High water table - deeper sump basin advisable? AI says no
Hi, I hope this is not against the subs rules. We purchased a new construction home in the northeast in an area with a high water table around 2021 and our basement flooded during Hurricane Ida. Since then I've tried to become more knowledgable on how to mitigate the flooding and after hiring about 4 or 5 local plumbers I realize this is probably outside of their expertise. I've been turning to AI for advice - which I know can also get me into trouble. So that's why I'm here.
Here's our setup for context. The builders put two sump pumps connected via the interior perimeter drain on opposite sides of the house with the secondary pump sitting a bit higher.
The primary pump runs 24/7 and we've replaced it 3 times since we moved in. It sits in a standard 18x24" basin and pumps to the sewer. The secondary pump will only activate if the primary fails and it pumps to the storm drain underground. We also have a generator. There's 3 pipes going into the primary basin (I believe two from the interior perimeter drain and one from outside).
The plumbers and basement waterproofing companies who have looked at our situation all give contrary advise with some advising to set the primary pump at the extreme top of the basin right below the basement floor (where the pump may run continuously for 40+ minutes and be off for an hour) and others advising to put it all the way on the bottom (where it will be on for 10 seconds and off for 10 seconds - which they say will stop after 1 week).
I had forced the last plumber to install a Hydrocheck float switch which allows me to set the on and off points anywhere in the basin (we zip tied the Zoeller's float switch so that it's always on).
* Sump Pump: Zoeller M137 sitting on the bottom of the pit
* Off point: Close to the base of the pump and below all pipes in the basin
* On point: Completely above 2 of the inlet pipes and 3/4 up the 3rd inlet (the highest one).
When we first set this up the pump would run for ~6 minutes and be off for 12 minutes. But now it runs for 3.5 minutes and is off for 5.5 minutes which seems too frequent. Also, I noticed the drain from outside cannot fully drain into the sump basin as the Zoeller 137 pumps out the basin too quickly. And I feel we're in no better situation to handle a hurricane type storm than when we first moved in.
I thought installing a larger basin adjacent to this main basin would allow the primary pump to pump a bit longer while keeping the interior perimeter drains emptier. Zoeller sells a 30x36" basin and a 36x36" basin. And my idea was to connect this second basin with a 4" pipe at the bottom. Besides additional capacity, with the second basin I can have the pumps alternate to avoid burn out, or in the hurricane scenario, both run simultaneously. AI has advised against putting a deeper basin as it says I'll create a cone of depression where a greater amount of water will flow in at a higher rate:
>Google Gemini:
By deepening the pit, you increase the hydrostatic pressure difference between the surrounding soil and the empty basin. The water will rush in significantly faster, increasing the total volume of water your pump has to move without actually making your basement any drier.
Is AI right here? AI thinks I should go wider but not deeper with a second basin. No one makes a wider 24" basin so it would have to be custom. Local plumber friend thinks I'm overreacting and should leave it as-is. My wife thinks we should put a french drain on the outside and I'm open to that as well. If this was your house, outside of moving out, what would you do or who would you contact?