Nutrient Pollution

City of Franklin's Sewage Treatment Plant Can Reduce Phosphorus Pollution

The City of Franklin can significantly reduce discharges from its sewage treatment plant. TDEC must require the City to utilize its technology to restore the Harpeth to the required water quality standards.

City of Franklin's Ability to Reduce Phosphorus Pollution

High levels of nutrients like phosphorus are a problem for water quality and public health. Too much phosphorus can cause algal blooms, including toxic blue-green algae, which can cause health and environmental problems. CLICK HERE to learn more about the potential dangers of algal blooms.

National experts say current conditions on the Harpeth River are already past the tipping point for production of potentially toxic blue-green algae. We raised these issues, along with a number of other legal obligations applicable to the sewer plant, in our comments on the permit that TDEC issued in 2017.  New work since then has validated these comments, and they remain valid.

Franklin is completing expansion of its sewer plant to discharge 16 million gallons of sewage effluent per day.  TDEC proposes to issue a permit (the “Draft Permit”) for the operation of this expanded plant.  Unfortunately, despite the continued impairment of the river by pollution from Franklin’s plant, TDEC repeats many of the same mistakes it made in the last (2017) permit.  Therefore, Harpeth Conservancy must oppose the issuance of the Draft Permit in its current form.  To read Harpeth Conservancy’s complete comments on the Draft Permit, click HERE

Harpeth Conservancy blue heron logo

Tennessee Department of Environment and Conservation's Draft Permit Does Not Require Franklin to Use Taxpayer-funded Equipment to Reduce Pollution in the Harpeth River.

Franklin is building its sewer plant with public funds, including $100+ million in loans from Tennessee’s State Clean Water Revolving Loan Fund.  This new plant includes biological nutrient reduction capabilities as well as the chemical phosphorus capabilities required in the 2016 Settlement Agreement of the citizen suit brought by HC against the City for alleged permit violations. The Draft Permit itself acknowledges these capabilities:  

The biological treatment system, consisting of three oxidation ditches, will be modified to include a fermentation zone for more efficient nutrient removal and an alum feed system will be added for chemical phosphorus removal capabilities.

Even though the taxpayers of the State and of Franklin itself are paying for these systems, the draft permit has not required they use them to try to achieve the results of which they are capable. 

Additionally, there is no requirement that Franklin continue previous optimization efforts.  These are now described as merely voluntary measures.



Rather than fulfill its statutory obligation to restore the Harpeth River, by allowing Franklin to pollute far more than it is currently discharging, it appears that TDEC is attempting to illegally and prematurely reserve for the City capacity to pollute from its planned South “Clean Water Facility” to expand its discharge capacity to 24 MGD.  Such an attempt is in effect an attempt to issue a future permit without compliance with all the legal requirements therefor. 

The only so-called “requirement” in the permit is an “action level” that calls on Franklin to report to TDEC when its total monthly phosphorus discharge is greater than an average level of 1.3 mg/L during that month. When Franklin exceeds that action level, it is not a violation of the permit, but Franklin must report to TDEC and analyze and refine its operations to reduce total phosphorus levels to below the action level. The permit also now requires Franklin to submit an annual report on its efforts to optimize its plant to reduce nutrient pollution.

Franklin has done better at reducing phosphorus pollution over the years , which we have fiercely advocated for and appreciate.  Franklin now discharges approximately 62 pounds per day.  Franklin’s results are encouraging, and we commend them and encourage the City to continue to improve even more.  Unfortunately, even at Franklin’s current discharge levels the river is still impaired.  And, the Draft Permit allows Franklin to discharge almost THREE (3) times much phosphorus as it currently discharges!


Franklin Sewer Treatment Plant Phosphorus Discharge to the Harpeth River. Data were compiled from the City of Franklin Monthly Operating Reports (MORs)


For many years, the Harpeth Conservancy has been concerned that the Franklin sewage treatment plant was not being operated as efficiently as it could be or in compliance with legal requirements. In 2014 the Harpeth Conservancy was forced to file a citizen suit under the federal Clean Water Act when Franklin rebuffed attempts to resolve issues amicably (citizen suit available HERE). The Harpeth Conservancy raised a number of issues in that action, including repeated sewer overflows and Franklin’s failure to submit a nutrient optimization report as required by the discharge permit for the plant. We successfully settled that case, resulting in a number of improvements in the operations of the Franklin sewer plant.

On June 1, 2017, TDEC issued to Franklin the permit for the City’s sewer plant (permit available HERE). The fundamental problem in the permit issued by TDEC was that it failed to recognize that the Harpeth River is impaired by phosphorus pollution (and violates State water quality standards for dissolved oxygen) and is on the State’s 303(d) list. 

The Harpeth River is impaired for phosphorus downstream of the City of Franklin where the Franklin sewer plant is located. In addition, almost 50 river miles downstream are also below water quality standards.

According to TDEC’s 303(d) list, a biennial report of waters that are “impaired” and don’t meet the water quality standards TDEC itself sets, the cause of the phosphorus pollution is Franklin’s sewage treatment plant (and Franklin’s stormwater systems). To read the State’s 303(d) list, click here.

Franklin’s own monitoring data show that just one (1) river mile downstream from the plant, from 2002 to 2014, 73% of the load of total phosphorus in the Harpeth, and 50% of the river’s load of total nitrogen, are from the Franklin sewer plant when effluent is 15% or more of the river’s flow. During October 2016, the last drought period, the daily average amount of treated sewage effluent just one (1) river mile downstream from the plant was 55% of the entire river’s flow.  

Over the period of 2018 to 2022, Franklin’s sewer plant discharged approximately 62 pounds of phosphorus per day. At this level, the Harpeth River is impaired by phosphorus pollution. The 2017 permit allowed Franklin to discharge more than double the amount of phosphorus it was actually discharging. The permit allowed Franklin to discharge 174.5 pounds of phosphorus per day. By comparison, Georgia and Virginia have achieved phosphorus outputs of 8 to 13 pounds per day. 

This was one of the primary reasons the Harpeth Conservancy filed an appeal of the permit. Franklin also appealed its own permit, claiming either that no phosphorus limit is necessary, or that it should be allowed to discharge even more phosphorus! 

Harpeth Conservancy and Franklin subsequently dismissed their permit appeals. Harpeth Conservancy agreed to dismiss its appeal on the expectation that TDEC, Franklin, and other stakeholders would work to promptly complete the required pollution study and reduction plan (called a “total maximum daily load” or “TMDL”).  A copy of Harpeth Conservancy’s letter can be found here. To read Harpeth Conservancy’s press release on the permit dismissal click here.  Unfortunately, seven (7) years after it was first announced, the TMDL remains far from completion and there is not plan or schedule to complete it.

TDEC Has Yet to Complete the Harpeth River TMDL Seven (7) (!) Years Later

TDEC announced that a new pollution reduction study and plan (“Total Maximum Daily Load” or “TMDL”) was required and would be undertaken in July 2015.  Unfortunately, seven years later, TDEC is nowhere near completing the TMDL.  No load allocations, wasteload allocations, or any other of the required or recommended elements of a TMDL are even mentioned in the Draft Permit.  The ONLY reference to the TMDL announced in 2015 is the following statement:

Action level for total phosphorus has been developed in the absence of a TMDL for nutrients on the Harpeth River.

Reference to the current TMDL is even dropped even from the Draft Permit’s reopener clause. 

The Harpeth TMDL is particularly important as it is the first TMDL in the State of Tennessee to utilize a Water Quality Analysis Simulation Program (WASP) developed and calibrated by the U.S. Environmental Protection Agency (EPA) Region 4 for the Harpeth River.  The WASP model allows the user to calculate water quality and flow conditions in every stream segment in the watershed based on observed data that was periodically collected between 2012 and 2019.  This model can be immensely helpful to identify temporal and spatial trends in pollution loads and what pollution level is acceptable to satisfy state water quality criteria.  Once the Harpeth TMDL focused on nutrients and low dissolved oxygen is complete, the WASP model and methodology can be translated to other rivers and streams in TN for TMDL development.  Completion of the Harpeth TMDL must be a heightened priority for TDEC and all stakeholders within the next two years in order to establish “best practices” for a nutrient based TMDL especially in light of the sewer expansion proposals currently underway in Franklin and the Water Authority of Dickson County. The WASP model was provided to TDEC and other stakeholders in Spring 2021, over a year later, there has been little progress to identify load limits for the Harpeth River.

The CWA and TNWQCA Require TDEC to Set a Water Quality Based Effluent Limit (“WQBEL”) Required to Restore the Harpeth River, but the Draft Permit Improperly Fails to Do So

The federal Clean Water Act is designed to clean up the nation’s waters, with the goal of removing waters, such as the Harpeth River, from the State’s 303 (d) list of impaired waters. To do this, the State envisions a series of more stringent discharge limits until the waterbody in question meets water quality standards and it can be removed from the 303(d) list. At a minimum, all dischargers must employ technology-based effluent limits (“TBELs”).  If these are insufficient, then water quality-based effluent limits (“WQBELs”) must be imposed.   This can be done through a TMDL, but regulators cannot wait for a TMDL to be completed.   Permits are required to include “any more stringent limitation, including those necessary to meet water quality standards.” 

The law does not allow TDEC to put off setting a water quality-based effluent limit into the permit based on the fact that it is preparing a TMDL.

This is Tennessee law as well, as established by TDEC’s own rules, for example:

0400-40-05-.07 TERMS AND CONDITIONS OF PERMITS. (1) When a permit is granted it shall be subject to the provisions of T.C.A. §§ 69-3-101 et seq., these regulations, and any special terms or conditions the Commissioner determines are necessary to fulfill the purposes or enforce the provisions of that section. (a) … If more stringent effluent limitations are necessary to implement applicable water quality standards, to avoid conflict with an approved area-wide waste treatment management plan, or to comply with other state or federal laws or regulations, then they should be imposed in the permit.

Yet, TDEC’s draft permit ignores the CWA and its own rules to allow Franklin to continue to pollute the Harpeth River by setting a discharge limit far in excess of not only current discharge levels but also what the river can tolerate as established by TDEC’s continued designation of the river as impaired for nutrients.

Proper Permit Discharge Limits Can Easily Be Calculated, and Many Parties’ Calculations Agree and Must Be Used

It is possible to calculate now what a WQBEL for the Franklin STP should be.  Indeed, Dr. JoAnn Burkholder did so five (5) years ago.  HC’s review and updating of her calculations show that they remain valid.  Indeed, HC’s review shows remarkable consistency not only between its and Dr. Burkholder’s calculations, but also those of TDEC.  In short, failure to impose a WQBEL consistent with this consensus of experts would be arbitrary, capricious, and an abuse of discretion.

To review, Dr. Burkholder observed in 2016 as follows:

The numeric translators developed by TDEC should be reduced to reflect reference conditions. It is obvious that the “reference” streams selected by TDEC are not science-based and do not reflect reference or minimally impacted conditions, because their nutrient concentrations do not differ from concentrations in the other streams of subecoregions 71h and 71i, especially TN. Based on this assessment, the reference conditions used for numeric translators of the narrative criterion should be 170 µg TP/L (similar to TDEC’s numeric translator of 180 µg TP/L), and 610 µg TN/L (much lower than TDEC’s value of 920 µg/L).

HC’s Dr. Ryan Jackwood updated the following information about the Franklin STP and Harpeth River Nutrient Loading:

Monthly average TP effluent load for Franklin STP between March 2018 and April 2022 are approximately 63.0 lbs/day (see chart below). This date range was used to capture the effluent loads that occurred after treatment optimization for the removal of TP. The average TP load is almost three-times lower than the permit limit of 174.5 lbs/day (derived from annual load limit of 63,693 lbs/year). It is important to note that the annual limit of 63,693 lbs/year (on a rolling annual average) is the same limit from the previous permit under the “old” STP with the assumption that the “new” WRF will have the capability to reduce TP concentration and essentially maintain the current TP load. Thus, the TP permit limit should reflect this improved capability for treatment. For example, if the “new” plant under the Draft Permit limit averaged two-times more TP load then is currently happening with the “old” plant, the monthly average load would be 126 lbs/day (45,990 lbs/year), which is still well below the Draft Permit limit BUT would result in higher TP loads in the Harpeth River (already impaired for nutrients).
Critical periods of concern for the Harpeth River occur when flow is low, and the Franklin STP is contributing a disproportional amount of TP to the river. For example, during low flow conditions assuming an average TP concentration in the river for the days with lowest 10% of flow (This equals 0.49 mg TP/L; Dr. Burkholder’s calculations yielded a very similar result of 0.494 mg TP/L).
7Q10 = 1.848 MGD (2.861 cfs) – TDEC revised for Draft Permit (Appendix V). This statistic is based on April 2014 through March 2021 after the removal of the lowhead dam per the permit rationale. This is almost 3.5 times higher than 0.54 MGD that has been the 7Q10 applied to several versions of the permit. The use of the USGS SW Stat tool will vary the output. Since the 7Q10 is a regulatory driver and affects management decisions and calculations in the TMDL effort, it will be valuable to determine the most appropriate data set to use to set the 7Q10 with the TMDL technical group. It could be that the data set TDEC has used in the draft permit is most appropriate, but it is a significant change from the prior value for the 7Q10 statistic.

The effluent and loading values from March 2018 to April 2022 for the Franklin STP can be calculated using the City’s own monthly operating report (“MOR”) dataset, as follows:

First, Dr. Jackwood has re-calculated the 95th percentiles of the following values, without prejudice to HC’s objections to TDEC’s misuse of those values:

  • TP Load in Effluent = 83.091 lbs/day Annual Rolling Average (only includes July 2018 to April 2022)

Dr. Jackwood then updated Dr. Burkholder’s calculation of a WQBEL as follows:

Qs = 7Q10 flow rate = 1.848 (from Draft Permit and is different from prior permits)

Cs = Harpeth River TP or TN concentration (data from WASP model)

Qd = Proposed flow from Franklin STP = 12 mgd or 16 mgd

Cd = Calculated concentration from Franklin STP to achieve Target TP in Harpeth

Qr = Downstream flow in Harpeth = Qs + Qd

TTP/N = Target TP/N concentration in Harpeth downstream of FRANKLIN STP

12 MGD: Cd = 0.132 mg TP/L to achieve 0.180 mg TP/L– Note that this concentration is determined by TDEC ecoregion report for nutrient criteria development.

16 MGD: Cd = 0.144 mg TP/L to achieve 0.180 mg TP/L– Note that this concentration is determined by TDEC ecoregion report for nutrient criteria development.

  • Science-based WQBELs for TP and TN should be developed for setting the final permit levels for these pollutants, based on target concentrations in the receiving river water of 180 µg TP/L (0.180 mg/L) and 640 µg TN/L. This analysis suggests that the WQBEL for TP in the summer season should be 130-140 µg TP/L (0.13 to 0.14 mg/L), and the WQBEL for TN should be 1000 µg TN/L (1.00 mg/L). Based on the available information on river water quality and Franklin STP design, these WQBELs for TP and TN can be achieved through BNR technology already available or planned to be available at the FRANKLIN STP.

Numeric targets for TP concentration and TN concentration in the Harpeth in the section at the Franklin STP discharge based on Water Quality Analysis Simulation Program (WASP) model:

A “current conditions” and “natural” model were developed and calibrated by the EPA.  Based on 75th and 90th percentiles for the different models, target concentrations were be calculated, as follows:

Red line = Current conditions in Harpeth River – 90 percentile = 0.546 mg TP/l; 75 percentile = 0.380 mg TP/l Black line = “Natural” conditions in Harpeth River (i.e. reference conditions) – 90 percentile = 0.207 mg TP/l; 75 percentile = 0.380 mg TP/l
Red line = Current conditions in Harpeth River – 90 percentile = 2.25 mg TN/l; 75 percentile = 1.20 mg TN/l Black line = “Natural” conditions in Harpeth River (i.e. reference conditions) – 90 percentile = 0.67 mg TN/l; 75 percentile = 0.37 mg TN/l

The “natural” model was built by EPA in the WASP model to represent reference conditions for the Harpeth and can be utilized to quantify target TP or TN concentration desired for the Harpeth River.  0.176 mg TP/L and 0.207 mg TP/L calculated from the “natural” model are the 75th and 90th percentile concentrations from this reference model and are virtually identical to the 0.180 mg TP/L numeric target independently calculated by TDEC for the state numeric translator using reference stream data and not the WASP model

In short, there is a remarkable concurrence between the values yielded by the various parties’ calculations.   TDEC can and must utilize this consensus between its own and various experts to set a WQBEL for the Franklin STP NOW.

Progress and Future Goals

TDEC and Franklin know what is required to reduce phosphorus pollution to restore the Harpeth River.  Indeed, Franklin has already used huge amounts of taxpayer monies to install pollution reduction systems, but inexplicably is not even required to try to use them!  The TMDL pollution reduction plan is nowhere near completion seven (7) years after it was announced. 


To  remedy this intolerable situation, TDEC must revise the Draft Permit to include a Water Quality Based Effluent Limit (“WQBEL”) at the levels calculated by the many experts who have already examined the issues.  This WQBEL must be in place until the TMDL is completed.  And TDEC must formulate a plan and schedule for finishing the TMDL. It must no longer be allowed to languish – too much is at stake. 

 CLICK HERE to learn more about the Harpeth River TMDL and how the Harpeth River is pushing for a science-driven, transparent, speedy process to put the river on the path to restoration!

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