public comments - dnrdnr.mo.gov/env/wpp/tmdl/docs/2020-bear-3960-comments.pdf · 2020-01-27 ·...

Draft Revised Total Maximum Daily Load (TMDL)

for

Bear Creek (WBID 3960)

PUBLIC COMMENTS

Public Notice September 27 – November 12, 2019

Missouri Department of Natural Resources Water Protection Program

PO Box 176 Jefferson City, MO 65102-0176 800-361-4827 / 573-751-1300

INTRODUCTION U.S. Environmental Protection Agency regulations require that total maximum daily loads, or TMDLs, be subject to public review (40 CFR 130.7). The Missouri Department of Natural Resources placed the draft revised TMDL for Bear Creek on a 45-day public notice and comment period from September 27 through November 12, 2019. All comments received are included in this document. Comments were received from the following groups or individuals: • U.S. Environmental Protection Agency, Region 7 • City of Kirksville

Missouri – Revised Bear Creek TMDL November 12, 2019

1

Background and Rationales for the development of a Revised TMDL

Bear Creek is a classified stream (WBID: 3960). The designated uses for this stream include Irrigation,

Livestock/Wildlife Protection, Warmwater Habitat, Human Health Protection, Whole Body Contact

Recreation (Category B) and Secondary Contact Recreation. Prior to 2014, Bear Creek was an unclassified

stream (WBID: 115U-01). In 2008, Bear Creek was impaired due to violations of Missouri’s General

Water Quality Criteria to protect aquatic life and biological aquatic communities. In 2010, the Bear Creek

TMDL was developed in accordance with Section 303(d) of the Clean Water Act. Though the cause of

this impairment was unknown pollutants, the dissolved oxygen (DO) parameter was used to estimate

the allowable TMDL load because this DO parameter provides a robust indicator of assessing a

waterbody’s overall ability to support aquatic life. According to the water quality data sampled at

various locations in Bear Creek, 50% of the DO measurements were below the State’s DO Criterion (5

mg/L) in August from 1975 to 2002. In 2009, 63 of the DO measurements were taken at eight monitoring

locations. Of those 63 DO measurements, 7 measurements were below 5 mg/L.

A close analysis of these DO datasets showed that the Kirksville WWTP was the leading source

contributing the low DO concentrations in Bear Creek during the low flow condition. Another important

contributor that linked to the low DO concentrations was the sediment transport from the watershed -

as it contains high organic materials that can consume a significant amount of DO in the stream when

they decompose. To mitigate the low DO levels and ensure that Bear Creek achieves the State’s DO

criterion, the effluent’s nutrient levels of the Kirkville WWTF and the sediment transport in the

watershed should be managed properly. Therefore, the QUAL2K model and total suspended solids (TSS)

are used in the revised TMDL. The former determines the nutrient’s permit limits for the Kirksville

WWTF and the latter quantifies the sediment load for Bear Creek as the TSS parameter is a good

surrogate to evaluate the sediment-bound organic materials. To calculate the TSS TMDL load, a load

duration curve (LDC) is utilized. This revised TMDL removes a nutrient LDC that used the ecoregion-

reference values in the original TMDL because the occurrence of the low DO problems at the low flow

condition is associated primarily with the Kirksville WWTF. Thus, by setting the facility’s nutrient permit

limits would warrant a significant improvement of the low DO condition in Bear Creek. This revised

TMDL does not allocate the nutrients load for the nonpoint sources for the low flow condition because

the nonpoint sources have very little effect on the DO concentrations in Bear Creek.

Technical Comments for Bear Creek QUAL2K Model

Development of Hydraulic Rating Curves

The rating curves for the sampling locations were derived, based on the measured stream hydraulic and

hydrologic data collected in 2009. These rating curves were used to determine the reach’s rating curves

used in the model. A new rating curve was developed for the impaired segment in 2019 and was shown

in Figure 1, along with the original segment’s rating curve. As indicated in the figure, the 2019 rating

curve did not properly characterize the observed flow-velocity relationship. Figure 2 shows the flow-

depth relationships for Reach 2. Likewise, the flow-depth relationship determined in 2019 did not

represent the appropriate flow-depth relationship identified in 2009. Therefore, there is a need to revise

the 2019’s rating curves for the model.


2

Denitrification in Sediment

Sediment denitrification transfer coefficient (SDTC) is defined as the velocity that nitrate diffuses into the sediment where the nitrate is denitrified to nitrogen gas. According to the QUAL2K documentation,

this coefficient value ranges from 0 to 1. The SDTC value was set at the maximum value of 1 for the

entire segment as this coefficient was adjusted at the model’s rate section. This adjustment suggests the

segment (Reaches 1 - 9) was under the anoxic condition. However, the denitrification rate used for the

water column was only 0.05 per day, indicating that the stream was not at the anoxic condition. This

water-column denitrification coefficient typically ranges from 0 to 2 per day as recommended by the

literature.

Headwater Nutrient Boundary Condition

Table 1 shows the model parametrization and the water quality data collected in 2009. As indicated in

the table, the 2009 model was set up based on the water quality data collected on July 15 because on

this date Bear Creek represented the critical flow condition. The nutrient concentrations were below the

reference condition suggested by EPA. The nutrient concentrations measured in 2009 were comparable

to the nutrient conditions recorded in 2002. The 2019 model was not calibrated appropriately for the

two major reasons. First, the organic N was assigned to zero while organic P was present in the stream

(102 µg/L). Based on the monitored nutrient data, the organic N and P coexisted in the stream. For

example, the organic N and P concentrations on August 25 were 362 and 51 µg/L, respectively. The

other reason was that, during the four sampling events (2 in July and 2 in August), ammonium

concentrations were all below the instrument detection limit (500 µg/L). However, the ammonium

concentration of 844 µg/L was assigned to the model, which exceeded the detection limit.

2019 2009 14-Jul 15-Jul 25-Aug 26-Aug

Flow (m3/s) 0.006 0.010 0.002 0.008 0.029 0.018

Organic N (µg/L) 0 491 521 492 362 289

Ammonium (µg N/L) 844 250 < 500 < 500 < 500 < 500 Less than Detection limit (500 ug N/L)

Nitrate (µg N/L) 300 290.5 166 291 179 170

Organic P (µg/L) 102 81 56 81 51 47

Inorganic P (µg/L) 0 6 4 6 4 4

Table 1. Model parametrization and water quality data collected in 2009.

2009 Water Quality DataRemarkParameter

QUAL2K Model

Reference condition: TN = 855 µg/L and

TP = 92 µg/L.

On 8/15/2002 (low flow condition), flow

= 0.003 m 3 /s, nitrate = 200 µg N/L,

ammonium = 50 µg N/L, ON = 740 µg/L,

TP = 135 µg/L (MDNR's WQX data).


3

Sediment Oxygen Demand – Percent coverage of sediment and algae

The calculation of sediment oxygen demand (SOD) in QUAL2K was based on the decomposition and transport of particulate organic matter from the water column. This organic matter was closely associated with the several factors including the percent coverage of algae and sediment and the prescribed SOD as well as the nutrient concentrations (Table 2). The coverage of algae and sediment was determined, based on the streambed substrate (see Table 6 in the 2009 sampling report). In general, a reach with higher silt/clay content was given a higher SOD coverage while a higher algae coverage was assigned to a reach with a higher sand/gravel/boulder value. For the 2019 model, the headwater (Reach 1) had zero values for these two coverages while the rest of the reaches had 100% SOD coverage. The algae coverage was all below 50%, except for Reach 3 (50%). The setting of these coverages was not in line with the substrate conditions, suggesting that the model’s setting did not appropriately reflect the actual stream condition. The prescribed SOD variable was a calibration factor that is used to account for the local condition such as the organics associated with the sediment. No prescribed SOD was assigned to the 2009 model because the nutrient concentrations and the algae/SOD coverage used in the model characterized the SOD condition seen in Bear Creek. In contrast, the prescribed SOD was needed for the 2019 model. Though the prescribed SOD could be used to account for the local condition, the use of this prescribed SOD might be simply a result of the incorrect setting of the coverage and headwater nutrient condition.

Water Quality in Tributaries – Nutrients and Dissolved Oxygen

The watersheds of the ten tributaries are primarily agricultural areas, according to the 2011 National Land Cover Database. The water quality of these tributaries was estimated using the headwater and/or the streams that have land use similar to the tributaries. Table 3 shows the water quality data used in the 2019 and 2009 model. The tributary’s nutrient data used in the 2009 model was based on the headwater nutrient concentration. However, elevated ammonium concentrations were assigned to the 2019 model. Similarly, high organic P concentrations were assigned to Tributaries 6 and 7. In addition, zero organic N and nitrate concentrations were used in the model.

Bottom Bottom Prescribed Bottom Bottom Prescribed

Algae SOD SOD Algae SOD SOD

Coverage Coverage gO2/m2/d Coverage Coverage gO2/m2/d

Reach 1 - - - Reach 1 50.00% 50.00% -

Reach 2 15.00% 80.00% 5.00 Reach 2 50.00% 50.00% -

Reach 3 50.00% 100.00% 4.00 Reach 3 50.00% 50.00% -

Reach 4 50.00% 50.00% -

Reach 5 65.00% 35.00% -

Reach 5 22.00% 100.00% 0.25 Reach 6 80.00% 10.00% -

Reach 6 12.00% 100.00% 1.00 Reach 7 70.00% 20.00% -

Reach 7 15.00% 100.00% 1.00 Reach 8 50.00% 100.00% -

Reach 8 22.00% 100.00% 1.00 Reach 9 80.00% 20.00% -

Reach 4 30.00% 100.00% 1.50

Table 2. Algae and SOD coverage and prescribed SOD values used in the 2019 and 2009 model.

2009 Model

Reach Reach

2019 Model


4

Under the typical (or low) flow condition, these excessive ammonium and organic P concentrations were indicative of the sewage-like water entering the tributaries. However, no point sources were identified inside the watersheds of the agricultural tributaries. In nature, a stream with a detectable organic P concentration is always accompanying with a measurable organic N. Therefore, assigning measurable organic P values to the tributaries in the model, without the organic N concentrations, is also a questionable model parameterization. The nutrient data collected at North Fork South Fabius River (monitoring site – 75/20.9) were 943 µg/L for TN (nitrate = 130 µg N/L and ammonium = 238 µg N/L) and 127 µg/L for TP during the period from 2010 to 2014. Similarly, the TN and TP nutrient data collected at Troublesome Creek (74/35.6) from 2009 to 2010 were 710 µg/L and 90 µg/L, respectively (nitrate = 130 µg N/L and ammonium = 175 µg N/L). These two streams are located in the same ecoregion as Bear Creek and had comparable nutrient concentrations as those occurred in the headwater. These nutrient data also demonstrated that the high nutrient values used for the tributaries in the 2019 model were not appropriate.

Effluent Water Quality – Kirksville Wastewater Treatment Facility

Table 4 summarizes the DO and nutrient values used in the 2019 and 2009 models for the Kirkville WWTF. As shown in the table, the nutrient concentrations were much less the calculated concentrations based on the data between Sites 1 and 2. For example, organic N concentration was assigned to a zero value for the 2019 model. However, the calculated organic N value was 2,378 µg/L. Under the low flow condition on August 8, 2002, the measured concentration for organic N was 2,540 µg/L. The organic N value used in the 2009 model was 2,500 µg/L. Likewise, the nitrate concentration used in the 2019 model was 867 µg/L. However, the calculated nitrate value was 10,277 µg/L. The nitrate concentration used in the 2009 model was 10,400 µg/L. The large differences in the nutrient concentrations between the 2009 model the calculated data reveal that the nutrient values used in the 2019 model was not appropriately and therefore the model should be revised.

DO Fast CBOD ON Ammonia N Nitrate + Nitrite N OP Inorganic P Alkalinity pH

Inflow mean mean mean mean mean mean mean mean mean

Name km m3/s mg/L mgO2/L ugN/L ugN/L ugN/L ugP/L ugP/L mgCaCO3/L s.u.

Trib 2 11.50 0.0010 2.00 5.50 1855.00 97.00 40.00 7.50

Trib 3 10.99 0.0200 2.00 6.00 1500.00 440.00 40.00 7.50

Trib 4 9.91 0.0001 2.00 6.00 1600.00 97.00 40.00 7.50

Trib 5 9.34 0.0001 2.00 6.00 3255.00 97.00 40.00 7.50

Trib 6 8.93 0.0001 2.00 6.00 3255.00 1200.00 40.00 7.50

Trib 7 6.62 0.0010 2.00 7.00 4255.00 1600.00 40.00 7.00

Trib 8 6.15 0.0010 2.00 7.00 2255.00 97.00 40.00 7.00

Trib 9 4.51 0.0200 2.00 4.00 5255.00 97.00 40.00 7.00

Trib 10 1.40 0.0200 2.00 4.00 4255.00 97.00 40.00 7.00

DO Fast CBOD ON Ammonia N Nitrate + Nitrite N OP Inorganic P Alkalinity pH

Inflow mean mean mean mean mean mean mean mean mean

Name km m3/s mg/L mgO2/L ugN/L ugN/L ugN/L ugP/L ugP/L mgCaCO3/L s.u.

Trib 1 12.52 0.005 3.13 5.59 242.00 500.00 290.50 60.90 26.10 100.00 7.05

Trib 2 12.01 0.001 3.13 5.59 242.00 500.00 290.50 60.90 26.10 100.00 7.05

Trib 3 10.92 0.005 3.13 5.59 242.00 500.00 290.50 60.90 26.10 100.00 7.05

Trib 4 10.33 0.002 3.13 5.59 242.00 500.00 290.50 60.90 26.10 100.00 7.05

Trib 5 9.88 0.001 3.13 5.59 242.00 500.00 290.50 60.90 26.10 100.00 7.05

Trib 6 7.49 0.001 3.13 5.59 242.00 500.00 290.50 60.90 26.10 100.00 7.05

Trib 7 7.09 0.003 3.13 5.59 242.00 500.00 290.50 60.90 26.10 100.00 7.05

Trib 8 5.38 0.005 3.13 5.59 242.00 500.00 290.50 60.90 26.10 100.00 7.05

Trib 9 1.40 0.003 3.13 5.59 242.00 500.00 290.50 60.90 26.10 100.00 7.05

Trib 10 0.01 0.002 3.13 5.59 242.00 500.00 290.50 60.90 26.10 100.00 7.05

Table 3. Water quality data used in the 2019 and 2009 models.

2009Location

2019Location


5

Original QUAL2K –

The Kirksville WWTF was upgraded in June 2019. The previous design flow was 3.16 million gallon per

day (MGD). The permit limits for the TN and TP were 0.855 and 0.092 mg/L, respectively. With this

upgrade, the facility has an expanded design flow of 4 MGD. Because there was no phytoplankton data

collected in 2009, the phytoplankton simulation and evaluation were neglected in the model.

Based on the Discharge Monitoring Reports (DMRs) of Kirksville WWTF, the annual average ammonium

level in its effluent was 1.01 mg N/L during the recent years from 2015 to 2019, which was 50% less than

the average value (2.28 mg/L) between 2006 and 2014 (Figure 3). Likewise, the annual average BOD5

was 5.38 mg/L during the 2018-2019 period. The average BOD5 value from 2006 to 2017 was 19.61

mg/L, which was about four times higher than the 2018-2019 average (Figure 4). These two values were

used to help determine the nutrient targets (or permit limits) for the Kirksville WWTF.

Figure 5 shows the longitudinal profile of DO for the proposed nutrient targets (TN = 5.0 mg/L and TP =

0.5 mg/L) for the Kirksville WWTF under the critical flow condition. As indicated in the figure, the

minimum DO concentrations were above the DO criterion. Table 5 shows the nutrient wasteloads for

the Kirksville WWTF. To meet the DO criterion, the TN and TP permit limits should be set at 167.4 and

16.7 lbs/day, respectively. The permit limit for the ammonium should be set at 1.0 mg N/L while the

BOD5 limit should be set at 6.5 mg/L (CBOD5 = 5.0 mg/L).

DO

(mg/L)

Organic N

(µg/L)

Ammonium

(µg N/L)

Nitrate

(µg N/L)

Organic P

(µg/L)

Inorganic P

(µg/L)

2019 Model 7.00 0 2755 867 520 0

2009 Model 6.00 2,500 620 10,400 4,000 1,800

Calculated Average (2009) 6.27 2,378 250 10,277

2002 (MDNR's WQX Data) - 2,540 180 11,250

TP = 4,993

TP = 9,440

Table 4. Nutrient concentrations assigned to the 2019 and 2009 QUAL2k models for Kirksville Wastewater Treatment Facility.


6

Evaluation of a New Kirksville WWTF’s Permit – DO Simulation

MNDR recently submitted a permit for Kirkville WWTF. This new permit has the effluent nutrient

limitations; 1.6 mg N/L for ammonium (daily maximum), 6 mg/L for TP (quarterly average) and 23 mg/L

for TN (annual average). This new permit also includes 23 and 15 mg/L for BOD5 for weekly and monthly

averages, respectively. Figure 3 shows the longitudinal DO plot for the facility that has the following

permit limits; 12 mg /L for BOD5, 1.0 mg N/L for ammonium, 15.7 mg/L for TN and 3 mg/L for TP. As

indicated in the figure, the minimum DO does not meet the State’s DO Criterion starting at the distance

of 1.86 miles (about 3.0 kilometers) below the Kirksville WWTP.

Design Flow (MGD) Concentration (mg/L) Wasteload (lb/day)

BOD5 4 6.5 217.6

Ammonium (as N) 4 1 33.5

Total Nitrigen 4 5 167.4

Total Phosphorus 4 0.5 16.7

Table 5. Wasteload calculated for Kirksville Wastewater Treatment Facility.


7

Technical Comments for TSS LDC and TMDL Calculation

TSS LDC – Selection of TSS Target

The new Kirksville permit has the TSS limitations; 45 mg/L for weekly average and 30 mg/L for monthly

average. Based on the Discharge Monitoring Reports (DMRs) of Kirksville WWTF, the weekly average

values show a decreasing trend from 2006 to 2019 (Figure 7). The results of analyzing annual TSS

averages show that the average TSS for the last two years was 9.03 mg/L (9.71 mg/L for 2018 and 8.36

mg/L for 2019). This average value was twice less than the average value (19.90 mg/L) from 2006-2015

(Figure 8). The average of these two periods was about 15.0 mg/L, which is three times smaller than the

weekly permit limit.


8

The results of TSS analysis show that the 25th percentile of all TSS data listed in Table B2 ranged 7.5 to

15 mg/L. If one-half of the detection limit were used, the 25th percentile of the TSS data would be 7.5

mg/L. If the detection limit were used, the 25th percentile of the TSS data would be 15 mg/L. The

recommended ecoregional reference TSS criterion (Ecoregion 40) is 15.5 NTU. This reference target is

equivalent to 16.35 mg/L. Using the concentration of 15 mg/L for setting up the TSS target would

warrant a significant reduction of sediment-organic materials deposited in the stream bottom.

TMDL Calculation – Low Flow Condition

The loading calculation for the nutrients for the low flow condition was based on the design flow (4

MGD or 6.2 cfs) of Kirksville WWTF. MO defines the low flow is the flow between 90th to 100th

percentile flow exceedance, wth an average flow (6.42 cfs) at the 95th percentile flow exceedance. This

average flow is actually the design flow. Since the nonpoint sources have very little effect on the DO

levels at the low flow condition, using the design flow in calculation represents that the calculated

nutrient loads are the maximum loads that Bear creek can receive without violating the State’s DO

criterion. These maximum nutrient loads are the wasteload for the Kirksville WWTF. However, Table 13

shows that the wasteload allocations are different from the permitted wasteloads. Please verify.

TMDL Calculation – MS4 at Low Flow Condition

At the low flow condition, the flow above the Kirkville WWTF is 0.0128 cfs (or 0.000036 cubic meter per

second). This flow was then used to calculate the nutrient loads for the headwater, using the nutrient

data collected on August 25-26, 2009. These calculated loads should be the loads from the nonpoint

sources (i.e., load allocation). However, Table 16 shows these loads are the MS4 nutrient loads. Please

verify.

public comments - dnrdnr.mo.gov/env/wpp/tmdl/docs/2020-bear-3960-comments.pdf · 2020-01-27 ·...

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