Source Water Assessment Program
Delineation Methods
3.1 Wellhead Protection Areas for Ground Water Systems
3.1.1 Community Public Water Supply Systems
Delineations for WHPAs for Community Public Water Supply wells have been drawn using the cylindrical displacement method and the EPA computer model, WHPA2. Wellhead Protection Area boundaries from both methods completely enclose the 20 year Time of Travel (TOT) areas. The 20 year TOT was decided upon by the Technical Advisory Committee during the development of the Wellhead Protection Program.
Most existing WHPAs in Nebraska have been delineated by the cylindrical displacement method. As communities request or prepare to do an “on-the-ground” inventory, cylindrical displacement WHPAs will be re-drawn using WHPA2 by NDEQ. Any WHPA delineations done under contract with NDEQ will be computer modeled. With this SWAP submittal, NDEQ is officially making WHPA2 delineations the preferred WHPA delineation method for Community Public Water Supply Systems if necessary hydrologic information is available. Community PWSSs will be the highest priority for completing delineations.
3.1.2 Computer Modeled Delineation
The same basic information needed to delineate WHPAs using the cylindrical displacement method is needed when using the computer model WHPA2 or WHAEM (or other computer modeling methods, see section 2.4). The “Data Sheet for Delineation of a Wellhead Protection Area” is shown in Appendix B. Basic information needed from the PWS includes:
- system name, well name
- well location and characteristics
- geologic information from well log
- average annual pumpage
Additional information needed to use the computer model to delineate the WHPA includes:
- ground water flow direction
- ground water gradient (related to ground water velocity)
- aquifer characteristics (hydraulic conductivity)
- river or aquifer boundaries
For more information on the WHPA2 (EPA, March 1991) or WhAEM (Haitjema, et al, 1994) computer models the reader is encouraged to review the model documentation. To see the difference between the cylindrical displacement method and the WHPA2 computer model, see the example below. Display Graphic Example
3.1.3 Fixed Radius on all Non-Community PWSSs
The fixed radius WHPA method was chosen for Non-Community PWSSs (Transient and Non-Transient) for the following reasons:
- A lack of information about the well. Some PWSSs may not have a well log or even know when the well was drilled, making it difficult to use more scientific methods, such as computer modeling.
- NDEQ budget and time frame constraints may not allow computer modeled delineations done by the Federal deadline. There are over 750 Non-Community PWSSs in Nebraska.
- Title 179 NAC 2 - Regulations Governing Public Water Supply Systems (NHHS,1998). Public Water Supply Systems are required to control the area immediately around their well. These regulations will provide information on specific set back distances for potential contaminant sources.
- Title 124 - Rules and Regulations for the Design, Operation and Maintenance of Septic Tanks (NDEQ,1994). This regulation sets out the distances required between septic tanks and Public Water Supply Wells. This will provide information related to septic tanks as potential contaminant sources.
- An article from the Minnesota Department of Health titled “Pumping Effects of Transient Non-Community Wells on a Fixed Radius Approach to Delineating Wellhead Protection Areas” (MDOH, 1995). This paper summarizes a project that determined a fixed radius will protect drinking water users at a hotel and resort, from acute health effects. A copy of this article can be obtained from NDEQ upon request.
- A statewide emergency response program dealing with contaminant releases. NDEQ has an individual on call 24 hours a day to respond to emergency situations regarding chemical spills and releases. This program addresses the concern related to pesticides and other contaminants that are not tested for by Non-Community PWSSs.
- The maximum set-back distance listed in Title 179, NAC2 (NHHS, 1998) is 1000 feet. This 1000 feet encloses the 2 year Time of Travel for ten PWSSs examined. These representative PWSSs serve populations ranging from 790 to 1000 (the “average” system in Nebraska serves 919 people), with 27 wells. The WHPA2 modeled 2 year TOT ranged from 970 feet to nearly 1900 feet from the well. Non-Community wells do not typically yield this much water, so 1000 feet will enclose much more than a 2 year Time of Travel.
For the assessment that is made available to the public, Non-Community PWSSs may be located on County, NRD, or some regional basis for efficiency in delineation and the first level inventory.
3.1.4 Non-Transient, Non-Community Public Water Supply Systems
Delineations will be done using a fixed radius for all Non-Transient, Non-Community PWSSs. These systems serve 25 people or more, over 6 months out of the year, examples include rural schools and factories. The radius will be 1000 feet, based on Title 179 NAC2 sec.007 (NHHS, 1998). WHPAs may be redone using a computer model later, if necessary information is available, as time allows, or special needs for these systems arise. Non-Transient, Non-Community PWSS will be a higher priority than Transient, Non-Community PWSSs, but remain a lower priority than Community PWSSs for completing delineations.
3.1.5 Transient, Non-Community Public Water Supply Systems
Delineations will be done using a fixed radius for all Transient, Non-Community PWSSs. These systems serve 25 people or more, over 60 days out of the year. Examples of this type of system include state or local parks, highway or interstate rest areas, or rural cafes. The radius will be 100 feet, based on Title178, Chapter 12, Section 003 (NHHS, 1997). WHPAs may be redone using a computer model later, if necessary information is available, as time allows, or special needs for these systems arise.
The following table summarizes the distance of the fixed radius for delineation of Non-Community PWSSs:
Type of Non-Community PWSSs | fixed radius in feet |
| Transient | 100 feet |
| Non-Transient | 1000 feet |
3.1.6 Delineations of Non-Adjacent Recharge Areas
There are no areas non-adjacent to WHPAs in the State of Nebraska that recharge those WHPAs. Nebraska has no mountainous areas of remote recharge separated from a WHPA by exposed bedrock. These situations generally typify non-adjacent recharge areas. Additionally, Nebraska’s WHPAs enclose the 20 year Time of Travel contribution area, which is a very protective distance.
3.2 Surface Water Systems and Ground Water Under the Direct Influence
All Public Water Supply Systems using surface water (streams, rivers, and lakes) and wells considered ground water under the direct influence of surface water (GWUDI) will follow the same plan for the SWAP. GWUDI means “any water beneath the surface of the ground with significant occurrences of insects or other macroorganisms, algae, or large-diameter pathogens such as Giardia lamblia, or significant and relatively rapid shifts in water characteristics such as turbidity, temperature, conductivity, or pH which closely correlates to climatological or surface water conditions” (NHHS, 1998). Currently, there are less than 10 PWSSs whose source of water has been determined “surface water” or “GWUDI”. There are PWSSs in Nebraska that purchase drinking water from these systems, but assessments will not be done for those purchasing drinking water because they do not have a well or intake.
For systems determined to be GWUDI, NDEQ will delineate WHPAs using provided well information. These systems are required in Title 179, NAC2, 013.02B5 to exclude potential sources of microbiological contamination from the 1 year TOT. Title 179, NAC2, 013.02B5 specifies the one year TOT be determined using the following formula:
T= 3.14nbL2 divided by Q
where T = Time-of-Travel (days)
L = Distance from the well (feet)
n = Effective porosity (assumed to be 0.2 unless supporting evidence indicates otherwise).
b = Aquifer thickness (feet)
Q = Pumping rate (cubic feet per day)
Translated into a distance formula would read as follows:
= 
Delineations will be completed for the entire watershed to the state boundaries for each surface water system, starting at the intake. This will be called the Watershed Delineation Area (WDA). When the watershed extends into another state, the Source Water Assessment will list the neighboring state contacts. After SWAP description completion, a multi-state effort will be coordinated, with the help of EPA Region 7, to address multi-state watershed issues and emergency response concerns.
NDEQ will determine the 24 hour Time of Travel (TOT) zone for each WDA individually. This 24 hour TOT zone will be called the “Assessment Area.” The Assessment Area will be determined using high stream flow data (see figure below for example). NDEQ will also determine the 12 hour TOT, 6 hour TOT, and 3 hour TOT zones within the Assessment Area. The PWSS will determine and justify for which zone(s) it completes an “on-the-ground” inventory, when it does one.
The following formula and information explains how the Assessment Area (24 hour TOT zone) is determined:
Dist (miles) = 24 hour Time of Travel distance in miles
Vk (feet/second) = velocity of stream; measured in the field by various agencies (USGS, NDEQ, Nebraska Department of Water Resources, Nebraska Game and Parks Commission, etc.)
Flowk (cubic feet/second) = known flow of stream; calculated from stream velocity and stream length and depth (area), which was measured in the stream by various agencies (see agencies above)
Flow90 (cubic feet/second) = calculated flow of stream at 90% of measured high flow, determined using many data measurements by various agencies (see agencies above)
Display Diagram
3.2.1 Conjunctive Delineations of Surface Waters with Significant Hydrologic Connections
The existing WHP program addresses surface water bodies that intersect or are included in a WHPA (Italics in Section 2.4 show the change to the WHP program as explained).
The diagram below illustrates the concept of airline miles.
Display Diagram
3.3 Responsibility
The Nebraska Department of Environmental Quality will assume the responsibility for completing delineations. Delineations completed by sources other than NDEQ will be used for the SWAP whenever possible. Some examples of other sources include NeRWA, NRDs, PWSSs, and County Health Departments. It is possible that some of the delineations may be contracted with agencies, organizations, or private companies outside of NDEQ.
Nebraska Department of Environmental Quality
1200 "N" Street, Suite 400
P.O. Box 98922
Lincoln, Nebraska 68509
(402) 471-2186