Sump pump failure during storm or thaw
Brockton sits on heavy clay soil that doesn't drain — most basements rely on perimeter drain tile feeding a sump pit. Atlantic nor'easter rainfall (3+ inches over 24 hours) or March thaw saturates the soil and the sump pumps continuously; when the float sticks, the motor fails, or the power goes out, the water that should be ejected starts rising through the pit and across the floor.