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

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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

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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.

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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

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At 1.0 cfs conditions

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