SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Former ARCO Station N10168 441 W. Charter Way Page 2 of 3 vertically to the vadose zone for SVE recovery. URS selected the depth in response to SJC/EHD's previously expressed concern with sparging into the sand interval between 40 and 45 feet below surface grade (bsg). URS plans to test IAS feasibility with the whole system installed. SJC/EHD noted to URS on 20 June 2005 that the State Water Board Cleanup Fund (CUF) may balk at reimbursing for installation and operation of a complete remedial system (21 IAS sparge and SVE points) that was not shown to be effective for the site through a pilot test. URS stated it is USR's belief that ARCO was willing to assume the risks for installation of the complete system would not expect reimbursement from the CUF if it is ineffective. URS further stated during the 20 June 2005 conversation that this willingness would be put in writing. If this is so, SJC/EHD can approve installation of the IAS system. URS has proposed to construct the nested SVE and IAS wells by setting the IAS well screen from 36 to 38 feet bsg with filter pack sand from 33 to 38.5 feet bsg; a 2-foot bentonite seal from 31 to 33 feet bsg and cement grout from 27 to 31 feet bsg. The SVE well would then be installed over the grout. You may install the wells with this design, but the State of California requires that cement grouts be undisturbed for a minimum of 12 hours following emplacement, which may be cumbersome for installing 21 such wells. You may want to consider using bentonite grout for the whole interval between 27 and 34 feet bsg. The depth to groundwater near MW-1 has generally been less than 30 feet, although it has been as deep as 37 feet, so it seems likely that the lower portion of the seal should always be hydrated and uncompromised. URS agreed with this construction during a telephone conversation on 22 June 2005. SJC/EHD inquired of URS on the intended use or destruction of the existing vapor extraction wells on the site. URS responded that the existing vapor wells would be plumbed into the SVE system and utilized in accordance with their ability to extract contaminants and that sufficient access to all wells on the site would be maintained for proper well destruction at the conclusion of their usefulness. SJC/EHD is also concerned with the remedial needs of impacted groundwater in the sand unit directly underlying the silt unit targeted for IAS. URS plans to monitor the sand interval for a sufficient response to the SVE/IAS operation. URS assured SJC/EHD on 20 June 2005, that if the impacted groundwater in the sand unit does not exhibit a sufficient response to the SVE/IAS operation that they have room and the willingness to install a remediation system to address that groundwater. The proposed locations for the three new monitoring wells appear to be reasonable. The completion depth of the proposed wells is 30 feet bsg, which will keep the screen intervals in the silt and sandy silt interval. SJC/EHD expressed interest for monitoring the sand interval approximately 40 to 45 feet bsg if present in the area. URS agreed by telephone on 21 June 2005 to dual complete the wells with separate screen intervals to address both intervals of interest. SJC/EHD