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YVAfC ATC Associates Inc. 1]17 Lone Palm Avenue, Suite 201 Modesto,California 95351 209-579-2221 ASSOCIATES INC. Fax: 209-579-2225 that impacted groundwater had not been delineated vertically at the source area or north of MW-2. In correspondence dated May 21, 2009, the EHD noted that contaminants of concern had only been detected in groundwater samples collected from monitoring wells MW-2 and MW-3 since July 2006. Consequently, the EHD approved a change in the monitoring to the following: Monitoring Sampling Analytes Wells Frequency MW-2, MW-3 Semi Annually TPHg , BTEX Q2 /Q4 MW-1, MW-4, MW-5, and MW-6 Biannually TPHg, BTEX 02 -Odd ears TPHg = Total Petroleum Hydrocarbons —gasoline z BTEX = Benzene, Toluene, Ethylbenzene, and total Xylenes On December 2, 2009, Ms. Vicki McCartney and Mr. Nuel Henderson of the EHD met at the site with Mr. Gerald Thiemann, the site owner, and Ms. Jeanne Homsey and Mr. Mike Sonke of ATC. Following review of the previously completed investigative work of the site, Ms. McCartney and Mr. Henderson communicated that additional delineation of the dissolved-phase petroleum hydrocarbon plume in the groundwater north of the former tank pit was needed before the site could be presented for closure to the Regional Board. ATC responded with Additional Investigation Work Plan, dated January 14, 2010, which detailed the proposed activities associated with advancing two vertical soil borings at depths of approximately 38 and 63 feet bgs in two locations to collect groundwater samples. One location was proposed directly north of MW-2 and the second location was to be directly north of former boring CPT3-35. The work plan also included provisions for a third pair of borings to be advanced to the west if the groundwater samples obtained directly north of MW-2 contained significant concentrations of petroleum hydrocarbons. The EHD approved this work plan in correspondence dated March 2, 2010. On April 9, 2010, ATC supervised the advancement of two vertical adjacent hydropunch borings (HP4a and HP4b) approximately 55 feet north of the site to depths of approximately 38 and 63 feet bgs, respectively. Adjacent borings HP4a and HP4b were advanced on the north side of Second Street, directly gorth of existing well MW2. On April 13, 2010, boring HP5a was advanced to a depth of 3feet bgs, on the north side of Second Street, north of the former UST location and existing well MW3. On May 11, 2010, boring HP5b was advanced adjacent to HP5a. Geoprobe@ technology was used to advance borings HP4a and HP4b. In addition, hollow stem augers were utilized by Precision Sampling to advance borings HP5a and HP5b. This change in methodology was required due to difficult drilling conditions at depth which prevented the extensive utilization of direct push methods. Groundwater samples were collected from these borings and subsequently analyzed for TPHg by EPA Method 8015M and BTEX by EPA Method 8260B. Results were reported in ATCs Summary Report of Additional ; S:\Enviromental\62605-Thiemanns\REPORTS\WP-Well Abandonment 3