§ 107-2-1. Definitions.
(a)
Director means the Director of Land Development Services or designated agent.
(b)
Class I soils consist of Soil Nos. 11, 28, 33, 38, 39, 76, 79, 80, 81, 84, 85, 87, 88, and 90.
(c)
Class II soils consist of Soil Nos. 2, 7, 9, 31, 75, 77, 78, 92, and 93.
(d)
Class III soils consist of Soil Nos. 1, 8, 10, 29, 30, 32, 34, 35, 36, 37, 48, 49, 59, 60, 61, 62, 63, 64, 65, 74, 82, 83, 89, 91, 94, and 109.
(e)
Class IVA soils consist of Soil Nos. 13, 15, 17, 20, 21, 26, 27, 42, 43, 44, 47, 51, 52, 53, 54, 55, 56, 57, 69, 71, 73, 86, 103, and 106.
(f)
Class IVB soils consist of Soil Nos. 3, 4, 5, 6, 12, 14, 16, 18, 19, 22, 23, 24, 25, 27, 40, 41, 45, 46, 47, 50, 66, 67, 68, 70, 72, 95, 96, 97, 98, 99, 100, 101, 102, 104, 105, 107, and 108.
(g)
Geotechnical Report shall mean a geotechnical or foundation engineering study prepared in accordance with the design and construction criteria outlined in the Public Facilities Manual.
(h)
Major Addition is considered any addition or alteration to an existing residential structure of equal to or greater than 500 square feet in exterior footprint area, or equal to or greater than 50 percent of the exterior footprint area of an existing non-residential structure, when such addition entails grading or construction of foundations in problem soils.
(i)
Minor Addition is considered any addition or alteration to an existing structure of less than 500 square feet in exterior footprint area for residential structures, or less than 50 percent of the exterior footprint area of an existing non-residential structure, when such addition entails grading or construction of foundations in problem soils.
(j)
Problem Soils shall mean landslide susceptible soils, shrinking and swelling soils, soils with high water table conditions, soils containing hazardous material, buried waste sites, uncompacted and undocumented man-placed fills, and earthen structures that would require special precautions for safety during and after construction activity. Problem soils include areas of Marumsco soils, "marine clays," Class III soils, and Class IV soils, as shown and/or identified on the official map adopted by the Board of Supervisors or any other soil as determined by the Director of Land Development Services.
(k)
"Marine clay" is a term used locally for clay-rich sediments of the Cretaceous-Age Potomac Formation of the Atlantic Coastal Plain. The Potomac Formation, identified as unit Kp on USGS geologic maps, thickens from a few feet along the boundary with the Piedmont Province in the west to over one hundred feet along the eastern boundary of Fairfax County. As a result of removal of younger deposits that have since eroded away, the sediments are commonly over-consolidated. The "marine clay" sediments consist mostly of montmorillonite minerals (which results in a high potential for shrink and swell with variations in moisture) that are commonly classified as elastic SILT (MH) and fat CLAY (CH) by the Unified Soil Classification System. Due to physical and chemical weathering, "marine clay" in the uppermost 20 ft of the Potomac Formation are preferentially weakened along fractures, joints and parting planes, and can cause landslides many years after the slopes are created. Sand layers, often water-bearing, are frequently mixed with the "marine clay" layers. The clays and silts are subject to large changes in volume with soil moisture changes. Regulations in the Fairfax County Zoning Ordinance, regarding "Marine Clay" are only applicable to the areas mapped as "Previously Mapped Marine Clay."
(l)
Soil Number shall mean the identifying number assigned to a soil unit in the Soil Survey of Fairfax County prepared by the United States Department of Agriculture National Resource Conservation Service. (15-02-107; 14-11-107; 27-17-107; 10-18-107.)