Dump Site Operations and Water Unloading
Setting the dump site
Place the portable tank on firm, level ground clear of traffic, overhead wires, and drainage problems. Allow room for the tender to approach and leave without backing if possible. Position the tank so the tender's dump valve can discharge directly into it and a drafting pumper can reach the tank with a short, straight suction line. Use a strainer that stays off the tank bottom so it does not bury in sediment or draw air.
Unloading
Open the dump valve smoothly and fully. A partially open valve can chatter, spray, and slow the dump. Coordinate with the drafting pumper: if the pumper drafts faster than the tender dumps, the tank level falls and the pumper may lose prime; if the tender dumps faster than the pumper drafts, the tank overflows unless a second tank or pumper is used. A jet siphon can transfer water from one portable tank to another or help maintain flow.
Worked example
A tender dumps 2,000 gallons at 1,000 gpm, so the dump takes 2 minutes. The drafting pumper takes 500 gpm. During the dump, water accumulates at 1,000 - 500 = 500 gpm, or about 1,000 gallons over 2 minutes. Reasoning: the portable tank must have that freeboard, or a second pumper or tank must take the excess; otherwise water is lost and the site becomes unsafe.
Traps
Do not set the tank before confirming level ground and clearance. Do not bury the strainer or let the tank run dry while drafting. Do not dump onto the ground unless the incident plan approves it. Do not leave a dump valve partly open.