Laserfiche WebLink
M. Scott Mansholt - 2 - 27 September 2007 <br /> Chevron EMC <br /> Mountain House #5 <br /> Regional Water Board staff approved a workplan 7 May 2007 to advance three borings and <br /> collect soil and groundwater samples for analysis. During the investigation the borings were <br /> advanced north-northeast of the site to evaluate/delineate the lateral extent of affected <br /> groundwater downgradient of boring MW5-7. Depth to water was less than 10-feet. Analytical <br /> results for the groundwater samples were non detect for TPHd, BTEX (benzene, toluene, <br /> ethylbenzene, and xylenes), and for polynuclear aromatic hydrocarbons (PAHs). <br /> Water quality test results indicated that the shallow groundwater contained the following <br /> among other constituents: total dissolved solids (TDS) 1,130 mg/L, electrical conductivity <br /> 1 ,830 pmhos/cm, bicarbonate 495 mg/L, and chloride 228 mg/L. Compounds reporting <br /> greater than their respective Water Quality Objectives (WQOs) and/or Maximum Contaminant <br /> Levels (MCLs) were: iron at 0.977 mg/L, sodium 343 mg/L, boron 4.6 mg/L, manganese 97 <br /> mg/L, and sulfate 165 mg/L. Nitrogen compounds were below their respective WQOs or <br /> MCLs. <br /> SAIC concluded that the extent of impacted soil and groundwater had been delineated, <br /> additional investigations were not needed, and the company would prepare a screening level <br /> Environmental Risk Evaluation. In conjunction, a long-term Soil and Groundwater <br /> Management Plan would be included, or it would provide a "Letter of Intent" to prepare a Plan <br /> that would address residual crude oil encountered during future site development or <br /> improvements. <br /> Based on our review, Regional Water Board staff concur that impacted soil and groundwater <br /> have been adequately delineated, additional investigations are not needed, and a risk <br /> evaluation can be prepared in support of a no further action determination. <br /> If you have any questions or comments, please contact Dean Hubbard at (559) 445-5179. <br /> SHELTON R. GRAY C. DEAN HUBBARD <br /> Senior Engineering Geologist Engineering Geologist <br /> P.G. No. 6357 <br /> cc: Michael J. Infurna, San Joaquin County EHD, Stockton <br /> Lee Higgins, SAIC, San Ramon <br /> CDHIRIChevron 0VPIMtn.House5,soII1GW rpt,Sep107 <br />