Applicability of semi quantitative approach to assess the potential environmental risks for sustainable implementation of water supply schemes: a case study of Sri Lanka

Identification and quantification of environmental and socio-economic impact risks and effective monitoring of water projects are crucial for sustainable water resource management. Hence, the present study was conducted with the objectives of identifying potential environmental risks of different stages of the development of a new water supply scheme located in the wet zone of Sri Lanka, and categorizing identified impacts based on their significance. A rapid environmental assessment (REA) was followed to identify the upstream point source pollution and downstream water uses in the immediate catchment. Subsequently, a semi quantitative approach was conducted to screen the environmental, social, and economic risks concerning likelihood and sensitivity of the impact. Besides, an analysis of physico-chemical and biological parameters of water quality was conducted in the intake location. The semi quantitative method highlighted that low and medium risk with ecological impacts (50%), low risks towards sustainability of water source (75%), medium level constructional impacts (60%), and very high-level impacts at the operational stage were available (50%). A water quality monitoring program revealed that Escherichia coli count, total coliform bacterial count, and colour of the water were above the standard limits in the nearby freshwater source. In conclusion, a similar approach can be implemented worldwide as a reference to determine the potential socio-environmental consequences in water supply projects to minimize the adverse impacts. Through this study, sustainable mitigation measures were proposed accordingly to prevent the impacts and to strengthen the long-term viability of the new Rural Water Supply Scheme.

• Identifying potential environmental risks of new water supply projects is crucial for sustainable water resource management.
• Rapid environmental assessment and semi quantitative approaches can be applied to screen the socio-economic and environmental risks of water sanitization projects.
• Implementing a sustainable environment plan is vital to control environmental impacts.

INTRODUCTION
The renewable freshwater ecosystems encompass a fraction of 0.3% of total global water resources, where people consume this for drinking, irrigation, agriculture, aquaculture, recreation, transportation, and so on (Arthington ). However, over the next century, climate change and the growing disparity between supply and demand of freshwater might dramatically change the hydrological cycle. Even now, many parts of the world are already limited by the quantity and quality of available water (Arthington ). It is estimated that more than 1.1 billion people suffer without having access to improved drinking-water facilities and, besides, 0.2 billion people exist without improved sanitation (World Health Organization ). More than 70% of the world's rural population in developing countries do not have access to adequate water supply and sanitation facilities (World Bank ). In special consideration, developing countries that are located in tropical regions are severely affected by these issues (World Health Organization ).
The conditions are more critical in South Asian countries; it is stated that 40% of the population in East Asia suffer from improper sanitation and are affected by immobilizing the sanitation-related infirmities (United Nations ).
In catchments, even though monsoonal rain recharges the freshwater inputs, it is not surprising to find communities in tropical regions who do not have access to safe drinking water (Buytaert & De Bièvre ). The prime reasons are poverty, human-induced and natural stressors such as pollution, and ecosystem destruction (Cobbina et al. ). These activities increase the imbalance between the availability of safe drinking water and water consumption patterns within a catchment and may weaken the performance of the ecosystem services. For instance, human inputs and accelerated weathering cause an increase in the salinity of freshwater ecosystems.
Higher salinity level causes a reduction in the quality of drinking water (Kaushal et al. ). Furthermore, impairment of water quality is responsible for the rapid distribution of waterborne diseases. For example, there exists a positive relationship between the quality of drinking water and chronic kidney disease in the North Central Province of Sri Lanka (Wanigasuriya ). Shreds of evidence show that many agrochemicals infiltrate through the soil and contaminate the surface and ground, which leads to widespread waterborne diseases (Wanigasuriya ). Thus, existing freshwater resources in tropical regions are under severe stress, which forces governments to find immediate solutions for the increasing demand for safe drinking water.
To reach the targets of safe drinking water for regional communities, effective monitoring of safe management of water and sanitation services should be strengthened through- Through these efforts, conservation goals of access to proper sanitation and safe drinking water can be accomplished.
The rural water supply schemes (RWSS) are one of the key solutions for providing safe drinking water for rural communities to develop human capital to support the growth potential of rural areas. These projects are usually proposed to be managed by community-based organizations (CBOs) (World Bank ). However, the challenge facing the sector today is how to scale up these experiences in order to meet the target of the Sustainable Development Goals (United Nations ). The sustainability of a water supply scheme is defined as the maintenance of an acceptable level of services throughout the design life of the water supply system (Mimrose et al. ). To gain the maximum benefits from RWSS and to continue to function over a prolonged period by providing quality, quantity, convenience, continuity, and health to the community, the water and sanitation service should be maintained in a sustainable manner.
Sustainability of water supply and sanitation has mainly five dimensions: technical sustainability, financial sustainability, institutional sustainability, social sustainability and environmental sustainability (World Bank ). Further, a proper evaluation should be maintained from planning throughout the operational stage to maintain the above-mentioned sustainability criteria.
However, natural entities and anthropogenic derivates cannot be easily isolated. Therefore, when implementing remedies for improving drinking water and sanitation, a range of social (impacts on rural agricultural, flooding, safety hazards, social conflicts), environmental (siltation of water sources, over-extraction of water, ecosystem degradation, soil erosion), economical (damages to utilities) consequences may progress (Enéas da Silva et al. ). All these factors account for unsustainable standards in water supply and sanitation improvement projects, especially in rural communities (Behailu et al. ). Moreover, sustainable standards of drinking water supply in rural communities of developing countries are quite unsatisfactory (Akter et al. ). For instance, even though the environmental and social safeguards of these projects meet 25% of their standards in the beginning, most of the water supply systems in African and Asian countries fail before the second year after their inauguration (Taylor ).
Therefore, identification of potential impacts on social, technical, and environmental aspects of drinking water projects within the catchment is critical to the success of the project.
Hence, evaluation and recognition of possible risks and socioenvironmental impacts on water supply projects should be incorporated through feasibility studies to ensure the sustainability of the project. Also, understanding the socio-economic and environmental conditions and the project impact on the catchment area is a must. In a feasibility analysis, along with the social and environmental risks and impacts, the demand for safe drinking water should be also assessed.
Risk assessment is a complex and systematic process to identify and compare threats and vulnerabilities that can occur in any scenario and can be determined quantitatively or qualitatively. However, when it comes to environmental risk assessment, the availability of relevant long-term data is limiting in most locations, especially in developing nations. Thus, semi quantitative approaches are always recommended. Semi quantitative methods are used to describe the relative risk scale, and different scales are used to characterize the likelihood of adverse events and their consequences. For example, the risk can be classified into categories like 'low', 'medium', 'high' or 'very high' (Athearn ; Radu ; Tahar et al. ). There are few methods to quantify the potential environmental impacts.
Among those methods, the semi quantitative method used by Petts () can be employed to understand the likelihood and the sensitivity of the environmental impacts or risks that are associated with them to determine the sustainable mitigation measures. In addition, following water quality monitoring along with the semi quantitative assessment provides the platform to understand the variability of physical, chemical, and biological parameters of the source water at different times of the year. Thereby, it enables understanding of the receiving pollutant load and diversity of pollutant concentrations from the upstream areas of the water source. However, as catchments are subjected to various stresses, a systematic approach is essential to assess and monitor the resource usage options and environmental impacts in an integrative manner. This evaluation must reflect the representative dimensions including integrated issues and stakeholders, the role between the natural sciences, and anthropogenic aspects (Jakeman & Letcher ). In a scenario where the water intake is a river, the river banks should be protected to prevent contamination of the water. Presently, it is essential to design for water catchment protection planning for sustainable catchment management (Smith & Porter ) to ensure the safety of water for drinking and other ecological purposes. Therefore, having a semi quantitative approach to measure the risk and impacts of rural small-scale drinking water projects may facilitate researches to develop a similar framework to determine and carry out comprehensive sustainability studies before implementing similar types of small scale projects that lack long term socio-environmental data.
This study is based on Bulathkohupitiya Divisional Secretariat (DS) in Kegalle District, Sri Lanka ( Figure 1). The area currently has a water supply scheme that is managed by the National Water Supply and Drainage Board (NWSDB), Sri Lanka. However, it has been unable to meet the demand for the pipe-borne water supply in that region. A total of 2012 households (24.2% of the total population) do not have access to the consumption of pipe-borne treated water in that region. Thus, a new Rural Water Supply Scheme (RWSS) was initiated to provide safe pipe-borne drinking water to the population in above Grama Niladhari Divisions (GNDs). It is expected to serve a projected population of 6,600 (1,600 households) in the year 2038. The total water demand in the area in 2038 is estimated at 1,000 m 3 /day. It is expected that the provision of safe drinking water will contribute towards reducing the incidence of waterborne diseases and upgrade the livelihoods of the community. This project aims to contribute towards poverty reduction with improved However, integration of environmental components and quantifying environmental and ecological impacts during the rural water supply projects has not been well addressed. Therefore, the present study thus attempts to identify the potential environmental risks and impacts of different stages of the development of a new rural water supply scheme and to categorize those impacts based on their significance. Hence, the present study was carried out with three key objectives: (1) to determine the applicability of rapid environmental assessment (REA) using the semi quantitative analysis method in characterizing the potential socio-environmental impacts of rural water supply schemes, (2) to determine the usability of raw water quality assessments to understand the baseline status of the water source, and (3) to identify the sustainable mitigatory measures to minimize the identified socio-environmental impacts of the selected rural water supply scheme.

Study area
The study was carried out in Bulathkohupitiya (70 06 0 16″N and 80 20 0 11″E), which is approximately 70 m above the mean sea level and located in the wet zone of Sri Lanka.
The annual average rainfall varies between 2,500 mm and 3,000 mm and the annual average temperature varies between 18 C and 35 C (Department of Meteorology Sri Lanka ). The Ritigaha Oya (river) is the water source where the proposed intake weir to be constructed.
The project site consists mainly of mountainous terrain.
Geologically, this area consists of metamorphic hard rock.
The surface water sources are intermittent streams, creeks, and canals associated with surface runoff. There are no adequate groundwater sources available within the selected GNDs due to the higher terrain of the area. In terms of land uses, the project area contains Hevea brasiliensis (15%) and Camellia sinensis (10%), home gardens (40%), and others (35%) including paddy cultivation. However, cultivation takes place in only one season (May to the end of August).

Sampling procedure
Rapid environmental assessment (REA) for environmental screening REA was conducted to encounter pollution sources and downstream water users of Ritigaha Oya concerning the health, and the operational stage were screened through a checklist.
Risk quantification using semi quantitative risk assessment method All potential biological, physical, and chemical hazards that could be associated with the water supply and all the risks were assessed using semi quantitative risk assessment (Petts ; Scottish Natural Heritage ). The descriptive information on risk level, semi quantitative risk matrix approach with likelihood and sensitivity analysis and summary of overall risk scoring and rating for evaluation are represented in Tables 1-3, respectively.
The risk score was generated as a multiplication of severity (sensitivity) and probable frequency of occurrence (likelihood) of a certain hazardous event (Equation (1)) (Petts ).
The risk score value is ranged from 1 to 25, whereas the risk rating is ranged from very high (25-16 score) to low (5-1 score). The significance level of a certain hazardous event was assigned based on the educational judgement for the impacts on human health, aesthetic value, operation and maintenance cost ( Table 1).
The probable occurrence frequency of a certain hazardous event was categorized into five frequency levels, as daily, once a week, once a month, once a year, and more than once a year. The most suitable level for the respective hazard was selected based on educational judgement and experiences. Based on these details, risk scoring and rating were assigned (Table 3)

RESULTS AND DISCUSSION
Upstream point source pollution and downstream water users in RWSS with reference to intake location The produced immediate catchment map of Ritigaha Oya water source indicating the point sources pollution and Major Potential long-term health effects or chronic toxicity (for example chemical organic constituents; for instance pesticides, trihalomethanes (THMs), or inorganic constituents including Hg, Cd, Pb). System significantly compromised; high level of monitoring is required. Disruption to consumers in the supply.

5
Catastrophic Potential illness or acute toxicity (for instance microbial, chemical organic constituents; for example pesticide, or inorganic constituents; for example CN). Major impact for large population. Complete system failure.
downstream water users is shown in Figure 3. In terms of upstream point source pollution, two electricity generating powerhouses and two households were identified as the potential pollution sources. Residents used the river only for bathing purposes. Based on the questionnaire survey, it was identified that chemical fertilizer usage was minimal for those tea-cultivated lands.
The total catchment of a water source is a major component in an RWSS. However, the feasibility of monitoring all activities and scenarios taking place in a larger catchment is less effective when there are limited resources. Therefore, identification of anthropogenic and natural activities occurring in the immediate catchment of a water source or a water body is vital for the effectiveness and sustainability of RWSS (Najar & Khan ; WaSSIP ). The water extraction rate from the Ritigaha Oya for electricity generation is 1,500 L/s and in the dry period, the water extraction rate is reduced accordingly. In addition, all the extracted water is directed back to the Ritigaha Oya stream above. Therefore, flow alterations and volume reductions are at a minimal level.  The impacts on fish and other biota due to changes in river hydrology were also considered as a medium level risk. Ritigaha Oya water source provides a range of habitats for fish species such as Garra ceylonensis (National conser-

Sustainability of water source
Excessive algal growth in storage reservoirs and unsatisfactory condition of the microbiological quality of water was recorded as a high significance risk (Table 4). Possible  CaCO 3 ) ± SEM in mg/L, (f) mean total hardness (as CaCO 3 ) ± SEM in mg/L, (g) mean total nitrate ± SEM in mg/ L, (h) mean total iron (as Fe) ± SEM in mg/ L, (i) mean total coliform bacteria colonies ± SEM at 35 C/100 mL and, (j) mean E. coli bacteria colonies ± SEM at 44.5 C/100 mL.

Construction-related impacts
Increased accidents and public safety issues due to construction work, material, and machinery, occupational health and safety of workers and dust generation due to ground clearing, cutting trenches and material transportation, and unloading in the vicinity of social sensitive areas, were grouped under the high significant environmental risks during the construction phase (Table 4). Impacts from mining and querying, noise and sound pollution, air pollution from emissions, solid waste accumulation in construction sites, damage due to the water transmission line on utilities such as roads, dams, telephone, electricity lines from construction activities, and soil erosion in construction-related practices were listed as medium significant risks (Table 4).
A low impact could be generated on agriculture or other cultivation from wastewater, moving soil, and loss of land.
During the construction phase of this RWSS, a medium level risk may be generated due to the intake development.
Concrete, cement, sand, and other materials that are used for construction will wash downstream with water flow.  In terms of public health aspects, water stagnation resulting in pollution of water sources and increased risk of disease in project areas (e.g. filaria, malaria, hepatitis, gastrointestinal diseases) would be an impact. Therefore, RWSS should be designed to extract water responsibly, minimizing the pollution of the water source such that downstream users are also exposed to clean and safe river water.
Additionally, improper siting of latrines near water sources, bad odour, and mosquito breeding in damaged latrine pits would have effects. Inappropriate sitting, unhygienic environment for workers and solid waste disposal within the camp sites would also be generated and should be minimized by implementing the proper EMP (WaSSIP ).

Operational impacts
Waste disposal from the water treatment plant would be a high-risk impact (

CONCLUSION
Water is a fundamental human right. The safety of drinking water is an ongoing concern within the world. More than two million of them die, mostly children under the age of five years, due to lack of safe drinking water. Most of them are poor and live in the developing world. Developing nations in tropical regions are critically suffering from lack of suitable drinking water sources as well as poor sanitation. Thus, RWSS are a perfect solution for many developing nations to provide safe drinking water to communities, as the implementation and the maintenance cost is minimal.
However, many criticize these projects due to the high failure rates and environmental degradation. Therefore, identification of overarching socio-environmental and economical feature to maintain sustainable practices is essential.
This study broadly analyses the social, environmental, economical, and technical aspects of a rural water supply project in the wet zone of Sri Lanka, while highlighting the importance of using Rapid Environmental Assessment and the semi quantitative method to identify the potential environ-