KGS--CQS 12--Organic carbon and trihalomethane formation potential--Results

Kansas Geological Survey, Chemical Quality Series 12, originally published in 1991
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Results and discussion

Analytical results

Table 3 shows the concentrations of TFP and TOC in the untreated samples. The concentrations of the four individual THM species are given in µg/L and then summed to give TFP in µg/L and micromoles per liter (µM). The percentage chlorine (%Cl) is the percentage of the halogen atoms in the THMs composed of chlorine, the balance being bromine. The yield, in µmol of TFP per mg of TOC, is a calculated value. The chlorine demand is the amount of free chlorine consumed during the 96-hr incubation period in the subsample used for TFP analysis.

In table 3, as well as tables 4-6, a number of the values reported are below the detection limit. In computing the mean, sample standard deviation (SD), geometric mean (G. Mean), and median for a constituent, values less than the detection limit were assumed equal to one half of the detection limit. Geometric means and medians are reported because the concentrations of many constituents were not normally distributed.

Table 3--TFP and TOC in untreated ground-water samples.

Sample	CHCl₃ µg/L	CHCl₂Br µg/L	CHClBr₂ µg/L	CHBr3 µg/L	TFP			TOC mg/L	Yield µmoles/mg	Chlorine Demand mg/L
Sample	CHCl₃ µg/L	CHCl₂Br µg/L	CHClBr₂ µg/L	CHBr3 µg/L	µg/L	µM	%Cl	TOC mg/L	Yield µmoles/mg	Chlorine Demand mg/L
1	8.9	12.0	8.7	1.3	30.9	0.195	71	0.69	0.282	1.71
2	85.2	14.1	3.4	<0.1	102.7	0.816	95	3.31	0.247	10.61
3	91.2	22.8	7.2	<0.1	121.2	0.938	93	2.56	0.366	7.20
4	9.0	3.7	1.6	<0.1	14.3	0.106	88	0.36	0.294	1.95
5	1.7	2.2	9.0	12.7	25.6	0.121	31	0.48	0.252	7.20
6	7.5	16.2	28.5	19.4	71.7	0.375	47	1.04	0.361	1.71
7	36.1	32.2	24.4	4.9	97.6	0.635	74	1.90	0.334	2.44
8†	27.9	21.9	30.7	15.8	96.3	0.577	64	1.37	0.421	1.77
9	26.7	28.4	23.3	5.6	83.9	0.530	71	2.19	0.242	2.81
10	8.3	13.4	13.1	3.7	38.4	0.228	63	1.03	0.221	3.72
11	37.0	28.6	18.7	3.3	87.7	0.588	78	1.90	0.309	7.44
12	3.4	4.5	4.5	2.4	14.8	0.087	62	0.41	0.212	0.37
13	3.2	2.5	3.0	2.7	11.4	0.067	62	0.31	0.217	0.24
14	4.0	3.2	2.3	0.2	9.7	0.065	77	0.30	0.217	1.22
15	4.3	7.3	7.6	3.0	22.2	0.129	60	0.85	0.152	0.61
16	27.3	20.1	14.2	2.5	64.1	0.429	78	1.52	0.282	2.14
17	4.1	13.6	24.9	19.1	61.6	0.312	42	1.06	0.294	1.65
18	9.5	8.7	5.6	1.0	24.8	0.163	76	0.87	0.188	6.83
19	6.1	3.9	3.9	<0.1	14.0	0.094	78	0.45	0.209	1.34
20*	64.2	29.2	12.7	0.8	106.9	0.780	87	2.84	0.275	9.88
21	1.2	5.3	27.0	44.9	78.4	0.349	21	1.20	0.291	3.17
22	3.4	6.7	12.4	4.4	26.9	0.146	52	0.58	0.252	0.98
23	9.1	10.2	8.7	2.0	30.0	0.188	70	0.83	0.227	3.90
24	2.8	4.4	4.8	2.3	14.3	0.083	60	0.52	0.159	0.24
25†	3.5	11.5	22.2	19.6	56.8	0.283	39	1.34	0.211	<0.06
26	6.5	12.6	15.3	4.6	38.9	0.222	58	0.72	0.308	0.61
27†	<0.1	3.3	7.6	7.4	18.3	0.086	30	0.47	0.183	<0.06
28	4.5	5.3	3.8	<0.1	13.5	0.087	74	0.55	0.159	<0.06
29	3.1	4.1	4.3	1.4	12.9	0.078	64	0.49	0.158	0.06
30	4.3	18.4	33.1	21.6	77.5	0.393	42	1.54	0.255	1.83
31	3.6	13.4	19.7	10.4	47.1	0.248	47	1.00	0.248	1.16
32	35.7	27.5	19.4	3.4	86.0	0.573	77	2.43	0.236	2.32
33	1.1	4.3	8.5	5.9	19.8	0.100	41	0.60	0.166	0.12
34	3.4	5.2	5.4	1.9	15.8	0.093	62	0.50	0.186	<0.06
35	11.0	10.7	7.9	1.0	30.6	0.199	74	0.88	0.226	1.22
36	3.6	3.1	1.6	<0.1	8.3	0.057	80	0.27	0.210	0.85
37	1.5	2.1	1.7	<0.1	5.3	0.033	71	0.21	0.158	<0.06
38‡	<0.1	0.4	1.4	3.9	5.8	0.025	16	0.29	0.086	>24.40
39	0.3	1.3	3.6	4.0	9.2	0.044	31	0.31	0.141	7.63
40	4.2	10.7	12.7	5.7	33.4	0.184	54	0.98	0.188	0.24
41	9.6	17.9	22.3	9.4	59.2	0.334	57	1.27	0.263	0.61
42	7.4	12.4	15.6	6.4	41.8	0.238	58	1.10	0.216	3.48
43	5.9	15.0	29.3	23.2	73.5	0.374	42	1.02	0.366	7.93
44	0.4	6.5	7.2	3.1	17.3	0.090	46	0.50	0.180	0.06
45	3.4	6.8	8.1	3.4	21.8	0.123	57	0.80	0.153	0.55
46	1.3	3.7	4.6	1.9	11.4	0.063	53	0.36	0.174	<0.06
47	1.3	11.6	58.2	107	178.0	0.784	19	2.14	0.367	ND**
48	7.2	4.3	2.0	<0.1	13.5	0.096	84	0.37	0.257	ND
49*	52.6	43.5	32.9	5.5	134.4	0.885	76	2.45	0.362	9.94
50	2.3	3.9	5.2	2.2	13.6	0.077	57	0.48	0.160	6.34
Mean	13.5	11.7	13.3	8.2	46.7	0.281	61	1.03	0.242	2.69
SD	20.9	9.5	11.5	16.7	39.5	0.250	18	0.76	0.070	3.09
G. Mean	5.4	8.5	9.2	2.2	32.5	0.192	58	0.81	0.232	0.95
Median	4.3	10.2	8.7	3.3	30.6	0.188	62	0.84	0.227	1.65
This sample was filtered through a glass-fiber filter (934 AH) to remove suspended solids. †Free chlorine was detected in the untreated sample (this was not checked in samples 1-23 or 36-50, except for sample 8). ‡No free chlorine residual was detected following chlorination, perhaps due to the high concentration of H₂S. Therefore, the TFP and chlorine demand data for this sample were excluded from all statistical summaries and correlations. *Not determined

Table 4 shows the terminal THM concentrations of the finished water samples collected from public-water supplies (i.e. those using chlorine to disinfect the water). A majority of the samples still contained free chlorine at the time the water was analyzed for THMs. Table 5 shows the instantaneous THM and TOC concentrations for the finished water samples.

Table 4--Terminal trihalomethane concentrations in finished water samples.

Sample	CHCl₃ µg/L	CHCl₂Br µg/L	CHClBr₂ µg/L	CHBr3 µg/L	Term. THM			Yield* µmoles/mg	Free Chlorine Remaining
Sample	CHCl₃ µg/L	CHCl₂Br µg/L	CHClBr₂ µg/L	CHBr3 µg/L	µg/L	µM	%Cl	Yield* µmoles/mg	Free Chlorine Remaining
1	4.7	8.5	9.8	3.7	26.7	0.153	59	0.222	yes
3	53.9	18.6	9.5	1.4	83.5	0.617	88	0.241	yes
4	0.5	0.9	0.6	<0.1	2.0	0.012	70	0.033	no
5	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	<0.004	yes†
6	<0.1	1.0	7.5	31.1	39.5	0.165	10	0.118	no
7	12.0	17.7	24.8	16.9	71.4	0.394	54	0.296	yes
8	20.5	19.0	23.1	6.2	68.8	0.423	68	0.338	yes
9	<0.1	0.2	0.2	<0.1	0.3	0.002	52	<0.001	no
11	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	<0.002	no
12	<0.1	1.5	2.0	0.9	4.3	0.022	42	0.032	yes
13	<0.1	1.3	2.2	2.1	5.6	0.027	33	0.159	yes
14	<0.1	2.1	1.9	0.7	4.7	0.025	47	0.147	yes
16	12.9	15.1	12.1	2.1	42.2	0.266	71	0.169	yes
17	14.4	14.8	10.5	1.4	41.2	0.267	74	0.267	yes
18	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	<0.005	no
20	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	<0.001	no
24	0.8	1.6	3.3	3.4	9.1	0.046	40	0.208	yes
25	1.5	5.8	17.5	19.9	44.7	0.211	30	0.155	yes
27	<0.1	0.8	2.5	3.4	6.7	0.030	24	0.178	yes
28	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	<0.007	no
30	5.7	17.5	25.4	13.4	62.0	0.329	48	0.212	yes
32	10.3	15.0	13.9	3.3	42.5	0.257	66	0.105	yes
36	2.9	2.4	1.4	<0.1	6.7	0.045	80	0.182	yes
37	0.7	1.3	1.4	0.4	3.8	0.022	61	0.136	yes
38	0.5	1.2	4.0	5.1	10.8	0.051	30	0.106	yes
39	<0.1	0.7	4.0	10.7	15.4	0.066	14	0.095	yes
40	0.4	2.6	7.1	6.9	17.1	0.081	31	0.072	yes
42	0.3	<0.1	<0.1	<0.1	0.3	0.003	100	0.002	no
45	0.2	<0.1	<0.1	<0.1	0.2	0.002	100	<0.001	no
49	91.9	42.7	17.8	1.9	154.2	1.123	87	0.459	yes
50	1.6	4.6	10.7	10.4	27.2	0.133	37	0.278	yes
Mean	7.6	6.4	6.9	4.7	25.5	0.154	54	0.136	-
SD	18.8	9.5	7.9	7.2	34.4	0.237	25	0.118	-
G. Mean	0.6	1.4	1.8	0.9	6.1	0.037	47	0.044	-
Median	0.5	1.5	3.3	1.9	9.1	0.046	52	0.136	-
*Based on the TOC concentration of the sample analyzed for instantaneous THMs (except for samples 49 and 50, in which case the yield was based on the TOC value of the raw water sample). †The detection of free chlorine in this sample may have been an artifact. It is more likely that this sample contained combined chlorine and enough iodide ion to cause monochloramine to be mistaken for free chlorine (see table 5).

Table 5--Instantaneous THM and TOC concentration in finished water samples.

Sample	CHCl₃ µg/L	CHCl₂Br µg/L	CHClBr₂ µg/L	CHBr3 µg/L	Inst. THM			TOC mg/L	Yield* µmoles/mg	Free Cl₂ (Field) mg/L
Sample	CHCl₃ µg/L	CHCl₂Br µg/L	CHClBr₂ µg/L	CHBr3 µg/L	µg/L	µM	%Cl	TOC mg/L	Yield* µmoles/mg	Free Cl₂ (Field) mg/L
1	0.7	2.4	3.7	1.8	8.5	0.045	48	0.69*	0.065	2.5
3	19.3	10.4	5.6	0.6	35.9	0.254	84	2.56*	0.099	2.5
4	0.5	0.6	0.5	0.0	1.6	0.010	73	0.36*	0.028	0.2
5	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	0.83	<0.004	0.2 (1.3)†
6	<0.1	<0.1	1.2	5.7	6.9	0.028	7	1.40	0.020	0.5
7	3.1	4.3	6.9	4.5	18.8	0.103	53	1.33	0.077	2.0
8	12.4	0.9	1.4	1.0	15.7	0.120	91	1.25	0.096	4.0
9	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	2.48	<0.001	0.2
11	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	1.93	<0.002	0.2
12	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	0.69	<0.004	1.7
13	<0.1	0.5	1.0	1.3	2.8	0.013	28	0.17	0.076	1.0
14	<0.1	0.2	0.4	0.3	0.9	0.004	34	0.17	0.023	2.0
16	0.6	1.3	1.8	0.6	4.3	0.023	55	1.57	0.015	2.7
17	1.1	0.7	0.8	0.9	3.5	0.021	64	1.00	0.021	1.5
18	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	0.64	<0.005	0.2
20	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	2.08	<0.001	1.0
24	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	0.22	<0.014	1.0
25	<0.1	0.8	2.9	5.0	8.7	0.038	20	1.36	0.028	2.0
27	<0.1	<0.1	0.5	1.1	1.6	0.007	12	0.17	0.041	1.3
28	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	0.42	<0.007	0.2
30	1.3	1.9	3.7	3.3	10.2	0.053	46	1.55	0.034	4.0
32	0.4	1.1	2.1	0.5	4.1	0.022	51	2.44	0.009	1.3
36	<0.1	1.1	0.2	<0.1	1.3	0.007	63	0.25	0.030	2.7
37	0.3	<0.1	<0.1	<0.1	0.3	0.002	100	0.16	0.015	2.7
38	<0.1	0.2	0.4	<0.1	0.6	0.003	46	0.48	0.006	4.0
39	<0.1	0.1	0.4	<0.1	0.5	0.002	41	0.69	0.003	1.3
40	0.4	0.1	<0.1	<0.1	0.5	0.004	95	1.12	0.004	1.2
42	<0.1	<0.1	<0.1	<0.1	<0.4	<0.003	-	1.34	<0.002	0.2
45	0.3	<0.1	<0.1	<0.1	0.3	0.002	100	2.61	<0.001	0.2
49	42.4	27.3	12.4	1.3	83.4	0.586	83	2.45	0.239	2.0 (2.5)t
50	1.4	0.9	0.9	<0.1	3.1	0.021	78	0.48*	0.044	4.0
Mean	2.7	1.8	1.5	0.9	6.9	0.045	58	1.13	0.032	1.6
SD	8.4	5.1	2.6	1.6	16.0	0.112	28	0.81	0.048	1.3
G. Mean	0.2	0.3	0.4	0.2	1.4	0.009	49	0.81	0.011	1.0
Median	<0.1	0.2	0.4	<0.1	1.3	0.007	52	1.00	0.015	1.3
* Raw water TOC (other TOC values were determined on the treated sample taken for analysis of instantaneous THMs). † The total residual chlorine concentration was greater than the free chlorine concentration (the total concentration is shown in parentheses).

Table 6 gives the results of the geochemical analyses. The laboratory pH was generally higher than the field pH, as would be expected with the escape of CO₂. A large difference between field and laboratory conductance might indicate precipitation of minerals from the water after sampling, but the values were generally close. Ionic balances were computed for these results, and the greatest deviation from electroneutrality (the difference between meq/L of anions and meq/L of cations divided by their sum) was 1.87%.

Table 6--Results of the geochemical analysis.¹

No.	Temp °C	pH Fld	pH Lab	Cond Fld	Cond Lab	Ca mg/L	Mg mg/L	Na mg/L	K mg/L	Sr mg/L	HCO₃^- mg/L	SO₄^-2 mg/L	Cl^- mg/L	NO₃^- mg/L	NH₄⁺ mg/L	Ba µg/L	Fe µg/L	Mn µg/L	H₂S µg/L
01	12	6.95	7.40	740	663	106	14	15	1.6	0.5	371	36	5.2	0.1	0.1	490	1530	422	ND
02	15	6.95	7.50	940	908	123	35	29	5.4	0.9	588	15	6.6	<0.1	1.1	868	12900	713	ND
03	15	7.05	7.60	830	810	90	28	46	5.9	0.7	398	96	14	<0.1	0.7	674	11100	706	ND
04	16	7.05	7.60	550	562	90	13	16	1.1	0.8	352	12	2.2	<0.1	0.2	131	664	24	ND
05	19	7.70	8.00	1450	1300	20	8.2	251	2.7	1.0	333	19	248	<0.1	1.0	31	4300	36	1.0
06	11	6.95	7.45	950	1020	142	26	33	5.3	2.3	407	94	56	46	0.1	193	152	9	ND
07	15	7.05	7.90	660	685	69	17	43	11.0	0.6	241	95	40	2.0	0.1	371	93	769	ND
08	16	6.95	7.60	1450	1430	207	42	52	11.0	2.7	420	382	45	24	0.1	55	BQ	411	ND
09	14	7.15	7.60	1030	1098	138	17	68	12.0	0.7	381	154	74	17.0	0.1	207	311	545	ND
10	14	6.85	7.45	720	750	103	16	34	4.1	0.4	395	64	16	0.1	0.4	168	2630	837	ND
11	14	7.10	7.70	960	1000	140	28	34	6.0	1.6	457	119	43	0.1	0.7	108	7520	937	ND
12	15	6.35	6.80	310	333	30	6.9	24	2.1	0.2	86	46	19	20	<0.1	158	BQ	16	ND
13	14	7.10	7.65	530	570	89	9.0	17	2.5	0.4	292	21	26	4.2	<0.1	188	BQ	BQ	ND
14	14	7.10	7.60	380	412	58	7.5	18	1.2	0.3	208	20	6.1	21	<0.1	122	BQ	BQ	ND
15	14	7.15	7.60	850	909	94	14	84	1.0	0.4	391	46	73	19	<0.1	130	BQ	BQ	ND
16	16	7.05	7.50	780	830	124	26	18	1.3	2.4	485	54	13	6.7	0.1	218	BQ	BQ	ND
17	15	7.05	7.85	2250	2350	167	37	263	7.1	1.3	322	188	487	22	<0.1	65	947	BQ	ND
18	14	7.25	7.85	1130	1180	29	7.7	229	6.1	0.4	418	116	102	0.4	0.8	24	127	25	ND
19	15	7.15	7.80	620	602	82	14	29	2.5	0.5	389	13	4.9	0.2	0.1	231	175	395	ND
20	14	7.25	7.95	1010	1042	140	45	34	16.0	1.2	704	7.6	18	0.2	1.5	3840²	14000²	12400²	ND
21	8	6.35	6.90	1100	1160	44	14	168	2.9	1.2	155	61	226	40	0.3	45	27	211	ND
22	8	6.90	7.60	800	838	103	28	42	1.9	1.0	397	93	29	4.0	0.1	71	377	8	ND
23	9	7.10	7.90	710	650	76	23	29	3.8	1.1	401	18	12	0.1	0.5	190	811	126	ND
24	15	7.50	8.00	410	415	40	15	24	5.7	0.6	213	23	6.4	14	<0.1	82	BQ	BQ	ND
25	14	7.10	7.85	625	610	62	24	21	4.6	1.2	175	74	49	25	<0.1	86	70	BQ	ND
26	16	7.15	7.90	640	608	60	27	29	3.8	1.2	265	84	13	9.3	0.1	118	41	19	ND
27	16	7.05	7.85	710	730	65	27	50	4.5	1.5	224	162	16	14	<0.1	20	16	BQ	ND
28	15	7.35	8.10	385	400	53	5.7	22	3.2	0.3	193	18	11	20	<0.1	141	BQ	BQ	ND
29	15	7.30	8.00	500	492	75	9.0	14	3.0	0.5	261	14	14	16	0.1	206	145	BQ	ND
30	14	6.85	7.70	1000	1050	176	14	29	4.6	0.7	347	180	71	0.3	0.1	197	904	52	ND
31	14	6.95	7.60	850	885	124	19	28	6.6	1.1	371	75	38	49	<0.1	213	22	BQ	ND
32	13	7.15	7.55	785	820	126	10	35	4.8	0.7	333	95	46	3.3	<0.1	204	45	140	ND
33	16	7.35	7.85	3700	3500	93	30	622	9.1	1.3	251	286	853	5.8	<0.1	38	BQ	BQ	ND
34	12	7.50	8.00	935	827	41	11	120	2.9	0.5	257	82	79	7.0	0.1	37	32	BQ	ND
35	15	7.45	7.85	600	580	57	28	29	1.7	0.7	324	23	14	13	0.1	136	BQ	BQ	ND
36	18	7.10	8.00	480	451	47	22	18	3.9	0.7	234	50	4.8	<0.1	0.2	72	166	BQ	ND
37	19	7.20	8.05	450	423	49	18	14	1.8	0.1	176	64	14	0.1	0.1	82	44	7	ND
38	20	7.35	7.60	780	790	51	24	87	5.3	0.8	320	34	86	<0.1	0.3	357	BQ	BQ	7.5
39	23	7.25	7.85	1200	1140	70	34	125	7.6	1.3	323	96	169	<0.1	0.4	52	122	BQ	3.5
40	14	6.80	7.65	820	820	118	14	38	6.9	0.7	352	71	45	27	0.1	178	BQ	BQ	ND
41	14	6.95	7.60	1040	1030	137	20	65	4.9	0.6	475	107	46	15	0.1	115	846	117	ND
42	14	6.95	7.90	950	923	142	15	42	5.0	0.8	476	96	22	0.6	0.3	122	3470	669	ND
43	13	6.80	7.60	1620	1481	184	43	88	7.4	2.1	392	379	100	0.2	1.0	39	616	2620	ND
44	13	7.05	7.80	840	778	95	32	18	0.9	0.3	386	21	29	36	0.2	556	BQ	BQ	ND
45	13	6.95	7.60	1900	1670	303	54	32	2.3	5.3	401	687	31	3.1	0.1	26	924	14	ND
46	15	6.95	8.00	2200	1960	78	12	319	6.8	0.5	250	59	474	6.0	<0.1	203	651	37	ND
47	13	6.60	6.85	1590	1520	227	30	47	1.4	0.9	352	140	134	188	0.1	192	BQ	BQ	ND
48	16	7.15	7.45	590	560	86	12	22	1.1	0.4	335	24	2.2	0.1	0.2	12	396	48	ND
49	21	7.25	7.85	685	725	106	16	22	2.7	1.0	385	30	17	0.1	1.1	805	9270	1790	ND
50	22	7.25	7.45	785	830	69	29	60	6.2	0.8	326	83	54	<0.1	0.3	108	40	BQ	2.0
Mean	14.8	7.08	7.69	956	942	100	21	72	4.7	1.0	340	97	80	13.6	0.3	186	1258	240	-
SD	2.9	0.25	0.28	584	546	55	11	105	3.2	0.8	110	118	150	28.3	0.3	191	2887	495	-
GM	14.5	7.07	7.68	842	837	87	19	43	3.7	0.8	321	59	33	1.8	0.2	122	139	21	-
Med.	14.5	7.10	7.68	810	824	90	19	34	4.4	0.8	350	68	30	4.1	0.1	131	122	14	-
¹ Notation: Fld = Field value; Lab = Lab value Cond = Specific conductance in µmhos/cm BQ = Below quantifiable limit (26 µg/L for Fe and 4 µg/L for Mn) SD = Standard Deviation GM = Geometric Mean Med. = Median ² Sample 20 contained a substantial amount of sediment, and the acidified sample had to be filtered prior to analysis for Ba, Fe, and Mn. The high values for these constituents probably reflect dissolution of particulate matter and not the presence of dissolved minerals. These values were discarded in all statistical summaries and correlations.

TOC and TFP

The raw-water TOC concentrations (table 3) ranged from 0.21 to 3.31 mg/L with a median value of 0.84 and a mean of 1.03 mg/L. Fig. 3 shows the statewide distribution of TOC concentrations greater than and less than 1.0 mg/L. Values greater than 1 mg/L were found throughout the state but primarily in alluvial aquifers. All of the consolidated aquifers sampled had TOC concentrations below 1 mg/L. The highest values (i.e. those > 2.0 mg/L) were found exclusively in the eastern third of the state.

Figure 3--Statewide distribution of TOC concentrations (base map from Steeples and Buchanan, 1983).

TOC concentrations marked on map of state with low values circled (throughout state) and high valued not marked (eastern third).

The TFPs (table 3) ranged from 5.3 to 178 mg/L, with a median value of 30.6 µg/L, a mean of 46.7 µg/L, and a geometric mean of 32.5 µg/L. On the average, only about 61% of the THM-halogen atoms were chlorine, illustrating the importance of bromide in THM formation in Kansas. For 29 of the 50 samples, either CHClBR₂ or CHCl₂BR was the most abundant THM species, with another five samples dominated by CHBR₃. Sample 47 had anomalously high concentrations of brominated THMs, presumably due to an unusually high concentration of bromide in the raw water.

Of the 50 samples analyzed, only four (8%, all in Missouri or Neosho River alluvium) had TFPs exceeding the current MCL for THMs of 100 µg/L. However, 28 (56%) had TFPs exceeding 25 µg/L, and 45 (90%) had TFPs exceeding 10 µg/L. Hence, if the MCL were set at a substantially lower level, a significant number of water utilities relying on ground water as a source of supply might have difficulty complying with the new MCL.

TOC and TFP (µM) were very strongly correlated (r = 0.953), as shown in fig. 4 and table 7. This was expected based on the results of many previous investigations of THM formation in surface waters; this relationship is reflected in the relatively low standard deviation in TFP yield (± 25%, as shown in table 3). This demonstrates that TOC would be an excellent surrogate measure for THM formation, which might prove particularly useful in monitoring and regulatory efforts.

Figure 4--TFP as a function of TOC and aquifer type.

TOC and TFP plotted shows strong correlation.

Fig. 4 and table 7 also show the TOC and TFP concentrations for each of the three major aquifer types. The highest concentrations (TOC values > 1.5 mg/L and TFP values > 50 µg/L) were found exclusively in alluvial aquifers, including those of the Missouri, Neosho, Smoky Hill, and Republican rivers. Only two nonalluvial aquifer samples had TOC concentrations greater than 1 mg/L; one was from a glacial buried-valley aquifer and one was from the Ogallala Formation. The remaining nonalluvial aquifer samples had TOC concentrations ranging from 0.2 to 0.9 mg/L, a range which includes only three alluvial aquifer samples.

As shown in table 7, the mean TOC and TFP concentrations were substantially higher for the alluvial aquifer samples than for the samples from consolidated and unconsolidated aquifers. River waters often carry large organic loads, and other investigations (see Introduction) have shown that river waters generally have higher TOC concentrations than ground waters. The recharge and discharge relationship of a river and its adjoining alluvium is probably a major factor in the amount of TOC in samples from alluvial sources. Alluvial aquifers which are at least partially recharged by river waters would be expected to have higher TOC levels. Organic materials deposited along with the alluvial sediments might also impart a significant amount of TOC to alluvial waters.

Table 7--Statistical summary of TOC and TFP data by aquifer type.¹

Parameter	All Samples	Alluvial Aquifers (23)	Consolidated Aquifers (14)	Unconsolidated Aquifers (12)
TOC, mg/L	1.03 ± 0.76	1.59 ± 0.76	0.48 ± 0.22	0.65 ± 0.34
TFP, µg/L	46.7 ± 39.5	76.2 ± 37.6	16.3 ± 7.4	25.6 ± 21.1
TFP, µM	0.28 ± 0.25	0.47 ± 0.25	0.10 ± 0.05	0.14 ± 0.09
TFP Yield, µmoles/mgC	0.24 ± 0.07	0.29 ± 0.07	0.20 ± 0.05	0.20 ± 0.04
Percent Cl	61 ± 18	62 ± 19	63 ± 19	56 ± 18
Cl₂ demand	2.69 ± 3.09	3.70 ± 3.42	2.76 ± 3.19	0.99 ± 1.29
Correlation coefficients:
TFP, µg/L vs TOC	0.887	0.766	0.875	0.902
TFP, µM vs TOC	0.953	0.911	0.887	0.934
TFP yield vs TOC	0.531	0.187	-0.072	0.360
Cl₂ demand vs TOC	0.597	0.737	0.095	0.358
Cl₂ demand vs TFP, µg/L	0.565	0.708	0.201	0.476
Calculated demand vs. actual demand	0.853	0.965	0.848	0.906
¹ Excluding THM and Cl₂ data for sample 38, excluding sample 34 from the aquifer types, and excluding Cl₂ demand for samples 47 and 48.

Table 7 also presents some statistical information regarding TFP yields, which were, on the average, about 50% higher in the alluvial aquifers in comparison to the nonalluvial aquifers. The TFP yields did not vary much, suggesting that the organic matter in Kansas ground waters has somewhat similar characteristics from place to place. When grouped by aquifer type, TFP yields were not correlated with TOC concentration; the weak correlation (r = 0.531) for the entire sample set is an artifact resulting from the combining of different sample populations.

Chlorine demand

Chlorine demand, determined simultaneously with TFP, averaged 2.69 mg/L and ranged from < 0.1 mg/L to 10.6 mg/L, excluding sample 38 (table 3). As shown in table 7, the average chlorine demand was significantly higher for the alluvial aquifer samples than for the samples from consolidated and unconsolidated aquifers. TOC and TFP appear to be weakly correlated with chlorine demand for the grouping of all samples and for samples from alluvial aquifers (table 7), but this in an artifact caused by a cluster of alluvial aquifer samples which contained both high amounts of TOC (and TFP) and high concentrations of ammonium, iron, and manganese.

To determine how well the measured chlorine demand values would compare to those expected on the basis of the chemical constituents present in the samples, the chlorine demand for each sample was calculated using the formula: 5.91(NH₄⁺) + 0.63(Fe) + 1.29(Mn) + 8.34(H₂S) + TOC, where all concentrations are expressed as mg/L. (The first four terms are based on stoichiometry, assuming all of the Fe and Mn present in divalent form.) The average calculated chlorine demand was 6.1 mg/L, substantially higher than the average measured chlorine demand. There are several reasons why this should be so: 1) a few of the raw-water samples, including samples 8, 25, and 27, already had some chlorine in them at the time they were collected; 2) Fe and Mn were not necessarily present in a reduced state, because oxygen introduced into the samples during pumping and handling could have oxidized the Fe and Mn prior to chlorination; and 3) some of the H₂S may have escaped by volatilization. Nevertheless, the measured and calculated chlorine demands were strongly correlated for all samples (r = 0.853) and for each aquifer type (table 7).

Instantaneous and terminal THM concentrations

Samples from the 31 public water-supply wells were analyzed for terminal and instantaneous THM concentrations (THM and ITHM, respectively), and the results are shown in tables 4 and 5. Additional statistical information is presented in table 8, which includes a separate category for the 21 samples that had a free chlorine residual remaining at the end of the TTHM incubation period (the TTHM results for the other samples were questionable).

The finished-water TOC concentrations were determined on 26 of the 31 ITHM samples. As shown in table 8, the average finished-water and raw-water TOC concentrations were quite similar and raw-water TOC was strongly correlated with finished-water TOC, as would be expected. The raw-water TOC concentration for these samples averaged 1.04 ± 0.74 mg/L, in very close agreement with the raw-water TOC concentration of 1.03 ± 0.76 mg/L for all 50 samples. Hence these samples are a very representative subset.

Table 8--Statistical summary of ITHM and TTHM data.

Parameter	All (31) Samples	Selected Samples¹
Raw water TOC, mg/L	1.04 ± 0.74²	0.93 ± 0.69²
Finished water TOC, mg/L	1.09 ± 0.77²	0.86 ± 0.67²
ITHM, µg/L	6.95 ± 16	9.78 ± 18.9
TTHM, µg/L		35.6 ± 37.0
ITHM/RTHM		0.19 ± 0.15
ITHM/RFP	0.11 ± 0.13³	0.15 ± 0.14³
TTHM/TFP		0.78 ± 0.41³
Correlation coefficients:
ITHM vs TOC⁴	0.433	0.658
TTHM vs TOC⁴		0.819
TTHM vs TFP		0.926³
TOC, Finished vs Raw	0.822²	0.944²
¹Those 21 samples, excluding sample 5, for which the TTHM sample had a free chlorine residual at the end of the incubation period. ² Excluding samples 1, 3, 4, 49, and 50, for which finished water TOC was not determined. ³ Excluding sample 38 ⁴ Finished water TOC

The average ITHM concentration for all 31 samples was only 6.95 µg/L, and the average ratio of ITHM to TFP was only 11%. Similarly, for the 21 TTHM samples having a free chlorine residual, the average ratio of ITHM to TTHM was only 19%. Hence, the concentration of THMs in the finished water generally represented only a small fraction of the THM concentration to which the consumers have been exposed. ITHM concentrations were only weakly correlated with TOC (r = 0.433), reflecting the strong influence of other factors, such as temperature, reaction time, pH, and chlorine dosage, on the initial rate of THM formation.

The mean TTHM concentration was 35.6 ± 37.0 µg/L. Since the TTHM incubation conditions (4 days at 25°C [77°F]) were probably, in most cases, a bit more severe than those actually present in the distribution system, the TTHM values represent a conservative estimate of the THM concentrations actually present in the distribution system.

The TTHM concentrations were strongly correlated with TOC (r = 0.819) and very strongly correlated with TFP (r = 0.926), as would be expected when the THM formation reaction is allowed to go to completion in the presence of excess free chlorine. Hence, TOC and TFP appear to be useful as predictors of distribution system THM concentrations. However, the average ratio of TTHM to TFP (based on 21 samples) was only 78%. The difference is readily attributable to the more extreme conditions (pH and chlorine dosage) of the TFP analysis. A pH of 8.2 was used for the TFP analysis, whereas the average pH of the raw water was 7.1 (table 5), and the average free chlorine residual in the TFP samples was undoubtedly a bit higher than in the TTHM samples. Clearly, it would be better to simulate conditions in the distribution system if the goal is to predict the distribution system THM concentrations; however, the TFP analysis provides a superior basis for comparisons among water sources, which was a major goal of this study.

TOC as a function of depth

TOC is generally expected to decrease with depth due to adsorption and biodegradation of organic matter as the water percolates downward through the sediments. Also, wells screened closer to the ground level are generally more susceptible to contamination by high-TOC surface water percolating into the shallow ground water through cracks, fissures, permeable deposits, or poorly constructed wells. Therefore, the data were examined to see if there might be a relationship between TOC concentration and the depth of the top of the well screen, the mid-depth of the well screen, or the depth of the top of the well screen below the water table. A statistical summary of this examination is presented in table 9, and fig. 5 shows TOC, as a function of aquifer type, versus the depth of the top of the well screen.

Figure 5--TOC as a function of depth to the top of the well screen.

High values of TOC occur only at shallow depths (less than 100 feet).

Table 9--Correlation of TOC and well depth.

	All Samples	Alluvial Aquifers	Consolidated Aquifers	Unconsolidated Aquifers
	Linear Regression Correlation Coefficient¹
TOC vs depth to top of screen	-0.455(48)	-0.008(22)	-0.540(14)	-0.215(12)
TOC vs mid depth of well screen	-0.443(48)	-0.060(22)	-0.582(14)	-0.249(12)
TOC vs depth from water table to top of screen	-0.377(46)	+0.014(21)	-0.550(13)	-0.414(12)
¹ The number of samples included in the correlation is shown in parentheses (the necessary data were unavailable for several wells).

As shown in table 9, TOC was weakly correlated with depth when considering all of the samples or only those from consolidated aquifers, but there was no correlation between TOC and depth for the alluvial aquifers. This was true whether the depth was measured to the top of the screen, to mid-depth, or from the water table to the top of the screen. A close examination of fig. 5 reveals that the weak correlations for the consolidated aquifers are really artifacts due to a data cluster associated with the very deep open-hole wells (the six deepest wells). Similarly, the weak correlations for all of the samples are attributable to the combining of two different populations; the alluvial aquifers had, on the average, much higher TOC values than the other types and their top-of-screen depths were all less than 80 ft (24 m) The curvilinear relationship shown in fig. 5 suggests that an exponential curve might better fit the data, and indeed the correlation coefficient for a semilogarithmic plot was higher (-0.593), but this too is attributable to the combining of two different populations of aquifers. Thus, it can be concluded that there is a general trend of decreasing TOC with depth, but only because alluvial aquifers tend to be shallow and high in TOC.

Aquifer classification by water type

Fig. 6 is a modified Piper diagram summarizing the geochemical composition of the samples. Water-type assignments were made according to dominant contributions (>50%) of particular ions to the total milliequivalents per liter of cations or anions in solution. Samples not dominated by a particular cation or anion were designated as "Mix" types. A majority (27) of the samples were CaHCO₃ type waters, 15 of these being from alluvial aquifers (see table 10). All of the Equus Beds aquifer samples, three glacial buried-valley samples, and two Pennsylvanian aquifer samples also were CA-HCO₃ type waters.

Table 10--Classification of aquifers by water type.

Sample	Aquifer*	TOC(mg/L)
Ca-HCO₃ Type Waters
1	Kansas(A)	0.69
2	Missouri(A)	3.31
3	Missouri(A)	2.56
4	Pennsylvanian(C)	0.36
6	Kansas(A)	1.04
7	Smoky Hill(A)	1.90
9	Republican(A)	2.19
10	Solomon(A)	1.03
11	Smoky Hill(A)	1.90
13	Equus Beds(U)	0.31
14	Equus Beds(U)	0.30
15	Equus Beds(U)	0.85
16	Arkansas(A)	1.52
19	Glacial(U)	0.45
20	Missouri(A)	2.84
22	Glacial(U)	0.58
23	Glacial(U)	0.83
28	Big Bend(U)	0.55
29	Dakota(C)	0.49
31	Pawnee(A)	1.00
32	Smoky Hill(A)	2.43
37	Arbuckle(C)	0.21
40	Solomon(A)	0.98
42	Saline(A)	1.10
44	Permian(C)	0.50
48	Pennsylvanian(C)	0.37
49	Neosho(A)	2.45
Ca-SO₄ Type Waters
45	Permian(C)	0.80
Ca-Mix Type Waters
8	Republican(A)	1.37
25	Ogallala(U)	1.34
30	Walnut(A)	1.54
43	Solomon(A)	1.02
47**	Neosho(A)	2.14
Mix-Mix Type Waters
12	Dakota(C)	0.41
27	Ogallala(U)	0.47
39	Arbuckle(C)	0.31
Mix-HCO₃ Type Waters
24	Ogallala(U)	0.52
26	Cimarron(A)	0.72
35	Permian(C)	0.88
36	Arbuckle(C)	0.27
38	Arbuckle(C)	0.29
50	Arbuckle(C)	0.48
Na-HCO₃ Type Waters
18	Dakota(C)	0.87
34	Pleistocene(U)	0.50
Na-Cl Type Waters
5	Pennsylvanian(C)	0.48
17**	Arkansas(A)	1.06
21	Glacial(U)	1.20
33	Cimarron(A)	0.60
46	Big Bend(U)	0.36
A = alluvial, C = consolidated, U = unconsolidated *The ratio of Na to Cl in mg/L is less than 0.65.

Figure 6--Modified Piper diagram showing study samples.

Chemistry of samples plotted.

There does not appear to be any significant relationship between TOC and water type. The five Ca-Mix waters had TOC levels greater than 1.0 mg/L, ranging from 1.02 to 2.14 mg/L, but four of these samples were from alluvial aquifers. The Mix-Mix, Mix-HCO₃, and CaSO₄ waters all had TOC concentrations close to or less than the median concentration (0.8 mg/L), but only one of these samples came from an alluvial aquifer. Na-Cl type waters had TOC concentrations ranging from 0.36 to 1.20 mg/L.

Summary of geochemical data by aquifer type

A simple statistical analysis of the geochemical data according to aquifer type is presented in table 11. Inspection of the means and medians reveals that the mean and median concentration of every constituent was higher in the alluvial aquifers than in the consolidated and unconsolidated aquifers, with only three minor exceptions: 1) the mean and median pH values were slightly lower for the alluvial aquifers (meaning that the hydrogen ion concentration was actually higher); 2) the median NO₃^- concentration was highest for the unconsolidated samples; and 3) the median ammonium concentration was highest for the consolidated aquifers. Hydrogen sulfide was excluded from the data summary, because only four samples contained a detectable amount, but all four came from deep open-hole wells in consolidated aquifers.

Specific conductance, calcium, bicarbonate, sulfate, chloride, barium, iron, and manganese were, on the average, present in substantially higher concentrations in the alluvial aquifers. Hence, these parameters would be expected to be correlated (associated) with TOC even where no causal relationship exists. For this reason, it was necessary to examine the relationship between TOC and the inorganic constituents for each individual type of aquifer, as described in the following section. The consolidated-aquifer samples were, on the average, quite similar to the unconsolidated samples; however, the consolidated aquifer samples had slightly higher concentrations of the majority of constituents, especially bicarbonate, sulfate, and iron.

Table 11--Summary of geochemical data by aquifer type.

Constituent, units	All Aquifers (50)		Alluvial (23)		Consolidated (14)		Unconsolidated (12)
Constituent, units	Mean ± SD	Median	Mean ± SD	Median	Mean ± SD	Median	Mean ± SD	Median
Field pH, pH units	7.08 ± 0.25	7.10	7.01 ± 0.17	6.95	7.17 ± 0.30	7.23	7.07 ± 0.28	7.10
Field Spec. Cond., µmhos/cm	956 ± 584	810	1130 ± 677	950	826 ± 447	690	777 ± 495	668
Ca, mg/L	100 ± 55	90	132 ± 40	126	77 ± 69	63	70 ± 20	71
Mg, mg/L	21 ± 11	19	25 ± 10	26	21 ± 13	20	16 ± 8	14
Na, mg/L	72 ± 105	34	75 ± 129	35	67 ± 80	27	69 ± 90	29
K, mg/L	4.7 ± 3.2	4.4	6.3 ± 3.6	5.4	3.3 ± 2.2	2.5	3.4 ± 1.8	3.1
Sr, mg/L	1.0 ± 0.8	0.8	1.1 ± 0.7	0.9	1.0 ± 1.3	0.7	0.8 ± 0.4	0.6
HCO₃^-, mg/L	340 ± 110	350	399 ± 104	385	305 ± 90	325	274 ± 95	237
SO₄^-2, mg/L	97 ± 118	68	124 ± 102	95	92 ± 174	40	51 ± 44	35
Cl^-, mg/L	80 ± 150	30	96 ± 192	43	56 ± 73	24	78 ± 139	21
NO₃^-, mg/L	13.6 ± 28.3	4.1	18 ± 40	3.3	6.4 ± 11.0	0.1	14 ± 12	14
NH₄⁺, mg/L	0.3 ± 0.3	0.1	0.4 0.4	0.1	0.3 ± 0.3	0.2	0.1 ± 0.1	0.05
Ba, µg/L*	186 ± 191	131	256 239	193	139 ± 151	145	126 ± 67	126
Fe, µg/L*	1258 ±2887	122	2384 ±3972	464	499 ±1128	125	183 ± 280	22
Mn, µg/L*	240 ± 495	14	489 ± 658	276	13 ± 15	5	66 ±123	2
* Excluding sample #20

Correlation of TOC and inorganic constituents

The data were statistically analyzed to reveal any significant geochemical relationships that might exist between TOC and various inorganic constituents. As shown in table 12, only a few of the correlations were statistically significant, and most of the statistically significant correlations were artifacts due to the combining of different populations (e.g., TOC versus Ca, Mg, hardness, K, and HCO₃^- for all 50 samples) or to the presence of outliers (e.g., TOC versus HCO₃^- or Ba for the alluvial aquifers and TOC versus NO₃^- for the unconsolidated aquifers). Upon closer inspection, the only potentially significant relationships were those involving NH₄⁺, Fe, and Mn.

Table 12--Correlation of TOC and inorganic constituents.

Constituent	Linear Regression Correlation Coefficient
Constituent	All Aquifers (n=50)	Alluvial Aquifers (n=23)	Consolidated Aquifers (n=14)	Unconsolidated Aquifers (n=12)
pH	-0.175	0.178	0.121	-0.409
Specific Conductance	0.063	-0.294	0.457	0.008
Ca, mg/L	0.420**	0.061	0.337	-0.244
Mg, mg/L	0.290*	0.149	0.236	0.370
Hardness, mg/L as CaCO³	0.419**	0.101	0.327	0.007
Na, mg/L	-0.149	-0.328	0.263	0.012
K, mg/L	0.428**	0.203	-0.026	0.006
Sr, mg/L	0.131	-0.179	0.390	0.546*
HCO₃^-, mg/L	0.565**	0.507*	0.520*	-0.196
SO₄^-2 mg/L	0.057	-0.353	0.436	0.151
Cl^-, mg/L	-0.116	-0.334	0.021	0.042
NO₃^-, mg/L	0.150	0.013	0.184	0.594*
NH₄⁺, mg/L	0.500**	0.600**	0.183	0.395
NH₄⁺, mg/L¹	0.736**	0.676*	0.594	-
Ba, µg/L²	0.580**	0.681**	-0.132	-0.381
Fe, µg/L²	0.648**	0.669**	0.049	-0.044
Mn, µg/L²	0.449**	0.216	0.065	0.110
Fe + Mn, µg/L³	0.966**	0.991**	-	-
^* Statistically significant at the 5% level of significance ^** Statistically significant at the 1% level of significance ¹ With values ≤ 0.1 mg/L excluded (n = 19, 8, 9, and 2, respectively) ² Excluding sample #20 ³ Excluding sample #20 and values < 1000 mg/L (n = 9, 8, 1, and 0, respectively)

Figs. 7 and 8 show NH₄⁺ and Fe + Mn, respectively, as a function of TOC concentration for the alluvial aquifers. In each case, there is a subset of samples having an elevated concentration of NH₄⁺ or Fe + Mn in which the concentration is linearly related to TOC. The correlation of Fe + Mn with TOC was especially strong (r = 0.991) for alluvial aquifer samples having a concentration of Fe + Mn greater than 1,000 µg/L (table 12 and fig. 8). Interestingly, the subsets of samples high in NH₄⁺ and high in Fe + Mn are virtually identical, i.e. each of the alluvial aquifer samples having an NH₄⁺ concentration greater than 0.1 mg/L also had an Fe + Mn concentration greater than 1,000 µg/L. Also, for the alluvial aquifer samples having > 0.1 mg/L of NH₄⁺, NH₄⁺ is linearly correlated to both Fe + Mn (r = 0.893) and to TOC (r = 0.845) when sample 43 is excluded as an outlier. Sample 43 had a high NH₄⁺ concentration (1.0 mg/L) relative to its TOC concentration of 1.02 mg/L and, unlike the other high ammonium samples, it contained much more Mn than Fe. Sample 20 was not plotted in fig. 8, due to its excessive concentrations of Fe and Mn, but this sample had the highest concentration of NH₄⁺ (1.5 mg/L) among all the samples.

Figure 7--Ammonium as a function of TOC for alluvial aquifer samples.

Ammonium plotted against TOC.

Figure 8--Fe + Mn as a function of TOC for alluvial aquifer samples.

Fe + Mn plotted against TOC.

These results reveal two distinct populations of alluvial aquifers: one having elevated concentrations of NH₄⁺, Fe, and Mn, and the other having low concentrations of these constituents. Presumably, the former population is associated with reducing (anoxic or anaerobic) conditions, under which iron and manganese were solubilized and the NH₄⁺ released by biological activity could not be oxidized to nitrate. The TOC values of both populations vary over about the same range, but those for the population having high concentrations of NH₄⁺, Fe, and Mn are linearly related to those constituents. There are several possible explanations for this relationship:

Under more reducing conditions, higher concentrations of TOC may occur due to the decreased energy available to the microorganisms metabolizing the organic matter;
Increased TOC may be associated with the active microbial populations metabolizing Fe, Mn, and NH₄⁺; and
Higher concentrations of TOC may correspond to higher concentrations of Fe and Mn due to complexation of Fe and Mn by organic matter (and perhaps these complexes stimulate increased biological activity causing NH₄⁺ to rise as well).

In any event, these relationships are strong enough and interesting enough to merit further investigation, especially in view of the fact that all of the constituents involved pose significant problems in regard to treatment of potable water supplies.

Implications for THM control in Kansas

The current federal MCL for THMs for utilities serving more than 10,000 persons is 100 µg/L. The Kansas Department of Health and Environment (KDHE) also has applied this requirement to all new supplies and to small systems (serving less than 10,000 people) undergoing plant modifications. The federal standard is expected to be lowered, perhaps substantially, when the new standards for disinfection byproducts are released in the near future. Approximately 8% of the study samples had TFPs greater than 100 µg/L (the present MCL for THMs), but 56% had TFPs greater than 25 µg/L and 90% had TFPs greater than 10 µg/L. Hence, many water-supply systems using ground waters in Kansas might have difficulty in meeting a substantially lower THM limit.

The highest TFP concentrations were found in samples from alluvial aquifers, so it is clear that utilities using waters from alluvial sources would be the most greatly affected by a lower THM limit. Since many communities in Kansas, especially eastern Kansas, are largely dependent on alluvial aquifers as sources for public water supplies, special attention should be given to monitoring and control of THM concentrations in drinking-water supplies derived from these aquifers.

The four major alternatives to controlling THMs include 1) precursor removal, 2) use of an alternative disinfectant (eliminating the use of chlorine), 3) removal of THMs after they are formed, and 4) modification of the chlorination process to hinder the progress of the reaction. The simplest and most effective means of controlling THM formation for most water-treatment plants in Kansas is to modify the chlorination process and replace free chlorine with combined chlorine, since the latter does not form THMs. In Kansas, a free chlorine residual of 0.2 mg/L or a combined residual of 1.0 mg/L is required throughout the finished-water distribution system for disinfection purposes. Higher combined residuals are needed because combined chlorine is not as strong a disinfectant as free chlorine. There are several other advantages associated with combined chlorine: 1) it is more stable in the distribution system; 2) it can be used in higher concentrations than free chlorine, since it contributes less to taste and odor; and 3) it requires lower dosages of chlorine for waters already containing substantial concentrations of ammonium.

The use of combined chlorine in water supplies should only be implemented by those having adequate knowledge of the chemistry of chlorine and ammonium and the reactions between them, so that maximum disinfection can be achieved with minimum THM formation and a minimum of taste and odor problems. It also is important that any change in disinfection practice be carefully monitored to ensure that the microbial quality of the drinking water is not compromised.

The data also bear significant implications with regard to monitoring of water supplies for compliance with the THM regulations. Since TFP and TOC are very strongly correlated, TOC could be used as a surrogate measure of THM formation potential, and ground-water supplies having low concentrations of TOC could be exempted from monitoring for THMs. Also, because there was a strong correlation between the TFP and TTHM concentrations (with the former being generally higher), TFP analyses conducted in a centralized laboratory could be used as a substitute for TTHM analyses. The relationship between TOC and NH₄⁺, Fe, and Mn suggests that alluvial aquifers having high concentrations of Fe, Mn, and NH₄⁺ should receive the most immediate attention and closer monitoring.

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Kansas Geological Survey
Placed on web Nov. 6, 2012; originally published in 1991.
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