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Aquifer geochemistry and effects of pumping on ground-water quality at the Green Belt Parkway Well Field, Holbrook, Long Island, New York

Water-Resources Investigations Report 2001-4025

Prepared in cooperation with the Suffolk County Water Authority
By:
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Abstract

Geochemistry, microbiology, and water quality of the Magothy aquifer at a new supply well in Holbrook were studied to help identify factors that contribute to iron-related biofouling of public-supply wells. The organic carbon content of borehole sediments from the screen zone, and the dominant terminal electron-accepting processes (TEAPs), varied by depth. TEAP assays of core sediments indicated that iron reduction, sulfate reduction, and undetermined (possibly oxic) reactions and microbial activity are correlated with organic carbon (lignite) content. The quality of water from this well, therefore, reflects the wide range of aquifer microenvironments at this site.

High concentrations of dissolved iron (3.6 to 6.4 micromoles per liter) in water samples from this well indicate that some water is derived from Fe(III)-reducing sediments within the aquifer, but traces of dissolved oxygen indicate inflow of shallow, oxygenated water from shallow units that overlie the local confining units. Water-quality monitoring before and during a 2-day pumping test indicates that continuous pumping from the Magothy aquifer at this site can induce downward flow of shallow, oxygenated water despite the locally confined conditions. Average concentrations of dissolved oxygen are high (5.2 milligrams per liter, or mg/L) in the overlying upper glacial aquifer and at the top of the Magothy aquifer (4.3 mg/L), and low ( < 0.1 mg/L) in the deeper, anaerobic part of the Magothy; average concentrations of phosphate are high (0.4 mg/L) in the upper glacial aquifer and lower (0.008 mg/L) at the top of the Magothy aquifer and in the deeper part of the Magothy (0.013 mg/L). Concentrations of both constituents increased during the 2 days of pumping. The δ34S of sulfate in shallow ground water from observation wells (3.8 to 6.4 per mil) was much heavier than that in the supplywell water (-0.1 per mil) and was used to help identify sources of water entering the supply well. The δ34S of sulfate in a deep observation well adjacent to the supply well increased from 2.4 per mil before pumping to 3.3 per mil after pumping; this confirms that the pumping induced downward migration of water. The lighter δ34S value in the pumped water than in the adjacent observation well probably indicates FeS2 oxidation (which releases light δ34S in adjacent sediments) by the downward flow of oxygenated water.

Suggested Citation

Brown, C.J., Colabufo, Steven, and Coates, J.D., 2002, Aquifer geochemistry and effects of pumping on ground-water quality at the Green Belt Parkway Well Field, Holbrook, Long Island, New York: U.S. Geological Survey Water-Resources Investigations Report 2001–4025, 21 p., https://pubs.er.usgs.gov/publication/wri014025.

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Study Methods
  • Aquifer Geochemistry
  • Effects of Pumping on Ground-Water Quality
  • Conclusions
  • References Cited

Additional publication details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Aquifer geochemistry and effects of pumping on ground-water quality at the Green Belt Parkway Well Field, Holbrook, Long Island, New York
Series title:
Water-Resources Investigations Report
Series number:
2001-4025
Year Published:
2002
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
New York Water Science Center
Description:
v, 21 p.
Country:
United States
State:
New York
City:
Holbrook
Other Geospatial:
Long Island
Online Only (Y/N):
Y
Additional Online Files (Y/N):
N