MassDEP’s Experience with Field Reagent Blanks for PFAS Drinking Water Testing

Presented by Sage Grace, Massachusetts DEP
Contact Information: [email protected]

ABSTRACT

The “Prime Directive” for drinking water testing labs is to always follow the approved method as written. Exceptions are only allowed when the regulatory or certification entities require something more stringent than what the method requires. For PFAS drinking water testing, the approved methods require Field Reagent Blanks (FB) that are collected at the same time, and in the same manner, as the field samples. FB results are used to demonstrate that the field samples were collected without PFAS contamination in the field. This is a burden to the Public Water System (PWS), and the testing lab, to ensure that clean sample containers, preservatives, and field reagent water are used, and that they are kept free of PFAS throughout the sampling and sample transport process.

In this presentation we will give a brief overview of MassDEP’s regulatory background and experience with PFAS drinking water testing and examine how often samples are rejected due to contaminated FB. We will also discuss the suspected causes of contaminated FB and the risk to MCL compliance. While field sample results are only rarely rejected due to contaminated field blanks, we have an example from one lab where on-going contaminated field blank results was caused by an apparent false-positive PFAS compound. It took the lab months to figure this out, and it might have been overlooked without the availability of FB results.

The value of FBs is to protect a PWS from appearing to be out of compliance when there is sample contamination occurring during field sampling. Since PFAS chemicals are ubiquitous, it seems prudent to try to protect the PWS from being penalized by erroneously high results caused by field sampling contamination. We will examine the benefit versus the burden of field blanks for PFAS drinking water testing.