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R n 4 x THOMAS M. GAU DIRECTOR AP FRITZ BUCHMAN DEPUTY DIRECTOR MICHAEL SELLING DEPUTY DIRECTOR JIM STONE DEPUTY DIRECTOR ROGERJANES BUSINESS ADA41NISTRATOR Mr. Marty Hartzell, PG, CHG Senior Engineering Geologist Title 27 Permitting and Mining Unit Regional Water Quality Management Board 11020 Sun Center Drive #200 Rancho Cordova, California 95670-6289 May 14, 2014 11 P. O. BOX 1810 -1810 E. HAZELTON AVENUE STOCKTON, CALIFORNIA 95201 (209) 468-3000 FAX (209) 468-2999 www,sjgov.org/pubworks SUBJECT: ADDRESSING COMMENTS TO FINAL CONSTRUCTION QUALITY ASSURANCE REPORT, CORRAL HOLLOW SANITARY LANDFILL, SAN JOAQUIN COUNTY Dear Mr. Hartzell: This letter is sent in response to your letter of March 10, 2014 regarding questions about the Final Construction Quality Assurance (CQA) Report for the Corral Hollow Landfill Closure Extension Project. In your letter you requested that: 1. Verify that the integrity of geomembrane liner was not compromised due to over -compaction, use of improper particle size materials, and failure to install a minimum 12 -inch loose lift cover. County Response: The integrity of the geomembrane liner has not been compromised. According to the Daily Inspection Reports the loose lift cover was 18 -inches, and the maximum particle size was two (2) inches. The statements in the CQA report to the contrary were incorrect and did not reflect actual construction procedures; in fact the closure was constructed per the approved technical specifications. Please see Attachment A, responses from the County's engineering consultant GLA, for further clarification. Telephone conversations with Mr. Vinoo Jain of CVRWQCB indicated a concern that compaction of the vegetative soil over 88 percent could have threatened the integrity of the geomembrane, based on an interpretation that a maximum compaction limit of 88 percent was intended to protect the geomembrane. In actuality, the intended lower compaction was to facilitate vegetative growth rather than protect the geomembrane. To address this concern however, the County asked its consultant CB&I Environmental to analyze the geomembrane strength and the stresses applied to it by the equipment during compaction operations. This analysis verifies that the integrity of the geomembrane was not compromised. In fact, a factor of safety of two (2) is provided with the compactor directly on the geomembrane. With the specified minimum one -foot -thick cover soil lift between the compactor and geomembrane, a factor of safety above seven (7) is provided. Please see Attachment B, responses from the County's engineering consultant CB&I, for further clarification.