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Management of Alternative on-Site Wastewater Systems – a Case Study

Anish R. Jantrania, Ph.D., P.E.,
Office of Environmental Health Services,
Main St. Station Suite 117, PO Box 2448,
Richmond, VA 23218

Introduction

The basic utility requirements for any home includes water, electricity, gas and sewage. To develop residential areas in an environmentally responsible manner, it is essential to adequately manage wastewater generated from individual homes, along with other wastes. Although many areas in the country have relatively easy access to a central sewer system and a treatment plant, census data from the last three decades indicate that about 25 percent of homes are unsewered. These homes use some form of on-site (decentralized) wastewater system, most commonly a conventional septic system. An improperly designed and/or inadequately managed on-site system will pollute groundwater and/or surface water, and may even raise public health concerns.

There are many examples of environmental pollution from sub-standard conventional septic systems all over the country. In Massachusetts, the state Department of Environmental Protection (DEP) estimates that of the approximately 650,000 on-site wastewater systems in use, approximately half are substandard conventional septic systems or cesspools. Pollution problems from inadequate on-site systems in the state are extensive. Statewide, approximately two-thirds of the surface waters surveyed in a 1992 water quality study were found to be inadequate to support fishing or swimming, and in providing habitats for aquatic life due to water pollution. One of the leading causes of such a pollution problem is discharges from cesspools and substandard or failing septic systems. Similar problems from on-site systems can be found in other states.

Even on-site systems which function properly from a hydraulics perspective (no effluent ponding on ground surface or backup into home) can result in environmental contamination and pose public and/or environmental health risks. This is of particular concern in densely developed areas, where prevailing soil type, water table, and/or other site conditions can cause inadequately treated wastewater to enter groundwater and travel long distances. In order to adequately protect public and environmental health from on-site systems, selection of “appropriate” treatment and disposal systems for given soil and site conditions as well as permanent management of these systems are the most important issues.

Conventional Septic Systems

Besides the cesspool or pit-privy, the most commonly used wastewater system for individual homes is a conventional septic system which consists of a septic tank and a drain field for ultimate disposal of the septic tank effluent. A septic tank-soil drain field system is a cost effective, simple, and easy to maintain on-site wastewater treatment system that has application not only in rural America, but also, in newly developed suburban areas where city sewers are too expensive or too difficult to reach.

Despite their simplicity and advantages, conventional septic systems are not appropriate for all sites and soil conditions. In fact, many of the nation’s soils are classified as unsuitable or marginally suitable for the successful operation of a conventional septic system. When installed at an unsuitable site, a conventional system can experience two types of failures: an operational failure, which is noticeable by ponding of effluent on the ground surface or backup into the house; and a treatment failure, which, though difficult to detect, results in groundwater or surface water pollution from inadequately treated wastewater. Both of these failures can be prevented by careful site and soil evaluation prior to permitting a conventional septic system on a proposed site. Use of a “watertight” septic tank and an effluent filter (a simple device that lowers amount of solids exiting the tank) should be encouraged to improve functioning of a conventional septic system. Even on sites that are suitable for conventional septic systems, a long-term maintenance of the systems is a must in order to prevent the operation and/or treatment failure.

As indicated before, the conventional septic systems are relatively easy to maintain on a long-term basis. Regular pumping of the septic tank is to remove accumulated septage and scum is the primary maintenance requirement for the conventional septic systems. However, at what interval the septic tanks should be pumped (pumping frequency) is always questionable and there is not a “perfect” answer to this question. Routine inspection may be a better way to deal with this issue. An annual or semi-annual inspection of septic tanks can offer a better understanding of the overall performance of the conventional septic systems. Such an inspection can also allow for necessary maintenance of the effluent filter when one is present in the tank. Who can provide such a routine maintenance service for the conventional septic systems and at what cost, are obvious questions that should be addressed before making a regulatory requirement.

Alternative Septic Systems

In areas where marginal soil and site conditions (such as high water tables, shallow bedrock, or close proximity to surface water) do not allow for conventional septic tank effluent disposal, the effluent can be further treated by using one of many advanced (alternative) treatment systems. The objective of advanced treatment is to reduce the waste strength of the septic effluent (measured in terms of biological oxygen demand, suspended solids, nutrient, and fecal coliform bacteria count) so that the effluent can be disposed of without adverse impact on the environment. Selection of an advanced treatment systems is site-specific and is normally governed by state regulations. Maintenance and monitoring requirements for alternative systems are more intense compared to the conventional septic systems.

In order to evaluate field performance and public acceptance of alternative on-site systems, a National On-Site Demonstration Program is currently undertaken by the National Small Flows Clearinghouse. Gloucester, MA is one of several communities in the country investing the use of alternative on-site systems as an option to central sewering for abating coastal water pollution problem. The city has implemented seven pilot projects over the last two years. Since 1994, there have been five different treatment systems and four different disposal systems in operation and under monitoring. Table-1 presents the technical details on each project. The treatment systems include: recirculating sand filter, intermittent sand filter, Bioclere, Orenco trickling filter, and Waterloo Bio-Filter. The disposal systems include: Infiltration Chambers, pressure dosed trench, shallow trench, and sand-lined trench. Monitoring of these systems include monthly sample collection from septic tank, treatment devices, and groundwater monitoring wells; recording water usage; and collecting homeowners’ input about operational problems with the systems. A summary of monitoring data collected for about 18 months is presented in Table-2. The city is currently managing the systems and is working on developing a city wide management program to provide for a permanent operation and maintenance services for such systems.

As the on-site systems become complex, the operation and maintenance requirements increase and so is the cost of offering such services. The onsite inspection frequency may increase up to once a quarter or once a month inspection. Also, there will be a need for attending emergency situations. Most of the alternative treatment systems incorporate a mechanical component (a pump, a blower, or something equivalent) to move air through the system and/or to move the wastewater through the system. Such a component can fail anytime and will need immediate repair or replacement. At present, the alternative system relay on audio visual alarm system to indicate a “problem” with the mechanical component. The homeowner is responsible for calling the service entity when the system is in alarm conditions. This type of arrangement is not always efficient in identifying and reporting a “problem” with the system. Use of remote monitoring of alternative systems is a preferred option. Gloucester, MA is currently exploring use of a remote monitoring systems for its alternative sewage collection system as well as for alternative on-site systems.

Long-Term Management

A long-term, permanent, management of on-site systems is becoming more and more of an importance as the alternative treatment and disposal systems are installed to overcome soil and site constrains. It is important to recognize that even a conventional septic system needs permanent management in order for it to function adequately. A community thinking seriously about implementing a permanent management program for the on-site systems must develop a database for all the systems that are operating in the area, list what type of system is in use, and what is the minimum maintenance requirement for the system. Normally, a town or a county should take a lead in determining the cost of such a management program and set a user-fee similar to sewer fees charged for a central sewer system. Normally, a town or a county should take a lead in determining the cost of such a management program and set a user-fee similar to sewer fees charged for a central sewer system. Septic tank pumping as necessary is the minimum maintenance for maintenance of on-site systems and this task should be done in conjunction with a regular inspection program. If a mechanical component is present for advance treatment or disposal purposes, a remote monitoring system should be considered in order to better manage the system Adequate public and environmental protection can be achieved from the on-site system when permanent management system is in place.

SAMPLES ARE COLLECTED FROM:

  • UG = UP GRADIENT MONITORING WELL
  • STE = SEPTIC TANK EFFLUENT*
  • TRE = TREATED EFFLUENT*
  • DG = DOWN GRADIENT MONITORING WELL

* At Brierwood St., STE is Treated Effluent from ORENCO Trickling Filter and TRE is Effluent for the bottom of the Sand-Lined Bed. PILOT SYSTEMS IN GLOUCESTER
NOTE: S#1,2,3, and 4 are part of the first pilot project in operation since April 1994
S# 5,6, and 7 are part of the NODP in operation since December 1994

Table 1

S# Location Treatment Disposal
1 11 R colburn St.
Map # 157, Lot# 34
Total Area = 7,320
3 Bedroom
Recirculating Sand Filter
22’X5′ filter bed
24″ of Coarse Sand
Loading Rate = 3 1,000 Gal. ST
Infiltrator-Pressure Dosed Bed
Bottom 36″ Below Ground
18.75′ X 18′ Bed; 18 Units
Loading Rate = 0.98
2 62 High St.
Map #153, Lot #50
Total Area=18,150
4 Bedroom
Bio-Clere
Model #1612
1,000 Gal. ST
Pressure Dosed Bed
Bottom 24″ Below Ground
40′ X 12′ Bed; 3 Pipes
Loading Rate = 0.98
3 43 Langsford St.
Map #152, Lot #11
Total Area=8,250
4 Bedroom
Recirculating Sand Filter
30′ X 5′ filter bed
Recirc. Rate = 5:1
Loading Rate = 2.9,
1,000 Gal. ST
Infiltrator-Pressure Dosed Bed
Bottom 36″ Below Ground
31.25′ X 15′ Bed; 25 Units
Loading Rate = 0.94
4 10 Vale Ct.
Map #138, Lot #25
Total Area=25,100
5 Bedroom
Bio-Clere
Model #1612
Two 1,000Gal. ST(one w/EF)
Infiltrator-Pressure Dosed Bed
Raised Bed;48″ Fill;
62.5′ Bed;25 Units
Loading Rate = 0.98
5 7 Bittersweet Rd.
Map #117, Lot #28
Total Area=28,360
3 Bedroom
Waterloo Biofilter
6′ X 6′ Filter and 4′ deep media
Single pass, with ability to recirc.
Loading Rate = 9.2;
1,500 Gal. ST w/Ef PC
Gravity Trenches (2 pipes);
Bottom 48″ Below Ground;
90′ X 4′;D-Box in the middle
Loading Rate = 0.92
6 17 Brierwood St.
Map #125, Lot #41
Total Area=10,000
3 Bedroom
ORENCO Rec. Trickling Filter
RTF Installed in the ST
1,500 Gal. ST w/EF PC
Sand-Lined Bed (Insulated);
Bottom 24″ Below Ground;
65′ X 5′;12″ of sand
Loading Rate = 1.02
7 1166 Washington St.
Map #151, Lot #31
Total Area=20,963
3 Bedroom
ORENCO Intermittent Sand Filter;
100 ft.2; Single Pass Filter
Loading rate = 3.3
1,500 Gal. ST w/EF PC
Shallow Trenches (3 total);
Bottom 15″ Below Ground;
50′ X 1′ each 150 ft.2
Loading Rate = 2.2-6.6

Table 2

Parameters RSF ISF Bio- Filter Bioclere RTF*
** Colburn St. Langsford St. Washington St. Bittersweet Rd. High St. Vale Ct. Brierwood St.
BOD5(mg/l)………….. IN
……………………………..OUT
…………………………% Rem.
314
7
98
270
11
96
264
15
94
155
12
92
143
29
80
248
51
79
89
29
86
TSS (mg/l)………………IN
……………………………..OUT
…………………………% Rem.
7.8
6.8
8.1
6.9
6.7
6.8
7.1
7.3
7.8
7.4
7.0
7.2
6.4
6.5
O & G………………………IN
……………………………..OUT
………………………..% Rem.
37.0
2.3
94
40.9
7.3
82
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
54.3
2.7
95
45.8
4.8
90
N.A.
N.A.
N.A.
Conductivity…………. IN
(micromhos/cm)…OUT
…………………………% Rem.
885
806
1190
828
866
847
763
636
626
519
620
495
602
422

Table 3

Parameters RSF ISF Bio- Filter Bioclere RTF*
** Colburn St. Langsford St. Washington St. Bittersweet Rd. High St. Vale Ct. Brierwood St.
D.O………………….. IN
(mg/l)……………OUT
N.A.
N.A.
N.A.
N.A.
1.5
3.1
2.0
7.3
N.A.
N.A.
N.A.
N.A.
3.0
4.5
Chloride…………….IN
(mg/l)…………….OUT
N.A.
N.A.
N.A.
N.A.
61
68
67
66
N.A.
N.A.
N.A.
N.A.
60
53
Temperature…….IN
(Deg. C)………..OUT
N.A.
N.A.
N.A.
N.A.
13
12
14
13
N.A.
N.A.
N.A.
N.A.
17
11
Ammon.-H……..IN
(mg/l)……………OUT
63.9
17.5
102.3
20.3
54.1
37.5
56.1
26.5
24.8
7.6
41.4
14.2
16.7
11.8
Nitrate-N………..IN
(mg/l)……………OUT
0.5
38.8
3.3
51.4
0.2
13.4
0.1
23.0
0.3
12.8
0.1
7.0
2.6
4.0
Kjeld.-N…………..IN
(mg/l)……………OUT
95.1
22.0
150.0
27.2
76.0
47.9
78.0
32.9
39.0
14.0
78.3
22.2
29.5
18.1

Table 4

Parameters RSF ISF Bio- Filter Bioclere RTF*
** Colburn St. Langsford St. Washington St. Bittersweet Rd. High St. Vale Ct. Brierwood St.
Total-N……………….IN
(mg/l)……………….OUT
………………………% Rem.
95.6
60.8
36
153.3
78.6
49
76.2
61.3
20
78.1
55.9
28
39.3
26.8
32
78.4
29.2
63
32.1
22.1
71
Total-P………………..IN
(mg/l)……………….OUT
……………………..% Rem.
8.7
3.0
66
16.7
5.1
69
11.4
8.3
27
7.8
8.4
N.A.
7.5
6.4
15
10.0
4.8
52
6.5
4.5
53
MGAS…………………IN
(mg/l)……………….OUT ……………………..% Rem.
18.1
0.3
98
23.1
2.1
9.1
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
6.4
0.5
92
15.2
1.1
93
N.A.
N.A.
N.A.
F. Colif………………..IN 323,582 938,627 211,584 99,628 155,452 1,489,019 70,399
Coin./100ml)…..OUT
……………………..% Rem.
10,285
97
7,189
99
5,182
98
1,377
99
7,407
95
121,943
92
23,018
67

TABLE 5

Parameters RSF ISF Bio- Filter Bioclere RTF*
** Colburn St. Langsford St. Washington St. Bittersweet Rd. High St. Vale Ct. Brierwood St.
Total-N……………….IN
(mg/l)……………….OUT
………………………% Rem.
95.6
60.8
36
153.3
78.6
49
76.2
61.3
20
78.1
55.9
28
39.3
26.8
32
78.4
29.2
63
32.1
22.1
71
Total-P………………..IN
(mg/l)……………….OUT
……………………..% Rem.
8.7
3.0
66
16.7
5.1
69
11.4
8.3
27
7.8
8.4
N.A.
7.5
6.4
15
10.0
4.8
52
6.5
4.5
53