PETITIONED HEALTH CONSULTATION
SURFACE WATER AND SEDIMENT PATHWAYS
SOUTHERN WOOD PIEDMONT COMPANY
(NORFOLK SOUTHERN FACILITY)
MACON, BIBB COUNTY, GEORGIA
In this section, ATSDR evaluates environmental monitoring data to determine whether and to what extent wood preserving compounds (e.g., creosote and pentachlorophenol) are present in the surface water and sediment of the on-site drainage ditch, Dillon Branch Creek, and Freedom Park Pond (see Figure 2). ATSDR also evaluated the data for the presence of constituents (or elements of wood preserving compounds) such as polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) because they are common impurities in technical grade pentachlorophenol; these classes of compounds are commonly referred to as dioxins and furans, respectively. Information on the use and environmental fate and transport of wood preserving compounds is presented in Appendix E.
The following subsection provides a description of the area's surface water bodies, followed by a review of available surface water and sediment quality data and remediation activities and how they were evaluated by ATSDR.
The SWP site lies in a region of rolling terrain drained primarily by the southeasterly flowing Ocmulgee River and its tributaries. The surface water bodies located on or near the site include the on-site drainage ditch, Dillon Branch Creek, and Freedom Park Pond.
On-Site Drainage Ditch
The on-site drainage ditch is a shallow, partially and often densely vegetated creek, that traverses the SWP site (see Figure 2). The ditch originates northeast of the site (and reportedly receives discharge from Freedom Park Pond) and travels 2,000 feet through the site before it converges with Dillon Branch Creek along the site's southwestern perimeter (Geraghty & Miller, 1991a). A 1990 creek inspection reported extensive dry stretches interspersed with areas of stagnant water devoid of aquatic life and discolored sediment throughout the creek's length. Water depth in the stagnant areas ranged from 1 to 4 inches depths thus water flow is minimal and suspected to occur only following periods of heavy precipitation (Geraghty & Miller, 1991a). SWP has since excavated an approximately 200-foot long section of the contaminated sediment from the on-site drainage ditch and replaced it with clean fill (Davis, 1996).
An unauthorized path between Freedom Park and the drainage ditch suggests that trespassers may have had access to the ditch in the past. According to a Macon-Bibb County Health Department representative, however, the ditch has never been used for recreational activity (e.g., swimming, wading, fishing) (Taylor, 1996), as the ditch is inaccessible and unsuitable for such use because of its vegetated banks and low intermittent flow. Since 1992, public access to the site and the on-site ditch has been restricted by a perimeter fence.
Dillon Branch Creek
Dillon Branch Creek originates in an unnamed pond located approximately 3,500 feet north of the SWP site. The creek flows in a southeasterly direction toward the SWP site by abandoned commercial/industrial property that contains a former underground storage tank (UST) and several cement culverts. Domestic trash and debris found on or near the creek, including drums labeled for toluene diisocyanate and volatile organic compounds (VOCs), indicate that unauthorized dumping may have occurred. Further downstream (and still upstream of the site), a groundwater seep discharges into the creek, where an orange bacterial growth and oil sheen were observed at the seep (Geraghty & Miller, 1991a).
Dillon Branch Creek continues to flow in a southeasterly direction, eventually flowing along the western perimeter and through the southern (nonindustrial) portion of the SWP site (see Figure 2) before merging with the on-site drainage ditch. During a 1990 creek reconnaissance, noticeable reddish-brown discoloration of Dillon Branch Creek sediment immediately downstream of the merge was noted. The creek is characterized by a shallow water level that ranges in depth from 0.5 to 4 inches, and although the width of the creek varies from 8 to 20 feet the width of the water ranges from only 1 to 4 feet across the bed. Throughout most of its length, the creek's banks are very tall (up to 8 feet), steep, and show signs of erosion. The banks consist of a relatively thin layer of soil overlying a partly consolidated fluvial sedimentary deposit of coarse sand, pebbles, and cobbles. Dillon Branch Creek has eroded much of the bank and confining clay layer of the shallow aquifer; consequently, the westwardly moving groundwater may be releasing contaminants into the creek.
Downstream from the site, Dillon Branch Creek travels through an urban, residential area. Near the Hillcrest Avenue area, several large stormwater pipes drain into the creek. Dillon Branch Creek continues to flow through more residential areas until it merges with Rocky Creek.
Although Dillon Branch Creek travels through residential property, it not known with certainty whether and to what extent Dillon Branch Creek has been or is used for recreational purposes. The conditions of the creek (i.e., low flow and steep banks) and the lack of aquatic life are not favorable for access or recreational activity. These conditions also minimize the likelihood that Dillon Branch Creek will flood and overflow into neighboring residential areas.
Freedom Park Pond
Freedom Park Pond is located within Freedom Park (see Figure 3) and was formed following the construction of a dam that separates Freedom Park from SWP's on-site drainage ditch. It is believed to be fed by springs, seeps, and possibly leaking water mains (Davis, 1996). The city posted a sign at Freedom Park Pond warning people against swimming because no lifeguard was on duty at the pond. Although people do not swim in the pond, it is a popular fishing spot (Fortson, 1996). In 1995, the city emptied the pond in anticipation of the construction of baseball fields in that area (Davis, 1996; Talbert, 1996), and surrounded the site by a fence to restrict access; however, the baseball fields were never built. The Macon Parks and Recreation Department refilled the pond, stocked it with fish, including largemouth bass and catfish, and reopened it to the public for fishing in April 1997 (FPC, 1997).
ATSDR evaluates contamination in surface water and sediment by using comparison values (e.g., Maximum Contaminant Levels, Lifetime Health Advisories for Drinking Water, Reference Dose Media Evaluation Guides, and Environmental Media Evaluation Guides) to select chemicals requiring further evaluation. These comparison values represent the estimated contaminant concentrations in surface water or sediment that are not likely to cause adverse human health effects, given a standard daily ingestion rate and standard body weight. The comparison values are calculated from the scientific literature available on exposure and health effects. Because the comparison values do not represent thresholds of toxicity, chemical concentrations above comparison values do not necessarily pose health hazards.
With the exception of 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD), ATSDR and the U.S. Environmental Protection Agency (EPA) have not established comparison values or guidance levels for other dioxin and furan isomers. In the absence of comparison values, ATSDR uses toxic equivalents (TEQ) of 2,3,7,8-TCDD to estimate the risks associated with other dioxin and furan forms in environmental media. Appendix F describes the methodology used to derive dioxin and furan TEQs.
Processing waste from the SWP settling ponds was discharged into the on-site drainage ditch for several decades, resulting in a substantial contribution of contamination to the ditch. Only limited monitoring has been conducted to characterize the extent of contamination in the on-site drainage ditch and to determine whether site-related contaminants have migrated to nearby Dillon Branch Creek or Freedom Park Pond. No monitoring of fish for site-related contaminants (e.g., polycyclic aromatic hydrocarbons [PAHs], dioxins, and furans) has been conducted at Freedom Park Pond.
Surface Water Quality Data
Between 1984 and 1987, GAEPD collected three surface water samples from the on-site drainage ditch, seven surface water samples from Dillon Branch Creek at a location downstream of the site and near Hillcrest Avenue, and one sample from the off-site Freedom Park Pond. All samples were analyzed for sVOCs, including PAHs and pentachlorophenol, and selected samples were analyzed for volatile organic compounds (VOCs). Only the on-site drainage ditch contained contaminants in excess of ATSDR comparison values: pentachlorophenol was detected at 1,512 parts per billion (ppb) and the PAH naphthalene at 206 ppb (see Appendix B, Table 1). The off-site Dillon Branch Creek and Freedom Park Pond surface water samples contained levels of most PAHs below comparison values (see Appendix B, Table 2).
Sediment Quality Data
SWP collected sediment samples from the on-site drainage ditch, Dillon Branch Creek, and Freedom Park Pond.
On-Site Drainage Ditch
As part of a 1989 sampling effort, SWP detected wood preserving compounds (reported as light or heavy polynitroaromatic compounds) in five sediment samples collected from the on-site drainage ditch. To further characterize the nature and extent of contamination in the on-site drainage ditch, SWP collected 14 sediment samples from seven trenches cut into the ditch and analyzed the samples for PAHs and pentachlorophenol. Samples were collected at 2 feet and 8 feet below ground surface. Concentrations of the PAH benzo(a)pyrene (between 8.7 and 280 parts per million [ppm]) and other PAHs in the samples were greater than the ATSDR comparison value for benzo(a)pyrene of 0.1 ppm. The highest PAH concentrations were found in samples collected in the visibly stained area near the former wood preserving plant (north of Roff Avenue) (ETE, 1990). PAH concentrations decreased uniformly with distance from the wood preserving plant and no PAHs were present in samples collected from the southernmost section of the ditch where it joins Dillon Branch Creek. No pentachlorophenol was detected in any of the samples collected from the on-site drainage ditch.
SWP additionally analyzed three sediment samples from the most contaminated portion of the drainage ditch for dioxins and furans. Although 2,3,7,8-TCDD was present in the sediment at concentrations of 0.0000048 ppm at depths from 0 to 6 inches and 0.000013 ppm at depths from 12 to 18 inches, the less toxic octachlorinated isomer comprised the majority of the dioxin and furan mixture (see Appendix B, Table 3) (Geraghty & Miller, 1991b; ChemRisk, 1991). This pattern of high concentrations of the octachlorinated isomers (or hepta- or hexachlorinated isomers) in sediment is usually indicative of a local combustion source or wood preservative use (e.g., pentachlorophenol) (Bopp et al., 1991).
SWP has excavated an approximately 200-foot long section of the contaminated sediment from the on-site drainage ditch (Davis, 1996). Furthermore, they have removed visibly stained on-site soil, which is likely to reduce the contribution of contaminants to the on-site drainage ditch through surface runoff. SWP has not proposed any further remediation of the on-site drainage ditch.
Dillon Branch Creek
Eleven samples collected from Dillon Branch Creek at locations downstream of the SWP site were analyzed for metals (including lead, arsenic, and cadmium), VOCs, semi-volatile organic compounds, dioxins, and furans to determine whether site-related contaminants had migrated to off-site areas where people might contact surface water or sediment. Elevated levels of PAHs were detected in one sample, which was collected 800 feet downstream of the site and near an underground storage tank (UST), and dioxin and furan levels below ATSDR comparison values were present in Dillon Branch Creek. An ongoing groundwater recovery system is expected to reduce any contamination that may migrate toward Dillon Branch Creek via groundwater transport.
Table 4 (Appendix B) presents the dioxin and furan concentrations and corresponding TEQs detected in Dillon Branch Creek. Although the TEQs for dioxins and furans detected in Dillon Branch Creek are typical of levels found in sediment of nonindustrial areas, the distribution pattern of dioxins and furans in the samples (i.e., a majority of hepta- and octachlorinated isomers) suggests that these contaminants may be a result of local industrial sources or wood preserving compound use (Bopp et al., 1991). Groundwater and surface water entering the creek may be responsible for migration of the low levels of contaminants from the site to the creek.
Freedom Park Pond
Only one sediment sample was collected from Freedom Park Pond. The sample was analyzed for PAHs, VOCs, dioxins, furans, and metals, but the sample did not contain compounds associated with wood preserving activities at levels above the ATSDR comparison values (see Appendix B, Table 4) (ChemRisk, 1992).
As with Dillon Branch Creek, dioxins and furans in Freedom Park Pond are typical of levels found in sediment from
nonindustrial areas, and the distribution pattern of dioxins and furans in the samples (i.e., a majority of hepta- and
octachlorinated isomers) suggests that these contaminants may be a result of local industrial sources or wood preserving
compound use. The groundwater seep may be responsible for migration of the low levels of contaminants from the site to
Freedom Park Pond.
Although only limited environmental sampling has been conducted to characterize the extent of contamination in the surface water bodies on or near the SWP site, ATSDR considers the potential for human exposure to contaminants through surface water or sediment pathways to be minimal.
Elevated concentrations of PAHs were detected in the surface water and dioxins and furans were found in the sediment of the on-site drainage ditch. Regardless of the contaminants present, a public health threat exists only if people are exposed to the contaminated surface water or sediment. Currently, people are restricted from the site by a perimeter fence and SWP has removed the most contaminated areas of the on-site drainage ditch. SWP also intends to keep the site inactive for an indefinite period. Based on these measures, current exposure to contaminants in the on-site drainage ditch is unlikely and future human exposures are not expected to occur.
Trespassers who accessed the ditch via the unauthorized trail from Freedom Park in the past (prior to the installation of the site's fence) could have been exposed to wood preserving compounds, dioxins, and furans. Any exposure associated with trespassing near the ditch is not expected to pose a health hazard because of the infrequent nature of the exposure.
Contaminants (e.g., PAHs, dioxins, furans) at levels below the ATSDR comparison values were detected in the surface water and sediment collected from several locations along Dillon Branch Creek, including residential areas downstream of the site. Therefore, these levels are not expected to pose health hazards to people who contact the creek's surface water or sediment. In addition, other sources, including debris and stormwater pipes along the creek, are potentially contributing to contaminants detected in the creek. SWP site remediation measures, including the groundwater recovery system and sediment removal (from the on-site ditch), are expected to reduce potential migration of SWP site-related contaminants to the creek in the future.
Although the creek travels through residential areas downstream of the SWP site, no information is available to suggest that Dillon Branch Creek is used for recreational activity. The only evidence of human activity was the domestic trash and debris observed behind residential properties and adjacent to the creek. Furthermore, many sections of the creek are unsuitable for recreational activity (e.g., swimming, wading, fishing) because of their low flow, steep banks, and lack of aquatic life. Even if adults or children access the creek, they are likely to have only brief or infrequent skin contact with sediment or surface water. This type of exposure to the low levels of PAHs, dioxins, and furans found in portions of the creek is not likely to cause adverse health effects.
Site-related contaminants at levels below very conservative ATSDR comparison values were detected in the surface water and sediment samples taken from Freedom Park Pond. Swimming and other activities that might permit skin contact (e.g., wading) with surface water or sediment containing low levels of contaminants are not allowed at the pond, and a "No Swimming" sign is posted. According to the Macon Parks and Recreation Department, the sign is posted because no lifeguard is on duty, not because of contamination in the pond (Fortson, 1996). Direct exposures, if any, to the contaminants in the surface water or sediment, such as incidental skin contact, were probably brief and infrequent and not likely to pose a health hazard.
Although swimming is rare, many people fish at the pond; consequently, indirect exposures to dioxins or furans through consumption of Freedom Park Pond fish may have occurred or may be occurring. Certain fish species accumulate even the very low levels of contaminants, such as dioxins, that may be present in sediment. The highest concentrations appear in larger fish that have resided in the water body for the longest time. Because fish monitoring data are not available for Freedom Park Pond, ATSDR does not know with certainty whether Freedom Park Pond fish accumulated site-related contaminants, primarily dioxins or furans, to levels that could pose a health hazard.
ATSDR reviewed scientific literature to understand the relationship between dioxin-contaminated water or sediment and uptake by fish. Some scientific evidence indicates that fish primarily accumulate dioxin via ingestion of sediment (Sherman, 1992). In one study in which fish accumulated dioxins in excess of the Food and Drug Administration (FDA) guidance levels for dioxin in foodstuff (0.000025 ppm TEQs), the water body's dioxin sediment concentration ranged from 0.0000141 ppm TEQs to 0.000142 ppm TEQs (Ling, 1995; ATSDR, 1989). These dioxin sediment concentrations are approximately 8 to 80 times greater than the dioxin sediment concentrations found in Freedom Park Pond.
Another study investigated much lower water body sediment dioxin concentrations (0.000003 ppm TEQs to 0.000051 ppm TEQs), which fall in the same range as those concentrations found in Freedom Park Pond, and reported fish uptake of dioxin and furan to concentrations of 0.0000010 ppm TEQs to 0.000003 ppm TEQs, which are below the FDA guidance level (Petreas, 1992). Although difference in fish species and lipid content may influence uptake, elevated fish tissue concentrations appear to correlate to high dioxin sediment concentrations. On this basis, ATSDR does not expect that Freedom Park Pond fish would accumulate concentrations of the dioxins and furans present in sediment to levels associated with human health hazards.
Although ATSDR determined that dioxins and furans are not expected to accumulate in Freedom Park Pond fish to levels associated with human health hazards, fish sampling would provide useful data for interpreting potential health hazards from consumption of Freedom Park Pond fish.