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CALIFORNIA REGIOI\I kFATER QUALITY CONTROL BOARD• Cal/EPA <br /> CENTRAL VF LLEY REGION <br /> 3443 Routier Road, Suite A �.� .3 ii_ hLA1.1 h <br /> a� Sacramento,CA 95827-3098 <br /> Phone(916)255-300097 AUG 9 pi414 Pete Wilson,Governor <br /> FAX(916)255-3015 <br /> 18 August 1997 <br /> Ms. Julie Raming <br /> 133 Peachtree Street, NE (30303) <br /> P.O. Box 105605 W uG2pcc <br /> Atlanta, GA 30348-5605 <br /> PHASE 2 INVEST <br /> IGATIONAND RECOMMENDATIONS FOR FUTURE REMEDIAL ACTIONS, FORMER <br /> GEORGIA PACIFIC CORPORATION CHEMICAL PACKAGING PLANT, TRACY, SAN JOAQUIN COUNTY <br /> I have reviewed the 6 May 1997 report entitled Phase 2 Investigation and Recommendations for Future <br /> Remedial Actions submitted by Brown and Caldwell for the Georgia Pacific Corporation's (GP) former <br /> Chemical Packaging Plant in Tracy. The report discusses the installation of three monitoring wells and <br /> sampling results from these and other monitoring wells at the GP site. The report also evaluates remedial <br /> alternatives for chloroform present in ground water. <br /> GP believes the extent of chloroform in ground water has been adequately determined and recommends <br /> natural attenuation as the best remedial approach for the site. As noted in my comments below, I <br /> believe more information is needed to support GP's conclusion and recommendations. <br /> Chapter 4 Investigation Results <br /> The extent of chloroform has not been determined downgradient of BC-13 in the 75 to 85-foot zone as <br /> can be seen in the cross section in Figure 3. Chloroform in BC-13 was detected at 7.5 µgIl in February <br /> 1997. The extent of chloroform in this zone should be evaluated after three more quarters of sampling <br /> of BC-13. <br /> Chapter 5 Environmental Fate and Transport of Chloroform in the Subsurface <br /> Site Specific Attenuation Analysis <br /> GP has estimated the half-life of chloroform based on a primary first-order decay equation. <br /> Chloroform concentrations have been plotted versus time for five wells. The slope of a best fit line <br /> drawn through each data set was used to represent the decay constant (k) for chloroform in each well. <br /> Results of the five plots show chloroform half-lives ranging from 0.8 to 5.5 years. Based on a <br /> regression analysis of these plots and eliminat-,on of the two extreme half-lives for chloroform, GP has <br /> estimated the half-life of chloroform at the site as 2.5 years. <br /> The best line fit in the regression analysis is for the two wells in the source area, wells BC-4 and BC-5. <br /> It would be more appropriate to use the more conservative of these two half-lives to represent the <br /> half-life of chloroform in the source area where chloroform is present at higher concentrations, i.e., 5.5 <br /> years in BC-5. Similarly, it would be more appropriate to use the more conservative of the half-lives <br /> to represent the half-life of chloroform in the areas on the perimeter of the plume where the <br /> chloroform concentration is lower, i.e., 2.1 years in BC-14. <br /> Recycled Paper <br /> Our mission is to preserve and enhance the quality ofCalifornia's wafer resources,and <br />