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81-Armet Ground-Water Monitoring Report <br /> 13975 Highway 88-E <br /> Lockefard, Catlfornia <br /> NGA Project No. 10.90.104 <br /> Page 3 <br /> Ground water samples collected on September 22,1990 were analyzed <br /> for BTBX and TPH. The laboratory results (attached) indicate that <br /> BTjX and TPH were not detected in any of the monitor;.ng wells. <br /> Results of historical ground-water sampling at the site indicate <br /> that TPH and 3TEX concentrations have been declining since the <br /> initial sampling event in June, 1987. Benzene has historically <br /> been the petroleum constituent detected at the highest <br /> concentration at the site. The attached figures show historical <br /> benzene concentrations at monitoring wells plotted against sampling <br /> dates. These figures illustrate the dramatic decline in benzene <br /> concentrations in monitoring wells at the site. Petroleum <br /> constituents have not been detected at monitoring wells MW-1, Mw- <br /> 3, and MW-4 for a period in excess of one year. <br /> RECOMMENDATIONS <br /> NGA recommends that all monitoring wells at the site be sampled <br /> again in approximately six months. Should results of the next . <br /> sampling event indicate no detectible concentrations of petroleum <br /> constituents in ground ,water at the site, we will recommend that l <br /> this site be officially closed and that no additional sampling of ]l <br /> ground water be performed. <br /> The next bi-annual sampling event is scheduled for late March, <br /> 1991. The bi-annual monitoring report for this sampling event is <br /> i;... scheduled for submittal on or about April 20, 1991. <br /> RM(ARKS/SIGNATURSS <br /> The recommendations contained in this report represent our. <br /> professional opinions. These opinions are based on currently <br /> } available information and are developed in accordance with . <br /> currently accepted geologic and hydrogeologic practices at this <br /> time and location. Other than this, no warranty is implied or <br /> intended. <br /> E <br /> f NATIONS GROUNDWATER ASSOCIATES <br /> Darrell'L. Nations, R.G. <br /> Principal. Hydrogeologist <br /> .;alzfornia-Registered Geologist X4712-- ----___------- ---__-- ----- _---,---- <br /> DLN:dn <br /> : Enclosure6. <br /> cci Mr. Bob Phillips <br />