ARCHIVED REPORTS XR0006623 - Laserfiche WebLink

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S E C 0 R a, . On August 8, 9 and 10, 2001, GR installed four groundwater monitoring wells, three offsite and one deep onsite (MW-8 through MW-11) The three shallow offsite wells were installed to depths a ranging from 28 to 29 feet bgs The deep well, MW-11, was installed to a total depth of 79 feet bgs Soil samples collected from well borings MW-8, MW-9 and MW-10 were reported as ND for all analytes Sod sample MW-11-14, collected at 14 feet bgs, contained 1 7 parts per million ; (ppm) of MtBE Groundwater samples collected from wells MW-8, MW-9 and MW-10, were reported as ND for all analytes The only analyte detected in groundwater from well MW-11 was r MtBE at a concentration of 110 ppb (EPA Method 8260) On December 3 through December 7, 2001, SECOR International Incorporated (SECOR) performed a dual-phase extraction (DPE) event at the site The DPE was performed on wells MW-3 and MW-7, and operated for a total of 110 hours Flow rates during the test varied from 10 90 to 33 41 cubic feet per minute (cfm) and vacuum rates varied from 24 to 25 inches of mercury (in Hg) Over the course of the five day event, SECOR reportedly removed a total of 0 pounds (lbs) of TPHg, 0 01 lbs of benzene, and 6 64 lbs of MtBE The amount of hydrocarbons removed is based on laboratory samples collected during the test SECOR determined that the vacuum radius of influence was between 36 and 60 feet Approximately 20,830 gallons of groundwater were extracted during the DPE event Based on the low mass removal achieved with this test, SECOR concluded that DPE is not an effective remedial alternative for this site In December 2002, GR installed monitoring wells MW-12 and MW-13, and sparge points SP-A through SP-H, SP-J, and SP-K, and installation of two CPT probes (CPT-2 and CPT-3) to a maximum depth of approximately 140 feet bgs The CPT rig was equipped with an onboard G n computer system that provided a real time analysis of the subsurface conditions The CPT device creates a lithologic log of the boring by comparing the CPT tip resistance to sleeve friction on the CPT cone After collection of lithologic data, a groundwater sampling probe was advanced in a separate location (approximately 3 feet from the original probe) to obtain depth discrete groundwater samples The target depths of the discrete samples were determined utilizing lithologic information obtained from the advancement of the CPT At the target depth for groundwater sample collection, the sampling device retracts to expose disposable PVC screen allowing groundwater to enter the device Each groundwater sample was collected using a precleaned teflon bailer and then decanted into laboratory supplied containers Samples were handled as described in Appendix A CPT-2 had groundwater samples collected at depths of 75, 101, and 120 feet bgs, and CPT-3 was sampled at depths of 74, 100, and 125 feet bgs TPHg and BTEX constituents were not detected above laboratory detection limits in the groundwater samples analyzed from select depths in the CPT borings CPT-2 and CPT-3 Of the fuel oxygenates, MtBE and methanol were detected in the groundwater sample CPT-2 75 at concentrations of 2 0 and 2,700 ppb, respectively MtBE was detected in CPT-3 100 at a concentration of 6 8 ppb MtBE r and TBA were detected in CPT-3 125 at concentrations of 290 and 88, respectively In December 2002, an ozone sparge system was installed, connected to sparge wells, and brought online Groundwater has been monitored and sampled on a quarterly basis from 1991 to the present During the year of 1997, groundwater was not monitored or sampled During the second quarter groundwater flow was toward the north at a gradient of 0 002 ft/ft Maximum reported concentration of MtBE and TBA during the second quarter 2004 were 28 ppb (MW-11) and 100,000 ppb (MW-7), respectively Concentrations of MtBE, TPHg, and TBA continue to decline in site monitoring wells Further discussion of quarterly sampling is discussed below SENSTIVE RECEPTORS Also in April of 2001, GR conducted a well search and Sensitive Receptor Survey (SRS) in the '�