We recently purchased a ~20 year old house with no disclosed history of flooding.
Over the winter season, we've seen significant rainfall three times. Each storm, we've seen a substantial flood in our basement.
After the first flood, we engaged insurance, who brought in restoration services. The folks from that company dug up flooring after the second flood and discovered a very wet backwater valve pit. Pictured:
After the mold abatement and mitigation had been completed, we decided to leave the basement in disarray until another storm came to prove that the backwater valve pit was the source of our flooding problem.
Indeed, this past weekend we had ~100mm of rain, and the pit flooded. Luckily we minimized the amount of water taken in by opening up the backwater valve lid and the sewer system was able to take in the water. It drained all day at a high rate:
A video of water underneath the basement slab draining into the city sewer via the backwater valve access
A slight tangent: before we opened the lid, we saw seepage around the seams of our foundation and a few other points in the basement (around the grout of a toilet, around some now-sealed floor drains). When we opened the lid and let the water underneath our basement floor slab drain into the city sewer, the seepage stopped.
We will engage contractors on this project, but I thought I'd ask here, too:
- What could be causing this pit to flood now, and not before?
- What would you do to prevent it from flooding in the future?
- If we seal this leak, we won't have a way of draining the water under the basement floor slab... do you think the seepage we started to see will become a problem?
On (2): the house's eavestroughs and downspouts all seem to drain directly into underground drainage systems, so the first thing we plan to do is add elbows to these and direct the water away from the house.
We are also considering adding a sump pump—we do not currently have one.
Thanks in advance!