The Portland (NH) Press published a nice story on the significance and value to residents of geologic mapping by the New Hampshire Geological Survey. [right, simplified bedrock geologic map of New Hampshire. Credit, NHGS]
An example they gave was that,
After days of torrential rain in March and April, water wouldn't leave the basements of about 15 homes in a Rollinsford neighborhood. The pumping seemed endless, and officials in the Seacoast town needed a solution.
They found it with the New Hampshire Geological Survey office, which had a detailed map pointing out sand and clay layers underground - and an explanation for the continued flooding.
It showed a unique situation where the sand deposits were overlying clay layers, and the water could not percolate down," said David Wunsch, state geologist. "So the basements were flooding and the sand was flowing into the basements because residents were pumping the water so hard, and the foundations were being undercut."