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Comment Response For TR-74 <br />West Taylor Pond <br />Figure 1C-3 <br />1) Four separate samples of "borrow" material were collected, and their physical properties were <br />analyzed in the laboratory. None of the samples met the qualifications described in the <br />originally-approved design; the Plasticity Index of each fell short of that required to be classified <br />as either CL or CH. In other words, the fine-grained soils readily available consisted mainly of <br />silt (which is susceptible to "piping") rather than clay (which is plastic and binds together well). <br />The Acceptable Fill Materials note on the drawing was subsequently amended to allow the field <br />engineer to approve the use of other materials, following appropriate laboratory testing. Given <br />the lack of availability of more desirable borrow material, this change is understandable. <br />2) Silty material is not normally desirable for the construction of earthen dam structures. Because of <br />this fact, a drainage filter mat was incorporated into the design. The Division agrees with the <br />decision to add this feature to reduce the potential for a piping-related failure to occur. <br />Construction Report <br />3) The last sentence on Page 1 should refer to Attachment "A2" rather than "211. Please <br />correct this error. <br />Response: The requested change has been made with this submittal. <br />4) The seventh paragraph on Page 2 should refer to Attachment "Al" rather than "1". Please <br />correct this error. <br />Response: The requested change has been made with this submittal. <br />5) The second paragraph on Page 3 should refer to Attachment "A2 rather than " 2". Please <br />correct this error. <br />Response: The requested change has been made with this submittal. <br />6) According to the first paragraph on Page 4, the approved 24-inch flume was replaced by a 9-inch <br />version. <br />Please provide the Division with design calculations which illustrate that a 9-inch flume is <br />sufficient to carry the flow expected from dewatering the pond through the 18-inch CMP <br />that has been installed. <br />Response: Under the 10 year, 24 hour design storm assumptions for the West Taylor pond <br />presented in Volume 13, Exhibit 7, Item 20, (page Exh. 7-20C-24), the resultant <br />peak flow of 5.25 cfs occurs at a pond stage of 7471.51 feet. A Parshall flume <br />with a 9 inch throat can measure a flow of about 8.9 cfs under free flow <br />conditions. <br />Flow through a 9 inch Parshall flume can be expressed as: <br />Q=3.07h1.53,