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CLEARWA" TER t. R tt � �' ! ♦ C Eroerroa mental s.r ,ccs 1.0 INTRODUCTION This report, submitted by Clearwater Group, Inc (Clearwater) on behalf of Ruiz Grocery pertains to activities conducted at the Rutz Grocery located at 4491 West Durham Ferry Road in Tracy, California(Figure 1) The report summarizes the results of quarterly groundwater monitoring for the fourth quarter 1999 and also presents a workplan for proposed confirmation borings to evaluate the effectiveness of the soil vapor extraction (SVE) 1 air sparge (AS) system operated from October 1998 to September 1999 1 1 Site Background Two gasoline USTs and dispensers were removed from the site in 1988 Seven monitoring wells (NBV-1 through MW- 7), one groundwater recoFery well (RW-1), four soil vapor extraction wells (VW-i through VW-4) and two air sparge wells (SW-1 and SW-2) haze been installed at the site A domestic well (DW), screened in a deeper water bearing zone also exists at the site (Table 1) The extent of soil and water contamination has been delineated Based on historical investigation data it was calculated that approximately 5 050 lbs (842 gals) of gasoline �.ontaminants remained in the vadose zone Additionallv pilot testing for groundwater extraction soil vapor extraction and air sparQing were competed Based on cumulative site data, Clearwater recommended construction of a remediation system consisting of combined groundwater and soil vapor extraction with air sparQing The results of this work were presented in Clearwater's Problem Assessment Report, Feasibdirn Stiid,, and Remedial,action Plan dated February 21 1996 The SJCPHS/EHD did not fully concur with the recommended plan for remediation Following further discussion Clearwater submitted a Revised Remedial Action Plan dated November 12, 1996, which recommended remediation by only soil vapor extraction and air sparging The SJCPHSIEHD approved this pian in a letter dated November 6, 1996 In late summer 1998, a SVE/AS remediation system was installed at the site Wells RW-1, MW-1 MW-2 and VW-1 through VW-4 were used to extract soil vapors, which were treated by an electne catalytic oxidizer An air blower was used to deliver air to the subsurface via wells SW-1 and SW-2 The system was operational from October 1998 to the end of September 1999, which resulted in 6,638 hours of total system operation Contaminant recovery from the subsurface was dramatic at first,averaging approximately 21bs/hr during the first five months of operation However, by the July 1999, contaminant recovery rates had decreased dramatically to approximately 0 02 lbs/hr For the last three months of operation, influent TPHg levels only slightly exceeded laboratory detection limits Calculations indicate the SVE/AS system recovered a total of 7,377 lbs(or 1,209 gals)of gasoline from the subsurface by the end of September 1999 The amount of contamination recovered from the subsurface compared well to that calculated to be in the subsurface prior to remediation,indicating that the system had removed the vast majority of contaminants beneath the site Remediation efforts were also reflected by a marked decrease, over two orders of magnitude in groundwater contaminants in the source area Pnor to remediation, maximum concentrations of TPHg and benzene in groundwater had been 150,000 pg/L and 3,400µg/I.,respectively Following shut-down of the remediation system, maximum TPHg and benzene concentrations in groundwater were only 990 pg1L and 1 3 Wg/L, respectively, in November 1999 Clearwater recommended shut-down of the SVE/AS system at the end of September 1999 because operational data 40 indicated that it had reached a plateau contaminant recovery The SJCPHS/EED approved system shut-down in a letter dated September 20, 1999 In that letter,the SJCPHS/EHD indicated that groundwater beneath the site should continue D-107 4Q99 GW&WP Confirmation Borings 1 November 15 1999