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March 1998 Slump /nvestigation and Mitigatiw¢ Report ~ Page 7 4.3 DRILLING AND PIEZOMETER INSTALLATION On Sepcember 8, 1997, MWA installed six piezometers to evaluate groundwater conditions as shown in Table 1, Summary of Piezometer Completion Details and Monitoring Results. The stratigraphy and the approximate location of the slump are shown in Exhibit I-2, Schematic Cross-Sec[ion. Borehole logs are included in Appendix A. In all cases, the stratigraphy encountered during drilling was similar to that observed in the trench: organic soil to within the first 1 to 1'k feet, fill material three co ten feet bgs and bedrock below ten feet. The fill material observed during drilling consisted of gray, light brown, and yellowish brown silt with fine sand. The structure of this material was ofren mixed without continuity of bedding or laminations, indicating that is was backfill or reclaimed spoils. The bedrock consisted of dark brown or dark gray finely laminated siltstone with abundant calcite and sulfur precipitation as well as oxide staining along fracture surfaces. The upper portion of the bedrock was completely weathered to a silt with a gradational contact between weathered and unweathered bedrock.. The gray, strongly consolidated siltstone observed in the bottom of the trench was not clearly observed in the boreholes; however, there was a relatively stronger layer encountered in each borehole between 5 and 9 feet bgs that may have been the equivalent. Groundwater was not observed in any of the boreholes during drilling in September 1997. However, the soil moisture content did appear to increase near the top of the weathered bedrock in most of the boreholes. Additionally, the presence of calcite and sulfur precipitates, as well as oxide staining within the weathered bedrock indicated that water has moved through the system. Montgomery Wa[son Ameruas ' P.O. Boz 774018 "Steamboat Springs, Colorado ` 80477 (970J 8796260 Y'\AA\L.mp.W,iquian6(.my Fryon 1/]1NA,ly