A Geotechnical Investigation of Abandoned Strip Mines for Sanitary Landfill Purposes

Abstract

Five strip mine sites in northeastern Ohio were selected to investigate their suitability as sanitary landfills. Engineering properties of the mine spoil from each site were studied for possible utilization as a cover and as liner material. Detailed investigations were conducted to evaluate the geologic and hydro-geologic conditions at each site. The mine spoil can be generally classified as a well-graded sand with fines of low plasticity. Laboratory density values range from 99 to 124 pcf (1.59 to 1.99 Mg/m 3 ) whereas in-situ density values of end-dumped, uncompacted, spoil range from 75 to 118.5 pcf (1.20 to 1.90 Mg/m 3 ). Density vs. permeability curves indicate that the required permeability of a cover material (1 × 10 −5 cm/sec) can be obtained at approximately 90 percent relative compaction while some spoil material can meet liner specifications (1 × 10 −7 cm/sec) at a relative compaction of 95 percent or more. Permeability values of spoil compacted at maximum dry density and slightly wet of optimum moisture content range from 2.5 × 10 −7 to 5.6 × 10 −8 cm/sec whereas field infiltration tests yield permeability values ranging from 5 × 10 −3 to 5 × 10 −7 cm/sec. The in-situ values of moisture content generally fall on the wet side of the optimum. Slake durability indices range from 54.6 to 97.7 suggesting that shales in the mine spoil have medium to very high resistance to slaking. The engineering properties of the mine spoil indicate that it is highly suitable for use as a cover material but only marginally suitable for use as a liner material. Shale is the predominant rock type underlying the sites. Underclay, which greatly increases the suitability of a site as a landfill, is present at three of the five sites. Generally, no significant aquifers were found immediately below the sites. Most water supplies are obtained well below the land surface and would be hydrologically separated from surface operations by the intervening clay and shale. These investigations indicate that properly engineered abandoned strip mines can be environmentally sound for sanitary landfill purposes.