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0 0 WARNING: In a non -traffic installation, insure that the areas above the tanks will never be subject to traffic or other type loads. NOTE: These depths of cover are MINIMUMS in all cases. NOTE: Asphalt and concrete pads must extend a minimum of 12 inches beyond tank in all directions. NOTE: Maximum budal depth is 7 feet of cover over top of tanks. NOTE: Unattached manway riser (if present) must not transmit load from the concrete slab to the tank. There must be a minimum of 6 inch space between the bottom of the riser and the top of the tank. NOTE: Tanks of 10 foot diameter and 30,000 gallons and larger may require a deeper burial or thicker top slab to offset buoyancy. Contact Xerxes' Technical Service Department for further information. TANK SPACING NOTE: These are minimum spacings and must be increased as needed to accommodate deadmen or anchor slabs. Refer to Section 7 on tank anchoring. Always allow sufficient clearance to allow the deadmen to be set outside of the tank shadow. TOP VIEW FIGURE 4-5 STABLE SOIL CONDITIONS Where shoring is not required to maintain a vertical wall from top to bottom of the excavation, and the soil is stable, the minimum spacing between the sidewall or endcap of the tank and side of excavation must be 18 inches (24 inches for 12 foot tanks). If more than one tank is to be installed in the same hole, there must be at least 18 inches between the tanks. TOP VIEW FIGURE 4-6 UNSTABLE SOIL CONDITIONS If the soil has less than 750 lbs./sq. ft. cohesion as calculated from an unconfined compression test; or in soils having an ultimate bearing capacity of less than 3500lbs./sq. ft.; or where soil will not maintain a vertical wall, the excavation must allow a minimum space equal to 1/2 the diameter of the tank between the side and endcap of the tank and the excavation wall to enhance lateral soil resistance. The spacing between adjacent tanks, 18 inches, remains the same. A reinforced concrete slab may be required under the tank for the foundation in the pit bottom. 0 0 WARNING: ff the soil is extremely soft or inherently unstable, (e.g. peat, quicksand, muck, landfill, very soft or highly expansive clay, �1 etc.) Xerxes recommends that the tank owner seek the advice of a local foundation professional engineer. FILTER FABRIC The tank owner or his technical representative is responsible for determining whether filter fabric or an alternate filtering technique is appropriate for a specific installation. Filter fabric allows the passage of water but prevents the migration and mixing of native soil and the select backfill material. It helps preserve the integrity of the select backfill envelope which surrounds and supports the tank. Xerxes recommends that filter fabric be used when the tank may be installed in: • areas with frequently changing ground water conditions or areas subject to tidal fluctuations, • unstable soils such as cited above, • water conditions with silty soil. For further information concerning fabric specifications and installation procedures, consult the filter fabric supplier's installation guide or instructions. To install filter fabric, typically filter fabric manufacturers recommend that the installer line the excavation sides and bottom with the fabric. Overlap adjoining panels by at least 12 inches. Place backfill material on the panels around the edge of the hole to anchor them in place. In wet -hole conditions, use backfill material to sink and hold the fabric in place on the hole bottom. NOTE: Polyethylene film is not considered an effective material to prevent migration of pea gravel, crushed stone and native soil; it may tear or degrade while in service. 5. DRY HOLEINSTALLATION moi, CAUTION: Xerxes recommends that every site be thoroughly evaluated for the potential to trap water or otherwise subject the tank to a rise in the local water table. Xerxes recommends that all tanks be anchored in installations in which water may enter the hole. Failure to anchor the tank in a wet hole may damage the tank or surrounding property. Prepare a smooth level bed, 12 inches thick, of approved backfill material. Place the tank or tanks onto the bed. Do not set Xerxes tanks directly onto a concrete slab or on timbers, cradles or directly onto the hole bottom. Leveling: As the tank is being placed, set the tank pitch as shown on the site plans. Xerxes does not require that a tank be pitched. All pitch is determined by the tank owners specification. If a double wall tank is pitched, the monitor should be at the low end. Use the tops of the ribs to establish longitudinal level. Establish lateral level by placing the level across the top of a fitting, a manway or a collar. When the tank is placed, take the first diameter reading (Deflection reading "A" on the checklist). See Section 13 for instructions on taking deflection readings. If the tank is to be anchored, install the anchoring hardware at this time (See Section 7).