Surface water and geomorphology herrera report-oct 2005

SURFACE WATER AND GEOMORPHOLOGY
TECHNICAL REPORT

Pioneer Aggregates Mining Expansion
and North Sequalitchew Project

Prepared for

Huckell/Weinman & Associates

October 2005

Note:
Some pages in this document have been purposefully skipped or blank pages inserted so that this
document will copy correctly when duplexed.

SURFACE WATER AND GEOMORPHOLOGY
TECHNICAL REPORT

Pioneer Aggregates Mining Expansion
and North Sequalitchew Project

Prepared for

Huckell/Weinman & Associates
270 Third Avenue, Suite 200
Kirkland, Washington 98033

Prepared by

Herrera Environmental Consultants, Inc.
2200 Sixth Avenue, Suite 1100
Seattle, Washington 98121
Telephone: 206/441-9080

October 28, 2005

Contents

1.0 Introduction...............................................................................................................................1

2.0 Affected Environment...............................................................................................................3
Sequalitchew Creek ..................................................................................................................3
Stream Discharge ............................................................................................................5
Water Quality ..................................................................................................................6
Geomorphology ..............................................................................................................7
Hydraulic Modeling of Existing Conditions .................................................................11
Fort Lewis Diversion Canal....................................................................................................12
Canal Discharge ............................................................................................................13
Water Quality ................................................................................................................13
Sequalitchew Creek Springs ...................................................................................................14
Near-Shore Springs.................................................................................................................14
Kettle Wetland ........................................................................................................................15
Old Fort Lake..........................................................................................................................15
Pond Lake ...............................................................................................................................15
Brackish Marsh.......................................................................................................................16
Historical Geomorphic Conditions .........................................................................................16
Existing Geomorphic Conditions ...........................................................................................16
Nisqually Reach (Puget Sound) ....................................................................................17
3.0 Significant Impacts of the Proposed Action ...........................................................................19
Construction............................................................................................................................19
Stormwater Management ..............................................................................................19
Site Clearing and Grading.............................................................................................20
North Sequalitchew Creek Construction.......................................................................20
Access Road and Pedestrian Bridge Construction ........................................................26
Conveyer System Construction.....................................................................................27
Operation ................................................................................................................................27
Mining and Processing ...........................................................................................................27
North Sequalitchew Creek ............................................................................................27
Sequalitchew Creek.......................................................................................................32
Kettle Wetland ..............................................................................................................34
Fort Lewis Diversion Canal/Sequalitchew Lake...........................................................34
Old Fort Lake ................................................................................................................35
Pond Lake .....................................................................................................................35
Brackish Marsh .............................................................................................................35
Post-Reclamation Stormwater Management.................................................................36
Near-shore Springs........................................................................................................37
Shipping Activities........................................................................................................37

i

Impacts of the Project Alternative ..........................................................................................37
Water Resources............................................................................................................37
Geomorphology ............................................................................................................37
Impacts of the No Action Alternative.....................................................................................38
Monitoring and Mitigation Measures .....................................................................................38
Water Quality ................................................................................................................38
Geomorphology ............................................................................................................39
Significant Unavoidable Adverse Impacts .............................................................................40
Proposed Action............................................................................................................40
Project Alternative ........................................................................................................42
4.0 References...............................................................................................................................43

ii

Tables

Table 1. Discharge summaries (monthly means) for Sequalitchew Creek and Fort
Lewis Diversion Canal from 1977 through October 2004. ........................................49
Table 2. Water quality standards (freshwater) and designated uses (Chapter 173-
201A-200 WAC) (Ecology 2003) applicable to surface waters of the project
site including Sequalitchew Creek and the Fort Lewis Diversion Canal. ..................50
Table 3. Water quality data for Sequalitchew Creek collected in the ravine bordering
the southern boundary of the Glacier site from September 1999 to September
2000. ...........................................................................................................................51
Table 4. Water quality data for the Fort Lewis Diversion Canal collected near the
eastern boundary of the Glacier site from September 1999 to September
2000. ...........................................................................................................................53
Table 5. Brackish Marsh salinity measurements (ppt) collected during low, ebb, high,
and flood tides on April 14 and April 19, 2004..........................................................55
Table 6. Water quality standards (marine waters) and designated uses (Chapter 173-
201A-210 WAC) (Ecology 2003) applicable to the Nisqually Reach of Puget
Sound (Extraordinary Quality). ..................................................................................56
Table 7. Marine water quality data collected from Ecology’s long-term ambient water
quality monitoring station GOR001 in the Nisqually Reach of Southern Puget
Sound from October 1996 to September 2002. ..........................................................57
Table 8. Table of estimated ground water quality concentrations and North
Sequalitchew Creek Concentrations within the mine expansion area
compared to background concentrations in Sequalitchew Creek and
Washington State surface water quality standards (Chapter 173-201A-200
WAC) (from Pacific Groundwater Group [PPG 2005]).............................................58
Table 9. Best estimate of predicted annual average flows in Sequalitchew Creek with
the additional flows from North Sequalitchew Creek upstream and
downstream of the proposed confluence at RM 0.8 (Anchor 2004d).........................60
Table 10. Best estimate of peak storm flows in Sequalitchew Creek under existing and
future conditions (Anchor 2004d). .............................................................................61
Table 11. Estimated peak storm flows in the proposed North Sequalitchew Creek used
by Aspect to assess reclamation stormwater conditions within the mine
expansion area (Aspect 2004b)...................................................................................62

iii

Figures

Figure 1. Proposed Glacier Mine expansion area, surface water features, and surface
water monitoring stations, DuPont, Washington........................................................63
Figure 2a. Sequalitchew Creek reach boundaries and landslides mapped by
GeoEngineers..............................................................................................................65
Figure 2b. Sequalitchew Creek reach boundaries and landslides mapped by
GeoEngineers (continued). .........................................................................................67
Figure 3. Landslide and debris fans in the lower Sequalitchew Creek ravine as
interpreted from shaded relief lidar digital elevation model. .....................................69
Figure 4a. Sequalitchew Creek selected erosional and depositional areas for current
conditions based on hydraulic modeling results.........................................................71
Figure 4b. Sequalitchew Creek selected erosional and depositional areas for current
conditions based on hydraulic modeling results (continued). ....................................73
Figure 5. Potential depositional and erosional reaches predicted by hydraulic modeling
of existing conditions in Sequalitchew Creek (GeoEngineers 2004b). ......................75
Figure 6. Sequalitchew Creek outlet and Diversion Canal surface water flow directions,
DuPont, Washington...................................................................................................76
Figure 7. Kettle wetland water levels at the existing Glacier Mine site from July 1999
to October 2002 (CH2M Hill 2003a)..........................................................................77
Figure 8. Brackish Marsh salinity sample locations near the existing Glacier Mine,
DuPont, Washington...................................................................................................79
Figure 9. Historical maps of Lower Sequalitchew Creek. .........................................................81
Figure 10. Current conditions within the Brackish Marsh during low tide. ................................83
Figure 11. Potential depositional and erosional reaches predicted by hydraulic modeling
of proposed conditions in Sequalitchew Creek (GeoEngineers 2004b). ....................85
Figure 12a. Sequalitchew Creek erosional and depositional areas for proposed conditions
based on hydraulic modeling results by GeoEngineers..............................................87
Figure 12b. Sequalitchew Creek erosional and depositional areas for proposed conditions
based on hydraulic modeling results by GeoEngineers (continued). .........................89
Figure 13a. Sequalitchew Creek areas of potential adverse change based on hydraulic
modeling results by GeoEngineers. ............................................................................91
Figure 13b. Sequalitchew Creek areas of potential adverse change based on hydraulic
modeling results by GeoEngineers (continued)..........................................................93
Figure 14. Model predicted change in ground water level near Sequalitchew Creek..................95

iv

Surface Water and Geomorphology Technical Report

1.0 Introduction

This report provides surface water and geomorphology technical detail and support to the
Supplemental Environmental Impact Statement (SEIS) for the expansion of Glacier Northwest’s
mining operations in DuPont, Washington. Glacier Northwest proposes to expand its current
mining operations by approximately 200 acres by mining adjacent land located mostly to the east
of the current mine area. Under the proposed action, Glacier proposes to capture ground water
entering the mine expansion area from the east and convey it south to Sequalitchew Creek via
North Sequalitchew Creek, a newly constructed stream channel. The following technical report
describes surface water and geomorphic existing conditions (affected environment), as well as
analyzes potential impacts to surface water resources and geomorphology from the proposed
200-acre expansion. In addition, proposed monitoring and mitigation measures for the proposed
project are presented.

wp4 /02-02403-000 surface water and geomorphology tech report.doc

October 28, 2005 1 Herrera Environmental Consultants


2.0 Affected Environment

Major surface water resources within the vicinity of the existing mine and proposed mine
expansion area include: Sequalitchew Creek and its associated wetlands and springs, Fort Lewis
Diversion Canal, Sequalitchew Lake, Old Fort Lake, and the Nisqually Reach of southern Puget
Sound. In addition, numerous small kettle lakes and wetlands located in the vicinity of the
project are described below.

The proposed mine expansion area is located in the Chambers-Clover basin (Water Resource
Inventory Area [WRIA] 12), which has a drainage area of 171 square miles. This basin is
located within the Puget lowlands ecoregion and has an average annual precipitation of
approximately 40 to 44 inches/year (Anchor 2004c). Sequalitchew Creek (Segment No.
12-0019), located entirely within the Chambers-Clover Creek Watershed, drains a watershed
covering 38.4 square miles and discharges into the Nisqually Reach of Puget Sound (WDF
1975). The headwaters of the Sequalitchew Creek drainage basin are located in Kinsey Marsh
on the east side of Interstate 5 (I-5). Runoff from the Kinsey Marsh flows 3.8 miles in Murray
Creek into American Lake on the west side of I-5. The water level in American Lake (1,162
surface acres) occasionally overflows the outlet weir and discharges into Sequalitchew Lake
(81 surface acres) (Figure 1).

Sequalitchew Creek
Sequalitchew Creek is formed at the outlet of Sequalitchew Lake. The Sequalitchew Creek
channel downstream of Sequalitchew Lake extends for approximately 1.5 miles through Edmond
Marsh. The lower 1.5 miles of Sequalitchew Creek, between Edmonds Marsh and the Puget
Sound shoreline, descends through a steep-walled ravine that parallels the southern boundary of
the proposed mine expansion area and existing mine. The channel drops approximately 220 feet
in elevation in 7,750 feet (average slope of 2.8 percent) between Center Drive below the upland
plateau and the brackish marsh located directly upstream of the BNSF Railroad embankment.
The floor of the ravine gradually widens in the downstream direction from a minimum of 40 feet
at the ravine head to a maximum width of roughly 400 feet near the railroad embankment at the
brackish marsh.

Ravine slopes on either side of the stream channel over much of its length range from 30 to 80
percent for an average of 60 percent. Near the mouth, Sequalitchew Creek passes through a
240-foot long box culvert (5 feet wide and 5 feet high) under the Burlington Northern-Santa Fe
Railroad (BNSF) railroad tracks before discharging into Puget Sound. The lower 300 feet of
Sequalitchew Creek above the BNSF railroad tracks is tidally influenced as evidenced by tidal
channels and a Class 1 estuarine wetland (per the City of DuPont rating system and identified as
the Brackish Marsh throughout this section).

Several springs, which provide flow to Sequalitchew Creek, are located on the north and south
banks from approximately 0.6 to 1.1 miles upstream of the mouth. An abandoned small-gauge



railroad grade that parallels the north creek bank intercepts these springs and collects the runoff
in drainage ditches that are culverted under the rail bed and drain into Sequalitchew Creek. The
springs daylight along the side slopes of the ravine at the contacts between layers of different
permeobilites and provide most of the flow into Sequalitchew Creek along this reach (CH2M
Hill 2003b).

Natural conditions at the mouth of the creek were substantially altered by construction of the
BNSF RR along Puget Sound in 1912 (Andrews and Swint 1994). The railroad embankment
isolated the delta from shoreline processes along Puget Sound and transformed the delta into a
one-half-acre brackish marsh. Since construction of the embankment, the exchange of
freshwater and saltwater has occurred through the long box culvert beneath the railroad.

Historically, Sequalitchew Creek has been subjected to chronic and extensive sediment inputs
throughout the project area as a result of pre-project land use (i.e., deforestation of ravine slopes
and construction of the railroad grade). The dominant mechanisms delivering sediment to the
creek channel include erosion of poorly consolidated hillslopes, soil creep, shallow landslides,
slumping, and ground water seeps. The Sequalitchew Creek valley has the potential to
contribute sediment due to the underlying geology of relatively unconsolidated sediments and
high ground water table. Extensive forest clearing in the early 1900s likely increased the rate of
sediment input to the creek. Given that flows in Sequalitchew Creek were naturally moderated
by ground water and upstream wetlands, it is likely the sediment inputs resulting from forest
clearing overwhelmed the creek’s sediment transport capacity. When the quantity of sediment
input to a reach exceeds the output, sedimentation decreases the depth and increases the width of
flow, further diminishing the sediment transport capacity. Bar formation and increased flow
widths would have further aggravated erosion of adjacent hillslopes. Local bank erosion is
observed where the channel is wide under existing conditions. The Fort Lewis diversion canal
(an upstream system of weirs that diverts flow away from Sequalitchew Creek) built in the
1950s, further diminished the creek’s sediment transport capacity by reducing stream flows.

Historically, two potential pollutant sources existed near the DuPont mine site. Fort Lewis Army
Reservation Landfill No. 5 located 0.5 mile east-northeast of the mine site was used for the
disposal of reservation wastes from 1967 to 1990. The landfill was designated as a Superfund
site pursuant to the Comprehensive Environmental Response Compensation and Liability Act
(CERCLA), when in 1987, sampling indicated that the landfill had contaminated the ground
water with elevated levels of heavy metals and organic compounds (U.S. EPA 2003). Closure of
the landfill was begun in 1987. Additional sampling after the closure of the landfill found
contaminant concentrations in ground water samples below state and federal cleanup standards,
and on May 22, 1995, the site was deleted from the National Priorities List (U.S. EPA 2003).

The old DuPont Works Plant, located south of the existing mine site, manufactured forty grades
of dynamite including water gel, nitroglycerine, ammonia explosives, and black powder from
1909 to 1977. Several remedial actions have been taken to remove contaminated material from
the site after the Weyerhaeuser and DuPont companies signed a Consent Decree with the
Washington Department of Ecology in pursuant to the Model Toxics Control Act in 1991
(URS 2000). The final environmental impact statement (FEIS) proposed action involves

Herrera Environmental Consultants 4 October 28, 2005


constructing a golf course to provide a cap/containment facility for the former explosives plant
(URS 2000).

Stream Discharge
The hydrology of Sequalitchew Creek is characterized by three reaches: an upper, losing reach;
the ravine, a middle gaining reach; and a lower, losing reach (CH2M Hill 2003b). The upper
reach extends from the outlet of Sequalitchew Lake through Edmond Marsh to a point west of
Center Drive. This upper reach infiltrates to recharge the Vashon Aquifer (CH2M Hill 2003b).
As the stream approaches the western end of Edmond Marsh, flows infiltrate the highly
permeable Vashon outwash materials. Surface flows do not extend downstream past Edmond
Marsh, except during high flow conditions.

During the winter, flows are regulated by a series of outlet weirs designed to manage the level of
Sequalitchew Lake by diverting excess discharge into the Fort Lewis diversion canal. Several
beaver dams on the stream cause the level of the stream to rise and back up, forcing discharge
into the diversion canal (Aspect 2004a). The Army removed some of the beaver dams near
Sequalitchew Lake in the summer of 2004, as they have reportedly done historically. The
beavers typically rebuild the dams. Because of the very low stream gradient along this reach, the
beaver dams can cause the water to reverse its flow direction with a water level rise of 1 to 2
feet. Effect of the beaver dams results in water levels in upper Sequalitchew Creek and Edmond
Marsh that are higher than water levels at either end. Thus, Sequalitchew Creek discharges both
down its historical channel to the west and through the Diversion Canal to the northwest (Aspect
2004a) (Figure 1). In addition, one stormwater outlet from Fort Lewis flows into Hamer Marsh
and one flows into Bell Marsh, adding additional surface flow to the stream. See the Diversion
Canal discussion below for a more detailed description of surface water flow pathways.

The middle reach extends from west of Center Drive downstream through the ravine to the
“Kitsap Cutoff,” the northern edge of the Olympia beds (CH2M Hill 2003b). This reach is
typically dry between the west end of Edmond Marsh and the ravine springs (Aspect 2004a).
This higher gradient portion of the creek receives discharge from several small springs from both
the north and south sides of the steep-walled ravine (CH2M Hill 2001). These springs provide a
perennial water source for the creek (CH2M Hill 2001, 2003b).

The stream channel within the lower reach, which extends west of the Kitsap Cutoff to Puget
Sound, consists of the highly permeable sands and gravels of the DuPont Delta formation. This
permeable layer causes water within the creek to infiltrate and recharge the ground water of the
DuPont Aquifer, measurably decreasing the discharge of the creek compared to the middle reach
(CH2M Hill 2003b).

Sequalitchew Creek discharge has been monitored periodically for several decades. Two studies
conducted during the 1970s and 1980s measured discharge in lower Sequalitchew Creek. A
study by Thut et al. (1978) from 1977 to 1978 measured monthly discharges in Sequalitchew
Creek ranging from 0.1 to 12.8 cfs. Similar results were found by Firth (1991) from 1984 to
1987 in lower Sequalitchew Creek, where monthly discharge averaged between 1.0 and 9.4 cfs.




The most recent Sequalitchew Creek discharge data were collected by Aspect Consulting
(Aspect) (2004a) and CH2M Hill (2001, 2003a) (Table 1). CH2M Hill monitored Sequalitchew
Creek discharge from October 1999 through September 2002 at a monitoring station located
approximately 700 feet upstream of the mouth. Stream flow monitoring activities at this lower
monitoring station were subsequently assumed by Aspect, which has published discharge data
through October 2004 (Aspect 2004b). From November 1999 to October 2004, the mean
monthly discharge at the lower monitoring station ranged from 0.2 to 2.9 cubic feet per second
(cfs). In addition, Aspect began operating a second upper flow monitoring station located
upstream of the proposed confluence with North Sequalitchew Creek (Aspect 2004a). From
November 2003 to October 2004, the mean monthly discharge at the upper station has ranged
from 0.4 to 2.5 cfs. At both stations, the highest discharges were measured during the wet
season (November through June) and the lowest discharges were recorded at the end of the dry
season (October/November).

Discharge measured in the lower reach indicates the creek does not respond quickly to rainfall
events, with minimum flows often lagging 1 to 2 days after a major rainfall event (i.e., >0.50
inches in 24 hours) (CH2M Hill 2001). The presence of Sequalitchew Lake, several large
wetlands in the headwaters of the creek, and several beaver dams in the Sequalitchew Creek
headwaters help detain and retard stormwater runoff. Because the flows in the lower reach of
Sequalitchew Creek are supported by ground water discharge, there is a time lag in the stream’s
response to storm events. Water flow through the subsurface (downstream of Center Drive)
moderates the discharge rates creating the lag in stream flow response. In addition, very little, if
any, surface water from the mine site enters Sequalitchew Creek (CH2M Hill 2001). The
majority of the precipitation infiltrates the highly permeable gravel deposits of the DuPont Delta
and Vashon Drift units underlying the site (CH2M Hill 2001).

Water Quality
Surface water quality standards for the State of Washington are established by Ecology in
Chapter 173-201A WAC for the protection of public health and enjoyment, and designated
beneficial uses (Ecology 2003). Sequalitchew Creek is designated as a salmon core rearing and
migration stream (formerly as a Class AA [extraordinary] waterbody under the previous WAC
designation and described in the original EIS [City of DuPont 1993]) by Ecology). Changes to
the state’s water quality standards were adopted by Ecology on July 1, 2003 and were effective
August 1, 2003. Water quality sampling results are compared to applicable state water quality
standards in Table 2.

Section 303(d) of the CWA (and later revisions) requires all states to prepare lists of surface
water that are not expected to meet applicable water quality standards after implementation of
water quality based controls. This list, identified as the 303(d) list, is prepared by Ecology and
submitted to the U.S. EPA. The most current listing is the 2004 303(d) list. To-date,
Sequalitchew Creek has not been identified on Ecology’s 303(d) list as a threatened or impaired
waterbody and is therefore not part of any existing or proposed TMDL. However, on the current
303(d) list, Sequalitchew Creek is listed as a “waters of concern” (Category 2) due to dissolved
oxygen and temperature excursions beyond the applicable criteria (Ecology 2005a).



Sequalitchew Creek water quality was described in the original mine EIS, which characterized
the stream as having good water quality and generally meeting Class AA water quality standards
(City of DuPont 1993). As part of the North Sequalitchew Creek Project, water quality samples
were collected monthly in Sequalitchew Creek from September 1999 through September 2000
(CH2M Hill 2001), with three additional dissolved oxygen measurements collected during the
summer of 2002 (Table 3). In addition, a continuous temperature recorder was installed in
Sequalitchew Creek in July 2000 to record daily temperature through December 2002. Water
quality samples were collected approximately 700 feet upstream of the mouth of lower
Sequalitchew Creek at the lower Sequalitchew Creek discharge gauge (Figure 1).

The sampling results (September 1999 through September 2000) indicate the waters of
Sequalitchew Creek are generally cool, well oxygenated, with low concentrations of fecal
coliform bacteria. During monthly sampling, measurements of pH, temperature, dissolved
oxygen and fecal coliform bacteria met the applicable state criteria. Nitrate-nitrogen was
detected at levels ranging from 0.28 to 0.82 mg/L, within the range presented in the original
mine EIS (City of DuPont 1993). Total phosphorus concentrations were low to moderate, and
ranged from 0.015 to 0.034 mg/L, with an average of 0.021 mg/L. TSS concentrations were low,
with an average of 4 mg/L measured during sampling (CH2M Hill 2001). Because samples were
not analyzed for turbidity, compliance with this standard cannot be determined. However,
because of the well documented link between turbidity and TSS (Packman et al. 1999), the
turbidity may also have been low during sampling.

During sampling, dissolved cadmium and lead concentrations were detected at concentrations
exceeding state water quality chronic criteria for each metal (based on an average hardness of
44 mg/L) (CH2M Hill 2001). A dissolved cadmium sample collected in October 1999 measured
0.0009 mg/L, which exceeded the chronic criterion of 0.0006 mg/L. Two dissolved lead samples
collected in May and July of 2000, both measuring 0.002 mg/L, exceeded the chronic criterion of
0.0010 mg/L.

CH2M Hill collected additional water temperature and dissolved oxygen data in Sequalitchew
Creek as part of continued project monitoring. The continuous temperature gauge recorded two
exceedances of the state temperature criterion (16°C) during August 2001 (CH2M Hill 2003c).
In addition, three dissolved oxygen measurements were made during the summer of 2002 with
one measurement in July (9.2 mg/L) and one measurement in August (9.3 mg/L) that failed to
meet the state minimum criterion of 9.5 mg/L (CH2M Hill 2003c).

Geomorphology
Historical Geomorphic Conditions
Sequalitchew Creek has responded to a series of changes in flow and sediment regimes
throughout both geologic and more recent historical times. The ravine of lower Sequalitchew
Creek was initially formed by a series of meltwater floods during glacial retreat (GeoEngineers
2004b). Peak flows within the channel likely declined rapidly following retreat of the glacier
and cessation of meltwater floods. Erosion would have been further reduced as forest vegetation




became established. This post glacial reduction in sediment production, sediment-transporting
flows, and increased hydraulic roughness within Sequalitchew Creek resulting from the
accumulation of wood debris would have resulted in relatively little sediment export to Puget
Sound. Thus as sea level rose, the creek mouth was probably characterized by a shallow
embayment of open water such as depicted in historical maps of the creek and not a prominent
delta (see Brackish Marsh discussion below). Prior to European colonization, the creek would
have provided outstanding salmon habitat because of the perennial source of cold water,
excellent substrate, abundant cover and shade, and high pool frequency created by in-stream
large woody debris.

Historical accounts of resource use by indigenous cultures and early settlers in lower
Sequalitchew Creek provide qualitative evidence of significant perennial flow prior to settlement
of the region. Records from Euro-American explorers arriving in the 1780s suggest perennial
flow and habitat conditions within Sequalitchew Creek were sufficient to sustain a productive
salmon run that sustained the local tribal population. Discharge at the mouth of Sequalitchew
Creek was also used to support a trading post established in 1821 and a water-powered sawmill
that operated between 1859 and 1870. Later on, the E.I. DuPont de Nemours Company
constructed a small dam and hydroelectric plant in the ravine in the early 1900s and maintained
the dam until at least 1940 (Aspect 2004a). Drainage of Edmond Marsh for farming by the
1850s, and the development of Fort Lewis between 1908 and 1917, impacted flows to
Sequalitchew Creek by reducing the storage capacity in the watershed. By the 1950s, flooding
caused by increased runoff from impervious areas of Fort Lewis prompted construction of the
current network of weirs and the diversion canal at the outlet of Sequalitchew Lake (Aspect
2004a) (Figure 1).

Construction of the diversion canal in the 1950s substantially reduced flows in Sequalitchew
Creek. Prior to construction of the diversion canal, the peak discharge in Sequalitchew Creek for
the 2-year storm event was estimated to range from 40 to 120 cfs, with an average value of 70 cfs
(Aspect 2004a). Based on recent stream gauging and hydrologic modeling, the current estimate
of the 2-year peak discharge is 10 cfs (Aspect 2004a). This major reduction in flow followed a
period in which deforestation and development would have dramatically increased the sediment
supply to the creek. The combination of an increase in sediment supply and reduction in
sediment transport capacity is consistent with field evidence of sedimentation within the ravine.
This material is currently held in storage within the ravine and available for transport to
downstream depositional reaches in the event of increased flow. The principal sediment trap has
historically been the tidal area currently occupied by the brackish marsh immediately upstream
of the railroad grade, an area where sedimentation is likely to accelerate if stream flow is
increased without compensating measures to reduce sediment delivery and improve transport
capacity through the area of tidal influence (see Brackish Marsh discussion).

Field observations and the natural history of the region suggest sediment transport and storage
within the creek would have been significantly influenced by large trees and in-stream woody
debris. Large tree stumps observed on the slopes of the ravine indicate that wood recruitment to
the creek would have included logs far larger than the creek would have been able to move, and
thus logs and woody debris capable of influencing the creek morphology would have been



common. Large trees would also be expected to moderate erosion along adjacent hillslopes by
reinforcing creek banks and promoting a relatively narrow and deep channel. Deforestation of
the basin in the early 1900s is likely to have exposed the highly erodible glacial sediments to
erosion and severely accelerated sediment input to the creek and sedimentation within the
brackish marsh.

Existing Geomorphic Conditions
The existing geomorphic conditions of lower Sequalitchew Creek have been investigated for the
proposed mine expansion project through field reconnaissance and modeling efforts. Field
reconnaissance was completed in January 2004 by participants from GeoEngineers, CH2M Hill,
and Glacier Northwest (GeoEngineers 2004b). Existing conditions in the brackish marsh were
investigated by Anchor (2004c) during rising and falling tides in April 2004. Additional field
reconnaissance of Sequalitchew Creek was performed by Aspect (2004a) in April 2004 and by
Herrera in September 2003 and February 2005. Landslides were mapped in the field and
interpreted from high-resolution topography of the project site.

The ravine below Center Drive has been divided into four reaches based on geology (location of
Kitsap cutoff), extent of tidal influence, and channel morphology (GeoEngineers 2004b). Reach
numbering (1 through 4) is upstream to downstream. Stream stationing, extending from Station
00+00 at the mouth, approximately 50 feet downstream of the 5-foot box culvert: to Station
70+00 (7000 feet) at the upstream end of the ravine, was established for purposes of hydraulic
modeling and provides an additional reference for discussion (Figures 2a and 2b). The
uppermost reach of the ravine is typically dry from the west end of Edmond Marsh to the first
identified springs about 300 feet west of Center Drive. Flow at this location is intermittent.
Remnants of the old dam and power works are located here as well.

Reach 1 begins at Station 70+00 in the ravine, approximately 750 feet downstream from Center
Drive (Figure 2a). At this location, the ravine is roughly 60 feet wide and 40 feet deep. Reach 1
is located above the Kitsap Cutoff and is characterized by relatively low channel gradient and
numerous ground water seeps emerging along the Olympia-Vashon contact. The average
channel gradient varies from 1 to 2 percent, with the local maxima as great as 3.5 percent. The
bankfull channel depth varies from 0.3 to 3 feet. Channel width varies from 5-7 feet upstream
and increases to 15-40 feet near Station 35+00. Sediment comprising the channel bed is
dominated by small gravel and cobbles and interstitial coarse sand and fine gravel. Stream
morphology varies between a shallow, wide, braided channel spanning nearly the entire width of
the ravine, to a relatively narrow channel confined against the ravine wall and causing local
erosion. Deposition of sand within the active channel reflects the relatively low transport
capacity within Reach 1. Consistent with sedimentation, the channel has relatively few pools,
and the ones observed occur downstream of the wood debris obstructing flow.

Reach 2 extends from Station 30+00 to 18+00 and is located below the Kitsap Cutoff in
unconsolidated outwash sand and gravel (Figure 2b). Channel gradient increases to 2-3 percent
in Reach 2, with a local maximum of 4.5 percent. The width of the ravine bottom also increases
downstream from 30 to 50 feet. Channel widths and depths in Reach 2 vary dramatically from



5-40 feet and 0.3-3 feet, respectively. Local surface raveling and exposed sediment at the toe of
ravine slopes suggest active erosion by the stream in Reach 2. Where the channel widens, low-
relief gravel bars provide additional evidence of recent scour and deposition, despite historically
low flows. These observations clearly indicate that local sediment delivery from adjacent
hillslopes still occurs and is likely to increase if flows are increased, unless mitigating actions are
taken to keep erosive flows from abutting the hillslopes (such as placement of large woody
debris). Elsewhere, the stream bed is locally armored with cobbles up to 6 inches in diameter.
The downstream segment of Reach 2 between Stations 23+00 and 18+00 is similar to Reach 1
and consists of a poorly defined braided channel with little or no floodplain.

The width of the ravine increases in Reach 3 to about 250 ft at the downstream end of the reach
(Station 5+00) (Figure 2b). Similar to the transition from Reach 1 to 2, the transition from
Reach 2 to Reach 3 is marked by a change in channel morphology from a wide, shallow channel
to a narrow channel incised into alluvium. Downstream of Station 16+80, channel morphology
varies from a narrow channel confined against the toe of the ravine to a wide undefined channel
with intermittent mid-channel gravel bars. A berm constructed between Stations 9+00 and
11+50 deflects the stream channel to the south side of the ravine and separates the creek from a
10-foot deep pit excavated along the north side of the ravine. At Station 10+00, the creek flows
within a relatively narrow channel in the middle of the widening valley bottom and away from
the toe of the ravine.

Reach 4 consists of a straight, plane-bed channel extending through the brackish marsh to the
entrance of the box culvert at the foot of the railroad embankment (Figure 2b). The channel
flows situated along the north side of the valley with its bed located below the brackish marsh,
which forms the creek’s floodplain through Reach 4. The channel is armored with a layer of
coarse gravel and is 9-10 feet wide and 1.0-1.5 feet deep. The channel does have some vegetated
bars along its right bank indicating it has undergone periods of historic sedimentation. In
addition, there are several distinctive gravel splays or finger-like deposits of gravel on top of the
adjacent tidal marsh at the upstream end of the reach (Station 5+50). Channel gradient decreases
from 2 percent to approximately 1.5 percent at the transition from Reach 3 to the brackish marsh
at Reach 4. The gradient of the box culvert beneath the railroad embankment is 1.2 percent. The
hydraulic gradient through Reach 4 is largely governed by the inlet elevation of the box culvert
(-1.02 feet) and high tides, which can exceed 10 feet.

Woody debris within the creek has been recruited from adjacent hill slopes because there are
relatively few trees within the ravine bottom. The majority of pools in the creek are formed
downstream of logs and in places where the banks are stabilized by tree roots. Most of the wood
debris consists of small trees, branches, and shrubs. Woody debris is not present in the tidally
influenced segment of Sequalitchew Creek through the brackish marsh (Reach 4), reflecting low
wood recruitment rates, insufficient transport capacity in the upstream reaches, and a low supply
of bedload in Reach 4. The lack of wood within the brackish marsh also indicates that little
wood debris is moving down the stream (coincident with a low sediment transport capacity) and
what is moving downstream is trapped prior to reaching the brackish marsh. Some small wood
debris may be flushed to Puget Sound during low tides. But if any significant quantities were




reaching the brackish marsh, then deposits of wood debris would be found along the high water
margins of the marsh.

Ravine slopes throughout the reaches are vegetated by ground cover and a mixed deciduous-
coniferous forest. The gradient of side slopes within the ravine ranges from 30 to 80 percent.
Several landslide features were mapped during a field reconnaissance of the ravine above station
9+00 in January 2004 (GeoEngineers 2004b) (Figures 2a and 2b). Evidence of ancient
landsliding was noted at Stations 9+00 and 12+00 in Reach 3. These landslides are at least a
century old based on the presence of old-growth tree stumps in growth position on the surface of
both features. A more recent landslide deposit was mapped on the ravine floor in Reach 2 at
Station 23+50. This feature, a probable debris flow deposit, is about 40 years old based on the
size of the largest tree growing on the deposit (GeoEngineers 2004b). High-resolution LiDAR
topography of the project area became available after completion of field mapping. The
landslide features identified in the 2004 field reconnaissance are delineated on a map showing
the 2003 LiDAR of the project area (Figure 3). Material derived from historical or older
landslides and chronic soil creep forms a nearly continuous sediment wedge along the toe of
ravine slopes and serves as a readily available sediment supply when eroded by the creek. Local
erosion of the sediment wedge occurs at sites where the creek flows along the valley edge. At
these sites the sediment wedge has eroded and the hillslope is undercut and steepened
(GeoEngineers 2004b). Unvegetated banks and ravine slopes with exposed sediment indicate
ongoing input of sediment to the creek.

Based on observations of existing geomorphic conditions in the ravine, sediment production and
delivery processes appear to be dominated by the erosion of existing landslide deposits,
gravitational creep, surface weathering, and sediment mobilized by flow from seeps and springs.
Sediment derived from hillslopes is typically delivered to margins of the valley bottom where it
remains in storage until eroded or entrained by the creek.

Hydraulic Modeling of Existing Conditions
Existing hydraulic conditions in Sequalitchew Creek were evaluated by GeoEngineers (2004b)
using the HEC-RAS model. HEC-RAS is a one-dimensional hydraulic model developed by the
U.S. Army Corps of Engineers to estimate water-surface elevations for rivers and streams.
HEC-RAS is typically used to evaluate stage and velocity relationships in a river given the
channel geometry, roughness, and flow rate. The channel geometry used in the model was based
on cross sections surveyed from the outlet of the box culvert at Puget Sound to the upstream end
of Reach 1. Existing hydraulic conditions were simulated for the 2-, 5-, 10-, 25-, 50-, and
100-year recurrence storm flow events. Hydraulic conditions in Reach 4 were evaluated under
conditions of both high and low tide. Simulated flows were developed using recent gauge data
from lower Sequalitchew Creek and correlation with recent stream gauge data from adjacent
stream systems. Simulation outcomes were compared with existing bankfull elevations inferred
in the field in order to calibrate the simulated channel roughness.

Shear stress (i.e., force exerted on the bed by the stream) calculated by the HEC-RAS model
provided the necessary hydraulic parameters to evaluate the potential for sediment transport




(erosion) and deposition along various reaches of the lower stream reach (GeoEngineers 2004).
The total boundary shear stress is the stress exerted by flowing water on the streambed and
changes with discharge, flow depth, and channel gradient. Critical shear stress for the bed is the
stress required to initiate the movement of a particle and is an intrinsic property of the particle
mass, shape, and size range of other particles on the bed. Because Sequalitchew Creek is
armored with the coarsest particles, the critical shear stress for initial entrainment of the
streambed was scaled to twice the critical shear stress for the 70th percentile grain size
(GeoEngineers 2004b). Sediment deposition occurs when shear stress drops below the critical
particle shear stress.

The modeling results of the shear stress analysis by GeoEngineers (2004b) indicated potential
erosion in Reach 1 near Station 33+00 for storm events larger than the 2-year event (Figure 4a).
However, the majority of potential erosion sites are located in Reach 2, where streambed
gradients increase through the Kitsap Cutoff (Figure 4b). The results for Reach 3 indicate
potential erosion for the 2-year storm near Station 10+80, downstream of the berm and 10-foot-
deep depression. Two additional sites in Reach 3, at Stations 5+58 and 5+40, indicate potential
bed erosion at the 25- and 50-year storm events just upstream of the brackish marsh.

Results also identify sites where declining shear stress would cause deposition of sediment. The
shear stress analysis suggests a downstream pattern in the deposition of progressively finer
sediment sizes through Reach 3. For instance, all grains in transport and larger than 8.2 mm
would be deposited near Station 17+10 during 10-year flows, whereas grains larger than 6 mm
would be deposited at Station 10+05 during 25-year flows (Figure 4b). Likewise, during
100-year flows, the maximum grain size transported through these reaches declines in the
downstream direction from 12 mm at Station 17+10 to 10 mm at Station 10+05. Declining shear
stress through the brackish marsh indicates Reach 4 is aggrading under existing flow conditions.

Relative trends in bed erosion and sediment deposition within Reaches 1 through 4 have been
summarized by comparing the ratio between the simulated shear stress and critical shear stress
during the 100-year event along a longitudinal profile of the creek (Figure 5). A ratio greater
than 1 indicates conditions are favorable for sediment transport and bed erosion. When shear
stress falls below the critical particle shear stress, sediment currently in transport would be
deposited. Results of the shear stress analysis indicate Reaches 1, 3, and 4 act as sediment traps
while most of Reach 2 is subject to erosion and exporting sediment under existing conditions
(Figure 5). The simulated decline in shear stress to just a fraction of the critical shear stress is
consistent with current observations of sedimentation in Reaches 3 and 4 and historical filling of
the brackish marsh.

Fort Lewis Diversion Canal
The Fort Lewis Diversion Canal (Diversion Canal), which borders the western boundary of the
Fort Lewis Military Reservation, was constructed in the 1950s to convey stormwater runoff from
Fort Lewis to Puget Sound and to help control the water level in Sequalitchew Lake by serving




as an auxiliary outlet (Figure 1). Hydraulic structures (i.e., weirs) control the lake water level to
prevent inundation of Sequalitchew Springs located near the eastern end of the lake, which
serves as a major water source for Fort Lewis (CH2M Hill 2003b). The Diversion Canal is two
miles long with trapezoidal-shaped channel, which is approximately 15 to 20 feet deep with a
base width of 20 feet and 1H:1V side slopes (Aspect 2004a).

Sequalitchew Lake is located entirely on the Fort Lewis Military Reservation. The lake is
approximately 81 acres in size and is shallow, approximately 17 feet deep. An 18-foot-wide
concrete structure with wooden stop logs that can be raised or lowered to adjust the elevation of
the lake acts as the outlet diversion weir for the Diversion Canal (Aspect 2004a). The weir is
currently set at an elevation of 211.15 feet (by the army).

Stormwater runoff from the developed areas of Fort Lewis flows into the Diversion Canal,
downstream of the lake outlet. The stormwater runoff is conveyed under Sequalitchew Creek via
a culvert near the lake outlet (CH2M Hill 2003b). The Diversion Canal then routes water along
the western boundary of the Fort Lewis Landfill No. 5, ultimately discharging into the Puget
Sound near the Solo Point Sewage Treatment Plant (Woodward-Clyde 1990).

A series of weirs controls lake level and flows to the Diversion Canal and Sequalitchew Creek
(Figure 6). At low lake levels, an adjustable height weir directs flows from the lake to
Sequalitchew Creek, and at higher lake levels, lake outflow enters the Diversion Canal (CH2M
Hill 2003c). To maintain flows in Sequalitchew Creek, a second weir structure prevents
Sequalitchew Creek waters from flowing into the Diversion Canal. Beaver dams located
downstream of the lake outlet can cause Sequalitchew Creek waters to back up, causing more
water to flow into the diversion canal and reducing the flows to the creek (CH2M Hill 2003c).

Canal Discharge
Discharge data measured by CH2M Hill (2003c) and Aspect (2004a) indicate that much higher
discharge flows through the Diversion Canal in comparison to the Sequalitchew Creek discharge.
The average monthly discharge ranged from 2.0 to 21.9 cfs from December 1999 to November
2002 at Wharf Road (CH2M Hill 2003c) and from 1.5 to 11.3 cfs from May 2003 to October
2004 at the Diversion Weir (Aspect 2004a) (Table 1). In addition, daily winter storm discharge
was measured as high as 40 to 50 cfs (CH2M Hill 2001). Aspect (2004a) also measured the
discharge at three locations in the Diversion Canal to determine whether it was gaining or losing
discharge. Aspect (2004a) determined that the first reach between the diversion weir and
DuPont-Steilacoom Road gains discharge while the next two reaches lose flow at relatively
constant rates.

Water Quality
A discussion of Diversion Canal water quality was not included in the original mine EIS (City of
DuPont 1993). However, as a part of the baseline monitoring for the project, water quality
samples were collected on a monthly basis in the Diversion Canal from September 1999 through




September 2000 (Table 4). Samples were analyzed monthly for dissolved oxygen and water
temperature, and quarterly for conventional parameters and metals (Table 4). The analytical
results indicate that the waters of the diversion canal generally have good quality, with the
exception of elevated water temperatures during the late spring through early fall. During the
monitoring period, state criteria were met for dissolved oxygen, fecal coliform bacteria, pH, and
turbidity. A continuous temperature gauge was installed in July 2000, which recorded daily
water temperatures through August 2002. Water temperatures exceeding the state criterion were
measured during July, August, and September of 2000.

Additional temperature and dissolved oxygen data were collected in the Diversion Canal as part
of continued project monitoring (CH2M Hill 2003c). The continuous recording temperature
gauge recorded numerous exceedances of the state temperature criterion (16°C) during May
through September 2001 and from late April through August 2002 when the continuous gauge
was removed (CH2M Hill 2003c). In addition, three dissolved oxygen measurements were
recorded during the summer of 2002 which did not meet the state minimum criterion of 9.5 mg/L
(CH2M Hill 2003c).

Sequalitchew Creek Springs
Several springs discharging from the Vashon aquifer are located along the north and south banks
of the Sequalitchew Creek ravine, south of the existing mine and proposed mine expansion area.
One major spring located on the north bank and two smaller seeps located along the south bank
were sampled as part of the original mine EIS studies (City of DuPont 1993). The results of this
monitoring indicate that the spring waters are of good quality (City of DuPont 1993). No new
spring water quality or discharge data have been collected since completion of the original mine
EIS. Similar to Sequalitchew Creek, elevated nitrate-nitrogen concentrations have been
measured in these springs (City of DuPont 1993).

Near-Shore Springs
Several near-shore springs are located along the Nisqually Reach of Puget Sound, adjacent to the
western boundary of the existing mine site. Spring discharges originate from the DuPont Delta
aquifer (CH2M Hill 2001). The largest spring (Large Beach Spring) is located in the intertidal
zone approximately 1,600 feet north of the mouth of Sequalitchew Creek (Figure 1). This large
spring enters Puget Sound at approximately 4 feet above mean lower low water (MLLW).
Discharge data in the original mine EIS characterized the discharge from this spring as ranging
from 11 to 18 cfs, depending on tide height (City of DuPont 1993). More recent data (CH2M
Hill 2001) measured discharges of 9.1 and 14.9 cfs during September 1999 and August 2000,
respectively. Several smaller near-shore springs, located about 600 feet north of the large spring,
had discharge that ranged between 0.05 and 0.24 cfs (CH2M Hill 2001).

Based on the water quality data results presented in the previous mine EIS, waters of the large
near-shore spring generally exhibit good quality (City of DuPont 1993). Significantly high




concentrations of sodium and chloride in addition to high specific conductivity measurements
reported in the original mine EIS were attributed to saltwater intrusion into the spring (City of
DuPont 1993). Salinity data were collected once in 1999 as part of the North Sequalitchew
Creek project in the large beach spring and two smaller springs (CH2M Hill 2001). Salinity in
the large beach spring was 5.3 parts per thousand (ppt), and was 7.7 ppt and 15.3 ppt in each of
the smaller springs.

Kettle Wetland
The Kettle Wetland, located in a large closed depression (a geologic feature called a kettle) near
the center of the existing mine site, is approximately 2.5 to 3 acres in size (CH2M Hill 2001)
(Figure 1). This wetland is located within the Sequalitchew Creek drainage basin and is in
hydrologic continuity with the Vashon aquifer, where the surface water level is an expression of
the ground water table at that location (CH2M Hill 2003b). Based on the water quality data
presented in the previous mine EIS, the Kettle Wetland has fair to good water quality (City of
DuPont 1993).

Water levels in the kettle fluctuate seasonally, from 1-2 feet during the summer to 4-6 feet during
the winter. The open water component width also varies seasonally from 50 feet during the
summer to several hundred feet during the winter. Water levels in the wetland were monitored
intermittently by CH2M Hill at a staff gauge installed in the wetland in 1999 (CH2M Hill
2003a). Monthly water level data from July 1999 to October 2002 are presented in Figure 7.
During monitoring, water levels reached peak levels during the wet season (November through
June) and tended to drop with decreasing precipitation, especially during late summer and early
fall. At the staff gauge location, water levels over the monitoring period ranged from a high of
6.22 feet in December 1999 to the soil surface (0.63 feet) in October 1999.

Old Fort Lake
Old Fort Lake is a small kettle lake located south of Sequalitchew Creek and the proposed mine
expansion area (Figure 1). The lake is located on the former DuPont Works Site now owned by
the Weyerhaeuser Company. The lake is located in a kettle, and is supported hydrologically by
the shallow Vashon aquifer. Thus, lake water levels fluctuate seasonally and are a reflection of
the ground water table at this location. Old Fort Lake water quality data were not summarized as
part of the original mine EIS and water quality data were not collected in Old Fort Lake as a part
of the North Sequalitchew Creek Project.

Pond Lake
Pond Lake is a surface water, isolated, kettle depression wetland that is approximately 1.8 acres
in size located south of the Sequalitchew Creek (WSA 2005). Pond Lake is located between



Center Drive and Strickland Lake (Figure 1). Although Pond Lake has no surface water
connections to other surface waters, it is apparently connected with ground water and its surface
fluctuates throughout the year based on the local ground water elevation (WSA 2005). Pond
Lake water levels fluctuate greatly; and lake periodically dries out for extended periods of time,
such as, in 2001 and 2004 (WSA 2005). Pond Lake dries out completely at a ground water
surface elevation of approximately 201 feet above sea level. Pond Lake water quality data were
not summarized as part of the original mine EIS and water quality data were not collected in
Pond Lake as a part of the North Sequalitchew Creek Project.

Brackish Marsh
The brackish marsh is a one-half acre wetland located in the estuary of Sequalitchew Creek
(Figure 8). The brackish marsh is situated on the southwest side of the main Sequalitchew Creek
channel on the landward (upstream) side of the BNSF railroad berm (Figure 8). Historical
records indicate that the Sequalitchew Creek estuary was once an open embayment along Puget
Sound which would have had a tidal wetland fringe. Historical land use beginning with
construction of the railroad embankment and upland development, led to gradual infilling of the
Sequalitchew estuary, allowing emergent vegetation to become established. Infilling has further
transformed emergent wetlands to upland vegetation.

Historical Geomorphic Conditions
Early survey maps from the late 1880s and 1908 show Sequalitchew Creek draining into a small
embayment along the coast of Puget Sound at the present location of the brackish marsh
(Figure 9). Although construction of the railroad berm in 1912 isolated the mouth of
Sequalitchew Creek from Puget Sound (Andrews and Swint 1994), sedimentation from
deforestation of the basin likely initiated filling of the estuary, which probably consisted of a
shallow embayment with intertidal mudflats and wetlands partially separated from Puget Sound.
Topographic maps prepared after construction of the railroad embankment indicate the remnants
of the embayment still existed in 1939 and 1947 as an open-water lagoon behind the railroad
embankment (Figure 9). Aerial photography from 1990 and recent field reconnaissance indicate
that considerable filling of the former embayment during the late 1900s transformed the
saltwater lagoon into the current brackish marsh.

Existing Geomorphic Conditions
The brackish marsh drains through a dendritic network of tidal channels that flow away from
Sequalitchew Creek and merge into a main tidal channel, which then runs north along the
railroad embankment and joins the creek at the box culvert entrance (see Figure 8). The
hydrology and water level of the brackish marsh are tidally influenced by Puget Sound (Anchor
2004c). When the tide is 8 feet above mean lower low water (MLLW) or lower, flow in
Sequalitchew Creek remains within its channel and bypasses the brackish marsh directly to the




box culvert (Anchor 2004c). When the tide rises to 9 feet above MLLW, salt water inundates the
main tidal channel and fresh water from Sequalitchew Creek flows into the main dendritic
channel of the marsh (Anchor 2004c). When the tide reaches 10 feet above MLLW or higher,
the brackish marsh is completely inundated (Anchor 2004c).

Because the elevation of the culvert is within the intertidal zone, fresh water and sediment from
Sequalitchew Creek are temporarily impounded behind the railroad embankment during high
tide (Anchor 2004c). The impoundment creates conditions for the settling of fine-grained
sediment throughout the brackish marsh within the area of inundation, as well as deposition of
coarse bedload sediment where the creek enters the impounded area at the upper end of Reach 4.
Significant quantities of sediment have historically been deposited and retained in the brackish
marsh. During low tide, there is generally sufficient shear stress within the creek channel to
move sediments deposited during high tide out to Puget Sound. Deposition within the brackish
marsh is most likely to occur during high creek flow and high tides. These periods of deposition
contribute to the ongoing aggradation of the brackish marsh. Field reconnaissance conducted by
Herrera in February 2005 observed gravel splay deposits emanating from the main-stem channel
and covering portions of the marsh surface (Figure 10). The combination of historical survey
records and recent observations of coarse-grained alluvium several feet above sea level (in the
area of the former salt water embayment) indicate historical sedimentation and filling of the
wetland within the brackish marsh.

The current valley morphology and channelization of the creek into alluvial fan deposits is
consistent with the sedimentation predicted by the declining shear stress simulated within the
lower ravine and brackish marsh. HEC-RAS modeling conducted by Herrera of the mean high
water (MHW) (approximately 9.5 feet North American Vertical Datum [NAVD], 13.5 feet above
mean lower low water, see above), indicates that aggradation below Station 8+00 is tidally
influenced, particularly when high tide coincides with significant sediment transporting events.
Mean higher high water elevation to the 1988 NAVD is 10.5 feet and the highest observed water
was 13.9 feet (at Olympia).

During April 2004, salinity in the brackish marsh and the lower Sequalitchew Creek reach was
monitored on two separate occasions (Anchor 2004c). The salinity was measured at several
stations during low and high tides, including an ebb tide during the second monitoring event
(Table 5). The mid-depth salinity in the Sequalitchew Creek channel (SQ-1 through SQ-7)
ranged from 0.1 to 27.6 ppt while the main dendritic channel (SQ-12, SQ-16, and SQ-17)
mid-depth salinity ranged from 1.9 to 27.3 ppt. In general, salinity in the Sequalitchew Creek
channel remained low (0.1 ppt) unless it became inundated with saltwater. The main dendritic
channel tended to exhibit much higher salinity concentrations, especially during low tide periods
when the marsh was not inundated with saltwater (Anchor 2004c).

Nisqually Reach (Puget Sound)
The Nisqually Reach of Puget Sound separates Anderson Island from the Nisqually Delta and
borders the western shoreline of the project site. Water circulation in the Nisqually Reach is




determined by a complex mixture of forces, including tides, freshwater inputs, and winds (City
of DuPont 1993). The Nisqually Reach hydrologic characteristics and water quality were
described in the original mine EIS (City of DuPont 1993).

The Nisqually Reach is designated as an extraordinary marine water by Washington State
Department of Ecology (Ecology 173-201A-085) (Table 6). Ecology has established several
ambient water quality monitoring stations in the Nisqually Reach. The station used to
characterize Nisqually Reach marine waters in the original mine EIS (Station Id: NSQ001) has
not been monitored since July 1996. More recent water quality data are available from a nearby
station in the reach (Station Id: GOR001) and are used to update the following water quality
characterization (Ecology 2005). This station is located in Pierce County, just north of Anderson
and Ketron Islands (Figure 1). The water quality data collected at this station from 1996 through
2002 are summarized in Table 7. Data collected in 2001 and 2002 are provisional and have not
been finalized (Ecology 2005). Data were gathered at 0.5, 10, and 30 meters from October 1996
to January 2000 and thereafter, were collected from depths of approximately 1, 10, and 30 meters
(Ecology 2005b).

Monitoring data indicate that marine waters of the Nisqually Reach have fair to good quality.
During sampling, reach waters met state extraordinary criteria for pH and fecal coliform bacteria.
However, the state extraordinary water temperature criterion (13°C) was exceeded 29 times
during the late summer and fall (July through October). In addition, 45 dissolved oxygen
measurements during the monitoring period did not meet the state minimum criterion of 7.0
mg/L. Because turbidity was not monitored, compliance with this standard is undetermined.

The Nisqually Reach/Drayton Passage area is on Ecology’s final 2004 303(d) list of threatened
and impaired waterbodies for violations of the state standards for fecal coliform bacteria,
dissolved oxygen, pH, ammonia-nitrogen, and temperature (Ecology 2005a). The Nisqually
Reach/Drayton Passage area was also listed for fecal coliform bacteria on the 1996 list, but was
not placed on the 1998 list (Ecology 2005a).

Ecology has initiated a South Puget Sound Model Nutrient Study (SPASM), which addresses
concerns of eutrophication in South Puget Sound. However, to-date a TMDL (and proposed
clean-up action) has not been established for the Nisqually Reach addressing the fecal coliform
bacteria listing (McKee 2005). Ecology completed a quality assurance project plan for the
Henderson and Nisqually TMDL Study that summarizes the existing Nisqually Reach data and
presents a TMDL evaluation project design (Sargeant et al. 2003). That report will serve as a
background study for establishing the Nisqually Reach TMDL. Several excursions beyond the
criterion for dissolved oxygen at station NSQ001 were identified on Ecology’s 1998 303(d) list;
however, these excursions were found to be a result of natural causes and no formal listing was
made (Ecology 1998).




3.0 Significant Impacts of the Proposed Action

Construction
Construction activities associated with the proposed mine expansion would include site clearing
and grading, excavation of soils for the construction of North Sequalitchew Creek, pedestrian
bridge construction (over North Sequalitchew Creek), access road construction (culvert
placement), and conveyer system construction. All mining operation and processing facilities
were constructed as part of the original mine facility and are not located within the proposed
200-acre mine expansion area. Impacts from the construction of these facilities are described in
the original draft and final EIS for the mine (City of Dupont 1992, 1993). No additional
facilities would be constructed in either the new mine expansion area or in the processing area
that is already in operation with the existing permitted mine.

Glacier Northwest proposes dewatering to accommodate excavation and sand gravel extraction
below the existing ground water table. The proposed dewatering plan would require the
installation of a series of dewatering wells to pump and drawdown the Vashon aquifer so that
excavation could occur under mostly dry conditions. Ground water would be discharged into
Sequalitchew Creek at the approximate location of the proposed confluence with North
Sequalitchew Creek (RM 0.8). During construction, the mining operations would remove the
Vashon drift unit, located within the proposed mine expansion area. (See the ground water
technical report for the discussion of impacts to ground water quality and quantity (PGG 2005).

Stormwater Management
A sediment pond and an infiltration pond would be used during construction (and operation) for
the discharge of on-site stormwater (CH2M Hill 2003c). The sediment pond would be sized to
treat up to the 10-year storm event and to treat ground water base flow (i.e., approximately
10 cfs) not captured by the dewatering wells (CH2M Hill 2003c). The infiltration pond would be
sized to store and infiltrate the 100-year, 24-hour storm, including the 10 cfs of possible ground
water baseflow (CH2M Hill 2003c).

During mine excavation, stormwater runoff and some ground water baseflow would accumulate
in the bottom of the active excavation pit. This pit would be graded to allow for the captured
water to collect at a low point, which would serve as a temporary sedimentation pond. If
necessary, the collected water would be pumped to an on-site infiltration pond for discharge to
ground water.

Current mining activities are covered under a Surface Mining and Associated Activities General
Permit (WAG-50-1178) as part of the Ecology NPDES permit program. This permit covers the
discharge for process water and stormwater associated with sand and gravel operations.
Coverage under this permit allows for discharges to waters of the State of Washington subject to
permit conditions under both the construction and operational phases of mining.




Site Clearing and Grading
Mine expansion area clearing and grading would be phased with mining and construction
activities to minimize the area cleared at any one time. Site clearing and grading would consist
of the removal of the topsoil and stockpiling this material on-site for re-use during site
reclamation after mining operations have ceased.

An Erosion and Sedimentation Control (ESC) Plan would be prepared as part of the Stormwater
Pollution Prevention Plan (SWPPP) completed for the proposed mine expansion as a requirement
of the mine NPDES permit. With the employment of proper and usual ESC measures, impacts to
receiving waters during clearing and grading are expected to be negligible. ESC measures
outlined in this plan would minimize or eliminate impacts by providing adequate treatment
through the use of best management practices during site clearing and grading. Sediment and
erosion ESC measures proposed for the mine expansion area include:

Wetting roadways as necessary with water for dust control
Truck wheel washing prior to off-site travel
On-site infiltration of stormwater.

Within the mine expansion area, construction would remove vegetative cover and expose soils
leaving this area prone to erosion during runoff events. The rate of surface water runoff from
these areas could increase due to compaction of soils and lack of vegetative cover. If sediment
enters any water resources, increases in turbidity, suspended solids, and settleable solids could
occur. However, all storm water runoff on-site would be infiltrated to the shallow ground water
aquifer, and not reach Sequalitchew Creek (via surface flow). Therefore, impacts to surface
water resources are not expected.

Oil, grease, and total petroleum hydrocarbons (TPH) could leak or spill from construction
equipment or petroleum product storage facilities. If an uncontrolled spill occurred, there would
be the possibility that petroleum products could reach ground water under the construction area.
These products could pose a risk to water quality at high concentrations. Release of petroleum
hydrocarbons from heavy mining equipment and haul trucks is a significant concern to ground
waters, but can be prevented by mitigation measures such as strict prohibition of oil/fueling
dumping and contractual specification’s for accidental spill response and notification
requirements, and catchment control of parking/staging areas for construction equipment. The
mining SWPPP would include an Emergency Spill Cleanup Plan that outlines specific best
management practices (BMPs) as they relate to accidental spills of fuel and oil and clean up
provisions for any contaminated soils and construction waste.

North Sequalitchew Creek Construction
Construction of North Sequalitchew Creek would begin in the northern section of the proposed
mine, then proceed to the south along the eastern property boundary of the proposed mine
expansion area. Early phases of mining (approximately the first five years) would include the
construction of 4,000 feet of North Sequalitchew Creek.



During stream construction, an impoundment berm would be constructed at the southern most
end of the new stream channel, near its proposed confluence with Sequalitchew Creek, to collect
runoff and ground water seeping from the materials during excavation and mining. This
impoundment berm would remain in place during channel excavation to prevent turbid water and
sediment from entering Sequalitchew Creek.

As mining operations remove sand and gravel, the stream channel and riparian buffer area for
North Sequalitchew Creek would be excavated. The slope above the new stream would be
stabilized and planted. After the stream channel is constructed and the vegetation along the slope
and within the riparian corridors is established, pumping of the dewatering wells would be
reduced. As the pumping is reduced, seeps would develop along the eastern riparian slope face
and flow down to the channel. Measures to prevent erosion along this face may include piping
this seepage down the face to the stream (CH2M Hill 2003b). The Vashon Drift consists of two
aquifers, an upper and a lower aquifer, which are separated by a thin layer of till, and stratified
silty ice-contact deposits which act as a confining layer (i.e., aquitard) between the two aquifers.
Most of the flow to the new stream would come from the upper aquifer, which consists of top the
30 feet of the seepage face (CH2M Hill 2003b). The lower 40 feet of the seepage face would
consist of the lower aquifer, which would have much lower yields (CH2M Hill 2003b). In
addition, ground water would daylight within the newly established North Sequalitchew Creek
channel along the impermeable Olympia Beds.

As the pumping of the dewatering wells is decreased, the expected flow in North Sequalitchew
Creek would increase. As stream flows are established, flow would be monitored for total
suspended solids, turbidity, dissolved oxygen, and temperature (CH2M Hill 2003c). Due to the
lack of vegetative cover, sediment and fines would likely occur in runoff entering the stream.
During this period, the project proposes to route this water to sediment pond(s) for treatment
(CH2M Hill 2003c). North Sequalitchew Creek will be constructed with a variety of BMPs in
place that are intended to protect water quality and meet applicable water quality standards.
These BMPs would help reduce fines and suspended sediment that could potentially be
transported from North Sequalitchew Creek to the mainstem creek when the two systems are
connected.

After the flow into the stream has stabilized, the temporary impoundment berm would be
removed, allowing flows from North Sequalitchew Creek to join Sequalitchew Creek. Turbidity
levels may be elevated in both streams during the initial flow period when the streams are
connected after berm removal. The estimated average monthly discharge of North Sequalitchew
Creek in its lowest reach prior to entering the mainstem of Sequalitchew Creek is estimated to
range between 6.4 (October) and 8.7 (March) cfs (Anchor 2004d). Water quality for the new
stream is discussed below under Operational Impacts.

Sequalitchew Creek
During construction, surface water runoff from the mine expansion area would not discharge
directly to Sequalitchew Creek because all storm water runoff would be infiltrated on-site.
However, during construction, ground water (Vashon aquifer) in the mining area would be




intercepted by a series of dewatering wells and pumped to Sequalitchew Creek for discharge.
The dewatering wells would be used for dewatering the mine expansion area until North
Sequalitchew Creek is functioning and intercepts ground water flow. Pumped ground water
would be piped from the mine expansion area to the south, down the steep ravine where it would
discharge to Sequalitchew Creek via a rock pad and flow dissipater designed to prevent erosion
of the ravine hill slope and stream channel. The flow dissipater would be located at
approximately RM 0.8, near the proposed confluence of the two streams. The estimated
dewatering rates would range from 7 cfs to 15 cfs with an average of 10 cfs (CH2M Hill 2003c).
These volumes exceed the current flow in Sequalitchew Creek, where monthly average flows
range from 0.2 cfs (September) to 2.9 cfs (March) (Anchor 2004b). However, these dewatering
rates are well below the historic peak flows within the stream that occurred prior to the
construction of the Fort Lewis diversion canal.

Water Quality
During construction, dewatering water (ground water) would be pumped via pipe(s) to
Sequalitchew Creek for discharge. Because mine expansion area ground water quality data were
not available, ground water quality data ranges were extrapolated by Pacific Groundwater Group
(PGG) from water quality data collected as part of (1) the Landfill No. 5 Remedial Investigation
(Woodward Clyde 1990), and (2) the 2002 quarterly ground water monitoring results reported
for Landfill No. 5 by Anteon (2002) (PGG 2005). The range of predicted dewatering ground
water quality for select parameters are compared to Sequalitchew Creek background water
quality data and state surface water quality standards in Table 8. The estimated quality of the
existing ground water is generally good (PGG 2005).

Temperature, turbidity, and dissolved oxygen were not estimated by PGG because background
data for these parameters did not exist either as part of the Fort Lewis Remedial Investigation
(Woodward Clyde 1990) or part of the 2002 and 2005 quarterly ground water sampling at Fort
Lewis No. 5 landfill (Anteon 2002; PGG 2005). Further, they are not regulated parameters in
state ground water quality standards (Chapter 173-200-040 WAC) (Ecology 1990).

Fecal coliform bacteria are regulated by state ground water standards, but were not sampled as
part of the quarterly monitoring of Landfill No. 5 as reported by Anteon (2002). Because this
data did not exist, PGG (2005) did not establish a background fecal coliform bacteria
concentration for ground water in the vicinity of the site. However, the fecal coliform
concentrations in the ground water would likely be low. Near the mine expansion area, there is
not a significant subsurface fecal coliform bacteria source (i.e., septic systems, etc.). The City of
DuPont (including Northwest Landing) is a sewered community. Further, fecal coliform bacteria
do not survive in the subsurface environment for an extended period of time. Fecal coliform
bacteria are not expected to exceed the state surface water criterion of 50 CFU/100 ml in
Sequalitchew Creek.

During dewatering, the pumped ground water would be cool. In the project test wells, ground
water temperatures ranged between 8°C to 12°C (CH2M Hill 2003c), meeting the state surface
water standard of 16°C (Chapter 173-201A WAC). Because the dewatering water pumped from



the mine would be cool, it would not adversely impact Sequalitchew Creek water temperatures.
Similar to temperature, turbidity is generally not a concern with ground water. The pumped
ground water would not be allowed to discharge to Sequalitchew Creek until the wells have been
properly purged and developed, and are free of sediment which may have been introduced during
well drilling and installation.

The dissolved oxygen concentrations of the dewatering water may be lower than the state
minimum criterion of 9.5 mg/L; however, the project proposes to utilize a rock pad and
dissipater device that would aerate and increase the dissolved oxygen concentration in the water
within in the discharge to meet this state standard (CH2M Hill 2003c).

Based on ground water quality data presented by PGG (2005), both ammonia and nitrate
concentrations in the dewatering water would be within background range of the Sequalitchew
Creek concentrations measured by CH2M Hill during baseline project sampling (Table 8). The
predicted ammonia concentration in the ground water would be low (<0.1 mg/L) and would meet
state water quality standards. The estimated nitrate-nitrogen concentration in the ground water
would be low, and is expected to range between 0.0005 and 0.02 mg/L, which is lower than the
stream background which ranged between 0.28 and 0.82 mg/L (Table 8) (PGG 2005). Nitrate-
nitrogen is not a regulated parameter in the state surface water standards, but is a regulated
parameter in state ground water standards and state drinking water standards. Both standards set
the limit at 10 mg/L (Chapters 173-200-040 WAC and Chapter 246-290-310 WAC, respectively)
based on human health concerns.

Monitoring of the dewatering water is a required element of the State’s sand and gravel general
National Pollutant Discharge Elimination System (NPDES) permit. The permit requires
dewatering discharges to surface water be monitored for turbidity, TSS, pH, temperature, and oil
sheen.

During the last phase of construction, the berm between the active mine area and Sequalitchew
Creek would be removed to connect North Sequalitchew Creek and Sequalitchew Creek, so that
North Sequalitchew Creek discharge can flow into Sequalitchew Creek. During confluence
construction, the Sequalitchew Creek channel would be disturbed, likely causing some sediment
and fines to enter Sequalitchew Creek waters. Construction measures would employ BMPs to
help minimize turbidity and sediment impacts from berm removal and confluence construction.
In addition, when flows from North Sequalitchew Creek are introduced to Sequalitchew Creek,
sediment from the disturbed channel areas would have the potential to be washed downstream
causing temporary increases in turbidity.

Discharge
Based on preliminary work by CH2M Hill (2003c), the estimated dewatering rates would range
from 7 cfs to 15 cfs with an average of 10 cfs. Dewatering volumes would exceed the average
annual discharge in the stream of 1.4 cfs (from 1999 through 2004) below the proposed
confluence of North Sequalitchew Creek (Anchor 2004b). These discharge rates are well below
the historic range estimated for Sequalitchew Creek, where the 2-year storm flows were



estimated to range from 40 to 120 cfs prior to construction of the diversion canal by Fort Lewis
(Aspect 2004a).

Geomorphology
Increased flows from mine dewatering would affect existing sediment transport processes in
lower Sequalitchew Creek. Increased discharge from dewatering of the mine expansion could
entrain greater amounts of sediment stored in the ravine bottom. Localized sections of the
stream, particularly in Reach 2, already experience bed and bank erosion under the existing flow
regime. Likewise, most of Reaches 3 and 4 show evidence of recent sedimentation reflecting
insufficient transport capacity and inputs from Reach 2 and local bank erosion within Reach 3.
This situation is likely to remain constant in most of these segments even after flows are
increased – particularly in Reaches 3 and 4 which would be receiving more sediment from
Reach 2. Based on the downstream trend in declining shear stress (i.e., the force exerted on the
streambed by the water) reported by GeoEngineers (2004), sediment eroded from Reach 2 would
likely be deposited in the upper portion of Reach 3. The resulting sedimentation within Reach 3
would increase the potential for channel migration into unconsolidated and easily eroded
sediment along the toe of valley slopes during moderate to large flood events. This in-turn could
trigger localized erosion of the hillslopes which could further overwhelm the stream with
sediment beyond what the increased discharge would have the capacity to move.

Brackish Marsh
Water Quality
The brackish marsh located near the mouth of Sequalitchew Creek would experience increased
flows and water levels as ground water is pumped to the mainstem of Sequalitchew Creek
(upstream of the brackish marsh) during mine dewatering during construction. Flow increases in
the brackish marsh would be similar to those described above for Sequalitchew Creek, where
flows in the stream channel could increase by 7 to 15 cfs (average of 10 cfs) during construction
dewatering.

This initial increase in flow to Sequalitchew Creek would likely mobilize sediment and fines
downstream as the wetted-width of the channel is increased, and as fine sediments and organics
are washed downstream (Anchor 2004c). The project proposes to incrementally increase flows
to Sequalitchew Creek to limit the amount of erosion upstream in Sequalitchew Creek and
downstream deposition within the brackish marsh.

Sediment and fines entering the stream during dewatering activities could have the potential to
increase turbidity downstream within the brackish marsh. Turbidity is a regulated parameter in
the state surface water quality standards (Chapter 173-201a WAC). During construction
dewatering, the project would have to maintain turbidity that is within 5 NTU over the
background condition (in Sequalitchew Creek), as identified in the State’s surface water quality
standards, unless otherwise specified in construction or mining permits issued for the project.




The increase in the amount freshwater entering the stream could alter the salinity of the water in
the brackish marsh (Anchor 2004d). However, salinity is not a regulated parameter in state
surface water quality standards for either freshwater or marine waters. Significant changes in
salinity could, however, affect the plant and animal communities existing within the marsh.
These are discussed in the Plants and Animals section of the SEIS, 3.4.

Geomorphology
Increased flows in Sequalitchew Creek during construction have the potential to impact the
geomorphology and ecology of the estuary (Reach 4). The Sequalitchew Creek estuary consists
of two distinctive geomorphic process domains: (1) a fluvial corridor along the north side of the
ravine occupied by the stream channel, within which freshwater and sediment are not input to the
estuary; and (2) a tidal marsh system occupied by a dendritic tidal slough network and salt marsh
vegetation, within which salt water from Puget Sound is exchanged twice daily (i.e., a diurnal
tide cycle). The confluence of these two geomorphic processes is located immediately upstream
of the box culvert inlet. This domain configuration is characteristic of pocket estuaries
throughout Puget Sound where fluvial corridors become confined along the perimeter of
embayments by natural levees (created by deposition of coarse overbank sediments along margin
of stream channels). These natural levees effectively increase the depth of the stream which in-
turn increase sediment transport capacity and reduce the probability that tidal marshes are filled
and converted to upland by stream sedimentation. The boundary between these two process
domains in the Sequalitchew Creek estuary is not well defined. Most notably absent is a distinct
levee. Because of this, Sequalitchew Creek has periodically delivered sediment to the brackish
marsh with the resulting sedimentation filling portions of the salt marsh wetland.

The confluence of the tidal slough network and stream channel near the outlet to Puget Sound
also contributes to sustaining the tidal marsh domain. During low tides, the outflow discharge
from the tidal slough network effectively increases the stream discharge and sediment transport
capacity in a locale particularly susceptible to sedimentation. The volume of water that enters
and leaves between mean lower low water (MLLW) and mean higher high water (MHHW) is
referred to as a tidal prism. The greater the tidal prism, the greater the ability of the system to
sustain an outlet channel to Puget Sound.

Pocket estuaries in Puget Sound have been able to sustain salt marsh ecosystems for thousands of
years through the natural segregation of the freshwater dominated fluvial domain and the
saltwater dominated tidal marsh domain. This natural segregation inhibits sedimentation from
filling tidal salt marshes and converting them to freshwater floodplains. The process is reflected
in the fact that many pocket estuary tidal marshes are underlain by thick deposits of organic peat
(created by tidal marsh vegetation) and little or no inorganic sediment representative of stream
deposition. While the Sequalitchew Creek Estuary exhibits some of general attributes of an
undisturbed pocket estuary, it has undergone rapid, historic infilling uncharacteristic of an
undisturbed pocket estuary. Infilling of the Sequalitchew Creek estuary has resulted from
historic land disturbance within the watershed and ravine. This historic trend has continued
despite the reduced flow regime in the stream and is likely to accelerate if the stream discharge is
increased, unless mitigating actions are taken. Implementing changes to the stream that emulate


Surface water and geomorphology herrera report-oct 2005

Surface water and geomorphology herrera report-oct 2005

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