HomeMy WebLinkAboutSW3210801_Soils/Geotechnical Report_20210804July 28, 2021
NorthPoint Development, LLC
4085 Montgomery Road, Suite 310
Cincinnati, OH 45212
Attn: Mr. Michael Johnston
P: (614) 546-9850
E: mjohnston@northpointkc.com
Irerracon
GeoReport
Re: Supplemental Geotechnical Consulting Services — Seasonal High Water Table
1-85 Commerce Center
410 Webb Road
Salisbury, North Carolina
Terracon Project No. 71215021
Dear Mr. Johnston:
Terracon Consultants, Inc. (Terracon) has completed a seasonal high water table exploration for
the five planned stormwater ponds at the proposed 1-85 Commerce Center project located in
Salisbury, North Carolina. This study was performed in general accordance with our
Supplement to Agreement for Services, Reference No. P71215021, dated July 12, 2021. This
letter report presents the findings of the subsurface exploration.
Five (5) hand auger borings, SHWT-1 through SHWT-5, were performed to depths of
approximately 58 to 120 inches below the existing ground surface within the proposed
stormwater pond areas. The boring locations were located using the 1-85 Commerce Center —
Existing Conditions" plan sheet, EX1.1, dated 7/1/2021 provided by Brad Smith of Thomas &
Hutton. The ground surface at each hand auger boring was estimated based on the provided
topographic plan. A Site Location Plan and Boring Location Plan are included in the attachments.
The soils encountered were field classified according to the Unified Soil Classification System
as clays with varying amounts of sand (CL), silts with varying amounts of sand (ML), and sands
with varying amounts of silt (SM). Groundwater was encountered in boring SHWT-3 at a depth
of approximately 8.5 feet at the end of the day prior to backfilling. The remaining borings were
backfilled immediately after completion of hand auger activities. As such, groundwater was not
encountered in the remaining borings in the relatively short amount of time they were left open.
Saprolite was also encountered within three of our hand auger borings (SHWT-1, SHWT-2 and
SHWT-3) at depths of approximately 2.5 to 5 feet. Saprolite is a clay -rich material left over from
the weathering of igneous and metamorphic rocks. As a result of its formation, saprolite often
has quartz veins and color banding that are relics of the parent materials, rendering the
identification of hydric soil components within saprolite unreliable. Its composition leads to low
permeability and can act as an aquitard, which can result in a perched water table.
Supplemental Geotechnical Consulting Services — Seasonal High Water Table lrerracon
1-85 Commerce Center Salisbury, North Carolina
July 28, 2021 Terracon Project No. 71215021 GeoReport
The soil samples in the borings were observed for in situ moisture content as well as
redoximorphic features of the soil profile to estimate the seasonal high water table levels at each
boring location. Redoximorphic features (a gray or bluish -gray colored soil matrix) and mottles
are formed by the process of reduction, translocation, and/or oxidation of iron and manganese
oxides as the water table fluctuates. A soil layer exhibiting redoximorphic features can be
representative of the seasonal high water table level.
The following table summarizes the results of our hand auger borings:
Estimated
Approximate
Approximate
Approximate
Boring
Seasonal High
Elevation of
Boring
Depth
Boring
Water Table
Observed
Depth of
No.
Elevation
Saprolite
(feet)
Elevation -
Groundwater -
(feet)
(feet)
(feet)
(feet)
NE
5
SHWT-1 10 774 NE 4
SHWT-2
10
773
NE
NE
2.5
SHWT-3
10
762
758.7
753.5
3.5
SHWT-4
4.83
762
759
NE
NE
NE
NE
SHWT-5
5.25
766
762.7
Below existing ground surface.
Elevations referenced from Existing Conditions plan sheet EX1.1 dated 7/1/2021 provided by Thomas &
Hutton.
Saprolite can sometimes affect the ability to accurately determine seasonal high water table, due to the relic
characteristics of the parent material and the potential for perched water due to low permeability.
NE = Not Encountered
Soil science provides a powerful tool for interpreting the estimated average seasonal high
water table level throughout the year, even during dry seasons when water tables may not be
present. In many situations, trained personnel without a formal soil science education can
make reliable interpretations. However, in areas of unique and complex soil conditions or
disturbed sites careful consideration of the soil's morphology, the kind of parent materials, the
position of the soil in the landscape, and topography need to be assessed by a qualified soil
scientist before a determination can be made. Field determinations of water table depth are
typically made through the identification of redoximorphic features in the soil profile. Monitoring
wells and piezometers are used to determine actual water table depths, which are then used
for calibrating field indicators of a high water table.
Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff
and other factors not evident at the time the borings were performed. Therefore, observed
groundwater levels during construction or at other times in the life of the structure may be higher
or lower than the levels indicated above. The possibility of groundwater level fluctuations above
Responsive r Resourceful L r<eliable 2
Supplemental Geotechnical Consulting Services — Seasonal High Water Table ��jt`f`aCtN1
1-85 Commerce Center Salisbury, North Carolina
July 28, 2021 Terracon Project No. 71215021 GeoReport
or below the estimated limits should be considered when developing the design and construction
plans for the project.
We appreciate the opportunity to be of service to you on this project. If you have any questions
concerning this report, or if we may be of further service, please contact us.
Sincerely,
Terracon Consultants, Inc.
liam O. Frazier, P.G.
Project Geologist
Attachments: Site Location Plan
Exploration Plan
Christopher R. Briggs, P.E.
Geotechnical Department Manager
Responsive F Resourceful in Reliable 3
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EXPLORATION PLAN
1-85 Commerce Center Salisbury, Rowan County, North Carolina
July 28, 2021 Terracon Project No. 71215021
1 rerracon
GeoReport
Approximate SHWT Boring Location —
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DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES PLAN PROVIDED BY THOMAS & HUTTON