A digging boom assembly including a first section which is attached to a trencher and a second section that may be disconnected from the first section and replaced with another identically configured section of longer or shorter length. The boom assembly is attached to the trencher such that the first section always remains connected to the trencher while the second section may be selectively exchanged with another section of a different length thereby permitting variable digging depths. An auger attachment and a crumber attachment are connected to the first boom section, which remains attached to the trencher at all times. Thus, when the second boom section is disconnected and replaced with another section of longer or shorter length, the auger and crumber attachments do not have to be disassembled from the boom assembly.