Full Description

On December 8, 1993, the United States Environmental Protection Agency (EPA) Region III office issued a Boil Water Notice to the one million consumers of drinking water in the metropolitan Washington DC area that is produced by the Washington Aqueduct. Heavy rains had occurred in the Potomac Basin during the weekend of December 4-5, 1993. The WAD reported that at 5 pm on the evening of Monday, December 6, 1993, the turbidity of the raw water taken from the Potomac River increased from 86 NTUs to 130 NTUs without their operators increasing the alum dosage. This resulted in an overload to the filters and at 1 am on December 7, 1993, the filtered water turbidity was 6.5 NTUs, peaked at 9 NTUs at 2 am and 6.5 NTUs at 3 am. Under the Surface Water Treatment Rule, filtered water can at no time exceed 5 NTUs. EPA was alerted to the problem later that afternoon but a full assessment of the problem did not occur until the next day, and by 5 pm, a Boil Water Notice for all users of the WAD water was issued which advised consumers to boil their water for at least 1 minute. The Notice remained in place until 1:15 pm on December 11, 1993, after two consecutive days of cryptosporidium and giardia testing of the water in the distribution system tested negative. Fortunately, no disease outbreak occurred, and several studies and investigations were undertaken to determine how this problem occurred as well as identifying ways of making sure it did not occur again. This paper lists 14 factors identified as contributing to the problem and 10 recommendations implemented by the WAD including limiting filter runs, backwashing the individual filters, improving communications, installing alarms, and investigating all turbidity spikes.

Product Details

Published: 01/01/1995 ISBN(s): 0898678358 Number of Pages: 7File Size: 1 file , 310 KB