ARCHIVED REPORTS XR0008942 - Laserfiche WebLink

Home Browse Search

A M B R I A Mr Jeffrey Wong July 27,2005 SVE REEVALUATION SVE Well Placement Cambria reviewed the site soil analytical data, SVE well and boring locations, construction details, and SVE test data We present the soil boring and well construction data in Table 1, the soil analytical data in Table 2, the radius of influence data in Table 3, SVE analytical and mass removal data in Table 4, and a site map showing well and borings locations (Figure 2) Several soil borings have been drilled adjacent to the gasoline USTs at this site The highest MTBE concentrations detected in soil were from bonngs SB-1 (92 9 ppm at 25 fbg) and SB-4 i (46 6 ppm at 25 fbg), which were drilled during January 1999 Cambria notes that other borings drilled during this investigation also contained MTBE Boring SB-2, located approximately 5 5 feet from the USTs, contained up to 9 92 ppb MTBE, and SB-5, approximately 21 feet from the USTs,contained up to 0 548 ppm MTBE Subsequently, Cambria installed wells MW-1, MW-2, and MW-3 during November 1999 These wells, located approximately 22 to 30 feet from the USTs, contained MTBE at concentrations up to 2 13 ppb Cambria installed SVE wells SVE-1, SVE-2, and SVE-3 during September 2003 The wells are located within the area of impacted soil, bounded by MW-1, MW-2, SB-5, MW-3, and SB-2 Note that SVE-2 is only 7 5 feet from SB-1 and SVE-3 is b feet from SB-4 In addition, all three SVE wells are approximately 5 feet from the USTs However, no MTBE was detected (at reporting limit 0 0050 ppm)at any depth in any of these well borings Cambria maintains that these wells were placed in the previously impacted area, and the most reasonable explanation for these non-detect soil results is that the MTBE degraded and/or migrated through the soil during the four years that elapsed between the investigations and is no longer present at significant concentrations within the source area The SVE wells are located around the edge of presumed source area (the gasoline USTs) They were placed as close to the USTs as practically possible to avoid vacuum short-circuiting in the more permeable UST complex backfill soils (pea gravel) Ideally these wells would be placed in the UST complex However, such well placement is not feasible because the tanks remain in place Residual MTBE Concentrations in the Source Area During SVE testing, the induced vacuum observed at the adjacent SVE well was almost 4% of the vacuum applied at the extraction well Based on this data, Cambria estimated the radius of 5