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The Western Pacific Railroad's (WPR) Oroville yard, near Oroville, California, has been proposed for inclusion on the U. S. Environmental Protection Agency's National Priorities List (NPL). WPR operated the 90-acre railyard for almost 60 years until the railyard was purchased by Union Pacific Railroad (UPR) in 1983. The servicing and repair of railcars on the site generated petroleum product wastes, chlorinated solvent waste, and heavy metal wastes that have migrated into the soils of the area.

The WPR site is located on dredger tailings east of the Feather River, two miles south of Oroville. The Regional Water Quality Control Board (RWQCB) has identified three primary sources of contamination on site: a roundhouse or fueling area, an unlined surface impoundment, and an API oil-water separator. Most of the tarry substance (petroleum hydrocarbons) in the bottom of the surface impoundment was removed in a remedial action, although migration of metals and some petroleum hydrocarbons into groundwater may have occurred before the remediation. The API oil-water separator has been cleaned, and contaminated soil along the sides has been removed, but soils that may be contaminated remain beneath the underground structure. A water well on site, leased to the California Water Services Company (CWS) as a municipal well, was removed from service in 1984 when it was found to contain trichloroethane (TCA) and dichloroethylene (DCE) at concentrations slightly above the safe drinking water level. In 1987, when the safe drinking water level, or Maximum Contaminant Level (MCL), of DCE was increased, and when TCA was no longer detected, the well was returned to service. The extent of soil contamination in the roundhouse or fueling area is under investigation by the RWQCB.

A residential area composed of 25-50 single family dwellings is located on a small hill 100-200 feet to the northeast overlooking the dredger tailings. Other industries, also built over the dredger tailings, are in the vicinity of the site. These include Koppers and Louisiana Pacific to the south, two wood product companies that are NPL sites, a sewage treatment company to the north and west, and Olive Products. Activities at Koppers and Louisiana Pacific are thought to have contaminated the groundwater under those sites. The Feather River is west of the dredger tailings area. Directly west of the river is the Oroville Wildlife Area, a wetlands area encompassing 5,000 acres.

The limited data available on concentrations of contaminants on site and off site are not sufficient to determine if humans are being or have been exposed to levels of contamination that would be expected to cause adverse health effects. Furthermore, knowledge of the hydrogeology of the dredger tailings is 20 years old, and the potential for transport of contaminants is unclear. Sampling of soil and groundwater in the roundhouse or fueling area as well as additional sampling near the excavated surface impoundment is needed to determine if migration into the groundwater of heavy metals, chlorinated solvents, and petroleum hydrocarbons (including benzene, xylene, toluene, and ethylbenzene) has occurred. Sampling of on-site and off-site soil and biota for dioxins and furans is necessary to determine if the site is a source of the dioxin and furan contamination that has been discovered in the South Oroville area. Although there is no evidence at this time that WPR is the source, the burning of petroleum and chlorinated solvent wastes, such as took place at the pond on this site, has been known to generate dioxins and furans. Therefore, this site is classified as an indeterminate public health hazard.

No health concerns from this site have been documented by the Butte County Health Department, although concerns about exposures from the Koppers and Louisiana Pacific sites exist. Although no follow-up health activities are proposed at this time, the California Department of Health Services (CDHS) will continue to monitor this site. If data become available suggesting that human exposure to hazardous substances at levels of public health concern has occurred, or is likely to occur, CDHS and ATSDR will reevaluate this site for any indicated follow-up health activities.


A. Site Description and History

The Western Pacific Railroad Oroville Yard is at 900 Marysville-Baggett Road, two miles south of Oroville, California (Figure 1). The WPR site is divided by a railyard running north to south. The site contains four areas where on-site contamination has occurred; three of those areas are also considered sources of contamination.

The first area is a three-acre roundhouse or fueling area on the eastern side of the railyard, which contains 12 "inspection pits" where repair, servicing, and cleaning of railcars and locomotives took place. Those activities also included sandblasting, welding, cutting, and fabricating railcars and locomotive engines. The roundhouse was destroyed on September 10, 1976, in an electrical fire (DHS Preliminary Site Assessment, December 1983). Since 1970, the Solano Railcar Company has leased five acres from UPR, including the roundhouse area with the inspection pits. The Solano Railcar Company reportedly uses the property to fabricate railcars. Its operations include cutting, welding, sandblasting, and painting railcars. According to WPR, Solano Railcar Company discharged waste oils and grease generated from the fabrication of railcars into the surface impoundment until October 1987. Solano Railcar Company reported that its wastewater was similar to those generated by WPR (DHS, Preliminary Site Assessment, 1983).

According to Solano Railcar Company, no hazardous wastes are currently generated on the site. However, RWQCB personnel have indicated that stormwater runoff containing petroleum products that were formerly discharged to the surface impoundment are currently discharged into a ditch on the site (Ecology and Environment, Inc., Site Inspection Summary, 1988).

A second area of contamination was an underground American Petroleum Institute (API) oil-water separator, into which unknown quantities of wastewater containing oils, grease, and heavy metals including chromium, were discharged from the activities at the roundhouse or fueling area. The API separator was supposed to remove the organic petroleum products from the wastewater for recycling, and to discharge the aqueous effluent to the unlined surface impoundment on the western side of the railyard tracks (Figure 2).

A third area of contamination is the unlined surface impoundment that received the wastewater, along with grease, oil, and waste solvents that were incompletely removed, from the API separator. The discharge of wastewater containing petroleum products and solvents into the unlined surface impoundment took place from the 1950s, when the API separator was installed, until October 1987 when it was blocked off (DHS, Preliminary Site Assessment, 1983). Periodically, the pond was apparently set afire to burn off the layer of oil that formed (DHS, Preliminary Health Assessment, 1983, and personal communication from Butte County Environmental Health Officer, now retired).

Site vicinity Map
Figure 1. Site Vicinity Map

Plot Plan
Figure 2. Plot Plan

The surface impoundment was first investigated by staffmembers from the Abandoned Site Program. Sampling of soil beneath the asphaltic layer of the surface impoundment by the Department of Health Services (DHS) in October 1985 revealed the presence of heavy metals. Total chromium detected in all soil samples ranged from 52-228 ppm (DHS, Sample Plan, Western Pacific Railroad, 1985).

The RWQCB Toxic Pits Cleanup Act (TPCA) Unit investigated the site in November 1985, and the surface impoundment was listed as a TPCA pond. RWQCB issued Cleanup and Abatement Order No. 89-700, which required closing the surface impoundment and excavating the soil. At the request of UPR, Dames and Moore, the contractors for UPR, did waste classification studies of the surface impoundment in 1987. They reported heavy metals (specifically arsenic, barium, copper, nickel, and chromium) at concentrations below the total threshold limit concentration (TTLC) values; total petroleum hydrocarbons (TPH) concentrations from 1,409 mg/kg to 13,000 mg/kg; low levels of benzene, toluene, phenanthrene, acetone, methethylketone, methylene chloride, and chlorobenzene, acute oral LD50 above 5,000 mg/kg, pH within 2.0 to 12.5, no aquatic toxicity, and flashpoint greater than 140o F. Based on those data, and pursuant to Section 66305(c) of Title 22, Division 4, Chapter 30, California Code of Regulations, the excavated soil from the pond was classified as not hazardous for disposal purposes. That is, the pond was exempted from the requirements of the Toxic Pits Cleanup Act. It was cleaned up under the provisions of the Porter-Cologne Water Quality Act, and the excavated soil did not have to be placed in a Class I hazardous waste dumpsite.

RWQCB required that UPR block off the API separator outlet pipe to the surface impoundment as part of the closure process. UPR completed that task in October 1987. The in-ground API separator was cleaned out according to a workplan approved by RWQCB, and the oily grit in the bottom was considered a non-RCRA material and was transported to W. W. Gardner Construction in Erda, Utah (Dames and Moore, Pond Closure Report, 1990). The concrete holding tank was then filled in with soil. An above-ground API separator was installed in 1989 to replace the nonfunctional underground separator.

In January 1989, RWQCB issued a Cleanup and Abatement Order to Union Pacific and Solano Railcar Company to remove the tarry or asphaltic hydrocarbon residue remaining in the pond from periodic burning (RWQCB, 1989). Dames and Moore contracted with UPR to characterize and remove the liquid and sludge waste from the surface impoundment and to fill in the area with nearby dredger tailings from the Feather River. Solano Railcar Company has declared bankruptcy (RWQCB, 1989).

In December 1987, Dames and Moore installed four monitoring wells (MW-1 through MW-4 in Figure 2) in and around the surface impoundment area at depths of 49, 75, 71, and 75 feet, respectively. Total chromium was detected at 80 ppb in MW-1, a monitoring well adjacent to the surface impoundment on the northern side. Chromium was not detected in the other three monitoring wells.

A fourth area where contaminants have been detected is a WPR well leased to CWS as a municipal well, and operated on a seasonal basis. It was found to have dichloroethylene (DCE) concentrations ranging from 0.5 to 1.4 ppb and 1,1,2-tricloroethane ranging from 0.6 - 0.9 ppb in monthly monitoring events between 1984 and 1986. It was removed from service in 1984 when a safe drinking water level of 0.2 ppb for DCE was established. In 1986, the safe drinking level, or Maximum Contaminant Level (MCL), was raised to six ppb and the well was returned to service. After March 1987, no DCE was detected (California Water Service Reports on State Well # 19N/4E-201N, 1990).

B. Site Visit:

California Department of Health Services staffmembers working under the Cooperative Agreement with the Agency for Toxic Substances and Disease Registry (ATSDR), visited the site on May 14, 1990. Accompanying them were the regional representative for the Agency for Toxic Substances and Disease Registry, the project manager from the Regional Water Quality Control Board, an environmental engineer from Union Pacific Railroad, engineers from Dames and Moore, and the contractor for Union Pacific Railroad.

The site is on dredger tailings that appear as both slightly and abruptly rolling grassland composed of variously sized gravel, and upon which grow some grasses and some deciduous and evergreen trees. It is accessible by gravel roads from 5th Avenue and the from Marysville-Baggett Road, and it is not fenced.

There were no obvious chemical hazards other than some oily, standing water near the roundhouse. There were several minor physical hazards, such as the uncovered excavation where an underground tank had been, and an uncovered manhole where an unpermitted discharge appeared to be taking place.

A cluster of structures occupies the roundhouse or fueling area. Several employees of Solano Railcar Company were working on the five-acre portion of the area that has been leased to Solano Railcar Company since 1970, although we were told that Solano had declared bankruptcy. The only thing that remains of the roundhouse is the circular concrete depression where the engine turntable is located, and some central crane-type structures. Radiating from the circular concrete depression are the 12 concrete inspection pits where work on the engines and railcars continues to take place. The wastewater and oils were collected by a semicircular ditch which led to the underground API oil-water separator nearby. The ditch is now lined with concrete.

The roundhouse area did not appear to be very intensively used. Most of the buildings on site when the EPA's Hazard Ranking System evaluation was prepared have since been demolished. Three railcars, including an antique coach car, occupied the inspection pits. A dark green liquid was visible in a rectangular hole on the roundhouse switch area property. Weeds were growing over some of the rails leading from the roundhouse area.

The environmental engineer from UPR said that 30 railcars would occupy the rails, waiting to be repaired when the site would again be actively used.

The locations of the four monitoring wells are indicated by rectangular metal plates (Figure 2). Monitoring well 89-01 is north of the roundhouse switching area and north of the API separator; well 89-02 is east of the roundhouse switch area and east-northeast of an excavated, unpermitted, underground tank site next to the Solano Railcar Company offices; well 89-03 is south-southwest of the roundhouse switch area, and well 89-04 is north-northwest of it. An unpermitted underground storage tank near well 89-02 has been excavated, and the excavation was covered haphazardly with clear vinyl.

Two abandoned wells in the roundhouse area have been inspected and sealed by request of RWQCB (Figure 2). AW-1 is north of the roundhouse switchyard and north-northwest of the API separator. AW-2 is south of the Solano Railcar Company offices and a former oil storage tank.

The former location of the in-ground API separator is barely visible as a depression and an outline of concrete, and an above-ground API separator has been substituted. The in-ground API separator was cleaned out according to a workplan approved by RWQCB (see Site Description and History). The surface ditch that the tracks traversed has been replaced by an underground culvert. The above-ground API separator has not been leased to the Solano Railcar Company. An above-ground hose ran from an underground pipe from the inspection pits to a stormwater runoff ditch in an unpermitted discharge.

The surface impoundment was approximately 1,500 feet west of the area where the roundhouse once stood, across the UPR railyard tracks and at the edge of the UPR property (Figure 2). The pond measures about 200 feet by 100 feet. The impoundment has been excavated, and the surface of the impoundment is now composed of smooth river rocks of various sizes, sandy soil, sawdust from a nearby lumber yard, a few weeds, and several pine trees with bases several feet above the current soil line, indicating that soil replacement is incomplete.

Four monitoring wells (MW-1 thru MW-4) are located around the site of the surface impoundment. MW-1, which is contaminated, is just above the excavation, about 20 feet from a chain-link fence separating the UPR property from a wood storage yard. The ground is spongy with partially decomposed sawdust and wood shavings that apparently are blown through the chainlink fence from the nearby property. MW-2 is at the southeastern border in a depression marking the area where an additional excavation took place due to high levels of TPH. MW-3 is about 300 feet south of the excavated area, and MW-4 is about 100 feet south of the excavated area.

A cluster of buildings occupies a hill on the western side of the track. The buildings are used as offices by employees of UPR. The WPR well that contained DCE and TCA is next to those buildings, but the source of its contamination is not thought to originate in that area.

C. Demographics, Land Use, and Natural Resource Use

Demographics: The site is two miles south of Oroville, population 10,500. The closest residential area is on a hill on the northeastern side of Marysville-Baggett Road within 200 feet of the site. It is composed of 25 to 50 single family dwellings and is estimated to have between 125-250 residents. Most of the dwellings are not built on the dredger tailings.

Land Use: The WPR site is located on dredger tailings and gravel left from old gold mining activities. The dredger tailing area is bounded on the north by Highway 162, on the east and south by Marysville-Baggett Road, and on the west by Highway 70. The area of dredger tailings is used primarily for industrial purposes and as a wildlife refuge, although the residential development appears to be encroaching into that area. The industries include Koppers and Louisiana Pacific, two wood processing companies to the south that are on the NPL list, a sewage treatment company to the north and west, and Olive Products. The Feather River is west of the dredger tailings and the Oroville Wildlife Area, a 5,000 acre wetland, is west of the Feather River. It is a home for bald eagles, peregrine falcons, and the elderberry longhorn beetle, which have been designated by the federal government as endangered or threatened species (Ecology and Environment, Inc., Site Prioritization Criteria, 1990).

Natural Resource Use: The Feather River is used for recreation and sport fishing. An estimated 270,000 pounds of salmon and steelhead trout are caught annually within 20 miles downstream of the site. The river below the site is also a spawning area for salmon (Ecology and Environment, Inc., memorandum to Tom Mix, EPA Region IX, 1990).

The WPR well is leased to CWS to supplement the seasonal fluctuation in Feather River water volume. When the well is operational, the water is combined with water from the Feather River to provide drinking water for the residents of Oroville. Drinking water uptake from the river is seven miles upstream of the site (Ecology and Environment, Inc., Reference 8-Memorandum, 1988).

D. Health Outcome Data

On January 1, 1988, the state's Cancer Surveillance Program began collecting data through the California Tumor Registry for the region that includes Western Pacific Railroad and the surrounding areas. CDHS released the data for 1988 on February 18, 1991. (Ref.: California Department of Health Services. Cancer incidence and mortality. California, 1988. California Health and Welfare Agency, 1991.)

The California Birth Defects Monitoring Program began collecting data for Butte County in 1988. (Ref: Croen LA, GM Shaw and NG Jensvold. Birth defects monitoring program in California: a resource for epidemiologic research. Pediatric and Perinatal Epidemiology, 1991; 5 (in press). The pertinence of these two data bases to the Western Pacific Railroad site will be discussed further in the Public Health Implications Section of this preliminary health assessment.


No health concerns related to the WPR site have been reported to the Butte County Health Department. The retired environmental health officer for Butte County stated that he knew of no problems associated with the site, but that it was "a stinking mess" when they were burning the oil layer off the surface of the pond. He reported a domestic well due south of the site in a cluster of four homes, and four CWS wells within three miles of the site. They operate on a seasonal basis to supply up to 25 percent of Oroville's water supply (California Water Service Company communication, April, 1988).

The Butte County medical officer indicated that public concerns were focused on the other NPL sites, Koppers and Louisiana Pacific, located just south of this site. Citizen contact has been in relation to the off-site groundwater contamination from those sites, the investigation of possible human exposure to dioxins and furans from the 1987 fire at Koppers, and the subsequent discovery of off-site dioxin and furan contamination that antedated the fire. Appendix C contains copies of two informational letters sent to residents.

No comments were received during the public comment period for this site, which extended from August 12, 1991 until September 6, 1991. Notification of the public comment period appeared for one day each in the Oroville Mercury Register, the Sacramento Bee, and the Chico Enterprise.


Toxic Chemical Release Inventory Search Information

We conducted a search of the EPA Toxic Chemical Release Inventory (TRI) for the site and for the local area for the years 1987, 1988, and 1989, the years for which TRI data were available on line at the time this preliminary health assessment was written. The TRI contains information voluntarily submitted to EPA on estimated annual releases of toxic chemicals into the environment from active industrial facilities. The 1987, 1988, and 1989 TRI did not contain information on toxic chemical releases in the site area.

A. On-Site Contamination

The contamination in the roundhouse or fueling area, the surface impoundment, and the CWS well, are discussed individually in the following sections.

Roundhouse or Fueling Area
Soil: The roundhouse or fueling area soil was analyzed for total petroleum hydrocarbons (TPH) by EPA Method 3550/8015. That method is said to focus on hydrocarbons in the diesel range (C10-C20), and on motor oil (>C24). Figure 3 shows that TPH contamination in the fueling area soil exists at levels up to 24,000 parts per million (ppm) (Dames and Moore, Phase II Investigation Work Plan, 1990). The objective of the Phase II Investigation is to determine the vertical and horizontal boundaries of the TPH contamination.

Analysis for volatile organic compounds (VOCs) by EPA Method 8240 showed concentrations of 1,1-dichloroethylene at 2.9 parts per billion (ppb), and toluene at 71 ppb in the boring for monitoring well 89-04. Toluene was also found at 33 ppb in the boring for 89-02, and at 17 ppb in test pit 7 (TP-7) (Dames and Moore, Fueling Area Progress Report, 1989).

Analysis for semi-volatile organic compounds by EPA Method 8270 indicated the presence of phenanthrene and 2-methylnaphthalene in soil boring sample SB-11 and in the boring for monitoring well 89-04. The levels of phenanthrene were 1,800 ppb for 89-04 and 1,500 ppb for SB-11. The levels of 2-methylnaphthalene were 5,900 ppb for 89-04 and 1,700 ppb for SB-11 (Dames and Moore, Fueling Area Progress Report, 1989).

No analysis was performed for metals in the soil of the roundhouse or fueling area.

No analysis was performed for polychlorinated biphenyls (PCBs) in the soil of the roundhouse although work on transformers in engines and railcars has been known to result in soil contamination with PCBs at other sites.

Groundwater: VOC contamination in monitoring wells is shown on a schematic map in Figure 4 (Dames and Moore, Fueling Area Progress Report, 1989). In 1989 and 1990 monitoring, well number 89-02 had concentrations of l,l-dichloroethane (DCA), l,l-dichloroethene (DCE), and trichloroethene (TCE) above the MCLs.

Chemical Conc.(ppb) MCL(ppb)
1,1-dichloroethane 66 6
1,1-dichloroethylene 320 6
trichloroethylene 13 0.5
1,1,1-trichloroethane 59 200
chloroform 8.2 100

No other well samples showed contamination above the MCLs. No detectable aromatic volatile organics (EPA Method 602) or petroleum hydrocarbons (EPA Method 8015) were found in the groundwater (Dames and Moore, Fueling Area Progress Report, 1989). No analysis was performed for metals in the groundwater in the fueling area.

Phase I Soil Sampling Analytical Results
Figure 3. Phase I Soil Sampling Analytical Results

Ground Water Sampling Analytical Results
Figure 4. Ground Water Sampling Analytical Results

Air: No air monitoring data were found in any report.

Surface Impoundment
Soils: The surface impoundment was excavated and closed in 1989 in accordance with RWQCB Work Order 89-700 (Dames and Moore, Pond Closure Report, 1990). TPH was analyzed in soils by EPA Method 3055/8015, and arsenic, barium, and chromium were analyzed by EPA Method 6010. Method 3055/8015 is described in Appendix A. This sample preparation method allows escape of volatile compounds containing less than ten carbons, so there are no accurate data for compounds such as benzene, toluene, and xylene (California Analytical Laboratories, personal communication, July, 1990. California DHS Hazardous Materials Laboratory, personal communication, April, 1991). Therefore, the method more accurately quantifies total extractable hydrocarbons (TEH) rather than TPH.

The reports available for this Preliminary Health Assessment indicated that analyses for VOCs or semi-volatiles were not performed.

RWQCB required the following soil concentration levels for the drainage and/or containment structures during closure of the waste-oil surface impoundment:

Concentration in Soil

(mg TPH/kg soil) Containment Requirements
<500 Cover residual waste and grade surface to drain.
500 to 1000 Cover with low permeability material to Class III landfill standards. Waste discharge requirements and further ground water monitoring may be necessary.
>1000 Continue to excavate. If material is left in place with concentrations above 1,000 mg/kg, the site will be required to conform with Class II landfill standards, including waste discharge requirements and ground water monitoring.

Table 1 (Dames and Moore, Pond Closure Report, 1990) indicates that sample 9/89-10 contained 2,300 ppm TPH, so another 1.5 feet of soil was excavated. No further samples were taken to analytically confirm that TPH levels in soil had been reduced to less than 500 ppm TPH. In the upper excavation one sample, 9/89-12, contained 588 ppm TPH. No additional sampling was done and no further excavation was done.

The soil in the surface impoundment area was not analyzed for dioxins or furans. However, the periodic uncontrolled burning of petroleum products with VOC solvents in the surface impoundment might be expected to produce dioxins and furans which could deposit on the site (Weerasinghe and Gross, 1985).

Table 1 also shows the concentrations of metals in the surface impoundment after excavation (EPA Method 6010). The metals arsenic, barium, and chromium were reported to be present at concentrations below the TTLC levels (Dames and Moore, Pond Closure Report, 1990). The metals were analyzed in archived soil samples taken in 1988. The TTLC values listed in Title 22 of the California Code of Regulations are for classification of wastes removed from a site. Those values have been inaccurately described as indicating a concentration that is "health conservative" and that is not likely to cause adverse effects on human health following chronic exposure if the soils remain in place (Dames and Moore, Pond Closure Report, February, 1990). Furthermore, although the concentrations were below the TTLC, Title 22 specifies that wastes must be below soluble threshold limit concentration (STLC) values as well as TTLC values. There is no report that the Waste Extraction Test (WET) was performed to establish that the metal concentrations were below STLC values. TTLC levels are a measure of the total amount of a hazardous chemical, whereas STLC levels are a measure of the amount that is thought likely to leach into the groundwater. Both TTLC and STLC criteria must be met for a waste to be considered nonhazardous according to Title 22 of the California Code of Regulations.


Surface Impoundment Conc. (mg/kg)*
Sample ID Collection Date TPH Arsenic Barium Chromium

9/89-04 9/14/89 < 10 9.7 117 53
9/89-05 9/14/89 21 10 133 53
9/89-06** 9/14/89 < 10 10 142 54
9/89-07 9/14/89 21 9.6 143 69
9/89-10*** 9/21/89 2300 4.0 66 29
9/89-14 9/26/89 201 4.6 93.9 62.8
9/89-15 9/26/89 410 2.2 66.6 58.5
9/89-16** 9/26/89 205 2.9 77.4 70.6
Upper Excavation Conc. (mg/kg)*
9/89-08 9/21/89 23 8.4 121 48
9/89-09** 9/21/89 26 7.6 111 43
9/89-11 9/26/89 117 3.8 93.7 56.1
9/89-12 9/26/89 588 4.2 131 56.1
9/89-13 9/26/89 378 1.3 96.0 57.8

* The unit of mg/kg = ppm
** This is a duplicate of the preceding sample
*** Additional soil was removed after this sample was taken. No subsequent analysis was done to confirm decreased TPH level.
Total Petroleum Hydrocarbons (TPH) analyzed by EPA Method 8015 (Modified) and metals analyzed by EPA Method 6010.
Data taken from Dames and Moore, "Pond Closure Report," 1990.

The concentrations of metals in the surface impoundment before excavation, which were used by EPA to perform the Hazard Ranking System, appear below (Michael Pardee, DHS, Abandoned Site Program, Site Sampling, 1985).

Metal (total) Max conc. (mg/kg*) Av. Conc. (mg/kg*)

arsenic 32.8 15.7
barium 360.0 184.3
chromium 228.0 125

*mg/kg is ppm

The table below presents maximum and average metal concentrations along with the appropriate TTLC and STLC values after excavation. Levels of arsenic ranged from 1.3 -10 mg/kg, barium from 66 to 143 mg/kg, and total chromium from 29 to 70.6 mg/kg.

Metal (total) Max conc. (mg/kg*) Av. Conc. (mg/kg*) TTLC (mg/kg*) STLC (mg/l*)

arsenic 10.0 5.0 500 5
barium 143.0 104.0 10,000 100
chromium 70.6 50.0 500(VI) 5
      2,500(III) 560

* mg/kg and mg/l are also ppm (parts per million)

Groundwater: Groundwater monitoring wells (MW-1 through MW-4) were bored and installed in the surface impoundment area in December 1987. Figure 2 indicates their locations. Table 2, taken from the Dames and Moore Groundwater Monitoring Results, 1988, gives the analysis of metals by EPA Method 6010.


Monitoring Well Conc. (ppm)
Metal Detection Limit (ppm) MCL (ppm) MW-1 MW-2 MW-3 MW-4

Antimony 0.05   <0.05 <0.05 <0.05 0.05
Arsenic 0.10 0.05 <0.10* <0.10* <0.10* <0.10*
Barium 0.02 1.00 0.58 0.07 0.12 0.19
Beryllium 0.02   <0.02 <0.02 <0.02 <0.02
Cadmium 0.01 0.01 <0.01 <0.01 <0.01 <0.01
Chromium 0.02 0.05 0.08* <0.02 <0.02 <0.02
Cobalt 0.01   0.06 <0.01 <0.01 <0.01
Copper 0.01 0.00 0.09 <0.01 0.02 0.02
Lead 0.10 0.05 <0.05 <0.10* <0.10* <0.10*
Mercury 0.05 0.002 0.05* <0.05* <0.05* <0.05*
Molybdenum 0.01   <0.01 <0.01 <0.01 <0.01
Nickel 0.10   0.10 <0.10 <0.10 <0.10
Selenium 0.10 0.01 <0.10* <0.10* <0.10* <0.10*
Silver 0.01 0.05 <0.01 <0.01 <0.01 <0.01
Thallium 0.10   0.20 0.10 0.10 0.10
Vanadium 0.01   0.11 <0.10 <0.01 <0.01
Zinc 0.01 5.00 0.12 <0.01 0.02 0.01

Data from Dames and Moore, "Groundwater Monitoring Results," 1988.
The * indicates metal concentrations which may exceed the MCL or maximum safe drinking water level (Safe Drinking Water Act).

The table below shows the concentrations of the metals of concern in the groundwater below the excavated surface impoundment. As shown, analytical Method 6010 has detection limits which are greater than the MCLs, or drinking water standards, for the metals arsenic, lead, selenium, and mercury. Therefore, it must be assumed that the concentrations of these metals could exceed drinking water standards. Chromium, mercury, and lead exceeded or equalled both the detection limit and the MCL.

Metal Conc(ppm) MCL (ppm) Detect.Lim (ppm)
arsenic <0.10 0.05 0.10
lead 0.10 0.05 0.10
selenium <0.10 0.01 0.10
mercury 0.06 0.002 0.05
chromium 1.0 0.05 0.02

No monitoring data from these wells were available for review after excavation of the surface impoundment, although additional sampling events were mentioned in the text. When questioned, the contractor's geologist reported that "all data was (sic) in the Pond Closure Report" (Kevin Brown, Dames and Moore, communication, July 3, 1990). The Dames and Moore Pond Closure Report, 1990, "recommends that the monitoring wells MW-01, MW-02, MW-03, and MW-04 be properly abandoned and no further sampling be conducted in the pond area" because "no indication of contamination has ever been detected in any of these four wells, throughout the course of nearly two years of quarterly sampling and analysis." The data available for review on the concentration of metals in groundwater, compared to their MCLs, do not support that statement.

California Water Service Well

Groundwater: The WPR well leased by CWS showed persistent 1,1-dichloroethylene (DCE) contamination (0.5 - 1.4 ug/L or ppb) and sporadic 1,1,2-trichloroethane (TCA) contamination (0.6-0.9 ug/L) from 1984 through early 1987. The well was removed from service since the contaminants were present at concentrations slightly above the MCL for DCE and TCA of 0.5 ug/L. The water from that well and three others located within three miles was used to supply water on a seasonal basis when the Feather River volume was low. The groundwater was blended with Feather River surface water. The well was returned to service when the MCL for DCE was raised to six ppb. No TCA was detected after March 2, 1987, and the well has been back in service with undetected levels since then. Data are from CWS quarterly sampling reports (CWS communication, July 1990). Analysis for metals was performed in 1986 and 1987 according to Title 22 Inorganic Requirements, and lead, mercury, arsenic, barium, and chromium were not detected (CWS communication, July, 1990).

B. Off-Site Contamination

Groundwater: There was no information on analysis of off-site domestic drinking wells or commercial production wells for TPH, metals, or volatile lower chain hydrocarbons such as benzene, toluene, and xylene.

Soil: A 1987 fire at the Koppers Oroville wood preservative treatment plant, which is just south of the WPR railyard, prompted the California Department of Health Services (CDHS) to analyze soils for dioxins (Draper, W. et al., 1988). Octachlorodibenzodioxin (OCDD) was selected as a marker for tetrachlorodibenzo(p)dioxin (TCDD) because it can be measured in soil quickly and relatively inexpensively, and its environmental fate and mobility are similar to TCDD. Soil sampling locations from 30 sites were chosen to be representative of the area around the Koppers wood treatment plant. Soil OCDD was detected at 4 of the 20 sites sampled that were north of Koppers. The measured levels were 6.5, 34, 59, and 240 ug/kg or ppb. Those levels were not considered a cause for concern resulting from direct exposure to soil.

Air: There has been no off-site air monitoring.

Biota: The investigation of the possible environmental contamination with TCDD as a result of the fire at Koppers wood preserving plant included analysis of eggs from chickens that scratched for food in the soils of the area, and beef from an animal that grazed in the same area as some of the chickens. Eggs were not taken from the same sites as the soil samples because the soil sample sites had been randomly pre-selected from a grid map of the area, and the sites did not necessarily correspond to homesites where range chickens were kept. That investigation clearly showed that chickens in the area are accumulating dioxins from some source. Sampling and analysis of chicken food, soil, water, air, bedding, and other media indicated that the likely source of dioxins was the soil. The concentrations of dioxins and the isomer patterns in an animal that was slaughtered in 1985 were essentially identical to those in an animal slaughtered in 1988. This suggests the exposure source pre-dated the fire at Koppers in 1987 (R. Chang et al., 1989).

C. Quality Assurance and Quality Control

In preparing this Preliminary Health Assessment, ATSDR relies on the information provided in the referenced documents and assumes that adequate quality assurance and quality control measures were followed with regard to chain-of-custody, laboratory procedures, and data reporting. The validity of the analyses and conclusions drawn for this Preliminary Health Assessment is determined by the comprehensiveness and reliability of the referenced information.

D. Physical and Other Hazards

There is a potential for physical hazards on the WPR site. The site is not fenced, thus allowing access at many points. The pits, the excavated underground storage tank, an uncovered manhole containing an oily liquid, and other structures in the fueling area could be hazardous to children playing on the site. There were also standing pools of oily water.


A. Environmental Pathways

On-Site Soil to Groundwater Migration

Roundhouse Area: On-site soil contamination data from the roundhouse or fueling area show that migration of high concentrations of petroleum products into the deeper soil layers has occurred. In the roundhouse area, surface soil concentrations of petroleum products range up to 24,000 ppm, and 5,750 ppm has been detected at 15 feet below ground level. In the area near the underground API separator, petroleum products at concentrations up to 11,400 ppm were found to have migrated 12 feet below the surface.

The method of analysis used to measure TPH involved an extraction step that allowed the volatile hydrocarbons below C10, such as benzene, toluene, and xylene, to vaporize. However, a soil-gas survey, which was performed in 1988 in the roundhouse area, established the presence of benzene, toluene, and xylene in the soils. The data are given in ion counts that are not absolute concentrations. However, they are a time-weighted flux of particular volatile compounds in soil gas and they are proportional to the concentration of the compounds in wet soil and, in some cases, in shallow groundwater. Since ion counts for benzene, toluene, and xylenes were above background counts, the concentration of TPH in the soils should be higher than reported. Tetrachloroethylene was present above background counts; therefore volatile organochlorine compounds were also present. And although petroleum hydrocarbons are not very soluble in water, the amount that is soluble has the potential to be of health concern from chronic exposure. There was no analysis of groundwater for low carbon number compounds available for review.

No analysis of metals in the soils of the roundhouse area has been performed. Repair and maintenance activities that generated heavy metals took place in that area, and aqueous and organic effluents containing metals were subsequently transferred in a ditch from the roundhouse to the API separator and then to the surface impoundment. Thus the migration of metals into soils and groundwater in the roundhouse area seems likely to have occurred. However, there was no analysis of metals in the groundwater monitoring wells of the roundhouse area available for review.

Surface Impoundment: The soils of the surface impoundment, after excavation of about eight feet of soil, contain up to 588 ppm TPH (see Table 1). The actual concentration of TPH in the soil is likely to be higher than that, since the extraction step in the analytical method allowed low carbon number chemicals, such as benzene, ethylbenzene, xylene, and toluene to escape. No analysis for those chemicals in soil or groundwater was available for review. Those chemicals are only slightly soluble in groundwater, but chronic exposure to low concentrations of benzene in drinking water would be a health concern.

The surface impoundment soils after excavation were also found to contain maximum and average concentrations of arsenic, barium, and chromium, which were below the TTLC (see On-Site Contamination and Dames and Moore, Pond Closure Report, 1990). However, there was no report of a WET to determine if concentrations met STLC criteria, and the STLC criteria are a measure of the tendency of materials to leach into groundwater. Title 22 of the California Regulatory Code specifies that wastes must meet both TTLC and STLC criteria and "be shown through experience or testing to (not) (sic) pose a hazard to human health or environment because of its carcinogenicity, acute toxicity, chronic toxicity, bioaccumulative properties, or persistence in the environment" (see On-Site Contamination).

Groundwater monitoring data from the surface impoundment area (MW-01 to MW-04) suggest that metals have migrated into the groundwater, which is 22 feet below the surface. The lowest concentrations of arsenic, lead, mercury, and selenium that the analytical method could detect was two to ten times higher than the safe drinking water standards or MCLs (see On Site Contamination). Concentrations of chromium, lead, and mercury were found at concentrations above their respective MCL (Dames and Moore, Groundwater Monitoring Report, 1988). It is not known if the concentrations of arsenic and selenium in groundwater are of concern since the detection limit exceeded the MCL. Furthermore, the analytical method used is not considered accurate for arsenic, mercury, and selenium (see On-Site Contamination). The monitoring wells are not current sources of drinking water. Those wells have screened intervals of 29-49 feet (MW-1), 35-75 feet (MW-2), 31-71 feet (MW-3), and 35-75 feet (MW-4). The well designated MW-1, which the contractors' report suggested was upgradient of the surface impoundment, had the highest detectable metal concentrations (Dames and Moore, Pond Closure Report, 1990). However, that well also draws water from the shallowest aquifers (On-Site Contamination), and the shallow and deep aquifers are thought to be interconnected (Central Valley RWQCB, Geohydrology and Waste Disposal-Roundhouse Area South of Oroville, California, 1971). Thus, the only groundwater monitoring data that were available for review (Kevin Brown, communication, 1990), suggest that metals have migrated from the surface impoundment into the shallow groundwater. Background levels were not taken; therefore the severity of the contamination cannot be confirmed.

The on-site well, leased to CWS as a municipal well, is 400 yards south, and presumably downgradient from the excavated surface impoundment. The contamination by 1,2-dichloroethylene and TCA in the years 1984-1987 indicates that migration of VOCs from soils in other areas of the site has occurred. This contamination may have originated from the unpermitted underground tank in the roundhouse area, which is east of the well and across the railyard (RWQCB, personal communication, 1990). That well had no detectable levels of metals when sampled in 1986 and 1987. However, that well at 150 feet draws water from the deep aquifer, but the monitoring wells in the surface impoundment, where the only analysis of metals in groundwater has been performed, are screened at 49-79 feet and they draw water from the shallower aquifers. Studies of the Oroville yard site indicate a great potential for groundwater contamination because of the high permeability of the dredger tailings, a mixture of gravel, clay, and sand which extends 40 feet below the surface, the short distance to the shallow aquifer, and the interconnections between the shallow and deep aquifers (Department of Water Resources, 1971). Thus, the current lack of contamination in the CWS well may indicate low leaching rates due to the five-year drought and do not assure that heavy metals, low molecular weight petroleum hydrocarbons, and volatile aromatic compounds from the roundhouse and surface impoundment will not contaminate it in the future.

Potential for Groundwater Contaminants to Migrate Off-site

The site is on dredger tailings consisting of heterogeneous deposits of gravel, clay, and sand. Dredging for gold has mixed the surface gravel with the deeper and older geological formations. Groundwater occurs in an unconfined shallow perched aquifer approximately 22 feet below the surface, which has interconnections to the deeper aquifers (Department of Water Resources, 1971). The RWQCB Geohydrology Report concluded in 1971 that there were both natural and artificial interconnections between the shallow and deeper aquifers, so that wastes could reach the deeper groundwater. Therefore, the potential for off-site contamination of groundwater is great. However, no off-site groundwater sampling has been performed.

Potential for Airborne Contaminants to Migrate Off-Site

The contents of the surface impoundment were set afire periodically. The impoundment is thought to have contained varying amounts of aqueous solutions, chlorinated solvents, and such petroleum products as lubricating grease, diesel fuel, gasoline, and oil from the roundhouse area. Dioxins and furans have been reported to be products of the low-temperature combustion of mixtures such as those (Weerasinghe and Gross, 1985). Soot and flyash containing dioxins and furans may have been carried by the wind to the soils of the surrounding area. Sampling of soils, dust, vegetation, and stream vegetation in the area for dioxin and furan contaminants was performed by California DHS staff after the 1987 fire at the Koppers' wood treatment site (see Off-Site Contamination). Soils north of Koppers, in the area near the WPR site, contained dioxins in the ppb and ppt range. Chicken eggs from hens that foraged for food showed evidence of bioaccumulation, as did tissues of local ducks and dogs. Comparison of dioxin levels and isomer patterns in animal tissues slaughtered before and after the fire suggested that the dioxin contamination of soils pre-dated the 1987 fire (Chang, R. et al., 1989). Therefore, other sources in the region are being considered. On-site sampling and analysis is needed to determine if this burning was a source of dioxins and furans which migrated to soils in the surrounding area.

B. Human Exposure Pathways

Groundwater: Reports from the retired environmental health officer for Butte County (Communication, May 1990) and the CWS manager (Communication, July 1990), indicate that there are domestic wells and off-site industrial production wells that represent potential human exposure pathways. The identities and locations of those wells are found in Appendix 2, "The Well Inventory for Western Pacific Railroad."

The on-site CWS well, downgradient of the surface impoundment, does not currently show contamination. That well produced 58.8 million gallons of the 1,050.7 million gallons of water supplied by CWS in 1989 (CWS personal communication, July, 1990). Although the well was contaminated by 1,1-dichloroethylene and TCA that slightly exceeded safe drinking water standards in the years 1984-1987, the well was used only seasonally, and the water was blended with water from other CWS wells, and with Feather River water. Thus, there was no human exposure of health concern. It did not have metal contamination when last monitored in 1987 (Craig Gilmour, communication, July, 1990).

Air: The surface impoundment was set on fire periodically to burn off the upper level of organic hydrocarbons that would accumulate (Environmental Health Director, retired, personal communication, July, 1990). The burning petroleum products and chlorinated hydrocarbons have been known to produce dioxins and furans as products of combustion (Weerasinghe and Gross, 1985), and contaminated soot and flyash may be transported by wind to soils over a wide area.

Soil: Soil concentrations of OCDD, taken by California DHS scientists after the 1987 Koppers fire indicated that dioxins were not considered high enough to be a source of concern for dermal (skin) exposure, or from incidental ingestion while gardening (see Off-Site Contamination).

Biota: Analyses of dioxins and furans in beef and in eggs from locally raised range chickens are discussed in Off-Site Contamination. Those studies revealed that dioxins were present in beef before the Koppers fire, and that the eggs from range chickens and the beef from cattle that grazed in the area appeared to have bioaccumulated dioxins (Chang, et al., 1989; Goldman et al., 1989).

The elevated levels of dioxins in locally produced chicken eggs, coupled with the egg consumption information reported by consumers themselves, led DHS scientists to conclude that a significant risk from dioxin exposure exists for individuals who consume eggs from range chickens in the area of South Oroville (Goldman et al., 1989).

Serum samples were taken from residents in two exposed households and matched with rural comparison subjects. Preliminary dioxin data show statistically significant elevations of 2,3,7,8-tetra, penta and hexa dioxin levels in serum. Residents in a household where both dioxin-contaminated beef and eggs were found, and where the residence time was longer than two years, had even greater serum levels of 2,3,7,8-tetra, penta and hexa dioxins (Goldman et al., 1989). An apparent dose-response relationship exists with diet and/or duration of exposure.


Two areas of the WPR site have high concentrations of contaminants in surface soils and in deeper soils. Those contaminants may migrate through on-site groundwater to the well leased by CWS for municipal drinking water for Oroville and to domestic and industrial wells south of the site.

Surface impoundment soils contain petroleum products which appear to have migrated into the shallow groundwater. The analysis method for TPH in soil does not accurately measure benzene, xylene, and toluene, which can vaporize during the extraction step; therefore the concentration of those compounds in soil or shallow groundwater is not known. Groundwater around the surface impoundment may contain arsenic, lead, mercury, selenium, and chromium at concentrations two to ten times higher than the safe drinking water standards or MCLs (see On-Site Contamination).

Surface soils in the roundhouse area contain petroleum products, organochlorines, and possibly metals. That area has not been remediated, except for excavation of an unpermitted underground storage tank that has been proposed as a possible source of the groundwater contamination in one well in the roundhouse area. TPH contamination levels up to 24,000 ppm have been detected in soil borings; therefore the Phase II Investigation is designed to determine vertical and horizontal extent of the contamination. Organochlorines have been detected in the groundwater of the monitoring wells in the roundhouse area. However, the groundwater in the roundhouse area has not been analyzed for low carbon number petroleum products such as benzene, xylene, and toluene. The activities that took place in that area also make heavy metal contamination a possibility.

Periodic burning of the organic layer containing VOCs and petroleum products on the surface impoundment may have created dioxins and furans which could subsequently have been dispersed by the wind to surface soils in the area. Ingestion of soil by range chickens which scratch for food, and by locally grazed cattle would be a potential pathway for the bioaccumulation of dioxins and furans in the fat of those food sources for humans.

A. Toxicological Evaluation

Levels of possible exposure to site-related chemicals are not known, since there is inadequate data for on-site contaminant levels. Since the exposure level is not known, the toxicological response and implications cannot be known, since the response is proportional to the dose of a hazardous chemical. A description of the toxicological effects of the chemicals discussed and the exposure levels at which the effects occur appears below.

Arsenic: Arsenic is an element that has been classified as carcinogenic in human beings (class A) on the basis of human epidemiological data (EPA Carcinogen Assessment Group). A dose-response relationship has been seen between skin cancer prevalence rates and arsenic exposure in the drinking water. However, no increases in skin cancer were seen in persons exposed for up to ten years to water containing about 300 ppb arsenic, suggesting that there may be a threshold below which the dose of arsenic is insufficient to cause cancer. Because the number of persons studied was small, it was decided that this study was not sufficient to conclude that a threshold for arsenic-induced cancer exists. Doses as low as about 1-4 mg/day (20 - 60 ug/kg/day) in adult humans produce one or more characteristic signs of arsenic toxicity, such as gastrointestinal irritation, anemia, neuropathy, skin lesions, vascular lesions, and hepatic or renal injury (ATSDR, 1987).

Chromium: Chromium is found in two states, trivalent (III) and hexavalent (VI). Chromium III, the trivalent form, is considered almost innocuous and it is required as an essential nutrient in amounts of 50-200 ug/day (0.7-3 ug/kg/day) in adult human beings. Chromium VI, the hexavalent ion, has been classified as a known carcinogen in human beings due to increases in mortality from cancers of the respiratory tract in workers exposed to chromium-containing aerosols. Inhalation of 0.002 mg/m3 chromium can cause nasal irritation and mild lung effects. Chromium is poorly absorbed from the digestive system of human beings and chronic oral studies in rodents are inconclusive. While some studies in rodents have not identified adverse effects on toxicological endpoints, other studies have reported that, at high oral doses in female mice, chromium attacks the digestive system by causing hemorrhaging, ulceration, and tubular necrosis of the kidneys. In order to be consistent with a policy to protect public health, chromium is assumed to be carcinogenic by ingestion as well as by inhalation, but the potencies may vary by several orders of magnitude.

Lead: Lead is an element that affects the nervous system, the heme-hemoprotein system, the kidneys, and the reproductive system. Developmental defects measured as decrements in I.Q. are seen in offspring of mothers with 10-16 ug lead/deciliter (dl) of umbilical cord blood. Alterations in heme synthesis are found when blood concentrations of lead reach 15 to 30 ug/dl, and the concentration of free erythrocyte porphyrins is often used as an indicator of exposure. Anemia appears at 75 ug Pb/dl of blood in children, and at 80-85 ug Pb/dl of blood in adults. Calcium, phosphate, and iron may affect absorption of lead. The risk of premature birth increases four-fold as cord or maternal blood lead levels increase from less than 8 to greater than 14 ug/dl. The range of 10 to 15 ug/dl is considered to be the lowest observed adverse effect level (LOAEL) for developmental toxicity manifested as neurobehavioral deficits and reductions in gestational age and birth weight in human beings. Lead in humans is associated with reproductive toxicity such as miscarriages and decreased fertility and sperm abnormalities at 40 to 50 ug/dl. In rats, developmental reproductive defects are seen at 18 to 29 ug/dl in females, and at 30 ug/dl in males. There is no conclusive evidence about teratogenic effects.

Mercury: Mercury occurs in many chemical forms, including elemental, organic, and inorganic such as the chloride salt (mercuric chloride). Toxicity occurs only if mercury is in a form that can be absorbed. Absorption of metallic mercury is poor, whereas absorption of methyl mercury, the organic form, is complete. Organic mercury has historically been known to cause tremors, irritability, tics and mental problems; e.g., people who made felt hats in the past used mercury and could become "mad as a hatter," as in Alice in Wonderland. Intrauterine poisoning by methyl mercury can result in tremors, irritability, retardation and cortical blindness of the newborn.

Ingestion of metallic mercury usually results in diarrhea. Inhalation of metallic mercury at 130 ppb for three hours causes chest pains, coughing, and shortness of breath. Inhalation of metallic mercury for eight hours at levels of 5,400 ppb results in persistent irritability and lethargy and lack of sexual desire. At higher doses, mercuric chloride causes irritation, superficial corrosion of exposed tissues and chronic effects of kidney damage, intestinal hemorrhaging, and ulceration.

Benzene: Benzene is designated a class A carcinogen in human beings on the basis of epidemiological evidence in humans that it causes acute myelogenous and monocytic leukemia. Benzene is a hydrocarbon that at higher doses also causes hematological toxicity including myelocytic anemia, thrombocytopenia, and leukopenia. Although individual workers vary in their reactions to benzene, the toxicity appears to be a function of both exposure level and exposure duration. Chronic inhalation exposure to levels of approximately 10 ppm are associated with aplastic anemia and leukemia.

Toluene: Toluene is an aromatic hydrocarbon similar to benzene. Inhalation is the main route of exposure, and exposure is usually related to the workplace or to substance abuse (glue or solvent sniffing). Toluene is not considered carcinogenic, and the minimal risk level (MRL) of one ppm is designed to protect against adverse mental effects. Inhalation of 100 ppm for six hours causes fatigue, sleepiness, decreased manual dexterity, decreased color discrimination, and decreased accuracy in visual perception. Inhalation of 200-800 ppm initially causes excitatory effects such as exhilaration and lightheadedness, followed by development of narcosis, which is characterized by impaired intellectual, psychomotor and neuromuscular effects. A chronic exposure to 300 ppm for one to ten years will produce impaired memory. Cardiac arrhythmias and liver and kidney dysfunctions have been seen after very high exposures.

Xylene: Xylene is another hydrocarbon which produces most of its effects through inhalation. An exposure of 100 ppm for one day causes eye, nose, and throat irritation. Near 300 ppm exposures for one hour increase visual stimulus response times. Air concentrations of 460 ppm can change the lens of the eye.

PAHs: PAHs (polynuclear aromatic hydrocarbons) are part of a broad class of chemicals derived from petroleum products. Many compounds are of concern, such as benzo(a)pyrene, because they are classified as probable carcinogens in human beings. However, many compounds of similar structure are not carcinogenic. PAHs localize in body fat and in fatty tissues such as the breast. Metabolism occurs by cytochrome P450-dependant monooxygenases.

TPHs: TPH stands for total petroleum hydrocarbons. Petroleum hydrocarbons include a wide variety of organic compounds from low carbon number volatile chemicals (C6 - C10) such as benzene, xylene, and toluene, to the straight chain carbon compounds (C10 - C20) in diesel fuel, to high carbon number aromatic compounds such as benzo(a)pyrene. Some compounds are classified as carcinogens, and some are not. Straight chain carbon compounds (alkanes) of five or more carbons have strong narcotic properties. Solubility in water is highest for the low molecular weight aromatic compounds, then it decreases through the series: aromatics, alicyclic compounds, branched chain alkanes and n-alkanes. Within each series, solubility decreases with increasing molecular weight or carbon number.

1,1-Dichloroethane (DCA): 1,1-Dichloroethane is a chlorinated hydrocarbon which is classified as a possible (class C) carcinogen in humans based on limited data of an increased incidence of mammary gland tumors and a rare tumor of blood vessel linings in female rats, and of liver tumors and benign uterine polyps in mice. Inhalation of 500 ppm for extended periods of time can cause kidney damage.

1,1-Dichloroethylene (DCE): 1,1-Dichloroethylene is also known as vinylidene chloride. It can be produced in groundwater as a breakdown product of other volatile organochlorines. Consequently, it has frequently been found in drinking water in the United States at low concentrations. The safe drinking water concentration (MCL) is seven ppb. Although there are negative and inconclusive animal studies, 1,1-dichloroethylene has been classified as a possible carcinogen in humans (class C) because male mice with severe kidney damage were found to also have kidney tumors after inhalation exposure. Inhalation by mice of levels of 20 ppm for 90 days showed decreases in weight, and 200 ppm for 90 days resulted in liver cell vacuolization.

1,1,2-Trichloroethane (TCA): 1,1,2-Trichloroethane is a chlorinated solvent that causes temporary stinging and burning when it touches the skin. There is no other information on health effects in human beings. The safe drinking water level (MCL) is 0.6 ppb. Based on animal studies, it is classified as a possible carcinogen in human beings (class C) because it produces liver and endocrine (adrenal cortex) tumors in several strains of mice.

Trichloroethylene (TCE): Trichloroethylene is a solvent that has been shown to produce liver tumors in several strains of mice. It has also been used as an anesthetic because it depresses the central nervous system, resulting in incoordination and unconsciousness. An exposure of 100 ppm for eight hours inhibits psychophysiological performance. Levels of 170 ppm cause decreases in pulse rate and blood pressure. At one time, EPA classified trichlorethylene as a probable human carcinogen based on animal studies. EPA has withdrawn this classification while conducting a review of the carcinogenicity of trichloroethylene. The International Agency for Research on Cancer (IARC), has determined that trichloroethylene is not classifiable as to human carcinogenicity. Until more experimental evidence is available, either from human or animal studies, we cannot determine whether exposure to trichloroethylene is likely to cause cancer.

2,3,7,8-tetrachlorodibenzo(p)dioxin (TCDD) is the most potent of a group of chemicals known as dioxins and furans which are frequently found as contaminants in the manufacture of polychlorinated phenols, which involves combustion, and in soot, flyash, and many other products which have been burned. Municipal waste incinerators, coal and fossil fuel plants, chemical waste burners, fireplaces and wood stoves, gasoline and diesel powered combustion engines, charcoal grills, and cigarette smoke have been postulated to be sources of dioxins and furans (Weerasinghe and Gross, 1985). Most of our information about the effects of TCDD on human health has been obtained from studies of workers who were exposed to TCDD (R.D. Kimbrough et al., 1984), or of citizens exposed in accidents such as the one at Seveso, Italy. In many cases, precise exposure data are not available. However, it can be concluded that humans are not so sensitive to the toxic effects of TCDD as such animals as the guinea pig. In some cases, workers developed chloracne but no systemic illness. In other cases there have been complaints of weight loss, easy fatigability, aching muscles, insomnia, irritability, loss of libido, and sensory changes. The liver has become tender and enlarged, and decreased nerve conduction velocity has been reported (R. D. Kimbrough et al., 1984). Based on data on liver cancer or neoplastic nodules in rats and mice, TCDD is considered to be a class B2 or probable carcinogen in human beings.

B. Health Outcome Data Evaluation

Insufficient data currently exist to allow adequate characterization of exposure pathways. Additional data on possible human exposure concentrations are required to ascertain if people were exposed to site contaminants at concentrations high enough for adverse health effects to occur. That information would determine whether it is possible to use the available epidemiological health related data to define health affects from site contaminants. Therefore, further review of data from the Cancer Surveillance Program and the Birth Defects Monitoring Program does not appear necessary at this time.

Also, as discussed under the section on Health Outcome Data, the Cancer Surveillance Program began collecting data in 1988 for the region that includes the Western Pacific Railroad site. This cancer incidence information may ultimately be useful in a future cancer investigation, but with only one year of data, should be viewed carefully since background cancer rates for the population are undefined and the first year of cancer reporting usually results in underreporting.

The Environmental Epidemiology and Toxicology Branch of CDHS has been conducting studies in Oroville since 1985 related to pentachlorophenol contamination in the drinking water. Additionally, after the Koppers fire in 1987, CDHS investigated dioxin contamination in the surrounding community. Appendix C provides information released to the Oroville community in May 1991 about those studies. Although those studies may not directly involve the Western Pacific Railroad site, they are taking place in the same community.


From the information reviewed, this site is classified as an indeterminate public health hazard. This category is used for sites with incomplete information. The limited available data do not indicate that humans are being or have been exposed to levels of contamination from the site that would be expected to cause adverse health effects. However, the location and amount of contamination on site are not yet well characterized and analysis of all environmental media has not been done to determine if potential pathways for human exposure could be complete pathways.

The available data suggest that servicing and repair of railcars at the roundhouse area generated petroleum product wastes, VOC solvent waste, and heavy metal wastes which have migrated into the soils on site. It appears likely that those contaminants have migrated or will migrate into groundwater. If the source of VOC contamination in the on-site well leased to CWS was the unpermitted underground tank in the roundhouse area, migration of VOC contaminants from the roundhouse to deeper aquifers has already occurred. However, no humans were exposed to VOC contaminants from that well at concentrations exceeding safe drinking water standards. Analysis of off-site wells for VOCs, metals, and lower molecular weight petroleum products (less than C10) and of the on-site well for metals and lower weight petroleum hydrocarbons, is necessary to determine if human exposures are occurring.

The available data on the excavated surface impoundment, where wastewater from the roundhouse area was discharged, indicate that heavy metals have migrated into the shallow groundwater. Metals and lower molecular weight petroleum products from that area could also have migrated into the shallow groundwater on site. Since there are interconnections between the shallow unconfined aquifer and the deeper confined aquifer in the dredger tailings, contaminants may migrate into deeper aquifers on site and off site where humans could be exposed.

Dioxins and furans have been found within a mile of the site. Although there is no evidence that the WPR site is the source, the activities on-site make it a possibility. Therefore, on-site soils should be analyzed for dioxins and furans.


Site Characterization Recommendations

The available data on hydrogeology are from 1971 and were derived from out-of-date and inaccurate methods. The groundwater monitoring well data from the surface impoundment area suggest that the hydrogeology of the area should be studied to define the direction of groundwater movement and the potential for contamination.

The soils and the shallow and deep groundwater in the roundhouse area should be sampled and analyzed for heavy metals to determine the extent of groundwater contamination. Analytical methods with detection limits less than or equal to the MCL should be used.

Sampling and analysis of the groundwater under the excavated surface impoundment using a method with detection limits less than or equal to the MCLs should be performed to define the extent of migration of heavy metals into the aquifer.

The soils and groundwater in the excavated surface impoundment should be sampled and analyzed to determine if benzene, xylene, and toluene have migrated to soils and groundwater below the level of excavation of the surface impoundment. Analytical methods which preserve aromatic hydrocarbons are recommended, e.g., EPA Methods 5030/8020.

Measures should be taken to assure that the groundwater on site does not exceed maximum contaminant levels before developing any residential or commercial uses requiring domestic wells.

Soils on the site should be sampled for dioxins and furans to determine if the WPR site was a source for the dioxin contamination of soils, chicken eggs, and locally grazed cattle seen off site.

Records of Western Pacific Railroads should be obtained to better delineate activities on the site and to determine if analysis of soils for other such chemical contaminants as polychlorinated biphenyls (PCBs) should be performed.

Health Activities Recommendation Panel (HARP) Recommendations

In accordance with the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) as amended, the Western Pacific Railroad site has been evaluated for follow-up health activities. There are no indications that human beings have been or are being exposed to site-related contaminants at concentrations of public health concern. Therefore, this site is not being considered at this time for follow-up health activities. However, there is a need for further site characterization and sampling of on-site soils for metals, volatile organochlorine compounds, low molecular weight volatile polycyclic aromatic hydrocarbons, and dioxins and furans to determine potential human exposure pathways of concern. In addition, the source of the identified off-site dioxin and furan contamination in the Oroville area is not known at the present time. However, the site and other sites in the area are considered possible sources of the off-site dioxin and furan contamination. The California Department of Health Services will continue to investigate all possible sources. If data become available suggesting that human exposure to hazardous substances at levels of public health concern has occurred or is likely to occur, ATSDR will reevaluate the site for any indicated follow-up health activities.


Public Health Actions Planned

Based on HARP recommendations, at this time ATSDR and CDHS are not planning any follow-up health activities. The Regional Water Quality Control Board will consider incorporating additional hydrogeological data, and the sampling of soil and groundwater for heavy metals, benzene, xylene, and toluene into the workplan being developed for the Remedial Investigation/Feasibility Study. Additional sampling of on-site soils for dioxin and furans and other possible contaminants will also be considered. The Regional Water Quality Control Board will continue to work with Union Pacific Railroad to delineate the extent of the diesel fuel contamination in the fueling area and to investigate the appearance of chlorinated solvents in the area between the excavated tank near the roundhouse and the California Water Service well. ATSDR and CDHS will coordinate with the appropriate agencies regarding actions to be taken in response to those recommendations provided in this preliminary health assessment for which no plan of action has yet been developed.



  1. California Regional Water Quality Board -- Central Valley Region. "Oroville Oil Seep, Butte County." Sacramento, CA. July 1985.

  2. Capouya, Renee. "Contact Report with Ray Taylor, California Water Service Co." EPA file reference #11. September 1987.

  3. Capouya, Renee. "Contact Report with Sara Demzler, Central Valley Regional Water Quality Control Board." EPA file reference #12. September 1987.

  4. Central Valley Regional Water Quality Control Board. "Geohydrology and Waste Disposal -- Roundhouse Area South of Oroville, California." Sacramento, CA. October 1987.

  5. Central Valley Regional Water Quality Control Board. "Sampling Summary Filed Notes Union Pacific Railroad Sump, Oroville." Sacramento, CA. August 1987.

  6. Chang, Ruth, Douglas Hayward, Lynn Goldman, Martha Harnly, Jennifer Flattery, Robert Stephens. "Foraging Farm Animals as Biomonitors for Dioxin Contamination." Chemosphere 19: 1-6, 481-486, 1989.

  7. Dames and Moore. "Fueling Area Progress Report Union Pacific Railroad Sump Oroville, CA." Sacramento, CA. March 1989.

  8. Dames and Moore. "Ground Water Monitoring Results UPRR -- Oroville." Sacramento, CA. March 1988.

  9. Dames and Moore. "Phase II Site Investigation Work Plan Union Pacific Railroad Fueling Area, Oroville, CA." Sacramento, CA. April 1990.

  10. Dames and Moore. "Pond Closure Report Union Pacific Railroad, Oroville, CA." Sacramento, CA. February 1990.

  11. Dames and Moore. "Waste Classification Union Pacific Railroad Runoff Pond Oroville, CA." Sacramento, CA. January 1988.

  12. Department of Health Services. "Preliminary Assessment Summary Western Pacific Railroad." Sacramento, CA. December 1983.

  13. Department of Health Services. "Sample Plan Western Pacific Railroad." Sacramento, CA. October 1985.

  14. Department of Water Resources. "Ground Water Quality Investigation Roundhouse Area, Oroville, California." Sacramento, CA. June 1973.

  15. Draper, William M., Jane Phillips, Martha Harnly, Robert Stephens. "Assessing Environmental Contamination from a Pentachlorophenol Fire: Screening Soils for Octachlorodibenzo-p-dioxin." Chemosphere 17: 1831-1850, 1988.

  16. Ecology and Environment, Inc. "Site Inspection Summary of Western Pacific Railroad, Oroville, California." San Francisco, CA. June 1988.

  17. Goldman, L.R., D.G. Hayward, J. Flattery, M.E. Harnly, D.G. Paterson, Jr., L.L. Needham, D. Siegel, R. Chang, R.D. Stephens, K.W. Kizer. "Serum Adipose and Autopsy Tissue PCDD and PCDF Levels in People Eating Dioxin Contaminated Beef and Chicken Eggs." Chemosphere 19(1-6): 841-848, 1989.

  18. Goldman, L.R., D.G. Patterson, Jr., L.L. Needham, J. Flattery, M. Harnly, D. Siegel, and R.D. Stephens. "Serum PCDD and PCDF Levels in People Eating Dioxin Contaminated Beef and Chicken Eggs." Manuscript in Preparation.

  19. Kimbrough, Renate D. Henry Falk, Paul Stehr and George Fries. "Health Implications of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) Contamination of Residential Soil." Journal of Toxicology and Env. Hlth. 14:47-93, 1984.

  20. Nelson, Lisa. "Contact Report with Jim Bailey, California Water Service Co." EPA file reference #8. March 1989.

  21. Nelson, Lisa. "Contact Report with Phil Woodward, California Regional Water Quality Control Board, Region 5." EPA file reference #18. March 1989.

  22. Noffke, Julie. "Contact Report with Ron Rogers, Department of Fish and Game, Wildlife Management." EPA file reference #14. April 1988.

  23. Noffke, Julie. "Contact Report with Sara Demzler, Central Valley Regional Water Quality Control Board." EPA file reference #10. May 1988.

  24. Stumph, Terry, Acting Chief Laboratory Support Section, Environmental Services Branch, OPM. "Review of Analytical Data for Case 5114/1677Y Western Pacific Railroad." San Francisco, CA. January 1986.

  25. Taylor, Raymond H. ("Monitoring Results for California Water Service Company Well on UPRR property.") EPA file. San Jose, CA. 1986.

  26. U. S. Environmental Protection Agency. "Western Pacific Railroad Co. Oroville, CA." National Priorities List. July 1989.

  27. Weerasinghe, N.C.A. and M.L. Gross. "Origins of Polychlorodibenzo-p-dioxins (PCDD) and polychlorodibenzofurans (PCDF) in the Environment" p. 133 - 151. In: Dioxins in the Environment, M.A. Kamrin and P.W. Rodgers, Editors, Hemisphere Publishing Corp. New York, 1985.



Susan Ann Knadle, Ph.D., DABT
Staff Toxicologist
Hazardous Waste Toxicology Section*
Office of Health Hazard Assessment

Jennifer Rous, B.S.
University of California at Davis
Student Intern in the Hazardous
Waste Toxicology Section*

Diana M. Lee, MPH
Research Scientist
Environmental Epidemiology and Toxicology Program

Jane Riggan, MSW
Community Relations Coordinator
Impact Assessment, Inc., Consultant to
Environmental Epidemiology and Toxicology Branch


Gwendolyn Eng
Regional Operations, Region IX
Office of the Assistant Administrator

William Nelson
Regional Operations, Region IX
Office of the Assistant Administrator


Burt J. Cooper, M.S.
Environmental Health Scientist
Division of Health Assessment and Consultation
Remedial Programs Branch
State Programs Section

*Before 7/19/91, the Hazardous Waste Toxicology Section was a section under the Environmental Epidemiology and Toxicology Branch within the California Department of Health Services.


This preliminary health assessment was prepared by the California Department of Health Services under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health assessment was initiated.

Burt J. Cooper
Technical Project Officer, SPS, RPB, DHAC

The Division of Health Assessment and Consultation, ATSDR, has reviewed this health assessment and concurs with its findings.

Director, DHAC, ATSDR

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