We see a lot of field blank contamination. The stack test companies usually explain this a “laboratory artifacts” or “false positives.” How much “blank contamination” should be accepted?

There is no general rule as for a acceptable blank contamination.  Of course, you do not want to have your target analytes as part of the “blank contamination” above the method detection limits (MDLs).

As specified in the individual methods, the following “blank contamination” levels are required to be met before the sorbent is allowed to be used in the sample train:

• Method 0010 (Semi-volatile):  4 mg/kg of total chromatographable organics (TCO);
• Method 0030 (Volatile):  2 ng/1.6 g of target specific analyte;
• Method 0050 (HCl/Cl2):  Reagent blank less than 10 % of the sample values; and
• Method 0060 (Multi-metals):  Reagent blank less than 2 ug/L of each target metals.