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Home My WebLink AboutGEO-Tech Review BLD2006-00467 - BLD Engineering / Geo-tech Reports - 6/8/2006 1 SON STA7-, � MASON COUNTY �P MC PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER o Shelton, Washington 98584 S N = r N 1 0 2� Y OJ �O 1864 DATE: June 8, 2006 INTER-DEPARTMENTAL COMMUNICATIONS TO: Kell McAboy PARCEL # 322325215003 FROM: John Sliva, Programs Engineer-PW BUILDING PERMIT NUMBER: BLD2006-00467 SUBJECT: Geo-Assessment Review NAME: Comsia Doug & Brenda Kell, The Geological Assessment with an addendum dated June 5, 2006 prepared for the proposed single-family two-story residence located at 141 E. Spruce in Union has been received and reviewed by Public Works. The addendum was a letter requested from Bradley-Noble Geotechnical Services. The addendum addressed ground water conditions at the site which were not included in the Geological Assessment. The assessment with the addendum appears to satisfactorily address County requirements for a Geological Assessment. The assessment reveals the extreme slopes are 11 degrees (19% slope) to 18 degrees (32% slope) from the drawing profile. Slopes at the structure and drainfield appear to be 19% from that profile. The author indicates soils can support standard spread footings. The author concluded that in their opinion the residence may be constructed at the indicated location without risk of loss or damage due to earth movements. The author further indicated that a geotechnical report is not appropriate or warranted for the proposed construction on the lot. I recommend accepting the assessment as satisfying the requirements for a County required Geological Assessment. Recommendations and comments contained in the report should be incorporated into the site development plans and made conditions for permit issuance. Not mentioned in the report is the fact that the area is mapped as Alderwood Ac soils. It important that adequate erosion and sediment control features need to be implemented during land disturbing activities to protect neighboring properties and State waters from adverse stormwater runoff impacts. The migration or release of silty water or mud from the applicant's property will be considered a violation of County and State water quality protection regulations. Please feel free to contact me at 724 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, John Sliva Programs Engineer Bradley-Noble Geotechnical Services a(P' A Division of The Bradley Group, Inc. PO Box 12267, Olympia WA 98508-2267 Phone 360-357-7883 9 FAX 360-867-9307 22 May 2006 1 Doug & Brenda Comsia 70 E. Harstine Forest Drive V Shelton, Washington 98584 Subject: Geotechnical assessment of the north facing slope on your property at 141 E. Spruce Street in Union, Washington, Mason County Tax Parcel Number 322325215003. Dear Mr. & Mrs. Comsia: As requested, we visited the above property in order to develop an opinion on slope stability and erosion potential of the site soils. Our work consisted of a site visit, review of available geologic information, our field conversation on proposed development, review of the site plan provided to us, and preparation of this report. The project site is located on the north side of Spruce Street. The property on the east side will include a vacated portion of Spruce Street. We found the upper portion of gentle slope. At the edge of the upper level the lot adjacent to Spruce Street to have a p g 1 P g area, there is another short slope down to another area of low relief. This area has the drain field installed. At the north edge of this area, the slope steepens down to the north towards an alley that is undeveloped in the toe area. The natural slope is well vegetated. Using a Brunton Pocket Transit, we were able to determine the average slope at this property by measurements from the top and toe G areas accessed by the alley. We found the native slopes to be in the 18 to 21 degree y/range (33 to 36%o_slope). This slope then is less than a 2:1 (horizontal to vertical). We noted that the slope flattens to the west of this property.,51opes less than 2:1 or 26 degrees are considered by the geotechnical profession to be stable, as the slope angle is less than the angle of internal friction of even loose granular soils. A slope of less than 2:1 in the 2003 International Building Code (IBC)is considered to be a safe slope not k requiring special geotechnical evaluation. / Examination of the slope did not indicate that mass wasting events have developed on this slope. No topographic features associated with mass wasting events was observed. Trees growing on the slope were vertical which suggests stability. We expect that soil creep, the slow downslope movement of the near-surface active soil zone is the only major erosional process working on the slope. 06050501 Page I of 3 06050501 Page 2 of 3 We understand that your proposed development will be a two-story, wood-frame residence that will incorporate a low daylight basement section with a floor to ceiling height of six feet or less. This is not habitable space and is proposed for storage. We agree with this design approach, as we expect that there exists some sidecast fill placed at the north edge of the upper bench. Construction of the daylight storage area will extend footings below any fill section and aid in keying the structure to the slope. To verify our interpretation of site geology, we referred to Geologic Map of the Shelton I:100,000 Quadrangle, Washington by Robert L. Logan, 2003, and published by the Division of Geology and Earth Resources, Department of Natural Resources. This area is mapped as Qga, Continental Glacial Deposits, Fraser Glaciation, Vashon Stade, Advance outwash, Late Wisconsinan. These soils in this area are glaciofluvial sands and gravels. Relative Slope Stability of the Southern Hood Canal Area, Washington by Mackey Smith and R. J. Carson, 1977, published by the Division of Geology and Earth Resources, Department of Natural Resources places this area in site Class 2, areas believed to be stable under normal conditions. These are areas that lack known failures, generally steeper than 15% and underlain by overconsolidated soils. e expect that site excavation will expose the dense sands and gravels of the advance outwash. These soils crop out in the_road cuts of this area. These soils can support >f standard spread foundations. Design of footings using Table 1804.2 in the IBC for a soil �S Class of Material type 4 is permissible. Structural fill material placed for support of garage slabs must be in conformance with the minimum requirements of Appendix J, Section J 107 for fills. To ensure a dry storage area, attention to perimeter drainage is required. At the base of the perimeter footings supporting foundation walls, a footing drain is to be installed. We recommend the use of rigid plastic pipe as it is more resistant to deflection and crushing during backfilling than the flexible ADS type of pipe. Use of a high quality water proof membrane sprayed onto the foundation walls is recommend in place of damp proofing using asphalt emulsion. Placement of bac ill a inst foundation walls must be in conformance with the requirements of Section 1 ,2 Placement of Backfill and � foundation. i 1803.3 Site Grading in the IBC to prevent ponding of water against the With excavation to construct the daylight storage area, we expect that height of cuts wilUxceed four feet. You and your contractor need to be aware that once forms or foundation walls exceed four feet in height, the void between the cut slope and forms or foundation walls is considered to be a trench under the Department of Labor and Industries Standards. All slopes then are to be cut or shored as specified in Chapter 296-155 WAC, Part N, Excavation, Trenching and Shoring. We recommend a soil type C be used for control. 06050501 Page 3 of 3 Water collected from footing drains and roof rain leaders is to be carried below the drain field for infiltration. For the roof rain leader collection system, we recommend the use of rigid plastic pipe with glued watertight joints. The roof rain leader collection system and the footing drains may be connected to a common discharge line at an elevation such that back up into the footing zone cannot occur. The site plan did not indicate if the property extended to the toe of slope area adjacent to the alley way. If the property does extend to the toe area, collected storm water should be conveyed to this area for infiltration. No concentrated-flows of storm water are to be_discharged over the slope. These concentrated flows can create areas of localized saturation and induce slope instability and accelerated erosion. We also recommend clean-outs in all storm water lines to allow for future maintenance. Based on our field observations, research, and understanding of the proposed development for this lot, it is our opinion that the residence may be constructed at the indicated location without risk of loss or damage due to earth movements. Attention to � --------- - --� control of storm water is required-to_ensur -ashy_storagg_area—dry, With the area being underlain by dense overconsolidated granular soils and at slope angles less than the angle of internal friction for these soils, we do not consider the preparation of a geotechnical report appropriate or warranted for the proposed construction on this lot. If you have any questions, or if we may be of additional service to you on this project, please contact us at our Olympia office. Cordially, BRADLEY-NOBLE GEOTECHNCIAL SERVICES `e of Y1 a S' ; �J David C. Strong, L.E.G. <�c �29 P`'Sed Geo�a DAVID C. sTPoNG Bradley-Noble Geotechnical Services A Division of The Bradley Group, Inc. / PO Box 12267, Olympia WA 98508-2267 Phone 360-357-7883 • FAX 360-867-9307 5 June 2006 RECEIVED JUN u 8 2W6 RECEIVED Doug & Brenda Comsia JUN 0 ' 2006 70 E. Harstine Forest Drive MAS(INCOUP��'I'li�l�l�10RK$ Shelton, Washington 98584 426 W. CEDAR ST. Subject: Additional information requested by Mason County Planning for your new home site at 141 E. Spruce Street in Union, Mason County Tax Parcel Number 322325215003. Dear Mr. & Mrs. Comsia: I received a telephone call from Mason County Planning about the report I prepared for you on the above property. Their comment was that I did not discuss springs or seeps on the slope and their potential to adversely affect your site development. In visual examination of the slope, I did not observe springs or seeps and therefore did not include a discussion in the report. Based on my field observations, the downslope flow of storm water is in the shallow surface soils. With the low angle of the slope, we do not consider that these flows to be destabilizing. We expect that springs or seeps may develop downslope of your property where the underlying Skokomish gravels crop out and are overlain by permeable soils. At the horizontal distance from your property, these would not have and adverse effect on you. We do recommend that you control your storm water from the site as discussed in our report to protect the slope from concentrated flows. If we may be of additional service in obtaining your permit please contact us at our Olympia office. V � 6v1 Cordially, n� � BRADLEY-NOBLE GEOTECHNICAL SERVICES ^ e at W aoil ah�� David C. Strong, L.E.G. 112, 9 'use o\°o' u1 d G 06050502 V11" OiV Ib C. Page I of I � V_ Q � a lit JIL � fs 19 MOW In IL ►. 14 F a-r !' 19 :: mw ,. ,.. ! ti T22NR3W • - �� 4. r REC;ETV- MAN ( 1 J1 6 MASUiv -,ji\ITY re 1 S b io °.ol �rvs rll � S c� � f 4e _ v'72 ooP ell 1s 7 I a�-b