Picture This: Baltimore County's Grease Map

Sewage overflows are unpleasant and unsanitary messes.

Normally, waste water from all of the toilets, sinks and tubs in Baltimore County—about 35 million gallons every day, according to public works officials—is conducted through miles of underground pipelines to treatment plants in the city.

There were 158 sewage overflows in Baltimore County in 2011, ranging from a trickle to millions of gallons, according to a database maintained by Maryland Department of the Environment.

The most common cause of sewage overflows is lines clogged with fats, oils and grease, known in public works-speak as FOG. Fats and grease congeal in drain pipes and sewage lines, according to sanitary engineers, contributing to overflows during heavy rainfall.

Backed-up sewage flows into homes and through neighborhoods, following the terrain downhill to the nearest body of water and ultimately into Chesapeake Bay, explained county public works spokesperson David Fidler.

While doing research for stories about sewage overflows last fall, I encountered an unusual document that piqued my interest--a "grease map" of Baltimore County. I wanted to know more about why the county has a grease map and what it meant.

In 2005, Baltimore County signed a consent decree to settle a lawsuit filed in U.S. District Court by the Environmental Protection Agency for repeated violation of the federal Clean Water Act.

As part of the settlement, Baltimore County agreed to develop a plan to prevent sewage overflows. Officials are required to keep track of grease-generating facilities (GGFs) in the county, which are a source of FOG.

According to public works officials, restaurants are the most common commercial sources of FOG. Restaurants are required to have grease traps, and can face fines for waste violations, but sanitary engineers said that some spillage of FOG down drains happens anyway.

The map above shows the location of grease-generating facilities in Baltimore County. Not surprisingly, GGFs cluster very closely around major streets. According to public works officials, GGFs also correlate very closely to neighborhoods with chronic sewage overflows.

To see if your neighborhood is affected by sewage overflows, search the Maryland Reported Sewer Overflow Database maintained by MDE.

Aside from restaurants, other sources of GGFs are automobile repair shops and residences where people pour oil and grease down the drain.

Sanitary engineers discourage people from allowing cooking oil, grease or rendered fats to go down drains. Any fat that is solid at room temperature--such as butter, animal fat and hydrogenated vegetable oils—will solidify in your drain system and sewage line.

Pour cooled cooking oil and fats into a container—such as a coffee can or a tin can—and dispose along with your trash. Use paper towels to mop grease from pans and dishes before washing.

Reducing the oils and fats down the drain is better for your home, better for the neighborhood, and better for Chesapeake Bay.