1990 Soil Ratings


The soils information below and the published maps are for general soil information; site specific investigations are recommended for more precise data. For more information, please contact the Department of Public Works and Environmental Services at 703-324-1720, TTY 711 or the Northern Virginia Soild and Water Conservation District at 703-324-1460, TTY 711

Soil Ratings

Soil No. Soil Name 1 Problem Class2 Foundation Support3 Drainage4 Septic Drainfields5 Infiltration Trenches6 Erosion Potential7 Other Notes8
1 Mixed Alluvial A Poor-F,B,W Poor-F,W Poor-F,W Poor-F,W Low Hyd
2 Chewacla A Poor-F,B,W Poor-F,W Poor-F,W Poor-F,W Low Hyd
3 Congaree A Poor-F,B,W Poor-F,W Poor-F,W Poor-F,W Low -
5 Wehadkee A Poor-F,B,W Poor-F,W Poor-F,W Poor-F,W Low Hyd
6 Hyattsville B Fair-B,W Marg-W Poor-W Poor-W Low -
8 Worsham A Poor-B,W,C Poor-W,C,S Poor-W,C,S Poor-W,C,S Low Hyd
10 Glenville B Fair-B,W Marg-W Poor-W Poor-W Mod -
11 Bermudian A Poor-F,B,W Marg-F,W Poor-F,W Poor-F,W Low -
12 Rowland A Poor-F,B,W Poor-F,W Poor-F,W Poor-F,W Low Hyd
13 Bowmansville A Poor-F,B,W Poor-F,W Poor-F,W Poor-F,W Low Hyd
14 Manassas B Fair-B,W Marg-W,R Poor-W,R Poor-W,R Mod -
15 Muck A Poor-F,B,W Poor-F,W Poor-F,W Poor-F,W Low Hyd
18 RockyLand (Acidic) C Good Marg-R Poor-R Poor-R High -
19 Very Rocky Land (Acidic) C Good Marg-R Poor-R Poor-R High -
20 Meadowville B Fair-B,W Marg-W Poor-W Poor-W Mod -
21 Manor C Good Good Good Good High -
23 Captina B Fair-B,W Marg-P,S Poor-P,S Poor-P,S Mod -
24 Elioak C Good Good Good Good High -
26 Bertie B Marg-B,W Marg-W,S Poor-W,S Poor-W,S Mod -
27, 29 Legore C Good Marg-R Poor-R Poor-R Mod -
28 Montalto (sil) C Good Fair-R Marg-R,S Marg-R,S Mod -
30 Huntington A Marg-F,W Marg-F,W Poor-F,W Poor-F,W Low -
31 Lindside A Poor-F,B,W Poor-F,W Poor-F,W Poor-F,W Low -
32 Fairfax (sil) B Good Marg-P Marg-P,S Marg-P,S High -
33 Melvin A Poor-F,B,W Poor-F,W Poor-F,W Poor-F,W Low Hyd
34 Woodstown B Fair-W Marg-W Poor-W Poor-W Low -
35 Manteo C Good Marg-R Poor-R Poor-R High -
37, 38 Beltsville B Fair-P Marg-P Poor-P,S Poor-P,S Mod -
39 Othello A Poor-B,W,C Poor-W,C Poor-W,C Poor-W,C Low Hyd
40 Mecklenburg A Fair-B,C,P Fair-C,P,R Poor-C,P,R Poor-C,R Mod -
41 Rocky Land-Iredell A Marg-B,C,P Marg-C,P,R Poor-C,P,R Poor-C,R Mod -
42 Very Rocky Land-Iredell A Marg-B,C,P Marg-C,P,R Poor-C,P,R Poor-C,R Mod -
43 Masada (grl) C Good Good Marg-S Marg-S Mod -
44 Caroline B Marg-B,C Marg-C Poor-C Poor-C Mod -
45 Matapeake C Good Fair-S Fair-S Fair-S Mod -
46 Mattapex B Marg-B,P Marg-P,S Poor-P,S Poor-P,S Mod -
47 Dragston B Marg-B,W Marg-W Poor-W Poor-W Low -
48 Iredell A Poor-B,C,P Marg-C,P,R Poor-C,P,R Poor-C,P,R Mod -
49 Lunt (fsl) A Marg-U,B,C,P Fair-C,P Marg-U,C,P Marg-U,C,P Mod US
50 Iredell-Mecklenburg (st) A Marg-B,C,P Marg-C,P,R Poor-C,P,R Poor-C,P,R Mod -
51 Keyport B Fair-B,W,C Fair-W,C Marg-W,S Marg-S Mod -
52 Elbert-Iredell A Poor-B,W,C Poor-W,C,R Poor-W,C,R Poor-W,C,R Low Hyd
53 Lenoir B Marg-B,W,C Marg-W,C Poor-W,C Poor-W,C Mod -
54 Sassafras C Good Good Good Good Mod -
55 Glenelg C Good Good Good Good High -
56 Kempsville B Good Fair-P,S Marg-S,P Marg-S Mod -
57 Brecknock (l) C Good Fair-R Marg-R Marg-R Mod -
59 Orange A Poor-B,C,P Poor-C,P,R Poor-C,P,R Poor-C,P,R Mod As
60 Appling C Good Good Fair-S Fair-S High -
61 Loamy/Gravelly Sediments A Marg-U,C,P Marg-C,P Marg-U,C,P Marg-U,C,P High US
62 Brecknock (sil) C Good Fair-S,R Marg-R,S Marg-R,S Mod -
63 Louisburg C Good Good Marg-R Marg-R High -
64 Silty/Clayey Sediments A Marg-U,B,C,P Marg-C,P Poor-U,C,P Poor-U,C,P High US
65 Colfax B Marg-B,W Marg-S,W Poor-W,S Poor-W,S Mod -
66 Lloyd C Good Fair-S Fair-S Fair-S Mod As
67 Penn (fsl) C Good Fair-R Marg-R Marg-R High -
68 Roanoke A Poor-F,B,W,C Poor-F,W,C Poor-F,W,C Poor-F,W,C Low Hyd
69 Enon A Marg-B,C Marg-C Marg-C Marg-C High As
70 State B Fair-F,B,W Fair-F,W Marg-F,W Marg-F,W Low -
71 Bucks (sil) C Good Fair-S Marg-R,S Marg-R,S Mod -
72 Bucks (l) C Good Fair-S Marg-R,S Marg-R,S Mod -
73 Penn (sil) C Good Marg-R,S Poor-R Poor-R High -
75 Penn (l) C Good Marg-R Poor-R Poor-R High -
76 Calverton (l) A Poor-B,W,C Marg-W,C,R Poor-W,C,R Poor-W,C,R Mod -
77 Penn (sh sil) C Good Marg-R Poor-R Poor-R High -
78 Calverton (sil) A Poor-B,W,C Marg-W,C,R Poor-W,C,R Poor-W,C,R Mod -
79 Kelly A Poor-B,C,P Marg-C,P,R Poor-C,P,R Poor-C,P,R Mod -
80 Croton A Poor-B,W,C Poor-W,C,R Poor-W,C,R Poor-W,C,R Low Hyd
83 Galestown C Good Good Good Good Mod -
84 Fallsington A Poor-B,W Poor-W Poor-W Poor-W Low Hyd
85 Elkton A Poor-B,W,C Poor-W,C Poor-W,C Poor-W,C Low Hyd
86 Klej B Fair-B,W Marg-W Poor-W Poor-W Low -
87 Wickham C Good Fair-S Marg-S Marg-S Mod -
88 Hiwassee (sil) C Good Fair-S Marg-S Marg-S Mod -
89 Tidal Marsh A Poor-B,F,W Poor-F,W Poor-F,W Poor-F,W Low Hyd
90 Augusta (vfsl) B Fair-F,P Marg-F,P Poor-F,P,S Poor-F,P,S Mod -
91 Birdsboro B Marg-B,F,W Marg-F,W Poor-F,W Poor-F,W Mod -
92 Raritan B Marg-B,F,W Marg-F,W Poor-F,W Poor-F,W Mod -
104 Catlett C Good Fair-P,R Poor-P,R Poor-P,R Mod -
110 Augusta (l) B Fair-F,P Marg-F,P Poor-F,P,S Poor-F,P,S Mod -
112 Augusta (sl) B Fair-F,P Marg-F,P Poor-F,P,S Poor-F,P,S Mod -
113 Fairfax (gr sil) B Good Marg-P Marg-P,S Marg-P,S High -
114 Masada (fsl) C Good Fair-S Marg-S Marg-S Mod -
115 Hiwassee (fsl) C Good Fair-S Marg-S Marg-S Mod -
116 Christiana B Marg-B,C Marg-C Poor-C Poor-C Mod -
117 Fresh Water Marsh A Poor-F,B,W Poor-F,W Poor-F,W Poor-F,W Low Hyd
118 Marine Clay A Poor-U,B,C,P Marg-C,P Poor-U,C,P Poor-U,C,P High US
120 Altavista B Fair-F,W Marg-F,W Poor-F,W Poor-F,W Low -
128, 129 Montalto C Good Fair-R Marg-R,S Marg-R,S Mod -
132 Mayodan C Good Fair-S Marg-S Marg-S Mod -
141 Rocky Land-Orange A Marg-B,C,P Marg-C,P,R Poor-C,P,R Poor-C,R Mod As
142 Very Rocky Land-Orange A Marg-B,C,P Marg-C,P,R Poor,C,P,R Poor-C,R Mod As
148 Iredell-Mecklenburg A Poor-B,C,P Marg-C,P,R Poor-C,P,R Poor-C,P,R Mod -
149 Lunt (sil) A Marg-U,B,C,P Fair-C,P Poor-U,C,P Poor-U,C,P Mod US
152 Elbert-Orange A Poor-B,W,C Poor-W,C,R Poor-W,C,R Poor-W,C,R Low Hyd
232 Fairfax (l) B Fair-C,P Marg-S,P Marg-S,P Marg-S,P High -
273 Readington B Good Marg-P,R Poor-P,R Poor-P,R Mod -
~ Fill/Made Land A -- -- -- -- -- --

Explanation of Ratings, Descriptions and Footnotes

On the maps, soil boundaries are identified by dashed lines. Soil properties tend to change gradually between soil types. As a result, the soil boundaries are general in nature and should not be scaled directly from the maps when analyzing individual building sites. In addition, small areas of differing soil types, too small to separate because of the map scale, may occur within a larger soil map unit.

Field symbols are used to identify soil types on the Fairfax County Soil Identification Maps. The symbols, illustrated below, identify the type of soil, slope class, and long term surface erosion.

Example: Soil Map Symbol: 55B2; Soil Number = 55, Slope Class = B, Erosion Class = 2.

The Slope Class on the soil maps is not to be confused with the Problem Class designations from Soil Ratings Chart, i.e., the Problem Class will not be found on the soil maps. The slope and erosion classes on the maps are as shown below.

Slope Classes Potential Erosion Symbols
A 0-2 percent + - Soil Accumulation (Low)
B 2-7 percent 0 - No Erosion (Low)
C 7-14 percent 1 - Slight Erosion (Low)
D 14-25 percent 2 - Moderate Erosion (Mod)
E 25+ percent 3 - Severe Erosion (High)

Key to Ratings

Good = No significant problems in natural undisturbed soils.

Fair = Minor potential problems affecting design or construction.

Marginal = Significant problems that must be considered in design and construction.

Poor = Major problems that must be addressed during the design and construction to ensure satisfactory performance of structures.

 

Key to Problems and Characteristics

B = Low bearing values for foundation support.

C = Clays with moderate to high shrink-swell potential often having slow to very slow permeability rates.

F = Flooding hazard following storm events.

P = Perched groundwater above restrictive soil or rock layers.

R = Shallow depth to bedrock.

S = Slow permeability rates.

U = Potentially unstable slopes from massive slope failure or slope creep.

W = High seasonal groundwater tables in drainage way or low lying areas.

1SOIL NAMES

Soil names are taken from the Soil Survey of Fairfax County, Virginia, Series 1955, No. 11, Issued May 1963. Additional soils, not in the original survey, have been included in revised soil maps of Fairfax County. The USDA Soil Conservation Service has continued to revise and update its list of soils for Virginia since the original soil survey was completed. Ranges in properties and interpretations for use of some soils were modified as more information was gathered, and some names were changed. As a result, some soil names used in Fairfax County today may not coincide in properties and interpretations with the same soil name elsewhere in Virginia. Interpretations are based on observations and data gathered by Fairfax County.

2PROBLEM SOIL CLASS

Letter designations A, B or C are assigned to each soil type according to the severity of soil problems and the potential difficulty of analyzing and correcting these problems. These designations serve as a guide to determine if a geotechnical engineering study is required for site development. Chapter 107 (Problem Soils Ordinance) of the Code of the County of Fairfax, Virginia clearly states that no construction shall occur on land containing Cretaceous-age Potomac Group clays (sometimes called marine clay), other shrinking and swelling clays, or on land where high groundwater conditions exist until adequate safeguards have been taken. Regardless of soil type, the builder must provide a warranty for the foundation against structural defects for a period of five years from the date of transfer of record title or possession. (Virginia Code § 55-70.1)

PROBLEM CLASS A Soils:
Class A soils are problem soils. The problems associated with these soils include unstable slopes and land slippage, high shrink-swell clays, poor foundation support, high water table conditions, etc. Geotechnical problems must be addressed with adequate engineering evaluations and designs prior to development. A geotechnical engineering report, prepared according to the geotechnical guidelines in Fairfax County Public Facilities Manual (PFM) and the Building Code, is mandatory for all construction and grading within these problem soil areas. The geotechnical report must be prepared by, or under the direction of, a professional engineer experienced in soil and foundation engineering. The engineering evaluation and report must be submitted for approval, and the recommendations incorporated into the grading plans as requirements for construction prior to plan approval. (PFM 4-0301.1). Construction inspections and certifications are required from the Engineer-of-Record. The soil types or conditions included in this group are:

(1) Cretaceous-age Potomac Group clays (marine clays).
(2) Other high shrink-swell soils in the Coastal Plain.
(3) High shrink-swell clay soils of the Iredell and Orange Soils Groups in the Triassic Basin and Piedmont Upland.
(4) Soils with a seasonal high water table at or near the surface for prolonged periods and low bearing strength (poor foundation support).
(5) Alluvial or floodplain soils.
(6) Uncontrolled fill, Made Land/Disturbed Land, e.g., old mines, landfills, etc.

The installation of linear structures such as storm sewer or sanitary sewer lines, usually do not require geotechnical report submission. The only exception would be in cases where such construction activity might trigger movement in adjoining slopes. Notes addressing placement of backfill and OSHA excavation requirements are sufficient in most cases. Some additions to residential structures and minor commercial buildings (those exempt from site plan submission requirements) usually only require engineered foundation design submitted with building permit application. All other cases require a soil report waiver or exemption as provided under Chapter 107 of the County Code.

PROBLEM CLASS B Soils:
Class B soils are problem soils that primarily have wetness and drainage problems that can be addressed on the construction plans with appropriate geotechnical notes and drawings, such as foundation drain details for basements and crawl spaces. Geotechnical investigation by an engineer is recommended; however, the submission of the resulting report for separate county approval may not be required under the following circumstances:

  • Class A type problem soil is not on the property.
  • The site /grading plans incorporates geotechnical notes and drawings addressing the items such as foundation drains, overlot drainage, compacted fill requirements (acceptable material, lift thickness, density testing, frequency of testing, etc). Construction inspections notes are required as shown in PFM 4-0402.1 and 4-0402.2.
  • Project does not require pile foundations, geopiers, mat foundation, ground modification; such as dynamic compaction, stone columns, vibra compaction chemical stabilization, etc.
  • Geotechnical reports are not required under any other county regulation or building codes.

PROBLEM CLASS C Soils:
Class C soils are not considered problem soils for foundations. These soils typically have few problems that would adversely affect most residential uses. Geotechnical investigation by an engineer is recommended; however, the submission of the resulting report for separate county approval may not be required under the following circumstances:

  • Building foundation footprint is not within 25 feet of Class A problem soil. The 25 feet margin allows for errors in mapping of the soils. If the building footprint is within 25 feet of Class A soil, a report or waiver is required.
  • Project does not require pile foundations, geopiers, mat foundation, ground modification; such as dynamic compaction, stone columns, vibra compaction chemical stabilization, etc.
  • Geotechnical reports are not required under any other county regulation or building codes.

Construction on engineered fill over Class C soils will require geotechnical engineering specifications on the site, grading or construction plans. The notes must address the placement of fill, material quality, and frequency of testing.

Major construction projects involving multi-story buildings, mat foundation, deep foundation, deep excavations, sheeting and shoring, retaining walls, embankments, ground modification, etc., require geotechnical report submission in compliance with the building codes.

3FOUNDATION SUPPORT

Foundation support ratings are based on empirical observations and experience. Unstable slopes, soft or compressible soils with low bearing values, high shrink-swell clays, high seasonal water tables, and flooding potential will adversely affect foundation support. In some problem soils, shallow bedrock may provide high bearing values; however, the bedrock may not to be continuous, or may require blasting for the foundation subgrade.

4DRAINAGE

Soil conditions that affect drainage around yards, crawl spaces, and basements include depth to seasonal high water table, permeability, landscape position, and potential for flooding. Soils with a "Poor" rating have a seasonal high water table at or near the surface, slowly permeable layers, or are subject to frequent flooding. A "Good" rating refers to permeable soils with a seasonal water table well below the ground surface.

5SEPTIC DRAINFIELDS

Suitability for a septic drainfield is based on the criteria for subsurface soil absorption systems defined by the commonwealth of Virginia Sewage Handling & Disposal Regulations and Chapter 68 (Individual Sewage Disposal Facilities) of the Fairfax County Code. Ratings are based on depth to seasonal high water table, bedrock, or other restrictive layer, landscape position, flooding potential, slope, presence of shrink-swell clays and permeability. Suitability for alternative on-site disposal systems were not factored into the rating. These general ratings should be used only for preliminary planning and evaluation. On-site evaluations are necessary to determine actual soil conditions and suitability.

6BEST MANAGEMENT PRACTICES (BMP) INFILTRATION TRENCHES

Suitability for infiltration trenches used in storm water control is based on depth to seasonal high water table, bedrock or other restrictive layer, slope, landscape position, flooding potential, and permeability. These general ratings should be used for preliminary planning and evaluation only. Site evaluations are necessary to determine actual soil conditions and suitability. Technical guidance in planning and designing BMP infiltration trenches can be found in the Northern Virginia BMP Handbook available from the Engineers and Surveyors Institute, telephone: 703-207-0688, TTY 711, or the Northern Virginia Regional Commission, telephone: 703-642-0700, TTY 711.

7EROSION POTENTIAL

Erosion potential, applies to soils under construction site conditions. Erodibility is affected by texture (relative proportion of sand, silt and clay), rock content, permeability, structure and slope (natural or man-made).

Low = Soils are not highly erodible, except on steep unprotected cuts. Sheet erosion of less that 0.05 inches can be expected on unprotected soils during a severe storm.

Moderate = Soils are moderately erodible on B slopes, highly erodible on C slopes or greater. Sheet erosion of 0.05 to 0.25 inches, plus rill and shallow gully erosion, can be expected on unprotected soils during a severe storm.

High = Soils are highly erodible, even on B slopes. Soil loss in excess of 0.25 inches from sheet erosion and formation of numerous gullies can be expected on unprotected soils in a severe storm.

8OTHER NOTES

As -- Bedrock With Naturally Occurring Asbestos

These soils occur within a geologic formation known as the Piney Branch Complex, locally known as greenstone. Naturally-occurring asbestos minerals, predominantly actinolite and tremolite, are known to occur in this formation. Excavations in bedrock or earth moving activities within this formation may expose these minerals to the atmosphere, allowing the fibers to become airborne.

Personnel working in or around this geologic area should be alerted to this potential health risk. For construction activities in this area, dust control and worker protection measures must be implemented. Excavated rock materials from the Piney Branch formation are not to be used as an aggregate. All exposed rock materials must be covered after construction. The Health Department, Telephone: 703-246-3561, TTY 711, should be contacted for information regarding worker protection and dust control.

Hyd -- Hydric Soils

Soils labeled Hyd are predominantly hydric soils. Hydric soils are saturated, flooded, or ponded long enough during the growing season to develop anaerobic (oxygen-deprived) conditions in the upper part. Soils labeled Hyd+ may consist of predominantly hydric soils in low areas and adjacent to streams or other hydric soils. In other areas, these soils will to be predominantly non-hydric.

Hydric soils are one of three criteria used to delineate wetlands. According to the Federal Manual for Identifying and Delineating Jurisdictional Wetlands, a jurisdictional wetland must have three essential characteristic: (1) wetland hydrology (soils are inundated or saturated with water for prolonged periods during the growing season), (2) hydrophytic vegetation (plants adapted to withstand saturated conditions), and (3) hydric soils.

Non-tidal wetlands are regulated under Section 404 of the Clean Water Act. The U.S. Army Corps of Engineers and the Environmental Protection Agency (EPA) are responsible for making determinations of wetlands regulated under the Clean Water Act. A permit must be obtained from the Corps of Engineers in many cases where construction is planned in wetlands.

The presence of hydric soils on the Fairfax County Soil Identification Maps provides a good indication of the extent and probability of wetlands, but does not necessarily mean that the site is a jurisdictional wetland. Other wetland criteria may not be present, or small areas of nonhydric soils may be included in the hydric soil mapping units. A detailed site evaluation is necessary to confirm the presence of, and delineate the extent of, wetlands.

US -- Unstable Slopes

These soil types are susceptible to slope instability on natural slopes. Slope movement may be accelerated by construction activities. Slope stability analyses must be performed using acceptable engineering methods.

Slope stability refers to long-term (permanent) stability in original ground. For most soils, the maximum final slope should not be steeper than 3:1 (horizontal:vertical). The soils noted US generally require permanent slopes of 5:1 or flatter where marine clays are present. Fill slopes require engineering designs and compaction to ensure long-term stability.

Temporary slopes such as in excavations or trenches must be designed in accordance with OSHA standards.

DAMS

Geotechnical requirements for the submission of reports are contained in the PFM, Chapter 6, Section 1605. The article contains a rating of the different soil types for dam use such as; embankment materials, embankment foundation, core, seepage potential, etc. It should be noted that a soil rated poorly for foundation support and general construction work may be rated suitable for certain components of a dam or landfill. A geotechnical engineer must be consulted for site specific investigations.


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