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09.10.2008 - GeoEngineers GEOENGINEER� September 10, 2008 City of Tigard 13125 SW Hall Boulevard Tigard, Oregon 97223 Attention: Mr. Dennis Koellermeier Subject: Geotechnical Engineering Recommendations Tigard Library Pond Outfall Tigard, Oregon File No. 4025-003-02 INTRODUCTION This report presents geotechnical engineering recommendations for constructing an outfall protection structure for the pond at the Tigard Library in Tigard, Oregon. Figure 1 shows the location of the site with respect to surrounding topography. PROJECT BACKGROUND The pond is located in the southeast corner of the site is contaminated with arsenic. This pond is within the flood plain of Fanno Creek. The outfall for the pond drains into Fanno Creek which is adjacent to and east of the pond. The outfall area has been eroding for some time, creating an erosional channel between Fanno Creek and the pond. The Oregon Department of Environmental Quality (DEQ) is concerned that Fanno Creek will continue to erode the outfall channel and contaminated sediment from the pond will enter Fanno Creek. The City of Tigard requested that we provide geotechnical engineering recommendations for protection of the pond outfall channel. Based on conversations with Clean Water Services, we understand that up to 100 square feet of area can be disturbed within the Fanno Creek flood plain without vegetation mitigation. SITE CONDITIONS We visited the site on August 22, 2008 to observe existing site conditions and collect data to design an outfall protection structure. The general layout of the pond and creek are shown on the plan view on the attached Figure 2. At the time of our observation,the pond level was roughly 6 to 8 feet higher than the adjacent creek level. The pond and creek are separated by a berm that was presumably constructed many years ago to restrict Fanno Creek from flooding the property. A channel has been eroded through the berm between the pond and Fanno Creek where the pond outfall is located. The channel ranges from approximately 4.5 to 6 feet deep. Soils observed in this channel consist of silt. Minor amounts of water were present in the pond during our reconnaissance. $9li1SC1pnG11+TechrtoiPf9y 1 W55 SSM Sequoia Pkwy teteyaone 903.1124,9274 Bailie`1419 taoetmtta 945.8,24S9y0 , . Pr}ltlAlodri1i 97724 weaslte; ww+ gpaen)9taadts eQip City of Tigard September 10, 2008 Page 2 OUTFALL PROTECTION RECOMENDATIONS We recommend placing aggregate fill within the channel between the pond outfall and Fanno Creek to reduce the potential for erosion of the outfall area. In order to keep the disturbance area limited to 100 square feet or less, the fill will be on the order of 10 feet long, beginning at the pond outfall. The final length of the outfall protection should be based on detailed measurements made at the time of construction, and in no case should exceed 100 square feet, unless vegetation mitigation is planned in accordance with Clean Water Services' requirements. Details of the proposed fill area are shown on Figure 3. The following paragraphs present specific recommendations for protection of the outfall. • Silt fence should be placed at the downstream end of the outfall channel to restrict soils from entering Fanno Creek during construction. • Organic topsoil should be stripped from the outfall protection area and stockpiled on site for later use. The approximate limits of grading are shown on Figure 3. In no case should grading disturb more than a 100 square foot area. • After stripping the topsoil, the subgrade should be prepared by excavating the channel and keyway as shown on Figure 3. The channel should be excavated just enough to square off the channel to facilitate rock placement and compaction. The keyway should have a minimum depth of 2 feet and a minimum width of 4 feet. • Place a woven geotextile over the prepared subgrade, as shown on Figure 3. The geotextile should conform to the following specifications. Property Test Method Value AOS ASTM D4751 60 max. Permittivity ASTM D4491 0.2 sec-' Grab Tensile ASTM D4632 315 lbs. Burst Strength ASTM D3786 500 psi Puncture Resistance ASTM D4833 112 lbs Tear Strength ASTM D4533 112 lbs UV Resistance ASTM D4355 70% • Place and compact 8" quarry spalls in lifts to the top of the pond outfall as shown on Figure 3. The quarry spalls should consist of hard, durable angular quarry stone with a maximum particle size of 8 inches. The quarry spalls should be fairly well graded between coarse and fine particle sizes and should be free of silt, clay or other earth material in quantities greater than 5 percent by weight. The quarry spalls should not contain debris or organic material. ■ The quarry spalls should be walked in to an unyielding state using trucked equipment, the excavator bucket or similar method in lifts no thicker than 16 inches. Rip rap should be placed as the quarry spall fill level is raised. • Place two courses of 24-inch diameter rip rap on the outside of the quarry spalls as shown on Figure 3. The rip rap should be placed such that there is maximum contact between adjacent boulders. The rip rap shall consist of hard, durable angular quarry stone with a maximum File No,4025-003-02 GEOENGINEERS� City of Tigard September 10, 2008 Page 3 dimension of 30 inches. The rip rap shall be free of silt, clay, or other earth materials in quantities greater than 5 percent by weight, and shall contain no debris or organic material. The rip rap fill should be reasonably well graded and the largest stones should have a maximum dimension not exceeding 30 inches. The rip rap fill should meet the following specifications: Size Percent Passing 30 inches 100% 24 inches 50-100% 18 inches 30-50% 12 inches 15-30% • After completion of the work, remove silt fence and place native seed and straw over disturbed areas. Top soil may also be placed over disturbed areas to promote re-vegetation. LIMITATIONS We have prepared this geotechnical engineering report for use by the City of Tigard for the Tigard Library Pond located at the Tigard Library on Hall Boulevard in Tigard, Oregon. We provided 01.11- services urservices at the request of Mr. Dennis Koellermeier of the City of Tigard in general accordance with our services agreement dated June 14, 2007. 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. 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. Please refer to Attachment A titled "Report Limitations and Guidelines for Use" for additional information pertaining to use of this report. File.No. 4025-003-02 GEOENGINEERS� City of Tigard September 10, 2008 Page 4 We appreciate the opportunity to provide services to the City of Tigard for this project. Please call if you have any questions concerning this report or if we can be of further assistance. Yours very truly, GeoEngineers, Inc. PRt) GINZ, /O 1, Brian C. Ranney, C.E.G. i Project Geologist r L LEO I David L. Thielen, P.E. Principal BCR:DLT:gaw P:\414025003\02\Finals\4025003028 Pond Outfall.doc Attachments: Figure 1 —Vicinity Map Figure 2 —Pond Outfall — Existing Conditions Figure 3 —Pond Outfall — Protection Details Attachment A—Report Limitations And Guidelines For Use Two copies submitted 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. Copyright©2008 by GeoEngineers,Inc. All rights reserved. File No. 4025-003-02 GEOENGINEERirZ.) "� � ' _� ter t;� �^r'�« �•• �I�� +►� • i �, a � � f r � r y � `y.„•♦: a �� }f ��� �� ��# � rA n. ^ r” C. t «Yam • l ♦« « « in „ f �, • •r r ,mss.. • k it �i E ff ? � r ♦ ,, .+° .tee. + ' m ' v , d ,rr rt w rt* site , '• `c ; " M� MI '.A-i + ,tea .�4, �_ • � 'Q� � • r � w « � r • * �fii���7^ ! i '' •.� ' Glx .a':tTtY,E� ^� r } t �• -�^t' +. . me�qq.. i,.• t*1 r f Map creat �v"it� < �0���6'N.-bond ,a0"gr ey t ' r�� `�; NATIONAL , �� _ PAIS /17 GEOGRAPHIC l - EEE v tEX3pAS t 05/17J07 Vicinity Map Q N Tigard Library o , Tigard, Oregon 10C N G. WENGINEERS Figure 1 EXISTING CONDITIONS—GENERALIZED CROSS SECTIONS NOT TO SCALE A A' _B B � 4.5 11 l 9' Berm C 4.5' 1 26 —"4 FOnno Creek C' GENERALIZED PLAN VIEW � NOT TO SCALE ,Accumulated Soil F`n0 Creek C' I B -- s" — B' 00 0 N 00 O Co A A' 3 � CN' "'Pond Outfoll 04 z h C O co � 3 2Pond� N Legend — — Stream O .o }-- Slope arrow points down hill C a A-A' Cross section Pond Outfall - Existing Conditions 0 Q Notes: U t.This drawing is for information purposes.It is intended to / N Tigard Library C) assist in showing features discussed in an attached g ' C) document.GeoEngineers,Inc.can not guarantee the Tigard, Oregon O accuracy and content of electronic files.The master file is N stored by GeoEngineers,Inc.and will serve as the official C) record of this communication. pp GMENGINEER� Figure 2 v 2.Location of all features shown area approximate. a- Reference:Base drawing was a sketch provided by GeoEngineers field staff. OUTFALL PROTECTION RECOMMENDATIONS NOT TO SCALE Fill to level of Pond Outfall 8" Quarry Spalls % g. A A' B Geotextile Fabric Excavate square channel bottom to facilitate rock placement textile Fabric —Geo W24" Dia Rip—Rap Pond Outfall-_.0 �� Keyway i 2H i2H 0 24" Dia Rip—Rap Geotextile Fabric ———� MIN. 8" Quarry spoils �� F nnno filled to level of Excavate Keyway Creek C' Pond Outfall �4' MIN _ °n=Creek Place Silt Fence prior C' to beginning work �\ OD I o g g' N I 00 Approximate limits of grading shall be limited to 100 sq ft of area in plan view or less no A A' -Pond Outfall m ' 3 � a N LL Z v N G C. Cl) 3 Pond- U,) CD Legend — — Stream O aSlope arrow points down hill 0A—A' Cross section a Pond Outfall - Protection Details 0 Q Notes: U 1.This drawing is for information purposes.It is intended to C) assist in showing features discussed in an attached Tigard Library M document.GeoEngineers,Inc.can not guarantee the Tigard, Oregon o accuracy and content of electronic files.The master file is UD stored GeoEngineers,Inc.and will serve as the official of �. record of this communication. pp G M E N G I N E E R Figure � 2.Location of all features shown area approximate. 3 a- Reference:Base drawing was a sketch provided by GeoEngineers field staff. GEOENGINEERS ATTACHMENT A REPORT LIMITATIONS AND GUIDELINES FOR USE 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 This report has been prepared for use by the City of Tigard for protection of the outfall area of the pond in the southwest corner of the Tigard Library site in Tigard, Oregon. 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. Our report is prepared for the exclusive use of our Client. No other party may rely on the product of our services unless we agree in advance to such reliance in writing. This is to provide our firm with reasonable protection against open-ended liability claims by third parties with whom there would otherwise be no contractual limits to their actions. Within the limitations of scope, schedule and budget, our services have been executed in accordance with our Agreement with the Client and generally accepted geotechnical practices in this area at the time this report was prepared. 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 use by the City of Tigard for protection of the outfall area of the pond in the southwest corner of the Tigard Library site in Tigard, Oregon. 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. • 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. • project ownership. Developed based on material provided by ASFE,Professional Firms Practicing in the Geosciences;www.asfe.org. File No. 4025-003-02 Page A-1 September 10,2008 GWENGINEERS� 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 geotechnical or 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 and laboratory 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. GEOTECHNICAL ENGINEERING REPORT RECOMMENDATIONS ARE NOT FINAL Do not over-rely on the preliminary construction recommendations included in this report. These recommendations are not final, because they were developed principally from GeoEngineers' professional judgment and opinion. GeoEngineers' recommendations can be finalized only by observing actual subsurface conditions revealed during construction. GeoEngineers cannot assume responsibility or liability for this report's recommendations if we do not perform construction observation. Sufficient monitoring, testing and consultation by GeoEngineers should be provided during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork activities are completed in accordance with our recommendations. Retaining GeoEngineers for construction observation for this project is the most effective method of managing the risks associated with unanticipated 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 can also misinterpret a geotechnical engineering or geologic report. Reduce that risk by having GeoEngineers participate in pre-bid and preconstruction conferences, and by providing construction observation. File No. 4025-003-02 Page A-2 September 10, 2008 GWENGINEERS� DO NOT REDRAW THE EXPLORATION LOGS Geotechnical engineers and geologists prepare final boring and testing logs based upon their interpretation of field logs and laboratory data. To prevent errors or omissions, the logs included in a geotechnical engineering or geologic report should never be redrawn for inclusion in architectural or other design drawings. Only photographic or electronic reproduction is acceptable, but recognize that separating logs from the report can elevate risk. GIVE CONTRACTORS A COMPLETE REPORT AND GUIDANCE Some owners and design professionals believe they can make contractors liable for unanticipated subsurface conditions by limiting what they provide for bid preparation. To help prevent costly problems, give contractors the complete geotechnical engineering or geologic report, but preface it with a clearly written letter of transmittal. In that letter, advise contractors that the report was not prepared for purposes of bid development and that the report's accuracy is limited; encourage them to confer with GeoEngineers and/or to conduct additional study to obtain the specific types of information they need or prefer. A pre- bid conference can also be valuable. Be sure contractors have sufficient time to perform additional study. Only then might an owner be in a position to give contractors the best information available, while requiring them to at least share the financial responsibilities stemming from unanticipated conditions. Further, a contingency for unanticipated conditions should be included in your project budget and schedule. 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. 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. File No.4025-003-02 Page A-3 September/0,2008 GWENGINEERS� BIOLOGICAL POLLUTANTS GeoEngineers' Scope of Work specifically excludes the investigation, detection, prevention or assessment of the presence of Biological Pollutants. Accordingly, this report does not include any interpretations, recommendations, findings, or conclusions regarding the detecting, assessing, preventing or abating of Biological Pollutants and no conclusions or inferences should be drawn regarding Biological Pollutants, as they may relate to this project. The term "Biological Pollutants" includes, but is not limited to, molds, fungi, spores, bacteria, and viruses, and/or any of their byproducts. If Client desires these specialized services, they should be obtained from a consultant who offers services in this specialized field. File No.4025-003-02 Page A-4 September 10,2008 GMENGINEERS�