What Causes a Fiberglass Septic Tank to Crack?

Installation

• Fiberglass septic tanks are easily damaged during installation if they’re dropped or hit. The crack may not even be noticeable until a few years later, when the tank is pumped. One sign that you may have a crack is if the effluent levels are unusually low, but the drain plug is intact.

Vehicles

• Don’t drive or park your vehicle over the septic tank unless the tank is protected with a vehicle-rated septic tank cover; the weight of your car could crush the tank, causing it to crack or even causing the tank to collapse. Nothing larger than a child’s bicycle should ever be driven over the tank or the leach field.

Soil

• Septic systems depend on soil to filter wastewater, and soil texture and composition affect how well the septic system performs. Clay soil is prone to expanding and contracting with water absorption, and this can damage fiberglass septic tanks and cause them to crack. Some clay minerals can expand up to 30 percent in volume when they absorb water. This problem is worse in areas that have wet and dry seasons. A soil survey test can identify how much soil will expand when it’s wet. Soil scientists assign a figure called the cole value to soils they test. This figure describes how much 100 inches of dry soil will expand when wet. Soil that expands 6 inches when wet has a cole value of 0.06. Soil with a value higher than that can cause your fiberglass tank to crack. Knowing your soil’s cole value will help you determine what kind of septic system you need.

Inspection

• The only way to tell if your septic tank is cracked is to do a visual inspection when the tank is pumped. Never enter a septic tank to examine it. Since the effluent will drain out through the crack, any cracks that are present will probably be located at the level of the effluent. If the effluent level is noticeably lower than the level of the tank outlet, your fiberglass tank is most likely cracked.

Repair/Replace

• If the lid to your septic tank is cracked, it can be replaced, but a crack to the tank itself probably means you’ll need a new tank. The price of a new tank varies depending on the size of the tank and where you live, but expect to pay around $1,000 for the tank and at least another $1,000 to $2,000 to have it installed, as of time of publication.