On introductory-level water treatment exams, flow is expressed as "number of gallons within a given frame of time." The four primary expressions of flow on introductory-level exams are gallons per minute (gpm), gallons per hour (gph), gallons per day (gpd), and million-gallons per day (MGD) .
When flow is expressed as gpm, gph, or gpd, the number before the gpm, gph, or gpd is written without any type of abbreviated notation. As examples, one thousand gallons per minute is written as "1,000 gpm", one hundred thousand gallons per hour is written as "100,000 gph", and ten million gallons per day is written as "10,000,000 gpd".
When flow is expressed as MGD, the full six-digit million number is never written before the MDG. A flow of ten million gallons per day, correctly written as 10,000,000 gpd, is not correctly written as 10,000,000 MDG. Ten million gallons per day, written in the MGD form, is "10 MDG".
Before beginning the practice portion of this post, it is important to understand the difference between MGD and MG. Both expressions are written with the same type of abbreviated notation, but MGD contains a timeframe (per day), which denotes flow. The term "MG", or million-gallons, has no timeframe attached to it. The term "MG" can express flow, under the right conditions, but it can also be used to denote capacity or quantity, such as a 2.5 MG clearwell or a 1.25 MG elevated tank.
For introductory-level water treatment operators, writing one million gallons per day as 1 MGD is easy. Writing ten and one-half million gallons per day as 10.5 MGD is also easy. But many introductory-level water treatment operators start to experience a problem when they have to write less than one million gallons per day in the MGD form.
To convert gallons into million-gallon notation, multiply the gallons by .000001 and add the abbreviation MGD or MG, depending on the context in which the million-gallon notation is used. The figure .000001 is a decimal point that is followed by five zeros and a 1. Below are several examples to illustrate how easily gallons can be converted into the million-gallon form.
PULL OUT YOUR CALCULATOR AND TRY EACH OF THESE PROBLEMS FOR YOURSELF. YOU MUST KNOW THIS INFORMATION IN ORDER TO ANSWER SEVERAL QUESTIONS ON YOUR EXAM. THESE EXAMPLES ARE PROBABLY MORE COMPLICATED THAN THE QUESTIONS ON THE EXAM, BUT IF YOU CAN PERFORM THESE PROBLEMS, YOU'LL HAVE NO DIFFICULTY AT ALL WITH ANY OF THE MILLION-GALLON CONVERSIONS ON YOUR EXAM.
3,250,000 gallons x .000001 = 3.25 MG
45,000 gallons x .000001 = .045 MG
999,999 gallons x .000001 = .999999 MG
(This is actually one gallon away from being 1 MG.)
1 gallon x .000001 = .000001 MG
(This is 999,999 gallons away from being 1 MG.)
655,000 gallons x .000001 = .655 MG
351,200 gallons x .000001 = .3512 MG
17,600 gallons x .000001 = .0176 MG
18,379,000 gallons x .000001 = 18.379 MG
To check and verify that your calculation is correct, multiply your MG figure by 1,000,000. You should get the original figure with which you started. You will need to use this procedure also if you are asked to convert MG or MGD into gallons.
3.25 MG x 1,000,000 = 3,250,000 gallons
.045 MG x 1,000,000 = 45,000 gallons
.999999 MG x 1,000,000 = 999,999 gallons
.000001 MG x 1,000,000 = 1 gallon
.655 MG x 1,000,000 = 655,000 gallons
.3512 MG x 1,000,000 = 351,200 gallons
.0176 MG x 1,000,000 = 17,600 gallons
18.379 MG x 1,000,000 = 18,379,000 gallons
VERY IMPORTANT NOTE: Whenever a test question or math problem requires an answer that involves a large number of gallons, be sure to ascertain if the answer should be in gallons or in million-gallons. Frequently, introductory-level math questions will ask "how many million gallons" are involved in a certain situation. But test questions can also ask "how many gallons" are involved in a situation. Always assess if questions involving large numbers of gallons are asking for the answer to be in gallons or in million gallons.