The fill materials may consist of rock, gravel, sand, or soil, or a mixture thereof,
but shall not contain any debris or organic matter. The fill material shall be spread
in a series of layers each not exceeding six inches in thickness after compaction.
After the fill material is placed and compacted, the compaction density shall be a
minimum of ninety percent of the maximum density as determined by the modified soil
compaction test, designated as AASHO T180-57 or ASTM D1557-58T tests in "Standard
Specifications for Highway Materials and Methods of Sampling and Testing," published
by the American Association of State Officials, 1961. These requirements may be waived
by the director if the permittee submits an engineer's report stating that the required
compaction density can be met with a thicker layer of fill, or substantiating why
the required ninety percent compaction density cannot be obtained with the fill material
to be used.
