4 years ago

Preliminary Engineering Report - Fauquier County

Preliminary Engineering Report - Fauquier County

treatment system that is

treatment system that is capable of meeting Level 1 reuse standards with minimal additional enhancements. In the future, if bus washing or other uses which require Level 1 treatment wish to be pursued, the County will request that DEQ re-assess the facility and additional operational improvements and monitoring requirements can be implemented. To meet the effluent standards for onsite water reuse, the following facilities are proposed (Phase I): Leachate Pretreatment: The biological pretreatment system will be maintained by expanding the volume of the existing Pond #1 located along the eastern edge of the property and relocating the existing aeration system and treatment media from Pond #2 into Pond #1. Pond #2 is planned for demolition as future landfill cell construction takes place, but will remain in place in the near term to serve as an emergency equalization basin to buffer severe storm events if needed. Once plans for additional cells are completed pond two may be decommissioned. Pond #1 will provide an equivalent replacement of approximately 1 million gallons. Upgrades to the existing system will be made with the objective to enhance the pretreatment process. Package Post-Treatment System: A package-type treatment system, utilizing either an activated sludge Membrane Bioreactor (MBR) process or a Moving Bed Bioreactor (MBBR) process with Ultra-Filtration (UF) Membranes, will be installed to further treat the leachate to meet the reuse standards. Both systems will require pre-screening of the influent. Final selection of the post-treatment system will be made during the design stage. Effluent Disinfection: The reuse standards include limits on bacterial parameters for the effluent, requiring disinfection. It is proposed that a ultra-violet (UV) disinfection system be provided. Alternatively, chlorine disinfection may be considered (using sodium hypochlorite). Water Reuse Storage Tanks and Pumping Station: Two 40,000 gallon ground-level steel tanks will be installed at the site for storage of treated effluent. A duplex packaged pumping station will draw from the tanks to deliver flow to either the irrigation system or the dust control trucks. The pumping station will have provisions for storage tank recirculation and a small amount of chlorine will be dosed to the treated effluent to reduce the potential for algae growth. Post Treatment Equalization Storage: An in-ground earthen-lined storage basin will be installed with a holding capacity of up to 1.5 million gallons for final treated leachate effluent. This will provide capacity to store effluent for a longer duration if seasonal weather conditions preclude onsite water reuse for an extended period, without the need to haul and dispose leachate offsite. A portion of this basin may also be divided and dedicated for raw leachate storage with an impervious geo-textile liner to provide additional flexibility in overall leachate handling. N:\18469-000\Engineering\Reports\April 2012 PER\18469 PER Treatment System 7-31-2012_AM.docx Page 3

The existing landfill site and proposed modifications are shown on Figures C-1, C-2 and C-3, and a process schematic is depicted on Figure P-1. A planning level budget estimate has been developed for the facility with a total project budget of $1.7 million. II. PROJECT BACKGROUND The landfill currently utilizes two geo-membrane lined collection ponds to capture leachate generated by five lined municipal solid waste cells. Cell 1 is open and active while Cells 2, 3, 4 and 5 have been temporarily capped. The basins are identified as Pond #1 and Pond #2. Pond #1 collects leachate from Cells 4 and 5 and has a storage capacity of 700,000 gallons with an average depth of approximately 6 feet. Pond #2 collects leachate from Cells 1, 2 and 3 and has a storage capacity of approximately 900,000 gallons with an average depth of approximately 8 feet. Leachate is recycled periodically through the cells with up to 6,000 gallons per day (permitted) per cell. Leachate from Pond #1 can be pumped to Pond #2 and vice versa. The characteristics of the leachate with respect to organics, inorganics and metal constituents are typical of that of leachate for a MSW landfill, with high concentrations of Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and nitrogen (ammonia). 1. Existing Leachate Pretreatment Process Description and Treatment Capabilities: As a result of TKN and ammonia-nitrogen limits imposed in the WWTPs NPDES permits, the smaller local POTW plants have been reluctant to accept the raw or recycled leachate without further treatment. In 2005, Pond #2 was upgraded with a submerged aeration system and submerged media to support biological treatment of the leachate and provide reduction of BOD, TKN and ammonia. This upgrade was undertaken to improve the leachate quality to a level that would better enable the local wastewater treatment plants to accept the leachate. The biological system installed utilizes the AquaMats Biofiltration® process. This process consists of submerged biological growth media that contains large and small pores to support the bacteriological growth to achieve nitrification of the ammonia present in the leachate. Aeration and circulation for the treatment system is provided by two positive displacement blowers, one in operation and one on standby. An aeration header distributes air to surface deployed submerged fine bubble membrane diffuser units via five equally spaced feeder trunk lines. Since the installation in 2005 the pretreatment system in Pond #2 has provided a consistent and significant reduction in BOD and TKN/ammonia as well as total suspended solids (TSS). Table 1 summarizes available data collected over the recent years. Generally, BOD ranges from 20- 100 mg/L and with very low ammonia levels (less than 5 mg/L) when the treatment N:\18469-000\Engineering\Reports\April 2012 PER\18469 PER Treatment System 7-31-2012_AM.docx Pond #2 Treatment System Page 4

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