PUBLIC HEALTH ASSESSMENT
MADISON METROPOLITAN SEWERAGE DISTRICT SLUDGE LAGOONS
TOWN OF BLOOMING GROVE, DANE COUNTY, WISCONSIN
The Madison Metropolitan Sewerage District has operated the Nine Springs WastewaterTreatment Plant since 1933. In 1942 a 52-acre lagoon was constructed for storing sludgeproduced from its sewage treatment process. By the 1960s, the District added a second lagoon(86 acres) adjacent to the first lagoon. In 1974, the District began a program to recycle sludgefrom the lagoons by incorporating it into the soils of nearby croplands. This is referred to as theMetrogro Program. In 1982, the District discovered that some of the sludge in the lagoonscontained polychlorinated biphenyls (PCBs) above 50 parts per million. Most of the lagoonsludge contained PCBs below 50 parts per million. However, some concentrations exceeded 200parts per million. The District's sludge monitoring system has ensured that only sludge withPCB concentrations below 50 parts per million were used in the Metrogro Program. The 50 partsper million limit represents the upper limit for land application under the federal ToxicSubstances Control Act. In 1990 the portion of the lagoon system with PCB concentrationsabove 50 parts per million was added to the U.S Environmental Protection Agency (EPA)National Priorities List of Superfund Sites.
There is no evidence of public exposure to chemicals from the lagoons at levels that would resultin adverse health effects, and the Wisconsin Bureau of Public Health (WBPH) is not aware ofany reports of unusual numbers of disease near this site. The lagoon system is located in a largewetland area without nearby residential areas. Due to the location of the lagoons and the limitedopportunity for direct contact with the PCB contaminated sludge, the site does not pose a publichealth hazard. The remedial investigation for the site found that the PCBs are effectivelycontained in the lagoons, and are not migrating to the groundwater or adjacent surface waters. Workers and members of the public interested in bird watching have access to the site andlagoons themselves. Exposures related to worker and bird watcher access to the site does notpose a public health hazard. The selected remedy for the site includes consolidating and cappingthe contaminated sludge. The remedy will also include continued monitoring and maintenanceactivities, as well as deed restrictions on future uses of the site. This remedy will keep peoplefrom contacting contaminants on the site.
During the evaluation of the lagoon sludge, concerns were raised about the sludge applied tofarm fields in the Metrogro program. Because the PCB concentrations in the sludge used in theprogram were below 50 parts per million, the applications are in compliance with EPArequirements. This assessment does not evaluate sludge spreading of the low-level PCBcontaminated sludges. Because the spreading of low level PCB contaminated sludges is a topicof statewide interest, the Wisconsin Department of Natural Resources (WDNR) has established aPCB work group to develop policy recommendations that will be protective of public health andthe environment. WBPH is working with this group, and will update those who expressed aninterest in the sludge spreading issues and the progress of the working group.
The Madison Metropolitan Sewerage District (District) sludge lagoons were added to the U. S.Environmental Protection Agency's (EPA) National Priorities List in 1990. Located in the townof Blooming Grove, south of Madison (population of 191,000) and Monona (population of8,600), the lagoons occupy 138 acres in a wetland next to the District's sewage treatment plantnear the intersection of Moorland Road and Raywood Road. The wetland lies on the westernshore of Lake Waubesa. This 2,080-acre lake is the third in a series of four, interconnected lakeswithin the Yahara River watershed . Nine Springs Creek flows along the southern and easterndikes of the lagoon and empties into Lake Waubesa. A drainage ditch flows along the northerndikes of the lagoons and empties into Nine Springs Creek.
The lagoons overlie lacustrine soils of peat, silt, and clay. The thickness of these soils rangesfrom less than five feet at the western edge of the site to about eighty feet at the center. A siltysand glacial till, ranging from zero to over seventy feet in thickness, underlies the lacustrinedeposit. A lower silt and clay unit occurs in some areas at depths of over fifty feet, and a lowertill unit occurs at depths of over one hundred feet. Cambrian age sandstone bedrock at depths ofless than one hundred to over two hundred feet underlies the glacial deposit. The bedrock servesas the drinking water aquifer for the cities of Madison and Monona [16, p.4.2]. There are nocontinuous, impermeable, geologic barriers to separate water from the lagoons completely fromthe underlying bedrock aquifer. The wetland surrounding the lagoons generally serves as a localgroundwater discharge area [17, p.6]. In other words, groundwater in this area appears to flowtoward the ground surface rather than down toward the bedrock.
The District constructed andbegan storing digested sewagesludge in its first lagoon in 1942. The fifty-two acre facility,surrounded by soil berms, wasexpanded in 1968 with theaddition of an eighty-six acrelagoon adjacent to the east side ofthe original lagoon [1, p.1.10]. The lagoons contain sludge,consisting of three to twentypercent solids, and supernatant[1, Tab.5.6]. In 1970, a 150-footsection of the northern dike of thenew lagoon broke and eighty-fivemillion gallons of sludge andsupernatant flowed into NineSprings Creek and Lake Waubesa. A fish kill followed due todecreased oxygen levels. In 1973a section of the southern dike ofthe new lagoon failed and nearlyreleased additional sludge[14, p.A1]. The dike system hassince been stabilized, but theDistrict decided that the best long-term protection of the nearby lake and river system was to remove the sludge and to restore theoriginal sedge meadow [15, p.2].
In 1975, the District began a "Metrogro" program to apply sludge as a fertilizer on nearbyagricultural lands. By 1988, roughly 28,000 acres of agricultural land had received digestedsludge [15, p.A3]. All newly produced sludge and 23,000 dry tons of old sludge had beenremoved from Lagoon #1 [15, p.2].
In 1982, the District discovered that some of the old sludge contained PCBs at concentrationsexceeding 50 parts per million (ppm) dry weight. "Old" sludge refers to sludge that hadoriginally been stored in the lagoon system. In 1994, the District stopped storing new sludge inthe lagoons. It constructed three six-million gallon storage tanks to hold new sludge until itcould be applied to area farmlands .
In 1991, the District started building dikes on the east side of Lagoon #1 to facilitate permanentremoval of old sludge. All of the sludge and some of the underlying peat was removed from thisarea and applied to croplands. In 1993, the District removed another 10 acres of Lagoon #1. In1995, the District began removing the remainder of the sludge from Lagoon #1. Final sludge andpeat removal from Lagoon #1 will be completed in 1997. The District added several new dikesto the western part of Lagoon #1 to facilitate the sludge removal.
Two dikes now divide Lagoon #2 into three sections. The western section contains sludge withPCB concentrations greater than 50 mg/kg. Results of additional sampling conducted in January1996 identified additional segments outside of the western most section of Lagoon #2 ascontaining sludge with PCB concentrations greater than 50 ppm. These sections are the onlyparts of the lagoon system subject to Superfund regulation. The District plans to apply sludgefrom the remainder of the lagoons to croplands .
In 1990, the District began planning a remedial investigation and feasibility study of the lagoonsystem. This study did not evaluate the croplands receiving lagoon sludge containing PCBs atless than 50 mg/kgdry weight. During Phase I of the remedial investigation, the Districtcollected preliminary field samples followed by comprehensive sampling. Phase II of theremedial investigation in 1993 provided additional samples of groundwater, wetland soils, andcreek sediment. Figure 3 shows the spacial distribution of PCB concentrations above and below50 ppm. As indicated earlier, portions of the lagoon sludge have already been removed andspread on farm lands. Those areas are also identified in Figure 3. The selected remedy for thesite involves constructing dikes and consolidating sludge containing PCB concentrations at orabove 50 ppm. Lagoon areas not already covered by natural vegetation would then be coveredwith soil and seeded. The site will continue to be monitored and the vegetation will bemaintained. A future deed restriction will also be placed on the property to ensure that futureuses do not interfere with the selected remedy.
The remedial investigation report was completed in January 1994 . A feasibility study wascompleted in September of 1996. The District prepared a baseline risk assessment of the lagoonsthat was also completed in September 1996 . The remedial investigation reported thefollowing conclusions:
- The peat acts as a capture zone that restricts migration of sludge constituents to theaquifer beneath the lagoons.
- Results indicate that groundwater is not affected by the lagoon sludge constituents.
- Nine Springs Creek and north ditch surface water results do not show contamination ismigrating through the dike walls.
- Sample results show no indication of sludge or contaminant migration.
- The sludge lagoons, including the 1970 dike failure, have not affected the wetland soilsadjacent to the North Ditch.
Because the PCB concentrations in the sludge were below 50 parts per million, the applicationsare in compliance with EPA requirements. This assessment does not evaluate sludge spreadingof the low-level PCB contaminated sludges. Because the spreading of low level PCBcontaminated sludges is a topic of statewide interest, the Wisconsin Department of NaturalResources (WDNR) has established a PCB work group to develop policy recommendations thatwill be protective of public health and the environment.
Two representatives of WBPH and a representative of WDNR met with two representatives ofthe Madison Metropolitan Sewerage District at the site on April 26, 1989. The group observedthe site from the dikes surrounding the two lagoons. A six-foot, chain-link fence topped withthree strands of barbed wire forms a barrier between the western side of the site and Raywoodand Moorland roads. "No trespassing" signs are posted on the fence. The six-foot, chain-linkgate at the entrance is open only during normal business hours. Wetlands, a drainage channel,and Nine Springs Creek surround the remainder of the site.
Lagoon #1 consists of two sections separated by a dike. The District's representatives said thatsampling in 1986, unlike that in 1983 and 1984, showed that most of the sludge from the westernlagoon contained less than 50 ppm PCBs. Most of this sludge was removed in 1987 and used inthe Metrogro program. A clamshell dredge was being placed in Lagoon #2 to remove sludge thatcontains PCBs at less than 50 ppm. District officials said that all of the sludge removed from thelagoon will be pumped to the plant for sampling. Those loads that contain concentrations ofPCBs less than 50 ppm will be incorporated into farm land in the Metrogro program, and allloads containing more than 50 ppm will be pumped, through a separate pipe, back to Lagoon #2.
The site visit team discussed other routes by which lagoon contaminants may potentially escapefrom the lagoons. PCBs may volatilize to the air from lagoon water. Some contaminated lagoonwater could seep from the lagoons to the surrounding creek and drainage ditch. Woodchucks andmuskrats have burrowed many holes into the dikes and may increase the permeability of thestructures. The District regularly mows dike vegetation to eliminate cover for these rodents andto reduce the rate of burrowing. The District has installed a dike stability monitoring system thatallows the District to identify areas of structural weakness in the dike and to prevent anotherfailure. Another possible route discussed through which some contaminants may escape is inwaterfowl that feed in the lagoons. Several Canada geese and ducks were feeding in the lagoonsat the time of the site visit. Sewerage district staff mentioned that many species of water birdsfrequent the lagoons and that bird watchers from the area often visit the site. They also said thathunting occurs in the wetlands adjacent to the site . WBPH has continued to visit this site atleast annually in conjunction with meetings of the District's advisory committee for the remedialinvestigation and feasibility study.
The site is located at the southeast border of Madison and about three-quarters of a mile south ofMonona. North, east, and south of the lagoons is an 800-900 acre wetland in public ownership. The Madison Metropolitan Sewerage District sewage treatment plant is directly across a roadwest of the lagoons. A small crew of District workers dredges sludge from the lagoons andtransfers it to trucks that transport the material for disposal on agricultural land. A mobile homepark of about 250 units is about 1,000 feet southwest of the site. South of the site are agriculturallands. Approximately twenty rural residences are within a mile south of the lagoons and obtaindrinking water from the sandstone bedrock aquifer about 200 - 300 feet below the ground surface[10, p.7]. A railroad track is about 150 feet north of the lagoons, and several small industries areabout 1,500 feet north. Madison Well #5 is 1,100 feet west of the site, and Monona Well #3 is3,500 feet north [10, p.3].
HEALTH OUTCOME DATA
"Health outcome data" is a phrase referring to records of death and disease. When there isevidence that people near a site have been exposed to contaminants at levels that could lead to anincrease in rates of death or disease, a review of health outcome data may be appropriate. Areview also may be appropriate if there are reports of unusual clusters of diseases near a site. There is no evidence of public exposure to chemicals from the lagoons at levels that would resultin health effects, and WBPH is not aware of any reports of clusters of chronic disease near thissite.
On December 11, 1990, a representative of WBPH attended a public meeting on disposal optionsfor handling sludge generated from the sewage treatment plant in the future. District officialspresented results of meetings with an advisory committee consisting of local citizens, publicofficials, and area farmers. Citizens at the meeting asked questions about the effects of heavymetals in the sludge and about protection of groundwater quality in areas where sludge is appliedto agricultural lands. Concerns were raised about the PCBs in sludge applied to agriculturallands.
WBPH also solicited public health concerns at two public meetings about the sludge lagoons:one on December 3, 1991, and another on January 28, 1994. In addition, WBPH has participatedin meetings of the District's advisory committee for the remedial investigation and feasibilitystudy of the lagoons since 1990. Citizens at these meetings asked some questions about thefindings of the District's studies and about the pathways of exposure to be investigated, but theydid not express concern that people are being exposed to hazardous chemicals. Several localnewspaper articles have covered the issue of industrial contamination in sewage sludge applied toagricultural land. While some stories and letters to the editor have emphasized the carefulregulation and monitoring involved in applying sewage sludge to cropland [18, 19, 6, 7], othershave questioned the merit of allowing any increase in persistent, toxic substances on agriculturalland, given the uncertainty about toxic effects, the adequacy of monitoring, and possibleenvironmental transport of PCBs [9, 6, 8]. An additional meeting was held in November 1996. At this meeting questions were again asked about the health implications of the low-level PCBcontaminated sludges spread on agricultural soils.