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California Reglonal Water Quality Antrol Board Central Valley Region , Robert Schneider,Chair Winston H.Hickox Gray Davis Secretaryfor Sacramento Main Office Governor Environmental Internet Address: http://www.swreb.ca.gov/rwgcb5 Protection 3443 Routier Road,Suite A,Sacramento,California 95827-3003 RE Phone(916)255-3000•FAX(916)255-3015 NOV 0 5 16 October 2001 ENVIROA'f- T. PER[o,j il ,C"` C'4jj0 Mr. Richard Powell Department of the Navy Pacific Plaza 2001 Junipero Serra Blvd., Suite 600 Daly City, CA 94014-1976 DRAFT GROUNDWATER MONITORING REPORT OPERABLE UNIT I AND OPERABLE UNIT 4, GROUNDWATER MONITORING PROGRAMS JANUARY 1998 TO APRILIMAY 2000, NAVAL COMPUTER AND TELECOMMUNICATIONS STATION(NCTS), SAN DIEGO DETACHMENT STOCKTON, STOCKTON, CA We have reviewed the Draft groundwater Monitoring Report Operable Unit 1 and Operable Unit 4, Groundwater Monitoring Programs January 1998 to April/May 2000, Naval Computer and Telecommunications Station (NCTS), San Diego Detachment Stockton,Stockton, CA dated June 2001 prepared by Tetra Tech EM Inc. The draft report presents (1)results of site-specific groundwater sampling events conducted between January 1999 and April/May 2000 (including site background and relevant historical data), and (2) interpretation of data, conclusions and recommendations. The report is well prepared. The information presented is well organized and concise. We generally concur with the information, conclusions and recommendations presented in this report. Our comments are provided below: 1. Although we prefer to see iso-concentration(plume) maps as much as possible, we believe that it is not appropriate to draw plume maps without sufficient data from nearby monitoring points. If a sufficient number of data points are not available either due to lack of monitoring locations or if no monitoring was conducted during a particular monitoring event, we suggest presenting a site map showing the concentration value next to the sampling point. A footnote should be included stating that a plume map is not presented due to lack of sufficient data points to make a meaningful interpretation. For example, in Figure 4-1B, the plume map shown for 1,2- Dichloroethene in groundwater for March 1999 is based on data from fewer monitoring points compared to the previous monitoring event in January 1999 (fewer wells were sampled in March 1999). It is not appropriate to show the non-detect (ND) contour of the plume based on data from the specific monitoring event. Well W-90 previously(in January 1999) had a concentration of 56 micrograms/liter, but as there was no data in March 1999 for this well, the ND contour shows a reduction in plume size. The same situation applies to the vinyl chloride plume map for California Environmental Protection Agency 0a Recycled Paper The energy challenge facing California is real. Every Californian needs to take immediate action to reduce energy consumption. For a list of simple ways you can reduce demand and cut your energy costs,see our Web-site at http://www.swrcb.ca.gov/rwgcb5