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Site History • 14000 Highway 88,Lockeford,CA Time Oil Property No 04-049 The highest concentrations of hydrocarbons appear to remain onsite in the vicinity of the pump Islands (MW- 1) and sidegradient of the former tank bed (MW-5) The groundwater plume does not appear to be migrating to any great extent When compared to the October 1998 sampling event, hydrocarbon concentrations remained relatively unchanged In each of the wells Additional monitoring data will be collected to further evaluate the extent of the dissolved hydrocarbon plume A copy of SECOR's "Quarterly Monitoring Report, January — March 1999" dated April 27, 1999, was forwarded to the appropriate regulatory agencies on April 30, 1999 Workplan for Installation of Air Sparging Wells— May 1999 Based on SECOR's "Corrective Action Plan" dated September 8, 1998, vapor extraction and air sparging appear to be the most feasible technologies for remediating hydrocarbon-impacted soils and groundwater associated with the subject site SECOR estimates that a total of ten existing wells (W-1 through W-8, MW-1 and MW-3) can be incorporated into a vapor extraction system, which would influence the entire plume of impacted soil and nearly the entire plume of impacted groundwater Four new wells will be required to conduct air sparging within the plume of impacted groundwater In order to proceed with the Installation of the proposed remediation system, SECOR generated a workplan for the completion of the following scope of work Four soil borings will be advanced in the vicinity of the former tank system Samples will be collected from each boring at 5-foot intervals or at changes in lithologies to assist in further characterizing site soils Three of the borings will be advanced to a depth of approximately 90 feet bgs, whiie the fourth boring will be advanced to a depth of approximately 100 feet bgs to address deeper hydrocarbon impacts in the vicinity of MW-1 Because the site has already been adequately assessed, soil samples collected during the installation of the air sparging wells will not be submitted for analyses • Two-inch diameter air sparging wells will be installed in each of the borings for use in the proposed remediation system Based on previously observed site conditions, SECOR estimates that each well will be installed with two feet of screened casing at the bottom of each boring, followed by blank casing to the ground surface Following installation, the sparge wells will be properly developed • At the conclusion of field activities, a summary of field observations will be included In the quarterly groundwater monitoring report following the well installation A copy of SECOR's "Workplan for Air Sparge Well Installation" dated May 19, 1999, was forwarded to the appropriate regulatory agencies on June 7, 1999, by SECOR In faxed correspondence dated September 29, 1998 Second Quarter 1999 Groundwater Sampling Results—April 1999 On April 26, 1999, samples were collected from each of the groundwater monitoring wells (MW-1 through MW-10) at the subject site by a representative of SECOR Prior to purging, the depth to water in each well was measured to evaluate elevation, flow direction, and gradient Groundwater with a southerly flow direction and a gradient of 0 03 ft/ft was encountered in the wells at depths of 64 96 feet to 77 00 feet below ground surface Free product was not encountered in any of the wells Since the January 1999 sampling event, groundwater elevation increased in MW-3 by 0 02 feet and in MW-9 by 0 06 feet, while it decreased in the remaining wells by 0 01 feet to 1 00 feet These changes resulted In an 23