ARCHIVED REPORTS_XR0005732 - Laserfiche WebLink

Home Browse Search

S E C O R . DISCUSSION Total petroleum hydrocarbons as gasoline (TPHg) were reported in two of the ten monitoring wells sampled this quarter at concentrations of 2,500 parts per billion (ppb, MW-1) and 110 ppb (MW-3) Benzene was reported in one of the ten monitoring wells sampled at a concentration of 420 ppb (MW-1) Methyl tert-butyl ether (MtBE), analyzed using EPA Method 82606, was detected in seven of the ten wells sampled at concentrations ranging from 0 52 ppb (MW-5) to 99 ppb (MW-7) 1,2-dichloroethane (1,2- DCA) was reported in seven of the ten monitoring wells at concentrations ranging from 0 62 ppb (MW-8) to 33 ppb (MW-3) MW-2 and MW-4 were not sampled because the wells were dry Due to a car parked over well MW-9, the well was not accessible for sampling Although the laboratory reported that all samples were analyzed past the recommended hold time, chemical concentrations were generally consistent with historical data, with the exception of the MtBE in MW-3, which was detected at its highest historical level in the well at 56 ppb this quarter Additionally, domestic well WSW and well DW-2 were sampled for TPHg, BTEX, MtBE, and other fuel oxygenates/additives, all of which were reported as non-detectable above the laboratory method reporting limits The direction of groundwater flow within shallow wells (MW-1 through MW-10) was northwest to north, at a gradient ranging from 0 002 ft/ft to 0 007 ft/ft The direction of groundwater flow within deep wells (DMW-1 through DMW-3) was to the southwest, at a gradient of 0 003 ft/ft Groundwater elevations in shallow monitoring wells MW-1 through MW-10 decreased by an average of 2 43 ft, while groundwater elevations in deep monitoring wells DMW-1 through DMW-3 decreased by an average of 2 02 ft SECOR is performing granulated activated carbon treatment on well DW-1 Influent and effluent water samples are taken monthly and reported under separate cover in monthly performance summaries DW- 2 and the onsite water supply well (WSW) are incorporated into the quarterly monitoring and reporting Analytical data from DW-2 is included in Tables 4 and 5 Certified laboratory analytical data are included In Attachment B This report presents our understanding of existing conditions at the subject site The conclusions contained herein are based on the analytical results, and professional judgment in accordance with current standards of professional practice, no other warranty is expressed or implied SECOR assumes no responsibility for exploratory borings or data reported by other consultants or contractors ATTACHMENTS: • Table 1 —Groundwater Elevation and Analytical Data • Table 2—Fuel Oxygenates Analytical Data • Table 3—Groundwater Gradient Data • Table 4—Domestic Well Analytical Data • Table 5--Domestic Well Fuel Oxygenates and Nitrate/Nitrite Analytical Data Figure 1 —Shallow Groundwater Elevation Contour Map • Figure 2— Deep Groundwater Elevation Contour Map • Figure 3—Groundwater Chemical Concentration Map • Attachment A—Field and Laboratory Procedures • Attachment B—Certified Laboratory Analytical Report, Chain-of-Custody Documentation, and Field Data Sheets cc Mr James Barton, Regional Water Quality Control Board - Central Valley Region (RWQCB-CVR) Ms Lori Duncan, SJCPHS Ms Madeline Scannavino, 5463 Cherokee Rd , Stockton, CA 95205 I I WRC0105951QMRS120M4QMR03 doc