On-site sewage facilities can treat residential sewage very efficiently if designed properly for the on-site conditions. But a shallow water table in the soil treatment zone is a particularly hazardous condition for OSSFs.
Standard gravity-fed systems that rely on subsurface soil treatment will fail during periods when a shallow water table is present in the 4-foot treatment zone.
Of all the limitations that must be examined as part of an on-site evaluation (texture, gravel, soil restrictive horizons, slope, floodplain), seasonal shallow groundwater is without a doubt the most difficult to analyze.
All of the other limitations can be assessed by a simple and direct site evaluation in the field. But with shallow groundwater, the evaluator is almost always basing his or her evaluation on indicators, and not on direct observation. This simple fact introduces considerable uncertainty into the process, increasing the chances that a bad call will be made, with the resulting surfacing of untreated sewage. A major public hazard by any measure.
What does this soil color pattern indicate about shallow groundwater? What about the picture above?
These two soils have very clear indicators of soil saturation or lack thereof. Do you know which is which? Do you know you could be sued for making the wrong call,especially since there is little doubt about these indicators?
Do you know how to “read” the landscape?
This landscape has “water-gathering” positions or areas and water-shedding positions. Which positions are likely to have seasonal shallow groundwater tables? You will know when you finish this course.
What about this flat landscape?
Could you make a determination about soil saturation even if no mottles were present? The “Bubba” test could help you!
This is an 8-hour TCEQ-certified (1487) course for the OSSF program.
This course is designed to help the site evaluator and others protect public health in the face of uncertainty, and to reduce their own liability from bad calls.