Large Subsurface Treatment Large Subsurface Treatment Systems in MinnesotaSystems in Minnesota

Brett Ballavance, P.E.Brett Ballavance, P.E.

MPCA, DuluthMPCA, Duluth

New Wave of Wastewater TreatmentNew Wave of Wastewater Treatment

Aging Infrastructure in MinnesotaAging Infrastructure in Minnesota

2005 WINS Study (Wastewater Infrastructure Needs 2005 WINS Study (Wastewater Infrastructure Needs Survey)Survey)– 57% of MN sewer systems are 30 years old or older57% of MN sewer systems are 30 years old or older– 14,668 miles of sewer system in the state14,668 miles of sewer system in the state– Statewide average age of WW treatment facilities is 22 yearsStatewide average age of WW treatment facilities is 22 years

Jan. 2006 Report to the LegislatureJan. 2006 Report to the Legislature

Over $3.4 billion of need in Over $3.4 billion of need in the state right now for the state right now for sewer systems & sewer systems & treatment plantstreatment plants

Covering over 1,000 Covering over 1,000 wastewater projectswastewater projects

State Revolving Fund/WIF State Revolving Fund/WIF is providing $121 million is providing $121 million this year for ~30 projectsthis year for ~30 projects

$250-$300 million $250-$300 million requested each yearrequested each year

At the same time federal At the same time federal funding is being reduced funding is being reduced (cut 30% in last 2 years)(cut 30% in last 2 years)

Growth of MSTSs & LSTSs in MNGrowth of MSTSs & LSTSs in MN

Big increase in the # of Big increase in the # of LSTSs in MinnesotaLSTSs in Minnesota– ~109 LSTSs in the state~109 LSTSs in the state

– Approx. 76% permitted in Approx. 76% permitted in last 7 yearslast 7 years

Nearly 880 domestic Nearly 880 domestic MSTSs in stateMSTSs in state

Agency is responding by Agency is responding by creating new toolscreating new tools– Design Guidance for LSTS (3Design Guidance for LSTS (3rdrd version version

soon)soon)

– New chapter 7081 rules for MSTSNew chapter 7081 rules for MSTS

Cluster System TermsCluster System Terms ISTSISTS

– Individual Sewage Individual Sewage Treatment SystemTreatment System

– Single home systemsSingle home systems MSTSMSTS

– Medium-sized Sewage Medium-sized Sewage Treatment SystemTreatment System

– Cluster, less than Cluster, less than 10,000 gpd of flow10,000 gpd of flow

LSTSLSTS– Large Subsurface Large Subsurface

Treatment SystemTreatment System– Cluster, greater than Cluster, greater than

10,000 gpd of flow10,000 gpd of flow

6A

3A

2B

1A

2A

1B

3B

4A

9B

20A

4B

8A

5B

22A

20B

10B

5A

8B

11A

13A

24B

22B

11B

21A

12B

24A

10A

31B

16A

21B 28B

27A

23A

18B

25A

27B

29A

13B

9A

18A

14B

30B

26B

36B28A

31A

25B

34A

16B

12A

6B

19A

26A

52A

7A

17A

17B

14A

19B

48A

35B

32A

33A

15A

23B

7B

15B

36A

29B30A

New Discharge Impact Map as a Result ofAnnandale-Maple Lake Court of Appeals Decision

and Minnesota River Dissolved Oxygen TMDL

0 30 60 90 120Miles

Disclaimer: Map is based on information obtained through discussion with communities and industries and represents information that could change.

­Source information as of:

October 27, 2005

Draining to Lake Pepin, Nutrient Impairment

MN River Low DO TMDL Area

Nutrient impaired lake watersheds

Three mile buffer

Ammonia

Low DO

Ammonia and Low DO

Biota Impairment

Annandale-Annandale-Maple Lake Maple Lake Court CaseCourt Case

Undersewered Undersewered Areas in Minn.Areas in Minn.

19961996

Summary of LSTSs in Minn.Summary of LSTSs in Minn.

109 total109 total Region w/ Most: Metro Region w/ Most: Metro

(36) followed by (36) followed by Brainerd (35)Brainerd (35)

County w/ Most: County w/ Most: Sherburne (15) followed Sherburne (15) followed by Washington (12) & by Washington (12) & Scott (10)Scott (10)

~2.5 million gpd total ~2.5 million gpd total treated by LSTSstreated by LSTSs

Typical LSTS Flow DiagramTypical LSTS Flow Diagram

Use with the permission of North American Wetland EngineeringUse with the permission of North American Wetland Engineering

Secondary Treatment Tech.Secondary Treatment Tech.

Recirculating sand filters: 22Recirculating sand filters: 22 Constructed wetlands: 12Constructed wetlands: 12 Recirculating gravel filters: 10Recirculating gravel filters: 10 AdvanTex textile filters: 9AdvanTex textile filters: 9 FAST units: 7FAST units: 7 Peat filters: 4Peat filters: 4 SBRs: 2 (?)SBRs: 2 (?) None: 36None: 36

Starting Point – LSTS GuideStarting Point – LSTS Guide

LSTS Guide HighlightsLSTS Guide Highlights

Do I need a MPCA permit?Do I need a MPCA permit? Preliminary Site Evaluation (up front Preliminary Site Evaluation (up front

planning)planning) Soils Evaluation/BOD and TSS treatmentSoils Evaluation/BOD and TSS treatment Pathogen Treatment Pathogen Treatment Nitrate Nitrogen TreatmentNitrate Nitrogen Treatment Areal Drainfield SizingAreal Drainfield Sizing

LSTS Guide HighlightsLSTS Guide Highlights

Phosphorus TreatmentPhosphorus Treatment Hydrogeologic EvaluationHydrogeologic Evaluation Septic Tank Sizing and Design IssuesSeptic Tank Sizing and Design Issues Sewer System DesignSewer System Design Permit Application SubmittalPermit Application Submittal

Do I Need a State Permit?Do I Need a State Permit?

30-homes requirement 30-homes requirement being eliminated ?(likely)being eliminated ?(likely)

Old state permit thresholdOld state permit threshold– 10,000 gpd or10,000 gpd or– 30-homes or more30-homes or more

New state permit thresholdNew state permit threshold– Just the 10,000 gpdJust the 10,000 gpd

Preliminary Site EvaluationsPreliminary Site Evaluations

New version of guide will have more of an New version of guide will have more of an emphasis on first doing an up front desktop emphasis on first doing an up front desktop analysis.analysis.

Main goal is to identify potential problem Main goal is to identify potential problem issues & to justify a more detailed and costly issues & to justify a more detailed and costly evaluation of the site.evaluation of the site.

More resources listed.More resources listed.

Soils EvaluationSoils Evaluation 11stst & 2 & 2ndnd version – PSS version – PSS

preferredpreferred

33rdrd version – PSS version – PSS required ?(likely)required ?(likely)

Soil sizing factorsSoil sizing factors– 2 lists down to 12 lists down to 1– All for pretreated effluentAll for pretreated effluent– ?? May change???? May change??

Pathogen TreatmentPathogen Treatment

No changes to this No changes to this section.section.

Yet we are considering Yet we are considering requiring monitoring requiring monitoring wells directly below the wells directly below the middle of the drainfield middle of the drainfield to monitor both to monitor both mounding height and mounding height and to take fecal samples to take fecal samples to evaluate to evaluate performance.performance.

Nitrate Nitrogen ConcernsNitrate Nitrogen Concerns Some older LSTSs have Some older LSTSs have

high N levels in wellshigh N levels in wells Some areas have high Some areas have high

background levelsbackground levels LSTSs/MSTSs contribute to LSTSs/MSTSs contribute to

this problemthis problem Agency developed LSTS Agency developed LSTS

nitrogen policynitrogen policy– Treat (denitrify) to 10 mg/lTreat (denitrify) to 10 mg/l– Or model to show Or model to show

compliance at property compliance at property lineline

Nitrogen Policy ChangesNitrogen Policy Changes

Previous policy/guide – 3 optionsPrevious policy/guide – 3 options– End-of-Pipe 10 mg/l total nitrogenEnd-of-Pipe 10 mg/l total nitrogen– Model 10 mg/l at boundary & install gw wellsModel 10 mg/l at boundary & install gw wells– Model 5 mg/l at boundary & no wells neededModel 5 mg/l at boundary & no wells needed

New policy/guide – 2 optionsNew policy/guide – 2 options– End-of-Pipe 10 mg/l total nitrogenEnd-of-Pipe 10 mg/l total nitrogen– Model 10 mg/l at boundary & install gw wellsModel 10 mg/l at boundary & install gw wells

Tertiary Treatment - DenitrificationTertiary Treatment - Denitrification

So far 3 technologies So far 3 technologies approvedapproved

11 total systems but 3 11 total systems but 3 technologiestechnologies

Fall under the heading of:Fall under the heading of:– ““Denitrification processes Denitrification processes

with supplemental substrate with supplemental substrate addition”addition”

– Carbon source addition, Carbon source addition, attached growth denitattached growth denit

Approved Denit SystemsApproved Denit Systems

Chemical (carbon source) additionChemical (carbon source) addition– Acetic acid approved for 10 cases so farAcetic acid approved for 10 cases so far– ““Fresh” wastewater carbon source for 11thFresh” wastewater carbon source for 11th– Methanol, “Micro C”, etc. also workMethanol, “Micro C”, etc. also work

Basic concept of this type of denitBasic concept of this type of denit– Nitrify in the secondary treatment unitNitrify in the secondary treatment unit– Denitrify in subsequent unit by adding a carbon Denitrify in subsequent unit by adding a carbon

source with attached growth on a substratesource with attached growth on a substrate

DenitrificationDenitrification

HeterotrophicHeterotrophic

BacteriaBacteria

NONO33- - + Organic Matter + Organic Matter N N22 + CO + CO2 2 + OH + OH- - + H + H22OO

NONO33-- can be reduced, under anoxic conditions, to N can be reduced, under anoxic conditions, to N22 gas gas

through heterotrophic biological denitrification as through heterotrophic biological denitrification as shown in the following unbalanced equation:shown in the following unbalanced equation:

Approved Denit SystemsApproved Denit Systems

NAWE Denit UnitNAWE Denit Unit– Nitrified in gravel filter (typical)Nitrified in gravel filter (typical)– Denitrified in subsequent tank with carbon source Denitrified in subsequent tank with carbon source

addition & fixed growth on plastic mediaaddition & fixed growth on plastic media

FAST Denit UnitFAST Denit Unit– MicroFAST for secondary treatmentMicroFAST for secondary treatment– NitriFAST – for further nitrificationNitriFAST – for further nitrification– ABC-N – anoxic denit. ZoneABC-N – anoxic denit. Zone

Fessel Denit UnitFessel Denit Unit

Phosphorus ChangesPhosphorus Changes

500 feet is the new 500 feet is the new trigger for when to trigger for when to evaluate for evaluate for phosphorusphosphorus– Within 500 feet of a Within 500 feet of a

surface water evaluate surface water evaluate adsorption capacity of adsorption capacity of soils for life of systemsoils for life of system

Previous policy was Previous policy was 300 to 2,640 based on 300 to 2,640 based on soil texturesoil texture

Linear Loading RateLinear Loading Rate

Dropping the linear Dropping the linear loading rate section of loading rate section of the guide because it is the guide because it is thought that thought that groundwater mounding groundwater mounding analyses capture this analyses capture this concern for horizontal concern for horizontal movement of water movement of water more appropriately.more appropriately.

Groundwater MoundingGroundwater Mounding

All projects must All projects must evaluate potential for evaluate potential for groundwater mounding groundwater mounding regardless of nitrogen regardless of nitrogen option chosenoption chosen

Thus all LSTS projects Thus all LSTS projects involve some level of involve some level of hydrogeo work beyond hydrogeo work beyond soils analysissoils analysis

Hydrogeological EvaluationsHydrogeological Evaluations

Require investigations into items such as:Require investigations into items such as:– Hydraulic PermeabilityHydraulic Permeability (i.e. slug tests, pumping (i.e. slug tests, pumping

testing, laboratory tests, estimates from grain-testing, laboratory tests, estimates from grain-size distribution)size distribution)

– Aquifer (saturated) ThicknessAquifer (saturated) Thickness (deep borings, (deep borings, hydrogeologic atlas, nearby well boring records)hydrogeologic atlas, nearby well boring records)

– Specific YieldSpecific Yield (literature data, laboratory tests) (literature data, laboratory tests)

Septic Tank Sizing ChangesSeptic Tank Sizing Changes STEP/STEG or community STEP/STEG or community

tankstanks Third option would be a Third option would be a

clarifier – continuous solids clarifier – continuous solids removalremoval

Fourth option would be an Fourth option would be an engineered design or engineered design or vendor/product-specific vendor/product-specific designdesign– Performance-basedPerformance-based

Monitor tank effluent for Monitor tank effluent for secondary treatment design secondary treatment design compliance (lbs BOD/day)compliance (lbs BOD/day)

ConclusionConclusion

LSTSs/MSTSs are likely going to continue LSTSs/MSTSs are likely going to continue as a part of our infrastructureas a part of our infrastructure

Use LSTS Guide as starting point in designUse LSTS Guide as starting point in design Treatment is easy – getting water in ground Treatment is easy – getting water in ground

is often not easy (mounding)is often not easy (mounding) Follow the nitrogen policyFollow the nitrogen policy Plan for system management and O&MPlan for system management and O&M If designed, constructed, and operated well If designed, constructed, and operated well

– can be a viable part of our infrastructure– can be a viable part of our infrastructure

Questions/CommentsQuestions/Comments

For more information call or email me at:For more information call or email me at:– 218/723-4837218/723-4837– Email: Email: brett.ballavance@pca.state.mn.usbrett.ballavance@pca.state.mn.us

Design Guidance for Large Subsurface Design Guidance for Large Subsurface Wastewater Treatment Systems (LSTS)Wastewater Treatment Systems (LSTS)– http://www.pca.state.mn.us/water/wastewater-engineerihttp://www.pca.state.mn.us/water/wastewater-engineeri

ng.htmlng.html Nitrogen PolicyNitrogen Policy

– http://www.pca.state.mn.us/publications/wq-wwprm1-10.http://www.pca.state.mn.us/publications/wq-wwprm1-10.pdfpdf