Chloride Dispersion across Silt Deposits in a Glaciated Bedrock River Valley

Abstract

Soil and groundwater from the Neponset River floodplain deposit that receive high concentrations of deicing agents from nearby highways were investigated. The silty sand floodplain is separated by a silty aquitard from the underlying aquifer that serves as a public water supply. We made a transport-based assessment of the capacity of the aquitard to protect the underlying aquifer. One hundred seventeen soil samples and 469 groundwater samples collected during a period of 4 yr from boreholes and 10 wells grouped in two well clusters were analyzed for dissolved Cl concentration. The soil characterization and groundwater monitoring results agreed, showing a very slow change in subsurface Cl contamination with time. These data also calibrated a vertical one-dimensional advective-dispersive transport model across the deposits. Advective transport dominated only in the top 3.37 m of the floodplain deposit, with dispersion being the main transport mechanism below this depth. Due to the silty nature of the aquitard, dispersion rather than diffusion was the main transport mechanism into the floodplain-aquitard system. Soil and groundwater quality data confirmed a Cl concentration at the floodplain surface near the highway runoff drainage outlets of 2450 mg L. The model estimated a vertical dispersivity at the site of 8 mm and a vertical hydrodynamic dispersion coefficient of 3.71 × 10 m s. These data confirmed the aquitard's capacity to contain deicing agents, protecting the underlying aquifer from contamination.

Remediation Potential of Borehole Thermal Energy Storage for Chlorinated Hydrocarbon Plumes: Numerical Modeling in a Variably-Saturated Aquifer

“…As a consequence, natural attenuation of the contaminant plume through volatilization and subsequent release into the atmosphere is a rather slow process. The above conclusion is expected to be valid in most subsurface conditions since the vertical dispersivity of 0.05 m assumed in this study is already a relatively high value in natural aquifers (Rotaru et al, 2014). molar fractions in both liquid and gas phases.…”

A simple contaminant fate and transport modelling tool for management and risk assessment of groundwater pollution from contaminated sites

“…Vertical dispersivity (z) 0.005 m f) a) Ratio of molar masses: Y VC-DCE = (62.5 g/mol) / (96.4 g/mol) b) Assessed from soil and water concentrations found from site descriptions in Jørgensen et al (2007a;2007b) c) Assumed to be the same as I d) Assessed from site descriptions in Jørgensen et al (2007a;2007b) e) Assessed from site description in Jørgensen et al (2007a;2007b) using Darcy's Law f) Chosen from an interval found from a literature review (Chiang et al, 1989;Mallants et al, 2000;Rivett et al, 1994;Robertson et al, 1991;Rotaru et al, 2014;Schulze-Makuch, 2005). Intervals are: α L 0,2-1 m, α T 0,0025-0,3 m, and α V 0,008-0,01 m. Figure 7a shows the vertical model results and the observed concentrations.…”

Screening and Degradation Mechanism of a Cold‐Resistant Nitrobenzene‐Degrading Microorganism

“…Less attention has been given to the degradation of nitrobenzene at low temperature. In nature, most soil and groundwater temperatures are around 10 to 12 8C, with the annual change , 0.1 8C (Wang et al, 2005;Rotaru et al, 2014;Kurylyk et al, 2013;Gunawardhana and Kazama, 2011;Wang et al, 2014). This temperature is inhibitory to the growth and metabolism of most microorganisms; this, in turn, greatly compromises their ability to degrade organic matter (Nemecek-Marshall et al, 1993;Lu et al, 2010;Wu et al, 2006;Cindy et al, 2014).…”