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i <br /> i <br /> Ann Cerney,j <br /> Page 2 <br /> lab results it appears�jsoil samples were taken at twenty--five (25) <br /> and thirty,` (30) feet below ground surface. Results indicated that <br /> all other peaks quantitated as Benzene existed at 2 ppm and 6 ppm <br /> at the above respective depths. One water !sample was -taken from <br /> this monitoring well. The sample results were non--detect at ,twenty, f <br /> (2 0) parts 'per billion 1� (ppb) . The detectionlimit recommended for' <br /> use today is 5 ppb, Given the high detection limit, the need for j <br /> confirmation sampling and gradient determination PHS/EHD does not' <br /> feel confident that groundwater has not been impacted. <br /> The lead agency providing oversight at the time the above work was' <br /> completed was California Regional Water Quality Control Board, <br /> Central Valley Region:° PHS/EHD has contacted their office and <br /> verified that this site remains on the contaminated site list. <br /> PHS/EHD 3is now the'.j lead agency providing oversight for' # <br /> investigation and remediation of sites contaminated from, leaking7 <br /> underground storage tanks. The LUFT Manual, "Regional Board, Staff' <br /> Recommendations for Initial Evaluation and Investigation of <br /> Underground Tanks" and "Appendix All are ' guidance documents that <br /> PHS/.EHD uses in evaluating sites. Seasonal high groundwater,, shown` <br /> on the San ;Joaqui_n County Flood Control .1986, is thirty (30) <br /> feet below ground surface for this site. ,Since 'soil contamination <br /> appears to ;E exist at twenty--five (25) and thirty (30) feet:, below' <br /> ground surface a groundwater investigation is required. Accordingi <br /> to the above documents; if the groundwater gradient for. this site I. <br /> can be documented at an adjacent site, the minimum investigation` a <br /> would be installation of one monitoring well placed within ten (10) <br /> feet of the 'tank excavation in a down-gradient position. If the <br /> groundwater gradient cannot be documented, a minimum of three (3) <br /> monitoring !' wells mustl! be installed to 'determine the ., gradient. 1 <br /> After review of the results from the minimum investigation' :PHS/EHD { <br /> will comment on whether further investigation is warranted. AF <br /> proposalfor the above work and a request to be placed in' the' Local! <br /> Oversight, Program should be submitted to 'PHS/EHD. i <br /> If you have any questions, contact Margaret Lagorio, SeniorlREHS, ' <br /> at (209) 468-3449. <br /> Jogi Khanna, <br /> M.D. , M.P.H. <br /> Health Of icer <br /> :,'22 <br /> .Ld <br /> urie A. � C RENS, Program Manager <br /> ,Environmental Health Division <br /> LAC/ML:nr <br /> c: Steffen Robertson.�jand Kirsten } <br /> s, <br /> 15311 'N E 90th Street <br /> Redmond, WA 98052 <br /> 3 <br />