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USGS1997

Natural attenuation of chlorinated volatile organic compounds in a freshwater tidal wetland, Aberdeen Proving Ground, Maryland

Ground-water contaminant plumes that are flowing toward or currently discharging to wetland areas present unique remediation problems because of the hydrologic connections between ground water and surface water and the sensitive habitats in wetlands. Because wetlands typically have a large diversity of microorganisms and redox conditions that could enhance biodegradation, they are ideal environments for natural attenuation of organic contaminants, which is a treatment method that would leave the ecosystem largely undisturbed and be cost effective. During 1992-97, the U.S. Geological Survey investigated the natural attenuation of chlorinated volatile organic compounds (VOC's) in a contaminant plume that discharges from a sand aquifer to a freshwater tidal wetland along the West Branch Canal Creek at Aberdeen Proving Ground, Maryland. Characterization of the hydrogeology and geochemistry along flowpaths in the wetland area and determination of the occurrence and rates of biodegradation and sorption show that natural attenuation could be a feasible remediation method for the contaminant plume that extends along the West Branch Canal Creek. The aquifer, which received contaminants in the past from sources that were located upgradient of the current eastern boundary of the wetland, is about 40 to 45 feet thick in the study area. The overlying wetland sediments consist of two distinct layers that have a combined thickness of about 6 to 12 feet--an upper unit of peat and a lower unit of silty to sandy clay or clayey sand. Head distributions show strong vertical gradients, and flow directions are predominantly upward through the wetland sediments. Tidal fluctuations, however, cause some reversals in ground-water-flow directions and changes in discharge locations, which affect the distribution and transport of contaminants. The average linear velocity of ground water is estimated to be about 2 to 3 feet per year along vertical flow lines in the wetland area, and the total ground-water discharge along a 1-foot-wide strip of the wetland extending from the eastern wetland boundary to the creek is in the range of 0.13 to 0.25 feet squared per day. The major parent contaminants in the aquifer were trichloroethylene (TCE); 1,1,2,2-tetrachloroethane (PCA); carbon tetrachloride (CT); and chloroform (CF). The aquifer was typically aerobic, but ground water in the wetland sediments became increasingly anaerobic along the upward flow direction. Iron-reducing conditions were predominant in the lower wetland sediment unit composed of clayey sand and silt, and methanogenesis was predominant in an upper unit composed of peat. Total concentrations of VOC's and the relative proportions of parent compounds to anaerobic daughter products changed substantially as the contaminants were transported upward through these changing redox environments. Concentrations of the parent compounds TCE and PCA ranged from about 100 to 2,000 micrograms per liter in the aquifer beneath the wetland, whereas concentrations of daughter products were low or undetectable. In contrast, the parent compounds commonly were not detected in ground water in the wetland sediments, but the daughter compounds 1,2- dichloro-ethylene (12DCE), vinyl chloride (VC), 1,1,2-trichloroethane (112TCA), and 1,2-dichloroethane (12DCA) were observed. 12DCE and VC were the dominant daughter products in the wetland sediments, even where PCA was the primary parent contaminant discharging to the wetland. The presence of these daughter products in water in the wetland sediments indicates that TCE and PCA are degraded by reductive dechlorination reactions in the naturally anaerobic wetland sediments. Although production of daughter products was observed, total concentrations of the VOC's decreased upward through the 6- to 12-feet-thick wetland sediments and were less than 5 micrograms per liter near the surface. The daughter products are apparently further degraded by these anaerobic processes to non-chlorinated, non-toxic endproducts, or are removed by other attenuation processes such as aerobic degradation or volatilization. Several sets of anaerobic microcosms, some amended with TCE concentrations of 400 or 990 micrograms per liter (3.0 or 7.5 micromoles per liter) and one amended with PCA concentration of 480 micrograms per liter (2.9 micromoles per liter), were constructed in the laboratory using wetland sediment and ground water from the study area. These microcosm experiments confirmed field observations that 12DCE and VC are the dominant daughter products from anaerobic biodegradation of both TCE and PCA. Production of 112TCA and 12DCA also was observed in the PCA-amended microcosms, but concentrations were lower than those of 12DCE and VC. These results indicate that degradation of PCA occurs through both hydrogenolysis and dichloroelimination pathways under anaerobic conditions. Daughter products were not observed in sterile controls, except for relatively low concentrations of 12DCE in the PCA-amended controls, suggesting that the reactions were predominantly microbially mediated. Parent and daughter concentrations in the microcosms decreased to less than 5 micrograms per liter in less than 34 days under methanogenic conditions, thus showing extremely rapid biodegradation rates in these organic-rich wetland sediments. Maximum potential rate constants for biodegradation of TCE and PCA, which were calculated from the microcosm exper-iments assuming first-order degradation rates, ranged from 0.10 to 0.31 per day under methanogenic conditions, corresponding to half-lives of 2 to 7 days. The rate constant for TCE biodegradation under sulfate-reducing conditions was 0.045 West Branch, Aberdeen Proving Ground, Maryland 3 per day (half-life of 15 days), which is lower than under methanogenic conditions. These estimated rate constants for the wetland sediments are two to three orders of magnitude higher than those reported in the literature for TCE biodegradation in microcosms constructed with sandy aquifer sediments. Aerobic biodegradation rates for cis-12DCE, trans-12DCE, and VC were in the same range as those measured for TCE and PCA under anaerobic conditions in microcosm experiments. Thus, production of these daughter products by anaerobic biodegradation of TCE and PCA could be balanced by their consumption where oxygen is available in the wetland sediment, such as near roots and land surface. In the aerobic microcosm experiments, biodegradation of cis-12DCE, trans-12DCE, and VC occurred only if methane consumption occurred, indicating that methanotrophs were involved in the process. Aerobic biodegradation was fastest for vinyl chloride and slowest for TCE in the microcosm experiments. These results agree with other laboratory and field studies that have shown faster degradation by methane-utilizing cultures when the compounds are less halogenated. Equilibrium sorption isotherms were measured in 24-hour batch tests and used to estimate distribution coefficients ( K d 's) to describe the ratios of sorbed to aqueous concentrations of PCA and the daughter products cis-12DCE, trans-12DCE, and VC. The estimated K d's for PCA, cis-12DCE, trans-12DCE, and VC were about 2.3, 1.8, 2.4, and 1.3 liters per kilogram of sediment, respectively. Sorbed concentrations of PCA, cis-12DCE, and trans-12DCE in the wetland sediments, therefore, would be expected to be about twice the concentration measured in the water, whereas sorbed concentrations of VC would not be much greater than the aqueous concentrations. Coefficients of retardation, which were calculated using the K d 's and an advective flow velocity of about 2 feet per year, indicate that sorption alone would cause the movement of the contaminants in the wetland sediments to be 6 to 10 times slower than the advective ground-water flow. Biodegradation and sorption, therefore, are significant natural attenuation mechanisms for chlorinated hydrocarbons in these wetland sediments. The relatively thin layers of wetland sediments are critical in reducing contaminant concentrations and toxicity of the ground water before it discharges to the wetland surface and the creek, and natural attenuation in the wetland sediments could be an effective remediation method for the ground-water contaminants.

Maryland↗
USGS1999

External quality-assurance results for the National Atmospheric Deposition Program/National Trends Network, 1995-96

The U.S. Geological Survey operated four external quality-assurance programs for the National Atmospheric Deposition Program/National Trends Network (NADP/NTN) in 1995 and 1996: the intersite-comparison program, the blind-audit program, the interlaboratory- comparison program, and the collocated-sampler program. The intersite-comparison program assessed the precision and bias of pH and specific-conductance determinations made by NADP/NTN site operators. The analytical bias introduced during routine handling, processing, and shipping of wet-deposition samples and precision of analyte values was estimated using a blind-audit program. An interlaboratory-comparison program was used to evaluate differences between analytical results and to estimate the analytical precision of five North American laboratories that routinely analyzed wet deposition. A collocated-sampler program estimated the precision of the overall precipitation collection and analysis system from initial sample collection through final storage of the data. Results of two intersite-comparison studies completed in 1995 indicated 94.6 and 94.4 percent of the onsite pH determinations met the NADP/NTN accuracy goals, whereas 97.2 and 98.3 percent of the specific-conductance determinations were within the established limits. The percentages of onsite determinations that met the accuracy goals in 1996 were slightly less for both pH and specific-conductance than in 1995. In 1996, 93.2 and 87.5 percent of onsite pH determinations met the accuracy goals, whereas the percentage of onsite specific-conductance measurements that met the goals was 93.9 and 94.9 percent.The blind audit program utilizes a paired sample design to evaluate the effects of routine sample handling, processing and shipping on the chemistry of weekly precipitation samples. The portion of the blind audit sample subject to all of the normal onsite handling and processing steps of a regular weekly precipitation sample is referred to as the bucket portion, whereas the portion receiving only minimal handling is referred to as the bottle portion. Throughout the report, the term positive bias in regard to blind-audit results indicates that the bucket portion had a higher concentration than the bottle portion. The paired t-test of 1995 blind-audit data indicated that routine sample handling, processing, and shipping introduced a very small positive bias (a=0.05) for hydrogen ion and specific conductance and a slight negative bias (a =0.05) for ammonium and sodium. In 1995, the median paired differences between the bucket and bottle portions ranged from -0.02 milligram per liter for both ammonium and nitrate to +0.002 milligram per liter for calcium. Although the paired t-test indicated a very small positive bias for hydrogen ion, the median paired difference between the bucket and bottle portions was 0.00 microequivalents per liter, whereas for specific conductance, the median paired difference between the bucket and bottle portions was 0.200 microsiemens per centimeter in 1995. The paired t-test of blind-audit results in 1996 indicated statistically significant bias for 6 of the 10 analytes. Only chloride, nitrate, hydrogen ion, and specific conductance were not biased in 1996. However, the magnitude of the bias in 1996 was very small and only of limited importance from the viewpoint of an analytical chemist or data user. The median paired differences between the bucket and bottle portions ranged from -0.02 milligram per liter for both ammonium and chloride to +0.006 milligram per liter for calcium. For hydrogen ion, the median paired difference between the bucket and bottle portions was -0.357 microequivalent per liter; for specific conductance, the median paired difference between the bucket and bottle portions was 0.00 microsiemens per centimeter in 1996. Surface-chemistry effects due to different amounts of precipitation contacting the sample collection and shipping container surfac

Water-Resources Investigations Report↗
USGS2002

Natural attenuation of chlorinated volatile organic compounds in ground water at Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington

The U.S. Geological Survey (USGS) evaluated the natural attenuation of chlorinated volatile organic compounds (CVOCs) in ground water beneath the former landfill at Operable Unit 1 (OU 1), Naval Undersea Warfare Center, Division Keyport, Washington. The predominant contaminants in ground water are trichloroethene (TCE) and its degradation byproducts cis-1,2-dichloroethene (cisDCE) and vinyl chloride (VC). The Navy planted two hybrid poplar plantations on the landfill in spring of 1999 to remove and control the migration of CVOCs in shallow ground water. Previous studies provided evidence that microbial degradation processes also reduce CVOC concentrations in ground water at OU 1, so monitored natural attenuation is a potential alternative remedy if phytoremediation is ineffective. This report describes the current (2000) understanding of natural attenuation of CVOCs in ground water at OU 1 and the impacts that phytoremediation activities to date have had on attenuation processes. The evaluation is based on ground-water and surface-water chemistry data and hydrogeologic data collected at the site by the USGS and Navy contractors between 1991 and 2000. Previously unpublished data collected by the USGS during 1996-2000 are presented. Natural attenuation of CVOCs in shallow ground water at OU 1 is substantial. For 1999-2000 conditions, approximately 70 percent of the mass of dissolved chlorinated ethenes that was available to migrate from the landfill was completely degraded in shallow ground water before it could migrate to the intermediate aquifer or discharge to surface water. Attenuation of CVOC concentrations appears also to be substantial in the intermediate aquifer, but biodegradation appears to be less significant; those conclusions are less certain because of the paucity of data downgradient of the landfill beneath the tide flats. Attenuation of CVOC concentrations is also substantial in surface water as it flows through the adjacent marsh and out to the tide flats. Attenuation processes other than dilution reduce the CVOC flux in marsh surface water by about 40 percent by the time the water discharges to the tide flats. Despite the importance of natural attenuation processes at reducing both the contaminant concentrations and the contaminant mass at OU 1, natural attenuation alone was not effective enough in the year 2000 to meet current numerical remediation goals for the site. That was in part due to the relatively short distance between the landfill and the adjacent marsh, and in part due to the extremely high CVOC concentrations directly beneath the landfill. Phytoremediation activities had some apparent effect on contaminant concentrations in ground water and surface water, but ground-water redox conditions to date (2000) were not affected by the February 1999 asphalt removal for tree planting. The poplar trees in the phytoremediation plantations were not yet mature in 2000, so the lack of discernible changes to date is understandable. Concentration changes of some redox-sensitive compounds suggest that increased recharge following asphalt removal diluted ambient landfill ground water. CVOC concentrations increased in some downgradient wells in both the northern and southern plantations after asphalt removal, whereas CVOC concentrations decreased in some upgradient wells in the southern plantation. A clear increase in CVOC concentrations in marsh surface water followed asphalt removal, apparently from increased contaminant discharge in ground water beneath the southern plantation. The results of the natural attenuation evaluation suggest than minor modifications to the current sampling plan may be beneficial to understanding the future impacts of phytoremediation and natural attenuation on the fate and distribution of CVOCs at OU 1.

Washington↗
USGS2003

Resurvey of quality of surface water and bottom material of the Barataria Preserve of Jean Lafitte National Historical Park and Preserve, Louisiana, 1999-2000

The quality of water and bottom material in the Barataria Preserve of Jean Lafitte National Historical Park and Preserve, Louisiana, was surveyed from March 1999 to May 2000. Organochlorine, chlorophenoxy acid, and organophosphorus pesticides; polychlorinated biphenyls (PCB's); and trace elements were analyzed in surface water and bottom material from three sites previously sampled in a 1981-82 survey. Surface water at six sites was sampled and analyzed for selected nutrients and major inorganic ions based on their importance to human health, the health of the marshes of the Barataria Preserve, or their usefulness in tracking the circulation of Mississippi River water in the Barataria Preserve. Southern Louisiana was in a moderate to severe drought during most of the sampling period, which elevated salinity in the Barataria Preserve for at least 8 months. Specific conductance values were less than 3,000 µS/cm (microsiemens per centimeter at 25 degrees Celsius) in surface water throughout the Barataria Preserve from March through September 1999. Specific conductance values increased over the next 2 months and then remained between 5,000 and 6,000 µS/cm. The herbicide 2,4-D was detected in water at the two sites sampled in August 1999 but not at any site during the two other sampling times. Iron, manganese, and the trace elements copper, nickel, and zinc were detected in dissolved and whole-water samples at all three sites. Nitrite+ nitrate, as nitrogen, concentrations ranged from less than 0.002 to 0.19 mg/L (milligrams per liter). Ammonia, as nitrogen, concentrations ranged from less than 0.01 to 0.16 mg/L. Orthophosphate, as phosphorus, concentrations ranged from less than 0.002 to 0.14 mg/L. Calcium, magnesium, potassium, sulfate, and chloride concentrations in surface water were elevated due to the marine influence on the composition of surface water in the Barataria Preserve during the sampling period. Sulfate and chloride concentrations reached 379 and 2,830 mg/L, respectively. Polychlorinated biphenyls, chlordane, and DDT were detected in bottom material. Trace elements were detected in bottom material at all three of the sampled sites. Arsenic concentrations ranged from 4 to 9 µg/g (micrograms per gram) and lead concentrations from 20 to 31 µg/g. Mercury concentrations also were above laboratory reporting levels (LRL's) for bottom material at all three sites. The herbicide 2,4-D was detected in surface water during both surveys. Other organic compounds were not detected in surface water. Mercury and chromium were detected in surface water at all three sites during the 1981-82 survey but were below LRL?s during the 1999-2000 survey. Changes in chemical characteristics of bottom material occurred during the years between the 1981-82 and 1999-2000 surveys. DDT decreased in the bottom material at Bayou Segnette near Barataria. DDE, a degradation product, increased at this site, indicating that over time, DDT concentrations are decreasing in bottom material. PCB's were present in similar concentrations (Bayou Segnette near Barataria) or increased (Bayou Segnette 4.6 miles below Westwego) from 1981-82 to 1999-2000. Cadmium concentrations consistently decreased by half or more at all three sites from 1981-82 to 1999-2000. Mercury concentrations were consistently lower at all three sites in the 1999-2000 survey, but the differences from the 1981-82 survey were small. Chromium concentrations increased at two of the three sites from 1981-82 to the present survey. At the third site, no chromium value was available for the earlier survey. Concentrations of copper and nickel increased in bottom material at the two sites on Bayou Segnette, but decreased at Kenta Canal northwest of Westwego. Probable Effects Levels (PEL's) and Interim Sediment Quality Guidelines (ISQG's) concentrations, as tabulated by the Canadian Council of Ministers of the of the Environment, were used to assess the probability of biological impairment in the Barataria Preserve. PEL’s are concentrations of a chemical at or above which some biological impairment is likely. ISQG concentrations are those at or below which biological impairment is unlikely. Concentrations of 2,4-D and trace elements, when detected in surface water, were substantially lower than levels at which biological impairment could be expected. Concentrations of organic compounds in bottom material were at most less than 25 percent of PEL’s, and usually much lower. Arsenic, cadmium, copper, and lead concentrations in bottom material were generally slightly above or lower than ISQG concentrations in both surveys, although arsenic was as high as 53 percent of PEL’s at one site in the 1999-2000 survey. All other trace elements in bottom material were present in concentrations lower than ISQG concentrations.

Louisiana↗
USGS1998

Seasonal and spatial variability of nutrients and pesticides in streams of the Willamette Basin, Oregon, 1993-95

From April 1993 to September 1995, the U.S. Geological Survey conducted a study of the occurrence and distribution of nutrients and pesticides in surface water of the Willamette and Sandy River Basins, Oregon, as part of the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program. About 260 samples were collected at 51 sites during the study; of these, more than 60 percent of the pesticide samples and more than 70 percent of the nutrient samples were collected at 7 sites in a fixed-station network (primary sites) to characterize seasonal water-quality variability related to a variety of land-use activities. Samples collected at the remain ing 44 sites were used primarily to characterize spatial water- quality variability in agricultural river subbasins located throughout the study area.This report describes concentrations of 4 nutrient species (total nitrogen, filtered nitrite plus nitrate, total phosphorus, and soluble reactive phosphorus) and 86 pesticides and pesticide degradation products in streams, during high- and low-flow conditions, receiving runoff from urban, agricultural, forested, and mixed-use lands. Although most nutrient and pesticide concentrations were relatively low, some concentrations exceeded maximum contaminant levels for drinking water and water-quality criteria for chronic toxicity established for the protection of freshwater aquatic life. The largest number of exceedances generally occurred at sites receiving predominantly agricultural inputs. Total nitrogen, filtered nitrite plus nitrate, total phosphorus, and soluble reactive phosphorus concentrations were detected in 89 to 98 percent of the samples; atrazine, simazine, metolachlor, and desethylatrazine were detected in 72 to 94 percent of the samples. Fifty different pesticides and degradation products was detected during the 2-1/2 year study.Seasonally, peak nutrient and pesticide concentrations at the seven primary sites were observed during winter and spring rains. With the exception of soluble reactive phosphorus, peak nutrient concentrations were recorded at agricultural sites during winter rains, whereas peak pesticide concentrations occurred at agricultural sites during spring rains.Spatially, although nutrients were detected slightly more often in samples from the northern Willamette Basin relative to the southern Willamette Basin, concentration distributions in the two areas were similar. About 75 percent more pesticides were detected in the northern basin; however, two-thirds of the pesticide detections in the southern basin were larger in concentration than for the same pesticides detected in the northern basin.Nutrient and pesticide concentrations were associated with percent of upstream drainage area in forest, urbanization, and agriculture. Nutrient concentrations at forested sites were among the smallest observed at any of the sites sampled. In addition, only one pesticide and one pesticide degradation product were detected at forested sites, at concentrations near the method detection limits. The highest nutrient concentrations were observed at agricultural sites. Further, the largest numbers of different pesticides detected were at agricultural sites, at concentrations generally larger than at most other land-use sites. Three pesticides--dichlobenil, prometon, and tebuthiuron--were detected more frequently at a site receiving predominantly urban inputs.

Water-Resources Investigations Report↗
USGS1998

Trace elements in streambed sediment and fish liver at selected sites in the Upper Colorado River Basin, Colorado 1995-96

Trace elements were analyzed in streambed-sediment samples collected from 16 sites and in fish-liver samples collected from 14 sites in the Upper Colorado River Basin in Colorado as part of the National Water-Quality Assessment program. Sites sampled represented agricultural, mining, mixed, and urban/recreation land uses and background conditions. The results for 15 trace elements in streambed-sediment and in fish-liver samples are presented in this report. Fourteen of the selected trace elements were detected in streambed-sediment samples collected at all sites. Twelve of the selected trace elements were detected in fish liver at more than 50 percent of the sites. Cadmium, copper, selenium, and zinc were selected for a more detailed analysis. Cadmium, copper, and zinc concentrations in streambed sediment were highest at mining land-use sites in the Southern Rocky Mountains physiographic province. Selenium concentrations in streambed sediment were highest at an agricultural land-use site in the Colorado Plateau physiographic province. The concentration of trace elements in streambed sediment generally increased as particle size decreased. Concentrations of trace elements in fish liver generally did not follow the same relation to land use as concentrations in streambed sediment; however, cadmium concentrations in fish liver were highest at a mining land-use site in the Southern Rocky Mountains physiographic province, and selenium concentrations in fish liver were highest at an agricultural land-use site in the Colorado Plateau physiographic province. Copper and zinc concentrations in fish liver were highest at mixed land-use sites. Comparison of streambed-sediment and fish-liver concentrations to two other similar NAWQA studies in the Rocky Mountain region generally indicated similar patterns in relation to land use for streambed sediment, but not for fish liver. Cadmium, copper, and zinc concentrations in streambed sediment were highest at sites affected by mining in all three study units. Selenium concentrations in streambed sediment did not indicate relations among the three study units when compared to land use. Cadmium in fish liver was highest at sites affected by mining in all three study units. Copper, selenium, and zinc in fish liver did not indicate relations among the three study units when compared to land use.

Colorado↗
USGS2001

Relations among rainstorm runoff, streamflow, pH, and metal concentrations, Summitville Mine area, upper Alamosa River basin, southwest Colorado, 1995-97

The upper Alamosa River Basin contains areas that are geochemically altered and have associated secondary sulfide mineralization. Occurring with this sulfide mineralization are copper, gold, and silver deposits that have been mined since the 1870's. Weathering of areas with sulfide mineralization produces runoff with anomalously low pH and high metal concentrations; mining activities exacerbate the condition. Summer rainstorms in the upper Alamosa River Basin produce a characteristic relation between streamflow and pH; streamflow suddenly increases and pH suddenly decreases (commonly by more than 1 pH unit). This report evaluates changes in pH in the upper Alamosa River Basin during July, August, and September 1995, 1996, and 1997 to examine possible adverse environmental effects due to rainstorm runoff. Ninety-three percent of the rainstorms occurring during 1995?97 produced runoff throughout the entire basin. Out of 54 storms, only 3 storms were isolated to the river reach upstream from the streamflow-gaging station Alamosa River above Wightman Fork, and only 1 storm was isolated to the river reach between the streamflow-gaging stations Alamosa River below Jasper and Alamosa River above Terrace Reservoir. Although most rainstorm runoff events occurred throughout the entire basin, pH changes were highest in parts of the basin that receive runoff from hydrothermally altered areas. The three principal altered areas within the basin are the Jasper, Stunner, and Summitville areas. Only limited mining occurred in the Stunner altered area, and yet significant decreases in pH values occur due to runoff from this area. Even after environmental restoration activities are completed at the Summitville Mine, the main stem of the Alamosa River may continue to be adversely affected by runoff from the Stunner and Jasper altered areas. A comparison of measured pH with Federal and State of Colorado water-quality standards and Toxicological Reference Values indicates pH was too low to support aquatic life in many parts of the basin for extended periods of time. Added stresses from sudden decreases in pH due to rainstorm runoff compound the adverse effects. Discharge of effluent from the Summitville Mine impoundment can significantly decrease pH in the Alamosa River downstream to Terrace Reservoir. A release of only 3 cubic feet per second from the impoundment decreased pH by at least 1 standard unit at all downstream sites. Low-flow years may pose a substantial risk to aquatic organisms within and downstream from Terrace Reservoir. During 1996, the basin had a low-flow year, and water storage and pool size of Terrace Reservoir were significantly reduced. The pH of water discharging from Terrace Reservoir was anomalously low during late August and September 1996, possibly due to geochemical interactions between sediment and the water column within the reservoir. In general, an inverse log-log relation exists between pH and the logarithm of dissolved metal concentrations, but the relations generally are not significant enough to confidently predict metal concentrations based upon measured pH values.

Water-Resources Investigations Report↗
USGS1996

Assessment of water quality, nutrients, algal productivity, and management alternatives for low-flow conditions, South Umpqua River basin, Oregon, 1990-92

This report is an evaluation of the effects of nutrient loading on water quality in the South Umpqua River Basin. The study was done by the U.S. Geological Survey in cooperation with Douglas County, Oregon. Five wastewater-treatment plants were shown to contribute less than 15 percent of the flow, but more than 90 percent of the nitrogen and phosphorus, in the South Umpqua River during low streamflows in summer. These nutrient inputs were associated with, and largely responsible for, the dense growth of periphytic algae that covered the rocky channel and produced biomass values as large as 340 grams of ash-free dry weight per square meter. The nighttime respiration of periphytic algae caused violations of the Oregon water-quality standard, which requires a dissolved oxygen concentration of at least 90 percent of saturation, at most sites along the South Umpqua River. Photosynthesis by algae during daylight resulted in many exceedances of the Oregon pH standard of 8.5. Net productivity, calculated from hourly measurements of dissolved oxygen concentrations, was as much as 3.8 grams of oxygen per square meter per day. The magnitude of productivity increased with increases in dissolved inorganic nitrogen concentration and load. The large amount of nutrient uptake by algae resulted in lowered nutrient concentrations downstream from nutrient point sources. Management alternatives for the South Umpqua River Basin include several methods to reduce nutrient concentrations and loads. The reduction of dissolved-inorganic-nitrogen and soluble- reactive-phosphorus loads from wastewater- treatment-plant effluent would reduce the frequency of violations of water-quality standards. Flow augmentation probably would decrease water-quality problems in the river, but it is difficult to predict the magnitude of the effects of increased velocity and decreased temperature on algal growth. Land application and storage of wastewater-treatment-plant effluent during the summer months would reduce the input of nutrients from point sources. Three exceedances of the Oregon standard for fecal coliform of 200 colonies per 100 milliliters were associated with large streamflows, suggesting that nonpoint sources affect the river during periods of high runoff. Fecal-streptococcus counts were larger than historical values and require confirmation. Ammonia from wastewater-treatment-plant effluent, high pH values, and high temperatures present a potential for chronic ammonia toxicity in the lower reaches of the South Umpqua River; however, actual violations of standards for chronic concentrations were not detected because of diel fluctuations in pH and water temperature.

Oregon↗
USGS2000

Mountain-front recharge along the eastern side of the Middle Rio Grande Basin, central New Mexico

Mountain-front recharge, which generally occurs along the margins of alluvial basins, can be a large part of total recharge to the aquifer system in such basins. Mountain-front recharge occurs as the result of infiltration of flow from streams that have headwaters in the mountainous areas adjacent to alluvial basins and ground- water flow from the aquifers in the mountainous areas to the aquifer in the alluvial basin. This report presents estimates of mountain-front recharge to the basin-fill aquifer along the eastern side of the Middle Rio Grande Basin in central New Mexico. The basin is a structural feature that contains a large thickness of basin-fill deposits, which compose the main aquifer in the basin. The basin is bounded along the eastern side by mountains composed of crystalline rocks of Precambrian age and sedimentary rocks of Paleozoic age. Precipitation is much larger in the mountains than in the basin; many stream channels debouch from the mountainous area to the basin. Chloride-balance and water-yield regression methods were used to estimate mountain-front recharge. The chloride-balance method was used to calculate a chloride balance in watersheds in the mountainous areas along the eastern side of the basin (subareas). The source of chloride to these watersheds is bulk precipitation (wet and dry deposition). Chloride leaves these watersheds as mountain-front recharge. The water-yield regression method was used to determine the streamflow from the mountainous watersheds at the mountain front. This streamflow was assumed to be equal to mountain-front recharge because most of this streamflow infiltrates and recharges the basin-fill aquifer. Total mountain-front recharge along the eastern side of the Middle Rio Grande Basin was estimated to be about 11,000 acre- feet per year using the chloride-balance method and about 36,000 and 38,000 acre-feet per year using two water-yield regression equations. There was a large range in the recharge estimates in a particular subarea using the different methods. Mountain-front recharge ranged from 0.7 to 15 percent of total annual precipitation in the subareas (percent recharge). Some of the smallest values of percent recharge were in the subareas in the southern part of the basin, which generally have low altitudes. The larger percent-recharge values were from subareas with higher altitudes. With existing information, determining which of the mountain- front recharge estimates is most accurate and the reasons for discrepancies among the different estimates is not possible. The chloride-balance method underestimates recharge if the chloride concentration used in the calculations for precipitation is too small or the chloride concentration in recharge is too large. Water-yield regression methods overestimate recharge if the amount of evapotranspiration of water that infiltrates into the channel bed of arroyos during runoff from summer thunderstorms is large.

Water-Resources Investigations Report↗
USGS1997

Ground-water development and the effects on ground-water levels and water quality in the town of Atherton, San Mateo County, California

The installation of at least 100 residential wells in the town of Atherton, California, during the 198792 drought has raised concerns about the increased potential for land subsidence and salt water intrusion. Data were collected and monitor ing networks were established to assess current processes and to monitor future conditions affect ing these processes. Data include recorded pump age, recorded operation time, and measured pumpage rates from 38 wells; water levels from 49 wells; water chemistry samples from 20 wells, and land-surface elevation data from 22 survey sites, including one National Geodetic Survey estab lished bench mark. Geologic, lithologic, climato logic, well construction, well location, and historical information obtained from available reports and local, state, and Federal agencies were used in this assessment. Estimates of annual residential pumpage from 269 assumed active residential wells in the study area indicate that the average annual total pumping rate is between 395 and 570 acre-feet per year. The nine assumed active institutional wells are estimated to pump a total of about 200 acre- feet per year, or 35 to 50 percent of the total resi dential pumpage. Assuming that 510 acre-feet per year is the best estimate of annual residential pumpage, total pumpage of 710 acre-feet per year would represent about 19 percent of the study area's total water supply, as estimated. Depth-to-water-level measurements in wells during April 1993 through September 1995 typically ranged from less than 20 feet below land surface nearest to San Francisco Bay to more than 70 feet below land surface in upslope areas near exposed bedrock, depending on the season. This range, which is relatively high historically, is attributed to above normal rainfall between 1993 and 1995. Water levels expressed as hydraulic heads indicate the presence of three different hydrologic subareas on the basis of hydraulic-head contour configurations and flow direction. That all measured hydraulic heads in the study area from April 1993 through September 1995 were above sea level indicates that saltwater intrusion was unlikely during this period. The chemistry of 20 well-water samples is characterized as a calcium magnesium carbonate bicarbonate type water. There is no evidence of saltwater intrusion from San Francisco Bay; how ever, water samples from wells nearest the bay and bedrock assemblages indicate a greater concentra tion of dissolved constituents and salinity. Dissolved-solids concentrations of water samples from wells in these areas exceeded 1,000 milli grams per liter, and several samples contained a substantial fraction of sodium and chloride. Water hardness for the 20 wells sampled averaged 471 milligrams per liter as calcium carbonate, which is classified as very hard. One well sample exceeded the primary maximum contaminant level for drinking water in nitrate, several wells exceeded the secondary maximum contaminant level for chloride and sulfate, and all wells sampled exceeded the secondary maximum contaminant level for total dissolved solids. Land-subsidence and the resultant damage because of excessive ground-water pumping, in combination with periodic drought, have a well- documented history in the south San Francisco Bay area. Land-elevation surveying data from 1934 to 1967 indicate that subsidence ranged from 0.1 to approximately 0.5 foot in the vicinity of the study area. It could not be determined from land- surface elevation surveying data from 1993 whether subsidence is currently occurring in the study area.

Water-Resources Investigations Report↗
USGS2003

Trends in concentrations of polychlorinated biphenyls in fish tissue from selected sites in the Delaware River basin in New Jersey, New York, and Pennsylvania, 1969-98

Polychlorinated biphenyl (PCB) concentrations in fish tissue collected during the 1990's from selected sites in the Delaware River Basin were compared with concentrations in fish tissue collected during 1969-88. Data collected by State and Federal agencies on concentrations in whole-body common carp ( Cyprinus carpio ) and white sucker ( Catostomus commersoni ), and edible portions of American eel ( Anguilla rostrata ), smallmouth bass ( Micropterus dolomieu ), and channel catfish ( Ictalurus punctatus ) during 1969-98 were compiled to define temporal trends in concentrations of PCBs in fish tissue from selected segments of the Delaware River, Lehigh River, Schuylkill River, and Brandywine Creek. The Delaware River in the vicinity of Trenton, New Jersey and Yardley, Pennsylvania (above the tidal influence) had the largest long-term data set among the sites considered for this study and was the only site with sufficient data for statistical analysis. A general pattern of decline in PCB concentrations during 1969-98 was apparent for this river segment. PCB concentrations in whole-body white sucker from this lower Delaware River segment declined during 1969-98 from a highest concentration of 7 micrograms per gram ( μ g/g, wet weight) in a sample collected during 1972 to 0.26 μ g/g (wet weight) in a sample collected during 1998. PCB concentration was negatively correlated with year (Spearman rank correlation -0.46, p < 0.08, n = 15); especially after removal of a sample from 1977 with an unusually low concentration (Spearman rank correlation -0.53, p = 0.05, n = 14). PCB concentrations in edible flesh of American eel declined during 1975-95, from a highest concentration of 3.8 μ g/g (wet weight) in a sample collected during 1976 to less than the reporting limit of 0.26 μ g/g (wet weight) in samples collected during 1993 and 1995. PCB concentrations in most samples (for species considered in this study) collected from the lower Delaware River exceeded the National Academy of Sciences and National Academy of Engineering (NAS/NAE) wildlife guideline level of 0.5 μ g/g during the 1970's and 1980's, and decreased to below this level during the 1990's. No samples of edible portions of game fish exceeded the U.S. Food and Drug Administration (FDA) tolerance level by the mid 1980's. However, the PCB concentration in a smallmouth bass fillet sample that was collected during 1998 (0.37 μ g/g) exceeded the Pennsylvania fish-consumption advisory level of 0.06 μ g/g, and the concentrations in whole-body common carp and white sucker collected during 1998 (1.10 μ g/g and 0.26 μ g/g, respectively) exceeded the New York State Department of Environmental Conservation wildlife criterion concentration of 0.11 μ g/g. (The concentration in carp also exceeded the 1973 NAS/NAE wildlife guideline concentration of 0.5 μ g/g.) Graphical analysis of PCB concentrations in whole white sucker and (or) edible portions of American eel from the upper Delaware River, lower Delaware River, middle Schuylkill River, and Brandywine Creek indicate a decline from the 1970's and (or) 1980's to the middle to late 1990's. Temporal trends in PCB concentrations in white sucker samples from the lower Lehigh and Schuylkill Rivers during 1979-98 are less clear; the PCB concentration (wet-weight basis) from a sample collected in 1998 from the lower Lehigh River was similar to that from a sample collected in 1979, and concentrations actually increased during 1982-98. Similarly, PCB concentrations in samples of white sucker and American eel from the lower Schuylkill River were highly variable over time.

New Jersey, New York, Pennsylvania↗
USGS1996

Trends in nutrients and suspended solids at the Fall Line of five tributaries to the Chesapeake Bay in Virginia, July 1988 through June 1995

Water-quality samples were collected at the Fall Line of five tributaries to the Chesapeake Bay in Virginia during a 6- to 7-year period. The water-quality data were used to estimate loads of nutrients and suspended solids from these tributaries to the non-tidal part of Chesapeake Bay Basin and to identify trends in water quality. Knowledge of trends in water quality is required to assess the effectiveness of nutrient manage- ment strategies in the five basins. Multivariate log-linear regression and the seasonal Kendall test were used to estimate flow-adjusted trends in constituent concentration and load. Results of multivariate log-linear regression indicated a greater number of statistically significant trends than the seasonal Kendall test; how-ever, when both methods indicated a significant trend, both agreed on the direction of the trend. Interpre- tation of the trend estimates for this report was based on results of the parametric regression method. No significant trends in total nitrogen concentration were detected at the James River monitoring station from July 1988 through June 1995, though total Kjeldahl nitrogen concen- tration decreased slightly in base-flow samples. Total phosphorus concentration decreased about 29 percent at this station during the sampling period. Most of the decrease can be attributed to reductions in point-source phosphorus loads in 1988 and 1989, especially the phosphate detergent ban of 1988. No significant trends in total suspended solids were observed at the James River monitoring station, and no trends in runoff- derived constituents were interpreted for this river. Significant decreases were detected in concentrations of total nitrogen, total Kjeldahl nitrogen, dissolved nitrite-plus-nitrate nitrogen, and total suspended solids at the Rappahannock River monitoring station between July 1988 and June 1995. A similar downward trend in total phosphorus concentration was significant at the 90-percent confidence level, but not the 95-percent confidence level. These decreases can be attributed primarily to reductions in nonpoint nutrient and sediment loads, and may have been partially caused by implementation of best management practices on agricultural and silvicultural land. Flow-adjusted trends observed at the Appomattox, Pamunkey, and Mattaponi monitoring stations were more difficult to explain than those at the James and Rappahannock stations. Total Kjeldahl nitrogen and total phosphorus increased 16 and 23 percent, respectively, at the Appomattox River monitoring station from July 1989 through June 1995. Total phosphorus concentration increased about 46 percent at the Pamunkey River monitoring station between July 1989 and June 1995. At the Mattaponi River monitoring station, decreases in dissolved nitrite-plus-nitrate nitrogen were offset by increases in total Kjeldahl nitrogen, resulting in no net change in total nitrogen concentration from October 1989 through June 1995.

Water-Resources Investigations Report↗
USGS1996

Hydrogeology of the interstream area between Ty Ty Creek and Ty Ty Creek tributary near Plains, Georgia

This report is part of an interdisciplinary effort to identify and describe processes that control movement and fate of selected fertilizers and pesticides in the surface and subsurface environments in the Fall Line Hills district of the Georgia Coastal Plain physiographic province. This report describes the hydrogeology of the interstream area between Ty Ty Creek and it's tributary near Plains, Sumter County, Georgia. Geologic units of interest to this study are, in ascending order, (1) the Tuscahoma Formation, a bluish gray, silty clay; (2) the Tallahatta Formation, a fine-to-coarse, poorly sorted quartz sand that is divided into an upper and lower unit; and (3) the undifferentiated overburden, which consists of fine to medium poorly sorted sand, silt and clay. Continuous-core samples indicate that the unsaturated zone includes the undifferentiated overburden and the upper unit of the Tallahatta Formation, and attains a maximum thickness of about 52 feet (ft) in the southern part of the study area. The Claiborne aquifer in the study area consists of the lower unit of the Tallahatta Formation and ranges in thickness from 3 ft near Ty Ty Creek tributary to about 20 ft in the upland divide area. It is confined below by the clayey sediments of the Tuscahoma Formation. The Claiborne aquifer in the study area generally is confined above by an extensive clay layer that is the base if the upper unit of the Tallahatta Formation. Fluctuations in the amount of vertical recharge to the aquifer result in areal and temporal changes in aquifer conditions from confined to unconfined in parts of the study area. Hydraulic conductivity of the aquifer ranges from 3.5 to 7 feet per day. The transmissivity of the aquifer is approximately 50 feet squared per day. Water-level data indicate the potentiometric surface slopes to the south, southeast, and southwest with a gradient of about 87 to 167 feet per mile. The shape of the potentiometric surface and the direction of groundwater flow remains relatively unchanged during high and low water-level periods. Water levels in the Claiborne aquifer fluctuated by a maximum of 6 ft during the period from January to December 1991. Recharge to the Claiborne aquifer consists of a local and regional flow component. Lateral ground-water flow (regional flow) into the study area is dependent on regional hydraulic controls (pumpage, stream discharge, and rainfall). The rate of lateral movement of ground water is dependent on the hydraulic conductivity of the saturated zone, the hydraulic gradient, and other hydraulic factors, and is considered to be relatively constant. Local recharge enters the ground-water system as rainfall that percolates down to the water table. Annual water-level fluctuations in the Claiborne aquifer indicate that the majority of regional and local recharge occurs in the interstream area with recharge decreasing downslope to the streams. Ground water discharges to Ty Ty Creek and it's tributary throughout the year during low and high water-level periods.

Georgia↗
USGS1992

Sediment transport, particle sizes, and loads in lower reaches of the Chippewa, Black, and Wisconsin Rivers in Western Wisconsin

Hydraulic and sediment data were collected at three sites on the Chippewa River (near Caryville, at Durand, and near Pepin); at one site near Galesville on the Black River; and at one site at Muscoda on the Wisconsin River during water years 1976-83. This report summarizes an interpretation of those data by providing (1) a description of the relation of suspended sediment, bedload, and total-sediment discharge to water discharge; (2) a description of particle-size characteristics of bed material, bedload, and suspended sediment; and (3) estimates of annual and average annual suspended load, bedload, and total-sediment load for water years 1974-83. Direct measurement with a Helley-Smith bedload sampler and calculations by the modified-Einstein procedure were used to estimate bedload. Single equations describe the suspended- and totalsediment transport-rate relations for Chippewa River at Durand and main channel at Pepin, and the Black River near Galesville. Two equations were needed to define the transport- rate relations for the Chippewa River near Caryville and Wisconsin River at Muscoda. Bed material at all sites except Chippewa River near Caryville were of similar particle size and exhibited little variation with time or location in the river cross sections. Median diameter at these sites ranged from 0.35 to 0.84 mm (millimeter). At Chippewa River near Caryville, median diameter ranged from 0.42 to 15 mm. Helley-Smith bedload at Chippewa River at Durand and near Pepin, Black River near Galesville, and Wisconsin River at Muscoda were of similar particle size. About 57 to 65 percent of bedload at all sites except Chippewa River near Caryville was in the 0.4- to 0.6- mm size range. About 50 percent of bedload at Chippewa River near Caryville was in the 0.5- to 1.0-mm size range. Suspended sediment at all sites except Chippewa River near Caryville was in the sand-size range; the average median diameters were between 0.17 and 0.22 mm. At Chippewa River near Caryville, 60 percent (on the average) of suspended sediment was finer than 0.062 mm. Average annual total-sediment load and the percentage transported as bedload were determined for a 10-year period (water years 1974-83)(October 1,1973-September 30, 1982). These loads and percentages were, respectively, 123,000 tons and 35 percent at Chippewa River near Caryville; 1,073,000 tons and 61 percent at Chippewa River at Durand; 940,000 tons and 44 percent at Chippewa River near Pepin; 277,000 tons and 43 percent at Black River near Galesville; and 558,000 tons and 49 percent at Wisconsin River at Muscoda.

Wisconsin↗
USGS1993

Hydrology and water quality of Powers Lake, southeastern Wisconsin

This report describes the hydrology and water quality of Powers Lake, a recreational lake in a densely populated area of southeastern Wisconsin, from October 16, 1986 - October 15, 1987. The hydrologic budget for the study period showed that direct precipitation on the lake and ground water were dominant sources of water entering the lake (37 and 36 percent, respectively) and that streamflow dominated the outflow. Surface runoff contributed 27 percent of the inflow-23 percent from Powers Lake inlet and 4 percent from shoreline drainage. Streamflow through Powers Lake outlet accounted for 62 percent of the outflow and evaporation accounted for 38 percent. Based on the streamflow from Powers Lake outlet, the lake's hydraulic residence time was 3.8 years. During the study period, precipitation was 27.16 inches or 4.08 inches below long-term (1951-80) average. The data were adjusted or normalized to represent an average year of precipitation and runoff to help evaluate the water quality of the lake for an average year. For an average year, precipitation dominated inflow (42 percent), followed by ground water (32 percent), Powers Lake inlet (21 percent), and shoreline drainage (5 percent). Streamflow through Powers Lake outlet accounted for 61 percent of an average year's outflow budget and the remaining 39 percent was evaporation. Based on an average year's streamflow from Powers Lake outlet, the lake's hydraulic residence time was 4.2 years. Phosphorus budgets were prepared for the study period and for an estimated normal year. The phosphorus budget for the study period showed that, of the total inputs (516 pounds), surface runoff contributed the largest amount; shoreline drainage contributed 44 percent, and Powers Lake inlet contributed 36 percent. Direct precipitation contributed 11 percent; ground water, 2 percent; and septic systems, 7 percent. Of the total outputs, 83 pounds (16 percent) was lost from the lake via the outlet; 433 pounds (84 percent) was lost to the sediments as the phosphorus that was attached to particles settled to the lake bottom. An estimated phosphorus budget for a normal year showed that of the total inputs (744 pounds), surface runoff contributed the largest amount; Powers Lake inlet contributed 45 percent and shoreline drainage contributed 35 percent. Precipitation contributed 9 percent; ground water, 1 percent; and septic systems, 10 percent. The health of the lake was evaluated using Carlson's Trophic State Index and Vollenweider's model. Carlson's Trophic State Index showed that Powers Lake was moderately enriched and in the mesotrophic range. Comparison of guidelines from Vollenweider's model showed that the total phosphorus input for the study period and for an estimated average year would not cause eutrophic conditions.

Wisconsin↗
USGS1996

Hydrogeology of the alluvial aquifers at the Pueblo Depot Activity near Pueblo, Colorado

In 1992, the U.S. Army Corps of Engineers and the U.S. Army Pueblo Depot Activity requested that the U.S. Geological Survey study the hydrogeology of the Pueblo Depot Activity, a 36-square-mile facility that has been operated by the U.S. Army since 1942. The purpose of the study was to provide an updated hydrogcological framework to facilitate the investigation of specific sites on the facility that might require remediation. This report describes the hydrogeology of the alluvial aquifers beneath the facility and the distribution of specific conductance of ground water in those aquifers. The Pueblo Depot Activity is underlain by two alluvial aquifers: (1) The terrace alluvial aquifer, which is a southernmost, downgradicnt part of an erosional remnant of an extensive terrace deposit; and (2) the Chico Creek alluvial aquifer, a smaller alluvial system along Chico Creek. These aquifers primarily consist of sand separated by clay layers and are underlain by the almost impermeable Pierre Shale of Upper Cretaceous age. The bedrock surface, which has an average slope of 28 feet per mile to the south-southeast, is relatively regular beneath the northern two-thirds of the terrace deposits at the Pueblo Depot Activity, but forms an irregular surface of troughs, hills, and ridges in the southwestern part of the terrace alluvium. Saturated thickness of the terrace aquifer ranges from 0 to about 45 feet. The bedrock surface beneath the Chico Creek aquifer slopes about 31 feet per mile to the south. Saturated thickness of the Chico Creek alluvium ranges from 0 to about 30 ft, but generally is less than 15 ft. Total thickness of the Chico Creek alluvium in the saturated area ranges from 16 to 41 ft. Water in the terrace alluvial aquifer generally flows southward, except in the southwestern part where directions of flow are complex. Measured hydraulic conductivity ranges from 0.4 to 400 feet per day (median 26 feet per day). Estimates for vertically averaged ground-water-flow velocity range from 0.02 to 3 feet per day (median 0.9 foot per day). Water in the Chico Creek alluvial aquifer generally flows southward to the Arkansas River alluvium. Measured hydraulic conductivity ranges from 14 to 310 feet per day (median 42 feet per day). Estimates for vertically averaged ground water-flow velocity range from 0.5 to 4 feet per day (median 0.7 foot per day). Specific conductance of ground water in the terrace alluvial aquifer generally is less than 800 microsiemens per centimeter; the smallest values were observed in the north-central part of the Pueblo Depot Activity. In the southwestern part of the terrace alluvial aquifer, values varied in an irregular pattern, and values as large as 3,300 microsiemens per centimeter were measured locally. Water in the terrace alluvial aquifer was dominated by the sodium cation and usually by the bicarbonate anion, and sulfate usually was present in substantial (and locally predominant) concentrations. Measured specific conductance of water in the Chico Creek alluvial aquifer ranged from 683 to 1,460 microsiemens per centimeter. This water was dominated by the sodium cation and by the bicarbonate and sulfate anions; sulfate was more predominant to the south.

Colorado↗
USGS1999

Occurrence of organochlorine compounds in whole fish tissue from streams of the lower Susquehanna River Basin, Pennsylvania and Maryland, 1992

Tissue samples of whole body white sucker ( Catostomus commersoni ) were collected at 15 sites and smallmouth bass ( Micropterus dolomieu ) were collected at 5 sites during 1992 in the Lower Susquehanna River Basin to determine the occurrence and distribution of 28 selected organochlorine compounds as part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Program. Only 12 of the 28 compounds occurred at concentrations greater than the 5 µg/kg reporting limit (total PCB’s reporting limit is ‹50 µg/kg and toxaphene is ‹200 µg/kg). The most frequently reported compounds were p,p ’-DDE (reported in all tissue samples), total polychlorinated biphenyls (PCB’s), and trans-nonachlor. High concentrations of p,p’ -DDE and low concentrations of the other DDT metabolites for the Lower Susquehanna River sites indicate no recent influx of DDT. Comparison with historical data from the Lower Susquehanna River Basin shows a decline of organochlorine concentrations within the basin. In 1987, Quittapahilla Creek had the highest concentrations of p,p’ -DDE in a national survey of contaminant occurrence in fish tissue conducted by the U.S. Environmental Protection Agency. This stream ranked the highest for total DDT of the 20 NAWQA studies started nationally in 1991. Total DDT concentrations were higher in agriculture-dominated (>50 percent) sites than in forest-dominated (>50 percent) sites with the exception of Deer Creek and Big Beaver Creek. These two sites are located more in grazing areas that lack a substantial crop-land use. Concentrations of total PCB’s were highest in basins with greater than 10 percent urban land use excluding the larger river sites. Concentrations of total chlordane were highest at sites with greater than 70 percent agricultural and 10 percent urban land use. Regional comparisons of total DDT, total PCB’s, and total chlordane in white sucker tissue from the Lower Susquehanna, Hudson (in New York), and Connecticut River Basins showed that median concentrations of total DDT were different (p=0.05), with the Lower Susquehanna Basin being the lowest. Total PCB’s and total chlordane medians were similar. Comparison of the data from national and regional studies with data from this local study showed concentrations of p,p’ -DDE in the Lower Susquehanna River Basin are similar to those nationwide and lower than the concentrations measured in the Northeast. PCB concentrations in the Lower Susquehanna River Basin and the Northeast were higher than those nationwide.

Water-Resources Investigations Report↗
USGS2002

SUTRA: A model for 2D or 3D saturated-unsaturated, variable-density ground-water flow with solute or energy transport

SUTRA (Saturated-Unsaturated Transport) is a computer program that simulates fluid movement and the transport of either energy or dissolved substances in a subsurface environment. This upgraded version of SUTRA adds the capability for three-dimensional simulation to the former code (Voss, 1984), which allowed only two-dimensional simulation. The code employs a two- or three-dimensional finite-element and finite-difference method to approximate the governing equations that describe the two interdependent processes that are simulated: 1) fluid density-dependent saturated or unsaturated ground-water flow; and 2) either (a) transport of a solute in the ground water, in which the solute may be subject to: equilibrium adsorption on the porous matrix, and both first-order and zero-order production or decay; or (b) transport of thermal energy in the ground water and solid matrix of the aquifer. SUTRA may also be used to simulate simpler subsets of the above processes. A flow-direction-dependent dispersion process for anisotropic media is also provided by the code and is introduced in this report. As the primary calculated result, SUTRA provides fluid pressures and either solute concentrations or temperatures, as they vary with time, everywhere in the simulated subsurface system. SUTRA flow simulation may be employed for two-dimensional (2D) areal, cross sectional and three-dimensional (3D) modeling of saturated ground-water flow systems, and for cross sectional and 3D modeling of unsaturated zone flow. Solute-transport simulation using SUTRA may be employed to model natural or man-induced chemical-species transport including processes of solute sorption, production, and decay. For example, it may be applied to analyze ground-water contaminant transport problems and aquifer restoration designs. In addition, solute-transport simulation with SUTRA may be used for modeling of variable-density leachate movement, and for cross sectional modeling of saltwater intrusion in aquifers at near-well or regional scales, with either dispersed or relatively sharp transition zones between freshwater and saltwater. SUTRA energy-transport simulation may be employed to model thermal regimes in aquifers, subsurface heat conduction, aquifer thermal-energy storage systems, geothermal reservoirs, thermal pollution of aquifers, and natural hydrogeologic convection systems. Mesh construction, which is quite flexible for arbitrary geometries, employs quadrilateral finite elements in 2D Cartesian or radial-cylindrical coordinate systems, and hexahedral finite elements in 3D systems. 3D meshes are currently restricted to be logically rectangular; in other words, they are similar to deformable finite-difference-style grids. Permeabilities may be anisotropic and may vary in both direction and magnitude throughout the system, as may most other aquifer and fluid properties. Boundary conditions, sources and sinks may be time dependent. A number of input data checks are made to verify the input data set. An option is available for storing intermediate results and restarting a simulation at the intermediate time. Output options include fluid velocities, fluid mass and solute mass or energy budgets, and time-varying observations at points in the system. Both the mathematical basis for SUTRA and the program structure are highly general, and are modularized to allow for straightforward addition of new methods or processes to the simulation. The FORTRAN-90 coding stresses clarity and modularity rather than efficiency, providing easy access for later modifications.

Water-Resources Investigations Report↗