>John Welbourn is the Environmental Engineering Manager for
>the Engineering and Environmental Compliance (EEC) of the
>Public Works Department for the City of Mountain View. EEC
>was formed in 1994 principally to ensure regulatory compliance
>throughout the period of landfill closure projects, now
>complete, and thereafter throughout the 30-year post closure
>maintenance period. Mr. Welbourn is a past president of the
>Founding Chapter of the Solid Waste Association of North
>America (SWANA) and was appointed by Governor Wilson to serve
>on the Local Government Technical Advisory Committee, an
>advisory committee to the California Integrated Waste
>John will describe his role in the landfill activities and
>discuss the new micro turbine project now being designed by
>SCS Engineers. Two new micro turbines are to be installed by
>summer 2003 at the landfill gas flare station and at the sewage
>lift station. They will utilize landfill gas in the production
>of electricity for use at those facilities located in Shoreline
>at Mountain View.
John Welbourn began his talk by giving us a tour of the Shoreline site, using a mixture of high altitude and ground level pictures. The site of the dump has now been mostly converted into a golf course, windsurfing lake, Shoreline Amphitheater (and parking), and wetlands habitat. There are a few spots reserved for other uses, like the flares where the landfill gas has been burnt since about '92, and the speaker went over those.
For many of the ground level views, John juxtaposed a picture taken in the late 1980s with the current state of the place, so that we could vividly see the changes. Most of the changes have made the place much more esthetically appealing. A few, like moving the access road and paving it have also made it easier for crowds to get out of Shoreline after a Concert. Shoreline is now a nice Regional Park, and many people don't know that it sits on about fifty feet of solid trash and demo waste, most of what the Peninsula (including San Francisco) created during the time it was open.
Welbourn explained that the trash was covered with a layer of clay about one to two feet thick, on top of which is a layer of soil one to two feet thick. The soil gives the plants that add to the appearance of the park a place to root, and it also prevents the clay from drying out and cracking, which would break the seal.
Under the clay is a web of tubing with up to eight inches of vacuum pressure that pulls the gasses generated inside the landfill towards the station where it is currently flared through three burners. Because the landfill is expected to subside ten to fifteen feet before stabilizing, the pipes have hinges and expansion joints to prevent breakage during this process. The gas is mostly carbon dioxide and methane, with some other stuff which is filtered out before it can be burned.
The microturbines look like boxes about seven feet high. They will fit on a concrete slab about ten feet by twenty feet near the current flares. Welbourn explained that until about 1992, they were extracting the methane from the landfill gas and selling it to PG&E as Natural Gas. The problem with this was that the cleaning required to make it market ready was so expensive that the project never made financial sense. However, microturbines are less picky about their fuel, and the power generated is an offset for the power they would have had to buy, making the payback timeframe in the cost analysis 3 to 5 years.
The Microturbines are a small line item among the costs associated with the dump. The City of Mountain View issued $25 Million in bonds to cover the cost of closing the dump, most of which has been spent to make the park what it is now. Ongoing costs from this day forward are about $1.5 million per year. Welbourn expects the facility to be providing enough methane gas to run the Microturbines for more than forty years into the future.