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Home My WebLink AboutGEO-Tech Review BLD2004-00930 - BLD Engineering / Geo-tech Reports - 6/21/2004 STA 7- 0 LG MASON COUNTY A° N PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER p � 2 Shelton,Washington 98584 yr, O °J ,f4 DATE: June 20, 2004 INTER-DEPARTMENTAL COMMUNICATIONS TO: Tammi Clark,DCD -Planner T I N T}-� T� BE KEG►, FROM: Alan A. Tahja,P/W- Co. Hydr. Engr. WO#PLG-04 PARCEL FILE SUBJ: Geo-Tech Assessment Review NAME: Grohe SFR(a, 145 E Spruce St. BLD2004-00930 Tammi, The geotechnical assessment prepared for the proposed Marc Grohe Single Family Residence (SFR)to be constructed at 145 E Spruce Street,Union, has been received and reviewed by Public Works. The report appears to satisfactorily address County requirements for geotechnical assessments. The assessment's author indicates that, in his opinion,the proposed development of the property will not cause stability problems for either the subject property or neighboring properties,and that a more detailed investigation(report)is not warranted. From the contents of the assessment, I recommend accepting the report as satisfying the County's requirement(s) for stability investigation and geotechnical reporting. Recommendations contained in the assessment should be incorporated into the site's development and made conditions for permit issuance. Adequate erosion and sediment control features need to be implemented during land disturbing activities to protect neighboring properties and State waters from adverse stormwater runoff impacts. The migration or release of silty water or mud from the applicant's property will be considered a violation of County and State water quality protection regulations. In summary,the geotechnical assessment appears acceptable, and the proposed residential development of the property should be allowed to proceed, subject to the engineering geologist's recommendations. Please feel free to contact me at County extension 461 if you have any questions regarding these comments,or if you feel any features need further discussion or attention. Sin a ely- L , v Al n A. Tahja File: H: \WP\GEO\Assessments\Grohe.doc r WORK ORDER - PUBLIC WORKS DEPT.- py Oats: U 1"1- (% _ R7 Work order PERMIT M (�I.Q a%r y-W 30 Number. 1 r-2Y� Requested'by: Authorized by: r1i Date: i Type of Work: CHARGE TO: NAME AGENCY/COMPANY SILLING ADDRESS ' PHONE Pub.Works Person in Charge: (c) Protect Time Une: (from-to dates) a TO� PM16d SW dada: EsthdoclOgsh Date: ' 3 Z2 AplxnodRfsEe I+cKxs: ESTIMATED TOTAL i'S: COST ESTIMATE • (D) JE& ngum Aub(sS31 FrIngs N TOTAL$ >� TOTAL n EQUIPMENT USED: I MATERIAL.USED: (F) AcWA Cost BARS: PROD A: DATE Eml+byea Nerve. � Hours Fringe N TOTAL$ EQUIPMENT USED: m Una $& TOTAL L MATERIAL USED: TOTAL ALL (a) GILLED DATE INV# PAID DATE RECI cvs _ SOH E L N rn g z c� P IN m v "' rn � o 0 al Geologic Assessment Proposed Residence 145 East Spruce Street Union, Washington July 22, 2003 For Marc Grohe G e o E n g i n e e r s File No. 10854-001-00 Geo 1 Engineers July 22, 2003 Marc Grohe P.O.Box 428 Union,Washington 98592 Attention: Marc Grohe Geologic Assessment Proposed Residence 145 East Spruce Street Union,Washington File No. 10854-001-00 INTRODUCTION We are pleased to present our geologic assessment for the property located at 145 East Spruce Street in Union, Washington. The project site is located approximately as shown on the Vicinity Map,Figure 1. We understand that current development plans call for the construction of a single-family residential structure on the site. The residence will be located in the southwest portion of the site approximately as shown on the Site Plan, Figure 2. We further understand that cuts of 2 to 3 feet are envisioned to establish proposed finish grade in the building area. We understand that Mason County has requested a geologic assessment of the site slopes. Mason County's Resource Ordinance requires a geotechnical report that addresses erosion and landslide hazards, if the subject property contains slopes greater than 40 percent, or if the subject property contains slopes greater than 15 percent and geologic contacts, springs and groundwater seepage is present. If there is a question regarding the presence of landslide or erosion hazards, Mason County's Resource Ordinance also allows for the submission of a Geologic Assessment. PURPOSE AND SCOPE The purpose of our services is to observe the existing site conditions as a basis for developing an opinion regarding the potential for landslide hazards at the site,and to present our findings and conclusions in a written Geologic Assessment prepared to address Mason County's requirements of a Geologic Assessment, as presented in Chapter 17.01.100 Section EA. Geolingineers,Inc. 1101 Fawcett Ave.,Suite 200 Tacoma,WA 98402 Telephone(253)383-4940 Fax(253)383-4923 www.geoengineers.com Printed on recycled paper. Marc Grohe July 22,2003 Page 2 Our specific scope of services includes: 1. Observing surface soil and groundwater conditions in the vicinity of the subject property. 2. Reviewing soil logs prepared by others for the planned septic drainfield at the site. 3. Observing surface slope conditions. 4. Reviewing readily available geologic maps of the site and vicinity. 5. Submitting a written letter summarizing our observations and opinions regarding landslide hazards at the site. Our scope of services and budget does not include slope stability analysis. We developed our opinion regarding the stability of the slopes based on site observations and our experience. You provided written authorization for our services on July 11,2003. SITE CONDITIONS PUBLISHED GEOLOGY AND SOIL CONDITIONS The upland area on which the subject property is located is underlain by soils deposited in connection with a series of several regional glaciations, together with the granular soils deposited between those glacial periods. The most recent glacial event concluded about 10,000 years ago. Except for the immediate ground surface deposits, all of the older materials have been over- ridden by past glaciers and are very compact. The geologic map of southeast Mason County (Molenaar and Noble, 1970) indicates that the soils in the vicinity of the subject property consist of glacial till (Qvt) and glacial advance outwash (Qva) deposited during the Vashon glaciation. Till typically consists of a very dense mixture of cobbles and coarse pebbles in a binder of clay and silt. Till typically has relatively low permeability and serves as an aquiclude allowing perched water to form within and above it. Glacial advance outwash typically consists of dense sand and gravel and has moderate to high permeability. The Coastal Zone Atlas for Mason County (Washington Department of Natural Resources, 1980) indicates the site is located in an area classified as being stable with respect to landslide potential. SITE RECONNAISSANCE We completed a limited geologic reconnaissance of the subject property on July 16, 2003. The irregularly shaped property encompasses approximately 1%2 acres. Existing single-family residential lots are situated to the southwest and northwest of the property. Undeveloped woodland bounds the site on the south and McReavy Road bounds the site on the east. The southwest portion of the property, where the residence will be located has been cleared of trees. The remainder of the property has a dense vegetative cover of shrubs, deciduous trees and second growth fir trees. G e o E n g i n e e r s File No. 1 0854-00 1-00 Marc Grohe July 22,2003 Page 3 A hand drawn topographic site plan you provided for our review includes information for the proposed building area of the site that has been cleared for development. The plan indicates slopes in the vicinity of the proposed building area are typically inclined gently to moderately down to the north and east with declinations typically in the range of about 10 to 20 percent. Slopes to the north of the building area, in the vicinity of the proposed drainfields are inclined gently to moderately down to the north with declinations typically in the range of about 20 to 30 percent. Field measurements we performed on site using a hand level are generally consistent with the information you provided for our review. In addition, we estimate the slope near the north property boundary is typically inclined at between 30 and 40 percent. A cut slope on the west side of McReavy Road opposite the site is inclined at about 50 percent. No standing water or groundwater springs/seeps were observed on the site at the time of our visit. No evidence of deep-seated slope instability was observed on or directly adjacent to the proposed building location,or on the slopes to the north and east of the proposed building area. We also observed subsurface conditions exposed in three existing shallow test pits located in the proposed drainfield area. The soil exposed in the test pits comprised glacial drift consisting of dense silty sand with gravel and silty gravel with sand. We did not observe subsurface seepage in the test pits. CONCLUSIONS LANDSLIDE HAZARD AREAS Classification A landslide hazard area is defined by Mason County Resource Ordinance, as one or more of the following: 1. Areas of historic failures including areas of unstable old and recent landslides. 2. Areas with artificial oversteepened or unengineered slopes. 3. Areas with slopes containing soft or liquefiable soils. 4. Areas with all three of the following: • Slopes steeper than 15 percent and, • Hillsides intersecting geologic contacts with a relatively permeable sediment overlying a relatively impermeable sediment or bedrock and, • Springs or groundwater seepage. 5. Areas oversteepened or otherwise unstable as a result of stream incision, stream bank erosion and undercutting by wave action. 6. Any area with a slope of 40 percent or steeper with a vertical relief of 10 feet or more, except areas composed of consolidated rock. Based on the results of our review and reconnaissance, it is our opinion the site does not meet the technical criteria for a landslide hazard area. Based on the geologic information presented above and our field observations of the subject property and the area surrounding the subject G e o E n g i n e e r s File No. 10854-001-00 Marc Grohe July 22,2003 Page 4 property, it is our opinion that further geotechnical evaluation of the landslide risk to this property is not necessary for the proposed development. In our opinion, the proposed septic drainfield location is appropriate with respect to site slope conditions. Slope Maintenance Excessive disturbance and/or poor site drainage can destabilize slopes. At no time, should loose uncontrolled fill, including yard waste, be cast over or placed on the slopes. Proper slope drainage is imperative for long-term slope stability. The influx of water is a major factor in the destabilization of slopes. At no time, should surface water be discharged to, or near, site slopes or retaining structures. Surface water from downspouts, foundation drains,upslope retaining wall drains and runoff, the driveway and other surfaces should be collected and discharged to an approved receptacle. SEISMIC HAZARD Potentially liquefiable soils were not observed during our visit to the property. Based on our reconnaissance and geologic review, it is our opinion the potential for liquefaction of site soil during earthquakes is low. LIMITATIONS We have prepared this assessment for use by Marc Grohe for the property located at 145 East Spruce Street in Union,Washington. Our services were provided to evaluate certain geologic risks for a planned single-family residential structure to be located on sloping property. We have not been supplied a detailed plan of the proposed improvements. Our recommendations are intended to maintain the overall stability of the site and to reduce the potential for future property damage related to earth movements, drainage or erosion. However, all construction on slopes involves risk, only part of which can be mitigated through qualified engineering and construction practices. Favorable performance of structures in the near term does not imply a certainty of long-term performance, especially under conditions of adverse weather or seismic activity. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this report was prepared. No warranty or other conditions, express or implied, should be understood. Please refer to Attachment A titled "Report Limitations and Guidelines for Use" for additional information pertaining to use of this report. G e o E n g i n e e r s File No. 10854-001-00 Marc Grohe July 22,2003 Page 5 We appreciate the opportunity to serve you on this project. We trust the above provides the information you require. Please contact us if you have questions or if we can be of further assistance. Yours very truly, H.SOUS �e�pF WAS y9f�`� GeoEngineers,Inc. o, P 25824 �� C GIST ox? 0 L EN Gang H. Squires,P.E.,L.E.G. Associate EXPIRES 10/23/4 3 GHS:jm TACO\10\10854001\00\Finals\1085400100R.doc Disclaimer:Any electronic form,facsimile or hard copy of the original document(email,text,table,and/or figure),if provided,and any attachments are only a copy of the original document. The original document is stored by GeoEngineers,Inc.and will serve as the official document of record. Enclosures: Figure 1 —Vicinity Map Figure 2—Site Plan Attachment A—Report Limitations and Guidelines for Use G e o E n g i n e e r s File No. 10854-001-00 > I A — ° � Mid ��,!fj r •- t „ •�� Ej ' S !i Q K O 1N 1 5 N 3t. ! Umoo - z� S -SITE o 11K A \ z—t Ifi .r t7ot fJr% ! , 5 1 ' t o 4 • • + 5 - - - f _ a 3 -o t G jv1 I - p - .4 - " CD - It Ln Data Source: Topography from Sure!Maps at scale of 1:24k. Co 0 oAll locations are approximate. 0 2000 4000 Q v - N / Lambert Conformal Conic SCALE IN FEET o Washington State Plane South / North American Datum 1983 0 0 � Note: This drawing is for information purpose. It is intended to assist 00 o in showing features discussed in on attached document. j It is unlawful to copy or reproduce all or any part thereof, whether for personal use or resale, without permission. 0 a- �� VICINITY MAP Geo� ,Engineers Q �/ FIGURE 1 PROPERTY \ . BOUNDARY - � N I \ • PROPOSED SEPTIC DRAIN FIELD 1 q ,.� (DESIGN BY OTHERS) � o O I I cr, N VACATED ALLEY VACATED ALLEY o W I � I � I 0 U W ' m Z 0 in cn PROPOSED HOUSE m I af w in / zQ Y � I / 0 SPRUCE STREET / 0 0 o /0 a Ln 0 /_o 0 a // 0 o 0 / 0 0 0 40 80 Ln o Notes: 1. The locations of all features shown are approximate. 2. This figure is for informational purposes only. It is intended to assist in the identification of features APPROXIMATE SCALE IN FEET discussed in a related document. Data were compiled from sources as listed in this figure. The data i sources do not guarantee these data are accurate or complete. There may have been updates to the SITE PLAN data since the publication of this figure. This figure is a copy of a master document. The master hard �� o copy is stored by GeoEngineers, Inc. and will serve as the official document of record. Geo��Engineers FIGURE 2 Reference: Site plan provided by Marc Grohe. ATTACHMENT A REPORT LIMITATIONS AND GUIDELINES FOR USE G e o E n g i n e e r s File No. 1 08 54-001-00 ATTACHMENT A REPORT LIMITATIONS AND GUIDELINES FOR USE' This attachment provides information to help you manage your risks with respect to the use of this report. GEOTECHNICAL SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES, PERSONS AND PROJECTS We have prepared this report for use by Marc Grohe and his consultants for use in evaluating geologic hazards at the proposed residence to be located 145 East Spruce Street in Union, Washington. This report is not intended for use by others, and the information contained herein is not applicable to other sites. GeoEngineers structures our services to meet the specific needs of our clients. For example, a geotechnical or geologic study conducted for a civil engineer or architect may not fulfill the needs of a construction contractor or even another civil engineer or architect that are involved in the same project. Because each geotechnical or geologic study is unique, each geotechnical engineering or geologic report is unique, prepared solely for the specific client and project site. No one except Marc Grohe and his consultants should rely on this report without first conferring with GeoEngineers. This report should not be applied for any purpose or project except the one originally contemplated. A GEOTECHNICAL ENGINEERING OR GEOLOGIC REPORT IS BASED ON A UNIQUE SET OF PROJECT-SPECIFIC FACTORS This report has been prepared for Marc Grohe and his consultants. GeoEngineers considered a number of unique, project-specific factors when establishing the scope of services for this project and report. Unless GeoEngineers specifically indicates otherwise, do not rely on this report if it was: • not prepared for you, • not prepared for your project, • not prepared for the specific site explored,or • completed before important project changes were made. For example, changes that can affect the applicability of this report include those that affect: • the function of the proposed structure, • elevation, configuration,location, orientation or weight of the proposed structure, composition of the design team, or • project ownership. Developed based on material provided by ASFE,Professional Firms Practicing in the Geosciences;www.asfe.org. G e o E n g i n e e r s A-1 File No. 10854-001-00 If important changes are made after the date of this report, GeoEngineers should be given the opportunity to review our interpretations and recommendations and provide written modifications or confirmation,as appropriate. SUBSURFACE CONDITIONS CAN CHANGE This geologic report is based on conditions that existed at the time the study was performed. The findings and conclusions of this report may be affected by the passage of time,by manmade events such as construction on or adjacent to the site, or by natural events such as floods, earthquakes, slope instability or groundwater fluctuations. Always contact GeoEngineers before applying a report to determine if it remains applicable. MOST GEOTECHNICAL AND GEOLOGIC FINDINGS ARE PROFESSIONAL OPINIONS Our interpretations of subsurface conditions are based on field observations from widely spaced sampling locations at the site. Site exploration identifies subsurface conditions only at those points where subsurface tests are conducted or samples are taken. GeoEngineers reviewed field data and then applied our professional judgment to render an opinion about subsurface conditions throughout the site. Actual subsurface conditions may differ, sometimes significantly, from those indicated in this report. Our report, conclusions and interpretations should not be construed as a warranty of the subsurface conditions. A GEOTECHNICAL ENGINEERING OR GEOLOGIC REPORT COULD BE SUBJECT TO MISINTERPRETATION Misinterpretation of this report by other design team members can result in costly problems. You could lower that risk by having GeoEngineers confer with appropriate members of the design team after submitting the report. Also retain GeoEngineers to review pertinent elements of the design team's plans and specifications. CONTRACTORS ARE RESPONSIBLE FOR SITE SAFETY ON THEIR OWN CONSTRUCTION PROJECTS Our geotechnical recommendations are not intended to direct the contractor's procedures, methods, schedule or management of the work site. The contractor is solely responsible for job site safety and for managing construction operations to minimize risks to on-site personnel and to adjacent properties. G e o E n g i n e e r s A-2 File No.10843-001-00 READ THESE PROVISIONS CLOSELY Some clients, design professionals and contractors may not recognize that the geoscience practices (geotechnical engineering or geology) are far less exact than other engineering and natural science disciplines. This lack of understanding can create unrealistic expectations that could lead to disappointments, claims and disputes. GeoEngineers includes these explanatory "limitations"provisions in our reports to help reduce such risks. Please confer with GeoEngineers if you are unclear how these "Report Limitations and Guidelines for Use"apply to your project or site. GEOTECHNICAL, GEOLOGIC AND ENVIRONMENTAL REPORTS SHOULD NOT BE INTERCHANGED The equipment, techniques and personnel used to perform an environmental study differ significantly from those used to perform a geotechnical or geologic study and vice versa. For that reason, a geotechnical engineering or geologic report does not usually relate any environmental findings, conclusions or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Similarly, environmental reports are not used to address geotechnical or geologic concerns regarding a specific project. BIOLOGICAL POLLUTANTS GeoEngineers' Scope of Work specifically excludes the investigation, detection, prevention, or assessment of the presence of Biological Pollutants in or around any structure. Accordingly, this report includes no interpretations, recommendations, findings, or conclusions for the purpose of detecting, preventing, assessing, or abating Biological Pollutants. The term `Biological Pollutants" includes, but is not limited to, molds, fungi, spores, bacteria, and viruses, and/or any of their byproducts. G e o E n g i n e e r s A-3 File No. 1 0843-00 1-00