Scope of Work.pdf
PDF 309 KB Posted
- Attached to
- Confined Aquifer Sustainability Study
- Solicitation number
- NPSS1 PEAA 2027000051 1
- Issued by
- Denver County, Denver City, Colorado
About this file
This Scope of Work document outlines a Confined Aquifer Sustainability Study required by the Colorado Division of Water Resources (DWR) and the State Engineer for the Rio Grande Basin (Water Division No. 3). The study must be completed by March 15, 2029—ten years from the March 15, 2019 effective date of the Rules Governing the Withdrawal of Groundwater in Water Division No. 3. The DWR will contract with a private consulting firm specializing in San Luis Valley hydrogeology and experienced with the Rio Grande Decision Support System (RGDSS) to investigate aquifer inflows and outflows, estimate historical water levels and artesian pressures from 1978 through 2000, and examine relationships between groundwater withdrawals, climatic conditions, and system water levels. The project comprises four tasks: Task 1 investigates inflows and outflows from the Confined Aquifer System and evaluates effects of pumping and climate conditions; Task 2 evaluates five potential estimation methods (Thiessen Polygon Composite Head, Linear Interpolation using Reference Wells, Model Infill, Water Budget Approach, and Historic Consumption); Task 3 recommends preferred methodologies; and Task 4 documents findings in a comprehensive report. Key deliverables include completion of the study by September 30, 2028, submission of a draft report by October 31, 2028, and a final report by March 15, 2029.
The consulting firm's technical expertise will focus on understanding aquifer system dynamics, estimating historical water levels and artesian pressures, and analyzing the interrelationship between climate conditions, hydrogeologic conditions, and groundwater withdrawals from both confined and unconfined aquifers. The final report and study recommendations will enable the State Engineer to determine preferred methodologies for maintaining sustainable water supply in the Confined Aquifer System and managing artesian pressures, potentially informing amendments to the existing Rules. The document does not specify pricing terms, contract duration beyond the completion date, set-asides, or funding sources.
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Scope of Work Division of Water Resources’
Confined Aquifer Sustainability Study
Background The State Engineer is required to complete a Confined Aquifer Sustainability Study no later than 10 years from the effective date of the Rules Governing the Withdrawal of Groundwater in Water Division No. 3 (The Rio Grande Basin) and Establishing Criteria for the Beginning and End of the Irrigation Season in Water Division No. 3 for all Irrigation Water Rights (“Rules”). The Rules were approved by the Water Court on March 15, 2019 and were effective on that day. Therefore, the study and associated report are due to the State Engineer by March 15, 2029. The purpose of this study is to provide the State Engineer with the information needed to (a) more fully understand and model inflows to and outflows from the Confined Aquifer System, (b) better estimate the 1978 through 2000 water levels and Artesian Pressures in the Confined Aquifer System, and (c) further investigate the relationship between groundwater withdrawals, climatic conditions, movement of water through the system and the water levels and Artesian Pressures in the Confined Aquifer System. The results of the study will then be used by the State Engineer to determine preferred methodologies for maintaining a Sustainable Water Supply in the Confined Aquifer System and for managing artesian pressures. If needed, the State Engineer will propose reasonable amendment(s) to the Rules based upon this study.
The Division of Water Resources (DWR) will contract with a private consulting firm specializing in the hydrogeology of the San Luis Valley and its underlying aquifers, and with extensive experience with the Rio Grande Decision Support System (RGDSS), to provide technical expertise on the inflows to and outflows from the Confined Aquifer System, the impact of these inflows and outflows on water levels and artesian pressures within the Confined Aquifer System, and the relationship between climate conditions, hydrogeologic conditions, and groundwater withdrawals from both the Unconfined Aquifer and the Confined Aquifer System.
Objectives
1) Completion of a Confined Aquifer Sustainability Study by September 30, 2028.
2) Preparation and submittal of a draft report to the State Engineer documenting the Confined Aquifer Sustainability Study by October 31, 2028.
3) Preparation and submittal of a final report to the State Engineer by March 15, 2029.
Approach
Rules 8.1.1 to 8.1.3 of the Rules require the State Engineer to complete a Confined Aquifer Sustainability Study and prepare a report of that study by March 15, 2029. This scope of work breaks the Confined Aquifer Sustainability Study and associated documentation into four tasks:
Task 1: Investigate inflows to and outflows from the Confined Aquifer System
Task 1 corresponds to the requirements of Rule 8.1.2a and 8.1.2c and involves an investigation of the inflows to and outflows from the Confined Aquifer System, an evaluation of the effects of Confined Aquifer and Unconfined Aquifer pumping, climate conditions, and hydrogeologic conditions on water levels and artesian pressures in the Confined Aquifer System. An evaluation of recharge, surface water conditions, and other inflows to and outflows from the Confined Aquifer System are also included in Task 1.
Task 2: Evaluate potential methods to better estimate the 1978 through 2000 water levels and artesian pressures in the Confined Aquifer System
Task 2 corresponds to the requirements of Rule 8.1.2b and involves an evaluation of potential methods to better estimate the 1978 through 2000 water levels and artesian pressures in the Confined Aquifer System. Five potential methods have been identified and are discussed in greater detail below.
Method 1: Theissen Polygon Composite Head The first method involves measuring water levels in wells that produce from the Confined Aquifer System. Each water level is assigned an area by constructing Thiessen Polygons and assigning an associated weight. Composite head is then calculated for the Confined Aquifer System using water level measurements and associated weights. Composite head has been tracked since 2015 by DWR for the Confined Aquifer System and for the following RGDSS model response areas: Alamosa La Jara, Conejos, Saguache and San Luis Creek.
Method 2: Linear Interpolation using Reference Wells The second method involves using Reference Wells, nearby wells with recorded water levels during the period 1978 to 2000, to estimate what water levels would have been from 1978 to 2000 at other nearby wells. Linear regression is applied to the water level dataset for the Reference Well to determine the data trend. The Reference Well data trend is then applied to the existing monitoring well water level data to hindcast an estimated 1978 to 2000 water level.
Method 3: Model Infill The third method involves using the RGDSS model to hindcast estimated water levels at existing monitoring well locations for the period 1978 to 2000. These historic estimated water levels would then be used to calculate composite head using the same approach discussed in Method 1 above.
Method 4: Water Budget Approach The fourth method involves using a water budget approach. Streamflow and pumping will be evaluated and related to historic sustainable water levels to estimate sustainable pumping volumes.
Method 5: Historic Consumption The fifth method involves reviewing historic consumption data and comparing it to historical sustainable water levels to estimate sustainable consumption levels.
The chosen consulting firm will complete a preliminary evaluation of each of these methods to determine feasibility. If warranted, a more in-depth evaluation will be completed. Additional methods may also be evaluated.
Task 3: Identify preferred methodologies to better estimate the 1978 through 2000 water levels and artesian pressures in the Confined Aquifer System
Task 3 corresponds to the requirements of Rule 8.1.3 and involves recommending preferred methodologies to the State Engineer to better estimate the 1978 through 2000 water levels and artesian pressures in the Confined Aquifer System. Recommendations will be based on the evaluation completed in Task 2.
Task 4: Prepare a report documenting the Confined Aquifer Sustainability Study
Task 4 corresponds to the requirements of Rule 8.1.3 and involves writing a report which documents the work completed under Tasks 1 through 3. A draft of the report will be provided to the State Engineer by October 31, 2028, with a final report provided by March 15, 2029.
Schedule
The chosen consulting firm will complete the Scope of Work on or before March 15, 2029, including the submittal of a final report documenting the Confined Aquifer Sustainability Study, the results of that study, and recommendations based upon the study.
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