My neighbors have septic systems. Because soils can vary greatly. You neighbors may have installed their septics when the rules were more relaxed or even before the county started regulating septic systems at all. It is very important for your protection as well as the protection of the environmental that your property is properly tested in the area where your septic system will be so that you get a system that will last you a long time and not cause problems later. I'm right next to a subdivision.
Soils can vary tremendously over even short distances.
It would be irresponsible of us to allow the installation of a septic system on a site where we have no direct evidence o its suitability for such a project. Typically, you have a radius of 30 feet around your two test holes in which to install your septic system. This is why it's so important that you place your test holes in the area where you think you're going to put your septic system. It may be wise for you to dig additional holes at the time your site assessment is done in order to have more flexibility in the placement of your septic system. When a subdivision is developed, an engineer is required to do a certain amount of site testing along the lines of our site assessments.