Implementation of New
York State ’s Source
Water Assessment Program in Nassau and Suffolk Counties
Authors: Daniel O’Rourke, Project Hydrogeologist, CDM
Mary Anne Taylor, P.E., Project Manager,
CDM
CDM, 100 Crossways Park,
Phone:
(516)-496-8400
Fax: (516)-496-8864
E-mail:
orourkede@cdm.com
The federal Safe Drinking Water Act (SDWA)
Amendments of 1996 created a Source Water Assessment Program (SWAP) to evaluate
existing and potential threats to the quality of public drinking water
supplies. The New York State Department
of Health (NYSDOH) Bureau of Water Supply Protection developed the New York
State SWAP Plan, and directed the implementation of the Plan for the over 1,300
public supply wells that provide drinking water to nearly 3 million people in
Assessment of each well
required:
- Delineation
of its source water recharge area;
- Determination
of the prevalence of various contaminants associated with land use and
point sources within each well’s source water area; and
- Evaluation
of each well's susceptibility to potential contamination based on the
prevalence of contaminants within the source water area, the
model-estimated time of travel to each well, and the contaminant
characteristics
Three existing tools were used creatively to
evaluate the potential impact of man’s activities and complete the Source Water
Assessments. Successful
implementation of this project required application of three-dimensional groundwater
models, integration of the model output with GIS summaries of land use types
and point source locations, and use of a carefully planned database to organize
information relating land use types and point source data and relate it to the
potential to cause groundwater contamination.
While groundwater models are routinely applied to
assist in evaluating water quality impacts, the scale of application for SWAP
is believed to be unique. Traditional
source water area delineations have incorporated a number of simplifying
assumptions that result in parabolic shaped source water areas located
immediately upgradient of each well.
Long Island’s public supply well network consists of hundreds of wells,
many of which are screened deep within the aquifers and that have contributing
or source water areas located miles away from the well, as shown by figure
1. This is particularly true of public supply
wells screened within the Lloyd aquifer along
Figure 1 – Location and Size of Source Water Areas
Depend upon Well Characteristics
Water supply pumping at all of these wells
simultaneously also modifies the regional flow fields, such that the
contributing areas are not regularly shaped zones, but complex shapes that fit
together like “pieces in a puzzle”, as shown by figure 2. A complex three-dimensional modeling
framework was required to consider the simultaneous water supply pumping of
hundreds of wells.
The land
uses and specific facilities (point sources) within each well’s model estimated
source water area were inventoried and their potentials to contaminate ground
water (contaminant prevalence) were assessed independently for each of four
contaminant categories (microbials, nitrates, volatile organic chemicals (VOCS)
and pesticides). The overall potential for these potential contamination
sources to be present within a supply’s source water area was aggregated, to
develop a “contaminant prevalence rating” for each contaminant category.
The source water assessments also evaluated the
well’s “sensitivity” to each of the four types of contamination, the likelihood
that contamination would reach the well, considering the model-estimated time
of travel to each well, and the fate and transport of those contaminants. Finally, each well’s “susceptibility” to
each of the four categories of contamination was assessed, based upon the
assigned ratings for contaminant prevalence and sensitivity.
Figure 2 – Source Water Areas Fit Together Like Puzzle Pieces (only select source water areas shown).
The Long Island SWAP shows how complex regional problems can be resolved with carefully planned integration of existing technologies. A Microsoft Accessâ database was used to integrate well data, groundwater model results, and ArcInfoâ compiled-land use and contaminant source summaries in each travel time of zone for each well. The criteria for assessing contaminant prevalence, sensitivity and susceptibility were also incorporated into the database. Using the data and criteria, database functions were developed to quickly generate the land use and point source contaminant prevalences, well sensitivities and susceptibilities, and to automatically compile the ratings into individual well assessment reports. Due to the sheer volume of data and the number of well reports required, manual compilation and report generation using other techniques would have been nearly impossible. Simultaneously simulating multiple wells with the groundwater models, processing the information using ArcInfoâ and a carefully designed database proved to be crucial.
Well-specific reports, including a series of tables, figures and the
characteristics of the source water area, along with a summary of the data
characterizing each well, were prepared. These resources are now available to Long
Island water managers for use in their continuing work to protect and preserve
the
Acknowledgements
The contributions of New York State Department of Health,
Nassau County Department of Health and Public Works Water Management Unit,
Suffolk County Department of Health Services, and the New York State Department
of Environmental Conservation, to the development of the SWAP for
References
Heywood,
B.J., M.A. Taylor, M. Labiak, R.H. Fitzgerald, D.E. O'Rourke, B.M. Harley,
2004. Use of
Integrated Groundwater Modeling And GIS Tools In The Development of Source
Water Assessments For 1,300 Wells In Nassau And Suffolk Counties, Long Island,
New York, AWRA Annual Spring Specialty Conference GIS and
Water Resources III Nashville, TN, May 17-19, 2004.
CDM. November 1990.
CDM. March 1998.
CDM. October 2003.
Nassau
County Department of Health (NCDH). 2002. Water Quality Database – Public
Supply Wells (unpublished data).
Nassau
County Department of Health (NCDH). 2002. Point source database
(unpublished data).
New
York State Department of Environmental Conservation. 2002.
Database (unpublished data).
New
York State Department of Health. 2003.
Summary Report, 53 p.
OMB
Watch Right to Know Environmental Databases. 2002.
http://www.rtknet.org/rtkdata.php
Suffolk
County Department of Health Services (SCDHS). 2002. Facilities Database
(unpublished data).
Suffolk
County Department of Health Services (SCDHS). 2002. Water Quality Database –
Public Supply Wells (unpublished data).
United States Environmental Protection Agency. 2002. Envirofacts database,
http://www.epa.gov/enviro/index_java.html.