Question

describe how groundwatersl samples are collected and list what parameter needs to be monitored before samples can be collected

Answer 1

Purging is done prior to collecting sample. The purpose of well purging before groundwater sampling is to ensure that the samples will be representative of the groundwater and contaminant levels in the vicinity of the well. In the field, before sampling any groundwater, the well must first be purged until pH, specific conductance (SC) and temperature (T) readings stabilize. The purpose of
wellbore purging is to evacuate the stagnant water in the well casing prior to sampling so
as to provide a representative sample of in-situ groundwater with minimum disturbance of the flow system and the collected sample.

groundwater samples are collected by following methods

1.low flow sampling

In this method GW samples are collected for a specific depth within a well screen interval. The rate of removal must be kept minimum so that the sampling pump will not draw stagnant water from the water column above and below the pump. This method is most applicable to aquifer with medium to high permeability. Low flow purging is done prior to low flow sampling. Positive displacement pumps are used for low flow sampling.

2. Peristaltic pump sampling

Peristaltic pumps are compact having few moving parts and portable. It operates by a circular motion creating a vacuum in an intake line drawing from the monitoring well. The vacuum draws groundwater up to the pump, where the water is dispensed from the end of the tubing. Tubing used for peristaltic pump sampling should be disposed of after one use.

3. Bailer Sampling

The bailer consists of a rigid tube with a check valve at the bottom and a means to attach a line to the top. The check valve allows water in to the interior chamber of the bailer as it is lowered into the saturated zone. When the bailer is raised the check valve is forced shut and a water sample can be retrieved from the well. The check valve allows water in to the interior chamber of the bailer as it is lowered into the saturated zone.

Parameters need to be monitored before collecting samples are :

Measurements of pH, temperature, and specific conductance are used to establish that the well has stabilized before sampling may begin. Other parameters, such as oxidation
reduction potential, alkalinity, and dissolved oxygen, are measured at the time of
sampling because the dissolved gases may react during the holding time.Prior to going to field for collecting samples all the equipments and their power supply must be checked.