So we now know what the minimum volume of the wet well should be to handle all inflowrates. We now need to select our wet well shape and size. This is an iterative process. A good place to start is by sizing the minimum hatch dimensions as this sets the minimum well diameter.

First determine the horizontal dimensions of the pumps by referring to the technical information sheets for your selected pump. Some important dimensions are shown in the following example:

The minimum length of the hatch is the distance between where the guide rail bracket mounts onto the hatch edge and the front of the pump. This is typically shown on the pump technical sheet.

To determine the minimum width of the hatch, use the following equation:

Hatch Width = (Number Of Pumps * Pump Width) +

[(Number Of Pumps – 1) * Minimum Pump Spacing]


Each pump manufacturer typically has a recommended spacing between each pump. Consult your selected pump manufacturer to determine these dimensions. The purpose of this spacing is to prevent the pumps from competing with each other in the case that they are running at the same time. Jensen Precast recommends that the minimum spacing between the outer edge of the pump to the wet well wall correlates to the pump spacing dimension. Below is an example of Homa Pumps recommended spacing from outer edge of pump to outer edge:


When specifying the hatch for the system, remember to address the following considerations:

  • Loading Criteria
Rating Live Load Uses
Pedestrian 300 lbs per sq foot Area of pedestrian traffic only
H-10 Incidental 8,000 lbs dual wheel load 16,000 lbs per axle Area of limited smaller vehicle traffic
H-20 Incidental 16,000 lbs dual wheel load 32,000 lbs per axle Limited access area of vehicle traffic
H-20 Full Vehicle Traffic 16,000 lbs dual wheel load 32,000 lbs per axle plus 30% Impact Factor Area of direct continuous vehicle traffic
As defined Per specifications Airports, Ports, Other special applications
  • Frame Features and Options
    • Material
      • Steel (galvanized, painted, or powder coated)
      • Aluminum (anodized optional)
      • Non-skid surfaces
  • Water/Gas tight
  • Trough frames
  • Gasket frames
  • Safety grates
  • Integral Unistrut/Nut rails for upper guide rail brackets
  • bituminous coating on exterior surfaces in contact with concrete