Welcome To the Background page of The Frontier Fertilizer Superfund Oversight Group



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The public first became aware of the Frontier Fertilizer site in 1983 when a dog fell into a liquid-filled pit on the property and later died of pesticide poisoning. Formerly the location of pesticide and fertilizer sales, this hazardous waste site on Second Street near Mace Boulevard is a continued source of concern and controversy in the community.

From 1972 until 1983, Frontier Fertilizer personnel dumped residual pesticides from drums and tanker trucks onto the ground and into unlined pits on the property. These pesticides leaked into the groundwater and now form a contaminated plume lying between 30 and 130 feet below ground surface and reaching over 800 feet north of the original disposal basin. Soil on the site in the vicinity of the disposal basin is also highly contaminated. Local, state and federal agencies have investigated the groundwater and soil contamination since 1983. Contaminant removal began in 1992.

In 1994, the Federal Environmental Protection Agency (EPA) placed the Frontier Fertilizer site on the National Priorities List (NPL) and declared it a Federal Superfund Site. Since 1994, EPA has studied the site and repaired, upgraded and expanded an existing contaminant monitoring and removal system put in place by the State. EPA is currently in the process of developing and implementing a final remedy for treatment of the groundwater and soil contamination.

Also in 1994, the non-profit Frontier Fertilizer Superfund Oversight Group (FFSOG) organized to work with EPA during the cleanup process. FFSOG has received grants from EPA totaling roughly $140,000 to aid them in this effort. FFSOG's role is to understand and monitor the nature and extent of the contamination and the cleanup process, assess current and potential impacts on the community, inform the community of progress, and to ensure that community concerns and needs are addressed. The FFSOG's primary concerns are continued contaminant migration in the groundwater, development that could slow or impede cleanup, and health and economic risks associated with the contamination.

In 1996-7, the city of Davis approved the Mace Ranch 11 housing development north of the site. Contaminated groundwater now underlies part of this development.

The contamination in the groundwater moves in three water-bearing zones containing sand and /or gravel separated by clay aquitards. The two shallow zones (S1 and S2) are 10 to 20 feet thick and within 90 feet of land surface. A third, deeper water-bearing zone, the A1 aquifer, lies between 110 and 130 feet below land surface. The city of Davis does not get drinking water from this aquifer, but from the deeper A2 aquifer.

The contaminated groundwater flows horizontally from 50 to 500 feet per year depending on agricultural and municipal pumping, seasonal climate changes, and other factors. The primary contaminants (chemicals of concern or COCs) in the groundwater are the soil fumigants dibromoethane (EDB), dibromochloropropane (DBCP) and dicholorpropane (DCP). ECB and DBCP are suspected carcinogens and have been banned from use. There is also a second plume of carbon tetrachloride (CCl4) to the east that apparently did not originate at the Frontier Fertilizer site.

EPA Site Investigations
When the USEPA took over the site, they installed more monitoring, injection and extraction wells and increased the pump and treat flow. They began their own remedial action investigation, looking further into the extent of groundwater and soil contamination and found that, despite the clean-up efforts, the contamination continued to spread horizontally and vertically in the groundwater. This continued spread of contamination, especially underlying the neighborhood north of Arroyo Drive in Mace Ranch, prompted system re-evaluation. Upon evaluation, EPA’s contractor found many problems with the extraction system including damaged wiring, overloaded electronic components, and discontinuous well operation.

In fall of 2000, EPA completed system repairs and upgrades, bringing all 16 extraction wells on line. Subsequent groundwater monitoring data showed that, though the upgrades improved capture, the system still was not completely containing the plume. Contamination continued to spread both vertically and horizontally in some areas. The continued spread was most evident in the neighborhood north of Arroyo Drive. In fall 2000, EPA began installation of three new high-capacity wells on Caricia as a first step in increasing contaminant capture in the neighborhood.

During this time also, EPA began work on a Feasibility Study (FS) and treatment options for clean-up of highly contaminated soil and a possible Dense Non-Aqueous-Phase Liquid (DNAPL) a the site. (The DNAPL would be composed of undiluted pesticides and other hazardous chemicals that moved down from the disposal basin and remain in the shallow aquifer.) The DNAPL and contaminated soil act as a source of continued movement of contamination to the groundwater and must be removed or treated.

In 2002, EPA completed another series of groundwater and soil samplings. Data showed that the system was still not fully containing the plume of contaminated groundwater. Data also showed that, while contaminant concentrations generally decreased in the upper two groundwater-bearing zones, contaminant concentrations increased in some locations in the A1 aquifer. High concentrations of contamination also remained in the shallow groundwater-bearing zones and in soil near and underlying the original disposal pits. Tests to confirm the presence of a DNAPL were inconclusive. The apparent continued downward movement of contaminants concerned the FFSOG. If unchecked, continued downward movement could eventually endanger the city's main drinking water aquifer.

Complex factors affect contaminant movement and capture. These include pumping from the aquifers, climate, and on the nature of soils and aquifer materials. Starting in March and continuing through August, growers throughout the region pump groundwater for irrigation. This pulls water down from the shallow groundwater zones and causes downward movement to the A1 aquifer and deeper. This probably accounts for at least some of the downward movement of contamination into the A1 aquifer from the upper water-bearing zones.

Contaminant Concentrations
During its investigations, EPA defined the extent of high concentrations of contaminants in groundwater in the vicinity of the "source area" in the region of the old disposal basin and in the other high-concentration area in the vicinity of Arroyo and Caricia in the Mace Ranch neighborhood north of the site. Data showed that contaminant concentrations in the S2 in a small area just north of the former disposal basin were as high as 1 million times the EPA drinking water standard. Data also showed contaminant concentrations in other areas in the S1 and S2 as high as 30,000 times the EPA drinking water limits. In the S1 and S2 in the vicinity of Arroyo and Caricia in Mace Ranch 11, EPA measured concentrations as high as 620 times the EPA drinking water limit. Water from these two zones is not used for irrigation or drinking. In the A1, the highest contaminant concentration recently detected was 1000 times the EPA drinking water limit. This aquifer is used for irrigation but not for drinking water.

The solvent carbon tetrachloride (CCl4) is also present in the groundwater and at concentrations as high as 240 times drinking water limits in the area immediately north of the Frontier site and 50 times the drinking water standards in some areas in the groundwater underlying the Mace Ranch neighborhood north of the site. Concentrations of contaminants are at or below EPA drinking water limits in most of the groundwater underlying the neighborhood.

Toxic Gases
During its investigations, EPA found that toxic gases from the groundwater plume were volatilizing and moving into the atmosphere above the plume. These gases were found from the site of the old disposal basin all the way into the neighborhood north of the site where several homes overlie the plume. EPA’s Risk Assessment showed that the gases in the area of the homes were too low to pose a health risk, but residents were still concerned with exposure. A relatively new issue arose when it was acknowledged that some of the chemicals rising into the atmosphere are endocrine disrupters and known reproductive toxins. EPA's risk assessment was based on exposure to carcinogens. Reproductive toxins were not considered and very little is known about how long-term exposure to them affects especially developing endocrine systems. After further study and analysis of data, EPA’s toxicologist believed that the risks due to exposure to endocrine disrupters would be too low to be of concern.

Based on groundwater monitoring data, beginning in 2003, EPA and their contractor, CH2MHill began designing and constructing and expanded system for extracting, transporting and removing the contaminants from the groundwater. EPA installed large capacity extraction wells near the former disposal basin and near the area of high contamination in the Mace Ranch neighborhood north of the site. Data also indicated that carbon tetrachloride was high on the eastern portion of the site and the neighborhood. EPA installed new monitoring wells on Cresta Court to follow this plume.

Feasibility Study
Once the extraction system was upgraded and expanded, EPA continued working on the FS to look at alternatives for the final remedy for removal of contamination in the soil and aquifer materials. There was still a great deal of investigation and analysis needed at the site before a final remedy would be determined.

As part of the FS, EPA proposed to conduct bench-scale treatability studies using soil and groundwater from the site to look at various methods for removing the soil and aquifer contaminants. Proposals included use of 0 valent iron dehalogenation, microbial break-down of the contaminants, and heating with an electrical current to volatilize, capture and treat the contaminants. Recent data had also shown that nitrates were three times their MCLs, so EPA had to also consider them in the groundwater cleanup.

Treatability studies using the 0 valent iron and microbial break down were unsuccessful. The microbial tests failed due to excessively high contaminant concentrations. The FFSOG felt this might indicate the presence of a DNAPL and that EPA must continue to assume its presence in clean-up plans.

In July of 2005, the FFSOG reviewed a draft Thermal Treatment Study Test Plan. The FFSOG’s main concern with the plan was that there was no determination of how the method will work at the site itself. Even if the heat treatment works in the treatability study, there was no guarantee that it would work in the field. Heat treatment has been used at other sites, but not on these COCs. In response to these concerns, EPA consulted with vendors for the heat treatments, who felt that this method would work at this site.

In April of 2006, the FFSOG received the draft FS for comments. The FFSOG developed a set of Community Acceptance Criteria as part of the process to evaluate the FS alternatives. The FS proposed to look at several options including microbial breakdown of contaminants, heat treatment, pump and treat only, and combinations of the three. The FFSOG pointed out that there is no evidence anywhere that the microbial treatment would work on the COCs. It would probably work on the nitrates and sulfates. There were also questions about how deep the heat treatment would be effective. The FS was apparently flawed in that none of the treatments appeared to reduce clean-up time below that of pump and treat alone. There were also concerns with the heat treatment in that the FS did not address the issue of escape of volatilized chemicals to the neighborhood or use of vapor emission controls, capture and treatment of volatilized toxic gases. Data from groundwater monitoring also indicated that the system was still allowing horizontal and vertical movement of contaminant in the groundwater. This is a problem that EPA also must address in the final remedy.

Proposed Plan
The Proposed Plan for the final remedy was released in June 2006. The FFSOG submitted comments, many critical of the PP. The PP included four basic components: Continued groundwater pumping and removal of contaminants; continued groundwater monitoring; injection and application of beer fermentation process waste for biological degradation of contaminants; and thermal treatment of soil and groundwater to remove contaminants. The FFSOG’s primary concerns were related to the proposed bioremediation using injected beer fermentation waste and air quality issues related to thermal treatment.

The biological treatment was the most controversial part of the plan. There is no scientific evidence anywhere to indicate that microbes will degrade the site contaminants. The key justification to include the microbial method was to reduce nitrate concentrations, but EPA is under no mandate to treat the nitrates. They are currently removed at the city’s waste water treatment plant.

There were also still concerns with the proposed thermal treatment. There was no discussion or provision for determining breakdown products of the heat treatment or whether or not they might be toxic. EPA did agree to do further studies to look at possible dangerous daughter products of thermal degradation and to ensure their degradation.

Other concerns included lack of performance criteria for clean-up and the failure of the pump and treat system to fully contain the plume.

Despite the FFSOG’s and community members’ concerns with the PP, the Record of Decision (ROD), based on the PP and public comments, was released in September of 2006. While many of the FFSOG’s and community’s concerns were addressed in the ROD, many were not. However, EPA ensured the FFSOG that they were committed to addressing all the issues either in the design phase or during implementation of the final action. EPA is also committed to full containment of contaminants and clean-up to MCLs.

For informataion regarding the Frontier Site or the FFSOG contact Pam Nieberg.