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C-BUILDING HILLSLOPE <br />1 <br />1 <br /> <br />1 <br /> <br />This section provides information about a potentially unstable slumped portion of the <br />hillslope between the Goat Trail and the previous C-Building access route. Monitoring of the <br />hillslope was initiated in mid-1996 using the method described in the Inventory Methods section <br />of this document. It was believed that the slump was "seep-fed" and had existed for an extended <br />period of time based on the mature hydrophytic-mesic vegetation found at the site. In previous <br />years, the slump remained active due to road ditch maintenance along the access route [o the C- <br />Building. The maintenance consisted of removing material from the road ditch at the toe of the <br />slump. As a result, the slump continued to creep downslope into the ditch along to the access <br />route. In conjunction with reclamation activities associated with the conveyor system in late <br />1996, this route was closed and reclaimed in accordance with the Goat Trial reclamation plan. It <br />was anticipated that discontinued maintenance of the route would allow [he toe to remain intact <br />and stabilize the slump. <br />The slump exhibited slight movement during the first monitoring period. Movement <br />' measured along the upper transect consisted of a two inch displacement occurring at both the east <br />and west stakes. Movement measured along the lower transect consisted of a three inch <br />displacement at the east stake and a one inch displacement at the west stake. <br />1 <br />1 <br />1 <br /> <br />1 <br />In 1998, the slump and additional surrounding azea experienced significant movement. <br />Movement along the upper transect consisted of a total displacement of 60 inches at the east <br />stake and 57 inches at the west stake. Movement along the lower transect consisted of a total <br />displacement of 33 inches at the east stake and 31.5 inches at the west stake. A visual inspection <br />confirnred that a seep does exist along the interface of differing lithologies in the upper portion of <br />the slump area. Apparently, the abnormal winter and spring conditions enabled a substantial <br />amount of moisture to infiltrate into cracks and fissures in the bedrock material above the slump. <br />The moisture subsequently exited the bedrock at the lithologic interface via the seep and <br />saturated the unconsolidated surface soils to the point of liquefaction. Additional visual <br />inspections indicate the slump material is draining and resting comfortably with the toe <br />supported by the reclaimed C-Building access road. The stakes within the slump area along the <br />upper transect were realigned in late 1998 for future monitoring. <br />' Observations in 1999 indicate the slump area has not exhibited additional movement due <br />to spring melt. The in-slump stakes along the lower transect will be realigned for future <br />monitoring. Based on the observations made to date, P&M believes the most prudent course of <br />' action is to continue to monitor the slump to determine if it has reached stability through self- <br />draining and a large toe configuration. <br />' Observations made during the 2000 inspection indicated no movement in either the upper <br />or lower transects. Therefore, P&M will continue to monitor the slump to verify it has reached <br />stability through self-draining and a large toe configuration. <br />1 <br />' 16 <br />