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6.2.1.4.When using select crushed stones,they must con- 7. EXCAVATION REQUIREMENTS form to the specifications of ASTM C 33,size numbers 7 or 8. See FIGURE 6-1 and Xerxes Primary Backfill Requirements, 0 WARNING APPENDIX B,for additional information on backfill material Follow OSHA regulations for tank excavations.Collapse of specifications. excavation walls could result in death or serious injury. 6.2.2.Xerxes recommends that the supplier of backfill material 7,1. GENERAL provides written certification that the material conforms to 7,1.1.The installing contractor must take all necessary pre- ASTM C 33,ASTM D 446,AASHTO M 43,and any other appli- cautions in or near a tank excavation.These precautions cable specifications. should include but are not limited to the following: 6.2.3.If primary backfill material which meets these specifications 7.1.1.1.Locate and protect any utility installations near the ex- is not available,contact technical support at Xerxes Minneapolis, cavation before opening the excavation. MN,for information on alternate materials,installation instructions for alternate materials and the process for approval. 7.1.1.2.Secure the walls of the excavation. 6.3. SECONDARY BACKFILL 7.1.1.3.Prevent exposure to hazardous fumes from the excavation. 6.3.1.Material is to be clean,free-flowing,and free of large 7.1.1.4.Avoid hazards associated with water accumulation in rocks,roots,organic materials,debris,ice and snow.Backfill the excavation. material shall not be frozen or contain lumps of frozen material 71 1.5.Erect barricades,etc.,to prevent unauthorized vehicle at any time during installation. or pedestrian traffic. 6.3.2.Material must be compacted to achieve a minimum of 7.1.1,6.Inspect,a minimum of once a day,the excavation and 85 percent standard proctor density. surrounding area during the entire installation process. 6.3.2.1.Do not use rammer-type compactors over the top of 7.1.2.For additional information on excavation,trenching and the tank. shoring safety practices,consult OSHNs Standard,Part 1926, 6.3.3.Material must be installed in 12-inch to 24-inch lifts Subpart P(Excavations),650-652;and"Fall Protection Rules compatible with the compaction equipment used. and Regulations." 6.3.4.In some conditions,frost heave may be encountered 7.1.3.The minimum clearance dimensions given in this section when using secondary backfill.Therefore,consider any frost- are important to the successful installation of a tank. related problems that may occur. 7,1.3.1.Additional clearances may be necessary due to fed- 6.3.5.Specifications for secondary backfill material and com- eral,state or local regulations,safety requirements or opera- paction above the fitter-fabric layer may be determined by the tional requirements.Follow all applicable regulations and requirements of the piping,surface slab or roadway. safety practices. 6.3.6.Refer to applicable codes or standards for base course 7.1.3.2. For additional requirements and specifications,con- and sub-base course material and compaction requirements. sult all applicable federal,state and local codes and regula- 6.3.7.The following are examples of acceptable secondary tions.See SECTION 1 for additional information. backfill material: 7.2. EXCAVATION AND TANK LOCATION 6.3.7.1.clean native backfill 7.2.1.Xerxes recommends that the tank owner seek the advice of a local foundation professional engineer to determine the proper 6.3.7.2.coarse sand or gravel. placement of a tank excavation near any existing structure(s). 6.3.8.One hundred percent(100%)of all backfill material must pass through a 1-inch sieve. I CAUTION 6.3.9.Install a layer of geotextile fitter fabric over the entire surface Improper placement of the excavation may result in damage of primary backfillmaterial before secondary backfill is placed.See to the tank and/or property damage. SEC710N9 for information regarding geotextile fabric. 7.2.2.The tank owner and/or the owner's technical represen- tative is responsible for determining the proper placement of a 6.3.9.1.All joints in the filter fabric must be overlapped amini- tank excavation. mum of 12 inches. 6.3.9.2.Geotextile fabric must overlap onto the tank and exca- 7.2.3.In general terms,the size of the excavation is deter- vation surface a minimum of 12 inches. mined by: 6.3.10.See Xerxes Split Backfill Instructions,APPENDIX C,for 7.2.3.1.the number of tanks to be installed more Information regarding this alternative. 7.2.3.2.the size of the tanks to be installed. 7.2.4.The location of a tank can be affected by the location of nearby structures.When selecting a tank site,care must be taken to avoid undermining the foundations of existing struc- tures or new buildings to be constructed.See FIGURE 7-1. 11