4.1.2.6 Description of Primary Treatment Technology for Alternative 6, Bioremediation This alternative would include CSPB of all contaminated soil, rock, and sediment along with portions of the PCB-contaminated municipal and industrial wastes. Figures 4-21 and 4-22 present material flow diagrams for Scenario 1 and Scenario 2 respectively. About 87 percent of typical municipal solid waste is considered potentially treatable and includes all components except for metal and rubber and leather. About 10 percent of industrial wastes are expected to be rags, cardboard, wood, and other materials amenable to CSPB. The treatable components should be crushed or shredded to reduce their size, allow for better mixing with other materials, and increase contact between microorganisms and PCB-contaminated wastes that would otherwise not be able to support microbial growth. This alternative would also include in situ biological treatment of contaminated lagoon sludge at the Winston-Thomas Sewage Treatment Plant. Prior to CSPB, this alternative would include the following activities: site preparation; excavation of contaminated materials; sorting of the contaminated materials at the sites to separate the nonhazardous waste from the hazardous waste (Scenario 1 only); transportation and disposal of the nonhazardous waste at a solid waste landfill (Scenario 1 only); transportation of the PCB-contaminated waste to the CTF; sorting and screening of the PCB-contaminated materials to separate biodegradable materials from nonbiodegradable materials; and transportation, treatment, and disposal of nonbiodegradable PCB- contaminated material at a TSCA landfill or incinerator. Unlike other pre-engineered, patented treatment systems used in other alternatives, biological treatment typically involves the use of readily available, off-the-shelf equipment and indigenous microorganisms. The equipment comprising a biological treatment system is typically installed and integrated in the field instead of consisting of a prefabricated system. Both CSPB and in situ biological treatment most likely require sequential anaerobic-aerobic treatment. During the first phase, anaerobic bacteria would dechlorinate highly chlorinated PCB congeners that aerobic bacteria are unable to metabolize. The resulting, less-chlorinated congeners are then susceptible to destruction by aerobic bacteria during the second phase. For CSPB, sequential anaerobic-aerobic treatment would involve the following steps: construction of biotreatment cells at the CTF, placement of the contaminated materials in the cells, creation of anaerobic conditions in the cells to allow anaerobic treatment to continue until sampling and analysis indicate that adequate dechlorination has occurred, and aeration of the materials to provide aerobic treatment. If this alternative is selected, other CSPB configurations may be evaluated during the remedial design phase. Biotreatment cells would be sized to contain the required batch volume. The required batch volume depends on the number of batches needed to treat the entire volume of contaminated materials. The number of batches would be determined based on the targeted treatment period of 11 years and the time required for anaerobic and aerobic microbial processes to adequately biodegrade PCBs in soil. This time may include an initial lag time to allow stimulation and growth of microbial populations that have been inactive for a period of time because of the unavailability of substrates (GECRD 1994). Bench- and pilot-scale studies using the PCB-contaminated materials from the CD sites are required to determine microbial process kinetics before full-scale design and implementation of this alternative; however, 2 years is a conservative estimate of the total time required for initiation and completion of anaerobic and aerobic treatment based on observations during previous bench- and pilot-scale studies (PRC 1995e). The 2-year estimate for treatment could allow treatment of about five batches within the total allowable remediation time of 11 years. Treatment of five batches of contaminated soil, rock, sediment, and the biodegradable portions of the PCB-contaminated municipal and industrial wastes could result in a batch size of about 43,600 and 76,000 yd3 for Scenarios 1 and 2, respectively. By placing these materials in CSPB cells at a depth of 10 feet, the required treatment area can be provided by constructing about 26 cells under Scenario 1 and 46 cells under Scenario 2 with dimensions of 30 feet by 150 feet. These dimensions are averages within a cell and may vary from top to the bottom of the cell walls if the walls are sloped to provide stability. Construction of multiple long and narrow cells is advantageous over construction of fewer large cells because contaminated materials can be placed in narrow cells from outside of the cells. This procedure eliminates the need to drive earthmoving equipment into the cells, which would compact the soil and reduce its porosity and might damage the geomembrane, leachate collection piping, or aeration piping. The use of multiple cells also allows for better monitoring and control of the individual cells. Aeration would be provided by drawing air through the soil under vacuum by blowers attached to horizontal perforated piping running through the soil. Although PCBs are not very volatile, other volatile contaminants may be present in the blower exhaust that would be removed using vapor-phase activated carbon. The spacing of the horizontal piping would be based on the effective radius of influence, which is the distance from the piping to the furthest point an adequate vacuum exists to create a pressure gradient that causes air flow to the piping. The radius of influence depends on the permeability of the soil and the characteristics of the blower used. The radius of influence would be determined during pilot-scale testing using pressure monitoring probes. Using a conservative estimate of 30 feet for the required spacing, the cells can be constructed with one main header pipe running down the center of each cell with lateral pipes located at 30-foot intervals along the header pipe that extend out to the edges of the cells. Because low air flow rates are typically required for biological treatment, one large blower should be able to provide adequate aeration to at least four cells using a common header system so that a total of about seven and twelve blowers will be needed to aerate the 26 and 46 cells under Scenarios 1 and 2, respectively. Valves would be used to control the air flow in each cell. During the anaerobic phase of treatment, the aeration piping should be open to the atmosphere to passively vent methane gas. Organics in the vented gas can be treated using activated carbon. An impermeable cover is needed to create anaerobic conditions by preventing the soil from contacting oxygen in the atmosphere and to contain the heat generated by anaerobic microbial processes, which are enhanced at elevated temperatures. A cross-sectional drawing of a typical biotreatment cell is shown in Figure 4-23. The biotreatment cells would be constructed of concrete retaining walls and floors or of earthen berms with an impermeable geomembrane lining the earthen floor. Because of the large treatment area required, earthen retaining walls and floor with a geomembrane liner are more cost-effective than concrete for this application. The cell floors would be graded to promote flow of leachate to a leachate collection system consisting of perforated piping placed in a sand layer overlying the geomembrane liner. In addition to promoting drainage into the piping, the sand layer would protect the liner during placement of the contaminated materials. Collected leachate would be recycled back into the soil after addition of any necessary amendments such as organic substrate, inorganic nutrients, or bacterial inoculum. Before amendment addition, the leachate may be treated using activated carbon to remove solubilized PCBs and other contaminants not biodegraded if accumulation of these contaminants in the recycled solution is a concern. The leachate would flow by gravity into a common collection sump. The leachate would be pumped from the sump into a tank where the amendments would be added and then through the amendment solution distribution system. The sump and tank would be equipped with high- and low-level alarm switches to control the liquid level. Additional tanks may be required to contain excess leachate during rain events. The amendment solution would be distributed throughout the soil by applying the solution to the surface of the soil and allowing it to percolate down through the soil. To avoid the need to remove the synthetic cover during anaerobic treatment to apply the amendment solution, use of perforated piping in trenches is more applicable than use of a spraying system. During placement of the contaminated materials in the cells, the materials could be placed in lifts and amendment solution applied to each lift to provide a more uniform distribution of amendments at startup. After CSPB at the CTF is completed, the treatment residuals would be transported to the disposal location for landfilling. If the PCB concentrations in the residuals are greater than 2 ppm, the residuals should be sent for disposal at an appropriate landfill or incinerator. Residuals containing less than 50 ppm PCBs could be disposed of in a solid waste landfill with written approval from the State. The CTF would then be decontaminated and closed. In situ biological treatment of the contaminated lagoon sludges at the Winston-Thomas Sewage Treatment Plant site should first require pumping of the liquids from the lagoon for on-site treatment and discharge to a permitted outfall or to the Dillman Road sewage treatment plant. Lagoon water treatment and discharge is discussed in greater detail in Section 3.2.2. Because of the large area of the lagoon (about 17 acres) and the low sludge thickness (about 8 inches) (EAI 1993), the most practical approach to in situ biological treatment of the lagoon sludge is to section off an area of the dewatered lagoon using berms to create a cell within the lagoon and to transfer all of the contaminated sludge into this cell for treatment. A 2-acre cell would significantly reduce the area that must be controlled during treatment and would result in a manageable sludge depth of about 6 feet within the cell. The lagoon sludges from outside the cell would be pumped into the cell, and the sludges from the drying beds and digesters would also be transferred to the cell. Based on sampling of the underlying clay layer, contaminated clay in hot- spot areas would be removed, sheared to make the PCBs within the clay available for treatment, and transferred into the cell. As much of the clay layer as possible should remain intact to allow it to continue to provide a protective barrier to leachate migration. Within the cell, mechanical mixing equipment would be installed along with a network of perforated piping to distribute solution containing amendments such as organic substrate, inorganic nutrients, and bacterial inoculum. During installation of equipment in the cell, the sludge in the cell may first need to be pumped out of the cell and into the rest of the lagoon. After equipment installation is completed, all of the sludge could then be pumped into the cell for treatment. Mechanical mixing equipment that could be used includes rotating impellers, dredges, open-faced pumps, or mechanical rakes mounted on booms, bridges, or floats. Floats would be secured using mooring lines and poles. Depending on the amount of shearing force that the mixing equipment imparts to the cell bottom, installation of small concrete pads may be required on the cell bottoms beneath the mixing equipment to prevent the clay layer from breaching. The cell should also be equipped with a network of perforated piping to vent methane gas during anaerobic treatment and to distribute air provided by a blower during aerobic treatment. As discussed for the CSPB cells, blower exhaust and vented methane gas could be treated if these emissions are a concern. Anaerobic treatment may also require covering the sludge in the cell with an impermeable geomembrane to prevent atmospheric oxygen from aerating the sludge and to enhance anaerobic microbial processes by containing heat. An alternative to mechanical mixing and use of an air distribution system would be to continuously pump the sludge from the lagoon, inject amendment solution into the pipeline, and pump the amended solution back into the lagoon. The return pipeline would be connected to a series of eductors or other outlet devices spaced throughout the cell to distribute and mix the amended sludge. The inlet to the pipeline and the outlet devices would be located beneath the sludge surface, which would allow the synthetic liner to be readily placed over the sludge during anaerobic treatment. During the aerobic phase of treatment, oxygen would also be injected into the pipeline. If the solids content of the sludge is so high that the sludge cannot be pumped readily, some of the lagoon water could be left in the lagoon and mixed with the sludge to decrease the solids content. This approach to in situ biological treatment was used successfully at the French Limited Superfund site (DEVO 1992). The cell would be located to allow existing lagoon berms to be used on one or two sides of the cell. These berms would need to be built up, and completely new berms would need to be constructed on the other sides of the cell. The existing berm along the lagoon's west side should not be used because Clear Creek runs along this side of the lagoon and PCBs would be released directly to the creek if this berm breaches or overflows. Bioremediation Support Requirements Bioremediation support requirements include site preparation and mobilization requirements, a treatment building, utilities, pretreatment of contaminated materials, and post-treatment of residuals. Site Preparation and Mobilization Requirements At the CTF, about 26 cells with average dimensions of 150 by 30 feet are required under Scenario 1 and about 46 cells are required under Scenario 2. The area required for each cell will be increased by the base width of the earthen berms surrounding the cell. The berm base width will depend on the berm slope needed to provide stability to the berm. If a slope of 2:1 (run:rise) is used, a 10-foot berm should have a base width of 40 feet. Using the original cell dimensions of 150 by 30 feet as the average dimension from the bottom to the top of the cell, the total base dimensions required for each cell, including the berm base widths, should be 210 by 90 feet. The cells at the CTF must be spaced and configured so that trucks can bring the soil to the cells and earth-moving equipment, such as a front-end loader, can move between the cells while placing the material in the cells. The proposed location for the CTF does not provide enough area to accommodate all required cells and equipment under either scenario. The in situ cell at the Winston-Thomas Sewage Treatment Plant should require an area of about 2 acres within the existing 17-acre lagoon. Sufficient space is also required outside the cells for external equipment, including blowers and accessories, leachate collection sumps with pumps, and amendment solution storage and mixing tanks with pumps. The blowers and accessories may be skid-mounted or mounted on a small, concrete pad. An enclosure or a roof to protect this equipment from the weather is not necessary but may be desirable because of the long duration of the project. Setup of support facilities, such as an office, sanitary facilities, and a water supply source, may also require additional space. The berms for CSPB cells can be constructed by partially excavating the cells and using the excavated soil to form the berms. Berm construction will require the use of earth-moving equipment, such as bulldozers and front-end loaders. Construction of the berms for the in situ cell may require soil from outside the lagoon and use of similar earth-moving equipment. The equipment required to construct the cells, including earth-moving equipment, piping, synthetic liners, pumps, blowers, and tanks, is easily mobilized and can be transported on public roads. Building Because operation of the biological treatment at the CTF requires one full-time operator, a building with an office and sanitary facilities could be needed. An on-site laboratory may also be included in this building, but it will likely be more cost-effective to use an off-site laboratory to perform the analyses for PCB congeners because the analysis requires expensive laboratory equipment and skilled personnel. The building should also include an area for storage of the amendments needed to make the amendment solution. The inorganic nutrients purchased could be in the form of agricultural-grade fertilizers, which are typically available as granular solids; therefore, these solids may need to be protected from precipitation. Utilities The only utilities required for biological treatment are electricity and water. The electrical power source should be sufficient to power the blowers and pumps at the CTF and to power pumps and possibly mechanical mixing equipment at the Winston-Thomas Sewage Treatment Plant. During amendment solution preparation, water will be required to make up water that is lost to evaporation or is captured as soil moisture. Pretreatment Pretreatment may also be required to shear any excavated pieces of clay or other tightly bound soils and to shred or crush certain components of PCB-contaminated municipal or industrial wastes in order to increase the bioavailability of PCBs. Amendment distribution piping and aeration piping can be spaced more closely if transfer limitations are not resolved by additional materials handling and pretreatment. The lagoon sludges at the Winston-Thomas Sewage Treatment Plant site are not expected to contain solid wastes and capacitors, and material mixing should adequately homogenize the sludges. Post-treatment Biological treatment should be determined complete based on analysis of sludge samples. If the 2-ppm cleanup standard is applied and treated sludge meets this standard, the treatment residuals could be excavated and transported to the disposal facility and landfilled. If treatment does not meet the applied 2-ppm standard, treatment residuals should be removed and transported off site for disposal at an appropriate permitted landfill or incinerator. Treatment residuals containing less than 50 ppm may be disposed of in a solid waste landfill with written approval from the State.