§ 19.07.025. Appendices.

APPENDIX A. ON SITE WASTEWATER TREATMENT SYSTEM REQUIREMENTS FOR SECONDARY DWELLING UNITS ON PARCELS LESS THAN TWO ACRES IN SIZE

The regional water quality control board criteria for a new septic system specifies a maximum density of one residence per acre unless soil and other constraints for sewage disposal are found to be "particularly favorable". Septic system density may then be increased to one residence per half acre.

(1)

Separate treatment systems shall be used for each dwelling. An application, plans and a site evaluation report meeting the requirements of this title shall be submitted for each system.

(2)

All other technical requirements of this title, and Titles 22 and 23 shall be met.

APPENDIX B. PERCOLATION TEST AND BORING PROCEDURES

Percolation and boring tests shall be performed by or under the supervision of a licensed qualified engineer.

(1)

Percolation test procedure.

a.

Test hole openings shall have an 8 12-inch diameter, or be 7 11-inches on the side, if square. The walls should be vertical.

b.

The bottom of the test hole should correspond with the bottom of the proposed trench and shall be covered with 2 inches of gravel.

c.

Presoak the test hole overnight, prior to testing. For sandy soils, presoak until water level stabilizes, see (2)a. below.

d.

The height of the water shall be refilled to initial height of between 8 and 10 inches over the gravel after each reading.

e.

The surface of the hole shall be uncompacted: any cobbles protruding from the surface shall be left in place.

(2)

Measurements.

a.

In sandy soils in which two consecutive measurements show that six inches of water seeps away in less than 25 minutes, the test shall be run for an additional hour with measurements taken every ten minutes, making sure to re-fill the hole after each measurement. The drop that occurs during the final ten minutes shall be used to calculate the percolation rate. Field data shall show the two 25 minute readings, along with the six 10 minute readings.

b.

In all other than sandy soils, pre-soak (fill) and wait overnight. If necessary, refill the hole the next day. Obtain at least 12 measurements per hole over at least 6 hours with a precision of at least 0.25 inch. Intervals between readings shall be approximately thirty minutes. The drop that occurs during the last 30 minutes is used to calculate the percolation rate. Field data shall show the twelve 30 minute readings.

(3)

Testing Procedure for Dry Wells (Seepage Pits) Performance Test.

a.

The hole diameter shall be between 6 and 8 inches. The test depth shall be equal to the depth of the proposed dry well, plus sufficient depth to prove proper setback to groundwater and impervious material.

b.

Carefully fill the hole with clear water to a maximum depth of 4 feet below the surface of the ground, or if cuts are anticipated, to the depth of the assumed inlet.

c.

All holes shall be pre-soaked for 24 hours unless the site consists of sandy soils containing little or no clay. In sandy soils where the water on two consecutive readings seeps away faster than half the wetted depth in 25 minutes or less, refill the hole with water, and pre-soak for an additional two hours. After the two hour pre-soak, the test may then be run. The time interval between measurements shall be taken at ten minutes and the test run for one hour. Refill to original depth after each reading.

d.

For all other soils, the percolation rate measurement shall be made on the day following pre-soak as described above. After 24 hours have elapsed, refill the hole to the proposed inlet depth. The fall of water should be measured every half hour over a five hour period. Refill the hole after each half-hour reading. During the last or the sixth hour, do not refill the hole after the half hour reading. Be sure to check the total hole depth every half hour as well to see if any caving has occurred.

e.

Readings will be in min/inch just like they are for leachlines. Rates are set by the regional water quality control board. Utilize 0.3 gallons per square foot per day for disposal rate, and 375 gallons per day average daily flow per household, up to four bedrooms.

f.

Seepage pits will not be allowed when percolation rates are slower than 55 minutes per inch.

(4)

Exploratory Borings. An exploratory boring is a hole excavated or drilled in the area where the disposal field is proposed in order to determine the type of soil, moisture content, and depth of the seasonal high water table or impervious material.

a.

All borings must extend to a minimum depth of ten feet below the bottom of the proposed disposal system so as to determine the depth of the water table, bedrock, and all impervious material within ten feet of the bottom of the disposal system. Minimum depth of any boring is 15 feet or stated refusal.

b.

When percolation results are faster than 1 minute an inch, the exploratory boring shall be drilled to a depth of 50 feet below the depth of the proposed disposal system. For percolation results between 1-4 minutes an inch, the boring shall be drilled to a depth of 20 feet below the proposed disposal system.

c.

A log of the soil profile shall be conducted and included as part of the written percolation test.

d.

All borings used to check for groundwater shall stay open a minimum of 24 hours prior to the final reading and groundwater check. Water levels are to be recorded at the highest discovered level following the 24 hour period. If any groundwater is encountered that may affect the subsurface sewage disposal, an evaluation by a qualified professional, shall be given in the conclusion section of the percolation report.

e.

Measurements of depth to seasonal high groundwater shall be conducted from November 1st to April 1st unless otherwise specified by the building official.

f.

In areas with seasonal high groundwater, a groundwater level monitoring well shall be installed to a minimum depth of ten feet in the area of a proposed wastewater dispersal system. Groundwater monitoring wells shall be a minimum of 3 inch PVC pipe and shall have a removable cap. The top 18 inches around the pipe shall be sealed with Bentonite or other suitable sealer to prevent surface pollutants from intruding into the well. Below 18 inches, the pipe shall be perforated. Monitoring wells shall not be deeper than 15 feet, unless required by the building official. If an impermeable layer is present at a depth of less than ten feet below the ground surface, the depth of the groundwater level monitoring well shall be decreased to the depth of the impermeable layer.

(Ord. No. 3343, § 1, 12-6-16)