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S E C 0 R 7-Eleven Store #32262 • Site Assessment Report December 12, 2003 Page 4 Well Installation Shallow Wells - The five shallow wells (MW-1 through MW-5) were constructed using 2-inch diameter polyvinyl chloride (PVC) blank casing and 0 020-inch-slot well screen The well screen was installed from 7 feet bgs to 17 feet bgs A sand filter pack was placed within the annulus of the well from the bottom of the boring to approximately one foot above the top of the well screen The annulus of the well was sealed with two feet of bentonite on top of the sand, and a portland cement/bentonite grout to the surface An 8-inch-diameter, traffic-rated, watertight street box was installed to protect the well from surface traffic Well construction details are summarized in Table 3 Deep Well - In order to minimize the risk of cross-contamination of the deeper groundwater, a conductor casing was set through the shallow groundwater zone to a depth of 32 feet bgs in the = deep groundwater monitoring well (MW-6D) The well was drilled and sampled to a depth of 32 feet bgs using 8-inch diameter HSAs The borings were then drilled out using 15-inch diameter hollow stem augers and a 83/4-inch diameter steel conductor casing was set and tremae grouted in place through the augers using neat cement The grouted conductor casing was allowed to setup for a period of 24 hours prior to drilling to total depth in the well The well was drilled from 32 to 51 feet bgs using 8-inch diameter HSAs and constructed using 2-inch diameter PVC blank casing with five feet of 0 020-inch-slot well screen set from 46 to 51 bgs A sand filter pack was placed within the annulus of the well from the bottom of the boring to approximately one foot above the top of the well screen The annulus of each well was sealed with four feet of bentonite on top of the sand followed . by a portland cement and bentonite grout to the surface A traffic-rated, watertight street box was installed to protect the wells from surface traffic �k Morrow Surveying, a certified surveyor for the State of California, surveyed the locations of the newly installed wells The top of casing of the newly installed wells were surveyed to within 001 feet ° relative to mean sea level A copy of Morrow's well survey map is included in Attachment D Well Development and Groundwater Sampling On October 24, 2003, SECOR developed wells MW-1 through MW-5, and MW-6D, by surging and bailing groundwater from the well Approximately 10 well casing volumes of groundwater were purged from each new well, until pH, temperature, and conductivity readings stabilized Parameters monitored during development and well purging included pH, conductivity, and temperature : (Appendix C) Purge water from well development and sampling was stored in 55-gallon drums on site, pending offsite disposal Following well development, groundwater samples were collected from the new wells Well purging �4 and sampling equipment was thoroughly cleaned prior to purging and sampling each well The sampling procedure for the 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 The well was purged of approximately three casing volumes of water (or to t dryness) using a submersible pump or bailer The equipment and purging methods used for the sampling event are noted on the field data sheets included in Attachment C During purging, temperature, pH, and electrical conductivity were monitored 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 ^,t 32262 Assessment Report SECOR Intematlonal Incorporated r