Septic Risk Assessment

Lake Sunapee Protective Association (LSPA) hired FB Environmental (FBE) through a Local Source Water Protection Grant from NHDES, and with support from USEPA, to start a Septic System Vulnerability Assessment for an area around Mountainview Lake.

This mapping and data inventory tool helped visualize areas where wastewater pollution from a potential failed septic system in that area was most likely to occur, or where it would do the most damage if it occurred.

The analysis combined several environmental datasets (soils, wetlands, surface waters, and flood zones) to understand where the landscape is naturally more or less vulnerable to septic system impacts. After this pilot project with FBE, LSPA staff took on the challenge of mapping and analyzing the rest of the watershed.

This map was created to visualize the vulnerability of Merrimack and Sullivan Counties to septic failure based on the co-occurrence of numerous environmental factors.

Overlapping risk factors indicate a greater risk to health and safety should a septic system fail or malfunction, because the resulting waste will have a more direct route to nearby waterbodies and swimming areas.

The limitations composing this map are based on soil limitations (such as filtering capacity, flooding, ponding, depth to bedrock, slope, depth to saturated zone, seepage, subsidence, large rocks, and non-rated soils such as sand/gravel pits or rock outcrops), the presence of wetlands, highly transmissive aquifers, flood zones, and distance to streams and lakes.

The total risk scores were binned into categories of low (scores 0-1), moderately low (1-2), moderate (2-3), moderately high (3-4), and high (4+) risk.

Tips for using the map on the left!

The top left corner arrow opens the map details, the legend, and the basemap gallery.

The bottom right tools allow you to navigate the web map here on our website. Hover over each icon to see what they do.

We recommend clicking the second icon from the top to Open in Map Viewer for full exploration of the map and layers.

You can zoom in and out with your mouse’s scroll wheel, and click on the polygons to see what that polygon was ranked.

The total risk score is close to the bottom of the attribute table above SHAPELength and SHAPEArea when you click on a polygon.

There are often many small polygons next to each other or overlapping each other. When you click on the map, toggle between the layers in the bottom left of the pop-up window.