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PUBLIC HEALTH ASSESSMENT

HIPPS ROAD LANDFILL
JACKSONVILLE, DUVAL COUNTY, FLORIDA


ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS

In this section, we review the environmental data collected at the site, evaluate sampling adequacy, select contaminants of concern, and list the maximum concentration and detection frequency for the contaminants of concern in the various media (that is, water, soil, and air). We select contaminants of concern based on the following factors:

  1. Concentrations of contaminants on and off site. Although background concentrations are useful in determining if contaminants are site-related, contaminants are only eliminated from further consideration if both the background and on-site concentrations are below standard comparison values. This is necessary to assess the public health risk to all contaminants detected, whether site-related or not.
  2. Field data quality, laboratory data quality, and sample design.
  3. Community health concerns.
  4. Comparison of maximum on- and off-site concentrations with published ATSDR standard comparison values. ATSDR's published standard comparison values are media-specific concentrations used to select contaminants for further evaluation. They are not used to predict health effects or to set clean-up levels. Contaminants with media concentrations above an ATSDR standard comparison value do not necessarily represent a health threat, but are selected for further evaluation. Contaminants with media concentrations below an ATSDR standard comparison value are unlikely to be associated with illness and are not evaluated further.
  5. Contaminants without ATSDR standard comparison values, but which have toxicological information published in documents called ATSDR toxicological profiles. These profiles are chemical-specific and contain a variety of toxicological information found in the scientific literature.

We used the following ATSDR standard comparison values (ATSDR 1993a), in order of priority, to select contaminants of concern:

  1. EMEG--Environmental Media Evaluation Guide--derived from ATSDR's Minimal Risk Level (MRL) using standard exposure assumptions, such as ingestion of two liters of water per day and body weight of 70 kg for adults. MRLs are an estimate of daily human exposure to a chemical likely to be without an appreciable risk of noncancerous illnesses.
  2. CREG--Cancer Risk Evaluation Guide--calculated from EPA's cancer slope factors, is the contaminant concentration that is estimated to result in no more than one excess cancer per one million persons exposed over a lifetime.
  3. RMEG--Reference Dose Media Evaluation Guide--derived from EPA's Reference Dose (RfD) using standard exposure assumptions. RfDs are an estimate of daily human exposure to a chemical likely to be without an appreciable risk of noncancerous illnesses.
  4. LTHA--Lifetime Health Advisory for Drinking Water--EPA's estimate of the concentration of a contaminant in drinking water at which illnesses are not expected to occur over a lifetime of exposure. LTHAs provide a safety margin to protect sensitive members of the population.

Because of the community's concern about the health effects of all contaminants, especially cancer-causing agents, we used the lowest value for either the EMEG or CREG when selecting contaminants of concern. This ensured the selection of the maximum number of contaminants for further evaluation.

Over 130 contaminants have been detected in various environmental media near the site (Table 1, Appendix B). Using the methodology described above, we eliminated 28 chemicals detected in various media at concentrations below their standard comparison values from further consideration (Table 2, Appendix B). Sixty-three other chemicals had no standard comparison values, and the human health data were insufficient to determine their public health significance, requiring us to eliminate these contaminants from further consideration as well (Table 3, Appendix B). We divided the remaining contaminants into two broad categories: contaminants with drinking water standards and contaminants of concern. We evaluated these categories separately. pH and the eight contaminants in the contaminants with drinking water standards category include inorganic chemicals found at the site that have primary or secondary drinking water standards established in Florida but do not have published comparison values. We discuss our findings for contaminants in this category in the Public Health Implications section below. We classified the remaining 35 contaminants as contaminants of concern. These contaminants are:

Arsenic
Barium
Benzene
Beryllium
Bromodichloromethane
Cadmium
Chlorobenzene
Chlorodibromomethane
Chloroform
Chromium(VI)
Cobalt
Cresol (total)
Cyanide
DDT
1,4-Dichlorobenzene
1,1-Dichloroethane
1,2-Dichloroethane
1,2-Dichloropropane
Di(2-ethylhexyl)phthalate
1,2-Diphenylhydrazine
Hexachloroethane
Lead
Manganese
Mercury
Methylene Chloride
Naphthalene
Nickel
n-Nitrosodiphenylamine
PCBs (total)
Selenium
1,1,2,2-Tetrachloroethane
Tetrachloroethene
Tin
Trichloroethene
Vinyl Chloride

We summarize the environmental sampling data for the contaminants of concern in Tables 4 through 13, Appendix B. In nearly all cases, the laboratory analyses did not specify the valence of the chromium detected. Since hexavalent chromium (that is, chromium(VI)) is the most toxic form of the metal, we assumed all chromium detected to be hexavalent chromium. Similarly, some laboratory analyses did not specify the isometric form of dichlorobenzene. When this specification was not made, we assumed the dichlorobenzene detected to be the para isomer (that is, 1,4-dichlorobenzene, also known as p-dichlorobenzene), the most toxic form. These assumptions are the most protective of public health. In addition, because the sampling around the site focused on the seven PCB mixtures that together comprised 98% of the PCBs sold in the United States (ATSDR 1993q), this health assessment focuses on these same seven mixtures. These PCB mixtures contain: Aroclor-1016, -1221, -1232, -1242, -1248, -1254, and -1260.

ATSDR standard comparison values are used only to select contaminants of concern for further consideration. Identification of a contaminant of concern in this section does not necessarily mean that exposure will be associated with illnesses. Identification serves to narrow the focus of the public health assessment to those contaminants most important to public health. When we selected a contaminant of concern in one medium, we also reported that contaminant in all other media. We evaluate the contaminants of concern in subsequent sections and determine whether exposure has public health significance.

To identify industrial facilities that could contribute to the contamination near this site, we searched the 1987, 1988, 1989 and 1990 EPA Toxic Chemical Release Inventory (TRI) data bases. EPA developed TRI from the chemical release information (air, water, and soil) provided by certain industries. The Hipps Road Landfill site is in the 32222 zip code area. Our TRI search of this zip code revealed no industries reporting releases of chemicals found at levels of concern at this site.

In this assessment, we discuss the contamination that exists on the site first and separately from the contamination that occurs off the site.

A. On-site Contamination

For the purposes of this evaluation, we defined "on-site" as the area within the fenced boundaries of the Hipps Road Landfill at present (Figure 7, Appendix A). This area includes not only the landfill, but also the area used by the groundwater treatment system.

We compiled data in this subsection from the following sources: BESD samples (BESD 1983a); Duval CPHU samples (FHRS 1981b, 1983c); EPA's 1984 site screening study, 1985 draft RI/FS work plan, and 1985 RI field work (EPA 1985a, 1985c, 1986d); CompuChem's private well samples (CompuChem 1988); Disposal Safety's groundwater contamination assessment (Disposal Safety 1990); Golder Associates' groundwater recovery system design report (Golder Associates 1990). We reviewed several other reports containing on-site sample data results (EPA 1985b, 1986a, 1986b, 1986c; ATSDR 1986) but determined these data had already been presented in and counted from earlier reports.

In counting the number of analyses for a contaminant, we used raw data whenever these data were available to us. In some cases, such as in our review of the remedial investigation data, we could only count the results presented in the report's summary data tables because the raw data were not available from EPA or other governmental agencies. Therefore, we acknowledge the total number of samples for some contaminants is likely greater than the number we show in our data tables, and some contaminants may have been analyzed for that are not identified in the summary reports we examined. When we were able to identify duplicate samples among the many reports we reviewed, we counted these samples only once.

Overall, we found the number of on-site samples and analyses too few to fully characterize the nature and extent of soil or water contamination at the site. Our having only summary data to review from some sources may have contributed to our finding small sample numbers for some contaminants. In addition, Disposal Safety's review of the 1985 RI solvent analyses found holding times were greatly exceeded, indicating that concentrations for these compounds may be underestimated (Disposal Safety 1990). Finally, most on-site samples were collected only one time from any given sample point; consequently, we do not have the data to examine how contaminant concentrations might have changed over time. These deficiencies precluded our determining if individual contaminants of concern were site-related or not.

On-site Surface Soil (0-3 inches deep)

There is no record of surface soil samples (0-3 inches deep) being collected on site. Although EPA collected soil samples at three locations on site, they did not specify sample depths (EPA 1985c). We consider the results from these EPA soil samples under the subsurface soil category. The RI report mentions collection of two on-site surface soil samples for dioxin analysis, but does not give the sample depths or present the analytical results (EPA 1986d); therefore, we do not use these data in our analysis. The lack of surface soil samples is a significant data gap for this public health assessment because there were homes on site, and family members played or gardened in on-site soils. Without sample data, we cannot evaluate the potential health effects from the resident's exposure to on-site surface soils. Nevertheless, there is no need to collect on-site surface soil samples in the future because the landfill is capped, the on-site homes are gone, and site access is restricted.

On-site Subsurface Soil (deeper than 3 inches)

Between 1984 and 1985, EPA collected on-site subsurface soil samples at 20 locations in the landfill (Figure 8, Appendix A). In 1984, EPA collected soil samples (unspecified depth) at three locations on the eastern side of the landfill. The EPA report identified two of the samples as composites, but did not identify the sample type for the third (EPA 1985c). In 1985, EPA collected subsurface soil samples from 17 boreholes in the landfill. EPA took these composite samples at depths ranging from 15 - 26.5 feet, and used the sample results to identify the chemical waste composition and distribution within the landfill (EPA 1986d). In our analysis, we used raw data from EPA's site screening report and summary data from the RI.

During the RI, EPA collected one soil sample for background data. They collected this sample while drilling a temporary well less than ¼ mile from the landfill boundary (EPA 1986d). Because this sample was taken within the area we judged likely to be affected by the site, we did not consider this sample point representative of background conditions. Consequently, we did not use data from this point for background information in our analysis.

Sixteen contaminants of concern were detected in on-site subsurface soils (Table 4, Appendix B). Four of these (arsenic, cadmium, di(2-ethylhexyl)phthalate, and 1,2-diphenylhydrazine) were found in concentrations above their respective comparison values for soil, and four others (chromium, 1,4-dichlorobenzene, lead, and nickel) are known or suspected cancer-causing agents. Six contaminants of concern (benzene, chlorobenzene, cyanide, manganese, mercury, and methylene chloride) were found in concentrations below their respective comparison values. The other two detected contaminants of concern (naphthalene and tin) did not have comparison values for soil. Eighteen contaminants of concern were not detected, and one contaminant of concern was not analyzed for in the on-site subsurface soils.

For the purposes of this public health assessment, there were not enough samples taken or analyses done to fully characterize on-site subsurface soil quality. In a couple of cases, such as for arsenic and lead, there were enough analyses to characterize on-site subsurface soil contamination by these substances. However, for most compounds, there were too few analyses to fully characterize on-site subsurface soil contamination. Nevertheless, there is no need to collect more on-site subsurface soil samples as long as the site remains undisturbed, the fence and cap continue to be maintained, and the on- and off-site groundwater continue to be monitored. If any of these conditions are not met or if there are plans to develop the site in the future, a comprehensive study of the landfill's contents will need to be conducted.

On-site Sediment

Between 1983 and 1985, various parties collected on-site sediment samples in at least 4 pond or ditch locations (Figure 9, Appendix A). In 1983, BESD sampled one on-site pond at the request of a private citizen. The BESD data did not include a map of the sample location, and we could not determine which on-site pond was sampled. (This sample location is not included in Figure 9, Appendix A.) BESD did not identify the collected sample as grab or core (BESD 1983a). During the 1984 site screening study, EPA collected one sediment sample from an on-site pond 75 feet east of the landfill, and another sediment sample from a drainage ditch immediately south of the landfill. EPA did not indicate if the samples taken were grab or core (EPA 1985c). During the 1985 RI fieldwork, EPA collected grab samples from two ponds each 75 feet east of the landfill for inclusion in the remedial investigation. The two ponds EPA sampled during the RI were different from the pond sampled during the site screening study (EPA 1986d). In our analysis, we used raw data from BESD and EPA's site screening report, and summary data from the RI.

EPA was the only investigator to collect a background sediment sample. During the RI, they collected this sample from an intermittent stream approximately 10,000 feet south of the site (EPA 1986d). The acceptability of this sample as representative of true background conditions is questionable for several reasons. First, the sample point is nearly two miles south of the site and not in the proper location (that is, not upgradient) to determine if the site is having an effect on pond sediments. Second, on-site ponds are groundwater-fed, not stream-fed. Third, a road crosses the background stream and is the likely source of lead found in the background sediment. Fourth, at least six of the contaminants found in the background sediment have not been found in the area around the site. For these reasons, we do not consider CDM's background sample adequate, and we do not include these data in our analysis.

Ten contaminants of concern were detected in on-site sediments (Table 5, Appendix B). Two of these (arsenic and PCBs) were found in concentrations above their respective comparison values for soil, and two others (chromium and lead) are known or suspected cancer-causing agents. Four contaminants of concern (cyanide, 1,2-diphenylhydrazine, manganese, and mercury) were found in concentrations below their respective comparison values. The other two detected contaminants of concern (cobalt and cresol) did not have comparison values for sediment. Twenty-five contaminants of concern were analyzed for but not detected in the on-site sediments.

For the purposes of this public health assessment, site investigators did not collect enough samples to fully characterize on-site sediment quality. Nevertheless, site cleanup activities have eliminated the on-site ponds and ditches, and no more samples can be collected.

On-site Surface Water

Between 1983 and 1985, various parties collected on-site surface water samples in at least 4 pond or ditch locations (Figure 10, Appendix A). In 1983, BESD sampled one on-site pond at the request of a private citizen. The BESD data did not include a map of the sample location, and we could not determine which on-site pond was sampled (BESD 1983a). (This sample location was not included in Figure 10, Appendix A.) During the 1984 site screening study, EPA collected one surface water sample from an on-site pond 75 feet east of the landfill, and another surface water sample from a drainage ditch immediately south of the landfill (EPA 1985c). During the 1985 RI fieldwork, EPA collected surface water samples from two ponds each 75 feet east of the landfill for inclusion in the remedial investigation. These two ponds were different from the pond EPA sampled during the site screening study (EPA 1986d). In our analysis, we used raw data from BESD and the EPA site screening report, and summary data from the RI.

EPA was the only investigator to collect a background surface water sample. They collected this sample from an intermittent stream approximately 10,000 feet south of the site (EPA 1986d). We do not consider this sample representative of true background conditions because the sample point is too far from the site and in an unsuitable location, the background stream does not feed any of the ponds, and outside sources seem to be contributing contaminants to the background stream.

Four contaminants of concern detected were detected in on-site surface waters (Table 6, Appendix B). One of these (DDT) was found in a concentration above its comparison value for water, and two others (manganese and mercury) were found in concentrations below their respective comparison values. The other detected contaminants of concern (tin) did not have a comparison value for water. Thirty-one contaminants of concern were analyzed for but not detected in the on-site surface water.

For the purposes of this public health assessment, site investigators did not collect enough samples to fully characterize on-site surface water quality. Nevertheless, site cleanup activities have eliminated the on-site ponds and ditches, and no more samples can be collected.

On-site Shallow Groundwater - Boreholes and Monitor Wells

Between 1983 and 1989, many parties sampled on-site shallow groundwater in boreholes or monitor wells to determine contaminant identity and migration. Over the years, site investigators sampled 21 on-site sample points multiple times (Figure 11, Appendix A). Four reports presented these data (EPA 1985a, 1986d; Disposal Safety 1990; Golder Associates 1990). In our analysis, we used raw data from the Golder Associates report and summary data from the draft RI, final RI, and Disposal Safety reports.

Of the four reports, only the remedial investigation presented background sample data information. This report identified one monitor well as a background sample point, but did not identify which private wells were considered background sample points (EPA 1986d). For our analysis, we did not consider the selected monitor well an adequate background sample because it was less than ¼ mile from the landfill boundary and within the area we judged likely to be affected by the site. We could not evaluate the adequacy of the referenced background private well sample points because we did not know their locations. In order to examine background shallow groundwater quality, we selected 11 private wells within a one-mile radius around the site and used their data to assess background conditions. We had well depth information for 2 of the 11 wells, confirming they were in the shallow aquifer. We assumed the other 9 wells to also be in the shallow aquifer because this is common for private wells in the area (FDER 1983a, 1983c). The 11 background wells were located at homes southeast of the site (Hilma, Worthington, and Shindler Roads), south of the site (Brett Forest Drive and Brett Forest Court), west of the site (Old Middleburg Road), and north of the site across Mile Branch Creek (Marlee and Shindler Roads). FHRS sampled these private wells between 1990 and 1993. We considered these background sample results to also apply to earlier sample results because of the slow movement of groundwater in the area. The analytical results showed both lead and manganese in the background shallow groundwater. Only one of the eleven background wells had detectable levels of lead. Without more information about this well, we cannot determine if this result represents background contamination or is an artifact of well construction or water storage in this particular well before sampling. All background wells had detectable levels of manganese in low concentrations, indicating this metal naturally exists in the shallow groundwater around the site. One background well, the same well having detectable lead, had a manganese concentration above the comparison value.

Twenty-five contaminants of concern were detected in on-site shallow groundwater (Table 7, Appendix B). In comparing sample data to background data, the maximum values for both lead and manganese were significantly higher than background concentrations; 19 other contaminants (arsenic, barium, benzene, cadmium, chlorobenzene, chloroform, chromium, 1,4-dichlorobenzene, 1,1-dichloroethane, 1,2-dichloroethane, di(2-ethylhexyl)phthalate, mercury, methylene chloride, naphthalene, nickel, n-nitrosodiphenylamine, PCBs, selenium, and vinyl chloride) were also above background levels. Four contaminants (beryllium, cobalt, cresol, and cyanide) did not have background data for comparison.

Of the 25 contaminants of concern detected, 14 (arsenic, barium, benzene, beryllium, chlorobenzene, cyanide, 1,2-dichloroethane, di(2-ethylhexyl)phthalate, manganese, mercury, n-nitrosodiphenylamine, PCBs, selenium, and vinyl chloride) had maximum concentrations above their respective comparison values for water. Six more chemicals (cadmium, chromium, 1,4-dichlorobenzene, 1,1-dichloroethane, lead, and nickel) are known or suspected cancer-causing agents. One monitor well contained chloroform in trace amounts. The study presenting this datum did not report the detection limit for chloroform (EPA 1985a); without this information, we cannot determine if chloroform exceeds the 6 µg/l (micrograms per liter) comparison value. Two contaminants of concern (methylene chloride and naphthalene) were found in concentrations below their comparison values for this media. The remaining two detected contaminants of concern (cobalt and cresol) did not have comparison values for water. Ten contaminants of concern were analyzed for but not detected in the on-site shallow groundwater.

For the purposes of this public health assessment, it is equivocal if the sample results adequately characterize on-site shallow groundwater quality. In some cases, such as for arsenic and benzene, there were enough analyses to characterize on-site shallow groundwater contamination by these substances. In other cases, such as for 1,2-diphenylhydrazine and hexachloroethane, there were too few analyses to fully characterize on-site shallow groundwater contamination by these compounds. Nevertheless, EPA should continue monitoring on-site groundwater to ensure changes in the composition or migration of the contaminant plume are discovered as quickly as possible.

On-site Shallow Groundwater - Private Wells

Between 1981 and 1985, FHRS and EPA sampled six on-site private wells to determine the extent of groundwater contamination and the threat to public health. In 1988, CompuChem sampled these private wells. In our analysis, we used raw data from FHRS and CompuChem (FHRS 1981b, 1983c; CompuChem 1988), and summary data from the RI and Disposal Safety reports (EPA 1986D; Disposal Safety 1990). We used data from 11 off-site private wells as background information for our analysis.

Ten contaminants of concern were detected in on-site private wells (Table 8, Appendix B). In comparing sample data to background data, the maximum value for lead was significantly higher than its background concentration. The maximum concentration for manganese was within background range. Seven other detected contaminants (arsenic, barium, cadmium, chloroform, mercury, methylene chloride, and nickel) were also above background levels, and one contaminant (tin) did not have background data for comparison.

Of the ten contaminants of concern detected, two (arsenic and methylene chloride) was found in concentrations above their respective comparison values for water, and three others (cadmium, lead, and nickel) are suspected cancer-causing agents. Manganese, a naturally occurring element in the area, was found in concentrations below its comparison value, as were barium, chloroform, and mercury. The other detected contaminant of concern (tin) did not have a comparison value for water. Sixteen contaminants of concern were not detected, and the remaining 9 contaminants of concern were not analyzed for in the on-site private wells.

For the purposes of this public health assessment, investigators did not collect enough samples to fully characterize on-site private well water quality. Nevertheless, site cleanup activities have eliminated the on-site homes and their private wells, and no more samples can be collected.

On-site Air

There is no record of air samples being collected on site prior to August 1993. Although EPA collected air samples during the 1985 RI fieldwork, these were general monitoring measurements from an HNu meter, an OVA meter, an explosimeter, and a dust monitor (EPA 1986d). These instruments yield general quantitative results applicable to monitoring site safety conditions; they do not yield the qualitative and precise quantitative data needed for a public health assessment. Therefore, we did not use these data to evaluate environmental contamination at the site. The lack of air samples from the past is a significant data gap for this public health assessment because there were homes on site, and nearby residents played or scavenged in the landfill. Without past sample data, we cannot fully evaluate the potential health effects from the resident's exposure to on-site air.

Presently, there is an air stripper on site to remove solvents from the groundwater. In August and September 1993, Golder Associates performed a trial run to evaluate the stripper's performance, and found the stripper was removing solvents from the groundwater and expelling them into the on-site air (Golder Associates 1993a). Because site access is restricted, nearby residents are not likely to be exposed to on-site air contaminants. We evaluate the movement of this contaminated air off site and the need for additional samples in our discussion of off-site air contamination.

On-site Biota

There is no record of biotic samples being collected on site. The lack of biotic samples is a significant data gap for this public health assessment because area residents ate vegetables from their gardens and fish from on-site ponds. Without sample data, we cannot evaluate the potential health effects from the resident's exposure to on-site biota. Nevertheless, there is no need to collect on-site biotic samples in the future because the these food sources no longer exist.

B. Off-site Contamination

For the purposes of this evaluation, we defined "off-site" as the area outside the fenced boundaries of the Hipps Road Landfill but within the area we consider likely to be affected by the site. We defined the affected area as: the area within approximately ¼ mile of the landfill's perimeter, the area directly north of the site to Mile Branch Creek and northeast of the site to Shindler Road, and the area southwest of the site along Exline Road (Figure 12, Appendix A). In considering private well data from this area, we used data from homes on both sides of a street, even if only one side of the street was within the ¼-mile boundary. Our definition of the affected area included groundwater contamination likely to result from the known contaminant plume northeast of the site, the mounding of water when the landfill was uncapped, and possible groundwater flow southwest from the site. Our definition encompassed an area larger than the federal cleanup area. By incorporating areas around the site where groundwater flow is likely as well as where it is known, we were better assured of identifying the maximum values of potentially site-related chemicals for use in our analysis.

We compiled data in this subsection from the following sources: FDER samples (FDER 1983f); BESD samples (BESD 1983a); Duval CPHU samples (FHRS 1981b, 1983c, 1984, 1990, 1991, 1992, 1993d); EPA's 1984 site screening study, 1985 draft RI/FS work plan, and 1985 RI field work (EPA 1985a, 1985c, 1986d); Disposal Safety's groundwater contamination assessment (Disposal Safety 1990); and Golder Associates' groundwater recovery system design report, baseline groundwater sampling study, and air stripper report, (Golder Associates 1990, 1992, 1993). We reviewed several other reports containing off-site sample data results (EPA 1985b, 1986a, 1986b, 1986c; ATSDR 1986) but determined these data had already been presented in and counted from earlier reports.

In counting the number of analyses for a contaminant, we used raw data whenever these data were available to us. In some cases, such as in our review of the remedial investigation data, we could only count the results presented in the report's summary data tables because the raw data were not available from EPA or other governmental agencies. Therefore, we acknowledge the total number of samples for some contaminants is likely greater than the number we show in our data tables, and some contaminants may have been analyzed for that aren't identified in the summary reports we examined. In several reports, sample locations were not precisely identified. When an incomplete sample point description contained enough information to judge it to be within the affected area, we included the sample in our off-site analysis; when a sample description did not contain enough information to judge its approximate location, we excluded the sample point from our analysis. Finally, when we were able to identify duplicate samples among the many reports we reviewed, we counted these samples only once.

In comparing soil and water data values on and off site, we noticed some contaminants of concern were found in higher concentrations off site than on site for the same media. Similarly, the RI asserted cadmium, lead, and chloroform were not site-related for various reasons (EPA 1986d). Because on-site contamination was insufficiently characterized, we could not determine if these irregularities represented contamination from other sources or were statistical artifacts of the unequal sampling among these locations.

Off-site Surface Soil (0-3 inches deep)

There is no record of surface soil samples (0-3 inches deep) being collected off site. The lack of surface soil samples is a significant data gap for this public health assessment because there are homes off site, and family members continue to play or garden in off-site surface soils. Without sample data, we cannot evaluate the potential health effects from the resident's exposure to off-site surface soils. Therefore, we recommend EPA collect one surface soil sample (0-3 inches deep) from the part of each private yard, bordering the southern eastern, northern, and western site boundaries, that is most likely to have received surface soils blown off site. We recommend these soils be analyzed for inorganics, pesticides, base neutrals, and acid extractables including: arsenic, barium, beryllium, cadmium, chromium, cobalt, cresol, DDT, di(2-ethylhexyl)phthalate, 1,2-diphenylhydrazine, hexachloroethane, lead, manganese, mercury, naphthalene, nickel, n-nitrosodiphenylamine, PCBs, selenium, and tin.

Off-site Subsurface Soil (deeper than 3 inches)

In 1985, EPA collected off-site subsurface soil samples at seven locations around the landfill to determine the nature and extent of off-site subsurface soil contamination. EPA collected these samples from the two water-bearing units of the surficial aquifer while drilling off-site temporary monitor wells. EPA took seven subsurface soil samples from the Sand aquifer at depths ranging from 29 - 60.5 feet, and five subsurface soil samples from the Limestone aquifer at depths ranging from 69 - 130 feet (EPA 1986d). Although site investigators collected subsurface soil samples from areas most likely to be contaminated by groundwater (deep in the Sand aquifer and in the top of the Limestone aquifer), residents are not likely to be exposed to these soils. Consequently, subsurface soils that residents might come in contact with through gardening or digging activities are uncharacterized.

For the purposes of this public health assessment, site investigators did not collect enough samples or perform all of the analyses needed to adequately characterize off-site subsurface soil quality that residents were exposed to. Nevertheless, we do not expect solvents which might be transported to these soils to remain because of the high volatility and water solubility of these compounds. Likewise, we do not expect substances that adsorb to soils or have a low water solubility to have a transport mechanism allowing them to permeate subsurface soils below a couple of inches. Therefore, we do not recommend EPA collect off-site subsurface soil samples.

Off-site Sediment

Between 1983 and 1985, BESD and EPA collected off-site sediment samples in at least four pond, ditch, or creek locations (Figure 13, Appendix A). In 1983, BESD sampled one pond, presumed to be off-site, at the request of a private citizen. The BESD data did not include a map of the sample location, and we could not determine where the sampled pond was located. (This sample location is not included in Figure 13, Appendix A.) BESD did not identify the collected sample as grab or core (BESD 1983a). In 1985, EPA collected grab samples from a pond 300 feet east of the site, another pond 1,900 feet north of the site, a creek (Mile Branch Creek) 4,000 feet northeast of the site, and a storm water ditch 1,000 feet south of the site. EPA used these samples to determine the nature and extent of contamination off site. EPA also collected a sediment sample from an intermittent stream 10,000 feet south of the site for background information (EPA 1986d), but we did not use these data in our analysis because they did not represent background conditions. In our analysis, we used raw data from BESD and summary data from the RI.

Five contaminants of concern were detected in off-site sediments (Table 9, Appendix B). One of these (PCBs) was found in a concentration above its comparison value for soil, and two others (chromium and lead) are known or suspected cancer-causing agents. One contaminant of concern (barium) was found in a concentration below its comparison value. The other detected contaminant of concern (cresol) did not have a comparison value for sediment. Four contaminants of concern were not detected, and the remaining 26 contaminants of concern were not analyzed for in the off-site sediments.

For the purposes of this public health assessment, site investigators did not collect enough samples or perform all of the analyses needed to adequately characterize off-site sediment quality. Without adequate sample data, we cannot fully evaluate the potential health effects from the resident's exposure to off-site sediment. Therefore, we recommend EPA collect one sediment sample every 150 feet for the first 500 feet of every storm water drainage system leaving the site. These systems include: the storm water swales along the sites northern and western borders, the cypress pond along the site's eastern boundary, and any other storm water conduits leaving the site. In addition, we recommend collection of two sediment samples from the ground depression immediately northeast of the intersection of Hipps and Bunion Roads. We recommend these sediments be analyzed for inorganics, pesticides, base neutrals, and acid extractables including: arsenic, barium, beryllium, cadmium, chromium, cobalt, cresol, DDT, di(2-ethylhexyl)phthalate, 1,2-diphenylhydrazine, hexachloroethane, lead, manganese, mercury, naphthalene, nickel, n-nitrosodiphenylamine, PCBs, selenium, and tin.

Off-site Surface Water

Between 1983 and 1985, BESD and EPA collected off-site surface water samples in at least four pond, ditch, or creek locations (Figure 14, Appendix A). In 1983, BESD sampled one pond, presumed to be off-site, at the request of a private citizen. The BESD data did not include a map of the sample location, and we could not determine which off-site pond was sampled (BESD 1983a). (This sample location is not included in Figure 14, Appendix A.) In 1985, EPA collected surface water samples from a pond 300 feet east of the site, another pond 1,900 feet north of the site, a creek (Mile Branch Creek) 4,000 feet northeast of the site, and a storm water ditch 1,000 feet south of the site. EPA used these samples to determine the nature and extent of contamination off site. EPA also collected a surface water sample from an intermittent stream 10,000 feet south of the site for background information (EPA 1986d), but we did not use these data in our analysis because they did not represent background conditions. In our analysis, we used raw data from BESD and summary data from the RI.

Five contaminants of concern were detected in off-site surface waters (Table 10, Appendix B). One of these (PCBs) was found in a concentration above its comparison value for water, and two others (chromium and lead) are known or suspected cancer-causing agents. One contaminant of concern (manganese) was found in a concentration below its comparison value. The other detected contaminant of concern (cobalt) did not have a comparison value for water. Four contaminants of concern were not detected, and the remaining 26 contaminants of concern were not analyzed for in the off-site surface waters.

For the purposes of this public health assessment, site investigators did not collect enough samples or perform all of the analyses needed to adequately characterize off-site surface water quality. Without adequate sample data, we cannot evaluate the potential health effects from the resident's exposure to off-site surface waters. Presently, there are two issues concerning storm water runoff. First, contaminants may be entering the cypress pond east of the site through groundwater recharge from the site. Neighborhood children play in the storm water ditches draining this pond. We recommend 1 surface water sample be collected from the cypress pond to determine if solvents (VOCs) are present in this water body. pH should be measured on all surface water or groundwater samples collected, and additional analyses for metals should be conducted if the pH is low. Second, residents also report the retention ponds for the air stripper have overflowed several times with runoff entering the residential yards east of the site (Hipps Road residents, pers. comm.). For example, after heavy rains in October 1992, the retention ponds reportedly overflowed and flooded the off-site cypress pond. One resident, living on property east of and contiguous to the site, noticed oily-looking fluids overflowing from the landfill onto his property (Norman 1994). The dirt bulging in the storm water control structures and the gaps in the plastic sheeting along the site's eastern boundary, seen during our May 23 and November 18, 1994 site visits, suggest retention pond overflow and storm water runoff may still be a problem at the site. In addition, site overflow going into the cypress pond east of the site subsequently flows into to storm water ditches that children play in. To determine if contaminants are present in storm water leaving the site, we recommend flood water be sampled in the cypress pond and in the site's perimeter ditches at 50 foot intervals within 12 hours of the next reported flooding event. In the cypress pond, at least one sample should be collected at the surface to capture oils or other substances less dense than water, and at least one other sample should be collected from below the pond's surface. Flood water samples should be measured for pH and analyzed for inorganics, pesticides, purgeables, base neutrals, acid extractables, and any contaminant of concern not covered by this list. Additional analyses for metals should be conducted if the pH is low. Furthermore, if the landfill's cap is somehow breached in the future, then a comprehensive study of the landfill's off-site surface waters will need to be conducted.

Off-site Shallow Groundwater - Monitor Wells

Between 1983 and 1993, many parties sampled off-site shallow groundwater in monitor wells to determine contaminant identity and migration, and to identify the contaminant plume boundaries for cleanup. Over the years, site investigators sampled 35 off-site sample locations multiple times at varying depths (Figure 15, Appendix A). Several reports and individual sample analyses contained these data (Disposal Safety 1990; EPA 1985a, 1986d; FDER 1983f; Golder Associates 1990, 1992, 1993a). In our analysis, we used raw data from three sources (FDER 1983f; Golder Associates 1990, 1993a) and summary data from the other four. We used data from 11 off-site private wells as background information for our analysis.

Twenty-seven contaminants of concern were detected in off-site shallow groundwater (Table 11, Appendix B). In comparing sample data to background data, the maximum values for both lead and manganese were significantly higher than background concentrations. Twenty-two other detected contaminants (arsenic, barium, benzene, cadmium, chlorobenzene, chlorodibromomethane, chloroform, chromium, 1,4-dichlorobenzene, 1,1-dichloroethane, 1,2-dichloroethane, di(2-ethylhexyl)phthalate, mercury, methylene chloride, naphthalene, nickel, n-nitrosodiphenylamine, selenium, 1,1,2,2-tetrachloroethane, tetrachloroethene, trichloroethene, and vinyl chloride) were also above background levels. The three remaining detected contaminants (beryllium, cobalt, and cresol) did not have background values for comparison.

Of the 27 contaminants of concern detected, 16 (arsenic, benzene, beryllium, cadmium, chlorodibromomethane, chloroform, 1,2-dichloroethane, di(2-ethylhexyl)phthalate, manganese, methylene chloride, naphthalene, n-nitrosodiphenylamine, 1,1,2,2-tetrachloroethane, tetrachloroethene, trichloroethene, and vinyl chloride) had maximum concentrations above their respective comparison values for water. Five more chemicals (chromium, 1,4-dichlorobenzene, 1,1-dichloroethane, lead, and nickel) are known or suspected cancer-causing agents. Four contaminants of concern (barium, chlorobenzene, mercury, and selenium) were found in concentrations below their respective comparison values. The other two detected contaminants of concern (cobalt and cresol) did not have comparison values for water. The remaining eight contaminants of concern were not detected in the off-site shallow groundwater.

In 1991, Disposal Safety tested the water at one monitor well in the vicinity of the groundwater contaminant plume for the presence of the prescription drug components pentobarbital, meprobamate, and phensuxamide. Pentobarbital was detected in the one groundwater sample taken at a concentration of 1 µg/l. Attempts to develop methods to extract the other two compounds in sufficient quantities failed (Disposal Safety 1991). These results suggest medical wastes may have been disposed of in the landfill. If medical wastes were disposed of at the site, low-level radioactive wastes may also be present in the fill material.

For the purposes of this public health assessment, sample results adequately characterize off-site shallow groundwater quality in the vicinity of the plume northeast of the site, with the exception of radionuclides. EPA should continue monitoring off-site groundwater in this area to ensure changes in the composition or migration of the contaminant plume are discovered as quickly as possible. In addition, EPA has not fully investigated groundwater movement in directions other than to the northeast of the landfill nor the possibility of off-site plumes in these directions. In fact, the remedial investigation's groundwater contaminant transport analysis diagrams show a groundwater flow gradient east and southeast of the site, in addition to the somewhat steeper gradient northeast (EPA 1986d). Moreover, groundwater movement in the area west of the site has been in question since FDER's initial investigation in 1983 (FDER 1983c), and remained undefined after the RI's groundwater contaminant transport analysis (EPA 1986d). Therefore, EPA should initially investigate groundwater movement within ½-mile around the eastern, southern, and western site boundaries and delineate the extent of groundwater contamination in this area. If contaminant plumes are found in these directions, the scope of this groundwater investigation will likely need expansion. All ground water analyses should include metals, other inorganics, purgeables, base neutrals, acid extractables, and radionuclides.

Off-site Shallow Groundwater - Private Wells

Between 1981 and 1993, various parties sampled approximately 90 off-site private wells to determine the extent of groundwater contamination and the threat to public health. In our analysis, we used raw data from FHRS (FHRS 1981b, 1983c, 1984, 1990, 1991, 1992, 1993d) and EPA's site screening study (EPA 1985c), and summary data from the RI and Disposal Safety reports (Disposal Safety 1990; EPA 1986d). For background information, we used data from 11 off-site private wells outside of the area of concern.

Twenty contaminants of concern were detected in off-site private wells (Table 12, Appendix B). In comparing sample data to background data, the maximum values for both lead and manganese were significantly higher than background concentrations. Seventeen other detected contaminants (barium, benzene, bromodichloromethane, chlorodibromomethane, chloroform, 1,4-dichlorobenzene, 1,1-dichloroethane, 1,2-dichloroethane, 1,2-dichloropro-pane, di(2-ethylhexyl)phthalate, hexachloroethane, mercury, methylene chloride, nickel, tetrachloroethene, trichloroethene, and vinyl chloride) were also above background levels. The final detected contaminant (cresol) did not have a background value for comparison.

Of the 20 contaminants of concern detected, 12 (benzene, bromodichloromethane, chlorodibromomethane, chloroform, 1,2-dichloroethane, di(2-ethylhexyl)phthalate, hexachloroethane, manganese, methylene chloride, tetrachloroethene, trichloroethene, and vinyl chloride) had maximum concentrations above their respective comparison values for water. Five more chemicals (1,4-dichlorobenzene, 1,1-dichloroethane, 1,2-dichloropropane, lead, and nickel) are suspected cancer-causing agents. Two contaminants of concern (barium and mercury) were found in concentrations below their respective comparison values. The other detected contaminant of concern (cresol) did not have a comparison value for water. Fourteen contaminants of concern were not detected in the off-site private wells, and one contaminant of concern was not analyzed for in any private well samples.

An examination of private well sampling frequencies shows very few private wells were sampled between 1981-1985, even fewer were sampled between 1986-1989, and many were sampled between 1990-1993. Considering that drinking water complaints reportedly began as early as 1972 (Keneagy 1991), there was a time period of approximately 18 years during which private well water quality was virtually uncharacterized. Many of the highest contaminant concentrations were measured during the 1983-1985 time period. We cannot know if these values were the peak exposure concentrations. Therefore, for the purposes of this public health assessment, investigators did not collect enough samples to adequately characterize private well water quality prior to 1990. However, investigators collected enough samples to characterize off-site private well water quality from 1990-1993 for most contaminants, with the notable exceptions of beryllium, cresol, cyanide, DDT, and tin. Nevertheless, FHRS should continue analyzing private well samples near the site to ensure any new wells contaminated by plume migration are discovered as quickly as possible. Radionuclides should be added to the list of contaminants currently analyzed for. If further groundwater studies show contamination in other areas around the landfill, private wells in these areas will need to be sampled. Concerned citizens close to known or suspected groundwater contamination areas should limit their exposure by connecting their homes to the public water supply where it is available, using public water for all home uses including car washing and irrigation, and properly plugging their private wells so that they are not available for future use by any party.

In addition to the private well sampling described above, FHRS also sampled private wells outside of the area of concern, in the area we called "off-site". We reviewed approximately 100 sample results collected between 1990-1993, and located within a 1-mile radius of the landfill boundaries. Between 1992-1993, there were nine isolated spots of mostly low-level groundwater contamination. Contaminants found in these locations were: "other volatiles" at two homes east of and about ½ mile from the site (Hipps Road); chloroform, p-cymene, di-n-butylphthalate, lead, mercury, styrene, or 1,2,4-trimethylbenzene at four homes east-southeast of and about ½ mile from the site Shindler Road); chloroform, bromodichloromethane, and chlorodibromomethane at one home southeast of and about 1 mile from the site (Walden Road); di(2-ethylhexyl)phthalate or lead at three homes south-southeast of and about ½ mile from the site (Bunion Drive); lead at one home south of and about ½ mile from the site (Taylorfield Road); lead or "other volatiles" at three homes south of and about 1 mile from the site (Brett Forest Drive and Brett Forest Court); barium, benzene, 1,1-dichloroethane, 1,1-dichloroethene, xylenes, or heptachlor at three homes southwest of and about ½ mile from the site (Sun Lane); ethylbenzene and "other volatiles" at one home west of and about ½ mile from the site (Hipps Road); and chromium or lead at two homes northwest of and about ½ mile from the site (Loves Drive). Heptachlor and styrene were new contaminants; heptachlor was found in concentrations below its comparison value (CREG), but styrene, a suspected cancer-causing agent, did not have a CREG value for comparison. Nearly all of the other contaminants were found in concentrations smaller than the maximum values already described in this assessment; however, one home had a new maximum value for lead, and another home had new maximum values for chloroform, bromodichloromethane, and chlorodibromomethane.

Nearby residents are concerned these latter results indicate the landfill's groundwater contaminant plume is much larger than currently believed. They contend the apparent random distribution of the contaminants simply could reflect the randomness of the private well sampling in the area. This is one possible explanation. Alternatively, because these contaminants are found in many household products (such as cosmetics, cleaners, paints, varnishes, paint and varnish removers, plumbing products, and pesticides), the contamination could result from residents' washing product residues into household septic systems or dumping unwanted products on the ground. We do not have enough information to determine which of these possibilities is most likely. Nevertheless, these results support our recommendation that a more comprehensive examination of groundwater flow and contamination is needed in the eastern, southern and western directions from the site.

Finally, the shallow depths and slow movement of Mile Branch Creek, observed during our May 1994 visit, suggest groundwater contaminants not captured by the air stripper treatment system might flow under this creek rather than be discharged into it, as suggested by the RI (EPA 1986d). Therefore, we recommend Duval CPHU periodically test the private wells of homes north of the creek for contaminants of concern and radionuclides.

Off-site Air

There is no record of air samples being collected off site. Although EPA collected air samples during the 1985 RI fieldwork, these were general monitoring measurements from an HNu meter, an OVA meter, an explosimeter, and a dust monitor (EPA 1986d). These instruments yield general quantitative results applicable to monitoring site safety conditions; they do not yield the qualitative and precise quantitative data needed for a public health assessment. Therefore, we did not use these data to evaluate environmental contamination off site. The lack of air samples from the past is a significant data gap for this public health assessment because of the residents' potential exposure to airborne contaminants in and around their homes. To estimate past exposure to volatile contaminants, we used the computer software Risk*Assistant (1993) to predict airborne concentrations of solvents volatilized from groundwater, based on their maximum concentrations in groundwater.

To estimate present and future exposure to airborne contaminants from the air stripper, we used a different model to predict off-site solvent concentrations from on-site air measurements taken during the air stripper's 1993 trial run and performance test. During this trial run, Golder sampled on-site air at three locations to ensure the newly installed air stripper was working as predicted and was not posing a public health threat (Figure 16, Appendix A). The sample points were at the top of the air stripper tower, 1,000 feet northeast of the stripper tower along the eastern fenced boundary, and 1,300 feet northwest of the stripper tower along the northern fenced boundary. For the first five days of the air stripper's operation, Golder collected 24-hour composite samples at all three sample locations. For the last 16 days of the trial run, Golder collected 24-hour composite samples only at the top of the air-stripper tower (Golder Associates 1993a). For our analysis, we used raw data from the trial run.

Prior to air stripper operation, Golder collected two composite samples (an eight hour and a twenty-four hour) at the northernmost sample location along Hipps Road. In addition, we consider the August 26 air samples taken from the two locations north of the tower to be background because the wind was predominately from the northeast on that day and blew the stripper emissions away from these sample points. The analytical results showed methylene chloride in the background air. This methylene chloride could be coming from the landfill itself or from solvent uses in the surrounding area.

Because it is unrealistic to assume nearby residents will breathe air in concentrations found at the top of the air stripper, we examined the data from the closest sample point. However, this sample point was 1,000 feet northeast of the tower, and the closest resident lives approximately 300 feet east of the tower. To predict air concentrations for this resident, we contacted the Florida Department of Environmental Protection's (formerly known as FDER) Air Modeling and Assessment Section in Tallahassee. They used a model called "Screen 2" to predict the dilution with distance from the air stripper (EPA 1992a). This model predicted the highest concentrations likely at various distances assuming worst case weather conditions of a gentle breeze with little dispersion. To check the accuracy of the model, we compared the predicted dilution to the actual concentrations measured at the two northernmost sample points on August 25, a day when the wind was predominately from the south. In general, the dilution predicted by the model is consistent with actual measured concentrations; therefore, we used the predicted concentrations at 300 feet for our analysis.

Nine contaminants of concern were detected at the top of the tower and are predicted to be present in off-site air (Table 13, Appendix B) at the closest residence. One of these (1,2-dichloroethane) is likely to be found in a concentration above its comparison value for air. Two more detected contaminants of concern (1,1-dichloroethane and vinyl chloride) are known or suspected cancer-causing agents. Four contaminants of concern (benzene, methylene chloride, tetrachloroethene, and trichloroethene) are likely to be in concentrations below their respective comparison values. The remaining two detected contaminants of concern (chlorobenzene and 1,2-dichloropropane) did not have comparison values for air. Four contaminants of concern were not detected at the top of the tower, and the remaining 22 contaminants of concern were not analyzed for in the on-site air.

For the purposes of this public health assessment, investigators collected enough samples to fully characterize on-site air quality resulting from the air stripper. Because the air stripper is an on-going pollution source in a residential community, we recommend EPA collect and analyze the water influent to the air stripper at least monthly for the first three months of operation, and at least every three months for the duration of operation. These samples should be analyzed for all of the volatile organic compounds already detected in the groundwater at this site, as well all of the volatile organic compounds already detected in the air from the air stripper. If any influent sample result exceeds the maximum detected concentration measured during the air stripper's trial run, we recommend re-evaluation of the influent data to determine if adverse health effects are likely.

Nearby residents are concerned metals in the groundwater may be emitted as aerosols from the air stripper. Golder reports they have placed a demister screen on the top of the air stripper to intercept any aerosols formed during the air-stripping process. Droplets formed on the demister drop back into the air stripper and are not released into the air (FHRS 1994b).

Off-site Biota

There is no record of biotic samples being collected off site. The lack of biotic samples is a significant data gap for this public health assessment because area residents ate vegetables from their gardens. Presently, there is no need to collect off-site biotic samples because the off-site contaminants presently detected in groundwater and air are not expected to significantly accumulate in plants. However, if the off-site samples we have recommended above reveal the presence of contaminants that bioaccumulate, we may request biotic sampling.

C. Quality Assurance and Quality Control

We requested a data review summary from EPA, but were told one does not exist for this site (Patsy Goldberg, pers. comm.). Although the remedial investigation contained a quality assurance/quality control (QA/QC) assessment asserting the RI data could be used with confidence (EPA 1986d), Disposal Safety's review of the solvent analyses found excessive holding times (exceeded by 70-110 days), suggesting that concentrations for these compounds may be underestimated (Disposal Safety 1990). Because we do not have the raw data and sample sheets to review, we cannot evaluate this assertion. Nevertheless, we used these data in our analyses because they are the only data we have for many contaminants measured during this time period. The 1988 CompuChem QA data showed methylene chloride was present in the blank. Because the methylene chloride concentration in the blank was close to detected well sample concentrations, we did not consider this compound to be detected in wells of this sample set. The quality assurance data we reviewed from the Golder reports (Golder Associates 1990, 1993a) indicated those data were reliable. We did not have QA/QC data for Golder's baseline groundwater sampling study (Golder Associates 1992), but we assumed these data were valid because the results were consistent with other data we had about the detected contaminants. Most of the FHRS private well data had information on trip blanks accompanying them, indicating these data were also reliable (FHRS 1981b, 1983c, 1984, 1990, 1991, 1992, 1993d). In cases where we did not have QA/QC information, we assumed these data were valid, since the environmental samples were collected and analyzed by governmental agencies or their contractors. In preparing this public health assessment, we relied on the information provided by these agencies or contractors and assumed that site investigators followed adequate quality assurance and quality control measures followed in regard to chain-of-custody, laboratory procedures, and data reporting, with the noted question about the RI data. The validity of the analysis and conclusions drawn for this public health assessment are determined by the completeness and reliability of the referenced information.

In each of the preceding On- and Off-site Contamination subsections, we evaluated the adequacy of the data to estimate exposures. We assumed that estimated data (J) and presumptive data (N) were valid. This second assumption errs on the side of public health by assuming that a contaminant exists when actually it may not exist.

D. Physical and Other Hazards

In 1988, Golder conducted a methane gas survey at the site to assess the fire/explosion hazard at the site and to determine the need for a gas venting system in the landfill's cap. The survey did not find any methane being generated at the site. Golder Associates concluded if methane were to be generated by the site in the future, the gas could escape through the soil cover; therefore, it would not accumulate under the cover or move laterally underground (Golder Associates 1989a). Consequently, we expect the fire/explosion hazard from methane gas at the site to be negligible.

During our site visits, drowning seemed to be a potential physical hazard if someone were to accidentally fall into the retention ponds. The ponds are about 4½ feet deep, and the slope of the sides is 2:1 (Golder Associates 1989b) which should enable adults and older children to easily climb out. However, children less than five feet tall might drown if the pond were full. The potential for this problem currently exists, since the site's fence on the western boundary (Exline Road) has a large hole through it, enabling trespassers to enter the site.

PATHWAYS ANALYSES

To determine if nearby residents are exposed to contaminants migrating from the site, we evaluated the environmental and human components of exposure pathways. Exposure pathways consist of five elements: a source of contamination, transport through an environmental medium, a point of exposure, a route of human exposure, and an exposed population.

An exposure pathway can be eliminated if at least one of the five elements is missing and will never be present. We categorize exposure pathways that are not eliminated as either completed or potential. For completed pathways, all five elements exist and exposure to a contaminant has occurred, is occurring, or will occur. For potential pathways, at least one of the five elements is missing, but could exist. For potential pathways, exposure to a contaminant could have occurred, could be occurring, or could occur in the future.

In this analysis, "on-site" is defined as the area within the fenced boundaries of the Hipps Road Landfill (Figure 7, Appendix A), and "off-site" is defined as the area outside of the fenced boundaries and within the area of we judged likely to be affected by the site (Figure 12, Appendix A). Much of the exposure information comes from interviews with nearby residents (FHRS 1993b, 1993c; Hipps Road residents, pers. comm.).

A. Completed Exposure Pathways

For a summary of the completed exposure pathways at this site, refer to Table 14, Appendix B.

Subsurface Soil Pathway

In the past, adult residents had contact with on-site subsurface soils (that is, soils more than three inches deep) as they scavenged materials out of the landfill. Neighborhood children had contact with on-site subsurface soils as they scavenged materials from and dug forts into the fill material while playing at the site. Exposure to subsurface soil contaminants occurred via skin absorption and incidental ingestion. Since the landfill is now capped and site access is restricted, nearby residents are not likely to be exposed to on-site subsurface soil contaminants in the present or future.

Sediment Pathway

In the past, neighborhood children played in the sediments of dried storm water swales and on-site ponds. Exposure to sediment contaminants occurred via skin absorption and incidental ingestion. Because site access is restricted and cleanup activities eliminated the ponds and storm water swales on site, neighborhood children are not likely to be exposed to on-site sediment contaminants in the present or future. However, neighborhood children are likely to be exposed to sediment contaminants from past storm water run off in off-site swales and ditches in both the present and future.

Surface Water Pathway

In the past, neighborhood children played in storm water swales and swam in on- and off-site ponds. Nearby residents also swam in Mile Branch Creek. Exposure to surface water contaminants occurred via skin absorption and incidental ingestion. Because site access is restricted and cleanup activities eliminated the ponds and storm water swales on site, neighborhood children are not likely to be exposed to on-site surface water contaminants in the present or future.

Shallow Groundwater Pathway

Prior to 1987, on-site and off-site homes drew potable water from private wells in the contaminated Sand aquifer. Exposure to shallow groundwater contaminants occurred via ingestion, as well as skin absorption and inhalation of solvents. Because on-site homes were vacated and demolished as a part of cleanup activities, residents will not be exposed to on-site shallow groundwater in the present or future. In contrast, many off-site homes in or near the contaminant plume still use private well water. Exposure to off-site shallow groundwater contaminants will continue in the present and future for residents using private well water close to the plume.

Air (Tower Effluent) Pathway

As a part of site cleanup activities, the responsible parties have installed an air-stripping tower to remove solvents from the groundwater. Solvents will be emitted in tower effluent and are likely to be blown off-site in both the present and future. Exposure to off-site air contaminants is likely via inhalation.

B. Potential Exposure Pathways

We categorize the following exposure pathways as potential because there are no environmental data measuring contaminant types or amounts. Without these data, we cannot fully evaluate the contribution of each potential pathway to the residents' total exposure. For a summary of the potential exposure pathways at this site, refer to Table 15, Appendix B.

Surface Soil Pathway

In the past, residents living on and off site may have been exposed to surface soil contaminants (that is, 0-3 inches deep) in their yards both by playing and gardening in the soil. In addition, adults and children visiting the landfill to scavenge or to play may have had contact with landfill surface soil contaminants. Exposure to surface soil contaminants may have occurred via skin absorption, incidental ingestion, and inhalation of dust. Since the landfill is now capped and site access is restricted, nearby residents are not likely to be exposed to on-site surface soils in the present or future. However, residents may be exposed to off-site surface soil contaminants in the present and future as they continue to play and work in their yards.

Surface Water Pathway

In the present and future, neighborhood children are expected to continue to play and swim in off-site storm water ditches, potentially exposing them to site-related contaminants via skin absorption and incidental ingestion. Nearby residents may also be exposed to any contaminants entering Mile Branch Creek from the groundwater contaminant plume northeast of the site.

Air (Odor) Pathway

In the past and present, nearby residents complained about landfill odors and worried about their possible exposure to airborne contaminants. Exposure to air contaminants may have occurred via inhalation and skin absorption. Since site access is now restricted, nearby residents are not likely to be exposed to on-site air contaminants in the present or future. However, nearby residents may be exposed to off-site air contaminants in the present and future as the wind blows air off site.

Biota Pathway

In the past, neighborhood children fished in the ponds adjacent to the landfill, and ate squirrels and other small game from the site. Furthermore, nearby residents ate vegetables from their gardens. Exposure to contaminants in biota may have occurred via ingestion of plant and animal tissue. Because the on-site ponds and gardens are now gone, nearby residents will not be exposed to on-site fish or garden vegetables. However, nearby residents may be exposed to contaminants in biota in the present and future by eating vegetables or small game from the site. In addition, nearby residents may be exposed to contaminants in biota in the present and future by eating fish from Mile Branch Creek, if plume contaminants reach sediments in this water body.

C. Eliminated Pathways

We did not evaluate a pathway for deep groundwater (that is, the Floridan aquifer) because we do not know of any exposure points to this media or have any sampling data from this aquifer.

We do not believe a pathway for off-site subsurface soil exposure exists. Contaminated groundwater from the site flows mostly downward before moving horizontally (EPA 1986d). Contaminants have been found in the Sand and Limestone aquifers at depths unlikely to be accessed by residents. Residents are concerned local flooding will bring these contaminants to the shallow soils where they can be exposed through gardening or other digging activities. Yet, when flooding occurs, we do not expect any solvents to remain in these soils because of the high volatility and water solubility of these compounds. Likewise, we do not expect substances that adsorb to soils or have a low water solubility to have a transport mechanism allowing them to permeate subsurface soils at shallow depths. Similarly, we expect any contaminants attached to on-site soil particles and later blown off site to remain within the surface soil layer.

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