2 Colo. Code Regs. § 402-6-9
The following aquifer characteristics established by these rules (in addition to the specific yield values set forth in Rule 6) are deemed presumptive: the elevation of the top or bottom of any of the Denver Basin Aquifers at a specific location; and the number of feet of saturated aquifer materials in any of the Denver Basin Aquifers at a specific location. If an applicant or permittee submits site specific data satisfactory to the State Engineer which support the use of a different value for one or more of the above aquifer characteristics, then, for the purpose of determining the allowed average annual amount of withdrawal from the well and the interval from which the well may withdraw water, the State Engineer shall modify the aquifer characteristic or characteristics accordingly. Such site specific data may include, but are not limited to, geophysical logs. Such use of site specific data shall not be deemed to be a modification of these rules. In determining whether an applicant or permittee has rebutted one or more of the above presumptive aquifer characteristics, nothing in this rule shall preclude the State Engineer from considering any other site specific data available to him.
2 CCR 402-6-9