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HomeMy WebLinkAboutPublic Comments submitted at hearings official hearing (2) Technical Review Geotechnical/Geologic Assessment and Addendum Capital Hill PUD Branch Engineering (Feb 6, and May 30, 2017) March 7, 2018 Prepared for: Capital Hill PUD Response Committee Laurel Hill Valley Neighborhood Association Fairmount Neighbors c/o Tom Bruno brunoassoc@aol.com TABLE OF CONTENTS Page INTRODUCTION..............................................................1 SLOPE MOVEMENT FEATURES MAPPED BY DOGAMI AROUND PUD..............2 SCARPS MAPPED BY APPLICANT’S ENGINEERING GEOLOGIST...................3 SLOPE MOVEMENT FEATURES MAPPED BY GEOSCIENCE........................3 INADEQUATE AND BIASED ASSESSMENT AREA................................4 CARELESS AND SHODDY WORK...............................................5 STRUCTURAL GEOLOGY AND THE DIP-SLOPE FAILURE ISSUE...................7 PUD DESIGN EXACERBATES EXISTING SLOPE STABILITY ISSUES................8 CONCLUSIONS AND RECOMMENDATIONS....................................10 LIST OF FIGURES Follows Page Context of PUD on LiDAR Hillshade Map...........................................2 Landslides in Vicinity of PUD Included on DOGAMI’s SLIDO Map......................2 Closer View of SLIDO Landslides in Immediate Vicinity of PUD.........................2 Branch Eng. Map of Scarps and Test Pit from Geotechnical Assessment....................3 Geomorphic Evidence of Slope Movement in Vicinity of PUD...........................3 Closer View of Slope Movements Mapped on Basis of Geomorphology....................3 Branch Test Pit Locations Relative to Mapped Geomorphic Features......................4 Scale Issue on Branch Area Slope Hazard Map........................................5 “No Build Area” on Entire Lots 18 & 19 on Branch Area Slope Hazard Map................5 Buildable Area on Lots 18 and 19 on Other PUD Maps.................................5 Location of Cross Section Shown on Next Figure......................................7 Dip-Slope Failure Concept.......................................................7 Slope Movements on Google Earth Image...........................................8 Proposed “Level Spreaders” Location Relative to Slope Movements.......................8 LIST OF APPENDICES Appendix A:Site Photos Appendix B:ASTM Method D-2488 (Visual Manual Procedure). ii Capital Hill PUD Geotechnical Review, GeoScience, Inc. 3/7/18 INTRODUCTION This report presents the results of a review of available information regarding the issues of slope stabilityand soil erosion in the area proposed for the Capital Hill PUD. The work included review of the applicant’s geotechnical consultant’s report (Branch Engineering 2/6/17) and an addendum to that report (Branch Engineering, 5/30/17), stormwaterplans for the PUD, published maps of landslides from DOGAMI, and original mapping of likely slope movement features in the vicinity of the PUD on LiDAR “hillshade” maps. The review was performed for the Capital Hill PUD Response Committee consisting of members of the Laurel Hill Valley Neighborhood Association and the Fairmount Neighbors. The review was conducted in its entirety by Dr. Gunnar Schlieder, an Oregon Certified Engineering Geologist with 29 years of experience working in the Eugene area. The review was tailored to address several portions of Eugene Code Chapter 9, including EC 9.6710 (Geological and Geotechnical Analysis) and EC 9.8320 (6) (TPUD Approval Criteria General -PUD will not present a risk to public safety...). At present it is unclear whether EC 9.6710 (Geological and Geotechnical Analysis) is applicable to the proposed development because the status as an Acknowledged Goal 5 Resource is unknown. On the one hand, the application addresses the approval criteria as if it were not included in the City’s Acknowledged Goal 5 Inventory and presents a map indicating that the subject propertyis not included. But on page 20 of the Staff Report staff indicates "...the subject property is included on the City’s acknowledged Goal 5 inventory, per the April 12,1978 Scenic Sites Working Paper... ". However, that working paper and its presumed map is not in evidence, and nowhere to be found on the City's web site. In fact, none of the information about Goal 5 resources on the City's web site includes the subject property. Judging from the title "Scenic Sites Working Paper" it would indicate that this was a preliminary document, and not officially adopted by City Council. EC 9.8320(6) Requires that: T he PUD will notbe a significant risk to public health and safety, including but not limited to soil erosion, slope failure, stormwater or flood hazard, or an impediment to emergency response. The Eugene Code is silent on the details of implementing this code provision but does address the issueof geotechnicalrisk and its assessment under EC 9.6710. If EC 9.6710 is not applicable, this leaves no guidance in the code on how to address the issue of geotechnical risk in the specific case of this PUD. Therefore, it appears that a prudent approach would be to at least use the provisions of EC 9.6710 as guidance. The applicant’s representatives apparently agree with this approach as they purport to have conducted the equivalent of a Level 2 Geotechnical Assessment per EC 9.6710. Therefore, this review addresses the geotechnical hazards of the site as relevant to both EC 9.6710 and EC 9.8320 (6). By necessity, the review focuses on the issues of slope stability and soil erosion which affect the planned PUD to a large degree. The applicable code sections are quoted as following: 1 Capital Hill PUD Geotechnical Review, GeoScience, Inc. 3/7/18 EC 9.6710 Geological and Geotechnical Analysis. (1) Purpose of Geological and Geotechnical Analyses: is to ensure that public and private facilities in developments in areas of known or potential unstable soil conditions are located, designed, and constructed in a manner that provides for public health, safety, and welfare. and EC 9.8320 (6) Tentative Planned Unit Development Approval Criteria - General (6) The PUD will not be a significant risk to public health and safety, including but not limited to soil erosion, slope failure, stormwater or flood hazard, or an impediment to emergency response. SLOPE MOVEMENT FEATURES MAPPED BY DOGAMI IN VICINITY OF PUD DOGAMI (Department of Geology and Mineral Industries) has mapped numerous apparent landslide features in the vicinity of the proposed Capital Hill PUD. This mapping is based partlyon geomorphic expression of slope movements in the area and partlyon field-verified reports of landslides which have occurred during the presence of white people in the area. The SLIDO (Statewide Landslide Inventoryand Database for Oregon) map can be accessed online at www.oregongeology.org/sub/slido/index.htm. DOGAMIis in the process of updating this mapping using newlyavailable LiDAR technology, which provides significantly better topographic information than was available with conventional topographic maps, however this update process has not yet been completed. The figure on the following page shows the larger vicinityof the Capital Hill PUD, from the area th of 30 Avenue in the south to nearly the bridge of I-5 over the Willamette River in the north. The base map was generated by GeoScience from a LiDAR DEM (Digital elevation Model) available from DOGAMI. The “hillshade map” was created through QGIS, a GIS program. The calculation of the shaded relief map was performed with the “virtual sun” located at an azimuth of 190 degrees (SSW) and 30 degrees up from horizontal. These angles were chosen to enhance geomorphic features on the steep east-facingslope of the ridge, which are in dark shadows if the conventional virtual illumination from the NW is utilized. The PUD is shown in dark pink. The following page includes the outlines of landslides mapped by DOGAMI. Whereas it is correct that the SLIDO map does not include landslides within the PUD itself, it does include two larger slope movements below the southeast portion and northeast corner of the proposed PUD, which are located less than 100' and 200' from the boundary of the PUD, respectively. Two smaller slides are indicated on SLIDO to be less than 150' from the PUD. It is interesting to note that the overwhelming number of landslides mapped in this area on SLIDO are located on east-facing slopes. The explanation for this phenomenon is provided in the section on “Dip-Slope Failure” below. 2 Capital Hill PUD Geotechnical Review, GeoScience, Inc. 3/7/18 SCARPS MAPPED ON PUD BY APPLICANT’S ENGINEERING GEOLOGIST Whereas the Staff report may be correct that no landslides are shown mapped on SLIDO on the proposed PUD itself, the blanket statement that no landslides were mapped there is patently false. The applicant’s own Engineering Geologist mapped two “scarps” within the PUD in what is now Lot 16, with one located in the vicinity of the proposed driveway and one a little farther downslope. “Scarps” are the steep slope segments that form the upper boundary of a moving landslide block as the sliding block drops and slides downslope. The presence of this landslide feature is th acknowledged by the applicant’s own geotechnical consultant in the 5/30/2017 Addendum (p.1, 5 paragraph): “One location in the southeast portion of the site was mapped as the upper section of a landslide area; subsequent site design omitted development in this area”. Whereas GeoScience agrees with the first part of this statement, the second part is incorrect. The current PUD design indicates that grading for the driveway for Lots 16 and 17 will occur directly on top of the upper scarp with the likely building area for Lot 16 located below the driveway. Therefore, the apparent building area for this lot will be located on top of a landslide the presence of which is acknowledged by the applicant’s geotechnical professional. No subsurface exploration was conducted in this area to define the problem (further discussion in “Inadequate and Biased Assessment Area”, below). SLOPE MOVEMENT FEATURES MAPPED BY GEOSCIENCE Given that DOGAMI’s update of the slope movement mapping in the area is not yet complete and, given our familiarity with the immediate area, GeoScience determined that it would be beneficial to conduct our own geomorphic mapping of probable slope movement features in the area. The figures on the following pages illustrate the results. Based on the geomorphology alone, it is quite clear that significant slope movements have occurred on the east-facing slope of the ridge in the recent geologic past. The outlines of these movements are shown in yellow. Scarps delineating the head of slides areshown with short lines attached on the downslope side of the outline of the movement. Areas with arrows indicate movement directions of the resulting landslide deposits. In most cases in the Eugene-Springfield area, slope movements initially consisting of sliding blocks, which tend to disintegrate with movementand turn into “earthflows”. These then form lobate landforms at the base of the slope which move downhill by soil creep and localized much more rapid movements of several feet to tens of feet within days. Such lobate forms are clearly discernible at the base of the steep east-facing slope of the ridge on which the PUD is proposed to be constructed. In the vicinity of Floral Hill Drive, the lobes exhibit uneven “hummocky” topography typical of landslide deposits. Moreover, in areas of the most recent and rapid movement, larger coniferous trees are absent, allowing for significant brush to cover the deposit, which causes minor problems with the LiDAR mapping. These areas are identifiable on the 3 Capital Hill PUD Geotechnical Review, GeoScience, Inc. 3/7/18 hillshade map by their “faceted” appearance. Movement directions of the lobes of the deposit are shown on the maps with arrows. However, it must be pointed out that GeoScience’s mapping within the PUD is based not only on LiDAR interpretation but also on observations during a visit to the PUD property in March of 2014. At the time, the PUD plans were in the very earlystages, and the layout of the PUD was as yet unknown. However, observations were made both of trees and exposures of the local rock (Eugene Formation) on the east-facing steeper slope in the eastern part of the proposed PUD property. In the areas shown as slope movements on the accompanying figures, coniferous trees are either affected significantly by movement or are absent, which can, in itself, be an indicator of movement. Whereas trees are affected by different types of movement, the effects for the different movement types aredifferent. Simple soil creep, caused by shrinking and swelling of expansive soil in this area generally results in long, sweeping downslope bends of the trunks as the base of the tree is rotated downslope and responds. In this case, many of the conifers (where present), show alternating bends in multiple directions (up-, down-, and side-slope) within single trunks. Examples of such deformation are shown in the site photos in Appendix A. Such deformation is typically associated with sliding movements of smaller portions of the slope. As the soil moves in smaller increments, the trees growing in the moving area are rotated, and then, when movement stops, the trees compensate for the rotation of the trunks. If the movement is too severe, the tree is killed, either by falling or disruption of its root system. It is notable that larger fir trees are relatively sparse in the steep areas on Lots 15, 16, and 17 and the adjoining “preservation area”. Trees are much denser on portions of Lots 13 and 14, which, according to the geomorphology are located in an area not recently affected by slope movements (see site photos). In those areas the trees show deformation attributable to soil creep only. In-place Eugene Formation is exposed in cuts made for both Capital Drive and also for the front yard of the residence at 2808 Capital Drive, located immediately S of the PUD property. At the latter location, the Eugene Formation consists of a fossiliferous (pelecypod-, or clam-fossils) fine- to medium-grained sandstone dipping eastward at a shallow angle. Given these observations on and near the site, it is apparent that there are at least two lines of evidence (geomorphic and tree evidence) that much of the east-facing slope of the ridge has been, and likely is, subject to slope movement (landslide) in the very recent geologic past. INADEQUATE AND BIASED ASSESSMENT AREA Given the plethora of evidence of existing large-scale slope movements both in the immediate vicinity as well as within the proposed PUD, it appears that a thorough investigation and definition of these movements would be appropriate to satisfy the requirements of both EC 9.6710 and EC 9.82320 (6). EC 9.6710 (4) and (5) require that subsurface exploration be conducted in all Tentative PUDs where the slope exceeds 10%. The applicant did perform some subsurface exploration using shallow backhoe or trackhoe test pits. In all, Branch Engineering excavated 10 test pits, the locations 4 Capital Hill PUD Geotechnical Review, GeoScience, Inc. 3/7/18 of which areshown on the figure on the followingpage. All test pits were located in the more gently sloping area at the top of the ridge. None of them were excavated on the steeper slopes or in the immediate vicinity of the landslide mapped by the applicant’s Engineering Geologist. The easternmost test pit (TP-5)was located on Lot 13 directly in the area between the two apparent slope movements affectingthe PUD. Even TP-8, which easily could have been placed at the mapped scarp on Lot 16, was placed around 100 feet from thereat the far (northern) boundary of Lot 15. No test pits at all were installed on the southernmost two lots despite significant geomorphic evidence of slope movement being present. No test pits at all were installed in the area later slated for installation of the storm-water discharge for much of the eastern half of the PUD. The 10 test pits describe an area that is on the order of 2.7 acres, which represents around 20% of the entire PUD’s area. Had these test pits all been located in the much steeper eastern portion of the site, they might have provided valuable information to address EC 9.6710 and EC 9.8320. However, as it is, the test pits were installed in the most gently sloping portion of the PUD and provide no information whatever regarding the issue of stability of the east-facing slope. This is clearly insufficient to satisfy both EC 9.6710 and EC 9.8320. CARELESS AND SHODDY WORK In addition to being conducted in over inadequate area most likely not to produce information potentiallydetrimental to the PUD’s design, both the field work itself (test pit logging) and its interpretation are abominably poor. The Branch Engineering Report indicates that ASTM Method D-2488 (Visual-Manual Procedure) was used to classify the soils encountered in the test pits according to the Unified Soil Classification System (USCS). This is a Standard Method used bymany geotechnical engineers. The pertinent pages from the ASTM Manual are included in Appendix B. However, there is scant evidence on the actual test pit logs that this method was actuallyapplied. There are no mention of dry strength tests, toughness values, dilatancy, sand sizes, etc. It would have been nice to have included at least some of these parameters in order for other professionals to verify that the method was indeed used and the classification is correct. On the other hand, the term used on Branch’s logs to describe the plasticityof the decomposed sandstone “slightly plastic” is not one of the options presented in Table 11 of the ASTM Method, which indicates that the plasticity is supposed to be described as “Nonplastic, Low, Medium, or High”. As a result, it is doubtful that a Standard Method was actually used to classify the soil according to the USCS as purported by Branch Engineering. This is all the more likely as the results of the Free 5 Capital Hill PUD Geotechnical Review, GeoScience, Inc. 3/7/18 Swell Tests conducted accordingto an Indian standard method indicate that much of the soil at the site is significantlyexpansive (Free Swell results ranging from 30 to 50%, with 3 of 4 samples in the 35 - 50% high range) . Expansive soils require the presence of expansive clay minerals, and none of the test pit logs make any mention of clay. The presence of clay is actually indicated in the USDA Soil Survey, which indicates that the soil in the area where the test pits were excavated (Philomath soil, # 108) consists of Lean Clay (CL) and Fat Clay (CH) soil rather than Silty Sand (SM). conducted, the use of the field data for conclusions As careless as the field work appears to have been is even worse. All test pit logs indicate that the test pits ended in variably decomposed “sandstone”, which is consistent with GeoScience observations. However, in the May 30, 2017 Addendum, on th page 1, 5 Paragraph, we find the following sentence: “The test pits and observations showed the majority of the development site was underlain by the stable volcanic rock material.” Both the report with the test pit logs and the addendum arestamped by Ron Derrick. P.E., G.E., a geotechnical engineer and Gary Sandstrom, a Certified Engineering Geologist. It is unfathomable to me how two professionals in the geologic/geotechnical field could classify sandstone as This is a Geology 101 question. “volcanic rock”. This incorrect classification may appear meaningless and without importance to a lay person, but in reality, the rock type and structure at this site have a significant influence on the stability of the slope. This is discussed further in the Section “Structural Geology and the Dip-Slope Failure Issue”, below. Additional errors are found on the “Area Slope Hazard Map” presented byBranch Engineering with the addendum on May 30, 2017. In the left-hand lower corner the map states: “Scale: 1" = 1000' (8.5" x 11")” The eastern boundary of the PUD is 2.43 inches long on the map. This would indicate that the PUD extends 2,439' in a N-S direction. This is incorrect. The PUD is only around half that long. That means that the actual scale of the map is apparently 1" = 500'. Of course that results in the landslides mapped by DOGAMI to be twice as close to the PUD as the map purports with its scale. Moreover, the “No Build” area on the map is significantly more inclusive than in the other PUD plans. Whereas the applicant’s “hazard map” shows that all of Lots 18 and 19 are to be included in the “No Build” area, the PUD plans show buildable area in the upper half of the . Given the steepness of the slope on these lots (up to 73% in the buildable area), the “No Build” lots designation appears appropriate. But non-conservatively, this was not considered in the PUD plans. 6 Capital Hill PUD Geotechnical Review, GeoScience, Inc. 3/7/18 STRUCTURAL GEOLOGY AND THE DIP-SLOPE FAILURE ISSUE As discussed above, under the previous section, the applicant’s geotechnical consultants misidentify the rock type underlying the PUD, assuming that the ridge is underlain by igneous rock, when, in realityit is underlain by sedimentary rock. However, this is a very important distinction. The sedimentary rock making up the ridge consists of the Eugene Formation which is a shallow marine deposit made up not only of sandstone, but a complex rock unit consisting of interbedded sandstone, siltstone, claystone, and weathered volcanic ash beds. Throughout the Eugene/Springfield area, these bedded sedimentaryrocks dip generally to (are inclined toward) the east. Based on the observations in the front yard of 2808 Capital Drive, the easterly dip is true in this vicinity also. The result is similar to a stack of cards tilted in an eastward direction. Planes of weakness caused either by the bedding in therock or by weak beds themselves, such as clayeydecomposed ash layers, are much more likely to slide in a direction parallel to the eastward-inclined bedding than westward, where failures are forced to break through the package of bedded rocks (seefigure on the next page). This is reflected in the DOGAMI SLIDO map of the larger area, where clearly the majority of the mapped slides originate on east-facing slopes. This propensity for east-facingslopes to be less stable than west-facingslopes is caused not only by inclined planes of weakness, but also by groundwater flow and discharge areas. Precipitation falling onto the entire ridge partially sinks into the ground and some of it infiltrates into more permeable beds in the rock (e.g. sandstone), flowing initially downward, until it encounters an impermeable stratum (e.g. siltstone or claystone). Because this stratum will be following the general eastward- dipping trend, the water then “runs down-dip” on top of the impermeable unit. In this manner, not only water fallingon the east-facing slope of the ridge will be transmitted to base of that slope, but also some water fallingon the west-facing slope of the ridge. Where this water exits the rock underlying the slope on the east-facing slope, it emerges as seeps. If the rock in that vicinityis covered with an impermeable clayey soil layer, the water will build up in the rock until the pressure is sufficient to either break through the soil layer or dislodge portions of the soil layer by reducing the friction holding them in place in manner very similar to the oil pressure in a car’s engine. This results in sliding of portions of the slope. Such “excess pore pressure” is very likely responsible for most of the multitude of slope movements on east-facing slopes of the hills in the Eugene- Springfield area. The applicant’s geotechnical assessment either does not recognize this fact (as indicated bythe remark regardingthe presence of “stable volcanic rock”) or ignores the presence of the dip slope and fails to investigate the portion of the PUD most sensitive to dip slope failures in an area where groundwater could develop significant pore pressures. Instead, the subsurface exploration was limited to the low-sloping area at the top of the ridge. 7 Capital Hill PUD Geotechnical Review, GeoScience, Inc. 3/7/18 PUD DESIGN EXACERBATES EXISTING SLOPE STABILITY ISSUES Given that the assessment has been conducted in a manner which is both slip-shod and intentionally limited to the areas of the PUD most likely to be without slope stability issues, the design is seemingly unfettered by geotechnical constraints. Whereas it might be possible to design the PUD to effectively address these real issues, its current design exacerbates existing slope stability problems. Parts of the infrastructure (mostlythe driveways to lots 8/9, 16/17 and 19/20) and the building pads for lots 8 through 19 will be located along the top of the steep east-facing slope. On these twelve lots, the slope of the proposed buildable area ranges from 40 to 73(!) %, with an average of 56%. The result is that fill embankments will need be placed at the top of the steep slope, which, in some cases will be designed with slopes to 1.5H : 1V (67%), which is in itself quite “optimistic”. Normally, fill slopes are designed to not exceed 2H : 1V. The excessively steep fill slopes are employed here to limit the eastward and downslope extent of the toe of the fills which would likely reach the eastproperty line of the PUD or even the Ribbon trail if installed at appropriately conservative slope angles. However, even the 1.5H : 1V slope angle will not suffice at Lots 18 and 19 to achieve a catch point within the confines of the buildable envelope for any fill. In essence, constructing fills in the upper portions of the east-facing slope results in loading the top of the slope, which increases driving force. Given that there are already indications both on and immediately adjacent to the PUD property that this slope is undergoing slope failure, it is quite clear that any adverse change to the equilibrium will result in re-activation of existing slope movements or generation of new ones. However, not only does the PUD as currently designed increasethe driving force at the top of This the slope, but it also decreases the resting force in at least one area at the toe of the slope. will occurin the area immediately east of the SW corner of Lot 13 and the SE corner of Lot 14, where the two 38-ft. level spreaders are proposed to be located. Per the proposed plan these storm water discharge systems are to dispose of the storm water which is generated from most of Cupola Drive and the 19 or 21 lots adjacent to it (Lots 7 – 17, 33, 34, and 27 – 32, plus possibly Lots 18 and 19). The Level Spreaders are proposed to be designed for a maximum discharge of 0.16 cfs (cubic feet per second) each for a total discharge of 0.32 cfs over an approximately 70-ft. wide stretch of slope. While this doesn’t seem like a large number, one must consider the units used. One cubic foot is 7.48 gallons, and there are 60 seconds in a minute. As a result, this seemingly small number is actually 144 gallons per minute. In comparison, a garden hose runningat full capacity is around 5 gpm. Therefore, the design discharge of these two level spreaders is the equivalent of nearly 29 garden hoses running full bore. And all of this water is discharged onto a segment of 50% slope that is located 104’ from the Ribbon Trailand above several residences along Floral Hill Drive (see figures on the following pages). It is impossible to see how this design: Does not result in severe soil erosion and running muddy wateronto and across the Ribbon A) Trail; and Does not result in a localized increase in pore pressures near the base of the steep slope. B) 8 Capital Hill PUD Geotechnical Review, GeoScience, Inc. 3/7/18 As far the second point is concerned, addingwaterto an already unstable slope is NEVER a good idea. And in this case, the discharge is proposed to occurdirectly above the larger of the two active slides mapped by DOGAMI below the central portion of the proposed PUD. That slide is mapped less than 200’ from the proposed location of the level spreaders. According to their geotechnical assessment report and addendum, it appears that Branch Engineering did not perform assessment of the conditions at or below the proposed location of the level any spreader stormwater discharge point. Therefore, the only information that can be utilized is DOGAMI’s map, which clearly indicates a slide directly below the discharge point. Of course, since DOGAMI’s map was generated mostly using remote sensing techniques, it is likely that they missed other slide areas in the immediate vicinity of this dip-slope system. So it is unlikely that therewill be any area along the eastern boundary of the proposed PUD where it would be appropriate to use this method of stormwater discharge. 9 Capital Hill PUD Geotechnical Review, GeoScience, Inc. 3/7/18 CONCLUSIONS AND RECOMMENDATIONS Conclusions The field work conducted for the Geotechnical/Geologic Assessment of the Capital Hill PUD by Branch Engineering does not satisfy the requirements of EC 9.6710 (5)(b) or (4)(c), in that it: 1.The subsurface exploration was conducted on 20% or less of the subdivision property. 2.The subsurface exploration did not extend into the areas most likely to be subject to slides. 3.The field work cannot be shown to have been conducted according to Standard Methods. The report on the assessment and its addendum contain numerous errors, all of which make it appear that the area is safer and more stable than it is in reality. 4.The addendum presents that the PUD will be constructed on “stable volcanic rock”, when, in reality, the site is underlain by an east-dipping sedimentary rock assemblage. 5.The scale of the “Area Slope Hazard Map” makes nearby DOGAMI-mapped slides appear twice as far from the PUD as they are in reality. 6.That same map indicates that lots 18 and 19 are located entirely within the “No Build Area”. The subdivision plans indicate otherwise. 7.Independent mapping of the area using state-of-the-art LiDAR hillshade maps and on-site tree evidence indicates that significant portions of the eastern part of the PUD have been and are subject to landslides. The PUD’s design also fails to satisfy the requirements of EC 9.8320 (6): 8. The design of the subdivision, with fills in the upper portion of the steep east-facing slope and concentration of storm-water in the pore-pressure sensitive lower portions of the site combine to both increase driving forces for slides at the top of the slope and decrease resisting forces at the bottom. In a system alreadysubject to slope movements this will have a highly destabilizing effect. 9. The level spreaders proposed to be employed to discharge the storm-water from the eastern portion of the PUD aredesignedto dump 144 gallons per minute of water on a slope with a gradient of 50%. This is the equivalent of about 29 garden hoses running full bore and will result in mud and water running across the Ribbon Trail. From there, the waterwill run directly into a landslide mapped by DOGAMI and then continue to several residences along Floral Hill Drive. 10.The professionals who prepared the Geotechnical/Geologic Assessment appear to either not understand the local geologic system, or not to care, placing the interests of the developer ahead of the people along portions of Floral Hill Drive in the Laurel Hill Valley who will be the recipients of both the storm-water discharge and potentially resulting landslides of various forms. 10 Capital Hill PUD Geotechnical Review, GeoScience, Inc. 3/7/18 CAPITAL HILL PUD Geotechnical Assessment Review By Gunnar Schlieder, Ph.D., CEG REVIEW INCLUDED: Branch Engineering: Geotechnical/Geologic  Assessment Capital Hill PUD (2/6/17) Branch Engineering: Addendum to above  (5/30/17) DOGAMI Publications  LiDAR Interpretation  Field Observations  REVIEW ADDRESSES: EC 9.6710 (Geologic and Geotechnical Analysis)  EC 9.8320 (6) (TPUD Approval Criteria –General)  PUD will not be a risk to public health and safety…  CONTENT: Review of Published Landslide Data • Interpretation of LiDAR Maps • Problems with the Applicant’s Work • Field Work Issues • Interpretation Issues • Other Issues • The Real Issue • The PUD makes it worse! • PUBLISHED LANDSLIDE MAPS DOGAMI SLIDO LIDAR INTERPRETATION This is my own interpretation. PROBLEMS WITH APPLICANT’S WORK A. Issues with the Field Work INADEQUATE AND BIASED COVERAGE Area Assessed: 2.7 Acres = 20% of PUD Area. Insufficient! Not Only Insufficient! Only Assessed the Low-sloping Portion of the PUD. No Assessment of the Steep East- facing Slope! No Assessment of Area with Indications of Landslides! Biased! ISSUES WITH METHODOLOGY Report States that ASTM Method D-2488 was Used for Soil Classification. The Test Pit Logs Indicate Otherwise. “Slightly” plastic is NOT a Valid Outcome of Using this Method. BUT THERE ARE BIGGER ISSUES WITH THE INTERPRETATION! According to the Logs, EVERY Test Pit Found “Sandstone”. SINCE WHEN IS “SANDSTONE” A VOLCANIC ROCK???? The Report and Addendum BOTH Were Stamped by a Geotechnical Engineer and a Certified Engineering Geologist. This is a Geology 101 Mistake! You Might Ask “So What? Why Does That Matter?” We’ll Get to That… THE DIP-SLOPE FAILURE ISSUE Remember the Sandstone vs Volcanic Rock? It matters because Sedimentary Rocks are usually BEDDED and Volcanic Rocks Aren’t. Except at Rattlesnake Ridge in WA. Which is currently sliding. But that’s a digression. THE PROPOSED PUD WILL MAKE THINGS WORSE! Fills will be added to the top of the steep  Slope. This increases driving forces. Water will be concentrated at the bottom of  the steep slope. This decreases resisting forces. YOU MAY SAY IT’S ONLY 0.32 CFS But how much is that really? 1 cfs= 7.48 gallons. There are 60 seconds in a minute 0.32 x 7.48 x 60 = 144 gpm Equivalent to 29 garden hoses running full bore. Onto a 50% slope. 100’ from Ribbon Trail Above a landslide mapped by DOGAMI! EC 9.6710: The field work conducted for the Geotechnical/Geologic Assessment of the Capital Hill PUD by Branch Engineering does not satisfy the requirements of EC 9.6710 (5)(b) or (4)(c), in that: 1.The subsurface exploration was conducted on 20% or less of the subdivision property. 2.The subsurface exploration did not extend into the areas most likely to be subject to slides. 3.The field work cannot be shown to have been conducted according to Standard Methods. The report on the assessment and its addendum contain numerous errors, all of which make it appear that the area is safer and more stable than it is in reality. 4.The addendum presents that the PUD will be constructed on “stable volcanic rock”, when, in reality, the site is underlain by an east-dipping sedimentary rock assemblage. 5.The scale of the “Area Slope Hazard Map” makes nearby DOGAMI-mapped slides appear twice as far from the PUD as they are in reality. 6.That same map indicates that lots 18 and 19 are located entirely within the “No Build Area”. The subdivision plans indicate otherwise. 7.Independent mapping of the area using state-of-the-art LiDAR hillshademaps and on-site tree evidence indicates that significant portions of the eastern part of the PUD have been and are subject to landslides. EC 9.8320 (6) The PUD’s design also fails to satisfy the requirements of EC 9.8320 (6): 8. The design of the subdivision, with fills in the upper portion of the steep east-facing slope and concentration of storm-water in the pore-pressure sensitive lower portions of the site combine to both increase driving forces for slides at the top of the slope and decrease resisting forces at the bottom. In a system already subject to slope movements this will have a highly destabilizing effect. 9. The level spreaders proposed to be employed to discharge the storm-water from the eastern portion of the PUD are designed to dump 144 gallons per minute of water on a slope with a gradient of 50%. This is the equivalent of about 29 garden hoses running full bore and will result in mud and water running across the Ribbon Trail. From there, the water will run directly into a landslide mapped by DOGAMI and then continue to several residences along Floral Hill Drive. 10.The professionals who prepared the Geotechnical/Geologic Assessment appear to either not understand the local geologic system, or not to care, placing the interests of the developer ahead of the people along portions of Floral Hill Drive in the Laurel Hill Valley who will be the recipients of both the storm-water discharge and potentially resulting landslides of various forms. THERE CAN ONLY BE ONE RECOMMENDATION: TheTentativePUDapplicationfortheCapitalHillPUD mustbedeniedbecausetheGeotechnical AssessmentfailstosatisfyEC9.6710(4)(b)and(5)(b) andthePUD’sdesignfailstosatisfyEC9.8320(6).