In considering landfill regulations and liner design requirements in 1988, the EPA undertook extensive technical evaluations of various liner system designs, including the appropriateness of various liner systems in karst geology similar to that found in the Boone/St. Joe formations in Northwest Arkansas. The EPA then concluded that a single composite liner system provided a sufficient level of environmental protection even in karst geology.

Over the years, ADEQ has reviewed extensive information regarding the geology of the Boone/St. Joe formations in Northwest Arkansas, which are characterized as immature karst geology, and determined that landfills can be safely sited in this area. To address public concerns regarding such formations, ADEQ and the Tri-County Solid Waste District implemented new regulations in 1995 to require additional safeguards, specifically double composite liner systems for new landfill units that locate in the Boone/St. Joe formations.

Large portions of other states have mature karst geology where municipal solid waste landfills are routinely sited, permitted and responsibly operated. These include the states of Florida, Pennsylvania, and West Virginia. Almost the entire state of Florida is underlain by the most developed, mature karst geology in the country and yet Florida requires only a single composite liner system, which is far less stringent than the double composite liner system required by ADEQ and the Tri-County Solid Waste District.

Geologic Column: Note 50 to 90 feet of relatively impermeable soils separate the surface from the underlying Boone Formation.

The anatomy of a landfill includes:

The Tontitown Landfill's double composite liner system consists of a primary composite liner and a secondary composite liner on the bottom, both of which are designed to provide an impermeable layer to protect groundwater.

The landfill's secondary composite liner system consists of two feet of clay barrier layer (or an engineered equivalent approved by ADEQ) and a very durable high-density polyethylene (HDPE) plastic liner that is chemical resistant to corrosion and damage. The secondary composite liner system provides a double protection standard to the primary composite liner system. The primary liner system, which contains the waste and collects leachate, also consists of two feet of clay (or an engineered equivalent) and the HDPE liner.

A blanket of geotextile fabric, composed of synthetic, felt-like fibers, is laid above the primary liner system, along with a geonet made of mesh-like plastic. Together, these prevent fine clay particles from clogging the leachate collection layer.

Strict construction guidelines must be followed in constructing the liner systems, which are summarized below: