20021271 Ver 1_Modifications_20030124

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SPAULDING & NORRIS, PA
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Civil Engineering & Planning
January 24, 2003
Mr. Todd St. John
NC Division of Water Quality
Central Office
2321 Crabtree Boulevard
Suite 250
Raleigh, NC 27604-2260
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Re: Major Amendment for 401 Water Quality Certification for Autumn Park PUD
Holly Springs, Wake County
DWQ # 02-1271
S&N Project # 308-01
Dear Mr. St. John,
On January 17, 2003, we had a telephone conversation about Autumn Park PUD (Holly Springs,
Wake County) and the need for further evidence of the proposed reduction in impervious surface
area. This letter is in response to your request for additional information to substantiate the
impervious coverage will be less than 30% for this project.
The original PCN Application for this project was submitted on August 8, 2002. Attached to the
PCN is a plan sheet titled "Autumn Park Subdivision -Wetlands Impact Analysis (C-22)". On
the top, right corner of this plan, a table titled "Project Data" lists various detailed information
about the project. This table lists the project total acreage as 49.468 acres. This project acreage
was entered as the total acreage of the site in Section XI of the PCN Application. What I failed to
notice about this table when preparing the PCN Application, was that it only accounts for the
single-family home portion of the project. Hence, the townhome portion of the project is not
included in the listed total acreage in the "Project Data" table. The actual total acreage of the site,
57.755 acres, is accurately listed on the wetlands survey supplied by Mrs. Amanda Jones of the
US Army Corps of Engineers, Raleigh Regulatory Field Office. This wetland survey supplied by
Mrs. Jones was also included with the August 8, 2002, PCN Application. This error on my part
accounted for a reported total site area that was 8.287 acres (17%) less than the actual site area. If
the correct total site acreage had been reported in Section XI of the PCN Application, the initial
proposed impervious area would equate to 36.7% (21.2 acres impervious / 57.755 acres total x
100) versus the reported 42.9%.
I submitted a letter to you dated November 20, 2002, in which I explain the methods used to
reduce the total proposed impervious acreage for this project. As stated in this letter, the
reduction in proposed impervious area will be achieved by slightly reducing the average home
size and by constructing homes closer to the front yard setback than was originally planned for
this development. The effect of placing the homes closer to the front yard setback is that
driveway length is reduced. Please understand that the Owner of this project has control over
what floor plans are available to future homeowners as well as their placement on this site.
Through these mechanisms, the Owner has committed to a maximum average impervious area
per single family home lot of 1,900 ft and 1,500 f~ per townhome unit. These, self-imposed
limitations on impervious area require that the Owner sell a smaller average product. However,
the Owner has chosen this reduction in total impervious surface area over the installation of
Phone: [phone] ~ Fax: [phone] ~ 972 Trinity Road ~ Raleigh, North Carolina 27607

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several BMPs on the site. The calculations provided with the letter dated November 20, 2002,
indicate a 3.96 acre reduction in total proposed impervious area when compared to the 21.2 acres
of proposed impervious surface listed in Section XI of the August 8, 2002, PCN Application.
Since there are 194 single family units and 50 townhome units planned for this project, this
equates to an average reduction of 707 ft2 of impervious surface area per unit. While this does
equate to a substantial reduction in desired average home size, it still allows for a product that is
very comparable to several other subdivisions and townhome developments in the Holly Springs
area.
The DWQ letter dated January 15, 2003, requesting additional information states that "the plan
approved along with the 401 Water Quality Certification, issued October 3, 2002, appear to be
essentially the same plans as those submitted December 23, 2002." Please note that the plans
submitted on both dates do not indicate building footprints or driveways for the single family
home portion of the project, hence there is no reason for the plans to have changed. Also please
note that there is no mention in any correspondence of altering streets, sidewalks or greenway
locations in order to achieve the desired reduction in impervious area for this project. The
previouslyproposed reduction in impervious area relied solely on the reduction of building and
driveway footprints.
The November 20, 2002, letter I submitted to you mentioned that the Owner was in the process of
requesting permission from the Town of Holly Springs to change the proposed greenway from an
impervious surface material to a pervious material (mulch, wood chips, gravel, etc.). Since the
date of this letter, the Owner has received verbal approval to change the proposed greenway trails
to mulch instead of asphalt. This change reduces the total impervious surface for the project by
another 17,149 ft . A revised impervious surface calculation sheet is provided for your reference.
After changing the greenway to mulch, the total proposed impervious surface is reduced to
733,667 ft . This equates to an impervious surface coverage of 29.2%.
I trust that these explanations and calculations will provide the requested additional substantiating
information to prove that the project's total impervious surface will in fact be less than 30% at
completion. Thank you in advance for your time spent reviewing this request. Please call me if
you have any questions, comments or concerns about this request or if you require additional
information to process this request.
Sincerely,
Scott MitchelT,~E, LSS
Environmental Engineer/Scientist
cc: Mr. Mitchell Huff, Grossman Communities of NC, Inc.

Impervious Surface Calculations
Revised 01-24-2003
for
Autumn Park PUD
Holly Springs
Wake County
Property Size = 57.755 acres or 2,515,807.8 ft2
30% of Property Size = 17.327 acres or 754,742.3 ft2
Impervious Surface Area Required for Infrastructure
Sin le Famil ft2 Townhomes ft2 Total ft~
Streets 196,935 49,716 246,651
Sidewalk, 36,106 7,310 43,416
Total. = 290, 067
Impervious Surface Area Required for Homes
Number of Lots Average Impervious - Total Impervious Area
Area r Lot (ft2 1 ft2
Single Family 194 1;900 368,600
Townhomes 50 1,500 75,000
Total = 443, 600
1 Includes all impervious area proposed for private lots (home, driveway, patio, walkway, etc.)
Total Proposed Impervious Surface Area for Project =
290,067 ftZ + 443,600 ft2 = 733.667 ft2
Percent of Property Covered by Impervious Surface at Full Build Out =
(733,667 ft2 / 2,515,807.8 ft2) x 100 = 9.2 °/