Report of Geotechnical Investigation

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i I� with persistent ground water, while the oxidized soil zone is not related to a persistent ground . water condition. ( The ground water surface within an unconfined aquifer is generally a subdued reflection of the' I ground surface. Groundwater flows from recharge areas in higher ground to discharge areas in lower ground and water bodies such as wetlands, streams, rivers and lakes. Ground water and perched water surfaces at the project site may vary or fluctuate due to ground surface drainage, site topography and climate. Seasonal or longer periods of drought or excess precipitation cause such variation and fluctuation too. �ONSTRUCTION CONSIDERATIONS GROUND WATER IMPACT As stated in the GROUND WATER section of this report, water was detected in Borings 1 and 2 near depths of 8 and 9 feet respectively. The Boring Logs reveal that supraglacial till was pred6minantly encountered in the borings to their bottom depths. The till appears to have both oxidized and unoxidized soil zones. The oxidized zone extends down to depths near 13 feet and it has given this zone its mottling, brownish and lighter colors. The oxidized zone is not related to a persistent ground water condition. The unoxidized soil zone underlies the oxidized zone, and it extends from depths near 13 feet to the bottom of the borings. It has dark gray color and no mottling from lack of soil oxidation, which is associated with a persistent ground water condition. As stated in the SITE CONDITION section of this repo�t, a large natural wetland lies a few blocks northeast of the lot, and its water surface appears to be nearly 20 feet lower than the lot. This • surface is a manifestation of the ground water level in this area. A smaller natural wetland lies neariy one-half mile northwest of the lot, and it appears to be on the order of 20 feet lower than this lot. The water surface of this smaller wetland is an indicator of the ground water level in this area. Based on water levels of these wetlands and dark gray unmottled soil encountered in the borings near a depth of 13 feet, the persistent ground water level across the lot is near a depth of 13 feet in the borings. The Federal Housing Administration (FHA) sets housing construction standards that can guide construction of residential buildings. Based on these standards, we recommend placing the lowest building floor at least 4 feet above the maximum anticipated ground water level (a persistent ground water condition near a depth of 13 feet in the Borings). When it becomes evident that ground water may adversely affect the project site, a geotechnical engineer from our company should be consulted to review this condition with respect to corrective action. Storm water will infiltrate through the oxidized zone to the unoxidized zone, especially during the Spring wet season. This water will drain slowly to the unoxidized zone, because clayey supraglacial till retards rapid downward drainage. Nevertheless, residential house construction Allied Projed 05039 5 July 31, 2005