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• 4.8.5.3 Infiltration Monitoring <br />Pre-mining infiltration rates have been documented by soil type per Appendix G Part IV. Post-mining <br />infiltration rates were measured on regraded and retopsoiled areas in 1983-1986. Three infiltration tests <br />using a double ring infitrometer were made at three locations in each plt during each year. At each loca- <br />tion, three separate infiftrometer readings were taken and the average results used to characterize the <br />stte. Tests were run during periods of low antecedent soil moisture condltions (Aug. and Sept.), Sample <br />sttes were marked in the field and re-sampled each year. This provided data for the same sites over the <br />life of the permit and indicate trends in increasing or decreasing infiltration rates. <br />Many factors related to local soil properties influence infiltration rates on premine and postmine lands. <br />These factors inGude surface and subsurface texture, abrupt horizon changes, porosity, permeability, <br />structure and cracking, depth, mineralogy, organic matter content, slope, aspect, and nature of the parent <br />rock. Some local soils are shallow wlth high organic content and often overlay fractured sandstone rock. <br />Water seeping through fractures in the parent rock, as well as lateral subsurface flow, may contribute to <br />high intake rates. High intake rates may also be attributed to unencumbered water movement through <br />the soil profile. Some soils are moderatey deep and overlay stratfied Gay shales. These soils have a <br />high Gay content, most likely predominantly montmorillonlte. Clays characteristically have low infiltration <br />rates due to swelling of Gay minerals when saturated with water. <br />• Considerable variability in infiltration rates exist between years on postmined land. When comparing <br />premine to postmine data, the postmine inflttretion rates all fall within the established premine infiltration <br />limits wtth tha exception of the North Ashmore site in 1988 (fable 4.8-14). Postmine infiltration rates <br />ranged from a high of 22.9"/4 hrs to a low of 1.33"!4 hrs. Based on the data presented on postmine infix <br />tretion rates, Trapper proposed and the Division approved discontinuing infiltration sampling in 1987. <br />Flowever, Trapper may re-evaluate postmine infiltration monitoring at some future date. <br />• <br />4-247b <br />~~~ <br />NfAY 13 199 <br />