ARCHIVED REPORTS_XR0007871 - Laserfiche WebLink

Home Browse Search

i MW AA Working To Restore Nature and within a radius of about 20 feet of the former 1,000 gallon gasoline UST tank pit A soil vapor extraction system was constructed at the site and began operating July 23, 1993 Quarterly groundwater monitoring results have shown detectable levels of petroleum hydrocarbons in the monitoring wells in the past (Table 1) ' GROUNDWATER SAMPLING AND GRADIENT EVALUATION RESNA personnel performed the latest quarterly groundwater monitoring of monitoring wells ' on June 2, 1994 At the direction of SJCPHS in correspondence dated May 10, 1994, the number of wells to be sampled has increased from three to six Field work consisted of measuring depth-to-water (DTW) levels and collecting groundwater samples from wells MW-1 ' through MW-6, and submitting groundwater samples for laboratory analysis Water level measurements were collected from wells MW-1 through MW-6 The depth to water ranged from 64 28 to 69 99 feet below top of well casing elevation In general, groundwater elevations have increased an average of 1 70 feet since March 17, 1994 The water level data were used to develop the groundwater elevation contour map (Plate 3) Assuming that horizontal isotropic conditions prevail, groundwater in the uppermost aquifer beneath the site flowed in an easterly direction The hydraulic gradient on June 2, 1994 was calculated to be 0 0006 ft/ft or about 3 feet/mile These data indicate a flatter gradient but no change in direction when compared with the previous quarterly monitoring results A summary of groundwater monitoring data is presented in Table 2 Groundwater elevations are referenced to feet mean sea level ' Groundwater samples were collected from six shallow groundwater monitoring wells, MW-1 through MW-6 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 No evidence of measurable floating product or hydrocarbon vapor was noted in the water samples Samples ' were then collected from each well using disposable bailers Purge water was contained in 55 gallon DOT approved drums and stored on-site pending proper disposal ' The groundwater samples collected from each well were submitted with Chain of Custody Record to Sequoia Analytical Laboratories of Redwood City, California, a State Certified ' laboratory (State Hazardous Waste Testing Laboratory Certification No 1210) Samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg), total petroleum hydrocarbons as diesel (TPHd), and benzene, toluene, ethylbenzene, and total xylenes (BTEX) utilizing EPA ' methods 8015/8020 Groundwater well purge and sample logs are provided in Appendix A 54Wi6\QUARTLYI3QMR1994 ORF 2 1