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i <br /> April 20, 1990 <br /> Because ground-water samples collected by G-R are analyzed to the <br /> parts per billion (ppb) range for many compounds, extreme care is <br /> exercised to prevent contamination of samples When volatile or <br /> semi-volatile organic compounds are included for analysis, G-R <br /> sampling crew members %k ill adhere to the following precautions in the <br /> field <br /> 1 A clean pair of new, disposable gloves are worn for each well <br /> being sampled <br /> When possible, samples are collected from known or suspected <br /> wells that are least contaminated (i a background) followed <br /> by wells in increasing order of contamination <br /> 3 Ambient conditions are continually monitored to maintain <br /> sample integrity <br /> When known or potential organic compounds are being sampled for, the <br /> following additional precautions are taken <br /> I All sample bottles and equipment are kept away from fuels and <br /> solvents When possible, gasoline (used in generators) is <br /> stored awav from bailers, sample bottles, purging pumps, etc <br /> 1 <br /> Bailers are made of Teflon or Stainless Steel Other <br /> materials such as plastic may contaminate samples with <br /> phthalate esters which interfere with many Gas Chromatography <br /> (GC) analyses <br /> i 3 Volatile organic ground-water samples are collected so that <br /> air passage through the sample does not occur or is minimal <br /> (to prevent volatiles from being stripped from the samples) <br /> sample bottles are filled by slowly running the sample down <br /> the side of the bottle until there is a positive convex <br /> meniscus over the neck of the bottle, the Teflon side of the <br /> 1 septum (in cap) is positioned against the meniscus, and the <br /> cap screwed on tightly, the sample is inverted and the bottle <br /> lightly tapped The absence of an air bubble indicates a <br /> successful seal, if a bubble is evident, the cap is removed, <br /> more sample is added, and the bottle is resealed <br /> 4 Extra Teflon seals are brought into the field in case seals <br /> are difficult to handle and/or are dropped Dropped seals are <br /> considered contaminated and are not used When replacing <br /> seals or if seals become flipped, care is taken to assure that <br /> the Teflon seal faces down <br /> Sample analysis methods, containers, preservatives and holding times <br /> are shown on Table I <br /> Vfjoffler -- ryan inc (415) 7837500 Page 10 <br /> general and envuanmenlal conlraelors <br />