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BACKGROUND West Las Positas Boulevard, between Hacienda Drive and Stoneridge Drive, was constructed in the early 1980s as part of the Hacienda Business Park Phase 1 development. The road parallels the Arroyo Mocho as it runs east-west in Pleasanton. The road consists of three lanes of traffic in each direction with landscaped medians, including mature trees. The roadway was constructed with 3.5 inches of asphalt on 6 to 8 inches of aggregate base, over the top of a subgrade that consists of high plasticity, silty clay. Due to the high plasticity of the subgrade, the upper 13 to 15 inches of the subgrade were lime treated instead of compacted during construction to obtain a firm and unyielding surface on which to build the road improvements. City-owned water, sewer, recycled water, and storm lines run under the paved sections of the street. The street has a history of localized settlement and differential movement. The City has implemented several maintenance repair projects over the years to try and remediate the uneven roadway and curb and gutters that are experiencing pavement distress and/or settlement. As part of the 2007 Annual Resurfacing Program, West Las Positas Boulevard received an overlay treatment and base repairs, bringing the roadway back to its original grades. Within a few years, the street showed signs of movement, causing concern about the premature failure of the overlay. By November 2011 , the curb lane near Tassajara Creek and in the eastbound direction had settled to a point that it created a safety concern, requiring the lane to be closed to vehicular traffic. To address the roadway repair as a result of the settling, the West Las Positas Boulevard at Tassajara Creek Street Repair Project, CIP No. 11504, was authorized under the 2011-12 Capital Improvement Program. In 2010, a geotechnical investigation was performed by Kleinfelder, a geotechnical consultant, to determine the possible causes of the ongoing settlement near Tassajara bridge. Numerous potential causes of the settlement were presented. However, no definitive cause of the settlement was identified. In 2012, ENGEO Incorporated, another geotechnical consultant, was authorized by the City to provide engineering and construction recommendations for the repair of the roadway near Tassajara bridge. ENGEO's opinion was that this section of roadway was constructed over a former "marsh and lagoon" area. The "marsh and lagoon" deposits consist of soft, compressible soils with high moisture content that led to roadway damage as the soil layers swelled and compressed. Roadway construction has applied additional loads over the soft soils, causing localized soil swelling and settlement. It was recommended by ENGEO that the distressed areas should be repaired by replacing the existing soil under the pavement surface with lightweight engineering fill material (cellular concrete). They advised that doing so would eliminate or reduce the severity of future settlement in the area currently showing distress. In 2013, Fanfa, Inc. completed the West Las Positas Boulevard at Tassajara Creek Street Repair Project, CIP No. 11504, for $253,684, implementing ENGEO's repair recommendations. The roadway profile was restored to the design grade near the Tassaraja Creek crossing and Fiesta Drive. Approximately 500 cubic yards of existing soil under the severely distressed area was replaced by lightweight cellular concrete material and approximately 1,200 square feet of the less severely distressed area was Page 2 of 5