The Small Flows Journal Volume 1, Issue 1, Fall 1994

N

A

C L E A R I N G H O

MALL FLOW

S

A collection of 

professional papers 

on the study of onsite 

and small community 

wastewater issues.

The

Flows

Small

Journal

Volume 1, Issue 1, Fall 1994

N

ATIONAL SMALL FLOW

S

C L E A R I N G H O U S E
The Small Flows Journal Volume 1, Issue 1, Fall 1994

From the Editor ................................................................................... 2

by Jill Ross

Save The Bay's "Toxic Diet" Project .................................................... 3

by Diana Wilder

A Small Community Success Story:

How Pressure Sewers and a Community Septic Tank

are Protecting the Environment at Cuyler, New York ....................... 11

by James V. Feuss, P.E.

R. Paul Farrell, P.E.

Peter W. Rynkiewicz

A Study of Scum Control in Septic Tanks ........................................... 17

by Frank Pearson, Ph.D., P.E.

Manuscript Guidelines and Call for Papers........................................ 24

The Small Flows Journal

Sponsored by:

U.S. Environmental Protection Agency

Haig Farmer, Project Officer

Municipal Support Division

Office of Wastewater

Enforcement and Compliance

Washington, D.C.

National Small Flows Clearinghouse

West Virginia University

John L. Mori, Ph.D., Manager,

WVU Environmental Services and

Training Division

Patricia Miller, Ph.D., Technical Advisor

Jill A. Ross, Editor-in-Chief

Cathleen Falvey, Managing Editor

Jim Williams, Editorial Assistant

Betsy Noullet, Graphic Designer

Interational Standard Serial Number

1079-1531

The Small Flows Journal

National Small Flows Clearinghouse

West Virginia University

P.O. Box 6064

Morgantown, WV 26506-6064

1-800-624-8301

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The Small Flows Journal is funded by

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products constitute endorsement or

recommendation for use.

Printed on Recycled Paper

N

ATIONAL SMALL FLOW

S

C L E A R I N G H O U S E

1

Contents ontents

NA

C L E A R I N G H O

MALL FLOW

S

A collection of 

professional papers 

on the study of onsite 

and small community 

wastewater issues.

The

Flows

Small

Journal

Volume 1, Issue 1, Fall 1994

NATIONAL SMALL FLOWS

C L E A R I N G H O U S E
The Small Flows Journal Volume 1, Issue 1, Fall 1994

2

FFrom the Editor rom the Editor

I

n answer to the interest expressed by

readers of the Small Flows newsletter

and a general demand for technical

information about cost-effective

wastewater treatment systems for small

communities, the staff of the National

Small Flows Clearinghouse (NSFC) is

pleased to present our first issue of The

Small Flows Journal. We hope that The

Small Flows Journal will help to satisfy

the demand for this information

by providing a forum for the

exchange of ideas and methodologies for solving small flows

issues.

The papers presented in this first

issue cover a variety of problems

that may be encountered by small

communities searching for ways

to improve their wastewater

treatment systems. “Save The Bay’s ‘Toxic

Diet’ Project” and “A Small Community

Success Story: How Pressure Sewers and

a Community Septic System are Protecting

the Environment at Cuyler, New York”

both present case studies of communities

that successfully implemented programs

to improve the quality of life for their

citizens. In “Save The Bay’s ‘Toxic Diet’

Project,” methods for identifying and

reducing nonindustrial toxics to the

influent stream are offered. “A Small

Community Success Story” describes,

step-by-step, a community’s decision to

upgrade its sewage disposal system, and

how it accomplished this goal in the face

of severe budget constraints. In “A Study

of Scum Control in Septic Tanks,” the

results of the author’s study could be

applied by a small community facing

similar problems maintaining septic tank

systems. All of these articles deal with

issues that are commonly faced by small

communities.

To ensure the quality of the material

published in The Small Flows Journal,

each manuscript is juried by the journal’s

Editorial Review Board. Board members

(listed on this page) were chosen based on

their distinguished accomplishments and

contributions to this field. All manuscripts

submitted are reviewed by three members

of the Editorial Review Board. Furthermore, the process is completely anonymous, meaning that the identity

of the author is not revealed to

the reviewers during the review

process, and the identities of the

reviewers also remain confidential. This procedure ensures that

authors feel free to submit their

work and that the process

remains fair.

We hope you will enjoy reading

this issue of The Small Flows Journal as

much as we enjoyed preparing it, and that

you will wish to continue receiving it. To

sign up for a free subscription, please fill

out and return the subscription information card on the back cover (no postage is

necessary). Also, we’d very much appreciate you passing the extra card along to a

colleague.

Finally, we’d love to hear your comments

on the journal. Please call or write to let

us know what you think. If you wish to

submit a manuscript for consideration for

publication in The Small Flows Journal,

see the call for papers on page 24.

Sincerely,

Jill A. Ross

Editor-in-Chief

The Small Flows Journal

NAT

CLEARIN

AL SMALL F

EARINGHOU

ATIONAL SMA

Editorial Review Board

From the Editor

James Converse, Ph.D.

Agricultural Engineering

Department

University of Wisconsin

Brian Cooper, P. Eng.

Simcoe Engineering Group, Ltd.

Pickering, Ontario

Donald Gray, Ph.D.

Professor of Civil Engineering

West Virginia University

Anish Jantrania, Ph.D., P.E.

Engineering Consultant

City of Gloucester, MA

Craig Jowett, Ph.D., P. Eng.

Research Associate Professor

Waterloo Centre for

Groundwater Research

University of Waterloo

Jim Kreissl

Environmental Engineer

U.S. Environmental

Protection Agency Center for

Environmental Research

George Loomis, Ph.D.

Natural Resources

Science Department

University of Rhode Island

Karen Mancl, Ph.D.

Associate Professor of

Agricultural Engineering

The Ohio State University

Richard A. Otis, P.E.

Vice-President

Ayres and Associates

Madison, WI

Sherwood Reed, P.E.

Consultant and Principle

Environmental Engineering

Consultants

Norwich, VT

A.R. Rubin, Ph.D.

Extension Specialist and

Associate Professor

North Carolina State University

George Tchobanoglous, Ph.D.

Professor of Civil Engineering

University of California at Davis

Jerry Tyler, Ph.D.

Associate Professor

University of Wisconsin
The Small Flows Journal Volume 1, Issue 1, Fall 1994

Save The Bay's "Toxic Diet"

by Diana Wilder

Preventing water pollution is easier and more cost-effective than cleaning it up, and

although progress has been made in curbing industrial pollutants in larger communities,

small, nonindustrial communities lack strategies for reducing unregulated toxics sources

to the influent stream. This article outlines one environmental organization’s model for

reducing these toxics sources that can be used to help small communities nationwide.

U

nder the Clean Water Act’s 1987

toxic discharge requirements,

wastewater treatment facilities

face increasingly strict limits for

heavy metals and other nonconventional

pollutants. While industrial discharges are

the primary targets of most toxic reduction

strategies and pretreatment efforts, most

minor (and a number of major) wastewater

treatment facilities have no significant

industrial inflows. In nonindustrial

communities, pipe corrosion, households,

and small businesses are the likely sources

of toxics to the influent stream. Reducing

toxics loadings from these unregulated

sources is now a critical issue for small,

nonindustrial wastewater treatment

facilities nationwide.

However, comprehensive toxic reduction

strategies specifically appropriate for these

small flow plants, which comprise the

majority of wastewater treatment facilities

in the U.S., are not yet developed. In the

absence of adequate toxic source reduction

strategies, smaller treatment plants must

consider adding costly effluent “polishing” facilities (EPA, 1989), and

small, nonindustrial communities

are least able to afford

these expensive

upgrades.

In an effort to help one

small town to comply

with the Clean

Water Act

requirements,

Save The Bay, a

local environmental organization, developed a cost-efficient methodology for

identifying and reducing the community’s

nonindustrial toxic sources.

 The Toxic Diet Project

Save The Bay is a private, membersupported nonprofit environmental

organization based in Providence, Rhode

Island, and is dedicated to the restoration

and protection of Narragansett Bay and its

watershed. For the past eleven years, Save

The Bay has compiled and published a

report titled “The Good, The Bad, and The

Ugly” (GBU), an evaluation of the

National Pollutant Discharge Elimination

System (NPDES) permit compliance for

publicly-owned treatment works discharging to the watershed.

The 1993 GBU report revealed a disturbing trend: publicly-owned small flow

treatment facilities have a difficult time

meeting NPDES limits for metals (Save

The Bay, 1993). The town of Northbridge,

Massachusetts, on the Blackstone River is

one of the publicly-owned treatment works

in noncompliance for metals (Camp,

Dresser, & McKee, 1994). To help

Northbridge and other small-flow wastewater treatment facilities meet their permit

limits, Save The Bay initiated the Toxic

Diet project. The goal of the Toxic Diet is

to develop a national model designed to

improve the quality of the nation’s waters

by reducing nonconventional pollutant

loadings to small, nonindustrial wastewater

treatment facilities.

3

SSave The Bay’s “Toxic Diet” Project ave The Bay’s “Toxic Diet” Project
The Small Flows Journal Volume 1, Issue 1, Fall 1994

pollution control—cannot be derived

without human value judgments. The use

of mixing zones and dilution factors, also

often politically influenced, further

complicates the process (GAO, 1994b).

In response to the growing uncertainty of

toxicity assessment and the ambiguity of

federal and state mandates, some national

and international

organizations, including

the International Joint

Commission on the

Great Lakes, favor

pollution prevention and

“zero discharge” of

toxic substances

(Jackson, 1993). The

precautionary approach

rejects the current

regulatory emphasis on

pollution “control”

rather than elimination

(Wilder, 1994). Source reduction, rather

than elimination, is a less threatening and

more politically acceptable incarnation of

the precautionary principle in the U.S.

 An Emphasis on Prevention

The Toxic Diet is based on the idea that

reducing the total amount of toxics in use

is the cheapest, easiest, and cleanest way

for a community to maintain and improve

its environmental quality. As a nation, we

spend far more on cleaning up our

pollution problems than on preventing

them. The U.S. spends $115 billion per

year on pollution control; this figure is

expected to rise to $170 billion annually

by the year 2000. At the same time, less

than one percent of the EPA’s annual

budget is dedicated to source reduction

(GAO, 1994a). At this time, if a small

community wishes to pursue the pollution

prevention approach, it must do so largely

on its own initiative. The Toxic Diet

will provide communities with a

workable model for achieving toxic

source reduction.

Northbridge’s current NPDES permit

contains strict effluent limits for three

metals: copper, lead, and zinc. The limits

Diana Wilder

. . . reducing the total

amount of toxics in use is

the cheapest, easiest, and

cleanest way for a

community to maintain

and improve its

environmental quality.

4

 The Control of Toxics

 through NPDES

Even with full NPDES implementation

and compliance, a watershed might still be

impaired due to the cumulative impact of

multiple pollution sources and long-term

chronic impacts. In response to this

possibility, the U.S. Congress included

Section 303(d) of the Clean Water Act.

This section directs states to identify

impaired waters in which water quality

standards cannot be met through technological controls.

The Blackstone River is currently identified as an impaired body of water. In

1991, the U.S. Environmental Protection

Agency (EPA) and the Massachusetts

Department of Environmental Protection

(MADEP) organized the Blackstone River

Initiative to translate water quality

standards into more stringent controls

(EPA and MADEP, 1992). The Clean

Water Act requires states to establish total

maximum daily loadings (TMDLs) for

each pollutant of concern affecting

impaired waters. A TMDL is an estimate

of a body of water's assimilative capacity.

Assimilative capacity is the assumed

property of a body of water's that enables

it to accommodate a certain amount of

pollution without damage (EPA, 1993).

There are several problems with the use of

assimilative capacity. First, if we attempt

to estimate a level of pollution below

which there are no harmful effects, we

have fallen prey to the “null hypothesis”—

the logical impossibility of universal

negative proof. Second, the causal

relationships between specific pollutants

and specific environmental effects are not

well understood (Jackson, 1993). This

scientific uncertainty severely limits our

ability to determine threshold capacities

for specific pollutants in specific ecosystems. Lastly, actual translation of a TMDL

into permit limits for individual dischargers under NPDES is politically challenging. Definitions of “acceptable levels of

impact” and “harm” or “damage to the

environment”—all necessary elements of

a TMDL’s “scientific” approach to water
The Small Flows Journal Volume 1, Issue 1, Fall 1994

Save The Bay's "Toxic Diet"

are strict in part because the publiclyowned treatment works discharges to a

small tributary of the Blackstone River.

Faced with a choice between dilution

(relocating the treatment facility’s outfall

pipe to discharge directly to the

Blackstone River) or pollution prevention

(reducing metals levels to meet the new

permit limits), the town decided to pursue

source reduction as the best long-term

solution.

Average concentrations of copper and lead

in Northbridge’s treated effluent (0.07

mg/l Cu, 0.04 mg/l Pb) exceed the average

monthly limits by a factor of ten (permit

limits are 0.008 mg/l Cu, 0.002 mg/l Pb).

These concentrations have the potential to

cause lethal and sublethal (reproductive

and/or developmental) impacts to the

aquatic life in the receiving water. Zinc is

less problematic, but still worrisome

(treated effluent averages 0.27 mg/l, with

the permit limit set at 0.068 mg/l). The

challenge lies in identifying the sources of

metals loadings, determining the percent

of contribution for each identified source

to total loadings, assessing the feasibility

of source reduction for each source

identified, and successfully implementing

pollution prevention strategies to attain the

desired permit limits.

According to existing toxic reduction

models, industrial sources and specific

industry types (such as drycleaners or

photographic studios) are the easiest

targets for source reduction. However,

Northbridge and many other small

wastewater treatment facilities do not have

this luxury. Two of the town’s three

industrial sources have already implemented pollution prevention procedures

and discharge very little to the sewage

treatment plant (only seven percent of the

treatment facility’s influent is industrial).

SAVE THE BAY

5

In communities like Northbridge, and in

municipalities where industries are

moving toward closed-loop systems, more

attention must be focused on other

sources. Since the majority of wastewater

treatment plant influent in Northbridge

comes from households and small

businesses, the Toxic Diet will serve as a

model for source reduction of toxics in

small communities, and it will help larger

urban publicly-owned treatment works

that have reached the limit of industrial

pretreatment.

 Project Phase I

The first phase of the Toxic Diet is

currently underway in Northbridge and is

expected to be completed in 1995. The

project involves a source assessment of

four discharger types: industrial, residential, small business, and the drinking water

conveyance system. A preliminary mass

balance will be derived from data obtained

by ongoing sampling of residential,

commercial, and isolated industrial trunk

lines. The following steps outline the

Phase I source assessment methodology:

1 Identify categories of dischargers to

the Northbridge sewer system and

evaluate the loading of copper, lead,

and zinc (pollutants of concern)

through waste audits, mass balances,

and trunk line sampling prior to and

following discharge connections.

2 Identify small quantity generators

discharging to the sewer system and

evaluate loadings of copper, lead, and

zinc through waste audits, mass

balances, and sampling prior to and

following discharge connections.

3 Assess and quantify the loading of

copper, lead, and zinc from the

drinking water conveyance system

and identify the local water supplier’s

schedule for implementation of

corrosion control facilities and the

expected reduction in loading associated with those improvements.
The Small Flows Journal Volume 1, Issue 1, Fall 1994

but the cumulative

impact of thousands of

individual households

can add up to a

significant percentage

of a wastewater

treatment facility’s

total metals loadings

(Dickey, 1991).

As a first step, we

evaluated the methodologies available for

determining per capita

contribution for the

toxics of concern. The

procedure commonly

used is to collect

purchasing data on

consumer goods from

local grocery and

supply stores and use

a series of mathematical formulas to arrive

at a per capita loading (Dickey, 1991). In

Northbridge, many residents work outside

of town and do their shopping elsewhere.

The integrity of loadings derived from this

type of calculation and data sources are

therefore questionable.

To solve this problem, we

designed a household product

use survey for spreadsheet and

statistical analysis. The survey

will identify consumer products

used, and the amount and

frequency of use by residents.

Residential loadings for the

metals of concern will be

calculated using a database of

consumer product metals

loadings developed by Phillip

Dickey of the Washington

Toxics Coalition.

A door-to-door survey effort

was initiated in October 1993

and a “project thermometer”

was installed on the town

common to help increase

awareness of the survey effort

(see photo 1 on page 8). To

Diana Wilder

6

0.90

0.85

0.80

0.75

0.70

0.65

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.01

Cu (ppm)

Figure 1. Toxic Diet Project, Northbridge, MA. Average copper (Cu) in 

residential effluent from five trunk line sites. Regions 1, 2, and 5 sampled 

over four (4) 24-hour periods. Regions 3 and 4 sampled over three (3) 

24-hour periods. Samples were composited by time of day (morning, 

afternoon, evening). Samplings conducted by Save The Bay between 

March and June 1994.

Key: Region 1: Rockdale

Region 2: Benson Rd.

Region 3: New Village

Region 4: Whitin Woods

Region 5: Linwood

Average ppm copper, residential effluent 

(0.44 ppm)*

Average ppm copper, POTW total influent

(0.18 ppm)

* flow-weighted; M=28%, A=40%, E=32%.

NOTE: Residential loadings shown here include loadings from 

source water, source-to-tap corrosion, and domestic uses.

A:

B:

A

B

Morning 

(6:00am - 12:00pm) 

Afternoon 

(1:00pm - 9:00pm)

Evening 

(10:00pm - 5:00am)

FIGURE 2

Average Pb (ppm) in

Residential Effluent in

Northbridge, MA

0.90

0.85

0.80

0.75

0.70

0.65

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.01

Pb (ppm)

Morning 

(6:00am - 12:00pm) 

Figure 2. Toxic Diet Project, Northbridge, MA. Comparison of average lead 

(Pb) concentrations in residential effluent from five trunk line sites and total 

POTW influent lead level. Regions 1, 2, and 5 sampled over four (4) 24-hour 

periods. Regions 3 and 4 sampled over three (3) 24-hour periods. Samples 

were composited by time of day (morning, afternoon, and evening). 

Samplings conducted by Save The Bay between March and June 1994.

Key: Region 1: Rockdale

Region 2: Benson Rd.

Region 3: New Village

Region 4: Whitin Woods

Region 5: Linwood

Average ppm lead, residential effluent 

(0.28 ppm)*

Average ppm lead, POTW total influent

(0.08 ppm)

* flow-weighted; M=28%, A=40%, E=32%.

NOTE: Residential loadings shown here include loadings from 

source water, source-to-tap corrosion, and domestic uses.

A:

B:

A

B

Afternoon 

(1:00pm - 9:00pm)

Evening 

(10:00pm - 5:00am)

FIGURE 1

Average Cu (ppm) in

Residential Effluent in

Northbridge, MA

4 Assess base-line residential contributions of copper, lead, and zinc through

a program of sampling in isolated

residential trunk lines and survey

consumer behavior to identify home

product usage and behaviors that may

significantly affect loading of the

pollutants of concern.

In Northbridge, the problem of isolating

each categorical discharger’s contribution

to the waste stream is simplified by the

town’s physical layout. There are purely

residential areas with sewer access points

that guarantee isolation. Town industries

and small businesses are also well-placed

to provide information before and after

discharge points. Monthly sampling of

source waters, wastewater treatment

facility influent and effluent, and

household tap water (first flush) are

also under way.

Residential Assessment

Everyday household products, such as

laundry detergent, shampoo, soap, and

general cleaners, contain trace amounts of

metals and other toxics. A single

household’s contribution is insignificant,
The Small Flows Journal Volume 1, Issue 1, Fall 1994

1.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.20

Zn (ppm)

Figure 3. Toxic Diet Project, Northbridge, MA. Comparison of average zinc 

(Zn) concentrations in residential effluent from five trunk line sites and total 

POTW influent lead level. Regions 1, 2, and 5 sampled over four (4) 24-hour 

periods. Regions 3 and 4 sampled over three (3) 24-hour periods. Samples 

were composited by time of day (morning, afternoon, evening). 

Samplings conducted by Save The Bay between March and June 1994.

Key: Region 1: Rockdale

Region 2: Benson Rd.

Region 3: New Village

Region 4: Whitin Woods

Region 5: Linwood

Average ppm zinc, residential effluent 

(0.723 ppm)*

Average ppm lead, POTW total influent

(1.570 ppm)

* flow-weighted; M=28%, A=40%, E=32%.

NOTE: Residential loadings shown here include loadings from 

source water, source-to-tap corrosion, and domestic uses.

A:

B:

A

B

3.50

2.00

Morning 

(6:00am - 12:00pm) 

Afternoon 

(1:00pm - 9:00pm)

Evening 

(10:00pm - 5:00am)

Save The Bay's "Toxic Diet"

date, 250 surveys have been completed—

enough to begin analysis.

In conjunction with the survey, residential

wastewater was sampled over a fourmonth period, from March to June 1993

(see photo 2 on page 9). Samples were

collected in five isolated residential

regions over three to four days using an

Isco model #1680 automatic sampler. One

250 ml. sample was taken per hour over

each 24-hour period. Samples were

preserved to < 2 pH with HNO3

 according

to standard procedure. Each day’s round of

24 samples was composited manually into

three time-specific categories (morning,

afternoon, and evening) corresponding to

periods of high and low water use. This

time-specific data will be compared to

survey questions, which measure the time

and frequency of certain household

cleaning chores, water consumption

patterns associated with these activities,

and product metals loadings to help

determine specific activities that contribute

significant amounts of metals to the

influent stream.

The four-month

residential

sampling phase

was completed in

June 1994. During

the sampling

phase, residential

effluent comprised roughly

one third (30

percent) of total

wastewater

treatment facility

inflow. Preliminary analyses

indicate that

copper, lead, and

zinc levels

fluctuate according to the time of

day and from

region to region

(fig. 1-3). A

comparison of

average residential and total

treatment facility influent metals levels

show that residential concentrations of

copper (fig. 1) and lead (fig. 2) are diluted

by nonresidential inflows containing

lower levels of these metals, while zinc

levels increase dramatically: a residential

average of 0.701 mg/l compared to 1.57

mg/l Zn in publicly-owned treatment

facility influent (fig. 3). This indicates

significant zinc loadings from nonresidential sources. Subsequent analyses of

drinking water and first-flush samples will

determine the percentage of metals

loadings in residential effluent attributable

to source water and corrosion.

Small Business Assessment

INFORM, a nonprofit research organization, found that many businesses do not

pursue pollution prevention because they

do not believe such practices will improve

their operations or save them money

(INFORM, 1985). Such perceptions exist

because business owners and managers

are largely unaware of inefficiencies in

their operations. Therefore, the best

approach for small business and industry

is based on business owner/operator

education.

To accomplish this goal, Save The Bay, in

cooperation with the Massachusetts Office

of Technical Assistance (MOTA) and the

Town of Northbridge, organized two

workshops to inform small businesses of

the free technical advisory services

available through MOTA’s outreach

program. Upon invitation, MOTA personnel or volunteers trained in pollution

prevention assessment conduct free audits

of business operations. These audits are

confidential, which should allay the fears

and concerns of business owners. Following the audits, technical advisors assess

the information and recommend alternative processes. The information provided

by waste audits indicate estimated source

reduction potentials for each business

type. This information will be combined

with trunk line sampling prior to and after

sewer tie-ins. From this base line data,

Save The Bay will develop a pollution

prevention strategy specifically designed

7

FIGURE 3

Average Zn (ppm) in

Residential Effluent

in Northbridge, MA
The Small Flows Journal Volume 1, Issue 1, Fall 1994

for each business shown to be of

significance.

For the businesses requiring capital outlay

to improve their processes, Save The Bay

will assist in obtaining low- or no-interest

loans. Community involvement, fostered

by citizen participation in the survey and

concerns that stem from a rate-supported

facility, will help in implementing

pollution prevention strategies.

Drinking Water Conveyance Systems

A major study of residential service lines

in Sacramento, California, revealed that

water distribution systems can significantly increase metals concentrations

before the water is used by residents

(Burnham, 1994). According to the study,

the composition of conveyance pipes

determines what type of metals leach into

the passing water; newer systems tend to

show increased levels of copper and zinc,

while older systems show higher levels of

lead, mercury, and zinc. Therefore, the

ages of the houses, businesses, and water

conveyance systems in the region are

significant factors in estimating loadings

sources for these specific metals.

To estimate metals loadings from drinking

water pipe corrosion, first-flush samples

of standing tap water were taken at ten

residential sites over a period of eight

months in conjunction with an ongoing

corrosion control study. Metals concentrations from these sites will be averaged

based on the distance of the sample sites

from the source wells and the ages of

residences taken from the household

surveys to estimate total corrosion

loadings from the drinking water conveyance system.

 Project Phase II

In Phase II of the Toxic Diet project,

potential source reduction for the pollutants of concern will be evaluated through

the application of both pollution prevention technologies currently available and

best management procedures. In the case

of the drinking water conveyance system,

Diana Wilder

the potential for further reduction of

loadings from enhanced corrosion control

methods will be assessed.

Other Source Reduction Options

In the course of this study, several

additional areas of concern emerged.

These concerns arose as we expanded our

scope to assess all significant additives to

the wastewater stream. Additives to

drinking water for corrosion control and

disinfection additives at the treatment

plant itself can significantly impact the

publicly-owned treatment work’s ability to

meet permit limits. Consequently, these

factors were included for evaluation.

Wastewater Treatment Operations

Wastewater treatment facilities are

themselves sources of several

nonconventional pollutants, primarily

chlorine and dechlorinating substances.

Several options are available to reduce the

use of toxics at the treatment plant.

As a nonchemical

process, ultraviolet

(UV) light has emerged

as a viable, feasible, and

cost-effective disinfection method for smallto medium-flow

publicly-owned

treatment works (EPA,

1991a). EPA studies

show that UV light is an

effective germicidal

agent. UV light leaves

no residual, does not

interact with chemicals

in wastewater, and will

not result in the

formation of toxic

compounds. UV light

can be produced onsite

and has no adverse

safety concerns for

plant staff or nearby

communities. However,

UV light does have its

limitations. In particular, it requires effluent

8

PHOTO 1

A "project thermometer"

is installed on Northbridge’s

town common to publicize

Save The Bay's survey effort.
The Small Flows Journal Volume 1, Issue 1, Fall 1994

Save The Bay's "Toxic Diet"

with relatively low total

suspended solids (TSS)

to ensure effectiveness.

The benign nature of

UV light contrasts

strongly with chlorine, a

highly toxic chemical.

Chlorine is dangerous to

transport, leaves a toxic

residual, and can

combine with other

wastewater elements to

create trihalomethanes

(THMs), potential

cancer-causing agents.

Cost is most likely the

reason that chlorine is

used by publicly-owned

treatment facilities.

Compared to UV, ozone,

and other disinfection

alternatives, chlorination/dechlorination

appears to be relatively

inexpensive. But when

the human health and safety concerns of

chlorination and the negative side effects

of dechlorinating chemicals (sulphur

dioxide and sodium sulfites or sulfite salts)

are taken into account (the creation of

sulfates and subsequent reduction in

dissolved oxygen; and equipment corrosion), they may outweigh any immediate

cost savings. In addition, dechlorination

may not remove 100 percent of the

chlorine residue, THMs, and halogenated

organics remaining after chlorination.

Corrosion Control

Although drinking water utilities can have

significant impacts on the environmental

and operational goals of wastewater

treatment facilities, they are regulated

under a separate set of federal and state

requirements using human health criteria.

Because humans are at the top of the food

chain, safe drinking water standards for

metals and other bioaccumulative toxics

are often less strict than aquatic life

criteria under NPDES. The lower standards for drinking water creates problems

for the publicly-owned wastewater

treatment facility, especially when the

drinking water utility is privately owned.

Drinking water corrosion control programs may result in additional long-term

costs to municipal treatment facilities

(Elmund et al., 1986). Specifically, the use

of sodium hexametaphosphate and other

precipitating agents will increase the

amount of solids in the wastewater stream,

resulting in additional sludge treatment

and removal costs for wastewater treatment plants.

In 1986, the public water utility in Fort

Collins, Colorado, considered the effects

of drinking water corrosion control on

wastewater treatment. This holistic

approach resulted in the elimination of

certain phosphate-based corrosion control

compounds from consideration.

According to the Fort Collins study, the

addition of sodium bicarbonate and lime

can significantly reduce copper and lead

corrosion without imposing additional

treatment costs on the wastewater treatment facility. A five- to six-fold copper

and lead reduction was achieved in Fort

Collins by adding sodium bicarbonate and

lime to the drinking water supply. By

1992, 90th percentile concentrations for

copper were down to .002 mg/l and .166

mg/l for lead. The utility is now considering the use of carbon dioxide (CO2

) in

place of sodium bicarbonate as an even

cheaper alternative (Elmund et al., 1986).

In communities where the drinking water

supply system is privately owned, as it is

in Northbridge, publicly-owned treatment

works will need to find some means, legal

or otherwise, to influence decisions on

additives and treatment methods. Options

for exerting control include the outright

purchase of the utility, strict enforcement

of sewer use ordinances (treating the

water company as an indirect discharger),

and/or cost-sharing arrangements for

improved corrosion control.

PHOTO 2

Northbridge residential

wastewater is sampled in

conjunction with the Save

The Bay survey.

9
The Small Flows Journal Volume 1, Issue 1, Fall 1994

NAT

CLEARIN

AL SMALL F

EARINGHOU

ATIONAL SMA

 Conclusions

When Phase I is completed in 1995, it will

be the town’s responsibility to institutionalize recommended source reduction

strategies. These may include mandates on

piping for drinking water and wastewater,

water conservation, product or chemical

bans (such as the Palo Alto, California,

ban on copper sulfate), or local limits.

Measured reductions in the loadings of

metals to the Northbridge publicly-owned

wastewater treatment facility will determine the project’s success. It is our hope

that the Toxic Diet will provide a way for

nonindustrial communities across the

country to adopt pollution prevention as a

proactive, common-sense strategy for

NPDES permit compliance.

 Acknowledgements

The Toxic Diet Project acknowledges the very

generous support of The Pew Charitable Trusts; the

Blackstone River Valley National Heritage Corridor;

21st Century Environment, Inc.; Isco, Inc.; Robert

Ferrari, Ferrari Engineering, Inc.; Alison McDeedy,

ESS, Inc.; and the residents of Northbridge, MA. The

opinions expressed in this report are those of the

author and do not necessarily reflect the views of the

Pew Charitable Trusts or our other supporters.

 References

Burnam, Jack II, et al. 1994. Source control: testing

program traces toxic discharges from residential

households, Water, Environment, & Technology,

(January): 44-48.

Camp, Dresser, & McKee, Inc. 1994. Draft report:

town of Northbridge, Massachusetts NPDES

permit compliance. Cambridge, MA.

Dickey, Philip. 1990. A database of safer substitutes

for hazardous household products (phase I).

Report by the Washington Toxics Coalition for

the Municipality of Metropolitan Seattle.

Seattle, WA.

Elmund, Keith G, et al. 1986. Corrosion control with

low alkalinity, low hardness surface waters.

Aurora, CO: Black & Veatch Consulting Engineers.

INFORM, Inc. 1985. Cutting chemical wastes. New

York, NY: INFORM, Inc.

Jackson, Tim, ed. 1993. Clean production strategies:

developing preventive environmental management in the industrial economy. Boca Raton, FL:

Lewis Publishers.

Save The Bay. 1993. Special report. The good, the

bad, and the ugly: toxic pollution in

Narragansett Bay and its tributaries. 1992

Wastewater Treatment Plant Performance

Review. Providence, RI: Save The Bay, Inc.

Diana Wilder

Diana Wilder is Save The

Bay’s toxics specialist.

She holds a B.A. in history

from the University of

California, Santa Barbara,

and an M.S. from the

University of Michigan’s

School of Natural Resources. Diana’s primary

interests are water

quality, pollution prevention, and promoting

environmental stewardship through public

education. She previously

worked with the Global

Rivers Environmental

Education Network

(GREEN), and she coordinated the University of

California’s Environmental

Studies Program at Santa

Barbara, where she also

served as lecturer.

For more information on

the Toxic Diet, contact

Diana Wilder at Save The

Bay, 434 Smith Street,

Providence, RI 02908.

(401) 272-3540

Diana Wilder

U.S. Environmental Protection Agency (EPA). 1989.

1988 Needs Survey. Office of Water. Washington,

DC: EPA.

______. 1991. Design manual: municipal wastewater disinfection. Washington, DC:

EPA 625/1-86/021.

______. 1993. Water quality standards handbook,

second edition. Office of Water: Washington,

DC: EPA 823/B-93-002.

______ / Massachusetts Division of Water Pollution

Control. 1992. Blackstone river assessment

phase one (dry weather study) interim report of

data. EPA Region I, Boston, MA: EPA.

U.S. General Accounting Office (GAO). 1994a.

Pollution prevention: EPA should reexamine the

objectives and sustainability of state programs.

Report to the Chairman, subcommittee on

Environment, Energy, and Natural Resources,

Committee on Government Operations, House of

Representatives. (January 1994) Washington,

DC: GAO PEMD-94-8 .

______. 1994b. Water pollution: poor quality

assurance and limited pollutant coverage

undermine EPA’s control of toxic substances.

Report to the Chairman, Subcommittee on

Superfund, Ocean, and Water Protection,

Committee on Environment and Public Works,

U.S. Senate. (February 1994) GAO PEMD-94-9.

Wilder, Robert J. 1994. Prevention rather than cure.

Nature. 369, no. 30 (June): 700.

10
The Small Flows Journal Volume 1, Issue 1, Fall 1994

PROPERTY LINE

OBSERVATION 

WELL

20' MIN.

SEPTIC TANK #1

OBSERVATION 

WELL

4" GATE VALVES

6" GATE VALVES

DOSING CHAMBER 

DBL. ALT. SIPHON

4" PVC PIPE

SEPTIC TANK #2

VALVE PIT

4" PVC PIPE PRESSURE SEWER DISCHARGE 

CHAMBER W/SURGE RELIEF 

VALVE

OBSERVATION 

WELL

OBSERVATION 

WELLS

OBSERVATION 

WELLS

4" PERFORATED PVC 

DISPOSAL PIPE (TYP.)

OBSERVATION 

WELL

100' TYP.

SLOPE 1/32"/FT.MAX (TYP)

FIELD THREE

FIELD ONE FIELD TWO

FIELD FOUR

100' TYP. SLOPE 1/32"/FT.MAX (TYP)

20' MIN.

6" PVC

6" PVC 6" PVC

6" PVC

N

 Small Community Success Story: Small Community Success Story:

C

uyler is an unincorporated hamlet

of about 130 people located in the

Township of Cuyler, a rural area of

upstate New York approximately

40 miles south of Syracuse. Cuyler is

literally a crossroads community, being

situated at the junction of New York State

Route 13, several county routes, and a

former major railroad route. It is economically depressed, agriculturally oriented,

and has many homes well over a century old.

In the early 1970s, the Cortland County

Health Department and Cuyler citizens

became concerned over the aesthetic and

public health consequences of individual

septic systems, which failed seasonally,

and of numerous surreptitious “straight

pipes” into drainage ditches. The county

health department was presented with the

dilemma of finding a way to solve this

serious problem within their very limited

AA

How Pressure Sewers and a Community Septic System are

Protecting the Environment at Cuyler, New York

by James V. Feuss, P.E.; R. Paul Farrell, P.E.;

and Peter W. Rynkiewicz

resources. The county board of health

modified the public health engineer’s job

to include the title of town engineer for

the town of Cuyler. Thus was born one of

the earliest “self-help” projects in

New York State (NYS), though that term

was not yet in general use (Feuss and

Farrell, 1994).

Wastewater Treatment

The county health department evaluated

many options to abate the public health

hazard in Cuyler. Surface discharge

options were eliminated by a New York

State Department of Environmental

Conservation (NYDEC) study that

determined that none of the streams

within a reasonable distance had the

required assimilative capacity. In response

to the town’s need for a “minimum

maintenance” and “zero discharge”

treatment plant, a system containing two,

5000-gallon septic tanks, dosing siphons,

and soil absorption systems was chosen.

The system was designed so that the tanks

can be operated individually, in series, or

in parallel. To compensate for a high

natural water table, the soil absorption

system was constructed by bringing in

1605 m3

 (2100 yd3) of fill, which was

placed over existing pasture land. The soil

absorption system consisted of 730 m

(2400 ft) of trench, divided into four equal

sections. The overall plan of the treatment

system is shown in figure 1, and the

profile is shown in figure 2.

A Small Community Success Story

A low pressure sewer system using grinder pumps was installed, mainly by volunteers and town

residents, to upgrade a small town’s sewage disposal system. Performance of the system has

consistently met or exceeded expectations. The case study presented in this article proves that a

small community with severe budget constraints can work together to provide a healthier environment for its residents.

11

FIGURE 1

Overall Plan of

Cuyler Treatment System
The Small Flows Journal Volume 1, Issue 1, Fall 1994

115

110

105

100

95

90

2 + 30 2 +20 2 + 10 2 + 00 1 + 90 1 + 80 1 + 70 1 + 60 1 + 50 1 + 40 1 + 30 1 + 20 1 + 10 1 + 00 0 + 90 0 + 80 0 + 70 0 +60 0 + 50 0 + 40 0 + 30 0 + 20 0 + 10 0 + 00 

EXISTING GRADE

DIVERSION DITCH

VALVE BOX SEPTIC TANK #2

SEPTIC TANK #1

PRESSURE 

SEWER 

DISCHARGE 

CHAMBER DOSING 

CHAMBER

END 6" DISTRIBUTOR 

PIPE (FIELD ONE)

END DISTRIBUTOR FINISH GRADE PIPE (FIELD THREE)

VALVE 

ELEVATION

PIT

1

3

1 3

FEET

Normal operation calls for using one

section on each side with alternate dosing.

These sections are in operation for 12 to

24 months while the other two sections

“rest” to permit them to restore their

absorption capacity biologically. Eight

monitoring wells were strategically placed

to ensure that no downstream plume went

beyond permissible boundaries. The

groundwater gradient is toward a wetland

on the north side of NYS Route 13.

 Design of Pressure Sewers

Many options were considered for the

proposed wastewater collection system.

Conventional gravity sewers would have

been extremely expensive due to the depth

of cuts required to retrofit service connections to existing homes. In addition, two

pumping stations and a major road cut

would have been necessary. On the basis

of information gathered from technical

reading and attendance at an occasional

seminar, the county public health engineer

decided that low pressure sewers using

grinder pumps warranted further investigation. This interest was reinforced by the

favorable results of a pressure sewer

demonstration project that had been

recently completed in Albany, New York

(Carcich, Hetling, and Farrell, 1972). This

work had been done jointly by the

research unit of the NYDEC and the

Environment/One Corporation. The

project was supported by a research grant

from the U.S. Environmental Protection

Agency (EPA), and the report has become

a classic on

pressure

sewers.

Environment/One,

a leading

manufacturer of grinder pumps based in

Schenectady, was contacted for product

information and application engineering

inputs to a preliminary piping system

design. The original collection system

design specified an H-shaped layout with

two main branches and one main connecting the two branches, serving the 41

buildings (mostly single family residences

with a few multi-family homes) in the

village. Piping was sized to minimize

friction loss, while achieving adequate

velocities to assure a self-cleansing

system. The

maximum

pump site

elevation

difference is

12.8 m (42 ft)

and the

maximum

total dynamic

head is

calculated to

be 20.25 m

(66.5 ft)

James V. Feuss, P.E.; R. Paul Farrell, P.E.; and Peter W. Rynkiewicz

12

FIGURE 2

Treatment System Profile

FIGURE 3

Detailed Plans of Cuyler

Sewer System

PVC Pipe -- Type SDR-21

Nominal Size Length-m Length-ft

32 mm (11

/4 in.) service laterals 1100 3600

50 mm (2 in.) main 850 2800

75 mm (3 in.) main 275 900

TABLE 1

Total Length of Pipeline

by Size

VALVE PIT

CLEAN OUT

GRINDER PUMP AND 

HOUSE CONNECTION

RAILROAD RIGHT OF WAY

PVC PRESSURE LINE

N

NYS Route 13
The Small Flows Journal Volume 1, Issue 1, Fall 1994

Although the current site required more

engineering, it was much more agreeable

to all. Patient but persistent negotiations

eventually led to the acquisition of this

site and a right-of-way for much of the

pressure pipeline along an abandoned

railway track bed (Rechlin, 1986).

The project was truly a self-help venture.

The county assistant public health

engineer supervised construction and

served as clerk of the works. A local

engineering firm prepared the final plans

and specifications for a minimal fee. A

civic-minded local attorney provided, at

no cost, legal services to include permit

filing, bond applications, and one condemnation. The fill was hauled by the

town and county highway departments,

and the final grading was done by

volunteers.

Total construction costs at the time of

installation (1978) amounted to $166,100,

or $4,153 per house, which is less than

one third of the estimate of $574,300

($14,357 per house) for a gravity sewer

and conventional treatment option. The

construction cost also included the

upgrading of the electrical service to 220

volts for most of the houses, which was

not included in the original estimate. This

cost savings plus a partial grant and a

long-term low-interest loan from the

Farmer’s Home Administration were the

keys to economic feasibility.

The debt is being retired systematically,

and the annual cost per home has been

declining each year. In 1994, the annual

debt service was $105 per household.

Operating cost and reliability data from

start up in 1978 to the present are summarized in table 2. Numbers for the first five

years were taken directly from the Roy F.

Weston evaluation (1983) funded by the

EPA. Data for 1986 through 1993 are

courtesy of Cuyler’s town clerk, who in

April 1994 searched the town records and

made copies for the authors of all sewer

system invoices (Jackson, 1994). These

recent data have been analyzed and

presented in the same format as in the

Weston report. The result is an accurate

A Small Community Success Story

(Weston, 1983). As shown in figure 3, the

chosen piping layout is without loops.

House connections are 32 mm (11/4 in.)

PVC, and the mains are 50 mm (2 in.) and

75 mm (3 in.) SDR-21 PVC. Fire hose

connections were installed in the valve pits

so that sections of the piping could be

bypassed if repairs were needed. To

conform to the anticipated frost penetration depth in Cortland County, the mains

were buried 1.2 m (48 in.) below grade.

Total length of pipeline by size is shown in

table 1, and a plan view of the collection

system is provided in figure 3.

 Economic Factors

An available land area suitable for the

community septic system was found,

albeit with some difficulty. The originally

proposed site had good soil characteristics,

but its proximity to a historic cemetery led

to vehement objection by Cuyler residents.

13

500

450

400

350

300

250

200

150

100

50

0

78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93

Year

TOTAL* Cost / house / year - $

Average $251 per House per Year

* Includes collection, treatment, operation and maintenance and debt service

No Data 1983-85

Start-up—Partial Year

FIGURE 4

Total System Cost Per

House Per Year

(1992 dollars)

TABLE 2

Operating Cost and

Reliablility Data
The Small Flows Journal Volume 1, Issue 1, Fall 1994

and detailed history (except for missing

records from 1983–85) spanning the 17-

year life of the system. The total annual

system costs (collection, treatment,

operation, maintenance, and debt service)

are shown in figure 4. These do not

include individual electric expenditures,

which typically amount to 200 kwhr or less

per year.

Grinder pump operation and maintenance

costs on a per house basis, excluding the

individual electric bills, are shown in

figure 5. These annual costs have been

adjusted to 1992 dollars using the Consumer Price Index to compensate for

inflation (Department of Commerce,

1993). Annual costs as expressed in

constant (’92) dollars, have averaged $63

per pump per year for the 17 years since

operation began. Because the system is so

small and parts are quantity purchased at

irregular intervals, the annual costs exhibit

a noticeably cyclic tendency. The per

pump cost for operation and maintenance

is also plotted on figure 5 as a moving

three-year average, which smooths out the

peaks and valleys and gives a more useful

long-term figure for budgeting purposes.

These pumps have static-type level

sensors with no moving parts in contact

with sewage; consequently, there are no

additional hidden preventative maintenance expenses.

 Operation and Maintenance

The system went into full-time operation

in 1978. Performance has consistently met

or exceeded expectations since that time.

Cuyler is too small to have a formal public

works department, so the occasional

James V. Feuss, P.E.; R. Paul Farrell, P.E.; and Peter W. Rynkiewicz

FIGURE 5

Operation and Maintenance

Costs Per Pump (1992

dollars)

14

Average $63/pump/year

$140

$120

$100

$80

$60

$40

$20

$0

'78 '79 '80 '81 '82 '83 '84 '85 '86 '87 '88 '89 '90 '91 '92 '93

Year

Operation & maintenance cost per pump -($/year)

Pump operation & maintenance $/house

No data 1983-85

3 yr moving average

Start up—partial year

10

9

8

7

6

5

4

3

2

1

0

'79 '80 '81 '82 '83 '84 '85 '86 '87 '88 '89 '90 '91 '92 '93

Year

MTBSC - years

Cuyler N.Y. Cumulative MTBSC* - 4.6 years

* MTBSC = Mean Time Between Service Calls - Years

No Data 1983-85

repairs are done part time by local

residents. Three spare cores (the pump,

grinder, and motor—all in a single unit

that is easily pulled out and replaced)

purchased as part of the original capital

investment are used whenever onsite

repair is not convenient. Service training,

replacement parts, and an occasional core

or motor overhaul are readily available

from a nearby distributor or direct from

the factory.

The cumulative mean time between

service calls (MTBSC) for the project is

4.6 years over the total project life as

shown in figure 6. MTBSC is calculated

by dividing the total number of pumps by

the cumulative average to date service

calls per year. This record is impressive,

especially in light of the fact that the

average age of this pump population is

now greater than 15 years. Grinder pump

design has been subject to continuous

improvement since 1978, but the Cuyler

pumps contain none of these refinements.

A few years ago, former town supervisor

Bob Randall estimated that nearly

one-fourth of the

41 positive displacement grinder

pumps had “not

been touched since

they were originally installed.”

Detailed review of

the data furnished

by the town clerk

shows Randall’s

rough guess was

FIGURE 6

Grinder Pump Reliability
The Small Flows Journal Volume 1, Issue 1, Fall 1994

A Small Community Success Story

pretty accurate. During the past eight

years, there were eight homes (one fifth)

with zero service calls and 16 homes that

required one call. Several of the homes

with multiple calls experienced “shortterm callbacks,” indicating a lack of

training or knowledge needed to fix a

problem correctly the first time. The

poorest reliability record was at a house

that has averaged one call per year. The

complete distribution of calls per house is

plotted as figure 7.

A post-construction evaluation of Cuyler’s

alternative approach was made for the

EPA in 1983 by the consulting firm, Roy

F. Weston, Inc. (1983). The report indicated that after five

years of operation, all

three objectives of the

project (i.e., low cost,

zero discharge, and low

maintenance) had been

achieved and the

system was operating

entirely within expectations. Following are

three important

findings from that

Weston report:

1 . . . although the total cost actually

expended exceeds the $150,000

town-imposed limit, it came very close

to the original estimate, and does

substantiate the fact that the benefit of

lowest possible capital cost was

achieved. This is especially true when

the cost estimates are adjusted to

1978 dollars.

15

16

14

12

10

8

6

4

2

0

0 1 2 3 4 5 6 7 8 9

Number of Service Calls Per House

Number of houses

Distribution of 77 service calls during 1986-93

The average was 1.9 calls in eight years

FIGURE 7

Service Call Frequency

Distribution

PHOTO 1

Cortland County Public

Health Director, Jim Feuss

points out the site of

community septic tank and

soil absorption system.

2 The benefit of discharge elimination

would appear to be completely

achieved.

3 Overall, the operational responsibilities associated with this system have

been easily managed by the small rural

community of Cuyler. The benefits of

minimizing operating costs and

operational requirements, and maximizing system reliability has been

achieved (Weston, 1983, 2-6).

Effluent grab samples taken from the

dosing siphon chamber over a four-week

period during the spring of 1994 averaged

85 mg/l suspended solids. If the influent is

assumed to be 310 mg/l, which is typical

of the Albany Pressure Sewer Demonstration, then the suspended solids removal

efficiency is 73 percent. These results

further substantiate the conclusion from

earlier research that the pre-grinding of

sewage by a grinder pump has no adverse

effect on its ability to settle (Carcich,

Hetling, and Farrell, 1972).

Although the treatment system is designed

for low maintenance, some maintenance is

still required. The septic tanks must be

pumped at least once every two years, and

the operation of the valves and dosing

siphon should be checked monthly.

Maintenance of the system has been

inconsistent in the past; valves have

frozen, the dosing counter has become

inoperable, and solids have entered the

leachfield. The Cortland County Health

Department is currently working with the
The Small Flows Journal Volume 1, Issue 1, Fall 1994

LOWS

ARINGHOUSE

SMALL FLOWS

OUSE

NATIONAL SMA

CLEARINGH

ONAL SM

James V. Feuss, P.E.; R. Paul Farrell, P.E.; and Peter W. Rynkiewicz

16

James V.

Feuss, P.E.

James V.

Feuss, PE,

graduated

from Rutgers

University in

1960 with a

degree in

sanitary

engineering.

He has served as Public Health Director

for Cortland County, New York, for the

last 16 years and as public health

engineer since 1970. He was the

assistant regional director for Region II

of the National Air Pollution Control

Administration, founder and director of

the Suburban Air Pollution Commission

(West Orange, New Jersey) and served

as the technical consultant on Water

and Waste Treatment for Wallace and

Tiernan, Inc.

technical marketing, and engineering

management in the fields of fluids

handling, wastewater processing

equipment, and home appliances.

Previously, Farrell worked for 19 years

at General Electric Company where he

developed, under contract to the

American Society of Chemical Engineers

and the EPA, the first prototype grinder

pump for low pressure sewer systems.

He continues to work with grinder

pumps and pressure sewer systems at

Environment/One Corporation.

Peter W.

Rynkiewicz

graduated

from Cornell

University in

1992 with a

B.S. in

Agricultural

Engineering

and currently serves as the assistant

public health engineer for Cortland county.

Peter W.

Rynkiewicz

If you would like more information about

this article, you can contact Paul Farrell

at Environment/One Corporation, 2773

Balltown Road, P.O. Box 773,

Schenectady, NY 12301; or James Feuss

and Peter Rynkiewicz at Cortland County

Health Department, Division of

Environmental Health, 60 Central Ave.,

P.O. Box 5590, Cortland, NY 13045.

R. Paul Farrell

Jr., P.E.

R. Paul Farrell,

Jr., P.E., is

manager of

engineering at

Environment/

One Corporation in

Schenectady,

NY. His

experience includes product design,

development, applied research,

town to improve routine and preventative maintenance.

 Conclusions

The Cuyler experience illustrates that

a tiny community with limited

resources can, within severe construction and operating cost constraints,

provide itself with effective lowmaintenance sewage disposal and a

healthy, more pleasant environment.

To date, the Cuyler grinder pump

pressure sewer and community septic

system have been performing well

above initial expectations for 17 years

with affordable operating and debt

service costs.

While replacing some of the original

steel gate valves with PVC ball valves

in the summer of 1994, an accumulation of sludge was found in most of

the tile field lines. The town has

embarked upon a program to clean all

of the treatment system lines and to

ensure proper operation of the

alternate dosing system. The original

design of the leachfield facilitates

repair because it allows the isolation

of each of the four fields. Once again

the county board of health has

amended the senior author’s job duties

to include serving as the town’s

engineer to oversee repairs and the

operation and maintenance of the

treatment system. These recent repairs

exemplify the on-going cooperative

relationship between Cuyler residents

and the health department. Both are

pleased and very proud of their joint

accomplishments.

 Acknowledgements

We would like to thank John S. MacNeill Jr.,

P.E., P.C., who provided engineering plans and

specifications for the project; Lynn Jackson,

Cuyler’s town clerk, who provided information

from the town records; and John T. Ryan Jr.,

Esq., who provided legal assistance to the Town

of Cuyler during the project.

 References

Carcich, Italo G., Hetling, Leo J., and Farrell, R.

Paul. 1972. A pressure sewer system demonstration. EPA R2-72-091, U.S. Environmental

Protection Agency: NTIS-PB 214 409

Feuss, James V. and Farrell, R. P. 1994. How

pressure sewers are protecting the

environment. Clearwaters, NY Water

Environment Association Magazine.

23 (winter).

Jackson, Lynn. 1994. Conversation with R. Paul

Farrell, April.

Rechlin, Michael. 1986. The process of

innovation in rural wastewater treatment.

Ph.D. diss., College of Environmental

Science and Forestry. State University of

New York, Syracuse.

Roy F. Weston, Inc. 1983. I/A technology

assessment post-construction evaluation of

Cuyler, New York, grinder pump-pressure

sewer and soil-absorption system. Interim

Report for U.S. Environmental Protection

Agency.

U.S. Department of Commerce. 1993. Statistical

abstract of the United States. Bureau of the

Census, Washington, DC.
The Small Flows Journal Volume 1, Issue 1, Fall 1994

ST AREA

1 MILE

REST AREA

1 MILE

by Frank Pearson, Ph.D., P.E.

A roadside rest area using septic tanks can serve as a laboratory for the study of scum

control. The author had the unique opportunity to test and observe several approaches,

the results of which are reported in this article. Ideas for improving septic tank designs to

help prevent scum accumulation are also offered.

Septage pumping had emptied the tanks

six weeks before the tests began. Two of

the northbound septic tanks were less

heavily loaded and accumulated insufficient scum to study scum control. The

four remaining Westley septic tanks were

studied. Three such tanks have conventional tee inlets, and one tank has a drop

inlet in which inflow enters above the

water level in the septic tank.

Field evaluations also considered two

septic tanks at a roadside rest area near the

town of Turlock, located toward the east

side of the Central Valley. The Turlock

septic tanks both have drop inlets, which

formed plunge pools through the scum at

the inlet manholes. So broad were these

plunge pools that attempts to measure the

scum depth by probing at the manholes

were abandoned.

 Biological Additives

Initial testing focused on enzymatic

additives, which CADOT had selected.

The additive doses and application

methods reflected the respective manufacturers’ general recommendations. However, no waste-specific additive dose

versus response characteristics were

available. Each supplier suggested trials to

determine the requisite dose, but no

standardized additive evaluation protocols

and criteria were available for such trials

and neither were the necessary time or

funding.

Early field tests and laboratory tests

delivered the specified additive dose in

one initial application. Later, in consultation with suppliers, doses were split into

A Study of Scum Control in Septic Tanks

17

R

oadside rest areas contribute to the

comfort and safety of highways all

across the U.S. More than half

of the rest areas operated by the

California Department of Transportation

(CADOT) use septic tanks to dispose of

wastewater from toilet facilities.

At some well-frequented roadside rest

areas in California, scum accumulates

rapidly in the inlet compartments of the

septic tanks, largely from toilet paper used

in the restrooms. Occasionally, scum

blocks the septic tank inlet lines, and

frequently, septage needs pumping more

than once a year. Substituting toilet paper

rated for septic tanks reportedly failed to

control the scum, so other control methods

were investigated. This article describes

the study and its results, and offers some

solutions for scum control.

Scope of the Tests

Scum control tests were conducted in

septic tanks at the Westley roadside rest

areas, located in an isolated area near the

junction of Interstates 5 and 580 at the

western edge of California’s Central

Valley. Laboratory tests were also

performed for this site. The Westley

site has separate northbound and

southbound rest areas, each

with three septic tanks. Two

such tanks each serve both

women’s and men’s restrooms,

while the third tank serves the

recreational vehicle (RV) dump

station. Each Westley septic tank has four

precast concrete cells in series, of 17 m3

(4500 gal) total capacity.

SScum Control in Septic Tanks cum Control in Septic Tanks

A Study of
The Small Flows Journal Volume 1, Issue 1, Fall 1994

two or three applications through the field

test runs. The test septic tanks differed

according to inlet type, waste type, and

loading. To help distinguish the effects of

additives and tanks on scum, additives

were rotated among the tanks in later runs.

 Field Methods

Field tests monitored how treatments and

conditions affected the depth of scum

exposed at manholes at either end of the

inlet compartments of the four Westley

test septic tanks. Field test runs initiated

by pulverizing the scum at each manhole

using a paddle plunger. Then additive was

blended into the scum at the inlet manholes of the three treated septic tanks,

while the fourth control tank received no

additive.

After pulverizing the scum and dosing

additive-treated scum, the depth of scum

was measured

at each

manhole. The

measurement

device was a

calibrated rod

hinged at one

end to a

200-mm (8-

in.) diameter

sheet metal

plate.

Initially, the

plate set to the vertical was sliced through

the scum. Then the plate was rotated to

the horizontal and pulled up until resistance was felt as the plate contacted the

underside of the scum layer. This permitted reading the scum depth as the rod

calibration mark opposite the upper

surface of the scum. As many as four

depth measurements were obtained over

the exposed scum surface, with fewer

readings from

shallow or fluid

scum layers.

The field tests

comprised five

runs over the three

months available.

Early runs lasted

up to four weeks

but later runs were

briefer. Over the

course of each run,

fresh waste

entering the tanks

replenished the

scum removed

(sunken) by the

control measures

tested. Scum depth

measurements

were nominally

timed on the first,

fourth, and tenth

days after initially

pulverizing the

scum. The following plotted and

tabulated results

show the actual

timings and

TABLE 1—

Decreases (in Millimeters)

from Initial Scum Depth

During Field Runs

Vertical dotted lines mark pulverization of scum, triangles mark additive doses 600 

300

0

300

0

300

0

300

0

Scum depth, mm

Tank 1: drop inlet, additive-dosed, restroom waste

Tank 2: tee inlet, no additve, restroom waste

Tank 3: tee inlet, additive-dosed, restroom waste

Tank 4: tee inlet, additive-dosed, RV dump waste

0 10 20 30 40 50 60 70 80

Days from start of first run

18

FIGURE 1

Scum Depth Histories for

Four Westley Septic Tanks

Septic Tank 1

Restroom Waste

Septic Tank 2

Restroom Waste

Septic Tank 3

Restroom Waste

Septic Tank 4

RV Dump Waste

NO. OF DAYS

RUN NO.

ADDITIVE

DECREASEADDITIVE

DECREASEADDITIVE

DECREASEADDITIVE

DECREASE

Drop Inlet Tee Inlet

1

Mean

4

Mean

10

to

15

Mean

1

2

3

4

5

1

2

3

4

1

2

3

4

B3

B3

B3

A3

C2

––

none

none

B1

none

––

none

none

none

none

––

3

/4

3

/4

3

/4

1

/4

3

/4

280

286

352

264

236

284

304

278

212

––

265

262

0

112

50

106

none

none

none

none

none

none

none

none

none

none

none

none

none

none

none

none

26

178

160

126

58

110

102

150

160

––

137

76

18

46

50

48

C2

C2

C1

B3

B

––

none

none

C1

B1

–– 

none

none

none

none

––

3

/4

3

/4

3

/4

3

/4

1

/4

126

50

114

98

––

97

136

58

96

––

97

66

-88

-8

––

-10

A3

A3

A1

A1

A1

––

none

none

A1

A1

––

none

none

none

none

––

1

/4

1

/4

3

/4

3

/4

38

140

172

90

58

100

122

72

108

––

101

76

-38

84

-88

9

E.g., a decrease of 250 denotes a scum layer some 250 mm less deep 

than at the start of the run. Depth decrease values shown in boldface

differ from zero at the 95% level of statistical significance, by Student's 

t - test. Additive designation A33

/4 signifies some 33/4 kg of Additive A. 

Additve doses listed for day 1 include the dose at the start of the run.

by Frank Pearson, Ph.D., P.E.
The Small Flows Journal Volume 1, Issue 1, Fall 1994

A Study of Scum Control in Septic Tanks

magnitudes of additive doses and depth

measurements.

 Field Results

In the text to follow, septic tanks numbered 1 through 4 serve, respectively, the

northbound-east, southbound-east, and

southbound-west restrooms, as well as the

southbound RV dump. The letters A, B,

and C distinguish the additives. In the inlet

manholes of tanks 1 through 4, initial

scum depths were 330, 280, 510, and 250

mm (13, 11, 20 and 10 in.) respectively,

averaged over the five runs. Corresponding

initial depths in the second manholes

averaged 75, 25, 75, and 25 mm (3, 1, 3

and 1 in.), so shallow that effects of

treatment were minor. All scum depths

mentioned below refer to measurements

made in the inlet manholes.

Figure 1 presents scum depth histories for

the four septic tanks, showing when the

scum was pulverized at the start of the

runs and when additive was dosed. Table 1

lists the additive doses, with decreases

from the initial scum depth on the first,

fourth, and tenth days of the runs, and

figure 2 shows the mean decrease from the

initial scum depth during the five runs.

Invariably, the scum mat became shallower during the first day after pulverizing

the scum. From the first to the fourth day,

the scum depth usually fell slightly. After

the fourth day, the scum depth increased at

a rate of some 15 to 25 mm/day (0.6 to 1.0

in./day) as the incoming waste replenished

the scum. Figure 2 reveals the effects of

certain conditions on the decrease in scum

depth after pulverization; namely, the

effects of septic tank inlet type, additive

versus no additive, and restroom waste

versus RV dump waste. Consider the

mean scum depth decreases on the first

day of the runs.

During the first day of the runs, scum

depths declined more in the drop inlet

tank; i.e., by 280 mm (11 in.) in tank 1

with a drop inlet, compared with a mean

of 100 mm (4 in.) in tanks 2 through 4

with tee inlets. Among tee inlet septic

tanks, the scum depth declined about the

same in additive-treated tanks as in the

additive-free tank, and the same in tanks

receiving restroom waste scum as in the

RV dump station tank.

 Statistical Analysis of Field

 Scum Depth Decreases

The field data suggest a statistical

hypothesis for testing; i.e., that decreases

in scum depth were primarily associated

with the type of septic tank inlet rather

than with the presence or choice of

additive. The switching of additives B and

C between tank 1 (drop inlet tank) and

tank 3 (a tee inlet tank) after run 3 of the

field tests permits testing of that hypothesis. For that purpose, regression analysis

of day 1 scum depth decrease data yield

the coefficients d, e, and f in the following

equation:

F = dD + eE + f (1)

in which:

F = day 1 scum depth decrease,

in millimeters;

d, e, and f = numerical coefficients, in

millimeters; and

D and E = Boolean variables identifying the additive type and

inlet type, thus:

D = 0 for additive C,

D = 1 for additive B,

E = 0 for a tee inlet,

E = 1 for a drop inlet.

19

300

250

200

150

100

50

0

Scum depth decrease, mm

Tank 1: drop inlet, additive-dosed, restroom waste 

Tank 2: tee inlet, no additive, restroom waste

Tank 4: tee inlet, additive-dosed, RV dump waste

Tank 3: tee inlet, additive-dosed, restroom waste

Days from start of run

0 2 4 6 8 10

FIGURE 2

Average Scum Depth

Decreases in Five Runs
The Small Flows Journal Volume 1, Issue 1, Fall 1994

by Frank Pearson, Ph.D., P.E.

Regression analysis of the scum depth

decrease data in table 1 yields the

solution:

F = 5D + 185E + 120 ± 56 (2)

The coefficient of the inlet parameter,

e = 185 mm (7.3 in.), exceeds the coefficient of the additive parameter, d = 5 mm

(0.2 in.). The respective partial correlation

coefficients are 0.85 and 0.04. Thus, day 1

scum depth decreases relate more strongly

to the tank inlet type than to the choice

between additives B and C.

Substituting appropriate values for D and

E in equation 2 describes the trend of day

1 scum depth decreases. For example,

with drop inlets (E = 1) and Additive B

(D=1), the scum depth decrease according

to the regression is F = 5x1 + 185 x 1 +

120 ± 56 = 310 ± 56 mm (12.2 ± 2.2 in.).

In case the strong effect of inlet type may

have obscured any effect of additive on

scum depth decrease, day 1 mean scum

depth decreases were compared among tee

inlet tanks. However, Student’s t-test

showed no difference between those

means at the 95 percent significance level.

Nor did depth decreases differ significantly between the restroom waste tanks

and the RV dump station waste tank.

 Laboratory Tests

Laboratory tests can complement field

tests by permitting generally closer

scrutiny of processes, better control of

conditions, and greater replication than

FIGURE 3

Scum Disintegration in Eight

Laboratory Test Columns

FIGURE 4

Septic Tank Scum Layer

Growth Characteristics

20

300

200

150

100

Additive A Additive B Additive C No Additive

Scum depth, mm 300

200

150

100

50

slope = -.19 ± .05 slope = -.22 ± .03 slope = -.20 ± .02 slope = -.29 ± .04

slope = -.34 ± .03 slope = -.44 ± .06

entire 

scum 

layer 

sank

slope = -.23 ± .03

Days from start of run

10 20 50 10 20 50 10 20 50 10 20 50 100

10 20 50 10 20 50 10 20 50 10 20 50 100

1.0

0.8

0.6

0.4

0.2

0.0

Relative scum depth, X

Asymptote

-0.1 -0.2 -0.3 -0.4 -0.5 -0.6

Scum disintegration curve slope, -q

Relative scum accumulation time, T

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

field tests can provide. Laboratory column

and batch reactors loaded with septic tank

scum from the Westley southbound rest

area simulated the operation of septic

tanks. Column reactors simulated the

disintegration of a scum mat in a septic

tank, while batch reactors characterized

the drainage and density of scum.

The Westley scum was homogenized,

screened, and divided. Additive-treated

portions received measured doses of the

additives A, B, or C, and the prepared

scum was loaded into the reactors.

Preliminary tests showed that the batch

reactors worked poorly in daylight, so the

batch reactors were kept in darkened

cabinets, and the column reactors were

covered.

 Column Reactor Tests

Each column was a vertically-mounted

1320-mm (52-in.) length of 73-mm (2.9-

in.) bore clear Plexiglas tubing, stoppered

at the

bottom, and

piped to

maintain a

constant, but

adjustable,

level of

municipal

wastewater.

Two liters

(0.53 gal) of

Westley

scum floated
The Small Flows Journal Volume 1, Issue 1, Fall 1994

depth of scum at unit time, p, may have

approximated the calculated depth of each

initial two-liter charge of scum in a 73

mm (2.9-in.) diameter column, which

amounts to 478 mm (18.8 in.). Substituting these p and q with t = 15 days in

x = pt-q yields a calculated scum depth of

x = 244 mm (9.6 in.). At 15 days, the

observed depths in the additive-free

columns were some 240 and 255 mm

(9.5 and 10 in.).

For a septic tank in the field, the rate of

change of scum depth may be the scum

supply rate minus the disintegration rate.

Functionally, x’=r-qpt-q-1, where r = scum

supply rate, mm/day. Substituting for t,

the differential equation governing scum

depth reduces to x’ = r - qp-1/q

x1+1/q.

Then the scum layer would grow to a

limiting depth at which x’ = 0, which

is (rq-1p1/q)

q/(1+q)

.

For simplicity, normalize scum depth to

X, the fraction of the limiting scum depth.

The normalized limiting scum depth is

unity. Also, normalize time to T, the ratio

of actual time to characteristic time,

T = t

1

/t

2

. Here, t

1

 is the actual scum

accumulation time since the tank was

emptied. Characteristic time, t

2

 , is the

time taken to attain the limiting scum

depth at the prevailing scum supply rate

without any disintegration of scum.

When normalized, the scum supply rate

becomes unity. The normalized differential equation governing scum depth is

dX/dT = 1 - X1+1/q. Figure 4 shows the

relative scum depth and accumulation

time as fractions of maximum depth and

characteristic time. In practice, the

asymptote might be considered to approximate the growth of a scum layer,

with a uniform increase in depth until a

steady-state depth is attained. The steadystate depth and the time to attain it depend

on the scum supply rate and scum

disintegration test results as described

above.

It becomes possible to compare the

steady-state scum depth as estimated from

column test results with field observations

A Study of Scum Control in Septic Tanks

21

on the wastewater. Wastewater was

replaced approximately every week.

Additive-dosed scum received 1 kg/m3 (1

g/L) of additive A, B, or C. The eight

columns gave two columns for each

additive and two additive-free columns.

During the 72 days of column operation,

the floating layers of scum progressively

disintegrated into the wastewater. Total

solids levels in the wastewater increased

through the columns. Grab samples of

wastewater displaced weekly from beneath

the scum layers in the columns showed an

average of 0.67 kg/m3

 (670 mg/L) total

solids, compared with 0.37 kg/m3 (370

mg/L) in column influent. Figure 3 shows

scum depth versus time in the columns, as

log-log plots. The frames show regression

lines and numerical slopes with standard

errors. In one column with the steepest

slope, the entire layer of scum sank during

the test. The slopes were significant at

95 percent for all columns.

Line slopes were more consistent among the additive-free

columns than among treated

columns. For each additive, the

slopes of lines for the treated

columns bracketed the slopes

for additive-free columns. The

regression slopes were compared between additive-treated

columns and untreated controls.

For that purpose, a Boolean

additive variable was incorporated into the regression, as

described previously for field

data. In no case was the

Boolean variable significantly correlated

with scum depth. So no additive was

shown to significantly affect scum

disintegration in the columns.

Figure 3 shows that disintegration kinetics

of a scum layer obey x = pt-q, in which

x = scum depth, t = time, and p and q are

constants, with q values shown as the

slopes of the regression lines.

For the additive-free control columns, the

slopes are -0.23 and -0.29, or approximately -0.25. Also for illustration, the
The Small Flows Journal Volume 1, Issue 1, Fall 1994

No lime, pH 5.8 Limed, pH 8.4

Relative density Relative volume

Additive dose, grams per liter

0.9

0.8

0.7

0.6

0.5

0.4

1.00

0.98

0.96

0.94

0.92

0.90

KEY

Additve A x

Additive B +

Additive C -

No additive

x

+

- -

+x -

+x

+

x + +

- x

- -

x

x

+- +x

- x

+

-

x

+ - x x

- + +

0.1 1 10 0.1 1 10

-

of limiting scum depth at a particular

scum supply rate. One estimator of the

scum supply rate is the rate of recovery of

scum depth at the end of the field runs,

which was quite similar among tanks, as

figure 2 shows. Table 1 (or figure 2)

shows this rate of recovery as r = 25

mm/day (1 in./day) in the septic tank with

the most well-defined recovery, tank 1.

For a scum accumulation rate of 25

mm/day (1 in./day), the limiting scum

depth estimated from column test results

would be (rq-1p1/q

)q/(1+q)= 350 mm (13.8

in.), based on q = 0.25 and p = 478 mm

(18.8 in.) as imputed for additive-free

columns. Accumulation of scum at 25

mm/day (1 in./day) would take 14 days to

attain the 350-mm (13.8-in.) limiting

depth. For comparison, when the field

tests began, the actual depth of scum in

tank 1 was 380 mm (15 in.), six weeks

after pumping the septic tanks. Furthermore, in field tests the scum layer in tank

1 recovered most of that initial depth in

about two weeks, as figure 1 shows. Thus,

an estimate of steady state scum depth

based on column test results matched the

observed scum depth in the field. However, column tests do not address whether

or how certain field conditions such as

septic tank hydraulics or sludge gasification may affect scum disintegration

kinetics.

 Batch Reactor Tests

The batch reactors were 500 mL Erlenmeyer (conical) flasks. Duplicate reactors

by Frank Pearson, Ph.D., P.E.

FIGURE 5—

Scum Volume and Densities

in Batch Reactors

received 500 mL of

scum treated with

additives A, B and C,

at doses of 0.1, 0.1 and

10 kg/m3 (1 kg/m3 =

1 g/L). Quadruplicate

control batch reactors

received 500 mL of

additive-free scum. The

reactors were weighed

before and after filling. In another

identical set of reactors, the scum was

dosed with slaked lime from pH 5.8 to

pH 8.4, because neutralizing the acidity of

the scum might have promoted

biodegradation.

After 28 days in storage, any free water

was poured off. The reactors were

weighed and scum volumes were measured approximately against the flask

calibrations. Scum densities were computed. Figure 5 shows the resulting

relative volume and density of the scum in

the unlimed and limed reactors. Relative

volume is the residual scum volume as a

fraction of its initial 500 mL volume,

being less than unity because water drains

from the scum. Relative density is the

density ratio of scum to water, which must

be less than unity in order for the scum to

float.

For unlimed scum, the drainage of water

during the test approximately halved the

scum volume. Relative volumes averaged

0.52, varying little with additive dose.

Relative densities averaged 0.96. At all

doses of additive B, and at the highest

dose of additive A, the dosed scum was

denser than the

additive-free

scum, though

such dosed

scum was still

generally less

dense than

water.

Liming evidently weighted

the scum,

because most

aliquots of

22

REMOVE THIS TEE 

AND BEND TO 

CONVERT TO 

DROP INLET

FIGURE 6

Schematic Diagram of Septic

Tank Tee Inlet and Drop Inlet
The Small Flows Journal Volume 1, Issue 1, Fall 1994

limed scum sank; relative densities at the

end of the tests averaged 1.01. Relative

volumes averaged 0.93, varying little with

additive dose.

 Conclusions

Scum exists only because it is buoyant.

Lighter-than-water wastes such as fat and

oil always float and should be removed

from the waste if significant. Test column

results show that the toilet paper-derived

scum would sink, possibly by disentraining gas bubbles from the heavierthan-water paper solids. Field results

emphasize agitation as a scum control

measure in septic tanks, particularly in

conjunction with a drop inlet. Sinking the

scum could prolong septage pumping

intervals by exposing the solids to the

degrading sludge. Field results showed

that a drop inlet controlled scum better

than conventional tee inlets did—based on

scum thickness measurements at the inlet

manholes—and that no biological additive

used significantly controlled the scum.

Various methods of mechanical agitation

could help reduce the contribution to

septic tank scum from heavier-than-water

materials such as paper. The simplest

method would be hand plunging at

intervals of perhaps one-half the time

taken for excessive scum to accumulate.

Other mechanized agitation methods

include mechanical paddling, hydraulic

jetting, and pneumatic sparging.

Agitation for scum control would appear

mostly suited to septic tanks larger than

domestic size. Whatever the septic tank

size, agitation should only be used in a

tank with multiple compartments. In a

single compartment septic tank, a drop

inlet or any other agitation would tend to

disrupt settlement and risk the discharge of

excessive solids to the leach field. In any

case, multiple compartment septic tanks

are advisable to avoid high levels of solids

in the effluent, due to agitation of the tank

contents by gas released from the degrading sludge, particularly in summer.

A Study of Scum Control in Septic Tanks

NAT

CLEARIN

AL SMALL F

EARINGHOU

ATIONAL SMA

Alternatively, to lessen or avoid a need for

external agitation, a septic tank might be

designed to safely retain a depth of scum

that disintegrates as fast as it accumulates.

Field observations and laboratory column

test results suggest that for toilet paper

scum mats in septic tanks, deeper mats

disintegrate faster. Deeper scum mats

submerge more, where hydrostatics tends

to dislodge bubbles. For any given rate of

scum supply to the septic tank, the scum

mat will tend to deepen until its rate of

disintegration (plus the rate of any loss of

scum to the septic tank outlet) equals the

scum supply rate.

Septic tank designers might provide

sufficient freeboard in a tank to retain the

limiting depth of scum corresponding to

the prevailing scum supply rate and

disintegration kinetics.

The septic tank inlet should enter at a

level above the limiting scum surface.

Provision for easy conversion between a

conventional tee inlet and a drop inlet

could be advantageous in a multiplecompartment septic tank subject to scum

mat formation. Figure 6 illustrates a

possible arrangement which permits

simple modification to raise the water

level so as to increase scum storage

volume if needed.

 Acknowledgements

Appreciation is expressed for the constructive

suggestions and expert assistance the author

received during this project from S. Bennett P. John,

Ted Bakker, John Williams, and William Nokes, all of

the California Department of Transportation, as well

as for astute comments from anonymous reviewers.

Lettie Mae Kaack, who contributed to the project

report, and the author were affiliated with the

University of California at Berkeley during the test

program. Government funding in partial support of

this study came from the U.S. Department of

Transportation, Federal Highway Administration,

and the California Department of Transportation.

This article reflects the views of the author, who is

responsible for the facts and the accuracy of the data

presented. The contents do not necessarily reflect the

official views or policies of the State of California or

the Federal Highway Administration.

Frank Pearson

Frank Pearson, Ph.D., P.E., is

a task force member for the

forthcoming Water Environment Federation manual of

practice on energy conservation in wastewater

treatment, and was part of

an American Society of Civil

Engineers' structural

inspection team formed

after the 1994 earthquake in

Southern California. Now

retired, his work experience includes, most

recently, an administrative

research position at the

University of California at

Berkeley, where onsite

wastewater disposal was

among his favorite topics.

For more information on

scum control in septic tanks,

contact Frank Pearson,

Ph.D., P.E., at 325 Sparrow

Drive, Hercules, CA 94547-

1508. (510) 799-4217

23
The Small Flows Journal Volume 1, Issue 1, Fall 1994

CLEARIN

AL SMALL F

EARINGHOU

ATIONAL SMA

1 Manuscripts should be printed on

8.5 by 11 inch paper and be double

spaced. The left margin should be

1.5 inches and the right margin

should be 1 inch.

2 Manuscripts should be accompanied

by an abstract of 150 words or less.

3 Authors are requested to follow the

directions given in the American

Society of Agricultural Engineers’

Guide for Refereed Publications,

Monographs, and Textbooks for

preparing the text, tables, and figures

of the manuscript. Contact the

National Small Flows Clearinghouse

to obtain a copy.

4 Manuscripts should not exceed 3,000

words, including text, tables, figures,

and reference list if applicable.

5 Manuscripts that are prepared on a

personal computer or Macintosh

should be submitted in WordPerfect

5.1, Microsoft Word, or ASCII

format. Files should include (in this

order) abstract, text, footnotes,

references, and tables. Figures

prepared on a computer should be

submitted on diskette as separate files

(*.tiff or *.eps) with accompanying

“camera-ready” copy. Photographs

should be limited to those that are

essential to the understanding of the

text. The photographs should be

sharp, glossy, black-and-white prints

identified on the back. Submit

electronic files on 3.5 inch diskettes,

an original of the manuscript, and

three printed copies to the editor.

6 Evaluations of manuscripts not

accepted for publication will be sent

to the principal author.

7 Manuscripts (and diskettes) not

accepted for publication will be

returned if requested by the principal

author.

8 Manuscripts should not be submitted

to another publication before or while

under review by The Small Flows

Journal.

9 All manuscripts go through a blind

review. Therefore, the title page of the

manuscript should be on a separate

page from the remainder of the

manuscript. The author’s name(s)

should not appear in the manuscript

except as a reference citation.

10 Authors of manuscripts accepted for

publication will be required to

transfer copyright to the National

Small Flows Clearinghouse, publisher

of The Small Flows Journal.

11 Authors warrant that the manuscript

is original except for excerpts and

illustrations from copyrighted works

as may be included with the permission of the copyright owners, such

permission to be obtained by the

authors at their expense.

12 Submit all manuscripts to:

Jill Ross, Editor-in-Chief

The Small Flows Journal

National Small Flows

Clearinghouse

West Virginia University

P.O. Box 6064

Morgantown, WV 26506-6064

Call for Papers:

Deadline for manuscripts

for Volume 1, Issue 2 of The

Small Flows Journal:

February 15, 1995

Papers accepted in the

following categories:

- technology/research

- operation and maintenance

- regulations

- management

- finance

- public education

Call 1-800-624-8301 if you

need further information.

24

MM anuscript Submission Guidelines anuscript Submission Guidelines
The Small Flows Journal Volume 1, Issue 1, Fall 1994 ✂

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EDITOR, THE SMALL FLOWS JOURNAL

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MORGANTOWN, WV 26506-9900

FIRST CLASS MAIL PERMIT NO. 6 MORGANTOWN, WV

POSTAGE WILL BE PAID BY THE ADDRESSEE

BUSINESS REPLY MAIL
The Small Flows Journal Volume 1, Issue 1, Fall 1994

National Small Flows Clearinghouse

West Virginia University

P.O. Box 6064

Morgantown, WV 26506-6064

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