At least two wells shall extend to a depth of at least 6 feet (1829 mm) below the ground surface and shall be a minimum of 3 feet (914 mm) below the designed system depth. However, with layered mottled soil over permeable unmottled soil, at least one well shall terminate within the mottled layer. Monitoring at greater depths shall be required, where necessary, due to site conditions. The site evaluator shall determine the depth of the monitoring wells for each specific site. All depths shall be approved. The monitoring well shall be a solid pipe installed in a bore hole. The pipe size shall be a minimum of 1 inch (25 mm) and a maximum of 4 inches (102 mm). The bore hole shall be a minimum of 4 inches (102 mm) and a maximum of 8 inches (203 mm) larger than the pipe (see Appendix A, Figure A-2).