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Slug-Test Analysis of Selected Wells at an Earthen Dam Site in Southern Westchester County, New York

Open-File Report 2019-1102
Prepared in cooperation with the New York City Department of Environmental Protection
By: , , and 
https://doi.org/10.3133/ofr20191102

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Abstract

In 2005, the U.S. Geological Survey began a cooperative study with the New York City Department of Environmental Protection to characterize the local groundwater-flow system and identify potential sources of seeps on the southern embankment of the Hillview Reservoir in southern Westchester County, New York. The earthen embankment comprises low-permeability glacial clays that were excavated from the site and rest on a veneer of low-permeability glacial deposits that overlie crystalline bedrock. At least two groundwater-flow zones—one shallow and the other deep—overlie the bedrock at the reservoir. As part of the study, slug-test data from 38 screened wells were analyzed to determine the hydraulic conductivity of the sediments in the groundwater-flow zones. Slug-test data were collected from 12 wells at the Hillview Reservoir during August 2007 and from 25 wells at the reservoir and 1 monitoring well south of the reservoir in northern Bronx County in June 2012.

Hydraulic conductivity values at the reservoir ranged from 0.0012 to 2 feet per day. On the southern embankment, hydraulic conductivity ranged from 0.0026 to 1 foot per day for wells screened in the shallow saturated zone; 0.0012 to 2 feet per day for wells screened in the deep saturated zone; and 0.021 to 0.27 foot per day for wells screened in the toe of the southern embankment, where the deep and shallow saturated zones coalesce. A hydraulic conductivity of 0.016 foot per day was determined for a well partially screened in the crystalline-bedrock aquifer, which potentially indicates an interconnection of transmissive fractures near the bedrock surface. The results of four slug-out tests are also included in this report to quality assure the hydraulic conductivity estimates from the slug-in test analysis. The results of the four slug-out tests were within 8 percent of slug-in test results, with an average of less than 2 percent.

Suggested Citation

Noll, M.L., Chu, A., and Capurso, W.D., 2019, Slug-test analysis of selected wells at an earthen dam site in southern Westchester County, New York: U.S. Geological Survey Open-File Report 2019–1102, 14 p., https://doi.org/10.3133/ofr20191102.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Slug-Test Methods and Well Installation
  • Slug-Test Analysis
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Slug-test analysis of selected wells at an earthen dam site in southern Westchester County, New York
Series title Open-File Report
Series number 2019-1102
DOI 10.3133/ofr20191102
Year Published 2019
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) New York Water Science Center
Description Report: vi, 14 p.; Data Release
Country United States
State New York
County Westchester County
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details