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Environmental Cleanup Plan for AOC 65
Section 5 - Groundwater Recharge Study
A groundwater recharge study will be conducted at AOC 65 to assess the nature, rate, and extent of groundwater recharge and flow in the fractured limestone underlying the site. The study will also assess how the groundwater flow affects migration of VOCs and performance of the SVE system. The groundwater recharge study data will assist in determination of potential contaminant flow paths and migration rates in soil and rock beneath AOC 65. A description of the recharge study is included in the AOC 65 Treatability Test Plan, Parsons, April 2002, submitted to CSSA.
5.2 - Piezometer Design and Installation
Six piezometers will be constructed as part of the groundwater recharge study to be conducted at AOC 65. Results from the geophysical surveys will be used to assist in locating piezometers along groundwater flow features. Final screened intervals will be located within zones containing features of interest (fractures, high VOC levels in soil gas) discovered during packer testing (Section 5.4).
Each piezometer will be completed with 25-foot screened intervals selected to provide complete coverage of the entire upper 150-foot profile of the unsaturated formation. Each borehole will be continuously cored during drilling. Additional information regarding the piezometer design and construction is included in Section 3.1 of the AOC 65 Treatability Test Plan, Parsons, April 2002.
5.3 - Weather Station Design and Installation
A weather station will be installed on the west side of Building 90 near the nested piezometers to continuously monitor weather and hydrologic conditions in the groundwater recharge study area. The weather station will be fitted with a rain gauge, and will be connected to down-hole transducers in each of the six piezometers. A solar powered data recorder capable of transmitting real-time data to CSSA, either through telemetry or telephone lines, will be secured at the weather station to record readings from the rain gauge and each transducer. The data collected will measure rainfall intensity and assess migration patterns and rates of water flow into the various screened intervals of each nested piezometer.
Soil gas samples will be collected from selected VEWS during the extraction packer test to be performed as part of installation of the deepest piezometer (150 feet). The intervals selected for packer testing will be based on lithologic descriptions of continuously sampled cores plus results of geophysical testing. Results of the packer test will provide guidance regarding the appropriate screen depth for the AOC 65 SVE system. Soil gas samples will be collected from up to eight separate depth and analyzed for VOCs by USEPA analytical method TO-14.
Groundwater will be collected from each piezometer following significant rainfall events (greater than 1.0 inch) and analyzed for VOCs by method 8260. Samples are proposed for collection approximately 24 hours after the rainfall event begins, and then again 48 and 96 hours later. No well development or purging will be conducted prior to sample collection, and samples will be collected with dedicated or disposable miniature bailers. It is assumed that no more than one significant rain event will occur per month. Additional information on analytical sampling to be conducted as part of the groundwater recharge study is included in the Draft AOC 65 Treatability Study Sampling and Analysis Plan Addendum, Parsons, April 2002.
Each of the six piezometers and six VEWs (see Section 6.0) will be sampled for ethane, ethene, and methane by analytical method RSK-175 in addition to other natural attenuation parameters for chlorinated systems.
A tracer test of the groundwater may also be considered to assess movement of TCE in groundwater through the fracture system.