ARCHIVED REPORTS_XR0005187 - Laserfiche WebLink

Home Browse Search

FOURTH QUARTER,2002 GROUNDWATER MONITORING REPORT AND ADDITIONAL ASSESSMENT REPORT JAMAR OIL DISTRIBUTION MARCH 2003 Both the Modesto and Riverbank formations are part of the Great Valley sedimentary sequence of rocks which fill the large Great Valley sedimentary basin which was originally formed as a forearc basin between the Sierran arc to the east and the subduction zone to the west Stockton is located within the San Joaquin Valley which consists of the southern two thirds of the Great Valley province The northwesterly flowing San Joaquin River and its tnbutanes are the main drainage feature of the San Joaquin Valley According to the CPT logs generated during the January 13-16, 2003 site investigation, the subject site vicinity area is underlain primarily by interbedded silt and clay within the first 110-feet of the surface Two units with a higher percentage of sand were encountered in each of the three CPT holes, one at approximately 65 to 70-feet below ground surface (bgs) and one at approximately 100 to l 10-feet bgs The CPT logs are discussed in more detail in the Cone Penetrometer Testing section of this report According to the USGS Stockton East, 7 5 Minute Quadrangle, which covers the subject site, the closest surface water body is Mormon Slough, which hes approximately 1400-feet South- southeast of the subject site and is crossed by Oro Avenue Past quarterly monitoring at the subject site has shown the direction of groundwater flow to be south-southeast Summary of Previous Investigations In 1995, a 300 gallon waste oil UST and a 500 gallon kerosene UST were excavated and removed from the site No environmental issues were documented with the removal of these tanks In December 1998, two 6,000 gallon and one 10,000 gallon gasoline USTs were excavated and removed from the site and replaced with a two compartment 20,000 gallon UST meeting EPA and State of California upgrade requirements Sora samples taken in conjunction with the tank removal contained detectable concentrations of petroleum hydrocarbons and on January 27, 1999, an Unauthorized Release form was filed with the County An additional Unauthorized Release was filed with the County on June 11, 1999 In response to a directive from the County, John P Cummings & Associates (JPCA) conducted a subsurface investigation on September 8-9, 1999, by installing and sampling three monitoring wells(MW-1, MW-2, and MW-3) MW-1, MW-2, and MW-3 were drilled to approximately 78 feet bgs, 74 feet bgs, and 74 feet bgs, respectively and sampled every 5 feet Groundwater samples were collected from the three wells on September 23, 1999 2