5 Colo. Code Regs. § 1002-11.24

Current through Register Vol. 47, No. 11, June 10, 2024

Section 5 CCR 1002-11.24 - DISINFECTION BYPRODUCT PRECURSORS RULE

11.24(1)Applicability and Definitions for Disinfection Byproduct Precursors

(a) For all community and non-transient, non-community surface water systems that use conventional filtration treatment, the supplier must comply with the disinfection byproduct precursor requirements specified in this rule.

(b) "DISINFECTION BYPRODUCT PRECURSORS" means the natural organic and inorganic compounds that react with chemical disinfectants in water to form disinfection byproducts.

(c) "ENHANCED COAGULATION" means the addition of sufficient coagulant for improved removal of disinfection byproduct precursors by conventional filtration treatment.

(d) "ENHANCED SOFTENING" means the improved removal of disinfection byproduct precursors by precipitative softening.

(e) "PAIRED TOC SAMPLE SET" means one source water TOC sample and one treated water TOC sample collected at the same time during normal operating conditions.

(i) The source water TOC sample must be representative of influent water quality.

(ii) The treated water TOC sample must be collected before or at the point of combined filter effluent turbidity monitoring and must represent the treated water.

(f) "SPECIFIC ULTRAVIOLET ABSORPTION" or "SUVA" means specific ultraviolet absorption at 254 nanometers, an indicator of the humic content of water. It is a calculated parameter obtained by dividing a sample's ultraviolet absorption, in 1/m, at a wavelength of 254 nm (i.e., UV254) by its concentration of dissolved organic carbon, in mg/L.

11.24(2)Treatment Technique Requirements for Disinfection Byproduct Precursors

(a) For each conventional filtration treatment plant, the supplier must comply with one of the following:

(i) The disinfection byproduct precursor treatment technique by meeting the Step 1 TOC removal requirements as specified in 11.24(5).

(ii) The disinfection byproduct precursor treatment technique requirements by meeting at least one of alternative compliance criteria specified in 11.24(7).

(iii) The disinfection byproduct precursor treatment technique by meeting the Step 2 TOC removal requirements as specified in 11.24(6).

(iv) Have a disinfection byproduct precursor waiver as specified in 11.24(6)(j).

(b) For compliance with the Step 1 or Step 2 TOC removal requirements, the supplier must operate with enhanced coagulation or enhanced softening.

11.24(3)Sampling Requirements for Disinfection Byproduct Precursors Treatment Technique Requirements

(a) To determine compliance with the disinfection byproduct precursor treatment technique requirements, the supplier must sample TOC and source water alkalinity as specified in this section, 11.24(3) and as identified in the monitoring plan developed under 11.5(3)(a)(v).

(b) For each conventional filtration treatment plant, the supplier must collect one routine paired TOC sample set and one routine source water alkalinity sample each month.

(i) The source water alkalinity sample must be collected at the same time as the paired TOC sample set and must be representative of influent water quality.

(c) The supplier may reduce the sampling frequency to quarterly at each treatment plant if the RAA of the monthly treated water TOC sample results meets one of the following criteria:

(i) Is less than (<) 1.0 mg/L for one year.

(ii) Is less than (<) 2.0 mg/L for two consecutive years.

(d) If the supplier is sampling at a reduced sampling frequency and the RAA of quarterly treated water TOC sample results is greater than or equal to (>=) 2.0 mg/L, the supplier must return to the routine monthly sampling frequency.

(e) For suppliers that intend to comply with the disinfection byproduct precursor treatment technique requirements by meeting one of the alternative compliance criteria specified in 11.24(7)(b)(v-vii), the supplier must also sample the necessary optional parameters to demonstrate compliance with the applicable alternative compliance criteria (i.e., specific ultraviolet absorption or magnesium hardness) at the same locations and sampling frequency as the paired TOC sample set.

11.24(4)Compliance Options for Disinfection Byproduct Precursors

For each conventional filtration treatment plant, the supplier must comply with the Step 1 TOC removal requirements under 11.24(5), unless one or more of the following criteria are met:

(a) The supplier complies with at least one of the alternative compliance criteria specified in 11.24(7).

(b) For systems using enhanced coagulation, the Department approves the supplier to comply with the Step 2 TOC removal requirements specified in 11.24(6).

(c) The supplier has a Department-approved waiver from enhanced coagulation requirements as specified in 11.24(6)(j).

11.24(5)Step 1 TOC Removal Requirements

To comply with the Step 1 TOC removal requirements, the supplier must achieve the applicable Step 1 required TOC percent removals in Table 11.24-I based on the source water TOC sample results and the source water alkalinity sample results collected under 11.24(3).

(a) For systems that use softening, the supplier must comply with the Step 1 required TOC percent removal based on the source water TOC sample results and the far-right column, Source water alkalinity >120 mg/L, regardless of the source water alkalinity sample results collected under 11.24(3).

TABLE 11.24-I STEP 1 TOC PERCENT REMOVAL REQUIREMENTS
	Source water alkalinity, mg/L as CaCO3
	0-60	>60-120 removal	>120
Source water TOC, mg/L	Required step 1 TOC percent
>2.0-4.0	35.0	25.0	15.0
>4.0-8.0	45.0	35.0	25.0
>8.0	50.0	40.0	30.0

11.24(6)Step 2 TOC Removal Requirements

(a) For systems using enhanced coagulation, if the supplier fails to achieve the Step 1 TOC removal requirement and the alternative compliance criteria, either due to water quality parameters or operational constraints, the supplier must apply to the Department for approval of alternative minimum TOC removal requirements (Step 2 TOC removal requirements) as specified in this section, 11.24(6), and if approved comply with the Step 2 TOC removal requirements.

(b) No later than three months after the system fails to comply with the Step 1 TOC removal requirements and the alternative compliance criteria, the supplier must:

(i) Complete bench- or pilot-scale testing to determine the recommended Step 2 TOC

percent removal.

(ii) Apply to the Department for approval of the recommended Step 2 TOC percent removal.

(A) If approved, this value is the Step 2 required TOC percent removal that will be used for determining compliance with the Step 2 TOC removal requirements.

(iii) Include the results of the bench- or pilot-scale testing in the Step 2 TOC removal requirements application.

(c) For the required bench- or pilot-scale testing, the supplier must incrementally add 10 mg/L of alum, or equivalent addition of iron coagulant, to a representative source water sample until the pH is reduced to a level less than or equal to ([LESS THAN EQUAL TO]) the applicable Step 2 target pH specified in Table 11.24-II.

(i) If the source water alkalinity is less than or equal to ([LESS THAN EQUAL TO]) 60 mg/L and the pH is reduced to less than (<) 5.5 before significant TOC removal occurs, the supplier must adjust the pH to between 5.3 and 5.7 until a TOC removal of less than (<) 0.3 mg/L per incremental addition of alum, or equivalent addition of iron coagulant, is reached.

TABLE 11.24-II STEP 2 TARGET pH
Source water alkalinity (mg/L as CaCO3)	Target pH
0-60	5.5
>60-120	6.3
>120-240	7.0
>240	7.5

(d) At the coagulant dose of alum, or equivalent addition of iron coagulant, where the TOC removal is less than (<) 0.3 mg/L, the supplier must calculate the recommended Step 2 TOC percent removal from the results of the bench- or pilot-scale testing as follows:

(i) The recommended Step 2 TOC percent removal is equal to:

(1-(treated water TOC result ÷ source water TOC result)) x 100

(e) The results of the bench- or pilot-scale testing shall be used by the Department to assess the recommended Step 2 TOC percent removal submitted by the supplier.

(i) If the Department approves the recommended Step 2 TOC percent removal, the Department may make the Step 2 required TOC percent removal retroactive for the purposes of determining compliance.

(f) Until the Department approves the recommended Step 2 TOC percent removal, the supplier must either comply with the Step 1 TOC removal requirements as specified in 11.24(5) or the alternative compliance criteria as specified in 11.24(7).

(g) If approved by the Department, the Step 2 required TOC percent removal supersedes the Step 1 required TOC percent removal specified in Table 11.24-I.

(h) If the supplier completes a new bench- and pilot-scale test and the Department approves a new Step 2 required TOC percent removal, the previous Step 2 required TOC percent removal will no longer be effective.

(i) The supplier may operate the treatment plant at any coagulant dose or pH necessary to achieve the Step 2 required TOC percent removal as long as it is consistent with other requirements of the Colorado Primary Drinking Water Regulations.

(j) The supplier may apply to the Department for a waiver from enhanced coagulation requirements if the water is deemed to contain TOC not amenable to enhanced coagulation.

(i) The water is deemed to contain TOC not amenable to enhanced coagulation if the TOC removal in the bench- or pilot-scale testing is consistently less than (<) 0.3 mg/L of TOC per incremental addition of alum at all dosages, or equivalent addition of iron coagulant.

11.24(7)Alternative Compliance Criteria Requirements for Disinfection Byproduct Precursors

(a) If the supplier complies with any of the alternative compliance criteria in any quarter, the supplier is not required to comply with the Step 1 or Step 2 TOC removal requirements for that quarter.

(b) The alternative compliance criteria are as follows:

(i) The LRAA of the source water TOC sample results is less than (<) 2.0 mg/L.

(ii) The LRAA of the treated water TOC sample results is less than (<) 2.0 mg/L.

(iii) Sample results demonstrate all of the following:

(A) The LRAA of source water TOC is less than (<) 4.0 mg/L.

(B) The LRAA of source water alkalinity is greater than (>) 60 mg/L (as CaCO3).

(C) The RAAs of TTHM and HAA5 samples are less than (<) 0.040 mg/L and 0.030 mg/L, respectively.

(iv) For systems using only chlorine for primary disinfection and maintenance of the residual disinfectant concentration in the distribution system, the RAA of the TTHM and HAA5 sample results are less than (<) 0.040 mg/L and 0.030 mg/L, respectively.

(v) The LRAA of source water SUVA is less than or equal to ([LESS THAN EQUAL TO]) 2.0 L/mg-m.

(vi) The LRAA of finished water SUVA is less than or equal to ([LESS THAN EQUAL TO]) 2.0 L/mg-m.

(vii) For systems using softening, the LRAA of removed magnesium hardness is greater than or equal to (>=) 10 mg/L (as CaCO3).

(viii) For systems using softening, the LRAA of treated water alkalinity is less than (<) 60 mg/L (as CaCO3).

11.24(8)Compliance Determination for Step 1 and Step 2 TOC Removal

(a) To determine compliance with the Step 1 or Step 2 TOC removal requirements, the supplier must calculate compliance quarterly based on a LRAA as follows:

(i) Determine the actual monthly TOC percent removal.

The actual monthly TOC percent removal is equal to: (1-(treated water TOC sample result ÷ source water TOC sample result)) ×t; 100

(ii) Determine the required monthly TOC percent removal:

(A) If the supplier is determining compliance with the Step 1 TOC removal requirements, refer to Table 11.24-I for the Step 1 required TOC percent removal.

(B) If the supplier is determining compliance with the Step 2 TOC removal requirements, use the Department-approved Step 2 required TOC percent removal.

(iii) Determine the monthly removal ratio.

The monthly removal ratio is equal to: (actual monthly TOC percent removal ÷ required monthly TOC percent removal)

(A) If one or more of the following conditions apply, the supplier may substitute a value of 1.0 for the monthly removal ratio in that month:

(I) The source water or treated water TOC sample result(s) is less than (<) 2.0 mg/L.

(II) The source water or finished water SUVA is less than (<) 2.0 L/mg-m.

(III) For systems using enhanced softening, treated water alkalinity is less than (<) 60 mg/L (as CaCO3).

(IV) For systems using enhanced softening, removed magnesium hardness (as CaCO3) is greater than or equal to (>=) 10 mg/L.

(iv) Determine the LRAA of the monthly removal ratios.

(b) For new or reclassified systems that now meet the applicability of this rule, the supplier must begin determining compliance after collecting 12 months of data.

11.24(9)Treatment Technique Violations and Response for Disinfection Byproduct Precursors

(a) If the supplier fails to comply with any of the alternative compliance criteria and the LRAA of the monthly removal ratios is less than (<) 1.00 as calculated for Step 1 or Step 2 TOC removal requirements, a disinfection byproduct precursors treatment technique violation occurs.

(b) In the event of disinfection byproduct precursors treatment technique violation, the supplier must:

(i) Notify the Department no later than 48 hours after the violation occurs.

(ii) Distribute Tier 2 public notice as specified in 11.33.

11.24(10)Reporting Requirements for Disinfection Byproduct Precursors

(a) The supplier must submit all of the following information no later than the 10^th of the month following the end of each quarter in which samples were collected:

(i) The number of paired TOC sample sets collected during the last quarter.

(ii) The location, date, and results of each paired TOC sample set and each associated alkalinity sample collected during the last quarter.

(iii) If the supplier is complying with either the Step 1 or Step 2 TOC removal requirements as specified in 11.24(5) and 11.24(6):

(A) For each month in the quarter that paired TOC sample sets were collected, the monthly removal ratio for each paired TOC sample set and the required TOC percent removal.

(B) Compliance calculations for determining TOC percent removals as specified in 11.24(8).

(C) Whether the system is in compliance with the Step 1 or Step 2 TOC removal requirements as specified in 11.24(5) and 11.24(6) for the last four quarters.

(iv) If the supplier meets one or more of the alternative compliance criteria as specified in 11.24(7):

(A) The alternative compliance criterion that the supplier is using for compliance and whether the system is in compliance with that particular alternative compliance criterion.

(B) For systems meeting the criteria specified in 11.24(7)(b)(i) or 11.24(7)(b)(iii), the LRAA of source water TOC.

(C) For systems meeting the criterion specified in 11.24(7)(b)(ii), the LRAA of treated water TOC.

(D) For systems meeting the criteria specified in 11.24(7)(b)(iii), the LRAA of source water alkalinity.

(E) For systems meeting the criteria specified in 11.24(7)(b)(iii) or 11.24(7)(b)(iv), the RAA for both TTHM and HAA5.

(F) For systems meeting the criterion specified in 11.24(7)(b)(v), the LRAA of source water SUVA.

(G) For systems meeting the criterion specified in 11.24(7)(b)(vi), the LRAA of finished water SUVA.

(H) For systems meeting the criterion specified in 11.24(7)(b)(vii), the LRAA of monthly removed magnesium hardness (as CaCO3 in mg/L).

(I) For systems meeting the criterion specified in 11.24(7)(b)(viii), the LRAA of treated water alkalinity.

(b) The Department may complete the calculations and determine whether the treatment technique was met, instead of having the supplier report that information.

5 CCR 1002-11.24

38 CR 07, April 10, 2015, effective 4/30/2015

41 CR 11, June 10, 2018, effective 6/30/2018

41 CR 23, December 10, 2018, effective 12/30/2018

43 CR 07, April 10, 2020, effective 4/30/2020

43 CR 17, September 10, 2020, effective 9/30/2020

45 CR 24, December 25, 2022, effective 1/14/2023