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Mike Infurna [EH] <br /> From: Amy Terrell [aterrell@waterboards.ca.gov] <br /> Sent: Tuesday, February 05, 2008 5:33 PM <br /> To: jack_badey@unifirst.com <br /> Cc: WPipes@geomatrix.com; gbibler@goodwinprocter.com; tcosgrave@harvardprojects.com; <br /> Mike Infurna [EH] <br /> Subject: 819 hunter, stockton CA <br /> Attachments: Table 1.xls; Figures 1-4.pdf <br /> �l <br /> Table 1.xls(34 KB) Figures 1-4.pdf(2 <br /> MB) <br /> Mr. Badey, <br /> Your California consultant, Mr. Pipes of Geomatrix Consultants, provided me with a stand- <br /> alone Monitoring Well Work Plan in a 1 February 2008 email transmittal for the Unifirst <br /> facility at 819 Hunter Street in Stockton. Central Valley Regional Water Quality Control <br /> Board (Regional Water Board) staff have reviewed the monitoring well work plan (text <br /> below, plus attachments) along with the December 2007 Additional Groundwater Investigation <br /> Results Report also prepared by Geomatrix Consultants. Regional Water Board staff <br /> conceptually concur with the work plan provided that the following changes and cautions be <br /> implemented. <br /> 1. Two of the borings shall be continuous cores. This is to better understand the <br /> lithology governing the complex distribution of constituents observed in the grab <br /> groundwater samples. <br /> 2 . All monitoring well screen lengths except MW-5A shall be 10 feet or shorter. MW-5A, <br /> the water table well screen, may remain 20 feet as proposed. The shorter screen lengths <br /> are to help prevent contaminants from migrating from one water-bearing zone to another. <br /> 3 . MW-6 should have its screen interval target the 75-80 feet depth encountered in boring <br /> B-4, instead of the 57-62 feet depth proposed. <br /> 4. Final placement of the screen interval shall be guided by the on-site lithologic log. <br /> 5. Care shall be taken not to install screens that bridge confining layers that appear to <br /> be present in some borings between 62 and 85 feet. <br /> The narrative of the monitoring well work plan states that the lateral and vertical extent <br /> of dry cleaning solvents has been determined. Regional Water Board staff believe that <br /> this statement is premature. For example, In Boring B10, PCE was detected at 480 ug/L at <br /> 101 feet, and TCE was detected at 15 ug/L at 145 feet depth. No monitoring well intervals <br /> are proposed at 145 feet. Boring B4 contained 800 ug/L PCE at 80 feet, the base of the <br /> boring. It is reasonable to assume that contaminants are also deeper than 80 feet in this <br /> location. From the distribution of contaminants identified to date, there does not appear <br /> to be a continuous confining layer limiting downward movement. Nonetheless, the <br /> monitoring well network will go a long ways towards locating and quantifying the bulk of <br /> the distribution. <br /> Regional water Board staff do concur that there appears to be additional sources of low <br /> levels of PCE in the neighborhood, and Unifirst may be looking at comingled contaminants. <br /> Unifirst is commended on the speed at which it has proceeded with investigation. The grab <br /> groundwater borings yielded a lot of information about the distribution, the monitoring <br /> wells will provide repeatable measuring points corroborating the grab groundwater data, <br /> and the boring logs should provide clues to the lithology governing this distribution. <br /> Please prepare an investigation report that includes a description of the well <br /> installation, the boring logs, any difficulties or deviations from the work plan that were <br /> encountered, groundwater sample results, and recommendations. This investigation report <br /> 1 <br />