Impervious Site needs to meet Pervious Pre-Development Conditions

[msf58]

Adding a small 4,000 sf storage warehouse on a ~6 acre developed site. There is a small drainage ditch across the north end of the property which discharges from a 15" CMP into the county ROW. At first, this project was pretty cut and dry. I simply increased the ditch capacity enough to account for the slight increase in runoff. The entire site is currently gravel, which was used in my original pre-development calculations.

However, upon receiving comments back from the county, there has been quite a bit of work done on the site without permit. A little side note, the owner is the contractor in this case. Anyway, the county has no record of 6 acres of gravel on the site, as well as a few of the more recent building additions.

Anyway, to my current problem: I have to match pre-development conditions from the latest site plan the county has on record. This means that I cannot account for the gravel surface currently in place, and have to match the drainage of a pervious site with my almost totally impervious site. I have figured I will need 70,000 cf in additional storage, which I just do not have with the configuration of the site. Any ideas or resources to point me in the right direction? Thanks!

 

[eyeforgeotech]

What about getting the existing work on site registered/surveyed/permitted with the county so the work you have to do for this new storage warehouse is based on what is actually there now? I'm sure it will cause delays as I don't imagine the county works fast but could save a ton of costs vs. having to add 70,000 cf additional storage.