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ADVISORY - ACTIVE SOIL GAS INVESTIGATIONS <br />Hand held multi-gas monitors equipped with a hydrogen sulfide sensor may also be <br />used. The RL should be equal to or less than 0.5 ppmv, be at least one microgram per <br />liter or sensitive enough to allow for a modeled ambient air concentration at the soil <br />surface. <br />7.2.1 Sample Containers <br />The following sample containers are recommended for hydrogen sulfide: <br />Black polymer gas sampling bags fitted with polypropylene valves or equivalent. <br />Clear polymer gas sampling bags can be used, stored and/or transported <br />provided they are protected from light; <br />100 mL gas-tight glass syringe or gas-tight glass bulb fitted with an inert valve <br />and wrapped in aluminum foil; and <br />Passivated stainless steel canister. Note that recovery of hydrogen sulfide in <br />passivated stainless steel canisters will deteriorate naturally with time with <br />repeated hydrogen sulfide sampling. <br />7.2.2 Hydrogen Sulfide Field Collection <br />Hydrogen sulfide samples should be analyzed by a hand-held instrument within 30 <br />minutes of collection to minimize sample degradation from reaction with the container <br />surfaces. If a hand-held instrument is not used, hydrogen sulfide samples should be <br />analyzed as follows: <br />Within 30 minutes of collection using GC procedures; <br />Within 24 hours of collection if duplicate samples are collected and analyzed; or <br />Within 6 hours of collection in polymer gas sampling bag using ASTM D5504 <br />with no surrogate addition needed. <br />7.2.3 Precautions Particular to Hydrogen Sulfide <br />Contact with oxygen and moisture should be avoided because hydrogen sulfide <br />is extremely unstable; <br />Due to the high reactivity of hydrogen sulfide gas, avoid contact of hydrogen <br />sulfide samples with metallic or other active surfaces during sample collection, <br />storage, and analysis; <br />Ensure GC components do not react with the sample. Typically, glass-lined <br />injection ports, thick-film capillary columns and silcosteel® lined tubing are used <br />to avoid loss of hydrogen sulfide during analysis; <br />Exposure of samples to light should be minimized to prevent photodegradation; <br />and <br />July 2015 41