SW3221001_SHWT Report_20230216

Civil - Geotechnical - Surveying
February 8, 2023
Mr. Ken Foster
Ridgeline Corporation
PO Box 39
Cornelius, NC 28031
Reference: Brighton Park Subdivision
Seasonal High -Water Table Evaluation
CESI Project Number 220143.000
Mr. Foster:
Peryour request, Concord Engineering & Surveying, Inc. (CESI) has performed an evaluation
of seasonal high-water table (SHWT) within the location of four of the seven storm detention
ponds (BMP's) for the Brighton Park Subdivision project in Mt. Pleasant, North Carolina. It is
noted that SHWT data was not warranted for BMP #3 and #6. These ponds will be
constructed within fill sections of the project.
On February 24, 2022, hand auger borings were performed at staked locations for BMP
locations #1, #2, #4, and #5. Once the hand auger boring was compete and initial data logged,
the test boring was allowed to acclimate. On March 7, 2022 CESI returned to the site to
observe the conditions and backfill the auger hole. The following is the data acquired and the
seasonal high water level recommendations.
BMP #1 SHWT
Ground (Hub) Elevation 611.29
Bottom of Hand Auger Boring 606.79 (auger refusal)
Water Level on March 7t" (11-day duration) not encountered
Proposed Bottom of Sand 609.0
2' Sand to SHWT Separation Elevation 607.0
45 Spring Street, SW P.O. Box 268 Concord, NC 28026-0268 704-786-5404
www.cesicgs.com NC License No. C-0263

A hand auger boring was advanced adjacent to the survey stake where auger refusal was
encountered at 4.5' below ground level. We offset multiple times on a radius of approximately
7' from the survey stake. Auger refusal was again encountered at corresponding elevations.
No groundwater was encountered at the time of hand auger boring or after an 11-day duration.
Based on our observations it was determined that the seasonal high groundwater table
elevation at the BMP #1 test location is deeper than 606.79. It was noted that prior to
auger refusal, we encountered leaf litter and topsoil underlain by fine sandy SILT (ML) soils.
The actual elevation of the SHWT could not be confirmed due to the presence of refusal
rock. However, it is our understanding that this location can be raised slightly (2.4')
to meet the design requirements.
BMP #2 SHWT
Ground (Hub)Elevation 643.11
Bottom of Hand Auger Boring 627.61
Water Level on March 7t" (11-day duration) not encountered
Proposed Bottom of Sand 630.00
2' Sand to SHWT Separation Elevation 628.00
A hand auger boring was advanced adjacent to the survey stake to a depth of 15.5' below
ground surface. Grass and topsoil underlain with fine sandy SILT (ML) soils was encountered
in the auger cuttings. No groundwater was encountered at the time of hand auger boring or
after an 11-day duration. Based on our observations it was determined that the seasonal
high groundwater table elevation at the BMP #2 test location is deeper than 627.61.
This elevation supports the use of a sand filter basin at the current location and
elevation.
BMP #3 SHWT
Ground Elevation
Proposed Bottom of Sand
Seasonal High -Water Table
623.0
625.5
Deeper than 623.0
BMP #3 will be constructed in a fill section. A minimum of 2.5' of clearance to SHWT will be
achieved.
45 Spring Street, SW P.O. Box 268 Concord, NC 28026-0268 704-786-5404
www.cesicgs.com NC License No. C-0263

BMP #4 SHWT
Ground (Hub)Elevation 627.21
Bottom of Hand Auger Boring 622.21
Water Level on March 7t" (11-day duration) 623.71
Proposed Bottom of Sand 628.40
2' Sand to SHWT Separation Elevation 626.40
A hand auger boring was advanced adjacent to the survey stake to a depth of 5' below ground
surface. The auger cuttings consisted of leaf litter underlain by fine sandy SILT (ML) soils. No
groundwater was encountered at the time of hand auger boring. However, stabilized
groundwater was encountered 3.5' from the surface at the 11-day duration mark. Based on
our observations it was determined that the seasonal high groundwater table elevation
at the BMP #2 test location is approximately than 623.71.
This elevation supports the use of a sand filter basin at the current location and
elevation.
BMP #5 SHWT
Ground (Hub) Elevation 610.73
Bottom of Hand Auger Boring 607.23 (auger refusal)
Water Level on March 7t" (11-day duration) not encountered
Proposed Bottom of Sand 610.00
2' Sand to SHWT Separation Elevation 608.00
A hand auger boring was advanced adjacent to the survey stake where leaf litter, topsoils and
fine sandy SILT (ML) soils were encountered with hand auger refusal at 3.5' below ground
level. It was noted that the auger refusal elevation is deeper than the required 2' bottom of
sand separation, so no offsets were performed. No groundwater was encountered at the time
of hand auger boring or after an 11-day duration. Based on our observations it was
determined that the seasonal high groundwater table elevation at the BMP #6 test
location is deeper than 607.23.
This elevation supports the use of a sand filter basin at the current location and
elevation.
45 Spring Street, SW P.O. Box 268 Concord, NC 28026-0268 704-786-5404
www.cesicgs.com NC License No. C-0263

BMP #6 SHWT
Ground Elevation 606.0
Proposed Bottom of Sand 615.5
Seasonal High -Water Table Deeper than 606.0
BMP #3 will be constructed in a fill section. Approximately 9.5' of clearance to SHWT will be
achieved.
We appreciate the opportunity to be of service to you and we look forward to helping you
through project completion. If you have any questions, please feel free to call.
Respectfully submitted,
�C A rRf '�fr
r
27837 2 1 U �(i✓
QN 4�
James G. (Jay) Eaves III, PE
Division Engineer
45 Spring Street, SW P.O. Box 268 Concord, NC 28026-0268 704-786-5404
www.cesicgs.com NC License No. C-0263

eirignton ParK - bftl�i fiorings uiap
Feature 1
r
CE M P-2
?4
• IL
fJ
`BMP-3
(BMP-4
`BMP-5 `BMP-6
Google Earth i!O
ol
OR . x �oaios'S'61
Z A�'
W, W,
0 ft