Series: Colorado Water Law Basics #12 - The Relationship between SB-213 and SB-5

Figure 1: Denver Basin aquifer system map.

If you live in the Colorado Front Range, you likely have drunk water from the Denver Basin aquifer system. This massive aquifer system goes from Greeley to the north, Colorado Springs to the south, Limon to the east, and the Hogback ridge (Dakota Group geologic formation) to the west. The Denver Basin is a geologic structural basin shown in Figure 1 and consists of four major water-bearing aquifers. In stratigraphic sequence in the order of their depth, they are: 1) The Dawson aquifer; 2) Denver aquifer; 3) Arapahoe aquifer; and 4) Laramie-Fox Hills aquifer

The basin can be up to 3,000 feet deep, with the deepest area centered around the Parker area.

The Doctrine of Prior Appropriation does not apply in the Denver Basin, but this does not mean that water rights and legal dates are not an issue. There are several water laws specific to the Denver Basin. This blog focuses on the two significant statutes related to water rights within the Denver Basin: Senate Bill 213 (1973) and Senate Bill 5 (1985); I will explain what these are and how they affect water users within the Denver Basin.

Prior to the passage of Senate Bill 213 in 1973, a landowner could obtain a permit for a Denver Basin aquifer, or multiple aquifers, simply through land ownership, with the permitted volume merely based on need. A water right that was adjudicated prior to Senate Bill 213 is now referred to as a pre-213 water right because these rights have special provisions not applicable to other Denver Basin water rights permitted after the effective date of Senate Bill 213. Pre-213 rights refer to any water right permitted prior to May 5, 1973.

Senate Bill 213 set forth several provisions related to Denver Basin groundwater rights for the first time. These include:

• Water developed from Denver Basin aquifers was presumptively considered to be nontributary.

• It established a minimum useful life of the aquifers.

• Water supply availability was tied to land ownership.

What do these provisions mean relative to Senate Bill 213?

Under Senate Bill 213, all Denver Basin aquifer water was presumptively considered to be nontributary. This meant all of the water produced could be used and reused to extinction. However, no specific definition of “nontributary” was included in Senate Bill 213.

Senate Bill 213 established the 100-year rule, also known as the useful-life concept. The 100-year rule specifies that “the minimum useful life of the aquifer is 100 years” and, therefore, to achieve this useful life, annual withdrawals are limited to 1 percent of the appropriated volume of water. For example, if the total appropriated volume of water beneath a property is 100 ac-ft, the annual withdrawals are limited to 1 ac-ft per year.

The 100-year useful life of the Denver Basin aquifers was then used as part of the methodology to tie water supply available for appropriation to a specific property. A Denver Basin groundwater right permitted after Senate Bill 213 is limited to the groundwater within the specified aquifer under the owner’s property. This concept is illustrated in Figure 2, where the water in each aquifer layer is quantified beneath a property. This volume of water is determined by the formula:

V = ((A)*(b)*(Sy))/100

Where, V = annual volume available for appropriation (ac-ft/yr)

A = surface area of the property (ac)

b = saturated thickness of the aquifer (ft)

Sy= specific yield of the aquifer (dimensionless)

Nontributary groundwater available for appropriation was considered to be the drainage portion of the water in the formation, i.e., the specific yield of the formation and not the porosity.

While the land ownership concept can be applied for all Denver Basin aquifer water rights after the enactment of Senate Bill 213, there was a problem with rights that had already been granted prior to Senate Bill 213. A water right permitted prior to May 5, 1973 can extend outside of a property boundary, so the question arose of how to deal with the situation where a pre-213 right overlaps onto another property that is appropriating its Denver Basin rights based on land ownership. A methodology was developed to address this issue so there would be no double counting of available water due to the overlapping of pre-213 and post-213 rights.

Figure 2: Denver Basin water appropriation.

Figure 3: Example of map indicating cylinders (circles) of appropriation.

To make sure that pre-213 rights are protected and post-213 rights acknowledge the pre-existing rights, all water rights in the Denver Basin permitted prior to May 5, 1973 have been assigned a volume equal to the volume appropriated by that pre-213 well in the form of a cylinder that extends through the entire depth of the aquifer and is centered on the well (commonly referred to as a “cylinder of appropriation”). A cylinder was adopted as the means to protect pre-213 rights as it provided a simple way to calculate the volume that needs to be protected and is somewhat representative of the water to be appropriated around the well. The formula for establishing the cylinder of appropriation is:

r = sqrt((V)/((Sy)*(b)*(π)))

Where, r = radius of the circle of appropriation

V = annual volume available for appropriation (ac-ft/yr)

Sy = specific yield of the aquifer (dimensionless)

b = saturated thickness of the aquifer (ft)

π = pi (3.141)

Based on this cylinder of appropriation (example shown in Figure 3), which is shown as a circle surrounding the well in plan view based on the above formula, any overlap of the circle onto adjacent land is reduced from the annual volume available for appropriation (A) in the formula for the annual volume of available appropriation on that adjacent land. In this way, the more “senior” pre-213 right is protected and the more “junior” post-213 right has its rights reduced to protect the previously permitted right.

Plan view areas of the pre-213 cylinders of appropriation are available to download from the DWR map viewer: The layer is called “DWR admin Data” and the sublayer is titled “Pre-213 Cylinder.”

Senate Bill 213 controlled the permitting of Denver Basin groundwater until a numerical model was developed in the early 1980s that evaluated not only Denver Basin groundwater pumping but also its potential hydraulic effect on stream systems that transect the basin on the surface. This model indicated that some pumping of Denver Basin water in some aquifers and at some locations may affect stream flow by greater than 0.1 percent of the cumulative water pumped over that 100-year period. Therefore, there was a movement to define nontributary groundwater more closely in the Denver Basin: the result was Senate Bill 5.

Because of the re-interpretation of the effect of pumping Denver Basin aquifer water on surface streams, Senate Bill 5 modified the interpretation of nontributary groundwater by adding an additional term “not-nontributary” groundwater (see also LWS Aug. 11, 2020 blog). In addition, “nontributary” was defined for the first time.

While nontributary water was defined as continuous pumping for 100 years that will not affect stream flow by greater than 0.1 percent of the cumulative water pumped over that 100-year period, not-nontributary water was defined as the opposite, i.e., continuous pumping for 100 years will affect stream flow by greater than 0.1 percent of the cumulative water pumped over that 100-year period. To define the areas of the Denver Basin that are nontributary versus not-nontributary, the Denver Basin Rules Maps were produced for each aquifer: https://dnrweblink.state.co.us/dwr/DocView.aspx?id=3121553&dbid=0&cr=1 (cookies must be enabled to view). These maps define the line that delineates nontributary water on one side of the line and not-nontributary water on the other side of the line. For more information on the Denver Basin Rules for not-nontributary water, see our August 11, 2020 blog.

The practicality of Senate Bill 5 is that there is now a major difference in the development of Denver Basin aquifer water, depending on whether the water is considered to be nontributary versus not-nontributary. If the water being developed is nontributary, that water can be developed by showing ownership of the water beneath a specific parcel of land. Conversely, the inclusion of the new type of Denver Basin aquifer water, not-nontributary, is that prior to use of this water an augmentation plan is required so that both pumping and post-pumping depletions are augmented. How these depletions are evaluated is described in the August 11, 2020 LWS blog post. In practice, this means that it is more complicated to develop not-nontributary water than nontributary water.

LWS personnel have been involved in permitting and adjudicating Denver Basin aquifer water rights for over 40 years; Mr. Lytle has overseen the installation of over 50 Denver Basin wells, including wells in all of the principal aquifers. If you have questions or needs related to the development of Denver Basin aquifer water rights, please give us a call (303-350-4090) or send LWS an email.

Bruce Lytle, P.E. bruce@lytlewater.com

Chris Fehn, P.E., P.G. chris@lytlewater.com

Ben Bader ben@lytlewater.com

Anna Elgqvist, E.I. anna@lytlewater.com