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Erica Crosby and Allen Sorenson - CDMG ENV 250.04 <br />November 9, 2004 <br />Page 2 <br />the pressure difference. This of course effects stabilization of field parameters even in a flow through <br />cell. Often, gas passes through the interface of the water elevation probes as the wells are being <br />sampled causing the effect of a rapid increase or decrease of water level when in fact it is just a gas <br />bubble passing through. <br />During a third party oversight sampling event where a team of water sampling professionals from the <br />USGS spent more than two weeks with us sampling as we sampled, the gas evolution from the deeper <br />aquifer wells provided significant challenges to collecting the samples and recording the "true" water <br />level. A great deal of patience and skill is required. In cases where a continuous water level probe <br />records a ground water sampling event the pressure changes can also be noted in the recorded data. <br />Removing even a small sample volume from a two inch well at over 1,400 feet of depth can result in <br />the release of gases for a significant time period. Monitoring of the production lines indicates that in <br />addition to carbon dioxide, there is also methane and other C6 gases present to be released. The <br />incidence at monitoring well 19-2 during drilling where a drill rig burned after methane was ignited is <br />conclusive to the amount of gases present. <br />The third party oversight by the USGS of our sampling and analytical program experienced very similar <br />issues with matrix interferences requiring dilutions, reactivity and precipitation of solids. No report from <br />the USGS is available regarding this project because it took nearly iwo years for the USGS laboratory <br />to complete the analysis of one monthly round of ground water samples and present their findings at a <br />meeting. Their issues were the same as the ones we have experienced from our contract laboratory <br />but we had the advantage of years of experience and past data to streamline the work. The USGS <br />concluded verbally that our sampling and analytical and QA/QC program are robust and yield <br />representative data. <br />The instrumentation used to monitor the field parameters has a much shorter life in this application <br />than I have experienced in other monitoring programs where the water is not so harsh to the electronic <br />components due the abrasiveness and corrosivity of the media being sampled. Many attempts were <br />made at significant expense ($50,000 plus) to develop a functional temperature, conductivity, and <br />elevation probe that would work in the dissolution surface wells. Three sets of the probes failed after <br />only a short time in the wells due to problems with the corrosive nature of the water. <br />It is a standard practice to acidify ground water samples to a pH < 2 in the field. It is nearly impossible <br />to acidify many of these samples to a pH < 2. The buffering capacity of the high bicarbonate water <br />would require a significant volume of acid to meet this condition. The lab acidifies the samples and <br />also experiences difficulties with the reactive nature of the water. Many metals, organic carbon and <br />nitrate/nitrite analysis are affected by the difficulty in acidifying the samples. <br />Solids precipitate out of the samples making it difficult to field filter and to analyze in the lab. In order <br />to analyze the samples they must be diluted and smaller aliquots of the sample are used which can <br />adversely impact the detection level. It is not uncommon for the lab to run many of the samples <br />several times before quality assurance/ quality control standards required by the lab are met. Solids <br />clog the nebulizer on both the ICP and ICPMS so based on the TDS or the conductivity of the samples, <br />appropriate dilutions are done. Solids also precipitate out in the sampling equipment interfering with <br />ball valve seating and bladder membrane expansion and contraction. <br />During the initial analysis when baseline samples were being collected columns were ruined on <br />analytical instruments in the laboratory due to the long-term matrix interterence of non-target analytes. <br />Dilutions of the samples were made to attempt to avoid this problem. Many analytical determinations <br />