Infiltration Basins - Contributing Drainage Area - Maryland

[PMAB32]

What is the allowable maximum drainage area for infiltration basins? I'm looking at the Virginia BMP Clearinghouse specs and they say 2 acres Maryland's manual is conflicting - it says no more than 5 acres in one section and then no more than 10 acres in another section. And of course I have a designer pushing the limit and trying to do it for 13 acres. Do you guys ever justify higher drainage areas when you have high infiltration rates, say 4.91 in/hr? min rate is 0.5 in/hr.

 

[Twinkie]

I've always done it by loading ratio ... 8:1 DA to footprint and 5:1 impervious to footprint.

In SEPA ... we have been hanging our hats on this for quite some time: Link

It says DRAFT because it is not Official PADEP guidance, but it has been widely used for quite some time now.

 

[PMAB32]

thanks! By footprint you mean surface area?

 

[Twinkie]

Yes .... the surface area ... bottom of the BMP

 

[Ekenny_G]

In Maryland, the maximum drainage area should be less than 5 acres for infiltration basins.
Now, the only infiltration practices used in Maryland are Infiltration Trench and Infiltration Basins. MDE may allow a higher infiltration rate with a higher drainage area if you show that the "extra" drainage area is mostly open space/Pervious areas.