Ground water that is considered non-tributary on the front-range is contained in the Denver Basin. This basin is 6,700 square miles in area and is estimated to contain 250 million acre-feet of recoverable water. The basin stretches from Colorado Springs on the south to Greeley on the north and Denver on the west to Limon on the east. Today, the Denver Basin provides much of the water used to satisfy growth in Douglas County. However, associated with this growth have been a decline of water levels in wells and a reduction in well yields. Publicity regarding the declining yield per well has created a variety of positive reactions in the water users and providers community.

Historically, computer models by the various state and federal agencies have assumed the Denver Basin to be hydraulically connected to the South Platte River and to the numerous tributary creeks and streams. In addition, it was assumed that the four aquifers in the basin are hydraulically connected vertically. These assumptions provide a modeled prediction of high ground water levels and high ground water production far into the future. Moreover, these modeling assumptions also suggested injury to surface water rights. However, in the 10 to 15 years since these model predictions were made, water levels have declined on average of 30 feet per year in the Arapahoe aquifer with no reported injury to the surface water rights. Therefore, the hydraulic connections assumed historically in the models are currently believed to be incorrect.

When non-tributary water rights are calculated, only the water that is physically contained in the sandstones beneath a given property is a part of the water right. The hydraulic head, or that fraction of the water as measured by a water level in a well that rises above the aquifer, is not a part of the water right. Consequently, for years the entire basin produced water that was not a part of individual or collective water rights, nor is it part of any surface right. Moreover, the hydraulic head in the basin represents less that one percent of the entire water resource. Given that (a) the hydraulic head is a small fraction of the available water, (b) hydraulic head was never a part of the right, and (c) the aquifer is still full, there is only one potential conclusion: aquifer yields under confined conditions represent a temporary condition and long-term yields will continue to diminish as the regional hydraulic head diminishes. What initial well yields were in the past (prior to 1980) and how they will diminish in the future is a function of many geologic and engineering factors, including location and pumping by all wells in the basin. In many parts of the basin, the yields are expected to diminish to approximately 20 percent of the expected yield of a well drilled prior to 1980. The largest portion of the projected decline in well yield is expected in the next 10 to 20 years. Therefore, the last 99 percent of the resource is expected to be produced at approximately 20 percent of the pre-1980 rates.

It is also recognized that water levels measured in wells represent an instantaneous measure of the hydraulic head of the sands intercepted by the screened interval of a well. Without piezometric measurements of each sand in an aquifer, a water level in a well that intercepts multiple sands may not accurately reflect saturated thickness of the combined or individual sands. Therefore, care must be exercised in interpretation of saturated thickness based solely on water levels in wells that interconnect multi-sand aquifers.

Given that historical model studies gave unrealistic expectations regarding well yields, water users and providers alike are concerned about predictions regarding future yield from wells. While this collective concern is understandable, given the history, the primary problem with wells has always been the difficulty with summer peaking. Generally, normal winter demand is about 20 percent of the summer peaking demand. Therefore, having a management storage vessel (Rueter-Hess Reservoir) that allows full time pumping to smooth the peaking issue, interconnections with other providers, and importation of water are prudent management steps for water providers. As always, tying the cost of imported water specifically to peaking water demand will shave demand. Aquifer storage and recovery, surface storage, imported water, and pricing will collectively play a role in the future of both water providers and consumers.

Given all of the drawbacks, it is important to remember that non-tributary ground water can be used and reused to extinction. In the future, water providers will not be able to rely solely on non-tributary ground water for water supply, especially for summer peaking; however, it is reasonably certain that non-tributary ground water will remain an important water supply source.

Therefore, while the source of future water supplies and their costs force new planning considerations as compared to the historical status quo, the steps being taken by Douglas County water providers individually and collectively are prudent and well advised. The Castle Pines North Metropolitan District recently completed two extremely important studies. The first study that was completed by the engineering firm of Camp Dresser McKee was an Integrated Water Resource Plan, which specifically addressed the long term sustainability of the Denver Basin aquifer. Additionally, this plan provided comprehensive information on historical and projected demands, conservation water savings, and renewable supply opportunities. These renewable water supply and management opportunities consist of a variety of water supply and management options, including new surface water supplies, conservation, conjunctive use of ground water and surface water, and water reuse. Castle Pines North also has made water rights filings on Plum Creek in 2004 and is in the process of decreeing these rights. Castle Pines North is one of sixteen entities that are participating in the reallocation of Chatfield Reservoir and is negotiating for storage space within the Rueter Hess Reservoir. The District is currently evaluating renewable water supply opportunities and pursing various water supply partnerships with other water suppliers within the Denver Metro region.

In addition to securing renewable water, the District has embarked on a comprehensive water conservation effort. In August 2006, the Castle Pines North Metropolitan District became the first entity within the State of Colorado to develop a water conservation plan under the Colorado Water Conservation Board’s recently adopted guidelines for water conservation plans. The District also has an extensive reuse program, which provides nearly 240 acre-feet per year of reclaimed wastewater to The Ridge Golf Course for irrigation use.

The Castle Pines North Metropolitan District is committed to securing a renewable water supply for the residents of Castle Pines North. The Board and the management team fully understand the need to act now to secure the needed water supply for this community so that the transition from non-renewable Denver Basin wells to a permanent source renewable surface water can be made as quickly as possible.

For additional information, please contact James McGrady, District Manager, at 303-242-3262, or John C. Halepaska at 303-794-1335 or john@halepaska.com.