Dilution and volatilization of groundwater contaminant discharges in streams

Abstract

An analytical solution to describe dilution and volatilisation of a continuous groundwater contaminant plume into streams is developed for risk assessment. The location of groundwater plume discharge into the stream (discharge through the side versus bottom of the stream) and different distributions of the contaminant plume concentration (Gaussian, homogeneous or heterogeneous distribution) are considered. The model considering the plume discharged through the bank of the river, with a uniform concentration distribution was the most appropriate for risk assessment due to its simplicity and limited data requirements. The dilution and volatilisation model is able to predict the entire concentration field, and thus the mixing zone, maximum concentration and fully mixed concentration in the stream. It can also be used to identify groundwater discharge The dilution model can also provide recommendations for sampling locations and the size of impact zones in streams. This is of interest for regulators, for example when developing guidelines for the implementation of the European Water Framework Directive.3

Legacy of a Chemical Factory Site: Contaminated Groundwater Impacts Stream Macroinvertebrates

“…The concentration of VC in the HZ at S4 exceeded the Danish groundwater quality criterion (0.2 µg L -1 ) by up to a factor of 1,000 (Table 1). The decreasing concentrations of chlorinated compounds downstream of the site S4 probably reflect a combination of volatilization (Aisopou et al 2015) and dilution due to significant inflow of less contaminated GW (see Table 3). The overall stream discharge increased approximately 100% from the upstream location S7 to the downstream site S1.…”

Contaminant mass discharge to streams: Comparing direct groundwater velocity measurements and multi-level groundwater sampling with an in-stream approach

“…The contaminant mass discharge is defined as the total contaminant mass per unit time that passes through a control plane that is oriented perpendicular to the groundwater flow direction, and that extends over the entire width and depth of the plume (Basu et al, 2006;ITRC, 2010). When assessing the risk posed to a stream, the contaminant mass discharge is especially us eful, since it can be used to simulate prospective in-stream contaminant concentrations (Aisopou et al, 2015).…”

Evidence of Spatio‐Temporal Variations in Contaminants Discharging to a Peri‐Urban Stream

“…A preliminary conceptual model was developed using extra stream water samples (in addition to the first set of measurements collected), which consisted of five points along each of the first five transects (T1–T5, Figure ) in order to document the mixing pattern of the CAHs in the stream water. This was supported by application of a 2D advection‐dispersion model of pollutant mixing in streams (Aisopou et al ; Lemaire ) to evaluate the potential location of the discharge to the stream from source zone A (i.e., with respect to chainage, streambed or streambank seepage), and to estimate the CMD and mixing conditions. These results were then used to design all other monitoring campaigns: these consisted of three points per transect for transects T1 and T4, and one point in transect T6 and T7 where fully mixed conditions (see In‐Stream Contaminant Mass Discharge section) were achieved (see Figure for all transect locations).…”

“…The in‐stream concentration is generally dependent on both the transverse and depth location of the sample within a control transect. For most streams, however, the depth is usually small compared to the width and the vertical mixing occurs over a relatively short distance (Fisher ; Aisopou et al ). At a certain distance, downstream of the discharge location, the contaminant will therefore be completely mixed in the vertical direction and the contaminant concentration is then only dependent on the transverse location of the sample.…”