Site Investigation

The Site Investigation page is where you enter the soil test results from the Sewage Enforcement Officer’s site evaluation. This data determines the absorption area, compatible system types, and overall design feasibility.

System Sizing Method

Select one of three system sizing methods at the top of the page:

Percolation Rate

The standard method for most residential designs. Most of these values can be found on the Site Investigation and Percolation Test Report. This method requires:

• perc rate (min/in) Valid range is 3 to 180 min/in.
• depth to limit zone (in) Valid range is 10 to 120 in.
• slope at bed (%) Valid range is 0 to 25 %
• building flow rate (# or gal/day) This value is either the number of bedrooms for a residence (1-9) or the flow rate to design to in gal/day. Internally the number of bedrooms is converted to a daily flow rate for calculations (3 bedrooms = 400 gpd).

Hydraulic Linear Loading Rate (HLLR)

An alternate method used when a soil scientist has evaluated the site. It is typically used for shallow soils (< 20 in limit zone). The values should be found in the soil scientist’s report for the site. This method requires:

• HLLR (gal/ft/day) — valid range: 2.0 to 7.0
• Infiltration Loading Rate (gal/sq ft/day) — valid range: 0.2 to 1.6
• depth to limit zone (in) Valid range is 10 to 120 in.
• slope at bed (%) Valid range is 0 to 25 %
• building flow rate (# or gal/day) This value is either the number of bedrooms for a residence (1-9) or the flow rate to design to in gal/day. Internally the number of bedrooms is converted to a daily flow rate for calculations (3 bedrooms = 400 gpd).
• Soil Scientist Name — the professional who performed the evaluation
• Soil Description — description of soil conditions from the professional

Stream Discharge

Available only for designs prepared by a licensed Professional Engineer. Stream discharge designs bypass soil infiltration entirely and discharge treated effluent to a surface waterway. This method has separate, additional regulatory requirements.

• building flow rate (# or gal/day) This value is either the number of bedrooms for a residence (1-9) or the flow rate to design to in gal/day. Internally the number of bedrooms is converted to a daily flow rate for calculations (3 bedrooms = 400 gpd).

Best Technical Guidance (BTG)

If the site is a repair of an existing failing system, you may check the BTG box. This invokes Best Technical Guidance provisions which may allow relaxed design criteria. BTG designs require a written justification that you will provide on a later page.

How It Affects Later Pages

This page has the largest downstream impact of any wizard page:

• The absorption area is calculated from your infiltration data and flow rate. This drives tank sizing, bed/mound dimensions, and material quantities.
• The available system types on the System Type page are determined based on your data method and values. The summary section on this page shows which design guidance categories (Standard, Alternate, Experimental, BTG, PE-Required) are available for your entered site conditions.
• If you change infiltration data after completing later pages, those pages will reset because the underlying calculations have changed. It will also trigger the need for the design to be repurchased if you have already finalized the design.

Tips

• The summary area updates as you enter data, showing which design rules are available. Check this before proceeding to confirm you have the design flexibility you expect.
• If the design has been saved and printed, critical data fields may be locked to prevent accidental changes. Unlocking those fields and making changes will trigger a repurchase.