Statistics-Based Approach for the Evaluation of Groundwater Metal Concentrations at a Paper Mill Landfill Site, 1995 Environmental Conference Proceedings

Ching-Gang Peng, John M. Fox, and

Jeff S. Ubl

Barr Engineering Company

Jim Jackson & Allan Meadows

Boise Cascade Corporation

The release of contaminants from solid waste deposited in landfills to groundwater is an area of considerable interest to environmental regulatory agencies as well as the regulated community. Increasingly, environmental regulatory agencies are establishing groundwater intervention limits at defined compliance boundaries downgradient of the landfill perimeter. When concentrations of groundwater parameters are present in groundwater upgradient of the landfill, establishing a background upper range is necessary to aid in setting of intervention limits. However, establishing the background upper range concentration for a given parameter is complicated if sample analytical results are reported below the instrument limit of detection (LOD). This paper describes statistical procedures that were used in the evaluation of groundwater quality with the objective of establishing the upper range background metal concentrations at Boise Cascade’s Moonlight Rock paper mill landfill near International Falls, Minnesota. Development of background upper range concentrations was based on monitoring data collected from nine monitoring wells which are upgradient of the existing landfill. The type of statistical procedure employed is dependent on the percentage of values below the LOD for each metal. Metals were grouped into one of five categories for the purpose of selecting the applicable statistical procedure. The mean and standard deviation were computed and the representative upper range concentrations were determined by calculating the one-sided upper tolerance limit. The statistics-based approach demonstrates a scientific and systematic analysis of groundwater monitoring data.