Wet wells are vertical cylinders built into pond edges. They supply irrigation water to submersible pumps. In the Northeast US, we use four or six foot diameter concrete risers for new installations or to replace rusted corrugated metal pipe. These cylinders or risers are sold as interlocking sections. The bottom section should have a 6″solid concrete base.
To replace a wet well, first detach and/or remove the suction line and any other pump connections. In some cases, a new concrete cylinder with a bored suction line hole can be lowered into the metal pipe.
The horizontal suction pipe is fed through the precast hole a few feet above the concrete base. I suggest using DR11 HDPE pipe (Not double wall drainage type pipe) for this pipe run. A wire cage mounted at the suction end will keep out debris and be cheap insurance against power failure.
If the method described above won’t work, a full well replacement must be done. Pond water pressure complicates wet well replacements because the contractor must first remove all the old pump components then block pond water from the wet well excavation. Typical water diversion techniques include cofferdams, diversion bags and berms.
- Cofferdams are vertical steel panels driven into the pond floor in a line or radius. They are very expensive and cannot be used on clay or synthetic lined ponds.
- Large diversion bags perform the same role and they don’t require piercing the pond floor. They can leak water no matter how tight you install them.
- Berm construction involves constructing of an earthen wall or layered sandbag wall in the pond that radiates from the wet well work limit. Lowering pond levels will simplify diversion installations.
Another method of wet well replacement involves excavating a hole installing twenty or so feet from the pond edge and old wet well. Some fill the old wet well with clay. In this case, no water diversion is needed. . The existing pond edge serves as the diversion as the concrete sections are installed.
After the wet well is installed and a new concrete foundation pad poured, a new perpendicular channel is dug from the edge of the pond to the wet well. This new channel is a few feet deeper than the bottom of the supply pipe and is also wide enough to deliver proper water volume. In some cases a modified suction line will supply water to the pump. In other cases, pumps may need realignment to fit supply needs. It’s good practice to line the new channel with geofabric topped with six inches of rip-rap stone.