R-2822 B (2)

STATE OF NORTH CAROLINA
DEPARTMENT OF TRANSPORTATION
PAT MCCRORY ANTHONY J. TATA
GOVERNOR SECRETARY

MAILING ADDRESS:
NC DEPARTMENT OF TRANSPORTATION
GEOTECHNICAL ENGINEERING UNIT
1589 MAIL SERVICE CENTER
RALEIGH NC 27699-1589
TELEPHONE: [phone]
FAX: [phone]

www.ncdot.gov/doh/preconstruct/highway/geotech
LOCATION:
CENTURY CENTER COMPLEX
ENTRANCE B-2
1020 BIRCH RIDGE DRIVE
RALEIGH NC

July 8, 2013

MEMORANDUM TO: Greg Thorpe, PhD
Manager, PDEA

ATTENTION: Wilson Stroud
Project Development Engineer

FROM: John Pilipchuk, P.G., P.E.
State Geotechnical Engineer

TIP: R-2822B
COUNTY: Graham
DESCRIPTION: NC 143 from Buffalo Creek to SR 1127

SUBJECT: Hot Rock testing on New Alignment Alternative

There has been concern expressed that no testing of potentially acidic rock will be conducted on
the New Alignment alternate for this project. This is understandable due to the presence of acid
producing rock in the region, most notably on the further-west sections of the Cherohala Skyway
and US 129 north of this project.

I have attached the previous report on this topic and the actual results of testing along the existing
Alternates 1 and 4. I’ll be brief about the direct rationalization not to test at this time for the New
Alignment alternate:

1) The Geotechnical Investigation performed in the 1970’s along the New Alignment did
not address the topic. However, it did reveal that this proposal would not have a large
amount of fresh rock excavation. The one cut to the north of the proposed bridge would
have the most quantity. There are also no direct rock outcrops at the surface.
2) The proximity of the tested Alternates 1 and 4, and their relationship to the underlying
geology allow us to correlate related bedding planes (similar geology). Alternates 1 and 4
were tested along the length and produced results that are not hot.
3) This does not mean that there is no hot rock on the New Alignment proposal, it just gives
insight as to the likelihood and potential strength, both of which are low.
4) For corridor selection purposes hot rock does not present itself as a vital factor that might
favor the selection of one alternate over another.
R-2822B Page 2 of 2

5) The New Alignment proposal is currently lightly developed with difficult overland
access. It has been investigated previously and most of the information exists to
commence with Geotechnical Recommendations. If it is chosen as the preferred route
then we would necessarily perform more investigation with respect to the actual planned
details such as specific cuts, bridge foundations, etc. It is at this time that we would
perform additional testing for hot rock.

In conclusion, the mitigation for hot rock is very specific on a site by site basis and is
usually not generated until an Alternate is chosen. The previous testing lets us draw some
reasonable conclusions about hot rock through this section and do not think it is a factor
in the alternate selection process. Based on our knowledge of the geology we also do not
anticipate it on the New Alignment.

If there are any questions regarding the geotechnical issues, please contact Jody Kuhne, LG, PE.,
Regional Geological Engineer. 828-298-3874.

Attachments:

GEU Scoping report, Hot rock, 8/26/2010
Scan of previous Hot Rock test results and locations

STATE OF NORTH CAROLINA
DEPARTMENT OF TRANSPORTATION
BEVERLY EAVES PERDUE EUGENE A. CONTI, JR.
GOVERNOR SECRETARY

MAILING ADDRESS:
NCDOT WESTERN REGIONAL
GEOTECHNICAL OFFICE
COURIER: 05-13-09

TELEPHONE: [phone]
FAX: [phone]

WEBSITE: WWW.DOH.DOT.STATE.NC.US
LOCATION:
WESTERN REGIONAL
GEOTECHNICAL OFFICE
5253 Z MAX BOULEVARD
HARRISBURG, NC 28075

August 26, 2010

TO: Wilson Stroud, Project Development Engineer, PDEA

FROM: Jody Kuhne, PG, PE, Project Engineering Geologist, GEU

PROJECT: R-2822B, NC 143 from Buffalo Creek to SR 1127

RE: Geologic Scoping and Hot Rock

BACKGROUND

I have reviewed information from the Geotechnical Engineering Unit concerning this
project. There have been three points in time for which we have data:

1) 1973 – A full subsurface investigation was performed. There is no alignment
given, I can surmise that this was for a new alignment.
2) 1995 – GEU has general page of scoping comments, indicates need for further
study on hot rock. No other apparent highlights or concerns were noted pending
alignment selection.
3) 2001 - Documentation at this time seemed to favor an Improve Existing trend.
Materials and Tests had an operating Acidic rock lab in place in Asheville and 23
samples were tested from the existing corridor. These would have been taken
from rock cuts along the highway and the number suggests that all areas of
concern were tested.

The 2001 Hot Rock results and sample locations are included with this memo.

HOT ROCK

Acidic runoff is produced when sulfate-bearing rock is exposed to air and water. This
usually occurs naturally at a very slow rate, although quite rapidly as far as mineral
weathering is concerned. This means that weathered rock, unless it was extremely acidic
when fresh, has already lost this component. So typically this is a concern for
construction when we intend to excavate fresh rock quickly from cuts and foundations.
The results are typically presented as Net Neutralization Potential (NNP). NNP is a
negative number for acidic rock (harmful) and positive (unharmful) for basic rock.

CONCLUSIONS

A review of GEU data shows that our typical sampling coverage was performed along the
existing alignment through the Subject interval in 2001. These results show universally
positive results indicating that acid producing rock is not present. The geologic units
involved do have areas of hot rock but the results for this project also correspond to
positive results from testing nearby at a bridge replacement project near the entrance to
Joyce Kilmer Forest several years ago.

The GEU does not think that special treatment is needed for rock excavation, as far as its
chemical environmental impact is concerned. Especially for an Improve Existing option.

Please contact Jody Kuhne of the GEU for further questions.

Attachments:

Map of sample locations
NNP sample results

5-13-13