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Wm. J. Hunter & Associates 2220 Loma Vista Dr <br /> RegEstered Geologists <br /> _' 7?i'"; i�;� r{,_ HEAL iiSacramento, CA 95825 <br /> �etroleum & Mineral Appraisers i't=es`I ' c� ^t�r�� (916) 972-7941 <br /> S 5 S N 12 <br /> PM 2: 4 6 FAX (916) 972-1683 <br /> May 26, 1995 <br /> Steven Sasson, Sr REHS <br /> San Joaquin County Health Department <br /> Environmental Health Division <br /> 445 North San Joaquin Street <br /> Stockton, Ca 95202 <br /> Ref Eighth Quarterly Groundwater Monitoring Report for 814 E <br /> Charter Way, Stockton, Site Code 1061 <br /> Dear Mr Sasson; <br /> We am enclosing a copy of the field report, water analysis, and <br /> maps showing groundwater_'gradients and lanes of equal concentra- <br /> tions of Benzene & TPHG -The-field work was performed on March ' <br /> 17, 1995 by-De1-Tech- Geotechnica7l Support Services as directed by <br /> our office <br /> The attached EXHIBIT A, shows the contours on the top of the <br /> groundwater taken March 17 ; EXHIBIT B summarizes the nine (9) <br /> hydraulic gradients measured to date on the property All of the <br /> • data indicate a rather stable gradient to the northeast This is <br /> consistent with both regional data and that measured at the <br /> Darpetro site to the northwest of the Morita property <br /> EXHIBIT C shows the approximate contours based on lines of equal <br /> concentration from the March 17, 1995 sampling event . EXHIBIT D <br /> shows lines of equal concentration of THPG from that date . Both <br /> maps indicate an increase in levels towards the downgradient <br /> well , MW-2 , which agrees closely with prior results . <br /> As mentioned in previous reports, a mayor soil & groundwater <br /> plume exists to the north which is centered on the Darpetro site <br /> to the northwest of the Morita property Monitoring well data <br /> from that project, taken on January 19, 1995 was reviewed by our <br /> staff and supports our belief that some, if not all, of the <br /> contamination measured in the groundwater from the Morita site is <br /> from that source . EXHIBIT E shows approximate lines of equal <br /> concentration of TPHG based on 12/7/1994 data from Morita Bros <br /> and 1/19/95 data from Darpetro, the closest comparable dates for <br /> which we have information Of course, other interpretations are <br /> possible, but it appears reasonable to conclude that the ground- <br /> water plume covers both the Darpetro & Morita sites <br /> Based upon gradient data and contamination levels obtained to <br />�l 1 <br />