5. Nature and Extent of Area-Wide Soil Contamination (continued)

Recommendations on How Information on the Nature and Extent of Area-Wide Soil Contamination Should be Communicated

The Task Force recommends that information on the nature and extent of area-wide soil contamination be communicated using a combination of maps and accompanying narrative information that emphasize the need for individual property evaluations to determine with certainty whether area-wide soil contamination is present.

Maps can be a highly effective way to communicate available information about potential locations of area-wide soil contamination to the public. In addition to communicating information about potential locations of area-wide soil contamination to the public, the maps recommended by the Task Force serve a variety of purposes, including helping the Agencies to identify areas where an alternate approach under MTCA might apply (see Section 10) and helping the Agencies and local jurisdictions prioritize and focus efforts where area-wide soil contamination is more likely. For the Tacoma and Everett smelters, Ecology, several local jurisdictions, and other organizations have collected and continue to collect data on where arsenic and lead soil contamination is likely to be present based on emissions, wind deposition, and results of a number of soil sampling events, and have developed maps to communicate this information. These maps were an important factor in the Task Force deliberations. Task Force recommendations related to maps are discussed later in this section.

Maps also have significant limitations. As discussed earlier in this report, the precise boundaries of area-wide soil contamination are not, and likely will not be, identified and therefore cannot be mapped. Even where area-wide soil contamination is likely, the actual distribution and concentrations of arsenic and lead in soil vary greatly over short distances. Because of this limitation, the Task Force emphasizes that maps can be used only to communicate where elevated levels of arsenic and lead in soil are more likely to be present relative to other areas in Washington State. Maps do not show where elevated levels of arsenic and lead have actually been found, and many properties within identified area-wide soil contamination locations may, if sampled, be shown to have concentrations of arsenic and lead that are below MTCA cleanup levels.

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Individual Property Evaluations

Because of the limitations of maps, an individual property assessment is the only way to know with certainty whether a property is affected by area-wide soil contamination. The Task Force believes that individual property evaluations are an important step for people to understand the potential for area-wide soil contamination where they live or work. These assessments are more important than locating a property on one of the maps discussed later in this report, because of the variability in the distribution of arsenic and lead and other limitations of mapping. To support individual property evaluations, the Task Force has created the following flowchart. Individuals who follow the flowchart and determine that there is a high probability of area-wide soil contamination at their property should implement individual protection measures and maintain good soil cover, and may want to consider soil testing, particularly if there is a high potential for exposure.

Figure 2: Individual Property Evaluation Flowchart  (click figure to enlarge in new window)

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Maps of Potential Area-Wide Soil Contamination

To supplement individual property evaluations, the Task Force recommends use of maps. The Task Force discussed maps at length and considered many different individual maps and mapping options. From these deliberations a number of themes emerged:

• The locations of area-wide soil contamination cannot be precisely mapped. Individual property evaluations are the only way to know with certainty whether a property is affected by area-wide soil contamination.
  
• Maps are a useful communication device, and are an effective way to show where area-wide soil contamination is more or less probable so that individuals can make knowledgeable choices about whether to carry out individual property evaluations. However, care should be taken to avoid misinterpretation of maps.
  
• Because of the limitations of maps, the Task Force believes strongly that maps should always be accompanied by information that describes what the maps show and the limitations of data on which the maps were based.

The Task Force recommends two tiers of maps and accompanying information for smelter emissions and historical uses of lead arsenate pesticides:

• Tier 1: The first tier of maps and accompanying information should identify the general areas in the state where elevated levels of arsenic and lead soil contamination are more likely to be present based on historical smelter emissions and historical use of lead arsenate pesticides. Information accompanying Tier 1 maps should emphasize that maps do not show areas that have been found to be contaminated, but simply show where contamination is more likely relative to other places. Tier 1 information should be designed to raise general awareness about area-wide soil contamination in the widest possible audience and to help users decide whether to look at the second tier of more detailed maps and informational tools for more information.
  
• Tier 2: The second tier of maps and accompanying information should identify where area-wide soil contamination is likely to be present on more detailed, smaller scale maps of smelter plumes and historical orchard areas, where these areas are known. Information accompanying Tier 2 maps should include flowcharts and/or other informational tools to help individuals determine whether arsenic and lead soil contamination is likely to be present based on the location and land-use history of individual properties and whether to implement individual protection measures or other responses, including soil sampling.

Examples of Tier 1 maps are included below (see Figures 3 and 4); examples of smaller scale Tier 2 maps are included in Appendix I. The Task Force emphasizes that the maps included in this report are only examples prepared to support Task Force deliberations. The example smelter emission maps are based largely upon ongoing mapping and sampling efforts associated with the Tacoma, Everett, and Harbor Island smelter cleanup actions. The smelter emission map for the Northport and Trail, BC smelters is based upon a historical study of the observed effects of sulfur dioxide emissions (another smelter emission contaminant released along with arsenic and lead) on vegetation. The example lead arsenate pesticide maps show estimates of the areas potentially affected by the use of lead arsenate pesticides based upon three different types of data sources: 1) the peak historical acreage in apple and pear tree production by county during 1905-47 (Figure 4), 2) a county-wide application of the land-use information in the individual property evaluation flowchart, and 3) locations of historical orchards identified based on aerial photographs from 1947.

It is important to reiterate that while maps show a greater or lesser probability of encountering elevated levels of arsenic and lead soil contamination based on proximity to historical sources, individual property evaluations are needed to confirm if elevated levels of arsenic and lead are actually present. Due to the variability of the nature and distribution of area-wide soil contamination, properties outside of areas identified on maps may contain elevated levels of arsenic and lead, while properties inside areas identified on maps may not, in fact, have elevated levels of arsenic and lead. The maps in this report include disclaimers to explain these limitations so that individuals are not given a false sense of assurance or concern about whether their property likely is affected by area-wide soil contamination.

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Figure 3: Areas Potentially Affected by Historical Smelter Emissions, Based on Data Available as of January 2003  (click figure to enlarge in new window)

Figure 4: County Acreage Potentially Affected by Historical Use of Lead Arsenate Pesticide  (click figure to enlarge in new window)

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