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�m,r.Rr -.,.a..�,.,R.r rzro^"�Rlo".".�...+,�.•.�.*m�rs..•.owa�ra.rmms+sr�gm^m�re�«,nvm+ < �.� �wm,na^,y*+�s•+m-—��w,�.r,^�wr�e+R`+rmr F` Ms Linda Turcatte September 14 1995 f Page 2 iThe San Joaquin Public Health Services Environmental Health Division (SCPHSEHD) has required further investigation to include refinement of the delineation of the extent of contamination and to evaluate possible options for the re►nediation of contamination at the site, suggested alternatives include excavation, bioventing, and passive bioremediation Site Setting The site is situated in the southern portion of the Sacramento Valley, the northern portion of the Great Valley physiographic province The site is underlain by Pleistocene deposits of the Modesto formation The Great Valley is underlain by several thousand feet of sediments of Cretaceous and younger age Boring logs indicate a clayey subsurface soil sequence The topography in the area of the site is very flat, the general slope is to the west Duck Creek is an ephemeral stream approximately 1,000 ft to the south and Mormon Slough is approximately 1 mi to the north Site groundwater elevation data have indicated that groundwater has been approximately 72 ft below surface grade, it has fluctuated within a range of approximately 5 ft over the times measured (Table 3) Scope of Work SJCPHSEHD has indicated that they will require feasibility testing of remedial actions and additional borings to delineate the lateral extent of contamination The proposed Scope of Work includes drilling and installing three tient wells, installing a blower for vapor extraction, and feasibility testing We propose to install three vent wells and to use the existing monitoring well as an observation/monitoring/infection point We believe that this program will provide the best results and significantly reduce costs and time required to accomplish the remedial action A blower should be installed to extract vapor from the soil and to draw oxygen into the contaminated zone The proposed system design will also allow infection of nutrients to stimulate the bioremediation which is naturally occurring in the soil, to add biological agents if necessary, and will allow the venting process to focus within the contaminated zones Drilling and Sampling We propose to install at least three vent wells at the site which will be constructed using 4-in diameter casing with 0 10-in slots One vent well will be located within the previous excavation, one on the east side of the excavation, and one near the west sid'- tit the excavation They will be installed to a depth of approximately 65-70 ft with slotted intervals between 30 and `.� 70 ft The well within the excavation will be designated the primary vapor extraction well, the " Lusi-i GLOSCIENCEs s 3