Dump Site Selection: Soft Ground, Septic Field, and a Posted Bridge
The shuttle incident commander asks you to scout a dump site at the end of a 900-ft gravel driveway. The driveway is 10 ft wide, with soft shoulders after 1.5 in. of rain. At the end is a pasture with a 4% side slope; a septic system drain field lies under the only obvious turnaround area. The proposed dump point is 300 ft beyond a bridge posted at 12 tons on the direct route. The alternate route adds 2.1 miles and ends at a paved equipment yard with room to turn. Your tankers are 2,000 gal and 2,500 gal; both have 8-inch rear dump valves, and the 2,000-gal unit also has a 3-inch side dump. The portable dump tank is 2,500 gal. A 2,500-gal tanker at legal gross is roughly 27 tons, well over the bridge posting. The IC wants the first tanker dumping within 10 minutes.
1. Evaluate the proposed pasture site and recommend where to dump. Use the specific constraints in your answer.
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The pasture site fails on three counts. First, access: a 10-ft gravel driveway with soft shoulders does not allow two tankers to pass and gives almost no margin for an 8.5-ft-wide truck; a loaded tanker that drops a rear wheel off the edge can roll. Second, the dump tank cannot be level on a 4% side slope; a portable tank on that slope will distort, the dump valve will not drain completely, and the tank can shift. Third, the only turnaround is over a septic drain field, which can collapse under a 27-ton tanker, and the direct route crosses a 12-ton bridge that the loaded tanker cannot legally or safely cross. I would recommend the paved equipment yard on the alternate route: it is 2.1 miles farther, but it has room to turn, a hard level surface, no bridge restriction, and no septic hazard. The extra travel time is small compared with a recovery or injury.
2. If the IC orders use of the pasture site anyway, how do you position the tanker and dump tank, and what limits do you set?
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If directed to use the pasture, I would keep the tanker on the gravel driveway and not drive onto the pasture. I would place the portable dump tank on the widest, most level hard spot available, using timber or prefabricated pads to spread the load and bring it within about 1% level. I would use the 3-inch side dump on the 2,000-gal tanker if the rear dump would discharge onto soft ground, and I would dump at a reduced rate so the tank does not surge and the driveway edge is not loaded. I would not put the 2,500-gal tanker over the septic field or the bridge. I would set a spotter at the driveway entrance, limit speed to walking pace, and stop operations if the ground rutted more than a few inches. If no level pad can be made, I would decline the site and ask the IC to move the dump point.
3. What site marking and radio communication do you complete before the first tanker arrives?
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Before the first tanker arrives I would mark the entrance with cones and reflective tape, designate one-way travel and a turnaround point, and mark the dump tank with a visible flag or light. I would establish a separate radio channel or a clear tactical channel for the shuttle, confirm radio coverage at the dump site, and assign a dump-site officer if staffing allows. I would give the first tanker a short brief: approach speed, spotter location, dump valve to use, tank level, and where to go after dumping. I would also tell the IC the bridge restriction and the actual round-trip time so the shuttle rate is based on the alternate route, not the direct route.