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The NASM Dulles Center project area is located on an approximately 200-acre tract of land in Fairfax County, Virginia, lying within and adjacent to Washington Dulles International Airport (see Figure 1-1, Figure 1-3). It is to the south of the airport's main terminal building and adjacent facilities, north of Route 50, west of Route 28, and east of airport and industrial park facilities. One small segment of the project area is located east of Route 28 and outside of the airport property; this 30-acre segment is part of the proposed Barnsfield Road interchange at Gate 4 and Route 28.
The project area consists of three adjoining parcels of land. The proposed development will not utilize the entire project area; most building development will be confined to a more or less central portion of 185 acres bordered by Highway 50 on the south. This is referred to as the central parcel. Automobile and aircraft access to this portion, storm water management, and/or parking may require use of portions of two peripheral parcels, referred to as the north parcel and the east parcel.
The north parcel is a wedged-shaped piece of approximately 110 acres that will be used for construction of an aircraft taxiway providing access from the existing runway to the proposed hangers. The east parcel, which lies between the central project site and Route 28, consists of approximately 150 acres. The east parcel may be used to develop roads for vehicle access from Route 28 for NASM Dulles Center visitors and for overflow parking. Figure 3-1 shows the proposed Area of Potential Effect within the three Smithsonian parcels.
Fairfax County has zoned the project area as land to be used for Public, Government and Institutional facilities. Fairfax County has also designated land adjoining Cain Branch up to its major fork in the middle of the project area as an Environmental Quality Corridor (EQC). EQCs are designated by Fairfax County to identify, protect, and enhance ecologically valuable land and surface waters. An EQC includes the area of a stream or wetland and a 100-foot buffer zone. The Cain Branch EQC is discussed in detail in D&M's Wetlands Delineation Report (Canfield and Wiley 1996).
With the exception of some logging that occurs on the site under arrangement with the MWAA, the project area is currently undeveloped. Gravel and paved access roads run throughout the area. Currently the main access routes to the project area are through Gate 1 off of Route 50 and Gate 4 off of Route 28.
The project is located within the Virginia Piedmont physiographic province, west of the fall line that divides the Coastal Plain from the Piedmont region.
Climate. The project area experiences a continental, humid, temperate climate. Winters are relatively mild and summers are generally warm. However, seasonal temperatures vary considerably. The difference between the summer and winter mean temperature is approximately 68o Fahrenheit. The average annual growing season is approximately 175 days. The average annual precipitation is 40 inches. Generally, most of the precipitation occurs in the spring and summer.
Topography and Drainage. Topography is relatively level across most of the project area, with overall slopes of approximately 2 percent toward the southwest. Several small streams traverse the site, including Cain Branch and two other Cub Run tributaries. As they occur starting from the southern end (Route 50) of the project site, they are:
Of these, only the main stem of Cain Branch is listed as a perennial stream; the remainder are considered intermittent streams. Limited areas with greater than average slope occur along the water courses; the area of greatest relief lies to the south of Cain Branch. Elevation in the project area ranges from 300 to 330 feet above mean sea level (msl). Areas to the north and east of the project area drain northward, emptying into the Potomac at Difficult Run, several miles up river from Washington, D.C.
The groundwater table generally follows the contours of the surface where the residual soils are thick, and is in the rock where the soil is thinnest. Perched water tables (i.e., ones with a restricted downward flow of water) are common in the project area where the upper soils have weathered to low permeability silts and clays over the sandstones, silt stones, mudstones, shales and diabase intrusives.
Jurisdictional Wetlands. During the period from October 1995 through June 1996, Dames & Moore conducted investigations to determine whether jurisdictional wetlands (as defined under Section 404 of the Clean Water Act) were present on an irregularly shaped approximately 240-acre parcel of land encompassing the project area. Approximately 25 acres of wetlands were delineated within the assessment area.
Ecology. The existing vegetative cover of the site is shaped by the past and current uses of the property. For much of the past two hundred years the Dulles site has been used for both row cropping and livestock grazing agriculture. Relict furrows are discernible under much of the young forest cover, and evidence of old pasture fencing is common. Older trees in the range of 50 to 100 years occur as fence-line markers or along stream corridors. But only in the past 30 to 40 years has the majority of the land been left fallow. Much of it has been planted with pine trees, but most has been allowed to proceed along successional lines through natural processes, toward a locally supported deciduous forest climax community.
The Dulles property contains diverse habitats capable of supporting a wide variety of wildlife species. Mammals in the project area include white-tail deer (Odocoileus virginianus), raccoon (Procyon lotor), gray squirrel (Sciurus carolinensis), woodchuck (Marmota monax), beaver (Castor canadensis), striped skunk (Mephitis mephitits), eastern chipmunks (Tamias striatus), eastern cottontail (Sylvilagus floridanus), and red squirrel (Tamiasciurus hudsonicus).
Most of the birds identified are associated with the oak-hickory and Virginia and loblolly pine forests which dominate the study area. The streams and associated riparian areas supply habitat for several species of turtles, frogs, salamanders and small fish. No Federally-listed or Virginia-listed threatened or endangered faunal species have been identified within the Area of Potential Effect.
Geology. The site is located near the western edge of Fairfax County, Virginia, in the Piedmont physiographic province. The site is underlain by sedimentary and crystalline rocks of the Triassic Lowland Province. The Triassic lowlands were formed by tectonic activity, when faulting created basins within Piedmont rocks. During the Triassic and Jurassic ages the surrounding highlands were eroded and the sediments were deposited in the lowlands. The coarser sediments were deposited first, forming conglomerates found along the eastern and western edges of the basins, while the finer sediments were deposited further out in the basins forming sandstones, siltstones, mudstones and shales. Climatic fluctuations and continued tectonic activity caused variations in the depositional environments, resulting in interfingering and interlayering of the deposits. Also during this time, igneous material penetrated into the basins and their sediments, forming intrusive bodies of diabase and metamorphosing adjacent sedimentary rocks.
In this region soils are mostly residual; they were formed from the in-place chemical weathering of the parent rock. The degree of weathering decreases with depth, and the deeper soils may retain a structure similar to the parent rock (i.e., joints, fractures and bedding). Other soils are alluvial, having been deposited by streams. Depth to bedrock varies from 0 to 30 feet in the conglomerates and over the diabase and from 0 to 20 feet in the sandstones, siltstones, mudstones and shales. The presence of boulders or less weathered materials within the residual soils is possible, especially in the soils underlain by diabase. The proposed site for the NASM Dulles Center is underlain by unmetamorphosed siltstone, mudstone and shale, possibly with lesser amounts of interbedded sandstone.
Soils of the project area have been mapped in the Soil Survey of Fairfax County, Virginia (SCS 1963). Five soil types are found in the project area: Calverton (Cb), Croton (Ck), Penn shaley (Pm,Pn,Ph), Readington (Rb), and Rowland (Rg) silt loams. The Calverton, Croton and Rowland soils have alluvial origins; the Penn and Readington soils are residual. The soil profiles consist of 1 to 2 feet of silty clay (Unified Soil Classification System ML/CL), which overlies low to high plasticity silts and clays (USCS MH,CL and CH) for most of the site (Rb, Cb and Ck soils) and very low plasticity soils (USCS GC and ML) for the other areas (Pn,Pm,Ph and Rg soils), which grade to completely to highly weathered rock. Depth to bedrock is generally deeper in the alluvial soils (typically ranging from approximately 2 to 8 feet in depth), than in the residual soils (typically ranging from approximately 1 to 4 feet in depth). In general, the soils in the project area have the potential to support significant agricultural productivity.
A broad picture of archeologically relevant paleoenvironmental conditions is available for the region surrounding the project area. Thus, despite the fact that little paleoenvironmental work has been done in Fairfax County, the work of Carbone (1976), Delcourt and Delcourt (1986), Gardner (1982, 1987) and Johnson (1986) allows us to construct the following general outline. The purpose of the outline is to identify the late pleistocene and early holocene environmental conditions encountered by the prehistoric Native Americans who inhabited the region.
Substantially different climatic conditions prevailed in Fairfax County during the late pleistocene than is the case today, even though the area was never directly affected by pleistocene glaciation. The earliest documentation of the region occurred over 11,000 years ago, at a time of receding glacial ice sheets, warming temperatures, and rapid transition in plant communities. The late pleistocene was characterized by ubiquitous open parkland interspersed with occasional strands of coniferous and deciduous trees; this vegetation shifted in the early holocene to primarily deciduous forest with limited parkland.
By approximately 5,000 years ago, an alternating series of oak-hickory and southeastern oak-pine communities had become characteristic of the area. Notwithstanding a number of climatic fluctuations and reversals, the general warming trend continued. Finally, by about 3,500 years ago, the climate and plant communities stabilized at approximately modern conditions. A shift in animal communities of the region also occurred during the transition from pleistocene to holocene. Most significant from the point of view of human subsistence, a number of large pleistocene fauna became extinct or moved northward. Deer, bear, and beaver become the main game animals available for Native Americans, as the ecological setting came to resemble those described in Section 3.3 above.
|Introduction||Chap. 2: Historic Preservation Compliance|
|Chap. 3: Project Area Description||Chap. 4: Background Research|
|Chap. 5: Field Investigations||Chap. 6: Laboratory Investigations|
|Chap. 7: Archeological Findings of Phase I Survey||Chap. 8: Archeological Findings of Phase II Survey|
|Chap. 9: Summary and Recommendations||Chap. 10: Bibliography|
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