I often receive questions from homeowners about their septic systems. It’s no surprise that they are usually about a specific problem they are having. Recently I received a different kind of question. A person was being relocated for work and was looking at houses in different locations outside a metropolitan area. The question was how to find out if there are problems with high groundwater in the area. This homeowner had lived in a home where the septic system was replaced due, at least in part, to the presence of saturated soil near the surface; and the person did not want to have the same problem in a new home.

Service providers recognize the value of knowing soil and water conditions in the area where they work. When a call comes in from a homeowner about a problem, you anticipate before you even leave the shop some of the conditions you are likely to encounter. As you head to the location, you are already planning for the process of troubleshooting the system.

However, what if you are relatively new to the business or area? Where do you find information on soils and water tables? One answer is to visit the local planning and zoning office (you need to know them anyway to get permits and inspections); your local soil and water conservation district office (usually located near planning and zoning); and state environmental and natural resource agency offices (for me, this is the Department of Natural Resources). All of these agencies can point you toward sources of information on not only water tables and aquifers, but also flood plains and soil information.

A geologic atlas prepared by the state or U.S. Geological Survey, while providing information on the presence and depths of regional aquifers, usually does not show water tables, which we are most concerned with for siting and operation of individual wastewater treatment systems. I say this not because the information isn’t useful, but because the depths of even near-surface aquifers are usually well below the soil zones where we install our systems. We should be aware of them because we want to make sure our systems treat the wastewater before it moves into these aquifers.

WETLANDS A CONCERN

The presence of wetlands (water at or near the surface) and periodic or seasonal perched water tables or saturated zones in the soil are of most concern to us. In the past, I have discussed soil characteristics used during site evaluations to identify these conditions. To refresh your memory, these are “redoximorphic features.” If you want to know something about these conditions before you leave for the site, the soil survey for your county or region is a primary source.

In the past, I would have told the homeowner or service provider to visit the county soil and water conservation district office for a hard-copy report for the county. One flaw in this approach was that all county soil surveys were not conducted at the same time. While the soil map has not changed, the understanding of the soils and their physical and chemical characteristics continues to get better as more data is collected by the Natural Resources Conservation Service and its state university partners. Fortunately, there is now an online tool to look up soils survey information, and the data and interpretations are kept up to date.

The maps and data are available at websoilsurvey.nrcs.usda.gov or simply type “web soil survey” in your browser. More than 95% of the country is mapped. Except for the most remote areas, maps and information are available. Online surveys still present soil lines on a photographic background indicating boundaries between soil types.

Once on the website, locate the parcel you are interested in by either using the zoom function provided or inputting GPS coordinates, county, address, township, range or section. An area of interest can be outlined, and the soil map can be accessed. Data is found on the soil map units found on the site and soil series descriptions. Along with data tables covering physical and chemical characteristics, it covers suitability and limitations for various uses.

ONLINE MAPPING

Having this information does not mean you don’t have to do any work in the field, but it gives you information to help guide your fieldwork, whether it’s a site evaluation for a new system or troubleshooting a problem for a homeowner. Soil surveys identify areas with similar soils and landscape properties and delineate those areas as unique mapping units. These units are delineated on soil properties (texture, color, structure and organic matter) and depth to water table, saturated zones, bedrock and other limiting characteristics.

The online maps have the same scale limitations for site work as the hard-copy versions. At the scale of most surveys, the smallest delineation is 2 to 5 acres in size. Since we work in areas on a lot of 2,000 to 3,000 square feet, we still have to evaluate the soil at the location to see if the soil properties fit our proposed use.

One other point on map units is that, by definition, up to 30% of the map unit can be of soils varying from the soil as mapped. These inclusions, as they are called, are also in the description. Looking at the data for those inclusions, as well as the primary soil mapped, will provide a clearer picture of what you will find at your site when you evaluate the soil.

By looking at the soil survey, the homeowner who submitted the question could determine the probability of encountering problems with water tables on the properties being considered. This can help the person ask the right questions when evaluating each property and might be factored into the purchase price.