Municipal Solid Waste (MSW) Landfills

MDL's and PQL's

Issue 1: If a laboratory has multiple instruments which are used for an analysis such as VOCs, is it appropriate to report a combined MDL for a particular analyte which is the maximum 99% confidence level detection limit for the multiple instruments? For example, if the MDL for instrument A is 0.1 ug/L and for instrument B is 0.3 ug/L, and some samples are analyzed on each instrument, would it be appropriate for the report to list 0.3 ug/L as the MDL for all samples?

Response: The MDL is based upon instrument specific data and therefore the reporting of sample results should reflect this. OAC Rule 3745-27-10(C)(1) requires that the analysis methods used produce an accurate representation of ground water quality. Therefore, all data should be reported with the MDL for the instrumentation used to determine the result.

Issue 2: Would it be appropriate to report somewhat "sanitized" MDLs for an range of say 0.1 to 0.4 ug/L, and the sanitized MDL would be 0.5 ug/L for all VOCs?

Response: For each instrument, once the MDL has been accurately calculated, it should not be changed.

Issue 3: Is it necessary to determine MDL in every sample matrix?  At a typical landfill there may be wells of high and low dissolved solids content.  TDS can affect the 99% confidence level detection level.  Is laboratory pure water considered to be representative of ground water?

Response: It is not necessary to determine the MDL in every sample matrix.  For a representative MDL, an actual sample matrix (not laboratory reagent water) would be preferred.  Unfortunately, there is no known definitive test that will be able to take care of all sample matrix issues.

Issue 4: You indicated that Ohio EPA has no specific instructions for calculating a PQL from an MDL, and that a PQL does not necessarily need to be 5 to 10 times the MDL.  The definition of PQL (or US EPA EQL) includes reference to the lowest level that can be achieved within the "specified limits of precision and accuracy." What are the specific limits of precision and accuracy required for OAC Rule 3745-27-10 reporting? The context of the US EPA definition refers to data quality objectives that are to be specified for the project. We are not aware of what precision and accuracy limits should be applied for this subject.

Response: OAC Rule 3745-27-10(C)(10) requires that the PQL for the analysis being reported be included with the submission of the analytical results.  There is no rule that specifies how the PQL is calculated, although Ohio EPA recommends that a description of how the PQL was calculated be included in submittals, to make it quicker and easier for the agency to evaluate the PQL used against the rule requirements.

Letter to Consultants Regarding Use of RL's and PQL's
Letter to Owner/Operators Regarding Use of RL's and PQL's