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Stantec April 24,2009 Ms. Kristi Shelton Stantec will monitor wind velocity and direction using a portable wind-speed meter and a wind sock or similar device. The real-time particulate monitoring data will be used to determine if immediate response actions are needed to control fugitive dust emissions during remediation activities, such as changes to dust control (use of water or soil stabilizers)or excavation methods. The data can also be used to modify the PPE worn by site workers, should control methods be ineffective. The California Division of Occupational Safety and Health (OSHA) has set a limit of 10 milligrams per cubic meter(mg/m3)for nuisance particulate dust in areas where workers may be exposed (Cal-OSHA, 2001). In order to be conservative and due to the possibility of chemicals of concern in air, the particulate concentration of 1 mg/m3 will be considered the first action level, at which point engineering controls(dust suppression using water or soil stabilizers or delayed work)will be implemented to reduce particulate concentrations. A second action level at a particulate concentration of 2.5 mg/m3 will require the donning of respirators in addition to increased engineering controls. At the particulate concentration of 10 mg/m3, work will stop until particulate concentration is decreased. Measurements of wind speed and direction will be made periodically throughout the day and recorded on field data sheets. Real-time particulate monitoring will be performed by a qualified professional familiar with the equipment and its use. Data will be automatically logged by the device and real-time measurements will be used to guide site operations. Dust generation will be controlled by spraying water on soils prior to and during excavation. The need for water application will be monitored visually and using the action level of 1 mg/m3. Stantec anticipates receiving water used for dust suppression from a nearby fire hydrant under a use permit from the City of Stockton. Installation of Shoring The northwest wall of the excavation will be shored with sheet piling to protect the fence marking the property line directly adjacent to the excavation. The sheet piling will be advanced to approximately 23 feet bgs, and extend approximately five feet beyond the proposed lateral extent of excavation as a method of keying in to undisturbed soils. The remaining three sidewalls will be sloped as necessary at approximately 2:1 grade to prevent sloughing of material into the excavation. The excavation work will be overseen by a competent professional, and sloping of sidewalls will be directed as appropriate. Excavation of Soils Prior to the start of the excavation, all health and safety, dust control, and related equipment and materials will be prepared and positioned for immediate use as necessary. Meteorological and dust monitoring will be conducted during work activities and controls will be used as appropriate, to minimize any impacts to existing facilities, on-site workers, and the public. The proposed scope of work consists of removal of approximately 146 tons of soil, from an area approximately 15 feet by 15 feet centered on well MWA excavated to 11 feet bgs. Stantec has included a contingency of approximately 25 tons to provide for removal of additional material based on results of the pre- excavation soil investigation, or on results of post-excavation soil sampling.