Table 10—Periods of Operation, and Quantities Filtered.
Month.Number of filter runs ended after:Number of days since previous:Million gallons filtered since previous:
Scraping.RakingScraping.Raking
Scraping.Raking.Max.Min.Ave.Max.Min.Ave.Max.Min.Ave.Max.Min.Ave.
1909.
July140894467.4000229.01106.27163.289000
August80745160.4000175.54124.94152.581000
September130985368.3000237.52114.37161.702000
October185813259.9433339.4206.0978.78132.35996.5071.5182.708
November82794453.4473742.0168.1982.32112.60399.0090.2394.615
December34626161.3635057.3135.77128.33132.647144.35106.11125.940
1910.
January94957988.0887277.0204.38146.58178.461189.48152.33170.735
February14999999.0935171.0205.73205.73205.730192.98118.85158.890
March34120110113.7108101104.3275.96257.36265.493249.68224.49238.993
April10121266284.81292165.3295.96104.13181.972307.5745.22142.448
May32863869.7553243.5186.6481.66150.230102.1569.7985.978
June1321006179.712978103.5213.70130.85171.059181.25167.84174.540
Year 1909‑10103391263271.11292166.6295.9681.66159.151307.5745.22143.832
Fiscal years:
1905-067101953891.1000497.45116.66240.379000
1906-0710141992477.0321421.7466.1269.76220.693103.2832.1376.870
1907-08143771801154.963728.6477.1928.20146.912165.2517.0875.775
1908-09128501351149.9931334.2298.0839.26125.617244.1941.4188.439

In re‑sanding a filter, it is first filled with water to the proposed depth of the sand layer. The outlet end of the hose is connected to a 3‑in. pipe which is supported on a boat, and the sand is discharged through this pipe at the point required. Work is first begun at the far end of the filter, and it is gradually filled by swinging the boat from side to side and backing it by degrees to the front end.

At first it was feared that a small quantity of mud would be deposited on the surface of the old sand, and that this mud would ultimately cause subsurface clogging. For this reason, when this method was first adopted, a man was required to rake the sand very thoroughly in front of the discharge. Later, it was found that by giving the end of the discharge pipe a slope of about 45° downward from the horizontal, the force of the current of sand and water could be depended on to cut the old surface of sand to any required depth, and move it ahead together with the new sand, thus completely breaking up the possible mud layer between the old and new sand layers. After having used this method almost exclusively for 15 months, in which time eleven filters have been re‑sanded, and 24,531 cu. yd. of sand have been replaced, there seems to be no indication of an increased initial loss of head. The sand is very compact, and has no apparent tendency to separate into different sizes. The general appearance is similar to that of very fine sand on the seashore. The filters re‑sanded in this way have been considerably more efficient than those in which the sand was replaced with carts, and as yet, no harmful results have been noted. The rate at which the sand is replaced is shown in [Table 12], and the cost of labor for sand handling is given in detail in [Table 14], which shows that quite a perceptible saving has been effected by the hydraulic method.

The figures showing the cost for sand handling do not include any charge for the quantity of water used, that item having been carried on the pumping‑station account.

Table 11—Quantities of Sand Removed.
Month.No. of filters scraped when last treatment was:Cubic yards when last treatment was:Depth, in inches, when last treatment was:
Scraping.Raking.Scraping.Raking.Scraping.Raking.
Max.Min.Ave.Max.Min.Ave.Max.Min.Ave.Max.Min.Ave.
1909.
July140338121190.60002.510.901.415000
August80356149218.50002.651.111.631000
September8052497178.60003.900.721.330000
October9515093115.8301121169.01.120.690.8622.240.901.256
November2213488111.013281106.51.000.650.8250.980.600.790
December02000133126129.50000.990.940.965
1910.
January24155112133.5195121147.81.150.830.9901.450.901.100
February04000390160225.80002.901.191.678
March14489489489.0262179214.33.643.643.6401.951.331.593
April41217284119.3230146178.81.280.620.8851.711.091.331
May12320320320.0249241245.02.382.382.3801.851.791.820
June02000203190196.50001.511.411.460
Year 1909-10493752484176.739081181.03.900.621.3142.900.601.373
Fiscal Years:
1905-0671060071250.00004.470.531.799000
1906-0794253652259.0398276337.04.000.561.9312.952.052.500
1907-08815352746190.241135118.43.920.211.5073.060.210.881
1908-09925058055169.547281177.54.310.411.2593.510.601.317
Table 12—Rates of Sand Handling.
DateSand removed from filters.Sand replaced in filters.
Ejector hours.Cubic yards of sand removedAverage rate in cubic yards per hourEjector hours.Cubic yards of sand removedAverage rate in cubic yards per hour
1906.
April492535.2.........
May3802,5116.6.........
June5673,2805.8.........
July9315,3765.8.........
August1055335.1.........
September3151,8926.0.........
October1,0675,1735.8.........
November1689355.6.........
December2031,0735.3.........
1907.
January3992,9747.3.........
February1401,1398.1.........
March1158787.6.........
April4273,1037.3.........
May1339397.0.........
June1056746.4.........
July7466.6.........
August905746.4.........
September3061,3966.5.........
October2731,7016.2.........
November2021,2586.8.........
December3042,1385.9.........
1908.
January5463,7086.8.........
February987767.9.........
March3152,8329.0.........
April4693,7758.1.........
May1821,4147.8.........
June2802,0577.4.........
July280-1/22,6839.6.........
August327-1/22,8088.6.........
September4023,3718.4.........
October3082,6968.7.........
November47-1/23337.0.........
December153-3/41,2688.3.........
1909.
January119-1/21,0558.8.........
February161-1/21,4799.2.........
March1441,46510.2.........
April214-3/42,26010.51882,40512.8
May219-3/42,22310.11902,19611.5
June3553,0968.72433,05412.6
July312-1/42,7078.7425-1/24,0509.5
August218-3/41,9559.064-1/26209.6
September172-1/21,3607.94082,8427.0
October2031,8709.2261-1/42,3509.0
November543977.400...
December623826.200...
1910.
January1047036.800...
February106-1/21,0589.928-1/437113.1
March9898510.0721,00814.0
April268-3/42,85210.7134-1/42,15916.1
May58-3/469311.8171-3/43,04217.7
June58-3/464210.99-3/416617.0

The cost for pumping water for sand handling, including all labor, materials, and repairs, amounts to $0.06 per cu. yd. of sand ejected and washed, and $0.03 per cu. yd. for replacing.

In addition to the water used for carrying the sand which is being replaced, it is customary to keep a slight upward flow in the filter, thus using about 500,000 gal. of filtered water per day for this purpose. Assuming the value of this water to be the total cost for pumping, filtering, etc., or $3.80 per 1,000,000 gal., the cost per cubic yard of sand replaced would be about $0.02 when one ejector is used, and $0.01 when two are in operation.

It is not considered absolutely necessary to have an upward flow of water in the filter which is being re‑sanded, and it is not always done. It was used, however, as an additional safeguard against the formation of a stratum of mud between the old and new layers of sand while the hydraulic method was in an experimental stage.

The quantities of sand removed from the filters per scraping and the rates of sand handling are shown in Tables [11] and [12].