Thanks to Bob Burry of Burry’s Waterproofing for this informative article:

How does water get into a basement that appears to be sealed tight? The answer is through hydrostatic pressure.When your house is built a hole is dug for the foundation.The block walls are erected, the house is built, a basement floor is poured, and then the dirt is filled back in against the walls of your home. That is called backfilling. Water infiltration problems occur because the dirt backfilled is not as dense as the soil that was not disturbed, despite the best efforts of the builder. Water then lays against the foundation walls of your home and over the years and over the decades creates channels and can work its way down to where it actually gets under the footer and under your basement floor. When very heavy rains or large snow melts occur, the weight of the water outside the walls presses down on the water under your floor and forces it up through the invisible seam where the wall and floor and footer meet. Water always seeks its own level.This is called hydrostatic pressure.

The problem can be corrected by having a professional company install a sub-floor drainage system in the basement.This entails removing the floor about 12 inches from the walls, digging a trench, and installing a 4 inch perforated drain pipe next to the footer. Clean stone is added to the trench with the pipe and the pipe slopes to a sump pump. Weep holes are drilled into the bottom course of the cement block to drain the wall and drain board covers the holes and directs the water to the piping system. The system is cemented shut and is completely under the floor.

Prices on this type of system can vary greatly so it is always advisable to get several estimates and always ask for plenty of references that have telephone numbers to call.

Bob Burry, 111 Hess Blvd, Lancaster PA 17601 560-2096 if you have a need!