DEP Environmental Protection Invoices, 1999-2001

NYC 9/11 Public Portal Document o1/oi/2Xi 16:12 518-402-7659 EPWSP PAGE 03/05

The turbidity requirement in both the SWTR and State Sanitary Code is a key provision intended to protect against adverse health effects from exposure to pathogens in drinking water. These requirements are designed to decrease the risk from waterborne microbial pathogens by limiting levels of particulate material in drinking water. Excess turbidity interferes with disinfection and can provide a shelter for pathogens by reducing their exposure to attack by disinfectants. Evidence exists that controlling turbidity is a competent safeguard against pathogens in drinking water. The operational changes to control the release of the high levels of turbid water in the Ashokan Reservoir West Basin and the flow reductions from the Ashokan Reservoir East Basin have not been sufficient in reducing the overall turbidity load from the Catskill system into Kensico Reservoir.

While the raw water turbidity leaving Kensico Reservoir has not yet exceeded the 5 NTU regulatory limitation, without the addition of alum and sodium hydroxide, such an exceedance is imminent. In the City's After Action Report on the application of alum and sodium hydroxide in 1996 the City demonstrated that the addition of alum and sodium hydroxide was able to control turbidity in the Catskill water system and limit its impact on turbidity levels in Kensico Reservoir, such that at no time did the Kensico effluent points exceed the SWTR 5 NTU limit. The addition of alum and sodium hydroxide is the only known feasible alternative readily available to the City at this time.

A public health hazard is defined in Department regulations as "an existing or imminent condition which can be responsible for or cause illness, injury or death and for which immediate corrective or remedial action is required"(10 NYCRR Section 5-1.1 (ar)). Disinfection which is inadequate to destroy harmful microorganisms or to maintain a specific chlorine residual is one example of a public health hazard. (See 10 NYCRR Section 5-1.1 (ar) (5)). The addition of alum and sodium hydroxide would be an "immediate corrective or remedial action" that has been demonstrated to reduce turbidity levels in the Kensico Reservoir.

Therefore, given the high turbidity levels in water entering Kensico Reservoir and the potential imminent development of a public health hazard, we approve your request to add alum and sodium hydroxide as outlined in the January 8, 2001 protocol attached to your approval request with the following additional conditions:

1. the City must first obtain approval from the New York State Department of Environmental Conservation (NYSDEC);

2. the City must notify this office before starting the alum and sodium hydroxide application;

3. the City must notify this office of the proposed alum and sodium hydroxide dosage and any changes in dosage, and receive approval of such changes before commencing the feeding or altering of alum and sodium hydroxide;

4. the City keypoint and limnological monitoring protocol must be implemented as proposed in the attachment to Mr. Hoffer's January 8, 2001 letter to Ms. Duke of NYSDEC Region 3 subject to the following provisions:

NYC-WTC 000137777