FAQ: On the Soil Parameters screen, why are there two input values for the affected soil area and the length parallel to the wind direction?

There has been some confusion with regards to the affected soil area and the length parallel to the wind direction in the Soil Parameters section. In both the RBCA Tool Kit and the RBCA Tool Kit for TRRP, the Soil Parameter screen looks like this...

RBCA Tool Kit Soil Input Screen

The confusion lies in the left-hand column of entries where there are two input values for the affected soil area and the length of soil parallel to the assumed wind direction. The reason for the two different inputs is because those values may differ for those calculating risk under the construction worker scenario. The right side values are for the construction worker, while the left side values are for the general case. These numbers may be different for a construction worker, who could be in closer contact with the soil than a normal commercial or residential receptor.

The construction worker scenario appeared in the draft of the ASTM RBCA standard, but not in the finalized version. It is included in the RBCA Tool Kit as an additional receptor type available to the user.

This two value types are indicated at the top of the number columns (circled in the screen shot above in red). However, the column headers are grayed out on the screen, and the purpose of the two different values was not clearly explained in the manual.

Similarly, the purpose for the two values in the volumetric water/air content in part 2: Surface Soil Column, is to differentiate between the vadose zone and the capillary fringe.