Septic Setbacks and a Floodplain Casing
A licensed driller is asked to site a new 4-inch PVC domestic well on a 2-acre lot in Pike County. The proposed location is 55 ft from a 1,000-gallon septic tank, 70 ft from the nearest lateral of the absorption field, 30 ft from a fenced cattle pen, 40 ft from the property line, and 90 ft from a neighbor's 30-ft hand-dug well. The lot lies in a FEMA floodplain. The driller proposes a 6-inch borehole, 4-inch casing to 90 ft, a pitless adapter, and casing extending 8 inches above grade. The annular space is to be filled with bentonite from 40 ft to surface; below 40 ft, the hole will be left open. The health department asks for the siting and construction review before issuing a local permit.
1. Evaluate the proposed separations. Which Illinois minimum setbacks are met or not met, and what should the driller do?
Read the worked answer
Compare each distance with the Code minima:
- Septic tank: 55 ft is greater than 50 ft, so this separation is met.
- Absorption field: 70 ft is less than the required 75 ft, so this fails.
- Cattle pen/animal feedlot: 30 ft is less than the required 50 ft, so this fails.
- Property line: 40 ft; the state well code does not set a general property-line setback, but local zoning or easements may. Verify before approving.
- Neighbor's hand-dug well: 90 ft; there is no state separation from another private well, but a shallow dug well is a potential contamination pathway, so keep the new well uphill and up-gradient where possible. The location cannot be approved as proposed. The driller should relocate the well so it is at least 75 ft from the absorption field and 50 ft from the cattle pen, or have the owner relocate those features. Do not treat the 40-ft property line as automatically fatal without checking local rules, but do not ignore it. A variance, if available, would need support from the local authority; the driller should not start construction while two mandatory separations fail.
2. Review the casing height and annular seal. What changes are required, and how should the grout be placed?
Read the worked answer
Casing at 8 inches above grade fails the 12-inch minimum; in a FEMA floodplain the casing should extend at least 24 inches above grade, or be protected to an equivalent height so floodwater cannot enter the annular space or well head. The 6-inch borehole with 4-inch casing leaves only a 1-inch annulus, which is below the Code's minimum annular space for reliable grouting (at least 1.5 inches). Use a 7-inch or larger borehole for 4-inch casing, or reduce to 3-inch casing in the 6-inch hole. The seal must be continuous from the bottom of the casing to ground surface, not just from 40 ft upward. Place grout by positive-displacement tremie from the bottom up, with centralizers, in one continuous operation; do not free-fall bentonite chips. If the lower hole is left open, contamination can migrate up the annulus. The pitless adapter is acceptable only if it is an approved unit and the casing is sealed around it.
3. The owner wants to keep the location and simply extend casing to 120 ft. Does that fix the problem?
Read the worked answer
No. Extending casing changes the vertical pathway but does not correct horizontal separation failures: the well would still be 70 ft from the absorption field and 30 ft from the cattle pen. It also does not raise the casing to floodplain height unless the extension is brought above grade. A deeper casing can even create a longer annulus that must be sealed. The driller must fix the siting or obtain a proper variance from the authority having jurisdiction if one exists; otherwise the well should not be constructed at that location. Additional casing is not a substitute for required setbacks.