Modeling analyses for fort lewis jblm drinking water system, aspect 2009

TECHNICAL MEMORANDUM
Modeling Analyses for Fort Lewis
Sequalitchew Springs and Lake Area
Prepared for: CalPortland

Project No. 040001-012 June 10, 2009

401 Second Avenue S, Suite 201 Seattle, WA 98104 Tel: (206) 328-7443 Fax: (206) 838-5853 www.aspectconsulting.com

a limited liability company

ASPECT CONSULTING

Contents

Introduction ......................................................................................................... 1
Conceptual Model ............................................................................................... 1
Outwash Gravel Aquifer .........................................................................................2
Surface Water Features and Groundwater Interaction ..........................................2

Summary of Current Modeling Effort ................................................................ 3
Updated Model .......................................................................................................4
Sequalitchew Lake Model ......................................................................................4
Sensitivity Analyses................................................................................................5

Model Boundary Conditions .............................................................................. 6
Current Conditions Model Runs .............................................................................6
Future Conditions Model Runs...............................................................................7

Results of Additional Modeling Analyses......................................................... 7
Original EIS Model .................................................................................................7
Updated Model .......................................................................................................8
Sequalitchew Lake Model ......................................................................................8
Sensitivity Analyses................................................................................................9

Conclusions ...................................................................................................... 10
References ........................................................................................................ 10
Limitations......................................................................................................... 11

List of Tables
1 Wetland and Diversion Canal Monitoring Data
2 Recharge Estimates
3 Boundary Conditions and Hydraulic Conductivities, Original EIS Model
4 Boundary Conditions and Hydraulic Conductivities, Updated Model
5 Boundary Conditions and Hydraulic Conductivities, Sequalitchew Lake
Model
6 Water Balance Summary, Updated Model

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7 Water Balance Summary, Sequalitchew Lake Model
8 Water Balance Summary, Dry Year Sensitivity Analysis
9 Water Balance Summary, Constant Flux Sensitivity Analysis
10 Calibration Results

List of Figures
1 Area Map
2 Hydrogeologic Cross Section, Showing Current and Predicted Water
Levels

List of Appendices
A Model Configuration and Boundary Conditions
B Modeling Results
C Sensitivity Analyses

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Introduction
This technical memorandum is prepared to provide additional information on
groundwater modeling used to predict drawdown associated with the North Sequalitchew
Creek project. Additional modeling analyses were performed for the Fort Lewis
Department of the Army Public Works. The modeling analyses focused on the upper
Sequalitchew Creek basin area around Sequalitchew Lake to address any potential for
impact to the Fort Lewis Sequalitchew Springs water supply source.
In conducting this analysis, we updated a number of the original model inputs using the
last 4 years of monitoring data. Monthly monitoring is being conducted throughout the
Sequalitchew Creek basin and we used these data to adjust recharge assumptions for the
drainage canal and water levels in the wetland areas. We also explicitly incorporate
Sequalitchew Lake into the model as a major surface water feature in the area that is
believed to be in hydraulic connection with groundwater. Finally, we conduct a
sensitivity analysis looking at the worst-case dry year conditions, and the effect of
changing boundary conditions in the area of the Sequalitchew Springs.
The revisions made to the model for this effort refine predicted surface water and
groundwater interactions occurring upgradient of the mine because they incorporate the
past four years of collected monitoring data, and Sequalitchew Lake, into the model. As
with the previous modeling work (discussed in the EIS, the City’s Staff Report, and
incorporate Glacier Northwest technical reports), the updated model results indicate
drawdown at the Sequalitchew Springs area will be immeasurable.
The following sections of this report summarize the conceptual model of the project area,
summarize the scope of the current modeling effort, provide information on model
boundary conditions in each of the model layers, and present a summary of the findings
from the modeling analyses.
This report should be reviewed in conjunction with other reports prepared for the project
to get a full understanding of the area hydrogeology, interrelationships with the surface
water system, and magnitude of the work completed for the North Sequalitchew Creek
project. A list of the key reports is provided in the References section of this Technical
Memorandum.

Conceptual Model
The conceptual model describes the physical geologic and hydrologic conditions
understood to exist in the area of the proposed mine expansion and forms the basis for the
numerical model developed to predict groundwater drawdown as a result of the project.
The conceptual model is based on numerous studies conducted in the basin over the past

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decade, including extensive field investigations and on-going long-term water level and
streamflow monitoring.
The following sections describe the conceptual understanding of the surface and
groundwater system in the project area as it relates to the groundwater model
development and predictive analyses. Figures 1 and 2 provide a plan map and
hydrogeologic cross-section of the basin area modeled for the project.

Outwash Gravel Aquifer
The mine-expansion project lies within a thick glacial outwash sequence near Puget
Sound just north of the Sequalitchew Creek canyon and east of the existing mine. The
outwash includes the very coarse-grained, surficial, Steilacoom Gravel flood deposits,
overlying older Vashon outwash. The water table is found at relatively shallow depths of
15 to 25 feet in the expansion area, east of the “Qob Truncation” (formerly called the
Kitsap Cutoff). West of the Qob Truncation, the water table is found at a depth of roughly
190 feet in the existing mine. The Qob Truncation causes a unique hydrogeologic feature
where groundwater in permeable outwash gravels drops roughly 160 feet in 800 feet (0.2
ft/ft) over the edge of the truncated Olympia Beds (Qob) aquitard. Figure 2 illustrates this
steep hydraulic gradient within the current mine site.
Four aquifer pumping tests were conducted along the east side of the proposed expansion
area to determine hydraulic properties of the outwash throughout its depth (CH2M Hill,
2000). These testing data, along with studies conducted for Fort Lewis Landfill 5 (WWC,
1991) and the DuPont Works site (Hart Crowser, 1994), provide the hydraulic parameters
for the Vashon Aquifer layers in the model and were used to subdivide the Vashon
Aquifer system into multiple layers to better represent the outwash aquifer stratification
(CH2M Hill, 2003).
The surficial Steilacoom Gravels are highly permeable and are known to rapidly infiltrate
precipitation and stormwater. The gravels form a relatively flat outwash plain in the area,
in the center of which is a series of five large wetlands—referred to as Bell, McKay,
Hamer, Sequalitchew Creek, and Edmond Marshes. The wetlands occur in areas where
large ice blocks, stranded during the glacial flood outbursts, later melted forming kettle
depressions lined with finer-grained lower permeability materials. These features store
water for a much longer time. The wetland sediments were sampled and lab tested for
permeability throughout the wetland complex. These permeability data were used to
incorporate the wetland areas into the groundwater model (Aspect Consulting, 2004a).

Surface Water Features and Groundwater Interaction
The principal drainage features in the Sequalitchew Creek watershed include
Sequalitchew Creek, the Diversion Canal, and the series of interconnected wetlands
through which these drainages flow (See Figure 1). The bulk of the surface water
originates at Sequalitchew Lake and from several Fort Lewis stormwater facilities on the
southeast project boundary. Both the Diversion canal and Sequalitchew Creek drain
excess surface water from Sequalitchew Lake and the wetland complex to Puget Sound
during high precipitation periods. A weir at the outlet of Sequalitchew Lake maintains the

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lake level at a target elevation of 211 feet to protect the Sequalitchew Springs water
supply source at the east end of Sequalitchew Lake.
Sequalitchew Springs are a highly productive discharge of groundwater at the east end of
Sequalitchew Lake. The springs supply the majority of Fort Lewis’s water supply needs,
which can range up to 8,000 gpm during peak summer periods (James Gillie, personal
communication, 2008). The Fort Lewis Springs are formed where the water table
between American Lake (at an elevation of 329 to 233 feet) and Sequalitchew Lake (at
211 to 213 feet) intersects ground surface. Overflow at the Springs feeds Sequalitchew
Lake. The lake is believed to be hydraulically connected to groundwater in the outwash,
like other lake features that have been monitored in the area.
Figure 2 presents a Hydrogeologic Cross Section that illustrates the steep gradient
between American Lake and Sequalitchew Lake where the Sequalitchew Springs occur
and a much flatter gradient around Sequalitchew Lake and through the wetland complex.
The flat gradient is due to the strong hydraulic connection between the groundwater and
surface water in the area around and east of DuPont –Steilacoom Road. The gradient
becomes very steep near the existing mine site approximately 3 miles west of the Springs,
where the underlying Olympia Beds aquitard is not present and groundwater discharges
to Puget Sound. The cross section shows both the existing water table (solid green line)
and the predicted water table (dashed green line) with the North Sequalitchew Creek
project.
The water sources to the groundwater system include a combination of direct
precipitation, infiltrating surface water, and groundwater inflow. The wetlands and lake
act as sources of recharge to groundwater when surface water elevations are higher than
groundwater elevations, and groundwater discharges to the surface water features when
groundwater elevations are higher than surface water. Groundwater also enters the project
area as underflow from American Lake and regional groundwater inflow derived from
upgradient recharge. Precipitation, flow between groundwater and surface water, and up-
gradient inflow are all included in the model.

Summary of Current Modeling Effort
A groundwater flow model was initially developed for the North Sequalitchew Creek
Project to evaluate environmental impacts (see City of Dupont Environmental Impact
Statement [EIS] for the project) from the mining project. The model area covers an
approximately 10 mi2 area as shown in Figure 1. The original model developed by CH2M
Hill (2003) was modified by Aspect Consulting to address a revised mining plan and
findings from detailed field investigations conducted in the upstream wetlands and stream
channels (Aspect Consulting, 2004a and b). The City of DuPont’s hydrogeologic
consultant for the EIS, Pacific Groundwater Group, also participated in the model design
and in review of the analytical results. The model used for predicting impacts as part of
the EIS will be referred to as the Original EIS Model.
This report discusses modifications to the Original EIS Model and analyses conducted
based on recent discussions and input from Fort Lewis consulting engineers (James

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Gillie, Senior Engineer, Versar and Mike Truex, Senior Program Manager, Pacific
Northwest National Laboratory).
The model consists of two separate model runs, one reflecting current conditions and the
other future conditions with the mine expansion and new tributary to Sequalitchew
Creek. The potential effect of the project on wetlands and Fort Lewis Sequalitchew
Springs was evaluated by estimating drawdown, or change in groundwater elevations,
between the current conditions and future conditions model runs.

Updated Model
For this additional modeling effort, two sets of revised conditions were developed. The
first model, referred to as the Updated Model incorporated additional wetland water level
and diversion canal flow data collected since the Original EIS Model was developed.
Changes to develop this Updated Model included:
• Setting the heads in the wetlands (modeled as river cells) equal to the average
wetland water levels measured between March 2004 and February 2009 (see
Table 1). The original EIS model used wetland water level data from April 2004,
which are slightly higher than the average values measured since that time.
Depending on the wetland, the head applied in the Updated Model was reduced
by 0.11 to 0.86 feet.
• Eliminating the additional recharge assigned to the diversion canal model cells.
The Original EIS Model applied 2.7 cubic feet per second (cfs) of recharge to
cells along the diversion canal to represent seepage losses. The estimated seepage
loss was based on the difference in measured streamflows between canal gaging
locations DC-1 and DC-3 in the spring of 2004. Review of the current database of
monthly flow measurements indicates there is considerable variability in losses
from the canal as shown in Table 1. The most significant change in seepage loss
occurred following the beaver dam removals in December 2005 and January
2006. Since that time there has been less seepage loss. On an annual basis, flow
changes in the canal range from a loss of 1.9 cfs to a gain of 0.6 cfs, with an
overall average loss for the period of record of 0.5 cfs. Based on these data it was
determined that losses from the canal may not be as significant a source of
recharge as initially modeled, so these model cells were set equal to the areal
precipitation recharge rate.

Sequalitchew Lake Model
The Original EIS Model did not explicitly include Sequalitchew Lake as a model
boundary, primarily because significant drawdown effects were not expected to
propagate that far. The original focus was on the wetland complex located closer to the
mine site because drawdown beneath the wetlands was of potential concern.
To better represent hydrogeologic conditions at Sequalitchew Lake and the Fort Lewis
Springs a second set of model revisions were made. The resulting model, referred to as
the Sequalitchew Lake Model (for the purposes of this memorandum), incorporates the
changes made in the Updated Model, and explicitly models groundwater interaction with

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Sequalitchew Lake using river boundary conditions. The head applied to the river
boundary condition for Sequalitchew Lake was set at 211 feet, the target lake elevation to
prevent intrusion of lake water to the Fort Lewis Sequalitchew Springs (Shapiro and
Associates 1997 and Northwest Hydraulic Consultants 2007). The vertical hydraulic
conductivity used for the river bed was 0.23 feet per day (ft/day), equal to 1/100th of the
low end of the range of estimated horizontal hydraulic conductivity values for the
shallow outwash deposits (Woodward-Clyde, 1991).

Sensitivity Analyses
A sensitivity analysis was performed on the Sequalitchew Lake Model to assess:
• The effects of an extreme dry year condition; and
• Evaluate effect of the constant head boundary condition between Sequalitchew
Lake and American Lake on estimated drawdown by replacing the constant head
boundary by a constant flux (wells) boundary.
The dry year conditions modeled were essentially a “drought” year. The dry year
condition used the minimum water levels measured in the marshes (See Table 1) and
assumed a water level of 208 feet in Sequalitchew Lake. In addition, the dry year
sensitivity analysis was performed using reduced recharge rates and reduced groundwater
inflow rates at the upgradient model boundary as discussed below.
Recharge rates were evaluated using Vacarro, et. al (1998) as shown in Table 2.
Precipitation data used to estimate recharge are from the McMillan Reservoir station,
with a period of record of 1942 through 2008. Recharge rates are estimated for a range in
land use types. The modeled area is generally undeveloped, except for the residential
areas of the City of DuPont and developed areas of Fort Lewis within the southern and
northern model domain. The average recharge rate used in the Original EIS Model and
the Updated Model is 19.8 inches/year, which we considered a reasonable representation
of the average conditions for the area land use (less than undeveloped, but greater than
for built up or residential).
For the dry year condition, we used the lowest recorded annual precipitation at McMillan
Reservoir of 22.1 inches in 1952. This is 35% of the average precipitation, thus, using
this relationship we reduced the recharge rate to 6.9 inches/yr from the average recharge
rate.
In addition, groundwater inflow across the upgradient boundary was reduced to account
for the dry year conditions. The average saturated thickness in the top model layer at the
upgradient boundary is 15 feet. The monitoring data from SRC-MW-2, the well closest to
the upgradient boundary, indicates the minimum water level to be 3 feet lower than the
average water level. Based on these data, the saturated thickness (and by extension the
transmissivity) in the top model layer along the upgradient boundary was reduced by
about 20% to account for the dry conditions.
A second sensitivity analysis was conducted to assess the effect of the constant head
boundary condition between Sequalitchew Lake and American Lake on estimated
drawdown. This was assessed by replacing this boundary condition with a constant flux

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boundary condition. Additional details on the boundary conditions and model runs are
provided in the following sections.

Model Boundary Conditions
Appendix A presents figures showing model boundary conditions for each of the eight
model layers for both the current conditions and future conditions model runs for the
Sequalitchew Lake Model. The locations of the boundary conditions are identical for the
Original EIS Model, the Updated Model, and the Sequalitchew Lake Model, with the
exception that the river boundary conditions representing Sequalitchew Lake on Layer 1
of the Sequalitchew Lake Model are not included in the other two models.
Tables 3 through 5 summarize the values applied to the boundary conditions for each of
the three models. Boundary conditions applied in the current condition and future
condition model runs are described below.

Current Conditions Model Runs
Boundary conditions for the current conditions model runs are shown in Appendix A and
include:
• A constant head (shown in blue) boundary applied in the area between American
Lake and Sequalitchew Lake. A constant head value of 211 feet was used in the
Original EIS Model and the Updated Model. In the Sequalitchew Lake Model heads
along this boundary were increased slightly to maintain inflow to the model across
this boundary. Final constant head values applied in the Sequalitchew Lake Model
ranged from 211.25 feet at the north end to 212.05 feet at the south end of the
boundary. A constant head boundary with head values ranging from 184.1 to 190.2
feet was also applied at the downgradient model edge along the trace of North
Sequalitchew Creek.
• A constant flux boundary (shown in red) applied along the upgradient boundary south
of Sequalitchew Lake. This boundary was modeled using the MODFLOW well
package. Flux values were developed based on a calibrated model run of the Original
EIS Model using constant heads along this boundary. This boundary represents
regional groundwater inflow that is expected to be controlled by upgradient recharge.
A constant flux boundary was considered appropriate, as regionally derived inflow
across this boundary is not expected to be influenced by changes in groundwater
elevations due to the North Sequalitchew Creek project.
• Recharge from and discharge to the wetlands was modeled using the MODFLOW
river boundaries (shown in green). The head applied to at each wetland in the
Updated Model and the Sequalitchew Lake Model were the average of the water
levels measured in the wetlands between March 2004 and February 2009. The
vertical hydraulic conductivity of 0.08 ft/d was selected as the average laboratory-
measured values from marsh sediment samples. In the Sequalitchew Lake Model the

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vertical hydraulic conductivity applied to boundary conditions representing
Sequalitchew Lake was 0.23 ft/day, equal to 1/100th of the low end of the range of
estimated horizontal hydraulic conductivity values for the shallow outwash deposits.
In the Original EIS Model and the Updated Model, Sequalitchew Lake was not
modeled with river cells.
• Discharge to Sequalitchew Creek downstream from the wetlands was modeled using
drain boundary conditions (shown in yellow). Drain boundary conditions were also
used to model discharge at the Olympia Beds (Qob) Truncation along the west side of
the model.
• Areal recharge from precipitation was applied throughout the model, except in the
wetlands and, for the Sequalitchew Lake Model, in Sequalitchew Lake. Recharge was
set at 19.8 inches/yr for all models. The Original EIS model included higher recharge
of 740 inches/yr along the diversion canal to represent seepage losses from the canal.
This is equivalent to a seepage loss of 2.7 cfs along the canal.

Future Conditions Model Runs
Boundary conditions for the Future Conditions model runs are also presented in
Appendix A, following the Current Model Conditions. The downgradient constant head
and drain boundary conditions were modified from the current conditions model runs to
create the future conditions model runs. To do this the downgradient constant head
boundary condition was removed and replaced by drain boundaries to represent
groundwater discharge to the expanded mine and the constructed North Sequalitchew
Creek. The upgradient constant head, recharge, constant flux, and river boundary
conditions remain the same for the future conditions model runs.

Results of Additional Modeling Analyses
The following sections summarize the changes in groundwater elevation, inflow and
outflow, and resulting drawdown predicted based on:
• Updating the wetland surface water elevations and diversion canal recharge
conditions in the Original EIS Model (Updated Model), and
• Incorporating Sequalitchew Lake into the model (Sequalitchew Lake Model).
Figures showing the results of the modeling analyses are presented in Appendix B.
Tables 6 and 7 provide a water balance summary of the components of each model.

Original EIS Model
Groundwater elevation contours and drawdown estimated with the Original EIS Model
are presented in Appendix B. This model, which does not incorporate any connection to
the surface water of Sequalitchew Lake, shows approximately 0.3 feet of drawdown at
the west end of the lake and 0.2 feet of drawdown near the middle of the lake. Not

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allowing for the interaction of groundwater with Sequalitchew Lake is a conservative
assumption with regard to estimated drawdown near the lake because the lake will act to
recharge the groundwater system when groundwater elevations are below the lake
elevation.

Updated Model
The Updated Model indicates that removing the additional recharge from the diversion
canal and reducing the modeled water levels in the wetlands results in a slight decrease in
modeled groundwater elevations, primarily near Sequalitchew Lake and the diversion
canal. However, the predicted drawdown is virtually identical to the drawdown predicted
with the Original EIS Model. Based on these results it appears that the modeled
drawdown is not very sensitive to recharge from the diversion canal or variations in head
in the wetlands. Groundwater elevation contours and drawdown estimated with the
Updated Model are presented in Appendix B following the figures for the Original EIS
Model.
A summary of water balance terms for the current conditions and future conditions model
runs are provided in Table 6. The water balance shows that about 90 percent of the
inflows to the model are from areal recharge and recharge from the wetlands, with the
remaining 10 percent coming from regional groundwater inflow and underflow from
American Lake along the upgradient boundary. Virtually all of the upgradient inflow
occurs in the upper two layers of the model, which represent the high hydraulic
conductivity portions of the outwash aquifer.

Groundwater elevation contours and drawdown contours for the Sequalitchew Lake
Model are presented in Appendix B following the Updated Model. The Sequalitchew
Lake Model indicates a pronounced decrease in drawdown near the lake and springs
relative to the Updated Model and Original EIS Model, with 0.2 feet of drawdown at the
west end of the lake and 0.1 feet of drawdown near the middle of the lake. The shape of
the drawdown contours near the lake in the Sequalitchew Lake Model are also different
than predicted with the Updated Model due to attenuation of the drawdown by induced
recharge from the lake.
A summary of water balance terms for the current conditions and future conditions model
runs are provided in Table 7. Similar to the Updated Model, the water balance shows that
about 90 percent of the inflows to the model are from areal recharge and recharge from
the wetlands and lake, with the remaining 10 percent coming from regional groundwater
inflow and underflow from American Lake along the upgradient boundary. For the
current conditions model run the overall water balance and the inflows to the model from
the wetlands and lake are essentially the same as the Updated Model, despite modeling
Sequalitchew Lake with river boundaries. In this model, Sequalitchew Lake acts as a
flow-through lake, with groundwater discharging to the lake from the northeast and south
and lake water recharging groundwater to the west and north of the lake. This is
consistent with monitoring data that show the diversion canal periodically gains water in
the reach near the lake. Net modeled discharge from the lake to groundwater (i.e.,

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outflow from the lake to groundwater minus inflow to the lake from groundwater) is
about 11,000 cubic feet per day, or 0.13 cfs.
The water balance for the future condition model run shows an increase in groundwater
inflow across the constant head boundary between American Lake and Sequalitchew
Lake of about 0.1 cfs and an increase in inflows from the wetlands of about 0.5 cfs
relative to the current condition model run. The net modeled discharge from the lake to
groundwater also increases by about 0.14 cfs. This increase in losses from the lake to
groundwater is not likely to significantly affect surface water elevations in the lake, as
discharge measured at the diversion canal weir, which measures discharge coming
primarily from the lake, averages approximately 6 to 7 cfs. Based on the results of this
model, the induced groundwater recharge from Sequalitchew Lake and the wetlands will
attenuate groundwater drawdown to less than 0.1 feet approximately ½ mile west of the
Fort Lewis Sequalitchew Springs.
Table 10 provides a comparison of current conditions model results to measured
groundwater elevations. The data match reasonably well except in the area of CHMW-3S
and D, which is located within the western portion of the mine expansion area, and is the
well that is furthest away from the wetlands and lake that are being evaluated with these
additional model runs. The match is best in the area of Sequalitchew Lake (MW-SL-1
and SRC-MW-2).

Sensitivity Analyses
Consideration of a drought year condition and substitution of the upgradient constant
head with a constant flux boundary condition were selected as sensitivity analyses to be
performed on the Sequalitchew Lake Model, in discussion with the Fort Lewis engineers.
Appendix C presents water level and drawdown contours for the dry year sensitivity
analysis and drawdown contours for the constant flux boundary condition sensitivity
analysis. Tables 8 and 9 summarize the water balance for these sensitivity runs.
The dry season current conditions analysis indicates groundwater elevations significantly
lower than with the Sequalitchew Lake Model. For example, the 210-foot contour
extends all the way to the east end of Sequalitchew Lake, while in other model runs this
contour is near the middle or west end of the lake. The modeled drawdown however, is
virtually identical to the modeled drawdown for the Sequalitchew Lake Model, with 0.2
feet of drawdown predicted at the west end of the lake and 0.1 feet of drawdown
predicted near the middle of the lake. The water balance for this sensitivity analysis
(Table 8) shows increased recharge of groundwater from the wetlands and Sequalitchew
Lake, and increased groundwater discharge to Sequalitchew Lake. The water balance also
shows increased inflow across the constant head boundary between American Lake and
Sequalitchew Lake.
For the constant flux boundary condition sensitivity analysis the current condition model
run was unchanged from the Sequalitchew Lake Model. In the future condition model run
the constant head boundary condition between American Lake and Sequalitchew Lake
was replaced with a constant flux boundary. Modeled drawdown is similar to the
modeled drawdown for the Sequalitchew Lake Model, although the 0.1-foot drawdown
contour forms a narrower envelop around Sequalitchew Lake. Inspection of the water

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balance shows essentially no change in the losses of water from Sequalitchew Lake to
groundwater relative to the Sequalitchew Lake Model.

Conclusions
The modeling analysis indicates groundwater drawdown upgradient of the project area
will be minor because changes in the groundwater elevation (i.e. drawdown) will be
offset by induced recharge from the area surface water bodies. This will occur primarily
in areas where there is direct hydraulic connection between the surface water and
groundwater; for example, the area between the Sequalitchew Lake outlet and DuPont
Steilacoom Road. In this area, monitoring data indicate the diversion canal gains flow
due to groundwater discharge. Taken together, the monitoring data and modeling
analyses indicate that drawdown propagating towards Sequalitchew Lake will be offset
by a reduction in the groundwater discharge to the diversion canal at the west end of the
lake. The induced recharge near the lake outlet will also help to maintain the lake level
desired to prevent backflow to the water supply system at the springs.
The monitoring data and modeling indicate the amount of induced recharge will be small,
roughly one-tenth of the current natural surface water recharge rate. This amount is less
than the natural variability seen due to seasonal and annual precipitation patterns.
The hydrogeologic cross section provides perspective on the groundwater level changes
expected to occur from construction of the new Sequalitchew Creek tributary. The cross-
section uses monitoring data to show current conditions and the modeling analysis to
show the predicted drawdown under future conditions. The vertical scale on the
hydrogeologic cross section is exaggerated 40 times over the horizontal scale in an
attempt to show the change in water level (drawdown) expected from the project. Even at
this great exaggeration it is virtually impossible to show the small amount of change
expected to propagate into the upgradient groundwater-surface water system beyond
about ½-mile from the east edge of the project area.

References
Aspect Consulting, 2004a, Technical Memorandum, Surface Water and Groundwater
System with Predictions on Effect to Wetland Hydrology Upstream of Proposed
North Sequalitchew Creek, July 21, 2004.
Aspect Consulting, 2004b, Supplemental Report, Surface Water and Groundwater
System, North Sequalitchew Creek Project, Prepared for Glacier Northwest,
December 13, 2004.
Aspect Consulting, 2007, 2005-2006 Water Resource Monitoring Data Report, North
Sequalitchew Creek Project, Prepared for Glacier Northwest, May 2007.

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CH2M Hill, 2000, Groundwater Investigation Report, North Sequalitchew Creek Project,
DuPont, Washington, June 2, 2000.
CH2M Hill, 2003, Draft Final Groundwater Modeling and Analysis Report, North
Sequalitchew Creek Project, DuPont, WA, Prepared for Glacier Northwest, May
2003.
City of DuPont, 2007, Final Supplemental EIS (SEIS), Glacier Northwest DuPont Area
Expansion and North Sequalitchew Creek Project, May 2007.
Hart Crowser, 1994, Draft Remedial Investigation, Former DuPont Works Site, DuPont,
Washington, Volume 1, Prepared by Hart Crowser, Inc., for Weyerhaeuser
Company & E.I. DuPont de Nemours &Co., December 22, 1994.
Northwest Hydraulic Consultants, Inc., Sequalitchew Springs Source Water Protection
Project, Performed by AHBL, Inc. (project 204689) and. (project 21380),
Prepared for the USACE Seattle District in cooperation with Fort Lewis Public
Works, August 2007.
Pacific Groundwater Group, 2006, Groundwater Impact Analysis, Expansion of Glacier
Northwest’s Pioneer Aggregate Mine, DuPont, Washington, Prepared for Huckell
Weinman and Associates, technical report supporting the SEIS, April 27, 2006.
Shapiro and Associates, Inc., 1997, Lake-Level Management Plan for Sequalitchew
Lake.
Truex, M.J., Johnson, C.D., Cole, C.R., 2006, Numerical Flow and transport Model for
the Fort Lewis Logistics Center, DSERTS No. FTLE-33, Fort Lewis Public
Works, Building 2102, Fort Lewis, WA.
Vaccaro, J.J., Hansen, A.J. Jr., Jones, M.A., 1998, Hydrogeologic Framework of the
Puget Sound Aquifer System, Washington and British Columbia, USGS
Professional Paper 1424-D.
Woodward-Clyde Consultants, 1991, Fort Lewis Landfill No. 5 RI/FS, Remedial
Investigation Report, Volume 1, Submitted to the Corps of Engineers Seattle
District, October 1991, Draft Final.

Limitations
Work for this project was performed and this report prepared in accordance with
generally accepted professional practices for the nature and conditions of work completed
in the same or similar localities, at the time the work was performed. It is intended for the
exclusive use of CalPortland for specific application to the referenced property. This
report does not represent a legal opinion. No other warranty, expressed or implied,
is made.

PROJECT NO. 040001-012 JUNE 10, 2009 11

Table 1 - Wetland and Diversion Canal Monitoring Data
North Sequalitchew Creek, Dupont, Washington
Project 040001-012
Wetland Monitoring Data
Water Level Elevations in Feet Value used in
Wetland Minimum Maximum Average Original EIS Model
Edmond Marsh 209.64 211.37 211.03 211.14
Sequalitchew Creek Marsh 210.57 212.67 212.09 212.27
Hamer Marsh 211.67 215.05 213.64 214.24
McKay Marsh 213.57 217.35 215.54 215.95
Bell Marsh 215.63 219.11 217.57 218.43
Period of Record is March 2004 through February 2009

Diversion Canal Monitoring Data
Change in Flow along Diversion Canal in cfs 1
Year Range Average
2004 -3.1 to -0.6 -1.9
2005 -3.1 to -0.2 -1.5
2006 -4.3 to 1.1 -0.6
2007 -0.6 to 3.3 0.6
2008 -1.7 to 3.0 0.5
Period of Record -4.3 to 3.3 -0.5
Values summarized from monthly flow measurements between March 2004 and December 2008.
Negative values indicate decrease in flow, positive values indicate increase in flows.
The original EIS model included 2.5 cfs of recharge from the diversion canal.
1
Change recorded as difference in flow between gaging station DC-1 and DC-3.

Aspect Consulting
06/10/2009 Table 1
V:040001 North Sequalitchew CreekDeliverablesSequalitchew Springs MemoNSC_Modeling_Tables Page 1 of 1

Table 2 - Recharge Estimates
Project 040001-012

Parameter Average (1942 - 2008) Minimum (1952)
Precipitation 41.5 22.1
Recharge by Land Use Type
Undeveloped 25.0 8.7
Residential 18.7 6.5
Built Up 12.5 4.4
Urban 0.0 0.0

All values are in inches per year.
Recharge calculated using Equation (6) from Vacarro, et al. (1998) for recharge to coarse-
grained deposits.
Average and minimum precipitation from precipitation data for McMillan Reservoir, with period
of record of 1942 through 2008.

Aspect Consulting
06/10/2009 Table 2
V:040001 North Sequalitchew CreekDeliverablesModeling Analysis MemoNSC Modeling (042609) Page 1 of 1

Table 3 - Boundary Conditions and Hydraulic Conductivities
Original EIS Model
Project 040001-012

Boundary Condition Parameter Value Units
Areal Recharge
Diversion Canal Leakage Recharge rate 740 inches/yr
Wetland Areas Recharge rate 0 inches/yr
All other areas Recharge rate 19.8 inches/yr
Constant Head
Upgradient Boundary Head 211 feet
Downgradient Boundary
(current conditions only) Head 184.1 to 190.2 feet
River
Edmond Marsh Head 211.14 feet
Vertical conductivity 0.08 ft/d
Sequalitchew Creek Marsh Head 212.27 feet
Hamer Marsh Head 214.24 feet
McKay Marsh Head 215.95 feet
Bell Marsh Head 218.43 feet
Constant Flux (Wells)
Layer 1 Flux 123,316 ft3/day
Layer 3 Flux 3 ft3/day
Hydraulic Conductivity
Layer 1 Horizontal conductivity 1,800 ft/d
Layer 31 Horizontal conductivity 0.3 ft/d
Layer 41 Horizontal conductivity 50 ft/d

Notes:
See Attachement 4 for model output.
Horizontal to vertical hydraulic conductivity anisotropy in all layers is 10:1
1
Higher hydraulic conductivity values were applied at the west corner of the model near
Old Fort Lake. In layers 3 through 5 the hydraulic conductivity in this area is 1,800 ft/d and
in layer 6 the hydraulic conductivity is 500 ft/d. Hydraulic conductivity values for other model
layers were applied uniformly throughout each layer.

Aspect Consulting
06/10/2009 Table 3

Updated Model
Project 040001-012

Areal Recharge
Diversion Canal Leakage Recharge rate 19.8 inches/yr
Constant Head
Upgradient Boundary Head 211 feet
River

Notes:
See Attachement 5 and Table 5 for model output.
1

Aspect Consulting
06/10/2009 Table 4

Project 040001-012

Areal Recharge
Diversion Canal Leakage Recharge rate 19.8 inches/yr
Constant Head
Upgradient Boundary Head 211.25 to 212.05 feet
River
Sequalitchew Lake Head 211 feet

Notes:
See Attachement 6 and Table 6 for model output.
1

Aspect Consulting
06/10/2009 Table 5

Table 6 - Water Balance Summary, Updated Model
Project 040001-012
Inflows - Current Conditions
Component Layer Rate (ft3/d) Rate (cfs) Percent of Total
Recharge 1 953,999 11.0 62%
River (wetlands) 1 434,868 5.0 28%
Upgradient Constant Head 1 8,896 0.1
Upgradient Constant Head 3 2 0.0
Total 13,808 0.2 1%
Wells (Constant Flux) 1 123,316 1.4
Wells (Constant Flux) 3 3 0.0
Total 133,031 1.5 9%
Total Inflows 1,535,705 17.8 100%

Outflows - Current Conditions
Downgradient Constant Head 1 -53,195 -0.6
Downgradient Constant Head 3 -3,727 0.0
Downgradient Constant Head 4 -475 0.0
Downgradient Constant Head 6 3,554 0.0
Total -278,468 -3.2 18%
Drains 1 -31,061 -0.4
Drains 2 -38,271 -0.4
Drains 3 -15,214 -0.2
Drains 4 -32,289 -0.4
Drains 5 -88,941 -1.0
Drains 6 -104,318 -1.2
Drains 7 -159,912 -1.9
Drains 8 -761,316 -8.8
Total -1,231,322 -14.3 82%
Total Outflows -1,509,789 -17.5 100%

Aspect Consulting
06/10/2009 Table 6

Table 6 - Water Balance Summary, Updated Model
Project 040001-012
Inflows - Future Conditions
Recharge 1 953,999 11.0 61%
River (wetlands) 1 479,365 5.5 31%
Total 4,518 0.1 0%
Total 133,031 1.5 8%
Total Inflows 1,570,913 18.2 100%

Outflows - Future Conditions
Drains 1 -81,235 -0.9
2 -105,412 -1.2
3 -6,910 -0.1
4 -14,276 -0.2
5 -41,801 -0.5
6 -88,108 -1.0
7 -200,802 -2.3
8 -1,028,192 -11.9
Total -1,566,737 -18.1 100%
Total Outflows -1,566,737 -18.1 100%

Aspect Consulting
06/10/2009 Table 6

Table 7 - Water Balance Summary, Sequalitchew Lake Model
Project 040001-012
Recharge 1 953,999 11.0 61%
River (wetlands) 1 414,537 4.8
River (Sequalitchew Lake) 1 37,661 0.4
Total 452,197 5.2 29%
Total 18,892 0.2 1%
Total 133,031 1.5 9%
Total Inflows 1,558,119 18.0 100%

River (Sequalitchew Lake) 1 -26,114 -0.3 2%
Total -287,193 -3.3 19%
Drains 1 -31,534 -0.4
Drains 2 -37,776 -0.4
Drains 3 -15,028 -0.2
Drains 4 -32,368 -0.4
Drains 5 -89,413 -1.0
Drains 6 -104,452 -1.2
Drains 7 -149,029 -1.7
Drains 8 -768,302 -8.9
Total -1,227,903 -14.2 80%
Total Outflows -1,541,209 -17.8 100%

Aspect Consulting
06/10/2009 Table 7

Table 7 - Water Balance Summary, Sequalitchew Lake Model
Project 040001-012
Recharge 1 953,999 11.0 59%
Total 501,730 5.8 31%
Total 24,447 0.3 2%
Total 133,031 1.5 8%
Total Inflows 1,613,206 18.7 100%

Drains 1 -84,255 -1.0
2 -109,672 -1.3
3 -8,762 -0.1
4 -15,088 -0.2
5 -43,033 -0.5
6 -88,990 -1.0
7 -204,505 -2.4
8 -1,041,958 -12.1
Total -1,596,264 -18.5 99%
Total Outflows -1,618,417 -18.7 100%

Aspect Consulting
06/10/2009 Table 7

Table 8 - Water Balance Summary, Dry Year Sensitivity Analysis
Project 040001-012
Recharge 1 331,857 3.8 29%
Total 514,938 6.0 46%
Total 173,987 2.0 15%
Total 108,367 1.3 10%
Total Inflows 1,129,149 13.1 100%

Total -136,099 -1.6 12%
Drains 1 -15,942 -0.2
Drains 2 -20,608 -0.2
Drains 3 -10,202 -0.1
Drains 4 -21,663 -0.3
Drains 5 -60,696 -0.7
Drains 6 -85,594 -1.0
Drains 7 -126,813 -1.5
Drains 8 -565,318 -6.5
Total -906,836 -10.5 80%
Total Outflows -1,129,406 -13.1 100%

Aspect Consulting
06/10/2009 Table 8

Table 8 - Water Balance Summary, Dry Year Sensitivity Analysis
Project 040001-012
Recharge 1 332,473 3.8 28%
Total 555,685 6.4 47%
Total 178,530 2.1 15%
Total 108,367 1.3 9%
Total Inflows 1,175,055 13.6 100%

Drains 1 -32,219 -0.4
2 -41,809 -0.5
3 -5,598 -0.1
4 -9,824 -0.1
5 -23,491 -0.3
6 -62,413 -0.7
7 -150,427 -1.7
8 -782,639 -9.1
Total -1,108,420 -12.8 93%
Total Outflows -1,190,406 -13.8 100%

Aspect Consulting
06/10/2009 Table 8

Table 9 - Water Balance Summary, Constant Flux Sensitivity Analysis
Project 040001-012
Recharge 1 953,999 11.0 61%
Total 452,197 5.2 29%
Total 18,892 0.2 1%
Total 133,031 1.5 9%
Total Inflows 1,558,119 18.0 100%

Total -287,193 -3.3 19%
Drains 1 -31,534 -0.4
Drains 2 -37,776 -0.4
Drains 3 -15,028 -0.2
Drains 4 -32,368 -0.4
Drains 5 -89,413 -1.0
Drains 6 -104,452 -1.2
Drains 7 -149,029 -1.7
Drains 8 -768,302 -8.9
Total -1,227,903 -14.2 80%
Total Outflows -1,541,209 -17.8 100%

Aspect Consulting
06/10/2009 Table 9

Table 9 - Water Balance Summary, Constant Flux Sensitivity Analysis
Project 040001-012
Recharge 1 953,999 11.0 59%
Total 503,456 5.8 31%
Total 151,956 1.8 9%
Total Inflows 1,609,410 18.6 100%

Drains 1 -84,158 -1.0
2 -109,540 -1.3
3 -8,748 -0.1
4 -15,058 -0.2
5 -42,977 -0.5
6 -88,924 -1.0
7 -204,325 -2.4
8 -1,041,173 -12.1
Total -1,594,903 -18.5 99%
Total Outflows -1,614,192 -18.7 100%

Aspect Consulting
06/10/2009 Table 9

Table 10 - Calibration Results
Project 040001-012

Observed Water Levels Modeled Residual
Well ID Minimum Maximum Average Water Levels (Average - Modeled)
CHMW-1 188.65 198.43 192.50 191.70 0.80
CHMW-2-D 190.08 196.89 192.87 187.09 5.78
CHMW-2-S 190.00 196.84 192.93 187.46 5.47
CHMW-3-D 189.58 200.15 194.40 180.77 13.63
CHMW-3-S 181.35 200.83 194.67 183.07 11.59
CHMW-4-D 190.88 205.07 195.14 192.73 2.41
CHMW-4-S 193.04 202.87 197.34 193.00 4.35
MW-EM-1D 201.69 208.86 205.87 199.26 6.61
MW-EM-2D 209.17 211.29 210.74 205.98 4.76
MW-EM-3 210.34 212.83 212.07 209.27 2.80
MW-SL-1 209.82 212.56 211.39 209.41 1.98
SRC-MW-2 210.67 217.28 213.74 211.90 1.84

Modeled Versus Observed Water Levels
220

215
Modeled Water Level in Feet

210

205

200

195

190

185

180
175

170
170 175 180 185 190 195 200 205 210 215 220
Observed Water Level in Feet

Water level data collected approximately monthly from 2003 through 2008.
Model results are for the Sequalitchew Lake Model.

Aspect Consulting
06/10/2009 Table 10

Modeling analyses for fort lewis jblm drinking water system, aspect 2009

Modeling analyses for fort lewis jblm drinking water system, aspect 2009

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