After reading this article you will learn about method of sampling for still water and well.
Sample Collecting Method for Still Water:
In still water, samples generally are collected at multiple sites and at multiple depths. The number of sampling sites and the depths where samples will be collected is depending on objectives and the physical, chemical, and biological characteristics of the water body.
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Thief-type samplers are usually used to collect still water samples:
Collection of samples from still water:
i. For organic compounds:
Select equipment with fluorocarbon polymer, glass, or metal components if components will directly contact samples to be analyzed for organic compounds. Do not use plastics other than fluorocarbon polymers.
ii. Inorganic constituents:
Select equipment with components made of fluorocarbon polymer or other relatively inert and uncolored plastics or glass if components will directly contact samples to be analyzed for inorganic constituents. Do not use metal or rubber component for trace-element sampling.
(i) Thief-Type Sampler:
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If the sampler operates as a point-source bailer, follow below mentioned steps. Pulling the bailer up will trigger the upper check valve to seal off the sample from the water overlying the targeted depth.
a. Lower opened sampler to the desired depth while minimizing disturbance of the water column.
b. Isolate the sample by activating the mechanism that closes the sampler.
c. Raise the sampler from the water body.
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d. Dispense sample to sample bottle or composting/splitting device using CH/DH techniques.
i. If using a bailer, drain sample through the bottom-emptying device.
ii. If sample compositing and (or) splitting is required, ensure that all particulates in the sampler are transferred with the sample by swirling the sample gently to keep particulates suspended and pouring the sample quickly into the churn or cone splitter.
e. Repeat steps a through d if more sample is needed from the same depth for that vertical section.
(ii) Pump Sampler:
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a. Lower the pump or pump-sample tubing (attached to a weighted line) to the desired sampling depth.
b. Turn on the pump about three sample-tubing volumes to field rinse the pump, tubing, and other sample-collection or -processing equipment. Discard rinse water.
c. Direct sample flow into collection container(s) until sufficient sample volume has been collected.
d. Repeat steps a through c, if another depth and (or) vertical section is to be sampled.
If a second sample from a different depth or vertical section will be composited, either:
(1) Clean and field rinse the splitter after processing the first sample and before collecting the second sample, or
(2) Use another clean splitter.
Sampling from Well:
Well purging removes standing water from the borehole. The purpose of purging is to reduce chemical and biochemical artifacts caused by the materials and practices used for well installation, well construction and well development, and by reactions occurring within an open borehole or annular space between a well casing and borehole wall.
The purging process forms a continuum with that of sample withdrawal. Sample withdrawal is the process by which sample water transported for collection and processing, after the well has been purged.
Purge volume and purge time could be estimated by following method:
