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Joe Lentini - 2 - 5 November 2009 <br /> Shell proposes to install three shallow monitoring wells in the vicinity of each of the Trenches 2 <br /> and 3 and four shallow monitoring wells in the vicinity of Trench 4. Each of these shallow <br /> monitoring wells will be screened in first encountered groundwater with screen intervals <br /> anticipated to extend from 20 to 35 feet below ground surface. In addition, two deeper <br /> monitoring wells with screen intervals of 105 to 115 feet and 145 to 155 feet will be installed <br /> along with one of the shallow monitoring wells near the location of boring B-69, which <br /> contained 730,000 pg/L of TPHc at 110 feet below ground surface. <br /> Shell also proposes to install a cluster of three sentinel monitoring wells northwest of the areas <br /> investigated so far to assess whether the known groundwater pollution extends towards the <br /> water supply wells. In order to assist with the construction of the screen intervals of these <br /> sentinel wells, Shell proposes to first advance a cone penetration test (CPT) boring at that <br /> location to 150 feet below ground surface and to collect discrete-depth groundwater samples <br /> from identified permeable zones using Hydropunch sampling equipment. Proposed well <br /> construction details based on the CPT data will be discussed with Central Valley Water Board <br /> staff before proceeding to well drilling. <br /> The shallow monitoring wells will be installed using a hollow-stem auger or roto-sonic drill rig. <br /> The deeper monitoring wells will all be installed using a roto-sonic drill rig to limit the potential <br /> for cross-contamination between separate water-bearing zones. Proposed source area <br /> monitoring well borings, located along the former pipeline alignment and the deeper well <br /> borings will be continuously sampled for soil description and screening of organic vapors using <br /> a photo-ionization detector (PID). Soil samples for soil description and PID screening will be <br /> collected at 5-foot intervals in the up and down gradient monitoring well boreholes. Selected <br /> soil samples will be submitted for laboratory analysis. All monitoring wells will be constructed <br /> with 2-inch diameter schedule 40 PVC casing. The monitoring wells will be developed, <br /> surveyed, and sampled. Soil and groundwater samples will be analyzed for total petroleum <br /> hydrocarbons as diesel (TPHd) and TPHc using EPA Method 8015M and benzene, toluene, <br /> ethylbenzene, and total xylenes (BTEX) using EPA Method 8260B. In addition, selected soil <br /> samples will be analyzed for hydraulic conductivity, pore fluid saturation, porosity, bulk density, <br /> moisture content, organic content, and grain size. <br /> Central Valley Water Board staff concurs with the proposed scope of work. The report for the <br /> proposed scope of work is due to this office by 5 February 2010. Provide at least one week <br /> notice of the field schedule prior to commencing field activities. If you have any questions <br /> regarding this letter, you may contact me at (916) 464-4665 or by email at <br /> ncasebeer@waterboards.ca.gov. <br /> Nathan Casebeer, P.G. <br /> Engineering Geologist <br /> Private Sites Cleanup Unit <br /> cc: Mr. Jeff Gaarder, Conestoga-Rovers & Associates, Sonoma <br /> Mr. Mike Infurna, San Joaquin County Environmental Health Department, Stockton <br /> Ms. Eileen Nottoli, Allen Matkins Leek Gamble & Mallory LLP, San Francisco <br /> Mr. Shailendra Ganna, Shell Global Solutions (US) Inc., Houston, TX <br /> Mr. David Corliss, Golden State Developers, Walnut Creek <br />