What laboratory tests must be done on grab samples?
The answer to the question is B, pH. Proper sampling is necessary for accurate laboratory analysis. Tests such as pH and dissolved oxygen must done on grab samples as the samples degrade (change) drastically over a brief period. Some analysis such as BOD and TSS can be done on composite samples which are drawn over periods of time and do not change as much. If you are unsure of what tests require grab or composite, simply review your NPDES permit. Understanding the difference between grab and composite samples and what analysis requirements are key to proper and reliable laboratory operations.
Using a flow rate of 600 gpm and a detention time of four hours, calculate the volume of the basin in gallons.
The correct answer is C, 144,000. Understanding detention time calculations can help prevent water treatment upsets and help with trouble shooting. The formula for theoretical detention time is volume in gallons divided by flow rate. In this example, we must convert the flow rate to gallons per hour and multiply by the detention time to solve for the basin volume in gallons.
600 * 60 minutes = 36,000 gallons per hour
36,000 gallons per hour * 4 hours = 144,000 gallons
