When bridge abutments or fill areas must impinge on water areas, it 

 is necessary to reduce the encroachment to meet flood protection require- 

 ments. The cross-sectional area of a waterway should in no case be 

 reduced to less than that which can adequately pass the 100-year maximum 

 flood waters. 



4.9 GROUNDWATER SUPPLY - SUBPROJECT 9 



Many onshore OCS facilities are big users of fresh water, often 

 pumped from groundwater aquifers in the coastal area. Such facilities as 

 refineries, petrochemical complexes, and platform fabrication yards may 

 withdraw particularly large amounts of groundwater. If withdrawal exceeds 

 safe limits, aquifers may become contaminated with salt or the land surface 

 may sink or both. 



Principal causes of saltwater intrusion into coastal aquifers include 

 (1) rapidly developing coastal areas where demands for fresh water over- 

 draw the aquifer, (2) canal or navigation construction that may dig into 

 ground levels providing direct access between surface saltwater and 

 freshwater aquifer soils, and (3) land-use changes which increase acreages 

 of impervious area and disrupt the natural recharge of aquifers. 



4.9.1 Summary 



Water supply systems for OCS-related demands are primarily concerned 

 with groundwater extraction. Groundwater resources are under growing 

 pressure in coastal communities and are increasingly pumped for industrial 

 and domestic water use. In California, Florida, Louisiana and New York, 

 groundwater aquifers have already been overpumped and have become 

 contaminated by saltwater intrusion. Other coastal areas are rapidly 

 approaching this situation. With as little as two percent contamination 

 by salt water, a drinking water supply cannot meet federal potable water 

 standards. 



While land subsidence is not a common problem, the adverse effects of 

 the instances of its occurrences are so severe as to make it a problem of 

 general concern. The solution to protecting groundwater and land resources 

 from saltwater intrusion and land subsidence is sound and comprehensive 

 water management. A total management program provides for groundwater, 

 surface water, and reused water supplies to be inventoried and utilized in 

 a coordinated plan of "conjunctive" management. Where extensive withdrawal 

 may cause saltwater intrusion in the freshwater supply, a water control 

 program is implemented to reduce the harmful amounts withdrawn and 

 allocate the water resources according to historical uses [85]. 



A comprehensive water management plan requires information on the 

 supply of groundwater, the source of replenishment of aquifers (recharge 

 areas), the potential for contamination and depletion, and the 

 possibilities for reclaiming wastewater and minimizing unnecessary water 

 consumption. 



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