Lower Issaquah Valley
Issaquah, Washington
Farallon Consulting, L.L.C.
April 3, 2020
Introduction
Farallon Consulting, L.L.C. (Farallon) has prepared this addendum (Addendum) to the Per- And Poly-Fluoroalkyl Substances Characterization Study Work Plan, Lower Issaquah Valley, Issaquah, Washington dated 2018, prepared by Farallon (2018) for Eastside Fire & Rescue (EFR) (Work Plan), to present the work elements and rationale to further characterize the nature and extent of per- and poly-fluoroalkyl substances (PFAS) in soil and groundwater in a portion of the Lower Issaquah Valley in Issaquah, Washington (Figure 1).
This Addendum addresses Task 2 of the Interagency Agreement dated December 3, 2019 between the Washington State Department of Ecology (Ecology) (2019) and EFR (IAA). The work described in this Addendum is being performed as a joint effort by EFR, Ecology, and the City of Issaquah (collectively Parties) to evaluate and reduce potential future impacts to human health and the environment associated with historical releases of PFAS. Characterization work described herein will further delineate select source areas of PFAS in soil; further evaluate the transport pathway from these identified source areas into groundwater at identified areas of interest; and further refine the distribution of PFAS impacts to groundwater at down-gradient locations from confirmed sources.
Although PFAS are not currently regulated as hazardous substances under federal or Washington State law, the characterization work will be performed consistent with the requirements of the Washington State Model Toxics Control Act Cleanup Regulation (MTCA), as established in Chapter 173-340 of the Washington Administrative Code (WAC 173-340). Data collected as part of the characterization work described in this Addendum may be used to support future cleanup actions if determined to be in line with requirements applicable at such time.