1. Common Abbreviations & Symbols Decoded
Septic drawings utilize standardized plumbing and engineering shorthand. Use this cheat sheet to decode your property's drawing:
| Symbol / Acronym | Full Technical Term | Function & What to Look For |
|---|---|---|
| ST / TANK | Septic Tank | Primary treatment chamber; drawing will indicate gallon capacity (e.g., 1000G ST). |
| D-BOX / DB | Distribution Box | Small junction chamber directing effluent evenly into absorption trenches. |
| CO | Cleanout | Vertical PVC access riser from the main house sewer line for snake access. |
| LF / EF | Leachfield / Effluent Field | Perforated lateral pipes embedded in washed gravel or plastic chambers. |
| INV / ELEV | Invert Elevation | The bottom inside elevation of a pipe, establishing critical gravity fall slopes. |
| PUMP / DT | Pump Chamber / Dosing Tank | Secondary pressurized tank for uphill or alternating field distribution. |
2. Understanding Triangulation & "Tie" Measurements
Contractors do not record GPS coordinates on historic diagrams. Instead, they use triangulation ties. The diagram will show two straight dashed lines extending from permanent structural corners of your house to the center of each tank lid:
- Example: A line labeled
28' 6"from the Northwest house foundation corner, and a second line labeled34' 2"from the Southwest porch corner. - How to locate the tank in your lawn: Have two people hold tape measures anchored at those exact two foundation corners. Walk out into the yard until the two tape measures cross at their specified lengths. The intersection point marks the exact center of the buried tank lid.
3. Elevation Drop and Gravity Fall Specifications
Standard gravity-fed septic systems require a consistent downward grade. The sewer pipe leaving the home must slope between 1/8-inch to 1/4-inch per foot (approx. 1% to 2% fall). Steeper drops can cause liquids to outrun solids, creating blockages, while shallower slopes cause sluggish drainage.
4. Mandatory Buffer Setbacks to Verify Before Remodeling
When planning a swimming pool, backyard patio, detached garage, or driveway addition, consult your as-built drawing to ensure you do not encroach on statutory exclusion zones:
- Private Potable Water Wells: Minimum 50 to 100 ft buffer from both tank and drainfield.
- Property Boundary Lines: Minimum 5 to 10 ft buffer.
- Building Foundations & Basements: Minimum 5 to 10 ft from tank, 10 to 20 ft from absorption field.
- Surface Water Bodies (Streams, Lakes, Ponds): Minimum 50 to 100 ft buffer.
Frequently Asked Questions
What are tie measurements on an as-built drawing?
Tie measurements are precise linear distances recorded by the installer from two permanent structural points (usually distinct exterior house corners or foundation benchmarks) intersecting directly over the tank lids and distribution box.
What does D-Box mean on a septic plan?
D-Box stands for Distribution Box. It is a small concrete or polymer junction box situated between the septic tank and the drainfield that distributes liquid effluent equally into each absorption trench line.
What are typical mandatory setbacks for septic systems?
Nationwide environmental health codes typically mandate that a septic tank maintain a minimum 5 to 10-foot setback from property lines and foundation footings, and a 50 to 100-foot buffer from private potable drinking water wells, streams, and lakes.
This technical reference is prepared by County Septic Records utilizing standardized regulations published by the US Environmental Protection Agency (EPA), state departments of health, and national onsite wastewater recycling standards.