Which class of soil is considered unsuitable for standard systems?

Class 4 soils are considered unsuitable for standard septic systems because they typically have poor drainage characteristics. This classification often includes soils that contain a high proportion of clay or have a very fine texture, which leads to slow percolation rates. Poor drainage can result in the wastewater not being absorbed properly, leading to potential system failure, surface pooling, or contamination of nearby water sources. Therefore, designs for these types of soils require specialized systems or additional engineering considerations to ensure proper sewage treatment and disposal. In contrast, Classes 1b, 2, and 3 generally possess better drainage capabilities, making them more suitable for standard systems.