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Emergency Response Plan In Action
Northwest Well Field Chemical Overfeed

On Friday, February 29, 2008 the District responded to a number of residents phone calls regarding complaints describing “slimy water” coming out of their faucets. District personnel responded immediately to ascertain the extent of the situation and immediately began corrective actions. These actions and the excellent employee response mitigated the severity of the situation and kept to a minimum the area and number of consumers affected.

It was determined that a small slug of sodium hydroxide was released to the system and attributed to a backsiphonage condition at well no. 4 located in the Northwest Well Field located off of Ontario Avenue. The Nassau County Department of Health (NCDOH) was alerted to the situation and in a cooperative manner worked with the District to minimize the effects. At no time throughout this episode did MWD obtain a field pH reading of >10 which would have triggered enhanced mandatory consumer notification under the Emergency Response Plan.

It was also decided to put into effect the Nassau County Office of Emergency Management (NCOEM) Reverse 911 system to the affected area. With assistance from the Districts Engineer, the boundaries of the area to be notified were determined in coordination with the NCDOH. Although a minimum number of glitches were encountered, once the decision was made to utilize the Reverse 911 system, the majority of consumers in the affected area were notified within 20 minutes.

In addition, after discussion with the NCDOH it was decided to obtain 10 water samples from within the affected area and have the Districts laboratory perform the necessary sampling all of which fell below a pH level of 7.69. MWD personnel responded to consumer phone calls until 7:00 pm after which, stand-by personnel continued to receive calls until midnight and also responded to calls on Saturday, March 1st. In addition, after discussion with the Board of Commissioners, the site was declared an emergency and District personnel proceeded with all work necessary to confirm the emergency declaration and to eliminate the potential for a future recurrence. The Massapequa Water District also retained the Engineering firm of Holzmacher, McLendon and Murrell, P.C. (H2M) to perform an objective evaluation of the incident and prepare a report pursuant to the requirements of Section 17(d) of Article VI of the Nassau County Public Health Ordinance. A representative of H2M reviewed the pertinent information related to the incident and proceeded to conduct an inspection of the Northwest Well Field. The inspection focused on the caustic treatment system and supply well (Well no. 4) in operation at the time of the reported incident.

Based on the post incident inspection performed, H2M concurred with the Superintendent that the sodium hydroxide incident most likely occurred because of the following:

• The air relief valve on Well no. 4 may have temporarily stuck closed which created a vacuum that overcame the existing pressure regulator on the caustic line thereby siphoning caustic into the well piping prior to discharge to the system.

• The combination of an inoperable swing check valve on Well no 4 in conjunction with a wafer check further upstream then allowed there to be no system pressure at the point of injection.


The comprehensive post incident inspection did not determine any other definitive causes related to the incident. The Water District has completed the implementation of the necessary improvements in order to prevent the occurrence of such incident from happening again at the NWWF.


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