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<br />Seismic Vulnerability Study <br /> <br />Task 2 Updated Seismic Vulnerability Study <br /> <br />Based on the findings from Task 1, we will update the vulnerability study to reflect the <br />current (2009) status of the Redwood City water system. This updated analysis will <br />include the following: <br /> <br />· Field data for steel tank shell thicknesses (we will collect this data using a non- <br />destructive probe which measures the thickness of steel using sound). This will <br />supplement any data available from fabrication drawings or corrosion / dive <br />inspections within the tanks made in the last 20 years or so. <br /> <br />· Comparison of tank / reservoir seismic failure modes to latest codes, guidelines <br />and standards. We will do this assuming the tank / reservoir is full (at overflow <br />level), in comparison to either the 475-year or 2/3 of the 2,475 year motions or the <br />84th percentile not-to-exceed motions for aM 7.9 event on the nearby San <br />Andreas fault. We will make these comparisons assuming "code" values for R <br />(legally the minimum) as well as elastic performance (as done in the nuclear <br />industry). We will show the PGA level at which there is no expected damage, as <br />well as how the existing tanks / reservoirs might perform under higher levels of <br />PGA. For each tank or reservoir, we will quantify the level ofPGA at which we <br />believe it "fails" code; or it is likely to be functionally damaged (uncontrolled loss <br />of water contents). Failure modes to be considered: tank shell buckling (steel <br />tanks); hoop stress overloads (steel tanks); damage to anchorage (steel tanks); <br />damage to attached pipes (inlet, outlet, overflow, drain) due to tank shell uplift <br />(steel tanks) or differential settlements (all tanks and reservoirs). For reservoirs <br />(like Carson), we will check liner capacity; roof diaphragm capacity; beam / <br />column connections. For concrete tanks, we will check the performance of the <br />seismic cables (lower level); concrete stops; roof-wall connections. <br /> <br />· We will provide similar results for pump station buildings. This will include <br />evaluation of the buildings (and critical equipment within) for earthquake loading. <br /> <br />· Latest geologic hazard information will be used to evaluate the performance of <br />buried distribution and transmission pipes in the Redwood City system. This will <br />include mode than 50 new geotechnical borings that we have collected in the <br />Redwood City area for other water projects (SFPUC new BDPL 5, where G&E is <br />the pipeline designer) and other sources. <br /> <br />· We will update the calculations of damage to pipelines due to updated <br />liquefaction hazards, as well as ground shaking, landslide and sympathetic offset <br />in the Serra fault zone. The calculations per pipe will be based on Redwood City's <br />GIS ObjectID. For planning purposes, we assume that this will be done using <br />EXCEL-type models. Should the available electronic databases from Redwood <br />City be suitable, we may adopt this information into G&E's SERA software. <br />SERA is a special purposes program to perform seismic vulnerability analyses for <br />water and power systems. Should G&E use SERA, it will provide a working copy <br />to Redwood City at no cost at the completion of the work. G&E licenses SERA <br /> <br />October 9, 2009 <br /> <br />Page 3 <br />