11.1  Groundwater quality

Every three years CICL conducts a groundwater salinity survey of all piezometers in the CIA. This survey was conducted during winter 2001. In total, 216 piezometers were sampled in the upper Shepparton aquifer (5-12m piezometer depth) and 433 were sampled in the lower Shepparton aquifer (12-35m piezometer depth). Contour maps have been produced by interpolation using ArcView GIS and Spatial Analyst. Figure 11.1 shows the groundwater salinity for the 5-12m and 12-35m depth ranges.

Figure 11.1  Groundwater salinity

Table 11.1 is a summary of the data presented in Fig 4.28. It shows a breakdown of the number of piezometers in each salinity range for both 5-12m and 12-35m piezometers.

Table 11.1  Piezometer salinity data in various ranges

Figure 11.2 illustrates that from 1998 to 2001 there have been large areas experiencing increases in groundwater salinity in both the upper and lower Shepparton aquifers. The negative numbers show the areas that have experienced a decrease in groundwater salinity and the positive numbers show those areas that have experienced an increase in groundwater salinity. Substantial increases in salinity for the lower Shepparton aquifer have occurred in the western areas of the Coly and Argoon regions as well as in the middle of the Argoon region (see figure 10.1). Less extensive areas of substantial salinity increase have also been mapped in the west of the Coly and Argoon regions for the upper Shepparton aquifer. Decreases in groundwater salinity (of lesser magnitude than the increases discussed above) have occurred in both aquifers for the Boona, Coly and Yamma regions. These areas tend to lie in the east of the CIA as well as in the centre of the Coly Region. Most of the Boona region has experienced a decline in groundwater salinity.

Figure 11.2  Groundwater salinity change from 1998 to 2001

Table 11.2 indicates that most regions have experienced increases in groundwater salinity in both the upper and lower Shepparton aquifers since 1998. As is also indicated in Figure 11.2, the largest increase in groundwater salinity was calculated for the Argoon region. Most of the overall changes calculated however are not large when compared to the changes mapped for some areas in Figure 11.2, or when compared to the actual groundwater salinities mapped for the whole CIA in Figure 11.1.

Table 11.2  Median groundwater salinity (mS/cm) by region