CONTENTS

 

Abstract

Introduction

Purpose and scope

Location of study area

Methods of study

Seismic-reflection survays

Borehole-geophysical logs

Water-level data

Water-quality data

Previous investigations

Acknowledgments

Hydrogeology

Stratigraphy

Bedrock

Lloyd aquifer

Raritan clay

Magothy aquifer

North Shore aquifer

North Shore confining unit

Upper glacial aquifer

Seismic-reflection survey

Borehole-geophysical logs

Precipitation

Ground water

Pumpage

Water levels

Upper glacial aquifer

Magothy aquifer

Lloyd and North Shore aquifers

Water quality

Chloride

Volatile organic compounds

Inorganic constituents and metals

Extent of saltwater intrusion

Saltwater wedges A and B

Saltwater wedge C

Saltwater wedge D

Other saltwater wedges

Summary and conclusions

References cited

 

FIGURES

 

1. Map showing location of Great Neck and Manhasset Neck peninsulas, and of seismic-reflection profiles, Nassau County, N.Y.: A. General location map. B. Location of Great Neck study area

2. Map showing locations of public-supply wells, observation wells, and golf-course wells within the Great Neck Peninsula, Nassau County, N.Y.

3. Map showing surface altitude of bedrock underlying Great Neck, N.Y.

4. Hydrogeologic sections on Great Neck, N.Y.

A. Section A-A´

B. Section B-B´

C. Section C-C´

D. Section D-D´

5-10. Maps of Great Neck, N.Y., showing extent and upper surface altitude of selected hydrogeologic units:

5. Lloyd aquifer

6. Raritan clay

7. Magothy aquifer

8. North Shore aquifer

9. North Shore confining unit

10. Upper glacial aquifer

11. Section showing interpreted stratigraphy along seismic-reflection profiles E-E´, F´-F, and G´-G off Great Neck, N.Y.

A. E-E´ in Long Island Sound

B. F´-F in Little Neck Bay

C. G´-G in Manhasset Bay

12. Geophysical logs of test well N12581T, Great Neck, N.Y.

13. Hydrograph showing water levels measured at four selected wells during 1992-93 tidal study on Great Neck, N.Y.

14-15. Maps of Great Neck, N.Y., showing water levels in August 1995:

14. Water-table altitude

15. Potentiometric-surface altitudes in the Lloyd and North Shore aquifers

16. Graphs showing chloride concentrations and pumpage at selected public-supply wells on the Great Neck, N.Y., peninsula: A. Well N5884, 1957-95. B. Wells N30 and N31, 1952-86. C. Well N1926, 1948-67

17. Map showing chloride concentrations in Lloyd, North Shore, and upper glacial aquifers, Great Neck, N.Y., 1996

18. Hydrogeologic section showing extent of saltwater wedge A, Great Neck, N.Y.

19. Graph showing chloride concentrations and pumpage at public-supply wells (A) N687 and (B) N2214 on Great Neck, N.Y., 1950-96

20. Graph showing chloride breakthrough curve at public-supply wells (A) N1298 (1952-96) and (B) N3443 (1951-96), screened in the Lloyd aquifer, Great Neck, N.Y.

 

TABLES

 

1. Generalized description of the hydrogeologic units underlying the Great Neck peninsula, N.Y.

2. Total annual pumpage from the Great Neck peninsula, by aquifer, 1992-96