SITE INFORMATION AND CORRESPONDENCE_FILE 2

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i) E San Joaquin County DIRECTOR Environmental Health epartment Donna Heran,ASSISTANT REHS { �o� ca ASSISTANT DIRECTOR f = i , F2� 600 East Main St r et Laurie Cotulla, REHS : i ; MU" Stockton, California 95 02-3029 PROGRAM COORDINATORS •'. Carl Borgman, REHS Cq •.: ;:-:. AP Website: www.s ov.or /ehd Mike Huggins,REHS, RDI (�FORta 19 Margaret Lagorio,REHS Phone: (209) 468-34.20 Robert McClellon,REHS Fax: (209)464-01313 Jeff Carruesco, REHS, Rol Kasey Foley, REHS I1C WILLIAM BERGVALL DEC 14 Z FORMER AMERICAN FOREST PRODUCT 2977 YGNACIO VALLEY ROAD, 4241 WALNUT CREEK, CA 94598 RE: FORMER AMERICAN FOREST PRODUCT 2601 WEST LANE STOCKTON CA San Joaquin County Environmental Health Depar ment (EHD) has reviewed site data and the Revised Draft Work Plan and Prelimina Site Hydrologic Conceptual Model Additional 1,2-DCA Investigation (WP) dated May4, 2007, submitted on your behalf by URS Corporation Americas (URS) and has the following comments. In the WP, URS proposes to investigate data gaps for 1,2-dichloroethane (1,2-DCA) by installing four monitoring wells DMW-10, DMW- 1 downgradient to the north, and DMW-12, and DMW-13 crossgradient to the east and west. The proposed construction of these wells is to be similar to monitoring well MW-9, screen interval 60 to 70 feet below surface grade (bsg), which is in the intermed ate ground water zone approximately 52-72 feet bsg. The DMW-9 water sample contain and 24 micrograms per liter (,Ug/1) 1,2- DCA during 1s'quarter 2007. EHD approves the proposed installation of DMW-10, DMW-12, and DMW-13 but does not approve DMW-11. The proposed location ar DMW-11 is downgradient from DMW-10 and would not be a useful data point if D W-10 shows no impact of 1,2-DCA. If DMW-10 is shown to be impacted, an additional downgradient monitoring well may be appropriate. Upon review of site data, it appears that 1,2-DCA has not been adequately delineated in the shallow ground water zone approximately 32 to 52 feet bsg or in the deeper groundwater zone approximately 80 to 90 feet bsg. As for the shallow groundwater zone, DMW-6 (screened 32 to 52 feet bsg) contained 19 gll 1,2-DCA during first quarter 2007 and is delineated toward the southwest by DMW- (screened 30 to 65 feet bsg) which has not been impacted by 1,2-DCA. There are no other monitoring wells on-site screened in this shallow ground water zone. EHD recommends that additional groundwater monitoring wells be installed to delineate 1,2-DCA impact in the shallow g Per g round water zone. As for the dee groundwater zone, DMW-8 (screened 80 to 90 feet bsg) has shown no impact of 1,2-DCA. However, DMW78 is not located in the impacted source area and is screened infine grained soil, therefore, the vertical delineation of 1,2-DCA is not convincingly demonstrated. EHD recommends that a CPT boring for grab water samples be advanced in close proximity to the source area to delineate the vertical extent of 1,2-DCA impacted groundwater.