ISO 5667-22:2010 pdf free download – Water quality一Sampling 一 Part 22: Guidance on the design and installation of groundwater monitoring points.
4.4 Installation design
4.4.1 Monitoring point installation
There are three major types of monitoring point installation for collection of groundwater samples. These are:
a) single screened or unscreened wells, boreholes or piezometers [Figure 2 a) and b)];
b) nested piezometers in a single borehole completion [Figure 2 c)];
c) discrete horizon or multi-level samplers [Figure 2 d) and e)];
The advantages and disadvantages of each are shown in Table 4.
4.4.2 Locating response zone
The response zone is that part of the monitoring point open to the aquifer or geological formation from which a groundwater sample is to be collected. Its location is a function of the monitoring objectives, including the required depth, and the type of liquids. Factors that can influence response zone design include:
a) range of water table elevations;
b) presence of NAPL;
c) thickness of unit to be monitored;
d) hydraulic performance requirements;
e) avoidance of vertical flows and cross-contamination.
Long response zones should be avoided where possible, as these can induce vertical flow and contaminant movement and may therefore disturb the natural flow patterns and geochemistry. They may also form preferential pathways for contaminant migration. In this part of ISO 5667, long response zones are assumed to be greater than 3 m.
Where monitoring for the presence of DNAPLs is required, users should note that the lower parts of most screen lengths do not contain slots or holes, as this is where the threads are located. Where the intention is to measure DNAPL at the base of a permeable unit, the hole should be slightly over-deepened to permit DNAPL sitting at the base of the unit to enter the GQMP, although care should be taken to ensure that DNAPL does not infiltrate deeper into the aquifer system. Where this approach has been adopted, allowance should be made in subsequent measurements of DNAPL thickness to take account of the “sump” created at the bottom of the GQMP.
4.4.3 Multi-level monitoring
Multi-level monitoring (MLM) systems represent a cost-effective and efficient method of installing a number of GQMPs through an aquifer system where an understanding of vertical hydrogeological processes and contaminant distribution is required.
Introducing materials into a previously undisturbed environment can result in chemical and biological alteration of both the materials and the groundwater. This in turn may reduce material performance, e.g. through clogging or failure through weakening and collapse. If the groundwater is altered, the samples obtained may not be representative, which may compromise the objectives of monitoring. Consequently, materials and method of installation are major considerations in the design process. Some considerations are:
i) the chemical environment in which the installation is placed — aggressive environments (saline, free-phase, low or high pH) rapidly degrade or corrode some materials;
ii) effect of materials on contaminants, such as sorption, oxidation, reduction;
iii) effect of contaminants on materials: corrosion, solution, strength, leaching.