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 water alkalinity 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. Prior to September 21, Northwest River raw water color, alkalinity and pH averaged approximately 250 color units, 35 mg/L as CaCO_3 and 6.5 respectively. By October 10, raw water color approached 1,000 cu, alkalinity fell below 10 mg/L as CaCO_3 and pH was as low as 5.5. On the fourth of October (TOC) levels in the Northwest River were as high as 75 mg/L. During this period, the Northwest River WTP was feeding 330 mg/L alum at a coagulation pH of 5.6. The coagulation pH was critical to achieve removal of natural organic material and color. Because of the drastic and rapid changes in raw water quality, there were several occasions when potable water production using the surface
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