Soils Subsurface Sewage Disposal Systems

Subsurface sewage disposal systems (SSDS) consist of a house sewer, a septic tank followed by a leaching system, any necessary pumps and siphons, and a groundwater control system upon which the operation of the leaching system depends. This interpretation focuses mainly on the septic tank leaching field and groundwater control system Soil Potential Ratings Soil potential ratings indicate the relative quality of a soil for a particular use compared to other soils in a given area, in this case the State of Connecticut. The rating criteria were developed by a committee of State and local sanitarians, engineers, and installers. The soils data was provided by the USDA Natural Resources Conservation Service (NRCS), and the performance and site conditions for a typical system were defined. This information provided a standard against which various combinations of properties of soils within Connecticut could be compared. The engineering and installation practices used to overcome various soil limitations were listed, and their costs estimated. This information was used to identify limitations and costs associated with installing an SSDS on each soil in Connecticut. Soils with no or minor limitations for the installation of an SSDS were rated the highest. Conversely, soils requiring extensive site modification and design were rated the lowest. The ease of system installation, and therefore cost, formed the basis of the rating scheme. Rating Classes The rating class definitions refer to installation of an SSDS that meets State and local health code regulations. Soils with high potential have characteristics that meet the performance standard. A typical system can be installed at a cost of "x", which represents the going rate for installing an SSDS. The actual value of x varies depending upon many factors unrelated to soil properties. The cost of installing a leaching field is expressed as a multiple of x and called the cost factor. For example, a cost factor of 3x to and 3.5x means that the estimated cost of installing a leaching field in the particular soil ranges from 3 to 3.5 times more than that of installing a field in a soil with high potential. The cost factors provide relative estimates of the costs of installing an SSDS. The soil potential ratings and associated cost factors, assuming a typical system, are defined below. High Potential - These soils have the best combination of characteristics or have limitations that can be easily overcome using standard installation practices. The cost factor is 1x to 2.0x. Medium Potential - These soils have significant limitations, such as low percolation rate, that generally can be overcome using commonly applied designs. The cost factor ranges from 2.0x to 2.5x. Low Potential - These soils have one or more limitations, such as low percolation rate and depth to seasonal high water table, that require extensive design and site preparation to overcome. The cost factor ranges from 2.5x to 3.5x. Very Low Potential - These soils have major soil limitations, such as depth to bedrock, that require extensive design and site preparation to overcome. A permit for an SSDS may not be issued unless the naturally occurring soils meet the minimal requirements outlined in the State health code. It is unlikely that these soils can be improved sufficiently to meet State health code regulations. The cost factor ranges from 4.25x to 6.0x. Extremely Low Potential - These soils have multiple major limitations, such as flooding and depth to seasonal high water table, which are extremely difficult to overcome. A permit for an SSDS may not be issued unless the naturally occurring soils meet the minimal requirements outlined in the State health code. It is unlikely that these soils can be improved sufficiently to meet State health code regulations. Not Rated - Areas labeled Not Rated have soil characteristics that show extreme variability from one location to another. The work needed to overcome adverse soil properties cannot be estimated. These areas commonly are urban land complexes or miscellaneous areas. An on-site investigation is required to determine soil conditions at the site. This data set is a digital soil survey and generally is the most detailed level of soil geographic data developed by the National Cooperative Soil Survey. The information was prepared by digitizing maps, by compiling information onto a planimetric correct base and digitizing, or by revising digitized maps using remotely sensed and other information. This data set consists of georeferenced digital map data and computerized attribute data. The map data are in a soil survey area extent format and include a detailed, field verified inventory of soils and miscellaneous areas that normally occur in a repeatable pattern on the landscape and that can be cartographically shown at the scale mapped. The soil map units are linked to attributes in the National Soil Information System relational database, which gives the proportionate extent of the component soils and their properties.