SW3230601_Sand Filter MDC Quick Questions -1_20230808

Holland, Brianna
From: David Ledford <[e-mail]>
Sent: Tuesday, August 8, 2023 7:00 AM
To: Holland, Brianna
Subject: [External] Fw: Sand Filter MDC Quick Questions
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Question for Jim Farkas
Email#1
I David Ledford, RLA
Landscape Architect
2730 Maiden Highway
Lincolnton, NC 28092
704-530-7880
----- Forwarded Message -----
From: David Ledford <[e-mail]>
To:[e-mail]<[e-mail]>
Cc: David Ledford <[e-mail]>
Sent: Thursday, May 25, 2023 at 10:18:11 AM EDT
Subject: Sand Filter MDC Quick Questions
Jim,
Been a while since we last talked. Hope everything is well in Raleigh.
I know you are overworked by the sounds of it talking with other designers.
I remember those days with Lincoln County and the volume of plans.
The reason for writing is to get a few MDC answers for a sand filter design.
I haven't submitted to the State in a while, mainly to local municipalities for
review and they have their own additional requirements too.
As always trying to get what's need but not over-design for the heck of it.
Items in Questions:
1) Is there a maximum depth over the sand filter area for the Vt (treatment volume).
I know there is a maximum 6' depth for the sand filter with a mention of peak
attenuation if needed. I'm planning on a 3'Vt depth over the sand filter portion.
2) Is there any peak attenuation requirement for a sand filter with the State.
As above there was only a mention of it with the depth IF NEEDED and the
as-built certification asks about if the bypass device is set at or above the
storage volume (Vt?).
3)What is the minimum depth of the stone or gravel layer on the top of the sand
filter surface. Not labeled in the detail or section but is usually 2" depth in most
municipalities with the requirement.
1

4) What is the requirement for underdrain protection with regard to the only mention
of the minimum sand layer depth and then the minimum sand layer depth above
the underdrains. The open bottom detail shows sand beside the underdrain no
protection mentioned. Would it be filter fabric, stone layer, or both.
5) Could the even flow distribution be accomplish with a rip rap energy dissipater
added at the end of the perforated riser pipe outlet in the sand filter as allowed
by Mecklenburg County. If not, are there any examples that you have or know
of that have been approved and used for this type of outlet.
6) Is there a checklist for either a sand filter submittal or a typical overall submittal
that you use or is listed on the website somewhere. I like to try to have all the
needed info for a good review package.
Thanks for your time.
David
J. David Ledford, RLA
Landscape Architect
2730 Maiden Highway
Lincolnton, NC 28092
704-530-7880
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