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Ryegrass LPL and Ryegrass Balefill Landfill Upgradient Groundwater <br />Investigation <br />Kittitas County Solid Waste <br />lined 500,000-gallon septage lagoons were constructed to the west replacing the unlined lagoons <br />(Ecology 2012). <br />Biosolids were placed into the lagoons for removal of liquids then the waste was either used as daily <br />cover in the Balefill Landfill until its closure or land applied at the Facility including below the LPL <br />prior to its construction in 1996, near well B3 south of the LPL, east of the Balefill Landfill, and on <br />the southeast corner of the Facility (Figure 2). The biosolids program is continuing to operate at the <br />two lined septage lagoons through a separate permit with Ecology. <br />Periodic sampling of the underdrains of the lined LWELs is completed as part of the operations of the <br />biosolids program. Previous evaluations in 2016 identified leaks from the westernmost LWEL that <br />were then repaired. Additional sampling has been completed to evaluate LWEL leakage from the <br />lined storage ponds. The lagoons and biosolids are managed following the Plan of Operation Liquid <br />Waste Evaporation Lagoons (Parametrix 2022). <br />Hydrogeology <br />3.1 Geologic Setting <br />The current evaluation of the geology and hydrogeology of the Facility is described in the <br />Hydrogeologic Investigation Report (HWA 2023). The HWA 2023 report updated previous evaluations <br />completed in 2004 (HWA 2004). A brief summary is included below: <br />■ Soils are mapped as Argabak very cobbly loam, Argabak-Vantage complex, and the Palerf- <br />Vantage complex (NRCS 2024), consist of cobbly loam averaging in thickness of <br />approximately 6-inches up to 35-inches in channels. <br />■ Surface geology is mapped as the Frenchman Springs member of the Wanapum Basalt (DNR <br />1994) locally known as the Gingko Flow/Gingko basalt. Outcrops of the Vantage Interbed are <br />also located nearby. <br />■ Subsurface geology consists of the massive and columnar basalt that transitions to the <br />bottom flow zone comprised of palagonite, pillow basalts, and petrified wood overlying the <br />sandstone, siltstone, claystone of the Vantage Interbed. The depth to the Vantage Interbed <br />ranges from 70 to 170 feet below ground surface (bgs) near the Facility. <br />■ The Shallow Aquifer is located in the bottom flow zone of the Gingko basalt perching above <br />the Vantage Interbed. Groundwater below the LPL predominantly flows to the west- <br />southwest. <br />■ Numerous springs occur south and west of the Facility where the Vantage Interbed outcrops <br />within the shallow channels. <br />■ The Vantage Interbed overlies the Grande Ronde Basalt. <br />3.2 Groundwater Monitoring History <br />Figure 3 displays the locations of the existing monitoring wells and the planned additional well, B8. <br />Groundwater monitoring at the Facility started in 1993. Three monitoring wells, B2, B3, and B4, were <br />installed south of the Balefill Landfill. A fourth location, B1, was abandoned and a well was not <br />constructed due to limited groundwater accumulation in the open borehole (PGG 1991). Well B2 <br />includes shallow and deep completions. The shallow completion is 38 feet deep and dry. In 2000, <br />April 2024 1 553-1763-010 <br />Revised May 2024 <br />