ARCHIVED REPORTS_XR0012855 - Laserfiche WebLink

Home Browse Search

• s , Ozone Microsparge Well and System Installation Report—Former Tosco(Unocal)Service Station No 6981 February 1,2002 _ In August 1999„GR installed three groundwater monitoring wells (MW-14 through MW-16), one groundwater sparging well (VW-7) and advanced one soil boring (VW-9) These groundwater monitoring wells replaced the wells that were abandoned in February 1996 In April 2000, the service station building and all related facilities were removed from the site,' including two 12,000-gallon double-wall steel gasoline USTs Soil samples were collected from y beneath the USTs, product lines, acid dispenser islands Any potentially impacted soil was overexcavated 'A total of approximately 200 cubic yards of potentially impacted soil was excavated from beneath the northwest and southeast dispenser islands and product lines immediately north of the west UST In addition, the UST pit was excavated to a depth of 21 feet bgs All of the soil t samples were reported as not detected except for 2 73 parts per million (ppm) of TPHg beneath the a northeast dispenser island at 4 75 feet bgs and 38 3"ppm°of TPHg and 0 125 ppm of xylenes beneath , the product lines northeast of the northwest dispenser island at a depth of 4 feet bgs t Groundwater has been monitored on a quarterly basis since 1990 and sampled at the site on a quarterly or semi-annual basis since April 1993 Floating product or sheen has never been observed in any of the wells Historically, petroleum hydrocarbon concentrations in the groundwater have' ranged from not detected to 78,000 parts per billion (ppb) of TPHg (well VW-2), not detected to, 28,000 ppb of benzene (well MW-5), and not detected to 4,900 ppb of MtBE (well VW-3) Groundwater data for the third quarter 2001 sampling event on September 12 and 13, 2001 ranged from not detected to 34,000 parts per billion (ppb) of TPHg (well VW-7), not detected to 870 ppb of benzene (well VW-7), and not detected to 310 ppb of MtBE (well VW-4) Historically, depth to groundwater has risen from approximately 51 to 53 feet bgs in 1993 to 30 to 32 feet bgs in t y September 2001 Groundwater flow has been to the northeast with the hydraulic gradient ranging from 0 002 to 0 013 feet/feet 1 FIELD ACTIVITIES ; Field work was performed in accordance with the GR Site Safety Plan No 140124 12, dated ' November 1, 2001 GR Field Methods and Procedures are included in Appendix A Underground Service Alert (USA) was notified prior to beginning drilling activities Drilling and well installation was performed under SJCPHS-EHD permit No 279SS A copy of the drilling permit is included in Appendix B Thirteen on-site soil borings were drilled on November 19 and 20, 2001 and completed as ozone microsparge wells SP-1 through SP-13 Ozone microsparge wells SP- 1 through SP-10 were installed to approximately 65 feet bgs and,ozone microsparge wells SP-11 through SP-13 were installed to approximately 40 feet bgs The well borings were drilled using two truck-mounted drill rigs equipped with eight-inch diameter hollow stem augers by Cascade Drilling, Inc (#C57 717510) A GR geologist observed the drilling and well installation activities and described the construction of each well (Appendix B) The well borings were not lithologically logged or sampled due to their proximity to a previously logged and sampled borings Well locations are shown on Figure 2 , r •. 14012412 ' 3