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Total Dissolved Solids (TDS)
<br /> TDS concentrations in groundwater samples collected from select monitoring wells on December 23,
<br /> 2002, prior to system startup, were in the range of 560 mg/L to 1,400 mg/L. The TDS concentrations in
<br /> groundwater samples collected on January 14 and February 12, 2003, were in the range of 490 mg/L to
<br /> 1,300 mg/L.
<br /> Petroleum Hydrocarbons and Oxygenates
<br /> The highest concentrations of TPHG, benzene, and MTBE detected in onsite monitoring wells since the
<br /> quarterly monitoring began at the site were at 55,000 gg/L (MW-6), 18,000 µg/L (MW-8), and 85,000 pg/L
<br /> (MW-6), respectively. These elevated concentrations were observed in quarterly monitoring events prior
<br /> to the operation of ozone injection system.
<br /> Since the operation of ozone injection system, the highest concentrations of TPHG, benzene, and MTBE
<br /> detected in onsite monitoring wells were at 33,000 gg/L (MW-6), 6,900 Ag/L (MW-4), and 67,000 pg/L
<br /> (MW-6), respectively. The historical TPHG, benzene and MTBE concentration variation over time at
<br /> select monitoring wells (MW-4, MW-5, MW-6, MW-7, and MW-8) are illustrated graphically in Figures 4
<br /> through 8).
<br /> During the recent quarterly sampling event (February 26, 2003), MTBE was detected in groundwater
<br /> samples collected from monitoring wells MW-1, MW-3 through MW-6, and MW-8 through MW-10. MTBE
<br /> concentrations ranged from 0.63 lag/L to 31, 000 µg/L, with the highest concentration detected at MW-6.
<br /> The reporting (detecting) limits for TPHG and/or benzene were elevated during analysis of groundwater
<br /> samples collected from wells MW-4, MW-6, and MW-8 due to dilutions performed by the laboratory in
<br /> order to quantify a target analyte. TPHG was detected in groundwater sample collected from MW-10 at
<br /> 120 µg/L. Benzene was detected in groundwater samples collected from MW-4 (6,900 pg/L) and MW-8
<br /> (5,000 Ag/L). Toluene, ethyl benzene, ETBA, TBA, TAME or EDB were not detected in any of
<br /> groundwater samples collected on February 26, 2003. Analytical results of TPHG, benzene, and MTBE
<br /> for groundwater samples collected on February 26, 2003 are presented in Figure 9.
<br /> LIMITATIONS
<br /> This report was prepared in general accordance with accepted standards of care that existed at the time
<br /> this work was performed. No other warranty, expressed or implied is made. Conclusions and
<br /> recommendations are based on field observations and data obtained from this work and previous
<br /> investigations. It should be recognized that definition and evaluation of geologic conditions is a difficult
<br /> and inexact art. Judgments leading to conclusions and recommendations are generally made with an
<br /> incomplete knowledge of the subsurface conditions present. More extensive studies may be performed to
<br /> reduce uncertainties. This report is solely for the use and information of our client unless otherwise noted.
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