5 Colo. Code Regs. § 1002-42.15
The provisions of C.R.S. 25-8-202; 25-8-203; 25-8204 provide the specific statutory authority for adoption of these regulatory provisions. The Commission has also adopted, in compliance with C.R.S. 24-4-103(4), the following statement of basis and purpose.
BASIS AND PURPOSE
The public water supply systems considered for classification and standards setting include four (Brighton, Fort Lupton, Fort Morgan and Sterling) on which the Commission delayed final action following the May, 1993 site-specific ground water classification hearing. The specified areas proposed for classification for three of these systems (Fort Lupton, Fort Morgan and Sterling) were developed by the "Northern Group" a consortium of the four cities and three area Water Conservancy Districts (Northern Colorado, Central Colorado, and Lower South Platte). The specified area for the City of Brighton was developed by an independent consultant.
The Commission agreed to delay the classification of the four wellfields for eighteen months. The additional time was requested to allow the Northern Group to develop the specified areas for classification using a model and database which they argued would provide more accurate specified areas and consequently greater confidence. The Northern Group also indicated that the additional time was needed to explain the proposal to municipal officials and area agricultural interests, and to seek their understanding, support, and concurrence.
The Commission directed the Northern Group to return for a hearing in the fall of 1994 with alternative specified areas for consideration. If alternatives for the four systems were not forthcoming, the Commission indicated that the Division's classification proposals for the four public water systems would be re-introduced for consideration.
Classification of the Town of Meeker's wellfield was delayed from the June 7, 1994 hearing on site-specific ground water classifications to allow the Town and the Rio Blanco County Commission to collect additional data to support revising the figure indicating the specified area. The Commission agreed to delay consideration until November, 1994.
The figure indicating the specified area for the Town of Meeker's wellfield was developed initially by the Division using the WHPA 2.1 semi-analytical model.
The specified area for the San Arroyo Creek Basin of the Morgan County Quality Water District's wellfield was developed by an independent consultant and reviewed and concurred with by the Division. The specified areas for the Towns of Eckley, Las Animas and Haswell were developed by the Division using the wellhead protection area or WHPA 2.1. Model developed for the U.S. EPA for use in delineating WHPAs for the wellhead protection program.
Participation in the hearing by the Town of Las Animas was solicited by the Division as it was to have been included in the two previous site-specific hearings and was unable to for a variety of reasons. The remaining systems (Eckley, Haswell, and Morgan County Quality Water) approached the Division independently seeking assistance and/or concurrence to have their wellfields classified.
The specified area for the Town of Eckley covers an area five miles upgradient of the Town's wells. The expanded area, considerably larger than the five year time of travel usually recommended by the Division, was developed at the request of Town's Board of Trustees.
All of the public water systems considered for classification at this hearing rely on ground water as a source of drinking water, and in the aggregate provide drinking water to 45,361 Colorado residents. Compliance records maintained by the Division's Drinking Water Section indicate that the systems that are the subject of this hearing consistently meet the Safe Drinking Water Act requirements for the delivery of potable water at the tap with chlorination as the sole means of disinfection. This is an indication that the ground water resource is of relatively good quality, and worthy of the protection provided by classification and standards setting.
Site-specific classification of ground water begins with the identification of the use of the water. In this instance, and those of previous site-specific hearings, the identified uses are domestic and agricultural. Both uses have been documented through the well records maintained by the State Engineer's Office. The corresponding water quality standards, found in Tables 1 through 4 of the "Basic Standards for Ground Water" 3.11.0 (5 CCR-1002-8), are designed to protect the uses.
The specified areas for the Northern Group cities of Fort Lupton, Fort Morgan and Sterling, to which the use classifications and standards are to apply, were determined through the use of the new "wellhead analytic element model" . Referred to as the WhAEM Model, it is a steady state ground water flow model designed to delineate capture zones for the wellhead protection program. It allows modeling of all features which influence ground water movement and is therefore very suitable for application to the varying hydrogeological situations found in Colorado.
Data used by the Northern Group in the WhAEM Model to determine the specified areas included: location and seasonal pumping rates of the cities' wells and the surrounding irrigation wells; aquifer properties such as hydraulic conductivity, thickness, and soil porosity; location and amount of ditch seepage and deep percolation of on-farm irrigation practices; and the location and elevation of constant head boundaries such as rivers and reservoirs. The WhAEM Model uses the data input to create water table contour plots which are compared to existing USGS data bases to verify that the model is calibrated, this is an important feature in gaining acceptance and confidence in the model.
The WhAEM Model is being developed for the U.S. EPA, and once completed, will supplement use of the semi-analytical WHPA 2.1 Model in the development of wellhead protection areas. Selection of an appropriate model in developing wellhead protection areas or areas for classification will generally be determined by the hydrogeologic conditions present in the subject aquifer.
WhAEM is based on the superposition or adding together of separate analytical functions that describe different features that effect ground water flow. WhAEM has functions or elements for well pumping, canal seepage, irrigation and rain infiltration, and river and reservoir gains or losses to the ground water aquifer. WhAEM can model numerous wells, canals, rivers and irrigation systems with the data input to WhAEM based on the x, y map coordinates of the elements. WhAEM also has the option of using digitized map files as input through its graphical pre-processor, GAEP.
WhAEM separates capture zones into subzones characterized by different sources of water. For example, WhAEM displays how much water to a well comes from each of multiple sources such as a river, canal, and irrigation infiltration. WhAEM plots time related capture zones with any time increment. WhAEM can display 30 day increments out to 300 days or 1 year increments out to 5 years (time increment used for Northern Group modeling) or any other combination. The WhAEM output can also zoom in on a specific part of the aquifer to display water table contours and capture zones in detail.
With its versatility and flexibility for incorporating numerous hydrogeologic features and interactions, WhAEM provides the tool needed to investigate future water management alternatives for the protection of the subject wellfields. Proposed recharge areas can be modeled to determine whether the localized ground water mounds from this recharge can keep pollutants away from wells.
The specified area for the City of Brighton was developed independently using the USGS Modflow Model. Two of the Conservancy Districts working with the Northern Group provided the consultant working with Brighton irrigation well pumping and canal seepage data in the Brighton area.
The WHPA 2.1. Model was used to develop the specified areas for the Towns of Eckley, Las Animas and Haswell, and to verify the figure proposed for the Morgan County Quality Water District. This model was also applied in developing the initial figure for the Town of Meeker's wellfield.
The Division used the modular, semi-analytical ground water flow model to define the areas specified for classification. The wellhead protection area or WHPA 2.1 Model was designed to assist the state and local technical staff with the task of wellhead protection area (WHPA) delineation. The model is PC-based and very user friendly.
The WHPA Model can be divided conceptually into two major sections. The computational section contains the Fortran programs that compute the capture zone(s) for a given physical scenario. All of the "number crunching" is performed by these computational modules. The second section of the WHPA model is the user-interface. The interface provides for data entry and review of the results.
The WHPA model contains four independent computational modules used to delineate capture zones. Three of the modules contain semi-analytical capture zone solutions that allow for a variety of simulated circumstances. Available aquifer types covered include confined, leaky-confined, and unconfined with areal recharge. The fourth module is a general particle tracking module that may be used as a postprocessor for two-dimensional numerical models of ground water flow. In developing the specified areas for the site-specific ground water classification proposal, the Division relied most heavily on two of the four computational modules available through the WHPA Model; namely the General Particle Tracking (GPTRAC) module and the Multiple Well Capture Zone (MWCAP) module.
GPTRAC delineates time-related capture zones for pumping wells in homogeneous aquifers with steady and uniform ambient ground water flow. The aquifer may be of infinite areal extent, or may be bounded by one or two (parallel) streams and/or barrier boundaries. The effects of well interference are accounted for. It also delineates time-related capture zones around pumping wells for steady ground water flow fields.
The Division selected a five year time of travel (TOT) as it was recommended in the state wellhead protection plan as an adequately protective timeframe for the majority of Colorado's aquifers. Time of travel refers to the time required for ground water to move through saturated strata (the aquifer) from a specific point to a well.
MWCAP delineates steady-state time-related (5 years), or hybrid capture zones for pumping wells in homogeneous aquifers with steady and uniform ambient ground water flow. The aquifer may be infinite in areal extent or the effects of nearby stream or barrier boundaries can be assessed. If multiple wells are examined, the effects of well interference are ignored.
There are two major assumptions common to both of the computational modules used. The first is that the aquifer is at steady state. "Steady state" is an idealization of the dynamic conditions that exist in the aquifer and the well during ground water withdrawal. The second assumption is that flow in the aquifer is horizontal (two dimensional in areal view).
The WHPA Model was run using information supplied by the public water systems and by the Division. Typically this consisted of (a) well logs, which contain the well location, geologic log, the well diameter, the length of the perforated casing, and the production rate in gallons per minute; (b) transmissivity; (c) porosity; (d) ground water gradient; and, if available, (e) the aquifer boundaries. If the public water system was unable to provide the information in (b) through (e), the Division consulted references such as the U.S. Geological Survey's Water Supply Papers, investigation series maps, open file reports and hydrologic atlases.
The use of classifications and standards adopted by the Commission for the specified areas surrounding the nine public ground water systems indicated in figures 29 through 37 serve as the basis for permitting and remedial actions undertaken by various local, state and federal regulatory agencies responsible for protecting ground water. Application of the classifications and standards is triggered by these actions; the regulation in and of itself is not self-implementing.
The site-specific classification and standards regulation serves as a means of protecting the ground water and by law, cannot cause material injury to water rights (Colorado Water Quality Control Act, C.R.S. 25-8-104(1)).
The Division and the Northern Group both worked diligently to explain the classification proposal, the modeling, and to educate and gain support for ground water classification and protection.
The Northern Group met individually in March, 1994, with the cities of Fort Lupton, Fort Morgan and Sterling to obtain data on the wells, A meeting with the Division was held in April to explain the modeling approach and the progress to date.
In May, 1994, the Northern Group met with the Weld County Commissioners to explain the ground water classification requirements. The Commissioners were interested in the potential implications on land use, and in the City of Fort Lupton's proactive involvement in managed recharge to protect ground water quality.
In June, the Northern Group presented the results of the modeling efforts to the Fort Lupton Water Board and City Council, and received a very favorable response. As a follow up, the City plans to join with the three Conservancy Districts to apply for a Section 319 non-point source grant to implement a managed artificial recharge project to protect alluvial ground water. This effort is expected to be an example and demonstration for other ground-water dependent communities.
Similar meetings to present the modelling results and explain the classification process are scheduled in early July before the Fort Morgan and Sterling City Councils.
The Division's outreach efforts included meeting with the consultant for the Morgan County Quality Water District to explain the process, and numerous phone contacts with the systems not represented in the Northern Group to explain the process and respond to questions. The Division made a presentation to a joint public meeting of the Town of Meeker and the Rio Blanco County Commission on July 12, 1994 to review and explain the classification proposal for the Town's wellfield, and to respond to questions.
PARTIES TO THE RULEMAKING HEARING
5 CCR 1002-42.15