Oil changing.

Oil Trivia

One gallon of used oil can foul a million gallons of drinking water. Used oil can contain such contaminants as lead, magnesium, copper, zinc, chromium, arsenic, chlorides, cadmium, and chlorinated compounds. Oil poured down drains or onto the ground can work its way into our ground and surface waters and cause serious pollution. One gallon of used oil can foul a million gallons of drinking water. Federal reports indicate that used motor oil accounts for more than 40 percent of the total oil pollution of our nation’s harbors and waterways.
http://www.calrecycle.ca.gov/usedoil/info/