20150539 Ver 1_Microsoft Outlook - Memo Style (2)_20150625

Smith, Cherri L
From:
Robinson, Jason
Sent:
Thursday, June 25, 2015 3:31 PM
To:
Jamie and Michelle; Smith, Cherri L
Cc:
Donnie Adams
Subject:
RE: Parkview Subdivision, Clayton, NC
Jamie,
We're good with these responses /revisions.
In order to expedite the review process, you can send two copies of the revised letter and plans to the regional office to
Cherri Smith's attention.
Thanks,
I
Jason T. Robinson, P.E.
Raleigh Regional Office
Water Quality Regional Operations
Division of Water Resources, DENR
919 - 791 -4249
E -mail correspondence to and from this address may be subject to the North Carolina Public Records Low and moy be disclosed to
third parties.
From: Jamie and Michelle [mailto:jamie .michelle.guerrero @gmail.com]
Sent: Thursday, June 25, 2015 2:19 PM
To: Robinson, Jason; Smith, Cherri L
Cc: Donnie Adams
Subject: Parkview Subdivision, Clayton, NC
Jason,
Below are responses to your comments. If you have any questions or additional comments let me know. I will print and
mail the hard copies of the revised cover letter and plans.
1) It appears that the cover letter(dated May 22) has a few discrepancies from what is shown on the maps and other
forms. In the "Stormwater and Diffuse Flow" section of the letter, it seems that the paragraph describing "Impact Area
B -1" is actually describing Area B -2 (two scour holes, high flow bypass). It seems that the paragraph describing "Impact
Area B -2" is actually describing Area B -3 (splitter box and a standard 40 ft. long level spreader used to treat. 077
cfs). This would need to be corrected.
Cover letter is revised as requested.
2) Area B -2 shows two scour holes as opposed to actual "level spreaders" ( "level spreaders" are described in Chapter 8
of DENR's Stormwater BMP Manual).
Why were scour holes chosen instead of an actual level spreader?

I initially tried using two -100 ft. long level spreaders but due to site constraints, minimum lot
requirements, and setback requirements, there was not enough space to install the level spreader
without encroaching on the lots. I spoke with Carlos Bagley, Environmental Manager for Johnston
County, about establishing a permanent stormwater utility easement for a traditional level spreader
on the residential lots. He had concerns that based on his experience, level spreaders on residential
lots are typically not being maintained, damaged, or even removed by homeowners despite
easements and protective covenants written to protect the devices. So based on these difficulties, I
am proposing the preformed scour holes.
Based on NCDOT design criteria, scour holes can be effective up to flows of 10 cfs and the
bottom width dimensions should be a minimum of three times the diameter of the pipe
discharging to the scour hole. The revised design shows a larger bottom width than the
minimum required for a 6" pipe (5'x 5') and a much smaller flow (approx. 1 cfs) than the
maximum limit for scour holes. With this "over- design" of the proposed scour hole, diffuse
flow should easily be achieved.
b. If scour holes are used, they should not be referred to as "level spreaders ", as the term "level
spreader" should only be used for devices that meet the requirements of "level spreader" as described
in Ch 8 of the BMP Manual. Therefore, the term "level spreader" should be removed from the
documents and plans when describing the scour holes.
Plans and documents have been revised.
c. Page 3 of 4 of the plans shows the plan detail for the scour holes. More detail should be provided
for the construction of the scour holes, including the profile detail. Information should also be included
about the depth, width (b1, b2, t1,t2) and slope of the two scour holes and the type of rip rap and filter
fabric to be used. An example of a profile view of a scour hole and dimensions can be found in the
DOT's BMP Toolbox, particularly page 4 -3. It would be helpful to include a table on the plans that
describes the dimensions for each scour hole, as well as the Q10 discharge into each scour hole.
Plans and details have been revised as suggested.
3) The bypass pipe on Impact Area B -2 discharges into a FES with dissipater pad into Zone 1 of the pond buffer. We
would prefer the discharge and dissipater pad to be located farther away from the edge of the pond and discharged into
Zone 2 (thus decreasing the buffer impact area and allowing the discharge more contact time with the buffer before
reaching the pond). Could this be done?
There is an existing farm path around the pond that the developer will likely use as a future greenway as an
amenity. The bypass pipe was extended to go underneath and discharge just below the path in order to avoid having
to install an additional culvert underneath the path. Also discharging the bypass near the edge of water reduces the
risk of scouring occurring at the outlet and possibly creating a gully through the buffer to the pond.
4) On the overall plan there are several areas that show short piping and what appears to be very small dissipater pads
near the buffers. An example is one that appears to be routed to the bypass channel in impact area B -3. There's also
one at Impact Area B -2 that slightly encroaches into Zone 2 of the buffer. What are those?
I apologize for the confusion because I inadvertently left the erosion control layer on in the drawing. The pipes you
are referring to are the skimmer outlets for the temporary skimmer basins that will be removed once the site is
stabilized and vegetated once construction activities are complete. I have revised the plan and turned off this layer.
Thanks,
PEI

Jamie Guerrero, PE, CPSWQ
PNTA Environmental Consultants
34 Castlewood Drive
Clayton, NC 27520
(919) 624 -8825