ARCHIVED REPORTS XR0002735 - Laserfiche WebLink

Home Browse Search

z 4 •4 'ti 1 , S E C 0 R Ms Lori Duncan February 9, 2004 Page 5 1 Based to the revocable permit issued by the City of Stockton, remedial piping crossing Harding Way would have to be completed a minimum of 2 feet beneath an existing 48-inch storm drain running east/west in Harding Way The bottom of the storm drain is approximately 10 feet below ground surface (bgs) requiring the horizontal boring to be 12 feet bgs Based on the required depth of the boring and the construction methods of horizontal borings, several boring pits would have to be installed onsite, offsite in the city right-of-way, and offsite on adjacent private property 2 Re-permitting the Harding Way crossing to trenching would require trenching to 12 feet and shoring of the trench which is cost prohibitive 3 Extraction wells EW-3, EWA and EW-5 yield little water during batch extraction events Offsite interim remedial action by batch groundwater extraction was restarted In September 2003 due to the continued evaluation of connecting offsite wells to the onsite extraction system Batch groundwater extraction events are completed on a weekly basis from wells EW-2, EW-3, EW-4, EW- 5, and EW-7 and approximately 30,770 gallon of groundwater have been extracted from offsite wells ` since September 2003 and treated through the onsite remediation system Batch extraction events 4'a will continue until an acceptable offsite remedial strategy is implemented Chemical concentrations in both on and offsite wells are showing significant downward trends due to the onsite remediation and offsite interim remediation A summary of groundwater batch extraction events is included in Table 4 and site groundwater analytical data including first quarter 2004 sampling results are include in Table 5 Graphs of chemical concentrations vs time in wells on and offsite are included In Attachment A _4 • REVISED OFFSITE REMEDIAL ACTION PLAN 'Al Based on the continuing difficulty of installing extraction piping across Harding Way, SECOR � recommends that an offsite ozone sparge (OS) system be installed rather than completing AA connection of offsite wells EW-2, EW-3, EW-4, and EW-5 back to the onsite remedial system Well EW-7 will be connected to the onsite remedial system because crossing Harding Way is not required Installation of the offsite OS system will require limited access to the Taco Bell property across d Harding Way for installation of an OS system remedial compound The OS system will destroy petroleum hydrocarbons and fuel oxygenates beneath the site With subsurface soils consisting predominantly of mixtures of silt and sand within the upper portion of the saturated zone, the 41 introduction of ozone through several OS points would directly destroy dissolved petroleum hydrocarbons and MtBE and stimulate in-situ aerobic biodegradation of dissolved petroleum ' hydrocarbons and petroleum hydrocarbons in the saturated zone by increasing subsurface oxygen concentrations The installation of OS points along the north side of Harding Way would act as a , barrier, inhibiting migration of dissolved petroleum hydrocarbons and MtBE further downgradient of the site r' Conceptual Design of the OS System q A total of 6 OS points (OS-1 through OS-6) are proposed as a barrier along the north side of Harding Way The locations of the wells were selected based on an assumed 15-foot ozone radius of 1P influence, and therefore will be installed on 30 foot centers A work plan for the installation of the OS X_ points is included in the following section 4 J 11ARCOla9321workplans\Revised IRAP&WP doc r