Wastewater Treatment Facility Plan Amendment 2 Staples,Minnesota April2018 - Submitted by

 
Wastewater Treatment Facility Plan Amendment 2 Staples,Minnesota April2018 - Submitted by
Wastewater Treatment Facility Plan
  Amendment 2
  Staples, Minnesota         April 2018

Submitted by:
Bolton & Menk, Inc.
7533 Sunwood Drive NW #206
Ramsey, MN 55303
P: 763-433-2851
F: 763-427-0833
Wastewater Treatment Facility Plan Amendment 2 Staples,Minnesota April2018 - Submitted by
Certification

                                Wastewater Treatment Facility Plan
                                        Amendment 2

                                                        for

                                      City of Staples, Minnesota

                                                W13.104619

                                                 April 2018

                                                I hereby certify that this plan, specification or report was
                                                prepared by me or under my direct supervision, and that I
                                                am a duly Licensed Professional Engineer under the laws of
                                                the State of Minnesota.

                                                By:
                                                         Paul Saffert, P.E.
                                                         License No. 43485

                                                Date:         April 25, 2018

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Wastewater Treatment Facility Plan Amendment 2 W13.104619
Wastewater Treatment Facility Plan Amendment 2 Staples,Minnesota April2018 - Submitted by
Table of Contents
        I.      INTRODUCTION ...................................................................................................................... 1
                     PURPOSE....................................................................................................................... 1
                     BACKGROUND .............................................................................................................. 1
        II.     DESIGN CONDITIONS.............................................................................................................. 2
                     PLANNING PERIOD ....................................................................................................... 2
                     CUSTOMER/USER PROJECTIONS .................................................................................. 2
                     WASTEWATER FLOWS .................................................................................................. 3
                     WASTEWATER LOADINGS ............................................................................................ 7
                     MERCURY...................................................................................................................... 9
                     BIOSOLIDS................................................................................................................... 10
                     CURRENT EFFLUENT LIMITS ....................................................................................... 11
                     FUTURE EXPECTED EFFLUENT LIMITS ........................................................................ 11
        III.    EVALUATION OF EXISTING FACILITIES .................................................................................. 13
                     TREATMENT FACILITY ................................................................................................. 13
                     FACILITY CONDITION .................................................................................................. 14
        IV.     WASTEWATER TREATMENT FACILITY IMPROVEMENTS ...................................................... 31
                     GENERAL ..................................................................................................................... 31
                     WASTEWATER TREATMENT FACILITY IMPROVEMENTS ............................................ 31
                     FACILITY CLASSIFICATION ........................................................................................... 36
        V.      RECOMMENDATION ............................................................................................................ 37
                     RECOMMENDATION................................................................................................... 37
                     PROJECT FUNDING ..................................................................................................... 37
        VI.     CONSTRUCTION COST ESTIMATE ......................................................................................... 39
                     GENERAL ..................................................................................................................... 39
                     CAPITAL COSTS ........................................................................................................... 39
                     OPERATIONAL COSTS ................................................................................................. 40
                     TOTAL PROJECT COST ................................................................................................. 40
                     USER RATES ................................................................................................................ 41
        VII.    IMPLEMENTATION ............................................................................................................... 42
                     IMPLEMENTATION SCHEDULE ................................................................................... 42

Figures
        Figure 2.1: Historical and Projected Populations ............................................................................ 3
        Figure 2.2: Historical Flow Data ...................................................................................................... 5
        Figure 2.3: Historical CBOD5 and TSS Loading................................................................................. 8
        Figure 3.1: Existing Static Screen .................................................................................................. 15
        Figure 3.2: Static Screen Supports ................................................................................................ 16
        Figure 3.3: Eutek Teacup Grit Removal System ............................................................................. 17
        Figure 3.4: Trickling Filter Arm ...................................................................................................... 18
        Figure 3.5: Trickling Filter Mechanism .......................................................................................... 19

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Wastewater Treatment Facility Plan Amendment 2 W13.104619
Wastewater Treatment Facility Plan Amendment 2 Staples,Minnesota April2018 - Submitted by
Figure 3.6: Bypass Pipe Leak ......................................................................................................... 20
        Figure 3.7: Aeration Basin Splitter Box ......................................................................................... 21
        Figure 3.8: Aeration Basin Air Header Hoist ................................................................................. 22
        Figure 3.9: Aeration Basin and Return Sludge Piping ................................................................... 22
        Figure 3.10: Older Clarifier ............................................................................................................ 23
        Figure 3.11: Influent to Older Clarifier .......................................................................................... 24
        Figure 3.12: Newer Clarifier .......................................................................................................... 24
        Figure 3.13: Chlorine Contact Basin .............................................................................................. 25
        Figure 3.14: Lime Feed System ..................................................................................................... 26
        Figure 3.15: Aerobic Digesters ...................................................................................................... 27
        Figure 3.16: Chlorine Enclosure .................................................................................................... 28
        Figure 3.17: Blowers...................................................................................................................... 29

Tables
        Table 2.1     Population Projections .................................................................................................... 2
        Table 2.2     Average Daily Flows - City of Staples............................................................................... 4
        Table 2.3     Determination of Design Flows - City of Staples ............................................................. 6
        Table 2.4     Historical Influent Loadings - City of Staples ................................................................... 7
        Table 2.5     Design Wastewater Flows and Loadings - City of Staples ............................................... 9
        Table 2.6     WWTP Mercury – City of Staples ................................................................................. 10
        Table 2.7     Biosolids Land-Applied – City of Staples ....................................................................... 10
        Table 2.8     Effluent Limits - City of Staples...................................................................................... 11
        Table 2.9     Future Expected Effluent Limits - City of Staples .......................................................... 11
        Table 3.1     Staples WWTF Unit Process Summary .......................................................................... 13
        Table 4.1     Alternative 1: Moderate Improvements to Optimize Current Processes ..................... 32
        Table 4.2     Alternative 2: Rehabilitation of Existing Facility with the Addition of Flow
                      Equalization ................................................................................................................... 33
        Table 4.3     Alternative 3: Rehabilitation of Facility with Addition of Extended Aeration Process . 34
        Table 4.4     Alternative 4: New Extended Aeration Activated Sludge Treatment Facility ............... 36
        Table 6.1     Capital Cost Estimates for Recommended Alternative 4 .............................................. 39
        Table 6.2     Operations & Maintenance Cost Changes – City of Staples.......................................... 40
        Table 6.3     Total Annual Project Costs– City of Staples .................................................................. 40
        Table 6.4     Estimated User Rates City of Staples ............................................................................ 41
        Table 7.1     Project Implementation Schedule - City of Staples ....................................................... 42

Appendix
        Appendix A: Preliminary Cost Estimates
        Appendix B: City Council Presentation Materials

Prepared by: Bolton & Menk, Inc.                                                                                                   Table of Contents
Wastewater Treatment Facility Plan Amendment 2 W13.104619
Wastewater Treatment Facility Plan Amendment 2 Staples,Minnesota April2018 - Submitted by
I.   INTRODUCTION
             PURPOSE
             This report provides the City of Staples, Minnesota with recommendations for wastewater
             facility improvements, including a prioritized list of items for repair or replacement.
             Recommendations are based on input from the city staff, a visual inspection of the
             infrastructure, and an evaluation of facility requirements in accordance with the current
             recommended practice.
             Section 2 provides a review of the current design conditions. An evaluation of the existing
             facility is provided in Section 3. Alternatives for wastewater treatment facility improvements
             are discussed in Section 4, with costs presented in Section 5 and the proposed project
             implementation in Section 6.
             BACKGROUND
             The Staples Wastewater Treatment Facility was originally constructed in 1965 and expanded
             in 1991. The aeration basins, two of the final clarifiers, the chlorine contact tank, and the
             aerobic digesters were originally constructed in 1965. A new pretreatment and control
             building, trickling filter and one final clarifier were added in 1991. In 1997, the city replaced
             the influent main lift station. Since 1991, the city has maintained the facility, replacing parts
             and rehabilitating pumps and equipment as necessary, but no significant rehabilitation or
             construction has been done on the facility itself. Overall, the existing system can be effective
             to treat the facility’s current flows and loadings, but the facility requires significant
             rehabilitation and upgrades.
             Additionally, the city staff has noted that when there are high flows (typically in excess of 0.5
             million gallons per day), the aeration basins and the final clarifier splitter box experience
             some overflow and vortex issues that are of concern. The city is interested in ways to remedy
             these issues, as well as recommendations for general rehabilitation or improvements
             necessary to allow the facility to operate appropriately over the next few permit cycles.
             Finally, the facility has limited biosolids digestion and storage capacity. MPCA regulations
             require sludge be stabilized before land application. Because of the limited capacity, the City
             of Staples has been required to use lime to stabilize the sludge prior to land application,
             which is year-round. This system is inefficient and potentially dangerous, as lime can be a
             very dangerous chemical if improperly stored or handled.

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                               Page 1
Wastewater Treatment Facility Plan Amendment 2 Staples,Minnesota April2018 - Submitted by
II. DESIGN CONDITIONS
             PLANNING PERIOD
             Wastewater treatment facilities are typically designed based on a 20-year planning period, as
             it is generally not feasible to make numerous changes in the capacity of a wastewater
             treatment facility. In addition, a 20-year planning period is required for the project to be
             eligible for funding assistance with the Public Facilities Authority (PFA).
             A design year of 2035 is used for this evaluation. Projected wastewater flows and loadings
             are determined using a combination of population trends and expected commercial and
             industrial growth. There are currently no significant industrial users in the City of Staples,
             though there is a nearby hospital that sends wastewater to the facility. As hospital waste is
             typically similar to domestic waste, all projections are based on typical domestic strength
             wastewater.
             CUSTOMER/USER PROJECTIONS
                   1.     Domestic and Commercial Projections
                          A number of methods are used to predict population trends, including a review of
                          historical city and county population trends and various mathematical
                          projections. A combination of methods is involved in projecting the future
                          population.
                          Table 2.1 summarizes the historical and projected populations for the city of
                          Staples and Wadena and Todd Counties as reported by the Minnesota State
                          Demographic Center. The City of Staples straddles the boundary line between the
                          two counties. As shown in Table 2.1 and Figure 2.1, the projected population
                          followed a decreasing trend from 2006 through 2010, but is projected to begin
                          increasing through 2035. The design population for the year 2035 for the City of
                          Staples is 3,189 people.

                                             Table 2.1 Population Projections

                             Year      City of Staples      Todd County      Wadena County

                             2006         3,149           24,469           13,615
                             2010         2,981           25,200           14,110
                             2015         3,005           25,720           14,470
                             2020         3,050           26,230           14,830
                             2025         3,095           26,620           15,210
                             2030         3,142           26,630           15,300
                             2035         3,189           26,660           15,440
                            Source: Minnesota Office of Geographic and Demographic
                            Analysis/State Demographic Center

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Wastewater Treatment Facility Plan Amendment 2 Staples,Minnesota April2018 - Submitted by
Figure 2.1 - Historical and Projected Populations
                                                       City of Staples, Todd County, and Wadena County
                         3,500                                                                                                         30,000

                                                                                                                                                Todd and Wadena Counties Population
                         3,000                                                                                                         25,000
City of Staples Population

                         2,500                                                                                                         20,000

                         2,000                                                                                                         15,000

                         1,500                                                                                                         10,000

                         1,000                                                                                                         5,000
                              2000           2005         2010         2015         2020         2025        2030       2035       2040
                                                                                    Year
                                                             City of Staples       Todd County          Wadena County

                                                           Figure 2.1: Historical and Projected Populations

                                          WASTEWATER FLOWS
                                          The City of Staples National Pollutant Discharge Elimination System (NPDES) Permit allows
                                          for an influent average wet weather (AWW) flow of 0.68 million gallons per day (MGD) and
                                          a peak flow of 1.3 MGD. A historical summary of the influent flows of the Staples
                                          Wastewater Treatment facility for the past ten years is presented in Table 2.2 and Figure 2.2.

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Wastewater Treatment Facility Plan Amendment 2 Staples,Minnesota April2018 - Submitted by
Table 2.2 Average Daily Flows - City of Staples

                                                                                                                                         Monthly
                        2003         2004         2005       2006       2007       2008        2009       2010       2011       2012
       Month                                                                                                                             Average
                        (gpd)        (gpd)        (gpd)      (gpd)      (gpd)      (gpd)       (gpd)      (gpd)      (gpd)      (gpd)
                                                                                                                                          (gpd)
  January              319,871      307,097      304,323    334,419    301,323    256,387     256,194    275,871   289,677     276,516   292,168
  February             308,179      325,759      294,250    312,107    301,500    245,966     259,321    311,250   290,536     266,000   291,487
  March                306,226      341,710      303,226    321,645    303,258    258,000     312,387    379,419   325,645     269,516   312,103
  April                366,767      352,133      392,867    396,367    454,867    335,300     404,467    358,867   427,867     294,167   378,367
  May                  441,097      362,258      394,194    406,903    417,935    372,613     339,968    353,581   493,452     369,774   395,177
  June                 500,233      367,067      512,933    339,233    404,867    393,233     318,433    363,200   484,233               401,853
  July                 612,968      407,935      427,258    297,968    319,452    329,323     351,677    412,548   406,452               402,723
  August               414,548      369,742      379,710    286,161    292,968    284,613     326,645    463,161   410,387               377,418
  September            343,433      396,767      376,467    299,167    294,300    273,333     292,033    377,867   310,433               343,985
  October              330,129      410,323      420,903    298,355    333,323    332,000     363,645    344,397   296,194               338,504
  November             320,633      360,367      388,033    283,033    301,767    286,067     417,833    354,867   296,500               341,020
  December             316,323      326,935                 288,419    269,452    259,129     352,419    316,903   264,806               317,852
  Yearly
  Average              381,701      360,674      381,288    321,982    332,917    302,164     332,919    359,328   358,015     295,195

  Note: A blank space indicates a month where no flow data was available.

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Wastewater Treatment Facility Plan Amendment 2 Staples,Minnesota April2018 - Submitted by
Figure 2.2 - Historical Flow Data
                                            Staples Wastewater Treatment Facility

        Flow (MGD)

                                                           Month-Year

                            Average Daily Flow (MGD)                          Permitted AWW Flow (MGD)
                            Maximum Daily Flow (MGD)                          Permitted Peak Flow

                                              Figure 2.2: Historical Flow Data

                     The average daily flow peaks in the spring months each year, but the spring peaks are less
                     than the permitted average wet weather flow. The maximum daily flow also peaks during the
                     spring months and, in 2010 and 2011, exceeded the permitted AWW flow. These large
                     fluctuations in influent flow to the treatment facility are attributed to infiltration and inflow
                     (I/I). I/I flows are heavily influenced by seasonal and precipitation events and are present in
                     essentially all gravity collection systems. The City of Staples is committing to an infiltration
                     and inflow reduction program over the next few years in an effort to reduce these large
                     fluctuations in flow.
                     The Minnesota Pollution Control Agency (MPCA) has guidelines for determining flow
                     projections. Future projections developed for different climactic conditions as described. The
                     Average Dry Weather (ADW) flow is based on the flow with no inflow due to precipitation
                     and/or snow melt and no infiltration due to high groundwater. The ADW flow typically
                     occurs in winter months or in very dry summer months. This flow corresponds with water
                     pumped from the drinking water source.
                     The Average Wet Weather (AWW) flow, or peak month flow, is the daily average flow for
                     the wettest 30 consecutive days for mechanical treatment systems such as Staples. AWW
                     flow is based on flow with infiltration due to high groundwater and typical inflow due to
                     precipitation and/or snowmelt. This flow usually occurs in spring and early summer. The
                     Peak Hourly Wet Weather (PHWW) flow is the peak flow during the peak hour of the day at
                     a time when the ground water is high and a five-year storm is occurring. The Peak
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Wastewater Treatment Facility Plan Amendment 2 Staples,Minnesota April2018 - Submitted by
Instantaneous Wet Weather (PIWW) flow is the peak instantaneous flow during the day at a
             time when the ground water is high and a twenty-five year one-hour storm event is occurring.
             This flow is used for sizing pumps and piping systems.
             An MPCA Determination of Design Flows worksheet was prepared using historical
             wastewater treatment facility flow data from the past five years. This worksheet is presented
             in Table 2.3.

                           Table 2.3 Determination of Design Flows - City of Staples

  A)      For Determination of Peak Hourly Wet Weather Design Flow (PHWW)                          gpd
   1      Present peak hourly dry weather flow                                                  1,104,000
   2      Present peak hourly flow during high ground water period (no runoff)                  1,700,000
   3      Present peak hourly dry weather flow [same as (1)]                                  - 1,104,000
   4      Present peak hourly infiltration                                                    = 596,000
        Present hourly flow during high ground water period and runoff at point of
    5 greatest distance between Curves Y and Z
          Present hourly flow during high ground water (no runoff) at same time of day as -
   6    (5) measurement
   7      Present peak hourly flow                                                               =
   8      Present peak hourly inflow adjusted for a 5-year 1-hour rainfall event                    199,000
   9      Present peak hourly infiltration [same as (4)]                                            596,000
  10      Peak hourly infiltration cost effective to eliminate                                   -     0
  11      Peak hourly infiltration after rehabilitation (where rehabilitation is cost effective) = 596,000
  12      Present Peak hourly adjusted inflow [same as (8)]                                         199,000
  13      Peak hourly inflow cost effective to eliminate                                         -     0
  14      Peak hourly inflow after rehabilitation (where rehabilitation is cost effective)       = 199,000
  15      Population increase __0__ @ _100_ gpcd times 2.5 (peaking factor)                            0
  16      Peak hourly flow from planned industrial increase                                            0
  17      Estimated peak hourly flow from future unidentified industries                               0
  18      Peak hourly flow from other future increases                                                 0
  19      Peak hourly wet weather design flow [(1)+(11)+(14)+(15)+(16)+(17)+(18)]                  1,899,000

       For Determination of Peak Instantaneous Wet Weather Design Flow
                                                                                                     gpd
  B) (PIWW)
  20   Peak hourly wet weather design flow [same as (19)]                                          1,899,000
       Present peak hourly inflow adjusted for a 5-year 1-hour rainfall event [same as
                                                                                               -   199,000
  21 (8)]
  22   Present peak inflow adjusted for a 25-year 1-hour rainfall event                       + 271,000
  23   Peak instantaneous wet weather design flow                                             = 1,971,000

  C)      For Determination of Average Dry Weather Design Flow (ADW)                                 gpd
  24      Present average dry weather flow                                                         241,000
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25      Population increase __494__ @ _100_ gpcd                                                 +     49,400
  26      Average flow from planned industrial increase                                            +        0
  27      Estimated average flow from other future unidentified industries                         +        0
  28      Average flow from other future increases                                                 +        0
  29      Average dry weather design flow [(24)+(25)+(26)+(27)+(28)]                               =     290,400

  D)      For Determination of Average Wet Weather Design Flow (AWW)                                       gpd
  30      Present average dry weather flow                                                               241,000
  31      Average infiltration after rehabilitation (where rehabilitation is cost effective)       +     292,200
  32      Average inflow after rehabilitation (where rehabilitation is cost effective)             +      97,400
  33      Population increase __494__ @ _100_ gpcd                                                 +      49,400
  34      Average flow from planned industrial increase                                            +        0
  35      Estimated average flow from future unidentified industries                               +        0
  36      Average flow from other future increases                                                 +        0
  37      Average wet weather design flow [(30)+(31)+(32)+(33)+(34)+(35)+(36)]                     =     680,000

             The ADW flow determined by this worksheet is 0.29 MGD and the AWW flow is 0.68
             MGD. These flows are similar to the existing design flows, which were determined in 1991.
             There are several reasons why the design flows from 1991 may match the current design
             flows, including conservative planning in 1991.

             WASTEWATER LOADINGS
             Pollutant loadings for the design year are required to size a wastewater treatment facility.
             Projected loadings are calculated by determining a pounds-per-capita-per-day (lb/capita/day)
             value for five-day carbonaceous biochemical oxygen demand (CBOD5), total suspended
             solids (TSS), and phosphorus (P) and multiplying this value by the projected population.
             Historical loading rates and per-capita values for the City of Staples are presented in Table
             2.4.

                            Table 2.4 Historical Influent Loadings - City of Staples

       Parameter                                            2007      2008     2009      2010          2011

       Population                                       3,146        3,131    3,099    2,981       2,976
       CBOD5: Influent Load (lb/day)                         627      535      553        509          409
       CBOD5: Per Capita Load (lb/day)                       0.199    0.171    0.178     0.171       0.138
       TSS: Influent Load (lb/day)                            694      564      578       500         534
       TSS: Per Capita Load (lb/day)                         0.221    0.180    0.187     0.168       0.179
       Phosphorus: Influent Load (lb/day)                    19.91    17.27    22.12     20.60       15.36
       Phosphorus: Per Capita Load (lb/day)                 0.0063   0.0055   0.0071    0.0069      0.0052

             Figure 2.3 presents a chart of the historical CBOD5 and TSS loadings.

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Figure 2.3 - Historical CBOD5 and TSS Loading
                                                          Staples Wastewater Treatment Facility

        Influent Loading (lb/day)

                                                                         Month-Year

                                                      Influent CBOD5                      Permitted CBOD5
                                                      Influent TSS                        Permitted TSS

                                                     Figure 2.3: Historical CBOD5 and TSS Loading

                                    The existing loadings have spiked over the permitted CBOD5 loading of 730 lb/day and the
                                    permitted TSS loading of 850 lb/day on a regular basis over the past ten years. The influent
                                    CBOD5 typically peaks during the spring months and exceeded the permitted and design
                                    values almost every year. The influent TSS follows a similar trend.
                                    Existing flows and loadings are used in conjunction with projected growth to develop design
                                    flows and loadings. Design parameters are presented in Table 2.5.

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Table 2.5 Design Wastewater Flows and Loadings - City of Staples

                                        Parameter                                Value       Unit
         Design Year                                                              2035         -
         Design Population                                                        3,791     persons
         Average Dry Weather (ADW) Flow                                           0.290      MGD
         Average Wet Weather (AWW) Flow                                           0.680      MGD
         Peak Hourly (PHWW) Flow                                                  1.90       MGD
         Peak Instantaneous (PIWW) Flow                                           1.97       MGD
         Biochemical Oxygen Demand, Carbonaceous 5-day (CBOD5)                     730      lb/day
         Total Suspended Solids (TSS)                                              850      lb/day
         Total Phosphorus (P)                                                      27       lb/day
         Total Mercury Monthly Average (Hg)                                        10         ng/l

             MERCURY
             Approximately two-thirds of the water on Minnesota’s 2014 Impaired Waters List is due to
             mercury. Mercury is a powerful neurotoxin that can enter the environment through a variety
             of methods such as volcanoes, burning fossil fuels, mining, metal processors, and gas
             combustion. The mercury often ends up in the bottoms of lakes and oceans where it
             accumulates in fish. As humans eat the fish, they are exposed to the mercury which
             accumulates in their bodies and can become toxic. The MPCA is implementing a TMDL by
             2025 to reduce the mercury released into the environment. Identifying the potential sources
             of the mercury is the first step in minimizing the discharge of mercury from the wastewater
             treatment facility into rivers and streams. The following is a list of activities or businesses
             which may have historically shown the potential to be significant sources of mercury.
                 •    Hospitals
                 •    Dentists
                 •    Electroplaters
                 •    Metal Finishers
                 •    Schools
                 •    Septic Haulers
                 •    Industrial Laundries
                 •    Laboratories
                 •    Veterinary Clinics
                 •    Printing Industry
                 •    Pottery and Arts
                 •    Automobile Service
                 •    Painting and Paint Stripping
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•   Landfill Leachate
                 •   Scrap Dealers

                                 Table 2.6 WWTP Mercury – City of Staples
                  Date             Influent Mercury (ng/l)         Effluent Mercury (ng/l)
          January 2014                       0.01                            20
          January 2015                       158                             17
          July 2015                          307                             26
          January 2016                        48                              9
          July 2016                          117                             8.8
          January 2017                       135                              6
          July 2017                           24                             2.5
          January 2018                       21.7                           5.88
                Average                     101.3                           11.9

              According to the U.S. Environmental Protection Agency (US EPA) data, typical mercury
             concentrations in wastewater treatment facility effluents ranges from 1 to 20 ng/l.

             BIOSOLIDS
             Sludge produced by the biological process is either injected or surface-sprayed on agricultural
             land. The City of Staples has a contract with a local land-owner to allow biosolids to be
             spread on a year-round basis. Lack of storage capacity forces the city to continuously using
             lime to stabilize the biosolids and then loading it out for land application. Table 2.7 below
             shows the amount of biosolids that was land-applied by the city over the past nine years.

                             Table 2.7 Biosolids Land-Applied – City of Staples

                             Year                     Amount Applied
                             2004                      870,400 gallons
                             2005                      771,200 gallons
                             2006                      838,400 gallons
                             2007                      766,400 gallons
                             2008                      806,400 gallons
                             2009                      523,200 gallons
                             2010                      646,400 gallons
                             2011                      758,400 gallons
                            Average                    787,700 gallons

             The existing aerobic digesters have a total volume of 152,000 gallons. The recommended
             amount of biosolids storage for any facility is at least 180 days to achieve appropriate
             stabilization and allow for a condensed period of land-application. Based on the above
             information, the City of Staples generates an average of 2,000 to 2,200 gallons of biosolids
             per day. With the addition of phosphorus removal, as required by the Facility’s permit, there
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is estimated to be an additional 100 to 150 gallons of biosolids generated per day. Total
             biosolids generated per day is estimated to be approximately 2,300 gallons; therefore, in order
             to meet the recommendation of 180-days of storage, a total of 415,000 gallons of storage is
             required.
             CURRENT EFFLUENT LIMITS
             Current effluent limits require a monthly average CBOD5 concentration of 25 mg/L or less
             and a TSS concentration of 30 mg/L or less. In addition, an 85% removal of CBOD5 and TSS
             is required. Projected effluent limits for CBOD5 and TSS are not anticipated to change in the
             next permit renewal cycle. The facility now also has a phosphorus mass loading limit, which
             is new with the current permit cycle. Existing effluent limits are summarized in Table 2.8.

                                  Table 2.8 Effluent Limits - City of Staples

                           Parameter                                      Limit
                                                              25 mg/l monthly, 85% Removal
                          5-Day CBOD
                                                            40 mg/l max. calendar week average
                    Dissolved Oxygen (DO)                             Monitor Only
                    Fecal Coliform Bacteria
                                                                  200 organisms/100 mL
                       (May - October)
              Hardness, Calcium and Magnesium                         Monitor Only
                         (as CaCO3)
                              pH                                         6.0 - 9.0
                Total Kjeldahl Nitrogen (TKN)                         Monitor Only
                      Total Phosphorous                         939 kg/year (2070 lb/year)
                    Total Residual Chlorine                       0.038 mg/L daily max.
                                                              30 mg/l monthly, 85% Removal
                 Total Suspended Solids (TSS)
                                                            45 mg/l max. calendar week average

             FUTURE EXPECTED EFFLUENT LIMITS
             The existing NPDES permit must be renewed every six years. With the upcoming renewal,
             the MPCA has kept most of the permit parameters the same, but the facility will now have a
             new mercury limit. The MPCA will phase in the new mercury limit if the facility makes
             improvements to the facility to meet the mercury limit. If the facility does not make
             enhancements to meet the mercury limit, the facility immediately fall under the final mercury
             limit.
             The new permit levels are show in Table 2.9.

                         Table 2.9 Future Expected Effluent Limits - City of Staples

                           Parameter                                      Limit
                                                              25 mg/l monthly, 85% Removal
                          5-Day CBOD
                                                            40 mg/l max. calendar week average
                    Dissolved Oxygen (DO)                             Monitor Only
                    Fecal Coliform Bacteria
                                                                  200 organisms/100 mL
                       (May - October)

Prepared by: Bolton & Menk, Inc.                                                             DESIGN CONDITIONS
Wastewater Treatment Facility Plan Amendment 1 W13.104619                                              Page 11
Hardness, Calcium and Magnesium                         Monitor Only
                         (as CaCO3)
                              pH                                         6.0 - 9.0
                Total Kjeldahl Nitrogen (TKN)                         Monitor Only
                      Total Phosphorous                         939 kg/year (2070 lb/year)
                    Total Residual Chlorine                       0.038 mg/L daily max.
                                                              30 mg/l monthly, 85% Removal
                 Total Suspended Solids (TSS)
                                                            45 mg/l max. calendar week average
                                                             50 ng/l daily maximum (interim)
                         Total Mercury                           17 ng/l maximum (final)
                                                              10 ng/l monthly average (final)

Prepared by: Bolton & Menk, Inc.                                                             DESIGN CONDITIONS
Wastewater Treatment Facility Plan Amendment 1 W13.104619                                              Page 12
III. EVALUATION OF EXISTING FACILITIES
             TREATMENT FACILITY
             The existing wastewater treatment facility consists of an influent lift station, a manually
             cleaned static bar screen, a cyclone grit removal system, two 46,000-gallon aeration basins,
             three final clarifiers, a chlorine contact basin, and four 38,400-gallon biosolids digester tanks.
             This section reviews the treatment capacity for the various unit processes at the Staples
             WWTF based on current design recommendations. This review indicates that the existing
             facility is adequate to meet the proposed design average wet weather flow, but is undersized
             to meet the proposed peak flow of 1.9 MGD.

                                Table 3.1 Staples WWTF Unit Process Summary

                                                                                   Maximum Available Capacity
           Parameter             Value         Units         Design Criteria         AWW        PWW       CBOD5
                                                                                    (MGD)      (MGD)      (lb/day)
   Static Screens
    Number                         2                           PIWW each
    Bar Spacing                  0.060         Inches                                0.680
    Volume                         10          ft3/MG
   Grit Removal
    Number                         1          centrifugal                            0.680
                                                system
    Unit Size                      54       inch diameter
    95% Capture Size              100           micron
    Grit volume                    5            ft3/MG
   Trickling Filter
    Diameter                       24            foot
    Area                          452             ft2
    Depth                          6             feet            min 6 ft
    Peak Hydraulic Loading        1.99         gpm/ft2                                          1.30
    BOD Loading                   242        lb/1000 ft3                                                    700

   Aeration Basins
    Number                        2                                 2+
    Dimensions                20 x 35        feet
    Sidewater Depth              12          feet           >10 ft and < 30 ft
    Volume                    124,000      gallons
    Freeboard                 0.25 – 2       feet                >1.5 ft
    Detention Time
      ADW Flow                  10.2        hours
      AWW Flow                   4.4        hours
      PHWW Flow                  1.6        hours
    BOD Loading                  30    lb/day/1000ft3
2 units (1965)               8.5              feet          min 12 ft
     1 unit (1991)                 10              feet          min 12 ft
    Surface Area                 1,260              ft2
    Surface Settling Rate
     ADW Flow                     230          gpd/ft2
     AWW Flow                     540          gpd/ft2                             0.68
     PHWW Flow                   1,507         gpd/ft2
The screenings dump from the trough directly into a dumpster on the level below.
                          The screenings are not adequately dewatered and are taken to the landfill in a
                          rather wet state. This situation may soon need to change as landfill or waste
                          management regulations evolve and move towards requiring a drier waste to
                          allow disposal. Static screens may not be the best application to produce the
                          desired screenings.

                                      Figure 3.1: Existing Static Screen

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Figure 3.2: Static Screen Supports

                   3.     Cyclone Grit Remover
                          Grit is removed with a Eutek Teacup cyclone grit removal system. The system
                          was installed in 1991 and is in poor condition. The exterior of the Teacup is
                          showing large amounts of rusting and flaking. This equipment has reached the
                          end of its useful life and replacement is recommended.

Prepared by: Bolton & Menk, Inc.                                            EVALUATION OF EXISTING FACILITIES
Wastewater Treatment Facility Plan Amendment 2 W13.104619                                            Page 16
Figure 3.3: Eutek Teacup Grit Removal System

                   4.     Trickling Filter
                          The trickling filter is contained in a square room and has a motor actuated rotor
                          and four trickling arms. The trickling filter has no recirculation feed which
                          reduces the effectiveness of the process. The rotor mechanism and granular
                          media are original from 1991. The mechanism is rusting and the rotor arms have
                          significant leaks at the end, as well as plugged openings along the arms. The
                          typical lifespan of granular filter media is 20 years and the media is currently 27
                          years old. The media has likely reached the end of its lifespan, though it has not
                          been tested.
                          The trickling filter bypass pipe leaks where it enters the tricking filter effluent
                          trough and repairs are required.

Prepared by: Bolton & Menk, Inc.                                                EVALUATION OF EXISTING FACILITIES
Wastewater Treatment Facility Plan Amendment 2 W13.104619                                                Page 17
Figure 3.4: Trickling Filter Arm

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                          Page 18
Figure 3.5: Trickling Filter Mechanism

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                            Page 19
Figure 3.6: Bypass Pipe Leak

                   5.     Aeration Basins
                          The trickling filter is followed by a four-way splitter structure and two aeration
                          basins. Each basin has two influent flow locations. The basins were constructed
                          in 1965 and the air piping is original to that construction. The basin is
                          constructed for a modified step influent and short hydraulic and solids retention
                          times.
                          The existing basins appear to be in poor condition, though a full inspection
                          cannot be completed until they are emptied and cleaned. The air piping, headers,
                          and diffusers are in poor condition and should be replaced. New equipment
                          improves the efficiency of oxygen transfer to the water.

Prepared by: Bolton & Menk, Inc.                                              EVALUATION OF EXISTING FACILITIES
Wastewater Treatment Facility Plan Amendment 2 W13.104619                                              Page 20
Figure 3.7: Aeration Basin Splitter Box

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                             Page 21
Figure 3.8: Aeration Basin Air Header Hoist

                            Figure 3.9: Aeration Basin and Return Sludge Piping
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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                          Page 22
6.     Final Clarifiers
                          The splitter box leading to the clarifier has three slide gates. The gates are no
                          longer functional and do not allow the city to isolate a clarifier. The structure
                          hydraulics cause overflow and unintentionally bypass the new clarifier in high
                          flow situations.
                          The system has three rectangular final clarifiers. Two were constructed in 1965
                          and one in 1991. All three have the original arms and piping. Chains and
                          sprockets were replaced as needed on all three clarifiers. The motors were rebuilt
                          and gearboxes replaced on the older clarifiers within the past five years.
                          The clarifier structures are generally in fair condition, but the arms, piping, slide
                          gates and baffle walls are in poor condition for all three clarifiers. The design of
                          the clarifiers does not meet existing standards on depth associated with chemical
                          addition necessary for nutrient control. A new mercury limit will be added to the
                          next wastewater discharge permit, and the inefficiencies of the final clarifiers
                          pose potential for NPDES permit violations.

                                          Figure 3.10: Older Clarifier

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                               Page 23
Figure 3.11: Influent to Older Clarifier

                                         Figure 3.12: Newer Clarifier

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                              Page 24
7.     Return Sludge System
                          The return activated sludge (RAS) system was constructed in 1965 and is in very
                          poor condition. The RAS splitter box which divides the returned sludge between
                          the two aeration basins is extremely rusted and in poor structural condition.
                          Return sludge is pumped by two vertical centrifugal pumps which are an
                          outdated model. The pumps are in need of rebuilding or replacement and parts
                          are very difficult to find and can be expensive.
                   8.     Chlorine Contact Basin
                          The chlorine contact basin is a concrete structure constructed in 1965. The
                          structure is in generally fair condition, but the basin is inadequately sized for
                          current and proposed peak flows. The tank has concrete baffle walls which are
                          four feet apart.
                          At the beginning of the chlorine contact tank is the draw for a heat exchange
                          system that the city uses to provide heat to some of the Public Works buildings.
                          Because this draw is after the chlorine injection point, the system can only be
                          used during the winter months when the system is not being chlorinated. If the
                          draw would be relocated to before the chlorine injection point, the system could
                          be used year-round and provide both heating and cooling.
                          Dechlorination is achieved at the end of the chlorine contact basin using liquid
                          chemical stored nearby.

                                     Figure 3.13: Chlorine Contact Basin

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                              Page 25
9.     Aerobic Digesters
                          There are four rectangular aerobic digester tanks. Two structures were
                          constructed in 1965 and two in 1991. The diffusers were all new in 1991. There
                          are significant concrete repairs necessary on the interior of the basins.
                          The capacity of the existing digesters equals approximately 50 days of sludge
                          storage. Due to MPCA sludge stabilization requirements and the limited storage
                          capacity, the city uses lime to stabilize the sludge prior to land-application.
                          Because this was not intended in the original design, the city has a cobbled-
                          together lime stabilization process that is potentially dangerous and is not cost
                          effective. Lime is added to one basin each week on average and the process is
                          time consuming and expensive. Longer biosolids storage time would allow for
                          the lime stabilization process to be eliminated.

                                       Figure 3.14: Lime Feed System

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                             Page 26
Figure 3.15: Aerobic Digesters

                   10.    Chemical Feed Systems
                          The facility currently feeds chlorine, sodium bisulfite, polymer, and a flocculant
                          to meet effluent limits.
                          a)       Chlorine System
                          The city feeds gas chlorine to the beginning of the chlorine contact tank and to
                          the RAS influent. The chlorine system is in fair condition and can continue to be
                          used. The chlorine system is currently stored in an open enclosure outside of the
                          facility that does not provide adequate weather protection during the winter
                          months. Beginning this year, the city is feeding chlorine to control filamentous
                          on a year-round basis, and a weather-tight enclosure is necessary. In addition,
                          the chlorine should be stored in a secure location.

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                              Page 27
Figure 3.16: Chlorine Enclosure

                          b)       Polymer System
                          The polymer system is located inside of the old control building and is in good
                          condition. However, the system is not isolated from the other equipment in the
                          room, particularly the heat exchanger, and does not have sufficient containment.
                          The operators feel that the polymer pumps are not ideal for continuous use and
                          would like to see them replaced.
                          c)       Dechlorination
                          The city feeds sodium bisulfite as a method of chemical dechlorination. This
                          system includes a chemical tank, containment, a chemical feed pump, tubing, and
                          an injection port. Since sodium bisulfite in solution freezes at approximately 45
                          degrees Fahrenheit, a weatherproof shelter with heating system was constructed.

                          d)       Phosphorus Removal
                          The city added a chemical feed system for use in phosphorus removal in the fall
                          of 2013.

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                            Page 28
11.    Blowers
                          There are three positive displacement blowers located in the basement of the old
                          control building. These blowers provide air for the aeration basin diffusers and
                          the aerobic digester diffusers. The blowers were installed in 1991 and have been
                          partially submerged in water and repaired several times since then. They are
                          considered to be at the end of their useful lives and in need of replacement.

                                             Figure 3.17: Blowers

                   12.    Pumps and Piping
                          There are six pumps throughout the facility: two RAS pumps, two scum pumps,
                          and two sludge loadout pumps. The six pumps are identical vertical centrifugal
                          pumps; four of which were installed in 1967 and two in 1991. They have all been
                          rebuilt several times and are an outdated model that is very difficult to find parts
                          for, and it is recommended these pumps be replaced as the expected life of
                          equipment is 20 years.
                          In general the piping and valves throughout the facility are in fair condition.
                          There are several valves that will likely need to be replaced through this project.
                   13.    Control Buildings
                          There are two controls buildings at this facility. The old control building was
                          originally constructed in 1965 and is now used for secondary uses. The main
                          floor contains the heat exchanger, the polymer system, and the electrical panel
                          for the equipment installed in 1965. The basement contains the blowers, pumps
                          and piping, and pressure filter for facility water.

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                              Page 29
The new control building was constructed in 1991 and contains the pretreatment
                          units and trickling filter, the electrical system for all of the equipment installed in
                          1991, and the office.
                          The old control building is in poor condition and is not being fully utilized. The
                          new control building is in good condition and generally needs little repair work.
                   14.    Sludge Tanker Truck
                          The city has a new sludge tanker truck that is used year-round for sludge loading
                          and land-application. Because the old truck was stored in the basement of the
                          control building, wastewater fumes have caused the electrical system to degrade
                          and replacement is required for several items.

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Wastewater Treatment Facility Plan Amendment 2 W13.104619                                                Page 30
IV. WASTEWATER TREATMENT FACILITY IMPROVEMENTS
             GENERAL
             In the following paragraphs, several categories of alternatives are given general
             consideration. Alternative solutions include: 1) optimization of operation and/or rehabilitation
             of existing facilities, 2) regionalization, or 3) construction of a new facility.
             Optimization of operation and rehabilitation/expansion of existing facilities includes
             improvements to the facility and site to make the treatment process more effective and
             efficient. Components of the existing facility are in fair condition, but the process will not
             meet future effluent limits or treatment goals.
             Construction of a new or expanded facility is proposed to be completed on the existing site.
             Various construction options are discussed further in this report.
                   1.     Optimization of Operation and/or Rehabilitation of Existing Facilities
                          The existing facility has maintained adequate treatment to meeting effluent
                          requirements. However, the facility’s proposed peak flow is higher than the
                          current design peak flow. The existing system potentially could be rehabilitated
                          and improved to provide required capacity and ensure future effluent quality
                          remains adequate.
                   2.     Regionalization
                          This category includes the possibility of diverting wastewater from the city to the
                          wastewater treatment facility of a nearby community. A lift station with large
                          pumps and a significant length of forcemain is typically required for
                          regionalization, along with the demolition or mothballing of the existing
                          treatment facility.
                          The flows from the City of Staples are quite large and regionalization for this
                          quantity of wastewater would be very difficult. Due to the distance and costs
                          associated with regionalization in comparison to the magnitude of the required
                          facility improvements, regionalization was not considered feasible at this time.
                   3.     Construction of a New Facility
                          The current facility is a mechanical treatment facility with continuous discharge.
                          The current treatment processes are adequate to meet existing effluent limits.
                          The facility may not be able to meet the new mercury limit. Based on existing
                          sampling, the facility would have violated the proposed limit in the past five
                          years. Construction of a new mechanical facility would require the demolition of
                          the existing facility and the construction of a new facility, which would contain
                          similar processes to the existing one. Constructing a new facility would allow
                          the City of Staples to effectively and reliably treat the wastewater to permitted
                          standards.
             WASTEWATER TREATMENT FACILITY IMPROVEMENTS
             The recommended improvements discussed in this section are based on optimization and
             rehabilitation of the existing facility. There are four alternatives discussed:
             •   Alternative 1: Moderate Improvements to Optimize Current Processes
             •   Alternative 2: Rehabilitation of Facility with Addition of Flow Equalization
             •   Alternative 3: Rehabilitation of Facility with Addition of Extended Aeration Process

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•   Alternative 4: Construction of New Extended Aeration Activated Sludge Treatment
                   Facility
                       1.   Alternative 1: Moderate Improvements to Optimize Current Processes
                            Alternative 1 includes a significant rehabilitation of all existing unit processes
                            and modification of the chlorine contact basin to increase length-to-width ration.
                            In addition, it includes constructing a new return activated sludge (RAS) system,
                            and provided adequate containment for chemical feed systems. Table 4.1 presents
                            a summary of the recommended improvements, based on the condition of the
                            processes described above in Section 3.

               Table 4.1 Alternative 1: Moderate Improvements to Optimize Current Processes

Pretreatment                           •   Rebuild static screen gear boxes
                                       •   Construct new static screen support structure
                                       •   Install screenings/dewatering press
                                       •   Replace centrifugal grit removal system
Trickling Filtration                   •   Replace trickling filter drive and arms
                                       •   Replace media
                                       •   Install recirculation pipe/pumps
                                       •   Install bypass pipe to bypass portion of flow to filter
Aeration                               •   Replace fine bubble diffusers and air piping
                                       •   Replace RAS system
                                       •   Replace the blowers
                                       •   Raise the elevation of the wall at the effluent end of the basins
Final Clarification                    •   Replace piping and mechanism parts as required
                                       •   Add baffle walls to prevent short-circuiting
Disinfection                           •   Remove existing baffle walls and install new fiberglass baffle walls
                                           2’ apart from each other
                                       •   Install sulfur dioxide system for dechlorination
Biosolids Storage and Handling         •   Construct a 265,000 gallon biosolids holding tank
                                       •   Modify loadout piping to accommodate new tank
                                       •   Provide exterior loadout area
Chemical Phosphorus Removal            •   Install ferric chloride feed system for phosphorus removal
Other Chemical Feed Systems            •   Rehabilitate existing “old” control building into chemical building
                                           with rooms for ferric chloride, polymer, chlorine, and sulfur
                                           dioxide or sodium bisulfate
Pumps and piping                       •   Rehabilitate RAS, scum, and sludge loadout pumps as needed
                                       •   Provide a recirculation pump for the trickling filter
                                       •   Replace some valves and piping throughout the facility as needed
Control Building                       •   None
Miscellaneous                          •   Repair or rehabilitate steel building over aeration/biosolids
                                           storage area as necessary

                            Alternative 1 allows the city to continue to use the processes that the operators
                            are familiar with, rehabilitates equipment that is in poor condition, and provides
                            dedicated and safe spaces for all chemicals.
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Alternative 1 does not include any improvements that would allow the facility to
                          operate more efficiently under current peak flow events or meet the proposed
                          peak flows. However, the city intends to research and implement an infiltration
                          and inflow reduction program and hopes to eliminate a portion of those peak
                          flows.
                          The reliance on unit processes, piping, and some valves that have been in service
                          since 1965 (50+ years) exposes the city to risk of significant future costs. This
                          risk is too great and is not further considered.
                          Replacing the chlorine contact tank baffle walls with fiberglass baffles only 2-
                          feet apart will increase the contact time in the basin to approximately 21 minutes
                          at the existing peak flow of 1.3 MGD and to 14.5 minutes at the proposed peak
                          flow of 1.9 MGD.
                   2.     Alternative 2: Rehabilitation of the Facility with the Addition of Flow
                          Equalization
                          Alternative 2 includes moderate to extensive rehabilitation of the pretreatment
                          processes, the trickling filter, and the existing aeration basin, as well as
                          construction of a flow equalization basin, two new final clarifiers, and a new
                          chlorine contact chamber. A summary of these recommendations is provided in
                          Table 4.2 below.

   Table 4.2 Alternative 2: Rehabilitation of Existing Facility with the Addition of Flow Equalization

 Pretreatment                          •    Rebuild static screen gear boxes
                                       •    Construct new static screen support structure
                                       •    Install screenings/dewatering press
                                       •    Replace centrifugal grit removal system
 Trickling Filtration                  •    Replace trickling filter drive and arms
                                       •    Replace media
                                       •    Install recirculation pipe/pumps
                                       •    Install bypass pipe to bypass portion of flow to filter
 Aeration                              •    Replace fine bubble diffusers and air
                                       •    Replace RAS system
                                       •    Replace the blowers
                                       •    Raise the elevation of the wall at the effluent end of the
                                            basins
 Final Clarification                   •    Construct two new 35-foot diameter circular final clarifiers
                                       •    Provide automatic wasting
 Disinfection                          •    Construct new chlorine contact basin
                                       •    Install sulfur dioxide or sodium bisulfite system for total
                                            chlorine residual reduction
 Flow Equalization                     •    Construct a 1.0 million gallon flow equalization basin (75-foot
                                            diameter, 30-foot depth) and associated piping
 Biosolids Storage and Handling        •    Convert the existing final clarifiers and chlorine contact
                                            chamber into additional biosolids storage (add approximately
                                            100,000 gallons or 40 additional days of storage)
                                       •    Replace the coarse bubble diffusers in the existing storage
                                            tanks

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•   Extend sludge loadout piping out of garage so that loading
                                             into a larger tank is possible
                                         •   Potentially replace existing tank truck with larger truck or
                                             tractor and tank combination
  Chemical Phosphorus Removal            •   Install ferric chloride feed system for phosphorus removal
  Other Chemical Feed Systems            •   Rehabilitate existing “old” control building into chemical
                                             building with rooms for ferric chloride, polymer, chlorine, and
                                             sulfur dioxide or sodium bisulfate
  Pumps and piping                       •   Replace RAS, scum, and sludge loadout pumps
                                         •   Provide a recirculation pump for the trickling filter
                                         •   Replace valves and piping throughout the facility as needed
  Control Building                       •   Rehabilitate existing MCCs, including consolidating both MCC
                                             units in the “new” control building
                                         •   Repair or replace building HVAC as required
  Miscellaneous                          •   Repair or rehabilitate steel building over aeration/biosolids
                                             storage area as necessary

                            Alternative 2 allows the city to continue using the existing processes that the
                            operators are familiar with and provides flow equalization, dedicated and safe
                            spaces for all chemicals, and rehabilitates or replaces equipment in poor
                            condition. It provides dechlorination and phosphorus removal systems as
                            required by the Facility’s most recent NPDES permit. This alternative provides
                            new final clarifiers which will allow the facility to easily handle current and
                            proposed peak flows and a new chlorine contact tank that has adequate chlorine
                            contact time and sufficient space for dechlorination. It also provides some
                            additional biosolids storage, though it may not provide enough holding time to
                            complete eliminate the lime stabilization process. Other aspects to consider
                            include the fact that the proposed flow equalization basin is quite large for the
                            property and the improvements only provide 100 days of sludge storage, while
                            180 days is recommended.
                            The reliance on unit processes, piping, and some valves that have been in service
                            since 1965 (50+ years) exposes the city to risk of significant future costs. This
                            risk is too great and is not further considered.
                       3.   Alternative 3: Rehabilitation of Facility with Addition of Extended Aeration
                            Process
                            Alternative 3 includes rehabilitation of the pretreatment processes and the
                            trickling filter, as well as construction of an activated sludge process and a new
                            chlorine contact chamber. A summary of the recommendations for this
                            alternative can be seen below in Table 4.3.

      Table 4.3 Alternative 3: Rehabilitation of Facility with Addition of Extended Aeration Process

Pretreatment                            •    Rebuild static screen gear boxes
                                        •    Construct new static screen support structure
                                        •    Install screenings/dewatering press
                                        •    Replace centrifugal grit removal system
Trickling Filtration                    •    Replace trickling filter drive and arms

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•   Replace media
                                        •   Install recirculation pipe/pumps
                                        •   Install bypass pipe to bypass portion of flow to filter
Aeration                                •   Construct three chamber concrete aeration basin with a hydraulic
                                            retention time of 18 hours
Final Clarification                     •   Construct two new 35-foot diameter circular final clarifiers
                                        •   Provide automatic wasting
Disinfection                            •   Construct new chlorine contact basin
                                        •   Install sulfur dioxide or sodium bisulfite system for total chlorine
                                            residual reduction
Biosolids Storage and Handling          •   Convert the existing aeration basin, final clarifiers and chlorine
                                            contact chamber into additional biosolids storage
                                        •   Replace the coarse bubble diffusers in the existing storage tanks
                                            and install coarse bubble diffusers in the existing aeration basin
                                            (for use in biosolids storage)
                                        •   Extend sludge loadout piping out of garage so that loading into a
                                            larger tank is possible
                                        •   Potentially replace existing tank truck with larger truck or tractor
                                            and tank combination
Chemical Phosphorus Removal             •   Install ferric chloride feed system for phosphorus removal
Chemical Mercury Removal                •   Install ferric chloride feed system for mercury removal
Other Chemical Feed Systems             •   Rehabilitate existing “old” control building into chemical building
                                            with rooms for ferric chloride, polymer, chlorine, and sulfur
                                            dioxide or sodium bisulfite
Pumps and piping                        •   Replace RAS, scum, and sludge loadout pumps
                                        •   Replace valves and piping throughout the facility as needed
Control Building                        •   Rehabilitate existing MCCs, including consolidating both MCC
                                            units in the “new” control building
                                        •   Install electrical as necessary for new process equipment
                                        •   Repair or replace building HVAC as required
Miscellaneous                           •   Repair or rehabilitate steel building over biosolids storage area as
                                            necessary

                           Alternative 3 provides rehabilitated and new process equipment for the entire
                           facility, does not require flow equalization, and provides additional biosolids
                           storage space. It also provides dechlorination and phosphorus removal systems as
                           required by the Facility’s most recent NPDES permit. With the additional sludge
                           storage space, there will be approximately 150 days of sludge storage. As a
                           result, the biosolids will have time to thicken and will potentially be able to meet
                           required standards without the addition of lime stabilization. However, this
                           alternative does not provide 180 days of sludge storage as recommended and will
                           require the operators to learn and operate a new treatment process.
                           The reliance on unit processes, piping, and some valves that have been in service
                           since 1965 (50+ years) exposes the city to risk of significant future costs. This
                           risk is too great and is not further considered.
                      4.   Alternative 4: New Extended Aeration Activated Sludge Treatment Facility
                           Alternative 4 includes the construction of a new extended aeration activated
                           sludge treatment facility. The existing facility would be abandoned due to age,
 Prepared by: Bolton & Menk, Inc.                                WASTEWATER TREATMENT FACILITY IMPROVEMENTS
 Wastewater Treatment Facility Plan Amendment 2 W13.104619                                           Page 35
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