CORRESPONDENCE_2012 - Laserfiche WebLink

Home Browse Search

0 0 W J� Mr. Michael Carroll - 2 - 10 May 2012 Corral Hollow Sanitary Landfill 2. Hydrologic Report: The hydrologic report (hereafter"Hydro Report") states that a landfill v-ditch collects and drains precipitation from approximately 16.98 acres. The peak calculated flow volume in the landfill v-ditch from a 24-hour 100-year storm event is 23.34 cubic feet per second (cfs). The Discharger proposes that this landfill v-ditch be lined with erosion control blanket prior to hydroseeding. The specification for the North American Green C125 Erosion Control Blanket states that it has a functional longevity of 36 months (3 years). On the other hand the Hydro Report states that a Caltrans v-ditch drains approximately 4.33 acres and has a peak calculated flow volume of 8.42 CFS during a 24-hour 100-year storm event. Yet, the Caltrans v-ditch which has less peak flow volume is a concrete lined v-ditch. Also, the Caltrans v-ditch drains 1/4 of the area of the landfill v-ditch (4.33 acres versus 16.98 acres) yet has 1/3 the runoff(8.42 cfs versus 23.34 cfs). It is unclear if the software program determined that more precipitation would percolate into the ground at the previously covered landfill area than in the Caltrans area, thus reducing the flow volume in the landfill v-ditch. Another major concern is that the landfill v-ditch which conveys higher precipitation flows than the Caltrans v-ditch yet is lined with a less permanent erosion resistant material will have a constant erosion control maintenance issue in preventing rills and gullet's from forming in the landfill v-ditch during the life of the project. 3. Drawings-Sheet 6 Detail#4: Detail#4 shows that the Geocomposite Drainage Layer Will be extended to contact the existing 1 foot barrier soil. This configuration provides a leakage path. An alternative method that might be considered is shown in the attached markup drawing. The Geocomposite Drainage Layer extension is replaced with LLDPE Liner underneath the drainage layer. Secondly, the barrier soil is extended over the LLDPE Liner to form an overlapping joint. 4. Construction Quality Assurance Plan Sections 5.1 & 5.2: The conformance testing for the Geocomposite Drainage Layer (5.1) and Linear-Low Density Polyethylene (LLDPE) Geomembrane calls for"minimum of one test per 100,000 square feet installed'. The total installed area is less than 2 acres (87,120 sq ft). It is unclear if the Discharger plans to only take one sample of each material for conformance testing? For less than 100,000 sq ft of total installed area (small project) it is recommended that the Discharger take more than one sample for comparison of the results. It is our understanding that the manufacturer's recommendation of one sample per 100,000 square feet is based on their assumption that most projects are ,typically larger than 2 acres at landfills. 5. Shell Oil Pipeline Access: The previous design had provisions to place barrier panels such that the panels could be readily removed to access the Shell pipeline. It is not clear if this design feature has been deleted in order to maintain continuity and strength of the LLDPE Liner. It is not clear what arrangements have been made with the owners of the Shell pipeline to provide access/maintenance of the pipeline and how this would affect the performance of the landfill cover extension project. 6. Conformance with Manufacturer's recommended site preparation and installation procedures: Board Staff has not verified that the site preparation and installation procedures in the Discharger's specifications conform to the liner manufacturer's installation specifications. Board Staff has relied on the Discharger/Consultant's professional responsibility to translate the manufacturer's specifications concisely and completely into the Discharger's design and construction quality assurance specifications. Any deviations from the manufacturer's installation specifications should be immediately brought to Board Staffs attention in an accompanying letter.