SR0080452_SSNL - Laserfiche WebLink

Home Browse Search

Appendix A Site Closure Request July 2,2010 Speedy Foods-Stockton Page 7 of 13 In Ground Zero's Groundwater Monitoring Well Destruction Workplan dated June 9, 2010, Ground Zero proposed to destroy groundwater monitoring wells MWS, MW7, MW8, MW10, MWll, MW14B, MW17B, MW18C, MW19D and extraction well EW2. In a letter dated June 15, 2010, EHD approved the request. These wells are scheduled to be destroyed between July 15, 2010 and July 16, 2010. Ground Zero recommends that the remaining wells be properly destroyed per San Joaquin County well destruction standards once site closure is granted. Monitoring well and extraction well logs are included in Attachment A and the well construction details are summarized in Table 3. 9.0 Groundwater Elevation Data Groundwater elevation has been monitored onsite since October 1999. During this time, depth to water has fluctuated between approximately 56 and 76 feet bgs. The groundwater table fluctuated between 24 and 44 feet below mean sea level. Groundwater flow direction has varied on the site from north-northeast to east. However, the predominant direction of flow has been to the northeast. Groundwater gradient has ranged from 0.001 feet per foot (ft/ft) to 0.01 ft/ft with the usual gradient approximately 0.003-0.008 ft/ft. Hydrographs of the four designated groundwater bearing zones have been included in Attachment C. Groundwater elevation data is summarized in Table 4. 10.0 Results of Sample Analyses The following tables are included in this report: • Table 4: Historical Groundwater Analytical Results • Table 5: Current Groundwater Analytical Results (February 2010) • Table 6: Summaryof Soil Analytical Results 11.0 Discussion of Contaminant Mass Changes Based on contamination concentrations fiom drilling investigations conducted between 1999 and 2004, Ground Zero estimated that were approximately 525 pounds(lbs)of TPHg and 67 lbs of MTBE remaining in soil. Prior to groundwater treatment, Ground Zero estimated that were approximately 52 lbs of TPHg and 39 lbs of MTBE remaining in groundwater. The 2004 contaminant mass estimates are sununarized in Table 7. Analytical results obtained during the installation of vapor extraction well VW2 in 2005 suggested that the original mass estimates in soil were under-estimated. Changes in containinant mass are related to active soil and groundwater remediation actions as well as natural attenuation. A discussion of the remaining contaminant mass is included in Section 15.0. Below is a brief summary of contamination removed by soil and groundwater remediation activities: • Approximately 166 yd of excavated soil from the UST pit were removed from the Site. • Between August 2001 and December 2003 approximately 180 gallons of free product/water mixture was removed by hand bailing methods. ----- -- -- ----- • The GWTS treated 4,457,049 gallons of petroleum impacted groundwater and removed approximately 125 lbs of TPHg, 14 lbs of benzene, and 44 lbs of MTBE.