Section 906.40  Fill Material

a)         Below Absorption Area

1)         A mound system shall be provided with a fill material beneath the absorption area (trenches or bed).  One of the following fill materials shall be used.

A)        FA-1

B)        FA-2

C)        FA-3

D)        FA-8

E)        FA-9

2)         These materials are classified and graded in accordance with Illinois Department of Transportation, Division of Highways specifications for fine aggregate.  These materials shall meet the gradation specifications as shown for these five fine aggregates in Appendix A, Exhibit B.

b)         Above the Absorption Area.  The cap (area above the bed or trenches) shall consist of a topsoil to allow plant growth.  Sands are not allowed since they drain rapidly and allow more infiltration of precipitation into the absorption area.  Topsoil shall be placed to a depth of 6 in. over the entire mound to promote good vegetation cover.  The cap soil shall be seeded and fertilized.