Source Water Assessment Program
Vulnerability Analysis
5.1 Vulnerability Definition
For purposes of Nebraska’s SWAP, the terms susceptibility and vulnerability are interchangeable. Nebraska has chosen to use the word vulnerability because of its use in Nebraska Health and Human Services’ (NHHS) Sanitary Survey Program and statewide familiarity with the term in the public drinking water supply industry. Both the SDWA Amendments and EPA’s SWAP Guidance encourage the use of existing information and coordination with other programs. Using the existing Sanitary Survey for the first phase of the vulnerability analysis is a use of effective information and cooperation between programs. The following chart shows examples of the information examined and recorded when a Sanitary Survey is completed by NHHS (see Appendix C for a complete blank vulnerability form).
Sanitary Survey Inspection Categories | Examples |
| Records | Water-Quality, Quantity, Use, Lab Reports |
| Wells | Site- Access, Drainage, Encroachment |
| Pumps | Base- Seal, Motor Mount, Bolts |
| Well House Mechanical | Piping- Supports, Ties, Sleeves, Corrosion |
| Auxiliary Equipment | Chemical- Safety, Storage, Controls, Pump |
| Storage Tanks | Condition- Structural, Corrosion, Leaks |
| Truck Fill Location | Backflow Prevention- Vacuum Breaker |
| Distribution System | Material Storage and Spare Parts |
| Operating Practices | New Construction and Abandonment |
| Miscellaneous | Wellhead Encroachment Policy, Emergency Plan |
| Treatment Plant | Sites, Structures, Buildings and Bins, Waste Handling |
A Public Water Supply System’s vulnerability to contamination is based on several factors:
- the integrity of the well (ground water) or intake (surface water) construction
- the geologic environment, including depth to water, presence of retarding sediments in the subsurface (ground water)
- the nature of the surface water source and watershed - large lake, small stream, large river, etc.
- the locations of potential contaminant sources in the WHPA or WDA
Nebraska is proposing a two phase Vulnerability Assessment, much like the two level Contaminant Source Inventory. The database search that was done as the level one Contaminant Source Inventory will be provided to NHHS field representatives to aid them in completing a Sanitary Survey for a PWSS. The existing Sanitary Survey vulnerability determination will be used for the first phase, and a more detailed vulnerability analysis of the PWSS will be done using the information from the “on-the-ground” inventory of potential contaminant sources (Section 4) and specific site information. This second vulnerability will be called a Contamination Potential Rating (CPR).
The first phase vulnerability analysis will assist PWSSs in focusing their local voluntary protection activities on the wells and locations that are more vulnerable to contamination. As Contamination Potential Ratings are completed, PWSSs will also benefit from this advanced analysis when assessing resources and protection activities for the Assessment Area (24 hour Time of Travel) in the watershed or the Wellhead Protection Area. It is also possible that results of the second phase vulnerability will be coordinated in the future to the Drinking Water State Revolving Loan Fund (DWSRF) priority list.
5.2 Ground Water Systems
5.2.1 Phase One - Existing Sanitary Survey Program
The Nebraska Health and Human Services (NHHS) visits all Public Water Supply Systems to conduct a Sanitary Survey. The phase one vulnerability analysis for the Source Water Assessment will not change from the existing NHHS Sanitary Survey rating. Community PWSSs are visited once every three years and Non-Community PWSS are visited once every five years. Current regulations require PWSSs to take “actions as necessary to protect the system and its components from encroachments which are likely hazards to the safety of the drinking water quality, or which could have a substantial impact on system pressure or economies delivered by the system” (NHHS, Title 179 NAC2.008.02F, 1998). The Sanitary Survey is a vulnerability assessment done within 1000 feet of a well. A well is given a rating of vulnerable or not vulnerable to contamination. Specific components of a PWSS are evaluated in a sanitary survey, including source water, treatment, storage, the distribution system, and maintenance. A copy of the form used by NHHS, listing the specific details that are recorded, is included as Appendix C.
The phase one vulnerability analysis 1000 feet review distance is not inclusive of the entire source of drinking water for the PWSS. However, it has been determined that for a “middle” sized PWSSs well, 1000 feet is inclusive of the 2 year Time of Travel zone within the WHPA. This 1000 foot radius may include as much as the 5 year Time of Travel (this 5 year Time of Travel is not routinely calculated for the WHP program). This zone is the most crucial area to protect and NHHS’s regulations reflect this need.
NDEQ intends to use all existing sanitary survey data with cooperation from NHHS to make a “first round” vulnerability analysis. This first phase vulnerability analysis will be accessed in NHHS’s files for the initial Source Water Assessment given to the PWSS (Section 6). It should be noted that no changes will be made to this already existing sanitary survey program and vulnerability assessment. PWSSs may challenge the “vulnerable” or “not vulnerable” rating given to them by NHHS (this form is also included in Appendix C). Being rated “vulnerable” usually means the PWSS may not be eligible for additional monitoring waivers.
5.2.2 Phase Two - More Detailed Vulnerability Analysis
A more detailed vulnerability analysis will be made by NDEQ after the results of the voluntary “on-the-ground” contaminant source inventory by the PWSS (or individuals, agencies, or organizations helping with inventories) are given to NDEQ. A review of available PWS well information from the WHP file and Safe Drinking Water Information System (SDWIS - EPA’s database of PWS information and violations) will be undertaken and a table completed (see Table 5.2). A Vulnerability Score will be the result of filling out the table. The scores will fall into different ranges, high to low, that will compare vulnerability of PWSS across the state (see Table 5.1). It should be noted that vulnerability scores will be ranked differently for Community ground water systems, Non-Community ground water systems, and surface water systems. This means a score of 40 does not mean the same thing for the above noted categories (see Table 5.7). The second phase vulnerability determination is independent of the initial rating by NHHS’s sanitary survey. This second phase vulnerability determination will help PWSS prioritize and plan local protection activities.
Table 5.1 Vulnerability Scores Ranking for Ground Water Community PWSSs
| High Vulnerability | Medium Vulnerability | Low Vulnerability |
| > 65 | 45 - 65 | < 45 |
It is likely that more information about the well(s) and local geology will be needed after an initial review of the WHP file is completed. NDEQ will work with the local PWS operator, the NHHS field representative and any other organizations which may have more site specific information available (Nebraska Rural Water Association, Natural Resources Districts, University Nebraska Lincoln-Conservation and Survey Division, local County Health Departments, etc.). NDEQ may contract with consultants, agencies, or organizations to complete this task. A PWSS may hire a consultant or engineer to complete this task, as an addition to a local WHP program. Vulnerability Analyses done by consultants and engineers on behalf of the PWS will be reviewed by NDEQ for completeness and adequacy prior to acceptance. By NDEQ performing or reviewing all of the Contamination Potential Ratings, statewide consistency will be maintained.
Table 5.2 - Second Phase Vulnerability Analysis for Ground Water Community PWS wells - ranking by well or by well field, only if wells are in close proximity and share similar characteristics.
| Characteristic | Point System |  | |
| Depth to water |
- < 10 feet
- 10 - 50 feet
- > 50 feet
| choose one |
|
| Vadose (unsaturated) zone (zone above water table) |
- all sand and/or gravel
- 1 - 15 feet of clay present
- > 15 feet of clay present
| choose one |
|
| Age of well |
- constructed before May, 1977
- constructed after May, 1977, but before May, 1986
- constructed (or reconstructed) after May, 1986
| choose one |
|
| Potential contaminant source within WHPA1 - includes potential nonpoint2 sources |
- inside 2 year Time of Travel
- within 2 year to 10 year TOT
- outside 10 year TOT
- none
| choose highest value |
|
| Transportation corridors within WHPA |
- main line railroad or pipeline
- major highway or interstate intersection
- state or federal highway or interstate
- county roads or city/village streets
- none
| choose highest value |
|
| Average PWSS nitrate as nitrogen concentration over last 5 years |
- below or equal to 5 ppm
- between 5 - 7 ppm
- between 7 -10 ppm
- at 10 ppm or above
| choose one |
|
| Detection of any contaminant regulated under drinking water quality standards in last 5 years (not including coliform) |
- none
- any at or below 50% MCL
- any above 50% MCL, but < MCL
- any at or above MCL or Administrative Order
| choose one |
|
| Existing land use or zoning ordinances for water quality concerns or protecting PWSS |
- none
- county
- local WHP program
| choose one |
|
| Natural Resources District Ground Water Management Area in place |
- none
- Phase I
- Phase II higher
| choose one |
|
Footnotes:
- Potential contaminant sources from “on-the-ground” inventory and from NDEQ database search.
- Nonpoint sources are usually associated with agricultural production where fertilizers and pesticides are applied. Pasture or wooded land are not usually included as potential nonpoint sources of contamination.
5.2.3 Explanation of Table Characteristics
Depth to Water
Shallow depth to the ground water table elevation makes a well more vulnerable to contamination than a deeper ground water level.
Vadose (Unsaturated) Zone
The zone between the surface and the saturated sediments that define the ground water table transmit recharge and contaminants downward. The type of sediments that comprise this zone are very important in determining how fast or even if contaminants will move toward the ground water. Sand and gravel transmit contaminants much faster than clay.
Age of well
May, 1977 was the date of the original Nebraska Safe Drinking Water Act, requiring plans and specs to be submitted after this date. Consideration may be given to PWSSs that submitted plans and specifications to NHHS prior to the 1977 date, even though they were not required.
Potential or existing contaminant source within WHPA - including potential nonpoint sources
Potential contaminant sources within a WHPA indicate a possible threat to nearby or existing well(s). NDEQ feels that any potential source of contamination should be treated equally and that proximity to PWS wells is more important than the type of contaminant. Existing active ground water or soil remediation or monitoring will be included here. Nonpoint sources of contamination (see section 2.2.3), such as irrigated and fertilized corn fields, may also increase the risk of nitrate as nitrogen or pesticide contamination to the PWSS. This characteristic also includes potential sources of bacterial contamination, such as septic systems.
Transportation corridors within WHPA
These potential sources were likely identified in the “on-the-ground” second level inventory. However, they offer the unpredictable threat of accidental spills that should be factored into the vulnerability analysis.
Average PWSS nitrate as nitrogen concentration over last 5 years
One of Nebraska’s most widespread and serious threats to drinking water quality is nitrate as nitrogen (Maximum Contaminant Level = 10 ppm). In many places, nitrates have increased over the past five to ten years and many domestic and public water supply wells have been impacted. Higher nitrate concentrations in PWSS wells indicates vulnerability to further nitrate increases.
Detection of any other contaminant in last 5 years (not including bacteria detections)
The detection of contaminants other than nitrate and bacteria over the last 5 years indicates the PWSS may be vulnerable to contamination. Bacteria is not included here because sampling for it is from the system (at someone’s home or business) and not at the well or Point of Entry. This sampling reflects more on the sampling point and procedures rather than the source of water. Potential sources of bacterial contamination will be addressed during the “on-the-ground” inventory.
Existing land use or zoning ordinances for water quality concerns
This characteristic is given points that will lower the PWSS’s vulnerability rating if controls (county or local zoning, ordinances, etc.) are in place to help prevent impacts to the PWSS’s water quality. An example of county zoning to protect water quality might relate to the size and number of confined animal feeding operations in a county.
Natural Resources District Ground Water Management Area in place
As in the characteristic explained above, points are given that will lower the vulnerability rating if a Ground Water Management Area (GWMA) is in place. Please refer to Section 2.2 for an explanation of GWMAs and the types of protective activities that may occur in them.
5.2.4 Non-Community PWSS
For Non-Community PWSS (both transient and non-transient), the same phased approach to vulnerability assessments will be taken as for Community PWSS, but on a less detailed scale. The first phase will be simply NHHS’s “vulnerable” or “not vulnerable” rating, based on the results of the Sanitary Survey (done once every five years for Non-Community PWSSs).
For the second phase, an area-wide approach will be used. All non-community PWSSs in a county will be plotted on a county, NRD, or some regional map. Ground water nitrate concentrations for the county (or NRD) from the University of Nebraska - Water Center Clearinghouse project (soon to be accessible on the Nebraska Natural Resources Commission internet web site) will be plotted or assessed within a one mile radius of the PWS well(s). Regional nitrate concentrations, PWSS monitoring violations, and regional depth to water will be taken into account for this CPRs.
Table 5.3 Second Phase Vulnerability Analysis for Non-Community PWSS
| Characteristic | Point System | |
| Monitoring detections of regulated contaminant not meeting drinking water quality standards in last 5 years (including coliform) |
|
|
| Regional nitrate concentrations |
- average < 7 ppm in 1 mile radius
- average > 7 ppm in 1 mile radius
|
|
| Regional depth to water |
|
|
Table 5.4 Vulnerability Scores Ranking for Non-Community PWSS
| High Vulnerability | Medium Vulnerability | Low Vulnerability |
| 20 | 15 | 0 - 10 |
As more information about these types of vulnerability assessments become available, NDEQ will consider refining this process. If deemed necessary, NDEQ will submit a SWAP amendment to EPA.
5.2.5 Vulnerability by Well, Wellfield, or by System
Currently, NHHS determines vulnerability for individual wells, unless several wells use a common Point of Entry (POE). This same rating by well or Point of Entry will be used for the first phase of vulnerability analysis in the SWAP.
For the second phase of the SWAP vulnerability analysis, NDEQ will look at wells in the same contiguous Wellhead Protection Area for a common vulnerability rating. Often PWSSs will have more than one wellfield, separated by more than a mile. Each separate Wellhead Protection Area will be rated using the appropriate table from this section. This second phase rating does not change the rating given by NHHS in the Sanitary Survey process, it is intended to be used for planning purposes.
5.3 Surface Water Systems
Surface water systems undergo the same Sanitary Survey with NHHS as the ground water PWSSs. The same two phased approach will be used for these systems, as explained above. The following table (Table 5.5) reflects modifications needed for the surface water systems.
Table 5.5 Second Phase Vulnerability Analysis for Surface Water Systems
| Characteristic | Point System | | |
| Integrity of intake, from last NHHS inspection |
| choose one |
|
| Size of Watershed Delineation Area (WDA) |
- > 35 square miles
- < 35 square miles
| choose one |
|
| Potential contaminant source within Assessment Area2 -- includes potential nonpoint3 sources and permitted discharges |
| choose one |
|
| Transportation corridors within Assessment Area (24 hour TOT) |
- main line railroad or pipeline
- major highway or interstate intersection
- state or federal highway or interstate
- county roads or city/village streets
- none
| choose
highest value |
|
| Detection of any contaminant regulated under drinking water quality standards in last 5 years (not including coliform) |
- none
- any at or below 50% MCL
- any above 50% MCL, but less than MCL
- any at or above MCL or Administrative Order
| choose highest value |
|
| Existing land use or zoning ordinances for water quality concerns |
- none
- county
- local Watershed Protection program or project4
| choose highest value |
|
Footnotes:
- From NDEQ database search, within the Assessment Area (24 hour TOT).
- Potential contaminant sources from “on-the-ground” inventory
- Nonpoint sources are usually associated with agricultural production where fertilizers and pesticides are applied. Pasture or wooded land are not usually included as potential nonpoint sources of contamination.
- Local Watershed Protection program or project could be a CWA 319 project, Nebraska Environmental Trust project, or other local/state program to protect the watershed and/or educate the public.
Table 5.6 Vulnerability Scores Ranking for Surface Water Community PWSS
| High Vulnerability | Medium Vulnerability | Low Vulnerability |
| > 40 | 20 - 40 | < 20 |
5.3.1 Explanation of Table Characteristics
Many of the Vulnerability Analysis characteristics are the same between ground water and surface water systems. Please see section 5.2.3 for these common explanations.
Table 5.7 Summary of Different Types of PWSSs Vulnerability Scores
Type of PWSS | High Vulnerability | Medium Vulnerability | Low Vulnerability |
| Community, Ground Water | >65 | 45-65 | <45 |
| Non-Community, Ground Water | >20 | 15 | 0-10 |
| Surface Water | >40 | 20-40 | <20 |
Integrity of Intake, from Last NHHS Inspection
Nebraska Health and Human Services routinely inspects surface water intakes as part of their Sanitary Survey program and ongoing work with PWSSs. Integrity of an intake structure for a surface water system should include:
- Withdrawal of water from more than one level if quality varies with depth (most often in a lake, but if the potential exists for a chemical spill it may also apply to a river).
- Should be a valve at each inlet and also a valve in the pipeline in case inlet valves are damaged/malfunction.
- Adequate protection against damage by ice, anchors, etc.
Integrity and safety of the intake to accident are evaluated in this inspection and reflect on the vulnerability of the system to contamination.
Size of Watershed Delineation Area (WDA)
A PWSS in a larger WDA will be more vulnerable to contamination than a smaller one due to a greater number of potential sources.
Existing Land Use or Zoning Ordinances for Water Quality Concerns
Counties may have controls (zoning, ordinances, etc.) that are protective of water quality. Local sponsors (such as NRDs, City of Omaha, etc.) have implemented watershed or lake projects that put Best Management Practices on the land and help educate land owners about surface water quality. Points are given for these types of projects that could lower a PWSS’s vulnerability.
5.4 Responsibility
The Nebraska Department of Environmental Quality will assume the responsibility of compiling the data from the Sanitary Survey Program with assistance from the Nebraska Health and Human Services, for the first phase of the vulnerability assessment/analysis. NDEQ will also undertake the CPRs for a PWSS, after the results of the voluntary “on-the-ground” inventory are given to NDEQ. In addition, the state or its contractors/cooperators will do a CRP (including a second round CSI within 3 hour TOT) for all Surface Water systems in Nebraska by May 2003. The goal for the Contamination Potential Ratings is to complete 90% of the PWSSs by the year 2010. A new Source Water Assessment, reflecting the Contamination Potential Rating, will be sent to the PWSS. An explanation of how the new vulnerability score was determined will be provided. The PWSS owner will be required to make this Assessment known and available to the public as explained in Section 6.
Nebraska Department of Environmental Quality
1200 "N" Street, Suite 400
P.O. Box 98922
Lincoln, Nebraska 68509
(402) 471-2186