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STANDARD OPERATING PROCEDURE FOR LOW-FLOW DRAWDOWN GROUNDWATER SAMPLE COLLECTION nvTRODUCTIorI The purpose of this standard is to provide a method,which minimizes the impact of purging on groundwater chemistry,and to minimize the volume of water disposed. This will take place by placing the pump intake within the screen interval and by keeping the drawdown at a level of 0.33 feet (4 inches) until the water quality parameters have stabilized and collection is complete. The SOP was developed by the Superfund/RCRA Groundwater Forum and ASTM Procedure D6771-02. SUMMARY This SOP should be used at monitoring wells which have a screen or an open interval with a length of ten feet or less. The pump intake should be placed at or near the known source of the contamination within the screened interval. It is critical to place the pump intake at the same depth for each successive sampling event. This argues for the use of dedicated sampling devices whenever possNe., which will stay undisturbed in the well. The pump intake sho:::d n of be placed near the bottom of the screened interval to avoid disturbing any sediment that may have settled at the bottom of the well. Neither should well depth measurements be taken until after sampling is completed,for the same reason. Water quality indicator parameters and water levels must be measured during purging. Stabilization of the parameters and water levels are a required precursor to sample collection. Water quality parameters are the following: electrical conductance (eH), dissolved oxygen (DO), turbidity, oxidation-reduction potential (ORP), pH, and temperature (T). Prior to conducting field work,information on well construction should be obtained,i.e.,well construction diagram,screen interval,etc. NECESSARY EQUIPMENT • S WL indicator and interface probe. • Sampling pump(if not dedicated)—Submersible.or bladder pumps with adjustable controls. Peristaltic pumps can be used when depth to pump intake is 27 feet below ground surface(bgs)or less. • Tubing—One-foot of silicone tubing across peristaltic pump is preferred to optimize pump performance,and polyethylene drop tubing (dedicated to well). Drop tubing can be inserted into silicone tubing. Available sizes are: Size 15 silicone 0.19 1D/0.17 x 0.25 poly, Size 24 silicone 0.25 1D/0.25 x 0.375 poly, Size 36 silicone 0.38 ID10.375 x 0.5 ID poly. • Power Source —Rechargeable battery pack or car battery is preferred. If a fuel-powered generator is used, it must be placed downwind of the sampling area. AC outlets can also be used with extension cords. • Flow measurement device—Graduated cylinder and watch with a second had. • Multi-Parameter meter with flow-through-cell (FTC) — Parameters which must be monitored are pH, ORP, eH, DO, turbidity,and T. Daily calibration must take place throughout the sampling event. • Decontamination Supplies(non-dedicated)—Distilled water,tap water,sprayer,20 gal.containers,brushes,detergent. • Laboratory sample bottles,vials, sample preservation supplies,labels,chain-of-custody(CDC)forms,coolers,ice. e Approved H&S Plan,Workplan, Field Sampling Plan,JSA to provide direction of work. • Well construction data and water quality data from previous sampling event. • Well keys and site map of well locations. Groundwater sampling logs Calculator • In-line filters, if needed(dissolved metals). • Ferrous Iron sample kit(Hatch Kit),if ferrous iron is to be sampled. • Poly sheeting that may be placed on the ground around the wellhead. • PPE as specified in the Site H&S Plan. • Air monitoring equipment as specified in the Site H&S Plan. • Tool Box a Drums or buckets for purge water. • Refer to Field Checklist for Checic/Check Procedures for field supplies that may not be listed here. • The sample tubing diameter. PURGING AND SAMPLING PROCEDURES Pre-Samp_l'u►�Activities 1. Sampling locations must begin at the monitoring well with the least contamination.