Absorption Area Adjustments
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The Absorption Area Adjustments page lets you adjust the footprint of the absorption area.
Constraining Dimensions
If site conditions limit the physical footprint available for the absorption area, you can constrain the width, the length, or both. The wizard will attempt tp adjust the bed geometry to fit within your constraints while still meeting the required absorption area and pertinent regulations.
Sewers uses these constraints and any area adjustments below to adjust the sizes and aspect ratio of the absorption area. The software attempts to make a best fit based on minimizing the difference in areas between the design footprint and the constraining area you specify while following applicable regulations such as minimum widths and required minimum aspect ratio. Generally some variance from the regulations is allowed when designing under “Best Technical Guidance (BTG)”.
Constraint Options
| Option | What It Constrains | When Available |
|---|---|---|
| none | No constraint applied | Always |
| on aggregate footprint | Constrains the aggregate (gravel) layer dimensions | Percolation-based systems with ESM, at-grade, or Eljen GSF mound discharge |
| on sand footprint | Constrains the sand layer dimensions (larger than aggregate) | Percolation-based systems with ESM or Eljen GSF mound discharge |
| on berm footprint | Constrains the outer berm dimensions (largest overall) | Percolation-based systems with ESM, at-grade, or Eljen GSF mound discharge |
When a constraint is selected, enter the width and length in feet. The wizard will attempt to fit the absorption area within those dimensions. There are very real limitations: the software fits to your constraints by altering the aspect ratio of the footprint. Aspect ratios have minimums based on system type and slope that must be maintained. Choosing BTG may relax those minimums.
Adjusting the Area
Adjust Area
Area reductions are only permitted on some system configurations. Area reductions require SEO approval and non-economic justification. Setting a maximum area is only allowed when invoking “Best Technical Guidance”. This software does NOT enforce the amount of a size reduction. It is up to you as designer to make that choice and to defend it.
| Option | Effect | Requires Justification |
|---|---|---|
| no adjustment | Use the calculated absorption area as-is | No |
| take allowed percentage reduction | Reduce the area by a percentage (e.g., 33% for aerobic, 40% for advanced secondary treatment) | Yes |
| set minimum area | Override the calculated area with a specific minimum in square feet | No |
| set maximum area | Cap the area at a specific maximum in square feet | Yes — only available under Best Technical Guidance (BTG) |
Percentage Reduction
When you select a percentage reduction, enter the reduction percentage. The software will use as much of the reduction as is possible but never more. The amount actually taken will be often be less due to some modularity of sizing a system and regulation constraints. GSFs are especially troublesome in this respect.
Maximum Area (BTG Only)
Setting a maximum area is only available when the Best Technical Guidance (BTG) flag is checked on the Site Investigation page. This allows you to cap the absorption area for repair situations where site space is limited. A written justification is required.
Justification
If you select a percentage reduction or set a maximum area, a justification text area appears below the adjustment controls. You must provide a written justification explaining why the area adjustment is appropriate for this site. The wizard will not let you proceed without it.
Tips
- The summary area shows the current absorption area in real time as you make changes. Check it before proceeding.
- Dimension constraints are useful when the property has physical obstructions (buildings, property lines, steep grade changes) that limit where the absorption area can go.
- If you constrain dimensions too tightly, the wizard may not be able to fit the required area. Review the summary to confirm the geometry is what you want.
- Best Technical Guidance generally opens up possibilities otherwise unavailable.