HomeMy WebLinkAboutWPO201400087 Plan - As-built 2023-01-13 (2)Geoff Elsie
From: Frank Pohl
Sent: Friday, January 13, 2023 10:22 AM
To: Geoff Elsie
Cc: Emily Cox
Subject: RE: LM - Lofts at Meadowcreek Biofilter
Attachments: LM C.20 VSMP 2015-09-03 Plotted 2015-05-01.pdf
Geoff,
Please print this email to PDF and save it to CV. Save it as "plans -as -built' and let me know if you need help. I already
uploaded the attached PDF but forwarding to you FYI.
Thanks,
Frank
Frank V. Pohl, PE, CFM
County Engineer
Albemarle County
foohl0albemarle.org
434-296-5832 x7914
401 McIntire Road, North Wing, Charlottesville, VA 22902
From: Richard Park<rpark@pinnacleconstructionva.com>
Sent: Tuesday, March 8, 2022 12:51 PM
To: Frank Pohl <fpohl@albemarle.org>
Cc: Geoff Elsie <gelsie@albemarle.org>
Subject: LM - Lofts at Meadowcreek Biofilter
CAUTION: This message originated outside the County of Albemarle email system. DO NOT
CLICK on links or open attachments unless you are sure the content is safe.
Frank,
Per our previous discussions, the biofilter at Lofts at Meadowcreek is not draining as specified. We had F&R collect and
analyze samples of the filter media and it has insufficient sand and excess soil fines which are causing this lack of
permeability. We have reviewed the VA DEQ Stormwater Design Specification No. 9 for Bioretention and propose the
following to remedy this issue:
1. Remove the existing shrubs and trees (which have mostly drowned) and mulch
2. Remove the existing biofilter media down to the top of the small stone layer ("pea gravel' on the detail below)
3. Assess the small stone choker layer to make certain it is sufficiently permeable
4. In lieu of the 24" depth of V1.9 biofilter media, Install =20" deep layer of sand with =4" of V1.9 biofilter media
on top
5. In lieu of the Tree, Shrub, and Herbaceous Plants planting template, use the Turf and Tree planting
template. To this end we will eliminate the shrubs shown on the original plan, plant (4) suitable trees in the
1
biofilter area (smaller trees than the sycamore shown on the original plan as it will quickly outgrow the available
space and its leaf litter is a continuous problem), sow the Ernst Rain Garden Mix onto the surface of the V1.9
topping layer, then cover with turf which will provide a great nurse cover and prevent the Rain Garden Mix from
being displaced before becoming established.
Relevant info from Specification No. 9:
Section 6.6 (page 25):
Alternative to Mulch Cover. In some situations, designers may consider alternative surface
covers such as turf, native groundcover, erosion control matting (coir or jute matting), river
stone, or pea gravel. The decision regarding the type of surface cover to use should be based
on function, cost and maintenance. Stone or gravel are not recommended in parking lot
applications, since they increase soil temperature and have low water holding capacity.
Media for Turf Cover, One adaptation is to design the filter media primarily as a sand filter
with organic content only at the top. Leaf compost tilled into the top layers will provide
organic content for the vegetative cover. If grass is the only vegetation, the ratio of compost
may be reduced.
Section 6.8 (page 26):
and tree. This option is a lower maintenance version of the tree -shrub -herbaceous
the mulcn layer is replaced by turf cover. 1 rees are
to prevent damage during mowing operations.
Since we will not be mowing this area, mulched islands are neither needed nor desired.
See proposed revisions below (in color) to the original cross section detail from Sheet C.20 (attached).
1C
3
PEA
GRAVEL
FILTER STONE
VDOT NO. 57
AGGREGATE
BIORETENTION SOIL
MIXTURE IN
ACCORDANCE TO
VIRGINIA BMP
CLEARINGHOUSE
SPECIFICATIONS,
LATEST EDITION
TOP OF —
MULCH
ELEV.=428.50
Ernst Conservation Seeds Rain Garden
Mix with sod nurse crop cover
i
3" MULCH
f
2'
3"
12"
PROVIDE MINIMUMS BOTTOM OFF L-6" DIA.
6" SUMP BELOW BIORETENTION PERFORATED
UNDERDRAIN FACILITY=425.00 UNDERDRAIN
BIORETENTION FILTER SECTION
NOT TO SCALE
have highlighted the proposed trees from the original plan Sheet C.22. Yellow— sycamore; purple — redbud; green —
maple. This is a fairly small space for four trees, particularly with a sycamore.
9