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Underground FRP Tank

Underground fiberglass tanks are a proven solution for below-grade water storage across municipal, industrial, and commercial projects. Fiberglass construction does not rust, crack, or require protective coatings, delivering a longer service life with minimal maintenance.

Available for potable water, fire suppression, stormwater, rainwater, irrigation, and wastewater applications in 8', 10', and 12' diameters from 5,000 to 50,000 gallons. Each tank is custom-configured to the project; water type, site conditions, and burial requirements must be confirmed before ordering.

AWWA D120 / NFPA 22 / NSF 61 Certified

Download Spec Sheet

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Spec List

  • Water type: potable, fire suppression, rainwater, stormwater, irrigation, or wastewater
  • 8' diameter: 5,000 to 20,000 gallons, 10' diameter: 10,000 to 40,000 gallons. & 12' diameter available upon request
  • Standards: AWWA D120, NFPA 22, NSF 61 compliant options to align with AHJ specifications
  • Manway size: 24", 30", or 36" bolted. Traffic-rated H20 or non-traffic design must be specified
  • Fuel storage also available: UL 1316, NFPA 30 / 30A

Features

  • Non-corrosive FRP, maintenance-free, watertight, custom-configured per project
  • Custom configured for project requirements
  • Compliance options available for AWWA D120, NFPA 22, and NSF 61
  • H20 structural design available for traffic-area installations
  • Accessory options include manways, flanges, vents, hydrants, ladders, straps, and anchor systems
  • Anchoring options available for high water table and site-specific conditions

Applications

  • Potable water storage with NSF 61 compliance available
  • Fire suppression reserves designed to NFPA 22 requirements
  • Rainwater harvesting and stormwater management systems
  • Irrigation water storage for commercial, municipal, and agricultural use
  • Wastewater containment applications
  • Dual-use potable water and fire suppression storage in a single tank where permitted by the AHJ
  • Fuel and petroleum storage options available
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Underground FRP Tank Details

An underground FRP tank is a fiberglass-reinforced plastic vessel engineered for below-grade installation. Fiberglass does not rust like steel or crack like concrete, requires no protective coatings, and delivers a longer service life with minimal maintenance. Tanks are lightweight relative to concrete alternatives, which simplifies transport and placement, and each unit is custom-configured to the project based on stored product, site conditions, and operational requirements.

These tanks are used wherever surface space is limited or above-ground storage is not practical. Common applications include potable water supply, fire suppression reserves, rainwater harvesting, stormwater management, irrigation, fuel storage, and wastewater containment. Below-grade placement eliminates above-ground structural and aesthetic requirements and provides some natural insulating properties. Where the project and AHJ permit it, a single tank can serve dual purposes, combining potable water and fire suppression storage.

Standards compliance is available for AWWA D120, NFPA 22, and NSF 61 depending on the application. H20 structural design is available for traffic-area installations. Confirm which standards apply to your project and jurisdiction during quoting.

Specialist Support for Your Storage Project

Talk with a specialist for practical guidance and equipment recommendations.

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Frequently Asked Questions

Common questions about underground FRP tanks and what to expect during the quoting and installation process.

What is an Underground FRP Tank?

An underground FRP tank is a buried fiberglass storage vessel used when above-ground placement is not practical. FRP is specified for underground service because it resists corrosion and requires no cathodic protection. Single-wall and double-wall configurations are available depending on the application.

What are the burial requirements?

Non-traffic areas typically require 24" of backfill cover, or 12" backfill plus 4" reinforced concrete. Traffic areas (HS20, 32,000 lbs/axle) require 36" backfill, or 18" backfill plus 6" reinforced concrete. Traffic pads must extend 12" beyond the tank in all directions. Confirm requirements with the manufacturer; inadequate cover can void the warranty.

What backfill material is required for an Underground FRP Tank

Approved backfill is pea gravel or crushed stone conforming to ASTM C-33. Sand, limestone, crushed concrete, and seashells are prohibited. Backfill must be placed in lifts and worked under the full tank length to eliminate voids. Geotextile fabric is required in areas with high groundwater, unstable soil, or low bearing capacity.

What anchoring options are there for the Underground FRP Tank

Three methods are available: deadmen anchors, a concrete anchor pad, and overburden burial. The right approach depends on water table depth, soil conditions, and burial depth. In wet-hole conditions, ballasting may also be required. Hold-down strap systems (FRP straps with galvanized cast iron hooks) are used with deadmen and anchor pad configurations. Confirm the method against manufacturer anchor charts before installation.