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County engineer recommends drop inlet to fix Castle Mountain Trail Center parking drainage; estimate $20,000–$25,000
Summary
A county engineer and facilities staff told commissioners that runoff from Circle Drive is pooling on the Castle Mountain Trail Center parking lot and recommended installing a drop inlet into the existing 24-inch storm sewer to collect water; staff estimated the fix at about $20,000–$25,000.
County engineering staff briefed the Natrona County Board of County Commissioners on drainage problems at the Castle Mountain Trail Center parking area and recommended installing a drop inlet to route pooled water into an existing 24-inch storm sewer.
Mike (county roads/engineering) said survey shots show the handicap parking pads have only a 0.03-foot fall and that to correct drainage by regrading the pads would require cutting down 13 inches — an impractical solution that would undermine the surface. He described a steep grade coming from Circle Drive that flattens to about 1 percent before the parking area, creating a location where runoff cannot turn east and ponding occurs.
"The water comes off Circle Drive at a 6% grade... It gets down to 1% and then you try and turn it east at 1 or less percent, and that just doesn't work," Mike said. He recommended installing a drop inlet that would collect water at the low spot and feed the existing storm pipe; engineers estimated mobilization and installation would bring the total cost to about $20,000–$25,000. Mike said the basin would be deep (the existing downstream line is about 7.5 feet deep) and would not freeze or clog under normal conditions.
Staff discussed other options — adding base material, constructing a valley pan or paving portions of the lot — and warned those approaches would either fail to fix the underlying conveyance issue or would be more expensive and still require adequate drainage. Mike said adding gravel without addressing the conveyance would only lead to repeated saturation and loss of the added material.
Commissioners asked for an engineer’s written recommendation to document the fix; Park Board and county staff said CEPI (consulting engineers) had already performed surveys and that obtaining a short written design/specification before contracting would be appropriate. Commissioners agreed to pursue cost estimates and directed staff to return with a firm scope and written engineering recommendation so the board could authorize work and funding.
No contract authorization occurred at the meeting; commissioners asked staff to explore contractor availability this fall and to provide a written engineer opinion and cost estimate.
