Looking for grey haired wisdom please

Looking for grey haired wisdom please on an urban airport hangar drainage design

Project:

Design grading plan for two pleasure type airport hangars 40’ X 150’ on rectangular parcel 148’ (north south) X 178’ (east west) with asphalt pavement between.

Facts:

Common rule of thumb for satisfactory drainage to sufficient outlet: minimum 1% on stiff stuff (concrete/asphalt) and 2% on green stuff (grass)

2 catch basins at east end at corners of leasehold lands with sump inverts 3’+/- deep about 7‘ east of east walls of both proposed hangar buildings

Catch basins’ rims less than about 1.5’ below existing ground that splits about half way on north south line between east west sections

Ditch out front (west end) at paved service road is 26’ +/- from face of both proposed hangar buildings and is so flat its present south outlet is higher than its inlet at north end by 0.05’

Extreme northern end elevation of edge of asphalt service road (36’+/- west from face of proposed hangar buildings) within 0.02’ of southern end and about 1.5 ‘ above ditch and about same elevation of both front (western) corners of leasehold lands

Existing hangar to south has about a 10’ sideyard (we have 5’) and has a finished floor about 1.5’ higher than the common front corner and about 0.5’ ish lower than our general high point at the east west split along the northern edge

Do I give the impression the land is F-L-A-T and we are about 1’ above the existing finished floor of the hangar to the south ?

By coming up 2% from CB to edge of accessway to taxiway, then 1% to C/L of paved accessway between the two buildings (about less than 58’ apart), then @1% to split of east west sections we end up with a proposed finished floor (FF) about 2.7’ above the CBs

The slope to both buildings will be 1% at the split east/west drainage split point or about 0.6’.

But, at the eastern and western ends of the buildings the asphalt to the FF will have a slope of about 4.8% +/- or about 1.5’

This is too steep for hand pushing small planes but good for drainage.

The existing drainage tile for drainage of the catch basins is about 3’; deep under sod and to run to the pipe joining them would be under asphalt and at best about 2.5’ maximum cover under the proposed asphalt with suspiciously little frost cover even with styrofoam over.

A Heatline might be a saving matter for the pipe solution but …………………… looking for wisdom without leaving a pile of frozen ‘stuff’ created by the Winter’s diurnal temperature change, snow ice etc.

Average yearly rainfall is 32” with freezing conditions from November through May possible as we do have seasons here.

Landlord municipality does not want common boundary swales too, so we have to use eavestrough at least along the exterior roof lines on the north and south buildings’ north and south sides.!!!!!!!

Wisdom much appreciated.

Thank you

Derek