PFAS MCP Immediate Response Actions and Conceptual Site Model Development

Per- and polyfluoroalkyl substances (PFAS) were detected in water samples collected from our client’s on‐site public water supply well in March 2022, as part of the quarterly sampling required by the MassDEP drinking water program. The reported detection of PFAS started an inquiry by MassDEP and prompted a site audit.  The MassDEP required the sampling of private water supply wells within 500 feet of the property. As a result of the initial private water supply well sampling, MassDEP issued a Notice of Responsibility (NOR) to our client on September 6, 2022, for concentrations of PFAS6 detected in three private water supply wells, some of which exceeded the MassDEP’s PFAS Drinking Water Maximum Contaminant Level (MCL) of 20 nanograms per liter (ng/L).  

Since the initial identification of PFAS in residential water supply wells, GZA has worked with our client to undertake Immediate Response Actions (IRAs) including sampling of residential wells, expansion of the residential sampling area, notifications to residents and MassDEP, installation of Point-of-Entry Treatment (POET) systems, and POET systems maintenance and monitoring. To date, the reach of the residential private water supply sampling has extended over 1,800 feet from our client’s on‐site public water supply well.  In addition, GZA and our client held an informational meeting early in the project for nearby residents to explain what PFAS are, the MCP response actions being undertaken, plans for POET system installations and residential sampling.

Challenge

The source of the PFAS in the area groundwater is unknown.  Chemicals were not historically manufactured at our client’s facility, but rather raw materials were mixed to customers’ specifications.  PFAS are present in the Town’s municipal wells and are a known regional groundwater contamination issue.  However, none of these documented PFAS contamination sources are in the vicinity of our client’s site and neighboring properties. 

Solution

GZA employed various investigation methods to develop a Conceptual Site Model with multiple lines of evidence to evaluate potential sources of PFAS in the vicinity of our client’s site, while continuing to perform MCP IRA activities.  
Actions included:

• GZA installed shallow groundwater monitoring wells around the facility to evaluate the possible presence of PFAS in the overburden aquifer.  Shallow soil samples and groundwater samples were collected to evaluate the potential for PFAS contamination and in an attempt to locate a Site PFAS source.
• GZA reviewed the client’s records of chemicals used at the facility for the possible presence of potential PFAS-containing chemicals.
• GZA developed windrose plots of the PFAS compounds and concentrations measured in the on-site production wells, on-site groundwater monitoring wells, and nearby residential private wells to evaluate the PFAS signatures in the area and create a graphical presentation of the data.
• GZA performed a Principal Component Analysis (PCA) of the analytical data to reveal groups within the data set to differentiate different sources of PFAS groundwater contamination.
• GZA identified two distinct plumes (a regional plume that is not Site-related and a smaller localized plume that appears to be Site-related). 
• GZA is currently performing a bedrock investigation to further identify potential sources of PFAS to the bedrock water supply wells at the Site and in the neighboring residences, and to confirm bedrock groundwater flow patterns in the Site vicinity. 

Benefit

GZA pooled their resources, from chemists to hydrogeologists to GIS specialists, to develop a Conceptual Site Model using numerous aspects of the site data in various methods, including PFAS signature evaluation, while keeping the client moving forward with MCP response actions, including the continued sampling and monitoring of private water supply wells and working toward a Phase II CSA.