The Environmental Survey Laboratory at Kalpakkam, India carries out elaborate monitoring programme involving atmospheric, terrestrial and aquatic samples for radioactivity to evaluate the impact of operating two pressurised heavy water reactors. This paper presents the evaluation of 25 y (1983-2008) data. Statistical analysis of the environmental data for different radionuclides showed that the data best fits log-normal distribution. The data analysed showed that fission products such as ¹³⁷Cs, ⁹⁰Sr and ¹³¹I were due to global fallout only. A ratio of 0.2 was obtained for ⁹⁰Sr to ¹³⁷Cs in air filter samples, only during Chernobyl accident period. The transfer factor of ¹³⁷Cs and ⁹⁰Sr for rice was computed to be 0.23 and 0.03 and vegetables 0.25 and 0.10, respectively. Activation products ³H and ⁴¹Ar are the only radionuclides that are related to MAPS operation. A strong correlation (r = 0.9) was observed between ³H activity in air and ³H discharged to the atmosphere. A similar correlation (r = 0.8) was observed in ³H concentration in seawater and ³H discharged in the liquid waste. The annual internal dose due to ³H and annual external dose due to ⁴¹Ar evaluated in the last 25 y show that the members of the public received less than 2% of the dose limit (1 mSv y^-1) set by ICRP 72.