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<br /> MONITORING WELL SAMPLING AND GROUNWATER GRADIENT EVALUATION
<br /> A
<br /> ATC personnel performed the latest quarterly groundwater monitoring of eight monitoring wells on July 8,
<br /> 2005. The on-site water supply wells (DWI and DW2) were sampled on September 8, 2005, due to
<br /> scheduling conflicts with maintenance personnel. Field work consisted of measuring depth-to-water levels in
<br /> the monitoring wells, collecting groundwater samples from all wells, and submitting groundwater samples
<br /> for laboratory analyses. Water level measurements were collected from groundwater monitoring wells MW-
<br /> 1 through MW-8. The depth to water ranged from 7.01 to 8.63 feet below top of well casings. The water
<br /> level data were used to develop the groundwater elevation contour map (Figure 3). Shallow groundwater
<br /> flow beneath the site was generally toward the north during the monitoring event. The average hydraulic
<br /> gradient on July 8, 2005, was calculated to be approximately 0.003 ft/ft or approximately 16 feet/mile. The
<br /> data indicate a groundwater gradient that is generally consistent with previous groundwater gradients
<br /> observed at the site. A summary of groundwater monitoring data is presented in Table 1. Groundwater
<br /> elevations are referenced to feet above mean sea level.
<br /> Groundwater samples were collected from monitoring wells MW-1 through MW-8. Prior to collection of
<br /> groundwater samples a minimum of three well casing volumes were purged from each well. The pH,
<br /> electrical conductivity, and temperature were measured and allowed to stabilize before groundwater samples
<br /> were collected. Samples were then collected from each well using disposable bailers. Purge water was
<br /> contained in 55-gallon DOT approved drums. Groundwater well purge and sample logs are provided in
<br /> Attachment 1.
<br /> u The groundwater samples collected from each well were submitted with Chain-of-Custody Record to State-
<br /> certified Argon Laboratories Inc. (Environmental Laboratory Accreditation Program Certification No.
<br /> 2359). The samples collected from MW-1 through MW-8 were analyzed for TPHg by EPA Method 8015M;
<br /> BTEX by EPA Method 802113; MTBE, tert-amyl methyl ether (TAME), TBA, di-isopropyl ether (DIPE),
<br /> ethyl-tert-butyl ether (ETBE), 1,2-dichloroethane (1,2-DCA), and 1,2-dibromoethane (EDB) by EPA
<br /> Method 826013; nitrate and sulfate by EPA Method 300.0; alkalinity by EPA Method 310.1; carbon dioxide
<br /> by method SM531OB; and dissolved ferrous iron by method HACH 8146. The samples collected from the
<br /> on-site supply wells were analyzed for TPHg by EPA Method 8015M; BTEX by EPA Method 802113; and
<br /> MTBE, TAME,TBA,DIPS,ETBE, 1,2-DCA, and EDB by EPA Method 8260B.
<br /> LABORATORY ANALYTICAL RESULTS
<br /> Petroleum hydrocarbons were not detected in the samples collected from the on-site water supply wells.
<br /> TPHg was detected in the groundwater samples collected from MW-2, MW-3, and MW-4 at concentrations
<br /> of 810 micrograms per liter (µg/1), 88 µg/1, and 420 µg/1, respectively. Benzene was detected in the
<br /> groundwater samples collected from MW-2, MW-3, and MW-4 at concentrations of 210 µg/l, 26 µg/1, and
<br /> 7.5 µg/1, respectively. Toluene was detected in the groundwater samples collected from MW-2 and MW-4 at
<br /> concentrations of 6.2 µg/1 and 1.1 µg/1,respectively. Ethyl benzene was detected in the groundwater samples
<br /> collected from MW-2, MW-3, and MW-4 at concentrations of 37 µg/1, 2.0 µg/1, and 3.3 µg/1, respectively.
<br /> Xylenes were detected in the groundwater samples collected from MW-2 and MW-4 at concentrations of 20
<br /> µg/1 and 15 µg/1, respectively. MTBE was detected in the groundwater samples collected from MW-1, MW-
<br /> 2,MW-3,MW-4,and MW-5 at concentrations of 1.6 µg/1,9.8 µg/1, 3.2 µg/l, 1.1 and 0.9 µg/1, respectively.
<br /> s:\Environmenta111786I\reports\3gmr2005.doc 3 ATC Associates Inc.
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