Version: FINAL
EA Project No.: 1664401
August 2026
Prepared by:
EA Engineering, Science, and Technology, Inc., PBC
600 Stewart Street, Suite 800
Seattle, Washington 98101
Prepared for:
City of Edmonds
121 Fifth Avenue North
Edmonds, Washington 98020
Link to report extracted from September 8, 2026 City Council meeting agenda:
Summary
EA Engineering, Science, and Technology, Inc., PBC (EA) conducted this desktop study to evaluate published literature, regulatory guidance, and publicly available local information relevant to potential per- and polyfluoroalkyl substance (PFAS) sources and transport pathways in the Deer Creek Critical Aquifer Recharge Area (CARA). The review focused on PFAS occurrence in urban and residential stormwater, atmospheric deposition and precipitation, built-environment materials, consumer and commercial products, and stormwater infiltration pathways that may be relevant to aquifer recharge settings.
The literature indicates PFAS can occur in urban stormwater and may be transported through developed watersheds via runoff from roads, roofs, paved areas, landscaped surfaces, school properties, recreational areas, and stormwater conveyance systems. In aquifer recharge settings, stormwater infiltration may represent a plausible pathway for PFAS movement toward groundwater; however, the significance of this pathway is highly site-specific and depends on stormwater concentrations, pretreatment, infiltration design, vadose-zone conditions, aquifer properties, dilution, travel time, and compound- specific PFAS behavior. Therefore, PFAS presence in stormwater should be treated as a pathway of concern but not as direct evidence of aquifer impact without supporting groundwater or vadose-zone data.
Atmospheric deposition is also a relevant potential input pathway. Published studies and agency materials indicate PFAS can be transported through the atmosphere and deposited through rainfall and dry deposition, including in areas without an obvious single point source. As a result, PFAS detected in developed recharge areas may reflect a combination of regional/background atmospheric inputs, stormwater runoff mobilization, and localized material or land-use sources rather than one dominant source category.
The review also found that PFAS use is broadly documented in built-environment and consumer-product categories relevant to residential and mixed-use urban settings. Potential source categories include roofing materials, exterior coatings, sealants, waterproofing products, treated textiles, carpets, consumer products, artificial turf, playground surfaces, and other outdoor polymeric or weather-exposed materials. The strength of evidence varies by material class. The evidence is strongest for documented PFAS use in coatings, textiles, carpets, consumer goods, exterior building products, and certain artificial turf components. Direct field-scale runoff data for specific residential materials, ordinary pavement products, and some landscaping materials remain more limited. Accordingly, these materials should be considered plausible diffuse PFASsource categories during source-screening efforts, while recognizing their relative contribution in Deer Creek cannot be quantified from the current desktop record alone.
Publicly available Deer Creek-specific technical information appears limited. The available record primarily consists of city permitting and planning materials, Washington State Department of Ecology (Ecology) guidance, public issue-history materials, litigation-related documents, and Washington analog studies rather than detailed, Deer Creek-specific PFAS fate-and-transport investigations. City materials confirm Deer Creek is a mapped CARA and projects within the Deer Creek and 228th Street CARA require city coordination before stormwater design, confirming the area is already treated as aquifer-sensitive in local permitting. Planning materials also indicate projected growth within Edmonds is concentrated in the Edmonds Marsh, Deer Creek, and Shell Creek watersheds, making development patterns and stormwater management directly relevant to the Deer Creek pathway evaluation.
Madrona K-8 School has become a focal point in the local PFAS concern context. Publicly available issue-history and litigation materials report PFAS detections in stormwater and bioretention planter soils at or near the school site and identify concerns regarding stormwater discharge through underground injection control wells above the Deer Creek aquifer. Reported stormwater concentrations in the litigation materials include values up to 32.2 nanograms per liter (ng/L) perfluorooctanoic acid (PFOA) and 18.9 ng/L perfluorooctane sulfonate (PFOS); however, those materials do not present the reported detections as direct aquifer groundwater results. These materials are important for understanding the local concern and potential pathway questions, but they should be treated as public-issue history and litigation context rather than final technical determinations of source attribution, groundwater impact, or aquifer contamination.
When compared with published urban stormwater literature, the reported Madrona stormwater PFAS concentrations appear broadly consistent with values reported in other urban runoff studies, although the reported PFOA concentration is near the upper end of some comparable datasets. This supports the conclusion that the reported stormwater detections warrant attention in a recharge-sensitive setting but do not, by themselves, prove a unique source mechanism or aquifer impact.
Stormwater-management alternatives within the Deer Creek CARA should also be evaluated in the context of the ultimate disposition of stormwater. Most of the CARA lies within closed drainage basins, where stormwater that is not managed through engineered infiltration may pond and ultimately infiltrate naturally unless it is collected and conveyed elsewhere. Other portions of the CARA may discharge toward Deer Creek, creating a distinct surface-water pathway. Consequently, prohibiting an engineered infiltration facility does not necessarily eliminate subsurface recharge or PFAS transport; it may instead change where infiltration occurs or redirect PFAS- bearing stormwater to another receptor. The relative protectiveness of engineered infiltration, natural infiltration, and non-infiltration alternatives therefore depends on site- specific hydrology, infiltration configuration, source-water quality, available controls, and receptor relationships.
Overall, the current record supports a multiple-lines-of-evidence conceptual model for the Deer Creek CARA. Plausible PFAS inputs include atmospheric deposition, diffuse urban stormwater, weather-exposed built-environment materials, landscaping and recreational materials, and household or commercial product-related sources. Stormwater may then transport PFAS through engineered infiltration, natural infiltration, stormwater conveyance, or surface-water discharge pathways depending on local drainage and site conditions.
The available information is sufficient to support targeted source-control measures and a tiered, risk-differentiated approach to stormwater and infiltration management, but it is not sufficient to identify a single dominant PFAS source, quantify the relative contribution of individual sources or pathways, or determine whether reported stormwater detections have resulted in aquifer impacts. Accordingly, source control should be emphasized where controllable PFAS inputs can be reduced before runoff is generated, while infiltration and other stormwater-management decisions should consider system configuration, hydrogeologic conditions, source-water quality, pretreatment where they are relied upon as a protective measure, monitoring, and the ultimate receiving pathway.
Key data gaps include the limited availability of Deer Creek-specific PFAS sampling data, incomplete source-area characterization, uncertainty regarding stormwater routing and drainage boundaries, limited information regarding engineered and natural infiltration pathways, incomplete characterization of surface-water and groundwater connectivity, limited hydrogeologic and vadose-zone information, and the need for complete PFAS-specific quality assurance (QA)/quality control (QC) documentation. These limitations currently prevent quantitative comparison of PFAS loading associated with engineered infiltration, natural infiltration, and surface-water discharge pathways.
Future work should prioritize well-documented stormwater and source-area sampling, drainage and infiltration-infrastructure mapping, characterization of closed-basin and direct-discharge areas, review of existing groundwater and surface-water information, and targeted evaluation of higher-priority source materials. Where warranted by project scale or pathway risk, additional hydrogeologic, groundwater, vadose-zone, pretreatment-performance, or receiving-water monitoring could be used to evaluate hydraulic and chemical connections and