ORIGINS, INFLUENCES AND CONTRIBUTIONS OF ILLINOIS STATE GEOLOGICAL SURVEY TO LANDFILL STUDIES AND GROUNDWATER PROTECTION

Segregation of wastes from potable water resources is a foundation of modern sanitation and public health. Studies of landfills, as part of groundwater protection, arose as a derivative of geologic mapping for land use and water supply in metropolitan Chicago in the 1960s.

Cooperative geologic mapping projects encouraged county sanitarians to contact Illinois State Geological Survey hydrogeologists to obtain technical information and professional opinions regarding the impact of landfills on the environment. Provision of timely hydrogeologic information from office and field studies provided information for 100s of landfills and led to research studies regarding landfill siting investigations and experimental covers and liners. Results of those studies guided professional practice, and promulgation of regulations and guidelines which continue in use.

Among the notable findings and investigative tools have been:

• piezometer construction in and around landfills shows development of a groundwater mound in refuse;

• samples drawn from piezometers over time, depth and successive sampling episodes show inconsistent chemistry;

• refuse must be separated by a minimum of 30 feet, preferably 50 feet, from any water- producing zone;

• knowing the geology of sites is necessary to understanding hydrogeology and groundwater contaminant flow;

• some soil types can allow piping and development of open holes in earthen covers;

• soil chemistry and physics provide insight into hydrogeology and cation exchange;

• hydraulic conductivity of remolded samples differs considerably from field tests in vertical and angle borings;

• infiltration of meteoric water through landfill covers can be determined by remote sensing;

• earthen covers rise and fall more than 30 mm because of temperature and moisture changes;

• temperature, electrical earth resistivity, and geophysical surveys can delimit leachate plumes; and

• aquifer sensitivity maps used for planning, regulation, and public health were based upon depths of waste burial;

Methods are being developed to identify defects on covers of more than 3,400 closed landfills using publicly-available aerial photography and lidar. Furthermore, proposals to map leachate plumes using Helicopter Time domain ElectroMagnetic resistivity (HTEM) technology are in development.