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Minimum Burial Depth Traffic Loads (4' - 10' diameter tanks) • Tanks need a minimum cover depth of 36" backfill or • 18" of backfill plus 6" of reinforced concrete.* *When mechanical anchoring is required, 6', 8' and 10' diameter tanks must be buried a minimum of 36". Note: • The reinforcements in the concrete traffic slab must be properly sized for job conditions to assure concrete surface pad integrity. (12' diameter tanks) • Tanks need a minimum cover of 38" backfill plus 6" of asphalt or 6" of reinforced concrete. A6. Filter Fabric Why use filter fabric? • It prevents the migration of pea gravel with native soil. • It helps maintain the integrity and stability of backfill materials. Owens -Coming requires the use of filter fabric for the following types of installations: • Tidal conditions. • Areas subjected to frequently changing ground water levels. • Unstable soils (muck or landfills, see section A4). • Water conditions with silty soil. For other types of installations, the responsibility for determining if a filter fabric is appropriate for a specific tank installation remains with the tank owner or technical representative. Installing Filter Fabric — Dry Hole • Line the sides and bottom with filter fabric. • Overlap adjoining fabric panels at least 12". • Place some backfill on top of the filter fabric to hold it in place. Installing Filter Fabric — Wet Hole • Backfill ballast is necessary to sink and hold the fabric to the bottom of the hole. Suitable brand name filter fabrics are listed below. Call the phone numbers listed for local distributors. Manufacturer Product Phone Reemay, Inc. TYPAR 3401 (800) 284-2780 TYPAR 3341 (615) 847-7000 Phillips Fibers SUPAC 4NP (800) 374-6606 (803) 242-6600 Hoechst Celanese TREVIRA S1120 (800) 845-7597 Corporation (hole depth less than 10') (803) 579-5269 TREVIRA S1125 (hole depth greater than 10' deep) • DO NOT use polyethylene as a filter fabric because it will degrade over time. A7. Anchoring It is the responsibility of the tank owner or the owner's technical representative: • To determine if mechanical anchoring is required for a specific job site. • To consider all potential sources of water, such as: ❑ Underground water table. ❑ Rain water run-off, etc. What is the purpose of anchoring? Mechanical anchoring is used to secure the tank in conditions where the tank could become buoyant (i.e. water in the hole). There are two common methods of mechanical anchoring: • Concrete anchor pad. -Deadman anchors. Note: Both methods require the use of Fiberglas anchor straps. When do you need to anchor your tank? If water can enter the hole, Owens -Coming recommends that tanks be mechanically anchored unless the minimum burial depth from tank top to grade is as follows (unless noted otherwise, assumes no turbine enclosures, sumps, or manway risers are installed; assumes water to grade and tank empty). Tank Diameter Minimum Burial Depth (s.f. of 1.2) when Mechanical Anchoring may not be required O O O 4' 30" 26" 34" 6' 48" 44" 48" 60" 8' 58" 54" 10' 74" 1 70" 78" 12' Requires Anchoring o Assumes no concrete slab. o Assumes a reinforced concrete traffic slab thickness of 8". o Assumes 42" sealable turbine enclosure and no top slab.