PFAS bioavailability and plant tolerance. Comparative assessments reported in the literature suggest that hemp's rapid biomass production and adaptability may offer advantages over other phytoremediation species. However, limitations in PFAS degradation and ecological risks, such as PFAS accumulation in pollen, persist. Integration of soil amendments and microbial inoculants shows potential to enhance hemp growth rates and PFAS tolerance; however, further testing and field validation are required. This review underscores hemp's potential as a sustainable phytoremediation agent and a component of integrated PFAS remediation strategies, while highlighting the need for standardized protocols and risk assessments to ensure environmental safety and practical scalability.
Monitored natural attenuation (MNA), primarily via biodegradation, is a cost-effective approach to managing large and dilute groundwater plumes formed by 1,4-dioxane. However, impacts of prior treatments, such as aerobic bioremediation strategies, on the subsequent attenuation of 1,4-dioxane are poorly understood. In this study, bench-scale microcosms were conducted with groundwater collected from seven monitoring wells located along the 1,4-dioxane plumes at two sites where propane biosparging (and bioaugmentation) were previously employed. Over 4 weeks of incubation, significant 1,4-dioxane removal was observed in microcosms prepared with groundwater samples from four locations within the proximity of historical treatment zones. First-order attenuation rates were in the range of 0.02 to 1.11 day(-1), corresponding to half-lives between 0.6 and 32.0 days. Concurrently, a meta study was conducted by compiling groundwater data from > 900 monitoring wells across the U.S. Bulk 1,4-dioxane degradation/attenuation half-lives were estimated in the range from 109 to 6405 days (R-2 > 0.5). The majority (96%) of the estimated half-lives were less than 3000 days with the shorter half-lives (i.e., faster rates) generally observed at higher 1,4-dioxane concentrations (i.e., > 20 & micro;g/L). Propane biosparging exhibited significantly shorter half-lives (i.e., a median half-life of 445 days) than MNA and pump and treat technologies. Additionally, 1,4-dioxane half-lives after the start of propane biosparging treatment were an order-of-magnitude shorter than those prior to this treatment, which may also explain the additional orders-of-magnitude decreases in half-lives in MNA-mimicking microcosms. Together, these findings indicate that propane biosparging not only accelerates immediate 1,4-dioxane removal but also "primes" microbial communities for enhanced long-term attenuation.
ABSTRACT This paper reports on a US project‐based treatability study conducted for a confidential client and focuses on the long‐term leaching of benzene and metals from soil surrogates containing 20% (S2X) or 40% (S4X) acid tar by volume (where X denotes the testing phase) and their stabilization/solidification (S/S) mix designs (M2X or M4X) formed with grouts of powdered ladle slag (PLS), a 60/40 (w/w) blend of Type IL Portland Cement (PC), and Grade 120 NewCem (NC) slag cement, and, in some mixes, bentonite (B). Long term semi‐dynamic leaching tests modified (M) for use with hydrocarbons (EPA 1315M) were performed on S/S‐treated soil surrogates cured for 28 days. Percent leaching reductions (%LRs) were calculated by comparing quasi‐steady‐state benzene concentrations from EPA 1315M to the effective solubility of benzene in the untreated soil surrogates (318 mg/L for S22; 406 mg/L for S42). Minimum %LR values of 93.7% and 92.8% were observed for M22 mixes tested with and without 0.5% B, respectively. Parallel testing was conducted using freshly mixed (FM) M22 materials placed in a specialized extractor, where benzene leached into an overlying water cap beneath a continuously exchanged headspace over 91 days. The mass transfer rates from the FM tests compared very well with those from the EPA 1315M tests beginning around day 35, coinciding with the end of the startup period for the 28‐day cured samples. The strong agreement of these data essentially validated the accuracy and effectiveness of the polydimethylsiloxane (PDMS) liner used in the EPA 1315M test. The corresponding EPA 1315M leaching of most trace heavy metals (Sb, As, Be, Cr, Co, Cu, Pb, Mo, Ni, and Ag) were at or below their respective method detection limits for all leaching intervals for all mix designs. Cd, Se, and Zn showed similar performance with a few outliers. Ba concentrations were between 20 and 100 µg/L. Mo and V concentrations from the pH‐dependent leaching (EPA 1313) test never exceeded 10 µg/L and were up to 100 times lower than those from the untreated soil surrogates at the same pH. After the 63‐day EPA 1315M test, the unconfined compressive strength of the test samples was at least 689 kPa (100 lb/in 2 ) greater than their 28‐day values.
For decades, crude oil spills have been a serious environmental challenge which have led to the establishment of crude oil remediation intervention values (CRIV) by different national agencies to regulate the release of toxic petroleum hydrocarbons via these spills. To ascertain the suitability of these CRIV in crude oil-polluted agricultural sites, the impact of five CRIV on the nutritional composition of two green leafy vegetables (GLV) and associated human health risk was investigated using standard analytical procedures. Briefly, high-performance liquid chromatography was used in determining the composition of the sugars while inductively coupled plasma mass spectrometer and atomic absorption spectrometer were utilized in quantifying the levels of minerals in the harvested samples. This was followed by human health risk assessment based on the evaluation of non-carcinogenic and carcinogenic risks. CRIV at 3000 and 5000 mg/kg total petroleum hydrocarbons (TPH) reduced the fructose and glucose contents of Lactuca sativa whereas the sucrose level was enhanced at 10,000 mg/kg TPH. All the tested CRIV had no statistically significant effect (p > 0.05) on the Na/K ratio of Brassica oleracea as well as the F/G and Ca/P ratios of L. sativa. Among the studied nonessential heavy metals, only the samples' Pb contents were below the FAO/WHO Codex maximum level. Multivariate statistical analysis indicated that the 10,000 mg/kg TPH treatment GLV samples' nutrients were the most impacted by the crude oil stress which also primarily had the highest non-carcinogenic and cancer risk levels. The investigation revealed the potential of some crude oil concentrations in agricultural sites to alter the physiology of GLV and their nutritional composition. Consequently, use of CRIV at TPH concentration of <= 3000 mg/kg is recommended to protect the quality of GLV from such sites and to safeguard against possible cancer risk.
Questions have recently been raised about the suitability of using porewater samples collected with suction lysimeters to estimate per- and polyfluoroalkyl substances (PFAS) mass discharge in the vadose zone. Multiple lines of evidence were evaluated to determine if porewater samples collected during a data gaps investigation in the former fire training area (FFTA) at Ellsworth Air Force Base were reproducible and representative. Lines of evidence used include supplemental geologic and hydrogeologic data, which show the presence of a semi-continuous silt/clay layer directly above the water table throughout much of the FFTA, and gravimetric moisture content results that demonstrate vertical water flow at a depth of 15 ft is substantially limited due to semi-arid climatic conditions. Radial diagrams were used to visually demonstrate that there was negligible variability in porewater concentrations caused by varying sample yields in the deep zone. Additional lysimeters installed in the FFTA during the remedial investigation did not result in a significant difference in the estimated vertical mass discharge, which demonstrates that the number of lysimeter sampling points in this area is sufficient. Strong attenuation in PFAS soil concentrations with depth validates the order(s) of magnitude reduction between shallow and deep porewater concentrations observed near the former burn pit. Vadose zone PFAS mass discharge is shown to be 4%-19% of groundwater mass discharge below the water table for regulated constituents. Recommendations for field data collection and estimation of PFAS mass discharge in the vadose zone are presented.
