ChapterIII(a) - Pollution Control Board, Assam

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EIA Report Proposed INDAdept G Project – Guwahati Refinery Chapter 3Weathering in SchistOutcrops of these rocks, either big or small, are found in the hills and some along thequarries, road-cuttings and some slope cuttings..Quartz veinQuartzites are limited in extent and small dimension quartzites are found in theKamakhya foothills and Nabagraha. Pegmatites of varied dimension occurring as lenses andveins are found almost in all quarries. Quartz veins are also common.The geological succession of Guwahati (Maswood, 1981) is shown below:PrecambrianPegmatite, quartz, feldspar, quartzo feldspathic veinFine grained graniteGrey porphyritic granitePink granite, granite gneiss, feldspathic quartziteHornblende biotite schists, hornblende pyroxene granulite, biotitesillimanite schists, biotite schist40
EIA Report Proposed INDAdept G Project – Guwahati Refinery Chapter 3The rocks in the study area are under the influence of weathering. The area is located in atropical belt, where a warm and humid climate is prevalent. This aids to the chemicalweathering processes. Rainwater is the main agent of chemical weathering. Weathering ispronounced near Jorabat along the Guwahati-Shillong road, Chandrapur Road and Noonmati-Kharghuli road. Because of the weathering, the rocks have become loose and friable in nature.The rate of weathering decreases as one proceeds toward the Kamakhya hills. This is becauseof the difference in the lithology. The rocks in and around Kamakhya are granitic which arehard and intact, whereas the rocks around Jorabat are schistose. Excavations, deforestation inrecent years have resulted in exfoliation. The slope stability is also affected. During the lastfew years, the city has witnessed some major landslides in which several lives were lost.Works on the geotechnical properties of these rocks have shown that the rocks are suitable forconstruction purpose.3.4. Climate and Meteorology3.4.1. General featuresThe climate of the study area is generally humid and tropical. A hot and humid premonsoonfrom March to May, a prolonged southwest monsoon or rainy season from June toAugust, a pleasant post-monsoon or retreating monsoon from September to November and acold pleasant winter from December to February are the typical characteristics of the generalclimate. Summer runs concurrently with the later part of the pre-monsoon season andcontinues throughout the monsoon season.The four climatic seasons viz. pre-monsoon, monsoon, post-monsoon and winter couldbe considered as comprising of(i)(ii)(iii)(iv)Pre-monsoon: March to May,Monsoon: June to August,Post-monsoon: September to November andWinter: December to February.Sometimes, the monsoon commences in mid-May and ends in mid-September or later.Therefore, the boundaries between the seasons are not very rigid.Guwahati's climate is generally described as temperate. The city's average yearlytemperature is recorded at 24 degree Celsius (76 °F). Average high temperature is recorded at29 degree Celsius (85 °F), while the average low at 19 degree Celsius (67 °F). The highestrecorded yearly temperature is 40 degree Celsius (104 °F), while the lowest recorded yearlytemperature is 5 degree Celsius (41 °F). December, January and February are the coldest andJune, July, August and September are the hottest. Average yearly precipitation is 161.3 cm(63.5 inches) with an average number of 77.3 rainy days. June and July are the wettestmonths. Extreme high level of humidity, many a times at more than 80/90 percent oftencreates discomfort during summer.41
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ChapterIII(a) - Pollution Control Board, Assam

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