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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Chapter III w Background Information <br /> <br />Bedrock was encountered in B I 0 I and B I 02 at a depth of 48 to 50 feet, and a depth of 15 <br />feet in B103. The bedrock is an highly weathered sandstone that is soft and friable, weakly <br />cemented, similar to the bedrock that is exposed in both abutments. Simplified boring logs for <br />B I 0 I through B I 03 are shown on Figure III-4. Groundwater was encountered in all three borings <br />during drilling. The depths of groundwater encountered during drilling are present in Table III-3. <br /> <br />Table 11I-3 <br />Groundwater Depths at Time of Drilling <br /> <br />Boring Groundwater Depth (ft) <br />BiOI 25.5 <br />BI02 45.0 <br />BI03 10.0 <br /> <br />Open-standpipe observation wells were iflstalled in BIOI and BI03 upon completion of <br />the hole. The wells consist of2-inch nominal di<lmeter flush-jointed PVC pipes with a bottom <br />screen section. The length of the screen section is 5 feet for B I 0 I and 10 feet for the hole was <br />backfilled with concrete sand. The top of the wells is sealed with approximately 3 feet of <br />bentonite chips, and then protected with a 6-inch.-dimater lockable surface casing. Table III-4 <br />lists the well readings taken for the observation wells. <br /> <br />Table 11I-4 <br />Well Readings Three Weeks after Installation <br /> <br />Well No. Water Depth (31i7/99) Water depth (4/8/99) <br />BIOI 43.0 43.0 <br />BI03 9.0 9.0 <br /> <br />The water levels in Well BIOI are about 18 feet lower than that observed during drilling <br /> <br /> <br />of the borehole. The observed water levels in W~ll BIOI are also inconsistent with the <br /> <br /> <br />observations of the samples and sampler during drilling. During drilling of BIOI, the sampler <br /> <br /> <br />and the samples below a depth of 25 feet were w~t, indicating that the fill was saturated below <br /> <br /> <br />that depth. It is not known why this well does not probably record the water level in the <br /> <br />embankment, since the well screen is backfilled with a clean 10-20 silica sand. Because of these <br /> <br /> <br />inconsistencies, the water levels observed in Well B 101 are considered to be unreliable, and a <br /> <br />water depth 25 feet is taken as the depth of the phreatic surface in the embankment at that <br /> <br />Monument Lake Dam Feasibility Study <br /> <br />17 <br /> <br />BDVLE <br />