Introduction

Maryland and the District of Columbia have abundant and economically important surface-water resources. Annual precipitation in these two areas is about 42 inches (U.S. Geological Survey, 1990, p. 291). In addition, an average of 30,000 million gallons per day enters the streams of Maryland and the District of Columbia from adjacent States. In 1985, surface-water withdrawals supplied public water-supply needs for 68 percent of the population of Maryland and 100 percent of the population of the District of Columbia (U.S. Geological Survey, 1990, p. 291). In addition to public supply, the streams and estuaries in the area also provide transportation, recreation, and scenic beauty. Water-Quality in most of the 93,000 miles of streams has been described as "good and stable," although problems exist locally (Maryland Department of the Environment, 1988, p. 5).

Land use (fig. lA) and physiography (fig. 1B) affect the use and quality of stream water. Land in Maryland is about 11 percent urban, 41 percent agricultural, 44 percent forest, and 4 percent wetland (Maryland Department of the Environment, 1988, p. 16). Areas of the State that are drained by surface water are mostly cropland, pasture, woodland, and forest; woodland and forest cover most of the land in the larger river basins that have substantial out-of-State drainage. The State contains parts of five physiographic provinces-- Coastal Plain, Piedmont, Blue Ridge, Valley and Ridge, and Appalachian Plateaus. Surface water is the major source of water supply in the four more densely populated provinces north and west of the Fall Line (the boundary separating the Coastal Plain and Piedmont provinces) because the consolidated rock that underlies the area has limited Groundwater storage capacity.

The combined 1990 population of Maryland and the District of Columbia was 5.4 million (U.S. Bureau of the Census 1990 decennial census files). Population is centered mainly in the Baltimore and Washington, D.C., metropolitan areas (figs. 1C and 2). Many urban areas had a substantial decline in population from 1970 to 1990, whereas rural areas had rapid growth and development. Most of this significant growth and urban development has been in central Maryland near Baltimore and Annapolis, and Washington, D.C. (U.S. Bureau of the Census decennial census files).

Figure 1. Land use, physiography, and population in Maryland and the District of Columbia. A, Major land uses. B, Physiographic divisions. C, Population distribution in 1990. (Sources: A Major land uses modified from Anderson. 1967. B, Physiographic divisions from Fenneman, 1946; landforms from Thelin and Pike, 1990. C. Data from U.S. Bureau of the Census 1990 decennial census files.)

Water-Quality Monitoring

Water-quality data obtained from analyses of water samples collected at monitoring stations are stored in the U.S. Geological Survey's (USGS) National Water Information System and the U.S. Environmental Protection Agency's (EPA) national data base known as STORET. Water-quality and streamflow data are reported by water year--the 12 months from October 1 through September 30. A water year is identified by the calendar year in which it ends. For example, water year 1991 comprises October 1, 1990, through September 30, 1991.

The data used in this summary of stream water quality in Maryland and the District of Columbia were obtained from water samples collected at six monitoring stations at which data collection is systematic and continuing (fig. 2). Analyses of water samples collected at these stations are the basis for the discussion and graphic summary (fig. 3) of stream water quality conditions during water years 1987-89 and for the discussion and graphic summary (fig. 4) of stream water-quality trends. Water samples were collected and analyzed by using standard methods approved by the USGS (Britton and Greeson, 1987; Fishman and Friedman, 1989; Ward and Harr, 1990) or by using equivalent methods. If a method of sample collection or analysis changed over time, data from an analysis were included in the evaluation of recent stream water-quality or of stream water-quality trends only if the change in method did not affect the comparability of the data.

In addition to monitoring the quality of streams and reservoirs for public-supply withdrawals and in stream fisheries, the USGS and the Maryland Department of the Environment (MDE) monitor stream water where it reaches the Chesapeake Bay estuary. The River Input Program (formerly Fall Line monitoring) is a cooperative data-collection program conducted by these two agencies. The purpose of the program is to monitor the flow of nutrients from major tributaries to the bay. Sampling stations for this program are located near the "hydrologic fall line," where the streams become affected by tides. This point is often near the Fall Line, where the Piedmont meets the Coastal Plain.

Water-Quality Conditions

In 1988, the MDE (1988, p. 95) assessed the quality of the State's streams. About 93 percent of the stream miles fully supported, 5.4 percent partially supported, and 1.7 percent did not support the uses designated by the State for purposes of water-pollution control and monitoring. Common causes for use impairment were excessive concentrations of nutrients, sediment, and bacteria from agricultural and urban runoff, mining, municipal discharges, land disposal, and industrial discharges. Other important water-quality concerns in the State are stream acidification in western Maryland due to mine drainage and acid precipitation, pesticides such as chlordane in agricultural runoff, and the effects of organic and trace-metal toxic substances from industrial sources.

The following discussion of stream water-quality in Maryland and the District of Columbia is organized by river basin (fig. 3). Where physiographic and land-use characteristics in different basins are similar, the discussion of those basins is combined. Graphs in figure 3 summarize certain aspects of stream water-quality in the basins for water years 1987-89. The graphs show frequency distributions of data values that represent concentrations of selected constituents in stream water and measurements of selected physical properties of stream water. These constituents and properties are dissolved oxygen, fecal coliform bacteria, total alkalinity (as calcium carbonate), dissolved sulfate, dissolved solids, dissolved nitrite plus nitrate (as nitrogen), and dissolved phosphate (as phosphorus). The data are reported in milligrams per liter (mg/L) and colonies per 100 milliliters (col/100 mL). Sources and environmental significance of each constituent and property are described in table 1.

Water-quality at each monitoring station is the result of geological, chemical, biological, and hydrologic processes that occur over a large area. Water-quality problems that affect aquatic life or public health only locally are not fully represented in this summary.

Choptank River

The Choptank River drains a large part of the Coastal Plain on the Delmarva Peninsula. This area consists of uplands having soils that range from poorly drained to well drained (Hamilton and others, 1989). Land cover in the drainage basin is mainly cropland, woodland, pasture, and forest. Average discharge of the Choptank River at site 1, which is near the hydrologic fall line of the river, is about 130 cubic feet per second (ft³/s). The effects of agriculture (primarily excessive bacteria and nitrogen in runoff) on the stream and downstream estuary are the primary water-quality concerns in this basin.

The sedimentary deposits underlying the Choptank River are composed of sand and clay that are not readily dissolved. Thus, median concentrations of alkalinity (12 mg/L) and dissolved solids (96 mg/L) at site 1 were the lowest for any of the six monitoring stations. Low alkalinity values reflect the susceptibility of the Choptank River to acidification; the pH at site 1 had a median value of 6.5, which was less than those at all other sites. Acidic precipitation often causes a temporary decline in the stream-water pH and an increase in dissolved-aluminum concentrations. Concentrations of other constituents at site 1 were characteristic of a stream that is little contaminated.

Figure 2. Selected water-quality monitoring stations, type of statistical analysis, and geographic features in Maryland and the District of Columbia. (Sources: Major land uses modified from Anderson, 1967; other data from U.S. Geological Survey files.)

Susquehanna River

The Susquehanna River system extends throughout central Pennsylvania and New York; drains the Piedmont, Valley and Ridge, and Appalachian Plateaus provinces; and transports more freshwater into Maryland and the Chesapeake Bay (average discharge of 41,000 ft³/s) than any other source. Agriculture, mining, and urbanization are the primary activities that affect water-quality in the basin. In Maryland, the Susquehanna River supplies the cities of Havre de Grace and Baltimore and is expected to supply the increasing demand for water needed to support growth in northeastern and central Maryland. The Susquehanna River, the largest river on the East Coast, is known for its fisheries and serves as spawning grounds for a variety of fish. Storm runoff causes increased suspended-sediment concentrations that result in reservoir siltation and inhibit aquatic life by increasing turbidity. Extreme storm runoff (greater than about 400,000 ft³/s) scours the reservoirs and redeposits the sediment in the upper Chesapeake Bay. In addition, contamination of water and sediment by toxic chemicals has recently become an important topic because of the scarcity of data concerning these materials and their possible effects on the Chesapeake Bay.

Site 2 is located at the outflow of the Conowingo Dam. During low flow, dissolved-oxygen concentrations commonly decrease to critical levels downstream from the dam. However, dam operators attempt to maintain sufficient flow to prevent this depletion. The median dissolved-oxygen concentration at site 2 was 11.3 mg/L, but 10 percent of the samples had concentrations of less than 4.4 mg/L, which is less than the State standard of 5.0 mg/L for water-contact recreation, aquatic life, and water supply (Maryland Department of the Environment, 1989, p. 5). Concentrations of fecal coliform bacteria at site 2 (median, 15 col/100 mL) were the lowest at any of the six stations. The median nitrite plus nitrate concentration (1.2 mg/L) was the second highest in samples from the six stations, and the median phosphate concentration (0.008 mg/L) was the lowest. With the exception of dissolved oxygen, the constituent concentrations at site 2 indicate that water-quality in the main stem of the Susquehanna River has been little degraded by activities in the drainage basin.

Figure 3. Water-quality of selected streams in Maryland and the District of Columbia, water years 1987-89. (Source: Data from U.S. Geological Survey files.)

Table 1. Sources and environmental significance of selected water-quality constituents and properties (Source: Compiled by the U.S. Geological Survey, Office of Water-Quality)

Patuxent River

The Patuxent River drains parts of the Piedmont province in central Maryland. The long-term average discharge as of 1989 was 362 ft³/s at site 3. Site 3 is near the hydrologic fall line and monitors little drainage from the Coastal Plain. The major land uses in the basin are agricultural, but water quality in the river also is affected by urban development. Water-use classification for the Patuxent River is water-contact recreation, aquatic life, and shellfish harvesting in the estuarine part of the river (Maryland Department of the Environment, 1988, p. 225). The primary reasons for impairment of these uses are eutrophication and bacterial contamination. Eutrophication occurs when large concentrations of nutrients and organic matter encourage rapid algal growth, which increases turbidity and causes oxygen depletion when algae and other aquatic vegetation die and decompose. Primary sources of nutrients and bacteria are municipal discharge, agricultural and urban runoff, and waste disposal.

During 1987-89, fecal coliform bacteria had a median concentration of 220 col/100 mL and had several occurrences of concentrations greater than 1,000 col/100 mL. Concentrations frequently did not meet State standards for water-contact recreation, aquatic life, and water supply (Maryland Department of the Environment, 1989, p. 5). Median nitrite plus nitrate (1.8 mg/L) and phosphate (0.04 mg/L) concentrations at site 3 were the highest or among the highest for the six monitoring stations (fig. 3). The concentrations of the selected water-quality constituents recorded at site 3 are greater than would be expected in an uncontaminated stream.

Potomac and Shenandoah Rivers

The Potomac River, which is the second largest tributary to the Chesapeake Bay, drains 11,570 square miles of diverse physiography. Geology and land use in the basin are important contributors to water-quality characteristics of the river. In the Potomac River basin, three water-quality monitoring stations (sites 4-6) were used to assess water-quality conditions during 1987-89. Site 4 monitors drainage from the upper part of the Potomac River basin, including drainage from the Appalachian Plateaus and Valley and Ridge provinces. Major water-quality issues in the upper basin are coal mining, forestry, raw- and treated-sewage effluent, acid precipitation, and toxic substances such as dioxin from paper mills. Site 5 is on the Shenandoah River in West Virginia. The Shenandoah River drains the eastern part of the Valley and Ridge province and joins the Potomac River at Harpers Ferry, W. Va. Water-quality in the Shenandoah River greatly affects water-quality in the Potomac River in Maryland. Site 6 is downstream from sites 4 and 5 and monitors additional drainage from areas of the Piedmont and Blue Ridge provinces. The largest Maryland stream in the drainage area upstream from site 6 and downstream from the mouth of the Shenandoah River is the Monocacy River, which drains the Piedmont province in central Maryland west of the Patuxent River basin.

Of samples collected at the three monitoring stations, those from site 5 had the highest median concentration of alkalinity (114 mg/L), sulfate (51 mg/L), and dissolved solids (219 mg/L) (fig. 3). The magnitude of these concentrations is due primarily to the dissolution of easily weathered limestone and dolomite in the Shenandoah River basin. At site 4, the median concentrations of alkalinity (66 mg/L), sulfate (48 mg/L), and dissolved solids (167 mg/L) were characteristic of drainage from the three western Maryland physiographic provinces. Downstream at site 6, less mineralized water from the Piedmont and Blue Ridge provinces mixes with streamflow from upstream (sites 4 and 5). This dilution yielded median sulfate (37 mg/L) and dissolved-solids (167 mg/L) concentrations at site 6 that were lower than would have resulted from mixing drainage from basins upstream at sites 4 and 5. Alkalinity concentrations at site 6, however, indicate that the Potomac River maintains its buffering capacity at this downstream monitoring station.

Median nitrite plus nitrate concentrations were nearly equal at sites 4-6, although higher concentrations were more common at site 6. Agricultural runoff from the Piedmont province and municipal discharges from the Washington, D.C., metropolitan area are probable sources of the higher nitrite plus nitrate concentrations at site 6. Bacterial contamination continues to be a concern in the basin. Median concentrations of fecal coliform bacteria were less than 100 col/100 mL at sites 4-6. However, 25 percent of the samples had concentrations larger than 300 col/100 mL at site 4 and 440 col/100 mL at site 6 and occasionally exceeded the State standard for water-contact recreation, aquatic life, and water supply. Constituent concentrations at these three stations reflect water-quality that is substantially affected by geology and human activities.

Water-Quality Trends

Trend analysis is a statistical procedure used to detect changes in stream water quality at a monitoring station over time. For this report, water-quality data from six monitoring stations (fig. 2) were analyzed for trends by using the seasonal Kendall test (Hirsch and others, 1982), a method used extensively by the USGS. The graph (shown below) of the dissolved nitrite plus nitrate concentration in the Susquehanna River at site 2 illustrates the trend inferred from the concentration data and demonstrates the variation in water-quality that is common in streams.

When possible, constituent-concentration data were adjusted for changes in streamflow to preclude identifying a trend in concentration that was caused only by a trend in streamflow. The data were not adjusted when (1) more than 10 percent of the samples had concentrations lower than the minimum reporting limit for the analytical method used or (2) streamflow was controlled substantially by human activities. When the concentration data could not be adjusted for streamflow, trends were determined directly from the concentration data.

Statewide trends in concentrations of selected constituents in stream water and in measurements of selected physical properties of stream water are shown on maps in figure 4. On each map, a trend is indicated at a monitoring station only if the data from that station were suitable for use in the trend analysis. For more information on the suitability criteria and on the trend-analysis procedure used for this report, see Lanfear and Alexander (1990).

Dissolved Oxygen

The dissolved-oxygen concentration in a stream is controlled by several factors, including water temperature, air temperature and pressure, hydraulic characteristics of the stream, photosynthetic or respiratory activity of stream biota, and the quantity of organic material present. A trend in dissolved-oxygen concentrations commonly is directly or indirectly the result of human activities. Generally, an upward trend in dissolved-oxygen concentrations indicates improving stream water-quality conditions and a downward trend indicates deteriorating conditions.

No trend in dissolved-oxygen concentrations was detected in data from the six monitoring stations (fig. 4). Dissolved-oxygen concentrations at all monitoring stations, with the exception of occasional measurements at site 2, were acceptable by State standards during 1980-89. However, Bahner and others (1990, p. 1) reported an apparent long-term (1950-89) decline in dissolved-oxygen concentrations in the Chesapeake Bay, although no recent trends were discernible. Continued efforts to decrease nutrient loads in stream water might result in future increases in dissolved-oxygen concentrations at the six monitoring stations as well as in the Chesapeake Bay.

Fecal Coliform Bacteria

Fecal coliform bacteria are used as indicators of fecal contamination from humans and other warm-blooded animals. Such contamination can introduce disease-causing viruses and bacteria into a stream.

No trend in fecal coliform bacteria concentrations was detected in data from the six monitoring stations (fig. 4). Bacteria concentrations in stream water might have been expected to decrease as a result of nutrient-management practices such as controls on animal waste in runoff and improvement in wastewater-treatment facilities. However, the effects of these practices might not yet be apparent at these monitoring stations.

Alkalinity

Alkalinity is a measure of the capacity of the substances dissolved in the water to neutralize acid. In most natural waters, alkalinity is produced mainly by bicarbonate and carbonate (Hem, 1985, p. 106), which are ions formed when carbon dioxide or carbonate rock dissolves in water.

Urban and industrial development has increased as a result of population growth in the Patuxent River basin during 1980-89. Larger quantities of urban runoff, industrial discharges, and municipal wastewater-treatment-plant effluent resulting from this development are probable causes of increasing alkalinity at site 3 (fig. 4).

Dissolved Sulfate

The major natural sources of sulfate in streams are rock weathering, volcanoes, and biochemical processes (Hem, 1985, p. 113). Human activities such as mining, waste discharge, and fossil-fuel combustion also can be important sources. A shortened trend-analysis period was used for sulfate because data from analyses performed prior to water year 1982 are not comparable to data from subsequent years.

No trend in dissolved-sulfate concentrations was detected at any of the six monitoring stations during 1982-89 (fig. 4). Although the State has administered two programs since 1977 to reclaim abandoned mining operations and to regulate discharges from existing mine operations that are known sources of sulfate in the upper Potomac River basin (Maryland Department of the Environment, 1988, p. 50), no downward trend was detected at either site 4 or site 6 on the Potomac River.

Dissolved Solids

Dissolved solids in stream water result primarily from rock weathering but also can be introduced as a byproduct of human activities (table 1). Concentrations generally are greatest in streams draining basins underlain by rocks and soils that contain easily dissolved minerals.

Possible reasons for the upward trend in the dissolved-solids concentration in the Patuxent River at site 3 (fig. 4) are increased contaminant loads in runoff as a result of urbanization and agricultural practices and increased discharges from municipal and industrial facilities. The drainage area upstream from site 3 is much smaller than that of other basins where urban development might affect dissolved-solids concentration; thus, the effects of localized changes might be more apparent at site 3 than at other sites.

Dissolved nitrite plus nitrate

Nitrite and nitrate are oxidized forms of nitrogen that together constitute most of the dissolved nitrogen in stream water. Nitrite readily oxidizes to nitrate in natural waters; therefore, nitrate generally is by far the more abundant of the two (Hem, 1985, p. 124).

Figure 4. Trends in water-quality of selected streams in Maryland and the District of Columbia, by water years. (Source: Data from U.S. Geological Survey files.)

Sources of nitrite and nitrate include fertilizers and animal wastes in agricultural runoff, atmospheric deposition, and discharges from municipal wastewater-treatment facilities. In 1985, Maryland, Virginia, and Pennsylvania entered into the Chesapeake Bay Agreement, which stated that those States would decrease the quantity of nutrients entering the Chesapeake Bay by 40 percent. Management programs are being implemented by each State to meet this water-quality goal. However, these programs had not been in place long enough to prevent the upward trends in nitrite plus nitrate concentrations during 1980-89 at sites 2 and 3 on the Susquehanna and Patuxent Rivers (fig. 4), whose drainage basins are affected by runoff from urban and agricultural areas.

Dissolved Phosphate

Phosphate is the oxidized form of phosphorus and the only form of significance in most natural waters. Small quantities of dissolved phosphate commonly are present in streams as a result of rock weathering. Normally, concentrations are no more than a few tenths of a milligram per liter (Hem, 1985, p. 126) and usually are much lower. Higher concentrations can indicate contamination from human activities (table 1).

In an effort to decrease the nutrient input to the Chesapeake Bay, Maryland issued a statewide ban in 1985 on the sale and use of phosphate-based detergents. The decrease in phosphate concentration in the Patuxent River at site 3 (fig. 4), downstream from several municipal wastewater-treatment-plant discharges, is attributable to the ban. The decreasing phosphate concentration in the Susquehanna River at site 2 is not obviously attributable to the ban because most of the drainage basin is outside the State and is not directly affected by the legislation. Also, the Susquehanna River basin is much less urbanized. However, concentrations might have decreased because the distribution areas for sale of nonphosphate-based detergents extend into adjacent States that have not banned use of phosphate-based detergents. Improved agricultural practices that require less use of phosphate fertilizer throughout Maryland and Pennsylvania also might have contributed to the downward trend. Streams that had no trend in phosphate concentrations are in drainage basins that are less affected by agriculture and urban development than those of the Susquehanna and Patuxent Rivers.

Water-Quality Management

Stream water-quality is regulated primarily by MDE, although the Departments of Agriculture and Natural Resources have limited water-quality management authority in agricultural areas and in wetlands and scenic-river corridors, respectively. The MDE establishes water-quality standards; performs regulatory, enforcement, and inspection activities for point and nonpoint sources of pollution; and coordinates water-quality programs of other State agencies. This authority is provided through various water-pollution articles in the Code of Maryland regulations. In addition, the MDE is responsible for implementing the Federal Clean Water Act in Maryland and for writing a biennial water-quality-assessment report (Maryland Department of the Environment, 1988) that is submitted to the EPA and the U.S. Congress in accordance with section 305(b) of the Federal Clean Water Act.

Several statewide and regional advisory panels, composed of citizens and professionals, advise the State on stream water-quality matters. Statewide panels include the MDE State Water-Quality Advisory Committee, the Coastal Advisory Committee, and the Scenic and Wild Rivers Review Board of the Department of Natural Resources. Regional advisory panels are usually associated with specific watersheds. These panels include the Monocacy River Commission, the Patuxent River Commission, and the Severn River Commission. Other local or special-interest advisory groups include the Anacostia River Advisory Board, the Magothy River Commission, "Trout Unlimited," and Save Our Streams.

Maryland cooperates with other States and their governments on regional water-quality management issues through the following interstate commissions: the Chesapeake Bay Commission, the Interstate Commission on the Potomac River Basin, the Susquehanna River Basin Commission, and the Ohio River Sanitation Commission. All but the Interstate Commission on the Potomac River Basin have Federal participants.

Water-quality monitoring, which has increased since the early 1970's as a direct result of the Clean Water Act, provides information for management purposes. The Chesapeake Bay Monitoring Program provides baseline information as well as data about the management of the bay and its tributaries. The uses stream water-quality monitoring program has provided long-term information about constituent loads and trends for several of the largest tributaries to the Chesapeake Bay.

The District of Columbia Water Pollution Control program is administered by the Water Resources Management Division (WRMD) of the Environmental Regulation Administration in the Department of Consumer and Regulatory Affairs. This agency acts as the primary regulatory agency for enforcing Federal and District laws and regulations related to water pollution control. The program functions include: setting water-quality standards, monitoring water-quality and reporting water-quality trends, certifying National Pollutant Discharge Elimination System permits, and planning and environmental review of water pollution control (Mohnsin Siddique, Water Resources Management Division, written commun., 1992).

The WRMD also cooperates with many local and regional agencies to develop regional strategies for water pollution monitoring and assessment and participates in restoration efforts of the Chesapeake Bay. Many of these programs, which respond to different management control strategies, focus on the Potomac Estuary and its tributaries (District of Columbia Government, 1992, p. 8).

Selected References

Anderson, J.R., 1967, Major land uses in the United States, in U.S. Geological Survey, 1970, National atlas of the United States of America: Washington, D.C., U.S. Geological Survey, p. 158-159.

Bahner, L.H., Reynolds, R.C., and Batiuk, R.A., 1990, Volumetric analysis of dissolved oxygen trends in the Chesapeake Bay--Preliminary findings: Annapolis, Md., Chesapeake Bay Program, unpaginated.

Britton, L.J., and Greeson, P.E., eds., 1987, Methods for collection and analysis of aquatic biological and microbiological samples: U.S. Geological Survey Techniques of Water-Resources Investigations, book 5, chap. A4, 363 p.

District of Columbia Government, 1992, The District of Columbia water-quality assessment: Washington, D.C., 140 p.

Fenneman, N.M., 1946, Physical divisions of the United States: Washington, D.C., U.S. Geological Survey special map, scale 1:7,000,000.

Fishman, M.J., and Friedman, L.C., eds., 1989, Methods for the determination of inorganic substances in water and fluvial sediments: U.S. Geological Survey Techniques of Water-Resources Investigations, book 5, chap. Al, 545 p.

Hamilton, P.A., Shedlock, R.J., and Phillips, P.J., 1989, Groundwater-quality assessment of the Delmarva Peninsula, Delaware, Maryland, and Virginia--Analysis of available water-quality data through 1987: U.S. Geological Survey Open-File Report 89-34,71 p.

Hem, J.D., 1985, Study and interpretation of the chemical characteristics of natural water (3d ed.): U.S. Geological Survey Water-Supply Paper 2254, 263 p.

Hirsch, R.M., Slack, J.R., and Smith, R.A., 1982, Techniques of trend analysis for monthly water-quality data: Water Resources Research, v. 18, no. 1, p. 107-121.

Lanfear, K.J., and Alexander, R.B., 1990, Methodology to derive water-quality trends for use by the National Water Summary Program of the U.S. Geological Survey: U.S. Geological Survey Open-File Report 90-359, 10 p.

Maryland Department of the Environment, 1988, 1985-1987 Maryland water quality inventory: Baltimore, Maryland Department of the Environment, various pagination.

_____1989, Code of Maryland Regulations 26.08.02 Water-Quality: Baltimore, Maryland Department of the Environment, 32 p.

Thelin, G.P., and Pike, R.J., 1990, Digital shaded relief map of the conterminous United States: Menlo Park, Calif., U.S. Geological Survey digital image processing, scale 1:3,500,000.

U.S. Geological Survey, 1990, National water summary 1987--Hydrologic events and water supply and use: U.S. Geological Survey Water-Supply Paper 2350,553 p.

Ward, J.R., and Harr, C.A., eds., 1990, Methods for collection and processing of surface-water and bed-material samples for physical and chemical analyses: U.S. Geological Survey Open-File Report 90-140, 71 p.

Prepared by Joel D. Blomquist, U.S. Geological Survey; "Water-Quality Management" section by J. Shermer Garrison, Maryland Department of the Environment

For Additional Information:

District Chief
U.S. Geological Survey
8987 Yellow Brick Road
Baltimore MD, 21237