SAMPLING PLAN
It is important to prepare a good sampling plan. The plan will describe where, what, why, how and when you will be sampling, and who will be doing it. The sampling plan should be prepared in consultation with stakeholders and field and laboratory technicians. The main steps associated with groundwater sampling are presented in Figure 2, and such planning is the first step in this workflow.
When designing a monitoring or sampling plan, issues of possible hazards as well as standard behaviour at the sampling site should be considered. By observing basic safety rules you will minimise the risk of accidents and ensure safety of the members of your sampling group.
Build your groundwater sampling plan around the following questions (modified from Waterwatch (2005)).
• Why are you field sampling?
• Who will use your data?
• How will the data be used?
• How will the data be achieved?
• What will you sample?
• What data quality do you require?
• What methods will you use?
• Where will you sample?
• How will the sample be preserved?
• When and how often will you sample?
• Who will be involved and how?
• How will the data be managed and reported?
• How will you ensure your data are credible?
• What potential hazards are there associated with the sampling?
• How can these hazards be mitigated?
CRITERIA FOR SAMPLING
Existing bores in a study area largely define the potential sites for groundwater sampling, however natural features (such as springs) or artificial features (such as mine shafts or pits) can also be used for groundwater access. It is a common practice to sample surface water bodies and rainfall to integrate with the groundwater chemistry. Different criteria can determine which bores are to be sampled, including the:
• spatial and depth distribution allowing reasonable representation across and within the target aquifer(s)
• spatial distribution to allow development of cross sections parallel and perpendicular to regional groundwater flow paths
• depth to water level ranging from shallow to deep groundwater systems (including perched and multiple aquifers). Some nested or multi-stemmed piezometers may need to be sampled to investigate chemical variations with depth (from the shallow watertable aquifer to deeper confined systems)
at a site
• representation of the various land uses covering broad acre agriculture, various crops types, irrigation practices, industrial or urban areas. Sampling needs to be carried out to address the groundwater contamination potential with particular reference to nutrients, pathogens and pesticides
• representation of sampling to describe the recharge and nature and extent
of groundwater/surface water interaction. Hence, bores may be selected on
the basis of being close to surface water sites (such as streams, lakes, wetlands and estuaries)
• representation of the diversity of groundwater use in the area, including irrigation, stock, domestic and town water supply, and
• logistical issues that define bore accessibility, such as bore ownership, operating condition, road access and the existence and nature of bore equipment (such as an installed pump).
FREQUENCY AND DURATION OF SAMPLING
The frequency and duration of groundwater sampling (Table 2) is an important issue that should be considered when designing a sampling plan. For example, if the monitoring is for a basic groundwater resource assessment it is recommended quarterly sampling for groundwater levels, annual sampling for basic quality indicators (e.g., electrical conductivity (EC) and temperature (T)) and as-need basis for other quality parameters (Table 2). Collection of long-term (one or more decades) water level data is recommended for better understating issues associated with groundwater availability and sustainability (USGS, 2001).
Table : Indicative monitoring frequency for various groundwater monitoring purposes (adapted from
Timms et al., 2009).
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* Including barometric pressure measurement at the bore site, # NSW Groundwater Quality Protection Policy,
^ Depending on Groundwater Quality Protection Level.
** Selection of appropriate water quality parameters for testing depends on the purpose of monitoring, possible contaminants and constraints on the cost of analyses.
Figure : Steps in groundwater sampling
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