MADISON METROPOLITAN SEWERAGE DISTRICT SLUDGE LAGOONS
TOWN OF BLOOMING GROVE, DANE COUNTY, WISCONSIN
ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS
This section describes contamination and other hazards associated with the Madison Metropolitan Sewerage District. Contaminants of concern are selected for further analysis and are discussed in following sections. Areas considered to be "on-site" are the sludge lagoons themselves. All other areas are considered to be "off-site." Detailed accounts of each sample and results from analysis can be found in the Remedial Investigation (RI) report for the site and in WDNR site files.
ON-SITE CONTAMINATION
PCBs are the primary contaminants of concern at this site. Several heavy metals (arsenic, barium, cadmium, chromium, lead, mercury, and zinc) are present in the sludge but not at levels of health concern [1, p.5.9; 5, p.F11]. The PCBs occur primarily in the lagoon sludge. The physical and chemical properties of PCBs are such that they adsorb readily to organic matter. Table 1 shows that PCB concentrations in sludge in Lagoon #2 are relatively high (1-170 ppm) in comparison to concentrations in the supernatant (0.0028 ppm). It is unlikely that PCBs are migrating beyond the peat layer at the bottom of the lagoons. During the remedial investigation, PCBs were detected in two of the five core samples taken of the upper peat layer directly beneath the sludge.
Table 1
Polychlorinated Biphenyls (PCBs) On-Site (ppm)
Madison Metropolitan Sewerage District Sludge Lagoons
| Medium | Low | High | |
Year | Reference |
| East Lagoon Sludge | 31 | 202 | (Dry wt.) | 1984 | 22 |
| 6 | 185 | (Dry wt.) | 1987 | 23 | |
| 2.51 | 170.0 | (Dry wt.) | 1991 | 1 | |
| West Lagoon Sludge | 15 | 164 | (Dry wt.) | 1984 | 22 |
| 7 | 86 | (Dry wt.) | 1986 | 23 | |
| 1.1 | 26.0 | (Dry wt.) | 1991 | 1 | |
| Underlying peat | ND.* | 0.43 | (Dry wt.) | 1984 | 16 |
| ND | 4.4 | (Dry wt.) | 1991 | 1 | |
| Lagoon supernatant | 0.003 | 0.007 | 1984 | 22 | |
| 0.00078 | 0.0028 | 1991 | 1 | ||
| Groundwater | <0.0005 | <0.0005 | 1989 | 16 | |
| ND | ND | 1991 | 1 | ||
*ND = Not detected. | |||||
Concentrations of PCBs are not uniformly distributed throughout the lagoon system. Table 1 is a summary of sample results from the lagoons from 1984 to 1991.
Two sources of evidence suggest that volatilization of PCBs from the lagoons is not significant. First, chromatograms of PCBs from Lagoon #2 show little "weathering," or loss of PCB peaks. Second, a study of aerobic digestion of PCBs in sludge found that active "air stripping" of PCBs in the biological reactors volatilized less than two percent of the total amount of PCBs removed from the sludge. Because air contact with sludge in the lagoons is considerably less than that in the reactors, one would expect a lower rate of volatilization from the lagoons [11, pp.28-29].
OFF-SITE CONTAMINATION
Groundwater
Future PCB contamination of groundwater is not expected to occur even if water from the lagoons migrates to the groundwater. PCBs attach themselves quite strongly to soil and particularly to sludge material. This prevents them from moving through the soils into the groundwater. There is not a continuous, impermeable barrier between the lagoon sludge and the bedrock aquifer. However, the properties of the PCBs themselves prevent them from contaminating the groundwater beneath the lagoons. The shallow soil deposits under much of the lagoon area are not very permeable. Shallow groundwater flow in this unit is inconsistent because of variation in precipitation and the volume of water in the lagoons. The wetlands surrounding the lagoons serve as a local discharge area for groundwater. The remedial investigation report concluded that PCBs are not migrating from the site in groundwater. PCBs were not detected in groundwater (with limits of detection less than 0.0005 ppm). PCBs were not detected in monitoring wells installed at the site or in the nearby municipal water supply well [1].
Surface Water and Sediments
As the District removed sludge from Lagoon #1, the dikes around that lagoon were found to be resistant to seepage. Even when the water level outside the lagoon was five feet higher than the level inside, there was no visible seepage through the dike. Because Lagoon #2 is made of dredged material rather than fill, there may be some seepage. Some lagoon water also flows through a pipe that carries overflow water back to the sewage treatment plant. A release of sludge and supernatant, likely containing PCBs, occurred when Lagoon #2's dike failed in 1970.
Fishery
Concentrations of PCBs are generally higher in carp than in other species of fish in the same area [17, pp.11-12]. Carp are both fatty fishes and bottom feeders. They accumulate more PCBs than other fishes because the highest concentrations of PCBs in the drainage channel are in the sediments and because PCBs tend to accumulate in fats. In 1983, WDNR analyzed two composite samples of carp from the drainage channel adjacent to the lagoons and found PCBs at 0.52 ppm and 0.58 ppm. Such concentrations are typical of those found in fish in the general area. The U.S. Department of Agriculture (USDA) and WBPH standard for PCBs in fish is 2 ppm.
Table 2
Polychlorinated Biphenyls (PCBs) Off-Site (ppm)
Madison Metropolitan Sewerage District Sludge Lagoons [1],[15]
| Medium | Low | High | Sample Year |
| Surface water | <0.0002 | <0.0002 | 1983 |
| ND.* | ND | 1991 | |
| Groundwater | <0.0001 | <0.0001 | 1983 |
| ND | ND | 1991-3 | |
| Sediment | <0.2 | 13 | 1983 |
| ND | 1.85 | 1991-3 | |
| Fish (carp) | <0.2 | 0.52 | 1983 |
*ND = Not detected | |||
PHYSICAL HAZARDS
No physical hazards were apparent outside of the area where access is restricted. Access is restricted by a six foot, chain-link fence topped with strands of barbed wire. On-site physical hazards of the sludge lagoons are not significantly different from those bird watchers may encounter in other wetland settings.
This section describes exposure scenarios for known (completed) exposures and for exposures that may have occurred or could occur in the future (potential).
COMPLETED EXPOSURE PATHWAYS
WBPH has no evidence that anyone has been exposed to PCBs from the lagoons. Therefore, there are no completed exposure pathways at this site.
POTENTIAL EXPOSURE PATHWAYS
The baseline risk assessment performed for the site as part of the EPA remedial investigation process accurately characterizes the potential on-site exposure pathways into the following three general scenarios:
2) Bird watchers permitted to enter the lagoon area. This scenerio assumes that the bird watchers or "birders" would occasionally leave the footpaths and enter the lagoons themselves. This activity is not expected to occur frequently if at all.
3) Local residents who may be exposed to PCBs transported from the site through the air. Trespassers were also included in this scenario; however, the bird watcher scenario would represent the trespasser scenario as well. Because the facility is locked after business hours, children would not likely be on the site alone or without being seen; therefore, the lagoons do not pose a significant hazard to children.
WBPH has reviewed the human health portion of the baseline risk assessment for the site and concurs with its conclusions for on-site exposure pathways. The conclusions of the risk assessment for each pathway is discussed in the Toxicological Implications section of this report. For more information about the assumptions and on-site risks evaluation, please refer to the Baseline Risk Assessment. [2]
The following section includes a discussion of health effects from potential exposure to PCBs at the site.
TOXICOLOGIC EVALUATION
The baseline risk assessment performed for the site as part of the EPA remedial investigation process characterizes the risks from potential on-site exposure pathways[2]:
1) The exposure assessment for employees did not identify a noncancer related health hazard. The overall potential increased lifetime cancer risk is five in one million.
2) The exposure assessment for bird watchers also did not identify a noncancer related health hazard. The overall potential increased lifetime cancer risk to bird watchers is three in one million. This risk estimate was derived with the assumption that bird watchers would leave the trail approximately 30 times per year over a 30 year period.
3) The exposure assessment for local residents did not identify a noncancer related health hazard. The overall potential increased cancer risk to local residents is less than one in one million.
WBPH reviewed the baseline risk assessment for the site, compared the results with exposure dose estimates as calculated by public health assessment guidance, and concurs with its conclusions for risks associated with on-site exposure pathways. These low increases in theoretical cancer risk do not constitute a public health hazard. Each of the potential increased cancer risks, though already quite low, are reduced further by the implementation of the selected remedy for the site. Based on the results of the baseline risk assessment, WDOH finds that exposure to on-site sludges does not pose a public health hazard. For more information about the assumptions and on-site risks evaluation, please refer to the Baseline Risk Assessment. [2]
Experiments with laboratory animals have shown that some PCB mixtures, at very high doses, produce such adverse effects as liver damage, skin irritations, reproductive and developmental effects. Therefore, it is prudent to consider that such effects are possible in people [20]. Caution is justified because PCBs readily accumulate in body fat, cross a mother's placenta, and pass in breast milk from mothers to nursing infants. For these reasons, embryos, fetuses, and nursing infants receiving PCBs from exposed mothers may be more sensitive to the toxic effects of PCBs [20]. Because some PCB mixtures have caused cancer in laboratory animals, EPA classifies them as "probable human carcinogens"[20, pp.100-101].
COMMUNITY HEALTH CONCERNS EVALUATION
This section is an evaluation of the health concerns that have been posed by the community living near the Madison Metropolitan Sewerage District Site.
WBPH reviewed WDNR and EPA criterion for agricultural application approvals for heavy metals and has found it to be protective of public health. WDNR strictly controls the deposition of heavy metals in sludge on agricultural lands. WDNR has adopted risk-based lifetime loading limits for heavy metals under 40 CFR Part 503 in their sludge management rule (NR 204). The quality of the sludge determines both the annual loading rate and the site lifetime [5, p.F9]. Annual application rates may not exceed the nitrogen requirement of the crop grown. WDNR inspects and approves all land application sites prior to their initial use. Because the application of metals to agricultural soils is controlled in this manner, this health assessment does not review data on the accumulation in soil of metals from sludge.
The purpose of lifetime loading limits for metals in sludge spread on agricultural fields is to recognize that persistent contaminants accumulate in the soils with each application. However, PCBs are generally considered to be persistant compounds and may also be expected to accumulate in soils with subsequent sludge applications. There are no lifetime loading limits for PCBs in existing sludge spreading regulations. The sludge PCB concentration is the only direct limiting factor (below 50 parts per million PCBs). The Metrogro Program is in compliance with state and federal requirements for the application of low-level PCB sludges.
This assessment does not evaluate sludge spreading of the low level PCB contaminated sludges. Because the spreading of low level PCB contaminated sludges is a topic of statewide interest, WDNR has established a PCB working group to develop policy recommendations that will be protective of public health and the environment. WBPH will update those who have expressed interest in the sludge spreading issues on the progress of the working group.
