SW6210907_Soils/Geotechnical Report_20210930

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
August 10, 2021
Re: Seasonal High -Water Table Identification and Soil Infiltration Rates: Proposed Gas Station
(Timberland Ranch). Hoke County, NC (PIN 594060001097)
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 366'
(approximately 15' below ground surface).
SATURATED HYDRAULIC CONDUCTIVITY (Kt)
Soils within the proposed stormwater BMP device typical of those within the Candor Sand series. Candor
Sands are very deep and excessively drained soils with moderately high rates of permeability. Infiltration
rates were measured to determine the suitability for installation of a stormwater infiltration BMP.
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
Borin6 #
SHWT
Munsell Color
Ksat 91
Ksat 42
Ksat #3
Ksat 94
(feet below
Notation
round surface
I
15'
SY 8/1
0-7'
7-9.5'
9.5-13'
13-15
SHWT
2.5Y 7/1
LS/SL
Perched water
SL/SCL
Crs LS
elevation: 366'
1
1 22" / hour
f Not Measured
3" / hour
15" / hour

Scott Cole, NCLSS
312 Copples Road Ext
Asheboro, NC 27205
[phone]
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,
ScX01e
North Carolina Licensed Soil Scientist
� SOIL SC�F�
`. •�
�"9lF ) 262)