Wastewater Treatment Facility Plan Amendment 244315AD6-8633-4D56-A3F9... · Wastewater Treatment Facility Plan. Amendment 2. Staples, Minnesota April 2018. Submitted by: Bolton &

Wastewater Treatment Facility PlanAmendment 2Staples, Minnesota April 2018

Submitted by:Bolton & Menk, Inc.7533 Sunwood Drive NW #206Ramsey, MN 55303P: 763-433-2851F: 763-427-0833

Prepared by: Bolton & Menk, Inc. Certification Wastewater Treatment Facility Plan Amendment 2 W13.104619

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

Prepared by: Bolton & Menk, Inc. Table of Contents Wastewater Treatment Facility Plan Amendment 2 W13.104619

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

Prepared by: Bolton & Menk, Inc. Table of Contents Wastewater Treatment Facility Plan Amendment 2 W13.104619

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. INTRODUCTION Wastewater Treatment Facility Plan Amendment 2 W13.104619 Page 1

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.

Prepared by: Bolton & Menk, Inc. DESIGN CONDITIONS Wastewater Treatment Facility Plan Amendment 2 W13.104619 Page 2

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


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.

5,000

10,000

15,000

20,000

25,000

30,000

1,000

1,500

2,000

2,500

3,000

3,500

2000 2005 2010 2015 2020 2025 2030 2035 2040

Todd

and

Wad

ena

Coun

ties P

opul

atio

n

City

of S

tapl

es P

opul

atio

n

Year

Figure 2.1 - Historical and Projected PopulationsCity of Staples, Todd County, and Wadena County

City of Staples Todd County Wadena County


Table 2.2 Average Daily Flows - City of Staples

Month 2003 (gpd)

2004 (gpd)

2005 (gpd)

2006 (gpd)

2007 (gpd)

2008 (gpd)

2009 (gpd)

2010 (gpd)

2011 (gpd)

2012 (gpd)

Monthly Average

(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.


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

Flow

(MG

D)

Month-Year

Figure 2.2 - Historical Flow DataStaples Wastewater Treatment Facility

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

Maximum Daily Flow (MGD) Permitted Peak Flow


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

5 Present hourly flow during high ground water period and runoff at point of

greatest distance between Curves Y and Z

6 Present hourly flow during high ground water (no runoff) at same time of day as

(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

B) For Determination of Peak Instantaneous Wet Weather Design Flow

(PIWW) gpd

20 Peak hourly wet weather design flow [same as (19)] 1,899,000

21 Present peak hourly inflow adjusted for a 5-year 1-hour rainfall event [same as

(8)] - 199,000

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


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.


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.

Influ

ent L

oadi

ng (l

b/da

y)

Month-Year

Figure 2.3 - Historical CBOD5 and TSS LoadingStaples Wastewater Treatment Facility

Influent CBOD5 Permitted CBOD5Influent TSS Permitted TSS


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


• 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


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

5-Day CBOD 25 mg/l monthly, 85% Removal 40 mg/l max. calendar week average

Dissolved Oxygen (DO) Monitor Only Fecal Coliform Bacteria

(May - October) 200 organisms/100 mL

Hardness, Calcium and Magnesium (as CaCO3)

Monitor Only

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.

Total Suspended Solids (TSS) 30 mg/l monthly, 85% Removal 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

5-Day CBOD 25 mg/l monthly, 85% Removal 40 mg/l max. calendar week average

Dissolved Oxygen (DO) Monitor Only Fecal Coliform Bacteria

(May - October) 200 organisms/100 mL


Hardness, Calcium and Magnesium (as CaCO3)

Monitor Only

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.

Total Suspended Solids (TSS) 30 mg/l monthly, 85% Removal 45 mg/l max. calendar week average

Total Mercury 50 ng/l daily maximum (interim)

17 ng/l maximum (final) 10 ng/l monthly average (final)

Prepared by: Bolton & Menk, Inc. EVALUATION OF EXISTING FACILITIES Wastewater Treatment Facility Plan Amendment 2 W13.104619 Page 13

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

Parameter Value Units Design Criteria Maximum Available Capacity AWW (MGD)

PWW (MGD)

CBOD5 (lb/day)

Static Screens Number 2 PIWW each Bar Spacing 0.060 Inches 0.680 Volume 10 ft3/MG Grit Removal Number 1 centrifugal

system 0.680

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 <40 lb/day/1000 ft3 504 Influent Loading w/ 30% CBOD removal by trickling filter MLSS concentration 2500 mg/L 1,000-3,000 mg/L Solids Retention Time 8 days Final Clarifiers Number 3 Dimensions 12 x 35 feet Sidewater depth


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 <1,200 gpd/ft2 1.51 Weir Loading Rate ADW Flow 2,010 gpd/lf AWW Flow 4,720 gpd/lf 1.03 PHWW Flow 13,200 gpd/lf <20,000 gpd/lf 2.88 RAS Pumps Number Capacity 300 gpm 15-100% AWW Chlorine Contact Basin Number 1 Total Volume 11,100 gallons Detention Time ADW Flow 55 minutes AWW Flow 23.5 minutes PHWW flow 8.4 minutes >15 minutes 1.07 Aerobic Sludge Digesters Number 4 Dimensions 17 x 24 feet Depth 12.5 feet Total Volume 152,000 gallons

FACILITY CONDITION

The unit processes at the existing wastewater treatment facility range in condition from fair to poor. Generally speaking, age appears to be a preliminary indicator of the structural condition. The typical expected life span of equipment in a wastewater facility is approximately 20 years, and the typical life expectancy of a structure is 50 years.

1. Influent Lift Station

The influent lift station was constructed in 1997 and has had regular maintenance over the past 17 years. The lift station consists of high lift pumps and a grinder to reduce the size of solids in the wastewater. The grinder was rehabilitated by the city in 2010. The lift station structure is in good condition and needs no improvements at this time.

2. Manually Cleaned Static Screens

The static screens were installed in 1991 and are in poor condition. The screens have been well maintained and the troughs were replaced recently. The screens are manually cleaned and the auger that removes the screenings is in need of a new gear box.

The steel platform which supports the screens is in poor condition, showing significant rusting and degradation.


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


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.


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.


Figure 3.4: Trickling Filter Arm


Figure 3.5: Trickling Filter Mechanism


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.


Figure 3.7: Aeration Basin Splitter Box


Figure 3.8: Aeration Basin Air Header Hoist

Figure 3.9: Aeration Basin and Return Sludge Piping


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


Figure 3.11: Influent to Older Clarifier

Figure 3.12: Newer Clarifier


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


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


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.


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.


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.


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.

Prepared by: Bolton & Menk, Inc. WASTEWATER TREATMENT FACILITY IMPROVEMENTS Wastewater Treatment Facility Plan Amendment 2 W13.104619 Page 31

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


• 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.


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


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


• 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.


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


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 • 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.


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,


excessive cost of rehabilitation, and inability to meet the treatment guidelines outlined in the facility permit. The new facility would consist of new pretreatment, aeration basins, final clarifiers, disinfection, chemical feed, and biosolids handling. A summary of the recommendations for this alternative are in Table 4.4

Table 4.4 Alternative 4: New Extended Aeration Activated Sludge Treatment Facility Pretreatment • New fine screen with press

• New vortex grit removal system Aeration • Construct three chamber concrete aeration basins 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 • Construct new buried concrete tanks for biosolids storage. Coarse bubble diffusers will be added to the first tank with a submersible mixer in the second tank

• Submersible pump for biosolids removal • A sludge load-out station will be constructed

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 • Construct new Chemical Feed Rooms for ferric chloride, polymer,

chlorine, and sulfur dioxide or sodium bisulfite Pumps and piping • New pumps and piping for the new treatment system Control Building • New MCCs for the new equipment

Alternative 4 provides a new robust facility that can better handle the diurnal flows and can provide effective treatment to meet the Facility’s permit standards as well as all current codes. The chemical feed will have dedicated rooms with proper ventilation and security. This alternative would allow for sufficient sludge storage to meet the 180 days of storage without the lime stabilization. Flow equalization would not be necessary with this alternative and the trickling filter would be eliminated. The existing Control Building will be utilized as garage and maintenance space.

FACILITY CLASSIFICATION

The MPCA classifies wastewater treatment facilities with a points system based on population, effluent limits, and treatment processes. The City of Staples WWTF is currently classified as a Class B facility. With the inclusion of a phosphorus and mercury effluent limit on the city’s NPDES permit, the points value of the Facility’s existing classification is near the top of the Class B range. A preliminary review indicates all four alternatives will keep the facility in the Class B range. The staffing of each alternative will be similar with the exception of reduced biosolids handling requirements associated with the new facility.

Prepared by: Bolton & Menk, Inc. RECOMMENDATION Wastewater Treatment Facility Plan Amendment 2 W13.104619 Page 37

V. RECOMMENDATION RECOMMENDATION

After careful consideration of all the design information, the condition of the existing facilities, required effluent limits, and all treatment alternatives, it is recommended to construct Alternative 4: New Extended Aeration Activated Sludge Treatment Facility. This alternative is able to meet the effluent limits for the design flows in 2035 and provide reliable service to the city. This recommendation is believed to provide Staples with the best long-term treatment of wastewater and investment into the required infrastructure. This alternative is operator friendly and eliminates lime addition and addresses all the condition of the existing facility. Additionally, this system is flexible and easily expandable to account for more stringent limits and future flows.

PROJECT FUNDING

There are several alternatives that the city can consider for project funding.

1. Bonding

The city could sell general obligation, local improvement, or revenue bonds in order to raise the capital costs to improve the treatment facility. The proceeds of the bonds would need to be repaid, either through property taxes, assessments, or user charges to the system.

2. Assessment

A portion of the capital costs of the project can be assessed to local property owners under Minnesota Statute 429. Using this method, a one-time assessment could be levied and repaid over a period of 10 to 20 years. This cost could help offset some monthly increases in user fees and permit use of general obligation bonding.

3. Rural Development (RD) Loan

The city may be eligible to secure a loan or grant through Rural Development for the wastewater improvements. Repayment could be through an increase in local property tax rates, user fees or assessments. A portion of the project costs may be eligible for grant funding as a part of this program depending on the economic status of the residents of the city.

In order to be considered for Rural Development monies, a Preliminary Engineering Report (PER) must be completed and submitted to RD. This provides specific treatment and financial information for RD to consider.

Rural Development uses an Equivalent Dwelling Unit (EDU) calculation for assisting in determining the amount and type of funding for which a community is eligible. The preliminary EDU calculations for the City of Staples indicate that it is unlikely the project would be eligible for grant financing, but loan financing may still be available. The PER would provide more specific information on the city’s eligibility.

4. State Revolving Fund Loan (through the PFA)

The loan program was created under the State Revolving Fund (SRF) provisions in the Federal Clean Water Act to provide financial assistance for water pollution control projects. Minnesota’s revolving loan program provides loans to municipalities for planning, design and construction of wastewater treatment projects. The loans are typically for a 20-year period at an interest rate of two to

Prepared by: Bolton & Menk, Inc. RECOMMENDATION Wastewater Treatment Facility Plan Amendment 2 W13.104619 Page 38

four percent. The loan monies are administered through the Public Facilities Authority. To be eligible for PFA funding, the city must submit this Facilities Plan for review and approval by the Minnesota Pollution Control Agency.

Revenue for loan repayment is typically generated by user rates, availability charges or assessment.

5. Point Source Implementation Grant (PSIG)

The MPCA and PFA jointly administer Point Source Implementation Grant programs funded by the Clean Water Legacy money. The grant programs provide a 50 percent grant on eligible portions of the project for up to $7,200,000 for TMDLs, mercury, and phosphorus.

Prepared by: Bolton & Menk, Inc. CONSTRUCTION COST ESTIMATE Wastewater Treatment Facility Plan Amendment 2 W13.104619 Page 39

VI. CONSTRUCTION COST ESTIMATE GENERAL

Published and unpublished data on costs for similar kinds of construction were utilized to prepare the preliminary construction cost estimates presented below. Annual inflation rates for this type of construction have ranged from approximately 4 percent to 6 percent in recent years. The cost estimates presented are intended for use as a guideline in the decision process. Once preparation of final drawings and specifications is underway, the cost estimates can be refined.

CAPITAL COSTS

The estimated capital costs for the recommended improvement is presented in Table 6.1. As shown on the itemized preliminary cost estimate, engineering, construction observation, and administration are included.

Table 6.1 Capital Cost Estimates for Recommended Alternative 4

Item Alternative 4 Mobilization, Bonds, and Insurance $ 400,000 Flow Equalization Basin N/A Rebuild Static Screen N/A Rebuild Screenings Dewatering Press N/A Repair Grit Removal N/A New Fine Screen, Press, and Grit Removal $ 1,100,000 Trickling Filter N/A Aeration Basin (including concrete, diffusers, and piping)

$ 700,000

Blowers $ 100,000 RAS System $ 100,000 Final Clarifiers $ 600,000 Chlorine Contact Basin $ 150,000 Dechlorination System $ 25,000 Ferric Chloride System $ 100,000 Biosolids Storage $ 1,100,000 Biosolids Handling $ 100,000 "Old" Control Building $ 150,000 New Chemical Feed Systems $ 50,000 Pumps and Piping $ 750,000 Electrical and Controls $ 740,000 HVAC $ 245,000 Miscellaneous N/A Contingencies (10%) $ 641,000 Subtotal $ 7,051,000 Engineering, Administration, and Legal $ 1,410,200

Total

$ 8,461,200


OPERATIONAL COSTS

The estimated annual operational costs include labor, utilities, chemicals and other non-capital related expenditures. Because exact operational costs were not known, these costs are estimated based on experience with other facilities and knowledge of chemical and other costs. Table 6.2 below shows the estimated operational costs changes from the facility’s existing operational costs.

Table 6.2 Operations & Maintenance Cost Changes – City of Staples

Item Alternative 4 Electric Utilities $ 16,000 Chemical Costs (Dechlorination/Ferric Chloride) $ 120,000 Total O & M Cost Adjustment $ 136,000

TOTAL PROJECT COST

Based on project financing for 20-years at 3 percent annual interest, the total annual project costs are summarized in Table 6.3.

Table 6.3 Total Annual Project Costs– City of Staples

Alternative 4 Total Capital Cost $ 8,461,200 Annual Capital Cos $ 569,000 O & M Cost Adjustment $ 136,000

Total Annual Project Cost $ 705,000 Total Present Worth Cost $ 10,484,500

Costs are annualized with a 3 % rate over 20 year period


USER RATES

An increase in user rates will likely be necessary to finance the proposed treatments, unless the city has a significant amount of money in wastewater reserves or has recently raised user rates to account for an upcoming improvements project. The current wastewater user rates are $3.35 per 100 cubic feet of drinking water plus a monthly base rate of $15 per connection. Revenue generation is estimated based on 1,043 connections. See Table 6.1 for estimated user rates for each alternative (based on the annual costs presented in Table 6.3). These rates assume that the user rate must include the operations costs for the existing system, as well as the increased O & M costs with the recommended changes.

Table 6.4 Estimated User Rates City of Staples

Base Rate Cost/100 cubic feet Average Bill (500 cubic feet)

Current $15.00 $3.35 $31.75

Alternative 4 $18.00 $7.65 $56.25

Prepared by: Bolton & Menk, Inc. IMPLEMENTATION Wastewater Treatment Facility Plan Amendment 2 W13.104619 Page 42

VII. IMPLEMENTATION IMPLEMENTATION SCHEDULE

The proposed implementation schedule for the wastewater treatment facility improvements is presented in Table 7.1.

Table 7.1 Project Implementation Schedule - City of Staples Item Date City approves concept of wastewater treatment alternative May 2018 Submit a Revised Facility Plan to MPCA May 2018 MPCA reviews and approves Facility Plan June 2018 City requests placement on the 2019 IUP July 2018 City receives notification of placement on 2019 IUP and funding programs September 2018 Prepare plans and specifications Fall 2018 MPCA reviews and approves plans and specifications Spring 2019 Advertise, bid and award construction contract Summer 2019 Initiate construction Summer 2019 Start Up New Facility Spring 2021

Prepared by: Bolton & Menk, Inc. Wastewater Treatment Facility Plan Amendment 2 W13.104619

Appendix A: Preliminary Cost Estimates


Capital Cost Estimates

Item Alternative 1 Alternative 2 Alternative 3 Alternative 4 Mobilization, Bonds, and Insurance $ 250,000 $ 400,000 $ 400,000 $ 400,000 Flow Equalization Basin N/A $ 950,000 N/A N/A Rebuild Static Screen $ 80,000 $ 80,000 $ 80,000 N/A Rebuild Screenings Dewatering Press $ 70,000 $ 70,000 $ 70,000 N/A Repair Grit Removal $ 100,000 $ 100,000 $ 100,000 N/A New Fine Screen, Press, and Grit Removal N/A N/A N/A $ 1,100,000 Trickling Filter $ 250,000 $ 250,000 $ 250,000 N/A Aeration Basin (including concrete, diffusers, and piping) $ 150,000 $ 150,000 $ 700,000

$ 700,000

Blowers $ 100,000 $ 100,000 $ 100,000 $ 100,000 RAS System $ 100,000 $ 100,000 $ 100,000 $ 100,000 Final Clarifiers $ 250,000 $ 600,000 $ 600,000 $ 600,000 Chlorine Contact Basin $ 50,000 $ 150,000 $ 150,000 $ 150,000 Dechlorination System $ 25,000 $ 25,000 $ 25,000 $ 25,000 Ferric Chloride System $ 100,000 $ 100,000 $ 100,000 $ 100,000 Biosolids Storage $ 550,000 $ 325,000 $ 350,000 $ 1,100,000 Biosolids Handling $ 150,000 $ 100,000 $ 100,000 $ 100,000 "Old" Control Building $ 150,000 $ 150,000 $ 150,000 $ 150,000 New Chemical Feed Systems $ 50,000 $ 50,000 $ 50,000 $ 50,000 Pumps and Piping $ 200,000 $ 350,000 $ 750,000 $ 750,000 Electrical and Controls $ 350,000 $ 450,000 $ 450,000 $ 740,000 HVAC $ 50,000 $ 150,000 $ 150,000 $ 245,000 Miscellaneous $ 100,000 $ 100,000 $ 100,000 N/A Contingencies (10%) $ 312,500 $ 475,000 $ 477,500 $ 541,000 Subtotal $ 3,437,500 $ 5,225,000 $ 5,252,500 $ 7,051,000 Engineering, Administration, and Legal $ 687,500 $ 1,045,000 $ 1,050,500 $ 1,410,200

Total $ 4,125,000 $ 6,270,000 $ 6,303,000

$ 8,461,200


Appendix B: City Council Presentation Materials


City Council Presentation to be added at a later date

Documents

Wastewater Treatment Facility Plan Amendment 244315AD6-8633-4D56-A3F9... · Wastewater Treatment Facility Plan. Amendment 2. Staples, Minnesota April 2018. Submitted by: Bolton &