ARCHIVED REPORTS_XR0010777 - Laserfiche WebLink

Home Browse Search

(VAI A S S O C I A T E S I N C not anticipated the change of scope will exceed the amount previously pre-approved by the Fund on November 1997 QUARTERLY MONITORING ACTIVITIES ATC performed quarterly groundwater monitoring and sampling on July 13, 2000 Field work included measuring the depth-to-water in wells MW1 through MW6 and purging and sampling the water from wells MW2, MW3, and MW4 in addition to the nearby Thornton No 2 Municipal Supply Well (Supply Well) The samples were analyzed for the presence of dissolved petroleum hydrocarbons Depth to water measurements were collected on July 13, 2000 from monitoring wells MW1 through MW6 Groundwater beneath the site generally flows in a westerly direction at an average gradient 0 001 ft/ft, or approximately 5 28 feet/mile, with apparent mounding in vicinity of MW3 Historically groundwater beneath the site generally flows in a westerly direction Groundwater monitoring data are summarized in Table 1 A groundwater gradient map for the July 13, 2000 monitoring episode is shown on Figure 2 Groundwater samples were collected from wells MW2, MW3, and MW4 after purging and . stabilization of physical parameters (pH, electrical conductivity, and temperature) The monitoring wells were purged and sampled according to ATC's Field Procedures on file with PHS/EHD Monitoring well purge logs are included in Attachment 1 Furthermore, ATC coordinated with San Joaquin County Utility Maintenance Division personnel and collected a water sample from the sampling port of the Supply Well Collected groundwater samples were placed on ice and transported under chain-of-custody to State-certified Sequoia Analytical laboratory (FLAP #1210) Samples were analyzed for benzene, toluene, ethylbenzene, xylenes (BTEX) by EPA method 8020, and TPHg by EPA method modified 8015 RESULTS Laboratory analyses detected only concentrations of TPHg at 704 parts per billion (ppb), toluene at 0 661 ppb, ethylbenzene at 19 2 ppb, and xylenes at 3 93 ppb in the sample collected from well MW4 The water sample collected from MW4 reported benzene was below the laboratory detection limit of 0 500 ppb Groundwater samples collected from wells MW2, MW3, MW4, and the nearby Supply Well contained no detectable concentrations of BTEX or TPHg These analytical results are generally consistent with historical levels Analytical results are summarized in Table 1 Laboratory reports and chain-of-custody documentation are presented in Attachment 2 w 1625821quartlyl2gr-2000 doc 4