LMG_Correspondence_20190927

4LMG
LAND MANAGEMENT GROUP
a DAVEA company
September 27, 2019
TO: Mr. Paul Wojoski
NC Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699
RE: Carroll at the Avenue; New Hanover County, NC
401 WQC Application; Additional Information
DWR Project 2017-1606
Dear Mr. Wojoski:
Thank you for your comments dated July 12, 2019 and July 17, 2019 on the IP/401 WQC application that
was submitted for the Carroll at the Avenue project in Wilmington, NC. Below is a response to each of your
comments.
Overall the Division is concerned with our ability to certify a project that results in such a large quantity of
resource loss (and no mitigation — but understanding that mitigating for open water loss is extremely
difficult). It's also concerning that the project was originally designed and permitted/certified with an
infeasible alternative. Those concerns aside, the Project Narrative outlines two alternatives other than the
preferred. I've listed them below with some further questions for analysis:
1. Alternative 1 -Site Plan from Nationwide Application
a. High costs to install this system was cited as rendering this alternative infeasible (Project Narrative,
Page 7) — what is this cost as a percentage of the total project cost/total projected revenue from the
development?
RESPONSE: The main reason this alternative was not feasible was because of the poor soils within the
site. In order to make infiltration feasible, the project would need to be reduced in scope to a point
where it is no longer economically feasible to the developer.
b. Minimal areas of open space were cited as rendering this alternative infeasible — how much area is
needed for the system? How does this amount of area impact the proposed project? Would it render the
site undevelopoble?
RESPONSE: The specific amount of open space that would be needed to make infiltration feasible would
vary depending on the infiltration rates of the soils within the open space provided. Given the amount
of impervious cover proposed in the site plan and the average infiltration rate across the site, the
required underground infiltration system area would need to be approximately 193,000 sf. However,
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the area available for use outside public rights of way, utilities corridors, and buildings is 87,000 sf.
Other factors are shallow depth to the seasonal high water table, which would require excessive fill on
the site to provide adequate cover, and varying infiltration rates from poor to adequate.
2. Alternative 2 — Stormwater Pond in Uplands
a. Projected lost future revenue ($28 million) was cited as rendering this alternative infeasible. (Project
Narrative, Page 8) What is this projected lost revenue as a percentage of the overall project projected
revenue?
As noted in the application, placing a stormwater pond in uplands would result in the loss of Building 10
and its associated parking. This building is expected to generate approximately $28 million in future
revenue, which is 11% of the total projected revenue for the entire project.
b. The project site is listed as 44.5 acres and the stormwater pond required is 3.4 acres. Is the parcel still
developable with a stormwater pond in uplands?
Reducing the scope of the project by 3.4 acres in order to construct a stormwater pond in uplands
would result in a project that is economically infeasible to the developer.
3. Other Alternatives to consider for analysis.
a. The project cites 42.8% impervious surface — what ways to reduce impervious surface were
considered?
The project will provide pervious pavement options that will reduce runoff and disconnect areas of
impervious coverage from the collection system and the wet detention basins. This will be achieved
by using pervious surfaces such as pavers and/or pervious concrete on surface parking spaces to
minimize surface runoff to Howe Creek. Surface parking outside of the 575' setback will also
include pervious pavers and/or pervious concrete.
It should also be noted that there is currently 289,238 sf (14.9%) of impervious surface currently
existing within the site that will be removed. The project will add approximately 541,887 sf or 28.0% of
additional impervious surface.
b. What other stormwater management systems were considered and why are they infeasible?
RESPONSE: The engineer evaluated using underground infiltration pipe in a stone trench. This option
was evaluated since it can handle and treat large volumes of stormwater runoff and is not limited to
small volumes. The two limiting factors on this type of system are separation from seasonal high-water
table, 24-inches minimum, and suitable soils that allow for a reasonable infiltration rate. One other
limiting factor with this project is the few areas on -site that will support this system. This type of
system is not installed within public or private rights of way, so we are limited to parking areas and
open spaces. We must also keep clearances from public water and sanitary sewer mains that also
traverse the property to service the proposed buildings. With that said, we simply ran out of feasible
areas to have an underground infiltration system that stores the 1.5-inch volume and the difference in
pre vs. post for the City of Wilmington peak attenuation requirements. This system will also require
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3805 Wrightsville Avenue, Suite 15 • Wilmington, NC 28403

large amounts of fill on the site in order to get the separation between the seasonal high water and the
top of the system. We concluded this option was not feasible.
Have private contractors provided analysis or quotes for alternative systems?
RESPONSE: No. Once it was determined that alternative systems would not be able to treat the amount
of stormwater to be generated by the project, these systems were not considered further, and
estimates were not obtained.
if cost renders the option infeasible, please provide cost in terms as a percentage of overall project cost.
RESPONSE: These systems were considered infeasible because they could not treat the amount of
stormwater to be generated by the project.
Two systems for consideration that our stormwater engineer brought to my attention include:
i. Bio-cells
RESPONSE: Bio-retention cells are primarily used for water quality and for very small drainage areas.
These types of systems are not used for large scale stormwater management, but rather smaller
components of an overall system. This type of BMP may still be used for this project but will not make
up the difference in treatment volume from the underground infiltration system. Bio-retention systems
also require good soil media to work as intended.
ii. Stormfilter by Con -tech
RESPONSE: Stormfilters are used for water quality treatment only. Since this project is in a jurisdiction
where peak attenuation for the 25-year storm event is required, we would still need to provide
additional underground storage to meet that requirement. This falls into the same issue with
underground infiltration, which is not enough room to install it.
I hope this response adequately addresses your concerns and that a 401 WQC can be issued at this time.
Please let me know if you have any other questions.
Sincerely,
mssigned b;54""�Kim WilliaDae:20;:
Kim Williams
Environmental Scientist
Cc: Mr. Roy E. Carroll II, 347 MCO, LLC
Mr. Rob Balland, Paramounte Engineering, Inc.
www.lmgroup.net • [e-mail] • Phone: [phone] • Fax: [phone]
3805 Wrightsville Avenue, Suite 15 • Wilmington, NC 28403

4LMG
LAND MANAGEMENT GROUP
a DAVEYI company
September 27, 2019
TO: Ms. Rachel Capito
U.S. Army Corps of Engineers
69 Darlington Avenue
Wilmington, NC 28403
RE: Carroll at the Avenue; New Hanover County, NC
Response to Comments; Individual Permit Application
Action ID# SAW-2017-02531
Dear Rachel:
Thank you for your comments dated August 16, 2019 regarding the IP application that was submitted
for the Carroll at the Avenue project in Wilmington, NC. Below is a response to each of your comments.
Comment #1: Alternative #2 mentions locating stormwater ponds in uplands, but there is no mention of
utilizing the two available uplands outparcels, which are currently not designed as part of the
development as an alternative location for the stormwater feature.
RESPONSE: Each outparcel is sized to accommodate a 43,000-sf office building, which is estimated to
be sold for approximately $9 million. Therefore, placing a pond here would result in losing
approximately $18 million of income. This is not economically feasible for the developer. Additionally,
the outparcels are located on the highest elevations of the overall property and would require
stormwater to be pumped to this location, which is not feasible. Finally, this area is located in an area
of high visibility to passing motorists on Military Cutoff Road and it does not make financial sense to
place a pond at this location.
Comment #2: Evaluate redesigning the parking adjacent to building 10 to utilize the available space in
that area for stormwater features.
RESPONSE: The office building requires a minimum of 445 parking spaces and there are 220 surface
spaces around the building. The remainder would be covered in the parking structures. Eliminating
parking for the office building would result in a further deficit for parking around the office building.
Additionally, easements and setbacks exist in this area. A sanitary sewer easement and powerline
right-of-way run along the eastern property boundary behind Building 10. The City of Wilmington
(COW) has a conservation resource setback measured off the wetlands in this area and development is
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3805 Wrightsville Avenue, Suite 15 • Wilmington, N[ 28403

limited. The COW allows up to 50% of the setback to be disturbed and only 25% of the setback can
include impervious surface.
I hope this response adequately addresses your concerns and that an Individual Permit can be issued at
this time. Please let me know if you have any other questions.
Sincerely,
Digitally signed by Kim Williams
Kim Williams Date: 2019.09.27 15:15:17
-04'00'
Kim Williams
Environmental Scientist
Cc: Mr. Roy E. Carroll II, 347 MCO, LLC
Mr. Rob Balland, Paramounte Engineering, Inc.
www.imgroup.net • [e-mail] • Phone: [phone] • Fax: [phone]
3805 Wrightsville Avenue, Suite 15 • Wilmington, NC 28403