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PAYMENT <br /> RECEIVED <br /> SAN J. rlf t•' JiV 1� � PUBLIC HEALTH "tftw. <br /> :E,� L ENVIRONMENTAL -EA�,rH I)IV;S! <br /> ON <br /> September 1G; 1996. <br /> PAYMENT <br /> 305 Sguth Hutchins Street RECEIVED <br /> Lodi 'California ;a::, .: '; l <br /> AN ON14 <br /> RU.18 ICI-tI ALTH SEIIV CES <br /> Mr..Mi l bfi=,Senior R.EHS ENViRCN!-1 .TAt.H JH iu15f0N <br /> lel <br /> Public;Health Ser*ices AY' EIVT <br /> Environmental Health Division RECEIVED: <br /> 304 Weber Avenue,Third Floor <br /> P. O. Box 388 SAN JQAQl}'IN CouNTY <br /> Stockton,California;95201 PUBLIC HEAT TH SERVICES <br /> ENVIRONMENTAL HEALTH D,I.UiSiQN. <br /> Dear H1r..Infurna: <br /> Please find enclosed,the output ftoin a 100 year simulation using Version 2.5 of SESQIL for Windows. <br /> The simulation was carred out in response to your request following your review of our August 1996 <br /> Case Closure Report on the site at 305 South Hutchins Street in Lodi <br /> As you requested,this most recent SESt3IL simulation models the vertical movement of benzene in the <br /> unsaturated zone in the vicinity of soil boring EB-8 at the 305 South Hutchins Street site. The water table <br /> was assumed to be about 40;feet below the surface,as you requested. We have not evaluated the water <br /> level data upon which you base this assumption,in fact,the simulation provided in our August report used <br /> a ground water depth of 55 feet,which corresponds more closely with several years of actual water level <br /> measurements at the site. The current water table depth that we used in our original simulation is likely to <br /> be more accurate for the purpose of input to simulations, With the possible exception of the water table <br /> depth used, parameter values that are considered realistic were selected as input to the model. The soil <br /> between the ground surface and the water table was assumed to be all sand. Three major layers were used <br /> in the model_ The uppermost layer represents the vadose zone from the ground:surhtce to the top of the <br /> Contaminated soil zone The second.layer represents the contaminated soil zone. Ile third or bottom layer <br /> represents the vadose zone beneath the contaminated soil zone. These layers are 610, 150f and 460 cm <br /> thick, respectively,in tl rno&.I.. The;total modeled vadose zone thickness is 1220cm... The otteirn layer in, <br /> the model is divided into 10: to provide better resolution of the advance of the pollutant front. <br /> The printed output:from the:100 year SESOIL run has been annotated to indicate the source and or <br /> mtionale'for parameter values used.. The area over which the benzene is assumed to be applied m a pulse <br /> corresponds to the area ofa circle with radius of 6 feet: (The closest boring tobboring EB-8 is GB-3;about. <br /> 12 feet. my. Na benzene was detected. n soil from.GB-3. Therefore,it:is assumed that the benzene;. <br /> contamination in.soil extends:from EB.-g.in all.directions to a distance of six Jr6d, N'o-b+enzene`was,found.in <br /> soja borings G0--10;TV VW k.GB-9;or GB4) <br /> Daniel,Mann,Johnson,&Mendenhall Piannirrg <br /> NASA Ames Research.Center,MIS 19.41 Aithifectu* <br /> Moffett Federal Airfield Engineering <br /> California 94035-1400 Program/Cod3truetion <br /> Telephone:415/604.4286 Fax:415/968-2063: Management <br />