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Preliminary Engineering Report - Fauquier County

Preliminary Engineering Report - Fauquier County

system is operating

system is operating optimally. At times, particularly during the colder season or when large quantities of raw leachate are transferred to Pond #2 the ammonia levels may increase, however, concentrations are brought down relatively quickly by increasing the air supply and recirculating the treated effluent. With the current leachate flows the hydraulic retention time (HRT) in Pond #2 ranges from 90-180 days. TABLE 1 Pretreated Leachate Effluent Sample Data (Pond #2) BOD Total P Ammonia TKN Nitrate TSS Date mg/L mg/L mg/L mg/L mg/L m/L pH 3/7/2006 88 205 11 8.63 3/21/2006 145 207 14 8.6 4/4/2006 50 201 15 8.49 4/25/2006 69 23.2 19 7.96 5/1/2006 72 100 11 8.18 5/15/2006 68 1 1 7.98 5/30/2006 12 10 4 8.11 6/12/2006 14 2.32 6 8.24 6/26/2006 86 3.09 9 8.21 7/10/2006 56 3.26 17 8.17 7/24/2006 35 3.73 4 8.22 8/7/2006 28 1.98 4 8.28 8/21/2006 54 1 4 8.04 9/5/2006 15 1 4 7.84 9/18/2006 33 1.81 2 7.88 10/2/2006 37 1 5 8.06 10/30/2006 10 5.32 3 7.97 11/27/2006 80 2.37 5 7.99 12/11/2006 12 2.67 3 8.19 12/27/2006 20 13.8 6 8.24 1/8/2007 40 31.9 31 8.11 1/23/2007 28 56.5 17 8.62 4/4/2007 45 120 58 8.58 1/13/2010 22 27 8.4 6/10/2010 1.47 213 7/20/2010 1.71 28 5/9/2011 20 2.22 0.72 1.75 376 11.3 To further improve the pretreatment process for total nitrogen by removal of nitrates through denitrification, an attempt was made to modify the aeration system mode of operation to create “anoxic”-like conditions in the front of the Pond. This was done by significantly reducing the air flow N:\18469-000\Engineering\Reports\April 2012 PER\18469 PER Treatment System 7-31-2012_AM.docx Page 5

in the first two air headers where the leachate enters, while at the same time recycling the pretreated nitrate-rich leachate through the existing pump station. The “anoxic” zone, the nitrate in the recycle flow and the carbon (BOD) present in the incoming leachate provides for conditions to achieve some degree of denitrification for overall total nitrogen removal. Table 1 shows the nitrate levels from a sample taken on June 10, 2010 (213 mg/L nitrate) at the start of the test and shows the nitrate levels by July 20, 2010 (28 mg/L nitrate) indicating a significant reduction in nitrate concentration. Currently, the system is operated in fully aerated mode and nitrate levels in the effluent from Pond #2 are in the range of 200-300 mg/L. Although the landfill is located in close proximity to the Town of Warrenton, the Town currently does not wish to provide a physical connection to their wastewater system since the landfill is outside of the Town’s service area. The Town of Warrenton is also currently not accepting pump and haul leachate from the facility. The landfill currently pumps and hauls pretreated leachate to the Fauquier County Water and Sanitation Authority (FCWSA) Remington WWTP or to the RECO Industrial Treatment facilities in Richmond for disposal. 2. Existing Leachate Daily Production Quantities: The last three years of landfill leachate hauling records were reviewed for estimating the leachate quantities, summarized in Table 2. Offsite Leachate Disposal Volumes Annual Volume of Leachate Hauled Offsite (gallons) Equivalent Average Daily Volume of Leachate (gallons) TABLE 2 Annual Leachate Disposal Volumes FY 2010 (July 2009 – June 2010) N:\18469-000\Engineering\Reports\April 2012 PER\18469 PER Treatment System 7-31-2012_AM.docx FY 2011 (July 2010 – June 2011) FY 2012 (July 2011 – June 2012) 1,876,225 3,176,121 2,480,281 5,140 8,702 6,795 The average daily leachate flow over the last three years is approximately 6,900 gallons per day. The highest annual production was from July 2010 to June 2011 with an average 8,700 gallons per day. The variations in landfill leachate production correlate directly with wet weather precipitation. Experience indicates that during wet weather periods, the landfill cells can generate as much as 12,000 to 15,000 gallons of leachate per day. During extended periods with little or no precipitation, as little as 5,000 to 10,000 gallons per week of leachate may be generated. The depth of the leachate within the pond can be varied from approximately 6 feet to 8 feet to allow for equalization during wet weather periods. 3. Management of Leachate Pretreatment System: During the cold weather months, the water temperature in the Pond can drop to 8⁰ C or lower. These lower temperatures result in reduced biological activity and less reduction in TKN and ammonia within the pond making it less favorable for offsite disposal at the local POTWs. To Page 6

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