Los Angeles County Department of Land Development Division Draft
Drill at least one boring to a minimum depth of 30 feet below the planned bottom of each proposed percolation basin. Additional borings must be performed in the area to establish continuity of subsurface materials. Each exploratory boring must be logged by a certified engineering geologist or soils engineer by either downhole logging or via samples obtained through the use of a continuous sampler.
Create an excavation bottoming at the invert of the proposed basin. It is recommended that the consultants test a limited area through the use of an open-ended standpipe. The standpipe must be a minimum of 5 feet in diamater. The outer edge of the standpipe must be sealed in order to eliminate water loss from around the base.
Presaturate the excavation, via the standpipe, for at least one week prior to performing testing. Maintain a constant head of at least 18 inches of water in the standpipe at all times during the presoak period.Presaturate the excavation, via the standpipe, for at least one week prior to performing testing. Maintain a constant head of at least 18 inches of water in the standpipe at all times during the presoak period.
Perform percolation testing using sediment-laden water. A minimum sediment load of 1000 Nepthelometric Turbidity Units (NTU) is required. Sediment loading must be carred out by directly adding sediment to the standpipe based upon water usage and the amount of load required to produce the required NTU. This must be accomplished on a daily basis. The sediment shall be collected from a nearby source area and shall be screened to reflect the anticipated sediment load grain size distribution. Maintain a constant 18 inches of head in the standpipe and record usage utilizing a continuous data logger.
Once the usage stabilizes continue testing for a minimum of two weeks. Stabilization is defined as 2 weeks of consecutive daily readings with average variations of no more than 10 percent of the daily usage in gallons. In addition the mean trend line of the readings after stabilization must remain constant (<1% deviation).
Allow sediment water to percolate completely and perform the recommended annual maintanence procedures on the test area.
Perform a retest utilizing the same methodology as described in the Testing above, once maintance has been performed.
Perform an additional retest utilizing the same methodology as described above, but without maintenance of the basin.
Based on the results of testing the consultant must recommend a long-term percolation rate (in inches per day) to be utilized in the design of the percolation basin. The basis of recommendation must be the result of the retest utilizing maintenance. (which retest - with or without maintenance?)
Prepare and submit a report which discusses the testing procedures, includes conclusions, and provides recommendations for maintenance.
Land Development Division must be notified at least 72 working hours prior to initiation of testing.
Basins will not be approved in areas that will receive fill during grading operations.