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SFPUC June 10, 2020 Page 12 At least two persons, wearing clean, powder-free nitrile gloves at all times, are needed on a sampling crew. Samplers should follow these procedures to ensure high-quality samples: • Collect samples only into pre-cleaned sample bottles. • One person ("dirty hands") touch and open only the outer bag of all double-bagged sample bottles, avoiding touching the inside of the bag. • The other person ("clean hands") reach into the outer bag, open the inner bag, and remove the clean sample bottle. • Position the sampler downstream of the sample point, approaching and collecting from downstream facing upstream. • "Clean hands" collect the sample directly, without any intermediate container, if possible. If necessary, strap the sample bottle onto a clean sampling pole and slowly submerse it in the water. • Triple-rinse bottles with the sample water(unless they contain preservative). • After a grab sample is collected, or when a clean item must be re-bagged, thus in the opposite order from which it was removed. • Change gloves whenever something not known to be clean has been touched. • Adhere to the following rules while collecting samples: o No smoking. o Never sample near a running vehicle or other motor. o Do not eat or drink during sample collection. o Do not breath, sneeze or cough in the direction of an open sample bottle. All bottles should be acid-cleaned, double-bagged and stored in coolers with wet ice for delivery to the laboratory. Mercury samples may be collected into pre-acidified sample bottles(each with 5 mL of HCl) for preservation. Laboratory analysis of total mercury in water should follow USEPA Method 245.1 with a reporting limit of 0.2 pg/L and detection limit of 0.05 ug/L. While less sensitive than Method 1631 E, these limits are still well below the thresholds of interest(2-200 ug/L) and the maximum potential concentration (55 ug/L). Data quality objectives are±25% for spike recoveries and lab control recovery standards. One mercury field blank or one field duplicate should be collected per event. Duplicate and blank results should be used in data interpretation, with no threshold for acceptability. Pond Sediment Samples Three surficial sediment samples should be collected annually from Grit Pond#I (assuming at least one UV lamp break occurs and its water is discharged to the pond since the previous sediment sample was collected), monitoring the top 2 centimeters of sediments. This uppermost layer is most biologically relevant and where mercury in seeping water would form complexes with soil organic matter(USEPA, 1997). Sediments should be collected using a clean, 2-cm-high, stainless steel scoop. Multiple samples should be composited from representative areas (that is, aggregating samples from multiple points in a 2-foot radius around the sampling site) into a plastic bag and homogenized. Each sediment sample should be transferred into 8-ounce clear, glass, wide-mouth bottles with a