Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p41
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 41/117)
Character Range: 461556–464645

variety of methods depending on the level of acceptable uncertainty. Commonly used methods include:
    * literature approaches (screening level data only)
  -       literature values based on grain size/lithology descriptions
  -       hazen formula with grain size analysis
    * aquifer tests
  -       slug tests that provide an indication of local hydraulic conductivity at the well bore
    -       pumping tests that provide information on a much larger volume of aquifer compared with slug tests
    -       tracer tests (in which the travel time of a conservative anion such as chloride is monitored between two points over time to directly estimate velocity).

More information on literature-based and aquifer test methods can be found in Fetter (2001) and other standard hydrogeology textbooks.

In general, aquifer testing involves the determination of a range of hydraulic properties within an aquifer. This is accomplished by stressing the aquifer at a test well, either by the addition or removal of water (or an equivalent volume of water using a weight or 'slug') and measurement of the hydraulic response at one or more observation wells within the test area. Depending on the type of aquifer testing carried out, it is possible that groundwater monitoring wells could be used either as test wells and/or observation wells.

However, most aquifer test methods require specific well construction procedures such as screening of the full aquifer thickness. Further information on aquifer testing can be found in Standard AS 2368 (1990) and Kruseman and de Ridder (1994).

Using pumping tests to determine average hydraulic conductivity in an area of severe groundwater contamination can be undesirable (for example, where there is a risk of exacerbating DNAPL contamination) and in these circumstances less intrusive methods should be considered. Alternatively, where aquifer properties do not vary significantly, it may be possible to perform aquifer testing outside the impacted area.

8.3              Delineating groundwater contamination

    8.3.1          Lateral delineation of groundwater contamination
The groundwater monitoring bore network should cover an appropriate study area to delineate the lateral extent of the contamination; define background groundwater quality, the groundwater flow system for the geological units of interest; and to assess the risk to relevant receptors. Generally the number of monitoring wells should be sufficient to define, at an appropriate scale, the lateral and vertical extent of the plume exceeding relevant assessment levels (for example, GILs, HILs, HSLs and/or site-specific risk-based criteria) and to understand any seasonal or longer-term variation in groundwater flow direction and rate of plume advance or retreat.

For large and/or complex sites with VOCs and/or SVOCs, consideration may be given to reducing uncertainty in lateral and vertical contaminant distribution by using various screening tools to identify and delineate contamination in both the vadose and saturated zones. These tools include soil vapour