Reso 2011-192 - Laserfiche WebLink

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POTENTIALLY ISSUES Geology /Soils (continued) POTENTIALLY SIGNIFICANT LESS THAN SIGNIFICANT UNLESS SIGNIFICANT No SOURCES IMPACT ISSUES MITIGATION IMPACT INCORPORATED Leandro Municipal Code regulating excavation activities and the construction of foundations and retaining walls, as well as the San Leandro Grading Ordinance regulating grading activities, drainage and erosion control. Therefore, compliance with the NPDES permit process and the California Building Code requirements would minimize potential impacts from erosion during and after project construction and would ensure that potential geology and soils impacts are less than significant. Mitigation Measure #12: Applicant shall comply with the NPDES requirements that must incorporate permanent post - construction Best Management Practice (BMP) of the California Regional Water Quality Control Board and the City of San Leandro Building and Engineering Departments. The BMP shall be reviewed and approved by the City's Engineering Department prior to the issuance of a Grading Permit. of Alameda County and the site is generally flat and level, with a slight downslope towards the southeast. The northeast end of the site is an enclosed, paved area used for long -term parking and equipment storage. The center and southwest end of the site is occupied by an existing office building with paved parking and planter areas with trees and low shrubs Surrounding the building on three sides. The geology of the area consists of fine- grained dominated soil sequences inter- bedded with coarse -grain dominated soil sequences. Based on field exploration, the subsurface conditions encountered appear typical of those found in the geologic vicinity and include a layer of pavements less than 1 foot thick, overlying a layer of black, stiff to very stiff, moderately plastic clay, extending to approximately 3 '/2 feet below the pavement surface. Beneath the black clay, borings encountered a layer of brown, stiff, low to moderate - plasticity clay with traces of fine sand, extending to approximately 8 feet below grade. This layer is overlain by a layer of olive -brown to light brown, stiff, low plasticity sandy clay extending to approximately 13 to 18 feet. Groundwater was encountered at between 27 to 28.5 feet and fluctuations in the groundwater table can be expected with changes in seasonal rainfall, urbanization and construction activities at or in the vicinity of the site. Lateral spreading occurs when sloping ground or ground near a free face is underlain by a Iiquefied layer and begins to slide downslope or towards the free face. There is no free face close to the site and the slope of the site is not sufficient to cause lateral spreading within the site. An acceptable degree of soil stability would be achieved for expansive, liquefaction -prone and compressible soils by incorporating soil treatment programs such as replacement, grouting, compaction and drainage control during the excavation and construction phases of the project in order to address site - specific soil conditions. Mitigation Measure #13: Applicant shall be required to completely remove all existing surface and subsurface structures prior to grading. If any of the following are encountered: concrete, septic tanks, gas and oil tanks, storm inlets, machinery, equipment, debris and trash, these should also be removed, with the exception of items specified by the owner for salvage. Ornamental trees to be removed - should be properly grubbed to adequately remove all major root systems. In addition, all underground structures must be located on the grading plans so that proper removal may be carried out. Mitigation Measure #14: A qualified geotechnical consultant shall be required to observe the removal of subsurface structures and be notified in ample time to ensure that no subsurface structures are covered and that the root systems from grubbing operations are completely removed. If a qualified geotechnical consultant is not contracted to observe demolition and removal of existing structures, backhoe investigation in the areas of demolition shall be performed prior to commencement of mass grading. Mitigation Measure #15: The applicant shall be required to excavate, remove and recompact potentially liquefiable soil. In -site ground densification, for example, compaction with vibratory probes, dynamic consolidation, compaction piles, compaction grouting, etc., shall be conducted. Ground modification techniques, such as permeation grouting, columnar jet grouting, deep soil mixing, stone columns, gravel or other drains shall be implemented, and deep foundations shall be put in place to mitigate potential liquefaction- induced settlement impacts. 2450 Washington Avenue Apartments 10 October 2011