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Response to CGS Comments Lincoln Elementary School Mode ization 750 E. Yosemite Avenue Manteca, Califomia Page 2 Adjusted maximum Considered Earthquake Spectral Response Accelerations Snss 0.908 SNH 0.907 Design Spectral Acceleration SDs 0.605 SDI 0.605 We recommend using the following design values: SDs 0.61 SDI 0.61 Section 6.2 LIQUEFACTION, SEISMIC SETTLEMENT POTENTIAL, Condor has made the following corrections to the Liqutefaction analysis: • Layer 6 ilea beea. broken out auto Layer 6 "w`ath an Ar -value of i i aatd J. , er 7 with an Al -value of 8. ® The layers 6 and 8 (now 9) are described in the Material Type as Cohesive Soil even though they are non -plastic because the model only presents the option of selecting the USCS classification of ML (silt) with thss setting. We concur that this does not affect calculations. • The fines content of layers 6 and 8 (now 9) have been reduced to 60% to represent silt values. e The Energy Ratio (Cr) has been reduced to 80%. • The rod length correction (CR) has been changed to 6.0. ® The sampler correction factor (Cs) has been unchecked so that it will not be applied. Using the above corrections and adjustments, Condor reran the liquefaction analysis at three different groundwater depths. Model Run Calculated Settlement 5/15/15 with groundwater at 10 feet below ground su ce 1.16 inches (original run) 11/4/15 with groundwater at 6.6 feet below ground surface 3.95 inches 11/4/15 with groundwater at 10 feet below ground surface 3.21 inches 11/4/15 with groundwater at 19.8 feet below ground surface 1.82 inches Recommendations Our previous recommendations were provided based on the total liquefaction surface settlement of I to 2 inches (pg. 8). The above revised calculations indicates that the surface settlement would be 2 to 3 inches at the recommended design groundwater depth of 10 feet to 20 feet; and as high as 4 inches if the groundwater were to rise to the historic (1956) levels. Due to the shallow footing depths relative to the settlement values at shallow depths, bearing failure is not a risk. The design criteria due to potential liquefaction settlement are therefore vertical displacements across a building footprint. We previously estimated differential settlement across a typical building footprint to be 0.5 to I inch. We are revising this estimate to I to 3 inches across a building footprint. Based on the modest change in the calculated liquefaction settlement and estimated differential settlement, we have not revised the over -excavation depth, but reconfirm that foundation excavations should be inspected at the time of construction, and inspection and testing be performed during grading W CONDOR