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0 • <br /> Mr.Bob Trommer April 4,20011 <br /> Underground Storage Tank Clean Up Fund—Cal EPA j <br /> Page 3 <br /> I <br /> i <br /> i <br /> Connection to Existing Conveyance System <br /> SECOR engineers reviewed the available documents regarding connection to the existing conveyance <br /> system. Based on the information provided, it appears that costs outlined in Table 1 for connecting the: <br /> new well to the existing conveyance system arejustified within certain parameters. Any modifications: <br /> that may need to be made to the existing system to accommodate additional pressure, volume, or: <br /> distance conveyed may result in added cost. The parameters considered in the cost of completion <br /> should include surveying, trenching, laying the pipe, connections, pressure testing, refilling the <br /> trenches, grading, and replacement of landscaping or cultural features (curbs, sidewalks etc.) <br /> However,because of a lack of details about the planned conveyance system,a detailed evaluation could <br /> not be made. <br /> Area Hydrogeologic Data Review <br /> SECOR reviewed documents provided by the California Department of Water Resources (DWR) <br /> regarding well completion information, well logging data,and boring logs for wells completed within a <br /> I/2 mile radius of the site. These reports revealed that, historically, six irrigation wells near Delta <br /> College have been drilled to an average depth of 322 feet bgs with a maximum depth of 345 feet bgs <br /> (Appendix Q. These wells are constructed with varying screened intervals to capitalize on prevailing <br /> aquifer conditions. The screened or perforated intervals of these wells, as well as the RIW, are <br /> presented in Figure 2. The primary aquifer tapped by these wells appears to be a sand layer and <br /> intervening clay between 260 and 295 feet bgs with minor amounts of water produced from thinner <br /> sand lenses between 295 and 345 feet bgs. The screened intervals in these wells reasonably correlates <br /> with the production zone (higher resistivity) in the test boring between 260 and 295 feet bgs near the <br /> lower portion of the well indicated by B on Figure 2. Production from these wells is reported to be <br /> between 1400 gallons per minute(gpm)to 2850 gpm. The latter production rate of 2,850 gpm is from <br /> the RIW,which incorporates the deepest and largest screened intervals. <br /> i <br /> SECOR also consulted the City of Stockton Municipal Utilities Department (MUD) for general <br /> information regarding well construction and aquifer state of 22 wells used by the City.of Stockton. In a <br /> personal communique with officials of MUD on April 3,2001,it was learned that well depths between <br /> 200 feet bgs.(older wells)and 500 feet bgs are common with some as deep as 600 feet bgs. Most well's <br /> have screened intervals below 250 feet bgs to assure the highest quality potable water and avoid <br /> possible incurrence of a saline front via aquifers above 200 feet bgs. Productive aquifers with water <br /> suitable for irrigation exist between 90 and 140 feet bgs, however it was noted that, depending on <br /> location,overdraft of these aquifers might lead to a salinity problem in the future. <br /> Recommendations and Conclusions <br /> The following modifications and considerations regarding the well design are based on our evaluation <br /> of the information obtained as described in the previous paragraphs. <br /> I <br /> i Casing should be set from the surface to 260 feet to seal off the upper water-bearing zone, The <br /> shallower portion is apparently impacted by petroleum hydrocarbons and the.lower portion of <br /> this zone may be impacted by saline water in the near future. <br /> i <br /> EACHent ReportslMirptsV)cltaCWSW.doc-00,jes:2 <br />