WA-1119_13261_CA_RPTS_20191009

3502 Hayes Road • Monroe, North Carolina 28110
113 West Firetower Road, Suite G • Winterville, North Carolina 28590
Phone [phone] • [phone] • Fax [phone]
October 9, 2019

Mr. Jeff Welti
North Carolina Department of
Environmental Quality-UST Section
Washington Regional Office
943 Washington Square Mall
Washington, North Carolina 27889

Re: October 2019 Boom Installation and
Plume Stability Analysis
Perrytown Service Station
526 Sand Hill Road
Colerain, Bertie County
Incident No. 13261
GRI Project No. 2858

Dear Mr. Welti:

Geological Resources, Inc. (GRI) presents this information to complete the scope of work that was
requested and approved as Task Authorization No. 13261-47 for the above referenced site (Figure 1).
Please find enclosed the applicable site location map, site map and GSI Mann-Kendall Toolkit for the
above referenced site.

The absorbent boom was replaced in RW-1 on October 9, 2019. An immeasurable amount of free
product was observed in the used absorbent boom. The used boom was transferred to a drum that was
secured on-site upon completion of the event.

A GSI Mann-Kendall plume stability analysis was completed for monitoring wells MW-2, MW-10, MW-
25, MW-26 and MW-27 on October 9, 2019, at the direction of the NCDEQ incident manager. The
results of the plume stability analysis indicate that contamination is decreasing in MW-2 and MW-27; is
probably decreasing in MW-10 and no trend could be established for MW-25 and MW-26.

Please do not hesitate to contact the undersigned at [phone] if you have any questions or require
additional information.

Perrytown Service Center
October 2019 Boom Replacement and
Plume Stability Analysis
Page 2 of 2

3502 Hayes Road • Monroe, North Carolina 28110
113 West Firetower Road, Suite G • Winterville, North Carolina 28590
Phone [phone] • [phone] • Fax [phone]

Sincerely,

Geological Resources, Inc.

William Regenthal, P. G.
Branch Operations Manager
Enclosures: Site Location Map, Site Map and GSI Mann-Kendall Toolkit
cc: file
Evaluation Date:Job ID:
Facility Name:Constituent:
Conducted By:Concentration Units:ug/L
Sampling Point ID:MW-2 MW-10 MW-25 MW-26 MW-27
Sampling Sampling
Event Date
1 14-Jul-09 1720 FP
2 5-Apr-10 1820 437
3 1-Dec-10 1500 268 218 844 282
4 6-Mar-12 399 316 513 2580 177
5 3-Dec-12 1770 835 0 219 318
6 28-Aug-14 145 789 320 29.6 128
7 3-Sep-15 1680 FP 61.2 469 2.7
8 16-May-16 207 252 0.4 0 24
9 28-Nov-16 188 174 0 0 170
10 28-Dec-17 51.3 554 119
11 12-Jun-18 0 132 610 195 125
12 19-Feb-19 253 2.9
13 27-Mar-19 360 215 2340 1570 112
14
15
16
17
18
19
20
Coefficient of Variation:0.96 0.63 1.65 1.35 0.78
Mann-Kendall Statistic (S):-38 -21 5 -9 -25
Confidence Factor:99.6%94.0%65.7%79.2%97.0%
Concentration Trend:Decreasing Prob. Decreasing No Trend No Trend Decreasing
Notes:
1.At least four independent sampling events per well are required for calculating the trend. Methodology is valid for 4 to 40 samples.
2.Confidence in Trend = Confidence (in percent) that constituent concentration is increasing (S>0) or decreasing (S<0): >95% = Increasing or Decreasing;
≥ 90% = Probably Increasing or Probably Decreasing; < 90% and S>0 = No Trend; < 90%, S≤0, and COV ≥ 1 = No Trend; < 90% and COV < 1 = Stable.
3.Methodology based on "MAROS: A Decision Support System for Optimizing Monitoring Plans", J.J. Aziz, M. Ling, H.S. Rifai, C.J. Newell, and J.R. Gonzales,
Ground Water, 41(3):355-367, 2003.
DISCLAIMER: The GSI Mann-Kendall Toolkit is available "as is". Considerable care has been exercised in preparing this software product; however, no party, including without
limitation GSI Environmental Inc., makes any representation or warranty regarding the accuracy, correctness, or completeness of the information contained herein, and no such
party shall be liable for any direct, indirect, consequential, incidental or other damages resulting from the use of this product or the information contained herein. Information in
this publication is subject to change without notice. GSI Environmental Inc., disclaims any responsibility or obligation to update the information contained herein.
GSI Environmental Inc., www.gsi-net.com
BENZENE CONCENTRATION (ug/L)
9-Oct-19
Perrytown Service Center Benzene
GSI MANN-KENDALL TOOLKIT
for Constituent Trend Analysis
William Regenthal
13261
0.1
1
10
100
1000
10000
02/08 07/09 11/10 04/12 08/13 12/14 05/16 09/17 02/19 06/20Concentration (ug/L)Sampling Date
MW-2
MW-10
MW-25
MW-26
MW-27