Vernier Water Depth Sampler User Manual

Page 3

·Tel. 1-800-299-5469 e-mail us: [email protected] visit our

O:\_VST PAPERWORK\SENSOR PAPERWORK\SENSOR BOOKLETS\WDS\150101.DOC

November 27, 2006

Obtain a water sample from a lake or stream. To measure the dissolved oxygen content,

fill a small glass bottle with the water sample. Be careful not to agitate the water or get any air
bubbles trapped in the bottle. Fill the bottle to overflowing. Make your determination of the
dissolved oxygen content using the water in this glass bottle. There are many standard chemical
tests available to make this determination. Follow the procedure presented with the test kit you
have. Remember to record the kit name on your data sheet so that others will know the test
method used.

To measure the 5 day BOD, fill a clean large jar about 3/4 full with the sample water,

cover, and shake vigorously for about one minute. Determine the amount of dissolved oxygen in
this water using standard oxygen testing procedures. Record this value on your data sheet.

Pour this aerated sample water into a smaller stoppered bottle that has been completely

wrapped in foil or painted black to keep the light out. Make sure the bottle is filled to overflowing
and that there are no trapped air bubbles present before sealing the bottle with the cap. Place the
bottle in a warm dark place for about 5 days. At the end of this time determine the dissolved
oxygen content. Subtract this value from the value recorded when the sample was new and just
shaken. This difference in dissolved oxygen levels is the 5 day BOD for the site where the sample
was taken. Record this value on your data sheet.

The following are some rough limits to compare your data with:

1 to 2 ppm BOD

Little biodegradable waste

3 to 5 ppm BOD

Relatively clean water

6 to 9 ppm BOD

High levels of waste, many bacteria

10 + ppm BOD

Extremely polluted water

pH Testing:

The pH of the water can be tested using standard pH test paper. Tear off approximately 3

inches of test paper and immerse it in the water sample. Let it stand for a few seconds then
remove it from the water and immediately compare it with the color chart found on the test paper
dispenser. Record the pH value on your data sheet. Liquid pH tests may be used to provide more
accurate results.

pH scale numbers range from 0 to 14. Pure distilled water was given the neutral pH value

of 7. The strongest acids approach 0 and the strongest bases approach 14. Pure rain has a slightly
acidic pH of 5.6. Rain and snow can pick up particles that are suspended in the air. If the rain
picks up sulfur and nitrous oxides it will be more acidic. Most fish can tolerate pH ranges from 5
to 9 but the best range falls between 6.5 and 8.2. If water that is more acidic than normal comes in
contact with certain chemicals and metals, the acid may cause these substances to become more
soluble or more toxic than normal. For instance, a fish that can stand a pH as low as 4.8 may die
at a pH of 5.5 if low concentrations of iron, aluminum, lead, or mercury are present.
Phosphates: