WORK PLANS - Laserfiche WebLink

Home Browse Search

GeosyntecO consultants EVS®models were generated for the Site 3, Site 4,Central,and Landfill Areas using the island-wide data set described above as well as available grab-groundwater data included in the project database that was collected between 2006 and 2016(Table 3).A mid-screen elevation was assigned as the elevation(Z value) for each sample location based on well installation and surveyed top of casing measurements provided by ERS.The Site 3 model was generated with data from 27 wells and 16 grab-groundwater samples. The Site 4 model was generated with data from 25 wells and 7 grab-groundwater samples. The Central Area model was generated with data from 71 wells and 7 grab-groundwater samples and the Landfill Area model was generated with data from 143 wells and 21 grab-groundwater samples. Non-detect flags are used as input for the plume interpretations at locations where groundwater samples were collected but chemical concentrations were below the Reporting Limit(RL).Non-detect flags were replaced by 10%of the reported RL values during the interpolation. Monitoring well sample results for wells not sampled since 2006 and grab-groundwater sample results prior to 2006 were compared to the current COC extents in the EVS® model. Data collected prior to 2006 was not used in the EVS® model, which is intended to represent the current distribution of COCs in groundwater.Of the monitoring wells not sampled since 2006, only three wells had COC detections at concentrations greater than the MCL.Monitoring wells W-259,W-263,and W-265 in the Building 30 cluster of wells in the northern portion of the island were last sampled in 2000 and had VC detections between 0.8 and 1.9 micrograms per liter(µg/L).The VC MCL is 0.5 µg/L.Based on the stable VC concentration trends for these wells based on historical data,VC likely remains near or below the MCL for these wells today. Of the grab-groundwater samples collected prior to 2006, only one had COC concentrations above MCLs in an area outside the current extent of the plume. This grab sample collected in 2005 from the northern portion of the landfills at an unspecified depth had reported VC and benzene concentrations above the MCL at concentrations of 11 and 3.7 µg/L, respectively. Cis-1,2-DCE was reported below the MCL at 3.7 µg/L.This grab sample was approximately 150 feet to the east of wells W-084,W-189,and W-183,which are screened at three unique depths in the aquifer. VOCs were historically detected at these wells but are now below MCLs. RRI Groundwater Monitoring Work Plan 16 1 June 2018