Soil Physical Properties at an Abandoned Mine in Central USA.

Relatively little information exists for soil physical characteristics of mine wastes in the central USA.  The Tri-State Mining District of southeast Kansas, southwest Missouri, and northeast Oklahoma produced lead and zinc from 1871 to the 1970s. In May 2006 an experiment was established to determine if soil amendments could decrease the bioavailability of heavy metals in the mine waste.  Seven treatments on two different sites near the town of Galena KS, called Site A and Site B, were established, as follows: (1) CO, non-amended control; (2) LC, low compost (45 Mg/ha); (3) HC, high compost (269 Mg/ha); (4) LCL, low compost (45 Mg/ha) + lime as Ca(OH)₂ (11.2 Mg/ha); (5) HCL, high compost (269 Mg/ha) + lime as Ca(OH)₂ (11.2 Mg/ha); (6) LCLB, low compost (45 Mg/ha) + lime as Ca(OH)₂ (11.2 Mg/ha) + bentonite (50 g bentonite/kg compost); and (7) HCLB, high compost (269 Mg/ha) + lime applied as Ca(OH)₂ (11.2 Mg/ha) + bentonite (50 g bentonite/kg compost).  The treatments were replicated three times per site in a randomized complete block. The soil physical properties were not studied in 2006.  In November, 2014, 8.5 years after the addition of the amendments, the plots were sampled and water content (WC), bulk density (BD), unsaturated hydraulic conductivity (k) were measured. Wet-aggregate stability was tested, and geometric mean diameter (GMD) and mean weight diameter (MWD) indexes were calculated.  Dry-aggregates were collected and GMD and GSD (geometric standard deviation) were calculated. Significant treatment effects were observed 8.5 years after treatment establishment, especially at Site B.  The WC, BD, and k parameters had significant treatment differences at Site B, but no one treatment consistently improved soil physical properties.  For the dry-aggregate size distribution test, the CO and HC treatments at Site B had the highest fraction of <0.84 mm dry aggregates, called the wind erodible fraction (WEF), and the LCLB and HCLB treatments had the lowest WEF. The results showed that the WEF of these mine waste materials can be reduced for over 8 years by adding a combination of compost, lime, and bentonite.