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i Subsurface Investigation Report Installation of Wells MWS,MW6, and MW7 640 N El Dorado Street, Stockton, CA Soil and groundwater samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) and diesel (TPHd) using EPA method 8015B, TRPH using EPA method 418 1, benzene, toluene, ethylbenzene, and xylenes (BTEX) using EPA method 8021B, oxygenated gasoline additives using EPA IMethod 8260B, and VOCs using EPA method 8260 2.3 Well Construction A Geoprobe 6600 direct push/auger rig was used to install groundwater monitoring wells MW5 through MW7 ' Based on the lithology and the initial depth to groundwater observed during drilling, well MW5 was screened from 18 to 38 feet bsg and wells MW6, and MW7 were screened from approximately 17 feet bgs ' to 37 feet bsg The wells were constructed of 2-mch diameter, Schedule 40 PVC casing and 0 010-inch slot screen The filter pack consists of#3 silica sand from the bottom of the well to approximately 2 feet above the top of the screened interval The annular seals consist of 2 feet of hydrated bentonite pellets overlain by I neat cement grout to the ground surface The wells were completed with traffic-rated well boxes completed to grade level, and equipped with locking well caps Boring/well construction logs are included in Appendix 2 ' 2.4 Well Development and Groundwater Sampling On June 3, 2003, a Ground Zero technician developed the new wells (MWS, MW6 and MW7) and collected groundwater samples Water levels were monitored prior to well development using an electronic water level indicator ' Wells MW5, MW6, and MW7 were developed by surging, bailing and pumping until turbidity was minimized Physical parameters (temperature, pH, and electrical conductivity) were measured during the development process Groundwater samples were collected from each well after physical parameters had ' stabilized and water levels recovered to at least 80% of pre-purged levels Samples were placed in an ice chest at a temperature of 4° Centigrade and submitted to Argon Laboratory under chain of custody protocol The samples were analyzed for TPHg, TPHd, TRPH, BTEX, and VOCs using the analytical ' methods previously described Well development/purge logs are included in Appendix 3 2.5 Well Surveying ' As required by AB 2886, the wellhead elevations of the new monitoring wells were surveyed by a Registered Surveyor to a horizontal accuracy of less than one meter and a vertical accuracy of 0 01 feet ' On June 3, 2003, Morrow Surveying surveyed the latitude and longitude of the site wells relative to the North American Datum (NAD83), and surveyed the wellhead elevations relative to City of Stockton Benchmark No 27 A site map showing monitoring well locations, latitude and longitude coordinates ' and wellhead elevations is included in Appendix 3 2.6 Limited Pump Test to Evaluate Free Product Recovery Rates ' A proposed limited pump test to evaluate the feasibility of increasing the recovery rate of free product • into well MW3 could not be conducted due to falling groundwater elevations 1 -3- 1