Chapter Two: Water Quality Trends of the Upper Basin
Drinking Water Supply
In the early 1890s, the main source of drinking water for our nation’s capital, Washington, DC, was shallow wells and springs. Unsafe drinking water from these shallow wells and springs was responsible for the majority of cases of typhoid fever and diarrheal disease. During an 11-year period ending on March 1, 1898, 2,150 deaths were reported from typhoid and typhomalarial fevers (1).
Also in the 1890s, an epidemic of typhoid fever occurred in Cumberland, Maryland, and three weeks later there was also an increase in the number of typhoid fever cases in Washington, DC. Typhoid fever was reported in other towns in the Upper Basin, including Staunton, Harpers Ferry, Elk Garden, Westernport, Frederick, and Hagerstown (1). It was a well-known fact that for many years Washington, DC enjoyed an unenviable notoriety because of the large number of cases of typhoid fever and diarrheal disease that occurred there annually.
In the late 1890s, Potomac River water began replacing shallow wells and springs as the major source of drinking water. However, muddy water continued to flow in the drinking water mains. At the turn of the century, about 75 million gallons per day (mgd) of Potomac River flow was diverted and used for drinking water, fire protection, and other domestic needs for the Washington, DC area. The actual domestic water use was about 50 mgd (2).
In 1905, slow sand filtration of the river water began, with chlorination becoming routine in 1923. The construction of the Dalecarlia Complex, which included rapid sand filtration, began in June 1921. The construction of the early phase of the Dalecarlia Complex was completed in 1928.
Since the 1960s, the diversion of Potomac River water for drinking water supply has increased dramatically. In the early 1960s, about 200 mgd was diverted (see below). Since the early 1990s, the diversion has been about 400 mgd. In addition to the Washington, DC Dalecarlia intake, four other intakes are withdrawing Potomac River water, with a total diversion of about 400 mgd or about 5% of the average flow of the Potomac River.
The diversions for the years 1900 to 1930 were based on Dalecarlia facility records and consumption data in the Washington Aqueduct report (2). Diversions from 1930 to 2000 were estimated by the USGS (see chart below).
21 Total Potomac River Water Diversions for the Water Supply of the Washington, DC Metropolitan Area 450
Total diversions (1930 to 2000) were calculated as the difference between 400 USGS station 01646502 (Potomac River near Washington DC, adjusted for diversions) and station 01646500 (Potomac River near Washington DC). Diversions from 1900 to 1930 were based on water consumption 350 data times 1.539 using the Washington Aqueduct 1852-1992 Report.
300
250
200 Prior to 1905, raw water was not treated. Diversions at Great Falls for Corps of Engineers supply to DC began before 1900. 150 Slow sand filtration began in 1905. Chlorination routine in
Total Diversions, mgd 1923. Dalecarlia Complex completed in 1928, including rapid sand 100 filtration. Rockville Water Filtration Plant began operating in 1958. WSSC's Potomac Filtration Plant began operating in 1961. 50 Fairfax Water Filtration Plant (City of Fairfax) began operating in 1961. Fairfax County Water Authority (Fairfax County) began operating in 1985. 0 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Years
Source: USGS Drinking Water Quality
Water quality monitoring of the drinking water withdrawn from the Potomac River provides a long historical record of the changes in the quality of the Potomac River above Washington, DC. Monitoring of the Potomac River as a drinking water source began in the mid-1900s and expanded in the 1920s. Currently, there are five water supply intakes above Washington, DC. Three of the intakes are more on the Maryland side and two are more on the Virginia side. The location of the intakes provides a means of assessing any riverine side-to-side chemical variability. As presented in Chapter One, the nitrate levels are higher on the Maryland side than on the Virginia side.
Water Quality Trends
In the 1886 monthly bacteriological examination of the Potomac River above Washington, DC, the number of colon bacteria ranged from 200 to 3,000 cells per cubic centimeter (1). When routine monitoring began in the 1920s, the coliform levels increased from about 100 to over 100,000 most probable number (mpn) per 100 ml (see below). Monthly monitoring of the Upper Estuary began in the late 1930s, also shown below.
22 Annual Average Total Coliform Concentrations of the Potomac River and its Estuary 10,000,000 Potomac River Water Intake Potomac Estuary at Woodrow Wilson Bridge Upper Estuary total From 1888 to coliform levels were 1,000,000 1898, there were greatly reduced 2,150 deaths by chlorination of in DC area from wastewater effluents typhoid and and reduction of typhomalarial amount of untreated fever; deaths also wastewater 100,000 reported in the Upper Basin
10,000 Chlorination of the drinking water began in 1923 In 1897, first bacteriological 1,000 survey of the Potomac River Basin was Total Coliform in mpn/100 ml conducted At Chain Bridge and nine other stations 100 in the Upper Estuary, salmonella isolates were recovered in 1967
DC Health Department banned swimming 10 in the Upper Potomac Estuary in 1971
1885 1890 1895 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Years
In the 1930s, the total coliform densities were about 1,000 to 2,000 mpn per 100 ml in Potomac River water. Total coliform densities continued to increase, reaching a maximum of about 20,000 mpn in the late 1980s. In the 1990s, coliform densities decreased to about 1,000 mpn. However, the total coliform densities increased to about 10,000 mpn during high river flows in 2003.
For the period from the 1930s to 1967, coliform densities in the Potomac Estuary at Woodrow Wilson Bridge Station were about two orders of magnitude higher than that in untreated drinking water. The high coliform levels in the Potomac Estuary at Woodrow Wilson Bridge Station were due to the discharge of raw sewage and the lack of chlorination of wastewater discharges. In the early 2000s, coliform densities were lower in the Upper Estuary than in the untreated drinking water due to year-round chlorination of the POTW effluents.
The average annual untreated drinking water quality for five parameters—alkalinity, hardness, total residue, chlorides, and sulphates—are shown below.
23 Potomac River at Great Falls Drinking Water Quality Trends
250.0
Alkalinity Hardness T Residue Chlorides SO4
200.0
150.0
100.0 Concentration in mg/l
50.0
0.0
1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Years
All five parameters have increased logarithmically, as can be seen in the chart above. During the period from the 1920s to 2003, the total residue, which is both dissolved and particulate matter, increased from 100 mg/l to 200 mg/l. The hardness of the drinking water has also doubled, increasing from about 60 mg/l to 120 mg/l during the period from 1905 to 2003. During this 98-year period, the alkalinity increased from 55 to 85 mg/l.
Sulphate concentrations have increased from about 20 mg/l to 35 mg/l during the 1925- 1965 year period. Since the late 1960s, sulphate levels have been decreasing. Chloride concentrations have increased 10-fold, going from about 2 mg/l in 1905 to over 20 mg/l in the early 2000s.
The average annual pH and alkalinity trends of the untreated river water, a measure of the acidity of the river, are presented below.
24 Potomac River Drinking Water Intake pH and Alkalinity Trends 100 9.0
90 8.5 Alkalinity pH 80 8.0
70 7.5 pH Units Alkalinity in mg/l 60 7.0
50 6.5
40 6.0
1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Years
As presented above, the pH of the river has increased about one-half of a unit, while the alkalinity has increased from 55 to 85 mg/l.
The USGS recently analyzed water-quality trends for three New England Rivers: the Connecticut, Blackstone, and Merrimack (3). Similar water-quality trends for these three rivers were observed for total residue, sulphates, and chlorides as for the Potomac River.
Temperature
As shown in the figure below, the average annual temperature of the Potomac River at the water intake has significantly increased over the past century. There appears to have been a slight increase in air temperature—about 2 degrees F. The large increase in river temperature was probably due to two large thermal-electric generating plants in Maryland above Washington, DC.
25 Potomac River Basin Average Annual Water Intake Temperatures and MD Surface Air Temperatures 68.0
66.0 River Temperature Air Temperature 64.0
62.0 F
o 60.0
58.0 Degree
56.0
54.0
52.0
50.0
1895 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Years
The average annual temperature of the Potomac River in 1897 was about 51.5oF. By 1999, it had increased to over 66oF, an increase of over 15.5oF. In 2003 (a high river flow year), the average temperature was 10 degrees lower at 56oF.
Nixon, et al, (4) compiled a 117-year coastal water temperature record from Woods Hole, Massachusetts. While there was some cooling of coastal temperatures during the 1960s, there was a significant warming from 1970 to 2002 at a rate of 0.04oC per year.
26 Monthly Mean Temperature USGS and DC Water Intake Potomac River 1978-2000 100.0
90.0 y = 0.8766x + 10.226 R2 = 0.9109 80.0 F o 70.0
60.0
50.0
40.0
30.0 USGS Chain Bridge Temperature 20.0
10.0
0.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 DC Intake Temperature oF
There is a strong correlation between the USGS and Dalecarlia average monthly temperatures (see above). Thus, the increase appears to be real.
Nutrients and Major Ions
Except for a few years where there are lost data, the water quality nitrate and chloride concentrations of the Upper Potomac River are available since 1905, as presented below.
Potomac River Drinking Water Intake Nitrate & Chloride Trends 30.000 3.00
25.000 2.50 Chlorides
Nitrate 20.000 2.00
15.000 1.50 Chlorides mg/l Nitrate as N mg/l 10.000 1.00
5.000 0.50
0.000 0.00
1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Years
27 The FWPCA began complete nutrient water quality analysis of the basin’s streams in 1965. The current USGS water quality monitoring program for the Potomac River Basin began in 1979. We explored various statistical models to estimate TN fluxes from the early monthly water quality nitrate data using TN/NO3 flux relationships. The linear model for the TN/NO3 flux relationship is presented below.
Potomac River Water Supply NO3 Monthly Fluxes Versus USGS TN Monthly Fluxes 1979-2002 500
450 y = 1.2894x - 1.5856 R2 = 0.8684 400
350 /month 2 300
250
200
150 USGS TN in kg/km
100
50
0 0 50 100 150 200 250 300 350 400
2 Drinking Water NO3 as N in kg/km /month
The TP concentrations from 1905 to 1964 are based on extrapolations from the relationship between TP and TN fluxes, as presented below.
Upper Potomac River Basin USGS TN Versus USGS TP Flux Data 1985-2002 45
40 y = 0.083x - 1.2412 R2 = 0.8584 35
30 /month 2 25
20
15 USGS TP in kg/km
10
5
0 0 50 100 150 200 250 300 350 400 450 USGS TN in kg/km2/month 28 The two extrapolations allowed us to estimate the monthly TP and TN riverine fluxes from the Upper Basin for the period 1905 to 1964. These estimates are vital in reconstructing the historical contributions from the Upper Basin. When the monthly riverine fluxes are divided by the monthly river flows, flow-weighted concentrations can be estimated.
Except for silica, the major nutrient concentrations of K, nitrates, and TP have all increased over the past century, as presented below.
Potomac River at Great Falls Water Quality Nutrient Concentration Trends 100.0 Potassium Silica TP Nitrates as N COD
10.0
1.0
Concentrations in mg/l 0.1
0.0 TP data from 1905 to 1964 based on extraolations
1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Years
The NO3 concentrations have increased 300%, from 0.5 mg/l in 1905 to about 2.0 mg/l in the 1990s. The TP levels have increased 100%, from 0.06 mg/l to 0.13 mg/l during the same time period, while potassium has increased 200%, from 1.0 mg/l to 3.0 mg/l. The silica concentrations have not varied significantly over the past 50 years.
29 A comparison of the historical NO3 trends of the Potomac River with two other major Middle Atlantic river basins that are also used as drinking water sources, the Schuylkill and the Delaware, is presented below. The comparison suggests that the nitrate concentrations in all three rivers have increased by 300% (see below).
Nitrate as N Concentration Trends Delaware, Schuylkill, and Potomac River Water Supply Intakes 3.50 Delaware Schuylkill Potomac 3.00
2.50
2.00
1.50
1.00 Concentration in mg/l
0.50
0.00
1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Years
For all three rivers, the major increase in NO3 concentration was during the period from 1955 to 1975. Similar increases in NO3 concentration have been reported in the New England Rivers by the USGS (3). For the past 30 years, there was a downward trend in TP for these rivers. This downward trend in TP concentration is probably due to the reduction of phosphorus in soaps and detergents in the 1980s.
30 The comparison of historical chloride concentration trends indicates that in the late1910s, the Cl levels in the Schuylkill and Delaware were about 5.0 mg/l, while the Potomac River was about 2.0 mg/l (see below).
Chloride Concentration Trends Delaware, Schuylkill, and Potomac River Water Supply Intakes 45.0 Delaware Schuylkill Potomac 40.0
35.0
30.0
25.0
20.0
15.0 Concentration in mg/l 10.0
5.0
0.0
1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Years
Since the early 1900s, the chloride concentration in the Potomac River has increased 1,000%, from about 2.0 to 22.0 mg/l. The Schuylkill has increased 830%, from about 6.0 to about 59.0 mg/l, while the Delaware has increased 360%, from 5.0 to 23.0 mg/l.
Similar to NO3, the major increase in chloride concentration began in 1955. Chloride concentrations, however, were still on the increase in the early 2000s.
Upper Basin Water Quality
The first major compilation from various sources of water quality data of our nation’s rivers was published by the USGS in 1925 (5). In this report. four stations in the Upper Basin had monthly analyses for a minimum of one year (table below).
31 Clark USGS Clark DC Intake Potomac Potomac Potomac Potomac Potomac Potomac Cumberland Cumberland Cumberland Brunswick Brunswick Brunswick 1906-7 1993 % Change 1906-7 1993 % Change mg/l mg/l % mg/l mg/l %
HC03 13.7 37.5 173.9 25.7 99.3 286.1
SO4 44.9 118.0 163.1 34.5 32.0 -7.3 Cl 5.0 21.2 327.4 3.2 18.0 471.4
NO3 0.7 4.4 522.9 7.9 Ca 8.6 42.0 126.3 20.2 32.0 58.8 Mg 3.6 10.0 180.9 6.8 8.0 17.1 Na 6.1 17.0 178.2 2.0 10.6 419.6 K 1.1 2.3 113.0 2.8 Silica 6.4 5.1 -19.7 6.1
Clark USGS Clark USGS Shenandoah Shenandoah Shenandoah Potomac Potomac Potomac Millville Millville Millville Great Falls Chain Br. Great Falls 1906-7 1993 % Change 1921 1993 % Change mg/l mg/l % mg/l ml/l %
HC03 47.2 134.4 184.6 43.1 100.2 132.5
SO4 4.4 16.1 263.4 19.8 26.0 31.2 Cl 2.1 10.4 386.0 3.3 11.4 248.6
NO3 1.9 4.8 160.2 3.8 7.9 110.1 Ca 22.9 34.7 51.9 22.7 29.0 27.8 Mg 5.9 11.5 96.2 5.4 7.6 42.1 Na 3.9 8.2 112.4 2.9 14.2 393.1 K 1.0 2.4 140.0 1.4 2.3 65.5 Silica 10.7 4.9 -54.2 6.5 5.6 -14.4
The USGS data for 1993, shown in the table above, was from the same stations as the Clark data, except for the Brunswick Station for which DC intake data were used for 1993. Except for silica, there were large increases of the major ions in the Potomac River at Cumberland, with NO3 increasing over 500%. At the Brunswick Station, both Cl and Na increased over 400%.
32 For the Shenandoah Station the increases were not as pronounced except for SO4 and Cl, which increased 263% and 386% respectively. The increases at the Great Falls/Chain Bridge Station were not as large as for the long-term Washington, DC drinking water intake monitoring data. This may be due in part to the fact that the NO3 and Cl levels in the intake water increased significantly from 1905 to 1921. Therefore, the DC intake waters better represent the Upper Basin above Brunswick.
The USGS Chain Bridge Station, which is below Great Falls, more accurately represents the entire Upper Basin, including the Shenandoah sub-basin. Thus, the two concentration data sets must be used separately. In Chapter Four, which addresses Upper Basin riverine export fluxes, statistical loading relationships are also presented that facilitate the use of the more long-term water intake data.
The first Upper Basin nutrient survey was conducted in 1966 (6). The sub-basins with the highest TP concentrations, as shown below, were the Antietam, Opequon, and Monocacy.
Sub-basin TP as P N02+NO3 TKN mg/l mg/l mg/l
North Br. 0.176 0.378 0.784 South Br. 0.030 0.296 No Data Conococheague 0.108 1.593 No Data Antietam 0.659 1.429 0.338 Opequon 0.499 2.149 0.269 Shenandoah 0.117 0.670 0.580 Monocacy 0.388 1.740 0.693 Potomac River at GF 0.125 0.903 0.273
The sub-basins with the highest nitrate concentrations were the Conococheague, Antietam, Opequon, and Monocacy watersheds.
33 1992 1994 1999 1940’s 1960’s 1970’s 1980’s UM – AL BOM BOM
Town of pH = 2.9 pH = 4.5 – 5.2 pH = 6.7 Kempton
Laurel Run @ pH = 6.5 pH = 2.8 – 3.3 pH = 3 - 3.7 pH = 2.9 – 3.5 pH = 5.5 – 6.7 pH = 5.7 Dobbin Road
Wilson pH = 3.9 – 4.8 pH = 7.0 pH = 3.5 – 6.5 pH = 6.6 – 7.5 pH = 6.8
Bayard pH = 3.6 pH = 4.2 – 6.7 pH = 6.5 – 7.5 pH = 6.8
Buffalo Creek pH = 2 – 3.2 pH = 6 – 6.0
Steyer pH = 2.3 – 3.3 pH = 3.9 – 5.4 pH = 6.7 – 7.7 pH = 7.0
Shallmar pH = 4.2 pH = 6.5 – 7.2 pH = 6.7 – 7.7 pH = 7.2
Abrams Creek pH = 3 - 4 pH = 4.7 – 5.1
Kitzmiller pH = 2.4 – 4.7 pH = 4.6 – 5.6 pH = 6.5 – 7.0 pH = 6.7 – 7.5 pH = 7.3
Three Forks Run pH = 3.2 pH = 2.1 – 3.3 pH = 3.1 – 4.0 pH = 2.9 – 3.8 pH =5.4
Elklick Run pH = 4 – 7.5 pH = 6.2 – 6.9
Barnum pH = 2.7 – 4.9 pH = 4.7 – 4.9 pH = 6.9
Beryl pH = 3.8 – 4.5 pH = 2.7 – 3.6 pH = 5.6 – 6.9 pH = 6.8
pH LEGEND: = less than 4.0 = 4.0 – 5.5 = more than 5.5
Coal Mine Drainage
In the 1840s, part-time coal mining began in the headwaters of the Upper Basin west of Cumberland, Maryland. Coal was shipped down the Potomac River in flat-bottomed barges. When the railroad came to Cumberland, it was used to ship coal to market. By 1873, annual coal production was about 614,000 tons. In 1970, annual production in the Upper Basin was about 1,600,000 tons in Maryland and about 3,600,000 tons in West Virginia. In 2002, both Maryland and West Virginia annual coal production was at an all- time high of 4,800,000 and 148,900,000 tons respectively.
The 1898 “Drainage Basin of the Potomac” report (7) identified Georges Creek, a tributary of the North Branch, as greatly impacted by the drainage of about 20 coal mines. The waters of Georges Creek were “exceeding bad” although “perfectly clear.” The rocks of the stream were highly colored with oxides of iron.
Chemical analysis of the stream indicated:
Combined SO2 0.735 grains per liter or 48 mg/l Free SO2 0.106 grains per liter or 6.8 mg/l
A 1975 ICPRB report titled “Non-Point Pollution in the Potomac River Basin” indicated that acid mine drainage (AMD) profoundly affected over 140 miles of streams and rivers of the North Branch (8). The report further stated that all 140 miles of stream were devoid of fish life and contained virtually no natural biological communities. The streams had low pH waters caused by acid mine drainage.
The history of AMD in the North Branch is detailed in a report, “The Recovery of the North Branch: 1940 to 2000 and Beyond,” (9). A program to reduce AMD was begun in the late 1980s. Beginning in the early 1990s, lime dousers and other passive systems were installed to neutralize AMD. The program also included Successive Alkalinity Producing Systems (SAPS).
Data from the report show a dramatic improvement in pH, as presented in the chart below as obtained form the authors. The pH of 8 of the 13 streams in the 1940s to 1980s were often below 3.0 pH units. Starting in the early 1990s, the pH of the streams improved as the acid mine drainage from the coal mines was reduced.
By 1995, the water quality of the streams had improved to such an extent that Maryland stocked trout in the North Branch for the first time. Today, acid mine drainage is mainly due to abandoned, gravity-flowing coal mines.
34 1992 1994 1999 1940’s 1960’s 1970’s 1980’s UM – AL BOM BOM
Town of pH = 2.9 pH = 4.5 – 5.2 pH = 6.7 Kempton
Laurel Run @ pH = 6.5 pH = 2.8 – 3.3 pH = 3 - 3.7 pH = 2.9 – 3.5 pH = 5.5 – 6.7 pH = 5.7 Dobbin Road
Wilson pH = 3.9 – 4.8 pH = 7.0 pH = 3.5 – 6.5 pH = 6.6 – 7.5 pH = 6.8
Bayard pH = 3.6 pH = 4.2 – 6.7 pH = 6.5 – 7.5 pH = 6.8
Buffalo Creek pH = 2 – 3.2 pH = 6 – 6.0
Steyer pH = 2.3 – 3.3 pH = 3.9 – 5.4 pH = 6.7 – 7.7 pH = 7.0
Shallmar pH = 4.2 pH = 6.5 – 7.2 pH = 6.7 – 7.7 pH = 7.2
Abrams Creek pH = 3 - 4 pH = 4.7 – 5.1
Kitzmiller pH = 2.4 – 4.7 pH = 4.6 – 5.6 pH = 6.5 – 7.0 pH = 6.7 – 7.5 pH = 7.3
Three Forks Run pH = 3.2 pH = 2.1 – 3.3 pH = 3.1 – 4.0 pH = 2.9 – 3.8 pH =5.4
Elklick Run pH = 4 – 7.5 pH = 6.2 – 6.9
Barnum pH = 2.7 – 4.9 pH = 4.7 – 4.9 pH = 6.9
Beryl pH = 3.8 – 4.5 pH = 2.7 – 3.6 pH = 5.6 – 6.9 pH = 6.8
pH LEGEND: = less than 4.0 = 4.0 – 5.5 = more than 5.5
Source: Mills and Davis, Frostburg University
BOM = Bureau of Mines
UM-AL = University of Maryland-Appalachia
35 Annual Monthly Variability
We initially examined the monthly variability of K and nitrate concentrations as a function of the monthly river flow for the Potomac River above Washington, DC (see figure below).
Annual Variability for River Flow, Nitrate, and K for the Potomac River above Washington, DC 5.00 100,000 Nitrate K Flow 4.50 90,000
4.00 80,000
3.50 70,000
3.00 60,000
2.50 50,000
2.00 40,000 River Flow in cfs Nitrate and K in mg/l 1.50 30,000
1.00 20,000
0.50 10,000
0.00 0
1993 1993 1994 1994 1995 Years 1993-1995
In March of 1993 and 1994, river flows were over 60,000 cfs and the nitrate and K concentrations were both about 2.0 mg/l. By July of 1993 and 1994, river flows were less than 5,000 cfs and K concentrations increased to over 3.0 mg/l—and continued to increase to over 4.0 mg/l—as the river flow remained low and was fed mainly by groundwater.
During the low river flows of August of 1993 and 1994, nitrate concentrations decreased to less than 1.0 mg/l as a result of biological activity in the watershed. However, in late August of both years, biological activity in the Upper Basin began to go dormant, the demand for nitrogen decreased, and riverine nitrate levels began to increase. This decrease—followed by an increase—suggests biological activity and chemical properties play an important role in nutrient export out of the watershed.
Another way of viewing the effect of river flow, biological activity, and chemical activity on the K and NO3 riverine concentrations can be seen for a low-flow year, 1999, and a high-flow year, 1996, in the scatter plots below. In the scatter plots, the monthly data points are connected chronologically, beginning in January and ending in December.
36 Potomac River K and Nitrate Versus River Flow 1999 Ave Flow = 6,376 cfs 4.500 Nitrate K 4.000
3.500
3.000 Jan-99
2.500 Dec-99
2.000
Jan-99 1.500
River K and Nitrate in mg/l Dec-99
1.000
0.500
0.000 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 River Flow in cfs
Potomac River K and Nitrate Versus River Flow 1996 Ave Flow = 27,800 cfs 4.00 Nitrate K 3.50
3.00
2.50 Dec-96 Jan-96
2.00 Dec-96 Jan-96
1.50
River K and Nitrate in mg/l 1.00
0.50
0.00 0 10,000 20,000 30,000 40,000 50,000 60,000 River Flow in cfs
37 For a low-flow stream discharge year (6,376 cfs) such as in 1999, riverine NO3 levels were less than 1.50 mg/l and decreased as the river flow decreased. In the warm biologically active summer low stream-flow months, the nitrate levels were often less than 0.50 mg/l, while the K concentrations were usually the highest, over 3.00 mg/l.
As can be seen the scatter plots above, at high river flow conditions (27,800 cfs), such as in 1996, the K and NO3 levels are elevated during all months. The concentrations of both nitrate and potassium were over 2.00 mg/l for most of the 12 months of 1996. During both the low-flow and high-low years, the potassium levels decreased as the river flows increased.
The annual variability of two important nutrients—silica and total phosphorus—for the low-flow year, 1999, is presented below.
Upper Potomac River Basin Silica and T Phosphorus Versus River Flow Average Flow = 6,376 cfs 1999 10.0 0.200
9.0 0.180
8.0 0.160
7.0 0.140
6.0 0.120
5.0 Dec-99 TP 0.100
4.0 Jan-99 TP 0.080 River Silica in mg/l
3.0 0.060 River Phosphorus in mg/l Jan-99 Silica 2.0 0.040
1.0 Dec-99 Silica 0.020
0.0 0.000 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 River Flow in cfs The silica and phosphorus concentrations followed very similar monthly flow patterns, as presented above. This suggests that both silica and phosphorus are similarly influenced by river flows, biological activity, and chemical properties of the watershed. After each annual cycle, silica and phosphorus tend to come to a state of equilibrium or homeostasis. Under low river flow conditions, a conservative-inactive water quality parameter such as hardness has a concentration versus river flow inverse linear relationship, as presented in the third graph below.
For the low-flow summer months, which are the biologically active months, the silica and phosphorus concentrations were over 5.0 mg/l and 0.06 mg/l respectively. This suggests that there is sufficient silica and phosphorus for riverine phytoplankton growth. The lowest silica concentrations were during November through February. The silica and hardness concentrations followed very different monthly flow patterns, as presented below. Both have groundwater and weathering of minerals as their major sources.
38 Upper Potomac River Basin Silica and Hardness Versus River Flow Average Flow = 6,376 16.0 1999 160.0
14.0 Silica 140.0 Hardness Linear 12.0 (Hardness) 120.0
10.0 100.0
8.0 80.0
6.0 60.0 River Silica in mg/l River Hardness in mg/l
4.0 40.0
Jan-99 2.0 20.0 Dec-99
0.0 0.0 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 River Flow in cfs
Under low river flow conditions, the hardness concentration versus river flow had an inverse linear relationship, as presented above. During the colder months of December, January, and February 1999, silica levels were the lowest. The reason for these low levels during the cold months is unknown. The factors affecting the movement of all nutrients need to be further examined and is beyond the scope of this treatise.
Total Residue, Suspended Solids, Dissolved Solids, and Major Ions
Since the 1920s, the total residue of the Potomac River at the drinking water intake has increased from about 100 mg/l to 200 mg/l, as shown below.
Potomac River at Fall Line Total Residue and Major Ion Trends 700
Total Residue Major Ions 600
500
400
300
200 Total Residue and Major Ions in mg/l
100
0 2000 2005 1995 1925 1930 1905 1965 1960 1915 1935 1910 1950 1970 1945 1955 1940 1920 1975 1985 1990 1980 Years
The major ions have increased from about 55 to 100 mg/l during this same 1920-2005 period, as presented above.
39 For five-year periods beginning in 1975, the Potomac River average annual concentrations of total residue (TR), suspended solids (SS), major ions, and dissolved solids (DS) are presented below.
5-Year SS DS Major Ions TR Period mg/l mg/l mg/l mg/l 1975-79 97.1 88.1 90.7 188.6 1980-84 75.0 88.3 109.3 209.6 1985-89 82.5 81.6 111.2 262.7 1990-94 34.4 92.3 100.5 204.3 1995-99 45.0 94.3 91.1 191.1
Average 66.8 88.9 100.6 211.3
Using the average ratio of SS/Major Ions of 66.8/100.6 (see above), we estimated that SS levels in the 1920s were about 35 mg/l. Using the average ratio of SS/TR of 66.8/211.3 (see above), we also estimated that the SS levels in the 1920s were about 32 mg/l. These two similar estimates suggest that since the 1920s, the SS concentration has doubled from about 33 mg/l to 66 mg/l, even though the amount of farmland has decreased from 75% to 35%. These higher concentrations may be due to higher spring river flow pulses and may possibility be associated with increases in impervious surfaces.
Heavy Metal Concentrations in the Major Middle Atlantic Rivers
The first stream sampling and chemical analysis of the major rivers of the Northeast Shelf using “clean methods” was conducted in the late 1980s (10). The dissolved trace metal concentrations for five of the rivers of the Middle Atlantic area, including the Potomac River, are presented below.
River Dissolved Trace Metal Concentrations in ug/l
Cd Co Cu Ni Pb Zn Delaware 0.010 0.022 0.672 0.220 0.017 0.398 Susquehanna 0.004 0.128 1.267 2.132 0.013 0.161 Potomac 0.024 1.162 0.988 1.000 0.024 0.278 Rappahannock 0.013 0.075 0.986 0.316 0.013 0.091 James 0.010 0.059 0.824 0.511 0.031 0.077
Average 0.013 0.356 1.016 0.990 0.020 0.152
While the dissolved trace metal concentrations varied among the five rivers, the Potomac River had the highest Cd and Co levels.
40 The total metal concentrations, which include both dissolved and particulate forms, are shown below.
River Total Metal Concentrations in ug/l
Cd Co Cu Ni Pb Zn Delaware 0.014 0.034 0.771 0.527 0.075 1.183 Susquehanna 0.025 2.045 2.590 5.199 0.646 6.679 Potomac 0.035 1.529 1.508 1.887 0.361 3.948 Rappahannock 0.023 0.257 1.608 1.017 0.298 2.425 James 0.020 0.239 1.261 0.948 0.262 1.721
Average 0.023 0.821 1.548 1.916 0.328 3.191
The Potomac River had the highest total Cd levels, while the Susquehanna River had the highest levels for the other five metals.
Water Quality Assessment of the Upper Basin in 1969
A water quality assessment of the Upper Basin was conducted in response to a recommendation adopted by the conferees of the Potomac River-Washington Metropolitan Area Enforcement Conference (11). Two special surveys were conducted in July and August 1969. The analysis included bacteria, DO, BOD, nutrients, pesticides, temperature, turbidity, and chlorophyll.
Key findings were:
1. Fecal coliform levels were high in the North Branch, South Branch, Conococheague Creek, Opequon Creek, Antietam Creek, North and South Forks of the Shenandoah River, and Monocacy River. 2. Low DO occurred (less than 3 mg/l) in the North Branch, Monocacy River, and South Fork of the Shenandoah River. 3. Most analyses for chlorinated hydrocarbon pesticides were negative; however, significant quantities of dieldrin and DDT were measured in Antietam Creek. 4. Nutrient levels were highest in Opequon Creek, Antietam Creek, and Monocacy River. 5. The effects of coal mine drainage were confined to the North Branch.
41 The river temperature data from the August 18, 1969 synoptic survey provides a further indication of the impact of thermal discharges, as presented below.
Main Stem Potomac River Location Along the Main Stem oF
Paw Paw 77.0 Brosius 78.8 Williamsport 79.7 Shepherdstown 80.6 Point-of-Rocks 80.6 Great Falls 82.4
Sub-basins Near Main Stem Shenandoah 77.0 (Front Royal) Monocacy 80.6 (Route 28 Br.)
As the Potomac River flowed from Paw Paw to Great Falls, its temperature increased from 77.0oF to 82.4oF, for an increase of 5.4oF. The river temperature of the Shenandoah near the confluence with the Potomac was the same as the main stem Potomac at Paw Paw, 77.0oF. The river temperature of the Monocacy about its confluence with the Potomac was also elevated at 80.6oF.
USGS NAWQA (National Water-Quality Assessment) Studies, 1979-1990 and 1992- 1996
The USGS NAWQA 1979-1990 study was a water-quality assessment of the Potomac River Basin (12). It included a detailed description of the basin and an analysis of available nutrient data from 1979 to 1990. Nutrient sources, concentrations, loads, and mass budgets were quantified.
As part of the NAWQA program, the USGS (13) evaluated seven major water-quality characteristics of selected stream sites of the Potomac River Basin for the period 1992 to 1996. Results from the Potomac River were compared to other NAWQA study sites throughout the nation.
42 Key findings were:
1. Nutrient and pesticide concentrations at several Potomac River Basin stream sites were among the highest in the nation. 2. PCBs and organic chlorine pesticides were detected in streambed sediments and/or in aquatic tissues at all sample sites. The levels at four sites ranked among the highest in the nation. 3. Elevated levels of chlordane and lead were detected in the North Branch, Anacostia River, and Acotink Creek. 4. Mercury was detected in all sediment samples, with the highest levels in the South River of the Shenandoah River sub-basin.
Stream habitat and fish communities were most degraded in highly agricultural or urban area streams.
Maryland’s Middle Potomac River Basin Environmental Assessment
In 1966, the MD DNR conducted an assessment of the water quality and habitat in the Middle Potomac River Basin (14). All of the streams surveyed had summer dissolved oxygen levels greater than 5.0 mg/l. Excessive loading of oxygen-demanding matter was not a problem. However, elevated nitrate-nitrogen concentrations were observed in 83% of the streams surveyed.
USGS Trend Study 1985-2003
In a recently published report (15), the USGS estimated the water quality trends for 31 sites within the Chesapeake Bay Basin using parametric methods. The trend analysis involved the use of non-transformed and transformed data. Trend analysis focused mainly on flow-adjusted river concentration.
A summary of the USGS trend results for the 12 sites of the Upper Potomac Basin are presented below:
Parameter No Significant Upward Downward Trend Trend Trend
TN 1 2 9 TP 1 2 9 Sediments 7 0 5
Except for two sites that had upward trends, the USGS flow-adjusted trends for TP and TN were downward for nine sites.
43 The trends in flow-adjusted river concentrations for the Upper Basin at Chain Bridge for the 1985-2003 period are presented below.
2000-2003 Flow-adjusted Measured Parameter Concentration Slope Concentration (mg/l) (mg/l) TN 1.79 -.0060 1.87
NO3 NA +.0014 1.23 TP 0.09 +.0095 0.14 DIP NA +.0113 0.04 Sediments 73.00 +.0525 49.60
No trends were presented for loads. Flow-adjusted TN concentrations exhibited little downward change, while DIN, TP, DIP, and sediments increased. The flow-weighted TN and TP concentrations were higher, 2.25 and 1.50 mg/l respectively, than the flow- adjusted concentrations of 1.79 and 0.096 mg/l respectively. The measured-unadjusted TN and TP concentrations were also higher than flow-adjusted concentrations.
Water Quality Studies in the Headwaters of the Potomac Basin in West Virginia
Poultry production in the Potomac Headwaters of West Virginia has increased dramatically since the early 1990s (see Chapter Three). The Potomac Headwaters Interagency Water Quality Office (PHIWQO) was established in 1963 to protect the Headwaters while maintaining strong agricultural industries.
PHIWQO water quality studies were initiated in 1994. The 1994 study did not indicate high nutrient concentrations at any site (16). The Cacapon Institute began an intensive study of the Headwaters of the Cacapon Basin in 1997. The final report includes an attempt to relate land use to water quality impacts (17).
Elevated nutrient levels were observed at some of the sampling sites in the 1997 study. Although poultry production continued to increase in the early 2000s, the impact on nutrient concentrations in the river was undefined in this study.
Since 1947, the West Virginia Department of Environmental Protection (WVA DEP) has maintained four fixed-site monitoring stations in the Upper Basin. Using the WVA DEP water quality monitoring data plus the FWPCA 1966 nutrient data, water quality trends for the Shenandoah, Opequon, Cacapon, and South Branch Potomac sub-basins for alkalinity, chlorides, nitrates, total phosphorus, and sulphates are presented below.
44 Water Quality Trends for Shenandoah River
Alkalinity Chlorides Nitrates as N TPhosphorus SO4 1000.00
100.00
10.00
1.00
0.10 Water Quality Trends in mg/l
0.01
09/18/4603/01/6108/00/6603/17/6804/21/7007/25/7210/23/7410/14/7603/07/7808/07/7912/02/8005/04/8208/03/8312/11/8408/18/8608/11/8709/27/8810/16/8910/15/9002/10/9206/29/9310/18/9412/08/9703/13/02 Sampling Date
Water Quality Trends for Cacapon River
Alkalinity Chlorides Nitrates as N TPhosphorus SO4 1000
100
10
1
0.1
Water Quality Trends in mg/l 0.01
0.001
09/19/4610/20/4906/05/6205/06/6305/00/6611/03/7602/20/7907/08/8103/04/8410/30/8511/12/8610/22/8709/27/8808/28/8907/10/9006/04/9105/06/9205/05/9304/05/9403/07/9509/02/9706/13/0003/11/03 Sampling Date
45 Water Quality Trends for Opequon River
Alkalinity Chloride Nitrates TPhosphorus SO4 1000.0
100.0
10.0
1.0
0.1 Water Quality Trends in mg/l
0.0
04/00/6631-Jul-67 20-Jul-7605-Jul-77 09-Sep-4706-May-63 17-Mar-6801-Jun-6908-Dec-7006-Jun-7223-Oct-7329-Apr-75 04-Jun-7801-May-7908-Apr-8003-Mar-8102-Feb-8220-Oct-8207-Jun-8309-May-8430-Sep-8707-May-8910-Apr-9103-Aug-9222-Jun-9426-Mar-9728-Mar-0017-Dec-02 Sampling Date
Water Quality Trends for South Branch Potomac
Alkalinity Chlorides Nitrates TPhosphorus SO4 1000
100
10
1
0.1
Water Quality Trends in mg/l 0.01
0.001
08/26/4711/29/6006/05/6212/09/6309/18/6706/03/6910/18/7101/22/7409/15/7505/03/7710/17/7802/05/8007/14/8111/16/8205/23/8411/21/8505/06/8707/26/8809/18/8909/19/9001/13/9207/22/9312/06/9409/02/9803/11/03 Sampling Date
46 A summary of the water quality trends for the four sub-basins is presented in the table below.
Sub-basin Alkalinity Chlorides Nitrates T Phosphorus Sulphates
Shenandoah no change no change upward ++ upward + downward - Opequon no change upward + no change downward - upward + Cacapon downward - upward + upward ++ downward - no change South Branch no change downward- upward++ downward- upward+
The largest upward trends were for nitrates in the Shenandoah, Cacapon, and South Branch sub-basins. These three sub-basins are major poultry production areas.
References for Chapter Two
1. 53th U.S. Congress, (1898), Bacteriological Examination of the Potomac River, U.S. Senate, 2nd Session, Document No. 211.
2. Ways, H.C., (Undated), The Washington Aqueduct, 1852-1992, US ACE, Dalecarlia Complex, Washington, D.C., pp 186.
3. Robinson, K.W., J.P. Campbell, & N.A. Jaworski, (2003), Water-Quality Trends in New England Rivers During the 20th Century, USGS, Water-Resources Investigations Report 03-4012, pp 20.
4. Nixon, S.S., et al, (2004), A One Hundred and Seventeen Year Coastal Water Temperature Record form Woods Hole, Massachusetts, Estuaries, 27:397-404.
5. Clarke, F.W., (1924), The Composition of the River and Lake Waters of the United States, USGS, Professional Paper 135, Washington, D.C.
6. Jaworski, N. A., (1969), Nutrients in the Upper Potomac River Basin, U.S. Department of the Interior, Federal Water Pollution Control Administration, Middle Atlantic Region, Chesapeake Technical Support Laboratory, pp 40.
7. USGS, (1898), Potomac River, Nineteenth Annual Report, 1897-98, Part IV, Hydrography, Washington, D.C.: 134-162.
8. Palmer, R.N., (1975), Non-Point Pollution in the Potomac River Basin, ICPRB, Technical Publication No. 75-2, Washington, D.C. pp 71.
9. Mills, J.S. & T.L. Davis (2000), The Recovery of the North Branch: 1940 to 2000 and Beyond, MDDE & Frostburg University, Frostburg, MD, pp 11.
47 10. Windom, H.L., (1996), Riverine Contributions to Heavy Metal Inputs to the Northeast Shelf Ecosystem, The Northeast Shelf Ecosystem: Assessment, Sustainability and Management, Blackwell Science, Cambridge, MA, pp 313- 325.
11. Aalto, A.A., et al, (1969), Upper Potomac Water Quality Assessment, Nutrients in the Upper Potomac River Basin, U.S. Department of the Interior, Federal Water Pollution Control Administration, Middle Atlantic Region, Chesapeake Technical Support Laboratory, Technical Report No. 17.
12. Blomquist, J.D., et al, (1996), Water-Quality Assessment of the Potomac River Basin: Description and Analysis of Available Nutrient Data, 1970-1990, U.S. Geological Survey Water-Resources Investigations Report 95-4221, pp 98.
13. Ator, S.W., et al, (1998), Water Quality in the Potomac River Basin, Maryland, Pennsylvania, Virginia, West Virginia, and the District of Columbia, 1992-96, U.S. Geological Survey Circular 1166, pp 38.
14. Dail, H.D., et al, (1998), Middle Potomac River Basin: Environmental Assessment of Stream Conditions, MD DNR, Resource Assessment Service, CBWP-MANTA-EA-98-5, pp 28.
15. Langland, M.J., et al, (2004), Changes in Stream flow and Water Quality in Selected Sites in the Chesapeake Bay, 1985-2003, USGS, Scientific Investigation Report 2004-529, pp 50.
16. Mathes, M.V., (1966), Stream water quality in the headwaters of the South Branch Potomac River basin, WVA, 1994-95, and Lost River basin WVA, 1995, USGS Administrative Report in Potomac Headwaters Agriculture Report, PHIWQO.
17. Cacapon Institute, (2002), Water Quality Studies in the Cacapon River’s Lost and North River in West Virginia, High View, WVA, pp 34.
48