Study of Septic Tank Wastewater Distribution in Soil

In general, people use septic tanks for household wastewater management, but most of them do not meet health requirements and sni regulations, resulting in polluted shallow groundwater. Because of these issues, the author conducted a laboratory simulation of septic tank wastewater seepage on a small scale. This research was carried out in a 100 cm x 100 cm x 40 cm glass box. The aim of this study was to determine the distribution distance, flow rate, and travel time of septic tank wastewater in a horizontal direction wihtin a glass container. The study used statistical analysis to examine the horizontal spread of septic tank effluent in a glass box. The distribution simulation was performed using laboratory tests a ratio 1:10 according to the existing conditions and soil physical properties were tested. Contaminant parameters including the concentration of Escherichia coli and ammonia (NH3N) were analyzed based on distance and time. The number of samples tested in this study was 40 arranged transversely. The results of soil physical property tests included specific gravity of 2,648%, plastic limit of 16,443%, liquid limit of 25,906%, plastic index of 9,463%, sieve analysis of 17,51%, moisture content of 13%, organic matter of 6,12% and permeability 5,388 x 10−5 cm/s. The results of Escherichia coli concentration tests at showed that the concentration was 1,6 x 104 (mpn/100 ml) at the closets distance from the source of spread and 0,92 x 104 (mpn/100 ml) at the farthest distance. The ammonia (nh3n) concentration at the closest distance from the source of spread was 1,30 (mg/l) and the farthest distance was 0,97 (mg/l). The simulation results of the horizontal spread of septic tank wastewater in a glass box at a distance 81 cm required a travel time of 425 minutes (7 hours 5 minutes) with a septic tank wastewater spread speed/flow rate 8,4 x 10−5 liter/minute.


Introduction
There are two types of waste water that come from household activities, referred to as non-toilet waste water or greywater, and toilet waste water or blackwater.If not handled properly, blackwater can cause severe harm to the environment.To solve this problem, septic tanks are typically utilized.These tanks are buildings that locally treat and break down human waste, usually for use by the community.However, many of these systems are not up to the health standards that are required.[1] the reason for choosing this building model is its cost-effectiveness both during the construction phase and while in operation.These types of buildings are typically constructed within the vicinity of the family home [2].
The ministry of public works has established the sni: 03-2398-2017 standard for creating septic tanks that meet the indonesian national standard.This standard outlines the proper processes for constructing septic tanks, including maintaining a distance of 1.5 meters between the septic tank and infiltration areas, 1239 (2023) 012026 IOP Publishing doi:10.1088/1755-1315/1239/1/012026 2 10 meters from clean water wells, and 5 meters from rainwater infiltration wells [3].However, in reality, community septic tanks are often designed without following these regulations.These septic tanks are often located in densely populated areas and are positioned around three meters away from wells.As a result, there is a risk of polluting shallow groundwater.Consuming this polluted water can lead to negative health consequences.
A decline in water quality may occur due to inadequate sanitation, for example, leakage of wastewater from septic tanks, leading to contamination of shallow groundwater.The quality of groundwater is ascertained using microbiological indicators such as Escherichia coli and ammonia (NH3N).The level of pollution is determined by factors such as the hydrogeological conditions, soil type, depth of groundwater table, and distance of wells from sanitation facilities.This results in the escalation of both chemical and bacterial pollutants, breaching health standards [4].
The factors that affect the movement or transport of contaminants in the soil are the rate of degradation of the contaminants; the greater the rate of degradation, the less the contaminants or pollutants reach deeper into the soil.The pore size in the soil is not uniform in small-pore conditions with a certain flow rate, which will cause the liquid to be stationary or stagnant.Another influencing factor is the mass transfer process by diffusion.The rate of diffusion in dry soil is smaller than in wet soil, which indicates that the movement of contaminants in water will be faster during the rainy season compared to the dry season [5].
The problems discussed in this research are to determine distribution distance, flow rate, and travel time of septic tank wastewater horizontally using glass box modeling and temporary test scale of 1:10 cm taking into account the influencing factors such as the physical properties of the soil and the parameters found in the septic tank such as Escherichia coli and ammonia (NH3N).The approach used to collect data uses simple statistical analysis approach to examine how the distance between each location affects the distribution about Escherichia coli and ammonia (NH3N) bacteria, as well as their physical characteristics soil affects the spread of bacteria.

Methodology
The research was conducted for six months, from june to november 2022, which included secondary data collection, primary data collection (sampling), laboratory testing, glass box making, observation of pollution spread, data processing and analysis.Soil sampling in medan marelan district, north sumatra.The research will be conducted at the water laboratory of the department of environmental engineering, faculty of engineering, university north sumatra.
In this study, the soil sample will be placed in a glass box of 100 cm x 100 cm x 40 cm, and then the bacteria Escherichia coli and ammonia (NH3N) will be tested based on flow rate, time, and distribution distance.
The following stages of soil sample preparation for research are as follows: a. Sampling of land is one point in kelurahan terjun, marelan field district, with the undisturbed soil sample method referring to sni 03-4148-1996.with a depth of 1 m, it consists of two layers of soil.b.Testing of soil physical properties includes type weight (GS), detail size analysis, soil textures, liquid limit (LL), plastic limit (PL), plastity index (PI), organic materials, permeability, and soil water rate in the laboratory hall of industrial research and standardization (BARISTAND) and laboratory of soil mechanics, civil engineering, USU.Because soil properties and behavior vary so much, classification systems group soils into general categories where they share the same physical properties.Soil classification is also useful for a detailed study of the state of the soil as well as the need for testers to determine the technical properties of the soil [6].
The soil classification systems that are commonly used are the unified soil classification system (USCS) and the american association of state highways and transporting officials (AASHTO).AASHTO system classifier based on grain size and plasticity criteria so classifying the soil requires testing the grain analysis of the soil and the atterberg limits.
-Specific of gravity The weight value of a soil varies depending on the condition of the soil structure, and the specific gravity of the particles of the soil also shows the density of the particles as a whole.From testing, specific gravity was obtained.From the test results in the laboratory, it was found that the specific gravity of the soil at a temperature of 270 °C was 2.648, referring to the soil being classified as organic silt.

-Plastic limit
The test is carried out by grinding the soil on a flat surface until the soil has cracks.From the plastic limit test obtained the results of the plastic limit test obtained an average water content of 16.443%.

-Liquid limit
The value of the water content used is expressed in percent by testing for the liquid limit using a device called a casagrande.From the liquid limit test obtained the results of the liquid limit test were carried out several times with different water contents, with the number of strokes ranging from 15 to 40.Then the water content and number of strokes were calculated to determine the water content at 25 strokes [7].The liquid limit value was 25.906%.

-Plasticity indeks
The following is a table of data from the Atterberg limits testing results: PI = LL -PL PI = 25.906%-16.443%PI = 9.463% From the results of these calculations obtained liquid limit (LL) of 25.906% and for the value of the plastic limit (PL) of 16.443%.As for the plasticity index value of 9  ), where the F value is less than 35% and passes the sieve.b.Granular soils are classified as a-1 to a-3.Soil a-2 is classified as granular soil but still contains silt and clay.Thus, the land is classified as group a-2 or a-2-4.This is because the sieving analysis test found that the percentage of the fraction passing sieve number 200 was 17.51% less than 35%, and the nature of the fraction that passed sieve number 40 had a liquid limit of 25.906% less than 40% and a plasticity index of 9.463% less than 10%.c.The results of the sieving analysis test showed that the soil samples were included in groups a-2-4, which were gravel and sand, which were silt or clay with very good to good properties.

-Water content
Based on table1, it is known that the available water content is 13%, and the ability of the soil to hold water is influenced by several factors that affect water holding capacity, including coarse-textured soils, organic matter, and fine-textured soils.The higher the organic matter, the higher the water content [8].

-Organic ingredients
Based on table1, it is known that the organic matter content is 6.12%.In soils containing sand, the organic matter content of the soil can change the soil structure from single grain to clump, thus increasing the degree of structure and aggregate size, or increasing the class of structure from fine to medium or coarse, thereby increasing the capacity of the soil to drain water.The more organic matter in the eating soil, the higher the water content at field capacity as a result of increasing medium-sized pores (meso) and decreasing macropores, so that the water holding capacity increases and has an impact on increasing the availability of water in the soil [9].-Permeability Tests were carried out to determine the coefficient of permeability by using the falling head method for water flow through fine-grained soils.The smaller the permeability value, the more difficult it is for water to penetrate the granules, and vice versa [10].From the permeability test with the falling head, the permeability value was 5.388 × 10 -5 and it was classified as a silt soil type.c.Testing the early content of bacteria Escherichia coli and ammonia (NH3N) at the environmental health and disease control engineering room (BTKLPP).The following work method will be carried out as follows: a.The dried soil sample is placed in a glass box of size P:L:T (100 cm x 100 cm x 40 cm).b.Disposal of 6800 ml of septic waste tank at a constant flow rate through the glass box, where the waste has been covered by 3 mm with a length of 96 cm at the specified time.c.After the wastewater is discharged at a certain time, 10 grams of soil will be taken diagonally at 40 designated points.d.The sample will be placed in a 100 ml transparent tube.e.The sample will be treated with soil dilution after it is tested for bacteria, Escherichia coli, and ammonia.
(NH3N).f.After the research is completed, the calculation of the flow rate of the spread of septic tank wastewater in the glass box will be carried out using Darcy's law equation.Q = k i A

Results and discussion
The simulation was carried out on a glass box by testing 40 points with a distance of 2 cm diagonally on the ground for each point to determine the concentration of Escherichia coli and ammonia (NH3N) originating from septic tank wastewater of 6 liters at an elevation or slope of 50 degrees, taking into account the factors in the form of distance, travel time, and speed of spread of septic tank wastewater, which are influenced by the physical properties of the soil and the permeability of the soil.

Table 4. Research results at 1 hour time
Based on the table above, there are 6 test points with a different distance of 2 cm for each point and 1 hour of travel time.From these results, the highest concentration of Escherichia coli was found at points 1, 2, 4, 5, and 6 at 1.6 x 10 4 (MPN/100 ml) and the lowest value at point 3 at 0.046 x 10 4 (MPN/100 ml).At the concentration of ammonia, the highest value is at point 3 of 3.20 mg/l, and the lowest value is at point 6 of 0.013 mg/l.Table 5.

Research results at 2 hour time
Based on the table above, there are 6 test points with a different distance of 2 cm for each point and 1 hour of travel time.From these results, the highest concentration of Escherichia coli was found at point 12 at 1.6 x 10 4 (MPN/100 ml) and the lowest value at points 10 and 11 at 0.024 x 10 4 (MPN/100 ml).In the ammonia concentration, the highest value is at point 10 of 0.571 mg/l, and the lowest value is at points 11 and 12 of 0.013 mg/l.Table 6.

Research results at 3 hour time
Based on the table above, there are 6 test points with a different distance of 2 cm for each point and 1 hour of travel time.From these results, the highest concentration of Escherichia coli was found at point 13 at 1.6 x 10 4 (MPN/100 ml), and the lowest value at point 16 was 0.047 x 10 4 (MPN/100 ml).At the ammonia concentration, the value for each point is constant at 0.013 mg/l.

Table 7. Research results at 4 hour time
Based on the table above, there are 4 test points with a different distance of 2 cm for each point and 1 hour of travel time.From these results, the highest concentration of Escherichia coli was found at points 19 and 21 at 1.6 x 10 4 (MPN /100 ml), and the lowest value at point 20 was 0.22 x 10 4 (MPN /100 ml).In the Based on the table above, there are 6 test points with a different distance of 2 cm for each point and 1 hour of travel time.from these results, the highest concentration of Escherichia coli was found at points 24, 26, and 27 of 1.6 x 10 4 (MPN/100 ml) and the lowest value at point 28 of 0.094 x 10 4 (MPN /100 ml). in the ammonia concentration, the highest value is at point 26 of 0.482 mg/l, and the lowest value is at point 23 of 0.013 mg/l.Table 9. Research results at 6-hour time Based on the table above, there are 6 test points with a different distance of 2 cm for each point and 1 hour of travel time.From these results, the highest concentration of Escherichia coli was found at point 31 at 1.6 x 10 4 (MPN/100 ml) and the lowest value at points 29 and 30 at 0.35 x 10 4 (MPN/100 ml).In the ammonia concentration, the highest value is at point 29 of 1.71 mg/L, and the lowest value is at point 33 of 0.22 mg/L.Table 10.Research results at 7 hour time Based on the table above, there are 6 test points with a different distance of 2 cm for each point and 1 hour of travel time.From these results, the highest concentration of Escherichia coli was found at points 37, 38, and 40 at 1.6 x 10 4 (MPN/100 ml), and the lowest value at point 36 was 0.079 x 10 4 (MPN/100 ml).At the ammonia concentration, the highest value was at point 38 of 2.54 mg/l, and the lowest value was at point 37 of 0.244 mg/l.
Determination of the distance between the spread of septic tank wastewater in this study used a glass box with the dimensions p:l:h (100:100:40) cm, the distance at each point was 2 cm, 40 points diagonally, and Escherichia coli concentration testing was carried out.And ammonia (NH3N) to determine the distribution distance of septic tank wastewater in the field.Based on the picture above, the distribution distance is not affected by contaminants originating from the septic tank wastewater; this is also proven by the product moment correlation analysis as follows: In the picture above, the significant value of the distance variable and Escherichia coli contaminants is 0.899, and ammonia (NH3N) is 0.263, where the values for both are greater than 0.05, which means that there is no correlation.The results of the product moment correlation analysis show that there is no significant relationship between the distance of distribution and the concentration of contaminants originating from the septic tank wastewater.This happens because bacteria will move horizontally and vertically down along with water, urine, or rainwater that seeps in.The distance of movement of bacteria will vary greatly depending on various factors, including soil physical properties and permeability.According to [11], the pattern of soil contamination by bacteria can reach 11 meters horizontally and 2 meters vertically.Bacteria can move up to a distance of 30 meters from the source point within 33 hours.In addition, there is a rapid decrease in the number of bacteria along the distance due to effective filtration and the death of the bacteria.
As for the travel time for septic tank waste water distribution in this study, the travel time for spreading leaky septic tank wastewater will flow to the ground through 40 points diagonally which have been determined.The closer to the source, the higher the risk of contamination caused by the distance being too close to the septic tank wastewater source.Based on measurements of the distance and time of distribution of the septic tank wastewater source to the farthest point in the study, the following results were obtained; The results of the product moment correlation analysis in the picture above have a significant value for the distance and time variables of 0.000, which means that a smaller value (0.05) has a relationship or correlation.In this figure, there is a pearson correlation of 0.998 with a degree of relationship between the two variables, namely a very strong correlation, and the form of the relationship is positive, which means that the farther the distance for spreading, the longer it takes for the spread of septic tank wastewater to be needed [12].
From the experimental results with glass box modeling obtained from 40 points at a distance of 81 cm, it takes 425 minutes (7 hours and 5 minutes) to spread septic tank wastewater.In the existing conditions, with a distance of 8.1 meters, it takes 3 days for the spread of septic tank wastewater.
The flow rate of the distribution of septic tank wastewater is the same as the movement of water in the soil which is part of the hydrological cycle.The movement of water in the soil, generally moving with a

Figure
Figure 1.Research flowchart

Figure 2 .
Figure 2. Appears on the research design

Figure 3 .
Figure 3. Side view of contaminant flow rate

Figure 4 .
Figure 4. (a) graph of Escherichia coli contaminated soil distance and concentration, (b) graph of distance and concentration of soil contaminated ammonia (NH3N)

Figure 6 .
Figure 6.(a) graph of the effect of distance on travel time, (b) distance and travel time pearson correlation test

Table 1 .
Soil physical properties testing Sieving analysis test to obtain soil gradation values for soil classification sieve analysis is an analysis carried out to obtain soil grain gradations (grain size distribution), namely by vibrating dry soil samples through a set of sieves with different sieve hole diameters and then arranging them from top to bottom with sieve diameter sizes from the largest to the smallest.In testing, the sieving analysis refers to sni 3423:2008.The test results of the soil sieving analysis that passed no.200 are 17.51%.Based on the AASHTO classification system, there are two categories for determining soil classification: the percentage of soil that passes filter number 200 and the percentage that passes filter number 40.Soil classification based on aashto is carried out as follows: a.The AASHTO classification system distinguishes soils into two general classifications, namely granular matter (35% passes sieve no.200) and silt-clay soil (>35% passes sieve number 200).The general classification of soil samples includes granular soil types.This is due to the sieving test number 200 of 17.51% (F

Table 2 .
Contaminant parameter testing on sterile soil d.Dry the sample in the oven at a temperature of 105-1100 °c for 4 hours and count the remaining water content in the soil.Testing the early content of Escherichia coli and ammonia (NH3N) at the environmental health and disease control engineering unit (BTKLPP).
Preparation of waste water samples in the following studies: a. Sampling of septic tank waste water from residential homes refers to SNI 69-8959-2008.

Table 3 .
Testing of septic tank wastewater contaminants

Table 8 .
the highest value is at point 20 of 0.317 mg/l, and the lowest value is at point 19 of 0.013 mg/l.Research results at 5-hour time