Septic Drain Field Remediation

7/30/2019 Septic Drain Field Remediation

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Septic Drain Field

RemediationSoils 401 Section 001Joseph P. Smith

3/29/2013


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Introduction

Septic systems are commonly used as a sewage holding and treatment option when city

wastewater treatment plants are not available. Septic systems consist of three major parts: a

toilet, a septic tank, and a drainage field. The septic tank is designed as a box with one inlet and

one outlet. The box is sized to be long enough to allow the large particles to settle and form

sludge by the time they reach the end of the box. These solids are digested by bacteria through

anaerobic (no air) or aerobic (with air) digestion. A layer of scummy film will form and float on

top of the fluids in the tank. The outlet is designed so that only water will be discharged from

the tank. The outlet is built above

the sludge and a baffle wall is added

to prevent the scum from escaping.

The outlet water is released through a

drainage field for a natural treatment.

I will focus my project on how to

amend a failing drainage field in a

septic system.

A proper drainage field is designed for percolation in soil before the effluent reaches the

bedrock and water table. Soil acts as a filter for the septic water, removing the surplus of organic

material that sewage is composed of. The soil functions to remove biochemical oxygen demand

(BOD), phosphorous, and salts. When a soils hydraulic capacity is very low (i.e. clay), the

water will not percolate through the soil quickly enough and the drainage field will not be

Image 1: soil absorption and purification layersabove the water table (Septic Systems andTheirMaintenance).


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effective. Moreover, the water in the septic system will back up. To create an effective drainage

field, the soil surrounding the drainage field will have to be altered. Conversely, having soil that

is too coarse and porous will not effectively treat sewage because the water will pass through the

soil too quickly. When this happens, organics do not have time to attach to soil. Drain fields can

fail for numerous other reasons including soil compaction from vehicles driving over the drain

field, system overload from increased use in a short period of time, and root systems clogging or

disrupting the system (Owens and Rutledge, n.d.). It is my goal to create a soil remediation plan

at a site with a failing septic system. Keep in mind that septic system installation and

remediation costs money. For the duration of the report, it will be assumed that the builder is

willing to spend money for a quality and long lasting product.

Site and Soil Description

Merigold, Bolivar County, Mississippi


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Image 1: Site (Google Maps)

Soils at site

o Brittain silt loam, nearly level phase (forestdale)o Dowling clay (sharkey)o Forestdale silty clay loam, nearly level phase

The problem at the site occurs in all three soil types because they all have very low hydraulic

conductivities (Rycroft and Amer, 1995). This is problematic because with low conductivity,

water cannot drain from the septic tank and the potential for a sewage backup arises. Sewage

water will pond on top of the drain field, causing damage to the land above it. The location is in

Bolivar County, MS, just outside of the town of Merigold. To get to the site, drive north from

Merigold on Park Street. The site is on the left of the road (west). The site is on farmland and a

small stream runs through the site. There are roads within 500 feet of the soil site boundary. As

the site is for a septic tank, there are homes in proximity of the site. I am going to take a

hypothetical look at a builder buying a plot of land and building a house on the site. For this

project, the landowner wants to include a septic system in the field. As the depth of soil

increases, the soil characteristics vary slightly. With an increase in depth, the pH increases,

cation-exchange capacity decreases, hydraulic conductivity slightly increases, water content

decreases, and percent clay does not follow any set pattern. The soils clay contents are all very

high which causes low hydraulic conductivity in the soils. In a septic system, septic water is

released through a drainage field to trickle through the soil. This removes the high organic

content from the water before it enters the bedrock and water table. In the case of soils with a

low hydraulic conductivity (i.e. clay), septic water cannot pass through the soil to reach the water

table (Owens and Rutledge, n.d.). This causes backups in the septic system and leads to septic

failure. See the appendix section for site soil characteristics.


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Literature Review

Jones and Taylor focused on laboratory research to determine changes in soil hydraulic

conductivity with respect to time after effluent application. Clogged pores were thought to lead

to reduced hydraulic conductivity and consequent septic system failure. The experimental results

show that clogging in septic system sands happens based on the cumulative effluent load. There

were found to be three phases of clogging. The rate of clogging in the initial phase is seen by

reduction of hydraulic conductivity that is directly proportional to the volume of effluent

percolated. This occurs because of organic solids deposited at the sand and gravel interface.

Clogging rates are significantly slower in the second phase. In the second phase, organic

material deposited is nearly equal to organic materials leaving the system so essentially no

clogging occurs. The third stage sees a high rate of clogging and a rapid decrease in K. It is

concluded that an absorption system should function without clogging for a long time if the

second phase of clogging could be extended for a longer period of time. Soil clogging occurs 3-

10 times faster under anaerobic conditions because air converts some deposited organic material.

Sands with high initial K clog slower than sands with relatively low initial K value (Jones and

Taylor, 1964).

Clogging Stage % of initial hydraulic

conductivity after completion ofstage

Phase Rate

Initial 100 -

Phase I 25 Moderate-Rapid

Phase II 10 SlowPhase III 1 Very Rapid

Table 1: Three phases on drain field soil clogging (Jones and Taylor, 1964).


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Jones and Taylor showed that hydraulic conductivity experiences an enormous decrease

from its initial value. The data is important because we want to idealize conditions that lead to

maximized phase II duration. The important thing to take away from this chart is that once phase

II is complete, phase III occurs at a very rapid rate. Phase III clogging leads to a very low

hydraulic conductivity (for example, 0.3 in/h compared to initial of 30 in/h) and possible system

failure.

From your home, sewage goes to a

septic tank before the effluent water

containing high amounts of organics and

salts is filtered through the drain field. In a

drain field, effluent goes to a trench where is it

distributed to a layer of gravel that sits above soil. It has been found that effluent is well treated

at the soil/gravel interface (Gill et al, 2007) which causes a great deal of organic build up at the

interface (Jones and Taylor, 1964). This buildup reduced permeability and can lead to system

failure. To deal with this buildup, every year or so, effluent should be sent to a second drain

field so that the first drain field can be rejuvenated (McKinley and Siegrist, 2010). The

rejuvenation takes place when naturally occurring microbes digest the built up organic material

in the soil and at the soil/gravel interface. If this isnt done, septic drain fields will not last as

long as their potential life span.

At the site in Merigold, MS, the clay soil is not good for septic system installation. As

previously discussed, clay soil does not have a high enough hydraulic conductivity to keep

effluent under the soil surface. This will lead to water damaged lawns and system backups.

Image 2: Typical septic system (Owens andRutledge, n.d.)


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Sewage can back up as far as the inside of your house, creating serious health hazards (Lindbo,

et al, n.d.).

Soils that are too wet will have gray spots. These soils should be avoided because wet

soils will not allow effluent to drain well. Additionally, wet soils do not treat effluent as well as

dry soils because wet soils lack oxygen. Oxygen treats effluent by removing pathogens and

other contaminants that can get into drinking water when soil is too wet (Lee and Jones, n.d.).

There are a number of soil characteristics to look for when designing a septic drain field.

First, the soils should not be too clayey or too sandy. Soil with too much clay will not drain well

and soil with too much sand will drain too fast so that effluent does not have proper exposure

time to be treated. The soil should be gently sloping so that is does not reach the water table too

fast to treat effluent. It should be permeable enough to allow effluent transport. Areas with

rocks near the surface should be avoided because rocks block effluent transport. Areas with

vegetation should be avoided as large root systems will interfere with the drain fields ability to

function ("Septic Systems and Their Maintenance").


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Source Fact

"Drainfield Rehabilitation."Pipeline Winter 2005: 1-

7. wvu.edu. Web. 28 Mar. 2013.

Soil fracturing can be used to open soil

for better hydraulic conductivity andpermeability.

Gill, L.W., OSulleabhain, C., Misstear, B.D.R., and

Johnston, P.J. 2007. The Treatment Performance ofDifferent Subsoils in Ireland Receiving On-Site

Wastewater Effluent. Journal of EnvironmentalQuality 36:1834-1855.

Most septic tank effluent treatment takes

place in the distribution gravel and thefirst 300 mm of subsoil.

Jones, J.H., and Taylor, G.S. 1964. Septic Tankeffluent through sands under laboratory conditions.

Soil Science Vo. 90, No. 5:301-309.

Under aerobic conditions, soil cloggingby deposited organics occurs in three

phases. The first and third phases show

rapid declines in hydraulic conductivity.However, the second stage shows low tono decline in hydraulic conductivity. If

the second phase of clogging can beextended, the performance of soil

absorption septic systems can bedramatically improved.

McKinley, J.W., and Siegrist, R.L. 2010.Accumulation of Organic Matter Components in Soil

under Conditions Imposed by Wastewater Infiltration.Soil Sci. Soc. Am. J. 74:1690-1700.

Effluent should be redirected to a seconddrain field to give the first drain field

time to recover. Naturally occurringmicrobes digest built up organic matter at

the soil/gravel interface.

Lee, Brad, and Jones, Don. "Septic Systems in

Flooded and Wet Soil Conditions."Home &Environment. Purdue Extension, n.d. Web. 29 Mar.

2013..

Wet soils do no treat effluent because

there is no oxygen present to removepathogens and other contaminants.

Lindbo, David, Rashash, Diana and Michael Hoover.

"Soil Facts."North Carolina State University. NorthCarolina Cooperative Extension, Web. 28 Mar. 2013.

.

Backups can reach the inside of your

house, creating serious health hazards.

Owens, Phillip, and Rutledge, Moye. "Septic DrainField Design and Maintenance."Phosphorous Best

Management Practices. USDA, n.d. Web. 28 Mar.2013.

.

Clay soils will not allow wastewater toinfiltrate fast enough to remain below the

soil surface.


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Ransom, M. D., W. W. Phillips, and E. M. Rutledge.

1981. Suitability for septic tank filter fields andtaxonomic composition of three soil mapping units in

Arkansas. Soil Sci. Soc. Am. J. 45:357-361.

For septic drain fields, soils with a slope

greater than 15% are rated severe by theSoil Conservation Service.

Radcliffe, D.E., West, L.T., and Singer, J. 2005.

Gravel Effect on Wastewater Infiltration from SepticSystem Trenches. Soil Sci. Soc. Am. J. 69:1217-

1244.

With a greater difference in gravel to

biomat hydraulic conductivity, gravelmasking increases and effluent flow

slows.

Rycroft, David, and Mohamed Amer. "Prospects forthe Drainage of clay soils."FAO Irrigation and

Drainage PaperRome (1995): 19-22. Print.

Soils with low hydraulic conductivity(clay), will drain more slowly than soils

with high conductivity.

"Septic Systems and Their Maintenance."

Department of Soil Science at NC State University,

Main Page. N.p., n.d. Web. 28 Mar. 2013..

Gently sloping, thick, permeable soils are

best for drain fields. Soil should not have

gray spots as these indicate that it isexcessively wet. It should not be toosandy or clayey.


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Solutions

The proposed problem is to fix a failing septic system. In the situation at hand, a

prospective builder wants to install a septic system in a low permeability clay soil. It is

important to note that septic systems can fail for many reasons other than low permeability clay

soil. This section will look at solutions for installing a septic system in clay soil as well as fixing

a failed system after installation.

To create an effective septic drain field, the clay soil will have to be addressed. One way

to do this is to fracture the soil (Drainfield Rehabilitation), a process similar to hydraulic

fracturing in shale formations to extract natural gas. In this process, a pneumatic hammer

punctures the soil and creates many small holes. Air is pumped into the holes to crack the soil.

Polystyrene pellets, used to prop the fractures open, are injected into the soils. This process

creates a higher permeability in the clay soil.

Another way to install a septic drain field in clay soil is to do a complete overhaul and

excavate the clay. The area would be backfilled with a soil that is better suited for drainage and

effluent filtration. If the soil is too wet, perimeter drainage systems will have to be installed to

ensure a dry drain field.

Once the drain field has been installed, failures can arise from floods, increased water

usage over a short period of time, organic buildups in soil or at the gravel/soil boundary, and

vegetation root systems clogging the drain field. To fix the problem, soil fracturing and a

complete system rebuild are options. Another option to fix the problem of organic buildup is

blasting high pressured water through the system to break up chunks of organics. Vacuums are


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used to gather the excess material pumped through the system. Installing a second drain field is

another way to fix the problem of organic buildup (McKinley and Siegrist, 2010).

Discussion

When installing anything, septic system included, it is a good idea to start things the right

way. Soil fracturing is a plausible short term fix for compaction, but it does not give a drain field

the proper starting point. The use of soil fracturing has been met with varied results and it is

only legal in certain states (Drainfield Rehabilitation). This is evidence enough that soil

fracturing should not be used at installation to create a drain field. While expensive, the decision

to excavate the clay soil and replace it with a more suitable soil will be the best long term option

at installation. It is beneficial to initially install two drain fields to avoid organic buildup over

years of use.

The options for system failures that occur in the later stages of a septic systems life vary.

It is important to diagnose the cause of system failure. If the system fails due to organic buildup,

reinstalling soil for the drain field is not necessary and is very expensive. Assuming the builder

did not initially install two drain fields, a second drain field should be built so microbes can

digest organic buildup while the opposite drain field is used. If the builder had installed two

drain fields initially, the problem would be unlikely to occur.

If the failure occurs from overuse, it is a good idea to conserve water for a while to let

ponded effluent infiltrate the soil. Other measures should not be necessary in this case. If root

systems interfere with the drain field, it is a good idea to remove them. Again, other measures

should not be necessary in this case.


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Conclusion

To install an effective septic system in clay soil, a complete overhaul must be done. The

clay soil should be excavated and replaced with a gently sloping soil that does not contain too

much clay or too much sand. The soil at the site has high water content, so perimeter drains

should be installed around the drain field to keep the soil dry. To reduce future organic buildup,

the builder should install two drain fields that can be used at different times (one in use while the

other rejuvenates).

Once installation has been completed, the easiest fix for many problems is prevention.

The owner should avoid system overload by conserving water. To do this, the owner should

avoid doing multiple loads of laundry, dished, etc. in the same day. The owner should avoid

driving on the land above the drain field to avoid soil compaction. The owner should not plant

trees or shrubs near the drain field to avoid root systems clogging or disturbing drainage.


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Literature Cited

"Drainfield Rehabilitation."Pipeline Winter 2005: 1-7. wvu.edu. Web. 28 Mar. 2013.

Gill, L.W., OSulleabhain, C., Misstear, B.D.R., and Johnston, P.J. 2007. The Treatment

Performance of Different Subsoils in Ireland Receiving On-Site Wastewater Effluent. Journal of

Environmental Quality 36:1834-1855.

Jones, J.H., and Taylor, G.S. 1964. Septic Tank effluent through sands under laboratory

conditions. Soil Science Vo. 90, No. 5:301-309.

McKinley, J.W., and Siegrist, R.L. 2010. Accumulation of Organic Matter Components in Soil

under Conditions Imposed by Wastewater Infiltration. Soil Sci. Soc. Am. J. 74:1690-1700.

Lee, Brad, and Don Jones. "Septic Systems in Flooded and Wet Soil Conditions."Home &Environment. Purdue Extension, n.d. Web. 29 Mar. 2013.

.

Lindbo, David, Diana Rashash, and Michael Hoover. "Soil Facts."North Carolina StateUniversity. North Carolina Cooperative Extension, Web. 28 Mar. 2013.

.

Owens, Phillip, and Moye Rutledge. "Septic Drain Field Design and Maintenance."Phosphorous

Best Management Practices. USDA, n.d. Web. 28 Mar. 2013..

Ransom, M. D., W. W. Phillips, and E. M. Rutledge. 1981. Suitability for septic tank filter fields

and taxonomic composition of three soil mapping units in Arkansas. Soil Sci. Soc. Am. J.45:357-361.

Radcliffe, D.E., West, L.T., and Singer, J. 2005. Gravel Effect on Wastewater Infiltration fromSeptic System Trenches. Soil Sci. Soc. Am. J. 69:1217-1244.

Rycroft, David, and Mohamed Amer. "Prospects for the Drainage of clay soils."FAO Irrigation

and Drainage PaperRome (1995): 19-22. Print.

"Septic Systems and Their Maintenance."Department of Soil Science at NC State University,Main Page. N.p., n.d. Web. 28 Mar. 2013. .

"Web Soil Survey." USDA Natural Resources Conservation Service. N.p., 22 Feb. 2013. Web.22 Feb. 2013. .


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Appendix

Location: Bolivar County, MS

AOI 47.1 acres

Soil Acres in AIO

Bd 1.Brittain silt loam, nearly

level phase (forestdale)16.9

Dc 2. Dowling clay (sharkey) 25.3

Fe 3.

Forestdale si lty clay

loam, nearly level

phase

4.9

0-25 cm 25-50 cm 50-100 cm 100-150 cm 150-200 cm

Bd 5.3 5.3 5.9 6.2 6.2

Dc 6.8 6.8 6.8 7.4 7.5

Fe 5.3 5.3 5.9 6.2 6.2

0-25 cm 25-50 cm 50-100 cm 100-150 cm 150-200 cm

Bd - - 10.5 10.5 10.5Dc 39.6 27.9 27.9 23 22.2

Fe - - 9.2 9.2 9.2

Soil pH

Chemical Properties

Cation-Exchange Capacity, milliequivalens per 100 grams)


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0-25 cm 25-50 cm 50-100 cm 100-150 cm 150-200 cm

Bd 1.7 0.21 1.9 2.7 2.7

Dc 0.2 0.21 0.21 0.89 1

Fe 1.7 0.21 1.9 2.7 2.7

0-25 cm 25-50 cm 50-100 cm 100-150 cm 150-200 cm

Bd 32.2 33.3 30.4 29 29

Dc 40.3 44 44 40.2 39.6

Fe 33.2 33.3 30.3 28.9 28.9

0-25 cm 25-50 cm 50-100 cm 100-150 cm 150-200 cm

Bd 34.6 47.5 30.5 22.5 22.5Dc 61.2 75 75 60 57.5

Fe 37.9 47.5 30.5 22.5 22.5

Saturated Hydraulic Conductivity, mm/s

Water Content, One-Third Bar (%)

% Clay

Physical Properties

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Septic Drain Field Remediation