&EPA
United States
Environmental Protection
Agency
Region 10
1200 Sixth Avenue, Suite 900
Seattle WA 98101
March 2013
EPA910-R-13-003
SUPPORT DOCUMENT FOR SOLE
SOURCE AQUIFER DESIGNATION OF
THE BAINBRIDGE ISLAND AQUIFER
SYSTEM
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SUPPORT DOCUMENT
FOR SOLE SOURCE AQUIFER DESIGNATION
OF THE BAINBRIDGE ISLAND AQUIFER SYSTEM
Prepared by
U.S. Environmental Protection Agency, Region 10
Office of Environmental Assessment for:
Drinking Water Unit,
Seattle, Washington 98101
March 2013
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TABLE OF CONTENTS
INTRODUCTION 5
Purpose 5
Sole Source Aquifer Program 5
Petition 6
Community Involvement 6
GEOGRAPHY 7
Climate 7
HYDROGEOLOGY 7
BOUNDARIES 10
GROUND WATER QUALITY 10
POTENTIAL FOR CONTAMINATION 11
POPULATION AND DRINKING WATER CONSUMPTION 11
ALTERNATIVE DRINKING WATER SOURCES 12
CONCLUSION 12
REFERENCES 15
FIGURES
Figure 1. Petitioned Bainbridge Island and surrounding area
Figure 2. Surficial geology of Bainbridge Island
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FINAL SUPPORT DOCUMENT FOR SOLE SOURCE
AQUIFER DESIGNATION OF THE BAINBRIDGE ISLAND
AQUIFER SYSTEM
INTRODUCTION
Purpose
This document summarizes readily available information and
describes the technical and legal basis for the proposed U.S.
Environmental Protection Agency (EPA) designation of the Bainbridge
Island aquifer system as a sole source aquifer. All technical information
presented in the document is referenced from the petition submitted to
EPA.
Sole Source Aquifer Program
The Sole Source Aquifer Program is authorized by the Safe Drinking
Water Act of 1 974 (Safe Drinking Water Act, Public Law 93-523 42 U.S.C.
300 et.seq). Section 1424(e) of the Safe Drinking Water Act states:
"If the Administrator determines, on his own initiative or upon
petition that an area has an aquifer which is the sole or principal drinking
water source for the area and which, if contaminated, would create a
significant hazard to public health, he shall publish notice of that
determination in the Federal Register. After the publication of any such
notice, no commitment for Federal financial assistance (through a grant,
contract, loan guarantee, or otherwise) may be entered into for any
project which the Administrator determines may contaminate such
aquifer through a recharge zone so as to create a significant hazard to
public health, but a commitment for Federal assistance may, if authorized
under another provision of law, be entered into to plan or design the
project to assure that it will not so contaminate the aquifer."
EPA defines a sole or principal source aquifer as an aquifer or
aquifer system which supplies at least 50 percent of the drinking water
consumed in the area overlying the aquifer, and for which there is no
alternative source or combination of alternative drinking water sources
which could physically, legally and economically supply those dependent
upon the aquifer (U. S. EPA, 1 987). For convenience, all EPA designated
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sole or principal source aquifers or aquifer systems are often referred to
simply as "sole source aquifers".
Although EPA has authority to initiate sole source aquifer
designations, the agency has a longstanding history of only responding
to petitions. Until 1 987, EPA accepted sole or principal source aquifer
petitions which contained a minimum amount of information. This
practice changed when EPA released the Sole Source Aquifer Petitioner
Guidance document in February of 1 987. The guidance clarifies the
definition and acceptable delineation of a sole or principal source aquifer,
and describes how to petition EPA.
Petition
The EPA Region 10 Drinking Water Unit in the Office of Water and
Watersheds received a draft sole source aquifer petition dated August 5,
2009 from Melanie Keenan and Malcolm Gander, individuals and
residents of Bainbridge Island.
Additional information was requested by EPA from the petitioners
and was submitted to EPA postdated July 9, 2010. On August 12, 2010
the petitioners were informed by EPA that their submittal was complete
and the technical review could begin. In January 201 2 comments by the
petitioners were incorporated into this draft technical support document
and received by Rl 0 Drinking Water Unit in the Office of Water and
Watersheds.
Community Involvement
In February 201 2, EPA began developing the community outreach
plan for this potential designation. The Agency designed a
communication strategy. This guided our efforts to ensure that the
community and interested stakeholders were informed of EPA's actions
and had the opportunity to be meaningfully involved.
A public comment period of forty-five days from April 20 through
June 4, 201 2 was announced in the Bainbridge Islander local newspaper
and announced via mailings and email. The mailings and emails also
included a Fact Sheet that discussed the project and where to review the
project documents. On April 20 the Draft Technical Support Document
and the original petition were posted on a dedicated web site
(http://go.usa.gov/PzJ). Hard copies of the above referenced project
documents were also available for public review at the Bainbridge Island
Library Reference desk and at the Bainbridge Island City Hall.
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EPA received a total of seven comments. Two of the comments
were from the petitioners. Of the five remaining comments four were in
support of the designation and one had questions.
GEOGRAPHY
The petitioned area is Bainbridge Island (Figure 1). The Island's
hydrogeologic characteristics are similar to the following Puget Sound
islands whose aquifers have already been designated as sole source
aquifers by EPA: Camano, Whidbey, Marrowstone, Guemes, and Vashon-
Maury. The island has a total of 53 miles of seawater shoreline. Interior
plateaus reach maximum elevations of 300 to 400 feet above mean sea
level. The island can be divided into 12 drainage basins and is primarily
a mixture of developed land and variably forested areas. The Olympic
Mountains are located 40 miles northwest and the Cascade Mountains are
50 miles to the east (Keenan and Gander, 2009).
Climate
Bainbridge Island has a mid-latitude, wet-coast marine climate with
relatively cool, dry summers and mild, rainy winters. Summer
temperatures average in the 70s during the day and 50s at night, winter
temperatures are generally in the 40s during the day and 30s at night.
Rainfall ranges from 34 to 36 inches per year (Keenan and Gander, 2009).
HYDROGEOLOGY
Geology
The following information was extracted from the petition (Keenan
and Gander, 2009).
At least six advances and retreats of Pleistocene continental
glaciers over the last 300,000 years has shaped the present-day
landscape and underlying hydrostratigraphy of the Island (Easterbrook
1 994). This resulted in the deposition of large volumes of
unconsolidated glacial and interglacial material (mixtures of sand, silt,
clay and gravels), which are host to the aquifers of the Island. Other
geologic units are present on the Island and have less importance from a
hydrologic standpoint. These units include surficial Quaternary alluvial
deposits, and Tertiary sedimentary rocks, which are exposed at the
southern end of the Island on the up-thrown side of a major east-west
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trending fault that transects the Island. Figure 2 presents a surficial
geologic map of the Island.
The Quaternary alluvium unit includes recent stream, lake,
floodplain, beach, and peat deposits. These are generally thin and
discontinuous surficial deposits that cover less than one percent of the
study area.
The Vashon deposits are the youngest glacial deposits on the
Island (Easterbrook 1 968; Easterbrook 1 994). They consist of poorly
sorted sand and gravel of the Vashon recessional outwash (Qvr). Below
the Qvr is the much more extensive Vashon till (Qvt), which comprises the
majority of the Island's surficial exposures. The Qvt is a mixture of
unstratified clay through boulder size detritus. Below the Qvt is the
Vashon advance outwash (Qva), composed of sand and silty sand with
lesser amounts of gravel and occasional lenses of silt. Locally, the
Lawton Clay (Qvl) lies below the Qva and consists of clay and silt
deposited in lakes that formed ahead of the advancing Vashon glacier.
Below the Vashon deposits are alternating groups of nonglacial and
glacial unconsolidated sedimentary deposits, which have been variably
named by several earlier workers. This early glacial period's deposits are
not as evident as the Vashon, but are present above sea level.
Delineation of the glacial units is further complicated by yet another
earlier interglacial and then glacial episode that are present in some
outcrops above sea level. Older glacial/interglacial episodes are evident
in well logs and do not outcrop.
The aforementioned east-west fault at the south end of the Island
juxtaposes unconsolidated Pleistocene sediments to the north with
Tertiary sedimentary bedrock in the south. The Tertiary bedrock, which
is mantled by Vashon glacial deposits, is the oldest material on the
Island. The bedrock consists of shale, sandstone, and conglomerate
deposited in a marine environment, and have been assigned to either the
Blakely Formation or the Blakely Harbor Formation.
Aquifer System
The following information was extracted from the petition (Keenan
and Gander, 2009).
Large volumes of unconsolidated glacial and interglacial materials are
host to the aquifers on Bainbridge Island. Six principal aquifers have
been identified on the Island:
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1) Perched Aquifer System (PA) - This aquifer occurs in Vashon
advance glacial outwash, which consists of fine to medium-grained
silty sand with interspersed gravelly units. About 4 percent of the
wells on the island are reportedly completed in this unit, and the
producing zone is generally > 200 feet (ft) above mean sea level
MSL.
2) Semi-Perched Aquifer (SPA) - This aquifer occurs in a mixture of
non-glacial and glacially-derived sands and gravels. About 25
percent of the wells on the island are completed in this unit, and
the producing zone is generally between 100 and -20 ft MSL.
3) Sea Level Aquifer (SLA) - This aquifer has been tentatively assigned
to glacial deposits referred to as the Salmon Springs Drift. It is the
most widely used aquifer with 53 percent of the wells completed in
this unit, and the producing zone is 40 to -230 ft MSL.
4) Glaciomarine Aquifer System (GMA) - This aquifer ranges in
composition from clay, silt, and silt-rich sand, to sand and gravel.
It also contains interspersed zones of organic material, which
indicates a non-glacial origin for this unit. About 2 percent of the
island wells are completed in this unit. Several of the island's deep
production wells are screened in the top of this aquifer, and the
producing zone is typically -400 to -76- ft MSL.
5) Fletcher Bay Aquifer System (FBA) - This is the deepest of the six
main aquifers encountered on the island. It is composed of sand
and gravel with subordinate amounts of silt and silty sand. Wells in
this unit are typically screened between
-690 to -1,010 ft MSL. Although less than 1 percent of the island's
wells are completed in this unit, the metered Kitsap Public Utility
District (KPUD) and City of Bainbridge Island Fletcher Bay Aquifer
(GOBI FBA) wells provide approximately 30 percent of the estimated
total water production on the island.
6) Bedrock Aquifer System (BAS) - This aquifer is a minor source of
groundwater on the island. Less than one percent of the wells are
completed in this unit. The wells are screened in sedimentary
rocks of the Blakely Harbor and Blakely Formations, and are located
on the south end of the island.
On-lsland precipitation is the only source of aquifer recharge in the
SSA. Approximately thirty-four to thirty-eight inches of rain falls annually
on Bainbridge Island, with the majority of that occurring in the winter
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months. All of the water from the aquifers, as well as lakes, ponds, and
streams, originates from precipitation on the island.
The ability of the Island to meet water demands in the future depends
largely on production from the Fletcher Bay Aquifer System, which
currently produces the most for the City of Bainbridge Island. The
Fletcher Bay Aquifer System has been correlated with deep aquifers on
Kitsap Peninsula; however, there is no evidence that the two are
hydraulically connected. The Fletcher Bay Aquifer System is not an
unlimited source, and its recharge area and recharge rates are poorly
understood.
Another important source of groundwater resources on the Island is
the Sea Level Aquifer System. Future increases in production have been
recommended to be taken from this System, particularly in the north and
central portions of the Island. The Sea Level Aquifer system is not an
unlimited source, and its recharge area and recharge rates are unknown.
BOUNDARIES
The petitioned aquifer is presented in Fig. 1. The Bainbridge Island Sole
Source Aquifer boundaries are representative of an aquifer system that
encompasses the entire Bainbridge Island area. The aquifer area is
bounded on all sides by Puget Sound. The vertical extent of the aquifer
system at depth includes all potable water-bearing geologic units
underlying the island.
The Bainbridge Island Sole Source Aquifer boundaries were
determined by following aquifer definitions from EPA Guidance (EPA,
1 987). The Guidance states that petitioners may request designation for
part of an aquifer, an entire aquifer, or an aquifer system. A petitioner
can request designation for part of an aquifer if that portion is
hydrogeologically separated from the rest of the aquifer. A petitioner can
also request designation for an aquifer system to the extent that all
aquifers in the system are hydrogeologically connected.
GROUND WATER QUALITY
A comprehensive study of the drinking water quality on Bainbridge
Island has never been completed due to lack of funding. In general,
groundwater quality on the Island is good. Iron and manganese are the
most common analytes found to exceed the Federal Maximum
Contaminant Level (MCL). High iron and manganese can cause a
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somewhat objectionable odor, taste, or color, but generally are not
considered a health problem.
POTENTIAL FOR CONTAMINATION
The aquifer system is vulnerable to contamination due to potential
seawater intrusion, accidental spills, petroleum products, small
hazardous waste generators, household hazardous waste disposal,
leachate from the closed Island landfill, leachate from the incompletely
remediated Wyckoff Superfund site in Eagle Harbor, or leachate from
Washington Department of Ecology listed Hazardous Sites such as the
former Unocal Station on Winslow Way (WDOE 201 la), the Strawberry
Plant site on Weaver Road (WDOE 2011 b), and the Winslow Way West &
Madison Avenue North site (WDOE 2011 b), failing septic systems,
fertilizers, pesticides and herbicides, improperly abandoned wells, and
the impact of population growth. The aquifer system is also vulnerable to
contamination from open ground water situations such as sand and
gravel mining operations.
POPULATION AND DRINKING WATER CONSUMPTION
The population of Bainbridge Island is approximately 23,290. It is
estimated the population will increase to 25,474 by 2020, and 28,1 95 by
2030. One hundred percent of the current population on the island
obtain their drinking water from the petitioned aquifer. The sole source
aquifer system on the Island underlies the entire Island. Actual usage
was calculated by multiplying population by an estimated per capita
consumption rate, which includes municipal, domestic, commercial,
irrigation, fish propagation, and stock watering uses, and also includes
an estimate of water use from claims and users of wells that are exempt
from water rights. The 1 990 population number of 1 5,736 was
multiplied by an average use of per capita value of 1 32 gallons per day
which yielded an annual continuous consumption total of 1,442 gpm.
The projected 2014 annual continuous consumption total was calculated
to be 2,067 gpm. This may represent approximately 1 8 percent of the
estimated total groundwater resource; however, the actual groundwater
resource is unknown based on a lack of data (Keenan and Gander, 2009).
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ALTERNATIVE DRINKING WATER SOURCES
EPA guidance requires that petitioners demonstrate not only that
an aquifer supply 50 percent or more of the drinking water for the area,
but also that there are no alternative sources or combination of sources
which could physically, legally, and economically supply all those who
depend upon the aquifer system for drinking water (EPA, 1 987). The
petitioners for the Bainbridge Island Aquifer System have adequately
demonstrated that there are no additional sources of drinking water that
are economically available.
Each of the potential alternative sources that the petitioner
evaluated has limitations on quantity or quality of an economically
feasible alternative water source and/or the feasibility of development.
There are no potential surface water bodies as a source for drinking
water and the two alternatives scenarios of piping water across Agate
Pass Bridge to the Island or installation of a desalination plant are both
considered cost-prohibitive at this time, and as such are not considered
alternative sources of drinking water. Therefore none of the potential
alternative sources qualify as Alternative Drinking Water Sources as
defined in the EPA Petitioners Guidance.
CONCLUSION
A sole source aquifer system must supply at least 50 percent of the
drinking water consumed within the natural boundaries of the aquifer
system, and there can be no economically or legally available alternative
source that could supply the entire population living in the area. The
Bainbridge Island Aquifer System supplies all of the drinking water to
people living in the petitioned area, and there are no economical and
legally available alternative sources of water. Given these conditions, the
Bainbridge Island Aquifer System meets the criteria of EPA designation as
a sole or principle source aquifer under Section 1424(e) of the Safe
Drinking Water Act.
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122°50
122*30'
122°20'
47°50' -
47'40'
47"30' —
EXPLANATION
Location subsequent figure:
WASHINGTON
Figure location
Base from U.S. Geological Survey digital data, 1:24.000, 1988
Universal Transverse Mercator projection, rone 11
North American Datum of 1983
10 MILES
8 10 KILOMETERS
Figure 1. Map of the proposed Bainbridge Island sole source aquifer, USGS
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FIGURE 3.3
GEOLOGIC SURFACE MAP
MODIFIED FROM DEETER. 1979
BAIWRDGE ISLAND LEVEL II BASIN ASSESSMENT
Figure 2. Geology of Bainbridge Island, City of Bainbridge Island, 2000.
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REFERENCES
City of Bainbridge Island, 2008, City of Bainbridqe Island Stop Work
Order, Triangle Sand Pit, Fletcher Bay Road and Lynwood Center Drive,
Bainbridqe Island Washington, July.
City of Bainbridge Island, 2000, City of Bainbridqe Island Level II
Assessment. An Element of the Water Resources Study. 70 pages.
Keenan, Melanie and Gander, Malcolm, 2009, Bainbridqe Island Sole
Source Aquifer Designation Petition, 65 pages.
U.S. Environmental Protection Agency, 1987, Sole Source Aquifer
Designation Petitioner Guidance, 30 pages.
U.S. Geological Survey, 2011, Conceptual Model and Numerical
Simulation of the Groundwater-Flow system of Bainbridqe Island,
Washington, Scientific Investigations Report 2011-5021, 96 pages.
Washington Department of Ecology, 2011 a, Confirmed & Suspected
Contaminated Sites List, Bainbridge Island City Strawberry Plant Site,
August 1 6.
Washington Department of Ecology, 2011 b, Hazardous Sites List. Unocal
Station 4388, August 31.
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