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Engineering,Planning, Corporate Office: Environmental Sciences and &ASSOCIATES,INC. 605 Third Street 760.942.5147 Profeaaional9Fams jpr Comptes Projevh Management Services Encinitas,California 92024 Fax 760.632.0164 20 November 2000 736-15 Kim Schwab Regional Water Quality Control Board Sacramento,rCAad, Suite A ��Q \�\`�� RE: Transmittal of Laboratory Analyses for Hexavalent Chromium, Marley Cooling Tower Company, 150 N. Sinclair Avenue, Stockton, CA. Dear Ms. Schwab: Transmitted herewith are the results of laboratory analyses for hexavalent chromium (Cr(VI)) of groundwater samples collected from 59 monitor, municipal supply, irrigation, and domestic wells as requested by the Regional Water Quality Control Board(RWQCB) and specified in our letter dated July 28, 2000. Two wells, MSI and MSD were not sampled because they were not accessible. The groundwater samples were collected between 11 -_16 October 2000. Laboratory reports are attached and the results are presented in tables and maps (Table 1, Figures I and 2). The analyses were conducted by California Laboratory Services (CLS) of Rancho Cordova, CA using method 7199 with a detection level of 0.5 micrograms per liter(ug/1). CLS is a state-certified laboratory. The results can be summarized as follows: • The results are generally consistent with previous analyses for total dissolved chromium considering that most of the previous analyses had detection limits of 10 ug/1. • The results indicate that there is no detectable Cr(VI) in the active municipal water supply wells CWS -52 and CWS-62 (Table 1 and Figure 2). The groundwater sample from inactive municipal water supply well CWS-20 contained 3.1 ug/l of Cr(VI). Well CWS-20 has been inactive since approximately 1988. • The results indicate that Cr(VI) is present in 6 of the seven domestic wells located south of main street in concentrations ranging from 1.2 ug/l to 8.8 ug/l (Table 1 and Figure 1). The concentrations of total dissolved chromium in these wells ranged from 20 ug/l to less than the detection limit of 10 ug/l before July 2000. Concentrations of total dissolved chromium in these wells ranged from 1 ug/l to 11 ug/l in July 2000. • No Cr(VI) was detected in deep zone monitor wells perforated below 200 feet below land surface.