Cleanup Levels Research Articles

Formerly used defense sites on Unalaska Island, Alaska: Mapping a legacy of environmental pollution.

Unalaska Island, Alaska, served as a US military base during World War II. The military installed bases on Unalaska and nearby islands, many of which were built adjacent to Unangan communities. The military used toxic compounds in its operations and left a legacy of pollution that may pose health risks to residents and local wildlife. The goals of this study were to identify hotspots of contamination remaining at Unalaska formerly used defense (FUD) sites, evaluate the risk posed by arsenic, and examine "no US Department of Defense action indicated" (NDAI) status determinations for FUD sites near communities. We compiled soil chemistry data from remediation reports prepared by the US Army Corps of Engineers at 18 FUD sites on and near Unalaska. Nine had past and/or active remediation projects and on-site sampling data. Eight sites did not have sampling data and were characterized as NDAI. One site was listed as closed. For the nine sites with sampling data, we compiled data for 22 contaminants of concern (COC) and compared concentrations to soil cleanup levels for human health (18 AAC 75.341). We mapped contaminant concentrations exceeding these levels to identify hotspots of contamination. We found that concentrations of some of the 22 COC exceeded Alaska cleanup levels despite remediation efforts, including diesel range organics, arsenic, and lead. The highest COC concentrations were at the FUD site adjacent to the City of Unalaska. A quantitative risk assessment for arsenic found that the risk of exposure through drinking water is low. We highlight concerns with NDAI designations and current remedial practices at remote FUD sites located adjacent to communities. Our data suggest the need for further remediation and monitoring efforts on Unalaska for certain contaminants and research to examine potential threats to human and animal health associated with these sites. Integr Environ Assess Manag 2024;20:1420-1431. © 2024 SETAC.

Electron beam remediation of soils impacted with heavy hydrocarbons

During electron beam (EBeam) irradiation, high-energy electrons can generate physical and chemical changes in a substance such as chain scission and cross-linking. Irradiation of soil is shown to be an effective technology for rapid reduction of Total Petroleum Hydrocarbons (TPH) in crude oil impacted soils. An experimental apparatus for batch treatment of 100 g soil samples was built and tested using a 10 MeV, 15 kW electron beam. The samples were a variety of crude oil impacted soil samples with TPH contents ranging between 1.6 and 32% by mass. Soils of initial TPH up to 9.1% (dry weight basis) TPH levels were reduced to below a target cleanup level of 1% with irradiation doses ranging from 700 kJ/kg to 1100 kJ/kg and treatment times less than 200 s, with maximum soil temperatures less than 450 °C. Soils with elevated moisture content required higher dosages or preliminary drying. EBeam treatments resulted in 1) reduction for both light and heavy hydrocarbon, 2) generation of new light hydrocarbons, and 3) generation of fixed carbon, indicating that the mechanisms of electron beam remediation include radical induced reactions at relatively low temperature and relatively short time scales and not simply thermal desorption effects.

Development of updated RfD and RfC values for medium carbon range aromatic and aliphatic total petroleum hydrocarbon fractions

ABSTRACT Using total petroleum hydrocarbon (TPH) measurements as a tool for assessing potential human health risks associated with exposures to petroleum products in the environment poses unique challenges, as TPH represents highly variable and complex mixtures containing hundreds of individual chemicals with wide-ranging chemical and physical properties. Current risk assessment practice generally involves analysis of environmental samples for various TPH fractions and summation of risk across those fractions. The United States Environmental Protection Agency (USEPA) derived provisional toxicity criteria for low, medium, and high carbon range aromatic and aliphatic hydrocarbon fractions over a decade ago. These criteria have been used, in whole or in part, to derive risk-based cleanup levels for TPH contamination in soil and groundwater. Herein, we evaluate and update oral and inhalation toxicity criteria for two of these fractions – medium carbon range aromatics and aliphatics – using, where applicable, newer data, updated modeling techniques, and new/alternative analyses of certain endpoints, human relevance, and uncertainty. The results of the analyses support an ~10-fold increase in the USEPA provisional reference concentration (p-RfC) values from 0.1 mg/m3 to 1 mg/m3 for both medium carbon range aromatics (different uncertainty factor) and aliphatics (new study and different judgment of toxicity data from existing study). Compared to the USEPA provisional oral reference dose (p-RfD) values for the medium carbon range aromatics and aliphatics of 0.03 mg/kg-day and 0.01 mg/kg-day, respectively, the present analyses suggest the RfD for medium carbon range aromatics could be increased >6.6-fold to 0.2 mg/kg-day (updated modeling and different uncertainty factors), and the RfD for medium carbon range aliphatics could be increased ~20-fold to 0.2 mg/kg-day (new study). These updated toxicity criteria could be used by regulatory agencies to reevaluate risk-based screening levels or by risk managers to support cleanup levels for medium carbon range aromatics and aliphatics, while still ensuring adequate health protection. Implications: Petroleum products represent complex mixtures of hydrocarbons broadly comprised of aliphatic compounds (straight-chain, branched-chain, and cyclic alkanes and alkenes) and aromatic compounds such as benzene, alkylbenzenes, and polycyclic aromatic hydrocarbons. The complex nature of petroleum products presents challenges for assessing potential health risks associated with exposure to petroleum hydrocarbon contamination in the environment. It has been over ten years since the U.S. Environmental Protection Agency derived provisional toxicity criteria for low, medium, and high carbon range aromatic and aliphatic hydrocarbon fractions. In that time, risk assessment guidance and tools have evolved, and new studies have been published. Our analyses indicate that current provisional toxicity criteria for medium carbon range aromatics and aliphatics fractions are overly conservative by approximately an order of magnitude.

Differences Between US EPA and EU related to PFAS/PFOS Contamination: Implications for Clean-up and Policy

BACKGROUND AND AIM: The US EPA has no national regulatory authority for per- and polyfluoroalkyl (PFAS/PFOS) classes of nonstick ‘Teflon’ compounds. The biggest US suppliers were Dupont/Chemours and 3M; in the EU they were 3M, Miteni, and Daikin. By contrast to the US, the European Union (EU) has published guidance providing safe exposure and clean-up levels for soil and water. With new EPA leadership, we seek to understand what levels of safety and clean-up might be adopted. METHODS: We examined the environmental health literature to comprehend where new national standards may be set, and how those differ from EU. PFAS/PFOS are persistent in the environmental and no longer manufactured. The C 8 Science panel linked workplace exposure to PFAS/PFOS to testicular and kidney cancer, elevated cholesterol, liver and chronic kidney disease, reduced fertility, thyroid and hormone problems, and immune dysfunction. RESULTS:Currently there are no EPA maximum concentration levels (MCL) for water. There was 2019 Congressional attempt to regulate Teflon chemicals under Superfund; to categorize PFAS/PFOS as hazardous substances. Because there was no agreement on the level of clean-up of military firefoam PFAS, it was left out of the legislation. Therefore, US states set differing notification and drinking water remediation levels ranging from 1 to140 ppt; states of MI, NJ, NY, and CA have been leaders in defining regulatory levels. The EU 2021 Drinking Water Directive mandates a 0.5 µg/l limit, and EU Chemicals Agency has developed standards for food, packaging, soil, and the workplace. CONCLUSIONS:A big issue will be the cost of remediation. We note the major producer corporations are also where best clean-up technologies are housed. The new EPA will account for the impacts of PFAS/PFOS on worker and disadvantaged communities. Although it will require a balancing of safe remediation and cost, we predict regulatory concentrations will be between 10 to 40 ppt. KEYWORDS: PFAS, policy and practice, international collaboration

Applicability of an anionic-nonionic surfactant in p-cresol contaminated soil washing: Finding the optimal mixing ratio.

In this study, the parameters influencing p-cresol removal efficiency in soil washing method were investigated. Primarily, extraction efficiencies of three Tween series surfactants (Tween 20, Tween 60, Tween 80) with 10mM concentration were compared. Tween 80 showed the best results since its value (55%) was 4% and 13% higher than that of Tween 60 and Tween 20. The impact of mixed surfactant on extraction rate was examined by employing a mixture of Tween 80 and one anionic surfactant (sodium dodecyl sulfate) with different molar ratio as the main washing solution. The results denoted that the molar ratio of 3:2 (SDS:Tween80) could enhance the extraction rate up to 38% compared to using SDS and Tween 80 alone. Regarding the initial p-cresol concentration in the collected sample, the cleanup level (390mg/kg) could only be achieved using the mixed-surfactant. Thus, the minimum required surfactant concentrations to hit the target level was calculated to be 3.54g/L of Tween 80 and 2.105g/L of SDS (molar ratio of 0.27 SDS:Tween80). Studying the role of surfactant concentration indicated that its increment from 10mM to 20mM, which is way above all the reagents' critical micelle concentration (CMC), does not affect the removal rate considerably. The same results were obtained comparing the effect of washing time in three different levels (30min, 60min and 90min). However, temperature showed to be a more significant parameter as it could enhance the results up to 20% (for SDS).

Large-volume electric field-assisted multiphase extraction of malachite green from water samples: A multisample device and method validation

In this work, a new large-volume multiphase, multi-sample electroextraction device was developed and applied to selectively extract malachite green (MG) from water samples. This device was easily constructed with ordinary materials and capable of extracting ten samples simultaneously, obtaining MG preconcentrated on a solid support, to fit into a pipette tip. A multi-well plate was applied to extract MG from aquaculture water samples, and the extracts containing the desorbed MG were analysed by LC-DAD and LC-MS/MS. The signals from both detectors were used in two independent validation procedures. Linearity, matrix effect, selectivity, precision, trueness, and limits of detection and quantification were all evaluated. For both detectors, linearity was demonstrated in the range of 0.5–5 μg L−1 (R2 > 0.98). Matrix effect was insignificant for LC-DAD only, and the average preconcentration factor was about 60 times. Recoveries ranged from 94 to 113% for LC-DAD and 95–115% for LC-MS/MS analysis. ANOVA was applied to estimate the standard deviation under repeatability (6.96–8.61% for LC-DAD and 5.98–7.41% for LC-MS/MS) and within-reproducibility (6.96–8.61% for LC-DAD and 6.56–7.41% for LC-MS/MS) conditions. The limits of detection and quantification for LC-MS/MS analysis were 4.29 and 28.74 ng L−1, respectively, while, for LC-DAD, these limits were 14.29 and 95.81 ng L−1, respectively. The results demonstrated that the developed method was suitable for determining MG in water samples, and the large-volume multiphase, multi-sample electroextraction device proved to be a powerful sample preparation technique to obtain high clean-up and large preconcentration levels, which are of paramount importance for environmental applications.

Numerical study of the building pressure cycling method for evaluating vapor intrusion from groundwater contamination.

Vapor intrusion (VI) risk assessments determine the cleanup level of groundwater in the absence of ingestion. In recent VI investigations, the building pressure cycling (BPC) method has been applied to help minimize ambiguity caused by temporal variability of indoor air samples that are important to risk assessments, and, consequently, determine groundwater cleanup level accurately. In this study, we use a three-dimensional numerical model to examine the dynamic migration of VOCs from groundwater after the application of BPC. First, we validated the numerical model with field measurements. Then, the verified model is used to investigate the effects of site-specific features in determining the performance of BPC operation. At last, we summarize past field applications of BPC to examine the simulated results. Our study indicates that the BPC-induced indoor depressurization can increase the building loading rate in the first 2-3 h, which would then drop to 2-3 times of that with natural conditions in most cases of groundwater contamination. In some cases involving a strong source, e.g., a vapor source above the capillary fringe or a groundwater source with sandy soil above the groundwater level, the normalized building loading rates can be maintained as high as 4-9 without decrease after the first 2-3 h. Significantly higher increase in building loading rate may indicate a potential presence of a preferential pathway between the groundwater contamination and concerned building.

Objective ranges of soil-to-dust transfer coefficients for lead-impacted sites

Residential yard soil and indoor dust datasets from eight communities near historical mining, smelting, and refining operations were used to quantify soil track-in, an important factor in evaluating indoor exposures to soil metals and to set residential soil cleanup levels. Regression analyses were used to derive slopes that represent mass soil-to-dust transfer coefficients or MSDs. Lead concentration data were available for all datasets. Arsenic data were available for six of the eight datasets. Cadmium and zinc data were available for one dataset, allowing limited comparison of MSDs for lead with other metals. Covariates that could indicate potential indoor sources of metals, such as house age and indoor heating source, were examined by multivariate regression analysis when available (three datasets). Covariates that could affect soil track-in, such as the amount of bare soil in the yard or having pets, were examined by stratified linear regression analysis when available (two datasets). Most of the R-squared values for lead, cadmium and zinc indicate a good to moderate fit (≥0.25), but for arsenic most indicate a poor fit (<0.25). Significant MSDs for models with a good to moderate fit range from 0.14 to 0.47 for lead, and 0.12 to 0.43 for the other metals (arsenic, cadmium, and zinc). The treatment of outliers was a significant methodological factor affecting the slope of the regressions. Substantial variability is expected among soils at residences due to both physical characteristics of each property and the ways in which residents interact with their home. Survey data providing information on various factors affecting soil track-in help to refine MSD estimates. For three of the datasets, covariate data were available that improved model fit by multivariate or stratified regression analysis for lead. When multivariate or stratified regression analyses were performed, the estimated MSD varied as little as <1% to as great as 200% depending on the dataset, but all estimates were below 0.4. Notably, the MSDs were lowest for the three datasets with the highest soil lead concentrations, i.e., those with average soil lead concentrations greater than 300 mg/kg after outlier removal. For five of the six datasets that had both arsenic and lead sampled, arsenic MSDs were much less than the lead MSDs; however, only two of the sites’ arsenic models had significant MSDs and adequate fit. Cadmium and zinc were only included in one dataset, limiting our ability to draw any conclusions from comparison to those MSDs. The results of our study are consistent with prior studies suggesting that MSDs for metals without internal sources are 0.3–0.4, and application of MSDs in that range will provide more reliable exposure estimates than the 0.7 default value used by the United States Environmental Protection Agency in the Integrated Exposure Uptake Biokinetic (IEUBK) Model.

Rationale for Soil‐Gas Sampling to Improve Vapor Intrusion Risk Assessment in China

Rationale for Soil‐Gas Sampling to Improve Vapor Intrusion Risk Assessment in China

EPA recommends cleanup level for PFOS and PFOA in groundwater

With a number of caveats, the US Environmental Protection Agency is recommending the cleanup of groundwater tainted with more than 70 parts per trillion of either of two widespread polyfluorinated chemicals. The EPA’s April 25 draft interim recommendations would apply only to groundwater that is a current or potential source of drinking water and would not have the legal force of regulations. They would also apply only in states that lack what the agency deems an “appropriate” drinking-water standard for the two chemicals, perfluorooctanoic acid (PFOA) and perfluorosulfonic acid (PFOS). The recommendations follow the EPA’s 2016 health advisory limit of 70 ppt for PFOS and PFOA, individually or combined, in drinking water. The two substances, which are no longer commercially produced in the US, contaminate groundwater across the nation and the world. In many areas, the pollution stems from military bases and airports that for years used firefighting foams containing

Modeling capillary fringe effect on petroleum vapor intrusion from groundwater contamination

At contaminated sites, indoor inhalation of volatile organic compounds from groundwater contamination, known as vapor intrusion (VI), is an important exposure pathway to determine groundwater cleanup level. Based on empirical analysis, US EPA concluded that there is a low probability for vapors from fuel hydrocarbons dissolved in groundwater to induce indoor concentrations that exceed risk-based standards, and recommended 6 feet vertical building-source separation distance as the risk screening tool for such cases. In this study, we examine this recommendation by performing numerical modeling to investigate the detailed effects of the capillary fringe on petroleum vapor biodegradation and attenuation. First, the numerical model is validated by comparison with laboratory data and field measurements in US EPA's database. Then the verified model is used to simulate two scenarios involving the capillary fringe effect, one with a groundwater source at various depth and the other with a soil gas source located above the groundwater level. For a groundwater contaminant source, the capillary fringe plays a significant role in VI by controlling the soil moisture content and oxygen availability, thus affecting the soil gas concentration biodegradation and attenuation. Specifically, the capillary fringe effect can significantly decrease the indoor air concentration by decreasing upward diffusion rates of hydrocarbon, increasing the thickness of the aerobic zone, and enhancing aerobic biodegradation. As a result, it is highly unlikely for sources located at groundwater level to induce unacceptable vapor intrusion risks, supporting US EPA's recommendation. Moreover, the simulations suggest that the vertical smear zone of residual light non-aqueous liquid contamination, induced by temporal fluctuations of groundwater level, may lead to a potential threat to indoor air quality for a short vertical source-building separation distance, and thus requires more attention. The sensitivity test of the numerical model also indicates that it is the vertical separation distance between building foundation and the top of the smear zone instead of the smear zone thickness that should be given more attention during the investigation.

Natural Background and Anthropogenic Arsenic Enrichment in Florida Soils, Surface Water, and Groundwater: A Review with a Discussion on Public Health Risk.

Florida geologic units and soils contain a wide range in concentrations of naturally-occurring arsenic. The average range of bulk rock concentrations is 1 to 13.1 mg/kg with concentrations in accessary minerals being over 1000 mg/kg. Florida soils contain natural arsenic concentrations which can exceed 10 mg/kg in some circumstances, with organic-rich soils often having the highest concentrations. Anthropogenic sources of arsenic have added about 610,000 metric tons of arsenic into the Florida environment since 1970, thereby increasing background concentrations in soils. The anthropogenic sources of arsenic in soils include: pesticides (used in Florida beginning in the 1890’s), fertilizers, chromated copper arsenate (CCA)-treated wood, soil amendments, cattle-dipping vats, chicken litter, sludges from water treatment plants, and others. The default Soil Cleanup Target Level (SCTL) in Florida for arsenic in residential soils is 2.1 mg/kg which is below some naturally-occurring background concentrations in soils and anthropogenic concentrations in agricultural soils. A review of risk considerations shows that adverse health impacts associated with exposure to arsenic is dependent on many factors and that the Florida cleanup levels are very conservative. Exposure to arsenic in soils at concentrations that exceed the Florida default cleanup level set specifically for residential environments does not necessarily pose a meaningful a priori public health risk, given important considerations such as the form of arsenic present, the route(s) of exposure, and the actual circumstances of exposure (e.g., frequency, duration, and magnitude).

It Is Time to Move Beyond the Linear No-Threshold Theory for Low-Dose Radiation Protection.

The US Environmental Protection Agency (USEPA) is the primary federal agency responsible for promulgating regulations and policies to protect people and the environment from ionizing radiation. Currently, the USEPA uses the linear no-threshold (LNT) model to estimate cancer risks and determine cleanup levels in radiologically contaminated environments. The LNT model implies that there is no safe dose of ionizing radiation; however, adverse effects from low dose, low-dose rate (LDDR) exposures are not detectable. This article (1) provides the scientific basis for discontinuing use of the LNT model in LDDR radiation environments, (2) shows that there is no scientific consensus for using the LNT model, (3) identifies USEPA reliance on outdated scientific information, and (4) identifies regulatory reliance on incomplete evaluations of recent data contradicting the LNT. It is the time to reconsider the use of the LNT model in LDDR radiation environments. Incorporating the latest science into the regulatory process for risk assessment will (1) ensure science remains the foundation for decision making, (2) reduce unnecessary burdens of costly cleanups, (3) educate the public on the real effects of LDDR radiation exposures, and (4) harmonize government policies with the rest of the radiation scientific community.

Pollution potential of the wastes of used oil treatment plants and their possible remediation techniques

In this research, wastes of used oil treatment plants have been studied for their pollution potential and geotechnical characteristics. A random sampling plan was used to collect 11 samples from the dump site. Moreover, statistical analysis indicated that six samples were required to prepare a representative sample for the wastes. Thus, a mixed sample was prepared to determine moisture content, pH, Atterberg limits and density of the waste. The analysis of organic compounds and heavy metals showed the presence of total petroleum hydrocarbons (TPH) and Barium as the main pollutants. The results also showed waste as a fine-grained soil heavily contaminated by petroleum hydrocarbons. The mean concentration of TPH was more than 216 g/kg, which is 832, 108 and 433 times greater than the acceptable cleanup levels for diesel range organics, oil range organics and TPH, respectively. Nevertheless, heavy metals concentrations are lower than proposed cleanup levels for industrial area. The moisture content, pH, liquid limit, plastic limit, plastic index and density of the mixed sample were 12.26%, 9.6, 25.91, 15.83, 10.08 and 1.22 g/cm3, respectively. After that, several remediation techniques were evaluated to propose the best one based on the physical and chemical properties of the waste, the applicability of the method and implementation costs. Finally, solidification/stabilization technique using organophilic clay as the stabilizer, incineration and bioremediation techniques was recommended for cleanup of the site.

1,4‐Dioxane Soil Remediation Using Enhanced Soil Vapor Extraction (XSVE): II. Modeling

Abstract1,4‐Dioxane is a volatile organic compound that is fully miscible in water, allowing it to sequester in vadose zone pore water and serve as a long‐term source of groundwater contamination. Conventional soil vapor extraction (SVE) removes 1,4‐dioxane; however, substantial 1,4‐dioxane can remain even after other colocated chlorinated solvents have been remediated. A field demonstration of “enhanced SVE” (XSVE) with focused extraction and heated injection was conducted at former McClellan AFB, CA, achieving 94% reduction in soil concentrations. A screening‐level tool, HypeVent XSVE, was created to assist in system design and data reduction and to anticipate how operating factors affect XSVE performance (e.g., cleanup level, remediation time, etc.). It assumes well‐mixed conditions, and combines an energy balance, mass balances for water and contaminant, and a temperature‐dependent 1,4‐dioxane Henry's Law constant. User inputs include the target treatment zone size, initial 1,4‐dioxane and soil moisture concentrations, and ambient site and injection/extraction conditions (temperature, humidity). Projections based on inputs representative of demonstration site conditions adequately anticipated the observed macroscopic field results. Sensitivity analyses show that removal increases with increasing heated air injection temperature and relative humidity and decreasing initial soil moisture content.

Assessment of residential soil contamination with arsenic and lead in mining and smelting towns of northern Armenia

Environmental characterization was conducted in one mining and one smelting community in Armenia, Akhtala and Alaverdi, respectively. The aim of the study was to quantify the levels and possible origins of arsenic and lead in the residential soil of these communities, and measure the relationship between those levels in the soil, and its proximity to the industrial source.In total, 459 soil samples were tested in the communities using an X-Ray Fluorescence (XRF) spectrometer. The study team followed standard protocols during the process of soil collection, processing, testing and quality assurance procedures. We compared arsenic and lead concentrations with the Maximum Allowable Concentrations (MAC), Clean up Level (CL) and Highest Background Level (HBL). We, also calculated the Geoaccumulation index (Igeo) and Enrichment Factor (EF). To identify the possible origin of contamination we performed linear regression, principal component analysis (PCA) and interpolation using the distance of each sampling point from the smelter smokestacks, sampling point elevation and measured content of arsenic and lead for Alaverdi.The results showed that in the smelting town of Alaverdi, 75.6% of soil samples exceeded Clean up Level for arsenic and 24.0% for lead. In the mining town of Akhtala, 3.2% of all soil samples exceeded Clean up Level for arsenic and 27.1% for lead. Pollution levels in the towns studied were classified as moderate to strongly polluted. In Alaverdi, both distance and elevation were statistically significant predictors for elevated arsenic and lead levels in residential soil. In Alaverdi, the PCA resulted in three components, one of which consisted of As, Pb, Mn, Cu and Zn, suggesting influence of copper-smelter emission on contamination. In Akhtala, the PCA resulted in four components. Anthropogenic influence was found in two components. One was related to the operation of a smelter during the Armenian Bagratid dynasty in the 10th century (the component consists of Pb, Cu, Zn and Ba) and the other, to later industrial activities (the component consists of As, Cr, Ti, Fe and Co).This study contributes to the evidence on levels of environmental contamination in mining and smelting communities worldwide.

Incorporating life cycle assessment with health risk assessment to select the ‘greenest’ cleanup level for Pb contaminated soil

Green and sustainable remediation (GSR) has emerged as one of the most important pioneering directions in the environmental remediation field. The GSR concept calls for maximizing the ‘net environmental benefit (NEB)’ by taking into account not only the environmental benefit, but also the life cycle environmental cost of remediation operations. However, existing literature to date has not examined how cleanup levels may affect the NEB. In this paper, we proposed a framework that combines life cycle assessment with health risk assessment to derive cleanup levels for remediating contaminated land. This method goes beyond the traditional approach, which focuses on acceptable risk levels to site users. It takes into account the number of potential receptors, as well as life cycle secondary environmental impacts, in order to select the ‘greenest’ cleanup level which maximizes the NEB. A case study was conducted using this framework for a school site with Pb contamination. In comparison with the regulatory guidance value of 255 mg/kg applicable at the time of project implementation, the newly selected optimum cleanup level of 800 mg/kg could increase the NEB by 3%, while reducing economic costs by 36%. The study indicated that as the cleanup level became more stringent, the detrimental secondary impacts of remedial operations increased exponentially, whilst the beneficial primary impact tailed off with diminishing returns. It also showed that more stringent criteria would lead to the cleanup of more widespread areas contaminated by diffusive sources rather than point sources. Overall, the study confirmed our hypothesis that an optimum cleanup level exists when considering both environmental benefit and environmental cost, and the ‘greenest’ cleanup level could be quantitatively determined by calculating NEBs with the proposed framework.

An evaluation of different soil washing solutions for remediating arsenic-contaminated soils

Soil washing is a promising way to remediate arsenic-contaminated soils. Most research has mostly focused on seeking efficient extractants for removing arsenic, but not concerned with any changes in soil properties when using this technique. In this study, the removal of arsenic from a heavily contaminated soil employing different washing solutions including H3PO4, NaOH and dithionite in EDTA was conducted. Subsequently, the changes in soil physicochemical properties and phytotoxicity of each washing technique were evaluated. After washing with 2 M H3PO4, 2 M NaOH or 0.1 M dithionite in 0.1 M EDTA, the soil samples’ arsenic content met the clean-up levels stipulated in China’s environmental regulations. H3PO4 washing decreased soil pH, Ca, Mg, Al, Fe, and Mn concentrations but increased TN and TP contents. NaOH washing increased soil pH but decreased soil TOC, TN and TP contents. Dithionite in EDTA washing reduced soil TOC, Ca, Mg, Al, Fe, Mn and TP contents. A drastic color change was observed when the soil sample was washed with H3PO4 or 0.1 M dithionite in 0.1 M EDTA. After adjusting the soil pH to neutral, wheat planted in the soil sample washed by NaOH evidenced the best growth of all three treated soil samples. These results will help with selecting the best washing solution when remediating arsenic-contaminated soils in future engineering applications.

Practical Perspectives of 1,4‐Dioxane Investigation and Remediation

1,4‐Dioxane (dioxane) is a contaminant of emerging concern that is classified by the U.S. Environmental Protection Agency as a likely human carcinogen. Dioxane has been used as a minor or major ingredient in many applications, and is also generated as an unwanted by‐product of industrial processes associated with the manufacturing of polyethylene, nonionic surfactants, and many consumer products (cosmetics, laundry detergents, shampoos, etc.). Dioxane is also a known stabilizer of chlorinated solvents, particularly 1,1,1‐trichloroethane, and has been commonly found comingled with chlorinated solvent plumes. Dioxane plumes at chlorinated solvent sites can complicate site closure strategies, which to date have not typically focused on dioxane. Aggressive treatment technologies have greatly advanced and are clearly capable of achieving lower parts per billion cleanup criteria using ex situ advanced oxidation processes and sorption media. In situ chemical oxidation has also been demonstrated to effectively remediate dioxane and chlorinated solvents. Other in situ remedies, such as enhanced bioremediation, phytoremediation, and monitored natural attenuation, have been studied; however, their ability to achieve cleanup levels is still somewhat questionable and is limited by co‐occurring contaminants. This article summarizes and provides practical perspectives on dioxane analysis, plume stability relative to other contaminants, and the development of investigation tools and treatment technologies.

Evaluating the spatial distribution of pollutants and associated maintenance requirements in an 11 year-old bioretention cell in urban Charlotte, NC

Bioretention cells (BRCs) are an increasingly popular Stormwater Control Measure used to mitigate the hydrologic and water quality impacts of urbanization. Previous BRC research has demonstrated a strong capacity for pollutant removal; however, long-term sequestration of pollutants within soil media can elevate concentrations to levels fostering environmental and human health risks. Soil media samples were collected from an 11 year-old BRC in Charlotte, NC, and analyzed for the accumulation and spatial distribution of zinc, copper, and phosphorus. Pollutant distribution varied significantly with respect to depth and ordinate distance from the BRC inlet. Zinc concentrations (0.9–228.6 mg kg−1 soil) exceeded environmental thresholds and phosphorus concentrations (5.1–173.3 mg kg−1 soil) increased from initial levels by a factor of seven; however, notable accumulation was restricted to the BRC forebay. Maximum zinc and copper concentrations in soil media did not exceed 1% of mandatory cleanup levels and with regular maintenance of the forebay, the effective life of BRC media should exceed the life of the developments they treat.