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Wagoner County Rural Water District #4 DRAFT WASTELOAD ALLOCATION REPORT
NPDES#: OK0043257
Contents
1. Problem Definition .............................................................................................................. 2 2. Endpoint Identification ....................................................................................................... 2 3. Source Analysis .................................................................................................................. 2
3.1. Point Sources ...................................................................................................... 2 3.2. Non-Point Sources ............................................................................................... 3 3.3. Background ........................................................................................................ 3
4. Linkage between Sources and Receiving Water .................................................................... 3 4.1. Model Inputs ....................................................................................................... 3 4.2. Maximum Assimilative Capacity ............................................................................ 4
5. Margin of Safety ................................................................................................................ 4 6. Allocations ......................................................................................................................... 4 7. Final Recommendations ...................................................................................................... 4 8. Public Participation ............................................................................................................. 4 9. References ........................................................................................................................ 5 Appendix A - Desktop Model .................................................................................................... 7
List of tables and figures
Table 1 Maximum Assimilative Capacity ............................................................................................... 4 Table 2 Allocations ............................................................................................................................. 4
Figure 1 Wagoner Co. RWD #4 WWTF and Receiving Stream (Coal Creek) ............................................. 6
Draft Wasteload Evaluation for Wagoner Co. RWD #4
February 2018 Page 2 of 13
1. Problem Definition
Wagoner County Rural Water District (RWD) #4 is currently operating an aerated lagoon which discharges to an
unnamed tributary of Coal Creek (OKWBID #OK121500010270_00). Wagoner Co. RWD #4 has formally
requested to increase their design flow from 0.5 MGD to 0.850486 MGD. The primary concern of ODEQ is the
threat of in-stream organic enrichment and low dissolved oxygen (DO) due to the increase in discharge of treated
municipal wastewater.
This waterbody assessment addresses instream organic enrichment and Dissolved Oxygen (DO) through the use
of point source wasteload allocations of DO-demanding substances (CBOD and Ammonia). It also accounts for
non-point source impacts through the use of conservative kinetic inputs/assumptions and the use of Sediment
Oxygen Demand (SOD) to calculate the Load Allocation (LA).
Since the unnamed tributary is not listed in Appendix A of the Oklahoma Water Quality Standards (OAC 785:45),
it is assumed to have the designated use of Warm Water Aquatic Community (WWAC). Coal Creek is listed in
the Oklahoma Water Quality Standards as having the following beneficial uses:
Agriculture
Aesthetics
Warm Water Aquatic Community (WWAC)
Primary Body Contact Recreation
Public and Private water Supply
Fish Consumption
Coal Creek was considered as attaining its beneficial uses based on the default protocol because it wasn’t
assessed for any beneficial uses. This WLA has been developed in order to ensure that the limits assigned to the
discharge are stringent enough to maintain DO standards under critical conditions.
2. Endpoint Identification
The Oklahoma Water Quality Standards define DO criteria for two flow regimes: critical low-flow and nuisance
conditions. The critical low-flow will be either 7Q2 or 1.0 cfs, whichever is greater. Nuisance condition applies
only when there is no upstream flow.
The following numerical dissolved oxygen criteria for WWAC apply to the unnamed tributary to Coal Creek:
Critical Low-Flow Condition (7Q2)
Summer (Jun–Oct): 5.0 mg/L
Spring (Apr–May): 6.0 mg/L
Winter (Nov–Mar): 5.0 mg/L
Nuisance Condition (zero upstream flow)
Year-round: 2.0 mg/L
Oklahoma antidegradation policy (OAC 785:45-3) requires protecting all waters of the state from degradation
of water quality. The allocated loadings/concentrations in this report were set with regards for all elements of
the Oklahoma Water Quality standards that include the antidegradation policy.
3. Source Analysis
3.1. Point Sources
Wagoner Co. RWD #4 Wastewater Treatment Facility (WWTF)
Facility Legal Description: N½, SW¼, S18, T18N, R16E, I.M.,
Point of Discharge (POD): N½, SW¼, S18, T18N, R16E, I.M., or
Latitude: 36o 02' 13.003" N*
Longitude: 95o 38' 57.408" W*
* 1927 North American Datum
Draft Wasteload Evaluation for Wagoner Co. RWD #4
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Current Wasteload Allocation (WLA):
Permitted Flow: 0.5 MGD
Summer Limits (Jun–Oct): 15 mg/L CBOD5, 50 mg/L TSS, 4 mg/L NH3-N, 5 mg/L DO
Spring Limits (Apr-May): 15 mg/L CBOD5, 50 mg/L TSS, 6 mg/L NH3-N, 5 mg/L DO
Winter Limits (Nov–Mar): Lagoon Secondary with 5 mg/L DO (25 mg/L CBOD5, 90 mg/L TSS)
3.2. Non-Point Sources
The allocations in this waterbody assessment are driven by critical instream dissolved oxygen conditions (low-
flow and high temperature) as defined in the Oklahoma Water Quality Standards. Low-flow conditions, by
definition, assume little or no runoff. This assumption, combined with the use of background loadings from
upstream flow and conservative kinetic inputs, accounts for any non-point source (NPS) impact that may exist
in the study area.
3.3. Background
The following background conditions of the unnamed tributary to Coal Creek were used:
Flow (7Q2): 1.0 cfs
CBOD5: 2.0 mg/L
Ammonia: 0.15 mg/L
DO: 85% saturation at the regulatory seasonal temperature
4. Linkage between Sources and Receiving Water
The links between sources and the receiving streams can be established through typical water quality models such
as spreadsheet mass balance, desktop Streeter-Phelps model, modified Streeter-Phelps model (SOD included),
QUAL2E, QUALTX, SWAT, and HSPF etc. The more complicated a model becomes, the better it represents the
system being studied. However, a complex model also requires more data. According to the complexity of the
problem, available data and policy, Oklahoma’s desktop model is chosen for the project.
The Oklahoma’s desktop model is based on the modified Streeter-Phelps equation. The modified Streeter-Phelps
model can be found in Oklahoma Continuing Planning Process.
4.1. Model Inputs
The water quality model used to determine the impact of DO-demanding substances on the in stream DO
concentration is based on a modified version of the Streeter-Phelps equation. The primary kinetic inputs were
derived from literature values and the past WLAs performed by Oklahoma Department of Environmental
Quality.
Unnamed Tributary to Coal Creek
Proposed Permitted Flow: 0.840486 MGD
CBOD decay rate (K1): 0.30/day for Summer and Spring, 0.35/day for Winter
Reaeration rate for Reach 1(K2): 17.03/day
NBOD decay rate (Kn): 0.30/day
CBOD settling rate (Ks): 0.03/day
Sediment Oxygen Demand (SOD): 0.11 g/ft2/day
Hydraulic parameters were estimated using topographic map data and general assumptions. They are as follows:
Stream Slope: 10.4 ft/mi
Side Slope: 0.10 ft/ft
Manning’s “n”: 0.06
7Q2 for the unnamed tributary to Coal Creek was assigned 1.0 cfs because there is no data available for the
stream. The model outputs are included in the Appendix.
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4.2. Maximum Assimilative Capacity
The model was used to determine the stream’s maximum assimilative capacity during various seasons under
regulatory flow condition of 1.0 cfs or 7Q2 whichever is greater. To do this, the concentration of CBOD5 and
NH3-N of the point source are increased at the same rate until the predicted instream DO reaches the DO criteria.
The resultant mass loading represents the maximum assimilative capacity of the stream for DO-demanding
substances. The maximum assimilative capacity is measured in terms of dissolved oxygen as shown in the
following table.
Table 1 Maximum Assimilative Capacity
Season Maximum Assimilative Capacity
(lbs/day)
Summer (Jun–Oct) 950.6
Spring (Apr–May) 947.6
Winter (Nov–Mar) 2,717.1
The complete model results are attached.
5. Margin of Safety
The CPP specifies a 20% margin of safety (MOS) for uncalibrated, simple source models. This is implemented
in the model by increasing the inputs of DO-demanding substances (CBOD5 and NH3-N) proportionally until
the DO criteria are met. The quantified MOS is equal to 20% of maximum wasteload allocations. Together with
the MOS, load allocation, wasteload allocation and reserved capacity are calculated in the model and will be
presented in the next section.
6. Allocations
Wagoner Co. RWD #4 WWTP discharges into an unnamed tributary of Coal Creek about 9.4 miles upstream
from the confluence. In modeling this wasteload allocation, the DO recovers before reaching Coal Creek. The
allocation of loads calculated by the desktop model was shown in the following table.
Table 2 Allocations
Season Load Allocation
(lb/day)
Wasteload Allocation
(lb/day)
MOS (20%)
(lbs/day)
Reserved Capacity
(lbs/day)
Summer 319.3 362.4 190.1 78.8
Spring 51.5 362.4 189.5 344.2
Winter 101.0 362.4 543.4 1,710.2
7. Final Recommendations
The following changes are recommended for inclusion in the Oklahoma Water Quality Management Plan (208
Plan).
Wagoner Co. RWD #4 Wastewater Treatment Plant
Proposed Design Flow: 0.840486 MGD
Summer Limits (Jun–Oct): 15 mg/L CBOD5, 50 mg/L TSS, 4 mg/L NH3-N, 5 mg/L DO
Spring Limits (Apr-May): 15 mg/L CBOD5, 50 mg/L TSS, 4 mg/L NH3-N, 6 mg/L DO
Winter Limits (Nov–Mar): 15 mg/L CBOD5, 50 mg/L TSS, 4 mg/L NH3-N, 3 mg/L DO
8. Public Participation
This Draft WLA report will be submitted to EPA for technical approval. After technical approval is received, the
proposed permit limits will be sent for public comments. Public comments received during this period will be
responded to and become part of the WLA report.
Draft Wasteload Evaluation for Wagoner Co. RWD #4
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9. References
1. Title 785, Oklahoma Administrative Code, Chapter 45 Oklahoma’s Water Quality Standards, State Of Oklahoma,
2007.
2. Oklahoma Desktop Model – One Reach, version 3.1, Watershed Planning Section, Oklahoma Department of
Environmental Quality, Oklahoma City Oklahoma, 2008.
3. Oklahoma Continuing Planning Process, 2006 edition, Oklahoma Department of Environmental Quality, State
of Oklahoma, 2006.
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Figure 1 Wagoner Co. RWD #4 WWTF and Receiving Stream (Coal Creek)
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Appendix A - Desktop Model