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Wastewater Reclamation System For The Salisbury School. Prepared by WMC Consulting Engineers Inc. John A. Wengell. Salisbury School. Background Conditions. Student Population Fluctuates between 230 students to 300 students 50 Faculty Members & 70 Staff Members
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Wastewater Reclamation System For The Salisbury School Prepared by WMC Consulting Engineers Inc. John A. Wengell
Background Conditions • Student Population Fluctuates between 230 students to 300 students • 50 Faculty Members & 70 Staff Members • Water Usage 23,200 GPD (Averaged- School in Session) • Population Fluctuates – Added 15% Variation = Average 26,700 GPD • Design Flow with a 50% Safety factor (DEEP requirement) = 40,000 GPD
Proposed Wastewater Options • Connect to the Town of Salisbury wastewater treatment system (2+ miles) • Construct a standard type leaching system • Install a pretreatment system and disperse effluent via low pressure to constructed leaching bed with an additional leaching layer • Install a pretreatment system and disperse effluent via low pressure to constructed leaching bed and thru a series of wetland cells
Wastewater Selection • Use of enhanced pretreatment with deemed cost effective • On Site disposal allows for groundwater reclamation into existing groundwater system • Variety of enhanced pretreatment options approved by DEEP • Reduction of cost with installation of wetland cells over additional leaching layer needed to achieve 21 days of travel time
System Components • Zenon Systems (Cycle-Let) Technology consisting of pretreatment, anoxic and aerobic stage biological treatment, ultra-filtration membrane separation, carbon adsorption and UV disinfection • Constructed Fill Leaching System • Constructed Wetland Cell System
Zenon Systems (Cycle-Let) Technology • Zenon System is capable of treating Nitrogen to levels less than 10 mg/L • Zenon System is capable of treating Total Phosphorus to levels less than 2 mg/L • Researched and proven to remove total coliform to levels < 2.2 MPN/100ml and virus to levels exceeding 99.998% • Performance around State
Constructed Fill Leaching System • Effluent dispersed via low pressure dispersal system into leaching bed (18” Washed Stone) • Effluent flows thru a constructed fill layer 24” thick of unsaturated material • To avert concerns of mounding a 12” blanket drain of highly permeable material was placed below the leaching fill • Allowed to break out at the toe of slope into a collection swale
Constructed Wetland Cell System • Wetland Cells were designed to provide 100% bacteria/virus removal back-up to the Zenon System • Wastewater treatment via constructed wetlands can provide high levels of bacteria and virus removal efficiencies at Hydraulic Residence Times (HRTs) of five to seven days • To comply with DEEP requirements the Wetland Cells were designed to have an HRT of a minimum of twenty one days.
Wetland Cell Design • Cells were designed to retain 21 days of inflow minus losses • Inflow = Treatment Plant design Flow plus a 50% safety factor, Direct Rainfall into the cells and overland flow from run-off • Losses = Infiltration, Evaporation, Transpiration and Cell Overflow • Conservatively Losses were only computed for Evaporation
Wetland Cell Design • Inflow (7,255 c.f./day) – Losses (567 c.f./day) = 6,688 c.f./day • Storage of 140,448 c.f. necessary for 21 day requirement • Approximately 69,000 s.f. of pond area at a 2’ depth was constructed • Discharge Rate of 35 gpm spread over 150’ long level spreader
