PUBLIC HEALTH ASSESSMENT
GBF & PITTSBURG DUMPS
ANTIOCH, CONTRA COSTA COUNTY, CALIFORNIA
The California Department of Health Services (DHS) has prepared this public health assessment under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). The public health assessment is a mechanism to provide the community with information on the public health implications of specific hazardous waste sites and identify those populations for which further health actions or studies are indicated.
The GBF/Pittsburg Landfill(s) site recieved municipal waste from the mid 1940s until March 1992. During the 1960s and 1970s, hazardous solid and liquid wastes including heavy metals, pesticides, volatile organic compounds, polychlorinated biphenols, acids, phosphorus ordinance, and medical waste were also disposed of at the site. During this period, numerous complaints were filed by the community about chemical odors from the site and symptoms of burning eyes and irritated lungs. In recent years, community concerns have been addressed through community meetings and fact sheets. In the course of preparing this public health assessment, we did not discover any current community health concerns.
Exposure to airborne contaminants to on-site workers and nearby community members did occur in the past, but data are not available to evaluate those exposures. The site currently poses no apparent public health hazard, and conditions are not expected to change in the future. The potential for inhalation exposure from releases of contaminated soil gas does exist, but those possible exposures would be below levels of health concern. No other potential present or future completed exposure pathways have been identified.
Significant future exposure to site-related contaminants is unlikely if: 1) migration of groundwater contamination is controlled; 2) remediation efforts reduce groundwater contamination to below levels of health concern; 3) no future drinking water wells are placed in areas of known contamination until remediation has reduced contaminant concentrations below levels of health concern; 4) any future excavation/construction projects at the site take the necessary precautions to insure that workers are not exposed to contaminants above levels of health concern; 5) deed restrictions restrict future development of the site; 6) the landfill gas collection and destruction system adequately controls the lateral transport of landfill gas; and 7) the cap is strictly maintained.
ATSDR and CDHS has made recommendations to reduce and prevent exposure to contaminants and to better characterize the contamination at and nearby the site. Follow-up health activities are not indicated at this time. As additional data becomes available, ATSDR and the California Department of Health Services may reevaluate this site for any indicated follow-up health activities.
The California Department of Health Services (CDHS) has prepared this public health assessment under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). ATSDR, located in Atlanta, Georgia, is a federal agency within the United States Department of Health and Human Services. ATSDR is authorized under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980 to conduct health assessments at hazardous waste sites on the National Priorities List. This public health assessment evaluates the public health significance of the GBF/Pittsburg Landfill site and is based on a review of environmental monitoring data, a site visit, and consultation with involved agencies and the public.
The GBF/Pittsburg Landfills (site) occupies 88 acres located northeast of the intersection of Somersville Road and James Donlon Boulevard in Antioch, Contra Costa County, California. A site location map is provided in Figure 1 (Appendix A). The site consists of two contiguous smaller properties which formerly operated as separate landfills which were consolidated in 1987 (1). As shown in Figure 1, the former GBF landfill comprised the eastern 63-acre parcel of the site, and the former Pittsburg landfill comprised the western 25-acre parcel of the site.
The 88-acre property and surrounding smaller parcels were owned by the J. Prewett family from 1904 to 1974, when property ownership transferred to the GBF Company. On December 20, 1977, the 88-acre property and surrounding smaller parcels was transferred to Silvio and Mary Garaventa, the current owner of the property.
Former Pittsburg Landfill
The former Pittsburg landfill was leased by the City of Pittsburg in 1946 for use as a municipal solid waste disposal facility. A land use permit was granted November 5, 1958, by the Contra Costa County Board of Supervisors to the City of Pittsburg for the disposal of municipal waste. From 1946 until 1992, at least four different companies operated the landfill for the City of Pittsburg. The Pittsburg Landfill was permitted to accept Group II and Group III materials only. However, historical records indicate that industrial liquid wastes were also disposed at the Pittsburg Landfill (1). In 1975, 20,000 pounds of "M-2 Incendiary Oil Thickener" containing magnesium paste, gasoline and isobutyl methacrylate (as hazardous materials) was deposited on the site (2). In 1987, Contra Costa Waste Service, Inc. (CCWS) consolidated waste disposal operations on the Pittsburg Landfill and the adjacent GBF landfill and established the Contra Costa Sanitary Landfill (a Class III facility). The Contra Costa Sanitary Landfill accepted municipal waste until March 1992.
Former GBF Landfill
The former GBF Landfill property was operated under a land use permit granted March 8, 1960, by the Contra Costa County Board of Supervisors. The Contra Costa Waste Service, Inc. (CCWS) leased the property from the J. Prewett family in 1958 for the purpose of operating a solid waste disposal facility. CCWS established such a facility on the northwest corner of the property. Historical records indicate that operations in the early 1960s included disposal of municipal waste and garbage, as well as containerized and liquid industrial wastes. Most of the municipal and solid waste (garbage) went into a central dumping area; old tires, out-dated medical supplies and drugs, barrels/drums of solvents, acids and other liquid materials were placed in trenches (2).
In the mid 1960s, Industrial Tank Inc. (IT) sub-leased a portion of the property from CCWS for the purpose of disposing liquid industrial waste. The IT Class I and II waste disposal facility consisted of ten unlined ponds. Liquid wastes (acids, solvents, oils, sulfonation tars, sludges, liquid metal wastes, etc.) were deposited in the ponds and allowed to evaporate to the atmosphere and percolate into the ground. Unknown quantities and types of phosphorous ordinance from the Department of Defense were also disposed of at the facility (2).
Both the former GBF and Pittsburg Landfills had several incidents of underground fires, pond fires, fires in trenches and explosions during the 1960s and 1970s (1). During one such fire on March 16, 1973, evidence of beryllium scrap was found in a trench next to one of the IT ponds. Because of concern over the potential for inhalation of beryllium fumes, 15 Riverview Fire District firemen were sent to the hospital for medical evaluations (1).
During the years 1960-1974, numerous complaints about both the Pittsburg and GBF facilities were filed by the community with the Bay Area Air Quality Management District (BAAQMD)(1) and other agencies. Complaints ranged from "smells bad", "looks bad, smells worse", "odors drifting off-site", to "parts of my home are disintegrating due to the site" (2). Complaints of strong oily and chemical odors were accompanied by symptoms of burning eyes and irritated lungs. An inspection conducted by the BAAQMD in 1973 revealed evidence of corrosion of metal surfaces on structures and residential areas located north and east of the site.
IT operated its percolation and evaporation ponds under waste discharge permits issued by the California Regional Water Quality Control Board (RWQCB), Central Valley Region. The permits stated that IT "shall not cause a pollution of usable ground or surface waters", and shall not "cause a nuisance by reason of odors or unsightliness" (2). In 1974, as a result of the complaints, fire hazards, urban build-up within 100 yards, and concern by the RWQCB that wastes could migrate from the property and contaminate groundwater in the area, the RWQCB ordered the owners and operators of the facility to convert the site from a Class I to a Class II facility.
From May 1974 through May 1978, Industrial Tank, Inc. closed the ten ponds and converted the property to a Class II disposal facility. The conversion process consisted of draining the waste oil ponds, adding Group II and III materials as absorbents to the acid ponds, covering with clean dirt, and then capping with impervious clay. In addition, closure procedures called for placement of leachate collection systems and groundwater monitoring wells. However, these wells were placed too shallow and were always dry (2). Industrial Tank, Inc. disposed municipal waste above and around the former liquid waste ponds until 1987, when CCWS consolidated waste disposal operations on the GBF and Pittsburg Landfills and established the Contra Costa Sanitary Landfill, which accepted municipal waste until March 1992. The site is currently undergoing closure activities, including capping the landfill with one foot of clay and three feet of soil.
History of Agency Involvement
In a November 1, 1977 report by the Contra Costa County Health Services Department (CCCHSD) to the Contra Costa County Board of supervisors, the author stated that the "...GBF disposal site at present does not constitute an imminent hazard to the health of residents of the adjacent properties" (2).
At a July 24, 1979 meeting of the Antioch City Council and Antioch Development Agency, the California Department of Toxic Substances Control (DTSC)(2) noted that "... most of the liquids were transported elsewhere in 1974 and solid waste added to absorb the remaining residues; that the site is being closed in a manner which poses minimum hazard(s) to public health and the environment" (2).
In 1983, the Property Evaluation Unit (PEU) of DTSC determined that there was not sufficient threat to public health and safety from the site to warrant prohibition of development of the Mira Vista Hills Unit #9 subdivision directly south of the site (2).
In April, 1984, a Preliminary Assessment was prepared by the staff of the Abandoned Site Assessment Program of DTSC for both landfills. The recommendation of this Preliminary Assessment was that no further action be taken (2).
In 1985, the PEU completed a second review of the site in response to a letter dated March 4, 1985, in which the Antioch Unified School District asked DTSC for information "... on the potential for a health hazard associated with construction of a school within the Mira Vista Hill Unit Number 9". PEU staff reviewed files at DTSC, RWQCB, BAAQMD, I.T. Headquarters, and the Riverview Fire District headquarters. Based on this review, PEU staff recommended that a plan for insuring access control for both facilities be developed, and a moratorium on development for all surrounding undeveloped land within 2,000 feet of the perimeter of the GBF site until the site has been fully characterized (3).
In August 1986, the Site Evaluation Program of DTSC evaluated the site using a standardized EPA hazardous waste ranking system. The site received a score of 77 (priority is given to sites scoring 28.5 or higher)(4). In October 1986, DTSC was notified by the RWQCB and CCCHSD that significant quantities of volatile organic compounds and heavy metals were found in six groundwater monitoring wells constructed on the perimeter of the site. The CCCHSD staff surveyed domestic water wells within three miles of the site and found them to be free of any contaminants (5).
Meetings held November 5th and 13th, 1986, involved representatives of CCCHSD, RWQCB, DTSC, BAAQMD, DHS Epidemiological Studies Section and the California Integrated Waste Management Board (IWMB). These meetings focused on how to best characterize the groundwater contamination and other potential exposure pathways. The BAAQMD agreed to do monitoring of ambient air quality and soil gas at the site (2).
At a January 13, 1987 meeting between all concerned agencies, the discussion concerned the public health significance of the data collected to date and identified further measures to be taken to assure that there was not current exposure to the general public from the site. The data reviewed included the ambient air and soil gas data from sampling conducted by BAAQMD in December 1986. The consensus of the participants was that public health was not currently being impacted through exposure to ambient air or groundwater (2). A sampling plan was agreed upon to assess subsurface gas migration from the site to nearby subdivisions. This was done in response to the high levels of methane detected in December 1986 by the BAAQMD in several of the gas monitoring wells constructed at the perimeter of the site (5). Low levels of methane were found in the utility vaults and water boxes of surrounding homes.
On January 26, 1987, the Contra Costa County Health Services Department released a report to the Contra Costa County Board of Supervisors which reviewed the existing information about the site and evaluated the potential for adverse public health impact (6).
During the early part of 1987, a public task force was organized by a member of the Contra Costa County Board of Supervisors. The purpose of the task force was to gather as much information about the site as possible and to expedite remediation of the site. Members of the task force include Antioch City Council Members, regulatory agencies involved (DTSC, CCCDHS, RWQCB, BAAQMD, WMB), the League of Women Voters, the Sierra Club, Public Works for City of Antioch, Riverview Fire District, and a resident near the site (2). This task force is described further in the Community Health Concerns section.
In July 1987, the DTSC completed a Preliminary Assessment Summary report for the site which reviewed the existing information about the site and potential routes of exposure (2). DTSC issued a remedial action order (RAO) to a group of identified responsible parties on September 25, 1987 and amended in June 1988. The RAO required a remedial investigation, a public health and environmental evaluation, a feasibility study and a full remedial action plan be submitted by the identified responsible parties.
In March 1988, DTSC completed a community relations plan for the GBF/Pittsburg Landfill(s) site (7). The purpose of the plan was to define any community concerns and informational needs about the site and encourage and ensure two-way communication between the community and DTSC.
The respondents group (i.e., the responsible parties responding to the RAO) submitted a preliminary public health and Environmental Evaluation report to DTSC in 1988 which was based on existing data at the time (8). The report served as the basis for Public Health and Environmental Evaluation.
The site was first proposed for the National Priorities List (NPL) on the Update 7 list in June 1988. The U.S. Environmental Protection Agency (EPA) subsequently revised the Hazard Ranking Score for the site based on public comments and additional information received. The revised score was below the cut-off score for inclusion on the NPL; therefore, the site was removed from consideration in October 1989.
The Agency for Toxic Substances and Disease Registry (ATSDR) completed a preliminary public health assessment for the site on July 18, 1990 (9). Based on existing information at the time, ATSDR concluded that the site was of potential public health concern but that environmental media had not been adequately analyzed for health assessment purposes.
The remedial investigation was conducted during 1990 and 1991 and was submitted to DTSC in August 1991 (1). The public health and environmental evaluation was submitted to DTSC in December 1991 (10), and the feasibility study was submitted to DTSC in February 1992. The DTSC, BAAQMD, RWQCB, and EPA submitted comments to the draft reports. The reports are currently in the process of being revised.
Under the revised Hazard Ranking System, a new HRS package was completed in September 1991 and the site was again proposed for inclusion on the NPL on the Update 12 list.
DTSC is overseeing contaminant characterization and remediation work required in the RAO. The California Integrated Waste Management Board and RWQCB are overseeing the closure of the Contra Costa Sanitary Landfill (i.e., the Class III landfill established in 1987).
During the morning of September 23, 1992, David Borgeson, Diana Lee, and Jane Riggan from the ATSDR/CDHS cooperative agreement project and the project manager and community relations coordinator from DTSC toured the site under the direction of a representative of Contra Costa Disposal. Access to the site is restricted by a fence around its periphery. At the time of the site visit, closure operations including capping the entire site were under way. An on-site landfill gas flare unit was burning gases collected via a landfill gas collection system. The flare unit is 44 feet tall and 11 feet six inches wide, and is surrounded by an eight foot cyclone fence.
While walking from the eastern border of the site to the center of the site, several members of the site visit team noticed strong landfill gas odors. The time was approximately 12:00 noon; the ambient temperature was approximately 75 degrees Fahrenheit. The source(s) of the odor was not determined.
Construction debris and some garbage was observed at the former Antioch Landfill adjacent to the sites western border. Access to the former Antioch Landfill property is not restricted. Burned vegetation existed in the Markley Creek bed just north of the former Antioch Landfill and adjacent to the northwest corner of the site. According to the representative of Contra Costa Disposal, a transient population had been living in the creek bed and were believed to have started the fire.
Cattle were observed grazing on the pasture land located west and south of the site. Residential neighborhoods were located northeast, east and southeast of the site.
Demographics and Land Use
The site is located on hilly terrain in the southwest corner of the city of Antioch. Farmland and residential communities surround the site. The nearest residences are located approximately 300 to 600 feet to the east and northeast of the site. Currently, undeveloped or open space properties exist to the northwest, west, and south of the site (1).
The various land uses in the vicinity of the site are graphically depicted in Figure 2. The site is presently zoned as open space by the March 1989 Contra Costa County Proposed Revised General Plan. The properties directly south and east of the site are also zoned as open space. Directly west and southwest of the site are two former landfills, the Antioch Dump site which closed in 1968 and the Lynch Landfill which closed in 1975. These properties are designated as permanent open space (1).
The Los Medanos Tank Farm located to the northwest of the site operated from 1913 to 1980 as a crude oil storage facility. During 1986-1988, various site investigations, groundwater quality monitoring and site restoration studies were conducted at the former tank farm and the property is currently planned for residential development as the Meadowlands project (1). An additional crude oil storage facility was built in 1925 in an area east of the Los Medanos Tank Farm. This facility, referred to as a large oil reservoir, consisted of an above-ground, concrete-floor storage facility with a capacity of 3,000,000 barrels. In 1972, the oil reservoir was decommissioned and removed prior to the construction of the Gentrytown residential development in this area (1).
Existing residential developments are located north, east and south of the site. The residential developments to the north are separated from the site by the Contra Costa Canal. The residential developments to the east and south are separated from the site by open space properties.
The population of the City of Antioch is approximately 62,000. According to the 1990 Census, 10,715 people live in 3,616 housing units within approximately two miles of the site. Thirty-two percent of this population is under 18 years of age. The racial/ethnic distribution is 80% white, 12% hispanic, 4% Asian and Pacific Islander, 2% black, and 1% American Indian. Based on observations from the site visit, the community in the vicinity of the site appears to be predominantly middle income.
As shown in Figure 2, three additional residential developments are currently proposed for construction in the vicinity of the site: 1) Meadowlands to the northwest of the site with 4,568 units; 2) Sky Ranch to the west of the site with 853 units; and 3) Mira Vista Hills located to the south of the site with 487 units (1).
Natural Resources Use
The site is located hydraulically upgradient of the Pittsburg groundwater basin. The basin is recharged by precipitation in the Markley Creek watershed as well as other drainage basins to the south of the site.
Groundwater exists at variable depths in the vicinity of the site. The current depth to groundwater ranges from about 40 feet to over 100 feet below ground surface in the site vicinity (1). This upper saturated zone may extend down to about 140 feet below ground surface or more. A deeper saturated zone exists below depths of 300 to 360 feet below ground surface; an extensive base to this deeper aquifer has not been identified (1). Regional groundwater flow direction is to the north. Most domestic wells in the vicinity of the site are screened between 100 and 200 feet below ground surface.
Over pumping from the Pittsburg basin main aquifer in the early 1900's reversed the subsurface flow directions and caused brackish water intrusion from the river system, which led to the degradation of the local water quality. The city of Antioch, including the residential subdivisions in the vicinity of the site, is serviced by the Antioch public water system.
Contamination has not impacted this system (5). In 1986 the Contra Costa County Health Services Department identified existing domestic wells within three miles of the GBF site. Seven wells closest to the site were tested and found to be free of contamination. Another inventory of water wells located within two miles of the site was performed as part of the remedial investigation in July 1990. This inventory discovered a total of 70 groundwater wells within two miles of the site. The current status of several of these wells was not determined. Currently, no wells near the site are potentially impacted by the groundwater contaminant plume and hence are not part of the ongoing testing program.
The primary drainage course in the vicinity of the site is Markley Creek, an effemoral stream channel which drains the foot hills to the south. The Markley Creek was dry from the mid 1980's through 1990-1991, while the remedial investigation work was done. The heavy precipitation of 1992-1993 may have caused Markley Creek to flow.
The Contra Costa Canal runs west along the northern property boundary. The canal is a cement lined, man-made waterway used for drinking water, irrigation and industry. There are four intakes along the canal within 15 miles downstream of the site which supply approximately 327,500 people with drinking water (1). The canal is fenced and is not used for fishing.
Sources of existing health related data in California that may be useful in evaluating hazards from environmental exposures include the California Birth Defects Monitoring Program, the California Cancer Surveillance Program, birth certificates, death certificates, and medical records which may exist in employment records, physicians offices, and local hospitals and clinics. The pertinence of these data bases to the site will be discussed in the Public Health Implications section of the public health assessment.
Complaints of strong oily and chemical odors, burning eyes and irritated lungs were filed by the nearby community during the early 1970s. The residents of the Gentrytown development bordering the site on the north and west sides complained of both oily and chemical odors and garbage odors. According to the Antioch Fire Department (now the Riverview Fire District), fires and explosions at the site raised residents concerns about the toxicity of the fumes and the immediate danger to nearby homes (7). Three major fires occurred in the early 1970s. A DTSC report noted that even in the absence of a fire, vapors from the evaporation ponds were thick enough to be mistaken for smoke (7).
A citizen's group was organized in 1985 to address issues related to the site. In 1986, the detection of contamination in groundwater monitoring wells installed at the perimeter of the site raised concerns about possible contamination of the drinking water. A public task force was organized in 1987 to gather as much information about the site as possible and to expedite remediation of the site. The task force is made up of representatives from Contra Costa County Board of Supervisors, Antioch City Council Members, regulatory agencies involved (DTSC, CCCDHS, RWQCB, BAAQMD, WMB), the League of Women Voters, the Sierra Club, Public Works for City of Antioch, Riverview Fire District, and a resident near the site. The task force has been meeting approximately two times a year and is still a viable group. At the task force meetings, reports from the regulatory agencies are made, concerns of the public are addressed, and further actions by the agencies and responsible parties are explained (2).
DTSC and CCCHSD has prepared and distributed five fact sheets updating the community about the site investigation and remedial efforts. A June 1989 community meeting was attended by approximately 50 people and an October 1990 community meeting was attended by about 30 people. Questions raised at these meetings were identified as major topics of concern and were answered in the fact sheets.
Community concerns in recent years have focused primarily on complaints about the sanitary landfill. In meetings that we held with staff from regulatory agencies, county health officials, city officials from Antioch, and a community representative, the general consensus was that concern has lessened since the closing of the landfill in March 1992.
In the course of preparing this public health assessment, we did not discover any current community health concerns. The following health concerns were raised by the community in the past.
- Which chemicals are lying beneath the landfill in the old hazardous waste disposal site and what is their long-term impact on residents living near the site?
- What is the extent of groundwater contamination? Can I be assured that it will never affect the drinking water supply?
- Are air pollutants from the sanitary landfill or the old hazardous waste disposal site being emitted from the methane gas collection and flare system at the site?
- What studies have been done to check for contamination of soil in the residential area as a result of fires at the site?
- Can cancer or birth defects be caused from the chemicals deposited at the hazardous waste site?
The public health assessment for the GBF/Pittsburg Landfill(s) was released for public comment from June 30 until July 30, 1993. Requests for public comment were published in the West County Times and the Antioch Daily Ledger. The public health assessment was made available for review at the Pittsburg and Antioch public libraries. Comments were received from the Environmental Division of the Contra Costa County Health Services Department and the state Department of Toxic Substances Control. These comments have been incorporated into the report. No comments were recieved from local residents.
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 following criteria were used to select contaminants of concern: 1) concentrations of contaminants on-site and off-site and frequency of detection; 2) field data quality, laboratory data quality, and sample design; 3) comparison of on-site and off-site concentrations with comparison (i.e., health guidance) values; and 4) community health concerns. If a contaminant is selected for follow-up in one medium, it is evaluated in all media potentially impacted. Comparison values used to select contaminants of concern at the site include the following:
EMEG = Environmental Media Evaluation Guide
RMEG = Reference Dose Based Media Evaluation Guide
CREG = Cancer Risk Evaluation Guide
LTHA = Lifetime Health Advisory for drinking water
MCLG = Maximum Contaminant Level Goal
MCL = Maximum Contaminant Level
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 noncarcinogenic 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 an 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, noncarcinogenic, health effects.
EPA has developed health based, non-regulatory Health Advisories (HAs) for some chemicals in drinking water. HAs represent a concentration below which no adverse health effects are expected to occur for a given exposure period. For example, a Lifetime Health Advisory (LTHA) is considered to be protective for exposure over an entire lifetime. HAs are protective against noncarcinogenic effects only; therefore, HAs are not given for chronic exposure to known or probable human carcinogens (LTHAs may be given for group C - "possible" human carcinogens). A margin of safety is included to protect sensitive members of the population.
MCLGs and MCLs are developed by EPA under the authority of the Safe Drinking Water Act. MCLGs are non-enforceable goals, set at levels which would result in no known, or anticipated, adverse health effects with an adequate margin of safety. MCLs are enforceable standards set as close to MCLGs as possible. In addition to health factors, MCLs are also required by law to consider the technological and economic feasibility of removing the contaminant from the water supply. The limit that is set must be feasible given the best available technology (e.g., practical quantification level) and treatment techniques.
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 noncarcinogenic 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 noncarcinogens, there are levels of exposure (i.e., thresholds), below which no adverse effects are expected to occur.
Carcinogenic chemicals detected in water, air and soil at the site were evaluated and selected for follow-up using Cancer Risk Evaluation Guide (CREG) values for water, air and soil, respectively. CREGs are media specific values which serve as an aid in selecting contaminants of concern that are potential carcinogens. CREGs are derived from EPA cancer slope factors according to ATSDR guidance (11). 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 excess lifetime cancer risk of one-in-a-million.
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 of getting cancer from all other causes during our lifetime. When we say there is a one-in-a-million excess cancer risk from a given exposure to a chemical, we mean that each individual exposed to that chemical at that level over his or her lifetime has a one-in-a-million 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-million, and, in fact, may be zero.
The Toxic Chemical Release Inventory (TRI) 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 at a site and in the area surrounding a site, and whether they may be causing an additional environmental burden to the community. We searched the TRI for the years 1987, 1988, 1989 and 1990 (the years for which TRI data were available on-line at the time this public health assessment was written).
We searched the TRI for releases from the 94509 zip code area, which includes the GBF/Pittsburg Landfill(s) and most of the City of Antioch. During the years 1987-1990, the TRI contained reports of releases of a total of 22 different chemicals from six different companies in the City of Antioch. The companies are not in the immediate vicinity of the GBF/Pittsburg Landfill(s). The 22 chemicals are listed in Table 1 (Appendix B). Summaries of discharge quantities for each year are provided in Table 2.
Contaminants in On-Site Surface Soil
The site stopped accepting municipal waste in March 1992 and is currently in the process of being capped with one foot of clay and three feet of clean soil. Contra Costa County currently inspects the site monthly for leachate seeps. After closure of the landfill, the county will inspect the site quarterly for leachate seeps. A seep was observed by DTSC staff in 1985. A field inspection during the remedial investigation work in January 1991 noted one small area which was partly saturated along the northeast graded slope of the site (1). No seeps were observed during our site visit.
Contaminants in On-Site Subsurface Soil and Waste
The former disposal ponds are covered with between 30 and 50 feet of refuse and soil. The information regarding the types of hazardous materials disposed of at the site is very sketchy. Direct sampling of waste on-site was not carried out as part of the remedial investigation partly due to the potential physical and chemical hazards (1).
Waste disposed at the site included containerized liquid, semi-solid and solid hazardous materials including drummed or boxed chemical and industrial waste and medical waste, a large quantity of M-2 incendiary oil thickener, and municipal solid waste and refuse. Liquids and sediment were sampled from the waste disposal ponds in 1975, prior to closure operations, by the Bay Area Air Pollution Control District. Liquid samples had high concentrations of chloride, nitrate, titanium dioxide, calcium, sodium, potassium, zinc, ammonia, and phenol. Mud samples had a range of concentrations for several trace metals as well as other inorganic and organic constituents (1). A list of hazardous substances known or suspected of being deposited at the site is provided in Table 3.
Contaminants in On-Site Sediments
Two sediment samples were collected from one location (the only location with surface water on-site) at the southeast corner of the site in June 1990 and April 1991. The sample was tested for metals, volatile and semi-volatile organic compounds, pesticides, PCBs, and herbicides. The results were non detect or low and similar to background (1). Contaminant concentrations did not exceed comparison values in on-site sediment and no contaminants were selected for follow-up.
Contaminants in On-Site Groundwater
The groundwater monitoring network for the remedial investigation consisted of 21 shallow aquifer and six deeper aquifer monitoring wells. Of these, nine shallow aquifer monitoring wells and three deeper aquifer monitoring wells exist at the perimeter of the site. Groundwater samples were collected and analyzed during two monitoring events in the summer and fall of 1990 (1). A total of 24 contaminants were detected in groundwater on-site at levels exceeding comparison values and were selected for follow-up. The contaminants of concern, along with the maximum concentration detected and comparison values, are presented in Table 4. The principal groundwater contaminants include trichloroethylene (TCE), tetrachloroethylene (PCE), 1,2-dichloropropane (1,2-DCP), carbon tetrachloride, vinyl chloride, chloroform, phenol, acetone and benzene, and some heavy metals.
Contamination in On-Site Surface Water
During the remedial investigation, site information and historical and current topographic maps and aerial photographs were reviewed to evaluate local drainage patterns, pathways for surface runoff from the site, and the nature and location of nearby surface water bodies. Surface water has been observed in a topographic depression in the southeast corner of the site. On March 20, 1990, one surface water sample was collected from a small pond at the southeast corner of the site and analyzed (1). No chemicals were detected above comparison values and no contaminants in on-site surface water were selected for follow-up.
Contaminants in On-Site Soil Gas
On-site soil gas sampling conducted by the BAAQMD in December 1986 detected low to high ppm values of perchloroethylene, vinyl chloride, TCA, and TCE (5). A soil gas collection and destruction system was installed at the site in 1988 and has been in operation since. As part of the remedial investigation, soil gas testing was conducted at three locations in June 1990 within the landfill. Two sampling locations were on the west or Pittsburg side, and one location was on the east or GBF side. Samples were collected at a depth of about five feet below the landfill cover at these locations.
To evaluate migration of soil gas, seven gas probes along the perimeter of the site were screened for total organic hydrocarbons with an organic vapor analyzer (OVA) on June 7-8, 1990. According to the sampling plan, if a sample had total organic hydrocarbons greater than 100 ppm, an additional sample would be obtained for further analysis for VOCs. One probe along the northern border of the site had a total organic vapor concentration at levels above the OVAs upper quantitation limit of 1,000 ppm. An additional gas sample was collected from this location and submitted for laboratory analysis. The other gas probes had concentrations at or below the background level of 0.8 ppm. Three probes were resampled in October 1990. Total organic vapor concentrations in these probes did not exceed the background concentration of 3.6 ppm (1). On-site soil gas contaminants and maximum concentrations detected are provided in Table 5.
None of the seven gas probes along the perimeter of the site had documentation on how the probes were constructed. For this reason, the California Integrated Waste Management Board (IWMB) has stated that they do not regard the data from the probes as valid (12). IWMB staff has required Contra Costa Waste Services to construct all new gas probes and resample. This data was not available for review at the time this health assessment was prepared.
Contaminants in On-Site Air
Ambient air monitoring was performed in December 1986 by the BAAQMD. With the exception of chloroform, airborne VOCs were detected at levels below average ambient air monitoring stations in the Bay Area (5). This monitoring occurred while the landfill was in operation and is not representative of current site conditions. Nor is it representative of conditions in the 1960s and 1970s when the Class I facility was active. Some on-site air sampling occurred during a fire in 1977, and is discussed under "Contaminants in Off-site Air".
Air immediately above the surface cover was sampled on July 18 and August 1, 1990. This surface-air sampling was done at three locations and involved continuously screening air three inches above the disposal site surface along a prescribed course over a 50,000 square foot grid during a 25 minute period. Screening was done using an OVA which analyzed for methane. Where methane concentrations exceeded 100 ppm, the sampling plan specified collection of an ambient sample and submittal for laboratory analysis. One location detected a methane concentration of 140 ppm. However, when verification sampling was carried out at this location on August 1, 1990, the maximum concentration of methane detected was 93 ppm. No laboratory analysis was done of the constituents (1).
Ambient air sampling was specified as an optional task in the remedial investigation work plan to be done in the event that surface-air sampling or soil gas characterization indicated significant emissions from the site. Based on the findings of the completed sampling, the contractor concluded that ambient air sampling was not necessary and was not performed.
An on-site landfill gas collection system and flare unit has been in operation at the site since 1988. The flare is 44 feet tall and 11 feet six inches wide. There is an eight foot cyclone fence around the flare unit. According to the BAAQMD permit, at least 99.7% of chlorinated hydrocarbons must be destroyed by the flare unit; 0.3% may be released to the ambient air.
The remedial investigation sampling plan specified that inlet and outlet gases from the flare be analyzed once for dioxins and furans. The contractor chose not to do this because of the rigorous testing procedures required (1). Rather, they did a review and comparative evaluation of existing data and testing data reported for other comparable landfill sites. Actual testing for the destruction efficiency of dioxins and furans may still be required by DTSC. Destruction efficiency for other contaminants must be checked on a regular basis as required by a BAAQMD permit.
Due to the limited information on past contaminant levels, and the current closure operations including capping the entire site, no on-site ambient air contaminants were selected for follow-up.
Contaminants in Off-Site Soil and Sediment
Periodic field inspections of the stream channel of Markley Creek were conducted by the remedial investigation contractor in 1990 to identify evidence of seeps caused by leachate. No evidence of seeps was observed (1).
In June 1990 and April 1991, a total of four surface soil samples were collected from two different locations within the Markley Creek bed potentially impacted by surface runoff. A background sample was collected from the creek bed to the west of the site. One additional off-site surface sediment sample was taken from a surface drainage course east of the site. Each sample was tested for metals, volatile and semi-volatile organic compounds, pesticides, PCBs and herbicides (1). No contamination at levels of public health concern was detected and no contaminants were selected for follow-up in off-site soil or sediment.
The remedial investigation concludes that contamination has not migrated into the Markley Creek bed north of the site, although this conclusion is based on only four samples from two sampling locations.
Contaminants in Off-Site Surface Water
The primary surface water body near the site, Markley Creek, has been dry since the mid 1980s. Sediment samples were collected to evaluate possible contamination of Markley Creek, as described above. A surface runoff berm and the depth to groundwater have kept the concrete-lined Contra Costa Canal from being impacted by site-related contamination.
Contaminants in Off-Site Groundwater
Of the 21 wells in the groundwater monitoring network, 12 shallow aquifer monitoring wells and three deeper aquifer monitoring wells exist off-site. Groundwater samples were collected and analyzed during two monitoring events in the summer and fall of 1990 (1). A total of 17 contaminants were detected in groundwater off-site at levels exceeding comparison values and were selected for follow-up. Contaminants of concern, along with the maximum concentration detected and comparison values, are presented in Table 6.
The principal groundwater contaminants include trichloroethylene (TCE), tetrachloroethylene (PCE), 1,2-dichloropropane (1,2-DCP), carbon tetrachloride, vinyl chloride, chloroform, and benzene. Phenol and acetone also exist off-site, but at levels below comparison values and were not selected as contaminants of concern in off-site groundwater. Relative to the site, three distinct patterns of contamination exist in the upper aquifer: to the east, by a predominance of 1,2-DCP, acetone and benzene; to the north, by a predominance of acetone, chloroform and phenol; and to the west, by a predominance of TCE, PCE and carbon tetrachloride (1).
Well surveys were conducted in 1986 and 1990. In 1986, staff from the Contra Costa County Health Services Division tested seven wells closest to the site and did not detect any contamination (5). Currently, no wells near the site are potentially impacted by the groundwater contaminant plume and hence are not part of the ongoing testing program.
Contaminants in Off-Site Soil Gas
Utility vaults and water boxes in residential areas adjacent to landfills were screened in February 1987. Low levels of methane were reported.
The remedial investigation reported that of the nine perimeter gas probes screened in 1990, only one probe had methane at levels above about one part per million. It then stated that based on these data, landfill-gases are not migrating off-site in the subsurface in the vicinity of the monitoring probes (1). This is probably true for most of the probes, although one probe along the northern border of the site had methane at >1000 ppm; landfill gas is likely migrating off-site in the subsurface in the vicinity of this probe.
An off-site soil gas survey was conducted in April 1990 as part of the remedial investigation. Based on the results of this survey, it appears that methane is migrating off-site, but only to a limited extent. Methane was only detected at four off-site locations (out of 35 locations tested), and at very low levels. These locations were near the perimeter of the site; one location was near residences to the north of the site.
Soil gas samples were collected from a total of approximately 100 locations off-site, north and east of the site. Except for four profiles (where samples were taken at 5, 10, and 15 foot depths) all sampling was conducted at five feet below land surface.
The subsurface gas samples were analyzed for carbon tetrachloride, chloroform, methylene chloride, trichloroethylene (TCE), tetrachloroethylene (PCE), and methane. Detection limits were 0.0001 micrograms or less per liter of soil gas for all compounds other then methane, for which the detection limit was 0.01 ug/L (1). Concentrations detected were in the low to very low parts per billion range.
Approximately 50 samples were also evaluated for vinyl chloride, 1,1-dichloroethylene, 1,1,1-trichloroethane, 1,2-dichloroethane, benzene, toluene, ethylbenzene, xylenes, and Freon-113 (13). Concentrations detected were in the low to very low parts per billion range. Two of six field blanks detected hits of 1,1-dichloroethylene, 1,1,1-trichloroethylene, 1,2-dichloroethane, benzene, toluene, ethylbenzene, and xylenes. However, the chemicals in the blanks were not quantified. Vinyl chloride was detected only once, at a level of 2.0 ppbv. Benzene was detected in one sample and one field blank. Ethylbenzene was detected in two samples and in one field blank. Freon-113 was detected once, in a field blank. The maximum concentrations of the contaminants found in the off-site soil gas survey are presented in Table 7.
On several occasions between 1973 and 1975, vapors from the ponds were thick enough to have been mistaken for smoke. Inspection of homes in October 1973 revealed evidence of corrosion of metal surfaces in the direction of the landfill, possibly due to windblown fumes from the acid evaporation ponds. Clearly, ambient air contamination did exist in the past at the site.
Unfortunately, ambient air data downwind from the site during the 1960s and early 1970s is not available. During a fire at the site on August 1-2, 1977, the BAAQMD and a consultant for IT, Inc. conducted ambient air sampling to determine whether there were toxic materials present in the emissions from the fire. The sampling was done because the fire was in a former chemical waste pond which had been filled with paper pulp, and because firemen were overcome by acidic-smelling fumes. The BAAQMD samples were collected on August 1 and August 2 and analyzed for sulfur dioxide, hydrogen sulfide, methyl mercaptan, lead, beryllium, sulfate, and total suspended particulates (14). The consultant to IT conducted sampling on August 2 and analyzed for lead, beryllium, chromium and asbestos (15).
The BAAQMD conducted sampling at the site and within the smoke plume near homes on Arthur Way, just east and downwind from the site. The results of the BAAQMD presented here are limited to how they were presented in memorandum. Five compounds - hydrogen sulfide, sulfur dioxide, methyl mercaptan, beryllium, and lead, were not considered to be of concern by the BAAQMD, either for residential exposure near the site or occupational exposure on the site. Hydrogen sulfide was detected up to 50 ppb, sulfur dioxide was detected up to 15 ppb, methyl mercaptan was not detected, beryllium was not detected or barely, and lead levels did not exceed the existing State standard and were comparable to regional background levels.
Sulfate in samples taken in the residential area was not detected at levels above the State standard and was at levels similar to regional background. Particulate sulfates on-site were high at 230 ug/m3.
In a 2-hour and a 1/2 hour sample taken in the residential area, total suspended particulates averaged 250 and 380 ug/m3. These high concentrations resulted from the sampler being directly in the plume of the fire. BAAQMD personnel noted that while the sample was being taken, the smoke plume was typical of that from burning wood - somewhat acrid and dusty, and concluded that the irritating pollutant was wood smoke from burning wood pulp.
The overnight particulate average was lower, about 60 ug/m3, apparently due to a shift of plume direction (14). The state 24-hour standard for suspended particulates was 100 ug/m3 and is currently 50 ug/m3. By comparison, regional background 24-hour averages during the later 1970s ranged from 38 to 124 ug/m3. Total suspended particulates on-site were much higher; the concentration of a half hour sample was 6,628 ug/m3.
The sampling conducted by a consultant to IT revealed similar results. No asbestos fibers were seen in five samples collected. Levels of lead, beryllium and chromium were below existing health guidance values and were comparable to regional background levels.
The BAAQMD conducted ambient air sampling on December 11 & 17, 1986 by request of the Contra Costa County Health Services Department. Results from two monitoring stations at the site were compared to data from the Community Station Network, which consists of five stations: San Jose, Fremont, San Francisco, Richmond and Concord. With the exception of chloroform, which was somewhat higher than data from the Community Station Network, most compounds were generally lower at the site than at the Community Station Network locations (5).
Since the magnitude of ambient air contamination in the 1970s is unknown, and given the current closure operations including capping the entire site, no off-site ambient air contaminants were selected for follow-up.
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.
Observations made at the time of the site visit did not detect any physical or other hazards that would be expected to present a particular threat to the community or to on-site workers. The landfill gas flare unit is fenced and access to the landfill gas extraction wells will be restricted as well. Access to the site is limited by a fence surrounding the property.
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 related to the site is also of concern, these pathways 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) transport through an 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 (11).
Exposure pathways are classified as either completed, potential, or eliminated. Completed exposure pathways include all five elements. 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 will not exist in the future. Human exposure pathways are evaluated for each environmental medium possibly impacted by site-related chemicals. The toxicological implications of the various exposure pathways identified as being of concern will be evaluated in the Public Health Implications section.
Two completed exposure pathways were identified and are summarized in Table 8. One completed pathway may have impacted workers who came into contact with actual waste material or contaminated soil in the past. These workers could have been exposed via incidental ingestion and/or via skin absorption. The number of potentially exposed workers and the nature and magnitude of exposure is unknown.
A second completed pathway existed in the past when on-site workers and nearby residents were likely exposed to airborne contaminants via inhalation. As indicated above, on several occasions between 1973 and 1975, vapors from the ponds were thick enough to have been mistaken for smoke. During this period, numerous complaints of burning eyes, irritated lungs, and strong oily or chemical odors were received by local and State agencies from the residents of the Gentrytown development (single family dwellings) north and east of GBF. Clearly, ambient air contamination did exist in the past at the site. The number of persons potentially exposed via ambient air was probably in the thousands. However, insufficient information is available on the actual number of exposed persons, exposure frequency and duration, air contaminants, and magnitude of contamination.
Both of the completed exposure pathways do not currently exist and are not likely to exist in the future. No completed exposure pathways involving groundwater, surface water or biota were identified.
Two potential exposure pathways were identified and are summarized in Table 9. The pathways involve ambient and indoor air on and near the site. Both pathways identified could currently exist or could exist in the future.
Ambient Air Potential Pathway
The ambient air potential pathway could exist if there is release of landfill gases to the ambient air via cracks in the surface of the landfill. The landfill is currently undergoing capping. Although this is a potential pathway, significant exposure is not expected to occur as long as the cap is well maintained. Exposure to contaminants from the flare unit was evaluated in the baseline risk assessment and was not found to be a pathway of concern. The nearest residences are located approximately 2,200 feet east of the flare.
Indoor Air Potential Pathway
A second potential pathway is the potential impact of soil gas contaminants on indoor air quality in neighboring residential units. Based on the soil gas survey conducted in 1990, it appears that methane is migrating off-site, but only to a limited extent. Methane was only detected at four off-site locations, and at very low levels. These locations were near the perimeter of the site; one location was near residences to the north of the site. No discussion was made in the remedial investigation about the patterns of VOCs in the soil gas as compared to groundwater contamination, although it was concluded that soil gas contaminants appear to be related to VOCs present in groundwater. This may be true, however, regardless of the source, low levels of VOCs do exist in soil gas in residential properties near the site. The potential impact of this exposure pathway was not evaluated in the public health and environmental evaluation completed by the respondents group in December 1991.
No indoor air testing has been done in homes adjacent to the site. However, a soil gas survey conducted in 1990 included multiple sampling locations in the adjacent community. An estimate of the elevation in indoor volatile organic compound (VOC) concentration resulting from subsurface contamination may be obtained by assuming that VOCs are transported into buildings in an analogous fashion to radon. The ratio of indoor concentration to soil gas concentration is called an attenuation coefficient (16). We estimated the potential concentrations inside residences near the GBF/Pittsburg Landfill(s) by multiplying the maximum concentration detected in off-site soil gas by an attenuation coefficient for radon (16).
No potential pathways involving soil, groundwater, surface water, or biota are considered likely to exist.Potential exposure pathways involving on-site soil/waste were considered unlikely to exist because future construction or excavation activities are unlikely, given the requirements for maintaining the integrity of the landfill cap. If such activities did occur, it is unlikely that significant worker exposures would occur if appropriate personal protection equipment is used.
Potential exposure pathways involving groundwater in the future are considered unlikely to exist. The city of Antioch, including the residential subdivisions in the vicinity of the site, is serviced by the Antioch public water system. Contamination has not impacted this system (5). Currently, no wells near the site are potentially impacted by the groundwater contaminant plume and hence are not part of the ongoing testing program. Federal and State agencies are currently determining the most appropriate way to control the migration of contamination in groundwater and cleanup existing contamination. A system of extraction and treatment has been proposed. Given the ongoing monitoring program and regulatory requirements, it is unlikely that contamination would migrate undetected and impact municipal or private wells in the vicinity of the site.
No potential exposure pathways involving surface water were identified. The bottom of the concrete-lined Contra Costa Canal is about 35 feet above the current level of groundwater (1). A berm exists which keeps surface runoff from entering the canal. Existing sampling data does not indicate that the Markley Creek bed has been impacted by site-related contaminants at levels of concern. Lastly, there are no past, current, or future pathways by which consumable biota would be impacted by site-related contaminants.
As discussed in the Pathways Analyses section, the only completed exposure pathways identified at the site were for past conditions. No completed pathways were identified under current and future, particularly for conditions during the 1960s and 1970s conditions. A significant health threat does not appear to have existed from ambient air exposure based on what limited data we have on past ambient air exposures near the site (i.e., results of sampling during the 1977 pulp fire and sampling in 1986). However, without adequate knowledge of the types and magnitude of ambient air contamination during the 1960s and early 1970s, is not possible to assess the toxicological implications of such exposure.
As described above, we estimated indoor air concentrations of VOCs in soil gas using an attenuation coefficient (see Reference 16). With an estimate of possible exposure point concentrations, it was possible to estimate the risk to the residents. Based on this assessment, it was concluded that this pathway does not pose an apparent public health hazard.
The California Birth Defects Monitoring Program does not have information on birth defects in the community near the site for the exposure period of concern (i.e., the 1960s and early 1970s). Likewise, the California Cancer Registry does not have data covering this period. For this reason, as well as other factors such as lack of exposure information, we do not believe that these data bases would be useful in better defining the potential impact of the site on the surrounding community.
A cluster of anencephaly and spina bifida birth defects was observed in the Antioch-Pittsburg area in 1979-1980. Of an estimated 2,000 births to residents in the Antioch-Pittsburg area, 10 cases of anencephaly and spina bifida were identified between March 1979 and November 1980. Only two would have been expected on the basis of a reported annual incidence rate. Investigators conducted a review of environmental health records, medical records, site visits to homes of cases, and a case-control study. However, they were not able to implicate any particular exposure as the cause for the increased incidence. The homes of cases were not located within one mile of a major industrial factory or toxic chemical dump site (17).
In the course of preparing this public health assessment, we did not discover any current community health concerns. In this section, we will address health concerns raised by the community in the past. Several of these questions have already been answered in fact sheets prepared by DTSC and CCCHSD (4,18).
- Which chemicals are lying beneath the landfill in the old hazardous waste disposal site and what is their long-term impact on residents living near the site?
- What is the extent of groundwater contamination? Can I be assured that it will never affect the drinking water supply?
- Are air pollutants from the sanitary landfill or the old hazardous waste disposal site being emitted from the methane gas collection and flare system at the site?
- What studies have been done to check for contamination of soil in the residential area as a result of fires at the site?
- Can cancer or birth defects be caused from the chemicals deposited at the hazardous waste site?
Between the 1960s and 1974, ten unlined evaporation ponds were filled with a variety of liquid industrial waste including acids, solvents, oils, sulfonation tars, sludges, and liquid metal wastes. The limited information on possible levels of past exposure preclude an assessment of long-term health effects. When the hazardous waste disposal site was closed, the ponds were drained and much of the site was covered with non-hazardous waste.
Groundwater contamination has moved slowly off-site. However, nobody is using contaminated groundwater for drinking water or other purposes. Most of the Antioch residents use the municipal water supply, which is surface water from the Delta and not groundwater. All the wells in the area which are in use have been tested and are not contaminated.
Because large amounts of methane are produced by decomposing garbage, it is often necessary to have methane collection systems at landfills to reduce odors and lesson fire hazards. The flare is designed to destroy the gases. The temperature must be monitored to ensure that the gases are destroyed as completely as possible. Results of destruction efficiency studies indicated that average destruction efficiencies are at least 90%. Given the destruction efficiencies, and the distance from the flare unit to residential locations, significant exposures from the flare unit should not occur.
Most of the concern about ambient air is from the vapors coming off of the liquid evaporation ponds during the 1960s and early 1970s. Significant deposition of hazardous airborne particulates is not expected, based on a review of existing site information. Existing information on suspended particulates obtained during a paper pulp fire in 1977 does not indicate that a health hazard existed for residents during this particular fire.
A very large number of chemicals have been deposited at the GBF/Pittsburg Landfill(s) site. Many of these chemicals have been shown to cause or potentially cause both cancer and birth defects. In order for a chemical to pose a health risk, however, a completed exposure pathway must exist, in which a chemical comes into contact with and enters the body. Fortunately, no apparent risk of cancer or birth defects exists from the site under current or future conditions. The lack of exposure information on past exposures makes it difficult to determine the risk of cancer or birth defects under past conditions. A significant health threat did not exist from ambient air exposure based on what limited data we have on past ambient air exposures near the site (i.e., results of sampling during the 1977 pulp fire and sampling in 1986).
1. Formerly the Bay Area Air Pollution Control District.
2. Prior to 1991, the DTSC was organized as the Toxic Substances Control Division within DHS.