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4" STABLE SOIL 'U ti 4'. f 16" 18" i9" DRY t2" '48] CONDITIONS 36" sic NOTE:Numbers in brackets[] is, 18" I z" refer to 12'tanks. Tanks not subjected to traffic loads must have a minimum cover depth of 24[48]inches of backfill,or 12[36]inches backfill plus STABLE SOIL CONDITIONS 4 inches of reinforced concrete or 6 inches of asphalt Where shoring is not required to maintain a vertical wall from.top to bottom of the excavation,the minimum spacing between the sidewall or endcap of the tank and side of excavation must be 18 inches(24 inches for 12'tanks).If more than one tank is to be installed in the same hole,there must be at least 18 inches between the tanks. l 36" 1/2 48" CONDI(ONS TANK D[A. UNSOIBLE 18" TRAFFiC S NOTE:Numbers in brackets[] referto 12'tanks. NVAEW K MEMMEM Tanks in high water areas not subjected to traffic loads must have a 1/2 TANK DIA. 1/2 TANK DIA. minimum of 36[48]inches of backfill covering. 111111011111 111011111011011111101111 WARNING:in a non traffic installation,insure that the areas above the tanks will never be subject to traffic loads. III NOTE:These depths of corer are MINIMUMS in all cases. NOTE:Asphalt and concrete pads must extend a minimum of 12 Inches beyond UNSTABLE SOIL CONDITIONS tank In all directions. If the soil has less than 750 IbsJsq.ft.cohesion as calculated from NOTE:Maximum burial depth is 7 feet of cover over top of tanks. an unconfined compression test;or in soils having an ultimate NOTE Unattached manway riser['d present)must not transmit load from the slab bearing capacity of less than 3500 IbsJsq.ft.;or where soil will not to the tank.There must be a minimum 6 inch space between the bottom of the riser maintain a vertical wall,the excavation must allow a minimum and the top of the tank. space equal to 1/2 the diameter of the tank between the side and endcap of the tank and the excavation wall.The spacing between TANK SPACING adjacent tanks,18 inches remains the same. NOTE:Time are minimum spacings and must be increased as needed to accommodate deadmen or anchor slabs.Refer to Section 7 on tank anchoring. FILTER FABRIC Always allow sufficient clearance to allow the deadmen to be set outside of the The tank owner or his technical representative is responsible for tank shadow determining whether filter fabric or an aftemate 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 backfill material.It preserves the integrity of the backfill envelope which supports the tank. Polyethylene film is not considered an effective material to prevent migration of pea gravel and native soil;it may tear or degrade while in service. Xerxes recommends that filter fabric be used when the tank may be installed in: •areas with frequently changing ground water conditions or treas subject to tidal fluctuations, •unstable soils such as bog,swamp,landfill or mud, •water conditions with silty soil.