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it The City of Everett The Floyd & Snider Team Everett Landfill/Tire Fire Site V The BFS evaluated the potential impact to deep aquifer quality that could be caused by installation of pile foundations driven through the landfill and underlying aquitard. The evaluation concluded that due to aquitard consistency, horizontal -favoring groundwater flow gradients, and general compliance of leachate with cleanup levels, either driven or drilled pile foundations could be installed at the landfill without risk to the groundwater pathway. This conclusion is supported by monitoring results from the deep aquifer directly down -gradient of the Snohomish County Transfer station, which was constructed 25 years ago with steel pipe piles driven through the thickest areas of refuse and into bearing sands below. This CMCP proposes methods to measure that the deep aquifer remains in compliance following pile installation. Additionally, a one-time sampling event at many locations throughout the landfill is proposed to determine whether there are any zones of the landfill at which leachate quality is significantly different from the results acquired from previous monitoring. If these results indicate that there are areas of the landfill where a breach between the shallow and deep aquifers could cause an exceedance of cleanup standards in the deep aquifer, pile foundations in those areas will be restricted to augercast construction. The recommended alternative for the direct contact pathway will require developed area covers to isolate buried landfilled materials, with associated institutional and property management controls to ensure cover materials are not penetrated without proper construction and repair procedures. Developed area cover includes building slabs, pavements, and clean soil for landscaped areas and utility corridors. Special construction requirements will be required to protect the health and safety of construction workers, and minimize off -site impacts of construction activities. These construction requirements include: dust and odor controls, erosion controls, dewatering procedures, extra health and safety training for construction crews and construction performance monitoring and inspection to ensure compliance. The recommended alternative allows on -site relocation and capping of excavated refuse during construction, and maintains site access controls to undeveloped portions of the site. The recommended alternative for the surface water pathway includes those measures recommended under existing conditions, as well as implementing construction practices and stormwater management requirements unique to the landfill setting that will prevent surface water runoff of contamination and its conveyance to the adjacent drainage ditches. 2.3 MONITORING TYPES AND OBJECTIVES The purpose of this CMCP is to ensure that necessary and appropriate evaluation, performance and confirmational monitoring, inspections and reporting of results are implemented for the Everett Landfill/Tire Fire Site. Monitoring and inspections are necessary to document compliance with cleanup standards and ensure protection of human health and the environment. This plan also describes triggers for implementing contingency measures and what those contingency measures would entail. Each pathway is described separately. However, quarterly site inspections for the direct contact and groundwater pathways have been coordinated and combined into me inspection event. Gas pathway inspections and monitoring will completed by trained and qualified technicians only. docs\j ompli Oce Monitoring Everett t-an\CMCDF maker- final Compliance Monitoring and Contingency Plan docslCompliance Monitoring PIan1CMCP 11-10-OO.doc p 9 9 Y FINAL - March 2001 Page 2-4