SW6210903_Soils/Geotechnical Report_20210914

Scott Cole, NCLSS
312 Copples Road Ext
Asheboro, NC 27205
[phone]
Double D Engineering, PLLC
Attn: Mr. Lee Humphrey
150 S. Page Street
Southern Pines, NC 28387
July 12, 2021
Re: Seasonal High -Water Table Identification and Soil Infiltration Rates: Carolina Crossing; Hoke
County NC Parcel (Altparno) 4768 (N. Horace Walter Road)
Soil conditions and infiltration rates were evaluated and measured on the above -referenced property
within the proposed storm water BMP device. Work was conducted in accordance with Parts A-2 and C-
1 of the North Carolina Department of Environmental Quality Stormwater Design Manual. Soil samples
were evaluated with a hand auger.
SEASONAL HIGH WATER TABLE IDENTIFICATION
Seasonal High Water Table depth is determined by field evaluation for soil wetness conditions which are
indicated by the presence of redoximorphic (redox) features with a chroma of 2 or less (in Munsell color
notation) in mottles or the horizon matrix. Colors of chroma 2 or less due to relic minerals from parent
material (underlying rock), anaerobic activity created by placement of fill material, or soil textural class
transitions (perched water) are not considered as indicators for seasonal high water. Upon determination
of SHWT depth, an additional 6" will be deducted from the observed depth to account for capillary fringe
water movement above the SHWT. Stormwater infiltration trenches are designed to ensure the lowest
point is at least two feet above the Seasonal High Water Table (SHWT).
The SHWT for this project was identified within the proposed BMP device at elevation 326'
(approximately 12' below around surface).
SATURATED HYDRAULIC CONDUCTIVITY (Ksat)
Soils evaluated across most of this property are typical of those within the Autryville Loamy Sand series
(AuA). These are deep, well drained soils with varying rates of permeability. Infiltration rates were
measured to determine if soil conditions were suitable for the installation of stormwater infiltration
trenches. Infiltration rates were measured using a Johnson Constant Head Permeameter. Measurements
were recorded at varying intervals until equilibrium was reached.
A summary of observations within the proposed Stormwater BMP Device is shown in the table below.
BMP Device Site #1
Borin¢ #
SHWT
(feet below
round surface
Munsell Color
Notation
Ksat # t
Ksat #2
Ksat #3
Ksat 94
1
12'
2.5Y 8/1
0-3'
Y-12'
N/A
N/A
SHWT
2.5Y 7/1
Loamy Sand
Sandy Loam
elevation: 321'
18" / hour
8" / hour
2
12'
2.5Y 8/1
0-3'
3'-6'
6'-9'
10,
SHWT
2.5Y 7/1
Loamy Sand
Sandy Loam
Perched water
Sandy
elevation: 325'
18" / hour
8" / hour
(exp. Clay)
Loam /
Not Measured
Sandy Clay
Loam
4" / hour

Scott Cole, NCLSS
312 Copples Road Ext
Asheboro, NC 27205
[phone]
Boring #
SHWT
Munsell Color
Ksat 41
Ksat #2
Ksat 43
Ksat #4
(feet below
Notation
round surface
3
14'
2.5V 8/1
0-3'
3'-7.5'
7.5%10'
12'
SHWT
2.5V 7/1
Loamy Sand
Sandy Loam
Perched water
Sandy
elevation: 326'
18" / hour
8" / hour
(exp. Clay)
Loam /
Not Measured
Sandy Clay
Loam
4" / hour
CONCLUSION
Field evaluation of hydraulic conductivity provides estimations of soil infiltration rates; however,
methods used to measure these rates can influence the results. Side walls of the bore hole are "smeared"
by the soil auger as the hole is prepared and loose soil in the bottom of the hole is placed in suspension
when water is applied; both of these factors negatively influence water infiltration rates. To help
overcome these issues, after excavation of each infiltration trench, it is recommended the trench bottom
and sidewalls be raked and dusted with pulverized limestone. These are practices that have been in place
within the on -site wastewater industry to help loosen the soil and aid in restoration of soil structure.
I am pleased to be of service in this matter and can be contacted at your convenience should you have any
questions concerning information within this report.
Thank you,
Scott Cole
North Carolina Licensed Soil Scientist
40
N
/7