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Wrd0tei! bYuvo ticwtr Prugec't L"a�shr r Pifi�il, EC�;tiitir Vnon i, Gur Pvc0d: Nutubar: l..l G••t):i.lSa. May1.6, 2,00"1 compacted native soil may be designed using a net allowable bearing capacity of 1,000 pounds per square foot (psf) for dead plus live loads. Lateral resistance for the vaults may be provided by assuming passive pressure acting against the side of the vault equal to 350 pounds per cubic foot (pcf) equivalent fluid pressure. Lateral resistance may also be provided by computing friction between the bottom of the vault and the soil. A coefficient of friction of 0.50 should be utilized. X044 G®roV�c��to®V�� G®� QRf� H1fe0@s We understand the wet wells will extend to a depth of about 20 to 25 feet below the existing ground surface, Based on our field explorations, it appears the wet wells will bear in sand soils. The wet wells will be constructed with precast concrete barrel sections placed on mat slab foundations. In our opinion, the wet well foundations can be supported on undisturbed, stable native soils. The foundations can be designed for a net allowable bearing capacity of 3,000 psf for dead plus live loads. This bearing capacity may be increased by 1/3 for the temporary loads such as seismic. Based on our field explorations, dewatering o`r the wet well excavations will be required. The dewatering should lower the water table to at least 3 feet below the bottom of the wet well foundation. The soils at the bottom of the wet well excavations are likely to be saturated and unstable at the time of construction, if this is the case, the wet well foundations may be overexcavated 12 inches and a layer of crushed gravel may be placed to provide a stable platform on which to construct the foundations. Depending on the soil conditions encountered at the time of construction this gravel shall be wrapped in a layer of non -woven geotextile fabric, such as Mirafi 140N or Propex 4535 or equivalent, to reduce the potential for fines to migrate into the gravel. Since groundwater was encountered at a depth of about 8 feet below the existing ground surface, for the foundations will need to resis uplift Forces. This can be accomplished by extending the foundations past the edge of the wet wells and using the weight of soil above the foundations to resist the uplift forces. For calculating purposes a buoyant unit weight of the soil can be taken as 60 pounds per cubic foot for soils below a depth of 8 feet. For soils above a depth of 8 feet, a moist unit weight of 120 pounds per cubic foot may be used. The mass of soil resisting uplift forces can be taken as a prism extending up from the edge of the mat slab foundations at a slope of 3/4:1 (H:V) to the top of the existing ground surface. The wet wells should also be designed to resist lateral earth pressures. The lateral earth pressure on a below grade wall depends on the height of the wall, type of backfill, slope of the backfill surface, and allowable horizontal movement on top of the wall. At -rest earth pressures should be used for walls that will not be free to rotate at the top; active NEIL O. ANDERSON AND ASSOCIATES 903 Inah aniol Miy • F.od;, (�A 95240 c )2007 Nei! O. Anderson & Associates. nc.