u.s environmental protection agency

Onsite Wastewater Treatment Systems Manual:

A Performance Based Approach forDesigning and Managing Onsite Wastewater

Systems

U.S Environmental Protection Agency

In the beginning . . . .

And thou shalt have a Paddle upon thy Weapon, and it shall be:

When thou wilt ease thyself abroad, Thou shalt dig therewith,

and shalt Turn Back and Cover that which Cometh from Thee

Deuteronomy 23:13

Where we’ve been . . .

2002 USEPA Onsite Manual

Complements the 1980 Design Manual

Promotes the use of design performance requirements

Advocates perpetual management of all systems

Focuses on risk-based assessments

Available on theInternet and CD

How to access the OWTS Manual

CDs are available at www.epa.gov/owm/onsiteThe online version is available at:

http://www.epa.gov/ORD/NRMRL/

To order a printed version, send a request to:

U.S. EPA/NSCEPP.O. Box 42419

Cincinnati, Ohio 45242-0419

Send an email to [email protected] call 1-800-490-9198 or (513) 489-8190

Summary of manual contents

Background and use of OWTSs Management of onsite systems System performance

requirements Treatment processes and

technologies Treatment system selection

Note:

The Onsite Wastewater Treatment Systems Manual is not intended to determine

appropriate or inappropriate uses of land.

The manual presents information that can be used to select appropriate technologies and management strategies to minimize

risks to human health and water resources in areas not connected to centralized

sewage systems.

Background and use of OWTSs

Current shortcomings

Lack of clear performance requirements Few O&M or management programs Watershed/regional impacts often

ignored Poor public outreach and education Little coordination with planning,

zoning, water resource, and other agencies and stakeholders

Reasons for concern

Public health Water quality Property

values Community

quality-of-life

OWTS pollutants of concern

Nutrients and bacteria from a variety of sources are primary pollutants in

the U.S.

Onsite systems are a source of nutrients and bacteria

Onsite system malfunction rates

U.S. Census Bureau Reports 7-10% National Small Flows Clearinghouse 10% Nelson, Dix, Shepard Survey up to 70% ???

Best professional judgement; failure definitions varied

A significant number of community water systems list onsite systems as a potential contaminant source for drinking water supplies . . .

Buttermilk Bay Assessment

Nitrogensource

Nitrogenconcentration

Loading rate Flow/recharge Totalloading

Onsitewastewatersystems

40 mg/L 6.72 lbN/person/yr

55gal/person/day

(165 gal/dwelling)

66,940 lb

Fertilizer fromlawns

NA 0.9 lb N /1000ft2/yr

18 inches / year 13,721 lb

Fertilizer fromcranberrybogs

NA 15.8 lbsN/1000 ft2/yr

NA 6,378 lb

Pavementrunoff

2.0 mg/L 0.42 lbsN/1000 ft2/yr

40 in/year 1,723 lb

Increasing demand for groundwater

POPULATION GROWTH 100% increase in public

water withdrawals (1960 - 1995)

Food production needs

URBAN SPRAWL Concentrates demand Leads to reductions in

ground water recharge

ECOSYSTEM MAINTENANCE Water supplies are needed to maintain

sensitive ecosystems and/or endangered species (e.g., Pacific NW, FL)

Public Water Supply Withdrawals

0

5

10

15

20

25

30

35

40

45

Withdrawals 1960 - 1995B

illi

on

s o

f G

allo

ns

Per

Day

1970 1975 1980 1985 1990 19951960 1965

Elevated nitrate concentrations in groundwater in Kent County,

MI

Nitrogen sources include agriculture and lawn fertilizers, atmospheric deposition, onsite systems

Source: Kent County Health Dept.

Source Water Assessment & Protection Program

(168,000 PWSs Must Have Complete Assessments By 2003)

1,645(98%)

953(91%)

2,080(98%)

675(95%)

1,687(94%)

8,146(91%)

2,645(96%)

4,211(96%)

2,023(97%)

736(97%)

2,101(95%)

1,274(95%)

6,865(89%)

Puerto Rico490 (74%)

550(96%)

718(96%)

1,329(97%)

1,079(93%)

1,732(93%)

8,352(98%)

1,932(94%)

2,701(94%)

1,199(89%)

1,820(87%)

11,724(99%)

5,801(93%)

1,485 (88%)

702(63%)

2,572(92%)

6,607(94%)

1,527(90%)

1,173 (79%)

4,837(96%)

12,350(98%)

5,939(95%)

1,414(94%)

7,511(97%)

3,776(96%)

10,389(97%)

3,815 (98%)

551 (97%)

4,279 (95%)

712 (67%)

10,630(97%)

2,103(98%)

1,347 (95%)

2,156 (98%)

1,628 (85%)

479 (94%)

3,705 (98%)

141(74%)

1. Delineate Source Water area

2. Contamination source inventory

3. Susceptibility Determinations

4. Public distribution & discussion of findings

Source Water Assessments 2003 Source Water Protection

5. Establish local SW protection risk management measures

6. Develop Contingency Plans

1996 SDWA

Management of onsite systems

Chapter 2 of the OWTS manual deals with system management

The USEPA Office of Water has developed guidelines and a handbook for managing onsite and clustered systems

Management:traditional management

focus . . . .

Permitting: prescribed limits on acceptable sites; prescribed system designs

Installation: oversight of construction and installers and/or licensing, registration

O & M: homeowner booklets and brochures, tank pumping info

Corrective actions: repair or replacement upon receipt of verified complaints

Performance-based management focus:

Performance requirements based on relative risk to valued surface and ground water resources

Management of all systems based on technology and risk assessments Simple systems installed at low densities farther

away from valued resources = lower management intensity

Complex systems or those installed at high densities near valued resources = managed more intensively

Performance-based management elements

Cooperative watershed planning: specifying the necessary water quality to permit a specific use at a specific location downstream of the onsite treatment systems

Performance-based design: requiring specific treatment levels

Operation: renewable system permits, periodic inspections

Maintenance: requiring tank pumping at regular intervals, maintenance contracts

Corrective actions: replacement requires new performance-based designs

Siting and design: Designing a system that meets performance

requirements based on site conditions rather than requiring the site to meet prescriptive

criteria (lot size, soil permeability, depth to groundwater, etc.) needed for the approved system type

System management: Management programs that provide perpetual

system oversight to protect public health, water resources, property

values

What constitutes a performance-based approach?

Overview of performance-based approach

Wastewater characterization

Site evaluation Design boundary

identification & characterization

Regulatory requirements for system performance

Residential wastewater sources/flows

Toilet 26.7%

18.5 gpcd

Shower 16.8%

11.6 gpcd

Bath 1.7%

1.2 gpcd

Clothes washer 21.7%

15.0 gpcd

Dishwasher 1.4%

1.0 gpcd

Faucets 15.7%

10.9 gpcd

Leaks 13.7%

9.5 gpcd

Other domestic 2.3%

1.6 gpcd

Total gpcd = 69.3

Residential wastewater characterization:

flow and strength analyses

Estimate: average daily flows

(or use meter info) hourly and

instantaneous peak flows

wastewater strength (composition) using similar-facility comparisons or sampling info

Wastewater strength can vary considerably

Assessing site conditions

Preliminary review Soil surveys, aerial

photos, geology, slopes

Info from adjacent systems, installers

Reconnaissance survey Landscape

position, vegetation, buildings, drainage, topography

Identification of prospective sites

Assessing site conditions

Consider broader planning needs Clustering of systems

can improve performance, lower capital & O/M costs

Detailed evaluation Soil profile analyses via

backhoe pit Characterize subsurface

wastewater flow path Groundwater

assessment (redox, wells, maps, etc.)

Identify design boundaries

... places where conditions change abruptly… in subsurface infiltration systems, the soil is part of the treatment system.

Infiltrative surface (biomat location)

Restrictive horizons; perched water tables Surface of saturated zone

(groundwater) Point at which performance must

meet water quality goals (SW/GW discharge, point of re-use, spray irrigation, etc. as required by regs)

Common design boundaries

Close-up of trench system design boundaries

Identify desired performance requirements of regulatory

agencies

Assess cumulative ecosystem impacts TMDLs, 303(d) lists Source water

protection (MCLs) Watershed

restoration action strategies

Anti-degradation requirements

Protection of public health No surfacing or well pollution

Protection of water resources Groundwater (pathogens,

nitrate) Surface waters (pathogens,

nutrients) Meet overall water quality

standards Consider existing/planned

system requirements and impacts System densities, critical areas Water resource sensitivities

Identify desired performance requirements (cont.)

Consider source water protection areas when establishing performance

requirements

Surface Water

Ground Water

Performance requirements should also consider watershed-scale

impacts

Assess design boundary loadings

Loadings to treatment system components controls sizing, technology

selection Loadings to the infiltrative

surface controls size of infiltration system

Loadings to restrictive horizons controls vertical placement of

SWIS Loadings to groundwater

controls vertical placement, may limit type

Lateral view of an effluent plume showing its movement through the soil toward design boundaries

Typical treatment train components

Septic tank(s) Single or multiple compartments Watertight; sized for peak flows Equipped with effluent screen to

protect SWIS

Subsurface wastewater distribution Trenches filled with gravel Gravelless trenches (chambers) Pressure-dosed systems

Alternative systems

Treatment train components (cont.)

Alternative systems Mounds, at-

grades, intermittent or recirculating filters

Aerobic units Vegetated

submerged beds

Chapter 4 topics: processes & technologies

Conventional OWTSs Soil based treatment and

distribution systems Use of alternative and

advanced pretreatment systems

Fact sheets for classes of alternative treatment systems and special issues

Treatment processes: components of a conventional soil-based system

Desirable SWIS characteristics

Width: < 3 ft. wide Length: Must meet contour load limits Orientation:Along landscape contours Vert. Placement: High in soil profile; 2 ft

GW/BR Dosing: Uniform over infiltrative surface Landscape pos: Ridge lines, hilltop, shoulder

slopes Drainage: Moderate- to well-drained site

BOD=150 BOD=30 BOD=150 BOD=30

0.2 0.6 0.25 0.150.2 0.5 0.25 0.13

0.4 0.7 0.50 0.180.6 1.0 0.75 0.250.2 0.5 0.25 0.13

0.2 0.6 0.25 0.150.4 0.8 0.50 0.200.2 0.5 0.25 0.13

0.4 0.6 0.50 0.150.6 0.8 0.75 0.20

0.2 0.00 0.05

0.4 0.6 0.50 0.150.6 0.8 0.75 0.20

0.2 0.3 0.25 0.080.4 0.6 0.50 0.15

0.2 0.3 0.25 0.08

0.50 0.25

Shape

Texture

Coarse sand, sand,

loamy coarse sand, loamy sand

Single grain Structureless

Structure

Grade

0.4 1.0

Fine sand, very fine

sand, loamy fine sand, loamy, very fine

sand

Single grain Structureless

Coarse sandy loam,

sandy loamPrismatic, blocky,

granular

WeakModerate, strong

Massive Structureless

PlatyWeak

Moderate, strong

Fine sandy loam, Very

fine sandy loam

Massive StructurelessPlaty Weak, mod.,

Prismatic, blocky,

granular


Prismatic, blocky,

granular


Loam


Silt Loam


Prismatic, blocky,

granular


Sandy clay loam, clay

loam, silty clay loam

MassivePlaty

Prismatic, blocky,

granular

StructurelessWeak, mod.,


Moderate, strong

Sandy clay, clay, s ilty

clay

MassivePlaty

Prismatic, blocky,

granular

StructurelessWeak, mod.,

Weak

Hydraulic Loading

(gal/ft2-day)

Organic Loading

(lbs BOD/1000ft2-day)

0.8 1.6 1.00 0.40

Loadings

How well does soil treatment work?

Very well . . . IF the topography, soil types, and groundwater levels meet requirements.

Source: University of Minnesota Extension

Drip lines high in the soil profile enhance treatment

Can be used on sloping sites with trees, etc.

Dispersal system options:drip irrigation

Other Chapter 4 topics

Aerobic treatment units (ATUs)

Media filters (ISFs and RSFs)

Fact sheets for about a dozen families/classes of available treatment units

Chapter 5:

Treatment system

selection

New system design approach

Rehabilitation of failed onsite system

Failure analysis: types of failure and effects

Failure analysis:

onsite wastewater

failure diagnosis and

correction procedure

Failure analysis:

onsite wastewater

failure diagnosis and

correction procedure

(cont.)

Onsite manual relationship toclustered treatment systems

Systems with capacity to serve 20 or more people per day defined as Class V Injection Wells under US EPA’s Underground Injection Control (UIC) Program Registration and groundwater protection States may have more stringent requirements

Site evaluation issues Design issues Management issues

Cluster site evaluation

Evaluation of ground water mounding potential

Additional contour loading and performance boundary analysis

Additional downstream flow and plume analysis

Cluster system design

Multiple fields (totaling ~ 200% sizing) rotated into/out of service

Greater need for uniform distribution (pressure or drip)

Monitoring well requirements

Cluster system management

Responsible management entity generally required

Proactive inspection and monitoring program required

Additional involvement in planning and oversight of residuals management, land use planning, and O & M programs

Status of EPA Alternative Sewers Manual

EPA supplies are presently exhausted for hard copy distribution

Manual can be viewed on web at www.epa.gov/ttbnrmrl/ by browsingpublications and typing in 625/1-91/024

http://www.epa.gov/ttbnrmrl/

Cluster systems planning

handbook is posted at

http://www.ndwrcdp.org/userfiles/WUHT014

5_web1.pdf

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