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.
Background
The 400-acre site of the currently proposed Village Farms Davis residential development project is bordered on the northeast side by the former 31-acre City of Davis waste disposal site. Historical records indicate the waste disposal activities at the Site began in the 1940s as an open burn dump. Operation as a direct-bury Class III landfill began in 1969 and received waste from residential, commercial, and industrial clients and construction debris until 1975, after which no additional waste was received.
Yearly records of the number of truckloads received were used by the City of Davis to estimate that approximately 300,000 tons of mixed waste was deposited in the landfill during its operation. The City of Davis also reported that NO hazardous classified waste had been disposed of at the landfill.
Figure 1 – Old Davis Landfill Vicinity Map
The Site was also used as the location of the former City of Davis Waste Water Treatment Facility, which included 5 surface water aeration ponds and a processing facility (Figure 2). The inactive ponds remain at the Site but the processing facility has been demolished and removed. An active Go-Kart racing facility, and an active Paint Ball facility currently occupy the southern portions of the former landfill site.
Figure 2 – Old Davis Landfill Site Map
Summary of Well Monitoring Findings
Periodic water sample testing from a series of seven monitoring wells both on the old landfill site (3 wells), on the Village Farms Davis project site (3 wells), and on the east side of Poleline Rd adjacent to the Wildhorse Golf Course (1 well) has been performed since 1992.
Concentrations of Water Contaminants – Pre-Covell Village EIR (Before 2005)
The early history of testing for contaminants (including vinyl chloride) is summarized best in the Draft Environmental Impact Report (DEIR) for Covell Village issued in 2004 from which partial excerpted sections are quoted below;
“Old Davis Landfill, County Road 28H.
Vadose soil impacts were not detected immediately beneath the landfill facility. Trace level volatile organic compound (VOC) concentrations were detected in the downgradient wells including vinyl chloride, trichloroethylene, cis-1,2-dichloroethylene, 1,2-dichloropropoane and 1,4-dichlorobenzene. Elevated selenium, chloride and nitrate were further reported for the downgradient wells. D&M concluded that groundwater downgradient of the former landfill facility had been impacted by landfill leakage with some contaminant levels above California Maximum Contaminant Levels. In 1996, D&M prepared an Evaluation Monitoring Report (EMP) for the former landfill facility….Only one VOC (1,2-DCP) was detected in groundwater samples obtained from the onsite CPT probes at concentrations ranging from 0.72 to 1.2 ug/l. VOCs were not detected in any of the onsite wells during four sampling events performed in 1995 and 1996. Based on the low levels detected, D&M recommended no further action, with semi-annual groundwater monitoring.
Groundwater Sampling in 2003
The results of sampling in February 2003 did not indicate detectable VOCs in any of the monitoring wells. Only dichlorodifluoromethane was detected in onsite wells HLA-MW1 & 2 and DM-MW4 at concentrations ranging from 1.5 to 6.4 ug/l between 1999 and 2002. The CVRWQCB completed a Monitoring Report Compliance Checklist for the landfill facility in March 2002 confirming that formal monitoring should continue in addition to a determination of background water quality.
Groundwater Sampling in 2004
The Report states that the aforementioned groundwater wells were sampled on Tuesday, February 10, 2004. The results showed little change in inorganic aqueous chemistry. One organic compound, dichlorodifluoromethane (Freon-12), was detected at monitoring well DM1. This compound has been detected onsite in the past and the concentration of 5.1 parts per billion (ppb) was slightly higher than the previous results of 3.90 ppb. Both levels are well below the State’s Action Limit for drinking water standards.
Subsequent to the issuance of the DEIR, numerous Comments to the DEIR were submitted indicating that the continued presence of vinyl chloride constituted a future risk to inhabitants of the proposed Covell Village project. This was addressed in the Response to those Comments in the Final EIR (FEIR) subsequently issue, as follows;
“According to both the City of Davis Public Works Department and GEOCON Consultants, the statement on page 11-5 of the 1997 Jones & Stokes Covell Center EIR is incorrect, because vinyl chloride has not been detected in either groundwater or vapor samples collected from the monitoring wells located on the Covell Village property. As further stated by GEOCON Consultants in March 2005, review of the source document referenced in the 1997 EIR (Evaluation Monitoring Report and Proposed Corrective Action Plan, Old Davis Landfill prepared by Dames & Moore, dated June 1997) does not corroborate the statement that vinyl chloride was detected on the Covell Village property. Vinyl chloride was detected in well DM-MW3 located on the City-owned landfill property during the initial groundwater sampling events performed in March and July 1992 at concentrations of 2.0 and 2.7 ppb, respectively. Subsequent sampling performed by the City's consultant (Dames & Moore) between September 1992 and August 1996, including five cone penetrometer test (CPT) groundwater samples collected from the Covell Village property, did not indicate detectable levels of vinyl chloride. Biannual groundwater sampling performed by the City of Davis since 1999 has only resulted in one detection of vinyl chloride; 2.8 ppb in well DM-MW2 located on northern portion of the City-owned landfill property in February 2001. The lack of persistent detections suggests that vinyl chloride is not present in groundwater beneath the former landfill or adjacent Covell Village property as a stable migrating plume”
Concentrations of Water Contaminants – Post Covell Village EIR Monitoring (2012 – 2019)
Subsequent to the defeat of Measure X at the polls and pursuant to an order from the Central Valley Regional Water Quality Board (CVRWQCB), the City again began testing of the groundwater in the 7 test wells from from 2012 – 2018 on an annual basis and then twice in 2019 (the later two tests to see if any seasonal variation occurred in sample concentrations). In 2018 the City retained the consulting engineers, Wallace Kuhl Associates to evaluate the well water test results and recommend an appropriate course of action, if any.
A report detailing the findings of constituents in the groundwater beneath both the landfill and the Village Farms Davis site prepared by the City’s contractor, Wallace Kuhl Associates (Semi-Annual Monitoring Report, Fourth Quarter 2019– Old Davis Landfill, WKA No. 12395.01P, January 23, 2020). According to this report, there was no groundwater contamination by any heavy metals or volatile organic compounds (VOCs) in excess of their established Maximum Concentration Level (MCL) and none of the samples showed the presence of any vinyl chloride contamination at all.
A Change in the Direction of Underlying Groundwater Flow
Generally, groundwater flow beneath Davis is toward the east. However, groundwater testing during the early 1990s indicated the directional flow of groundwater beneath the former landfill site was toward the south and southwest. According to the analysis performed at the site by Dames and Moore in 1997, groundwater flow was generally toward the south during fall – spring changing toward the southwest during the summer months. At the time, “this was attributed to increased pumping of groundwater at the Hunt-Wesson Plant to the southwest of the landfill…during the onset of the tomato canning season…from late-June to mid-October groundwater pumping at the plant is on the order of 2 to 2.5 million gallons per day compared to approximately 400,000 gallons per day in the off season”. It was reported this dropped local groundwater levels on the order of 7 ft. thus establishing the downgradient flow from the landfill through the Covell Village site towards the Hunt Wesson Cannery.
By 2019, however, the City’s consulting engineers had determined that the directional groundwater flow had completely changed direction as a result of discontinuance of groundwater pumping at the Hunt-Wesson plant which closed in 1999 (Wallace Kuhl Associates (Semi-Annual Monitoring Report, Fourth Quarter 2019– Old Davis Landfill, WKA No. 12395.01P, January 23, 2020). Their report stated that, “The groundwater contours generated based on groundwater-surface elevations indicate that on October 22, 2019, the groundwater gradient was northeast at a gradient of 0.009 feet per foot. Figure 3 depicts groundwater surface elevation contours for the modeled potentiometric groundwater-surface at the Site”.(Emphasis added).
Thus even if further contamination leakage from the landfill site commenced in the future, it will migrate away from the Village Farms Davis development site. The groundwater gradient is graphically shown in the following figure.
Figure 3 – Groundwater Directional Map
Final Assessment of the Former Davis Landfill Site
A final assessment of the former Davis Landfill Site was made by the City’s contractor, Wallace Kuhl Associates in a report entitled Site Characterization Report – Old Davis Landfill, WKA No. 12395.01P, June 20, 2020. The main findings excerpted from this report follow (with bold emphasis added).
“4.0 2019 GROUNDWATER SAMPLING AND ANALYSIS
No metal concentration in groundwater exceeded its established EPA Primary MCL Maximum Concentration Limit. No VOC was detected at a concentration that exceeded its established EPA MCL.
5.0 CONCLUSIONS
Beginning in September 2012, the City of Davis Department of Public Works Utilities & Operations resumed groundwater monitoring at the Site. Analysis was limited to VOCs. In 2019 the City of Davis retained WKA to conduct groundwater monitoring.
WKA conducted second and fourth quarter 2019, groundwater monitoring and sampling at the Site in June and October of 2019, respectively…Analytical results from the Fourth Quarter 2019, sampling event revealed that Nitrate was detected is groundwater samples at a concentration exceeding its MCL of 10 mg/L. Manganese, Sulfate, and Selenium were detected at concentrations exceeding their respective secondary MCL.
6.0 RECOMMENDATIONS
- Terminate quarterly groundwater monitoring and abandon wells DM-MW-1 through DM-
MW-5, as well as HLA-MW-1 and HLA-MW-2.
- WKA recommends that the State Water Board close the case and issue a No Further Action ruling for the Site.”
REFERENCES
All data on the site and groundwater contamination for this report was obtained from the following pertaining to the former landfill site. Copies are available upon request.
- Solid Waste Water Quality Assessment Report, Report for Old Davis Landfill, Dames and Moore, January, 1993
- Evaluation Monitoring Report and Proposed Corrective Action Plan – Old Davis Landfill, Dames and Moore, June 1997
- Covell Village Draft Program Level Environmental Impact Report, SCH# 2004062089, Raney Planning and Management, December, 2004
- Covell Village Final Program Level Environmental Impact Report, SCH# 2004062089, Raney Planning and Management, May, 2005
- Semi-Annual Monitoring Report, Fourth Quarter 2019– Old Davis Landfill, WKA No. 12395.01P, Wallace Kuhl Associates, January 23, 2020
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