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11 E LCRS Design - Area 2B Foothill Sanitary Landfill Sizing of the pump within the Area 2B sump will based on predicted flows from the HELP analysis completed for this report, and based on average daily flows that can be expected based on actual daily leachate generation records from Area 2A because they likely provide more realistic estimates of potential average flows due to leachate recirculation at the facility. The peak daily leachate generation prediction from the HELP model is 1,235 ft3/day/acre, or about 30,900 ft3/day for the entire 25 acre Area 2B expansion. The average daily leachate generation per acre as established from actual leachate records for Area 2A is roughly 236 ft3. For the 25 acre Area 2B the total average leachate generation is estimated to be 5,500 ft3 per day. The noted leachate generation rates for average and peak translate to 160.5 gpm and 28.6 gpm for peak and average leachate generation rates. Pump design will be carried out by McIntire Electric, who will consider twice the flow volumes estimated in this report to comply with governing regulations. Pump designs will be presented in a separate calculation package. Leachate generation estimates for Area 2B are presented in the HELP model output included as Attachment 1 of this report. The County will operate the sump pump(s) as necessary to generally maintain less than 12 - inches of liquid head above the composite liner system. Leachate will be pumped directly to an onsite leachate tank and disposed of by the County in accordance with the WDRs. 4.0 LEACHATE GENERATION ANALYSIS 4.1 General The leachate generation of the FSLF's Area 2B was estimated by modeling the water balance of the proposed facility using the model Hydrologic Evaluation of Landfill Performance (HELP), version 3.07 (Schroeder et al., 1994). The HELP model was used to calculate the maximum impingement rate for drainage layer transmissivity calculations, as well as the calculated maximum leachate head on the liner. Leachate generation potential for this analysis was evaluated for the critical active cell condition of the landfill for side slope and base LCRS and was also investigated for final filling with current design elevations (145 -foot waste fill). Additionally, a final fill condition considering a 300 -foot waste was considered to provide information for the County's decision making process with regard to landfill planning. 4.2 HELP Model Description The HELP model is a 'quasi 2-dimensional' deterministic water balance model that uses daily climate data, soil and refuse characteristics, and liner system design data to predict the movement of water into, within, and leakage out of the landfill boundaries. The US Army Corps of Engineers first generated the HELP model in 1983 under a contract with the United States Environmental Protection Agency (USEPA). Documentation of Version 3.0 of the HELP model can be found in Schroeder et al., (1994). 4.3 Landfill Profiles Simulated Peak daily leachate generation potential is typically highest during the early stages of landfill operations when a relatively thin (i.e., 15 foot) layer of waste has been placed across the entire floor of the cell. As waste thickness increases, the storage capacity of the landfill tends to Project No. AU17.1254 I LCRS Design 4 May 2018