WORK PLANS - Laserfiche WebLink

Home Browse Search

M CDIM Standard Operating Procedure 4.1 Soil Vapor Sampling "°'"""'"' Rev.1 6/30/2022 placed on top of the sand layer. Another 0.5 feet of sand is then poured over the nested well probe. A layer of hydrated bentonite' will typically follow. For temporary wells, if only one sample depth is required (single vapor well), the bentonite layer is poured to-surface. If additional sample depths are needed, a sand layer is deposited at each desired sample depth. Bentonite layers are to be poured between the sand intervals and poured to the surface. Every additional nested well probe is to be embedded within a sand layer of at least 1 foot thickness. For permanent wells, the layering process is the same as temporary installment, only, cement grout is poured to-surface on top of the dry bentonite. To protect the probe, a well monument box containing the probe tubes is to be set flush with the newly grouted surface. The tubes should remain in the well box between sample events and be secured by a closed ball valve on its free end. A figure depicting typical single and nested soil vapor well construction is provided as Attachment 2.1. After cleaning the hole surroundings of dust and debris, the shroud may be placed over the well and setup can begin. 3.3 Sample Preparation, Collection, and Closure 3.3.1 Equipment Purging and sampling equipment is constructed from a variety of materials. Inert materials (e.g., Teflon, stainless steel), with respect to known or anticipated contaminants, should be used whenever possible. The project work plans or protocols will describe the type of equipment to be used in further detail. An example of a typical soil vapor sample canister and matching sampling train is available in Attachment 3.1. Key equipment relevant to both the Vapor PinTm and vapor well approaches to soil vapor sampling include, but is not limited to: 1. Sample port(e.g., Vapor Pin TM, single, or nested vapor well probe), 2. Sample canister(Summa), 3. Flow controller/ regulator, 4. Shroud, 5. Tracer gas (helium or equivalent), 6. Tracer gas detector, 7. Tubing (typically'/4-inch outer-diameter[OD]) and fittings, and 8. Syringe/air pump. Bentonite used in single or nested well instillation will typically arrive packaged in its dehydrated state. When appropriate, the dehydrated bentonite is to be poured down the well with frequent doses of water. The addition of water to dehydrated bentonite produces a binding, cement-like consistency, and creates a seal around the tubing to prevent ambient air intrusion into the soil-gas probe. 4