But there is a difference between being familiar with a product and being able to effectively use it. “Most contractors have used trash pumps from time to time, but not always in the most efficient manner pertaining to use or maintenance,” says Williamson.
“We have found many contractors will not properly set up even a single trash pump dewatering system,” says Nute. “Too often, very little thought goes into making a ‘system’ that is efficient. Things like an inadequate suction hose, too much debris or solids to pump efficiently, too long a run of undersized hose or pipe, kinks and obstructions in the discharge line are present. Pumps are too often sized in an isolated environment and not thought of as a system.”
Trash pumps often provide a good short-term solution. “If the jobsite is not too large or deep, and the project will only continue for a short duration, a simple trash pump could be an effective and inexpensive solution for your dewatering needs,” says Williamson. “However, each and every jobsite presents different challenges. In the same jobsite, two excavations less than 25 ft. apart could require completely different systems to run successfully.”
Another more complex solution is the wellpoint pump. “Wellpoint pumps are useful because they should handle significant amounts of air and be able to prime and re-prime on a regular basis,” says Aldridge. “The limits are that due to the design of these pumps, they do not handle large solids.”
Wellpoint pumps are intended to pump clean water/effluent for wellpoint and sock dewatering. A typical 6-in. wellpoint pump is capable of pumping 1,500 gpm with head pressures of 100 ft. or more. The objective is to lower the groundwater table to drain excavation sites.
Unlike a trash pump, the objective with a wellpoint pump is to keep groundwater from entering an excavation in the first place by lowering its level. “Wellpoint systems offer a good way to keep water out of a jobsite, and once installed, typically require minimal maintenance,” says Williamson. “Wellpoint systems may be cost prohibitive for short-term projects, but very appropriate for longer durations.”
Don’t overlook submersible pumps. “If electrical power is available on site, an electric submersible pump can be a simple and inexpensive dewatering solution,” says Williamson. However, he cautions, “It is not always efficient to use whatever pump is available on site. Put some thought into the job and select a proper fit.”
“Submersibles are an excellent choice when the static lift is greater than when an end drive centrifugal will work,” says Nute. “Typically, in depths of 20 ft. plus, submersibles need to be considered. The availability of line or temporary power needs to be considered, as well as the type of product to be pumped.”
In some instances, access to the site, the depth of the excavation or elevation changes create challenges for an above-ground pump. “Submersible pumps are an excellent choice in the instance when suction lift is a challenge for an above-ground system,” says Aldridge. Typically, the limit for such systems is 28 ft., depending on the pump performance and flow requirements. Submersibles don’t face this limitation, and will not be disabled if an area floods.
“Submersible pumps work well regardless of site depth,” says Williamson. “Above-ground pumps are limited through the laws of physics to a maximum depth of 29 to 30 ft. Submersible pumps can be very efficient when sized correctly, and will use less space on a crowded jobsite. If the submersible is a quality brand and used properly, it is very low maintenance and nearly labor free.”
Some of the latest advancements in dewatering revolve around submersible pumps. “Slimline submersible pumps are now available to fit inside pipes as small as 8 in. in diameter,” says Williamson. “Since the footprint is so small, contractors are able to place perforated casing pipes with a pump nearly anywhere on a jobsite. Special floats can be used for confined spaces, which turn the slimline pump on and off, depending upon water levels.”