Water Tables and Basements

When we bought our home (built in 1907), I called in a favor from an electrician friend of mine to upgrade the 60-amp to a 100-amp service. Having worked together in New Hampshire where many of our projects were on sites full of ledge, he smirked when he told me: “Here, you go try and drive this 12-foot copper grounding rod!” No more than 10 minutes later I came in and said, “How much of the rod should remain above grade?”

It turns out our home, right in the middle of a steep, shaley, ledgey, slope, must have been built on a ton of free-draining fill, making our basement dry and that rod a piece of cake to drive nearly 12 feet into the ground.

But for both new construction and existing homes, isn’t there a better way to figure out just what soil, rock, and water challenges your site will pose? Actually, there are three great online resources and a couple of others that take just about all the chance and guesswork out of determining site conditions.

Web Soil Survey

Being originally trained as an agronomist, I first went to our Vermont soil specialist, Thomas Villars. He sent me a Word document, “How Get Site-Specific Information on the Representative Depth to the Shallow Water Table for Soils In Vermont Using the NRCS Web Soil Survey.”

There are several different ways to use the NRCS Web Soil Survey, but it’s pretty easy to use the “Area of Interest” (AOI) tab to get you zeroed in on a crystal clear aerial map, and then click the Soil Map tab to get the soil type overlay on the aerial map. Under the Soil Data Explorer tab is a sub-tab “Soil Properties and Qualities,” and then another sub-tab called “Water Features,” giving you “Depth to Water Table” for each soil type in your area of interest.

USGS Groundwater Watch

The U.S. Geological Survey has several databases related to ground water.  For builders and remodelers, the most useful of these resources are probably the Active Groundwater Level Network and the Long-term Groundwater Data Network. Each is fed by records from over 850,000 wells drilled over the last 100 years. The data are pretty thin for Vermont and probably for other sparsely populated areas around the country, but there's tons of data for many highly populated regions of the U.S.

Local historical societies and the Library of Congress

Trying to piece together just why our section of Fairview Street in Brattleboro is a rarity — flat, with tons of fill — I got help at the Brattleboro Historical Society (BHS). I was directed to a web site called Old-Maps.com, where I found a great resource, “Early Maps of Brattleboro” . This narrated collection of maps explains a lot about local land use, but strangely, very little about our section of Brattleboro. A quick trip to the BHS led to file cabinets full of street photos, and perhaps more importantly, to a volunteer — a neighbor of mine — who suggested a web site from the Library of Congress called Chronicling America.

Amazingly, this database has hundreds of local newspapers from all over the country — all digitized — for the years extending from 1789 to 1925. You have to be patient, but searching based on your street name or family names you know to have lived in homes for more than one generation can sometimes lead to the history of your lot’s use.

Two resources that are likely to have the deepest local knowledge are the head of your Department of Public Works and local excavators. They have years of experience digging around and knowledge of local water tables.

Finally, here is a checklist to use to determine depth-to-water table on your sites.