Onsite Wastewater Treatment Systems

Municipal Officials Conference:

Managing Onsite Wastewater Treatment Systems

to Protect Long Island’s Waters

March 25, 2014

George Loomis

New England Onsite Wastewater Training Program @ URI

• We are a USDA, state and training class fee funded program

• Outreach through URI Cooperative Extension

• Coverage area: Regions 1&2 – New England, NY, NJ, PR &

USVI

• Provide third party, non-biased technical assistance

• Clientele includes federal and state regulatory agencies,

communities, NGOs, wastewater professionals, homeowners

• Conduct approx. 50 classes a year reaching over 1,800

wastewater practitioners and decision makers

• We perform onsite wastewater research

• Work closely with local and state regulatory programs

NEOWTC @ URI

Long Island and Block Island Sound

What we will cover –

1) Conventional OWTS basics

2) Cesspools

3) Contaminant treatment potential

4) System management - inspection and tank

pumping

5) Intro - Advanced treatment technologies (more

in afternoon session talk)

1) Conventional septic system has

3 main components

Septic tank Soil absorption area

Source: URI Cooperative Extension, New England Onsite Wastewater Training Center

D-Box

Conventional Septic Tank

Inlet

sludge

scum

As scum and sludge layers build and come closer

together, the retention time becomes less and

solids removal efficiency drops, as well as BOD and

FOG removal

Conventional D-Box

Operates on trickle flow

to the lowest pipe invert

D-Box leveling

devices readjust

outlet pipe inverts.

Manufacturers make these for

various pipe sizes.

Separation distance

Defined as: The distance between the base

of a drainfield and the elevation of

the seasonal high water table (or a

restrictive layer)

This varies with jurisdiction. Nassau Co. has a minimum separation to SHWT of 24”

Suffolk Co. has a minimum separation to SHWT of 36”

Drainfield options

Drainfield sizing criteria

• Depends on the soil type

• Number of bedrooms

• The design of a soil treatment area also

depends on the type of system.

• Leaching pools are designed differently

than pipe on stone (tile drainfields).

Min. separation distance to water

table = 3 or 4 feet (Rhode Island)

• In 2008, galleys prohibited in RI for new construction

• Block Island will phase out existing ones

• Produces a deep

installation base

(8 ft.)

• Poor oxygen

diffusion

• Poor aerobic

treatment

potential

2’

8’ 2’

10”-14”

3.5’+/-

Alternative system (shallowest chamber type for shallow SHWT)

Leaching pools

6’

Typical 4 bedroom leaching pool design

(for SHWT 9’ or greater)

8’

Typical 4 bedroom leaching pool design

(for SHWT 11’ or greater)

14’

Typical 4 bedroom leaching pool design

(for SHWT 17’ or greater)

25’ max

A very deep installation

Concentrated footprint

Small infiltrative surface

• NO septic tank

• Substandard system

• Antiquated and inadequate

• Often violates vertical separation distance regulations

• In coastal areas - may be tidally connected

• Prioritize replacement with approved system

2) Cesspools

Source: URI Cooperative Extension, New England Onsite Wastewater Training Center

2) Cesspools defined -

Dry-fit, or minimally

mortared: Concrete

block, brick, fieldstone

Into which flows

sanitary sewage from

a structure

Impractical - solids

storage and liquid

infiltration

Treatment and safety

issues

3) Pollutants common in septic

tank effluent

• TSS, BOD5

• Nutrients - nitrogen, phosphorus

• Volatile organic chemicals (VOCs)

• Pathogenic organisms

- Helminths (septic worms)

- Protozoa

- Bacteria

- Viruses

Vadose zone wastewater treatment

Controlling factors –

• Environmental

Temp., moisture,

oxygen levels

• Wastewater char.

Loading rates,

strength, types

of pollutants

• Soil properties

Physical, chemical,

biological

• Retention time

Unsaturated soil

Water table

Saturated soil

Biomat

Soil-based wastewater treatment

The Goal :

• Unsaturated conditions

• Thin film flow of wastewater

around soil particles

• Pore space in between

particles and/or soil peds

(structural units of soil)

• Gases and air move

in/out

When organic inputs exceed removals and all

soil pore spaces are clogged, then hydraulic

failure occurs.

Failure defined (usually in regs):

Surfacing wastewater = off site movement of

contaminants, loss of treatment, water quality

impairment, and environmental and public

health risks

Source: URI Cooperative Extension, New England Onsite Wastewater Training Center

Biochemical reactivity in soils

• 99% of soil bioreactivity is within 10 – 20 inches of soil surface

Sources:

“Introduction to Soil Microbiology”, Second Edition – Martin Alexander - John Wiley & Sons,1977.

"Soil Microbiology" Selman Waksman - John Wiley & Sons, 1952.

MOST OWTS regs promote deep drainfield placement, well below this reactive zone

Summary - Nitrogen removal in

conventional septic systems

• Less than 15 percent removal in septic tank

• Septic tank effluent composed of organic-N

and ammonium-N

• Limited ammonium adsorption by soil below

drainfield

• Ammonium conversion to nitrate-N

• Nitrate-N very mobile and conservative

• 10 ppm EPA nitrate-N drinking water standard

Summary - Phosphorus (P) removal in

conventional septic systems

• Phosphorus adsorbed to iron, aluminum,

manganese, calcium, and magnesium in

soils

• P removal depends on soil surface area

• Sands have far less surface area than finer

soil particles

• P saturation can and does occur

• Wet soils conditions result in iron removal, so less P removal potential

Summary - Wastewater

microorganism movement

Organism Approx. Size Mobility

Potential

Helminths

Protozoa

Bacteria

Viruses

sand

c. silt

f. silt - c. clay

v.f. clay

low

high

Enhanced removals with aerobic soils and long retention times

Summary –

Emerging contaminants of concern

• Pharmaceuticals

• Antimicrobials

• Endocrine disrupters

• Personal care products (PCPs)

Removals based upon complex biochemistry –

and they are compound and site specific

Aerobic soil conditions and long retention times

are key treatment factors

Life cycle of an unmanaged

conventional septic system

---------- Years----------

T0 Tff Thf siting

design

permitting

installation

home first

occupied

system

hydraulically

fails

// (first flush)

USE

T = time

4) Management

The onsite system

O&M image crisis

Anything beyond

nothing seems like

too much !

Onsite wastewater industry challenge

• Managed centralized treatment plants

• Unmanaged conventional systems

• Managed advanced treatment onsite

systems

Conventional system inspections and tank pumping

Identifies problems Creates an inventory

Protects –

•Owner investment

•Public health

•Water quality

•Resources

•Property values

Managed systems last longer than neglected ones

Costs - $250 (pumping) and $50 to150 (inspection)

Frequency – every 3 to 5 years

Onsite Wastewater Treatment System

Inspector Training Class

Dates & Times:

April 22 – 23, 2014 (2-day class) 8:00 am – 5:30 pm (registration at 7:30 am)

or

April 24 – 25, 2014 (2-day class) 8:00 am – 5:30 pm (registration at 7:30 am)

Location:

Oyster Bay Community Center, Church Street, Oyster Bay, NY 11771

Cost: FREE (normal cost $450)

Class size is limited to 25 people, so please register early to assure a seat.

5) Alternative technology

treatment train

1. Primary treatment zone

2. Alternative technology

Secondary treatment 3. Drainfield - Dispersal and advanced secondary / tertiary treatment 4. Controls - timers

• Totally unsewered watersheds

• 30 - 50 % of systems are cesspools

• Very permeable unconfined aquifers

• Groundwater contamination risk

• 8 houses / acre on shallow wells

• Surface water eutrophication risk

• Shellfish closures

Water quality standards for coastal pond systems

• 0.3 - 0.5 mg/l TN and 14 counts / 100 ml F. coliform

Typical application for I&A technologies

Rhode Island southern coast

Advanced treatment technologies approved in RI

ca.1996

• RUCK

• ATUs

• Single pass sand filters

• Recirc. sand filters

• Early textile filters

• Foam biofilters

• Shallow narrow pres. drainfields

• Bottomless sand filters - early

• Modular peat filters

• Textile filters

• Fixed activated sludge systems

• Bottomless sand filters – current

• Denite upflow filters

• Trickling filters

• UV disinfection

• Soil treatment area renovation technologies ca.2014

ca.1983

N removal systems

Bottomless sand filter

Thanks for your attention!

George Loomis

GLoomis@uri.edu

401. 874. 4558

http://www.uri.edu/ce/Cwq/OWT/index.htm