A0009_GEO_EIS_Acidic_Rock_Final_Assessment

STATE OF NORTH CAROLINA
DEPARTMENT OF TRANSPORTATION
ROY COOPER ERIC BOYETTE
GOVERNOR SECRETARY

Mailing Address:
NC DEPARTMENT OF TRANSPORTATION
GEOTECHNICAL ENGINEERING UNIT
1589 MAIL SERVICE CENTER
RALEIGH, NC 27699-1589

Telephone: [phone]
Customer Service: 1-877-368-4968

Website: www.ncdot.gov
Location:
1020 BIRCH RIDGE DRIVE
RALEIGH, NC 27610

November 11, 2020

MEMORANDUM TO: Wanda Austin, PE
Division 14 Project Development Engineer

ATTENTION: Amy Sackaroff, AICP
Senior Transportation Planner, Stantec

FROM: Jody Kuhne, LG, PE
Regional Geological Engineer, NCDOT GEU

STATE PROJECT: 32572, A-0009
COUNTY: SWAIN/GRAHAM
DESCRIPTION:

SUBJECT:
US 74 Corridor from US 129 at Robbinsville to 2 miles East of
NC 143/NC 28 intersection at Stecoah

Acidic Rock Testing Results, Improve Existing Alternate

The Geotechnical subsurface investigation for the Improve Existing Alternate has been ongoing
through summer and fall, 2020. In the process, fresh testing samples were taken along the
alignment in the proximity of the Anakeesta/Weyhutty formation. This formation is noted for
having rock mineralization that generates acidic runoff, particularly when excavated and exposed
to air and water.

The NCDOT Geotechnical Engineering Unit has recommended A-0009 alignments that avoid the
acidic rock issue since 1981. This is mostly because the values, volumes and treatment are highly
customized and potentially extremely expensive. Also, the Special Provision and
Recommendations for dealing with the issue are not possible until a specific route is thoroughly
investigated, which is generally difficult to estimate for the EIS process on a long roadway.

To that end, the attached results and locations indicate that the Improve Existing Alternate does
avoid this particular problem. There will be more sampling from rock coring, but these results are
from all exposed rock cut areas that were most likely to have the issue.

Sample Interpretation

The attached table shows the indicator we are looking for in the “CaCO3” column, which has

A-0009, Acidic Rock pg 2

been referenced in other project literature as the Net Neutralization Value, NNP. The more
negative this number, the more acid producing potential exists. Depending on the general
neutralization capacity NCDOT projects typically haven’t had an issue requiring treatment with
bulk averages of -10.

Since this alignment met a general recommendation to avoid acid producing rock formations, the
low level of this measure confirms this as a reasonable choice.

Recommendations

1) No specific treatment or material handling will be required for excavation on this project.

2) No specific water chemistry testing or monitoring is recommended with respect to this
issue, outside of other erosion control and water quality preservation items required for
the project.

3) Durable excavated rock material, if approximating Class I or II rip rap, or Class VII in the
NCDOT Standard Specifications may be used to construct 1.5:1 rock embankments
parallel to streams, if this is desirable to reduce the project footprint.

Please contact Jody Kuhne, NCDOT GEU at 828-779-9482 or [e-mail] with questions
regarding this report.

Page 1 of 2
Date: 11/6/2020 Galbraith Laboratories, Inc. Test Report
Prepared for:
Matthew Brewer
Carolinas Geotechnical Group
2400 Crownpoint Executive Dr
Charlotte, NC 28227
email: [e-mail]
Carolinas Geotechnical Group, PLLC/AA-0001C 2400-20-068
Robbinsville, NC
Paste pH
Neutrali
zation
Potentia
l
Potential
Acidity
CaCO3
(Def)/Sur Fizz
Total
Sulfur*Pyritic Sulfur
******%%
Lab ID Sample ID - - - - - - - - - - - - - - - EPA 600/2-78-054 - - - - - - - - - - - - - - - ASTM D4239ASTM D2492-77
M-1018 Hand Sample 1, Date 10/6, Container-Plastic bag, Spl. Type- Rock 5.52 0.50 1.25 -0.8 None 0.040 0.030
M-1019 Hand Sample 2, Date 10/6, Container-Plastic bag, Spl. Type- Rock 6.18 0.72 0.15 0.57 None 0.005 0.024
M-1020 Hand Sample 3, Date 10/6, Container-Plastic bag, Spl. Type- Rock 6.15 2.47 0.08 2.4 None 0.003 0.018
M-1021 Hand Sample 4, Date 10/6, Container-Plastic bag, Spl. Type- Rock 6.54 2.07 0.25 1.82 None 0.008 0.036
M-1022 Hand Sample 5, Date 10/6, Container-Plastic bag, Spl. Type- Rock 6.07 1.70 0.07 1.6 None 0.002 0.019
M-1023 Hand Sample 6, Date 10/6, Container-Bag, Spl. Type- Rock 5.92 0.18 0.34 -0.16 None 0.011 0.012
M1024 Hand Sample 7, Date 10/6, Container-Bag, Spl. Type- Rock 5.85 0.48 0.00 0.5 None 0.000 0.011
M-1025 Hand Sample 8, Date 10/6, Container-Bag, Spl. Type- Rock 8.42 5.63 0.17 5.46 None 0.006 0.037
M-1026 Hand Sample 9, Date 10/6, Container-Bag, Spl. Type- Rock 6.39 0.78 0.16 0.6 None 0.005 0.018
M-1027 Hand Sample 10, Date 10/6, Container-Bag, Spl. Type- Rock 6.99 2.32 0.31 2.01 None 0.010 0.021
M-1028 Hand Sample 11, Date 10/6, Container-Bag, Spl. Type- Rock 5.87 1.73 0.69 1.0 None 0.022 0.011
M-1029 Hand Sample 12, Date 10/6, Container-Bag, Spl. Type- Rock 9.44 4.70 0.00 4.70 None 0.000 0.067
M-1030 Hand Sample 13, Date 10/6, Container-Bag, Spl. Type- Rock 6.93 0.83 0.05 0.8 None 0.002 0.070
M-1031 Hand Sample 14, Date 10/6, Container-Bag, Spl. Type- Rock 6.48 0.74 0.19 0.55 None 0.006 0.021
M-1032 Hand Sample 15, Date 10/6, Container-Bag, Spl. Type- Rock 9.44 4.72 0.00 4.7 None 0.000 0.081
M-1033 Hand Sample 16, Date 10/6, Container-Bag, Spl. Type- Rock 9.33 4.25 0.10 4.15 None 0.003 0.057
M-1034 Hand Sample 17, Date 10/6, Container-Bag, Spl. Type- Rock 8.63 4.14 0.21 3.93 None 0.007 0.056
Page 2 of 2
M-1035 Hand Sample 18, Date 10/6, Container-Bag, Spl. Type- Rock 9.49 5.95 0.15 5.80 None 0.005 0.169
M-1036 Hand Sample 19, Date 10/6, Container-Bag, Spl. Type- Rock 9.71 37.62 0.17 37.45 Slight 0.005 0.065
M-1037 Hand Sample 20, Date 10/6, Container-Bag, Spl. Type- Rock 9.54 3.67 0.01 3.66 None 0.000 0.733
** Tons of CaCO3 per 1000 tons of material * The quantitation limit for sulfur was 0.010%
PROJECT REFERENCE NO.SHEET NO.
FEET
0
A-0009C
200 400
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