MatCon

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In early April 1999, Wilder Construction Company installed a Modified Asphalt Technology for Waste Containment (MatCon) cap over a contaminated Superfund Site at Dover AFB, Delaware. This installation was also a demonstration project under the Superfund Innovative Technology Evaluation (SITE) program. The SITE program evaluates the applicability of innovative technologies to real world contamination problems. The installation of the demonstration cap was observed by Mr. David Carson of the EPA SITE Program Office.

Physical Description of Cap: The Dover AFB site, known as the Lindane Source Area, was divided into three areas for capping, see Figure 1. Approximately one-half of the site was paved with conventional asphalt concrete normally specified by Dover AFB for road paving. Of the remaining portion approximately one-half was capped using four inches of dense graded MatCon and one-half using MatCon with leak detection.

The leak detection system consists of two impermeable layers of MatCon with an open-graded (permeable) layer of MatCon sandwiched in-between. The permeable layer was installed to provide a space and pathway for fluids to be collected and directed to a sump for detection.

The leak detection system was constructed using a four-inch thick base layer of impermeable MatCon sloped to drain to the Northeast corner. An open-graded layer was placed on top of the base layer in four sections (pads), see Figure 2. Plastic pipes were placed into the Northeast corners of each open graded pad to direct fluids to sumps that will be installed along the north edge of the cap. The areas between and around the open-graded pads were filled-in using impermeable MatCon to form barriers isolating the open-graded pads from each other and the edges of the cap. A four-inch thick layer of MatCon was then placed over the drainage pads and barriers.

The four-inch thick section of impermeable MatCon was installed after construction of the three-layer section.

Construction: Wilder furnished the modified asphalt binder to local asphalt producer, Tilcon who manufactured the asphalt concrete and provided it to paving contractor Ralph Cahill & Son who performed the installation of the cap. MatCon binder was delivered to Tilcon's local asphalt plant in tanker trucks. The binder was loaded into heated storage tanks that had been drained free of Tilcon's standard asphalt binder. A load of gravel was run through the production process without any asphalt binder to clean the asphalt plant. MatCon was then produced in the plant using the specified gradation of aggregate, MatCon binder and standard asphalt production procedures.

Cahill delivered the MatCon to the project site in standard end-dump trucks timed to keep material laydown continuous while minimizing truck wait times at the site. The MatCon was installed using a conventional asphalt-paving machine. Each MatCon lift was placed at full depth to produce a four-inch compacted cover. Placement proceeded in continuous 10-foot wide strips running east to west starting along the north edge of the site, see Figure 3. This laydown sequence assured that all joints would be hot within each MatCon section of the cap.

A 10-ton vibratory compactor followed the paving machine using both vibratory and non-vibratory passes over the mat. Density testing was performed after compaction using a Troxler Nuclear density Gauge. The density gauge was calibrated to provide a percentage of total compaction reading. The roller performed additional passes over the mat until the density was at least 97% to correspond to less than 3% air voids in the MatCon. Quality control testing was performed at both the plant and at the site.

Testing and Analysis: As part of the SITE demonstration program, the EPA will design and perform tests on the completed cover and material samples taken from the cover to assess applicability of the technology to various uses as a cover and as a liner system. The EPA will publish results upon completion of their testing. Any preliminary test results or interim reports issued by the EPA will be added to this site as we receive them.

Wilder took its own samples from the site and performed tests on them. Test results from an independent certified lab were less than 1 x 10^-8 cm/sec permeability for the dense graded MatCon. Wilder also demonstrated the flow characteristics of the drainage layer during construction by running a full flowing stream of water from a 3 inch diameter hose onto the open graded MatCon mat prior to covering it with the dense graded layer. The entire stream of water flowed through the drainage layer with no surface collection of the water.

Conclusion: This third-party test data met, actually surpassed, MatCon's performance specifications and RCRA requirements. This project also demonstrated that MatCon could be successfully applied on an actual Superfund Site project by a local asphalt concrete supplier and a local qualified asphalt paving contractor using their own personnel and equipment.