For the most part underground fiberglass tank manufacturers have similar backfill requirements. The standard backfill is pea gravel or crushed rock. If using pea gravel it must be 3/4 minus. Three quarter minus is round, washed, free flowing rock 1/8”-3/4” in diameter. No more than 5% may pass through a #8 sieve. If you decide to go with crushed rock the installation guidelines is going to require 1/8” - 1/2” diameter.
Sometimes the construction zone has ideal native soil, and in efforts of saving money the contractor may elect to use it. The contractor would send in a sieve analysis to the manufacturer to get a alternate materials approval.
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A: Seven feet.
If you work with Fextex on your project, you can bury the fiberglass tank at least seven feet. We commonly see tanks being buried much deeper, where burying one deep into the teens is not out of the question with proper engineering and installation. Not only should the structural integrity of the vessel be taken into consideration, but just as importantly, please consider your accesses. Are you going to be using PVC risers or fiberglass extensions? How many do you have, and how can we assure they stay watertight? These are often times the weakest part of the installation. www.fextex.com
Underground fiberglass tank warranties are typically good for 1 year. This includes wastewater, fire protection, rainwater collection and storm water suppression tanks. The exception is the 30 year warranty for a NSF potable water tank. The corrosion barrier on all these tanks are manufactured very similar. The potable water tank has an interior NSF listed vinyl ester resin built to NSF standards. A Xerxes potable water tank is one of the only tanks manufacturered that is NSF Listed. Most of their competition merely builds tanks to NSF standards. You can view the standard warranties attached to this post. For more information visit us at www.fextex.com
Underground tank warranties Link
You can collect 0.62 gallons of water per square foot of roof space, per inch of rainfall. With factors such as evaporation, splash out, leaks, overflow from gutters and first flush we use a collection efficiency percentage of 75-85%. Example: (0.62 x .85 x 1500 x 36) Seattle WA. Annual Rainfall 36 Inches Sqaure Feet of Roof Area 1500 Rainwater Collection Efficiency 85% Gallons of Water Per Square Foot/ Per Inch 0.62 Total Annual Rainwater Collected 28,458 Gallons If you would like to learn more visit us at www.fextex.com
Septic Tank Design 101 What must first be determined is the waste stream source & strength - ie. laundromat, RV dump site, restaurant, residential home etc. Next, determine the design flow- Historical flow data is the pr method to determine the daily flow rate. In a new development where flow date is not available, design flow is commonly established by the number of bedrooms and/or people using the facility(s) .ie: With residential waste strength sewage assuming 30 ea. 3 bedroom homes @ 120 gallons per bedroom =360 gallons per home. (WA state standards) the design flow would be (10,800 gallons per day) Multiply your that design flow by 1.5-3x. Therefore the recommended tank size would be 16,200-32,400 gallons liquid capacity. Liquid capacity does not account for any required volume above the invert of the outlet. You may also need to consider state or local regulations for total volume requirements. Currently Washington State requires 20% reserve flow. Next we determine the tank configuration- First decide whether the tank will be single or dual compartment. If a dual compartment tank is selected the baffle wall will typically split the tank 2/3 & 1/3 (from the inlet side). Next the size of inlets, outlets and baffle tees (if applicable) are determined. The gravity line running to the septic tank usually dictates the plumbing size in the septic tank. Riser openings (typically 24”, 30” or 48” diameter) are usually spaced 10’ apart along the length of the tank shell. Effluent filters can be added to the outlet of the septic tank (sized per specific manufacturer’s recommendations) for filtering of solids. If there is a potential for standing groundwater; or if the installation will be in an area with a rainy climate and poor draining soils then anti-buoyancy measures must be implemented. The Designer must determine the “worst case scenario” ground water level. Once determined buoyancy calculation and anti-flotation measures can be implemented. For more info www.fextex.com
Are you thinking about incorporating a fiberglass tank into your plan set? Are you uncertain how many LEED points you can qualify for? See below, or download our attachment for a clear understanding. If you need further help, visit us at www.fextex.com LEED® Credits for Water Efficiency (WE) WE Credit 1.1 – (2) points Water Efficient Landscaping: Reduce by 50% WE Credit 1.2 – (2) points Water Efficient Landscaping: No Potable Water WE Credit 2 – (2) points Innovative Wastewater Technologies WE Credit 3 – (2-4) points Water Use Reduction LEED® Credits for Sustainable Sites (SS) SS Credit 6.1 – (1) point Stormwater Design: Quantity Control SS Credit 6.2 – (1) point Stormwater Design: Quality Control SS Credit 7.2 – (2-4) points Heat Island Effect – Roof: Vegetative Roof Surfaces Regional LEED® Credits MR Credit 5 – (1-2) points Regional Materials RP Credit 1 – (0-4) points Regional Priority
An underground fiberglass tank costs $2.00 per gallon delivered. O.K. it’s not that simple, but if you are looking for a shot from the hip and don’t wan’t to sweat the details, $2.00 per gallon is your number. This is by far Fextex’s most asked question, and to better answer it we must uncover what you are truly looking for. Let’s assume you are storing water (waste-water, potable water, rainwater collection, storm-water detention, etc) I can now tell you are looking for a S.W.T. single walled tank. Approx tank Shell cost: 10K-20K gallons of storage = approx $1.20 per gallon for the tank shell 22K-40K gallons of storage= approx $1.50 per gallon for the tank shell 41K-50K gallons of storage= approx $2.25 per gallon for the tank shell The rest of your costs are in the fittings, accessories and freight.