Geology topics

R. J. Shedlock

Publications and source records attributed to R. J. Shedlock.

8 recordsLinked to original sources

USGS1993

Hydrology and chemistry of groundwater and seasonal ponds in the Atlantic Coastal Plain in Delaware, USA

The hydrochemistry of small seasonal ponds was investigated by studying relations between ground-water and surface water in a forested Coastal Plain drainage basin. Observation of changes in the water table in a series of wells equipped with automatic water-level recorders showed that the relation between water-table configuration and basin topography changes seasonally, and particularly in response to spring recharge. Furthermore, in this study area the water table is not a subdued expression of the land surface topography, as is commonly assumed. During the summer and fall months, a water-table trough underlies sandy ridges separating the seasonal ponds, and maximum water-table altitudes prevail in the sediments beneath the dry pond bottoms. As the ponds fill with water during the winter, maximum water-table altitudes shift to the upland-margin zone adjacent to the seasonal ponds. Increases in pond stage are associated with the development of transient water-table mounds at the upland-margin wells during the spring. The importance of small local-flow systems adjacent to the seasonal ponds also is shown by the similarities in the chemistry of the shallow groundwater in the upland margin and water in the seasonal ponds. The upland margin and surface water samples have low pH (generally less than 5.0), and contain large concentrations of dissolved aluminum (generally more than 100 μg 1 −1 ), and low bicarbonate concentrations (2 mg l 4 or less). In contrast, the parts of the surficial aquifer that do not experience transient mounding have higher pH and larger concentrations of bicarbonate. These results suggest that an understanding of the hydrochemistry of seasonally ponded wetlands requires intensive study of the adjacent shallow groundwater-flow system.

Journal of Hydrology↗

USGS1993

Pesticides in shallow groundwater in the Delmarva Peninsula

A regional study of the areal and depth distribution of pesticides in shallow groundwater in the Delmarva Peninsula of Delaware, Maryland, and Virginia was done to (i) relate the pesticides detected to landscape and shallow subsurface features, and (ii) evaluate aquifer vulnerability and the potential contamination of drinking-water supplies. Water samples collected at 100 wells from 1988 to 1990 were analyzed for concentrations of 36 pesticides, four metabolites, and other constituents. The most commonly detected residues were atrazine, cyanazine, simazine, alachlor, metolachlor, and dicamba. Concentrations were low; few exceeded 3 µg L −1 . Most detections correlate with the intensive use of these herbicides in three widely distributed and commonly rotated crops—corn ( Zea mays L.), soybean [ Glycine max (L.) Merr.], and small grain—particularly if grown in well-drained soils. Most detections occurred in samples collected from shallow wells screened within 10 m of the overlying water table. The shallow depth distribution of most residues is consistent with their suspected history of use (ca. 20 yr), and patterns in shallow groundwater flow in the surficial aquifer in the study area. The areal and depth distributions of detectable residues in groundwater did not correlate with a vulnerability index, nor any of the component scores developed to estimate that index using the DRASTIC method. The shallow depth of most detections also indicates why few samples from water-supply wells in this study had measurable concentrations of pesticides; most supply wells are deeper than 10 m below the water table. The low number of contaminated samples from supply wells implies that deep groundwater currently (1992) used for drinking generally does not contain detectable pesticide residues.

Journal of Environmental Quality↗

USGS1993

Water-quality assessment of the Delmarva Peninsula, Delaware, Maryland, and Virginia--Effects of agricultural activities on, and distribution of, nitrate and other inorganic constituents in the surficial aquifer

Agricultural applications of inorganic fertilizers and manure have changed the natural chemical com- position of water in the surficial aquifer through- out the Delmarva Peninsula. Nitrate, derived from nitrification of ammonia in inorganic fertilizers and manure, is the dominant anion in agricultural areas. Concentrations of nitrate in 185 water samples collected in agricultural areas ranged from 0.4 to 48 mg/L as nitrogen, with a median concen- tration of 8.2 mg/L as nitrogen. Nitrate concen- trations exceeded the U.S. Environmental Protection Agency's maximum contaminant level for drinking water of 10 mg/L as nitrogen in about 33% of the 185 water samples. Groundwater affected by agricultural activities contains significantly higher concentrations of dissolved constituents than does natural groundwater. Concentrations of calcium and magnesium are higher because of liming of soils, and concentrations of potassium and chloride are higher because of applications of potash, a supple- ment to the nitrogen-based fertilizers. Alkalinity concentrations commonly are decreased because the bicarbonate ion is consumed in buffering reactions with acid that is produced during nitrification. Effects of agricultural activities on groundwater quality are not limited to the near-surface parts of the aquifer underlying farm fields. Elevated concentrations are common in aerobic water at or near the base of the aquifer, 80 to 100 ft below land surface. The median concentration of nitrate in water beneath agricultural areas collected from 24 wells deeper than 80 ft below land surface was 8.5 mg/L as nitrogen, and concentrations in 9 of these water samples exceeded the maximum contaminant level. Regional variations in concentrations of nitrate and other agriculture related constituents in the surficial aquifer in the Delmarva Peninsula depend on a number of factors that include geomorphology, geology, soils, land use, and groundwater-flow patterns. (USGS)

Delaware, Maryland, Virginia↗

USGS1989

Preliminary analysis of the shallow ground-water system in the vicinity of the Grand Calumet River/Indiana Harbor Canal, northwestern Indiana

The shallow groundwater system in the vicinity of the Grand Calumet River-Indiana Harbor Canal, Indiana was analyzed from June 1985 to May 1986. This analysis was done to obtain detailed information about the physical characteristics of the Calumet aquifer and the shallow groundwater flow system. 36 shallow wells were installed and sediment samples were collected at 26 sites. Water level measurements were made in 45 wells. Data indicate that the aquifer consists of fine-grained to medium-grained sand, locally overlain by slag fill. Aquifer thickness is 0 to 65 ft. This aquifer is underlain by about 100 ft of glacial till and lacustrine clay that overlies carbonate bedrock of Silurian age. Broad, low-relief water table mounds occur between the major surface water drains. The crests of these mounds form major east-west-trending water table divides. Northwest of the Indiana Harbor Canal (IHC), a narrow water table ridge parallels the Lake Michigan shoreline and connects to a somewhat circular, low mound northwest of the IHC. Shallow groundwater generally flows from these water table mounds to the major streams or to Lake Michigan. Groundwater also flows to small ditches, wetlands, and sewer lines. Stream/aquifer relations along the Grand Calumet River/IHC were quite complex. Digital model simulations of a conceptual north-south section near the middle of the study area indicate that discharge of groundwater to small ditches and leaky sewer lines has lowered the water table by several ft from predevelopment levels. Simulations also indicate that downward leakage to the bedrock may have contributed to the decline in the water table.

Indiana↗

USGS1987

Ground-water-quality assessment of the Delmarva Peninsula, Delaware, Maryland, and Virginia; project description

In April 1986, the U.S. Geological Survey began a pilot program to assess the quality of the Nation 's surface water and groundwater resources. This National Water-Quality Assessment (NAWQA) program is designed to acquire and interpret information about a wide range of water quality issues. Three groundwater pilot projects have been started, including the project on the Delmarva Peninsula, which covers eastern Maryland and Virginia and most of Delaware. The objectives of the Delmarva project are to: (1) investigate regional groundwater quality on the Delmarva Peninsula, emphasizing a description of the occurrence of trace elements and manmade organic compounds; (2) relate groundwater quality to land use and geohydrologic conditions; and (3) provide a general description of the location, nature, and possible causes of selected water quality problems prevalent in the study area. The shallow aquifer system and the deeper aquifers used for public water supply will be addressed. The shallow aquifer system in the Delmarva Peninsula consists of permeable unconsolidated sand and gravel. Flow systems are localized and small-scale. Farming is common on the peninsula, and the migration of agricultural chemicals to the groundwater system is a local water quality concern. To assess the water quality of the groundwater resources, a regional survey for a wide range of constituents will be conducted in all of the pilot projects to provide a representative sample of groundwater analyses for a national assessment of groundwater quality. Results of this survey may be used as a baseline to monitor future water quality trends. (Lantz-PTT)

Open-File Report↗

USGS1986

Shallow ground-water flow, water levels, and quality of water, 1980-84, Cowles Unit, Indiana Dunes National Lakeshore

The Cowles Unit of Indiana Dunes National Lakeshore in Porter County, northwest Indiana, contains a broad dune-beach complex along the southern shoreline of Lake Michigan and a large wetland, called the Great Marsh, that occupies the lowland between the shoreline dunes and an older dune-beach complex farther inland. These lacustrine sediments form a surficial aquifer that extends from the Lake Michigan shoreline to the northern edge of the Lake Border moraine. Water levels and water quality in the surficial aquifer were monitored from 1977 to 1984 near settling ponds on adjacent industrial property at the western end of the Cowles Unit, Seepage from the settling ponds from 1967 to 1980 created a water-table mound that extended north into the shoreline dune complex and caused perennial flooding of several intradunal lowlands on National Lakeshore property. Since 1980, when the settling-pond bottoms were sealed, these intradunal lowlands contained standing water only during periods of high snowmelt or rainfall. Water-level declines following the cessation of seepage ranged from 6 feet at the easternmost settling pond to nearly 14 feet at the westernmost pond. No general pattern of water table decline was observed in the Great Marsh or in the shoreline dune complex at distances greater than approximately 3,000 feet east or north of the settling ponds. Since the settling ponds were sealed, the concentration of boron has decreased while concentrations of cadmium, arsenic, zinc, and molybdenum in shallow ground water downgradient of the ponds show no definite trends in time. Arsenic, boron and molybdenum have remained at concentrations above those of shallow ground water in areas unaffected by settling-pond seepage.

Indiana↗

USGS1986

Review of the hydrologic data-collection network in the St. Joseph River basin, Indiana

The St. Joseph River Basin data-collection network in the St. Joseph River for streamflow, lake, ground water, and climatic stations was reviewed. The network review included only the 1700 sq mi part of the basin in Indiana. The streamflow network includes 11 continuous-record gaging stations and one partial-record station. Based on areal distribution, lake effect , contributing drainage area, and flow-record ratio, six of these stations can be used to describe regional hydrology. Gaging stations on lakes are used to collect long-term lake-level data on which to base legal lake levels, and to monitor lake-level fluctuations after legal levels are established. More hydrogeologic data are needed for determining the degree to which grouhd water affects lake levels. The current groundwater network comprises 15 observation wells and has four purposes: (1) to determine the interaction between groundwater and lakes; (2) to measure changes in groundwater levels near irrigation wells; (3) to measure water levels in wells at special purpose sites; and (4) to measure long-term changes in water levels in areas not affected by pumping. Seven wells near three lakes have provided sufficient information for correlating water levels in wells and lakes but are not adequate to quantify the effect of groundwater on lake levels. Water levels in five observation wells located in the vicinity of intensive irrigation are not noticeably affected by seasonal withdrawals. The National Weather Sevice operates eight climatic stations in the basin primarily to characterize regional climatic conditions and to aid in flood forecasting. The network meets network-density guidelines established by the World Meterological Organization for collection of precipitation and evaporation data but not guidelines suggested by the National Weather Service for density of precipitation gages in areas of significant convective rainfalls. (Author 's abstract)

Indiana↗

USGS1984

Shallow ground-water flow and drainage characteristics of the Brown ditch basin near the East Unit, Indiana Dunes National Lakeshore, Indiana, 1982

Brown ditch drains wetlands between three parallel ridges of sand dunes near the East Unit of Indiana Dunes National Lakeshore in Poter County, Indiana. Dune and lacustrine sands form a surficial aquifer that is the source of base flow to the ditch. Profiles established in July and August 1982 show that the average streambed slope of the ditch in the Lakeshore (0.19 percent) is six times that of the upstream east reach in the adjacent town, The Pines (0.03 percent). Although the ditch contains debris and vegetation, the reach in the Lakeshore seems to convey all the base flow it receives. In contrast, the upstream east arm contains several ponded sections where flow is sluggish. Digital model simulations show that dredging to form a uniformly graded streambed and eliminate ponding in the upstream east arm of the ditch south of The Pines could lower the water table 0.2 to 2.0 feet in The Pines. Lowering the ditch stage in the Lakeshore by 0.5 to 1.0 foot would cause additional water-table decline of less than 0.5 foot in The Pines. Lowering the ditch stage both in the Lakeshore and in The Pines could lower the water-table in the Lakeshore by nearly 1.0 foot. (USGS)

Water-Resources Investigations Report↗