Duration of Mandatory Replacement
The previous rule required water systems with LSLs that continue to exceed the lead AL after the installation of treatment to annually replace a minimum of 7 percent of the initial number of LSLs in their distribution system. The Primacy Agency could require systems that did not install the required treatment also to initiate LSLR and/or to replace LSLs at a faster replacement rate. Systems could discontinue LSLR if they no longer exceed the lead AL for two consecutive six month tap sampling periods.
To estimate the average time a CWSs would continue LSLR before being eligible to stop LSLR, EPA:
 Identified CWSs with a reported milestone of "LSLR." This milestone indicates systems that are required to initiate LSLR.
 Assumed the Primacy Agency would only require LSLR if a system had a continued lead ALE after installing CCT. Thus, the analysis was restricted to only those CWSs with CCT (see Section 4.3.3) and at least one lead ALE prior to the date a system was required to initiate replacement of LSLs, i.e., the "Event Actual Date." EPA applied these criteria to limit the analysis to 85 CWSs that EPA assumed initiated LSLR in response to the rule as opposed to voluntary replacement. If the "Event Actual Date" month was June through September, then a 1/2 year of LSLR was assumed for that same year. However, if the "Event Actual Date" month was October through December of a given year, it was assumed that LSLR began in January of the following year. If more than one "Event Actual Date" was reported to SDWIS/Fed, EPA used the earliest one.
 Identified all lead ALEs (i.e., lead 90[th] percentile levels above 15 ug/L) since the "Event Actual Date."
 Determined the length of time from the "Event Actual Date" to the end of the period in which the CWS no longer had a lead ALE for two consecutive six month tap sampling periods and could discontinue LSL replacements. If no 90[th] percentile was reported, EPA assumed that the system had no lead ALE. Any subsequent ALE(s) were also counted toward the years of LSLR until the system again had two subsequent tap sampling periods without a lead ALE.
The estimated average number of years of replacements based on 85 CWSs was 3 years. For additional details, see the file "Derivation of LSLR_Time_Span_Analysis_CWS_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300.
For NTNCWSs, EPA applied the same average estimate of 3 years because there was less milestone data for NTNCWSs as compared to CWSs in SDWIS/Fed.
Discussion of Data Limitations and Uncertainty
See Section <IP_ADDRESS> for a discussion of data uncertainty associated with SDWIS/Fed. EPA conservatively assumed that NTNCWSs would replace LSLs for 3 years; however, the timeframe may be shorter since NTNCWSs typically have fewer service connections, own their entire service line. EPA further assumed that NTNCWSs with fewer than 7 estimated LSLs (i.e., those serving 10,000 or fewer people) will replace their LSLs within one year.
Lead and Copper Tap Levels
The analyses described in this section draw from multiple sources to characterize baseline water quality including lead levels at customer's taps. Lead 90[th] percentile data were obtained from SDWIS/Fed, along with information on systems' CCT status. EPA also used information from 12 states, Region 9 tribes, and a web search of individual system LSLR programs to identify systems with LSLs. As previously discussed, SDWIS/Fed does not identify which systems have LSLs, only those that are required to initiate LSLR.
The remainder of this section is organized as follows:
 Section <IP_ADDRESS> explains the derivation of the percentage of systems with: 1) no trigger level exceedance (TLE) or ALE, 2) a TLE, or 3) an ALE as a function of LSL and CCT status:
 Prior to implementation of the final LCRR (i.e., baseline conditions).
 During the first year of implementation of the final LCRR when LSL systems must collect a fifth liter sample from available sites served by LSLs in lieu of a first liter sample from 50 percent of sites served by LSLs as required under the previous rule.
 Section <IP_ADDRESS> provides the likelihood of an individual lead sample being greater than 15 ug/L.
 Section <IP_ADDRESS> provides the likelihood that a system exceeds the copper AL of 1.3 mg/L but not the lead AL.
Percent of Systems with No TLE or ALE, a TLE, or ALE
The discussion of the percent of systems that fall into one of three lead 90[th] percentile classifications is presented in three subsections as follows:
         <IP_ADDRESS>.1: Previous Rule
         <IP_ADDRESS>.2: Final LCRR
         <IP_ADDRESS>.3: Discussion of Data Limitations and Uncertainty
Previous Rule
As described in Chapter 3, the LCRR includes a new trigger level (TL) of 10 ug/L whereby a system with a lead tap sample 90th percentile level above 10 ug/L but at or below the existing AL of 15 ug/L (i.e., has a TLE) will be subject to additional requirements. For the purposes of estimating the costs of the final rule, EPA first estimated the proportion of systems that would be classified into one of three lead 90[th] percentile categories prior to implementation of the LCRR (i.e., under the baseline or previous rule) as follows:
 No TLE or ALE: the lead 90[th] percentile level is at or below 10 ug/L,
 A TLE: the lead 90[th] percentile value is above 10 ug/L but at or below 15 ug/L, or
 An ALE: the lead 90[th] percentile level is above 15 ug/L.
The presence or absence of CCT and LSLs can impact lead 90[th] percentile levels; thus, EPA further characterized this analysis based on LSL.
The estimated percent of systems with no TLE or ALE, a TLE, and an ALE is based on SDWIS/Fed historical 90[th] percentile lead tap sample data from 2007 to 2015. EPA recognizes that there are uncertainties in predicting the future 90[th] percentile ranges from historical SDWIS/Fed data. Also, the Agency recognizes that these uncertainties could have a significant impact on estimated costs and benefits of the final LCRR. To provide a range of costs and benefits that reflects this uncertainty, EPA generated a "low" and "high" estimate of baseline conditions as detailed in the following four steps:
Step 1  -  Identified "Low" and "High" 90th percentile level based on historical data: EPA reviewed all lead 90th percentile data from 38,707 CWSs that reported to SDWIS/Fed for monitoring conducted between 2007 and 2015 and excluded those results that were: 1) negative sample values (Maryland only) and 2) values > 1,500 ug/L, which is 100x higher than the AL. From the remaining results 37,286 CWSs, EPA selected the minimum lead 90th percentile level between 2007 and 2015 for the "low" estimate and the maximum lead 90th percentile for the "high" estimate.
Step 2  -  Designated systems by LSL status: Data were grouped according to LSL status for analysis. LSL status for individual systems is not available in SDWIS/Fed; therefore, EPA reached out to states that had collected LSL inventory information and EPA Regions (for tribal systems) and conducted web searches to identify for which systems or additional states sufficient information was available to definitely determine if a system had any LSLs or no LSLs. Exhibit 4-18 summarizes the information from 6,978 systems that were assigned a "yes" / "no" LSL status based on this effort. For additional detail on systems' LSL determination for individual states, see file "Derivation of State LSL Status. _Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
As shown in Exhibit 4-18, information on LSL status was available for systems in 12 states and Region 9 tribal systems, as well as select systems identified in web searches. In all, the number of systems with known LSL status represents approximately 14 percent of the total CWS inventory of 50,067, with information collected from more than 50 percent of states. Column D indicates the percentage of all CWSs for which EPA has known LSL status information. The fact that EPA is constrained by the available data that represents 14 percent of total systems results in a high degree of uncertainty around these estimated percentages for systems falling into the no TLE or ALE, a TLE, or an ALE category. For systems serving > 1M, EPA obtained system-level LSL estimates from available sources (see the data summary table provided as Exhibit B-2 in Appendix B).
Exhibit 4-18: Number of CWSs with LSL Determination Based on State, Tribal, and Web Data1
                                    Source
            Number of Systems per State or Region 9 Tribal Systems
              Number of systems with "YES" LSL determination
               Number of Systems with "NO" LSL determination
                     Percent of CWSs with Known LSL Status

                                       A
                                       B
                                       C
                                  D = (B+C)/A
California
                                                                          2,832
                                                                              6
                                                                              0
                                                                           0.2%
Hawaii2
                                                                            117
                                                                              0
                                                                            117
                                                                           100%
Illinois
                                                                          1,762
                                                                            321
                                                                            891
                                                                            69%
Indiana
                                                                            455
                                                                            117
                                                                            224
                                                                            75%
Louisiana
                                                                             71
                                                                              0
                                                                             36
                                                                            51%
Maryland
                                                                            250
                                                                             23
                                                                            171
                                                                            78%
Michigan
                                                                          1,053
                                                                            172
                                                                            595
                                                                            73%
Nevada3
                                                                            201
                                                                              0
                                                                            201
                                                                           100%
North Carolina
                                                                          2,197
                                                                             59
                                                                          2,138
                                                                           100%
Ohio
                                                                          1,205
                                                                            179
                                                                            712
                                                                            74%
Washington
                                                                            691
                                                                             72
                                                                              1
                                                                            11%
Wisconsin
                                                                            568
                                                                            131
                                                                            414
                                                                            96%
Region 9 Tribes
                                                                            276
                                                                              0
                                                                            276
                                                                           100%
Systems Serving > 1M
                                                                             21
                                                                             13
                                                                              6
                                                                            90%
Web Searches4

                                                                            138
                                                                             17

TOTAL5

                                                                          1,179
                                                                          5,799

Notes:
[1] The data presented in this exhibit were compiled from numerous state surveys, as well as a web search of systems with prior or ongoing LSLR programs and were updated through May 2020. Determinations of whether systems had LSLs within each state were dependent on the information provided in the states' survey. (For additional detail on systems' LSL determination for individual states, see file "Derivation of State LSL Status_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.) Note that this exhibit does not show counts of CWSs that reported "unknown" LSL status or for which the data were insufficient for EPA to determine the system's LSL status. Only those systems whose LSL status was known are described here.
2 The LSL information for the State of Hawaii was extracted from an April 9, 2016 Associated Press article that stated no drinking water systems in Hawaii have lead pipes.
3 The LSL information for the State of Nevada was submitted as a public comment on the proposed LCRR, by the Nevada Division of Environmental Protection, stating that no drinking water systems in Nevada had documented LSLs. Refer to Attachment A that is available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
4 The web search identified LSL status information for systems from 21 states plus Washington, D.C. For more details, see file "Derivation of State LSL Status_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
5 Note that there was overlap with some of the systems with known LSL status in individual states, systems identified through web searches, and those that serve more than 1 million people.

Step 3  -  Identified systems with reported lead 90[th] percentile results and known LSL status: EPA identified which systems had at least one reported lead 90[th] percentile value in SDWIS/Fed between 2007 and 2015 and known LSL status. This subset of 4,424 systems was used for the remainder of the analysis described in step 4. Of the 4,424 systems, 23 percent (1,031 systems) were identified as having LSLs and 77 percent (3,393 systems) were identified as having no LSLs.
Step 4  -  Estimated the Percentage of CWSs in Each Category: Based on Steps 1 through 3, EPA assigned each CWS to the category of: 1) no TLE or ALE, 2) a TLE, or 3) an ALE based on each system's LSL status.
Exhibit 4-19 presents the "low" and "high" estimates of the percentage of systems in each lead 90[th] percentile category by LSL status. The "low estimate" is based on the lowest 90[th] percentile lead value reported to SDWIS/Fed from 2007 to 2015; the "high estimate" is based on the highest 90[th] percentile lead value reported to SDWIS/Fed from 2007 to 2015. Based on the "low estimate," the percentage of systems without LSLs having an ALE was slightly higher than that of systems with LSLs, which is counterintuitive but may be reflective of the limitations of the known LSL status dataset. For the categories TLE and no TLE/ALE, systems with LSLs had a slightly higher percentage than those without LSLs. For the "high estimate," the differences between systems with and without LSLs was greater. As expected, a higher percentage of systems with LSLs were classified as having an ALE or TLE than those without LSLs.
Exhibit 4-19: Percent of CWSs with No TLE or ALE, a TLE, and an ALE (Baseline Conditions)
                                   Category
                                    No LSLs
                                   Has LSLs
                                 Low Estimate
No TLE/ALE (P90 <=10 ug/L)
                                                                            97%
                                                                            99%
           <= 5 ug/L
                                                                            94%
                                                                            85%
           >5 and <=10 ug/L
                                                                             3%
                                                                            14%
TLE (10 ug/L < P90 <= 15 ug/L )
                                                                             0%
                                                                             1%
ALE (P90 > 15 ug/L)
                                                                             2%
                                                                             0%
                                 High Estimate
No TLE/ALE (P90 <=10 ug/L)
                                                                            87%
                                                                            79%
           <= 5 ug/L
                                                                            68%
                                                                            49%
           >5 and <=10 ug/L
                                                                            19%
                                                                            30%
TLE (10 ug/L < P90 <= 15 ug/L)
                                                                             7%
                                                                            12%
ALE (P90 > 15 ug/L)
                                                                             6%
                                                                             9%

Acronyms: ALE = action level exceedance; CWS = community water system; LSL = lead service line; P90 = lead 90[th] percentile level; TLE = trigger level exceedance.
Notes:
    Includes CWSs with known LSL status that also reported at least one 90[th] percentile value to SDWIS/Fed between 2007 and 2015.
    Totals may not add due to independent rounding.
    For additional detail, see file, "Derivation of Initial P90 Categorization_Baseline_Final Rule," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Minimal data were available on the LSL status for NTNCWSs. Thus, the above analysis could not be conducted for NTNCWSs. However, an analysis was conducted to evaluate the likelihood of the NTNCWSs' 90[th] percentile values falling into the three lead 90[th] percentile categories without the consideration of LSL status. The likelihoods for the NTNCWSs were very similar to those calculated for CWSs. Based on this comparison and the lack of LSL information for NTNCWSs, EPA assumed the same estimated percentages for NTNCWSs as those presented in Exhibit 4-19 for CWSs. For additional detail, see file "Derivation of Initial P90 Categorization_CWS_NTNCWS Compare_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Final LCRR
EPA estimated the percent of CWSs with no TLE or ALE, a TLE, or an ALE using historical SDWIS/Fed 90[th] percentile tap sample data (as done for the previous rule) with two important adjustments:
 An adjustment to reflect the new requirement for LSL systems to collect all samples from LSL sites where possible, as opposed to the previous rule minimum of 50 percent of samples being collected from LSL sites.
 An adjustment to reflect new requirements for LSL systems to collect fifth liter samples from LSL sites instead of first liter samples.
These two adjustments are discussed separately below.
    Adjustment to reflect that all LSL system lead tap samples come from LSL sites instead of 50 percent
EPA recognizes that there is uncertainty in the impact of this new requirement on 90[th] percentile lead tap sample levels. EPA also recognizes that the approach used to make the adjustments may have a significant impact on costs and benefits of the final LCRR. To provide a range of costs and benefits that reflects this uncertainty, EPA developed both low and high multipliers for the adjustment of lead 90[th] percentile values to provide bounding around the uncertain impact of this LCRR requirement.
Slabaugh et al. (2015) evaluated LCR compliance data from 17 systems over 72 tap sampling periods, comparing the lead 90[th] percentile concentrations based on samples collected from all LSLs (either Tier 1 sites -- single family structures, or Tier 2 sites -- multiple-family residences) to lead 90[th] percentiles based on samples collected from both LSL and non-LSL sites. The median 90[th] percentile for LSL only sites was 8.95 compared to a median 90[th] percentile of 6.63 from all monitoring sites. The ratio of the median 90[th] percentiles for LSL sites compared to all sites was 8.95/6.63 = 1.35. EPA selected this value (1.35) as a "high" multiplier, meaning that 1.35 was applied to all 90[th] percentile lead values for LSL systems to reflect the potential impacts of sampling from only LSL sites to predict the initial lead categorization under the final LCRR. This adjustment value may be biased high because the median 90[th] percentile value for the 1,031 systems with LSLs (from among the 4,424 systems used in EPA's analysis) was only 2.8 ug/L. This 90[th] percentile value of 2.8 ug/L corresponded with the 9.8 percentile for the 72 tap sampling periods from the Slabaugh et al. (2015) dataset using all sampling sites (that is, for samples taken from all sites, there are 7 of the 72 tap sampling periods, or 9.8 percent, with 90[th] percentile lead values less than or equal to 2.8 ug/L). Ideally, this analysis would have been done at the system level, but EPA did not have access to the dataset of 72 tap sampling periods from the 17 systems. Thus, EPA could not confirm if the data from the tap sampling periods varied among the 17 systems and if system(s) above the AL were overrepresented as 9.8 percent of the rounds exceeded the AL. This is inconsistent with the historical SDWIS/Fed 90[th] percentile data at the system level and may be due to systems' exceeding the AL being on 6-month monitoring whereas the systems at or below the AL might be monitoring annually or triennially.
As an alternative approach, EPA also compared 90[th] percentile values for the LSL samples to that for all sample data. From the Slabaugh et al. data, EPA determined that the corresponding 90[th] percentile value for those samples taken only at Tier 1 or Tier 2 LSL tap sampling sites was 2.81 ug/L, versus the 90[th] percentile value of 2.80 ug/L for samples taken at all sites indicated above. The ratio of these two values, 2.81/2.80 = 1.004 was selected by EPA as a "low" multiplier, again meaning that 1.004 was applied to all 90[th] percentile lead values for LSL systems to reflect the potential impacts of sampling from only LSL sites to predict whether the system has no TLE or ALE, a TLE, or an ALE under the final LCRR.
EPA combined the low and high adjustment factor from Slabaugh et al. (2015) with the low and high 90[th] percentile values under the previous rule, to produce a "low" and "high" likelihood of being in each 90[th] percentile category under the final LCRR. As a summary, the assumptions for the "low" and "high" percent of CWSs with no TLE or ALE, a TLE, and ALE for adjustment 1 are as follows:
 "Low" estimate: minimum 90[th] percentile lead value from SDWIS/Fed from 2007 to 2015, and low multiplier (1.004) for 90[th] percentile values for LSL systems.
 "High" estimate: maximum 90[th] percentile lead value from SDWIS/Fed from 2007 to 2015, and high multiplier (1.35) for 90[th] percentile values for LSL systems.
2) Adjustment to reflect taking a fifth liter sample as opposed to the first liter for LSL systems
EPA expects that the fifth liter sampling for LSL systems will increase the percent of systems with a TLE or ALE. To estimate the probability that a system having LSLs would fall into each of the three lead 90th percentile categories as a result of a requirement that they use a fifth liter sample, EPA used paired first and fifth liter data from 133 systems in Michigan at LSL locations that were collected in 2019. The ratio of the fifth to the first liter lead concentrations was calculated for each of these 133 systems. Note that there was insufficient data to allow for calculation of separate fifth to first liter ratios with respect to CCT status. Overall, the ratios ranged from 0.003 to 889, with a median value of 1.22 and 10th and 90th percentile values of 0.12 and 3.21, respectively. The ratio of the average fifth liter value to the average first liter value was 1.85.
For this analysis, all 133 ratios were applied to the 90th percentile values for each of the 4,424 systems of known LSL status that have LSLs. Specifically, the ratios were applied to the low and high 90th percentile values for systems having LSLs to account for LSL systems taking all fifth liter, rather than first liter, samples. The fifth to first liter ratios were not applied to the non-LSL systems.
The resulting sets of adjusted 90th percentile values were then gathered into the various subsets of systems based on LSL status to obtain the probabilities of being in each of the three categories of no TLE or ALE, a TLE, or an ALE. Exhibit 4-20 presents the "low" and "high" estimates of the percentage of systems in each lead 90[th] percentile category by LSL status.
Exhibit 4-20: Number and Percent of CWSs with No TLE or ALE, a TLE, and an ALE (Final LCRR)
                                   Category
                                    No LSLs
                                   Has LSLs
                                 Low Estimate
No TLE/ALE (P90 <=10 ug/L)
                                                                            97%
                                                                            89%
           <= 5 ug/L
                                                                            94%
                                                                            77%
           >5 and <=10 ug/L
                                                                             3%
                                                                            13%
TLE (10 ug/L < P90 <= 15 ug/L)
                                                                             0%
                                                                             5%
ALE (P90 > 15 ug/L)
                                                                             2%
                                                                             6%
                                 High Estimate
No TLE/ALE (P90 <=10 ug/L)
                                                                            87%
                                                                            58%
           <= 5 ug/L
                                                                            68%
                                                                            40%
           >5 and <=10 ug/L
                                                                            19%
                                                                            18%
TLE (10 ug/L < P90 <= 15 ug/L)
                                                                             7%
                                                                            12%
ALE (P90 > 15 ug/L)
                                                                             6%
                                                                            30%
Acronyms: ALE = action level exceedance; CWS = community water system; LCRR = Lead and Copper Rule revisions; LSL = lead service line; P90 = lead 90[th] percentile level; TLE = trigger level exceedance.
Notes:
    Includes CWSs with known LSL status that also reported at least one 90[th] percentile value to SDWIS between 2007 and 2015.
    Totals may not add due to independent rounding.
    For additional detail, see file, "Derivation of Initial P90 Categorization_Final Rule," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.

Discussion of Data Limitations and Uncertainty
There are several factors that introduce uncertainty into the initial lead 90[th] percentile classification as follows:
Use of historical SDWIS/Fed Data to predict future 90[th] percentile levels.
Uncertainty in predicting the effects of sampling from 100 percent LSLs.
Reliance on an incomplete universe of systems with known LSL status.
Representativeness of first and fifth liter sampling results from a single state (Michigan).
Variability of the ratio of first and fifth liter sampling results from a single state
Each of these limitations are described in more detail below.
       Use of Historical SDWIS/Fed Data
As described previously in this section, EPA recognizes the uncertainty in using historical SDWIS/Fed data to predict future 90[th] percentile values by developing "low" and "high" end estimates of the percent of CWSs with no TLE or ALE, a TLE, or an ALE under the previous rule.
       Uncertainty in Predicting the Effects of Sampling from 100 Percent LSLs
For the final LCRR, there is additional uncertainty in the effect of LSL systems being required to take all samples from LSL sites instead of the 50 percent minimum as required under the previous rule. EPA addressed this uncertainty by having a low and high estimate based on data provided in Slabaugh et al. (2015) paper.
       Reliance of Incomplete Universe of Systems with Known LSL Status
An important factor in the analyses to determine a system's initial lead 90[th] percentile categorization is the distinction between systems with LSLs and systems without LSLs. Limited data are available that indicate a system's LSL status; thus, EPA conducted a series of analyses to evaluate the representativeness of the subset of 4,424 CWSs with known LSL status as follows:
Compared the subset of 4,424 CWSs to all 50,067 CWSs in the SDWIS/Fed inventory.
Compared the subset of 4,424 CWSs to all 32,862 CWSs with at least one reported lead 90[th] percentile level during 2007 - 2015.
Determined the geographic representation of the 4,424 CWSs.
Each of these analyses are described in more detail below.
Comparison of Known LSL Status Subset to All CWSs
To help characterize the uncertainty of the subset of 4,424 with known LSL status and lead 90[th] percentile data used to determine a system's initial lead 90[th] percentile classification, EPA compared this subset to the 50,067 active CWSs in SDWIS/Fed. As shown in Exhibit 4-21, although most of the 4,424 CWSs were those serving 3,300 or fewer people, they only represented 7 percent of all small CWSs. The subset of the 4,424 CWSs serving 3,301 to 50,000 people and serving more than 50,000 people comprised 17 percent and 21 percent of all CWSs that serve these size categories, respectively. The data set of known LSL status systems is therefore less robust in its representation of water systems serving fewer than 3,300 people. The data set is consistent in the degree of representation across the larger size categories representing water systems serving between 3,301 and 50,000 people and those serving greater than 50,000 people.
Exhibit 4-21: Percent of CWSs with Known LSL Status to All CWSs by System Size
                         System Size
Population Served

                             Number of Active CWSs
          CWSs with Known LSL Status and Lead 90[th] Percentile Data

                               Number of Systems
                              Percent of All CWSs

                                       A
                                       B
                                    C = B/A
<= 3,300
                                                                         40,784
                                                                          2,808
                                                                             7%
3,301 to 50,000
                                                                          8,305
                                                                          1,410
                                                                            17%
> 50,000
                                                                            978
                                                                            206
                                                                            21%
Total
                                                                         50,067
                                                                          4,424

Source: SDWIS/Fed, 3rd quarter 2016 frozen dataset. Also see file, "Extent of P90 Data.xlsx" for additional information.
Notes:
General: Refer to Section <IP_ADDRESS>.1 and Exhibit 4-18 for more details on the development of the universe of systems with known LSL status.
A: Includes all active CWSs in SDWIS/Fed based on 3rd quarter 2016 frozen dataset.
B: Includes systems with known LSL status (either presence or absence of LSLs) and at least one reported lead 90[th] percentile value to SDWIS/Fed during the 9-year analysis period of 2007 - 2015. Lead 90[th] percentile values for this subset of systems were used to determine a system's initial lead 90[th] percentile classification.

Comparison of Known LSL Status Subset of All CWSs with Reported Lead 90[th] Percentile Data
EPA compared the subset of systems with known LSLs status and reported lead 90[th] percentile values to the larger set of CWSs with at least one reported lead 90[th] percentile value (but unknown LSL status) in SDWIS/Fed for 2007 - 2015. The first step was to generate the percentage of CWSs placed into each of the three lead 90[th] percentile categories (based on the maximum or "high estimate" lead 90[th] percentile value for 2007  -  2015) by system size and CCT status using the larger dataset of 32,862 CWSs (i.e., 37,286 minus 4,424 CWSs) for which LSL status is unknown and the 4,424 CWSs with known LSL status. The results of this lead 90[th] percentile assessment are shown in Exhibit 4-22. Next, EPA used a z-test to statistically evaluate the proportions for systems in each lead 90[th] percentile category for the two sets of systems. For all system sizes and CCT status groups, the resulting z-values fell within the critical range, indicating that differences in proportions observed between the two sets were not statistically significant. See file "P90_Unknown LSL vs LSL Known Status CWSs_Final Rule.xlsx" for additional information.
Exhibit 4-22: Comparison of P90 Data for CWSs with At Least One Reported Value to the Set of CWSs with Known LSL Status and P90 Data by Three P90 Ranges, System Size, and CCT Status (Percent) Using the Baseline/High Estimate
                                  System Size
                                      CCT
                                    Percent

                                P90 <=10 μg/L
                        10 ug/L < P90 <= 15 ug/L
                               P90 >15 μg/L

                                w/ Reported P90
                      Reported P90 & Known LSL Status
                                  Difference
                                w/ Reported P90
                      Reported P90 & Known LSL Status
                                  Difference
                                w/ Reported P90
                      Reported P90 & Known LSL Status
                                  Difference

                                       A
                                       B
                                    C = A-B
                                       D
                                       E
                                    F = D-E
                                       G
                                       H
                                    I = G-H
<= 3,300
No
                                                                          86.1%
                                                                          85.4%
                                                                           0.7%
                                                                           6.4%
                                                                           7.7%
                                                                          -1.3%
                                                                           7.5%
                                                                           6.9%
                                                                           0.6%
<= 3,300
Yes
                                                                          82.5%
                                                                          81.6%
                                                                           0.8%
                                                                           6.9%
                                                                           7.5%
                                                                          -0.6%
                                                                          10.7%
                                                                          10.9%
                                                                          -0.2%
3,301-10K
No
                                                                          90.4%
                                                                          88.2%
                                                                           2.2%
                                                                           6.3%
                                                                           8.3%
                                                                          -2.0%
                                                                           3.3%
                                                                           3.5%
                                                                          -0.2%
3,301-10K
Yes
                                                                          89.8%
                                                                          88.1%
                                                                           1.7%
                                                                           6.2%
                                                                           6.2%
                                                                           0.0%
                                                                           4.0%
                                                                           5.7%
                                                                          -1.7%
10,001-50K
No
                                                                          91.2%
                                                                          89.9%
                                                                           1.3%
                                                                           6.0%
                                                                           7.1%
                                                                          -1.1%
                                                                           2.8%
                                                                           3.0%
                                                                          -0.2%
10,001-50K
Yes
                                                                          90.9%
                                                                          85.1%
                                                                           5.9%
                                                                           5.4%
                                                                           9.3%
                                                                          -3.9%
                                                                           3.7%
                                                                           5.6%
                                                                          -1.9%
> 50K
No
                                                                         100.0%
                                                                         100.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
> 50K
Yes
                                                                          91.3%
                                                                          81.5%
                                                                           9.8%
                                                                           5.5%
                                                                          13.2%
                                                                          -7.7%
                                                                           3.2%
                                                                           5.4%
                                                                          -2.1%
Acronyms: LSL = lead service line; P90 = lead 90[th] percentile.
Source: SDWIS/Fed 3[rd] Quarter Frozen Dataset, current through June 30, 2016. All see file, "P90_Unknown LSL vs LSL Known Status CWSs_Final Rule.xlsx" for additional detail.
Notes:
A, D, G: Includes all 33,816 CWSs that equals all 37,286 CWSs with at least one reported P90 value minus the 4,424 CWSs with both a reported P90 value and known LSL status (i.e., presence or absence of LSLs).
B, E, H: Includes the subset of 4,424 CWSs with both a reported P90 value and known LSL status.

Geographic Representativeness of Known LSL Status Subset
EPA recognizes that using the subset of systems with known LSL status for the analysis may under or over represent 90[th] percentile results from specific geographic regions. To evaluate the potential impacts of this uncertainty, EPA grouped known LSL status systems into three geographic regions: 1) Midwest (Illinois, Indiana, Michigan, Ohio, and Wisconsin), 2) East (Maryland and North Carolina), and 3) West (California, Nevada, and Washington). The 90[th] percentile values for these groups and for the full set of known LSL status systems are shown in Exhibit 4-23. Note that Cornwell et al. (2016) reported a higher proportion of LSL systems in the Midwest and Northeast compared to the rest of the United States; however, EPA recognizes uncertainty in not representing other geographic regions.
Exhibit 4-23: Number and Percent of CWSs with No TLE or ALE, a TLE, and ALE  -  Comparison of Results from Three Geographic Regions with Known LSL Status Using the Baseline/High Estimate
                                   Category
                                    No LSLs
                                   Has LSLs

                                Number of CWSs
                                    Percent
                                Number of CWSs
                                    Percent

                                    No CCT
                                    Yes CCT
                                    No CCT
                                    Yes CCT
                                    No CCT
                                    Yes CCT
                                    No CCT
                                    Yes CCT
                      East (North Carolina and Maryland)
No TLE/ALE (P90 <=10 ug/L)
                                                                            242
                                                                            367
                                                                            83%
                                                                            86%
                                                                             12
                                                                             34
                                                                           100%
                                                                            83%
TLE (10 ug/L < P90 <= 15 ug/L)
                                                                             17
                                                                             17
                                                                             6%
                                                                             4%
                                                                              0
                                                                              1
                                                                             0%
                                                                             2%
ALE (P90 > 15 ug/L)
                                                                             31
                                                                             44
                                                                            11%
                                                                            10%
                                                                              0
                                                                              6
                                                                             0%
                                                                            15%
          Midwest (Illinois, Indiana, Michigan, Ohio, and Wisconsin)
No TLE/ALE (P90 <=10 ug/L)
                                                                          1,119
                                                                            709
                                                                            85%
                                                                            88%
                                                                            253
                                                                            421
                                                                            83%
                                                                            79%
TLE (10 ug/L < P90 <= 15 ug/L)
                                                                            115
                                                                             59
                                                                             9%
                                                                             7%
                                                                             34
                                                                             64
                                                                            11%
                                                                            12%
ALE (P90 > 15 ug/L)
                                                                             80
                                                                             42
                                                                             6%
                                                                             5%
                                                                             17
                                                                             49
                                                                             6%
                                                                             9%
                   West (California, Nevada, and Washington)
No TLE/ALE (P90 <=10 ug/L)
                                                                            142
                                                                             19
                                                                            91%
                                                                            90%
                                                                             33
                                                                             20
                                                                            85%
                                                                            91%
TLE (10 ug/L < P90 <= 15 ug/L)
                                                                             10
                                                                              2
                                                                             6%
                                                                            10%
                                                                              4
                                                                              2
                                                                            10%
                                                                             9%
ALE (P90 > 15 ug/L)
                                                                              4
                                                                              0
                                                                             3%
                                                                             0%
                                                                              2
                                                                              0
                                                                             5%
                                                                             0%
                       All Systems with Known LSL Status
No TLE/ALE (P90 <=10 ug/L)
                                                                          1,784
                                                                          1,161
                                                                            87%
                                                                            87%
                                                                            301
                                                                            518
                                                                            84%
                                                                            77%
TLE (10 ug/L < P90 <= 15 ug/L)
                                                                            149
                                                                             80
                                                                             7%
                                                                             6%
                                                                             38
                                                                             84
                                                                            11%
                                                                            13%
ALE (P90 > 15 ug/L)
                                                                            129
                                                                             90
                                                                             6%
                                                                             7%
                                                                             20
                                                                             70
                                                                             6%
                                                                            10%
Acronyms: ALE = action level exceedance; CCT = corrosion control treatment; CWS = community water system; LSL = lead service line; P90 = lead 90[th] percentile level; TLE = trigger level exceedance.
Notes: Includes only systems with known LSLs status. See Exhibit 4-18 for the breakdown by state. Also, as explained in footnote 30, additional state data were available to EPA for systems with known LSL status for the final rule as compared to the proposed rule. For the proposed rule, a total of 3,870 systems with known LSL status were used in the analysis versus a total of 4,424 systems with known LSL status in the final rule analysis.

Representativeness of First and Fifth Liter Data from a Single State
Data from the State of Michigan were used to estimate the impact on the lead 90[th] percentile levels that are based on fifth liter vs. first liter samples under the final LCRR for LSL systems. As described earlier, ratios of fifth liter 90[th] percentile values to first liter 90[th] percentile values from 133 systems in Michigan were applied to 90[th] percentile values from the 4,424 systems with known LSL status to estimate the likelihood of systems under the final LCRR having an ALE, TLE, or no ALE/TLE. EPA recognizes the uncertainty introduced in using data from a single state that may not represent the values on a national level. However, the Michigan data represent actual compliance monitoring data collected recently from all systems within the state, as opposed to using historical sampling data from a smaller subset of systems that may have had lead issues (e.g., the "profile" data from five systems that was used for the proposed LCRR).
Likelihood of an Individual Lead Sample Exceeding 15 ug/L
As detailed in Chapter 3, Section 3.4.5 EPA is requiring all systems to take specific actions in response to any single lead tap sample that is above 15 ug/L. Individual sample results are not available in SDWIS/Fed; therefore, EPA used available compliance monitoring data from the State of Michigan to calculate the likelihood of an individual sample being greater than 15 ug/L based on system size, LSL status, and the three lead 90[th] percentile categories of: 1) no TLE or ALE, 2) a TLE, or 3) an ALE. The analysis for the final LCRR used fifth liter samples for systems with LSLs and first liter samples for systems without LSLs from the Michigan dataset using the following steps:
Step 1  -  Categorized Michigan systems as with or without LSLs based on compliance monitoring data as follows:
 EPA assumed 132 CWSs have LSLs because the system provided first and fifth liter lead samples as required by Michigan's new regulation and were identified as having LSLs in their online inventory information (Michigan EGLE, 2020).
 EPA assumed 251 CWSs have no LSLs because the system submitted only first liter data and did not report any LSLs in the online inventory information.
Step 2  -  Calculated lead 90[th] percentile levels: EPA calculated lead 90[th] percentile values for CWSs as described below. The purpose of this step is to categorize each dataset by: 1) no TLE or ALE, 2) TLE, or 3) an ALE so that the likelihood of a sample being above 15 ug/L can be calculated for each 90[th] percentile category separately.
 For all systems with LSLs, to approximate the lead 90[th] percentile value if all samples were collected from LSL sites and all samples are fifth liter samples (new requirements in the final LCRR), EPA calculated a lead 90[th] percentile value using all fifth liter concentrations. (Note that fifth liter samples were only used in the 90[th] percentile calculation if they could be paired with first liter samples from the same system, date, and address.) EPA used this 90[th] percentile to categorize the dataset by: 1) no TLE or ALE, 2) a TLE, or 3) an ALE.
 For all systems with no LSLs, EPA calculated the 90[th] percentile using all first liter concentrations data for each dataset and used this information to categorize the dataset by: 1) no TLE or ALE, 2) a TLE, or 3) an ALE.
Step 3  -  Calculated the likelihood of a sample > 15 ug/L: EPA calculated the proportion of samples above 15 ug/L for each 90[th] percentile category. Results are shown in Exhibit 4-24.
Systems with LSLs had a higher likelihood of having a sample above 15 ug/L when they had a lead ALE (25.4 percent) compared to those without LSLs (22.7 percent). The likelihood for having a sample above 15 ug/L in the lead 90[th] percentile concentration category of TLE was not consistently higher or lower between systems with and without LSLs when looking at the three size categories together. As shown in Exhibit 4-24, some of the system size strata with no ALE/TLE, a TLE, and an ALE contained very few to no samples (e.g., systems with LSLs serving <= 3,300 people with a TLE). Therefore, EPA combined the size categories and included the likelihoods for all systems by LSL stratum, i.e., with LSLs and without LSLs, as inputs in the SafeWater LCR model. For additional detail on the number and percent of samples in the Michigan dataset that were greater than 15 ug/L, see file "Derivation of Probability_Sample_Above_15_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Note that the Michigan dataset does not include first and fifth liter data for NTNCWSs. Therefore, EPA assumed the same likelihood for NTNCWSs as those presented in Exhibit 4-24 for CWSs.
Exhibit 4-24: Percent of Individual Lead Sample Result Above 15 ug/L Based on Michigan CWSs with Known LSL Status for Final LCRR
                                  LSL Status
                                  System Size
Number of Michigan lead samples associated with calculated P90 values that were:
Number of Michigan lead samples > 15 ug/L associated with calculated P90 values that were:
Percent of Michigan lead samples > 15 ug/L associated with calculated P90 values that were:

                                  <=10 μg/L
                                 (No TLE/ALE)
                                   10 ug/L
                          < P90 <= 15 ug/L (TLE)
                                 >15 μg/L
                                     (ALE)
                                  <=10 μg/L
                                 (No TLE/ALE)
                                   10 ug/L
                          < P90 <= 15 ug/L (TLE)
                                 >15 μg/L
                                     (ALE)
                                  <=10 μg/L
                                 (No TLE/ALE)
                                   10 ug/L
                          < P90 <= 15 ug/L (TLE)
                                 >15 μg/L
                                     (ALE)

                                       A
                                       B
                                       C
                                       D
                                       E
                                       F
                                    G = D/A
                                     H=E/B
                                     I=F/C
Has LSLs
<=3,300
                                                                            232
                                                                              0
                                                                             48
                                                                              1
                                                                              0
                                                                             22
                                                                           0.4%
                                                                           0.0%
                                                                          45.8%

3,301  -  50,000
                                                                          1,385
                                                                            444
                                                                            246
                                                                             20
                                                                             27
                                                                             56
                                                                           1.4%
                                                                           6.1%
                                                                          22.8%

>50,000
                                                                            280
                                                                            184
                                                                             84
                                                                              2
                                                                             11
                                                                             18
                                                                           0.7%
                                                                           6.0%
                                                                          21.4%

Total
                                                                          1,897
                                                                            628
                                                                            378
                                                                             23
                                                                             38
                                                                             96
                                                                           1.2%
                                                                           6.1%
                                                                          25.4%
No LSLs
<=3,300
                                                                          1,509
                                                                             26
                                                                             22
                                                                              3
                                                                              4
                                                                              5
                                                                           0.2%
                                                                          15.4%
                                                                          22.7%

3,301  -  50,000
                                                                          1,104
                                                                              0
                                                                              0
                                                                              6
                                                                              0
                                                                              0
                                                                           0.5%
                                                                           0.0%
                                                                           0.0%

>50,000
                                                                            258
                                                                              0
                                                                              0
                                                                              1
                                                                              0
                                                                              0
                                                                           0.4%
                                                                           0.0%
                                                                           0.0%

Total
                                                                          2,871
                                                                             26
                                                                             22
                                                                             10
                                                                              4
                                                                              5
                                                                           0.3%
                                                                          15.4%
                                                                          22.7%
Acronyms: ALE: action level exceedance; P90 = lead 90[th] percentile level; TLE = trigger level exceedance.
Notes:
    Due to the low number of results for some size categories, the SafeWater LCR model uses the total percentage of systems with and without LSLs presented in bold in Columns G through I as inputs in the SafeWater LCR model. The bold percentages in Column G corresponds to SafeWater LCR model data variable pp_above_al_bin_one, those in Column H to pp_above_al_bin_two and those in Column I to pp_above_al_bin_three.
    EPA assumed a zero percent likelihood of a sample being greater that 15 ug/L for systems serving 1,000 or fewer people that are on a 9-year monitoring waiver because to meet the waiver requirement, these systems must be free of any lead-containing plumbing materials in their distribution system including the buildings they serve.
    For additional detail, see file "Derivation of Probability_Sample_Above_15_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.

Discussion of Data Limitations and Uncertainty
Recent data from the State of Michigan were used to estimates the likelihood of a single sample result above 15 ug/L for systems with LSLs as compared to systems without LSLs. While there is uncertainty in the national representativeness of the data (i.e., does lead tap sample data from Michigan represent lead tap data from other states), there are advantages to the use of these data. The Michigan data contains more than 5,800 individual lead sample results from systems with and without LSLs, with both first and fifth liter sampling results.
Systems with Copper Only ALEs
The previous rule sets an AL concentration of 1.3 mg/L for copper. If a system exceeds the AL in more than ten percent of tap water samples collected during any monitoring period (i.e., if the 90[th] percentile level is greater than the AL), the system has not violated the rule but must conduct additional actions such as CCT steps, WQP monitoring, and source water monitoring. EPA reviewed SDWIS/Fed 90[th] percentile copper data from 2012 through 2015 to identify systems that had exceeded the copper AL but not the lead AL.
The average annual percentage of all CWSs exceeding the copper AL during this time period is shown in Exhibit 4-25 by size, CCT status, and source type and was extremely low. For CWSs with CCT, the percentages ranged from 0 percent for CWSs serving 50,000  -  100,000 people and those serving above 1 million people to 2.3 percent for ground water systems serving 501  -  1,000 people. The overall percentage of CWSs with CCT and a copper ALE was 1 percent. For those without CCT, all systems serving above 50,000 people were assumed to be b3 systems and had no copper ALEs. No CWS size or source category had a copper ALE percentage above 0.8 percent and, overall, all CWSs without CCT had an estimated copper exceedance percentage of less than 0.5 percent. For a detailed derivation, see "CWS Inventory Characteristics_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Similar information is shown in Exhibit 4-26 for NTNCWSs. The overall percentages of NTNCWSs with a copper ALE were 3.4 percent and less than 1 percent for NTNCWSs with and without CCT, respectively. For additional detail, see "NTNCWS Inventory Characteristics.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Note that for the cost estimates presented in Chapter 5 for the LCRR and Appendix B for the previous rule, EPA made a simplifying assumption no system with CCT would have a copper ALE, because < 1 percent of CWSs and < 3.5 percent of NTNCWSs were estimated to have a copper ALE. See Chapter 5, Section <IP_ADDRESS>.1and Appendix B, Section B.5.1 for additional detail.
Exhibit 4-25: Average Percent of CWSs that Had Any Copper Only ALE from 2012 - 2015
                                 Size Category
                             Average (2012 - 2015)

                                   with CCT
                                  without CCT

                                 Ground Water
                                 Surface Water
                                  All Sources
                                 Ground Water
                                 Surface Water
                                  All Sources
<=100
                                                                           2.2%
                                                                           0.7%
                                                                           1.7%
                                                                           0.4%
                                                                           0.7%
                                                                           0.4%
101 - 500
                                                                           1.5%
                                                                           0.7%
                                                                           1.2%
                                                                           0.4%
                                                                           0.8%
                                                                           0.4%
501 - 1,000
                                                                           2.3%
                                                                           0.5%
                                                                           1.6%
                                                                           0.4%
                                                                           0.6%
                                                                           0.4%
1,001 - 3,300
                                                                           1.8%
                                                                           0.3%
                                                                           1.1%
                                                                           0.5%
                                                                           0.5%
                                                                           0.5%
3,301 - 10,000
                                                                           1.1%
                                                                           0.2%
                                                                           0.5%
                                                                           0.3%
                                                                           0.3%
                                                                           0.3%
10,001 - 50,000
                                                                           0.8%
                                                                           0.2%
                                                                           0.4%
                                                                           0.2%
                                                                           0.3%
                                                                           0.2%
50,001 - 100,000
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
100,001 - 1M
                                                                           0.4%
                                                                           0.1%
                                                                           0.1%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
>1M
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%

All Sizes
                                                                           1.6%
                                                                           0.3%
                                                                           1.0%
                                                                           0.4%
                                                                           0.6%
                                                                           0.4%
Source: "CWS Inventory Characteristics_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Note: EPA estimated that 11 CWSs are b3 systems, serve 50,001  -  1 million people, and have no CCT. No b3 systems serve more than 1 million people. Refer to Section 4.3.3 for EPA's approach for estimating the number of b3 systems based on SDWIS/Fed data.
Exhibit 4-26: Average Percent of NTNCWSs that Had Any Copper Only ALE from 2012 - 2015
                                 Size Category
                             Average (2012 - 2015)

                                   with CCT
                                  without CCT

                                 Ground Water
                                 Surface Water
                                  All Sources
                                 Ground Water
                                 Surface Water
                                  All Sources
<=100
                                                                           4.3%
                                                                           0.7%
                                                                           3.8%
                                                                           0.7%
                                                                           1.1%
                                                                           0.8%
101 - 500
                                                                           3.9%
                                                                           2.1%
                                                                           3.7%
                                                                           0.7%
                                                                           1.3%
                                                                           0.7%
501 - 1,000
                                                                           3.3%
                                                                           1.0%
                                                                           2.9%
                                                                           0.7%
                                                                           1.6%
                                                                           0.8%
1,001 - 3,300
                                                                           3.6%
                                                                           1.4%
                                                                           2.9%
                                                                           0.8%
                                                                           0.8%
                                                                           0.8%
3,301 - 10,000
                                                                           1.0%
                                                                           1.3%
                                                                           1.2%
                                                                           1.0%
                                                                           0.0%
                                                                           0.9%
10,001 - 50,000
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
50,001 - 100,000
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%

100,001 - 1M
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%

>1M

All Sizes
                                                                           3.9%
                                                                           1.3%
                                                                           3.4%
                                                                           0.7%
                                                                           1.2%
                                                                           0.8%
Source: "NTNCWS Inventory Characteristics_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Note: Three NTNCWSs serve 50,001  -  1 million people and each have CCT. No NTNCWS serves > 1 million people.
Treatment Plant Characterization
This section explains the baseline inputs for the following treatment-related PWS characteristics:
 Entry points per system
 Average daily flow
 Design flow
 pH of finished water
 Orthophosphate (PO4) dose
For additional detail and values used in this EA, see the file, "Derivation of Baseline CCT Characteristics_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
As described in Section 4.2.2, EPA developed the likelihood of a CWS's having 1 to 50 entry points using data from the 2006 CWSS. For example, ground water CWSs serving 101 to 500 people have a 72 percent chance of having one entry point, a 12 percent chance of having two entry points, and a 10 percent chance of having three entry points. For systems serving greater than one million people, EPA gathered system-specific information on the number of treatment plants and flow and used this information wherever available. EPA assumes that NTNCWSs always have one entry point since they tend to be single facilities covering a small geographical area.
Average daily production flow and design flow per system are based on regression equations from the EPA Report, Geometries and Characteristics of Public Water Supplies (USEPA, 2000). The average daily flow and design flow are functions of the population served, with different equations for source water type (surface or ground water), ownership (public or private) and for purchased and non-purchased systems. The flow was then divided by the number of entry points to calculate the flow per treatment plant for the system (assuming each entry point has one treatment plant). As a conservative estimate, the flow-population regression equations for CWSs were also used for NTNCWSs.
EPA evaluated historical SDWIS/Fed data to determine the proportion of systems with CCT that use pH adjustment, orthophosphate treatment, or both. This analysis is detailed in Chapter 5, Section <IP_ADDRESS>.1.
Baseline pH levels and orthophosphate (PO4) dosages are also important inputs in calculating the incremental costs of the final LCRR. EPA used the SYR3 ICR dataset to characterize the distribution of finished water pH for those systems that have CCT installed and those that do not under baseline conditions. EPA also estimated the distribution of PO4 dosages for large, medium, and small systems with and without LSLs. See the file, "Derivation of Baseline CCT Characterization_Final Rule.xlsx" for additional detail and for final baseline pH and PO4 input values used to develop costs and benefits for this EA.
Discussion of Data Limitations and Uncertainties
EPA recognizes that there is uncertainty in assuming a system's total flow is divided equally among each entry point because a single system may have a mix of large and small plants to support their population. There is also uncertainty in using the equations from the 2000 Geometries Document (USEPA, 2000) to predict future average daily and design flow based on a system's retail population. Water use efficiency has increased substantially since the 1980's, with a major improvement between 2005 and 2010 (Rockaway et al., 2011). A 2016 Water Research Foundation study reported a 22 percent decline in indoor water use (WaterRF, 2016). Several factors have contributed to increases in water efficiency. Technological changes, supported by policy, increased the efficiency of water use. For example, the Energy Policy Act of 1992 required water efficiency standards for fixtures, including shower heads, toilets, and washing machines. Water recycling and increased efficiency of power generation also reduces freshwater use. The economic downturn of 2008 contributed to the drop in water use and the increase in use of water-efficient fixtures, xeriscaping, and other demand side management measures contributed to reduction in per capita use as well. The trend of lower residential water use could result in lower flow per population and, lower treatment costs as compared to predicted values in this EA.
Lead and Copper Tap and WQP Monitoring Schedules
Under the previous rule, systems were allowed to reduce the frequency and, in some cases, the number of samples for required lead and copper tap and WQP monitoring if they met certain criteria. Section <IP_ADDRESS> provides a summary of the requirements and the methodology used by EPA to estimate the percent of systems on reduced lead and copper tap sampling schedules. Section <IP_ADDRESS> provides the same analysis for reduced WQP monitoring.
Lead and Copper Tap Monitoring
Under the previous rule, systems on routine (semi-annual) lead and copper tap sampling could have qualified for reduced sampling by meeting specific criteria. These criteria varied for the three broad LCR system size categories. Reduced monitoring allows a system to collect lead and copper tap samples from a reduced number of sites on an annual, triennial, or 9-year tap sampling monitoring schedule; the number of sampling sites for reduced monitoring is the same under the previous and final rules. The reduced monitoring criteria are presented in detail in Exhibit 4-27 and apply to both CWSs and NTNCWSs.
Exhibit 4-27: Criteria for Reduced and Increased Lead and Copper Tap Sampling under the Previous Rule
                       Tap Sampling Monitoring Frequency
                                   Criteria
Reduced Monitoring Criteria (Collect Reduced Number of Samples)[1]
Annual
<= 50,000: No lead or copper ALE for 2 consecutive 6-month tap sampling periods.
All sizes: No lead ALE and meet OWQP specifications for 2 consecutive 6-month tap sampling periods.[2]
Triennial
<= 50,000: No lead or copper ALE for 3 consecutive years.
All sizes: No lead ALE and meet OWQP specifications for 3 consecutive years.
All sizes: Meet 40 CFR 141.81(b)(3).[3]
All sizes: Meet accelerated reduced monitoring criteria in 40 CFR 141.86(d)(4)(v).[4]
9-year[5]
<= 3,300 only: Lead and copper 90[th] percentile levels are <= 0.005 mg/L and <= 0.65 mg/L, respectively, and plumbing materials are free of lead- and copper-containing materials.
Increased Monitoring Criteria (Collect Routine Number of Samples)[1]
Semi-Annual
<= 50,000: Lead or copper ALE.
All sizes: Lead ALE or has an OWQP excursion for more than 9 days in a 6-month period.
Acronyms: ALE = action level exceedance; OWQP = optimal water quality parameter.
Notes:
1 The number of sampling sites for reduced monitoring is specified in 40 CFR 141.86 and is the same under the previous and final rules. Refer to Exhibit 3-7 in Chapter 3 for a comparison of the reduced lead and copper criteria under the previous rule and final LCRR.
2 OWQPs are measured to determine whether a system is operating its CCT at a level that most effectively minimizes the lead and copper concentrations at users' taps.
3 In the final rule, a water system is deemed to have optimized or re-optimized corrosion control if it submits results of tap water monitoring in accordance with 40 CFR 141.86 demonstrating that the 90[th] percentile tap water lead level is less than or equal to the lead practical quantitation level of 0.005 mg/L and meets the copper AL for two consecutive 6-month tap sampling monitoring periods.
4 Criteria in 40 CFR 141.86(d)(4)(v) were met if for 2, consecutive, 6-month monitoring periods the system has 90[th] percentile lead and copper levels of < 0.005 mg/L and < 0.65 mg/L, respectively.
[5] To qualify for a 9-year monitoring waiver, systems had to meet the following criteria in 40 CFR 141.86(g): 1) serve <= 3,300 people; 2) demonstrate that its distribution system and service lines and all drinking water supply plumbing, including plumbing conveying drinking water within all residences and buildings connected to the system, are free of lead-containing materials and/or copper-containing materials; and 3) all lead and copper 90[th] percentile levels cannot exceed 0.005 mg/L and 0.65 mg/L, respectively.
EPA determined a system's lead tap sampling monitoring schedule at the start of rule implementation primarily based on its lead ALE history and size. For systems without CCT, EPA further categorized these systems according to whether or not they received a 9-year monitoring waiver (meaning that they are only required to conduct lead and copper tap compliance monitoring once every 9 years). EPA assumed that these systems meeting the following criteria would receive the 9-year monitoring waiver from their Primacy Agency:
 A CWS or NTNCWS that:
          Serves 1,000 or fewer people and has no lead or copper ALEs during 1993 through 2015.
          Has a first reported date on or after January 1, 1989. The first reported date may indicate when the system became operational.
 A CWS that meets the definition of a mobile home park as follows:
 System has a primary service type of "Mobile Home Park" or "Mobile Home Park Principal Residence" reported to SDWIS/Fed.
 System has a primary service type of "Residential Area" and "Mobile", "Trailer," or "MHP" in their name.
Exhibit 4-28, below, provides a summary of the criteria used to estimate the various lead and copper tap sampling monitoring schedules based on information reported to SDWIS/Fed.
Exhibit 4-28: SDWIS/Fed Criteria Used to Estimate Lead Tap Sampling Monitoring Schedules
                             Monitoring Frequency
                                  Description
Semi-Annual
System's latest lead or copper ALE occurred after 12/31/2014. Thus, the system did not have two consecutive 6-month monitoring periods without a lead ALE.
All sizes: Lead ALE or had an OWQP violation (59 violation).
Annual (Reduced)1
System's latest lead or copper ALE occurred between 1/1/2012 and 12/31/2014. Thus, the system had two consecutive 6-month monitoring periods without a lead ALE.
Triennial (Reduced)[1]
System's latest lead or copper ALE occurred before 1/1/2012; or
System's latest lead or copper 90[th] percentile result that was at or below the AL was reported for a sampling period between 1.5 and 5 years,[2] or
System does not have any reported lead or copper 90[th] percentile results,[3] or
System serves >50,000 and meets the b3 criteria.
9-year[1 ,4]
CWS: Is a mobile home park, had no lead or copper exceedances during 1993 - 2015, the SDWIS/Fed first reported date is on or after January 1, 1989, population served is <= 1,000, and does not have CCT.
NTNCWS: Had no lead or copper exceedances during 1993 - 2015, the SDWIS/Fed first reported date is on or after January 1, 1989, population served is <= 1,000, and does not have CCT.
Source: For additional information see "Derivation of Pb Schedules_CWS_Final Rule.xlsx" and "Derivation of Pb Schedules_NTNCWS_Final Rule.xlsx," both available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Notes:
[1] Systems on annual, triennial, or 9-year monitoring collect samples at the reduced number of sites specified in the rule (see 40 CFR 141.86(c).
2The length of the tap sampling period was determined by the difference between the sampling period begin and end dates. EPA assumed if the difference was greater than 1 year, but the system did not meet the 9-year monitoring criteria, it was on triennial monitoring.
3 The previous rule only requires Primacy Agencies to report 90[th] percentile levels to SDWIS/Fed that are above the lead AL for systems serving <= 3,300 people and above the copper AL for any size system.
4 SDWIS/Fed does not have a milestone or other required reporting that identifies systems on 9-year monitoring. Although the rule allows systems serving <= 3,300 people to qualify for 9-year monitoring, EPA assumed only a subset of systems serving <= 1,000 people met this requirement. EPA further assumed only water systems that became active after January 1, 1989 (based on the first reported date) would qualify for 9-year monitoring. EPA selected this date because it is well after when systems stopped using LSLs and when all states had to adopt the lead provisions (i.e., by August 6, 1988) that limited the amount of lead in plumbing materials.
Based on the criteria in Exhibit 4-28, the majority of CWSs are on triennial monitoring. Specifically, for those with CCT depending on system size and source water type, EPA estimated approximately 87 percent to 100 percent will be on triennial monitoring. For those without CCT, EPA estimated that all systems serving more than 50,000 people will meet the b3 criteria and be on triennial monitoring. Across the smaller system sizes and source water types EPA found that approximately 91 to 99 percent of CWSs will be on the triennial schedule. See Exhibit 4-29 and Exhibit 4-30, for additional detail on CWSs with CCT and without CCT, respectively.
Exhibit 4-29: Estimated Percentage of CWSs with CCT on Various Lead Tap Monitoring Schedules by Size and Source Type
                                 Size Category
                          CWS with CCT: Surface Water
                          CWS with CCT: Ground Water

                                    6 Month
                                    Annual
                                   Triennial
                                    9 Year
                                    6 Month
                                    Annual
                                   Triennial
                                    9 Year
<=100
                                                                           1.6%
                                                                           4.1%
                                                                          94.3%
                                                                             0%
                                                                           4.1%
                                                                           8.5%
                                                                          87.4%
                                                                             0%
101 - 500
                                                                           1.9%
                                                                           4.0%
                                                                          94.1%
                                                                             0%
                                                                           2.0%
                                                                           5.6%
                                                                          92.3%
                                                                             0%
501 - 1,000
                                                                           1.4%
                                                                           4.2%
                                                                          94.4%
                                                                             0%
                                                                           2.7%
                                                                           4.4%
                                                                          92.9%
                                                                             0%
1,001 - 3,300
                                                                           1.1%
                                                                           2.5%
                                                                          96.4%
                                                                             0%
                                                                           2.0%
                                                                           3.9%
                                                                          94.1%
                                                                             0%
3,301 - 10,000
                                                                           0.5%
                                                                           1.8%
                                                                          97.7%
                                                                             0%
                                                                           1.3%
                                                                           2.8%
                                                                          95.9%
                                                                             0%
10,001 - 50,000
                                                                           0.3%
                                                                           1.7%
                                                                          98.0%
                                                                             0%
                                                                           0.9%
                                                                           2.4%
                                                                          96.7%
                                                                             0%
50,001 - 100,000
                                                                           0.8%
                                                                           2.1%
                                                                          97.2%
                                                                             0%
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                             0%
100,001 - 1M
                                                                           1.8%
                                                                           2.4%
                                                                          95.9%
                                                                             0%
                                                                           0.0%
                                                                           1.6%
                                                                          98.4%
                                                                             0%
>1M
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                             0%
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                             0%
Source: For additional information, see "Derivation of Pb Schedules_CWS_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Notes:
    Refer to Exhibit 4-28 for the criteria EPA applied to determine systems' lead and copper tap monitoring schedules and Section 4.3.3 for the criteria EPA used to identify systems with and without CCT.
    Systems on annual, triennial, or 9-year monitoring collect samples at the reduced number of sites specified in the rule (see 40 CFR 141.86(c)).
Exhibit 4-30: Estimated Percentage of CWSs without CCT on Various Lead Tap Monitoring Schedules by Size and Source Type
                                 Size Category
                        CWS without CCT: Surface Water
                         CWS without CCT: Ground Water

                                    6 Month
                                    Annual
                                   Triennial
                                    9 Year
                                    6 Month
                                    Annual
                                   Triennial
                                    9 Year
<=100
                                                                           1.5%
                                                                           3.2%
                                                                          93.4%
                                                                           1.9%
                                                                           1.1%
                                                                           2.6%
                                                                          91.1%
                                                                           5.2%
101 - 500
                                                                           1.5%
                                                                           4.3%
                                                                          91.9%
                                                                           2.2%
                                                                           1.0%
                                                                           2.5%
                                                                          93.9%
                                                                           2.6%
501 - 1,000
                                                                           1.6%
                                                                           3.4%
                                                                          93.8%
                                                                           1.1%
                                                                           0.6%
                                                                           2.0%
                                                                          96.2%
                                                                           1.1%
1,001 - 3,300
                                                                           1.8%
                                                                           1.7%
                                                                          96.5%
                                                                           0.0%
                                                                           0.6%
                                                                           2.5%
                                                                          97.0%
                                                                           0.0%
3,301 - 10,000
                                                                           0.6%
                                                                           1.5%
                                                                          97.9%
                                                                           0.0%
                                                                           0.5%
                                                                           1.3%
                                                                          98.2%
                                                                           0.0%
10,001 - 50,000
                                                                           0.6%
                                                                           1.1%
                                                                          98.3%
                                                                           0.0%
                                                                           0.1%
                                                                           1.1%
                                                                          98.8%
                                                                           0.0%
50,001 - 100,000
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                           0.0%
100,001 - 1M
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                           0.0%
>1M

Source: For additional information, see "Derivation of Pb Schedules_CWS_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Notes:
    Refer to Exhibit 4-28 for the criteria EPA applied to determine systems' lead and copper tap monitoring schedules and Section 4.3.3 for the criteria EPA used to identify systems with and without CCT.
    Systems on annual, triennial, or 9-year monitoring collect samples at the reduced number of sites specified in the rule (see 40 CFR 141.86(c)).
    The gray shaded cells denote that there were no CWSs serving >1M people without CCT in the CWS inventory.
Exhibit 4-31 and Exhibit 4-32 provide similar information for NTNCWSs with CCT and without CCT, respectively. EPA estimated that most NTNCWSs will also be on a triennial monitoring schedule. Specifically, EPA estimated that depending on system size and source water type about 75 percent to 100 percent of NTNCWSs with CCT and about 85 to 100 percent without CCT will be on a triennial schedule.
Exhibit 4-31: Estimated Percentage of NTNCWSs with CCT on Various Lead Monitoring Schedules by Size and Source Type
                                 Size Category
                        NTNCWS with CCT: Surface Water
                         NTNCWS with CCT: Ground Water

                                    6 Month
                                    Annual
                                   Triennial
                                    9 Year
                                    6 Month
                                    Annual
                                   Triennial
                                    9 Year
<=100
                                                                           4.5%
                                                                           2.7%
                                                                          92.9%
                                                                           0.0%
                                                                           5.5%
                                                                          13.6%
                                                                          81.0%
                                                                           0.0%
101 - 500
                                                                           6.4%
                                                                           6.4%
                                                                          87.2%
                                                                           0.0%
                                                                           6.0%
                                                                          11.7%
                                                                          82.3%
                                                                           0.0%
501 - 1,000
                                                                           2.0%
                                                                           3.9%
                                                                          94.1%
                                                                           0.0%
                                                                           5.6%
                                                                          10.9%
                                                                          83.5%
                                                                           0.0%
1,001 - 3,300
                                                                           2.8%
                                                                           4.2%
                                                                          93.0%
                                                                           0.0%
                                                                           3.8%
                                                                          13.8%
                                                                          82.4%
                                                                           0.0%
3,301 - 10,000
                                                                           0.0%
                                                                           5.0%
                                                                          95.0%
                                                                           0.0%
                                                                           0.0%
                                                                          12.0%
                                                                          88.0%
                                                                           0.0%
10,001 - 50,000
                                                                           0.0%
                                                                          11.1%
                                                                          88.9%
                                                                           0.0%
                                                                           0.0%
                                                                          25.0%
                                                                          75.0%
                                                                           0.0%
50,001 - 100,000
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                           0.0%
100,001 - 1M
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                           0.0%

>1M

Source: For additional information, see "Derivation of Pb Schedules_NTNCWS_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Notes:
    Refer to Exhibit 4-28 for the criteria EPA applied to determine systems' lead and copper tap monitoring schedules and Section 4.3.3 for the criteria EPA used to identify systems with and without CCT.
    Systems on annual, triennial, or 9-year monitoring collect samples at the reduced number of sites specified in the rule (see 40 CFR 141.86(c)).
    The gray shaded cells denote that there were no surface water NTNCWSs serving 100,001 to 1M people with CCT and no NTNCWSs serving > 1M in the NTNCWS inventory.

Exhibit 4-32: Estimated Percentage of NTNCWSs without CCT on Various Lead Tap Monitoring Schedules by Size and Source Type
                                 Size Category
                       NTNCWS without CCT: Surface Water
                       NTNCWS without CCT: Ground Water

                                    6 Month
                                    Annual
                                   Triennial
                                    9 Year
                                    6 Month
                                    Annual
                                   Triennial
                                    9 Year
<=100
                                                                           7.2%
                                                                           7.2%
                                                                          84.8%
                                                                           0.7%
                                                                           2.4%
                                                                           3.7%
                                                                          93.8%
                                                                           0.1%
101 - 500
                                                                           3.3%
                                                                           4.6%
                                                                          90.8%
                                                                           1.3%
                                                                           1.9%
                                                                           4.6%
                                                                          93.5%
                                                                           0.1%
501 - 1,000
                                                                           3.2%
                                                                           0.0%
                                                                          96.7%
                                                                           0.0%
                                                                           1.4%
                                                                           2.9%
                                                                          95.7%
                                                                           0.0%
1,001 - 3,300
                                                                           6.4%
                                                                           0.0%
                                                                          93.4%
                                                                           0.0%
                                                                           1.3%
                                                                           5.1%
                                                                          93.6%
                                                                           0.0%
3,301 - 10,000
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                           0.0%
                                                                           1.4%
                                                                           4.1%
                                                                          94.6%
                                                                           0.0%
10,001 - 50,000
                                                                           0.0%
                                                                         100.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                           0.0%
                                                                         100.0%
                                                                           0.0%
50,001 - 100,000

100,001 - 1M

>1M

Source: For additional information, see "Derivation of Pb Schedules_NTNCWS_Final Rule.xlsx," available in the docket at EPA-HQ-OW-2017-0300 at www.regulations.gov.
Notes:
    Refer to Exhibit 4-28 for the criteria EPA applied to determine systems' lead and copper tap monitoring schedules and Section 4.3.3 for the criteria EPA used to identify systems with and without CCT.
    Systems on annual, triennial, or 9-year monitoring collect samples at the reduced number of sites specified in the rule (see 40 CFR 141.86(c)).
    The gray shaded cells denote that there were no NTNCWSs serving greater than 50,000 people without CCT in the NTNCWS inventory.

Discussion of Data Limitations and Uncertainty
As previously discussed, for systems serving 3,300 or fewer people, the previous rule required Primacy Agencies to only report those lead 90[th] percentile values that exceed the lead AL of 15 ug/L, but to report all lead 90[th] percentile values for larger water systems. To determine if systems in this smallest size category were underrepresented, EPA estimated the percentage of systems with any reported lead 90[th] percentile data during 2007 - 2015 within this size category, as well as for systems serving 3,301 to 50,000 people and greater than 50,000 people. As shown in Column C of Exhibit 4-33 below, lead 90[th] percentile data were reported for only 69 percent of all CWSs in this smallest size category compared to 98 percent in the larger two categories. EPA also estimated the percentage of CWSs in which only lead exceedance data were reported to try to assess any bias in reporting for the smallest size category. As shown in Column F of Exhibit 4-33, in general, both exceedances and non-exceedances were reported for approximately 98 percent of systems in the smallest size category, and essentially all of those in the highest two categories (1 system serving 3,301  -  50,000 people reported lead ALE data only). This indicates that Primacy Agencies tended to report exceedance and non-exceedance data for even the smallest size category.
Exhibit 4-33: Estimated Number and Percentage of CWSs with Reported Lead ALEs Only
                         System Size
Population Served
                                   All CWSs
             All CWSs w/ any Reported Lead 90[th] Percentile Data
                All CWSs w/ Reported P90 Data Above the AL Only

                                    Number
                                    Number
                              Percent of All CWSs
                                    Number
                              Percent of all CWSs
                      Percent of Any w/ Reported P90 Data

                                       A
                                       B
                                    C = B/A
                                       D
                                    E = D/A
                                    F = D/B
<= 3,300
                                                                         40,784
                                                                         28,185
                                                                            69%
                                                                            574
                                                                             1%
                                                                             2%
3,301 to 50,000
                                                                          8,305
                                                                          8,141
                                                                            98%
                                                                              1
                                                                             0%