8331 Sierra College Blvd., Suite 208 Roseville, CA 95661 Phone: 916.757.6150 Fax: 916.787.6191 www.wreco.com Memorandum Date: June 30, 2015 To: Keith D. Rhodes, PE – T.Y. Lin International From: Michael Wilson, PG, CEG – WRECO Subject: South County Corridor Project –Preliminary Geotechnical Memorandum INTRODUCTION Scope of Services This memorandum was prepared in support of the Feasibility Study for the South County Corridor (SCC) Project (Project). This memorandum evaluates the potential geotechnical/geologic impacts and mitigation measures for the Project. Project Description The SCC is a planned east-west 4-lane divided expressway connecting State Route 99 (SR 99) to Interstate 5 (I-5) in the southern portion of Stanislaus County and bypassing the Cities of Patterson and Newman. The SCC Feasibility Study will analyze potential traditional and multi-modal corridor alignments that will enhance the east-west transportation link for all travel modes in southern Stanislaus County. Key goals of the Feasibility Study are as follows: • Provide an efficient movement of goods and people for all modes of travel statewide • Improve safety through the roadway widening and improvements, limiting access to the expressway facility and divided traffic lanes • Enhance local, regional and statewide connectivity • Improve air quality and noise • Promote an increase of local and regional investments • Promote the support of General Plans applicable within the project limits • Assess the feasibility including planned land use, transportation and environmental issues • Develop project development and implementation strategies Figure 1 is an aerial map showing the Project study area and Figure 2 is a map identifying the existing SCC and proposed SCC alternative alignments. Project Need Stanislaus County is a vital hub for the movement of agricultural (farm to market) and other goods, both locally grown/produced and those that pass through the region, which links northern and southern California as well as the Bay Area. The lack of an efficient and direct travel route between | Civil Engineering | Water Resources | Environmental Compliance | Geotechnical Engineering | 1 8331 Sierra College Blvd., Suite 208 Roseville, CA 95661 Phone: 916.757.6150 Fax: 916.787.6191 www.wreco.com SR 99, SR 33, and I-5 in the southern part of Stanislaus County has become a pressing concern to the region. Of primary concern is the amount of regional and interregional traffic generating congestion within the Patterson city limits and surrounding areas. This traffic congestion, noise, and related safety issues are of a larger concern to the region which depends on an efficient and safe transportation system to deliver manufactured and agricultural goods both regionally and inter-regionally. In addition, the centrally located nature of Stanislaus County has made it an ideal location for the distribution of goods through the Central Valley. The SCC will be key to the continued success of these industries. The existing corridor is part of the 39.7 mile County Route J17 (CR J17) established in 1960 that runs through Stanislaus and Merced counties. The section of CR J17 (Sperry Road, E. Las Palmas Avenue, and W. Main Street) between SR 99 and I-5 functions as an agricultural trade corridor that extends 18 miles between the Cities of Turlock and Patterson. This section of CR J17 is generally a 2-lane highway through rural areas; although, the facility has 4-lane segments within the city limits of Turlock and 3-lane segments within the city limits of Patterson. East Las Palmas Avenue on the east side of town has 100 year old palm trees that prevent widening the road. Trucks experience approximately ten traffic signals along Sperry Road, East Las Palmas Avenue, and West Main Street to get from I-5 to SR 99. Since Patterson is becoming a west side hub for commerce distribution, the existing corridor route is heavily use and is often congested. | Civil Engineering | Water Resources | Environmental Compliance | Geotechnical Engineering | 2 8331 Sierra College Blvd., Suite 208 Roseville, CA 95661 Phone: 916.757.6150 Fax: 916.787.6191 www.wreco.com Figure 1, SCC Study Area Map | Civil Engineering | Water Resources | Environmental Compliance | Geotechnical Engineering | 3 8331 Sierra College Blvd., Suite 208 Roseville, CA 95661 Phone: 916.757.6150 Fax: 916.787.6191 www.wreco.com Figure 2, SCC Project Map Source: TYLIN International, 2015. South County Corridor Conceptual Alignments, Overall Project Map, Level 2 Alignments, Exhibit 1 of 1, Scale 1” = 10,000’ | Civil Engineering | Water Resources | Environmental Compliance | Geotechnical Engineering | 4 8331 Sierra College Blvd., Suite 208 Roseville, CA 95661 Phone: 916.757.6150 Fax: 916.787.6191 www.wreco.com EXISTING CONDITIONS Physical Setting Climate The climate of Stanislaus County (within San Joaquin Valley) is classified as mild Mediterranean, with warm semi-arid to arid conditions. There is one wet season during the year, with 90-percent of the precipitation occurring October through April. Snow in the valley is infrequent, and occurs once in about every seven years. Precipitation ranges from 5- to 7-inches annually in the San Joaquin Valley and from 7- to 12-inches annually on the surrounding terraces, foothills, and mountains. In the San Joaquin Valley, the last frost in spring is generally in February or early March and the first frost in fall is late in November or early December. In the mountains, the last frost typically in spring is early in May and the first frost in fall for some areas is early in October. Summers are generally cloudless, hot, and dry with temperatures commonly exceeding 100-degrees F and rarely are less that 51-degrees F. Winters are typically mild and fairly humid. December and January are characterized by frequent fog or low clouds which occur mostly at night. Winter temperatures typically range from the low 30’s at night with daytime temperatures in the 50’s. A study of wind-speed records suggest that wind-speeds can attain velocities of 30- to 45-miles per hour about once in 2-years. As often as once in 50-years wind-speeds have reached 60- to 65-miles per hour, and at 100-year intervals they can reach 65- to 75-miles per hour. Topography The Project consists of relatively flat topography with a slight rise in elevation in the west, near I-5. The elevation range is approximately 40 feet to 200 feet, with the San Joaquin River being the lowest and I-5 being the highest. Grassland and farmlands are the dominant habitats throughout the area (USGS, 20151-6). Regional Geology The Project is located on the eastern edge of the Diablo Range Mountains. The Diablo Range is located within the California Coast Ranges subdivision of the Pacific Coast Ranges. The Diablo Range Mountains are nearly 200 miles long and start near the Carquinez Strait in Contra Costa County east of Oakland to the north and stretches south to Orchard Peak near where State Route 46 crosses over the Coast Ranges at Cholame in northwestern Kern County. The Diablo Range Mountains form the western wall of the Central Valley and are paralleled by the U.S. Route 101 to the west and by I-5 to the east. The Diablo Range Mountains are characterized by steep mountainous topography to the west that level out towards the valley on the east. The west side of the Project is located near the western boundary of the northern portions of the San Joaquin Valley, near the Cities of Patterson and Newman, while the eastern side of the Project is located near Turlock near the center of the valley, in Stanislaus County. The physiographic location of the subject site is within the Great Valley Geomorphic Province. The province encompasses the San Joaquin and Sacramento valleys’ and is bounded by the Sierra Nevada Mountains to the east, the | Civil Engineering | Water Resources | Environmental Compliance | Geotechnical Engineering | 5 8331 Sierra College Blvd., Suite 208 Roseville, CA 95661 Phone: 916.757.6150 Fax: 916.787.6191 www.wreco.com Coast Ranges to the west, the Transverse Range (Tehachapi Mountains) to the south, and the Klamath Mountains to the north. The San Joaquin Valley is a structural trough that covers 2,374 square miles, which makes up the southern two-thirds of the Great Valley Geomorphic Province. The San Joaquin Valley extends from the Stockton-Tracy area on the north to the Transverse Ranges on the south. The southern San Joaquin Valley basin is bounded by the Temblor Ranges on the west, the Sierra Nevada Mountains on the east, and the San Emigdio and Tehachapi mountains to the south. The west side of the basin consists of a tightly folded anticlinorium, which is sub-parallel to the San Andreas Fault. The east side of the valley is a broad homocline. The valley surface is relatively flat and is underlain by thousands of feet of alluvial (river), lacustrine (lake), and marine (ocean) deposits that have accumulated in an elongate, asymmetrical sedimentary basin to form the structural trough as the adjacent mountain ranges elevated. The main axis of the San Joaquin basin is north-northwestern trending along the valley’s main drainage axis. During the late Mesozoic and to the early and middle Cenozoic eras (approximately 20 to 100 million years before present), deposition of thousands of feet of marine sediments occurred within the Great Valley. Continental deposits (generally alluvium) of late Tertiary and Quaternary age (approximately 20 million years ago to present) overlie these marine sediments. A total of 32,000 feet of continental deposits and underlying marine sediments were deposited into the San Joaquin Valley trough (or subbasin) during periodic inundation by the Pacific Ocean and by erosion of the surrounding mountains. Project Site Geology Based on the Geologic Map of the San Francisco and San Jose Quadrangle (Wagner, et al, 1991), the Project site is underlain by soils belonging to the Fanglomerate, Valley Springs and Tesla formations’ on the western margin of the project (along I-5) and alluvial fan soils, Dos Palos alluvium (within the San Joaquin River floodplain) and Modesto formation trending eastward towards the center of the valley (Figure 3).