Water percolation in different sediment media: a study of sediment capabilities in

landfill systems

By: Dayton Brown and Tyler Greenwood

ED 4260

For: Matt Roy and Wayne Melville

February 28, 2014

Brown and Greenwood

Water percolation in different sediment media: a study of sediment capabilities in

landfill systems

Introduction

The process of water percolation effect’s everyday life on earth as water

slowly makes its way from the earth’s surface from rainwater toward the

groundwater system. However, the contents in the water are not always beneficial

to the surrounding areas health and well being, with landfill sites acting as potential

threats of pollution to an ecosystems overall health. In an attempt to keep the

ground water clean, landfill sites use techniques to contain contamination above the

groundwater system. Clay is used in a variety of forms to decrease the amount of

contaminant movement through subsurface soils (Sarabian and Rayhani 2013;

Hamdi and Srasra 2013; Zhan et al. 2014). These forms include a compact clay layer

that absorbs water, while also creating a barrier between the topsoil contaminants

and the subsoil beneath the layer (Hamdi and Srasra 2013). Along with the compact

layers, a technology known as a geosynthetic clay liner, a layer made from a mesh

material and clay, is laid down prior to the development of a landfill with a similar

goal of keeping contaminants out of the groundwater system in mind (Sarabian and

Rayhani 2013).

When developing landfills there are selected sediment characteristics that

are adhered to when constructing a layer that will restrict the movement of

contaminated water to the groundwater system. The ideal material consists of small

sized sediment particles that create small pores or “pore spaces” that make it

difficult for water to move through the layer due to hydrogen bonding of the water

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molecules and the surrounding sediment (Hamdi and Srasra 2013; Sarabian and

Rayhani 2013). The material also must not expand or contract significantly when

water is added or removed (Hamdi and Srasra 2013). If this occurs the layer is

susceptible to leaking, allowing the contaminated solution to move toward the

groundwater system.

Geosynthetic clay liners, made of mesh materials and clay, have been

implemented into landfill sites in an attempt to create a less permeable layer to

restrict the movement of contaminated water to the groundwater system (Sarabian

and Rayhani 2013). In attempt to create a model to show how geosynthetic clay

liners are affected in the environment, Sarabian and Rayhani (2013) looked at the

effect annual weather patterns have on the clay liners. The study revolved around

subjecting one geosynthetic layer to constant temperatures, and another to varying

cycles of heat to study the differences in water retention between each liner

(Sarabian and Rayhani 2013). It was found that heat caused the geosynthetic layer

to have adverse effects when studying the water retention and permeability of the

layer (Sarabian and Rayhani 2013). It was concluded that prolonged exposure to

environmental conditions creates problems in the layers permeability (Sarabian and

Rayhani 2013). As a result, it was determined that the clay liners should not be

exposed above ground for a long period of time in order to combat against the

adverse affects that the environment places on the materials (Sarabian and Rayhani

2013). While the study we conducted did not delve into the specifics of different

environmental conditions on the sediment, the study has the capabilities to be

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expanded on in the future to incorporate how different climatic zones act on the

sediment types.

Studies found that uncontrolled landfill areas account for a substantial

amount of solution movement through the sediment (Zhan et al. 2014). This

wastewater can be hazardous to the surrounding area if the water is left

unrestrained. An uncontrolled landfill site in southeastern China relied on the

natural clay sediment of the area to contain the contaminated surface water of the

landfill (Zhan et al. 2014). In this particular case the pollution had travelled 9m into

the sediment over a 17-year period (Zhan et al. 2014). While this is a single case,

there appears to be a correlation between the effect of contamination and the

absence of an impermeable clay layer that restricts the movement of water from the

upper horizons (Zhan et al. 2014). The implementation of clay barriers appears to

be an integral part of a landfill site to stop contamination of ground water.

While the impermeable barrier that the clay produces is an essential part to

containing the pollution on site, there is also an emphasis on the material that can

be used to cover the clay boundary (Sarabian and Rayhani 2013). It has been

determined that a “poorly graded sand subsoil” is the best material to place above

the barrier to ensure the correct amount of moisture reaches the clay layer,

ensuring that the barrier does not fail due to environmental forces (Sarabian and

Rayhani 2013). The goal here is to incorporate sediment that will allow water to

keep the layer moist, while allowing the clay compound to contain the contaminated

water in the upper horizons (Sarabian and Rayhani 2013).

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Furthermore, sand can act as a water filter when it is implemented with the

correct mixture of materials (Janzen et al. 2009). Janzen et al. (2009) researched the

affect of micro-pollutants from wastewater on soils, specifically on how to filter the

contamination that was present in the water. By layering gravel, sand, and peat, it

was found that micro-pollutants could be retained and broken down in the

boundary layer due to bacteria (Janzen et al. 2009). The layers of media allow for

optimal water retention that replicates the characteristics of a natural wetland

(Janzen et al. 2009). The research took the simulation a step further and created a

reed filled top layer to allow for further retention (Janzen et al. 2009). While this

may not be a feasible implementation strategy for landfills as bulldozers are

continually moving the topsoil, it may be something that landfills can find a solution

to ensure pollutants are separated as much as possible.

By subjecting different types of sediment to higher than normal quantities of

water in the environment, we will be modeling the water percolation and retention

capabilities of different sediment media. By using an exaggerated amount than what

would be seen in nature, we are able to see how the sediments react to extreme

conditions to find which sediment types are able to create a boundary layer in

landfill sites. The sediments being studied are: sand, potting soil, grade “A” gravel

and clay. By using the different sediment types our aim is to develop a spectrum that

will identify which sediments retain water or restrict water movement.

Furthermore, by subjecting the sediment samples to a contaminated mixture

of 60 parts antifreeze and 40 parts water, we can test the pH of the residual liquid to

see the filtration capabilities of the different sediment samples. To replicate rainfall

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the sediment will be subject to 3 trials of water treatment to see if the pH remains

the same over time, or if the contamination is flushed from the sediment. By

conducting this we hope to determine which sediments can be used as an acceptable

impermeable layer in landfill sites and which sediments can be used as a topsoil to

help remove harmful contaminants.

Hypothesis:

We believe that the test will show differentiation in sediment permeability.

Based on an understanding of water movement through sediment, we believe the

A1 gravel will be the most permeable material and let the most water through. This

will be followed by sand, soil and finally clay as the material that will be the least

permeable, letting minimal amounts of water through, if any at all.

When studying the effect the sediments have on filtration we believe that the

clay will filter the liquid the best, bringing the pH of the antifreeze-water solution

back to an acceptable pH of around 7. This is due to the small size of the clay

particles that allow the sediment to pack together and retain the contaminants. The

second best filter sediment will be soil, followed by sand, and A1 gravel last due to

its inability to retain water, allowing the liquid to flow through readily.

Methods

Preparation for the following experiment required the collection of the four

sediments (sand, potting soil, grade “A” gravel and clay) being investigated from an

area in the Fort Frances/Rainey River District in Northwestern Ontario. Each media

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deposit was found in an open environment thus the consistency of foresaid media is

indefinite due to possible natural influences. Approximately 1,182.5 ml of each

sediment was collected to account for the potential for error and multiple trials.

The experiment was commenced in a closed environment so no external

environmental forces could affect the results. Each experimental trial was subject to

error due to the approximate measurement of the media as a volume quantity.

The simulated landfill area was modeled by cutting a 2 litre Pop bottle into

two sections. A full cut was made at the point where the bottle begins to taper into

the spout; the top section served as our simulated landfill where each sediment

form was individually tested, while the bottom served as a collecting basin for the

liquids that leached through. Medical gauze was then cut into approximately 10cm x

10cm squares creating a screen to hold sediment within the upper section of the

bottle, yet allow liquid to percolate through the sediment. This screen was then

securely wrapped onto the nozzle of the pop bottle with the use of an elastic band.

After the screen was secured, the top section of the bottle was then placed within

Figure 1: Sediment samples from Rainy River District, Northwestern Ontario

Gravel Sand Soil Clay

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the remaining section of the bottle with the nozzle facing down to ensure sediment

was able to be retained, creating our simulated landfill.

`

Each sediment type was investigated independently with 236.5 ml of

sediment poured into the pop bottle top. Before each trial we ensured a wastebasket

appropriate for holding the mix of liquid and sediment was available.

Water Trials

236.5 ml of water was measured and poured over the sediment at a

consistent rate for all trials. At this point we began the stopwatch, timing for 2

minutes for each trial. After the 2 minutes had expired we removed the simulated

landfill, being careful not to spill the sediment or liquid that may still be percolating.

After the top “landfill” section of the pop bottle was removed we poured the

liquid that had collected into the bottom basin for measurement. After recording the

Figure 2: Pop bottle simulated landfill apparatus filled with sand media.

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results we rinsed all equipment of residue so no contamination with future tests

occurred.

Antifreeze Trials

The initial set up was identical for both trials in regards to simulated landfill

and screen procedures. Basin procedures differed due to nature of the liquid and pH

assessments. An alternative wastebasket was available to dispose of all

contaminated media. After the liquid percolated through the sediment and collected

in the basin a sample of the liquid was inserted into the pH test kit tube. 2 drops of

phenol red was then introduced and the resulting color of the liquid is interpreted

on the pH scale.

Procedures were duplicated for all sediment types and appropriate pH levels

were recorded. The sediment contaminated with antifreeze was then disposed of in

an environmentally friendly manner.

Figure 3: pH testing kit analyzing antifreeze sample after percolation through sand.

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Results

From our trials we looked to assess the differences between 4 media types in

regards to the amount water allowed to percolate through the sediment. As an

extension we studied if the different medias served as a filter for contaminated

liquids by measuring the pH of the residual percolated liquid. From our results we

observed how the different media types affected the rate of water percolation with

sand allowing the most water, 150ml, to travel through the media within the 2-

minute trial time. Clay was the most impermeable media type allowing only 5 ml of

water to percolate through within the 2 minutes. This is depicted in Figure 4,

showing the different amount of liquid that percolated through the media contents

in the 2 minutes.

In regards to the antifreeze, pH trials were unfortunately inconclusive. The

sand trials showed small improvements with the residual water pH becoming

slightly less basic in trial 2, but due to procedural faults the margin of error

discounts any results.

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Table 1: Data Results of h20 percolation & ph trials between media types.

Figure 4: Graph depicting the amount of water (ml) that percolated through each of the media types.

Gravel Soil Clay Sand0

20406080

100120140160

H20 Percolation Through Media Types

Media Types

H2

O (

ml)

10

H2O

(mL)

Antifreeze 1

(ph)

Antifreeze 2

(ph)

Antifreeze 3

(ph)

Antifreeze 4

(ph)

Gravel 20 N/A N/A N/A N/A

Soil 100 7.7 N/A N/A N/A

Clay 5 N/A N/A N/A N/A

Sand 150 7.7 7.6 7.7 7.7

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Discussion

In an attempt to recreate the effect that sediments can have on restricting

groundwater contaminants, we subjected different types of sediment to higher than

normal quantities of water. By doing so our intention was to create a model showing

the percolation of water through various types of sediment to assess retention and

filtration abilities of the different sediment types. Controlling the amount of

groundwater contamination is essential to preserve the surrounding ecosystem and

potential threats of pollution to societies, thus the development of landfills requires

the consideration of the surrounding sediment composition.

By comparing the retention of different sediment types (sand, potting soil,

grade “A” gravel and clay) we determined that clay serves as the most impermeable

media, while sand served as the least. This supports the basis of landfills largely

being placed on clay beds to decrease the amount of contaminant movement

Trial 1 Trial 2 Trial 3 Trial 47.54

7.58

7.62

7.66

7.7

Antifreeze Percolation Through Sand Media

Test Trial Number

An

tifr

eeze

pH

Figure 5: Graph depicting the change in antifreeze pH after four trials of percolation through sand sediment.

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through subsurface soils, as outlined by Hamdi and Srasra (2013) and Sarabian and

Rayhani (2013). The “A” gravel was determined to be the 2nd least permeable, which

was a surprise for us since was assumed it would be the most permeable sediment

type in our hypothesis. We credit this to the composition of the sediment mixed in

with the gravel, which when saturated became a type of impermeable material

made up of small sediment particles. The sand showed that it allowed a significant

quantity of liquid to percolate through its media, while the soil permitted slightly

less. This shows that soil and sand are poor choices to control ground water

contamination within a landfill.

Throughout our Antifreeze pH trials we encountered various complications

when attaining results. The sand had the most recordable results because the pH

color comparison was somewhat readable, where the antifreeze became slightly

more transparent after each filtration cycle. We can suspect that this was due to the

sand acting as a filter and retaining some antifreeze, allowing the water to travel

though, thus diluting the sample. For all the other sediment types the

contamination of the sediment discolored the liquid making the color comparison

unreadable. This was a complication that we were not expecting, but may have been

able to be remedied by using pH testing strips rather than a phenol drop method.

We are able to hypothesize that this would give a better result, however sediment

contamination may result in similar inabilities to confidently read the pH. The most

practical way of reading the results would be to subject the residual liquid to further

filtration to strain sediment particles even further, which in turn would skew the

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data. Future studies may benefit by testing for something other than pH, as the

indicating process may be difficult to determine.

Our rational for each trial being two minutes long was based on initial sand

and soil trials where the liquid had percolated through the media in less than two

minutes. Although unrealistic compared to a real life application, we felt that on the

scale of our design two minutes was adequate. In future trials we could implement

more trials over an extend period of time to account for the persistent amounts of

groundwater that an actual landfill receives, which also could examine how different

sediment types become packed down. Other adjustments can be applied in future

studies to avoid potential errors. Most importantly we feel increasing the surface

area of the model landfill will allow more liquid to pass through the media, rather

than all the sediment and liquid being bottlenecked into a 1 inch opening. The use of

various other screens could also be investigated to determine if the size of the holes

affected the flow of the liquid into the basin.

Testing the permeability of the sediments was a successful experiment with

results that challenged our hypothesis. By implementing the adjustments to the

logistical development of the experiment we believe that further investigations

regarding sediment percolation can be more successful.

Conclusion

By subjecting the sediment samples to the water tests we were able to

determine that the best sediment for creating an impermeable layer in a landfill is

either clay or grade “A” gravel due to the water retention qualities of both. While

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both the clay and gravel reacted similarly to the water simulations, if we determine

the sediment type based on the characteristics outlined by Hamdi and Srasra (2013)

and Sarabian and Rayhani (2013) the homogenous small particle size of the clay

would be favoured over the mixture of large and small sediment sizes that make up

the gravel. However, it appears that if clay were unavailable, the “A” gravel would

act as a sufficient layer to restrict contaminant movement. While further studies are

needed to view the differences in percolation over a longer time period of time than

2 minutes, our initial findings appear to determine that it would make an acceptable

layer.

The soil and sand showed that they are unable to prevent large quantities of

water to percolate through the sediment samples. While this is the case, the sand

was able to retain 76.5 ml of water, and the soil was able to retain 86.5 ml of water.

By comparing how much water was initially poured over the sediment, and the total

water yield following percolation we discovered these quantities. This proves that

these soil types do have the capacity to retain a finite amount of water. Under

normal conditions layers of sand and soil may be able to retain a certain amount of

water before experiencing a surplus that would lead to deeper water percolation.

Having mentioned this, we understand the importance of the impermeable clay

layer below the topsoil to ensure percolation of contaminated water does not

persist to the groundwater system.

It is important to note that the filtration portion of the study, while

unsuccessful in all cases but the sand, was able to provide us with future inquiries

surrounding the affect of sediment on filtrating contaminated water. The sand

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showed small improvements on the pH of the contaminated liquid, although

because of procedural error we must discount the data. Future studies will need

better pH and contamination identification procedures to measure the cleanliness of

the residual percolated liquids. Furthermore, more trials will need to be done for

longer periods of time to see how environmental factors would act on contaminated

soils.

In order to determine the effect of water percolation in different sediment

media it was apparent that soils and sand retain a small amount of water, while the

gravel and clay prevent the water from percolating through. While this was a very

simplistic representation of how sediments are able to manipulate the percolation

of water, more advanced studies can be produced off of the concept. The 2-minute

time frame selected only worked for some tests, it will be necessary to determine

the length of time necessary for water to percolate through the clay and the gravel.

This will give us insight on the effect of the water on the clay and gravel over a

prolonged period of time. By doing so, further conclusions can be made to prove

that clay and gravel are acceptable boundary layer sediments.

References

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Hamdi, Noureddine, and Ezzeddine Srasra, 2009. Hydraulic conductivity study of

compacted clay soils used as landfill liners for an acidic waste. Waste

Management. 33, 60-66.

Janzen, Niklas, Stefan Banzhaf, Traugott Scheytt, Kai Bester, 2009. Vertical flow soil

filter for the elimination of micro pollutants from storm and waste water.

Chemosphere 77, 1358-1365

Sarabian, Tahmineh, and Mohammad T. Rayhani, 2013. Hydration of geosynthetic

clay liners from clay subsoil under simulated field conditions. Waste

Management 33, 67-73

Zhan, T.L.T., C. Guan, H.J. Xie, Y.M. Chen, 2014. Vertical migration of leachate

pollutants in clayey soils beneath an uncontrolled landfill and Huainan, China:

A field and theoretical investigation. Science and Total Environment 470-471,

290-298.

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