Last summer’s regional drought conditions sent confusing signals about effective effluent distribution


Question:

Last summer was dreadfully dry — good for leach fields, but bad for the pumping business. My question is this: Over certain fields, (almost everything here is trench and gravel) the drain lines showed dead surface vegetation above the lines, as opposed to the usual bright green and healthy strips such fields usually produce. In these cases, I suspect potential blockage due to root infusion, system age and lack of maintenance, etc. Still, should it just die? Surrounding vegetation, though drought-stricken, looks better. Could the gravel layer prevent access to deeper soil moisture? Could it be caused by flushed items?

Answer:

First, you stated the dry summer was “good for leach fields, but bad for the pumping business.” I’m not sure why this should be, unless tanks are pumped in your area only when the leach field is failing and effluent is coming to the surface or the toilet is backing up.

If the trenches are full of effluent, the grass should be green over all of the trenches. The effluent reaches soil above the trench rock and capillary action pulls the moisture up for the plant roots. But full trenches also mean the septic system is at capacity.

Your first comment indicates that septic systems in your area are pumped only when trenches are full and people have sewage backing up. When there is a lot of rain, the extra moisture does not let as much effluent percolate into the wet soil. The onsite system does not take as much wastewater, the sewage backs up and you get called.

In dry years the soil absorbs and draws more liquid away from the trenches. The trenches may only be part full. The sewage does not back up, people don’t have the “failing” systems, so you are not getting called.

NEW TRENCHES?

You said some drain lines show dead surface vegetation above the lines, as opposed to the usual bright green strips such fields usually produce. The surrounding vegetation was suffering from the drought, but looked better than over the trenches.

There may be several reasons for this. First, the trenches may be relatively new and effluent isn’t reaching the top of the trench rock and contacting the topsoil. With only a little effluent in the trench rock, the only way for moisture to get up to the soil would be as vapor. Under severely dry conditions the vapor may not supply enough moisture to the vegetation above the trench rock.

What kind of effluent distribution is being used for multiple trench systems in your area? If drop boxes are being used, the first trench or trenches will be full of effluent and show green strips. Trenches farther along the drop box line may not have any effluent, so the only moisture for the grass is provided by rainfall. The grass above these trenches will be dry.

If distribution boxes are used, the area for the drainfield is level and the system is new, there will be only a little effluent in the bottom of each trench. The grass roots will not get enough moisture from this effluent to stay green under dry weather conditions.

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Are trenches in your area installed with inspection pipes? If so, you could open a pipe cap and find out if there was effluent in a trench and, if so, the depth of the effluent.

SHALLOW TOPSOIL

Maybe there is not much soil depth above the rock layer in the trench. The grass roots or other vegetation above the trench will not have much depth of soil from which to get water when there is no effluent in the trench. Between the trenches, the original soil will allow the roots to penetrate deeper and have access to more water.

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Under the dry conditions you describe, the extra soil depth still may not contain enough water to keep the grass green. But the plants between the trenches with the deeper root system would look a little better than the plants directly above the trenches.

How much soil cover is usually placed over the trench rock in your area? If the depth of soil is 6 inches or less, as it should be, there will not be enough moisture in the soil above the trench rock to keep the surface vegetation growing when it is really dry.

The backfill soil placed over the trenches may also be of a different texture than the original topsoil, which exists in the area between the trenches. When a trench is being excavated, the soil is piled up beside the excavation with the topsoil on the bottom of the pile. The topsoil likely will not be replaced above the trench rock.

You asked about blockage from root infusion. Grass roots, or any roots, are not going to grow into trench gravel that is full of effluent. If the effluent percolates out into the soil where there is also soil air with oxygen, the roots will be there.

You asked about the age of systems and lack of maintenance. I don’t believe “lack of maintenance” has anything to do with the situation you describe. Lack of maintenance will affect the life of the onsite system, but should have nothing to do with the growth of grass under wet or dry conditions. I also don’t believe anything “flushed” down the drain would have an effect on what you are describing.

SCHEDULED MAINTENCE

I recommend you establish a program with your customers to have their tanks pumped and cleaned on a regular basis rather than waiting until their sewage backs up. Then wet or dry years will not affect your pumping business.

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