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Mr Kyle Christie July 21, 1995 Page 2 . Prior to sampling, the wells were purged of a minimum of three well casing volumes or until evacuated using a pump or bailer After purging, each well was sampled using a disposable bailer. All groundwater samples were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX) and total petroleum hydrocarbons as gasoline (TPH-G) by U S Environmental Protection Agency (EPA) Method 503018020, and 8015 Modified Field data sheets and cham-of-custody documentation are included in Exhibit A Results and Discussion The general groundwater flow direction beneath the site on April 25 and 26, 1995, was to the northeast under a hydraulic gradient of approximately 0 003 (Figure 1) Since groundwater monitoring began in April 1987, the general groundwater flow direction has ranged from north to east at this site The hydraulic gradient measured this quarter is within the range of previously reported gradients The groundwater data collected from well ATR-8 was not used for contouring this quarter because the data appears to be anomalous with past data The Field Data Sheet prepared for this well by Emcon indicates that the well casing was covered with water at the time of sampling. Depth-to-water on April 25 and 26, 1995 ranged from 8 51 feet below the top of the well casing (TOC) in well ATR-8 to 12 90 feet below TOC in well ATR-1. Since the last quarterly monitoring event (February 28, 1995), water-level elevations in all the measured monitoring wells except ATR-8 have decreased an average of 0.30 feet. The water-level elevation in well ATR-8 increased 0 28 feet. Summaries of depth- to-water measurements and calculated groundwater elevations are presented in Table 1 Table 2 lists past and present groundwater flow directions and hydraulic gradients for this site. Benzene concentrations this quarter were nondetectable in all sampled wells except ATR-4 and SMW-1 Benzene was 19 micrograms per liter (pg/1) in well ATR-4, and 470 pg/l in well SMW-1. The detection limit for benzene is 0 5 µg/1. These concentrations are within the range of previously reported values. TPH-G concentrations were nondetectable in all the sampled wells except ATR-4, ATR-5,and SMW-1. TPH-G was 1100 µg11 in well ATR-4, 83 pg/1 in well ATR-5, and 5100 pg/l in well SMW-1 The detection limit for TPH-G is 50 µg/1 These concentrations are consistent with previous values Analytical results of groundwater samples are summarized m Table 3 The complete laboratory report for the sampling event is presented in Exhibit A Figure 2 shows TPH-G and BTEX concentrations for this sampling event A soil vapor extraction and treatment/air sparging (SUET/AS) system has been designed for this site An Authority-to-Construct permit (Permit No. N-3413-1-0, issued March 10, 1995 and expiring March 10, 1997) has been obtained from the San Joaquin Valley Unified Air Pollution Control District for this site. The system design has been submitted to the City of Tracy Planning Department, and approved with modifications. Constriction of the remedial system is planned for the third quarter 1995. Use or disclosure of data contained on this sheet is subject to the restriction specified at the beginning of this document 2043NRFP RTS\2ND95Q7R RPT