2 Colo. Code Regs. § 402-7-8

Current through Register Vol. 47, No. 20, October 25, 2024

Rule 2 CCR 402-7-8 - Determination of Allowed Annual Amount of Withdrawal

The allowed annual amount of withdrawal from a well permitted pursuant to Section 37-90-137(4), C.R.S. shall be determined based on the following criteria:

A. The allowed average annual amount of withdrawal shall be based on an aquifer life of 100 years in accordance with Section 37-90-137(4)(b)(I), C.R.S. The allowed average annual amount of withdrawal for all of the wells on the overlying land shall not exceed one percent of the total amount of water, exclusive of artificial recharge, recoverable from a specific aquifer beneath the overlying land. However, the allowed annual amount of withdrawal may exceed the allowed average annual amount of withdrawal as long as the total volume of water withdrawn from the well or wells does not exceed the product of the number of years since the date or dates of issuance of the well permit or permits or the date or dates of determination or determinations of right to ground water by the water court, whichever comes first, times the allowed average annual amount of withdrawal.

B. The total amount of water recoverable from a specific aquifer from a well or wells shall be determined by multiplying the number of acres of overlying land as adjusted by Rule 8.C., if necessary, by the average number of feet of saturated aquifer materials in the aquifer underlying those lands by the average specific yield of those saturated aquifer materials. The allowed average annual amount of withdrawal shall be 1% of the total recoverable water. In the case of aquifers to which the above formula does not apply, e.g., fractured formations, the total amount of water recoverable shall be determined in accordance with an appropriate methodology, as determined by the State Engineer.

C. If the cylinder or cylinders of appropriation of a well or wells meeting the requirements of Section 37- 90-137(5), C.R.S. overlap the overlying land claimed in the application, the number of acres of overlying land claimed in the application shall be reduced by the number of acres of the cylinder or cylinders of appropriation which overlap the land, unless the water court has determined some other acreage to represent the cylinder or cylinders of appropriation which overlap the land. The area of the cylinder of appropriation of a well meeting the requirements of Section 37-90-137(5), C.R.S. shall be computed as defined in Rule 4.A.7), making the following assumptions, if necessary:

1) In the event that the well meeting the requirements of Section 37-90-137(5), C.R.S. does not fully penetrate the aquifer, the radius of the cylinder of appropriation for that well shall be calculated assuming that it does fully penetrate that aquifer.

2) In the event that a well meeting the requirements of Section 37-90-137(5), C.R.S. is constructed so as to produce water from more than one aquifer, cylinders of appropriation shall be calculated for each aquifer. The production of the well from each aquifer shall be allocated in proportion to the historical production of the well from each aquifer. If no data are available to show what the production from each aquifer was, the production shall be divided equally between the aquifers.

3) In the event that the specific yield for a well meeting the requirements of Section 37-90-137(5), C.R.S has not been specified by decree, it shall be assumed to be the same as for the well for which an application for a permit is being evaluated, absent site specific data for the existing well.

4) In the event that the thickness of saturated aquifer materials for a well meeting the requirements of Section 37-90-137(5), C.R.S. has not been specified by decree, the thickness of saturated aquifer materials shall be assumed to be that thickness existing at the time of the issuance of the permit, registration of the well with the State Engineer, or decree, whichever was earlier.

5) In the event that a well meets the exemptions specified in Section 37-92-602(1), C.R.S., the area of the cylinder of appropriation shall be considered to be zero.

D. The specific yield value to be used in calculating the allowed average annual amount of withdrawal must be an average value representative of the ground water which underlies the overlying land and must be a weighted average for the saturated aquifer materials within the specific aquifer. If the State Engineer has established the specific yield of an aquifer or portion thereof by rule, an applicant or permittee may submit to the State Engineer site specific data which were obtained pursuant to either Rules 8.D.1), 2), 3) or 4), and the State Engineer shall consider those data in determining the allowed average annual amount of withdrawal. If the State Engineer has not established the specific yield of an aquifer or portion thereof by rule, he may require, as a condition of approval on the well permit, the applicant to obtain site specific data for specific yield pursuant to Rules 8.D.1), 2), 3) or 4). If a permittee is unable to obtain site specific data, the State Engineer shall assign a specific yield value. Specific yield data must be submitted to the State Engineer within sixty days of the tests. Specific yield tests must be done in accordance with the following criteria:

1) If cores are collected, the depths for collecting either side hole or down hole vertical cores shall be selected by the applicant or his consultant, but they must be obtained from within that portion of the aquifer materials which are claimed to be saturated. Laboratory tests must be conducted on a minimum of three samples from each well within the total claimed saturated aquifer materials from each well.

2) Laboratory tests for specific yield must be made on undisturbed samples which can be cut from either sidewall or vertical cores. The particular procedure for sample preparation and testing of coarse and medium textured materials shall comply with the American Society for Testing and Materials (ASTM) Standards as described by ASTM Designation D 2325-68, as reapproved in 1981, which appears on pages 363 through 369 in the 1985 Annual Book of ASTM Standards Volume 04.08 Soils and Rock; Building Stones, and which is hereby incorporated by reference into this rule. This rule does not include later amendments to or editions of the incorporated material. Certified copies of the complete text of the material incorporated shall be maintained by the Office of the State Engineer and shall be available for public inspection during regular business hours. Certified copies of the material incorporated shall be provided at cost upon request. The title and address of the employee of the Office of the State Engineer who will provide information regarding how the incorporated material may be obtained or examined is: Assistant State Engineer for Ground Water, 1313 Sherman Street, Room 818, Denver, Colorado 80203. The number of tests conducted on a sample and the specific negative pressures may vary, but, as a minimum, values must be obtained at tensions (negative pressures) of 10, 30, 100, 300, and 450 feet of water. Laboratory test data shall be plotted as a moisture content-tension curve. The appropriate value of specific yield for the sample will be the lesser of the specific yield for the test conducted at the greatest negative pressure or the value coinciding for the negative pressure in feet which is equal to the thickness of the aquifer or portion thereof at the well site.

3) In unconfined aquifers, the State Engineer shall accept an aquifer or well test ascertaining the specific yield of the aquifer at the location of the well.

4) The applicant, prior to well construction, may request the State Engineer to consider the use of substitute laboratory procedures for determining specific yield, the use of geophysical logging procedures which measure specific yield directly, or the use of other methods to determine specific yield. The State Engineer shall evaluate the request and either approve or disapprove the alternate method and inform the applicant accordingly.

E. The number of feet of saturated aquifer materials shall be determined as follows:

1) The number of feet of saturated aquifer materials from a specific aquifer will be calculated from analysis of geophysical logs meeting the minimum log requirement described in Rule 9 or by application of valid Rules & Regulations applying to a particular aquifer. The appropriate value for use in determining the allowed average annual amount of withdrawal will be an average value for the saturated aquifer materials which underlie the overlying land. The applicant may be required to demonstrate that the individual aquifer materials are in fact saturated in order to claim those zones in the calculation of saturated aquifer materials.

F. The State Engineer shall require an applicant or permittee who wishes to submit site specific data to establish the average specific yield value or average number of feet of saturated aquifer materials underlying the overlying land to furnish data obtained from more than one site, if necessary, to determine an average value for the land. Data obtained for a specific site shall be presumed to be representative of aquifer characteristics within 1,320 feet of that site.

2 CCR 402-7-8