HomeMy WebLinkAboutRS_Geotechnical_180925_v1.pdfRevised Geotechnical Report
King County South Treatment Plant
Biogas and Heat Systems Improvements
Renton, Washington
January 6, 2017
Submitted To:
Mr. Ian McKelvey
Brown and Caldwell
701 Pike Street, Suite 1200
Seattle, Washington 98101
By:
Shannon & Wilson, Inc.
400 N 34th Street, Suite 100
Seattle, W ashington 98103
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TABLE OF CONTENTS
Page
1.0 INTRODUCTION ..................................................................................................................1
2.0 PROJECT AND SITE DESCRIPTION .................................................................................1
3.0 PROJECT SITE GEOLOGY .................................................................................................2
3.1 Puget Rock Group (Renton Formation) .....................................................................2
3.2 Alluvial Fan Deposits .................................................................................................2
3.3 Organic Deposits ........................................................................................................2
3.4 Floodplain Deposits ....................................................................................................2
3.5 Fill ..............................................................................................................................2
4.0 EXISTING SUBSURFACE EXPLORATIONS ...................................................................3
5.0 SUBSURFACE EXPLORATION AND LABORATORY TESTING .................................3
6.0 SUBSURFACE CONDITIONS .............................................................................................4
7.0 CONCLUSIONS AND RECOMMENDATIONS .................................................................5
7.1 Seismic Design Considerations ..................................................................................5
7.1.1 Site Class ......................................................................................................5
7.1.2 Seismic Design Parameters ..........................................................................5
7.1.3 Earthquake-induced Geologic Hazards........................................................6
7.2 Foundations ................................................................................................................7
7.2.1 Spread Footings ...........................................................................................7
7.2.2 Mat Foundation ............................................................................................7
7.2.3 Stone Column Ground Improvement ...........................................................8
7.2.4 Driven Steel Piles .........................................................................................8
7.2.5 Augercast Piles.............................................................................................8
7.3 Lateral Load Resistance .............................................................................................9
7.4 Site Grading and Excavation ....................................................................................10
7.5 Fill Placement and Compaction ...............................................................................10
7.6 Wet Weather Earthwork ...........................................................................................10
7.7 Construction Monitoring ..........................................................................................11
8.0 LIMITATIONS ....................................................................................................................11
9.0 REFERENCES .....................................................................................................................13
TABLE OF CONTENTS (cont.)
Page
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TABLE
1 Seismic Design Parameters ......................................................................................5
FIGURES
1 Vicinity Map
2 Site and Exploration Plan
3 Generalized Subsurface Profile A-A’
4 Generalized Subsurface Profile B-B’
5 Estimated Axial Augercast Pile Resistance 12-inch Diameter – Post-Seismic
6 Estimated Axial Augercast Pile Resistance 24-inch Diameter – Post-Seismic
APPENDICES
A Subsurface Explorations
B Geotechnical Laboratory Results
C Important Information About Your Geotechnical/Environmental Report
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REVISED GEOTECHNICAL REPORT
KING COUNTY SOUTH TREATMENT PLANT
BIOGAS AND HEAT SYSTEMS IMPROVEMENTS
RENTON, WASHINGTON
1.0 INTRODUCTION
This revised report presents the results of our subsurface explorations and geotechnical
assessment for the proposed design and construction of new biogas and heat exchange facilities
(Facility) at the King County Wastewater Treatment Division’s South Plant, located as shown in
the Vicinity Map, Figure 1. This report is revised to clarify our recommendations for foundation
design following review comments received from the Owner’s technical review staff.
The project will consist of a gas upgrading room and a boiler or HXT building. The new facility
is expected to replace the existing scrubbers in phases while existing facilities maintain the
ability to deliver biogas. Our services have been performed in general accordance with our
Professional Services Subcontract 24825, Standard Subcontract for Geotechnical Services, King
County – South Plant Biogas and Heat Systems Improvements. Our services included review of
existing subsurface data, performing two subsurface explorations, and performing engineering
analyses to develop recommendations for foundation design and associated earthwork for the
project.
2.0 PROJECT AND SITE DESCRIPTION
The proposed Facility will be located in a vacant field at the north side of the King County South
Plant. It will be constructed directly west of the existing digesters and Solids MCC Building.
The Facility will be placed between Road “N” and Road “X.” The majority of the proposed
Facility site is located at a topographically high point within the plant area on a mound of fill that
slopes up from surrounding ground surface by approximately 10 feet. We understand that this
mound is to be removed and the project site is to be graded to surrounding surface elevation.
According to drawing G3142, provided by Brown and Caldwell, the gas upgrading room will be
88 feet long by 65 feet wide, and the HXT building will be 58 feet long by 40 feet wide. We
understand that maximum loads applied by the Facility are expected to not exceed 1,500 pounds
per square foot. At this time, we do not know the magnitude of individual column loads.
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3.0 PROJECT SITE GEOLOGY
Our experience with projects at this location and our recent subsurface exploration indicates that
the following geologic units (as encountered from lower to higher elevation) are present at the
project site:
3.1 Puget Rock Group (Renton Formation)
The site is underlain by rock consisting of the Renton Formation, which is part of the Puget Rock
Group. It consists of dark brown to grayish-brown, fine- to coarse-grained, iron-oxide-stained
sandstone exhibiting a varying degree of weathering, with beds of coal, carbonaceous siltstone,
and claystone. Existing rock outcroppings and the results of subsurface explorations indicate
that the bedrock contact dips sharply to the south and the east. The Renton Formation is
typically encountered during subsurface explorations around the north and west sides of the
South Plant.
3.2 Alluvial Fan Deposits
Alluvial fan deposits consist of varying thickness of loose to dense, gray to dark gray sand and
sand with gravel. Silty sand containing shells and wood fragments also occur within this
formation. Alluvial fan deposits generally possess a relatively high shear strength and low
compressibility.
3.3 Organic Deposits
The sediments comprising this formation consist of peat; soft, organic silts; and clayey silts.
Their thickness appears to decrease from west to east at the South Plant. These deposits exhibit
low shear strength and high compressibility.
3.4 Floodplain Deposits
The floodplain deposits consist of very loose to medium dense sand and silt layers. They exhibit
considerable variation in their engineering properties due to their depositional nature.
3.5 Fill
Fill at the project site consists of a silty sand layer of variable thickness. Our subsurface
explorations indicate that fill is present to depths of about eight to 25 feet below ground surface
(bgs) at the location of the proposed Facility. The thickness of this layer is greatest below the
center of the fill mound.
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4.0 EXISTING SUBSURFACE EXPLORATIONS
The logs of soil borings and test pits performed near the site since 1982 are presented in
Appendix A, Subsurface Explorations. The locations of the explorations are shown in the Site
and Exploration Plan, Figure 2. We reviewed the explorations to estimate the approximate
elevation of bedrock at the project site. As shown in the Cross Sections provided in Figures 3
and 4, only two of these explorations, Boring B-301 and Test Pit 2, encountered sandstone at
relatively high elevations. These explorations were performed to the west and the southwest of
the proposed Facility site, and their results reinforce the assessment that Renton Formation
sandstone dips to the east across the South Plant grounds. The remaining previous explorations
generally encountered alluvial sand and silty sand, as well as floodplain deposits, but did not
encounter bedrock.
5.0 SUBSURFACE EXPLORATION AND LABORATORY TESTING
Our recent explorations consisted of two borings performed at the approximate locations shown
in the Site and Exploration Plan, Figure 2. The borings were performed on the southeast and
northwest sides of the proposed Facility site. The borings, designated B-1 and B-2, were drilled
on July 15 and 22 by Holocene Drilling, Inc. (Holocene) of Puyallup, Washington, under
subcontract to Shannon & Wilson, Inc. Holocene used hollow-stem auger techniques to drill
boring B-1 and mud rotary techniques to drill boring B-2. Boring B-1 was drilled to a depth of
approximately 91.5 feet and boring B-2 was drilled to a depth of approximately 121.5 feet. Both
borings were observed by a geologist or engineer from our firm who visually identified the
retrieved soils, obtained representative soil samples, and compiled logs of the explorations. A
Soil Classification and Log Key is presented in Figure A-1 of Appendix A, and logs of the
borings are presented in Figures A-2 and A-3.
We detected a hydrocarbon odor at a depth of about 25 feet while drilling boring B-1. A sample
from this depth was collected and delivered to Fremont Analytical, Inc. of Seattle, Washington,
for environmental testing to assist with disposal characterization of exploration-derived waste.
Lab analysis did not detect petroleum hydrocarbons within the sample.
The geotechnical laboratory testing program was directed towards determining index properties
of the native soils. The tests performed in our Seattle laboratory included water content analysis
and analysis of grain size distribution. The water content tests were conducted in accordance
with ASTM International (ASTM) Designation: D2216, Standard Test Methods for Laboratory
Determination of Water (Moisture) Content of Soil and Rock by Mass. The grain size
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distribution tests were conducted in accordance with ASTM Designation: D422, Standard Test
Method for Particle-Size Analysis of Soils. The results of the water content tests are shown in
the boring logs, Figures A-2 and A-3, and the results of the grain size distribution tests are shown
in Appendix B.
6.0 SUBSURFACE CONDITIONS
The results of borings B-1 and B-2 indicated that the subsurface soils below the proposed
Facility location are comprised of the following layers:
Holocene Fill, consisting primarily of very loose to medium dense, brown, silty sand
with gravel. Fill was encountered from the surface to a depth of about 25 feet bgs at
boring B-1 and about 8 feet bgs at boring B-2.
Holocene Alluvium, consisting primarily of medium dense to very dense, gray to dark
gray, poorly graded sand and poorly graded sand with gravel. This layer extended to
about 80 feet bgs at boring B-1 and 85 feet bgs at boring B-2.
Layers of floodplain and organic deposits, such as Holocene Lacustrine and Holocene
Estuarine. These soils consisted primarily of medium stiff to hard silt and peat, and
were found scattered within the Holocene Alluvium material. Layers ranged in
thickness from about 2 to 22 feet. A layer of soft to stiff, gray silt was encountered
from 8 to 30 feet bgs, and a layer of very soft to soft, gray silt was encountered from
about 40 to 60 feet bgs at boring B-2.
Decomposed sandstone, representative of Renton Formation rock. This material was
very low strength and completely to highly weathered. Coal was found interbedded
within the layer, and coal clasts were observed throughout the layer. The sandstone
was encountered at a depth of about 80 feet bgs at boring B-1 and 111 feet bgs at
boring B-2, indicating that its elevation at the proposed Facility site is highly variable
depending on location, and dips down to the east.
Groundwater was observed at about 30 feet bgs (elevation 106 feet) at boring B-1. Mud rotary
drilling at boring B-2 prevented accurate measurement of the groundwater level. Previous
explorations near the site of the proposed Facility found groundwater at higher elevations than
boring B-1. For example, Boring 202, located as shown in Figure 1 and presented in
Appendix A, encountered groundwater at a depth of 2 feet (elevation 111 feet). However,
groundwater levels at this boring were recorded in April. Groundwater elevation at the South
Plant grounds is likely dependent on seasonal weather patterns, and excavation during the winter
months may encounter groundwater at much higher elevations than 106 feet. Wet weather
earthwork is discussed further in Section 7.6.
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7.0 CONCLUSIONS AND RECOMMENDATIONS
7.1 Seismic Design Considerations
7.1.1 Site Class
The proposed Facility site is underlain primarily by loose to medium dense sands and
silts to a depth of about 50 to 60 feet. Given the nature of these sediments and their
susceptibility to liquefaction discussed in Section 7.1.2, we have identified the site classification
as Site Class E.
7.1.2 Seismic Design Parameters
Seismic design of the Facility will be based on levels of ground motion anticipated for
events with different return periods. The 2015 International Building Code (IBC) design code is
based on levels of ground motion anticipated for an event with a 2,500-year recurrence interval,
while the Basic Safety Earthquake-1 (BSE-1) hazard level is based on levels of ground motion
anticipated for an event with a 475-year recurrence interval (International Code Council, 2015).
We estimated seismic design parameters for the 2,475-year earthquake using the mapped
spectral accelerations provided by the U.S. Geological Survey (USGS) and the site classification
procedures outlined in IBC 2015 1615. We estimated seismic design parameters for the
475-year earthquake using the USGS probabilistic seismic hazard deaggregation tool and the
conversion factors given in ASCE/SEI 7.11 (2010). The maximum considered spectral
accelerations for short periods and the 1-second period are shown in Table 1, as well as the
mapped SS and S1 values in the vicinity of the site and the soil response coefficients FA and FV
corresponding to Site Class E.
TABLE 1
SEISMIC DESIGN PARAMETERS
Return
Period
(years) SS (g’s) S1 (g’s) FA FV
SMS
(g’s)
SM1
(g’s)
SDS
(g’s)
SD1
(g’s)
2,475 1.46 0.54 0.9 2.4 1.31 1.30 0.87 0.87
475 0.67 0.22 1.2 3.2 0.81 0.70 0.81 0.70
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We estimated that the site-class adjusted peak ground acceleration is 0.55g for the
2,475-year return period and 0.36g for the 475-year return period.
7.1.3 Earthquake-induced Geologic Hazards
Earthquake-induced geologic hazards that may affect a given site include ground surface
fault rupture; liquefaction and its associated effects (e.g., loss of shear strength, bearing capacity
failure, loss of lateral support, ground oscillation, slumping, lateral spreading, and settlement);
and slope instability. The following provides a brief discussion of these hazards.
The project site is located about 5 to 6 miles south to southwest of the Seattle Fault Zone.
This is considered to be an active fault structure by the USGS. However, the potential for
ground surface rupture is not a design issue at the subject site due to its distance to the fault zone
and the relatively long repeat times for fault movement.
Soil liquefaction is a phenomenon in which pore pressure in loose, saturated, granular
soils increases during ground shaking to a level near the initial effective stress, resulting in a
reduction of shear strength of the soil (quicksand-like condition). As a result of this reduction in
shear strength, ground settlement and lateral spreading (ground movement on very gentle slopes)
can occur. Results from boring B-1 indicate that liquefaction may occur at the proposed Facility
site within soil layers between about 30 to 60 feet bgs during an earthquake with a 2,475-year or
475-year recurrence interval. This is due to the relatively loose nature of the soils below the
groundwater level. Differential settlement of the ground surface should be expected under these
conditions. For planning purposes, we recommend assuming that differential settlement could be
about 50 percent of the total settlement across the length of any given structure. The actual
amount of differential settlement will depend on the load distribution and soil-structure
interaction.
In our opinion, shallow spread footings bearing in soils at the proposed Facility site will
be susceptible to liquefaction-induced settlements, while mat foundations or deep-foundation
elements such as piles or shafts bearing in denser soils below approximately 60 feet bgs will
mitigate structural settlement due to liquefaction. Section 7.2 discusses foundation
considerations.
Current plans call for the existing mound to be removed and the proposed Facility to be
constructed on a relatively flat site. Slope instability due to ground shaking is therefore low and
not considered a design issue for this project.
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7.2 Foundations
We understand that various factors will influence the selection of a foundation for the proposed
Facility. Among these are cost considerations, competency of load-bearing subsurface soils, and
allowance for building settlement under static and dynamic conditions. We understand that the
Facility may have a basement, which would affect total depth of excavation and condition of
bearing soils at the mat foundation bearing elevation. Based on our additional analyses of
liquefaction-induced settlements and discussions with the project structural engineer, we
recommend that the facility be supported on a mat foundation. We assume that the mat
foundation will bear at or below elevation 123 feet where medium dense silty sand is present as
the subgrade soil.
Five foundation systems that have been considered for this project are discussed below:
7.2.1 Spread Footings
Spread footings are the most common type of foundation due to their ease of installation
and relatively low cost. On dense, competent soils, spread footings would typically provide
adequate resistance to loads comparable to those proposed for the Facility. The existing mound
has likely compressed (preloaded) the underlying fill; however, the fill layer extends to 25.5 feet
below the top of the mound. Therefore, variable fill materials will be present below the base of
the proposed Facility and the preloading effects cannot be relied upon for isolated spread
footings.
Spread footings are susceptible to differential settlement when constructed on variable fill
materials and potentially liquefiable soils. We do not recommend the use of spread footings due
to the risk of static differential settlement and the risk of differential settlement due to
liquefaction following an earthquake.
7.2.2 Mat Foundation
Although more expensive than traditional spread footings, a mat foundation would reduce
the potential for differential settlement by evenly distributing structural loads. This foundation
type offers more structural continuity and flexural strength than a system of spread footings, and
would provide better stability on loose soils and soils that may liquefy. A mat foundation would
limit overall settlement at the proposed Facility, including settlement brought on by seismic
conditions. A mat foundation may be designed for a maximum allowable bearing pressure of
1,000 pounds per square foot, which is intended to not exceed the preload stress that the bearing
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soils have experienced in the past due to the mound of fill that currently exists on the building
site. We understand that the structural engineer will perform finite element modelling of the
building and mat foundation. For finite element modelling we recommend assuming a modulus
of subgrade reaction, k, of 200 pounds per square inch per inch.
7.2.3 Stone Column Ground Improvement
Stone column installation uses a vibrator to create a shaft of densely compacted crushed
rock. This type of foundation would improve the stability of subsurface soils at the proposed
Facility site, and may be installed through layers of silt, such as those found at depths of about 10
to 20 feet bgs. If stone columns are selected, we would recommend they extend down to the
dense soil layer encountered at 65 and 60 feet deep in borings B-1 and B-2, respectively. This
foundation method could significantly reduce the risk of static and dynamic settlement. Stone
column installation is relatively expensive and may cause localized vibration during installation
that may affect nearby buildings and buried utilities.
7.2.4 Driven Steel Piles
Driven steel piles would significantly reduce settlement by transferring structural loads to
deeper, competent sands and gravels. Driven piles also reduce soil export volumes and provide
an instant field verification of pile capacity. Pile driving produces significant noise, and we
understand that this may prohibit its use at the proposed Facility site.
7.2.5 Augercast Piles
Augercast pile installation consists of drilling a hollow-stem auger to the required depth,
then injecting grout as the auger is removed. Reinforcing steel is then lowered into the hole.
Installation costs are typically lower than those of cast-in-place piers and driven piles, and noise
and vibration levels are much lower than those with driven piles. Augercast piles can be
installed to depths of 80 to 90 feet, which would provide embedment into dense alluvial material
at the proposed Facility site. Transferring loads to this layer would mitigate the risk of both
static and dynamic settlement, as the majority of structural loads would bear in non-liquefying
soils.
Based on our subsurface explorations and engineering analyses, we recommend that the
proposed Facility be supported on this type of foundation if a pile foundation is selected. We
performed a preliminary analysis of augercast pile capacity at the project site using an in-house
computer program. The analysis used a single-pile case and did not consider group effects. It is
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our opinion that seismic loading conditions control deep foundation design based on the results
of our analysis. Post-earthquake settlements in liquefied soils could induce downdrag loads on
augercast piles on the order of 95 kips or 190 kips for 12-inch- and 24-inch-diameter piles,
respectively. The short-term downdrag loading caused by liquefaction can typically be
accommodated by the piles’ ultimate capacity, with the net result being a temporary reduction to
the factor of safety used in the design of the piles. Depth versus allowable pile bearing capacity
for the seismic case is shown in Figures 5 and 6. Although we anticipate that the end-bearing
depth for augercast piles will be about 75 to 80 feet bgs, pile lengths may differ across the site
due to variable elevation of the alluvial layer. Unit cost pricing for augercast piles should be
included in the project budget. A contingency for extra pile costs should be included in the
project budget.
Our analysis considered 12-inch- and 24-inch-diamater augercast piles and assumed that
the top 10 feet of fill near boring B-1 will be excavated before pile installation. Other pile
diameters may be appropriate and should be evaluated after the project structural engineer has
determined vertical and lateral foundation loads. We should be retained to assist the structural
engineer in determining the optimum pile type, size, and depth for the anticipated column loads.
It is our opinion that augercast pile foundations would experience relatively minor
settlements during loading. We estimate total augercast pile settlements would be less than
½ inch. Because of the granular nature of the end-bearing soils, these settlements would be
primarily elastic and would occur as the load is applied. No long-term static settlements of
earthquake-induced settlements are anticipated.
7.3 Lateral Load Resistance
Lateral loads may be resisted by pile foundations, friction along buried walls, and by passive soil
resistance against buried portions of a foundation. Footings or mat foundations (if used) that
bear in the existing fill may be designed using a coefficient of base friction of 0.4. Passive soil
resistance against the buried portions of foundations may be calculated based on an equivalent
fluid density of 300 pounds per cubic foot. This value for passive soil resistance includes a
factor of safety of 1.5 on the ultimate soil strength in order to limit allowable lateral
deformations. This value is based on the assumption of a horizontal surface extending beyond
the footing for a distance of at least two times the depth of embedment. Passive resistance
should be ignored in the upper 12 inches unless it is specifically required for lateral stability and
the backfill in this zone is densely compacted structural fill. It should be ignored entirely if
future development could result in removal of the soils providing lateral resistance.
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7.4 Site Grading and Excavation
Excavations can be accomplished with conventional excavating equipment, such as a dozer,
front-end loader, or backhoe. For planning purposes, we recommend that temporary
unsupported open-cut slopes in the very loose to medium dense fill be no steeper than 1.5
Horizontal to 1 Vertical. We recommend that all exposed cut slopes be protected with a
waterproof covering during periods of wet weather to reduce sloughing and erosion. Final
grades should slope away from the Facility to prevent ponding of water next to the structure.
7.5 Fill Placement and Compaction
Some backfill may be required for locations around and under Facility foundations and over
subsurface pipe trenches. In our opinion, the on-site fill that was observed in the upper 24 feet of
boring B-1 and upper 8 feet of boring B-2 is acceptable for use as trench backfill and backfill
around structures.
Any fill placed beneath structures should consist of imported structural fill. Structural fill should
consist of relatively well-graded sand or sand and gravel having a maximum particle size of
about 3 inches. It should contain less than 20 percent fines (material passing the No. 200 sieve,
based on the ¾-inch minus fraction) and, during wet weather or wet conditions, it should contain
no more than 5 percent fines. Structural fill should not contain organics or deleterious material.
All fill should be placed in horizontal lifts and compacted to at least 95 percent of its Modified
Proctor maximum density (ASTM D1557), and should be verified to be in a dense and
unyielding condition. The thickness of loose lifts should not exceed 10 inches for heavy
equipment compactors and 6 inches for hand-operated compactors.
7.6 Wet Weather Earthwork
Earthwork would most easily be accomplished during the normally drier months of June through
mid-October. It is our opinion that earthwork performed during the wet-weather months will
prove more costly. The condition of silty sand will deteriorate rapidly when exposed to moisture
and construction activity. If shallow foundations are used, this could lead to deeper footing
excavations than anticipated. The following recommendations are applicable if earthwork is to
be accomplished in wet weather or in wet conditions:
Fill material should consist of clean, granular soil, of which not more than 5 percent
by dry weight passes the No. 200 mesh sieve, based on wet-sieving the fraction
passing the ¾-inch sieve. The fines should be non-plastic. Such soil would need to
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be imported to the site. The identification of suitable wet-weather backfilling
material should be made by a geotechnical engineer from our firm experienced in
wet-weather construction.
The ground surface in the construction area should be sloped and sealed with a
smooth-drum, vibratory roller or equivalent to promote the rapid runoff of
precipitation, to prevent surface water from flowing into excavations, and to prevent
ponding of water. Soils that become too wet for compaction should be removed and
replaced with clean granular soil.
Excavation and placement of structural fill material should be observed on a full-time
basis by a geotechnical engineer or technician experienced in wet-weather earthwork
to determine that all unsuitable materials are removed and suitable compaction and
site drainage is achieved.
Covering work areas, soil stockpiles, or slopes with plastic; sloping, ditching, sumps,
dewatering, and other measures should be employed as necessary to permit proper
completion of the work. Bales of straw and/or geotextile silt fences should be
strategically located to control soil movement and erosion.
The above recommendations for wet weather earthwork should be incorporated into the contract
specifications.
7.7 Construction Monitoring
We recommend that Shannon & Wilson, Inc. be retained to monitor the geotechnical aspects of
construction activities at the site including the preparation of subgrades for the structure (if
shallow foundations or slab-on-grade floors are utilized), installation of piles, augercast piles, or
stone columns (if deep foundations are utilized), and compaction of structural fill or backfill. If
driven steel piles or augercast piles are installed, we recommend that a Shannon & Wilson, Inc.
representative be on site for the entire installation.
Unanticipated soil conditions are commonly encountered and cannot be fully determined by
merely taking soil samples or test borings. Such unexpected conditions may require the
Contractor to make adjustments in his procedures to attain a properly constructed project. Some
contingency fund is recommended to accommodate potential extra costs related to unexpected
conditions.
8.0 LIMITATIONS
The analyses, conclusions, and recommendations presented in this report are based on the site
conditions as they presently exist and assume that the explorations are representative of the
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9.0 REFERENCES
American Society of Civil Engineers, 2010, Minimum design loads for buildings and other
structures (3rd printing): Reston, Va., American Society of Civil Engineers, ASCE
Standard ASCE/SEI 7-10.
International Code Council, Inc., 2015, International building code: Country Club Hills, Ill.,
International Code Council, Inc., 690 p.
5
405
167
Renton
Lake Washington
Tukwila
dale
Seattle
PROJECT
LOCATION
SW
Oa
k
es
Ave
VICINITY MAP
FIG. 1
Map adapted from aerial imagery provided by
Google Earth Pro, reproduced by permission
granted by Google Earth ™ Mapping Service.
NOTE
Filename: J:\211\22210\001\21-1-22210-001 Vic Map.dwg Date: 01-05-2017 Login: mjmSeattle
Washington
Project
Location
90
5
97
MT
21-1-22210-001
King County South Biogas Plant
Renton, Washington
January 2017
0 3,000 6,000
Approximate Scale in Feet
A
A'B-403B-202B-301BB'B-501TP-2B-1B-221-1-22210-001FIG. 2Geotechnical and Environmental ConsultantsSHANNON & WILSON, INC.SITE AND EXPLORATION PLANKing County South Biogas PlantRenton, WashingtonJanuary 2017Filename: J:\211\22210\001\21-1-22210-001 Plan & Profile.dwg Layout: Site Plan Date: 01-05-2017 Login: mjm
B-1ABoring Designation andApproximate LocationTest Pit Designation andApproximate LocationGeneralizedSubsurface Profile(See Figures 3 and 4)LEGENDApproximate Facility LocationMap adapted from aerial imagery provided byGoogle Earth Pro, reproduced by permissiongranted by Google Earth ™ Mapping Service.NOTEMTTP-20100200Approximate Scale in Feet
7-22-2016?Approximate Elevation in Feet 150SouthwestANortheastA'B-403B-2B-202B-301500(Proj. 15' NW)(Proj. 36' NW)(Proj. 81' NW)(Proj. 17' NW)10010-15-19824-6-19823-16-1983???SANDSTONE(Renton Formation)Sand and Silt(HoloceneAlluviual andLacustrine)SANDSTONE(Renton Formation)Dense to very denseSand and GravelSand and Silt(HoloceneAlluviual andLacustrine)Sand and Silt(Holocene Alluviualand Lacustrine)??????Approximate Elevation in Feet 150500100B-B'Approximate ExistingGround Surface atTime of Boring21-1-22210-001FIG. 3Geotechnical and Environmental ConsultantsSHANNON & WILSON, INC.GENERALIZED SUBSURFACEPROFILE A-A'King County South Biogas PlantRenton, WashingtonJanuary 2017Filename: J:\211\22210\001\21-1-22210-001 Plan & Profile.dwg Layout: A-A' Date: 01-05-2017 Login: mjm
050100Vertical Scale in FeetVertical Exaggeration = 2XBoring DesignationProjected Distance and DirectionApproximate Elevation in FeetApproximate Geologic ContactBottom of BoringDate of Completion(Proj. 17' NW)??10-15-1982LEGENDB-3010100200Horizontal Scale in Feet(Elev. ~29')(Elev. ~118')(Elev. ~113')(Elev. ~127')(Elev. ~114')
7-22-2016Approximate Elevation in Feet 150WestBEastB'B-2500(Proj. 82' S)100??SANDSTONE(Renton Formation)Dense to very denseSand and GravelSand and Silt(HoloceneAlluviual andLacustrine)Approximate Elevation in Feet 150500100A-A'TP-2(Proj. 0')200200B-1(Proj. 0')B-501(Proj. 0')SANDSTONE(Renton Formation)Sand and Silt(HoloceneAlluviual andLacustrine)?????????Approximate ExistingGround Surface atTime of Boring/Test Pit7-15-201611-21-19836-26-1981(Elev. ~182')(Elev. ~136')(Elev. ~127')(Elev. ~135')21-1-22210-001FIG. 4Geotechnical and Environmental ConsultantsSHANNON & WILSON, INC.GENERALIZED SUBSURFACEPROFILE B-B'King County South Biogas PlantRenton, WashingtonJanuary 2017Filename: J:\211\22210\001\21-1-22210-001 Plan & Profile.dwg Layout: B-B' Date: 01-05-2017 Login: mjm
050100Vertical Scale in FeetVertical Exaggeration = 2XBoring or Test Pit DesignationProjected Distance and DirectionApproximate Elevation in FeetGroundwater Level During DrillingApproximate Geologic ContactBottom of Boring or Test PitDate of Completion(Proj. 82' S)??10-15-1982LEGENDB-2(Elev. ~29')0100200Horizontal Scale in Feet
GENERAL NOTES
1. The analyses are based on a single augercast pile and do not
consider group action of closely spaced augercast piles (closer than
2.5 diameters, center to center). Once final pile group sizes and
spacings are determined, the axial capacity of the pile group should
be re-evaluated.
2. Total augercast pile capacity is a summation of its side and base
resistances. Ultimate resistances shown on the plot above do not
include a factor of safety (FS).
ASSUMED SUBSURFACE
PROFILE
Based on Nearby Exploration:
B-1
0
10
20
30
40
50
60
70
80
0 50 100 150 200
DEPTH (feet)ULTIMATE RESISTANCE (kips)
Side Resistance (Seismic)
Base Resistance (Seismic)
Total Resistance
Estimated Liquefied Zone
Estimated Liquefied Zone
Add Downdrag Loads to Other
Foundation Loads
Loose to medium dense,
gray, Silty Sand with Gravel
(SM)
0'
Medium stiff to stiff, OL/ML
14'
Medium dense, dark gray,
Poorly Graded Sand (SP)
18'
Hard, brown Silt (ML)28'
Medium dense to dense,
dark gray, Poorly Graded
Sand (SP)
31'
Loose to medium dense,
gray-brown, Silty Sand (SM)
38'
Dense, dark gray, Poorly
Graded Sand with Gravel (SP)
54'
Decomposed Sandstone
70'
Subsurface profile assumes
~10 feet of excavation to
remove fill mound
King County South Biogas Plant
Renton, Washington
Geotechnical and Environmental ConsultantsSHANNON & WILSON, INC.FIG.5
ESTIMATED AXIAL AUGERCAST
PILE RESISTANCE
12-INCH DIAMATER -POST -SEISMIC
January 2017 21-1-22210-001
GENERAL NOTES
1. The analyses are based on a single augercast pile and do not
consider group action of closely spaced augercast piles (closer than
2.5 diameters, center to center). Once final pile group sizes and
spacings are determined, the axial capacity of the pile group should
be re-evaluated.
2. Total augercast pile capacity is a summation of its side and base
resistances. Ultimate resistances shown on the plot above do not
include a factor of safety (FS).
ASSUMED SUBSURFACE
PROFILE
Based on Nearby Exploration:
B-1
0
10
20
30
40
50
60
70
80
0 100 200 300 400 500
DEPTH (feet)ULTIMATE RESISTANCE (kips)
Side Resistance (Seismic)
Base Resistance (Seismic)
Total Resistance
Estimated Liquefied Zone
Estimated Liquefied Zone
Add Downdrag Loads to Other
Foundation Loads
Loose to medium dense,
gray, Silty Sand with Gravel
(SM)
0'
Medium stiff to stiff, OL/ML
14'
Medium dense, dark gray,
Poorly Graded Sand (SP)
18'
Hard, brown Silt (ML)28'
Medium dense to dense,
dark gray, Poorly Graded
Sand (SP)
31'
Loose to medium dense,
gray-brown, Silty Sand (SM)
38'
Dense, dark gray, Poorly
Graded Sand with Gravel (SP)
54'
Decomposed Sandstone
70'
Subsurface profile assumes
~10 feet of excavation to
remove fill mound
King County South Biogas Plant
Renton, Washington
Geotechnical and Environmental ConsultantsSHANNON & WILSON, INC.FIG.6
ESTIMATED AXIAL AUGERCAST
PILE RESISTANCE
24-INCH DIAMATER -POST -SEISMIC
January 2017 21-1-22210-001
21-1-22210-001
APPENDIX A
SUBSURFACE EXPLORATIONS
21-1-22210-001-R1f-AA/wp/lkn 21-1-22210-001
A-i
APPENDIX A
SUBSURFACE EXPLORATIONS
TABLE OF CONTENTS
FIGURES
A-1 Soil Description and Log Key (3 sheets)
A-2 Log of Boring B-1 (2 sheets)
A-3 Log of Boring B-2 (3 sheets)
A-4 Boring No. B-403 (Converse Consultants) (2 sheets)
A-5 Log of Test Pit No. 2 (Converse Ward Davis Dixon
A-6 Boring No. B-301 (Converse Consultants)
A-7 Boring No. 202 (Converse Consultants) (2 sheets)
A-8 Boring No. B-501 (Converse Consultants)
21-1-22210-001
APPENDIX B
GEOTECHNICAL LABORATORY RESULTS
21-1-22210-001-R1f-AB/wp/lkn 21-1-22210-001
B-i
APPENDIX B
GEOTECHNICAL LABORATORY RESULTS
TABLE OF CONTENTS
FIGURES
B-1 Grain Size Distribution Plot, B-1
B-2 Grain Size Distribution Plot B-2
21-1-22210-001
APPENDIX C
IMPORTANT INFORMATION ABOUT YOUR
GEOTECHNICAL/ENVIRONMENTAL REPORT
Page 1 of 2 1/2017
SHANNON & WILSON, INC.
Geotechnical and Environmental Consultants
Dated:
Attachment to and part of Report 21-1-22210-001
Date: January 6, 2017
To: Mr. Ian McKelvey
Brown and Caldwell
IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL/ENVIRONMENTAL
REPORT
CONSULTING SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES AND FOR SPECIFIC CLIENTS.
Consultants prepare reports to meet the specific needs of specific individuals. A report prepared for a civil engineer may not be adequate
for a construction contractor or even another civil engineer. Unless indicated otherwise, your consultant prepared your report expressly
for you and expressly for the purposes you indicated. No one other than you should apply this report for its intended purpose without
first conferring with the consultant. No party should apply this report for any purpose other than that originally contemplated without
first conferring with the consultant.
THE CONSULTANT'S REPORT IS BASED ON PROJECT-SPECIFIC FACTORS.
A geotechnical/environmental report is based on a subsurface exploration plan designed to consider a unique set of project-specific
factors. Depending on the project, these may include: the general nature of the structure and property involved; its size and
configuration; its historical use and practice; the location of the structure on the site and its orientation; other improvements such as
access roads, parking lots, and underground utilities; and the additional risk created by scope-of-service limitations imposed by the
client. To help avoid costly problems, ask the consultant to evaluate how any factors that change subsequent to the date of the report
may affect the recommendations. Unless your consultant indicates otherwise, your report should not be used: (1) when the nature of
the proposed project is changed (for example, if an office building will be erected instead of a parking garage, or if a refrigerated
warehouse will be built instead of an unrefrigerated one, or chemicals are discovered on or near the site); (2) when the size, elevation,
or configuration of the proposed project is altered; (3) when the location or orientation of the proposed project is modified; (4) when
there is a change of ownership; or (5) for application to an adjacent site. Consultants cannot accept responsibility for problems that may
occur if they are not consulted after factors which were considered in the development of the report have changed.
SUBSURFACE CONDITIONS CAN CHANGE.
Subsurface conditions may be affected as a result of natural processes or human activity. Because a geotechnical/environmental report
is based on conditions that existed at the time of subsurface exploration, construction decisions should not be based on a report whose
adequacy may have been affected by time. Ask the consultant to advise if additional tests are desirable before construction starts; for
example, groundwater conditions commonly vary seasonally.
Construction operations at or adjacent to the site and natural events such as floods, earthquakes, or groundwater fluctuations may also
affect subsurface conditions and, thus, the continuing adequacy of a geotechnical/environmental report. The consultant should be kept
apprised of any such events, and should be consulted to determine if additional tests are necessary.
MOST RECOMMENDATIONS ARE PROFESSIONAL JUDGMENTS.
Site exploration and testing identifies actual surface and subsurface conditions only at those points where samples are taken. The data
were extrapolated by your consultant, who then applied judgment to render an opinion about overall subsurface conditions. The actual
interface between materials may be far more gradual or abrupt than your report indicates. Actual conditions in areas not sampled may
differ from those predicted in your report. While nothing can be done to prevent such situations, you and your consultant can work
together to help reduce their impacts. Retaining your consultant to observe subsurface construction operations can be particularly
beneficial in this respect.
Page 2 of 2 1/2017
A REPORT'S CONCLUSIONS ARE PRELIMINARY.
The conclusions contained in your consultant's report are preliminary because they must be based on the assumption that conditions
revealed through selective exploratory sampling are indicative of actual conditions throughout a site. Actual subsurface conditions can
be discerned only during earthwork; therefore, you should retain your consultant to observe actual conditions and to provide conclusions.
Only the consultant who prepared the report is fully familiar with the background information needed to determine whether or not the
report's recommendations based on those conclusions are valid and whether or not the contractor is abiding by applicable
recommendations. The consultant who developed your report cannot assume responsibility or liability for the adequacy of the report's
recommendations if another party is retained to observe construction.
THE CONSULTANT'S REPORT IS SUBJECT TO MISINTERPRETATION.
Costly problems can occur when other design professionals develop their plans based on misinterpretation of a
geotechnical/environmental report. To help avoid these problems, the consultant should be retained to work with other project design
professionals to explain relevant geotechnical, geological, hydrogeological, and environmental findings, and to review the adequacy of
their plans and specifications relative to these issues.
BORING LOGS AND/OR MONITORING WELL DATA SHOULD NOT BE SEPARATED FROM THE REPORT.
Final boring logs developed by the consultant are based upon interpretation of field logs (assembled by site personnel), field test results,
and laboratory and/or office evaluation of field samples and data. Only final boring logs and data are customarily included in
geotechnical/environmental reports. These final logs should not, under any circumstances, be redrawn for inclusion in architectural or
other design drawings, because drafters may commit errors or omissions in the transfer process.
To reduce the likelihood of boring log or monitoring well misinterpretation, contractors should be given ready access to the complete
geotechnical engineering/environmental report prepared or authorized for their use. If access is provided only to the report prepared for
you, you should advise contractors of the report's limitations, assuming that a contractor was not one of the specific persons for whom
the report was prepared, and that developing construction cost estimates was not one of the specific purposes for which it was prepared.
While a contractor may gain important knowledge from a report prepared for another party, the contractor should discuss the report with
your consultant and perform the additional or alternative work believed necessary to obtain the data specifically appropriate for
construction cost estimating purposes. Some clients hold the mistaken impression that simply disclaiming responsibility for the accuracy
of subsurface information always insulates them from attendant liability. Providing the best available information to contractors helps
prevent costly construction problems and the adversarial attitudes that aggravate them to a disproportionate scale.
READ RESPONSIBILITY CLAUSES CLOSELY.
Because geotechnical/environmental engineering is based extensively on judgment and opinion, it is far less exact than other design
disciplines. This situation has resulted in wholly unwarranted claims being lodged against consultants. To help prevent this problem,
consultants have developed a number of clauses for use in their contracts, reports, and other documents. These responsibility clauses
are not exculpatory clauses designed to transfer the consultant's liabilities to other parties; rather, they are definitive clauses that identify
where the consultant's responsibilities begin and end. Their use helps all parties involved recognize their individual responsibilities and
take appropriate action. Some of these definitive clauses are likely to appear in your report, and you are encouraged to read them closely.
Your consultant will be pleased to give full and frank answers to your questions.
The preceding paragraphs are based on information provided by the
ASFE/Association of Engineering Firms Practicing in the Geosciences, Silver Spring, Maryland
400 NORTH 34TH STREET, SUITE 100
P.O. BOX 300303
SEATTLE, WASHINGTON 98103
206-632-8020 FAX 206-695-6777
TDD 1-800-833-6388
www.shannonwilson.com 21-1-22210-002
December 8, 2017
Mr. Ian McKelvey
Brown and Caldwell
701 Pike Street, Suite 1200
Seattle, WA 98101
RE: GEOTECHNICAL REPORT ADDENDUM, BIOGAS AND HEAT SYSTEMS
IMPROVEMENTS PROJECTS, KING COUNTY SOUTH TREATMENT PLANT,
RENTON, WASHINGTON
Dear Mr. McKelvey:
We are pleased to submit this letter to serve as an addendum to our Revised Geotechnical Report
for the South Treatment Plant Biogas and Heat Systems Improvements project dated
January 6, 2017. This addendum summarizes our recent geotechnical evaluation of three
geotechnical issues that were not addressed in our previous report:
1. Infiltration rates to aid in the design of stormwater infiltration facilities
2. Pavement sections for a small area of driveway/parking
3. Evaluation of coal mine hazards
Our services were performed in accordance with Amendment No. Three to the Subcontract
between Brown and Caldwell and Shannon & Wilson, Inc. for Geotechnical Services, dated
June 5, 2017.
STORMWATER INFILTRATION RATES
Shannon & Wilson staff visited the proposed project site from October 9 to 12, 2017, to perform
pilot infiltration tests (PITs) to evaluate suitability of soils for infiltration facilities. Clearcreek
Contractors (Clearcreek), under subcontract to Shannon & Wilson, Inc., excavated three test pits
designated TP-1, TP-2, and TP-3 at locations determined by the project civil engineer, Davido
Consulting Group. The approximate locations of the test pits are shown on the attached
Ian McKelvey
Brown and Caldwell
December 8, 2017
Page 2 of 7
21-1-22210-002-L1f.docx/wp/s 21-1-22210-002
Figure 1 – Test Pit Locations. Clearcreek used a vacuum truck to pothole and locate subsurface
utilities prior to excavating the pits. Previously unknown utilities were encountered at all three
test pit locations before and during excavation. Photo 1 shows a presumed electrical conduit
running east to west at TP-2 at a depth of approximately 3 feet below ground surface (bgs).
Photo 1: Electrical Conduit Running East to West at TP-2.
Clearcreek used a mini excavator to excavate the test pits. TP-1 was excavated to a depth of
approximately 7 feet bgs, while TP-2 and TP-3 were excavated to a depth of approximately
10 feet bgs. Soils encountered during excavation generally consisted of dense, silty sand and
gravel, followed by soft, gray silt. After excavation, we performed PITs at each of the test pits.
PITs were performed in accordance with the 2017 City of Renton Surface Water Design Manual.
We filled each test pit with water to a depth of approximately 12 inches, then allowed the base of
the PITs to soak for six hours. We then performed constant head and falling head tests.
Ian McKelvey
Brown and Caldwell
December 8, 2017
Page 3 of 7
21-1-22210-002-L1f.docx/wp/s 21-1-22210-002
We observed relatively little infiltration at all three PITs during the constant and falling head
tests. At TP-1, we observed an infiltration rate of approximately 0.02 inch/hour (without
correction factor), while PIT data at TP-2 and TP-3 indicated negligible infiltration rates. Based
on these observations, in our opinion, water infiltration facilities are unfeasible at the depths
tested in all three PITs.
Following testing, Clearcreek backfilled the test pits with previously excavated soils. We spread
grass seed on the disturbed ground surface at TP-1 and TP-2, as shown in Photo 2. We also
marked the surfaces of each backfilled test pit location at areas where unknown subsurface
utilities were encountered.
Photo 2: Grass Seed Spread on TP-1. White Line Indicates an Unknown Utility Observed.
PAVEMENT SECTION DESIGN
We understand that a relatively small section at the proposed Facility will be paved for vehicle
access and parking. This paved area or areas will likely experience vehicle loading comparable
Ian McKelvey
Brown and Caldwell
December 8, 2017
Page 4 of 7
21-1-22210-002-L1f.docx/wp/s 21-1-22210-002
to current loading conditions at the South Plant. During our recent site visits, we did not observe
significant damage to the existing roadways, indicating that current pavement design at the South
Plant is adequate for anticipated traffic and loading conditions. We recommend adopting the
existing roadway construction methods when designing for new paved areas around the Facility.
If as-builts are unavailable, or if construction methods of existing roadways cannot be
determined before new paved sections are designed, we recommend referring to Table 4.3 of
Chapter 4 of the 2016 King County Road Design and Construction Standards. In our opinion,
the native soil subgrades have resilient modulus values of 10,000 pounds per square inch or
greater. For commercial access roads, King County recommends 6 inches of hot mix asphalt and
6 inches of crushed surfacing base course. This is based on a design equivalent single axle load
of less than 2,500,000 trips.
COAL MINE HAZARD EVALUATION
The City of Renton has designated the proposed Facility site as located within a critical area
consisting of a moderate coal mine hazard. The site has this designation because it is within
approximately 200 feet of a mapped historical coal mine consisting of a series of mine adits
extending north from the former mine entrance near the northeast corner of the Cogeneration
Building, as shown on the City of Renton map below:
Ian McKelvey
Brown and Caldwell
December 8, 2017
Page 5 of 7
21-1-22210-002-L1f.docx/wp/s 21-1-22210-002
According to the reference documents linked to the City’s sensitive areas website, County Map
K29 (King County, 1997 1), this mine operation belonged to the Diamond Coal Company. No
other information is available. Based on the relatively specific mapped location of the adits
1 County, King, 19970224, Coal Mine Hazards: King County, King County, WA.
http://www5.kingcounty.gov/gisdataportal/Default.aspx
Ian McKelvey
Brown and Caldwell
December 8, 2017
Page 6 of 7
21-1-22210-002-L1f.docx/wp/s 21-1-22210-002
associated with the Diamond Coal Company mine, it is our opinion that the mine adits do not
extend beneath the footprint of the proposed Heat and Energy Recovery building or the proposed
thermal oxidizer.
During our 2016 subsurface investigation, summarized in our January 6, 2017 report, we
advanced two borings to depths of about 91.5 to 121.5 feet bgs at the location of the proposed
Heat and Energy Recovery building. Boring results indicated that the project site is underlain by
sandstone bedrock consisting of the Renton Formation at depths ranging from 80 to 111 feet bgs.
This formation is known for containing coal beds, some used for mining purposes. The soils
above the bedrock consist of alluvial sediments that were not associated with coal mines.
Previous subsurface explorations, including borings and test pits by others, also did not locate
coal mining evidence at the Heating and Energy Recovery building site. Our recent TP-3 and
test pits previously performed by others nearby the proposed thermal oxidizer site did not expose
evidence of mining activity. In our opinion, there is no subsurface or surface evidence of past
mining activity at the proposed Facility site and there is low probability that construction of the
proposed Facility is at risk of coal mine hazards such as subsidence. Coal mine hazards are not a
design issue that require mitigation for the proposed project.
CLOSURE AND LIMITATIONS
This letter was prepared for the exclusive use of Brown and Caldwell and King County to aid in
design of the King County South Treatment Plant Biogas and Heat Systems Improvements. This
letter should be relied on for factual data only, and not as a warranty of subsurface conditions,
such as those interpreted from our observations. The conclusions and recommendations
contained in this letter are based on site conditions observed during our site visit.
Within the limitations of the scope, schedule, and budget, the conclusions and recommendations
presented in this letter were prepared in accordance with generally accepted professional
geotechnical engineering principles and practices in the area at the time this letter was
prepared. We make no other warranty, either express or implied.
The scope of our services for this project did not include any environmental assessment or
evaluation regarding the presence or absence of wetlands or hazardous or toxic materials in the
soil, surface water, groundwater, or air on, below, or around the site. Shannon & Wilson, Inc.
1
2
3
4
5
DESIGNED/DRAWN:
PROJECT ENGINEER:
PROJECT ACCEPTANCE:
DESIGN APPROVAL:
CONTRACT NO:
DRAWING NO:
PROJECT FILE NO:SCALE:
FACILITY NUMBER:
DEPARTMENT OF NATURAL RESOURCES & PARKS
WASTEWATER TREATMENT DIVISION
DATE:
SHT NO / TOTAL REV
NO:BORDER FILE EDITION: KCWTD-2015R0-Dsize-TB-Border1
2
3
4
5
E F G HBCDA
CHECKED:REFERENCE1"0P:\King County\148642 KC SP Biogas and Heat Sys Imp\_CAD\2-SHEETS\G-GENERAL\224-1123636G0000008.dwg | Layout: Layout1PLOTTED: Mar 30, 2017-09:35:46am By SPlancicXREFS: KCWTD-2015R0-Dsize-TB-Border.dwgIMAGES:SOUTH TREATMENT PLANT
BIOGAS AND HEAT SYSTEMS IMPROVEMENTS
MAR 2017
15-xxxxxxx
NO REVISION DESCRIPTION BY APVD DATE
E F G HBCDA
PRELIMINARY ISSUE DRAWING
30% DESIGN
APRIL 2017 S. Hildreth
G0000008
J. Bolton
T. Ingraham
G. Newman
None
0
R. Bard
Page 1 of 2 1/2017
SHANNON & WILSON, INC.
Geotechnical and Environmental Consultants
Dated:
Attachment to and part of Report 21-1-22210-002
Date: December 8, 2017, 2017
To: Mr. Ian McKelvey
Brown and Caldwell
IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL/ENVIRONMENTAL
REPORT
CONSULTING SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES AND FOR SPECIFIC CLIENTS.
Consultants prepare reports to meet the specific needs of specific individuals. A report prepared for a civil engineer may not be adequate
for a construction contractor or even another civil engineer. Unless indicated otherwise, your consultant prepared your report expressly
for you and expressly for the purposes you indicated. No one other than you should apply this report for its intended purpose without
first conferring with the consultant. No party should apply this report for any purpose other than that originally contemplated without
first conferring with the consultant.
THE CONSULTANT'S REPORT IS BASED ON PROJECT-SPECIFIC FACTORS.
A geotechnical/environmental report is based on a subsurface exploration plan designed to consider a unique set of project-specific
factors. Depending on the project, these may include: the general nature of the structure and property involved; its size and
configuration; its historical use and practice; the location of the structure on the site and its orientation; other improvements such as
access roads, parking lots, and underground utilities; and the additional risk created by scope-of-service limitations imposed by the
client. To help avoid costly problems, ask the consultant to evaluate how any factors that change subsequent to the date of the report
may affect the recommendations. Unless your consultant indicates otherwise, your report should not be used: (1) when the nature of
the proposed project is changed (for example, if an office building will be erected instead of a parking garage, or if a refrigerated
warehouse will be built instead of an unrefrigerated one, or chemicals are discovered on or near the site); (2) when the size, elevation,
or configuration of the proposed project is altered; (3) when the location or orientation of the proposed project is modified; (4) when
there is a change of ownership; or (5) for application to an adjacent site. Consultants cannot accept responsibility for problems that may
occur if they are not consulted after factors which were considered in the development of the report have changed.
SUBSURFACE CONDITIONS CAN CHANGE.
Subsurface conditions may be affected as a result of natural processes or human activity. Because a geotechnical/environmental report
is based on conditions that existed at the time of subsurface exploration, construction decisions should not be based on a report whose
adequacy may have been affected by time. Ask the consultant to advise if additional tests are desirable before construction starts; for
example, groundwater conditions commonly vary seasonally.
Construction operations at or adjacent to the site and natural events such as floods, earthquakes, or groundwater fluctuations may also
affect subsurface conditions and, thus, the continuing adequacy of a geotechnical/environmental report. The consultant should be kept
apprised of any such events, and should be consulted to determine if additional tests are necessary.
MOST RECOMMENDATIONS ARE PROFESSIONAL JUDGMENTS.
Site exploration and testing identifies actual surface and subsurface conditions only at those points where samples are taken. The data
were extrapolated by your consultant, who then applied judgment to render an opinion about overall subsurface conditions. The actual
interface between materials may be far more gradual or abrupt than your report indicates. Actual conditions in areas not sampled may
differ from those predicted in your report. While nothing can be done to prevent such situations, you and your consultant can work
together to help reduce their impacts. Retaining your consultant to observe subsurface construction operations can be particularly
beneficial in this respect.
Page 2 of 2 1/2017
A REPORT'S CONCLUSIONS ARE PRELIMINARY.
The conclusions contained in your consultant's report are preliminary because they must be based on the assumption that conditions
revealed through selective exploratory sampling are indicative of actual conditions throughout a site. Actual subsurface conditions can
be discerned only during earthwork; therefore, you should retain your consultant to observe actual conditions and to provide conclusions.
Only the consultant who prepared the report is fully familiar with the background information needed to determine whether or not the
report's recommendations based on those conclusions are valid and whether or not the contractor is abiding by applicable
recommendations. The consultant who developed your report cannot assume responsibility or liability for the adequacy of the report's
recommendations if another party is retained to observe construction.
THE CONSULTANT'S REPORT IS SUBJECT TO MISINTERPRETATION.
Costly problems can occur when other design professionals develop their plans based on misinterpretation of a
geotechnical/environmental report. To help avoid these problems, the consultant should be retained to work with other project design
professionals to explain relevant geotechnical, geological, hydrogeological, and environmental findings, and to review the adequacy of
their plans and specifications relative to these issues.
BORING LOGS AND/OR MONITORING WELL DATA SHOULD NOT BE SEPARATED FROM THE REPORT.
Final boring logs developed by the consultant are based upon interpretation of field logs (assembled by site personnel), field test results,
and laboratory and/or office evaluation of field samples and data. Only final boring logs and data are customarily included in
geotechnical/environmental reports. These final logs should not, under any circumstances, be redrawn for inclusion in architectural or
other design drawings, because drafters may commit errors or omissions in the transfer process.
To reduce the likelihood of boring log or monitoring well misinterpretation, contractors should be given ready access to the complete
geotechnical engineering/environmental report prepared or authorized for their use. If access is provided only to the report prepared for
you, you should advise contractors of the report's limitations, assuming that a contractor was not one of the specific persons for whom
the report was prepared, and that developing construction cost estimates was not one of the specific purposes for which it was prepared.
While a contractor may gain important knowledge from a report prepared for another party, the contractor should discuss the report with
your consultant and perform the additional or alternative work believed necessary to obtain the data specifically appropriate for
construction cost estimating purposes. Some clients hold the mistaken impression that simply disclaiming responsibility for the accuracy
of subsurface information always insulates them from attendant liability. Providing the best available information to contractors helps
prevent costly construction problems and the adversarial attitudes that aggravate them to a disproportionate scale.
READ RESPONSIBILITY CLAUSES CLOSELY.
Because geotechnical/environmental engineering is based extensively on judgment and opinion, it is far less exact than other design
disciplines. This situation has resulted in wholly unwarranted claims being lodged against consultants. To help prevent this problem,
consultants have developed a number of clauses for use in their contracts, reports, and other documents. These responsibility clauses
are not exculpatory clauses designed to transfer the consultant's liabilities to other parties; rather, they are definitive clauses that identify
where the consultant's responsibilities begin and end. Their use helps all parties involved recognize their individual responsibilities and
take appropriate action. Some of these definitive clauses are likely to appear in your report, and you are encouraged to read them closely.
Your consultant will be pleased to give full and frank answers to your questions.
The preceding paragraphs are based on information provided by the
ASFE/Association of Engineering Firms Practicing in the Geosciences, Silver Spring, Maryland