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STRATUM GROUP
1451 Grant Street, Bellingham, W A 98225
Phone (360) 714-9409
DEe 1 2 2006
June 2, 2006
Bruce and Theresa Lockwood
2945 SE Cleveland Drive
Portland, OR 97080
Re: Geology Assessment
Tax Parcel 602133020
Bee Mill Road
Jefferson County, Washington
Dear Mr. and Ms Lockwood:
Stratum Group is pleased to present the results of our geology assessment of the above
referenced property adjacent to a shoreline bluff. The purpose of this geology assessment was to
1) determine the suitability of the property for the siting of a residence, 2) qualitatively evaluate
the risk of slope failures, and 3) provide general site development and maintenance
recommendations for development of the property adjacent to a potentially unstable bluff. Based
on my investigation of the site and vicinity, it is my opinion that the site is suitable for
development as a residential property provided the recommendations presented in this report are
followed. This assessment included a visual inspection ofthe property, slopes on and in the
vicinity of the property, the shoreline at the base of the bluff, and a review of available geologic
mapping in the area.
SCOPE OF SERVICES
The scope of our services included the following:
1) Conducted a site visit to visually inspect the subject property and vicinity
including the bluff slope conditions, slope conditions on and in the vicinity of the
property and shoreline conditions.
2) Observed surface soil conditions on the shoreline slope and the upland portion of
the property at the top of the bluffby excavating shallow hand dug test pits.
3) Prepared this report summarizing our findings, including an evaluation of the
feasibility of building a residence on the subject property, a qualitative evaluation
ofthe shoreline bluff stability, recommendations for site development, and
recommendations for further investigation, if necessary.
June 2,2006
Tax Parcel 602133020, Bee Mill Road, Jefferson County, W A
Geology Assessment
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 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' x 60' Quadrangle. Washington (Yount,
Minard and Dembrof, 1993) indicates the property is underlain by recessional glacial outwash
deposits. The Geologic Map of West-Central Jefferson County. Washington (Birdseye, 1976)
indicates the subject property and the bluff exposed on the subject property are underlain by ice-
contact stratified drift.
My observations on the bluff face and within road cuts to the west of the subject property are
generally consistent with the mapping described above. However, the upland and uppermost
portion of the bluff is underlain by glacial till. The lower portions of the shoreline bluff are
underlain by stratified sand and gravel with silt and clay and cobbles. This stratified unit
underlying glacial till is consistent with Birdseye's interpretation of this unit being an ice contact
deposit. Yount, Minard and Dembrof (1993) include ice contact deposits within their description
of recessional glacial outwash. However, based on my observations the stratified deposits on the
bluff slope were either deposited by water flowing under the glacial ice or are preglacial outwash
deposits that were subsequently over ridden by glacial ice. The stratified sediments are very
compact indicating ice compaction and the majority of the cobbles are from locally derived
bedrock consistent with the overlying the unit.
The important point of this interpretation is that the stratified sediments are very compacted and
are very resistant to erosion from wave action due the compact nature of the unit. Recessional
units tend to be much less compacted and are much more subject to erosion.
SPECIFIC SITE OBSERVATIONS
The location of the subject property is indicated on the attached site vicinity map. A schematic
site plan for illustrative purposes is provided in Figure 2. The subject property consists of a very
gently sloping upland area bounded on the northeast by a steep shoreline bluff. The shoreline
bluff slopes down to a gravel beach on the shore of an estuary inlet associated with Spencer
Creek. The creek and estuary flows into Jackson Cove, a bay off of Hood Canal. The upland area
and most of the steep shoreline bluff are tree-covered with a mix of mature Douglas fir and
madrone trees. The understory consists of thick moss, salal, evergreen huckleberry and
Rhododendrons (in bloom at the time of my site visit).
Stratum Group
File:5,I,06,C
2
June 2, 2006
Tax Parcel 602133020, Bee Mill Road, Jefferson County, W A
Geology Assessment
The shoreline bluff is approximately 25 feet high and has an overall slope average of
approximately 70 degrees; however, portions of the bluff are vertical at the shoreline. Despite the
very steep slope, the shoreline bluff slope is well vegetated with mature trees. The soils
underlying the bluff slope consist of extremely compact sand and gravel with silt and cobbles.
Most of the trees on the bluff slope are mature trees.
The beach along the shoreline consist of a cobble and gravel beach primarily made up oflocally
derived bedrock fragments eroded out ofthe shoreline bluff. Upland plants are growing on the
upper most portion of the beach indicating that tide levels and waves rarely reach the toe of the
steep shoreline bluff. However, a portion of the steep shoreline bluffhas been undermined along
the subject property and it appears that a small slide took place this past winter. This event likely
was associated with a very high tide and storm surge event that took place in early February
2006. Shoreline bluff toe erosion took place along many bluffs within the northern inland waters
of Washington State during that event.
A trail from the upland area down to the beach cuts across the steep shoreline slope. The trail is a
very narrow foot trail. No erosion or slope problems are present on this slope associated with the
trail. However, the slope below a portion of the trail along the mid-section of the trail has been
undermined by erosion at the base of the 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 upland portion of the property such that bluff erosion or landsliding would
not threaten the structure within the expected life of the structure (75 years) as long as our
recommendations are followed. I recommend a set back distance of at least 25 feet from the top
of the steep bluff slope. It is my opinion from an engineering geology standpoint that this
distance will be adequate to allow for expected bluff face failures that will result from the
periodic erosion of the base of the bluff by wave action and ravelling of the exposed soils on the
bluff face as well as any possible minor settlement along the upper slope.
I do not anticipate that the development of the subject property will cause any negative impacts
on the stability of the slope as long as the following recommendations are followed.
Because the bluff is an eroding bluff, slope failures should be expected to occur on a periodic
basis. The only way to prevent continued erosion of the base of the bluff would be to construct
hard armoring at the shoreline at the base of the bluff. However, the eroding bluff acts as a feeder
bluff (erosion of the bluff provides sediment) for the beaches northwest and southeast of the
subject property, and any shoreline armoring will have a negative impact on properties down drift
from the bluff as well as the beach in front of the subject property. The construction of shoreline
Stratum Group
File:5.I ,06,C
3
-..,
June 2, 2006
Tax Parcel 602133020, Bee Mill Road, Jefferson County, W A
Geology Assessment
armoring on other properties may cause an increase of erosion of the subject property. The
owner ofthe subject property should contact Jefferson County officials regarding any proposed
shoreline protection projects along the bluff or any shoreline protection construction. There are
currently no shoreline-armored areas along this stretch of coastline.
Soils on the upland portion of the property appear to be relatively well drained. Roof drains and
any drainage around the home should be discharged into a perforated dispersion pipe and
infiltrated into the ground at least 30 feet from the top of the steep shoreline bluff.
Site grading soils or debris, landscape debris, or any other material should not be disposed of
over the bluff face or placed at the top of bluff or placed on the steep ravine slopes. Over time
debris will break down and form an unstable mass that will slide damaging the slopes below.
Native vegetation, particularly tress and low native brush within 20 feet of the top ofthe bluff
should be disturbed as little as possible. If trees are thinned or limbed for view purposes on the
bluff face, all debris should be removed from the bluff face. Limbing and topping of trees should
be limited to maintaining the view corridor only and the native brush understory should be left in
place.
A septic drain field should not have any have any adverse affects on the stability of the bluff as
long as the drain field is located at least 50 feet from the top of the bluff.
Stratum Group appreciates the opportunity to be of service to you. Should you have any
questions regarding our reconnaissance please contact our office at (360) 714-9409. 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.
Sincerely yours,
r,'fij..,~mGr~ !Y
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Dan McShane, M.Sc., L.E.G.
Licensed Engineering Geologist
Stratum Group
File:5,],06.C
4
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