Environmental impact assessment

In short

Environmental impact assessment (EIA) is a formal, legally mandated study that predicts the environmental consequences of a proposed project before it is sanctioned, and prescribes measures to avoid, reduce or compensate those consequences. In India it is statutory: the EIA Notification S.O. 1533(E) of 14 September 2006, issued under Section 3 of the Environment (Protection) Act, 1986, makes prior environmental clearance (EC) compulsory for the project types listed in its Schedule. EIA is the single most examined topic in environmental management papers, in UGC-NET/GATE Environmental Science and Engineering, and in interviews at consultancies (NABET-accredited firms), industry EHS departments, and regulators (CPCB, SPCBs, MoEFCC). Day to day it is the work of EIA coordinators, functional area experts (FAEs), monitoring teams and compliance officers who file half-yearly compliance reports.

Explained

What EIA is, its objectives and its forms

• Definition: a systematic process of identifying, predicting, evaluating and mitigating the biophysical, social and other relevant effects of development proposals prior to major decisions being taken and commitments made.
• Objectives: inform the decision-maker; integrate environment into project design; identify mitigation early (cheaper than retrofitting); ensure public participation; create an auditable record.
• Principles: prevention is better than cure; precautionary principle; polluter pays; "no net loss"; proponent pays for the study but it must be objective.
• Related but distinct studies:
  • IEE/rapid EIA - one season (three months) of baseline data; comprehensive EIA - all three or four seasons (monsoon usually excluded for baseline sampling).
  • SEA (strategic environmental assessment) - applied to policies, plans and programmes, not single projects; not yet statutory in India.
  • SIA (social impact assessment) - people, livelihoods, R&R; statutory separately under the Right to Fair Compensation and Transparency in Land Acquisition, Rehabilitation and Resettlement Act, 2013.
  • Cumulative impact assessment (CIA) - combined effect of many projects in one basin or cluster (used for hydropower cascades, river basins, industrial clusters).
  • Risk/hazard assessment and disaster management plan - mandatory chapter for MAH (major accident hazard) units.
  • LCA (life cycle assessment) - cradle-to-grave product impacts (ISO 14040/14044); an EIA is site- and project-bound.
  • Environmental audit/statement - post-operation; Form V under the Environment (Protection) Rules, 1986 is filed annually by 30 September (an *ex post* check, unlike EIA which is *ex ante*).

The Indian legal and institutional framework

• Enabling law: Environment (Protection) Act, 1986, Section 3(2)(v) and Rule 5 of the Environment (Protection) Rules, 1986 → EIA Notification, 2006 (as amended many times; a consolidated Draft EIA Notification 2020 was published but, to the best of current knowledge, has not replaced the 2006 notification).
• Schedule of the 2006 notification lists 8 sectors (mining/primary extraction; primary processing; materials production; materials processing; manufacturing/fabrication; service sectors; physical infrastructure including Environmentally Sensitive Areas; building/construction, townships and area development).
• Category A: appraised at the Centre by an Expert Appraisal Committee (EAC), clearance granted by MoEFCC. Larger projects and all projects needing inter-state or special handling.
• Category B: appraised by the State Expert Appraisal Committee (SEAC), clearance granted by the SEIAA (State Environment Impact Assessment Authority). Where no SEIAA exists, the file goes to the Centre as Category A.
• B1 needs an EIA report; B2 does not (clearance on Form 1/Form 1A and a pre-feasibility report plus EMP). The split is decided at screening.
• General condition (GC): a Category B project becomes Category A if it lies wholly or partly within 5 km of a notified protected area, critically polluted area, eco-sensitive area or an inter-state/international boundary (distances have been relaxed by specific amendments for some sectors - check the current notification).
• Specific condition (SC): sector-specific trigger written into the Schedule entry itself.
• Related clearances that run in parallel: Forest Clearance under the Van (Sanrakshan Evam Samvardhan) Adhiniyam, 1980 (the Forest Conservation Act renamed by the 2023 amendment); Wildlife clearance from the NBWL; CRZ clearance under the Coastal Regulation Zone Notification, 2019; Consent to Establish and Consent to Operate from the SPCB under the Water Act, 1974 and Air Act, 1981; authorisation under the Hazardous and Other Wastes Rules, 2016.
• Portal: all applications are filed online on PARIVESH (Pro-Active and Responsive facilitation by Interactive, Virtuous and Environmental Single-window Hub).
• Accreditation: EIA consultant organisations must be accredited by NABET (QCI), sector- and category-wise; the report names the EIA Coordinator and Functional Area Experts (air AP, water WP, ecology EB, noise NV, soil SC, land use LU, socio-economic SE, risk RH, hydrology HG, solid waste SW, air quality modelling AQ).
• Appeals: against grant or refusal of EC, to the National Green Tribunal under the NGT Act, 2010, normally within 30 days (extendable by 60 days for sufficient cause).
• Validity of EC (indicative, as amended): river valley 10 years, mining up to 30/50 years as per the amendment applicable, nuclear 5 years, other projects commonly 10 years for commencement of construction; always quote the condition in the specific EC letter rather than a remembered number.

The four statutory stages, step by step

1. Screening - only for Category B: the SEAC decides from Form 1 (and Form 1A plus a conceptual plan for construction projects) whether a full EIA (B1) is required or not (B2).
2. Scoping - the EAC/SEAC issues the Terms of Reference (ToR), ideally within 60 days of a valid application, listing the issues, study area, seasons and modelling to be covered. Standard ToR exist for many sectors; a site visit may be ordered. Category A projects start here (no screening).
3. Public consultation - two components:
   • a public hearing at the site or close to it, conducted by the SPCB/UTPCC, advertised in one major national and one regional-language daily, normally with a minimum 30-day notice; the SPCB has about 45 days to complete it and send the proceedings;
   • written responses invited from other concerned persons. Exempted categories include most modernisation within the existing premises without capacity increase, expansions in notified industrial estates with prior EIA, highway expansion in existing right of way, and all Category B2 projects; nuclear, defence and strategic projects are handled specially. Issues raised must be addressed and the final EIA/EMP revised accordingly.
4. Appraisal - the EAC/SEAC examines the final EIA, EMP, public-hearing proceedings and the proponent's presentation, then recommends grant (with conditions) or rejection; the regulatory authority decides, normally within 45 days of the recommendation, and the EC letter is put in the public domain.
5. Post-clearance: half-yearly compliance reports (1 June and 1 December) uploaded on the portal and the company website; monitoring by the MoEFCC Regional Office/SPCB; violation can attract action under Section 15 of the EP Act and NGT orders.

Contents of an EIA report (the 10 generic structure chapters)

1. Introduction - proponent, consultant, statutory basis, ToR compliance table.
2. Project description - location (lat/long, toposheet), layout, process, raw material, water and power demand, effluent and emission quantities, solid waste, manpower, cost.
3. Analysis of alternatives - site, technology, raw material, and the "no project" option; the chapter is mandatory where the site is not fixed.
4. Description of the environment (baseline) - study area usually a 10 km radius from the project boundary; one season (other than monsoon) minimum.
5. Anticipated environmental impacts and mitigation measures - construction phase and operation phase, each attribute separately.
6. Environmental monitoring programme - parameters, locations, frequency, responsibility, cost.
7. Additional studies - public consultation, risk assessment, disaster management plan, R&R, natural resource conservation.
8. Project benefits - physical and social infrastructure, employment, improvement in quality of life.
9. Environmental cost-benefit analysis - only if specifically asked for in the ToR.
10. Environmental management plan (EMP) - administrative structure, capital and recurring cost, implementation schedule.

Plus summary and conclusion (executive summary) and disclosure of consultants. The executive summary is translated into the local language for the public hearing.

Baseline data: what is measured, and against which Indian standard

• Ambient air: PM10, PM2.5, SO2, NO2, CO, O3, NH3, Pb, benzene, BaP, As, Ni compared with the National Ambient Air Quality Standards, 2009 (CPCB) - PM10 annual 60 µg/m³ and 24-h 100 µg/m³; PM2.5 annual 40 and 24-h 60; SO2 annual 50, 24-h 80; NO2 annual 40, 24-h 80 (industrial, residential and rural, same values). Normally 8 stations, twice a week, 24-hourly, over one season.
• Meteorology: wind speed and direction, temperature, humidity, rainfall; a windrose fixes the downwind sampling stations and the model domain.
• Water: surface and ground water sampled for the parameters of IS 10500:2012 (drinking water) and compared with CPCB's designated best-use classes A to E; effluent against the industry-specific standards in Schedule I of the Environment (Protection) Rules, 1986.
• Noise: Leq day and night against the Noise Pollution (Regulation and Control) Rules, 2000 - industrial 75/70, commercial 65/55, residential 55/45, silence zone 50/40 dB(A) Leq (day 6 a.m.-10 p.m.).
• Soil, land use and geology: texture, pH, EC, organic carbon, SAR, heavy metals; land use from satellite imagery.
• Ecology: flora and fauna lists, Schedule I species under the Wild Life (Protection) Act, 1972, forest types, aquatic ecology; a wildlife conservation plan where applicable.
• Socio-economic: demography from the latest Census, occupation, literacy, health, amenities, R&R needs, archaeological sites.
• Traffic: existing and project-added volumes, level of service (IRC methods).

Methods of impact identification and prediction

• Ad hoc / expert judgement - quick, cheap, subjective; used for screening.
• Checklists - simple, descriptive, questionnaire or scaled-weighted checklists; good for completeness, poor on interaction.
• Matrices - Leopold matrix (100 project actions × 88 environmental characteristics; each cell gets magnitude and importance on 1-10 with sign) - the classic examination answer; stepped/cross-impact matrices show secondary effects.
• Networks and impact trees - Sorensen network traces cause-condition-effect chains and reveals indirect impacts.
• Overlays / GIS - transparent map layers or raster suitability analysis; excellent for siting linear projects (roads, canals, transmission lines).
• Index/scoring methods - Battelle Environmental Evaluation System (EES): 78 parameters in 4 categories (ecology, physical/chemical, aesthetics, human interest), quality converted to a 0-1 value function and weighted with parameter importance units (PIU) out of 1,000.
• Simulation and predictive models - AERMOD/ISCST3/CALPUFF for air dispersion, QUAL2K/QUAL2E for river water quality, MODFLOW for groundwater, FHWA/CoRTN or ISO 9613 for noise propagation, SPM/ALOHA/PHAST for consequence analysis of releases.
• Weighting methods - Delphi technique, analytic hierarchy process, paired comparison for assigning importance.
• Significance criteria: magnitude, extent, duration, reversibility, probability, sensitivity of the receptor and compliance with a standard; "significant" normally means a standard is breached or an irreplaceable receptor is affected.

Mitigation, EMP and the limitations of EIA

• Mitigation hierarchy: avoid → minimise → rectify/restore on site → reduce over time → compensate/offset (plantation, CER, biodiversity offset) → monitor.
• Typical mitigation: ESP/bag filter and stack height per CPCB formula, ETP/STP with zero liquid discharge where ordered, rainwater harvesting, green belt (commonly a third of the plot area for large industry, three rows of trees along the boundary), acoustic enclosures, HW storage on an impervious platform, CER (corporate environmental responsibility) spend as a percentage of project cost set project-wise by the EAC.
• EMP elements: organisational chart with an environment cell, budget (capital + O&M), schedule, monitoring protocol, reporting, emergency plan, closure/decommissioning plan (mine closure plan for mining).
• Advantages: prevents costly design mistakes, legal defensibility, finance eligibility (banks and the IFC Performance Standards/Equator Principles require it), public legitimacy.
• Limitations and criticisms (examined often): proponent funds the study, so bias and "cut-and-paste" reports occur (the NGT has quashed ECs on such grounds); one-season baseline misses seasonality; cumulative and induced impacts are poorly handled; weak post-clearance monitoring capacity; public hearing can be a formality; ex post facto clearance for violation cases has been repeatedly struck down by courts (the Supreme Court in *Common Cause* and *Vanashakti*-line judgments has taken a strict view - the position on regularising violations has been litigated repeatedly, so check the current law before relying on it); screening thresholds encourage deliberate under-sizing of projects.

Key points

• EIA - an *ex ante*, predictive study of a project's environmental effects, with mitigation; environmental audit is the *ex post* check.
• Legal basis - EIA Notification S.O. 1533(E) dated 14-09-2006 under Section 3 of the Environment (Protection) Act, 1986; applications on the PARIVESH portal.
• Four stages - screening (Category B only), scoping (ToR), public consultation, appraisal; then grant/refusal of EC with conditions.
• Category A vs B - A appraised by the EAC and cleared by MoEFCC; B by the SEAC and cleared by the SEIAA; B1 needs an EIA, B2 does not.
• General condition - proximity (nominally 5 km) to a protected, eco-sensitive, critically polluted area or a state/international boundary escalates B to A.
• Form 1 / Form 1A - the application and screening documents; Form 1A with a conceptual plan is for building and township projects.
• Study area - normally 10 km radius; baseline for one non-monsoon season (rapid) or three/four seasons (comprehensive).
• Public hearing - conducted by the SPCB, advertised in national and regional dailies with about 30 days' notice; exempted for B2, most in-premises modernisation and strategic projects.
• Leopold matrix - 100 actions × 88 characteristics, each cell scored for magnitude and importance 1-10.
• Battelle EES - 78 parameters, 4 categories, value functions 0-1, 1,000 parameter importance units.
• Models to name - AERMOD/CALPUFF (air), QUAL2K (river), MODFLOW (groundwater), ALOHA/PHAST (risk).
• Mitigation hierarchy - avoid, minimise, restore, reduce, compensate, monitor; EMP carries the cost and the responsibility.
• NAAQS 2009 - 12 parameters; PM10 60 µg/m³ annual, PM2.5 40 µg/m³ annual; same limits for industrial and residential areas.
• Noise Rules 2000 - 75/70, 65/55, 55/45, 50/40 dB(A) Leq for industrial, commercial, residential and silence zones (day/night).
• Compliance - half-yearly reports on 1 June and 1 December; monitoring by the MoEFCC Regional Office and SPCB.
• NABET accreditation of the consultant and named FAEs is mandatory for an acceptable EIA report.
• Appeal - to the NGT within 30 days of the EC order (extendable by 60 days).
• Parallel clearances - Forest (Van Adhiniyam, 1980 as amended 2023), wildlife (NBWL), CRZ Notification 2019, CTE/CTO from the SPCB.

Formulas and examples

Example 1 - Battelle-type aggregate index. A thermal plant's EIA scores four parameters:

ΔEIU = 306.0 − 367.0 = −61.0 PIU, i.e. a net deterioration of 61/550 ≈ 11.1% of the assessed value. Air quality alone loses 63 PIU, so it is the red-flag parameter and the EMP must target it (ESP efficiency, FGD, stack height, green belt).

Example 2 - incremental ground-level concentration and NAAQS check. A boiler stack emits SO2 at 40 g/s. Wind speed at stack height u = 4 m/s; effective stack height H = 60 m; at the distance of maximum concentration, class-C stability gives σy = 150 m, σz = 60 m. Baseline 24-h SO2 (98th percentile) = 28 µg/m³.

• Q = 40 g/s = 40 × 10⁶ µg/s.
• π·u·σy·σz = 3.1416 × 4 × 150 × 60 = 113,097 m³/s (dimensionally µg/m³ per µg/s).
• Q/(π u σy σz) = 40 × 10⁶ / 113,097 = 353.7 µg/m³.
• Exponent: H²/(2σz²) = 3,600 / (2 × 3,600) = 0.5 → e^−0.5 = 0.6065.
• C = 353.7 × 0.6065 = 214.5 µg/m³ (this is the short-term, worst-case centre-line value).
• Resultant 24-h value = 28 + 214.5 ≈ 242 µg/m³ against the NAAQS 24-h limit of 80 µg/m³ → fails by a wide margin. Mitigation needed: FGD/low-sulphur fuel to cut Q, or a taller stack - note C falls roughly as Q, so an 80 µg/m³ target with the same geometry needs the incremental part below 52 µg/m³, i.e. emission cut to 40 × (52/214.5) ≈ 9.7 g/s, about a 76% reduction.

Example 3 - river assimilation after an ETP discharge. River upstream: Q = 12 m³/s, BOD = 2 mg/L. Effluent: 8 MLD at BOD 30 mg/L (the general inland-surface-water limit in Schedule I is 30 mg/L).

• Qe = 8 MLD = 8,000 m³/day ÷ 86,400 s = 0.0926 m³/s.
• Load upstream = 12 × 2 = 24 g/s equivalent units; load effluent = 0.0926 × 30 = 2.778.
• Cmix = (24 + 2.778) / (12 + 0.0926) = 26.778 / 12.0926 = 2.21 mg/L.
• Increase = 0.21 mg/L; Class C inland water (drinking with conventional treatment) allows BOD ≤ 3 mg/L, so the discharge is acceptable on BOD - but the same calculation must be repeated for ammonia, phosphate, COD, temperature and in the lean season flow (say 1.2 m³/s), where Cmix = (2.4 + 2.778)/(1.2926) = 4.01 mg/L, which breaches 3 mg/L. Lean-flow assessment is the point of the exercise.

Example 4 - noise: combined level and distance attenuation. Three DG sets each at 95 dB(A) at 1 m, plus a compressor at 92 dB(A) at 1 m, at the plant boundary 50 m away (point sources, no barrier).

• Combined at 1 m: 3 × 10^9.5 = 3 × 3.162×10⁹ = 9.487×10⁹; compressor 10^9.2 = 1.585×10⁹; total = 1.107×10¹⁰ → Lp = 10 log10(1.107×10¹⁰) = 100.4 dB(A).
• Attenuation to 50 m: 20 log10(50/1) = 20 × 1.699 = 34.0 dB.
• Boundary level = 100.4 − 34.0 = 66.4 dB(A), below the industrial daytime limit of 75 dB(A), so the day limit is met; at night the industrial limit is 70 dB(A), also met, but a residential receptor 50 m beyond the boundary (total 100 m → 20 log10(100) = 40 dB, a further 6 dB) would see ≈ 60.4 dB(A), breaching the residential night limit of 45 dB(A) - hence acoustic enclosures (−20 to −25 dB) and a green belt are prescribed.

Example 5 - screening the category. A 0.6 MTPA cement grinding unit is proposed 3.5 km from the boundary of a notified wildlife sanctuary.

• Cement plants above the Schedule threshold are listed; a stand-alone grinding unit of this size would ordinarily be appraised as Category B by the SEAC.
• The site is within 5 km of a protected area → the General Condition applies → it is treated as Category A, appraised by the EAC with clearance by MoEFCC, and additionally needs NBWL recommendation because it is within the 10 km eco-sensitive zone default.
• Consequence: ToR from the EAC, full EIA with three-season baseline if the EAC so directs, public hearing (not exempt), and a wildlife conservation plan. (Thresholds and the GC distance have been amended sector-wise - verify against the notification in force.)

Where it is used

• EIA consultancies and engineering firms - NABET-accredited houses and the environment divisions of WAPCOS, MECON, NEERI, TCE, L&T, AECOM and Ramboll prepare ToR applications, baseline programmes, dispersion modelling and EMPs; entry roles are FAE-trainee and EIA coordinator.
• Industry EHS departments - cement, steel, thermal power (NTPC), refineries (IOCL/BPCL/HPCL), pharma clusters in Hyderabad and Gujarat, chemical estates: obtaining EC, then filing half-yearly compliance and annual Form V, and defending conditions before the EAC/SPCB.
• Regulators and public bodies - MoEFCC, SEIAA/SEAC secretariats, CPCB and SPCBs (public hearings, CTE/CTO), NHAI and metro rail corporations (DMRC, MMRDA), port trusts under CRZ, and panels of the NGT.
• Infrastructure and real estate - building and area-development projects above the Schedule 8(a)/8(b) thresholds need EC with Form 1A, a conceptual plan, STP, rainwater harvesting and waste segregation; often bundled with GRIHA or IGBC certification.
• Finance and due diligence - banks, PE funds and multilaterals apply the IFC Performance Standards and Equator Principles; ESDD (environmental and social due diligence) analysts read EIAs to price risk.
• Monitoring and laboratory services - NABL-accredited and MoEFCC-recognised labs do the air, water, soil, noise and ecology baselines that an EIA chapter 4 rests on.

Interview questions

• Q: Under which law is EIA mandatory in India, and which notification governs it? A: The Environment (Protection) Act, 1986 (Section 3) read with Rule 5 of the EP Rules, 1986; the operative instrument is the EIA Notification S.O. 1533(E) of 14 September 2006, as amended.
• Q: What are the four stages of the EC process? A: Screening (only for Category B), scoping and issue of ToR, public consultation, and appraisal by the EAC/SEAC leading to grant or refusal of clearance with conditions.
• Q: How do Category A and Category B differ, and what is B2? A: Category A is appraised by the central EAC with clearance by MoEFCC; Category B by the SEAC with clearance by the SEIAA. B2 projects are exempt from preparing an EIA report and from the public hearing; B1 must do both.
• Q: What is the General Condition? A: A rule in the 2006 notification that upgrades a Category B project to Category A if it lies within a prescribed distance (nominally 5 km) of a protected area, critically polluted area, eco-sensitive area or inter-state/international boundary.
• Q: Which projects are exempt from public hearing? A: All B2 projects, most modernisation within existing premises without capacity increase, expansion of highways inside the existing right of way, projects in notified industrial estates already covered by an EIA, and defence/strategic projects.
• Q: What is the usual study area and baseline season? A: A 10 km radius around the project boundary, with at least one non-monsoon season of primary data; the EAC may direct three seasons for sensitive or large projects.
• Q: Explain the Leopold matrix and its weakness. A: A 100 × 88 interaction matrix in which each project-action/environment-characteristic cell is scored for magnitude and importance on a 1-10 scale; the weakness is subjectivity and that it cannot show indirect or cumulative chains - a network method does that.
• Q: What does the EMP contain, and who pays for it? A: The mitigation measures, monitoring programme, organisational structure, implementation schedule and capital plus recurring budget; the project proponent bears the cost, and it becomes an enforceable condition of the EC.
• Q: A project's predicted incremental PM10 is 20 µg/m³ and the baseline 98th percentile is 95 µg/m³. Is it acceptable? A: No - the resultant 115 µg/m³ exceeds the 24-h NAAQS of 100 µg/m³, so emissions must be cut, the layout changed or the capacity reduced before clearance.
• Q: What is the difference between EIA and environmental audit? A: EIA is predictive and done before approval; an environmental audit (the annual Form V environmental statement) verifies actual performance of an operating unit against its consents and the EMP.
• Q: Can a project that started work without EC be regularised later? A: Ex post facto clearance has been repeatedly held impermissible by the courts; violation cases are dealt with under special procedures and penal action under Section 15 of the EP Act, and the legal position has changed with litigation, so the current judgment and any standard operating procedure in force must be checked.
• Q: Why is a "no project" alternative included? A: It gives the decision-maker the counterfactual baseline against which the project's net environmental cost and benefit are measured, and it tests whether the stated need can be met otherwise.
• Q: Where do you appeal against an environmental clearance? A: To the National Green Tribunal under the NGT Act, 2010, normally within 30 days of the order, extendable by up to 60 days for sufficient cause.

Common mistakes

• Writing "EIA clearance" - the study is the EIA; the permission is the environmental clearance, granted by MoEFCC or the SEIAA, not by the EAC (which only appraises).
• Saying every project needs screening - Category A projects skip screening and begin at scoping; screening exists to split B into B1 and B2.
• Confusing scoping with screening: screening decides *whether* an EIA is needed, scoping decides *what the EIA must cover* (the ToR).
• Comparing the incremental modelled concentration alone with the NAAQS - the standard applies to the resultant value (baseline + increment), and to the correct averaging period.
• Mixing up averaging periods and units in noise and air work: adding decibels arithmetically instead of logarithmically, or comparing a 1-hour prediction with a 24-hour or annual standard.
• Treating the public hearing as the end of the process, or forgetting that the final EIA must be revised to answer the issues raised in it.
• Quoting remembered thresholds, EC validity periods and the 5 km General Condition distance as fixed - they have been amended sector-wise many times; always cite the notification in force.
• Forgetting that EIA is only one of several permissions: forest, wildlife, CRZ and the SPCB's Consent to Establish/Operate are separate and can each stop a project.

Related topics

Environmental laws in India · Environmental monitoring and analysis · Disaster management · ESG and sustainability reporting · Climate change and carbon accounting · Waste management rules: plastic, e-waste and biomedical