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. A special soil features layer (point and line features) is optional. This layer displays the _location of features too small to delineate at the mapping scale, but they are large enough and contrasting enough to significantly influence use and management. 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.

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. A special soil features layer (point and line features) is optional. This layer displays the location of features too small to delineate at the mapping scale, but they are large enough and contrasting enough to significantly influence use and management. 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.

This data set is based upon the 2011 soil survey prepared by the US Department of Agriculture-Natural Resources Conservation Service. The 2011 soil survey was prepared to National Cooperative Soil Survey standards and utilized nationally recognized names for soil types. The 2018 soil map legend is identical to the 2011 legend, but the soil boundaries have been shifted to better correlate with topography and land use. This map was officially adopted by the Board of Supervisors in 2018. All construction plans submitted to the County for permits that require the inclusion of soils mapping should reference the 2018 soils map.

The soil classification areas from the 1990 soil survey for Fairfax County. Not all areas of Fairfax County were classified during this project so there are areas that do not have soil information.

Marumsco soils in Fairfax County. Marumsco soils are mapped in complexes with other soil types. The complexes are highly variable and consist of combinations of clays, silts, sands, and gravels. They may also be problematic. In steep areas that contain clays known as "marine clays" slope stability can be a problem. In addition, structures constructed on clays found in this complex could suffer foundation distress if adequate precautions are not taken during design and construction.

Potential asbestos containing soils in Fairfax County. These soils are mapped over naturally asbestos-containing bedrock. Safety precautions must be taken during construction. Orange soils, which overlie a majority of this geology, also contain shrinking-swelling clays which can cause foundation distress.

Table of properties of soil types. One to many relate with the Soils 2018 layer.

Non-marine clay shrink swell soils in Fairfax County. These are soils containing other shrinking-swelling clays that can lead to foundation distress if precautions are not taken during design and construction.

These areas were mapped as marine clays in previous surveys. Marine clays are high shrink-swell soils that can cause foundation distress. They are sometimes referred to as Potomac Clays or Deltaic Clays.

This polygon dataset is composed of subsets from Fairfax County’s current soil inventory, recorded floodplain, and Resource Protection Area (RPAs) layers. Layer subsets are identified using the Virginia Department of Conservation and Recreation (DCR) definition/criteria for “environmentally sensitive sites”in 4VAC50-85-10 and merged into a single ESA polygon layer.

This preliminary experimental lithogeochemical map shows the distribution of rock types in the Virginia and Maryland parts of the Chesapeake Bay watershed. The map was produced digitally by classifying geologic-map units according to composition, mineralogy, and texture; rather than by age and stratigraphic relationships as shown on traditional geologic maps. This map differs from most lithologic maps in that the lithogeochemical unit classification distinguishes those rock units having key water-reactive minerals that may induce acid neutralization, or reduction, of hosted water at the weathering interface. The validity of these rock units, however, is independent of water chemistry, because the rock units are derived from geologic maps and rock descriptions. Areas of high soil carbon content, and sulfide metal deposits are also shown. Water-reactive minerals and their weathering reactions yield five lithogeochemical unit classes: 1) carbonate rock and calcareous rocks and sediments, the most acid-neutralizing; 2)carbonaceous-sulfidic rocks and sediments, oxygen-depleting and reducing; 3) quartzofeldspathic rocks and siliciclastic sediments, relatively weakly reactive with water; 4) mafic silicate rocks/sediments, oxygen consuming and high solute-load delivering; and, 5) the rarer calcareous-sulfidic (carbonaceous) rocks, neutralizing and reducing. Earlier studies in some parts of the map area have related solute loads in ground and stream waters to some aspects of bedrock lithology. More recent preliminary tests of relationships between four of the classes of mapped lithogeochemical units and ground water chemistry, in the Mid-Atlantic area using this map, have focused on and verified the nitrate-reducing and acid-neutralizing properties of some bedrock and unconsolidated aquifer rock types. Sulfide mineral deposits and their mine-tailings effects on waters are beginning to be studied by others. Additional testing of relationships among the lithogeochemical units and aspects of ground and surface water chemistry could help to refine the lithogeochemical classification, and this map. The testing could also improve the usefulness of the map for assessing aquifer reactivity and the transport properties of reactive contaminants such as acid rain, and nitrate from agricultural sources, in the Chesapeake Bay watershed.