U.S. Department of the Interior Section 4.0 MM S Minerals Management Service Description of Affected Environment 4.0 DESCRIPTION OF THE AFFECTED ENVIRONMENT 4.1 PHYSICAL RESOURCES For purposes of describing the physical resource characteristics of the proposed action area, this material is presented in the following seven subsections: geology, noise, physical oceanography, climate and meteorology, air quality, water quality, and electrical and magnetic fields. 4.1.1 Regional Geologic Setting The site of the proposed action is located in the Atlantic Coastal Plain physiographic province. The geomorphologic setting can best be described as glacially produced. The surficial expression of Cape Cod and Nantucket Sound were formed during the advance and retreat of the last continental ice sheet in the northeastern United States, part of the Laurentide glaciation, and the subsequent erosion and reworking of the glacial deposits during the Holocene (10,000 years ago to the present) sea-level rise. Figure 4.1.1-1 (see Appendix A for all Figures) presents an interpretation of the glacial processes that formed Cape Cod and Nantucket Sound. In the area of the proposed action, the maximum advance of the last continental glaciation is marked by the advance of the Cape Cod ice lobe, and the formation of terminal moraines on Martha’s Vineyard and Nantucket, estimated at approximately 20,000 years ago. During this advance, it is thought that subglacial tunnel valleys carrying meltwater and sediment, extended south from Cape Cod to the ice margin near Martha’s Vineyard and Nantucket, and eroded into the underlying fine grain sediments (Uchupi, E. and Mulligan, A.E., 2006). As the continental ice sheet retreated, a proglacial lake formed in Nantucket Sound, resulting in the deposition of clays and fine sand. During this retreat, the ice sheet stalled along the southern shore of Cape Cod, depositing unstratified, poorly-sorted, ice-contact deposits of silt, clay, sand, gravel, and boulders (see area “III” in Figure 4.1.1-1). As ice-sheet retreat continued, this unstratified glacial deposit formed a dam and a second glacial lake formed to the north (see area “IV” in Figure 4.1.1-1). Fine- grained sediments were deposited into this second glacial lake. As the ice-sheet continued to retreat, this second dam, located along the southern shore of present day Cape Cod, failed, and the glacial lake on Cape Cod joined glacial Lake Nantucket. This event was followed by failure of the dam that formed Lake Nantucket, resulting in extreme erosion of the glacial lake and basement sediments. As the ice-sheet continued to retreat, fluvial deposition resulted in the formation of outwash plains on Cape Cod and Nantucket Sound (U.S. Geological Survey [USGS], 2006a; Uchupi, E. and Mulligan, A.E., 2006). As the ice-sheet continued to retreat, another glacial lake formed to the north, in Cape Cod Bay, north of the present day Cape Cod outwash plains and the moraine that formed in central Cape Cod. The water level in this glacial lake was higher than today’s sea-level, and groundwater seeps formed on the outwash plain. The unique combination of sand and gravel outwash plains and plenty of source water emanating from the seeps resulted in the formation of straight fluvial valleys that flowed south across the present day Cape Cod outwash plains and Nantucket Sound (Mulligan, A.E. and Uchupi, E. 2004; USGS, 2006a). During this glacial event, world-wide sea-level was hundreds of feet lower than current levels, and the Earth’s crust was depressed by continental glacial loading. As the Laurentide ice sheet continued to melt, sea-level continued to rise, ultimately transgressing over the present day offshore sediments in the project area, drowning the lower reaches of the straight fluvial valleys that had formed, eroding and reworking the glacial deposits along the southern Cape Cod coastline and in Nantucket Sound, a processes that continues today (USGS, 2006a). Cape Wind Energy Project 4-1 January 2009 Final EIS U.S. Department of the Interior Section 4.0 MM S Minerals Management Service Description of Affected Environment Figure 4.1.1-2 presents the present day regional onshore surficial geology of Cape Cod, Martha’s Vineyard, and Nantucket. Figure 4.1.1-3 presents the present day regional surficial geology of Nantucket Sound. Figure 4.1.1-4 presents surface sediment types in the proposed action area of Nantucket Sound. To further understand the regional sedimentary features, two regional geologic cross sections were constructed. Figure 4.1.1-5 presents the locations of two cross sections, identified as A-A′ and B-B′. Figure 4.1.1-6 presents the geologic cross section A-A′, which begins onshore in southwestern Cape Cod, extends through the site of the proposed action in Nantucket Sound, and continues to Nantucket Island. Figure 4.1.1-7 presents geologic cross section B-B′, which begins on Martha’s Vineyard, extends through the site of the proposed action, and continues onshore in the mid-Cape Cod region. 4.1.1.1 Site-Specific Studies Analysis Field studies were completed to further refine the understanding of the geology at the site of the proposed action as it relates to the seafloor, sub-seafloor, and onshore cable route. Studies were targeted to detail water depths, surface and sub-surface sediment types, seafloor morphology, sub-seafloor stratigraphy, and natural or man-made obstructions as they relate to installation, operation, and decommissioning of the proposed facilities. Benthic and archaeological samples were incorporated into the geotechnical field programs, where applicable (Report No. 4.1.1-1). Integrated marine geophysical/hydrographic surveys and geotechnical/sediment sampling programs were conducted in 2001, 2002, 2003, 2004, and 2005 on Horseshoe Shoal and along the proposed transmission cable route from the ESP to the proposed landfall location in Yarmouth. Numerical modeling and engineering analysis of site specific data related to oceanographic processes was performed to assess, simulate, and predict potential impacts to geologic resources for installation and operation of the proposed action. The studies included: Report No. 4.1.1-2 Simulation of Sediment Transport and Deposition from Cable Burial Operations in Nantucket Sound for the proposed energy Project; Report No. 4.1.1-3, Estimates of Seabed Scar Recovery from Jet Plow Cable Burial Operations and Possible Cable Exposure on Horseshoe Shoal from Sand Wave Migration; Report No. 4.1.1-4, Analysis of Effects of Wind Turbine Generator Pile Array of the Project in Nantucket Sound; Report No. 4.1.1-5, Revised Scour Report; Report No. 4.1.1-6, Conceptual Rock Armor Scour Protection Design,; Report No. 4.1.1-7, Hydrodynamic Analysis of Scour Effects Around Wind Turbine Generator Piles, Use of Rock Armor and Scour Mats, and Coastal Deposition and Erosion; and, in Report No. 4.1.1-8, Seabed Scour Control Systems Scientific Design Station Report. A detailed summary of these studies is presented in Section 5.3.1.1. As detailed in Section 5.3.1.1, if the proposed action is authorized, the applicant would conduct additional geophysical/hydrographic surveys, geotechnical/sediment sampling vibracore sampling, and cone penetration test samples along the proposed 115 kV cable routes and along the inner-array 33 kV cable routes to finalize design parameters. All future survey and sampling methods will be site specific and coordinated with MMS. 4.1.1.1.1 Marine Geophysical/Hydrographic Surveys The marine geophysical/hydrographic surveys were designed to collect remote sensing data to evaluate wind tower installation feasibility, gather data to support the foundation design process, and to support the analysis of the surface and subsurface sediments on Horseshoe Shoal and the proposed submarine transmission and inner-array cable routes. Surveys included: • Hydrographic measurements with a fathometer to determine water depths; Cape Wind Energy Project 4-2 January 2009 Final EIS U.S. Department of the Interior Section 4.0 MM S Minerals Management Service Description of Affected Environment • Side-scan sonar to evaluate surface sediments, seafloor morphology and potential surface obstructions; • Seismic profiling with high frequency (HF) (high resolution; limited penetration below the seafloor) and low frequency (low resolutions; deeper penetration beneath the seafloor) acoustic sources; and • Magnetometer surveys to identify ferrous objects at the surface or shallow subsurface areas; combined with a differential Global Positioning System (GPS) to document the precise location of anomalies. Figure 4.1.1-8 illustrates the locations of the 2001, 2003, and 2005 marine geophysical and hydrographic vessel tracklines, as they relate to the proposed action facilities. Following completion of the field survey, the digital data files were processed at the surveyor’s mainland facility, then reviewed and interpreted by staff and a marine archaeologist (for potential cultural resources). Digital hydrographic files were corrected for tidal fluctuations to report water depths at MLLW. Side scan sonar and magnetic intensity data were interpreted to delineate acoustic targets and magnetic anomalies. 4.1.1.1.2 Geotechnical Investigations Two marine sediment sampling methods, vibracoring and sediment boring were used to advance sediment sampling devices below the seafloor surface to collect, sample, and analyze representative sediments from the site of the proposed action. The information gathered during these studies was used to correlate the geophysical data collected to actual sediment characteristics where WTG foundations are proposed in deep sediment (85 ft [26 m] below the seafloor) and along shallow electrical inner-array cable routes in shallow sediment depths (targeted for 6 ft [1.8 m] below the seafloor). In addition, soil borings and test pits were completed along the onshore transmission cable route to confirm the surficial materials expected to be encountered during transmission cable installation.