EPA 910/9-87-167F	United States	Region 10
Environmental Protection	1200 Sixth Avenue
Agency	Seattle WA 98101	September 1967
Office of Ground Water
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SUPPORT DOCUMENT FOR DESIGNATION OF
THE NORTH FLORENCE DUNAL AQUIFER
AS A SOLE SOURCE AQUIFER
Prepared by
the Office of Ground Water
U.S. EPA Region 10
Seattle, Washington 98101
September 1987
H'C-pcrty of U.S. Environmentai
pro'^ciijp		 *
•' Ajcncy uo.-sry MD-?08
DEC ¦ 0 19Q7
,200 SiyM Avenue/Seznio 
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SUPPORT DOCUMENT FOR DESIGNATION OF THE NORTH FLORENCE
DUNAL AQUIFER AS A SOLE SOURCE AQUIFER
INTRODUCTION
Sole Source Aquifer Program
The Safe Drinking Water Act, Public Law 93—523, was signed into law on
December 16, 1974.1 This act provides the statutory basis for designation
of sole source aquifers by the Environmental Protection Agency. Section
1424(e) of the 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."
Petition
On June 2, 1985, the Region 10 Office of the Environmental Protection Agency
(EPA) received a petition from Shirlee J. Gardinier, a citizen of Florence,
Oregon, requesting that EPA designate the North Florence Dunal Aquifer as a
sole source aquifer.2 The petitioner provided EPA with additional
technical information on July 30, 1985. A Federal Register notice
announcing receipt of the petition and requesting public comment was
published on November 13, 1985.3 Another Federal Register notice,
published on March 3, 1986, announced the publication of a support document
and requested further public comment through August 1, 1986.4 A final
public comment period was opened between August 25, 1987 and
September 21, 1987 to provide an opportunity for review of the recently
revised boundaries of the sole source aquifer area.
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Purpose
This document represents a summary of available information which will serve
to provide the basis for an EPA decision regarding sole source aquifer
designation. Those interested in more detailed information may consult the
references listed at the end of the report.
GENERAL DESCRIPTION OF THE NORTH FLORENCE DUNAL AREA
Location
The North Florence Dunal Aquifer represents a hydrologically isolated
portion of an extensive dunal aquifer system located along the south-central
Oregon coastline. The entire dunal aquifer system, whose width ranges from
less than one mile to over three miles, extends almost 60 miles from Coos
Bay north to Heceta Head. The dunal area north of the Siuslaw River, herein
referred to as the North Florence Dunal Aquifer, represents about 15 percent
of the aquifer length and covers roughly 19 square miles.
The area originally petitioned for sole source aquifer status included only
the unconsolidated sand deposits between the Siuslaw River and Sutton
Creek. However, available information suggests that the sand dune area
north of Sutton Creek is not hydrologically separate from the rest of the
aquifer. Also, part of the bedrock surface east of the dunes supplies
runoff into lakes which are hydrologically connected to the aquifer.
Therefore, it seems appropriate to include these areas into the sole source
aquifer area. A more thorough description of the boundaries associated with
the aquifer occurs later in this report, as does a map (Attachment 1) which
delineates those boundaries.
Climate
A temperate marine climate with distinct wet and dry seasons prevails in the
area. Temperature records from Reedsport, located 20 miles south of
Florence, show an average annual temperature of 52 degrees (Farenheit). The
July-August temperature averages 61 degrees whereas the January temperature
averages 45 degrees.5 Rainfall at Florence averages 65 inches per year
with about 80% occurring between the months of October and March.5
Population
Over 8,000 people reside in the North Florence Dunal Area, including about
4,500 within the city limits of Florence.6.1 Since tourism forms the
principal industry of the area, the population fluctuates somewhat on a
seasonal basis. Nearly one tenth of the area residences are classified as
seasonal by the 1980 national census.8 July and August traffic counts
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along the coastal highway are double those registered during the winter
months (about 10,000 vehicles per day versus roughly 5,000 vehicles per
day)9. According to the Lane County planning staff, about 15,000 people
will reside in the area by the year 2,000 and, ultimately, the population
may approach 25,000.6
Geology
BEDROCK UNITS
The wind-blown sand of the dunal aquifer rests upon a wave-cut terrace of
sedimentary and igneous bedrock. Sandstone and siltstone beds, whose grains
are cemented by clay minerals and calcite, crop out along most of the
eastern boundary of the aquifer.6,10 These beds were exclusively
correlated with the middle Eocene Tyee Formation until 1974. Since then,
some investigators have grouped the strata with the Flournoy Formation while
others hold to the original correlation.11.^ The upper Eocene Yachats
Basalt crops out along the northeastern margin of the aquifer for about one
mile. This complex assemblage of volcaniclastic rocks and ancient lava
flows erodes less easily than the sedimentary bedrock as evidenced by the
rocky headland of Yachats Basalt north of the dunal aquifer.'0 Springs
and wells in the bedrock units yield only very small amounts of water.5
UNCONSOLIDATED MATERIAL
Surface expressions of the sand cover have been categorized into three
groups: active dunes, stabilized dunes, and deflation plains.1(^ Active
dunes are those areas with little or no vegetation covering them which move
freely in response to the wind. Stabilized dunes, as the name implies,
represent those areas covered by enough vegetation to hold the sand in
place. Recently stabilized dunes contain a cover of grasses and shrubs
whereas forests cover dunes which were stabilized decades ago. Deflation
plains are areas eroded by wind (deflated) down to the summer water table
elevation. These marshy wind-scoured depressions generally expand during
the winter and spring as the water table rises. Active dunes observed
presently encroaching upon forested areas illustrate the dynamic nature of
the sand-covered land surface. Surface cuts and boreholes, which show
multiple buried soil horizons and peat beds, indicate a history of continual
sand movement.
Numerous borehole records combined with a seismic survey by Oregon State
University have allowed fairly detailed characterization of the aquifer
portion between Sutton Creek and the Siuslaw River. Key findings from
subsurface investigations include: (1) unconsolidated sand thicknesses
average 100-200 feet; (2) since the sand lies upon a flat bedrock surface,
topographic highs in the dunes generally represent thicker accumulations of
wind-blown sand; (3) abrupt thinning occurs not only along the eastern and
northern aquifer margin, as would be expected, but also around a buried sea
stack located under the coastal highway northwest of Clear Lake; (4) the
lower one-third of the sand is largely impermeable because of plastic clay
between the sand grains.6.!3
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Desposition by wind has produced a sand body of quite uniform grain size and
fairly uniform grain composition. According to sieve analysis of samples
taken just north of Florence, 96-99 percent of the grains are of medium- and
fine-grained sand size.5 Mineralogical studies along the Oregon coast
have shown that dune sands contain 70-99 percent quartz with the higher
amounts of quartz generally found furthest from the ocean.14 Chemically
unstable rock fragments account for most of the balance.15 The uniformly
sand-sized particles, when saturated, can hold and transmit large quantities
of water.
Hydrology
A favorable combination of geologic and climatic factors make the dunal
aquifer an immense dynamic reservoir of ground water. Laboratory studies
suggest that mobile ground water accounts for 32 to 35 percent of the
aquifer volume.5. Measured permeabilities range from 270 to 600 gallons
per day per square foot.5 From a water development standpoint, the thick
accumulation of porous and permeable sand will yield in excess of 150
gallons per minute to properly constructed wells.5 Natural recharge and
discharge in 1963, when the area was less urbanized, was estimated at 3000
acre feet per year for each square mile of the aquifer.5 Although ground
water withdrawals have increased significantly since then, natural discharge
still greatly exceeds consumption.
Approximately 85 percent of the rain which falls upon the sand-covered
surface percolates into the water table.5 Locally, discontinuous buried
soil layers and peat beds, both partly cemented by iron oxides, act to
retard veritical movement.5»6 However, on a large scale, ground water
moves rapidly and almost uniformly towards a discharge point. In fact,
tritium age dating indicates that water in the aquifer replaces itself at
least every 30 years.6
The North Florence Dunal Aquifer discharges principally into the Pacific
Ocean and Siuslaw River. Multiple seeps and springs occur along the
coastline and riverbank, although areas of quicksand indicate that the
aquifer discharges mostly as underflow.5 The water table slopes westward
at about 10 feet per 1,000 feet and southward at about 5 feet per 1,000 feet
from its highest portion, located west of Mercer, Col lard, and Clear
Lakes.13 Munsel Creek intercepts some of the ground water flowing towards
the Siuslaw River. Likewise, Sutton Creek and Berry Creek intercept some of
the westward moving ground water before it discharges into the Pacific.5>6
The string of lakes along the eastern boundary of the aquifer are a minor
discharge area. However, the aquifer supplies a significant amount of water
to the lakes, especially during the summer months when surface water inflow
decreases and withdrawals from Clear Lake are increased. Hydrographs
comparing lake levels with aquifer levels strongly suggest a hydrologic
connection between the surface and ground water supplies.5 More refined
studies estimate that the aquifer supplies at least 27% of Clear Lake's
annual water supply and a much higher proportion during the dry season.^
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Few streams cross the dunal area since most rainfall quickly infiltrates to
the water table. Those streams which do flow across the area (Munsel Creek,
Sutton Creek, and Berry Creek) originate in upland areas of relatively
impermeable bedrock. Where streams flow across the sand they are
hydrologically connected with the ground water system. In fact, effluent
ground water provides most of the flow of Sutton and Munsel Creeks at their
points of discharge.6
Aquifer and Designated Area Boundaries
The North Florence Dunal Aquifer encompasses the entire continuous body of
sand located north of the Siuslaw River and east of the Pacific Ocean. The
surface contact between bedrock and the unconsolidated sand forms the
northern and eastern boundary of the designated area as far south as Mercer
Lake. The boundary between bedrock and the dunal aquifer has been drawn on
the basis of a surface geological map published in 1974 by the Oregon
Department of Geology and Mineral Industries.10 In addition to the dunal
sand area itself, steep drainage areas east of Col lard, Clear, Ackerley, and
Munsel Lakes have been included in the designated area because those lakes
are hydrologically connected to the aquifer.5,6 Therefore, the surface
drainage divide located just east of the lakes forms the eastern boundary of
the designated area from Mercer Lake south to the Siuslaw River.
Ground Hater Quality
From a human health standpoint, the aquifer provides water of good quality.
However, naturally high concentrations of dissolved iron require treating
the water for aesthetic reasons. The naturally high dissolved iron content
apparently results from weakly acidic ground water (pH of 5.6 to 6.2)
reacting with the iron-rich minerals found in some sand grains.6
Potential for Contamination
Rapid infiltration rates into the sand cover combined with a shallow water
table make the North Florence Dunal Aquifer highly susceptible to
contamination from surface activity. Despite the relatively rapid flow of
ground water through the aquifer, water soluble contaminants introduced near
the surface may remain in the ground water system for nearly 60 years.6
Immiscible contaminants, such as petroleum distillates, would spread rapidly
if spilled onto the permeable sand cover but would resist flushing by
natural ground water flow.
Possible sources of aquifer contamination include fuel storage tank failure,
improper storing or handling of hazardous materials, accidental spills of
hazardous material transported across the aquifer, septic tank effluent,
storm runoff, pesticides, and chemical fertilizers. The lakes located along
the eastern margin of the dunal area would suffer from any contaminants
introduced into that portion of the aquifer which recharges the lakes.
Direct leaching from septic tanks located in sand-covered areas adjacent to
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the lakes could seriously downgrade the quality of Clear Lake - the only
surface source of drinking water presently used in the area.1(>
Localized overpumping of the aquifer near the ocean could result in
saltwater intrusion. However, population projections by the Lane County
Planning Staff suggest that such overdrafts are unlikely.
Hater Supply Systems
Drinking water for the sole source area comes almost exclusively from two
water districts. The City of Florence serves areas within the city limits
whereas the Heceta Water Distrist serves residents outside of Florence.
Florence produces most of the water it consumes from two city owned and
operated wells. A treatment plant near the wells precipitates and filters
out the iron in addition to providing chlorination.17 The city purchases
supplemental water from the Heceta Water District during seasonal periods of
increased demand. The Heceta Water District pumps water from Clear Lake and
distributes it after chlorination. As of 1985, withdrawals from Clear Lake
by the water district accounted for about 18% of annual outflow from the
lake.1f> Although the Heceta Water District has only a few hundred
connections fewer than Florence, a much higher percentage of its customers
are seasonal residents. Accordingly, annual production by the Heceta Water
District averages less than half that of the City of Florence.
Alternative Sources
Locally available surface water cannot qualify as a truly alternative source
because of the hydrologic connection between surface water and ground water
across the dunal surface. For instance, aquifer recharge to Clear Lake
during the summer months, when surface inflow drops sharply and water
consumption rises dramatically, already represents a significant part of the
lake's inflow. Therefore, additional pumping from Clear Lake would, in
essence, simply represent additional pumping from the aquifer.
Coastal lakes south of the Siuslaw River, such as Woahink Lake, have been
suggested as an alternative water source. However, installing a water
treatment system, pumping units, storage facilities, and transmission lines
would significantly increase consumer costs. Furthermore, the coastal lakes
south of the Siuslaw River are hydrologically connected to a dunal aquifer
which is as vulnerable to contamination as the North Florence Dunal Aquifer.
Streams which originate in the bedrock uplands east of the aquifer lack the
year-around flow needed to meet water consumption in the area. Original
studies of the dunal aquifer at Florence were conducted over 25 years ago
because surface streams and wells drilled into bedrock could not meet the
growing water needs of the area.^ Any reservoir construction projects
designed to provide a steady supply of surface water would face serious
obstacles which include: (1) steep topography susceptible to landslides;
(2) bedrock units which present engineering difficulties; and (3) silting
problems associated with runoff from heavily logged slopes.8 These
obstacles alone would raise costs to prohibitive levels.
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TABLE 1
ANNUAL WATER CONSUMPTION WITHIN THE
SOLE SOURCE AQUIFER AREA
1. Ground Water Use
City of Florence
Individual Wells
Total Ground
Water Use
Volume in
Mi 11 ion
Cubic ft.
29.3a
0.2<*
29.5
Approximate
Number of
Connections
1600b
30e
1630
Approximate
Population
Served
4565c
81f
4646
2.*Surface Water Use
Heceta Water
District
City of Florence
Total Surface Water
Use
11. 5g
2.3J
13.8
1237^	37501
Supplemental Use Only
1237	3750
3. TOTAL (all sources) 43.3
2867
8396
4. Surface Water as a Percentage of Total Water Use in the Area: 32%
5. Ground Water as a Percentage of Total Water Use in the Area: 68%
* All surface water withdrawals are from Clear Lake. The North Florence
Dunal Aquifer is hydrologically connected with Clear Lake and provides about
27% of its annual inflow.16
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TABLE 1 NOTES
a) Source:
b)	Source:
c)	Source:
d)	Source:
e)	Source:
f)	Source:
g)	Source:
h)	Source:
i)	Source:
j)	Source:
The City of Florence estimates that its recently
rehabilitated wells presently produce about 600,000 gallons
per day, which is equivalent to 29.3 million cubic feet per
year. Iron precipitation problems will probably cause
production to drop and generate another workover treatment at
some point in the future.
Approximate number of connections according to the City of
Florence.
Oregon Blue Book,
State.
1987-88, published by the Secretary of
Annual consumption was estimated by assuming 30 connections
each use 150 gallons per day throughout the year.
Number of residences estimated by the Heceta Water District
as within the sole source aquifer area which are not served
by a public water supply system.
Estimated number of connections was multiplied by 2.7 to
arrive at this figure.
1985-1986 water production which was used by Heceta Water
District customers rather than sold to the city of Florence.
Connections on record with the Heceta Water District.
Number of people served was estimated as between 3500 and
4000 by the Heceta Water District.
The City of Florence used 31.6 million cubic feet during
1985-1986. The difference between that consumption figure
and present annual well production capacity of 29.3 million
cubic feet equals 2.3 million cubic feet.
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CONCLUSIONS
An aquifer must supply 50 percent or more of the drinking water for an area
in order to receive designation as a sole source aquifer. Ground water
directly supplies about 68% of the drinking water in the North Florence
area. Furthermore, ground water partly recharges the one source of surface
water used as drinking water. No feasible alternative sources to the North
Florence Ounal Aquifer system exist in the area. Therefore, contamination
of the aquifer would "create a significant hazard to public health."1
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REFERENCES
1.	Safe Drinking Water Act, Public Law 93-523.42 U.S.C. 300 et. seq.
2.	Sole Source Aquifer Petition and	related material received by the U.S.
Environmental Protection Agency,	Seattle, Washington, June 2, 1985 and
July 30, 1985.
3.	Federal Register, Volume 50, No.	219, November 13, 1985, p. 46828-46829.
4.	Federal Register, Volume 51, No.	41, March 3, 1986, p. 7335.
5.	Hampton, E.R., 1963, Ground Water in the Coastal Dune Area Near
Florence, Oregon: U.S. Geological Survey Water Supply Paper 1539—k.
6.	Christensen, R. and Rosenthal, G., 1982, North Florence Dunal Aquifer
Study: Lane County and Lane Council of Governments, Eugene, Oregon, 174
P-
7.	Roberts, B., 1987, Oregon Blue Book 1987-88, Secretary of State, Salem,
Oregon, p. 353.
8.	Personal communication with Clair Van Bloom of the Lane Council of
Governments about tract #701 of the 1980 national census on
September 23, 1987.
9.	Personal communication with William Randall of the Oregon Department of
Transportation on September 23, 1987.
10.	Schlicker, H. G.; Deacon, R. J.; Newcomb, R. C.; and Jackson, R. L.,
1974, Environmental Geology of Coastal Lane County: Oregon Department
of Geology and Mineral Industries, Bulletin 85, 116 p.
11.	Personal communication with E. M. Baldwin, Professor of Geology at the
University of Oregon, on July 30, 1987.
12.	Personal communication with John Beaulieu, State Geologist of Oregon,
on July 31, 1987.
13.	Couch, R.; Cook, J.; Connard, G.; Troseth, S.; and Standing, W., 1980,
Seismic Measurements of the Dunal Aquifer of Florence, Oregon, A Final
Report of the Lane Council of Governments: Geophysics Group of the
School of Oceanography at Oregon State University.
14.	Cooper, W. S., 1958, Coastal Sand Dunes of Oregon and Washington:
Geolgical Society of America, Memoir 72, 169 p.
15.	Twenhofel, W. H., 1946. Mineralogical and Physical Composition of the
Sands of the Oregon Coast from Coos Bay to the Mouth of the Columbia
River: Oregon Department of Geology and Mineral Industries, Bulletin
30, 64 p.
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16.	Christensen, R., 1985, Phosphorus Acumulation in the Clear Lake
Watershed: Lane County Land Management Division of the Department of
Public Works, 81 p.
17.	Kirby, R. A.; Strong, C. H.; Stoner, J. L.; and Chappell, J., 1979,
Coastal Domestic Water Supply Study: Lane County Environmental Health
Division, 93 p.
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ATTACHMENT 1
NORTH FLORENCE DUNAL AREA
SOLE SOURCE AQUIFER DESIGNATED AREA
MAP
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PAGE NOT
AVAILABLE
DIGITALLY
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