Contaminant Transport in a Municipal Drinking Water Supply: A Steady-state Approach to Estimate Rate and Uncertainty

Abstract

Contaminant transport is generally considered to be a key factor when assessing and classifying the environmental risk of polluted areas. In the study presented here, a steady-state approach was applied to obtain estimates of the transit time and concentration of the pesticide metabolite BAM (2,6-dichlorobenzoamide) at a site where it is contaminating a municipal drinking water supply. A Monte Carlo simulation technique was used to quantify the uncertainty of the results and to evaluate the sensitivity of the used parameters. The adopted approach yielded an estimated median transit time of 10 y for the BAM transport from the polluted site to the water supply. Soil organic carbon content in the unsaturated zone and the hydraulic conductivity in the saturated zone explained 44% and 23% of the uncertainty in the transit time estimate, respectively. The sensitivity analysis showed that the dilution factor due to regional groundwater flow and the soil organic carbon content at the polluted site explained 53% and 31% of the uncertainty of concentration estimates, respectively. In conclusion, the adopted steady-state approach can be used to obtain reliable first estimates of transit time and concentration, but to improve concentration predictions of degrading contaminants, a dynamic model is probably required.

Modeling subsurface transport in extensive glaciofluvial and littoral sediments to remediate a municipal drinking water aquifer

“…A former forest-plant nursery situated in Piparböle, about 1.5 km up-gradient from the water-extraction wells ( Fig. 2), is the source of the contaminant (Bergvall et al, 2007). The nursery, which was active between 1956 and 2002, cultivated mainly spruce and pine seedlings.…”

“…2), soil samples were collected at 40 cm intervals, down to the groundwater table, in November 2003. Details of the sampling have been reported previously (Bergvall et al, 2007) and the results are summarized in Table 1. The soil water content was first analyzed every 0.2 m by the oven-drying The water content data obtained by the oven-drying method was used to calibrate the vadose zone model.…”

“…We estimated the drainage from the stream to the aquifer by measuring the stream discharge above and below the aquifer-crossing, Table 1. Analysis of soil samples taken in six, 5 to 10 m deep, soil profiles from the nursery site, including data from Bergvall et al (2007), and slug tests carried out in the aquifer (Fig. 2).…”

“…This means that 19 kg of the active substance, dichlobenil, was applied to 4 % of the total nursery area between 1976 and 1991; this is considered to be a conservative estimate (Bergvall et al, 2007). However, since the soil has been repeatedly mixed over the years, we assumed the same load of pesticide over the entire nursery area (i.e.…”

“…Pesticides and their degradation products are some of the most common contaminants reported in European countries (Lapworth et al, 2006;Cerejeira et al, 2003;Papastergiou and PapadopoulouMourkidou, 2001;Schiavon et al, 1995) and in the US (Barbash et al, 2001;Kolpin et al, 1998). In Sweden, there are about 1900 municipal drinking-water plants that draw their supplies from natural or artificial groundwater.…”