1. How do I use the TPH values in the Tier I Look Up Table when comparing them to the TPH reports received from the laboratory? Answer

The Modified TPH values in the Look Up Table have different values in each of the three columns sub-titled gasoline, diesel/#2 fuel oil and #6 oil (heavy oil). Modified TPH is Total TPH minus the BTEX compounds.

Use the column that describes the type of petroleum source that has created the contaminated site. For example, if the source is gasoline, the lab report is compared to the Modified TPH criteria under the gasoline column. The Look Up Table value in the gasoline column is the not the allowable level of C6-C10 hydrocarbon as reported by a laboratory. The Look Up Table value is to be compared to the total petroleum hydrocarbon measured at the site less the concentration of the BTEX parameters.

If two products have spilled and mixed (i.e. gasoline and diesel) use the lowest value under either the gasoline or diesel columns. If two contaminants are present on the same site but clearly separated, they may be treated as two different source areas using the appropriate column criteria.

2. Can I use the Tier I Look Up Table criteria with off-site impacts? (For example if I have on-site Commercial receptors and off-site residential receptors.) Answer

Yes, but subject to the following conditions:

  • The site and any adjacent property are consistent with the default conditions for the Tier I Look Up Table. The defaults are found in the Atlantic PIRI Reference Documentation on the web site.
  • Use the correct Tier I criteria for the receptor that may be at risk. (If the adjacent off-site receptor is Residential, the hydrocarbon concentrations in soil and groundwater at the property boundary must meet the Tier I Residential criteria.)
  • Ensure that the off-site criteria will also be met in the future. This can be done by either presenting monitoring data showing steady state conditions or by groundwater modeling. Steady state means that the observed concentrations within the plume remain constant or decrease with the passage of time.
3. Are Tier I Look Up Table criteria applicable to sites with basements? Answer

Tier I Look Up Table criteria were calculated based on slab on grade construction assuming one meter of clean surface soils below the slab overlying the impacted sub-surface soils.

The RBCA model developers assumed that a source would not be located beneath a building (i.e., tank installation) and that contaminant migration from the source tank would migrate below the building in a manner which results in a clean 0 to 1.0 meter soil zone below the existing slab on grade structure. The Atlantic RBCA model does not consider advection when calculating indoor air impacts.

Tier I criteria may be used for residential furnace oil contamination (#2 fuel oil) in typical cases. The Atlantic PIRI Committee considered several furnace oil tank release scenarios using Tier II assessment where the product is near the basement wall and floor (next to approximately 30% of the wall/floor area). The Tier II scenario calculations assumed impacted soil and groundwater within 10 cm of the basement floor and walls and produced higher remedial criteria than the Tier I Look Up Table.

As such, use of the Tier 1 criteria at sites is reasonable for many sites with basements, however, the Site Professional is responsible for comparing the site to the other Atlantic PIRI default conditions before using the Look Up Table. This specifically includes the condition of the floor and walls for cracks and dirt floor sections, including sumps with open bottoms.

How are basements considered at Tier II?

If a basement exists, the site-specific depth to contaminated soil or groundwater should be calculated from the basement floor, not the ground surface.

If you conduct Tier II calculations on a building with a basement you should consider the buried sections of walls that can transmit vapours to the interior. This can be done by considering the sum of the basement wall and floor area in contact with soil as the modified floor area and recalculate a new Building Volume / Area Ratio (Screen 8.4). When calculating the building volume, only the basement height should be used since complete mixing of basement air and first floor air is unlikely. Ensure that the Building Volume / Area figure is placed in the correct exposure box for your site (Residential or Commercial).

4. How can I justify use of the Tier I Look Up Tables if the groundwater table at my site is less than the 3.0 metres below ground surface (BGS) used by Atlantic PIRI as the default condition? Answer

In general, if site conditions do not match the Tier I default parameter assumptions, Tier II should be used. Nevertheless, Tier I subsurface soil criteria are conservative for groundwater depths less than 3 m below the building floor slab due to conservative modelling assumptions. If the groundwater is within 1 m of the slab, Tier II should be used to develop groundwater SSTLs.

5. What is the difference between silt/clay and sand/gravel in the Tier I Look Up Table? Answer

A coarse grained soil (sand/gravel) is defined as material having greater than 50% (by dry weight) particles equal to or larger than 75 microns (200 mesh) in diameter. Materials with less than 50% sand-sized particles are considered fine-grained soil (silt/clay). If no seive data is available, then the lowest applicable number should apply until a seive test is performed.

6. Is the construction worker protected by the Tier I Look Up Table? Answer

Yes. Assuming surface soil contact by all potential receptors, the construction worker is a less sensitive receptor than either the residential or commercial receptor in the Tier I Look Up Table.

7. Can the Atlantic RBCA software be used for contaminants other than petroleum hydrocarbons? Answer

At present, Version 2 of the Atlantic RBCA software is sanctioned for use only with TPH and BTEX. The physical/chemical properties and toxicological data has been reviewed and updated for these compounds. Although the current release of the software contains similar data for many other compounds, these data have not been reviewed to ensure that they are up-to-date and appropriate for use in Canada. As a result, the Atlantic RBCA software model cannot be generally sanctioned for use with chemicals other than TPH and BTEX.

However, the concepts of risk assessment and management apply to non-petroleum contaminants under the Atlantic RBCA process adopted by the Atlantic Provinces. Site Professionals calculate such risks for a Tier 3 assessment.

8. Does the Atlantic RBCA software calculate cumulative risks? Answer

The use of cumulative risks in developing remediation objectives for contaminated sites is appropriate for chemicals that have the same biological end-points. The current Atlantic RBCA model uses cumulative risks for dealing with TPH and BTEX. However, for chemicals that have differing biological end-points, the summation of exposures or risks is not toxicologically sound and has little practical meaning.

The User Guidance manual outlines how cumulative risks are considered in the RBCA process. It also clearly indicates that the use of the Atlantic RBCA model for compounds other than BTEX and TPH can only be done in consultation with local regulators. Such consultation would also likely require input from a toxicologist or similar professional who can properly address the issues relating to interactive effects between chemicals.

The Site Professional must also consider the potential for cumulative risks from exposure to the same chemical through multiple pathways (e.g., indoor air and potable water). At many sites, one exposure pathway will be the critical pathway; however, the Site Professional should consider all possible exposure pathways in the site assessment process. Version 2 of Atlantic RBCA contains a Cumulative Risk Worksheet to facilitate this type of evaluation.