HomeMy WebLinkAboutBLD2007-00286 Geotechnical Report I
SHANNON F�WILSON, INC. COLOR
ALASKA
' �� COLORADO
CEOTECHNICAL AND ENVIRONMENTAL CONSULTANTS CALIFORNIACALIFOA
MINNESOTA
MISSOURI
OREGON
WASHINGTON
I
1 October 4, 2012 DE C E O V
I1.1 OCT 222012
Mr. Gary Colley
Platt Irwin Law Firm JEFFERSON COUNTY
I 403 S. Peabody DEPT.OF COMMUNITY DEVELOPMENT
Port Angeles, WA 98362
IRE: ENGINEERING GEOLOGIC EVALUATION OF
RESIDENTIAL PROPERTY AT 311 VICTORIA LOOP, CAPE GEORGE,
IJEFFERSON COUNTY, WASHINGTON
Dear Mr. Colley:
IAt your request, we have completed an evaluation of the engineering geologic aspects of a
residential property at 311 Victoria Loop in Jefferson County, Washington. The purpose of our
Iwork was to review the geologic conditions and the past history of the site to evaluate the
feasibility and relative risk of habitation of the newer of two residences on the site. We
Iunderstand that the houses on the site are no longer occupied and both have been declared unsafe
(red-tagged) due to landslide hazard.
1 The scope of our services included a review of existing publicly available geologic maps, a site
visit on August 21, 2012, a review of pertinent documents provided by Ms. Leslie Johnson of
First Federal Savings & Loan, discussions with you and Ms. Johnson regarding my findings, and
Sthe preparation this letter report.
I
Our work was authorized by you in a letter dated August 9, 2012.
MATERIALS REVIEWED
I • Reports by the Stratum Group (chronologically):
— Geology Stability Inspection, 291 Victoria Loop, Port Townsend, Washington for
I
Elma Berry dated October 23, 2004.
— Geology Stability Inspection, 291 Victoria Loop, Cape George Colony,
I — Washington for Katherine Kent dated June 20, 2005.
Geology Stability Inspection, 291 Victoria Loop, Cape George Colony,
Washington for Katherine Kent dated June 24, 2005.
I400 NORTH 34TH STREET•SUITE 100 LOG �TEM
P.O. BOX 300303
SEATTLE, WASHINGTON 98103 1 �J 21-1-21762-001
206 632 8020 FAX 206 695 6777 4
I TDD: 1.800.833.6388 ,t
www.shannonwilson.com 9 fa O ) 5
Mr. Gary Colley
Platt Irwin Law Firm SHANNON&WILSON,INC.
I, October 4, 2012
Page 2 of 7
— Occupancy of ExistingHome, 291 Victoria Loop, Cape George Colony,
Y p, p g
Washington for Katherine Kent dated May 31, 2006.
— Old Septic Tank and Slope Stability, 291 Victoria Loop, Cape George Colony,
Washington for Katherine Kent dated August 4, 2006.
1 — Location of Proposed Home, 291 Victoria Loop, Cape George Colony,
Washington for Katherine Kent dated October 29, 2007.
— Site Inspection, 291 Victoria Loop, Cape George Colony, Washington for
Katherine Kent dated April 9, 2008.
- Site Inspection, 291 Victoria Loop, Cape George Colony, Washington for
Katherine Kent dated August 4, 2008.
■ Other reports and correspondence (chronologically):
- Coastal Zone Atlas, Jefferson County, Washington, 1978, Washington
Department of Ecology.
— Permit Case Summary for 311 Victoria Loop, 1979—2011, Jefferson County,
Washington.
— Soil Hole Logs and septic design calculations, January-May 2006, Mike Deeny.
- Septic System Preliminary Design, Parcel #937800119 (7 sheets), May 23, 2006,
Creative Design Solutions.
- Septic Permit Application, May 31, 2006, Katherine Kent (applicant).
— Septic Disposal Permit, August 4, 2006, Jefferson County Department of
Community Development.
— Septic System, Parcel #937800119, Record Drawing(2 sheets), February 28,
2009, Creative Design Solutions.
— Rapid Evaluation Safety Assessment Form, March 19, 2012, Jefferson County
Building Department.
— Taxpayer's Claim for Reduction of Assessments Resulting from Destroyed Real
or Personal Property or Loss of Value in a Declared Disaster Area, March 20,
2012, Katherine Kent (applicant).
SITE DESCRIPTION
The residential property is located on the western edge of the Cape George Colony in
northeastern Jefferson County, about 5 miles west of Port Townsend as shown in Figure 1. The
property is one of several residences that border a steep to precipitous bluff overlooking the
Strait of Juan de Fuca. The plateau on which 311 Victoria Loop is located is about 120 feet
Ci fTEM
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Mr. GaryColley
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Platt Irwin Law Firm SHANNON&WILSON,INC.
October 4, 2012
Page 3 of 7
above the shoreline. Below the edge of the bluff, the ground drops about 40 feet near vertically,
to the west of which is a gently inclined bench or terrace about 50 feet wide. The slope then
drops steeply about 80 feet down to the beach. The beach is presently covered with trees, rocks,
and other landslide debris.
There are two structures on the subject site, as shown in the site sketch, Figure 2. The older,
abandoned building is very close to the edge of the bluff; 14.5 feet east at the southern end and 7
feet east at the northern end. A concrete patio to the west of the building is partially undermined,
as shown in Figures 2 and 3. A newer, recently abandoned residence is adjacent to the eastern
edge of the older structure. The western wall of the newer structure is presently about 60 feet
east of the bluffs edge at the southern end of the building and about 54 feet east of the bluff at
the northern end of the building. No earth cracks or building cracks indicative of earth
movement were observed above the bluff
A septic tank that was formerly located on the ground between the older house and the bluff s
edge is presently sitting on the mid-slope bench about 50 feet below the top of the bluff A white
polyvinyl chloride pipe that was apparently connected to the septic tank currently sticks out of
the slope,just below the top of the bluff. A new septic system is installed in the space to the
north of the newer residence, as indicated in Figure 2.
SITE HISTORY
We do not know the date of the construction of the original house; however, records indicate that
the original septic system was approved in 1976. In 1997, the septic tank of the original house
was, "exposed on the bluff due to bluff erosion." In 2006, "a building permit to demolish an
existing house and leaving cement foundation was finaled (sic) on October 15, 2007." This is
the structure identified above as the original, older residence. It appears that the superstructure
was demolished, leaving the basement, which is presently accessible only from the western patio.
A building permit, "for a single family residence with attached garage" was approved on
December 3, 2007. This is the structure referred to above as the newer residence. The"final,
final"building inspection for this residence was dated March 25, 2009.
Engineering geologic evaluations were performed for 311 Victoria Loop between June 20, 2005,
and August 4, 2008, by the Stratum Group. Reports by the Stratum Group document
assessments and recommendations for siting the new residence, including geologic risk,
occupancy limitations for the older residence, general site development guidelines, setbacks from
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I
Mr. Gary Colley
Platt Irwin Law Firm October 4, 2012 SHANNON&WILSON,INC.
Page 4 of 7
the bluffs edge for the new house, and the advisability of keeping in place the older residential
basement structure.
GEOLOGIC AND BLUFF CONDITIONS
The geologic conditions as exposed in the bluff are well documented in three Stratum Group
reports in 2004 and 2005. They will not be repeated herein. We have no disagreement with the
geologic characterization of the site by the Stratum Group.
The bluff on the subject and surrounding properties is recognized as unstable on maps in the
Coastal Zone Atlas (CZA)produced by the Washington Department of Ecology; classified as
either"unstable" or"unstable old slide." It is difficult to locate 311 Victoria Loop exactly on the
CZA map,but it appears to be in the latter category. In our opinion, this property and adjacent
bluff-bordering properties can be categorized as landslide-prone, actively unstable, or sensitive
Islope.
In the site description of the June 24, 2005, report by the Stratum Group, the uppermost vertical
' bluff to the west of the older house was reported to be about 15 feet high. Based on visual
observation, we estimate the height to presently be about 40 feet. Other descriptive text in the
Stratum Group reports indicates that the bluff has been active in the past several years. Based on
several reports by the Stratum Group, the newer house was to be set back 65 feet from the edge
of the bluff in 2008. Stakes were placed and verified in the field for this setback distance.
During out recent site visit, the western wall of this structure is presently about 60 feet east of the
bluffs edge at the southern end of the building(regression of about 5 feet) and about 54 feet east
of the bluff at the northern end of the building (regression of about 11 feet).
In the June 24, 2005, Stratum Group report, a bluff regression rate of 4 inches per year was
estimated. Over a 100-year structure life, the bluff regression was estimated to be about 33 feet.
The Stratum Group added two slab failures 15 feet wide plus a rounding up of 2 feet to yield the
recommended 65-foot setback.
Assuming
ssu ing that the new residence was built 65 feet from the bluff edge at both the north and
south corners of the house, the bluff regression rates since 2008 range from approximately
2.75 feet (33 inches) to 1.25 feet (15 inches) per year, respectively. It is unknown whether the
bluff regression occurred gradually or in large pieces during this time period; however, we
suspect that a block fall (one of the two assumed by the Stratum Group) could have occurred due
separation of the septic tank plumbing or could have caused the tank plumbing to separate.
LOG ITEM
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Mr. GaryColley
e Y
Platt Irwin Law Firm SHANNON eiWILSON,INC.
111 October 4, 2012
Page 5 of 7
CONCLUSIONS AND RECO
MMENDATIONS
In our opinion, remedial measures to slow or temporarily stop the regression of the bluff on the
subject or adjacent properties are not practical or financially reasonable. Measures commonly
used to arrest or decrease slope movement, such as drainage, slope buttressing, or retaining
walls, may be impractical, very expensive, or require constant maintenance. Additionally, work
along the shoreline would be subject to exhaustive permitting with questionable favorable results
and a poor chance of approval by Jefferson County and State of Washington permitting agencies,
in our opinion. Without extensive subsurface exploration and groundwater monitoring, it is
111 unclear which remedial measure(s) would be the most effective here.
If the rate of regression were to revert to that estimated by the Stratum Group, the risk to the new
residence would be relatively low over the next 100 years. However, if the regression rate of the
last 4 years is the new normal, then the bluff could move back to the residence in less than 20
years. It has been our experience that such Puget Lowland bluffs move episodically; that is,
shorter periods of movement followed by longer periods of quiescence. Such rates can be
rendered meaningless in the event of strong seismic shaking.
' We understand that the older basement foundation will remain in place, and we agree with this
recommendation. It has been our experience that the regression of a landslide headscarp is
commonly slowed or temporarily stopped once it reaches the foundations of a structure. In this
case, much depends on storm activity, the retention of the landslide debris on the middle and toe
of the bluff, and groundwater levels within the upland plateau.
In our opinion, the risk posed by continued bluff erosion and movement to the newer residence is
relatively low at this time; however, the exact number of years in which the risk becomes high or
the condition may become dangerous cannot be estimated with a high degree of precision or
certainty. It is unlikely that the high rate of the past 4 years will continue, in our opinion. The
newer house could be occupied at this time with a low risk; however, the length of safe
occupancy is unknown and should be reassessed as the bluff continues to regress in the future.
As previously stated in the Stratum Group reports, some actions can be taken to reduce the risk
of landsliding/bluff regression at this site. They include:
1. Native vegetation should not be disturbed on the property.
2. No materials should be placed on or over the bluff.
LCt17-
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Mr. Gary Colley
Platt Irwin Law Firm SHANNON&WILSON,INC.
tOctober 4, 2012
Page 6 of 7
the beach byfuse-welded high
3. All storm drain lines should be directed either to g
density polyethylene pipe or to stormwater collection facilities away from the bluff
4. Slope stakes to measure the location of the bluff edge should monitored and
recorded by the owner at least twice a year.
5. If a block of more than 5 feet wide is observed to fall from the bluff, an engineering
geologist or geotechnical engineer should assess the bluff conditions.
6. An evaluation of other possible strategies to reduce bluff erosion rates (e.g., walls,
subsurface drains) would require subsurface explorations and engineering analyses.
LIMITATIONS
The conclusions and recommendations in this letter report are based on a visual examination of
the surface conditions as they existed during the time of our site visit. No subsurface
explorations were performed for this study. This work has been performed using practices
consistent with geologic and geotechnical industry standards in the region; however,prediction
of slope movements or bluff regression rates with certainty is not possible with currently
available scientific knowledge. As with any steep slope, there are always risks of instability that
present and future owners must accept. Such risks include seismic shaking, groundwater levels,
heavy precipitation, water leaks, pipe breaks, improper or inappropriately directed drainage, lack
of maintenance for drains and vegetative cover, filling or saturation on the property, record rain
or snow falls, or other actions, events, or unknown conditions that could cause slope instability.
If site conditions described in this letter report change, we should be advised immediately so that
we can review those conditions and reconsider our conclusions and recommendations.
Opinions and recommendations included in this letter report are presented to assist the Platt
Irwin Law Group in decisions regarding the disposition of the subject property. Shannon &
Wilson has included the enclosed, "Important Information About Your Geotechnical/
Environmental Report," to assist you and others in understanding the use and limitations of our
reports.
r
I
1
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Mr. Gary Colley
Platt Irwin Law Firm SHANNON&WILSON,INC.
A October 4, 2012
Page 7 of 7
IWe appreciate the opportunity to be of service. If you have any questions or comments, please
contact me.
ISincerely,
ISHANNON & WILSON, INC.
I °��0 Was,,',
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\ njjeeeriog 6eo{ovst4.
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I1 William Thomas Laprade
I William T. Laprade, L.E.G.
Senior Vice President
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Enc: Figure 1 —Vicinity Map
I Figure 2— Site Plan
Figure 3 —Photo 1, Bluff Edge Looking North
Figure 4—Photo 2, Concrete Patio Looking South
I Figure 5 —Photo 3, Bluff and Undermined Patio Looking East
Important Information About Your Geotechnical/Environmental Report
I
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Map adapted from aerial imagery provided by
Google Earth Pro, reproduced by permission
E granted by Google Earth TM Mapping Service October 2012 21-1-21762-001
ro SHANNON &WILSON, INC. FIG. 1
- Geotechnical and Environmental Consultants
111
SHANNON & WILSON INC. Attachment to and part of Report 21-1-21762-001
- Geotechnical and Environmental Consultants
' Date: October 4,2012
- To: Mr.Gary Colley
Platt Irwin Law Firm
I
I IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL/ENVIRONMENTAL
REPORT
111
CONSULTING SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES AND FOR SPECIFIC CLIENTS.
IConsultants 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
Iexpressly 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.
ITHE 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
Ifactors. 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
Imay 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,
Ior 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.
ISUBSURFACE CONDITIONS CAN CHANGE.
Subsurface conditions may be affected as a result of natural processes or human activity. Because a geotechnical/environmental report
Iis 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
Iwere 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.
LOG0 i E::.
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A REPORTS CONCLUSIONS ARE PRELIMINARY.
The conclusions contained in your consultant's report are preliminary because they must be based on the assumption that conditions
Irevealed 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
Iapplicable 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.
ITHE 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
Iprofessionals to explain relevant geotechnical,geological,hydrogeological,and environmental findings,and to review the adequacy of
their plans and specifications relative to these issues.
IBORING 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
Igeotechnical/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.
I 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
I 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
I 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.
IREAD RESPONSIBILITY CLAUSES CLOSELY.
Because geotechnical/environmental engineering is based extensively on judgment and opinion, it is far less exact than other design
I 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
I 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.
I The preceding paragraphs are based on information provided by the
ASFE/Association of Engineering Firms Practicing in the Geosciences,Silver Spring,Maryland
I
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