16 Del. Admin. Code § 4462-12.0

Current through Register Vol. 28, No. 7, January 1, 2025

Section 4462-12.0 - Disinfectant Residuals, Disinfection Byproducts, and Disinfection Precursors

12.1 General requirements: The requirements of this section constitute national primary drinking water regulations.

12.1.1 The regulations in this section establish criteria under which community water systems (CWSs) and non-transient, non-community water systems (NTNCWSs) which add a chemical disinfectant to the water in any part of the drinking water treatment process must modify their practices to meet MCLs and MRDLs in subsections 9.2.1.2 and 1.19.3 respectively, and must meet the treatment technique requirements for disinfection byproduct precursors in subsection 12.9.

12.1.2 The regulations in this section establish criteria under which transient NCWSs that use chlorine dioxide as a disinfectant or oxidant must modify their practices to meet the MRDL for chlorine dioxide in subsection 1.19.3.

12.1.3 EPA has established MCLs for TTHM and HAA5 and treatment technique requirements for disinfection byproduct precursors to limit the levels of known and unknown disinfection byproducts which may have adverse health effects. These disinfection byproducts may include chloroform; bromodichloromethane; dibromochloromethane; bromoform; dichloroacetic acid; and trichloroacetic acid.

12.2 Compliance Dates

12.2.1 CWSs and NTNCWSs. Unless otherwise noted, systems must comply with the requirements of this section as follows. Surface water or ground water under the direct influence of surface water systems serving 10,000 or more persons must comply with this section beginning December 16, 2001. Surface water or ground water under the direct influence of surface water systems serving fewer than 10,000 persons and systems using only ground water not under the direct influence of surface water must comply with this section beginning December 16, 2003. All systems must comply with these MCLs until the date specified in subsection 14.1.3.

12.2.2 Transient NCWSs. Surface water or ground water under the direct influence of surface water systems serving 10,000 or more persons and using chlorine dioxide as a disinfectant or oxidant must comply with any requirements for chlorine dioxide and chlorite in this section beginning December 16, 2001. Surface water or ground water under the direct influence of surface water systems serving fewer than 10,000 persons and using chlorine dioxide as a disinfectant or oxidant and systems using only ground water not under the direct influence of surface water and using chlorine dioxide as a disinfectant or oxidant must comply with any requirements for chlorine dioxide and chlorite in this section beginning December 16, 2003.

12.3 Each CWS and NTNCWS regulated under subsection 12.1 must be operated by qualified personnel who meet the requirements specified by the Division and are included in a State register of qualified operators.

12.4 Control of disinfectant residuals. Notwithstanding the MRDLs in subsection 1.19.3, systems may increase residual disinfectant levels in the distribution system of chlorine or chloramines (but not chlorine dioxide) to a level and for a time necessary to protect public health, to address specific microbiological contamination problems caused by circumstances such as, but not limited to, distribution line breaks, storm run-off events, source water contamination events, or cross-connection events.

12.5 For compliance with this section systems must use analytical methods in accordance with 40 CFR 141.131(a); 40 CFR 141.131(b)(1-2); 40 CFR 141.131(c)(1-2); and 40 CFR 141.131(d) (1-6. Copies may be obtained from the Office of Drinking Water.

12.5.1 Analysis under this section for disinfection byproducts must be conducted by laboratories that have received certification by EPA or the Division, except as specified under subsection 12.7.2.1.3. To receive certification to conduct analysis for the contaminants in subsection 9.2.1.2, the laboratory must carry out annual analyses of performance evaluation (PE) samples approved by EPA or the Division. In the analyses of PE samples, the laboratory must achieve quantitative results within the acceptance limit as specified in 40 CFR 141.131(b)(2).

12.5.2 A party approved by the EPA or the Division must measure residual disinfectant concentration.

12.6 Monitoring requirements - General requirements:

12.6.1 Systems must take all samples during normal operating conditions.

12.6.2 Systems may consider multiple wells drawing from a single aquifer as one treatment plant for determining the minimum of TTHM and HAA5 samples required, with the approval of the Division.

12.6.3 Failure to monitor in accordance with the monitoring plan required under subsection 12.11 is a monitoring violation.

12.6.4 Failure to monitor will be treated as a violation for the entire period covered by the annual average where compliance is based on a running annual average of monthly or quarterly samples or averages and the system's failure to monitor makes it impossible to determine compliance with MCLs or MRDLs.

12.6.5 Systems may use only data collected under the provisions of this section or 61 FR 24368, May 14, 1996 to qualify for reduced monitoring.

12.7 Monitoring requirements for disinfection byproducts:

12.7.1 TTHM and HAA5

12.7.1.1 Routine monitoring. Systems must monitor at the frequency indicated in the following table:

Type of system	Minimum monitoring frequency	Sample location in the distribution system
Surface water or ground water under the direct influence of surface water system serving at least 10,000 persons	Four water samples per quarter per treatment plant	At least 25% of all samples collected each quarter at locations representing maximum residence time. Remaining samples taken at locations representative of at least average residence time in the distribution system and representing the entire distribution system, taking into account number of persons served, different sources of water, and different treatment methods.¹
Surface water or ground water under the direct influence of surface water systems serving from 500 to 9,999 persons	One water sample per quarter per treatment plant	Locations representing maximum residence time.¹
Surface water or ground water under the direct influence of surface water system serving fewer than 500 persons	One sample per year per treatment plant during month of warmest water temperature	Location representing maximum residence time¹. If the sample (or average of annual samples, if more than one sample is taken) exceeds MCL, system must increase monitoring to one sample per treatment plant per quarter, taken at a point reflecting the maximum residence time in the distribution system, until system meets reduced monitoring criteria in subsection 12.7.1.4.
Systems using only groundwater not under the direct influence of surface water using chemical disinfectant and serving at least 10,000 persons.	One sample per quarter per treatment plant.²	Locations representing maximum residence time.¹
Systems using only groundwater not under the direct influence of surface water using chemical disinfectant and serving fewer than 10,000 persons.	One sample per year per treatment plant² during the month of warmest water temperature.	Locations representing maximum residence time.¹ If the sample (or average of annual samples, if more than one sample is taken) exceeds MCL, system must increase monitoring to one sample per treatment plant per quarter, taken at a point reflecting the maximum residence time in the distribution system, until system meets reduced monitoring criteria in subsection 12.7.1.2.

¹ If a system elects to sample more frequently than the minimum required, at least 25% of all samples collected each quarter (including those taken in excess of the required frequency) must be taken at locations that represent the maximum residence time of the water in the distribution system. The remaining samples must be taken at locations representative of at least average residence time in the distribution system.

² Multiple wells drawing from a single aquifer may be considered one treatment plant for determining the minimum number of samples required, with Division approval.

12.7.1.2 Reduced monitoring. Systems may reduce monitoring, except as otherwise provided, in accordance with the following table:

If you are a...	If you have monitored at least one year and your...	You may reduce monitoring to this level.
Surface water or ground water under the direct influence of surface water system serving at least 10,000 persons which has a source water annual average TOC level, before any treatment, <4.0 mg/L.	TTHM annual average <0.040 mg/L and HAA5 annual average <0.030 mg/L.	One sample per treatment plant per quarter at distribution system location reflecting maximum residence time.
Surface water or ground water under the direct influence of surface water system serving from 500 to 9,999 persons which has a source water annual average TOC level, before any treatment, <4.0 mg/L.	TTHM annual average <0.040 mg/L and HAA5 annual average <0.030 mg/L.	One sample per treatment plant per year at distribution system location reflecting maximum residence time during month of warmest water temperature.
Systems using only groundwater not under the direct influence of surface water using chemical disinfectant and serving at least 10,000 persons.	TTHM annual average <0.040 mg/L and HAA5 annual average <0.030 mg/L.	One sample per treatment plant per year at distribution system location reflecting maximum residence time during month of warmest water temperature.
Systems using only groundwater not under the direct influence of surface water using chemical disinfectant and serving fewer than 10,000 persons.	TTHM annual average <0.040 mg/L and HAA5 annual average <0.030 mg/L for two consecutive years or TTHM annual average <0.020 mg/L and HAA5 annual average <0.015 mg/L for one year.	One sample per treatment plant per three year monitoring cycle at distribution system location reflecting maximum residence time during month of warmest water temperature, with the three-year cycle beginning January 1 following the quarter in which the system qualifies for reduced monitoring.

Note: Any Surface water or ground water under the direct influence of surface water system serving fewer than 500 persons may not reduce its monitoring to less than one sample per treatment plant per year.

12.7.1.3 Monitoring requirements for source water TOC. In order to qualify for reduced monitoring for TTHM and HAA5 under subsection 12.7.1.2, surface water or ground water under the direct influence of surface water systems not monitoring under the provisions of subsection 12.9.1 must take monthly TOC samples every 30 days at a location prior to any treatment, beginning April 1, 2008 or earlier, if specified by the Division. In addition to meeting the other criteria for reduced monitoring in subsection 12.7.1.2, the source water TOC running annual average must be <4.0 mg/L (based on the most recent four quarters of monitoring) on a continuing basis at each treatment plant to reduce or remain on reduced monitoring for TTHM and HAA5. Once qualified for reduced monitoring for TTHM and HAA5 under subsection 12.7.1.2, a system may reduce source water TOC monitoring to quarterly TOC samples taken every 90 days at a location prior to treatment.

12.7.1.4 Systems on a reduced monitoring schedule may remain on that reduced schedule as long as the average of all samples taken in the year (for systems which must monitor quarterly) or the result of the sample (for systems which must monitor no more frequently than annually) is no more than 0.060 mg/L and 0.045 mg/L for TTHMs and HAA5, respectively. Systems that do not meet these levels must resume monitoring at the frequency identified in subsection 12.7.1.1 in the quarter immediately following the quarter in which the system exceeds 0.060 mg/L and 0.045 mg/L for TTHMs and HAA5, respectively. For systems using only groundwater not under the direct influence of surface water and serving fewer than 10,000 persons, if either the TTHM annual average is >0.080 mg/L or the HAA5 annual average is >0.060 mg/L, the system must go to increased monitoring identified in subsection 12.7.1.1 (sample location column) in the quarter immediately following the monitoring period in which the system exceeds 0.080 mg/L or 0.060 mg/L for TTHMs or HAA5s respectively.

12.7.1.5 Systems on increased monitoring may return to routine monitoring if, after at least one year of monitoring their TTHM annual average is <0.060 mg/L and their HAA5 annual average is <0.045 mg/L.

12.7.1.6 The Division may return a system to routine monitoring at the Division's discretion.

12.7.2 Chlorite. Community and non-transient non-community water systems using chlorine dioxide, for disinfection or oxidation, must conduct monitoring for chlorite.

12.7.2.1 Routine monitoring

12.7.2.1.1 Daily monitoring. Systems must take daily samples at the entrance to the distribution system. For any daily sample that exceeds the chlorite MCL, the system must take additional samples in the distribution system the following day at the locations required by subsection 12.7.2.2, in addition to the sample required at the entrance to the distribution system.

12.7.2.1.2 Monthly monitoring. Systems must take a three-sample set each month in the distribution system. The system must take one sample at each of the following locations: near the first customer, at a location representative of average residence time, and at a location reflecting maximum residence time in the distribution system. Any additional routine sampling must be conducted in the same manner (as three-sample sets, at the specified locations). The system may use the results of additional monitoring conducted under subsection 12.7.2.2 to meet the requirement for monitoring in this paragraph.

12.7.2.1.3 A party approved by EPA or the Division must measure daily chlorite samples at the entrance to the distribution system.

12.7.2.2 Additional monitoring. On each day following a routine sample monitoring result that exceeds the chlorite MCL at the entrance to the distribution system, the system is required to take three chlorite distribution system samples at the following locations: as close to the first customer as possible, in a location representative of average residence time, and as close to the end of the distribution system as possible (reflecting maximum residence time in the distribution system).

12.7.2.3 Reduced monitoring.

12.7.2.3.1 Chlorite monitoring at the entrance to the distribution system required by subsection 12.7.2.1.1 may not be reduced.

12.7.2.3.2 Chlorite monitoring in the distribution system required by subsection 12.7.2.1.2 may be reduced to one three-sample set per quarter after one year of monitoring where no individual chlorite sample taken in the distribution system under subsection 12.7.2.1.2 has exceeded the chlorite MCL and the system has not been required to conduct monitoring under subsection 12.7.2.2. The system may remain on the reduced monitoring schedule until either any of the three individual chlorite samples taken quarterly in the distribution system under subsection 12.7.2.1.2 exceeds the chlorite MCL or the system is required to conduct monitoring under subsection 12.7.2.2, at which time the system must revert to routine monitoring.

12.7.3 Bromate.

12.7.3.1 Routine monitoring. Community and non-transient non-community systems using ozone, for disinfection or oxidation, must take one sample per month for each treatment plant in the system using ozone. Systems must take samples monthly at the entrance to the distribution system while the ozonation system is operating under normal conditions.

12.7.3.2 Reduced monitoring.

12.7.3.2.1 Until March 31, 2009, systems required to analyze for bromate may reduce monitoring from monthly to once per quarter, if the system demonstrates that the average source water bromide concentration is less than 0.05 mg/L based upon representative monthly bromide measurements for one year. The system may remain on reduced bromate monitoring until the running annual average source water bromide concentration, computed quarterly, is equal to or greater than 0.05 mg/L based upon representative monthly measurements. If the running annual average source water bromide concentration is [GREATER THEN OR EQUAL TO]0.05 mg/L, the system must resume routine monitoring required by subsection 12.7.3.1.

12.7.3.2.2 Beginning April 1, 2009, systems may no longer use the provisions of subsection 12.7.3.2.1 to qualify for reduced monitoring. A system required to analyze for bromate may reduce monitoring from monthly to quarterly, if the system running annual average bromate concentration is [LESS THEN OR EQUAL TO]0.0025 mg/L based on monthly bromate measurements under subsection 12.7.3.1 for the most recent four quarters, with samples analyzed using Method 317.0 Revision 2.0, 326.0 or 321.8. If a system has qualified for reduced bromate monitoring under subsection 12.7.3.2.1 that system may remain on reduced monitoring as long as the running annual average of quarterly bromate samples [LESS THEN OR EQUAL TO]0.0025 mg/L based on samples analyzed using Method 317.0 Revision 2.0, 326.0, or 321.8. If the running annual average bromate concentration is >0.0025 mg/L, the system must resume routine monitoring required by subsection 12.7.3.1.

12.8 Monitoring requirements for disinfectant residuals.

12.8.1 Chlorine and Chloramines.

12.8.1.1 Routine monitoring. Systems must measure the residual disinfectant level at the same points in the distribution system and at the same time as total coliforms are sampled, as specified in Section 7.0.

12.8.1.2 Reduced monitoring. Monitoring may not be reduced.

12.8.2 Chlorine dioxide.

12.8.2.1 Routine monitoring. Community, non-transient non-community, and transient non-community water systems that use chlorine dioxide for disinfection or oxidation must take daily samples at the entrance to the distribution system. For any daily sample that exceeds the MRDL, the system must take samples in the distribution system the following day at the locations required by subsection 12.8.2.2, in addition to the sample required at the entrance to the distribution system.

12.8.2.2 Additional monitoring. On each day following a routine sample monitoring result that exceeds the MRDL, the system is required to take three chlorine dioxide distribution system samples. If chlorine dioxide or chloramines are used to maintain a disinfectant residual in the distribution system, or if chlorine is used to maintain a disinfectant residual in the distribution system and there are no disinfection addition points after the entrance to the distribution system (i.e., no booster chlorination), the system must take three samples as close to the first customer as possible, at intervals of at least six hours. If chlorine is used to maintain a disinfectant residual in the distribution system and there are one or more disinfection addition points after the entrance to the distribution system (i.e., booster chlorination), the system must take one sample at each of the following locations: as close to the first customer as possible, in a location representative of average residence time, and as close to the end of the distribution system as possible (reflecting maximum residence time in the distribution system).

12.8.2.3 Reduced monitoring. Chlorine dioxide monitoring may not be reduced.

12.9 Monitoring requirements for disinfection byproduct precursors (DBPP).

12.9.1 Routine monitoring. Surface water or ground water under the direct influence of surface water systems which use conventional filtration treatment (as defined in Section 1.0) must monitor each treatment plant for TOC no later than the point of combined filter effluent turbidity monitoring and representative of the treated water. All systems required to monitor under this paragraph must also monitor for TOC in the source water prior to any treatment at the same time as monitoring for TOC in the treated water. These samples (source water and treated water) are referred to as paired samples. At the same time as the source water sample is taken, all systems must monitor for alkalinity in the source water prior to any treatment. Systems must take one paired sample and one source water alkalinity sample per month per plant at a time representative of normal operating conditions and influent water quality.

12.9.2 Reduced monitoring. Surface water or ground water under the direct influence of surface water systems with an average treated water TOC of less than 2.0 mg/L for two consecutive years, or less than 1.0 mg/L for one year, may reduce monitoring for both TOC and alkalinity to one paired sample and one source water alkalinity sample per plant per quarter. The system must revert to routine monitoring in the month following the quarter when the annual average treated water TOC [GREATER THEN OR EQUAL TO]2.0 mg/L.

12.10 Bromide: Until April 1, 2009, systems required to analyze for bromate may reduce bromate monitoring from monthly to once per quarter, if the system demonstrates that the average source water bromide concentration is less than 0.05 mg/L based upon representative monthly measurements for one year. The system must continue bromide monitoring to remain on reduced bromate monitoring.

12.11 Monitoring plans. Each system required to monitor under this Section 12.0 must develop and implement a monitoring plan. The system must maintain the plan and make it available for inspection by the Division and the general public no later than 30 days following the applicable compliance dates in subsection 12.2. All Surface water or ground water under the direct influence of surface water systems serving more than 3,300 people must submit a copy of the monitoring plan to the Division no later than the date of the first report required under subsection 12.6. The Division may also require the plan to be submitted by any other system. After review, the Division may require changes in any plan elements. The plan must include at least the following elements.

12.11.1 Specific locations and schedules for collecting samples for any parameters included in this section.

12.11.2 How the system will calculate compliance with MCLs, MRDLs, and treatment techniques.

12.11.3 If approved for monitoring as a consecutive system, or if providing water to a consecutive system, under the provisions of subsection 1.16.2, the sampling plan must reflect the entire distribution system.

12.12 Compliance requirements:

12.12.1 General requirements.

12.12.1.1 Where compliance is based on a running annual average of monthly or quarterly samples or averages and the system's failure to monitor for TTHM, HAA5, or bromate, this failure to monitor will be treated as a monitoring violation for the entire period covered by the annual average. Where compliance is based on a running annual average of monthly or quarterly samples or averages and the system's failure to monitor makes it impossible to determine compliance with MRDLs for chlorine and chloramines, this failure to monitor will be treated as a monitoring violation for the entire period covered by the annual average.

12.12.1.2 All samples taken and analyzed under the provisions of this section must be included in determining compliance, even if that number is greater than the minimum required.

12.13 Disinfection byproducts.

12.13.1 TTHMs and HAA5s

12.13.1.1 For systems monitoring quarterly, compliance with MCLs in subsection 9.2.1.2 must be based on a running annual arithmetic average, computed quarterly, of quarterly arithmetic averages of all samples collected by the system as prescribed by subsection 12.7.1. If the running annual arithmetic average of quarterly averages covering any consecutive four-quarter period exceeds the MCL, the system is in violation of the MCL and must notify the public pursuant to subsection 4.2, in addition to reporting to the Division pursuant to subsection 12.15. If a PWS fails to complete four consecutive quarters' monitoring, compliance with the MCL for the last four-quarter compliance period must be based on an average of the available data.

12.13.1.2 For systems monitoring less frequently than quarterly, compliance must be based on an average of samples taken that year under the provisions of subsection 12.7.1. If the average of these samples exceeds the MCL, the system must increase monitoring to once per quarter per treatment plant and such a system is not in violation of the MCL until it has completed one year of quarterly monitoring, unless the result of fewer than four quarters of monitoring will cause the running annual average to exceed the MCL, in which case the system is in violation at the end of that quarter. Systems required to increase monitoring frequency to quarterly monitoring must calculate compliance by including the sample that triggered the increased monitoring plus the following three quarters of monitoring.

12.13.2 Bromate. Compliance must be based on a running annual arithmetic average, computed quarterly, of monthly samples (or, for months in which the system takes more than one sample, the average of all samples taken during the month) collected by the system as prescribed by subsection 12.7.3. If the average of samples covering any consecutive four-quarter period exceeds the MCL, the system is in violation of the MCL and must notify the public pursuant to subsection 4.2, in addition to reporting to the Division pursuant to subsection 12.13. If a PWS fails to complete 12 consecutive months' monitoring, compliance with the MCL for the last four-quarter compliance period must be based on an average of the available data.

12.13.3 Chlorite. Compliance must be based on an arithmetic average of each three sample set taken in the distribution system as prescribed by subsection 12.7.2. If the arithmetic average of any three sample set exceeds the MCL, the system is in violation of the MCL and must notify the public pursuant to subsection 4.2, in addition to reporting to the Division pursuant to subsection 12.15.

12.14 Disinfectant residuals.

12.14.1 Chlorine and chloramines.

12.14.1.1 Compliance must be based on a running annual arithmetic average, computed quarterly, of monthly averages of all samples collected by the system under subsection 12.8.8.1. If the average of quarterly averages covering any consecutive four-quarter period exceeds the MRDL, the system is in violation of the MRDL and must notify the public pursuant to section 4.2, in addition to reporting to the Division pursuant to subsection 12.15.

12.14.1.2 In cases where systems switch between the use of chlorine and chloramines for residual disinfection during the year, compliance must be determined by including together all monitoring results of both chlorine and chloramines in calculating compliance. Reports submitted pursuant to subsection 12.6 must clearly indicate which residual disinfectant was analyzed for each sample.

12.14.2 Chlorine dioxide

12.14.2.1 Acute violations. Compliance must be based on consecutive daily samples collected by the system under subsection 12.8.2. If any daily sample taken at the entrance to the distribution system exceeds the MRDL, and on the following day one (or more) of the three samples taken in the distribution system exceed the MRDL, the system is in violation of the MRDL and must take immediate corrective action to lower the level of chlorine dioxide below the MRDL and must notify the public pursuant to the procedures for acute health risks in subsection 4.2 in addition to reporting to the Division pursuant to subsection 12.15. Failure to take samples in the distribution system the day following an exceedance of the chlorine dioxide MRDL at the entrance to the distribution system will also be considered an MRDL violation and the system must notify the public of the violation in accordance with the provisions for acute violations under subsection 4.2 in addition to reporting to the Division in accordance with subsection 12.15.

12.14.2.2 Non-acute violations. Compliance must be based on consecutive daily samples collected by the system under subsection 12.4.8.2. If any two consecutive daily samples taken at the entrance to the distribution system exceed the MRDL and all distribution system samples taken are below the MRDL, the system is in violation of the MRDL and must take corrective action to lower the level of chlorine dioxide below the MRDL at the point of sampling and will notify the public pursuant to the procedures for non-acute health risks in subsection 4.2 in addition to reporting to the Division pursuant to subsection 12.15. Failure to monitor at the entrance to the distribution system the day following an exceedance of the chlorine dioxide MRDL at the entrance to the distribution system is also an MRDL violation and the system must notify the public of the violation in accordance with the provisions for non-acute violations under subsection 4.2 in addition to reporting to the Division in accordance with subsection 12.15.

12.14.3 Disinfection byproduct precursors (DBPP). Compliance must be determined as specified by subsection 12.16.3. Systems may begin monitoring to determine whether Step 1 TOC removals can be met 12 months prior to the compliance date for the system. This monitoring is not required and failure to monitor during this period is not a violation. However, any system that does not monitor during this period, and then determines in the first 12 months after the compliance date that it is not able to meet the Step 1 requirements in subsection 12.16.2.2 and must therefore apply for alternate minimum TOC removal (Step 2) requirements, is not eligible for retroactive approval of alternate minimum TOC removal (Step 2) requirements as allowed pursuant to subsection 12.16.2.3 and is in violation. Systems may apply for alternate minimum TOC removal (Step 2) requirements any time after the compliance date. For systems required to meet Step 1 TOC removals, if the value calculated under subsection 12.16.3.1.4 is less than 1.00, the system is in violation of the treatment technique requirements and must notify the public pursuant to subsection 4.2, in addition to reporting to the Division pursuant to subsection 12.15.

12.15 Reporting and recordkeeping requirements:

12.15.1 Systems required to sample quarterly or more frequently must report to the Division within 10 days after the end of each quarter in which samples were collected, notwithstanding the provisions of subsections 4.1.1, 4.1.2, 4.1.3, 4.1.7 and 4.1.8. Systems required to sample less frequently than quarterly must report to the Division within 10 days after the end of each monitoring period in which samples were collected.

12.15.2 Disinfection byproducts. Systems must report the information specified in the following table:

If you are a...	You must report1...
System monitoring for TTHM and HAA5 under the requirements of subsection 12.7 on a quarterly or more frequent basis	1. The number of samples taken during the last quarter. 2. The location, date, and result of each sample taken during the last quarter. 3. The arithmetic average of all samples taken in the last quarter. 4. The annual arithmetic average of the quarterly arithmetic averages of this section for the last four quarters. 5. Whether, based on subsection 12.15.1, the MCL was violated.
System monitoring for TTHMs and HAA5 under the requirements of subsection 12.7 less frequently than quarterly (but at least annually).	1. The number of samples taken during the last year. 2. The location, date, and result of each sample taken during the last monitoring period. 3. The arithmetic average of all samples taken over the last year. 4. Whether, based on subsection 12.15.1, the MCL was violated.
System monitoring for TTHMs and HAA5 under the requirements of subsection 12.7 less frequently than annually.	1. The location, date, and result of the last sample taken. 2. Whether, based on subsection 12.15.1, the MCL was violated.
System monitoring for chlorite under the requirements of subsection 12.7.	1. The number of entry point samples taken each month for the last three months. 2. The location, date, and result of each sample (both entry point and distribution system) taken during the last quarter. 3. For each month in the reporting period, the arithmetic average of all samples taken in each three samples set taken in the distribution system. 4. Whether, based on subsection 12.15.3, the MCL was violated, and how many times it was violated each month.
System monitoring for bromate under the requirements of subsection 12.7.	1. The number of samples taken during the last quarter. 2. The location, date, and result of each sample taken during the last quarter. 3. The arithmetic average of the monthly arithmetic averages of all samples taken in the last year. 4. Whether, based on subsection 12.15.2 the MCL was violated.

1 The Division may choose to perform calculations and determine whether the MCL was exceeded, in lieu of having the system report that information.

12.15.3 Disinfectants. Systems must report the information specified in the following table:

If you are a...

You must report¹...

System monitoring for chlorine or chloramines under the requirements of subsection 12.8.

1. The number of samples taken during each month of the last quarter.

2. The monthly arithmetic average of all samples taken in each month for the last 12 months.

3. The arithmetic average of all monthly averages for the last 12 months.

4. Whether, based on subsection 1.19.3.1, the MRDL was violated.

System monitoring for chlorine dioxide under the requirements of subsection 12.8.

1. The dates, results, and locations of samples taken during the last quarter.

2. Whether, based on subsection 1.19.3.1, the MRDL was violated.

3. Whether the MRDL was exceeded in any two consecutive daily samples and whether the resulting violation was acute or non-acute.

¹ The Division may choose to perform calculations and determine whether the MRDL was exceeded, in lieu of having the system report that information.

12.15.4 Disinfection byproduct precursors and enhanced coagulation or enhanced softening. Systems must report the information specified in the following table:

If you are a...

You must report¹...

System monitoring monthly or quarterly for TOC under the requirements of subsection 12.9 and required to meet the enhanced coagulation or enhanced softening requirements in subsections 12.16.2.2 or 12.16.2.3.

1. The number of paired (source water and treated water, prior to continuous disinfection) samples taken during the last quarter.

2. The location, date, and result of each paired sample and associated alkalinity taken during the last quarter.

3. For each month in the reporting period that paired sample were taken, the arithmetic average of the percent reduction of TOC for each paired sample and the required TOC percent removal.

4. Calculations for determining compliance with the TOC percent removal requirements, as provided in subsection 12.16.3.1. 5. Whether the system is in compliance with the enhanced coagulation or enhanced softening percent removal requirements in subsection 12.16.2 for the last four quarters.

System monitoring monthly or quarterly for TOC under the requirements of subsection 12.9 and meeting one or more of the alternative compliance criteria in subsections 12.16.1.2 or 12.16.1.3.

1. The alternative compliance criterion that the system is using.

2. The number of paired (source water and treated water, prior to continuous disinfection) samples taken during the last quarter.

3. The location, date, and result of each paired sample and associated alkalinity taken during the last quarter.

4. The running annual arithmetic average based on monthly averages (or quarterly samples) of source water TOC for systems meeting a criterion in subsections 12.16.1.2.1 or 12.16.1.2.3 or of treated water TOC for systems meeting the criterion in subsection 12.16.1.2.2.

5. The running annual arithmetic average based on monthly averages (or quarterly samples) of source water SUVA for systems meeting the criterion in subsection 12.7.1.2.5 or of treated water SUVA for systems meeting the criterion in subsection 12.16.1.2.6.

6. The running annual average of source water alkalinity for systems meeting the criterion in subsection 12.16.1.2.3 and of treated water alkalinity for systems meeting the criterion in subsection 12.16.1.3.1.

7. The running annual average for both TTHM and HAA5 for systems meeting the criterion in subsection 12.16.1.2.3 or 12.16.1.2.4.

8. The running annual average of the amount of magnesium hardness removal (as CaCO3, in mg/L) for systems meeting the criterion in subsection 12.16.1.3.2.

9. Whether the system is in compliance with the particular alternative compliance criterion in subsections 12.16.1.2 or 12.16.1.3.

¹ The Division may choose to perform calculations and determine whether the treatment technique was met, in lieu of having the system report the information.

12.16 Treatment Technique for Control of Disinfection Byproduct (DBP) Precursors:

12.16.1 Applicability.

12.16.1.1 Surface water or ground water under the direct influence of surface water systems using conventional filtration treatment (as defined in Section 1.0) must operate with enhanced coagulation or enhanced softening to achieve the TOC percent removal levels specified in subsection 12.16.2 unless the system meets at least one of the alternative compliance criteria listed in subsections 12.16.1.2 or 12.16.1.3.

12.16.1.2 Alternative compliance criteria for enhanced coagulation and enhanced softening systems. Surface water or ground water under the direct influence of surface water systems using conventional filtration treatment may use the alternative compliance criteria in subsections 12.16.1.2.1 through 12.16.1.2.6 to comply with this section in lieu of complying with subsection 12.16.2. Systems must still comply with monitoring requirements in subsection 12.9.

12.16.1.2.1 The system's source water TOC level, measured according to 40 CFR 141.131(d)(3), is less than 2.0 mg/L, calculated quarterly as a running annual average.

12.16.1.2.2 The system's treated water TOC level, measured according to 40 CFR 141.131(d)(3), is less than 2.0 mg/L, calculated quarterly as a running annual average.

12.16.1.2.3 The system's source water TOC level, measured as required by 40 CFR 141.131(d)(3), is less than 4.0 mg/L, calculated quarterly as a running annual average; the source water alkalinity, measured according to 40 CFR 141.131(d)(1), is greater than 60 mg/L (as CaCO3), calculated quarterly as a running annual average; and either the TTHM and HAA5 running annual averages are no greater than 0.040 mg/L and 0.030 mg/L, respectively; or prior to the effective date for compliance in subsection 12.2, the system has made a clear and irrevocable financial commitment not later than the effective date for compliance in subsection 12.2 to use of technologies that will limit the levels of TTHMs and HAA5 to no more than 0.040 mg/L and 0.030 mg/L, respectively. Systems must submit evidence of a clear and irrevocable financial commitment, in addition to a schedule containing milestones and periodic progress reports for installation and operation of appropriate technologies, to the Division for approval not later than the effective date for compliance in subsection 12.2. These technologies must be installed and operating not later than June 16, 2005. Failure to install and operate these technologies by the date in the approved schedule will constitute a violation of National Primary Drinking Water Regulations.

12.16.1.2.4 The TTHM and HAA5 running annual averages are no greater than 0.040 mg/L and 0.030 mg/L, respectively, and the system uses only chlorine for primary disinfection and maintenance of a residual in the distribution system.

12.16.1.2.5 The system's source water SUVA, prior to any treatment and measured monthly according to 40 CFR 141.131(d)(4), is less than or equal to 2.0 L/mg-m, calculated quarterly as a running annual average.

12.16.1.2.6 The system's finished water SUVA, measured monthly according to 40 CFR 141.131(d)(4), is less than or equal to 2.0 L/mg-m, calculated quarterly as a running annual average.

12.16.1.3 Additional alternative compliance criteria for softening systems. Systems practicing enhanced softening that cannot achieve the TOC removals required by subsection 12.16.2.2 may use the alternative compliance criteria in subsections 12.16.1.3.1 and 12.16.1.3.2 in lieu of complying with subsection 12.16.2. Systems must still comply with monitoring requirements in subsection 12.9.

12.16.1.3.1 Softening that results in lowering the treated water alkalinity to less than 60 mg/L (as CaCO3), measured monthly according to 40 CFR 141.131(d)(1) and calculated quarterly as a running annual average.

12.16.1.3.2 Softening that results in removing at least 10 mg/L of magnesium hardness (as CaCO3), measured monthly according to subsection 12.2.2 and calculated quarterly as an annual running average.

12.16.2 Enhanced coagulation and enhanced softening performance requirements.

12.16.2.1 Systems must achieve the percent reduction of TOC specified in subsection 12.16.2.2 between the source water and the combined filter effluent, unless the Division approves a system's request for alternate minimum TOC removal (Step 2) requirements under subsection 12.16.2.3.

12.16.2.2 Required Step 1 TOC reductions, indicated in the following table, are based upon specified source water parameters measured in accordance with 40 CFR 141.131(d). Systems practicing softening are required to meet the Step 1 TOC reductions in the far-right column (Source water alkalinity >120 mg/L) for the specified source water TOC:

Step 1 Required Removal of TOC by Enhanced Coagulation and Enhanced Softening for Subpart H Systems Using Conventional Treatment^1,2

Source Water TOC	Source water alkalinity, mg/L as CaCO³ (in percentages)
	0-60	>60-120	>1203
>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

¹ Systems meeting at least one of the conditions in subsections 12.16.1.2.1 through 12.16.1.2.6 are not required to operate with enhanced coagulation.

² Softening systems meeting one of the alternative compliance criteria in subsection 12.16.1.3 are not required to operate with enhanced softening.

³ Systems practicing softening must meet the TOC removal requirements in this column.

12.16.2.3 Surface water or ground water under the direct influence of surface water conventional treatment systems that cannot achieve the Step 1 TOC removals required by subsection 12.16.2.2 due to water quality parameters or operational constraints must apply to the Division, within three months of failure to achieve the TOC removals required by subsection 12.16.2.2, for approval of alternative minimum TOC (Step 2) removal requirements submitted by the system. If the Division approves the alternative minimum TOC removal (Step 2) requirements, the Division may make those requirements retroactive for the purposes of determining compliance. Until the Division approves the alternate minimum TOC removal (Step 2) requirements, the system must meet the Step 1 TOC removals contained in subsection 12.16.2.2.

12.16.2.4 Alternate minimum TOC removal (Step 2) requirements. Applications made to the Division by enhanced coagulation systems for approval of alternative minimum TOC removal (Step 2) requirements under subsection 12.16.2.3 must include, as a minimum, results of bench- or pilot-scale testing conducted under subsection 12.16.2.4.1 and used to determine the alternate enhanced coagulation level.

12.16.2.4.1 Alternate enhanced coagulation level is defined as coagulation at a coagulant dose and pH as determined by the method described in subsections 12.16.2.4.1 through 12.16.2.4.5 such that an incremental addition of 10 mg/L of alum (as aluminum) (or equivalent amount of ferric salt) results in a TOC removal of [LESS THEN OR EQUAL TO] 0.3 mg/L. The percent removal of TOC at this point on the ``TOC removal versus coagulant dose'' curve is then defined as the minimum TOC removal required for the system. Once approved by the Division, this minimum requirement supersedes the minimum TOC removal required by the table in subsection 12.16.2.2. This requirement will be effective until such time as the Division approves a new value based on the results of a new bench- and pilot-scale test. Failure to achieve Division-set alternative minimum TOC removal levels is a violation of National Primary Drinking Water Regulations.

12.16.2.4.2 Bench- or pilot-scale testing of enhanced coagulation must be conducted by using representative water samples and adding 10 mg/L increments of alum (as aluminum) (or equivalent amounts of ferric salt) until the pH is reduced to a level less than or equal to the enhanced coagulation Step 2 target pH shown in the following table:

Enhanced Coagulation Step 2 Target pH

Alkalinity (mg/L as CaCO³)	Target pH
0 - 60	5.5
>60 - 120	6.3
>120 - 240	7.0
>240	7.5

12.16.2.4.3 For waters with alkalinities of less than 60 mg/L for which addition of small amounts of alum or equivalent addition of iron coagulant drives the pH below 5.5 before significant TOC removal occurs, the system must add necessary chemicals to maintain the pH between 5.3 and 5.7 in samples until the TOC removal of 0.3 mg/L per 10 mg/L alum added (as aluminum) (or equivalent addition of iron coagulant) is reached.

12.16.2.4.4 The system may operate at any coagulant dose or pH necessary (consistent with other NPDWRs) to achieve the minimum TOC percent removal approved under subsection 12.16.2.3.

12.16.2.4.5 If the TOC removal is consistently less than 0.3 mg/L of TOC per 10 mg/L of incremental alum dose (as aluminum) at all dosages of alum (or equivalent addition of iron coagulant), the water is deemed to contain TOC not amenable to enhanced coagulation. The system may then apply to the Division for a waiver of enhanced coagulation requirements.

12.16.3 Compliance Calculations:

12.16.3.1 Surface water or ground water under the direct influence of surface water systems other than those identified in subsections 12.16.1.2 or 12.16.1.3 must comply with requirements contained in subsections 12.16.2.2 or 12.16.2.3. Systems must calculate compliance quarterly, beginning after the system has collected 12 months of data, by determining an annual average using the following method:

12.16.3.1.1 Determine actual monthly TOC removal, equal to: (1-(treated water TOC/source water TOC)) X 100.

12.16.3.1.2 Determine the required monthly TOC percent removal (from either the table in subsection 12.16.2.2 or from subsection 12.16.2.3).

12.16.3.1.3 Divide the value in subsection 12.16.3.1.1 by the value in subsection 12.16.3.1.2.

12.16.3.1.4 Add together the results of subsection 12.16.3.1.3 for the last 12 months and divide by 12.

12.16.3.1.5 If the value calculated in subsection 12.16.3.1.4 is less than 1.00, the system is not in compliance with the TOC percent removal requirements.

12.16.3.2 Systems may use the provisions in subsections 12.16.3.2.1 through 12.16.3.2.5 in lieu of the calculations in subsections 12.16.3.1.1 through 12.16.3.1.5 to determine compliance with TOC percent removal requirements.

12.16.3.2.1 In any month that the system's treated or source water TOC level, measured according to 40 CFR 141.131(d)(3), is less than 2.0 mg/L, the system may assign a monthly value of 1.0 (in lieu of the value calculated in subsection 12.16.3.1.3) when calculating compliance under the provisions of subsection 12.16.3.1.

12.16.3.2.2 In any month that a system practicing softening removes at least 10 mg/L of magnesium hardness (as CaCO3), the system may assign a monthly value of 1.0 (in lieu of the value calculated in subsection 12.16.3.1.3) when calculating compliance under the provisions of subsection 12.16.3.1.

12.16.3.2.3 In any month that the system's source water SUVA, prior to any treatment and measured according to 40 CFR 141.131(d)(4), is [LESS THEN OR EQUAL TO]2.0 L/mg-m, the system may assign a monthly value of 1.0 (in lieu of the value calculated in subsection 12.16.3.1.3) when calculating compliance under the provisions of subsection 12.16.3.1.

12.16.3.2.4 In any month that the system's finished water SUVA, measured according to 40 CFR 141.131(d)(4), is [LESS THEN OR EQUAL TO]2.0 L/mg-m, the system may assign a monthly value of 1.0 (in lieu of the value calculated in subsection 12.16.3.1.3) when calculating compliance under the provisions of subsection 12.16.3.1.

12.16.3.2.5 In any month that a system practicing enhanced softening lowers alkalinity below 60 mg/L (as CaCO3), the system may assign a monthly value of 1.0 (in lieu of the value calculated in subsection 12.16.3.1.3) when calculating compliance under the provisions of subsection 12.16.3.1.

12.16.3.3 Surface water or ground water under the direct influence of surface water systems using conventional treatment may also comply with the requirements of this section by meeting the criteria in subsection 12.16.1.2 or 12.16.1.3.

12.16.4 Treatment technique requirements for DBP precursors. The Division identifies the following as treatment techniques to control the level of disinfection byproduct precursors in drinking water treatment and distribution systems:

12.16.4.1 For Surface water or ground water under the direct influence of surface water systems using conventional treatment, enhanced coagulation or enhanced softening.

16 Del. Admin. Code § 4462-12.0

24 DE Reg. 794(2/1/2021)
25 DE Reg. 713( 1/1/2022) (Final)