HomeMy WebLinkAbout821262008 Geotech AssessmentSHANNON WILSON, INC. ~~~~~
GEOTECHNICAL ArlD ENVIRONMENTAL CONSULTANTS ''t954-2004
May 18, 2004
~~~~~~~~
The Rosauer Co. LLC
1818 Westlake Avenue N., Suite 320 ~~ '~+ 1. ~~~~
Seattle, WA 98109
,~~~E~~SQ~ ~,~~~~ Q~~
Attn: Mr. Robin Rosauer
RE: GEOLOGIC SLOPE STABILITY E'~ALUATION, PARADISE BAY ROAD
PROPERTY PARCEL N0.8212~21~~b}, PORT LUDLOV~, WASHINGTON
JEFFERSON COUNTY DEPARTMENT OF COMMUNITY DE'~ELOPMENT
CASE # MLA04-Oaa53}
Dear r. Rosauer:
This letter report summarizes our observations, conclusions, and recommendations regarding
slope stability and development of the property referenced above for asingle-family residence.
.,
In a letter to you dated March 9, 2004, Jefferson County indicated that this property is located in
a Landslide Hazard area and that a geotechnical report would be required to assess the stability
of the site. Consequently, we have prepared this report in accordance with the Unified
Development Code far Jefferson County to evaluate the potential for slope movement and
provide recammendationsfnr development of the site with respect to slope stability. Our ,
conclusions and recommendations are based on observations made during our visit to the site on
May 15~, 2004; available published geologic, topographic, and sail maps; previous work by
Shannon & Filson an properties south of the site; and undated building and site plans provided
by your civil engineer, Mr. Michael Anderson. This work has been performed in general
accordance with our proposal to the Rosauer Co., dated April ZZ, 2004, and authorized by you on
Apri126, 2004.
SITE DESCRIPTION
The site is located between Paradise Bay Road and Hood Canal, approximately 2 miles north of
the Hood Canal Bridge (see Figure 1) on a hiltside that slopes down to the northeast toward
400 NORTH 34TH STREET • SUITE 100 21-I-20107-001
P.O. BOX 300303
SEATTLE, WASHINGTON 98103
206.632.8020 FAX 206.695.617?
TDD: 1.800833.6388
The Rosauer Co. LLC
Attn: Mr, Robin Rosauer
May 1 S, 2004
Page 2
SHANNON F~WILSON,IN~.
Hood Canal. The property is approximately 845 to 1,195 feet long (east-west) by approximately
130 to 250 feet wide (north-south).
The topography across the site rises from sea level at Hood Canal, to about 120 feet to the
southwest. from east to west, the topography includes the following,
- A beach.
- A steep, waterfront slope (approximately 35 to 45 feet high) that slopes up to the
southwest at about 34 to 53 degrees (may be near-vertical in local areas).
- A relatively flat upland that slopes up to the southwest at about 4 to ~ 10 degrees.
A small creek in an approximately 25-foot-deep ravine is located along the north property line
(see Figure 1). The sides of the ravine are sloped at about 30 to 36 degrees.
In general, the waterfront slope is steepest and highest near the south property line and becomes
the shortest and least steep where the creek and ravine meet the beach near the north property
line. Near the south property line, abowl-shaped depression is located at the crest of the
waterfront slope. The depression is approximately 25 to 30 feet wide parallel to the crest of the
slope, about 15 feet deep, and extends back into the upland portion of the slope approximately
15 feet.
Vegetation on the upland portion of the site typically consists of Douglas fir, cedar, and maple
trees up to 3 ~/2 feet in diameter with scattered, smaller alder trees. Undergrowth in the upland
portion of the site includes sword fern and salmon berry. The vegetation on the steep waterfront
slope where it is the flattest in the vicinity of the ravine includes alder, maple, and cedar trees up
to 3 feet in diameter. The trunks of many of the trees on this portion of the waterfront slope are
bowed down slope, which is indicative of soil creep. Soil creep is the slow, gradual downslope
movement of near-surface soils under the effects of gravity and water and occurs on most slopes
to some degree. To the south, the trees on the waterfront slope are typically alders I-foot or
smaller in diameter. Undergrowth on the waterfront slope includes salmon berry, thimbleberry,
and other broad-leafed hydrophilic vegetation.
21-I-2UI47-oat-i,llwp/lkd 2I-1-20101-0a1
The Rosauer Co. LLC
Attn: Mr. Robin Rosauer
May ~ S, 2004
Page 3
SHANNON F~WIL.SON, INC.
At the tlme of our slte vlslt, water flaw in the creek is estimated to have been on the order of at
least 10 gallons per minute or more. Slight seepage or damp conditions were observed on
non-vegetated portions of the waterfront slope between the beach level and about 15 to 20 feet
below the crest of the slope.
GEOLOGIC CONDITIONS
Published geologic maps of the area indicate that the upland portion of the site is underlain by
Pleistocene-age ~+17,000 years old} Vachon Advance outwash with a cap of younger,
Pleistocene-age (13,500 to 17,000 years old} Vashan Lodgement Till on the lower portion. of the
upland site. Along the waterfront slope, the geologic maps indicate that the Vachon Advance
outwash is underlain by older, undifferentiated, stratified pre-Vachon sediments. The
undifferentiated, pre-Vachon sediments may consist of bath glacial and non-glacial deposits and
may include stratified sand, gravel, silt, clay, and peat. rThepre-Vashan sediments are not
lithified tare not rack}. The overlying Vachon Advance Outwash typically consists of sand with
lesser amounts of silt and gravel. The advance outwash was deposited on the pre-existing land
surface, in front of the continental Vashan Stade ice sheet that advanced from Canada across the
Puget Sound region approximately 17,000 years ago. Lodgement till is typically an unsorted
mixture of clay, silt, sand, and gravel with occasional cobbles and boulders that was deposited
directly beneath the ice sheet as the glacier advanced over the area. The Vachon Lodgement Till
was deposited directly beneath the Vashon Stade ice sheet. The ice sheet that overrode the till,
and the underlying soils (including the advance outwash and pre-existing soils} is estimated to be
on the order of 3,000 to 4,000 feet thick in this area. Consequently, the till and the underlying
soils have been compacted to a very dense or hard state.
Subsurface explorations were not performed at this site for this evaluation. However, the soils
observed in the steep waterfront slope at the site confirm the presence of Vashon Advance
Out~vash and pre-Vashon sediments. Specifically, pre-Vashon sediments observed in
near-vertical, 3- to 4-foot high exposures on the waterfront slope just above beach level and at
the mouth of the creek include hard, gray, clayey silt. Conjugate joints were observed at about
1-foots acings at apparent dips of 45 and 60 degrees in the face of the exposures. Near the
p
2~-i-2ola~-ooi-~.~~~~iv~a 21-1-20107-001
The Rosauer Co. LLC
Attn: Mr. Rabin Rosauer
May 1 S, 2004
Page 4
SHANNON WILSON, IIV~.
south property line below the bowl-shaped depression, pre-Vashon sediment consisting of hard,
gray, clayey silt was observed in exposures to within approximately 15 feet of the crest of the
slope the bottom of the bowl}, and appeared to include same sand and gravel. Within the bowl
the upper 15 feet of the slope}, brown, trace-ta-slightly gravelly, silty sand was. observed. The
brown, sandy soil likely corresponds to the advance outwash indicated on geologic maps at the
site.
Since the retreat of the glacier, the upper few feet of the very dense~hard soil has loosened and
weathered and topsoil, colluvium, andlor slide deposits have developed at the ground surface,
colluvium is weathered material that has reached its present location due to the farces of water
and gravity and is typically found on, and at the base of steep slopes. Slide deposits are also
present at various locations on the beach at the base of the waterfront slope.
C4NCLUSIUNS AND RECOMMENDATIONS
Slope Stability
~ealagic hazard maps indicate that the waterfront slope is unstable and is the location of recent
landslides. Slope movements appear to be associated with the oversteepened condition of the
waterfront slope and with perched groundwater on the clayey silt sails at the. top of the pre-
~ashon sediment. The following provides a description of the processes affecting the stability of
the slopes.
The waterfront slope is the result of ongoing wave erosion and oversteepening at the toe of the
slope. The hard glacially overridden soils that underlie the slope may have been slowly eroded
or spalled from the near-vertical faces caused by wave erosion. In addition, while the very dense
or hard glacially overridden soils maybe stable at relatively steep slopes ~e.g., 40 degrees or
steeper}, the relatively loose topsoil and colluvium that weather from these soils are not as
competent and are susceptible to movement on slopes on which the underlying glacial soils are
relatively stable. Movement of the topsoil or colluvium may occur as slow soil creep or as
relatively shallow surficial slides. with enough time, movement of colluvium, topsoil, andlor
slide debris toward the base of the waterfront slope would result in a flatter, more stable slope.
2~-~-za~a~-oo~-L}iw~n~a 21-1-2010?-001
The Rosauer Co. LLC
Attn: Mr, Robin Rosauer
May 18, 2004
Page 5
SHANNON ~WiLSON, INC.
However, wave erosion at the toe of the waterfront slope does not allow the slide deposits,
colluvium, or topsoil to accumulate at the toe and maintains the slope in an over-steepened
condition.
In addition the constant oversteepening .by wave erosion at the base of the slope and shallow
surficial slides, it appears that somewhat deeper=seated slope instabilities and movements occur
along the crest of the slope. As previously indicated, slight seepage was observed on portions of
the waterfront slope below where groundwater apparently perches above the relatively
im envious pre-Vashon clayey silt. Perched groundwater zones on slopes have been the location
p
of numerous slides in the region. Within the slope at the site, groundwater moves down through
the more pervious sand units and perches on the top of the less pervious, clayey silt layers about
15 feet below the crest of the slope. where the sandlsilt contact daylights at the face of a slope,
seeps develop from the perched groundwater and supports the zones of hydrophilic vegetation
observed on the slope. Loose topsoil, colluvium, or slide debris on the slope in the vicinity of
the seeps and springs may become saturated, with a resulting increase in soil weight and
reduction in effective shear strength. fihe increase in soil weight and reduction in strength may
cause shallow slope movements. In addition, deeper-seated slope movements may also occur as
the perched groundwater may effectively decrease the soil shear strength along sand! clayey silt
contact.
It appears that the bowl-shaped depression at the crest of the waterfront slope near the south
property is the result of such a moderately deep-seated instability. Based an our observations,
the bowl is the head scarp of a recent slide. These observations include the bare slopes within
and immediately downslope of the scarp where the vegetation was removed as a result of a slide.
The vegetation that has since grown back consists primarily of small ~3- to 4-foot-tall} alder
saplings. we also observed slight groundwater seepage on the bare portions of the slope below
the scarp, which appears to originate on the slope near the base of the bowl or head scarp.
Finally, a large maple (including 15- to 20-foot-diameter root ball} was laying an the beach. It
appears that the maple had been located above the slide scarp and fell to the beach when the
underlying soils within the head scarp slid.
21-~-2o~a~-jai-Ll/wpllkd 21-1-20147-001
The Rosauer Co. LLC
Attn: Mr. Robin Rosauer
May 18, 2004
Page b
SHANNON ~WiLSON, 9N~.
Other large trees lying on the beach south of the property indicates that similar slope instabilities
have occurred periodically on this slope on this and adjacent properties. Similar slope
movements should be expected in the future as the wave erosion at the toe of the waterfront
slope continues to keep the slope in an aversteepened condition and groundwater continues to
perch on the sandlclayey silt contact. In this regard, there is some risk of future instability
present on all hillsides, which the owner must be prepared to accept. Such instability could
occur because of future water line breakslleaks, uncontrolled drainage, unwise development in
adjacent areas, or other actions or events on a slope that may cause sliding. The following
provides further discussion of risk reduction measures that maybe effective at this site. Provided
that the risk reduction measures discussed in this letter are implemented, it is our opinion that the
proposed development would not adversely impact the stability of adjacent properties.
Measures to Reduce the Risk Posed by Slope Movement
In general, the risk of soil movement on a slope can be deduced by not oversteepening a slope
4e.g., do not excavate the toe of the slope} and not increasing the weight on a slope ~e.g., do not
place yard debris or fill on or at the crest of the slope}. The risk of soil movement on a slope can
also be reduced by maintaining a slope as dry as possible ~e.g., locate septic drain fields away
from the slope, route roof downspouts and yard drains away from the slope, and minimize the
amount of surface water that could flow down the face of the slope}, and covering the slope with
proper vegetation. The following provides additional recommendations toreduce the risk of soil
movement affecting development of this site.
Building Setback
The measures discussed above may reduce the risk of sail movement on a slope. One of
the most cost-effective measures to reduce the potential impact of slope movement is to provide
an adequate building setback so that if soil movement on the slope does occur, the hazard to the
structure is minimal. An appropriate setback is a function of the rate or risk of slope movement
~regressian rate}, the design life of the structure, and the risk the owner of the structure is willing
to assume. The regression rate for the slope is unknown. However, based on the size of the
larger trees on the slope, it is our opinion that the average regression rate is relatively low ~e.g.,
an the order of a few inches per year}. While the average rate maybe relatively low, please note
2~-1-20107-001-L11wpNcd 21-1-2UI07-001
The Rosauer Co. LLC
Attn: Mr. Robin Rosauer
May 18, 2004
Page 7
SHANNON F~WtLSON, INC.
that there maybe several years where no noticeable regression occurs, and other times where
regression of several feet may occur ~e.g,,15 feet at the scarp near the south property line}.
Based on these observations, inferences, and our experience, we recommend a minimum
buildin setback of 50 feet from the crest of the steep waterfront slope. Along the south property
,~
line, the edge of the slide scarp should be considered the crest of the slope. In our opinion, this
minimum setback from the crest of the slopes is prudent given the observed recent movement.
Based on the size of the observed scarp along the south property line, this minimum setback
would allow for two to three events to occur without impacting the stability of structure located
at a 50-foot setback from the existing crest. We also recommend a minimum building setback of
at least 25 feet from the edge of the ravine. greater risk reduction can be achieved with larger
building setbacks.
Septic Drain Field Location
~.
The septic drain field should be located as far as practical from the waterfront slope and
ravine. By placing the septic drain field as far as practical from the slopes, the potential for
water from the drain field to find its way down onto less pervious soils, increase seepage and
decrease stability is reduced. We recommend that a minimum 50-foot setback from the crest of
the waterfront slope and 20 feet from the crest of the ravine be used.
Drainage
In general, reducing the amount of water entering and discharging onto a slope can
reduce the risk of slope movement. Drains should be constructed and maintained to collect water
from im ermeable surfaces that may be associated with the proposed development (e.g., roof,
p
decks, patios, and driveways} and directed in a tightline to a suitable discharge point. In our
opinion, a location near the base of the ravine would provide a suitable discharge point. The
discharge paint should be constructed to allow dispersion of the water and dissipation of energy
to reduce the potential far erosion. Discharge onto a mat of b-inch-minus quarry spans,
extending 6 feet in the direction of flow would be one method to provide water dispersion and
energy dissipation,
21-t-20107-001-Lllwp/Ikd 21-1-20147-001
The Rasauer Co. LLC
Attn: Mr, Robin. Rosauer
May 18, 2004
Page 8
SHANNON WILSON, iNC.
In addition to surface drainage, we recommend that footing drains be installed around the
perimeter of the residence and on the upslope side of interior footings to improve subsurface
drainage in the immediate vicinity of the structure. Footing subdrains should consist of slotted,
4-inch-diameter minimum, plastic pipe bedded in washed, 3I8-inch pea gravel. Typical
installation details far these drains are shown in Figure 2. Figure 2 also includes subdrainage
and foundation wall backfill recommendations. ~n-site soils will likely not be suitable for use as
drainage sand and gravel. Note that the perimeter subdrain invert should be located at least 18
inches below the lowest adjacent grade. Roof or other drains should not be connected to the
footing subdrains. The discharge from footing drains should be routed by means of a tightline to
a suitable discharge point as previously discussed. AlI outside grades should slope away from
the residence.
Based on our understanding of the limited, single-residence development of this property,
it is our opinion that the anticipated discharge of water collected from impermeable surfaces and
footing drains as outlined above will not significantly affect the pre-development drainage
conditions on the adjacent properties.
Impermeable surface around the proposed building ~e.g., paved drives} should be
minimized to reduce potential changes in the existing site drainage characteristics and impacts on
adjacent sites.
Erasion Hazard
we note that according to published U.S. Department of Agriculture USDA} sail maps, surficial
soils on the upland portion of the site are classified as Kitsap series silt loam on o to 15 percent
slopes and Belfast silty clay loam on slopes of 2 percent of flatter. The USDA maps indicate that
these soils have Wane to moderate erosion hazard. The soils on the steep waterfront slope are not
classified but based on steepness of the slope and our field observations, the erosion hazard for
soils on the slope is relatively high. To reduce the potential for soil erosion and associated
hazards, the fallowing wet weather earthwork recomrn~endations are presented. Provided that
these wet weather earthwork recommendations and prudent construction practices are used, it is
z~-i.2alo7-ao~-LifWpro~a 21-1-20107-001
The Rosauer Co. LLC
Attn: Mr. Robin Rosauer
May 1 S, 2044
Page 9
SHANNON f~WILSON, INC.
anticipated that the future earthwork for the proposed development will not significantly affect
soil erosion and associated hazards on the site.
wet V4~eather Earthwork
1n western Washington, wet weather generally begins about mid-October and continues
through about mid-May, although rainy periods may occur at any time of the year. Therefore, it
would be advantageous to schedule earthwork during the normally dry weather months of mid-
May through mid-October. Earthwork performed during the wet winter months will generally
prove more costly.
The following recommendations are applicable if earthwork is to be accomplished in wet
weather ar in wet conditions:
- Fill material should consist of clean, granular soil, of which not more than 5 percent by
dry weight passes the No. 240 mesh sieve, based an wet-sieving the minus 3/a-inch
fraction. Any fines should benon-plastic.
- The ground surface in and surrounding the construction area should be sloped and sealed
with asmooth-drum roller to promote runoff of precipitation away from work areas and
to prevent ponding of water.
~ Earthwork should be accomplished in small sections to reduce exposure to wet
conditions. If there is to be vehicular traffic over the exposed subgrade during
construction, the size or type of e9uipment may have to be limited to prevent soil
disturbance or the subgrade may need to be protected ~e.g., covered with a minimum
~ inches of compacted crushed rock}.
- No sail should be left exposed to moisture or uncompacted. A smooth drum vibratory
roller, or equivalent, should be used to seal the surface. Soils that become too wet for
compaction should be removed and replaced with clean crushed rock.
- Excavation and placement of structural fill during wet weather should be observed on a
full-time basis by a geotechnical engineer for his representative} experienced in wet
weather earthwork, to determine that all unsuitable materials are removed and suitable
compaction is achieved.
Zi-~-zolQ~-oo~.i~i~~nr~a 2I - I-24147-401
The Rosauer Ca. LLC
Attn: Mr. Robin Rosauer
May 1 S, 204
Page 1 U
SHANNON F~WlLSON, INC.
Havering work areas, soil stockpiles, ar slopes with plastic, sloping, ditchin , installin sum s
g g p,
dewatering, and other measures should be employed, as necessary, to permit ro er tom letion
pp p
of the work. Straw bales andlar geotextile silt fences should be aptly located to control soil
movement and erosion.
LIIVIITATIaNS
The conclusions in this letter report are based on site conditions visually observed Burin our
g
reconnaissance at and around the site and inferred from published geologic, soils, to o ra hit
pg P
and hazard maps and assume that observed conditions are representative of the subsurface
conditions throughout the site; i.e., the subsurface conditions are not significantly different from
those inferred from the site reconnaissance or indicated an geologic maps. If, Burin subse cent
g ~
site activities {e.g., construction}, subsurface conditions different. from those inferred in this letter
are observed or appear to be present, we should be advised at ante so that we can review those
conditions and reconsider our conclusions where necessary.
within the limitations of scope, schedule, and budget, the conclusions presented in this letter
were prepared in accordance with generally accepted geologic engineering principles and
practices in this area at the time this letter report was prepared. we make no other warrant ,
y
either express ar implied.
This letter report was prepared for the use of Mr. Rosauer and his engineer in the evaluation of
the stability of this site. with respect to possible future construction, it should be made available
far information on factual data only and not as a warranty of subsurface conditions, such as those
interpreted from the site visits and discussion of geologic conditions included in this letter re ort.
P
Please note that the scope of our services did not include any environmental assessments or
evaluation regarding the presence or absence of wetlands or hazardous ar toxic material in the
soil, surface water, groundwater, or air on, or below, ar around this site. we are able to rovide
P
these services and would be pleased to discuss these with you if the need arises.
zt-~-Zaio~-aoi-Lit,~pr~a 2~-1-2o1o7-Oa1
The Rosauer ~o. LLG
Attn; Mr. Robin Rosauer
May 18, 2004
Page 11
SHANNON F~WI~SON, INC.
Shannon & Wilson has prepared the enclosed, "Important Information About Your Geotechnical
Report," to assist you in understanding the use and limitations of our report.
We appreciate the opportunity to provide geologic services to you, and are available to answer
any questions regarding our observations, conclusions or recommendations contained in this
letter report.
Sincerely,
SHANNON & WILSON, INC.
~a~e ~~ W ~h~~ r
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Wi[(iam Jose h Perkins
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William J. Perkins, L.E.G.
Sensor Principal Engineering Geologist
JEffERSON COUNTY BCD
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Enclosures: Figure I - ~licinity Map
Figure ~ - Subdrainage & Backfilling
Important Information About Yaur Geotechnical Report
c: Mr. Michael J. Anderson
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0 112 1
Scale in Miies
NOTE
Map adapted from 1;24,004 USGS topographic map of
Port Ludlow, ~IIIA quadrangle, dated 1953,
photorevised 1913, and Lofall, UVA quadrangie, dated
1953, photorevised 1968.
Wall
Sloped to Drain
Away from
Structure
Drainage Sand &
Pavement yr 10" to 15" ~ ~ Gravel ar Washed
Impervious Sail 4 ° Pea Gravel
o~
1$~~ ° o Q Damp Proofing
Backfill Meeting Gradation Min
Requirements for Structural Fill o
See Note 2} °o o Weep Hales
° See Note 1} Vapor Barrier
Op
Excavation Slope vo
' o
Floor Slab
Contractor's Responsibility
_
'A
p'04Q`p
.Q
~ D " ~' ~ n'~ G 4 Q a
~ fl
poao 0a 0~Q18 Mm.4a~a
••0
0 Q
0
0
6"Min. Cover of Pea Gravel
~6" Min. on Sides of Pipe} 2" #0 4" Washed 4"Min
Pea Gravel
Subdrain Pipe
Not to S cale
Drainage Sand & Gravel with
the Following Specifications;
°/° Passin
Sieve Size t~Weight
1-112" 100
314" 94 to 140
114" l5 to 104
No. 8 65 to 92
Nv. 30 20 to 65
Na. 50 5 to 20
No. 140 0 to 2
Eby wet sieving} 4non-plastic}
z
v
0
r
.~
0
0
N
T
r
0
m
0
4"minimum diameter perforated or slatted pipe;
tight joints; sloped to drain ~6"1100' min. slope};
provide clean-outs.
Perforated pipe holes X3116" to 1!4"dia.} to be in
lower half of the pipe with lower quarter segment
unperforated for water flaw.
Slotted pipe to have 118" maximum width slots.
`~ NOTES
1. Drainage gravel beneath floor slab should be
hydraulically connected to subdrain pipe on the
down-slope side of the structure only. Use of 2"dia.
weep holes as shown is ane applicable method.
2. Imparted structural fill should consist of well-graded
granular soil with not more than 5°/° fries Eby weight
based on minus 314" portion} passing No. 200 sieve
Eby wet sieving} with no plastic fines.
3. Backfill within 18" of wall should be compacted with
hand-operated equipment. Heavy equipment should
not be used for backflf, as such equipment operated
near the wall could increase lateral ear#h pressures
and possibly damage the wall.
4. All backfill should be placed in layers riot exceeding
4" loose thickness and densely compacted. Beneath
-paved or sidewalk areas, compact to at least 95 % of
Modified Proctor maximum dry density ~ASTM:
D1551-70, Method C}. Otherwise compact to 92°la
minimum.
SHANNON & VUELSON, ANC. Attachment to and part of Report 21-I-20107-00i
Geotechnical and Environmental Consultants
Date: May 18, 2004
To: The Rosauer Co. LLC
Attn: Mr. Robin Rosauer
IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAVENVIRONMENTAL
REPORT
CONSULTING SERVICES ARE PERFORMED FGR SPECIFIC PURPOSES AND FOR SPECIFIC CLIENTS.
Consultants prepare reports to meet the specif c needs of specific individuals. Areport 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 geotechnicaUenvironmental report is based on a subsurface exploration plan designed to consider a unique set ofproject-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 utjlit~es; 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:~`~l}when the nature of the proposed project is changed (for
example, if an office building will be erected instead of a parking garage, ar 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; 43} when the location ar 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 geotechnicaUenvironmental 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 geotechnicaUenvironmental 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
vase 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.
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