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1991 Fourth Quarter Groundwater Monitoring Report November 25, 1991 <br /> Stephens Marine, Stockton, California W0147.00 <br /> laboratory analyses to date. The laboratory reports and chain-of-custody documentation are <br /> presented in Attachment 2. <br /> CLQSURI <br /> E <br /> i <br /> Three underground storage tanks consisting of two 4,000 gallon regular gasoline tanks and one <br /> ' 4,000 gallon diesel tank were removed in December 1988. A 1,000 gallon premium gasoline <br /> tank was removed in April 1988. The tanks appeared to be in good condition when excavated <br /> and removed. No free product was encountered in the water at the bottom of the tank <br /> excavation. The water sample collected from within the tank pit contained low levels of <br /> dissolved TPHG at 5.9 parts per million (ppm) (WaterWork, January 1989). <br /> Subsequent to verbal approval from San Joaquin Local Health District, Environmental Health <br /> Division on March 2, 1989, contaminated soil was excavated and removed from the tank <br /> excavation immediately prior to the installation of new tanks, The soil was disposed of at <br /> Forward Landfill in Stockton, California. The new tanks consisted of double-walled steel tanks <br /> with a fiberglass wrap tied down to a concrete slab. A leak detection system meeting 1989 <br /> requirements was also installed at this time. i <br /> In order to investigate the extent of possible groundwater impact three monitoring wells were <br /> installed on August 14, 1989; soil samples collected from the 5 and 8 foot (capillary fringe) ' <br /> intervals did not record any petroleum hydrocarbons above method detection limits(WaterWork, <br /> September 1989). Groundwater.�sampleVcbllected afte well�developmentfo n�,August`I8;�1�989 , <br /> rt 100 HD-in, <br /> . Y PtiNiW2 ani} 11U ppm` HDdn W31(WaterWork, September 1989). <br /> Ncz��arornatic;consti,tuents��r¢�TEH6were�cietected:� <br /> Between the August 18, 1989 and January 7, 1991 sampling events, minimal levels of BTEX <br /> intermittentlywere in groundwater samples from the three wells. Ortlyonceclldlany <br /> f the,_a tgytes :eix State�M=.*mum{CotauimentjI.evcls (�1QI,F137/ (3, 3 7,ppb°betizen Since <br /> January 7, 1991 all analytes tested reported no concentrations at or above Method Detection <br /> Limits. TheHowlevelsafcbssolved hydrocarbgnsazdetected ins-.erlier:sanplingeventshkliaye' <br /> � <br /> po,sssibl �y�,been r rrkW*ted,byvnatural$,hipdegractatinn pxc cesses # <br /> Based on the fact that no source for groundwater contamination remains at the site and that no <br /> evidence of groundwater contamination has been observed during the last four q«arters of <br /> sampling RESNA requests closure for the unauthorized release investigation at the Stephens <br /> Marine site. RESNA proposes to discontinue groundwater monitoring at the site pending a <br /> recommendation from the San Joaquin County Public Health Services to the Central Valley <br /> Regional Water Quality Control Board for case closure. When closure approval is received, the <br /> three monitoring wells will be abandoned in accordance with County and State Regulations. <br /> L,. SMIX10123.WP 2 <br />