Lecture 14 Water quality asssessment.pdf

WATER QUALITY IMPACT  Water is an essential resource  sustains life on earth, and the presence of abundant liquid water is what makes the earth unique amongst known planets. 96% of the earth’s free water is sea water, and 3% is ice and snow – so liquid fresh water only constitutes 1% and is a r...

WATER QUALITY IMPACT  Water is an essential resource  sustains life on earth, and the presence of abundant liquid water is what makes the earth unique amongst known planets. 96% of the earth’s free water is sea water, and 3% is ice and snow – so liquid fresh water only constitutes 1% and is a relatively scarce resource. In many parts of the world, lack of enough clean water is likely to be one of the most critical issues of the twenty-first century.  WATER QUALITY ASSESSMENT IN EIA  Scoping Introduction The water environment  susceptible to pollution. It is particularly important  develop thorough inventory of materials that will be used (and of how they will be stored and used) during both the construction and operational phases of a project (Atkinson 1999). The EA strongly advocates the use of scoping checklists which is abridged from an EA checklist, e.g. by omitting impacts on components such as traffic, landscape and heritage).  The water assessment is almost certain to overlap with other EIA components, so early liaison between consultants is important. It is also essential to focus on key impacts and receptors, and a competent hydrologist should be employed at the scoping stage. In a few cases the impact area may be confined to the project site and its immediate surroundings, but hydrological impacts are likely to be more widespread. This can hinder accurate determination of the impact area, and early estimates may have to be revised in the light of information obtained during the assessment process.  Methods and levels of study Difficulties Many hydrological variables, Collection of field data is difficult, Time-consuming, and Requires sampling over extended periods. Thus impose severe limitations on the range and depth of field survey work It is important to make maximum use of existing data by means of the desk study.  Some sources of information are given in Table. Different organizations referred  hold more information than that shown, and in the case of development types for which EIA is mandatory, it is obligatory for the relevant EPA to provide the developer (at a cost) with any relevant information in their possession Physical models, the mathematical and statistical analysis of input data are sometimes used. Some calculations  hand calculator or computer spreadsheet Detailed modeling  software packages, many of which can be run on PCs Limitations some software is expensive, Models need expert hydrologist/hydraulic engineer, competent hydrologist input predictions have a degree of uncertainty and should be validated throughout the life of a project. Baseline studies on water quantity  Methods : Survey and modeling methods Catchments Most of the hydrological variables considered in an EIA are studied in the context of the relevant catchment, and it is therefore important to obtain information on its characteristics (boundary/area and drainage patterns, geomorphology, geology and soils, land cover/use) General information can be found in sources such as LEAPs, Ordnance Survey (OS), geological and soil survey papers or digitized maps, digital terrain models/maps etc. Precipitation and evapotranspiration Precipitation data from the nearest weather station or MO. Rainfall–runoff modelling  rainfall depth– duration–frequency data, or to obtain long-term records from which such information can be extracted. rainfall data, e.g. to correlate variations in stream flows to localized rainfall patterns. Rainfall can be measured using rain gauges/recorders.  Infiltration and overland flow For small areas e.g. on a steep slope : Point measurements. Large areas : Factors such as slope, soil properties, vegetation cover, and amount of impermeable surfaces, that can indicate runoff potential, and are incorporated in rainfall–runoff models Water in the ground In both the unsaturated (vadose) zone and the saturated zone  water storage and flow. For example, if a project is likely to affect soil drainage, it may be important to consider moisture levels and water retention and flow properties of local soils. Data source : MO or soil moisture contents can be measured  water retention properties or field capacity and saturated hydraulic conductivity can be estimated  based on texture of a soil If the project may have a significant impact on groundwater abstraction rates  local aquifer’s storage capacity and storage level patterns is needed.  Surface waters Important issues  current conditions of standing waters and watercourses, their vulnerability to changes in runoff, abstraction, and interference with river corridors and floodplains.  To assess the vulnerability of standing water bodies data needed on area, depth and volume/capacity, elevation, site catchment, recharge and discharge regime, water level ranges and variability, and reservoir operating schedules. The desk study  recharge/discharge data for inflow/outflow streams For length of river  important to know how flows respond in times of heavy rainfall or drought. Stream flows can be measured by stream gauging and/or estimated by rainfall–runoff models. BASELINE STUDIES ON WATER QUALITY  Introduction Water quality can be assessed by chemical or biological methods. Chemical methods involve analysing water samples for a range of variables (nitrate, oxygen, pH, etc.). Advantage:  levels that can be compared with statutory standards;  they are the only available method for assessment of groundwaters.  Chemical methods of assessment (focusing on impact on human health) Phosphorus, Nitrate Chlorophyll a, Organic matter, Biochemical oxygen demand (BOD), Chemical oxygen demand (COD), Metals (Al, Cu, Cd, Hg, Pb, Zn, Ca, Mg, Na, K) and Micro-organics, Ammonia , Hydrogen , sulphide ,Cyanide , sediment , Pathogens , Dissolved oxygen, pH Alkalinity, Electrical conductivity , Temperature  Levels of chemicals  vary considerably seasonally, throughout the day, and over quite short distances. Biological indicators of water quality Most groups of freshwater organisms have been used as indicators  macroinvertebrate families (not species) are by far the most widely used taxa in Britain and Europe. Other bioindicators are available. Diatoms  river water quality , long-term changes in lake water & quality, particularly of acidification. assessing eutrophication changes in fish populations with time Various plant and animal species bioaccumulate toxins, and some are used in ecotoxicological studies using bioassay techniques. The most common organisms in Pakistan are  a) total coliforms b) faecal coliforms c) faecal streptococci and d) Salmonella. IMPACT PREDICTION Because of the complex, dynamic nature of hydrological systems, accurate prediction of impacts is often difficult, and there are bound to be uncertainties, which must be admitted in the EIS. Changes without the development These can be assessed in relation to past, present and predicted trends. Predicting impacts on water quantity Typical questions that should be considered are– is the project likely to significantly: affect river channel/corridor, standing water or wetland features increase flood risk reduce surface and/or groundwater levels and increase the risk of river low flows. Predicting impacts on water quality Point source pollution and non-point source pollution are used Predicting significance of impacts Impact significance will depend on impact magnitudes and the sensitivity and value of receptors  Mitigation If a project is likely to cause a significant increase in flood risk or water pollution  strong presumption in favor of the relocate or no action alternatives. Flow detention structures and storm reservoirs redesign, Software like WATERSHEDSS can assist in the selection of suitable mitigation/management practices. These can include the use of natural and constructed wetlands Monitoring Monitoring is particularly important for the water component of EIAs and should be prescribed for both the construction and post-development phases.