WTC site damage assessment map, Sept 21, 2001

NYC 9/11 Public Portal Document

There is an underground retaining wall beneath the WTC site that was constructed in the 1960s to prevent the flooding from the Hudson River and shallow groundwater. As many as 1,100 of the anchors to bedrock, known as tiebacks, will eventually be coimected to the retaining wall as support structures. The retaining wall was built to lend stability to the soil around the WTC site and keep groundwater from flooding the area CHie New York Times 2001a).

Environmental Impacts

Groundwater is not a potable water source and would not be used for drinking water at any proposed facility. Construction of aboveground facilities would not affect or be affected by shallow groundwater. Building support structures, utilities, and subway repair/re-construction involving tunneling activities would require de-watering. Shallow groimdwater is impacted by releases that have occurred in the vicinity of the WTC. Extensive subsurface construction and tunneling would be relatively deep and groundwater removal (dewatering) during excavation and construction would be necessary. Dewatering activities may result in generation of groundwater with minor amounts of contamination. The groundwater generated during dewatering would need to be sampled and tested prior to disposal to the stormwater system or to an approved facility that can accept the waste as characterized. Handling of shallow groundwater during dewatering would need to conform to standards established for health, safety, and environmental protection. The presence of possibly contaminated shallow groundwater would result in the need for remediation or the development of dewatering specifications and permitting to address this concern. Construction methods and techniques would be implemented by the responsible party, as appropriate, to avoid shallow groundwater impact. Tunneling and other excavation may require the use of a watertight slurry wall to surround the excavation area or the use of pressurized tunnel boring rqaehines to pass beneath city streets. If long-term groundwater removal in this area occurs, a change in the groimdwater flow direction may occur; howeve-, this is deemed an insignificant effect. After construction, no significant impact to groundwater resources would occur.

3.2 BIOLOGICAL RESOURCES

3.2.1 FLORA

Because the lower Manhattan area has been developed for intensive urban land use no natural vegetative cover remains. Existing vegetative cover consists of ornamental species used for lanH-'-aping in and aroimd the buildings, and along park esplanades on the Hudson River edge. A mix of herbaceous, shrub and tree vegetation was used for landscaping as plaimed by the Battery Park City Authority.

3.2.2 FAUNA

The re-development and repair of existing facilities and infrastructure within the urban landscape of lower Manhattan makes resource use by wildlife difficult. Those species

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