Water Supply, Sanitation and Environment

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This section covers surface and groundwater sources and their selection, water impurities and quality parameters, water-related diseases, drinking water quality standards, and the estimation of water demand.

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Sources of Water Source Type Examples & Selection Considerations Surface water Rivers, lakes, ponds, reservoirs; generally more accessible in large quantity but more prone to pollution/turbidity variation, usually requiring more extensive treatment Groundwater Springs, dug wells, tube wells/boreholes drawing from aquifers; generally better initial quality (natural filtration through soil/rock) but can have high mineral content and is vulnerable to over- extraction and contamination near polluting sources Selection factors Quantity (adequacy for present & future demand), quality, reliability (seasonal variation), proximity/cost of conveyance, and legal/environmental considerations Impurities, Hardness & Alkalinity Suspended impurities: visible particulate matter (silt, clay, organic debris) causing turbidity, removable by sedimentation/filtration.

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Colloidal impurities: very fine particles that do not settle by gravity alone, requiring coagulation to remove.

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Dissolved impurities: minerals, gases, and salts fully dissolved in water, not removable by simple sedimentation/filtration.

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Hardness (caused mainly by calcium and magnesium salts) is classified as temporary (carbonate) hardness (bicarbonates, removable by boiling) and permanent (non-carbonate) hardness (chlorides/sulphates, requiring chemical treatment such as lime-soda or ion exchange to remove).

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Alkalinity is the water's capacity to neutralize acids, due mainly to bicarbonates, carbonates, and hydroxides; it is relevant to coagulation efficiency and corrosion control.

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Water-Related Diseases & Prevention Waterborne diseases (pathogens ingested directly, e.g. cholera, typhoid, diarrhoeal diseases), water- washed diseases (linked to inadequate quantity for hygiene, e.g. skin/eye infections), water-based diseases (pathogen has an aquatic host stage, e.g. schistosomiasis), and water-vector diseases (transmitted by insects breeding in/near water, e.g. malaria, dengue).

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Prevention centres on safe water supply (protected sources, adequate treatment, safe storage), adequate sanitation, and hygiene education.

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Drinking Water Quality Standards & Demand Estimation Drinking water quality standards (e.g.

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Nepal Drinking Water Quality Standards, WHO guidelines) specify limits for physical (turbidity, colour, taste, odour), chemical (pH, hardness, specific ions, heavy metals), and bacteriological (coliform/E. coli count) parameters.

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Water demand comprises domestic, industrial, commercial, public (institutional), and fire demand, plus an allowance for losses/wastage; it is estimated using per-capita demand (litres/capita/day) and projected population, with design accounting for peak factors (hourly and daily peak demand relative to average demand) to size supply components adequately.

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This section covers intake structures and their siting, pipe materials/joints/valves/fittings, break pressure tanks, service reservoirs, and the design of branch and looped distribution systems.

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Intakes Types of intakes: river intake, reservoir/dam intake, lake intake, and infiltration gallery (a perforated conduit laid in a water-bearing stratum near a river/lake bed, drawing filtered water); the choice depends on the source type and site conditions.

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Factors in selecting an intake location: availability of adequate water quantity even in dry season, best available water quality, easy accessibility for construction/operation, location upstream of pollution sources (e.g. away from sewage outfalls), and stability of the site (e.g. away from erosion-prone riverbanks).

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Pipe Materials, Joints, Valves & Fittings Component Types/Purpose Pipe materials Cast iron (CI)/ductile iron (DI) — durable, commonly used for mains;

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PVC/HDPE — corrosion- resistant, lightweight, widely used for distribution; steel — high strength, used for large transmission mains; asbestos cement (AC) — older installations, largely phased out due to health concerns Joints Socket-and-spigot, flanged (for above-ground/valve chambers, allowing easy dismantling), and mechanical/push-fit joints (allow some flexibility, used for buried pipelines) Valves Sluice (gate) valve — isolates sections for maintenance; check (non-return) valve — prevents backflow; air valve — releases trapped air/prevents vacuum; scour (drain) valve — empties/flushes a pipe section Fittings Tees, bends, reducers, and other components used to change pipe direction, diameter, or to branch the pipeline Break Pressure Tanks & Service Reservoirs A break pressure tank (BPT) is an open, small storage structure installed along a pipeline on steep terrain to dissipate excess hydrostatic pressure (by breaking the pipeline into shorter hydraulic segments), protecting downstream pipes/fittings from bursting under excessive pressure.

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A service reservoir balances the (often variable) rate of supply from the source/treatment works against the (also variable) rate of consumer demand, and provides emergency storage (e.g. for fire-fighting or supply interruptions); its capacity is commonly determined as a fraction (e.g. roughly a third to a quarter) of the average daily demand, or more precisely via a mass-balance (demand-supply pattern) analysis.

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Distribution System Layouts A branch (dead-end/tree-type) system has pipes branching from a main line with no interconnection between branches; simple to design and lay, but water at dead ends can stagnate, and a pipe failure can cut off supply to the entire downstream branch.

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A looped (grid/circular) system interconnects pipes to form closed loops, allowing water to reach any point from more than one direction; more reliable (supply can be maintained around a failed section) and reduces stagnation, but is more complex to design (often requiring iterative methods such as Hardy Cross for pipe network analysis) and generally more costly to construct.

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This section covers the sequence of unit processes used in water treatment, from screening through disinfection, softening, and miscellaneous treatments for taste, odour, iron, and manganese.

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Treatment Train Overview Process Purpose Screening Removes floating and coarse debris (leaves, sticks, trash) from raw water, protecting downstream equipment Plain sedimentation Gravity settling of suspended (settleable) particles in a quiescent basin, without any chemical addition Sedimentation with coagulation Chemical coagulants (e.g. alum) are added to destabilize colloidal particles, allowing them to aggregate and settle, which plain sedimentation alone cannot achieve Flocculation Gentle, prolonged mixing following coagulant dosing, promoting collisions between destabilized particles so they aggregate into larger, more readily settleable/filterable flocs Filtration Passing water through a granular medium (sand, sometimes with gravel/anthracite layers) to remove remaining fine suspended matter and turbidity not removed by sedimentation Disinfection Inactivation/destruction of pathogenic microorganisms, commonly via chlorination, and also by UV irradiation or ozonation, to make water microbiologically safe Softening Removal of hardness (calcium/magnesium ions), via the lime-soda process (chemical precipitation) or ion exchange (resin-based) Filtration Types Slow sand filters: operate at low filtration rates, rely on a biological layer (schmutzdecke) at the sand surface for purification (including some pathogen removal), require minimal chemical pretreatment, but need large land area and periodic scraping/cleaning of the surface layer.

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Rapid sand filters: operate at much higher filtration rates, require prior coagulation-flocculation- sedimentation pretreatment for effective performance, occupy less land area, and are cleaned by backwashing (reversing flow to dislodge accumulated solids) rather than scraping.

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Miscellaneous Treatments Aeration: exposing water to air, which adds dissolved oxygen, and helps release dissolved gases (e.g. carbon dioxide, hydrogen sulphide, associated odours) and oxidize certain dissolved substances.

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Removal of iron and manganese: typically achieved by aeration (to oxidize soluble ferrous/manganous forms to insoluble ferric/manganic forms) followed by sedimentation/filtration to remove the resulting precipitates.

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Removal of colour, odour, and taste: commonly achieved using activated carbon (adsorption of organic compounds responsible for colour/taste/odour), sometimes combined with aeration or oxidation (e.g. with chlorine, within safe limits) as needed.

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This section covers the estimation of wastewater quantity, sewerage system types, design criteria and shapes/materials of sewers, and the construction of sewers and their appurtenances.

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Quantity of Wastewater & Sewerage System Types The quantity of wastewater generated is commonly estimated as a percentage (typically around 70–80%) of the water supplied, since not all supplied water returns as wastewater (some is lost to evaporation, irrigation, leakage, etc.).

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A separate system conveys sanitary sewage and stormwater in separate pipe networks — sewers can be sized for sewage flow alone (smaller, more consistent flow, avoiding dilution of sewage with stormwater at the treatment plant).

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A combined system conveys both in a single network (simpler, cheaper to construct initially, but sewers must be sized for peak stormwater flow, and can overflow untreated combined flow during storms).

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A partially separate system allows some stormwater, such as roof/yard drainage, into the sanitary sewer while the bulk of stormwater is conveyed separately.

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Design Criteria, Shapes & Materials Aspect Key Points Design criteria Sewers are designed to flow under gravity, generally as open-channel (partially full) flow; a minimum (self-cleansing) velocity is required to prevent deposition of solids, while a maximum velocity limit prevents erosion of the pipe material; adequate slope and a minimum practical pipe size are also specified Shapes of sewers Circular — most common, structurally efficient, easy to manufacture/lay; egg-shaped — maintains higher velocity at low (dry-weather) flows by concentrating flow in a narrower invert, useful for combined sewers with highly variable flow; horseshoe — used for larger sewers/tunnels, offering good structural and hydraulic properties Sewer materials Reinforced cement concrete (RCC) — common for larger sewers; vitrified clay — durable, corrosion- resistant, traditional choice for smaller sewers;

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PVC/HDPE — lightweight, corrosion-resistant, increasingly common; cast iron — used where high strength or specific conditions (e.g. under roads, exposed crossings) are needed Construction & Sewer Appurtenances Sewer construction involves trenching, careful bedding and alignment (to maintain the design slope/gradient), pipe-laying, jointing, and backfilling, with attention to groundwater control and trench safety during construction.

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Sewer appurtenances: manholes (access points at changes of direction/gradient/junctions, and at regular spacing, for inspection and maintenance); drop manholes (allow a sewer to drop in elevation at a manhole without excessive velocity, via an internal drop pipe); catch basins/inlets (collect stormwater runoff from the surface into the sewer, often with a sediment-trapping sump); inverted siphons (used where a sewer must dip below an obstruction, such as a stream or utility line, then rise again, flowing full under pressure through that section); and ventilating shafts (allow release of sewer gases and admit air, aiding ventilation and reducing odour/corrosion/gas hazards).

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This section covers the characteristics and decomposition of sewage, BOD and COD, primary and secondary (biological) treatment processes, wastewater disposal methods, sludge/solid waste disposal, and on-site sanitation via latrines and septic tanks.

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Characteristics & Decomposition of Sewage Sewage is examined for physical characteristics (colour, odour, temperature, turbidity/solids content), chemical characteristics (pH, BOD, COD, nitrogen, phosphorus, and other constituents), and biological characteristics (presence of pathogenic and indicator microorganisms).

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Organic matter in wastewater decomposes via aerobic decomposition (in the presence of oxygen, producing relatively inoffensive, stable end products such as carbon dioxide and water) or anaerobic decomposition (in the absence of oxygen, producing malodorous, sometimes flammable/toxic gases such as methane and hydrogen sulphide) — treatment processes are designed to favour controlled, efficient decomposition.

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BOD and COD Parameter Meaning BOD (Biochemical Oxygen Demand) The amount of dissolved oxygen consumed by microorganisms in biologically degrading organic matter in a sample, standardly measured over 5 days at 20°C (BOD5); reflects the biodegradable organic pollution load COD (Chemical Oxygen Demand) The amount of oxygen equivalent required to chemically oxidize both biodegradable and non- biodegradable organic matter in a sample using a strong oxidizing agent; obtained faster than BOD and is typically numerically higher, since it also oxidizes non-biodegradable organics that BOD does not capture Primary & Secondary Treatment Primary treatment physically removes floating and settleable solids: screening (coarse debris), grit removal (dense inorganic particles like sand/grit, via a grit chamber designed to allow grit to settle at a controlled velocity while keeping lighter organic matter in suspension for downstream treatment), and primary sedimentation (settleable organic solids, forming primary sludge).

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Secondary (biological) treatment uses microorganisms to degrade remaining dissolved/colloidal organic matter: sewage/trickling filtration (wastewater trickles over a fixed bed of media colonized by a microbial biofilm), the activated sludge process (wastewater is aerated in a tank together with a suspended, actively growing microbial floc, with a portion of settled sludge returned to maintain the microbial population), and oxidation ponds (shallow ponds relying on natural, largely algal-bacterial symbiotic processes for treatment, needing minimal mechanical input but larger land area and longer retention time).

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Disposal & On-site Sanitation Disposal by dilution discharges treated (or sometimes only partially treated) effluent into a receiving water body; the oxygen sag curve describes the resulting dip and gradual recovery of dissolved oxygen downstream (as biodegradation consumes oxygen faster than natural reaeration initially replenishes it, before reaeration eventually dominates), modelled quantitatively by the Streeter-Phelps equation relating the oxygen deficit to deoxygenation and reaeration rate constants over time/distance downstream.

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Disposal by land treatment applies wastewater to land (e.g. irrigation, infiltration), using the soil-plant system to further treat/assimilate the wastewater, sometimes with beneficial reuse for irrigation.

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Sludge and solid waste disposal involves thickening (concentrating sludge), digestion (further stabilizing organic content, often anaerobically, producing biogas), dewatering, and final disposal or reuse (e.g. as soil conditioner, subject to appropriate safeguards).

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A latrine (e.g. pit latrine) provides basic on-site excreta disposal without water-borne conveyance; a septic tank is a small-scale, on-site primary treatment unit (settling + partial anaerobic digestion) typically followed by a soakage/leach pit or field for effluent disposal, commonly used where a piped sewerage system is unavailable.

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This section covers the tiered framework of environmental assessment in Nepal (BES, IEE, EIA), the governing legal/regulatory framework, and the types and mitigation of disasters.

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Levels of Environmental Assessment Level Description BES (Brief Environmental Study) A relatively simple, less detailed environmental review applied to projects with limited anticipated environmental impact, typically involving smaller-scale interventions IEE (Initial Environmental Examination) A more detailed study than a BES, applied to projects with moderate potential environmental impact, to identify significant issues and determine whether a full EIA is warranted or whether mitigation measures at the IEE level suffice EIA (Environmental Impact Assessment) The most comprehensive level of assessment, required for large-scale projects or those with potentially significant environmental impacts, involving detailed baseline studies, impact prediction/evaluation, alternatives analysis, and a detailed environmental management plan Legal & Regulatory Framework Nepal's environmental assessment requirements are governed by the government's Environment Protection Act and associated Rules/Regulations, which specify which categories/scales of projects require BES, IEE, or EIA, and lay out the procedures for study preparation, public consultation, review, and approval by the competent authority before project implementation can proceed.

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The tiered (BES/IEE/EIA) system allows assessment effort to be proportionate to a project's likely environmental significance, avoiding unnecessary burden on low-impact projects while ensuring rigorous scrutiny for high-impact ones.

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Disasters and Mitigation Types of disasters: natural disasters (earthquake, flood, landslide, fire, drought, and similar events arising from natural processes) and human-induced (anthropogenic) disasters (arising from human activity or failure, e.g. industrial accidents, certain fires, some landslides triggered by construction/deforestation).

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Disaster mitigation measures are structural (engineering interventions such as earthquake-resistant construction, flood embankments/levees, slope stabilization works) and non-structural (land-use planning/zoning, early warning systems, public awareness and preparedness, building codes and their enforcement, and emergency response planning) — combining both is generally necessary for effective disaster risk reduction.