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CORROSION CONTROL STUDY
PIPE LOOP STUDY
REPORT SUPPLEMENT FOR THE
EXPANDED EXECUTIVE SUMMARY
PREPARED FOR:
CITY OF FLINT
By
Cornwell Engineering Group, Inc
as a subcontractor to
Arcadis
Cornwell Engineering Group
712 Gum Rock Court
Newport News, VA 23606
(757) 873-1534
January 18, 2021
ii
TABLE OF CONTENTS
Table of Figures ............................................................................................................................. iii
List of Tables ................................................................................................................................. iv
Introduction ..........................................................................................................................1
Current Conditions ...............................................................................................................1
WTP and Distribution System Water Quality .........................................................1
Lead in the Distribution System: LCR and Residential Sampling Data ................12
Pipe Loop Study Methods and Materials ...........................................................................17
Set Up and Equipment ...........................................................................................17
Daily Operations ....................................................................................................21
Sampling procedures and Analytical methods .......................................................24
Coupon Study Methods and Materials ...................................................................26
Study Operational Adjustments and Events ..........................................................26
Pipe Loop Water Quality ...................................................................................................30
Lead Service Line Rigs Water Quality ..................................................................30
Galvanized Pipe and Brass Fixture Loops .............................................................36
References ..........................................................................................................................40
iii
TABLE OF FIGURES
Figure 1 Weekly median pH at CSII and Tap (1/1/2016 – 6/30/2020) ................................. 4
Figure 2 WTP Tap pH Control Chart (1/1/2016 – 6/30/2020) .............................................. 4
Figure 3 pH percentile of all distribution system sites, excluding CSII (1/1/2016 –
5/22/2020) ............................................................................................................... 5
Figure 4 pH in the distribution system by WQP monitoring site (12/13/2017 -
5/22/2020) ............................................................................................................... 6
Figure 5 Orthophosphate residual at CSII and Tap (1/1/2016 – 6/30/2019) ......................... 7
Figure 6 Orthophosphate residual at CSII and Tap Control Chart (1/1/2016 –
6/30/2019) ............................................................................................................... 7
Figure 7 Orthophosphate residual in the distribution system by WQP monitoring
site (12/13/2017 - 5/22/2020).................................................................................. 8
Figure 8 Tap Alkalinity and DIC (1/1/2016 - 6/30/2020) ..................................................... 9
Figure 9 DIC in the distribution system (12/13/2017 - 5/22/2020) ..................................... 10
Figure 10 Free chlorine residual at CSII and Tap (1/1/2016 - 6/30/2020) ............................ 11
Figure 11 Free chlorine residual in the distribution system (12/13/2017 - 6/30/2020) ......... 12
Figure 12 Percent of lead measurements by compliance period ........................................... 14
Figure 13 Percentile distribution of 1st and 5th L samples in both 2019 compliance
periods ................................................................................................................... 15
Figure 14 Percent of lead measurements of 1st and 5th L samples for both 2019
compliance periods ............................................................................................... 16
Figure 15 Percentile distribution of lead by sample period and volume ............................... 17
Figure 16 Example LSL Rig (left) and Galvanized/Fixture Rig (right) ................................ 19
Figure 17 Early Operational Changes and Total Lead, using D1 and D2 as an
Example. ............................................................................................................... 29
Figure 18 Flowrate and Key Operational Adjustments on Total Lead using D1 and
D2 as an Example. ................................................................................................ 29
Figure 19 Measured temperature for flowing samples from the LSL rigs (5/9/2019 –
8/21/20) ................................................................................................................. 31
Figure 20 Measured free chlorine for flowing samples from the LSL rigs (5/9/2018 –
8/21/2020) ............................................................................................................. 32
Figure 21 pH box-plot for LSL rig flowing samples during 1.2gpm-Dose1 ........................ 33
iv
Figure 22 pH box-plot for LSL rig flowing samples during 1.5gpm-Dose1 ........................ 33
Figure 23 pH box-plot for LSL rig flowing samples during 1.4gpm-Dose2 ........................ 34
Figure 24 Orthophosphate box-plot for LSL rig flowing samples during 1.2gpm-
Dose1 .................................................................................................................... 35
Figure 25 Orthophosphate box-plot for LSL rig flowing samples during 1.5gpm-
Dose1 .................................................................................................................... 35
Figure 26 Orthophosphate box-plot for LSL rig flowing samples during 1.4gpm-
Dose2 .................................................................................................................... 36
Figure 27 Measured temperature for flowing samples from the galvanized and
fixture rigs ............................................................................................................. 37
Figure 28 Measured free chlorine for flowing samples from the galvanized and
fixture rigs ............................................................................................................. 37
Figure 29 Flowing sample pH from the galvanized and fixture rigs ..................................... 38
Figure 30 Flowing sample orthophosphate from the galvanized and fixture rigs ................. 39
LIST OF TABLES
Table 1 Changes to target WQPs on December 13, 2017 .................................................... 1
Table 2 Treatment chemicals used at Flint WTP ................................................................. 2
Table 3 Median CSII, Tap, and Distribution System WQPs ............................................... 2
Table 4 Historical 90th percentile lead and copper for LCR compliance .......................... 14
Table 5 Pipe Rig Study Test Material Information ............................................................ 20
Table 6 Timer-Operated Flow Schedule ............................................................................ 21
Table 7 Weekly Operator Schedule ................................................................................... 22
Table 8 Flow-Dose Analysis Periods for LSL Rigs by Operational Characteristics ......... 31
1
INTRODUCTION
This document serves as a supplement to the Pipe Loop Study Expanded Executive Summary. The
Expanded Executive Summary included a brief discussion of pipe loop study operations and
included loop study lead data, statistical analyses, and final optimal corrosion control treatment
(OCCT) recommendations for the City of Flint, MI.
This supplement provides further information regarding the loop study methods and materials,
current conditions in the distribution system, and discussion relating loop study data to current
distribution system conditions.
CURRENT CONDITIONS
The recommendations from the pipe loop study include maintaining the current target
orthophosphate residual at 3.5 mg/L PO4 until it is determined that all lead service lines (LSLs)
have been removed from the distribution system. This recommendation was based on the pipe loop
results, as well as LCR sampling data that showed that lead levels have decreased over time and
are currently relatively low: the second-half of 2019 compliance period had a 90th percentile of 4
µg/L. Flint is also rapidly replacing their lead service lines.
This section therefore provides a detailed analysis of current distribution system water quality
parameter (WQP) conditions, which are important to assess in relation to lead sampling data to
ensure Flint is maintaining stable distribution system conditions conducive to effective CCT
moving forward.
WTP and Distribution System Water Quality
Data from Flint WTP monthly operating reports were available from 2016 through June 2020 and
WQP monitoring data were available from late 2015 through mid-May 2020. For most analyses,
data were used after the official interim changes in target treatment on December 13, 2017 for
monitoring at the entry point and the Enhanced Water Quality Monitoring (EDWM) sites in place
in the distribution system (MDEQ 2017). Changes to target WQPs are shown in Table 1. No new
interim targets were set in the distribution system. This time period was determined to be the most
representative of current operating conditions at the Flint WTP and throughout the distribution
system, which is important when drawing conclusions from pilot data in the context of full-scale
impacts.
Table 1 Changes to target WQPs on December 13, 2017
Parameter Unit EP Target EP Range EDWM
Target
EDWM
Range
pH s.u. 7.5 7.2 – 7.9 7.5 7.2 – 7.9
Orthophosphate Residual mg/L as PO4 3.6 3.3 – 4.0 3.3 3.1 – 4.5
Free Chlorine Residual mg/L 1.5 – 1.8 1.4 – 1.9 -- --
2
Daily data from monthly operating reports (MORs) and weekly Enhanced Water Quality
Parameter Monitoring (EWDM) reports were utilized to assess Great Lakes Water Authority
(GLWA) influent water as measured at Control Station 2 (CSII), adjusted water quality as
measured at the plant tap, and distribution system water quality. The MORs also contained the
distribution system TCR free chlorine data used in this analysis. All location-specific WQP data,
excluding free chlorine measurements, were obtained from the available weekly EWDM reports.
Currently the Flint WTP adds chemicals for additional treatment to boost pH (when necessary),
free chlorine residual, and orthophosphate residual of purchased GLWA water. The chemicals
used and the dose median and ranges are shown in Table 2. Typical WQPs, as measured at CSII,
tap, and throughout the distribution system are shown in Table 3.
Table 2 Treatment chemicals used at Flint WTP
Chemical Purpose Unit Dose Median Dose Range
Orthophosphate*
(Phosphoric Acid) Corrosion Inhibitor mg/L as PO4 2.4 0.7 – 2.8
Sodium Hypochlorite Disinfection mg/L as Cl2 1.1 0.7 – 1.7
25% Caustic Soda pH adjustment mg/L 4.0 0.8 – 7.4
*Note: This is dose not orthophosphate residual. GLWA water entering the plant already has
orthophosphate residual around 1.2 mg/L as PO4
Table 3 Median CSII, Tap, and Distribution System WQPs
Measured Parameters Unit
CSII
(pre-
Adjust)
Tap Distribution
System
pH s.u. 7.3 7.6 7.6
Alkalinity mg/L as CaCO3 80 84 84
Total Hardness mg/L as CaCO3 102 102 102
Non-Carbonate Hardness mg/L as CaCO3 32 34 --
Calcium mg/L 28 28 28
Magnesium mg/L 7.8 8.0 --
Chloride mg/L 15 15 15
Sulfate mg/L 16 -- 17
Orthophosphate mg/L as PO4 1.3 3.6 3.5
Free Chlorine Residual mg/L 1.0 1.7 1.5
Calculated Parameters
Dissolved Inorganic Carbon (DIC) mg/L as C 21.2 21.1 21.1
CSMR mg/mg 0.93 -- 0.88
Parameters in Table 3 were analyzed due to their importance in CCT. Trending and analysis of
individual parameters will be discussed throughout this section.
3
For some parameters, control charts were developed as a way to characterize the consistency or
variability of the measurements and concentrations over a certain time period. Control charts
presented are Shewhart median control charts as described in Cornwell et al. (2015) and Grant
(1964). Control charts calculations involve grouping data and then identifying the median and
range of each group to characterize the data over a specific time period. The overall median of
these group medians plotted as a constant value over the given time period. Upper and lower
control limits (UCL and LCL, respectively) are based on this median and the overall median of
group ranges (i.e., median variability within the groups). The group medians are plotted as
individual data points. If group medians typically fall within the UCL and LCL, that indicates less
variability in the data. MOR data in these control charts were grouped weekly.
pH
Figure 1 presents weekly median pH measurements for CSII and the plant tap. Influent CSII
GLWA weekly median pH from 2016 to mid-2020 typically varied from about 7.2 to 7.5 with few
exceptions. CSII weekly median pH exhibited noticeable variability over the time period analyzed,
but the overall distribution of measurements did not appear to change dramatically over time. In
early 2017, the target pH leaving the tap was raised to 7.5. MORs showed the addition of 25%
caustic soda beginning in February 2017. Figure 1 shows the median pH coming from the tap
increased closer to a target pH of 7.5 mid-2017. Figure 2 is a control chart of the pH data at the
Flint WTP tap after pH adjustment, analyzed in two different time periods, before and after the
increase in pH set in December 2017 (Table 1). Figure 2 shows periods of time where median tap
pH falls outside of the UCL and LCL, which indicates room for improvement in pH consistency
leaving the plant.
4
Figure 1 Weekly median pH at CSII and Tap (1/1/2016 – 6/30/2020)
Figure 2 WTP Tap pH Control Chart (1/1/2016 – 6/30/2020)
5
The pH in the distribution system increased as well once the Flint WTP began dosing caustic.
Figure 3 shows a percentile distribution by year for all of the distribution system WQP monitoring
sites in the EWDM reports, excluding CSII. This figure shows a general increase in pH distribution
after 2017. It also shows that 2018-2020 distributions of pH measurements were similar and
relatively consistent. The 10th percentile to 90th percentile range was 7.39 to 7.72 in 2019 and 7.42
to 7.64 for 2020 (through 5/22/2020).
Figure 4 is a modified box plot of pH values at each distribution system site from 12/13/2017
through 5/22/2020 (after the target WQP changes outlined in Table 1). The median pH of all of
these sites during this time period at each site ranges from 7.53-7.65. Figure 4 shows little
variability in the middle fifty percent of distribution system pH data, with the difference between
the seventy-fifth and twenty-fifth percentiles of each site being less than 0.2. Figure 4 also shows
that the pH in the distribution system is overall well maintained within the target range of 7.2 –
7.9. The minimum pH at sites #14 (1) and #4 were both <7.2. These were singular values for both
sites and the next lowest value for sites #14 (1) and #4 during this time period was 7.27 and 7.20,
respectively.
Figure 3 pH percentile of all distribution system sites, excluding CSII (1/1/2016 – 5/22/2020)
6
Figure 4 pH in the distribution system by WQP monitoring site (12/13/2017 - 5/22/2020)
Orthophosphate
Orthophosphate residual, already present in the water purchased from GLWA, is boosted at the
Flint WTP and acts as a corrosion inhibitor in the distribution system. The orthophosphate residual
in finished GLWA water entering the WTP is about 1.2 mg/L as PO4. When the water reaches the
Flint WTP, phosphoric acid is added in order to increase orthophosphate residual to a target
residual of 3.6 mg/L PO4 (Table 1). The current target range requires the orthophosphate at the
entry point to be maintained within 3.2 mg/L PO4 to 4.5 mg/L PO4. Figure 5 and Figure 7 show
that orthophosphate residual leaving the WTP and in the distribution system has been well
maintained.
Figure 5 displays measured phosphate residual data from CSII and at the tap over time, which
visually appears to be relatively stable for both locations. Similar to orthophosphate at the tap, the
distribution system does not have much variation in the measured values at each WQP monitoring
site. Figure 6 is a control chart of the same data and shows that the orthophosphate residual at the
tap is well controlled. The bounds of the UCL and the LCL are relatively close to the median of
group medians, signifying low variability in weekly measurements. Additionally, the low number
of values outside these limits show that measurements are consistent and well controlled near the
overall median of group medians. Keeping the orthophosphate controlled as shown is essential to
maintaining the water chemistry entering the distribution system.
7
Figure 5 Orthophosphate residual at CSII and Tap (1/1/2016 – 6/30/2019)
Figure 6 Orthophosphate residual at CSII and Tap Control Chart (1/1/2016 – 6/30/2019)
8
Figure 7 is a modified box plot of orthophosphate measurements in the distribution system. This
figure shows that orthophosphate residual was well maintained in the distribution system, with no
values below 3.0 mg/L PO4 at any of the WQP sites. The median orthophosphate concentration
was typically close to 3.5 mg/L PO4, and each site has relatively consistent measurements: the
middle fifty percent of data, also known as the interquartile range (IQR), is contained within a
small range for each site.
Figure 7 Orthophosphate residual in the distribution system by WQP monitoring site
(12/13/2017 - 5/22/2020)
Alkalinity and Dissolved Inorganic Carbon
Dissolved inorganic carbon (DIC) was calculated for paired pH and alkalinity data from 2016 to
mid-2020 for CSII, tap, and distribution system WQP sites. Alkalinity and DIC from the tap are
shown in Figure 8. DIC and alkalinity data show similar trends over the time period analyzed. DIC
ranged from 18 to 19 mg/L as C, until around July 2017 when alkalinity and DIC both increased
and became more variable. Both parameters appear to have become more stable mid-2018, as
shown in Figure 8. After December 13, 2017, when target WQPs were changed, the alkalinity
ranged from 66 – 100 mg/L as CaCO3 and DIC ranged from 17 – 26 mg/L as C. DIC is a function
of both pH and alkalinity, so changes in pH have some effect on the calculated value.
9
Figure 8 Tap Alkalinity and DIC (1/1/2016 - 6/30/2020)
DIC in the distribution system appears stable with a median at all WQP sites around 21 mg/L as
C, as shown in Figure 9. Data included in Figure 9 spans the same time period of about two and a
half years as shown previously in Figure 7.
10
Figure 9 DIC in the distribution system (12/13/2017 - 5/22/2020)
Free Chlorine and Scale Analysis
Maintaining proper free chlorine residual is important for controlling bacteria and other
microbiological organisms that may be present in drinking water. GLWA water entering the water
treatment plant, measured at CSII, typically has a free chlorine residual within the range of 0.8 to
1.0 mg/L, shown in Figure 10. Beginning in June 2016, sodium hypochlorite has been added at the
Flint water plant to boost the free chlorine residual leaving the plant. Currently, the chlorine
residual is boosted to a target concentration of about 1.5 to 1.8 mg/L (Table 1). Maintenance of
free chlorine residual in the distribution system, in addition to disinfection, is important for
ensuring pipe scales are stable if crystalline oxidized lead compounds are found in pipe scales
(lead (IV)).
Free chlorine affects the oxidation and reduction potential (ORP) of the water, which has the
potential to impact pipe scales in the distribution system (Schock & Lytle 2011). A decrease in
ORP could lead to solids that are stable with higher ORP to transition into more soluble lead (II)
compounds (Lytle & Schock 2005). Pipe scale analyses on harvested Flint pipes completed by
Williams et al. (2018) showed crystalline layers near the pipe wall contained some oxidized lead
(IV), plattnerite (PbO2). Williams et al. (2018) mentions that this layer closest to the pipe wall was
mostly lead (II) compounds “cerussite (PbCO3) and lead phosphate” and contained “hydrocerussite
(Pb3(CO3)2(OH)2)” as well as the more soluble lead (II) oxide “litharge (PbO)”. Additionally,
Cornwell conducted scale analysis for two LSLs in late-2017 (Cornwell Engineering Group 2018).
11
Pipes were cleaned, sent to the University of Florida (UF), and scale layers were extracted by
visual and textural differences with assistance from Cornwell staff. One of the pipes, indicated in
Cornwell Engineering Group (2018) as F-Pb-2300, was the same pipe used in the study indicated
as A1 as shown in Table 5. Amorphous aluminum and magnesium were found, as well as
crystalline lead (IV) (plattnerite) in both pipes and lead (II) (hydrocerussite) in only F-Pb-2300
(A1). The presence of plattnerite in both analyses suggests maintaining free chlorine residual, and
therefore ORP, could be influential on the stability of some LSL scales when lead pipes persist in
the Flint distribution system.
Figure 10 shows that the free chlorine concentration leaving the WTP is typically within 1.6 to 1.8
mg/L.
Figure 10 Free chlorine residual at CSII and Tap (1/1/2016 - 6/30/2020)
Figure 11 displays a modified box plot of free chlorine residual measurements in the distribution
system at the Total Coliform Rule (TCR) monitoring sites from December 2017 through June
2020, sorted by descending median free chlorine residual which ranges from 1.1 to 1.8 mg/L. All
of the sites during this time period had a median free chlorine residual above 1.0 mg/L, though site
19 had minimum values below 0.2 mg/L.
12
Figure 11 Free chlorine residual in the distribution system (12/13/2017 - 6/30/2020)
Lead in the Distribution System: LCR and Residential Sampling Data
Flint is currently monitoring for lead and copper rule (LCR) compliance on a semi-annual basis.
In addition to sampling for compliance, the City collects supplemental lead data from residential
homes in order to further monitor the concentration of lead in the distribution system. The
compliance samples are the only ones that are used for determining potential action level
exceedance, but additional sampling and sampling methods are also helpful to provide more
insight to the distribution system. One of the additional sets of data collected is in the Flint’s
Residential sampling database. This data includes 250 mL, 750, and 1 L samples from different
residences in the City.
To supplement data obtained from the pipe loop studies, lead data from the distribution system
were used to compare to data from the pilot study. This analysis is shown in the accompanying
Expanded Executive Summary document. The 5th L compliance samples were used to make
comparisons with current system data to values obtained from the harvested lead service line pipe
loop study. Residential data (250- and 750-mL samples from the tap in the Flint distribution
system) were used to make comparisons to pipe loop data from the galvanized and brass fixture
loops.
For both the samples analyzed for loop studies by Cornwell, compliance, and the residential lead
data analyzed by Flint, the reporting limit for lead was 1 µg/L. Cornwell used the reporting limit
of 1 µg/L for measured values below the reporting limit, while EGLE uses 0 µg/L for analysis on
13
values below the reporting limit. In order to stay consistent with values used by EGLE, data listed
as 0 µg/L was kept at 0 and not changed to match Cornwell’s procedures for data analysis.
LCR Data
In 2018, revisions were made to Michigan’s lead and copper rule. These new revisions require a
second sample to be taken at homes with a lead service line in addition to the first liter draw (EGLE
2018). The second sample, at liter five from the tap, is intended to capture water that is more
representative of the service line. The highest lead and copper results from the two samples are
then used for compliance calculations of the 90th percentile. The 2018 Michigan LCR sampling
revisions were implemented beginning in the first compliance period of 2019. Additional
revisions, including lowering of the lead action level from 15 to 12 µg/L, will go into effect in
January 1, 2025 (EGLE 2018).
Flint has received two follow up or routine lead and copper tap monitoring and reporting violations
(SDWIS Violation Code 52). These violations occurred in the compliance periods beginning on
July 1, 2019 and January 1, 2020. These violations were issued when Flint failed to provide the
minimum number of samples required for compliance (60 samples). According to EGLE,
compliance is determined using only Tier 1 samples. Because the service line material is unknown
at the time samples are being collected, the City confirmed the service line materials after all of
the samples were collected. Revisions in the 2018 Michigan LCR also included changes in the
“tiering” for sampling sites. These revisions removed “copper with lead solder” from Tier 1 sites
and changed the designation to Tier 3 sites beginning in the 2019 compliance period. Therefore, if
only Tier 1 sites are used in compliance calculations, homes without lead pipes as service line
material or household plumbing are currently excluded from compliance sampling and results
(even if lead solder is present). Because Flint has been replacing Tier 1 sites at such a rapid rate,
EGLE has allowed Tier 2 sites to be used for compliance as well. Once all of the lead service lines
have been replaced, the Flint will move to the Tier 3 or “Other” category for compliance.
Flint switched back to GLWA water in mid-October 2015 and began adding orthophosphate in
early December 2015. Table 4 shows that for the compliance period immediately following the
switch back to GLWA and the addition of corrosion inhibitor (2016 January-June), Flint still had
a 90th percentile above the action level at 20 µg/L. After this compliance period, the 90th percentile
for lead has been below the current action level of 15 µg/L. Copper has been historically well
below the action level of 1300 µg/L in each compliance period, as shown in Table 4.
Data that was analyzed for compliance in the 2019 July-December period was only comprised of
49 samples. 123 total samples were taken during the sampling period, but only 49 of these were
Tier 1 sites.
14
Table 4 Historical 90th percentile lead and copper for LCR compliance
Compliance Period 90th Percentile Lead (µg/L) 90th Percentile Copper (µg/L)
2016 January-June 20 170
2016 July-December 12 120
2017 January-June 7 150
2017 July-December 6 90
2018 January-June 6 90
2018 July-December 4 50
2019 January-June 6 89
2019 July-December 4 60
Figure 12 shows that the percentage of lead samples in each compliance period that are below
detect has also increased since 2016. This visually shows lower lead values are more frequent than
they were in earlier sampling periods.
Figure 12 Percent of lead measurements by compliance period
The changes to the LCR implemented in the 2019 compliance period also updated the sampling
procedure to require the collection of a 1st and 5th L sample instead of just 1st L at each location.
The maximum lead value between these two samples at each LCR sample location is used for
15
compliance (EGLE 2018). Comparison of the percentile distribution of lead concentration between
the 1st and 5th L samples shown in Figure 13 show that the values between the two are similar, but
the 1st L is slightly higher. The 1st L sample is more representative of sources from household
plumbing while the 5th L is more representative of concentrations in the service lines. The
distributions look similar in both compliance periods. Figure 14 shows the same data but is
presented as the percentage of lead concentration in six different bins.
Figure 13 Percentile distribution of 1st and 5th L samples in both 2019 compliance periods
16
Figure 14 Percent of lead measurements of 1st and 5th L samples for both 2019 compliance
periods
Residential Sampling Data
Sequential sampling can be used to help identify the location of the lead source in the household
plumbing. Residential sampling involved sampling the first 250 mL and then immediately
sampling the next 750 mL as a separate sample. These two samples can indicate where the lead is
present within the first 1 L that comes from the customer’s tap. Residential data sampling was
initiated as supplemental to compliance data to help monitor lead and copper in customer homes.
Data analyzed in this section were from June 5, 2017 through August 20, 2020. The time periods
analyzed were separated into two 6-month periods per year, January through June and July through
December. These sample periods are similar to the compliance LCR periods but residential
samples in this data set were not used for compliance. Data were used up to the 2020 January
through June sampling period.
Figure 15 shows the percentile distribution of the 250- and 750-mL samples for the earliest set of
data available (2016 January-June) to the first half of 2020 (2020 January-June). Figure 15
supports observation of an overall reduction in lead observed from 2016 to 2020 in the previous
two figures. These percentile distributions show the 250 mL sample distributions in both years
may have slightly higher lead values overall. However, this difference in lead concentration
between the two sample volumes within the same sampling does not appear to be substantial.
17
Figure 15 Percentile distribution of lead by sample period and volume
PIPE LOOP STUDY METHODS AND MATERIALS
Set Up and Equipment
Water Sources
Water utilized during the equilibration of test materials was Flint WTP finished water, accessed
via hose bibs near the rigs. During the study period, test materials flowed with GLWA water routed
from Control Station #2 (CSII), with varying orthophosphate doses as test conditions dictated. This
water needed to be routed outside for a portion of the distance from CSII to the pipe rig study
location inside the plant. Water pressure was reduced to a target flowing pressure of under 20 psi
prior to entering the rigs via a pressure reducing valve (PRV). The main header line from CSII
connected to header manifolds which connected to the individual hoses for each rig. A bypass
valve was installed to serve as a bleed line in an effort to prevent the hose from freezing during
colder weather.
Pipe Rig Design
An example LSL rig and an example galvanized/faucet rig are shown in Figure 16.
Four LSL rigs located in the Flint WTP flowed with finished Flint water prior to the start of this
study as part of previous research by others, described in Williams et al. (2018). These four rigs
contained four harvested LSLs each, for a total of sixteen LSL pipes that were available for testing.
18
Each LSL was approximately 48” in length, though this length varied, with an internal diameter
(ID) of ¾” (Williams et al. 2018). Water entered the rigs from a hose connection near the bottom
of the rack. Flow control and measurement was possible at the rig- and pipe-level via diaphragm
valves and rotameters. Each pipe was able to get a different orthophosphate dose on the LSL racks
due to each pipe having a chemical feed check valve and static mixer, allowing for greater
flexibility in the test conditions. There were sample taps per-pipe after the static mixers which
were originally used for flowing sample collection but it was apparent that flowing samples
collected at this location increased the flowrate of the pipe, thus diluting the sample. Once noticed,
flowing sample collection was adjusted to the same sample valve used for stagnation metals
sampling, located after the test material. An electrically actuated ball valve, controlled by a timer
on the rig, was located on the effluent line of each rig. For this study, the timers were also
connected to an outlet which allowed for power-cycling the orthophosphate pumps to feed
chemical only when the valve was open.
Four additional rigs were set up in early March 2019 to supplement the data generated from the
LSL rigs with data from harvested galvanized pipe (instructions to outside personnel providing
these pipes for testing were to only provide galvanized lines previously preceded by lead) and new
brass fixtures. These newer racks contained one chemical feed port on the rig header, allowing
each rig to only test one orthophosphate dose condition. Flow measurement was possible for the
rig itself and for individual pipes and flow control was achieved by diaphragm valves located on
each pipe prior to the test materials. The three galvanized lines were located on the top shelf of the
rack. Five brass faucet-bodies were daisy-chained and connected to Schedule 40 PVC on the shelf
below the galvanized lines. Similar to the LSL racks, a timer controlled an electrically actuated
ball valve on the effluent line and an electrical outlet located on the rig for the orthophosphate feed
pumps.
The harvested LSLs and galvanized pipes were connected to the PVC piping by plastic tubing
fitted over the test material attached to the PVC and test material by hose clamps. Threaded
connections on the new brass fixtures allowed for direct connection to the PVC piping by using
fittings.
19
Figure 16 Example LSL Rig (left) and Galvanized/Fixture Rig (right)
Lead Service Lines and Materials Description
The harvested LSLs and galvanized pipe were removed from the distribution system by others as
part of ongoing replacement efforts in Flint. The harvested LSLs were mostly already connected
to the rigs, apart from “Pipe 1” on each rig (e.g. A1, B1, etc.) which were harvested and placed in
the rigs in late 2017. Table 5 shows the known information regarding the harvested materials from
the distribution system. The five brass fixtures daisy-chained together per rig were the faucet body
portions of the Proplus Model KF1885.
20
Table 5 Pipe Rig Study Test Material Information
LSL Rigs (Rigs A – D) Galvanized/Fixture Rigs (Rigs E – H)
Study
ID Material Location ID†
Stud
y ID Material Location ID
A1 Harv. LSL 2300 Vernon Ave.‡ E1 New Brass N/A
A2 Harv. LSL 2614-02 E2 Harv. Galvanized 1921 Chippewa St
A3 Harv. LSL 2614-03 E3 Harv. Galvanized 2302 Basset Place
A4 Harv. LSL 2614-01 E4 Harv. Galvanized 1715 Tacoma
B1 Harv. LSL 2317 Vernon Ave.‡ F1 New Brass N/A
B2 Harv. LSL 742-2 F2 Harv. Galvanized 1219 Mann
B3 Harv. LSL 742-4 F3 Harv. Galvanized 518 E 12th St
B4 Harv. LSL 742-3 F4 Harv. Galvanized 2465 Gibson St
C1 Harv. LSL 2417 Vernon Ave.‡ G1 New Brass N/A
C2 Harv. LSL 2301-3 G2 Harv. Galvanized 1232 Roosevelt
C3 Harv. LSL 2301-2 G3 Harv. Galvanized 3310 Clairmont
C4 Harv. LSL 2301-4 G4 Harv. Galvanized 1115 W 2nd
D1 Harv. LSL 2402 Vernon Ave.‡ H1 New Brass N/A
D2 Harv. LSL 749-1 H2 Harv. Galvanized 708 Stockton St
D3 Harv. LSL 749-3 H3 Harv. Galvanized 714 Oak
D4 Harv. LSL 749-4 H4 Harv. Galvanized 601 Asylum
Notes: † LSL location IDs are the written identifier codes on the existing tags, present before
the start of the present study
‡ These pipes have “Vernon St.” written on the tags, but this street does not exist in Flint,
and therefore was assumed to be Vernon Ave.
Timer Flow Schedule
Each pipe rig had a digital timer which controlled power to an outlet and the rig’s electrically
actuated ball valve based on the set schedule. The LSL rig timer schedule during the equilibrated
lead period used for data analysis is shown in Table 6. Table 6 also shows the galvanized and
fixture rig schedule, which was adjusted in late 2019 to increase stagnation time to eleven hours
from the previous eight hours.
21
Table 6 Timer-Operated Flow Schedule
LSL Rigs (Rigs A – D) Galvanized/Fixture Rigs (Rigs E – H)
Time Valve Position Time Valve Position
12:00 am Closed 10:00 am Open
2:30 am Open 10:30 am Closed
3:00 am Closed 12:30 pm Open
11:00 am Open 1:30 pm Closed
11:30 am Closed 3:30 pm Open
2:00 pm Open 4:00 pm Closed
3:00 pm Closed 6:30 pm Open
4:30 pm Open 7:00 pm Closed
5:00 pm Closed 10:30 pm Open
7:30 pm Open 11:00 pm Closed
8:00 pm Closed
11:30 pm Open
Study Equipment
There were two general categories of equipment utilized for this study apart from the pipe rigs
themselves: chemical feed equipment and sampling and analytical equipment. The chemical feed
equipment consisted of the peristaltic pumps, pump heads, and other items necessary to dose
orthophosphate to rigs during periods of flow. Peristaltic pump drives were outfitted with multiple
stacked pump heads in order to feed the same dose to multiple pipes. Pump-specific tubing was
utilized for carrying the orthophosphate dilution from the storage tanks to the chemical feed ports
on the rigs. The feed tubing was inserted into the existing chemical feed ports on each pipe using
a tubing adapter. As mentioned previously, the peristaltic pumps were plugged into a timer-
controlled outlet to ensure orthophosphate was only dosed during periods of flow. The
orthophosphate product utilized for this study was a sodium-neutralized orthophosphate product,
trade name Shannon Chemical Corp. SLI-5179. This product is specified as 36% by weight
orthophosphate as PO4 (Shannon Chemical Corporation).
Daily Operations
Cornwell had a dedicated engineering staff member on site as rig operator to complete daily tasks
required to produce data for this study. Tasks included sample collection for stagnating and
flowing samples, flowing sample WQP analysis, chemical feed dilution preparation, collecting
flow and pressure readings, performing rig maintenance as necessary, and ensuring data was
logged and entered into the data sheets.
The schedule shown in Table 7 summarizes the operational tasks regularly performed by Cornwell
throughout the week and these individual tasks are described in more detail below. The discussion
in this section applies primarily to the period of the study which was determined to have
equilibrated lead which was used for analysis and to make recommendations, as described in the
loop study Expanded Executive Summary document. This time period will occasionally be
22
referred to in this section as the study analysis period. Major operational changes will be discussed
in a separate portion of this section.
Table 7 Weekly Operator Schedule
TASK † MON TUE WED THU FRI
Collect Stagnation Samples
(Lead)
Collect Stagnation Samples
(PO4) ‡
Collect Flowing Samples and Test
(pH, Temperature, PO4) (Cl2 - weekly)
Record Rig Pressure and Flow x3 x3 x3 x3 x3
Record Individual Pipe Flow x3 x3 x3 x3 x3
Record Chemical Pump Flow x3 x3 x3 x3 x3
Record Daily Cumulative Flow
Record Daily Chemical Dilution Usage
Upload Data using Data Sheet and Excel File
Create Chemical Feed Dilution As
Needed
As
Needed
As
Needed
As
Needed
As
Needed
Adjust Pump Tubing/ Troubleshoot Pumps As
Needed
As
Needed
As
Needed
As
Needed
As
Needed
Note: † Sample collection frequency was adjusted based on holidays and operator availability on
a case-by-case basis
‡ Stagnation water quality parameters collected from June 2019, typically on a regular
basis
Stagnant Sample Collection
Prior to the first flow period on a stagnation sampling day, labels were first filled out and applied
to sample bottles. Stagnant samples were collected from all pipes near the end of the longest
stagnation period of the flow schedule shown in Table 6. Prior to collecting the samples for each
pipe, it was important to first close the manual ball valves located after the test materials and waste
a set amount of water which was not in contact with the test material. After samples were collected,
half of the samples were prepared for filtered lead analysis each sampling period such that each
pipe had one filtered lead sample per week. Clean syringes and new syringe filters were used to
filter 50 mL of sample into clean, labelled bottles. Chain of custody (COC) forms for the collected
samples were filled out and a tracking file was updated when samples were packed for shipment.
Typically, once per week beginning in June 2019, stagnant samples were collected and analyzed
for orthophosphate at the end of the stagnation period similar to stagnation lead samples.
Flowing Sample Collection
During the equilibrated period used for lead data analysis, flowing water quality was typically
analyzed twice per week as shown in Table 7. Free chlorine per-rig was typically measured weekly.
23
This schedule allowed time to perform the “bathtub-fill” events on Fridays, which will be
discussed in the General Operations and Maintenance portion of this section. Samples were
collected, as feasible, over the course of the workday flow periods depending on the rigs sampled
on a given day. Sample pH, temperature, orthophosphate, and free chlorine were measured for
flowing samples according to the procedures described in the Sampling Procedures and Analytical
Methods section of this document.
Prior to the first flow period, a sample from the sample tap was collected from one of the rigs for
conditioning the pH probe before flowing samples were collected. When both sets of rigs were
operating with GLWA water and varying orthophosphate doses, timer schedules were staggered
to ensure each set of rigs had enough flow available. This staggered schedule enabled the operator
to pull samples from as many pipes as possible from the LSL rigs (Rigs A-D), test WQPs on these
samples, then collect as many samples as possible from the galvanized and fixture rigs (Rigs E-H)
once the first flow period for these rigs began. Between sampling events, the pH probe was
reconditioned in water from the GLWA bleed line. After all flowing samples are analyzed, the pH
probe was stored in storage solution and the lab area was cleaned and organized. During the time
period used for lead data analysis, the pH probe was cleaned and calibrated weekly, typically on
Monday.
General Operations and Maintenance
When on-site, the rig operator visually assessed the rigs to detect potential leaks. When a leak was
detected at the connection to the test material, it was fixed by tightening the hose clamps in place.
Leaks found at any other connection on the rig were resolved by undoing the connection, removing
damaged thread tape, applying new thread tape, and securing the connection. Flint WTP staff
provided additional maintenance assistance as necessary.
Daily cumulative flows for rigs A-D were recorded between flow periods 2 and 3. Remaining
dilution volume was recorded after flow period 3. Flowing pressure and flow rates were recorded
for each pipe during each flow period during which an operator was on site. During the side-by-
side coupon study, water would be taken from the appropriate pre-LSL tap during flow period 2
to prepare coupon samples.
Rig flowing pressure, rig flow rate, and individual pipe flow rate were typically recorded three
times each day an operator was on site. Instantaneous flow meters (rotameters) allowed for the
flow rate to be visibly observed and recorded by the operator and pressure was recorded from the
pressure gauge situated on the common line near the beginning of each rig, shown in Figure 16.
Cumulative flow was recorded daily from flow totalizers on each pipe (LSL rigs) and each rig
(galvanized and fixture rigs). The volume of orthophosphate dilution remaining was also recorded
daily in order to track usage. Stagnant samples were taken for lead analysis approximately twice
per week. Chemical feed rates were reviewed after each water quality parameter test. Pump rates
were initially set based on concentration calculations and were adjusted using the ratio method as
needed throughout the study. Rig pressures and flows, individual pipe flows, and chemical pump
24
flows were recorded daily. Operating procedures included documenting readings from either flow
meters, flow totalizers, or the digital pump displays. Chemical use per day was recorded daily by
reading the graduation on the storage tanks. The chemical use and flow totals were used as a double
check on the flow rates and timer operation. Pump tubing was adjusted for the peristaltic pumps
at least weekly or more frequently if conditions dictated. Tubing was adjusted by opening the pump
head and drawing an unused section of tubing into the pump head before closing it again. Sections
of tubing were replaced after the entire section had been used in the pump head.
Typically, every Friday beginning in February 2019, LSLs were put through a “bathtub fill” event.
These pipes would be allowed to flow at 3 gpm of unadjusted GLWA water for 30 minutes. This
process was completed once every three weeks per pipe. During this time, chemical feed lines
were inspected and adjusted as necessary.
Chemical Dilution
Chemical dilutions of orthophosphate product Shannon Chemical Corp SLI-5179 were prepared
as needed according to ratios set by feed calculations and expected usage rates. For example,
beginning in May 2019, storage tank “OS-1” was prepared with a 1:400 dilution. Unadjusted
GLWA water was utilized as dilution water which negligibly impacted the amount of phosphate
in the feed stock. Dilutions were prepared during periods of stagnation by first adding the measured
SLI-5179 to the storage tank, filling to the 100 L line with GLWA water, and stirring.
Sampling procedures and Analytical methods
Sampling Procedures
Flowing samples were originally analyzed 3 times per week for pH, temperature, and
orthophosphate. Once the “bathtub fill” events began, these analyses were performed twice per
week to accommodate the new workload. Flowing samples were taken by manual sample grabs
from the sample taps downstream of the test materials after allowing pipes at least five minutes to
flow before sampling. After the sample tap valve was opened, the ball valve downstream of the
tap needed to be actuated in order for water to flow from the tap. The first 500-750 mL of water
was wasted from each line on a rig. The manual ball valves were then reopened and the sample
taps closed to allow the rig to return to its typical flowing state. This process was repeated for
every line on one rig. After allowing all lines to return to their standard flowing state,
approximately 400 mL was collected from each line by manually actuating the sample taps and
closing the post-tap ball valve. These samples were used to immediately analyze pH and
temperature and to measure orthophosphate residual. This process was repeated for each rig. The
same flowing sample process was used to measure free chlorine for one pipe on each rig.
Lead stagnation samples were collected typically twice weekly, one sample from each pipe.
Sample bottles were prepared by affixing a label that indicated the line to be sampled, the date and
time of the sample grab, sampler name, sample number and analysis to be completed. After
preparing the sample bottles, samples were collected after water had stagnated in the test materials
25
for approximately eight hours (LSL rigs) or eleven hours (galvanized and fixture rigs). These
samples were collected by manually closing all ball valves immediately downstream of the sample
taps. Taps were individually manually actuated and the appropriate volume of water was wasted
from each line on a rig into a graduated cylinder. The amount to be wasted was determined using
volume calculations as well as a profile analysis and was 80 mL for each of the brass lines, varied
from 95 to 130 mL for LSLs, and varied from 95 to 250 mL for the galvanized pipes. Stagnation
sequential samples were also collected during the study to help assess wastage calculations. After
wasting, a sample of approximately 250 mL was collected in an appropriately labeled sample
bottle. This process was repeated for each rig until all lines had been sampled. Once per week, an
aliquot of the stagnation sample from each test material was passed through a 0.45 µm pore
diameter MCE filter to assess filtered lead. These samples were filtered by drawing approximately
25 mL of the sample into a clean syringe, attaching a new 0.45 µm pore diameter MCE filter, and
expelling the sample through the filter into an appropriately labeled, new or cleaned sample bottle.
This process was done twice for each sample to have a total filtered sample volume of
approximately 50 mL. There were instances in which the filtered lead exceeded the total lead for
the same sample. This will be discussed further in the Study Operation Adjustments and Events
section of this document.
Analytical Procedures
Temperature and pH were measured using a Hanna Edge pH meter and accompanying probe as
soon as possible after collecting the flowing grab sample. Meter calibration and probe cleaning
occurred typically weekly during the study analysis period. Before collecting the flowing samples,
the probe was first removed from the storage solution and immersed in a stagnation sample to
allow the probe to equilibrate. Flowing and stagnation samples were collected on different days of
the week, allowing this sample to not affect other sampling efforts. As soon as feasible after
collecting samples, the probe was immersed in the test samples and the operator collected readings
for temperature and pH. Samples were all measured in cleaned glass beakers and stirred with a
magnetic stirrer rod and associated stirring plate during sample analysis. This process was
completed for other samples, and if necessary, the probe was temporarily stored in the stagnation
sample used for probe equilibration between flow periods. After sampling was finished for a given
day, the probe was reinserted into storage solution and the station was cleaned.
Sample orthophosphate was measured using a Hach DR900 and Orthophosphate sample kits (trade
name Hach Test N’ Tubes) according to Hach Method 8048. Due to this method having a stated
range maximum of 5.0 mg/L as PO4, a 1:2 dilution was performed for all samples coming from
lines with target orthophosphate concentrations of 5.0 mg/L as PO4 using a 100 mL volumetric
flask and TenSette pipet. The measurements for these lines were recorded as presented by the
instrument, but calculations in the analysis files corrected for this dilution.
Free chlorine was measured using the Hach DR900 according to Hach Method 8021. Samples
were measured typically weekly due to this parameter not being deliberately adjusted for the study.
26
Stagnation samples tested for total or filtered lead were sent to Cornwell Laboratories in Newport
News, VA for analysis via EPA Method 200.9. After receipt in Newport News, samples were
acidified in the sample bottle to a pH of less than 2.0 using 1:1 HNO3.
Coupon Study Methods and Materials
A limited coupon study was conducted alongside the pipe loop study in order to provide further
information regarding the lead solubility of the water entering the harvested LSLs. At first, sixteen
total lead coupon assemblies were set up onsite for testing. These assemblies consisted of a lead
coupon hanging from a plastic hook superglued to a plexiglass piece. The original conditions tested
consisted of duplicates collected twice per week from pipes of each target orthophosphate dose.
Four additional coupons were tested using water from the 3.5 mg/L as PO4 target orthophosphate
dose but with different immersion periods: two coupons were immersed in fresh water every day
an operator was on-site and two different coupons were immersed in new water every week. In
October 2018, many of these conditions were discontinued and only select coupons were
continued. Single replicates of the GLWA water, 2.0, 3.0, 4.0 and 5.0 mg/L as PO4 twice per week
conditions were continued. Both duplicates of the 3.5 mg/L as PO4 twice per week conditions
continued. The side-by-side coupon study was discontinued in January 2020.
Fresh water for coupon samples was collected from LSL rigs after orthophosphate dosage but
before water contacted the test materials. At least five minutes after the beginning of a flow period,
water was drawn from the pre-LSL sample tap into a clean, labeled coupon sample bottle from a
pipe with the appropriate orthophosphate test condition. Coupon assemblies were then carefully
transferred from the previously stagnating water to the freshly collected water. The bottles were
filled as much as possible and the coupon assemblies did not have holes in order to allow for
samples to be headspace free when stagnating.
As mentioned in the Expanded Executive Summary document for this study, the LSL rig sample
taps utilized for this coupon study were noted to increase flow for the line being sampled
potentially due to no upstream flow control. For this reason, flowing samples were collected from
the sample taps immediately following the test materials starting in July 2018. However, for the
purposes of this coupon study, samples continued to be collected from before the LSLs. Therefore,
fresh coupon water during this coupon study likely contained slightly less orthophosphate than the
target orthophosphate typically flowing through the pipes being sampled.
Study Operational Adjustments and Events
This section aims to provide a summary of major operational changes or events during the entire
study period, beginning when Cornwell was first onsite and extending into the study analysis
period. A significant amount of information in this section has also been presented in the study
Expanded Executive Summary document.
27
Lead Service Line Rigs
In March 2018, Cornwell staff arrived on site and began collecting samples. Rigs A, B, and D were
switched to GLWA water plus sodium orthophosphate dilution, if applicable, on April 5, 2018.
Rig C was switched to GLWA water plus caustic soda dilution and appropriate orthophosphate
doses on April 9, 2018. In early May 2018, the caustic feed was turned off for Rig C, effectively
creating triplicate pipes for the 1.2, 2.5, 3.0, and 4.0 mg/L as PO4 conditions. From May 22, 2018
ball valves post-LSLs were closed prior to stagnation sampling to isolate the individual test
materials and from July 23, 2018 flowing samples were collected post-LSL in order to prevent
orthophosphate dilution in samples collected. In July 2018 and early August 2018, initial wastage
was included in the flowing sample collection procedures. Figure 17 shows the impact of the above
operational changes on total lead, using pipes D1 and D2 as an example. There are several data
points in these figures higher than the maximum y-axis values, but the scales were zoomed in to
show trends. Note the increase in apparent particulate lead during the 1 gpm operational period
beginning around the same time post-LSL ball valves were closed prior to stagnation sampling.
Pressures were increased for the LSL rigs in early October 2018 due sample taps not flowing post-
LSL when opened during a rig flow period. Pipe C3 disconnected shortly after in mid-October
2018, pressures were then decreased, and pipe C3 was reconnected with new vinyl tubing a few
days later. This tubing connects to the outer diameter of the LSLs and the PVC piping. However,
this new tubing failed several days after reinstallation and was replaced again with thicker tubing.
In December 2018, tubing sections began to be replaced with braided vinyl tubing post-LSLs. It
was also observed approximately at this time that pipes did not appear to be flowing full or there
was trapped air in the tubing connecting the LSLs to the PVC piping. Attempting to resolve this
issue without major rig modifications failed. Also, in December 2018 a stagnation sampling
flowrate of about 0.5 gpm was enacted and pH meter calibration and cleaning increased to weekly.
Another LSL disconnected in late December 2018, and by the end of January 2019 all of the post-
LSL tubing was replaced with braided tubing.
Several further operational adjustments were made in an attempt to understand erratic lead levels
noted in the rigs. Filtered lead samples were regularly collected beginning on February 12, 2019.
Between February 18 and 19, 2019, pipes D1 and D2 operated at 1.5 gpm, several pipes were
operated for 30 minutes at 3 gpm, and investigative sampling efforts occurred. Despite a low-flow
bleed line, a header freeze occurred before the morning of February 28, 2019. Once thawed, all
pipes were adjusted from 1.0 to 1.2 gpm on February 28, 2019. Once header freezing was no longer
a concern, all pipes were again adjusted up to 1.5 gpm on May 20, 2019.
The regular schedule of “bathtub-fill” events, which consisted of adjusting LSLs to 3 gpm for
thirty minutes every three weeks, began in May 2019 and flowing water quality parameters were
adjusted to twice per week to accommodate. Stagnant orthophosphate began to be collected once
per week on Fridays in June 2019. To illustrate the impact of increasing the pipe flowrates and
beginning a regular schedule of exposing pipes to 3 gpm for 30 minutes, Figure 18 shows D1 and
D2 lead data from early September 2018 onward delimited by target flowrate. For analysis
28
purposes, data collected during the short 1.5 gpm period for pipes D1 and D2 between February
18 and 19, 2019 were not included in the 1.5 gpm data used for the comparisons described in Table
8 and the Expanded Executive Summary report. Pipes D1 and D2 were maintained at the same
orthophosphate target dose for the entire duration of the test. All other pipes were switched to a
different target dose than the original test conditions on February 24, 2020, but D1 and D2
maintained a target orthophosphate concentration of 3.5 mg/L as PO4 throughout the study.
The bathtub fill event procedure was adjusted in August 2019 in order to prevent potential
orthophosphate feed interruptions after an operations error caused the 4.0 mg/L as PO4 conditions
to not have phosphate for a few days in July 2019. Orthophosphate doses were refined in
September 2019 to get more consistent readings closer to targets. The bleed line flow rate needed
to be increased after another line freeze on December 11, 2019 which depressurized the rigs and
potentially drained the rigs for a period of time before rigs were flowing again in the second flow
period of the day. The pre-LSL vinyl tubing ruptured for pipes A1 and A2 in January 2020 and for
pipe C3 in February 2020 and these tubing connections were reattached by plant maintenance staff
before the Cornwell operator could replace the connections with braided tubing.
In early 2020, it was noticed that the number of samples where the filtered lead exceeded the total
lead appeared to increase and the difference between the two readings also increased albeit at the
low lead levels being measured. Suspected samples were re-run by the laboratory and data files
were updated. However, this issue again came up in May 2020. The exact cause of the difference
was never determined but out of precaution washed laboratory bottles for filtered lead analysis
were no longer used and bottles were switched to entirely new bottles for all lead samples in June
2020. Also, all Flint samples were run by themselves on the instrumentation following extensive
machine clean out.
29
Figure 17 Early Operational Changes and Total Lead, using D1 and D2 as an Example.
Figure 18 Flowrate and Key Operational Adjustments on Total Lead using D1 and D2 as an
Example.
30
Galvanized and Fixture Rigs
The galvanized and fixture rigs were assembled in March 2019 in order to assess orthophosphate
dose performance on materials other than LSLs due to the rapid replacement of LSLs in the Flint
distribution system. These rigs flowed in a limited operations capacity during the equilibration
phase when the pipes flowed on finished Flint water. Stagnation samples were collected twice per
week for these lines. Four galvanized pipes were available shortly after the rigs were built, but the
remaining eight galvanized pipes were not delivered until fall 2019.
Stagnation time was increased for these newer rigs on December 16, 2019 from eight hours to
eleven hours. Stagnation sampling waste volume was adjusted December 19, 2019. All pipes
remained on finished Flint water until rigs were switched to GLWA water with varying target
orthophosphate doses, using SLI-5179 dilution, on April 20, 2020. Regular data collection
occurred for these rigs beginning on April 23, 2020. On June 17, 2020, the target flowrates for the
galvanized lines and brass fixture lines were adjusted to 1.5 gpm and 1.0 gpm, respectively.
In September 2019, the automatic effluent ball valve for Rig F was noted to have a slight leak
during stagnation and this issue was believed to be solved at the time. However, in late July 2020
and early August 2020, the automatic ball valves were noted to be apparently leaking during
stagnation and were adjusted accordingly. In mid-September 2020 these valves were checked and
adjusted, if necessary, and regularly checked to ensure no leakage during stagnation. Similar to the
LSL rigs, filtered lead samples showed much higher lead numbers than the total lead figures for
certain periods of time, especially in early 2020 and May 2020. Certain suspect samples were rerun
and washed bottles were no longer used for sample collection beginning in early June 2020.
PIPE LOOP WATER QUALITY
The rig water quality and operational data presented in this section is shown for the time periods
coinciding with the study analysis periods used to make recommendations. For the LSL rigs,
therefore, data presented in this section is shown for samples or measurements collected within
the flow-dose analysis periods shown in Table 8, or between May 9, 2019 and August 21, 2020.
Table 8 is reproduced from the Expanded Executive Summary document for reference. For the
galvanized and fixture rigs, these data were collected between when the rigs were switched to
GLWA water in late April 2020 through August 20, 2020.
Lead Service Line Rigs Water Quality
This section presents the WQPs for the LSLs for each of the four different lead service line loop
flow-dose periods as outlined in Table 8. As mentioned previously, the Cornwell rig operator
regularly collected data for pH, temperature, orthophosphate, and free chlorine. Additionally, the
rig operator checked individual pipe and rig flows, rig pressures, daily totalized flow, chemical
feed flowrates, and orthophosphate dilution remaining.
31
Table 8 Flow-Dose Analysis Periods for LSL Rigs by Operational Characteristics
Operational Time
Period ID
Phosphate Dose
Regime
Target Flowrate per
Pipe (gpm) Date Range
1.2 gpm-Dose1 Original (Dose 1) 1.2
5/09/19 to 5/19/19
and
11/1/19 to 2/23/20
1.5 gpm-Dose1 Original (Dose 1) 1.5 5/20/19 to 10/31/19
1.2 gpm-Dose2 Switched (Dose 2) 1.2 2/24/20 to 6/15/20
1.4 gpm-Dose2 Switched (Dose 2) 1.4 6/16/20‡ to 8/21/20†
Notes:
† Statistical analyses completed for data through 8/13/20
‡ Stagnation lead samples collected 6/16/20 prior to the flowrate change
Figure 19 shows temperature measured during flowing sample collection for all samples collected
from the LSL rigs, with each flow-dose period indicated on the figure. Flowing temperature varied
seasonally and peak temperatures typically occurred in August or early September. Note these
readings were collected on flowing water samples and it is possible that the ambient temperature
could have impacted stagnant water temperature in the pipes, though this parameter was not
measured.
Figure 19 Measured temperature for flowing samples from the LSL rigs (5/9/2019 – 8/21/20)
32
Figure 20 shows free chlorine measurements during the study which were collected per-rig,
typically once per week. Disinfectant residual was not supplemented during the test period and
varied seasonally. However, measured free chlorine was typically above 0.75 mg/L as Cl2. The
lowest free chlorine residuals were measured in the late summer of 2019, with the minimum of
0.20 mg/L measured from the Rig A flowing sample in early August 2019.
Figure 20 Measured free chlorine for flowing samples from the LSL rigs (5/9/2018 –
8/21/2020)
Flowing water pH was measured regularly from samples collected from the LSL rigs, typically
twice per week during the study analysis period. Measured pH was generally between 7.4 and 7.6
s.u. excluding occasional variability and lower than typical measurements in early-June 2019.
Figure 21, Figure 22, and Figure 23 show the distribution of pH measurements for the 1.2gpm-
Dose1, 1.5gpm-Dose1, and 1.4gpm-Dose2 data collection time periods, respectively.
Measurements in these figures were grouped by the target orthophosphate for the pipes during the
flow-dose time period analyzed. Summary data for the 1.2gpm-Dose2 time period is not shown
due to these data not being utilized for statistical analyses as described in the Expanded Executive
Summary document. Figure 22, Figure 23, and Figure 24 show that pH measured in the rigs were
typically similar between orthophosphate doses and flow-dose data analysis periods.
33
Figure 21 pH box-plot for LSL rig flowing samples during 1.2gpm-Dose1
Figure 22 pH box-plot for LSL rig flowing samples during 1.5gpm-Dose1
34
Figure 23 pH box-plot for LSL rig flowing samples during 1.4gpm-Dose2
Figure 24, Figure 25, and Figure 26 show the distribution of flowing sample orthophosphate
measurements during 1.2gpm-Dose1, 1.5gpm-Dose1, and 1.4gpm-Dose2, respectively. Figure 26
shows that orthophosphate measurements during 1.5gpm-Dose1 were more variable than the other
analysis periods and slightly lower than targets.
35
Figure 24 Orthophosphate box-plot for LSL rig flowing samples during 1.2gpm-Dose1
Figure 25 Orthophosphate box-plot for LSL rig flowing samples during 1.5gpm-Dose1
36
Figure 26 Orthophosphate box-plot for LSL rig flowing samples during 1.4gpm-Dose2
Galvanized Pipe and Brass Fixture Loops
WQPs were also measured for the galvanized pipe and brass fixture rigs. However, due to each rig
having identical water quality, samples were only analyzed per-rig for pH, temperature,
orthophosphate, and free chlorine. These parameters were typically measured twice per week
except for free chlorine which was typically measured once per week.
The galvanized and fixture rigs were kept at constant orthophosphate dose during the study period,
so there are no distinct dose periods as there were in the LSL rigs. The flow rate was changed
during the study analysis period for these rigs but the measured lead concentrations did not indicate
that this change in flow rate had an impact on lead levels and therefore the flow periods were not
analyzed separately. The study period for these rigs was much shorter than the LSL rigs. Figure
27 shows temperature measurements for flowing samples from the galvanized and fixture rigs
varied seasonally from 7.6 to 21.9°C.
Similar to the LSL rigs, the free chlorine residual measured from flowing samples was relatively
high throughout the test period with a median of about 0.90 mg/L. Figure 28 shows free chlorine
measurements from flowing samples were highest in the colder months at around 1.0 mg/L and
decreased to about 0.8 mg/L once water temperatures were over 20°C.
37
Figure 27 Measured temperature for flowing samples from the galvanized and fixture rigs
Figure 28 Measured free chlorine for flowing samples from the galvanized and fixture rigs
38
Figure 29 shows measured pH for the galvanized and fixture rig flowing samples through 8/20/20
was generally between 7.4 and 7.6, with some variations.
Figure 29 Flowing sample pH from the galvanized and fixture rigs
Figure 30 shows the measured orthophosphate from flowing samples collected from the galvanized
and fixture rigs through 8/20/20. Figure 29 and Figure 30 together show that as orthophosphate
dose target increased between rigs, measured pH decreased slightly. Although the orthophosphate
product utilized for this study was a pH neutralized sodium orthophosphate, measured pH appeared
to be slightly affected by orthophosphate dose. Figure 29 shows the magnitude of difference was
not large, but it was noticeable and consistent.
39
Figure 30 Flowing sample orthophosphate from the galvanized and fixture rigs
40
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