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FIELD PROTOCOL Low-Flow Sampling Technique This sampling technique is based on EPA document 540/S-95/504 (April 1996) and on ASTM Procedure D6771-02. Before the static groundwater level from the Monitoring Wells is measured, wells are opened and allowed to equilibrate. The Depth To Water (DTW) and floating product level, if present, is measured with a Solonist Water level Indicator and a KECK Interface Probe— 100', respectively. ,i These instruments are accurate to the nearest 0.01 foot. If necessary, groundwater depths are subtracted from wellhead evaluations, including corrections for product thickness, for gradient evaluation by multiplying product thickness (PT) by a correction factor 0.8 and subtracting from the DTW(Adjusted DTW=DTW-- [PT x 0.8]). ' Prior to collection of groundwater samples, sample tubing or a submersible pump is slowly and carefully inserted to the depth equivalent to midway down the screened interval so as not to disturb the standing water column above the screened interval and not to stir up colloidal particles or sediment. In some cases, dedicated tubing may be present in the well. (Shallow wells — 27 ft or shallower) The tubing is connected to a peristaltic pump and a Horiba Water Quality Monitor Model U-22XD meter with a flow-through cell. (Deeper wells — 28 ft or deeper) The tubing is connected to an appropriate submersible Mpump and to a Horiba Water Quality Monitor Model U-22XD meter with a flow-through cell. LGroundwater is slowly pumped while simultaneously monitoring the DTW and adjusting the pump rate until no or minimal drawdown is observed. Drawdown greater than 0.33 ft results in a reduction of pumping rate or a temporary shut down. Once the pumping rate is stabilized at a rate not exceeding 0.5 L/min, temperature, pH, specific conductance, redox, dissolved oxygen, and turbidity are measured. Environmental parameters are monitored according to the table below. When three consecutive readings show the parameters are stabilized, a groundwater sample is collected from the tubing port in front of the flow through cell of the meter. Conductance Dissolved Oxygen Redox Potential pH Turbidity (eH) (DO) (ORP) (NTU) . t3% t 3 pg/L t 10 millivolts I t 0.1 pH units t 3% Water samples are collected from the tubing and carefully poured into 40-milliliter (ml) glass vials preserved with hydrochloric acid. The vials are filled so as to produce a positive meniscus and sealed with a cap containing a Teflon® septum, and examined for air bubbles to avoid headspace that would allow volatilization to occur. The labeled samples are promptly transported on ice in a thermally insulated ice chest, accompanied by a Chain of Custody Record, to a California-certified laboratory. The quantity of water purged from each well is determined by the volume present in the purge buckets.