Installing With Management in Mind

After a good soil evaluation and design, there are many things an installer can do to ensure a high-quality, long-lasting system.
Installing With  Management in Mind
Access to the system is important for future management. Here, access to a pressure distribution lateral is provided so the that lateral can be periodically cleaned

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In previous columns we have discussed various aspects of installing onsite systems with an eye toward future management. Now we'll take a fresh look at the issue and try to be a little more comprehensive in our approach.

We feel that installing for management ensures good installations that will last a long time. It is interesting that even some state codes specify that systems should be installed in a manner that ensures they last at least 20 years, yet offer no insight on what such a system looks like or what the key elements are to make sure that longevity is delivered.

According to the glossary put forth a few years ago by the Consortium of Institutes for Decentralized Wastewater Treatment, system management is defined as all the steps necessary to conduct operational inspections, maintenance, monitoring and compensation. For systems to be managed properly, they must be installed with all of these activities in mind.

Start with design

A management program such as that administered by a responsible management entity provides the framework for maintaining the onsite wastewater treatment infrastructure. For management to succeed and for the systems to be good, work must start way back at the soil and site evaluation phase.

If a bad soil or site call is made, the system has no chance of operating properly into the future, but if the system is properly sited, has easy access for maintenance, is used properly by the owner, and receives proper care, including the required maintenance and reporting, these systems can be managed for much longer than a normal 20-year horizon.

Assuming the site evaluation and design were done properly – and that includes sizing the system correctly and identifying any limiting conditions such as wet soil and bedrock to ensure proper separation for treatment – what can the installer do to create a good system?

Excavate with care

First, be aware of the elevation of the bottom of the system. Do not over excavate – it is critical to ensure that the required vertical separation
distance from limiting conditions is maintained. Over-digging causes additional expense, so just from the pure economic standpoint, do only the required excavation.

Only excavate when the soil is dry enough. Do not excavate if the soil's moisture content allows it to be molded or rolled into a ribbon. Do not excavate into frozen soil, since this will cause smearing and compaction. Both the site and the infiltrative surface where effluent is applied need to be protected from compaction and smearing.

To prevent compaction, the site should be protected from unwanted traffic. Use of tracked rather than wheeled equipment can help. There should be no cutting or filling on the site, and the area should be protected after installation.

For the infiltrative surface, do not drive upon it. Limit foot traffic on the infiltrative surface during placement of the media. Use low-ground-pressure equipment, and work from the upslope side of the system when placing the media.

Choose the right stuff

Use only proper materials. This includes piping, sewage tanks, treatment system media and backfill. House sewers, supply line piping and distribution pipes must be properly bedded where necessary, and properly glued and attached.

The backfill over supply pipes and the house sewer pipe should not contain rocks, include frozen material, or be organic soil. It should be clean backfill material that is free of soil clods that do not flow over and around the piping.

Any sewage tanks installed in the system should be watertight and of sound materials. This means any risers, the lid and all openings must be properly sealed. The tanks need to properly set on bedded material where appropriate and set level. Piping into and out of the tanks needs to be properly supported, and the proper backfill must be used when filling around and over the tanks.

If the distribution media for the soil treatment unit is rock, it needs to be the proper size, and also durable, hard and clean. When rock is used, it is the installer's responsibility to ensure that the material used meets those requirements. If a gravelless product is used, whether chambers or polystyrene blocks or pellets, it is up to the manufacturer to ensure that the material meets the durability and strength requirements of the system.

If rock is used, hardness is important. The rock should not break into smaller pieces when it is handled. If a penny can scratch the rock without the rock flaking and crumbling, it meets the hardness criteria. The rock should be 3/4 to 2 1/2 inches in diameter and have less than 1 percent fine material (silt- and clay-size particles). If there is a large cloud of dust associated with the rock, the installer should visit the quarry to insist that clean rock be provided.

Keep it clean

When sand media is used for a mound or a media filter, it also needs to be clean. For mounds, there should be no more than 5 percent fines in the material. This can be readily field-tested using the jar test, where two inches of sand are added to a straight-sided quart jar full of water and shaken. If the layer on top of the sand in the jar after two hours exceeds 1/8 inch, the sand is dirty and should not be used.

How the media is handled on the site is also important. Rock or sand should not be stockpiled in a place, or handled in a manner, that would allow fine soil material to be introduced to the material. One source of potential contamination is dirty equipment, such as backhoe buckets covered with soil material from trench excavation.

This is a brief rundown of some installation procedures that make a quality system. Other important aspects include providing access for future maintenance, ensuring proper use and, when necessary, monitoring system performance. We will cover these topics in coming issues, all the while keeping in mind that the objective here is to manage the systems for the long term.



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