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<br /> <br />CONSULTING ENGINEERS / LAND SURVEYORS <br /> <br />2150 Hwy. 6 & 50, Grand Junction, CO 81505-9422 . 970/242.5202 . FAX 970/242-1672 <br /> <br />March 9, 2003 <br /> <br />Silt Water Conservancy Disuict <br />P.O. Box 8 <br />Silt, CO 81652 <br /> <br />ATTN: <br /> <br />Scot Dodero, Manager <br /> <br />RE: <br /> <br />Harvey Gap Dam Seepage, Preliminary Remediation Cost Estimates. <br /> <br />Scot: <br /> <br />As requested, we are providing cost estimates of various options for addressing the seepage <br />problems after having visited the site and reviewed additional information. There are <br />generally two issues to be addressed - the possibility of progressive removal of material <br />from the embankment, abutment or foundation and the possible existence of voids resulting <br />from historic removal of such material. Methods for addressing each of these issues are <br />discussed in this letter. <br /> <br />If the entry areas for the seepage could be identified with confidence, decisions regarding <br />the means to address these two issues would me much clearer. Based on the 1909 <br />enlargement plans and the geologic information presented in existing reports, it seems more <br />likely than not that the area where the seepage water enters the bedrock is within an <br />approximate 5,000 sq ft area in the vicinity of the spillway. Comparison of the 1909 plans <br />with the existing field conditions suggests that the original spillway excavation shown on <br />those plans has since been filled in and a new concrete spillway structure has been <br />constructed on the fill. If it is correct that this is the area of seepage, it would sufPciently <br />narrow down the entry area to allow for adequate evaluation of mitigation options. <br />However, if the subsurface conditions are different than indicated by the plans and <br />geologic evaluations, decisions made on the basis of this initial indication could prove to be <br />erroneous. Therefore, we are presenting below three possible methods for trying to <br />confinn the entry areas: <br /> <br />1. Dyes could be used to try and identify shoreline reservoir currents toward the <br />seepage entry areas. This could be done with the reservoir at gage elevations between 47 <br />and 49 and would involve the following: <br /> <br />a. Close the outlet at the desired reservoir level at least a day prior to the dye <br />test in order to dampen out outlet discharge currents. <br /> <br />b. Dye the reservoir surface at isolated locations along the shoreline and <br />observe the travel directions of the dye. <br />