DESIGNING A TRACER DISTRIBUTION SYSTEM FOR A VERTICAL LANDFILL EXPANSION

摘要

Vertical expansion of an existing landfill facility represents an excellent approach to provide additional landfill airspace. However, the New York State Department of Environmental Conservation (NYSDEC) Solid Waste Management Regulations mandate that landfill expansions to existing facilities must maintain separate groundwater monitoring for the purpose of differentiating potential water quality impacts from existing and new cells. Since any liner leaks from the existing and new cells would impact the same groundwater flow system, conventional groundwater monitoring approaches to differentiate water quality impacts would not be possible. The use of a chemical tracer system in the vertical expansion supplies the mechanism to monitor the facilities separately in conformance with NYSDEC requirements. Within the context of groundwater flow and contaminant transport, a tracer is a substance carried by groundwater that provides information on the potential contaminants that might be transported in the groundwater system. Fluoride was selected as the tracer of choice because of its anticipated geochemical behavior (not readily attenuated in the groundwater system) and its uniqueness to the groundwater environment. Without the quality of uniqueness, a monitoring program sensitive enough to detect small leaks from a landfill would not be possible. The tracer distribution system will allow introduction of fluoride as sodium fluoride solution into a network of distribution piping, located above the geocomposite component of the leak detection zone of the vertical expansion. There are really two main elements to this type of project; the geochemical and the engineering design. The geochemical element involves assessment of the viability of utilizing fluoride as the tracer solution and required concentrations. The design element pertains to the development of a system to introduce the tracer solution uniformly into the secondary overliner. This paper will present the development and features of the system and the challenges faced with respect to the two elements.