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Former Beacon Station 112474 June 16,2003 Stockton California Revision to Work Plan Addendum intervals identified deeper than 130 feet bsg (the total depth of the CPT-1 boring) and at total depth of the boring. All groundwater samples shall be analyzed as described in the Work Plan Addendum. The data obtained from the site CPT characterization (including data from the previous CPT-1 boring and CPT groundwater sampling) shall be evaluated for the purpose of locating and designing the additional monitoring wells MW-15 and MW-16. The location and construction of the monitoring wells proposed on the basis of the results of the CPT investigation described above shall be specified in an addendum to this revised Work Plan Addendum. If groundwater analytical results from the CPT borings indicate hydrocarbon impacts, the data shall be used to propose depth-discrete monitoring wells to verify the analytical results. If groundwater analytical results from the CPT borings indicate no hydrocarbon impacts, the data shall be considered to represent delineation and additional monitoring Fvells 117111 not be necessary in those' areas. The total depth and screened interval of monitoring well MW-13 shall be approximately 150 feet bsg but ultimately evaluated in the field on the basis of stratigraphic data collected during drilling of the well and that collected from the CPT-2 and CPT-3 stratigraphic logs. Continuous core shall be collected below 130 feet bsg from the monitoring well MW-13 boring to supplement stratigraphic data in that area. At the request of EHD, a CPT boring (13-11) shall be advanced at the location shown on Figure 2 for the purpose of collecting a soil sample at approximately 80 feet bsg. The soil sample is to evaluate the EHD concern that a secondary source of hydrocarbons in soil may �a.. be present in that area and is causing the hydrocarbon concentrations in groundwater from monitoring well MW-1 (screened 75 to 90 feet bsg) to be higher than those in monitoring well MW-9 (screened 56 to 76 feet bsg). Please call Horizon at 916-939-2170 if you have any questions. Sincerely, Eq GFopo HORIZ ENVIRONMENT c �`- 4 REXFORD x SMITH u' No. 53 7 Rexford Smith `;A Re istered Geologist No. 530O CA��4 Gary D. Barker Senior Project Manager Attachment: Figure 2 cc: Mr. Joe Aldridge, Ultramar Inc. AddmRev6-03 Project No. 1474.13 2 HORIZON ENVIRONMENTAL INC.