AWWA ACE54277

AWWA ACE54277 The Chemistry of Catastrophe: Hurricane Floyd: The Chesapeake Experience
Conference Proceeding by American Water Works Association, 06/01/2001

Harr, Karen;Hecht, Philip M.

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Hurricane Floyd's effects were felt in the Hampton Roads, Virginia area on Wednesday and Thursday, September 15 and 16, 1999. The hurricane deposited up to 20-inches of rainfall in some areas causing major flooding. The effects of regional flooding were especially detrimental to the operation of water treatment plants in the Southeastern Virginia and North Carolina areas. The City of Chesapeake's Northwest River Water Treatment Plant (WTP) experienced significant and catastrophic changes to raw water quality due to the meteorological impact of Hurricane Floyd. Due to the tremendous amount of rainfall deposited in the Hampton Roads area, the Dismal Swamp overflowed into the Northwest River watershed causing raw water total organic carbon (TOC) and color levels to increase dramatically. This was accompanied by a marked decrease in raw wateralkalinity and pH. The impacts to treatment of the overflow event lasted more than five months. The effects of Hurricane Floyd did not begin to significantly impact raw water quality until September 21. At that time, raw water color began to rise while alkalinity and pH began to decrease. Because of the drastic and rapid changes in raw water quality, there were several occasions when potable water production using the surface water source ceased for several hours. At times, many plant staff worked 16 to 18 hour shifts to control pretreatment chemistry and maintain drinking water production. Following the passage of Hurricane Floyd river levels slowly receded, however pools of highly organic water remained impounded above normal river stage. During subsequent rainfall events, the impounded pools overflowed and caused Northwest River raw water organic levels to increase. The variance in raw water TOC continued into February, 2000. This paper presents the data associated with pretreatment chemistry and the struggle to maintain high quality potable water due to a catastrophic meteorological event. Includes reference, tables, figures.