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San Joaquin County Environmental Health Division Recommended Groundwater Sampling Guidelines San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) is providing these guidelines to increase the confidence and reliability of the groundwater sample results. Variance from these guidelines may result in a lower confidence level and results may not be recognized as representative of actual site conditions. Recommended Procedures 1. All wells should be measured for depth to water (DTW) and total depth (TD) prior to purging the wells. A water/oil interface probe should be used when free product is suspected. Field notes should include the condition of the well in and around the traffic box, stove pipe, well seal protection, obvious odors, general site conditions and weather conditions. All requested data should be collected in field notes and included in subsequent reports. 2. Wells should be purged using either a pump that minimally disturbs groundwater or by hand bailing using a bailer. At least three to five casing volumes should be purged, using DTW and TD measurements to calculate casing volume, or until water from the well has been shown to be stabilized, using pH, temperature and electrical conductivity data gathered at frequent intervals before and during the purging process. 3. Purging instruments should be decontaminated between wells by thorough cleaning and rinsing between sampling to prevent cross contamination or the introduction of cleaning agents. 4. After the appropriate volume of water is removed and before a sample is collected, another DTW measurement should be taken and recorded. If the well has not recovered to 80% of the original depth, within a reasonable amount of time (<1 hour) a sample may be collected. The recharge condition should be noted in the field notes. S. Wells should be sampled in the order of the cleanest well to the most contaminated well, if prior information is available. 6. Volatile, semi-volatile or non-volatile samples should be collected in the appropriate pre-chilled containers for the analysis requested. If no preservative is used, then the samples must be analyzed within 7 calendar days of the date of sampling. If preservative is used samples must be completely analyzed within 14 days of the date of sampling. 7. Samples should be collected using a bailer or a pump 1. During sample collection, the volatile sample container should be filled with no observable air bubbles. No headspace should be present in the sample container once the container has been capped. To avoid dilution of the preservative, sample containers should not be overfilled. Samples should be collected to minimize contact with the atmosphere to prevent the loss of volatile constituents from the sample. When appropriate travel blanks should be collected. 8. The samples should be stored in an insulated ice chest cooled with ice to ensure that the samples achieve 4° C. 9. Chain of Custody forms must be complete. Mail couriers must also be noted on the chain of custody and supported with documentation. Chain of Custody forms must be legible. Notation should be made on the chain of custody by the receiving lab indicating the condition and temperature of the samples. 1-pumps used for purging or sampling collection should have good flow controllability to permit low flow rates, <100 milliliter per minute, for sampling volatile chemical constituents. Pumps should be simple to operate, durable, portable, cleanable and should minimize the physical and chemical disturbance of the groundwater to avoid conditions which would interfere with the collection of a representative sample. For more information, please contact the site mitigation unit at (209) 468-3450. 2/15/95