2012-09-10_REVISION - M1982090 (5)

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Mr. Oswald/M -1982- 090 /TR -04 September 10, 2012 Page 5 of 6 the girders, 5 "x5 "x5/16" angle iron will be welded between the girders (at 45° and 90 °) as crossbracing. The pipe will rest on '/4 "x5" gussets, end plates, and bearing plates that are elevated above the crossbracing between the girders and radiused to fit the outside diameter of the pipe (36 "). Every 5 feet along the length of the beams, 1/8"x5" steel straps (radiused at 36 ") will be wrapped around the top of the pipe and bolted to the angle iron between the girders using 5/8" threaded rod. Where practicable, the steel materials and fasteners will be galvanized, stainless, or painted to prevent corrosion. DRMS: The non - functional Parshall flume that is currently on site will be replaced, presumably to be able to monitor discharge flows. Will the new Parshall flume be galvanized steel construction or a durable non -metal composite material? There is no mention of any problem with the current concrete structure around the Parshall flume, nor that replacement of it is needed. Please clarify if replacement work is needed for the concrete structure around the Parshall flume. CBCI: The replacement flume is currently anticipated to be a 12" Parshall flume manufactured by Plasti -Fab, Inc. in Tualatin, Oregon. This flume will be designed to accommodate 160 to 7,200 gallons per minute. Plasti -fab describes the composition of their flumes as, "Full length, molded fiberglass reinforced polyester laminated in one piece. The interior surface will have 10 to 15 mil white gelcoat backed by a resin rich layer of resin and chopped glass forming a water and chemical resistant surface. The remainder of the laminate shall be fiberglass reinforced polyester containing not less than 30% glass content by weight. The thickness of the walls and floor of the flume shall not be less than 1/4 inch." The concrete structure surrounding the flume is in excellent condition. The only segment of the concrete structure to be replaced will be the wing containing the pipe intake (see Photos 3 and 4 of the original submittal of TR -04). There may be some concrete and grouting needed beneath and along the walls of the replacement flume to ensure that it is level, secured properly, and sealed. DRMS: Since nearly all work related to portal rehab has the potential to increase sediment loading of the portal discharge, the sediment pond and its conveyance pipe must be installed before the portal work may proceed. Please confirm. CBCI: The sequence of construction activities described in the TR and in this response letter are as follows: 1. Excavation of the sedimentation pond simultaneous with stockpiling of excavated materials 2. Construction of pond outfall 3. Installation of the discharge conveyance simultaneous with grading and stockpiling of GA1 and GA2 4. Installation of new Parshall flume at pipe intake 5. Construction of equipment storage building simultaneous with 14L portal construction 6. Snow shed construction 7. 14 Level drift rehabilitation