To: Garth Oksol P.E. From: Randy Reynolds RTC. File: Date: November 6, 2008 Revised January 14, 2009

Transcription

1 Memo To: From: Randy Reynolds RTC File: Date: November 6, 2008 DESIGN MEMORANDUM: Task B.3 Geotech Reference: Geotechnical Feasibility Investigation - Plan Line Study for the SouthEast Connector Stantec Consulting was retained by RTC of Washoe County to perform a plan line study for the SouthEast Connector project. The initial phase of this project consists of refining the location of the roadway corridor within an approximate 1500 foot corridor width. The objective of the geotechnical feasibility investigation is to determine soil, bedrock, and groundwater conditions in this corridor area and provide information on potential construction difficulties to assist in determining the optimum location of the roadway. Geotechnical information for this study is based on existing soils/groundwater information from previous studies including the corridor study for the Tahoe-Pyramid Link completed by SEA Engineers in the early 1980 s. No additional subsurface explorations were performed for this investigation. This design memorandum addresses Task B.3 - Geotechnical Feasibility Investigation of the Corridor Study Area. This investigation will be completed with the following information: 1. Compilation of existing soils/groundwater information within the corridor area; 2. Discussion of predominant soils/bedrock types and approximate groundwater depths within the corridor area; 3. Summary of seismic conditions including major fault systems that may influence major structure design, soil liquefaction potential, and lateral spread; 4. Summary of geologic hazards including rock fall and slope stability potential; 5. Discussion of available embankment and stabilizing fill material; 6. A discussion of potential design and construction difficulties including subgrade soil stability issues and bedrock excavation. The geotechnical investigation for the SouthEast Connector project will be completed in three different phases: corridor study feasibility investigation (current investigation), preliminary geotechnical investigation, and final geotechnical investigation. The preliminary investigation will be for the entire corridor, while the final geotechnical investigation will be completed with each construction phase, if more than one, of the project. V:\52801\active\ \report\Final Report\6_Appendix A - Geotechnical Investigation\SE Conn_memo_RTC_RAR_ doc

2 Page 2 of 21 The area covered by this investigation is shown on Plates 1A to 1C in Appendix A. 1.0 PROJECT DESCRIPTION The SouthEast Connector is proposed to extend from the intersection of US 395 and State Route 431 (Mount Rose Highway) to the intersection of Sparks Boulevard and Greg Street. The segment of the SouthEast Connector that will be investigated with this study extends from the intersection of South Meadows Parkway and Veteran s Parkway to the intersection of Sparks Boulevard and Greg Street for a total length of about 5 ½ miles. The remaining southern portion of this roadway that extends from the intersection of US 395 and State Route 431 (Mount Rose Highway) to South Meadows Parkway has been completed. The SouthEast Connector will be a high access control arterial roadway consisting of potentially 6 travel lanes (3 travel lanes in each direction). The initial construction phase of the roadway may include 2 travel lanes in each direction. Additional lanes may be constructed depending on the development of traffic volumes. Several water way crossings including Steamboat Creek, Boynton Slough, and the Truckee River are anticipated. A viaduct, or elevated roadway above the existing ground surface, will be constructed over the Truckee River floodplain corridor area that may extend from Greg Street to Cleanwater Way. To provide a reference for this geotechnical feasibility investigation, the corridor area was divided into 4 different roadway segments as presented in Table 1. TABLE 1 - ROADWAY SEGMENTS Roadway Segments Location 1 South Meadows Parkway to Alexander Lake Road. This segment of the roadway extends northward from South Meadows Parkway to the physiographical area known as Huffaker Narrows. A detention dam is proposed to be constructed at Alexander Lake Road. 2 Alexander Lake Road to Mira Loma Drive. This roadway segment extends through the Butler Ranch area. 3 Mira Loma Drive to Pembroke Drive. This portion of the corridor extends through the Rosewood Lake Golf Course. 4 Pembroke Drive to Greg Street. The majority of this segment of the corridor extends through the University Farms area.

3 Page 3 of Site Conditions The proposed roadway corridor is located at the base of the western flank of the Virginia Range within the east-central portion of the Truckee Meadows. Based on a regional topographic map, the proposed corridor area slopes gently to the north with a slope gradient of about 2 to 3 percent. Several existing roadways cross the corridor area: Alexander Lake Road, Mira Loma Drive, Pembroke Drive, and Cleanwater Way. Specific site conditions will be discussed for the different roadway segments in Sections 2.1 to Roadway Segment #1 - South Meadows Parkway to Alexander Lake Road This roadway segment is primarily located between Huffaker Hills to the west and the Virginia Range to the east. Steamboat Creek is located within the central portions of this area flowing in a northerly direction to the Truckee River. Steamboat Creek represents the topographic lowpoint in this segment of the roadway corridor and the topography appears to gently slope toward Steamboat Creek from either side of the valley. Active borrow pits are located near this roadway segment (refer to Section ). Formerly irrigated fields were located in this area and vegetation consists of thick grasses and small bushes. Picture #1 shows the roadway corridor south of Alexander Lake Road. Picture #1- Looking south along the proposed corridor area from Alexander Lake Road 2.2 Roadway Segment #2 - Alexander Lake Road to Mira Loma Drive The majority of this corridor area is located between Huffaker Hills to the west and the Virginia Range to the east. Picture #2 shows a gently sloping alluvial fan that extends into the roadway

4 Page 4 of 21 corridor originating from the Virginia Range. The alluvial fan is located within the southern portion of this segment of the roadway. Steamboat Creek is located at the base of the alluvial fan and flows northward along the base of the low-lying hillsides of the Virginia Range. Picture #2 - Looking north along the proposed corridor area from Alexander Lake Road Vegetation consists of scattered grasses and small bushes within the southern end of this roadway segment and thick grasses and small bushes within the northern end. Picture #3 shows the roadway corridor looking south of Mira Loma Drive. Prominent rock outcrops are also shown in the hillsides east of the corridor area. Picture #3 - Looking south along the proposed corridor area from Mira Loma Drive

5 Page 5 of Roadway Segment #3 - Mira Loma Drive to Pembroke Drive This segment of the roadway traverses through Rosewood Lakes Golf Course along the west side of the Hidden Meadows Residential area. Rosewood Lakes Golf Course is located west of Steamboat Creek. Picture #4 shows the southern portion of this roadway segment east of Steamboat Creek. This area is relatively flat with moderately thick vegetation consisting mostly of small bushes. Residences are shown in the background, which appear to be elevated approximately 10 feet above the proposed corridor grade. Picture #4 - Looking north along the proposed corridor area from Mira Loma Drive Toward the northern end of this roadway segment, Boynton Slough, which originates west of the corridor area, intersects with Steamboat Creek. Picture #5, looking south of Pembroke Drive, shows the confluence area of these water ways.

6 Page 6 of 21 Picture #5 - Looking south along the proposed corridor area from Pembroke Drive 2.4 Roadway Segment #4 - Pembroke Drive to Greg Street The southern portion of this roadway segment is located within formerly irrigated fields along the base of the Hidden Valley residential area. As shown in picture #6, this area is relatively flat and consists of patchy areas devoid of vegetation, barbed-wire fences, and isolated residences. Steamboat Creek flows in a meandering pattern along the base of the Virginia Range before intersecting with the Truckee River. Vegetation consists of scattered bush and grasses with isolated trees. Picture #6 - Looking north along the proposed corridor area from Pembroke Drive

7 Page 7 of 21 Cleanwater Way is located within the central portions of this roadway segment. Picture #7 shows the view south of Cleanwater Way, which shows thick grasses and localized barbed-wired fences. Picture #7 - Looking south along the proposed corridor area from Cleanwater Way Picture #8 was taken from Cleanwater Way on the existing bridge over Steamboat Creek and shows irrigated fields within the University Farms area. The banks of Steamboat Creek in this area have estimated heights of 7 to 10 feet. The roadway corridor extends through University Farms, over the Truckee River, and intersects with Greg Street. The banks of the Truckee River have a height of about 15 feet. An existing paved walking path is located at the top of the northern bank of the river. Picture #8 - Looking north along the proposed corridor area from Cleanwater Way

8 Page 8 of Compilation of existing soils/groundwater information within the corridor area The determination of existing geotechnical and groundwater conditions within the corridor was derived from several sources including existing geologic maps and an corridor study for the Tahoe-Pyramid Link completed by SEA Engineers in The following documents were reviewed for this investigation: Geologic Map, Vista Quadrangle, Nevada Bureau of Mines and Geology, Geologic Map, Steamboat Quadrangle, Nevada Bureau of Mines and Geology, Tahoe/Pyramid link Corridor Study, SEA Engineers, Preliminary Geotechnical Investigation Bella Vista Ranch, Matrix Construction Services Inc., The Tahoe Pyramid Link Alignment Study, 1983, included preliminary exploration of that roadway alignment with both exploratory test pits and borings. The exploratory test pits allow for a more detailed geologic description of the upper portion of the geotechnical profile than the exploratory borings. The exploratory borings were completed in areas where heavy structures such as bridges or large culverts were anticipated. No additional subsurface investigation was conducted as part of this geotechnical feasibility investigation. The approximate locations of the test borings and test pits for the 1983 study are shown on Plates 1A to 1C in Appendix A. Logs of the test borings and test pits are presented as Plate 2 Logs of Test Borings/Pits. Sections 4 and 5 describe the field exploration and laboratory testing for that exploration study. 4.0 Exploration 4.1 Test Pits As part of the 1983 alignment study, a series of 46 exploratory test pits were excavated at approximate 1000 foot centers. Twenty-five (25) of those exploratory test pits are within the current study area and are included in this report. The maximum depth of the exploratory test pits was 10 feet. 4.2 Drilling A total of ten (10) exploratory borings were reported with the 1983 alignment study. Four (4) exploratory borings were drilled with the 1983 alignment study, and six (6) borings were provided from an investigation for the Reno-Sparks Joint Sewer Treatment Plant in The borings were drilled using 6-inch-outside-diameter (O.D.), 3-¼ inch-inside-diameter (I.D.) continuousflight augers. The maximum depth of exploration was 43 feet below the existing ground surface. The native soils were sampled in-place every 2 to 5 feet by use of a standard 2-inch OD splitspoon sampler driven by a standard 140-pound drive hammer with a 30-inch stroke. The number of blows to drive the sampler the final 12 inches of an 18-inch penetration into undisturbed soil provides an indication of the density or consistency of the material.

9 Page 9 of LABORATORY TESTING 5.1 Index Testing Samples of significant soil types were analyzed in the 1983 investigation to determine their in situ moisture content (ASTM D 2216), grain size distribution (ASTM D 422), and plasticity index (ASTM D 4318) with the results of these tests presented in Appendix B. 5.2 R-value Testing A total of 9 resistance value tests (ASTM D 2844) were performed on representative samples of subgrade soils. R-value testing is a measure of subgrade strength and expansion potential that can be correlated with resilient modulus and used in design of flexible pavements. Results of the R-value tests are presented in Appendix B. 6.0 REGIONAL PHYSIOGRAPHIC SETTING The Truckee Meadows is located along the western margin of the Basin and Range physiographic province and the eastern border of the Sierra Nevada physiographic province. One of a series of north-trending basins in northwestern Nevada, the Truckee Meadows are bordered on the west by the Carson Range, a spur of the Sierra Nevada s, on the Southeast by the Virginia Range, and on the northeast by the Pah Rah Range (Cohen and Loeltz, 1964). The Wedekind Hills trend northerly from north of the Truckee Meadows and Peavine Mountain stands to the northwest. Northeast-southwest trending volcanic bedrock forms the Huffaker Hills, the boundary between the lower and upper (southern) Truckee Meadows. The ranges bordering the Truckee Meadows area are deeply dissected, complex, fault-block mountains composed of igneous, metamorphic, and sedimentary rocks. These ranges have been broken into troughs and ridges by normal faults. The Sierra Nevada and the subordinate Carson Range consist largely of granodiorite and other granitic rocks emplaced into complex sequences of metamorphic bedrock. However, southwest of the Truckee Meadows, the Carson Range consists primarily of volcanic bedrock. The Virginia Range, Pah Rah Range, Wedekind Hills, and Huffaker Hills differ from the main Carson Range in that they are composed of a higher percentage of volcanic rocks. Topographic relief of the mountains resulted principally from uplift and warping associated with movement along normal faults, however, internal structure, volcanism, erosion, and sedimentation were also major factors in the formation of the present land forms (Cohen and Loeltz, 1964). The valleys are structural depressions that are partially filled with unconsolidated and partially consolidated subaerial and lacustrine deposits. Valley-fill alluvium in the Truckee Meadows was estimated to be greater than 1,000 feet thick (Thompson and Sandberg, 1958). The Truckee River, the principal stream/water course in the area, has its headwaters in the Sierra Nevada s south of Lake Tahoe. Flowing eastward out of the mountains, the river follows a meandering course eastward through the Truckee Meadows and discharges from the valley through a narrow, steep-walled canyon between the Virginia and Pah Rah Ranges.

10 Page 10 of GEOLOGIC AND GENERAL SOIL CONDITIONS Sedimentation in the Truckee Meadows has been in progress at varying rates since the formation of the block faulted basin. Most of the sediments, including the coarse grain, gravelly sands that underlie the majority of the Truckee Meadows, were deposited quite abruptly in the post-glacial period during torrential flooding. With the advent of a warm, drier climate, the volume and size distribution of sediment transported was greatly reduced and the sedimentation process became largely limited to the reworking of earlier deposits. A review of the referenced geologic maps for the Steamboat and Vista Quadrangles indicates that the roadway corridor lies within flood plain deposits of the Truckee River and Steamboat Creek. These deposits primarily consist of fine-grained sands with variable quantities of silt or clay and localized zones of organics. Geologic conditions presented are primarily based on field exploration performed with the previously referenced 1983 Tahoe-Pyramid Link Study and will be discussed separately for each of the different roadway segments. 7.1 Roadway Segment #1- South Meadows Parkway to Alexander Lake Road The geotechnical profile within this roadway segment is primarily derived by floodplain deposits from Steamboat Creek. Alluvial fan deposits from adjacent hillsides are also interfingered with these floodplain deposits. Consequently, the soils within this roadway segment are highly variable and complexly interbedded. The different soil types encountered consist of clayey sands, silty sands, poorly graded sands, sandy silts, and sandy clays. Individual soil layers range in thickness from a few inches to 6 feet. The thicker fine-grained layers are located toward Huffaker Narrows near Alexander Lake Road. An exploratory boring was drilled to approximately 40 feet at Alexander Lake Road. The upper portions of the geotechnical profile encountered generally consisted of medium stiff to stiff sandy clays to a depth of 30 feet below the existing ground surface. Below 30 feet, to the depth of exploration, medium dense gravelly sands to poorly graded sands were encountered. Based on SPT blow counts, the relative density of the granular soils was loose to medium dense and the consistency of fine-grained soils was medium stiff to stiff. 7.2 Roadway Segment #2 - Alexander Lake Road to Mira Loma Drive This segment of roadway is located within a closed basin area, which predominantly collected fine-grained floodplain deposits. Based on this depositional environment, the geotechnical profile encountered primarily consisted of lean clays with sand and sandy silts to the depth explored of approximately 10 feet below the existing ground surface. Fine-grained soils were overlain by a veneer of poorly graded sands in localized locations. The referenced preliminary geotechnical investigation by Matrix Construction Services indicates similar soil conditions as encountered with the previous 1983 study. Their investigation also included drilling an exploratory boring to depths of 20 feet below the existing ground surface. A granular soil profile was encountered consisting primarily of poorly graded sand with clay and poorly graded gravels with sand and clay from a depth of 10 to 20 feet below the existing ground surface.

11 Page 11 of 21 Near Alexander Lake Road the corridor may traverse alluvial fans and bedrock outcrops. Alluvial fans generally consist of coarse-grained granular soils comprised of silty sands with gravels. The bedrock consists of volcanic breccias and mud flows of the Tertiary Period Kate Peak Formation. The volcanics are exposed as both massive rim rocks and rounded, weathered bedrock hills. 7.3 Roadway Segment #3 - Mira Loma Drive to Pembroke Drive The geotechnical profile encountered is generally similar to the soils encountered for Roadway Segment #2. The geotechnical profile primarily consisted of fine-grained floodplain deposits; however, within several exploratory test pits, fine-grained soil deposits were encountered interbedded with granular soil layers. Fine-grained soil deposits primarily consist of lean clays with sand and sandy silts to the depth explored. Granular interbedds consist of silty sands and clayey sands. An exploratory boring was drilled to approximately 40 feet at Pembroke Drive. The upper portions of the geotechnical profile encountered generally consisted of slightly stiff to stiff sandy silt to depths of about 15 feet below the existing ground surface. Below 15 feet to the depth of exploration, dense to very dense gravelly sands to poorly graded sands were encountered. 7.4 Roadway Segment #4 - Pembroke Drive to Greg Street During the 1983 study, this roadway segment was explored by both exploratory test pits and borings. Exploratory borings were drilled within the roadway corridor north of Cleanwater Way and the exploratory test pits were excavated between Cleanwater Way and Pembroke Drive. Eight exploratory borings were drilled to depths ranging from 25 to 35 feet. In general, the geotechnical profile encountered can be characterized as three different soil horizons. The uppermost soil horizon consisted of sandy silts to depths of about 8 to 13 feet below the existing ground surface. Below these depths, to approximately 25 feet below the existing ground surface, medium dense silty sands were encountered. The lowermost soil horizon encountered consisted of medium dense to very dense gravelly sands to poorly graded sands. Complexly interbedded fine-grained and granular soils deposits were encountered between Cleanwater Way and Pembroke Drive. The geotechnical profile is influenced by both alluvial fan material deposited from the adjacent hillside and floodplain deposits from a meandering segment of the Steamboat Creek. This geomorphic environment accounts for the complex interfingering of fine grained and granular soils. Fine grained soils consisting of sandy silts to sandy clays were generally encountered within the upper 1 to 2 feet of the profile. Granular soils consisting of silty sands to poorly graded sands were generally encountered below 2 feet with thicknesses ranging from 4 to 8 feet. 8.0 GROUNDWATER CONDITIONS Groundwater levels were measured at the exploratory locations completed with the referenced investigations and should be considered approximate, especially since the measurements were obtained in It should be understood that fluctuations in the water table may occur due to rainfall, temperature, seasonal runoff or adjacent irrigation practices. Consequently, the

12 Page 12 of 21 groundwater elevation may change from the levels measured during field exploration. Construction planning should be based on assumptions of possible variations. If desired, more accurate groundwater levels could be assessed by installing peizometers and monitoring the groundwater levels. However, the proposed roadway corridor area is located near existing open water courses such as the Boynton Slough or Steamboat Creek and the groundwater level elevations will likely be close to the water levels present within these water courses. Groundwater levels measured as part of the referenced 1983 study are presented in Table 2. TABLE 2 - MEASURED GROUNDWATER TABLE LEVELS Roadway Segments Groundwater Levels 1 1 The groundwater table is generally shallow and ranged from about 2 ½ to 4 feet below the existing ground surface. 2 The groundwater table is generally shallow and ranged from about 1 to 6 feet below the existing ground surface within the basin area. Within the alluvial fan area, the groundwater table was not encountered at a depth of 10 feet below the existing ground surface. Groundwater levels encountered by Matrix Construction Services Inc. in 2005 ranged from 2 to 6 feet in this area. 3 The groundwater table was encountered at a depth ranging from 1 to 10 feet below the existing ground surface. 4 The groundwater table ranged from about 5 to 15 feet below the existing ground surface. The deeper groundwater table was encountered within the northern portion of this roadway segment. Notes: 1. Groundwater levels are based on the time of measurement and may fluctuate as previously noted.

13 Page 13 of 21 Reference:Geotechnical Feasibility Investigation - Plan Line Study for the SouthEast Connector 9.0 Soil Chemistry An environmental study to fully address soil chemistry considerations is beyond the scope of this investigation; however, based on the present available information, a preliminary discussion of some of the potential concerns with soil chemistry is provided. Soil chemistry testing was not completed with this feasibility study or the 1983 study. However, other referenced reports for soils within the corridor area and also near the corridor did complete limited soil chemistry investigations. Based on these reports, the prevalent soil chemical concerns are soluble sulfates, boron, and arsenic. Mercury was also encountered from a study provided to us by RTC within the Butler Ranch area. It has been our experience that this area typically contains elevated levels of boron, arsenic, and soluble sulfates. Except for soluble sulfates, there is not any construction mitigation required for boron and arsenic. Soluble sulfates are salts that can be detrimental to concrete and depending on the levels of soluble sulfates special concrete mix designs are required. Boron can be detrimental to plant life. Typically, cut material derived from bedrock areas, adjacent to the roadway corridor, has been used as fill soils for development areas without material chemistry constraints. However, it would be prudent to test bedrock areas for typical chemical constituents to determine if the levels are higher than the threshold levels measured for the alluvium soils SEISMIC HAZARDS 10.1 Seismicity Much of the Western United States is a region of moderate to intense seismicity related to movement of the crustal masses (plate tectonics). By far, the most active regions, outside of Alaska, are along the San Andreas Fault zone of western California. Other seismically active areas include the Wasatch Front in Salt Lake City, Utah, which forms the eastern boundary of the Basin and Range physiographic province, and the eastern front of the Sierra Nevada s, which is the western margin of the province. The project site lies near the eastern base of the Sierra Nevada, within the western extreme of the Basin and Range Liquefaction Liquefaction is a nearly complete loss of soil shear strength that can occur, during an earthquake, as cyclic shear stresses generate excessive pore water pressure between the soil grains. This phenomenon is generally limited to unconsolidated sands (up to 35 percent nonplastic fines) lying below the groundwater table to depths of 50 feet below the existing ground surface. The higher the ground acceleration caused by a seismic event, or the longer the duration of shaking, the more likely liquefaction is to occur. Earthquake hazard maps are not available for the proposed roadway corridor area; however, since the roadway will predominantly be traversing fine-grained alluvium and basin filled sediments, it is anticipated that the majority of the large structures planned within the roadway corridor will likely need to be designed for the potential of soil liquefaction. The geotechnical profile encountered within the exploratory borings verifies the presence of potentially liquefiable soils, especially the roadway segment north of Cleanwater Way. Predominantly granular, loose to medium dense, fine-grained sands were encountered below the ground water table within this V:\52801\active\ \report\Final Report\6_Appendix A - Geotechnical Investigation\SE Conn_memo_RTC_RAR_ doc

14 Page 14 of 21 segment of the roadway. Although a soil liquefaction analysis was not performed with this investigation, based on experience with these soils and recorded SPT blow counts, they are likely susceptible to soil liquefaction. The geotechnical profile encountered within the exploratory boring (1983 study) at Pembroke Lane indicated a limited zone with potentially susceptible liquefiable soils located between 12 to 16 feet below the existing ground surface. Below these depths, the soil profile consists of a dense to very dense sand and gravel horizon not generally susceptible to soil liquefaction. The exploratory boring at Alexander Lake Road indicates that the majority of the geotechnical profile encountered consists of predominantly of low to medium plastic clays, which are likely not susceptible to soil liquefaction. However, below the uppermost clay soil horizon, the soils are predominantly granular and based on the density of these soils are likely marginally liquefiable. In summary, detailed geotechnical exploration and studies will be required to determine soil liquefaction; however, based on this feasibility study, liquefaction mitigation measures during construction will likely be required. Typically, construction mitigation techniques include compaction grouting or the construction of stone columns that dissipate excess groundwater pressures Faults The following information regarding earthquake faulting relates to the general roadway corridor vicinity. Specific earthquake faulting information in relationship to the preferred roadway alignment (34-40 combined alignment) is presented in Appendix C. To determine the location of mapped earthquake faulting, a review of several published references was completed, as follows: Vista Quadrangle Geologic Map by Bell and Bonham (1987) Steamboat Quadrangle Geologic Map by Bell and Bonham (1993) Local Quaternary Faults and Associated Potential Earthquakes in the Reno and Carson City Urban Areas by depolo (1996) Earthquake Occurrence in the Reno-Carson City Urban Corridor by depolo (1997) Based on a review of these documents, two primary fault zones are located near, or through the proposed roadway corridor (Refer to Plates A-1a to A-1c in Appendix C for approximate fault locations). The first fault zone is known as the Huffaker Hills Faults that consist of a series of short, northeast trending, parallel faults through Huffaker Hills. A fault trace, as part of this fault zone, is shown as extending through the roadway corridor within the Butler Ranch area, immediately south of Mira Loma Road. The fault is queried, indicating its existence is uncertain. Although, these faults are classified as not active with the last movement occurring along the fault zone during Quaternary time (Bonham and Bell, 1983), they are associated with one of the most pronounced and persistent seismicity trends in the region. This seismicity trend exists from about the Huffaker Hills to the southwest and intersects the active Carson Range Front (depolo, 1996).

15 Page 15 of 21 The second fault zone is known as the Eastern Reno Basin Fault Zone, which consists of several mapped north to south trending, range bounding faults located at the base of the western flank of the Virginia Range. This fault zone is defined as a series of short, discontinuous fault scarps and side-hill benches within a deeply eroded range front. The most recent reported earthquake event along this fault zone was in the Late Quaternary time period (Trexler and Pease, 1981). The total length of this fault zone is about 13 miles; however, it is uncertain whether earthquake segments involve the entire 13 miles, or the Huffaker Hills area may act as a barrier, and shorter earthquake segments may actually occur to the south and north of Huffaker Hills. Based on this consideration, the reported maximum earthquake magnitude within this fault zone ranges from 6.5 to 6.8 (depolo, 1996). The only mapped segment of this fault zone which may trend through the proposed roadway corridor area is located between Cleanwater Way and Greg Street. This segment of the fault is dashed, meaning that the location of the fault is inferred. Within this location are Holocene sediments which may be covering deeper earthquake scarp zones. It is generally accepted that the maximum credible earthquake that would affect this project would originate from the frontal fault system of the Eastern Sierra Nevada and have an earthquake magnitude on the order of 7 to 7.5. The most active segment of this fault system in the Reno area is located at the base of the mountains near Thomas Creek, Whites Creek, and Mt. Rose Highway, some 5 to 9 miles southwest of the project site. The criteria for evaluation of Quaternary earthquake faults has been formulated by a professional committee for the State of Nevada Seismic Safety Council, but is not yet adopted by the State or Counties. These guidelines are consistent with the State of California Alquist-Priolo Act of 1972, which defines Holocene Active Faults as those with evidence of displacement within the past 10,000 years (Holocene time). Those faults with evidence of displacement during Pleistocene time (10,000 to 2,000,000 years before present) are classified as either Late Quaternary Active Fault or Quaternary Active Fault. Both of the latter fault designations are considered to have a decreased potential for activity than the Holocene Active Fault. Based on the referenced fault map, the faults in the vicinity of the project are considered either Late Quaternary Active Fault or Quaternary Active Fault. The mapped faults within the roadway corridor area are considered Quaternary Active Faults with a less potential for movement than Holocene Active Faults. Also, these faults are not welldefined and, consequently, are dashed, meaning that their location is inferred. The roadway corridor area may cross faults at two locations: Roadway Segments 2 and 4. The fault within roadway segment 4 is shown just east of the intersection of Sparks Boulevard and Greg Street and, consequently, is likely avoidable. However, the fault trace located within roadway segment 2 is not avoidable unless the roadway is routed within volcanic bedrock areas, east of the Butler Ranch area. Additional investigation by examining aerial photos and possibly exploratory trenching could be performed to try to define the location of the fault trace within Roadway Segment 2. However, it is our opinion that based on the existing information this fault likely poses a low risk of movement during the service life of this roadway. Also, because of the inferred location of this fault, even with additional investigation, an accurate location of this fault may never be determined. Based on a review of the referenced Preliminary Geotechnical Investigation for Bella Vista Ranch, a fault study was being conducted by Valkyrie Consulting to assess the age and future activity this fault. It is recommended to try to obtain this report to provide additional information on this fault trace.

16 Page 16 of Lateral Spread Lateral displacement, or lateral spread, is the horizontal movement of surficial soil layers as a consequence of soil liquefaction. Horizontal soil movement occurs due to the effect of dynamic earthquake generated inertial forces and static gravitational forces. Lateral spread generally occurs on sloped terrain or movement to a free face, such as a steep embankment. Since potentially liquefiable soils exist along the proposed corridor area and the terrain is relatively flat, the mostly likely occurrence of lateral spread will be near the vertical faces of creek beds or cut and fill slopes overlying liquefiable soils SEISMIC DESIGN PARAMETERS Seismic design parameters are based on site-specific estimates of spectral response ground acceleration as designated in the 2006 IBC. The benefit of this approach is that a response spectrum can be developed from this data and based on the period of the structure, a spectral acceleration for that structure can be determined. The spectral response acceleration values are based on structures underlain by bedrock. Acceleration values may amplify or attenuate depending on the subsurface geologic conditions. Therefore, the building code provides a correction factor to modify the acceleration values depending on the subsurface geologic conditions. Sites are classified based on the soil profile type as presented in Table 3. TABLE 3 SITE CLASSIFICATION DEFINITIONS Site Classification A B C D E F Soil Profile Type Description Hard Rock Rock Very Dense Soil and Soft Rock Stiff Soil Profile Soft Soil Profile Soil Type Requiring Site-Specific Evaluation The soil/bedrock profile classification is based on two criteria: density (primarily for soils based on SPT blow count data) or hardness (based on shear wave velocity primarily for bedrock sites). These two criteria have to be determined to a depth of 100 feet below the ground surface. Based on the findings of this investigation, the site classification may vary from a C to F along the corridor area DISCUSSION AND RECOMMENDATIONS 12.1 General Information The roadway corridor area is located overlying a variety of different material types ranging from fine-grained soils (silts and clays) to coarse-grained soils (sands and gravels) and even localized areas of bedrock. The predominant uppermost soil strata encountered within the roadway corridor area is comprised of fine grained soils (silts and clays) with low support characteristics. Because of the shallow ground water table within the majority of the proposed corridor area, the native soils are prone to instability and stabilization construction techniques will likely be

17 Page 17 of 21 required. Roadway cut material from bedrock areas or material derived from coarse-grained alluvial fans could be utilized for stabilization; however, these areas are localized and sufficient quantities of imported stabilization material will likely be required. Due to the predominant uppermost fine-grained soil strata and shallow groundwater table, foundation support for structures will likely require deep foundations. Also, potential scour depths from Steamboat Creek and the Truckee River will likely mandate the use of deep foundations. Deep foundations will likely consist of drilled shafts, but driven piles may also be applicable for some of the structures. Soil liquefaction will also be an issue to consider and typical construction mitigation consisting of either compaction grouting or stone columns will likely be required Design Consideration for the Roadway Corridor Design consideration for the roadway corridor will be presented separately for the different roadway segments Roadway Segment #1- South Meadows Parkway to Alexander Lake Road Near surface soils encountered are predominantly fine-grained granular soils. An R-value test result of 12 was obtained on a soil sample from TP-19A, which indicates that these soils have weak subgrade support characteristics. A shallow groundwater table was encountered and unstable soil conditions should be anticipated. Typical soil stabilization construction methodology used in the South Meadows area consists of elevating the roadway, where possible, and placing a coarse initial layer of structural fill. Typically, 2 feet of stabilizing fill has been used; however, within softer areas, thicknesses of 3 to 4 feet were required. It is anticipated that the thicker sections of stabilization fill will be required within the roadway section near Alexander Lake Road. A combination of stabilization fill and geotextile has also been utilized with success. As an option, depending on the existing groundwater elevations, instead of elevating the roadway to accommodate stabilizing fill, soft soils could be overexcavated and replaced with stabilizing fill. Because of shallow groundwater elevations, the preferable stabilization method is to elevate the roadway and utilize an initial coarse-grained structural fill layer. Three potential borrow pit sources, that would provide imported rock and structural fill, are located close to this roadway segment. These potential borrow pits are as follows: Mira Loma Pit: This pit is located east of the planned corridor location near Alexander Lake Road. The Mira Loma Pit is located on BLM property and is under the jurisdiction of NDOT. All permitting of this pit is through NDOT. Bella Vista Pit: This is a private pit. The last potential borrow source is unnamed and is a private pit located west of the roadway corridor and south of Alexander Lake Road. This is an active pit in which an existing volcanic knob is being mined for structural fill. The ownership and available of the material from this area is unknown at this time. An aerial photo showing the location of these pits is presented as Plate 3 in Appendix A.

18 Page 18 of Roadway Segment #2- Alexander Lake Road to Mira Loma Drive Near surface soils encountered are predominantly fine-grained soils consisting of sandy silts and clays. An R-value test result of 7 was obtained on a soil sample from TP-14A, which indicates that these soils have weak subgrade support characteristics. As with Roadway Segment #1, shallow groundwater table was encountered and unstable soil conditions should be anticipated. Because of the extremely weak soil conditions and shallow groundwater conditions, it is anticipated that at least 4 feet of stabilizing fill will be required to provide a construction platform for the roadway. It is our opinion that the most efficient construction method to accommodate the stabilizing fill is to elevate the roadway; however, limited overexcavation and replacement with stabilizing fill is also an option. It is recommended that the roadway alignment is located overlying the coarse-grained alluvial fan deposits within the southern end of this roadway segment. If the roadway is located through bedrock areas, excavated material could be utilized as stabilizing fill. Coarse-grained alluvial fan deposits and unaltered and competent bedrock should provide adequate subgrade support for the roadway. It should be advised that if the roadway traverses through bedrock areas, blasting may be required for excavation. Rockfall mitigation will also likely be required and could consist of excavating horizontal benches and constructing rock fences within the cut slope, or netting may have to be placed over the slope face. Rock catchment areas may also be required at the base of the slope. Any major cut slope will likely be within bedrock areas. It is anticipated that, for the most part, cut slopes within bedrock areas will be stable. However, depending on the fracture and weathering patterns, wedge type slope failures may occur. It is anticipated that the majority of these failures could be mitigated by flattening the slope gradient, but some areas may need to be stabilized by rock bolting Roadway Segment #3 - Mira Loma Drive to Pembroke This roadway segment traverses through the existing Rosewood Golf Course and soil conditions and groundwater levels are similar to that encountered within Roadway Segment #2. An R- value test result of 4 was obtained on a soil sample obtained fromtp-8a, which indicates that these soils have weak subgrade support characteristics. As with the other roadway segments, the combination of extremely weak soil and shallow groundwater conditions will likely promote subgrade soil instability and it is anticipated that at least 4 feet of stabilizing fill will be required to provide a construction platform for the roadway. It is our opinion that the most efficient construction method to accommodate the stabilizing fill is to elevate the roadway; however, limited overexcavation and replacement with stabilizing fill is also an option. This roadway segment will also cross the Boynton Slough and Steamboat Creek. Large box culverts, con-span type bridges may be used for these water crossings. It is anticipated that considerable thicknesses of stabilizing fill, approximately 4 to 6 feet, may be required below box culverts. For bridge structures, deep foundations will be required.

19 Page 19 of Roadway Segment #4- Pembroke to Greg Street Soil conditions are similar to Roadway Segment #3; however, the groundwater table is not as shallow as the other roadway segments. Consequently, subgrade instability susceptibility is not as great and, therefore, the required thickness of stabilizing fill will likely be reduced, ranging from 2 to 4 feet. Native soils have weak subgrade support characteristics, as evidenced by R- value test results that ranged from 2 (TP-1A) to 6 (TP-6A). This roadway segment will also cross the Steamboat Creek and the Truckee River. A viaduct will be constructed and because of the soft, near surface soil conditions and scour concerns, deep foundations, likely consisting of drilled shafts, will be required. As previously mentioned, soil liquefaction mitigation will likely be required. Unless the roadway is routed adjacent to the existing hillside, from a geotechnical perspective, there isn t a preferable route within this roadway segment. Soils are likely more granular and provide better subgrade soil support near the hillside area; however, this corridor would likely require more crossings over Steamboat Creek and would traverse the existing fault in this area Summary of Design Considerations for all Roadway Segments (Table 4) TABLE 4 - SUMMARY OF DESIGN CONSIDERATIONS FOR ROADWAY SEGMENTS Roadway Segments Anticipated Design R-values Summary of Roadway Design Considerations 1 Alluvium soil areas: 5 to 15 Bedrock or coarse-grained alluvial fan areas: 40 to 80 1 Combination of weak subgrade soils and shallow groundwater will necessitate the use of a stabilizing fill subbase layer. 2 Alluvium soil areas: 5 to 10 Bedrock or coarse-grained alluvial fan areas: 40 to 80 1 Combination of weak subgrade soils and shallow groundwater will necessitate the use of a stabilizing fill subbase layer. Bedrock areas will likely require blasting for excavation and rockfall mitigation. Cut material could be utilized as stabilizing fill. 3 & 4 5 to 10 Combination of weak subgrade soils and shallow groundwater will necessitate the use of a stabilizing fill subbase layer. Deep foundations will likely be required for bridge structures. Mitigation for soil liquefaction will likely be required. Notes: 1. Estimated R-values. Need to verify with testing.

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21 Page 21 of 21 REFERENCES Bell, J. W. and H. F. Bonham, 1987, Geologic Map, Vista Quadrangle: Nevada Bureau of Mines and Geology, Map 4Hg. Bonham, H. F. and J. W. Bell, 1993, Geologic Map, Steamboat Quadrangle: Nevada Bureau of Mines and Geology, Map 4Fg. depolo, C.M., 1996, Local Quaternary Faults and Associated Potential Earthquakes in the Reno and Carson City Urban Areas, Nevada, Nevada Bureau of Mines and Geology. depolo, C.M. et al, 1997, Earthquake Occurrence in the Reno-Carson City Urban Corridor, Seismological Research Letters, Volume 68, May/June, pages International Building Code, 2003; International Code Council, Inc. Matrix Construction Services Inc., Preliminary Geotechnical Investigation Bella Vista Ranch, April 26, 2005, Project Number Nevada Earthquake Safety Council, 2006, Guidelines for Evaluating Potential Surface fault Rupture /land Subsidence Hazards in Nevada. SEA Engineers Inc., Corridor Study Tahoe/Pyramid Link, October 21, 1983, project No: Standard Specifications for Public Works Construction, 2007 (Washoe County, Sparks-Reno, Carson City, Yerington, Nevada).