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| Publications— Data Series |
U.S. Geological Survey Data Series 292
By Peter J. Cinotto
This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.
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This report presents the results of a study by the U.S. Geological Survey (USGS), in cooperation with the Chester County Water Resources
Authority (CCWRA), to update the drought-trigger water levels for the Chester County observation-well network. The Chester County observation-well
network was established in 1973 through a cooperative agreement between the CCWRA and the USGS to monitor local ground-water levels
and trends and to determine drought conditions.
In 1990 and again in 1997, drought-warning and drought-emergency water-level triggers were determined for the majority
of wells in the existing Chester County observation-well network
of 23 wells. Since 1997, the Chester County observation-well network expanded to 29 wells, some of the original wells were destroyed, and
additional monthly water-level observations were made to allow for better statistical relations. Because of these changes, new statistics for
water-level triggers were required.
For this study, 19 of the 29 wells in the observation-well network were used to compute drought-trigger water levels. An additional "drought-watch
water-level trigger" category was developed to make the Chester County drought-trigger water-level categories consistent with those implemented by
the Pennsylvania Department of Environmental Protection (PaDEP). The three drought-trigger water-level categories, as defined by PaDEP are
1) "drought watch" when at the 75th-percentile level; 2) "drought warning" when at the 90th-percentile level; and 3) "drought emergency" when at
the 95th-percentile level.
A revised methodology, resulting from longer periods of record representing ground-water and climatic conditions and changes in local water use,
has resulted in some observed differences in drought-trigger water levels. A comparison of current drought-trigger water levels to those calculated
in 1997 shows the largest mean annual change in percentile values was in northeastern Chester County. In this northeastern region, the average
90th-percentile water levels changed by as much as 1.84 feet (17.5 percent) from those determined in 1997. Other observation wells in the county
generally exhibited a smaller mean annual change in percentile values; a typical change was less than 0.5 foot. While most revisions in the
drought-trigger water levels generally can be attributed to different methodology and (or) the additional years of data collected under existing
climatic conditions, anthropogenic influences, such as the cessation of local pumping stresses, also were shown to cause changes in the
drought-trigger water levels determined in this study.
Abstract
Introduction
Purpose and Scope
Overview of the Chester County Observation-Well Network
Methods for Determination of Drought-Trigger Water Levels
Use of Drought-Trigger Water Levels
Drought-Trigger Water Levels for Wells in the Chester County Observation-Well Network
Comparison to Previous Studies
Summary
References Cited
This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.
View the full report in PDF 726 KB
For more information about USGS activities in Pennsylvania contact:
Director
USGS Pennsylvania Water Science Center
215 Limekiln Road
New Cumberland, Pennsylvania 17070
Telephone: (717) 730-6960
Fax: (717) 730-6997
or access the USGS Water Resources of Pennsylvania home page at:
http://pa.water.usgs.gov/.