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<br />Ground Water &Construction <br /> <br />Characteristics <br /> <br />Ground water can be one of the most cost I y--even <br />ruinous--factors in construction and land development if it <br />i 5 not understood and taken into cons 1 derat i on in the <br />planning phases of a project. ~ater is the primary cause of <br />the ground moving--up, down or laterally--because of its <br />capabi I lty of changing the chemical and physical nature of <br />rocks and soils. 'f'latar activates swelling and <br />hydrocompacting (collapsing> soi 15 and is a major factor in <br />slope instability. <br /> <br />The value of any development is affected, directly and <br />indirectly, by the long term impacts of :Jround water. The <br />lack of it or the over abundance of it is one of the most <br />prevalent and fundamental reasons for financial distress in <br />the bu i I ding and I and deve I opment bus i nasses. Its <br />significance is evidenced by outright 105595, delays, <br />lawsuits, improper or inadequate use of a site and post <br />construction corrective measures. <br /> <br />Aggravating Circumstances & Consequences <br /> <br />Elementary practices such as roof and pavem~nt storm runoff, <br />sewage treatment, landscaping and land grading can upset the <br />existing natural ground water regimen and create new <br />situations that did not exist prior to development. <br />3asements may flood, foundations sink or be pushed upward to <br />affect an entire structure and underground uti I ities as well. <br />Pavelnents may bul]e or cave in as ground water is affected by <br />land-use changes on the surface of the ground. Planning <br />projects with knowledge of the pre-develop~ent ground water <br />cond i t ions and ana I ys i s of ant i c i pated post-deve I opment <br />conditions may indicats the desirabi I ity of mitigation <br />measures before full development. The cost of prevention is <br />ordinar] Iy far cheaper than tryin] to correct and repair <br />damage from Jround water related causes. <br /> <br />24 <br /> <br />rl i::lh ground water tab I as Ii m i t t and use and may requ i re <br />special construction methods. Lowering the water table by <br />draining low-lying areas and then Ii II ing them with 5011 15 a <br />common practice which frequently alters local ground water <br />conditions. <br /> <br />Mitigation <br /> <br />Ground water is an area-~ide matter which can be managed to <br />the short and long term benefit of surfaca lands. It is to <br />the advantage of contractors and developers to know in <br />advance what their project wi I I do to ground water and what <br />ground water may do to it. <br /> <br />Case History <br /> <br />A southern Aurora subd i vis i on was deve loped in the ear I y <br />1970 '5 when the groundwater tab I e was 20 leet be I ow the <br />surface. Piecemeal development, changing of drainage <br />patterns during development, and excessive lawn watering over <br />the sandy so ils ra i sed the water tab I e and caused chron I c <br />basement flood i ng. ilr1any homeowners put in sump pumps and <br />shal low lawn-watering wel Is. Damage 15 estimated at $1,000 <br />to $4,000 each to several hundred homes. lntegrated surface <br />drainage, non-basement homas, and an area-wide dewatering <br />system could have prevented such high water table damage. <br />The city estimated residents were sprinkl ing 45 inches of <br />water on their lawns annually, thus contributing to the <br />problem. <br />