Hydrologic Monitoring in the Central Pine Barrens

Science Center Objects

The Long Island Central Pine Barrens (CPB) is a large, preserved region of pristine ecological habitat located in eastern parts of Suffolk County, Long Island, NY. The 106,500-acre CPB encompasses portions of the Towns of Brookhaven, Riverhead, and Southampton, and is a core part of the larger Long Island Pine Barrens Maritime Reserve (fig. 1). The CPB overlies portions of Long Island’s federally designated sole-source drinking-water aquifer, and encompasses part of the watersheds for two of the four major rivers on Long Island; the Carmans and Peconic Rivers.

map of Long island in shades of green with markers for gw wells and stream sites

Figure 1Click here open an interactive map of the location of USGS stream-discharge, groundwater-level, and water-quality monitoring stations within the Central Pine Barrens region of Long Island, NY.​​​​​​​ (Public domain.)


The effects of development within and surrounding the CPB region present a risk to the quality and quantity of ground and surface water in this sensitive ecosystem. Continued development in the area has increased water-supply demands, and added impervious surfaces that reduce direct groundwater recharge and increase storm-water runoff. Additionally, encroaching urbanization has increased the potential for anthropogenic contamination from fertilizer and pesticide application, and from onsite wastewater-disposal systems.

The U.S. Geological Survey (USGS) has partnered with the Central Pine Barrens Commission, the Town of Brookhaven, the Suffolk County Water Authority, the Suffolk County Department of Health Services, and the New York State Department of Environmental Conservation to provide extensive long-term water-quality and water-quantity monitoring within the CPB region. The monitoring program provides natural-resource managers, stakeholders, and the public with a comprehensive baseline of water-resource conditions that can be compared to future hydrologic conditions to identify potential areas of ecohydrologic concern that may result from encroaching development or other stressors within the CPB.

Water-Quality Monitoring

Water-Quality Sampling in Streams

To understand the effects of point and non-point contamination sources on the streams within the CPB the USGS collects water samples from seven locations along two streams; 5 sites along the Carmans River (01304990, 01304995, 01304998, 01305000, 01305040) and 2 sites along the Peconic River (01304440, 01304500). Peconic River sites are sampled two times a year (spring and fall) and Carmans Rivers sites are sampled four times a year (seasonally). Each water sample collected is analyzed for nutrients, major inorganic constituents, and alkalinity. Analysis of pesticides and pharmaceutical constituents occurs annually for samples from select sites. A schedule of the stream-sampling effort is shown in Table 1.

table of Water-quality sampling schedule at streams within the Central Pine Barrens

Table1: USGS water-quality sampling schedule at streams within the Central Pine Barrens region. [Tasks listed by Federal Fiscal Year (FFY); “X” indicates a sample collected for nutrients, major inorganics, and alkalinity; “*” indicates a sample collected for pesticides and pharmaceuticals. Physical parameters (pH, dissolved oxygen, water temperature, specific conductance, and turbidity) are collected during each sample visit]  (Public domain.)

Groundwater-Quality Sampling

The groundwater-aquifer system underlying the CPB region consists of a series of mostly unconsolidated stratified sediments comprised of sand, gravel, silt and clay (fig. 2). The uppermost aquifer (upper glacial aquifer), contains the water table and is generally comprised of Pleistocene outwash and ice-contact deposits. Beneath the upper glacial aquifer lies the Cretaceous Magothy and Lloyd aquifers.

Water-table aquifer wells and deeper supply wells have been sampled by the USGS in previous years for select projects. The most recent groundwater samples were collected in 2018 from six water-table aquifer wells within the CPB region (fig. 1) were sampled in 2018 by the USGS, to provide a water-quality dataset documenting shallow-groundwater quality conditions. Samples collected from these wells were analyzed for nutrients, major inorganics, alkalinity, pesticides, volatile- organic compounds, pharmaceuticals, and per- and polyfluoroalkyl substances (PFAS).

blue and gray illustration of Long Island aquifers

Figure 2. Generalized cross section of Long Island showing the main aquifers and confining units (Cohen and others, 1968) (Public domain.)

Water-Quantity Monitoring

Groundwater Levels

Groundwater-level elevations are measured by the USGS at wells located  in within the CPB monthly and annually. In 2019 at 29 wells were measured monthly , and annually at an additional 17 wells were measured annually (fig. 1). Three wells equipped with water-level recorders provide continuous data used to document water-table fluctuations in the region related to changes in precipitation and water usage. The data also provides insight into changing locations of stream start-of-flow along the Carmans and Peconic rivers.

These groundwater-elevation measurements collected in the CPB region are part of a larger USGS monitoring program that provides information on the altitude of the water table, and the deeper Magothy and Lloyd aquifers, throughout most of Long Island. This larger network is funded through USGS cooperation with State, County, and local partners, and provides the information needed for various water management, ecological, and engineering issues, and for the production of USGS water-level maps, depth-to-water maps, and hydrological-study reports.

 Stream Discharge

Nearly all of the water flowing in streams and moving through lakes on Long Island is derived from groundwater, therefore, they provide a window to the overall health of the underlying aquifer system. If the water table is lowered due to drought, pumping, or sewering, the ecosystems of these streams, lakes, and wetlands can be adversely impacted.

The USGS assess streamflow conditions in the CPB region, by collecting discharge measurements at 7 locations two times per year (spring and fall) at the two largest streams; 5 locations along the Carmans River and 2 along the Peconic River (fig. 1). These measurements supplement the continuous data collected by the USGS at permanent-gaged locations along both rivers that is funded through a cooperative program with State, County, and local agencies.

Additional stream discharge will be measured by the USGS during one water-quality sampling event (spring or fall) at both Carmans and Peconic River gaged locations (01304500, 01305000) and at the ungaged downstream Carmans River location (01305040 ) to help assess the contaminant load for each stream. A sample collection timeline is provided in Table 1.

Additional information on USGS hydrologic monitoring activities throughout Long Island is available from the “U.S. Geological Survey Hydrologic Monitoring on Long Island, New York” Project Webpage or from the New York Water Science Center Homepage

2019 Summary of Data Collection within the Central Pine Barrens Region