Groundwater monitoring sites Albemarle-Pamlico drainage basin

The areal ground-water quality studies of the Albemarle-Pamlico Drainage describe general characteristics of shallow ground water (ground water that occurs within 50 feet of the land surface) and specific characteristics of shallow ground water under selected land uses. On a National basis, shallow ground water was selected because it is most susceptible to contamination from the land surface. Several deep public supply wells were also sampled in areas of cones of depression caused by pumping . This was done to determine if deep supply wells appeared to be intercepting contaminants introduced in water from shallow aquifers.

Ground-water quality was investigated in the Albemarle-Pamlico Basin through statistically based land-use and study-unit surveys and flow-path study. All three components emphasized the study of shallow aquifer systems. These studies were designed to characterize the effects of corn and soybean agriculture and urban activities on shallow ground-water quality. Synoptic studies also were conducted to address particular questions about ground-water quality over large areas.

The land-use survey focused on agricultural land use. Urban uses also were investigated, but results were not included because of sampling problems encountered during the study. These results will be discussed in a planned report. Because corn and soybean agriculture is so important in the Albemarle-Pamlico Drainage and is representative of this type of agriculture in the eastern United States, this particular land use was selected to investigate possible regional and national water-quality effects. Twenty-six sites across the Coastal Plain, which were used for growing corn and soybeans, were randomly selected. Wells were installed on 21 of these sites. Another 5 shallow supply wells in these same areas were sampled to determine if contaminants from the fields appeared to be reaching nearby domestic supply wells.

The study-unit survey wells were randomly selected to represent general shallow ground-water quality in the Coastal Plain without a targeted land use. These wells were used to compare water-quality data from targeted land-use wells in the same area to evaluate possible effects associated with the particular land use investigated. Wells that could be included for selection were those equipped with submersible pumps and good well-construction and location information. Many of these wells were typically existing USGS or State observation wells used for long-term water-level monitoring. Most wells occured in areas of recharge and none were sited in stream discharge areas. Several were shallow supply wells, which were equipped with submersible pumps. About 7 deep public-supply wells were also sampled in the vicinity of known pumping cones to evaluate possible pumping-induced contamination.

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Physiographic province is either O, outer Coastal Plain, or I, inner Coastal Plain; these are defined as follows: The eastern boundary of the outer Coastal Plain is the Atlantic Ocean. The eastern boundary of the inner Coastal Plain is the Suffolk Scarp; the western boundary is the Fall Line, which delineates the Piedmont physiographic province.
Station type is either DS, rural domestic supply well; LU, land-use well (related to corn and soybean agriculture); SU, study-unit survey well; or MU, municipal supply well.

Water samples were analyzed for physical properties, major ions, nutrients, pesticides, and volatile organic compounds (see list below). Radiochemicals, such as radium and uranium isotopes and radon, were included in the study-unit survey.

gw, ground-water sample; sw, surface-water sample; IT, incremental titration; mg/L, milligram per liter; cfs, cubic foot per second; µS/cm, microsiemen per centimeter; ft, foot; gpm, gallon per minute; mm of Hg, millimeter of mercury; µg/L, microgram per liter; pci/L, picocurie per liter

* Minimum reporting limit (MRL) - not MDL

Land-Use Survey

Land-use surveys were conducted to characterize ground-water quality associated with particular land uses. Corn and soybean agriculture and urban land-use studies were conducted.

Agricultural land use (installed well)

• Land-Use Setting: Agricultural: 13,349 mi² of Coastal Plain area. Sampling occurred only in corn- and soybean-growing areas. Wells were installed in or on the edge of corn and soybean fields.

• System Description: Primarily the unconfined surficial aquifer was sampled throughout the Coastal Plain; however, several wells are placed in the uppermost confined aquifer, including the Yorktown, Peedee, or upper Cape Fear aquifers. Coastal Plain topographic conditions vary from well-drained areas of high topographic relief dissected by streams to broad, poorly drained flats. Well depths range from 6 to 33 feet below land surface, with a median depth of about 11 feet.

• Site Selection: The Coastal Plain area was divided into about 1,000 cells. Twenty cells were randomly selected, and corn- and soybean-growing areas were identified in these cells by county Natural Resource Conservation Service (NRCS) personnel. Wells were installed in or on the edge of corn and soybean fields. One of these wells was not sampled; only a QAQC (blank) was performed. Total number of wells: 20; Wells randomly selected: yes; Wells installed: 20; Wells previously installed: 0.

Agricultural land use (domestic-supply well)

• Land-Use Setting: Agricultural and residential: 13,349 mi² of Coastal Plain area. Sampling occurred only at rural residences in corn- and soybean-growing areas in wells previously installed at residences for household or farm supply.

• System Description: Confined aquifers, primarily, were sampled throughout the Coastal Plain, including the Castle Hayne, Yorktown, Peedee, and Pungo River aquifers; a few wells were screened in the unconfined surficial aquifer. Coastal Plain topographic conditions vary from well-drained areas of high topographic relief dissected by streams to broad, poorly drained flats. Well depths range from 10 to 288 feet below land surface, with a median depth of 170 feet.

• Site Selection: Domestic-supply wells were selected adjacent to the 20 randomly selected agricultural land-use wells (mentioned above). If this was not possible, domestic-supply wells near corn and soybean fields were sampled. Total number of wells: 17; Wells randomly selected: no; Wells installed: 0; Wells previously installed: 17.

Urban land-use study, Virginia Beach

• Land-Use Setting: Urban: Virginia Beach, Virginia. Land use generally is urban, although many land uses are represented, including public schools, city parks, industrial, residential, agricultural, and forested wetland. The city of Virginia Beach covers about 270 mi², including a water-surface area of 51 mi². Samples were all from the northern, more developed half of the city.

• System Description: Virginia Beach is in the outer Coastal Plain. (Note: Suffolk Scarp delineates the inner and outer Coastal Plain.) Land elevations range from 0 to 25 feet above sea level. Poorly drained to well-drained soils were formed in marine and fluvial sediments; other soils include very poorly drained organic material and excessively drained sandy eolian sediments. Wells are screened in the unconfined Columbia aquifer or the confined Yorktown/Eastover aquifer. The top of the Yorktown/Eastover aquifer is about 90 feet below land surface at Virginia Beach. Well depths range from 35 to 95 feet below land surface, with a median depth of 65 feet.

• Site Selection: Wells were selected from the Virginia Department of Environmental Quality (DEQ) monitoring well network. All available wells were used. NOTE: One of these wells (364745076004304) also was sampled as part of the outer Coastal Plain study-unit survey. Total number of wells: 15; Wells randomly selected: no; Wells installed: 0; Wells previously installed: 15.

Study-Unit Survey

Existing wells in the Coastal Plain were randomly selected to represent general shallow ground-water quality in the inner and outer Coastal Plain. Data from these wells were used to evaluate water-quality data from the agricultural land-use wells in the same area to determine possible effects associated with corn and soybean agriculture. Wells that were selected were equipped with submersible pumps, were well constructed, and had complete location information available. Many of the wells were existing USGS or State observation wells used for long-term water-level monitoring. All wells were located in areas of recharge. Several were shallow supply wells equipped with submersible pumps. Seven deep public-supply wells also sampled in the vicinity of known pumping cones of depression to evaluate possible pumping-induced contamination.

Study-unit wells, inner Coastal Plain

• Land-Use Setting: Nontargeted land use: The 8,880-mi² inner Coastal Plain was sampled without targeting any particular land use. (Note: Suffolk Scarp delineates the inner and outer Coastal Plain.)

• System Description: Inner Coastal Plain topographic conditions vary from well-drained areas of high topographic relief dissected by streams to broad, poorly drained flats. The wells are screened primarily in the surficial and Yorktown aquifers. Well depths range from 11 to 67 feet below land surface, with a median depth of 20 feet.

• Site Selection: Wells were selected from the North Carolina Division of Environmental Management ambient monitoring network wells, Virginia DEQ monitoring wells, and USGS climatic-effects network wells. The inner Coastal Plain area was divided into about 1,000 cells. Twelve cells were randomly selected, and wells near the center of these cells were identified. (Search radius was as large as needed to select a well in the database.) Total number of wells: 12; Wells randomly selected: yes; Wells installed: 0; Wells previously installed: 12.

Study-unit wells, outer Coastal Plain

• Land-Use Setting: Nontargeted land use: The 4,469-mi² outer Coastal Plain was sampled without targeting any particular land use. (Note: Suffolk Scarp delineates the inner and outer Coastal Plain.)

• System Description: The outer Coastal Plain consists of low, flat, poorly drained plains separated by shallow, widely spaced streams and estuaries. In general, the farther from the stream, the wetter the soil and thicker the organic-rich surface. Fourteen wells are screened in the unconfined surficial aquifer; one well is screened in the confined Yorktown aquifer. Well depths range from 5 to 75 feet below land surface, with a median depth of 23 feet.

• Site Selection: Wells were selected from the North Carolina Division of Environmental Management ambient monitoring network wells, Virginia DEQ monitoring wells, and USGS climatic-effects network wells. The outer Coastal Plain area was divided into about 500 cells. Fifteen cells were randomly selected, and wells near the center of these cells were identified. (Search radius was as large as needed to select a well in the database.) NOTE: One of these wells (364745076004304, lus3) also was sampled as part of the Virginia Beach urban land-use study. Total number of wells: 15; Wells randomly selected: yes; Wells installed: 0; Wells previously installed: 15.

Study-unit deep municipal wells, inner Coastal Plain

• Land-Use Setting: Nontargeted land use: The 8,880-mi² inner Coastal Plain was sampled without targeting any particular land use. (Note: Suffolk Scarp delineates the inner and outer Coastal Plain.)

• System Description: The two Kinston, N.C., municipal wells are screened in the Black Creek aquifer; well depths are about 420 and 480 feet below land surface. The two Franklin, Va., municipal wells are screened in the Paleocene Series and upper Cretaceous aquifer system; well depths are about 590 and 610 feet below land surface.

• Site Selection: Deep municipal wells were selected in areas of major drawdown. Total number of wells: 4; Wells randomly selected: no; Wells installed: 0; Wells previously installed: 4.

Study-unit deep municipal wells, outer Coastal Plain

• Land-Use Setting: Nontargeted land use: The 4,469-mi² outer Coastal Plain was sampled without targeting any particular land use. (Note: Suffolk Scarp delineates the inner and outer Coastal Plain.)

• System Description: The two Aurora, N.C., municipal wells are screened in the Castle Hayne aquifer; well depths are about 325 and 350 feet below land surface.

• Site Selection: Deep municipal wells were selected in areas of major drawdown. Total number of wells: 2; Wells randomly selected: no; Wells installed: 0; Wells previously installed: 2.

Study-unit well, Great Dismal Swamp (reference)

• Land-Use Setting: Reference site: 13,349 mi² of Coastal Plain area was sampled only at one well in the Great Dismal Swamp.

• System Description: Great Dismal Swamp National Wildlife Refuge was established in 1974 to restore and maintain the natural biological diversity that existed prior to drainage and logging operations that began in 1763. The refuge consists of about 167 mi² of forested wetlands, less than half the original size of the swamp, and includes the 5-mi² Lake Drummond. Well depth of the reference well is 5 feet below land surface.

• Site Selection: One background well installed in Great Dismal Swamp. Total number of wells: 1; Wells randomly selected: no; Wells installed: 1; Wells previously installed: 0.

Flow-Path Survey

Flow-path studies are intended to answer questions about processes controlling ground-water contamination. Several wells along a flow path were installed and sampled for various chemicals. Records of pesticide and fertilizer applications were obtained to relate water quality with land-use practices. Other factors, such as geology and soil and aquifer chemistry, were considered to distinguish human from nonhuman factors affecting ground-water and surface-water quality.

Flow-path well, Pete Mitchell (<50 feet)

• Land-Use Setting: Agricultural: The 17-mi² Pete Mitchell Swamp drainage basin is 59 percent cropland and pasture, 35 percent forest, 4 percent forested wetland, and 2 percent residential. The primary crops in this basin are soybeans, corn, and cotton.

• System Description: The unconfined aquifer in this Coastal Plain basin is composed of soils derived from large river valleys that drain both the Piedmont and Coastal Plain, flood-plain systems, and other post-Miocene deposits. Wells are screened in the unconfined surficial aquifer. Well depths range from 7 to 14 feet below land surface, with a median depth of about 11 feet.

• Site Selection: Wells were installed either to characterize the shallow flow system in the Pete Mitchell basin or to sample along a flow path in this basin. Total number of wells: 10; Wells randomly selected: no; Wells installed: 10; Wells previously installed: 0.

Flow-path instream well, Pete Mitchell (<50 feet)

• Land-Use Setting: Agricultural: The 17-mi² Pete Mitchell Swamp drainage basin is 59 percent cropland and pasture, 35 percent forest, 4 percent forested wetland, and 2 percent residential. The primary crops in this basin are soybeans, corn, and cotton.

• System Description: The unconfined aquifer in this Coastal Plain basin is composed of soils derived from large river valleys that drain both the Piedmont and Coastal Plain, flood-plain systems, and other post-Miocene deposits. This well is located in a drainage ditch, Pete Mitchell Swamp Canal, which was hand-dug about 100 years ago. The well is screened in the unconfined surficial aquifer. The canal bottom is dredged annually, so elevation changes frequently; well depth is approximately 2 feet below the canal bottom.

• Site Selection: Well was installed at discharge point of a flow path in the Pete Mitchell Basin. Total number of wells: 1; Wells randomly selected: no; Wells installed: 1; Wells previously installed: 0.

Flow-path domestic well, Pete Mitchell (<50 feet)

• Land-Use Setting: Agricultural: The 17-mi² Pete Mitchell Swamp drainage basin is 59 percent cropland and pasture, 35 percent forest, 4 percent forested wetland, and 2 percent residential. The primary crops in this basin are soybeans, corn, and cotton.

• System Description: The unconfined aquifer in this Coastal Plain basin is composed of soils derived from large river valleys that drain both the Piedmont and Coastal Plain, flood-plain systems, and other post-Miocene deposits. One well is screened in the unconfined surficial aquifer; well depth is 28 feet below land surface. The other well is screened in the confined Yorktown aquifer; well depth is 40 feet below land surface.

• Site Selection: Domestic wells were sampled to characterize the shallow flow system in the Pete Mitchell basin. Total number of wells: 2; Wells randomly selected: no; Wells installed: 0; Wells previously installed: 2.

Flow-path domestic well, Pete Mitchell (>50 feet)

• Land-Use Setting: Agricultural: The 17-mi² Pete Mitchell Swamp drainage basin is 59 percent cropland and pasture, 35 percent forest, 4 percent forested wetland, and 2 percent residential. The primary crops in this basin are soybeans, corn, and cotton.

• System Description: Soils in this area are derived from large river valleys that drain both the Piedmont and Coastal Plain, and flood-plain systems. These wells are screened in the confined Black Creek aquifer. Well depths are about 120 and 170 feet below land surface.

• Site Selection: Domestic wells were sampled to characterize the flow system in the Pete Mitchell basin. Total number of wells: 2; Wells randomly selected: no; Wells installed: 0; Wells previously installed: 2.

Flow-path temporary well, Pete Mitchell (<50 feet)

• Land-Use Setting: Agricultural: The 17-mi² Pete Mitchell Swamp drainage basin is 59 percent cropland and pasture, 35 percent forest, 4 percent forested wetland, and 2 percent residential. The primary crops in this basin are soybeans, corn, and cotton.

• System Description: The unconfined aquifer in this Coastal Plain basin is composed of soils derived from large river valleys that drain both the Piedmont and Coastal Plain, flood-plain systems, and other post-Miocene deposits. Wells are screened in the unconfined surficial aquifer. Well depths range from approximately 3 to 11 feet below land surface, with a median depth of about 6 feet.

• Site Selection: Temporary wells were installed to characterize the shallow flow system in the Pete Mitchell basin. Total number of wells: 4; Wells randomly selected: no; Wells installed: 4; Wells previously installed: 0.

Flow-path municipal well, Pete Mitchell (>50 feet)

• Land-Use Setting: Agricultural: The 17-mi² Pete Mitchell Swamp drainage basin is 59 percent cropland and pasture, 35 percent forest, 4 percent forested wetland, and 2 percent residential. The primary crops in this basin are soybeans, corn, and cotton.

• System Description: Soils in this area are derived from large river valleys that drain both the Piedmont and Coastal Plain, and flood-plain systems. This well is screened in the confined upper Cape Fear aquifer. Well depth is 180 feet below land surface.

• Site Selection: A municipal-supply well was sampled to characterize the flow system in the Pete Mitchell basin. Total number of wells: 1; Wells randomly selected: no; Wells installed: 0; Wells previously installed: 1.

Flow-path monitoring well, Pete Mitchell (<50 feet)

• Land-Use Setting: Agricultural: The 17-mi² Pete Mitchell Swamp drainage basin is 59 percent cropland and pasture, 35 percent forest, 4 percent forested wetland, and 2 percent residential. The primary crops in this basin are soybeans, corn, and cotton.

• System Description: Soils in this area are derived from large river valleys that drain both the Piedmont and Coastal Plain, and flood-plain systems. This well is screened in the confined Black Creek aquifer. Well depth is approximately 98 feet below land surface.

• Site Selection: A North Carolina Division of Environmental Management monitoring well was sampled to characterize the flow system in the Pete Mitchell basin. Total number of wells: 1; Wells randomly selected: no; Wells installed: 0; Wells previously installed: 1.

Flow-path monitoring well, Lizzie (<50 feet)

• Land-Use Setting: Agricultural: The 1.5-mi² drainage basin is approximately 60 percent cropland, 20 percent forested wetland, 15 percent forest, 3 percent confined hog operation, 1 percent pasture, and 1 percent residential. The primary crops in this basin are soybeans and corn.

• System Description: Soils along the flow path in this Coastal Plain basin consist primarily of nearly level, well-drained and moderately drained soils with loamy subsoil in the uplands, and nearly level, poorly drained loamy soils in the flood plains. One well is screened in the confined Yorktown aquifer; other wells are screened in the unconfined surficial aquifer. Well depths range from 7 to 50 feet below land surface, with a median depth of about 14 feet.

• Site Selection: Wells were selected to sample along a shallow flow path in the Lizzie basin. One well was installed in the streambed where discharge occurs. Total number of wells: 6; Wells randomly selected: no; Wells installed: 1; Wells previously installed: 5.

Synoptic Studies

Three special synoptic studies were designed to investigate the relation between ground-water quality and surface-water quality. These studies included the collection of ground water from the streambed, bed-sediment samples, and surface-water samples.

• Ground-water synoptic, February and March 1994
• Ground-water synoptic, June 1994
• Ground-water synoptic, September 1995
• Surface-water synoptic, August - September 1995