Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p42
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 42/117)
Character Range: 464371–467374

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 sampling (refer Section 9) and the membrane interface probe (MIP) and laser-induced fluorescence (LIF) tools (refer Sections 7.2.4 and 7.2.5 respectively). These tools can also be used in a reactive or adaptive field sampling program.

Although the number of bores, locations, depths and screen intervals are site-specific, groundwater site investigations require as a minimum:
    * one upgradient bore to establish the quality of groundwater entering the site (one for each aquifer or geological unit of interest)
    * two or three bores to monitor groundwater quality immediately downgradient and also lateral to each contaminant source (for each aquifer or geological unit of interest).
Sites with significant contamination and/or complex hydrogeology will require numerous bores at various depths to assess the lateral and vertical extent of contamination and the nature of any temporal variation.

The initial investigation bores should be:
    * close to each potential contamination source
    * installed with similar construction techniques to minimise sources of variation and uncertainty in the data
and, where appropriate,
    * screened across the water table to locate any LNAPL and to identify contamination derived primarily from surface spills and leaching.
The number, spacing and depth of follow-up wells are site-specific considerations that should be informed by the CSM. The installation of bores without consideration of hydraulic gradient and conductivity values may result in bores being sited at improper spacings.

However, as a general guide for plumes estimated to be <200 m long, well spacing should be of the order of 2050 m in the direction of groundwater flow and 1020 m perpendicular to flow. Well spacing should generally be less than 10 m for the delineation of source zones.

Consideration should be given to installing one or more 'sentinel' wells to monitor the migration of an expanding or detached plume or to provide confirmation of the continued absence of contamination at a particular location. For example, in some situations it may not be possible to delineate the position of the contaminant plume front due to logistical constraints such as the presence of buildings. However, in this case an acceptable approach would be to install sentinel wells upgradient of the relevant receptors to provide an early warning of any significant plume advance. The location of the sentinel wells would ideally allow the implementation of management actions to protect the receptor if the plume were to advance significantly.

    8.3.2          Vertical delineation of groundwater contamination
Source: Clements et al. (2009)
Delineation of vertical variability in groundwater chemistry is