CORRESPONDENCE_1982-1983 - Laserfiche WebLink

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August 26, 1983 Project 116-1.4 - 2 - 3. Drain pipe perforations are placed only along the under side of the drain pipe as a mechanism to mimimize clogging or siltation from suspended solids. Each round of perforations will contain three holes separated by 450 angle spacing. Each round will be spaced at 6 inches from the previous round. The leachate drain pipe will be underlain by a minimum four inch thickness of Class 2 permeable drain material. The drain pipe will be covered by eight inches of Class 2 permeable drain material and one additional foot of the drainage blanket which covers the entire trench floor. 4. The two leachate drain cross sections shown on Figure 2 include the smaller scale drawing design to show the drain trench, the drain pipe, the filter blanket and the slope of the trench floor with respect to the east trench wall. The other design detail is an enlargement of the first and is intended only to show the perforation detail in the pipe and the angle of separation between the drilled perforations. The drain trench will be 1 foot deep and 1.5 feet wide. 5. The additional dimensions requested will be added to the drawings and attached to this communication. 6. Directional indications will be provided on Plate 1 as requested. The following comments relate to the leachate retention pond and provide the clarification requested: - The leachate retention pond was sized using rainfall records from the winter of 1982-83 because these data exceed the 100 year frequency event. For this reason we have designed the pond to hold 24 inches of accumulated rainfall in both the retention pond and the waste retention area. An additional 2 feet of freeboard is included to . provide an additional safety factor against overflow. - Based upon our telephone conversation of this date, we have decided to use a 20 mil, low density polyethylene liner in the leachate retention pond. This liner will be fabricated off site by utilizing the method of heat treating along seams to effect a proper seal. The seams will be placed vertically with respect to sidewall embankments. The pond liner will contain no horizontal seams which can be easily separated when a load is placed on the liner. The 20 mil liner, if necessary, can be vented along the upper edge of the embankment wall if wind billowing and subsequent tearing becomes a problem. The 20 mil liner will be anchored in an anchor trench with GBetac_ lssociates