SITE INFORMATION AND CORRESPONDENCE

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Sent By: Stratus Environmental, Inc; - 530 642 1760; May-2-00 2:19PM; Page 314 Workrilan Addmj= ARCO Facility No.5469 Stockton,California Page 2 in a resealable plastic bag„ and stored in an ice-chilled cooler. The samples will remain chilled until relinquished to a State-certifmd analytical laboratory. Strict chain-of-custody procedures will be followed from the time the samples are collected until the tune the samples are relinquished to the laboratory. Soil contained in the retraining brass tubes will be screened for volatile organic compounds using field insoutnentation equipped with a photoionization detector (PID). Delta will record PID readings, soil types, and other pertinent geologic data on the borehole log. Three soil samples will be submitted for chemical analysis from each boring, the sample exhibiting the highest PID response, the sample from just above first-encountered groundwater,and the sample collected from the bottom of the boring. Development of the monitoring well will consist of surging with a surge block and pumping. Development will continue,to the extent practical, until the development water runs clean and pH and conductivity measurements stabilize. After well development and stabilization of the water levels, water levels and the quantity of well volumes removed from the well will be recorded. The elevation of the top of each well caging will be surveyed by a California licensed surveyor. A rninimum of 48 hours after the groundwater monitoring wells arc installed, the wells will be purged and groundwater samples will be collected. The samples will be collected using a disposable bailer, transferred to laboratory-supplied glass vials, and placed in an ice-chilled cooler. The samples will remain chilled until relinquished to a State-certified analytical laboratory. Strict chain-of-custody procedures will be followed from the time the sample is collected until the time it is relinquished to the laboratory. Additional Laboratory Analysis in addition to the laboratory analyses specified in the February 28,2000 workplan,soil and groundwater samples will be analyzed for Methanol,Ethanol,EDB,and 1,2-DCA using EPA Method 8260. Samples will be submitted on a regular-tum-around basis. Schedule Upon receiving approval of this workplan addendum, the proposed work will be scheduled and a well permit application package will be submitted to PHS/EHD. We anticipate that it will require a minimum of three weeks after receiving the well permit for a drilling contractor to become available. Fieldwork, including well development and sampling, should be completed within three weeks of initiation. The assessment report will be submitted to the regulatory agencies within six weeks of receipt of all analytical.reports,