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Revised Proposal for Geotechnical Pavement Investigation BSK Proposal GL21-21837B W. Las Positas Boulevard September 15,2021 Pleasanton, California Page 2 changed, BSK will consider appropriate modifications,subject to the standards of care to which we adhere as professionals. PROJECT UNDERSTANDING AND ANTICIPATED SUBSURFACE CONDITIONS It is our understanding that West Las Positas Boulevard has experienced settlement and cracking over many years and has exhibited accelerated settlement over the last 10 years. The more severe surface manifestations have occurred between 1-680 and Santa Rita Road. It is also our understanding, based on discussions with you and our knowledge in the area, that the settlement issue is not limited to the roadway but is widespread in this area, affecting homes and other structures. During our site walk it was noted that a significant number of storm drain crossings have settled across both the eastbound and westbound lanes. It is our understanding, based on discussions with you,that the settlement is confirmed to have affected the storm drains themselves and is not limited to the roadway materials above the storm drain. We also understand that most of the fire lines in this area have recently been replaced due to damage to the lines resulting from settlement. The previous geotechnical studies conducted in the roadway near Tassajara Creek, which investigated settlement issues near the bridge, did not identify any obvious near-surface causes for the pavement and utility settlement. The 2010 Kleinfelder report advanced borings to a maximum depth of 25 feet below the existing ground surface (BGS) and encountered primarily lean clay, up to 10 feet of which were identified as fill. The 2012 Engeo report advanced 7 CPTs around the area of the Tassajara Creek crossing to a depth of 35 feet BGS and encountered primarily stiff clays.The subsurface data provided in the other geotechnical reports surrounding the roadway indicate similar soils to a depth of approximately 45 feet BGS, below which layers of sand and gravel were encountered. We understand that the City is not interested in doing a research project to evaluate the exact cause(s) of the settlement, but that an approach is needed to mitigate the situation such that continued, persistent settlement and subsequent extensive repairs to the roadway are significantly reduced. It is our understanding that the City would like to consider the use of geotextiles to strengthen the subgrade under the roadway to lessen cracking and the differential nature of the settlement. It is also our understanding that a new bike lane is proposed within the current shoulder areas. If the project understanding described above is incorrect, please notify us immediately so that we may review and possibly revise our proposed scope of services presented herein. SCOPE OF SERVICES Our scope of services will include a subsurface investigation, laboratory testing, and report that includes geotechnical conclusions and recommendations, and possible mitigation options for the project. We have formulated our scope of services to evaluate the following items within our borings: • Subgrade conditions within upper 7 to 10 feet BGS, including moisture content and density, soil type,expansion potential, resistance(R)value, and relative compaction, 1