Drain Rock For Septic Systems

By Robert Jones May25,2023

drain rock for septic systems

Conventional gravity septic systems employ a drain field where wastewater percolates through soil to be further treated by microbes; this area is commonly known as a leach field.

Leach lines are trenches filled with washed rock/gravel that is levelled to flow level where a perforated pipe lies, then more rock is placed to cover it and paper or another suitable filter material is added as an additional barrier to stop soil filtering down into it.

Structural Support

Septic tanks and their leach fields require extensive ground space, with soil that can absorb the dissolved elements found in wastewater. An inadequately draining or compacted soil cover over a septic system may result in unpleasant wet areas, plumbing issues in your home and costly component replacement needs. To help avoid this from occurring, many municipalities and septic tank installation professionals recommend the use of gravel as the ideal surface material to use throughout its drain field area.

Leach lines are typically constructed by digging a trench filled with washed gravel that measures 2 inches in size. A perforated pipe then rests atop this gravel at an even grade before more gravel is spread over it to cover it – this allows sewage to trickle through rock into soil for treatment.

Although crushed stone is an effective building material, septic leach fields perform much better when constructed from clean washed pea gravel that’s slightly smaller than what was originally used to fill trenches. Smaller grains allow more waste to be processed at once.

A 2-bedroom home typically requires at least 200 square feet of gravel if installed in sandy soil with coarse particles, according to Eco-Nomic. The amount required depends on both the size of the septic tank and soil composition surrounding it. For instance, in sandy soil that’s being treated by the system a minimum 200-square-foot bed needs to be covered with gravel according to Eco-Nomic.

Gravel isn’t the only construction material suitable for use as a septic tank bed; other options may include sand, recycled tires chopped into chunks of certain sizes and concrete blocks that have been wet-baked. Whatever material is chosen as part of your septic tank bed should resist soil erosion while being free from large rocks and frozen matter to minimize risk to your tank and ensure reliable performance.

For optimal protection of your septic system and surrounding drain field, avoid driving on its leach field or planting vegetable gardens nearby, as well as keeping pets and children away from it. Additional good septic-system maintenance tips include keeping the tank lid closed and not using your septic system as a trash can by disposing of items like cigarette butts, tissues, cotton swabs, paper towels coffee grounds sanitary products kitty litter or cigarette waste in toilets.

Storage Capacity

No matter the age or state of your septic system, it must have sufficient storage capacity during periods of heavy use to avoid overflowing and backing up into your home. Furthermore, proper tank storage can reduce pumping frequency.

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One way to increase septic system storage capacity is to add multiple chambers to your tank. Depending on your household size and the volume of waste generated by each fixture, this could have an enormous effect on how much wastewater your septic system can store.

An alternative approach is increasing the size of your drain field, which helps distribute waste over a larger surface area than is typical with traditional systems, helping prevent overflow and other waste-related issues from taking over your septic tank. This type of septic system works effectively in various soil conditions and locations and may prove cost-effective for multiple households.

Traditional septic systems operate by transporting waste away from the house through an underground pipe which connects to a leach field, or drain field, via an open holed pipe and connecting with one of several trenches filled with washed gravel, covered by an impermeable membrane to keep out dirt, dust, and other debris that would prevent effluent from filtering down into soil and being treated by microbes.

Leach fields should be designed according to expected waste/sewage flow rate and number of fixtures installed in dwelling occupancies or estimated wastewater/sewage design flow rate for commercial occupancies as defined by Table H 201.1 of California Code of Regulations. It is advised that at minimum two compartments be constructed in order to store at least 500 gallons (1892 L) each compartment or as specified by Authority Having Jurisdiction.

To ensure optimal functioning of a leach field, it must be constructed from high-grade gravel. Poor-grade gravel may block oxygen from reaching septic pipes, preventing evapotranspiration and leading to overflows and backups. Furthermore, large enough stones must be chosen so as not to crush septic pipe installations.


Drain rock provides essential filtration capabilities for both gravel-filled septic tank trenches and leach fields, helping keep waste from your home from polluting the soil around it and entering groundwater, protecting bacteria that process waste while simultaneously helping the soil absorb wastewater more easily as it seeps into it. A quality gravel such as shale may be preferable.

A conventional septic system operates via drainage. A pipe runs from the septic tank to a drain field that slowly diffuses sewage into the soil over time – necessary to protect people and wildlife from toxic septic tank chemicals as well as stop an overwhelming surge of waste entering an area quickly. To protect its integrity further, drainage pipes are usually surrounded by layers of clean gravel approximately 1″ or smaller in diameter around their drainage pipe.

Septic tanks are concrete or plastic structures that store waste until microbes in them can process it, with oil and grease floating to the top as scum, solid waste sinking to the bottom as sludge, and effluent being released back into the environment. A typical septic tank typically holds its full load for 24 hours until its capacity has been depleted and then it empties.

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Unfortunately, this doesn’t always go to plan; sometimes the soil in a drain field may not be dense enough to filter and cleanse sewage properly, resulting in backup into homes, pooling on earth surfaces and polluting nearby groundwater and bodies of water.

To avoid this issue, ensure your drain field is appropriately sized for the needs of your family, with drainage pipe running at least 2 feet below any underground obstacles. Have your septic system inspected every two to three years, adding a reserve drain field when necessary. Alternatively, if the leach field in an area too sandy or swampy for effective functioning cannot function effectively, a sand filter could be an alternative solution.


Septic systems provide homeowners with wastewater disposal systems on remote properties when city sewer pipes cannot reach. Instead of sending effluent liquids directly into a treatment plant, this type of system relies on pipes, leach lines and soil. Effluent liquids from homes are carried to drain fields where bacteria treat it further while drain fields have percolation pathways designed to permit percolation through layers of gravel into groundwater below and the gravel helps retain liquid until its absorption into groundwater; keeping soil free of flooding issues.

Installing a septic system requires selecting rocks of appropriate sizes. Too-small gravel slows the flow, leading to backup in your house, while too-large rock prevents effluent from flooding the soil and damaging its integrity. In general, ideal gravel sizes for this task include clean washed stones with an average diameter of 1.5 inches or greater and an experienced supplier can recommend which variety would work best with your system.

A gravel/stone system has long been employed as an effective design solution. Effluent exiting the septic tank enters an underground trench of gravel covered by geofabric to keep dirt from entering filtering stones, with perforated drainfield pipes buried into its layers of gravel to collect perfluent from various drainfields; each finger of gravel covers individual perforated pipes buried into its layers, filtering bacteria out before groundwater seepage.

Fiberglass and composite plastic tanks offer more eco-friendly alternatives than gravel/stone systems, providing an almost watertight seal more durable than metal tanks in rocky soils and providing near-watertight seals that won’t leak like metal tanks do. Fiberglass tanks may also be the better option in areas with limited access to rock resources.

Regular maintenance of the septic tank and drainfield is necessary to ensuring its smooth functioning, and should be checked by a licensed inspector on an ongoing basis. For monitoring purposes, installing monitoring ports within the drainfield bed allows inspectors to view any standing liquid (ponding) within it – usually one at the natural soil interface up to grade and another one placed atop of drain rock is sufficient to accomplish this goal.

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