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City of Stockton Redevelopment Agency B34604.OIa ' February 16, 2001 Page A -3 Prior to sampling a monitoring well, a minimum of 3 well casing volumes will be purged using a clean, stainless steel submersible pump or a disposable bailer equipped with a length of new rope. Disposable bailers and rope lengths will be used once, and discarded. After 3 casing volumes of water have been removed from the well,purging will continue until measured field parameters(pH, specific electrical conductivity, and temperature)have stabilized. Purging data will be recorded on the Well Sampling log. ' After purging,groundwater parameters will be measured. The temperature,electrical conductivity, and pH will be measured using a Hyda ® model 910 meter or equivalent. If required, oxygen content will be measured in the well usina Oxyguard®MKl portable dissolved oxygen meter and ' probe or equivalent. If required, red n/oxidation potential will be measured using a Orion® portable redox meter, model 290A or a uivalent. All meters will be calibrated consistent with ' manufacturer's recommendations prior to use. Some monitoring wells are expected to be evacuated to dryness after removing fewer than three casing volumes. These low-yield monitoring wells will be allowed to recharge for as long as 24 hours. Samples will be collected as soon as the monitoring wells have recharged sufficiently to allow sample collection. If insufficient water has recharged after 24 hours,the monitoring well will ' be recorded as "dry" for the sampling event Purged water will be containerized in Department of Transportation-approved drums,and stored on ' site in an area inaccessible to the general public. The purged water is typically characterized either by sampling,or on the basis of the groundwater sample analytical results. Twining can recommend an appropriate method for disposition oft(ie purged water. Disposal will be the responsibility of the client. Water samples will be transferred into sample containers supplied by the analytical laboratory. Sample containers will be labelled and pl ced in an ice-cooled chest,equipped with a thermometer, for transport to the laboratory. The tempe ture inside the ice-cooled chest will be recorded on chain of custody documents when samples art: placed in the chest, and when they are received by the laboratory. Samples will be maintained t a temperature of approximately 4 degrees Centigrade. Standard Operating Procedures for EaUlDment Decontamination: Proper decontamination ' procedures reduce the potential for: cross contamination among sample locations;and introduction of contamination from outside sources. ' Before,during,and following drilling op rations,drilling equipment is thoroughly cleaned using a high pressure hot water(steam)washer. team cleaning condensate will be containerized for later disposal. Generally, disposal will be the client's responsibility. ' Sampling equipment and any tools,measuring devices, or other equipment which will contact soil or any media being assessed will be washed in a low-phosphate soap and water solution, and rinsed in clean water before each use. The type of soap used will depend upon project requirements.