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O DEPTH OF EXCAVATION EXCAVATION SIZE U The hole must be deep enough to provide sufficient Stable Soil Conditions bedding and cover depth as determined by the type of Jsurface pavement and loading. NFPA 30 and 31 should Where shoring is not required to maintain a vertical wall J1Wbe consulted as well as local codes. from top to bottom of the excavation, the minimum spacing between the sidewall or endcap of the tank and Tanks subjected to - _=_ - ZI side of excavation must be 24 inches (61 cm). traffic loads must have 6" a cover depth of at N I� H--p 6„ If more than one tank is to be installed in the same hole, least 30 inches (76cm) there must be at least 24 inches (61 cm) between the !I �if � of backfill plus 6 inches tanks. - (15cm) of asphalt. An _ 1 acceptable alternativeTRAFFIC III u is a minimum of 18 30 _ DRY CONDITIONS Stable inches (46cm) of 12" Soil backfill plus 6 inches -� �_ �I� (15cm) of steel re-bar S - reinforced concrete. Tanks subjected to = traffic loads and high ---- water must have a 8„ 6 24"� 24 minimum of 30 inches24 =11' _ C"F (76cm) of backfill and °IIII-I II��"II either 8 inches (20cm) =1 _ FIT, _ =-'r -fILI,=I = of asphalt or 6 inches - p 30" (15cm) of steel re-bar 30�� TRAFFIC CONDITIONS ` reinforced concrete. ] 12„ '" Unstable Soil Conditions If the soil has less than 750 lbs/sq. ft. cohesion as cal- culated from an unconfined compression test;or in soils Tanks not subjected to having an ultimate bearing capacity of less than 3500 traffic loads must have lbs/sq. ft.; or where soil will not maintain a vertical wall, a minimum cover 24" the excavation must allow a minimum space equal to 1/2 depth of 24 inches 4 12" the diameter of the tank between the side and endcap (61 cm)of backfill,or 12I - �- of the tank and the excavation wall. The spacing be- inches (30cm) backfill -- fi tween adjacent tanks, 24 inches (61 cm), remains the plus 4 inches (10cm) _ DRY - same. of steel re-bar rein- - coNNioloNs p forced concrete. - - TRAFFICf'I'� Unstable 1.„I � ; , '/z Soil I -' 12' Tank �I;II Dia. Tanks in high water areas not subjected to traffic loads must have _ a minimum of 36 - 1- inches (91 cm) of 36" '/z Tank _}I 24" backfill covering. Dia. t - WET - D', ilk - ,_' 1 7m 3nCONDITIONS -' rNO - TRAFFIC 12" NOTE: MANWAY RISER MUST NOT REST ON THE TANK. There must be a minimum six-inch space between the bottom of the riser and top of the tank. NOTE: These depths of cover are MINIMUMS for high water areas without traffic over the tank. NOTE:Asphalt and concrete pads must extend a minimum of 12 inches (30cm)beyond tank in all directions. NOTE: Maximum burial depth is 7 feet(2.1 meters)of cover over top of tanks.