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Mr. Kyle Christie January 11, 1995 11 Page 2 t�l Quarterly Monitoring Results and Discussion The groundwater flow across the site is generally to the south with a hydraulic gradient of approximately 0.002. Water-level data are listed in Table 1. Table 2 shows historical hydraulic gradients and groundwater flow directions. Figure I illustrates groundwater contours and the groundwater flow direction. Well W-213 was not used for contouring, as this well is completed in a deeper zone than the other wells. Wells W-2A and W-4 were not used in contouring because these wells were dry. Well W-10 was not used in contouring because it was inaccessible. The approximate southern flow direction and gradient of 0.002 are within the ranges previously reported. On September 28, 1994, the depth-to-water ranged from 65.60 feet in well W-8 to 67.15 feet in well W-IA. Water-levels in the monitoring wells decreased an average of 3.39 feet between June 23, 1994 and September 28, 1994. Well W-2A has been dry since August 1993, with the exception of last quarter when the water-level elevation was -20.30 feet. The reason for last quarter's change in water-level is unclear. Current and historical analytical results are summarized in Table 3. The complete laboratory report and chain-of-custody documentation, for the quarterly sampling are presented in Exhibit A. Benzene was detected in well W-3, and toluene was detected in well W-5. No other BTEX or TPH-G constituents were detected in any of the sampled wells. The detection limits for benzene and TPH-G are 0.5 and 50 micrograms per liter (pg/1), respectively. The reason for the presence of benzene in the sample from well MW-3 is unknown at this time. BTEX and TPH-G had not been detected in that well during all four quarters of 1993. BTEX and TPH-G constituents started showing up in this well during the first quarter of 1994, at levels relatively close to the detection limits. GTI was contracted by ARCO to conduct the 1994 sampling at this and other sites, and the first quarter of 1994 was the first time that GTI sampled this facility. The presence of toluene in the sample from well MW-5 is suspicious in that well MW-5 has not contained any BTEX or TPH-G constituents since February 1992. However, toluene is a common ingredient in permanent marking pens and is also used - extensively in laboratories Toluene may be present in the MW-5 sample because a permanent- _ marking pen may have been used to label the sample bottle, or because of laboratory contamination. However, the exact cause is unknown at this time. The presence (or absence) of contaminants in wells MW-3 and MW-5 will be verified in future quarterly sampling events. Status-of"Site Remediation This section provides a description of the remediation system and discusses the effectiveness of the remediation system operation. Use or disclosure of data contained on this sheet is subject to the restriction specified at the beginning of this doctunent. 1318\REP0RTs\3RD94QTR.R Pr