Mid-Atlantic Power Pathway Chalk Point Substation to Indian River ...

Mid-Atlantic Power Pathway Environmental Review Document
Chalk Point Substation to Indian River Substation Volume II – Environmental Analysis of
April 13, 2011 Chalk Point Substation to MD/DE State Line
1.1 GEOLOGY
This section provides information on the geological resources associated with the installation and
operation of the Chalk Point Substation to Maryland/Delaware State Line Project (Project) in Prince
George’s, Calvert, Dorchester and Wicomico Counties, Maryland. Geological resources reviewed
include the geologic and topographic setting, mineral resources, and geologic hazards that might exist at
the converter stations and along the transmission line route. Existing conditions are addressed first in
Section 1.1.1 followed by an analysis of potential Project impacts to those resources in Section 1.1.2.
1.1.1 Existing Conditions
The Project is located within Maryland and is classified as within the Embayed Section of the Coastal
Plain Physiographic Province. The Coastal Plain is a seaward sloping plain extending from Cape Cod,
Massachusetts to the southern tip of Florida. In Maryland, it consists of a fairly flat to moderately rolling
upland and a flatter lowland. The eastern boundary of the Coastal Plain is sea level, as it includes
shorelines of the major estuaries and the Atlantic Ocean. The western boundary extends into central
Maryland well northwest of the proposed Project area. The Coastal Plain is underlain with an eastward
thickening clastic wedge of gently southeast-dipping sediments overlying crystalline basement rocks.
These sediments are mostly unconsolidated sand, gravel, silt, and clay of both terrigenous and marine
origin. The Embayed Section of the Coastal Plain is characterized by estuaries and embayments
attributed to the drowning of river mouths and formation of barrier islands associated with post-glacial
sea-level rise.
Within this physiographic province and section, the Project crosses four physiographic regions: Western
Shore Lowland Region, Western Shore Upland Region, Delmarva Peninsula Region, and Chesapeake
Bay Estuary Region (Figure 1.1-1). The Western Shore Lowland Region is comprised of a series of low
(generally below 50 feet in elevation) and flat fluvial and estuarine terraces, beaches, and drowned river
mouths that fringe the Western Shore Uplands. This Region extends some distance up the valley of the
Patuxent River. Sediments underlying this region are generally quartzoses and, silt, clay, and gravel.
Gravels may be quartz, quartzitic, or lithic (e.g., granitic rocks from the Piedmont). The Project is located
within the Patuxent Estuaries and Lowlands District of this region, which is characterized as a broad, flatbottomed
valley flanked by fluvial-estuarine terraces (Reger and Cleaves 2008). A summary of the
physiographic regions, districts, and areas crossed by the existing Project right-of-way is provided in
Table 1.1-1.
The Western Shore Upland Region extends from the fall line towards the estuary; the boundary is the
base of the usually prominent slope transition to the Western Shore Lowlands (roughly at an elevation of
40 feet). A flat to rolling upland surface underlain by Cretaceous to Pliocene sediments, the region has
markedly higher elevations and greater relief than the Eastern Shore. Fluvial and estuarine terraces flank
the major drainages, most notably the Patuxent River. The Project is located within the Prince Frederick
Knobby Upland District of this region, which consists of moderately to well-dissected uplands with
numerous hillocks between the Patuxent and Chesapeake watersheds. Within this district, the Project is
in the vicinity of the Calvert Cliffs Area but the Project does not contain cliffs, characterized by high
cliffs in an eroding shoreline made up of mainly Miocene strata. Cliff retreat here is primarily by mass
wasting. There is little or no beach along nearly the entire length of the cliffs.
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