Skip directly to search Skip directly to A to Z list Skip directly to site content

PUBLIC HEALTH ASSESSMENT

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 MadisonMetropolitan Sewerage District. Contaminants of concern are selected for further analysis andare discussed in following sections. Areas considered to be "on-site" are the sludge lagoonsthemselves. All other areas are considered to be "off-site." Detailed accounts of each sampleand results from analysis can be found in the Remedial Investigation (RI) report for the site andin 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 levelsof health concern [1, p.5.9; 5, p.F11]. The PCBs occur primarily in the lagoon sludge. Thephysical 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) incomparison to concentrations in the supernatant (0.0028 ppm). It is unlikely that PCBs aremigrating 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 beneaththe sludge.

Table 1.

Polychlorinated Biphenyls (PCBs) On-Site (ppm) Madison Metropolitan Sewerage District Sludge Lagoons

MediumLowHigh    
    
YearReference

East Lagoon Sludge31202(Dry wt.)198422
 6185(Dry wt.)198723
 2.51170.0(Dry wt.)19911
West Lagoon Sludge15164(Dry wt.)198422
 786(Dry wt.)198623
 1.126.0(Dry wt.)19911
Underlying peatND.*0.43(Dry wt.)198416
 ND4.4(Dry wt.)19911
Lagoon supernatant0.0030.007 198422
 0.000780.0028 19911
Groundwater<0.0005<0.0005 198916
 NDND 19911

*ND = Not detected.

Concentrations of PCBs are not uniformly distributed throughout the lagoon system. Table 1 is asummary 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 PCBsin the biological reactors volatilized less than two percent of the total amount of PCBs removedfrom the sludge. Because air contact with sludge in the lagoons is considerably less than that inthe 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 thelagoons migrates to the groundwater. PCBs attach themselves quite strongly to soil andparticularly to sludge material. This prevents them from moving through the soils into thegroundwater. There is not a continuous, impermeable barrier between the lagoon sludge and thebedrock aquifer. However, the properties of the PCBs themselves prevent them fromcontaminating the groundwater beneath the lagoons. The shallow soil deposits under much ofthe lagoon area are not very permeable. Shallow groundwater flow in this unit is inconsistentbecause of variation in precipitation and the volume of water in the lagoons. The wetlandssurrounding the lagoons serve as a local discharge area for groundwater. The remedialinvestigation report concluded that PCBs are not migrating from the site in groundwater. PCBswere not detected in groundwater (with limits of detection less than 0.0005 ppm). PCBs werenot 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 beresistant to seepage. Even when the water level outside the lagoon was five feet higher than thelevel inside, there was no visible seepage through the dike. Because Lagoon #2 is made ofdredged material rather than fill, there may be some seepage. Some lagoon water also flowsthrough 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 dikefailed 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 thanother fishes because the highest concentrations of PCBs in the drainage channel are in thesediments and because PCBs tend to accumulate in fats. In 1983, WDNR analyzed twocomposite samples of carp from the drainage channel adjacent to the lagoons and found PCBs at0.52 ppm and 0.58 ppm. Such concentrations are typical of those found in fish in the generalarea. The U.S. Department of Agriculture (USDA) and WBPH standard for PCBs in fish is 2ppm.

Table 2.

Polychlorinated Biphenyls (PCBs) Off-Site (ppm)
Madison Metropolitan Sewerage District Sludge Lagoons [1],[15]

MediumLowHighSample Year

Surface water<0.0002<0.00021983
 ND.*ND1991
Groundwater<0.0001<0.00011983
 NDND1991-3
Sediment<0.2131983
 ND1.851991-3
Fish (carp)<0.20.521983

*ND = Not detected

PHYSICAL HAZARDS

No physical hazards were apparent outside of the area where access is restricted. Access isrestricted by a six foot, chain-link fence topped with strands of barbed wire. On-site physicalhazards of the sludge lagoons are not significantly different from those bird watchers mayencounter in other wetland settings.

PATHWAYS ANALYSIS

This section describes exposure scenarios for known (completed) exposures and for exposuresthat 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 investigationprocess accurately characterizes the potential on-site exposure pathways into the following threegeneral scenarios:

    1) District Employees exposed during routine monitoring and maintenance of the lagoons anddikes. During routine maintenance and monitoring of lagoons and dikes, the District employees may be exposed to sludges. However, typical health and safety precautions, such as wearing gloves and coveralls, tend to minimize or eliminate contact with the sludge.

    2) Bird watchers permitted to enter the lagoon area. This scenerio assumes that the bird watchersor "birders" would occasionally leave the footpaths and enter the lagoons themselves. Thisactivity 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 wouldrepresent 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 notpose a significant hazard to children.

WBPH has reviewed the human health portion of the baseline risk assessment for the site andconcurs with its conclusions for on-site exposure pathways. The conclusions of the riskassessment 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 theBaseline Risk Assessment. [2]

PUBLIC HEALTH IMPLICATIONS

The following section includes a discussion of health effects from potential exposure to PCBs atthe site.

TOXICOLOGIC EVALUATION

The baseline risk assessment performed for the site as part of the EPA remedial investigationprocess 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 healthhazard. The overall potential increased lifetime cancer risk to bird watchers is three in onemillion. This risk estimate was derived with the assumption that bird watchers would leave thetrail 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 exposuredose estimates as calculated by public health assessment guidance, and concurs with itsconclusions for risks associated with on-site exposure pathways. These low increases intheoretical cancer risk do not constitute a public health hazard. Each of the potential increasedcancer risks, though already quite low, are reduced further by the implementation of the selectedremedy for the site. Based on the results of the baseline risk assessment, WDOH finds thatexposure to on-site sludges does not pose a public health hazard. For more information about theassumptions 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 developmentaleffects. Therefore, it is prudent to consider that such effects are possible in people [20]. Cautionis justified because PCBs readily accumulate in body fat, cross a mother's placenta, and pass inbreast milk from mothers to nursing infants. For these reasons, embryos, fetuses, and nursinginfants 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 classifiesthem 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 communityliving near the Madison Metropolitan Sewerage District Site.

  1. Citizens have asked about the effects of heavy metals in the lagoon sludge applied toagricultural lands.

    WBPH reviewed WDNR and EPA criterion for agricultural application approvals for heavymetals and has found it to be protective of public health. WDNR strictly controls the depositionof heavy metals in sludge on agricultural lands. WDNR has adopted risk-based lifetime loadinglimits for heavy metals under 40 CFR Part 503 in their sludge management rule (NR 204). Thequality 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. WDNRinspects and approves all land application sites prior to their initial use. Because the applicationof metals to agricultural soils is controlled in this manner, this health assessment does not reviewdata on the accumulation in soil of metals from sludge.

  2. Concerns were raised about the PCBs in sludge applied to agricultural lands.

    The purpose of lifetime loading limits for metals in sludge spread on agricultural fields is torecognize that persistent contaminants accumulate in the soils with each application. However,PCBs are generally considered to be persistant compounds and may also be expected toaccumulate in soils with subsequent sludge applications. There are no lifetime loading limits forPCBs in existing sludge spreading regulations. The sludge PCB concentration is the only directlimiting factor (below 50 parts per million PCBs). The Metrogro Program is in compliance withstate 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 beprotective of public health and the environment. WBPH will update those who have expressedinterest in the sludge spreading issues on the progress of the working group.


Next Section       Table of Contents

  
 
USA.gov: The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #