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BACKGROUND <br /> West Las Positas Boulevard, between Hacienda Drive and Stoneridge Drive, was <br /> constructed in the early 1980s as part of the Hacienda Business Park Phase 1 <br /> development. The road consists of three lanes of traffic in each direction with a <br /> landscape median that includes mature trees. The roadway was constructed with three- <br /> and-a-half inches of asphalt on six to eight inches of aggregate base and 13 to 14.5 <br /> inches of lime-treated subgrade that consists of expansive, silty clays. The road <br /> parallels the Arroyo Mocho, and Tassajara Creek intersects the roadway near the <br /> boulevard's most severe roadway deformations. City sewer, water and storm lines run <br /> under the paved sections of the street. <br /> The street and adjacent properties have had a history of localized settlement and <br /> differential movement. The City has provided maintenance repairs several times to <br /> remediate the uneven roadways and curbs that are experiencing pavement distress <br /> and/or settlement. <br /> As part of the 2007 Annual Resurfacing Program, West Las Positas Boulevard received <br /> an overlay treatment and base repairs, bringing the roadway back to original grades. <br /> Within a few years, the street showed signs of movement and concern was raised about <br /> the premature failure of the overlay. By November 2011, the curb lane near Tassajara <br /> Creek and in the eastbound direction had settled to a point that it created a safety <br /> concern, requiring the lane to be closed to vehicular traffic. To address the roadway <br /> repair due to the settling, the West Las Positas Boulevard at Tassajara Creek Street <br /> Repair Project, CIP No. 11504, was authorized under the 2011/12 Capital Improvement <br /> Program. <br /> In 2010, a geotechnical investigation was performed by Kleinfelder to determine the <br /> possible causes of the ongoing settlement. Numerous potential .auses of the settlement <br /> were presented. However, no definitive cause for the settlement was identified and it <br /> was deemed necessary to obtain a second opinion from a different geotechnical <br /> consultant. <br /> In 2012, ENGEO Incorporated, a geotechnical consultant, was approached for a second <br /> opinion and was authorized by the City to provide engineering and construction <br /> recommendations for the repair. ENGEO's opinion is that this section of roadway was <br /> constructed over a former marsh and lagoon area. The marsh and lagoon deposits <br /> consist of soft, compressible soils with high moisture content that lead to the damage as <br /> the deep soil layers swell and compress. Roadway construction has applied additional <br /> loads over the deep, soft soils, causing localized soil swelling and settlement. ENGEO <br /> recommended that the distressed areas should be repaired by replacing the existing soil <br /> under the pavement surface with a lightweight engineering fill material (cellular <br /> concrete). Doing so should eliminate or reduce the severity of future settlement in the <br /> area currently showing distress. <br /> In 2013, Fanfa, Inc. completed the West Las Positas Boulevard at Tassajara Creek <br /> Street Repair Project, CIP No. 11504, for $253,684, implementing ENGEO's repair <br /> recommendations. The roadway profile was restored to the design grade near the <br /> Tassaraja Creek crossing and Fiesta Drive. Approximately 500 cubic yards of existing <br /> soil under the severely distressed area was replaced with lightweight cellular concrete <br /> material and approximately 1,200 square feet of less-severely distressed area was <br /> Page 2 of 4 <br />