HomeMy WebLinkAbout701283001 Geotech Assessment (2008)
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STRATUM GROUP
1451 Grant Street, Bellingham, W A 98225
Phone (360) 714-9409
February 25, 2008
Fred and Lorraine Pleines
1755 Bogachiel Way
Forks, WA 98331
Re: Geology Hazard Evaluation, Shoreline Bluff
Tax Parcel 701283001
Quilcene, W A
Dear Mr. and Ms Pleines:
Stratum 'Group is pleased to present the results of our geology hazard evaluation of the above
referenced property on a shoreline bluff. The purpose of this geology evaluation was to
qualitatively evaluate the risk of slope failures impacting the proposed residence on the subject
property and provide general site development and maintenance recommendations. This
evaluation included a visual inspection ofthe property and vicinity, a visual inspection ofthe
slopes on the property and vicinity, review of available geologic mapping in the area, and
inspectio~ of the shoreline at the base of the bluff. '
I had previously evaluated this site in 2001. Since that time I have gained a better understanding
of the terrace located on the property where the proposed building area is located and the slopes
above based on work on other properties to the north of the subject property. This updated report \
reflects a minor alteration in my interpretation of the geology of the site.
The property is located on an approximately 500-foot high bluff on the east side of the Bolton
Peninsula. The location of the property is indicated on Figure 1. The property is approximately 5
acres in size and is located in the southwest 1/4 of Section 28, Township 27, Range 1 W W.M.
SCOPE OF SERVICES
The scope of our services included the following:
1) Conducted a site visit to visually inspect the subject property including the slope
conditions, shoreline conditions, and relevant conditions in the vicinity of the
property .
2) Observed surface soil conditions on the slope and on the uplands above the slope.
3) Prepared this report summarizing out findings, including a qualitative evaluation
J V ,r-<r. Tr" 'of the slope stability in regards to the proposed residence on the property, .
l1l:1-:r L~,f KVE D recommendations for site development, and recommendations for further
investigation, if necessary.
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February 25, 2008
Tax Parcel 70 I 228300 I, Qui1cene, W A
Geologic Evaluation of Shoreline Bluff
GENERAL GEOLOGY
Northwestern Washington has been occupied by continental glaciers at least tour times during
the Pleistocene Epoch (1.6 million to 10,000 years ago). During these glacial and accompanying
interglacial periods, the underlying bedrock was eroded and a relatively thick layer of glacial
related and interglacial fluvial sediments were deposited over the underlying bedrock in the
vicinity ofthe subject property.
The Geologic Map of Surficial Deposits in the Seattle 30' by 60' Quadrangle, Washington
(Yount, Minard, ,and Dembroff, 1993) indicates the bluff is underlain by undifferentiated
Pleistocene deposits. These deposits are described as consisting of poorly exposed gravel, sand,
silt, and clay of uncertain provenance. The Geologic Map of East-Central Jefferson County,
Washington (Birdseye, 1976) indicates the ~horeline and bluff exposed on the subject property
and vicinity is underlain glacial till and Pre- V ashon stratified deposits. The glacial till is
described as consisting of a mixture of clay, silt, sand and gravel and is in a very compact
condition. Birdseye indicated that there are three glacial till deposits on the bluff in the vicinity of
the property, the Possession Till, the Double Bluff Till and the Vashon Till. The Pre-Vashon
stratified deposits are described as consisting of sand, gravel, silt and clay deposited prior to the
last ice age.
Observations on the subject property, slopes in the vicinity of the property and upland areas
above the subject property are generally consistent with the mapping described above. One
exception described below is the presence of glacial ice contact/ice wasting deposits on a portion
of the property. ~.
Glacial till is present at an exposure along the beach a short distance south of the subject
property. Glacial till is also present on the property below the proposed building site and the
beach. However, these two till exposures are not likely the same unit, as the thickness of the unit
ifit were a single unit would have to be on the order of 125 feet. In addition, stratified silts and
sands are present below the till on the subject property and on the steep shoreline slope south of
the property. The till exposed on the beach is probably the Possession Till and the till observed
below the building site on the subject property is probably the Double Bluff Till. However,
without age dates this correlation can not be confirmed~ Vashon Glacial Till underlies the upper
elevations of the Bolton Peninsula and is present on the top of the bluff west of the subject
property.
Stratified sediments on the bluff at the subject property and in the vicinity consist primarily of
stratified sand and gravel deposits, fine sand and silt layers and peat layers. The silt, clay and peat
deposits as well as sand and gravel with high silt or clay content are very compact condition due
RECEIVED
Stratum Group File: 2.25.08
APR 0 3 2008
JEFFERSU,~ ~UUNTY DCD
2
February 25,2008
Tax Parcel 70 I 228300 I, Qui1cene, W A .
Geologic Evaluation of Shoreline Bluff
the fact that a thick layer of glacial ice has over ridden them. Most of the sands and gravel layers
on the bluff contain enough silt that they are in a fairly compact condition. However, two areas of
looser sand , and gravel are present on the steep slope. An approximately 10-foot layer of loose to
medium dense sand is located on thelower slope of the subject property. This layer appears to be
discontinuous and does not define a distinct geomorphic feature across the slope. Loose to
medium dense sand and gravel is located on the upper slopes of the bluff west of the subject
property and below the Vashon Till at the top of the bluff.
Glacial ice contact/ice wasting deposits are present on the topographic bench area on the subject
property. These deposits consist of aNery chaotic rnix of sand and gravel and blocks and
fragments of compact stratified deposits mixed together. Topographic features in this bench area
are consistent with features found on glacial terrace benches and are not related to any current
geomorphic processes.
The Relative Slope Stability in East-Central Jefferson County, Washington (Birdseye, 1976) ~ap
indicates slopes in the vicinity of the subject property are unstable and identifies areas of recent .
landsliding in the immediate vicinity of the subject property.
Observations confirm that most of the slopes on the subject property and the vicinity are
generally unstable or potentially unstable. Numerous recent small shallow soil slides are present
on portions of the subject property and in the viCinity of the subject property. The implications
and relative threat to the subject property and the siting of a residence on the subject property are
discussed in detail in the following sections.
SPECIFIC SITE OBSERV A TIONS
The subject property is approximately 5 acres in size. A sketch map and cross section of the
property with pertinent features indicated are provided in Figures 2 and 3. Most of the property
slopes steeply towards the east. The east boundary of the property is Dabob Bay and the property
slopes up from the water with an overall slope angle of approximately 38 degrees. The west
boundary of the property is at an elevation of approximately 340 feet. The slope continues up
above the property to an elevation on approximately 500 feet. The slope is mostly tree-covered
with mature Douglas fir, western red cedar, alder and big leaf maple with an understory of
bracken fern, salal and other brush.
An access road crosses the property from the south to the north near the approximate mid slope
of the property. This road accesses the property as well as properties south of the subject
property. The proposed building site area is located on a relatively level cleared area adjacent to
this road. This level area ranges from approximately 50 to 75 feet wide. The road is immediately
adjacent to thi]{~CiEfVlB:D t,he level area. The entire width ofthe level area and the
Stratum Group File: 2.25.08
APR 0 3 2008
3
,JEffERSON COtiNTY DeD
February 25, 2008
Tax Parcel 701228300 I, Quilcene, W A
Geologic Evaluation of Shoreline Bluff
road is approximately 110 feet.
The slope angle above the road is approximately 19 degrees for a distance of approximately 75
feet and then steepens to 25 to 35 degrees for 150 feet and then becomes approximately 45
degrees with a few areas that are much steeper west ofthe western boundary of the property. The
slope above this steep area becomes very gentle.
The slope below the proposed building area drops steeply to the east at angle of ranging from
approximately 40 to 50 degrees for a distance of 50 feet. Below this steep section, the slope angle
lessens to an angle of approximately 30 degrees down to another small level area approximately
100 feet below the proposed building area. This level area is approximately 20 feet wide and is
accessed from the north via a steep road/trail that was cut down the slope from the north. The
road is a cut and fill road. Hence the slopes above and below the road are steeper than the
adjacent slopes. The level are is approximately 15 to 20 feet above the beach.
Along the beach a few slope failures are apparent along the shoreline south and north of the
subject property. All ofthese the slope failures appear to be relatively shallow soil failures due to
the steepness of the slope. The primary cause of slope failures is from undermining of the slope
by wave action at the beach. As the slope is undermined the lower portions of the slope fail first
and the slope failures progress up the slope. Ultimately the slope failures will progress up to the
top of the bluff. However, no slides that involved the entire bluff slope were observed anywhere
on the bluff in the vicinity of the subject property. The landslide debris from these slides acts as a
natural protection for the base of the bluff until over thne the debris is washed away and the
process of progressive slope failures up the shoreline bluff repeats itself. Most of the soil exposed
at the base of the bluff along the shoreline in the vicinity of the subject property appeared to
consist oflandslide failures.The time period between these failures has been generally sufficient
to allow for the growth of mature trees on the landslide soils. Hence, most of the slopes above the
beach in the vicinity of the subject property and on the property itself are heavily wooded.
Based on the presence of 100 year old or older Douglas firs and madrones on most of the bluff
slope on this stretch of coast line, and the consistent geology along this portion of the coast, it
appears that the frequency of slope failures that remove all the trees has been less frequent than
100 years.
As noted above in the geology section soils under lying the subject property consist primarily of
stratified silts, fine sand, peat, sand and gravel, and glacial till. The proposed building area and
the lower portions of the slope west of the proposed building area are underlain by ice contact
and ice wasting deposits. A schematic cross section sketch illustrates the approximate locations
of the units observed.
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1i\\.1WCElIVE D
Stratum Group
File: 2.25.08
A?R 0 3 ;::..3
4
"---,-r, n ' I
Ith cnJON COU~ IT DCD
February 25,2008
Tax Parcel 7012283001, Quilcene, WA
Geologic Evaluation of Shoreline Bluff
One inactive slide is located on the lower slopes of the property below the proposed building
area. The slide appears to be the result of oversteepening of the slope from erosion at the base of
the bluff combined with the steepening of the slope years ago by cutting the road and level area
into the base of the steep slope.
CONCLUSIONS AND RECOMMENDATIONS
Based on my visual inspection of the subject property and vicinity, I conclude that a residence
can be located on the relatively level area on the mid-section of the property as indicated in the
site plan sketch. A residence located at this site should not be at risk from bluff erosion or
landsliding that would threaten the structure within the expected life of the structure (75 years) as
long as our recommendations are followed.
The relatively level building area on the mid-portion of the slope adjacent to the road is
approximately 250 feet long. The building should be setback from the top of the steep slope a
minimum of30 feet. Any building should also be set back a minimum of30 feet fromthe'base of
the slope along west side of the road on the subject property. '
A deck may be constructed within the setback from the top of the steep slope as long as it is not
an integral part of the structure of the residence. That is if a slope failure occurs, the deck will
detach from the house.
Native vegetation, particularly tress and low native brush on the slope between the building site
and the steep slope below the building site should"be disturbed as little as possible. No trails or
grading should be performed on the steep slope below the building site. If trees are thinned or
limbed for view purposes, no debris should be placed on the top of the bluff. Some thinning of
trees growing between the top of the bluff face and the home site should not cause any problems
as long as the native brush understory is left in place. Thinning and trimming of trees on the bluff
slope should be limited to topping of alders and maples and limbing for view corridors of
Douglas fir and western red cedar. Any debris from thinning on the bluff slope itself should be
removed from the slope.
All storm water run off from the roof gutters should be routed away from the bluff face. Storm
water can be directed into a~ infiltration area south and downslope of the proposed residence .
towards an existing drainage swale. .
The septic drain field may be located either north or south of the proposed building site. If
located south of the proposed building the topography of the area will direct subsurface flow
away from the steep slope. If the drain field is located north of the proposed building site, the
drain field should be located at least 30 feet from the top of the steep slope.
RECEIVED
Stratum Group File: 2.25.08
APR 0 3 2008 5
JEFfERSDN LUu~TY DCD
February 25, 2008
Tax Parcel 701228300 I, Quilcene, W A
Geologic Evaluation of Shoreline Bluff
Maintaining healthy native vegetation cover both on the uplands and on the slope will best
control long term erosion. Blackberry .vines should be removed from the slope and not allowed to
spread as they can crowd out desirable plants and do not provide effective erosion control.
Yard waste and other deleterious material should not be placed on or over the slope. Such
material smothers vegetation, retains water and acts to destabilize the slope.
CLOSURE
Please note that there are inherent risks associated with lots near or adjacent to steep slopes.
These are risks that the building owner should recognize and be willing to accept. If conditions
appear different than those described in this report, or other concerns arise, we request that we be
notified so we can review those areas and modify our recommendations as required.
We appreciate the opportunity to be of service to you. Should you have any questions regarding
please contact our office at (360) 714-9409.
Sincerely yours,
Stratum Group
Dan McShane, M.Sc., L.E.G.
Licensed Engineering Geologist
RECEIVED
Stratum Group
File: 2.25.08
APR 03 2008
6
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STRATUM GROUP
1451 Grant Street, Bellingham, W A 98225
Phone (360) 714-9409
December 11,2007
Fred and Lorraine Pleines
1755 Bogachiel Way
Forks, W A 98331
Re: Geology Hazard Evaluation, Shoreline Bluff
Follow up inspection
Tax Parcel 701283001
Quilcene, W A
Deaf Mr. and Ms Pleines:
I visited the property on December 9, 2007 to determine if any changes had taken place since my
original site evaluation dated August 1,2001. No changes have taken place on the property since
my original report. The day I visited the subjec~ property was less than one week after a very
heavy rainfall event had impacted the area. No slides or erosion was evident anywhere on the
property.
Stratum Group appreciates the opportunity to be of service to you. Should you have any
questions regarding please contact ollr office at (360) 714-9409.
Sincerely yours,
lJ:r~
Dan McShane, M.Sc., L.E.G.
Licensed Engineering Geologist
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STRATUM GROUP
1451 Grant Street, Bellingham, WA 98225
Phone (360) 714-9409
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August 1,2001
Fred and Lorraine Pleines
1755 Bogachiel Way
Forks, WA 98331
Re: Geology Hazard Evaluation, Shoreline Bluff
Tax Parcel 701283001
Quilcene, W A
Dear Mr. and Ms Pleines:
Stratum Group is pleased to present the results of our geology hazard evaluation of the above
referenced property on a shoreline bluff. The purpose of this geology evaluation was to
qualitatively evaluate the risk of slope failures impacting the proposed residence on the subject
property and provide general site development and maintenance recommendations. This
evaluation was limited to a visual inspection of the property and vicinity, a visual inspection of the
slopes on the property and vicinity, review of available geologic mapping in the area, and
inspection of the shoreline at the base of the bluff. '
The property is located on an approximately 500-foot high bluff on the east side of the Bolton
Peninsula. The location of the property is indicated on Figure 1. The property is approximately 5
acres in size and is located in the southwest 1/4 of Section 28, Township 27, Range 1 W W.M.
SCOPE OF SERVICES
The scope of our services included the following:
1) Conducted a site visit to visually inspect the subject property including the slope
conditions, shoreline conditions, and relevant conditions in the vicinity of the
property.
2) Observed surface soil conditions on the slope and on the uplands above the slope.
3) Prepared this report summarizing our findings, including a qualitative evaluation of
the slope stability in regards to the proposed residence on the property,
recommendations for site development, and recommendations for further
investigation, if necessary.
-
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jEffERSOt-l c(}Ul\fi DC!>>
August 1,2001
TaxParce17012283001, Quilcene, WA
Geologic Evaluation of Shoreline Bluff
GENERAL GEOLOGY
Northwestern Washington has been occupied by continental glaciers at least four times during the
Pleistocene Epoch (1.6 million to 10,000 years ago). During these glacial 'and accompanying
interglacial periods, the underlying bedrock was eroded and a relatively thick layer of glacial
related and interglacial fluvial sediments were deposited over the underlying bedrock in the
vicinity of the subject property.
The Geologic Map of Surficial Deposits in the Seattle 30' by 60' Quadrangle, Washington
(Yount, Minard, and Dembroff, 1993) indicates the bluff is underlain by undifferentiated
Pleistocene deposits. These deposits are described as consisting of poorly exposed gravel, sand,
silt, and clay of uncertain provenance. The Geologic Map of East-Central Jefferson County.
Washington (Birdseye, 1976) indicates the shoreline and bluff exposed on the subject property
and vicinity is underlain glacial till and Pre- V ashon stratified deposits. The glacial till is described
as consisting of a mixture of clay, silt, sand and gravel and is in a very compact condition.
Birdseye indicated that there are three glacial till deposits on the bluff in the vicinity of the
property, the Possession Till, the Double Bluff Till and the Vashon Till. The Pre-Vashon stratified
deposits are described as consisting of sand, gravel, silt and clay deposited prior to the last ice
age.
Observations on the subject property, slopes in the vicinity of the property and upland areas above
the subject property are consistent with the mapping described above. Glacial till is present at an
exposure along the beach a short distance south of the subject property. Glacial till is also present
on the property below the proposed building site and the beach. However, these two till
exposures are not likely the same unit, as the thickness of the unit if it were a single unit would
have to be on the order of 125 feet. In addition, stratified silts and sands are present below the till
on the subject property. The till exposed on the beach is probably the Possession Till and the till
observed below the building site on the subject property is probably the Double Bluff Till.
However, without age dates this correlation can not be confirmed. Vashon Glacial Till underlies
the upper elevations of the Bolton Peninsula and is present on the top of the bluff west of the
subject property.
Stratified sediments on the bluff at the subject property and in the vicinity consist primarily of
stratified sand and gravel deposits, fine sand and silt layers and peat layers. The silt, clay and peat
deposits as well as sand and gravel with high silt or clay content are very compact condition due
the fact that a thick layer of glacial ice has over ridden them. Most of the sands and gravel layers
on the bluff contain enough silt that they are in a fairly compact condition. However, two areas of
looser sand and gravel are present on the steep slope. An approximately lO-foot layer ofloose to
medium dense sand is located on the lower slope of the subject property. This layer appears to be
discontinuous and does not define a distinct geomorphic feature across the slope. Loose to
Stratum Group
File: 7.5.01
2
August 1,2001
TaxParce17012283001, Quilcene, WA
Geologic Evaluation of Shoreline Bluff
~J~
St.? 1 ~ "i.\W i
j\:HlRSOl-l CO\Jl-Ili \)C\)
medium dense sand and gravel is located on the upper slopes of the bluff west of the subject
property and below the Vashon Till at the top of the bluff.
The Relative Slope Stability in East-Central Jefferson County. Washington (Birdseye, 1976) map
indicates slopes in the vicinity of the subject property are unstable and identifies an area of recent
landsliding in the immediate vicinity of the subject property.
Observations confirm that slopes on the subject property and the vicinity are generally unstable.
Numerous recent small shallow soil slides are present on the subject property and in the vicinity of
the subject property. The implications and relative threat to the subject property and tlie siting of
a residence on the subject property are discussed in detail in the following sections.
SPECIFIC SITE OBSERV A nONS
The subject property is approximately 5 acres in size. A sketch map and cross section of the
property with pertinent features indicated are provided in Figures 2 and 3. Most of the property
slopes steeply towards the east. The east boundary of the property is Dabob Bay and the property
slopes up from the water with an overall slope angle of approximately 38 degrees. The west
boundary of the property is at an elevation of approximately 340 feet. The slope continues up
above the property to an elevation on approximately 500 feet. Th~ slope is mostly tree-covered
with mature Douglas fir, western red cedar, alder and big leaf maple with an understory of
bracken fern, salal and other brush.
An access road crosses the property from the south to the north near the approximate mid slope
of the property. This road accesses the property as well as properties south of the subject
property. The proposed building site area is located on a relatively level cleared area adjacent to
this road. This level area ranges from approximately 50 to 75 feet wide. The road is immediately
adjacent to this area and is upslope from the level area. The entire width of the level area and the
road is approximately 110 feet. A sketch map of this area is provided in Figure 4.
The slope angle above the road is approximately 19 degrees for a distance of approximately 75
feet and then steepens to 25 to 35 degrees for 150 feet and then becomes approximately 45
degrees with a few areas that are much steeper near the western boundary of the property. The
slope above this steep area becomes very gentle.
The slope below the proposed building area drops steeply to the east at angle of ranging from
approximately 40 to 50 degrees for a distance of 50 feet. Below this steep section, the slope angle
lessens to an angle of approximately 30 degrees down to another small level area approximately
100 feet below the proposed building area. This level area is approximately 20 feet wide and is
accessed from the north via a steep road/trail that was cut down the slope from the north. The
Stratum Group
File: 7.5.Q1
3
,.;: (} ."'i."" ,t~"":.
,h ,'. .. """:"
August 1,2001
Tax Parcel 7012283001, QIiilcene, WA
Geologic Evaluation of Shoreline Bluff
JEFFERSON COUNTY Den
road is a cut and fill road. Hence the slopes above and below the road are steeper than the
adjacent slopes. The level are is approximately 15 to 20 feet above the beach.
Along the beach a few slope failures are apparent along the shoreline south and north of the
subject property. All of these the slope failures appear to be relatively shallow soil failures due to
the steepness of the slope. The primary cause of slope failures is from undermining of the slope by
wave action at the beach. As the slope is undermined the lower portions of the slope fail first and
the slope failures progress up the slope. Ultimately the slope failures will progress up to the top of
the bluff. However, no slides that involved the entire bluff slope were observed anywhere on the
bluff in the vicinity of the subject property. The landslide debris from these slides acts as a natural
protection for the base of the bluff until over time the debris is washed away and the process of
progressive slope failures up the shoreline bluff repeats itself Most of the soil exposed at the base
of the bluff along the shoreline in the vicinity of the subject property appeared to consist of
landslide failures. The time period between these failures has been generally sufficient to allow for
the growth of mature trees on the landslide soils. Hence, most of the slopes above the beach in the
vicinity of the subject property and on the property itself are heavily wooded.
Based on the presence of 100 year old or older Douglas firs and madrones on most of the bluff
slope on this stretch of coast line, and the consistent geology along this portion of the coast, it
appears that the frequency of slope failures that remove all the trees has been less frequent than
100 years.
As noted above in the geology section soils under lying the subject property consist of stratified
silts, fine sand, peat, sand and gravel, and glacial till. A schematic cross section sketch illustrates
the approximate locations of the units observed.
Several old slides are apparent on the subject property. One inactive slide is located on the lower
slopes of the property below the proposed building area, and two slides are located on the slopes
above the proposed building area. The lower slide appears to be the result of oversteepening of
the slope from erosion at the base of the bluff combined with the steepening of the slope years ago
by cutting the road and level area into the base of the steep slope.
The two upper slides appear to have been the result of slope colluvium and topsoil sliding on the
steep slope over the underlying compact soils. The colluvium that builds up on this slope is
partially the result of loose sand and gravel that has been collecting on the slope from a sand and
gravel unit above the very steep slope to the west of the subject property. Water seeps are present
at the top of the compact silts and peat deposits within the base of the loose sand and gravel. It
appears that during times of soil saturation some slope failures have spilled down onto the slope
on the west side of the property. This loose soil material has accumulated over the underlying
very compact silts, sands and gravels and is susceptible to sliding during periods of wet weather.
Stratum Group
File: 7.5.01
4
August 1,2001
Tax Parcel 7012283001, Quilcene, W A
Geologic Evaluation of Shoreline Bluff
St~ 1 ~ LUUl
,lfffEIISON COUNTt DCD
CONCLUSIONS AND RECOMMENDATIONS
Based on our visual inspection of the subject property and vicinity, we conclude that a residence
can be located on the southern portion of the relatively level area on the mid-section of the
property as indicated in the site plan sketch. A residence located at this site should not be at risk
from bluff erosion or land sliding that would threaten the structure within the expected life of the
structure (75 years) as long as our recommendations are followed.
The relatively level building area on the mid-portion of the slope adjacent to the road is
approximately 250 feet long. We recommend that proposed residence be constructed on th~
southern 70 feet of this area. The building should be setback from the top of the steep slope a
minimum of25 feet, and should be no closer than 30 feet from the base of the slope above the
building site. This location is such that slides above the proposed building site will be directed
north or south of the building site due to the topography of the slope above the proposed building
site.
A deck may be constructed within the setback from the top of the steep slope as long as it is not
an integral part of the structure of the residence. That is if a slope failure occurs, the deck will
detach from the house.
Native vegetation, particularly tress and low native brush on the slope between the building site
and the steep slope below the building site should be disturbed as little as possible. No trails or
grading should be performed on the steep slope below the building site. If trees are thinned or
limbed for view purposes, no debris should be placed on the top of the bluff Some thinning of
trees growing between the top of the bluff face and the home site should not cause any problems
as long as the native brush understory is left in place. Thinning and trimming of trees on the bluff
slope should be limited to topping of alders and maples and limbing for view corridors of Douglas
fir and western red cedar. Any debris from thinning on the bluff slope itself should be removed
from the slope.
All storm water run off from the roof gutters should be routed away from the bluff face. Storm
water can be directed into an infiltration area south and downslope of the proposed residence
towards an existing drainage swale.
he septic drain field may be located either north or south of the proposed building site. If located
uth of the proposed building the topography of the area will direct subsurface flow away from
e steep slope. If the drain field is located north of the proposed building site, the drain field
ould be located at least 50 feet from the top of the steep slope.
Stratwn Group
File: 7.5.01
5
August 1,2001
Tax Parcel 7012283001, Quilcene, WA
Geologic Evaluation of Shoreline Bluff
Maintaining healthy native vegetation cover both on the uplands and on the slope will best control
long term erosion. Blackberry vines should be removed from the slope and not allowed to spread
as they can crowd out desirable plants and do not provide effective erosion control.
Yard waste and other deleterious material should not be placed on or over the slope. Such
material smothers vegetation, retains water and acts to destabilize the slope.
CLOSURE
Please note that there are inherent risks associated with lots near or adjacent to steep slopes.
These are risks that the building owner should recognize and be willing to accept. If conditions
appear different than those described in this report, or other concerns arise, we request that we be
notified so we can review those areas and modifY our recommendations as required.
We appreciate the opportunity to be of service to you. Should you have any questions regarding
please contact our office at (360) 714-9409.
Sincerely yours,
~ ~ ~ 0.. ..
Stratum Group
Dan McShane, M.S.
Geologist
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Stratum Group
File: 7.5.01
6
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