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Summary of Annual Hydrologic Conditions - 2000

Volume 3: Water-Quality

Surface Water-Quality

Water year 2000 was marked by generally normal amounts of rainfall and stream discharge with noticeable increases in the late summer months. Monthly total precipitation was greater than long-term (1961-90) mean monthly precipitation during June through September at the Newark and Atlantic City National Weather Service stations and during August and September at the Trenton station (fig. 1). All monthly mean discharges at the three stream-discharge index stations, South Branch Raritan River at High Bridge, Great Egg Harbor River at Folsom, and Delaware River at Trenton, were within the range of historical (period of record prior to 2000 water year) maximum and minimum monthly mean values (fig. 2). Monthly mean discharge was greater than long-term (1960-90) median monthly values during June to August at the High Bridge station, August and September at Folsom, and March to September at Trenton.

Specific conductance (SC) is often used as an indicator of the concentration of dissolved solids. It is generally inversely related to stream discharge. The maximum monthly mean SC value for water year 2000 at the continuous monitoring station on the Delaware River at Trenton was recorded for September (fig. 3). The lowest monthly mean stream discharge for the year also was in September. The minimum monthly mean SC and the maximum monthly mean discharge were in March. Monthly mean SC values were lower than long-term (1968-99) mean monthly SC values during March to August when stream discharges were greater than long-term (1961-90) median monthly discharges. Monthly mean SC values were greater than long-term mean monthly SC values during November, January, and February when stream discharges were less than long-term median monthly discharges. All monthly mean SC values were within the range of historical (1968-99) maximum and minimum monthly mean SC values.

Figure 1. Monthly precipitation
at three National Weather
Service stations.
Figure 2. Monthly mean
discharge at index
gaging stations.
Figure 3. Monthly mean
specific conductance at Delaware
River at Trenton, New Jersey.
Figure 1 Figure 2 Figure 3

The monthly mean water-temperature values for the continuous monitoring station on the Delaware River at Trenton for water year 2000 were within the range of historical (1968-99) maximum and minimum monthly mean values (fig. 4). Monthly mean values recorded in November, December, January, and March were greater than long-term (1968-99) mean monthly values and were a result of unseasonably warm air temperatures during the winter season. According to the Northeast Regional Climate Center of Cornell University in Climate Impacts, the Northeast region continued a trend of warmer-than-normal months from December to March. The exception occurred during late January to early February when temperatures changed abruptly, averaging about 8 to 10 degrees below normal. Monthly mean values recorded in June through September were less than long-term mean monthly values and were caused by unseasonably cool spring and summer seasons. According to Climate Impacts-July 2000, in New Jersey, July 2000 was the second coolest July of record (1895-1999), with a statewide monthly average air temperature of 70.9°F (21.6°C).

Dissolved oxygen (DO) concentration generally exhibits an inverse relation to water temperature. As water temperature decreases, oxygen concentration increases; as water temperature increases, oxygen concentration decreases. DO, therefore, varies seasonally; yearly maximums occur in winter and yearly minimums occur in summer. Occasionally water clarity, sunlight variations, and algal photosynthesis and respiration rates affect the temperature-DO relation; extremes of DO concentration can occur irrespective of temperature extremes. The monthly medians of daily maximum and minimum DO concentrations at the continuous monitoring station on the Delaware River at Trenton for the 2000 water year were within the range of historical (1968-99) extreme monthly median values (fig. 5). The highest monthly median of the daily maximum DO concentrations, 15.2 milligrams per liter (mg/L), and the year's lowest monthly mean water temperature of 1.6°C, were recorded in February. The lowest monthly median of the daily minimum DO concentrations, 8.0 mg/L, was recorded in July and September; the year's highest monthly mean water temperature of 24.1°C was recorded in July.

Figure 4. Monthly mean water
temperature at Delaware River
at Trenton, New Jersey.
Figure 5. Monthly medians of daily
maximum and minimum
dissolved-oxygen concentrations at
Delaware River at Trenton, New Jersey.
Figure 4 Figure 5

 


Water-Column Nutrients and Common Ions in, and Physical Characteristics of, New Jersey Streams

Analyses for water-phase concentrations of total and filtered nutrients, filtered common ions, and biochemical oxygen demand (BOD) were performed on surface-water samples from 107 sites in the U.S. Geological Survey (USGS)/New Jersey Department of Environmental Protection (NJDEP) Cooperative Ambient Stream Monitoring Network (ASMN). Samples were collected at each site four times a year -- November to December, February to March, May to June, and August to September. Sites were classified in five categories. Six Background sites were located in undisturbed areas. Twenty-two Watershed Integrator sites were located at the farthest downstream point, not affected by tide, in one of the large drainage basins in each of the twenty watershed management areas, except areas 9 and 16. These sites reflected the cumulative effects of various land uses and point-source discharges. Each Land Use Indicator site monitored the effects of one of four designated land uses (undeveloped, agriculture, mixed, and urban) that occurred in each watershed management area. Ten of the Land Use Indicator sites were designated agriculture, 5 mixed, 13 undeveloped, and 13 urban. Statewide Status sites represented a randomly selected population of New Jersey streams; two sites were selected in each of the 20 watershed management areas. Seven of the Statewide Status sites were located at existing Watershed Integrator or Land Use Indicator sites. The Delaware River Main Stem category consisted of five sites. Water-column samples were collected at each site to assess water-quality constituents that might have been used as environmental indicators statewide. In addition to the regularly scheduled sampling, a Watershed Reconnaissance study is conducted annually to meet specific project needs. The purpose of the Watershed Reconnaissance study in water year 2000 was to assess 2-to-5-day diurnal dissolved oxygen levels at a subset of the network sites. This is discussed further in the section Ambient Stream Monitoring Network Reconnaissance Study.

Distributions of water temperature and concentrations of constituents measured in water-column samples collected during water year 2000 are presented in figures 6a and 6b as a function of site category, excluding the Delaware River Main Stem site category. Plots are presented for dissolved oxygen in percent of saturation during the growing season (April through October), water temperature, silica in filtered water, total ammonia, nitrite plus nitrate in filtered water, total nitrogen, total phosphorus, BOD, total dissolved solids (parameter code 70300), and filtered organic carbon. The analyzing laboratory used two different methods and reporting conventions for establishing the minimum concentration above which a quantitative measurement can be made. These reporting conventions were minimum reporting level (MRL) and laboratory reporting level (LRL). LRL was computed as twice the long term method detection level (LT-MDL). Values reported by the analyzing laboratory as less than the MRL or LRL were included in each distribution but were reported as a value equal to one-half the MRL or LT-MDL.

Figure 6a. Distribution of selected constituents in filtered and unfiltered surface water, and physical characteristics of surface water from 102 sites in the Ambient Stream Monitoring Network, water year 2000. Figure 6b. Distribution of selected constituents in filtered and unfiltered surface water, and physical characteristics of surface water from 102 sites in the Ambient Stream Monitoring Network, water year 2000.
Figure 6a Figure 6b

The lowest medians for water temperature, BOD, and concentrations of silica and total dissolved solids (TDS) were recorded at Background sites. The median values of silica in filtered water for all site types ranged from 5 to 9.2 milligrams per liter (mg/L). Samples from Statewide Status sites, which represent a random population of New Jersey streams, had a median silica concentration of 8.1 mg/L. Streams affected by wastewater and road salt runoff are likely to have high levels of TDS; samples from urban and Watershed Integrator sites had the highest median concentrations. In contrast, samples from Background sites had the lowest median TDS concentrations.

Box plots for the nutrient species (filtered ammonia, filtered nitrite plus nitrate, total nitrogen, and total phosphorus) seem to indicate that human activities are the greatest contributors to measurable nutrient levels in streams (fig. 6b). The highest median concentrations of ammonia and phosphorus were measured in samples from agricultural land use, urban land use, and Watershed Integrator site types, and most likely resulted from private, industrial, and municipal sewage; animal waste; and chemical fertilizers. As expected, samples from Background sites had the smallest range of concentrations and the lowest median concentrations.

The range of median concentrations of filtered organic carbon in samples from New Jersey streams historically has been from 4.0 to 5.0 mg/L. Median values measured in samples during water year 2000 ranged from 2.6 to 4.9 mg/L at all seven site types. Some undeveloped sites were located on streams that drained swamps and wetlands. Therefore, samples from undeveloped sites had the largest range of filtered organic carbon concentration, 1.25 to 30.41 mg/L, and the highest median concentration and highest value of all site types.

 


Trace Elements, Volatile Organic Compounds, and Organic Pesticides in New Jersey Streams

The presence of trace elements, volatile organic compounds (VOCs), and pesticides in New Jersey streams continued to be of great interest to water-resource managers and the public in general. The USGS/NJDEP ASMN has demonstrated that many of these trace elements and organic compounds were present under ambient conditions in many New Jersey streams but at low concentrations.

Concentrations and frequencies of detection of selected whole-water recoverable trace elements, VOCs, and pesticides in samples from Background and Statewide Status sites are presented in figures 7a, 8, and 9, and tables 1, 2a, and 2b. Selected whole-water-recoverable and filtered trace elements with a high percentage of detections in samples (greater than 75 percent) are presented in box plots (fig. 7b). Constituents with a lower percentage of detections in samples are presented in scatter plots (fig. 7a). A detected compound is one whose value is reported to be greater than or equal to the laboratory's MRL. Estimated values, which were determined to be greater than the LT-MDL but less than the LRL, were included in the data for the scatter plots. They were marked with an "E" in the water-quality tables. Refer to "Laboratory Measurements" in the Introduction for additional information about estimated concentrations. Values reported by the analyzing laboratory as less than the MRL or LRL were included in the box plot distributions but were reported as a value equal to one-half the MRL or LT-MDL. The six Background sites were located in relatively pristine areas of New Jersey, such as state forests or national parks. Water-quality data from these sites constitute a baseline with which to compare the water quality of other sites. The 40 randomly chosen Statewide Status sites provide a general overview of the water quality in the state and the aerial distribution of those compounds. Samples analyzed for trace elements, VOCs, and pesticides were collected when the compounds were most likely to have been detected, during August and September, February and March, and May and June, respectively. Boron in filtered water was analyzed for in samples collected throughout the 2000 water year from all 107 sites in the ASMN. Data from the five Delaware River Main Stem sites were excluded from the distribution of boron in filtered water in figure 7b.

Concentrations and frequencies of detection of selected whole-water-recoverable trace elements in samples from New Jersey streams are shown in figure 7a. Beryllium, cadmium, mercury, selenium, and silver were not detected in any sample and so were not included in the figure. Data from the Background sites indicated infrequent detection and, when detected, low concentrations of trace elements. Of the six trace elements presented, chromium was detected twice; arsenic, boron, copper, and nickel were detected once; and lead was not detected in samples from Background sites. In contrast, these trace elements were detected in greater concentrations and frequencies in samples from Statewide Status sites.

Distributions of selected whole-water-recoverable and filtered trace elements in samples from selected sites in the ASMN are shown in figure 7b. Barium and manganese were detected in concentrations greater than the reporting limits in all 46 samples. Iron was detected in concentrations greater than the LRL in all but 2 of the 46 samples. Zinc was detected at greater than the MRL in all but 4 of the 46 samples, and filtered boron was detected at greater than the LRL in all but 32 of the 433 samples. Concentrations of boron in filtered water could result from human activities; samples from urban land-use sites had the highest median concentration and the highest single value. The median concentrations of boron in filtered water, whole-water-recoverable barium, iron, manganese, and zinc were lower in samples from Background sites than in samples from Statewide Status sites.

Concentrations and frequencies of detection of VOCs detected in samples from New Jersey streams are shown in figure 8 (those detected more than once) and are listed in table 1 (those detected only once). Samples were analyzed for the presence of 34 VOCs in each of 45 samples. Refer to individual station records to view concentrations from all 34 compounds in table form. Of the 14 compounds detected, only 2, chloroform and methyl tert-butyl ether (MTBE), were detected at low concentrations in samples from Background sites. The most frequently detected VOC, MTBE, was detected in 60 percent of all samples. The next most frequently detected VOC, Chloroform, was detected in 20 percent of all samples. VOCs are synthetic chlorinated compounds that are used as industrial solvents and degreasers; household and dry-cleaning agents; additives in paint, varnish, and adhesives; and components of, and additives to, gasoline.

Table 1. Volatile organic compounds, detected only once, at selected sites in the Ambient Stream Monitoring Network, water year 2000.
[SS, statewide status; E, estimated]
CONSTITUENTCONCENTRATION
(micrograms per liter)
SITE TYPE
ChlorodibromomethaneE.1176SS
1,1 Dichloroethane0.1378SS
Ethyl etherE.1356SS
meta+para-XyleneE.1070SS
Toulene0.1485SS
Trichloroethane0.4137SS
Tricholorfluoromethane0.2614SS

 

 

Figure 7a. Concentration and frequency of detection of selected whole-water-recoverable trace elements in samples from selected sites in the Ambient Stream Monitoring Network, water year 2000. Figure 7b. Distribution of selected whole-water-recoverable and filtered trace elements in samples from selected sites in the Ambient Stream Monitoring Network, water year 2000. Figure 8. Concentration and frequency of detection of volatile organic compounds detected at selected sites in the Ambient Stream Monitoring Network, water year 2000.
Figure 7a Figure 7b Figure 8

Concentrations and frequencies of detection of organic pesticides in samples of filtered water from New Jersey streams are shown in figure 9 (those detected more than once) and listed in tables 2a (those with estimated concentrations) and 2b (those detected only once). Forty-seven compounds were analyzed for using USGS National Water Quality Laboratory schedule 2001; refer to "Laboratory Measurements" in the Introduction for the complete list. Twenty-four pesticides were detected in samples from Statewide Status sites and four in samples from Statewide Status and Background sites. Five of the detected compounds were insecticides-- Diazinon, Carbaryl, Carbofuran, Dieldrin, and Malathion. The remaining compounds were herbicides. The pesticides most frequently detected in the 45 samples collected were Metolachlor and Atrazine, which were detected in 87 percent of the samples; Deethylatrazine, in 80 percent; Prometon, in 60 percent; Simazine, in 51 percent; and Carbaryl, in 44 percent. Four widely used herbicides (Metolachlor, Atrazine, Deethylatrazine, and Prometon) were detected in samples from one or more Background sites; no insecticides were detected in samples from Background sites. One or more pesticides were detected in 36 of 39 samples (92 percent) from Statewide Status sites. One or more pesticides were detected in three of six samples (50 percent) from Background sites. The pesticides that were frequently detected in samples from throughout the State were present in low concentrations.

Table 2a. Frequency of detection of pesticides in filtered water detected at selected sites in the Ambient Stream Monitoring Network, water year 2000.
[All values are estimated due to poor recovery or poor precision]
CONSTITUENTSTATEWIDE STATUSBACKGROUND
Carbaryl20 of 390 of 6
Carbofuran2 of 390 of 6
Deethylatrazine34 of 392 of 6
Terbacil2 of 390 of 6

Table 2b. Pesticide concentrations in filtered water, detected only once, at selected sites in the Ambient Stream Monitoring Network, water year 2000.
[SS, statewide status; E, estimated]
CONSTITUENTCONCENTRATION
(micrograms per liter)
SITE TYPE
ButylateE.00177SS
EPTCE.00241SS
Pronamide0.00714SS
TerbuthylazineE.00310SS

 

Figure 9. Concentration and frequency of detection of pesticides in filtered water from selected sites in the Ambient Stream Monitoring Network, water year 2000.
Figure 9

 


Ambient Stream Monitoring Network Reconnaissance Study

Field characteristics and concentrations of constituents in surface water monitored continuously at 18 selected stations during August or September 2000 are presented in figures 10a and 10b. The 18 stations included 12 stations in the Ambient Stream Monitoring Network, 3 continuous water-quality monitoring stations, and 3 miscellaneous sites. The monitors at the continuous water-quality monitoring stations are permanent installations. The other 15 stations had temporary installations in place for 2 to 5 days. Monitoring took place during the late summer months. The study was intended to observe incidents of base-flow extremes of water temperature and percent of oxygen saturation and to document the occurrence and magnitude of diurnal dissolved oxygen fluctuations that cannot be observed during normal site visits between 8a.m. and noon. Of the 12 ASMN sites, 6 were Background sites, 3 were Land Use Indicator sites, and 3 were Watershed Integrator sites. Data from Background sites were needed to understand fluctuations of diurnal dissolved oxygen (DO) in pristine watersheds and to compare with data from other sites. The Land Use Indicator, Watershed Integrator, and miscellaneous sites were chosen on the basis of historical DO super-saturation (greater than 120 percent of saturation) or low DO (less than 60 percent of saturation).

Temperatures at the Background sites typically were lower than at other sites because of their locations in forested watersheds. The DO concentrations at the Background sites were greater than 6 mg/L, except at site 01466500, McDonald's Branch in Lebanon State Forest. This site is recharged by ground water that typically has low concentrations of DO. The minimum DO values at the other sites ranged from 4.0 to 8.6 mg/L. The maximum values ranged from 4.5 to 11.3 mg/L. Three sites exhibited minimum percent of DO saturation values less than 60 percent-- Background site 0146500, McDonald's Branch in Lebanon State Forest; Miscellaneous site 01379000, Passaic River near Millington; and agriculture Land Use Indicator site 01464515, Doctors Creek at Allentown. They historically have had low DO values during routine sampling visits. Three sites exhibited maximum percent of DO saturation values greater than 110 percent-- Watershed Integrator site 01398102, South Branch Raritan River at South Branch; undeveloped Land Use Indicator site 01440000, Flat brook at Flatbrookville; and Delaware River Main Stem site 01463500, Delaware River at Trenton. They historically have had high DO values.

Four sites-- 01378560, 01381800, 01391100, and 01391500-- had wide variation of minimum, mean, and maximum specific conductance (SC) measured during respective periods of record. These sites are different from those with extreme values (<60 percent and >110 percent) of percent of DO saturation. The lowest continuously monitored pH occurred at two Background sites, 01411955 and 01466500.

Figure 10a. Field characteristics and
concentrations of constituents in
surface water at selected stations
in the Ambient Stream Monitoring
Network during August or
September, 2000.
Figure 10b. Field characteristics and
concentrations of constituents in
surface water at selected stations
in the Ambient Stream Monitoring
Network during August or
September, 2000.
Figure 10a Figure 10b

 



Groundwater-Quality

The Ambient Ground-Water-Quality Network (AGWQN) was designed to monitor the quality of ground water at or near the water table. Shallow ground water is generally the first and most significantly affected part of the ground-water system, and the quality of this water is directly related to human activities at land surface. The USGS/NJDEP AGWQN has four goals. The first goal is to assess the status of ground-water quality by examining the concentrations of various constituents that can be used as environmental indicators. The second goal is to assess water-quality trends by examining data collected on a 5-year cycle. The third goal is to determine the effects of land use on shallow ground-water quality, and the final goal is to identify threats from non-point sources and to identify emerging or new environmental issues of concern to the public.

The network consists of 150 shallow wells distributed throughout New Jersey within three land-use types. Sixty wells are, or will be located, in agricultural areas, 60 in urban/suburban areas, and 30 in undeveloped areas within New Jersey's five watershed management regions (WMR)--the Passaic, the Raritan, the Upper Delaware, the Lower Delaware, and the Atlantic Coastal. These five WMRs were further divided into 20 watershed-management areas (WMA). Every year approximately 30 sites are sampled in one or several of the five WMRs. The full cycle of 150 wells will be completed in five years.

Thirty shallow wells were sampled in 2000. Fourteen wells are in the Lower Delaware Region of New Jersey and are distributed throughout WMA 17-20 (fig. 11). Sixteen wells are in the Atlantic Coastal Region and are distributed throughout WMA 13-16. Twenty-two wells are screened in the Kirkwood-Cohansey aquifer system; one in the Mount Laurel Sand; one in the undifferentiated sediments of Holocene, Pleistocene, Pliocene, or Miocene age; one in the Merchantville Formation; one in the Upper Aquifer of the Potomac-Raritan-Magothy aquifer system; two in the Englishtown aquifer system, and two in the Marshalltown Formation (table 3). The wells have polyvinyl-chloride casings and range in depth from 8 to 49 feet. Three were drilled in 1996; the other 27 were drilled during March through September 2000. Samples from the wells were analyzed for physical characteristics, major ions, nutrients, trace elements, organic constituents, and gross alpha and beta radioactivity. The tables of chemical constituents are in the section, "Water-Quality Records at Miscellaneous Ground-Water Sites."

Figure 11. Location of sites in the Ambient Ground-Water-Quality Network, water year 2000.
Figure 11

 

Table 3. Hydrogeologic unit and land use at 30 wells sampled as part of U.S. Geological Survey-N.J. Department of Environmental Protection (cooperative) Ambient Ground-Water-Quality Network, water year 2000.
[WMA, Watershed Management Area; VOCs, volatile organic compounds; mg/L, milligrams per liter; NO2+NO3, nitrite plus nitrate; dis, dissolved; -, no data; <, less than; ft bls, feet below land surface; 121CKKD, Kirkwood-Cohansey aquifer system; 111HPPM, Undifferentiated sediments of Holocene, Pleistocene, Pliocene, or Miocene age; 211MRSL, Marshalltown Formation; 211MLRL, Mount Laurel Sand; 211MCVL, Merchantville Formation; 211EGLS, Englishtown aquifer system; 211MRPAU, Upper Aquifer system of the Potomac-Rartian-Magothy aquifer system]
NJ-WRD well numberWMA numberHydrogeologic unit aquifer codePredominant land use1 Water type
(dominant cation-anion)
Dissolved oxygen
(mg/L)
Nitrogen NO2+NO3 dissolved
(mg/L)
Number of pesticides detected2 Number of VOCs detected2Number of trace elements detected2Well depth
(ft bls)
15120715121CKKDAgriculturalMagnesium-NO2+NO35.45611724.0
11115417121CKKDAgriculturalPotassium-sulfate2.6126None517.7
15151417121CKKDAgriculturalCalcium-NO2+NO310.5114None624.2
15151518111HPPMAgriculturalSodium-chloride1.1.3192612.7
15151618121CKKDAgriculturalCalcium-nitrate7.713None2629.5
33093918211MRSLAgriculturalCalcium-NO2+NO34.6104None519.5
25079020211MLRLAgriculturalSodium-chloride.3.173None414.2
29140213121CKKDUndevelopedSodium-chloride6.0<.05None148.0
29140313121CKKDUndevelopedSodium-sulfate5.6<.05None1210.5
29140413121CKKDUndevelopedMagnesium-sulfate4.6.75NoneNone217.3
29140513121CKKDUndevelopedSodium-chloride4.1<.05None1318.0
01140214121CKKDUndevelopedIron-Sulfate1.0<.05NoneNone411.5
05149614121CKKDUndevelopedSodium-sulfate9.3.1None1216.0
05149714121CKKDUndevelopedSodium-sulfate5.0<.05None1113.8
05150114121CKKDUndevelopedAluminum-sulfate5.3<.05NoneNone417.5
01140015121CKKDUndevelopedSodium-sulfate.7<.05None1313.5
07084215121CKKDUndevelopedAluminum-sulfate1.8<.05NoneNone314.0
09051016121CKKDUndevelopedCalcium-bicarbonate1.8<.05NoneNone311.0
11115217121CKKDUndevelopedSodium-chloride6.7<.05None1312.0
11115317121CKKDUndevelopedSodium-chloride4.7<.05None1232.5
05150219121CKKDUndevelopedSodium-sulfate4.5<.0521539.0
01140114121CKKDUrbanSodium-sulfate1.1.44None1512.5
01124015121CKKDUrbanSodium-NO2+NO31.714None2519.0
01140315121CKKDUrbanSodium-chloride3.41.412423.0
09050915121CKKDUrbanCalcium-sulfate8.81.7NoneNone325.0
07100418211MCVLUrbanIron-chloride-<.0563318.7
07100518211EGLSUrbanSodium-chloride.5<.0523413.6
05149819211MRSLUrbanMagnesium-chloride4.57.9None1626.0
05149919211MRPAUUrbanCalcium-bicarbonate.2<.05None1449.0
05150019211EGLSUrbanCalcium-chloride2.1.542None219.5
1Land use based on New Jersey Department of Environmental Protection 1986 ITU with subsequent field verification.
2Includes compounds with estimated concentrations, defined as positive detections of a compound, but measured as less than the laboratory's reporting levels.

 


Common Ions, Nutrients, and Trace Elements in, and Physical Characteristics of, Shallow Ground Water

Plots of selected constituent concentrations measured in ground-water samples collected throughout the Lower Delaware and Atlantic Coastal regions during August and September 2000, as a function of land-use designation, are shown in figures 12 through 15. Constituents with a high percentage of detections in the samples (greater than 75 percent) are presented in box plots (figs. 12a and 12b). Values reported by the analyzing laboratory as less than the MRL, or LRL if applicable, were included in each box plot but were reported as a value equal to one-half the MRL or LT-MDL. Constituents with a lower percentage of detections in the samples also are presented in scatter plots (figs. 14 and 15). The scatter plots include estimated values that were determined to be greater than the LT-MDL but less than the LRL. Refer to "Laboratory Measurements" in the Introduction for additional information about estimated concentrations. The trilinear diagrams in figures 13a, 13b, and 13c, and the "Water Type" column (column 5) in table 3 are grouped by land-use type and summarize the major ion chemistry of the water from each well.

The box plots highlight the differences in ground-water chemistry among wells located in areas with agricultural, undeveloped, and urban land-use designations. Median water temperature and median concentrations of hardness, total dissolved solids, chloride, manganese, iron, and organic carbon were lower in samples from wells in undeveloped areas than in those in other land-use areas (figs. 12a and 12b). Median concentrations of chloride and iron were greatest in samples from wells in urban areas. The median concentration of iron, for instance, was two orders of magnitude greater in samples from wells in urban areas than in samples from wells in undeveloped areas. The lowest median DO concentration, approximately 2 mg/L, was measured in water from wells in urban areas; the median concentration in water from wells in agricultural and undeveloped areas was from 4 to 5 mg/L. The highest median concentration of aluminum, 602 micrograms per liter (µg/L), was measured in samples from wells in undeveloped areas; the lowest median concentration, 65 µg/L, was measured in samples from wells in urban areas. The highest median concentrations of zinc, 19 µg/L, was measured in samples from wells in both undeveloped and urban areas. Agricultural practices appear to have the greatest effect on calcium and magnesium concentrations; the highest median concentration of hardness, 78 mg/L as calcium carbonate, was measured in samples from wells in agricultural areas.

Figure 12a. Distribution of selected constituents in filtered water in, and physical characteristics of, ground water from 30 sites in the Ambient Ground-Water-Quality Network, water year 2000. Figure 12b. Distribution of selected constituents in filtered water in, and physical characteristics of, ground water from 30 sites in the Ambient Ground-Water-Quality Network, water year 2000.
Figure 12a Figure 12b

 

Figure 13a. Trilinear diagram showing the distribution of major ions in ground-water samples from 14 sites in undeveloped land-use area in the Ambient Ground-Water-Quality Network, water year 2000. Figure 13b. Trilinear diagram showing the distribution of major ions in ground-water samples from seven sites in agricultural land-use area in the Ambient Ground-Water-Quality Network, water year 2000. Figure 13c. Trilinear diagram showing the distribution of major ions in ground-water samples from nine sites in urban land-use area in the Ambient Ground-Water-Quality Network, water year 2000.
Figure 13a Figure 13b Figure 13c

Concentrations of ammonia nitrogen were low in samples from all three land-use types (fig. 14). Frequencies of detection of concentrations above the MRL of 0.03 mg/L in samples from wells in urban, undeveloped, and agricultural areas were 33, 21, and 14 percent, respectively. The highest median nitrite plus nitrate concentration, 10.90 mg/L, was measured in samples from wells in agricultural areas; the lowest, 0.41 mg/L, was measured in samples from wells in undeveloped areas. The lowest frequency of detection, 14 percent, was for samples from wells in undeveloped areas. Frequencies of detection of concentrations of ortho-phosphorus above the MRL of 0.01 milligrams per liter in samples from wells in urban, undeveloped, and agricultural areas were 33, 0, and 29 percent, respectively.

The following trace elements were detected at concentrations greater than their respective reporting limits in samples from wells with all three land-use designations: arsenic, with an MRL of 0.9 µg/L; barium, MRL of 1.0 µg/L; chromium, LT-MDL of 0.4 µg/L; copper, MRL of 1.0 µg/L; and selenium, MRL of 0.7 µg/L (fig. 15). Barium was detected in 100 percent of the samples. Arsenic, chromium, copper, and selenium were detected most frequently in samples from wells in agricultural areas (57, 57, 86, and 86 percent of those wells, respectively). Cadmium was detected in just one sample from a well with an urban land-use designation. Lead was detected in four samples (three of the samples were from wells in agricultural areas), and mercury was detected in three samples (two of the samples were from wells in agricultural areas). Silver was not detected at any well and, therefore, is not included in the figure.

 

Figure 14. Concentration and frequency of detection of selected nutrients in filtered ground water from 30 sites in the Ambient Ground-Water-Quality Network, water year 2000. Figure 15. Concentration and frequency of detection of selected trace elements in filtered ground water from 30 sites in the Ambient Ground-Water-Quality Network, water year 2000.
Figure 14 Figure 15

 


Volatile Organic Compounds and Organic Pesticides in Shallow Ground Water

A list of the frequencies of detection of volatile organic compounds (VOC) detected in ground-water samples collected throughout the Lower Delaware and Atlantic Coastal regions is presented in table 4. Each sample was analyzed for the presence of 34 VOCs. Only VOCs detected in one or more samples are listed in table 4. Refer to individual station records to view concentrations of all 34 compounds in table form. Chloroform was the most frequently detected VOC (43 percent of all samples) in samples from wells in all land-use areas. The second most frequently detected VOC, Methyl tert-butyl ether (20 percent of all samples), was detected in samples from wells in urban and agriculture areas. The third most frequently detected VOC, Toluene, was detected in 1 of 14 samples from wells in undeveloped areas and in 1 of 9 samples from wells in urban areas. 1,4-Dichloropropane, cis-1,2-Dichloroethene, Dichlorobromomethane, Diisopropyl ether, tert-Pentyl methyl ether, and Tetrachloroethylene were each detected only once.

Table 4. Frequency of detection of volatile organic compounds detected in ground water at 30 sites in the Ambient Ground-Water-Quality Network.
[AG, agriculture; UR, urban; UN, undeveloped]
 SITE TYPE
CONSTITUENTAGURUN
1,4 Dichloropropane1 of 70 of 90 of 14
Chloroform2 of 73 of 98 of 14
cis-1,2 Dichloroethene0 of 71 of 90 of 14
Dichlorobromomethane1 of 70 of 90 of 14
Diisopropyl ether0 of 71 of 90 of 14
tert-Pentylmethyl ether0 of 71 of 90 of 14
Methyl tert-butyl ether1 of 75 of 90 of 14
Tetrachloroethylene0 of 71 of 90 of 14
Toluene0 of 71 of 91 of 14

 

Concentrations and frequencies of detection of organic pesticides in filtered ground-water samples collected throughout the Lower Delaware and Atlantic Coastal regions are shown in figure 16 (those most frequently detected) and listed in tables 5a (those with estimated concentrations) and 5b (those detected only once). Forty-seven compounds were analyzed for using USGS National Water Quality Laboratory schedule 2001; refer to "Laboratory Measurements" in the Introduction for the complete list. The plots include estimated values that were determined to be greater than the LT-MDL but less than the LRL. The most frequently detected pesticides in samples from wells in all land-use areas were Metolachlor (23 percent), Atrazine (20 percent), Deethylatrazine (17 percent), Simazine (10 percent), Prometon (10 percent), Alachlor, Carbaryl, Dacthal, and Diazinon (7 percent each). Ten widely used herbicides and four widely used insecticides were detected in samples from seven wells in agricultural areas. The most frequently detected herbicides in samples from wells in agricultural areas were Metolachlor (71 percent), Atrazine (57 percent), Deethylatrazine (57 percent), Alachlor (29 percent), Simazine (29 percent), and Dacthal or DCPA (29 percent). The insecticides Carbaryl, Diazinon, Dieldrin, and p,p-DDE were each detected once in samples from wells in agricultural areas. Six widely used herbicides and two widely used insecticides were detected in samples from nine wells in urban areas. The most frequently detected herbicides in samples from wells in urban areas were Atrazine, Metolachlor, and Prometon (22 percent each); the insecticides Carbaryl and Malathion were each detected once. Diazinon, an insecticide, and Propanil, an herbicide, were the only two compounds detected in samples from wells in undeveloped areas.

Table 5a. Frequency of detection of pesticides in filtered ground water at 30 sites in the Ambient Ground-Water-Quality Network.
[All values are estimated due to poor recovery or poor precision; AG, agriculture; UR, urban; UN, undeveloped]
 SITE TYPE
CONSTITUENTAGURUN
Carbaryl1 of 71 of 90 of 14
Dacthal2 of 70 of 90 of 14
Deethylatrazine4 of 71 of 90 of 14
Diazinon1 of 70 of 91 of 14
Prometon1 of 72 of 90 of 14

Table 5b. Pesticide concentrations in filtered water, detected only once, at selected sites in the Ambient Ground-Water-Monitoring Network.
[AG, agricultural; UR, urban; UN, undeveloped; E, estimated]
CONSTITUENTCONCENTRATION
(micrograms per liter)
SITE TYPE
Dieldrin0.0134AG
EPTC0.031AG
MalathionE.0037UR
Molinate0.0126AG
p,p´-DDEE.0026AG
Pebulate0.0194UR
PropanilE.0034UN
Tebuthiuron0.0272AG

 

Figure 16. Concentration and frequency of detection of pesticides in filtered ground water from 30 sites in the Ambient Ground-Water-Quality Network, water year 2000.
Figure 16

 

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