I-28_Laboratory Quality Assurance Split Sampling Study-2020

CITY OF
DURHAM
Date:
To:
From:
Subject:
Introduction
9/28/2020
Memo
John Loperfido- Environmental Planning & Compliance Manager
Joseph Smith- Monitoring & Assessment Supervisor
Laboratory Quality Assurance Split Sampling Study-2020
As part of the City of Durham's (COD) quality assurance efforts, split sampling studies are
routinely conducted to assess lab variability and if data quality objectives are being met. This
study plan describes a three-way split of samples to be analyzed by laboratories including
Environmental Conservation Laboratories Inc. (ENCO, Cert. # 591), South Durham Wastewater
Reclamation Facility (SDWRF, Cert. #176), and the North Carolina Division of Water Resources
Central Laboratory (NCDWR Central Laboratory), which is also responsible for the issuance of
lab certification for chemical analyses. This study will also compare analyte results from
sampling conducted by staff with the COD Stormwater & GIS Division (SW & GIS) to those
collected by staff with the North Carolina Division of Water Resources Raleigh Regional Office
(RRO). The last split sampling study was conducted in 2017.
The COD Stormwater & GIS Services Division collects routine ambient water quality samples
for chemical analyses. These samples consist of nutrients, including ammonia (NH3), nitrate
and nitrite (NO),), total Kjeldahl nitrogen (TKN), and total phosphorous (TP), metals including
copper (Cu), calcium (Ca), magnesium (Mg), and zinc (Zn), total suspended solids (TSS), fecal
coliform, and biochemical oxygen demand (BOD5).
The NCDWR Ambient Monitoring System (AMS) consists of monthly routine monitoring for
physical and chemical parameters at 329 active stations, nine of which are located within the
County of Durham. These sites are sampled by staff from the RRO. Routine chemical
parameters monitored monthly as part of the AMS include NH3, NO., TKN, TP, fecal coliform
and turbidity. In addition to monthly samples hardness and TSS are collected quarterly.
Study design
In coordination with laboratory and RRO staff (Table 1), the COD Stormwater & GIS Services
Division will conduct split sampling at three sites normally sampled by RRO staff as part of the
AMS program. Samples will be collected in a single day at the three NCDWR ambient
monitoring stations listed below in (Table 2).
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Table 1 Key Contacts for the Laboratory Quality Assurance Split Sampling Study-2020
Laboratory/
Contact
Title
Phone
Email
Agency
Env. Planning
919-560-4326
SW & GIS
Christine Cailleret
& Comp.
ext. 30276
Christine. Cailleret(cDdurhamnc.gov
Coord.
ENCO
Amanda Gaines
Project
Manager
919-467-3090
againes a(a)encolabs.com
SDWRF
James Blake
Sr. Laboratory
919-560-4386
James. Blake(a)durhamnc.gov
Manager
ext.35533
NCDWR
Ellen Stafford
Laboratory
919-733-3908
EIIen.Stafford(a ncdenr.gov
Manager
ext. 213
Ambient
NCDWR
Kristen Slodysko
Monitoring
919-743-8411
Kristen. Slodysko ncdenr.gov
System Coord.
Table 2 Ambient Monitoring Stations to be Sampled for the Laboratory Quality Assurance Split Sampling Study- 2020
Station
Location description
Latitude, Longitude
B3039000
NEW HOPE CRK AT CONCRETE IMPOUNDMENT
35.88582,
-78.96528
J0770000
ENO RIV AT US 501 NR DURHAM
36.07197,
-78.90864
J1330000
ELLERBE CRK AT SR 1636 NR DURHAM
36.05949,
-78.83224
Sampling will be conducted by COD staff alongside RRO staff for one sampling event during the
month of October. A final date will be decided, and labs will be notified of the intent to collect at
least 72 hours prior to the sampling event dependent on RRO staff scheduling. The study will
begin in October 2020 and extend to the spring of 2021. Tasks for this study are shown in the
project timeline below (Table 3).
Table 3 Project Timeline for the Laboratory Quality Assurance Split Sampling Study -2020
Task
2020
2021
0)
a
C
U)
o
o
z
o
LL
Q
Q
Study Plan
X
X
Sample Collection
X
Laboratory Analysis
X
X
X
Data Compilation/ Data Review
X
X
Data Analysis
X
X
Draft report
X
X
Final Report
X
Response to COVID-19
Due to the ongoing pandemic, standard sampling methodology will be modified to facilitate
social distancing. Namely, staff will be limited to at a minimum of 6 feet in proximity to one
another during "side by side" sampling with one another.
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Sampling Methodology
In conjunction with RRO staff, members of the COD Stormwater & GIS Division will collect
concurrent triplicate grab samples from each site once for the analytes shown below (Table 4)
using methodology outlined in the Water Quality Unit's Standard Operating Procedures for
Water Chemistry Sampling v 1.1. Staff from the RRO will collect their routine monthly samples
including ammonia (NH3), nitrate and nitrite (NO2+NO3), total Kjeldahl nitrogen (TKN), and total
phosphorous (TP), fecal coliform and turbidity, as well as any quarterly samples if scheduled.
Samples will only be collected once from all three sites by COD staff.
Table 4 Analyte Grouping and Preservation of Samples to be Collected for the Laboratory Quality Assurance Split
Sampling Study- 2020
SDWRF Lab
ENCO Lab
NCDWR Lab
Analyte/ Reporting Units
Hold Time
Preservatives
Preservatives
Preservatives
/ Sample
/ Sample
/ Sample
Bottle
Bottle
Bottle
Ammonia (NH3,2SO4,
mg/L as N)
H2SO4,3
1 L Plastic,
250 mL
500 mL
Nitrate + Nitrite (NO., mg/L as N)
all nutrient
Plastic, all
Plastic, all
Total Kjeldahl Nitrogen (TKN, mg/L as N)
28 days
samples
nutrient
nutrient
collected in
samples
samples
Total Phosphorus (TP, mg/L as P)
single bottle
collected in
collected in
single bottle
single bottle
Total Suspended Solids (TSS, mg/1)
7 d
1 L Plastic
500 mL
500 mL
Plastic
Plastic
Biological Oxygen Demand (BOD5, mg/L)
48 hr.
1 L Plastic
1 L Plastic
1 L Plastic
Calcium (Ca, mg/L)
1+1 HNO3,
1+1 HNO3,
1+1 HNO3,
Magnesium (Mg, mg/L)
250 mL
250 mL
500 mL
Plastic, all
Plastic, all
Plastic, all
Hardness (Calculated, mg/L as CO3)
6 mo.
metals
metals
metals
Total Copper (Cu, pg/L)
samples
samples
samples
collected in
collected in
collected in
Total Dissolved Zinc (Zn, pg/L)
single bottle
single bottle
single bottle
1+1 HNO3,
1+1 HNO3,
1+1 HNO3,
250 mL
250 mL
250 mL
Plastic,
Plastic,
Plastic,
all metals
all metals
all metals
Dissolved Copper (Cu, pg/L)
samples
samples
samples
6 mo.
collected in
collected in
collected in
Dissolved Zinc (Zn, pg/L)
single bottle,
single bottle,
single bottle,
field filtered
field filtered
field filtered
through a
through a
through a
0.45pm
0.45pm
0.45pm
cartridge
cartridge
cartridge
filter
filter
filter
Sample bottles used by COD staff will be treated identically pre and post sampling. Following
collection samples will be placed in Ziplock bags prior to storage on wet ice. Sample bottles will
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be pre -preserved and will not be rinsed with site water. Each laboratory will receive three sets of
samples, one from each site listed in table 2.
Physical parameters will also be collected in -situ at each site by COD staff in accordance with
the Water Quality Unit's Standard Operating Procedures for Field Measurements and
Observations v 1.1 (Table 5). A YSI Pro Plus and Hach model 2100P turbidity meter will be
used. The same physical parameters, with the exception of turbidity, will be collected by RRO
staff using a multiparameter probe with similar accuracy and resolution. RRO staff will collect
turbidity as a laboratory analyzed sample to be completed by the NCDWR Central Laboratory.
Field readings from the turbidity meter will be compared to these samples.
Table 5 Physical Parameters to be Collected for the Laboratory Quality Assurance Split Sampling Study- 2020
Parameter
Equipment Used
Range of
Resolution
Accuracy
Measurement
Temperature (°C)
YSI Pro Plus w/Quatro
-5 to 70°C
±0.1 °C
±0.2°C
Cable
YSI Pro Plus w/
Dissolved oxygen (%)
Quatro Cable
0 to 500%
0.1 %
±2%
(galvanic sensor
Dissolved oxygen
YSI Pro Plus w/
±2% of the reading or
(mg/L)
Quatro Cable
0 to 50 mg/L
0.01 mg/L
0.2 mg/L, whichever is
(galvanic sensorgreater
Specific Conductance
YSI Pro Plus w/
0 to 200
0.001
0.5% of reading or
(pS/cm2 @ 25°C)
Quatro Cable
mS/cm2
mS/cm2
0.001 mS/cm,
whichever is greater
pH (s.u.)
YSI Pro Plus w/
0 to 14 units
0.01 units
±0.2 units
Quatro Cable
Turbidity NTU
Hach Model 2100P
0 — 1000 NTU
± 2%
0.01 NTU
Data Analysis and Reporting
Following submittal, the samples will be analyzed, and the data will be reviewed by the
individuals responsible for data validation according to the laboratories' respective QA/QC
protocols before release to the Monitoring & Assessment Group Supervisor. The relative
percent difference (RPD, Equation 1) between pairs of individual analyte results will then be
calculated and used to measure the agreement between laboratories on individual analytes.
Equation 1 Relative Percent Difference to be Used for the Laboratory Quality Assurance Split Sampling Study- 2020
X1 — X2
RPD = x 100
(X + X2)/2
Relative percent difference will also be calculated and reported for analyte values between COD
staff and RRO staff. A final report summarizing these differences in respective analytes will be
prepared following final qualification of all data from the respective laboratories.
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Appendix I Laboratory Reporting Limits and Analytical Methods
SDWRF Lab
ENCO Lab
NCDWR Lab
Analyte
Reporting
Method
Reporting
Method
Reporting
Method
Limit
Limit
Limit
SM
EPA 350.1
Ammonia (NH3)
0.04 mg/L
4500NH3D
0.10 mg/L
EPA 350.1
0.02 mg/L
Rev 2.0
1997
1993
Nitrate & Nitrite
EPA 300.0
EPA 353.2
(NOx)
0.04 mg/L
Rev. 2.1
0.10 mg/L
EPA 353.2
0.02 mg/L
Rev. 2.0
1993
1993
Total Kjeldahl
EPA 351.2
EPA 351.2
Nitrogen (TKN)
0.17 mg/L
Rev. 2.0
0.50 mg/L
EPA 351.1
0.20 mg/L
Rev. 2.0
1993
1993
Total
EPA 365.3
EPA 365.1
Phosphorus
0.03 mg/L
(1978)
0.10 mg/L
EPA 365.4
0.02 mg/L
Rev. 2.0
TP
1993
Total
Suspended
2.5 mg/L
SM 2540 D-
2.5 mg/L
SM 2540 D
6.2 mg/L
SM 2540 D-
Solids TSS
1997
1997
Biological
SM 5210 B-
SM 5210 B-
Oxygen Demand
2.0 mg/L
2001
2.0 mg/L
SM 5210 B
2.0 mg/L
2001
BODs
Hardness
(calculated)
1.0 mg/L
SM 2340 B
1.0 mg/L
SM 2340 B
1.0 mg/L
SM 2340 B
SM 3111 B-
EPA 200.7
Calcium (Ca)
0.061 mg/L
1999
0.10 mg/L
EPA 200.7
0.10mg/L
Rev 4.4
1994
SM 3111 B-
EPA 200.7
Magnesium (Mg)
0.020 mg/L
1999
0.10 mg/L
EPA 200.7
0.10mg/L
Rev. 4.4
1994
EPA 200.8
Total Copper
EPA 200.8
Rev 5.4
(Cu)
0.04 pg/L
Rev. 5.4
10 tag/L
EPA 200.7
2.0 tag/L
(1994) EPA
(1994)
200.7 Rev
4.4 1994
EPA 200.8
EPA 200.8
Rev 5.4
Total Zinc (Zn)
0.03 pg/L
Rev. 5.4
10 pg/L
EPA 200.7
10 pg/L
(1994) EPA
(1994)
200.7 Rev
4.4 1994
EPA 200.8
Dissolved
EPA 200.8
Rev 5.4
Copper (Cu)
0.04 pg/L
Rev. 5.4
10 pg/L
EPA 200.7
2.0 pg/L
(1994) EPA
(1994)
200.7 Rev
4.4 1994
EPA 200.8
Dissolved Zinc
EPA 200.8
Rev 5.4
(Zn)
0.03 pg/L
Rev. 5.4
10 pg/L
EPA 200.7
10 pg/L
(1994) EPA
(1994)
200.7 Rev
4.4 1994
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CITY OF DURHAM
Department of Public Works
Stormwater & GIS Services
2020 Laboratory Quality Assurance Split Sample Study
July 15th, 2021
CITY OF
DURHAM
2020 Laboratory Quality Assurance Split Sample Study- DRAFT
Executive Summary
As part of the City of Durham's (COD) quality assurance efforts, split sampling studies are conducted to assess
lab variability and if data quality objectives are being met. This memo describes findings of the 2020 three-way
split sample study of field work conducted on October 27th, 2020. For this study, split samples were collected
by City staff and submitted to laboratories including Environmental Conservation Laboratories Inc. (ENCO,
Cert. #591), South Durham Wastewater Reclamation Facility Laboratory (SDWRF, Cert #176), and the North
Carolina Division of Water Resources Central Laboratory (NCDWR). Samples were collected in conjunction
with staff from the NCDWR Raleigh Regional Office (RRO) and the NCDWR Ambient Monitoring System
(AMS). Due to an erroneous chain of custody form, calcium (Ca), hardness, magnesium (Mg), dissolved
copper (Cu), and dissolved zinc (Zn) were not analyzed by the SDWRF laboratory. Additionally, computer
failure resulted in the loss of Nitrate and Nitrite (NO. as N) results from the SDWRF Laboratory. Data analysis
of the 2007 High Rock Lake replicate samples comparison conducted by LimnoTech Environmental
Consultants at the request of the NC Division of Water Quality, which documented acceptable relative percent
difference (RPD) values between 20% and 40%. For this memo the RPD was calculated for each reported
sample, with a recommended maximum RPD of +/- 30%. Overall comparisons showed exceedances of the
30% limit in 58% of these comparisons (n=69). Also of note were significant variances for five-day biological
oxygen demand (BOD-5) and Total Suspended Solids (TSS) from the NCDWR Central Laboratory in
comparison to both SDWRF and ENCO results, although BOD-5 results from the NCDWR Central Laboratory
were heavily qualified. Additional samples were collected by RRO staff as part of routine ambient monitoring by
the state. However, these results have not been finalized for release at the time of writing this memo.
Preliminary comparisons between unqualified results collected by RRO staff and qualified results collected by
COD staff that were both submitted to the NCDWR laboratory do not show substantial differences of concern.
Results are further discussed below.
Methodology
In coordination with laboratory and RRO staff, the COD Stormwater & GIS Services Division conducted split
sampling at three sites normally sampled by RRO staff as part of the AMS. Samples were collected on October
27th 2020 at the three NCDWR ambient monitoring stations listed below in Table 1.
Table 1. Ambient Monitoring Stations Sampled as part of the Laboratory Quality Assurance Split Sampling Study- 2020
Station
Location description
Latitude, Longitude
B3039000
NEW HOPE CRK AT CONCRETE IMPOUNDMENT
35.88582,-78.96528
J0770000
ENO RIV AT US 501 NR DURHAM
36.07197,-78.90864
J1330000
ELLERBE CRK AT SR 1636 NR DURHAM
36.05949,-78.83224
Weather conditions from the prior three days indicate an average temperature of 620 F, with accumulative
rainfall of 0.12 inches. Field notes indicate that samples were collected in normal baseflow. A stainless steel
bridge sampler basket was used to collect all samples at B3039000. Physical parameters were collected using
a calibrated ProPlus multiparameter water quality meter and a Hach Turbidimeter. Physical parameters
included dissolved oxygen (DO), temperature (°C), pH (s.u), specific conductivity (pS/cm3), and turbidity (NTU).
Following collection, samples were submitted to laboratories for analysis following their respective standard
operating procedures. Reporting limits and methodology for the analysis of samples by respective laboratories
is shown below in Table 2.

Table 2 Laboratory Reporting Limits and Analytical Methods- 2020 Laboratory Quality Assurance Split Sampling Study. Values may be higher than method detection limits reported
below.
Analyte
SDWRF Lab
ENCO Lab
NCDWR Lab
Reporting
Limit
Method
Reporting
Limit
Method
Reporting
Limit
Method
Ammonia (NH3) as N
0.04 mg/L
SM 4500NH3D (1997)
0.10 mg/L
EPA 350.1
0.02 mg/L
EPA 350.1 Rev 2.0 (1993)
Nitrate & Nitrite (NOx) as N
0.04 mg/L
EPA 300.0 Rev. 2.1 (1993)
0.10 mg/L
EPA 353.2
0.02 mg/L
EPA 353.2 Rev. 2.0 (1993)
Total Kjeldahl Nitrogen (TKN)
0.17 mg/L
EPA 351.2 Rev. 2.0 (1993)
0.50 mg/L
EPA 351.1
0.20 mg/L
EPA 351.2 Rev. 2.0 (1993)
Total Phosphorus (TP)
0.03 mg/L
EPA 365.3 (1978)
0.10 mg/L
EPA 365.4
0.02 mg/L
EPA 365.1 Rev. 2.0 (1993)
Total Suspended Solids (TSS)
2.5 mg/L
SM 2540 D-1997
2.5 mg/L
SM 2540 D
6.2 mg/L
SM 2540 D-1997
Biological Oxygen Demand (BOD-5)
2.0 mg/L
SM 5210 B-2001
2.0 mg/L
SM 5210 B
2.0 mg/L
SM 5210 B-2001
Hardness (calculated)
1.0 mg/L
SM 2340 B
1.0 mg/L
SM 2340 B
1.0 mg/L
SM 2340 B
Calcium (Ca)
0.061 mg/L
SM 3111 B-1999
0.10 mg/L
EPA 200.7
0.10mg/L
EPA 200.7 Rev 4.4 (1994)
Magnesium (Mg)
0.020 mg/L
SM 3111 B-1999
0.10 mg/L
EPA 200.7
0.10mg/L
EPA 200.7 Rev. 4.4 (1994)
Total Copper (Cu)
0.04 pg/L
EPA 200.8 Rev. 5.4 (1994)
10 pg/L
EPA 200.7
2.0 pg/L
EPA 200.8 Rev 5.4 (1994)
EPA 200.7 Rev 4.4 (1994)
Total Zinc (Zn)
0.03 pg/L
EPA 200.8 Rev. 5.4 (1994)
10 pg/L
EPA 200.7
10 pg/L
EPA 200.8 Rev 5.4 (1994)
EPA 200.7 Rev 4.4 (1994)
Dissolved Copper (Cu)
0.04 pg/L
EPA 200.8 Rev. 5.4 (1994)
10 pg/L
EPA 200.7
2.0 pg/L
EPA 200.8 Rev 5.4 (1994)
EPA 200.7 Rev 4.4 (1994)
Dissolved Zinc (Zn)
0.03 pg/L
EPA 200.8 Rev. 5.4 (1994)
10 pg/L
EPA 200.7
10 pg/L
EPA 200.8 Rev 5.4 (1994)
EPA 200.7 Rev 4.4 (1994)

Upon receipt of all data, the Monitoring and Assessment Group Supervisor and Ambient Monitoring
Coordinator reviewed data for completeness and calculated the relative percent difference using the formula
shown below in Equation 1. It should be noted that this RPD equation removes the absolute value from the
difference from the average portion of the normal RPD formula, which maintains negative values deemed
useful to assess if a laboratory routinely reported higher or lower values in comparison.
RPD = 100 x X1 — X2
(X1 + X2)
2
Equation 1 Relative Percent Difference, modified
Results
Physical parameters recorded by WQU staff are shown below in Table 3. Analytical results from each
laboratory are shown below in Table 4. Comparisons of the relative percent difference of those values are
shown on the following pages in graph form. The relative percent difference formula allows for the comparison
between two data points, so each laboratory was paired twice for analysis. No further statistical analysis was
performed on this data set.
Table 3 Physical parameters recorded by WQU Staff the three Ambient Monitoring locations, 2020 Laboratory Quality Assurance Split
Sampling Study
Parameter
B3039000
J0770000
J 1330000
DO, mg/L
6.5
9.0
7.8
DO, % Saturation
72
92
84
Temperature, °C
19.0
16.7
19.2
pH, S.U.
6.4
6.6
7.1
Sp. Conductivity NS/cm3
355
102
410
Turbidity, NTU
6.8
5.6
1.9

Table 4 Reported Values for all Parameters, 2020 Laboratory Quality Assurance Split Sampling Study. All values reported using laboratory significant figures.
Parameter
BOD-5, mg/L
TP, mg/L
NO, as N, mg/L
NH3 as N, mg/L
TKN, mg/L
Hardness, mgCaCO31L
Ca, µg/L
Total Cu, µg/
Dissolved Cu,
Total Zn. ua/!
Dissolved Zn, µg/L
U - The analyte was analyzed for, but not detected to the level shown, adjusted for actual sample preparation data where applicable.
G4- Estimated. Evidence of toxicity was present. Reported Value from Highest dilution.
G5- Estimated. GGA standard recovery was < 198 +/-30.5 mg/L.
J- The reported value is between the laboratory method detection limit, and the method reporting limit.
D- The sample was analyzed at dilution.
B3039000
J0770000
J1330000
SDWRF
NCDWR
ENCO
SDWRF
NCDWR
ENCO
SDWRF
NCDWR
ENCO
2U
22G4,G5
2U
2U
11 G4,G5
2U
2U
18G4,G5
2U
0.19
0.11
0.16
0.11
0.02
0.03 J
0.12
0.07
0.092 J
-
3.7
3.8 D
-
0.2
0.2
-
1
1
0.07
0.03
0.045 U
0.05
0.2 U
0.045 U
0.05
0.02 U
0.045 U
1.15
0.91
0.84
0.79
0.4
0.55
1.22
0.74
0.95
4.2
6.2 U
2.5 U
2.5 U
17
4.1
5
16
2.5 U
-
67
44
-
36
21
-
83
55
-
5300
5410
-
3400
3430
-
6100
6040
-
18000
17500
-
8700
8540
-
23000
22000
2.42 J
2.30
1.96 J
1.02 J
2 U
1.6 U
2.66 J
2.4
1.6 U
-
2.0 U
1.6 U
-
2 U
1.6 U
-
2.3
1.6 U
12.34
16
20.7
0.91 J
10 U
4.4 U
13.09
16
17.2
-
14
15.7
-
10U
4.4U
-
15
16.8

BOD-5 showed elevated relative percent difference results between NCDWR and other laboratory results
(Figure 1). BOD-5 was not detected above method reporting limits (MRL) by the SDWRF or ENCO. As part of
the BOD-5 analysis, glucose- glutamic acid (GGA) is added to three test bottles along with seeded dilution
water. All three site results as reported by NCDWR were G4 qualified ("Estimated- Evidence of toxicity was
present. Reported value from highest dilution") and G5 qualified ("Estimated- GGA standard recovery was <
198 +/- 30.5 mg/L"). Recovery limits below expected values are associated with poor seed quality or quantity,
or the presence of a toxic material in dilution water, source of seed, or labware (American Public Health
Association, American Water Works Association, Water Environment Federation, 2012). Taken in conjunction
with non -detects for BOD-5 values from SDWRF and ENCO, this indicates potential lab contamination issues
with samples submitted to NCDWR.
BOD-5, RPD
200%
150%
100%
50%
30%
`s
0%
-30%-
-50%
-100%
-150%
AL
A SDWRF us. NCDWR
* SDWRF us. ENCO
. . NCDWR us. ENCO
-200%
B3039000 J0770000 J1330000
Station
Figure 1 BOD-5 Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
Overall, RPD for total phosphorus (TP) averaged 33% for all samples (Figure 2). However, higher variance
(RPD- 114%, 139%) was observed at J0770000 between the SDWRF results (0.11 mg/L) and others (0.02,
0.03 mg/L). TP was detected near or below the maximum MRL (ENCO, 0.10 mg/L) at sites J0770000 and
J1330000 and was J qualified. This J qualifier is normally attached to results below the method reporting limit
for that run of samples indicating that higher recovery than expected was observed in QA samples analyzed, or
that detected values were below the practical quantitative limit established by the laboratory. This may account
for the higher variance between samples observed, particularly at J0770000. Analysis of other possible
sources of interference include the overall amounts of total suspended solids recorded. TSS for all three sites
remained relatively low, with a median concentration of 4.2 mg/L, and a maximum reported value of 17 mg/ L
(NCDWR, J1330000). Since the RPD values in TSS ranged from -150% to 150%, sediment bound phosphorus
amounts could have fluctuated with the differing amounts of sediment detected at each lab. It should be noted
that samples were collected in the Fall, and leaf litter can also be a source of TP, potentially resulting in
differing amounts at the point of collection.

TP, RPD
200%
150%
100%
50%
30%
g 0%
m
-30%
-50%
-100%
-150%
ASDWRFvs.NCDWR
SDWRF us. ENCO
♦ NCDWR us. ENCO
-200%
B3039000 J0770000 J1330000
Station
Figure 2 Total Phosphorous (TP) Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
Ammonia (NH3 as N) was not detected in ENCO results with a reported MRL of 0.045 mg/L. This MRL is lower
than the 0.10 mg/L found in Table 2, and may be in error. NH3 was not detected at J1330000 by the NCDWR
lab (MRL=0.02 mg/L). However, all reported values remained relatively close to reported MRLs, so higher
SDWRF values are not indicative of an issue. Standard method 4500 D, used by SDWRF, uses an ammonia
selective electrode in contrast to the semi- automated colorimetry used by NCDWR and ENCO. These
differences in method, as well as the relatively low concentrations reported, may account for the elevated RPD
values observed above the 30% near method detection limits (Figure 3).
NH3, RPD
200%
SDWRF us. NCDWR
SDWRF us. ENCO
NCDWR us. ENCO
150%
100%
50%
30%
g 0%
e:
-30%
-50%
-200%
B3039000 J0770000 J1330000
Station
Figure 3 NH3 as N Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
Due to equipment failure, Nitrate and Nitrite as N (NO,, as N) values could not be reported by SDWRF. Results
from NCDWR and ENCO are shown below and were detected well above the MRL for each laboratory. RPD
averaged 2%, indicating strong overall agreement between both labs (Figure 4). ENCO analyzed a diluted
sample at B3039000 for unknown reasons, however, comparisons between both labs show this had minimal
effect on final results.

NOx, RPD
200%
150%
100%
50%
30%-......
d 0%
s
-30%------
-50%
-100%
-150%
.NCDWR vs. ENCO
-200%
B3039000 J0770000 J1330000
station
Figure 4 NO,, as N Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
Total Kjeldahl Nitrogen (TKN) was detected at or above the maximum MRL (ENCO, 0.5 mg/L) at sites
B303900 and J133000, and at slightly above the maximum MRL at J0770000. On average, SDWRF reported
values were 0.32 mg/L higher than reported values from ENCO and NCDWR, while NCDWR reported values
0.23 mg/L lower than average values from ENCO and NCDWR. SDWRF and ENCO results showed relatively
consistent agreement, with an average RPD of 31 % (Figure 5). The highest variance in RPD was observed at
J0770000 (mean= 44%), where relatively low values at or near the Maximum MRL may have resulted in
increased variance compared to the other two stations.
TKN, RPD
200%
. SDWRF us. NCDWR
* SDWRF us. ENCO
. NCDWR us. ENCO
150%
100%
AL
50%
.
30%- ...................
a.-......-......-.....................-0...-.....................-......-......0
a 0%
`s
♦■
-30%-.------------------------------------------------------------
..-.....................-......-.....
-..................
-50%
-100%
-150%
-200% -
B3039000 J0770000 J1330000
Station
Figure 5 Total Kjeldahl Nitrogen (TKN) Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
Total suspended solids (TSS), showed high variance with no RPD values meeting the recommended 30%
RPD limits (Figure 6). Turbidity values collected by field staff using a Hach turbidimeter show relatively low
values, indicative of low concentrations of suspended particulate matter in the water column. This is consistent
with the range of TSS concentrations, from non -detect to 17 mg/L, measured in this study. While the RPD
values were high, the magnitude of all TSS measurements were similarly low. Common interferences for TSS
analysis include over filtration resulting in filter clogging, inadequate resuspension of samples before

processing, and inadequate drying times (American Public Health Association, American Water Works
Association, Water Environment Federation, 2012). Samples were collected in October during the fall, so
particulate leaf matter may have caused interference. For TSS samples with a low filtered mass, resolution of
different laboratory scales can also lead to high RPD between samples measured using different scales.
TSS, RPD
200%
. SDWRF us. NCDWR
SDWRF us. ENCO
♦ NCDWR us. ENCO
150%
100%
50%
30%
S 0%
m
-30%
-50%
-200%
B3039000 J0770000 J1330000
Station
Figure 6 Total Suspended Solids (TSS) Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
Comparing ENCO and NCDWR results for hardness, no values met the recommended 30% RPD limit (Figure
7). Hardness was not analyzed by the SDWRF Laboratory.
Hardness, RPD
200°k
♦ NCDWR us. ENCO
150%
100%
50%
30%
S 0%
m
-30%
-50%
100%
150%
-200%
B3039000 J0770000 J1330000
station
Figure 7 Hardness Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
However, in the review of the accompanying calcium (Ca) and magnesium (Mg) data, relatively low variance is
observed. Table 5 below shows the hardness values as reported by ENCO and NCDWR as well as hardness
calculated using the Ca and Mg concentrations reported by both. Hardness was calculated using the Standard
Method (American Public Health Association, American Water Works Association, Water Environment

Federation, 2012) recommend formula shown in Equation 2. Hardness was not analyzed by the SDWRF
laboratory.
mg of CaCO3/L = 2.497 [Ca, mg/L] * 4.118 [Mg, mg/L]
Equation 2 Hardness, mg equivalent CaCO3/L, Laboratory Quality Assurance Split Sampling Study-2020
Table 5 Reported and Calculated Hardness From ENCO Results in Comparison to NCDWR, Laboratory Quality Assurance Split
Sampling Study-2020
Site
ENCO Reported,
m CaCO31L
ENCO Calculated,
m CaCO31L
NCDWR Reported,
m CaCO31L
NCDWR Calculated,
m CaCO31L
B3039000
44
66
67
67
J0770000
21
35
36
36
J1330000
55
80
83
83
As Table 5 shows, recalculated hardness values are very similar, indicating potential calculation errors by both
laboratories. RPD for calculated values average 2%.
Magnesium (Mg) concentrations were similar from ENCO and NCDWR, with an average RPD of -1 % (Figure
8). Mg was not analyzed by the SDWRF Laboratory.
Mg, RPD
200%
. NCDWR vs. ENCO
150%
100%
50%
30%
g 0%
m
-30%
-50%
-100%
-150%
-200%
B3039000 J0770000
Station
Figure 8 Magnesium (Mg) Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
Calcium (Ca) concentrations were similar from ENCO and NCDWR, with an average RPD of 3% (Figure 9). Ca
was not analyzed by the SDWRF Laboratory.

Ca, repo
200%
150%
100%
50%
30%
g 0%
o:
-30%
-50%
-100%
-150%
.NCDWR vs. ENCO
-200%
B3039000 J0770000 J1330000
Station
Figure 9 Calcium (Ca) Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
Total Copper (Cu) RPD values at site B3039000 all fell within the recommended 30% limit (Figure 10). Results
from J0770000 and J1330000 were more variable than for B3039000, with some results falling outside of the
recommended limits. In a comparison of laboratory results, reported concentrations were at or very close to
laboratory limits. This may have resulted in increased variance, Values from SDWRF at J0770000 were
reported below the MRL for ENCO at all stations and for NCDWR at station J0770000.
Total Cu, RPD
200%
150%
100%
50%
30%
n 0%
s
-30%
-50%
-100%
-150%
-200%
Station
ASDWRFvs.NCDWR
* SDWRF us. ENCO
♦ NCDWR us. ENCO
Figure 10 Total Copper (Cu) Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
For dissolved Cu, ENCO reported all values as U qualified, not detected above the MRL concentration of 1.6
pg/L, while NCDWR only reported concentrations above the MRL of 2.0 pg/L at one site J1330000 (2.3 pg/L).
Two of the three comparisons showed acceptable variance within the recommended 30% limit, while the third
showed an RPD of 36% (Figure 11). Overall, dissolved Cu showed reasonably good agreement between labs
at or near method detection levels. Dissolved Cu was not analyzed by the SDWRF.

Dissolved Cu, RPD
200%
150%
100%
50%
30%
d 0%
s
-30%
-50%
--------------------------------------------------------- * ------------------
* NCDWR vs. ENCO
-200%
B3039000 J0770000 J1330000
station
Figure 11 Dissolved Copper (Cu) Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
Total zinc (Zn) showed greater variance as compared to Total Cu, with an average RPD of -42% (Figure 12).
In general, values reported by ENCO were higher than those from the other laboratories. Total Zn was
detected at relatively low levels at J0770000 (SDWRF- 0.91 pg/L J, NCDWR- 10 pg/L U, ENCO- 4.4 pg/L U)
which increased RPD values at this site due to differences in detection limits by the respective laboratories
(Table 2). MRLs for the laboratories were 0.03 pg/L for SDWRF and 10 pg/L for ENCO and NCDWR.
Total Zn, RPD
200%
150%
100%
50%
30%
d 0%
s
-30% -------------------
-----------------------------------------------------
-50%
-100%
-150%
AL
-- I-------------------
-200% —
B3039000 J0770000 J1330000
station
♦ NCDWR vs. ENCO
Figure 12 Total Zinc (Zn) Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
Comparisons of dissolved Zn data between NCDWR and ENCO show good overall agreement (Figure 13).
Dissolved Zn was not detected above either laboratory's MRL at J0770000, resulting in a high RPD at this site
as shown below. Sites with dissolved Zn values above the MRL were within the recommended 30% range.
Dissolved Zn was not analyzed by SDWRF.

Dissolved Zn, RPD
200%
150%
100%
50%
30%
0%
-30%
-50%
-100%
-150%
-200%
B3039000 J0770000
station
J1330000
J
♦ NCDWR vs. ENCO
Figure 13 Dissolved Zinc (Zn) Relative Percent Difference, Laboratory Quality Assurance Split Sampling Study-2020
Summary
Results from this study were mixed with some comparisons for specific parameters for specific laboratories
meeting the recommended 30% RPD limit on RPD. Some RPDs that were higher than 30% were due in part to
differences in MRLs established by laboratories based on their internal QA process. This should not be
considered an issue in routine monitoring where elevated values and exceedances of water quality standards
are a concern. More notable are the exceedances of recommended RPD limits with BOD-5, TP, NH3 as N, and
TSS. While a reasonably good overall agreement was observed between SDWRF and ENCO for most values
in the data set. Values relating to BOD-5, TP, NH3 as N, and hardness showed significant variance among
laboratory results. This may in part due to the relatively low concentrations observed of these parameters
during baseflow conditions, and should not be considered an issue where elevated values and exceedances
are of primary concern. BOD-5 values reported from the NCDWR laboratory were qualified for low GAA
recovery, which, may have contributed to higher concentrations from that laboratory in comparison to SDWRF
and ENCO. Regarding TSS, no values fell within the accepted RPD range for any comparisons made between
the laboratories. Although, it should be noted that given the relatively low TSS concentrations and turbidity
values, TSS samples at or near the method reporting limit should be expected to have increased variance.
Bibliography
American Public Health Association, American Water Works Association, Water Environment Federation.
(2012). Standard Methods for the examination of Water and Wastewater 22nd edition. Washington
D.C.: American Public Health Association.