Monitored Natural Attenuation to Manage PFAS Impacts to Groundwater: Scientific Basis

Sites impacted by per- and polyfluoroalkyl substances (PFAS) pose significant challenges to investigation and remediation, including very low cleanup objectives, limited information on natural PFAS degradation processes in the subsurface, and the apparent mobility and persistence of PFAS. Consequently, monitored natural attenuation (MNA) may be considered less applicable to PFAS compared to biodegradable classes of chemicals such as petroleum hydrocarbons and chlorinated solvents that can completely biodegrade to innocuous end products. However, MNA has proven effective for certain non-degrading metals, metalloids, and radionuclides (e.g., chromium, arsenic, and uranium). To assess the applicability of MNA to PFAS, this paper reviews the fate and transport properties of PFAS in conjunction with the various physiochemical factors that control the subsurface movement of chemicals. This analysis demonstrates that two important retention processes: (1) chemical retention in the form of PFAS precursors, and (2) geochemical retention in the form of sorption and matrix diffusion to mitigate the movement and potential impacts of PFAS in groundwater that may form the scientific basis for applying MNA to PFAS contamination. This paper describes the scientific and regulatory basis for using MNA to manage PFAS-impacted groundwater.     

New maturation parameters based on naphthalene and phenanthrene isomerization and dealkylation processes aimed at improved classification of crude oils (Southeastern Pannonian Basin,Serbia)

Aiming at improved classification of crude oils, naphthalene and phenanthrene isomerization and dealkylation processes were considered in detail as a possible basis to select new maturation parameters. Crude oils originating from the Banat depression (Southeastern Pannonian Basin, Serbia) were used as objects of our study. Four new maturation parameters are proposed in this paper. Two of them are based on dimethylnaphthalene (DMN) and trimethylnaphthalene (TMN) isomerization reactions: DN_x = (1,3-DMN + 1,6-DMN)/(1,4-DMN + 1,5-DMN) and TNy = (1,3,6-TMN + 1,3,7-TMN)/(1,3,5-TMN + 1,4,6-TMN). The other two are based on demethylation of dimethyl-and trimethylphenanthrenes (DMP and TMP) into corresponding methylphenanthrenes (MP): MDR = ΣMP/ΣDMP and MTR = ΣMP/ΣTMP. The new parameters’ advantageous applicability was demonstrated by factor analysis, comparing them with maturation parameters known from literature. The text was submitted by the authors in English.     

Geochemical investigation and characterisation of Neogene sediments from Valjevo-Mionica Basin (Serbia)

Sediments from the Valjevo-Mionica Basin of Neogene age were investigated in this study using different geochemical methods. The results of the inorganic part analyses suggest that during genesis of the sediments, the contents of Na₂O, B and As changed the most, which indicates that genesis of the investigated sediments was followed by climate changes and volcanic activity. The quantity of other macro- and microelements did not vary significantly. Investigations of the organic substance showed that it is native organic matter, which has been preserved to a significant extent, formed predominantly of algal precursor organisms, which provided good quality, deposited under reducing conditions and that it is at a low maturity level. As it has been established that genesis of the investigated sediments was mostly affected by an arid climate with more intensive salinity, the aim of this study, was also to identify the processes which were the most affected by the change in salinity, as well as biomarkers which are the most sensitive to this change. The results led to the conclusion that the salinity increase in the depositional environment had a primary effect on the preservation of the organic substance and the formation of the mineral searlesite. In addition, it was noticed that besides the Sq/nC₂₆ ratio, the parameters nC₁₇/nC₂₇, CPI and Ph/nC₁₈, are also significantly sensitive to salinity change in a depositional environment in case of immature organic substance deposited under reducing conditions.     

Experimental study of rill bank collapse

Rill bank collapse is an important component in the adjustment of channel morphology to changes in discharge and sediment flux. Sediment inputs from bank collapse cause abrupt changes in flow resistance, flow patterns and downstream sediment concentrations. Generally, bank retreat involves gradual lateral erosion, caused by flow shear stress, and sudden bank collapse, triggered by complex interactions between channel flow and bank and soil water conditions. Collapse occurs when bank height exceeds the critical height where gravitational forces overcome soil shear strength. An experimental study examined conditions for collapse in eroding rill channels. Experiments with and without a deep water table were carried out on a meandering rill channel in a loamy sand and sandy loam in a laboratory flume under simulated rainfall and controlled runon. Different discharges were used to initiate knickpoint and rill incision. Soil water dynamics were monitored using microstandpipes, tensiometers and time domain reflectometer probes (TDR probes). Bank collapse occurred with newly developed or rising pre‐existing water tables near rill banks, associated with knickpoint migration. Knickpoint scour increased effective bank height, caused positive pore water pressure in the bank toe and reduced negative pore pressures in the unsaturated zone to near zero. Matric tension in unsaturated parts of the bank and a surface seal on the ‘interrill’ zone behind the bank enhanced stability, while increased effective bank height and positive pore water pressure at the bank toe caused instability. With soil water contents >35 per cent (sandy loam) and >23 per cent (loamy sand), critical bank heights were 0·11–0·12 m and 0·06–0·07 m, respectively. Bank toe undercutting at the outside of the rill bends also triggered instability. Bank displacement was quite different on the two soils. On the loamy sand, the failed block slid to the channel bed, revealing only the upper half of the failure plane, while on the sandy loam the failed block toppled forwards, exposing the failure plane for the complete bank height. This study has shown that it is possible to predict location, frequency and magnitude of the rill bank collapse, providing a basis for incorporation into predictive models for hillslope soil loss or rill network development. Copyright © 2006 John Wiley & Sons, Ltd.     

A simple method for effective multi-site generation of stochastic hydrologic time series

This paper presents an algorithm for generating stationary stochastic hydrologic time series at multiple sites. The ideas in this paper constitute a radical departure from commonly accepted methodologies. The approach relies on the recent advances in statistical science for simulating random variables with arbitrary marginal distributions and a given covariance structure, and on an algorithm for re-ordering the generated sub-sets of each synthetic year of data such that the annual auto-correlation of desired lag is maintained, along with the autocorrelations between the end of the preceding year and the beginning of the current year. The main features of the proposed algorithm are simplicity and ease of implementation. A numerical test is presented containing the generation of 1000 years of weekly stochastic series for four sites based on the 84 years of historical natural weekly flows from Southern Alberta in Canada.     

Analysis of the Relationship Between the Solar X-Ray Radiation Intensity and the D-Region Electron Density Using Satellite and Ground-Based Radio Data

Increases in the X-ray radiation that is emitted during a solar X-ray flare induce significant changes in the ionospheric D region. Because of the numerous complex processes in the ionosphere and the characteristics of the radiation and plasma, the causal-consequential relationship between the X-ray radiation and ionospheric parameters is not easily determined. In addition, modeling the ionospheric D-region plasma parameters is very difficult because of the lack of data for numerous time- and space-dependent physical quantities. In this article we first give a qualitative analysis of the relationship between the electron density and the recorded solar X-ray intensity. After this, we analyze the differences in the relationships between the D-region response and various X-ray radiation properties. The quantitative study is performed for data observed on 5 May 2010 in the time period between 11:40 UT?–?12:40 UT when the GOES 14 satellite detected a considerable X-ray intensity increase. Modeling the electron density is based on characteristics of the 23.4 kHz signal emitted in Germany and recorded by the receiver in Serbia.     

A Rapid Decision Support Tool for Estimating Impacts of a Vadose Zone Volatile Organic Compound Source on Groundwater and Soil Gas

Diminishing rates of subsurface volatile contaminant removal by soil vapor extraction (SVE) oftentimes warrants an in-depth performance assessment to guide remedy decision-making processes. Such a performance assessment must include quantitative approaches to better understand the impact of remaining vadose zone contamination on soil gas and groundwater concentrations. The spreadsheet-based Soil Vapor Extraction Endstate Tool (SVEET) software functionality has recently been expanded to facilitate quantitative performance assessments. The updated version, referred to as SVEET2, includes expansion of the input parameter ranges for describing a site (site geometry, source characteristics, etc.), an expanded list of contaminants, and incorporation of elements of the Vapor Intrusion Estimation Tool for Unsaturated-zone Sources software to provide soil gas concentration estimates for use in vapor intrusion evaluation. As part of the update, SVEET2 was used to estimate the impact of a tetrachloroethene (PCE) vadose zone source on groundwater concentrations, comparing SVEET2 results to field-observed values at an undisclosed site where SVE was recently terminated. PCE concentrations from three separate monitoring wells were estimated by SVEET2 to be within the range of 6.0–6.7 μg/L, as compared to actual field concentrations that ranged from 3 to 11 μg/L PCE. These data demonstrate that SVEET2 can rapidly provide representative quantitative estimates of impacts from a vadose zone contaminant source at field sites. In the context of the SVE performance assessment, such quantitative estimates provide a basis to support remedial and/or regulatory decisions regarding the continued need for vadose zone volatile organic compound remediation or technical justification for SVE termination, which can significantly reduce the cost to complete for a site.     

Assessing the role of alkaline soils on the carbon cycle at a playa site

Alkaline soils occupy approximately 5 % of the Earth’s land surface (7 million km), and this may increase due to the global trend towards increasing desertification, yet the extent to which these soils modulate carbon dynamics on regional and global scales is inadequately studied and poorly understood. Railroad Valley (RRV) playa (Nevada, USA) is a semi-arid playa with highly alkaline soils (pH > 10) and no vegetation. The extreme, alkaline environment and absence of vascular vegetation make RRV an ideal site to investigate the role of physiochemical processes of soil-atmosphere CO₂ exchange. Both field and laboratory investigations were conducted. This work shows how the atmospheric CO₂ mixing ratio decreases at nighttime at RRV playa to a value well below the average global background CO₂ concentration. Laboratory investigations using soil samples collected at RRV playa confirmed that CO₂ uptake by RRV playa soils occurs when temperatures are decreased. Both field and laboratory studies suggest that the alkaline RRV soil acts as a CO₂ reservoir during colder periods, such as at nighttime. These results highlight the importance of investigating carbon dynamics in previously understudied environments. Given how little information is available on the CO₂ flux in desert and semi-arid alkaline ecosystems lacking vegetation, our findings draw attention to these environments as becoming increasingly important for carbon fluxes on regional and global scales.     

Photocatalytic Degradation of Dye C.I. Direct Blue 78 Using TiO2 Nanoparticles Immobilized on Recycled Wool‐Based Nonwoven Material

This paper discusses the possibility of immobilization of TiO₂ nanoparticles onto recycled wool‐based nonwoven material, which can be utilized for removal of dyes from wastewater. The photocatalytic activity of TiO₂ nanoparticles deposited on the nonwoven material was evaluated in the aqueous solution of direct dye C.I. Direct Blue 78 under the UV illumination. Nonwoven material modified with TiO₂ nanoparticles provides complete removal of dye from the solution already after 4–6 h of UV illumination. However, photodegradation of the dye adsorbed on the nonwoven material was obtained within 24 h of UV illumination. The rate of dye adsorption and photodegradation depends on the amount of deposited TiO₂ nanoparticles. The increase of initial dye concentration induced decrease in photocatalytic efficiency of immobilized TiO₂ nanoparticles. The highest photodegradation rate was achieved in acidic conditions. Elevated temperatures positively affected the removal of dye from solution. Photocatalytic activity of TiO₂ nanoparticles deposited on nonwoven material was preserved after three photodegradation cycles.     

EFFECT OF ANNUAL RAINFALL AND RUNOFF COMPOSITION ON SEDIMENT YIELD IN SMALL WATERSHEDS

ＥＦＦＥＣＴＯＦＡＮＮＵＡＬＲＡＩＮＦＡＬＬＡＮＤＲＵＮＯＦＦＣＯＭＰＯＳＩＴＩＯＮＯＮＳＥＤＩＭＥＮＴＹＩＥＬＤＩＮＳＭＡＬＬＷＡＴＥＲＳＨＥＤＳＳｌｏｂｏｄａｎＰＥＴＫＯＶＩＣａｎｄＪｏｖａｎＳＴＥＦＡＮＯＶＩＣ（ＰｒｏｆｅｓｓｏｒｏｆＨｙｄｒａ...