2016-11-16_REVISION - M1987049 - Laserfiche WebLink

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Mr. Joe Lamanna November 11, 2016 Page 3 entering the system. In the transmission trench area, geofabric shall be installed around the gravel material to limit fine grained material from entering the system. The remaining depth of the trenches shall be backfilled with compacted native overburden or clay material. Cross sections of the construction in the collection and transmission sections of the underdrain system have been presented in Figures 4 and 5, respectively. At the outlet of the underdrain system, where it discharges to the McCann Ditch, a discharge structure shall be installed including concrete and rip-rap material to protect the McCann Ditch from erosion and tampering similar to the structure presented in Figure 6. At the upper end of the underdrain system to the south, the pipe will angle up and terminate at the surface with an access port covered by a manhole cover for cleanouts,when periodically necessary. All sections of the pipe installed in the underdrain system shall slope towards the discharge at a slope of no less than 0.5% (1 foot drop for every 200 feet horizontal). Steel plating should be installed above the trench in any location where vehicle traffic is expected. A contour map of the property area has been included as Figure 7 for additional reference information. Action Plan Construction of the proposed underdrain system should proceed consistent with the following construction action plan. The existing drainage channels should be maintained during any site activities to provide for drainage of flow away from the construction site. -Preliminary Investigation • Access the area with excavation equipment and investigate the depth to native gravel material at the location of the proposed collector trench. Depth to gravel may be as much as seven feet below the ground surface. For planning purposes, plan to complete at least five test pit excavations. We suggest that BBA have a representative on site for the test pit excavation processes to collect technical observations. -Trench Construction and Pipe Installation • Excavate a trench along alignment of collector and transmission trenches potentially with the aid of trench boxes. The depth of excavation and gravel backfill in the collector trench area should be to the depth of native gravel material.The gravel backfill material will likely extend as much as five to seven feet below the elevation of the perforated discharge pipe. The depth of the excavation and gravel in the transmission trench area should be no more than 6 inches deeper than the proposed pipe elevation. • As the trench is advanced, backfill trench with compacted gravel material to the pipe elevations specified for the pipe alignment in Figure 3 and install perforated pipe at the specified elevations.