INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue XIII September 2025
Special Issue on Innovations in Environmental Science and Sustainable Engineering
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“Mapping Potential Septic Contamination in Household
Groundwater Sources Using GIS: A Case Study of Trento, Agusan
del Sur”
Michael C. Cullantes and Jocel G. Cullantes
Department of Agricultural and Forestry, NEMSU, Sta. Josefa National High School, DepEd
DOI:
https://doi.org/10.51584/IJRIAS.2025.101300001
Received: 10 September 2025; Accepted: 16 September 2025; Published: 06 October 2025
ABSTRACT
This study examines the potential contamination of water sources by septic systems used by households in
Trento, Agusan del Sur, where site-specific conditions and local groundwater flow are often overlooked
when installing septic systems and wells. The research focuses on the risks posed to household water sources
by potential septage contamination, with water source and septic system locations identified through a
ground survey. The radial distances between septic systems and water sources were analyzed using
Geographic Information System (GIS) techniques, specifically Multiple Ring Buffer Analysis. Risk
assessments were based on the minimum standard distance of 10 to 30 meters, as outlined in the Code on
Sanitation of the Philippines, P.D. 856. The results reveal on a potential risk analysis using thematic mapping
and multiple-ring buffer analysis further illustrates that approximately 84% of wells are situated within a 10-
meter radius of septic tanks, classifying them as Very High Risk for contamination. In addition, only 6.64%
of households surveyed are aware of the standard septic-to-water source distance, suggesting a significant
gap in public awareness regarding sanitation safety standards. The study also highlights the reliance on water
refilling stations (62.1%) as the primary drinking water source, with 16.7% of households still depending on
wells, which are vulnerable to contamination. These findings highlight the necessity of stronger legislation,
increased public awareness, and better sanitary infrastructure in order to avoid waterborne illnesses and
protect public health.
Keywords: Septage Contamination, Septic System, Radial Distance, Risk
INTRODUCTION
Groundwater is a dependable water source every human can use. It is a critical source of drinking water,
particularly in developing countries where surface water may be inaccessible or unsafe (Carrard et al., 2019).
However, with humans' right to access this water source, these groundwater resources were exposed to threat
such as overutilization and is vulnerable to contamination from septic systems, which are widely used for
onsite wastewater disposal in peri-urban and rural areas. Septic systems are one of the groundwater sources'
most commonly recognized pollutants and contaminants. Inadequate construction, lack of lining, and
proximity to wells increase risks of groundwater pollution especially in in areas where property lots are
limited with considerably high densities of septic systems, shallow domestic wells and groundwater
contamination are susceptible to septic system leachate (Bremer & Harter, 2012).
In the Philippines, over 80% of households rely on septic. However, a significant portion of these systems do
not meet the standards outlined in the Revised National Code on Sanitation of the Philippines, P.D. 856 or
the Water Code of the Philippines. The Code specifies requirements such as watertight tanks, appropriate
size, a minimum distance of 25 meters from any well, and provisions for regular desludging through access
ports or manholes (USAID & DOH, 2008). Many of these are undersized, unlined, and poorly maintained,
which leads to untreated effluent leaching into aquifers (Bowyer, 2007). While previous research has
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue XIII September 2025
Special Issue on Innovations in Environmental Science and Sustainable Engineering
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addressed groundwater contamination risks (Bremer & Harter, 2012; Ochieng et al., 1992), few studies in the
Philippines have applied GIS-based spatial analysis to systematically evaluate household-level risks.
Additionally, the role of public awareness regarding sanitation standards remains underexplored.
The gap addressed by this study lies in the (1) lack of comprehensive risk assessments and data on the
potential contamination of water sources by mapping the proximity of septic tanks to wells in Trento using
GIS, (2) investigating and analyzing the distance between septic systems and household wells by
categorizing contamination risks based on distance thresholds and (3) analyzing household awareness of
septic-to-water source standards. By linking spatial and social dimensions of sanitation, this research
provides evidence for both academic discourse and local governance.
METHODOLOGY
Respondents and Study Area
The study was conducted in the Municipality of Trento, Agusan del Sur. Figure 1 shows the boundary layer
of Trento, Agusan del Sur- It has a land area of 555.70 square kilometers, constituting 5.56% of the
province's total area. The study's respondents were selected from the total household population of the
Municipality by employing stratified random sampling. This sampling method involved dividing a
population in the Municipality into smaller sub-groups known as strata or barangays. On the recent Census
of 2020, its population was 54,492; considering a 95% confidence level and 5 % marginal error, a sample
size of 467 household respondents was chosen as the study's respondents.
Figure 1. Map of Trento, Agusan del Sur
Data Preparation and Collection
The study's data collection includes a GPS field survey and responses from a semi-structured interview
questionnaire. A ground/field survey was conducted to identify the location of the water source and the
septic tanks using GPS to obtain their coordinates. The coordinates were inputted into the GIS platform in
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue XIII September 2025
Special Issue on Innovations in Environmental Science and Sustainable Engineering
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CSV format. These inputs were processed, transformed into shapefile, and then analyzed using the multiple-
ring buffer to generate a risk map for the potential contamination of the water well from the septic sources.
The ring buffer levels were established based on the Code on Sanitation of the Philippines on the standard
distance of septic tanks from the wells or any water sources. Three Risk Levels were considered in the
analysis: Very High Risk represented the 10 m radial distance between the septic and wells, High Risk for 20
meters, and Low to No risk corresponds to 30 meters. Further, data obtained from the survey questionnaire
were summarized using basic statistical techniques used for the descriptive analysis such as frequency count
and percentage. A correlation analysis (Chi-square test) was used to analyze the influence of level of
awareness to the choice of water source used by the respondents
RESULTS AND DISCUSSION
Household Latrine Facilities
Table 1 provides data on the types of latrine facilities used by households in various barangays, categorizing
them into different types based on the presence of septic tanks (ST), lining, or whether the facility is a
pour/flush latrine. The results indicate that a significant proportion of respondents already have access to
sanitation facilities. However, an alarming 73% of these facilities are either unlined or are considered open-
bottom septic systems. This condition mirrors national findings (USAID & DOH, 2008), where undersized
and poorly constructed septic tanks dominate. Such facilities directly increase risks of effluent seepage into
groundwater, as noted by Bremer & Harter (2012).
Furthermore, the absence of adequate lining in these systems may potentially allow untreated waste to seep
into the groundwater source and may pose severe public health risks, which can lead to the spread of
waterborne diseases. This underscores the urgent need for improved sanitation infrastructure and stricter
regulation to ensure that septic systems are properly constructed and maintained to safeguard public health
and the environment.
Multiple Ring Buffer Analysis Between Wells and Septic Units
The Potential Risk Analysis for households in the municipality was conducted using thematic mapping,
which defined the boundaries of each barangay. The analysis employed the geographic coordinates of wells
(water sources) and septic tanks, as depicted in Figure 2.a, where blue dots represent water sources and red
dots represent septic tanks. To assess the proximity between these two critical elements, multiple-ring buffer
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue XIII September 2025
Special Issue on Innovations in Environmental Science and Sustainable Engineering
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analysis was applied, as shown in Figure 2.b, which interpolates the distance between the water sources and
septic tank locations.
The analysis reveals significant overlap between the buffers of septic tanks, neighboring septic systems, and
wells, suggesting that many water sources are dangerously close to septic tanks. This phenomenon can be
attributed to the limited lot space and high neighborhood density in the area, which restricts the placement of
water sources and septic systems at adequate distances from one another. Given the high density and small
lot sizes, it is highly likely that septic systems and water sources are often located in close proximity within
the same household premise, exacerbating the risk of cross-contamination and potentially compromising the
safety of drinking water. This emphasizes the urgent need for urban planning and stricter regulations
regarding the spatial arrangement of sanitation systems and water sources to protect public health.
(a)
(b)
Figure 2. Coordinates of Water Source and Septic tanks of Households (a), Multiple Ring Buffer Analysis of
the Barangays (b)
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Risk Distribution of Wells
Figure 3 illustrates the wells categorized according to various risk levels, while Table 2 presents the
estimated percentages of wells assigned to each risk level based on the analysis. GIS buffer analysis revealed
that 84% of wells are within 10 meters of septic tanks, indicating Very High Risk (Table 2). Only 1% were
safely beyond 30 meters. Compared to U.S. and African studies (Bremer & Harter, 2012; Ajayi et al., 2022),
the contamination risk in Trento is significantly higher due to smaller residential lot sizes. Statista (2024)
reports that more than half of Filipino households occupy lots under 50 m², limiting spatial separation
between sanitation systems and water sources.
Figure 3. Map on the Risk Analysis of Wells
Table 2. Risk Distribution of Wells (n=467)
Septic-Water Source Distance Awareness
Table 3 shows the responses of the household of barangays on their awareness to Septic-Water Source
Distance based from the Code on Sanitation of the Philippines. Only 6.64% of the total households surveyed
are aware of the standard distance between water sources and septic tanks, amounting to 31 households out
of a total of 467 households.
Table 3. Household Responses Awareness
Response
Aware (%)
Not Aware (%)
Total
6.64
93.36
% = Percentage of total respondents (n=467)
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
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Figure 4. Household Awareness of Required Septic–Water Source Distance (n = 467)
Further, this suggests that a significant majority of households (93.36%) are not aware of these important
safety standards as shown in figure 4, which could lead to health risks due to contamination. Several
barangays, such as Salvacion, Santa Maria, San Isidro, Cebolin, San Ignacio, Basa, Cuevas, and Poblacion,
have a large number or even all households unaware of the standard distance. Notably, Poblacion has 118
households (25.27%) unaware, which is the highest in the table. The fact that Poblacion, a more urbanized
area, has such a high proportion of unaware households raises concerns about the adequacy of awareness
programs and the risks that might arise from such a lack of knowledge.
Drinking Water Source Used by Households
Figure 5 presents data on the primary sources of drinking water for different barangays (neighborhoods or
villages).
Figure 5. Correlation Between Water Source Preference and Level of Awareness
This breaks down these sources into three categories: Public Taps, Water Refilling Stations, and Wells. The
data showed that Water Refilling Stations are the most commonly used water source across all barangays,
contributing 62.1% (290 instances out of 467 total). Many barangays have a higher reliance on water
0 50 100 150 200 250 300 350 400 450 500
Wells
Public taps
Refilling stations
Total
Awareness Versus Choise of Water Source
Total Not aware Aware
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refilling, including areas like Kapatungan (25) and Poblacion (82), likely due to factors like local water
quality issues or insufficient public tap infrastructure. However, a manifestation of 16.7% reliance on wells
for drinking water is still a significant concern, particularly because wells are vulnerable to contamination
from septage and other pollutants.In addition, figure 4 also shows the distribution of drinking water sources
according to household awareness of the 25-meter sanitation standard. At first glance, households that are
aware and not aware of the standard appear to have very similar patterns of water source use: most rely on
refilling stations, followed by public taps, with wells being the least common. This visual impression is
confirmed by the chi-square test of independence, which indicated no significant association between
awareness and drinking water source, χ²(2, N = 467) = 0.04, p = .98. The negligible effect size (Cramer’s V
= 0.009) further suggests that awareness had virtually no influence on household water source choices.
This finding highlights a critical knowledge–practice gap in water, sanitation, and hygiene (WASH)
interventions. While awareness campaigns are intended to encourage safer water use, previous research
shows that knowledge alone rarely produces behavioral change in contexts where infrastructure,
affordability, and convenience strongly constrain options (Mosler, 2012). For example, even when families
understand the risks associated with wells near septic tanks, the lack of affordable alternatives and the
convenience of having an on-site source may compel them to continue using wells (Carrard, Foster, &
Willetts, 2019).
The dominance of refilling stations as the main drinking water source across both awareness groups also
reflects broader trends in the Philippines, where households increasingly purchase treated water due to
declining trust in groundwater quality (WHO & UNICEF, 2021). However, reliance on refilling stations is
closely tied to household income. Poorer families may still depend on wells and public taps despite
awareness of contamination risks, as has been documented in other Southeast Asian communities (Ercumen
et al., 2017).
Finally, the absence of a strong statistical relationship suggests that structural and socioeconomic constraints
outweigh awareness. Without stronger policy enforcement, expanded public water infrastructure, or
subsidies for safe alternatives, awareness campaigns alone may not meaningfully reduce groundwater
reliance in areas like Trento, Agusan del Sur. Similar findings have been noted in other WASH studies,
where enforcement and enabling environments are necessary to convert knowledge into sustainable practice
(USAID & DOH, 2008).
SUMMARY, CONCLUSION, AND RECOMMENDATIONS
Summary
The analysis presented several key findings on sanitation facilities, water sources, and related public health
risks in the municipality. A significant proportion of households (73%) rely on unlined or open-bottom septic
systems, which can lead to potential contamination of both soil and water sources and may increase the risk
of waterborne diseases. This situation aligns with earlier findings by USAID (2008) highlighting issues with
poorly constructed septic systems in the Philippines. A potential risk analysis using thematic maps revealed
that many wells are located within close proximity to septic tanks, with 84% of wells classified as Very High
Risk due to their location within a 10-meter radius of septic systems. The data also showed that a lack of
awareness about proper septic-to-water source distance is prevalent, with only 6.64% of households aware of
the standard distance requirements. Most households rely on water refilling stations (62.1%) as their primary
drinking water source, though 16.7% still depend on wells, further raising concerns about the vulnerability of
water sources to contamination.
Conclusion
This study demonstrates that improperly constructed and closely located septic systems may pose severe
contamination risks to household wells in Trento. With 84% of wells in Very High-Risk zones and only
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
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6.64% of households aware of sanitary distance standards, groundwater contamination poses a significant
public health threat. The high percentage of unlined septic tanks and the close proximity of septic systems to
wells emphasize the necessity for imperative action to improve septic infrastructure practices and
management. Furthermore, the lack of public awareness regarding the standard septic-to-water source
distance compounds the risks, as many households are unaware of the necessary safety protocols.
Additionally, while water refilling stations are commonly used, the continued reliance on wells for drinking
water, particularly in high-risk areas, remains a concerning factor for public health.
The study achieved its objectives by mapping contamination potential, analyzing risk categories, and linking
results with awareness data. The novelty lies in integrating GIS risk mapping with household knowledge,
bridging spatial and social dimensions of sanitation research. Findings underscore the urgency for action in
infrastructure, regulation, and community engagement.
Recommendations:
Based on the results the following recommendation below maybe considered:
1. Enhanced Public Awareness Campaigns: This is a low-cost but high impact stategy. Implement
extensive community education programs to raise awareness about the risks associated with improper
septic system construction and the importance of maintaining the correct distance between septic tanks
and water sources. This can be done through local workshops, informational materials, and media
outreach. Conduct barangay-level workshops, distribute IEC materials, and use radio/TV campaigns.
2. Monitoring and Compliance: Strengthen the monitoring and enforcement of sanitation codes,
particularly those that regulate the construction and maintenance of septic systems, ensuring that all
systems comply with established standards to safeguard public health.
3. Expansion of Safe Water Access: For a long-term plan and investment, provision and improvement
of public water infrastructure, particularly in barangays with high reliance on wells, to ensure the
availability of safe and potable drinking water. This could include expanding the coverage of public
taps and water refilling stations, or constructing additional water treatment facilities to reduce
dependency on potentially contaminated water sources.
REFERENCES
1. Ajayi, O. G., Nwadialor, I. J., Odumosu, J. O., Adetunji, O. O., & Abdulwasiu, I. O. (2022).
Assessment and delineation of groundwater potential zones using integrated geospatial techniques and
analytic hierarchy process. Applied Water Science, 12(12), 1–18. https://doi.org/10.1007/s13201-022-
01802-4
2. Bartolino, J., & Cunningham, W. (2003). Ground-water depletion across the nation (Fact Sheet 103-
03). U.S. Geological Survey. https://doi.org/10.3133/fs10303
3. Boberg, J. (2005). Liquid assets: How demographic changes and water management policies affect
freshwater resources. RAND Corporation.
4. Bowyer, J., Development Alternatives Inc., & USAID. (2007). Philippine Environment Governance 2
Project (EcoGov 2): Septage management in the Philippines—Current practices and lessons learned
(pp. 2–3). Development Alternatives Inc.
5. Bremer, J. E., & Harter, T. (2012). Domestic wells have high probability of pumping septic tank
leachate. Hydrology and Earth System Sciences, 16(8), 2453–2467. https://doi.org/10.5194/hess-16-
2453-2012
6. Calderon, J., & Gonzales, E. (2016). Methods of research and thesis writing (pp. 153–154). National
Bookstore.
7. Carrard, N., Foster, T., & Willetts, J. (2019). Groundwater as a source of drinking water in Southeast
Asia and the Pacific: A multi-country review of current reliance and resource concerns. Water, 11(8),
1605. https://doi.org/10.3390/w11081605
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue XIII September 2025
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Page 9
www.rsisinternational.org
8. Chanco, B. (2023, March 8). Water. Philstar.com.
https://www.philstar.com/business/2023/03/08/2249976/water
9. Dou, X. (2016). A critical review of groundwater utilization and management in China’s inland water
shortage areas. Water Policy, 18(6), 1367–1383. https://doi.org/10.2166/wp.2016.043
10. Ercumen, A., Pickering, A. J., Kwong, L. H., Arnold, B. F., Parvez, S. M., Alam, M., ... & Luby, S. P.
(2017). Do sanitation improvements reduce fecal contamination of water, hands, food, soil, and flies?
A review of evidence. International Journal of Hygiene and Environmental Health, 220(3), 329–340.
https://doi.org/10.1016/j.ijheh.2016.12.005
11. Fielding, K. S., Russell, S., Spinks, A., & Mankad, A. (2012). Determinants of household water
conservation: The role of demographic, infrastructure, behavior, and psychosocial variables. Water
Resources Research, 48(10). https://doi.org/10.1029/2012WR012398
12. Giordano, M. (2009). Global groundwater? Issues and solutions. Annual Review of Environment and
Resources, 34(1), 153–178. https://doi.org/10.1146/annurev.environ.030308.100251
13. Johnson, L. (2009). Geographic information systems in water resources engineering. Choice Reviews
Online, 47(2), 47-0889. https://doi.org/10.5860/choice.47-0889
14. Kitamura, Y., Yamazaki, E., Kanie, N., Edwards, B. D., Shivakoti, B. R., Mitra, B. K., Abe, N.,
Pandyaswargo, A., & Stevens, C. (2014). Linking education and water in the sustainable development
goals. Sustainability Science, 9(2), 181–192. https://doi.org/10.1007/s11625-013-0223-6
15. Mackay, J. D., Barkwith, A., & Guzman, M. A. L. G. (2019). PhiGO seasonal groundwater
forecasting system (p. 21). British Geological Survey.
16. Mosler, H. J. (2012). A systematic approach to behavior change interventions for the water and
sanitation sector. International Journal of Environmental Health Research, 22(5), 431–449.
https://doi.org/10.1080/09603123.2011.650156
17. Motho, M., Kolawole, O. D., Motsholapheko, M. R., & Mogomotsi, P. K. (2022). Influence of
household demographic and socio-economic factors on water demand in Ngamiland District,
Botswana. Water Science, 36(1), 48–59. https://doi.org/10.1080/23570008.2022.2048581
18. Ochieng, G., Ojo, O., Ogedengbe, K., & Ndambuki, J. (1992). Open wells, sanitary features,
pollutions and water qualities: Case study of Ibadan slums, Nigeria. International Journal of the
Physical Sciences, 6(13), 3062–3073. https://doi.org/10.5897/IJPS10.485
19. Pareño, E., & Jimenez, R. (2006). Basic statistics: A worktext. C&E Publishing, Inc.
20. Popkin, B. P. (1983). Guidelines for groundwater quality assessments for hazardous waste facilities.
Groundwater Monitoring & Remediation, 3(2), 65–70. https://doi.org/10.1111/j.1745-
6592.1983.tb01201.x
21. Shah, T., Molden, D. J., Sakthivadivel, R., & Seckler, D. (2000). The global groundwater situation:
Overview of opportunities and challenges (p. 21). International Water Management Institute.
https://doi.org/10.22004/ag.econ.113506
22. Statista. (2024, March 1). Share of households living in residential units Philippines 2022, by floor
area. https://www.statista.com/statistics/1240662/philippines-households-living-in-residential-units-
by-floor-area
23. USAID & Department of Health (DOH). (2008). Operations manual on the rules and regulations
governing domestic sludge and septage (pp. 3–5). AECOM International Development.
24. World Health Organization (WHO), & UNICEF. (2021). Progress on household drinking water,
sanitation and hygiene 2000–2020: Five years into the SDGs. WHO/UNICEF Joint Monitoring
Programme (JMP).
