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PUBLIC HEALTH ASSESSMENT

FRONTIER FERTILIZER
DAVIS, YOLO COUNTY, CALIFORNIA


ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS

This section presents the contaminants identified at the site and selects which of these contaminants are of potential health concern in each environmental medium. The environmental sampling conducted to date has detected many different contaminants. Certain contaminants in each medium are selected from all contaminants detected at the site in order to focus the public health assessment on contaminants most likely to pose a health risk. Their selection does not necessarily mean that a health threat exists, but only that they will be evaluated further in the assessment.

Subsequent sections will evaluate whether individuals have been or could be exposed to the contaminants of concern and will determine whether such exposures have public health significance. The existence of a public health hazard is dependent on the magnitude of contamination in the various environmental media and not the source; it is not our intent to attribute the contamination to particular sources.

Contaminants of concern at the site are selected primarily based on a comparison of detected concentrations with comparison (i.e., health guidance) values. Other criteria for selection include concentrations of contaminants on-Property and off-Property and frequency of detection, field data quality, laboratory data quality, sample design, and community health concerns. Comparison values used to select contaminants for further evaluation at the Frontier Fertilizer site include the following:

 
EMEG Environmental Media Evaluation Guide
RMEG Reference Dose Based Media Evaluation Guide
MCL Maximum Contaminant Level
CREG Cancer Risk Evaluation Guide
LTHA U.S. EPA's Drinking Water Lifetime Health Advisory

EMEGs are media specific values developed by ATSDR to serve as an aid in selecting environmental contaminants that need to be further evaluated for potential health impacts. EMEGs are based on non-carcinogenic end-points and do not consider carcinogenic effects. EMEGs are based on an ATSDR Minimal Risk Level (MRL). RMEGs are equivalent to EMEGs, but are derived from a U.S. EPA Reference Dose (RfD) instead of an MRL, according to ATSDR guidance. Both the MRL and the RfD are estimates of daily exposure to a chemical that is unlikely to cause adverse, non-carcinogenic, health effects.

MCL's are enforceable standards for contaminants in drinking water, developed by U.S. EPA under the authority of the Safe Drinking Water Act. In addition to health factors, MCL's are also required by law to consider the technological and economic feasibility of removing the contaminant from the water supply. The limit set must be feasible given the best available technology and treatment techniques. MCL's may be used as a comparison value if no other comparison values exist, or if the MCL is the most conservative of all existing comparison values for a particular contaminant. U.S. EPA's Lifetime Drinking Water Advisory (LTHA) defines a concentration in drinking water at which non-cancer adverse health effects would not be expected to occur.

In general, if a chemical is known or believed to cause cancer, a comparison value based on the carcinogenic properties of the chemical will be substantially lower than a comparison value based on its non-carcinogenic adverse effects. This is because it is generally assumed that there is no absolutely "safe" exposure levels to carcinogens (known as the no-threshold assumption), whereas for non-carcinogens, there are levels of exposure (i.e., thresholds), below which no adverse effects are expected to occur. Carcinogenic chemicals detected in soil at the site were evaluated and selected for follow-up using Cancer Risk Evaluation Guide (CREG) values for soil. CREGs are media specific values which serve as an aid in selecting contaminants of concern that are potential carcinogens. CREGs are derived from U.S. EPA cancer slope factors according to ATSDR guidance (15). Cancer slope factors give an indication of the relative carcinogenic potency of a particular chemical. CREG values represent media concentrations which are thought to be associated with an extra lifetime cancer risk of one-in-a-million.

A. TOXIC CHEMICAL RELEASE INVENTORY (TRI) SEARCH

The Toxic Release Inventory (TRI) maintained by the U.S. EPA contains information on estimated annual releases of toxic chemicals from active industrial facilities from 1987 to present. TRI data can be used to get a general idea of the current environmental emissions occurring in the area surrounding a site, and whether they may be causing additional environmental burden to the community.

We searched the TRI for the years 1987 through 1992 (the years for which TRI data were available at the time this public health assessment was written). The TRI data are organized by zip code. We searched for data from the two zip codes existing in the site vicinity, 95616 (Davis) and 95618 (El Macero). No records were found for zip code 95618 for any year.

Only one facility in the City of Davis zip code 95616 reported releases to the TRI during 1987-1992. This facility is located about 3-1/2 miles west of the Frontier Fertilizer Property. The facility reported a total release to land of 150,369 pounds of chemicals in 1987: 132,021 pounds of sodium hydroxide solution and 18,348 pounds of chlorine. The company reported zero releases to land during the years 1988-1992. The company reported a total release to air of 3,000 pounds during 1987-1992, resulting from a release of 750 pounds of chlorine to air each year during the period 1989-1992. No air releases were reported for the years 1987 and 1988. The company reported zero releases to water during the period 1987-1992. Due to the distance of this facility from the Frontier Fertilizer Property, releases as reported in TRI are not expected to impact the community near the site.

B. ON-PROPERTY CONTAMINATION

CONTAMINANTS IN SOIL ON PROPERTY

Several soil sampling investigations have been conducted at the site by different contractors and agencies since August 1983 (2). The soil samples have been analyzed for various organic and inorganic chemicals. Organic chemicals analyzed for have included EDB, DBCP, other halogenated volatile organics, carbamates, phenoxyacid herbicides, and organophosphate and organochlorine pesticides. The inorganic chemical analytes have included arsenic, barium, cadmium, cobalt, chromium, copper, nickel, lead, selenium, and zinc (2).

Multiple pesticides have been found in soil samples. The principal area where pesticides have been detected is at or near the former pesticide disposal basin. In addition, pesticide residues have been detected near the wash pad near the southern end of the pole barn, the ditch north of Second Street, and the ditch south of Second Street (2).

Surface Soil

The vast majority of soil samples collected over the years have been from depths of one foot below ground surface or deeper. The limited existing surface soil data are summarized below.

In June 1984, DTSC collected a surface soil sample at the center of the disposal basin (2). Although deeper soil samples contained high levels of EDB and other pesticides, no EDB was detected in the surface sample. Disulfoton and trifluralin were detected, but at levels below health comparison values (2). The detection limits and description of the quality of the data was not reported in the cited report. In February 1985, during the NEIC/FBI investigation, 12 soil samples were collected, some apparently at the surface (2). From the literature available for review, it is not known how many surface samples were taken, or the levels present. The NEIC/FBI detection limits for EDB and DBCP exceeded the health comparison values for these contaminants.

In a sample collected at six inches below ground surface in May 1985, no pesticides were detected (2). The cited report did not indicate the detection limits, describe the quality of the data, or indicate who collected and analyzed the samples. Four samples collected in July 1985 at a depth of about six inches below ground surface detected EDB, disulfoton, and parathion (2); the levels were below health comparison values.

In February 1987, four shallow soil samples (surface to six inches) were collected by DTSC around the former disposal basin and the pole barn. Several pesticides were detected, including endosulfan, 2,4-D, benefin, methomyl, and carbaryl (2). However, the levels were below health comparison values.

In September 1994, in preparation of widening Second Street onto part of the Frontier Fertilizer Property, the City of Davis conducted soil sampling in order to determine if any contaminants have migrated off the southern border of the Property via surface water runoff. The City of Davis's contractor, Kennedy/Jenks Consultants, collected a total of 79 soil samples about 20 north of the fence which marks the southern boundary of the Property. The soil sampling area was divided into two areas: Area A lies along the southwest portion of the Property and Area B lies along the southeast portion of the Property. Each area was divided into a 40-foot sampling grid system; samples were collected at the center of each sampling grid, unless overhead or subsurface obstruction prevented the collection. Soil samples were collected from depths of 1.0 - 1.5 feet bgs and 2.5 - 3.0 feet bgs in Area A and from depths of 0.5 - 1.0 feet bgs in Area B (30). The soil samples were analyzed for EDB, DBCP, volatile organic hydrocarbons (VOCs), organochlorine pesticides, organophosphorus pesticides, and carbamate pesticides. The only contaminant detected was DDT (at 0.16 ppm) in a soil sample collected in Grid 10 (near the center of the sampling area); however, the level was below the health comparison value. See Figure 8.

Subsurface Soil

Pre-excavation Data

Soil sampling was first carried out at the site by YCDPH in August 1983, when two soil samples were collected from the disposal basin. These samples contained 1,676 ppm disulfoton and 1,056 ppm EDB (1). Twenty-two soil samples collected from eight locations by YCDPH in March 1984 contained EDB, 1,2-DCP, DBCP, and other pesticides and herbicides (2). The inorganic chemical analysis revealed naturally occurring elements, such as, arsenic, barium, cadmium, cobalt, chromium, copper, nickel, lead, selenium, and zinc in the soil samples taken at depths between one to four feet (2). All levels, with the exception of cadmium, were within range of the levels commonly found in the soils in the western United States.

In June 1984, CDHS collected soil samples from the center of the pesticide disposal basin at six depths ranging from surface to five feet below ground surface. Although, as indicated above, no EDB and only low levels of other pesticides were detected in the surface sample, subsurface samples contained up to 2,770 ppm EDB, up to 3,250 ppm disulfoton, and up to 166 ppm trifluralin (2). The inorganic chemical analysis revealed naturally occurring elements were within range of the levels commonly found in the soils in the western United States.

In November 1984, CDHS collected soil samples from three depths within the disposal basin. At 4.5 feet below ground surface, EDB was detected at 215 ppm, along with 63 ppm disulfoton and 7 ppm ethyl parathion. At 8 feet below ground surface, EDB was found at 18 ppm; at 16 feet below ground surface, EDB was found at 11 ppm (2). The NEIC/FBI samples collected in February 1985 from 12 locations contained disulfoton up to 3,300 ppm, pebulate up to 3,000 ppm, trifluralin up to 480 ppm, alachlor up to 3,300 ppm, parathion up to 1 ppm, endosulfan up to 13 ppm, EDB up to 11,000 ppm, and DBCP up to 550 ppm (2).

Post Excavation Data

In 1985, much of the soil contamination in the pesticide disposal basin was excavated and taken off the Property. Soil sampling since then, however, has shown that subsurface soil contamination still exists in the area of the former disposal basin. The following discussion summarizes post excavation levels of subsurface soil contamination.

In December 1989, GTI collected soil samples from 53 locations on site, mostly near the pesticide basin (1). Samples were only analyzed for EDB, DBCP, and 1,2-DCP. The results revealed limited horizontal migration of these contaminants, with high levels in and near the former disposal pit dropping to non-detect 20 feet away. Subsurface soils contained EDB up to 3.5 ppm, 1,2-DCP up to 34 ppm, and DBCP up to 0.69 ppm.

In March 1993, U.S. EPA's contractor E&E collected 105 soil samples at four depths from 27 locations from the former pesticide disposal basin area (see Figure 4 and sample locations F01-F27 on Figure 5) (10). Depth intervals were 1-2, 8-9, 18-19, and 26-27 feet below ground surface. Samples were analyzed for carbon tetrachloride, EDB, DBCP, 1,2-DCP, and 1,3-DCP. In April and May 1993, E&E collected an additional 141 soil samples from 36 different locations (see sample locations F28-F62 and F65 on Figure 5 and Figure 6) (10). The depths were the same as the March sampling event. In addition to analyzing for EDB, DBCP, 1,2-DCP, and 1,3-DCP, these samples were analyzed for volatile organic compounds, organochlorine and organophosphate pesticides, and carbamate/urea pesticides.

EDB was found in subsurface soil at levels exceeding its CREG at 35 of the 63 locations tested by E&E. All 35 locations are in the general vicinity of the former disposal basin. EDB was also found at levels exceeding its CREG in the 1989 GTI investigation, also near the former disposal basin. Therefore, EDB is selected for follow-up in subsurface soil. DBCP was found in subsurface soil at levels exceeding its CREG at five of the 63 locations tested by E&E. All five locations are in the general vicinity of the former disposal basin. Therefore, DBCP is selected for follow-up in subsurface soil. In the E&E study, neither 1,2-DCP or 1,3-DCP were found at any depth at any location at levels exceeding their CREG values. The 1989 GTI investigation did find 1,2-DCP at a level exceeding its CREG near the former pit area; therefore, this contaminant is selected for follow-up.

Carbon tetrachloride was not detected in any soil samples. The detection limit for the March samples was 2 ppm; the April and May samples included samples collected near the concrete sump suspected of being a carbon tetrachloride source; the detection limit for these samples was 0.025 ppm. The CREG for carbon tetrachloride in soil is 5 ppm, therefore, this chemical was not selected for follow-up in this public health assessment based on its absence in the soil, however, it was selected based on its presence in groundwater (see next section).

Multiple other pesticides were detected on the property during the E&E investigation. Most of these contaminants were found at low levels and below health comparison values. Three pesticides detected: siduran, barban and methiocarb, were selected for follow-up because there was no comparison value for these compounds. These pesticides were also found in the general area of the former pesticide disposal basin.

In summary, a total of six contaminants are selected for follow-up in subsurface soil, and all contamination of concern is within the general area of the former disposal basin. Contaminants selected for follow-up in subsurface soil on-property, along with their maximum concentrations detected and health comparison values, are summarized in Table 1.

Table 1.

Contaminants Selected For Follow-up in Subsurface Soil on Property
Chemical Date Detected Max. Conc. Sample Depth (feet) Maximum Concentration (ppm) Comparison Value1(ppm) Comparison Value Source
EDB April/May 1993 26.5 24.5 0.06 CREG2
DBCP March 1993 1.5 61 0.5 CREG3
1,2-DCP Dec. 1989 20 34 10.3 CREG3
Barban April/May 1993 1.5 16 NA NA
Methiocarb April/May 1993 26.5 0.29 NA NA
Siduron April/May 1993 1.5 5.9 NA NA

1 See text above for description of the types of comparison values used.
2 CREG calculated using slope factor obtained from IRIS
3 CREG calculated using slope factor obtained from HEAST

CONTAMINANTS IN GROUNDWATER ON PROPERTY

Monitoring Wells

Between June 1985 and October 1987, a total of 13 monitoring wells were installed on Property to investigate the vertical and horizontal extent of groundwater contamination resulting from the former disposal basin. The locations of the wells are shown in Figure 7. Eight monitoring wells (AW3, AW4, AW5, AW6, MW-3A, MW-4A, MW-5A, and MW-5B) are screened in the S1 zone on the Property. Three monitoring wells (MW-4B, MW-5C and MW-33) are screened in the S2 zone on the Property. Two monitoring wells (MW-3C and MW-4C) are screened in the A1 zone on the Property. There are no monitoring wells screened in the A2 zone on Property; limited data on contamination of on-Property groundwater in the A2 zone are available from water samples collected from the former Labor Camp and ANDCO water supply wells.

Monitoring Wells

Since June 1985, several groundwater sampling investigations have been conducted by different contractors and agencies. Samples have been analyzed for pesticides and other contaminants. Nine contaminants have been detected in on-Property groundwater at levels exceeding health comparison values, and were selected for follow-up. These nine contaminants, their maximum concentrations detected, and health comparison values are presented in Table 2.

Several other contaminants have also been detected in on-Property groundwater over the years, but at levels below health comparison values. These contaminants include benzene, chloroform, diazinon, dibromomethane, 1,2-dichlorobenzene, 1,3-dichloropropene, 1,2-dichloroethene, disulfoton, methylene chloride, napthalene, tetrachloroethylene, toluene, 2,4,5-TP (Silvex), 1,2,3-trichloropropane, trichlorotrifluoromethane (Freon 113), and xylenes (1, 2, 9, 10, 16-21).

Results from E&E's 1993 groundwater investigation indicated that the concentrations of the majority of the contaminants have decreased in most of the wells since the previous groundwater investigation conducted in 1991 (10). In 1994, ICF Kaiser conducted a groundwater investigation which also concluded that the concentration of the majority of contaminants have decreased in most of the wells; however, in a few monitoring wells, the levels of contamination have increased (17, 37).

Contamination is predominantly confined to the S1 and S2; however, contaminant levels in the A1 aquifer has been rising; therefore, the groundwater pump-and treat system has been upgraded in order to remediate this situation (37).

Private Wells

The Labor Camp well and the ANDCO well were sampled in 1984, 1985, and in 1992 by different regulatory agencies. EDB and 1,2-DCP were detected in the Labor Camp well at levels exceeding health comparison values. Trace levels of several other contaminants were detected in the Labor Camp well, including 1,3-dichloropropene, chloroform, 1,2-dichloropropane, and Freon 113 (2, 17). In the ANDCO well, three chemicals were found at levels exceeding health comparison values, including 1,2-DCP at 8.3 ppb, 1,2-dichloroethane (1,2-DCA) at 3.3 ppb, and carbon tetrachloride at 2.7 ppb. Contaminants detected at levels below health comparison values included chloroform, benzene, toluene, 1,2,3-trichloropropane, 1,1,1-trichloroethane, trichlorotrifluoromethane (Freon 113), disulfoton, and 2,4,5-TP (2, 16, 18). Inorganic chemical analysis revealed naturally occurring elements, such as, boron, calcium, magnesium, manganese, nickel, potassium, silicon, sodium, and zinc in the Labor Camp well (18). For both ANDCO and Labor Camp wells, the levels of the naturally occurring elements detected were within range of the levels commonly found in the groundwater in the United States.

Table 2.

Contaminants Selected For Follow-up in On-Property Groundwater
Chemical Maximum Concentration In Each Zone (ppb) Comparison Value (ppb) Comparison Value Source
S1 Zone S2 Zone A1 Zone A2 Zone
Bromoform 7 ND ND NM 4 CREG
Carbon tetrachloride trace ND 3 ND 0.3 CREG
DBCP 0.13 1 ND ND 0.2 MCL
1,2-DCA 0.5 0.5 0.7 0.9 0.4 CREG
1,2-DCP 851 210 13* 8* 5 MCL
EDB 0.13 3.2 ** ** 0.0004 CREG
MCPP ND ND 270 ND 10 child RMEG
Propoxur ND ND 150 ND NA NA
Tetrachloroethylene 14 15 7 NM 5 MCL
TCE 1.4 4 1.4 0.4 3 CREG

ND = Not Detected
NA = Not Available
NM = Not Monitored
MCL = Maximum Contaminant Level
CREG = Cancer Risk Evaluation Guide
MCPP = 2-(4-chloro-2-methylphenoxy)propionic acid
Propoxur = 2-(1-methylethoxy)phenyl methylcarbamate
*    1,2-DCP was detected in the Labor Camp well at a level of 13 ppb. The Labor Camp well was screened in both the A1 and A2 zones. The maximum level of 1,2-DCP detected in the ANDCO well, which was screened only in the A2 zone, was 8 ppb.
**    EDB was detected in the Labor Camp well at a level of 14 ppb. The Labor Camp well was screened in both the A1 and A2 zones.

CONTAMINANTS IN AIR ON PROPERTY

Prior to the April 1985 excavation of soil from the disposal basin, limited on Property air monitoring was carried out to determine if workers needed to wear respirators during the excavation. The highest level of EDB in the ambient air samples collected near the pesticide disposal basin was 0.002 ppb. Air samples collected by personnel air monitors during well construction and soil sampling activities ranged from below the detection limits to 0.0001 ppb EDB. According to the California Health and Safety code (Title 8, section 5219), if EDB is greater than 0.1 ppm and up to 1 ppm, workers are required to wear supplied air respirators or self containing breathing apparatus. Since the levels of EDB was below 0.1 ppm, workers were not required to wear respirators. The air CREG for EDB is 0.0006 ppb. This value is meant as a screening tool to protect the general population. Since the excavation action was a temporary action, and since air concentrations did not exceed worker safety guidelines, no contaminants in on Property air were selected for follow-up. Of more concern would be longer-term exposures to on-Property workers when the site was active. Since there are no data on such exposure, it is considered a potential pathway and is discussed in the Pathways Analysis section.

On April 18 and 19, 1995, air monitoring was conducted during drilling activities at the Frontier Fertilizer site. Personal and ambient air samples were collected by Gillian air sampling pumps for EDB and DBCP. All results were non-detect (i.e., less than 1 ppbv) (37).

Soil Gas On Property

In 1992, Harding Larson Associates (HLA) conducted a soil gas survey to evaluate the distribution of carbon tetrachloride in the soil. Eight soil gas samples were collected on Property. The maximum concentration detected was 0.2 ppb (samples were collected in the former pesticide disposal basin and near the concrete sump). Although the level of carbon tetrachloride exceeded the health comparison value (air CREG is 0.01 ppb), carbon tetrachloride was not selected for follow-up in air. The air comparison values are media-specific concentrations that are used to select environmental contaminants for further evaluation. Because the contaminants were detected in the pore space surrounding the soil and not in the ambient air, it would be inappropriate to use the air CREG as a guideline.

C. OFF-PROPERTY CONTAMINATION

CONTAMINANTS IN SOIL OFF PROPERTY

In April 1985, approximately 1,100 cubic yards of contaminated soil from the pesticide disposal basin was excavated and treated at an agricultural field located three miles east of the site. Treatment consisted of spreading the excavated soil over 15-acres to a thickness of about 1-1/2 inches deep. The treatment enabled volatile pesticides to rapidly dissipate and aided degradation. This has been shown in a field pilot study that was completed in November 1984. In this pilot study, the concentration of EDB in the treated soil dropped from an initial level of 49,000 ppb to 276 ppb after about 2 weeks and to about 43 ppb after 4 weeks (2).

In 1993, U.S. EPA's contractor E&E collected soil samples from six locations about 10 feet to the north of the fence which marks the northern boundary of the Property, and is just north of the former disposal basin. The shallow most samples were taken at a depth of one foot below ground surface. No EDB, DBCP, 1,2-DCP or 1,3-DCP were detected in these samples. Disulfoton and linuron were detected in these samples, although at levels below health comparison values. EDB, but not DBCP or DCP, was detected at levels exceeding health comparison values in deep (about 26 feet below ground surface) soil at about the water table in five of these samples.

CONTAMINANTS IN GROUNDWATER OFF PROPERTY

Monitoring Wells

Several investigations have been conducted by different contractors and agencies over the past nine years to evaluate the extent of groundwater contamination off-Property.

A total of 26 monitoring wells have been installed off Property to characterize the horizontal and vertical extent of groundwater contamination. The locations of the wells are shown in Figure 7. Twelve off-Property monitoring wells (AW1, AW2, MW-6A, MW-6B, MW-7A, MW-7B, MW-8A, MW-9A, MW-10A, MW-11A, MW-12A, and MW-13A) are screened in the S1 zone. Eight off-Property monitoring wells (MW-6C, MW-7C, MW-8B, MW-9B, MW-10B, MW-11B, MW-12B, and MW-13B) are screened in the S2 zone. MW-2A is screened in both the S-1 and S-2 zones (31). MW-13C is screened in the A-1 zone (31). Four off-Property monitoring wells (MW1, MW-2B, MW-7D, and MW-9C) are screened in the A1 zone (1). There are no monitoring wells screened in the A2 zone off-Property.

A total of 17 contaminants have been detected in off-Property groundwater at levels exceeding health comparison values and were selected for follow-up. These 17 contaminants, their maximum concentrations detected, and health comparison values are presented in Table 3.

Several other contaminants have been detected in off-Property groundwater as well, but at levels below their health comparison values and were not selected for follow-up. These contaminants include carbon disulfide, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,1-dichloroethane, 1,2-dichloroethene, dichloromethane, ethylbenzene, toluene, 1,1,1-trichloroethane, trichloroethylene, trichlorofluoromethane, 1,2,3-trichloropane, trichlorotrifluoromethane (Freon 113), and xylenes (1, 2, 9, 10, 16, 17, 18, 19, 20).

As was the case for on-Property contamination, recent sampling events indicate that the levels of most of the contaminants in off-Property groundwater have been decreasing (10, 17). However, the concentrations of EDB and 1,2-DCP have increased in MW-11B which is screened in the S-2 zone and located approximately 450 feet north of the pesticide basin (17, 21). And for MW-7C, which is screened in the S2 zone and located about 100 feet north of the former disposal basin, the levels of EDB, 1,2-DCP and DBCP were found to have also increased (21). The level of EDB has also increased in two monitoring wells, MW-7D and MW-1 (37).

Contamination is predominantly confined to the S1 and S2 zone off Property. 1,2-DCP were detected in two of the four off-Property monitoring wells screened in the A1 zone and EDB has been detected in three of the four off-Property monitoring wells screened in the A1 zone (37). To date, no monitoring wells have been installed in the A2 zone on Property because of the relatively low levels of contamination detected in the A1 zone (13). In May 1995, U.S. EPA installed three temporary monitoring wells (called hydropunches) in the A1 zone (37).

Private and Municipal Wells

There are two private wells in the vicinity of the Property: the Anderson well located near the Anderson office building between 2nd Street and Mace Boulevard and the Mizuguchi well located approximately 50 feet west of the Property. During May 1984, the DTSC and the State Water Resources Control Board collected water samples from the Mizaguchi and Anderson wells, and the wells were sampled again by Frontier Fertilizer's contractors, Luhdorff and Scalmanini, in April 1985 and July 1985. No contaminants of concern were detected in either well (13, 34, 35, 36). The Mizaguchi well is no longer in use, whereas, the Anderson well is still being used (13). It is not clear whether the Anderson well is still being tested.

There are twenty-one City of Davis municipal wells; they are monitored approximately every 18 months. The closest well is located a quarter mile from the Property, whereas, the farthest well is located greater than four miles from the Property. None of these wells are contaminated (32).

Groundwater Plume

The principal contaminants at the site are EDB and 1,2-DCP. Based on recent investigations, the leading edge of the EDB contamination is beyond MW-11 in the S-1 and S-2 zones north of the site and beyond A-1 in MW-1 also north of the site. EDB does not appear to exist south of MW-4 (37). The 1,2-DCP contamination also extends beyond MW-11 north of the site in the S-1 and S-2 zones, beyond MW-1 north in the A-1 zone, and just appear at AW-6 on the southern boundary of the site (37).

Soil Gas Plume

Two plumes of carbon tetrachloride have been partially characterized. The highest concentration of carbon tetrachloride has been found near well cluster MW-12, located about 400 feet north of the property. The larger of the two plumes apparently extends about 600 feet north of the Property; its southern boundary has not been clearly defined. The larger plume most likely originated on the Property, possibly from a concrete sump located near the labor camp. However, soil and soil-gas investigations have been unable to identify a source (10). A second smaller plume was found near the former disposal basin. The smaller plume extends about 25 feet north of the Property and extends approximately 50 feet into the Property. The source of the smaller plume was most likely the former disposal basin.

CONTAMINANTS IN AIR OFF PROPERTY

Ambient Air

In October 1990, representatives from the Regional Water Quality Control Board (RWQCB) conducted a walk-around survey of the property to identify the location and the condition of the monitoring wells on property and off property. During the walk-around survey, the ambient air was monitored using a Gillian pump for EDB and DBCP. The levels of EDB and DBCP were less than 0.26 ppb and less than 0.32 ppb, respectively (23).

In 1992, during the soil gas investigation to evaluate the potential source area of carbon tetrachloride, HLA collected 5 ambient air samples. Four of the five air samples were collected at random locations north of the property in the vicinity of the monitoring wells. The highest level of carbon tetrachloride detected in the ambient air was 0.001 ppb (24). The air CREG for carbon tetrachloride is 0.01 ppb; therefore, carbon tetrachloride was not selected for followup in off-Property air.

Open Borehole and Well Head Space

In 1990, GTI collected 20 vapor samples in open boreholes during soil sampling and well installation activities. 1,2-DCP was detected in MW-7D at 39 ppb. No contaminants were detected in the other samples. In May 1991, representatives from the RWQCB collected air samples from the well head space of two wells during an inspection of the monitoring wells. The two monitoring wells were selected for sampling because they have shown in previous groundwater investigations to contain the highest levels of contamination. EDB and DBCP were detected in the head space of MW-7A at a level of 11.2 ppb and 2.4 ppb, respectively (25). In MW-7B, only EDB was detected (at a level of 3.7 ppb). In 1993, URS conducted a similar investigation for DTSC. EDB and 1,2-DCP were detected in MW-7C at 11 ppb and 350 ppb, respectively.

Table 3.

Contaminants Selected For Follow-up in Off-Property Groundwater
Chemical Maximum Conc. In Each Zone (ppb) Comparison Value (ppb) Comparison Value Source
S1 Zone S2 Zone A1 Zone A2 Zone
Benzene 130* 16* ND NM 1 CREG
Carbon tetrachloride 2,058*** 3,132*** ND NM 0.3 CREG
Chloroform 14 4 0.2 NM 6 CREG
2,4-DB 160 2 ND NM 80 Child RMEG
dibromochloromethane 17.2 ND ND NM NA NA
DBCP 130 750 ND NM 0.2 MCL
1,2-dichloroethane 3,009 22 ND NM 0.4 CREG
1,1-dichloroethene 17 1.9 ND NM 0.06 CREG
1,2-DCP 33,000 34,000 11 NM 5 MCL
1,3-Dichloropropene 48 ND ND NM 3 childRMEG
EDB 39,000 19,700 12 NM 0.0004 CREG
Isopropyltoluene trace ND ND NM NA NA
Methylene Chloride ** ** ND NM 0.2 CREG
1,1,2,2-Tetrachloroethane 20 160 ND NM 0.2 CREG
Tetrachloroethene 3500 26 17 NM 0.7 CREG
1,1,2-trichloroethane 13 2.4 ND NM 0.6 CREG
1,2,3-Trichloropropane 202 trace ND NM 40 LTHA

NM = Not Monitored
NA = Not Available
ND = Not Detected
CREG = Cancer Risk Evaluation Guide
MCL = Maximum Contaminant Level
child RMEG =Child Reference Dose Media Evaluation Guide
LTHA = Lifetime Health Advisory for Drinking Water
*    Higher levels were reported in the Ecology and Environment, Inc. report, however, these were estimated quantity due toexceeded holding times (22).
**    The estimated levels from the Ecology and Environment, Inc report were 150 ppb (22).
***    U.S. EPA's highest samples were a full order of magnitude below these values (which were obtained by the State of California Regional Water Quality Control Board, Central Valley Region).

Although the levels of DBCP, 1,2-DCP and EDB were detected in the well head space at levels exceeding their health comparison values (0.2 ppb for DBCP; 0.87 ppb for 1,2-DCP; and 0.006 ppb for EDB), they were not selected for followup. The air comparison values are media-specific concentrations that are used to select environmental contaminants for further evaluation. Because the contaminants were detected in the well head space and not in the ambient air, it would be inappropriate to use such values as a guideline. Furthermore, standard operating protocols mandate that monitoring wells must be capped at all times, except during sampling; therefore, there would not be any exposure to the community.

Soil Gas

Several soil gas surveys have been conducted by different contractors and agencies. The purpose of a soil gas survey is to provide preliminary data to aid in the identification of the location of sources of contamination in soils; however, it does not provide quantitative data on soil and groundwater contaminant levels.

In 1990, GTI collected two soil gas samples directly south of the MW-7 cluster. The samples were analyzed for EDB, 1,2-DCP and DBCP. At four feet below ground surface, no contaminants were detected. At 20 feet below ground surface, 1,2-DCP was detected at 720,000 ppb and EDB was detected at 1,900 ppb. In 1992, HLA conducted a soil gas survey to investigate the carbon tetrachloride plume and to try and identify its source. Thirty-one soil gas samples were collected off Property. The maximum concentration of carbon tetrachloride detected was 9.5 ppb from a sample collected near MW-12. In 1993, Entrix, Inc. conducted a soil gas investigation in order to resolve the issue of potential health risks posed by soil gas contaminated with EDB, 1,2-DCP, and benzene. Soil gas samples were collected within a 15 foot radius of MW-7 (the location of greatest groundwater contamination) and at depths down to 20 feet. No EDB, 1,2-DCP or benzene were detected in the 15 samples analyzed.

Although these investigations detected EDB, 1,2-DCP and carbon tetrachloride at levels exceeding their health comparison values (air CREG's are 0.0006 ppb, 0.87 ppb, and 0.01 ppb, respectively), they were not selected for follow-up. The air comparison values are media-specific concentrations that are used to select environmental contaminants for further evaluation. Because the contaminants were detected in the pore space surrounding the soil and not in the ambient air, it would have been inappropriate to use the air CREG as a guideline. Exposure to volatiles released to the ambient air or indoor air from subsurface contamination will be discussed in the Pathways Analysis section.

D. QUALITY ASSURANCE AND QUALITY CONTROL

In preparing this public health assessment, ATSDR and CDHS rely on the information provided in the referenced documents and assume that adequate quality assurance and quality control measures were followed with regard to chain-of-custody, laboratory procedures, and data reporting. The accuracy of the conclusions contained in this public health assessment is determined by the completeness and reliability of the referenced information.

E. PHYSICAL AND OTHER HAZARDS

Access to the site is limited by a fence surrounding the property. Physical hazards were noted on the site during the site visit. There were broken and rusted farm equipment abandoned south of the pole barn and north of the labor camps. There was a large pile of concrete rubble located south of the anhydrous ammonia tanks.

PATHWAYS ANALYSES

This section addresses the pathways by which human populations in the area surrounding the site could be exposed to contaminants at, or migrating from, the site. If it is determined that exposure to chemicals not necessarily related to the site is also of concern, this exposure will be evaluated as well.

When a chemical is released into the environment, the release does not always lead to exposure. Exposure only occurs when a chemical comes into contact with and enters the body. In order for a chemical to pose a human health risk, a complete exposure pathway must exist. A complete exposure pathway consists of five elements: 1) a source and a mechanism of chemical release to the environment; 2) a contaminated environmental medium (e.g., air, soil, water); 3) a point of human contact with the contaminated medium (known as the exposure point); 4) an exposure route (e.g., inhalation, dermal absorption, ingestion) at the exposure point; and 5) a human population at the exposure point (15).

Exposure pathways are classified as either completed, potential, or eliminated. Completed exposure pathways require that all five elements exist. Potential exposure pathways are either: 1) not currently complete but could become complete in the future, or 2) are indeterminate due to lack of information. Pathways are eliminated from further assessment if they are determined to be unlikely to occur.

A time frame given for each pathway indicates whether the exposure occurred in the past, is currently occurring, or will occur in the future. For example, a completed pathway with only a past time frame indicates that exposure did occur in the past, but does not currently exist and is not likely to exist in the future. Human exposure pathways are evaluated for each environmental medium possibly impacted by site-related chemicals. The toxicological implications of any completed exposure pathways identified will be evaluated in the Public Health Implications section.

A. COMPLETED EXPOSURE PATHWAYS

The only completed exposure pathway identified in this public health assessment involves the past use of water from the Labor Camp well on the Property (see Table 4). Since this well was decommissioned in 1992, this pathway existed in the past only; no current completed exposure pathways are identified. The exposed population consists of people drinking from or otherwise using water from the Labor Camp well from the early 1970's until 1992.

The Labor Camp structures were used to house farm workers from the early 1950s until 1972. Since pesticide operations and disposal at the Property did not begin until 1971, it is not expected that contamination resulting from these activities would have impacted the Labor Camp well water until about the mid 1970s. Therefore, exposed individuals probably consisted of workers on the Property beginning about the mid 1970s. Information on the number of potentially exposed individuals and use information (such as if well use continued after contamination was detected in 1984) was not located in the site literature available for review. This information was requested during preparation of this assessment, but was not received prior to completion of the report.

Only limited data exists on the nature and extent of contamination of water from the Labor Camp well. Two contaminants were detected in this well at levels exceeding comparison values. Specifically, EDB was detected at a level up to 14 ppb, and 1,2-DCP was found up to 13 ppb. Using several assumptions about factors such as the concentration of contaminants over time, exposure frequency, and exposure duration, we will calculate a quantitative estimate of exposure dose (i.e., an estimate of a daily exposure level) in the toxicological evaluation section, according to ATSDR guidance (15).

Only completed exposure pathways are evaluated for their toxicological risks. For the Frontier Fertilizer site, only one completed pathway was identified in the Pathways Analysis section. This pathway involved past exposure (no completed exposure pathways currently exist or are expected to exist in the future) of workers on the Property drinking from or otherwise using water from the Labor Camp well from the mid 1970s until 1992. Two contaminants were detected in this well at levels exceeding comparison values. Specifically, EDB was detected at a level up to 14 ppb, and 1,2-DCP was found at levels up to 13 ppb.

There are insufficient data on contaminant concentrations and water usage to accurately estimate exposures and risks from this pathway. However, likely maximum doses based on existing data were estimated to get a rough idea of whether or not the chemicals at the concentrations found could have potentially affected the health of Labor Camp well water users. Because it is thought that only workers and not residents were exposed to contaminants in the Labor Camp well, we only evaluated exposure and associated risk from drinking the water (e.g., we did not evaluate exposure from other domestic uses such as bathing). Additional information about actual usage of water from the Labor Camp well would allow a more realistic estimation of doses and associated risks from this pathway. The exposure and risk estimates for this pathway, along with the assumptions used, are provided in Tables 7-9. The toxicological implications of exposure to 1,2-DCP and EDB from drinking water from the Labor Camp well is discussed separately for each contaminant.

Table 4.

Completed Exposure Pathways
Contaminated Environmental Medium Time Frame Exposure Point Exposure Route Exposed Population
Groundwater Past On property Ingestion People drinking from Labor camp well from early 1970's until July 1992

B. POTENTIAL EXPOSURE PATHWAYS

Three potential exposure pathways were identified and are summarized in Table 5. Two of the pathways involve workers and others on the Property in the past while pesticide operations were taking place. These individuals were potentially exposed to contaminants via skin absorption, incidental ingestion, and inhalation. There was insufficient information in the literature available for review on the nature of possible exposures to evaluate these pathways.

The third potential exposure pathway is the potential future inhalation of carbon tetrachloride vapors which have migrated up from the plume of carbon tetrachloride contaminated groundwater. This plume could potentially impact workers in the future light industrial development planned for the land within about 600 feet north of the Property. Potential exposures to EDB and 1,2-DCP from vapors migrating from contaminated groundwater were evaluated in previous risk assessments and by DTSC in its border zone determination. Carbon tetrachloride has been documented in soil gas in the area north of the Property proposed for light industrial development. However, based on the material available for review, potential exposures and associated risks were not evaluated for carbon tetrachloride.

Table 5.

Potential Exposure Pathways
Contaminated Environmental Medium Time Frame Exposure Point Exposure Route Exposed Population Comments
Soil Past On property Skin absorption, incidental ingestion People on property Nature and magnitude of exposure occurring in the past is unknown
Air Past On Property Inhalation People on Property Nature and magnitude of exposure occurring in the past is unknown
Air Future Light Industrial area above groundwater plume within about 400 feet north of Property Inhalation Workers at exposure point Exposure to carbon tetrachloride not evaluated in existing risk assessments

C. ELIMINATED EXPOSURE PATHWAYS

Three exposure pathways were evaluated in this public health assessment, but were eliminated from further review because it was determined that they were unlikely to exist. Eliminated pathways are summarized in Table 6.

Two of the eliminated pathways involve current or future exposure to workers on the Property to contaminants via either skin absorption, incidental ingestion, or inhalation of vapors from soil contamination. The limited surface soil data does not indicate levels of soil contaminants at levels of concern. The lack of substantial levels of contamination of soil at the surface is expected. Because the principal contaminants such as EDB and 1,2-DCP do not adsorb tightly to soil particles and dissolve in water, these chemicals tend to move down through the soil to the groundwater. In the years since pesticide operations were stopped at the site, a combination of downward migration, volatilization to the air, and degradation by sunlight and microorganisms has substantially reduced contamination of surface soil. Fairly rapid reductions in contaminant levels were shown in the sampling conducted as part of the 1985 excavation and "land treatment" which was described in the Environmental Contamination and other hazards section. On the other hand, contaminant levels are of concern in subsurface soil. Construction or excavation workers on Property could potentially come into contact with the contaminants. However, significant exposure via this pathway is not expected to occur as long as personal protection equipment is used.

The only water supply well in use which has been impacted by groundwater contamination is the Labor Camp well, the sole water supply well used on Property. Exposure to contaminants from this well was discussed under completed exposure pathways above. Other water supply wells in the area include the City of Davis municipal water supply wells, the Barthel Mobile Home Park well, and a few private wells within several miles of the site. Contamination has not been documented in any of these drinking water wells. Currently, there are no drinking water supply wells in the area potentially impacted by the groundwater contaminant plumes. There are deed restrictions for both the Frontier Fertilizer Property as well as the Mace Ranch Park property, restricting the placement of groundwater wells. Given these deed restrictions, the groundwater monitoring program, and the establishment of a groundwater cleanup program at the site, future exposure to contaminants in groundwater is considered unlikely to occur. Furthermore, the City of Davis is proposing an ordinance that will strongly discourage private citizens from installing private groundwater wells (32).

Table 6.

Eliminated Exposure Pathways
Contaminated Environmental Medium Time Frame Exposure Point Exposure Route Exposed Population Comments
Soil Current, future On property Skin absorption, incidental ingestion, inhalation People on property coming into contact with subsurface soil Significant exposure via this pathway is not expected if personal protection equipment is used
Groundwater Future Off property Ingestion Users of well water in vicinity of property Exposure via this pathway will not occur as long as site remedial efforts are continued

PUBLIC HEALTH IMPLICATIONS

A. TOXICOLOGICAL EVALUATION

When individuals are exposed to a hazardous substance, several factors determine whether harmful effects will occur and the type and severity of those health effects. These factors include the dose (how much), the duration (how long), the route by which they are exposed (breathing, eating, drinking, or skin contact), the other contaminants to which they may be exposed, and their individual characteristics such as age, sex, nutrition, family traits, life style, and state of health. The scientific discipline that evaluates these factors and the potential for a chemical exposure to adversely impact health is called toxicology.

This section will evaluate the toxicological risks from each completed exposure pathway identified in the Pathway Analyses section. The approach used to evaluate the potential for non-carcinogenic (i.e., non cancer) adverse health effects to occur in an individual or population assumes that there is a level of exposure (i.e., a threshold level) below which non-cancer adverse health effects are unlikely to occur. The approach compares the exposure level (referred to as the dose estimate) with the threshold level (referred to as the toxicity value). The dose estimate is an estimate of exposure expressed in terms of the amount of contaminant (either in contact with or absorbed into the body) per unit body weight per unit time (e.g., mg contaminant per kg body weight per day, or mg/kg/day).

When the dose estimate for a contaminant exceeds the toxicity value for that contaminant, there may be concern for potential non-cancer adverse health effects from that contaminant. However, the dose estimate and toxicity values are developed using conservative assumptions of exposure and toxicity in order to be protective of human health. Although a dose estimate exceeding a toxicity value does indicate a health concern may exist, it does not necessarily mean that observable health effects in the exposed individuals are likely to exist.

Toxicity values used to evaluate non-carcinogenic adverse health effects include the ATSDR Minimal Risk Level (MRL) and the U.S. EPA Reference Dose (RfD). Both of these values are estimates of daily exposure to the human population (including sensitive subgroups), below which non-cancer adverse health effects are unlikely to occur (26). The MRL and the RfD only consider non-cancer effects. Since they are based only on information currently available, some uncertainty is always associated with the MRL and RfD. Uncertainty factors are used to account for the uncertainty in our knowledge of their danger.

When there is adequate information from animal or human studies, MRLs are developed for different routes of exposure, such as ingestion and inhalation. Separate non-cancer toxicity values are also developed for different durations of exposure. ATSDR develops MRLs for acute exposures (less than 14 days), intermediate exposures (from 15 to 364 days), and for chronic exposures (greater than one year). U.S. EPA develops RfDs for developmental exposures (less than 14 days), subchronic exposures (from two weeks to seven years), and chronic exposures (greater than seven years). For example, the chronic MRL or RfD for ingestion is set at a level to be protective against chronic (i.e., lifetime) exposures via ingestion. Both the MRL and RfD for ingestion are expressed in units of milligrams of contaminant per kilograms body weight per day (mg/kg/day).

The potential for carcinogenic health effects (i.e., cancer) to occur in an individual or population is evaluated by estimating the probability of an individual developing cancer over a lifetime as the result of the exposure. This approach is based on the assumption that there are no absolutely "safe" exposure levels to carcinogens (i.e., there is no safety threshold as there is for non-carcinogenic substances). U.S. EPA has developed cancer slope factors for many carcinogens. A slope factor is an estimate of a chemical's carcinogenic potency, or potential, for causing cancer.

If adequate information about the level of exposure, frequency of exposure, and length of exposure to a particular carcinogen is available, an estimate of excess cancer risk associated with the exposure can be calculated using the slope factor for that carcinogen. Specifically, to obtain risk estimates, the estimate of long-term exposure (expressed in the units milligrams contaminant per kilogram body weight per day or mg/kg/day) is multiplied by the slope factor for that carcinogen (expressed as the risk per mg/kg/day) (26).

Cancer risk is the likelihood, or chance, of getting cancer. We say "excess lifetime cancer risk" because we have a "background risk" of about one-in-four (1/4) of getting cancer from all other causes during our lifetime. If we say there is a "one-in-a-hundred-thousand" (1/100,000) excess cancer risk from a given exposure to a contaminant, we mean that each individual exposed to that contaminant at that level over his or her lifetime would be expected to have, at most, a one-in-a-hundred-thousand chance (above the background chance) of getting cancer from that particular exposure. In order to take into account the uncertainties in the science, the risk numbers used are plausible upper limits of the actual risk. In actuality, the risk is probably somewhat lower than one-in-a-hundred-thousand, and, in fact, may be zero.

TOXICOLOGICAL IMPLICATIONS OF EXPOSURE TO 1,2-DCP FROM THE LABOR CAMP WELL

Non-cancer Effects

Information concerning the toxicity of 1,2-DCP to humans were gathered from occupational exposure reports and accidental or intentional over-exposure cases. To date, there are no human exposure studies. In occupational industries, painters and metalworkers who handled solvents containing 10 to 40% 1,2-DCP developed adverse dermal changes, such as, dermatitis, redness, blisters, fluid accumulation, and other signs of skin toxicity. There has been several reported cases of poisonings due to accidental or intentional over-exposure to 1,2-DCP (27). 1,2-DCP mainly exerts its toxic effects upon the central nervous system, liver, and kidney. The adverse health effects discussed were the result of exposure to high levels of 1,2-DCP. The level of exposure that occurred as a result of using contaminated groundwater from the Labor Camp well would be lower than the levels in these case studies, therefore, the workers may not have experienced similar health effects.

We estimated the dose of 1,2-DCP that workers might be exposed to from drinking water from the Labor Camp well (see Tables 7 and 8 for exposure assumptions used and dose estimates). The dose estimate for 1,2-DCP was below the ATSDR chronic MRL. Therefore, non-cancer effects are not expected to occur from past ingestion of 1,2-DCP in the Labor Camp well.

Carcinogenic Effects

In carcinogenicity studies of 1,2-DCP, animals developed benign (non-harmful) liver tumors. A slight increase of mammary gland tumors were also noted. According to the International Agency for Research on Cancer (IARC), 1,2-DCP is not classified as a human carcinogen. Their conclusion was based on the limited evidence for the carcinogenicity of 1,2-DCP in animal studies and the lack of human data (27). However, both the United States and California Environmental Protection Agency's do consider 1,2-DCP a potential human carcinogen.

If we consider 1,2-DCP a potential carcinogen, and if we assume that there is no safe level of exposure to carcinogens, then workers who drank water from the Labor Camp well may have a small increased chance (i.e., 1 in 386,997) of getting cancer from exposure to 1,2-DCP.

TOXICOLOGICAL IMPLICATIONS OF EXPOSURE TO EDB FROM THE LABOR CAMP WELL

Non-cancer Effects

Adverse health effects are unlikely to occur in humans exposed orally to low levels of food or water contaminated by EDB. Doses that cause acute death in human and animals are relatively high (29). If EDB is immediately washed off the skin after contact, low levels of EDB are neither irritating to the surface of the skin nor rapidly absorbed through the skin. In one human study, volunteers were exposed to 0.5 ml of EDB. No dermal changes were observed in the volunteers. However, a burning sensation, inflammation, and blisters occurred when a cloth dressing was saturated with EDB and applied to the skin for 1 to 2 hours. In one animal study, only reddening of the skin occurred when EDB was applied on the skin. Additional adverse signs, edema and necrosis, occurred when a cloth dressing was saturated with EDB and applied to the skin.

Two fatal cases of occupational exposure to EDB were reported in the literature (28). Two workers died after collapsing in a pesticide storage tank containing residues of EDB. The primary route of exposure was skin contact with EDB; however, inhalation of EDB may have also contributed to the deaths. After EDB is absorbed through the skin, the liver and kidney are the target organs for toxicity. The principle cause of the two deaths was liver failure. There has been three cases of deaths caused by the intentional ingestion of high doses of EDB. However, the levels of exposure that have occurred as a result of using contaminated groundwater from the Labor Camp well would be lower than the levels in these case studies. In an animal study, lethal amounts of EDB applied to the skin was rapidly absorbed. If evaporation of EDB was prevented for 24 hours by a cloth dressing, death occurred within 4 days.

Two human studies have suggested that EDB may have adverse effects on fertility and sperm production (29). However, these studies had severe limitations and provide little or questionable evidence linking EDB and adverse fertility or sperm production. Animal studies have also indicated that high doses of EDB may have adverse effects to the male reproductive systems.

No Minimal Risk Level (MRL) was derived for EDB because of the lack of quantitative exposure data (29). Humans are susceptible to the short-term toxic effects of EDB from three routes of exposure, inhalation, dermal, and ingestion. With the exception of adverse reproductive effects in men due to occupational exposure, long-term effects of EDB have not been documented in humans. However, based on animal studies, there is a potential for certain adverse health effects, such as, liver and kidney damage, sperm abnormalities, and DNA damages, in humans exposed chronically (long-term) to low environmental levels of EDB from hazardous waste sites.

We estimated the dose of EDB that workers might be exposed to from drinking water from the Labor Camp well (see Tables 7 and 8 for exposure assumptions used and dose estimates). The dose estimate for EDB exceeded U.S. EPA Reference Dose (RfD) for EDB. Therefore, past exposure may have presented a non-cancer hazard to workers.

Carcinogenic Effects

In studies of EDB exposed workers, results did not show increases in the number of deaths or cancers. However, these studies had limitations and small increases in cancer may not have been detected (29). Studies in animals have shown that, via the inhalation route, EDB is a potent carcinogen, producing cancer in the upper respiratory systems, as well as in other organs and tissues throughout the body (29).

Our estimate of an upper bound extra lifetime cancer risk to workers from drinking EDB contaminated water from the Labor Camp well results in a moderate increased cancer risk (about 1 in 286).

Table 7.

Does Estimate Equation For Ingestion of Chemicals in Water From the Labor Camp Well
Dose Estimate (mg/kg-day) = (CW x IR x EF x ED) ÷ (BW x AT)
Where:
CW Chemical Concentration in Water (mg/liter)
IR Intake Rate (liters/day)
EF Exposure Frequency (days/year)
ED Exposure Duration (years)
BW Body Weight (kg)
AT Averaging Time (the period over which exposure is averaged, in days). For noncarcinogenic effects, it is the pathway-specific period of exposure (i.e., ED x 365 days/year). For carcinogenic effects, it is a 70 lifetime (i.e., 70 years x 365 days/year).
Variable Values Used:
CW: EDB: 0.014 mg/liter; 1,2-DCP: 0.013 mg/liter
IR: 2 liters/day
EF: 260 days/year
ED: 10 years
BW: 70 kg for adult (14)
AT: For noncarcinogenic effects: 10 years x 365 days/year = 3,650 days. For carcinogenic effects: 70 years x 365 days/year = 25,550 days.

Table 8.

Chronic Does Estimates For Ingestion of Chemicals in Water From The Labor Camp Well
Contaminant Non-cancer Effects (mg/kg/day) a Carcinogenic Effects (mg/kg/day)b
1,2-DCP 0.00026 0.000038
EDB 0.00028 0.000041

a Dose for evaluating noncarcinogenic effects. Exposure is averaged over the period or duration of exposure (i.e., AT = 10 years x 365 days/year).
b Dose for evaluating carcinogenic effects. Exposure is averaged over a 70 year lifetime (i.e., AT = 70 years x 365 days/year).

Table 9.

Ration of Dose to Non-Cancer Toxicity Value and Cancer Risk Estimates for Ingestion of Chemicals in The Labor Camp Well
Contaminant Non-cancer Toxicity Value (mg/kg-day) Non-cancer Toxicity Value Source Ratio of Dose to Toxicity Value EPA Cancer Slope Factor (mg/kg-day)-1 Chemical-Specific Cancer Risk
1,2-DCP 0.09 Chronic MRL 0.24 0.068 0.0000026 (i.e., about 1 in 400,000)
EDB 0.000057 RfD 5 85 0.0035
(i.e., about 1 in 300)

B. HEALTH OUTCOME DATA EVALUATION

Existing health databases such as the cancer and birth defects registries are generally useful if substantial exposures are documented or suspected for neighborhoods in the vicinity of a site. In the case of Frontier Fertilizer, community-wide exposures have not occurred. A review of disease statistics in the vicinity of the site would not help to define any potential impact on individuals on the Property who in the past may have been exposed to contaminants in water from the Labor Camp well.

C. COMMUNITY HEALTH CONCERNS EVALUATION

In this section, we will address specific health concerns raised by community members.

Has contaminated water gone down far enough to reach the municipal water supply?

    No. Small amounts of contamination from the site have gone down to the A2 zone, based on data from the former water supply wells on Property. Some municipal wells get water from this zone. However, based on available data groundwater contaminants from the site have not migrated very far off site. According to a representative of DTSC, there are currently no municipal water wells at risk of being contaminated with any contaminants from the site.

Could there be a problem if children played in the fields adjacent to Frontier?

    No. Based on the information and data available for review, there is no indication of or potential for significant levels of site-related contaminants to have impacted surface soils in fields near the site. There may be small releases of carbon tetrachloride to the air above the carbon tetrachloride plume. Long-term exposure to this chemical inside structures built over the plume might be of concern. However, any carbon tetrachloride escaping to the ambient air from soil gas would be rapidly diluted and would not pose a health hazard to children or others playing in the area.

Could any of the chemicals at Frontier Fertilizer cause air pollution in the surrounding areas?

    No. The contamination of concern at the site is in the subsurface soil and in the groundwater. Under current conditions, air releases either via fugitive dust or due to vapors is not a problem for residents. There may be small releases of carbon tetrachloride to the air above the carbon tetrachloride plume. The potential for exposure to this chemical should be assessed prior to development of the land over the carbon tetrachloride plume. No residential units will be constructed in the area.

Will site cleanup activities allow exposure to toxic chemicals to occur?

    Given the distance from the site to the nearest residence, exposure to the community during remedial actions is not likely to occur. U.S. EPA will provide community members with information about possible remedial actions for the site. Prior to implementing a remedial action, there will be a formal public comment period. Any concerns about exposures related to the particular remedial action would be addressed at that time.

Does the site currently pose any danger to the health of residents living closest to the site?

    No. As indicated above and evaluated in this assessment, the site does not currently pose any danger to the health of residents living closest to the site.

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