14.0 SOILS, GEOLOGY AND SEISMOLOGY
14.1 Applicability
This analysis will address constructibility issues - soils, bedrock location, topography and slopes, groundwater depth, and other geotechnical conditions, as documented in existing literature and, to the degree necessary, as investigated on-site and along interconnection routes. The Siting Board regulations also explicitly require an evaluation of geology and seismology. 16 NYCRR 1001.3(b)1(v). Furthermore, the Public Service Law requires that an Application contain, "as appropriate, geological... tsunami, [and] seismic" data. PSL164.1(a). The potential for active seismological faults and earthquakes that could cause ground motion, liquefaction, slope instability and deformation will therefore be addressed in the Application. The analyses to be performed are described below as well as in Stipulation 8.
14.2 Geotechnical Analysis
14.2.1 Existing Conditions
Soils on-site are a result of fill activity in the nineteenth century. Their suitability for supporting building foundations is considered poor. Piles are anticipated to be a potential method of support for the structure of the proposed Project. Bedrock is not likely to be encountered in any of the on-site excavations. The site is located in an area of the East River marked by soft soils and bedrock that is much deeper than along most of the East River. Grading and stability of slopes, other than those in temporary construction cuts and fills, should not be a concern because the site slopes very gently from the East River up toward Kent Avenue.
14.2.2 Further Information Requirements and Methodology
A further geotechnical site investigation will be conducted as necessary to characterize subsurface conditions in the immediate vicinity of the site for foundation design and construction, and may be reported upon in the Application. The geotechnical site investigation may consist of drilling, soil sampling, field observations, laboratory tests, and analyses that address foundation type, bearing capacity, settlement amount and rate, vibrations, liquefaction potential, seismic effects, and subgrade improvement. This information will assure that the Project is safely and adequately designed and constructed, given site-specific conditions.
The Application will include a report on the suitability of the soils actually found on-site through new or previously reported geotechnical investigation, including the suitability for construction purposes of each soil type, a description of its recharge/infiltration capacity, and a discussion of any dewatering that may be necessary during construction. Included in the Application will be a map delineating depth to bedrock and showing existing and proposed site contours.
14.3 Construction Techniques for Project and Interconnections
14.3.1 Steam Interconnection
The Application will assess alternative methods of steam interconnection construction, including directional drilling and tunnel boring. In addition, the possible use of the existing MTA tunnel will be discussed. The geotechnical composition below the East River will be presented on the basis of available literature. A conceptual work plan will be set forth, with descriptions of steam interconnection requirements, description of equipment to be used, impacts to bedrock geology, and contingency plans associated with directional drilling and/or tunnel boring.
14.3.2 Foundation Support
On the basis of the geotechnical investigation, the Application will identify the method of foundation support, and will provide sufficient technical details to establish the viability of the preferred support method.
14.3.3 Blasting and Pile Driving Analyses
TGE will examine the need for blasting associated with the construction at the Project site or interconnections. Although blasting is not anticipated, TGE will present a blasting plan. The plan will identify blasting operator qualifications, standard protocols, timing of discrete blasts, and what steps will be taken to ensure that any damage to adjacent structures can be avoided, or if it occurs - identified, mitigated, and compensated.
The Application will also examine pile driving, which may be used at the Project site. The Application will therefore include a preliminary plan describing the hours of pile driving operations and measures to ensure that neighboring buildings are not impacted by any Project-related pile driving. Included will be an identification and evaluation of reasonable mitigation measures regarding pile driving impacts, including the use of alternative technologies and/or location of structures, and including a plan for securing compensation for any damages that may occur due to pile driving.
14.4 Bedrock Faults and Seismology
The Application will report information on the bedrock geology that underlies the site and all interconnections. The bedrock foundations of New York City consist of a sequence of dense and stable crystalline rocks consisting of schist, gneiss, and marble that outcrop mainly in Manhattan and the Bronx. These rocks are overlaid unconformably in Queens by unconsolidated Cretaceous deposits and unconsolidated Pleistocene glacial and scattered postglacial material. The crystalline rocks of the Bronx, Manhattan, and eastern and northern Queens and Brooklyn provide the supporting foundation for major buildings and structures throughout the New York City region. These rock formations occur in two major units separated by a regional northeast-striking, eastward dipping thrust fault, known as Cameron's Line.
The Application will address the seismic risk for the Project site and interconnections. Earthquakes with Richter Magnitude greater than 6 are possible in New York City, although none are documented in the historic record. The probability of these significant earthquakes is low (about once every few hundred years), but can result in multi-billion dollar losses in a densely populated area such as New York City. To reduce the risk of earthquake damage in New York State, numerous seismic hazard reduction measures have become effective, including Seismic Building Codes. The New York State Building Code divides the state into four seismic zones, A, B, C, and D, with seismic zone factors of Z = 0.09, 0.12, 0.15, and 0.18, respectively (measuring effective peak acceleration in fractions of g, where g equals the earth's gravity acceleration). The seismic building code for New York State uses these four zone factors, which are based of an exceedance probability of 10% in 100 years. Brooklyn is in seismic zone C, indicating a region of intermediate seismic hazard. Per the Public Service Law, tsunamis will also be addressed.