Explaining Measured Units

We know that chromium-6 has been found in the Grants Pass water supply, but how much is there? The units expressed are in micrograms (µg/L) or parts per billion (ppb). One microgram is equivalent to one drop in 13,750 gallons. At the highest amount tested, it is less than 1/4 of a drop in 13,750 gallons! Another way to look at it is it is equivalent to less than 2 drops into an Olympic-sized swimming pool. The numbers are very small, and until fairly recently, could not even be tested for.