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Home My WebLink AboutSlope Assessment - PLN General - 6/30/2007 SLOPE ASSESSMENT 31 NE TI MA ROAD BELFAIR, WA CLIENT: MR. ROGER BURMASTER PO BOX 1651 BELFAIR, WA 98528 BY: N.L. OLSON AND ASSOCIATES, INC. 2453 BETHEL AVE. SE PORT ORCHARD, WA 98366 (360) 876-2284 n JOB NO. 6697- 07 39359 . JUNE 2007 N.L. OLSON & ASSOCIATES, INC. Engineering, Planning and Surveying May 20, 2006 Project Number: 6697-07 Attn: Mr. Roger Burmaster PO Box 1651 Belfair, WA 98528 Subject: Slope Assessment Proposed Outbuilding 31 NE Tima Road Belfair, WA 98528 Mason County Parcel#: 123292290050 Dear Mr. Burmaster; This report presents our findings of the slope assessment and subsurface investigation within the site. We appreciate the opportunity to be of service to you on this project. If we can be of further assistance or if you have any questions regarding this project, please contact our office. Sincerely, Eric Castleberry Wesle+RJo son, P.E. Staff Geologist Project Engineer P.O. Box 637•2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800)755-1282 Fax: (360) 876-1487 Q%ProjectslNLO FileslProjects%697-Burrnaster%Burmaster Final.doc TABLE OF CONTENTS INTRODUCTION .....................................................................................................................1 SITELOCATION....................................................................................................................... 1 SITECONDITIONS................................................................................................................... 1 PROPOSEDDEVELOPMENT..................................................................................................... 1 FIELD INVESTIGATION AND WATER WELL LOG INFORMATION..................................................... 1 AVAILABLE GEOLOGIC AND SOILS INFORMATION.......................................................................2 SLOPERECONNAISSANCE.......................................................................................................2 HISTORICAL LANDSLIDE RESEARCH.........................................................................................2 CONCLUSIONS & RECOMMENDATIONS.............................................................................3 REPORTLIMITATIONS..........................................................................................................3 VICINITY MAP &SITE PLAN...................................................................................FIGURE 1 CROSSSECTIONS..................................................................................................FIGURE 2 SLOPESTABILITY MAP .........................................................................................FIGURE 3 SLOPE ASSESSMENT PROPOSED OUT BUILDING 31 NE TIMA ROAD BELFAIR, WA 98528 INTRODUCTION This report presents the results of our field investigation for the referenced project. The assessment was done per Mason County Resource Ordinance, 17.01.100 landslide hazard areas, section E. special reports, page 6 of 15, as of December 27, 2006. In the following, we present our findings and conclusion for the proposed development. SITE LOCATION The property is located at the address of 31 NE Tima Road in Belfair, WA and by, section 29, township 23 north, range 1 west, in Mason County, Washington. The Vicinity Map for the property has been illustrated on Figure 1. SITE CONDITIONS The site is bordered to the east by a single-family residence, to the north by undeveloped land, to the south by a single-family residence and by undeveloped land to the west. The property is square in shape, roughly two and a half acres in size and previously developed with a single- family residence. The area of proposed development consists of a gradual slope, which descends from the north side of the property to the south side of the property, with gradients of 0 to 25 percent. A localized steep slope area of about 50 percent was observed north of the proposed building area and was the result of previous grading activity during placement of the existing residence. Beyond the proposed building area to the east the slope ascends at gradients of about 2 to 9 percent gradients towards a ridge and trends down to the east at gradients of 25 to 50 percent. The areas north and south of the proposed building has been logged and re-vegetated with weeds and grass. The slope area east of the proposed building has been logged and cleared of trees with branches and other woody material left in this area after the logging operation. PROPOSED DEVELOPMENT As presently conceived, a portion of the site is proposed for development. The proposed building footprint is rectangular and roughly 1,550 square feet in size. The structure will be one story and of light wood frame construction with a floor slab. The building's footing loads are anticipated to be light to moderate. We have shown the approximate building layout on the Site Plan - Figure 1. FIELD INVESTIGATION AND WATER WELL LOG INFORMATION The site's subsurface conditions were explored on June 7, 2007 by excavating two hand borings. The hand borings were excavated using posthole diggers and extended down 43 to 48 P.O. Box 637.2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 CAProjectsWLO Files\Projectsl6697-BurmasleABurmaster Final.doc Project No.6697-07 May 20,2006 Page No.2 inches below current site grades to evaluate the upper soils horizon. In general, our hand borings revealed the site is underlain by poorly graded sand with trace silt and gravel. Medium dense soil conditions were encountered 2.5 to 3 feet below current site grades. The water well log information indicated that sand composes the upper 90 feet of the soil horizon in this general area. During our subsurface exploration, perched groundwater and standing water conditions were not encountered. Based on the water well log information for this area, we anticipate a static ground water level at about 100 feet below current site grades. AVAILABLE GEOLOGIC AND SOILS INFORMATION The Washington Division of Geology and Earth Resource (WDGER), Geologic Map of Washington — Northwest Quadrant, dated 2002, has mapped the site as Quaternary sediments, dominantly glacial drift and includes alluvium. Glacial till consists of an unsorted, unstratified, highly compacted mixture of clay, silt, sand, gravel and boulders deposited by glacial ice. SLOPE RECONNAISSANCE As part of our fieldwork, the slope areas were examined for indications of slope instability during our reconnaissance performed on June 7, 2007. Indications of slope instability include head scarps, hummocky terrain, inconsistent patterns of vegetation, tension cracks, seepage zones and course grain material overlaying silt and clay soils. At the time of our reconnaissance, no slides or erosion were observed on the property and the site appeared stable. HISTORICAL LANDSLIDE RESEARCH A review of "Relative Slope Stability of Southern Hood Canal Area, WA, 1977" USGS Miscellaneous Investigation Series indicates the area in and around the property has been classified as Class 1, Class 2 and Class 3. Discussion of each class is provided in the following and the Slope stability mapping for the site has been illustrated on Figure 3. Class 1: Areas believed to be stable. Slope generally less than 15 percent, but may be greater locally in areas too small to be shown at the map scale. Largely comprises rolling uplands underlain by stable material such as young glacial till, mantled in places by a thin layer of sandy gravel or other permeable material; also includes flood plains, deltas, alluvial fans, and some beach deposits. Class 1 areas immediately adjacent to steep slopes of class 3 areas may be threatened by potential landsliding. Normal, proper engineering practices generally are adequate to insure stability in these areas. Class 2: Areas believed to be stable under normal conditions, but may become unstable if disturbed by man's activities, oversteepened by erosion, or subjected to strong seismic shaking. Slopes are generally steeper than 15 percent, but may be less in some areas of weak geologic materials. Includes areas underlain by; well drained sand and gravel, mostly on valley sides that lack known slope failures; glacial till with steep slopes; and bedrock. Class 3: Areas inferred to be unstable because slopes, generally greater than 15 percent, underlain by weak, unstable materials in which old or recently active landslides have occurred. P.O. Box 637. 2453 Bethel Avenue • Port Orchard,Washington 98366 Phone: 1(800)755-1282 Fax: (360) 876-1487 C:TrojectsWLO FilesTrojects16697-Burmaster\Burmaster Final.doc Project No.6697-07 May 20,2006 Page No. 3 Includes areas of sand and gravel on top of impermeable silt and clay, mostly along steep valley sides. The "Relative Slope Stability of Southern Hood Canal Area, WA, 1977" indicates the area of proposed development has been classified as Class 3. However, based on the slope gradients encountered in the proposed building area, in our opinion, the area of proposed development should be reclassified to class 1. The steeper slope areas that meet class 2 or 3 criteria are roughly one hundred feet east of the proposed building as illustrated on our cross sections. The steeper slope area immediately north of the proposed building were created by previous grading activity when the single-family residences was placed. In our opinion, the proposed building area has been adequately set back from the steep sloping areas along the north and south sides of the site. CONCLUSIONS Following our review of Mason County Resource Ordinance, Ordinance Number 77-93, we conclude that large scale sliding or deep-seated rotational failures resulting from the proposed construction appears negligible and the overall global stability of the proposed building area under the present site conditions and post construction appears good and an additional geotechnical engineering report will not be required for this proposed development. REPORT LIMITATIONS This report has been prepared for the client regarding the subject project. Information presented in this report has been collected and interpreted in a manner consistent with the level of care and skill ordinarily exercised by members of the profession currently practicing under similar conditions, and in accordance with sound and generally accepted principles consistent with normal consulting practice. No other warranty, expressed or implied, including (but not limited to) any warranty or merchantability or fitness for a particular use has been made. In the event that change in the nature, design, or location of the proposed construction is made, or any physical changes to the site occur, recommendations are not be considered valid unless the changes are reviewed by NLO and conclusions of this report are modified or verified in writing. Any site involving sloping terrain has inherent risk of earth movement. As a result, the CLIENT agrees to accept full responsibility for all risks associated with steep slopes. The CLIENT acknowledges that this risk cannot be completely eliminated and that engineering and geologic analysis is intended to reduce the inherent risk associated with slopes. No amount of geotechnical engineering and geologic analysis can provide a guarantee of stable slopes. Geotechnical engineering and geologic analysis are based heavily on subjective interpretation, professional judgment, and opinion regarding the physical conditions at a specific site. Subsurface conditions are only documented at those points where samples were taken and interpolation and extrapolation is necessary between and around sample locations. Conditions can vary between samples and can change over time due to natural processes and/or human P.O. Box 637.2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 CAProjects\NL0 Files\Projects16697-Burmaster%Burmaster Final.doc y I Project No.6697-07 May 20,2006 Page No.4 activity. Analyses and recommendations provided in this report are based in part upon the data obtained from the subsurface explorations. P.O. Box 637.2453 Bethel Avenue• Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 C:%ProjectsWL0 FilesTrojects%6697-Burtnaster%Burrnaster Final.doc Existingg_.._ Detached-- — E fisting Garage E -- --- Mobile Home i SITE FERN WAY x 0 0 0�� B 'sti Sh d � x ng o n .-- 0 5f Proposed Building Area A (1 ,575 SF) ° -;0 A VICINITY MAP �,r�:.x�-�.„;„_:�� NOT TO SCALE B SITE PLAN FIGURE 1 SCALE: 1 = 50 REVISIONS BY I DATE I FOR: NO. DATE BY DESCRIPTION DESIGNED ,A! SITE PLAN & VICINITY MAP ROGER B1651 ER DATE. NE 20. 2 L J N.L.OIsonBAssociates,lnc. PO BOX 1651 DATE:JUNE 20. zoos DR—E Engineering, Planning and Surveying 4�•�ma64 31 NE TIMA ROAD BELFAIR, WA 98528 BELFAIR, WA 98528 DRAwLNC NUMBER 076697 APPROVED (360) ens-zzB+ _ XXXXXX XXXXXX ACCEPTED 2453 BWW Avenue.P.O.Box 637,Port Orchard,WA SM _ / 2 A—A' CROSS SECTION (Looking North) - - - -- - - - - - -- 7 - - - - T- -- - -I- - -- T - - - -� - - - � - --- T- - - - - I - - - - -I- - -- -� 130 I I I I I I I I I I I I I 130 120 I- - -I - - - - I - -- I - - - - I -- - -I- - - -I - - - -I- - - - I - -- - I - - -I - - - - I - - - I 120 I I I I I I 110 I I PROPO ED I 1 I 6% I I I I I I I 110 27, BUILDI G 1 �% 100 I- -- - - - - — — - - - - -I- -- --I- - -- -I- - -I- - - - -+ - -- - >� - - - -I - - - - -- - - -I 100 I 35% I 1 1 1 90 I I 35ft ISET BACKI DISTANCL 114ft I I I I I I 90 I 80 1-- -- ---r - - - - -- ---I - - - - r -- - -1- - -- - - -- -1- - - - -� - - — - - - - - - --r- - - - -1 80 I 24% I I 70 60 -- -J - - - - L-- -- - - - - -I- -- - -1- - -- - - -- -1- - - --1 -- - - J-- - - - -1 - - - - J- - - - 60 I I I I I I I I I I I I I 300 250 200 150 100 50 0 SCALE: 1 "= 30' B-B CROSS SECTION (Looking West) DURING OUR RECONNAISSANCE, A LIMITED SLOPE SURVEY WAS r— — - — — —I—— — —— —T— — —I— — — —— —— —I——_ —_ T- — —_ I I I I I I I I I I I PERFORMED UTILIZING A HAND HELD (SUNTO TYPE PM-5/360PC) TO 170 I I I I I I I I I I I "° ESTIMATE SLOPE GRADIENTS AND A 300 FEET FIBERGLASS TAPE UTILIZED FOR SLOPE DISTANCE MEASUREMENTS. THE SURVEY SHOULD 160 — — -� — — —I— — — —— — — —I— — — J- — — -I — — —1—— — l- — — BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED AND 150 I I I I I I I I I I I 10 METHODS USED. I I I I I I I I I I 130 I I I 1 I I I 1 3 f I I I 130 NOTE ELEVATION ARE APPROXIMATE FINISH FLOOR EL=100 ESTABLISHED I__ _ I — — —I— — — I —— I — — —I— — — _ FOR THE PURPOSES OF THIS REPORT. 120 I I I I IPROP I I I 120 110 I I I 3% I I BUILC SED 17% L I I no FI LL 100= =100 0 50 100 ISO 200 250 SCALE: 1 40' BY DATE A FOR` ROGER BURMASTER SCALE AS90M REVISIONS , SECTIONS A-A & B-B N0. DATE BY DESCRIPTION DESIGNED `�J N.L.OISOnBASSOCIBtes,InC. PO BOX 1651 DATE:JUNE 20, 2007 �a�se DRAPING NUMBER CHE ED Engineering, Planning and Surveying �0 �MAL 31 NE TIMA RD BELFAIR, WA BELFAIR, WA 98528 076697 APPROVED (360) 876-2284 ACCEPTED 2453 Be"Am^P.O.Box 637.Port Orchard,WA 9066 owo�'" '_. 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