21-07 - 2021 Ditch Screening Structure Upgrade

The City of Gunnison is upgrading the potable water intake structure pipe off of an irrigation ditch on the northeast side of the City. The improvements include the following:
 

1. The existing 30” CMP pipe needs to be replaced from the intake to the splitter box. The current intake structure is a concrete headwall with a 30” CMP pipe. The new 30” HDPE dual wall pipe will have to overlap and be banded to this existing pipe at the headwall. The pipe will require several 45-degree vertical bends in order to avoid an existing 3-phase electrical feeder line. The exact depth of this electric line is unknown and will need to be potholed before construction to verify the depth before the pipe excavation begins. A minimum of 1.5’ of cover will need to be maintained over the new pipe. The finished grade above the new pipe may need to have on site fill added in order to maintain the required cover.  The pipe should have select backfill around it. This backfill should meet the pipe manufacturer specifications.

2. The existing splitter box will be demolished and replace with a new splitter box at the west end of the proposed pipe. This box will have interior dimensions of 48” x 48” and a depth of around 7.5’. The box is designed to sit above existing and finished grade and be deep enough to allow for clearance below the pipe inverts for slidegates, at least 0.2’ See the plan set for reinforcement requirements and other details. Two bollards will be added in front of the new splitter box.

3. Access to the headgate will be upgraded. A new 14’ wide gravel road will need to be graded in and topped with 1-1/2” washed rock.