Chapter 3

Source Water Delineation Approaches

The most important information needed to accurately delineate a source water assessment area is the location of the wells or intakes. DEQ, with assistance from the EPA, has located approximately half of the wells and intakes using Global Positioning System equipment. One of the first tasks will be to locate the remaining wells and intakes.

The Wyoming Geologic Survey has completed wellhead delineations and related Susceptibility Assessment Forms for approximately half of the 630 wells supplying noncommunity public water systems in the state. Susceptibility Assessment Forms were developed for use in the Wellhead Protection Program and will contain information useful during the contaminant inventory step of Source Water Assessment and Protection. The Susceptibility Assessment Form is included as Appendix F of the Wellhead Protection Program Guidance Document. Geologic and water resource studies for many Wyoming cities and towns are also available through work performed under the direction of Wyoming's Water Development Office. These studies contain information organized by county on the geology, lithology, water quality, water levels, and aquifer characteristics.

Additional, soon to be available resources, include Geographic Information Systems (GIS) maps of groundwater sensitivity and vulnerability to pesticides for each county within the state. A well characteristic information database is currently scheduled for completion during 1999, and will contain information on approximately 340 public water supply wells. These sources of information, in combination with those listed above, will enable the accurate delineation of source water areas.

3.2 Assessments in Wyoming

The development of a Source Water Assessment and Protection program and the assessment of all public water systems are mandatory in states which have primacy for administering the Safe Drinking Water Act rules and regulations within that state. Wyoming is the only state which does not have primacy. Consequently, Wyoming is not required to develop a Source Water Assessment and Protection program or complete source water assessments. DEQ and the Wyoming State Legislature, however, felt that a Source Water Assessment and Protection program could greatly benefit the citizens of and visitors to the state of Wyoming. The Wyoming legislature provided DEQ with the authority to set aside 10% of the federal Drinking Water State Revolving Fund to be used for conducting source water assessments.

Appendix B.

DEQ has made a commitment to conduct as many assessments as possible. As a first priority, DEQ will encourage all community and nontransient noncommunity systems to apply for assessments. These public water systems serve water to people which could be exposed to any contaminants in the water over a long period of time. These public water systems also account for the large majority of people being served by public water systems in Wyoming. All public water systems which use inherently vulnerable water sources will also be a high priority. These include systems using surface water or groundwater under the direct influence of surface water. Additionally, any public water system that has had contaminants detected in the finished water will be assigned a high priority.

3.3 Public Water Supply System Types

A public water system is any water system that serves 15 connections or 25 people per day for a minimum of 60 days per year. There are two basic types of public water systems: community and noncommunity systems. Noncommunity systems can be described as either transient or nontransient systems. Public water systems which purchase water from another water source are considered consecutive water systems. The definitions for each public water system type are listed below:

• Community public water systems are water systems that have at least 15 service connections used year-round by residents or that regularly provide water to at least 25 residents year- round. Examples include municipalities, water districts, and housing developments.

• Nontransient noncommunity public water systems are water systems that are not a community water system and which regularly provide service to at least 25 of the same persons for more than six months of the year where those persons are not full-time residents. Examples include schools, factories, mines, and office buildings.

• Transient noncommunity public water systems are water systems that serve a transient, non-residential population of at least 25 different people over a period of at least sixty days per year. Examples include campgrounds, rest stops, and resorts.

• Consecutive public water systems have no water source of their own, but obtain their water from another public water system. Mobile home parks and trailer courts are commonly consecutive public water systems.

3.4 Groundwater Systems

In order to protect groundwater supplies, community leaders and planners must have information regarding the surface and subsurface area surrounding a well or wellfield that contributes water to the public water system supply. Hydrogeologic conditions vary across the state and well depths range from tens to thousands of feet. The types and thicknesses of overlying materials that may protect the aquifer from contamination also vary. Because of the great range in hydrogeologic settings across Wyoming, the intrinsic sensitivity of groundwater to contamination varies greatly.

Methods and criteria used to delineate individual groundwater sources will reflect these hydrogeologic variations. Glacial till and alluvial aquifers adjacent to rivers and streams, bedrock aquifers exposed at or near the surface, karst, or fractured bedrock aquifers are the most sensitive to contamination from activities at the land surface. Conversely, deep or confined aquifers are less sensitive to contamination from surface activities. The delineation method used for each groundwater source will reflect the sensitivity of the aquifer. Groundwater sources that have the greatest need for protection will use the most conservative delineation methods. A public water system may always elect to use a more conservative delineation method in subsequent assessment efforts.

Delineation Methods for Groundwater Systems
Wyoming will use the delineation methods presented in the EPA-approved Wyoming Wellhead Protection Program Guidance Document to delineate groundwater source water assessment areas. Aquifer type (confined, unconfined, alluvial, etc.) or flow system type (porous, diffuse, or conduit) factor greatly into determining which delineation method is appropriate. A brief description of the most commonly used delineation methods follows. More detailed descriptions may be found in the Wyoming Wellhead Protection Program Guidance Document.

• Hydrogeologic and Aquifer Vulnerability Mapping: This method will be used where flow within the aquifer is primarily via conduits, which is typical in karst or fractured bedrock aquifers. Hydrogeologic mapping techniques use surface observations in combination with subsurface geologic data to identify aquifer boundaries and areas that may contribute water to the aquifer. Conduit flow aquifers have extremely variable flow patterns and rates, making times of travel difficult to predict. The entire aquifer may be delineated as the source water area if groundwater flow divides are not present.

• Analytical Models: Using models such as Simplified Variable Shapes, Wellhead Protection Area Model, and Wellhead Analytical Element Model will be the preferred method of delineation for wells in aquifers with either diffuse or porous flow conditions. These models require information on well pumping rate and screen length, aquifer hydraulic conductivity and gradient, and the saturated thickness of the aquifer. Calculations will be completed for both a two and a five year time of travel. A time of travel is the time that it will take for water to move from a specific location to the well. Analytical models should use as much site specific information as is possible.

• Calculated Fixed Radius: Another acceptable method for delineating source water areas is the calculated fixed radius. This method is applicable for wells producing from aquifers with either diffuse or porous flow conditions. Radii are calculated using aquifer porosity, well screen length, and pumping rate. Radii for both two and five year time of travels will be calculated. If insufficient information exists to calculate a fixed radius, average or estimated parameters will be used to estimate a calculated fixed radius.

• Arbitrary Fixed Radius: This method is the least accurate method and should only be used if a calculate a fixed radius cannot be estimated. In a deviation from the Wellhead Protection Program Guidance Document, the arbitrary fixed radius method may only be used in the following situations. Wells must be completed in porous or diffuse flow confined aquifers that are greater than 100 feet below the ground surface and have an intact, regionally expansive, low permeability confining layer overlying the aquifer. In such situations, the area within a 500 foot radius from the wellhead would be considered the source water area. However, recharge areas of the confined aquifer within an approximate five year time of travel must also be delineated using hydrogeologic and aquifer vulnerability mapping techniques.

Preferred Groundwater Delineation Methods Based On Public Water System Type

Community and nontransient noncommunity public water systems
Approximately one quarter of Wyoming's population is served by community or nontransient noncommunity groundwater public water systems. Community and nontransient noncommunity public water systems serve the same population daily. Because individuals served by these public water systems usually consume the water over long periods of time, more protective delineations are needed. DEQ will accept any delineation method except arbitrary fixed radius for these public water systems.
• Transient noncommunity public water systems
  Transient noncommunity public water systems typically do not serve the same individuals over a long period of time. They also rarely have jurisdiction over land use activities outside their property boundaries or extensive resources to develop and implement protection programs. The use of sophisticated delineation methods would be impractical in these circumstances. Source water assessment areas for transient noncommunity systems will be delineated using the calculated fixed radius method. The arbitrary fixed radius method may also be used if conditions exist as listed in the description of the arbitrary fixed radius method above.

• Consecutive public water systems
  Consecutive public water systems obtain their water from other public water systems. All consecutive public water systems that obtain water from a public water system for which an assessment have been done will be provided with copies of the assessment results. If a consecutive public water system requests an assessment and the public water system from which they obtain their water has not been assessed, an assessment on the public water system which provides the water may be conducted. The method used to delineate the public water system will be determined as outlined above.

Delineation of Inactive and Abandoned Wells
Wyoming will not conduct an assessment on inactive or abandoned wells unless the public water system requests that they be assessed and indicates that these wells will be reactivated in the future.

Delineation of Aquifer Recharge Areas
Recharge areas for porous or diffuse flow confined aquifers that are within a five year time of travel of a well will be delineated. A combination of hydrogeologic and aquifer vulnerability mapping methods as well as surface water delineation techniques will be used.

Included within the recharge area will be a 1000 foot wide buffer zone on both sides of all perennial streams for a distance of one mile upstream of the recharge area, or to the point where the stream becomes intermittent.

3.5 Surface Water Systems

Less than 10 % of all public water systems in Wyoming utilize surface water sources for drinking water. However, these 60 public water systems provide water to nearly two thirds of Wyoming's population. Several of Wyoming's large communities such as Casper, Cheyenne, and Laramie rely upon surface water to supplement drinking water supplies during certain times of the year.

Delineation of Surface Water Systems
In order to protect surface water supplies, community leaders and planners must have information regarding the area contributing water to the public water system. Potential sources of contamination located upstream from the drinking water intake could reach and possibly impact the water system. Water moving across the ground surface or through the upper layers of soil may move pollutants from the pollutant source to nearby bodies of water. Once in the water, pollutants can be transported downstream to the drinking water intake.

The source water assessment area will therefore be the entire watershed above the intake. Unlike most source water areas for groundwater systems, assessment areas for public water systems using surface water sources may encompass large areas of the land surface. Public water systems which use trans-basin diversions to supplement water supplies will require additional delineation. Trans-basin diversions are structures such as pipelines, ditches, or tunnels that move water from one watershed into another. The watershed upstream from each diversion point will be incorporated into the source water area of the public water system.

Preferred Surface Water Delineation Methods Based on Public Water System Type

• Community and nontransient noncommunity public water systems
  Source water assessment areas will include the entire watershed upstream from the intake. Watersheds above any trans-basin diversions which contribute water to the intake will also be included in this area.

• Transient noncommunity public water systems
  The entire watershed above the intake will be delineated as described above.

• Consecutive public water systems
  Assessments for consecutive surface water systems will be conducted if the public water system requests an assessment and the public water system from which they obtain their water has not been assessed. The public water system from which they obtain their water must also agree to have a source water assessment completed for their system. If the public water system from which they obtain their water has already been assessed, the assessment results will be forwarded to the consecutive public water system.

3.6 Other Delineation Methods

Conjunctive Delineation
Conjunctive delineation combines both groundwater and surface water delineation techniques. This type of delineation protects a public water system when both surface and groundwater drinking water sources are used, or when groundwater sources are influenced by surface water. Wells that can be influenced by surface water typically occur in karst, fractured flow, or alluvial aquifers. Shallow wells less than 100' deep may also be affected by surface water. Additionally, wells which have been determined to be under the direct influence of surface water using microscopic particulate analysis or other, similar techniques, will require conjunctive delineation.

In a conjunctive delineation, DEQ will delineate the source water area using both groundwater and surface water delineation methods. The methods which will be used and the situations in which each is appropriate have been described above.

Interstate Delineation
Watershed delineation boundaries may cross state lines and extend into South Dakota, Montana, Idaho, Utah, Colorado, and/or the Wind River Indian Reservation. Groundwater system assessment areas may also cross these boundaries. The assessment area will terminate at the Wyoming border or reservation border. The adjacent state or tribe will, however, be asked to notify DEQ of any potential contaminant sources that may affect the quality of water in the assessment areas. DEQ will, in turn, provide other states and the Wind River Indian Reservation with any information that they may request.

Area-Wide Delineation
The delineation of a larger area serving as the source water area for multiple public water systems may be useful in some situations. For example, groundwater in karst aquifers may travel very tortuous paths. The speed and direction of groundwater movement in karst aquifers can rarely be accurately determined, even with the aid of monitoring wells. In areas with large karst aquifers such as the Black Hills of Wyoming, the best way to protect all public water systems using this water is to protect the entire aquifer system. The result would be a large, region-wide or area-wide assessment area. Another appropriate use of area-wide assessments is where several public water systems have closely spaced wells or intakes that share the same hydrogeologic setting.

3.7 Delineation of Contaminant Inventory Zones

Zone 1 is the area immediately surrounding the well or intake. Contaminants released within this zone would have the greatest likelihood of reaching and affecting the quality of the water. Potential sources of contamination within Zone 1 are therefore of the greatest concern.

Zone 2 lies immediately beyond Zone 1. Contaminants released within this zone are within close proximity of the well or intake. Zone 2 for surface water systems includes an area upstream of the intake because contaminants could potentially reach the river system and be transported to the intake. Contaminants released within Zone 2 are of concern because the chances of them reaching the well or intake is still high.

Zone 3 is the area furthest from the well or intake. Contaminant sources within this zone are less likely to reach the well or intake in quantities which could affect water quality. Major sources of contamination within Zone 3 will still be noted. These potential sources of contamination should still be considered in source water protection planning efforts.

Groundwater

• Zone 1: Zone 1 is called the `Accident Prevention' or `Sanitary Protection Zone'. The Wellhead Protection Program Guidance Document defined this area to prevent the introduction of contaminants into the well. The Wellhead Protection Document suggests that potential sources of contamination within Zone 1 be strictly monitored, controlled, or excluded to prevent the introduction of contaminants into the aquifer. A thorough, comprehensive contaminant inventory will be conducted within this zone. Types of contaminant inventories are discussed in detail in Chapter 4 of this document.

  Zone 1 will be delineated as outlined in the Wellhead Protection Program Guidance Document. The default radius for Zone 1 is 100 feet. Zone 1 can be reduced to a 50 foot radius if the following conditions are met: 1) wells are completed (screened) across only one aquifer; 2) wells are constructed according to DEQ rules and regulations; 3) wells meet or exceed the minimum setback or isolation distances stipulated by DEQ rules and regulations; 4) the public water system has completed or provided adequate information to DEQ for the completion of the Susceptibility Analysis Form developed for the Wellhead Protection Program; and 5) a well has been determined to have a low or moderate susceptibility using this form.

• Zone 2: Zone 2 is called the `Attenuation Zone'. The Wellhead Protection Program Guidance Document delineated this area to protect wells from sources of microbial contamination. Microbial contaminants such as Giardia lamblia and Cryptosporidium parvum are largely attenuated within a few years of release into the groundwater. The majority of these pathogenic organisms will die within 2 years. Zone 2 will also provide sufficient time for emergency response, active cleanup, or the implementation of contingency plans if other contaminants are introduced into the aquifer. A comprehensive contaminant inventory will be conducted within this zone.

  Zone 2 will be delineated as outlined in the Wellhead Protection Program Guidance Document. Zone 2 will extend from the outer edge of Zone 1 to the two year time of travel boundary for porous and diffuse flow aquifers. In conduit flow aquifers, Zone 2 will be determined by hydrogeologic and aquifer vulnerability mapping.

• Zone 3: Zone 3 is called the `Remedial Action Zone'. The Wellhead Protection Program Guidance Document defined this area to include a large part of the aquifer which contributes water to the well. This zone needs to be sufficiently large to allow time to detect and respond to contaminants. The length of time between contaminant detection and when it reaches the well must be sufficient for either cleanup, well replacement, or the implementation of other contingency plan options. A limited contaminant inventory will be conducted within this zone.

  Zone 3 will also be delineated as outlined in the Wellhead Protection Program Guidance Document. Zone 3 will extend from the outer edge of Zone 2 to the five year time of travel boundary for porous or diffuse flow aquifers. Figure 3.1 illustrates Zones 1, 2, and 3 for a hypothetical well located in a porous or diffuse flow aquifer. If the aquifer is a conduit flow aquifer, Zone 3 will extend to the flow system boundaries or the lateral extent of the aquifer.

Figure 3.1 Zones 1, 2, and 3 for a hypothetical well drawing water from a porous or diffuse flow aquifer.

Contaminant Inventory Zones in Arbitrary Fixed Radius Delineations: In cases where the arbitrary fixed radius delineation method has been used to determine the wellhead protection area, Zone 1 will extend 50 or 100 feet, as described for other delineations. Zone 2 will be a 500 foot radius around the wellhead. A 500 foot radius is a reasonable estimate of a two year time of travel for porous flow confined aquifers in the state of Wyoming. A Zone 3 will not be delineated. A comprehensive contaminant inventory will be done in Zones 1 and 2.

Surface Water

• Zone 1: Zone 1 for surface water systems is also called the `Accident Prevention' or `Sanitary Protection Zone'. As with groundwater systems, this area will be delineated to prevent the introduction of contaminants into the intake. The area within a 100 foot radius of the intake will be considered to be Zone 1. A comprehensive contaminant inventory will be conducted within this zone. Contaminant inventories are discussed in detail in Chapter 4 of this document.

• Zone 2: This zone will extend upstream from the edge of Zone 1 for a distance of 15 valley miles on the mainstem and all perennial tributaries. A distance equivalent to an eight hour time of travel at high flow, if known, may also be used. Zone 2 will terminate at the watershed boundary, state or reservation boundary, or where the tributary streams become intermittent if these boundaries are less than 15 valley miles or an eight hour time of travel above the intake. If the distance between the intake and the next public water system upstream is less than 15 valley miles or an eight hour time of travel, Zone 2 will terminate at the upstream intake. If the upstream public water system has not conducted an assessment, Zone 2 will continue upstream past the intake as described above.

  Zone 2 will also extend laterally 1000 feet beyond each perennial streambank. The EPA requires contaminant inventory zones 1000 feet or more wide to identify possible sources of contamination that could affect water reaching the intake. Contaminants released within Zone 2 could reach the intake by being washed into the river or stream or by moving through the alluvial aquifer. A comprehensive contaminant inventory will be conducted within this zone.

• Zone 3: This zone will include the remaining delineated watershed. A limited contaminant inventory will be conducted within this zone. Figure 3.2 illustrates Zones 1, 2, and 3 for a hypothetical surface water intake.

  Figure 3.2 Zones 1, 2, and 3 for a hypothetical surface water intake.

  

  Intakes Below Lakes/Reservoirs: It is assumed that a lake or reservoir will retain water for longer than eight hours. Therefore, surface water sources which are located within an eight hour time of travel or 15 valley miles below a lake or reservoir will delineate Zones 1 and 3 as described above. Zone 2 will be delineated only up to the lake or reservoir. Figure 3.3 illustrates Zones 1, 2, and 3 for an intake below a lake or reservoir.

  Figure 3.3 Zones 1, 2, and 3 for a hypothetical surface water intake below a lake or reservoir.

  

  Intakes On Lakes/Reservoirs: It is assumed that a lake or reservoir will retain water for longer than eight hours. Therefore, surface water sources which are located on a lake or reservoir will delineate Zones 1 and 3 as described above. Zone 2 will consist of a 1000 foot boundary around the lake or reservoir high water line. Figure 3.4 provides an illustration of a surface water intake on a lake or reservoir.

  Figure 3.4 Zones 1, 2, and 3 for a hypothetical surface water intake on a lake or reservoir.

  

  Intakes On Or Below Lakes/Reservoirs With Short Retention Times: Zone delineations for surface water intakes located on or below a lake or reservoir where water entering the lake or reservoir may not be retained for an eight hour period before reaching the intake will need to completed on a case-by-case basis

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  Chapters
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  Glossary | Acronyms
  Appendices
  A | B | C | D
  Wyoming's Source Water Assessment Guidance Document Contents
  

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