WQ0002708_Monitoring (Information)_20190228

Ground Water
Monitoring Plan
Wrenn Road Facility Wastewater Irrigation
System

Garner, NC
February 26, 2019

hdrinc.com
555 Fayetteville Street Suites 900 & 210, Raleigh, NC 27601-3034
[phone]

February 26, 2019

Mr. Rick Bolich
NC Department of Environmental Quality
Division of Water Resources
Water Quality Regional Operations Section
Raleigh Regional Office
3800 Barrett Drive
Raleigh, NC 27609

Re: Ground Water Monitoring Plan
Permit No. WQ0002708
City of Raleigh Wrenn Road Facility Wastewater Irrigation System
Wake County, North Carolina
Dear Mr. Bolich,
On behalf of the City of Raleigh Public Utilities Department, we are resubmitting the Ground Water
Monitoring Plan requested in the approval for Permit Number WQ0002708 to support background
concentrations of manganese, iron and arsenic above the 15A NCAC 02L standards. The sampling
plan has been prepared with consideration to the guidance material suggested in the Permit
Approval letter: Aquifer Protection Section Policy for metals Determinations Required by Title 15A,
NCAC, Subchapter 2L (May, 2013) and Evaluating Metal in Groundwater at DWQ Permitted
Facilities: A Technical Assistance Document for DWQ Staff (NC DENR, July, 2012). Also, the
following US EPA groundwater monitoring guidance document was utilized: Statistical Analysis of
Groundwater Monitoring Data at RCRA Facilities-Unified Guidance: EPA 530/R-09-007.
Additionally, recommendations offered by DEQ during discussions with the City and HDR were
incorporated into the sampling plan.
In summary, the revised sampling plan will:
1. Install and develop four (4) background monitoring wells at the Wrenn Road Facility;
2. These wells will be sampled for iron, manganese, and arsenic bi-monthly for the first six (6)
months to develop background statistics for compliance monitoring;
3. Determine if 2010 sampling data is from the same population and for use in defining
background statistics for ground water monitoring;
4. Sample the new background wells for one (1) year on the same schedule used for
compliance monitoring to evaluate any time trends to consider in compliance assessments;
5. The new ground water monitoring wells will be m aintained such that resampling can be
accomplished in the future if necessary.
hdrinc.com
555 Fayetteville Street Suites 900 & 210, Raleigh, NC 27601-3034
[phone]

This package contains the following:
Attachment A – The ground water monitoring plan submitted to DEQ on February 28, 2017
Attachment B – Responses to comments provided to DEQ on October 7, 2017
Attachment C – The resubmittal to DEQ by the City/HDR on December 14, 2018, providing
revised background monitoring well locations
Attachment D – Meeting minutes from a meeting held with the City, HDR, Eagle Resources,
and DEQ on January 31, 2019
Attachment E – W ater well locations for the subdivision located adjacent to the Wrenn
Road Facility
Attachment F – Ground water well levels
Attachment G – A contour map of the proposed monitoring well locations
The groundwater permit WQ0002708 expires June 30, 2020. The I-540 project will impact the
Wrenn Road Facility and the compliance boundary. The exact timing of the I-540 project is
unknown at this time. The City will keep DEQ informed as to the progress of this project.
We have submitted a full package in order to hopefully help the review process. Should you have
any questions, please do not hesitate to call me at 919-232-6657. We look forward to hearing from
the NC Department of Environmental Quality.
Sincerely,
HDR Engineering Inc. of the Carolinas

Chris Brown, PE
Project Manager

Enclosures
cc: Chris Phelps, City of Raleigh
Dennis Lassiter, City of Raleigh
Whit Wheeler, City of Raleigh
Eric Lappala, Eagle Resources
Samantha Black, HDR
Manish Bhandari, HDR

A
Ground Water Monitoring
Plan – Submitted February
28, 2017

1

Proposed Monitoring Plan to Establish Background
Concentration of Iron and Manganese at the
Wrenn Road Sprayfields, Wake County, NC

North Carolina Non-Discharge Permit WQ0002708

Prepared for
City of Raleigh Pubic Utilities Department and
HDR Engineering of the Carolinas

April 1, 2016
(Revised February 1, 2017)

Eric G. Lappala, P.E., P.H.

Eagle Resources, P.A.
P.O. Box 11189
Southport, NC
www.eagleresources.com

i

Contents
Introduction ................................................................................................................................................. 1
Purpose ........................................................................................................................................................ 1
Model Analyses to select sites for background monitoring ........................................................................ 2
Sampling Design ......................................................................................................................................... 8
1. Identical and Independent Distributions of background and forward samples ..................... 8
2. Temporal Stationarity of Samples ............................................................................................. 10
3. Spatial Stationarity of Samples ................................................................................................. 10
4. Statistical Outliers ....................................................................................................................... 12
5. Use of Parametric Methods ........................................................................................................ 12
6. Minimum Number of Background Samples ............................................................................ 12
a) Additional Background Wells ................................................................................................ 13
b) Sampling to Establish Background ....................................................................................... 14
c) Initial Sampling Methodology Assessment ........................................................................... 14
Recommended Background Determination Methodology ....................................................................... 15
Conclusions ............................................................................................................................................... 16

Figures
Figure 1.-- Measured and modeled water level elevations in B-3, B-8, and B-9 ....................................... 3
Figure 2.-- Modeled concentrations of the modeled constituent in model layer 1 as of 12/31/15. ............ 5
Figure 3.-- Modeled concentrations of the modeled constituent in model layer 2 as of 12/31/15. ............ 6
Figure 4.-- Modeled concentrations of the modeled constituent in model layer 3 as of 12/31/15. ............ 7
Figure 5.-- Probability Plots for (Fe / 2L standard) and (Mn / 2L standard) for the 2010 study samples..
............................................................................................................................................................. 9
Figure 6.-- Probability plots of log-transformed values of (Fe 2L Standard) and (Mn / 2L Standard) for
the 2010 study samples. .................................................................................................................... 10
Figure 7.-- Log-transformed multiple of Fe (left panel) and Mn (right panel) multiples of the 2L
Standards for samples from the 2010 study. ..................................................................................... 11
Figure 8.-- Dissolved Fe and Mn plotted against each other showing little correlation between them. ... 12

Tables
Table 1.—Dissolved Fe and Mn from the 2010 study, their multiples of the 2L standards and the log
transform of the multiples of the 2L standards. .................................................................................. 9
Table 2.-- Coordinates of Proposed Background Monitoring Wells. ....................................................... 13
Table 3.-- Results of purging of compliance wells on February 5, 2016 and laboratory analyses for
dissolved Fe and Mn in samples taken at the end of purging.. ......................................................... 15

1
Introduction
NC DEQ has granted Permit WQ0002708 to the City of Raleigh (City) for the continued operation and
irrigation at the Wrenn Road Facility in southeastern Wake County. This permit is a renewal for the
permit of the same number that was in effect originally to permit the same facilities for the disposal of
wastewater effluent from the treatment facilities. The Wrenn road Facility stopped receiving domestic
wastewater in 2008. The spray irrigation facilities were modified to allow treatment of residuals from
the DE Benton Water Treatment Plant (DEBWTP). WQ0002708 was amended in 2012 for the spray
irrigation modifications and to change the influent waste source to residuals from the DEBWTP. The
spray irrigation permit was renewed in 2015. The sprayfields have been used since 1989 to dispose of
treated wastewater from the Garner wastewater treatment plant (Garner WWTP). The Town of Garner
operated the WR Sprayfields until the merger of the Garner water and sewer utility systems with the
City of Raleigh in July 2000. The City of Raleigh Public Utilities Department (CORPUD) has operated
the Garner wastewater plant and the WR Sprayfields since that date.

A comprehensive Hydrogeologic and Geochemical evaluation of the site was completed by Soil and
Environmental Consultants (S&EC) and Eagle Resources for the site in 2010 and approved by DEQ as
part of the application for the currently issued permit1,2,. These studies comprised the installation of
over 20 temporary piezometers, three monitoring wells, and groundwater flow, groundwater transport,
and geochemical modeling to assess both conditions prior to the application of residuals from the WTP
and to recommend loading rates to the sprayfields to assure that the likely depth to the watertable would
be compliant with the conditions of the permit.

Purpose
The permit was issued by DEQ with the condition that the City prepare a monitoring plan to assess the
background concentrations of arsenic, iron and/or manganese above the 15A NCAC .02L groundwater
standards (2L Standards). The 2010 reports documented concentrations of these constituents in samples
collected from piezometers and monitoring wells that exceeded the 2L Standards. The permit condition
also requested that CORPUD consider DWQ Staff guidance documents3,4 in preparing the plan.

These guidance documents include the statistical evaluation of data used to establish background
concentrations to account for spatial variations across complex sites. Because the piezometers from the
2010 studies have been abandoned, they and are no longer available to use for re-development and
sampling to provide this data. The three monitoring wells that have been used for compliance reporting
since the original permit was issued for the site (MW-B3, MW-B8, and MW-B-9) also are not adequate
in number or location to use for the establishment of background concentrations. These wells are not
located in areas where the 2010 study showed concentrations of the regulated metals to be above the 2L
Standards. Additionally, only three rounds of samples have been taken that have included analyses for
the metals of concern since the permit was issued and application of residuals was started in 2014.

The objective of this report is to present a plan for using data and analyses from the 2010 study
documents combined with data from additional monitoring locations to respond to the permit condition
to assess the background concentrations of iron and manganese at the facility.

1 Soil and Environmental Consultants, 2009, Site Analysis for Wrenn Road Wastewater Treatment Plant Spray Irrigation
system, Garner., Wale County, North Carolina
2 Eagle Resources, P.A., May 10, 2010, Groundwater Mounding Analysis and Groundwater Quality Assessment Wrenn Road
Wastewater Treatment Plan Spray Irrigation System Garner, Wake County, North Carolina
3 NC Division of Water Quality, July 2012: Evaluating Metals in Groundwater at DWQ Permitted Facilities: a Technical
Assistance Document for DWQ Staff.
4 NC Division of Water Quality, May 13, 2013: Aquifer Protection Section Policy for Metals Determinations Required by Title
15A North Carolina Administrative Code, Subchapter 2L.

2

Based upon the DEQ guidance documents, determination of the quality and quantity of background data
needed should consider the following:
“
1. Physical complexity of the site
a. Does site geology vary horizontally across the site
b. Are off-site wastes likely to migrate to and contaminate background or compliance
boundary wells
c. Have Hydrogeologic anomalies been identified?
d. Have wastes been disposed across particularly large or undocumented areas
e. Spatial extent and complexity of the waste disposal practices
2. Are background concentrations expected to be similar to 2L standards and/or similar to on-site
concentrations at the compliance boundary
3. Will site be used as a precedent for similar sites in the state
4. Will statistical proof be required to justify a non-compliance determination

At a minimum, collected data should measure maximum concentrations of permitted waste constituents
that exist at the compliance boundary and at ambient background locations, along with any spatial or
temporal trends. Moreover, sample numbers and locations should align with statistical data needs....

Therefore, background data should be collected from a hydraulically up gradient location (outside the
influence of site wastes) in immediate proximity to the site and within the same groundwater horizon
(depth/zone) as samples collected from compliance boundary wells. ….”

Model Analyses to select sites for background monitoring
The 2010 studies and analyses provide the documentation of the items listed above that define the
physical complexity of the site. The calibrated groundwater flow and transport model constructed for
those studies was based on site-specific data from borings, piezometers (19) monitoring wells (3), water
levels, tests for hydraulic conductivity, chemical and geochemical analyses of water samples. The
model was constructed using three layers: The Saprolite at the site was modeled as two layers each 17.7
feet thick which are referred to as the Upper Saprolite and Lower Saprolite respectively. The third layer
comprised Partially Weathered Rock (PWR) and was 15 feet thick.

Transient analyses using the model have been used to help identify those areas that are not likely to
have been impacted by migration of constituents in water applied to the Wrenn Road fields during 2014
and 2015. The initial water levels used for the transient analyses with the model were the steady state
values from the calibrated 2010 model which used a natural recharge rate of using a recharge rate of 15
inches per year. Monthly recharge for 2014 and 2015 used for model input was determined as follows:

Recharge on non-sprayfield areas = Precipitation – Evapotranspiration (ET); and (1)

Recharge on spray areas = Precipitation + Applied Effluent – ET. (2)

Precipitation for each month was taken from the grid centered on the site out of the 4km x 4km gridded
values from the National Precipitation Dataset from the PRISM website5. The PRISM datasets are

5 http://www.prism.oregonstate.edu/

3
computed using measurements from a wide range of monitoring networks that cover the conterminous
United States to which sophisticated quality control measures and a variety of modeling techniques are
applied and are available as daily, monthly and yearly time scales for the period from 1895 to the
present.

ET was taken from the global monthly ET 0.05 degree grid corresponding to the site from the MODIS
project6. This project is part of NASA/EOS project to estimate global terrestrial evapotranspiration from
earth land surface by using satellite remote sensing data. The MOD16 ET datasets are estimated using
Mu et al.’s improved ET algorithm (2011) over previous Mu et al.’s paper (2007a). The ET algorithm is
based on the Penman-Monteith equation (Monteith, 1965). Surface resistance is an effective resistance
to evaporation from land surface and transpiration from the plant canopy.

Applied effluent to each field for each month was computed using the volume applied as reported on the
Discharge Monitoring Reports (DMRs) provided by CORPUD and tables provided by HDR of the
percentage of spray heads applying to each soil type within each field that are included as Attachment 1
to this report. Attachment 2 provides a summary tabulation of the monthly effluent applied to each soil
type within each field. The unit rate applied effluent in equation (2) was determined by dividing the
volume applied by the area occupied by each soil within each field.

Modeled water level elevations in B-3, B-8, and B-9 for the period 2014 through 2015 are shown on
Figure 1 along with measured water level elevations for 2007 through 2015 Although water levels
fluctuate, they tend to fluctuate in unison over the site and model analyses show that the pattern of
groundwater flow that are determined by recharge and discharge areas does not change significantly.
.

Figure 1.-- Measured and modeled water level elevations in B-3, B-8, and B-9

6 http://www.ntsg.umt.edu/project/mod16
150
180.25
210.5
240.75
271
301.25
331.5
361.75
6/1/06 5/22/07 5/11/08 5/1/09 4/22/10 4/12/11 4/1/12 3/22/13 3/13/14 3/3/15 Water Level Elevattion, NAVD88 FeetB-3
B-8
B-9
B-3 Modeled Sy = 0.25
B-8 Modeled Sy = 0.25
B-9 Modeled Sy = .25

4
Transient transport analyses for 2014 through 2015 were conducted to assess potential migration of
COCs in effluent from DEB WTP and to locate areas where it is not likely to have impacted
groundwater and hence where background monitoring sites should be located. The source term used for
these analyses was an arbitrary constituent at a concentration of 10 arbitrary units applied to the areas
that received effluent during 2014 and 2015. Figures 2 through 4 show the modeled concentrations of
the arbitrary constituent as of December 31, 2015 for each of the modeled layers.

8
Sampling Design
DEQ has determined that the data from the 2010 report should not be used to establish background
values because the wells were not permanent and because their sampling may not have met the currently
recommended sampling methodology for metals. However, because the sample size is relatively large
(n = 21) from that study and to provide a guide to the approximate variability in concentrations of iron
and manganese over the site as an aid to establishing a background monitoring program to meet these
requirements, we have included that data its summary statistics in Table 1 as well as their as multiples
of the 2L standards. Their multiples of the 2L Standards are also shown on Figures 2 through 4 to
illustrate their spatial variability.

The USEPA guidance document7 on groundwater monitoring for compliance purposes which is
referenced in the DEQ guidance document provides the following six requirements for establishing
prediction limits for comparing background and future compliance samples:

1. Background and future sample measurements need to be identically and independently distributed;
2. Sample data do not exhibit temporal non-stationarity in the form of trends, autocorrelation, or other
seasonal or cyclic variation;
3. For inter-well tests (e.g., up-gradient-to-downgradient comparisons), sample data do not exhibit non-
stationary distributions in the form of significant natural spatial variability;
4. Background data do not include statistical outliers;
5. For parametric prediction limits, background data are normal or can be normalized using a
transformation; and
6. A minimum of 8 background measurements is available; more for non-parametric limits or when
accounting for multiple, simultaneous prediction limit tests.

1. Identical and Independent Distributions of background and forward samples
To assess the likely distributions of these data, probability plots for the multiples of the 2L standards are
shown in Figure 5. Examination of these plots and the value of the skew coefficients in Table 1 show
that the raw data is not normally distributed. However, the the log transform of the multiples of the 2L
standards closely approximate normal distributions as shown by the fit to the straight normal probability
line in Figure 6. Therefore, to meet the requirements 1 and 5 above, all background and forward
compliance samples should be log-transformed. Note that for both Mn and Fe a value of the log
transformed value of 0.0 for the multiple of the standard is equivalent to the 2L Standard (Value /
Standard = 1.0).

7 U.S. Environmental Protection Agency, March, 2009: Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities-
Unified Guidance: EPA 530/R-09-007, chapter 18, pp 18-4.

9

Figure 5.-- Probability Plots for (Fe / 2L standard) and (Mn / 2L standard) for the 2010 study samples..

Table 1.—Dissolved Fe and Mn from the 2010 study, their multiples of the 2L standards and the log transform of the multiples of the 2L
standards.

R² = 0.68701
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
0 50 100 150 200 250Z-ScoreFe / 2L Standard
R² = 0.7386
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 20 40 60 80 100Z -ScoreMn / 2L Standard
2010
Study
Well No.
Fe,
mg/l
Mn,
mg/l
Fe x
Std
Log Fe
x Std
Mn x
Std
Log Mn
x Std
MW-1 11.74 1.06 39.13 1.593 21.2 1.326
MW-2 6.37 0.63 21.23 1.327 12.6 1.100
MW-3 12.33 0.04 41.1 1.614 0.8 -0.097
PZ-1 3.83 4.43 12.77 1.106 88.6 1.947
PZ-2 11.69 4.11 38.97 1.591 82.2 1.915
PZ-3 3.02 0.56 10.07 1.003 11.2 1.049
PZ-4 26.28 2.16 87.6 1.943 43.2 1.635
PZ-5 30.2 3.16 100.67 2.003 63.2 1.801
PZ-6 69.14 3.46 230.47 2.363 69.2 1.840
PZ-7 23.6 0.43 78.67 1.896 8.6 0.934
PZ-8 31.94 0 106.47 2.027 0 n/a
PZ-9 6.92 0.84 23.07 1.363 16.8 1.225
PZ-10 6.96 0.55 23.2 1.365 11 1.041
PZ-11 1.41 0.02 4.7 0.672 0.4 -0.398
PZ-12 10.3 0.25 34.33 1.536 5 0.699
PZ-14 1.52 0.33 5.07 0.705 6.6 0.820
PZ-15 0.68 0.22 2.27 0.356 4.4 0.643
PZ-16 2.39 0.26 7.97 0.901 5.2 0.716
PZ-17 2.29 0.09 7.63 0.883 1.8 0.255
PZ-18 6.16 0.08 20.53 1.312 1.6 0.204
PZ-19 3.14 0.57 10.47 1.020 11.4 1.057
Mean 12.95 1.11 43.16 1.361 22.14 0.986
Median 6.92 0.55 23.07 1.363 11.00 1.045
Variance 260 2 2887 0.268 821 0.439
Std Dev 16.12 1.43 53.73 0.517 28.65 0.662
Skew 2.40 1.45 2.40 0.012 1.45 -0.340

10

Figure 6.-- Probability plots of log-transformed values of (Fe 2L Standard) and (Mn / 2L Standard) for the 2010 study samples.
Conformance with requirement 1 for compliance samples will have to be assessed by periodically determining
their log transformed values and plotting their distribution compared to the background distribution.

2. Temporal Stationarity of Samples
Conformance with Requirements 1 and 2 above will require the periodic assessment of time trends in
both background and compliance samples to assess whether such trends are consistent with each being
similarly distributed. The evaluation of the background and compliance samples should be evaluated for
temporal trends using regression and/or analysis of variance. These analyses will not be possible until a
sufficient number of compliance (and background) samples are available.

3. Spatial Stationarity of Samples
Examination of the spatial patterns of the log transformed values from the 2010 for Fe shows that
concentrations of Fe were elevated in the northwest portion of the property and Mn concentrations were
elevated in the northern portion of the property as shown in Figure 7. These patterns are likely the
result of increased weathering and leaching of the soils and saprolite from the uplands at the north end of
the property to the lowlands at the southern part of the property. These patterns are not apparently
correlated with either the presence or absence of application fields or with the modeled concentrations of
the arbitrary constituent shown in Figures 4 through 4.
R² = 0.98704
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0.000 0.500 1.000 1.500 2.000 2.500Z ScoreLog (Fe / 2L Standard)
R² = 0.97568
-2
-1.5
-1
-0.5
0
0.5
1
1.5
-0.500 0.000 0.500 1.000 1.500 2.000 2.500Z -ScoreLog(Mn / 2L Standard)

11

Figure 7.-- Log-transformed multiple of Fe (left panel) and Mn (right panel) multiples of the 2L Standards for samples from the 2010 study.
A similar spatial variability assessment should be made using new background data and compliance data
once a samples have been collected for at least one year on the current compliance schedule.

To further assess the spatial distribution of Fe and Mn, the log-transformed values of their respective
multiples of the 2L standards are plotted against each other for the 2010 study samples in Figure 8.
While there is a general trend in this relationship, the correlation coefficient between them is very low,
indicating a very weak relationship.

12

Figure 8.-- Dissolved Fe and Mn plotted against each other showing little correlation between them.
4. Statistical Outliers
The EPA guidance document lists two screening tools (Probability and Box Plots) and two formal
outlier tests (Dixon’s and Rosner’s) to identify statistical outliers8. The probability plots shown in
Figure 6 for the samples from the 2010 study show that there are no apparent outliers for the log-
transformed data for either Fe or Mn. Because samples from multiple time periods are not available for
the 2010 study samples, Box Plots to compare the values are not appropriate. However after a sufficient
number of additional background and compliance samples are available they may be useful in
identifying any outliers. Because there do not appear to be any statistical outliers for either the log-
transformed Fe or Mn data shown in Figure 6, it does not seem appropriate to apply either parameter.

5. Use of Parametric Methods
Using parametric methods to assess compliance with background requires that the background and
compliance data are both drawn from normal distributions or that the data can be transformed to normal
distributions. As shown in Figure 6 both Fe and Mn are log normally distributed and therefore at least
the data from the 2010 study meet this requirement.

6. Minimum Number of Background Samples
The EPA guidance document states that at least 8 samples should be available to establish background
for the use of prediction intervals for compliance assessment9. As few as three background observations
can be used to compute compliance but would result in a very large upper prediction limit for
background and would limit the statistical power of the test.

8 USEPA Unified Guidance document, Chapter 12.
9 USEPA Unified Guidance Document, p. 18-4.
R² = 0.1431
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
0 1 2 3 4 5Log(Mn / 2L Standard)Log(Fe / 2L Standard)

13

Although DEQ has determined as previously stated that the sample analyses from the 2010 study cannot
be used by themselves to establish background, it is our professional opinion that that dataset as well as
samples from the 1990 study can and should be use in conjunction with additional samples to achieve
this objective. As demonstrated in the previous five sections the 2010 dataset is a) larger than the
minimum of 8 required; b) shows that parametric tests for compliance can be used if the data is log-
transformed; c) shows that the spatial variability in Fe and Mn is the result of natural variability and not
the result of past applications to fields; and d) apparently does not contain statistically significant
outliers. The recommended monitoring plan utilizes this information from the 2010 samples in
conjunction with additional background samples to be obtained from new permanent background
monitoring wells.

With the exception of compliance well MW-B3, none of the existing wells on site meet the necessary
criteria to establish background. MW-B1 is the only well up-gradient of the fields. The remaining
compliance wells (MW-B-8 and MW-B9 and the three other permanent wells remaining on site (MW-1,
MW-2, and MW-3) are down gradient of the fields and therefore do not meet the DEQ criteria for
background wells going forward. However, data from the 2010 study for MW-1, MW-2, and MW-3 can
and should be use as part of the overall dataset used to establish background. The modeling analysis
shown in the previous section showed that there is the potential for Fe and Mn to have migrated in some
concentrations to these wells as the result of applications in 2014 and 2015 and therefore these and
future data from these wells should be excluded from the background analysis.

Because Fe and Mn were not required compliance parameters prior to the issuance of the current permit,
there is no data from the three compliance wells prior to 2015 for these parameters that could be used to
establish background.

a) Additional Background Wells
This plan recommends the installation and sampling of new wells at five (5) sites and sampled twice at 6
month intervals be used to establish background concentrations for iron and manganese. These sites
were selected based upon the transient model analyses discussed above the are shown on Figures 2
through 4 and were chosen to meet the criteria listed in the DEQ and EPA guidance. The coordinates of
these sites are shown in Table 2 below.

Table 2.-- Coordinates of Proposed Background Monitoring Wells.
Type 1 monitoring wells should be constructed at these sites that are screened from the depth of the
seasonal high water permanent watertable to the top of PWR. Based upon the 2009 S&EC
hydrogeologic report for the site the new wells will be approximately 25 feet deep and have ten (10) feet
of well screen. The preferred well construction method should be sonic or air rotary drilling to
eliminate blinding off of the formation by drilling muds with hydraulic rotary or smearing of the
formation by hollow stem auger methods.
Well No Easting Northing
P-MW-1 2126155 691193
P-MW-2 2124156 688177
P-MW-3 2123614 686726
P-MW-4 2125044 688180
P-MW-5 2126427 689422

14

The wells are to be constructed using new threaded 2-inch diameter PVC casing and wire-wound screen
with a number 10 (0.01 inch) opening. The wells are to be completed with a graded sand pack installed
in the annulus between the well screen and borehole wall from the bottom of the boring to two feet
above the top of the screened interval. A bentonite seal at least 1 foot thick is to be placed on top of the
sand pack and a concrete seal placed above it to the land surface. The wells are to be completed with
above-ground, lockable, protective metal well casings.

The new background wells should be developed using industry standard procedures as documented in
the DEQ guidance document. Pumping, surging, and bailing should be used in an effort to develop the
sand pack used so as to minimize the potential for fine sediment to enter the wells during the sampling
events. Development should continue until the produced water is visibly clear and preferably has a
turbidity of 10 NTU or less or the turbidity levels are stable (three consecutive turbidity measurements
do not vary by more than 10%).

b) Sampling to Establish Background
The newly constructed background wells and the three compliance wells should be sampled on a bi-
monthly basis for the first six months following their installation to develop an adequate sample
population for background assessment. Thereafter, these wells should be sampled on the same schedule
used for the existing three compliance wells (March, July, and November) for one year to assess any
longer term time trends. Low flow purging and sampling of all wells should be used to conform with the
DEQ guidance document10. Low flow well purging should continue until turbidity levels are less than
10 NTU or vary no more than 10% and field measured pH and water temperature are similarly stable.

c) Initial Sampling Methodology Assessment
An initial evaluation of low-flow purging and sampling was conducted of the three existing compliance
wells (MW-B-3, MW-B-8, and MW-B9) on February 5, 2016 by CORPUD staff using procedures
recommended by Eagle Resources to assess the ability to implement the procedures for obtaining valid
metal samples recommended by DEQ. Low flow well purging was conducted for approximately 30
minutes with pH, temperature and turbidity measurements made at approximately 7 minute intervals.
The wells were purged with the dedicated bladder pumps installed in each well controlled with a
GeoControl Pro system which filled the bladder for 20 seconds and discharged for 10 seconds, resulting
in a flow rate of 0.375 gallons per minute. The field measurements for this purging event are shown in
Table 3.

Water samples were taken at the end of the purging in pre-acidified sample containers supplied by the CORPUD
laboratory and the results of these analyses are shown in Table 3. It is apparent that the DEQ requirements for
low flow purging and sampling can be implemented for the compliance wells. While the turbidity in well MW-
B9 was slightly greater than 10 NTU, subsequent measurements were stable within 10% of the initial value.

10 NC Division of Water Quality, May 13, 2013: Aquifer Protection Section Policy for Metals Determinations Required by Title
15A North Carolina Administrative Code, Subchapter 2L.

15

Table 3.-- Results of purging of compliance wells on February 5, 2016 and laboratory analyses for dissolved Fe and Mn in samples taken
at the end of purging..
Recommended Background Determination Methodology
The following steps are recommended to implement the determination of background concentrations of
As, Fe, and Mn at the Wrenn Road Site:

1. Install and develop the five (5) new background monitoring wells as recommended herein;

2. Sample the background and compliance wells bi-monthly for six (6) months following the
installation and development of the new wells. The sampling should follow the recommended
low-flow purging, and field analysis for pH, Conductivity, Turbidity, and Temperature. Samples
taken should be analyzed in the CORPUD laboratory for As, Fe and Mn This will provide a
background sample size of 15 (5 wells x 3 samples) for each constituent. One duplicate should
be taken from one of the background wells that is randomly selected for each sampling round;

3. Prepare probability plots of the 15 sample results for each constituent using the log transform of
the raw values; and visually compare to the plots for the 2010 samples;

4. Conduct One-way Analysis of Variance (ANOVA) on the log-transformed values to assess
whether the new background results are from the same population as the 2010 samples;

5. If the ANOVA shows that the new and 2010 samples are from the same population, pool both to
1 8 16 23
0.38 3.00 6.00 8.63
pH 4.81 4.55 4.57 4.59
Temp Deg C 15.20 15.6 15.8 15.80
NTU 0.20 1.30 1.35 0.95
0.111
< .05
43.4
pH 4.80 4.74 4.83 4.79
Temp Deg C 14.80 15.1 15.1 15.10
NTU 2.43 2.00 1.48 1.86
0.109
0.148
189
pH 5.61 5.15 5.06 4.97
Temp Deg C 14.20 13.8 13.9 13.90
NTU 14.90 13.40 13.10 13.30
0.57
< .05
64.2
Dissolved Fe (mg/l)
Dissolved Mn (mg/l)
Conductivity (umhos/cm)
MW-B-9
Elapsed Time, Min
Purge Volume Gal
MW-B-3
MW-B-8
Dissolved Fe (mg/l)
Dissolved Mn (mg/l)
Conductivity (umhos/cm)
Dissolved Fe (mg/l)
Dissolved Mn (mg/l)
Conductivity (umhos/cm)

16
define the background statistics to use in compliance monitoring; or

6. If the ANOVA shows that the new and 2010 samples are not from the same population, use only
the new samples to define the background statistics to use in compliance monitoring; and

7. Sample the new background wells for one year on the same schedule used for the compliance
wells (March, July, and November) to evaluate any time trends in As, Fe, Mn to consider in
compliance assessments. Log transformation should be applied to all these data.

Conclusions
A recommended methodology for establishing the background statistics for the concentrations of
Arsenic (As) Iron (Fe) and Manganese (Mn) in groundwater at the Wrenn Road facility that can be used
in assessing compliance in the three compliance wells monitored at the site under the currently issued
permit WQ0002708. This methodology was prepared in response to a condition of the issuance of the
permit by NC DEQ.

Information on As, Fe, and Mn concentrations is available from the 2010 study at the site that was
collected before application of residual effluent from the Dempsey E. Benton Water Treatment Plant
began in 2014 under the permit. However, the wells used to collect these samples were temporary and
could not be re-sampled and the sample purging and collection methods used for that study were not
necessarily conformant with DEQ guidance for metals evaluation that was published in 2012 and 2013.
Consequently, additional background wells are recommended to be installed to supplement the 2010
data.

Five additional background wells are recommended at sites where modeling analyses conducted as part
of this plan showed that concentrations of mobile constituents contained in effluent applied in 2014 and
2015 were not likely to have reached.

The plan recommends sampling the new wells bi-monthly for six months to provide an adequate sample
size for assessing background concentrations of As, Fe, and Mn. To assess the additional value
provided by also considering the results from the 2010 study, statistical evaluations are recommended to
ascertain if data from the new wells is from the same population as that from the 2010 study. If so, all
the data should be pooled to provide a more robust sample size to establish the distributions and
statistics to use in compliance assessment. If these tests show that the new and 2010 data are not from
the same population only the new data should be used. This assessment concluded that to enable the use
of parametric tests for compliance that the raw As, Fe, and Mn concentrations should be log-
transformed.

To assess any time trends in background values of As, Fe, and Mn it is recommended that the
background wells be sampled for one year on the same schedule used for the compliance wells. The
background wells should be maintained in such as a condition that they can be resampled following this
period if necessary.

B
Responses to DEQ
Comments – Provided
October 7, 2017

Eagle Resources, P.Å.
215 West Moore Street Southport, NC 28461
919-345-1013 www.eagleresources.com

Rick Bolich, L.G.
Assistant Supervisor
N.C. Dept. of Environmental Quality
Division of Water Resources
Water Quality Regional Operations Section
Raleigh Regional Office
3800 Barrett Drive
Raleigh, NC 27609

[e-mail]

October 7, 2017

Subject: Groundwater Monitoring Plan for City of Raleigh Wrenn Road Facility Permit WQ0002708.

Dear Rick;
This letter responds to your email dated May 2, 2017 to Chris Brown of HDR regarding the location of
proposed new monitoring wells to establish ambient concentrations of iron and manganese in
groundwater at the Wrenn Road Facility. Our response to the issues you provided in that email are
attached.

Please contact us if you need any further information on this matter. We are available to meet with you
if necessary to discuss any additional information that you may need to approve the monitoring plan.

Sincerely yours,

Eric G. Lappala, P.E., P.H.

Attachment:
Response to additional information request

2

Comment:
The proposed background wells P-MW-1 and P-MW-5 appear to be in a topographically upgradient areas that
would be good locations for background assessment of groundwater conditions.

P-MW-2, P-MW-3. and P-MW-4 are not in locations suited to be background locations. They may be suitable
monitoring stations for site conditions affected by lagoon and spray field activities, but these locations are not
representative of background concentrations as they appear to be hydraulically downgradient of the waste
application areas. DWR recommends moving these two wells to a location that is unlikely to be impacted by
waste application.

Response:
The groundwater flow and transport modeling performed for this site demonstrate that all wells chosen to establish
background conditions, including P-MW-2, P-MW-3, and P-MW-4, are unlikely to have been impacted by the
application of water treatment residuals, even if they are within the boundaries of the facility. The objective of the
proposed monitoring plan is to establish statistically significant ambient background conditions that include any
contribution from applied wastewater effluent during that period.

The site was used previously by the Town of Garner and operated by the City of Raleigh to dispose of treated
wastewater effluent from 1989 through 2008 under permit WQ0002708 (Permit).
• Sampling and analysis for iron and manganese in groundwater was not required under that permit.
• The Eagle Resources 2010 study used to support the modification of the Permit detected elevated
concentrations of iron and manganese in temporary monitoring wells that were located within and down
gradient of fields that had been used for wastewater effluent from 1989 to 2008.
• Therefore, any concentrations of these constituents that are currently in groundwater are the result of both
their natural occurrence and any concentrations that may have been present in the wastewater effluent applied
under the permit from 1989 through 2008.

The application of water treatment residuals from the Dempsey E. Benton Water Treatment Plant under the amended
permit that was issued in 2012 began in 2014. The three-dimensional groundwater flow and transport model used in
the 2010 report was updated and used to assess the likely extent of migration of iron and manganese may have
occurred as the result of the application of water treatment residuals.

As documented in the 2010 report the migration of both iron and manganese in groundwater is influenced by the
complex geochemical interaction of these constituents with the soils, saprolite and weathered bedrock that underlie
the site. These interactions all act to attenuate the migration of iron and manganese relative to the migration of
groundwater via a variety of sorption processes. However, to provide the likely maximum extent of their migration
from the application of water treatment residuals, the updated model did not include any of these attenuation
processes.

The DEQ guidance document on establishing ambient background also requires that a statistically valid data set be
present that accounts for the spatial variability hydrogeologic conditions as well concentrations of the regulated
constituents that were present prior to the application of water treatment residuals. Because of the size and
complexity of the Wrenn Road site, it therefore is necessary to include monitoring sites that are within the boundaries
of the site and that may be apparently hydraulically down gradient of some application fields but that have not been
impacted by the application of water treatment residuals.

3

All the proposed monitoring wells locations were selected to meet above criteria. Locating additional wells only at
topographically up-gradient locations of all fields will not meet the requirement to account for this spatial variability
and account for presence of iron and manganese interior to the site that were detected in samples taken for the 2010
report that may have included a contribution from the application of wastewater effluent prior to 2008. Therefore,
we believe that it is scientifically appropriate to install monitoring wells at the proposed locations in order to establish
background conditions.

Comment:
Please use caution if you intend to use groundwater quality data from the 2010 Eagle Resources study and report
to establish background metals concentrations as some of the wells in this study had turbidity in excess of the
levels recommended in the NCDEQ July 2012 “Evaluating Metals in Groundwater at DWQ Permitted Facilities:
A Technical Assistance Document for DWQ Staff” as mentioned in previous correspondence. Please also note
filtered samples are not acceptable for use in establishing metals concentrations at permitted facilities in
accordance with the May 13, 2013 policy memo by Jay Zimmerman, “Aquifer Protection Section Policy for Metals
Determinations Required by Title 15A, North Carolina Administrative Code, Subchapter 2L”.

Response:
We intend to use only data that we deem in our professional opinion to be representative of background
conditions.

Comment:
DWR also recommends that any new compliance monitoring wells used to monitor potential impacts from waste
applications be placed at the review or compliance boundary.

Response:
We will consult with DWR on the location of any new compliance wells if they become necessary.

C
Ground Water Monitoring
Plan Resubmittal – Submitted
on December 14, 2018

555 Fayetteville Street, Suite 900, Raleigh, NC 27601
[phone]
hdrinc.com

Transmittal
Date: Friday, December 14, 2018
Project: City of Raleigh Wrenn Road Facility
To: Rick Bolich, L.G., DEQ
From: Chris Brown, PE, HDR
Subject: Groundwater Permit

We are sending you: ☒ Attached ☐ Under separate cover via the following items:
☐ Shop drawings ☐ Prints ☐ Plans
☐ Samples ☐ Specifications ☐ Copy of letter
☐ Change Order ☐ Other:

Copies Date No. Description
1 Dec 13 2018 Letter from Eagle Resources – Relocated Wells

These are transmitted as checked below:
☒ For your approval ☐ Approved as submitted ☐ Resubmit
☒ For your use ☐ Approved as noted ☐ Submit
☒ As requested ☐ Returned for corrections ☐ Return
☒ For review/comment ☐ Other:
☐ For bids due ☐ Prints returned after loan to us

Remarks: Mr. Bolich –

HDR Engineering, Inc. of the Carolinas (HDR) is pleased to provide DEQ with the above item. This is
a follow up to comments received at our Oct 2017 meeting. The team has been working with the
adjacent land owner on acquisition of property.

We would like to meet in Jan 2019 to discuss a path forward.

Please let us know if you have any questions.

Copy to: Dennis Lassiter, Chris Phelps, Whit
Wheeler, Jesse Walker, Tracy McLamb -
City of Raleigh; Eric Lappala, Eagle
Resources; Samantha Black, Manish
Bhandari - HDR

Signed: Chris Brown 919.677.9350
[e-mail]

Eagle Resources, P.Å.
215 West Moore Street Southport, NC 28461
919-345-1013 www.eagleresources.com
Rick Bolich, L.G.
Assistant Supervisor
N.C. Dept. of Environmental Quality
Division of Water Resources
Water Quality Regional Operations Section
Raleigh Regional Office
3800 Barrett Drive
Raleigh, NC 27609

[e-mail]

December 13, 2018

Subject: Groundwater Monitoring Plan for City of Raleigh Wrenn Road Facility Permit WQ0002708

Dear Rick,

This letter transmits the revised locations of the four (4) proposed background monitoring wells for the
subject facility that are shown on the attached map. Wells PMW-2 and PMW-3 will be installed on
property recently acquired by the City of Raleigh. Well PMW-3 is to be accessed for installation from
the adjacent subdivision which has provided permission for same. The location of PMW-1 has not
changed from the original monitoring plan We have moved the location of PMW-4 to the location
shown on the attached map to provide better access for drilling equipment.

We are available at your convenience to meet to discuss the monitoring plan and these locations if it is
necessary.

Sincerely yours,

Eric G. Lappala, P.E., P.H.
Attachments: Proposed monitoring well location map

City of
Raleigh
Public
Utilties
Department
Eagle Resources, P.A.
215 West Moore Street
Southport, NC 28461
919-345-1013
[e-mail]
Project No.
24041.1
1
FIGURE
Approved: EGL
Design data and recommendations included herein are provided as a
matter of information and should not be used for final design. Rely only on
hard copy bearing consultants original seal and signature
Location of proposed background moniitoring wells
Wrenn Road Facilty.
Date: 11/28/18
Proposed Background Monitoring Wells
Property Boundaries (Wake County GIS)
EXPLANATION
Well No.Easting Northing
PMW-1 2126151.11 691215.39
PMW-4 2125522.18 687848.49
PMW-2 2124505.08 691694.17
PMW-3 2121970.6 688486.31

D
Minutes from Resubmittal
Discussion Meeting –
Meeting Held on January 31,
2019

Meeting Minutes
Project: City of Raleigh – Wrenn Road Facility Ground Water Monitoring Plan
Subject: Meeting with City and DEQ
Date: Thursday, January 31, 2019
Location: DEQ Offices, 3800 Barrett Drive
Attendees: Chris Phelps – City of Raleigh
Rick Bolich – DEQ
Brion Byers – DEQ
Eric Lappala – Eagle Resources
Samantha Black – HDR
Manish Bhandari – HDR
Chris Brown – HDR

Goal of the Meeting
The goal of this meeting was to gain verbal approval of the Wrenn Road Facility Ground Water
Monitoring Plan so the City may proceed to the implementation and monitoring phase. An
additional goal was to make DEQ aware of changes that may come to the existing Wrenn Road
Facility following the future expansion of Interstate-540 (I-540).
History of the Wrenn Road Facilties Ground Water Monitoring Plan
A brief history of the Wrenn Road Facility Ground Water Monitoring Plan was provided during
the meeting as follows:
 The current permit (WQ0002708) was issued in 2015, and allowed the continued
operation of the Wrenn Road Facility. Part of this permit was the requirement that the
City monitor ground water wells for manganese, iron, and arsenic.
 In February 2017, a revised monitoring plan was submitted to DEQ.
 In May 2017, comments on the revised plan were received by DEQ.
 In October 2017, the City/HDR provided responses to DEQ comments, and a meeting
was held with the City, DEQ, and HDR to discuss these responses. Changes to some of
the background wells were requested by DEQ during this meeting.
 In 2018, the City obtained a parcel of land adjacent to the Wrenn Road Facility. This
parcel provided options for locating background wells. This parcel will provide easier
access to monitoring well #3.
 In December 2018, revised background well locations were submitted to DEQ for review.
These locations were selected based on fieldwork conducted by Eagle Resources and
the well driller. Two well locations were added to the west of the Wrenn Road Facility.

Revised Well Locations
There are four proposed monitoring wells (PMWs). PMW -4 was relocated to avoid a drilling
access issue, and it is now on the access road. DEQ is interested in the ground water flow
directions for PMW -4, and requested a 5-ft contour map of this site. Additionally, a water table
map and water levels were requested.
Wells will be drilled into partially weathered rock, and are not considered bedrock wells. It is
estimated that the depth of these wells will be less than 50 feet. The nearby subdivision ground
water well might influence PMWs if they are to be drilled into partially weathered rock. It was
suggested that a monitoring device be put in to observe the diurnal influence of the subdivision
well. The partially weathered rock is a relatively high permeability, and there is no significant
change in water level based on a recent study. The screening level of the PMWs will be from
the bottom, across the water table.
Impacts of I-540 to the Wrenn Road Facility
In the future, I-540 will be expanded on a portion of the Wrenn Road Facility. It is expected that
this expansion will result in the abandonment of at least one MW, consumed 15 to 16 acres of
irrigation land, and change the compliance boundary. The I-540 design-build project is in the
early stage of design, and it is anticipated that it will be one year until the design is complete. A
conceptual drawing of where I-540 will be located was provided in the agenda. The City will deal
with the changes caused by the I-540 expansion project when the design is closer to
completion. The PMWs will not be impacted by I-540.
It may be beneficial to submit the ground water monitoring plan once changes from the I-540
project are established since construction will impact the water table. However, the City will
need to submit a permit modification after the new compliance boundary is established.
Alternatively, having a plan in place prior to I-540 construction may be beneficial as well to get
background data collected before construction for comparison purposes.
The City plans to wait to abandon wells impacted by I-540 until they can no longer use
associated the spray irrigation area. Although 15 to 16 acres of land will be lost due to the I-540
expansion, the City currently has excess capacity. However, the permit will still need to be
modified to reflect the new capacity.
Action Items and Next Steps
 HDR/Eagle Resources to provide existing subdivision water well locations, ground water
well levels, well depth, and a contour map to DEQ.
 DEQ will review information and generate a ground water flow map.
 HDR to resubmit the revised Wrenn Road Facility Ground Water Monitoring Plan to DEQ
for review.
These minutes were prepared by Samantha Black with HDR> Please provide comments within
5 days of receipt to [e-mail] or 919-232-6638.

E
Water Well Locations for
Subdivision Adjacent to the
Wrenn Road Facility

1

Appendix E – Water Well Locations for
Subdivision Adjacent to the Wrenn Road Facility
HDR has identified three wells located within the Glen Creek Community:
1. Well 1: One drinking water well is completely developed, and is located on the north side
of the community (Figures 1 and 2).
2. Well 2: A second drinking water well has been drilled, but is not currently in use, and is
located the south side of the community (Figures 3 and 4).
3. Well 3: The third well is an irrigation well, which supplies irrigation water to the
community (Figures 5 and 6).
Table 1 provides a summary of these community wells, and the following figures show
photographs of wells and their locations relative to the closest proposed monitoring wells
(PMWs).
Table 1. Glen Creek Community Wells
Well Use Latitude, Longitude Closest PMW
1 Drinking Water 35.6466, -78.5855 PMW -2
2 Drinking Water 35.6363, -78.5937 PMW -3
3 Irrigation Water 35.6503, -78.5803 PMW -2

Figure 1. Existing Drinking Water Well Located on the North Side of the Glen Creek Community
2

Figure 2. Existing Drinking Water Well Location Relative to PMW-2

Figure 3. Future Drinking Water Well Located on the South Side of the Glen Creek Community

Figure 4. Future Drinking Water Well Location Relative to PMW-3
3

Figure 5. Existing Irrigation Well Located on the North Side of the Glen Creek Community

Figure 6. Irrigation Well Location Relative to PMW-2

F
Ground Water Well Levels

City of Raleigh Ground Water Monitoring Plan
Wrenn Road Facility
Ground Water Well Levels
B-3 MP Elev 346.00 B-8 MP Elev 226.46 B-9 MP Elev 247.94
Date DTW WL EL Date DTW WL EL Date DTW WL EL
3/9/2017 19.70 326.30 42803.00 20.50 205.96 42803.00 11.20 236.74
7/5/2017 20.60 325.40 42921.00 21.10 205.36 42929.00 12.10 235.84
11/7/2017 22.80 323.20 43046.00 23.60 202.86 42937.00 12.30 235.64
3/8/2018 22.00 324.00 43167.00 22.30 204.16 43046.00 12.20 235.74
7/5/2018 22.40 323.60 43286.00 23.00 203.46 43167.00 11.40 236.54
7/12/2018 22.60 323.40 43293.00 23.20 203.26 43286.00 12.60 235.34
11/8/2018 21.50 324.50 43412.00 22.70 203.76 43293.00 12.50 235.44

G
Contour Map of Proposed
Monitoring Well Locations

City of
Raleigh
Public
Utilties
Department
Eagle Resources, P.A.
215 West Moore Street
Southport, NC 28461
919-345-1013
[e-mail]
Project No.
24041.1
1
FIGURE
Approved: EGL
Design data and recommendations included herein are provided as a
matter of information and should not be used for final design. Rely only on
hard copy bearing consultants original seal and signature
Proposed background moniitoring wells, existing
compliance wells, topography, modeled steady state
watertable elevations, and measured water level
elevations in July 2018, Wrenn Road Facilty Date: 02/02/19
Compliance Wells and July 2018 Water Level
Background Wells
Property Boundaries (Wake County GIS)
Land Surface Elevation
Modeled Steady State Watertable 2014
EXPLANATION
Well No.Water Table Elev
MW-B-9 235.34
MW-B-8 203.26
MW-B-3 323.4

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HDR Engineering, Inc. of the Carolinas
555 Fayetteville Street
Suite 900
Raleigh, North Carolina, 27601
919-232-6600

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