Section 15.102 - Deep Observation Hole Test(1) The purpose of the deep observation hole test is to determine in accordance with 310 CMR 15.103 the soil profile in the proposed disposal area, the depth of overburden above ledge, bedrock or impervious layer(s), and to determine the observed ground-water elevation at the time of testing and to gather evidence to determine the adjusted ground-water elevation.(2) A minimum of two deep observation hole tests shall be performed in the presence of the Approving Authority at every proposed disposal area, two in the primary area and two in the reserve area. Additional testing shall be required if, in the opinion of the Soil Evaluator or the Approving Authority, there is evidence of inconsistent soil characteristics, the presence of ledge, or additional testing is necessary to properly assess site conditions within the proposed location to ensure that it can be installed entirely on soils and slopes in conformance with the requirements of 310 CMR 15.000. When a trench system is to be designed with the reserve area between the trenches, the Approving Authority may allow two deep hole observations if in the opinion of the Approving Authority the two deep holes adequately characterize the soils in both the primary and reserve areas.(3) Deep observation holes shall be excavated in two adjoining segments, the first ending at approximately the five-foot level to allow detailed examination by the Soil Evaluator without need for shoring, and an adjoining segment which shall extend to a minimum depth of four feet below the bottom elevation of the proposed soil absorption system but in no case less than ten feet below existing/natural grade unless such depth is unattainable due to bedrock or refusal or high groundwater, or where human safety may be in jeopardy.(4) Every deep observation hole shall be located from known and recoverable reference points or benchmarks so that it may be located on the system design plan with an accuracy of one foot. The location of the hole shall be defined as being half way between the side walls of the excavation at the point where the five foot deep segment adjoins the deeper segment.(5) It shall be the responsibility of the owner or agent to ensure that every deep observation hole is secured to prevent accidents whenever work is not in progress.