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"4 -'EOTECHNICAL ENGINE
ERING STUDIO::
AND ABANDONED MINE ASSESSMEN1
n
North 405 Upper and Lower Sites
Renton, Washington.
ae
Project No. T-3453 '
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errs Associates, Inc.
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Prepared for:
Opus Northwest, LLC
Bellevue, Washington
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December 17, 1997
CITY OF RE TON
RECEIVED
r
FEB 0 5 1999
c, TERRA ASSOCIATES, Inc.
Consultants in Geotechnical Engineering, Geology
�a and
Environmental Earth Sciences
December 17, 1997
Project No. T-3453
Mr. Harry DeMarre
Opus Northwest, LLC
200— 112th Avenue NE, Suite 205
Bellevue, Washington 98004
Subject: Geotechnical Engineering Study and Abandoned Mine Assessment
North 405 Upper and Lower Sites
Renton, Washington
References: 1. Report, Aerial Photograph Interpretation, Monster Road,prepared by Golder Associates,Inc.,
Reference No. 973-1212, dated November 26, 1997
2. .Report, Preliminary Abandoned Mine Assessment,prepared by Golder Associates, Inc.,
Reference No.973-1212, dated August 22, 1997
3. Preliminary Geotechnical Study,Oaksdale Business Park, prepared by Terra Associates,Inc.,
Project No. T-3453, dated February 15, 1997
Dear Harry:
As requested, we have completed a geotechnical engineering study and abandoned mine assessment for the above
subject project. Our work was conducted in accordance with your instructions and authorization.
The results of our study indicate that previous mining for coal did occur on the site predominantly in the western
portion of Parcel A, the upper site. This coal mining activity extracted a shallow coal seam from a depth of about
10 to 14 feet below existing surface grade using strip mining techniques. However, there is also evidence that
mine prospects or tunnels were advanced northeastward across the site at a depth below this upper mined out coal
seam. These mine prospects appear to extend beyond the extent of the surface mining operations and, therefore,
would impact the extreme northwest corner of the proposed building construction and the west portion of the
upper west parking lot. Fortunately, the prospects are relatively shallow and limited in nature (less than 25 feet
deep) and measures to mitigate the potential for surface collapse can readily be implemented concurrent with site
grading activities.
12525 Willows Road, Suite 101, Kirkland, Washington 98034 • Phone (425) 821-7777
Mr. Harry DeMarre
December 17, 1997
etailed discussion and recommendations regarding the above issue, along with geotechnical engineering
commendations for design and construction,are summarized in the attached report.
We trust the information presented is sufficient to meet your current needs. If you have any questions or require
additional informati 1.
IV_ J. Sc,
Sincerely your
TERRA AS T "Q
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T odore J. Sc
Principal Engi�ne-ewww
TJS:ts 1O"M &58/q S
Project No. T-3453
Page No. 17
TABLE OF CONTENTS
Page
1.0 Project Description 1
2:0 Site Conditions 2
2.1 Surface 2
2.2 Subsurface 3
2.3 Groundwater 4
3.0 Geologic Hazards 4
3.1 Coal Mines 4
3.2 Steep Slopes 5
3.3 Seismic 6
4.0 Discussion and Recommendations 6
4.1 General 6
4.2 Site Preparation and Grading 6
4.3 Slopes and Embankments 8
4.4 Excavations 8
4.5 Foundations 9
4.6 Slab-on-grade 9
4.7 Retaining Walls 10
4.8 Rockeries 10
4.9 Drainage -10
4.10 Utilities 11
4.11 Pavements 11
5.0 Additional Services 11
6.0 Limitations 12
Figures
Vicinity Map Figure 1
Exploration Location Plan Figure 2
General Slope Fill Detail Figure 3
Retaining Wall Drainage Detail Figure 4
Reinforced Fill/Rockery Cross-section Figure 5
Appendix
Field Exploration and Laboratory Testing Appendix A
Golder Associates, Inc. Reports Appendix B
Geotechnical Engineering Study
and Abandoned Mine Assessment
North 405 Upper and Lower Sites
Renton, Washington
1.0 PROJECT DESCRIPTION
The project will consist of developing the sites with office warehouse type structures. The structures will have a
clear span height of about 27 feet and will be constructed using precast concrete tilt up wall panels. Perimeter
wall loads are expected in the range of three to five kips per lineal foot with interior isolated columns supporting
the roof structure loaded to about 100 kips.
Based on drawings prepared by AHBL, dated October 22, 1997,the structure on the upper site will have its finish
floor constructed at Elev. 72. The structure on the lower site will have its finish floor constructed at Elev. 55.
Significant grading will be required at this site in order to establish these finish floor elevations, as well as the
perimeter parking and drive access routes. For the upper site, excavations or cuts into the existing south hillside
approaching a depth of 25 feet will be required to establish the parking and access grade along the south side of
the structure. The drawings by AHBL show that the lower six to eight feet of this cut will be vertical with a
backslope graded at an inclination of 2:1 (Horizontal:Vertical). Fill material, ranging in depth from 8 to about 12
eet will be required to establish desired building grade in the north-central portion of the structure and north
parking lot area. Off the north perimeter of the parking area,the fill is shown sloped at a gradient of 2:1.
The lower site will have its finish floor established at an elevation of 55. This will require excavations in excess
of 60 feet below existing grade into the adjacent eastern hillside. This cut is shown on the drawings prepared by
AHBL to be laid back at a finish inclination of 1:1 along the east perimeter of the structure. Along the western
and northern margins of the structure, fill material approaching a depth of 20 feet will be required to establish the
adjacent parking and drive access grades.
A stormwater biofiltration swale will be constructed along the west perimeter of the upper site, north of the lower
site. The biofiltration swale will have its center line grade established at Elev. 58 at the north end and Elev. 54 at
the south end. Along the swale centerline, a maximum excavation depth of about 30 feet will be required to
establish this Swale grade. An eight to ten-foot high rockery is shown along the east perimeter of the Swale,
supporting the vertical break in grade adjacent the east parking lot area.
An alternative building layout is also proposed for the upper site. This layout for Cascade Airgas, while having a
different building footprint, would require similar grading as that shown on the October 22, 1997 drawings by
AHBL.
The recommendations contained in the following sections of this report are based upon the above design features.
Should actual features vary or if changes are made, we should be informed and requested to review them in order
>supplement or amend our recommendations as required.
December 17, 1997
Project No.T-3453
2.0 SITE CONDITIONS
2.1 Surface
The site is bounded to the east and southeast by Monster Road and a METRO sewer treatment facility.
Warehouse facilities bound the site to the north. The Burlington Northern Railroad right-of-way bounds the site
to the southwest. An approximately 2-1/4 acre parcel owned by METRO extends northwest of Monster Road and
bounds the southern part of the subject property. A 15-foot wide water easement and 60-foot wide railroad
easement run along the eastern and western parts of the northern property line, respectively.
The site is situated on a hill surrounded by the Green River valley floor. Most of the eastern portion of the site
(Parcel 3) is open with nearly flat to gently sloping ground extending to the east and north. These slopes steepen
to a gradient of approximately 3:1 at the southern margin of Parcel 3 and lead off of the site toward the hill's peak
on the adjacent METRO property.
The northern margin of the site slopes downward toward the neighboring warehouse facility properties at an
overall inclination of approximately 2:1.. This slope continues westward into Parcel 4B where it turns southward
and runs toward the Burlington Northern right-of-way at the site's southwestern margin. The slope's height
ranges from approximately 40 feet at the northeastern comer of the site to 100 feet within Parcel 4B.
_n the vicinity of Test Pit-TP-1, we observed a north-south trending,approximately 30-foot wide mine adit that
formed an excavated trough extending down the face of the slope toward the northern property line. We also
noted an approximately six foot square opening in the ground east of the adit that was partially obscured by berry
brambles. The opening appeared to be a mine exploratory or ventilation shaft. The approximate locations of
these features are shown on Figure 2.
The southern part of the site contains southwest-facing slopes standing at grades of up to 3:1. Relatively level
areas are located adjacent to the top of a near-vertical 30 to 40-foot high cut made for construction of the adjacent
railroad. The cutslope appeared to expose weathered sandstone and did not show any seeps, springs, or
significant signs of instability. Portions of the cut were draped with chain-link fencing to provide protection
against rockfall.
A flat, marshy area is situated between the railroad spur and Burlington Northern line within the northwestern
corner of the site. At the time of our January 22, 1997 site visit, standing water covered most of this low-lying
area. Minor standing water was also noted at the eastern part of the site. No signs of recent surface water runoff
or erosion were noted during our visit. Vegetation at the site consisted of wild grasses and berry bramble within
the open, eastern part of the site. Mature coniferous and deciduous trees, and occasional blackberry brambles
covered the western sloped areas.
Page No. 2
December 17, 1997
Project No.T-3453
2.2 Subsurface
We explored subsurface conditions at the site by excavating five test pits at the upper site and three test pits at the
lower site on January 22, 1997. The results of our exploration, along with preliminary conclusions regarding site
development, were presented in a report dated February 15, 1997. Subsequent this report, Golder Associates, Inc.
was retained to complete a more detailed study to assess the coal mine hazard at the site. The ensuing site
exploration undertaken by Golder Associates,Inc. included the excavation of several test trenches which extended
to depths of 14 to 18 feet below existing site grade for lineal distances ranging from 5Q to over 400 feet. The
results of their study and preliminary conclusions were presented in reports dated August 22 and November 26,
1997. These reports are attached in Appendix B.
Following the Golder Associates, Inc. studies, on December 11 through December 15, 1997, we drilled three
additional soil test borings on the upper site. These borings were performed to further assess the coal mine
hazards at the site and to evaluate the excavation characteristics of the underlying rock formations. The locations
of the explorations completed by Golder Associates, Inc. and Terra Associates, Inc. are shown on the attached
Exploration Plan, Figure 2. The following provides a general summary of the conditions observed.
Near-surface soils at the site to depths of 1 to 2.5 feet were shown to consist of fill or topsoil composed of an
organic sandy to clayey silt to silty sand. Underlying these near-surface soils, layers of weathered sandstone,
clay, and silt, of the Renton formation were encountered. The weathered sandstone was generally noted to be in a
edium dense to dense condition with the clay and silt strata noted to be stiff to hard.
Very dense glacial till or till-like soils were also observed along the south portion of the upper site at.Test Pits TP-
2 and TP-3. These till or till-like soils were composed of a silty fine sand with gravel and contained occasional
cobbles and clasts of highly weathered sandstone. Below depths of approximately 10 to 15 feet, at.Test Trench
No. 6 and Test Boring B-2, slightly weathered to unweathered sandstone was observed. Underlying the south
slopes, large boulders were also noted overlying the Renton formation sandstone at Test Trench No. 2 and Test
Boring B-3.
As described in the attached Golder Associates, Inc. report, the area west of the upper site and north of the lower
site has been subject to previous grading activity from coal mining. The coal, which was shown to reside at a
relatively shallow depth of about 10 to 14 feet below, was extracted by strip mining with the area then reclaimed
following coal removal. Site exploration revealed coal mine spoils composed of silty sands, clays, coal
fragments, extended to depths of 10 to 18 feet below existing surface grades.
Detailed descriptions of soil conditions encountered are summarized on the test pit and test boring logs attached in
Appendix A. A narrative description of conditions observed at the test trenches excavated by Golder Associates,
Inc. is included with their reports attached in Appendix B.
Page No. 3
December 17, 1997
Project No. T-3453
2.3 Groundwater
We observed groundwater seepage of varying intensity at Test Pits TP-1 through TP-8 with the exception of Test
Pit TP-5. These test pits were excavated in January of 1997. No indication of groundwater seepage was observed
at the test trenches excavated by Golder Associates, Inc. in August of this year. We observed groundwater
seepage at depths varying from two to ten feet below existing surface grades. The seepage was occurring from
more pervious soil zones or the weathered rock horizon overlying relatively impervious strata of unweathered
sandstone or siltstone. As demonstrated by this study, groundwater seepage levels will fluctuate on a seasonal
and annual basis. Higher levels of groundwater seepage would be expected during the wet winter season with
seepage levels diminishing or becoming absent in the dry summer months.
3.0 GEOLOGIC HAZARDS
3.1 Coal Mines
There is both surficial evidence and evidence in the literature that indicates that coal mining activity occurred on
and adjacent the subject site. We provided a preliminary evaluation of this activity in our referenced February 15,
1997 report. Golder Associates, Inc. was retained to perform a more detailed assessment of the possibility for
abandoned mines to exist on the property. The results of their studies were summarized in two reports dated
August 22, 1997 and November 2.6, 1997, both of which are attached in Appendix B.
The results of the Golder Associates, Inc. studies indicate that mining activity on the site primarily occurred
Nithin the western portion of the upper site. The mining that occurred removed a relatively shallow coal seam
residing approximately 10 to 14 feet below existing surface grades using surface mining techniques. Once the
coal was extracted, the area was reclaimed with the excavated spoils. Test Trench No. 3, which was a 400-foot
excavation north to south across the site, delineated the approximate eastern extent of these surface mining
activities. The location of Test Trench No. 3 was surveyed in the field and is shown on attached Figure 2.
At Test Trench No. 1, a mine opening was observed at a depth of about 8 to 14 feet below existing surface grades.
As reported by Golder Associates, Inc., this trench probably encountered the remnants of the 207-foot long Black
River Mine slope. However, Golder Associates, Inc. indicated that the slope was mined in an easterly direction
below the elevation of the upper coal seam as encountered at Test Trenches No. 3, 7, and 8. Therefore, it was
speculated that there was a potential for a second lower seam to exist at the site. Golder Associates, Inc.
recommended further investigation at the site by drilling to determine whether a deeper coal seam than the one
that was observed in these trenches existed.
On December 11 through December 15, 1997, Terra Associates, Inc. followed Golder Associates, Inc.'s
recommendations and drilled three additional soil test borings at the site. Boring B-2 was drilled to a depth of 59
feet specifically to determine if there was a second lower coal seam which could have economically been
extracted by driving a tunnel from west to east across the site. The result of our additional exploration revealed
no such second lower seam. However, at Test Boring B-1, which was drilled in the area of Test Trench No. 4 and
the existing sink holes, we observed what appears to be remnants of a mine tunnel in the form of timber and coal
debris. This material was encountered at a depth of approximately 20 feet or at roughly site Elev. 50.
Page No. 4
December 17, 1997
Project No. T-3453.
The mine opening observed at Test Trench No. 1 was at approximately site Elev. 54. We believe that the opening
,bserved at Test Trench No. 1 and conditions observed at Test Boring B-2 represent shallow prospects which
were terminated when it was determined that a minable coal resource farther eastward into the site was not
available. Subsidence observed in the vicinity of Test Trench No. 4 is likely related to the collapse of this shallow
mine working.
Based on the results of the Golder Associates, Inc. studies and our subsequent exploration, we conclude that there
are undocumented mine workings which extend from the southwest to the northeast along the western portion of
the upper site. These workings are likely abandoned prospects and exist at a relatively shallow depth of 20 to 25
feet below existing site grade (Elev. 45 to 55). There is a risk that these relatively shallow tunnels could collapse,
resulting in surface sink holes if not mitigated. This risk would be present along the parking and drive areas west
of the structure on the upper site as well as the extreme northwest corner of the structure.
Proposed grading, particularly in the central and southern portions of this area of the site will require excavations
of 14 to 30 feet below existing surface grades. These excavation depths are equivalent to or extend below
previously mined depths at the site as indicated by our studies. It is likely that any mine workings in this area will
be uncovered and reworked by the planned grading. The exception to this occurs in the area of the existing sink
holes near Test Trench No. 4 as shown on the.Exploration Location Plan, Figure 2. Here, minimal grading of less
than two feet below existing surface grade will be required to establish desired construction elevation.
To mitigate the risk posed by undocumented mine workings below this area of the site, we recommend that this
.rea also be overexcavated to a minimum depth of 20 feet below current site grade with grade then restored with
uitably compacted structural fill as described in a subsequent section of this report. Alternatively, deep dynamic
compaction (DDC) can be used to consolidate the soils and collapse any undocumented mine workings. DDC
consists of dropping a heavy weight generally on the order of six to ten tons using a large crane from a height of
about 30 to 50 feet. The weight is dropped at the same location five to ten times to consolidate loose fills at
depth. Given the expected shallow workings; which may be present in this area, the energy delivered by the DDC
would also be expected to collapse any undocumented workings. Specific details for application of DDC at the
site can be provided if this option is selected.
3.2 Steep Slopes
As indicated by our exploration, the site is primarily underlain by competent soils and weathered block. Existing
slopes on the site, which range in inclination from near-vertical adjacent the railroad cut to the southwest, to
gradients of 2:1 south of the upper site, were noted to be in a stable condition with no indication of previous or
current landslides or slope instability. The near-vertical cut at the southwestern portion of the site was faced with
chain-link fencing to contain material falling or eroding off of the near-vertical cut. In our opinion, provided
recommendations contained in the following sections of this report are followed, site grading as proposed
resulting in cut slopes varying from 1:1 to 2:1 would remain stable and would not impact the current site stability
or that of adjacent properties.
Page No. 5
December 17, 1997
Project No. T-3453
'.3 Seismic
The Puget Sound area falls within Seismic Zone 3 as classified by the Uniform Building Code (UBC). Based on
the soil conditions encountered and the local geology, from Table 16J of the UBC, a site coefficient of 1.0 should
be used in design of the buildings. With the competent nature of the native soil and rock which underlies the site,
there would be no risk for soil liquefaction related impacts to the structures or associated utilities.
4.0 DISCUSSION AND RECOMMENDATIONS
4.1 General
Based on the results of our study, itds our opinion that there are no geotechnical constraints which would preclude
development of the sites as proposed. However, mitigation to eliminate the hazard associated with previous
mining activity as discussed in the coal mine hazard section of this report will be required within the western
portion of the upper site. It is recommended that this mitigation work occur concurrent with the start of site
grading activities.
Extensive excavations will be required at both sites to achieve desired construction grades. Initial soils excavated
from the sites to depths of 10 to 15 feet will consist of layers of silty sands, clays, silts, and weathered sandstone.
It is also likely that large boulders or fragments of intact bedrock will be encountered at excavation depths of 10
15 feet below current side grade. Below 15 to 20 feet, hard sandstone, associated with the Tukwila formation,
will be encountered. The soils contain a significant amount of fines and will not likely be suitable for use as
structural fill during wet weather conditions. Therefore, we recommend that mass grading activities at the site
only be contemplated during the drier summer months(June through October). In addition, the grading contractor
should be prepared to use hard rock excavating techniques, such as ripper claws and hard formation teeth, to
achieve the desired construction elevations. For the lower site, which will require excavations of 60 feet below
existing grade, blasting to facilitate excavation of the hard Tukwila sandstone formation may need to be
considered.
The following sections of this report provide detailed recommendations pertaining to the above issues, as well as
other geotechnical design considerations. These recommendations should be incorporated into the final design
drawings and construction specifications.
4.2 Site Preparation and Grading
To prepare the sites for construction, prior to excavation and placement of fill material, it will be necessary to
strip the organic surface layers. On the existing south and western slopes, surface stripping depths of four to six
inches should be expected to remove the organic topsoil. Along the lower flatter portions of the sites, site
explorations indicate surface stripping depths of one to two feet will be required. These soils will not be suitable
for use as structural fill, but can be used in nonstructural landscaping areas.
Page No. 6
December 17, 1997
Project No.T-3453
oncurrent with site excavations, mitigation work to eliminate the potential risks associated with undocumented
ine workings in the western portion of the upper site should be undertaken. As described previously, proposed
grading activity in the central and south portions of this area of the site should extend to a depth equivalent to or
below the depth of the mine workings as identified by our study. However,within the north portion of this area of
the site, additional excavation approaching 20 feet below existing grade should be planned. The approximate
limits where this overexcavation is recommended for the purpose of mitigating the mine hazard is shown on the
Exploration Location Plan, Figure 2. Once excavated, uncovering suspected mine workings or competent
bedrock material, the grade can be restored using structural fill. As described earlier, an alternative to this
overexcavation and refill procedure would be the use of DDC.
Prior to placing fill materials, stripped subgrades should be proofrolled with heavy construction equipment to
determine if any isolated soft and yielding areas are present. If such areas are found, and they cannot be stabilized
and placed by compaction, the affected soils should be overexcavated to firm bearing and replaced with structural
fill. Similar proofrolling should be performedon native subgrades, which will provide direct support for building
or pavement construction.
The soils at the site contain a.significant amount of fines and, in our opinion, would not be suitable for use as
structural fill during wet weather conditions. Therefore, we strongly suggest that grading activity only be
contemplated during the drier summer months (June through October). In addition, given the fines content of the
soil and the presence of weathered bedrock fragments of siltstone and sandstone, a sheeps foot compactor should
be used to compact the structural fills.
grading activities are planned during the wet weather season, or if they are initiated in dry weather and extend
into the winter, you should be prepared to import a relatively clean fee-draining pit run sand and gravel for use as
structural fill. Imported material for wet weather grading purposes should meet the following requirements.
U.S. Standard Sieve Size Percent Passing
3 inches 100
No. 4 75 maximum
No. 200 5
As an alternative to importing wet weather structural fill, consideration could be given to amending native soils
which are unstable due to excessive moisture using Portland cement or kiln dust. These additives, when mixed
uniformly with the soil, reduce the soils' moisture content and generally produce a workable and compactable
material. When compacted, the cement or kiln dust continues to hydrate with the soil, improving its strength and
decreasing its compressibility. If necessary, soil amendment of this nature can also be considered for utility
trench backfill soils.
Page No. 7
December 17, 1997
Project No.T-3453
tructural fills should be placed in uniform loose lifts not exceeding eight inches and then compacted to a.
...inimum of 95 percent of the soils' maximum dry density as determined by ASTM Test Designation D-698
(Standard Proctor). The moisture content of the soil at the time of compaction should be in the range of plus or
minus two percent of the soils' optimum moisture, as determined by this same method. In nonstructural areas,
and for utility trench backfill below a depth of four feet, the degree of relative compaction can be reduced to 90
percent.
4.3 Slopes and Embankments
Fill embankments should be graded with a finish slope inclination of no steeper than 2:1. Fill material used to
construct the embankment should be placed and compacted as a structural fill, as described in the preceding
section. Where the fill will be placed on existing slope gradients, in excess of 20 percent, it should be keyed and
benched into the native subgrade as shown on attached Figure 3.
Finish slope surface should be firmly compacted, trackwalked, and appropriately vegetated to reduce or prevent
erosion. Surface water runoff should not be allowed to flow in an uncontrolled fashion over the crest of the slope
or on the slope,face. If surface water is not directed away from the slope,it should be controlled in a swale and
either tightlined in a closed conduit down the slope face or in an appropriately lined channel.
"inish cut slopes exposing competent bedrock of the Tukwila or Renton formation can be laid back at finish
clinations of 1:1 to 2:1. For near-surface stability considerations, where the slope gradient exceeds 2:1, we
recommend the slope surface be covered with a permanent erosion control and stabilization geosynthetic material.
We recommend using a material, such as Enkamat S or equivalent, which is staked to the slope surface in
accordance with the manufacturer's recommendations. Once this material is placed, the slope surface should be
hydroseeded'with a hydroseed mix appropriate for the slope inclination.
4.4 Excavations
All site excavations must be completed in accordance with local, state, or federal requirements. Based on the
current Occupational Safety and Health Administration (OSHA) regulations, near-surface materials and existing
disturbed mine spoils would be categorized as a Group C soil. Accordingly, excavations within this material
which extend to a depth of greater than four feet should be laid back at an minimum inclination of 1.5:1. In our
opinion,temporary excavations which extend into the weathered bedrock and unweathered bedrock can be laid
back at minimum slope inclinations of 1:1 to 1/2:1, respectively.
The above information is provided solely for the benefit of the owner and other members of the project design
team. It should not be construed to imply that Terra Associates, Inc. assumes responsibility for job site safety.
Job site safety is the sole responsibility of the project general contractor.
Page No. 8
December 17, 1997
Project No. T-3453
".5 Foundations
The building may be supported on conventional spread foundations bearing on competent native soils or on
structural fills placed above competent native soils. Foundation subgrades should be prepared as recommended in
the Site Preparation and Grading section of this report. Perimeter foundations exposed to the weather should be at
a minimum depth of 1.5 feet below final exterior grades. Interior foundations can be constructed at any
convenient depth below the floor slab.
We recommend designing foundations obtaining support on competent native soils for a net allowable bearing
capacity of 4,000 ps£ Foundations bearing on structural fill should be proportioned for an allowable bearing of
2,500 psf. For short-term loads, such as wind and seismic, a 1/3 increase in this allowable capacity can be used.
With the expected building loads and these bearing stresses applied, the estimated total settlements fall in the
range of one-half to one inch, of which 1/4 to 3/4 inches would be differential in nature. The greatest magnitude
of differential settlement would occur at the transition from native bearing soils to structural fill. If required,
foundations spanning this transition can be stiffened to resist this bending.
For designing foundations to resist lateral. loads, a base friction coefficient of .4 can be used. Passive earth
pressures acting on the side of the footing can also be considered. We recommend calculating this later resistance
using an equivalent fluid weight of 350 pcf. We recommend not including the upper 12 inches of soil in this
computation because they can be affected by weather or disturbed by future grading activity. This value assumes
e foundation will be constructed neat against competent native soil or backfilled with structural fill as described
the Site Preparation and Grading section of this report. The passive value recommended includes a safety
factor of 1.5.
4.6 Slab-on-grade
Slabs-on-grade may be supported on the subgrade prepared as recommended in the Site Preparation and Grading
section of this report. Immediately below the floor slab, we recommend placing a four-inch thick capillary break
layer of clean, free-draining sand or gravel that has less than three percent passing the No. 200 sieve. This
material will reduce the potential for upward capillary movement of water through the underlying soil and
subsequent wetting of the floor slab.
Moisture can still be transmitted through the floor slab .by vapor transmission. This can be particularly
troublesome for floor covering adhesives. To guard against this occurrence where necessary, a durable plastic
membrane should be placed on the capillary break layer. The membrane should be covered with two inches of
clean, moist sand to guard against damage during construction and to aid in curing of the concrete.
Page No. 9
December 17, 1997
Project No. T-3453
4.7 Retaining Walls
The magnitude of earth pressure development on lower-level or retaining walls will partly depend on the quality
of the wall backfill. .We recommend placing and compacting wall backfill as structural fill. To guard against
hydrostatic pressure development, wall drainage must also be installed. A typical recommended wall drainage
detail is shown on Figure 4.
With wall backfill placed and compacted as recommended and drainage properly installed, we recommend
designing unrestrained walls for an active earth pressure equivalent to a fluid weighing 35 pcf. For retrained
walls, an additional uniform lateral pressure of 100 psf should be added. These values assume a horizontal
backfill condition and that no other surcharge loading, such as traffic or sloping embankments, will act on the
wall. If such conditions will exist, then the imposed loading must be included in the wall design. Friction at the
base of foundations and passive earth pressure will provide resistance to these lateral loads. Valued for these
parameters are provided in the Foundations section of this report.
4.8 Rockeries
Excavations along the south and east perimeters of the upper and lower sites, respectively, should expose dense
Renton or Tukwila sandstone. These conditions would be suitable to face with rockery construction to a
aximum height of eight feet. Rockeries should be constructed by an experienced rockery contractor in
;cordance with the Association of Rockery Contractors guidelines.
The excavation along the east perimeter of the biofiltration swale is expected to encounter disturbed mine spoils
along its northern portion. These soils will not be suitable to face with rockery construction. The fill should be
removed and replaced with structural fill that is reinforced with geogrid. A general reinforced fill/rockery section
is shown on attached Figure 5.
4.9 Drainage
Final exterior grades should promote free and positive drainage away from the site at all times. Water must not be
allowed to pond or collect adjacent foundations or within the immediate building area. We recommend providing
a gradient of at least three percent for a minimum distance of ten feet from the building perimeter, except in paved
locations. In paved locations, a minimum gradient of one percent should be provided unless provisions are
included for collection and disposal of surface water adjacent the structure.
Surface water must not be allowed to flow uncontrolled over the crest of the site slopes and embankments.
Surface water should be directed away from the slope crests to a point of collection and controlled discharge. If
site grades do not allow for directing surface water away from the slopes, then water should be collected and
tightlined down the slope face in a controlled manner.
Page No. 10
December 17, 1997
Project No.T-3453
bsurface
We recommend installing perimeter foundation drains below landscaped areas adjacent to the structures. Where
pavement extends to the structure perimeter and positive slope is provided away from the building, we do not
believe foundation drains are necessary.
.Drains, where installed, must be laid with a gradient sufficient to promote positive flow to a controlled point of
approved discharge.
4.10 Utilities
Utility pipes should be bedded and backfilled in,accordance with American Public Works Association (APWA) or
City of Renton specifications. At minimum, trench backfill should be placed and compacted as structural fill as
Y .
described in the Site Preparation and Grading section of this report. As noted, soils excavated on-site should be
suitable for use as backfill material during dry weather. However, at the time of our study, the soils' moisture
content appeared to be above optimum. Therefore, drying back or other means to condition the material may be
necessary to facilitate proper compaction. If utility construction takes place during the winter, it may be
necessary to import suitable wet weather fill or amerid native soils for utility trench backfilling.
4.11 Pavements
a.means to prepare a stable subgrade and pavement base, we recommend using a soil cement application. The
.,oil cement, or cement treated base (CTB), can be constructed using the native soils observed below the organic
surface layer. We recommend scarifying the top 12 inches of the subgrade and then blending in Type 1 Portland
Cement at a rate of 60 pounds per square yard of surface area. The cement should be blended uniformly with the
soils, with the mixture also moisture conditioned as necessary. The soil cement moisture should be within —1 to
+3 percent of optimum as determined by ATSM Test Designation D-698 (Standard Proctor) prior to compaction.
Once blended and conditioned, the soil cement should be compacted to a minimum of 95 percent of its maximum
dry density as determined by this ASTM standard.
Traffic at the facility will mainly consist of cars and light trucks with only occasional heavy traffic in the form of
tractor-trailer rigs and trash removal vehicles. We recommend that the pavement section constructed over the 12
inches of CTB consist of two inches of asphalt concrete (AC). The AC should meet WSDOT specifications for
Class B mix.
5.0 ADDITIONAL SERVICES
Terra Associates, Inc. should review the final design and specifications in order to verify that earthwork and
foundation recommendations have been properly interpreted and incorporated into project design. We should also
provide geotechnical services during construction in order to observe compliance with the design concepts,
specifications, and recommendations. This will also allow for design changes if subsurface conditions differ from
ise anticipated prior to the start of construction.
Page No. 11
December 17, 1997
Project No. T-3453
0 LIMITATIONS
We prepared this report in accordance with generally accepted geotechnical engineering practices. This report is
the property of Terra Associates, Inc. and is intended for specific application to the North 405 Upper and Lower
Sites project. This report is for the exclusive use of Opus Northwest, LLC and their authorized representatives.
No other warranty, expressed or implied, is made.
The analyses and recommendations presented in this report are based upon data obtained from the test pits and
test borings excavated on-site. Variations in soil conditions can occur, the nature and extent of which may not
become evident until construction. If variations appear evident, Terra Associates, Inc. should be requested to
reevaluate the recommendations in this report prior to proceeding with construction.
Page No. 12
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LEGEND:
•` •\"!\\�. //i. ii/ ti�i! t..._— is i i!''' -—' ` \ \ —
\ '� TEST PITS BY TERRA ASSOCIATES (1/97)
Uii
"�",•\ .\`4•`\'`r \\ `:`'\ � ��\ ''/ ce/.
gg I. TEST
BY GOLDER ASSOCIATES
(8/97)/ i\ ,it ` i RENCHTP-3
t
,�`.\,,, •\, /„/;,. �;,/,//ii isii, iiireiigili irk r, - " '1i �•:. �•,;,: \ `;\\\..\\>\ `\ '' TEST BORINGS BY TERRA AS
``,'':.` „•, ti C 1 I \\•,,: \� \b�\\,,, , \� \ SOCIATES (12/97)
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.;; REFERENCE:
`9G
SITE PLAN PROVIDED BY GOLDER ASSOCIATES\,� :::;;::`�.::::;:•_�:.;; p._O1J' ` JOB No. •9731212, P '
a° ,tip\ J.• :,`•;;,�or'a:°•s::aa,,,:.•,• _ i LATE 4, DATED 11/97.
:�r?y� , \:,\,.,�
o
.,\' .:`%�:-.-1�"�Win;� •�'
EXPLORATION LOCATION PLAN
TERRA NORTH 405 UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
\� .• •Geotechnical Consultants Proj. No.3453 Date DEC. 1997 Fi ure 2
9
SLOPE TO DRAIN
NEW STRUCTURAL FILL
MAXIMUM SLOPE GRADIENT: 2:1(H:V) —
2
1 it � •• ••.>. ..
EXISTING - -
GRADE
TYPICAL BENCH -
- MAY REQUIRE SUBDRAIN IF SEEPAGE
71111
` CONDITIONS ARE INDICATED
' ,.•: GRADE AFTER THE REMOVAL OF
TOPSOIL AND OTHER LOOSE SOILS
KEY CUT AND TOE DRAIN —
4" DIAMETER PERFORATED PIPE ENVELOPED
IN 1 cu.ft. 1/2" DRAINAGE GRAVEL
NOT TO SCALE
NOTES:
1. SLOPE SHOULD BE STRIPPED OF TOPSOIL AND UNSUITABLE SOILS PRIOR TO PLACING ANY FILL.
2. "BENCHES" SHOULD BE A MINIMUM OF 6 FEET WIDE.
3. "KEY" SHOULD BE MINIMUM 2 FEET DEEP AND 6 FEET WIDE, EXTENDING THE FULL LENGTH OF
THE SLOPE FACE.
4. FINAL SLOPE FACE SHOULD BE DENSIFIED BY COMPACTION.
5. PLANT OR HYDROSEED SLOPE FACE TO REDUCE EROSION POTENTIAL.
6. ALL STRUCTURAL ALL SHOULD BE COMPACTED TO 95% OF SOILS MAXIMUM DRY DENSITY PER
ASTM D-698 (STANDARD PROCTOR).
GENERAL SLOPE FILL DETAIL
TERRA NORTH 405 UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No.3453 Date DEC. 1997 Figure 3
12" MINIMUM WIDE
FREE—DRAINING GRAVEL
SLOPE TO DRAIN
1r
" . EXCAVATED SLOPE
(SEE REPORT FOR
APPROPRIATE
INCLINATIONS)
COMPACTED STRUCTURAL
BACKFILL
3 .� 1 r OVER THE PIPE
"
4 DIAMETER PVC 3" BELOW THE PIPE
PERFORATED PIPE
NOT TO SCALE
RETAINING WALL DRAINAGE DETAIL
;,:.,::.''� �' TERRA NORTH 405 UPPER AND LOWER SITES
r ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No. 3453 Date DEC. 1997 Figure 4
Swale for surface drainage control
.........._......
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-___ :reinforcement approved b ,:y:7=.__;xt.iy•.r=;:::? f=: � :Y
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- - -_ -- --=--
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P P ;_ apt.
-=r SDO 2 03.3(14)B and =_=
-_-_ = __- =_ __
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L_c'r....:S.c i:-:•.',.5v i=.hiP?_:i:'.:i Y•i� =-�'
c--
�_Crus ed rock filter?�_;:::::::.::::=»r:-:�;�i:,?-�s
-- ::_material between 2�i'-�s��_===`�'=%�X:••• _ - _
---rand 4- inch 312e.' s..•::a•- ............I s,.:..,•:;K;r:;-s:M.,ar'aY:::,xa:•;_;_.;;
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in� min.
Grade at Rockery face
i
Firm undisturbed 3 in. min
soil to be verified 12 in.
by Soil Engineer Keyway 'min. 4 in. minimum diameter
drain pipe surrounded by
gravel meeting WSDOT
Keyway should be sloped 9-03.12(2) specifications
down towards the face
being protected
GEOGRID REINFORCING SCHEDULE
Rockery Height No. of Grid Layers Grid Length (L)
4' 2 4'
6' 3 5'
8' 4 6.5'
NOT TO SCALE
NOTE:
Penetrations through geogrid for installation of guardrail can be made. Grid should be exposed and cut cleanly
and not ripped, torn or pulled by action of drilling auger. Cut dimension should not exceed 12 inches.
REINFORCED FILL/ROCKERY CROSS-SECTION
TERRA NORTH 405 UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
•.• .•.
Geotechnical Consultants Proj. No.3453 Date DEC. 1997 1 Figure' 5
APPENDIX A
FIELD EXPLORATION AND LABORATORY TESTING
North 405 Upper and Lower Sites
Renton,Washington
We explored subsurface soil conditions at the site by excavating eight test pits using a rubber-tired back hoe on
January 22, 1997. Subsequent this exploration, additional test pits were excavated in August 1997 by Golder
Associates, Inc. under a subcontract with our firm. Following their exploration on December 11 through
December 15, 1997 in accordance with Golder Associates, Inc.'s recommendations, we advanced three soil test
borings using a truck mounted drill rig. Test pits excavated at the site, both by Terra Associates, Inc. and Golder
Associates, Inc. extended to depths of 1.0 to 18 feet below existing surface grades. Test borings were drilled to
depths of 16 to 59 feet below existing grade. The approximate location of the field explorations are shown on
attached Figure 2. Logs for Test Pits TP-l'through TP-8 and Test Borings B-1 through B-3 are presented on
Figures A-2 through A-10. A'description of soil conditions encountered at the test trenches excavated by Golder
Associates,Inc. is summarized in narrative format in their reports attached in Appendix B.
Engineering geologists from Terra Associates, Inc. and Golder Associates, Inc. conducted the field explorations
and classified soil conditions encountered. Our representative maintained a log of each test pit, obtained
representative soil samples, and observed other site features pertinent to the proposed construction. All soil
samples were visually classified in accordance with Unified Soil Classification System (USCS) described on
Figure A-1.
epresentative soil samples obtained from Test Pits TP-1 through TP-8 and Borings 13-1 through B-3 were placed
in closed containers and taken to our laboratory for further examination and testing. The moisture content of each
sample was measured and is reported on the test borings and test pit logs. Atterburg limits evaluating the
plasticity characteristics of two representative samples were also performed. These test results are also recorded
on the test pit logs opposite the samples on which they were performed. Grain size analyses were also performed
on three of the samples,.the results of which are shown on Figures A-I I and A-12.
MAJOR DIVISIONS LETTER TYPICAL DESCRIPTION
SYMBOL
Clean GW Well-graded gravels, gravel-sand mixtures, little or no
GRAVELS Gravels fines.
_j a, (less than GP Poorly-graded gravels, gravel-sand mixtures, little or
O N More than 5/o fines) no fines.
U) v, 50% of coarse
.ccfraction is GM Silty gravels, gravel-sand-silt mixtures, non-plastic
a> > lar er than No. Gravels fines.
Z a Fn 94 sieve With fines
Q E o GC Clayey gravels, gravel-sand-clay mixtures, plastic fines.
(D �Cl Clean SW Well-graded sands, gravelly sands, little or no fines.
o SANDS Sands
Cl) �z (less than Poorly-graded sands or gravelly sands, little or no
tY = c More than 5% fines) SP fines.
Q 50% of coarse
O o fraction is SM Silty sands, sand-silt mixtures, non-plastic fines.
U g smaller than Sands
No. 4 sieve With fines SC Clayey sands, sand-clay mixtures, plastic fines.
Inorganic silts, rock flour, clayey silts with slight
J `—�°o SILTS AND CLAYS ML plasticity.
0)o
05 O CU N CL Inorganic clays of low to medium plasticity, (lean clay).
E o Liquid limit is less than 50%
in oZ N
W CD ' O L Organic silts and organic clays of low plasticity.
Z_ U-) c5a
W � .r W M H Inorganic silts, elastic.
SILTS AND CLAYS
W m CH Inorganic clays of high plasticity, fat clays.
7 0 � Liquid limit is greater than 50%
L OH Organic clays of high plasticity.
HIGHLY ORGANIC SOILS PT Peat.
DEFINITION OF TERMS AND SYMBOLS
J
w Standard Penetration 2" OUTSIDE DensityResistance in Blows/Foot I SPOON SAMPLER
ETER SPLIT
Very loose 0-4 2.4" INSIDE DIAMETER RING SAMPLER
`o Loose 4-10 OR SHELBY TUBE SAMPLER
Medium dense 10-30
Q Dense 30-50 1 WATER LEVEL (DATE)
< Very dense >50
Tr TORVANE READINGS, tsf
Standard Penetration Pp PENETROMETER READING, tsf
>- Consistency Resistance in Blows/Foot g DID DRY DENSITY pounds per cubic foot
v Very soft 0-2
`o Soft 2-4 LL LIQUID LIMIT, percent
Medium stiff 4-8 PI PLASTIC INDEX
Stiff 8-1.6 Very stiff 16-32 N STANDARD PENETRATION, blows per foot
Hard >32
TERRA UNIFIED SOIL CLASSIFICATION SYSTEM
NORTH 405 UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants
Proj. No. T-3453 Date DEC. 1997 Figure A-1
Test Pit No. TP-1
Logged by: KPR
Date: 1/22/97
Depth USCS/
Graph Soil Description W
TOPSOIL/FILL: Dark brown organic sandy SILT,very soft, moist.
1
CH Light gray-brown, mottled CLAY, fractured with original laminated
structure,stiff(qu=1.5tsf), moist, medium plasticity. 37.1
5
Light gray, mottled silty CLAY with siltstone and coal inclusions,
CL stiff(qu=1.5 tsf),fractured texture, moist, low plasticity. 35.5
Black COAL,fractured, moist,very soft. _
10 ray very me grain SANDSTONE,widely-spacedfractures,
hi hl weathered soft moist.
Test pit terminated at 12 feet.
Light and moderate perched groundwater seepage observed at 2 feet and
.15 10 feet respectively, No caving.
Test Pit No. TP-2
Logged by: KPR
i
Date: 1/22/97
Depth USCS/
0 _jGra h Soil Description W
OL SM TOPSOIL/FILL: Dark brown organic silty sand with few gravel
inclusions and occasional buried wood, loose, moist. 33.9
ML Brown, mottled sandy SILT with clay, stiff(qu=2.0 tsf), moist,
low plasticity, 28.1
5 Gray-brown silty very fine SAND with gravel, occasional cobbles,
and clasts of highly weathered sandstone,very dense, moist.
SM (Glacial Till)
10 16.0
Test pit terminated at 11 feet.
Very light perched groundwater seepage at 4 feet.
No caving.
15
TEST PIT LOGS
TERRA 405 NORTH UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants
Proj. No. T-3453 Date DEC. 1997 Figure A-2
Test Pit No. TP-3
Logged by: KPR
Date: 1/22/97
Depth USCS/
Graph Soil Description W
TOPSOIL: Dark brown organic clayey silt,very soft,saturated. 1
CL Gray, mottled silty CLAY,fractured,stiff(qu=1.0 tsf), moist,
low to medium plasticity. 35.6
5 Brown to blue-gray, mottled clayey SILT with occasional organic
fibers, laminated,very stiff to hard (qu=3.0 tsf), moist, medium LL=59
MH plasticity. 45.6 PL=35
PI=24
1
Gray, mottled silty fine SAND with few gravel inclusions,occasiona
10 1 SMJ, cobbles and rare 24 inch boulders,dense,wet to saturated.
(Till-like) 24.2
Test pit terminated at 12 feet. Ponded water at surface.
Moderate groundwater seepage at 8 feet. No caving.
15
Test Pit No. TP-4
Logged by: KPR
Date: 1/22/97
Depth USCS/
Graph Soil Description W
PT .-TOPSOIL,
ism], Red-brown(oxidized)silty fine SAND, medium dense, moist, 17.2
(completely weathered sandstone).
Light gray to orange(oxidized layers)fine SAND with silt, dense,
5 moist becoming saturated at 8 feet(completely weathered 13.9
sandstone).
'LL SP-SM
10 1
__=_ Gray to orange (oxidized zones) highly weathered SILTSTONE, 19.1
___= soft bedding structure occasional fractures moist.
Test pit terminated at 13 feet.
15 Heavy perched groundwater seepage at 8 feet.
No caving.
TEST PIT LOGS
TERRA 405 NORTH UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants
[Proj. No. T-3453 I Date DEC. 1997 1 Figure A-3
Test Pit No. TP-5
Logged by: KPR
Date: 1/22/97
Depth USCS/
Graph Soil Description W
0 . A A PT AA TOPSOIL: Dark brown organic sandy silt,wet.
Tan to orange (oxidized)silty fine SAND with trace gravel, medium 23.2
dense to 4 feet becoming dense, moist to wet. (completely
SM. weathered sandstone).
5
. • • Brown to orange-brown (oxidized stains)SANDSTONE, highly
• • • • • weathered, bedding structure,thin coaly seams,very fine grained,
10 . • . . . soft, moist.
19.8
Test pit terminated at it feet.
No groundwater seepage or caving observed.
15
Test Pit No. TP-6
Logged by: KPR
Date: 1/22/97
Depth USCS/
Graph
Soil Description W
0 (0 to 8 inches TOPSOIL)
Brown silty very fine to medium SAND with clasts of sandstone, 31.4
SM 4 foot boulder at 4 feet, disturbed texture, dense, moist
5 becoming saturated at 6 feet. _
• • • • • Yellow-tan fine-grained SANDSTONE, massive, highly weathered, 15.6
soft, moist.
10
Test pit terminated at 9.5 feet.
Moderate perched groundwater seepage observed at 6 feet.
No caving.
15
TEST PIT LOGS
TERRA 405 NORTH UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants
Proj. No. T-3453 Date DEC. 1997 1 Figure A-4
Test Pit No. TP-7
Logged by: KPR
Date: 1/22/97
Depth USCS/
Graph Soil Description W
0 FILL: Dark brown organic silt with clay,soft, moist, low plasticity.
MH Gray, mottled clayey SILT fractured,very stiff,(qu=2.25 tsf), LL=60
moist, medium plasticity. 28,3 PL=41
5 PI=19
Brown-gray, mottled sandy SILT,very fine sand, medium dense,
non-plastic,wet to saturated. 1
ML 26.9
10 --- ==74,.Dark graySILTSTONE,fractured moderate moderatelv weathered, o moist.
Test pit terminated at 10.5 feet.
Perched moderate groundwater seepage at 8 feet.
No caving.
15
Test Pit No. TP-8
Logged by: KPR
Date: 1/22/97
Depth USCS/
Gra h Soil Description W
0 OL FILL: Dark brown organic silt with clay,soft, moist, low plasticity.
21.1
Gray, mottled CLAY,fractured, thin laminae, stiff(qu=2.0 tsf),
CH most, medium plasticity.
5— 25.7
1
Silty very fine to medium SAND with gravel, clasts of weathered
SM sandstone and occasional 2 foot boulders, dense,saturated 15.8
becoming moist at 7 feet.
10
Test pit terminated at 10 feet.
Very light groundwater seepage and caving observed at 6 feet.
15
TEST PIT LOGS
TERRA 405 NORTH UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants
Proj. No. T-3453 Date DEC. 1997 Figure A-5
Boring No. B-1
Logged by: ABK
Date: 12/15/97 Approximate Elev.
Consistency/ a (N) Moisture
Soil Description Relative Depth E Blows/ Content
Density (ft ) I ft. (/o)
Note: Drill pad cut 2 feet below
existing grade.
FILL: Brown silt,scattered wood pieces
and organics, moist. Very
Soft 2
5 .
FILL: Gray, gray-brown and rust-mottled T
silt, scattered wood and organics,with J_ 8
laminations of sandy silt, increasingly Loose
sandy and more till-like with depth, moist. — 10
Stiff
I 10
15
FILL: Brown silt,very moist. Medium
Stiff
6
Sampled coal and wood pieces. 20
Loose
Z 10
25
Bedrock: SANDSTONE, gray.
Hard
= 50/4"
Boring terminated at 28 feet.
"Note: Poor recovery.
BORING LOG
TERRA NORTH 405 UPPER AND LOWER SITES
• ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-6
Boring No. B-2
Logged by: ABK
Date: 12/15/97 Approximate Elev.
Consistency/ Q (N) Moisture
Soil Description Relative Depth E Blows/ Content
Density (ft.) 0 ft. (%)
Organic Silt Topsoil,trace to little Gay, Soft
moist to very moist.
Gray, grayy-brown and rust-mottled
clayey SZT-, some dark orange staining, Very
Moist. Stiff
23
Orangish-brown SILTY SAND with 5
GRAVEL,fine to medium,few bedrock Medium
clasts,very cobbly with difficult drilling Dense
around 6 feet,wet at 8 feet.
33
Orange-brown and rusty CLAYEY SILT, 10
scattered pieces of coal, moist, 1/4 inch
lamination of dark brown organics at 9 Hard
feet.
50/6"
Gray CLAYEY SAND to SILTY SAND, 15
fine, moist.Water perched at about Very
12 feet. Dense
Gray SANDSTONE, partially laminated
._L_ 50
with organics, (Bedrock). Seam of coal 20
encountered at 19 feet. Hard
/4"
Continue with Rock Coring Log on next page...
BORING LOG
TERRA NORTH 405 UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-7
Rock Coring Log B-2
Project Feature: Elevation
Driller/Equipment: Geoboring Start Date
Sampler/Method: Cable Tool Finish Date
Coordinates:. Hole Diameter
Rock Mass PL
Elev. Depth Box Run%Rec./Graphic Classification and Rating or Remarks
(feet) # #• RQD Log Physical Condition RMRJ Q UCS'
End of auger and SPT sampling.
Bedrock,no coring.
25
1 100/55 BEDROCK: Sandstone, gray,fine-grained,
soft to medium hard,fractures with average
apparent dip of 15 to 35 degrees,some are
coal-filled or organic-filled.
30 2 100160
Coal from 32 to 33 feet.
1
35 3 100/80 Coal from 35 to 37 feet.
Interbedded coal and sandy clay from 39 to
40 4 40/40 49 feet. (Note: no recovery in run#5)
2 Circulation loss
from 39 to 49 feet.
45 5 0/0
NA
50 -
'Rock Strength Tests (in psi): Logged by: ABK
PL= PoiRt Load Test
UCS =UncW ned Compressive Strength
LU ROCK CORING LOG
TERRA NORTH 405 UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-8
Rock Coring Log B-2
Project Feature: Elevation
Driller/Equipment: Geoboring Start Date
Sampler/Method: Cable Tool Finish Date
Coordinates: Hole Diameter
Rock Mass PL
Elev. Depth Box Run%Rec./Graphic Classification and Rating or Remarks
(feet) # # RQD Log Physical Condition RMRJ Q UCS`
50 6 90/80
3 Interbedded coal and sandy clay from
53 to 55 feet.
55 7 100/80
4
60 -
Boring terminated at 58.9 feet.
65
70
75
"Rock Strength Tests.(in psi): Logged by: ABK
PL= Poiat Load Test
UCS =UncT8ned Compressive Strength
ROCK CORING LOG
TERRA NORTH 405 UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-9
Boring No. B-3
Logged by: ABK
Date: 12/15/97 Approximate Elev.
Consistency/ a (N) Moisture
Soil Description Relative Depth E Blows/ Content
Density (ft.) ft. M
Organic Brown Silt Topsoil Soft
Gray and gray-brown mottled SILT,
hairline fractures and scattered 15
organics,moist.
5
Very
Stiff to
Hard
Scattered seams of rocks and clasts,
silty sand, rusty spots, pocket of coal. 28
10
Scattered coal seams and dark
brown organics soil.
—L 48
Bluish-gray SILTY SAND,fine to Dense
medium,wet. 15
Boring terminated at 16 feet. .
Refusal on large boulder.
Redrilled 5 feet away and met with refusal at 8 feet.
BORING LOG
TERRA NORTH 405 UPPER AND LOWER SITES
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-10
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GRAIN SIZE ANALYSIS
NORTH 405 UPPER AND LOWER SITES
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\� • • � • RENTON, WASHINGTON
• Date DEC. 1997
APPENDIX B
GOLDER ASSOCIATES,INC.REPORTS
Golder Associates Inc.
4104-148th Avenue,N.E. _ = Golder
Redmond,WA 98052
Telephone(425)883-0777 �"soc afes
Fax(425)882-5498
August 22, 1997 Our ref: 973-1212
Terra Associates,Inc.
12525 Willows Road,Suite 101
Kirkland,WA 98034
ATTENTION:Ted Schepper
RE: PRELIMINARY ABANDONED MINE ASSESSMENT
Dear Ted:
Please find attached a copy of the preliminary report written by SubTerra.Please note
that SubTerra are waiting for test pit photographs to complement this report.
The major concerns are:
1) Lack of topographic control for location of topographic features and test pits etc.
These data are needed to better assess the relationship between the geology and
topographic features.
2) TT#1 found evidence for a mine opening. Due to its elevation,this feature
would imply a deeper coal seam than that viewed in TT#5 where a shallow un-
worked coal seam,situated about 10 feet below the surface was found. This
seam appears to have an apparent dip of approximately 10'to the north or
northeast rather than 35'indicated on the geological map.
3) Features hidden beneath the blackberries.Two sinkholes were observed near the
north west edge of the Parcel 3. The smaller hole (TT#4) was about 5 feet in
diameter,2 foot deep with vertical sides,i.e.,fairly fresh. A rusty,steel,1 inch
pipe was observed in the northern face of the hole. The second sinkhole was
much older and longer (--20 feet by --10 feet) with gently sloping sides.
Removal of the bush this weekend by Opus may reveal other features of
importance.
The work has answered some questions but raised a few more.To would advise the
following actions;
• Observe the site after the bush has been removed.
• Have a surveyor complete a map of the site complete with the locations of the
most recent test pits.
OFFICES IN AUSTRALIA,CANADA,GERMANY,HUNGARY,ITALY.SWEDEN,UNITED KINGDOM,UNITED STATES
August 22,1997 2 973-1212
• Investigate by drilling whether there is a deeper coal seam than the one we
followed in TT#3.
These issues can be discussed in the meeting that you are planning for next week
Please advise me of its timing in due course.
On a budgetary note,the test pitting took three hours longer than estimated due to the
number of features revealed beneath the blackberries and the difference in the dip of
the coal seam to the geological record. These costs amount to an increase of
approximately$700 which you were able to verbally approve during yesterday's
telephone conversation. This amount added to the approved budget to date bring the
total to$7,525. The budget must be about 95% complete at the time of writing.
I look forward to your reply after you have had a chance to review the preliminary
report.
Sincerely, '
i
GO ER IATES INC.
Ian B' op
Se ' r Geophysicist
I /psry
OB=bldoc
Golder Associates
Mining Engineering
Civil and Mining Rock Mechanics
7; �_ _: SubTerra, Inc. Mine Subsidence
Solid Waste Disposal
Tunnel Engineering
f Concrete/Shotcrete Technology
Construction Bid Documents
21 August, 1997
Dr. Ian Bishop
Associate
Golder Associates, Inc.
4104 148th Avenue NE
Redmond, WA 98052
Re: Visual Site Reconnaissance and Preliminary Abandoned Mine Assessment
Proposed Oaksdale Business Park in Renton, Washington
Dear Dr. Bishop:
At your request we have completed a visual site reconnaissance and preliminary, or Phase
1, abandoned mine assessment of the above subject site. The scope of work contained in
our August 11, 1997 proposal included:
1. Examination of abandoned mine plans available from the Washington State
Department of Natural Resources (DNR). We understand that you already
have the pertinent maps, however, we will review our fiche to determine
whether there are additional relevant records.
2. Digitizing the most recent plans for incorporation in an AUTOCAD drawing of
the site.
3. Retrieval and examination of the historical aerial photographs of the site.
4. A preliminary site reconnaissance to observe current conditions.
5. Evaluation of supplemental data and information (e.g., historical production
records) in our possession to determine the potential for the presence of
additional workings beyond those shown on the mine plans.
6. Planning a preliminary site investigation program designed to confirm or
refute the presence of additional workings.
7. Preliminary evaluation of potential impacts of the abandoned mines on the
developable site area.
This scope was subsequently extended to include a limited site exploration program
utilizing a trackhoe to dig up to eighteen (18)feet deep exploratory trenches. This program
was intended to confirm the presence of a coal seam dipping at 35 degrees and striking
east-west across the site for input to planning a more extensive, geophysical exploration
program.
8003 118th Avenue N.E., Kirkland, WA 98033 (206) 827-8003 FAX (206) 889-8150
SubTerra, Inc. Golder Associates 8/21/97
Monster Road Geophysical Investigation
Phase I Approach
As part of our assessment, we reviewed a preliminary geotechnical study by Terra
-Associates, Inc., dated February 15, 1997, in which the presence of abandoned mine
workings was noted. In addition to the data from the Tema report, a regional geologic map,
archival mine records, historical aerial photographs dating from 1936, and a detailed 1990
topographic map of the western portion of the site, prepared by BRH, Inc., were used in
completing our preliminary assessment and the preliminary plan of the site shown in
Drawing 1.
Preliminary investigations indicate that the underground workings located on the subject
site were probably part of the Black River mine, which had recorded production during the
1890's, but no further information or mine maps are available. Another abandoned mine,
the Diamond Mine is located to the east of Monster road at the approximate location shown
on Drawing 1. This mine was worked from 1927 until 1931 and produced approximately
6,000 tons of coal according to mine records maintained by the Division of Natural
Resources.
Additional un-recorded production occurred after 1890, as evidenced by the present
condition of the on-site workings and the visibility of on-going excavation in the 1936 aerial
photograph. The location and trend of caved workings or surface cuts and spoils piles that
were visible on the aerial photographs, were also identified during the visual site
reconnaissance. The approximate location of this area is shown on Drawing 1.
Because no mine maps or production records were available, the extent of the workings
and undermined areas can only be inferred. Additional information has been gleaned from
a.limited subsurface exploration program during which approximately 500 linear feet of
exploration trench was dug ranging from 4 to 18 feet in depth. A summary of the results of
the Phase I-study and limited site exploration is presented in the following paragraphs.
Results of the Preliminary Site Reconnaissance
A brief description of the site was provided in the February 1997 report by Terra
Associates, and will not be duplicated here. The focus of our site reconnaissance was
along the western edge of the approximate 150 foot tall bedrock hill that rises above the
Green River/Duwamish floodplain and forms the core of the subject parcel.
The west side of the subject bedrock hill is characterized by steep forested slopes with an
approximate forty-foot tall near vertical cut adjacent to Burlington Northern railroad tracks at
the southwest portion of the bedrock hill. An overgrown road grade ran in a north-south
direction along the west side of the bedrock hill from the railroad tracks to a point about 500
feet north of the tracks. At the northern end of the road an extensive area of modified land
was encountered. This area of modified land was visible in the 1936 air photo as an
extensive west-north-west trending excavation at this location. This site was also displayed
as a coal prospect in a 1948 regional geologic map of the area. The modified land
consisted of an east -west trending topographic depression into the hill slope that
measured about 150 feet east west by about 80 feet north-south.
2
SubTerra, Inc. Golder Associates 8/21/97
Monster Road Geophysical Investigation
The depression contained local spoils that contained good quality coal. The slopes along
the depression contained loose soil with coal fragments. Evidence of ongoing-raveling and
soil creep along these slopes was seen in the form of bowed and tilted trees. What
appeared to be the main spoils pile from these workings extended to the west and
downslope of the depression a distance of about 120 feet down the floor of the regional
floodplain. This apparent spoils pile was covered with heavy brush and was not assessed
during the field reconnaissance.
A continuation of the overgrown road grade extended in a southeasterly direction towards
the top of the hill and a broad north sloping area that was clear of trees but covered with
thick blackberries. Five test pits had been completed in this area during the February 1997
Terra and Associates study, but no evidence of the test pits could be found. We were _
particularly interested in locating test pit TP-1, which encountered coal to the east of the `
excavated area.
Our Initial Understanding of the Geology and Coal Seams
Our initial understanding of the geology of the site was based upon our visual
reconnaissance, data from the Terra and Associates test pits, and review of available
geologic literature. In general, the geology of the site appeared to consist of a thin veneer
of flat lying glacial sediments that were deposited atop relatively steeply dipping Eocene
age (about 50 million years ago) volcanic and sedimentary units that are part of the Puget
Group. At the subject site, the Puget Group rocks are represented by the volcanic related
Tukwila formation and sandstone and siltstone of the Renton Formation. The Renton
Formation is the host of a number of coal seams, one of which underlies the subject site,
as discussed below.
The glacial sediments on the property were deposited about 15,000 years ago during the
Vashon Stade of the Frazer glaciation. During this period a continental ice sheet, up to
about 3,000 feet thick in the Renton area, occupied much of the area known as the Puget
Lowland. At the project site, a dense, unsorted mixture of sand silt and gravel was
deposited at the sole of the advancing glacial ice sheet and these sediments are referred to
as lodgement till. The till was consolidated to a dense state by the weight of the ice and
typically is characterized by relatively high strength and relatively low permeabilities.
Based on the visual reconnaissance and test pit data, the till is estimated to be less than
about 10-15 feet thick across the site. Across the northern and western portion of the site
the till is apparently absent, as the sandstone was encountered at the surface in these
areas.
The Tukwila formation is exposed in the railroad cut along the southwest portion of the
parcel, and has previously been mapped by others elsewhere in the south half of the site.
This formation is characterized by andesitic lava flows and breccia, with conglomerates and
arkosic sandstones, that were deposited in a high-energy depositional environment.
The Renton formation conformably overlies the Tukwila formation and is characterized by
sediments deposited in a meandering stream type environment at the edge of the
continent. Interbedded sand and silt and clay were deposited as channel and overbank
3
SubTerra, Inc. Golder Associates 8/21/97
Monster Road Geophysical Investigation
(flood) deposits, as the ancient stream channels migrated back and forth across a broad
floodplain. The coal seams represent persistent swampy areas along the floodplain, that
gradually subsided and allowed accumulating organic matter to be buried and eventually
preserved as coal: Based on previous geologic mapping, the coal encountered at the site
has been correlated with the Black River Bagley coal seam.
Following deposition, both the Tukwila and Renton formations were folded and faulted
during the uplift of the Cascade Range. The folding and faulting caused many of the
originally flat-lying coal seams to slope (dip) steeply and to locally crop out at the surface.
In the area where the surface excavation was encountered, the Black River-Bagley coal
seam reportedly trends approximately west-north-west and dips 35 degrees down to the
north. The surface expression of the coal seam was therefore interpreted to form a line
across the south central portion of Parcel 3 based on available geologic data.
Results of the Trenching Program
A one day trenching program was carried out to further investigate the site and to provide
data for input to the geophysical investigation program. In the absence of survey control
and topographic data for Parcel 3, the trenches could only be very approximately located.
These very approximate locations are provided on Drawing 1. Highlights of the results of
the trenching program are presented below.
Test Trench No. 1 was located in an east-west trending depression thought to be a
collapsed mine access. Coal and wood fragments were first encountered at a depth of
about eight (8) feet. Numerous cut timbers were extracted between 8 and 14 feet and the
collapsed outline of a mine entry could be observed on either side of the trench. The
approximate-alignment of the opening was similar to the line of the syncline axis shown on
Drawing 1. A second test pit that was dug to a depth of 14 to 16 feet approximately 20 feet
east of TT#1 encountered spoils to a depth of about 14 ft but no evidence of the mine
workings.
Test Trench No. 2 was located east of TT#1 and was dug approximately 70 feet from the
south to the north on a bench immediately below the apparent highwall left by the workings
shown in the 1936 aerial photograph. No solid coal seams were encountered, however,
coal mine spoils existed to depths of at least 17 feet. An intermittent seepage occurred at
the base of the trench at a location approximately east-south-east of the opening observed
in TT#1, however, no evidence of collapsed workings was encountered. Native materials
were observed in the slopes at the north and south ends of the trench.
Test Trench No. 3 was located approximately 100 feet east of TT#2 and was dug from the
property line at the Metro fence north approximately 260 feet. This trench encountered
what appeared to be Tukwila formation at a depth of about 4 feet for the first 50 feet then
graded into the softer sandstone of the Renton Formation. Subsequent inspection
indicated that the first 50 feet of trench contained large boulders which were underlain by
Renton formation sandstone. Trace coal was encountered at a depth of 14 ft approximately
80 feet from the fence and a continuous 3-4 foot thick coal seam was encountered between
10 and 14 feet deep between 150 and 230 feet from the fence.
4
SubTerra, Inc. Golder Associates 8/21/97
Monster Road Geophysical Investigation
Test Trench No. 4 was located just north of the end of TT#3 in a six foot wide sinkhole. No
evidence of coal was found in the trench which was deepened to 18 feet. Weak , soft,
caving soils were encountered from the top to the bottom of the trench.
Test Trench No. 5 was excavated at right angles to TT#3 about 180 feet from the fence to
determine the eastwards extent of the coal seam. The coal seam was observed to thin out
and disappear in about 15 feet.
Test Trench No. 6 was located approximately 200 feet east of TT#3 and was dug from the
property line at the Metro fence north approximately 100 feet. No evidence of coal or
carboniferous materials was observed in sections of the trench that were dug to depths of
14 feet. Trenching in this area was curtailed so that sufficient time was available for
backfilling of all excavated trenches and exploration of the long depression along the
property line between Parcels 3 and 4-B.
Test Trench No. 7 was located in a north-south depression located approximately along the
north-south boundary between Parcel 3 and Parcel 4-B. This depression is approximately
twelve feet wide and appears to be a cut that was probably made to explore for coal. Coal
with an apparent thickness of about 6 feet was found about 1 foot below the ground surface
in the face of the north facing headwall. As the trench was extended towards the north, the
apparent dip of the top of the coal was observed to change from about 30" south to about
100 north. Part of the coal seam had been removed in the base of the trench.
Test Trench No. 8 was extended south from the start of TT#7 a distance of about twenty
feet. The coal seam disappeared just beyond the crest of the slope grading immediately
into yellow sand.
Interpretation of the Data
Without the benefit of production records or mine maps it is difficult to quantify the extent
and location of undermined areas. However, we would normally not anticipate that the
undermined areas would be large, as a large mine would have more difficulty avoiding a
State of Washington law circa 1900, that required all coal mine operators to file an annual
mine plan with the state. The extent of the excavation encountered during the field
reconnaissance, and the visibility of this excavation in the 1936 photo suggest that some
undocumented work took place after the Black River mine was reportedly abandoned in the
1890's.
The following interpretations are considered to be very preliminary. Inferred data and
information, including geologic contacts, dip, and dip and strike directions are very
approximate and based strictly on non-quantitative field observations.
1. Test Trench No. 1 probably encountered the remnants of the 207 ft long Black
River mine slope. There is inconclusive evidence that the encountered slope
was mined in an easterly direction, however, it was mined at a depth below the
coal seam encountered in Test Trench Nos. 3, 7 and 8. There is therefore some
potential for a second, lower seam to exist at the site.
5
SubTerra, Inc. Golder Associates 8/21/97
Monster Road Geophysical Investigation
2. A thin, 3 to 4 foot thick coal seam occurs at shallow depth beneath part of the
western 100 feet of Parcel 43 This seam strikes about east-south-east and dips
towards the north at between 100 and 200. It is unlikely that this seam would
have been mined using underground methods due to its relatively shallow depth.
3. No coal was discovered in areas east of Test Trench No.3. However, trenching
was not extended across the marked wetland area due to time constraints and
uncertainty regarding disturbance of the marked area. It is unlikely that
extensive coal workings underlie this part of the site, however, a relatively
inexpensive drilling program would confirm the presence or absence of mineable
coal seams at depths beyond those reachable by trenching.
4. The north-south trending depression located approximately on the property line
between Parcels 3 and 4-13 is believed to be an,exploratory dozer cut and may
well be the"prospect" mapped and referred to in Warren at al,(1945).
5. Very soft, caving soils underlying developed sinkholes were encountered to
depths of 18 feet in the northwest part of Parcel 3. There is no evidence that
these sinkholes are associated with coal mining, however, the encountered
conditions may pose constraints on site development. It is recommended that
Terra Associates conduct additional site investigation in this area.
6. It is likely that the ground west and immediately south of the depression,
including the area referred to as the"strip-pit from the 1936 air photo', has been
disturbed by mining.
This report was prepared for the exclusive use of Golder Associates, Inc., their Client Terra,
Associates, and Terra Associates client Opus Northwest, LLC and is considered to be a
preliminary investigation of the potential impacts of abandoned mines on the Monster Road
Property. We trust that the report is sufficient foryour present purpose.
Please feel free to call us if you have any questions regarding the enclosed materials. We
may be reached at (425) 827-8003.
Best Regards
Chris D. Breeds
President
References:
Warren, Norburath, Grivetti, and Brown, 1945. The Coal Fields of King County. Provides
location of the Diamond Mine and Black River prospects.
George Watkin Evans, 1912. Bulletin No. 3, The Coal Fields of King County. Chapter 5
contains a description of the Black River mine.
"In the north half of Section 24, T23N, R4E at Black River Junction, a mine
was opened in the latter part of the eighties. A small slope was sunk for a
distance of 207 feet on Pe bed which dips to the north at 25 degrees. At the
rr
6
SubTerra, Inc. Golder Associates 8/21/97
Monster Road Geophysical Investigation
foot of the slope, the bed flattened considerably, evidently approaching the
syncline that lies between this point and the beds that outcrop north of the
Columbia and Puget Sound railroad in Section 13.
No great amount of work was done here, but the writer is informed that what
coal was mined was of good quality. The mine was closed in 1892, and has
remained closed since that data.
Terra Associates, 1997. Preliminary Geotecnical Study Oaksdale Business Park Renton,
Washington. Prepared for OPUS Northwest LLC by Terra Associates, February 15, 1997.
Provides a description of the site and location of test pits and observed mine hazards.
Schasse, H., Koler, M.L., Eberle, N.A., and Christie, R.A., 1994. The Washington State
Coal Mine Map Collection, OFR 94-7, June 1994. Provides mine map locations and mine
production information.
7
Golder Associates Inc.
4104-148th Avenue,N.E. � = Golder
Redmond,WA 98052
Telephone(425)883-0777 socifes
Fox(425)882-5498 As
November 26, 1997 Our ref: 973-1212
Terra Associates, Inc.
12525 Willows Road, Suite 101
Kirkland,WA 98034
ATTENTION: Ted Schepper
RE: AERIAL PHOTOGRAPH INTERPRETATION,MONSTER ROAD
Dear Ted:
Following our telephone conversation of Tuesday,November 18, 1997, we understand
that your client, OPUS Northwest LLC does not wish to proceed with the complete
scope of works for the Phase II abandoned mine assessment at this time. These works
were detailed in a change order, dated November 3, 1997(GAI 1997). In particular,
OPUS does not wish to commit to drilling a borehole to investigate the potential
existence of a second coal seam on the site. Accordingly, this letter report details the
tasks completed to date and presents the analysis of the aerial photographs.
1. SUMMARY OF WORK TO DATE
The scope of works completed to date include:
Phase I
1. Examination of abandoned mine plans available from the Washington State
Department of Natural Resources (DNR).
2. Digitization of the most recent plans for incorporation in an AutoCAD drawing of
the site.
3. Retrieval and examination of the historical aerial photographs of the site.
4. A preliminary site reconnaissance to observe current conditions.
5. Evaluation of supplemental data and information (e.g. historical production records).
6. Planning a preliminary site investigation program designed to confirm or refute the
presence of additional workings.
7. Preliminary evaluation of potential impacts of the abandoned mines on the
developable site area.
8. Limited site exploration utilizing a track-hoe to dig eighteen (18) feet deep
exploratory trenches. The program was intended to confirm the presence of a coal
seam dipping at approximately 35 degrees to the north and striking east-west across
OFFICES IN AUSTRALIA,CANADA,GERMANY,HUNGARY,ITALY,SWEDEN,UNITED KINGDOM,UNITED STATES
November 26, 1997 2 973-1212
the site for input to the planning of a more extensive exploration program utilizing
geophysical or intrusive methods.
The Phase I exploration noted in.(8) above, revealed a thin 3-4 ft.thick coal seam beneath
part of the western 100 feet of Parcel A(a.k.a. Parcel 3) (TT3) and soft caving soils in the
northwest part of Parcel A(TT4). The located seam strikes east-southeast and dips
between 10 and 20 degrees to the north. An exploration trench dug approximately 200
feet east of the located coal seam did not encounter coal. A second trench (TTI) dug in a
hollow on the hillside on the northern edge of Parcel B (a.k.a.Parcel 4B) found evidence
for a second coal seam located approximately 40 feet below the seam described above.
The preliminary abandoned mine assessment reports should be read in conjunction with
this document(Golder Associates, 1997,Sub Terra 1997).
2. PHASE II
}
2.1. Original scope
The original objectives outlined in the change order for Phase H were to delineate areas
suitable for construction, areas that should only be used for parking, and areas that
should not be developed,based solely on abandoned mine issues. This was to be
accomplished by:
1. Adding features (buildings, earth movement and waste piles).from aerial
photographs to the AutoCAD Drawings of the site to better understand the history
of the site.
2. Drilling one or two boreholes to investigate whether a second, deeper and workable
coal seam is located within the site boundaries.
3. Completion of annotated photographic plates of the test trenches for incorporation
in a final report.
4. Preparation of a final report and recommendations for proposed building locations.
Items 2 and 4 have not been authorized by the client at the time of writing.
2.2. Annotated photographs of the test trenches
Annotated photographs of the test trenches dug by Sub Terra, Inc. are included with this
report. The information obtained from these trenches was detailed in the preliminary
abandoned mine assessment report presented to you in August. Note that the locations
of the test trenches presented in that report were based on measurement from fence
lines, and pre-date the detailed topographic survey completed in late October. The
updated locations of the test trenches can be seen on the attached plates.
The trenches were excavated to confirm the presence and state of a coal seam dipping at
35 degrees to the north. They were not dug or logged for the purpose of soil
characterization.
Golder Associates
November 26, 1997 3 973-1212
2.3. Survey Control
Following the submission of the preliminary report, all the blackberries were cleared
from Parcel A. This allowed a walk-over surface inspection of Parcel A and the
placement of test trench marker flags for the planned topographic survey. During this
walkover, the only extra features of interest noted were:
1. A wall footing denoted by a single line of red bricks 120 ft. west of TT4.
2. A gravel track running west from Monster Road,approximately 100 ft. south of
northern-most boundary of Parcel A.
3. Concrete foundation slabs adjacent to Monster Road.
Bush,Roed &Hutchins,Inc(BRH, 1997) supplied AutoCAD maps detailing the survey
control established at the site, the detailed topography and the locations of most of the
trenches completed as part of(8).above. The survey markers for test trenches TTl,TT2.
and TT8, the northern end of TT6, and the southern end of TT3, were not picked up by
the surveyor. The locations of these have been estimated from field measurements and
are shown on the plates. The locations of the two sinkholes and a wall foundation are
also shown. Note that a small iron pipe was located on the edge of TT4. TT4
investigated the most recent sinkhole.
The preliminary report described evidence for the existence of a mine portal in TTl.
This test trench was dug in an east-west orientated, topographic,depression that cuts
into the hillside. Assuming that this was a portal to a coal seam, the elevation of the
feature (64 ft.) indicates a deeper coal seam approximately 40 feet below the coal seam
viewed in TT3. Without a boring, we can make no comment as to the quality of any coal
in this seam or whether it would have been economic to mine.
3. AERIAL INTERPRETATION WORK
3.1. Introduction
To better understand the development history of the site, the aerial photographs of the
site for the years 1936, 1970 and 1995 were scanned into a computer. These date were
then merged with the AutoCAD survey map supplied by BRH. The best-fit results are
shown in the following plates:
Plate 1. 1936 aerial photograph overlain by site plan
Plate 2. 1970 aerial photograph overlain by site plan
Plate 3. 1995 aerial photograph overlain by site plan
By best fit, we mean that the relative position of the aerial photograph to the survey data
has been obtained by stretching the scanned photographic images to optimize their fit
relative to the 1997 topographic data set. This process entailed making some
assumptions about the positions of Monster Road, the rail track and other features.
Golder Associates
November 26, 1997 4 973-1212
However, the final fit appears to effectively match the survey data, so any errors in
matching the photographs should be of the order of several feet.
3.2. The Diamond Mine
This mine was located east of Monster Road.
A digitized copy of the mine map supplied by the DNR was overlain on to the 1936
aerial photograph (Plate 1,features labeled-m-). Note that this photograph was taken
four years after the last recorded workings in the Diamond mine (DNR 1997). A house
and an entrance way, (labeled bunker in the mine plan), were matched to corresponding
features on the 1936 photograph. Fitting the mine map to the photograph using these
features as reference points produced the result shown in Plate 1. It is interesting to note
that the mine portal, digitized from the mine map, correlates well with the end of a
linear feature, of similar orientation,located in the photograph. This feature is
interpreted as the approach cut running down to the mine portal. This same incised
feature is still evident on the 1970 photograph.
3.3. Features in Plot A and B
3.3.1. 1936 photograph.
This is the earliest aerial photograph of the site. It shows cultivated field above and
below the steep slope separating Parcel A from Parcel B. Within Parcel A, the
photograph reveals two major vehicle tracks running east-west from Monster Road and
one minor east-west vehicle track to the south. The northern pair of tracks run to a
collection of buildings, the largest of which is located 15 ft. north of the sinkholes
identified in Phase I.
Plate 1 indicates that TT3 runs along the eastern edge of a marked change in the
reflectivity of the surface materials. To the east, the surface appears uniform with well
defined boundaries, indicating a cultivated field or pasture. West of this line, and east of
the edge of the hillside,the surface is dark and patchy indicating a mixture of
uncultivated (vegetation) and disturbed ground. The two sinkholes are located in this
area. All the areas of disturbed ground are therefore located west of this trench.
The incised gully is not visible in this photograph (TT7) although clear on the 1970
photograph (Plate 2). This indicates that the gully interpreted as a prospect trench in the
preliminary report was dug after the 1936 photograph was taken.
One hundred feet east of TT3 there is a pronounced cut in the hillside, shown by a
shadow. A few feet east of this topographic feature, which still exists today, are two
parallel features which indicate that the crop, shown by the east west closely spaced
lines, is growing more poorly in this part of the field. These features are interpreted as
the influence of the foundations from a large pre-1936 building. Foundations can cause
this effect by reducing the soil cover, altering the local drainage and creating soils with
Golder Associates
November 26, 1997 5 973-1212
lower moisture and nutrient content.The brick foundation structure at the north end of
this feature (noted during the walkover survey)may be related to part of this structure.
The hillside that separates Parcel A and B shows lobes of material interpreted as end-
tipped mine spoil spreading down the side of the slope. Most of the surface of these
lobes shows significant vegetation.which would indicate some years of latency since the
bulk of the spoil was deposited. However, there appear to be several areas of disturbed
ground(poorly vegetated) which would indicate more recent mining activity.
3.3.2. 1970 photograph.
The Diamond Mine buildings are not evident on the photographs. Some of the
topographic features such as the feature interpreted as the approach cut are still evident.
The bunker road has been widened and extended towards what is now the Metro
works. This road appears to pass over the mine portal.
All the buildings in Parcel A have been removed and the farming has passed to pasture.
Cattle tracks (shown in white) run across the field and down into the old mine workings.
The central east-west track is still in use. The photograph indicates that the building that
must have occupied the concrete foundation slabs located adjacent to Monster Road
must have been built after 1936 but removed before 1970..
As noted in 3.3.1, the gully(TT7) is clearly visible in this photograph.
The land north of Parcel A and B has been re-graded, with the construction of a railway
spur and buildings.
3.3.3. 1995 photograph.
The Diamond mine site has been completely re-graded and no trace remains of the older
mining related features.
The top of the hill, south of Parcel A,is now fenced (METRO). Vegetation (blackberries)
have encroached across much of the site as the land has fallen into disuse and away
from farming.
There has been further development of the commercial buildings to the north of both
parcels.
The hillside on the south western side of Parcel B has been cut back and re-graded.
4. DISCUSSION
The aerial photographs cover most of the changes in land use between 1936 and the
present day. The history of this use appears to be fairly complete although the building
Golder associates
November 26, 1997 6 973-1212
adjacent to Monster Road (Parcel A) was,not photographed while erect. From some of
the surrounding artifacts present in the field,it is likely that it was a small farm.
The incised gully in to which TT7 was placed is not evident on the 1936 photograph,
which would indicate that it post dates the photograph. All the remainder of the mining
related features (spoil piles, strip mining, tracks etc.) present in the 1936 photograph are
situated west of TT3. East of TT3, and west of Monster Road, the ground appears to
have been used only for farming.
The study has relocated the survey plans for the Diamond Mine with some degree of
confidence. None of the recorded workings underlie the site.
This letter should be read in conjunction with the preliminary report produced in
August (GAI, 1997). At this stage, a full Phase II abandoned mine assessment has not
been completed because of the:potential for a deeper coal seam beneath Parcel A. We
trust that the report is sufficient for your present purpose.
Please feel free to call us if you have any questions regarding the enclosed materials. We.
may be reached at(425) 883-0777.
Sincerely,
GOLDER ASSOC fiS.INC.
i
Ian Bish .; h.D.
Senior f ophysicist
David P. Findley
Associate
IB/DPF/ta
nzeiti.doc
Golder Associates
November 26, 1997 7 973-1212
References
BRH, 1997. Topographic survey for Opus Northwest: Oakesdale Ave SW&Monster Rd,
Renton, King County,Washington. Bush,Roed &Hutchings, Inc., 21st October 1997.
DNR, 1997. Letter dated February loth, 1997 from Timothy Walsh (Washington State
Department of Natural Resources) to Terra Associates, detailing;
1. Production figures for the mine as reported to the Sate Mine Inspector:
year tonnage
1927 120
1928 698
1929 1,434
1930 3,839
1931 195
2. Copy of the mine map for the Diamond mine, scale ---1:30, no date.
GAI, 1997. Preliminary abandoned mine assessment, letter dated August 22, 1997
with report from SubTerra. Golder Associates.Inc., 973-1212.
SubTerra 1997. Visual site reconnaissance and preliminary abandoned mine assessment,
proposed Oaksdale Business Park in Renton, Washington. 21 August 1997.
Golder Associates
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to 14 feet beneath weathered sandstone and siltstone. South.
Plate 3 Test Trench #3 - Coal Seam in the
Weathered Renton Formation Project No. 97-26
SubTerra, Inc. Golder Associates, Inc. 11/26/97
Monster Road Geophysical Investigation
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Plate 4 Test Trench No. 4 - Existing Sinkhole with
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Project No. 97-26
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Plate 5 Test Trench No. 5 - Coal Seam Beneath
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Plate 8 Test Trench No. 8 - Shallow Coal Seam
Pinches Out to the South in Old Strip Pit
Area. Project No. 97-26