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Stantec • • <br /> April 13, 2009 <br /> Page 3 of 13 <br /> Reference: Response to RWQCB March 11, 2009 Letter <br /> Monitoring Well Destruction, Installation, and Additional Assessment Report <br /> (Assessment Report) describes the investigation. <br /> A few points of clarification are warranted. Well TS/MW-3D was installed to determine the <br /> vertical extent of groundwater impacts beneath the Tesoro Terminal and to facilitate pilot <br /> testing to mitigate impacts at onsite well TS/MW-2D. <br /> Due to heavy equipment operations on the Port of Stockton leased property near monitoring <br /> wells OW-3C and OW-3D these wells needed to be relocated. Wells OW-3C and OW-3D <br /> were destroyed and replacement wells OW-3CR and OW-3DR were installed approximately <br /> 200 feet to the south of the original well emplacements. A Plus Materials, operator of the <br /> leased property requested the well relocation to keep them out of the way of site operations. <br /> Monitoring wells PS/MW-20A and PS/MW-20B were installed as mid-point observation wells <br /> for the east ozone barrier to replace PS/MW-20 which was damaged during onsite <br /> operations. <br /> Wells PS/MW-20C and PS/MW-20D were the only wells installed to evaluate the potential <br /> for an upgradient source to impacts in well OW-51D. Stantec has presented evidence in <br /> several documents that OW-5D impacts are locally derived and not from the STTC <br /> terminals. <br /> 2 The 2 July 2008 Addendum to Work Plan for Additional Monitoring Well Installation <br /> specified that grab groundwater sampling would be conducted at 5-foot intervals during <br /> installation of the seven new monitoring wells. However, grab groundwater sampling was <br /> not conducted in the fine grained units at 140 and 150 feet bgs in boring TS/MW-2D. In <br /> addition, there is no evidence that any grab groundwater sampling was conducted in the <br /> other six boreholes. The lack of groundwater data from these boreholes and the <br /> petroleum hydrocarbons detected in the wells installed in the boreholes is evidence that <br /> the vertical and lateral extent of petroleum hydrocarbon pollution downgradient of the <br /> site remains undelineated. <br /> A few points of clarification are warranted. The RWQCB states above that "...grab <br /> groundwater sampling would be conducted at 5-foot intervals during installation of the <br /> seven new monitoring wells." There was no mention of this in the above-referenced <br /> document or ever any proposal for collecting grab groundwater samples at 5-foot intervals in the <br /> other wells. Groundwater grab samples was only proposed later regarding TS/MW-3D in the <br /> Addendum to Evaluation of Remedial Alternatives for D-zone Groundwater. <br /> The comment continues with: "However, grab groundwater sampling was not conducted in <br /> the fine grained units at 140 and 150 feet bgs in boring TS/MW-2D." This is consistent with <br /> the approved approach. The approach had always been to collect the groundwater grab <br /> samples from coarse-grained units, not fine-grained units, even after it was determined that <br /> greater depths than 135 feet bgs could be achieved with the Sonic equipment. Collection of <br /> reliable groundwater grab sample data from fine-grained low-permeability units is tenuous at <br /> best and was not proposed. <br /> I\ST rC-Stockton\Reports\Response to Comments\RWQCB Letter 3-11-09\STTC Response to RWQCB 3-11-09 Letter Final.doc <br />