Inventorying Potential Sources of Drinking Water Contamination

Barbara C. Cooper, Water Quality Education Specialist
Jane R. Frankenberger, Extension Agricultural Engineer
Fred Whitford, Coordinator, Purdue Pesticide Programs

What Is a Potential Contaminant
How Do You Conduct a
Contaminant Source Inventory?
What's Next?
Useful Publications
Sources for Maps and Aerial
Indiana Information Contacts
Clean, safe drinking water is vital to our communities, to our economy, and to our health. If your ground water becomes contaminated, it may be lost forever as a water supply or may require very expensive treatment to remain usable. The best way you can ensure safe water, now and for the future, is to protect the area around your drinking water supply wells from potential hazards.

This publication provides guidance for the public water supply operators and local wellhead protection planning team members who will guide the completion of the contaminant source inventory. It explains the process of identifying regulated and unregulated, present and past, potential contaminant sources within the wellhead protection area. It assumes that your wellhead protection planning team has defined and mapped your wellhead protection area using an appropriate delineation method. (See "Useful Publications" for Purdue Extension publications offering information on these topics.)
Wellhead Protection Planning Overview
  • Local planning team
  • Delineation of the wellhead protection area
  • Identification of potential sources of contamination
  • Management of the wellhead protection area
  • Contingency plan
  • Public participation, education, and outreach
  • Why Do a Contaminant Source Inventory?

    Indiana's Wellhead Protection Rule (327 IAC 8-4.1) requires community water supply systems to "complete an inventory of potential sources of contamination (regulated and non-regulated) within the wellhead protection area." This rule requires a search of existing databases of regulated sources, but a database search alone will not reveal all potential sources of contamination. Volunteers your team recruits must also travel through the wellhead protection area to do a site inventory. And you should supplement this information by seeking historical land use data from long-time community residents.

    By knowing what potential contamination sources exist near your drinking water supply wells, your community can help prevent ground water contamination through effective management of land activities. Experiences of other communities have shown that on average, wellhead protection is 27 times less costly than cleaning up a contaminated water source, according to the Environmental Protection Agency. Not only is wellhead protection a matter of common sense, it is a good idea from an economic point of view.

    What Is a Potential Contaminant Source?

    A potential contaminant is anything that might get into your drink-ing water that you would not want to drink. A source is a facility or land activity that could release a contaminant. While soil serves as a filter for many things that might otherwise enter the ground water, it is not capable of remov-ing everything. So it is important to prevent contaminants at or near the surface of the ground from seeping into the ground water.

    The most important potential sources of contamination to identify are those that are particularly hazardous to health and those occurring in large volumes. Some obvious potential sources of ground water contamination are hazardous chemicals that are stored, transferred, or used in the wellhead protection area.

    However, many other things are potentially hazardous to ground water. Other potential sources include abandoned wells, land-fills, animal feed lots, storage lagoons, abandoned underground storage tanks, quarries or mines, and septic systems. Former or abandoned gasoline stations, dry cleaners, and manufacturing facilities, even though no longer in operation, might also be potential sources of contamination. The contaminant source inventory is a list of all potential sources of contamination within the wellhead protec-tion area.

    How Do You Conduct a Contaminant Source Inventory?

    To complete an inventory of potential contaminant sources, your team will need to identify existing regulated and non-regulated sources, locate and identify them on a map, and tabulate the col-lected information about the sources. So one of your first tasks is to get base maps your team can use for organizing this data.

    1. Get Maps of the Wellhead Protection Area

    A Note on Map Scale

    A map is a representation of features on the land's surface,
    reduced to a size that can be viewed on a piece of paper. Every
    map has a specified scale that tells the user how much size
    reduction has taken place in the production of the map. An 8"x11"
    map of the world would be a smaller scale (and show less detail)
    than an 8"x11" map of your town. For a wellhead protection plan,
    IDEM requires the use of maps in which one inch on the map
    represents between 400 feet and 1000 feet on the ground. Map
    scales within this range will show enough detail to be
    easily readable.

    How do you know if a map or photo is at an acceptable scale for
    use in the contaminant source inventory? Most maps are labeled
    with a scale that is a ratio between one unit of distance on the
    map and a corresponding unit of distance on the ground. It is
    written as two numbers with a colon between. A scale of 1:200
    means that one inch on the map is 200 inches on the ground, or
    one centimeter on the map is 200 centimeters on the ground. The
    units, whether inches, centimeters, or something else, do not
    matter-the ratio is the significant information. To comply with
    the requirement in Indiana's Wellhead Protection Rule, the scale
    of your map must be between 1:4,800 (equivalent to one inch =
    400 feet) and 1:12,000 (one inch = 1000 feet).

    Maps are vital throughout the wellhead protection planning process. All the informa-tion gathered must be both tabulated and displayed on a map in the wellhead protec-tion plan submitted to the Indiana Depart-ment of Environmental Management (IDEM). If your area lies at the edge or corner of an existing map sheet, you may need to obtain more than one published map to cover your wellhead protection area.

    You will need at least three copies of your base map(s). One copy you will send to IDEM with your completed plan, one you will keep as a master copy for yourself, and one you will use as a working map to write and erase on as changes are made. You will also need to photocopy (and possibly en-large) the working copy of the base map and divide it into sections for use by volunteers who will help with the site survey of the wellhead protection area. The site survey process is described in more detail in a later section of this publication.

    Here are some options for types of maps your team can use as your base map. IDEM requires that you use either a USGS 7.5 minute topographic quadrangle or a map at a specific scale. (See the sidebar "A Note on Scale.") You can find information on where to acquire these maps at the end of this publication.

    * Engineering Map-If you had the wellhead protection area delineated professionally, you should have received from the consultant a map of the delineated wellhead protection area at a scale of between 1:4,800 and 1:12,000. (See "A Note on Map Scale.") Depending on the detail included, your team could reproduce and use this delinea-tion map as the base map for the contaminant source inventory.

    * Topographic Quadrangle Map-If you have a system small enough (pumping less than 100,000 gallons per day) you are eligible to apply to IDEM to use the 3000-foot radius as the wellhead protection area. You are required to submit a topographic quadrangle map showing the delineated wellhead protection area to IDEM (Figure 1). You can enlarge this map to double its normal size and use it as your base map.

    * Plat Map-Your team can also use a plat map as a base map, if it is of the appropriate scale. The advantage of using a plat map is that it already shows property boundaries and land ownership.

    * City or County Map-If your wellhead protection area can be indicated on a city or county map and it is the proper scale of between 1:4,800 and 1:12,000, your team could use the city or county map as a base map.

    * Aerial Photos-Aerial photography provides an option for the site survey portion of the contaminant source inven-tory. Because it is often difficult to get a clear photocopy, it is probably not the best choice for the base map. However, an advantage of aerial photos is that evidence of former hazardous land activities and present land activities can be identified, and that information can be transferred to your base map.

    No matter what type base map your team chooses, the delineated wellhead protection area should be clearly marked on the map (Figure 2). It is important that the map you choose as a base map is easy to read even when photo-copied.

    Once you get a suitable base map, draw the delineated wellhead protection area on it. The delineated wellhead protection area is the area for which you will gather infor-mation on potential contaminant sources.

    2. Gather Data.

    Your team must use two techniques to gather the information needed to identify potential contaminant sources. These include:

    * Reviewing records of regulated potential contamination sources in federal databases and in state and county databases and files, and

    * Traveling through the wellhead protection area observing land activities that may not be included in any databases.

    As you complete each of these data-collection processes, compile the data collected onto one copy of your map. This publication refers to the map on which you add or compile information as the "working map." Create a table to list the information related to each map entry. (See "Organize Data.") In large communities, there will a correspondingly large volume of data to be organized. So it is good to organize as you progress rather than waiting until all the information is collected.

    The Records Review

    Your database search should locate existing and former potential contaminant sources that are regulated by some government entity. Many potential sources of contamination, such as landfills, underground storage tanks, and pesticide storage sites, are regulated, and the records about such sites are public information. A search of existing databases will provide identification of regulated sources.

    You can obtain these records using one of two methods: by hiring a private consultant to complete a database search for your specific area or by searching the databases yourself using a computer with an Internet connection.

    You can hire a consultant to perform the search of federal and some state databases for hazardous materials, past reported spills, and underground storage tanks. The price depends on the complexity of the delineated wellhead protection area and will range between a few hundred and a few thousand dollars. Some of these providers will plot the data on a map and provide the data in a table, as necessary for compliance with Indiana's Wellhead Protection Rule. Some consultants who can provide these services are listed on the Web at http://www.ecn.purdue.edu/SafeWater/.

    Whether you hire a consultant or search the databases yourself, be aware that the databases may not be totally accurate. Through personal experience, someone on your wellhead protection planning team may be aware of changes that have occurred which make the information on the databases inaccurate. So check the database information for accuracy and consistency.

    Federal Database Search

    If you or someone on the wellhead protection planning team chooses to search the databases, visit http://www.epa.gov/enviro/ to find information about federally regulated facilities.

    As you search each of these databases, number and note the facilities you find in your wellhead protection area on your working map. You might choose a distinct shape mark to indicate each type of potential pollutant. If a facility is on a database, but is no longer in operation, indicate its position on the map, list it in the table, but note its status with a term descriptive of its condition, like "closed," "abandoned," or "removed."

    State and Local File Search

    State and county files of regulated materials often contain data that has not been computerized, but recorded on paper in various government offices. Historic records of land activities and uses may also be available. These data files must also be searched.

    Like the federal databases, the state and local data files can be searched in two ways, by hiring a consultant to do the search or by doing it yourself. Someone familiar with the process can search IDEM's files in three to eight hours. Some consultants who offer this service are listed on the Safe Water Web site. (See "Indiana Information Contacts.") This task is not recommended for anyone who is unfamiliar with the process. However, if you or someone on the planning team chooses to search the state and local files, you must be aware of the necessary files to include in your search.

    Include the state and county file search information on your working map. Once the database and file search information is on the map, you can enlarge sections for your wellhead protection planning team to use in the site survey for unregulated or otherwise unidentified potential sources.

    The Site Survey

    Federal and state databases are not 100% accurate, are focused on facilities using of large quantities of chemicals, and are incomplete with regard to smaller facilities. Also, the requirement to register underground storage tanks applies only to those in use after 1986 and only to those larger than 500 gallons. A facility that closed before current regulations were in effect could have left behind a source of contamination. Thus a more thorough survey performed by people who know the area will offer better protection for your water supply.

    This survey is usually completed by community volunteers who drive or walk through the designated wellhead protection area writing down observations about the various past and present activities taking place in an area. The process is often called a "windshield survey" because the observations are usually made through the windshield of a car. This type of site survey is the best way to obtain information on non-regulated hazardous materials that might be in the wellhead protection area.

    By getting community members to assist with the collection of this information you also raise awareness within the community of the importance of wellhead protection. Try recruiting these volunteers from local service organizations and retired citizens groups. Try also to get your local newspaper, radio station, and /or television station to publicize the event and to communicate the importance of gathering as much information as possible. For very small communities, posting of fliers and bulletins can be highly effective. Because successful wellhead protection depends on cooperation from everyone, educating the public about the goals and requirements of wellhead protection is essential.

    Most hazards to ground water are associated with certain activities. For example, fertilizer use and pesticide uses are associated with golf courses, residential and other lawns, and farms and other agricultural operations. Chemical solvents and oils are associated with machine shops, auto repair facilities, and certain industrial processes. To clean clothing, dry cleaning facilities use chemicals that are highly toxic to a drinking water supply. Armed with the base map showing the delin-eated wellhead protection area, a few community volunteers can map these and other unregulated activities that are potentially harmful to a drinking water supply.

    Historic land use data can be assembled through investigating old Chamber of Commerce membership files, historical maps and photos, Sanborn Insurance maps, and Soil and Water Conservation District aerial photos. A local history buff is a good resource for information. The collective memory of long-time residents is the best source for historic land use information, locations of abandoned wells and underground storage tanks, and other potential contaminant sources. You might also try asking the local newspaper to run an article requesting people with historical land use information to contact the local well-head protection planning team.

    Steps for Organizing a Site Survey

    1. Prepare the maps you will need. Enlarged copies of your existing working map (the map on which you add or compile information about the sites where regulated use and storage of hazardous materi-als occurs) should be used for the site survey. The people who will help with this part of the survey can verify the presence or absence of the regulated facilities found in the database search while they drive or walk through their portion of the wellhead protection area. If your wellhead protection area is large or complex, divide the wellhead protection area into sections small enough that a couple of people can drive through each section noting land activities and potential contaminant sources within a couple of hours. Create a separate map for each section to be surveyed.

    2. Assemble a group of community volunteers, and divide them into two-person teams. Try to let each pair choose a section they are familiar with to survey. Provide each survey pair with a large map of their specific area (Figure 3) and instructions on how to complete the survey. (See the "Guide for Wellhead Protection Survey Volun-teers" handout master copy included at the end of this publication.)

    3. Have the volunteers complete the survey and return their maps and notes to the coordinator, the person who will assemble the information from the various groups. The coordinator should also make sure each returned map has the names of the surveyors on it, in case there is a question about the information collected.

    4. After the coordinator collects the maps and inventory tables, have one person assemble and organize the information from all the working maps onto the master map and a master table. Each group of volunteer surveyors will have numbered the potential contami-nant sources in their particular section starting with the number "1." This information must be put onto the master map in a sequence that corresponds to the way it will be depicted on the table of potential contaminants. It is important that there is a one-to-one correspon-dence between the map and the table.

    5. Organize the original inventory sheets according to location, and keep them as an appendix for your on-site, master copy of the wellhead protection plan. Later in the wellhead protection planning process, they may be useful in developing your management strategy.

    3. Organize Data

    IDEM requires that three things be included in the contaminant source inventory section of the wellhead protection plan:
    1. Narrative description of the land uses in the wellhead protection area,

    2. Map showing land uses and locations of both regulated and unregulated potential contaminant sources, and

    3. Table corresponding to the map.

      The Narrative Description

      The narrative description you will eventually submit to IDEM with your completed wellhead protection plan should include background information on your community water supply system. Include what is known about its size and age, a description of the size of the wellhead protection area, and the land activities that are found in the wellhead protection area. As you can see in the sidebar, "Example of a Narrative Description," this does not have to be an elaborate or complicated document.

      Example of a Narrative Description

      The delineated wellhead protection area for Small Town,
      IN is an oval shape extending approximately 2000 feet
      to the north and 1200 feet south, east and west of the
      well, covering an area of approximately 200 acres. The
      well is six inches in diameter. This well pumps
      approximately 150,000 gallons per day and serves a
      population of 825 people.

      Slightly less than half of the delineated wellhead
      protection area (approximately 80 acres) is in commercial
      usage. The commercial area includes most of the
      downtown area and the country club. There is a small
      industrial area with a chemical manufacturing company.
      There is a small residential area on private septic
      systems, and the remainder of the wellhead protection
      area is in agricultural land use. Indiana Highway 32
      traverses the wellhead protection area about 1000 feet
      south of the wells.

      The Map

      The master map you will submit to IDEM with your wellhead protection plan should show all the inven-tory information collected for both regulated and non-regulated contaminant sources from all the working maps. Double-check to make sure that every potential contaminant source is shown on the map, and make sure the master map is at the proper scale. (See "A Note on Map Scale.") Before you send it to IDEM, remember to make a copy of this master map to keep with your other records.

      The Table of Potential Contaminant Sources

      The table that you submit to IDEM as the third component of the contaminant source inventory section of your wellhead protection plan should list the following information: Depending on the complexity and size of your wellhead protection area and on your access to computer resources, you may find it helpful to use a spreadsheet to keep track of the contaminant source inventory information. Table 1 shows an example of how the information gath-ered in the site inventory can be displayed.

      Table 1. Example of tabulated information on potential contaminant sources in the wellhead protection area.
      ID# Facility Name Address Site Type Contaminant Type Federal and State Site
      Identification Numbers
      Operating Status
      1 Bill's Service Center 231 Main St gas station gasoline, oil, BTEX RCRIS-IND000000000
      UST 000000
      2 MJB's Gas 2994 E. 6th gas station gasoline, oil, BTEX RCRIS-IN0000000000
      LUST 000000
      3 Auto Care 1337 N 14th St. auto repair solvent, oil, batteries, antifreeze RCRIS-IND000000000 operating
      4 Sam's Cleaners 831 Pine St. Laundry/
      Dry Cleaners
      PCE RCRIS-000000000000 operating
      5 city landfill 18 River Road landfill unknown CERCLIS IN0000000000 closed
      6 ChemCorp 200 Beck Rd. chemical research VOC, solvents, bromine TR-IND000000000
      7 BJ's Nursery Supply 321 Juniper Lane nursery and
      garden supply
      fertilizers, pesticides NA operating
      8 Circle R Dairy 250 SR 100 N dairy farm manure, fuel, oil, diesel UST 000000 operating
      9 Moose Lodge
      Country Club
      300 SR 100 W country club fertilizers, pesticides,
      swimming pool chemicals
      RCRIS-IN0000000000 operating
      10 State Highway 32   highway road salt, gasoline, oil spills from
      vehicular accidents
      NA open

      What's Next?

      By completing the contaminant source inventory, your wellhead protection planning team will have identified the most likely sources of contamination in your wellhead protection area. At that point, Your team can begin working on formulating management and contingency plans, and on developing a program for public education about well-head protection. You will find information on these topics in future Purdue Extension publications on wellhead protection planning.

      Useful Publications

      The following Purdue Extension publications provide information about other aspects of the wellhead protection process. You may find the following two Purdue Extension brochures to be useful in your community outreach efforts: All of the above publications and brochures are available free of charge through your county Purdue Extension office or by calling 1-888-EXT-INFO.

      The USEPA has an informative publication, "Wellhead Protection, A Guide for Small Communities," EPA/625/R-93/002, available free by calling 1-800-490-9198.

      Sources for Maps and Aerial Photos

      Topographic Maps

      Plat Maps

      Aerial Photos

      Indiana Information Contacts


      USEPA, 1995, "Benefits and Costs of Prevention: Case Studies of Community Wellhead Protection-Volume 1," USEPA, EPA 813-B-95- 005.

      USEPA, 1993, "Wellhead Protection: A Guide for Small Communities," a USEPA Seminar Publication, EPA/625/R-93/002.

      Whittman, Jack, 1996, "Wellhead Protection Guide," Center for Urban Policy and the Environment, School of Public and Environmental Affairs, Indianapolis, IN.

      Witten, Jon and Scott Horsley, 1995, "A Guide to Wellhead Protection," Planning and Advisory Service, American Planning Association, PAS Report #457/458.

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