Rationale for Re-evaluating the POTW Typical Pollutant Concentrations Used in the Nutrient Model

Background

The Water Pollutant Loading Tool Nutrient Model (Nutrient Model) (USEPA, 2017) calculates total nitrogen (TN) and total phosphorus (TP) loadings based on the type of facility (i.e., SIC code) and availability of discharge monitoring report (DMR) data. For facilities that do not have nitrogen and/or phosphorus DMR data available in the program system of record (Integrated Compliance Information System-National Pollutant Discharge Elimination System (ICIS-NPDES)), typical pollutant concentrations (TPCs) are used in the loading calculations. Currently, the Nutrient Model uses two methodologies to calculate TPCs.1

The first methodology groups the nitrogen and phosphorus concentration data available in ICIS-NPDES by SIC code, season, and facility flow class (<1 MGD, 1-5 MGD, and >5 MGD) and identifies the median TN and TP concentration for each group. For publicly owned treatment works (POTWs) (defined by SIC code 4952), the twelve TPCs for TN range from 6.71 mg/L to 8.96 mg/L, and the twelve TPCs for TP range from 0.78 mg/L to 1.61 mg/L. The Nutrient Model uses these TPCs in calculating TN and/or TP loads for POTWs having flow data available in ICIS-NPDES but no nitrogen and/or phosphorus DMR data.

The second methodology determines the median TN and TP concentration for each SIC code. For POTWs, the median TN and TP concentrations are 6.1 mg/L and 0.8 mg/L, respectively1. The Nutrient Model uses these TPCs in calculating TN and/or TP loads for POTWs having no flow data and no nitrogen and/or phosphorus DMR data in ICIS-NPDES.

1Note that the TPCs and median concentrations calculated using the Nutrient Model methodology change as data are added to ICIS-NPDES. The values shown above reflect those available on the Water Pollutant Loading Tool Nutrient Model website when accessed on October 19, 2017.

Need for Re-Evaluation

In a December 14, 2012, letter to the Natural Resources Defense Council (NRDC), USEPA noted: "where nutrient discharge monitoring data [for POTWs] do exist… generally it is at facilities that employ not just secondary treatment technology but also more advanced treatment technologies" (USEPA, 2012). Because lower TN and TP concentrations are anticipated from POTWs employing advanced treatment technologies, such as denitrification and phosphorus removal, TPCs derived using a dataset more reflective of POTWs employing advanced treatment may underestimate TN and TP concentrations for those POTWs without additional treatment for nutrients.

Earlier efforts by Pait (1993), Tetra Tech (1999), and USEPA (2007) considered treatment level in determining TPCs for TN and TP at POTWs (see Table 1 below). The TPCs derived using the current Nutrient Model methodologies are within the ranges calculated for POTWs employing advanced treatment, according to these earlier TPC derivation efforts.

A state-specific analysis of TN and TP effluent data recently completed by the Iowa Department of Natural Resources (DNR) also shows that TPCs calculated using the current Nutrient Model methodologies underestimate TN and TP concentrations for POTWs only employing secondary treatment. Under Iowa’s Nutrient Reduction Strategy, major POTWs are required to perform weekly influent and effluent monitoring for TN and TP. The Iowa DNR calculated the TPCs, shown in Table 2 below, using 2016 monthly average TN and TP effluent data from 54 major Iowa POTWs grouped by flow class.

While recognizing the inherent uncertainty in deriving TPCs for a subset of POTWs lacking TN and/or TP data in ICIS-NPDES, a re-evaluation of the Nutrient Model’s methods for calculating TPCs was recommended to provide TPCs for POTWs that are not likely to have additional treatment for nutrients.

Table 1. TPCs derived with consideration of POTW treatment level.
Treatment Level Source TPC
TN (mg/L) TP (mg/L)
Secondary Pait, 1993 11.2 7.0
Tetra Tech, 1999 11.2 2.0
USEPA, 2007 15 4
Advanced Pait, 1993 5.6 3.5
Tetra Tech, 1999 5.6 0.8
USEPA, 2007 11.2 2.0
Table 2. Iowa-specific TPCs.
Statistic Flow Class Sample Size2 Count of POTWs3 TPC
TN (mg/L) TP (mg/L)
Median <1 MGD 216 29 13.1 1.9
1-5 MGD 322 37 12.2 1.9
>5 MGD 102 11 21.5 2.4
Average <1 MGD 216 29 15.8 3.2
1-5 MGD 322 37 13.3 2.6
>5 MGD 102 11 24.7 2.9

2Sample size refers to the number of monthly average results.
3Some POTWs have monthly average results associated with more than one flow category. Total universe = 54 POTWs.

Why use average values?

The TPCs for TN and TP from POTWs or facilities with SIC code 4952 – sewerage systems – have been adjusted to reflect average values of monthly average data reported. Depending on individual permit requirements, some facilities may monitor daily (or multiple times a day then averaged to generate a daily sample), weekly (or multiple times in a given week then averaged to generate a weekly sample), or monthly (often several samples in a month averaged together, or the average of weekly or daily samples). Effluent concentrations of TN and TP at POTWs may be expected to vary due to several factors including influent concentration fluctuations and technology performance factors. A monthly average of TN and TP effluent concentration data from a facility captures those fluctuations while providing a typical effluent concentration value often based on several daily or weekly samples. Thus, a monthly average value can be a more accurate representation of any facility’s effluent concentration than a median value that discounts outliers while being less variable than daily or weekly samples and closer to a facility’s long term average concentration.

Additionally, in the Iowa DNR analysis previously noted, 2016 annual TN and TP loads were calculated for a subset of 51 Iowa POTWs using actual facility-specific monthly average flow and concentration data. The same load calculations were then performed except that the Iowa-specific TPCs, shown in Table 2 above, were used in place of the actual facility-specific monthly average concentration data. The loads calculated using the average TPCs were closer to those loads calculated using actual facility-specific concentration data than were the loads calculated using the median TPCs (Table 3).

Table 3. Comparison of 2016 TN and TP Loads (lb) for 51 Iowa POTWs calculated using:
  Facility-specific Mo Avg Conc Data Iowa-specific Average TPCs Iowa-specific Median TPCs
TN 12,903,407 13,758,347 12,032,294
TP 1,691,574 1,798,032 1,428,357

How the Hypoxia Task Force (HTF) TPCs were calculated

The following steps identify the process followed to generate the TPCs for TN and TP from major municipal wastewater treatment plant effluent in the twelve Hypoxia Task Force (HTF) Mississippi/Atchafalaya River Basin (MARB) states not likely to have additional treatment for nutrients.

  1. Identify from the HTF Point Source committee’s 2016 Report on Point Source Progress in Hypoxia Task Force States a list of a minimum of 10 (where available) randomly selected major POTWs from each of the 12 states with required monitoring for nitrogen and phosphorus parameters but without effluent limitations. The state of Iowa had done its own analysis on 54 Iowan facilities, with 12 months of data for the year 2016; that data was included in the analysis.
  2. Collect from EPA’s Environmental Compliance History Online (ECHO) portal the monthly discharge monitoring reports from facilities identified in step 1 for the months April 2014 – July 2017.
  3. From the DMR data downloaded, classify each facility into one of three categories based on the average of the facility’s reported monthly average flow in millions of gallons discharged per day (MGD): small (<1 MGD), medium (1-5 MGD), and large (>5 MGD).
  4. Create a master excel file with all the facility DMR data for TN and TP, linked through a data model identifying each facility’s flow class.
    1. Create an Excel 2016 PowerPivot pivot table to calculate the average TN and phosphorus concentrations.
      1. Filters:
        1. Perm_feature_nmbr: any, other than "influent" or "INF"
        2. Perm_feature_type_code: "EXO"
        3. Perm_feature_type_desc: "External Outfall"
        4. Parameter_desc: "Nitrogen, Total [as N]" and "Phosphorus, Total [as P]"
        5. Monitoring_location_desc: "Effluent Gross," "Effluent Option 1," Effluent Option 2," and "See Comment."
        6. Standard_unit_desc: "mg/L"
        7. Statistical_base_short_desc: "30DA AVG," "MO AVG", and "QTR AVG"
        8. Flow_Class: small, medium, large (user created)
      2. Columns:
        1. Flow Class (user created)
      3. Rows:
        1. npdes_id
      4. Values:
        1. Average of dmr_value_nmbr
        2. Median of dmr_value_nmbr
    2. Create slicers to easily toggle and filter out data:
      1. Flow Class
      2. State
  5. Analyze data
    1. a. Calculate an average value from monthly average TN and TP data points for all facilities and calculate the same for the three distinct flow classes.
    2. Caveats:
      1. Initial review indicated that all facilities within the "large" flow class from Indiana had average monthly average TP effluent concentrations well below 1 mg/L, indicative of treatment beyond national secondary treatment standards for POTWs. Due to time constraints, data from all Indiana facilities were removed from the analysis as staff was unable to splice out data from only the large Indiana facilities.
      2. TP values from the states of Minnesota and Wisconsin were also removed as those states have state laws requiring 1 mg/L effluent limit concentrations for TP at major POTWs.
      3. Facilities from Arkansas reported only nitrite + nitrate values which is not a full measure of TN (TN = nitrite + nitrate plus total kjeldahl nitrogen) and thus the analysis did not incorporate that data. Facilities from Indiana only reported daily maximum TN data, not 30-day or monthly average values so those data were also not incorporated in the analysis. Most facilities from Ohio and Minnesota reported nitrite + nitrate and total kjeldahl nitrogen separately. Due to time constraints, the analysis did not include the manual addition of those monthly average values to generate TN values for inclusion in the analysis.
      4. EPA did not verify, other than under the circumstances listed above in (5)(a)(i), whether the facilities it included in the analysis had received effluent limits for TP, TN, or both since the publishing of its 2016 Report on Point Source Progress in Hypoxia Task Force States. Also due to time and resource constraints, EPA did not independently verify that any of the facilities had effluent limits at any time from April 2014 – July 2017, or that the facilities are designed to treat beyond national secondary treatment standards.
  6. Results:
     
    Table 4. Results of Total Nitrogen TPC Calculations
    Total Nitrogen
    Flow Class Avg. of Monthly Avg. (mg/L) Median of Monthly Avg. (mg/L) Number of Distinct NPDES facilities Number of Samples 95% Confidence Range
    All 13.343 11.58 152 3129 13.147 - 13.539
    Large 13.586 10.9 25 533 13.145 - 14.027
    Medium 12.75 11.3 84 1760 12.497 - 13.003
    Small 14.436 12.945 43 836 14.022 - 14.85
    Table 5. Results of Total Phosphorus TPC Calculations
    Total Phosphorus
    Flow Class Avg. of Monthly Avg. (mg/L) Median of Monthly Avg. (mg/L) Number of Distinct NPDES facilities Number of Samples 95% Confidence Range
    All 2.439 1.86 199 4860 2.402 - 2.476
    Large 2.039 1.698 39 1030 1.991 - 2.087
    Medium 2.599 1.936 109 2690 2.545 - 2.653
    Small 2.422 1.8 51 1140 2.342 - 2.502
  7. List of facilities
     
    Table 6. List of Facilities4
    Name NPDES ID Flowclass Flow
    PLANO STP, CITY OF IL0020052 Small 0.736
    MILAN STP, VILLAGE OF IL0020214 Small 1
    FLORA STP, CITY OF IL0020273 Medium 1.14
    LITCHFIELD STP, CITY OF IL0020621 Medium 2.269
    DANVILLE SD IL0020788 Large 7.9
    MARSEILLES WWTP, CITY OF IL0021059 Medium 1.417
    MORRIS - MAIN STP IL0021113 Medium 2.31
    CREVE COEUR WWTP, VILLAGE OF IL0021237 Medium 1.149
    BONNIE BRAE FOREST MANOR SD IL0021261 Small 0.813
    GREATER PEORIA SANITARY AND SEWAGE DISTRICT IL0021288 Large 22.97
    O'FALLON STP, CITY OF IL0021636 Medium 3.397
    CHARLESTON STP, CITY OF IL0021644 Small 1
    JACKSONVILLE STP, CITY OF IL0021661 Medium 4.6
    STREATOR STP, CITY OF IL0022004 Medium 3.288
    WATSEKA STP, CITY OF IL0022161 Medium 1.491
    BENTON NORTHWEST STP, CITY OF IL0022365 Medium 1.52
    ST CHARLES EASTSIDE WWTF, CITY OF IL0022705 Medium 4.38
    GALESBURG SANITARY DISTRICT IL0023141 Large 8.07
    MENDOTA STP IL0023221 Medium 1.99
    MURPHYSBORO STP, CITY OF IL0023248 Medium 1.48
    FREEPORT STP, CITY OF IL0023591 Medium 4.71
    CLINTON SD STP IL0023612 Medium 1.44
    JERSEYVILLE STP, CITY OF IL0024465 Medium 2.06
    ALTON STP, CITY OF IL0027464 Large 9.35
    CARBONDALE NORTHWEST WWTP IL0027871 Medium 1.61
    EAST PEORIA STP #1, CITY OF IL0028576 Medium 4.25
    HERRIN STP, CITY OF IL0029165 Medium 2.03
    HIGHLAND STP, CITY OF IL0029173 Medium 1.49
    SPRING VALLEY WWTP IL0031216 Small 0.95
    SYCAMORE STP - NORTH PLANT IL0031291 Medium 2.88
    TROY STP, CITY OF IL0031488 Medium 1.65
    STOUGHTON CITY WWTF WI0020338 Small 0.9315
    SUSSEX VILLAGE WWTF WI0020559 Medium 1.9013
    ARCADIA CITY WWTF WI0023230 Medium 1.46715
    OREGON WI0020681 Medium 1.2748
    BEAVER DAM CITY WWTF WI0023345 Medium 4.157
    NEW ALBANY POTW MS0020044 Medium 1.9
    LAUREL POTW NUMBER 2 MS0020176 Medium 3
    PASCAGOULA POTW MS0020249 Medium 4.7
    BELZONI POTW MS0020371 Small 0.47
    WEST POINT POTW, WEST MS0020788 Medium 1.83
    HATTIESBURG NORTH LAGOON MS0020826 Medium 1.98
    WINONA POTW MS0021024 Small 0.8
    ESCATAWPA WWTP MS0021521 Medium 1.1
    VICKSBURG POTW MS0022381 Medium 3.41
    BROOKHAVEN POTW MS0024147 Medium 2
    WAYNESBORO POTW MS0024228 Small 0.975
    BATESVILLE POTW MS0024627 Medium 1.104
    WAVELAND POTW MS0027847 Medium 2.51
    HCUA, WEST BILOXI POTW MS0030333 Medium 4.04
    VERONA POTW MS0042048 Small 0.754
    JCUA, WEST JACKSON COUNTY POTW MS0045446 Large 5.1
    DIAMONDHEAD WATER AND SEWER DISTRICT MS0046078 Small 0.88
    GULFPORT POTW, NORTH MS0051756 Large 5.95
    ABERDEEN POTW, EAST MS0055581 Medium 2.65
    BEATTIES BLUFF WWTF MS0057517 Medium 3.91
    MCCOMB POTW MS0061077 Medium 2.75
    S5 KILN NORTHERN REGIONAL WWTP MS0061239 Small 0.33
    MONETT WASTEWATER TREATMENT PLANT MO0021440 Medium 2.2
    BOLIVAR WWTF MO0022373 Medium 1.57
    KC BLUE RIVER WWTF MO0024911 Large 27.5
    MSD LEMAY WWTP MO0025151 Large 103.5
    MSD COLDWATER CREEK WWTF MO0025160 Large 24.5
    CABOOL WWTF MO0026301 Medium 1.37
    SAVANNAH WWTF MO0026336 Small 0.454
    CALIFORNIA MO0023272 Medium 1.55
    MSD MISSOURI RIVER MO0004391 Large 23.7
    KENNETT WWTF MO0028568 Large 7.45
    FARMINGTON WEST WWTF MO0040312 Medium 1.6
    MISSOURI RIVER WWTF MO0058351 Medium 3.98
    FESTUS-CRYSTAL CITY STP MO0080632 Medium 1.96
    WARRENTON WWTP MO0087912 Medium 1.452
    NEVADA MO0089109 Medium 1.33
    PCRSD BRUSH CREEK FAC MO0119474 Small 0.69
    CHISHOLM MN0020117 Small 0.997
    MONTEVIDEO MN0020133 Small 0.908
    LUVERNE WWTF MN0020141 Medium 1.005
    NEW PRAGUE MN0020150 Small 0.804
    DETROIT LAKES MN0020192 Small 0.888424
    THIEF RIVER FALLS MN0021431 Large 8.6885
    MARSHALL MN0022179 Medium 2.5
    WINDOM WWTF MN0022217 Small 0.791
    MADELIA WASTEWATER PLANT MN0024040 Small 0.68
    NORTHFIELD WWTP MN0024368 Medium 2.08
    PRINCETON MN0024538 Small 0.37
    RED WING WWTP MN0024571 Medium 2
    ROCHESTER WWTF MN0024619 Large 12.6
    SAINT JAMES MN0024759 Small 0.803
    WORTHINGTON WWTF MN0031186 Medium 1.7
    BUFFALO MN0040649 Medium 1.003
    ALEXANDRIA LAKE AREA SSD MN0040738 Medium 2.726
    ST CLOUD WWTF MN0040878 Large 9.17
    WORTHINGTON INDUSTRIAL MN0031178 Medium 1.65
    GRAND RAPIDS MN0022080 Medium 3.145
    EAST GRAND FORKS MN0021814 Large 10.833
    ALBERT LEA WASTEWATER FACILITY MN0041092 Medium 3.8
    BROUSSARD, CITY OF LA0020613 Small 0.87
    ST. CHARLES PARISH COUNCIL - LULING OXIDATION POND LA0032131 Medium 1.68
    HAMMOND, CITY OF- SOUTH SLOUGH WETLAND WASTEWATER ASSIMILATION PROJECT LA0032328 Medium 4.6
    OAKDALE LA0033430 Medium 1.37
    THIBODAUX, CITY OF- WASTEWATER TREATMENT FACILITY LA0032948 Medium 3.29
    BREAUX BRIDGE, CITY OF LA0033014 Medium 1.15
    MANDEVILLE, CITY OF LA0038288 Medium 1.31
    TERREBONNE PH GOVT-HOUMA NORTH LA0040207 Large 6.83
    DENHAM SPRINGS, CITY OF LA0045730 Medium 2.44
    WALKER, TOWN OF LA0059951 Small 0.834
    TALLULAH, CITY OF- WASTEWATER TREATMENT PLANT LA0086576 Medium 2.7
    CHARLESTOWN MUNICIPAL WWTP IN0020508 Medium 1.01
    TELL CITY WWTP IN0021016 Medium 1.88
    INDIANAPOLIS BELMONT & SOUTHPORT ADVNCD WTP IN0023183 Large 65.8
    JEFFERSONVILLE WWTP IN0023302 Large 5.5
    NEW ALBANY WWTP IN0023884 Large 8.9
    NEWBURGH WWTP IN0023892 Medium 2.62
    SOUTH DEARBORN RSD IN0024538 Medium 3.51
    MADISON WWTP IN0025666 Medium 2.2
    EVANSVILLE WESTSIDE WWTP IN0032956 Large 13.8
    SPEEDWAY WWTP IN0032972 Medium 4.01
    EVANSVILLE EASTSIDE WWTP IN0033073 Large 13.1
    MOUNT VERNON WWTP IN0035696 Medium 2.08
    ERWIN STP TN0023001 Medium 1.013
    MORRISTOWN STP TN0023507 Medium 4.4
    ELIZABETHTON STP TN0023515 Medium 2.34
    MCMINNVILLE STP TN0023591 Medium 1.7
    OAK RIDGE STP TN0024155 Medium 3.7
    SHELBYVILLE STP TN0024180 Medium 3.1
    CHATT.-MOCCASIN BEND STP TN0024210 Large 66.2
    JOHNSON CITY KNOB CREEK STP TN0024236 Medium 2.43
    JOHNSON CITY STP TN0024244 Large 7.22
    SOUTH PITTSBURG STP TN0024295 Small 0.5
    ROANE COUNTY STP TN0024473 Small 0.27
    JACKSON ENERGY TN0024813 Large 8.131
    CROSSVILLE STP TN0024996 Medium 2.43
    BELLS LAGOON TN0026247 Medium 1.56
    WHITEVILLE STP TN0026590 Small 0.57
    LEBANON STP TN0028754 Large 6.74
    JOHNSON CITY REGIONAL STP TN0028789 Medium 1.94
    HALLS LAGOON TN0057291 Small 0.41
    COLLIERVILLE STP TN0057461 Medium 1.58
    LOUDON STP TN0058181 Large 8.29
    WHITE HOUSE STP TN0059404 Small 0.691
    PARIS TN0061271 Medium 2.55
    MUNFORD LAGOON TN0062499 Medium 1.096
    GREENVILLE STP KY0020010 Medium 1.06
    HAZARD STP KY0020079 Medium 1.87
    RWRA MAX RHOADS WWTP KY0020095 Large 8.735
    MAYSVILLE STP KY0020257 Medium 1.269
    HENDERSON STP KY0020711 Large 5.128
    BENTON STP KY0021172 Small 0.8947
    MORGANFIELD WWTP KY0021440 Medium 1.72
    ASHLAND STP KY0022373 Large 5.93
    BOWLING GREEN STP KY0022403 Large 7.63
    PADUCAH/MCCRACKEN JSA PADUCAH KY0022799 Large 7.87
    HARLAN STP KY0026093 Small 0.951
    SOMERSET STP KY0026611 Medium 2.62
    WILLIAMSBURG STP KY0028347 Medium 1.09
    PRINCETON STP KY0028401 Medium 1.026
    MANCHESTER STP KY0029122 Small 0.948
    GREENUP CO ENVIRONMENTAL COMM KY0048348 Medium 1.85
    MOREHEAD STP KY0052752 Medium 2.55
    MIDDLESBORO STP KY0072885 Medium 1.95
    CEDAR CREEK WQTC KY0098540 Medium 4.54
    DEREK R GUTHRIE WQTC MSD KY0078956 Large 33.37
    HONEY BRANCH REGIONAL STP KY0103578 Small 0.36
    ADEL CITY OF STP IA2503001 Small 0.372
    ATLANTIC CITY OF STP IA1509001 Medium 1.299
    BOONE CITY OF STP IA819001 Medium 2.696
    CEDAR FALLS CITY OF STP IA709001 Large 6.377
    CHARLES CITY, CITY OF STP IA3405001 Medium 1.655
    CHEROKEE CITY OF STP IA1811002 Medium 1.341
    CORALVILLE CITY OF STP IA5208001 Medium 2.600
    COUNCIL BLUFFS CITY OF STP IA7820001 Large 6.969
    CRESTON CITY OF STP IA8816001 Medium 1.530
    DAVENPORT CITY OF STP IA8222003 Large 34.928
    DES MOINES METROPOLITAN WRF IA7727001 Large 66.282
    DUBUQUE CITY OF STP IA3126001 Large 7.477
    EAGLE GROVE, CITY OF STP IA9926001 Medium 1.135
    ELDORA CITY OF STP IA4236001 Small 0.608
    ELDRIDGE, CITY OF SOUTH SLOPE IA8230003 Small 0.560
    EMMETSBURG CITY OF STP IA7428002 Small 0.605
    ESTHERVILLE CITY OF STP IA3218002 Medium 1.383
    FOREST CITY, CITY OF STP IA9525001 Medium 1.024
    FORT DODGE CITY OF STP IA9433003 Large 8.235
    GREENFIELD CITY OF STP IA140001 Small 0.366
    GRIMES, CITY OF STP IA7736001 Medium 1.872
    GRINNELL, CITY OF STP IA7930001 Medium 1.984
    GRUNDY CENTER CITY OF STP IA3833001 Small 0.603
    HARLAN CITY OF STP IA8335002 Small 0.796
    HUMBOLDT CITY OF STP IA4641001 Small 0.952
    INDEPENDENCE CITY OF STP IA1037001 Medium 1.469
    IOWA CITY, CITY OF (SOUTH) STP IA5225002 Large 9.523
    IOWA FALLS CITY OF STP IA4260001 Small 0.956
    IOWA GREAT LAKES SD IA3050901 Medium 2.944
    JEFFERSON CITY OF STP IA3742001 Small 0.937
    KNOXVILLE CITY OF STP IA6342001 Medium 1.428
    MAQUOKETA CITY OF STP IA4950001 Small 0.664
    MONTEZUMA CITY OF STP IA7950001 Small 0.364
    MOUNT PLEASANT (MAIN) IA4453001 Medium 1.341
    MOUNT VERNON CITY OF STP IA5758001 Small 0.453
    MUSCATINE CITY OF STP IA7048001 Medium 4.986
    NEW HAMPTON CITY OF STP IA1970001 Medium 1.333
    NEWTON CITY OF STP IA5059002 Medium 2.242
    OELWEIN CITY OF STP IA3353001 Medium 1.045
    OSCEOLA CITY OF STP IA2038002 Small 0.966
    OSKALOOSA (NORTHEAST) IA6273001 Small 0.891
    OSKALOOSA (SOUTHWEST) IA6273002 Small 0.994
    RED OAK CITY OF STP IA6950001 Medium 1.584
    SHELDON CITY OF STP IA7170001 Medium 1.508
    SHENANDOAH CITY OF STP IA3659001 Medium 1.405
    SIOUX CENTER CITY OF STP IA8486002 Medium 1.179
    SIOUX CITY CITY OF STP IA9778001 Large 12.589
    VINTON CITY OF STP IA688001 Small 0.964
    WASHINGTON CITY OF STP IA9271001 Medium 1.538
    WAVERLY CITY OF STP IA990001 Medium 1.342
    WEBSTER CITY, CITY OF STP IA4063001 Medium 1.757
    WEST BURLINGTON CITY OF STP IA2985001 Small 0.728
    WEST LIBERTY CITY OF STP IA7073001 Medium 1.265
    WINTERSET CITY OF STP IA6171001 Small 0.789
    TWIN CITY WWTP OH0020079 Medium 1.74
    WEST CARROLLTON WWTP OH0020133 Medium 1.18
    LEXINGTON WWTP OH0020257 Small 0.484
    HAMILTON CO POLK RUN WWTP OH0020419 Medium 4.56
    MILFORD STP OH0020451 Small 0.67
    MASSILLON WWTP OH0020516 Large 11.14
    BROOKVILLE WWTP OH0020605 Small 0.8
    BELPRE WWTP OH0020621 Small 0.76
    EATON WWTP & SEWER SYSTEM OH0020907 Medium 1.29
    LEBANON REGIONAL WWTP OH0021059 Medium 2.613
    HARRISON WWTP OH0021440 Small 0.95
    COLUMBIANA WWTP OH0021776 Medium 1.15
    WELLSTON WWTP NORTH OH0023507 Small 0.904
    ASHLAND WWTP OH0023906 Medium 4.22
    ATHENS WWTP OH0023931 Medium 2.33
    CITY OF CANTON OH0024350 Large 25.23
    CHILLICOTHE WWTP - EASTERLY OH0024406 Medium 2.22
    CITY OF CIRCLEVILLE OH0024465 Medium 1.57
    CITY OF COLUMBUS OH0024732 Large 72.1
    CITY OF COLUMBUS OH0024741 Large 81.1
    DAYTON STP OH0024881 Large 41.14
    EAST LIVERPOOL WWTP OH0024970 Medium 2.46
    ENGLEWOOD WWTP OH0025011 Medium 1.185
    FAIRBORN WATER RECLAMATION CENTER OH0025062 Medium 4.1
    FRANKLIN REGIONAL WWTP OH0025275 Medium 3.24
    HAMILTON WWTP OH0025445 Large 8.51
    MUDDY CREEK WWTP OH0025470 Large 12.17
    LANCASTER WPCF OH0026026 Large 5.52
    MARION WPC OH0026352 Large 7.96
    YOUNGSTOWN WWTP OH0028223 Large 29.8
    SHELBY OH0023540 Medium 1.805
    KENTON OH0025925 Medium 3.381
    BELLEFONTAINE OH0024066 Medium 2.525
    CLARKSVILLE LIGHT & WATER AR0022187 Medium 1.03
    CAMDEN WATER UTILITIES AR0022365 Medium 2.4
    GREENWOOD, CITY OF AR0022454 Medium 1.004
    BLYTHEVILLE, CITY OF-WEST WWTF AR0022560 Small 0.991
    BLYTHEVILLE, CITY OF-SOUTH AR0022578 Small 0.682
    FORT SMITH, CITY OF - "P" STREET WWTP AR0033278 Large 7.45
    PINE BLUFF BOYD POINT WW TREATMENT FAC AR0033316 Large 11.76
    DUMAS, CITY OF-WWTP AR0033987 Medium 1.148
    BRYANT, CITY OF - WWTP AR0034002 Medium 2.36
    STUTTGART WW TREATMENT PLANT AR0034380 Medium 1.617
    MENA WASTEWATER TREATMENT PLANT PLANT AR0036692 Medium 1.835
    SHERWOOD, CITY OF - NORTH FACILITY AR0037176 Small 0.43
    LRWU-FOURCHE CREEK WWTP AR0040177 Large 9.61
    VAN BUREN, CITY OF-NORTH WWTP AR0040967 Medium 1.103
    JONESBORO, CITY OF - CITY WATER & LIGHT EASTSIDE WWTP AR0043401 Large 8.71
    BARLING, CITY OF AR0048801 Medium 2.38
    CLINTON EAST WW TREATMENT FACILITY AR0048836 Small 1
    LITTLE ROCK WASTEWATER-LITTLE MAUMELLE WWTP AR0050849 Medium 2.13
    CONWAY-TUPELO BAYOU WWTP AR0051951 Large 5.113

    4Note: this list includes the facilities that were excluded from the analysis as identified in steps 5(a)(i),(ii), and (iii), above.

References

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Pait, A.S. et al. (analysis team). 1993 (December). The National Coastal Pollutant Discharge Inventory, Point Source Methods Document (PDF) (258 pp, 6.5 MB). National Oceanic and Atmospheric Administration (NOAA), National Ocean Service, Office of Ocean Resources Conservation and Assessment, Strategic Environmental Assessments (SEA) Division, Pollution Sources Characterization (PCS) Branch. Silver Spring, Maryland. Retrieved from https://repository.library.noaa.gov/view/noaa/2920/noaa_2920_DS1.pdf.

Tetra Tech, Inc. 1999 (September 8). Improving Point Source Loadings Data for Reporting National Water Quality Indicators, Final Report. Final Report. Prepared for: U.S. Environmental Protection Agency, Office of Wastewater Management (OWM). Contract #68-C-0014, Work Assignment 1-31. Tetra Tech, Inc., Fairfax, Virginia.

USEPA. 2007. Hypoxia in the northern Gulf of Mexico—An update by the EPA Science Advisory Board (PDF) (333 pp, 4.9 MB). U.S. Environmental Protection Agency, EPA Science Advisory Board. EPA-SAB-08-003. Retrieved from https://yosemite.epa.gov/sab/sabproduct.nsf/C3D2F27094E03F90852573B800601D93/$File/EPA-SAB-08-003complete.unsigned.pdf.

USEPA. 2012 (December 14). Letter to the Natural Resources Defense Council in response to a petition requesting that the USEPA publish updated information about secondary treatment nutrient removal capability and establish new technology-based nutrient limits as part of the secondary treatment standards (PDF) (14 pp, 667 K). U.S. Environmental Protection Agency, Washington, D.C. Retrieved from https://www3.epa.gov/npdes/pubs/ow_shapiro_nrdcpetition.pdf.

USEPA. 2017 (accessed October 19). Water Pollutant Loading Tool: About the Nutrient Model. U.S. Environmental Protection Agency, Washington, D. C. 

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