Against the rolling green hills of the Allegheny Mountains, Houston-based Waste Management's (WMI) Washington, Pa., landfill looks like any other. Even a closer look wouldn't reveal the site's most unusual feature, because it cannot be seen at all.

Buried 8.5 feet underground is a liquefied natural gas (LNG) storage tank, the fuel source for seven of Waste Management's refuse trucks.

Since 1997, WMI has used LNG trucks to collect the refuse generated by the area's 120,400 residents and 4,500 commercial and industrial accounts, which span 250-miles in five counties. The company's experience with LNG trucks is significant, and Waste Management reports that it has learned a few lessons.

The seven LNG trucks are equipped with Mack E7G natural gas engines. Making as many as 900 to 1,000 stops each day, the engines operate at zero to five miles per hour (mph), which is the worst of all duty cycles. Spark-ignited engines, such as the E7G, are less fuel efficient than diesel units. In fact, WMI shows that LNG fuel economy is 18 percent lower than diesel, even though LNG trucks have a lower average speed.

Despite poorer fuel economy, WMI's drivers prefer the LNG truck because there is no diesel odor, less engine noise and more power for heavy payloads - LNG trucks have 325 horsepower (hp), while diesel trucks have 300 hp. Other benefits to the Mack E7G truck are that it has a homogeneous, lean-burn fuel delivery system for optimum combustion. This reduces emissions of reactive hydrocarbons, particulate matter and nitrogen oxides. The trucks meet the U.S. Environmental Protection Agency's (EPA), Washington, D.C., low-emission vehicle (LEV) standard and the California Air Resources Board's low-nitrogen oxide (NOx) standard for heavy duty applications.

Another important aspect of the LNG truck is the way it refuels at the landfill. A LNG storage and refueling facility provides 30 gallons per minute from a 13,000-gallon underground tank. To store LNG underground, it is cooled to approximately -260degrees Fahrenheit. Once cooled, the atmospheric pressure will condense it from a gas to a liquid. Then, the LNG is stored in double-walled, vacuum-insulated tanks so that it remains cold.

In addition, according to the report, "Waste Management's LNG Truck Fleet Start-Up Experience," LNG Express, Houston, states that key benefits to using underground storage tanks include:

* "Shorter piping runs, no containment dike, and compactness of the facility reduces installation time;

* The soil protects the tank from thermal radiation, eliminating a fire risk;

* Reduced vapor dispersion and thermal radiation zones makes it easier to install tanks in densely populated areas; and

* Reduced exposure minimizes vandalism, accidents and sabotage."

According to Jerry Simmons, WMI's Washington, Pa.-based fleet manager; Ben Woods, a WMI district manager; and John Bartel, senior staff engineer for Mack Natural Gas Engines, Hagerstown, Md., the pilot project taught them:

* Communication is imperative. Keep participants informed on the project's progression from the start to finish.

* The project must have a champion and a nucleus of committed participants. Simmons says that Mack and WMI have gone the extra mile to ensure the project's success.

* A committed fleet manager can take the project to new heights.

* Pay attention to start-up issues, such as infrastructure, training, etc. This applies even if the fleet is small, Bartel says.

* Recognize that LNG vehicles are different from diesel trucks. Bartel emphasizes that the LNG trucks are not going to mix immediately with the diesel fleet. A person has to understand the system and be able to troubleshoot problems.

* Drivers need someone that they can talk to about the trucks. For example, if a driver senses something wrong with the truck, but does not know the problem because of the new technology, he needs to talk to someone who can give valuable advice.

* Install fueling infrastructure before purchasing trucks. If you don't install one above or below ground, the station is bound to have difficulties.

For more information on "Waste Management's LNG Truck Fleet Start-Up Experience," visit www.ccities.doe.gov/success/waste_management.shtml or contact the National Alternative Fuels hotline toll-free at (800) 423-1DOE.