Transactions of the American Society of Civil Engineers, vol. LXXII, June, 1911 / Water Purification Plant, Washington, D. C. Results of Operation.

by American Society of Civil Engineers; E. D. Hardy

Table 2—Tons of Suspended Matter Entering System, Etc.

Month.	Amount that would have entered the system if the gates had been left continuously open.	Number of hours gates were closed.	Amount shut out.	Amount deposited in Dalecarlia Reservoir.	Amount deposited in Georgetown Reservoir.	Amount deposited in McMillan Park Reservoir.	Amount entering filtration plant.	Total.
1909.
July	318	32.0	3	0	125	74	116	318
August	146	47.0	1	0	78	38	29	146
September	97	57.0	7	21	13	38	18	97
October	61	90.5	8	7	9	25	12	61
November	50	60.0	4	13	5	17	11	50
December	370	99.0	126	108	33	59	44	370
1910.
January	2,410	136.0	1,109	1,020	67	117	97	2,410
February	839	117.5	481	126	56	75	101	839
March	208	7.5	13	43	15	13	124	208
April	321	65.0	17	195	43	43	23	321
May	197	84.5	58	54	22	24	39	197
June	1,505	124.0	786	535	49	88	47	1,505
Total	6,522	920.0	2,613	2,212	515	611	661	6,522

In order to relieve the situation at such times, the expedient of raking was tried. This was first attempted with the filters filled with water; the effluent was first shut off in order to prevent a downward flow of water, and the filter was then raked or harrowed from boats. This method was not satisfactory, however, as the work was neither as uniform nor as thorough as necessary. Later, the filters were drained to the necessary depth, and the surface of the sand was thoroughly stirred with iron garden rakes. The filters were then filled with filtered water through the under‑drains and put in service.

This latter method proved so satisfactory that it has been resorted to at all times when the work was at all pressing. When the runs were of short duration, and the depth to which the mud had penetrated the filter sand was slight, a raking seemed to be nearly as effective in restoring the filter capacity as a scraping; it could be done in 8 hours by 3 laborers, and there seemed to be no ill effects from lowered efficiency.

Table 3—Turbidities.
Average by Months.
(United States GeologicalSurvey Standard.)

Month.	Great Falls.		Reservoirs:
			Dalecarlia Outlet.		Gerogetown Outlet.		McMillan Park Outlet.		Filtered water.
	Max.	Ave.	Max.	Ave.	Max.	Ave.	Max.	Ave.	Max.	Ave.
1905.
October	100	36	40	21	32	18	20	11	4	1
November	35	19	34	19	22	14	14	11	3	1
December	1,500	199	250	84	150	74	95	39	14	6
1906.
January	700	94	180	60	120	60	85	52	20	12
February	120	45	85	41	55	29	35	22	5	3
March	1,750	272	350	181	120	56	90	46	8	6
April	1,270	167	180	72	95	58	75	46	12	7
May	600	56	50	20	45	16	34	10	3	2
June	1,700	303	500	125	450	94	180	41	13	2
July	1,000	130	180	54	150	47	250	43	13	3
August	1,530	375	250	112	95	66	65	45	5	2
September	120	33	180	34	95	28	75	25	7	2
October	1,025	127	110	37	60	24	55	21	1	1
November	160	27	75	20	45	16	24	13	1	1
December	600	69	110	31	80	28	80	26	8	2
1907.
January	400	135	150	70	110	75	70	53	11	7
February	55	26	26	15	36	16	40	17	5	2
March	950	248	180	77	130	70	90	57	7	4
April	200	47	80	33	60	30	45	24	4	2
May	130	29	40	18	26	15	14	9	1	1
June	400	104	160	48	75	32	40	18	1	1
July	600	114	130	61	78	47	45	31	1	1
August	800	73	130	35	85	26	30	14	1	0
September	600	129	[1]	[1]	150	51	70	28	1	0
October	75	32	[1]	[1]	65	28	75	26	4	0
November	300	97	[1]	[1]	100	45	45	23	2	1
December	680	135	[1]	[1]	180	61	100	46	10	4
1908.
January	2,100	202	340	73	250	82	160	65	20	7
February	3,000	302	300	52	150	52	75	32	7	4
March	300	91	150	78	100	68	65	42	5	4
April	75	23	65	41	37	27	26	20	3	2
May	2,000	172	130	48	85	37	50	20	1	1
June	400	40	70	29	40	24	30	18	1	1
July	1,500	149	...	74	170	44	75	15	0	0
August	900	129	200	[1]	150	56	85	39	2	1
September	75	24	[1]	[1]	50	19	35	18	0	0
October	95	20	[1]	[1]	55	18	28	15	0	0
November	24	11	[1]	[1]	20	11	19	10	0	0
December	20	9	17	11	14	9	10	7	0	0
1909.
January	400	72	95	32	60	23	25	16	4	1
February	650	194	120	64	90	51	55	35	4	3
March	250	51	[1]	[1]	90	44	60	37	8	4
April	750	98	[1]	[1]	130	42	76	31	2	1
May	480	57	[1]	[1]	30	19	30	12	2	1
June	650	141	[1]	[1]	120	51	80	30	1	0
July	400	48	[1]	[1]	215	46	120	35	2	1
August	180	23	[1]	[1]	50	17	18	9	0	0
September	26	16	24	14	[1]	[1]	25	6	0	0
October	14	10	15	10	11	9	8	4	0	0
November	11	9	11	8	10	8	6	4	0	0
December	600	63	110	31	80	28	50	15	3	0
1910.
January	3,000	357	200	58	150	53	115	30	5	2
February	3,000	143	150	55	120	50	100	36	7	4
March	210	36	100	35	95	38	100	43	9	5
April	350	55	100	25	55	18	25	8	1	0[2]
May	300	33	55	19	50	17	28	13	1	0[2]
June	1,500	246	180	42	110	37	50	16	1	0[2]
Fiscal years.
1905-06[2]	1,750	133	500	70	450	47	180	31	20	5
1906-07	1,530	114	250	46	150	37	250	29	13	2
1907-08	3,000	117	340	53	250	45	160	31	20	2
1908-09	1,500	79	200	50	170	32	85	22	8	1
1909-10	2,100	86	200	30	215	29	120	18	9	1

[¹ Reservoirs out of service.]

[² October to June 30th.]

Table 4—Bacteria.
Averages by Months.

Month.	Reservoirs:
	Dalecarlia Inlet.	Dalecarlia Outlet.	Georgetown Outlet.	McMillan Park Outlet.	Filtered water.
1905.
October	...	...	...	210	80
November	...	...	...	150	27
December	...	15,500	...	3,800	60
1906.
January	...	2,800	...	1,500	39
February	2,900	4,100	1,800	550	16
March	1,800	1,100	900	650	19
April	3,300	1,700	700	400	22
May	425	210	95	65	17
June	7,900	4,600	325	220	17
July	13,500	600	475	160	26
August	8,700	1,100	1,200	190	14
September	425	250	140	135	14
October	2,300	950	650	270	16
November	1,800	1,100	1,200	220	12
December	6,900	3,800	3,600	700	45
1907.
January	4,400	2,400	2,200	950	70
February	1,000	950	1,000	700	45
March	11,500	8,300	7,200	3,600	65
April	3,700	2,100	1,400	475	21
May	750	350	325	130	26
June	2,300	1,000	600	100	18
July	2,700	575	350	160	17
August	3,000	275	425	80	17
September	6,200	[1]	1,900	230	32
October	1,400	[1]	950	275	27
November	8,900	[1]	6,600	1,500	27
December	16,000	[1]	9,600	4,300	190
1908.
January	11,000	8,700	9,400	3,700	190
February	11,500	6,000	5,000	2,800	75
March	4,600	4,000	2,900	1,300	30
April	700	450	250	120	13
May	9,500	1,100	650	325	17
June	750	120	110	95	12
July	4,900	...	400	150	8
August	1,600	325	300	100	12
September	325	[1]	200	80	11
October	375	[1]	325	140	8
November	550	[1]	300	200	12
December	800	750	375	170	23
1909.
January	11,000	2,700	1,600	700	31
February	8,000	3,500	2,400	1,300	60
March	3,800	[1]	2,600	1,000	39
April	2,200	[1]	1,400	550	12
May	900	[1]	350	140	16
June	3,400	[1]	1,200	170	21
July	550	[1]	500	250	33
August	400	[1]	325	55	18
September	325	240	[1]	70	18
October	350	275	250	130	20
November	600	500	500	180	13
December	21,000	9,100	5,900	4,500	250
1910.
January	76,000	78,000	88,000	52,000	800
February	45,000	35,500	31,000	17,500	350
March	9,900	7,600	7,400	4,800	80
April	7,900	4,100	3,500	650	29
May	1,230	810	830	448	28
June	3,660	930	800	324	27
Fiscal years:
1905-06	3,300[2]	4,300[3]	750[4]	850[2]	33[2]
1906-07	4,900	1,900	1,700	650	31
1907-08	6,360	2,700	2,900	1,300	55
1908-09	3,400	2,000	950	400	21
1909-10	14,300	13,900	10,900	6,890	143

[¹ Reservoirs out of service.]