ARCHIVED REPORTS_XR0004884 - Laserfiche WebLink

Home Browse Search

Monitoring Well Installation Report ID Quik Stop Market No 121 Page 9 site, near monitoring wells MW-3 and RW-1, and on the northwest side at MW-1 Perimeter wells MW-2, MW-5 and MW-7 are currently free of detectable TPHg and BTEX compounds Groundwater in the vicinity of monitoring well MW-3 and RW-I were reported to have the highest contaminant concentrations of TPHg and MTBE at the subject site It appears some TPHg and MTBE has migrated to a lower portion of the aquifer, at a depth of 33 to 43 feet, as detected in the water sample collected at MW-4 (Figures 5 and 6) Low concentrations (less than 10 ug/1) of MTBE were detected at the two perimeter wells, MW-5 and MW-7, located on the south and southeast sides of the site However, no petroleum hydrocarbon contamination was detected from the deepest site well (screened from 65 to 75 feet) as reported at MW-6 It appears vertical continuity of the aquifer is limited A review of the site hydrogeology data indicates monitoring well MW-6 is screened within a separate aquifer This is based on the fact that the hydrostatic water level was measured approximately 5 to 6 feet higher than the other seven site wells, which are screened at shallower depths The boring log from CPT-1 (located in the vicinity of monitoring wells MW-3, MW-4 and MW-6, Figure 2) shows two clay, clayey silt and sandy silt horizons between 43 and 47 feet and 54 and 66 feet Some localized "hard pan" material was noted in these soil horizons and appear to act as confining layers between the two aquifers Further the "hard pan" material appears to be an impediment to vertical contaminant migration as confirmed by the reported clean soil samples collected from depths of 50 and 60 feet, and water sample MW-6 being free of detectable petroleum hydrocarbons A majority of the soil contamination detected was in the vicinity of the fuel tank area, near recovery well RW-1 (Figures 7 and 8) Laboratory data show low concentrations of detectable TPHg and higher concentrations of detectable MTBE in the soil column from depths of 5 feet through 27 5 feet Further, soil contamination was also detected at depths of 10 and 15 feet in monitoring wells MW-4 and MW-5 It appears the soil concentrations, which were detected within the capillary fringe, suggest the shallow aquifer may be influencing the TPHg and/or MTBE concentrations at these locations Based on the information obtained and data reviewed, CCI recommends the following 1 A Dual-Phase Extraction Test be performed on recovery well RW-1, with a truck mounted, high-vacuum, liquid-ring pump with a thermal oxidizer system will be used to conduct the test The purpose of the test will be to determine whether vapor extraction is a viable option for cleaning the soil and groundwater in the vicinity of RW-1 The Dual-Phase Extraction Test will be operated for a minimum of S hours or until it can be determined whether this remediation technique can effectively remediate the groundwater at the site Based on the results of this test, Quik Stop will select the appropriate treatment system for the site, 2 CCI is currently attempting to obtain off-site permission to install two additional wells