Inventory Potential Sources of Contamination

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After the wellhead protection area has been delineated, the next step is to identify and locate potential sources of groundwater contamination in that area. Inventorying sources in a wellhead protection area is essentially creating a map of the features and land uses. Groundwater contamination, and resulting threats to your drinking water, can occur as a result of many types of land uses and activities. A source is a location where there is any activity having the potential to release contaminants into groundwater at a level of concern. Those activities may include transporting, storing, manufacturing, or using any potential contaminants.

An inventory of potential sources can serve several important purposes:

Groundwater Contaminants:

There are three broad categories of contaminants that reduce the quality of groundwater in Oregon. The three categories, with subcategories and common examples of each, are as follows:

1. Micro Organisms:

2. Inorganic Chemicals:

3. Organic Chemicals:

Contaminant releases to groundwater can occur on an area-wide basis or from a single point source. Major contaminants of concern on an area-wide or "nonpoint source" basis in Oregon are nitrates and pesticides. Nitrates are currently the most pervasive nonpoint source groundwater problem in Oregon. Sources that potentially contribute nitrates to the groundwater include high densities of septic systems, agricultural activities such as fertilizer application and confined animal feeding operations, and disposal of food processing wastes.

Major contaminants of concern on a "point source" basis in Oregon are volatile organic compounds (VOCs) and petroleum compounds. Point source groundwater contamination can come from not only industrial facilities, waste disposal sites, and large accidental spills, but from day-to-day operating practices associated with small businesses, abandoned single family water supply wells, and other residential-related activities commonly located in every community in Oregon.

Table 3-2 provides a good overview of potential sources of contamination and the contaminants that are associated with each source. The sources of groundwater contamination can be grouped according to many different criteria. Contaminants can reach groundwater from activities occurring on the land surface or below it. Table 3-2 can be used as a guideline for understanding the potential contaminants from the types of facilities listed on your inventory form.

There are many excellent resources available to provide additional information on groundwater, contaminant sources, and transport issues (see EPA, 1994; OTA, 1984; EPA, 1990). Our recommended approach to identifying potential sources is to be as thorough as possible.

Recruiting Volunteers:
A thorough inventory of potential contamination sources is an essential step in developing local wellhead protection plans. This process can be tailored to the specific needs and resources of the individual RMA(s) and Team. If your wellhead protection area is small or an adequate inventory can be conducted by the Public Works Director, for example, or members of the Team, you may not need to solicit volunteers for assistance. Most communities participating in a wellhead protection effort, however, will share the problem of not having the staff or resources to conduct a thorough inventory. One solution to this problem is recruiting volunteers from your local area. The knowledge of the citizens living in your local area is essential in identifying many of those activities which pose a threat to the drinking water. Using local citizen volunteers will not only improve the inventory outcome, but will reduce the overall costs of your wellhead protection plan.

Volunteers are precious local resources. They can be recruited from many different existing organizations, such as community service organizations, 4-H Clubs, Boy Scouts, Girl Scouts, League of Women Voters, high school groups, or a Team member can establish and coordinate a new group of volunteers.

One very successful example of using volunteers for an inventory was the recent utilization of the Retired Senior Volunteer Program (RSVP) in El Paso, Texas. This project is highlighted here not only because it successfully used an existing organization, but DEQ also strongly recommends the utilization of seniors in your community because they are invaluable sources of information.

Retired citizens of the community can provide the knowledge, manpower, and leadership needed to conduct an inventory of potential sources of contamination. Their availability, historic knowledge of the community, interest in intergenerational environmental concerns, and personal expertise make the retired persons of the community the ideal candidates for groundwater protection activities. Through their tradition of consistently strong local political involvement and numbers, older adults can ultimately affect a change in public opinion concerning the issue of groundwater protection.

RSVP is an ideal candidate for groundwater protection activities because RSVP is structured with a recruiting mechanism. Each RSVP project throughout the United States has an individual available to call and recruit the volunteers needed to conduct an inventory. RSVP also provides its volunteers with an insurance program involving accident, personal liability, and excess automobile liability insurance coverages. Oregon has 14 existing local networks throughout the state. Information on Oregon's RSVP program can be obtained from the RSVP office located at:
2256 NW Lovejoy

Portland, OR 97210

Telephone: 503-229-7787

Communities interested in involving RSVP volunteers should first consult their telephone directory under RSVP or Retired Senior Volunteer Program. If the community is unable to find such a listing they may contact the Portland office or the National Association of RSVP Directors, 703 Main St., Patterson, New Jersey 07503.

The Department of Environmental Quality can provide more information on the El Paso RSVP project for Oregon communities that are interested in using this as a tool to conduct their inventory. This approach to the inventory would most likely only be necessary in larger communities and/or large wellhead protection areas.


The methodology for accomplishing Step 4, the inventory of potential sources, can be summarized as follows:

A detailed description of each step is included below:

Check with your local county/city transportation, planning department, public works, or chamber of commerce to help you locate the best available map for the delineated area. Your base map used during the delineation step may be detailed enough. If you used a USGS topographic map at the typical 1
:2,000 scale, though, you may want to enlarge it to a 1:1,000 scale for use during the inventory step. Even larger scale maps, such as 1:800, are most convenient for urban areas. It is important to have a map at an appropriate scale that allows the Team and/or volunteers to plot each potential source on the map. Each source can be labeled or coded on the inventory map. A simple numbered mark or reference for each source on the map can also be cross-referenced to a separate list. An example of an inventory map is shown in Figure 3-9.

Figure 3-9: Example Inventory Map

Potential sources can be coded and cross-referenced to Form 3-1.

Example codes:











Land-use areas can be color-coded and labelled on the map.

Subsections of the base map can be copied to be used in the "field" during the inventory process. Then the Team and/or volunteers could continuously update one primary base map as they cover small segments within the delineated area. This will help ensure detailed coverage and avoid duplication of effort by the volunteers while conducting the inventory.

B. Collect existing sources of information:

At the local level, a substantial amount of information on historical, current, or future potential contamination sources exists in the form of routine records or documents in the county or city files. This is an excellent place for the Team and/or volunteers to begin. Specific sources of information for local data on land uses and activities may include:

When identifying land uses, it is important to consider not only existing uses but also the historical and future uses of the land. The historical uses often play a major role in the land's present capacity to contaminate groundwater. For example, land that was used for agricultural purposes at one stage should be researched to identify chemicals such as pesticides used, stored, or disposed of on-site. Historic or former gasoline stations and dump sites are easy to overlook but are considered high potential risks to groundwater. Searching records and/or interviewing long-time residents will help ensure that you do not overlook past sources of contamination.

Aerial photographs can be extremely helpful in identifying both present and historic land uses and activities. Aerial photos may be available at your county seat, planning, or transportation office. They can also sometimes be obtained from the Corps of Engineers, Soil Conservation Service, or from a commercial aerial photographer (listed in your local phone directory). Other resources include the larger colleges or universities in Oregon. The University of Oregon in Eugene also has an extensive collection of aerial photos of most of Oregon in their Photogrammetric Library.

In collecting existing sources of information, the Team will want to also query the state resource agencies for data which may be available on the wellhead protection area. There are databases at the Department of Environmental Quality, Water Resources Department, State Fire Marshall, Emergency Management, Oregon Health Division, and the Department of Geology and Mineral Industries. These databases contain information on existing permits related to water quality, underground injection, hazardous waste, solid waste, underground storage tanks, air quality, water supply wells, and data on the toxic release inventory, and cleanup sites. Appendix B provides a description of what data is available and where to find it. Collecting this type of information prior to conducting any field work should make the field effort much easier.

The level of effort necessary for collecting this information will vary according to the density of development. Older, larger communities may need to invest more time obtaining existing data and verifying it.

C. Divide the WHP area into different land uses:

To help structure the inventory approach, it is recommended that you divide your wellhead protection area into the following four land use categories:

A general land use overlay map can be prepared using the information gathered in Step 4B. This overlay map will help your Team establish the threat that land uses pose to the quality of your water supply. A good starting point for this map, if available, is your community's zoning map or current land use map, which allocates sections of your community for specific land uses, including residential, commercial, and industrial uses. These zones create concentrations of businesses or small industry. If these concentrations are located in close proximity to your well(s), they can potentially increase the threat to your drinking water. Aerial photos may also be very useful for dividing the wellhead protection area into the general land use categories if a zoning map is not available for your community.

The land uses/zones in your wellhead protection area can be fine-tuned or updated as the volunteers conduct the actual inventory. This will also help to make your Team's management strategy or approach easier to develop.

D. Prepare an inventory form:

To adequately identify potential sources of contamination, it is useful to prepare a comprehensive inventory form. This will not only ensure a more consistent approach by the volunteers, but it will help prevent omissions of potential contaminant sources. DEQ recommends that you use Form 3-1 .  This is considered to be a comprehensive list, although all potential sources of groundwater contamination are impossible to list. If the WHP area is subdivided and assigned to different individuals, this list can be copied to produce as many as are needed for volunteers to use. A final tally of each category can be conducted when they are compiled at the end of the inventory step.

The list in Form 3-1 can be expanded or adapted to more adequately apply to your particular wellhead protection area. This extensive list will not be appropriate for many of the drinking water sources in the rural areas of Oregon. It is recognized that there are significant variations in land uses and activities across the state, especially in agricultural activities. The Team may want to adapt this list to more adequately address their local area. It is important to encourage the volunteers to use the "other" categories on the inventory form as often as needed when they are not sure what a particular land use or activity is. Identifying by address/location and a brief description of the observed activities will allow adequate follow-up if more information is necessary.

E. Conduct a windshield survey and plot the existing data:

The level of actual field reconnaissance or "windshield survey" will depend upon the complexity of your wellhead protection area. In some cases, the entire inventory can be performed by a very knowledgeable individual in the office without any field work required. However, most Teams/volunteers will need to conduct a windshield survey using the inventory form prepared in Step 4D. This simply involves driving through the wellhead protection area, field checking the locations of potential sources identified during the previous data collection Step 4B, and noting any new potential sources that are seen during the survey. Some of the important things to look for during the windshield survey include old gas stations (evidence of pump "islands"), lagoons or basins where water is ponding, locations of long-term machine/auto repair sites, and obvious storage areas for chemicals, pesticides, wastes, etc. The Team may want to re-visit these areas and conduct a more in-depth assessment. It may be helpful for any Team or volunteer member that conducts the windshield survey to review the Table 3-2 list of potential sources. This will help them become familiar with the fact that there are wide varieties of potential sources in virtually every community.

Other tools that can be used to collect information for the source inventory includes door-to-door surveys or mail surveys. This may be particularly useful, for example, in areas where there are many abandoned wells or septic tanks.

Any other approach or combination of approaches that help ensure an accurate and complete inventory will contribute toward the success of your wellhead protection plan. There are many potential contamination sources that are difficult to identify. The Team can get additional technical assistance or information about conducting their inventory from DEQ.

It is important to recognize that local jurisdictions may not have the authority to access or inspect potential sources/facilities. Be sure to gain the property owners permission for access before entering the property for purposes of an inventory.

The primary objective of Step 4 is to prepare a map with the locations of potential sources. Using the detailed base map developed in Step 4A, plot the potential sources as accurately as possible. Figure 3-9 provides an example inventory map with potential sources, as well as the land uses, identified with numbers or codes keyed to the inventory list. Your potential source map will serve as the basis for developing your management strategy. Appendix C contains other actual inventory forms and maps from Oregon Communities.

F. Rank the estimated risks or threats:

The last step in the inventory process is to determine which of those potential contamination sources pose the greatest threat to your water supply. Classifying potential sources into general risk categories will be the simplest way to determine which sources pose the greatest threat. Identifying the high risk threats will provide input for developing a management strategy based on prioritized areas or individual sources.

Values of risk can be assigned to each potential source according to, for example:

For a densely developed or complex area, the Team could employ a fairly sophisticated method of ranking potential sources. EPA (1991) developed a risk screening tool to assess and rank the relative threats to groundwater supplies posed by potential contamination sources in 13 different major source categories. A risk score is calculated for each potential contaminant based on the likelihood and severity of well contamination. Scoresheets, datasheets, and forms are provided for use in the scoring process. Although this could provide an excellent tool for ranking individual risks, DEQ does not anticipate that this level of evaluation is necessary for most public water systems in Oregon.

DEQ has used Oregon-specific data, as well as EPA guidance, to develop a list of types of potential sources in each risk category. Table 3-3 provides a list in each higher, moderate, and lower risk categories. In this table, the criteria for placement in the specific categories was limited to historic release data such as (EPA, 1990b; DEQ, 1995), DEQ regulatory control data (Ross, 1994), and potential contaminant characteristics (DEQ, 1995; EPA, 1994). The most common types of facilities that are on the active DEQ cleanup list, for example, are considered higher risks to groundwater.

An essential assumption that must be made when considering potential risks to groundwater is that the facility or activity does not now or may not in the future employ good management practices or pollution prevention. This is important because it is the potential risk that we are attempting to determine. Ideally, most of these activities are conducted in a manner that minimizes the risk of a spill or "release" that could result in soil and groundwater contamination, threatening your water supplies. This is obviously one of the goals of developing a wellhead protection plan.

Your Team may want to make modifications to the risk categories in Table 3-3 based on local conditions, knowledge of operating practices, etc.

Keep in mind that the overall success of your WHP Plan is largely dependent upon identifying the potential sources and determining in the management step what, if any, practices should be employed to reduce the risks from these sources. During the management step, the Team will make more detailed assessments of the potential sources and the site-specific practices that may enable you to move many of the higher or moderate risks to the lower category. This can reduce the need for any management efforts for those facilities or activities that are employing good management practices.

Inventory References:*

DEQ, 1995. Waste Management and Cleanup Division, Environmental Cleanup Site Information (ECSI) Database, Oregon Department of Environmental Quality.

EPA, 1990a. Handbook, Ground Water, "Volume I: Ground Water and Contamination", EPA 625/6-90/0162, Office of Research and Development, Washington D.C. September 1990.

EPA, 1990b. A Review of Sources of Ground Water Contamination from Light Industry, EPA 440/6/9/005, Office of Water, Washington D.C., May 1990.

EPA, 1991. Managing Ground Water Contamination Sources in Wellhead Protection Areas: A Priority Setting Approach, EPA 570/9-91/023, Office of Water, Washington D.C., October 1991.

EPA, 1993. Seminar Publication, Wellhead Protection: A Guide for Small Communities, EPA/625/R-93/002, Office of Research and development, Washington D.C., February 1993.

EPA, 1994. Handbook, Ground Water and Wellhead Protection, EPA/625/R-94/001, Office of Research and development, Washington D.C., September 1994.

OTA, 1984. Protecting the Nation's Groundwater from Contamination, Vols. I and II, OTA-0-233 and -276, The Office of Technology Assessment, Washington D.C.

Ross and Assoc., 1994. Enhancing Technical Assistance and Pollution Prevention Initiatives at the Oregon Department of Environmental Quality, Ross and Associates, April 1994.


*EPA documents can generally be obtained free of charge from EPA by calling 513-489-8190.

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