SW6220802_Soils/Geotechnical Report_20220816

Adams Soil Consulting
1676 Mitchell Road
Angier, NC 27501
919-414-6761
Attention: Glenn Tew
July 13, 2022
Project #963
RE: Seasonal high-water table determination and infiltration analysis for proposed
commercial stormwater device (BMP) located adjacent.to the intersection of NC HWY 401
and Chalybeate Springs Road — Harnett County, NC
Mr. Tew;
Adams Soil Consulting (ASC) performed a site evaluation per your request on the above
referenced location. Profile descriptions can be supplied upon request. The purpose of the
evaluation was to determine the depth to the seasonal high-water table and establish baseline soil
infiltration rates (hydraulic conductivity (Ksat)) for stormwater BMP design calculations. Four
replications were evaluated at the proposed BMP site. Profile descriptions can be supplied upon
request.
The seasonal high water table determinations were made using soil indicators taken from profile
descriptions made at each site. The soil profile descriptions were made from hand auger borings.
The soil was most similar to the "Norfolk and/or Gilead" soil series. The subsoil clay mineralogy
found in the subsoil was considered to be slightly expansive in nature. Numerous soil borings were
made in the device area.
The Ksat data was collected in -situ from a constant head permeameter in the unsaturated zone of
the soil profile. The constant -head well permeameter technique was utilized for the Ksat analysis.
A detailed description of the method can be provided upon request. It is my professional opinion
that Ksat results would give a conservative estimate of instantaneous infiltration rates. Ksat rates
ranged from 0.352 inchesihour to 0.786 inches/hour and averaged 0.538 inches per hour based on
four readings. Based on these results I believe your design infiltration rate of 0.6 inchesihour to be
within a reasonable working range based on the collected field data. The Kast values were
measured at 18-24 inches below the existing soil surface (most restrictive zone).
The seasonal high-water table was determined to vary between 24-28 inches below the existing
soil surface at site elevation of 328', soil wetness indicators were identified at a minimum depth
of 24 inches in the soil profile.

It should be noted that the seasonal high-water table determinations were made based on observed
soil indicators and were not measured or monitored. The actual water table may vary from soil
indicators. This report represents the professional opinion of the evaluating scientist of the seasonal
high-water table depth for design purposes.
Additionally, the site was also evaluated for potential jurisdictional wetlands, streams,
and/or waters of the US. At the time of the evaluation, it was determined that
jurisdictional wetlands or streams were not present on the site. The US Army Corps of
Engineers was not contacted for a determination.
If you have any questions or concerns, please contact me at your earliest convenience.
Sincerely,
Alex Adams
NC Licensed Soil Scientist #1247