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Summary of Annual Hydrologic Conditions - 1999

Volume 3: Water-Quality

Surface Water-Quality

Three major climatic events affected the quantity and quality of New Jersey streams during the 1999 water year, October 1, 1998 to September 30, 1999--the drought during October 1998 through December 1998 (which began in August 1998), the drought of April 1999 to September 1999, and the drought-breaking rainfall of tropical storm Floyd on September 16, 1999. According to the Northeast Regional Climate Center of Cornell University, Climate Impacts-October, November, and December 1998, average rainfall amounts for those months were 76, 35, and 38 percent of normal, respectively. The following monthly average rainfall amounts, in percent of normal, were measured during the year's second drought: April, 64 percent; May, 75 percent; June, 52 percent; July, 41 percent; August, 117 percent. Also, the three National Weather Service monthly precipitation index stations--South Branch Raritan River near High Bridge, Great Egg Harbor River at Folsom, and Delaware River at Trenton (figure 1)--generally recorded below-average rainfall amounts for November, December, April, May, June, and July. In contrast, September 1999 was the second wettest September in 105 years of record. Statewide average rainfall was 9.4 inches (250 percent of normal) due, in large part, to the tropical storm. Monthly rainfall totals for September were well above normal at the three index stations (fig. 1).

Monthly-mean stream flows at the three index stations demonstrate the effects of the droughts and the tropical storm (fig. 2). Below-normal stream flows were recorded during October to December and April to August. The monthly mean flows for December at High Bridge and Folsom were less than the minimum monthly means for 81 and 74 years of record, respectively. The tropical storm in September was the main cause of above-normal stream-flow conditions at the three index stations for that month.

Drought conditions adversely affect the concentrations of trace elements, nutrients, organic compounds, and aquatic organisms because the low flow lessens the beneficial effects of dilution. This is evident in the inverse relationship between specific conductance and discharge. During the fall and winter drought, the monthly-mean specific conductance measured at the continuous monitoring station on the Delaware River at Trenton (01463500) consistently exceeded the 30-year maximum-monthly means (fig. 3). The November 1998 mean value of 233 µS/cm, the December 1998 mean of 228 µS/cm, and the January 1999 mean of 238 µS/cm exceeded the historical maximum-monthly means of 224 µS/cm, 214 µS/cm, and 237 µS/cm, respectively. The second drought during April to September 1999 continued the trend of above-normal monthly-mean values of specific conductance, but none of those values exceeded previously established maximums.

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 instantaneous peak for specific conductance for the year measured during January at the station on the Delaware River at Trenton was 468 µS/cm. The unusually high value was probably the result of the application of road salt, exacerbated by low-flow conditions. Similarly, specific conductance exceeded historical maximum-instantaneous values at the continuous monitoring stations at the Passaic River below Pompton River at Two Bridges (01389005) and the Ramapo River at Pompton Lakes (01388000) (records are listed in the water-quality tables).

The beneficial effects of dilution, as measured by specific conductance, can be seen during the relatively wet periods of January, February, and September 1999. According to Climate Impacts-January and February 1999, rainfall in January was 227 percent of normal and in February, 91 percent. Mean specific conductance for February, measured at the continuous monitoring station at Trenton, was 158 µS/cm; the 30-year mean was 170 µS/cm. Rainfall in September was 250 percent of normal, in large part, as a result of the 6.22 inches (measured in Newark) that fell during tropical storm Floyd on September 16. Following this event, new minimum-instantaneous values of specific conductance for the period of record were recorded at the Pompton Lakes and Two Bridges continuous-monitoring stations.

The drought, as well as the high ambient air temperatures experienced during July through September 1999, also affected water temperature. According to Climate Impacts, 1998 was the warmest year on record for the northeast region. The region's average temperature of 49.8 °C for the year exceeded the previous record of 49.5 °C set in 1953. Temperatures followed the same trend during January to March 1999 and May to September 1999. This is evident at the monitoring station on the Delaware River at Trenton where the monthly-mean water temperatures recorded throughout the year exceeded or equaled the 30-year mean, except in January (fig. 4). The monthly mean of 5.7 °C for December 1998 exceeded the 30-year maximum-monthly mean of 5.5 °C. The monthly mean of 28.1 °C for July 1999 exceeded the 30-year maximum-monthly mean of 27.8 °C. In July, record heat and drought conditions combined to set new maximum instantaneous water-temperature values for the period of record at the Pompton Lakes and Two Bridges monitoring stations.

Dissolved oxygen (DO) concentrations generally exhibit an immediate inverse relation to water temperature; as water temperature increases, oxygen concentration decreases. In streams that exhibit oligotrophic characteristics (low amounts of plant nutrients and abundant DO), yearly maximums for DO occur during winter, and yearly minimums occur during summer. At the Trenton monitoring station on the Delaware River, the monthly median of daily maximum values for November 1998 of 15.1 mg/L equaled the 30-year high (fig. 5). At the monitoring station on the Ramapo River at Pompton Lakes, the minimum instantaneous DO value for the period of record was recorded in early August when air temperatures were highest and stream flows were lowest. In streams that exhibit eutrophic characteristics (high amounts of plant nutrients, high algae populations, and resultant high algal respiration), photosynthesis drives DO concentrations to maximum values during daylight hours in summer. This process is noticeable in the DO data for Two Bridges, where DO concentrations reached the upper limit of the monitoring instrument (20.0 mg/L) on many days during the heat spell during July through September. High concentrations of DO occurred more frequently during this period because of drought conditions.

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 103 sites in the U.S. Geological Survey (USGS)/New Jersey Department of Environmental Protection (NJDEP) Cooperative Ambient Stream Monitoring Program (ASMP). Samples were collected at each site four times a year--November to December, February to March, May to June, and August to September. Sites are sorted into five categories. Six Background sites are located in undisturbed areas. Twenty-two Watershed Integrator sites are 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 reflect the cumulative effects of various land uses and point-source discharges. Land-use Indicator sites monitor the effects of the dominant land use in each watershed management area. Fifteen of the Indicator sites are designated agriculture, 13 forest, and 12 urban. Every year two randomly selected Statewide-Status sites are located within each of the 20 watershed management areas. Surface-water samples are collected at each site to assess water-quality constituents that may be used as environmental indicators statewide. Watershed Reconnaissance sites are selected annually according to specific project needs. The purpose of the Watershed Reconnaissance in water year 1999 was to assess the level of nutrients in bed sediments at a subset of the Land-use Indicator sites.

Distributions of constituent concentrations measured in water-column samples collected during water year 1999 are presented in figures 6a and 6b as a function of the Land-use Indicator type. Box plots are presented for dissolved oxygen in percent of saturation during the growing season, water temperature, silica in filtered water, total ammonia, nitrite plus nitrate in filtered water, total nitrogen, total phosphorus, BOD, boron in filtered water, total dissolved solids (parameter code 70300), and filtered organic carbon. Values reported by the analyzing laboratory as less than the minimum reporting level (MRL) are included in each distribution, but are reported as a value equal to one-half the MRL.

Figure 5. Figure 6a. Distribution of dissolved
oxygen, water temperature, filtered
silica, total ammonia, and filtered
nitrite plus nitrate in surface
water by land-use designation.
Figure 6b. Distribution of total nitrogen,
total phosphorus, biochemical oxygen
demand, filtered boron, total dissolved
solids, and filtered organic carbon in
surface water by land-use designation.
Figure 6a Figure 6b

The box plots for the nutrient species (ammonia, nitrite plus nitrate, total nitrogen, and total phosphorus) seem to indicate that human activities are the greatest contributors to measurable nutrient levels in streams. The highest median concentrations of ammonia and phosphorus were measured at agricultural land use, urban land use, and Integrator site types, and most likely result from private, industrial, and municipal sewage; animal waste; and chemical fertilizers. Land disturbances and diffuse non-point sources may account for the high median concentrations of nitrite plus nitrate and total nitrogen at forest and Status sites. As expected, Background sites have the smallest ranges of concentrations and the lowest median concentrations.

Concentrations of boron in filtered water also show the effects of human activities. Urban land-use sites, where household wastewater containing soaps and detergents is a major source, have the highest median concentrations. The distribution of silica in filtered water is uniform among all sites types and land uses, which demonstrates the abundance of silica in the environment.

The correlation between BOD and dissolved oxygen is demonstrated in figures 6a and 6b. BOD is a measurement of the amount of organic matter, dissolved and suspended in water, available for oxidation. Concentrations of BOD should be high in streams affected by human activity. As BOD levels increase, the consumption of DO increases, leaving less DO available to aquatic organisms. Background, forest, and agricultural site types that are unaffected by human activities generally exhibit higher median concentrations of DO and lower median concentrations of BOD. Urban sites exhibit the opposite trend, indicating the effects of human activities.

The range of filtered organic carbon in New Jersey streams historically has been from 4.0 to 5.0 mg/L. Median values measured during water year 1999 ranged from 2.5 to 4.0 mg/L. Forest site types usually have streams that drain swamps and wetlands and generally have the highest concentrations of filtered organic carbon concentrations ranging 5 to 60 mg/L. Accordingly, the box plot for concentrations in forest areas shows the widest range and greatest concentrations of filtered organic carbon.

Streams affected by wastewater and road salt runoff are likely to have higher levels of total dissolved solids (TDS). This is evident in the plot of TDS concentrations for urban and Integrator sites, which have the highest median concentrations. In contrast, Background sites have the lowest median values.

 

Whole-Water-Recoverable Trace Elements, Volatile Organic Compounds, and Filtered Organic Pesticides in New Jersey Streams

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

Plots showing concentrations and lists of frequencies of detection of whole-water-recoverable trace elements, volatile organic compounds (VOCs), and pesticides, at Background and Statewide-Status sites are presented in figures 7, 8, and 9; concentrations are listed in tables 1, 2a, and 2b. The six Background sites are located in relatively pristine areas of New Jersey, such as state forests or national parks. Water-quality data from those 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. Collection of water-column trace-element samples during August and September coincided with the collection of bed-sediment trace-element samples during low-flow conditions. Volatile-organic-compound and pesticide samples were collected when the compounds were most likely to be detected, during February and March, and May and June, respectively. For the purpose of analysis, only detected compounds present in one or more samples are shown in the figures. A detected compound is one whose value is reported to be greater than or equal to the laboratory's MRL. Estimated values are also included in the figures and are marked with an "E" in the water-quality tables. These values are greater than the long-term method detection level, but less than the MRL. Refer to "Laboratory Measurements" in the "Explanation of Records" for additional information about estimated concentrations.

Concentrations and frequencies of detection of whole-water-recoverable trace elements in New Jersey streams are shown in figure 7. Iron and manganese are not included because they are naturally abundant in the environment. Barium, beryllium, cobalt, mercury, and silver were not detected in any sample and, therefore, were not included. The data collected at Background sites indicate the natural occurrence and low concentrations of trace elements found in relatively undisturbed areas; of the nine trace elements presented, arsenic, boron, copper, lead, and nickel were detected only once. In contrast, these trace elements were detected in greater concentrations and frequencies at Statewide-Status sites. Although the following trace elements are naturally occurring at low levels in the environment, the concentrations detected in New Jersey streams could result from the indicated practices: arsenic from industrial-waste disposal and pesticide application; boron from household-waste disposal; cadmium from fertilizer application, fossil-fuel combustion, battery disposal, paint weathering, and industrial-waste disposal; chromium from fuel combustion, waste incineration, and metallurgical operations; copper, lead, and zinc leached from plumbing materials and carried by household wastewater; and nickel from metallurgical operations (Shelton, 5th edition).

Plots of the concentrations and frequencies of detection of VOCs in New Jersey streams are shown in figure 8 and are listed in table 1. Of the 10 compounds detected, only 2, chloroform and methyl tert-butyl ether (MTBE), were detected at Background sites in low concentrations. The presence of the two VOCs at both Background and Statewide-Status sites indicates how widespread these two compounds are in New Jersey streams. The following synthetic chlorinated compounds and MTBE do not exist in the natural environment, but are manmade for the indicated uses: 1,1-dichloroethane, industrial degreaser; 1,2-dichloroethylene, limited use as a solvent and preservative; tetrachloroethylene, dry cleaning solvent and industrial degreaser; 1,1,1-trichloroethane, industrial solvent and cleaner; trichloroethylene, industrial solvent, household cleaner, and additive in paints, varnishes, inks, and adhesives; and MTBE, gasoline additive (Shelton, 5th edition). The most frequently detected VOC, MTBE, was detected at 80 percent of all sites sampled, including five of the Background sites. The next most frequently detected VOC, chloroform, was detected at 23 percent of all sites sampled.

Table 1

 

Figure 7. Concentration and
frequency of detection of selected
whole-water-recoverable
trace elements.
Figure 8. Concentration and
frequency of detection of volatile
organic compounds.
Figure 7 Figure 8

Plots of the concentrations and frequencies of detection of organic pesticides detected in filtered water in New Jersey streams are shown in figure 9 and are listed in tables 2a and 2b. Forty-seven compounds were analyzed for using laboratory schedule 2001 (refer to the section titled "Explanation of the Records for the complete list). Of these, 26 were detected in one or more samples--25 at Statewide-Status sites, 8 at Statewide-Status and Background sites, and 1 at a Background site. Eight of the detected compounds are insecticides--chlorpyrifos, diazinon, carbaryl, carbofuran, azinphos-methyl, dieldrin, malathion, and the degradation product P,P`-DDE. The remaining compounds are herbicides. The pesticides most frequently detected in the 45 samples collected were metolachlor in 73 percent of the samples, atrazine in 67 percent, prometon in 56 percent, carbaryl and deethyl-atrazine in 49 percent, and simazine in 47 percent. Three widely used herbicides (metolachlor, atrazine, and deethyl-atrazine) were present at one or more Background sites. Their presence in relatively pristine areas indicates that wind currents and precipitation are potential modes of transport. One or more pesticides were detected at 29 of 39 (74 percent) of Statewide-Status sites. The pesticides that were frequently detected throughout the state were present in low concentrations.

Table 2a Table 2b

 

Figure 9. Concentration and
frequency of detection of
pesticides in filtered water.
Figure 10. Distribution of
ammonia plus organic nitrogen,
ammonia, phosphorus, and inorganic
plus organic carbon measured
in samples of bed material.
Figure 9 Figure 10

Distributions of concentrations of nutrients in stream-bed sediments are presented in figure 10 as a function of land use. The data were collected at 2 Background and 8 Land-use Indicator sites in water year 1998 and at 2 Background and 34 Land-use Indicator sites as part of the Watershed Reconnaissance study in water year 1999. Too few samples were collected from Background sites to present the distribution of concentrations in a box plot; therefore, the Background-site data are presented as scatter plots (fig. 10). The nutrients included in figure 10 are ammonia plus organic nitrogen, ammonia, phosphorus, and inorganic carbon plus organic carbon. Concentrations reported by the analyzing laboratory as less than the MRL are included in each summary, but are reported as equal to one-half the MRL. The highest median concentrations for the four nutrients occurred in the agricultural land-use type; however, because of the large variation in nutrient concentrations, as indicated by the 25th and 75th percentile concentrations at forest, agricultural, and urban land-use sites and the range at background sites, the concentrations at agricultural land-use sites may not be statistically different from the concentrations at other land-use and background sites.

 

Groundwater-Quality

The Ambient Ground-Water 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 was established to achieve 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 ground-water wells distributed randomly throughout New Jersey within three land-use types. Sixty wells are in agricultural areas, 60 in urban/suburban areas, and 30 in undeveloped areas within New Jersey's five watershed management regions (WMRs)--the Passaic, the Raritan, the Upper Delaware, the Lower Delaware, and the Atlantic Coastal. These five WMRs are divided into 20 watershed-management areas. Every year approximately 30 sites are sampled in one of the five WMRs. The full cycle of 150 wells is completed in five years.

Thirty shallow wells were sampled in 1999. Twenty-eight wells are located in the Lower Delaware Region of New Jersey and are randomly distributed throughout WMAs 17-20 (fig. 11). Two wells are located in the Atlantic Coastal Region, one well in WMA 15 and one in WMA 16. Twenty wells have open, screened, intervals in the Kirkwood-Cohansey aquifer system, two in the Vincentown aquifer, one in the Wenonah-Mt. Laurel aquifer, two in the Hornerstown formation, three in the Englishtown aquifer, one in the Manasquan formation, and one in the Marshalltown formation (table 3). The wells have polyvinyl-chloride casings, range from 10 to 51 feet in depth, and have open intervals within the outcrop areas of the individual aquifers listed above. Most of the wells were drilled within the last 3 years. Samples from the wells were analyzed for physical characteristics, major ions, nutrients, trace elements, organic constituents, and gross alpha and beta radioactivity.

Figure 11. Location of Ambient
Ground-Water Quality Network
sampling sites in the
Lower Delaware Region.
Figure 11

 

Table 3

 

Filtered Nutrients, Common Ions, and Physical Properties in Shallow Ground Water

Distributions of constituent concentrations measured in ground-water samples collected during late August and September 1999 as a function of land-use designation are shown in figures 12a and 12b. The plots include statistics for dissolved oxygen, water temperature, hardness, filtered ammonia, filtered nitrite plus nitrate, filtered ortho-phosphorus, total dissolved solids (parameter code 70300), and filtered organic carbon. Values reported by the analyzing laboratory as less than the MRL are included in each distribution, but are reported as a value equal to one-half the MRL. Trilinear diagrams show the distributions of major cations and anions in water samples collected from the 30 wells (figs. 13a, b, and c). The diagrams are grouped by the dominant land use around each well.

Figure 12a. Distribution of dissolved
oxygen, water temperature, hardness,
filtered ammonia, and filtered nitrite
plus nitrate in ground water.
Figure 12b. Distribution of filtered
ortho-phosphorus, total dissolved
solids, and filtered organic carbon
in ground water.
Figure 12a Figure 12b

Box plots show that the highest median values of hardness (fig. 12a) and total dissolved solids (fig. 12b) were measured at sites located in agricultural areas. Calcium or magnesium, both contributors to hardness is the dominant cation at 14 sites in agricultural areas. To counteract acidity resulting from the nitrification process, farmers usually apply calcium and magnesium to their fields. Acidification results from the release of hydrogen ions when ammonia is oxidized to nitrite, then nitrate, in the presence of oxygen and nitrifying bacteria. Sodium is the dominant cation at the remaining seven agricultural sites (table 3). The box plots also show that forest land-use sites have the lowest concentrations of hardness and total dissolved solids. Forested sites have lower percentages of calcium and magnesium than other land-use sites (fig. 13a).

Nitrification, the aerobic processes that convert ammonia to nitrate, was occurring at all land uses and is indicated by the plots for ammonia, nitrite plus nitrate, and dissolved oxygen (fig. 12a). Low median values of ammonia and high median values of nitrite plus nitrate correlate with high median values of dissolved oxygen. In anaerobic conditions, nitrification does not proceed: ammonia does not convert to nitrite then to nitrate. The five highest ammonia values, 0.03 to 0.37 mg/L, are related to low dissolved oxygen values, 0.2 to 2.7 mg/L, and low nitrite plus nitrate values, <0.05 mg/L.

Figure 13a. Trilinear diagram
showing the distribution of
major ions in ground water from
two wells sampled in forest
land-use areas in water 1999.
Figure 13b. Trilinear diagram
showing the distribution of
major ions in ground water from
21 wells sampled in agricultural
land-use areas in water 1999.
Figure 13c. Trilinear diagram
showing the distribution of
major ions in ground water from
five wells sampled in urban
land-use areas in water 1999.
Figure 13a Figure 13b Figure 13c

Differences in ground-water temperatures due to land use were not expected. Median values of water temperature in urban areas, however, were appreciably higher and had a smaller range than those in the agricultural and forested areas. The higher water temperatures found in urban areas could be the result of direct solar radiation and indirect radiation from buildings and paved areas. Although the water temperatures in agricultural and forest areas were comparable, the lowest median water temperatures were found in forest land-use areas and probably could be attributed to the natural tree canopy that shields the ground from solar radiation.

The highest median concentration of dissolved oxygen was measured in samples from wells in agricultural areas that are likely to contain well-drained and well-oxygenated soils. The lowest concentrations of dissolved oxygen were measured in forested areas where soils are likely to be rich in organic matter. Bacteria consume oxygen during the decomposition of organic matter.

No correlation was apparent for filtered organic carbon and land use. The median concentrations for all three land uses were about 1.0 mg/L.

 

Filtered Trace Elements, Volatile Organic Compounds, and Filtered Organic Pesticides in Shallow Ground Water

Plots of the concentrations and frequencies of detection of filtered trace elements in shallow ground water throughout the Lower Delaware Region are shown in figure 14. The plots include estimated values that were determined to be greater than the long-term method-detection level, but less than the MRL. Aluminum, iron, and manganese are not included because they are naturally abundant. No detections were reported for mercury or silver in any sample. Neither lead nor cadmium was detected in samples from wells located in predominantly urban land-use areas, although detections were expected. Barium, chromium, copper, and zinc were detected in all land-use types. The following trace elements were detected at similar frequencies in samples from wells in all three land uses. Barium was detected in 100 percent of wells, chromium in 33 to 40 percent, selenium in 29 to 40 percent, and zinc in 60 to 67 percent. Except for lead and cadmium, land use probably plays a minor role in the frequency of occurrence of filtered trace elements in the shallow ground-water systems of this region.

Figure 14. Concentration and
frequency of detection of selected
trace elements, in filtered water,
at 29 ground-water sites.
Figure 14

 

DA list of the frequencies of detection of volatile organic compounds (VOC) detected in shallow ground water throughout the Lower Delaware Region is presented in table 4. Eight of the 30 samples were analyzed for additional VOCs (laboratory schedule 2020); the VOCs analyzed for are listed with MRL's in the section titled "Explanation of Records". Chloroform was the most frequently detected VOC (23 percent of wells) at all predominant land-use types followed by MTBE (20 percent), toluene (17 percent), and tetrachloroethylene (10 percent). Chloroform, toluene, MTBE, and tetrachloroethylene were detected at 23, 18, 14, and 9 percent, respectively, of the 22 wells in agricultural areas. Chloroform and MTBE were detected at 40 percent of the five wells in urban areas. MTBE was the only VOC detected at any of the three wells in forested areas. The most frequently detected VOCs and the ranges of concentrations were: chloroform, 0.016 to 0.395 µg/L; MTBE, 0.200 to 8.44 µg/L; toluene, 0.005 to 0.200 µg/L; and tetrachloroethylene, 0.0129 to 0.4870 µg/L.

Table 4

Concentrations and frequencies of detection of pesticides detected in shallow ground water throughout the Lower Delaware region are presented in figure 15 and tables 5a and 5b. Estimated values are included. Forty-seven pesticides were analyzed using schedule 2001 (refer to the section titled "Explanation of Records" for the complete list). The most frequently detected pesticides at all site types were deethylatrazine (47 percent), atrazine (43 percent), simazine (37 percent), metolachlor (33 percent), prometon (20 percent), and P,P`-DDE (17 percent). Five widely used herbicides (deethylatrazine, atrazine, metolachlor, simazine, and prometon) and one insecticide (P,P`-DDE) were detected at 50, 45, 45, 36, 14, and 14 percent of 22 wells in agricultural areas, respectively. Deethylatrazine, atrazine, prometon, and simazine were detected at 60 percent of the five wells in urban areas. P,P`-DDE was detected in 20 percent of 5 wells in urban areas, and 33 percent of 3 wells in forested areas; it was the only pesticide detected in forested areas. The compounds most frequently detected in shallow ground-water samples--deethylatrazine, atrazine, simazine, metolachlor, and prometon--were also the most frequently detected in surface-water samples.

Figure 15. Concentration and
frequency of detection of pesticides
in filtered water detected
at 30 ground-water sites.
Figure 15

 

Table 5a Table 5b

 

Saltwater-Monitoring Network

The potability of ground water in the Coastal Plain of New Jersey depends primarily on its chemical quality, including contamination with saltwater. Chloride concentration is an accurate index of the extent and degree of saltwater contamination. The presence of high concentrations of chloride, however, is not definitive proof of active saltwater intrusion; high concentrations may represent a natural, static condition. Saltwater intrusion can be documented by analysis of periodically collected water samples. Saltwater intrusion is indicated by increases in chloride concentration over time rather than by a single concentration measured at one point in time.

In the 1940's, the USGS established a saltwater-monitoring network in the Coastal Plain of New Jersey to document the movement of saltwater into the freshwater aquifers. The USGS collects and analyzes water samples from USGS and NJDEP observation wells and selected domestic and agricultural supply wells. Chloride measurements are augmented by chloride-concentration data reported to the NJDEP by owners of public and industrial supply wells. During the 1999 water year, the USGS sampled water from forty-one wells in six counties. Chloride concentrations in these samples were supplemented by more than 6,000 values that were reported by hundreds of public and industrial supply well owners and are stored in NJDEP and USGS files.

During the 1999 water year, saltwater intrusion was evident in many communities along Raritan Bay, the Atlantic Coast, the Delaware Bay, and the lower Delaware River, and in central Gloucester County.

 

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