asia trail elephant facility - National Zoo - Smithsonian Institution

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ASIA TRAIL - ELEPHANT FACILITY SUPPLEMENTAL ENVIRONMENTAL ASSESSMENT 3.0 AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES This section describes the affected environment to document the existing conditions of the project area, and provide a technical baseline for the subsequent evaluation of impacts. Those resource disciplines that would potentially be affected by the project alternatives are included. This section also identifies the potential impacts of the proposed project and recommends appropriate mitigation measures. Potential impacts to resources within the project study area may include direct, indirect, and/or cumulative impacts. Direct impacts would be caused by the proposed action, and would occur at the same time and place as the action. Indirect impacts would be caused or influenced by the action and would occur later in time or further removed in distance. Cumulative impacts would result from the incremental impact of the proposed action, when added to the impact of other past, present, and reasonably foreseeable future actions. 3.1 Geophysical Resources The natural topography of the Zoo consists of a moderately to steeply sloping basin, descending eastward from the main entrance of the Zoo to the eastern Zoo boundary near Rock Creek (a change from approximately 210 feet (ft) to 55 ft in elevation, relative to mean sea level). The topography of the project area slopes moderately to the Zoo perimeter road to the north and gently to Olmsted Walk to the south. The natural topography of the proposed project site has been previously modified over time by the introduction of fill material to create animal exhibits (e.g., the cheetah and zebra exhibits) at this location. The soils of the project site are classified as urban land soils, which are soils that have been previously cut (excavated) and filled with other soil materials. The project site soils have been historically disturbed for exhibit construction and operation, and/or covered with impervious materials such as asphalt, concrete, and building materials. In steeply sloped areas of the site, soils may be mixed with bluestone, which was used to stabilize the soil from disturbance from animal traffic. There is no known history of soil contamination or previous use of contaminated fill at the project site. In the project area, natural soils overlie bedrock, generally at depths of 25 ft below the natural soil surface, based on recent geotechnical explorations on the site. Bedrock in the area may also occur at greater depths due to the placement of fill material during past development of previous and existing exhibits in the project area. The project area has mature and fully developed vegetative cover with few areas of exposed soil, except within the animal exhibit yards. Paved pedestrian pathways are provided around the animal exhibits. Overall, minor potential exists on-site for soil erosion and sediment transport due to stormwater runoff. Potential Geophysical Resource Impacts Under the Proposed Alternative, project site topography would be altered by demolition, grading, fill placement, excavation, and construction activities. However, there would not be major elevation or topographic profile changes to the project site. Excavated soils would not be anticipated to contain contaminants and would, therefore, be suitable for reuse on-site. SMITHSONIAN INSTITUTION – NATIONAL ZOOLOGICAL PARK 3-1
ASIA TRAIL - ELEPHANT FACILITY SUPPLEMENTAL ENVIRONMENTAL ASSESSMENT Project site soils would be subject to disturbance from demolition of existing exhibit infrastructure, clearing and grubbing of vegetation, and surface grading to prepare the site for the proposed facilities. The construction of the proposed elephant facility, which would occur in an area of previously disturbed fill material, would require regrading, and potentially the placement of additional fill material, to create level areas for the facility and its yards. It is not anticipated that bedrock would be encountered during construction due to the typical depth of bedrock on the site (25 ft or greater). Thus, there would be no anticipated construction complications (i.e. pile driving and/or blasting/drilling of rock outcrops) related to bedrock. Clearing of the project site and construction of the elephant facility may occur during the same time period as the on-going construction activities of Asia Trail Phase I. Therefore, the impacts to site topography, soils, and geology from this project would cumulatively contribute to the ongoing changes to topography; including the movement of soil within the Asia Trail project. However, the project area has been previously disturbed to establish animal exhibits. Therefore, there would be no impacts to original undisturbed soil and topography. In addition, there would be no cumulative impacts to geology. Overall, development of the elephant facility would likely result in minor impacts to topography, moderate temporary impacts to site soils, and no impact to geology. Mitigation The potential for soil erosion impacts during construction, due to the disturbance of on-site soils and vegetation, would be temporary and mitigated by the implementation of appropriate best management practices (BMPs) addressing soil erosion. If detected, contaminated soils would be collected, transported, and disposed of using appropriate BMPs for handling hazardous materials. 3.2 Water Resources Surface Water The project site is located in one of the larger, highly urbanized surface drainage areas in the District, with an impervious surface area estimated at 50 percent, based on D.C. standards for urban areas. The site naturally drains to Rock Creek, which is located along the Zoo’s eastern boundary. The project site does not include wetlands and is not within the Rock Creek floodplain. Rock Creek is a natural water body and a minor tributary to the Potomac River, which is part of the Chesapeake Bay Watershed. It meanders through the lower portions of the Zoo, separating the public area and animal exhibits of the Zoo from other parts of the Zoo to the south. Rock Creek is considered jurisdictional “waters of the United States,” subject to the regulatory control of the U.S. Army Corps of Engineers. Rock Creek is also a designated Special Waters of the District of Columbia (SWDC) and subject to the water quality requirements of the District of Columbia as currently maintained under US EPA agreements with the District Water and Sewer Administration (WASA). SMITHSONIAN INSTITUTION – NATIONAL ZOOLOGICAL PARK 3-2
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asia trail elephant facility - National Zoo - Smithsonian Institution

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