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4.9.4.1. This date that the vacuum was applied may be used as a reference under this procedure to evaluate the tank's integrity prior to installation. 4.9.4.2. Tanks shipped under vacuum must be under vacuum for a minimum of 7 days. If this requirement is not met, a pressure soap test is required. 4.9.4.3. The tank shipped under vacuum should be installed and backfilled with the vacuum intact if both of the following two conditions are met: • installation of the tank is to begin 7 days or more afterthe factory application of vacuum (as indicated on the shipping documents and/or tank labels) • the vacuum gauge shipped with the tank reads 12 inches of mercury [40 kPa] or more NOTE: Under certain field conditions (such as major changes in temperature, barometric pressure and/or altitude) and/or with certain equipment failure (such as freezing or sticking of gauge mechanism), the vacuum -monitoring method may not be an accurate enough test. 4.9.4.4. When in doubt, or when such conditions occur, see Pressure -Testing Sidebar for instructions on testing a dry, double-wall tank not under vacuum. 4.9.5. PRESSURE TESTING A DRY -MONITOR, DOUBLE-WALL TANK NOT UNDER VACUUM 4.9.5.1. See Pressure -Testing Sidebarfor instructions. 4.9.6. PRESSURE TESTING A DRY -MONITOR, DOUBLE-WALL MULTICOMPARTMENT TANK NOT UNDER VACUUM NOTICE Do not connect pressure source directly to the access fitting for interstitial -space monitoring. Pressurizing the interstitial space by itself could result in damage to the primary tank and/ortank failure. 4.9.6.1. See Pressure Testing Sidebarfor instructions. 5: INSTALLING TANKS 5.1. GENERAL S.I.I. Take safety precautions throughout the entire installation process. See the Introduction. 5.1.2. Use only approved backfill material. See section 1.2. 5.1.3. Do not mix approved material together with sand or in-situ soil. 5.1.4. Do not use in-situ soil as primary backfill material. 5.1.5. Typically, all excavated in-situ soil must be replaced with primary backfill material. 5.2. DRY -HOLE INSTALLATION 5.2.1. Before beginning tank installation, take a tank diameter measurement. See section 1 for instructions. 5.2.2. Record this measurement as Measurement#1 on theTank Installation Checklist. 5.2.3. Locate the excavation site according to instructions in section 1 5.2.4. Prepare the excavation according to instructions in section 1 and the following points: • When preparing the excavation, allow for an anchoring system (if used) and geotextile fabric (if used). See section 1. • When preparing the excavation, allow forthe appropriate depth of cover as specified in section 1. • If two or more tanks are to be installed in the same excavation hole, follow instructions in section 1. • If the tank has a bottom sump or fitting, prepare the excavation hole according to instructions in section 1. 5.2.5. If an anchor slab is needed, install it now. See section 1. 5.2.6. Where necessary, level the bottom of the excavation using primary backfill material, filling in any low areas. See section 1 for backfill requirements. 5.2.7. Geotextile fabric, if used, must be placed to separate the primary backfill material from all other in-situ soil and/or secondary backfill material. See section 1. 5.2.8. If deadmen are used, see section 1 for information on deadmen placement. • If deadmen are used and they are to be placed so that they are in the bedding or below the bottom of the tank, place the deadmen before preparing the backfill bedding. 5.2.9. Prepare a 12 -inch -thick [30 -cm -thick] smooth, level bed of approved primary backfill material on the bottom of the excavation or on top of slab. See section 1 for backfill requirements. NOTICE If anchor straps are used, bedding must be carefully leveled. Failure to follow this notice could result in straps being too short or too long, which could result in property damage. NOTE: If the excavation has soft soil conditions or if there might be difficulties controlling water accumulation, it is acceptable to increase the bedding thickness as needed. Set the tank anchors once the bedding thickness has reached a level 12 inches [30 cm] below the tank bottom elevation. 5.2.10. See section 2 regarding the use of lifting lugs to hoistthe tank when unloading and installing it. NOTICE Do not set tanks directly onto a concrete slab, timbers, cradles or in-situ soil. Failure to follow this notice could result in damage to the tank. 5.2.11. Place the tank or tanks onto the bed: • If deadmen are in place, centerthe tanks between them. • Align the tanks with anchors for proper placement of anchor straps. • As the tank is being placed, slope the tank according to site specifications. • Sloping of tanks may affect accuracy of calibration charts. • If a double-wall tank is sloped, the monitor should be at the low end in a tank with a dry interstitial space and at the high end in a tank with a wet interstitial space. NOTE: We do not require that a tank be sloped. However, sloping the tank may be required by the tank owner's specifications.