SW8021225_COMPLIANCE_20030326

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SWJ��J`�
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE
YYYYMMDD

3/13/2003 FAMILY DOLLAR 02007
CDC Infiltration Trench
10-year Storm
WATERSHED DATA
Total Drainage Area
s . ft. acres
76,230 1.75
Impervious Area
Land Use
sq. ft.
acres
buildings
7,812
0.18
arkin las halt
36,261
0,83
concrete
2,646
0,06
Offsite
0
0.00
Total
46,719
1.07
INFILTRATION SYSTEM:
% impervious = 0.613
= 61.3°%
say 62.0°%
CPRE =
0,25
CPOST = (°% imp.)(.95)+(1-0%
imp.)(.25)
=
0,68
110 =
7.23 in/hr
125 =
8.15 in/hr
alume of first two inches of runoff = impervious area(2/12) +(total area - impervious area) (2112) x .25
V= 97016.13 cu-ft
)Iume of Basin provided= (Area of FP + Area of Boftom)12 ' Depth of basin
Vtp= 9,714.00 cu-ft 45 elevation 3840 sf.
47 elevation 5874 sf.
DRAWDOWN TIME:
Depth ofintiltration system:
D= 2 ft.
Infiltration Rate of soils.
R= 18.4 in/hr
Drawdown time:
DDT= 1.30434783 hrs.
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RECEIVED
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3.25-03

INFILTRATION BASIN ANALYSIS FILENAME: G:IDATAIWPDATAIWQSIINBASIN1021225.WK1
PROJECT NUMBER: 021225 DATE: 23-May-03
PROJECT NAME: Family Dollar Shipyard Plaza
DRAINAGE BASIN: Cape Fear REVIEWER: L. Lewis
RECEIVING STREAM: Cape Fear River CLASS: SC
Index No.: CPF17 18-(71) If ORW, is site within the 575' AEC?
SITE AREA 1.75 acres DRAINAGE AREA: 7623 SF
IMPERVIOUS AREA CALCULATION
Rational C
BUILDINGS 7812 1
PARKING/ASPHALT 36261 1
CONCRETE 2646 1
OTHER
TOTAL
% IMPERVIOUS, 1= �. 3%n
ELEVATION OF SEASONAL HIGH WATER TABLE
REPORTED INFILTRATION RATE
SURFACE AREAS AND ELEVATIONS
:......::671: C :> T
Place a "1" here if Rational 1:
RV= .05f.009 (1)
FEET MSL
INCHES/HOUR
Elev. (ft) Area, sq ft
Inc. Volume Acc. Volume
BOTTOM 45 3840
0
0 0
TOP 47 5874
9714 9714
VOLUME 1 DEPTH 1 DRAWDOWN CALCULATION
DESIGN STORM, INCHES
2
DESIGN VOLUME
016;`: CUBIC FEET
TOTAL VOLUME AVAILABLE
:::>9714 CUBIC FEET
DEPTH OF RUNOFF
FEET
TIME TO DRAWDOWN
1 6l HOURS MUST BE <120
25 YEAR 24 HOUR STORM
Intensity, i = .33 inches 1 hour
Qr= C i A =
0.41 CFS
Qp through the bottom of the basin=
1.64 CFS Must be > Or
10 YEAR 10 MIN HIGH INTENSITY EVENT
Intensity, i = 6.3 inches 1 hour
Volume for 10 yr. 10 min. event =
4694.35 CF < 9714 CF
COMMENTS
Volume and drawdown are within Design Requirements.

December 3, 2002
Stormwater Narrative
Family Dollar
New Hanover County, NC
TE 02007
The proposed site for Family Dollar is lot 45 of Shipyard Plaza. The lot is 1.75 acres and
has 7,812 sf of proposed building, 2,646 sf of concrete sidewalk, and 36,261 sf of asphalt
parking and roadway.
Runoff will be treated by an infiltration basin system. The system will treat the total 1.75
acres with 46,719 sf of impervious area. The system is sized to meet the State's 1" and
the City's pre -post requirement. Runoff from the site will drain to a tributary of the Cape
Fear River, classification C-SW. Due to the high rate of infiltration within the soils and
additional sizing of the system, we request a vegetated filter for overflow not be required.

SEP-04-199Q 12:54
2IM'1ER DEVELOPMENT CO
1 910 762 1999 P.02/20
zjftmr Development Comwny
Law Projea No. 310004.1045
Page 2
08'UM
considered accurate only to the degree implied by the methods used. The approximate locations of
the borings are shown on Drawing No. 2 in the Appendix.
The borings were performed by a C,'iE 45 power drilling rig. Borings were drilled using wash
rotary techniques with a drilling slurry to stabilize the boreholes. Samples were taken by driving a
1-3/8 inch I.D. split -spoon sampler in general accordance with ASTIM D 1586 specifications at 2-
1/2 to 5 feet intervals. Representative portions of all samples were sealed in glass jars and
returned to our laboratory where they were visually classified by a geotechnical engineer in
general accordance with the Unified Soil Classificat on System (USCS).
Test boring records showing visual descriptions of the sail strata encountered and the sampling
and field test data are included in the Appendix. Information sheets describing L�e Unified Soil
Classification System and L4e terms and symbols used on the soil boring records are also included.
The evaluation and recommendations presented in this report were developed from our
interpretation of the general subsurface Conditions at the site based on information obtained from
;he soil borings. The stratification lines indicated on the boring records represent the approximate
boundaries between soil types. The t =itions may be more gradual in situ. Variations in soil
conditions can also occur between soil boring locations.
One sample from boring B-6, from a depth of one to five feet was submitted for permeability
.-sting.
SITE AND SUBSLWACE COND171IONS
Site Description
The proposed site is located southeast corner of Carolina Beach Road and Shipyard Boulevard in
Wilmington, North Carolina, as shown on Drawing No. 1 in the Appendix. The site is essentially
rectangular in shape with a gas station located in the north half with an overhead pump station
canopy, car wash, concession buildings. and asphalt paving. The southern half of the propemy is
lat. undeveloped and has a grass cover.
Subsurface Conditions .
The borings performed across the site generally revealed loose to dense fine sands containing
variable amounts of clay and silt to a depth of boring termination 20 ftet. A laver of loose to firm
clayey sands was encountered from approximateiy 6 to la feet BGS in baring B-2, 3, and 5.
Underlying the clayey Sands, a firm fine sand was encountered. These soils are classified as SP
and SC soils according to the Unified Soil Classification System. The upper sands have Standard
Penetration Test (SPT) resistance values (N-values) ranging from 9 to 16 blows per foot. The
underlying clayey sands have SPT values ranging from 10 to 36 blows per foot. The underlying
Fine sands have SPT values ranging from 14 to 50* blows per foot.
Asphalt overlying marl and gravel was encountered to a depth of one foot in the borings located
throughout the area of the old gas station. Loose sand was encountered in Boring B-s to a depth of
3 feet. This boritHk(TIVED
an area formerly occupied by an old UST tank pit which has
MAR' 2 6 2003 ' LAW
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PROJ # nCyE02122.5

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reportedly been removed. Fuel odors were apparent in samples collected from borings B-I and
B-4.
A soil sample from boring B-6 from 1.0 to 5.0 feet below ground surface was.laboratory tested for
permeability. The results of laboratory testing indicate a permeability of 1.3E-0_2 cmisec. f
Ground -Water Conditions
Accurate groundwater readings could not be made at the completion of the borings since a slurry
or "mud" was used in the drilling process. However, based on the observed soil moisture
conditions and ground -water measurements obtained :n open borehole monitoring wells 24 hours
alter drilling, we expect ground water is present be -we -ea 12 and 14 feei below the existing ground
surface. Ground -water observations are recorded on the Soil boring logs in the Appendix.
Fluctuations in the groundwater table may occur depending on variations in precipitation,
evaporation, and surface water runoff. The ground -water level is generally higher during, the
wetter months of the year (November to March).
RECONCKENDATIONS
Site Pre aration
u'e anticipate fill will be placed above existing grades in the prcaosed building areas to establish
sur:ace: drainage away from the structures. We assume no more than about one foot of fill will be
placed. We do not expect any significant lowering of existing grades over the remainder of the
site, except for an infiltration pond.
Site preparation should begin with demolition and removal of buildings associated with the
existing gas station. The existing mari encountered beneath the asphalt paving may remain in
place or be salvaged for use elsewhere on the site. All vegetaticn, topsoil, and unsuitable soil
should be stripped From proposed building and pavement areas in the southern parcel. The
strippings should be removed from the site or s-,cckpiled for use in landscaped areas. We
recommend a nominal snipping depth of one foot to remove surface vegetation and topsoil,
although deeper stripping may be necessarysn localized areas to allow for more complete removal
of unsuitable materials if encountered.
If areas of unstabie soils are observed during stripping, these soils should be undercut and replaced
with either compacted washed crushed stone (N.C-DOT No. 57 or 67) or compacted soil ill. In
general, we do not anticipate significant undercutting at this site based on shallow soil conditions
revealed by the borings.
Cnce demo Iitionlremoval and stripping is complete, the shallow sands in building and pavement
areas should be densifaed by vibratory rolling with a heavy -weight smooth steel drum vibratory
roller. The vibratory roller should make eight passes over each section of the building- and
pavement subgrades in order to improve the densiry of shallow sands in an effort to provide more
uniform subgrade support for compaction of structural fill and for floor slabs and pavements. The`
second set of four passes should be perpendicular to the first set of four passes. The geotechn'scal
., engineer or technician should observe the vitrratory rolling to ' elp identify localized areas of
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