Abstract
The representativity index R u is a measure used in assessing the chemical status of groundwater based on monitoring studies. This index is designed to describe the spatial homogeneity of the monitoring network. The general formula for calculating the index R u includes the following parameters: average distance to the nearest monitoring point, number of monitoring points, and size of the test area. Calculations to determine the representativity index for four different shapes of the theoretical test study with the same area and the same number of monitoring points have been done. These calculations suggest that the index value depends on the shape and the position of these points, and it is less dependent on the size of the surface. An assessment of the representativeness of the monitoring network for the different numbers and configurations of the piezometers around the Tychy-Urbanowice landfills based on the mentioned index has been done as well. The best and the worst configurations of the monitoring network for these landfill sites in mathematical terms have been presented in this paper. The results are surprising: the highest index value is obtained with a single measurement point. The calculations were performed with the area of landfill and the area limited by the range of piezometers as the exclusive test area. To choose the optimal test area, representativity indicator was calculated also for the monitoring network around waste landfills, including the buffer network behind the piezometers. The difference in the values of the representativity indicator for subsequent variants is astounding. The representativity index for the same monitoring network is about 20 % higher if we consider the test area limited by external piezometers, and higher by another 20 %, taking into account the 95-m buffer zone behind piezometers. Due to increase of the representativity index value with a different width of buffer zone, the mathematical calculations of the monitoring network’s representativeness should be supported by an analysis of the geological structure and hydrogeological conditions occurring in the analyzed area.
Highlights
The monitoring and representativeness of a sampling of groundwater is a difficult and complex process resulting from the substantial spatial variability of the groundwater composition, limited access to the aquifer and quite frequently, a conceptually inadequate model of the monitoring system with poorly defined recharge and discharge zones.It has to be mentioned that even in quite simple conditions with a limited spatial variability of groundwater composition, the reliability of three downgradient piezometers can be not appropriate from the point of view of groundwater pollution risk assessment (Witczak et al 2006).The monitoring network design depends on the objectives of the monitoring
Grath et al (2001) argued that the monitoring network, to enable a good estimate of the chemical status of groundwater, should be homogeneous, and proposed the following representativity index Ru, as a measure to evaluate this property by mathematical methods
To illustrate the behavior of the representativity index, at first we studied the relationship between different shapes of the area and the value of index
Summary
The monitoring and representativeness of a sampling of groundwater is a difficult and complex process resulting from the substantial spatial variability of the groundwater composition, limited access to the aquifer and quite frequently, a conceptually inadequate model of the monitoring system with poorly defined recharge and discharge zones. Environ Earth Sci (2016) 75:749 control the input of pollutants into the groundwater locally (point sources), and control the status of all groundwater bodies. In both cases, proper monitoring network design should include the same factors (e.g. geology, hydrogeology, recharge and discharge zones, the migration time of contaminants, land use and human impact, regulatory requirements) but could be different in some details, e.g.: the number and location of observation wells, their construction, the sampling frequency and the range of measurements taken according to environmental standards (Witczak et al 2006). A minimum number of three sampling points in groundwater monitoring network per groundwater body or potential pollution source (Grath et al 2001; Witkowski 2009) is required
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