Laserfiche WebLink
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 will 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 /> 2. When possible, samples are collected from known or suspected <br /> wells that are least contaminated (i.e. 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 /> 4W <br /> 1. All sample bottles and equipment are kept away from fuels and <br /> solvents. When possible, gasoline (used in generators) is <br /> stored away from bailers, sample bottles, purging pumps, etc. <br /> 2. 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 /> 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 /> 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 1. <br /> Page 10 <br /> 7t�effler — ryan InC. (415)783-7500 <br /> -. 9eneral and environmental c"Iraclors <br />