The Dyer Boulevard Landfill services all of Palm Beach County, Florida. It is located over the Turnpike Aquifer, an important local source of drinking water. When initially opened in 1968, it was one of several unlined landfills operated within the County. With time, it became a major disposal area for both municipal solid waste and sewage sludge.  In late 1970's, evidence of contamination of the shallow aquifer surrounding this high rise landfill was observed within the site's monitoring network. Under the terms of a consent agreement between Palm Beach County and the Florida Department of Environmental Regulation, executed in 1982, it was agreed that:

The Phase I (unlined) landfill was to be closed in an environmentally sound manner.

A new lined landfill was to be developed to provide for future solid waste disposal capacity.

An alternative means of wastewater treatment plant sludge and septic tank pumpings disposal was to be utilized.

Post, Buckley, Schuh & Jernigan, Inc. (PBS&J) was selected by Palm Beach County, and subsequently by the Solid Waste Authority of Palm Beach County (SWA) when it assumed responsibility for the landfill in 1983, to develop the closure design for the existing 190 acres ± of landfill cells in Phase I.  The closure design developed for the site included a low permeability 'top cap', well vegetated side slopes, and an integrated drainage system to capture and remove surface runoff, reducing percolation and subsequent leachate generation. The top cap was designed for installation over slopes of less than 10 percent, based on water balance calculations which indicated that only minimal percolation was anticipated through well vegetated landfill side slopes after installing erosion control products.  The selection of a geomembrane liner material for use in the top cap at the Dyer Boulevard Landfill proved to be an arduous task, with properties of various materials reported in differing units, or obtained using differing test methods. Suppliers assisted in the selection process by noting the superior properties of some geomembrane liner materials relative to competing materials. Plasticizer loss, ultraviolet degradation, questionable chemical resistance with respect to landfill gas exposure, and more limited elongation properties were cited as reasons to consider materials other than PVC. Environmental stress cracking, seaming difficulties, and poor strength characteristics upon exposure to bidirectional forces were cited as reasons to consider materials other than High Density Polyethylene (HDPE). 

PURPOSE AND SCOPE

During the past several years, geosynthetics testing has matured to the point at which properties of virgin materials ' are widely available and in many cases readily comparable. Data concerning the properties of liner materials which have been in service remain scarce, although there is a growing body of information concerning exposure in the laboratory to simulated in-service environments [1], [2].  The top cap material in-service at Dyer Boulevard provides an opportunity to examine the properties of material which has been in service for over five years. Properties of this material will be compared to the properties determined by quality assurance testing during its manufacture and installation, in an attempt to assess the change in properties resulting from material exposure. Excess material stored in a warehouse since its purchase in 1983/84 will serve as a control.

DESIGN AND SPECIFICATIONS

The site closure design included the placement of PVC sheet, soil bedding and cover material, a passive landfill gas venting system, drainage improvements, and seeding, mulching and sodding (erosion control) of the completed landfill. A typical cross section through the final cover is provided in Figure 1. Physical properties specified for the 20 mil PVC liner are presented in Table 1. Tensile strength at the seam was required to be at least 80 percent of that of the parent material, or 1760 psi. Also required in the specification was the sampling and testing of the production run for tensile strength and elongation at break.  General Contractor Crabtree Construction Company, Inc., purchased 3.32 million square feet of PVC material, Product Number 1951, manufactured by Dynamit Nobel of America, Inc. and fabricated by the Watersaver Company, Inc. The surface of the subgrade prepared as liner bedding was treated with Hyvar X-L Herbicide prior to placement and seaming of the liner panels. The coarse grained sand used for liner bedding and backfill was obtained by dredge from a near site borrow area.  One hundred and sixty-six panels of PVC, most of which measured 400 feet by 70 feet, were installed by Wright/Kohli Construction Company, a specialty liner subcontractor. Watersaver WS-70 splicing solvent was used for seaming the panels together.