The Small Flows Journal Volume 2, Issue 1, Winter 1996

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 2, Issue 1, Winter 1995

N

ATIONAL SMALL FLOW

S

C L E A R I N G H O U S E
The Small Flows Journal Volume 2, Issue 1, Winter 1996

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

by Cathleen Falvey

RESEARCH

Shallow Intermittent Sand Filtration:

Performance Evaluation ....................................................................................3

by Jeannie Darby, Ph.D., P.E.

George Tchobanoglous, Ph.D., P.E.

M. Asri Nor

David Maciolek

FEATURE

A Private Market Approach To Onsite Wastewater

Treatment System Maintenance ..................................................................... 16

by James Herring

Manuscript Guidelines....................................................................... 25

The Small Flows Journal

Sponsored by:

U.S. Environmental Protection Agency

Steve Hogye, 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, Publications Supervisor

Cathleen Falvey, Editor

Eric Merrill, Graphic Designer

International 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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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 2, Issue 1, Winter 1995

NATIONAL SMALL FLOWS

C L E A R I N G H O U S E
The Small Flows Journal Volume 2, Issue 1, Winter 1996

T

he National Small Flows

Clearinghouse (NSFC) is

pleased to present this second

issue of The Small Flows

Journal. We were overwhelmed by the

positive response to our first issue,

published in the fall of 1994, and we

hope to continue to inspire the same

level of enthusiasm from you, our

readers, with each issue to come.

Many of the comments we received

praised the articles for being directly relevant to you in your work

as sanitarians, public health officials, and engineers. We also

received many compliments on the quality of the information and

the style in which it was presented.

The two papers presented in this issue were selected with these

goals in mind. The first paper, Shallow Intermittent Sand Filtration:

Performance Evaluation" reports the results of a study by environmental engineers at the University of California, Davis on the

minimum media depth required to produce high quality effluent

from intermittent sand filters. ADD TWO SENTENCES HERE.

The second article, A Private Market Approach to Onsite Wastewater Treatment System Maintenance" is a feature article proposing a

new strategy for encouraging onsite system maintenance by

individual homeowners. This idea could

We hope that this long-awaited second issue meets or exceeds your

expectations. While word of the journal is still spreading we have

nearly 5,000 subscribers, unfortunately, enough manuscripts did not

successfully complete the peer review process in time to publish

two issues in 1995 as hoped.

Manuscripts are now being accepted for review for upcoming issues

of the journal If you would like to submit a manuscript, see the

manuscript submissions guidelines on page 28. Information cards

for free subscriptions are also found on page 28.We would very

much appreciate it if you would help to continue to spread the word

about The Small Flows Journal by passing these cards along to your

colleagues.

Sincerely,

Cathleen Falvey

Editor

The Small Flows Journal

2

FFrom the Editor rom the Editor NAT

CLEARIN

AL SMALL F

EARINGHOU

ATIONAL SMA

From the Editor

Terry Bounds, P.E.

Roseberg, OR

James Converse, Ph.D.

Biological Systems Engineering Dept., University of Wisconsin

Brian Cooper, C.E.T.

Simcoe Engineering Group, Ltd., Pickering, Ontario

Donald Gray, Ph.D.

Professor of Civil Engineering, West Virginia University

Michael Hines, M.S., P.E

Quantum Engineering Corporation, Knoxville, TN

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, Center for Environmental Research

U.S. Environmental Protection Agency

George Loomis

Research Soil Scientist

Natural Resources Science Dept., University of Rhode Island

Roger E. Machmeier, Ph.D., P.E

Professor Emeritus, University of Minnesota

Karen Mancl, Ph.D.

Associate Professor of Agricultural Engineering

The Ohio State University

Richard J. Otis, P.E.

Vice-President, Ayres and Associates, Madison, WI

Michael H. Ogden, P.E.

Southwest Wetlands Group, Santa Fe, NM

Sherwood Reed, P.E.

Consultant and Principal

Environmental Engineering Consultants, Norwich, VT

A.R. Rubin, Ph.D.

Extension Specialist and Associate Professor

North Carolina State University

Jerry Stonebridge

President, Stonebridge Construction, Inc., Langley, WA

George Tchobanoglous, Ph.D., P.E.

Professor of Civil Engineering, University of California at Davis

Jerry Tyler, Ph.D.

Associate Professor, University of Wisconsin

A.T. Wallace, Ph.D., P.E.

Professor, Department of Civil Engineering, University of Idaho

Ted Walker, R.E.H.S.

Sonoma County Health Department, Sonoma, CA

Editorial Review Board
The Small Flows Journal Volume 2, Issue 1, Winter 1996

Pell and Nyberg, 1989a,b,c; Pell et al.,

1990; Peeples et al., 1991).

Early filters, being relatively deep (approximately 2 meters) and lightly loaded,

were material-intensive and required large

land areas. These factors, combined with

potential for odor production, resulted in

few such filters being constructed after

1950. However, there is renewed interest

in intermittent sand filters as shallower

media depths and higher loading rates, and

special applications are being explored.

Because intermittent sand filters are

capable of producing high quality effluent

and have relatively low maintenance

requirements, they are well-suited to onsite

and small municipal applications. However, for the full potential of intermittent

sand filters to be realized, high quality

effluents need to be obtained reliably with

low capital and operating costs. Ideally,

filters constructed of shallow, locally

available common sand would produce the

3

I

ntermittent sand filtration is one

of the oldest known methods of

wastewater treatment and was

common in the U.S. before 1900 for

treating community sewage (EPA, 1980;

Marshall and Middlebrooks, 1974).

Wastewater is applied to granular media

beds in one or more doses per day such

that the media drain and reaerate between

doses. Excellent detailed descriptions of

the intermittent sand filtration process are

available elsewhere (Andersen et al.,

1985; Metcalf and Eddy, 1991).

Many studies of intermittent sand filters

have been conducted to investigate the

effects of various parameters on performance. Key among these are effects of

hydraulic loading rate (HLR), dosing

frequency (DF), and media characteristics

and depth (Grantham et al., 1949; Furman

et al., 1955; Schwartz and Bendixen,

1970; Marshall and Middlebrooks, 1974;

EPA, 1980; Siegrist and Boyle, 1981;

Anderson et al., 1985; Andreadakis, 1987;

Shallow Intermittent Sand Filtration:

Performance Evaluation

TECHNICAL

by Jeannie Darby, Ph.D., P.E.,

George Tchobanoglous, Ph.D., P.E.,

M. Asri Nor, and David Maciolek

ABSTRACT: Twelve shallow sand filters (0.38 m deep, nominal diameter of 1.2 m) were loaded

intermittently with primary effluent to evaluate effects of hydraulic loading rate (HLR), dosing

frequency (DF), and filter media characteristics on removal of biochemical oxygen demand (BOD)

and chemical oxygen demand (COD) , suspended solids (SS), turbidity, and organic and ammonia

nitrogen. Hydraulic loading rates between 0.041 and 0.652 m/d1

 were applied during an 85-day

period at DFs between 4 and 24 times/d. Media effective sizes (d10) ranged from 0.29 to 0.93 mm

with uniformity coefficients between 1.4 and 4.52. At an HLR of 0.163 m/d and a dosing frequency

of 24 times/d, effluent quality was excellent and comparable to effluent from advanced wastewater

treatment facilities. Specifically, average removal rates of between 90 and 99 percent for BOD, SS,

organic and ammonia nitrogen and turbidity, and at least 81percent for COD, occurred, regardless of media characteristics.

Shallow Intermittent Sand Filtration:

Performance Evaluation
The Small Flows Journal Volume 2, Issue 1, Winter 1996

required effluent quality at a high wastewater loading rate. To move toward this

ideal, the minimum media depth for

adequate treatment must be determined, as

well as the effect of sand characteristics,

loading rates, and dosing frequencies on

performance.

Little information is available in the

literature on the minimum media depth

required to achieve adequate treatment.

Previous research has indicated shallower

media depths (i.e., 0.5 to 1 m versus the

typical 2-plus m) may provide adequate

treatment especially when dosed at higher

frequencies (Grantham et al., 1949;

Furman et al., 1955). However, a thorough

investigation of filter performance with

sand depths shallower than 0.5 m has not

been published.

The objective of this research was to

investigate the effects of HLR, DF, and

filter media characteristics on removal of

biochemical oxygen demand (BOD),

chemical oxygen demand (COD), suspended solids (SS), turbidity, organicnitrogen (organic–N), and ammonia

nitrogen (NH3

–N) in shallow (0.38 m)

sand filters loaded intermittently.

Experimental Facilities

Twelve shallow sand filters were loaded

intermittently with effluent from the

primary settling tank of the University of

California, Davis (UCD) wastewater

treatment plant (WWTP). A plan view of

the experimental facilities is presented in

figure 1.

The filter units were constructed above

ground, using galvanized metal stock

water tanks with a depth of 0.61 m. The

nominal inside diameter of the tanks was

1.2 m with a range of ± 0.07 m. A

schematic cross-section of a filter is

shown in figure 2.

J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

4

FIGURE 1

plan view of experimental

facilities

Primary effluent

Plywood cover wrapped

 with polyethylene sheeting Halved 102 mm PVC

 pipe cover (typ.)

76 mm

51 mm

76 mm

381 mm

102 mm

Effluent outlet and

sampling port

38 mm PVC pipe underdrain

surrounded by 9-16 mm gravel

6 mm filed grooves

@ 102 mm on center (typ.)

3 mm mesh plastic screen

Washed pea gravel

layer 102 mm thick 9-16 mm gravel around drainpipe

Sand

Washed pea gravel

19 mm PVC pipe manifold

FIGURE 2

cross-section of filter unit

Experimental Methods
The Small Flows Journal Volume 2, Issue 1, Winter 1996

5

Shallow Intermittent Sand Filtration: Performance Evaluation

FIGURE 3

filter media particle size

distribution (average of

washed samples)

Because the filters were intended for

frequent dosing, the volume of influent

applied per dose would be insufficient to

flood the surface, resulting in uneven

distribution. Thus, an influent distribution

system was provided consisting of a

19-mm PVC pipe manifold with 3-mm

upward facing orifices. Each branch of the

manifold was covered with halved,

102-mm PVC pipe, and the whole system

was underlain with 76 mm of washed pea

gravel. A spacing of 130 to 170 mm

between each orifice resulted in 52

orifices for each filter unit. The underdrain

of the units consisted of 38-mm diameter

perforated PVC pipe surrounded with

washed 10- to 16-mm gravel in a layer of

washed pea gravel 102 mm deep. The

underdrain perforation was achieved using

6-mm filed grooves spaced at 102 mm

center to center. Ventilation was provided

through the open top surface and the

effluent overflow outlet.

To prevent the accumulation of falling

debris on the filter surface and reduce

algae growth in the system, a removable

plywood cover wrapped with plastic was

provided for each unit. The covers were

raised 76 mm above the tanks, and four

99.999

99.99

99.9

99

95

90

80

70

50

30

20

10

5

1

.1

.01

.001

0.1

Percent equal to or less than indicated size

Size of Mesh Opening, mm

1 10

Sand Type d ,mm 10 UC

Concrete 0.29 4.52

Filter 0.93 1.29

Filter 0.54 1.32

Filter 0.33 1.42

52-mm holes were cut through the plastic

sheet of each cover to provide aeration to

the filters.

The depth of the media in each filter was

381 mm. Two types of sand were used:

(1) concrete sand obtained from a local

ready-mix concrete company and (2)

cleaned and kiln-dried filter sand. Before

use, the concrete sand was washed to

remove clay and silt. The average grain

size distribution of the washed concrete

sand and filter sand is shown in figure 3.

The average effective size and uniformity

coefficient of the washed concrete sand

were 0.29 mm and 4.52, respectively.

Three effective sizes (0.33, 0.54, and 0.93

mm) of filter sand were used. The

uniformity coefficients of the filter sand

were less than 1.5.

Experimental Design and

Data Collection

Filter Design and Operating Parameters.

Design and operating parameters of the

filters are summarized in table 1. Four

sizes of sand (0.29, 0.33, 0.54, and 0.93

mm), four uniformity coefficients (1.29,

1.32, 1.42, and 4.52), five loading rates

(0.041, 0.081, 0.163, 0.326 and 0.652 m/

d), and three DFs (4, 12, and 24 times/d)2

were investigated. These parameters were

varied such that the effect of each parameter could be investigated systematically

and independently of the other three

parameters.

Sampling. Grab samples of the effluent

were collected through 13-mm sample

ports on each filter unit. The effluent was

allowed to flow continuously through the

sample ports to avoid settlement of

suspended solids. To observe the performance at system start-up, samples were

collected every other day during the first

two weeks of operation. Thereafter,

sampling was conducted once per week.

Approximately three liters of effluent

were collected from each filter unit using

1-L plastic sample bottles during each

sampling event. Samples of the influent
The Small Flows Journal Volume 2, Issue 1, Winter 1996

Expericmental Design and Data

the study is compared with typical septic

tank effluent, also in table 2. Values for

the primary effluent quality parameters

were generally in the lower one-third of

the range that is typical for septic tank

effluent.

Data pertaining to the effect of varied

parameters on performance of the intermittent sand filters are presented and

discussed in the following sub-sections.

Most of the discussion is focused on data

collected after the filters had been

operating three weeks and effluent quality

had stabilized. To determine whether

results from various filters were statistically different, hypothesis tests using

nonparametric (Wilcoxon signed-rank

6

TABLE 1

filter sand

characteristics and

applied loading

Parameter Average Range Average Range

Turbidity (NTU) 26.1 18 - 38 - -

COD (mg/L) 143.8 98 - 226 327 25 - 780

BOD5 

(mg/L) 75.1 38 - 105 138 7 - 480

TSS (mg/L) 29.1 20 - 38 49 10 - 695

NH3

-N (mg/L - N) 10.6 6.1 - 23.6 31 0.1 - 91

Nitrate + Nitrite (mg/L-N) 0.3 0.0 - 1.1 0.4 0.1 - 7.4

Organic N (mg/L -N) 4.6 3.3 - 6.2 - -

a Values, at approximately 10 a.m PST, from startup through day 86 of operation

(20 data points)

b Adapted from USEPA (1978)

This study a Septic tank effluentb

J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

were obtained each time

effluent sampling occurred.

Sampling continued for 85

days.

Laboratory Analysis.

Samples were analyzed for

turbidity, SS, BOD, COD,

NH3

-N, NO3-N, and organicN. Turbidity was measured

with a HACH Model 2100A

turbidimeter. Analyses of

BOD and SS were conducted

according to Standard

Methods (APHA, 1989).

Spectrophotometric analysis

for NH3-N, NO3-N, and

organic-N were conducted

using a HACH DR3000

spectrophotometer and

HACH methods (HACH DR3000 manual,

1985). Chemical oxygen demand was

analyzed by digestion followed by

colorimetric determination. Ammonia

nitrogen was analyzed using the

nesslerization method. Where interference

was suspected (i.e., turbidity greater than

2 NTU), the nesslerization analysis was

preceded by distillation. Nitrate was

analyzed using the modified cadmium

reduction method. Organic nitrogen was

analyzed using the nesslerization method

preceded by digestion and distillation

according to Standard Methods. Air

temperatures measured at a climatological

data collection facility 2 km from the filter

site at the same elevation are representative of those at the filter site and were

recorded. The actual temperature of the

media and wastewater were not measured

during the study.

Characteristics of the wastewater applied

to the filters during the study period are

presented in table 2. Because intermittent

sand filtration is most often used to treat

septic tank effluent or similar quality

wastewater, the primary effluent used in

Experimental Design and

Data Collection

TABLE 2

quality of wastewater applied

to filters

1 0.29 4.52 0.041 4 10.3

2 0.29 4.52 0.081 24 3.4

3 0.29 4.52 0.326 24 13.6

4 0.29 4.52 0.652 24 27.2

5 0.29 4.52 0.163 24 6.8

6 0.29 4.52 0.163 4 40.8

7 0.29 4.52 0.163 12 13.6

8 0.33 1.42 0.163 24 6.8

9 0.54 1.32 0.163 24 6.8

100.93 1.29 0.163 24 6.8

11 0.93 1.29 0.163 4 40.8

12 0.93 1.29 0.163 12 13.6

Filter

number

Effective

size, mm

Uniformity

coefficient, UC

Dosing

frequency,

times/d

Hydraulic

Loading

rate, m/d

Application

rate mm/dose

Parameter investigated Compare filters:

Hydraulic loading rate 2, 3, 4, & 5 and 1 & 6

Effective size 8, 9 & 10

Dosing frequency 5, 6, & 7 and 10, 11, & 12

Uniformity coefficient 5 & 8

Note: To investigate the effect of each parameter independently of others

the following comparisons were made:
The Small Flows Journal Volume 2, Issue 1, Winter 1996

carbon adsorption (Metcalf and Eddy,

1991). Effluent organic-N and NH3-N,

under these loading conditions, were

below levels listed in the same reference

as typical for activated sludge with

separate stage nitrification/denitrification.

When operated as described above, each

1.2-m diameter filter unit was able to treat

184 L/d of septic tank or similar quality

effluent to tertiary quality

levels.

In this research, removal rates

in filters dosed 12 times/d or

more, exceeded most removal

rates reported in the literature

employing DFs of 1 to 4 times/

d. The observed removal rates

for BOD, SS, NH3

-N, and

organic-N compare favorably

with the results of Furman et

al. (1955), where DFs of up to

24 times per day were used.

Most previous research used sand of

significantly greater depth than used in

this research; yet effluent quality observed

in this research was as good or better than

reported in previous research. In the

literature reviewed, only Peeples et al.

(1991) tested a filter with shallower media

than were used in this study (0.30 m vs.

0.38 m), and the performance reported

was noticeably worse. Peeples et al.

(1991) used media with a d10 of 0.44 mm

and a UC = 3.3 and employed a DF of 1

time/d at an HLR of 0.255 m/d. The

improved performance observed in this

study, compared to that of Peeples et al.

(1991), is probably due to increased DF (4

times/d or greater). Higher media temperatures may have been an additional factor.

The average air temperature from June

through August was 22.6 °C, which is

near the high-end of the range in the

previous studies that reported temperature.

Due to the filter design and intense solar

radiation, the filter media were probably

as warm as or warmer than the average air

temperature. Previous studies reported

increased removal rates at higher temperatures (Grantham et al., 1949; Pell et al.

1990; Schwartz and Bendixen, 1970).

7

test) and analysis of variance techniques

(ANOVA) were conducted. When the two

tests produced conflicting results, data

distributions were inspected for normality.

For normally distributed data, ANOVA

results were used. Otherwise, results of

Wilcoxon signed-rank tests were used.

Confidence levels used in all tests were 95

percent.

Overall Performance

A summary of the performance of filters

5, 7, 8, 9, 10, and 12 (loaded at 0.163 m/d

and dosed 12 or 24 times/d) is shown in

table 3. Effluent from these filters was of

excellent quality and (except for coliform

levels, which were not measured) would

be suitable for most disposal methods or

reclamation. In these filters, average

removal rates were 94 percent or better for

all parameters, and removal rates of

greater than 99 percent were common.

Effluent quality from the filters was

extremely stable, with only one excursion

from a very robust performance (one

effluent COD measurement, from one

filter, was 42 mg/L; otherwise the maximum would have been 20 mg/L). Filters

with lower HLRs had equal or better

performance, except when dosed at a

frequency of 4 times/d, which sometimes

resulted in worse performance.

At an HLR of 0.163 m/d and a DF of 12

times/d or greater, maximum effluent

values of BOD, COD, SS, and turbidity

(presented in table 3) were below levels

listed as typical for activated sludge

followed by granular media filtration and

Shallow Intermittent Sand Filtration: Performance Evaluation

TABLE 3

summary of treatment

achieved for filters loaded

at 0.163 m/d with dosing

frequency of 12 or 24

times/daya

Parameter Average Minimum Maximum Average Minimum Maximum

Turbidity 97 91 99 0.7 0.3 1.7

COD 94 81 >99 8.8 1.042

BOD5 99 97 >99 0.7 0.0 2.6

SS 98 94 >99 0.4 0.0 1.8

NH3

-N 99 99 >99 0.04 0.01 0.20

Organic N 95 90 >99 0.20 0.0 0.5

a Based on data collected from day 23 through day 86 of operation

(10 measurements per filter for each parameter)

Effluent concentration,

Percent removal mg/L except NTU for turbidity
The Small Flows Journal Volume 2, Issue 1, Winter 1996

8

J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

100

80

60

40

20

0

100

80

60

40

20

0

Percent COD Removal

Filter HLR, m/d

2

3

4

5

0.081

0.326

0.652

0.163

(b) DF = 4 times/d

(a) DF = 24 times/d

Filter HLR, m/d

1

6

0.041

0.163

0 10 20 30 40 50 60 70 80 90

Percent COD Removal

Day of Operation

FIGURE 5

effect of hydraulic loading rate on COD

removal at

(a) DF = 24 times/d and

(b) DF = 4 times/d

(d10 = 0.29 mm, UC = 4.52)

of DFs, from 4 to 24

times/d. It can be

seen in figure 4 how

stable the effluent

COD values were

relative to the

influent, especially

for filters dosed 12 or

24 times/d after 25

days of filter

operation. As DF

increased from 4 to

24 times per day,

average COD

removal improved

from 79.3 to 93.3

percent, an effect that

is discussed in more

detail below.

250

200

150

100

50

0 0 10 20 30 40 50 60 70 80 90

Day of Operation

COD, mg/L

Filter DF, times/d

11

12

10

Influent

4

12

24

Grantham et al. (1949) reported that

improvements in performance due to air

temperature increases were greater for

coarser sand and for shallower depth and

concluded that this was due to greater air

circulation with larger media and/or

shallower depths. The higher media

temperatures in this study may be a factor

in the performance, but no conclusions

can be drawn without an explicit focus on

the effects of temperature on filter

performance.

Influent and effluent COD concentrations

for three filters are shown in figure 4 to

illustrate overall removal of organic

material. Effluent data for filters 10, 11,

and 12 are shown because these filters

have the same sand effective size of

0.93 mm, the same relatively high loading

rate of 0.163 m/d, and represent the range

FIGURE 4

applied (influent) and

effluent COD from

three filters

(HLR = 0.163 m/d)
The Small Flows Journal Volume 2, Issue 1, Winter 1996

0.326 m/d) than for filters 5 and 6 (loaded

at 0.163 m/d). This increased loading also

caused filter 3 to clog, as evidenced by

effluent overflowing the filter housing

after 70 days in operation. When loaded at

an HLR of 0.652 m/d, filter 4 clogged

after only 20 days in operation, thus no

data comparable to other filters were

collected.

An HLR between 0.163 m/d and 0.326 m/d

appears to be the maximum sustainable

loading for the concrete sand beyond

which clogging occurs in less than three

months of operation. Sauer et al. (1976)

reported a similar threshold HLR between

0.2 and 0.57 m/d for a more uniform filter

sand (d10 = 0.45 mm, UC = 3.0) and DF of

4 to 13 times/d with media 0.61 deep. At

the higher HLR, Sauer et al. (1976)

reported an operating duration of 45 to 80

days while at the lower HLR, operating

duration exceeded 150 days. Furman et al.

(1955), applied an HLR of up to 0.280 m/d

without clogging in over five months of

operation in filters with media ranging

from 0.46 to 0.76 m deep, and d10 ranging

from 0.46 to 1.04 mm.

The early clogging of filter 4 (HLR =

0.652 m/d, DF = 24 times/d, d10 = 0.29

mm, UC = 4.52) in this study may be

attributed to the high HLR combined with

9

Shallow Intermittent Sand Filtration: Performance Evaluation

TABLE 4

effect of HLR on average

percent removala

 (d10 = 0.29

mm, UC = 4.5)

Effect of HLR on Performance

The effect of HLR on filter performance

was evaluated for concrete sand (d10 = 0.29

mm, UC = 4.52) at DFs of both 4 and 24

times/d. The effect of increasing HLR on

COD removal at both DFs is presented in

figure 5. Increasing the HLR from 0.081

to 0.163 m/d had little effect on COD

removal at a DF of 24 times/d. At this DF,

HLR increases to 0.326 and 0.652 m/d

caused noticeable decreases in COD

removal. At a DF of 4 times/d, the COD

removal in the filter dosed at 0.163 m/d

was slightly, but consistently, less than the

filter dosed at 0.041 m/d.

The response of COD to variation in HLR

is typical for all parameters studied, as can

be discerned from table 4, a summary of

the effect of increasing HLR on removal

rates for each parameter. Shading of

results in adjacent columns indicates that a

statistically significant difference existed

between those results. When dosed 24

times/d, increasing HLR from 0.081 to

0.163 m/d caused no statistically

significant decrease in removal for any

parameter except turbidity, which had a

very slight, but statistically significant

lower removal rate at the higher HLR. The

removal rates for all parameters were

significantly lower for filter 3 (loaded at

Turbidity 97.0±1.2 97.7±1.1 92.2±1.9 c 96.9±1.3 94.4±1.6

COD 94.9±2.094.3±3.4 71.6±20.7 c 96.3±1.092.1±2.1

BOD5 99.4±0.4 99.5±0.3 76.1±9.5 c 99.4±0.6 98.5±0.6

TSS 98.1±1.2 99.0±0.5 90.7±4.4 c 98.2±0.9 94.7±2.6

NH3-N 99.5±0.2 99.6±0.1 - 5.7±42.7 c 99.7±0.1 99.2±0.3

Organic N 97.4±2.0 96.0±1.8 82.3±3.4 c 99.3±0.7 93.5±2.9

Note: Shading of adjacent columns indicates that results exhibit a statistically significant difference

a Based on data collected from day 23 through day 86 of operation

(10 measurements for each parameter)

b Filter 3 clogged (overflowed) after 70 days in operation

c Filter 4 clogged (overflowed) after 20 days in operation

Parameter

Filter 4

0.652 m/d

Filter 1

0.041 m/d

Filter 6

0.163 m/d

Filter 3b

0.326 m/d

Filter 5

0.163 m/d

Filter 2

0.081 m/d

 Effect of HLR on average percent removala

(d10 = 0.29 mm, UC = 4.5)

 Dosing = 24 times/day Dosing = 4 times/day
The Small Flows Journal Volume 2, Issue 1, Winter 1996

100

80

60

40

20

0

100

80

60

40

20

0

Percent COD Removal

Filter DF, times/d

6

7

5

4

12

24

(a) d = 0.29 mm,

UC = 4.52

0 10 20 30 40 50 60 70 80 90

Percent COD Removal

Day of Operation

10

Filter DF, times/d

11

12

10

4

12

24

(b) d = 0.93 mm,

UC < 1.5

10

the relatively low permeability of the

concrete sand. Although permeability was

not measured, it can be seen in figure 3

that the concrete sand used in filters 1-7

had a fairly broad and even size distribution. This size distribution allows the

smaller sand particles to fill interstices

between large particles, resulting in

smaller and more convoluted pore spaces.

This condition encourages clogging of

remaining void spaces with suspended

solids and biological growth. In previous

studies in which wastewater of similar or

greater strength was applied at an HLR ≥

0.163 m/d without clogging, the UC of the

media was less than 3.3. EPA (1980) and

Metcalf and Eddy (1991) recommend a

UC no greater than 4.0.

Clogging reduces natural aeration, which

can lead to anaerobic conditions within

the filter. When filter 3 was taken out of

service and the media examined, the top

7.5 cm was found to be black. The

blackness was probably due to iron

sulfide, which is highly indicative of

anaerobic conditions, implying that

aeration had ceased due to clogging. The

same color was observed in the top 2.5 cm

of sand in filter 4, which clogged after

only 20 days in operation at HLR = 0.652

m/d. After resting filter 4 for three weeks,

the pea gravel on top of the sand and the

top 5.0 cm of sand were replaced. The

filter was again loaded at 0.652 m/d with

the DF increased to 48 times/d. After 10

days, this filter again clogged and overflowed, which may indicate that the media

porosity had been permanently reduced,

either by clogging or compaction.

Effect of Dosing Frequency

on Performance

Increasing the DF from 4 to 12 to 24

times/d generally improved the performance of the filters. The effect of DF on

COD removal is illustrated in figure 6.

Improvements were more dramatic for the

coarse filter sand (d10 = 0.93 mm) than for

the concrete sand (d10 = 0.29 mm).

Increasing the DF from 4 to 12 times/d

10

J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

resulted in obvious improvements in COD

removal in the coarser media and small,

but noticeable improvements with the

finer sand. At a DF of 12 times/d or

greater, removal rates were very high for

all parameters with all media types.

The excellent performance observed at

DFs of 12 times/d or greater may be

attributable to the manner of flow through

the media and the resulting hydraulics and

diffusion rates. At high DFs, the volume

of wastewater applied in any one dose is

small, e.g., 15.3 L at an HLR of 0.163 m/d

and a DF of 12 times/d. When distributed

over the surface area of the filter, this

15.3 L dose translates to an application

rate of only 1.36 mL/cm2 or 13.6 mm. If

the application rate does not exceed the

water holding capacity of the media, the

FIGURE 6

effect of dosing frequency on

COD removal at

HLR=0.163 m/d (a) d10=

0.29 mm, UC=4.52 and

(b) d10=0.93 mm, UC < 1.5
The Small Flows Journal Volume 2, Issue 1, Winter 1996

Shallow Intermittent Sand Filtration: Performance Evaluation

applied water flows over the sand grains in

a thin film allowing maximum oxygen

diffusion and maximum contact between

organics in the waste flow and the

microbial growth on the media. Thin-film

flow allows longer contact time between a

given parcel of applied wastewater and

attached microbes than would occur under

flow conditions resulting from a large dose

volume (low DF).

The effect of DF on removal efficiency for

all parameters can be discerned from

table 5, which is a comparison of average

removal in filters containing concrete sand

(d10 = 0.29 mm) with filters containing

coarse filter sand (d10 = 0.93 mm). As in

table 4, shading of results in adjacent

columns indicates that a statistically

significant difference existed between

those results. For the concrete sand,

increasing DF from 4 to 12 times/d

resulted in a slight, but statistically

significant increase in removal for

turbidity, COD, and organic N; increasing

DF from 12 to 24 times/d did not significantly increase the removal efficiency of

any parameter. For the coarse filter sand,

increasing the DF from 4 to 12 times/d

significantly improved the removal of all

parameters, and increasing DF from 12 to

24 times/d significantly improved the

removal of turbidity, BOD, and ammonia.

For both media types, increasing the DF

from 4 to 12 times/d had a greater effect

than increasing it from 12 to 24 times/d.

Consistent with the proposed

thin-film flow phenomenon,

increasing DF would have a

greater effect for large media

filters than small media

filters due to the difference

in water holding capacity.

Coarser media have a lower

water holding capacity than

fine media, and thus a

smaller dose volume (higher

DF) is required to promote

the thin-film flow pattern. In

general, these findings are

consistent with those of

Furman et al. (1955) who

reported that, with an

increase in DF, BOD and SS removal

improved slightly for media of d10 ≤ 0.31

mm, but improved substantially for media

with d10 ≥ 0.44 mm.

At a DF of 4 times/d, the removal rates in

the concrete sand were better than the

corresponding removal rates for the coarse

filter sand (see table 5). As DF was

increased (for a given HLR), the differences in removal rates between the two

media consistently decreased. These

results are consistent with the proposed

thin-film flow concept. Concrete sand has

a large unit wetted surface area relative to

the coarse filter sand. The large surface

area allows thin-film flow conditions to

occur at higher per-dose application rates,

i.e., relatively low DFs. Increasing DF for

a given HLR decreases the volume

applied per dose and allows thin-film flow

conditions in the coarser filter sand. Thus,

increasing DF (i.e., reducing the per-dose

application rate) may partially compensate

for lower unit wetted surface area of

coarser media. Coarser media, used with a

high DF, may be advantageous as they are

less likely to clog.

Effect of Media Size on Performance

An attempt was made to isolate the effect

of media size on filter performance using

very uniform filter sand (UC< 1.42) of

three sizes: d10 = 0.33 , 0.54, and 0.93 mm.

A fairly high loading rate of 0.163 m/d

11

Turbidity 94.4±1.6 97.3±1.2 97.7±1.1 77.0±4.9 96.0±1.6 97.0±1.8

COD 92.1±2.1 95.2±1.7 94.3±3.4 79.3±8.092.6±1.7 93.3±1.5

BOD5 98.5±0.6 98.8±0.8 99.5±0.3 87.0±5.8 98.7±0.4 99.2±0.4

TSS 94.7±2.7 97.8±1.5 99.0±0.5 77.0±8.5 97.2±0.9 98.6±0.9

NH3-N 99.2±0.3 99.7±0.1 99.6±0.1 98.7±1.9 99.4±0.3 99.6±0.1

Organic N 93.5±2.9 95.8±2.5 96.0±1.8 70.1±5.7 92.3±2.2 94.0±2.0

Note: Shading of adjacent columns indicates that results exhibit a statistically significant difference

a Average (± 95% confidence interval) of data collected from day 23 through day 86

of operation (10 measurements for each parameter).

Parameter

Filter 6,

4 times/d

Filter 7

12 times/d

Filter 5

24 times/d

Filter 11

4 times/d

Filter 12

12 times/d

Filter 10

24 times/d

d10 = 0.29 mm, UC = 4.52 d10 = 0.93 mm, UC = 1.29

Effect of dosing frequency on average percent removala

at HLR of 0.163 m/d

TABLE 5

effect of dosing frequency on

average percent removala

 at

HLR of 0.163 m/d
The Small Flows Journal Volume 2, Issue 1, Winter 1996

and DF of 24 times/d were used. The

removal efficiencies for turbidity, SS,

BOD, and COD for the three media

sizes are compared in figure 7.

Differences between the removal

efficiencies in the different media

sizes are difficult to discern. Slightly

higher turbidity removal in the finest

sand was the only statistically

significant difference.

Performance effects due to media

size appear to be affected by DF as

discussed previously. Grantham et al.

(1949) and Marshall and

Middlebrooks (1974) reported

increased removal rates with finer

sand with DFs of 1 or 2 times/d.

Furman et al. (1955) reported much

better removal rates for BOD and SS

and more nitrogen oxidation with

finer media when dosed two times

per day. However, when the DF was

increased to four times per day,

Furman et al. (1955) reported very

similar performance for fine and

coarse media. In this study, effect of

media size was compared using a DF

of 24 times/d and a moderate HLR; thus

only a small volume of wastewater was

applied per dose and effects of media size

were apparently overshadowed by the

high overall removal rates. If greater perdose application rates had been used

(same DF but larger HLR), differences in

removal rates between media of different

sizes may have been more apparent.

Effect of Uniformity Coefficient

on Performance

Removal rates for turbidity, SS, BOD, and

COD in two filters with sands of similar

effective sizes (d10 = 0.29 and 0.33 mm)

but different uniformity coefficients

(UC = 1.42 and 4.52) are shown in

figure 8. The same HLR (0.163 m/d) and

DF (24 times/d) were used in both filters.

The filter with more uniform sand

demonstrated a slight, but statistically

significant increase in turbidity and SS

removal. In the literature reviewed, the

12

effect of media uniformity on filter

performance was not explicitly explored.

Design recommendations call for media

UC of less than 4.0 (Anderson et al.,

1985; EPA, 1980). This recommendation

is intended to avoid clogging at higher

loading rates. The clogging of filters 3 and

4 at HLRs equal to or greater than 0.326

m/d was partially attributable to the wellgraded nature of the concrete sand (UC =

4.52) used as media.

At a lower HLR of 0.163 m/d and DF of

24 times/d, all media had high removal

rates and media uniformity did not appear

to have much effect on filter performance.

The lower per-dose application rates

favored thin-film flow conditions and

allowed excellent removal rates regardless

of media uniformity. As the per-dose

application rate increases, media uniformity apparently becomes more important

because it affects pore geometry and

conditions under which thin-film flow

occur.

J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

FIGURE 7

effect of media size on

removal of (a) turbidity, (b)

SS, (c) BOD, and (d) COD

(UC < 1.5, DF=24 times/d,

HLR=0.163 m/d)

Filter

8

9

10

0.33

0.54

0.93

100

80

60

40

20

0

Percent Removal

Day of Operation

100

80

60

40

20

00 20 40 60 80

Day of Operation

0 20 40 60 80

d10

(a) Turbidity

(b) SS

(c) BOD (d) COD

Percent Removal
The Small Flows Journal Volume 2, Issue 1, Winter 1996

listed as typical (Metcalf and Eddy,

1991) for activated sludge followed

by granular media filtration and

carbon adsorption; organic-N and

NH3-N were below levels listed in

same reference as typical for

activated sludge with separate stage

nitrification/denitrification. Based

on the above-listed loading and

dosing rates, each 1.2-m diameter

filter unit was able to treat 184 L/d

of septic tank or similar quality

effluent to tertiary treatment levels.

The deleterious effects of increases

in HLR, media size, or UC were

shown to be mitigated significantly

in certain situations by increasing

DF. The effects of DF were found to

be more significant for higher

values of HLR, coarser media, and

less uniform sand.

No single filter design or operating

parameter was found to adequately

predict the performance of intermittent sand filters. The effects of the

many parameters are interrelated in

a complex manner. However,

research focused on the per-dose

application rate and a characterization of the media pore geometry

together may provide insight for the

performance variation observed.

The excellent performance observed

at high DFs is hypothesized to be

the result of per-dose application

rates that allow development of

thin-film flow through the media

and subsequently maximum oxygen

diffusion and contact time.

Support for this research was provided

by the National Science Foundation

through a Presidential Young Investigator Award to J. Darby. The donation of equipment and technical

assistance by Harold Ball of Orenco

Systems, Inc. (Roseburg, Oregon) is

gratefully acknowledged.

For the conditions studied in this research,

the following conclusions can be drawn:

Intermittent sand filters with a

relatively shallow bed depth (0.38

m) are capable of producing

excellent quality effluent at an HLR

of 0.163 m/d when dosed 12 to 24

times/d with wastewater equivalent

to septic tank effluent. The minimum removal efficiencies observed

for BOD, SS, organic-N, and NH3-

N, are similar to the best removal

rates reported in the literature for

intermittent sand filters of greater

depth.

At an HLR of 0.163 m/d, with a DF

of 12/d or greater, the maximum

effluent values of BOD, COD, SS,

and turbidity were below levels

13

Conclusion

Filter

5

8

1.42

4.52

100

80

60

40

20

0

Percent Removal

Day of Operation

100

80

60

40

20

00 20 40 60 80

Day of Operation

0 20 40 60 80

UC

(a) Turbidity

(b) SS

(c) BOD (d) COD

Percent Removal

FIGURE 8

effect of media uniformity

coefficient on removal of (a)

turbidity, (b) SS, (c) BOD,

and (d) COD (d10=0.3 mm,

DF=24 times/d, HLR=0.163

m/d)

Acknowledgements

Shallow Intermittent Sand Filtration: Performance Evaluation
The Small Flows Journal Volume 2, Issue 1, Winter 1996

1 1 m/d is equivalent to 24.54 gal/ft2

•d 2

 1/8 inch orifice with a residual head of

8 ft.

American Public Health Association.

1989. Standard methods for the

examination of water and wastewater.

17th ed., Washington, D.C.

Anderson, D. L., R. L. Siegrist, and R. J.

Otis. 1985. Technology assessment of

intermittent sand filters. Municipal

Environmental Research Laboratory.

U.S. Environmental Protection Agency.

Cincinnati, Ohio. EPA 832/R-85/100.

Andreadakis, A. D. 1987. Organic matter

and nitrogen removal by an onsite

sewage treatment and disposal system.

Water Research 21, no. 5: 559-565.

Furman, T. D., W. T. Calaway, and G. R.

Grantham. 1955. Intermittent sand

filters—multiple loadings. Sewage and

Industrial Wastes (March): 260-276.

Grantham, G. R., D. L. Emerson, and A. K.

Henry. 1949. Intermittent sand filter

studies. Sewage Works Journal 21, no.

6:1002-1015.

Metcalf and Eddy. 1991. Wastewater

treatment. 3d. ed. San Francisco:

McGraw Hill.

Marshall, G. R., and E. J. Middlebrooks.

1974. Intermittent sand filtration to

upgrade existing wastewater treatment

facilities. Utah Water Research Laboratory, College of Engineering. Utah State

University at Logan.

Peeples, J.A., K.M. Mancl, and D.L Widrig.

1991. An examination of the role of

sand depth on the treatment efficiency of

pilot scale intermittent sand filters.

Proceedings of the 6th National Symposium on Individual and Small Community Sewage Systems (Chicago, December 16-17). ASAE publication n10-911.

St. Joseph, MI: ASAE

Pell, M., and F. Nyberg. 1989a. Infiltration

of wastewater in a newly started pilot

sand-filter system: Part I. Reduction of

organic matter and phosphorus. Journal

of Environmental Quality 18: 451-457.

______. 1989b. Infiltration of wastewater in

a newly started pilot sand-filter system:

Part II. Development and distribution of

the bacteria population. Journal of

Environmental Quality 18: 457-462.

______. 1989c. Infiltration of wastewater in

a newly started pilot sand-filter system:

Part III. Transformation of nitrogen.

Journal of Environmental Quality 18:

463-467.

Pell, M., F. Nyberg, and H. Ljungren. 1990.

Microbial numbers and activity during

infiltration of septic-tank effluent in a

subsurface sand filter. Water Research

24, no. 11: 1347-1354.

Sauer, D. K., W. C. Boyle, and R. J. Otis.

1976. Intermittent sand filtration of

household wastewater. ASCE Journal of

the Environmental Engineering Division

(August): 789-803.

Schwartz, W. A., T. W. Bendixen, and R. E.

Thomas. 1967. Project report of pilot

studies on the use of soils as waste

treatment media. In-house report

prepared for the Federal Waste Pollution

Agency. Cincinnati, OH.

Siegrist, R. L., and W. C. Boyle. 1981.

Onsite reclamation of residential

graywater. Proceedings of the Third

National Symposium on Individual and

Small Community Sewage Treatment.

ASAE:176-186.

Simons, A. P., and F. R. Magdoff. 1979.

Laboratory evaluation of design

parameters for mound system disposal of

septic tank effluent. Journal of Environmental Quality 8, no. 4: 486-492.

Tchobanoglous, G., and E. D. Schroeder.

1985. Water quality: characteristics,

modeling, and modification. Addison

Wesley Pub. pp. 120-121.

U.S. Environmental Protection Agency

(EPA). 1978. Management of small

waste flows. Municipal Environmental

Research Laboratory. Cincinnati, Ohio.

EPA 600/2-78-173.

______. 1980. Design manual. Onsite

wastewater treatment and disposal

system. Municipal Environmental

Research Laboratory. Cincinnati, Ohio.

EPA 625/1-80-012

J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

14

Notes

References
The Small Flows Journal Volume 2, Issue 1, Winter 1996

LOWS

ARINGHOUSE

SMALL FLOWS

OUSE

NATIONAL SMA

CLEARINGH

ONAL SM

Jeannie Darby, Ph.D., P.E.

Jeannie Darby is an associate

professor in the department of

civil and environmental engineering at the University of California

at Davis. She has a BSCE from

Rice University (Houston, TX), a

MSCE from Tufts University

(Medford, MA), and a Ph.D. in civil

engineering from the University of

Texas at Austin. She is a registered professional engineer.

George Tchobanoglous,

Ph.D., P.E.

George Tchobanoglous is a

professor emeritus in the department of civil and environmental

engineering at the University of

California at Davis. He has a

BSCE from the University of the

Pacific (Stockton, CA), a M.S. in

sanitary engineering from University of California at Berkeley, and

a Ph.D. in civil engineering from

Stanford University. He is a

registered professional engineer.

M. Asri Nor

and

David Maciolek

M. Asri Nor is an instructor in the

department of civil engineering at

the University of Technology,

Malaysia. David Maciolek is an

engineer at Larry Walker &

Associates in Davis, CA. At the

time of this research, both were

graduate students in the department of civil and environmental

engineering at the University of

California at Davis.

15

If you would like more information

about this article, write to Jeannie

Darby, Ph.D., P.E.; Department of Civil

and Environmental Engineering;

University of California at Davis;

116 Everson Hall; Davis, CA 95616.

Shallow Intermittent Sand Filtration: Performance Evaluation
The Small Flows Journal Volume 2, Issue 1, Winter 1996

I

n the United States, approximately 25

million private residences rely on

onsite wastewater treatment systems

(OWTS), such as septic tanks with

leach fields (Bureau of the Census, 1993,

165, table 12). When properly designed,

sited, constructed, and maintained, such

systems can provide an excellent, low-cost

means of treating waste with little risk to

human health or environmental quality.

However, inadequate system care can

result in system failure, with consequent

environmental and public health risks.

Virtually all jurisdictions in the U.S. have

regulations or programs to assure proper

OWTS siting, design, and construction—

but maintenance, the final step in OWTS

management, is much more troublesome

to control and is the most frequent source

of system decay and failure.

16

by John Herring

In response to problems with failing

systems, some communities regulate and

control OWTS maintenance through

management districts and other community programs. While these programs can

be very effective, their successful implementation often depends on widespread

community support.

In this article, some of the advantages and

limitations of current OWTS management

programs in the U.S. and Canada are

discussed, and an idea for an alternative,

insurance-based strategy for managing

OWTS maintenance is offered. The

proposed strategy allows for individual

participation by homeowners living in

communities where management districts

are impractical or unpopular.

Malfunctioning or failing onsite wastewater treatment systems (OWTS) are a significant

source of pollutants, adversely affecting hundreds of waterbodies nationwide. Currently,

system design, siting, and construction are fairly well-managed, with maintenance of

existing systems the remaining weak link. In this article, some limitations of traditional

regulatory approaches to OWTS management are discussed, and an alternative approach

using private-market catastrophic OWTS insurance is proposed and developed. Possible

advantages of an OWTS insurance approach include improved water quality, risk

reduction for homeowners and lending institutions, increased incentives for additional

research regarding OWTS management practices, and reduction in the need for publiclyfunded regulatory programs.

 Private Market Approach To

Onsite Wastewater Treatment

System Maintenance

AA Private Market Approach To

Onsite Wastewater Treatment

System Maintenance

FEATURE
The Small Flows Journal Volume 2, Issue 1, Winter 1996

17

of this extraordinarily valuable

resource (KWIC, 1993). Shoreline properties in this watershed

are economically critical. For

several of the municipalities,

shoreline properties constituting

only a few percent of total land

area contribute over half of all

property tax revenues. Keuka

Lake OWTS inspections,

performed by municipal officers,

include verification of adequacy

of baffles, checks for holes or

cracks, and a determination of

whether pumping is needed.

Funding for these inspections is

provided by fees for services and

by municipal support.

Many of the other successful

OWTS management programs discussed

in the literature were developed precisely

because of real or perceived threats to

public health or economic well-being. For

example, the Stinson Beach Water District

in Stinson Beach, California is the result

of direct threats to public health in an area

heavily dependent on water-based

recreation (Richardson, 1989). Groundwater sampling and testing of the residences

in the Stinson Beach area indicated 10

percent of the systems were malfunctioning.

Other examples include the onsite

management program in Fountain Run, in

south central Kentucky, where there was

greater than a 30 percent failure rate for

existing systems, with many additional

systems undersized by current standards

and “expected to fail in the near future”

(Otis, Robertson, and Kleinschmidt,

1981). The Westboro, Wisconsin district

was developed to deal with a situation in

which over 80 percent of all systems

discharged directly into a small stream

(Otis, Robertson, and Kleinschmidt,

1981). And in Virginia, the Arlington

County Chesapeake Bay Preservation

Ordinance, which requires five-year

pumping cycles for onsite systems (EPA,

1993, 4.116), clearly bases its legitimacy

on the issue of protecting the highly

significant Chesapeake Bay.

A Private Market Approach To Onsite Wastewater Treatment System Maintenance

KEUKA LAKE, NEW YORK

Economically critical

shoreline properties on

Keuka Lake, New York,

are protected by an

intermunicipal OWTS

maintenance agreement.

Regulating Maintenance

Typically, state or local health departments

promulgate standards for OWTS design

and siting criteria. Sound OWTS construction is usually achieved through onsite

inspection during the construction phase

by health department personnel, local

building inspectors, watershed inspectors,

or some other regulatory authority. In

many instances, backfill over a system is

prohibited until such an inspection occurs.

However, direct regulatory programs

aimed at managing OWTS maintenance

are rare and usually focus on remediation

of a direct threat to public health or

property values, or the protection of a

specific highly-valued waterbody.

An example of a preventive management

program aimed at protecting a highlyvalued waterbody is an intermunicipal

agreement among six towns and two

villages sharing frontage on Keuka Lake,

one of the New York Finger Lakes. The

agreement requires inspections for

systems within 200 feet (60.96 meters) of

the shoreline at least once every five years

as a means of protecting the high quality

 OWTS Management Programs
The Small Flows Journal Volume 2, Issue 1, Winter 1996

Assigning responsibility to existing

agencies, such as watershed inspectors or

local health departments, would simply

mean an increase in workload such that

significant staff additions would be

necessary. It also should be noted that

these estimated costs merely focus on

inspections, and do not include the

potential costs of remediating inadequate

systems.

In the absence of significant perceived

benefits, such a program is unlikely to

gain widespread community support,

especially because its successes (early

detection of OWTS problems) imply an

additional cost, sometimes substantial, to

affected homeowners. Mooers and Waller

(1994) note that in some communities in

Nova Scotia, the lack of a public perception that OWTS problems even exist has

resulted in the failure to adopt onsite

management programs. Therefore, while

the concept of a district or other public

utility as a mechanism for onsite system

maintenance has obvious advantages, it is

not a panacea. It appears to be an attractive alternative only if at least one of the

following conditions can be met:

there is a serious threat to health or

property values that a district might

reduce at less expense than central

sewers,

there is a widespread perception of a

threat to public health or the environment and a perception that central

sewers would be more expensive, or

the area is undergoing significant

new development, so that district

formation is a part of an overall

development package.

In a few instances, however, it appears that

districts can be developed and supported

by a community in the absence of a real or

perceived immediate threat, given a

population that is exceptionally committed to minimizing environmental impacts.

18

Examples of OWTS management

programs in Nova Scotia show the same

general trend. Mooers and Waller (1994),

in their survey of Nova Scotia’s OWTS

management districts, noted only three

successful districts since the 1982

legislation authorizing their formation. In

each case, significant problems led to

formation of the districts. In Port

Maitland, problems included failed

systems and direct discharge to ditches. In

Guysborough, a survey found that only 10

percent of the systems did not drain to

ditches or surface water. In Woods

Harbour, many systems were determined

to be malfunctioning.

Limitations of Current Programs

While the aforementioned examples of

managed OWTS maintenance have

largely been successful, expansion of such

direct regulatory programs to cover all

onsite systems is highly unlikely. One

reason is that, in many areas, the immense

cost associated with such an expansion

would require a significant increase in

public funds.

New York State, for example, has

approximately 1.5 million residential

OWTS, with Suffolk County accounting

for over 20 percent of that total (Bureau

of the Census, 1993, 224–230, table 66).

Straightforward calculations assuming

four inspections per person per day, or

1000 per year, mean that New York would

need 1500 new inspectors if annual

inspections were implemented. Even

inspection on a three-year cycle, as is

recommended under the Management

Measures Guidance for the Coastal

Nonpoint Pollution Control Program

(EPA, 1993, 4.114), would require 500

inspectors. Adding salary and benefits to

other program costs such as office space,

staff support, materials, etc., leads to a

cost estimate of at least 15 to 20 million

dollars per year. Whether generated

through fees for required services, as part

of a community’s general budget, or

through some form of special tax, these

costs would be borne by the public.

John Herring
The Small Flows Journal Volume 2, Issue 1, Winter 1996

A Private Market Approach To Onsite Wastewater Treatment System Maintenance

19

Despite the costs and limitations of a

public management district or utility

approach, the concept of controlling

OWTS maintenance is attractive from

both individual and societal perspectives.

Societally, the pollution avoided through

routine inspection and maintenance will

improve water quality in hundreds of

waterbodies nationwide. In New York

State alone, it is estimated that OWTS

pollution is the primary cause for over 180

waterbodies failing to meet designated use

standards. OWTS failures are a secondary

cause of pollution for an additional several

hundred waterbodies (DEC, 1993).

For the individual system owner, routine

inspections also can provide significant

benefits. Early detection of many malfunctions, such as loss of in-tank baffles,

allows early and inexpensive maintenance.

In addition, inspection normally includes

tank pumping, itself an important factor

extending a system’s useful life.

For a variety reasons, it seems that most

homeowners do not perform appropriate

routine OWTS maintenance despite

demonstrated benefits. The author has

been unable to locate any formal studies

showing voluntary high levels of

homeowner OWTS maintenance in the

absence of the same preexisting conditions

listed earlier as being important in

management district formation. Indeed, in

a survey conducted at the beginning of the

process leading to the Keuka Lake

intermunicipal agreement, a systematic

random sample of the records of 839

systems in the watershed showed that

fewer than 40 percent of systems had been

inspected in the previous ten years. Nearly

22 percent of systems in the watershed had

not been inspected in over 20 years

(Powell, Herring, and Anderson, 1988).

These findings, together with those of

Lemley (1995) and information from those

working in the field, lead to the conclusion

that it is not uncommon for homeowners

to focus on OWTS maintenance only after

gross failures occur.

Because properly designed and sited

systems do not require maintenance often,

homeowners are unlikely to incorporate

system maintenance as routine. Also,

when faced with the choice between the

certainty of spending a small amount of

money now versus the possibility of

having to spend a large amount in the

future, time preferences for money

reinforce the desire to avoid spending

money when there is no immediate

benefit.

The fact that OWTS maintenance can

often be delayed without immediate

repercussions can also lead to neglect.

Also, homeowners are sometimes unaware that OWTS maintenance is necessary, or even that they rely on onsite

treatment.

Education programs regarding OWTS

maintenance are sponsored by some

political jurisdictions, educational

associations, and other groups (see Mancl

and Magette, 1991). While such programs

can address some of the homeowner

maintenance issues discussed previously

and are virtually always a component of

OWTS management programs, education

programs are, at best, rarely completely

effective in changing behavior. Education

and outreach efforts are necessary but are

not usually sufficient in preventing

neglect, just as the posting of speed limit

signs does not obviate the need for

enforcement.

Preventing OWTS Failure

For the reasons above, it is not uncommon

for homeowners to focus on OWTS

maintenance until after gross failures

occur. When a system fails noticeably (for

example, with surface discharge), owner

inconvenience from such factors as odor

is usually sufficient to assure relatively

prompt remediation. Unfortunately,

remediation by owners is often predicated

on a clear and inconvenient failure, and

Advantages of Effective

OWTS Maintenance
The Small Flows Journal Volume 2, Issue 1, Winter 1996

corrective measures can be significantly

more expensive than preventive ones.

The first problem with preventing OWTS

failure is related to the difficulty of clearly

defining “failure.” Reliance on owner

action tends to imply a definition based on

obvious inconvenience, such as odor

problems, surface discharge, etc. Even

obvious symptoms of incipient failure,

such as transient surface ponding directly

over leach lines, may well be missed or

ignored by the homeowner. Symptoms

recognized by the homeowner usually

appear well after more subtle symptoms

of failure. Water quality impacts and

threats to public health can occur well

before the more obvious symptoms of

failure.

Implications of the increased OWTS

remediation costs include overall increased expenses for the homeowner

(public funds for the remediation of

failing private onsite systems are small

and are likely to remain so) and the

problem that some individuals will not be

able to remediate at all. Regulatory

officials are thus placed in the position of

enforcing against individuals who already

perceive themselves as victims, and who

cannot afford to remediate.

Given such undesirable alternative

solutions as property condemnation,

regulatory agencies are faced with simply

attempting to meliorate problems. While

the creative use of alternative onsite

systems can resolve problems in many

instances, cases still remain in which the

results are unsatisfactory from both

environmental and public health perspectives.

One approach that could offer a workable

OWTS maintenance alternative for

individual homeowners would be the

development of a private market in

catastrophic OWTS failure insurance.

Private insurers could offer policies,

perhaps as riders to existing homeowner

policies, that would cover the cost of

OWTS repair or replacement. Clearly,

insurers would have an incentive to

develop expertise to assess and reduce

risks of system failure in order to maximize their profits. An obvious approach to

doing so is to establish minimum maintenance standards that void the policy when

not met. Systems maintained according to

these minimums would, in fact, have a

reduced likelihood of failure, protecting

environmental and public health as well as

reducing overall costs to homeowners.

The concept of using insurance programs

to reduce pollution potential from private

homes is already being considered in New

York. In response to concern over

pollution potential in the New York City

watershed system, New York State has

announced that legislation will be introduced authorizing the creation of “. . . a

voluntary program of homeowner

insurance for underground home heating

oil tanks. Such insurance would cover the

cost of necessary soil and groundwater

remediation and thereby encourage

homeowners to investigate and report on

the conditions of their underground tanks,

and remediate identified problems” (New

York State, 1995, 10). The impetus for this

program is concern over public health—

the New York City water supply system

provides drinking water to over 9 million

people. Similar logic could be used to

extend the program to address OWTS

maintenance issues.

Insurers of onsite systems might offer a

range of options with policies, such as

varying deductibles. Thus, a very lowpriced policy with a high deductible

would not cover routine costs such as

periodic pumping, while a more expensive

policy could (for a hypothetical example

of OWTS coverage, see table 1). Such

policies would be, from the homeowner’s

perspective, analogous to a utility district,

allowing the homeowner to trade a lower

regular payment for protection from larger

unexpected costs. For example, the

Georgetown Divide Public Utility in

California includes inspections for onsite

systems in a large subdivision among its

20

John Herring

A Private Market Alternative
The Small Flows Journal Volume 2, Issue 1, Winter 1996

Coverage provided

Repair and replacement

costs up to $2,500

Repair or replacement of

existing system up to $5,000

Repair and replacement

costs up to $10,000. Up to

$1,000 design permitting

costs for alternative onsite

or special systems.

Deductible

High

Medium

none

Services Included

none

Inspection of System

Annual inspection of system

Annual household plumbing

 and water use audit

Pumping of tanks needed

Policy

Low–Cost

Standard

Deluxe

21

A Private Market Approach To Onsite Wastewater Treatment System Maintenance

services. Homeowners are charged $12.50

per month for the management of singlefamily systems (Dix, 1992).

To compare the private market plan to that

of public districts or utilities, first consider

a situation in which all homeowners

participate. The systems would have equal

beneficial impacts, in that maintenance

would be uniformly addressed. In each

case, the homeowner would pay a relatively low fee in order to avoid the

possibility of a much larger cost should the

system fail. The only difference under the

full participation scenario is that the fee

would be paid to a private insurer in one

case and a public utility in the other.

However, if support for OWTS maintenance is not universal, the two systems

would differ. With the insurance approach,

there is a direct correlation between those

supporting OWTS maintenance and

participation. Under the district plan, those

supporting maintenance can, if sufficiently

numerous and vocal, force a maintenance

program on those reluctant to participate.

The result under the district plan would be

high participation, assuming adequate

enforcement of the regulatory program is

included. If, however, those supporting

OWTS maintenance are not sufficiently

numerous or well-organized, their desire

for a district will be frustrated. In such a

case, the only maintenance that will occur

is that which can be attained through

voluntary means, such as education.

The above comparison assumes, for both

options, that each OWTS contributes

equally to pollution problems, or that the

relationship between likelihood of pollutTABLE 1

hypothetical example of

levels of OWTS insurance

coverage

ing and support for OWTS management is random. In most instances, a

relatively small portion of systems

constitute the majority of pollution

potential. This serves to increase the

difference between the two approaches. If we assume that those

owners most likely to pollute are also

most likely to oppose required

maintenance (because of the repair

costs it would impose), the insurance

strategy would provide some benefits

but not adequately deal with the

highest-risk cases.

On the other hand, the district approach could be expected to have one

of two results. If a sufficient majority

of homeowners were interested in

required maintenance (i.e., the

proportion of high-risk systems was

low), they could force the creation of a

program that would address the highrisk situations. If, however, those

opposing the district were capable of

blocking formation, there would be no

required maintenance for anyone. In

this sense, the district strategy may be

seen as a high-risk, high-payoff strategy.

Advantages of OWTS Insurance

Following are several points of interest

and possible benefits of the private

insurance approach to OWTS maintenance:

An insurance plan may allow for

the application of market forces to

minimize the costs associated with

OWTS management.

Just as individuals frequently

compare costs and services for autos

or homes, a private market system

will offer the opportunity for

competition to improve prices and

service to the homeowner. Estimates

of the cost of such insurance are, of

course, heavily dependent on

assumptions regarding such issues

as system life cycle and the extension to be expected through routine

maintenance, definitions of system

failure, and so on.
The Small Flows Journal Volume 2, Issue 1, Winter 1996

Insurers might consider site conditions

such as soil porosity and proximity to

water supplies (which affect the risk an

individual OWTS poses) in determining premium rates, the frequency of

appropriate inspections, and action

levels for remediation. Insurers might

elect to require that inspections be

performed by their staff or by individuals with specified credentials, such

as registered sanitarians.

Individual insurers would have the

burden of determining at what point

a system can be considered in

failure.

One major difficulty facing any

traditional OWTS regulatory inspection program is the determination of

failure, because OWTS failure is most

often a continuum rather than a single

catastrophic event. This problem

would be much less important under

an insurance plan, as individual

insurers might establish their own

systems of evaluation. Insurers would

thus balance the increased protection

from setting high standards (very early

warning of possible problems) with the

increased costs associated with the risk

reduction. It is to be expected that,

over time, some standardization would

occur. At a minimum, certain failure

“trigger points” would be set so as to

meet relevant public health and

environmental standards, so that the

insurance would actually protect the

homeowner. Clear trigger points would

probably include those currently

applicable in regulation, such as

surface discharge, and other possible

criteria such as the physical integrity

of tanks and lines (avoiding cracks),

evidence of solids flow into leach

lines, etc.

An insurance approach may encourage and generate funding for further

OWTS research.

Because of the direct economic

implications of setting specific points

of failure, insurers would have a

significant incentive to improve

22

Observed OWTS failure rates usually

range between one and five percent per

year (EPA, 1993, 4.114). Assuming a

catastrophic failure rate of one percent

per year with remediation costs

averaging $4000, a fee of forty dollars

per year should cover claims. Premiums must be higher to allow for

overhead costs and profit. In addition,

at least in the initial stages of such a

program, a significant margin for error

would be needed. This margin would

presumably be reduced as expertise

accumulated. It thus seems that a

premium of one hundred dollars per

year, competitive with costs of some

existing governmental districts, is

feasible. If policies were incorporated

as riders on existing homeowner

policies, administrative costs would be

minimized. With 25 million such

systems in the United States, the

potential market is significant.

Private insurers can be expected to

set maintenance standards for

OWTS policies in order to reduce

their costs.

Just as an insurer may encourage

proper maintenance for a home in

order to avoid later claims, OWTS

insurance would provide an incentive

for insurers to work with their customers to improve routine maintenance.

Examples of approaches include

offering differential premiums,

distributing educational pamphlets,

and establishing minimum maintenance requirements. Again, as with

traditional homeowner policies, the

insurer may reject or limit claims if

reasonable and customary maintenance

is not performed by the owner (e.g., if

the OWTS is never pumped or

inspected). Both insurer and insured

thus have strong incentives to improve

maintenance and reduce the likelihood

of failure.

Private insurance holds the promise

of allowing tailoring to site-specific

conditions, always an important

factor in OWTS management.

John Herring
The Small Flows Journal Volume 2, Issue 1, Winter 1996

tion. Just as most lending institutions

require insurance to protect against other

value-reducing problems such as fire, they

might require OWTS insurance.

Because OWTS management has not

historically been a major issue for such

institutions, an education program for

lending institutions would probably be

necessary. Such a targeted program might

be developed by water quality experts as

a long-term means of improving water

quality. Alternatively, private groups,

whether they be environmental interest

groups or associations focusing on the

insurance industry, might also assume the

role of educating lenders.

Adoption of OWTS insurance requirements by such federal lenders as HUD and

FHA would both introduce the concept to

the private sector and establish a market,

justifying private insurers in taking action

to develop their offerings. Alternatively,

having OWTS insurance might translate

into a small rebate on mortgage costs,

reflecting the risk reduction. This possibility is unlikely, however, unless a similar

reduction were applied to mortgages for

homes served by public sewerage.

A factor affecting lending institution

acceptance of OWTS insurance is the

recent growth of the secondary mortgage

market. This has led to pressure to

standardize mortgage terms and conditions, so that groups of mortgages may

more readily be “bundled” for resale. This

will initially act to discourage lender

requirements for OWTS insurance.

However, if the insurance provides

adequate risk reduction, some institutions

are likely to require it. Other factors, such

as proximity to potable water supplies,

may be important in the determination of

risk reduction. Once OWTS insurance is

required for some mortgages, the same

tendancy toward standardization should

act rapidly to increase the number of

institutions requiring the insurance.

23

A Private Market Approach To Onsite Wastewater Treatment System Maintenance

knowledge of such factors as efficiency

and life span of differing types of

systems under differing conditions and

the effectiveness of various best

management practices. As a further

parallel to existing insurance mechanisms, such information might be

generated in many ways. For critical

questions, insurers might themselves

fund research. The Insurance Institute

for Property Loss Reduction, for

example, funds research aimed at

reducing property losses due to natural

disasters, such as hurricanes and

earthquakes (McLean, 1995). In other

instances, research done under other

auspices could be used. The incentive

to improve understanding of OWTS

operation should improve both the

insurance market and OWTS maintenance over time.

Benefits of OWTS failure insurance to the

environment and insurers are clear. The

chief advantage for homeowners is in

terms of risk reduction. As such, acceptance of the plan will depend on

homeowner perceptions of risk. An

insurance program would provide additional opportunities for education programs. Also, because insurance premiums

are predictable, there would be an increased recognition that OWTS management is needed and can have direct

economic impact. Therefore, the insurance

strategy should not be considered a

replacement or substitute for educational

programs. Instead, they are complementary.

OWTS Mortgage Insurance

Perceived risk reduction as a driving force

is not limited to the homeowner. Approximately two-thirds of the owner-occupied,

one-family housing units in the United

States are currently covered by a mortgage

or other lien (Bureau of the Census, 1993,

224–230, table 66). Financial institutions

may be expected to recognize the risk

reduction potential of such an insurance

plan and take steps to encourage participa-
The Small Flows Journal Volume 2, Issue 1, Winter 1996

Existing regulations to ensure appropriate

OWTS maintenance are inadequate, and

public support for expansion of regulatory

authority through mechanisms such as

wastewater management districts or

utilities is limited except in specialized

circumstances. Voluntary programs, such

as education programs developed by

cooperative extension offices, cannot be

completely effective. Voluntary programs

also must overcome inherent disincentives

for establishing routine maintenance or

remediating failed systems, because it is

less expensive in the short-term for

unconcerned system owners to do nothing.

What is needed to ensure OWTS maintenance in areas without community programs, then, is an institutional mechanism

that internalizes the cost of OWTS

maintenance, thus reducing failure rates

and consequent public health and environmental problems.

In summary, a private market system for

catastrophic OWTS failure insurance could

provide an alternative approach to improving OWTS maintenance, the major

problem in overall OWTS management.

The insurance approach would offer risk

reduction for the homeowner, avoid the

need for a large and expensive governmental entity, and internalize costs which are

currently external. This strategy could

create new incentives for the development

and refinement of better OWTS maintenance practices, and may also affect siting

and design practices. Improved environmental quality and reduced threats to

public health are possible benefits of such a

system. Risk reduction aspects of the

proposal may also trigger support from

lending institutions, despite recent pressure

for standardization of mortgage provisions.

Dix, S.P. 1986. Case study no. 4—Crystal

Lakes, Colorado. National Small Flows

Clearinghouse. Morgantown: West

Virginia University.

Keuka Watershed Improvement Cooperative

(KWIC). 1993. A draft proposal to

protect and improve the quality of Keuka

Lake. Yates County Planning Office.

Penn Yan: New York.

Mancl, K. and W. Magette. 1991. Water

resources 28—maintaining your septic

tank. Cooperative Extension Service.

College Park: University of Maryland.

McLean, Dan D. 1995. Report of the

chairman. Remarks made at the Second

Annual Meeting of the Insurance Institute

for Property Loss Reduction. (November

14) Chicago.

Mooers, Jordan D. and Donald Waller. 1994.

Wastewater management districts—the

Nova Scotia experience. In Proceedings

of wastewater nutrient removal technologies and onsite management districts

conference. Waterloo Centre for Groundwater. (June 6) Waterloo, Ontario:

University of Waterloo.

New York State Department of Environmental Conservation (DEC). Division of

Water. 1993. Priority water problem list.

Albany: 7–15.

New York State Office of the Governor.

1995. Agreement in principle for the New

York City water supply. (November 2)

Albany.

Otis, Richard, Marc Robertson, and James

Kleinschmidt, 1981. Guide to wastewater

facilities planning in unsewered areas.

Small Scale Waste Management Project.

Madison: University of Wisconsin.

Powell, John, John Herring, and Thistle

Anderson. 1988. Keuka Lake septic

system survey final report. Yates County

Aquatic Vegetation Committee. Penn

Yan: New York.

Richardson, Mark S. 1989. Public management, operation and maintenance of onsite sewage systems. In Proceedings of

the 6th Northwest on-site wastewater

treatment short course. (September 18-

19) Seattle: University of Washington

U. S. Bureau of the Census. 1993. 1990

Census of housing: detailed housing

characteristics: Prepared by Housing and

Economic Statistics Division, Bureau of

the Census. Washington, D.C.

U.S. Environmental Protection Agency

(EPA). 1993. Guidance specifying

management measures for sources of

nonpoint pollution in coastal waters.

U.S. EPA Division of Water. Washington,

D.C.: 4.114–4.116.

NAT

CLEARIN

AL SMALL F

EARINGHOU

ATIONAL SMA

John Herring

John Herring is

currently a coastal

water quality specialist

with the New York

State Department of

State’s Division of

Coastal Resources

and Waterfront

Revitalization, and the

coordinator for New

York State’s Coastal

Nonpoint Pollution

Control Program. He

holds BS and Ph.D.

degrees in natural

resource management

from Cornell University, and an MS in

environmental health

from the Harvard

School of Public

Health. Previous

professional experience includes cooperative extension

agent, environmental

consultant, and

college professor in

both economics and

environmental science.

24

John Herring

Conclusion

References
The Small Flows Journal Volume 2, Issue 1, Winter 1996

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