[This Op-ed article was originally published in the Davis Enterprise on March 22nd in response to February 18th Davisite and Davis Vanguard articles in which Alan Pryor asserted that valid concerns related to contaminants associated with the proposed Village Farms Davis project, are “myths”. This is a slightly modified version of that article.]
By Steven Deverel, Marjorie Longo, and Robert Okamoto
There was a recent attempt to dismiss contaminant risks related to the proposed Village Farms project in north Davis. We herein summarize data and potential risks related to contamination from the adjacent Old Davis Landfill, Burn Area, and Wastewater Treatment Plant.
First, it was posited that contamination from the landfill has dissipated, per and poly fluoralkaline substances (PFAS) are not a health issue and that Village Farms Davis will not be built on the landfill.
Response
While the concentrations of analyzed volatile organic compounds associated with landfill have decreased over time, the EIR process did not adequately consider the contaminants associated with 30 years of burning of waste at the adjacent unlined Old Davis Landfill/Burn Site Specifically, dioxins and furans and higher molecular weight and carcinogenic polycyclic aromatic hydrocarbons (PAHs), such as benzo(a)pyrene, were not analyzed at the level of concern. Moreover, the boundaries of the burn site – as defined by the Department of Toxic Substance Control, include the extent of contamination generated by burning and disposal activities or by subsequent spreading of contamination by natural processes (such as wind, rain, flooding, and erosion) or human activities (such as grading and trenching) – are unknown and could include adjacent Village Farms property.
A key concern with the PFAS “forever chemicals” contamination documented at the project site is their presence in shallow groundwater and the potential for vapor intrusion. The extent of the PFAS shallow groundwater contamination has not been defined within the proposed development footprint adjacent to the landfill/burn site. However PFAS in the groundwater at the southern boundary of the Old Davis Landfill is as high as 1,600 parts per trillion (ppt) (measured in 2024), compared to 34 ppt in the groundwater under the middle of the Davis waste-water treatment plant (DWWTP) and 120 ppt in the DWWTP effluent (both estimated in 2021). PFOS, arguably the most toxic form of PFAS, is present at 1,500 ppt at the southern boundary of the Old Davis Landfill, 375-times higher than the target limit of 4 ppt in the DWWTP groundwater. The proposed drainage channel and residential property will be located within 100 ft of this location. The PFOS groundwater concentration was above this target limit on the Village Farms Property 1/3 of a mile away from its source at 39 ppt (measured in 2024). It is therefore highly likely that PFAS contamination is present in the shallow groundwater underlying the footprint of the proposed development south of the landfill/burn site.
EPA researchers[1] stated that “volatile per- and polyfluoroalkyl substances (PFAS) pose an inhalation exposure risk to occupants of buildings overlying a contaminated soil or a groundwater source.” There are also potential risk pathways via soil, food, surface water, and air[2]. Elevated groundwater PFAS concentrations at the southern margin of the landfill/burn site and upgradient of the project footprint are associated with the 4+ acres most recently used as a waste disposal site between June 1973 and July 1975 according to records at www2.calrecycle.ca.gov/; a time period that corresponds to the introduction of many disposable products containing these PFAS forever-chemicals.
Second, while it was acknowledged that there is potential infiltration of groundwater containing PFAS into the channel which is proposed at the boundary between the project footprint and the landfill/burn site it was stated that the channel depth will be above the maximum water table ever recorded and that the new channel will be lined with an impervious compacted clay layer to prevent any infiltration of groundwater into the Channel.
Response
The Partial Draft Response to EIR Comments stated that the proposed channel would include a geotextile or low permeability liner, not an impervious clay layer. Moreover, the infiltration rate of this proposed liner is listed at 2.4 X 10-5 inches per minute. To be effective at limiting PFAS migration into the proposed channel, this infiltration rate would need to be significantly lower than that of the subsurface clayey soils at Village Farms that conduct PFAS laden groundwater. However, the liner is unlikely to be effective because its infiltration rate is similar to those of clayey soils present on site.
Figure 4.8.3 of the Draft EIR show multiple events in which measured groundwater levels were at or above 26.5 feet above mean sea level which is the proposed channel depth thus indicating that groundwater levels periodically can be shallow enough to allow contaminated groundwater associated with the Old Davis Landfill/burn site to flow toward and into the proposed drainage channel. Groundwater levels in monitoring well HLA-MW-1 which is located at the southern boundary of the landfill and adjacent to the proposed canal were measured at or above 26.5 feet on 9 occasions based on data collected from 1992 to 2024 and reported in the 2024 Geochon report[3]. These and other data collected in the vicinity indicate that groundwater levels can remain elevated for months. Moreover, if it were possible to limit groundwater flow to the channel, this would likely cause higher PFAS-containing groundwater levels on adjacent properties. Geochon[4] recommended “that the proposed channel be designed with a base elevation above the groundwater elevation to limit the infiltration of groundwater into the channel that may be impacted by PFOA.”
The movement of PFAS to the proposed channel represents a potential threat to the ecosystem. Scientific studies demonstrate that exposure to PFAS in the environment may be linked to harmful health effects in humans and animals (https://www.epa.gov/pfas/pfas-explained.) Experimental studies that have revealed the long-term effects on animals include the alteration of thyroid functions, and the ability to induce carcinotoxicity[5]. PFAS are persistent in the environment and accumulate in the food chain[6].
Elevated selenium concentrations in shallow groundwater also represent a potential threat to the ecosystem. Concentrations in groundwater samples in 2024 ranged from 5.1 to 68 micrograms per liter. For comparison, a 0.2 microgram per liter level is recommended for protection of aquatic life in the Bay and Delta (https://epa.gov/wqs-tech/water-quality-standards-establishment-revised-numeric-criteria-selenium-san-francisco-bay).
We posit that further investigation and analysis are needed to adequately assess and mitigate the human and environmental health risks associated with the proposed Village Farms development adjacent to the landfill/burn area.
Steven Deverel, Ph.D. is a Professional Geologist and Certified Hydrogeologist and was a community technical advisor for the Frontier Fertilizer Superfund site, 1995 – 2022. Marjorie Longo, Ph.D. is Emeritus Professor of Chemical Engineering. Robert Okamoto is a retired Staff Air Pollution Specialist and former working group member who identifies significant adverse impacts on public health or environment, including air, water, or soil.
[1] Schumacher et al., Journal of hazardous materials, 464 (2024) 133025
[2] Ahrens et al. (2011). Environmental Science & Technology 45(19): 8098-8105
[3] Geochon Consultants, Inc., 2024, Drainage Channel Evaluation prepared from North Davis Land Company
[4] ibid
[5] Peritore et al. , International Journal of Molecular Science, 2023, 24, 11707
[6] Houde et al. , Environmental Science and Technology, 2011, 45, 7962-7973
Davisite 
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