No. TN0064041 ( Modified)

Authorization to discharge under the National Pollutant Discharge Elimination System ( NPDES)

Issued By Tennessee Department of Environment and Conservation Division of Water Pollution Control 401 Church Street 6th Floor, L & C Annex Nashville, Tennessee 37243 1534 Under authority of the Tennessee Water Quality Control Act of 1977 ( T. C. A. 69 3 101 et seq.) and the delegation of authority from the United States Environmental Protection Agency under the Federal Water Pollution Control Act, as amended by the Clean Water Act of 1977 ( 33 U. S. C. 1251, et seq.)

Discharger: Metro Nashville Airport Authority is authorized to discharge: treated aircraft deicing fluid and storm water runoff from Outfall 002, overflow from South and North Ponds from Outfalls 003 and 004, and storm water runoff from Outfalls SW1 through S11 from a facility located: in Nashville, Davidson County, Tennessee to receiving waters named: Sims Branch at miles 1.8 to Mill Creek at mile 1.6 to the Cumberland River at mile 194.5 ( Outfall 002); Sims Branch at miles 1.9 and 2.0 ( Outfalls 003 and 004), McCrory Creek to Stones River at mile 5.8 ( Outfall SW1), Sims Branch to Mill Creek at mile 1.6 to the Cumberland River at mile 194.5 ( Outfalls SW2, SW3, SW4, SW5, & SW6); and Mill Creek to the Cumberland River at mile 194.5 ( Outfalls SW7, S10, & S11)

in accordance with effluent limitations, monitoring requirements and other conditions set forth herein.

This permit shall become effective on: January 1, 2004 This permit shall expire on: February 28, 2005 Issuance date: December 16, 2003 Paul E. Davis, Director Division of Water Pollution Control ii CN 0759 RDAs 2352 and 2366 i TABLE OF CONTENTS Page PART I A. EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS ............................... 1 B. MONITORING PROCEDURES ..................................................................................... 4 1. Representative Sampling........................................................................................... 4 2. Sampling Frequency .................................................................................................. 4 3. Test Procedures......................................................................................................... 4 4. Recording of Results.................................................................................................. 5 5. Records Retention ..................................................................................................... 5 C. DEFINITIONS................................................................................................................ 5 D. REPORTING................................................................................................................. 6 1. Monitoring Results ..................................................................................................... 6 2. Additional Monitoring by Permittee ............................................................................ 7 3. Falsifying Reports ...................................................................................................... 7 E. SCHEDULE OF COMPLIANCE..................................................................................... 7 PART II A. GENERAL PROVISIONS .............................................................................................. 7 1. Duty to Reapply ......................................................................................................... 7 2. Right of Entry ............................................................................................................. 7 3. Availability of Reports ................................................................................................ 8 4. Proper Operation and Maintenance........................................................................... 8 5. Treatment Facility Failure........................................................................................... 8 6. Property Rights .......................................................................................................... 8 7. Severability ................................................................................................................ 9 8. Other Information....................................................................................................... 9 B. CHANGES AFFECTING THE PERMIT ...................................................................... 9 1. Planned Changes ...................................................................................................... 9 2. Permit Modification, Revocation, or Termination........................................................ 9 3. Change of Ownership .............................................................................................. 10 4. Change of Mailing Address...................................................................................... 10 ii C. NONCOMPLIANCE..................................................................................................... 10 1. Effect of Noncompliance.......................................................................................... 10 2. Reporting of Noncompliance.................................................................................... 11 3. Overflow................................................................................................................... 11 4. Upset ....................................................................................................................... 12 5. Adverse Impact ........................................................................................................ 13 6. Bypass ..................................................................................................................... 13 7. Washout .................................................................................................................. 14 D. LIABILITIES................................................................................................................. 14 1. Civil and Criminal Liability ........................................................................................ 14 2. Liability Under State Law ......................................................................................... 14 PART III A. TOXIC POLLUTANTS ................................................................................................ 14 B. REOPENER CLAUSE................................................................................................ 15 C. PLACEMENT OF SIGNS........................................................................................... 15 D. ANTIDEGRADATION.................................................................................................. 16 E. BIOMONITORING REQUIREMENTS......................................................................... 16 PART IV STORM WATER POLLUTION PREVENTION PLAN A. PLAN IMPLEMENTATION........................................................................................ 19 B. PLAN AVAILABILITY................................................................................................ 19 C. PLAN MODIFICATION ............................................................................................. 19 D. MONITORING PLAN................................................................................................ 19 PART V WASTELOAD ALLOCATION STUDY FOR SIMS BRANCH 1.0 INTRODUCTION ............................................................................................... 30 1.1 Background ....................................................................................................... 30 1.2 Purpose............................................................................................................. 30 iii 1.3 Scope of Work .................................................................................................. 32 2.0 WASTELOAD ALLOCATION STUDY ............................................................... 33 2.1 Work Plan.......................................................................................................... 33 2.2 Reconnaissance Field Survey........................................................................... 33 2.3 Time of travel Surveys ...................................................................................... 34 2.4 Calibrate Water Quality Model........................................................................... 38 2.5 Continuous Monitoring....................................................................................... 40 2.6 Model Validation................................................................................................ 40 2.7 Wasteload Allocation Modeling ......................................................................... 40 2.8 Final Report....................................................................................................... 41 3.0 SCHEDULE....................................................................................................... 42 ADDENDUM TO RATIONALE dated September 18, 2003 A 1 to A 8 RATIONALE I DISCHARGER........................................................................................................ R 1 II PERMIT STATUS.................................................................................................... R 1 III FACILITY DISCHARGES AND RECEIVING WATERS........................................... R 2 IV APPLICABLE EFFLUENT LIMITATIONS GUIDELINES.......................................... R 2 V PREVIOUS PERMIT LIMITS AND MONITORING REQUIREMENTS...................... R 2 VI HISTORICAL MONITORING AND INSPECTION .................................................... R 3 VII NEW PERMIT LIMITS AND MONITORING REQUIREMENTS................................ R 4 VIII BIOMONITORING REQUIREMENTS .................................................................... R 11 IX ANTIDEGRADATION ............................................................................................ R 12 X PERMIT DURATION............................................................................................. R 13 APPENDIX 1. FACILITY DISCHARGES AND RECEIVING WATERS............................................ R 14 2. PREVIOUS PERMIT LIMITS AND MONITORING REQUIREMENTS ...................... R 19 3. HISTORICAL MONITORING AND INSPECTION..................................................... R 21 iv 4. NEW PERMIT LIMITS.............................................................................................. R 29 VMJ TN0064041. DOC Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 1 of 40 PART I __________________________________________________________________________

A. EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS Metro Nashville Airport Authority is authorized to discharge treated aircraft deicing fluid and storm water runoff from Outfall 002, overflow from South and North Ponds from Outfalls 003 and 004, and storm water runoff from Outfalls SW1 through S11 to Sims Branch at miles 1.8 to Mill Creek at mile 1.6 to the Cumberland River at mile 194.5 ( Outfall 002); Sims Branch at miles 1.9 and 2.0 ( Outfalls 003 and 004), McCrory Creek to Stones River at mile 5.8 ( Outfall SW1), Sims Branch to Mill Creek at mile 1.6 to the Cumberland River at mile 194.5 ( Outfalls SW2, SW3, SW4, SW5, & SW6); and Mill Creek to the Cumberland River at mile 194.5 ( Outfalls SW7, S10, & S11). These discharges shall be limited and monitored by the permittee as specified below: PERMIT LIMITS  OUTFALL002 EFFLUENT LIMITATIONS MONITORING MONTHLY DAILY REQUIREMENTS EFFLUENT AVG. CONC. AVG. AMNT. MAX. CONC. MAX. AMNT. MSRMNT. SAMPLE CHARACTERISTIC ( mg/ l) ( lb/ day) ( mg/ l) ( lb/ day) FRQNCY. TYPE FLOW Report ( MGD) * Report ( MGD) * 1/ Week Instantaneous pH** Range 6.0  9.0 1/ Week Grab COD   Report  1/ Week Grab TOTAL SUSPENDED SOLIDS ( TSS) 30.0  Report  1/ Month Grab OIL & GREASE 10.0  15.0  1/ Month Grab DISSOLVED OXYGEN ( D. O.)   6.0 Minimum  1/ Week Grab TEMPERATURE, Effluent Report Effluent Temperature 1/ Week Grab NITROGEN, AMMONIA TOTAL 1.0  2.0  1/ Week Grab RECEIVING STREAM FLOW *** 1/ Week Grab 48 HR LC50 Survival, Reproduction, & Growth in 100% Effluent 1/ Quarter Composite ****

CBOD5 3.0  4.5  1/ Month Grab CBOD5 6.0  9.0  1/ Month Grab CBOD5 12.0  18.0  1/ Month Grab CBOD5 Report  Report  1/ Month Grab CBOD5 25.0  37.5  1/ Week Grab CBOD5 45.0  67.5  1/ Week Grab CBOD5 65.0  97.5  1/ Week Grab CBOD5 65.0  Report  1/ Week Grab Report ( CFS)

Receiving Stream Flow > 1.0 CFS and < 3.0 CFS Receiving Stream Flow > 0.5 CFS and < 1 CFS Receiving Stream Flow > 3 CFS Summer ( May 1 through September 30) Maximum Receiving Stream Temperature: 22 ° C Receiving Stream Flow > 0.5 CFS and < 1.0 CFS Receiving Stream Flow > 1 CFS and < 1.5 CFS Receiving Stream Flow > 0 CFS and < 0.5 CFS *****

Winter ( October 1 through April 30) Maximum Receiving Stream Temperature: 17 ° C Receiving Stream Flow > 0 CFS and < 0.5 CFS Receiving Stream Flow > 1.5 CFS * Flow shall be reported in Million Gallons per Day ( MGD). ** pH analyses shall be performed within fifteen ( 15) minutes of sample collection. *** Receiving stream flow is based on a 24 hour average value. Receiving stream flow will be measured at a location, and using methods approved by the division. **** To be conducted once in each quarter ( Jan Mar; Apr Jun; Jul Sep; Oct Dec) during which aircraft deicing is/ has occurred. See Part III for methodology. ***** Permittee should make every effort to prevent discharge when the flow of Sims Branch is below 0.5 cfs. However, if discharge is necessary, these limits apply. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 2 of 40 Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 3 of 40 Additional monitoring requirements and conditions applicable to all outfalls include:

There shall be no distinctly visible floating scum, oil or other matter contained in the wastewater discharge. The wastewater discharge must not cause an objectionable color contrast in the receiving stream.

The wastewater discharge shall not contain pollutants in quantities that will be hazardous or otherwise detrimental to humans, livestock, wildlife, plant life, or fish and aquatic life in the receiving stream.

Sludge or any other material removed by any treatment works must be disposed of in a manner which prevents its entrance into or pollution of any surface or subsurface waters. PERMIT LIMITS OUTFALL 004 EFFLUENT LIMITATIONS MONITORING MONTHLY DAILY REQUIREMENTS EFFLUENT AVG. CONC. AVG. AMNT. MAX. CONC. MAX. AMNT. MSRMNT. SAMPLE CHARACTERISTIC ( mg/ l) ( lb/ day) ( mg/ l) ( lb/ day) FRQNCY. *** TYPE FLOW Report ( MGD) * Report ( MGD) * 1/ Month Estimate pH** Report 1/ Month Grab CBOD5   Report  1/ Month Grab COD   Report  1/ Month Grab TOTAL SUSPENDED SOLIDS ( TSS)   Report  1/ Month Grab OIL & GREASE   Report  1/ Month Grab * Flow shall be reported in Million Gallons per Day ( MGD). ** pH analyses shall be performed within fifteen ( 15) minutes of sample collection. *** Once per month, or once per occurrence, whicever is less frequent.

PERMIT LIMITS EFFLUENT LIMITATIONS MONITORING MONTHLY DAILY REQUIREMENTS EFFLUENT AVG. CONC. AVG. AMNT. MAX. CONC. MAX. AMNT. MSRMNT. SAMPLE CHARACTERISTIC ( mg/ l) ( lb/ day) ( mg/ l) ( lb/ day) FRQNCY. TYPE ***

FLOW Report ( MGD) * Report ( MGD) * Semi annual Estimate pH ** Report Semi annual Grab CBOD5   Report  Semi annual Grab COD   Report  Semi annual Grab TOTAL SUSPENDED SOLIDS ( TSS)   Report  Semi annual Grab OIL & GREASE   Report  Semi annual Grab *

** pH analyses shall be performed within fifteen ( 15) minutes of sample collection.

*** OUTFALL SW1  Storm Water ( 3,192 acres) OUTFALL SW2  Storm Water ( 960 acres) OUTFALL SW7  Storm Water ( 492 acres)

The permittee shall provide the date and duration ( in hours) of the qualifying storm event( s) sampled; rainfall measurements or estimates ( in inches) of the storm event that generated the sampled runoff; the duration between the storm event sampled and the end of the previous measurable ( greater than 0.1 inch rainfall) storm event; and an estimate of the total volume of the discharge sampled. Flow shall be reported in Million Gallons per Day ( MGD).

Samples shall be collected within 30 minutes of initiation of flow during a storm event that is greater than 0.1 inches, and that occurs at least 72 hours after any previous storm event with rainfall of 0.1 inches or greater.

Note: Storm water runoff from Outfalls SW1, SW2, & SW7 is considered to be representative of storm water runoff from Outfalls SW1 through S11. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 4 of 40 Additionally, the disposal of such sludge or other material must be in compliance with the Tennessee Solid Waste Disposal Act, TCA 68 31 101 et seq. and the Tennessee Hazardous Waste Management Act, TCA 68 46 101 et seq.

Surfactants in the oil/ water separator would inhibit separation of oil from water. The Division proposes for MNAA to use Best Management Practices ( BMPs) in the use of soaps and detergents ( if used in the equipment cleaning) that may enter the oil/ water separator as part of their overall facility Storm Water Pollution Prevention Plan ( SWPPP).

The design, installation, and exact location of in stream flow monitoring system( s) for purposes of complying with monitoring requirements and effluent limitations at Outfall 002 should be done in consultation with and upon approval of the Division's personnel in Environmental Assistance Center  Nashville.

B. MONITORING PROCEDURES 1. Representative Sampling Samples and measurements taken in compliance with the monitoring requirements specified herein for Outfalls 002 and 004 shall be representative of the volume and nature of the monitored discharge, and shall be taken after treatment and prior to mixing with uncontaminated storm water runoff or the receiving stream. Samples and measurements taken in compliance with the monitoring requirements specified herein for Outfalls SW1, SW2, and SW7 shall be representative of the volume and nature of the storm water runoff.

2. Sampling Frequency Where the permit requires sampling and monitoring of a particular effluent characteristic( s) at a frequency of less than once per day or daily, the permittee is precluded from marking the " No Discharge" block on the Discharge Monitoring Report if there has been any discharge from that particular outfall during the period which coincides with the required monitoring frequency, i. e. if the required monitoring frequency is once per month or 1/ month, the monitoring period is one month, and if the discharge occurs during only one day in that period then the permittee must sample on that day and report the results of analyses accordingly.

3. Test Procedures a. Test procedures for the analysis of pollutants shall conform to regulations published pursuant to Section 304 ( h) of the Clean Water Act ( the " Act"), as amended, under which such procedures may be required.

b. Unless otherwise noted in the permit, all pollutant parameters shall be determined according to methods prescribed in Title 40, CFR, Part 136, as amended, promulgated pursuant to Section 304 ( h) of the Act. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 5 of 40 4. Recording of Results For each measurement or sample taken pursuant to the requirements of this permit, the permittee shall record the following information:

a. The exact place, date and time of sampling;

b. The exact person( s) collecting samples;

c. The dates and times the analyses were performed;

d. The person( s) or laboratory who performed the analyses;

e. The analytical techniques or methods used, and;

f. The results of all required analyses.

5. Records Retention All records and information resulting from the monitoring activities required by this permit including all records of analyses performed and calibration and maintenance of instrumentation shall be retained for a minimum of three ( 3) years, or longer, if requested by the Division of Water Pollution Control.

C. DEFINITIONS The Daily Maximum Concentration is a limitation on the average concentration, in milligrams per liter ( mg/ L), of the discharge during any calendar day. When a proportional toflow composite sampling device is used, the daily concentration is the concentration of that 24 hour composite; when other sampling means are used, the daily concentration is the arithmetic mean of the concentrations of equal volume samples collected during any calendar day or sampling period.

The Monthly Average Concentration, a limitation on the discharge concentration, in milligrams per liter ( mg/ L), is the arithmetic mean of all daily concentrations determined in a one month period. For the purpose of this definition, a frequency of 2/ Month is representative of 2 separate daily samples, each sample having been collected on a separate day during the monitoring period.

The Instantaneous Concentration ( Minimum or Maximum) is a limitation on the concentration, in milligrams per liter ( mg/ L), or other appropriate units, of any pollutant contained in the discharge determined from a grab sample taken at any point in time.

A Composite Sample, for the purposes of this permit, is a sample collected continually over a period of 24 hours at a rate proportional to the flow. Composite sample should be a combination of at least 8 sample aliquots of at least 100 milliliters, collected at periodic intervals during the operating hours of a facility over a 24 hour period. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 6 of 40 A Grab Sample, for the purposes of this permit, is defined as a single effluent sample of at least 100 milliliters collected at a randomly selected time over a period not exceeding 15 minutes. The sample( s) shall be collected at the period( s) most representative of the total discharge.

For the purpose of this permit, a Calendar Day is defined as any 24 hour period.

For the purpose of this permit, a Quarter is defined as any one of the following three month periods: January 1 through March 31, April 1 through June 30, July 1 through September 30, or October 1 through December 31.

For the purpose of this permit, Semi annually means the same as " once every six months." Measurements of the effluent characteristics concentrations may be made anytime during a 6 month period beginning from the issuance date of this permit so long as the second set of measurements for a given 12 month period are made approximately 6 months subsequent to that time, if feasible.

For the purpose of this permit, Annually is defined as a monitoring frequency of once every twelve ( 12) months beginning with the date of issuance of this permit so long as the following set of measurements for a given 12 month period are made approximately 12 months subsequent to that time.

A Qualifying Storm Event is one which is greater than 0.1 inches and that occurs after a period of at least 72 hours after any previous storm event with rainfall of 0.1 inches or greater.

D. REPORTING 1. Monitoring Results Monitoring results shall be recorded monthly and submitted monthly for Outfalls 002 and 004 using Discharge Monitoring Report ( DMR) forms supplied by the Division of Water Pollution Control. Likewise, DMRs shall be recorded semi annually and submitted semiannually for Outfalls SW1, SW2, and SW7. Submittals shall be postmarked no later than 15 days after the completion of the reporting period. The top two copies of each report are to be submitted. A copy should be retained for the permittee's files. DMRs and any communication regarding compliance with the conditions of this permit must be sent to:

TENNESSEE DEPT. OF ENVIRONMENT & CONSERVATION DIVISION OF WATER POLLUTION CONTROL COMPLIANCE REVIEW SECTION 401 CHURCH STREET L & C ANNEX 6TH FLOOR NASHVILLE TN 37243 1534 The first DMR is due February 15, 2004.

DMRs must be signed and certified by a responsible corporate officer as defined in 40 CFR 122.22, a general partner or proprietor, or a principal municipal executive officer or Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 7 of 40 ranking elected official, or his duly authorized representative. Such authorization must be submitted in writing and must explain the duties and responsibilities of the authorized representative.

The electronic submission of DMRs will be accepted only if approved in writing by the Division. For purposes of determining compliance with this permit, data submitted in electronic format will carry the same weight as data submitted on signed and certified DMR forms.

2. Additional Monitoring by Permittee If the permittee monitors any pollutant specifically limited by this permit more frequently than required at the location( s) designated, using approved analytical methods as specified herein, the results of such monitoring shall be included in the calculation and reporting of the values required in the DMR form. Such increased frequency shall also be indicated on the form.

3. Falsifying Reports Knowingly making any false statement on any report required by this permit may result in the imposition of criminal penalties as provided for in Section 309 of the Federal Water Pollution Control Act, as amended, and in Section 69 3 115 of the Tennessee Water Quality Control Act.

E. SCHEDULE OF COMPLIANCE Full compliance and operational levels shall be attained from the effective date of this permit.

PART II __________________________________________________________________________

A. GENERAL PROVISIONS 1. Duty to Reapply Permittee is not authorized to discharge after the expiration date of this permit. In order to receive authorization to discharge beyond the expiration date, the permittee shall submit such information and forms as are required to the Director of Water Pollution Control ( the " Director") no later than 180 days prior to the expiration date.

2. Right of Entry The permittee shall allow the Director, the Regional Administrator of the U. S. Environmental Protection Agency, or their authorized representatives, upon the presentation of credentials: Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 8 of 40 a. To enter upon the permittee's premises where an effluent source is located or where records are required to be kept under the terms and conditions of this permit, and at reasonable times to copy these records;

b. To inspect at reasonable times any monitoring equipment or method or any collection, treatment, pollution management, or discharge facilities required under this permit; and c. To sample at reasonable times any discharge of pollutants.

3. Availability of Reports Except for data determined to be confidential under Section 308 of the Federal Water Pollution Control Act, as amended, all reports prepared in accordance with the terms of this permit shall be available for public inspection at the offices of the Division of Water Pollution Control. As required by the Federal Act, effluent data shall not be considered confidential.

4. Proper Operation and Maintenance a. The permittee shall at all times properly operate and maintain all facilities and systems ( and related appurtenances) for collection and treatment which are installed or used by the permittee to achieve compliance with the terms and conditions of this permit. Proper operation and maintenance also includes adequate laboratory and process controls and appropriate quality assurance procedures. This provision requires the operation of backup or auxiliary facilities or similar systems which are installed by a permittee only when the operation is necessary to achieve compliance with the conditions of the permit. Backup continuous pH and flow monitoring equipment are not required.

b. Dilution water shall not be added to comply with effluent requirements to achieve BCT, BPT, BAT and or other technology based effluent limitations such as those in State of Tennessee Rule 1200 4 5. 03.

5. Treatment Facility Failure The permittee, in order to maintain compliance with this permit, shall control production, all discharges, or both, upon reduction, loss, or failure of the treatment facility, until the facility is restored or an alternative method of treatment is provided. This requirement applies in such situations as the reduction, loss, or failure of the primary source of power.

6. Property Rights The issuance of this permit does not convey any property rights in either real or personal property, or any exclusive privileges, nor does it authorize any injury to private property or any invasion of personal rights, nor any infringement of Federal, State, or local laws or regulations. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 9 of 40 7. Severability The provisions of this permit are severable. If any provision of this permit due to any circumstance, is held invalid, then the application of such provision to other circumstances and to the remainder of this permit shall not be affected thereby.

8. Other Information If the permittee becomes aware that he failed to submit any relevant facts in a permit application, or submitted incorrect information in a permit application or in any report to the Director, then he shall promptly submit such facts or information.

B. CHANGES AFFECTING THE PERMIT 1. Planned Changes The permittee shall give notice to the Director as soon as possible of any planned physical alterations or additions to the permitted facility. Notice is required only when:

a. The alteration or addition to a permitted facility may meet one of the criteria for determining whether a facility is a new source in 40 CFR 122.29( b); or b. The alteration or addition could significantly change the nature or increase the quantity of pollutants discharged. This notification applies to pollutants which are subject neither to effluent limitations in the permit, nor to notification requirements under 40 CFR 122.42( a)( 1).

2. Permit Modification, Revocation, or Termination a. This permit may be modified, revoked and reissued, or terminated for cause as described in 40 CFR 122.62 and 122.64, Federal Register, Volume 49, No. 188 ( Wednesday, September 26, 1984), as amended.

b. The permittee shall furnish to the Director, within a reasonable time, any information which the Director may request to determine whether cause exists for modifying, revoking and reissuing, or terminating this permit, or to determine compliance with this permit. The permittee shall also furnish to the Director, upon request, copies of records required to be kept by this permit.

c. If any applicable effluent standard or prohibition ( including any schedule of compliance specified in such effluent standard or prohibition) is established for any toxic pollutant under Section 307( a) of the Federal Water Pollution Control Act, as amended, the Director shall modify or revoke and reissue the permit to conform to the prohibition or to the effluent standard, providing that the effluent standard is more stringent than the limitation in the permit on the toxic pollutant. The permittee shall comply with these effluent standards or prohibitions within the time provided in the regulations that establish these standards or prohibitions, even if the permit has not yet been modified or revoked and reissued to incorporate the requirement. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 10 of 40 3. Change of Ownership This permit may be transferred to another party ( provided there are neither modifications to the facility or it's operations, nor any other changes which might affect the permit limits and conditions contained in the permit) by the permittee if:

a. The permittee notifies the Director of the proposed transfer at least 30 days in advance of the proposed transfer date;

b. The notice includes a written agreement between the existing and new permittees containing a specified date for transfer of permit responsibility, coverage, and liability between them; and c. The Director, within 30 days, does not notify the current permittee and the new permittee of his intent to modify, revoke or reissue, or terminate the permit and to require that a new application be filed rather than agreeing to the transfer of the permit.

Pursuant to the requirements of 40 CFR 122.61, concerning transfer of ownership, the permittee must provide the following information to the Division in their formal notice of intent to transfer ownership: 1) the NPDES permit number of the subject permit; 2) the effective date of the proposed transfer; 3) the name and address of the transferor; 4) the name and address of the transferee; 5) the names of the responsible parties for both the transferor and transferee; 6) a statement that the transferee assumes responsibility for the subject NPDES permit; 7) a statement that the transferor relinquishes responsibility for the subject NPDES permit; 8) the signatures of the responsible parties for both the transferor and transferee pursuant to the requirements of 40 CFR 122.22( a), " Signatories to permit applications"; and, 9) a statement regarding any proposed modifications to the facility, it's operations, or any other changes which might affect the permit limits and conditions contained in the permit.

4. Change of Mailing Address The permittee shall promptly provide to the Director written notice of any change of mailing address. In the absence of such notice the original address of the permittee will be assumed to be correct.

C. NONCOMPLIANCE 1. Effect of Noncompliance All discharges shall be consistent with the terms and conditions of this permit. Any permit noncompliance constitutes a violation of applicable State and Federal laws and is grounds for enforcement action, permit termination, permit modification, or denial of permit reissuance. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 11 of 40 2. Reporting of Noncompliance a. 24 Hour Reporting In the case of any noncompliance which could cause a threat to public drinking supplies, or any other discharge which could constitute a threat to human health or the environment, the required notice of non compliance shall be provided to the Division of Water Pollution Control in the appropriate Environmental Assistance Center within 24 hours from the time the permittee becomes aware of the circumstances. ( The Environmental Assistance Center should be contacted for names and phone numbers of environmental response personnel).

A written submission must be provided within five days of the time the permittee becomes aware of the circumstances unless this requirement is waived by the Director on a case by case basis. The permittee shall provide the Director with the following information:

i. A description of the discharge and cause of noncompliance;

ii. The period of noncompliance, including exact dates and times or, if not corrected, the anticipated time the noncompliance is expected to continue; and iii. The steps being taken to reduce, eliminate, and prevent recurrence of the noncomplying discharge.

b. Scheduled Reporting For instances of noncompliance which are not reported under subparagraph 2. a. above, the permittee shall report the noncompliance on the Discharge Monitoring Report. The report shall contain all information concerning the steps taken, or planned, to reduce, eliminate, and prevent recurrence of the violation and the anticipated time the violation is expected to continue.

3. Overflow a. " Overflow" means the discharge of wastes from any portion of the collection or treatment system other than through permitted outfalls. " Severe property damage" means substantial physical damage to property, damage to the treatment facilities which would cause them to become inoperable, or substantial and permanent loss of natural resources which can reasonably be expected to occur in the absence of an overflow. Severe property damage does not mean economic loss caused by delays in production.

b. Both sanitary sewer overflows and dry weather overflows are prohibited unless the following three ( 3) conditions are met:

i. The overflow is unavoidable to prevent loss of life, personal injury, or severe property damage;

ii. There are no feasible alternatives to overflow, such as the use of auxiliary treatment facilities, retention of untreated wastes, or maintenance Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 12 of 40 during normal periods of equipment down time. This condition is not satisfied if adequate back up equipment should have been installed in the exercise of reasonable engineering judgment to prevent an overflow which occurred during normal periods of equipment down time or preventative maintenance;

iii. The permittee submits notice of an unanticipated overflow to the Division of Water Pollution Control in the appropriate environmental assistance center within 24 hours of becoming aware of the overflow ( if this information is provided orally, a written submission must be provided within five days). When the need for the overflow is foreseeable, prior notification shall be submitted to the Director, if possible, at least ten ( 10) days before the date of the overflow.

c. The permittee shall operate the collection system so as to avoid overflows. No new or additional flows shall be allowed that will contribute to overflow discharges or would otherwise overload any portion of the system. No new or additional flows shall be added upstream of any point in the collection system which experiences chronic overflows ( greater than 5 events per year) or would otherwise overload any portion of the system. Unless there is specific enforcement action to the contrary, the permittee is relieved of this requirement after: 1) an authorized representative of the Commissioner of the Department of Environment and Conservation has approved an engineering report and construction plans and specifications prepared in accordance with accepted engineering practices for correction of the problem; 2) the correction work is underway; and 3) the cumulative, peak design, flows potentially added from new connections and line extensions upstream of any chronic bypass point are less than or proportional to the amount of inflow and infiltration removal documented upstream of that point. The inflow and infiltration reduction must be measured by the permittee using practices that are customary in the flow measurement industry and reported in an attachment to a Monthly Operating Report submitted to the local TDEC Environmental Assistance Center. The data measurement period shall be sufficient to account for seasonal rainfall patterns and seasonal groundwater table elevations.

4. Upset a. " Upset" means an exceptional incident in which there is unintentional and temporary noncompliance with technology based effluent limitations because of factors beyond the reasonable control of the permittee. An upset does not include noncompliance to the extent caused by operational error, improperly designed treatment facilities, inadequate treatment facilities, lack of preventive maintenance, or careless or improper operation.

b. An upset shall constitute an affirmative defense to an action brought for noncompliance with such technology based permit effluent limitations if the permittee demonstrates, through properly signed, contemporaneous operating logs, or other relevant evidence that:

i. An upset occurred and that the permittee can identify the cause( s) of the upset; Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 13 of 40 ii. The permitted facility was at the time being operated in a prudent and workman like manner and in compliance with proper operation and maintenance procedures;

iii. The permittee submitted information required under " Reporting of Noncompliance" within 24 hours of becoming aware of the upset ( if this information is provided orally, a written submission must be provided within five days); and iv. The permittee complied with any remedial measures required under " Adverse Impact."

5. Adverse Impact The permittee shall take all reasonable steps to minimize any adverse impact to the waters of Tennessee resulting from noncompliance with this permit, including such accelerated or additional monitoring as necessary to determine the nature and impact of the noncomplying discharge. It shall not be a defense for the permittee in an enforcement action that it would have been necessary to halt or reduce the permitted activity in order to maintain compliance with the conditions of this permit.

6. Bypass a. " Bypass" is the intentional diversion of wastewater away from any portion of a treatment facility.

b. Bypasses are prohibited unless the following three ( 3) conditions are met:

i. The bypass is unavoidable to prevent loss of life, personal injury, or severe property damage;

ii. There are not feasible alternatives to bypass, such as the use of auxiliary treatment facilities, retention of untreated wastes, or maintenance during normal periods of equipment down time. This condition is not satisfied if adequate back up equipment should have been installed in the exercise of reasonable engineering judgment to prevent a bypass which occurred during normal periods of equipment down time or preventative maintenance;

iii. The permittee submits notice of an unanticipated bypass to the Division of Water Pollution Control in the appropriate environmental assistance center within 24 hours of becoming aware of the bypass ( if this information is provided orally, a written submission must be provided within five days). When the need for the bypass is foreseeable, prior notification shall be submitted to the Director, if possible, at least ten ( 10) days before the date of the overflow.

c. Bypasses not exceeding limitations are allowed only if the bypass is necessary for essential maintenance to assure efficient operation. All other bypasses are prohibited. Allowable bypasses not exceeding limitations are not subject to the reporting requirements of 6. b. iii, above. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 14 of 40 7. Washout a. For domestic wastewater plants only, a " washout" shall be defined as loss of Mixed Liquor Suspended Solids ( MLSS) of 30.00% or more. This refers to the MLSS in the aeration basin( s) only. This does not include MLSS decrease due to solids wasting to the sludge disposal system. A washout can be caused by improper operation or from peak flows due to infiltration and inflow.

b. A washout is prohibited. If a washout occurs the permittee must report the incident to the Division of Water Pollution Control in the appropriate Environmental Assistance Center within 24 hours by telephone. A written submission must be provided within five days. The washout must be noted on the discharge monitoring report. Each day of a washout is a separate violation.

D. LIABILITIES 1. Civil and Criminal Liability Except as provided in permit conditions for " Bypassing," " Overflow", " Upset," " Diversion," and " Treatment Facility Failures," nothing in this permit shall be construed to relieve the permittee from civil or criminal penalties for noncompliance. Notwithstanding this permit, the permittee shall remain liable for any damages sustained by the State of Tennessee, including but not limited to fish kills and losses of aquatic life and/ or wildlife, as a result of the discharge of wastewater to any surface or subsurface waters. Additionally, notwithstanding this Permit, it shall be the responsibility of the permittee to conduct its wastewater treatment and/ or discharge activities in a manner such that public or private nuisances or health hazards will not be created.

2. Liability Under State Law Nothing in this permit shall be construed to preclude the institution of any legal action or relieve the permittee from any responsibilities, liabilities, or penalties established pursuant to any applicable State law or the Federal Water Pollution Control Act, as amended.

PART III __________________________________________________________________________

OTHER REQUIREMENTS A. TOXIC POLLUTANTS The permittee shall notify the Division of Water Pollution Control as soon as it knows or has reason to believe:

1. That any activity has occurred or will occur which would result in the discharge on a routine or frequent basis, of any toxic substance( s) ( listed at 40 CFR 122, Appendix D, Table II Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 15 of 40 and III) which is not limited in the permit, if that discharge will exceed the highest of the following " notification levels":

a. One hundred micrograms per liter ( 100 ug/ l);

b. Two hundred micrograms per liter ( 200 ug/ l) for acrolein and acrylonitrile; five hundred micrograms per liter ( 500 ug/ l) for 2,4 dinitrophenol and for 2 methyl 4,6 dinitrophenol; and one milligram per liter ( 1 mg/ L) for antimony;

c. Five ( 5) times the maximum concentration value reported for that pollutant( s) in the permit application in accordance with 122.21( g)( 7); or d. The level established by the Director in accordance with 122.44( f).

2. That any activity has occurred or will occur which would result in any discharge, on a non routine or infrequent basis, of a toxic pollutant which is not limited in the permit, if that discharge will exceed the highest of the following " notification levels":

a. Five hundred micrograms per liter ( 500 ug/ l);

b. One milligram per liter ( 1 mg/ L) for antimony;

c. Ten ( 10) times the maximum concentration value reported for that pollutant in the permit application in accordance with 122.21( g)( 7); or d. The level established by the Director in accordance with 122.44( f).

B. REOPENER CLAUSE If an applicable standard or limitation is promulgated under Sections 301( b)( 2)( C) and ( D), 304( B)( 2), and 307( a)( 2) and that effluent standard or limitation is more stringent than any effluent limitation in the permit or controls a pollutant not limited in the permit, the permit shall be promptly modified or revoked and reissued to conform to that effluent standard or limitation.

C. PLACEMENT OF SIGNS Within sixty ( 60) days of the effective date of this permit, the permittee shall place and maintain a sign( s) at each outfall and any bypass/ overflow point in the collection system. For the purposes of this requirement, any bypass/ overflow point that has discharged five ( 5) or more times in the last year must be so posted. The sign( s) should be clearly visible to the public from the bank and the receiving stream or from the nearest public property/ right of way, if applicable. The minimum sign size should be two feet by two feet ( 2' x 2') with one inch ( 1") letters. The sign should be made of durable material and have a white background with black letters.

The sign( s) are to provide notice to the public as to the nature of the discharge and, in the case of the permitted outfalls, that the discharge is regulated by the Tennessee Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 16 of 40 Department of Environment and Conservation, Division of Water Pollution Control. The following is given as an example of the minimal amount of information that must be included on the sign:

TREATED INDUSTRIAL WASTEWATER AND STORM WATER RUNOFF METRO NASHVILLE AIRPORT AUTHORITY ( Permittee's Phone Number) NPDES Permit NO. TN0064041 TENNESSEE DIVISION OF WATER POLLUTION CONTROL 1 888 891 8332 ENVIRONMENTAL ASSISTANCE CENTER  NASHVILLE INDUSTRIAL WASTEWATER AND STORM WATER RUNOFF OVERFLOW METRO NASHVILLE AIRPORT AUTHORITY ( Permittee's Phone Number) NPDES Permit NO. TN0064041 TENNESSEE DIVISION OF WATER POLLUTION CONTROL 1 888 891 8332 ENVIRONMENTAL ASSISTANCE CENTER  NASHVILLE STORM WATER RUNOFF METRO NASHVILLE AIRPORT AUTHORITY ( Permittee's Phone Number) NPDES Permit NO. TN0064041 TENNESSEE DIVISION OF WATER POLLUTION CONTROL 1 888 891 8332 ENVIRONMENTAL ASSISTANCE CENTER  NASHVILLE D. ANTIDEGRADATION Pursuant to the Rules of the Tennessee Department of Environment and Conservation, Chapter 1200 4 3. 06, titled " Tennessee Antidegradation Statement," and in consideration of the Department's directive in attaining the greatest degree of effluent reduction achievable in municipal, industrial, and other wastes, the permittee shall further be required, pursuant to the terms and conditions of this permit, to comply with the effluent limitations and schedules of compliance required to implement applicable water quality standards, to comply with a State Water Quality Plan or other State or Federal laws or regulations, or where practicable, to comply with a standard permitting no discharge of pollutants.

E. BIOMONITORING REQUIREMENTS The permittee shall conduct a 48 hour static acute toxicity test on two test species on the same samples of final effluent from Outfall 002. The test species to be used are Water Fleas ( Ceriodaphnia dubia) and Fathead Minnows ( Pimephales promelas).

The measured endpoint for toxicity will be the concentration causing 50% lethality ( LC50) of the test organisms. The LC50 shall be determined based on a 50% lethality as compared to the controls. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 17 of 40 Test shall be conducted and its results reported based on appropriate replicates of a total of five serial dilutions and a control, using the percent effluent dilutions as presented in the following table:

Serial Dilutions for Whole Effluent Toxicity ( WET) Testing Permit Limit ( PL) 0.50 X PL 0.25 X PL 0.125 X PL 0.0625 X PL Control % effluent 100 50 25 12.5 6.25 0 The dilution/ control water used will be a moderately hard water as described in Methods for Measuring the Acute Toxicity of Effluents to Freshwater and Marine Organisms, EPA/ 600/ 4 90/ 027F ( or the most current edition). Results from an acute standard reference toxicant quality assurance test for each species tested shall be submitted with the discharge monitoring report. Reference toxicant tests shall be conducted as required in EPA/ 600/ 4 90/ 027F ( or the most current edition).

Toxicity will be demonstrated if the LC50 is less than or equal to the permit limit indicated for each outfall in the above table( s). Toxicity demonstrated by the tests specified herein constitutes a violation of this permit.

Toxicity testing will be conducted using a 24 hour flow proportionate composite sample of final effluent. If, in any control more than 20% of the test organisms die in 48 hours, the test ( control and effluent) is considered invalid and the test shall be repeated within 30 days of the date the initial test is invalidated. Furthermore, if the results do not meet the acceptability criteria as defined in Methods for Measuring the Acute Toxicity of Effluents to Freshwater and Marine Organisms, EPA/ 600/ 4 90/ 027F, that test shall be repeated. Any test initiated but terminated before completion must also be reported along with a complete explanation for the termination.

The toxicity tests specified herein shall be conducted quarterly ( 1/ Quarter in each quarter during which aircraft deicing has occurred) for Outfall 001 and begin no later than 60 days from the effective date of this permit. The toxicity tests specified herein should be started as soon as, but not later than 1 week of receiving representative effluent sample from deicing operation( s).

In the event of a test failure, the permittee must start a follow up test within 2 weeks and submit results from a follow up test within 30 days from obtaining initial WET testing results. The follow up test must be conducted using the same serial dilutions as presented in the corresponding table( s) above. The follow up test will not negate an initial failed test. In addition, the failure of a follow up test will constitute a separate permit violation which must also be reported.

In the event of 2 consecutive test failures or 3 test failures within a 12 month period for the same outfall, the permittee must initiate a Toxicity Identification Evaluation/ Toxicity Reduction Evaluation ( TIE/ TRE) study within 30 days and so notify the Division by letter. This notification shall include a schedule of activities for the initial investigation of that outfall. During the term of the TIE/ TRE study, the frequency of biomonitoring shall be once every Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 18 of 40 three months. Additionally, the permittee shall submit progress reports once every three months throughout the term of the TIE/ TRE study. The toxicity must be reduced to allowable limits for that outfall within 2 years of initiation of the TIE/ TRE study. Subsequent to the results obtained from the TIE/ TRE studies, the permittee may request an extension of the TIE/ TRE study period if necessary to conduct further analyses. The final determination of any extension period will be made at the discretion of the Division.

The TIE/ TRE study may be terminated at any time upon the completion and submission of 2 consecutive tests ( for the same outfall) demonstrating compliance. Following the completion of TIE/ TRE study, the frequency of monitoring will return to a regular schedule, as defined previously in this section as well in Part I of the permit. During the course of the TIE/ TRE study, the permittee will continue to conduct toxicity testing of the outfall being investigated at the frequency of once every three months but will not be required to perform follow up tests for that outfall during the period of TIE/ TRE study.

Test procedures, quality assurance practices and determination of effluent lethality values will be made in accordance with Methods for Measuring the Acute Toxicity of Effluents to Freshwater and Marine Organisms, EPA/ 600/ 4 90/ 027F or the most current edition.

Results of all tests, reference toxicant information, copies of raw data sheets, statistical analysis and chemical analysis shall be compiled in a report. The report shall be written in accordance with Methods for Measuring the Acute Toxicity of Effluents to Freshwater and Marine Organisms, EPA/ 600/ 4 90/ 027F or the most current edition.

Two copies of biomonitoring reports ( including follow up reports) shall be submitted to the Division. One copy of the report shall be submitted along with the discharge monitoring report ( DMR). The second copy shall be submitted to the local Division of Water Pollution Control office address:

Environmental Assistance Center  Nashville Division of Water Pollution Control 711 R. S. Gass Boulevard Nashville, TN 37243 1550 PART IV __________________________________________________________________________

STORM WATER POLLUTION PREVENTION PLAN The discharger will develop, document and maintain the SWPPP pursuant to the requirements as set forth in the Tennessee Storm Water Multi Sector General Permit for Industrial Activities ( TMSP), Sector S, " Storm water discharges from establishments and/ or facilities including airports, air terminals, air carriers, flying fields, and establishments engaged in servicing or maintaining airports and/ or aircraft ( generally classified under Standard Industrial Classification ( SIC) code 45) which have vehicle maintenance shops, material handling facilities, equipment cleaning operations or airport and/ or aircraft deicing/ anti icing Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 19 of 40 operations," Part 3, " Storm Water Pollution Prevention Plan Requirements." For the details regarding plan requirements, see ATTACHMENT I. The plan shall be signed by either a principal executive officer of a corporation, the owner or proprietor of a sole proprietorship, or a partner or general partner of a partnership. The SWPPP developed and implemented shall contain, in addition to the requirements listed in the Tennessee Multi Sector SWPPP guidelines for establishments and/ or facilities including airports, air terminals, air carriers, flying fields, and establishments engaged in servicing or maintaining airports and/ or aircrafts, the following items:

A. PLAN IMPLEMENTATION The plan should be developed and available for review within 180 days after permit coverage. Facilities should implement the management practices as soon as possible, but not later than one year after permit coverage. Where new construction is necessary to implement the management plan, a construction schedule should be included. Construction should be completed as soon as possible.

B. PLAN AVAILABILITY The plan will be maintained by the discharger on the site or at a nearby office. Copies of the plan will be submitted to the Division of Water Pollution Control within ten working days of any request.

C. PLAN MODIFICATION The plan will be modified as required by the Director of the Division of Water Pollution Control.

D. MONITORING PLAN The storm water discharges will be monitored as required in Part I. Section A., Effluent Limits and Monitoring Requirements, applicable to storm water outfalls. For each outfall monitored, the surface area and type of cover, for example, roof, pavement, grassy areas, gravel, will be identified.

VMJ TN0064041. DOC Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 20 of 40 ATTACHMENT I Metro Nashville Airport Authority NPDES Permit TN0064041 Storm Water Pollution Prevention Plan Requirements Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 21 of 40 Storm Water Pollution Prevention Plan Requirements Storm water pollution prevention plans developed for areas of the facility occupied by tenants of the airport shall be integrated with the plan for the entire airport. For the purposes of today's permit, tenants of the airport facility include airline companies, fixed based operators and other parties which have contracts with the airport authority to conduct business operations on airport property which result in storm water discharges associated with industrial activity.

a) Contents of Plan. Each plan shall include, at a minimum, the following items:

( 1) Pollution Prevention Team. Each plan shall identify a specific individual or individuals as member( s) of a storm water Pollution Prevention Team who are responsible for developing the storm water pollution prevention plan and assisting the facility management in its implementation, maintenance, and revision. The plan shall clearly identify the responsibilities of each team member. The activities and responsibilities of the team shall address all aspects of the facility's storm water pollution prevention plan.

( 2) Description of Potential Pollutant Sources. Each plan shall provide a description of potential sources which may reasonably be expected to add significant amounts of pollutants to storm water discharges or which may result in the discharge of pollutants during dry weather from separate storm sewers draining the facility. Each plan shall identify all activities and significant materials which may potentially be significant pollutant sources. Each plan shall include, at a minimum:

( a) Drainage ( i) A site map indicating an outline of the drainage area of each storm water outfall within the facility boundaries, each existing structural control measure to reduce pollutants in storm water runoff, surface water bodies, locations where significant materials are exposed to precipitation, locations where major spills or leaks identified under paragraph 3. a.( 2)( c) ( Spills and Leaks) of this section have occurred, and the locations of the following activities where such activities are exposed to precipitation: aircraft and runway deicing/ anti icing operations; fueling stations; aircraft, ground vehicle and equipment maintenance and/ or cleaning areas; storage areas for aircraft, ground vehicles and equipment awaiting maintenance; loading/ unloading areas; locations used for the treatment, storage or disposal of wastes, liquid storage tanks, processing areas and storage areas. The map must indicate the outfall locations and the types of discharges contained in the drainage areas of the outfalls.

( ii) For each area of the facility that generates storm water discharges associated with industrial activity with a reasonable potential for containing significant amounts of pollutants, a prediction of the direction of flow, and an identification of the types of pollutants which are likely to be present in storm water discharges associated with industrial activity. Factors to consider include the toxicity of chemical; quantity of chemicals used, produced or discharged; the likelihood of contact with storm water; and history of significant leaks or spills of toxic or hazardous pollutants. Flows with a significant potential for causing erosion shall be identified. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 22 of 40 ( iii) The site map developed for the entire airport shall indicate the location of each tenant of the facility that conducts industrial activities as described in Part 1. a., and incorporate information from the tenants site map ( including a description of industrial activities, significant materials exposed, and existing management practices).

( b) Inventory of Exposed Materials   An inventory of the types of materials handled at the site that potentially may be exposed to precipitation. Such inventory shall include a narrative description of significant materials that have been handled, treated, stored or disposed in a manner to allow exposure to storm water between the time of 3 years prior to the date of issuance of this permit; method and location of onsite storage or disposal; materials management practices employed to minimize contact of materials with storm water runoff between the time of 3 years prior to the date of issuance of this permit; the location and a description of existing structural and nonstructural control measures to reduce pollutants in storm water runoff; and a description of any treatment of storm water runoff.

( c) Spills and Leaks   A list of significant spills and significant leaks of toxic or hazardous pollutants that occurred at areas that are exposed to precipitation or that otherwise drain to a storm water conveyance at the facility after the date of 3 years prior to the date of issuance of this permit. Such list shall be updated as appropriate during the term of the permit.

( d) Sampling Data   A summary of existing discharge sampling data describing pollutants in storm water discharges from the facility, including a summary of sampling data collected during the term of this permit.

( e) Risk Identification and Summary of Potential Pollutant Sources   A narrative description of the potential pollutant sources from the following activities: aircraft, runway, ground vehicle and equipment maintenance and cleaning; aircraft and runway deicing/ antiicing operations ( including apron and centralized aircraft deicing/ anti icing stations, runways, taxiways and ramps); outdoor storage activities; loading and unloading operations; and onsite waste disposal. The description shall specifically list any significant potential source of pollutants at the facility and for each potential source, any pollutant or pollutant parameter [ e. g., biochemical oxygen demand ( BOD5), oil and grease, etc.] of concern shall be identified.

Facilities which conduct deicing/ anti icing operations shall maintain a record of the types [ including the Material Safety Data Sheets ( MSDS)] and monthly quantities of deicing/ anti icing chemicals used. Tenants and fixed base operators who conduct deicing/ antiicing operations shall provide the above information to the airport authority for inclusion in the storm water pollution prevention plan for the entire facility.

( 3) Measures and Controls. Operators covered by this permit shall develop a description of storm water management controls appropriate for their areas of operation, and implement such controls. The priority in selecting controls shall reflect identified potential sources of pollutants at the facility. The description of storm water management controls shall address the following minimum components, including a schedule for implementing such controls: Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 23 of 40 ( a) Good Housekeeping   Good housekeeping requires the maintenance of areas which may contribute pollutants to storm water discharges in a clean, orderly manner.

( i) Aircraft, Ground Vehicle and Equipment Maintenance Areas   Permittees should ensure the maintenance of equipment is conducted in designated areas only and clearly identify these areas on the ground and delineate them on the site map. The plan must describe measures that prevent or minimize the contamination of the storm water runoff from all areas used for aircraft, ground vehicle and equipment maintenance ( including the maintenance conducted on the terminal apron and in dedicated hangars). Management practices or equivalent measures such as performing maintenance activities indoors, maintaining an organized inventory of materials used in the maintenance areas, draining all parts of fluids prior to disposal, preventing the practice of hosing down the apron or hangar floor, using dry cleanup methods, and/ or collecting the storm water runoff from the maintenance area and providing treatment or recycling should be considered.

( ii) Aircraft, Ground Vehicle and Equipment Cleaning Areas   Permittees should ensure that cleaning of equipment is conducted in designated areas only and clearly identify these areas on the ground and delineate them on the site map. The plan must describe measures that prevent or minimize the contamination of the storm water runoff from all areas used for aircraft, ground vehicle and equipment cleaning. Management practices such as performing cleaning operations indoors, and/ or collecting the storm water runoff from the cleaning area and providing treatment or recycling should be considered.

( iii) Aircraft, Ground Vehicle and Equipment Storage Areas   The storage of aircraft, ground vehicles and equipment awaiting maintenance must be confined to designated areas ( delineated on the site map). The plan must describe measures that prevent or minimize the contamination of the storm water runoff from these areas. Management practices such as indoor storage of aircraft and ground vehicles, the use of drip pans for the collection of fluid leaks, and perimeter drains, dikes or berms surrounding storage areas should be considered.

( iv) Material Storage Areas   Storage units of all materials ( e. g., used oils, hydraulic fluids, spent solvents, and waste aircraft fuel) must be maintained in good condition, so as to prevent or minimize contamination of storm water, and plainly labeled ( e. g., " used oil," " Contaminated Jet A," etc.). The plan must describe measures that prevent or minimize contamination of the storm water runoff from storage areas. Management practices or equivalent measures such as indoor storage of materials, centralized storage areas for waste materials, and/ or installation of berming and diking around storage areas should be considered for implementation.

( v) Airport Fuel System and Fueling Areas   The plan must describe measures that prevent or minimize the discharge of fuels to the storm sewer resulting from fuel servicing activities or other operations conducted in support of the airport fuel system. Where the discharge of fuels into the storm sewer cannot be prevented, the plan shall indicate measures that will be employed to prevent or minimize the discharge of the contaminated runoff into receiving surface waters. Management practices or equivalent measures such as implementing spill and overflow practices ( e. g., placing sorptive materials beneath aircraft during fueling operations), using dry cleanup methods, and/ or collecting the storm water runoff should be considered. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 24 of 40 ( b) Preventive Maintenance   A preventive maintenance program shall involve timely inspection and maintenance of storm water management devices ( e. g., cleaning oil/ water separators, removing debris from catch basins) as well as inspecting and testing facility equipment and systems to uncover conditions that could cause breakdowns or failures resulting in discharges of pollutants to surface waters, and ensuring appropriate maintenance of such equipment and systems.

( c) Spill Prevention and Response Procedures   Areas where potential spills which can contribute pollutants to storm water discharges can occur, and their accompanying drainage points shall be identified clearly in the storm water pollution prevention plan. The plan shall describe material handling procedures, storage requirements, and consider the use of equipment such as diversion valves. Procedures for cleaning up spills shall be identified in the plan and made available to the appropriate personnel. The necessary equipment to implement a clean up should be available to personnel.

( d) Source Reduction   Operators who conduct aircraft and/ or runway ( including taxiways and ramps) deicing/ anti icing operations shall evaluate present operating procedures to consider alternative practices to reduce the overall amount of deicing/ anti icing chemicals used and/ or lessen the environmental impact of the pollutant source.

( i) With regard to runway deicing operations, operators, at a minimum, shall evaluate: present application rates to ensure against excessive over application; metered application of deicing chemical; pre wetting dry chemical constituents prior to application; installation of runway ice detection systems; implementing anti icing operations as a preventive measure against ice buildup; the use of substitute deicing compounds such as potassium acetate in lieu of ethylene glycol, propylene glycol and/ or urea.

( ii) In considering source reduction management practices for aircraft deicing operations, operators, at a minimum, should evaluate current application rates and practices to ensure against excessive over application, and consider pretreating aircraft with hot water prior to the application of a deicing chemical, thus reducing the overall amount of chemical used per operation.

Source reduction measures that the operator determines to be reasonable and appropriate shall be implemented and maintained. The plan shall provide a narrative explanation of the options considered and the reasoning for whether or not to implement them.

( e) Management of Runoff   The plan shall contain a narrative consideration of the appropriateness of traditional storm water management practices ( practices other than those which prevent or reduce source( s) of pollutants) used to divert, infiltrate, reuse, or otherwise manage storm water runoff in a manner that reduces pollutants in storm water discharges from the site. The potential of various sources at the facility to contribute pollutants to storm water discharges associated with industrial activity [ see paragraph 3. a.( 2) ( Description of Potential Pollutant Sources)] shall be considered. Appropriate measures or equivalent measures may include: vegetative swales, reuse of collected storm water ( such as for a process or as an irrigation source), inlet controls ( such as oil/ water separators), snow Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 25 of 40 management activities, infiltration devices, and wet detention/ retention devices. Measures that the permittee determines to be reasonable and appropriate shall be implemented and maintained.

( i) Operators that conduct aircraft and/ or runway deicing/ anti icing operations shall also provide a narrative consideration of management practices to control or manage contaminated runoff from areas where deicing/ anti icing operations occur to reduce the amount of pollutants being discharged from the site. Structural controls such as establishing a centralized aircraft deicing facility, and/ or collection of contaminated runoff for treatment or recycling should be considered. Collection and treatment alternatives include, but are not limited to, retention basins, detention basins with metered controlled release, Underground Storage Tanks ( USTs) and/ or disposal to Publicly Owned Treatment Works ( POTW) by way of sanitary sewer or hauling tankers. Runoff management controls that the operator determines to be reasonable and appropriate shall be implemented and maintained. The plan should consider the recovery of deicing/ anti icing materials when these materials are applied during non precipitation events to prevent these materials from later becoming a source of storm water contamination. The plan shall provide a narrative explanation of the controls selected and the reasons for their selection.

( f) Inspections   In addition to or as part of the comprehensive site evaluation required under paragraph 3. a.( 4) of this section, qualified facility personnel shall be identified to inspect designated equipment and areas of the facility specified in the plan. The inspection frequency shall be specified in the plan, but at a minimum be conducted once per week during deicing/ anti icing application periods for areas where deicing/ anti icing operations are being conducted. A set of tracking or follow up procedures shall be used to ensure that appropriate actions are taken in response to the inspections. Records of inspections shall be maintained. The use of a checklist developed by the pollution prevention team is encouraged.

( g) Pollution Prevention Training   Pollution prevention training programs shall be developed to inform management and personnel responsible for implementing activities identified in the storm water pollution prevention plan of the components and goals of the plan. Training should address topics such as spill response, good housekeeping, aircraft and runway deicing/ anti icing procedures, and material management practices. The pollution prevention plan shall identify periodic dates for such training.

( h) Recordkeeping and Internal Reporting Procedures   A description of incidents ( such as spills, or other discharges), along with other information describing the quality and quantity of storm water discharges shall be included in the plan. Inspections and maintenance activities shall be documented and records shall be incorporated into the plan.

( i) Non storm Water Discharges ( i) The plan shall include a certification that the discharge points have been tested or evaluated for the presence of non storm water discharges. The certification shall include the identification of potential significant sources of non storm water at the site, a description of the results of any test and/ or evaluation for the presence of non storm water discharges, the evaluation criteria or testing method used, the date of any testing and/ or evaluation, and the onsite drainage points that were directly observed during the test. Certifications shall be Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 26 of 40 signed in accordance with Part I. D. 1. of this permit. Such certification may not be feasible if the facility operating the storm water discharge associated with industrial activity does not have access to an outfall, manhole, or other point of access to the ultimate conduit which receives the discharge. In such cases, the source identification section of the storm water pollution prevention plan shall indicate why the certification required by this part was not feasible, along with the identification of potential significant sources of non storm water at the site. A discharger that is unable to provide the certification required by this paragraph must notify the Division of Water Pollution Control in accordance with paragraph 3. a.( 3)( iii) ( below).

( ii) Sources of non storm water that are combined with storm water discharges associated with industrial activity must be identified in the plan. The plan shall identify and ensure the implementation of appropriate pollution prevention measures for the non storm water component( s) of the discharge. Any non storm water discharges that are not permitted under an individual NPDES permit should be brought to the attention of the Division's local Field Office ( see APPENDIX I).

( iii) Failure to Certify   Any facility that is unable to provide the certification required ( testing for non storm water discharges), must notify the Division of Water Pollution Control 180 days after the date of issuance of this permit. If the failure to certify is caused by the inability to perform adequate tests or evaluations, such notification shall describe: the procedure of any test conducted for the presence of non storm water discharges; the results of such test or other relevant observations; potential sources of non storm water discharges to the storm sewer; and why adequate tests for such storm sewers were not feasible. Non storm water discharges to waters of the State which are not authorized by an NPDES permit are unlawful, and must be terminated.

( j) Sediment and Erosion Control   The plan shall identify areas which, due to topography, activities, or other factors, have a high potential for significant soil erosion, and identify structural, vegetative, and/ or stabilization measures to be used to limit erosion.

( 4) Comprehensive Site Compliance Evaluation. Qualified personnel shall conduct site compliance evaluations during periods of deicing/ anti icing operations at appropriate intervals specified in the plan, but in no case less than once a year. Such evaluations shall provide:

( a) Areas contributing to a storm water discharge associated with industrial activity shall be visually inspected for evidence of, or the potential for, pollutants entering the drainage system. Measures to reduce pollutant loadings shall be evaluated to determine whether they are adequate and properly implemented in accordance with the terms of the permit or whether additional control measures are needed. Structural storm water management measures, sediment and erosion control measures, and other structural pollution prevention measures identified in the plan shall be observed to ensure that they are operating correctly. A visual inspection of equipment needed to implement the plan, such as spill response equipment, shall be made.

( b) Based on the results of the evaluation, the description of potential pollutant sources identified in the plan in accordance with paragraph 3. a.( 2) of this section ( Description of Potential Pollutant Sources) and pollution prevention measures and controls identified in the Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 27 of 40 plan in accordance with paragraph 3. a.( 3) of this section ( Measures and Controls) shall be revised as appropriate within 2 weeks of such evaluation and shall provide for implementation of any changes to the plan in a timely manner, but in no case more than 12 weeks after the evaluation.

( c) A report summarizing the scope of the evaluation, personnel making the evaluation, the date( s) of the evaluation, major observations relating to the implementation of the storm water pollution prevention plan, and actions taken in accordance with paragraph 3. a.( 4)( b) ( above) of the permit shall be made and retained as part of the storm water pollution prevention plan for at least 3 years from the date of the evaluation. The report shall identify any incidents of noncompliance. Where a report does not identify any incidents of noncompliance, the report shall contain a certification that the facility is in compliance with the storm water pollution prevention plan and this permit. The report shall be signed in accordance with Part I. D. 1. of this permit.

( d) Where compliance evaluation schedules overlap with inspections required under 3. a.( 3)( f), the compliance evaluation may be conducted in place of one such inspection. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 28 of 40 ADDENDUM I WASTELOAD ALLOCATION STUDY WORKPLAN FOR SIMS BRANCH METROPOLITAN NASHVILLE AIRPORT AUTHORITY One Terminal Drive, Suite 501 Nashville, Tennessee November 2001 Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 29 of 40 Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 30 of 40 1.0 INTRODUCTION 1.1 Background The Metropolitan Nashville Airport Authority ( MNAA) owns and operates the Nashville International Airport ( BNA), which is located within Davidson County as illustrated in Figure 1 1. The approximate geographical coordinates of the airport are 36 ° 08' 2" N Latitude 86 ° 40' 24" W Longitude. BNA is a medium sized, primarily commercial, airport that accommodates domestic and international passenger flights, commuter traffic, freight and courier transports, general aviation, and military flights.

Storm water runoff from BNA discharges to Mill Creek, Sims Branch, and McCrory Creek from ten ( 10) identified storm water outfalls. The majority of the airport that is actively engaged in industrial activities ( deicing, fueling, washing, etc) drains through one of four underground oil/ water separators to a storm pond, and then to the airport storm water treatment basin. Following treatment, storm water is currently discharged to Sims Branch under the authority of the expired NPDES Permit No. TN0064041 ( MODIFIED).

The Tennessee Department of Environment and Conservation, Division of Water Pollution Control ( TDEC WPC) is working on renewing the expired NPDES Permit and has issued the MNAA a Draft NPDES Permit No. TN0064041. The Draft permit contains proposed effluent discharge limitations on 5 day Biochemical Oxygen Demand ( BOD5) as well as other conventional parameters. BOD5 is a measure of pollution present in runoff from the airport, and results primarily from de icing and anti icing fluids.

In the years leading up to the issuance of the current Draft permit, MNAA consultants have conducted several intensive field studies and developed models of the receiving stream in order to suggest appropriate BOD5 limits to TDEC WPC. Unfortunately, the quality and type of data gathered, and consequently the modeling and proposed limits, was not deemed acceptable by TDEC WPC and have essentially been disregarded. Instead, the BOD5 limits proposed in the Draft NPDES permit were developed by TDEC WPC based on desktop modeling of the receiving stream with little corroborative field data.

1.2 Purpose Based on the method used to model the receiving stream and discharge, the model is likely conservative in nature and has resulted in overly stringent BOD5 effluent limitations for the MNAA. In other words, to be protective of the receiving stream, and in the absence of appropriate field data, TDEC WPC has used standard, conservative default model parameters in their model. If unable to remove sufficient BOD5 from the wastewater in the BNA treatment basin, the MNAA would be at risk of violating discharge permit limits or be forced to divert the discharge to the Nashville sanitary sewer system and pay surcharges. A properly conducted WLA and modeling study would generate a more accurate model of the receiving stream and Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 31 of 40 Figure 1 1 Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 32 of 40 could yield greater effluent BOD5 limitations for the MNAA and still be protective of the receiving stream.

With the concurrence of TDEC WPC, the MNAA will initiate a wasteload allocation and modeling study of Sims Branch in order to develop alternate effluent water quality limitations for the BNA storm water treatment pond discharge. The purpose of this document is to describe the elements of such a proposed study.

1.3 Scope of Work The specific tasks comprising the wasteload allocation study are listed below. The tasks are expounded upon in subsequent sections.

1. Develop approved study work plan.

2. Reconnaissance field survey of receiving stream.

3. Time of travel field studies.

4. Develop and calibrate water quality model.

5. Conduct continuous monitoring.

6. Validate model.

7. Wasteload allocation modeling.

8. Final report submittal. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 33 of 40 2.0 WASTELOAD ALLOCATION STUDY 2.1 Work Plan This document constitutes the Work Plan covering all components of a study to develop an assimilative capacity model of Sims Branch. The model will be used to develop discharge limits which are both equitable for the MNAA and protective of the receiving stream. It is the intention of the MNAA to submit this Work Plan to TDEC WPC for review and approval.

2.2 Reconnaissance Field Survey The first step in developing an accurate water quality model of Sims Branch is to conduct physical reconnaissance of the stream. There are several objectives of the reconnaissance survey, including establishment of an accurate system diagram/ map, as well as assessment of watershed conditions, land uses, and physical attributes of the stream. Due to the relatively short length of the receiving stream, and in order to ensure that model encompasses the full dissolved oxygen sag curve, the entire length of the stream will be reconnoitered.

Sims Branch will be walked from accessible headwater segments on the Airport property to the confluence with Mill Creek. Observations regarding stream conditions, habitat, and surrounding land uses along the extent of the stream will be documented with photographs and field notebooks. Detailed measurements of channel morphology ( width and depth) will be made approximately every 1,000 yards along the length of the stream, or as conditions warrant ( e. g., obvious change in hydrologic characteristics).

Field measurements will include determination of flow. The instantaneous flow will be determined by accurately measuring the cross section of the stream and then measuring in stream velocity using a rod mounted Pygmy current meter ( vertical shaft, rotating cup meter). All data will be recorded on standardized field forms and/ or stored in a handheld data logging device. The velocity measurements will be used to estimate time of travel and to provide definition for the next task in the study.

Several stations will be marked on the stream bank. The stations will be used as points of reference so that exact locations and distances can be determined during all subsequent in stream monitoring surveys and time of travel studies.

In situ water quality characteristics ( temperature, conductivity, and pH), including an initial synoptic DO profile, will also be measured during the reconnaissance survey. Additional in situ measurements which may be collected include secchi disk measurements for the determination of the amount of light penetration into the water.

The reconnaissance survey will be scheduled upon approval of this work plan by TDEC, but it is anticipated to occur sometime during late November/ early December of 2001. Prior to conducting the survey, accessible portions of the stream may be observed from vehicles in order to help plan the survey. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 34 of 40 2.3 Time of travel Surveys Background Time of travel surveys will be used to gather data for model calibration. When evaluating treated wastewater runoff quality from Airport operations there are two distinct scenarios which must be considered: 1) discharge during deicing season; and 2) discharge during the summer season. Both or either scenario may represent critical periods from a wasteload allocation perspective. First, the greatest pollutant loading contribution from Airport operations is expected during the winter since deicing and antiicing operations are more likely to occur. As discussed previously, deicing chemicals ( i. e., glycols) are the main source of BOD at the Airport. However, during the summer months background flow and temperature conditions in the receiving stream are expected to produce critical water quality conditions, and hence these summer conditions are normally used to represent the " worst case" discharge scenario and must be taken into account. In consideration of these two critical scenarios, two campaigns of time of travel studies are proposed: once during deicing season and once during summer.

Hydraulic parameters, water quality conditions, and kinetic reaction rates will be determined from data gathered during these studies. Flow and time of travel measurements are critical in the wasteload allocation process for determination of decay rates ( time dependent) required by the model and for establishment of the required hydraulic boundary conditions. Although the methodologies for these measurements are described separately, the time of travel, flow measurements, in situ water quality and samples for laboratory analyses will be taken concurrently during these intensive surveys.

The distance from the point of discharge from the Airport wastewater treatment pond to Mill Creek is approximately 2.5 miles ( according to USGS quadrangle map). Although the reconnaissance survey and the calibration studies will accurately delineate the time of travel and the D. O. sag curve in Sims Branch, it is anticipated that the sag point under all conditions will manifest itself prior to Mill Creek. If there is no sag point in Sims Branch prior to Mill Creek, the combined flow and additional dissolved oxygen mass contribution of Mill Creek is expected to completely mitigate the potential impact of the Airport discharge, although this scenario will also be addressed in the final report if applicable. Assuming a total travel time of less than two days, the calibration studies have initially been planned for two days each ( 48 hours), although this may be modified based on information gathered during the reconnaissance survey or first calibration study.

Note that due to the temperate climate in Nashville, only moderate amounts of deicing fluid are applied to aircraft. If the winter is milder than usual, there may not be much deicing fluid applied at all. It is also quite possible that if deicing fluid is applied to aircraft at the terminal gates or deicing pad during periods of little precipitation, the deicing fluid may take several days to reach the treatment basin if at all. In other words, depending on conditions there may not be any BOD load to be discharged to Sims Branch during the scheduled studies. In order to permit scheduling of the studies and to provide the best possible data for the modeling study, if there is insufficient BOD available for discharge it is proposed that the treatment basin be spiked with a quantity of propylene glycol to generate a measurable BOD load. Although spiked effluent will not be exactly representative of processed waste ( treated pond BOD may Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 35 of 40 be more recalcitrant because it has been treated), the dynamics of the receiving stream should be similar. The spiked BOD concentration will be 25 mg/ L or less, and will be controlled by careful analysis and dilution at the discharge.

Dye Time of Travel Flow will be gauged at least twice per day in Sims Branch near the dye mass during each study. In addition, the Sims Branch flow upstream from the Airport treatment pond discharge will be measured prior to injection of the dye. The stream flow will be determined from velocity and depth measurements using a Pygmy current meter on a wading rod in accordance with standard USGS standard gauging techniques. If there are significant tributaries contributing to stream flow, these will also be estimated. Normally, 1% of main stream flow is used as a criterion for defining tributaries as " significant."

Time of water travel for Sims Branch will be determined from both dye peak to peak travel time measured at 2 to 6 hour intervals over approximately a 2 day period and from selected locations where ISCO samplers will be positioned to collect the complete dye curve at up to 3 stationary points in the study area. On the first day of each calibration field study, a sufficient quantity of 20% Rhodamine WT, a fluorescent water tracing dye, will be instantaneously injected into Sims Branch upstream from the Airport discharge point to achieve a downstream concentration of 20 ppb or less. At this concentration, the dye should not be visible to the naked eye, but easily detectable by a fluorometer. Following injection, the dye peak will be measured about every 2 to 6 hours using a Turner Designs Model 10 AU or SCUFA Fluorometer with sensitivities of approximately 0.01 ppb and 0.04 ppb, respectively.

Sims Branch water from about mid depth will be analyzed at known fixed stations established during the reconnaissance study. Once fluorometer readings exceed background levels ( indicating the presence of the dye plume), measurements will be recorded at intervals ranging from approximately 2 to 15 minutes. Readings will continue until the peak is reached and dye readings recede to approximately 10 percent of the peak concentration. After the dye peak has passed a station, the equipment and personnel will move to the next downstream station to await the dye peak again in a similar manner.

In addition, ISCO samplers will be stationed at 2 to 3 locations along the study area to measure average dye mass time of travel. Discrete samples will be taken at approximately 15 to 30 minute intervals over a 4 to 8 hour period in order to delineate the dye curve. These data will then be used to determine the dye mass center which is analogous to the average time of travel. The stations will be located near the beginning of the dye study, the approximate midpoint and near the end of the dye study area. The peak to peak dye measurements will then be interpolated using these three points back to an average dye time of travel at each water quality station.

Time of travel data will be used with the flow data to develop v= aQ b relationships for each Sims Branch reach. The coefficient, a, and the exponent b, developed for each reach will be input into the QUAL2E model.

Distances will be determined based on miles as measured on the current 7.5 minute USGS quadrangle maps. The velocity of the River within the study area is believed to be on the order of 0.05 to 0.5 feet per second, dependent on flow conditions. Therefore, the dye mass will be Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 36 of 40 tracked for approximately 24 to 48 hours of travel or about 13,000 ft. Results from the bathymetric profiles, dye time of travel, and concurrent flow measurements will provide the hydraulic characterization necessary for determining velocity versus flow and depth versus flow relationships. The velocity versus flow relationships developed for each reach will be used in the wasteload allocation modeling.

Water Quality At each dye station, in situ water quality measurements and composite water samples for timeseries BOD and chemical analyses will be collected around the dye peak. In situ measurements and water samples will be collected for laboratory analysis at the approximate center of the stream from about mid depth at about 2 to 15 minute intervals around the dye peak. If a different sampling strategy ( e. g., widely dispersed and separate flow paths) is suggested by the reconnaissance study, the sampling strategy will be adjusted for the dye studies.

In situ water quality parameters will be collected concurrently with the dye time of travel study and include D. O., temperature, conductivity, and pH. Measurements of these parameters will be recorded at each dye station. Instruments to be utilized for these measurements include a Hydrolab Data Sonde 3 Multiprobe Logger ( Model D3S BS with Hydrolab Surveyor 3 Display Logger, Model SVR3 DL) or equivalent instrumentation. Several measurements will be made around the dye peak at each station. These measurements will be from the center of the channel at about mid depth in the water column. Again, if reconnaissance data indicate a different sampling scheme is required, then the dye study sampling scheme will be modified accordingly. In situ water quality will also be measured from any significant tributary to Sims Branch.

Instruments will be calibrated at the beginning of each study and at approximately 8 to 10 hour intervals during the field survey. The D. O. meters will be air calibrated following instrument manufacturer's recommendations. The pH meters will be calibrated using pH 7.0 and pH 10.0 standard buffers. The conductivity meters will be calibrated using prepared potassium chloride standards of 718 and 1,413 µ

/ cm.

Time Series BOD Time Series BOD samples will be prepared from river composite samples collected with the dye time of travel study. As previously mentioned, a composite river sample will be collected at each dye time of travel station by collecting a series of subsamples around the dye peak to create a 5 gallon composite sample at the station. Stream samples will be immediately covered and stored to minimize temperature extremes and potential temperature shock until the samples can be transported to the Airport laboratory. Samples will be transported to the laboratory for preparation of duplicate 2 L BOD bottles plus a 1 gallon makeup sample container. After initial D. O. readings, the BOD bottles will be incubated in coolers at 20 ° C. Samples will also be prepared for any other significant tributaries within the study area. In addition, time series BOD samples will be prepared for the background Sims Branch sample ( upstream from the Airport treatment basin discharge).

Once the water samples are brought to the laboratory, the samples will be vigorously shaken to aerate the samples to saturation. The sample will be allowed to stabilize for about 5 minutes. The sample will then be carefully siphoned into two 2 L BOD bottles and a 1 gallon Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 37 of 40 amber bottle. The two 2 L BOD bottles will serve as duplicate samples for measurement of oxygen utilization during the 90 day incubation period. The 1 gallon amber bottle will provide the additional sample required to makeup volume lost during the periodic D. O. readings. A 5 mL disposable pipette will be used to transfer makeup water from the bottle to each of the 2 L duplicate bottles. Additionally, the TKN and/ or ( NO2+ NO3) N samples will be obtained from the makeup bottle during the incubation period. After initial ( t0 or " time zero") readings are taken from the two duplicate samples and the lost volume is carefully replaced in the sample ( preventing oxygen transmittal), both samples will be sealed with air tight caps to prevent D. O. exchange. In addition, all samples will be covered with opaque material to prevent light penetration and potential algal productivity.

The D. O. will be monitored in the samples at frequent intervals including days 0, 0.5, 1, 2, 3, 4, 5, 7, 10, 15, 20, 25, 30, 35, 45, 60, 75 and 90. In addition, TKN and/ or ( NO2+ NO3) N samples will be withdrawn for analysis of nitrogenous activity on days 0 and 90.

Results from the 90 day time series BOD samples represent the ultimate carbonaceous and nitrogenous BOD. Since the 5 day BOD is required for permit limits and for MNAA's examination of their effluent quality, results from the long term ultimate BOD of 90 days will be converted to the appropriate 5 day value. A CBODu to BOD5 ratio will be estimated for this effluent and used in the QUAL2E model.

Water Samples for Chemical Analyses Water samples for chemical analyses will be collected from the 5 gallon composite time series BOD samples collected at each dye station. The samples will be analyzed for the following:

  Total Kjeldahl Nitrogen ( TKN);   Ammonia Nitrogen ( NH3 N);   Nitrite + Nitrate nitrogen ( NO2+ NO3 N);   Dissolved Orthophosphate ( Dissolved Ortho P);   Total Phosphate ( total PO4); and   Chlorophyll a.

Organic nitrogen is determined from the difference between TKN and NH3 N and total organic phosphorus is determined from the difference between total phosphates and orthophosphates. These samples will be prepared from composite water quality samples collected with the dye time of travel study. The same 5 gallon composite sample collected for the BOD sample will be used to fill the individual sample bottles for chemical analyses. Samples for chemical analyses will also be prepared from samples of the Sims Branch background and effluent. Grab samples for chemical analyses will be obtained for any other significant tributaries in the study area.

Diurnal D. O. Swing D. O. concentrations will be measured at specific stations over the diurnal cycle to estimate the influence of algal productivity and respiration on stream D. O. levels, as well as evaluate the target D. O. of 5 mg/ L required for the wasteload allocation modeling. For each calibration study, D. O. and temperature measurements will be recorded at approximately 2 to 3 stations Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 38 of 40 on a continuous basis. Diurnal D. O. measurements will be obtained during each dye survey period. Periodic checks of stream D. O. will be made independently at these fixed stations.

2.4 Calibrate Water Quality Model Water Quality Modeling Wasteload allocation modeling will be conducted using the USEPA wasteload allocation model QUAL2E. The QUAL2E model is widely used and accepted by both state and federal regulatory agencies and is acceptable to TDEC and USEPA Region 4. The model was developed for use as a water quality planning tool to set permit limits for point source dischargers of conventional constituents such as CBODu, organic nitrogen, and ammonia nitrogen, as well as to assist in determining the levels of treatment required for a constituent mass load. QUAL2E solves a one dimensional advection dispersion mass transport equation using the classic implicit backward difference numerical solution technique. Components of the general equation include dispersion, advection, constituent reactions, constituent interactions, and other sources and sinks.

The primary constituent being modeled is D. O. and therefore the model is driven by the factors which impact in stream levels of D. O. Some of these factors include the deoxygenation of ultimate carbonaceous biochemical oxygen demand ( CBODu), organic nitrogen conversion to ammonia, nitrification of ammonia, SOD, reaeration, temperature, flow, and algal productivity and respiration. Several of these parameters will be set based on data collected in the field and laboratory. Although model parameters can be simulated over time ( dynamic conditions), QUAL2E is limited to steady state hydraulic conditions. Since the boundary conditions for flow are expected to be constant, the model is referred to as quasi dynamic or quasi steady state.

For modeling purposes, the study area of Sims Branch will be divided into segments based on stream physical characteristics including stream depth, width, channel slope, and water timeof travel ( velocity). Water quality characteristics described by the calibration data set will be utilized in conjunction with the critical flow and temperature analysis to determine the rates and boundary conditions required for the developed model. The model will then be calibrated with the adjustment of certain water quality parameters within regulatory accepted ranges. Parameters involved in the calibration procedure include those which most affect the receiving water such as flow, D. O., carbonaceous BOD, organic nitrogen and ammonia nitrogen loadings. SOD will not be measured, and the model will use default values. In addition, an uncertainty analysis will be conducted to determine the degree of confidence placed in the model and resulting allocation.

Field Water Quality Model Input In situ water quality results for critical model parameters will be utilized for calibration of the developed model. Since these samples will be collected with the dye time of travel, the samples represent the water quality characteristics of a specific volume of river water ( slug) as it travels downstream from the Airport. In addition, since the water quality characteristics of this volume of water describe the physical, chemical, and biological reactions and interactions occurring as it travels downstream, these characteristics will be used to determine the decay Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 39 of 40 rates required for model development. The decay rates of concern in the model include those which affect the level of D. O. in the river and include the deoxygenation of BOD and nitrification processes resulting from the decay of organic nitrogen to ammonia nitrogen and ammonia nitrogen to nitrite nitrogen and then to nitrate nitrogen. Prior to entry into QUAL2E, rates must be adjusted from measured temperatures to the standard temperature accepted by the model.

The first order reaction rates that will be developed from analysis of concentration with time of travel downstream will include CBODu, organic nitrogen, and ammonia nitrogen. These rates will be independently determined and entered into the calibration model. No blind curve fitting of the model will be attempted and any adjustments to these rates will only be done after a careful review of the data sets.

Reaeration rates will be calculated using Tennessee/ EPA Region 4 guidance. Water elevation changes will be obtained from existing sources ( i. e., USGS quadrangles), and velocities will be modeled based on the equation V= aQ b, where a and b can be determined from multiple field measurements.

Results from the time series BOD samples will be utilized for two purposes. First, the CBODu concentrations determined for each of the samples collected with dye time of travel will be plotted versus the associated time of travel for each station. A first order curve fit of this plot ( exponential curve fit or a straight line on semilog paper) will be used to calculate the river CBODu deoxygenation rate, k1 or k r. The rates calculated will be used in the calibration and model. Secondly, the time series BOD analyses of CBODu for the river/ effluent dilution samples will be used to establish a CBODu/ BOD5 ratio. This ratio will be used to project the total mass CBODu loadings projected in the model to a BOD5 mass loading for establishing permit limits.

The oxygen utilized in the samples will be analyzed generally using Standard Methods ( APHA 1994), No. 5210 C, Ultimate BOD Test or another accepted method to characterize both the carbonaceous and nitrogenous kinetics of BOD.

Organic nitrogen and ammonia nitrogen results for the samples will be plotted versus time oftravel downstream. A first order curve fit of these data will be used to determine the organic nitrogen and ammonia nitrogen deoxygenation rates for input into the model.

Chlorophyll a results may also be input into the model to simulate primary productivity of algae if appropriate. The diurnal D. O. measurements will be used to project through sinusoidal curve fitting the minimum, maximum and average D. O. at each station. The midpoint of the diurnal D. O. fluctuation is used as the target D. O. for model calibration. The fluctuation in D. O. concentrations in Sims Branch resulting from algal productivity and respiration will be utilized not only during the calibration and validation of the developed model, but also to ensure that model allocations remain within regulatory limits.

Calibration The measured rates will be entered into the model and the model output will be compared against the individual field measured parameters ( e. g., CBODu, organic nitrogen, etc.) and D. O.. Adjustments to individual rates and parameters to better fit the individual curves and the Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 40 of 40 D. O. data will be done based on small adjustments to one rate at a time. Once the model is found to provide acceptable fits of the data, no further adjustments will be made.

Sensitivity Analysis Once the calibration model is completed, sensitivity analysis will be completed for each significant model rate and background parameter. These are adjusted one at a time about plus or minus 25 to 50 percent of the model rate or value. The most sensitive parameters are typically flow, water temperature, reaeration rate, and the CBODu deoxygenation rate.

2.5 Continuous Monitoring Having an adequate data set of in stream water quality data for Sims Branch under many varying conditions will be important in the development of an accurate and robust water quality model. Therefore, in addition to the intense time of travel field surveys, additional data will be gathered throughout the study period on an intermittent basis. Additional data will help refine the model and allow testing of predictions during development.

At least once per month during the study period between intensive time of travel surveys, in situ measurements of water quality parameters ( i. e., D. O., temperature, conductivity, pH) will be taken. Field personnel will walk the length of Sims Branch to Mill Creek and back again, taking the appropriate readings with a portable instrument at fixed stations identified during the reconnaissance study. The instrument will be appropriately calibrated prior to each assessment.

In addition, a Sims Branch " permanent" flow monitoring station will be established at the Airport access road retention dam. Sims Branch passes through long twin square culverts at the access road. A bubbler or other device for measuring depth of flow will be deployed. Using Manning's equation, culvert geometry, and the depth of flow through the culvert, the flow in Sims Branch can be accurately determined. The flows determined in this fashion will be checked against the field measured values using cross section and current meters. A permanent written or electronic record of daily flows will be generated.

2.6 Model Validation As in independent test of the calibration and robustness of the calibrated model, a new set of data ( not previously used during the calibration of the model) will be collected and compared to model predictions. The Model Validation field study will gather many of the same types of information as collected during the winter and summer time time of travel studies, but will be shorter and quicker. Use of Rhodamine WT tracer dye is not anticipated. However, measurements of flow, water quality, diurnal D. O., etc. will be conducted. If the model needs adjusting to accurately predict conditions encountered during the validation study, this will be noted and the appropriate changes made.

2.7 Wasteload Allocation Modeling Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 41 of 40 Once a water quality model has been satisfactorily calibrated, it will be used to determine the point source value of CBODu and NH3 N resulting in a D. O. sag curve which remains above the regulatory standard ( target D. O.). The CBODu values will then be converted into 5 day BOD values for establishing proposed permit limits. Using this method, wasteload allocations will be determined for the MNAA discharge for both summer and winter conditions, and at varying background flows in Sims Branch as appropriate.

2.8 Final Report Following completion of the wasteload allocation and modeling study, the MNAA will submit a final report summarizing all methodologies, data, and results to TDEC. The report will include maps and figures, with both tabular and graphical presentations of the study results, as well as any other information supplemental to the wasteload allocation study. Disks of the model inputs will be included. A recommended wasteload allocation plan will be prepared.

The final report will include, but not be limited to, the following:

  Summaries and data from all monitoring activities;

  Descriptions of methodologies applied during field data collection and laboratory analysis;

  Results of all modeling efforts ( calibration, validation, prediction);

  Study area maps and receiving system schematics;

  Hydraulic, water quality, and other parameters characterized during the field surveys and results;

  Projections of a WLA for the facility during winter and summer under varying flow conditions, and;

  Suggested permit limits and verbiage for inclusion in the final facility NPDES permit. Metro Nashville Airport Authority ( MNAA) NPDES Permit TN0064041 Page 42 of 40 3.0 SCHEDULE As discussed in the previous sections, the wasteload allocation study consists of many components. In order to ensure a successful study, it is necessary to schedule each component as carefully as possible. It is anticipated that the study as outlined in this Work Plan will be concluded by the summer of 2003, with the final report being submitted to TDEC on June 1, 2003. The proposed schedule for each task is outlined in Table 3 1.

Table 3 1. MNAA Sims Branch WLA Study Schedule No. Task Proposed Date( s) 1 Work Plan approval granted by TDEC 12/ 5/ 2001 2 Reconnaissance Study 12/ 10/ 2001   12/ 11/ 2001 3 Winter time of travel 12/ 27/ 2001   12/ 28/ 2001 4 Winter time of travel ( additional, if warranted) 1/ 3/ 2002   1/ 4/ 2002 5 Data reduction and analyses, time series BOD, etc. 1/ 4/ 2002   5/ 1/ 2002 6 Continuous in stream monitoring 2/ 1/ 2002   11/ 1/ 2002 7 Interim Report 6/ 1/ 2002 8 Summer time of travel 7/ 1/ 2002   7/ 2/ 2002 9 Summer time of travel ( additional, if warranted) 7/ 8/ 2002   7/ 9/ 2002 10 Data reduction and analyses, time series BOD, etc. 7/ 9/ 2002   11/ 1/ 2002 11 Validation study 12/ 30/ 2002   12/ 31/ 2002 12 Data reduction, analyses, and WLA modeling 12/ 31/ 2002   3/ 1/ 2003 13 Draft Final Report submitted to TDEC 5/ 1/ 2003 14 Final Report 6/ 1/ 2003 Every effort will be made to adhere to the dates listed in Table 3 1. However, due to the nature of field studies and uncertainties inherent with such studies, it may become necessary to adjust the dates somewhat. It is important to remain flexible to account for unanticipated changes that may be dictated by field conditions, weather, or even the data generated by earlier studies. Regardless of what changes may become necessary in the schedule, the overall completion date of June 1, 2003 will not be changed. Metro Nashville Airport Authority ( Addendum) NPDES Permit No. TN0064041 Page No. A 1 of A 8 ADDENDUM TO RATIONALE Metro Nashville Airport Authority PERMIT NO. TN0064041 September 18, 2003 Addendum prepared by: Mr. Vojin Janjic The Metropolitan Nashville Airport Authority ( MNAA) existing individual NPDES permit required MNAA to perform a Waste Load Allocation ( WLA) study. The purpose of the study is to determine the impact on water quality and to set permit limits for the discharge from the treatment facility which discharges to Sims Branch via Outfall 002.

The existing permit required that the overall completion date of June 1, 2003 for the WLA study must be met, regardless of what changes may become necessary in the details and interim reporting dates. After several revisions of the draft study were made according to division's recommendations, the final version was submitted in a timely manner, on May 30, 2003. The significance to meet this compliance date was to allow for sufficient time for this permit to be modified prior to the 2003/ 2004 deicing season. The purpose of this addendum to rationale is to summarize changes in effluent limitations and monitoring requirements at Outfall 002, based on the findings of the WLA study. The effluent limitations, monitoring requirements and other conditions for all other outfalls, as described in the NPDES Permit TN0064041, will remain unchanged.

Several stream characterization samples were collected as part of the Sims Branch WLA. The characterization sampling was performed during the different seasons of the year to provide data applicable to each season. Seasonal sampling was a key to this study because of the nature of discharge from MNAA. Deicing only occurs in the colder months of the year. For this reason, samples were collected and analyzed according to the typical bounds of the deicing season. A seven month period represents the potential months when deicing may occur. This period, the Winter Period, includes October through April of each year. These months also correspond to the wetter months of the year, thus providing additional assimilative capacity to deal with the discharged treated flow from Outfall 002. The remaining period of the year, the Summer Period, includes May through September. This period does not see any deicing activity. Additionally, flows are lower in Sims Branch, and since temperatures are higher, dissolved oxygen ( DO) is lower. Therefore, this period of the year is considered separately. Each of these seasons is reflected in sampling schemes, data analysis, and permit limits.

The Winter Event was performed on December 28 29, 2001. This was the first of the two extensive sampling efforts performed as part of the WLA. This twoday period is within two weeks of the midpoint of the winter period. The data obtained from the event provided a good characterization of the typical conditions during a Winter Period discharge from Outfall 002. 2.53 14.03 5.78 8.64 3.72 3.28 4.14 2.69 0 2 4 6 8 10 12 14 16 0 0.5 1 1.5 2 2.5 DISTANCE FROM CONFLUENCE WITH MILL CREEK ( MI) CBOD ( mg/ L) JB2 JB4 JB6 JB14 JB8 JB10 JB11 JB12 TRIB 5 TRIB 6 TRIB 4 STEP AERATOR EFF.

Ultimate CBOD concentrations for the Winter Metro Nashville Airport Authority ( Addendum) NPDES Permit No. TN0064041 Page No. A 2 of A 8 The Summer Event was performed on July 8 9, 2002. This was the second of the two extensive sampling efforts performed as part of the WLA. This two day period is within a few days of the mid point of the summer period. The data from this event characterizes the discharge from Outfall 002 during the warmer months of the year.

In addition to the Winter Event and Summer Event, environmental quality samples were also collected during several one day sampling events. The sampling was much less extensive and did not include ultimate carbonaceous biochemical oxygen demand ( CBODu) sampling as was included during the extensive Winter and Summer Events. Also, additional time of travel sampling was not performed. However, the data that was obtained during these events did provide sufficient information for a model validation scenario.

Once the field investigations and sampling events were complete, all relevant data available was gathered, and the task of organization and analysis was performed. The data was then used to develop and calibrate a model of Sims Branch. The model selected to perform the WLA study was the Qual2E model developed by the U. S. EPA. This model requires many types of data inputs to perform acceptable model runs. Although it is possible to perform model runs using default values, data developed through a study such as this one will result in a better and more reliable water quality model. Therefore, strict attention was given to an accurate assessment of all available data to improve the output from the Qual2E model runs.

The extensive environmental data collected during sampling events was analyzed and used to develop and calibrate the Qual2E model. The development and calibration of the Qual2E model was performed based on the period of the year to be evaluated. Each calibration was based on the major sampling event performed for each period of the year. The Winter Event ( December 28 29, 2001) was used as the base scenario for the Winter Period ( October   April). Likewise, the Summer Event ( July 8 9, 2002) was used as the base scenario for the Summer Period ( May   September).

Several conservative measures have been employed in the development of this model. Some noteworthy conservative aspects of the calibrated model for scenario assessment include:   A wide range of headwaters flow conditions is used to perform the scenarios;   The 75 th percentile flow was used for the discharge flow, even during very low flow headwaters conditions;   The outlying period for the Winter Period was April 30 ( deicing activity typically is over before April of every year); and   One half the diurnal flow variation was used for comparison of model results to the water quality standard ( 5.5 mg/ L versus the 5.0 mg/ L WQS). The conservative approach provided sufficient safety factors toward developing appropriate permit limits for the Outfall 002 discharge; however, some aspects of a worst case scenario 0 2 4 6 8 10 12 14 16 0 0.5 1 1.5 2 2.5 DISTANCE FRO CONFLUENCE WITH MILL CREEK ( MI) CBOD ( mg/ L)

model actual JB2 JB4 JB6 JB14 JB8 JB10 JB11 JB12 TRIB 5 TRIB 6 TRIB 4 STEP AERATOR EFF.

Winter Event CBODu Actual versus Model Metro Nashville Airport Authority ( Addendum) NPDES Permit No. TN0064041 Page No. A 3 of A 8 should still be evaluated. This was accomplished by performing scenarios for the outlying limits of the seven month and five month periods to evaluate the potential impact.

The ultimate purpose of this study is to provide a basis for recommending appropriate discharge limits for the MNAA Outfall 002. The flow of Outfall 002 represents the treated stormwater discharge from the main terminal and ramp areas of the Nashville International Airport property. The stormwater discharge includes flows from deicing activities during the winter months of the year.

There is always some element of BOD contained in airport discharge. However, levels remain very low during the Summer Period of the year. The major source of BOD in airport runoff is deicing fluid. Deicing only takes place during the cold periods of the year; the period is almost exclusively bound between the months of October and April of the year. Consequently, the limits recommended by this report are relevant to this timeframe. Limits are recommended for the period between October and April, and separate limits are recommended for the period between May and September. These are the same periods proposed by the division's personnel during the last permit review.

It is important to note the extensive range of variables that affect the impact of any pollutant source on a receiving stream. The discharge from Outfall 002 is a classic example. For any particular discharge flow, there is an associated CBOD concentration. This particular flow and concentration could have a range of impacts on the water quality of Sims Branch. Factors that influence these impacts include: weather conditions, air temperature, water temperatures ( Sims Branch and effluent), pre existing dissolved oxygen concentrations ( Sims Branch and effluent), pre existing CBOD concentrations in Sims Branch, and background flow of Sims Branch. It would be preferable to develop a matrix or a real time model as part of the discharge permit; however, this is not currently practical for the State of Tennessee or MNAA because of insufficient staff and resources. Such a concept is also limited because of the required time to evaluate CBOD levels in stream as well as in the Outfall 002 discharge. If future advancements are made in water quality sampling and analysis practices and the additional staff to perform such an evaluation were available, such a standard would provide a much more real time management of the water quality of Sims Branch.

The Winter Period recommendations are based on, a) model runs that show no DO concentration that dips below the water quality standard along the entire length of Sims Branch, and b) the evaluation of the technological capability of the treatment unit. The technological evaluation demonstrated that under certain influent conditions, even a 92% reduction of CBOD5 would yield concentrations in excess of 250 mg/ L. However, these conditions typically occur when flows are lower in Sims Branch and in the treatment unit. The critical period for CBOD5 concentrations is found when a great deal of deicing is required and relatively low rainfall or snow melt totals are available to carry the deicing fluids. Therefore, the major concern is during cold, dryer periods of the winter. When these periods occur and high influent concentrations are detected, flow into the treatment unit can be stopped and flows can be retained until additional stormwater is available for dilution and treatment. This option was exercised in December 2002. If the capacities of the treatment unit and retention ponds are exceeded when a high concentration is measured in the influent of the treatment pond, flow can be diverted to the Metro sanitary sewer collection system. This addresses the critical time for CBOD5 concentrations. Metro Nashville Airport Authority ( Addendum) NPDES Permit No. TN0064041 Page No. A 4 of A 8 The limits for higher flow periods are not problematic for the treatment unit because of the available dilution from stormwater. The permittee recommended the highest concentration allowed during the winter months to be 150 mg/ L for a single sample for any flow of 3 cfs or greater. This recommendation was based on model runs with the stream flow set at 3 cfs with a discharge concentration of 150 mg/ L. Although higher concentrations may be assimilated by Sims Branch at higher flows, concentrations are not critical at these higher flow conditions and the recommended 150 mg/ L concentration will further contribute to the protection of the health of Sims Branch.

The discharge permit limits recommended by the permittee for the Winter Period are presented in Table A. One sample was recommended per week during the Winter Period of the year because it is the critical period of the year for elevated CBOD concentrations in the discharge from Outfall 002.

Table A Permittee Recommended Water Quality Based Effluent Limits for the Winter Period ( October   April)