HYDROGEOLOGIC ISSUES AND NEW YORK STATE LANDFILL PERMITS

Recent landfill permitting in Upstate New York has required resolution of recurrent hydrogeologic issues: rapid/unpredictable groundwater flow through bedrock, Principal Aquifer determinations, and discrimination of contamination from multiple potential sources.

Landfill regulations state that bedrock subject to rapid or unpredictable groundwater flow must be avoided unless fugitive leachate cannot reach bedrock. The regulation implicitly refers to karst systems, but could also apply to settings where wide bedrock joints permit high velocity or non-laminar flow. No post-1993 decisions were based on calculated Reynolds numbers to demonstrate validation of Darcy’s Law. Fracture aperture and in-situ flow velocity measurements may be required--techniques not yet commonly used at Upstate landfill sites. Technical simplicity and successful use of the “lack of karst” precedent keep it in favor.

Regulations also demand that site selection consider proximity and hydrogeologic relationship to water supply sources. In New York parlance, Principal Aquifers are under-exploited/unused unconsolidated deposits with potential for major municipal water supply development. The State regulatory agency established certain aquifer size, sustainable yield and water quality criteria for Principal Aquifer determinations. Generally, however, little data exist for under-utilized aquifers beyond the applicant’s residential well surveys, test drilling, permeability testing and water quality testing. One Principal Aquifer determination was decided in favor of the landfill due to small size and lack of connection to larger nearby aquifers. A second case was decided in favor of a landfill because the aquifer actually consisted of weathered bedrock, not unconsolidated deposits, and exhibited poor water quality. A third case is pending.

Regulations state that new landfills cannot be located in areas where environmental monitoring and site remediation cannot be conducted. Arguments arise when landfills propose to expand adjacent to old, unlined cells where groundwater may be impacted. Monitorability arguments focus on geochemical differences between leachates from different waste streams and of different ages and the role of engineered liner systems in providing early indications of leak sources.