Question
We are collecting bids for a backyard patio.  We have water issues so we want
a very good base.  We have been instructed to use grade 9 fill versus grade 8
limestone, however, the contractors that are bidding are using grade 8
limestone.   could you tell us the difference and why one would recommend
grade 9 versus grade 8.  thanks  

Answer
You were instructed to ask for "grade 9" fill by whom? They might know of the subtle distinction.

The grading of fill material is generally governed by local or state development codes, so I would direct you to ask your city/county engineering office, or building inspector this question.  

Various State Department of Transportation or Roadway Department offices can also be of assistance, as well.  Road builders are constantly discussing such an exciting topic as "base grade integrity".  

Since you gave me no region, I am at a loss to direct you to the appropriate local agency.

If you have water issues, the grade of fill is not the most important item, good drainage AWAY from your patio is.  I would install some sort of hard-pipe drainage (like those found at ndspro.com), or at a minimum, make darn sure the direction of the patio slope is away from your dwelling.

Good luck!

~M