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Research about Nassau County, New York

Source-linked reports with geographic coverage including Nassau County, New York.

At least 19 recordsLinked to original sources
USGS2024

Analysis of factors affecting plume remediation in a sole-source aquifer system, southeastern Nassau County, New York

Several plumes of dissolved, chlorinated solvents, including trichloroethylene, have been identified in a sole-source aquifer near the former Northrop Grumman Bethpage Facility and Naval Weapons Industrial Reserve Plant sites in southeastern Nassau County, New York. Past investigations have documented that the groundwater contamination originated from this industrial area and now extends to the south, in the direction of groundwater flow. The intermixed plumes are commonly referred to as the “Navy Grumman groundwater plume.” Detailed groundwater-flow modeling was needed for the New York State Department of Environmental Conservation (NYSDEC) to evaluate design options necessary for the construction, operation, optimization, maintenance, and monitoring of a groundwater extraction and treatment cleanup plan selected in a December 2019 Amended Record of Decision by the NYSDEC to comprehensively address these plumes. Consequently, the NYSDEC began a cooperative study with the U.S. Geological Survey in 2020 to better understand the local hydrogeologic framework using two independent approaches to characterize aquifer heterogeneity and update an existing regional groundwater-flow model to provide transient boundary conditions for new inset groundwater-flow models of the plume area. We developed these detailed inset models for the two independent aquifer characterizations using history-matching techniques coupled with a novel approach to risk-based management optimization of the remedial design. We also used the updated regional model to assess this optimized groundwater extraction and treatment design for potential saltwater intrusion. The ensembles of parameters resulting from history matching provided a platform with which to evaluate capture by water-supply and remedial wells using particle-tracking techniques. Using the ensemble to select a risk stance, we performed multiobjective optimization to identify various configurations of remedial pumping that are consistent with external constraints and that favor potentially competing objectives. Multiple solutions provide tradeoffs that NYSDEC can consider. In general, pumping redistribution may help to prevent further contamination migration downgradient. These and other study results are intended to support decisions for the remedial design focused on the local area encompassing the full extent of the Navy Grumman groundwater plume.

New York↗
USGS2022

Nuclear magnetic resonance logging of a deep test well for estimation of aquifer and confining-unit hydraulic properties, Long Island, New York

A 1,200-foot deep well in southwestern Nassau County, Long Island, N.Y. was selected to evaluate the application of a nuclear magnetic resonance (NMR) logging tool. Technological advances in NMR borehole systems have allowed for reduced probe length and diameter, and focused measurement at specific diameters beyond the disturbed zone surrounding a well. This 3-inch-diameter NMR tool was specifically developed for use in deep 4-inch-diameter polyvinyl chloride cased wells common to Long Island. Selected intervals of the Magothy and Lloyd aquifers and the Raritan confining unit were logged for the evaluation. Unlike other petrophysical logs that respond to the rock matrix and fluid properties and are strongly dependent on mineralogy, NMR logs respond to the presence of hydrogen protons in the formation fluid to determine water fraction and pore-size distribution. NMR log analysis provided estimates of the clay-bound, capillary-bound, and mobile water fraction and hydraulic conductivity of aquifers and confining units penetrated by the well. NMR-estimated porosity and mobile water fraction for the Magothy aquifer (0.34 and 0.22 respectively), Magothy/Raritan(?) (0.35 and 0.30), Raritan confining unit (0.30 and 0.13), Raritan clay and silt (0.23 and 0.01), and the Lloyd aquifer (0.27 and 0.19) was determined from the NMR log. Hydraulic conductivity was estimated from the NMR-log data using the Schlumberger- Doll Research and sum of squared echoes equations with empirically derived constants for unconsolidated aquifers. Average hydraulic conductivity of the Magothy aquifer was 70 ft/d, the Raritan confining unit was 9.0 ft/d overall, the clay-rich lower part 0.24 ft/d, and the Lloyd aquifer was 56 ft/d. The coarse sandy Magothy/Raritan(?) unit between the Magothy aquifer and the top of the Raritan confining unit had the highest hydraulic conductivity of 345 ft/d. The hydraulic-conductivity estimates from the NMR log analysis for the Magothy and Lloyd aquifers were consistent with published values and that estimated for the Lloyd aquifer from a specific-capacity test at the well site.

New York↗
USGS2020

Analysis of remedial scenarios affecting plume movement through a sole-source aquifer system, southeastern Nassau County, New York

A steady-state three-dimensional groundwater-flow model based on present conditions is coupled with the particle-tracking program MODPATH to assess the fate and transport of volatile organic-compound plumes within the Magothy and upper glacial aquifers in southeastern Nassau County, New York. Particles are forward tracked from locations within plumes defined by surfaces of equal concentration. Particles move toward ultimate well capture and discharge to the general head and drain boundaries representing natural receptors in the models. Because rates of advection within coarse-grained sediments typically exceed 0.1 foot per day, mechanisms of dispersion and diffusion were assumed to be negligible. Resulting particle pathlines are influenced by hydrogeologic framework features and the interplay of nearby hydrologic stresses. Simulated hydrologic effects include cones of depression near pumping wells and water-table mounding near points of treated water recharge; however, remedial pumping amounts are balanced by treated-water return, and net effects at distant regional boundaries, including freshwater/saltwater interfaces, are minor. Once a steady-state model was developed and calibrated, eight hypothetical remedial scenarios were evaluated to hydraulically contain the volatile organic-compound plumes. Specifically, the remedial scenarios were optimized to achieve full containment by altering the pumping-well locations, adjusting the pumping rates, and adjusting the discharge locations and rates. Based on the results, total hypothetical extraction rates varied from about 5,462 gallons per minute during an anticipated near-future condition to about 13,340 gallons per minute during full hydraulic containment of all site-related compounds identified by the New York State standards, criteria, and guidance for environmental investigations and cleanup. Targeting of high-concentration zones of the plume increases the total amount of remedial pumpage necessary to capture all parts of the plume but may decrease the total amount of time necessary to operate a remedial system. Simulated time frames of advective transport ranged from about 12 years to capture zones with elevated concentrations of volatile organic compounds (mean particle travel time plus the standard deviation of travel time) to more than 100 years to capture all zones. Groundwater-flow model analysis indicates that all the optimal plume-containment scenarios would have negligible effects on streams and the saltwater-freshwater interface along the south shore of Long Island. Massapequa, Bellmore, Seaman, and Seaford Creeks are represented by using MODFLOW drain-boundary conditions. Saltwater-freshwater interfaces are represented by using MODFLOW general head-boundary conditions where the Magothy aquifer discharges upward into saline groundwater across the Gardiners clay confining unit and the Lloyd aquifer discharges upward into saline groundwater across the Raritan confining unit.

New York↗
USGS2014

Simulation of groundwater flow pathlines and freshwater/saltwater transition zone movement, Manhasset Neck, Nassau County, New York

A density-dependent groundwater flow and solute transport model of Manhasset Neck, Long Island, New York, was used to analyze (1) the effects of seasonal stress on the position of the freshwater/saltwater transition zone and (2) groundwater flowpaths. The following were used in the simulation: 182 transient stress periods, representing the historical record from 1920 to 2011, and 44 transient stress periods, representing future hypothetical conditions from 2011 to 2030. Simulated water-level and salinity (chloride concentration) values are compared with values from a previously developed two-stress-period (1905–1944 and 1945–2005) model. The 182-stress-period model produced salinity (chloride concentration) values that more accurately matched the observed salinity (chloride concentration) values in response to hydrologic stress than did the two-stress-period model, and salinity ranged from zero to about 3 parts per thousand (equivalent to zero to 1,660 milligrams per liter chloride). The 182-stress-period model produced improved calibration statistics of water-level measurements made throughout the study area than did the two-stress-period model, reducing the Lloyd aquifer root mean square error from 7.0 to 5.2 feet. Decreasing horizontal and vertical hydraulic conductivities (fixed anisotropy ratio) of the Lloyd and North Shore aquifers by 20 percent resulted in nearly doubling the simulated salinity(chloride concentration) increase at Port Washington observation well N12508. Groundwater flowpath analysis was completed for 24 production wells to delineate water source areas. The freshwater/saltwater transition zone moved toward and(or) away from wells during future hypothetical scenarios.

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USGS2011

Simulation of groundwater flow in a volatile organic compound-contaminated area near Bethpage, Nassau County, New York: A discussion of modeling considerations

The 2010 Bethpage groundwater-flow model (ARCADIS, 2010) was based on a steady state assumption. Although it is widely acknowledged that significant water-level changes have occurred in the past, the reviewed model does not represent changing water levels. The steady state approach limits the effectiveness of the following: 1. identification of sources of contamination, 2. analysis of model accuracy, 3. model calibration, and 4. simulations of future scenarios. Future plume movement was simulated in an incomplete manner through an unchanging groundwater-flow field. Available time-series information on temporal variation of factors affecting groundwater-flow dynamics includes: 1. public-supply pumping, 2. groundwater discharges from systems remediating volatile organic compound (VOC) plumes, 3. recharge and precipitation rates, and 4. water levels and streamflows. Transient phenomena that might be useful in future hypothetical simulations include pumping variations, redirection of containment-system waters for industrial use, and climate-change scenarios. Public-domain computer programs, U.S. Geological Survey guidance reports on transient-state calibration and uncertainty methods (Doherty and Hunt, 2010), and additional local and regional datasets are available to provide additional confidence in model evaluations and allow better evaluation of their limitations.

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USGS2004

Hydrogeology and Extent of Saltwater Intrusion in the Northern Part of the Town of Oyster Bay, Nassau County, New York: 1995–98

The Oyster Bay study area, in the northern part of Nassau County, N.Y., is underlain by unconsolidated deposits that form a sequence of aquifers and confining units. At least one production well has been affected by the intrusion of saltwater from Hempstead Harbor, Long Island Sound, and Cold Spring Harbor. Nineteen boreholes were drilled during 1995-98 for the collection of hydrogeologic, geochemical, and geophysical data to delineate the subsurface geology and the extent of saltwater intrusion. Continuous high-resolution marine-seismic-reflection surveys in the surrounding embayments of the Oyster Bay study area were conducted in 1996. New drill-core data indicate two hydrogeologic units—the North Shore aquifer and the North Shore confining unit—where the Lloyd aquifer, the Raritan confining unit, and the Magothy aquifer have been completely removed by glacial erosion. Water levels at 95 observation wells were measured quarterly during 1995–98. These data and continuous water-level records indicated that (1) the upper glacial (water-table) and Magothy aquifers are hydraulically connected and that their water levels did not respond to tidal fluctuations, and (2) the Lloyd and North Shore aquifers are hydraulically connected and their water levels responded to pumping and to tidal fluctuations. Marine seismic-reflection surveys in the surrounding embayments indicate at least four glacially eroded buried valleys with subhorizontal, parallel reflectors indicative of draped bedding that is interpreted as infilling by silt and clay. The buried valleys (1) truncate the surrounding coarse-grained deposits, (2) are asymmetrical and steep sided, (3) trend northwest-southeast, (4) are several miles long and about 1 mile wide, and (5) extend to more than 500 feet below sea level. Water samples taken during 1995–98 from three production wells and six observation wells screened in the upper glacial and Magothy aquifers contained volatile organic compounds in concentrations that exceeded the New York State Department of Health Drinking Water Maximum Contaminant Levels. High iron or nitrate concentrations were detected in water samples taken in 1997–98 from 39 observation wells. Previous high concentrations resulted in the shutdown of two production wells. Four distinct areas of saltwater intrusion in the Oyster Bay study area were delineated—three were in the upper glacial aquifer, and the fourth was in the Lloyd aquifer. Borehole-geophysical-logging data indicated that three of these saltwater "wedges" ranged from a few feet thick to more than 100 feet thick and had sharp freshwater-saltwater interfaces. Chloride concentrations in water from eight observation wells within these wedges in 1997 ranged from 125 to 13,750 milligrams per liter. One production well in Bayville has been shut down as of 1996 and others in the area may be affected by these saltwater wedges.

New York↗
USGS2002

Hydrogeology and extent of saltwater intrusion on Manhasset Neck, Nassau County, New York

Manhasset Neck, a peninsula on the northern shore of Long Island, N.Y., is underlain by unconsolidated deposits that form a sequence of aquifers and confning units. Ground water at several public-supply wells has been affected by the intrusion of saltwater from the surrounding embayments (Manhasset Bay, Long Island Sound, Hempstead Harbor). Twenty-two boreholes were drilled during 1992-96 for the collection of hydrogeologic, geochemical, and geophysical data to delineate the subsurface geology and the extent of saltwater intrusion within the peninsula. A series of continuous high-resolution seismic- reflection surveys was completed in 1993 and 1994 to delineate the character and extent of the hydrogeologic deposits beneath the embayments surrounding Manhasset Neck. The new drill-core data indicate two hydrogeologic units--the North Shore aquifer and the North Shore confining unit--where the Lloyd aquifer, Raritan confining unit, and the Magothy aquifer have been completely removed by glacial erosion. Water levels at selected observation wells were measured quarterly throughout the study. These data, and continuous water-level records, indicate that (1) the upper glacial (water-table) and Magothy aquifers are hydraulically connected and that their water levels do not respond to tidal fluctuations, and (2) the Lloyd and North Shore aquifers also are hydraulically connected, but their water levels do respond to pumping and tidal fluctuations. Offshore seismic-reflection surveys in the surrounding embayments, and drill-core samples, indicate at least four glacially eroded buried valleys with subhorizontal, parallel reflectors indicative of draped bedding that is interpreted as infilling by silt and clay. The buried valleys (1) truncate the surrounding coarse-grained deposits, (2) are asymmetrical and steep sided, (3) trend northwest-southeast, (4) are 2 to 4 miles long and about 1 mile wide, and (5) extend to more than 400 feet below sea level. Water from 12 public-supply wells screened in the Magothy and upper glacial aquifers contained volatile organic compounds in concentrations above the New York State Department of Health Drinking Water maximum contaminant levels, as did water from one public- supply well screened in the Lloyd aquifer and from two observation wells screened in the upper glacial aquifer. Five distinct areas of saltwater intrusion have been delineated in Manhasset Neck; three extend into the Lloyd and North Shore aquifers, and two extend into the upper glacial and Magothy aquifers. Borehole-geophysical-logging data indicate that several of these saltwater wedges range from a few feet to more than 125 feet in thickness and have sharp freshwater-saltwater interfaces, and that chloride concentrations within these wedges in 1997 ranged from 102 to 9,750 milligrams per liter. Several public-supply wells have either been shut down or are currently being affected by these saltwater wedges. Data show active saltwater intrusion in at least two of the wedges.

New York↗
USGS1997

Urbanization and recharge in the vicinity of East Meadow Brook, Nassau County, New York: Part 4 — Water quality in the headwaters area, 1988-93

Surface-water and ground-water quality in the East Meadow Brook headwaters area was monitored during 1988-93 to determine the effects of urban stormwater on water quality before, and for 1 year after, the construction of a stormwater-detention basin in 1992. Stormwater samples were collected from the stream during storms. Between storms, water samples were collected from the stream and from a network of monitoring wells in the headwaters area. The detention basin was constructed as part of a pilot project to increase aquifer recharge while decreasing the discharge of contaminated stormwater to coastal waters. Bacteria and road salt were the major contaminants detected in stormwater samples, and the concentrations of organic compounds and nutrients in the samples rarely exceeded New York State drinking-water standards. Lead and chromium were detected in only a few of the stormwater samples, and cadmium was not detected in any of the samples. Loads of most inorganic constituents in stormwater reflected the season and the magnitude of the storm and were proportional to the total stormwater volume measured at the headwaters area. Stormwater during the nonwinter (non-road-salting) season had a diluting effect on shallow ground water adjacent to the stream. Large amounts of sodium and chloride that entered the stream and ground water after road-salt applications to the Westbury drainage area affected the ground-water quality beneath and adjacent to the stream for several months. Concentrations of sodium and chloride in streamwater on March 6, 1989, reached 1,700 mg/L (milligrams per liter) and 2,700 mg/L, respectively, as a result of road salt washed in by stormwater. Median concentrations of sodium and chloride in wells in an area affected by road salt were generally several times higher than concentrations in shallow wells in unaffected suburban areas. Bromide-to-chloride ratios were used to distinguish road salt from atmospherically derived sea salt within the shallow aquifer and indicated that ground water was affected by road salt to a depth of 14 meters.

New York↗
USGS1988

Geohydrology of the Bethpage-Hicksville-Levittown area, Long Island, New York

A study of ground-water levels and flow in east-central Nassau County, N.Y. , began in October 1985. The 11.4 sqare-mile area encompasses parts of Bethpage, Hicksville, Levittown, Plainview, Plainedge, and Farmingdale. Approximately 1,200 ft of unconsolidated Cretaceous deposits and 50 to 100 ft of Pleistocene deposits overlie bedrock throughout the area. The unconsolidated deposits consist mostly of sand, gravel, silt, and clay and have good water-transmitting properties except where clay forms continuous layers that can impede groundwater flow. The area is mostly residential and industrial. Pumpage for public supply exceeds 10 million gallons per day, most of which eventually discharges from the ground-water system to tidewater as sewage outflow. Industrial pumpage during summer exceeds 10 million gallons per day, but most of the water is returned to the system through recharge basins. Ground-water levels in this area fluctuate seasonally in response to natural recharge, pumping, and use of recharge basins.

New York↗
USGS1985

Effects of sanitary sewers on ground-water levels and streams in Nassau and Suffolk Counties, New York; part 3: Development and application of southern Nassau County model

By 1990, sanitary sewers in Nassau County Sewage Disposal Districts 2 and 3 and Suffolk County Southwest Sewer District will discharge to the ocean 140 cu ft of water per second that would otherwise be returned to the groundwater system through septic tanks and similar systems. To evaluate the effects of this loss on groundwater levels and streamflow, the U.S. Geological Survey developed a groundwater flow model that couples a fine-scale subregional model to a regional model of a larger scale. The regional model generates flux boundary conditions for the subregional model, and the subregional model provides detail in the area of concern. Results indicate that the water table will decline by as much as 90% from conditions in the early 1970's. This report is one of a three-part series describing the predicted hydrologic effects of sewers in southern Nassau and southwestern Suffolk Counties.

New York↗
USGS1985

Estimated public-water supply and industrial-commercial ground-water withdrawals and returns in Nassau County, Long Island, New York, 1973-79

Nassau County, New York depends upon ground water for its freshwater supply. The primary water uses are for public-water supply and industrial-commercial purposes, which together accounted for 202 Mgal/d (million gallons per day) in 1975. Public-water suppliers withdrew 85 percent of their water from the Magothy Formation. About 133 Mgal/d was returned to the ground after use in 1975, and about 69; Mgal/d was discharged to tidewater. In addition, about 34 Mgal/d infiltrated into sewerlines in 1975 and was also discharged to tidewater. Because of the importance of this freshwater supply, the New York State Department of Environmental conservation reviews applications for the installation of wells and compiles data on pumpage throughout Long Island. It also reviews applications to discharge wastewater into the surface water and ground water of the State. This report summarizes the data filed with the New York State Department of Environmental Conservation for Nassau County during 1973-79. It presents data and estimates on withdrawals for public and industrial-commercial supply, returns to the ground, and discharges through sewer systems. It also includes information on population and land use.

New York↗
USGS1982

Ground-water pumpage in Nassau County, Long Island, New York, 1920-77: Introduction and user's guide to the data compilation

Pumpage data from about 2,100 wells used for public and nonpublic water-supply in Nassau County from 1920-77 have been collected and are available for public inspection at the U.S. Geological Survey office in Syosset, Nassau County. Except for wells in use before 1920, these data constitute the entire record available through 1977. The data are divided into two categories--pumpage from wells used for public supply, and pumpage from wells used mainly for industrial and commercial uses, designated as nonpublic water supply. Pumpage is tabulated by well or well field and is given by month or year with an annual total. The report serves as an introduction and user 's manual to the data, which are available for inspection but are not included in the report because they fill several hundred pages. The report describes the method of reporting pumpage on Long Island and how pumpage values were derived from the records. It also includes well-completion data and two maps showing the location of all wells.

New York↗
USGS1980

Nitrogen in ground water and surface water from sewered and unsewered areas, Nassau County, Long Island, New York

Data on nitrogen in groundwater and surface waters in the sewered and unsewered parts of Nassau County were analyzed to evaluate the principal sources of nitrogen and to determine what factors significantly affect its concentration in the upper glacial aquifer and the underlying Magothy aquifer. Nitrate data for water samples collected during 1952-76 show that: (1) median nitrate concentration of water in the sewered part of the entire thickness of the upper glacial aquifer is not significantly different (at the 0.95 confidence limit, N = 1400) from that in the unsewered area, (2) median nitrate concentrations in the upper 3 meters of the upper glacial aquifer are significantly lower (at the 0.90 confidence limit, N = 15) in the sewered area than in the unsewered area, (3) in the sewered area, water from 8 of 10 wells in the upper glacial aquifer shows significantly decreasing nitrate concentration with time, (4) total nitrogen concentrations in streams draining the sewered area are significantly lower than in those draining the unsewered area, (5) from more than 2,000 nitrate analyses of water in the Magothy aquifer collected from 1952-76, it was found that nitrate is present at all depths but that nitrate concentrations decrease with depth, and (6) although water from most Magothy wells having long-term nitrate records shows no significant change in nitrate concentration with time, where the change is significant, nitrate is increasing. (USGS)

New York↗
USGS1978

Reconnaissance for microbial activity in the Magothy aquifer, Bay Park, New York, four years after artificial recharge

Tertiary-treated sewage effluent was injected into the Magothy aquifer at Bay Park, Long Island, N.Y., between 1968 and 1973. In 1977, the microbial flora in water samples from the injection well and from three nearby wells were surveyed. Differences in the composition of the microbial flora among the four wells were found. A bacterial community dominated by facultative and obligate anaerobes, including two Clostridium species and methanogenic bacteria, was found at a well 6.1 m from the injection well. By contrast, except for isolation of Clostridium sphenoides from a well 30 m away, only obligate aerobes and facultative anaerobes were found in water from the injection well and the 30 m well. Only a small number of obligate aerobes were found in samples from a well 61 m away. These results suggest that nutrients in the recharge water formed an organically enriched zone to at least a distance of 6.1 m from the point of injection but not as far as 61 m. Extensive pumping at the end of the injection program apparently removed exogeneous nutrients near the injection well.

New York↗