Groundwater & Basement Water Intrusion in Leominster, MA

That is the thaw doing what the autumn rain set up. Dense till here drains slowly, so ground that took water in October is still holding it when the freeze arrives. When the snowpack melts in spring, that water is added to soil that never emptied, and the surplus goes wherever it can, which is often through a foundation wall. It is genuinely a seasonal event rather than a storm event, and it recurs annually.

That is worth treating carefully, because below-grade space in a converted mill was not built to be occupied. The walls are usually thick masonry set directly into wet ground with no drainage layer, and they were expected to be damp. Finishing that space traps moisture behind materials that do not tolerate it. If the conversion did not include a drainage system and a proper approach to the walls, the lower level will keep producing problems.

Assume very little, and design accordingly. Glacial till here was compacted under ice and it is dense, so water moves through it slowly. Practically that means a footing drain matters more than the grading above it, because surface improvements only address the water that has not yet soaked in. It also means a sump may run long after the rain has stopped, which is the system working rather than failing.