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FATE & TRANSPORT
GROUNDWAER MODELING
REPORT
STANLEY CREEK COUNTRY STORE
INCIDENT NO. 15573
STANLEY, GASTON COUNTY
NORTH CAROLINA
Prepared For:
Southeastern Geological Services
Post Office Box 441
Shelby, North Carolina 28151
BLE Project Number J23-19484-01
February 16, 2023
Fate & Transport Groundwater Modeling February 16, 2023
Stanley, Gaston County, North Carolina BLE Project No. J22-19484-01
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TABLE OF CONTENTS
1.0 INTRODUCTION.......................................................................................................................... 1
1.1 Project Background .......................................................................................................................... 1
1.2 Current Groundwater Quality .......................................................................................................... 1
2.0 FATE & TRANSPORT MODELING ......................................................................................... 2
2.1 BIOSCREEN Inputs ........................................................................................................................ 2
2.1.1 Hydrogeology .................................................................................................................................. 2
2.1.2 Dispersion ........................................................................................................................................ 2
2.1.3 Adsorption ....................................................................................................................................... 2
2.1.4 Biodegradation ................................................................................................................................. 2
2.1.5 General ............................................................................................................................................. 3
2.1.6 Source Zone Data ............................................................................................................................. 3
2.2 Predictive Modeling ......................................................................................................................... 3
2.2.1 Intersection with Stanley Creek ....................................................................................................... 3
2.2.2 Predicted Concentrations in Stanley Creek ...................................................................................... 3
3.0 CONCLUSIONS ............................................................................................................................ 5
Appendices
Appendix A SGS 2022 Semi-Annual Groundwater Monitoring Report
Appendix B Tables
Appendix C BIOSCREEN Inputs
Appendix D First Order Decay Coefficients Analysis
Appendix E BIOSCREEN Output
Appendix F StreamStats Report
Phase I ESA - 455 Mills Gap Road February 9, 2023
Arden, Buncombe County, North Carolina BLE Project No. J22-18805-01
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1.0 INTRODUCTION
Bunnell-Lammons Engineering (BLE) performed the fate & transport groundwater modeling effort in
general accordance with BLE Proposal No. P23-0178 dated January 27, 2023. BLE’s proposal was
accepted by Mr. Richard Kelly, P.G., with Southeastern Geological Services (SGS).
1.1 Project Background
The former Stanley Creek Country Store is located at 236 Mauney Road in Stanley, Gaston County, North
Carolina (herein referred to as the “Site”). BLE reviewed documents obtained via the North Carolina
Department of Environmental Quality (NCDEQ) Division of Waste Management (DMW) Laserfiche
Weblink. The store operated as a convenience store with gasoline and kerosene sales from 1972 from 1993.
In 1996, the underground storage tank (UST) system, comprised of one 1,000-gallon kerosene UST, one
4,000-gallon gasoline UST, and one 6,000-gallon gasoline UST was permanently closed by removal.
During the closure activities, a release of petroleum materials that impacted soil and groundwater was
detected.
Beginning in 1996, soil and groundwater remedial activities were performed at the Site. Those remedial
activities included soil removal, several aggressive fluid vapor recovery (AFVR) events, air sparge/soil
vapor extraction, and free product removal using Xitech pumps. It is our understanding that active
remediation activities have not occurred at the Site since 2016.
The incident is considered High Risk due to exceedances of the North Carolina Groundwater Quality
Standards (2L Standards) and the presence of several active water supply wells within 1,000 feet of the
release area.
It is our understanding that Mr. Brad Newton, the Site’s incident manager with the NCDEQ UST Section,
requested that groundwater modeling be performed to evaluate the potential impacts that the residual
groundwater contamination could have on Stanley Creek.
1.2 Current Groundwater Quality
Mr. Kelly provided BLE with a Semi-Annual Groundwater Monitoring Report prepared by SGS and dated
September 30, 2022. The report without the laboratory report is included in Appendix A.
The report indicates that the groundwater in the source area, in the vicinity of monitoring wells MW-1 and
VMW-1 and product test well PTW-1, has been remediated. However, residual groundwater contamination
in exceedance of 2L Standards remains downgradient of the source area and appears to be migrating toward
Stanley Creek, which is located approximately 160 feet southeast of the source area. The groundwater
contaminants of concern include benzene, toluene, ethylbenzene, xylene, methyl tert-butyl ether (MTBE),
and naphthalene. The zone of groundwater impacts is primarily located around monitoring well MW-2 and
product testing well (PTW-2), also known as P-2.
Phase I ESA - 455 Mills Gap Road February 9, 2023
Arden, Buncombe County, North Carolina BLE Project No. J22-18805-01
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2.0 FATE & TRANSPORT MODELING
BIOSCREEN is a software package developed by the United States Environmental Protection Agency
(USEPA) to simulate the natural attenuation of petroleum constituents in groundwater. For purposes of the
BIOSCREEN model, BLE assumed the groundwater contaminant plume to be represented by the migration
of benzene, toluene, and naphthalene, because those three contaminants of concern that have the most
stringent North Carolina 2B Surface Water Standards (2B Standards) and/or North Carolina In-Stream
Target Values for Surface Waters (In-Stream Target).
2.1 BIOSCREEN Inputs
The following sections provide a summary of the inputs selected for the modeling exercise. The inputs are
summarized in Table 1 and the subsequent sections correspond to the BIOSCREEN Input module (see
Appendix B).
2.1.1 Hydrogeology
BLE sourced slug test and hydraulic gradient information from the Comprehensive Site Assessment
Addendum Corrective Action Plan prepared by SGS and dated May 28, 1998. The linear groundwater
velocity was reported in monitoring well MW-7 and product testing well PTW-2, as 3.25 feet per year
(ft/year) and 0.35 ft/year, respectively. For purposes of this modeling exercise, BLE used the average of
the groundwater velocity at MW-7 and PTW-2 and this data presents the general groundwater velocities in
the area being evaluated. As such, the modeling simulation utilized a groundwater velocity of 1.8 ft/year.
2.1.2 Dispersion
Dispersion is essentially the migration of contaminants in groundwater caused by the spreading of mass
from highly concentrated areas to less concentrated areas. Dispersion is quantified by multiplying the
groundwater velocity by dispersivity coefficient. Dispersivity can be estimated using the length of the
historical dimensions of the groundwater contaminant plume, estimated to be around 170 feet.
2.1.3 Adsorption
The migration of contaminants in groundwater can be slowed via the presence of organics (i.e., carbon) in
the soil. A retardation factor of one represents no retardation and the migration rate of dissolved
contaminants is equal to that of the groundwater velocity. For modeling purposes, BLE used a retardation
factor of one for each compound as it represents the most conservative approach. This approach is
conservative as it is very common for retardation of contaminant migration to occur.
2.1.4 Biodegradation
The natural attenuation or biodegradation of petroleum compounds is commonly simulated using first order
decay coefficients. For purposes of the modeling effort, BLE assumes that 1st order decay of the benzene,
toluene, naphthalene contaminant plumes would occur. BLE estimated the first order decay coefficients
and subsequent half-life for benzene, toluene, and naphthalene by plotting the concentrations over time as
measured in either monitoring well MW-2 or product test well PTW-2 – with the selection determined by
which well exhibits the highest, current contaminant concentrations between the two wells for benzene,
toluene, and naphthalene. An exponential trend line matched to the plotted data sets and first order
equations for each trend line was obtained. The first order decay coefficients were sourced from each trend
line equation and the subsequent half-life was calculated by dividing 0.693 by the first order decay
coefficient. The analysis is included in Appendix B.
Phase I ESA - 455 Mills Gap Road February 9, 2023
Arden, Buncombe County, North Carolina BLE Project No. J22-18805-01
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2.1.5 General
The General section in the BIOSCREEN Input model establishes the modeled area by length and width.
For purposes of BLE’s model, the length varied by the distance from the well exhibiting the highest
concentration of the contaminant of interest and the subsequent distance from the well to Stanley Creek.
The contaminant plume width was kept consistent between models at 25 feet.
2.1.6 Source Zone Data
The saturated thickness of the contaminant plume was estimated to be 15 feet, based on a review of data
included in the Comprehensive Site Assessment Addendum Corrective Action Plan. The depth to bedrock
is around 27 feet below grade (BG) and the depth to water is roughly 12 feet BG, which would suggest a
saturated thickness in the unconfined aquifer of approximately 15 feet.
The source zone groundwater data was obtained from the current benzene, toluene, and naphthalene plume
data outlined in the 2022 the Semi-Annual Groundwater Monitoring Report.
The source 1st order half-life was set to <1 year as the portion of the groundwater plume being modeled is
approximately 40 feet from the source area. Therefore, BLE assumes that the effect of petroleum-impacted
soil impacting the groundwater contaminant plume in the model area is negligible.
2.2 Predictive Modeling
2.2.1 Intersection with Stanley Creek
The BIOSCREEN simulations were run in one-year time steps until the maximum contamination
concentration was measured at the predicted plumes intersection with Stanley Creek. The results are
summarized in Table 2. In summary, the predictive modeling indicates that benzene in the unconfined
aquifer will intersect Stanley Creek in 11 years (2033) at a concentration of 32 g/L. The model predicts
that toluene and naphthalene in the unconfined aquifer will intersect Stanley Creek in 25 years (2047) at
concentrations of 18.4 g/L and 16.8g/L, respectively.
2.2.2 Predicted Concentrations in Stanley Creek
The 7Q10 was estimated for Stanley Creek using an empirical equation sourced from Low-Flow
Characteristics of Streams in North Carolina – United States Geological Survey Water-Supply Paper 2403
dated 1993 and prepared by G.L. Giese and Robert R. Mason, Jr. The 7Q10 is defined as the annual
minimum 7-day consecutive low flow that on average will be exceeded in 9 out of 10 years.
The Site located in the Charlotte Milton Belt, thus, the 7Q10 is quantified as 0.196 x DA0.53, where DA
equals the drainage area in square miles. The DA was estimated to be 2.64 square miles using the United
States Geological Service (USGS) StreamStats website (see Appendix E). Therefore, the 7Q10 was
estimated to be 0.33 cubic feet (ft3) per second or 10.4 million ft3 per year.
BLE estimated the flux of contaminated groundwater intersecting Stanley Creek by multiplying the
groundwater seepage velocity (1.8 ft/year) by the area or window of groundwater flow estimated to be 15
feet (saturated thickness) multiplied by 25 feet, the estimated width of the contaminated plume at the
intersection of Stanley Creek. Therefore, the flux of contaminated groundwater intersecting Stanley Creek
is estimated to be 675 ft3per year.
Phase I ESA - 455 Mills Gap Road February 9, 2023
Arden, Buncombe County, North Carolina BLE Project No. J22-18805-01
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Using a standard mass balance equation, the predicted concentrations of benzene, toluene, and naphthalene
in Stanley Creek were estimated to be 0.001 g/L – less than the applicable 2B Standards and/or In-Stream
Target for benzene, toluene, and naphthalene.
Phase I ESA - 455 Mills Gap Road February 9, 2023
Arden, Buncombe County, North Carolina BLE Project No. J22-18805-01
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3.0 CONCLUSIONS
BLE performed groundwater modeling using BIOSCREEN software to estimate the potential impacts on
Stanley Creek caused by the migration and associated attenuation of the benzene, toluene, and naphthalene
groundwater contaminant plumes. The BIOSCREEN results suggest that benzene, toluene, and
naphthalene will be significantly less than their 2B Standards and/or In-Stream Target Values in Stanley
Creek. Therefore, BLE opines that there is a low potential for the residual petroleum groundwater
contaminant plume associated with the Stanley Creek Country Store to adversely impact the nearest surface
water receptor, Stanley Creek.
Appendix A
SGS 2022 Semi-Annual Groundwater
Monitoring Report
SOUTHEASTERN GEOLOGICAL SERVICES
PO Box 441
Shelby, NC 28151
704 481 8558
STANLEY CREEK COUNTRY STORE
TRANSMITTAL LETTER
The following report is issued in pdf format:
-) MO-4603_15573_CA_MRP_20220930.PDF
-) Stanley Creek Country Store
-) Incident # 15573
-) Semi-Annual Monitoring Report
-) 9-30-22
-) Facility ID: 0-015658
Richard Kelly
Chief Geologist
1
B. EXECUTIVE SUMMARY
The AS/SVE system was reactivated October 12, 2007 to remediate the contaminated
groundwater onsite. It was deactivated in May 2016. The following wells were sampled August
30, 2022 for this report: WSW-2, WSW-7, MW-2, MW-7, and P-2. The water supply wells and
MW-7 remain non-detect. Contaminant levels increased in both MW-2 and P-2.
C. TABLE of CONTENTS
Section D Site History & Characterization 1
Section E Site Assessment Information 1
Section F Free Product 3
Section G Soil Remediation 3
Section H Groundwater Remediation 3
Section I Conclusions 3
Section J Figures 3
Section K Tables 3
Section L Appendices 3
D. SITE HISTORY and CHARACTERIZATION
Stanley Creek Country Store is a former convenience store that sold petroleum products from an
underground storage tank system. A release occurred from the system and the groundwater was
impacted. The AS/SVE system was activated October 23, 2002 to remediate the contaminated
groundwater. It was temporarily shut down in October 2004 and activated October 12, 2007. It
was shut down in April 2016 as required by the DENR after reviewing the April 2016 semi-
annual monitoring report.
E. SITE ASSESSMENT INFORMATION
1.0 WATER SUPPLY WELL SAMPLING
1.1 Sampling Protocol
Water supply wells 2 &7 were sampled August 30, 2022. Both wells were sampled from an
outside tap after running the water at full strength for ten minutes. The taps were slowed before
taking the samples to prevent aeration. The samples were placed in laboratory provided 40 ml
vials, fixed with a chain of custody, and placed on ice for shipment between the field and
laboratory. They were delivered to PACE Analytical the same day.
2
1.2 Sampling Results
The samples were analyzed by methods 6200B and 504.1; no compounds were detected. The
analyses are attached.
2.0 MONITOR WELL SAMPLING
2.1 Sampling Protocol
Monitor wells 2 &7, and P-2 were sampled with new, disposable bailers after first gauging the
wells and then purging three well casing volumes. The samples were taken August 30, 2022 and
handled as described above.
2.2 Sampling Results
The samples were analyzed by EPA method 6200B and 504.1. Petroleum compounds were
detected in MW-2 and P-2. Some compounds were detected above their standard, but all were
below their gross contaminant level. The results show that the plume is restricted to the former
free product area (MW-2 and P-2). It is also evident that the contaminant levels of the former
free product area have been greatly reduced, as all compounds are below their gross
contaminated level. A summary follows.
MW-2: benzene, xylenes, MTBE, naphthalene, 1,2,4-Trimethylbenzene, and EDB > standard,
but < GCL,
MW-7: non-detect, and
P2: benzene, xylenes, naphthalene, n-Propylbenzene, and 1,2,4-Trimethylbenzene > standard,
but < GCL.
A comparison with the last sampling event follows:
All compounds increased in both MW-1 and P-2, after substantial decreases from the 8-21 to 3-
22 sampling events..
MW-2: BTEX/MTBE/Naphthalene increase,
MW-7: remain non-detect, and
P-2: BTEX/MTBE/Naphthalene increase,
The analytical results are presented in Table B-4, Table 1 is a historical summary of the sampling
results, and the laboratory analysis is attached. Individual BTEX maps are attached; a total
BTEX map showing all monitor and remediation wells is also attached. Time/concentration
graphs for MW-2 and P-2 are attached.
3.0 CREEK INVESTIGATION
The creek was checked and there was no sheen on the creek or emitting from the bank. The area
that was investigated is marked on the attached maps.
3
F. FREE PRODUCT – not applicable
G. SOIL REMEDIATION – not applicable
H. GROUNDWATER REMEDIATION - natural attenuation
I. CONCLUSIONS
Contaminant levels increased in MW-2 but they are consistent with the last several sampling
events. Contaminant levels increased in P-2, continuing the pattern of spring lows and fall highs.
Site cleanup has progressed well with the free product removed, concentrations in the former
free product area reduced to below gross contaminant levels, and all outlying monitor wells
below standard. The sampling shows that the plume remains restricted to MW-2 and P-2.
J. FIGURES
USGS Topographic Map
Water Supply Well Map
Site Map
Groundwater Flow Map: 8-30-22
Benzene Isoconcentration map
Toluene Isoconcentration map
Ethylbenzene Isoconcentration map
Xylenes Isoconcentration map
Total BTEX Isoconcentration map
MTBE Isoconcentration map
Naphthalene Isoconcentration map
K. TABLES
Table B-4 Summary of Groundwater Sampling Results
Table 1 Historical Groundwater Sampling
Table 2 Static Groundwater Levels
Table B-9 Static Groundwater Levels: Current and Historical
L. APPENDICES
Time vs Concentration Graphs: MW-2 & P-2 (both arithmetic and logarithmic scales)
Laboratory Analysis and Chain of Custody
Table B-4: Summary of Groundwater and Surface Water Sampling Results
Revision Date: 9-29-18 Incident Number and Name: 15573 Stanley Creek Country Store Facility ID#:
Analytical Method (e.g., VOC by SM6000B) or
Field Measurement (FM)6200B 6200B 6200B` 6200B 6200B 6200B 6200B 6200B 6200B 504.1
Contaminant of Concern/ Field MeasurementBenzeneTolueneEthylbenzeneXylenesMTBEIPENaphthalene1,2DCEEDBEDBWell or
SW ID
Date
Collected
Sample
ID
Incident
Phase
MW-2 8-30-22 MW-2 Monitor 136 489 318 2454 148 5 174 <2.5 <2.5 0.13
MW-7 “ MW-7 “ <1 <1 <1 <2 <1 <1 <2 <1 <1 <.020
P-2 “ P-2 “143 45 376 1125 12 <2.5 156 <2.5 <2.5 <.020
WSW-2 “ WSW-2 “ <1 <1 <1 <2 <1 <1 <2 <1 <1 <.020
WSW-7 “ WSW-7 “ <1 <1 <1 <2 <1 <1 <2 <1 <1 <.020
Minimum Reporting Limit (ug/l)
2L Standard (ug/l)1 600 600 500 20 70 6 0.4 0.02 0.02
GCL (ug/l)5000 260000 84500 85500 20000 70000 6000 400 50 50
NC 2B Standard or EPA National Criteria
(ug/l)
Results reported in ug/l ug/l =micrograms per liter GCL = gross contamination level
6200B rounded to whole numbers
Table B-4: Summary of Groundwater and Surface Water Sampling Results
Revision Date: 9-29-18 Incident Number and Name: 15573 Stanley Creek Country Store Facility ID#:
Analytical Method (e.g., VOC by SM6000B) or
Field Measurement (FM)6200B 6200B 6200B 6200B` 6200B` 6200B 6200B 6200B 3030C
Contaminant of Concern/ Field Measurementn-ButlybenzeneSec-ButylbenzeneTert-ButylbenzeneIsopropylbenzenen-PropylbenzeneStyrene1,2,4Trimethylbenzene1,3,5TrimethylbenzeneLeadWell or
SW ID
Date
Collected
Sample
ID
Incident
Phase
MW-2 8-30-22 MW-2 Monitor <2.5 <2.5 <2.5 15 41 9 531 180
MW-7 “ MW-7 “ <1 <1 <1 <1 <1 <1 <1 <1
P-2 “ P-2 “ <2.5 <2.5 <2.5 26 78 <2.5 680 193
WSW-2 “ WSW-2 “ <1 <1 <1 <1 <1 <1 <1 <1
WSW-7 “ WSW-7 “ <1 <1 <1 <1 <1 <1 <1 <1
Minimum Reporting Limit (ug/l)
2L Standard (ug/l)70 70 70 70 70 70 400 400 15
GCL (ug/l)6900 8500 15000 25000 30000 70000 28500 25000 15000
NC 2B Standard or EPA National Criteria
(ug/l)
Results reported in ug/l ug/l =micrograms per liter GCL = gross contamination level
6200B rounded to whole numbers
Benzene Toluene Ethylb.Xylenes BTEX MTBE IPE Naphthalene
Standard 1 29 600 500 20 70 21
GCL 5000 29000 29000 87500 20000 70000 15500
MW-2 1998-12 Free Product
2001-3 Free Product
2002-11 Free Product
2003-3 Free Product
2003-6 Free Product
2003-8 Free Product
2004-3 Free Product
2004-9 6500 34000 2100 15300 57900 1600 830
2007-7 325 310 149 537 1321 122 133
2008-3 3715 3878 1795 6290 15678 45 122
2008-9 4120 8500 2030 22570 37220 1070 <200 1280
2009-3 1470 5610 1030 5960 14070 360 <200 730
2009-9 1120 1890 575 2910 6495 397 19 660
2010-4 566 2480 548 3040 6634 218 9 329
2010-9 1110 4300 1040 6890 13340 328 <25 465
2011-3 1170 4360 950 5980 12460 411 <25 334
2011-10 782 3810 1670 9100 15362 358 <13 939
2012-3 833 3450 976 5160 10419 449 <13 675
2012-9 550 3140 719 4110 8519 301 <10 335
2013-3 50 88 66 1026 1230 15 <2 100
2013-10 284 2470 461 2370 5585 202 5 211
2014-3 211 1880 379 2770 5240 182 <10 199
2014-9 299 2680 616 3720 7315 237 <6 238
2015-3 379 2810 717 4270 8176 292 <10 307
2015-9 183 664 309 1486 2642 149 4 173
2016-3 270 2030 460 3050 5810 214 <10 244
Benzene Toluene Ethylb.Xylenes BTEX MTBE IPE Naphthalene
Standard 1 29 600 500 20 70 21
GCL 5000 29000 29000 87500 20000 70000 15500
MW-2 2016-9 151 554 326 1592 2623 158 5 274
2017-3 284 2170 540 4410 7404 632 <10 375
2017-9 230 1590 484 3290 5594 218 6 325
2018-2 247 1480 468 4160 6355 240 7 349
2018-9 71 76 19 989 1155 3 <1 65
2019-2 405 2810 1000 7000 11215 339 <13 456
2019-9 9 1520 1270 3670 6469 <2 <2 201
2020-3 229 1020 561 3220 5030 212 7 254
2020-8 195 605 542 2473 3815 141 6 285
2021-3 105 542 311 1978 2936 124 3 131
2021-9 110 250 310 1310 1980 86 3 130
2022-3 47 130 174 790 1141 40 1 108
2022-8 136 489 318 2454 3397 148 5 174
Benzene Toluene Ethtlb.Xylenes BETX MTBE IPE Naphthalene
Standard 1 29 600 500 20 70 21
GCL 5000 29000 29000 87500 20000 70000 15500
MW-7 1996-8 90 <1 <1 4 94 240 16
1998-12 2 <1 <1 <2 2 52 2
2001-3 Free Product
2002-11 Free Product
2003-3 Free Product
2003-6 Free Product
2003-8 Free Product
2004-3 Free Product
2004-9 <100 110 <100 2180 >2290 <100 <100
2007-7 <5 949 454 2418 3821 25 29
2008-3 <1 <1 3 15 18 <1 <1
2008-9 <5 12 <5 179 191 <5 <5 24
2009-3 <1 <1 <1 <2 <1 <1 <1 <2
2009-9 41 146 68 269 524 6 2 29
2010-4 1 1 4 14 20 <1 <1 <2
2010-9 3 23 18 87 131 1 <1 11
2011-3 <1 <1 <1 <2 <2 <1 <1 <2
2011-10 1 1 <1 10 12 1 <1 6
2012-3 <1 <1 <1 <2 <2 <1 <1 <2
2012-9 <1 <1 <1 <2 <2 <1 <1 <2
2013-3 <1 <1 <1 <2 <2 <1 <1 <2
2013-10 <1 <1 <1 <2 <2 <1 <1 <2
2014-3 <1 1 <1 <2 <2 <1 <1 <2
2014-9 <1 <1 <1 <2 <2 <1 <1 <2
2015-3 <1 <1 <1 <2 <2 <1 <1 <2
2015-9 <1 <1 <1 <2 <2 <1 <1 <2
2016-3 <1 <1 <1 <2 <2 <1 <1 <2
Benzene Toluene Ethtlb.Xylenes BETX MTBE IPE Naphthalene
Standard 1 29 600 500 20 70 21
GCL 5000 29000 29000 87500 20000 70000 15500
MW-7 2016-9 <1 <1 <1 <2 <2 <1 <1 <2
2017-3 <1 <1 <1 <2 <2 <1 <1 <2
2017-9 <1 <1 <1 <2 <2 <1 <1 <2
2018-2 <1 <1 <1 <2 <2 <1 <1 <2
2018-9 <1 <1 <1 <2 <2 <1 <1 <2
2019-2 <1 <1 <1 <2 <2 <1 <1 <2
2019-9 <1 <1 <1 <2 <2 <1 <1 <2
2020-3 <1 <1 <1 <2 <2 <1 <1 <2
2020-8 <1 <1 <1 <2 <2 <1 <1 <2
2021-3 <1 <1 <1 <2 <2 <1 <1 <2
2021-9 <1 <1 <1 <2 <2 <1 <1 <2
2022-3 <1 <1 <1 <2 <2 <1 <1 <2
2022-8 <1 <1 <1 <2 <2 <1 <1 <2
Benzene Toluene Ethtlb.Xylenes BETX MTBE IPE Naphthalene
Standard 1 29 600 500 20 70 21
GCL 5000 29000 29000 87500 20000 70000 15500
P2 1998-12 Free Product
2001-3 Free Product
2002-11 Free Product
2003-3 Free Product
2003-6 Free Product
2003-8 Free Product
2004-3 Free Product
2004-9 4700 11000 2400 11900 30000 1500 290
2007-7 417 309 185 612 1523 260 164
2008-3 512 2448 854 6214 10028 <20 81
2008-9 2740 4200 1540 23150 31630 <200 <200 1380
2009-3 <200 1190 904 5710 7804 <200 <200 <200
2009-9 236 1070 502 2545 4353 <5 <5 216
2010-4 192 4410 3100 16080 23782 <50 <50 974
2010-9 230 2100 3110 19800 25240 <25 <25 2120
2011-3 97 2070 1430 8970 12567 <50 <50 586
2011-10 87 2220 2630 14470 19407 <10 <10 1410
2012-3 75 946 1860 8900 11781 <13 <13 1330
2012-9 92 536 712 3226 4556 <3 <3 306
2013-3 244 1870 315 2491 4920 154 <5 163
2013-10 40 203 221 1129 1593 <1 <1 <2
2014-3 19 108 117 825 1069 <1 <1 71
2014-9 90 337 423 2070 2920 <1 <1 157
2015-3 14 64 108 445 631 <3 <3 54
2015-9 135 247 387 1855 2624 4 <1 150
2016-3 46 139 206 1183 1574 2 <3 103
Benzene Toluene Ethtlb.Xylenes BETX MTBE IPE Naphthalene
Standard 1 29 600 500 20 70 21
GCL 5000 29000 29000 87500 20000 70000 15500
P-2 2016-9 113 235 797 4700 5845 <6 <6 749
2017-3 38 115 423 3131 3707 265 <6 899
2017-9 95 108 157 1346 1706 11 <5 259
2018-2 8 33 142 820 1003 <1 <1 128
2018-9 96 102 24 1383 1605 5 <3 96
2019-2 54 44 180 722 1000 <3 <3 100
2019-9 173 4 111 9 297 12 <2 625
2020-3 34 24 118 374 550 <1 <1 58
2020-8 108 71 248 725 1152 4 <1 79
2021-3 15 21 131 546 713 <1 <1 113
2021-9 160 52 260 818 1290 14 1 61
2022-3 4 4 32 144 184 <1 <1 25
2022-8 143 45 376 1125 2666 12 <2.5 156
TABLE 2
Static Groundwater Levels 3/15/2022
wellhead level static
MW-1 100 9.44 90.56
MW-2 100.24 10.05 90.19
MW-3 97.91 8.39 89.52
MW-4 97.54 8.06 89.48
MW-5 101.24 10.05 91.19
MW-6 95.68 6.91 88.77
MW-7 98.09 8.55 89.54
P-2 99.27 9.29 89.98
VMW-1 99.9
Table B-9: Current and Historical Groundwater Elevations and Free Product Thickness
Revision Date: 2-6-19 Incident Number and Name: 15573 Stanley Creek Country Store Facility ID#:
Well ID
#Date
Screened Interval
(top of screen,
bottom of screen)
Depth to Water*
Uncorrected
(feet)
Free
Product
Thickness
(feet)
Depth to Water*
Corrected
for Free Product
Thickness(feet)
Top of
Casing
Elevation
(MSL)
Groundwater
Surface
Elevation
(MSL)
MW-2 8-30-22 ? - ?0 10.05 100.24 90.19
3-15-22 0 9.83 90.41
9-15-21 0 10.25 89.99
3-23-21 0 9.48 90.76
8-11-20 0 9.75 90.49
3-17-20 0 9.97 90.27
9-16-19 0 10.46 89.78
2-6-19 0 9.35 90.89
9-14-18 -0 10.01 90.23
9-22-17 -0 9.68 90.56
3-17 -0 9.75 90.49
9-14-16 -0 10.22 90.02
9-14-15 -0 9.73 90.51
MW-2 9-15-14 ? - ?0 8.43 100.24 91.81
“ 10-8-13 0 8.65 91.59
“ 3-24-14 0 7.93 92.31
*Depth to Water is measured from Top of Casing
Table B-9: Current and Historical Groundwater Elevations and Free Product Thickness
Revision Date: 2-6-19 Incident Number and Name: 15573 Stanley Creek Country Store Facility ID#:
Well ID
#Date
Screened Interval
(top of screen,
bottom of screen)
Depth to Water*
Uncorrected
(feet)
Free
Product
Thickness
(feet)
Depth to Water*
Corrected
for Free Product
Thickness(feet)
Top of
Casing
Elevation
(MSL)
Groundwater
Surface
Elevation
(MSL)
MW-7 8-30-22 ? - ?0 8.55 98.09 89.54
3-15-22 0 8.24 89.85
9-15-21 0 8.68 89.41
3.23-21 0 8.03 90.06
8-11-20 0 8.28 89.81
3-17-20 0 8.49 89.60
9-16-19 0 8.85 89.24
2-16-19 0 8.47 89.62
9-14-18 -0 8.08 90.01
9-22-17 -0 8.13 89.96
3-17 -0 8.30 89.79
9-14-16 -0 8.67 89.42
MW-7 9-14-15 ? - ?0 8.20 98.09 89.89
9-15-14 -0 6.87 91.22
10-8-13 0 7.20 90.89
3-24-14 0 6.47 91.62
Table B-9: Current and Historical Groundwater Elevations and Free Product Thickness
Revision Date: 2-6-19 Incident Number and Name: 15573 Stanley Creek Country Store Facility ID#:
Well ID
#Date
Screened Interval
(top of screen,
bottom of screen)
Depth to Water*
Uncorrected
(feet)
Free
Product
Thickness
(feet)
Depth to Water*
Corrected
for Free Product
Thickness(feet)
Top of
Casing
Elevation
(MSL)
Groundwater
Surface
Elevation
(MSL)
P-2 8-30-22 ? - ?0 9.29 99.27 89.98
3-15-22 0 9.03 90.24
9-15-21 0 9.43 89.84
3-23-21 0 8.65 90.62
8-11-20 0 8.91 90.36
3-17-20 0 9.15 90.12
9-16-19 0 9.65 89.62
2-6-19 0 8.81 90.46
9-14-18 -0 8.75 90.52
9-22-17 -0 8.80 90.47
3-17 -0 8.89 90.38
9-14-16 -0 9.42 89.85
9-14-15 -0 8.85 90.42
P-2 9-15-14 ? - ?0 7.58 99.27 91.69
10-8-13 0 7.84 91.43
3-24-14 0 7.19 92.08
*Depth to Water is measured from Top of Casing
0
10000
20000
30000
40000
50000
60000
70000
2004-92007-72008-32008-92009-32009-92010-42010-92011-32011-102012-22012-92013-32013-102014-32014-92015-32015-92016-32016-92017-32017-92018-22018-92019-22019-92020-32020-82021-32021-92022-32022-8MW-2
B E T X MTBE
1
10
100
1000
10000
100000
2004-92007-72008-32008-92009-32009-92010-42010-92011-32011-102012-22012-92013-32013-102014-32014-92015-32015-92016-32016-92017-32017-92018-22018-92019-22019-92020-32020-82021-32021-92022-32022-8MW-2
B E T X MTBE
0
5000
10000
15000
20000
25000
2004-92007-72008-32008-92009-32009-92010-42010-92011-32011-102012-32012-92013-32013-102014-32014-92015-32015-92016-32016-92017-32017-92018-22018-92019-22019-92020-32020-82021-32021-92022-32022-8P2
B E T X MTBE
1
10
100
1000
10000
100000
2004-92007-72008-32008-92009-32009-92010-42010-92011-32011-102012-32012-92013-32013-102014-32014-92015-32015-92016-32016-92017-32017-92018-22018-92019-22019-92020-32020-82021-32021-92022-32022-8P2
B E T X MTBE
Appendix B
Tables
1. Hydrogeology Value Units Comments
Seepage Velocity 1.8 feet/year Sourced from CSA Addendum CAP dated May 28, 1998 prepared by Southeastern
Geological Services. Average of seepage velocity measured at PTW-2 and MW-7.
2. Dispersion
Longitudinal Dispersivity 10.0 feet Calculated by BIOSCREEN using the Estimated Plume Length
Transverse Dispersivity 1 feet Calculated by BIOSCREEN using the Estimated Plume Length
Vertical Dispersivity 0 feet Default
Estimated Plume Length 170 feet Measured plume length
3. Adsorption
Retardation Factor 1 Conservative estimation
or
Soil Bulk Density Not used kg/L
Partition Coefficient Not used L/kg
FractionOrganicCarbon Not used unitless
4. Biodegration
Benzene
1st Order Decay Coefficient 0.18 per year Calculated by BIOSCREEN using the Solute Half-Life
or
Solute Half-Life 3.8000 year Calculated using the first order decay coefficient from the first order decay equation
discussed in Section 7.1.
Toluene
1st Order Decay Coefficient 0.18 per year Calculated by BIOSCREEN using the Solute Half-Life
or
Solute Half-Life 3.80 year Calculated using the first order decay coefficient from the first order decay equation
discussed in Section 7.1.
FractionOrganicCarbon Not used unitless
Naphthalene
1st Order Decay Coefficient 0.11 per year Calculated by BIOSCREEN using the Solute Half-Life
or
Solute Half-Life 6.33 year Calculated using the first order decay coefficient from the first order decay equation
discussed in Section 7.1.
FractionOrganicCarbon Not used unitless
5. General
Modeled Area Length 100 feet Length of model space to be viewed in the output.
Modeled Area Width 25 feet Width of model space to be viewed in the output
Simulation Time Various years Model ran in 1 year time steps identifying the maximum contaminant concentration in
groundwater at its intersection with Stanley Creek.
6. Source Data
Source Thickness 27 feet Unconfined aquifer thickness sourced CSA Addendum CAP dated May 28, 1998
prepared by Southeastern Geological Services.
Source Zone (benzene)0.143 mg/L Sourced from Semi-Annual Monitoring Report dated September 30, 2022 prepared by
Southeastern Geological Services.
Source Zone (toluene)0.489 mg/L Sourced from Semi-Annual Monitoring Report dated September 30, 2022 prepared by
Southeastern Geological Services.
Source Zone (naphthalene)0.174 mg/L Sourced from Semi-Annual Monitoring Report dated September 30, 2022 prepared by
Southeastern Geological Services.
Source Halflife (Inst. React.)Not used years
Source Halflife (1st Order)<1 years Simulates little to no benzene, toluene, and naphthalene in soil
cm/sec = centimeter per second
kg/L = kilograms per liter
L/kg = liters per kilogram
mg/L = milligrams per liter
Table 1 - Summary of BIOSCREEN Input Data
Stanley Creek Country Store, Incident 15573
236 Mauney Road
Stanley, Gaston County, North Carolina
BLE Project No. 19484-01
Benzene Toluene Naphthalene Benzene Toluene Naphthalene
11 32 0.001
25 18.4 16.8 0.001 0.001
NCAC 2B 1.19 11 NA
In-Stream Target NA NA 400
1Predicted contaminant concentration at the intersection with Stanley Creek
mg/L = micrograms per liter
NCAC 2B = North Carolina 15A NCAC 02B Water Quality Standards for Surface Waters
In-Stream Target = North Carolina In-Stream Target Values for Surface Waters
Stanley Creek is classified as WS-IV
NA = Not applicable
BIOSCREEN Output1 (mg/L)Time
(years)
Stanley Creek Result Following Mixing
(mg/L)
Table 2 - Summary of BIOSCREEN Output and Mixing Results
Stanley Creek Country Store, Incident 15573
236 Mauney Road
Stanley, Gaston County, North Carolina
BLE Project No. 19484-01
Appendix C
BIOSCREEN Inputs
Appendix D
First Order Decay Coefficients Analysis
y = 5E+11e-5E-04x
R² = 0.5993
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
37,000 38,000 39,000 40,000 41,000 42,000 43,000 44,000 45,000 46,000Benzene Concentration in Micrograms per LiterDays
PTW-2 Benzene Concentration Vs. Time
Half-life = 0.693/5E-04 = 3.79
y = 3E+11e-5E-04x
R² = 0.5742
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
37,000 38,000 39,000 40,000 41,000 42,000 43,000 44,000 45,000 46,000Toluene Concentration in Micrograms per LiterDays
PTW-2 Toluene Concentration Vs. Time
Half-life = 0.693/5E-04 = 3.79
y = 2E+07e-3E-04x
R² = 0.4224
0
200
400
600
800
1,000
1,200
1,400
39,000 40,000 41,000 42,000 43,000 44,000 45,000 46,000Naphthalene Concentration in Micrograms per LiterDays
MW-2 Naphthalene Concentration Vs. Time
Half-life = 0.693/3E-04 = 6.33
Appendix E
BIOSCREEN Output
DISSOLVED HYDROCARBON CONCENTRATION ALONG PLUME CENTERLINE (mg/L at Z=0)
Benzene Distance from Source (ft)
TYPE OF MODEL 0 10 20 30 40 50 60 70 80 90 100
No Degradation 0.000 0.002 0.062 0.035 0.017 0.006 0.002 0.001 0.000 0.000 0.000
1st Order Decay 0.000 0.002 0.032 0.014 0.005 0.002 0.000 0.000 0.000 0.000 0.000
Inst. Reaction 0.000 0.002 0.062 0.035 0.017 0.006 0.002 0.001 0.000 0.000 0.000
Field Data from Site
Time:
11 YearsNext Timestep
Prev Timestep
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Animation Recalculate This
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0 20 40 60 80 100 120Concentration(mg/L)Distance From Source (ft)
1st Order Decay Instantaneous Reaction No Degradation Field Data from Site
Return to
DISSOLVED HYDROCARBON CONCENTRATION ALONG PLUME CENTERLINE (mg/L at Z=0)
Toluene Distance from Source (ft)
TYPE OF MODEL 0 45 90 135 180 225 270 315 360 405 450
No Degradation 0.000 0.158 0.016 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
1st Order Decay 0.000 0.0184 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
Inst. Reaction 0.000 0.158 0.016 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
Field Data from Site
Time:
25 YearsNext Timestep
Prev Timestep
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Animation Recalculate This
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
0.160
0.180
0 50 100 150 200 250 300 350 400 450 500Concentration(mg/L)Distance From Source (ft)
1st Order Decay Instantaneous Reaction No Degradation Field Data from Site
Return to
DISSOLVED HYDROCARBON CONCENTRATION ALONG PLUME CENTERLINE (mg/L at Z=0)
Naphthalene Distance from Source (ft)
TYPE OF MODEL 0 45 90 135 180 225 270 315 360 405 450
No Degradation 0.000 0.064 0.007 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
1st Order Decay 0.000 0.0168 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
Inst. Reaction 0.000 0.064 0.007 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
Field Data from Site
Time:
25 YearsNext Timestep
Prev Timestep
Calculate
Animation Recalculate This
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0 50 100 150 200 250 300 350 400 450 500Concentration(mg/L)Distance From Source (ft)
1st Order Decay Instantaneous Reaction No Degradation Field Data from Site
Return to
Appendix F
StreamStats Report
StreamStats Report
Collapse All
Basin Characteristics
Parameter Code Parameter Description Value Unit
DRNAREA Area that drains to a point on a stream 2.64 square miles
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Time:2023-02-13 15:24:18 -0500