Troubleshooting soil treatment areas (STA) is a complex process as essentially all of the components of the STA are not visible and accessible for assessment or measurement. Principles for troubleshooting STA will be discussed. Essential initial inputs include: any permits for the system as well as the soil-site assessment; history of the home/business site development; surrounding and neighboring development that could influence the hydrology of the site; past and current use of the onsite wastewater system; troubleshooting of upstream components of the onsite wastewater system as well as the activities the home owner or business manager have placed on top of the STA. Once an assessment of current and past use status has been developed, intrusion into the STA through probing, coring, and/or digging will need to be performed to “ground truth” the problem. Examples will be provided to illustrate many of the common causes of poor performance of the STA of onsite wastewater systems that have been managed by one entity over a relatively long period of time as well as those managed by a relative new homeowner or business manager. In some instances, the STA may be able to be continued to be used at a lesser intensity with some renovation while in a many cases, new STA locations may need to be located and assessed if there is ample area to do so.