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-:-+ssl tls i _i--.f -:aim- -:; •}! -..-_..-.. - -�'u• -`---- - - `-- .._-- -------- -t - _� t' :rf�i/f/�rrrrfrrrs=:� ■ :rfrrt.�s�rs�.,;.s:.� (YVATC M A S S O C I A T E S I N C is generally consistent with the gradient observed last quarter. A summary of groundwater monitoring data is presented in Table 1. Groundwater elevations are referenced to feet above mean sea level. Groundwater samples were collected from monitoring wells MW-1 through MW-6. Prior to collection of groundwater samples a minimum of three well casing volumes were purged. The depth-to-water, pH, electrical conductivity, and temperature were measured and allowed to stabilize before groundwater samples were collected. Samples were then collected from each well using disposable bailers. Purge water was contained in 55-gallon DOT approved drums. Purge water from monitoring wells MW-1 and MW-6 from the previous sampling event did not contain detectable concentrations of petroleum hydrocarbons and was discharged to the ground { surface. Groundwater well purge and sample logs are provided in Appendix A. The groundwater samples collected from each well were submitted with Chain of Custody Record to Sequoia Analytical in Redwood City, California, ELAP Certification No. 1210. The samples were analyzed for TPHg and BTEX/MTBE by EPA methods 8015 and 8020, respectively. Groundwater analytical results are summarized in Table 2. The laboratory analytical reports are included in Appendix B. RESULTS OF LABORATORY ANALYSES f Results of the laboratory analysis of groundwater samples from the monitoring wells indicate the presence of petroleum hydrocarbons in groundwater from monitoring wells MW-2 and MW-3. TPHg and BTEX concentrations in wells MW-2 and MW-3 have increased since last quarter. Trace amounts of BTEX constituents were detected in wells MW-4 and MW-5. No petroleum hydrocarbons were detected in monitoring wells MW-1 and MW-6. MTBE was not detected in any of the wells. The analytical results are summarized in Table 2. ADDITIONAL SITE ACTIVITIES On May 27, 1999, ATC personnel supervised the transport and disposal of approximately 750 gallons of purge water stored on site. Prior to the purge water disposal, analytical data was supplied to Clearwater Environmental to profile the purge water for the appropriate disposal method. Clearwater pumped the 750 gallons of purge water into a vacuum truck and transported the purge water to Alviso, California where it was recycled by Alviso Independent Oil. Copies of the non-hazardous waste manifests are included in Attachment 3. w:1178611reportsl4gmr1998.doe 3 1