ARCHIVED REPORTS XR0011904 - Laserfiche WebLink

Home Browse Search

wells, soil samples were collected from the borings. On July 21, 1995, Smith Environmental developed and sampled monitoring wells MW-1, MW-2 and MW-3. Analytical results of the soil and groundwater samples collected indicated elevated concentrations of petroleum hydrocarbons were present in the soil and groundwater downgradient of the former gasoline UST locations. GROUNDWATER SAMPLING AND GRADIENT EVALUATION Smith Environmental personnel performed the latest quarterly groundwater monitoring of monitoring wells on April 22, 1996. Field work consisted of measuring depth-to-water levels in all wells and collecting groundwater samples from all wells and submitting groundwater samples for laboratory analysis. Water level measurements were collected from groundwater monitoring wells MW-1, MW-2, and MW-3. The depth to water ranged from 7.25 to 8.73 feet below top of well casing elevation. Groundwater elevations have decreased an average of 0.06 feet since January 25, 1996. The water level data were used to develop the groundwater elevation contour map (Figure 2). Assuming that horizontal isotropic conditions prevail, groundwater in the uppermost aquifer beneath the site flowed in a north-northwest direction. The average hydraulic gradient on April 22, 1996 was calculated to be 0.003 ft/ft or about 16 feet/mile. The data indicates a groundwater gradient that is consistent with the gradient last quarter. A summary of groundwater monitoring data is presented in Table 1. Groundwater elevations are referenced to feet mean sea level. Groundwater samples were collected from monitoring wells MW-1, MW-2, and MW-3. Prior to collection of groundwater samples a minimum of three well casing volumes were purged. The depth-to-water, pH, electrical conductivity, and temperature were measured and allowed to stabilize before groundwater samples were collected. Samples were then collected from each well using disposable bailers. Purge water was contained in 55 gallon DOT approved drums. Purge water from monitoring well MW-1 from the previous sampling event did not contain detectable concentrations of petroleum hydrocarbons and was discharged to the ground surface. The groundwater samples collected from each well were submitted with Chain of Custody Record to Argon Laboratories of Ceres, California, a State Certified laboratory (DOHS #1873). Samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg), and benzene, toluene, ethylbenzene, and total xylenes (BTEX)utilizing EPA methods 8015/8020. Groundwater well purge and sample logs are provided in Attachment A. RESULTS OF LABORATORY ANALYSES Water samples collected from each well were analyzed for TPHg, and BTEX using modified EPA methods 8015/8020. These results and cumulative results of laboratory analyses are summarized in Table 2. The Chain of Custody Record, laboratory analytical reports, and chromatograms are included in Attachment B. w:\95122\2QMR1996.doc • SMTH