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STATE OF CALIFORNIA—ENVIRONMENTAL =CTION AGENCY PETE WILSON,Govemor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— CENTRAL VALLEY REGION 3443 ROUTIER ROAD,SUITE A SACRAMENTO,CA 95827-3098 PHONE: (916)255-3000 96 N;011 —7 AM If: Ct_ FAX: (916)255-3015 J Y 6 November 1996 Mr. Tom Welch Westrec Properties 116633 Ventura Boulevard, 6th Floor Encino, CA 91436 TOWER PARK MARINA, 14900 W. HIGHWAY 12, LODI: REVIEW OF GROUNDWATER MONITORING REPORTS, SECOND AND THIRD QUARTERS, 1996 (SAN JOAQUIN COUNTY) Staff has reviewed the Second and Third Quarter, 1996, Reports for groundwater monitoring submitted by SECOR on behalf of Tower Park Marina. Staff also has reviewed the 14 August 1996 letter that accompanied the Second Quarter Monitoring Report. The monitoring was done in accordance with Monitoring and Reporting Program(MRP) Order No. 95-802. This letter responds to the 14 August letter from SECOR and both monitoring reports, and follows up telephone conversations with SECOR staff. GENERAL DISCUSSION OF THE MONITORING REPORTS: The reports indicate apparent seasonal fluctuations in depth to ground water, with groundwater rising in four of the five monitoring wells during the second quarter(measured in June 1996), compared to previous measurements in 1993 through 1995. The third quarter measurements (taken in September 1996) show a slight drop in groundwater elevations compared to the previous quarter readings,but still somewhat higher than pre-1996 levels. These results are to be expected following a dry summer. Monitoring well MW-2 behaved somewhat differently from the others: its water level dropped slightly compared to the first quarter(March 1996)reading. Analytical results show general decreasing trends in concentrations when all data since 1993 are considered for all wells and for all components. But during the last three monitoring rounds concentrations of several components have fluctuated, and in some cases, have shown increases above recent historical levels. This behavior may be attributable to rising groundwaters redissolving components from the soil profile. However, MW-2,the well that failed to show rising water levels during the last two sample rounds, exhibits the same general patterns of slight increase in concentration of some components. At the same time as these increases occurred, concentration of dissolved tph-d increased significantly in MW-3 (from 4000µ1L in December 1995 to 28,000µ/L in September 1996), and dissolved tph-g has reappeared in MW-3 over five of the six rounds of sampling(the exception being December 1995, a time of lowest recent historic groundwater levels). Over the same period of time,free product thickness has again increased in MW-3 -- an observation that is not necessarily consistent with rising groundwater levels. In