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3764Gold Camp Drive Delta s°ite 2°° ��. 7 C ? (1 F ti I IR1ao Cordova,CA 95670 Environmental 9 J 38-2085 Consultants,Inc. FAX:916/636-8385 September 4, 1997 Ms. Mary Meays San Joaquin County Department of Public Health Services Environmental Health Division 304 East Weber Avenue Stockton, California 95201-388 Subject: Addendum to Revised Work Plan for On-Site Assessment Holz Rubber Company 1129 South Sacramento Street Lodi, California Delta Project No. D096-090 Dear Ms. Meays: This letter is in response to your telephone conversation this morning with Mr. Eric Holm regarding the proposed activities at the subject site (Figure 1). In said conversation you requested additional information regarding construction details for the proposed ground water monitoring wells,backfill details on the proposed geoprobe, hand auger, and soil vapor probe borings, and treatment of soil generated during drilling activities. The following information is provided as an addendum to Delta Environmental Consultants, Inc.'s Revised Work Plan for On-site Assessment,dated June 30, 1997. Ground Water Monitoring Well Construction Details The six proposed ground water monitoring wells will be constructed of 2 inch diameter, flush-threaded, Schedule 40 PVC casing. The monitoring wells will be screened with 0.020 inch slotted screen extending from approximately 45 to 70 feet below surface grade (bsg) to allow for seasonal ground water table fluctuations. The annular space in each well will be filled with a filter pack consisting of No. 3 Lonestar sand from 2 feet above the well screen to the maximum depth of each well. A 2 foot thick bentonite transition seal will be placed above the filter pack. If ground water is present in the borehole at the depth of the bentonite seal,the bentonite (Wyo-Ben Envirplug medium)will be installed using a tremie pipe. The annular space above the bentonite seal will be filled with neat cement grout mixed at a ratio of one 94-pound sack of Portland cement to between 5 and 10 gallons of potable water. The neat cement grout will be placed in the annulus using a tremie pipe up to a depth of 30 feet bsg; from 30 feet bsg to the ground surface, the grout will be installed via gravity from the ground surface. A proposed construction detail for the monitoring wells is included in Enclosure A. The location of the wells is illustrated in Figure 2. Destruction of Geoprobe and Hand Auger Soil Borings, and Soil Vapor Probe Borin s The geoprobe and hand auger soil borings, and soil vapor probe borings will be backfilled with neat cement grout mixed at a ratio of one 94-pound sack of Portland cement to 5 to 10 gallons of potable water. Since the interval to be backfilled is anticipated to be dry and less than 30 feet in depth, the neat cement grout will be installed via gravity from the ground surface. If ground water is encountered in a Providing a Competitive Edge