ARCHIVED REPORTS_XR0004861 - Laserfiche WebLink

Home Browse Search

al +7 Quik Stop Market No 121 CCI Project No 12118-2 Page 3 One of the three deep (B-aquifer) wells (MW-6, MW-9 and MW-10), screened from 65 to 75 feet within the B-aquifer, was reported to have detectable MTBE Monitoring well MW-6 was reported to have 13 ug/L MTBE No other detectable compounds were reported in the three B- aquifer wells The results of the groundwater analysis are summarized in Table 2 The analytical reports from ChromaLab and chain-of-custody documents are attached in Appendix B Discussion Based on the groundwater data obtained during the quarterly sample round, it appears the groundwater continues to be impacted with petroleum hydrocarbons, mainly in the vicinity of Quik Stop Market's fuel tanks, located on the southeast side of the site, near monitoring wells MW-3, MW-4 and RW-1 (Figures 3 and 4) Groundwater samples collected from perimeter wells MW-1, MW-7, MW-11 and MW-12 were reported to be free of detectable TPHgBTEX and MTBE compounds Monitoring well MW-8 was reported to have 1 ug/L MTBE Groundwater in the vicinity of monitoring wells MW-3, MW-4 and RW-1 were reported to have the highest concentrations of MTBE at the subject site It appears MTBE has migrated to a • lower portion of the A-aquifer, to a depth of 33 to 43 feet, as detected in the water sample collected at MW-4 and continues to be detected in low concentrations in B-aquifer well MW-6, although at decreasing concentrations The other two B-aquifer wells, MW-9 and MW-10, were reported to be free of detectable petroleum compounds Groundwater measurements taken in ten of the shallow A-aquifer wells on January 9, 2002 indicated the depth-to-groundwater ranged from approximately 16 54 to 18 02 feet below the top of the well casings The water level in monitoring well MW-4 (screened in the A-aquifer from 33 to 43 feet) was measured at 16 92 feet below the top of the well casing The water table in the shallow A-aquifer has risen approximately 5 feet since the October 2001 sample round Groundwater contours in the A-aquifer monitoring wells indicate the groundwater flow direction is to the north-northeast at gradient ranging from 0 005 to 0 010 feet per foot (Figure 5) A groundwater gradient map for the B-aquifer was created and indicates a gradient of 0 001 feet per foot to the northwest (Figure 6) Quik Stop Markets, Inc has conduct a series of 8-hour dual-phase treatment events at the site since February 2001 The MTS events have been conducted monthly, using a mobile treatment system (MTS) operated by TRC of Concord, California During this quarter, two additional MTS events (for a total of 9 ) were conducted at the site in November and December, 2001 A review of the vapor concentration data from the last 9 MTS events indicates the vapor concentrations decreasing significantly to the extraction wells by the end of each 8-hour event . This trend appears to be confirmed by the groundwater samples, since the MTBE concentrations have decreased in the 3 wells with the highest concentrations (RW-1, MW-3