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{ R604 :UPDATE 11-JULY, 1992 - f�l i }g INTRODUCTION This report includes the work performed under the Confirmation` Soil Borings and MW-7 Installation Work Plan,, along with the events - -that have occurred at this site -since the 10th Update t { Status Report, that covered events through June 10 , 1992 . E 3 t As stated in our 8th Update Status report, the first phase of remediation to the above mentioned site, removing aged gasoline j ` range hydrocarbons from the soil in the vadose zone beneath the tank field and pump island areas , has been completed. The above i confirmation borings were to verify this. Upon drilling and ! ' sampling the borings , two small areas of soil contamination still exist, and the borings in these area were converted into vapor extraction wells . The following report documents the drilling, sampling, and well installation that occurred. ' LOCATION Regal Station 604 (parcel # 139-020-08 ) is located at 1448 N. El Dorado and Harding Way, Stockton, San Joaquin County , California. The site is in projected section 2 ; T1N; R6E; MDB&M at approximately 14 feet above mean sea level. Initial drilling (November, 1989 ) encountered ground water at approximately 32 feet below sea level ( 471 below the surface) and flowing in an east to i southeasterly direction, see figures 1 , 2 , and 3A. • UPDATE STATUS REPORT #11 , WELL SAMPLING AND ANALYTICAL TECHNIQUES Depth to ground water measurements were obtained from all of the ground water monitoring wells on July 24 , 1992 « Water samples were obtained from the newly installed and developed monitoring well , MW7 at this time by a Western Geo-Engineers sample technician working directly under a (WEGE) geologist . Top of casing elevations , as documented in previous reports , were used and MW7 elevation was surveyed using MW4 as a datum. Depth to top of fluid and ground water measurements were obtained using a clean product water interface probe. The probe , lowered into the well attached to a tape calibrated in 0 . 1 foot intervals , signals at the contact of floating product and at the top of ground water . The measurement is obtained from the calibrated tape reading adjacent to a reference point on the casing. The probe is cleaned with trisodium phosphate soapy water , with a distilled water rinse, before measuring the next well . Measurements are started at the historically cleanest wells and progressed to the dirtiest wells . All depth to ground water measurements were obtained prior to purging the wells for sampling. The depth to water is then j subtracted from the elevation of the casings reference point for a corrected ground water elevation. The ground water gradient contour map, Figure 4 , was then developed from these corrected readings . A computer generated gradient program was not used. .i More interpretive gradient maps were developed by calculating the page 1