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Mercury is a toxin that causes neurological impairments in adults, is particularly harmful for fetuses and children, and is deadly in severe cases, making it a worldwide health concern. Methylmercury (MeHg) is the environmentally relevant form of mercury (Hg) because it biomagnifies along the food chain. Methylmercury is mainly produced in aquatic sediments via methylation of inorganic Hg (Hg(II)) and transformed back via demethylation. Because transformation rates determine MeHg concentrations, quantification of methylation and demethylation rates is needed to inform management of MeHg. Published rate constants for Hg(II) methylation ( k m ) and MeHg demethylation ( k d ) vary greatly, stemming partly from differences in experimental methods. We conducted a comprehensive review of rate laws, evaluated published rate constants, and performed biogeochemical simulations to assess variability in reported k m and k d. Based on selected studies employing the same pseudo-first-order rate law and similar experimental methods, we found that k m = 0.04 ± 0.03 d − 1 is a reasonable range for wetland sediments. Over a number of environments, maximum k d was smaller at sites without Hg source ( k d = 0.5 d − 1 ) than at sites with identified Hg source ( k d = 1.8 d − 1 ). Larger variability and higher uncertainty in k d compared to k m highlight the need for more research on MeHg demethylation rates. This critical review: (a) aids the design of future experimental studies of k m and k d ; (b) provides guidance for comparing rate constants from different studies; (c) presents a biogeochemical reaction model to assess rate constants; and (d) informs selection of k m and k d values from the literature for use in model simulations. [ABSTRACT FROM AUTHOR]

Groundwater professionals require tools to evaluate a variety of technical issues related to per‐ and polyfluoroalkyl substances (PFAS). These include the potential impact of PFAS precursors on groundwater plumes of perfluoroalkyl acids (PFAAs). Numerical modeling results show that, by adjusting the mass loading rate, source zones with or without a precursor can produce similar PFAA plumes. However, if a precursor is present, it can impact PFAA plume concentrations and extend PFAA plume durations by decades. Additional research regarding in situ precursor transformation rates—and improvements in source area characterization—will further advance the predictive value of modeling. [ABSTRACT FROM AUTHOR]

Introduction Quality assurance and graphical presentation for ground water analyses are routine and yet essential tasks for anyone dealing with water quality and water chemistry (Drever 1997; Langmuir 1997). These [...]

Onondaga Lake is a 12-square-kilometer urban lake located in Syracuse, New York, USA. The legacy of industrialization and municipal development since the late nineteenth century resulted in impaired water quality and contamination of lake sediments. A comprehensive lake restoration plan was developed following two decades of intensive multidisciplinary technical studies. The restoration plan includes removal of approximately 1.5 million cubic meters of lake sediments (completed November 2014, one year ahead of schedule); transport of the dredge slurry through a 6.5-kilometer-long, double-walled pipeline; and dewatering in geotextile tubes strategically placed in a dedicated 20-hectare upland confined facility. More than 160 hectares of the lake received an engineered cap to isolate the remaining contamination after dredging and provide a habitat restoration surface. The deepest portion of the lake will be monitored for ongoing natural recovery. The restoration and design process involved close coordination and discussions with multiple regulatory agencies and stakeholders and was supported by several technical studies, including: 1) development of sediment and fish tissue remedial goals; 2) detailed evaluations of capping, dredging and upland containment, natural recovery, and nitrate addition to the lower part of the lake water column (to limit production of methyl mercury); and 3) integration of habitat restoration into the lake-wide cleanup effort. As one of the largest sediment capping projects constructed to date, the multi-function cap design incorporated several innovative components, including site-specific biodegradation and reactive media (activated carbon [AC] for contaminant sequestration and siderite amendment for pH control) to ensure remedial performance requirements for long-term chemical isolation and habitat restoration were met. The innovative capping concepts were developed through multiple years of field investigations, laboratory and bench-scale studies, and field pilot testing. In addition, state-of-the-science contaminant migration and cap effectiveness modeling studies were conducted to evaluate the required layering of the cap and to optimize the amendment media and required dosage for the various layers. Successful integration and regulatory acceptance of these unique design features provided opportunities for significant optimization of raw material needs (cap thickness and amendment dose). The innovative study methods also resulted in streamlined and efficient construction, while retaining environmental effectiveness. Construction began with a field pilot project in 2011, followed by full-scale field implementation in 2012; sediment removal was completed in 2014 and lake capping was completed in 2016. Details of the study methodology, analysis of amendment and cap effectiveness (laboratory testing and modeling), and construction verification methods and monitoring results are presented in this paper. [ABSTRACT FROM AUTHOR]

The article provides information that would be of great help to engineer or site evaluator in making a preliminary determination as to whether in situ bioremediation (ISB) has potential for cleaning up a particular site. Bioremediation is the process by which living organisms act to transform or degrade contaminants. ISB is effective when various microbiological, chemical, hydrogeological, geological and engineering elements are coordinating to create and optimize subsurface conditions.

Amending soils with mineral-based materials to immobilize contaminants is both old and new. Although mineral amendments have been used for decades in agriculture, new applications with a variety of natural and reprocessed materials are emerging. By sequestering contaminants in or on solid phases and reducing their ability to partition into water or air, amendments can reduce the risk of exposure to humans or biota. A variety of mineral types are commonly used to amend contaminated soils, with different modes of molecular-scale sequestration. Regulatory, social, and economic factors also influence decisions to employ mineral amendments as a treatment technology.