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r , <br /> from an undisturbed soil sample, placing this subsample in a clean glass jar, and <br /> sealing the far with aluminum foil secured under a nng-type threaded lid. The,lar <br /> was warmed for approximately 20 minutes, then the foil was pierced and the head- <br /> space within the jar was tested for total organic vapor, measured in parts per <br /> million as benzene (ppm, volume/volume). The instrument had been previously <br /> calibrated using a 100-ppm isobutylene standard (in air) and a sensitivity factor <br /> of 0 7,which relates the photo-ionization sensitivity of benzene (7 0 ppm) to that of <br /> isobutylene The results of the field testing are noted on the exploratory well logs. <br /> Monitoring Well Development and Sampling Procedures <br /> The wells were developed prior to sampling. The well development procedure <br /> consisted of surging the well with a 3-inch diameter plug to force the fine-grained <br /> material out of the sand pack Then the well was evacuated 10 casing volumes <br /> with a pump until the groundwater was clear and relatively free of sediment. <br /> The sampling procedure consisted of first measuring the water level in each well <br /> with an electronic water level indicator, and checking each well for the presence of <br /> separate-phase hydrocarbons (SPH) using an electronic oil/water interface probe. <br /> If the wells did not contain SPH, they were then purged of approximately four <br /> • casing volumes of water (or to dryness) using a centrifugal pump or disposable <br /> bailers During purging, temperature, pH, and electrical conductivity were <br /> monitored in order to document that these parameters were stable prior to <br /> collecting samples. After purging, the water levels were allowed to partially <br /> stabilize. Groundwater samples were collected using a Teflon bailer, placed into <br /> appropriate EPA-approved containers, labelled, logged onto chain-of-custody <br /> documents, and transported on ice to a state-certified laboratory Chain-of- <br /> custody documentation is presented as Attachment B <br /> Laboratory Procedures <br /> The analytical methods for determining the presence of total petroleum <br /> hydrocarbons calculated as gasoline, benzene, toluene, ethylbenzene, and xylenes <br /> are taken from EPA Methods 8015, 8020, and 5030. The above analytical methods <br /> utilize the purge and trap technique, with final detection by gas chromatography <br /> using a flame-ionization detector and a PID. All analyses were performed by a <br /> California-State certified laboratory. <br /> 31004002/MWINSTAL A-2 October 4, 1994 <br />