To: Board of County Commissioners
Through: Bryan Weimer, Director, Public Works and Development
Prepared By:
prepared
Loretta Daniel, Long Range Planning Program Manager and Larry Mugler, Planner/Project Specialist
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presenter
Presenter: Will Koger, Forsgren Associates, Inc., Consultant Team Leader
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Subject:
title
1:00 PM *Arapahoe County Water Supply Study
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Purpose and Request:
recommended action
The Water Supply Study (Study) consultants will be presenting a progress report at the study session. They have prepared a draft of the Study and will summarize the key findings and recommendations before releasing the draft for public comment.
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Background and Discussion: The purpose of the Study is to understand present and future conditions of water supply and demand, to identify efficiencies that can be achieved, and to take steps through comprehensive planning, development review, and regulatory processes to encourage best practices for water demand management, water efficiency, and water conservation. The overall intent of the Study is to ensure that land use decisions are made based on balancing the efficient use of limited water supplies with the needs of new residents, businesses, and industry to have a reliable water supply. Another important consideration was to develop an approach to evaluate the water supply for new development at an earlier stage in the development process.
The goals of the Study are to:
1. Close potential gaps between future supply and demand;
2. Improve water use efficiency; and
3. Extend the life of Denver Basin aquifers to sustain a long-term supply.
The Water Supply Study has a planning horizon of 2050 and expands on the scope of an earlier water study completed in 2001 and which was incorporated into the 2001 Arapahoe County Comprehensive Plan. Recommendations from this Study will be used to update the goals, policies, and strategies in the 2018 Water Supply Study as well as lead to new regulations in the Land Development Code.
The Study is funded through a combination of grants from the Colorado Water Conservation Board and ARPA funding provided by the Board of County Commissioners (BOCC). In November 2022, a contract was signed with a consultant team led by Forsgren Associates, Inc. and with LRE Water and Michael Baker International to carry out the Study with a maximum budget of $494,250.
An Advisory Committee comprised of representatives of the water suppliers and land use planners from the jurisdictions in the county provided guidance and comments for the Study. Three public meetings were held in 2024, one virtual and two in-person, to identify areas of concern and obtain comments. In addition, the public involvement process included an online survey (MetroQuest) which was open in early 2024 for the public to identify their concerns and ideas on a range of topics, including water supply, conservation, and water reuse.
Updates on the Study were provided at study sessions to the Board of County Commissioners (BOCC) on October 31, 2023, and the Planning Commission on November 14, 2024.
To provide an overview, the Water Supply Study includes 10 sections which are:
1. Introduction. This section explains the goals and objectives of the study and introduces the interactive map developed for this Study.
2. Stakeholder/Public Participation. An Advisory Committee was established with representatives of water providers and land use planners in the county’s jurisdictions. Public engagement consisted of a survey and three public meetings which provided opportunities for the public to identify their concerns and provide ideas.
3. Land Use & Socioeconomic Scenarios. Two growth scenarios were developed, in part based on the 2023 Colorado Water Plan. The projections include population and employment growth.
4. Water Providers. This section provides an overview of the water providers in the county and their service areas.
5. Projected Water Demands. Using the growth scenarios of Section 3, water demands were estimated for the water providers’ service areas.
6. Groundwater Analysis. This section identifies the available groundwater sources in the county and describes the results of the Petra modeling.
7. Water Supplies vs. Demands. This section uses the information and data in the previous water demand and groundwater supply information to compare water supplies to demands and identify potential gaps.
8. Water Management Strategies. Strategies such as water conservation are analyzed in detail and estimates of potential reductions are provided. The role of water reuse is also explained.
9. Recommended Policies. The Study concludes with policies for the County to implement.
10. Implementing Recommendations. This is a summary of the recommended policies and actions.
The draft Study and Appendices, which provide technical data and detailed information, are attached.
Groundwater Evaluation
The consultant team identified an approach using production factors based on the Petra modeling for the four Denver Basin aquifers in consideration. There have been previous actions and discussions about the 100-, 200-, and 300-hundred-year “rules” for groundwater. To summarize:
1. State law limits groundwater withdrawals to one percent per year with the intent that the well lasts 100 years. This is often referred to as the “100-year rule.”
2. The County’s 2001 Comprehensive Plan had a policy that limited wells to 50 percent of the state's one percent per year. This would extend the life of a well to 200 years.
3. The Planning Commission directed that the 2018 Comprehensive Plan include a policy with a goal of having wells last 300 years or implement a “300-year” rule.
Neither the policies from the 2001 nor 2018 Comprehensive Plans were incorporated into the Land Development Code.
The approach developed by the consultant team for the Study is based on the productivity of the aquifers in the county since the various aquifers have different groundwater availability. They have proposed applying production factors for each aquifer that would reduce the allowable annual withdrawals by 27 to 71 percent, depending on the aquifer source. As an average for the four aquifers, the production factor is less than the states, or 59 percent of the state’s calculations, as shown in the charts below.
Table 6-4. Comparison of Petra Computation of Physically Available Groundwater vs. Denver Basin Rule Computation (SB-5)
|
Name |
PETRA Groundwater Calculations |
Denver Basin Rule Computations |
Percent Physically Available vs Denver Basin |
|
|
Acre-ft/year |
Acre-ft/year |
% |
|
Denver Aquifer |
4,746 |
7,954 |
60% |
|
Upper Arapahoe Aquifer |
2,022 |
4,779 |
42% |
|
Lower Arapahoe Aquifer |
839 |
3,145 |
27% |
|
Laramie Fox-Hills Aquifer |
4,267 |
5,975 |
71% |
|
Total |
11,873 |
21,853 |
Weighted Average - 59% |
Figure 6-8. Comparison of Groundwater Availability (PETRA VS. SB-5)
The chart above illustrates the differences between the consultant’s Petra modeling and the states’ SB-5 rule. The groundwater available varies significantly for each aquifer.
These different “rules” have implications for the density of development. As an example, if a hypothetical parcel for development consuming groundwater was developed based on:
a. The state’s “100-year” rule, 100 residential units could be developed;
b. The consultant’s recommended allocation of 59 percent, 59 residential units could be developed, which would translate into a “170-year” rule;
c. A “200-year” rule, 50 residential units could be developed; and
d. A “300-year” rule, 33 residential units could be developed.
Fiscal Impact: The Study is on budget and expected to complete the effort within the approved budget.
Alternatives: The draft Study contains a number of recommendations. Before the Study is completed, the Planning Commission and the BoCC will consider adopting the recommendations as part of the Comprehensive Plan followed by possible changes to the Land Development Code.
Alignment with Strategic Plan:
☒Be fiscally sustainable
☒Provide essential and mandated service
☒Be community focused
Staff Recommendation: Following study sessions with the Planning Commission and the BOCC, the draft Water Supply Study will be posted on the project website (www.arapahoeco.gov/waterstudy) for review and comment by the public during the month of October. Staff seeks the BOCC comments on the draft Water Supply Study before the public review period in October. Given the detailed nature of the Study, staff realizes that more time may be needed for review of the Study, and the BOCC’s comments can be provided until the end of September.
Concurrence: The Planning Commission is reviewing the draft Water Study concurrently with the BOCC.