The URL can be used to link to this page

Report (69) Marjorie Wolfe Si ', irva Water Wolf Resources May 17, 2017 Page 2 of 18 lots 1100 and 1200. In addition to the scour of the bank face, the CMP culvert is sheared below grade approximately 20 feet north of the north bank face and stormwater flowing from the sheared culvert has scoured out a large void around the culvert. There are indications of ground subsidence on the surface above the void up to 15 feet north of the top of north bank above the buried CMP culvert. The landslide site area encompasses a hillside on the north bank of Derry Dell Creek to the south of two residential properties, tax lots 7300 and 7400. The landslide site area is shown on the Site and Exploration Plan Derry Dell Landslide, Figure 3. The landslide had been previously studied by Shannon&Wilson in 2009 and 2015. We produced a report, dated March 31, 2009, which evaluated conceptual landslide repair options. Conceptual repair options were never constructed, and we produced a second report, dated February 12, 2016,which focused on emergency mitigation measures and risk of damage to the residence located on tax lot 7400. In our 2016 report, we determined that the residential structure was not at imminent risk of damage, and the City decided not to implement emergency mitigation measures to improve landslide stability. REGIONAL GEOLOGY The project area lies within the Tualatin Valley along the northeastern margin of Bull Mountain, a dome-like uplift with apparent fault boundaries (Schlicker and Deacon, 1967 and Madin, 1990). The core of the uplift is made up of a series of basaltic lava flows known as the Columbia River Basalt Group, which flowed into the region between about 17 million and 6 million years ago. The Columbia River Basalt Group underlies much of the Portland metropolitan area and the Tualatin Valley at depth. The basalt is locally overlain by the Helvetia Formation, which is described by Schlicker and Deacon(1967) as poorly indurated sediments of laterized pebbly sand, silt, and clay, likely derived from erosion of the basalt. Helvetia Formation is generally found on slopes at elevations that range from about 200 and 900 feet. Bull Mountain is capped by a unit mapped by Schlicker and Deacon(1967) as Upland Silt. Commonly known as the Portland Hills Silt,this wind-blown deposit(loess) is derived primarily from the erosion of basalt and quartzite rocks east of the Cascade Mountains. At the base of Bull Mountain, and in the vicinity of the project area, Schlicker and Deacon (1967)mapped the near surface sediments as Willamette Silt. The Willamette Silt was deposited during the late stages of the last great ice age,between about 18,000 and 15,000 years ago, when a serried of glacial outburst floods inundated the Willamette Valley. A lobe of the continental GER—Derry Dell 24-1-04116-002 Marjorie Wolfe 14141 :,_ ° 1 ‘`„'. Water Wolf Resources May 17, 2017 Page 3 of 18 ice sheet repeatedly blocked and dammed the Clark Fork River in western Montana, which then formed an immense glacial lake called Lake Missoula. The lake grew until its depth was sufficient to buoyantly lift and rupture the ice dam,which allowed the entire massive lake to empty catastrophically. Once the lake had emptied,the ice sheet again gradually dammed the Clark Fork Valley and the lake refilled, leading to 40 or more repetitive outburst floods at intervals of decades (Allen and others, 2009). These repeated floods are collectively referred to as the Missoula Floods. During each short-lived episode, floodwaters washed across the Idaho panhandle,through eastern Washington's scablands, and through the Columbia River Gorge. When the floodwater emerged from the western end of the gorge, it spread out over the Portland and Tualatin Basins and up the Willamette Valley as far south as Junction City, depositing a tremendous load of sediment(O'Conner and others, 2001). The catastrophic floods deposited extensive gravel bars across east Portland and up to 50 feet of micaceous clay to fine sandy silt in the Tualatin Basin. The Willamette Silt laps onto the flanks of Bull Mountain and begins to thin around elevations of 250 feet. In the project area, the Upland Silt, or Portland Hills Silt, is similar to the Willamette Silt and is often indistinguishable from the Willamette Silt except for its occurrence above elevation 250 feet. The Derry Dell Creek project area is near the transition elevation between Willamette Silt and Portland Hills Silt,but appears to be underlain by Willamette Silt. SITE EXPLORATIONS AND LABORATORY TESTING Geologic Reconnaissance Stormwater Outfall A geologic reconnaissance of the stormwater outfall area was performed by David Higgins, a Shannon&Wilson Engineering Geologist, on February 21, 2017. The stormwater outfall consists of a buried 15-inch diameter CMP culvert with an outlet near the top of the north bank of Deny Dell Creek. The location of the buried 15-inch diameter CMP culvert and outlet is shown in Figure 2. Stormwater flowing from the outlet of the CMP culvert has scoured out the creek bank face,resulting in an eroded channel with 8 to 10 feet high, near vertical banks directly below the culvert. The eroded channel is approximately 8 feet wide with intact native clay and silt soil exposed in the side walls. Derry Dell Creek bank slopes adjacent to the eroded channel vary from 1 horizontal to 1 vertical (1 H:1 V)to 2H:1 V. The buried section of the CMP GER—Derry Dell 24-1-04116-002 Marjorie Wolfe `4- . ? ::,i ,,JC Water Wolf Resources May 17, 2017 Page 4 of 18 culvert is sheared below ground, approximately 20 feet north of the outlet. The sheared portion of the culvert is bent downward, and stormwater flowing from the sheared culvert has scoured out a void several feet wide around the outside of the culvert. The total width of the void is up to 4 feet in diameter and appears to extend back approximately 20 feet into the slope to where the culvert is sheared. There are indications of ground subsidence on the surface above the void up to 15 feet north of the top of north bank above the CMP culvert. In the subsidence area,the ground surface appears to have settled several inches. We did not observe ground cracks or other indications of slope instability adjacent to the buried CMP culvert on the Deny Dell Creek bank slopes adjacent to the scoured out channel below the culvert. It was raining during our reconnaissance, and stormwater was observed to be flowing both from the outlet of the CMP culvert and around the outside of the culvert,presumably from where the culvert was sheared. We did not observe groundwater seepage exiting the hillside or sidewalls of the scour channel during our reconnaissance. Landslide Area A geologic reconnaissance of the landslide area was performed by David Higgins, a Shannon&Wilson Engineering Geologist, on February 21, 2017. Two previous reconnaissances of the landslide area were performed by Shannon&Wilson on February 12, 2009, and December 30, 2015. Summary of observations are included in our 2009 and 2016 reports. The residences occupying tax lots 7300 and 7400 consist of two-level ranch style homes with the upper level at street grade and a lower level which daylights to the backyard. The backyard areas are level and extend approximately 25 feet from the house to points near the east property line. Behind the residence occupying tax lot 7400, a 5-foot-high concrete block privacy wall had been constructed by the homeowner on city property just beyond the property line. An iron gate is positioned in the wall near the southeast property corner. According to a survey made by WHPacific in 2009,the wall crosses about 5 feet over the property line into City property near the gate. A water feature with an electric pump is built into a rockery structure against the privacy wall at the extreme southeast corner of the yard. The wall was not plumb and was leaning outward several inches in the downslope direction. GER—Deny Dell 24-1-04116-002 Marjorie Wolfe x r's 3t,! Cr _ , Water Wolf Resources May 17, 2017 Page 5 of 18 The backyard lawn surface of tax lot 7400 was very moist at the time of each of our reconnaissance. The surface felt soft underfoot and our feet sunk into the surface when walking across. Three corrugated plastic drain pipes were observed exiting the ground behind the wall. Two pipes were suspended in the air and bowed down, crossing below the landslide scarp. One pipe was embedded in the debris. One of the suspended pipes was observed to be leaking water into the landslide debris field. It is not clear what the pipes were connected to,but as part of our 2009 study, during our first visit to the site on November 18, 2008,the homeowner, Mrs. Klettke, told us that the previous owner had installed the drain pipes to drain the back lawn. During our February 12, 2009, reconnaissance, we observed that the landslide had occurred just behind the concrete block privacy wall near the southeast property corner. The headscarp was located several feet below the gate and extended to the south, approximately 30 feet south of the property line between tax lot 7300 and 7400. Below tax lot 7400, at the nearest point,the headscarp was about 4 feet east of the south gate post and 9 feet east of the tax lot 7400 property boundary. Below tax lot 7300, the headscarp was approximately 12 feet east of the property boundary at the nearest point. A series of ground cracks and slumps were observed in soil upslope of the headscarp, which extended the active slide area to about 2 feet east of the wall. The slide was approximately 20 feet wide at the headscarp and about 40 feet wide at the toe. The slide was approximately 45 feet in length from the top of the headscarp to the toe of the landslide debris near the creek channel. The slide appeared to have been a debris slump forming a prominent bench in the mid-portion of the slide area, about 5 to 7 feet below the rim of the headscarp. The bench was the upper surface of a debris mound that,having failed from its original position, settled at the edge of the creek. During our December 30, 2015, reconnaissance, we observed that the norther portion of the previous landslide area had failed again as a debris flow landslide, increasing the overall size of the landslide to approximately 35 feet wide at the headscarp and about 50 feet wide at the toe. The northern portion of the headscarp had retrogressed upslope to about 1 foot away from the gate and wall. The headscarp prominent bench debris mound that had been 5 to 7 feet below the rim of the headscarp (as described in our February 12, 2009, reconnaissance)had slid away as a debris flow landslide, forming a debris field that extended into the creek channel. It appeared that much of the soil debris had been washed down stream. The remaining landslide debris GER—Derry Dell 24-1-04116-002 Marjorie Wolfe .r u" . F . Water Wolf Resources May 17, 2017 Page 6 of 18 extended from the headscarp to the creek channel and appeared to mound immediately adjacent to the creek. The headscarp of the landslide was near vertical, 12 to 13 feet high, and 10 to 12 feet wide. We also observed that there were ground cracks on the uphill side(west side) of the gate in the backyard of the residence at tax lot 1400, about 1 foot west of the wall. There were several cracks in the wall that were not present during our February 12, 2009, reconnaissance, and the wall appeared to now be leaning several inches further out of plumb than what had been observed in 2009. The entire length of the wall,parallel with the eastern property boundary,was observed to be leaning during both our 2009 and 2015 reconnaissance. During our February 21, 2017,reconnaissance, we found that overall landslide conditions were similar to what was observed in December 30,2015. However,we observed that ground cracks which were previously observed to be located about 1 foot west of the gate were now observed up to 3 feet west of the gate, extending further into the backyard area of tax lot 7400. In addition,blackberry brush had been cleared from the slope below tax lots 7300 and 7400 just prior to our reconnaissance, and we observed that hummocky ground landslide topography extends across the entire hillside below tax lot 7400 and a portion of tax lot 7300. The approximate headscarp and landslide limits are shown on Figure 3 and extend from about 35 feet south of the property boundary between tax lots 7300 and 7400,north to the boundary between tax lots 7400 and 7500,where a drainage swale is located between the two properties. The toe bulge was observed within the bank slope of Derry Dell Creek just above the base of the creek channel. We did not observe groundwater seepage exiting the hillside during our reconnaissance,but the surface of the backyard area of tax lot 7400 was saturated. Exploratory Borings The field exploration program included one solid stem auger boring, designated B-1, and seven hand augered borings, designated HA-1 through HA-7. The approximate locations of the explorations are shown on Figure 2 and Figure 3. Boring B-1 was drilled just above the landslide headscarp on February 18, 2009, as part of the City's initial landslide investigation and was originally presented in our Geotechnical Investigation letter dated March 31, 2009. Hand auger HA-1 was drilled on January 8, 2016, shortly after reactivation of the landslide and was originally presented in our Emergency Response letter dated February 12, 2016. Hand augers HA-2 and HA-3 were drilled below the existing outfall on February 21,2017,under the current GER—Derry Dell 24-1-04116-002 Marjorie Wolfe t ; i l f} Water Wolf Resources May 17, 2017 Page 7 of 18 scope of services. Hand augers HA-4 through HA-7 were drilled in the landslide area on February 22, 2017, also under the current scope of services. Boring B-1 was drilled to a depth of 25.5 feet using a hand-portable Little Beaver DR100 drill rig and 4-inch solid-stem flight augers. The drill rig was provided and operated by PLi Systems, Inc., of Hillsboro, Oregon. Disturbed samples were collected in Boring B-1 at 2.5-to 5-foot depth intervals in conjunction with standard penetration testing, which was performed in accordance with the Standard Test Method for Standard Penetration Test(SPT) and Split-Barrel Sampling of Soils (ASTM D1586). Hand Auger Borings HA-1 through HA-7 were manually drilled to depths ranging from 3.5 to 15 feet by Shannon&Wilson staff using hand auger tooling which creates an approximately 3-inch diameter hole. Representative disturbed samples were collected from the hand auger cuttings during drilling. All samples were sealed in the field to retain moisture and returned to our laboratory for additional examination and testing. Shannon&Wilson field staff were on site throughout the explorations to locate the borings, observe the drilling for B-1, auger Borings HA-1 through HA-7, collect samples, and log the materials encountered. We logged the material encountered in the boreholes in accordance with ASTM D2488 (Standard Practice for Description and Identification of Soils, Visual-Manual Procedure). Our Soil Description and Log Key is presented in Figure 4, and logs of the borings are presented on Figures 5 through 12. Laboratory Testing The samples we obtained during our field explorations were transported to our laboratory for further examination. We selected representative samples for a suite of laboratory tests. The testing program, including the explorations performed from 2009 through the present, consisted of moisture content analyses (ASTM D2216) and particle-size analyses (ASTM D1140). All testing was performed by Shannon&Wilson in accordance with applicable ASTM International standards. Results of the moisture content analyses and fines contents are presented graphically on the boring logs (Figures 5 though 12). Results of the particle-size analyses were used to refine our visual-manual soil descriptions and identifications in accordance with elements of the Standard Practice for Classification of Soils for Engineering Purposes(Unified Soil Classification System), ASTM D2487. The refined descriptions and identifications were incorporated into the boring logs. GER—Derry Dell 24-1-04116-002 Marjorie WolfeINC. Water Wolf Resources May 17, 2017 Page 8 of 18 SUBSURFACE CONDITIONS Geotechnical Units We grouped the materials encountered in our subsurface explorations into three geotechnical units, as described below. Our interpretation of the subsurface conditions is based on the explorations and regional geologic information from published sources. The geotechnical units are as follows: ➢ Fill—soft to medium stiff Silt(ML) and Silt to Lean Clay(ML/CL)with varying amounts of sand ➢ Landslide Deposits—Silt to Silt with Sand(ML) and Silt to Lean Clay(ML/CL) ➢ Willamette Silt—loose to medium dense/medium stiff to stiff Silt to Silt with Sand (ML),with lesser amounts of Lean Clay(CL) These geotechnical units were grouped based on their engineering properties, geologic origins, and their distribution in the subsurface. Contacts between the units may be more gradational than shown on the boring logs, and variations in subsurface conditions may exist between the borings. The sections below describe generalized characteristics for each geotechnical unit. SPT blow counts shown on the boring logs and discussed below are as counted in the field (uncorrected). Fill Fill was encountered near the landslide headscarp in Boring B-1 from the ground surface to a depth of 7 feet. It was also encountered near the outfall, in Hand Auger Borings HA-2 and HA-3, from the ground surface to depths of 2 feet and 1 foot, respectively. The encountered Fill generally included soft to medium stiff, gray to brown and orange-mottled, Silt(ML) and Silt to Lean Clay(ML/CL)with varying amounts of sand. The soil was typically moist and micaceous, with fine sand and low to medium plasticity. Trace fine gravel was observed in some samples. Trace to few organics were also observed. Two SPTs attempted in the Fill yielded N-values of 4 and 7 blows per foot(bpf). The natural moisture contents of two specimens were 31 and 32 percent. Landslide Deposits Landslide deposits were encountered at the ground surface in Hand Auger Borings HA-1 and HA-4 through HA7. Depths of the landslide deposits ranged from about 1.5 feet in HA-1 to GER—Derry Dell 24-1-04116-002 Marjorie Wolfe S9, JNOr. Water Wolf Resources May 17, 2017 Page 9 of 18 11 feet in HA-4. In general, the Landslide Deposits consisted of brown to gray or blue-gray and orange-mottled, Silt to Silt with Sand(ML) and Silt to Lean Clay(ML/CL)with trace to little fine sand. The soil was moist to wet and micaceous, and ranged from nonplastic to medium plasticity. Trace fine to coarse gravel was observed in some samples. Trace to few organics were also observed. The Landslide Deposits were differentiated from the underlying Willamette Silt primarily by relative ease of augering and the presence of a markedly disturbed texture. Natural moisture contents in the Landslide Deposits ranged from 31 to 49 percent, and averaged 36 percent. Willamette Silt All borings were terminated in Willamette Silt, with the deepest penetration being to a depth of 25.5 feet in Boring B-1. In general,the encountered Willamette Silt consisted of loose to medium dense/medium stiff to stiff Silt to Silt with Sand(ML),with lesser amounts of Lean Clay(CL). The soil was moist to wet and micaceous, with fine sand and nonplastic to medium plasticity. Trace to few organics were observed in some samples. SPT N-values in the unit ranged from 5 to 10 bpf and averaged 7 bpf. Natural moisture contents ranged from 26 to 38 percent, and averaged 33 percent. Groundwater In the vicinity of the outfall, groundwater was observed at depths of approximately 7.5 feet below the ground surface in Hand Auger Boring HA-2 and 2 feet below the ground surface in HA-3. In the landslide area, encountered groundwater depths ranged from approximately 8.5 feet in Boring B-1 to within inches of the ground surface in Hand Auger Boring HA-4. Free water was observed at a depth of approximately 19 feet in Boring B-1,between the time when drilling and sampling was completed and the hole was backfilled,but it is possible that the water level in the hole had not yet equilibrated to the static local groundwater level. Given the fine- grained nature of the materials at the site, it is likely that groundwater perches at various depths within the Landslide Deposits and Willamette Silt. No groundwater seepage was observed during reconnaissance or explorations. However, standing water was observed on the ground surface in the lawn are of tax lot 7400. GER—Deny Dell 24-1-04116-002 Marjorie Wolfe #{ it Water Wolf Resources May 17, 2017 Page 10 of 18 LANDSLIDE SLOPE STABILITY ANALYSES General Approach We performed slope stability analyses to evaluate the design of the creek bank repairs for the stormwater outfall area and the landslide area. Slope stability is influenced by various factors including 1)the geometry of the soil mass and subsurface materials,2)the weight of soil materials overlying the failure surface, 3)the shear strength of soils along the failure surface, and 4)the hydrostatic pressure(groundwater levels)present within the landslide mass and along the failure surface. The stability of a slope is expressed in terms of factor of safety(FS)which is defined as the ratio of resisting forces to driving forces. At equilibrium, the FS is equal to 1.0, and the driving forces are balanced by the resisting forces. Failure occurs when the driving forces exceed the resisting forces, i.e., FS less than 1.0. An increase in the FS above 1.0, whether by increasing the resisting forces or decreasing the driving forces, reflects a corresponding increase in the stability of the mass. The actual FS may differ from the calculated FS due to variations in soil strengths, subsurface geometry, failure surface location and orientation, groundwater levels, and other factors that are not completely known or understood. In this regard,we have used information developed from our field explorations, geologic reconnaissance and mapping, review of the previous slope stability analyses performed during previous studies performed within the landslide area, and our experience with similar materials to develop the stability analysis model in our computer software. Our analyses are based upon the assumption that subsurface conditions everywhere within the landslide mass are not significantly different from those encountered by the field explorations. We performed the slope stability analyses with the aid of the computer program SLOPE/W which performs both force and moment(Spencer)limits equilibrium analyses. The analysis model geometry for the Stormwater Outfall area was developed along the cross section A-A' shown in Figure 2. The analysis model geometry for the Derry Dell Landslide area was developed along the cross section B-B' shown in Figure 3. Based on local engineering practice on landslide projects and our professional judgement, we recommend that the FS should be 1.25 or greater for a stable permanent slope. GER—Derry Dell 24-1-04116-002 Marjorie Wolfe JINN INC. Water Wolf Resources May 17, 2017 Page 11 of 18 Soil Parameters Information from our subsurface explorations and laboratory testing, as well as from our previous experience on similar projects, was utilized in determining appropriate initial material strength and unit weight parameters for the various geologic units. Table 1 presents the geologic unit designations and the parameters utilized in our stability analyses. Through the construction of the rock embankments,most to all of the Landslide Debris and Fill will be removed. TABLE 1: MATERIAL PROPERTIES FOR SLOPE STABILITY ANALYSIS Wet Density'Net Friction Angle(p Cohesion C Soil Unit pcf Deg psf Fill—Soft SILT,trace sand 105 30 15 Willamette Silt 106 31 45 Landslide Debris 104 28 0 Stone Embankment 130 38 0 Results—Stormwater Outfall Area The final configuration for the rock embankment at cross section A-A' was analyzed for the static stability using the procedures discussed above. The geometry is presented in Figure 13. The FS was found to be greater than 1.25. The groundwater was modeled at approximately 7 feet below the ground surface at HA-2 and just 2 feet below the ground surface at HA-3 as discovered during field explorations. A detailed discussion of the rock embankment geometry is presented below. Results—Derry Dell Landslide Area The final configuration for the rock embankment at cross section B-B' was analyzed for the static stability using the procedures discussed above. One cross section was considered to be representative for the landslide area in this section of Derry Dell Creek channel because the landslide debris encountered in the exploration program was shallow and will be mostly removed during the installation of the rock embankment. The geometry is presented in Figure 14. The FS was found to be greater than 1.25. The groundwater was modeled at the surface for the section at the top of the slope because standing water was found in the backyard of the residence within tax lot 7400. At the toe of the slope,the groundwater was placed at the surface of the creek. GER—Derry Dell 24-1-04116-002 Marjorie Wolfe Water Wolf Resources May 17, 2017 Page 12 of 18 A detailed discussion of the rock embankment geometry is presented below. Seismic Slope Stability The seismic stability of the rock embankments at each section was performed using the maximum considered earth quake geometric mean peak ground acceleration(PGAM)which follows the guidance of ASCE 7-10. This corresponds to an event with a 2 percent probability of exceedance in a 50-year period(2,475-year-return period). PGAM was derived for the Derry Dell Creek site using USGS's US Seismic Design Maps web application. The site soils were determined to be representative of a Site Class E. The PGAM was calculated to be 0.378 g. The pseudostatic analysis was performed using SLOPE/W. A horizontal pseudostatic coefficient,kh, equal to one-half of the PGAM, or 0.189,was used in the analyses. Both slopes were found to have a FS of less than 1.0. These results indicate that the slopes are not stable during the analyzed seismic event(2,475-year earthquake). Because the two rock embankment sections are far enough from the neighboring structures that their failures do not pose a risk to the structure and life safety concerns, a FS less than 1.0 would not be unreasonable. It should be noted, however, that during an event such as this, it would be reasonable for the slopes to experience large deformations and would require repair afterwards. CONCLUSIONS AND RECOMMENDATIONS Based on our explorations and our slope stability analyses, we recommend that the slopes at both the stormwater outfall and landslide areas be stabilized using rock embankment with a shear key. The stable configuration of the rock embankment at both the Stormwater Outfall and Derry Dell Landslide can be sloped back at 1.5H:1 V. Geometry—Stormwater Outfall Area The geometry of the rock embankment for the Stormwater Outfall area is shown in Figure 13. The rock embankment will be no less than 3 feet wide at the top of the slope. The face of the rock embankment will be placed at a slope of 1.5H:1 V. This geometry will continue until the toe of the slope which will need to be placed a minimum of 2 feet below existing ground surface and a minimum of 2 feet below the final ground surface at the toe. The toe of the rock embankment may be required to go deeper to account for scour, which was not reviewed as part of our study. The base of rock embankment will be no less than 12 feet wide. From the deepest portion of the GER—Derry Dell 24-1-04116-002 Marjorie Wolfe -), :` ` .II, 1':- ° ti `,,'``'. Water Wolf Resources May 17, 2017 Page 13 of 18 - toe,the back slope of the rock embankment may vary based on the height of the slope. In no case shall this backslope be steeper than 1 H:1 V. Geometry—Derry Dell Landslide Area The geometry of the rock embankment for the Stormwater Outfall area is shown in Figure 14. The face of the rock embankment will be placed at a slope of 1.5H:1 V. This geometry will continue until the toe of the slope. At the toe of the slope,the shear key portion will be installed in a trench that shall be 6 feet deep and cut at a slope of 1 H:1 V. The rock embankment will be 6 feet wide at base. From the deepest portion of the toe,the back slope of the rock embankment will be 1H:1 V. The width of the rock embankment at the top of the slope will vary but will be no less than 8 feet wide at the top of the slope. Embankment Materials ODOT Stone Embankment Material, in accordance with the 2015 Oregon Standard Specifications for Construction(OSSC) Section 00330.16, should be used to construct the rock embankment. In our opinion, a drainage geotextile should be placed along the temporary excavation slope and bottom and sides of the excavation as a separation function between native soil and the rock embankment fill. Also, the geotextile will prevent possible long-term piping of the fines in the native soil into the voids in the stone embankment material due to seepage. We recommend that the geotextile should be consistent with ODOT riprap geotextile Type 2 following the guidance in Table 02320-1 of OSSC (2015) Section 02320.20. The properties are presented in Table 2. TABLE 2: RIPRAP GEOTEXTILE FABRIC MATERIAL PROPERTIES Geotextile Property Units Test Method Values Grab Tensile Strength lb ASTM D 4632 -Machine Direction 260(min.) -Cross Machine Direction 260(min.) Grab Elongation % ASTM D 4632 15(min.) Burst Strength psi ASTM D 3786 435(min.) -Diaphragm Method Puncture Strength lb ASTM D 4833 80(min.) Apparent Opening Size(AOS) in ASTM D 4751 No.70(max.) -US Standard Sieve Permittivity s-' ASTM D 4491 0.5(min.) GER—Derry Dell 24-1-04116-002 Marjorie Wolfe %. t _# .` .1 l ..r Water Wolf Resources May 17, 2017 Page 14 of 18 AT CONSTRUCTION CONSIDERATIONS General The rock embankment construction will include(1) site preparations, including clearing and grubbing; (2) excavation; and(3)placement of fill. These construction activities should generally be accomplished in accordance with the 2015 OSSC. Due to the relatively unstable nature of the existing landslide, in our opinion, construction of the proposed improvements should be performed during the dry season. In addition, we recommend that excavation and backfilling be completed in segments no greater than 75 feet in length(no greater than 75 feet of excavation open at any time), measured across the top of the excavation segment, to minimize aggravating slope stability conditions. It will be the Contractor's responsibility to monitor the site safety and take appropriate measures to maintain a safe work environment. A pre- and post-construction assessment should be made of nearby residences and the existing retaining wall to look for cracks and damage. In addition, the contractor should install and maintain a temporary stormwater diversion pipeline during work for the Stormwater Outfall area. In our opinion, the proposed improvements can be constructed with conventional earthwork equipment and tracked dumpers but will require removal of select trees. Temporary Cut Slopes Temporary cut slopes are typically the responsibility of the contractor and should comply with applicable local, state, and federal safety regulations, including the current OSHA Excavation and Trench Safety Standards. During excavation and construction for the rock embankment, localized unstable landslide debris may slide into the excavation along the temporary cut slope. The excavation for the toe of the rock embankment should be accomplished in accordance with _ OSSC (2015) Section 00330.44. Excavation and Groundwater Control Our opinion is that seepage along the excavation slopes may occur even during summer construction. Therefore, groundwater may accumulate in the bottom of the excavation. The contractor should provide a drainage path for the seepage water to escape, or a temporary dewatering system should be designed to remove accumulated seepage water in the excavation GER—Deny Dell 24-1-04116-002 Marjorie Wolfe 614 ,i AsJCI Sir f.,", Water Wolf Resources May 17, 2017 Page 15 of 18 area. The drainage system will most likely require use of sump pumps. Design of the temporary dewatering system is traditionally the responsibility of the contractor. In addition, water collected should be treated and disposed in a manner meeting local, state, and federal environmental regulations and requirements. Discharge water treatment may require use of filter bags or baker tanks prior to disposal. Fill Placement and Compaction Embankment construction(rock embankment) should follow the guidance in OSSC (2015) Section 00330.42. Any fill placed on slopes steeper than 3H:1 V should consist of ODOT Stone Embankment material. ODOT Stone Embankment material should be nominally compacted by track walking or worked in with an excavator bucket or non-vibratory roller. All fill subgrade steeper than 5H:1 V should be benched prior to placement of fill. LIMITATIONS The analyses, conclusions, and recommendations contained in this report are based on site conditions as they currently exist. Our conclusions and recommendations are based on our understanding of the project as described in this report and the site conditions as interpreted from the explorations, survey monuments, and survey topography provided by AKS. We have assumed that the explorations are representative of the subsurface conditions at the site of the proposed improvements and that subsurface conditions everywhere are not significantly different from those disclosed by the explorations. Within the limitations of the scope, schedule, and budget, the analyses, conclusions, and recommendations presented in this report were prepared in accordance with generally accepted professional geotechnical engineering principles and practice in this area at the time this report was prepared. We make no warranty, either express or implied. If, during construction, subsurface conditions different from those encountered in the field explorations are observed or appear to be present, we should be advised at once so that we can review these conditions and reconsider our recommendations where necessary. If there is a substantial lapse of time between the submission of the final design report and the start of work at the site, or if conditions have changed because of natural forces or construction operations at or adjacent to the site, we recommend that this report be reviewed to determine the applicability of the conclusions and recommendations concerning the changed conditions and/or the time lapse. GER—Derry Dell 24-1-04116-002 Marjorie Wolfet ° ' : x` C.{ Water Wolf Resources May 17, 2017 Page 16 of 18 This report was prepared for the exclusive use of Wolf Water Resources and the City of Tigard for the Derry Dell Creek at 118th Court Stream Bank Stabilization and Outfall Repair Project. This report is not a warranty of subsurface conditions, such as those interpreted from the exploration logs, including conclusions of subsurface conditions in other interpretive sections of the report. Unanticipated soil conditions are commonly encountered and cannot fully be determined by merely taking soil samples from borings. Such unexpected conditions frequently require that additional expenditures be made to attain properly constructed projects. Therefore, some contingency fund is recommended to accommodate the potential for extra costs. The scope of our geotechnical services did not include any environmental assessment or evaluation regarding the presence or absence of hazardous or toxic materials in the soil, surface water, groundwater, or air, on or below the site, or for evaluation of disposal of contaminated soils or groundwater, should any be encountered, except as noted in this report. Shannon&Wilson, Inc., has prepared a document, "Important Information About Your Geotechnical/Environmental Report,"to assist you and others in understanding the use and limitations of our report. This document is included as an attachment at the end of this report. GER—Deny Dell 24-1-04116-002 Marjorie Wolfe Water Wolf Resources May 17, 2017 Page 17 of 18 SHANNON & WILSON, INC. .IAT I F/FO <<- PRO,cFs / ((.01. 4(4 /,, OREGON OREGON 4(4 p DAVI HIGGINS 58419PE *' E 20 `� EiON co yENG ?\`' 1.2/3//,20/ 7 EXPIRES:/•2 34 Dave Higgins, CEG Risheng(Park) Piao, PE, GE Associate i Engineering Geologist Vice-President I Geotechnical Engineer SMM/JLJ:hrr Attachments Figure 1 Vicinity Map Figure 2 Site and Exploration Plan—Stormwater Outfall Figure 3 Site and Exploration Plan—Derry Dell Landslide Figure 4 Soil Description and Log Key Figure 5 Log of Boring B-1 Figure 6 Log of Boring HA-1 Figure 7 Log of Boring HA-2 Figure 8 Log of Boring HA-3 Figure 9 Log of Boring HA-4 Figure 10 Log of Boring HA-5 Figure 11 Log of Boring HA-6 Figure 12 Log of Boring HA-7 Figure 13 Slope Stability Analysis Results—Stormwater Outfall Figure 14 Slope Stability Analysis Results— Derry Dell Landslide Important Information About Your Geotechnical/Environmental Report GER—Derry Dell 24-1-04116-002 Marjorie Wolfe Water Wolf Resources May 17, 2017 Page 18 of 18 REFERENCES Allen, J.E., Burns, M., and Burns, S., 2009, Cataclysms on the Columbia: The Great Missoula Floods (2nd ed.): Portland, Oregon, Ooligan Press, 204 p. Madin, I.P., 1990, Earthquake-Hazard Geology Maps of the Portland Metropolitan Area, Oregon: Oregon Department of Geology and Mineral Industries, Open-File Report 0-90- 2, scale 1:24,000, includes Beaverton, Gladstone, Hillsboro, Linnton, Lake Oswego, Mount Tabor, Portland, and Scholls quadrangles. O'Connor, J.E., Sarna-Wojcicki,A., Wozniak, K.C., Polette, D.J., and Fleck, R.J., 2001, Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon: U.S. Geological Survey Professional Paper 1620, 52 p., 1:250,000. Schlicker, H.G. and Deacon, R.J., 1967, Engineering Geology of the Tualatin Valley region, Oregon: Oregon Department of Geology and Mineral Industries Bulletin B-60, 103 p., 5 app., 45 figs., 5 tables, 4 pls. incl. 1 geologic-hazards map and 1 depth-to-basalt map [all 1:48,000]. GER-Derry Dell 24-1-04116-002 t'� Washington t — — ( l_ t.,--:_7; Site Location —? r 1c. I . ' 'r L z_ . —'-.0' Idaho I l_ L� I —1 /-til '--i___/!-- - --1 1 �' I j -1 JI'')i/1 L ` l 1 1 Cs it l ` I -I - 1 California I Nevada Ju.t ,,Ln K,.‘. . SITE LOCATION STORMWATER OUTFALL SITE LOCATION DERRY DELL LANDSLIDE w. Sb`uChander Di C SW Duehllly CI ,. st :"-.'Mr;-,thud Hid; t�,� 0 J N. U, 0 N t4 N Rk rth.lesl 1 N N flontesso,l TO .Tuaiafin fi. h c a >. _ ,, x ft Sources: Esri, HERE,DeLorme, Intermap, increment P Corp.,GEBCO. �1 USGS, FAO, NPS,NRCAN,GeoBase,IGN, Kadaster NL,Ordnance Survey,Esri Japan,METI,Esri China(Hong Kong),swisstopo, o Mapmylndia,©OpenStreetMap contributors,and the GIS User it Community d z 0 0.0625 0.125 0.25 Derry Dell Creek at 118th Court o I---i I Streambank Stabilization and Outfall Repair `O Scale in Miles Tigard, Oregon 4 VICINITY MAP iii March 2017 24-1-04116-002 E co SHANNON toVVILSON,INC. FIG. 1 I.). Filename:T:1Projects124-1/4116 Derry DenitFigure 2 Site Map_Outfall.mxd Date:3/13/2017 Login:de ? r n , 1 n5 _ \ s5 s � / Tax,Lot 1100 7 . ; ,/ \'',''''::-/ '---1 , -r7Z---,4,---,!---,,',;,-',1W.-',--,- - -.-,-., ', ;.,--- - i _ _00#0.--__„,__ di 'a' yis\, s ,wwa I / tii c/ � ' 1‘t1c . . t *, q ,� : 1111ir `--i Ill, 1 i. J0 t fi �; FI-0YIrji � � �`•% tg ° � a t h t r !. 1 • P /'' d7 . 1 i. Fs i.DigitalGlobe.Ge Eye Earthste G giepb cs CNES/Airbus DS USDA.USGS, he Oof21 D-GN.3YId the GAS User Com�ltl nlry f LEGEND 0 15 30 60 Derry Dell Creek at 118th Court HA-1 V Designation and Approximate Location of Hand Auger 1 I I Streambank Stabilization and Outfall Repair B-1 Designation and Approximate Location of Boring Scale in Feet Tigard,Oregon A *A' Location and Designation of Slope Stability Analysis Models SITE AND EXPLORION PLAN u NOTES -n STORMWATER ATOUTFALL G) 1 Contours and existing features from drawing N ACAD-5746 CXMPL5746CXMPL-Model.dwg, March 2017 24-1-04116-002 provided by AKS Engineering and Forestry,LLC SHANNONbWII�SON;NC. FIG.2 on February 23,2017. - - I- Filename:T:Projects124-1\4116 Derry Dell\Figure 3 Site Map_LS.mxd Date:3/13/2017 Login:clv / / • '1--' :/f:'i'''I':i ''', ' '/'\'''I''' /' : t' ,/� III, D r r f/ ! � / x Lf, , / / 7 ;,.- Drain SW*' 'j` ix/l0. r1 //' ) r t ,.; rr 7 9 !j/It ,)H/adcarp ',// I I( %/1,, 4,/' 1 / ' ?, ' ''r` ` / I 1 1 1I I 'l// ,I,I , I / HA +,� HA\7)I 1.,1 Ali I //11 ' !r II//// '� �`� I,II1 i/%�,r•l/ ( / -1 ��1/1 ! t,ir,,,r \ l ,t1 1_r (r`// / ,/ , J 2 � '''` )vIt°\ !III '7/ . , , tr .'I I r.1 ,1 .1 / 1 :II 1 111/P l' til' T ' ' -/7-'---((il n Q°O 1/ /If / ,11( I1 x s jr, ,A \.oti Wall • 'i/7 11 //'///I/l1. // Ir JIII h, a+ 1 ll/'j) i I(//'if l//,f HA S.. ;`,>> / /,/: �II ��w Ground Crack ,_ ,11/1/,/,/ Ilk1 , /, :% ( _ I ! i'.,,,, l /PI;, \ ,/,/ ,,,, , 1 ,., , r" t t+I Ill ` <.. �✓ ';''B-1y//,I f /11�r f/`l j 1/1 '✓ "r 1 111,Jiro,Ili! / ks1 /r2//1) , ILII/ I " / t �1 l f I,/ illl 111 ,111'.:',', r, r )1 xIY �- -vz. J y%% ------- )/ c i ^=ate. '''1-/-1/';'•//f f t. 3 rx ..//,.1(, HA-4 "r �.-,1c,---_,,-.7,,,,,,/.,//y -r, 'o I it/4; of t • - % /l t J I(' '`l /(y fi ./ -V �` i(/f •'—t,'n 1 ,a I/{ / l/ /x 4 � - �� • � l 1 1Cff �I vv /^ 11�V /i/ ✓ diit / 1 / 1 f �‘„ //,III'\\tit r ___� (I ,I (/ /'111/ II{)(t lv. t I )((l III ',A r ------ Der -Dell Creek_ . '-" � f __________,____ .,„r-(";' ',';:::---:,--" / ,t, [1' ` * � ,,� -- -- Ji \L, —/ ti _ .-i 280 _ lI Soi c E=i.D'iglt�IGl he GeoEy Earth tar Geag,aph C _ AervGRID IGN,and the GIS User gtehr nary LEGEND 0 15 30 60 Derry Dell Creek at 118th Court HA-1 Designation and Approximate Location of Hand Auger I I I I Streambank Stabilization and Outfall Repair B-I 8 Designation and Approximate Location of Boring Scale in Feet Tigard,Oregon Approximate Area of Derry Dell Landslide SITE AND EXPLORATION PLAN A A' Location and Designation of Slope Stability Analysis Models T AAC) NOTES DERRY DELL LANDSLIDE 1. Contours and existing features from drawing w ACAD-5746 CXMPL5746CXMPL-Model.dwg, March 2017 24-1-04116-002 provided by AKS Engineering and Forestry,LLC SHANNONtomL80N.INC. FIG.3 on February 23,2017. - - PARTICLE SIZE DEFINITIONS DESCRIPTION SIEVE NUMBER AND/OR APPROXIMATE SIZE Shannon & Wilson, Inc. (S&W), uses a soil identification system modified from the Unified FINES <#200(0.075 mm=0.003 in.) Soil Classification System(USCS). Elements of the USCS and other definitions are provided on SAND this and the following pages. Soil descriptions Fine #200 to#40(0.075 to 0.4 mm; 0.003 to 0.02 in.) are based on visual-manualprocedures(ASTM Medium #401to#104(2 to 4.75 2 mm;0.02 to 0.081in Coarse #10 to#4 to mm;0.08 to 0.187 in.) D2488)and laboratory testing procedures (ASTM D2487), if performed. GRAVEL Fine #4 to 3/4 in. (4.75 to 19 mm;0.187 to 0.75 in.) S&W INORGANIC SOIL CONSTITUENT DEFINITIONS Coarse 3/4 to 3 in. (19 to 76 mm) z FINE-GRAINED SOILS COARSE-GRAINED CONSTITUENT (50%or more fines)' SOILS COBBLES 3 to 12 in.(76 to 305 mm) (less than 50%fines) 1 Silt,Lean Clay, BOULDERS > 12 in. (305 mm) Major Elastic Silt,or Sand or Gravel' Fat Clay3 RELATIVE DENSITY/CONSISTENCY Modifying 30%or more More than 12% COHESIONLESS SOILS COHESIVE SOILS (Secondary) coarse-grained: fine-grained: Precedes major Sandy or Gravelly' Silty or Clayey' N,SPT, RELATIVE N,SPT, RELATIVE constituent BLOWS/FT. DENSITY BLOWS/FT. CONSISTENCY 15%to 30% 5%to 12% <4 Very loose <2 Very soft coarse-grained: fine-grained: with Sand or with Silt or 4- 10 Loose 2-4 Soft Follows Minor major with Gravel' with Clayr3 10-30 Medium dense 4-8 Medium stiff constituent 30%or more total ° 30-50 Dense 8-15 Stiff coarse-grained and 15%or more of a >50 Very dense 15-30 Very stiff lesser coarse- second coarse- >30 Hard grained constituent grained constituent: is 15%or more: with Sand or with Sand or with Gravel WELL AND BACKFILL SYMBOLS with Gravelsn Bentonite %;o%; Surface Cement 'All percentages are by weight of total specimen passing a 3-inch sieve. \\\� Cement Grout %,,�>,,, Seal 'The order of terms is:Modifying Major with Minor. 'Determined based on behavior. // Bentonite Grout Asphalt or Cap Determined based on which constituent comprises a larger percentage. 'Whichever is the lesser constituent. (We+ :;"SS Bentonite Chips % Slough MOISTURE CONTENT TERMS Silica Sand Inclinometer or Dry Absence of moisture,dusty,dry Non perforated Casing to the touch • Gravel r Vibrating Wire Moist Damp but no visible water H Perforated or I I Piezometer Screened Casing Wet Visible free water,from below water table PERCENTAGES TERMS 1,2 Trace <5% Few 5 to 10% o STANDARD PENETRATION TEST(SPT) • Little 15 to 25% O SPECIFICATIONS Some 30 to 45% Hammer: 140 pounds with a 30-inch free fall. Rope on 6-to 10-inch-diam.cathead Mostly 50 to 100% m 2-1/4 rope turns, > 100 rpm 1Gravel,sand,and fines estimated by mass. Other constituents,such as Sampler: 10 to 30 inches long organics,cobbles,and boulders,estimated by volume. > Shoe I.D.= 1.375 inches 'Reprinted,with permission,from ASTM D2488-09a Standard Practice for Barrel I.D. = 1.5 inches m Description and Identification of Soils(Visual-Manual Procedure),copyright a Barrel O.D.=2 inches ASTM International,100 Barr Harbor Drive,West Conshohocken,PA 19428. N-Value: Sum blow counts for second and third A copy of the complete standard may be obtained from ASTM International, Nwww.astm.org. N 6-inch increments. a Refusal:50 blows for 6 inches or Derry Dell Creek at 118th Court (? less; 10 blows for 0 inches. s Streambank Stabilization and Outfall Repair NOTE:Penetration resistances(N-values)shown on Tigard, Oregon a boring logs are as recorded in the field and have not been corrected for hammer efficiency, overburden, or other factors. SOIL DESCRIPTION AND LOG KEY 0 CD March 2017 24-1-04116-002 E ° SHANNON&WILSON, INC. FIG. 4 Geotechnical and Environmentalonsultants Sheet 1 of 3 N C N UNIFIED SOIL CLASSIFICATION SYSTEM(USCS) (Modified From USACE Tech Memo 3-357,ASTM D2487,and ASTM D2488) MAJOR DIVISIONS GROUP/GRAPHIC SYMBOL TYPICAL IDENTIFICATIONS SS GWWell-Graded Gravel;Well-Graded • � O. OGravel with Sand Gravel '0. (less than 5% Gravels fines) GP •4' Poorly Graded Gravel;Poorly Graded (more than 50% 1, 6NI Gravel with Sand of coarse ',If' fraction retained •I on No.4 sieve) GM 1 Silty Gravel;Silty Gravel with Sand _ Silty or Clayey 1 Gravel + 'i COARSE- (mor fines)than 12/ GC Y /� SandyClayey Gravel;Clayey Gravel with GRAINED SOILS �% (more than 50% retained on No. SW . Well-Graded Sand;Well-Graded Sand 200 sieve) Sand . with Gravel (less than 5% fines) . Poorly Graded Sand;Poorly Graded Sands SP . Sand with Gravel (50%or more of • : •"' coarse fraction •I: I' 7'. passess the iehe No.4 Silty or SM .:I:i;l. •1� Silty Sand;Silty Sand with Gravel Clayey Sand •.I:•t:F:J'1:• (more than 12% t... fines) SC j Clayey Sand;Clayey Sand with Gravel ML Silt;Silt with Sand or Gravel;Sandy or Gravelly Silt Inorganic ,1,r Silts and Clays �`O Lean Clay;Lean Clay with Sand or (liquid limit less CL �� Gravel;Sandy or Gravelly Lean Clay than 50) FINE-GRAINED Organic Silt or Clay;Organic Silt or SOILS Organic OL ;' GraClave ly OOrganic Sth Sand orGt orraveClay Sandy or (50%or more /' passes the No. / Elastic Silt;Elastic Silt with Sand or 200 sieve) MH � / Gravel;Sandy or Gravelly Elastic Silt Inorganic Silts and Clays Fat Clay;Fat Clay with Sand or Gravel; (liquid limit 50 or CH Sandy or Gravelly Fat Clay more) / ►i Organic Silt or Clay;Organic Silt or r Organic OH M� Clay with Sand or Gravel;Sandy or .75 �► Gravelly Organic Silt or Clay M Z1, HIGHL - 0 O GANIC Primarily organic matter,dark in PT , „ Peat or other highly organic soils(see SOILS color,and organic odor ASTM D4427) z ci Placed by humans,both engineered The Fill graphic symbol is combined m FILL and nonengineered. May include with the soil graphic that best various soil materials and debris. represents the observed material o0 a NOTE: No.4 size=4.75 mm=0.187 in.; No.200 size=0.075 mm=0.003 in. cc g m NOTES m M 3 1.Dual symbols(symbols separated by a hyphen,i.e.,SP-SM,Sand �' with Sift)are used for soils with between 5%and 12%fines or when a the liquid limit and plasticity index values plot in the CL-ML area of Derry Dell Creek at 118th Court c? E, the plasticity chart. Streambank Stabilization and Outfall Repair 2.Borderline symbols(symbols separated by a slash,i.e.,CL/ML, Tigard, Oregon a Lean Clay to Silt;SP-SM/SM,Sand with Silt to Silty Sand)indicate 9 that the soil properties are close to the defining boundary between N two groups. SOIL DESCRIPTION N 3.The soil graphics above represent the various USCS identifications (i.e., GP,SM,etc.)and may be augmented with additional AND LOG KEY U symbology to represent differences within USCS designations. zo Sandy Silt(ML),for example,may be accompanied by the ML soil March 2017 24-1-04116-002 o• graphic with sand grains added. Non-USCS materials may be m represented by other graphic symbols;see log for descriptions. SHANNON&WILSON,INC. FIG. 4 M S Geotechnical and Environmental Consultants Sheet 2 of 3 N GRADATION TERMS ACRONYMS AND ABBREVIATIONS Poorly Graded Narrow range of grain sizes present or,within the range of grain sizes ATD At Time of Drilling present,one or more sizes are approx. Approximate/Approximately missing(Gap Graded). Meets criteria in ASTM D2487,if tested. Diam. Diameter Well-Graded Full range and even distribution of Elev. Elevation grain sizes present. Meets criteria in ft. Feet ASTM D2487,if tested. Fe0 Iron Oxide CEMENTATION TERMS' gal. Gallons Weak Crumbles or breaks with handling or Horiz. Horizontal slight finger pressure HSA Hollow Stem Auger - Moderate Crumbles or breaks with considerable finger pressure I.D. Inside Diameter Strong Will not crumble or break with finger in. Inches pressure lbs. Pounds PLASTICITY2 MgO Magnesium Oxide APPROX. mm Millimeter PLASITICTY MnO Manganese Oxide INDEX NA Not Applicable or Not Available DESCRIPTION VISUAL-MANUAL CRITERIA RANGE Nonplastic A 1/8-in.thread cannot be rolled <4% NP Nonplastic at any water content. O.D. Outside Diameter Low A thread can barely be rolled and 4 to 10% OW Observation Well a lump cannot be formed when Pounds per Cubic Foot drier than the plastic limit. pcf Medium A thread is easy to roll and not 10 to PID Photo-Ionization Detector much time is required to reach the 20% PMT Pressuremeter Test plastic limit. The thread cannot be ppm Parts per Million rerolled after reaching the plastic limit. A lump crumbles when drier psi Pounds per Square Inch than the plastic limit. PVC Polyvinyl Chloride High It take considerable time rolling o rpm Rotations per Minute and kneading to reach the plastic >20% limit. A thread can be rerolled SPT Standard Penetration Test several times after reaching the USCS Unified Soil Classification System plastic limit. A lump can be qu Unconfined Compressive Strength formed without crumbling when drier than the plastic limit. VWP Vibrating Wire Piezometer ADDITIONAL TERMS Vert. Vertical WOH Weight of Hammer Mottled Irregular patches of different colors. WOR Weight of Rods Bioturbated Soil disturbance or mixing by plants or Wt. Weight animals. Diamict Nonsorted sediment;sand and gravel STRUCTURE TERMS' in silt and/or clay matrix. Interbedded Alternating layers of varying material or color with layers at least 1/4-inch thick;singular:bed. Cuttings Material brought to surface by drilling. Laminated Alternating layers of varying material or color with layers less than 1/4-inch thick;singular: 1- Slough Material that caved from sides of lamination. 0 borehole. Fissured Breaks along definite planes or fractures with little resistance. z Sheared Disturbed texture,mix of strengths. Slickensided Fracture planes appear polished or glossy; N PARTICLE ANGULARITYAND SHAPE TERMS' sometimes striated. m Blocky Cohesive soil that can be broken down into small angular lumps that resist furtherAngular Sharp edges and unpolished planarobreakdown.ia_ surfaces. Lensed Inclusion of small pockets of different soils, ri Subangular Similar to angular,but with rounded such as small lenses of sand scattered through m edges. a mass of clay. Homogeneous Same color and appearance throughout. 3 Subrounded Nearly planar sides with well-rounded N edges. O Derry Dell Creek at 118th Court 0. Rounded Smoothly curved sides with no edges. 0 Streambank Stabilization and Outfall Repair th Flat Width/thickness ratio>3. Tigard, Oregon Elongated Length/width ratio>3. 'Reprinted,with permission,from ASTM D2488-09a Standard Practice for SOIL DESCRIPTION 2 Description and Identification of Soils(Visual-Manual Procedure),copyright ASTM AND LOG KEY vInternational,100 Barr Harbor Drive,West Conshohocken,PA 19428. A copy of the complete standard may be obtained from ASTM International,www.astm.org. z ZAdapted,with permission,from ASTM D2488-09a Standard Practice for March 2017 24-1-04116-002 o Description and Identification of Soils(Visual-Manual Procedure),copyright ASTM a' International,100 Barr Harbor Drive,West Conshohocken,PA 19428. A copy of SHANNON&WILSON, INC. FIG. 4 b the complete standard may be obtained from ASTM International,www.astm.org. Geotechnical and Environmental Consultants Sheet 3 of 3 N Total Depth: 25.5 ft. Northing: --647,609 ft. Drilling Method: Solid Stem Auger Hole Diam.: 4 in. Top Elevation: -270 ft. Easting: -7,611,926 ft. Drilling Company: PLi Systems Rod Type: AWJ Vert.Datum: NGVD29 Station: - Drill Rig Equipment: Little Beaver DR100 Hammer Type: Cathead Horiz.DatumNAD83(11)OSPN Offset: - Other Comments: SOIL DESCRIPTIONE/ev. o aNi c PENETRATION RESISTANCE,N (blows/ft.) Refer to the report text for a proper understanding of the a S m . ♦ Hammer Wt.&Drop: 140 lbs/30 inches subsurface materials and drilling methods. The stratification Depth E E 2 ra 'a lines indicated below represent the approximate boundaries (ft.) to rn f0 0 > N between soil types,and the transitions maybe gradual. 0 20 40 60 80 100 - Soft to medium stiff,gray-brown and • orange-mottled, Silt(ML); moist;trace fine • sand; low plasticity;micaceous. •• • • FILL . S-t111, • • 5 • Sample S-2 contained scattered black pockets • S-2 and thin seams of leafy organic material. 7 263.0 • Loose,gray and orange-stained, Silt with Sand 7.0 0 (ML); moist grading to wet at 8.5 ft;fine sand; S-3 nonplastic; micaceous;trace thin layers of 2 —7 Lean Clay(CL). m 10 0 WILLAMETTE SILT 0 -7 Z • 0 ln Samples S-4,S-5,and S-6 contain fine leafy s'5 07 organic material in thin horizontal laminae. — - - - i-. 15 • WS'S ___.. .._.... x 6 y m U i; 20 • J S-7 5 - 247.0 -- Loose to medium dense,gray, Silt with Sand 23.0 (ML);moist;fine sand; nonplastic; micaceous; • 0 7 faint horizontal laminations. 244.5 S-8 25 10 M o Completed: February 18,2009 25.5 oX 0 Q. S U) M 0 20 40 60 80 100 c9 LEGEND 0 Recovery(%) 0 i I Standard Penetration Test Q Groundwater Level ATD O %Fines(<0.075mm) • %Water Content 00 J Plastic Limit I -I Liquid Limit M O 3 Derry Dell Creek at 118th Court a Streambank Stabilization and Outfall Repair c? Tigard, Oregon 2 a NOTES 2 1.Refer to KEY for explanation of symbols,codes,abbreviations,and definitions. LOG OF BORING B-1 N 2.Groundwater level,if indicated above,is for the date specified and may vary. w 0 3.Group symbol is based on visual-manual identification and selected lab testing. 2 4.The hole location and elevation should be considered approximate. March 2017 24-1-04116-002 cc 1- SHANNON&WILSON, INC. FIG. 5 Geotechnical and Environmental Consultants f REV 3 Total Depth: 3.5 ft. Northing: -647,591 ft. Drilling Method: Hand Boring Hole Diam.: 3 in. Top Elevation: -254 ft. Easting: -7,611,945 ft. Drilling Company: Shannon&Wilson,Inc. Rod Type: Vert.Datum: NGVD29 Station: - Drill Rig Equipment: Hand Auger Hammer Type: Horiz.DatumNAD83(11)OSPN Offset: - Other Comments: SRefer to the report DESCRIPTION of the Elev. -6 d c PENETRATION RESISTANCE,N (blows/ft.) P proper understanding a .- t ♦ Hammer Wt.&Drop: subsurface materials and drilling methods. The stratification Depth E E 2 N a lines indicated below represent the approximate boundaries (ft.) lj as 0 > between soil types,and the transitions may be gradual. 0 20 40 60 80 100 Light brown, Silt(ML);wet; low plasticity;trace to little organic debris. LANDSLIDE DEPOSITS 252.1 Light brown to gray and orange-mottled, Silt 1.4 0 105 (ML);moist to wet; low plasticity; micaceous. WILLAMETTE SILT 250.0 Completed:January 8,2016 3.5 5 z 10 U) U a 0 -1 .................... 0 CD N1 F cci 15 X a. a. -J z x 0 20 40 60 80 100 LEGEND a Plastic Limit I--I Liquid Limit Natural Water Content Derry Dell Creek at 118th Court Streambank Stabilization and Outfall Repair Tigard, Oregon NOTES 1.Refer to KEY for explanation of symbols,codes,abbreviations,and definitions. LOG OF BORING HA-I r 2.Groundwater level,if indicated above,is for the date specified and may vary. C7 3.Group symbol is based on visual-manual identification and selected lab testing. ° 4.The hole location and elevation should be considered approximate. March 2017 24-1-04116-002 SHANNON&WILSON,INC. FIG. 6 Geotechnical and Environmental Consultants 2 REV 3 Total Depth: 15 ft. Northing: —647,427 ft. Drilling Method: Hand Boring Hole Diam.: 3 in. Top Elevation: —285 ft. Easting: —7,611,626 ft. Drilling Company: Shannon&Wilson,Inc. Rod Type: — Vert.Datum: NGVD29 Station: — Drill Rig Equipment: Hand Auger Hammer Type: — Horiz.DatumNAD83(11)OSPN Offset: — Other Comments: SOIL DESCRIPTION Elev. o a`ai c PENETRATION RESISTANCE,N (blows/ft•) Refer to the report text for a proper understanding of the . S11.? A Hammer Wt.&Drop: 140 lbs/30 inches subsurface materials and drilling methods. The stratification Depth , E 2 as - lines indicated below represent the approximate boundaries (ft.) to (7 a, between soil types,and the transitions maybe gradual. o 20 40 60 80 100 Brown, Silt with Sand to Lean Clay with Sand �'•• (ML/CL); moist;trace fine angular gravel;fine • S i G sand; low to medium plasticity;trace to few •♦ • organics; micaceous. FILL 283.0 r• • Yellow-brown,Lean Clay(CL); moist;trace to s-211little fine sand; medium to high plasticity;trace organics;trace iron-oxide stains; micaceous. WILLAMETTE SILT _ 280.5A'� � 0 Brown and orange-mottled, Silt with Sand 4.5 s-31 (ML); moist;fine sand; nonplastic to low 5 plasticity; micaceous. x Q Grades to wet at 7.5 ft. 1 HI it 10 g z it 0 J N. _ _...._ _... _....... ......_. m i:,- 0 0 270.0 15 X Completed: February 21,2017 15.0 0 O. Z a x CO - CO 0 20 40 60 80 100 J a LEGEND X a ® Grab Sample SZ Groundwater Level ATD Plastic Limit I---I Liquid Limit m J Natural Water Content l7 3 Derry Dell Creek at 118th Court Streambank Stabilization and Outfall Repair t? Tigard, Oregon 0 2 NOTES 0 1.Refer to KEY for explanation of symbols,codes,abbreviations,and definitions. LOG OF BORING HA-2 N 2.Groundwater level,if indicated above,is for the date specified and may vary. w O 3.Group symbol is based on visual-manual identification and selected lab testing. 0 4.The hole location and elevation should be considered approximate. March 2017 24-1-04116-002 re w SHANNON&WILSON,INC. FIG. 7 Q Geotechnical and Environmental Consultants REV 3 Total Depth: 7 ft. Northing: -647,412 ft. Drilling Method: Hand Boring Hole Diam.: 3 in. Top Elevation: -270 ft. Easting: --7,611,650 ft. Drilling Company: Shannon&1Mlson,Inc. Rod Type: - Vert.Datum: NGVD29 Station: - Drill Rig Equipment: Hand Auger Hammer Type: - Horiz.DatumNAD83(11)OSPN Offset: - Other Comments: SOIL DESCRIPTION Elev. o 2 v PENETRATION RESISTANCE,N (blows/ft.) Refer to the report text for a proper understanding of the a c .9- w ♦ Hammer Wt.&Drop: 140lbs/30 inches subsurface materials and drilling methods. The stratification Depth E E o to a lines indicated below represent the approximate boundaries (ft.) tj cli c. between soil types,and the transitions maybe gradual. 0 20 40 60 80 100 Dark brown, Silt to Lean Clay(MUCL); moist; . 04 s'G trace to little fine sand; medium plasticity;trace . 269.2 �• organics; micaceous. 1.0 FILLOr Brown to blue-gray and orange-mottled, Silt with Sand to Lean Clay with Sand(ML/CL); s • j moist to wet;fine sand; medium plasticity; ,_- 267.2 s m 3.0 trace organics; micaceous. J o Blue-gray and orange-mottled, Silt to Silt with Sand(ML);wet;fine sand; medium plasticity; trace to few organics; micaceous. 5 WILLAMETTE SILT SLJ • 263.2 Completed: February 21,2017 7.0 Q a z 10 Z z ................................. . t 0 J .... ................. n w M t- o o 15 X a a z Q h m 0 20 40 60 80 100 X LEGEND a } ® Grab Sample SZ Groundwater Level ATD ce o Plastic Limit I I Liquid Limit Natural Water Content M E, c Derry Dell Creek at 118th Court Streambank Stabilization and Outfall Repair 0. s Tigard, Oregon a NOTES 2 1.Refer to KEY for explanation of symbols,codes,abbreviations,and definitions. LOG OF BORING HA-3 N 2.Groundwater level,if indicated above,is for the date specified and may vary. w O 3.Group symbol is based on visual-manual identification and selected lab testing. 2 4.The hole location and elevation should be considered approximate. March 2017 24-1-04116-002 w SHANNON&WILSON, INC. FIG. 8 f Geotechnical and Environmental Consltants REV 3 Total Depth: 12.5 ft. Northing: --647,563 ft. Drilling Method: Hand Boring Hole Diam.: 3 in. Top Elevation: -251 ft. Easting: -7,611,930 ft. Drilling Company: Shannon&Wilson,Inc. Rod Type: Vert.Datum: NGVD29 Station: - Drill Rig Equipment: Hand Auger Hammer Type: Horiz.DatumNAD83(11)OSPN Offset: - Other Comments: SOIL DESCRIPTION -5 o c PENETRATION RESISTANCE,N (blowsi t.) Refer to the report text for a proper understanding of the a S .2 . A Hammer Wt.&Drop: 140 lbs/30 inches subsurface materials and drilling methods. The stratification Depth E E 2 to a lines indicated below represent the approximate boundaries (ft.) to (E 0 between soil types,and the transitions may be gradual. 0 20 40 60 80 100 Dark brown to gray, Silt(ML); moist to wet; sz tG trace to little fine sand; medium plasticity;trace to little organics;disturbed texture. _ 250.0 __ m 1.3 • Blue-gray and orange-mottled, Silt(ML); moist s-zn o to wet;trace to little fine sand;low to medium plasticity;trace to few organics;disturbed texture; micaceous. LANDSLIDE DEPOSITS 5 ......................... x a ................. z 10 z 240.2 ............ Blue-gray and orange-mottled, Silt(ML);moist 11.0 to wet;trace to little fine sand;low to medium plasticity;trace to few organics; micaceous. 238.7 WILLAMETTE SILT , 12.5 ........................ Completed: February 22,2017 I 0 15 0 a z x 0 20 40 60 80 100 LEGEND O } ® Grab Sample SZ Groundwater Level ATD Plastic Limit I-- Liquid Limit Natural Water Content 3 Derry Dell Creek at 118th Court Streambank Stabilization and Outfall Repair Tigard, Oregon u NOTES �1 2 1.Refer to KEY for explanation of symbols,codes,abbreviations,and definitions. LOG OF BORING HA-4 N 2.Groundwater level,if indicated above,is for the date specified and may vary. w 3.Group symbol is based on visual-manual identification and selected lab testing. 2 4.The hole location and elevation should be considered approximate. March 2017 24-1-04116-002 cc SHANNON&WILSON, INC. FIG. 9 Geotechnical and Environmental Consultants 2 REV 3 Total Depth: 10 ft. Northing: -647,643 ft. Drilling Method: Hand Boring Hole Diam.: 3 in. Top Elevation: -250 ft. Easting: --7,611,986 ft. Drilling Company: Shannon&Wilson,Inc. Rod Type: - Vert.Datum: NGVD29 Station: - Drill Rig Equipment: Hand Auger Hammer Type: Horiz.DatumNAD83(11)OSPN Offset: - Other Comments: SOIL DESCRIPTION Elev. o aNi c PENETRATION RESISTANCE,N (blows/t.) Refer to the report text for a proper understanding of the n a :? A Hammer Wt.&Drop: 140 lbs/30 inches subsurface materials and drilling methods. The stratification Depth E E 2 co a lines indicated below represent the approximate boundaries (ft.) e, cn between soil types,and the transitions maybe gradual. 0 20 40 60 80 100 Dark brown to gray, Silt to Lean Clay(ML/CL); s-1G moist to wet;trace to little fine sand;medium 249.2 7 plasticity;trace to little organics. f 1.0 Brown and orange-mottled, Silt to Lean Clay (ML/CL);moist to wet;trace fine to coarse s-.,n • gravel;trace to little fine sand; medium ``1i�ull plasticity;disturbed texture; micaceous. LANDSLIDE DEPOSITS 0 5 244.2 • Blue-gray and orange-mottled, Silt to Lean 6.0 Clay(ML/CL); moist to wet;trace to little fine S-3 sand; medium plasticity; micaceous. WILLAMETTE SILT x :T; 240.2 10 Completed: February 22,2017 10.0 z s it J r` CO r- 15 0 D. J z x 0 20 40 60 80 100 LEGEND a ® Grab Sample V Groundwater Level ATD Plastic Limit I----I Liquid Limit Natural Water Content Derry Dell Creek at 118th Court Streambank Stabilization and Outfall Repair Tigard, Oregon NOTES N 1.Refer to KEY for explanation of symbols,codes,abbreviations,and definitions. LOG OF BORING HA-5 2.Groundwater level,if indicated above,is for the date specified and may vary. w 0 3.Group symbol is based on visual-manual identification and selected lab testing. ° 4.The hole location and elevation should be considered approximate. March 2017 24-1-04116-002 SHANNON&WILSON, INC. FIG. 10 Geotechnical and Environmental Consultants REV 3 Total Depth: 10 ft. Northing: —647,687 ft. Drilling Method: Hand Boring Hole Diam.: 3 in. Top Elevation: —261 ft. Easting: --7,611,971 ft. Drilling Company: Shannon&lMlson,Inc. Rod Type: Vert.Datum: NGVD29 Station: — Drill Rig Equipment: Hand Auger Hammer Type: Horiz.DatumNAD83(11)OSPN Offset: — Other Comments: SOIL DESCRIPTION ,._o al 0 PENETRATION RESISTANCE,N (blows/ft.) Refer to the report text fora proper understanding of the a a ♦ Hammer Wt.&Drop: 140 lbs/30 inches subsurface materials and drilling methods. The stratification Depth E E 2 N a lines indicated below represent the approximate boundaries (ft.) U > N between soil types,and the transitions may be gradual. 0 20 40 60 80 100 Dark brown, Silt to Lean Clay(ML/CL);moist SiG to wet;trace to little fine sand; medium plasticity;trace to few organics;disturbed 259.0 • _ -1 texture; micaceous. J"- 1.5 Brown and orange-mottled, Silt to Silt with Sand(ML); moist;fine sand; nonplastic to low plasticity;disturbed texture; micaceous. LANDSLIDE DEPOSITS 5 . ............... .......... ................................... ... 253.5 Brown and orange-mottled, Silt to Silt with 7.0 Sand(ML); moist;fine sand; nonplastic to low plasticity; micaceous. WILLAMETTE SILT x E z 250.5 10 Completed: February 22,2017 10.0 Z it 0 ...................................... M 0 o 15 X O a .................... ........... .............................. 1 z a I m 0 20 40 60 80 100 J k X LEGEND a ® Grab Sample SZ Groundwater Level ATD Plastic Limit I----I Liquid Limit co J Natural Water Content C1 3 Derry Dell Creek at 118th Court Streambank Stabilization and Outfall Repair co Tigard,Oregon 0 NOTES - 1.Refer to KEY for explanation of symbols,codes,abbreviations,and definitions. LOG OF BORING HA-6 N 2.Groundwater level,if indicated above,is for the date specified and may vary. Lu O 3.Group symbol is based on visual-manual identification and selected lab testing. March 2017 24-1-04116-002 2 4.The hole location and elevation should be considered approximate. 1- SHANNON&WILSON, INC. W FIG. 11 Geotechnical and Environmental Consu nts 2 REV 3 Total Depth: 10 ft. Northing: --647,688 ft. Drilling Method: Hand Boring Hole Diam.: 3 in. Top Elevation: -255 ft. Easting: --7,611,987 ft. Drilling Company: Shannon&Wilson,Inc. Rod Type: Vert.Datum: NGVD29 Station: - Drill Rig Equipment: Hand Auger Hammer Type: Horiz.DatumNAD83(11)OSPN Offset: - Other Comments: SOIL DESCRIPTION o a PENETRATION RESISTANCE,N (blows/t.) Refer to the report text for a proper understanding of the Elev. subsurface materials and drilling methods. The stratification Depth E E R a Hammer Wt.&Drop: 140 lbs/30 inches lines indicated below represent the approximate boundaries (ft.) (>1) o > between soil types,and the transitions may be gradual. 0 20 40 60 80 100 Dark brown, Silt to Lean Clay(MUCL);moist 254.0 s'G 1 to wet;trace to little fine sand; medium / 0.5 plasticity;trace to little organics;disturbed i texture; micaceous. J _ Brown to gray and orange-mottled, Silt to Silt with Sand(ML); moist to wet;fine sand; nonplastic to low plasticity;disturbed texture; • -- - micaceous. s- G LANDSLIDE DEPOSITS SZ ........................ rff ............. . 249.5 Brown to gray and orange-mottled, Silt to Silt 5.0 5 with Sand(ML); moist to wet;fine sand; O nonplastic to low plasticity; micaceous. WILLAMETTE SILT o. x m z 244.5 Completed: February 22,2017 10.0 10 0 N. C, X 15 a a 2 co x m 0 20 40 60 80 100 LEGEND a. ® Grab Sample SZ Groundwater Level ATD Plastic Limit I----I Liquid Limit Natural Water Content Derry Dell Creek at 118th Court Streambank Stabilization and Outfall Repair Tigard,Oregon NOTES 2 1.Refer to KEY for explanation of symbols,codes,abbreviations,and definitions. LOG OF BORING HA-7 N 2.Groundwater level,if indicated above,is for the date specified and may vary. w 0 3.Group symbol is based on visual-manual identification and selected lab testing. 4.The hole location and elevation should be considered approximate. March 2017 24-1-04116-002 SHANNON&WILSON, INC. �f Geotechnical and Environmental Consltants 2 FIG. L REV 3 File:I:\EF\24-1 PDX\04100s\04116 Derry Dell Cree\DRAFTING\CAD\Sections 1_6_7_Deny Dell.dwg Date:03-13-2017 Author:clv Color Name Unit Weight(pcf) Cohesion'(psf) Phi'(°) Silty Fill 105 15 30 El Willamette Silt 106 55 31 0 Stone Embankment 130 0 38 290 A 3 Feet Factor of Safety= 1.3 A' °6 ° •?. 1:1 Maximum - Stone Embankment 280 � 1.5:1 j, 3 ar Approximate x ` ` Groundwater Elevation 270 -,,,,-,-....",'4, y �.,z 2 Feet . , -_. 260 xs 'rD a > 250 u 240 230 ` ; . . �� I " I I -25 -15 -5 5 15 25 35 45 55 65 75 85 95 105 Distance(Feet) 0 20 40 Derry Dell Creek at 118th Court Scale in Feet Streambank Stabilizaton and Outfall Repair Tigard, Oregon SLOPE STABILITY NOTES ANALYSIS RESULTS 11 1. Critical failure surface estimated using the entry and exit search criteria STORMWATER OUTFALL ,Q and the Spencer analysis method. 2. See Figure 2 for stability analysis location. March 2017 24-1-04116-002 W 3. See report text for additional information about analyses and SHANNON&WILSON,INC. assumptions. Geotechnical and Environmental Consultants FIG. 13 1 File:I:\EF\24-1 PDX\04100s\04116 Derry Dell Cree\DRAFTING\CAD\Sections 1_6_7_Deny Dell.dwg Date:03-13-2017 Author:clv Color Name Unit Weight(pcf) Cohesion'(psf) Phi'(°) fl Willamette Silt 106 55 31 ❑ Rock Embankment 130 0 38 B 8 Feet 275 270 �, r ,tzRock Embankment `�` to '2.. i'Z' ` 1.5:1 Approximate k�,; r ', a. . i Groundwater Elevation 1 , , , iso '":,,,,,ii,„•'„ 255 S 250 - ' o �r ` ti`a . ,•N5 r� ,1 -24 - ot y tw.<W 240 � a , ` a `235 e �� * ✓ "'i ✓-,1. �2: ` � r,- a4J ; 6i �I , ardit"• s z , # s 2 -. tY '" a, 220 ✓+ `a 4 a 215 .E ,< ., ., -, � ,'� '. .. . -25 -15 -5 5 15 25 35 45 55 65 75 85 95 Distance(Feet) 0 20 40 Scale in Feet Derry Dell Creek at 118th Court Streambank Stabilizaton and Outfall Repair Tigard, Oregon SLOPE STABILITY NOTES ANALYSIS RESULTS Ii 1. Critical failure surface estimated using the entry and exit search criteria DERRY DELL LANDSLIDE and the Spencer analysis method. , 2. See Figure 3 for stability analysis location. March 2017 24-1-04116-002 3. See report text for additional information about analyses and SHANNON&WILSON,INC. Geotechnical and Environmental Consultantsassumptions. FIG. 14 -III SHANNON &WILSON, INC. Attachment to and part of Report 24-1-04116-002 - Geotechnical and Environmental Consultants Date: May 17,2017 - To: Marjorie Wolfe Wolf Water Resources IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL/ENVIRONMENTAL REPORT CONSULTING SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES AND FOR SPECIFIC CLIENTS. Consultants prepare reports to meet the specific needs of specific individuals. A report prepared for a civil engineer may not be adequate for a construction contractor or even another civil engineer. Unless indicated otherwise,your consultant prepared your report expressly for you and expressly for the purposes you indicated. No one other than you should apply this report for its intended purpose without first conferring with the consultant. No party should apply this report for any purpose other than that originally contemplated without first conferring with the consultant. THE CONSULTANTS REPORT IS BASED ON PROJECT-SPECIFIC FACTORS. A geotechnical/environmental report is based on a subsurface exploration plan designed to consider a unique set of project-specific factors. Depending on the project, these may include: the general nature of the structure and property involved; its size and configuration; its historical use and practice; the location of the structure on the site and its orientation; other improvements such as access roads, parking lots, and underground utilities; and the additional risk created by scope-of-service limitations imposed by the client. To help avoid costly problems, ask the consultant to evaluate how any factors that change subsequent to the date of the report may affect the recommendations. Unless your consultant indicates otherwise,your report should not be used: (1)when the nature of the proposed project is changed (for example, if an office building will be erected instead of a parking garage, or if a refrigerated warehouse will be built instead of an unrefrigerated one,or chemicals are discovered on or near the site);(2)when the size,elevation, or configuration of the proposed project is altered; (3)when the location or orientation of the proposed project is modified; (4)when there is a change of ownership;or(5)for application to an adjacent site. Consultants cannot accept responsibility for problems that may occur if they are not consulted after factors which were considered in the development of the report have changed. SUBSURFACE CONDITIONS CAN CHANGE. Subsurface conditions may be affected as a result of natural processes or human activity. Because a geotechnical/environmental report is based on conditions that existed at the time of subsurface exploration,construction decisions should not be based on a report whose adequacy may have been affected by time. Ask the consultant to advise if additional tests are desirable before construction starts; for example,groundwater conditions commonly vary seasonally. Construction operations at or adjacent to the site and natural events such as floods,earthquakes,or groundwater fluctuations may also affect subsurface conditions and,thus,the continuing adequacy of a geotechnical/environmental report. The consultant should be kept apprised of any such events,and should be consulted to determine if additional tests are necessary. MOST RECOMMENDATIONS ARE PROFESSIONAL JUDGMENTS. Site exploration and testing identifies actual surface and subsurface conditions only at those points where samples are taken. The data were extrapolated by your consultant,who then applied judgment to render an opinion about overall subsurface conditions. The actual interface between materials may be far more gradual or abrupt than your report indicates. Actual conditions in areas not sampled may differ from those predicted in your report. While nothing can be done to prevent such situations, you and your consultant can work together to help reduce their impacts. Retaining your consultant to observe subsurface construction operations can be particularly beneficial in this respect. Page 1 of 2 1/2016 A REPORTS CONCLUSIONS ARE PRELIMINARY. The conclusions contained in your consultant's report are preliminary because they must be based on the assumption that conditions revealed through selective exploratory sampling are indicative of actual conditions throughout a site. Actual subsurface conditions can be discerned only during earthwork;therefore,you should retain your consultant to observe actual conditions and to provide conclusions. Only the consultant who prepared the report is fully familiar with the background information needed to determine whether or not the report's recommendations based on those conclusions are valid and whether or not the contractor is abiding by applicable recommendations. The consultant who developed your report cannot assume responsibility or liability for the adequacy of the report's recommendations if another party is retained to observe construction. THE CONSULTANTS REPORT IS SUBJECT TO MISINTERPRETATION. Costly problems can occur when other design professionals develop their plans based on misinterpretation of a geotechnical/environmental report. To help avoid these problems,the consultant should be retained to work with other project design professionals to explain relevant geotechnical,geological,hydrogeological,and environmental findings,and to review the adequacy of their plans and specifications relative to these issues. BORING LOGS AND/OR MONITORING WELL DATA SHOULD NOT BE SEPARATED FROM THE REPORT. Final boring logs developed by the consultant are based upon interpretation of field logs(assembled by site personnel),field test results, and laboratory and/or office evaluation of field samples and data. Only final boring logs and data are customarily included in geotechnical/environmental reports. These final logs should not,under any circumstances,be redrawn for inclusion in architectural or other design drawings,because drafters may commit errors or omissions in the transfer process. To reduce the likelihood of boring log or monitoring well misinterpretation,contractors should be given ready access to the complete geotechnical engineering/environmental report prepared or authorized for their use. If access is provided only to the report prepared for you,you should advise contractors of the report's limitations,asstiming that a contractor was not one of the specific persons for whom the report was prepared,and that developing construction cost estimates was not one of the specific purposes for which it was prepared. While a contractor may gain important knowledge from a report prepared for another party,the contractor should discuss the report with your consultant and perform the additional or alternative work believed necessary to obtain the data specifically appropriate for construction cost estimating purposes. Some clients hold the mistaken impression that simply disclaiming responsibility for the accuracy of subsurface information always insulates them from attendant liability. Providing the best available information to contractors helps prevent costly construction problems and the adversarial attitudes that aggravate them to a disproportionate scale. READ RESPONSIBILITY CLAUSES CLOSELY. Because geotechnical/environmental engineering is based extensively on judgment and opinion, it is far less exact than other design disciplines. This situation has resulted in wholly unwarranted claims being lodged against consultants. To help prevent this problem, consultants have developed a number of clauses for use in their contracts,reports,and other documents. These responsibility clauses are not exculpatory clauses designed to transfer the consultant's liabilities to other parties;rather,they are definitive clauses that identify where the consultant's responsibilities begin and end. Their use helps all parties involved recognize their individual responsibilities and take appropriate action. Some of these definitive clauses are likely to appear in your report,and you are encouraged to read them closely. Your consultant will be pleased to give full and frank answers to your questions. The preceding paragraphs are based on information provided by the ASFE/Association of Engineering Firms Practicing in the Geosciences,Silver Spring,Maryland Page 2 of 2 1/2016