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<br />., <br /> <br />time. Additionally, seismic events have the potential of opening joints, <br />increasing erosional forces or collapsing existing cavities. The recent seepage <br />monitoring has indicated, as John Blair noted, the possibility of a substantial <br />increase in seepage flow rates over time which, if representative of a trend, <br />would indicate significant increases in seepage flow path size. <br /> <br />2. The Martin and Wood report discussed the possibility of two remediation methods: <br /> <br />a. Installation of a synthetic liner. This could possibly be an inexpensive meam to <br />reduce or eliminate seepage. However, the key to success of this method is to <br />assure that the liner covers all or most of the seepage entry points and to make <br />provisions to assure that new entry points do not develop. Our expmence has been <br />that, while in some cases upstream lining has been successful, in other situations <br />accomplishment of these two goals is not necessarily as simple as it might appear. <br />Even obvious entry points do not necessarily reflect the source of the majority of <br />seepage. There also seems to be a tendency for seepage to seek new paths when <br />previous entry points have been cut off. The Martin and Wood report suggests that <br />the clayey shale geologic strata would likely constitute aquitards or layers which are <br />practically impervious to seepage flow. However, these clayey zones can include <br />joints, fractw"es and bedding planes which can transport water in a similar manner <br />to the more sandy layers. These openings can either be the result of geologic <br />processes or constrUction activities. Joints in clayey materials can be held open by <br />soluble minerals which leave open seepage paths as they dissolve. The implication <br />is that it cannot safely be assumed that only the sandstone layers provide seepage <br />entry areas and conduits. It is even possible that seepage entry points could be <br />located at some distance from the dam embankment. Therefore, it would be <br />advisable to conduct additional field investigations prior to undertaking a lining (or <br />grouting) project in order to attempt to more specifically identify probable seepage <br />entry areas. Following are discussiol\l\ regarding two options for further <br />investigations: <br /> <br />1. There are geophysical methods which have been used to identify seepage paths <br />in similar situations. Such information could be used to evaluate the potential <br />of using lining methods, to better locate target areas for grouting, or to identify <br />non-re8ervoir sources of seepage flow. It is estimated that the cost of <br />geophysical swveys would be on the order of $30,000. Additionally, field <br />geophysical surveys would need to be performed with the reservoir at both <br />levels which produce maximum seepage and levels at which minimum seepage <br />occurs. Therefore, the surveys would require the time necessary to cycle the <br />reservoir stage through minimum and maximum levels. <br /> <br />n. We have not had an opportunity to review any existing geotechnical <br />infonnation for the project. Unless the existing information is comprehensive in <br />the vicinity of the seepage, it would be valuable to drill additional test holes <br />along the dam crest in the area where seepage is occumng to more specifically <br />