40456 Federal Register / Vol. 56, No. 157 / Wednesday. August 14. 1991 / Proposed Rules 



depression, or seepage slope), subject 

 area has either. 



a. The soil, classified to the series 

 level, is on the national list of hydric 

 soils; or 



b. The soil, classified according to 

 "Soil Taxonomy", is a Histosol (except 

 Folists), Sulfaquent. Hydraquent. or 

 Histic Subgroup of Aquic Suborders; or 



c. Regional indicators of significant 

 soil saturation (as developed and 

 approved by Soil Conservation Service 

 soil scientists and the Federal 

 Interagency Committee for Wetlands 

 Delineation) are materially present. 



Hydric Soil Background 



Wetlands typically possess hydric 

 soils, but not all areas mapped as hydric 

 soil series are weUands (e.g., dry phases 

 that were never wetlands and drained 

 phases that represent former wetlands). 

 Hydric soils are defined as soils that are 

 saturated, flooded, or ponded long 

 enough during the growing season to 

 develop anaerobic conditions in the 

 upper part (U.S.DA. Soil Conservation 

 Service 1987). These soils usually 

 support hydrophytic vegetation under 

 natural (unaltered) conditions. 



National and State Hydric Soils Lists 



The SCS in cooperation with the 

 National Technical Committee for 

 Hydric Soils (NTCHS) has prepared a 

 list of the Nation's hydric soils (U.S.D.A. 

 Soil Conservation Service 1987). State 

 lists have also been prepared for 

 statewide use. The national and state 

 lists identify those soil series that 

 typically meet the NTCHS hydric soil 

 criteria according to available soil 

 interpretation records in SCS's soils 

 database. These lists are periodically 

 updated, so make sure the list being 

 used is the current one. The list while 

 extensive, does not include all series 

 that may have hydric members; these 

 soils may be determined as hydric when 

 they have evidence of wetiand 

 hydrology and hydrophytic vegetation. 

 The lists facilitate use of SCS county 

 soil surveys for identifying potential 

 weUands. One must be careful, 

 however, in using the soil survey, 

 because a soil map unit of a nonhydric 

 soil may have inclusions of hydric soil 

 that were not delineated on the map or 

 vice versa. Also, some map units (e.g., 

 alluvial land, swamp, tidal marsh, muck 

 and peat) may be hydric soil areas, but 

 are not on the hydric soils lists because 

 they were not given a series name at the 

 time of mapping. These soils meet the 

 NTCHS criteria for hydric soils. 



County Hydric Soil Map Unit Lists 



Because of the limitations of the 

 national and state hydric soil lists, the 



SCS prepared lists of hydric soil map 

 units for each county in the United 

 States. These lists may be obtained from 

 local SCS district offices and are the 

 preferred lists to be used when using 

 soil survey maps. The hydric soil map 

 unit lists identify all map units that are 

 either named by a hydric soil or that 

 have a potential of having hydric soil 

 inclusions. The lists provide the map 

 unit symbol, the name of the hydric soil 

 part or parts of the map unit, 

 information on the hydric soil 

 composition of the map unit, and 

 probable landscape position of hydric 

 soils in the map luiit delineation. The 

 county lists also include map units 

 named by miscellaneous land types or 

 higher levels in "Soil Taxonomy" that 

 meet NTCHS hydric soil criteria. 



Soil Surveys 



The SCS publishes soil surveys for 

 areas where soil mapping is completed. 

 Soil surveys that meet standards of the 

 National Cooperative Soil Survey 

 (NCSS) are used to identify areas of 

 hydric soils. These soil surveys may be 

 published (completed) or unpublished 

 (on file at local SCS field offices). 

 Published soil siuveys of an area may 

 be obtained from the local SCS field 

 office or the Agricultural Extension 

 Service office. Unpublished maps may 

 be obtained from the local SCS district 

 office. 



The NCSS maps contain four kinds of 

 map units: (1) Consociations, (2) 

 complexes, (3) associations, and (4) 

 undifferentiated groups. (Note: 

 Inclusions of unnamed soils may be 

 contained within any map imit; the 

 inclusions are listed in the description of 

 the soil map luiit in the soil survey 

 report.) Consociations are soil map units 

 named for a single kind of soil (taxon) or 

 miscellaneous area. Seventy-five 

 percent or more of the area is composed 

 of the taxon for which the map unit is 

 named (and similar taxa). When named 

 by a hydric soil, the map unit is 

 considered a hydric soil map unit for 

 wetiand determinations. However, small 

 areas vifithin these map units generally 

 too small to be mapped separately 

 (some areas are identified by "wet spot" 

 symbols) may not be hydric and should 

 be excluded in delineating weUands. 



Complexes and associations are soil 

 map units named by two or more kinds 

 of soils (taxa) or miscellaneous areas. If 

 all taxa for which these map units are 

 named are hydric the soil map unit may 

 be considered a hydric soil map unit for 

 wetiand determinations. If only part of 

 the map unit is made up of hydric soils, 

 only those portions of the map unit that 

 are hydric are considered in wetiand 

 determinations. 



Undifferentiated groups are soil map 

 units named by two or more kinds of ^ 



soils or miscellaneous areas. The soils in 

 these map units do not always occiu: 

 together in the same map unit but are 

 included together because some 

 common feattue such as steepness or 

 flooding determines use and 

 management. These map units are 

 distinguished from the others in that 

 "and" is used as a conjunction in the 

 name, while dashes are used for 

 complexes and associations. If all 

 components are hydric. the map unit 

 may be considered a hydric soil map 

 unit If one or more of the soils for which 

 the unit is named are nonhydric. each 

 area must be examined for the presence 

 of hydric soils. 



Use of County Hydric Soils Map Unit 

 Lists and Soil Surveys 



The county hydric soils map unit list 

 and soil surveys should be used to help 

 determine if the hydric soil criterion is 

 met in a given area. When making a 

 weUeind determination, one should first 

 locate the area of concern on a soil 

 survey map and identify the soil map 

 units for the area. The county list of 

 hydric soil map units should be 

 consulted to determine whether the soil 

 map units are hydric or potentially 

 hydric. If hydric soil map units or map 

 units with hydric soil inclusions are 

 noted, then one should examine the soil 

 in the field and compare its morphology 

 with the corresponding hydric soil 

 description in the soil survey report If 

 the soil's characteristics match those 

 described for hydric soil, then the hydric 

 soil criterion is met unless the soil has 

 been effectively drained. If soils have 

 been significanUy disturbed, either 

 mecharucally or hydrologically, refer to 

 the disturbed areas section. In the 

 absence of site-specific information, 

 hydric soils also may be recognized by 

 certain soil properties caused by 

 weUand hydrology conditions that make 

 soil meet the NTCHS criteria for hydric 

 soils. 



General Characteristics of Hydric Soils 



Due to their wetness during the 

 growing season, hydric soils usually 

 develop certain morphological 

 properties that can be readily observed 

 in the field. Anaerobic soil conditions 

 usually occuur due to excessive wetness 

 and they typically lower the soil redox ^ 

 potential causing a chemical reduction 

 of some soil components, mainly iron 

 oxides and manganese oxides. This 

 reduction affects solubility, movement 

 and aggregation of these oxides which is 

 reflected in the soil color and other 



