Segment 11 consists of the States of Delaware, Maryland, New Jersey, North Carolina, West Virginia, and the Commonwealths of Pennsylvania and Virginia. All but West Virginia border on the Atlantic Ocean or tidewater. Pennsylvania also borders on Lake Erie. Small parts of northwestern and north-central Pennsylvania drain to Lake Erie and Lake Ontario; the rest of the segment drains either to the Atlantic Ocean or the Gulf of Mexico. Major rivers include the Hudson, the Delaware, the Susquehanna, the Potomac, the Rappahannock, the James, the Chowan, the Neuse, the Tar, the Cape Fear, and the YadkinPeedee, all of which drain into the Atlantic Ocean, and the Ohio and its tributaries, which drain to the Gulf of Mexico.
Although rivers are important sources of water supply for many cities, such as Trenton, N.J.; Philadelphia and Pittsburgh, Pa.; Baltimore, Md.; Washington, D.C.; Richmond, Va.; and Raleigh, N.C., one-fourth of the population, particularly the people who live on the Coastal Plain, depends on ground water for supply. Such cities as Camden, N.J.; Dover, Del.; Salisbury and Annapolis, Md.; Parkersburg and Weirton, W.Va.; Norfolk, Va.; and New Bern and Kinston, N.C., use ground water as a source of public supply.
All the water in Segment 11 originates as precipitation. Average annual precipitation ranges from less than 36 inches in parts of Pennsylvania, Maryland, Virginia, and West Virginia to more than 80 inches in parts of southwestern North Carolina (fig. 1). In general, precipitation is greatest in mountainous areas (because water tends to condense from moisture-laden air masses as the air passes over the higher altitudes) and near the coast, where water vapor that has been evaporated from the ocean is picked up by onshore winds and falls as precipitation when it reaches the shoreline.
Some of the precipitation returns to the atmosphere by evapotranspiration (evaporation plus transpiration by plants), but much of it either flows overland into streams as direct runoff or enters streams as base flow (discharge from one or more aquifers). The distribution of average annual runoff (fig. 2) is similar to the distribution of precipitation; that is, runoff is generally greatest where precipitation is greatest. Runoff rates range from more than 50 inches per year in parts of western North Carolina to less than 12 inches in parts of North Carolina, Virginia, and West Virginia.
Parts of the seven following physiographic provinces are in Segment 11: the Coastal Plain, the Piedmont, the Blue Ridge, the New England, the Valley and Ridge, the Appalachian Plateaus, and the Central Lowland. The provinces generally trend northeastward (fig. 3). The northeastern terminus of the Blue Ridge Province is in south-central Pennsylvania, and the southwestern part of the New England Province, the Reading Prong, ends in east-central Pennsylvania. The topography, lithology, and water-bearing characteristics of the rocks that underlie the Blue Ridge Province and the Reading Prong are similar. Accordingly, for purposes of this study, the hydrology of the Reading Prong is discussed with that of the Blue Ridge Province.
The Coastal Plain Province is a lowland that borders the Atlantic Ocean. The Coastal Plain is as much as 140 miles wide in North Carolina but narrows northeastward to New Jersey where it terminates in Segment 11 at the south shore of Raritan Bay. Although it is generally a flat, seaward-sloping lowland, this province has areas of moderately steep local relief, and its surface locally reaches altitudes of 350 feet in the southwestern part of the North Carolina Coastal Plain.
The Coastal Plain mostly is underlain by semiconsolidated to unconsolidated sediments that consist of silt, clay, and sand, with some gravel and lignite. Some consolidated beds of limestone and sandstone are present. The Coastal Plain sediments range in age from Jurassic to Holocene and dip gently toward the ocean.
The boundary between the Coastal Plain and the Piedmont Provinces is called the Fall Line (fig. 3) because falls and rapids commonly form where streams cross the contact between the consolidated rocks of the Piedmont (fig. 4) and the soft, semiconsolidated to unconsolidated sediments of the Coastal Plain. The increase in stream gradient at the Fall Line provided favorable locations for mills and other installations that harnessed water power during the early years of the Industrial Revolution, and on most major rivers, the Fall Line coincides with the head of navigation.
The Piedmont Province is an area of varied topography that ranges from lowlands to peaks and ridges of moderate altitude and relief. The metamorphic and igneous rocks of this province range in age from Precambrian to Paleozoic and have been sheared, fractured, and folded. Included in this province, however, are sedimentary basins that formed along rifts in the Earth's crust and contain shale, sandstone, and conglomerate of early Mesozoic age, interbedded locally with basaltic lava flows and minor coal beds. The sedimentary rocks and basalt flows are intruded in places by diabase dikes and sills.
The mountain belt of the Blue Ridge Province forms the northwestern margin of the Piedmont in most of Segment 11. This belt consists mostly of igneous and high-rank metamorphic rocks but also includes low-rank metamorphic rocks of late Precambrian age and small areas of sedimentary rocks of Early Cambrian age along its western margin. In this report, the Reading Prong of the New England Province, which is an upland that extends from east of the Susquehanna River in Pennsylvania northeastward into New Jersey (fig. 3), is treated as part of the Blue Ridge Province. Part of the Reading Prong in Pennsylvania and New Jersey and a small part of the Piedmont Province in northeastern New Jersey have been glaciated. Glacial deposits completely or partly fill some of the valleys, and the eroding action of the glacial ice removed some of the rock from the ridges. Thus, the glaciated parts of the province have a smoother topography and less relief than other parts.
The Valley and Ridge Province is characterized by layered sedimentary rock that has been complexly folded and locally thrust faulted. As the result of repeated cycles of uplift and erosion, resistant layers of well-cemented sandstone and conglomerate form elongate mountain ridges and less resistant, easily eroded layers of limestone, dolomite, and shale form valleys. The rocks of the province range in age from Cambrian to Pennsylvanian. Parts of this province from central Pennsylvania into New Jersey have been glaciated, and glacial deposits fill or partially fill some of the valleys.
The Appalachian Plateaus Province is underlain by rocks that are continuous with those of the Valley and Ridge Province, but in the Appalachian Plateaus the layered rocks are nearly flat-lying or gently tilted and warped, rather than being intensively folded and faulted. The boundary between the two provinces is a prominent southeast-facing scarp called the Allegheny Front in most of the northern part of Segment 11 (fig. 5) and the Cumberland Escarpment in the southern part. The scarp faces the Valley and Ridge Province, and throughout most of the segment, the eastern edge of the Appalachian Plateaus Province is higher than the ridges in the Valley and Ridge. Like parts of the Reading Prong and the Valley and Ridge Province, the northern part of the Appalachian Plateaus Province in Pennsylvania has been glaciated. In the glaciated section, the surface is mantled by glacial drift, and the valleys are partly filled with glacial deposits.
The northwestern corner of Segment 11 contains a small part of the Central Lowland Province. This flat lowland is underlain by gently dipping sedimentary rocks, some of which are the same geologic formations as those of the Appalachian Plateaus Province. The two provinces are separated by a northwest-facing scarp. Because of the small area of the Central Lowland Province within the segment and the similarity of aquifer properties with those of the glaciated part of the Appalachian Plateaus Province, the two provinces are discussed together in this report.
The rocks and unconsolidated deposits that underlie Segment 11 are divided into numerous aquifer systems, aquifers, and confining units. An aquifer system consists of two or more aquifers and can be of two types, both of which are in Segment 11. The first type consists of aquifers that are vertically stacked and hydraulically connected-that is, the ground-water flow systems in the aquifers function in the same fashion, and a change in conditions in one of the aquifers affects the others. The Northern Atlantic Coastal Plain aquifer system is of this type. The second type consists of several aquifers that are not connected, but share common geologic and hydrologic characteristics and, accordingly, can best be studied and described together. The surficial aquifer system is of this type. The areas where each principal aquifer or aquifer system is exposed at the land surface or is the shallowest major aquifer are shown in figures 6 and 7. For purposes of this Atlas, the principal aquifers in Segment 11 (some of which include many local aquifers) have been grouped by physiographic province. The Coastal Plain Province has six aquifers that consist mostly of semiconsolidated rocks. The Piedmont and the Blue Ridge Provinces have three types of aquifers in consolidated rocks, locally overlain by unconsolidated deposits of the surficial aquifer system. The surficial aquifer system also locally overlies aquifers in two types of consolidated rocks in each of the Valley and Ridge and the combined Appalachian PlateausCentral Lowland Provinces. Some of the consolidated-rock aquifers are in more than one province; for example, limestone and dolomite aquifers are recognized in the Piedmont, the Blue Ridge, the Valley and Ridge, and the Appalachian Plateaus Provinces (fig. 7).
The aquifers and aquifer systems of Segment 11 can be grouped into three categories, depending on the degree of consolidation of the rocks and deposits that compose the aquifers. Rocks of Precambrian, Paleozoic, and early Mesozoic ages generally are consolidated; rocks of Cretaceous and Tertiary ages generally are semiconsolidated; and deposits of Quaternary age generally are unconsolidated. Some of the consolidated rocks, particularly those that underlie the Piedmont and the Blue Ridge Physiographic Provinces, are covered with unconsolidated material called regolith that is largely derived from weathering of the consolidated rocks.
Unconsolidated sand and gravel deposits that mostly occur as long, narrow bands in the northern and western parts of Segment 11 (fig. 6) compose the surficial aquifer system. Many of the sand and gravel deposits north of the limit of continental glaciation formed as glacial outwash that was deposited by meltwater from the ice sheets. Elsewhere, the sand and gravel are stream-valley alluvium that was deposited adjacent to the principal streams in the segment. Some of the stream-valley alluvium consists of reworked glacial outwash. Unsorted, unstratified deposits called till, emplaced by the continental ice sheets, are not aquifers.
Aquifers in semiconsolidated to consolidated rocks underlie most of Segment 11 (fig. 7). These aquifers, along with confining units that separate them in some places, are described according to physiographic province. Aquifers in some of the provinces extend underground far beyond the areas where they are mapped at or near the land surface; for example, the Potomac aquifer is exposed as only a narrow band along the northwestern boundary of the Coastal Plain, but underlies most of the Coastal Plain.
The Northern Atlantic Coastal Plain aquifer system consists mostly of semiconsolidated sand aquifers separated by clay confining units. Unconsolidated sands compose the surficial aquifer, which is the uppermost water-yielding part of the aquifer system; the system also includes a productive limestone aquifer. The Coastal Plain sediments are thin near their contact with the rocks of the Piedmont Province and, in places, might not yield as much water as the underlying igneous and metamorphic rocks that are an extension of Piedmont rocks.
Aquifers in the Piedmont and the Blue Ridge Provinces and the Reading Prong are predominately in metamorphic and igneous rocks. In some topographically low areas of the Piedmont, aquifers are in carbonate rocks (limestone, dolomite, and marble) and in sandstone of early Mesozoic age that fills large basins that formed as deep rifts in the Earth's crust. The carbonate rocks are the most productive Piedmont and Blue Ridge aquifers.
Folded sedimentary rocks of Paleozoic age underlie the Valley and Ridge Physiographic Province. The strata consist mostly of sandstone, shale, and limestone; coal is present
in these rocks in Pennsylvania and Virginia, and they locally contain minor dolomite and conglomerate. Locally, the rocks have been metamorphosed into quartzite, slate, and marble. Carbonate rocks are the most productive Valley and Ridge aquifers.
The Appalachian Plateaus aquifers are in Paleozoic sedimentary rocks that are flat-lying or gently folded. The rocks consist mostly of shale, sandstone, conglomerate, and carbonate rocks; coal beds are in rocks of Pennsylvanian age. Most of the water-yielding beds are sandstones of Pennsylvanian and Mississippian age; Pennsylvanian coals and Permian sandstones yield water, but the Permian strata are mostly shale. Carbonate rocks of Mississippian age are also productive aquifers in many places. Small volumes of water are obtained locally from conglomerate beds of Pennsylvanian age.
Segment 11 contains two major rock types-consolidated crystalline rocks and consolidated to unconsolidated sedimentary rocks. The crystalline rocks consist of numerous kinds of igneous and metamorphic rocks and are mostly in the Piedmont and the Blue Ridge Provinces. Consolidated sedimentary rocks are mostly in the Valley and Ridge and the Appalachian Plateaus Provinces. Sedimentary rocks in the Coastal Plain Province are mostly semiconsolidated, but some are unconsolidated. The extent of the different rock types is shown in figure 8.
The igneous and metamorphic rocks in Segment 11 crop out in a band that trends northeastward, is widest in North Carolina, and narrows northeastward (fig. 8). The band includes much of the rock of the Piedmont Province and most of the rock of the Blue Ridge Province and the Reading Prong. The crystalline rocks generally are resistant to weathering and erosion. According to radiometric dating, the ages of the crystalline rocks range from more than 1,200 million to 196 million years before present (Precambrian to Jurassic). Even though these rocks vary greatly in mineral composition and texture, they have similar hydraulic characteristics in that they generally have almost no pore spaces between mineral grains and contain ground water in joints and fractures.
Most of the rocks that underlie Segment 11 are sedimentary rocks that can be grouped into three categories-well-consolidated rocks of Paleozoic age, variably consolidated rocks of Triassic and Early Jurassic age in early Mesozoic rift basins, and semiconsolidated to unconsolidated rocks of Cretaceous and younger age. Unconsolidated Quaternary deposits that overlie crystalline rocks or consolidated sedimentary rocks in the northern and western parts of the segment are shown in figure 6.
Paleozoic sedimentary rocks extend from western and central Virginia through all of West Virginia, western Maryland, western and northern Pennsylvania, and a small part of northern New Jersey. Most of these rocks are exposed in the folded and thrust-faulted Valley and Ridge Province and in gently warped to flat-lying beds of the Appalachian Plateaus Province (fig. 9), but some are in the Piedmont Province of northern Maryland, eastern Pennsylvania, and northern New Jersey. ThePaleozoic sedimentary rocks consist of conglomerate, sandstone, siltstone, mudstone, shale, coal, limestone, and dolomite. The sandstone and limestone beds are the most productive aquifers in these rocks.
Lower Mesozoic (Triassic and Lower Jurassic) sedimentary rocks are in deep, elongate basins in the Piedmont Province (figs. 8 and 9). The basins formed in rifts in the Earth's crust and are oriented roughly parallel to the modern coast. Some incompletely mapped basins are buried beneath Coastal Plain sediments. The Newark Basin in north-central New Jersey and adjacent parts of New York and Pennsylvania is the largest early Mesozoic basin in eastern North America. The sedimentary rocks in the basins have been tilted and faulted, but are not metamorphosed and deformed to the same extent as the older rocks that surround the basins. The sedimentary rocks in the basins are primarily conglomerate, sandstone, shale, and siltstone, with minor limestone and coal. These rocks are interlayered with basalt flows and intruded by diabase dikes and sills. The conglomerate and sandstone are the most productive aquifers.
Semiconsolidated to unconsolidated sediments of Cretaceous and younger age in the Coastal Plain Province form a band that narrows toward the northeast and is parallel to the coast (fig. 8). The sediments, especially those of Cretaceous age, thicken greatly toward the coast in subsurface basins in Maryland, Delaware, and part of New Jersey but are much thinner on structurally high areas to the north and south. Most of the Coastal Plain sediments are sand, clay, and silt, with minor gravel and lignite; limestone is locally prominent, particularly in North Carolina. The sediments were deposited mostly in shallow marine environments when sea level was higher relative to the land surface than at present, or in the floodplains and deltas of rivers that drained the landmass to the north and west. The sands and limestones are the most productive aquifers.
All three categories of sedimentary rocks have been divided into numerous formations. The geologic and hydrogeologic nomenclature used in this report differs from State to State because of independent geologic interpretations and varied distribution and lithology of rock units. A fairly consistent set of nomenclature, however, can be derived from the most commonly used rock names. Therefore, the nomenclature used in this report is basically a synthesis of that of the U.S. Geological Survey, the Delaware Geological Survey, the Maryland Geological Survey, the New Jersey Geological Survey, the North Carolina Geological Survey, the Pennsylvania Bureau of Topographic and Geologic Survey, the Virginia Division of Mineral Resources, and the West Virginia Geological and Economic Survey. Individual sources for nomenclature are listed with each correlation chart prepared for this report.
Quaternary deposits are in the extreme northern parts of all the physiographic provinces except the Coastal Plain (fig. 6). These deposits are predominately unsorted and unstratified glacial material (till) that ranges in size from clay to coarse gravel and boulders. Sand and gravel are present as outwash deposits that formed along the glacial front (the southern limit of glaciation) and as Holocene alluvium in major river valleys.
The area mapped in figure 8 contains four broad geologic categories (fig. 9). From northwest to southeast, these are: flat to gently folded Paleozoic sedimentary rocks that underlie the Appalachian Plateaus and the Central Lowland Physiographic Provinces; the same types of rocks folded into a series of anticlines and synclines in the Valley and Ridge Physiographic Province; metamorphic and igneous rocks of the Piedmont and the Blue Ridge Physiographic Provinces that contain large areas of tilted sedimentary rocks and lava flows in early Mesozoic basins, and smaller areas of faulted and folded blocks of Paleozoic sedimentary rocks that have undergone various degrees of metamorphism; and gently dipping, semiconsolidated to unconsolidated sediments of the Coastal Plain Physiographic Province. The combination of rock type and geologic structure largely determines the hydraulic properties of the rocks. These factors, plus topography and climate, determine the characteristics of the ground-water flow system throughout the mapped area.
The concentration of dissolved solids in ground water provides a basis for categorizing the general chemical quality of the water. Dissolved solids in ground water primarily result from chemical interaction between the water and the rocks or unconsolidated deposits through which the water moves. Rocks or deposits composed of minerals that are readily dissolved will usually contain water that has large dissolved-solids concentrations. The rate of movement of water through an aquifer also affects dissolved-solids concentrations; the longer the water is in contact with the minerals that compose an aquifer, the more mineralized the water becomes. Thus, larger concentrations of dissolved solids commonly are in water at or near the ends of long ground-water flow paths. Aquifers that are buried to great depths commonly contain saline water or brine in their deeper parts, and mixing of fresh ground water with this saline water can result in a large increase in the dissolved-solids concentration of the freshwater. Contamination as a result of human activities can increase the concentration of dissolved solids in ground water; such contamination usually is local but can render the water unfit for human consumption or for many other uses.
The terms used in this report to describe water with different concentrations of dissolved solids are as follows:
Dissolved-solids concentration, in milligrams per liter
|Freshwater||Less than 1,000|
|Slightly saline water||1,000 to 3,000|
|Moderately saline water||3,000 to 10,000|
|Very saline water||10,000 to 35,000|
|Brine||Greater than 35,000|
FRESH GROUND-WATER WITHDRAWALS
Ground water is the source of public supply for almost 7 million people in Segment 11, or about 19 percent of the population in the seven-State area. About 2,600 million gallons per day was withdrawn from all the principal aquifers during 1985; 33 percent of this amount was withdrawn for public supply. Withdrawals by self-supplied industries and for mining accounted for 22 percent of the total water withdrawn.
Counties with the largest withdrawals in Segment 11 generally are those that contain large population centers. Such counties include those around Pittsburgh, Pa., the Philadelphia, Pa.Camden, N.J. area; and the parts of New Jersey in the New York City metropolitan area (fig. 10). Large withdrawals are associated with mining activity in eastern North Carolina and with paper manufacturing in southeastern Virginia. Fresh ground-water withdrawals for most water-use categories increased through 1985, according to a nationwide compilation of water-use data by the U.S. Geological Survey.
The largest withdrawals of ground water, 1,029 million gallons per day, were from the Northern Atlantic Coastal Plain aquifer system, which accounted for about 40 percent of all ground-water withdrawals in the segment during 1985 (fig. 11). Withdrawals from aquifers in the Piedmont and the Blue Ridge Provinces during the same period were 634 million gallons per day. Withdrawals from aquifers in the Valley and Ridge Province were 371 million gallons per day, primarily in Pennsylvania and Virginia. Withdrawals from unconsolidated sand and gravel aquifers of the surficial aquifer system were 320 million gallons per day. In the Appalachian Plateaus Province, withdrawals were 282 million gallons per day, most of which was withdrawn in Pennsylvania and West Virginia.