By Alan Pryor
Executive Summary and Conclusions
This article reports on potential groundwater contamination beneath the former Davis Landfill site north of the City of Davis on Poleline Rd. and the adjacent site proposed for the Village Farms Davis development project immediately south and southeast of the old landfill site.
During the contentious Measure X election in November, 2005 in which the proposed Covell Village project (on the same site as the current proposed development, Village Farms Davis) was rejected by voters, allegations were made that the site’s groundwater was contaminated by leaching of pollutants from the former Davis landfill site just north of the project. In particular, it was alleged that a carcinogen, vinyl chloride, was in the groundwater beneath the project site rendering the project unsuitable for development in as much as a deep well was proposed for the site to add to the City of Davis potable water supply.
In a recent City Council meeting (April 4, 2023) in which the possible timing of bringing peripheral projects before the voters were discussed, one public comment again stated that vinyl chloride was in the groundwater beneath the old Davis landfill and the proposed site for the Village Farms Davis project.
“The parcel itself has so many problems. It has toxics in the north end from the land fill site. The old land fill site was not lined so there is vinyl chloride leakage from the old land fill and it’s substantial. Vinyl chloride does not go away.”
These claims of vinyl chloride and other toxic compounds in the groundwater were based on data from the early 1990s though 2005 which showed some intermittent groundwater contamination (including some tests showing the presence of vinyl chloride) in shallow groundwater test wells beneath the old landfill and immediately to the south beneath the then proposed Covell Village project. These earlier monitoring well test results were reported in the EIR issued in the Covell Village EIR issued in 2005 and are further discussed below in the section entitled Summary of Well Monitoring Findings.
These reported findings were considered important at the time because, as stated above, the Covell Village project proposal included a new deep well on the project site to provide drinking water capacity for the proposed project and connecting into the City’s potable water supply network. Concerns were expressed that the shallow water contamination could worsen and impact the deep aquifer from which potable water would be drawn. Potentially compounding the problem was the discovery that the groundwater plume was migrating from the landfill toward the south and southwest in the direction of the proposed Covell Village project.
Annual testing of the monitoring wells subsequently occurred in the period since the Covell Village EIR from 2012 – 2019. These later tests showed a substantial reduction in groundwater contamination in the intervening years and the report from consulting engineers engaged by the City to evaluate the groundwater contamination showed the following results;
- NO Vinyl Chloride was found at all in any sampled groundwater from 2012 – 2019 nor were there ANY other VOCs (Volatile Organic Compounds) or metals found in any of the test well samples above the EPA's Primary Maximum Concentration Levels (MCLs) for drinking water.
- There were some measurements of nitrate (probably from past agricultural fertilization on the site) in the monitored wells that were in excess of Primary MCLs and some other naturally occurring minerals (selenium, manganese, and sulfate) that were intermittently in excess of Secondary MCLs but not hugely in excess of other well waters in the area.
However, these are NOT a human health concern because the groundwater beneath the Village Farms Davis project site will NOT be pumped and used for drinking water purposes. Instead, the project will rely on City of Davis municipal drinking water supplies as delivered to the rest of the City.
- The plume of groundwater beneath the former landfill site and the proposed development project site was most recently determined to be moving toward the northeast away from the Village Farms Davis project site as a result in changes in groundwater extraction rates in the area. Thus, even if there was very unlikely leaching from the landfill site future in the future it would NOT migrate in the direction of the proposed development project.
- Based on the sampling results from 2012 – 2019 indicating no detectable amounts of vinyl chloride and no amounts of volatile organic hydrocarbons (VOCs) or heavy metals in excess of established EPA MCLs, it was recommended that the City discontinue annual testing and request a No Further Action letter from the Regional Water Board thus confirming the area is no longer considered a threat to groundwater contamination.
These later test monitoring results from 2012 – 2019 are also further discussed below in the section entitled Summary of Well Monitoring Findings.
(more…)
Davisite 