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Home My WebLink AboutGeoTech Addendum for BLD2007-00806, 00807, 00808 - BLD Engineering / Geo-tech Reports - 7/6/2007 t ,r E N G I N E E R I N G \ I N C 309 WASHINGTON STREET NE • OLYMPIA WA 98501 • TEL:360 352-2477• FAX: 360 352-0179 www vectorengineennginc.com RECEIVED J UL - 9 2007 July 6,2007 MCCD - PLANNING Mr.Robert D.Fink,AICP Mason County—Department of Community Development Mason County Bldg 1 P.O.Box 279 Shelton,WA 98584 Subject: Geotechnical Report Request for Additional Information Permit#:BLD 2007-00806,BLD 2007-00807,and BLD 2007-00808 Parcel No. 122292290362,122292290363,& 122292290367 Applicant: Casey Thomas Planner: Rebecca Hersha VEI#: 7054-007 The geotechnical report prepared by Envirotech Engineering, 74 NE Hurd Road, Belfair, Washington 98528 for eight single family residence lots located in the NW '/4 NW '/4 Section 29 Township 22 North Range 1 West, Mason County was received and reviewed by Vector Engineering, Inc. The Department of Community Development requested the review for the purpose assisting the Department in determining the amount of potential for landslide activity and the proposed development would not cause significant adverse impacts or there is adequate geological information available on the area to determine the impacts of the proposed development and appropriate mitigating measures. The Department of Community Development reviews all development applications to determine if they are likely to be in or near a landslide hazard area per Mason County Resource Ordinance (MCRO), Geologically Hazardous Areas, Landslide Hazard Areas 17.01.100, Seismic Hazard Areas 17.01.102, and Erosion Hazard Areas 17.01.104 approved December 27,2006. The geotechnical report states the proposed residences are currently developed with paved roadways and have had clearing activities associated with the road development and site preparation. A site plan was provided with the report,which included a description of the size and location of the proposed drainfields and residences. Based upon preliminary review of the report, it is requested the following items are requested or be clarified before the review of the report is complete. Page 1 of 3 X:\7000 Files\7054 Mason County Geotech Reviews\7054-007 Mason_Co(Thomas)\Admin\Transmittal Letters\Geotechnical Report BLD 2007-00806 00807 00808 Review Reguest.doc Yi�lr "+tii`I Additional Information Requested 1. A geological assessment for B 07-00807; MCRO 17.01.100 E.1(d). The geotechnical report was sub ad of the geological assessment. However, development on the site is o within 3 eet of slopes over 40%. The nearest part of the proposed struc 70 feet away. 2. A discussion of the general geologic conditions in the general vicinity as required by MCRO 17.01.100 E.5(1). 3. A geologic map of the site showing the area of the proposed development, including the boundaries of the hazard, and associated buffers and setbacks MCRO 17.01.100 E.5(4). 4. A cross-section, which depicts the subsurface profile, drawn to scale as required by MCRO 17.01.100 E.5(5). 5. Calculations for the slope stability analysis for the static and seismic conditions. 6. Clarification whether drainfields are permitted within the landslide hazard buffer area. The drainfields are reported to not be expected to adversely affect the influence the slope stability for the planned building structures or critical slopes. However, the proposed drainfields for Lots 3A, 313, 4A, and 4B are within the 50 feet of the top of the 60 percent slope inside the buffer and are a concern because the slope would be constantly saturated. MCRO 17.01.100 D.6(a) requires a 50-foot buffer of undisturbed natural vegetation around a Landside Hazard Area or as recommended by the geotechnical engineer. 7. Clarification whether total cl g is pe tted within the landslide hazard buffer area. The clearing is proposed to t edge of the slope. MCRO 17.01.100 D.6(a) requires a 50-foot buffer of undi natural vegetation around a Landside Hazard Area or as recommended by the tec engineer. 8. Clarification whether Ids are pernutt within the landslide hazard buffer area. The drainfields are reported t not be ex ted to adversely affect the influence the P~ slope stability for the planned din structures or critical slopes. However, the proposed drainfields for Lots 3A, A, and 4B are within the 50 feet of the top of the 60 percent slope inside the buff d are a concern because the slope would be constantly saturated. MCRO .01. 0 D.6 a requires a 50-foot buffer of undisturbed natural vegetation#1und a Lan ide Hazard Area or as recommended by the geotechnical engineer. 9. Clarification on whether the geotec engineer can recommend a landslide buffer of less than 50 feet.MCRO 17.01.100 . a , 11 In the reviewer's opinion, the report does not provide sufficient information to determine the proposed drainfields and residences will not decrease slope stability at the site or on adjacent properties and the risk for such occurrence would be minimal. Page 2 of 3 XA7000 Files\7054 Mason County Geotech Reviews\7054-007 Mason_Co(Thomas)\Admin\Transmittal Letters\Geotechnical Report BLD 2007-00806 00807 00808 Review Reguest.doc The conclusions presented in this report are based on Vector Engineering, Inc.' understanding of the project requirements.Vector Engineering,Inc.warrants that its services were performed with the level of care and skill ordinarily exercised by members of the same profession currently practicing in the same locality under similar conditions. No other warranty or representation,expressed or implied,is included or intended hereunder. Please feel free to contact me if you have any questions regarding these comments. I look forward to receiving the items and clarifications to complete the review. Sincerely, (Signature) (Date) Russell W. La Force, P.E. Design Engineer Vector Engineering, Inc. 309 Washington Street NE Olympia, WA 98501 (360) 352-2477 Page 3 of 3 XA7000 Files\7054 Mason County Geotech Reviews\7054-007 Mason_Co(Thomas)\Admin\Transmittal Letters\Geotechnical Report BLD 2007-00806 00807 00808 Review Reguest.doc Geotechnical Report Addendum #1 Seabeck Developers Eight Single Family Residence Lots Parcel No's 12229 22 90361, 12229 22 90362, 12229 22 90363, 12229 22 90364912229 22 90365912229 22 903669 12229 22 903679 & 12229 22 90368 Mason County, Washington July 14, 2007 Project#0724 Prepared For: Seabeck Developers, LLC. 200 Bravo Terrace Port Orchard, Washington 98366 Prepared E�,: Envirotech Engineering 74 NE Hurd Road Belfair, Washington 98528 Phone: 360-275-9374 Fax: 360-275-4789 INTORDUCTION Envirotech Engineering (Envirotech) has completed this geotechnical addendum as an addition to the "Geotechnical Report for Seabeck Developers Eight Single Family Residence Lots" prepared June 6, 2007 by Envirotech Engineering. The referenced geotechnical report is for eight adjacent parcels of land identified as parcel numbers 12229-22-90361, 12229-22-90362, 12229-22-90363, 12229-22-90364, 12229-22-90365, 12229-22-90366, 12229-22-90367 and 12229-22-90368 located in Mason County, Washington (Project). This addendum will identify these parcels, respectively, as Lots' 1A, 2A, 3A, 4A, 1B, 2B, 3B and 4B. This addendum was prepared in order to satisfy Mason County requirements and provide additional information requested by Vector Engineering, Inc. in a letter dated July 6, 2007. This addendum is presented by providing additional information concerning the project in an item number format. The item numbers in the body of this addendum correspond to the item numbers in the Vector Engineering, Inc. letter found in Attachment A of this addendum. ITEM#1 Mason County, initially required geological assessments to be completed for Lots IA, 1B, 2A and 2B. Lots 3A, 3B, 4A and 4B were required to have geotechnical reports. However, Lots 2A and 2B require geotechnical reports due to development within 300 feet of slopes over 40%. Although Lots IA and 1B required geological assessments, Envirotech prepared a geotechnical report for all eight parcels. The geotechnical report and/or this addendum addresses, at a minimum, Mason County geotechnical report requirements for Lots 2A, 2B, 3A, 3B, 4A and 4B, and geologic assessment requirements for Lots I and 1B. ITEM#2 Per MCRO 17.01.100 E.5(1), "a discussion of general geologic conditions, specific soil types, groundwater conditions, the upslope geomorphology and location of upland water bodies and wetlands, and history of landslide activity in the vicinity" of the project is required for geotechnical reports. The reviewer requested only a discussion of the general geologic conditions, for the reason that the other requirements per MCRO 17.01.00 E.5(1) were addressed in the geotechnical report. Envirotech Engineering Geotechnical Addendum#1 Ph. 360-275-9374 Page 1 of 5 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62, -63, -64, -65, -66, -67. &-68 July 12, 2007 General Geologic Conditions In general, soils at the project are composed of materials from glacial advances. The geologic conditions as presented in the "Geologic Map of Washington," compiled by I Eric Schuster, 2002 indicates Quaternary sediments, Q8. Quaternary sediments are generally unconsolidated deposits, and dominantly deposited from glacial drift, including alluvium deposits. This project is located within the Puget Lowland. Typically, "lower tertiary sedimentary rocks unconformably overlie the Crescent Formation." as revealed in the Geologic Map. Initial sedimentary rocks were formed from shales, sandstones and coal deposits from rivers. During the Quaternary period, the Puget Lowland was covered by numerous ice sheets, with the most recent being the Fraser glacier with a peak of approximately 14,000 years ago. Upon the glacial retreat, the landscape was formed by glacial erosion glacial drift deposits. ITEM#3 A geologic map of the site showing the area of the proposed development, including the boundaries of the hazard, and associated buffers and setbacks per MCRO 17.01.100 E.5(5)is provided in Attachment B of this addendum. ITEM#4 A cross-section drawn to scale, which depicts the subsurface profile, is required per MCRO 17.01.100 E.5(5). A cross-section, drawn to scale, is provided in Attachment C of this addendum. ITEM#5 Calculations for the slope stability analysis for the static and seismic conditions are provided in Attachment D of this addendum. The Simplified Bishop Method was used for this site utilizing a spreadsheet program iterative approach. Various radii's and center points of the circle were selected until the lowest factor of safety was found. Center points and radn's were carefully chosen to exploit the weakest points of possible slip planes. In addition, conservative to ultra-conservative values were used in the slope stability analysis in regards to saturation of the upper slope. See Item #6 for additional information concerning septic drainfield parameters. In attachment D, two pages of spreadsheet indicate where the smallest factor of safety for static conditions were found (1.7). The spreadsheet is divided into "Input" values and Envirotech Engineering Geotechnical Addendum#1 Ph. 360-275-9374 Page 2 of 5 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62, -631, -641, -65, -66, -67. &-68 July 12. 2007 "Output" results. In the "Input" block, topography is indicated, estimated soil properties, surcharge amounts and location, and a cell for a trial radius. A conservative 75% slope was used in which this steep of a slope can only be found beyond the property lines of Lot 4B. Additional safety factors were built-in to the stability analysis, such as considering the top of slope as level instead of gently sloping down as indicated on-site, and estimating a slightly higher vertical relief than actual conditions represent. Soil input values were considered saturated in the upper 18 feet of soils,which greatly decreases cohesion, and to a lesser extent, the angle of internal friction. "Output" values included subroutines for calculating data required in the slope analysis, tables typical to the Simplified Bishop Method output, and factor of safeties manually typed based on changes in the trial radius for the given center of circle. Seismic conditions were estimated utilizing worst case scenario values from the static analysis, a horizontal acceleration coefficient of 0.15 as required by Mason County, and applying the aforementioned values to the stability charts shown in Attachment D. These stability charts were presented by the American Society of Civil Engineers (ASCE) in the "Journal of Geotechnical and Geoenvironmental Engineering," April 2002. ITEM#6 Clarification is required whether septic drainfields are permitted within the landslide hazard buffer area as indicated in the geotechnical report. Septic drainfields are permitted within 50 feet from the top of slope. Specifically, septic drainfields in the locations presented in the geotechnical report are permissible. The buffer depicted in the geotechnical report was provided for buildings only. However, further clarification is provided as follows: Since proposed building locations are known to be approximately 100 feet away from the steep slopes, an arbitrary and conservative location for building surcharges was established at 50 feet from the top of the steep slope. This arbitrary building surcharge location and proposed septic drainfield locations were used in the slope stability analysis. Additional building loads were applied at 200 feet from the top of slope that is indicative of the planned development on Lots 2A and 2B. Due to this distance and subgrade conditions on-site, factor of safeties from several trials were well above the trials provided in the attachments. Constant saturation of the subgrade due to the septic drainfiled is not expected nor a concern to the critical slope. The planned septic units were designed as mound systems where the absorption area will be entirely above the existing ground surface, and the treated water will be disbursed periodically throughout the day into the absorption area via Envirotech Engineering Geotechnical Addendum#1 Ph. 360-275-9374 Page 3 of 5 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62, -63, -64, -65, -66, -67.&-68 July 12, 2007 timed dosing. This type of septic system is required as a result of the upper 2 to 3 feet of existing subgrade conditions. These soils are dense to very dense, predominantly low plastic silt with few sand/ gravel and binding clay. Below this stratum is a very dense cemented soil, typically described as `hardpan.' Except for the few inches of topsoil, these soils have very little void space or continuous voids to freely allow groundwater flow. These soils exhibit a low permeability coefficient expected to be in the range of 5 X I T6 to 5 X 10'8 centimeters per second. Due to the relative impermeability of these soils, treated water from the septic absorption area is not expected to detrimentally penetrated the subgrade before the groundwater flows down the slope and away from the critical slope. As an extra pre-caution, the upper 18 feet of soils were considered saturated in the slope stability analysis which could probably occur if the ground was completely disturbed to a depth of 18 feet. Additional recommendations provided in this addendum is that no additional land disturbing activity, other than installing the planned septic system and associated vegetation removal, shall be permitted within 50 feet from the top of the slope. Any earthmoving activities, or barriers that impede the movement of ground and surface water shall be avoided. From the site visit, it appears that neither trees or large bushes are required to be removed from the septic components area due to the very low density of vegetation in these areas. ITEM#7 Clearing is not permitted on the face of critical slopes. Clearing is permitted within 50 feet from the top of the slope. However, this clearing is contingent upon re-working disturbed areas by compacting and light grading so that pre-existing conditions are maintained as much as possible. The above recommendation is provided in the geotechnical report. Removal of vegetation within 50 feet of the top of critical slopes for this project is a very low concern based on the following: • The vegetation in this area is very sparse, resulting in low disturbance if removal is completed. The sparse vegetation may be due to past clearing activities. If clearing had been done, there are no indication of cracks, saturation, ponding or any slope or erosion problems due to vegetation removal. • Due to the topography, virtually no stormwater will enter this area from upslope terrain Vegetation is not critical in this area in order to decrease groundwater flow through transpiration. Envirotech Engineering Geotechnical Addendum#1 Ph. 360-275-9374 Page 4 of 5 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62, -63. -64, -65, -66, -67, &-68 July 12, 2007 ATTACHMENT A VECTOR ENGINEERING,INC.LETTER I :w c >,. E N 6 1 N E E N I N 6\\N C 309 WASHINGTON STREET NE • OLYMPIA WA 98501 . TEL:360 352-2477• FAX: 360 352-0179 www.vedorenginestinginc.com RECEIVED JUL -9 2001 July 6,2007 MC CD - PLANNING Mr.Robert D.Fink,AICP Mason County—Department of Community Development Mason County Bldg 1 P.O.Box 279 Shelton,WA 98584 Subject:Geotechnical Report Request for Additional Information Permit#:BLD 2007-MO6,BLD 2007-00807,and BLD 2007-00808 Parcel No. 1222922903621,122292290363,& 122292290367 Applicant:Casey Thomas Planner: Rebecca Hersha VEI#: 7054-007 The geotechnical report prepared by Envirotech Engineering, 74 NE Hurd Road, Belfair, Washington 98528 for eight single family residence lots located in the NW t/4 NW'/4 Section 29 Township 22 North Range 1 West, Mason County was received and reviewed by Vector Engineering,Inc. The Department of Community Development requested the review for the purpose assisting the Department in determining the amount of potential for landslide activity and the proposed development would not cause significant adverse impacts or there is adequate geological information available on the area to determine the impacts of the proposed development and appropriate mitigating measures. The Department of Community Development reviews all development applications to determine if they are likely to be in or near a landslide hazard area per Mason County Resource Ordinance (MCRO), Geologically Hazardous Areas, Landslide Hazard Areas 17.01.100, Seismic Hazard Areas 17.01.102, and Erosion Hazard Areas 17.01.104 approved December 27,2006. The geotechmcal report states the proposed residences are currently developed with paved roadways and have had clearing activities associated with the road development and site preparation. A site plan was provided with the report,which included a description of the size and location of the proposed drainfields and residences. Based upon preliminary review of the report,it is requested the following items are requested or be clarified before the review of the report is complete. Page 1 of 3 X:\7000 Files\7054 Mason County Geotech Reviews\7054-007 Mason Co(Momas)Wdmin\Transmittal Letters\Geotechnical Report BLD 2007-00806 00807 00808 Review Reguestdoc i Additional Information Requested 1. A geological assessment for BLD 2007-00807; MCRO 17.01.100 E.l(d). The geotechnical report was submitted instead of the geological assessment. However, development on the site is also within 300 feet of slopes over 40%.The nearest part of the proposed structure is 270 feet away. 2. A discussion of the general geologic conditions in the general vicinity as required by MCRO 17.01.100 E.5(1). 3. A geologic map of the site showing the area of the proposed development, including the boundaries of the hazard, and associated buffers and setbacks MCRO 17.01.100 E.5(4). 4. A cross-section, which depicts the subsurface profile, drawn to scale as required by MCRO 17.01.100 E.5(5). 5. Calculations for the slope stability analysis for the static and seismic conditions. 6. Clarification whether drainfields are permitted within the landslide hazard buffer area. The drainfields are reported to not be expected to adversely affect the influence the slope stability for the planned building structures or critical slopes. However, the proposed drainfields for Lots 3A,3B,4A,and 4B are widen the 50 feet of the top of the 60 percent slope inside the buffer and are a concern because the slope would be constantly sativated. MCRO 17.01.100 D.6(a) requires a 50-foot buffer of undisturbed natural vegetation around a Landside Hazard Area or as recommended by the geotechnical engineer. 7. Clarification whether total clearing is permitted within the landslide hazard buffer area. The clearing is proposed to the top edge of the slope. MCRO 17.01.100 D.6(a) requires a 50-foot buffer of undisturbed natural vegetation around a Landside Hazard Area or as recommended by the geotecbnieal engineer. 8. Clarification whether drainfields are permitted within the landslide hazard buffer area. The drainfields are reported.to not be expected to adversely affect the influence the slope stability for the planned building structures or critical slopes. However, the proposed drainfields for Lots 3A, 38,4A,and 4B are within the 50 feet of the top of the 60 percent slope inside the buffer and are a concern because the slope would be constantly saturated. MCRO 17.01.100 D.6(a) requires a 50-foot buffer of undishnbed natural vegetation around a Landside Hazard Area or as recommended by the geotechnical engineer. 9. Clarification on whether the geotechnical engineer can recommend a landslide buffer of less than 50 feet.MCRO 17.01.100 D.6(a), In the reviewer's opinion,the report does not provide sufficient information to determine the proposed drainfields and residences will not decrease slope stability at the site or on adjacent properties and the risk for such occurrence would be minimal. Page 2 of 3 XA7000 Files\7054 Mason County Geotech Reviews\7054-007 Mason CO(Momas)Wdmin\Transmittal Letters\Geotechnical Report BLD 2007-00806 00807 00809 Review Reguest.doc Now The conclusions presented in this report are based on vector ralgmeenng,lac.- imuem sung of the project requirements.Vector Engineering,Inc.warrants that its services were performed with the level of care and skill ordinarily exercised by ambers of the same profession currently practicing in the same locality under similar conditions. No other warranty or representation,expressed or implied,is included or intended hereunder. Please feel free to contact me if you have any questions regarding these comments. I look forward to receiving the items and clarifications to complete the review. Sincerely, -"VV� .�v.+rt1�. C (Signature) Oate Russell W. La Force,P.E. Design Engineer Vector Engineering,Inc. 309 Washington Street NE Olympia,WA 98501 (360) 352-2477 Page 3 of 3 XA7000 Files\7054 Mason County Geotech Reviews\705"7 Mason Co([bomas)\Admin\Trmsmivat Leuers\Geotwhnical Report BLD 2007-00806 00807 00808 Review Reguest.doc ATTACHMENT C SUBSURFACE CROSS-SECTION I + w $� b a-0 w s w ¥ §_3 Ix k k -ja _j h QLL-_ o y §k �� E ƒ 2 yƒ §2f» -i u u _■$ §&§� G kd . ■V »� � �� k� � �� / W� § A w An § � ■ . -�2 � �a � . U� b Q� w C ® 0 5 a 5 OC w e � E� m F- �� ¥_j § §� z0U 2L- uw w �k ` Qa gn k� U § XZ�WU3 2—mow ! § q�h -J�2 Ce§ PI u § q /-JdAw& w Qa-®m®E c w�2 SONXm— k k§ � Q§§ 2k � � s> $ § � kk ATTACHMENT D SLOPE STABILITY SPREADSHEETS i i 2 a � t 2 ■ t � a k . o 0 k kCD e o % � $ a c �� 2 ■ o E 7 CL k 0 ■ � � � � �!j 2 § - - - - - �% CL 8 in � m � 9" f � a egCM - - - ogo 40X $ $ © o / 0 k A 2 co 2 co � & � § § � § g qq � � q E � �� § = = 2 » > � U > ■ ■ � � § 0 § xC _ o u x %© � C U U U @ '0 c CE SSl� Ww moe � -aw � co N � _ ■�� IS 16 � � k eU � � � S � � � k § i 009 m e N N E � kkkkkZ % % � � 0 ��02 L £ > @ LL � 0 @co ■ ■ zz � � � rPOD � ODIp� Mr WgM NOr � � tCto {. NOAaDc9Maf9MMN M M 1* M M co co M V O O O O O CD, O O O O M P- m Ln m V C iW) W) Axto �- rr � �+ C+) rrrrr N U U- cc 00000000000 � � m o 0 oo ci ti 8 8 N CM r r t r r r r r c g 1-- li oDc+� M � O �- NaOa et aaN � aD V 4fCtomv O t1� rt[� rtCrW V• N N t+ OCOCR "It IQ atM O V V MTM- � Mt� N O M N r -q N M r r n 'atCaDe= OV- NNMV � = O a � c m � to 0 q r OR OR q M 0 N O O Im C aD N I� aD M N OCVCVr co CCNMCr W pr aD WNN- aD l� 00M- a0O N � Om � daDD �lC�pDl �A11D 3 ' N c! t cg1ArrO yaD '� r � ap �ta� aC�D tC! a�- N " tC8 � ^ rm � Edwm NMI� ON NO m � 04NM � MMM V' V M c Z V NCArC, a� MrNl� � aDr C3 abG W M M �p C O O CC�� C� 0 1� co NCD r r r r r O O C O C ^N a LLL DO- ca m � Q E o� 00MODMC� Na, tt tMAaNO � m VM' � 'N�, C'7 � ,A � in V- NCM4C09 � � � w V C,4 m 'n N (nL ® NNM � CNCCth �t � f► E O Q = Z v apstMON- CO V OI� O C� cD rV ro� M4040co ONNc^o � � � � MO ooOOOC� O� aO - - I� aD e f r r r O O C Cl C m � LL �Ul 0- 0 E o r CDgtto r- M V C) 1- MrMQr IM+ � an0 OwOa, IiN �p rzuii�pg aDmN WMpp vi rr NNM V �T V et cif � C � � N � � � W ��+ ��. MrNOMr000 �t3 fn � rl� l� aDaD � rQ Wt� M �p W NSA 1� ILNCVrrrr m m N N M d M M V V J O Z w CIA C! GA W CiCDCtG) CCC� W O OOOA � aMD. 1� 1� NNCVIV NNNN " N rrrr: V r: C000C r r r r r r r r r r W co fb M 1A O N QLL �pMOi- rrr as W 09 � rNNf � pCptiap W 0 E � rNa7 �tgCpP. a00► � nZ r � Z �j a tc./C. a ve O ws ?fit lF^7 G c �r�Cc�►a' t3ls ' 71"f i fi E y la:' 370 e alre- ;r►c�.►a�f vt f 1 jo> r S. - /. 28 1 i i p F,S, _ 1,06 4 f 1 j 1 1 1 1.06 S. �,� Z i i i I F � 4 (8)10 9 _D-2 a � 30 >� 6 �g 6 6 5J04 � F e tsar 30 4 4 a 15 z k Q1 a kh=Q2 a °° 05 1 15 a 2S O 0.5 1 is 2 25 O 0.5 1 is 2 23 (b) w a3 3 2.1 F 2 2 0 FK�_ O-O N .., 100 11000 '001 kA=0.1 kM=0.2 ki-0.3 °o at a2 a3 a4 CA at as a3 as o5 °o Q1 a as as r� r� Fig.4. Safety factor for slopes subjected to quasi-static horizontal force sidered to be fiflly drained where dilation of the soil skeleton does make it possible to make an"educated guess"of the influence of not cause any change m the magnitude of the pore water pressure. pore water pressure on the stability of slopes. For the purpose of presenting the influence of the pore water on the stability of slopes,the distribution of the pore water pres- Quasi-Stack Selsmlc Etfisat sure is described by coefficient r" defined by Bishop and Mor- genstem(1960)es Seismic low on slopes are often considered in design by includ- ing quasi-atedc form due to seismic accelwation.While such an r = sr (g) aaalyak ignores the mumc process (acceleration history) and " Yh does not give any insight into the bebavior of the structure,it is where v=magnitude of the pore water pressure, y=roil unit routinely used m design.The kinematic approach of limit analysis weight,and h=depth of the point on the iihre sutfaee below the was used here to arrive at the data used to produce the charts in slope surface.Stabt7ity charts for slopes with r"equal to 0,0.25, Fig.4.Coefficient ka repro the intensity of horizontal accel- end 0.50 are presented in Fig.3.The data in the charts in Figs 3 eration as a fraction of the gravity acceleratian. The effect of was created using a computer progrnon written earlier (Micha- quasi-static forces was included in the analysis as an additional lowski 1995). work term in the eneW balance equation(1Michalowsld 1999). Coefficient r"is a ratter crude of accounting for the No pore water pressure was considered m calculabons with a pore water pressure in a slope. If a weft-defined Now net in a quasi-static seismic form The guesi-stabc approach is a crude slope is known,the eornegwxWing pore psessure distribution can approximation of seismic ells, and desires aslrolving mother be calculated and included explicitly in c0mPuftdO a Of the sta- simplified concept(rr)t0 deacxrbe the pose water pressure distri- bitty number(or the safety,factor).While such calculations are button,in addition to kk,may not be indicative of the true safety more accurate,preseni�iws of tie rewrite is charts would be dif- margin of slopes.Such charts would be en inappropriate tool for flcult because of the large number of variables needed to describe analyzirug the tardy dopes,ply liquefiable soils. realistic Now nets. While the net= of calculatiorrs with pare Safety factor F, represented is the charts as F/ten T, is an pressures described in Eq. (8) is rather approximate,the results increasing function of N• (or c/yH tan cp)up to some threshold 354/JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING/APRIL 2002 yoN.sTgrFo� MASON COUNTY o P A o H DEPARTMENT OF COMMUNITY DEVELOPMENT > S N Planning Division y7 N y ti P O Box 279, Shelton,WA 98584 of o (360)427-9670 1864 REQUEST FOR ADDITIONAL INFORMATION May 24, 2007 CASEY THOMAS 200 BRAVO TERRACE PORT ORCHARD WA 98366 Parcel No.: 122292290362 Project Description: New SFR Dear Applicant: t go(, f'W% You have submitted a permit application (case no. BLD2007-00807)for proposed construction or development in the county. Upon review of your application, I require additional information to complete the permit review process. Therefore, review of your application will not proceed until the necessary information is provided (see the comment section of this letter for details.) Once the information is submitted and the application is complete, I will continue to process your application accordingly. If the additional information is not provided to the County within 180 days of this request, the application shall expire and no further action on the proposed development shall take place. Please contact me at (360)427-9670, ext. 593 if you have questions. Sincerel r ebecca Hersha Land Use Planner Mason County Planning Department i s 0 z 5/24/07 Page 1 of 2 BLD2007-00807 Mode : INQUIRY REAL PROPERTY Auto Roll : OFF Parcel # 12229 22 90362 Rng 1 Twp 22 Sec 29 Tax Yr 2008 Taxpayer # SEAB 0247 SEABECK DEVELOPERS LLC T/P Chg Dt 4/11/2007 Title Owner # SEAB 0247 SEABECK DEVELOPERS LLC T/P Chg By DLB Contract Owner # Loan # Plat/Condo Type Code Blk Lot Unit Dock Description LOT: 2 SP #2233 PTN S 247 TR 36 N1/2 NW Assoc M/H Chg Dt 4/11/2007 Chg By DLB Chg Rs RV FS 03335:02 Tax Code 0210 1 403 A P3 F3 L H Land Use 9110 VACANT < 5AC Zoning Code Tax Stat TX TAXABLE Reval 2 Chg Rs F/P? Y Ac Land: Improved Unimproved Timberland Total Land Improvement Total AV Acres 114 1.14 Taxable 30, 000 30, 000 30, 000 Market New/C 0/AV Mob Home AV Sub Cd Int% Sr Cit Cd Reg Exmpt O/R Regular Taxable 30, 000 Lien Date AF # As-Tx Yr App # Agr # WINDOW (; Command Keys : 5, 6, 7, 9, 12 �P7 e ;n rce i 1��G ' .j�; �2229 22 go3(.Z RECEIVEC juN 12,1007 426 W. CEDAR 5 Geotechnical Report • Lots Family Residence Seabeck Developers Eight Single y J Parcel No's 12229 22 90361, 12229 22 90362, 12229 22 90363, I 12229 22 90364912229 22 90365, 12229 22 903669 12229 22 903679 & 12229 22 90368 Mason County,Washington ' June 6, 2007 Project#0724 !I { Prepared For: Seabeck Developers, LLC. 200 Bravo Terrace ' Port Orchard, Washington 98366 Prepand By: Envirotech Engineering 74 NE Hurd Road Belfair, Washington 98528 Phone: 360-275-9374 " ' Fax: 360-275-4789 TABLE OF CONT ENTS ' Page ' 1.0 INTRODUCTION 1 1.1 Project Description 1 1.2 Purpose of Investigation 2 ' 1.3 Scope of Work 2 2.0 SURFACE CONDITIONS 3 ' 2.1 General Observations 3 2.2 Topography 34 2.3 Drainage 3.0 SUBSURFACE INVESTIGATION 5 3.1 Field Methods 5 ' 3.2 Field Sampling 5 3.3 Field Testing 5 9 6 3.4 Subsurface Conditions ' 3.5 Soils Testing 7 3.5.1 Visual Classification 3.5.2 Limited Particle Size Analysis 7 4.0 CONCLUSIONS 8 5.0 ENGINEERING ANALYSIS AND RECOMMENDATIONS 9 5.1 Building Foundation Recommendations 9 ' 5.1.1 Bearing Capacity 9 5.1.2 Settlement 10 5.2 Lateral Earth Pressures 10 ' 5.3 Earthwork Construction Recommendations 10 5.3.1 Excavations 11 5.3.2 Placement and Compaction of Native Soils and Engineered Fill 11 5.3.3 Retaining Wall Backfill 12 5.3.4 Building Pads 12 5.3.5 Wet Weather Considerations 13 ' 5.4 Slope Stability and Erosion Control 13 5.4.1 Septic Drainfield Impacts 14 5.4.2 Building and Footing Setbacks 14 ! ' 5A.3 Erosion Control 15 5.4.4 Surface and Subsurface Drainage 16 5.4.5 Vegetation Considerations 16 5.5 Earthquakes and Liquefaction Potential 17 ' 6.0 LIMIT ATIONS 18 ' DIX APPEN ' Appendix A- Site Plan Appendix B - Soil Information ' Soil Cross-Section Soil Logs Well Reports ' General Stability Map Appendix C -Erosion Control e ' it E� ' t 1.0 INTRODUCTION ' Envirotech Engineering (Envirotech) has completed a geotechmcal investigation for eight adjacent parcels of land identified as parcel numbers 12229-22-90361, 12229-22-90362, 12229-22-90363, 12229-22-90364, 12229-22-90365, 12229-22-90366, 12229-22-90367 tand 12229-22-90368 located in Mason County, Washington (Project). This report will identify these parcels, respectively, as Lots' IA, 2A, 3A, 4A, 1B, 2B, 3B and 4B. As presented herein, this report includes information pertaining to the Project in this Introduction Section; observations of the property and surrounding terrain in the Surface Conditions Section; field methods and soils descriptions in the Subsurface Investigation ' Section, and, foundation, settlement, earthwork, lateral earth pressures, slope stability and erosion control in the Engineering Analysis and Recommendations Section. An initial evaluation of the Project was conducted by the Planning Division for Mason ' It was determined that Lots 3A, 3B, 4A f County Department o Community Development. and 4B are within 300 feet of slopes greater than 401/6, and subsequently will require a ' geotechnical report pursuant to Mason County Resource Ordinance pertaining to landslide hazard areas. In addition, a geotechnical assessment was determined to be necessary for Lots IA, 1B, 2A and 2B. An evaluation by Envirotech with a representative of the ' property owner/developer, Casey Thomas, was completed on June 1, 2007. Afterward, it was confirmed to prepare this geotechnical report for all eight parcels. This report r identifies the Project as eight parcels where feasible, and provides discussion for each individual parcel or group of parcels where necessary. During the above mentioned evaluation and site visit by Envirotech, surface and subsurface conditions were assessed. After completion of the field work and applicable Project research, Envirotech prepared this geotechnical report. 1.1 Project Description ' Information pertaining to J the Project was provided by the developer's representative. The Project is sited in which each Lot consists of approximately 1.25 to 2.0 acres of land, and will minimally consist of developing single family residences on each Lot. Currently, the land is vacant with paved access roads, wells and water lines. Although not installed, septic systems are designed and approved by the County Health Department. Three Lots (2A, 3A and 3B) have completed site plans, and the other five are currently being ' conceptualized. Nevertheless, general building areas and locations have been determined. The houses are anticipated to be two-story, 3 bedrooms, predominantly wood frame with concrete stem walls. Approximately 36 ft by 66 ft building envelopes are anticipated. i Building footprints with relation to site features are illustrated in the Site Map in Appendix A. Envirotech Engineering Geotechnical Investigation ' Ph. 360-275-9374 Page 1 of 18 Mason County Parcels 12229-22-90361. Fax: 360-275-4789 -62, -63. -64. -65, -W -67,&-68 June 6.2007 1.2 Purpose of Investigation ' The purpose of this geotechnical investigation was to evaluate the Project in order to provide geotechnical recommendations relating to the construction of the planned single family residence. The investigation included characterizing the general Project surface and subsurface conditions, and evaluating the suitability of the soils to support the planned site development. 1.3 Scope of Work In order to fulfill the purpose of investigation, the geotechnical program completed for the proposed improvements of the Project include: ' • Review project information provided by the Project owner/developer; • Conduct a site visit to document and photograph the site conditions that may influence the construction and performance of the proposed improvements; Define the general subsurface conditions of the site by observing several existing excavations within the Project, probing below the surface on each Lot, and review well logs from existing wells on and/or near the Project; i • Collect bulk samples at various depths and locations; • Perform soils testing to determine selected index properties of the soils that includes 16 visual classifications, and one limited particle size analysis; • Complete an engineering analysis supported by planned improvements, and the surface and subsurface conditions that were identified by the field investigation and soil testing;and, Establish conclusions based on findings, and make recommendations for foundations, slope stability, erosion control, earthwork construction requirements, and other considerations. i � 1 1 1 1 Envirotech Engineering Geotechnical Investigation Ph. 360-275-9374 Page 2 of 18 Mason County Parcels 12229-22-90361.. Fax: 360-275-4789 -62. -63. -64. -65, -66, -67. &-68 June 6, 2007 ' 2.0 SURFACE CONDITIONS ' Information pertaining to the existing surface conditions for the Project was gathered on June 1, 2007 by Michael Staten, geotechnical engineer with Envirotech. During the site visit, the type of geotechnical investigation was assessed, photographs were taken of the ' surface and surrounding areas, site features were documented that may influence construction, soil samples were collected from selected locations, and near-surface soils were visually classified. This Surface Conditions Section provides information on general observations, topography, vegetation, and drainage for the Project and surrounding areas that may impact the Project. 2.1 General Observations ' The Project is currently developed with paved roadways accessing the eight Lots as previously discussed in the Introduction Section. Each Lot has had past clearing activities associated with the road development and site preparation. The clearing of vegetation was ' not apparent on the face of the steep slopes that border Lots 3A, 3B 4A and 4B. Naturally, the Project consisted of moderate to highly dense vegetation, including firs, grasses, blackberries, and other trees and shrubbery common to the Northwest. Existing water wells located within 250 feet from the top of the steep slope were observed on Lot 3A Apparently, two additional wells were completed and installed on Lot 4A. Access to the Project's paved roadway network is accomplished via State Highway 3, approximately '/4 mile south of Sherwood Creek in Allyn, Washington. Observations of surface y conditions, other than what is presented in this section, can be found in the Slope Stability ' and Erosion Control Section of this report. ' 2.2 Topography The eight parce ls are situated within and near moderate to steep sloping terrain. Site t grades are gently sloping to moderately sloping where development is expected to take place. Ascending slopes in relation to the anticipated building pad locations for Lots 2A, 2B, 3A, 3B, 4A and 4B are relatively flat. Ascending slopes in relation to the anticipated building pad locations for Lots IA and 1B are slightly sloping. Steep descending slopes located on the west portion of Lots 3A, 3B, 4A and 4B range from approximately 30%to ' 65%, with a vertical relief of approximately 100 feet. Slopes near 30% are close to the south property line of Lot 3A, and slopes near 65% are on Lots 3B and 4A- The top of these steep slopes range from about 240 feet to 270 feet west of the west property lines of ' Lots 3A, 3B, 4A and 4B. Slopes of up to 75%appear to exist on the neighboring property directly north of Lot 4B. Envirotech Engineering Geotechnical Investigation ' Ph. 360-275-9374 Page 3 of 18 Mason Count} Parcels 1.2229-22-90361, Fax: 360-275-4789 -62. -63, -641, -65, -66. -67.&-68 June 6, 2007 The existing ground surface extending from the top of the steep slope to approximately the property line dividing Lots 3A, 3B, 4A and 4B with Lots 2A and 2B has a gentle ' grade of about 2% descending in an easterly direction. From the previously mentioned property line for a distance of about 225 feet, the easterly descending slope increase to ' approximately 7%. Moderately sloping terrain of approximately 25% extends the majority of Lots IA and 1B that descends to the State Highway 3 right-of-way. These moderate slopes have a vertical relief of about 40 feet. See the Site Map in Appendix A for an illustration of the general topography with respect to the planned development. 2.3 Drainage ' Stormwater runoff originating upslope from anticipated building locations are expected to be very minimal or none at all due to the existing topography. Lots IA and 1B will probably receive the greatest amount of runoff from the ascending slopes, however nothing detrimental if ordinary drainage provisions are completed. Drainage within the vicinity of the eight properties basically sheet flows on the sloping terrain. It is expected ' that all storm water originating to the east of the 63%top of slope extending on Lots 3A, 3B, 4A and 4B will eventually lead to the State Highway 3 right-of-way. Water originating to the west of the aforementioned top of slope is expected to sheet flow down the slope. Some water will be directed along natural small furrows, before emptying into Sherwood Creek that is located less than '/a mile west of the top of slope. During the site visit, running water was not present within 300 feet of the planned building locations. Excessive scour, erosion or other indications of past drainage problems were not observed at or near the Project. Overall, the earth near the Project surface consists of low permeable soils that is an engineering property relating to slow groundwater drainage. i `1 � t Envirotech Engineering Geotechnical Investigation ! ' Ph. 360-275-9374 Page 4 of 18 Mason County Parcels 12229-22-90361. Fax: 360-275-4789 -62. -63, -64_ -65. -66. -67, &-68 June 6. 2007 3.0 SUBSURFACE INVESTIGATION ' Information on subsurface conditions pertaining to the Project was gathered on June 1, 2007 by Michael Staten, geotechnical engineer with Envirotech. Specific information on field methods, sampling, field testing, subsurface conditions, and results from soil testing are presented in this section of the report. ' 3.1 Field Methods Information on subsurface conditions for the Project was accomplished by observing several excavations extending to depths ranging from approximately 2 feet to 3 feet below the existing ground surface. Additional information on subsurface conditions was collected ' by field testing, shallow probing near the expected building pad area, reviewing well logs originating from the subject property and/ or nearby properties, and general slope stability maps for the Project and surrounding areas. The slope stability map depicts general slope conditions, and is presented by the Washington State Department of Ecology. Appendix B has pertinent information on subsurface conditions for the Project, including the above mentioned slope stability map for the Project area, two test pit logs representative of the near surface soils for all eight Lots, two well logs, and a soil cross-section representing relative soil conditions based on the accumulation of subsurface information for the Project. 3.2 Field Sampling Two bulk samples were collected at the Project site at approximately 1.5 feet and 2.0 feet below the existing ground surface near anticipated building locations. The soil samples collected were secured and transported for laboratory testing. 3.3 Field Testing Relative density of the in-situ soils were acquired by recording the resistance from driving a'/2" steel bar into the site soils near the location of the proposed residences. These results generally indicated dense/very stiff soils in the stratification below the upper 12 inches to ' depths extending 3 feet below the ground surface. Very dense soils were identified at depths beginning at 2 feet to 3 feet below the existing ground surface in all 16 field testing locations throughout the Project. Envirotech Engineering Geotechnical Investigation . ' Ph. 3 otech Engineering Page 5 of 18 Mason County Parcels 12229-22-90361, Ph. 60-275-9374 -62, -63, -64. -65. -66. -67.&-68 June 6. 2007 i 3.4 Subsurface Conditions ' The Project subgrade within the depth of penetration at all testing, sampling and observed locations were composed of native soils, with no indications of borrowed fill. For engineering purposes, these native soils consist of distinguishable layers, as presented below. Soils within the upper 4 to 6 inches on all eight Lots contain an organic composition and soil mixture. These soils are neglected for bearing capacity and settlement concerns, and nearly negligible for the slope stability analysis. For Lots 1A, 1B, 2A, 2B, 3A and 4B, soils below the upper organic/ soil mixture to depths ranging from 2 feet to approximately 3 feet below the existing ground surface consists primarily of a moist, brown sandy silt QvIL) with gravel. Gravels are primarily content is mostly well-graded and subrounded. The sand Y fine and medium, with some coarse. The fines content is primarily a silt with some clay, and low plasticity. These soils were observed and tested to be dense. This same stratification limits on Lots 3B and 4A were very similar and maintained an identical engineering classification except these soils exhibited less gravel sized material. The soils below the aforementioned sandy silt with gravel layer on all eight Lots consisted of a very dense, relatively dry `hardpan' consisting of silty sand with gravel (S11 ). These very dense soils are expected to extend from 2 or 3 feet below the ground surface to approximately 15 to 25 feet below the existing ground surface. The gravel appears to be mostly coarse and rounded to subrounded. Sands are primarily medium, and fines are non- plastic. Below the very dense silty sand with gravel soils on each Lot, is expected to consist of dense silty sand (SM) with gavel soils to depths extending beyond 30 feet below the ground surface. Soils below 30 feet are not expected to significantly influence the slope ' stability or soil mechanics of this Project. Neither groundwater nor bedrock was encountered during the field exploration. feet below the Permanent groundwater is expected to be approximately 170 to 190 f existing ground surface beneath proposed building locations. According to the well logs, saturated conditions existed at 75 feet to 78 feet, and 105 feet to 110 feet below the ' ground surface. Envirotech Engineering Geotechnical Investigation Ph. 360-275-9374 Page 6 of 18 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62, -63, -64, -65. -66.-67.&-68 June 6.2007 3.5 Soils Testing The soil samples obtained at the Project site during the field investigation were preserved and transported for specific laboratory testing. Visual classification of soils was performed in the field. The following soil tests were performed in accordance to the American tStandards for Testing and Materials(ASTM): • 16 Visual Classifications(ASTM D2488);and, • 1 Limited Particle Size Analyses(ASTM D422). ' 3.5.1 Visual Classification The general results from the visual classification are presented in the aforementioned Subsurface Conditions Section from depths of up to 3 feet below the existing ground surface. Minor variations observed during the visual classification of particle size content (i.e. gravel, sand, fines), or isolated pockets within the soil stratification were insignificant in relation to the engineering properties of the soil. f3.5.2 Limited Particle Size Analyses A limited particle size analysis was performed on one soil sample collected at the s Project site. Only the No. 4 and No. 200 sieves were utilized in order to determine the gravel, sand and fines content of the individual soil sample. For a representative sample of the site soils near the building site at a depth of 18 inches, the gravel ' content was 12%, sand content was 17%, and a fines content of 71%. This laboratory test provided assurance for the accuracy of the visual classifications performed at the remaining locations of the Project. e ' f F � Envirotech Engineering Geotechnical Investigation Ph. 360-275-9374 Page 7 of 18 Mason Countv Parcels 12229-22-90361. Fax: 360-275-4789 -62. -63. -64. -65. -66. -67. & -68 June 6. 2007 ' 4.0 CONCLUSIONS ' The services described in this report were prepared under the responsible charge of Michael Staten, a professional engineer with Envirotech. Michael Staten has appropriate education and experience in the field of geotechnical engineering in order to assess ' landslide hazards, earthquake hazards, and general soil mechanics. According to the Coastal Zone Atlas, Volume 9, of Mason County, Washington, the Project is within three zones with relation to landslide activity. These zones includes Stable, Intermediate and Modified. Stable slopes are generally not prone to landslides due ' to small grades and accommodating geology. Historically, intermediate terrains have no known landslides. However, these sites are considered inherently hazardous due to the steep grades. Modified slopes usually do not have a history of landslide movements, and ' consist of significant excavating or filling as a result of development activities which must be accounted for in the slope stability analysis. Upon a more detailed analysis as presented in the Engineering Analysis and Recommendations Section of this report,the slopes within ! ' and near the expected developed Project appears to be stable. This is based on observations during the surface investigation, and an engineering analysis of the slopes using expected subsurface conditions and anticipated site development as presented in this ' report. The frost penetration depth is not expected to extend beyond 12 inches below the ground surface for this Project under normal circumstances and anticipated design features. The soils on-site have high frost susceptible characteristics and should be used only to the extents provided in this report. The planned site development will be on moderate slopes, and near high sloping terrain. Proper drainage provisions should be implemented where practical, including the £ ' recommendations herein in order to reduce the potential for damaging erosion or scour. ' Off-site impacts due to the expected development of this Project are not anticipated. It is our opinion that slopes on and near the Project are sufficiently stable for the development if the recommendations presented in this report are adhered to. In addition, sedunentation t control should be adequate when utilizing the erosion control recommendations as presented herein together with implementing appropriate erosion controls with the degree of care as expected from a licensed contractor. Envirotech Engineering Geotechnical Investigation Ph. 360-275-9374 Page 8 of 18 Mason County Parcels 12229-22-90361. Fax: 360-275-4789 -62, -63, -64. -651, -66. -67.&-68 June 6. 2007 5.0 ENGINEERING ANALYSIS AND RECOMMENDATIONS The following sections present engineering analysis and recommendations for the proposed improvements of the Project. These recommendations have been made available based on the planned improvements as outlined in the Introduction Section of this report; general observations of drainage and topography as summarized in the Surface Conditions Section; and, soil conditions that were identified by the field investigation and soils testing in the Subsurface Investigation Section. Engineering analysis and recommendations for the Project that is provided herein, includes pertinent information for foundations, settlement, slope stability, earthwork construction, lateral earth pressures, footing setbacks, surface and subsurface drainage, and erosion control. ' 5.1 Building Foundation Recommendations Recommendations provided in this section account for the site development of a two- story, single family residential structures for all eight lots. Below the upper 12 inches of native soil within the Project, there is apparently two distinguishable layers of soil that will influence the bearing capacity and settlement of the residential structure. The ' recommended allowable bearing capacities and settlements as presented below, consider the probable type of construction as well as the field investigation results by implementing practical engineering judgment within published engineering standards. Evaluations include classifying site soils, and deriving probable relative densities, unit weights and angles of internal friction of the in-situ soils based on observed field conditions and soil testing for this Project. 5.1.1 Bearing Capacity For the existing site conditions, bearing values should increase with depth. Existing m-situ soils at the Project site indicates that the structure can be established on ' shallow, continuous or isolated footings. Foundations shall be established on relatively undisturbed native soil. Alternatively, foundations may be constructed on selective re-compacted native soil or compacted engineered fill as described in the Earthwork Construction Recommendations Section of this report. Footing width 1 and depth recommendations shall be adhered to, and are based on a 2000 pounds per square feet(psf)maximum structural bearing pressure. For a bearing capacity requirement of no more than 2000 psf, a minimum of 15- inch wide footings shall be placed at a minimum of 12 inches below the final ground surface. These recommendations are made available based on adherence to the remaining recommendations that are provided in this report. W Envirotech Engineering Geotechnical Investigation Ph. 360-275-9374 Page 9 of 18 Mason County Parcels 12229-22-90361, ■- Fax: 360-275-4789 -62. -63, -64, -65, -66. -67, &-68 June 6. 2007 required at increments of every 5 feet of fill depth. A setback of 5 feet shall be I ' maintained between the building and the top of the building pad slope. 5.3.5 Wet Weather � the to Due es of subsurface soils, additional provisions may be required during I ' prolonged wet weather. Every precaution should be made in order to prevent free ' moisture from saturating the soils within excavations. If the bottom of excavations used for footing placement changes from a moist and dense/hard characteristic as presented in this report to muck or soft, saturated conditions, then these soils become unsuitable for foundation bearing material. If this situation occurs, a geotechnical engineer should be notified, or these soils should be completely removed and replaced with suitable compacted material as presented in this section. f 5.4 Slope Stability and Erosion Control Landslides and erosion are natural processes, and structures near slopes possess an inherent risk of adverse settlement, sliding or structural damage due to these processes. These risks cannot be eliminated for any site with moderate to steep sloping grades. Geotechnical engineering provides an acceptable factor of safety for building near sloping site conditions. These factor of safeties are based on engineering judgment, and engineering standards accumulated from years of academic and professional research by individuals in the field of geotechnical engineering. Surface sloughing or other types of surficial slope movements usually do not affect the ' deep-seated structural capability of the slope. However, excessive and/or repeated surficial slope movements, if not repaired, may represent a threat to the structural integrity of the slope. With appropriate drainage and erosion control provisions for this Project during and ' after construction, it is unlikely that this Project will experience excessive surficial movements. However, maintenance of the slope must be completed if the situation does arise in order to prevent the possibility of further surficial or deep seated slope movements ' that may be damaging to life and property. Most of the buildings for this Project is expected to be situated on a relatively flat grade ' and slightly sloping grades. The two structures on Lots IA and 1B, are anticipated to be on moderate slopes. The building pads on Lots 3A, 3B, 4A and 4B are at a conservative distance of no more than 120 feet from the top of steep slopes ranging from approximately ' 60% to 75%. During the site visit, there were no indications of deep-seated slope or surficial slope failures. Although the steep slopes that exist on-site signal a potential landslide or erosion hazard area, indications of past landslide or current slope failures were Envirotech Engineering Geotechnical Investigation Ph. 360-275-9374 Page 13 of 18 Mason Countv Parcels 12229-22-90361. Fat: 360-275-4789 -62, -63, -64, -65. -66, -67.&-68 June 6, 2007 not observed. Landslide indicators(none observed on-site)include: • Outwash of sediments near the bottom of the slope, • Fissures, tension cracks or naturally stepped land masses on the face or top of ' the slope, and parallel to the slope, • Fine, saturated subsurface soils, • Old landslide debris, • Significant bowing or leaning trees, or, • Slope sloughing or calving. The Simpli fied BishopMethod was used to analyze the stability of the Project's slopes utilizing expected site soils, topography, surcharges from expected site improvements, and various slip surfaces. Anticipated building loads, building pad loads, building pad cuts, or impacts from the planned septic drainfield are not expected to have any significant influence on the global stability of the slopes, provided that the setback requirements and recommendations in this report are adhered to. Based on the aforementioned Project criteria, observations, slope stability analysis, and the recommendations in this report, the Project has an acceptable factor of safety of over 1.5 relative to deep-seated slope failures for all eight parcels. 5.4.1 Septic Drainfield Lnpacts The approximate locations of the planned septic drainfields are presented on the Site Plan in Appendix A of this report. Based on these locations and the following recommendations, the drainfields for each Lot is not expected to adversely e influence the slope stability for the planned building structures or critical slopes. The planned residence on Lot IA should be located at least 20 feet upslope from its drainfield. It is also recommended to construct the residence on Lot 1B as close to the south property line as possible in order to prevent excess surcharges on the t potential saturated soils created from its drainfield. Special variances are not required for building setbacks, simply follow current ordinances. If these recommendations do not coincide with the final desired developments on Lots IA ' and 1B, Envirotech will provide additional recommendations for mitigating impacts from the septic drainfields. ' 5.4.2 Building and Footing Setbacks Anticipated surcharges from anticipated or possible planned site developments were used in the slope stability analysis. A worst-case scenerio was used for the steep slopes on the west portion of the Project that would be sufficient for Lots 3A, 3B, 4A and 4B. Provided that assumptions relating to construction occur as I ' Envirotech Engineering Geotechnical Investigation Ph. 360-275-9374 Page 14 of 18 Mason County Parcels 12229-22-90361. Fax: 360-275-4789 -62. -63, -64, -65. -66, -67, &-68 June 6. 2007 presented in this report, and the aforementioned recommendations pertaining to foundations are adhered to, the factor of safety for slope stability is sufficient for ' the following footing setback. • A minimum horizontal setback of 50 feet must be maintained between the bottom and outside edge of the structural footing to the face of the steep descending slopes ranging from about 60%to 75%located on the west portion of Lot's 3A, 3B, 4A and 4B. See the figure below and the Site Map in Appendix A for additional illustration. TOP 13F SMCTLW sLarE ' FACE 4 WN—� rWT" Minimum building setback requirements to adjacent and nearby existing slopes on Lot's IA, 1B, 2A and 2B are not of concern, except what is provided in the Septic ' Drainfield Impacts Section. 5.4.3 Erosion Control Minimal erosion control measures may be required during construction due to ' disturbing the topography. This will mostly depend on the timeliness of construction, and amount of rainfall during construction. Other sediment loss prevention that should be considered, if necessary, may occur due to wind-borne ' silts during dry weather, and tracking sediments off site with construction equipment. N the owner/ contractor chooses not to install erosion control prior to construction, the owner shall be prepared to immediately install appropriate erosion control prior to a large storm event or otherwise needed. Erosion control during construction should include minimizing the removal of !F , vegetation to the least extent possible. If necessary, erosion control measures during construction may include stockpiling cleared vegetation, temporary retention areas, silt fencing, intercepting swales, berms, straw bales, plastic cover or other standard controls. Any erosion control should be located down-slope and beyond the limits of construction and clearing of vegetation where surface water is expected to flow. If the loss of sediments appear to be greater than expected, or erosion control measures are not functioning as needed, additional measures must be implemented immediately. See Appendix C for sketches and notes regarding ' selected erosion control measures. Envirotech Engineering Geotechnical Investigation Ph. 360-275-9374 Page 15 of 18 Mason CountyParcels 12229-22-90361. Fay: 360-275-4789 -62. -63. -64, -65. -66, -67, &-68 June 6, 2007 Permanent erosion control completed after construction should include promoting the growth of vegetation within the exposed areas by seeding or an equivalent ' measure. Recommendations for seeding are provided in Appendix C. Additional erosion control measures that should be performed include routine maintenance and replacement, when necessary, of permanent erosion control, drainage structures and/or features. Further erosion control items and specifications may be found in the current "Stormwater Management Manual for Western Washington," prepared by the Washington State Department of Ecology Water Quality Program. 5.4.4 Surface and Subsurface Drainage Positive drainage should be provided in the final design for all planned residential buildings. Surface and subsurface drains should be adequately maintained during the life of the structure. Drainage shall include sloping the ground surface, driveways and sidewalks away from the Project structures. Foundation drains should be utilized for this Project if stem walls are retaining more than 1.5 feet of soil, which will help mitigate the excess moisture away from the structure. If used, the outlet for foundation drains shall be located downslope, and at least 5 feet away from the structure. It is also recommended to established foundation drains in a rock quarry or very gravelly, clean soils. If roof drains are utilized, water should be transported from the roof directly into a permeable medium that is downslope and at least 5 feet away from building foundations. If both roof drains and foundation drains are utilized, they should be ' installed as a separate drainage system, and not tie into each other. If drainage problems occur during or after construction, additional water ' mitigation may be required. This may include a combination of swales, berms, drain pipes or outlet protection in order to divert water away from the structure and/or reduce erosion. ' 5.4.5 Vegetation Considerations ' Vegetation is an excellent measure to minimize surficial slope movements and erosion on slope faces and exposed surfaces. As previously mentioned, existing surface conditions at the Project site appear to be sufficiently resistant to erosion hazards. Site development will require land disturbance and the removal of vegetation in building areas. Envirotech recommends to minimize removal of vegetation during and after construction near the building improvement areas as Envirotech Engineering Geotechnical Investigation 1 ' Ph. 360-275-9374 Page 16 of 18 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62, -63. -64, -65, -66, -67. &-68 June 6. 2007 much as possible. Vegetation should not be disturbed on the steep slope face on the west portion of Lots 3A, 3B, 4A and 4B except for trimming. For the moderate slopes east of the building footprints on Lots IA and 113, vegetation removal is permitted. However, ground disturbance should be avoided as much as ' possible in these areas, and it is recommended to allow stumps and roots to remain in place. For the land between the above mentioned areas which extends from the top of the steep 60%+ slopes to the building footprints on Lots IA and 1B, complete vegetation removal is permitted. However, disturbed ground should be lightly compacted and graded so that pre-existing conditions are maintained as much as possible. After construction, re-vegetation on exposed areas is recommended in order to reduce the potential for significant erosion. 5.5 Earthquakes and Liquefaction Potential Soils for this Project are primarily Type C, corresponding to the International Building Code (IBC) soil profiles. For this region, the seismic zone is 3, which yields a maximum ground acceleration of 0.33g. ! The potential for liquefaction or lateral spreading is believed to be very low for this Project. This is based on subsurface conditions such as soil characteristics and the lack of a shallow water table. k i Envirotech Engineering Geotechnical Investigation Ph. 360-275-9374 Page 17 of 18 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62, -63, -64. -65, -66, -67. &-68 June 6, 2007 "I ' 6.0 LIMITATIONS ' Due to the inherent natural variations of the soil stratification and the nature of the geotechnical subsurface exploration, there is always a possibility that soil conditions encountered during construction are different than those described in this report. Therefore, it is recommended that a qualified engineer observes and documents the construction, or Envirotech is promptly notified if project and subsurface conditions found on-site are not as presented in this report so that we can re-evaluate our ' recommendations. ' This report presents geotechnical design guidelines, and is intended only for the owner, or owners' representative, and project described herein. This report should not be used to dictate construction procedures or relieve the contractor of his responsibility. Any and all content of this geotechnical report is only valid on compliance with all recommendations provided in this report. The recommendations provided in this report ' are valid for the proposed development at the issuance date of this report. Changes to the site other than the expected development, changes to ordinances or regulatory codes, or broadening of accepted geotechnical standards may affect the conclusions and recommendations of this report. please contact Nfichael Staten at 360-275-9374 if you have any questions, comments, or require additional information. 0 CLYI� Sincerely, Envirotech Engm �Q, :• � Michael Staten,P. 0 Geotechnical Engin G[s'ctiR� 10 200 Envirotech Engineering Geotechnical Investigation Ph. 360-275-9374 Page 18 of 18 Mason County Parcels 12229-22-90361. Fax: 360-27�-4789 -62. -63. -64. -65. -66. -67.&-68 June 6, 2007 i I � I � ' sc v i PcH- im MET SILT FENCE �j IF NECESSARY(TYP)• �` rF ' � 3 PARCEL NO. 12229-22—%365 EXISTING 10 FT LOT 13 ® VIDE PAVED ACCESS ROAD ' « t PROPERTY CORNER (TYP) pT PARCEL ND. * 12229-22-90361 ' LOT 1A * NOTES, CONTROL IS TO BE USED IF PARCEL NIL M ! NECESSARY. GENERAL LOCATIONS, AND 12229-22-903" ivi ALTERNATIVES TO SILT FENCES NAY X g LOT 29 M UTILIZED AS EXPLAINED IN THE iG GEOTECMIICAL REPORT. ' 8 CONTOURS ARE NOT PRECISE, AND ONLY pr DEPICT GENERAL TOPOGRAPHIC CONDITIONS. 3 SECTION A—A IS LIMITED TO A SOIL !t3 PROFILE PROVIDED IN APPENDIX IR PARCEL NO. APPROXTE 12229-22-90362 LOCATIQIIMAff LOT 2A SEPTIC BRADFIELD (TYP) j APPROXIMATE ' LOCATION OF !*3�SOF DRIVEWAY CTYM \ � .1 APPROXIMATE i TPS \ LOCATION LOCATING OF �i \ FmTPRINT (TYP) i hi'i®\ !� SLOPE DIFFER * * \ FOR BUILDINGS APPROX ' \ i \ L � LEGEND mTMN TOP OF SLOPE SILT FENCE SLOPE DIRECTION A',y Qr _.--eon EXISTING CONTOJR PAL NO. * 4- Tin TEST PIT LOT 41222 Bid-9036@ ARCEI g � 4A !� ARCEL NO. LOT 3 PARCEL 22-90 LOT B 12229- 3A !� I PROJECT/ OWNER/ LOCATION SEABECK DEVELOPERS ` GEOTECHNICAL REPORT I SEABECK DEVELOPERS, LLC. PARCEL NOS. 12229 22 9036L —62, —63. ' tRt —64, —65, —66, —67 L —68 so MASON COMM WASHINGTON DESIGNERS ENVIROTECH ENGINEERING 74 NE HURD ROAD ' BELFAIR, WASHINGTON 98528 124 F7 t 360-275-9374 t0 SITE PLAN APPENDIX B SOEL INFORMATION ' ORIGINAL GRADE PROPOSED ANDY S L BUILDING ' GRAVEL (ML) (050 2' 3' ' SILTY SAND WITH GRAVEL (SM) VERY DENSE ' 15' - 25' \ \ SILTY SAND WITH GRAVEL (\) \ \ \ \ \ \ \ \ \ \ 10' - 20' SOIL CRO4S-3EMON(A-A) NOT TO SICALE NOTES. 1) BUILDINGS MAY BE CUT INTO SLOPE OR PLACED ON ENGINEERING FILL. 2) S❑IL PROFILE IS AS ACCURATE AS THE METHOD IMPLIES, 3) SEE GEOTECHNICAL REPORT FOR SPECIFIC INFORMATION ON CUT AND FILL REQUIREMENTS. PROJECT/ OWNER/ LOCATM SEABECK DEVELOPERS GEOTECHNICAL REPORT SEADECK DEVELOPERS, LLC. t PARCEL NOs. 12M 22 9036L -62, -63. -64, -0, -66, -67 E -0 ENMNEERi ENVIROTECH ENM EERM 74 NE HURD ROAD BELFAIR, VASHD GT13N 985M 360-275-9374 SOIL PROFILE TEST PIT LOG TEST PIT NUfv1FFR TF' 1 • ECr N& 0724 LoGem my.0 LICS CLEHr. slapirs. • r ;;• 229 r-WK a D ; r M WATAL DEM OF D,,,.a: O f M WA ------------- .....■ .....■ -----. -...-. ....-■ .-..m■ ..---. ....-■ .....■ --...■ .--.-■ -----. .---.■ .----. --...■ -....■ ■■■■■■ c TEST PIT LOG TEST PIT NUMBER y •JEM. Ssabw*on,,lnoopormC _ • r r: _ • • DATE OF :'• ' C •+ rDwslopsm • ft WA • • r. 1222M-00307 DRILL RIG: Me • • • • ELEVATION: INITIAL DEPTH OF E' WA FINAL DEFrH OF Insole r mmm�� wommom mmomom ommomm wommom omm�� mmommm wommom c ommmom wommom mom�� mmmomm mmoomm mmommm wommom mmomom mmm�� mmommm mommmm ommmom momomm wommom mom�� mmomom ommomm mmomom ommomm omm�� mmmmom womomm mmommm mmoomm momomm mom�� mmoomm momomm mommmm mmmmom mommmm mmm�� ommmmm mommmm momomm ' mmomom mom�� womomm mommmm mmommm ommomm momomm ommmom MEMNON c t PORT CURRENT /VET WATER WELL REPORT Notice Of Intent NO. WE05138 Drigihmr&l"�' Ear.gy,2''a.�'-.rerler.a ampy-ariaer ' i' o'i'li's Y Unique Ecology Well ID Tag No. AL 472 Construction/Decommission("x"in circle) �D J119ton D• Construction Water Right Permit No.EXEMPT WELL �p Decommission ORIGINAL INSTALLATION Notice Property Owner Name DEAN DEFRANK (UNIQUE CON .19( Iogy ' Q a I"7' of Intent Number Well Street Address HWY 3 (WELL 1) IMtOPOSHD USE: m Danslic D lodumtrisl D Muoicpd City ALLYN County MASON D DeWater D inipom D Tau wall ❑Otlwr Location NW 1/4-1/4 NW 1/4 Sec 29 Twr122N R1W EWM D creel TYPE OF WORN Ownex's mudhal of well(if seas tban oy)WELL 1 "- W WM Q ads 0 NowDee walla-d D Recovditiamw bbd.1 Dns ❑somd D (Lat/Lon Ddvm Cable m Raury D�� g(S,t,r Lot Deg Lot M in/S1x DIMENSIONS:Dismdarofwdl�_vacks,dri0ad fl• Still REQUIRED) Long Deg LDngMin/See ' Deplh ofasrpMud wan 200 fl CONSTRUCTION DETAILS Tax Parcel No. • 122292290367_ (Cortettion) Casing m Welded 6 Diem.from+2 ft to R Isstallmd: 8 Liwissaw Dunn.from fl.a ft CONSTRUCTION OR DECOMMISSION PROCEDURE Thratltd Dom.thvhn ft to fl Fom tjon: Describe by color.dutmaar.as orrunwisl and mnctue,and the load dad Perfinamro: YesRING, name ar*A WAMd M web SMOM PMW0 d;with s lent ON wtrY for each dnmga of Type of pafmator met iafomrtion. SE ADDITIONAL SHEETS IF NECESSARY. SIZE ofper6 in.by in.said M.ofper111_6am^fl m fl. MATERIAL FROM TO Scram ❑Yes 0 W ❑K-Pec L'acslian BROWN SILT BOUND SAND.GRAVEL 0 25 ' Maaafmaurar s Native BROWN SILTY SAND,GRAVEL 25 35 Type Model No. REDISH BROWN SILTY CLAY 35 45 Dialn Slat mine San ft to fl Disco Slaiva Eraa ft m fl BROWN SILTY SAND 45 65 GravdlPlltmrpaehnl Yes No St:zofgyvd/atmd COMPACT BROWN SAND,GRAVEL 65 75 ' Mawidsphhad5an fl m ft BROWN SILTY SAND,WET 75 78 Sm am Ses1:oYes C,No To tabs dapd?2( fl. BROWN SILTY CLAY 78 81 Malarial used at and BENTONITF CHIPS GRAY STICKY CLAY 81 86 Did may stay comro mmsabla waldt ❑Yes l;a No BROWN SILTY SAND 85 105 ' Typeefwalerl Deed Dfa uts SILTY BROWN SAND,WET 105 110 Method ofstaftsrayDA• BROWN SILTY SAND 110 138 PUMP: Mondhora w's Nams GRAY CLAY 138 1 W Type: N.P' GREEN CLAY,GRAVEL 180 190 WATER LEVZIS: IAndtula dDvmtios mhos tam seem Laval it RED COMPACT GRAVEL AND WATER 190 200 Stufo level 140 ft below top ofwmn Dale]1M _ Arleran p estan Ibs per square isrb Dse Arsesimm wMa is mstrolled by ' Valre.at. WELL TP3'1'S:Dtnwdovrs is amonmt taco level is lowered below almde scud Wmspuaptat=wb?DYaa 0No Ifymbywham Yield:-------AdJam wit fl.dnwd0am mfbr bra ' Yidd: olA11is.whh ft drmwdown mfla ball Yield:oin.wit fl.&W'&wa mflal hn Ramw:ry ekes(lase said;m xto usher pmyh started qV(Water/an/taeaurad)i al tad top to tram rend) Timm "W Lsvd Tune V.*W Level Time wow Lftw ' Date after: Bdkr vest gsl./moh.wit fl.drawdown mane Ira. ' Aie1g1_2Q _gs1Jerin.with utr185 fl.1br1 lla. Artesian flow &P-nL Date Teavensura of wm was a chemical analysis made?D Yes 0 No Start Data 7/B/O6 Completed Dale ZM/Ofl WELL CONSPRUC170N CER77FICATION: I oalsbucled andlor accept responsibility for construction of this well,and its compliance with all ' Washington gton well construction standards. Materials used and the information reported above are true to my best knowledge and belief. ash 0 Driller 0 Engineer OTrsiarre Nasm ftiwkM NELSON 42 Drimag Company ARCADIA DRILLING INC. D ilkr/Engii—fr—Siphmae 4- S� h .rf's. Addrest PO BOX 1790 ' Drillers aiseo Liam=No.IBM City,Stm,Zip SHELTON WA 9WA4 1fTRA1NEL Conersaces Driaer't 1.1=eascd Na Regiatrarios No ARCADD1098K1 sue 717/06 Drillar's Signalise ECY 050.1-20(Rev 3/05) Ecology is an Equal Oppommity Employer. L 1 R ' WATER WELL REPORT CURRENT MAR 12-2007 g Oriinal•1"copy-Ecdev.a copy-ewaer.3e1 copy-ddakr Notice of Intent No.W237286 ... .. .,.State i VFW 1, ALJ471 ' k t l t o c i Unique Ecology Well ID Tag No. 178 ttlnr>n�of ECoiogy Construction/Decommission("a"in circle) Construction Water Right Permit No.EXEMPT WELL Decommission ORIGINAL INSTALLATION Notice Property Owner Name UNIQUE CONSTRUCTION INC. ' ( of Intent Number Well Street Address HWY 3 _0 17bPROPOSED USE- Domestic indnow ❑ Mmaoipd City ALLYN County MASON ❑0dweler Imgsuon ❑Test Well ❑Odrer Location NW I/4-1/4 NW 1/4 Sec 29 Twn22N R1W r*4 ❑ duet TYPE OF WORK: owne's oombv ofwdl(if rtwce then me) WWM ❑j one ' m Now so ❑Ramc;trawd metw: >hg ❑Bored ❑Driven (LadLong(s,t,r Let Deg Let Min/See Deepenedgdbte ®� ❑ UI DIMSNSIOPS ne<ofwdl)�---iec drilled�Q Still REQUIRED) _R. Long Deg Long Min/See 0*11 of completed wall 210 R ' CONII'MUCrION DgTAILS Tax Parcel No. -122292290368 ( rr i e Codas m Welded I — Diem.from+2 R to 206 8. loommed: LveritWalled Diem from R.in CONSTRUCTION OR DECOMMISSION PROCEDURE 8 TMma " o .from R to II. Fotmaion.Describe by color.chwww,sue of o werial and madam and lie iiad and Paefem"m: Yesdd m No oaturs of the sawid ra each stramat pearrmook wpb at Inez one pay for each dtssrge or ' Type ofperforatorused_ infmnatm E ADDITIONAL SHEETS IF NECESSARY. SIZE of perf3< is by ice.and as of parts^fan R to^fl. MATERIAL FROM TO Sereesa 0 Yes ❑No 0 K-Pac Lawban 200 SILTY SAND,GRAVEL 0 2 Maubman's Name JOHNSON BROWN SILT BOUND SAND,GRAVEL 2 15 ' Type TTED Modd No- BROWN SILTY SAND,SOME GRAVEL 15 35 DwnStd sae.1Y10 fom 205 R ro 210 R Dent. Slos oa fiom R m ft. REDISH BROWN SILTY CLAY 35 45 GnvellFYeerpadw Yes 0 No 0 Sinofpaveltwtd BROWN SILTY SAND 45 65 Mauxialspbwed OUR R ro R COMPACT BROWN SAND,GRAVEL 65 75 Savhnsed-Oyes ❑No Towbode07 2D fl. BROWN SILTY SAND,WET 75 78 y,,maw aw in end BENTONITE CHIPS BROWN SILTY CLAY 78 81 Did any sna s earMea esamble water? ❑Yes O No GRAY STICKY CLAY 81 85 ' Troofwagn Depthofatrm BROWN SILTY SAND 85 105 Uied%w ofnehnstswoff SILTY BROWN SAND.WET 105 110 PUMP.Minghco esNaue BROWN SILTY SAND 110 138 Type: H.P. GRAY CLAY 138 180 ' wATtR I.BvtIS: lad�deva m*Iowa man sea level It GREEN CLAY,GRAVEL 180 190 Stoic kval 115 R below top of wdl Daft 7/4106 RED COMPACT GRAVEL AND WATER 190 200 Artmen pramts Iba persipme inch Dye GRAVEL,SOME SAND AND WATER 200 210 Anesion wow is camoYad by (cm vawe, ate. ' VnMX T2S78:Dnwdown is uammt wear kvd islowered below Inuit level Wes a pmrp cat atade?❑Yes 0 No Ifysa,by whm? Yield`pthain.with ft,ditawdown dkr ins. Yidd. PLh ice.witb fl.drawdown sfler hm. ' Ytdd�lJaio.wi6 R dmwdown after laa. 'Wea►siy dare(arse aatrn as saro wharpuny awed ao comer level raewww's'ora weft rop ro water levd) . Time Www Level Time WatrrLMI Tune W@WLevd Data of teM Boiler tat gain in.w'dh It dtawdown after less. Airiest 30 gd.hme with stern see M 100 fl.far 1_hrs. ' Artesine flow s p m-Dote Tempenswe of water Was a ehwmcal analysis made? ❑Yes ®No Start Dais 6129106 Completed Dale 714/06 WELL CONSTRUCTION CERTIFICATION: 1 construiled and/or accept responsibility for construction of this well,and its compliance with all ' Washington well construction standards. Materials.used and the information reported above are true to my best knowledge and belief. 0Driller OEnipaw OTrainec Naate N LSON 00 Drill-atgCwrywny ARCADIA DRILLING INC. Dnller/Eagineedfruaes Sigeattee_� �� Address PO BOX 1790 ' Driller w truna License No.1886 Cry,State,Zip SHELTON WA 98584 IfTRAINE6, Cmtreews Drinees Licensed No. RegistiVm No. ARCADD10981(1 Dote 7/5ft Driller's Signature :J ' ECY aSa-1-20(Rev 3WS) Ecology is n Egad Opp—ty E-pl%w- i r 1 f a _ w j cc f 1 r PA kq A a�- r 1 ' APPENDIX C ' EROSION CONTROL j i 1 1 GEOTEXTR E FABRIC WRAP Mr TRENCH TO AT LEAST ENTIRE BOTTOM OF TRENCH BEFORE PLACING GR4Tw r�PW WOOD POST ON SILT FENCE I2' DEEP, 8' WIDE EQUIVALENT ON BETTER ' FILLED WITH 3/4. THE TE FILTER CEMENT MANUAL TYPE LFOR M PUSET SOUND SPECIF O WASHED GRAVEL BASIN,'OR APPLICABLE COUNTY STANDARDS: DIRECTION OF WATER F1 OV— T L lEQTEXTI E FILTER FABRIC SHALL BE PUNCH D IN A EXISTING CONTDRUDA ROLL CUT TO THE LENGTH OF EACH BARRIER TO Gt01DNDSI RFACE AVOID USE OF JOINTS.IF JOINTS ARE►EOESSARY,FILTER FAMUC SWILL BE SPLICED TOGETER ONLY AT A SUPPORT POST WITH A T BICH OVERLAP AND SECURELY FASTENED AT BOTH DOS TO THE POST. 3.STANDARD FILTER FABRIC OWL BE FASTENED USD6 1' STAPLES OR TIE WIRES GOBS RINGS)0 4 IN SPACD& 4. POSTS SWILL BE SPACED AM PLACED AT DEPTHS INDICATED IN SILT FENCE SrrTffN THE DETAILS ON TIT SHEET,AND DRIVEN SECURELY INTO TIE N.TS. GRONN0. ' S WINE MESH SMALL E 2'X2'XI4 GAVE OR INDENT.THE WIRE MESH MAY BE ELIMINATED IF EMI A-STiENGTH FILTER GEOTEXTILE FABRIC FABRIC 0FR ,AND CLOSER POST SPACING IS USED. 2'><2' WOOD POST CTYP) 00 M M ��fi DE MESH 6J A TRENCH SMALL BE EXCAVATED ACCORZ MG TO THE BETALS ON 13 R EQWVALEMT OR BETTER THIS SHEET ALONG THE LIE OF THE POSTS 41D UPSLOPE FROM 16 FT MAX. O.C. THE SLT FENCE. 0.3 FT 7. SILT FENCES SHALL E LOCATED DOYNSIAPE FROM THE FT CLEARING LIMITS BE THE PROJECT. EXISTING GROUND SURFACE 2 12' DEEP, 8' WIDE TRENCH FILLED WITH 1 ' 3/4' TO 1 1/2' P.3 FT WASHED GRAVEL BOTTOM EXTENTS OF SILT FENCE - DETAIH PERMANENT EROSION CONTROL NOTES GEOTEXTD.E FABRIC N.T.S. SOD PLACEMENT L SOD FOR GRASS STALES SHALL E NACHDE CUT AT A 3/4-DM LMIPGRM TICK ESS AT GENERAL NOTES- THATCH. MOM RING.MEASUREMENTS FOR THICKNESS ESS SHALL EXCLUDE TGR GROWTH AND L SIOILD THE TEMPORARY EROSION no SEDIMENT CONTROL MEASURES NS STANDARD SIZE SECTIONS OF SOD FOR GRASS SVALES SHALL BE STRONG ENOUGH TO SHOWN ON THESE PLANS PROVE TO BE DADEQUATE DURING CONSTRUCTION, SUPPORT TEAR OWN WEIGHT AND RETAIN THEIR SIZE AN SHAPE WHEN SUSPENDED BY THE CTHE COL CONTRACTORSHALL INSTALL ADDITIONAL EROSION AND SEDIMENT END OF A 3 FOOT SECTOR FACILITIM 3 SOD FOR GRASS SWALES SHALL NOT E HARVESTED GR TRANSPLANTED WHEN B.ALL EROSION AND SEDIMENT CONTROL FACILITIES AND DEVICES SHALL E EXCESSIVELY DRY OR WET MOISTURE CONTENT MAY ADVERSELY AFFECT ITS SURVIVAL. INSPECTED DAILY AND 9063MTELY MAINTAINED,IF NECESSARY. 4 SOD FOR GRASS$VALES SMALL E HARVESTED,SLIVERED AND PLACED WITHIN A I ALL EROSION AND SEDI ENI CONTROL FACILITIES AND DEVICES SHALL E PERIOD OF 36 1OUIM LEFT IN PLACE UNTIL THE UPSLOPE AREAS HAVE BEEN PERMANENTLY STADILIZED SEEDING FOR RAW SLOPES TEMPORARY ERGRID/CONTROL NOTES, L BMW SEEDW4 INSTALL HEEDED SURFACE RUOFF CONTROL MEASURES SUCH/AS GRAWENT TERRACES. INTERCEPTOR DOLES,STALES.LEVEL SPREADERS AND SEDIMENT FOR ALL AREAS WHICH HAVE BEEN STRIPPED 0< VEGETATION OR EXPERIENCED P- THE SEED NEB SHALL BE FDII WITH HARASS FINE SURFACE, FO1 OVDIG SURFACE LAND DISTURBING ACTIVITIES,AND WHERE NO FURTHER VOW IS ANTICIPATED ROUpHENDO,PERFORM ALL OPERATIONS ACCROSS OR PERPENDICULAR TO THE SLOPE. FOR A PERIOD EXCEEDBO THE LISTED CRITERIA BELOW,ALL DISTURBED AREAS 3,SEEDING RECOMMENDATIONS,AS SHOWN BELOW.AID SHOULD E APPLIED AT THE RATE MUST BE IMMEDIATELY STABl=D WITH M IJODNG.LASS PLANTING GR OTHER OF 120 POURS PER ACRE APPROVED EROSION CONRRM.TREATMENT APPLICABLE TO THE TDE OF YEAR. 4.SEED BEDS PLANTED BETWEEN MAY 1 AID OCTOBER 31 WILL REDIARE DOUGA1T3N AND GRASS SEEDING MILE WILL ONLY E ACCEPTABLE DURING THE MONTHS OF OTHER MAINTENANCE AS NECESSARY TO FOSTER MD PROTECT THE ROOT STRUCTRE. APRIL TFE T samma MAY ALM BE AUGMENTED 3.SEED DEDS PLANTED BETWEEN NOVELBER 1 AID APRIL 30,ARMORING ff THE SEED BED IN T INTEREST NETTING O OSIER APPROVED BUTMSTTREATMENT. WILL BE NECESSARY,(w4 GEOTEXTI.EL JUTE MINT,CLEAR PLASTIC COVERINCA 6.FERTILIZERS ARE TO BE USED ACCORDING TO SUPPLBOW RETODEIDATMML MOATS DRY SEASON(NAY 1 THRI SEPTEMOER 30) — THE CLEARING OF LAND, SHOULD BE MI VU=ESPECIALLY ADJACENT TO WATER DOI I£S AID WETLANDS. DICLlO1NG THE REMOVAL OF EXISTING VEGETATION OR OTHER GROUND COVER. USE THE FOLLOWING RECOMMENDED SEED MIXTURE FOR EROSION CONTROL, GR A COUNTY MUST BE LIMITED TO ONLY AS MULTI LAIRD AS CAN RECEIVE APPROPRIATE APPROVED ALTERNATE SEED MIXTURE. PROTECTIVE COVER OR BE OTHERWISE STAJOI EMP AFTER HAVING BEER CLEARED OR OTHERWISE 319TRED,BY IS LATER THAN SEPTOW 30 OF A pR!>POtTIOq PURITY TION GIVEN YEAR: UNLESS IMMEDIATE STABILIZATON 3 SPECIFIED IN THE EROSDDN MILE A PORTIO � � � AND SEDIMENT CONTROL PLAN,ALL AREAS CLEWED GR OTHERWISE DDMRED WEIGHT ' MIST BE APPROrRIATELY SRABB.I2ED THROUGH THE USE ff MLCIOO,METTING, PLASTIC SIEETDIG,EROSION ILAIOCETS.FREE DRADNIIIG MATERIAL,ETC»BY ANNUAL RYE CLOL1tM MLTIFLOR110 40 98 90 SEPTEMSER 30 GR SOBER PER TE APPROVED PLAN O'ACTION.UNLESS OTHERWISE APPROVED BY THE COU TY. SEEDING, FERTILRING AND MRLC I G CHEWING TEST CA RIARA COOUTATp 40 97 80 OF CLEARED GR OTHERWISE DESTIRIED AREAS SHALL BE PERFOHED DURING CJMESTOVN.BANNER,SHADOW. KOCET THE FOLLOWING PERIOBSS MARCH 1 TO MAY 13,AND AUGUST 13 TO OCTO W L WHITE DUTCH REP 10 96 90 SEEDING AFTER OLoOO I VI.L BE DOE WHEN WH PHYSICAL COMPLETION THELETION E CrRIFOLIUM PROJECT IS IMMINENT AND THE ENVHIOENTAL CONDITIONS ARE CONDUCIVE TO SATISFACTORY GROVTL IN THE EVENT THAT PERAIENT STABL37ATMN IS NOT MULCHING POSSIBLE,AN ALTERNATIVE METHOD OF GROUND COVER,SUCH AS MU.CHRNy, NETTING. PLASTIC SHEETING,EROSION BLANKETS,E:TCJ.MUST BE INSTALLED BY L MATERIALS USED FOR M IXHING ARE REf00ENOE9 TO BE WOND NO LATER THAN SEPTEME SHOULD 000 R 3Q SHOD BE APPLIED AT A RATE OF I PONDS PER ACRE FIRER CELLULOSE,AND IN THE EVENT THAT CONSTRUCTION ACTIVITIES OR OTHER SITE DEVELOPMENTL MULCH SHOULD K APPLIED IN ALL AREAS VZTH E7WOED SLOPES GREATER THAN N ' ACTIVITIES ARE OR SHALL K ES N LEAST 4 CONSECUTIVE INSPECTION DAYS, THE 3 MULCHING SHAD BE USED IMMEDIATELY LY AFTER SEEDING GR IN AREAS WHICH CANNOT SHAUL BE RESPONSIBLE FOR THE DISPECTION O ALL BE SEEDED BECAUSE OF THE SEASON ALL AREAS REDOO G MULCH SHALL BE COVERED BY EROSION AND SEDIMENT CONTROL FACKMn IOEDIATELY AFTER S. tOVEMER L EVENTS,AND AT LEAST ONCE EVERY WEM THE OWNER/CONTRACTOR BE ILE FOR THE WUNTENANCE AND REPAIR O'ALL EROSION AN SHALL B SEDIMENT CONTROL FACILITIEL ' VET SEASON GICTDER E THRU APRIL 30) — ON SITES WERE U INTERUPTED / LOCATION THE PROJECT/ OWNERR ACTIVITY IS IN PROGRESS, THE CLEARING aF LAND,INCLUDINGINCLUDINGPROJ SEABEC DEVELOPERS E O'EXISTING VEGETATION MID OTEt GROUNDCOVER,SMA L E UNITED TO AS MUCH LAND AREA AS CAN BE COVERED OR STABILIZED WITHIN 24 FORS IN THE EVENT A MAJOR STORM IS PREDICTED AND/ OR EROSION AND GEOTECHNICAL REPORT SEOMIT TRANSPORT OT-SITE IS OBSERVED. SEADECIC DEVELOPERS.ED Up- ALL CLEARED OR DISTURB AREAS SMALL RECEIVE APPROPRIATE PROTECTIVE PARCEL NOS. 12M 22 90361, -62, -63, COVER OR BE OTHERWISE STABILIZED,SUCH AS MULCHING,NETTING,PLASTIC -64, -65, -66, -67 & -68 SHEETING,EROSION HLAIGWM FREE BRAVOS MATERIAL,ETC., WITHIN 3 DAYS AFTER HAVING BEEN CLEWED OR OTHERWISE DISTURED IF MOT BEING ACTIVELY VOICED. SILT FECDO,SEDIMENT TRAPS. SEDIMENT PONDS.ETC., DESIGMERP ENVIROTECH ENGUEERINCi WILL NOT BE VEVED AS ADEDIATE COVER IN AND OF T ES.ENDELV IN THE EVENT THAT ANY LAND AREA NOT BEING ACTIVELY WORKED REMAINS 74 NE HURD ROAD ' UNPROTECTED DR HAS BEEN NOT BEER APPROPRIATELY STABILIZED 3 DAYS AFTER HAVING WASHINGTOl1 98328 HAVING CLEARED,ALL CONSTRUCTION ACTIVITY ON THE SITE, EXCEPT FOR APPROVED EROSTDI AND SEDIMENT CONTROL ACTIVITY.SHALL IMMEDIATELY 360-27$-9374 CEASE UMTD.APPROPRIATELYPR TIMEROPEC OR ST AS AFORENDITIONEDLANDAREA"�BEEN EROSION CONTROL r Envirotech Engineering 74 NE Hurd Road Belfair,WA 98528 July 16, 2007 Att. Rebecca Hersha Mason County Department of Community Development PO Box 279 Shelton, Washington 98584 RE: Geotechnical Report for Parcel Number 122292290363, Stock#2003-0154 Dear Ms. Hersha, Please find enclosed, three copies of the Geotechnical Report Addendum #1 for the referenced project. This addendum should accompany the "Geotechnical Report for Seabeck Developers Eight Single Family Residence Lots" prepared June 6, 2007 by Envirotech Engineering. If you need any additional information, please do not hesitate to contact me at 360-275-9374. Best Regards, Michael Staten, P.E. Project Director BUS: 1-800-387-6806 CELL: 360-689-6045 FAX: 360-275-4789 HM OFFICE: 360-275-9374 EMAIL: envirotech_ak@hotmail.com Geotechnical Report Addendum #1 Seabeck Developers Eight Single Family Residence Lots Parcel No's 12229 22 90361, 12229 22 90362, 12229 22 90363, 12229 22 90364912229 22 90365912229 22 903669 12229 22 903679 & 12229 22 90368 Mason County, Washington July 14, 2007 Project#0724 Prepared For: Seabeck Developers, LLC. 200 Bravo Terrace Port Orchard, Washington 98366 Prepared By Envirotech Engineering 74 NE Hurd Road Belfair, Washington 98528 Phone: 360-275-9374 Fax: 360-275-4789 INTORDUCTION Envirotech Engineering (Envirotech) has completed this geotechnical addendum as an addition to the "Geotechnical Report for Seabeck Developers Eight Single Family Residence Lots" prepared June 6, 2007 by Envirotech Engineering. The referenced geotechnical report is for eight adjacent parcels of land identified as parcel numbers 12229-22-90361, 12229-22-90362, 12229-22-90363, 12229-22-90364, 12229-22-90365, 12229-22-90366, 12229-22-90367 and 12229-22-90368 located in Mason County, Washington (Project). This addendum will identify these parcels, respectively, as Lots' IA, 2A, 3A, 4A, 1B, 2B, 3B and 4B. This addendum was prepared in order to satisfy Mason County requirements and provide additional information requested by Vector Engineering, Inc. in a letter dated July 6, 2007. This addendum is presented by providing additional information concerning the project in an item number format. The item numbers in the body of this addendum correspond to the item numbers in the Vector Engineering, Inc. letter found in Attachment A of this addendum. ITEM#1 Mason County, initially required geological assessments to be completed for Lots IA, 1B, 2A and 2B. Lots 3A, 3B, 4A and 4B were required to have geotechnical reports. However, Lots 2A and 2B require geotechnical reports due to development within 300 feet of slopes over 40%. Although Lots IA and 1B required geological assessments, Envirotech prepared a geotechnical report for all eight parcels. The geotechnical report and/or this addendum addresses, at a minimum, Mason County geotechnical report requirements for Lots 2A, 2B, 3A, 3B, 4A and 4B, and geologic assessment requirements for Lots I and 1B. i ITEM#2 Per MCRO 17.01.100 E.5(1), "a discussion of general geologic conditions, specific soil types, groundwater conditions, the upslope geomorphology and location of upland water bodies and wetlands, and history of landslide activity in the vicinity" of the project is required for geotechnical reports. The reviewer requested only a discussion of the general geologic conditions, for the reason that the other requirements per MCRO 17.01.00 E.5(1) were addressed in the geotechnical report. Envirotech Engineering Geotechnical Addendum#1 Ph. 360-275-9374 Page 1 of 5 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62. -63, -64, -65, -66, -67, &-68 July 12, 2007 ... ...ierrarillfifIW111irm11�WY1r1�w�n ._,.... General Geologic Conditions In general, soils at the project are composed of materials from glacial advances. The geologic conditions as presented in the "Geologic Map of Washington," compiled by J. Eric Schuster, 2002 indicates Quaternary sediments, Qs. Quaternary sediments are generally unconsolidated deposits, and dominantly deposited from glacial drift, including alluvium deposits. This project is located within the Puget Lowland. Typically, "lower tertiary sedimentary rocks unconformably overlie the Crescent Formation." as revealed in the Geologic Map. Initial sedimentary rocks were formed from shales, sandstones and coal deposits from rivers. During the Quaternary period, the Puget Lowland was covered by numerous ice sheets, with the most recent being the Fraser glacier with a peak of approximately 14,000 years ago. Upon the glacial retreat, the landscape was formed by glacial erosion glacial drift deposits. ITEM#3 A geologic map of the site showing the area of the proposed development, including the boundaries of the hazard, and associated buffers and setbacks per MCRO 17.01.100 E.5(5)is provided in Attachment B of this addendum. ITEM#4 A cross-section drawn to scale, which depicts the subsurface profile, is required per MCRO 17.01.100 E.5(5). A cross-section, drawn to scale, is provided in Attachment C of this addendum. ITEM#5 Calculations for the slope stability analysis for the static and seismic conditions are provided in Attachment D of this addendum. The Simplified Bishop Method was used for this site utilizing a spreadsheet program iterative approach. Various radii's and center points of the circle were selected until the lowest factor of safety was found. Center points and radii's were carefully chosen to exploit the weakest points of possible slip planes. In addition, conservative to ultra-conservative values were used in the slope stability analysis in regards to saturation of the upper slope. See Item #6 for additional information concerning septic drainfield parameters. In attachment D, two pages of spreadsheet indicate where the smallest factor of safety for static conditions were found (1.7). The spreadsheet is divided into "Input" values and Envirotech Engineering Geotcchnical Addendum#1 Ph. 360-275-9374 Page 2 of 5 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62, -63, -64, -65, -66, -67, &-68 July 12, 2007 "Output" results. In the "Input" block, topography is indicated, estimated soil properties, surcharge amounts and location, and a cell for a trial radius. A conservative 75% slope was used in which this steep of a slope can only be found beyond the property lines of Lot 4B. Additional safety factors were built-in to the stability analysis, such as considering the top of slope as level instead of gently sloping down as indicated on-site, and estimating a slightly higher vertical relief than actual conditions represent. Soil input values were considered saturated in the upper 18 feet of soils,which greatly decreases cohesion, and to a lesser extent, the angle of internal friction. "Output" values included subroutines for calculating data required in the slope analysis, tables typical to the Simplified Bishop Method output, and factor of safeties manually typed based on changes in the trial radius for the given center of circle. Seismic conditions were estimated utilizing worst case scenario values from the static analysis, a horizontal acceleration coefficient of 0.15 as required by Mason County, and applying the aforementioned values to the stability charts shown in Attachment D. These stability charts were presented by the American Society of Civil Engineers (ASCE) in the "Journal of Geotechmcal and Geoenvironmental Engineering," April 2002. ITEM#6 Clarification is required whether septic drainfields are permitted within the landslide hazard buffer area as indicated in the geotechnical report. Septic drainfields are permitted within 50 feet from the top of slope. Specifically, septic drainfields in the locations presented in the geotechnical report are permissible. The buffer depicted in the geotechnical report was provided for buildings only. However, further clarification is provided as follows: Since proposed building locations are known to be approximately 100 feet away from the steep slopes, an arbitrary and conservative location for building surcharges was established at 50 feet from the top of the steep slope. This arbitrary building surcharge location and proposed septic drainfield locations were used in the slope stability analysis. Additional building loads were applied at 200 feet from the top of slope that is indicative of the planned development on Lots 2A and 2B. Due to this distance and subgrade conditions on-site, factor of safeties from several trials were well above the trials provided in the attachments. Constant saturation of the subgrade due to the septic drainfiled is not expected nor a concern to the critical slope. The planned septic units were designed as mound systems where the absorption area will be entirely above the existing ground surface, and the treated water will be disbursed periodically throughout the day into the absorption area via Envirotech Engineering Geotechnical Addendum#1 Ph. 360-275-9374 Page 3 of 5 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62, -63. -64. -65, -661, -67,& -68 July 12, 2007 timed dosing. This type of septic system is required as a result of the upper 2 to 3 feet of existing subgrade conditions. These soils are dense to very dense, predominantly low plastic silt with few sand/ gravel and binding clay. Below this stratum is a very dense cemented soil, typically described as `hardpan.' Except for the few inches of topsoil, these soils have very little void space or continuous voids to freely allow groundwater flow. These soils exhibit a low permeability coefficient expected to be in the range of 5 X 106 to 5 X 10' centimeters per second. Due to the relative impermeability of these soils, treated water from the septic absorption area is not expected to detrimentally penetrated the subgrade before the groundwater flows down the slope and away from the critical slope. As an extra pre-caution, the upper 18 feet of soils were considered saturated in the slope stability analysis which could probably occur if the ground was completely disturbed to a depth of 18 feet. Additional recommendations provided in this addendum is that no additional land disturbing activity, other than installing the planned septic system and associated vegetation removal, shall be permitted within 50 feet from the top of the slope. Any earthmoving activities, or barriers that impede the movement of ground and surface water shall be avoided. From the site visit, it appears that neither trees or large bushes are required to be removed from the septic components area due to the very low density of vegetation in these areas. TEEM#7 Clearing is not permitted on the face of critical slopes. Clearing is permitted within 50 feet from the top of the slope. However, this clearing is contingent upon re-working disturbed areas by compacting and light grading so that pre-existing conditions are maintained as much as possible. The above recommendation is provided in the geotechnical report. Removal of vegetation within 50 feet of the top of critical slopes for this project is a very low concern based on the following: • The vegetation in this area is very sparse, resulting in low disturbance if removal is completed. The sparse vegetation may be due to past clearing activities. If clearing had been done, there are no indication of cracks, saturation, ponding or any slope or erosion problems due to vegetation removal. • Due to the topography, virtually no stormwater will enter this area from upslope terrain. Vegetation is not critical in this area in order to decrease groundwater flow through transpiration. Envirotech Engineering Geotechnical Addendum#1 Ph, 360-275-9374 Page 4 of 5 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62, -63, -64, -65, -66, -67, &-68 July 12. 2007 • The roots are very shallow and sparse within this project due to the very dense and compact soils near the ground surface and lack of vegetation. Root structures which normally increase the `apparent cohesion' of a slope is very minor for this project. Slope stability analysis determines the deep-seated factor of safety where roots are not present for this project. Significant surficial slope movements due to vegetation removal is also not expected because of the lack of vegetation, slightly sloping terrain which provides a slower medium for water movement, soil characteristics of very dense and binding instead of loose, and the recommendations presented in the geotechnical report and addendum for maintaining pre-development conditions as much as possible. ITEM#8 This item is identical to Item#6. See Item#6 for addressing this comment. ITEM#9 A landslide buffer of less than 50 feet is feasible for this project. However, buildings and considerable land disturbance is not permitted within 50 feet of the top of slope. Tree cutting without ground disturbance and septic installation is permitted within 50 feet of the top of slope, but not on the face of the critical slope. These conclusions are based on favorable surface conditions where virtually all water beginning at the top of critical slopes will flow away from the slope face; subsurface conditions in which very dense and complementary soil structures and classifications exist; and, a conservative slope stability analysis provides a sufficient factor of safety for both static and seismic conditions. Items #1 through #7 provides additional details and more specific details in relation to these conclusions. Please contact Michael Staten at 360-275-9374 if you have any questions, comments, or require additional information. yCLYp� Sincerely, Envirotech Engineerin Michael Staten, P.E. 4304 Geotechnical Engineer ��G �� ti l A • Envirotech Engineering Geotechnical Addendum 41 Ph. 360-275-9374 Page 5 of 5 Mason County Parcels 12229-22-90361, Fax: 360-275-4789 -62, -63, -64, -65, -66. -67.&-68 July 12. 2007 ATTACHMENT A VECTOR ENGINEERING,INC. LETTER ATTACHMENT B GEOLOGIC MAP yr� �ncN-uo FEET Mom+ �ay� f sr,�rf 3 S PARCEL Na 12229-22-90365 EXISTING 10 FT LOT 1B ® PAVEDVIDE ACCESS ROAD F PROPERTY CORDER �. CTYP) PARCEL NQ 2229-22'90361 LOT « A NOTES, PARCEL NO. L CONTOURS ARE NOT PRECISE, AND ONLY 12229-22-903" DEPICT GENERAL TOPOGRAPM CONIOTIONS. R LOT 2B % 2. SECTION A-A 1S LIMITED TO A SOIL iG * CROSS-SECTION PROVIDED IN ATTACHMENT r- C. 3. THERE ARE NO EROSION HAZARDS OR F7 EARTHOWE HAZARDS FOR THIS PROJECT. 1t3� ® M 1f0 f t3'°T S TE 22�29'-22-`J0362 �OF ST LOT 2A SEPTIC BRADVIELD (TYP) 1* 41 APPROXNATE LOCATION 1t3 PT DRIVEVAY�CTM y \ \ 50F APPROXWTE �►'r \ \ OF B CATION \ FOOTPRINT CTM \ � \ Iva SLOPE BUFFER « « \ AND GROUND 44 4 \ \ DISTURBANCE \ ® LOCATION OF � TO SLOP OF SLOPE PARCEL NO. wf �Op 2229-22-90368 LOT 42 41 11y 4 �C ARCEL � 4A STq 1NM7 S LOT 32 PARCEL 12 3A PROJECT/ OVNER/ LOCATION* 4b SEABECK DEVELOPERS SLOPES OVER 401: EXTEND GEOTECHNICAL REPORT RNR� OVER 300 FEET NORTH MID SEAM= DEVELOPERS, LLC. ' t9 OVER 300 FEET SOUTH OF PARCEL NOs. 12229 22 90361, -62, -63, THE PROJECT LDUTS -64. -0, -66, V 7 6 -68 SHINGTON DESIGNEIh ENVIROTECH ENG04MRING 74 NE HURD ROAD BELFAIR, VASHINGTON 98528 124 FT t 360-275-9374 GEOLOGIC MAP ATTACHMENT C SUBSURFACE CROSS-SECTION � w � $ § La0 § § 0a0Q $ w �■ %B? Ib� >_j -tn) ,�Clul 2 §k �� a. $b� .9 - . ems k �m e &a� a_9b ® §0 0 U-iidL) w al §� §v� 9� §� 09L _Lapm § � �§ � � u� w �3 ¥ wLAJ CL�_ � 0 �� k _j� EjX a a -J § � e� � k �0Li bU_ e :3w w 2 Uw2 < < �� 2 . § <Q�222 X: 2 wuo § § qOb-j�2 E § 2LjCL�wS ` m SU �� § ( -J0O w& L a§ � 1m0 § c (X w �Z 2 SONX:n� N k, ■§�§ § � . 4X2 §a /§ � kk § � 1pl1I�IY�YII W1�IfL A�f�iMY IWWfilii�il�i1101 "-_ -_. ATTACHMENT D SLOPE STABILITY SPREADSHEETS � 2 � 6 r- ■ $ a ■ 7 e 0 k 230 ako / CL © § 0 c .n a m x ■ © r E 0 ƒ ' cl cc2 g £ — $ $ CRaC 2 § - - - - - =6 k � 0 Cl© 2N�N � - - �oVD go A2 o � � © & § o ocmCMCf) 1* 0 % @ » @O » co ■ cc o � 2 kkk 2 § x �o � ■ @@ # c IL U- U- e k § CV c � kIrak � � co co D ee � � 2 �222 � ® � $ @ 0 eLm ma £ � ooc « © o06 d § _ CM 0) « to COccc o e § § o 0 0 m2 2 0000 co 0P7 oo k cc 6 is £ » co @k@ $ @V) V) $ LL � o @45 ■ ■ Zz � � L : rt+ CDftaRP, Mc! 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E QO r r r r r r r r r V- A r r r r r r O O C 0 0 v t0 CA m tly m N = a� D aMO N O N co _ $ E y m �- Nersd� W 40l� 4040Q Naa � mmrt a� mO C� CO r r M Z N Z r te)10 tc)1O te)'0 �+ S -D-2 w g 830 f a S 5 S 16 WI 30 4 ; 4 15 2 kh=a1 2 kA=a2 2 T OPFI 05 1 is 2 25 0 03 1 is 2 2.5 0 0.5 1 is 2 2.S (b)4 (d) to 3 2.� s t ! � 2 ZS - g 2OLV 2 2 00,0 , 79 , kA=0.1 p ka=0.2 0�0001-1 k�=0.3 00 0.1 tO.2 0.3 a4 05 a1 a2 03 a4 G5 00 a, 0.2 0.3 a4 a5 uE r i� Fig.4. Safety factor for slopes subjected to quasi-static horizontal force sidered to be Hilly drained where dilation of the soil skeleton does make it possible to make an"educated guess"of the influence of not cause any change in the magnitude of the pore water pressure. pore water pressure on the stability of slopes. For the purpose of presenting the influence of the pore water on the stability of slopes,the distribution of the pore water pres- sure is described by coefficient r„ defined by Bishop and Mor- Quasi-Static Setsmk Effect genstein(ice)as Seismic loads an slopes are ohm considered in design by mclud- u ing quasi-satic form due to seismic acceleration.While such an rr= k (8) analysis ignores the seismic process (acceleration history) and does not give any insight into the behavior of the structure, it is where u—magnitude of the pore water pressure, 7—soil unit routinely used in desgpL The kinematic approach of limit analysis weight,and h—depth of die point on the Mur a surface below the was used here to strive at the data used to produce the charts in slope surface. Stability charts for slopes with r„equal to 0,0.25, Fig.4.Coefficient kn represents the intensity of horizontel aceel- and 0.50 are presented in Fig.3.The data in the c bwft in Fig.3 eration as a iiviction of the gravity accelemon. The effect of was created using a computer program written earlier (Micha- quitsi-static f°roces was included in the anokirsis as an additional lowski 1995). work in in the energy balance equdion(Michalowski 1998). Coefficient rg is a rather code manna of aceouming for the No pore water pressure was considered in calculations with a Pam water pressure in a slope. If a well-defined fbw net in a quasi-static seismic fi=e— The quasi-stir approach is a crude Slope is known,the correspondfng pore preemie distribution can approximation of seismic effects, and charts involving another be calculated and included explicitly in computations of the sta- simplified concept(r„)to describe the pee water pressure distri- Wity number(or the safety factor). While such calcubdicitis are bution,in addition to ki,WAy not be indicative of the true safety mac accurate,presenMon of die results in charts wouM be dif- margin of slopes.Such charts would be an inappropriate tool for ficult because of the large number of variables needed to describe analyzing the safety of slopes,pertclilaiy for liquefiable soils. realistic flow nets. While the nature of calculations with pare Safety factor r F, represented in the charts as F/tan 4p, is an pressures described in Eq. (8) is rather approximate, the results increasing function ofN' (or c/TH tan if)up to some threshold 354/JOURNAL OF GEOTECHNICAL AND GEOEPNVIRONMENTAL ENGINEERING/APRIL 2002 SeabGC.I�. (/�{/Gfa �s 7'�lrilh�G CaIGG�fas { o 71� C- oe" cot Z 3' C— fe p f 37 � �f e- ��►C�!n fin _ 0j 1 2s.3° ef' I Far fC = 0.2 2.25 n FS, = 1006 0,15 -71 s i 1 i