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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 consists of three lanes of traffic in each direction with a landscape median that includes mature trees. The roadway was constructed with three- and-a-half inches of asphalt on six to eight inches of aggregate base and 13 to 14.5 inches of lime-treated subgrade that consists of expansive, silty clays. The road parallels the Arroyo Mocho, and Tassajara Creek intersects the roadway near the boulevard's most severe roadway deformations. City sewer, water and storm lines run under the paved sections of the street. The street and adjacent properties have had a history of localized settlement and differential movement. The City has provided maintenance repairs several times to remediate the uneven roadways and curbs 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 original grades. Within a few years, the street showed signs of movement and concern was raised 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 due to 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 to determine the possible causes of the ongoing settlement. Numerous potential .auses of the settlement were presented. However, no definitive cause for the settlement was identified and it was deemed necessary to obtain a second opinion from a different geotechnical consultant. In 2012, ENGEO Incorporated, a geotechnical consultant, was approached for a second opinion and was authorized by the City to provide engineering and construction recommendations for the repair. ENGEO's opinion is 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 lead to the damage as the deep soil layers swell and compress. Roadway construction has applied additional loads over the deep, soft soils, causing localized soil swelling and settlement. ENGEO recommended that the distressed areas should be repaired by replacing the existing soil under the pavement surface with a lightweight engineering fill material (cellular concrete). Doing so should 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 with lightweight cellular concrete material and approximately 1,200 square feet of less-severely distressed area was Page 2 of 4