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01
City of Pleasanton
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2016
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010516
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12/29/2015 3:26:28 PM
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CITY CLERK
CITY CLERK - TYPE
AGENDA REPORT
DOCUMENT DATE
1/5/2016
DESTRUCT DATE
15Y
DOCUMENT NO
01
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Mitigation Measure 4.4-3e: Keyways equipped with a subsurface drainage system shall be constructed. <br /> Each keyway shall be keyed into firm natural materials unaffected by shrinkage cracks. The keyway shall <br /> be filled with materials derived from the Livermore Gravels compacted to 95 percent relative compaction <br /> for non-expansive materials and 90 percent relative compaction for expansive materials. The required <br /> depth of the keyways shall be determined in the field by the geotechnical engineer during grading. Fill <br /> above the keyways shall be benched into firm, competent soil or bedrock and drained as appropriate. <br /> Unless otherwise recommended by the Geotechnical Engineer, benches shall be constructed at vertical <br /> intervals of not less than five feet. <br /> Mitigation Measure 4.4-3f: Subsurface drainage systems should be installed in all key ways, swales or <br /> natural drainage areas, and landslide removal areas in accordance with the recommendations of the <br /> geotechnical exploration. Depending on the actual conditions encountered during grading, similar <br /> subsurface drainage facilities may be recommended within existing stock ponds, springs, low-lying areas, <br /> or at lots where wet conditions are encountered during excavation. In addition, new sources of seepage <br /> may be created by a combination of modified topography, future irrigation practices, and potential utility <br /> leakage. If discovered, these conditions should be brought to the attention of the Geotechnical Engineer <br /> so that remedial actions may be initiated, if necessary. <br /> Mitigation Measure 4.4-3g: Structural retaining walls shall be constructed in accordance with the <br /> recommendations of the geotechnical exploration and provided with drainage facilities to prevent the <br /> buildup of hydrostatic pressures behind the walls. <br /> Mitigation Measure 4.4-3h: Where steeper slopes greater than 3:1 are desired, supplemental slope <br /> stabilization measures such as geogrid enforcement and/or the use of select fill shall be employed. <br /> Drainage benches shall also be provided at a 30-foot minimum intervals, and construction shall follow the <br /> structural setbacks of the CBC. Accordingly, structures shall be: (I) set back from the top of the slope by <br /> a minimum of one-third of the slope height or a maximum of 40 feet; and (2) set back from the bottom of <br /> the slope by a minimum of one-half of the slope height or a maximum of 15 feet. Alternative setbacks <br /> may be addressed on a per lot and foundation design basis. <br /> Significant Impact <br /> Impact 4.4-4: Expansive soils and bedrock materials are present within project boundaries and <br /> construction on expansive soil could cause foundation and other structural failures, particularly at lots <br /> traversed by a cut/fill transition. <br /> Finding <br /> Changes or alterations have been required in, or incorporated into, the project which mitigate or avoid the <br /> significant effects on the environment. <br /> Facts in Support of Finding <br /> The City of Pleasanton has adopted the following measures which will reduce potential impacts related to <br /> expansive soils and bedrock materials to a less-than-significant level: <br /> Mitigation Measure 4.4-4: Cut lots shall be overexcavated 2 feet, scarified 12 inches, and recompacted <br /> so as to provide a zone of at least 3 feet of reworked and compacted soil. Additionally, cut/fill transition <br /> lots should be overexcavated so as to provide a minimum of 3 feet of a uniform thickness of engineered <br /> fill within the entire foundation area. In addition, exposed soils shall be kept moist by watering for several <br /> days before placement of concrete. <br /> LUND RANCH II(PUD-25)RESIDENTIAL PROJECT 12 FINDINGS <br />
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