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Example Annual Costs Per Home |
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1. Inspection: annual or with main treatment system:
a) Look for ponding or damp areas, odors, lush vegetation
b) If alternating beds, operate diversion valve to redirect flow (1-2 times/yr., in warm weather)
c) If distribution box: check levelness and level if necessary
d) For mounds: look for seepage around mound sides, and erosion. Perform landscaping necessary for erosion control.
e) For ET: look for erosion, evidence of misuse. Maintain stormwater drainage (bed crown. swales). Educate homeowner:
- avoid bed compaction by vehicles, people, animals
- maintain proper vegetation (mowed grass and shrubs, no gardens or trees)
- attention to water conservation and water-saving devices
2. Monitor area groundwater semi-annually for:
Monitor at least four wells, three hydraulically wells gradient at the limits of the waste management area, one hydraulically up gradient.
3. Educate homeowners in water usage and conservation practices.
Evapotranspiration is not usually used in Indiana because of the high annual rainfall and cold winters.
Inspections: no additional labor for leachfields
Mound and ET Bed landscaping:
Groundwater monitoring:
Sample analysis:
Parts and Supplies: $ 0
Equipment:
| Landscaping tools (shovel, hoe. rake. pick. etc.) | $91/2 yrs. |
| 1000 ml water sampler and rope | $46/5 yrs. |
| Total: | $55/1 yr. |
Power: $0
| Mound and ET landscaping: | 3 man-hr/bed * $6/man-hr * 20 M&ET bed / 120.00 home = | $3.00 |
| Groundwater Sampling: | 4 man-hrs * $6/man-hr / 120 home = | $0.20 |
| Sample Analysis: | 8 sample * $35/sample / 120 home = | $2.33 |
| Equipment: | $55.00 / 120 home = | $0.46 |
| Total: | (First Quarter 1982) = | $5.99 |
| Updated Total: | Total | OMR | 1982 OMR | |
| $5.99 | *3.49 | / 3.44 | = $6.08 |
These systems all discharge to groundwater and have similar O&M requirements therefore they are treated together.
The leachfield, is generally the least expensive to install, operate, and maintain, given proper design, siting, etc.
Mound and ET beds can be used where siting limitations preclude a standard leachfield, but are prone to failure if not properly attended. Mounds are often preceded by a septic effluent pump, treated earlier.
Descriptions of all beds are found in EPA (1980c). Laak (1980) describes leachfields.
Properly managed leachfields are generally problem free. Improper siting may cause effluent to enter the groundwater. Solids in the influent will cause bed clogging, resulting in odors, ponding, and/or in sewage "backing up" into the house.
Unlevel distribution boxes can cause surfacing of effluent on sloping sites. Mounds and ET beds are much more problem-prone and require very effective management. They are sensitive to hydraulic overloading, bed compaction inadequate stormwater drainage, and improper vegetation. Failure is generally characterized by surfacing effluent. Hoover et al. (1981) calculated a 50% mound failure rate f or the state of Pennsylvania. McKluskey ( 1982) estimated a 50% ET failure rate and 10% leachfield failures in Mill Canyon, Colorado, an area of problem soils.
Some O&M functions are needed to help avoid problems have been developed, including inspections, homeowner education, and groundwater monitoring. The groundwater monitoring program specified is a relatively inexpensive way for a community to detect an otherwise unapparent type of system failure. Homeowner education is absolutely essential as preventative maintenance of ET systems, since any of the conditions mentioned above will cause system failure.
All system components considered have an expected life of at least 20 years, and thus system rehabilitation may be considered a capital expense. However, provisions have been made here to include complete system repair in the economic evaluation, if desired, for areas which have an established failure rate for existing systems.
Estimates of repair costs were obtained from contractors noted earlier. These were supplemented with new system construction costs considering that repairs often consist of adding to the old bed at about half the cost of a new system.
The example calculation presents annual costs per home for a community with 100 leachfields, 10 mounds, and 10 ET beds. Thus the total is an average which most strongly reflects the costs for leachfields, which often predominate. Costs for complete system repairs are not included (failure rate equals 0.0 for illustration purposes only).