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0 <br /> Kennedy/Jenks/Chilton <br /> Mr. John Menke <br /> California Regional Water Quality Control Board <br /> 30 November 1989 <br /> Page 2 <br /> demonstrate appreciable amounts of petroleum hydrocarbons remain in soil , <br /> additional work may be proposed. <br /> The San Joaquin Air Pollution Control District has been contacted for <br /> permitting and approval of the aeration of the soil containing petroleum <br /> hydrocarbons. <br /> Task 3 is the construction of an additional monitoring well and sampling of <br /> all the monitoring wells on site. The proposed work is essentially <br /> satisfactory, but the filter pack material proposed (Page A-5, last paragraph) <br /> is Monterey No. 1C sand; the other monitoring wells at the site used No. 3 <br /> sand. The correct pack should be based on a sieve analysis, and you may make <br /> the determination at the time of well construction. In addition, I want to <br /> advise you that the Cal-Farm Supply site is located near two other sites <br /> identified as probable sources of ground water pollution. The Port of <br /> Stockton bulk fuel facility is to the southwest and is a suspected source of <br /> petroleum hydrocarbons; Pacific Molasses is to the northwest and is a <br /> suspected source of nitrates. Your investigation should consider the <br /> potential impact from these sites on ground water under Cal -Farm Supply. If <br /> you want additional information on the neighboring sites, please call Ms. <br /> Twila Leclerc at 361-5673. <br /> As was stated in our Preliminary Site Investigation Report (dated 14 July <br /> 1989) , a Monterey No. 1C sand was used as an artificial filter pack in the <br /> monitoring wells constructed at the site. A No. 1C was chosen for this site <br /> based on the fact that a 0.020-inch machine slotted well screen was used. <br /> According to the DHS Decision Tree Manual concerning the construction of <br /> monitoring wells the slot size and artificial filter pack should be matched so <br /> that approximately 15% of the artificial filter pack passes through the well <br /> screen (85% retention) . When using a 0.020-inch slot size a No. 1C sand <br /> satisfies this requirement. Kennedy/Jenks/Chilton has used this technique on <br /> several other sites with success in limiting the amount of turbidity in a <br /> sample. It should also be noted that turbidity (the primary reason for <br /> designing an artificial filter pack sand with relationship to the ambient <br /> formation) is primarily of concern when collecting groundwater samples for the <br /> purpose of metals analysis. Petroleum hydrocarbons are of concern at the Cal - <br /> Farm Supply Stockton Facility and turbidity is not of concern with <br /> relationship to these analyses. In addition, the formation was predominantly <br /> clay and the likelihood of some turbidity, regardless of well design, is <br /> expected in a clay formation which contains an indefinite amount of fines. <br /> Kennedy/Jenks/Chilton did research the surrounding area near the Cal -Farm <br /> Facility before the Preliminary Site Investigation was initiated. However, <br /> the results of the soil and groundwater laboratory analyses indicate that <br /> there isn't a concern in the soil or groundwater with respect to nitrate. The <br /> petroleum hydrocarbons that were detected in the soil and groundwater were <br /> only detected in two borings which were adjacent to the existing underground <br />