Safeguarding Our Water’s Purity

 

Safeguarding Our Water’s Purity

By Gerard Hillenbrand, P.E.

That was the intriguing subject of our chapter’s dinner meeting of Wednesday, November 15th 2006 at Mullen’s restaurant in Manhattan. The evening’s speaker was James Mueller, Director of Planning and Design, Bureau of Engineering Design and Construction, N.Y. City Department of Environmental Protection. The topic of Mr. Mueller’s Presentation was the new water filtration plant now under construction in Van Cortlandt Park in the Bronx. The subject of Mr. Mueller’s presentation has been submitted to our accreditation organization for eligibility to receive credit for one professional development hour toward continuing educational requirements in the state of New York. This technical dinner meeting was also co-sponsored by the Metropolitan Section of the American Society of Mechanical Engineers.

Mr. Mueller began his very effective slide presentation by introducing his associates from the D.E.P who were seated together at a table in the front of the meeting room. The Croton Watershed System is the oldest in N. Y. City’s water supply network, and was essentially completed in its present configuration in 1917. Periodic upgrades have been added including interconnections to the City’s third water tunnel initiated in 1970, and completion of the New Croton Aqueduct in 1993 which feeds into the Jerome Park Reservoir in the Bronx. The Croton Watershed System covers 375 square miles of area and contains 12 individual reservoirs and three major spillways. The system is entirely gravity fed and supplemented by two local pumping stations.

For some years now the federal government has been lobbying N.Y. City to further improve the quality of its drinking water, which had developed occasional problems with taste, odor, and clarity. The city responded with a program of purchasing additional watershed area upstate, reducing contaminants in ground water, and improving efforts to reduce agricultural and urban pollution from entering the water shed areas. Despite these initiatives, our city’s water has been unable to meet consistently the federal government’s new drinking water quality standards and regulations. The federal government then went to court to enforce the new regulations and this legal action led to a 1998 consent decree, entered into by the United States, the state and city of New York, to provide additional filtration for our city’s drinking water. The objective of this added filtration was to further reduce the presence of disease-causing organisms, such as those associated with nausea, cramps, diarrhea, associated headaches, and even cancer, birth defects and microbiological contamination.

In 2002 the original consent decree was further modified to mandate that N.Y. City evaluate and choose between three potential sites for the construction of a major filtration plant, tow sites in the Bronx and one in Westchester county. The specifications for this proposed plant were for a capacity of from90 to 290 million gallons of water per day with an average flow projected to be 144 million gallons per day. The three sites considered were:

  • Along the Harlem River in the neighborhood of Fordham Road west of the Jerome Park Reservoir.
  • At the Mosholu Golf Course, lying within Van Cortlandt Park.
  • At Eastview in Westchester County, on ciry owned property.

The proposed Harlem River site generated the most public opposition and its elimination from consideration was primarily a political rather than a technical decision. In addition, the area had significant zoning problem as well as major construction complexities. The proposed Eastview site had the advantages of providing large staging area with close proximity to existing tunnels for ease of connection and integration into facilities in the area, all without use and zoning limitations. However, the Eastview site had serious disadvantages such as local approvals from Westchester County, loss of property taxes on condemned city-owned property, and certain design limitations. These limitations include deeper excavations for the associated pumping station, water surge and over flow conditions, more expensive security requirements and Groton Watershed rehabilitation projects, along with more complex piping arrangements.

The Mosholu site would have a major impact on the Golf course, but offered major benefits. Among the benefits were no new zoning changes, complete underground construction enhancing security requirements, superior vehicular access, close proximity to the Croton Aqueduct, and minimum overall construction work resulting in lowest cost of all the alternatives. As a result, the city sought state legislation authorizing the use of the Mosholu Golf Course for the construction, operation and maintenance of a major filtration plant. This legislation was passed in 2003 and signed into law by the Governor shortly thereafter. The required Environmental Impact Statement, issued in 2004, also identified the Mosholu site as the preferred site for this facility. The city council approved the start of construction in the fall of 2004 and in 2005 preparation work began on the site, and as photographs showed, this work is now nearing completion with 75% of the excavation finished.

The final design of the filtration plant was approved in April, 2006 and bids were requested in June, 2006 with start of construction scheduled for February, 2007. Completion of the project is scheduled for May 2011 with operations starting in October 2011. The plant itself is projected to cost $1.4 Billion. The site preparation work is scheduled for completion in 2007 and will cost $1.17 Billion, the lowest of three bids ranging upward to $1.7 Billion. This preparation work also contains provisions for minimizing the impact of truck transport, noise and dust generation. The connecting tunnels into the Croton Aqueduct are expected to cost $200 Million. The inevitable change orders are to be processed within 9 months to 1 year after determination of need. Price and inflation indexing has been built in over the life of this five year project. After completion of the plant construction, the Golf Course will be restored and a Golf driving range will be constructed on the ground level roof covering the filtration plant.

The design of the underground filtration plant is, of course, state of the art. All collection tanks will be vented into the atmosphere and will odorless. Storage tanks for acids and chemicals, such as Chlorine and Florine compounds, will be connected to the water feeding system and controlled automatically via remote conveyor and mixing machinery. 48 individual filtration mechanisms will be employed and will include the necessary backwash and residual collection units. Ultraviolet units rated at 40 Million Joules per Square Centimeter, will also process the filtered water to achieve the highest levels of purity. Flocculation equipment will collect and eliminate the small, fluffy masses of impurities that the filtration units will generate. Disposal units are the wet well design type and contain sealed pumping stations to convey impurities to the surface for collection and transfer away from the site. The entire plant, including its electric system and piping schematic, is modeled in miniature to preclude any three-dimensional interference and missed connections.

This lecture was concluded with the usual interesting question and answer period. This lecture is typical of the type of technically current material presented at our periodic dinner meetings. We cordially invite all our chapter members to join us at future activities.

 Posted by at 4:03 pm