HomeMy WebLinkAboutApplication Files_82693_pg0446 T1L22ASSP�a�'.�n Rrrrict i ._ F r
f
l
Porous Asphalt Pavement
Porous asphalt pavement treats and infiltrates stormwater runoff by allowing
stormwater to pass through the asphalt surface and trickle through the underlying
gravel base and sand layer for water duality treatment. The use of porous asphalt
pavement effectively"replaces"an impervious parking lot area with a pervious
groundcover that allows infiltration. Porous asphalt will be installed in the two
parking lots located to the south and west of Studio Building 3. Test Pit data in this
area(see Appendix B)indicates a fine textured sandy loam mantle over a coarser
textured sand. Soil samples analyzed from these test pits indicate permeability rates
between 60 and 92 inches per hour at a depth of three feet below existing grade.
Monitoring wells were set in these test pits and a seasonal high groundwater table
(SHGWT)adjustment factor was applied.The SHGWT varied from elevation 48.0 to
53.0. In consideration of this data,the porous asphalt has been designed with greater
than a three-foot separation to seasonal high groundwater or bottom at elevation
59.0. The hydrologic model of this basin includes a safety factor of 2(per the"2004
Connecticut Stormwater Quality Manual,"Chapter 11 Section 11-P3 that reads that the
"recommended design infiltration rate is equal to one-half the field-measured
infiltration rate(i.e.,safety factor of 2)")and resultant infiltration rate of 29 inches per
hour.
J
' Hydrologic Information
For the proposed conditions hydrologic analysis,the site was divided into eighteen
drainage areas(see Figure 3).These areas discharge to the four design points where
peak discharge rates were evaluated for both existing and proposed conditions.A
full size proposed conditions plan is located in Appendix A.
Design Point 1 is the northwest property corner,adjacent to the CONRAIL tracks
and the intersection of Chapel Road and John Fitch Boulevard. Thirteen drainage
areas contribute to this Design Point:
> Drainage Area PR1A-This 1.8-+-acre area consists of a portion of the proposed
access drive from Ellington Road,a parking area,and existing vegetated land.
Runoff from this area will be treated and infiltrated in Biofiltration Basin 5,with
an overflow to Design Point 1.
> Drainage Area PR1B-This 1.9±-acre area will contain a portion of the access
drive to the studio. Runoff from this portion of roadway will be treated and
directed to an existing permeable basin near the access drive with potential
overflow to Design Point 1.
L
72189DrAnYeds17E78,WyW1�dsm9inagel 12 Proposed Conditions
72789 Ova(nage Report Jury tat t.doc p