In Washington State, used motor oil is classified as Household Hazardous Waste (HHW)
or Moderate Risk Waste (MRW). In the late 1980s permanent collection facilities for HHW were established
to replace hazardous waste "roundup" events because of the need for year-round collection and cost control.
The collection of hazardous materials from municipal waste streams has many benefits, including the recovery of
valuable resources and reducing toxicity to solid waste landfills and wastewater systems. In 1999 Washington
collected approximately 9.9 million pounds of HHW of which nearly 9.3 million pounds was used oil. About half of
the collected oil is recycled/reused, the other half is burned in "energy recovery" efforts. After used
oil, the next largest sources of HHW are oil based paint, latex paint, flammable liquids, and lead-acid batteries.
Most automotive service stations recycle used
oil today, but many Do-It-Yourselfers (mostly males in the 20 to 45
year-old age range) are fairly lackadaisical when it comes to proper
disposal. The Washington State Department of Ecology reports that
people who change oil themselves purchased an estimated 54 million
pounds of oil in 1998. Of this amount only 70%, or 38 million lbs.,
is recoverable. (Oil will be lost through combustion, residual amounts left
on engine parts, and inadvertent spillage and leaks.) The amount
recovered through used oil collections totaled 11.6 million pounds,
or 32% of the recoverable amount. Where did the rest of the
oil go in the state of Washington?
The recycled oil data for all 36 Washington counties is presented by year and by a 3-year
mean; values are expressed in lbs per capita. The 3-year mean county values are displayed in the accompanying histogram.
We see that there is a cluster of counties whose annual per capita oil recycling lies from 1.0 to 2.5 pounds. The
histogram is "skewed to the right" or "positively skewed", with a skewness value of 1.3.
As with all positively skewed histograms, the mean lies to the right of the median (mean = 1.82 lbs/person, median
= 1.65 lbs/person). The mean is pulled to the right of the median because of the high recycling efforts of
Asotin and San Juan counties. Students may want to compute annual rates of change for each county in the
years 1998 and 1999, or evaluate the connection (if any) between county oil recycling and other variables (income,
population, education, etc.).
Source: "Solid Waste in Washington State, 9th Annual Status
Report", Washington State Department of Ecology, December 2000,
Publication #00-07-037. http://www.ecy.wa.gov/