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Barbara Moore-Lewis Ibrinnongroup@gmail.com]
Tuesday, November 03, 2009 9:47 AM
David W. Johnson
Fwd: comments in response to notice of scoping
Comments for Scoping Meeting (2).doc; waterworksConsultantsWaterReview.pdf;
seawaterintrusion. pdf
Attached are my comments in response to the notice of scoping for preparation of a supplemental impact
statement (SEIS) to address zoning code admending, development agreement, and project-level environmental
review of the master plan for the Brinnon master planned resort (BMPR).
I'm attaching a letter, comments on water issues by Waterworks Consultants, and Island County's Seawater
Intrusion Policy. I would like all of these documents to be presented in full in the public record and all of them
to be considered in the scoping process.
As for an alternative to the BMPR, we have a number of residents who have e-businesses or telecommute.
Broadband for the entire community would be a minuscule investment compared to the cost of a resort. This
would allow the development of small businesses that are the backbone of this country and of this county,
instead of a large foreign-investment development, environmentally challenged development. This would be an
economic development that could be accomplished fairly quickly, bring revenue to the county that is steady,
and have minimal impact on the environment and the community.
Thank you for the opportunity to comment.
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1
T\'IED
Barbara Moore-Lewis
Comments for Scoping Meeting
October 28,2009
Emailed to DCD November 3,2009
Thank you for the opportunity to speak.
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o SubSurface Group LLC has prepared a document titled "Water Supply and
Groundwater Impact Analysis."
o The document is dated November 20,2008 and was date-stamped into the
Jefferson County Department of Community Development on April 1,2009.
o This document was sent for comment to state and local agencies, tribes, and
interest groups on June 30, 2008, after internal review by DCD.
o Comments were due to David Johnson July 17, 2009.
o Waterworks Consultants submitted comments on behalf of the Brinnon Group at
that time. Waterworks Consultants pointed out significant gaps in the information
needed to assess the Black Point hydrogeologic system. These comments are
attached.
o My remarks are based on the recommendations of Waterworks Consultants.
Summary of Recommendations for Additional Testing
To better understand the hydrogeologic response to the proposed water supply
management scheme in this relatively sensitive groundwater environment, each
of the components of the hydrologic cycle should be more accurately quantified.
In addition, the aquifer properties must be better defined to design a supply
system that does not overstress the aquifer. The following tests are
recommended in order to gather that information.
Aquifer properties
Aquifer testing - pump tests should be conducted for a minimum of 72 hours in
any wells that might be proposed for water supply purposes (American
Campground Well, Pleasant Tides Coop Well (Sam Boling Water System/Black
Point Water Company) and MW-2). Pump tests should be conducted for long
enough to generate a measurable drawdown in at least two monitoring wells in
the vicinity. Pumping rate at the Pleasant Tides Coop Well should include the
300 gpm for existing water rights plus the proposed new withdrawal.
! Pump testing at MW-2 should include installation of a monitoring well, at a
location that is as close as existing wells are to the eastern shoreline, in
line with the MW-2 well. Chloride testing of water pumped from the
aquifer should be done when the MW-2 is pump tested.
E Pump testing at the Pleasant Times Coop Well should include monitoring
for water level drawdown and for chloride at the other Black Point Water
Company wells, the Babare well, the Tudor well and the other Pleasant
Harbor Beach Tract Owners wells.
I
Barbara Moore-Lewis
Comments for Scoping Meeting
October 28,2009
Emailed to DCD November 3,2009
Seowater intrusion
Chloride content in groundwater should be determined in samples collected from
wells pumped adjacent to the marine shoreline over the duration of the pump
tests. At a minimum one sample should be collected prior to initiation of
pumping, another after at least l2 hours of pumping and a third shortly before
pumping is stopped. More samples provide more confidence in the data
collected, and the interpretations derived from that data. Chloride concentrations
between 100 and 200 mgll indicate wells atmoderate risk for seawater intrusion,
with 200 mg/l being the trigger for high risk, according to Island County's
Seawater Intrusion Policy (a copy is included with these comments as an
Attachment ).
Groundwater movement
Groundwater levels should be measured in every accessible well on the same
date, so that a groundwater elevation contour level map can be constructed that
is reliable for interpreting the direction(s) of groundwater movement. A better
understanding of the direction of groundwater movement will support a better
interpretation of the groundwater withdrawal impacts to private wells on the Black
Point Peninsula and seawater intrusion risk.
Woter Budget
The presentation of the water budget in the Report makes it impossible to assess
the individual components of the water budget, their relationship to each other,
and what data was used to derive them. A comprehensive explanation of the
water balance calculations must be provided. This should include:
E water budget equation used
E Values for each component the equation
Water Supply and Groundwater Impact Analysis, Pleasant Harbor Marina and Golf
Resort
Technical Review and Recommendations 9
E data, calculations and assumptions used to derive each value
In particular the following components need better delineation.
Precipitation
Precipitation should be monitored on the Black Point Peninsula site for the
duration of a year (concurrent with other monitoring data collection).
2
Barbara Moore-Lewis
Comments for Scoping Meeting
October 28,2009
Emailed to DCD November 3,2009
Recharge
Groundwater levels should be monitored with continuous electronic logs in the
three monitoring wells, and reported for the duration of a year to assess the
range of groundwater level variation, and the recharge resulting from
precipitation events. Precipitation monitoring should coincide with groundwater
level monitoring periods. Precipitation should be used to evaluate the changes in
groundwater levels associated with precipitation events (i.e. recharge)
Evopotranspiration
Evapotranspiration calculations, and the data and assumptions used in those
calculations needs to be presented in report form.
Streamflow
Stream flow emitting from the lake on the eastern margin of the Peninsula, and
flowing to the east shoreline should be monitored to assess the rate of surface
water runoff from the Peninsula.
Lake Level
Monitor lake (located in the central-eastern portion of Black Point Peninsula)
level elevation over the period of a year concurrent with other monitoring data collected.
Thank you for the opportunity to comment on these important environmental issues.
Barbara Moore-Lewis
PO Box 303
aJ
Re
Waterworks Consu ltants
4017 Willowbrook Lane
Bellingham, WA 98229
360-296-8084
Memo
To: Gerald Steel
From: Llyn Doremus
Date: July 17, 2009
Technical review of: Water Supply and Groundwater lmpact Analysis
Pleasant Harbor Marina and Golf Resort - November 20,2008 (SDEIS)
Recommendations for Additional Hydrogeologic Testing at Black Point
Background
The Pleasant Harbor Marina and Golf Resort is planned for construction on the
Black Point Peninsula in Hood Canal. The peninsula is surrounded by salt water
for more thanTSo/o of it's shoreline. At least 15 wells are located along the Black
Point eastern and northern shorelines that are at risk of seawater intrusion.
Hood Canal is known to have a serious problem with depleted dissolved oxygen
content, which has resulted in what has been termed a "dead zone". The dead
zone creates conditions where a wide range of sea life that requires dissolved
oxygen in the waters of their environment cannot survive. The depleted oxygen
condition is known to result from enhanced activity of bacteria and algae that is
promoted by discharge of nutrients (nitrogen and phosphorus) dissolved in
surface and groundwater to Hood Canal. The two conditions. seawater
surrounding the Black Point Peninsula and the potential for seawater intrusion to
degrade water quality in shoreline wells, and extreme sensitivity of Hood Canal
biologic health to the release of nutrients generate a very delicately balanced
hydrogeologic environment in which the Resort is proposed for construction.
The Resortwater supply for residential, commercial and irrigation purposes has
been proposed through a combination of rainwater capture, reuse, reclamation,
infiltration, and groundwater withdrawal processes. While the general scheme of
the suppty system has been outlined in previous documents, the specifics of how
each of the components will operate has not yet been accurately defined. The
potential for negative impacts of the various supply system components on the
delicately balanced hydrogeologic environment is high. A sophisticated
understanding of the Black Point hydrogeologic system is mandated to assess
potential for degradation from the proposed water supply scheme to dissolved
oxygen levels in Hood Canal, to seawater intrusion into the Black Point aquifer,
and for the design, maintenance and operation of that system to function without
degrading the Black Point aquifer and Hood Canal.
These comments address the hydrogeologic characterization presented in the
report: Water Supply and Groundwater lmpact Analysis, Pleasant Harbor Marina
and Golf Resorf by Subsurface Group, LLC. November 20, 2008 (Report) with
respect to the information necessary for characterization, design and operation of
a water supply system that does not degrade the Black Point aquifer. The
accuracy and completeness of the Report assumptions, information and
conclusions are assessed, and recommendations for additional testing to fill in
the information gaps in the Report are listed.
Hydrogeologic System
Groundwater moves through the sediments and rock, which, along with the other
water moving through the system, defines the hydrolgeologic system of a specific
site. Sediment tends to form in layers, which can be visualized as a "layer cake"
type configuration. Sediments and rock layers with a large percentage of void
spaces typically transmit water more quickly, which is termed a high permeability
hydrogeologic unit. Sediment layers that are more dense, with tiny void spaces
are termed "low permeability" or "impermeable". Low permeability sediment
layers impede downward migration (infiltration) of groundwater, and tend to
accumulate water on their upper surface. This is normally how unconfined
aquifers form. The permeability of an aquifer is usually determined by
conducting a pump test. With the exception of the single pump test of the
American Campground well, and the marginal data generated from that test,
there is no data presented on the aquifer properties of the various hydrogeologic
units on the Black Point Peninsula.
RECOMMENDATION FOR ADDITIONAL TESTING
The Report describes results from a pump test conducted in the American
Campground well for 48 hours to assess the permeability and other aquifer
properties in the well vicinity. The data generated by the test was found to
be insufficient to assess the aquifer properties, because the drawdown in
Water Supply and Groundwater lmpact Analysis, Pleasant Harbor Marina and Golf Resort
Technical Review and Recommendations 2
the monitoring wells was almost undetectable. Pump testing should be
conducted in all of the wells that are proposed for water supply purposes.
The pumping rate used should be equivalent to the rate at which water is
proposed for withdrawal for the water supply needs of the resort (at a
minimum 75 gallons per minute to provide lhe 121 acre feet annual use
projection), because of the likelihood that individual wells may be relied
upon for the full volume for the resort water demand when problems with
water level drawdown and seawater intrusion occur. The tests should be
run for sufficient duration (minimum 72 hours) to derive measurable
drawdown curve in at least one of the monitoring wells, so that reliable
aquifer properties can be calculated.
The direction of groundwater movement is defined by the groundwater gradient.
Groundwater moves from locations of high water elevation level to low elevation
discharging eventually to lower-elevation surface water bodies. The groundwater
elevation pattern often mimics the ground surface topographic elevation pattern.
Downgradient (lower groundwater elevation) locations manifest the affects of
groundwater movement and withdrawal in higher elevation locations. lt is
important to understand the directions of groundwater movement in order to
assess the magnitude and distribution of ground water level decreases
associated with groundwater withdrawal (pumping from wells). ln particular,
reduction in the groundwater levels in shoreline areas increases the risk of
seawater intrusion into water supply wells.
The Report presents an interpretation of groundwater flow direction towards the
center of the peninsula and then to the east (discharging into Hood Canal). The
groundwater surface elevation contours are illustrated in Figure 4 of the Report,
and suggest that a groundwater high point (at MW-2) dominates groundwater
flow direction on the entire peninsula. That single data point (MW-2 water level
elevation) is disproportionally valued in interpreting the groundwater flow
directions.
RECOMMENDATION FOR ADDITIONAL TESTING
Groundwater levels should be measured in every accessible Black Point
Peninsula well on the same date, so that a groundwater elevation contour
level map can be constructed that is reliable for use in interpreting the
direction(s) of groundwater movement. A better understanding of the
direction of groundwater movement will support a better interpretation of the
groundwater withdrawal impacts to private wells on the Black Point
Peninsula and seawater intrusion risk.
Water Supply and Groundwater lmpact Analysis, Pleasant Harbor Marina and Golf Resort
Technical Review and Recommendations 3
Diagrams of the Black Point Peninsula hydrogeologic system are presented in
the Report Figures 11 , 12 and 13. Much of the site is covered with dense, low
permeability till. About one third of the site has additional sediments deposited
on top of the till that are higher in permeability and allow water to migrate more
quickly through them. Water that migrates downward through these higher
permeability sediments might slow down and accumulate in a "perched" aquifer
upon encountering the underlying low-permeability till. There is no evidence of
perched conditions at this site presented in the Report.
Basalt bedrock is shown in Figures 13 in wells located on the northern part of the
site. The contribution of groundwater flow transmitted through bedrock to the
Black Point aquifer is not well characterized in the Report, nor is the bedrock
permeability, or the hydraulic connection between bedrock and the overlying
unconsolidated sediments. With the exception of the single pump test of the
American Campground well, and the marginal data generated from that test,
there is no data presented on the aquifer properties of the bedrock or
unconsolidated sediment hydrogeologic units on the Black Point Peninsula, or on
the hydraulic continuity between unconsolidated sediment units and the bedrock
underlying them. Further pump testing (as previously described) is necessary to
better define aquifer properties of the hydrogeologic units and the hydraulic
continuity with bedrock on the site.
Water Budget
A water budget uses estimates or measurements of each component of the
hydrologic cycle to assess the entire movement of water through a specific
hydrologic system annually. For the purposes of characterizing the impact of the
proposed water management scheme on the the Black Point Peninsula aquifer
and hydrogeology, the water budget should encompass the entire Peninsula. To
prevent or at least minimize detrimental impacts it is essential that the
components of the water budget are defined as accurately as possible.
A typical equation for a water balance is as follows.
Ppt=E+Q+dSn+6q
Where:
Ppt = annual precipitation
E = annual evaporation plus transpiration (evapotranspiration)
Q = stream flow or surface water runoff
dS. = the change in quantity that is stored as surface water for the year
(negative for a decrease in the water quantity in surface storage)
Water Supply and Groundwater lmpact Analysis, Pleasant Harbor Marina and Golf Resort
Technical Review and Recommendations 4
dSs = the change in the water quantity that is stored as groundwater for
the year (negative for a decrease in the groundwater storage, indicating a
drop in groundwater levels)
Surface Water Flow
Although surface water is not flowing onto the proposed Pleasant Harbor Resort
site, the quantity of water discharged from Black Point Peninsula as stream flow
impacts the water budget for the Peninsula. Accurate stream flow
measurements help reduce uncertainty in other portions of the hydrologic budget
that are more difficult to estimate. Stream flow emitting from the lake in the
eastern-central portion of Black Point Peninsula, as well as any other stream flow
on the Peninsula needs accurate assessment in order to calculate its contribution
to the water budget, and its influence on the other components of the budget.
RECOMM ENDATION FOR ADDITIONAL TESTING (Q)
Stream flow emitting from the lake on the easterncentral margin of the
Peninsula, and flowing to the east shoreline should be monitored to assess
the rate of surface water runoff from the Peninsula.
Surface Water Sforage
Surface water is typically stored in lakes and wetlands. To better understand the
changes in surface water storage that are ongoing under current conditions
(dSs), and that may be expected from the proposed use of kettles as water
storage facilities, the water stored in Lake (on the eastern margin of the
Peninsula) should be monitored for changes in lake elevation. lt is likely that the
lake is in hydraulic continuity with groundwater, and receives groundwater
discharge. A better delineation of lake level variations, and their relationship to
precipitation quantities and timing, and groundwater levels will improve the
understanding of how groundwater moves through the Peninsula hydrogeologic
system.
RECOMMENDATION FOR ADDITIONAL TESTING (dSS)
Monitor lake level elevation over the period of a year (concurrent with other
monitoring data collected).
Precipitation
Precipitation provides water that supports the various water uses and hydrologic
components. Annual precipitation at this site is poorly understood because of the
variability in precipitation along the north south extent of Hood Canal, and the
lack of monitored data collected in the Black Point Peninsula or Brinnon vicinity.
Water Supply and Groundwater lmpact Analysis, Pleasant Harbor Marina and Golf Resort
Technical Review and Recommendations D
RECOMMENDATION FOR ADDITIONAL TESTING (Ppt)
Precipitation should be monitored on the Black Point Peninsula for an entire
year. ln addition, the data available from the NOAA approved weather
station at location A5461 on the west side of Hwy. 101 across from
Pleasant Harbor should be analyzed. See Attachment t hereto.
Groundwater Storage
Groundwater that is stored in an aquifer is the amount of water that is added to
the aquifer over the course of the year (termed recharge) minus the amount
withdrawn or discharged from the aquifer. Recharge to an aquifer derives from
precipitation that infiltrates into the ground. Discharge from an aquifer typically
goes to stream flow (Q), or it may be pumped for water supply or irrigation
purposes, or, in this case, includes flow into Hood Canal to diminish salt water
intrusion into the fresh water supply. The difference between the amount
recharged and the amount discharged is the change in storage (dsg).
Quantification of recharge is an important factor in assessing the storage
changes in groundwater, as is quantification of the discharge.
Recharge of an aquifer results from vertical infiltration of precipitation that falls on
the ground surface overlying the aquifer. Aquifers are more rapidly recharged
when the sediment overlying the aquifer is of "high permeability" and when there
is high annual precipitation. Consider if the precipitation that infiltrates to
recharge the aquifer is half (50%), the standard assumption when data is not
available to calculate actual recharge rates. For this site the annual precipitation
rate is not well known, which makes the annual recharge rate even more difficult
to assess. Table 3 lists 55 inches for annual precipitation in Quilcene (the
closest site monitored). Half of this is 27 inches, or 2.3 feet. For this 220 acre
site, this provides an annual recharge of 504 acre feet (significantly less than the
783 acre feet claimed in the Report on page 17). The presence of low
permeability till will slow down groundwater infiltration, and likely reduce the rate
of groundwater recharge to the aquifer even further than estimated using these
assumptions.
There will be substantial additional evapotranspiration caused by the watering of
the golf course and other vegetation in the hot months of the year. This has not
been adequately considered.
RECOMMENDATION FOR ADDITIONAL TESTING (dsg)
Groundwater levels in the three monitoring wells (MW-1, MW-2 and MW-3)
should be monitored for at least one year, to determine the variation in
groundwater elevation. Precipitation should be monitored on the site for at
Water Supply and Groundwater lmpact Analysis, Pleasant Harbor Marina and Golf Resort
Technical Review and Recommendations 6
least one year to determine the actual precipitation received annually
(concurrently with other monitoring data collected). Analyses of recharge
quantities and rates should be done using monitored data, and presented in
the calculation of the water budget for the site. A separate set of
calculations should be done assuming serious drought conditions - perhaps
an estimated 500-year drought.
Quantification of groundwater discharge is calculated using measurements of
changes in groundwater elevation, stream flow measurements, pumped
quantities from the aquifer, and precipitation measurements. lt is important to
delineate the groundwater flow direction and to delineate locations of
groundwater discharge, to more accurately assess the annual amount of
groundwater discharging from the aquifer. The change in groundwater storage
calculated amount (dsg) relies upon an accurate estimation of annual
groundwater discharge and its relative value with respect to the annual recharge
amount. Additionally, discharge of groundwater from beneath the proposed
resort to Hood Canal, that contains contaminated landscaping chemicals
(especially nitrate and phosphorus) poses a significant risk to the environmental
health of Hood Canal.
Evapotranspiration
The information presented in the Report on estimations of evapotranspiration
(24.1 or 24.2 inches per year), need to be presented with data, formulas, tables,
and assumptions used in those calculations, as part of the comprehensive water
budget estimation.
Summary of Recommendations for Additional Testing
To better understand the hydrogeologic response to the proposed water supply
management scheme in this relatively sensitive groundwater environment, each
of the components of the hydrologic cycle should be more accurately quantified.
ln addition, the aquifer properties must be better defined to design a supply
system that does not overstress the aquifer. The following tests are
recommended in order to gather that information.
Aquifer properties
Aquifer testing - pump tests should be conducted for a minimum of 72 hours in
any wells that might be proposed for water supply purposes (American
Campground Well, Pleasant Tides Coop Well (Sam Boling Water System/Black
Point Water Company) and MW-2). Pump tests should be conducted for long
Water Supply and Groundwater lmpact Analysis, Pleasant Harbor Marina and Golf Resort
Technical Review and Recommendations 7
enough to generate a measurable drawdown in at least two monitoring wells in
the vicinity. Pumping rate at the Pleasant Tides Coop Well should include the
300 gpm for existing water rights plus the proposed new withdrawal.
. Pump testing at MW-2 should include installation of a monitoring well, at a
location that is as close as existing wells are to the eastern shoreline, in
line with the MW-2 well. Chloride testing of water pumped from the
aquifer should be done when the MW-2 is pump tested.
. Pump testing at the Pleasant Times Coop Well should include monitoring
for water level drawdown and for chloride at the other Black Point Water
Company wells, the Babare well, the Tudor well and the other Pleasant
Harbor Beach Tract Owners wells.
Seawater intusion
Chloride content in groundwater should be determined in samples collected from
wells pumped adjacent to the marine shoreline over the duration of the pump
tests. At a minimum one sample should be collected prior to initiation of
pumping, another after at least 12 hours of pumping and a third shortly before
pumping is stopped. More samples provide more confidence in the data
collected, and the interpretations derived from that data. Chloride concentrations
between 100 and 200 mg/l indicate wells at moderate risk for seawater intrusion,
with 200 mg/l being the trigger for high risk, according to lsland County's
Seawater lntrusion Policy (a copy is included with these comments as
Attachment 2).
Groundwater movement
Groundwater levels should be measured in every accessible well on the same
date, so that a groundwater elevation contour level map can be constructed that
is reliable for interpreting the direction(s) of groundwater movement. A better
understanding of the direction of groundwater movement will support a better
interpretation of the groundwater withdrawal impacts to private wells on the Black
Point Peninsula and seawater intrusion risk.
Water Budget
The presentation of the water budget in the Report makes it impossible to assess
the individual components of the water budget, their relationship to each other,
and what data was used to derive them. A comprehensive explanation of the
water balance calculations must be provided. This should include:
r water budget equation used
. Values for each component the equation
Water Supply and Groundwater lmpact Analysis, Pleasant Harbor Marina and Golf Resort
Technical Review and Recommendations 8
. data, calculations and assumptions used to derive each value
ln particular the following components need better delineation.
Precipitation
Precipitation should be monitored on the Black Point Peninsula site for the
duration of a year (concurrent with other monitoring data collection).
Recharge
Groundwater levels should be monitored with continuous electronic logs in the
three monitoring wells, and reported for the duration of a year to assess the
range of groundwater level variation, and the recharge resulting from
precipitation events. Precipitation monitoring should coincide with groundwater
level monitoring periods. Precipitation should be used to evaluate the changes in
groundwater levels associated with precipitation events (i.e. recharge)
Evapotranspiration
Evapotranspiration calculations, and the data and assumptions used in those
calculations needs to be presented in report form.
Streamflow
Stream flow emitting from the lake on the eastern margin of the Peninsula, and
flowing to the east shoreline should be monitored to assess the rate of surface
water runoff from the Peninsula.
Lake Level
Monitor lake (located in the central-eastern portion of Black Point Peninsula)
level elevation over the period of a year concurrent with other monitoring data
collected.
Water Supply and Groundwater lmpact Analysis, Pleasant Harbor Marina and Golf Resort
Technical Review and Recommendations 9
I r.o
SEAWATER INTRUSION TOPIC PAPER (Final)
Approved by WRdC: 2/3/05, Approved by BOCC 3/'16/05
Island County / !7RIA 6 Watershed Planning Process
Seawater Intrusion
Introduction
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Saltwater intrusion is the movement of saline water into a freshwater aquifer. Where the source of
this saline water is marine water, this process is known as seawater intrusion. The marine / saline
waters of the Puget Sound surround Island County and as a result, all of the aquifers in the county
that extend below sea level are at risk for seawater intrusion. The high mineral content (primarily
salts) of marine waters causes these waters to be unsuitable for many uses, including human
consumption. Thus if intrusion problems become extreme, they can render an aquifer and any wells
that are completed in that aquifer unusable for most purposes.
As a result of the above concerrrs, Island County has historically taken a leading role in
understanding and protecting its groundwater resources. The adoption of the Island County /
Washington State Department of Health - Salt Water Intrusion Policy in 1989 represented a
significant step toward this goal of protecting our aquifers. Fifteen years later, limitations of this
policy have become evident, and significant new scientific information has become available. This
topic paper provides an overview of current science and regulations, explores management options,
and makes recommendations for future resource protection efforts.
1.1 Groundwater and Seawater Intrusion
When an aquifer is in hydraulic connection with saline / marine waters such as the Puget Sound,
portions of the aquifer may contain saltwater while other portions contain fresh water. Freshwater is
slightly less dense (lighter) than saltwater, and as a result tends to float on top of the saltwater when
both fluids are present in an aquifer. There is a relationship based on the density difference between
saltwater and freshwater that can be used to estimate the depth to saltwater based on the thickness of
the freshwater zone above sea level. The relationship is known as the Ghyben-Heruberg relation
(Figure l). The boundary between the freshwater and the saltwater zones is not sharp but instead is
a gradual change over a finite distance, and is known as the zone of diffusion or the zone of mixing.
In Island County, all of our groundwater originates as
recharge from precipitation. This recharge creates a
pressure distribution within our aquifers that tends to
be highest in the center of the islands, lowering as you
approach the shorelines. The pressure distribution
leads to a flow in the aquifers that is vertically
downward near the center of the islands, then flowing
radially outward toward the shore (Figure 2).
Two mixing processes (diffusion and dispersion)
continuously move saltwater into the freshwater zone
Flow in the freshwater zone sweeps this mixed-
C:\My Documents\Word\WatershedPlanning\Seawater Intrusion final).doc
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F lSure
Puget
Sound
Editor: Doug Kelly
Z= Thiclaress of frchwater
below sea level
.& = Water level
above sea level
Freshwale,
z=1oh
w'[rere;
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SEAWATER INTRUSION TOPIC PAPER (Final)
Approved by WRAC: 2/3/}s,Approved by BOCC 3/1,6/05
Island County / WRIA 6 Watershed Planning Process
Figure 2
brackish water toward the shoreline where it discharges at submarine seeps. The processes of
recharge, flow, mixing, and discharge all work in unison to hold the interface position in a roughly
stationary position. A change to one or more of these processes can result in a change in the position
of the interface, an inland movement of the interface boundary known as lateral intrusion.
When a well is pumped, water levels in the vicinity of
the well are lowered, creating a drawdown cone
(Figure 3). If a saltwater zone exists in the aquifer
beneath the well, the saltwater will rise up toward the
well screen. This rising up of saltwater is known as
upconing and is the second type of seawater intrusion.
The previous figures describe various characteristics
of groundwater in coastal marine environments, from
the perspective of a single aquifer. In reality the
groundwater system in Island County is made up of
multiple layers of unconsolidated sand and gravel,Frgure 3
Editor: Doug Kelly C:\My Documents\Word\WateshedPlmning\Seawater Intrusion (Final).doc
)
Sea Level
Groundwater Flow
in a Marine
Island Environment
Drawdown and Upconing
Puntping
Sea Level
Puge{
Sound
Groundwater
Saline Seawater
Puget Sound
Silfine {koutdwatsr
GroundwaterFresh
Freshwater
Saftrvater