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The proposal for basement waterproofing in my home as given to me by AquaGuard Waterproofing Corporation called for a sump enclosure described as follows: “…drainage piping will empty into a 30″ sub-floor, commercial grade plastic container housing a heavy-duty submersible 1/2 horsepower pump.” In reality, the enclosures provided were only 22″ deep and 20 ” wide. The figure above captures this discrepancy or failure to provide what was described in the proposal. Beyond the fact that a smaller enclosure is generally cheaper as a material item, using an enclosure of significantly less volume also means less labor and savings to the basement waterproofing company. For example, the hole to be excavated is considerably smaller as is the amount of gravel needed to spread around the enclosure. WIth respect to the latter, it is highly questionable if they used any gravel at all; a failure in workmanship that we will discuss in a future posting.
Regardless of the advantages or disadvantages of AquaGuard using the smaller enclosure, it is a fair question to ask, what difference does it make if the enclosure is 30 or 22 inches deep? Put differently, what is the correct size of the sump enclosure?
Answering this question is very difficult because it is tied to questions like what amount of water is expected to flow into the enclosure. Put differently, what is the expected flow rate into the enclosure vice the expected discharge rate? I am in the process of collecting information on these and related questions as they speak to the following important considerations:
1. What range of flow rates does one expect into the enclosure?
2. Given the range of reasonable flow rates into the enclosure, what demands does this put on the volume or capacity of the enclosure and what size or capacity pump is needed to meet these demands while keeping the water from overflowing?
3. How does one size the combination of sump enclosure and pump to avoid overflowing on the one hand and short cycling of the pump on the other hand? Short-cycling refers to pumps that are constantly turning on and off, which is known to be especially hard on the devices. Short-cycling will lead to earlier pump failures and is to be avoided.
4. Perhaps most important of all, how does one estimate the above variables so one can make intelligent choices with respect to sump enclosure size and sump pump capabilities?
We will be exploring these issues in the future as I gather more information from various sump pump manufacturers and waterproofing professionals. For now, I’ll share part of an email exchange I had with an engineer for a major sump pump manufacturer. First, I’ve copied some comments I made to that individual. Then I’ll provide what I consider an insightful response from the engineer.
Thank you for your comments and insights. Over time I am gaining a better appreciation as to the difficulties in engineering the correct solution. In lieu of a careful assessment of actual water discharge needs, maybe the best an outfit can do is fall back to a “one size fits all” approach and the size that works best for them is the smaller pump. If I learn anything else, I’ll pass it along.
Your comment about using a one size fills all approach is spot on. Larger systems are usually easier as we have well-worn calculations to predict total daily flows, average flow rates and based on start/hr, select pumps and equipment. Unfortunately, when it comes to residential ground water removal systems, it is all over the place. Sometimes, a homeowner finds what he really needed was a commercial system. This would be a larger sump, 2 larger non-automatic pumps, separate control system to alternate the pumps, bring both on-line in an emergency situation, an alarm light & buzzer with dry contacts that allow for remote monitoring. Or, a .25 HP utility/sump pump, that operates a couple of months a year. In either case, the general contractor or home builder may not know if the particular location requires a basic system or one of the entry-level commercial packages. And material costs can easily be in excess of 10 times the cost of a basic system.
In future postings we’ll explore these issues as I believe, and I state again that I’m no expert in this field, these are all related to both the correct sizing of the sump pump installation and the need for more than a casual assessment of any particular basement seepage problem. With respect to what happened in my home, however, the issue of correct sizing is rendered ridiculous by how the enclosure was “prepared” and “installed” by AquaGuard’s hand-picked incompetent subcontractor. We turn next to those topics.