The facility reported three maximum daily concentrations for manganese in 2016, ranging from 49.9 ug/L (below both the AML and MDL) to 70.2 ug/L (above both the AML and MDL). Eight measurements (taken twice per year) have been reported since then with manganese concentrations ranging from 36.2 to 63.0 ug/L with an average of 53.0 ug/L. Removal using potassium permanganate as a catalyst for oxidation has shown promising results; however, it is not clear that additional treatment for manganese would be needed for the facility to comply with effluent limits derived from the economic analysis criteria. EPA estimated a range of costs to address manganese. On the lower end of the range of costs is implementing a P2 program. The upper end of the range is, in addition to a P2 program, the estimated cost of additional treatment by adding chemical precipitation to the treatment system, which would have similar costs as oxidation for manganese removal using potassium permanganate and which can be estimated using the selected cost estimation software. EPA assumed that the City of Phoenix WWTP could use its existing primary clarifiers for chemical precipitation. The estimated costs are summarized in Exhibit A-25.
Exhibit A-25: City of Phoenix WWTP Estimated Incremental Costs (230 MGD)
Parameter
Control Option
Capital Cost
Other One-Time Cost
O&M Cost
Annual Cost (3%)[a]
Annual Cost (7%)[b]
Manganese
Chemical Precipitation
                                  $28,600,000
                                      $0
                                   $992,000
                                  $2,914,369
                                  $3,691,638

Large Facility P2 Program
                                      $0
                                    $49,672
                                      $0
                                    $20,973
                                    $20,973

                Alternative Compliance Mechanism for Manganese

Large Facility P2 Program
                                      $0
                                    $49,672
                                      $0
                                    $20,973
                                    $20,973
TOTAL:
                               $0 - $28,600,000
                                    $49,672
                                 $0 - $992,000
                             $20,973 - $2,935,342
                             $20,973 - $3,712,611
Notes:
[a] Capital costs annualized over 20 years at a 3% discount rate. Other one-time costs are not annualized.
[b] Capital costs annualized over 20 years at a 7% discount rate. Other one-time costs are not annualized.
Pima County WRC - Arva Valley WRF (AZ0024121)
The Pima County Regional Wastewater Reclamation Department's Arva Valley Wastewater Reclamation Facility (Pima County Arva Valley WRF; NPDES permit number AZ0024121) is a POTW located approximately 10 miles southwest of Tucson, Arizona, and upstream from the Pasqua Yaqui Indiana Reservation. The receiving water for the Pima County outfalls is Black Wash, tributary of Brawley Wash, which flows into the Santa Cruz River Basin. The POTW has a service population of approximately 17,370 people within the unincorporated areas of Pima County and the Pasqua Yaqui Indian Reservation.
EPA developed this facility analysis based on the draft 2019 permit and fact sheet issued by the Arizona Department of Environmental Quality together with discharge monitoring reports from between 2016 and 2021. EPA assumes that these draft documents are representative of current permits.
Effluent and Treatment Process
The Pima County Arva Valley WRF has a facility design flow of 4.0 MGD. The permit includes effluent limitations for BOD, TSS, pH, E. coli, and total residual chlorine.
The treatment processes at the Pima County Arva Valley WRF consist of a biological nutrient removal oxidation ditch (BNROD), screening, secondary clarification, tertiary filtering and UV disinfection with possible, occasional chlorination disinfection (used when basin maintenance is required and or as an emergency backup system substitute for UV disinfection if required). The sludge handling facility consists of a sludge-holding tank, waste sludge thickener, and a sludge loading station. Thickened waste sludge is hauled by tanker truck to a Pima County conveyance system manhole that flows to the Agua Nueva WRF for further processing prior to land application.
Reasonable Potential Analysis
The available monitoring data for the facility indicates that there have been no discharges to surface water of any pollutant of concern for this analysis between 2016 and 2020.
Summary
EPA assumes that there will be no incremental costs for this facility.
Town of Florence WWTP (AZ0025208)
Located in Pinal County, Arizona, the Town of Florence South WWTP (NPDES permit number AZ0025208) is a major NPDES facility that treats domestic wastewater from commercial and residential sources. The POTW's service area includes a population of 11,000 people in the Tohono O'odham Tribe Town of Florence on the Florence Village Reservation, in addition to the Florence Prison System. Effluent limitations seek to maintain the Water Quality Standards listed in Arizona Administrative Code (A.A.C.) R18-11-101 et. seq.
EPA developed this facility analysis based on the draft 2020 permit and fact sheet from the Arizona Department of Environmental Quality, together with discharge monitoring reports from between 2016 and 2021. EPA assumes that these documents are representative of current facility operations.
Effluent and Treatment Process
The facility has a design flow of 2.5 MGD. It intermittently discharges treated effluent into an irrigation ditch for local agricultural use, recharges the effluent into on-site recharge containers, or discharges the effluent into the facility's receiving water, the Gila River, via Outfall 001. Treatment processes entail influent screening; grit removal; three (3) sequencing batch reactors (SBRs) using aeration, anoxic reaction, settling, and decanting; effluent equalization basin; reuse pump station; and three (3) recharge basins. The treated effluent passes through an ultra-violet (UV) contact chamber for disinfection; the chamber has a chlorination system as a backup.
Sludge is treated in aerobic sludge digesters, pressed, and then disposed of at the local Apache Junction Landfill Corporation.
Reasonable Potential Analysis
EPA had sufficient data to conduct reasonable potential analyses for E. coli, ammonia, chlorine, chloroform, cyanide, dichlorobromomethane, selenium, and zinc (shown in Exhibit A-26).
Exhibit A-26: Summary of Available Effluent Data for Town of Florence WWTP (ug/L)
Parameter
Effluent Data[a]
Detection Limit

Samples
50[th] Percentile
Maximum

Bacteria (E. coli; cfu/100 mL)
                                                                             51
                                                                           6.0
                                                                      2,420[b]
                                                                            -
Ammonia
                                                                             20
                                                                           405
                                                                         3,140
                                                                             10
Chlorine
                                                                             62
                                                                         ND[c]
                                                                        0.03[c]
                                                                             10
Chloroform
                                                                              3
                                                                             -
                                                                          8.46
                                                                           0.01
Cyanide
                                                                             19
                                                                         ND[d]
                                                                           7.0
                                                                              5
Chlorodibromomethane
                                                                              3
                                                                             -
                                                                          16.2
                                                                         0.0001
Selenium
                                                                             20
                                                                          0.30
                                                                           2.5
                                                                            0.6
Zinc
                                                                              9
                                                                              -
                                                                            63
                                                                           0.05
Notes:
[a] For aquatic life economic analysis criteria, the reasonable potential analysis uses an estimate of the 99[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration. For human health criteria, the reasonable potential analysis uses either 1) the 50[th] percentile concentration from the existing effluent data set if the effluent data set includes 10 or more observations or 2) an estimate of the 50[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration if the effluent data set includes fewer than 10 observations. Thus, this table does not include a 50[th] percentile calculated from the effluent data set when there are less than 10 observations.
[b] While the daily maximum for this facility was measured as 2,420 cfu/100 mL, the maximum of monthly averages was 6.58 cfu/100 mL.
[c] Reported value is below the DL.
[d] The data included both detected and non-detected concentrations. The 50th percentile (median) value was reported as "not detected."
Exhibit A-27 summarizes the RPA for all parameters with sufficient data. Based on the fact sheet for the facility's current permit, mixing zones are not authorized, so EPA assumed no dilution was available for purposes of this analysis.
Exhibit A-27: Summary of Reasonable Potential Analysis for Town of Florence WWTP (ug/L)
Parameter
Conc at Edge of Mixing Zone[a]
Applicable Criteria
RP

Acute
Chronic
HH
Acute
Chronic
HH
AL
HH
Bacteria (E. coli; cfu/100 mL)b
                                                                             --
                                                                             --
                                                                             --
                                                                             --
                                                                             --
                                                                             --
                                      N/A
                                      Yes
Ammonia
                                                                         17,700
                                                                         17,700

                                                                        11,000
                                                                         1,400
                                                                              -
                                      Yes
                                      N/A
Chlorine
                                                                           0.10
                                                                           0.10

                                                                             19
                                                                             11
                                                                              -
                                      No
                                      N/A
Chloroform
                                                                           47.6
                                                                           47.6
                                                                           10.2

                                                                             60
                                      N/A
                                      No
Cyanide
                                                                           36.2
                                                                           36.2
                                                                            NDc
                                                                             22
                                                                            5.2
                                                                            4.0
                                      Yes
                                      No
Chlorodibromomethane
                                                                           91.1
                                                                           91.1
                                                                           19.5
                                                                              -
                                                                              -
                                                                           0.66
                                      N/A
                                      Yes
Selenium
                                                                              -
                                                                           13.1
                                                                             ND

                                                                            1.5
                                                                            130
                                      Yes
                                      No
Zinc
                                                                            195
                                                                            196
                                                                             46
                                                                            120
                                                                            120
                                                                           2600
                                      Yes
                                      No
Notes:
[a] No dilution was used for this analysis.
[b] For bacteria, the facility was assumed to have reasonable potential if the maximum effluent concentration (see above exhibit) exceeds 100 cfu/100 mL.
[c] The data included both detected and non-detected concentrations. The 50th percentile (median) value was reported as "not detected."
As shown above, six parameters (bacteria, ammonia, cyanide, chlorodibromomethane, selenium, and zinc) have reasonable potential. Exhibit A-28 summarizes the average monthly and maximum daily effluent limitations that were calculated as part of the RPA for the Town of Florence WWTP.
Exhibit A-28: Summary of Calculated Limits for Parameters with Reasonable Potential for Town of Florence WWTP (ug/L)
Parameter
Limiting Criterion
Limits
Max Conc
Exceeds Limit?

AML
MDL

Bacteria (E. coli; cfu/100 mL)
                                      HH
                                                                            100
                                                                             --
                                                                         6.58 a
                                      No
Ammonia
                                      AL
                                                                          1,400
                                                                          5,500
                                                                          3,140
                                      Yes
Cyanide
                                      AL
                                                                            3.3
                                                                            9.6
                                                                            7.0
                                      Yes
Chlorodibromomethane
                                      HH
                                                                           0.66
                                                                            1.3
                                                                             16
                                      Yes
Selenium
                                      AL
                                                                            1.5
                                                                            5.9
                                                                            2.5
                                      Yes
Zinc
                                      AL
                                                                             61
                                                                            120
                                                                             63
                                      Yes
Note:
[a] While the daily maximum for this facility was measured as 2419.50 cfu/100 mL, the maximum of monthly average effluent concentration was 6.58 cfu/100 mL
Summary
This facility's permit specifies an average monthly limit of 126 cfu/100 mL, and a daily average of 575 cfu/100 mL for E. coli. Monthly average effluent data indicate that this facility met its existing monthly average effluent limits and limit derived from the economic analysis criterion for bacteria from 2016 to present. The facility data also show a significant reduction in daily effluent concentrations after 2016 (January 2017 to March 2021, range of 0 to 130 cfu/100mL). In the most recent months (January 2020 to April 2021) the monthly average effluent concentration was reported as 3 cfu/100 mL with a range of daily maxima from 0 to 8 cfu/100mL during that same period (only 3 measurements during that period were above 0). These data indicate that the existing facility can meet the effluent limit based on the economic analysis criterion as currently operated. Therefore, EPA estimated no incremental compliance cost for bacteria for this facility at this time.
The facility would meet the ammonia MDL of 5.5 mg/L derived from the economic analysis criteria; the daily maximum concentrations also meet the proposed AMD of 1.4 mg/L in all but one month. Based on the available effluent data, it appears that the current system may be able to operate to achieve WQBELs derived from the economic analysis criteria. Performing a process analysis or modeling exercise may allow the facility to identify process steps that are not consistently performing up to the limits of the technology and to assure compliance. For effluent ammonia concentration reductions, this analysis may require additional water quality testing at the facility to conduct a process analysis and identify how to modify the unit processes in the current system to perform in such a way as to meet effluent limits. Modifications may include additional aeration, extended times in nitrification reactors, addition of alkalinity, enhanced solids removal, and temperature control. EPA estimated the cost to this facility of implementing a process modeling program, water quality monitoring, and process modifications to reduce effluent concentrations of ammonia. For purposes of this analysis, EPA estimated these costs to be similar to the costs of a P2 program that might be implemented for other pollutants.
Data for cyanide are mostly reported as non-detect. Of the measurements taken since 2016, none exceeded the MDL of 9.6 ug/L, but 5 of the 19 measurements exceeded the AML of 3.3 ug/L. Additional sampling would confirm whether treatment such as GAC adsorption to remove cyanide is necessary for this facility or if the facility may be able to meet the cyanide WQBELs derived from the economic analysis criteria with a P2 program. If the facility is unable to consistently comply with the MDL and AML and additional treatment is potentially infeasible (e.g., may cause substantial and widespread socioeconomic impact), the facility could apply for a WQS variance to investigate the its best compliance options, which may include addition of adsorption to remove cyanide. As shown in Exhibit A-29, EPA estimated the cost to this facility of applying for a WQS variance and implementing a P2 program to reduce effluent concentrations of cyanide and, at the upper end of the range of costs, the cost of adding adsorption to the treatment system along with a P2 program.
Exhibit A-29: Town of Florence WWTP Estimated Incremental Costs (2.5 MGD)
Parameter
Control Option
Capital Cost
Other One-Time Cost
O&M Cost
Annual Cost (3%)[a]
Annual Cost (7%)[b]
Ammonia
Small Facility Process Analysis
                                      $0
                                    $16,557
                                      $0
                                    $9,934
                                    $9,934
Cyanide and Selenium
Adsorption
                                  $5,944,000
                                      $0
                                   $317,849
                                   $717,379
                                   $878,921

Small Facility P2 Program
                                      $0
                                    $33,144
                                      $0
                                    $19,868
                                    $19,868

           Alternative Compliance Mechanism for Cyanide and Selenium

Small Facility P2 Program
                                      $0
                                    $33,144
                                      $0
                                    $19,868
                                    $19,868

Variance Feasibility
Analysis
                                      $0
                                    $90,328
                                      $0
                                      $0
                                      $0

Variance Application
                                      $0
                                   $255,680
                                      $0
                                      $0
                                      $0
TOTAL:
                                $0 - $5,944,000
                              $49,701 - $395,709
                                 $0 - $317,849
                              $29,802 - $747,181
                              $29,802 - $908,723
Notes:
[a] Capital costs annualized over 20 years at a 3% discount rate. Other one-time costs are not annualized.
[b] Capital costs annualized over 20 years at a 7% discount rate. Other one-time costs are not annualized.
Data for chlorodibromomethane show that effluent concentrations exceed the MDL and AML. The data ranged 2.27 ug/L to 16.20 ug/L and averaged 9.17 ug/L. Treatment of trihalomethanes (THMs), like chlorodibromomethane, in wastewater can often be controlled at minimal cost by managing chlorination, such as reducing chlorine contact time, limiting sunlight exposure to the chlorine contact chamber, and modifying the pH. Reducing the precursors to the formation of THMs, however, can be far costlier in the wastewater treatment process using activated carbon, ion exchange, or membrane filtration. Since there are operational changes that can reduce the formation of chlorodibromomethane, EPA estimated no incremental compliance cost for chlorodibromomethane for this facility at this time.
Selenium data show 2 exceedances of the AML for selenium (1.5 ug/L) derived from the economic analysis criteria from 21measurements taken from 2016 to 2021; however, the average of daily maximum selenium concentrations was 0.46 ug/L and the maximum value was 2.5 ug/L. The maximum daily limit of 5.9 ug/L was not exceeded during this monitoring period. The facility may be able to meet the selenium effluent limits derived from the economic analysis criteria with a P2 program. If the facility is unable to consistently comply with the MDL and AML and additional treatment is potentially infeasible (e.g., may cause substantial and widespread socioeconomic impact), the facility could apply for a WQS variance to investigate the its best compliance options. In addition, if activated carbon adsorption is added for cyanide removal, an additional benefit of the treatment process is removal of selenium. Therefore, EPA estimated a range of cost for compliance with selenium limits derived from the potential baseline WQS. These estimates include the cost of a P2 program and variance application or a P2 program and treatment, with no incremental compliance cost for treatment if an activated carbon adsorption unit is used for both cyanide and selenium removal.
Data for zinc ranged from 0.03 to 63 ug/L for the daily maximum. Of the concentrations reported since 2016, none exceeded the MDL of 120 ug/L and only 1 of the 9 daily measurements exceeded the AML of 61 ug/L (reported at 63 ug/L). EPA estimated no incremental compliance cost for additional zinc removal for this facility at this time.
Coachella Valley Water District Mid-Valley WRP (CA0104973)
The Coachella Valley Water District Mid-Valley WRP No. 4 (Coachella Mid-Valley WRC; NPDES permit number CA0104473) is located in the Riverside County, California,. The facility serves a population of approximately 63,000 in the City of La Quinta and surrounding areas and discharges treated municipal wastewater to the Coachella Valley Storm Water Channel.
EPA developed this facility analysis based on the 2012 permit and fact sheet issued by the Colorado River Basin Regional Water Quality Control Board together with discharge monitoring reports from between 2016 and 2021.
Effluent and Treatment Process
Coachella Mid-Valley WRC has a treatment capacity of 9.9 MGD. The permit includes effluent limitations for CBOD, TSS, pH, cyanide, selenium, chlorine, and E. coli.
The treatment system includes consists of two treatment systems running in parallel; a lagoon
treatment system (7.0 MGD) and an activated sludge treatment system (2.9 MGD). The headworks system includes two pre-aeration ponds, automatic bar screens, conveyor, a washer-compactor, and a headworks building equipped with an air scrubber. Flow from the headworks is distributed to five treatment modules. Four of the treatment modules are part of the lagoon treatment system and one treatment module is part of the activated sludge treatment system. Each of the four lagoon treatment modules are comprised of four lined aerated lagoons and two lined polishing ponds (for a total of 16 aeration lagoons and 8 polishing ponds). All ponds are lined with a synthetic membrane liner. The activated sludge treatment system consists of two
activated sludge basins, two secondary clarifiers, and sludge handling facilities (including a gravity belt thickener and belt filter press). Combined effluent from the two systems is disinfected and dechlorinated, prior to discharge into the Coachella Valley Storm Water Channel.
Reasonable Potential Analysis
EPA had sufficient data from 2015 to 2020 to conduct reasonable potential analyses for the parameters shown in Exhibit A-30.
Exhibit A-30: Summary of Available Effluent Data for Coachella Mid-Valley WRC (ug/L)
Parameter
Effluent Data[a]
Detection Limit

Samples
50[th] Percentile
Max

Bacteria (E. coli; cfu/100 mL)
                                                                             61
                                                                       < 1.8
                                                                          130 b
                                                                            -
4-4'-DDT
                                                                              1
                                                                              -
                                                                           0.05
                                                                         0.0120
alpha-BHC
                                                                              1

                                                                           0.01
                                                                              -
alpha-Endosulfan
                                                                              1
                                                                              -
                                                                           0.01
                                                                          0.014
Ammonia
                                                                             28
                                                                           1800
                                                                           9400
                                                                             10
Arsenic
                                                                              3
                                                                              -
                                                                            2.5
                                                                            0.4
Chloride
                                                                              5
                                                                              -
                                                                        100,000
                                                                              4
Chlorodibromomethane
                                                                              6
                                                                              -
                                                                            2.6
                                                                          0.001
Chloroform
                                                                              9
                                                                              -
                                                                             42
                                                                           0.01
Chromium (III)
                                                                              3
                                                                              -
                                                                            2.3
                                                                              -
Chromium (VI)
                                                                              2
                                                                              -
                                                                           0.08
                                                                            0.3
Copper
                                                                              5
                                                                              -
                                                                             13
                                                                            0.5
Dichlorobromomethane
                                                                              9
                                                                              -
                                                                             12
                                                                          0.003
Nickel
                                                                              2
                                                                              -
                                                                            1.8
                                                                            0.5
Selenium
                                                                             17
                                                                           1.35
                                                                            2.2
                                                                            0.6
Silver
                                                                              1
                                                                              -
                                                                           0.52
                                                                            0.1
Solids, Dissolved and Salinity
                                                                             61
                                                                        497,000
                                                                        540,000
                                                                              -
Toluene
                                                                              1
                                                                              -
                                                                            1.0
                                                                           0.01
Zinc
                                                                              5
                                                                              -
                                                                           45.7
                                                                           0.05
Notes:
[a] For aquatic life economic analysis criteria, the reasonable potential analysis uses an estimate of the 99[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration. For human health criteria, the reasonable potential analysis uses either 1) the 50[th] percentile concentration from the existing effluent data set if the effluent data set includes 10 or more observations or 2) an estimate of the 50[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration if the effluent data set includes fewer than 10 observations. Thus, this table does not include a 50[th] percentile calculated from the effluent data set when there are less than 10 observations.
[b] While the daily maximum for this facility was measured as 130 cfu/100 mL, the maximum of monthly averages was not quantified (<1.8 cfu/100 mL).
In addition, all data for chlorine and cyanide were reported as below the DLs.
Exhibit A-31 summarizes the RPA for all parameters with sufficient data. The analysis assumes no dilution, as the permit does not authorize mixing zones for this POTW based on the nature of the receiving water and the nature of the effluent.
Exhibit A-31: Summary of Reasonable Potential Analysis for
Coachella Mid-Valley WRC (ug/L)
Parameter
Conc at Edge of Mixing Zone[a]
Applicable Criteria
RP

Acute
Chronic
HH
Acute
Chronic
HH
AL
HH
Bacteria (E. coli; cfu/100 mL)b
                                                                              -
                                                                              -
                                                                              -
                                                                              -
                                                                              -
                                                                              -
                                      N/A
                                      Yes
4-4'-DDT
                                                                              -
                                                                              -
                                                                          0.050
                                                                              -
                                                                              -
                                                                       0.000004
                                      N/A
                                      Yes
alpha-BHC
                                                                              -
                                                                              -
                                                                          0.010
                                                                              -
                                                                              -
                                                                       0.000058
                                      N/A
                                      Yes
alpha-Endosulfan
                                                                              -
                                                                              -
                                                                          0.010
                                                                              -
                                                                              -
                                                                              4
                                      N/A
                                      No
Ammonia
                                                                         29,200
                                                                         29,200
                                                                              -
                                                                         11,000
                                                                          1,400
                                                                              -
                                      Yes
                                      N/A
Arsenic
                                                                           13.2
                                                                           13.2
                                                                              -
                                                                            340
                                                                            150
                                                                              -
                                      No
                                      N/A
Chloride
                                                                        419,000
                                                                        419,000
                                                                              -
                                                                        860,000
                                                                        230,000
                                                                              -
                                      Yes
                                      N/A
Chlorodibromomethane
                                                                              -
                                                                              -
                                                                           1.60
                                                                              -
                                                                              -
                                                                           0.66
                                      No
                                      Yes
Chloroform
                                                                              -
                                                                              -
                                                                           20.1
                                                                              -
                                                                              -
                                                                             60
                                      N/A
                                      No
Chromium (III)
                                                                           12.9
                                                                           12.9
                                                                              -
                                                                            570
                                                                             74
                                                                              -
                                      No
                                      N/A
Chromium (VI)
                                                                           0.59
                                                                           0.59
                                                                              -
                                                                             16
                                                                             11
                                                                              -
                                      No
                                      N/A
Copper
                                                                           61.6
                                                                           61.6
                                                                           8.33
                                                                            4.4
                                                                            2.7
                                                                          1,300
                                      Yes
                                      No
Dichlorobromomethane
                                                                              -
                                                                              -
                                                                           5.24
                                                                              -
                                                                              -
                                                                           0.79
                                      N/A
                                      Yes
Nickel
                                                                           13.3
                                                                           13.3
                                                                           1.70
                                                                            470
                                                                             52
                                                                            180
                                      No
                                      No
Selenium
                                                                              -
                                                                            3.3
                                                                           1.35
                                                                              -
                                                                            1.5
                                                                            130
                                      Yes
                                      No
Silver
                                                                           6.86
                                                                              -
                                                                              -
                                                                            3.2
                                                                              -
                                                                              -
                                      Yes
                                      N/A
Solids, Dissolved and Salinity
                                                                              -
                                                                              -
                                                                        497,000
                                                                              -
                                                                              -
                                                                        250,000
                                      N/A
                                      Yes
Toluene
                                                                              -
                                                                              -
                                                                            1.0
                                                                              -
                                                                              -
                                                                             35
                                      N/A
                                      No
Zinc
                                                                            155
                                                                            155
                                                                           32.8
                                                                            120
                                                                            120
                                                                          2,600
                                      Yes
                                      No
Notes:
[a] No dilution was used for this analysis.
[b] For bacteria, the facility was assumed to have reasonable potential if the maximum effluent concentration (see above exhibit) exceeds 100 cfu/100 mL.
As shown above, 12 parameters have reasonable potential. Exhibit A-32 summarizes the average monthly and maximum daily effluent limitations that were calculated as part of the RPA for Coachella Mid-Valley WRP. The analysis shows a need for reductions of bacteria, chlorodibromomethane, copper, dibenzo(a,h) anthracene, dichlorobromomethane, and ideno(1,2,3-cd) pyrene in the discharge in order to comply with effluent limits derived from the proposed WQS.
Exhibit A-32: Summary of Calculated Limits for Parameters with Reasonable Potential for Coachella Mid-Valley WRC (ug/L)
Parameter
Limiting Criterion
Limits
Max Conc
Exceeds Limit?

AML
MDL

Bacteria
                                      HH
                                                                            100
                                                                            N/A
                                                                          1.8 a
                                      No
4-4'-DDT
                                      HH
                                                                      0.0000040
                                                                      0.0000080
                                                                           0.05
                                      Yes
alpha-BHC
                                      HH
                                                                       0.000058
                                                                        0.00012
                                                                           0.01
                                      No
Ammonia
                                      AL
                                                                          1,400
                                                                          4,800
                                                                          9,400
                                      Yes
Chloride
                                      AL
                                                                        190,000
                                                                        380,000
                                                                        100,000
                                      No
Chlorodibromomethane
                                      HH
                                                                           0.66
                                                                            1.3
                                                                            2.6
                                      Yes
Copper
                                      AL
                                                                            2.2
                                                                            4.4
                                                                             13
                                      Yes
Dichlorobromomethane
                                      HH
                                                                           0.79
                                                                            1.6
                                                                             12
                                      Yes
Selenium
                                      AL
                                                                            1.5
                                                                            2.0
                                                                            2.2
                                      Yes
Silver
                                      AL
                                                                            1.9
                                                                            3.8
                                                                           0.52
                                      No
Solids, Dissolved and Salinity
                                      HH
                                                                        250,000
                                                                        270,000
                                                                        540,000
                                      Yes
Zinc
                                      AL
                                                                             61
                                                                            120
                                                                           45.7
                                      No
Note:
[a] While the daily maximum for this facility was measured as 170 cfu/100 mL, the maximum of monthly average effluent concentration was < 1.8 cfu/100 mL.
Summary
Although the RPA indicates that the discharge from this facility has reasonable potential for bacteria, alpha-BHC, chloride, silver, and zinc, the maximum effluent concentrations do not exceed the AMLs or MDL.
DMR data show that effluent ammonia concentrations average 2,15 mg/L and ranged from 0.30 to 9.4 mg/L during the monitoring period that included 26 samples. The effluent limits derived from the economic analysis criteria are an AML of 1.4 mg/L and MDL of 4.8 mg/L. A facility upgrade may be necessary to meet these limits. EPA estimated the cost of adding a nitrification step to the existing treatment process.
Data for chlorodibromomethane and dichlorobromomethane show that the effluent routinely exceeds the AML and MDL derived from the economic analysis criteria. Treatment of THMs, like dichlorobromomethane and chlorodibromomethane, in wastewater can often be controlled at minimal cost by managing chlorination, such as through reducing chlorine contact time, limiting sunlight exposure to the chlorine contact chamber, and modifying the pH. Reducing the precursors to the formation of THMs, however, can be far costlier in the wastewater treatment process using activated carbon, ion exchange, or membrane filtration. Since there are operational changes that can reduce the formation of THMs, EPA estimated no incremental compliance cost for dichlorobromomethane or chlorodibromomethane for this facility at this time.
Analysis of copper data indicate that the concentration in all but 4 of the 5 available samples exceeds the AML of 2.2 ug/L and 3 of the 5 exceed the MDL of 4.4 ug/L. Selenium data indicate a range of concentrations from 1.0 to 2.2 ug/L. While only 1 of 17 data points exceeds the MDL of 2.0 ug/L, 3 exceed the AML of 1.5 ug/L. EPA estimated the incremental costs of a P2 program for copper and selenium along with additional treatment using chemical precipitation to meet effluent limits based on the economic analysis criteria. If the facility is unable to consistently comply with the MDLs and AMLs for copper and selenium and additional treatment is potentially infeasible (e.g., may cause substantial and widespread socioeconomic impact), the facility could apply for a WQS variance to investigate the its best compliance options. For this analysis, EPA assumed that the facility would implement a P2 program and apply for a variance for copper and selenium and estimated the cost of this alternative compliance mechanism.
The limited effluent data for 4,4'-DDT include 4 values reported as below the DL and 1 value reported as 0.05 ug/L. Additional data would be needed to determine whether it would be necessary to install additional treatment, such as GAC adsorption, to reduce the concentration of 4,4'-DDT in the effluent. In addition, all of the reported dissolved solids concentrations exceed the AML and MDL. EPA estimated the cost of a P2 program for 4,4'-DDT and dissolved solids along with additional treatment using GAC adsorption to comply with WQBELs derived from the economic analysis criteria. If the facility is unable to consistently comply with the MDLs and AMLs for 4,4'-DDT and dissolved solids and additional treatment is potentially infeasible (e.g., may cause substantial and widespread socioeconomic impact), the facility could apply for a WQS variance to investigate the its best compliance options. For this analysis, EPA assumed that the facility would implement a P2 program and apply for a variance for 4,4'-DDT and dissolved solids and estimated the cost of this alternative compliance mechanism.
Exhibit A-33 summarizes the estimated incremental costs for the Coachella Mid-Valley WRC.
Exhibit A-33: Coachella Mid-Valley WRC Estimated Incremental Costs (9.9 MGD)
Parameter
Control Option
Capital Cost
Other One-Time Cost
O&M Cost
Annual Cost (3%)[a]
Annual Cost (7%)[b]
Ammonia
Nitrification
                                  $3,978,548
                                      $0
                                   $131,200
                                   $398,621
                                   $506,747
Copper, Selenium,

Chemical Precipitation
                                  $5,136,287
                                      $0
                                  $1,955,690
                                  $2,300,929
                                  $2,440,519

Medium Facility P2 Program
                                      $0
                                    $66,230
                                      $0
                                    $30,908
                                    $30,908

           Alternative Compliance Mechanism for Copper and Selenium

Medium Facility P2 Program
                                      $0
                                    $66,230
                                      $0
                                    $30,908
                                    $30,908

Variance Feasibility
Analysis
                                      $0
                                    $90,328
                                      $0
                                      $0
                                      $0

Variance Application
                                      $0
                                   $511,360
                                      $0
                                      $0
                                      $0
4,4'-DDT, Dissolved Solids
Adsorption
                                  $18,139,164
                                      $0
                                   $263,900
                                  $1,483,137
                                  $1,976,109

Medium Facility P2 Program
                                      $0
                                    $66,230
                                      $0
                                    $30,908
                                    $30,908

     Alternative Compliance Mechanism for 4,4'-DDT and Dissolved Solids

Medium Facility P2 Program
                                      $0
                                    $66,230
                                      $0
                                    $30,908
                                    $30,908

Variance Feasibility
Analysis
                                      $0
                                    $90,328
                                      $0
                                      $0
                                      $0

Variance Application
                                      $0
                                   $511,360
                                      $0
                                      $0
                                      $0
TOTAL:

Notes:
[a] Capital costs annualized over 20 years at a 3% discount rate. Other one-time costs are not annualized.
[b] Capital costs annualized over 20 years at a 7% discount rate. Other one-time costs are not annualized.
Pagosa Area Water and Sanitation District - Vista WWTP (CO0031755)
The Pagosa Area Water and Sanitation District - Vista WWTP (Pagosa Area WWTP; NPDES permit number CO0031755) is a POTW located in Pagosa Springs, Colorado. The facility treats wastewater from the Pagosa Area Water and Sanitation District 1 in addition to wastewater from the Pagosa Springs Sanitation General Improvement District. The Pagosa Area WWTP discharges into Stevens Draw, Martinez Creek, and Stollsteimer Creek. The authorized discharge point is Outfall 001A.
EPA developed this facility analysis based on the 2019 permit and associated fact sheet issued by the Colorado Department of Public Health and the Environment together with discharge monitoring reports from between 2016 and 2021.
Effluent and Treatment Process
The Pagosa Area WWTP has a facility design flow of 3.9 MGD (3.75 MGD January to March), with effluent limitations for E. coli, total residual chlorine, total inorganic nitrogen, ammonia, BOD, TSS, iron, copper, lead, manganese, mercury and selenium. No information about treatment processes was available.
Reasonable Potential Analysis
EPA had sufficient data to conduct reasonable potential analyses for the parameters shown in Exhibit A-34.
Exhibit A-34: Summary of Available Effluent Data for Pagosa Area WWTP (ug/L)
Parameter
Effluent Data[a]
Detection Limit

Samples
50[th] Percentile
Max

Bacteria (E. coli; cfu/100 mL)
                                                                             63
                                                                          30.0
                                                                         120 b

Ammonia
                                                                             63
                                                                          2,000
                                                                         19,800
                                                                            10
Arsenic
                                                                             20
                                                                          1.45
                                                                           2.1
                                                                           0.4
Cadmium
                                                                             20
                                                                          0.50
                                                                          10.0
                                                                          0.05
Chloride
                                                                             20
                                                                        45,350
                                                                        62,900
                                                                             4
Chromium (III)
                                                                             20
                                                                          10.0
                                                                          12.0
                                                                             -
Chromium (VI)
                                                                             20
                                                                           8.0
                                                                          10.4
                                                                           0.3
Copper
                                                                             21
                                                                           3.2
                                                                          68.7
                                                                           0.5
Cyanide
                                                                             20
                                                                            10
                                                                            10
                                                                             5
Iron
                                                                             20
                                                                          70.5
                                                                           125
                                                                             1
Lead
                                                                             20
                                                                         0.500
                                                                          35.6
                                                                           0.6
Manganese
                                                                             20
                                                                          61.3
                                                                           129
                                                                           0.1
Nickel
                                                                             20
                                                                           3.2
                                                                           5.5
                                                                           0.5
Nonylphenol
                                                                             20
                                                                          3.20
                                                                          15.8
                                                                             -
Selenium
                                                                             20
                                                                           1.0
                                                                           2.6
                                                                           0.6
Silver
                                                                             20
                                                                          0.20
                                                                          0.30
                                                                           0.1
Zinc
                                                                             21
                                                                          22.2
                                                                          72.5
                                                                          0.05
Notes:
[a] For aquatic life economic analysis criteria, the reasonable potential analysis uses an estimate of the 99[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration. For human health criteria, the reasonable potential analysis uses either 1) the 50[th] percentile concentration from the existing effluent data set if the effluent data set includes 10 or more observations or 2) an estimate of the 50[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration if the effluent data set includes fewer than 10 observations. Thus, this table does not include a 50[th] percentile calculated from the effluent data set when there are less than 10 observations.
[b] While the daily maximum for this facility was measured as 120 cfu/100 mL, the maximum of monthly averages was 79 cfu/100 mL.
Exhibit A-35 summarizes the RPA for all parameters with sufficient data. No dilution was used, as the NPDES permit does not authorized mixing zones because effluent constitutes 100% of the flow.
Exhibit A-35: Summary of Reasonable Potential Analysis for Pagosa Area WWTP (ug/L)
Parameter
Conc at Edge of Mixing Zone[a]
Applicable Criteria
RP

Acute
Chronic
HH
Acute
Chronic
HH
AL
HH
Bacteria (E. coli; cfu/100 mL)b
                                                                             -
                                                                             -
                                                                             -
                                                                             -
                                                                             -
                                                                            -
                                      N/A
                                      Yes
Ammonia
                                                                         47,040
                                                                        47,040
                                                                              -
                                                                        11,000
                                                                         1,400
                                                                             -
                                      No
                                      N/A
Arsenic
                                                                          2.91
                                                                          2.91
                                                                              -
                                                                           340
                                                                           150
                                                                            -
                                      Yes
                                      N/A
Cadmium
                                                                          64.2
                                                                           61.8
                                                                              -
                                                                           1.8
                                                                          0.72
                                                                            -
                                      Yes
                                      N/A
Chloride
                                                                         77,420
                                                                         77,420
                                                                              -
                                                                       860,000
                                                                       230,000
                                                                            -
                                      No
                                      N/A
Chromium (III)
                                                                          5.25
                                                                           14.3
                                                                              -
                                                                           570
                                                                            74
                                                                            -
                                      No
                                      N/A
Chromium (VI)
                                                                          11.3
                                                                          11.0
                                                                              -
                                                                            16
                                                                            11
                                                                            -
                                      Yes
                                      N/A
Copper
                                                                           485
                                                                           485
                                                                          3.20
                                                                           4.4
                                                                           2.7
                                                                         1,300
                                      Yes
                                      No
Cyanide
                                                                          10.0
                                                                          10.0
                                                                          10.0
                                                                            22
                                                                           5.2
                                                                           4.0
                                      Yes
                                      Yes
Iron

                                                                           198
                                                                            -

                                                                         1,000
                                                                            -
                                      No
                                      N/A
Lead
                                                                           315
                                                                            315
                                                                            -
                                                                            65
                                                                           2.5
                                                                            -
                                      Yes
                                      N/A
Manganese
                                                                              -
                                                                              -
                                                                          61.3
                                                                              -
                                                                              -
                                                                            50
                                      N/A
                                      Yes
Nickel
                                                                          7.65
                                                                          7.65
                                                                          3.20
                                                                           470
                                                                            52
                                                                           180
                                      No
                                      No
Nonylphenol
                                                                          52.2
                                                                          52.2
                                                                            -
                                                                            28
                                                                           6.6
                                                                             -
                                      Yes
                                      N/A
Selenium

                                                                          4.27
                                                                          1.00

                                                                           1.5
                                                                           130
                                      Yes
                                      No
Silver
                                                                          0.35
                                                                              -
                                                                              -
                                                                           3.2
                                                                              -
                                                                             -
                                      No
                                      N/A
Zinc
                                                                           162
                                                                            163
                                                                          22.2
                                                                           120
                                                                           120
                                                                         2,600
                                      Yes
                                      No
Notes:
[a] No dilution was used for this analysis.
[b] For bacteria, the facility was assumed to have reasonable potential if the maximum effluent concentration (see above exhibit) exceeds 100 cfu/100 mL.
As shown above, 11 parameters have reasonable potential. Exhibit A-36 summarizes average monthly and maximum daily effluent limitations that were calculated as part of the RPA for the Pagosa Area WWTP.
Exhibit A-36: Summary of Calculated Limits for Parameters with Reasonable Potential for Pagosa Area WWTP (ug/L)
Parameter
Limiting Criterion
Limits
Max Conc
Exceeds Limit?

AML
MDL

Bacteria (E. coli; cfu/100 mL)
                                      HH
                                                                            100
                                                                              -
                                                                           79 a
                                      No
Ammonia
                                      AL
                                                                          1,400
                                                                          5,200
                                                                         19,800
                                      Yes
Cadmium
                                      AL
                                                                            0.5
                                                                            1.4
                                                                           10.0
                                      Yes
Chromium (VI)
                                      AL
                                                                             11
                                                                             12
                                                                           10.4
                                      No
Copper
                                      AL
                                                                            1.4
                                                                            4.4
                                                                           68.7
                                      Yes
Cyanide
                                      HH
                                                                            4.0
                                                                            4.0
                                                                           10.0
                                      Yes
Lead
                                      AL
                                                                            1.4
                                                                            4.7
                                                                           35.6
                                      Yes
Manganese
                                      HH
                                                                             50
                                                                             91
                                                                          128.5
                                      Yes
Nonylphenol
                                      AL
                                                                            4.9
                                                                             12
                                                                           15.8
                                      Yes
Selenium
                                      AL
                                                                            1.5
                                                                            2.7
                                                                            2.6
                                      Yes
Zinc
                                      AL
                                                                             61
                                                                            120
                                                                           72.5
                                      Yes
Note:
[a] While the daily maximum for this facility was measured as 120 cfu/100 mL, the maximum of monthly averages was 79 cfu/100 mL.
Summary
Although the RPA indicates reasonable potential for bacteria and chromium VI, actual effluent sampling results for these parameters meet the effluent limits for these parameters derived from the economic analysis criteria, so EPA estimated no incremental compliance costs for meeting these limits.
Reported effluent concentrations of ammonia since 2016 have ranged from below the DL to 19,800 ug/L. Reported concentrations are frequently above the AML and MDL derived from the economic analysis criteria, with values exceeding the MDL more than 36% of the time. A facility upgrade may be necessary. As summarized in Exhibit A-37, EPA estimated the cost of a facility upgrade to add an additional nitrification step to the treatment process.
The RPA indicates reasonable potential for cadmium, but actual reported concentrations comply with the MDL derived from the economic analysis criteria in 18 of the 20 measurements. The exceedances were in April and November 2020. However, reported concentrations exceeded the AML in all cases. Likewise, copper concentrations reported since 2016 ranged from1.0 to 68.7 ug/L and frequently exceed the effluent limitations derived from the economic analysis criteria. Furthermore, manganese was measured from August 2019 through March 2021. The 20 measurements ranged from 12.75 to 128.5 ug/L and the average was 61.8 ug/L. Manganese control (e.g., using potassium permanganate for oxidation) will be necessary to meet the AML of 50 ug/L and the MDL of 91 ug/L.As summarized in Exhibit A-37, EPA estimated the cost of a P2 program and adding chemical precipitation and filtration/oxidation to the treatment system for metals removal. If the facility is unable to consistently comply with the MDLs and AMLs for copper, cadmium, or manganese and additional treatment is potentially infeasible (e.g., may cause substantial and widespread socioeconomic impact), the facility could apply for a WQS variance to investigate the its best compliance options. Therefore, EPA also included estimates for the cost of a P2 program and variance application for copper, cadmium, and manganese.
Cyanide was measured from August 2019 through March 2021. The 20 measurements were all 10 ug/L, which exceeds the AML and MDL of 4.0 ug/L. Removal for cyanide can be achieved with GAC adsorption or pH adjustments and chlorine. Since the facility currently uses UV for disinfection, EPA estimated the cost for addition of a chlorine contact chamber and dechlorination. These costs are summarized in Exhibit A-37.
Lead was measured from August 2019 through March 2021. The 20 measurements ranged from 0.50 to 35.6 ug/L and the average was 2.26 ug/L. All the measurements were 0.50 ug/L except for a single measurement of 35.6 ug/L. Based on this information, at this time, additional treatment for lead does not appear to be needed. However, chemical precipitation to remove other metals or GAC to control cyanide would have the additional benefit of reductions in lead.
Nonylphenol was measured from August 2019 through March 2021. The 20 measurements ranged from 0.00 to 15.80 ug/L and the average was 1.23 ug/L. Nonylphenol control may be necessary to consistently meet the average monthly limit of 4.9 ug/L and the maximum daily limit of 12 ug/L. Optimizing the existing treatment processes (including biosolids removal) can be used to remove nonylphenol. Therefore, EPA estimated no incremental compliance costs for meeting nonylphenol limits. In addition, if GAC is installed to control cyanide, an additional benefit will be reductions in nonylphenol.
Selenium was measured from August 2019 through March 2021. The 20 measurements ranged from 1.0 to 2.6 ug/L and the average was 1.23 ug/L. Selenium control may not be necessary to meet the AML of 1.5 ug/L and the MDL of 2.7 ug/L. No reported values were greater than the MDL and most results were reported below the AML. Therefore, EPA estimated no incremental compliance costs for meeting selenium limits.
Zinc was measured from January 2016 through March 2021. The 21 measurements ranged from 6.7 to 72.5 ug/L and the average was 26.2 ug/L. Zinc control may not be necessary to meet the AML of 60 ug/L and the MDL of 120 ug/L. There was a single reported concentration (72.5 ug/L) that was greater than the AML. Therefore, EPA estimated no incremental compliance costs for meeting zinc limits.
Exhibit A-37: Pagosa Area WWTP Estimated Incremental Costs (3.9 MGD)
Parameter
Control Option
Capital Cost
Other One-Time Cost
O&M Cost
Annual Cost (3%)[a]
Annual Cost (7%)[b]
Ammonia
Nitrification
                                  $1,218,320
                                      $0
                                    $79,610
                                   $161,500
                                   $194,611
Cyanide
Chlorination (with Dechlorination)
                                  $2,504,713
                                      $0
                                   $215,100
                                   $383,456
                                   $451,527
Cadmium, Copper, Manganese
Chemical Precipitation
                                  $2,598,967
                                      $0
                                   $754,320
                                   $929,011
                                   $999,644

Small Facility P2 Program
                                      $0
                                    $49,671
                                      $0
                                    $29,802
                                    $29,802

      Alternative Compliance Mechanism for Cadmium, Copper, and Manganese

Small Facility P2 Program
                                      $0
                                    $49,671
                                      $0
                                    $29,802
                                    $29,802

Variance Feasibility
Analysis
                                      $0
                                   $135,492
                                      $0
                                      $0
                                      $0

Variance Application
                                      $0
                                   $383,520
                                      $0
                                      $0
                                      $0
TOTAL:
                            $3,723,033 - $6,322,000
                                  $49,671 -
                                   $568,683
                             $294,710 - $1,049,030
                                  $574,758 -
                                  $1,503,769
                                  $675,940 -
                                  $1,675,584
Notes:
[a] Capital costs annualized over 20 years at a 3% discount rate. Other one-time costs are not annualized.
[b] Capital costs annualized over 20 years at a 7% discount rate. Other one-time costs are not annualized.
CF Industries Nitrogen (IA0004014)
The CF Industries Nitrogen, LLC  -  Port Neal Nitrogen Complex (CF Industries Nitrogen; NPDES permit number IA0021784)  contains an ammonia plant, two nitric acid plants, two liquid urea plants, and a urea ammonium nitrate plant, all located in Woodbury County, Iowa, in Township 87N. CF Industries Nitrogen, LLC operates the facility. The industrial complex discharges treated industrial wastewater into the Missouri River, which is impaired for arsenic and habitat alteration. Outfall 001 combines waste streams from the plant.
EPA developed this facility analysis based on the 2015 permit as amended in 2018, which was issued by the Iowa Department of Natural Resources, together with discharge monitoring reports from between 2016 and 2021.
Effluent and Treatment Process
CF Industries Nitrogen has a design flow of 2.23 MGD. The permit stipulates effluent limitations for ammonia, nitrate nitrogen, organic nitrogen, and total residual chlorine. Treatment processes include septic tanks and leach fields that do not discharge to surface waters.
Reasonable Potential Analysis
EPA had sufficient data to conduct reasonable potential analyses for the parameters shown in Exhibit A-38.
Exhibit A-38: Summary of Available Effluent Data for CF Industries Nitrogen (ug/L)
Parameter
Effluent Data[a]
Detection Limit

Samples
50[th] Percentile
Max

Ammonia
                                                                             64
                                                                         35,020
                                                                        131,670
                                                                             10
Chlorine
                                                                             64
                                                                             80
                                                                            350
                                                                             10
Note:
[a] For aquatic life economic analysis criteria, the reasonable potential analysis uses an estimate of the 99[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration. For human health criteria, the reasonable potential analysis uses either 1) the 50[th] percentile concentration from the existing effluent data set if the effluent data set includes 10 or more observations or 2) an estimate of the 50[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration if the effluent data set includes fewer than 10 observations. Thus, this table does not include a 50[th] percentile calculated from the effluent data set when there are less than 10 observations.
Exhibit A-39 summarizes the RPA for all parameters with sufficient data. Critical low flow data used in this analysis were provided in the permit and were used to calculate dilution factors for use in the analysis. Where ambient data were not available, half the DL was used unless that value was above the applicable criteria.
Exhibit A-39: Summary of Reasonable Potential Analysis for CF Industries Nitrogen (ug/L)
Parameter
Conc at Edge of Mixing Zone[a]
Applicable Criteria
RP

Acute
Chronic
HH
Acute
Chronic
HH
AL
HH
Ammonia
                                                                         3,520
                                                                         3,520
                                                                              -
                                                                        11,000
                                                                         1,400
                                                                              -
                                      Yes
                                      N/A
Chlorine
                                                                          10.9
                                                                          10.9
                                                                              -
                                                                            19
                                                                            11
                                                                              -
                                      No
                                      N/A
Note:
[a] Calculated based on dilution factors for aquatic life acute (59), aquatic life chronic (59), human health non-carcinogens (82), and human health carcinogens (175) following the methods used in the fact sheet and based on flow conditions.
As shown above, the facility has reasonable potential for ammonia. Exhibit A-40 summarizes the average monthly and maximum daily effluent limitations that were calculated as part of the RPA for CF Industries.
Exhibit A-40: Summary of Calculated Limits for Parameters with Reasonable Potential for CF Industries Nitrogen (ug/L)
Parameter
Limiting Criterion
Limits
Max Conc
Exceeds Limit?

AML
MDL

Ammonia
                                      AL
                                    77,000
                                    200,000
                                  130,000[a]
                                      Yes

Summary
Since January 2016, the maximum daily effluent concentration of ammonia has not exceeded the proposed MDL and the average monthly concentration has not exceeded the proposed AML. The facility should be capable of meeting the proposed limits with its existing treatment processes, with optimization as needed. Consequently, EPA estimated no incremental compliance costs for meeting these limits.
MidAmerican Energy - Neal North Energy Center (IA0004103)
The MidAmerican Energy Company  -  Neal North Center (Neal North; NPDES permit number IA0004103) generates electricity for sale and distribution using coal with a thermal cycle that employs the steam water system as the thermodynamic medium. Neal North is located in Sergeant Bluff, Iowa, and discharges via three outfalls to the Missouri River: 003, 009, and 016. This industrial facility is located approximately 5 miles away from the Winnebago Tribe, also known as the Ho-Chunk Tribe.
EPA developed this facility analysis based on the 2017 permit issued by the Iowa Department of Natural Resources together with discharge monitoring reports from between 2016 and 2021.
Effluent and Treatment Process
Neal North has a facility design flow of 6.03 MGD. The permit includes effluent limitations for TSS, total iron, total copper, pH, selenium, aluminum, and chromium (VI) for Outfall 003. All three outfalls discharge into the Missouri River along a stretch of shoreline that is less than 2,000 feet long.
Reasonable Potential Analysis
The available monitoring data for the facility do not include observations for any parameter of interest between 2016 and 2020, including some months where the facility reported no discharge.
Summary
EPA assumes that there will be no incremental costs for this facility.
MidAmerican Energy - Neal South Energy Center (IA0061859)
The MidAmerican Energy Company  -  Neal South Center (hereinafter "Neal South;" NPDES permit number IA0061859 generates electricity for sale and distribution, using coal with a thermal cycle employing the steam water system as the thermodynamic medium. Neal South is in Salix, Iowa, and discharges to the Missouri River. The Missouri River is a Class A1 water, reflecting primary contact recreational uses. This industrial facility is located approximately 3 miles away from the Winnebago Tribe, also known as the Ho-Chunk Tribe.
EPA developed this facility analysis based on the 2017 permit (as amended in 2018) and associated rationale issued by the Iowa Department of Natural Resources, together with discharge monitoring reports from between 2016 and 2021.
Effluent and Treatment Process
Water is withdrawn from the Missouri River and used for once-through condenser cooling before returning to the River. This surface water is also used in some of the low-volume waste generating activities taking place at the facility. Well water is used in low-volume processes (reverse osmosis) and fire protection and for air preheater washing (non-chemical metal cleaning). Treated wastewater and river water are used in the bearing flush and seal water system. All waste streams from this facility are discharged to the Missouri River through several outfalls:
Outfall 001 discharges once-through condenser cooling water; it has an average monthly flow rate of 468 MGD and a maximum daily flow rate of 484 MGD. It has existing limits for temperature only, and the fact sheet notes that no other parameters are evaluated for this outfall since it is used for non-contact cooling water only and all concentrations are attributable to intake water from the Missouri River.
Outfall 004 discharges WTP filter backwash and rinse water, boiler blowdown, reverse osmosis reject, neutralized demineralizer waste, floor drains, oil water separator waste, coal combustion residual monofill leachate, and monofill stormwater runoff. It has an average monthly flow rate of 0.0833 MGD and a daily maximum flow rate of 0.161 MGD. It has limits for TSS, oil & grease, and acute toxicity.
Outfall 005 discharges underboiler quench water bath blowdown and has an estimated flow of 0.144 MGD.
Outfall 006 combines discharges from Outfalls 004, 005, and 008, stormwater runoff, and intermittent discharge from various water holding tanks and the fire protection system.
Outfall 007 discharges from the main condenser and has an identical location to Outfall 001; it has an average monthly flow of 302.4 MGD and a maximum daily flow of 320 MGD.
Outfall 008 infrequently discharges non-chemical metal cleaning wastes from the air heater wash pond at most once every two years.
Reasonable Potential Analysis
EPA had sufficient data to conduct reasonable potential analyses for chlorine for the three outfalls shown in Exhibit A-41. The facility has limitations and monitoring requirements for additional outfalls and parameters, but no data were available for RPAs; all data for Outfall 005 indicate that it is not operational.
Exhibit A-41: Summary of Available Chlorine Effluent Data for Neal South (ug/L)
Outfall
Effluent Data[a]
Detection Limit

Samples
50[th] Percentile
Max

001
                                                                             10
                                                                             45
                                                                             90
                                                                             10
006
                                                                             20
                                                                             20
                                                                             60
                                                                             10
007
                                                                             15
                                                                             30
                                                                            130
                                                                             10
Note:
[a] For aquatic life economic analysis criteria, the reasonable potential analysis uses an estimate of the 99[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration. For human health criteria, the reasonable potential analysis uses either 1) the 50[th] percentile concentration from the existing effluent data set if the effluent data set includes 10 or more observations or 2) an estimate of the 50[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration if the effluent data set includes fewer than 10 observations. Thus, this table does not include a 50[th] percentile calculated from the effluent data set when there are less than 10 observations.
Exhibit A-42 summarizes the chlorine RPA. Critical low flow data were provided in the permit and were used to calculate dilution factors for use in the analysis. Ambient data were not available for the receiving water, so EPA assumed background concentrations were equal to half the DL unless that value was above the applicable criteria, which is conservative assumption for chlorine.
Exhibit A-42: Summary of Chlorine Reasonable Potential Analysis for Neal South by Outfall (ug/L)
Outfall
Conc at Edge of Mixing Zone[a]
Applicable Criteria
RP

Acute
Chronic
HH
Acute
Chronic
HH
AL
HH
001[a]
                                                                            180
                                                                           61.5
                                                                              -
                                                                             19
                                                                             11
                                                                              -
                                      Yes
                                      N/A
006[b]
                                                                          0.110
                                                                         0.0100
                                                                              -
                                                                             19
                                                                             11
                                                                              -
                                      No
                                      N/A
007[c]
                                                                            257
                                                                           70.1
                                                                              -
                                                                             19
                                                                             11
                                                                              -
                                      Yes
                                      N/A
Notes:
[a] Calculated based on dilution factors for aquatic life acute (1.27), aquatic life chronic (3.73), human health non-carcinogens (4.82), and human health carcinogens (9.40) following the methods used in the fact sheet based on flow conditions.
[b] Calculated based on dilution factors for aquatic life acute (1533), aquatic life chronic (15319), human health non-carcinogens (21447), and human health carcinogens (47190) following the methods used in the fact sheet based on flow conditions.
[c] Calculated based on dilution factors for aquatic life acute (1.42), aquatic life chronic (5.22), human health non-carcinogens (6.91), and human health carcinogens (14.00) following the methods used in the fact sheet based on flow conditions.
As shown above, two outfalls have reasonable potential for chlorine. Exhibit A-43 summarizes the average monthly and maximum daily effluent limitations that were calculated as part of the RPA.
Exhibit A-43: Summary of Calculated Chlorine Limits for Neal South Energy Center by Outfall (ug/L)
Outfall
Limiting Criterion
Limits
Max Conc
Exceeds Limit?

AML
MDL

001
                                      AL
                                                                             13
                                                                             24
                                                                           90.0
                                      Yes
007
                                      AL
                                                                             13
                                                                             27
                                                                            130
                                      Yes

Summary
Although available effluent data indicate reasonable potential for chlorine at Outfall 001 and 007, there are no reported measurements of chlorine since the August 2017 discharge monitoring report. Furthermore, the current permit fact sheet notes that the facility does not chlorinate once-through cooling water and the current permit prohibits the discharge of chlorine from Outfalls 001 and 007. In addition, Outfall 006, where there was no reasonable potential for chlorine, is a stormwater discharge, and the facility is required to perform stormwater management and monitoring activities.
Based on the available data and the requirements of the current permit, EPA estimated no incremental compliance costs for this facility to comply with chlorine limits derived from the economic analysis criteria.
City of Pocatello WPCF (ID0021784)
The City of Pocatello WPCF (Pocatello WPCF; NPDES permit number ID0021784)  is a POTW located in, and owned and operated by, the City of Pocatello, Idaho. The facility serves the cities of Pocatello and Chubbuck, with a combined resident population of approximately 68,000. The facility is located within one mile upstream from Fort Hall tribal land. The secondary treatment plant discharges treated municipal wastewater to the Portneuf River. The collection system has no combined sewers.
EPA developed this facility analysis based on the 2012 permit and supporting fact sheet issued by EPA. EPA subsequently transferred authority for issuing the permit to the state of Idaho in 2018; however, an updated state-issued permit is not available online. For this analysis, EPA assumed that the 2012 permit and its associated fact sheet are representative of this facility. EPA also used available discharge monitoring reports from between 2016 and 2021 to conduct the RPA.
Effluent and Treatment Process
The Pocatello WPCF has a facility design flow of 12 MGD. The permit contains effluent limitations for BOD, TSS, E.coli, pH, total residual chlorine, ammonia, and total phosphorous.
Pocatello's WPCF process includes screen and grit removal, primary clarification, activated sludge and nitrogen reduction, final clarification, disinfection using chlorine gas and dechlorination using sulfur dioxide gas. The treated wastewater is then discharged to the Portneuf River. Solids are further processed using anaerobic digestion and a sludge lagoon for thickening the solids before they are distributed for beneficial use as a fertilizer on local agriculture fields owned by the City of Pocatello. In addition, the digestion process produces biogas which fuels cogeneration engines that produce electricity used within the Pocatello WPCF.
Reasonable Potential Analysis
EPA had sufficient data to conduct reasonable potential analyses for the parameters shown in Exhibit A-44.
Exhibit A-44: Summary of Available Effluent Data for Pocatello WPCF (ug/L)
Parameter
Effluent Data[a]
Detection Limit

Samples
50[th] Percentile
Max

Bacteria (E. coli; cfu/100 mL)
                                                                             64
                                                                            3.0
                                                                       2,419[b]
                                                                            -
Ammonia
                                                                             64
                                                                          1,440
                                                                         26,200
                                                                             10
Arsenic
                                                                             11
                                                                            1.5
                                                                            2.3
                                                                            0.4
Cadmium
                                                                             11
                                                                           0.05
                                                                           0.10
                                                                           0.05
Copper
                                                                             11
                                                                            6.0
                                                                             10
                                                                            0.5
Cyanide
                                                                             11
                                                                            2.5
                                                                            2.5
                                                                              5
Lead
                                                                             11
                                                                           0.25
                                                                           0.60
                                                                            0.6
Nickel
                                                                             11
                                                                            2.2
                                                                            3.0
                                                                            0.5
Selenium
                                                                             11
                                                                           0.50
                                                                            2.0
                                                                            0.6
Zinc
                                                                             11
                                                                             48
                                                                             68
                                                                           0.05
Notes:
[a] For aquatic life economic analysis criteria, the reasonable potential analysis uses an estimate of the 99[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration. For human health criteria, the reasonable potential analysis uses either 1) the 50[th] percentile concentration from the existing effluent data set if the effluent data set includes 10 or more observations or 2) an estimate of the 50[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration if the effluent data set includes fewer than 10 observations. Thus, this table does not include a 50[th] percentile calculated from the effluent data set when there are less than 10 observations.
[b] While the instantaneous maximum for this facility was measured as 2,419 cfu/100 mL, the maximum of monthly averages was 4 cfu/100 mL.
Exhibit A-45 summarizes the RPA for all parameters with sufficient data. Critical low flow data used in this analysis were provided in the permit and were used to calculate dilution factors for use in the analysis. Ambient data were not available for the receiving water, so EPA assumed background concentrations were equal to half the DL unless that value was above the applicable criteria.
Exhibit A-45: Summary of Reasonable Potential Analysis for Pocatello WPCF (ug/L)
Parameter
Conc at Edge of Mixing Zone[a]
Applicable Criteria
RP

Acute
Chronic
HH
Acute
Chronic
HH
AL
HH
Bacteria (E. coli; cfu/100 mL)b
                                                                              -
                                                                              -
                                                                              -
                                                                              -
                                                                              -
                                                                              -
                                      N/A
                                      Yes
Ammonia
                                                                         33,200
                                                                         29,200
                                                                              -
                                                                         11,000
                                                                          1,400
                                                                              -
                                      Yes
                                      N/A
Arsenic
                                                                            3.9
                                                                         4.0[c]
                                                                              -
                                                                            340
                                                                            150
                                                                              -
                                      No
                                      N/A
Cadmium
                                                                           0.13
                                                                           0.11
                                                                              -
                                                                            1.8
                                                                           0.72
                                                                              -
                                      No
                                      N/A
Copper
                                                                            9.8
                                                                            8.7
                                                                            1.5
                                                                            4.4
                                                                            2.7
                                                                           1300
                                      Yes
                                      No
Cyanide
                                                                            4.0
                                                                            3.5
                                                                           0.93
                                                                            22.
                                                                            5.2
                                                                              4
                                      No
                                      No
Lead
                                                                           0.87
                                                                           0.76
                                                                              -
                                                                             65
                                                                            2.5
                                                                              -
                                      No
                                      N/A
Nickel
                                                                            2.5
                                                                            2.2
                                                                           0.98
                                                                            470
                                                                             52
                                                                            180
                                      No
                                      No
Selenium
                                                                            3.4
                                                                            3.0
                                                                           0.19
                                                                              -
                                                                            1.5
                                                                            130
                                      Yes
                                      No
Zinc
                                                                             67
                                                                             61
                                                                             18
                                                                            120
                                                                            120
                                                                           2600
                                      No
                                      No
Notes:
[a] Calculated based on dilution factors for aquatic life acute (1.9), aquatic life chronic (2.2), human health non-carcinogens (2.7), and human health carcinogens (4.5) following the methods used in the fact sheet based on flow conditions.
[b] For bacteria, the facility was assumed to have reasonable potential if the maximum effluent concentration (see above exhibit) exceeds 100 cfu/100 mL.
[c] The concentration at the edge of the chronic mixing zone is greater than the concentration at the edge of the acute mixing zone because the ambient concentration is greater than the effluent concentration.
As shown above, bacteria, ammonia, copper, and selenium have reasonable potential. Exhibit A-46 summarizes the average monthly and maximum daily effluent limitations that were calculated as part of the RPA for the Pocatello WPCF.
Exhibit A-46: Summary of Calculated Limits for Parameters with Reasonable Potential for Pocatello WPCF (ug/L)
Parameter
Limiting Criterion
Limits
Max Conc
Exceeds Limit?

AML
MDL

Bacteria
                                      HH
                                                                            100

                                                                              4
                                      No
Ammonia
                                      AL
                                                                          2,600
                                                                         12,000
                                                                         26,200
                                      Yes
Copper
                                      AL
                                                                            5.0
                                                                            7.9
                                                                             10
                                      Yes
Selenium
                                      AL
                                                                            3.0
                                                                            8.7
                                                                            2.0
                                      No

Summary
Although the RPA indicates reasonable potential for bacteria and selenium actual effluent sampling results for these parameters meet the effluent limits derived from the proposed WQSi for these parameters, so EPA estimated no incremental compliance costs for meeting these limits.
The facility's current average monthly ammonia limits are 6.3 mg/L during Nov-June and 5.0 mg/L during July-Oct. The maximum daily limits are 16.4 mg/L during Nov-June and 13.0 mg/L during July-Oct. The limits derived from the economic analysis criteria are an AML of 2.6 mg/L MDL of 12 mg/L. DMR data suggest that the facility meets the current MDL about 84% of the time and the exceedances do not occur at predictable intervals. The facility currently meets the proposed MDL of 2.6 mg/L about 69% of the time. A treatment system upgrade may be necessary. As summarized in Exhibit A-47, EPA estimated the cost of a facility upgrade to add an additional nitrification step to the treatment process.
Copper data from April 2016 through April 2021 include 11 measurements ranging from 3.0 to 10 ug/L and averaging 6.2 ug/L. Most of the samples are less than the proposed MDL but greater than the proposed AML. To meet the AML, additional treatment may be necessary. As summarized in Exhibit A-47, EPA estimated the range of incremental cost to this facility of adding chemical precipitation along with implementing a P2 program to reduce effluent concentrations of copper. EPA assumed that the facility could adapt its existing primary clarifier for this process.
Exhibit A-47: Pocatello WPCF Estimated Incremental Costs (12 MGD)
Parameter
Control Option
Capital Cost
Other One-Time Cost
O&M Cost
Annual Cost (3%)[a]
Annual Cost (7%)[b]
Ammonia
Nitrification
                                  $5,460,000
                                      $0
                                   $145,700
                                   $512,698
                                   $661,085
Copper
Chemical Precipitation
                                   $826,000
                                      $0
                                   $134,270
                                   $189,790
                                   $212,239

Medium Facility P2 Program
                                      $0
                                    $33,115
                                      $0
                                    $15,454
                                    $15,454
TOTAL:
                                  $6,286,000
                                    $33,115
                                   $279,970
                                   $717,942
                                   $888,778
Notes:
[a] Capital costs annualized over 20 years at a 3% discount rate. Other one-time costs are not annualized.
[b] Capital costs annualized over 20 years at a 7% discount rate. Other one-time costs are not annualized.
City of Devils Lake WWTF (ND0020681)
The City of Devils Lake WWTF (Devils Lake WWTF; NPDES permit number ND0020681) is a POTW located in the City of Devils Lake, North Dakota. The facility services the City of Devils Lake, which had a population of 7,141 in 2020. Facility discharges are directed into Creel Bay at Devils Lake.
EPA could not locate permit documentation for this facility and based the analysis on discharge monitoring reports from between 2016 and 2021.
Effluent and Treatment Process
The Devils Lake WWTF is authorized to discharge domestic wastewater. The facility combines a Lemna system (which relies on the growth of duckweed to treat BOD, TSS, and inorganic contaminants) and facultative lagoon systems. The treatment system has a design flow of 5.50 MGD and consists of three waste stabilization ponds, the Lemna system, and an artificial wetland. Wastewater can be transferred from Cell 3 to the North Marsh (the artificial wetland) through Outfall 003. From the North Marsh, wastewater passes through the Lemna system. The North Marsh is located adjacent to the Devils Lake Municipal Airport's runway. Due to concerns about the number of birds present, the Devils Lake WWTF plans to use the North Marsh on an as needed basis for treatment or to address hydraulic issues and not as a routine part of treatment.
Reasonable Potential Analysis
EPA had sufficient data to conduct reasonable potential analyses for ammonia and nitrates as shown in Exhibit A-48.
Exhibit A-48: Summary of Available Effluent Data for City of Devils Lake WWTF (ug/L)
Parameter
Effluent Data[a]
Detection Limit

Samples
50[th] Percentile
Max

Ammonia
                                                                             18
                                                                          2090
                                                                         5,780
                                                                           100
Nitrates
                                                                              8
                                                                              -
                                                                           240
                                                                              2
Note:
[a] For aquatic life economic analysis criteria, the reasonable potential analysis uses an estimate of the 99[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration. For human health criteria, the reasonable potential analysis uses either 1) the 50[th] percentile concentration from the existing effluent data set if the effluent data set includes 10 or more observations or 2) an estimate of the 50[th] percentile effluent concentration statistically projected from the maximum observed effluent concentration if the effluent data set includes fewer than 10 observations. Thus, this table does not include a 50[th] percentile calculated from the effluent data set when there are less than 10 observations.
Exhibit A-49 summarizes the RPA for all parameters with sufficient data. Information about mixing zones authorized in the permit was not available; as such, EPA assumed a dilution factor of 10 for all parameters. Ambient data were not available for the receiving water, so EPA assumed background concentrations were equal to half the DL unless that value was above the applicable criteria.
Exhibit A-49: Summary of Reasonable Potential Analysis for City of Devils Lake WWTF (ug/L)
Parameter
Conc at Edge of Mixing Zone[a]
Applicable Criteria
RP

Acute
Chronic
HH
Acute
Chronic
HH
AL
HH
Ammonia
                                                                         1,796
                                                                         1,796

                                                                        11,000