Water Resources Research Act Program

Principal Investigators: Gary Denton, John Jenson, Mark Lander

Abstract: In 2012, USEPA released its third Unregulated Contaminant Monitoring Rule (UCMR3) (USEPA, 2012). Included in this list was the fluorinated organic compound, perfluorooctane sulfonate (PFOS). This recalcitrant chemical was once widely used in industry and is now considered an ubiquitous environmental contaminant. It is moderately water soluble (~600 mg/L) and has recently emerged as a drinking water contaminant of potential concern, having so far been detected in approximately 2% of public water systems across the Nation (Hu 2016). PFOS has also been shown to bioaccumulate in wildlife and target liver and blood proteins in mammalian species (ASTDR 2009, Lim et al. 2011). In 2009, USEPA issued a provisional drinking water health advisory (HA) for PFOS of 200 ng/L. A final HA of 70 ng/L was promulgated in May 25, 2016 (Federal Register 2016). The Guam Waterworks Authority (GWA) began monitoring PFOS in Guam’s groundwater in March, 2015. Two more rounds of sampling were conducted in September 2015 and August 2016. Overall, five production wells were identified as PFOS contaminated and levels in two of them were consistently above the USEPA's 70 ng/L benchmark. These two wells (A-23 and A-25) are high-production, sister wells and almost certainly draw water from the same perched aquifer in the Agana sub-basin. Based on the available data, they also appear to be impacted by the same PFOS source. PFOS concentrations in them ranged from 88-160 ng/L and 220-480 ng/L in A-23 and A-25 respectively. Both wells are currently offline because of this contamination and further PFOS monitoring has been discontinued. Plans are on the table to retrofit both wells with GAC filters although exactly when this will happen is uncertain. WERI sees merit in continuing to monitor both wells without interruption in order to determine if GACs are really necessary. This proposal therefore seeks funding to examine PFOS levels in well A-23 on a monthly basis, over a one year period, in order to get a better handle on projected attenuation rates. Rainfall data from within the catchment area will be collected over the same time frame. Well A-23 is chosen for study over A-25 because its location greatly simplifies the disposal of flushing water prior to sampling. The fact that this well is so close to A-25 suggests that it will also serve as a useful model for the latter well. The objectives of the study are to: a) identify any trends in PFOS concentrations within A-23 that suggest levels are increasing, stable, or on the decline; b) provide sufficient data to reliably determine whether or not remediation strategies are warranted to consistently meet the new HA if both of the above wells are brought back online; c) highlight the importance of rainfall as a primary transport mechanism controlling PFOS movement from its source to both sister wells; d) conduct supplementary studies to identify and delineate the most probable PFOS source or sources within the catchment basin.