ARCHIVED REPORTS XR0003356 - Laserfiche WebLink

Home Browse Search

SS E C 0 R 7-Eleven Store #14117 Quarterly Groundwater Monitoring Report (2Q2004) August 13, 2004 Page 3 also present in the soil samples indicated possible dry cleaner plume contributions (IT Corporation, 1999) On August 14, 2003, deep groundwater monitoring well (MW-8) and one soil boring (SB-1) were advanced on site SECOR summarized this assessment in the February 27, 2004 Additional Site Assessment Report and Fate and Transport Model, which also presented calculations of the lateral migration of dissolved MtBE in groundwater Per the request of the SJCEHD, groundwater monitoring and sampling is coordinated with a former Exxon site (currently a USA Gasoline station) immediately east of the 7-Eleven site MONITORING AND SAMPLING PROCEDURES The depth to water was measured to within 0 01 feet bgs in monitoring wells MW-1 through MW-6, and MW-8 from top of casing (TOC) using a water level indicator Dissolved oxygen concentrations were also measured in each well using a YSI Model 550A dissolved oxygen meter equipped with a down hole sensor MW-7 was not monitored or sampled due to a vehicle blocking access to the well Well purging and sampling equipment was thoroughly cleaned prior to purging and sampling each well The sampling procedure for each well included measuring the water level and checking for the presence of liquid-phase hydrocarbons (LPH), using either an electronic indicator and a clear Teflon® bailer or an oil-water interface probe Wells not containing LPH were purged of approximately three casing volumes of water (or to dryness) using a submersible pump or bailer The equipment and purging methods used for the current sampling event are noted on the field data sheets included in Attachment A During purging, temperature, pH, and electrical conductivity were monitored in order to document that these parameters were stable prior to collecting samples After purging, water levels were allowed to recover to 80% of the original levels prior to collection of the water sample Groundwater samples were collected using a disposable Teflon® bailer, placed into appropriate Environmental Protection Agency EPA approved containers, labeled, logged onto chain-of-custody documents, and transported on ice to a California state-certified laboratory Copies of the field notes are included in Attachment A GROUNDWATER SAMPLE ANALYSES AND RESULTS The groundwater samples collected from MW-1 through MW-6, and MW-8 were analyzed for TPHg, BTEX, and the fuel oxygenates MtBE, tert-butyl alcohol (TBA), diisopropyl ether (DIPS), ethyl-tert-butyl ether (EtBE), tert-amyl-methyl ether (TAME), 1,2-dichloroethane (1,2-DCA), and 1,2-dibromoethane (EDB) by EPA Method 8260B The certified laboratory analytical report and chain-of-custody documentation are presented as Attachment B Groundwater analytical results are presented on Figure 3, and are summarized in Tables 1 and 2 Hydrocarbon concentrations were generally consistent with historical data Dissolved concentrations of MtBE and TBA continue to decline in MW-4 . PURGE AND RINSATE WATER DISPOSAL Water generated during well sampling and equipment cleaning was pumped into a SECOR truck-mounted water tank The water was transferred into properly labeled 55-gallon drums 14117 04-2Q Report doc SECOR international incorporated