landfills: Glacial Till Acts As Natural Landfill Liner

Tim Kenyon

If a landfill liner had experienced no leaks in the last 12,000 years, you likely would say that the system had "withstood the test of time." And if the designers of an expansion for the Sioux Falls (S.D.) Regional Sanitary Landfill are correct, that is exactly what will happen.

This innovative conceptual design uses the relative impermeability of the state's unweathered glacial till as the landfill's bottom liner in combination with more traditional sidewall liners.

The landfill, which covers 400 acres, serves a population of approximately 175,000. It is the largest in the state, with waste receipts of 150,000 tons annually.

Last November, the South Dakota Board of Minerals and Environment granted the city of Sioux Falls a permit to operate and expand the landfill without a constructed bottom liner.

The natural liner concept, which was accepted unanimously by the board, reportedly will yield multimillion-dollar savings for the city in engineering, construction, maintenance and monitoring costs. This cost savings, along with the assurance of sufficient landfill space, will stabilize tipping fees and allow for the continued economic development of the Sioux Falls area.

Before the permit application was submitted to the state, LBG hydrogeologists conducted a comprehensive hydrogeologic evaluation of the existing and expansion landfill areas, and reviewed data provided by the South Dakota Geological Survey.

The assessment's results indicated that a clayrich glacial till to a depth of up to 150 feet underlies the site. The Wall Lake Aquifer, the area's primary groundwater resource, is underneath the glacial till.

The glacial till is extensively weathered and fractured up to 20 feet below land surface with a transition zone extending to the unweathered till at up to 45 feet below land surface. No significant sand layers or lenses were encountered within the landfill expansion area. Slug-test and permeameter test data indicated that the unweathered till has a hydraulic conductivity ranging from 10-7 to 10-9 centimeters per second, showing it to be relatively impermeable.

Carbon-14 age dating of the groundwater within the unweathered till showed it to be 12,000 to 20,000 years old. Analysis also showed that the groundwater has not been re-charged by water that was exposed to the atmosphere after 1953 - the year of the first hydrogen bomb test.

Direct observation of the glacial till in trenches excavated for the existing portion of the landfill confirmed that the till deeper than 40 to 45 feet below the land surface is not fractured, so it will not conduct fluids readily.

Based on the assessment's results, it was concluded that no significant lateral groundwater movement within the weathered glacial till had occurred in at least the last 12,000 years.

The expansion design proposed four north-south trending trenches excavated to 50 feet below land surface. The trenches will be up to 585 feet wide and 2,440 feet long. Leachate will flow by gravity to the trenches' south end for collection and removal. The final height will be 100 feet above land surface with a total landfill volume of 25.5 million cubic yards. At present disposal rates, the landfill expansion will last up to 60 years.

To be sure, this solution does not apply to every site. However, similar hydrogeologic conditions exist elsewhere in the upper Midwest, including North Dakota, Nebraska, Minnesota, Iowa, Wisconsin and Michigan, and perhaps in Ohio, Indiana and Illinois. In some of the Western states, such as Wyoming, Nevada, Colorado and Montana, impermeable sediments also are found at the surface.

While this type of design requires a greater density of geological data than a conventional design, the costs may be significantly less than installing and maintaining a constructed liner. In any case, a design that uses the site's hydrogeology is more likely to yield a cost-effective solution than an "off the shelf" approach.

Agreement Mack Trucks Inc., Allentown, Pa., and Eaton Corp., Clemmons, N.C., have announced a long-term supplier agreement to improve both companies' competitiveness in the heavy-duty truck market. According to the terms of the agreement, Eaton Fuller transmissions will become standard on all Mack CH model chassis.

Approval Arid Operations has received final approval from a Superior Court decision for the completion of its Mesquite Regional Landfill, located 35 miles east of Brawley, Calif., in Imperial County.

Acquisition Eastern Environmental Services Inc., Mt. Laurel, N.J., has completed its acquisition of the Ruben Smith Carting Co., Atlantic City, N.J. It also has signed definitive purchase agreements to acquire five collection companies in New York City and a collection company in Miami. The combined companies have annual revenues of approximately $20.1 million.

American Disposal Services Inc., Burr Ridge, Ill., has acquired 10 waste management companies located in New England, Missouri, Indiana, Ohio and Pennsylvania, bringing to 5`1 the company's total acquisitions since January 1993. The acquisitions were purchased using a combination of cash and stock.

Awards The American Forest & Paper Association has awarded its eight annual Best Paper Recycling Program Awards. Winners include: Manitowac County (Wis.) Materials Recovery Facility; Charleston County (S.C.) Department of Solid Waste/Recycling; Granger Recycling Center, Lansing, Mich.; Northwestern University, Ill.; Tree Musketeers, El Segundo, Calif.; and Rhode Island Resource Recovery Corp.

The California Integrated Waste Management Board, Sacramento, Calif., has presented the Walt Disney Co. with a "Waste Reduction Award Program of the Year" plaque. In 1996, the company recycled 80,000 tons of waste, saving $528,000 in disposal costs.

Contract Global Recycling Technologies Inc., Stoughton, Mass., has been awarded a contract by the Massachusetts Division of Operational Services for the recycling of spent mercury-bearing fluorescent lamps. The contract is available to all Massachusetts agencies, authorities and municipalities for one year with up to four option years.

Loans The California Integrated Waste Management Board, Sacramento, Calif., has approved $2,221,134 in loans to Evergreen Glass, Stockton; MBA Polymers, Richmond; and Vision Recycling, Almeada County.

New Facility Allison Transmission announces the opening of its new customer training facility in Indianapolis, Ind. The 13,000-square-foot facility offers courses on basic maintenance to more in-depth classes that cover hydraulic and electronic controls of the World Transmissions.

Re-Opening Med/Waste Inc., Opa Loca, Fla., has announced that its South Carolina waste incineration facility which suffered fire damage has been granted permission to reopen and resume normal operations by the S.C. Dept. of Health and Environmental Control.