A Guide To Water Well Casing and Screen Selection   -   35

9.4  APPENDIX IV

Water Sampling for Chemical Analysis

If possible, obtain sample bottles and directions for taking samples from the laboratory. Make arrangements to coordinate the collection, transportation, and testing of the samples so as to minimize delay in testing form pH, bacteria, and other constituents where time of standing may affect results.

When taking bacteriological samples, the bottle must be sterile and care must be exercised not to contaminate either the bottle or sample. Allow the sample tap to flow smoothly for at least one (1) minute before collecting sample. Do not flush at high rate first since this will disturb sediment in the sample pipe. Avoid touching the inside of the bottle cap or the lip of the bottle.

Samples for mineral analysis must be taken in clean bottles with plastic (non-metal) caps. Allow only enough air space for thermal expansion so as to minimize gain or loss of carbon dioxide. Avoid splashing or entraining air bubbles during collection.

When collecting samples from wells, temperature should always be taken, because this may provide a clue as to the average depth of the producing aquifers. The thermometer should have the scale engraved on the glass and the graduations should be such that you can estimate the reading to the nearest degree F. Allow the water to overflow a small plastic container (a polystyrene coffee cup is ideal). Immerse the thermometer in the cup and read the temperature after the reading has been constant for a minute or more.

Samples for dissolved oxygen are not difficult to take, but you must have the following equipment and reagents:

1. A ¼" O.D. polyethene tube that can be connected to the sample tap.
2. A special sample bottle with a tapered ground-glass stopper. It should have a capacity of approximately 250ml.
3. Three small (35 to 100ml) bottles equipped with screw-on rubber bulb dispensing pipettes. The pipettes should discharge approximately 0.5ml when the bulb is squeezed (an ordinary eye dropper is satisfactory).
   1. The first bottle contains a 40% solution of manganous sulfate MnSO42H2O.
   2. The second bottle contains alkaline iodine reagent consisting of 70gm of KOH and 150gm KI diluted to 100ml.
   3. The third bottle contains concentrated sulfuric acid. This is one of the most dangerous chemicals in common use and must be handled with great care.

Fill the sample bottle with water, using the plastic tube immersed almost to the bottom of the special bottle. Allow it to overflow so that 4 to 10 volumes have been displaced. Turn off the sample tap and withdraw the plastic tube, being careful to avoid introducing any air in the sample. Immerse the ever dropper containing the manganous sulfate under the surface of the water and add one ml (two squirts) of manganese sulfate reagent. Next add one ml of alkaline iodide reagent, taking pains to assure that no air bubbles are introduced when the reagent is added. Insert the stopper without trapping any air bubbles and mix the solution by rapidly inverting the bottle. A heavy floc of manganese hydroxide will form at this point. Allow this floc to settle for three (3) or four (4) minutes, remove the stopper carefully, add one ml of concentrated sulfuric acid. Again insert the stopper and mix by inverting the bottle.

The sample now contains a solution of iodine that is chemically equivalent to the initial dissolved oxygen. The solution is stable and can be transported to the laboratory for exact determination.

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