Hydrologic Soil Grouping Determination for Appalachian Minesoils.

The hydrologic soil group refers to the infiltration potential of the soil after prolonged wetting.  This classification system separates soils into four hydrologic groups (A, B, C, and D), based upon the intake and transmission of water under conditions of maximum yearly wetness. In the study of the hydrologic soil nature, soil properties that affect infiltration, such as bulk density, porosity and texture, should be considered. Associated factors that affect infiltration in the field are slope and vegetation. Surface coal mining is a common practice for extracting coal in West Virginia. This practice removes, changes, and in some cases destroys soil where mining takes place. Additionally, surface grading for stability during minesoil reclamation often causes high compaction. Therefore, it has been assumed that minesoils are somewhat poorly drained with low infiltration rates and high runoff potential. This assumption results in minesoils being classified in hydrologic soil group C. The objectives of this study were to determine the hydrologic soil grouping of a minesoil. Two study areas were selected on a reclaimed surface mine in Webster County, WV. Area 1 was selected to study the effect of vegetative cover and slope on surface hydrology while study area 2 was selected to study the hydraulic properties of the most compacted layer present in the profile of reclaimed minesoils, the compacted backfill. The properties measured to determine the minesoils hydrologic grouping included texture, bulk density, and saturated hydraulic conductivity. Study area 1 exhibited high infiltration and low surface runoff and erosion. Results obtained in area 1 showed that, although minimal, the effect of slope on hydraulic properties was greater than that of vegetative cover. Study area 1 had a higher fraction of rocks, more silt and more clay, while study area 2 had fewer rocks and a greater amount of sand. Bulk density values were higher in study area 2, with uncorrected bulk density values averaging 2.10 + 0.18 Mg/m³, as compared to 1.54 + 0.24 Mg/m³ in study area 1. Corrected bulk density values for study area 2 were 1.80 + 0.24 Mg/m³ while study area 1 exhibited corrected bulk density values of 0.91 + 0.17 Mg/m³. The saturated hydraulic conductivity values for study area 1 averaged 47.3 + 26.2 µm/s, while study area 2 had a much lower average of 3.0 + 2.7 µm/s. Higher bulk density values and lower Ks values confirm that the compacted backfill found in study area 2 was the most limiting layer in the minesoil profile.  The study findings lead to the conclusion that the hydrologic soil grouping for this minesoil should be hydrologic soil group A. In order to ensure that other minesoils are placed into the correct hydrologic soil grouping, future work should be done on more mine sites to determine whether similar hydrologic behavior may change an assumed hydrologic soil grouping. Such work should also be conducted over a longer period of time to study how soil hydrologic properties may change as minesoils become more developed.