SITE INFORMATION AND CORRESPONDENCE

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r • • Mr. Mike Nakagawa - 3 - 17 February 2000 It is interesting to note that nitrate concentrations are three orders of magnitude lower in the well that contained petroleum hydrocarbons in the greatest concentrations (MW-1). Ammonia concentrations are also more consistently present in this well than the other wells. This may suggest that oxidation- reduction reactions are taking place between the petroleum and nitrate compounds in the groundwater or vadose zone. The groundwater analytical results table (Table 2) does not indicate whether atrazine,prometon, and simazine were tested for in March 1999. The laboratory analytical sheets indicate the pesticides were analyzed for and not detected,which should be noted in the table. Second, Third and Fourth Quarters, 1999 MW-6 was unintentionally destroyed during weed abatement activities during the 1999 summer. Unfortunately, the well was well positioned and provided valuable information on both nitrate and groundwater elevations. IT recommends replacing the monitoring well. I concur. Koppel Stockton is on the property directly to the south of Cal Farm Supply and is also conducting a groundwater investigation for nitrate contamination. Since groundwater elevations at Cal Farm Supply indicate a complex gradient, IT and Koppel measured the groundwater elevations within four days of each other during June and September 1998, and during March,August and November 1999. The Koppel well nearest to Cal Farm Supply is KP-2,which is approximately 520 feet south of Cal Farm's MW-6, and 750 feet south-southeast of MW-3. The groundwater elevation in Koppel's KP-2 monitoring well was the same as MW-6 in June 1998, and was 0.6 feet higher in September 1998 and March 1999. This implies that during some periods of the year, groundwater travels from Koppel's northern border to the depression on the Cal Farm Supply southern portion. Data were not available for MW-6 for August and November 1999 since MW-6 had been destroyed. Elevations recorded in MW-6 were lower than the upgradient wells MW-3 and MW-9 during each of the four quarters of record, supporting the suggestion that a groundwater depression lies between Cal Farm Supply and Koppel Stockton. This apparent groundwater depression corresponds to a ground surface depression which ponds stormwater during wet periods. Beyond the influence of this depression, groundwater flows generally easterly at the Cal Farm Supply facility, and southeasterly at the Koppel Stockton facility. However,it is unusual to have a groundwater depression beneath a ponded area. The overall groundwater gradients are shallow, approximately 0.005 feet/foot, and it is also unusual to have a 0.6 foot groundwater elevation change in 500 feet when the overall gradient is 1,000 times shallower. Since accurate groundwater gradient information is important in this area of the property that borders another groundwater nitrate source, the wells at Cal Farm Supply should be resurveyed. This should be done when MW-6 is replaced. IT corrected the Analytical Results Table, and all nitrate entries are now listed as nitrate units. MW-6, downgradient of Cal Farm's facilities, consistently contains nitrate concentrations three times greater than other wells on the site. IT suggests that this may be attributable to Koppel's nitrate influence or stormwater runoff, since MW-6 is situated in a localized pond during the winter months.