To understand if groundwater contamination is a problem in an aquifer, it is necessary to know both the type and amount of contaminant in the groundwater system. We measure amounts of contaminants in terms of concentration. More specifically, we use the concepts of ppm and ppb, which are parts per million and parts per billion.

• PPM is simply the amount of contaminant units in 1,000,000 (1 million) units of groundwater.
• PPB is likewise the amount of contaminant units in 1,000,000,000 (1 billion) units of groundwater.
• You could make up your own concentration measurements as well, such as PPH (parts per hundred), which would be the amount of contaminant units in 100 units of groundwater. In fact we already use PPH but we call it percent, %. (1pph = 1/100 =1%)

Alt | Win

Use the animation to visualize what the part per (number) means, then answer the question: Which is a larger concentration, 1 PPM or 1 PPB?