Screening Analysis Example

The following example includes fictitious data created to illustrate the screening analysis process using one conservative screen. All ATSDR CVs were current when the example was developed. Health assessors must always use the most current ATSDR CVs and non-ATSDR screening levels available.

Step 1: Review Site Information and Sampling Data

Site background: A nursing home is located adjacent to a former dry-cleaning facility. Soil gas and groundwater sampling measurements indicated there is a potential for vapor intrusion into the nursing home, and indoor air samples were collected in response. Sampling was conducted to examine the possible presence of three particular contaminants in indoor air: tetrachloroethylene, trichloroethylene, and trans-1,2-dichloroethylene.

Sampling data: Eight air samples were collected inside the nursing home building. Results were reported in parts per billion (ppb), and the laboratory detection limit was 0.05 ppb for tetrachloroethylene and 0.75 ppb for the other contaminants.

Air Sampling Data (Collected in March)

^{ppb = parts per billion}

^{U = not detected above the detection limit of 0.75 ppb}

Air Sampling Data (Collected in July)

^{ppb = parts per billion}

^{U = not detected above the detection limit of 0.75 ppb}

Step 2: Identify Contaminants and Concentrations

Now, looking at the available sampling data from Step 1, identify each detected contaminant and its corresponding maximum concentration for screening (as noted, there are some exceptions to using the maximum for some air evaluations during this step). The table below shows the maximum concentrations detected among the eight samples. Both maximum concentrations were detected in Sample 4 from the March sampling event.

Maximum Concentrations in Air Sampling

^{ppb = parts per billion}

Step 3: Select Appropriate Screening Levels

Now, let’s see if ATSDR has Air CVs for these contaminants. Health assessors can use PHAST for this step. The table below shows the available media-specific ATSDR CVs for these contaminants.

Media-Specific ATSDR CVs

^{* ATSDR recommended CV
CREG = cancer risk evaluation guide
CV = comparison value
EMEG = environmental media evaluation guide}

^{Int = intermediate
NA = not available
ppb = parts per billion
RMEG = reference dose media evaluation guide}

As shown in this example, several ATSDR CVs are available. PHAST will choose the appropriate ATSDR CV to use for your scenario. The recommended ATSDR CVs identified in PHAST to use for this screening example are the 0.57 ppb CREG for tetrachloroethylene and the 0.040 ppb CREG for trichloroethylene.

Step 4: Conduct the Comparison and Identify Contaminants Requiring Further Evaluation

Now, you will compare the maximum concentrations identified in Step 2 with the recommended ATSDR CVs identified in Step 3. The table below shows the comparison.

The maximum concentration of 10 ppb for trichloroethylene exceeds the CREG of 0.040 ppb, so trichloroethylene will be retained for further evaluation. Note that the maximum concentration of trichloroethylene also exceeds the available EMEGs (chronic and intermediate) and the RMEG. Therefore, even though for screening purposes you are retaining the CREG (i.e., ATSDR’s CV for cancer effects), both cancer and non-cancer effects need to be evaluated in the next scientific component: the EPCs and Exposure Calculations Evaluation.

The maximum concentration of tetrachloroethylene is below its CV, so this is not retained (but refer to Step 5, which discusses other factors to consider).

Comparison of Maximum Concentrations and Recommended ATSDR CVs

^{CREG = cancer risk evaluation guide
ppb = parts per billion}

^{CV = comparison value}

CV PHAST Module Tables for the Example Scenario

^{CASRN = Chemical Abstracts Service Registry Number
Conc = concentration
CREG = cancer risk evaluation guide
CV = comparison value
EMEG = environmental media evaluation guide}

^{Int = intermediate
NA = not available
ppb = parts per billion
RMEG = reference dose media evaluation guide}

The CV Module in PHAST would provide users with these onscreen tables for the example scenario.

Description of PHAST Module Tables for the Example Scenario

Step 5: Check for Factors Warranting Further Evaluation

The last step of the process is to check for other factors that might warrant further evaluation. In this example, you would check if tetrachloroethylene (below its CV) represented a community concern, and if so, you might retain it for further evaluation. You would also compare the detection limit of 0.75 ppb for trans-1,2-dichloroethylene (examined in Step 1), which was not detected, to ATSDR CVs. The table below shows the results. As shown, the detection limit for trans-1,2-dichloroethylene was below the CVs, so a health assessor could eliminate it from further evaluation.

Comparison of Recommended CV for Trans-1,2-Dichloroethylene to Its Detection Limit

^{CREG = cancer risk evaluation guide
CV = comparison value
EMEG = environmental media evaluation guide
Int = intermediate}

^{NA = not available
ppb = parts per billion}

Overall Findings

Using the information from this example for Steps 1 through Step 5, one contaminant, trichloroethylene, requires further evaluation. That means you would carry it through to the next phase of the scientific evaluation: the EPCs and Exposure Calculations Evaluation. You will also, summarize the screening analysis process in your documents.