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Mr Mike Infurna Page 3 In response to the second comment in the letter, our rationale for the screened intervals proposed for the new shallow wells (45-75 feet) is to ensure that the wells remain usable for the longest possible period of time Hustoncal data indicate that groundwater in the site vicinity exhibits large seasonal depth fluctuations and extreme long-term fluctuations related to precipitation The seasonal range of fluctuation is over 10 feet and the cyclical range appears to be 50 feet or more During the drought of 1991 and 1992, groundwater levels at the adjacent U-Haul site had an approximate average depth of 83 bgs Depths rose somewhat between 1992 and 1994 and then began a significant rise following the breaking of the drought in 1994 Water levels peaked during the high precipitation years of 1997- 1999 The last two years have had approximately average precipitation and water levels have begun to drop If the long-term rainfall trend observed over the Iast century holds true, it is most likely that a period of below normal precipitation is beginning and water levels can be anticipated to drop substantially A graph of water levels in U-Haul well MW3 is included in Attachment C Within the last year (June 2001 through June 2002), groundwater has decreased 5 57 feet at the Harry's Auto site As shown by the projected trend(Attachment C), the groundwater level at Harrys Auto is anticipated to be approximately 63 feet bgs by September 2002 At thus depth, all site wells except for well MW1 and offsite well U-Haul MW7 will be dry By constructing the proposed offsite wells with deeper screens,the wells should remain usable for sampling for several years even under drought conditions If the proposed 30-foot screen length is unacceptable to EHD we propose the alternative of screening the wells from 50 to 75 feet Any Issues of screen flooding which may occur during non-drought years should not be of concern No free product related . to the Harrys Auto site will be present, and any contaminants that may be present will be in the dissolved state Permit applications for the proposed monitoring wells will be submitted to your office after having secured the necessary encroachment permits from the City of Stockton If you have any questions or comments please contact Ground Zero at your convenience RespectHly, Gro alysns,Inc Sean Garvey, Staff Geologist GREGORY P. STAHL d * No. 5023 'f Gregory P Stahl,RG 5023 CA Certified Hydrogeologist No 264 �lF OF CA kF Attachments cc Mr and Mrs John Ferraiolo Mr Marty Hartzell, CA Regional Water Quality Control Board Ms Marla Nahonn,Environmental Closures i %NGZA_PSISYS01`Data1GROUNDZEVIARRYSV2eporu\QMR1200212QM2002 doc