Groundwater Sampling
Quality Control and Quality Assurance
Quality control (QC) is a set of activities to measure and reduce error in the data quality, while quality assurance (QA) is a set of procedures to ensure the proper implementation of quality control and the quality of resulting data.
Piezometer
A piezometer determines the liquid pressure in a system by measuring the height to which a column of the liquid rises against gravity. The purpose of using a piezometer is to determine the level and flow pattern of groundwater.
The most basic type of piezometer is the standpipe piezometer which consists of a filter tip joined with a riser pipe that extends to a surface. Water flows through the filter tip, into the riser pipe and the reading is obtained using a water level indicator.
Water level indicator
A water level indicator is a device consisting of a measuring probe electrode, a signal indicator, and measuring tape. The signal indicator lights up when the measuring probe electrode touches the water.
Groundwater monitoring wells
Monitoring wells are wells with a small diameter that are usually used for level monitoring and water quality analysis. It has a permeable screen section at the bottom where the water is collected. The water in the tube rises and falls following the groundwater monitoring. The water level is usually measured by a submersible pressure transmitter. The groundwater level in an area or also known as the water table can be obtained by drilling a number of monitoring wells in an area.
Bailer
A bailer is a hollow tube used for obtaining groundwater samples from monitoring wells. To obtain the sample, the bailer is attached to a bailing cord and lowered slowly down the well until the top of bailer is below the groundwater surface. When the desired depth is reached and the weight of water closed the check valve, the bailer is pulled up.
Sampling frequency
Shallow groundwater wells/piezometers (<7 m) is sampled twice a month while deep piezometers (>7 m) is sampled once a month for water quality analysis. Open drains/irrigation channels are sampled once a month, recording both primary and secondary flow.
Equipment handling
Piezometers and water wells will be sampled using contamination-free bailer. All the equipments have to be decontaminated before use by washing them in detergent solution and then rinsing with tap water, and 3 more times of rinsing with distilled water. Groundwater from water wells and piezometers will be analyzed for chemicals of concern at different levels in the saturated groundwater zone.
Maximum handling time
The maximum holding time (MHT) is the longest time a sample can be stored between sample collection and analysis, before the results are significantly affected. Nitrate ion, phosphate ion, and pesticide residue samples will be analyzed within 24 hours of collection, while bacteria samples should be analyzed within 6 hours.