Millsboro 100,000-Gallon Elevated Effluent Storage Tank

Key Accomplishments

Johnston Construction Company

• JCC’s scope included site excavation, dewatering, foundation preparation, foundation installation, backfill and compaction, piping below the tank foundation, concrete encasement of piping, conduit bank installation, anchor bolt layout and installation, concrete and soil testing coordination, and related foundation support work.
• Major work included excavation and backfill for the tank foundation, installation of the foundation to bottom-of-elevation requirements, installation of Pittsburg Tank & Tower-provided anchor bolts, installation of inlet and outlet piping below the foundation, installation of two conduit banks, concrete encasement of piping, and dewatering of the site.
• The work required coordination with Pittsburg Tank & Tower Group, Sussex County, GHD, geotechnical engineers, testing agencies, utility providers, concrete suppliers, equipment providers, and project stakeholders.
• The project required compliance with AWWA D107 composite elevated tank requirements, geotechnical recommendations, OSHA safety requirements, Sussex County and GHD specifications, concrete construction requirements, excavation and backfill requirements, dewatering requirements, testing requirements, and project closeout requirements.
• The project included construction support for a new composite elevated tank consisting of a foundation, reinforced concrete support structure, and welded steel water tank. The tank specification identifies the tank capacity as no less than 100,000 gallons, with a bottom capacity level of elevation 181.00, maximum fill rate of 4,500 gallons per minute, maximum outlet rate of 4,000 gallons per minute, 12-inch inlet pipe, and 24-inch outlet pipe.
• JCC’s scope included labor, material, equipment, dewatering, shoring, rough grading, fine grading, foundation preparation, scarification, export material, and compaction required for the site excavation, foundation installation, and conduit bank work. The scope also included excavation and backfill required for foundation installation and compaction of the entire foundation/pad in accordance with the geotechnical report recommendations.
• The foundation work included installation of the foundation to the bottom elevation shown on the project drawings, including the concrete floor cap. JCC also included layout and installation of anchor bolts provided by Pittsburg Tank & Tower Group. The work required coordination with the tank contractor’s foundation requirements, geotechnical recommendations, foundation excavation inspections, testing requirements, and tank construction sequencing.
• Piping work included installation of piping below the tank foundation. The work authorization indicates that the piping was to extend 24 inches above grade inside the tank foundation and extend 10 feet beyond the edge of the tank foundation on the exterior. The piping scope also included concrete encasement, with inlet pipe identified as 12 inches and outlet pipe identified as 16 inches in the work authorization.
• The composite elevated tank specifications required communication and antenna cable provisions, including a bundle of six 6-inch Schedule 40 PVC conduits with long-radius 90-degree bends routed from exterior below grade to the interior support wall at the slab-on-grade. The specifications also required electrical and lighting work in accordance with AWWA D107.
• The geotechnical report identified the project site as part of the Inland Bays Regional Wastewater Facility Expansion – Elevated Effluent Storage Tank project in Millsboro, Delaware. The report stated that the project included construction of a new 100,000-gallon elevated effluent storage tank, and provided recommendations for site preparation, fill and backfill construction, foundation support, slab subgrade support, seismic site classification, groundwater, and dewatering.
• The geotechnical recommendations indicated that the tank structural elements should be supported on a mat foundation or ring foundation bearing on firm native subgrade or controlled structural fill. The original report noted that shallow foundations should not be supported in or above the fat clay layer unless unsuitable material was removed and replaced with high-quality structural fill.
• The work required attention to groundwater and dewatering conditions. The geotechnical report noted that groundwater was encountered during drilling at depths of approximately 14.5 to 15 feet below existing grade, and that groundwater could be encountered at shallower depths during construction depending on conditions. The contractor was advised to be prepared to dewater excavations and keep exposed subgrade areas dry during construction.

Concrete Services Division

• Concrete Services Division, LLC performed concrete forming, placement, finishing, curing, and accessory work for the Millsboro 100Kgal EWST project in Sussex County, Delaware.
• CSD’s scope included concrete work for the tank foundation, including footing forming, curved wall forming, footing placement, slab-on-grade placement, wall placement, float and screed work, trowel finishing, point and patch work, bagging, curing, and concrete accessory labor.
• Major work included mobilization and demobilization of concrete equipment, tools, and supplies; rental of form material; purchase of form lumber; installation and stripping of forms; concrete placement labor; concrete finishing labor and supplies; concrete curing labor and supplies; and concrete accessory labor.
• The concrete work required coordination with Johnston Construction Company, Pittsburg Tank & Tower Group, Sussex County, GHD, geotechnical engineers, concrete suppliers, testing agencies, pumping services, equipment providers, and project stakeholders.
• The work required compliance with Specification Section 13210 Composite Elevated Water Storage Tank, PTTG project specifications and foundation drawings, geotechnical recommendations, OSHA safety requirements, concrete construction requirements, testing requirements, and project closeout requirements.
• CSD performed the work under subcontract to Johnston Construction Company for the Millsboro 100Kgal EWST project. The CSD subcontract, No. 202504SC01, was dated effective April 24, 2025, and identified Concrete Services Division, LLC as the concrete subcontractor, Johnston Construction Company as the contractor, and the delivery location as Millsboro 100Kgal EWST in Millsboro, Delaware.
• The overall project included construction of a new composite elevated tank consisting of a foundation, reinforced concrete support structure, and welded steel water tank. The tank specification identified the tank capacity as no less than 100,000 gallons, with bottom capacity level elevation 181.00, maximum fill rate of 4,500 gallons per minute, maximum outlet rate of 4,000 gallons per minute, 12-inch inlet pipe, and 24-inch outlet pipe.
• CSD’s concrete scope included forming, placing, finishing, and curing associated with the tank foundation. The work included mobilizing and demobilizing concrete equipment, tools, and supplies to and from the jobsite; rental of form material; purchase of form lumber; installation and stripping of forms; concrete placement labor; concrete finishing labor and supplies; concrete curing labor and supplies; and concrete accessory labor.
• The concrete accessory work included labor for items such as PMJ, waterstop, caulk, and related concrete accessories. The subcontract also included winter protection labor, resteel placing labor on a time-and-material basis to JCC, resteel placing supplies on a time-and-material basis to JCC, unloading rebar labor with equipment by JCC, and setting anchor bolts on a time-and-material basis to JCC.
• CSD’s billing worksheet identified approximately 101 cubic yards of concrete work, 243.35 square feet of footing forming, 1,313.19 square feet of curved wall forming, 46.08 cubic yards of footing placement, 5.82 cubic yards of slab-on-grade placement, and 48.64 cubic yards of wall placement.
• The concrete finishing and curing scope included approximately 967.61 square feet of float and screed work, 314.16 square feet of trowel machine finishing, 1,313.19 square feet of point and patch work, 34.56 square feet of bagging, 2,838.30 square feet of total curing, and concrete accessory work associated with approximately 100.53 cubic yards.
• CSD coordinated concrete purchased by Johnston Construction Company, testing lab services paid for by JCC or the owner, concrete pumping services paid for by JCC, and rental of JCC and outside equipment paid for by JCC. The subcontract excluded excavation, backfill, stone subgrade, concrete material, concrete accessory material, concrete pumping rental, concrete testing services, retainage, and sales tax, while still including coordination of several of those items where required.
• The geotechnical report identified the project as the Inland Bays Regional Wastewater Facility Expansion – Elevated Effluent Storage Tank in Millsboro, Delaware. The report stated that the project included construction of a new 100,000-gallon elevated effluent storage tank and provided recommendations for site preparation, fill and backfill construction, tank foundation support, slab subgrade support, seismic site classification, groundwater, and dewatering.