Key Largo Wastewater Treatment District Biosolids Digester Project Description

The project consists of the work as depicted in the Contract Documents, including the plans and specifications. This narrative description of the work is intended only to assist in the general understanding of the scope of work and is not intended to modify the scope of work as defined in the plans and specifications.

Overview The work generally consists of demolition of several existing concrete structures, followed by construction of a pre-stressed concrete digester tank and associated equipment, piping and electrical elements. Following completion of construction and testing of the digester system, the WWTP staff will transfer biosolids from the existing tank currently being used as a digester, and the new digester will be placed into service.

The work also includes cleaning of the existing digester tank and installation of equipment to convert the tank into its original intended use as Sequencing Batch Reactor #3. After the tank is cleaned, the Engineer will inspect the tank and determine if any repairs are needed. The Contractor will then install the SBR equipment provided by the District and install the influent piping as shown on the plans. The nutrient analyzers will also be installed.

Following conversion of the tank to an SBR, the District staff will place the SBR into service and divert the flow from SBR #2 into SBR #3 for treatment. The Contractor will then clean SBR #2 for inspection by the Engineer and then proceed with the influent piping modifications and installation of the nutrient analyzers. When SBR #2 is completed, the District staff will transfer the flow from SBR #1 to SBR #2, allowing the Contractor to commence with the same scope of work on SBR #1.

A proposed phasing plan for the work is outlined on Sheet G-06. The phasing plan is for guidance only and can be modified by the Contractor as needed so long at the operation of the WWTP facility is not impaired. Two SBRs and a digester must be in operation at all times. The actual construction phasing is to be proposed by the Contractor and must be approved by the Engineer and the Owner.

Demolition The demolition work includes the following general items, including all associated piping, equipment, conduit, and other related items: • Concrete headworks platform and columns, including aluminum stairs and handrails, piping and screening equipment. • Concrete disinfection basins, equipment pads and chemical storage containment area. • Various concrete landings and equipment pads in the Biosolids Digester project area. Biosolids Digester The Biosolids Digester work consists of the following major elements and all associated piping, equipment, conduits and other related items: • 78’ diameter, 28’ tall pre-stressed concrete tank including pilings, foundation, stairs, walkways and handrails; • Jet aeration and mixing equipment system, including blowers, pumps, aeration/mixing header, piping and ancillary equipment; • Vacuum sewer truck dumping station slab, drains and pumps; • Centrifuge dewatering station including slab, drains and electrical supply; • Rotary drum sludge thickener, polymer blending equipment; • Digester analyzers, probes, transmitters and controls; • Motor control center, variable frequency drives and control panels for all electrical equipment associated with the digester/dewatering system

Conversion of SBR #3 The tank for SBR #3 has been used as a temporary digester. The work on this tank will include the followings items, including all ancillary equipment, piping, electrical and mechanical work: • Clean grit, rags, sediment and sludge from SBR #3 after the bulk of the liquid has been removed by District staff. Disposal fees for the removed solids will be paid by the District; • Provide safe access equipment for the Engineer for inspection of the tank; • Perform any necessary rehabilitative work as directed by the Engineer, using the $15,000 (per tank) allocation in the bid; • Removal of interim digester swing-arm decanter; • Installation of SBR decanter, probes and level controls; • Installation of influent piping; • Installation of nutrient analyzers

Modifications to SBRs #1 and #2 The work on each of the SBRs will include the following items, including all ancillary equipment, piping, electrical and mechanical work: • Clean grit, rags, sediment and sludge from SBR #3 after the bulk of the liquid has been removed by District staff. Disposal fees for the removed solids will be paid by the District; • Provide safe access equipment for the Engineer for inspection of the tank; • Perform any necessary rehabilitative work as directed by the Engineer, using the $15,000 (per tank) allocation in the bid; • Installation of influent piping; • Installation of nutrient analyzers