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Nis. Wendy Cohen 5/4/95 Page 2 2. Analysis of the soil and groundwater for glycol compounds and groundwater for semi-volatile organic compounds. As discussed with Mr. John Moody of your office, we will analyze soil and groundwater samples collected during this site investigation for ethylene glycol because under some circumstances ethylene glycol may form as an intermediate compound from the biodegradation of triethylene glycol. If ethylene glycol is not identified in any of the soil and groundwater samples collected during this study, it will not be included in the list of monitoring parameters during future routine groundwater sampling efforts. Conversations with chemists at analytical laboratories have revealed that the preferred method for analyzing soil and groundwater samples for ethylene glycol is by GC, rather than HPLC, due to its high water solubility. Therefore, we propose to test the soil and groundwater samples for ethylene glycol using GC methods. We do not propose to analyze the soil or groundwater samples for the other glycol compounds because, with the exception of ethylene glycol, glycol compounds are not regulated per Chapter 11, Title 22 of the California Code of Regulatons, nor are they contained in the water quality goals listed in Marshack (October 1986; revised September 1991). We do not beleive that the request for analyzing groundwater samples for semi-volatile compounds is warranted. Gas condensate liquids at this gas dehydrator station resemble a petroleum fuel, similar to kerosene, and as such, we propose to analyze all groundwater samples for TPH as gasoline, kerosene, diesel and motor oil, and BTEX compounds. This list of petroleum hydrocarbon analytes is consistent with the suggested list of chemical analytes for underground fuel tank cases presented in Regional Board Staff Recommendations for Initial Evaluation and Investigation of Underground Tanks. 3. Use of gradient information, in addition to soil boring results, in the selection of well locations. The Lathrop Gas Dehydrator Station is located in the San Joaquin Delta at a location relatively near the Middle River. As a result, it is possible that groundwater flow beneath the site may be influenced by tidal fluctuations. Therefore, taking a"snap shot" look at the groundwater gradient to direct well placement decisions may result in significant field judgment errors. The well locations provided in the workplan were designed to surround the groundwater plume as defined from the 1993 investigation results. As a result, regardless of the predominant groundwater flow direction,the proposed well locations should give adequate coverage for monitoring the lateral extent of the plume. As part of the workplan, we have proposed measuring groundwater levels at the site over a 24-hr period to determine if tidal fluctuations are observed in the groundwater levels at the site. If tidal fluctuations are observed in the groundwater levels at the site, the groundwater levels will be measured in several wells for a 72-hr period to determine the mean groundwater gradient direction.