Wastewater Treatment Plant Expansion and Improvements

As of April 26, 2023, project has been under construction since last month, and is expected to be completed in 3 years. The owner has determined a prequalified list of construction managers. Dorchester County owns and operates the Lower Dorchester Wastewater Treatment Plant (WWTP). The County has a National Pollutant Discharge Elimination System (NPDES) permit for an annual average design flow of 8 million gallon per day (mgd) with permit limits for expansion to 10 and 12 mgd. The WWTP is located 0.78 mile from the confluence with the Ashley River near the Charleston County line. The Lower Dorchester WWTP serves approximately 44,000 people. The majority of the influent flow is pumped to the WWTP. Dorchester County wishes to expand the Lower Dorchester WWTP to accommodate growth in the service area. The projected wastewater flow in the Lower Dorchester service area is anticipated to exceed the Lower Dorchester WWTP permitted capacity of 8 mgd over the next 20-year planning period. The County has currently committed 9 mgd of capacity at the Lower Dorchester WWTP. Additionally, the County has received firm requests for an additional 4.5 mgd of capacity, which is commensurate with the anticipated growth per the County's Comprehensive Plan. It is anticipated that the majority of the growth in the Lower Dorchester service area will occur within the next 5 to 10 years. Therefore, an expansion of the Lower Dorchester WWTP from 8 to 16 mgd is necessary to prepare for the anticipated near-term growth. The County is also anticipating growth in an area north of the Lower Dorchester service area, characterized as the Central Dorchester service area, within the next 5 to 15 years. An initial capacity of 4 mgd has been identified for a proposed Central WWTP with a future expansion to 8 mgd. The Preliminary Engineering Report (PER) for the proposed Central WWTP is being prepared as a separate document from this Basis of Design Report (BODR) for the Lower Dorchester WWTP expansion project. The proposed Central WWTP is discussed in this BODR due to the re-distribution of the County's ultimate oxygen demand (UOD) wasteload allocation between the two treatment facilities.

Division 02 -	Existing Conditions, Subsurface Investigation.
Division 03 -	Concrete, Precast Concrete.
Division 04 -	Masonry, Unit Masonry.
Division 05 -	Metals, Structural Metal Framing, Metal Fabrications.
Division 06 -	Wood, Plastics, and Composites, Rough Carpentry.
Division 07 -	Thermal and Moisture Protection, Dampproofing and Waterproofing, Thermal Protection.
Division 08 -	Openings, Doors and Frames, Windows, Hardware.
Division 09 -	Finishes, Painting and Coating.
Division 10 -	Specialties, Signage, Compartments and Cubicles, Emergency Aid Specialties, Fire Protection Specialties, Storage Assemblies.
Division 11 -	Equipment, Laboratory Equipment.
Division 14 -	Conveying Equipment.
Division 21 -	Fire Suppression, Fire-Extinguishing Systems.
Division 22 -	Plumbing, Instrumentation and Control for Plumbing, Plumbing Piping, Plumbing Equipment, Plumbing Fixtures.
Division 23 -	Heating, Ventilating, and Air Conditioning (HVAC), Instrumentation and Control for HVAC, HVAC Air Distribution.
Division 26 -	Electrical, Instrumentation and Control for Electrical Systems, Interior Lighting, Emergency Lighting, Exit Signs, Exterior Lighting.
Division 27 -	Communications, Structured Cabling, Data Communications, Voice Communications, Distributed Audio-Video Communications Systems.
Division 28 -	Electronic Safety and Security, Electronic Access Control and Intrusion Detection, Access Control, Intrusion Detection, Electronic Surveillance, Electronic Detection and Alarm.
Division 31 -	Earthwork, Earthwork Methods.
Division 32 -	Exterior Improvements, Flexible Paving, Rigid Paving, Curbs, Gutters, Sidewalks, and Driveways, Fences and Gates, Turf and Grasses.
Division 33 -	Utilities, Water Utilities, Storm Drainage Utilities, Electrical Utilities, Communications Utilities.
Division 44 -	Pollution and Waste Control Equipment, Common Work Results for Pollution and Waste Control Equipment, Air Pollution Control, Noise Pollution Control, Odor Control, Water Pollution Control Equipment, Solid Waste Control and Reuse, Waste Thermal Processing Equipment, Fluidized Bed Combustion Equipment, Rotary Kiln Incinerators, Pyrolysis Equipment, Hazardous Waste and Medical Waste Incinerators, Heat Recovery Equipment for Waste Thermal Processing, Synthesis Gas Cleanup and Handling Equipment.