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Percolation Reports and Septic Design

A percolation report is required for constructing an occupancy (residential or commercial) that will not be connected to sewer service. In these cases, a private sewage disposal system is necessary. These reports consist of trenching or drilling pits or borings and determining the percolation rate of the soil by measuring the amount of water that percolates (soaks) in a given amount of time. Once the percolation rate is obtained, a septic system may be designed. Designing a septic system takes experience and knowledge of the governing agency requirements and Uniform Plumbing Code.


Leach line systems are the most economical and are typically designed if the development allows. Leach lines are relatively shallow (less than 15’) horizontal perforated pipes with gravel, 60 to 100 feet in length. The size and length depends on the percolation rate and structure plumbing fixtures. In some cases multiple leach lines may be necessary.


If your parcel is steep, small, or in an area that does not percolate well, seepage pits may be required. Seepage pits are vertical borings, 4-6 feet in diameter, line with perforated concrete liners, 25 to 50 feet deep, also depending on the percolation rate and structure plumbing fixtures. In some cases, multiple pits and a pre-treatment system to prevent groundwater contamination may be required by the governing agency.


Due to the restrictions of designing a septic system, it is important to contact Bruin GSI, in most cases, before you purchase the property.

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