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* SEMI-ANNUAL SAMPLING EVENT REPORT OF 3118/04 SAMPLING PROCEDURE Monitoring wells were vented and purged by normal methods per standards of the industry (see Groundwater Field Report by Del-Tech Geotechnical Services attached) Purge pump rates were +l-0 5 gallons per minute in all monitoring wells Groundwater samples were extracted from each monitoring well using the check valve in tube technique Samples were transported on ice under chain of custody for delivery to Sherwood Labs for analysis WATER TABLE ELEVATIONS AND GRADIENT Soundings on the monitoring wells showed the groundwater elevation has raised+/-4 feet from the last soundings on 9/23/2003 The hydraulic gradient of the water table is bearing to the east at S=O 006 WATER SAMPLE ANALYSIS FINDINGS Monitoring well samples taken on 3/18/04 were very similar to the previous sample events when analyzed for BTEX and TPHg with the exception of MW-1 MW-1 was analyzed with non-detect TPHg compared to 81 8 ug/L for the previous event MW-3S continues to produce samples with BTEX compounds and TPHg as determined by EPA Method 5030/8015(M) TPHg in this well was analyzed at 883 ug/L The purgeable halocarbon 1,2-Dichloroethane,continues to be present in all of the wells with the exception of MW-4S (ND)and MW-4D(ND) Monitoring well MW-513 had the highest recorded values of the compound 1,2-Dzchloroethane at 28 ug/L MW-4D continues to produce positive results for Chloroform(1 3ug/L) and no other analyte (see . recap of data attached) CONCLUSIONS BTEX compounds in the monitoring well MW-3S remain in the same range as the past events This monitoring well is receiving the highest impact of all the wells due to TANK#1, the Stoddard Solvent tank, which is usually up gradient and Southwest of MW#3S Low concentrations of 1,2- Dichloroethane remain in monitoring wells MW-1,MW-2S,MW-2D,MW-3S,MW-3D and MW- 5S and MW-5D The continued low concentrations of chloroform in MW-4S & MW-4D defy the logic of the rest of the contamination plume RECOMMENDATIONS The author requests that all monitoring wells continue to be sampled to semiannual events to conserve financial resources �ESS/p Please contact this office at 209/ �i A �� ions arise from this report TL Respectfully submitted, va`, 2 p57707 + C,� � ca U NO r Foothill Engineering Mike Vlach"RCS �'�TF ,�O¢ cc Mrs Helen Higgins, 5815 Marg ace e#1 , Stockton CA 95219 2