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r r SEMI-ANNUAL SAMPLING EVENT REPORT OF 9/15104 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 +/-0 5 gallons per minute in all monrtonng wells, except for MW-5S which was purged at 2gpm until it went dry 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 dropped+/-6 2 feet from the last soundings on 3/18104 The hydraulic gradient of the water table is beanng to the east at S-0 009 WATER SAMPLE ANALYSIS FINDINGS Monitoring well samples taken on 9/15/04 were very similar to the previous sample events when analyzed for BTEX and TPHg MW-3S continues to produce samples with BTEX compounds and TPHg as determined by EPA Method 5030/8015(M) TPHg in MW-3S was analyzed at 542 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-5D had the highest recorded values of the compound 1,2-Dichloroethane at 37 ug/L MW-4D continues to produce positive results for Chloroform(1 1 ug/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 monrtonng 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-213,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 There are two compounds that continue to be above drinking water levels, benzene and 1,2- Dichloroethane Comparing current values to the initial values,shows a natural attenuation process is taking place RECOMMENDATIONS The author requests that all monitoring wells continue to be sampled in semiannual events to conserve financial resources CypFESSIoN Please contact this officeany questions arise from this report .G% CO �yy Respectfully submitted � C 57707 • Foothill E�in e�i�i EXP 12 31-05 * , �� Mike V ac PE s�q crv►� ��,�� cc Mrs Helen Higgins, 58 Sfa#16, Stockton CA 95219 2