Watershed Management for Potable Water Supply Assessing the New York City Strategy (2000) / Chapter Skim
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11 Wastewater Treatment
11 Wastewater Treatment
Pages 468-491
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From page 468... ...
Over 30,000 on-site sewage treatment and disposal systems (OSTDS) and 41 centralized wastewater treatment plants (WWTPs)
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From page 469... ...
ANALYSIS OF WASTEWATER TREATMENT PLANTS AND ON-SITE SEWAGE TREATMENT AND DISPOSAL SYSTEMS Impact Index The approach used by the committee views each reservoir in the water supply system as a "black box" that receives effluent from OSTDS and WWTPs. The volume and pollutant concentrations of OSTDS and WWTP effluent that are currently entering the Catskill/Delaware reservoirs represent a baseline "impact index" of 100 percent.
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From page 470... ...
BACT for WWTPs includes sand filtration, disinfection, phosphorus removal, and microfiltration, and all upgrades are scheduled for completion by 2002. Although not mandated in the New York City watersheds, BACT for OSTDS consists of aerobic treatment units (ATUs)
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From page 471... ...
Effluent Pollutant Concentrations Wastewater Treatment Plants. Determining the contribution of WWTPs to overall pollutant loading in a watershed is relatively straightforward.
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From page 472... ...
Quantitative increases in effluent from OSTDS caused by population increases can also be estimated using projected rates of population growth and average per capita wastewater production. The assumptions used for both WWTPs and OSTDS and the calculated values derived from these assumptions are given in Appendix D
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From page 473... ...
The impact index assumes that all systems without technology upgrades suffer a 5 percent failure rate, while those that install BACT have a zero percent failure rate. Finally, the EIS analysis implies that only those OSTDS residing within proscribed setback distances (between 100 and 500 ft)
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From page 474... ...
The potential for BACT to greatly improve effluent quality is shown dramatically in Figures 11-1 through 11-4. Role of Best Available Control Technology Wastewater Treatment Plant Effluent According to the impact index analysis, the largest reductions attributable to the use of BACT at WWTPs occurred with phosphorus, total suspended solids, and Cryptosporidium oocysts.
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From page 475... ...
The rightmost bar represents the loading of the parameter with BACT in place and population growth to 2010. Each bar is divided into two parts: one representing the percentage contribution from WWTPs (unshaded)
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From page 476... ...
476 WATERSHED MANAGEMENT FOR NEW YORK CITY FIGURE 11-2 Impact index for Neversink and Pepacton reservoirs.
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From page 477... ...
WASTEWATER TREATMENT FIGURE 11-3 Impact index for Rondout and Schoharie reservoirs.
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From page 478... ...
WATERSHED MANAGEMENT FOR NEW YORK CITY FIGURE 11-4 Impact index for Kensico and West Branch reservoirs.
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From page 479... ...
Because WWTPs in the Rondout and West Branch watersheds are already at or near BACT, population growth will begin to degrade water quality to below preBACT conditions almost immediately in those watersheds. In the Ashokan, Cannonsville, Pepacton, and Schoharie watersheds, where implementation of BACT will significantly improve effluent quality, over 100 years will be required to reach previous contaminant levels.
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From page 480... ...
Wastewater Treatment Plants Currently, BACT for new WWTPs discharging to surface waters is defined as sand filtration, disinfection, phosphorus removal, and microfiltration. The following effluent standards are also required, which the SPDES permits for these plants must be updated to reflect: · Phosphorus: 1.0 mglL for <50,000 gallons per day (gpd)
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From page 481... ...
Because of the higher cost of aerobic units, the passive septic tank and drainfield combination is invariably chosen. As previously mentioned, passive septic tank and drainfield combinations provide inferior treatment of residential wastewater compared to ATUs.
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From page 482... ...
SITING ISSUES On-Site Sewage Treatment and Disposal Systems Suitable locations for OSTDS described in the NYS DOH publication "Individual Residential Wastewater Treatment Systems Design Handbook" appear to be adequate (NYS DOH, 1996~. There must be 100 It separating OSTDS from nearby waterbodies and wetlands.
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From page 483... ...
Waivers are especially ill advised in areas that are environmentally sensitive or are of public health significance. Wastewater Treatment Plants The Watershed Rules and Regulations include a 60-day travel-time delineation that is used to regulate siting of new or expanding WWTPs in the Catskill/ Delaware watershed.
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From page 484... ...
Analysis The appropriateness of a 60-day travel time for source protection must first be framed in the context of what objective is to be achieved. In the absence of precise written documentation justifying the 60-day value, it is assumed that this concept is based on the belief that 60 days will provide sufficient time for decay of microorganisms from a properly treated wastewater, so as to have de minimus impact on microbial levels in the source water.1 In other words, travel time from the WWTP to the reservoirs is considered a barrier to pollution, much like chlorination or other treatment processes.
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From page 486... ...
Wastewater effluents discharging into the New York City watershed have substantially lower oocyst levels than do other WWTP effluents across the country. For example, Madore et al.
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From page 487... ...
Treatment Plant Mean Standard Deviation Delhi WWTP 0.74 1.76 Hunters Highland WWTP 0.69 3.36 Hobart WWTP 3.25 20.73 Tannersville WWTP 8.57 32.46 Stamford WWTP 2.26 9.85 Source: NYC DEP (1998b)
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From page 488... ...
In any event, consideration of both Giardia and Cryptosporidium information raises questions as to whether a 60-day travel time is sufficiently protective. Studies using the waters under question and sensitive viability assays (animal infectivity or perhaps cell culture in the case of Cryptosporidium)
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From page 489... ...
5. To make sure that the Continuous Backwash Upflow Dual Sand Filtration units represent BACT, wastewater treatment plants using this technology should be subject to rigorous long-term monitoring of particle counts and turbidity to verify that equivalency is maintained.
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From page 490... ...
8. Although declines in water quality related to WWTPs and OSTDS will occur with population growth, in most cases 40-100 years will pass before contaminant contributions from WWTPs and OSTDS reach preBACT levels.
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From page 491... ...
1996. Individual residential wastewater treatment systems design handbook.
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