Calculation of Local Limits

Transcription

1 Calculation of Local Limits for Metals Discharged to the Decorah Wastewater Treatment Plant Decorah, Iowa July South 17th Street, Suite 107 Ames, Iowa 50010

2 Calculation of Local Limits for Metals Discharged to the Decorah Wastewater Treatment Plant Decorah, Iowa July 2016

3 Local Limits Local limits are locally established restrictions on certain discharges to the sanitary sewer system. Local limits may be developed by publicly owned wastewater treatment works (POTWs) to ensure compliance with the requirements of the discharge permit (NPDES) and related government prohibitions and guidelines. The federal and state requirements do not take into account the site-specific factors at a POTW and local limits may be required to ensure that all discharges are in compliance. A POTW may need to impose local limits on an industrial user that are more stringent or cover more pollutants than an applicable categorical standard in order to ensure compliance with all aspects of their NPDES permit. Decorah is a growing community with several significant industrial users that discharge wastewater containing metals. Significant Industrial Users that have treatment agreements for metals include Stanley (formerly Acument Global Technologies North America Camar LLC), Gemini, Inc., and Deco Products. The IDNR adopted more stringent stream standards in 2006, which have resulted in significantly reduced amounts of metals that may be discharged in the plant s effluent. Preparation of local limits calculations is helpful for the City to get an overall understanding of the metals that are allowed to be discharged to the river, the amount that has been "allocated" to the existing industries, and the amount that is available to allocate to future or expanding existing industries. In March 2010, the IDNR issued a wasteload allocation (WLA), which was utilized to develop the NPDES permit for Decorah (based on 2006 revised Water Quality Standards, 2002 Permit Derivation Procedure, the 2000 ammonia criteria and the 2007 chemical criteria). The WLA provided the following Proposed Effluent Permit Limits for metals as shown in Table 1 below. Table 1 IDNR Wasteload Allocation Metals Conc (mg/l) Mass (lbs/d) Avg Max Avg Max Arsenic As Cadmium Cd Chromium VI Cr Copper Cu Cyanide CN Lead Pb Mercury Hg Molybdenum Mo NA NA NA NA Nickel Ni Selenium Se Silver Ag Zinc Zn FOX Engineering Associates

4 When issuing a city s NPDES permit, IDNR evaluates the treatment plant effluent data and existing treatment agreements and compares them to the proposed metal limits (such as listed in the table above). If there is reasonable doubt as to the plant s ability to comply with these limits, the permit writer will likely include the specific metal with the limits on the NPDES permit. Development of local limits involves working backwards from the effluent limits (as well as any restrictions on biosolids or amounts which could interfere with the treatment processes) to determine how much of each parameter may be allocated for industrial use. The essential steps in local limits calculations for metals are as follows: 1. Allowable Headworks Loading For each parameter or pollutant, the maximum allowable headworks loading (MAHL) is determined. This is the maximum amount of the pollutant that would not cause a POTW to violate any criterion of a permit or treatment process; i.e. not cause any exceedance of permit limits or interference with the treatment process. The MAHL calculations determine the maximum amount that can enter the plant that will not violate the limits for effluent quality, biosolids disposal, treatment inhibition, or water quality. A critical factor in this calculation is the percentage of each metal that is removed in the treatment process. The MAHL for each parameter is calculated using the percent of each metal that is removed or redistributed through the treatment process. For metals, the amount entering the plant is not actually destroyed, but is diverted to either the biosolids or the effluent flow streams. The majority of the metals end up in the biosolids portion of the treatment process, and this has historically been the area of concern for violation of land application limits on metals. However, recent very stringent stream standards have resulted in the effluent limits often being the more critical area of concern. The actual percent removal (or redistribution) of metals throughout the plant can be calculated using actual data or assumed values found in the EPA Local Limits Development Guidance, published in July 2004 (Appendix R Priority Pollutant Removal Efficiencies). The required detection limits must be very low in order to be less than the proposed permit limits, the Decorah staff have collected one week of influent and effluent data in order to provide a more accurate calculation of actual removal through the plant. When the City applied for the renewal of its NPDES permit, they submitted an extensive list of analyses from three days of effluent sampling, as was required for the application. At that time, the detection limits used for the metals testing were higher than most of the currently proposed effluent limits. IDNR s approach when the effluent value is less than the detection limit, is as follows: Evaluate the effluent data and assume that the actual effluent values are 50% of the detection limit If the resultant value is more than 50% of the proposed NPDES limit, the parameter is assumed to a probable source of violation and would be included in the permit. In order to have the ability to utilize actual data for the amount of each metal entering and leaving the treatment plant in the effluent, the city collected five days of influent and effluent data using laboratory methods for analysis with lower detection limits. The testing also produces 2 FOX Engineering Associates

5 data for calculation of percent removal of the metals as they pass through the plant. That data (collected in March and April 2016) is presented in Appendix A. The maximum allowable headworks loading (MAHL) is the amount of a particular pollutant which may be received at the POTW s headworks or first stage of treatment that will not cause excessive pass-through, interference with the treatment process, or violation of any known regulatory issues. The following Table 2 illustrates the values utilized for the plant removals, the resultant MAHL, and the limiting criteria for each of the metals of concern. It should be noted that the calculations to develop local limits are based on the average flows and concentrations for comparison to the proposed permit limits - not the amounts that the treatment facility is designed or rated to treat. Table 2 Maximum Allowable Headworks Limits (MAHL) Metals 1 POTW Removal (%) MAHL 2 Lbs/day Limiting Criteria Arsenic As 21% 0.21 Digestion Inhibition Cadmium Cd 80% 0.08 Sludge Disposal Chromium VI Cr 61% 0.64 Stream Standards Copper Cu 84% 1.31 Digestion Inhibition Cyanide CN 52% 0.21 Digestion Inhibition Lead Pb 91% 0.69 Sludge Disposal Mercury Hg 60% 0.02 Stream Standards Molybdenum Mo 55% 0.10 Sludge Disposal Nickel Ni 57% 0.48 Digestion Inhibition Selenium Se 29% 0.26 Sludge Disposal Silver Ag 31% 0.07 Stream Standards Zinc Zn 73% 7.63 Sludge Disposal 1 Calculated from data 2 Based on flows of 1.3 mgd 2. Maximum Allowable Industrial Loading (MAIL) The MAHL must be split or divided between the background amount from domestic/commercial sources (which are assumed to be uncontrollable and include infiltration and inflow) and the amount that may be allowed from industrial sources (assumed to be controllable) known as maximum allowable industrial loading (MAIL). The background or domestic concentrations for each parameter may be collected from municipal sanitary sewers, or the default summary of values found in the EPA manual noted above may be used (Appendix V Domestic Pollutant Loadings). The City collected domestic/background data on two days in March/April for use in this portion of the calculations. 3 FOX Engineering Associates

6 The MAHL and MAIL are calculated in terms of mass or lbs/day. In order to convert between mass and concentration (mg/l or parts per million), it is critical to have the flow data (million gallons per day). For purposes of this Local Limits Calculation, the domestic background levels for the metals utilize the annual average total plant influent flow (1.3 mgd) minus the actual average daily flow (0.018 mgd) from the industrial users known to have or be permitted to discharge metals. The following Table 3 illustrates the default data values for typical domestic wastewater from EPA and the domestic data collected from a domestic/commercial sewer in Decorah in March and April The collected domestic data has been utilized for the calculations and the resultant domestic/uncontrolled mass and the percentage of the MAHL that is attributed to domestic (uncontrolled) background for each metal is shown below. Table 3 Domestic/Uncontrolled Influent Data Metals Default EPA Domestic Concentration (Avg) Mar/Apr 2016 Data - Used for Domestic Level Domestic/Commercial (Uncontrolled) Mass mg/l mg/l lb/d % of MAHL Arsenic As % Cadmium Cd % Chromium VI Cr % Copper 1 Cu % Cyanide CN % Lead Pb % Mercury Hg % Molybdenum 1 Mo % Nickel Ni % Selenium Se % Silver Ag % Zinc 1 Zn % 1 Use default value rather than collected data The data in Table 3 indicate that the sewer sampled for domestic/commercial had some industrial wastewater as well. Conversations with Mike O Hara confirm that there is a manufacturer of screws which discharges to that sewer and probably contributed the excess concentrations of copper, molybdenum, and zinc. City staff may elect to provide a new sample of domestic/commercial wastewater, for the purposes of this report, the default values will be utilized for those three parameters. The domestic (uncontrolled) mass of each metal is subtracted from the MAHL to obtain the MAIL. Also subtracted from the MAHL is the amount that a city wishes to allot for future growth or reserve. For this report, 10% was used; some municipalities utilize up to 25%. Table 4 illustrates those calculations and reflects the MAIL to be allocated for metals. 4 FOX Engineering Associates

7 Table 4 Maximum Allowable Industrial Load (MAIL) all in lbs/day Metals MAHL Domestic & Commercial Growth or Reserve MAIL Arsenic As Cadmium Cd Chromium VI Cr Copper Cu Cyanide CN Lead Pb Mercury Hg Molybdenum Mo Nickel Ni Selenium Se Silver Ag Zinc Zn Industrial User Permit Limits The last stage of establishing local limits is to determine how the mass of each metal is to be distributed among the affected industries, so the difficult task of determining who gets what? in a manner considered by all to be fair is facilitated. There are three industries in Decorah that presently are permitted to discharge metals above the background domestic levels; they are Stanley (formerly names: Acument Global Technologies North America Camar LLC), Gemini, Inc., and Deco Products. Table 5 contains a summary of the existing permitted discharges from the three industries. 5 FOX Engineering Associates

8 Table 5 Permitted Discharges All in Average lbs/day Metals Stanley Permits Permits Permits (Acument Deco Gemini Total MAIL as % of as % of as % of Global) MAIL MAHL WLA Arsenic NA NA NA NA 0.17 NA NA NA Cadmium % 90% 215% Chromium % 73% 72% Copper % 43% 54% Cyanide % 84% 47% Lead % 17% 21% Mercury NA NA NA NA 0.02 NA NA NA Molybdenum NA NA NA NA 0.08 NA NA NA Nickel % 135% 10% Selenium NA NA NA NA 0.22 NA NA NA Silver % 91% 50% Zinc NA NA NA NA 5.24 NA NA NA The existing discharge data illustrate that the metals in the effluent are well below the levels that might cause a violation of the NPDES limits, sludge application limits, or stream standards. However, it is very significant to note that if the industries discharged the mass of metals that each is permitted, the City would be exceeding 100% of the allowed industrial mass of cadmium, cyanide and nickel, and more than 90% of the industrial mass of chromium and copper - possibly causing a violation. The City collected wastewater plant influent and effluent samples from in late March and early April 2016, using low enough detection limits that only a few values were less than detection limit. The purpose of this was twofold, to have adequate information to determine the actual loading into the plant and to calculate the percent removal through the treatment process. The resultant data is included in Appendix 1 and provides an average and a percent removal where there is adequate data. Using the average flow of 1.3 mgd, an average daily mass (lbs/day) has been calculated for the influent loading to the plant and is compared to the MAHL in the following Table 6. Table 6 -Influent Mass Comparison 6 FOX Engineering Associates

9 Metals Avg Conc (2016 data, mg/l) Avg mgd MAHL (lb/d) Influent as % of MAHL Arsenic % Cadmium % Chromium % Copper % Cyanide % Lead % Mercury % Molybdenum % Nickel % Selenium % Silver % Zinc % Conclusions The comparison between the total metals entering the treatment plant and the maximum allowable headworks loading (MAHL), shown in Table 6 above, illustrate that all of the metals are well within the MAHL and indicate that there is no anticipation of violation of any of the regulations or guidelines relating to the metals. However, the mass of metals that are permitted or potentially able to enter the plant are of concern. The comparison between the total permitted metals and the calculated maximum allowable industrial load (MAIL), shown above in Table 5, illustrate that the potential metals of concern are cadmium, chromium, copper, cyanide, and nickel. If the metal industries were to discharge the amounts of those metals that they are permitted, there could be violations of sludge regulations (ceiling concentrations) for land application, the stream standards, or the sludge digestion could be inhibited. While this is somewhat alarming, it remains a theoretical problem until such time that the industries begin discharging the permitted amounts. Many industries ask for more capacity than they actually need as a form of insurance against mishaps or for anticipated possible growth. We recommend that you meet with industries to explain the situation and negotiate revised treatment agreements that reflect their current needs and your existing capacity. Following is a brief description of each of the metals of concern and outline of the issues discussed in this report. The graphs document the calculated values for the amounts of each pollutant entering the plant as well as the actual amount and the permitted amount from the industries permitted for that pollutant. Bars two, three, and four add up to the first bar; the fifth bar is the influent loading based on the 2016 data; and the sixth bar is the permitted industrial mass. Ideally, the 2016 influent should be less than or equal to the sum of the domestic/commercial and the permitted amounts, reflecting that you are capturing the total influent to the plant in terms of metals. 7 FOX Engineering Associates

10 Arsenic (As) Allowed to be discharged to stream: 9.35 lbs/day Controlling factor for POTW: Digester Inhibition Max Allowable Headworks Limit: 0.21 lbs/day Max Allowable Industrial Limit: 0.17 lb/day POTW Influent (2016 data): 0.01 lbs/day Percent Removal in POTW: 21% (to solids) Cadmium (Cd) Allowed to be discharged to stream: lbs/day Controlling factor for POTW: Sludge Land Application Regulations Max Allowable Headworks Limit: 0.08 lbs/day Max Allowable Industrial Limit: 0.07 lb/day POTW Influent (2016 data): lbs/day Percent Removal in POTW: 80% (to solids) Currently Permitted to Industrial Customers: 0.07 lb/day 8 FOX Engineering Associates

11 Chromium (Cr) Allowed to be discharged to stream: 0.65 lbs/day Controlling factor for POTW: Stream Standards Max Allowable Headworks Limit: 0.64 lbs/day Max Allowable Industrial Limit: 0.52 lb/day POTW Influent (2016 data): 0.03 lbs/day Percent Removal in POTW: 61% (to solids) Currently Permitted to Industrial Customers: 0.47 lb/day Copper (Cu) Allowed lowed to be discharged to stream: 1.05 lbs/day Controlling factor for POTW: Digester Inhibition Max Allowable Headworks Limit: 1.31 lbs/day Max Allowable Industrial Limit: 0.59 lb/day POTW Influent (2016 data): 1.02 lbs/day Percent Removal in POTW: 84% (to solids) Currently Permitted to Industrial Customers: 0.57 lb/day 9 FOX Engineering Associates

12 Cyanide (CN) Allowed to be discharged to stream: 1.05 lbs/day Controlling factor for POTW: Digester Inhibition Max Allowable Headworks Limit: 1.31 lbs/day Max Allowable Industrial Limit: 0.59 lb/day POTW Influent (2016 data): 1.02 lbs/day Percent Removal in POTW: 84% (to solids) Currently Permitted to Industrial Customers: 0.57 lb/day Lead (Pb) Allowed to be discharged to stream: 0.56 lb/day Controlling factor for POTW: Sludge Disposal Max Allowable Headworks Limit: 0.69 lb/day Max Allowable Industrial Limit: 0.61 lb/day POTW Influent (2016 data): 1.02 lbs/day Percent Removal in POTW: 91% (to solids) Currently Permitted to Industrial Customers: 0.12 lb/day 10 FOX Engineering Associates

13 Mercury (Hg) Allowed to be discharged to stream: 0.01 lb/day Controlling factor for POTW: Stream Standards Max Allowable Headworks Limit: lb/day Max Allowable Industrial Limit: lb/day POTW Influent (2016 data): lbs/day Percent Removal in POTW: 60% (to solids) Currently Permitted to Industrial Customers: 0 lb/day Molybdenum (Mo) Allowed to be discharged to stream: NA Controlling factor for POTW: Sludge Disposal Max Allowable Headworks Limit: 0.10 lbs/day Max Allowable Industrial Limit: 0.08 lb/day POTW Influent (2016 data): 0.05 lbs/day Percent Removal in POTW: 55% (to solids) Currently Permitted to Industrial Customers: 0 lb/day 11 FOX Engineering Associates

14 Nickel (Ni) Allowed to be discharged to stream: 1.05 lbs/day Controlling factor for POTW: Digester Inhibition Max Allowable Headworks Limit: 0.48 lbs/day Max Allowable Industrial Limit: 0.32 lb/day POTW Influent (2016 data): 0.05 lbs/day Percent Removal in POTW: 57% (to solids) Currently Permitted to Industrial Customers: 0.65 lb/day Selenium (Se) Allowed to be discharged to stream: lb/day Controlling factor for POTW: Sludge Disposal Max Allowable Headworks Limit: 0.26 lb/day Max Allowable Industrial Limit: 0.22 lb/day POTW Influent (2016 data): 0.02 lb/day Percent Removal in POTW: 29% (to solids) Currently Permitted to Industrial Customers: 0 lb/day 12 FOX Engineering Associates

15 Silver (Ag) Allowed to be discharged to stream: 0.13 lbs/day Controlling factor for POTW: Stream Standards Max Allowable Headworks Limit: lbs/day Max Allowable Industrial Limit: lb/day POTW Influent (2016 data): lbs/day Percent Removal in POTW: 31% (to solids) Currently Permitted to Industrial Customers: lb/day Silver (Ag) 0.06 Lbs per Day MAHL MAIL 2016 Influent Permitted Zinc (Zn) Allowed to be discharged to stream: lbs/day Controlling factor for POTW: Land Application Regulations Max Allowable Headworks Limit: 7.63 lbs/day Max Allowable Industrial Limit: 5.24 lb/day POTW Influent (2016 data): 1.54 lbs/day Percent Removal in POTW: 73% (to solids) Currently Permitted to Industrial Customers: 0 lb/day 13 FOX Engineering Associates

16 Recommendations and Summary The purpose of the study was to develop local limits for metals that may be discharged into the City s sewer system from industrial customers without violating any of the regulations regarding sludge disposal or stream standards or recommendations for optimal treatment plant operations. The three industries in Decorah which are regulated via a treatment agreement for metals are Stanley, Deco, and Gemini. Based on the available data and EPA approved default values, data was input to the model developed by Paul Marshall at EPA - Region 7 for use by municipalities in this region to calculate local limits. The Local Limits model/calculations estimated the maximum allowable headworks loading (MAHL) and the maximum allowable industrial loading (MAIL) that would protect the treatment facilities from violation of the stream standards or sludge land application regulations, as well as prevent inhibition within the plant or inadvertent pass through of any metals into the stream. The model/spreadsheet will be provided to the City staff and copies of the pages are attached in Appendix 2. The model outputs indicate that Decorah has additional capacity based on the available data of what is actually entering and leaving the plant (both effluent and land applied sludge). The influent data from March and April 2016 samples indicate that a range of 3-78% of the MAHL for metals is being utilized. However, the permitted amounts of cadmium, nickel, and silver exceed 100% of the MAIL; permitted amounts of chromium and copper exceed 90% of the MAIL (see Table 5). This would indicate that the amount of most metals permitted is in excess of what is currently utilized by the industries and should be reduced to amounts that reflect what they actually need plus a small percentage for a buffer to avoid violations of the permits. For mercury and molybdenum, the data indicate that there are unpermitted amounts of these two metals that should be identified and permitted as industrial users. If Decorah were to choose to adopt local limits into the city code for their industrial customers, the MAIL amounts would be the local limits in total pounds/day from all industries. If the MAIL mass were translated to uniform concentration limits, using the total industrial flow of mgd, the resultant local limits in mg/l are shown in Table 7 below. Please note that the determination of how to distribute the local limits in either mass or concentration is a philosophical and/or political decision that must be a local decision based on the size, needs, equity, and impact to each city. For example, if justified, a city could allocate any percentage of any metal to one industry, leaving a smaller percentage to others. 14 FOX Engineering Associates

17 Table 7 - Local Limits Metals MAIL (lb/d) MAIL (mg/l) Arsenic Cadmium Chromium Copper Cyanide Lead Mercury Molybdenum Nickel Selenium Silver Zinc It is recommended that the City consider revising the treatment agreements to better reflect their actual discharge needs and provide a more realistic portrayal of the capacity for metals treatment in the City's wastewater treatment plant. This could become a more pressing need should another industry request to discharge metals into the City's sewer system in the future. 15 FOX Engineering Associates

18 Phone: / Fax: Web: Appendix 1 Data Collected by City Staff Utilized for Calculations

19 Decorah - Calculation of % Removal Through Treatment Plant Silver (Ag) Nickel Influent Effluent % Removal Influent Effluent % Removal 3/28/2016 Silver Ag < 50% 3/28/2016 Nickel Ni* % 3/29/2016 Silver Ag < 6% 3/29/2016 Nickel Ni* % 3/30/2016 Silver Ag < 53% 3/30/2016 Nickel Ni* % 3/31/2016 Silver Ag < < 0% 3/31/2016 Nickel Ni* % 4/4/2016 Silver Ag < < 0% 4/4/2016 Nickel Ni* < 60% AVG % AVG % Arsenic Lead Influent Effluent % Removal Influent Effluent % Removal 3/28/2016 Arsenic As < < 0% 3/28/2016 Lead Pb* < 94% 3/29/2016 Arsenic As % 3/29/2016 Lead Pb* % 3/30/2016 Arsenic As % 3/30/2016 Lead Pb* < 91% 3/31/2016 Arsenic As < 10% 3/31/2016 Lead Pb* % 4/4/2016 Arsenic As < 9% 4/4/2016 Lead Pb* < 91% AVG % AVG % Cadmium Zinc Influent Effluent % Removal Influent Effluent % Removal 3/28/2016 Cadmium Cd* % 3/28/2016 Zinc Zn* % 3/29/2016 Cadmium Cd* % 3/29/2016 Zinc Zn* % 3/30/2016 Cadmium Cd* E-05 < 93% 3/30/2016 Zinc Zn* % 3/31/2016 Cadmium Cd* E-05 < 72% 3/31/2016 Zinc Zn* % 4/4/2016 Cadmium Cd* E-05 < 75% 4/4/2016 Zinc Zn* % AVG E-05 80% AVG % Cyanide Molybdenum Influent Effluent % Removal Influent Effluent % Removal 3/28/2016 Cyanide CN < 92% 3/28/2016 Molybdenum Mo % 3/29/2016 Cyanide CN < < 0% 3/29/2016 Molybdenum Mo % 3/30/2016 Cyanide CN < % 3/30/2016 Molybdenum Mo % 3/31/2016 Cyanide CN < 19% 3/31/2016 Molybdenum Mo % 4/4/2016 Cyanide CN < < 0% 4/4/2016 AVG % AVG % Chromium Selenium Influent Effluent % Removal Influent Effluent % Removal 3/28/2016 Chromium Cr % 3/28/2016 Selenium Se % 3/29/2016 Chromium Cr % 3/29/2016 Selenium Se % 3/30/2016 Chromium Cr % 3/30/2016 Selenium Se % 3/31/2016 Chromium Cr % 3/31/2016 Selenium Se % 4/4/2016 Chromium Cr % 4/4/2016 Selenium Se % AVG % AVG % Copper Influent Effluent % Removal 3/28/2016 Copper Cu* % 3/29/2016 Copper Cu* % 3/30/2016 Copper Cu* % 3/31/2016 Copper Cu* % 4/4/2016 Copper Cu* % AVG %

20 3/28/2016 3/31/2016 Influent Effluent % Removal Influent Effluent % Removal Silver Ag < 50% Silver Ag < < 0% Arsenic As < < 0% Arsenic As < 10% Cadmium Cd* % Cadmium Cd* < 72% Cyanide CN < 92% Cyanide CN < 19% Chromium Cr % Chromium Cr % Copper Cu* % Copper Cu* % Nickel Ni* % Nickel Ni* % Lead Pb* < 94% Lead Pb* % Zinc Zn* % Zinc Zn* % Molybdenum Mo % Molybdenum Mo % Selenium Se % Selenium Se % 3/29/2016 4/4/2016 Influent Effluent % Removal Influent Effluent % Removal Silver Ag < 6% Silver Ag < < 0% Arsenic As % Arsenic As < 9% Cadmium Cd* % Cadmium Cd* < 75% Cyanide CN < < 0% Cyanide CN < < 0% Chromium Cr % Chromium Cr % Copper Cu* % Copper Cu* % Nickel Ni* % Nickel Ni* < 60% Lead Pb* % Lead Pb* < 91% Zinc Zn* % Zinc Zn* % Molybdenum Mo % Molybdenum Mo % Selenium Se % Selenium Se % 3/30/2016 Influent Effluent % Removal Silver Ag < 53% Arsenic As % Cadmium Cd* < 93% Cyanide CN < % Chromium Cr % Copper Cu* % Nickel Ni* % Lead Pb* < 91% Zinc Zn* % Molybdenum Mo % Selenium Se % Decorah Data collected for Local Limits Calculations Silver Arsenic Cadmium Cyanide Chromium Copper Nickel Lead Zinc Molybdenum Selenium Sewer System 3/28/2016 3/29/2016 3/29/2016 3/30/2016 4/4/2016 Average Default # Avg/Def ault < < % % % < < < % % % % % % % %

21 Appendix 2 Data and Summary Sheets from Local Limits Spreadsheet Model (Paul Marshall, EPA)

22 CITY: Decorah, Iowa 07/12/16 LOCAL LIMITS CALCULATOR Plant Non SIU Flow, MGD: SLDG To Disposal,MGD: acres per year for land app Data: TOTAL Flow, MGD: 1.3 SLDG Disposal %Solids: Q10, MGD: 24.4 SITE Use, Years: 100 Flow To Digsr: MGD: SITE Size, Acres: 300 Mar/Apr 2016 Data WLA 3/2/2010 NPDES Removal Efficiencies Domestic Safety Avg. Infl. AS Digestion Default Limit Primary Plant Level WQS Factor Cncntrn Inhibition Inhibition Data Entered Metal Industries Avg mgd Ag NA 31% NA 10% As NA 21% NA 10% Rockwell Collins 0 Cd* NA 80% NA 10% Decco CN NA 52% NA 10% Gemini Cr NA 61% NA 10% Stanley Cu* NA 84% NA 10% Total Hg NA 60% NA 10% NA Ni* NA 57% NA 10% Pb* NA 91% NA 10% Zn* NA 73% NA 10% Mo NA 55% NA 10% NA NA Se NA 29% % NA NA *HARDNESS DEPENDENT Domestic sampling included two industries DW Design Domestic Domestic Sources Estimator Daily avg Peak Sources Expansion Avg. Infl. Pop: 8089 persons lbs/day lbs/day lbs/day Factor Cncntrn lbs/cap/day lbs/day BOD 1700 NA % 150 BOD ,375 TSS 2000 NA % 180 TSS 0.2 1,618 TKN 340 NA % 30 TKN moly from screw coating NOTE: all values mg/l unless noted CONVERSIONS CFS TO MGD 1 CFS = mgd SLUDGE, DT/Y to MGD dt/y avg %sld mgd % = 0.01

23 SUMMARY OF MASS LOADINGS Maximum Allowable Maximum Domestic/commcl Industrial Load Allowable Headworks Current Sources (MAIL) Headwrks Load ACTUAL Loading % of % of lbs. (MAHL) Avg.Load as % of lbs. limit lbs. MAHL Reserve lbs lbs MAHL Ag % % % As % % % Cd % % % CN % % % Cr % % % Cu % % % Hg % % % Ni % % % Pb % % % Zn % % % Mo % % % Se % % % TOXIC POLLUTANTS SUMMARY UNIFORM CONCENTRATION LIMIT If APPLIED LIMITING CRITERIA mg/l Ag Ag NPDES #: As As Digstn Inhib: Cd Cd SLDG Dispsl: CN CN Digstn Inhib: Cr Cr NPDES #: Cu Cu Digstn Inhib: Hg Hg NPDES #: Ni Ni Digstn Inhib: Pb Pb SLDG Dispsl: Zn Zn SLDG Dispsl: Mo Mo SLDG Dispsl: Se Se SLDG Dispsl: