Onsite Wastewater Installation Assessment:
Phase 2 (2015 – 2018) Report
Onsite wastewater systems have been and will continue to be a viable option for the treatment of wastewater in areas not served by centralized wastewater treatment systems. Every state in the nation has a population served by decentralized (onsite) wastewater systems. However, the extent to which this treatment option is being utilized has not been measured nationally since the 1990 Census.
NESC, with support of industry and regulators, worked to gather data from years 2015 through 2018 on the installation of onsite wastewater treatment systems across the country. The first of two reports (Phase 1) focused on 2015 collected data. The second report (Phase 2), now available, expanded the Phase 1 dataset to include years 2016 through 2018. The Phase 2 report assesses the use of onsite wastewater treatment systems with new residential and commercial development during the time frame of 2015 through 2018.
DisclaimerThis report contains information about onsite wastewater systems provided by state regulatory agencies and local permitting agencies to the National Environmental Services Center (NESC). Information collected was for the years 2015 through 2018. This effort is composed of two phases: Phase 1) pilot survey for collection of 2015 data, and Phase 2) expansion of dataset to include 2016 – 2018.
Phase 2 collected data expanded the Phase 1 database to cover the time period of 2015 – 2018 while also revisiting failed contacts and correcting errors from Phase 1. The data compiled has been analyzed similarly to Phase 1; however, the terms used for system size were changed from single-family and large to residential and commercial, respectively. Total housing data in 2015 has changed from the Phase 1 report to use imputed data supplemented by data from the Census Bureau, in order to better reflect 6-month lag values. All housing permits were counted with a 6- month lag; i.e., permits in 2015 consist of permits from July 2014 to June 2015. The 6-month lag count is done in order to account for a 6-month construction period and number of finished constructions with an onsite wastewater treatment permit in the report year. This is further discussed in ‘Information Collection Methods’ section. Filling in missing data was done for states and local agencies that did not respond to Phase 1 and did respond to Phase 2. This is further discussed in the ‘National Overview’ section.
Phase 1 concluded with an 82% response rate from state regulatory and local permitting agencies. In comparison, Phase 2 concluded with a 45% response rate from state regulatory and local permitting agencies. This will lead to a discrepancy in permit totals and reliability of analysis when representing the nation. Changes to regulations, jurisdictions, or other administrative issues may have occurred in some states or local jurisdictions since Phase 1 information was collected. States, such as Alabama, shifted from a central state agency to local permitting. These changes are discussed further in the ‘National Overview’ and by state depending on the changes.
The privacy of the individuals submitting the information has been honored. Private funding supported NESC’s efforts to collect, compile, and report on the data. The contents of this report do not necessarily reflect the views and policies of West Virginia University (WVU), West Virginia University Research Corporation, WVU Energy Institute, or NESC, nor does the mention of trade names or commercial products constitute endorsement or recommendation for use.
While attempts were made to provide comparable, standardized data for all jurisdictions
in all 50 states, data storage and collection methods are not consistent across
jurisdictions making it impossible to do so. Data has been presented in a standard
format to the degree possible. It should be recognized all analysis is done
with the data sets provided. Percentages calculated in the report are rounded
to the nearest whole number for simplicity. The analysis includes large number
totals; therefore, rounded percentages may lead to deviations. These percentages
are meant for discussion purposes.
Onsite wastewater treatment systems (OWTS) have been and will continue to be a viable option for the treatment of wastewater in areas not served by centralized wastewater treatment systems. Every state in the nation has a population served by decentralized (onsite) wastewater systems. The measurement of OWTS utilization on a national scale has not been conducted since the 1990 Census. Currently, groups are working to have decentralized wastewater questions included in the American Community survey through the U.S. Census Bureau. However, this task will take several years to complete and at this time, there is no commitment to ensure the topic will be addressed in future surveys.
In response, the National Environmental Services Center (NESC) conducted a national assessment of onsite wastewater systems in 1993 and 1998. During the 1993 data collection, NESC contacted 3,490 health departments and received a 45% response rate via paper survey. The effort took almost three years to compile the data. This was followed by a second round of surveys in 1998 to all local permitting agencies with a similar response rate. NESC published the results of both surveys in a report titled, “National Onsite Wastewater Treatment: A National Small Flows Clearinghouse Summary of Onsite Systems in the United States, 1998.” Table 1 is a summary of the total permits reported. Refer to Appendix A for state by state summary; including new OWTS, repair/replace, and failing system totals.
Table 1. Historical onsite wastewater system permit data reported in 1993 and 1998 broken down by new, repair/replace, and failing.
1.1 Project Objective
The objective of this project was to conduct a national assessment of onsite wastewater system installations over the period of 2015 – 2018.
1.2 Project Activities Summary
NESC has gathered onsite wastewater system utilization data over the four-year span 2015 – 2018. This effort is composed of two phases: Phase 1 – pilot survey for collection of 2015 data, and Phase 2 – expansion of dataset to include 2016 – 2018. Phase 1 is the initial attempt to contact agencies for onsite system permit data pertaining to 2015. The compiled data allows permit data to be analyzed by size: single-family and large (terminology changed to “residential” and “commercial” in Phase 2), and type: new and repair/replace. Depending on the quality of the data received, repair/replace was further broken down by type of repair. The Phase 1 analysis led to the concept development of an Onsite System Utilization Rate (OSUR), a measure to calculate the percentage of new residential housings built with an onsite wastewater system permit. Phase 2 concluded this study by expanding the Phase 1 database to include 2015 – 2018, and utilizing the data, to determine trends in onsite wastewater system installation with relation to new housing construction as well as onsite system maintenance across the United States.
1.3 Report Content
This report is to convey the information obtained from state and local regulators/permitting authorities regarding onsite wastewater installations during 2015 – 2018. Specifically, the report first describes the methods used for information collection, data sources, and reliability. A national overview is provided to summarize permitting agency responses, and type of data collected. The data includes new, residential system permits; residential system repairs; new, commercial system (multi-family, commercial, institutional, etc.) permits; and commercial system repairs. This report also includes the calculated OSUR and their trends as well as decentralized infrastructure sustainability indicated by system replacement rates.
1.4 Potential Benefits of Report
Knowledge of the current trends and the status of existing OWTS will provide local, state, and federal government agencies with necessary information to appropriately allocate resources to ensure OWTS are providing necessary environmental and human health protections. This effort acknowledges centralized wastewater treatment is not a viable option, economically or environmentally, for everyone. Onsite systems, when properly sited and installed, provide as good if not better wastewater treatment and environmental protection as large-scale centralized systems. This effort exemplifies a) widespread reliance on decentralized wastewater treatment to properly treat wastewater across the United States, and b) the need to leverage appropriate resources to ensure continued environmental and public health protection. Manufacturers and contractors may utilize the report findings to identify market trends, opportunities, and potential coverage gaps.
2.0 Information Collection Methods
2.1 Onsite Wastewater Treatment System Information
NESC worked with the project sponsor to develop a state regulatory assessment survey via an online tool. NESC sent a request to state onsite regulatory agencies in all 50 states and solicited assistance from the State Onsite Regulators Association (SORA) to encourage its members to respond to the request. Data collected from the state regulatory agencies provided NESC with each state’s respective permitting structure and preliminary data regarding the number of new, residential, and commercial onsite system permits and onsite system repair permits. If the state agency maintains permit data, NESC requested the state share the local permitting level data. For state agencies not maintaining permit data, NESC compiled a contact list of local permitting authorities and requested they complete the online assessment about their local-level data.
2.2 Housing Information
NESC collected monthly housing data, constructed and manufactured, at the county level through the Census Bureau. Constructed housing permits are installation permits for housing units constructed onsite; whereas, manufactured housing installation permits are equivalent to housing units constructed offsite and delivered in modules. Both housing permits were counted with a 6-month lag; i.e., permits in 2015 consist of permits from July 2014 to June 2015. The 6-month lag count is done in order to account for a 6-month construction period and number of finished constructions with an onsite wastewater treatment permit in the report year. The information made available through the Census Bureau was limited at a county level and thus subsidized by estimates provided through an algorithm utilizing decennial historical housing percentages. These estimates were highly accurate in comparison to the data provided through the Census Bureau.
2.3 Sources of Data
The Census Bureau provided two sets of data in the “Residential building permits survey documentation county ASCII files” 1) estimates with imputation and 2) reported only. The estimates with imputation dataset include reported data for monthly respondents and imputed data for non-respondents and was utilized for this project. Reported data is composed of construction authorized by building permits submitted by local permit officials, and obtained through Form C-404, "Report of Building or Zoning Permits Issued and Local Public Construction." Mitigation of missing data is done by either Survey of Use of Permits (SUP) or imputation. The SUP is used to collect information on housing available only for about 850 areas for which Census Bureau interviewers list and sample the permits authorizing construction of new residential structures. For places not in the SUP, imputations assume the ratio of current month authorizations to those of a year ago should be the same for both respondents and non-respondents.
2.4 Reliability of the Data
Explicit measures of the effects of errors are not available. However, the Census Bureau has expressed the importance of detecting and correcting the operational errors of the data to a degree of “reasonableness and consistency.” These operational errors are attributed to many sources: inability to obtain information about all cases, differences in interpretation of questions, inability or unwillingness by respondents to provide correct information, and errors made in processing the data.
The reported statistics are also influenced by the following limiting factors:
The portion of building permit records is inherently limited since such records
do not reflect construction activity
outside of areas subject to local permit requirements. This portion is likely
to be minimal.
Building permit jurisdictions may close their books a few days before the end
of the month/year; therefore, totals may not strictly align with the calendar
- Roughly three percent of residential houses built in permit-issuing places are built without a permit according to a previous Census Bureau study spanning four years.
To the extent most of these limiting factors apply rather consistently over an extended period, they may not seriously impair the usefulness of building permit statistics as prompt indicators of trends in residential construction activity.
3.0 National SummaryThe Onsite Wastewater System Installation Assessment in 2015 (Phase 1) received an overall 82% response rate from state regulatory/permitting agencies. The follow-up survey for 2016 – 2018 (Phase 2) received an overall 45% response rate. Figure 1 compares county response rates across the United States for Phases 1 and 2.
Figure 1. County response rates to the Onsite Wastewater System Installation Assessment, Phase 1 and Phase 2.
The Phase 1 (2015) and Phase 2 (2016 – 2018) national maps shows response rates, in percentages, of county and/or state regulatory agencies: gray states provided no responses; orange states provided partial, city-level responses; blue states had a response rate less than 50%; light green states had a response rate greater than 50%; and dark green states had a 100% response rate.
Phase 1 was successful in reaching permit authorities in 47 states. Phase 2 was only able to contact 30 states; however, states with missing county level data were updated. Arizona was added to the list of successful surveys in Phase 2 from no data collected in Phase 1. Texas was moved from state total to county level data. Kentucky provided to the state total in Phase 2. Continued expansion of this database to make a thorough account of trends in the nation will be done with updates as data is collected.
3.1 Permitting Authority ResponsesPermitting authorities vary from state to state and vary within a state depending on system size, type, and/or location. Figure 2 depicts responses received from state regulatory agency representatives when asked to identify the level of government issuing onsite system permits within their respective state. In consideration of state versus local permit collection/handling, Alabama and Kansas have decentralized to local agencies due to cuts in funding. California and Kentucky are working toward a centralized permit collection system. Given the range of jurisdictions (i.e., level of government), collecting permit data is a difficult task for state agencies to regulating OWTS. During Phase 1, agencies were asked how permit data was tracked: 54% track permits with self-developed databases, 31% use spreadsheets, and the remaining 15% use purchased databases such as Digital Health Department or Health Space.
Figure 2. Level of governing authority related to onsite wastewater treatment system permits.
The assessment was broken down by the size of regulated OWTS in addition to function/use of the onsite system permit. Participants were given the following options to select if they regulate by size: 1) residential, residential onsite wastewater systems only; 2) commercial (multi-family, commercial, institutional) onsite wastewater systems only; 3) both residential and commercial, onsite wastewater systems, but separately; or 4) combined residential and commercial, onsite wastewater systems, without separation. Option 4 was added to Phase 2, as agencies reported back option 3 with the edit both onsite system sizes were recorded as a combined total with no separation.
Eighty-five percent of the survey respondents from Phase 1 stated they regulate both residential and commercial, onsite system applications; and the percentage decreased to 68% in Phase 2. A similar shift existed in the percentage of respondents that reported they regulate commercial system applications only, from 11% in Phase 1 to 6% in Phase 2. In contrast, the percentage of respondents that regulate only residential, residential applications increased from 4% in Phase 1 to 17% in Phase 2. The additional option in Phase 2 of combined residential and commercial permitting without separation by size, reporting at 8%, is a factor that contributes to the drop in the top category. Figure 3 illustrates this classification by size in number and percentage of total respondents for Phases 1 and 2. Other factors contributing to the shift between Phases 1 and 2 numbers may include the drop in participation of respondents, funding cuts leading to decentralized permitting, and the added option 4 as mentioned above.
Figure 3. Onsite wastewater treatment system permitting authority classification by size. White boxes are the number of total respondents while the graph illustrates percentage (%) of total respondents, including state and local agencies.
As an adjustment from Phase 1, an additional breakdown of the collected information was used. Participants were given the additional option to select if they regulate by function: 1) Flowrate, 2) Discharge (surface vs subsurface), 3) Use (commercial, domestic, etc.), 4) No factor of separation, and 5) Other. Option 1 gave respondents the choice to specify with most elaborating difference in definition of what is considered a residential permit by gallon per day (gpd). This assessment assumes residential is 2,500 gpd. This factor is not universal and varies by state/local agency. Other specifications are done by waste strength, water quality, pretreatment options, etc., with relation to commercial output. Figure 4 illustrates the percentages of respondents that denote onsite system permits by function. Appendix B summarizes the national assessment of permitting authority including information on agency authority and factors of separation for OWTS permit categorization (e.g., size, use, discharge).
Figure 4. Onsite wastewater treatment system permitting authority classification by function. White boxes are the number of total respondents while the graph illustrates percentage (%) of total respondents, including state and local agencies.
3.2 Size and Types of OWTS PermitsPhase 1 and Phase 2 reported a total of 282,147; 196,349; 203,786; and 191,378 onsite wastewater treatment systems were permitted and/or installed for 2015, 2016, 2017, and 2018, respectively. There is no national standard for size classification; and unfortunately, not all states distinguish between residential and commercial onsite systems. States that do separate by size have different measurements for categorization; size and function (e.g., flowrate, discharge, use, end treatment). Most states define residential and commercial in relation to the size of the system. The residential classification, on a national scale, refers to a system size of ~2,500 gpd. This term does not define the limit of the study; rather, clarifies the referenced system size by many of the states. State size definitions for a residential sized OWTS vary from 1,500 gpd and 5,000 gpd. The state-by-state size definitions are discussed in the state review section of this report but vary mainly due to climate and site soil type. Classification of OWTS by size, residential and commercial, is clarified by the end use of the system, refer to Appendix B. Table 2 provides total permits by size and the percentage of permit size to total permits. The percentages have remained constant through Phase 1 and 2.
Table 2. Documented national total onsite system permit breakdown by size in 2015 – 2018, (percentage of permit size to total permits).
New onsite systems associated with total permits accounting for ~70% of the permits issued in 2015 – 2018 with repair/replacement permits accounting for ~30% of total permits. The increase of 7% in permit type of total permits from 2015 (67%) to the following three years (~75%) can be explained by comparing the national response rate of Phase 1 (82%) to Phase 2 (~45%). The total number of new and repair/replace permits dropped significantly from 2015 to 2016. The significant decrease of ~70,000 in total OWTS permits from 2015 to the following three years can be explained by comparing the national response rate of Phase 1 (82%) to Phase 2 (~45%). There is a peak in total OWTS permits for 2017 at 219,910 total permits followed by the lowest number of permits at ~210,557 for 2018. Table 3 provides total values and percentages of new and repair/replace OWTS permits issued nationally.
Table 3. Documented national total onsite wastewater treatment system permit breakdown by type (new and repair/replace) in 2015 – 2018 (percentage of permit type to total permits).
Table 4 provides total values and percentages of new OWTS permits issued nationally in 2015 – 2018. New permits are broken down further by size (i.e., residential, commercial, and combined). Size is denoted by residential, commercial, and combined. The combined category represents states that do not separate by size. There is no change with the comparison of commercial and combined permits even with the change in response rate between 2015 – 2018. There is a decrease of ~31,000 new residential permits from 2015 to 2016. The significant changes in new residential permit totals and percentages from 2015 to the following three years can be explained by comparing the national response rate of Phase 1 (82%) to Phase 2 (45%). Notice the ~10,000 new residential permit increase for 2017. For 2017, there was an expected drop in residential permits with some states unable to report 2017 data (i.e., Oregon – no data available, Alabama – 33% response rate for 2017 and 2018).
Table 4. Documented national new onsite system permit breakdown by size and type in 2015 – 2018. Percentage of permit type to total permits.
Figure 5 provides a breakdown of new OWTS permits issued by size classification.
Combined permits represent data from those states that do not distinguish between
residential and commercial systems. In 2015, the total number of new OWTS permits
were 189,233 consisting of 69% residential, 1% commercial, and 29% combined size
classification. For 2016, the total number of new OWTS permits was 160,129 consisting
of 63% residential, 1% commercial, and 36% combined size classification. For
2017, the total number of new OWTS permits was 166,192 consisting of 66% residential,
1% commercial, and 33% combined size classification. For 2018, the total number
of new OWTS permits was 157,691 consisting of 62% residential, and 1% commercial
size, and 36% combined classification.
Figure 5. Documented new onsite wastewater treatment system permit breakdown by size.
Table 5 provides total values and percentages of repair/replace OWTS permits issued nationally in 2015 – 2018. Repair/replace permits broken down further by size (i.e., residential, commercial, and combined). The combined category represents states that do not separate by size. The significant changes in residential and combined repair/replace permit totals and percentages from 2015 to the following three years can be explained by comparing the national response rate of Phase 1 (82%) to Phase 2 (45%). There is a decrease of ~15,000 residential repair/replace as well as a decrease of ~24,000 combined repair/replace permits from 2015 to 2016. Notice the 40% increase of ~800 combined repair/replace permit for 2017 followed by the 34% decrease of ~1,000 combined repair/replace permits. There is a 20% increase of commercial repair/replace permits between 2015 and 2016 even with the decrease in response rate.
Table 5. Documented national repair/replace onsite wastewater treatment system permit breakdown by size in 2015 – 2018 (percentage of permit type to total permits).
Figure 6 provides a breakdown of repair/replace OWTS permits issued
by size classification. Combined permits represent data from those states that
do not distinguish between residential and commercial systems. The significant
changes in permit totals and percentages from 2015 to the following three years
can be explained by comparing the national response rate of Phase 1 (82%) to
Phase 2 (45%). For 2015, the total number of repair/replace OWTS permits was
91,130 consisting of 70% residential, 1% commercial, and 29% combined size categorization.
For 2016, the total number of new OWTS permits was 52,899 consisting of 94% residential,
2% commercial, and 4% combined size categorization. For 2017, the total number
of new OWTS permits was 53,718 consisting of 93% residential, 2% commercial,
and 5% combined size categorization. For 2018, the total number of new OWTS permits
was 52,866 consisting of 94% residential, 2% commercial, and 4% combined size
categorization. Phase 2 had consistent percentages for 2016, 2017, and 2018.
Figure 6. Documented repair/replace onsite wastewater treatment system permit breakdown by size.States that categorize the repair/replace permits include Alaska, Connecticut, Florida, Iowa, Idaho, Kansas, Kentucky, Massachusetts, Maryland, Missouri, and West Virginia. These permits are designated as tank, drainfield, tank & drainfield, or other. The other category includes any permits that do not fall under tank and/or drainfield categories. Some states have additional categories such as expansion, modification, or unspecified. These were included in the other category. States that separate by new, repair, and alterations (Georgia and Ohio) were not included in this breakdown. Figure 7 provides a breakdown of combined repair/replace OWTS permits issued by category. These permit total do not add up to the national repair/replace total permits as not all states categorize repair/replace permits.
Figure 7. Documented repair/replace onsite wastewater treatment system permit categorization:
tank, drainfield, tank & drainfield, drainfield expansion, or other.
3.3 Onsite System Utilization RateThe collected data was used to calculate an onsite system utilization rate (OSUR) for new housing, which is defined as the ratio of number of reported new, residential housing with onsite system permits to total new housing permits plus manufactured housing shipments with a 6-month lag for installation (Equation 1):
where OWTS permits are residential or combined (residential and commercial)
depending on data availability and total new housing (TNH) is the sum of
manufactured and constructed housing with a 6-month lag.
Data for housing permits and shipments was obtained from the U.S. Census Bureau and imputed with historical decennial data to fill in missing data. Residential housing permits used to calculate the OSUR are “lagged” by six months to account for the estimated time from the housing permit being issued to the onsite system installation. Where partial data from a state was collected (i.e., data from some but not all counties), the Adjusted OSUR was calculated based on the housing permits and mobile housing placements from the responding counties with reported onsite system installations (Equation 2):
where OWTS permits are residential or combined (residential and commercial)
depending on data availability; total new housing (TNH) is the sum of manufactured
and constructed housing with a 6-month lag; and (NH%) is new housing percentage
that is located within responding counties.
Residential OWTS permit data was collected from 48 states in 2015 (New Hampshire and Nevada did not report). Of the 48 states responding, 42 reported new and replacement systems separately, and the remaining six reported a combined total. Of the 42 responding states, 33 states separate residential and commercial onsite system permits. Definitions of residential and commercial systems vary from state to state. Each state’s agency authority and categorization of permit by size and function are shown in Appendix B. State definition and parameters of onsite wastewater treatment systems are provided within the individual state sections that follow the National Summary. Appendix D provides two tables of new OWTS permits for each state by type: residential and commercial in 2015 – 2018. Appendix E provides two tables of repair/replace OWTS permits for each state by type: residential and commercial in 2015 – 2018.
The numbers utilized in the OSUR calculation are dependent on the data availability for each state. The possible datasets used in the calculations are residential new installation or total new installation (combined, both residential and commercial) moving from left to right in Appendix D. When the OSUR calculation is dependent on data from total new installation (combined residential and commercial systems) or total permits (new installation and repair/replace), the OSUR value is expected to have a deviation from the actual OSUR value for the state. The OSUR calculated with total new installation (combined residential and commercial systems) is a minor source of deviation as the data from the states that reported residential and commercial systems separately. Table 4 suggests commercial onsite wastewater treatment system permits make up approximately one percent (1%) of all new installations when counted separated. Therefore, these states (Alabama, Hawaii, Louisiana, Maine, Nebraska) were included in the adjusted national OSUR calculation with the understanding a small deviation will be expected. The OSUR calculated with total permits (new installations and repair/replace installations) is a major source of deviation as the 2015 data set suggest repair/replace installations are approximately 33% of all installations ( Table 2). Therefore, these states (Arkansas, Delaware, Mississippi, New Mexico, Texas) were excluded from the adjusted national OSUR calculation. In addition, Vermont reported a significant portion of the new OWTS permits include a combination of boundary line adjustments, permit revisions, minor amendments, change of use, water supply permits, etc. Therefore, Vermont was removed from the adjusted national OSUR calculation.
The accuracy of the state’s OSUR value is dependent upon the available data as discussed previously, the county response rate, and total new housing within responding counties. In this report, county response is rated by low (< 40%), moderate (40 – 80%), or high (> 80%). Similarly, total new housing within responding counties will also indicate the percentage of housing included. For example, Oregon had a moderate county response rate of 67% with 87% of the housing within those responding counties. This gives a high probability that the OSUR is accurate for Oregon. An OSUR for responding counties was calculated based on new, residential housing and onsite system permits located within the counties, providing an accurate value for the county. As county response of new, residential housing within responding counties approaches 100%, the accuracy of the OSUR value increases. Refer to Appendix C for two tables on state data set reliability: a) inclusion/exclusion in adjusted national OSUR assessment, b) notes on reliability of state data set, c) survey response rate by county, and d) percentage of total new housing included for the adjusted OSUR.
Some state OSURs were unadjusted for several possible reasons including 1) low county response rate with >100% OSUR for the reporting counties, and 2) responses limited to city level agencies lacking defined borders. States with issues relating to (1) were typically large expansive areas with little urban populated areas, including Alaska, Iowa, Kansas, Montana, Oregon, and South Dakota. These states also indicate that agencies such as multi-county health departments or city-level agencies are the permit authority. States with issues relating to (2) were highly dense urban areas located in around northeast, including Connecticut, Massachusetts, and New Jersey. The data from these states was included in the overall national OSUR assessment with a ±1% deviance on the national OSUR value.
The OSUR values exceeding 100%, where new housing with onsite system permits exceeded the number of new housing permits, can be explained by various reasons: a) inability to separate system permits by size or type, b) allocation of permits from multi-county authorities, c) agency estimates, or d) unaccounted mobile housing placement. Other possible explanations do not fall within the scope of this report and require further review. Finally, several states have permit exemptions based on lot size and other factors. These states may not require a permit for an OWTS. These details are further explained within each state’s individual assessment.
All states except for Nevada and New Hampshire did not provide data for Phase 1 or Phase 2 data collection efforts. Table 6 shows 30 – 32% of new, residential housing units across the nation utilize an OWTS for 2015 – 2018. When no data is parsed and all permits for new OWTS and housing are taken into consideration, the national unadjusted OSURs were 26%, 20%, 19%, and 17% in 2015, 2016, 2017, and 2018, respectively. This is an inaccurate measurement to represent the nation but provides minimum OSUR values for 2015 – 2018. The adjusted totals remove commercial sized and unspecified OWTS permits as well as new housing totals from non-responsive counties. The national adjusted OSURs were 30%, 31%, 32%, and 29% in 2015, 2016, 2017, and 2018, respectively. For a complete view of all the data used to calculate the national adjusted OSUR, refer to Appendix F.
Table 6. National permit totals, percentage of total permits included in OSUR, with unadjusted and adjusted OSUR values.
Figure 8 are maps of OSUR across the nation in 2015 - 2018. The gradient
(dark to light) on the maps are state OSUR values from Very High (>75 %),
High (50 – 75 %), Moderate (25 – 50 %), Low (<25 %), to No Data Collected.
Few states divert from their respective gradient. Any significant changes are
due to differences in county response from Phase 1 to Phase 2. For example, Michigan
seems to peak in 2015; but, this is due to low response (20%) in Phase 1 versus
Very High response (100%) in Phase 2. States that did have consistent response
rates of 100% with significant changes in OSUR are: Colorado (±5%) peak in 2017,
Georgia (±5%) peak in 2015, Hawaii (±5%) peak in 2018, Kentucky (±12%) peak in
2015, Minnesota (±5%) peak in 2016, Oklahoma (±15%) peak in 2015, and Vermont*
(±73%) peak in 2018. If the adjusted national OSUR were to be limited to states
with 100% response rate for Phase 1 and Phase 2, the new OSUR values are 30%,
32%, 32%, and 30% for 2015 through 2018, respectively. Based on either conservative
adjustments or including all available datasets, the national OSUR calculation
maintains approximately one-third (1/3) of new housing rely on OWTS.
Figure 8. State OSUR in 2015, 2016, 2017, and 2018. Gradient of OSUR from Very High ( >75 % ), High ( 50 – 75 % ), Moderate ( 25 – 50 % ), Low ( 25 % ), to No Data Collected.
The states excluded from the national OSUR calculation include Arkansas, Delaware, Mississippi, New Hampshire, New Mexico, Nevada, Texas, and Vermont. Each state’s dataset contains one or more of the following issues: no data collected or no separation of new installation permits from repair/replace permits. Refer to Appendix C for notes on the inclusion/exclusion of state datasets from the national OSUR value.
3.4 Historical Comparison of OSUR
There are significant decreases in new housing permits and new housing with an onsite system permit when comparing the data from the 1998 report with the data collected in 2015 – 2018. The data provided from the 1998 report indicates new housing permit demand was much higher in 1993 and 1998 than new housing permits in 2015, a difference of greater than 100% (~750,000 permits, Table 7). Similarly, the data provided from the 1998 report indicates the demand for new housing with an onsite system had decreased from 1998 to 2015 by near 100% (~145,000 permits). A main reason for this discrepancy is data reliability. Specifically, the reliability of the data in terms of county response rate by state is not provided in the 1998 report. The only indicator of response rate is 48% of local agencies for the nation, and the number of local agencies that responded in 1993 (1,566); 1998 (1,546); and both 1993 and 1998 (917). Any reference to OSUR for the years of 1993 (21%) and 1998 (23%) are unadjusted. Therefore, it is assumed new housing with onsite system permit totals represent the state without an adjustment with the responding rate. This causes the state and national OSURs for 1993 and 1998 to be lower than actual OSURs. The national manufactured housing values for 1993 and 1998 were annual totals with no 6-month lag. This causes a small deviation from the actual OSUR value in accordance to how 2015 – 2018 OSURs were calculated (see sections 2.2 and 3.3).
When comparing unadjusted national OSURs, the rates are similar for 1993 and 1998 to the 2015 – 2018 rates (Table 7). The 2015 unadjusted OSUR may be higher due to higher county response rate (82%) versus the ~45% response rate for all other years. Even with drastic differences of total new housing permits, the unadjusted OSUR remained in the range of 18 – 26%. The unadjusted OSUR is not an accurate calculation of the nation and is considered the minimum OSUR value. The adjusted OSURs calculated for years 2015 – 2018 are a more accurate representation of real onsite system utilization rates for new housing, which show approximately 1/3 of new housing use an onsite system to treat wastewater.
Table 7. National overview of new housing permits, onsite wastewater treatment system permits, and resulting Onsite System Utilization Rate (OSUR).
3.5 Conclusion of National Assessment
National assessment effort of the Census Bureau for onsite wastewater treatment system utilization was halted after the 1990 Census. In response, the National Environmental Services Center (NESC) has conducted a national assessment of onsite wastewater treatment system (OWTS) permits in 1993, 1998, and 2015 – 2018. The OWTS data collected in this effort includes new, residential system permits; residential system repairs; new, commercial system (multi-family, commercial, institutional, etc.) permits; and commercial system repairs.
The combination of OWTS and new residential housing permits led to the concept development of OSUR, a measure to calculate the percentage of new residential housing built with onsite wastewater system permits. Conservatively, with data limitations in consideration and unadjusted for non-responding agencies, the national OSUR has consistently remained at 21 – 24 % from 1993 to 2018. The data limitations of the historical data set (1993 and 1998) does not allow for an adjusted value, other than removing new housing data from non-responsive states. The national adjusted OSUR value increases to 29 – 32% for 2015 – 2018, excluding non-respondent counties and inconsistent data format, refer to Table 7.
The national OSUR in 2015 is the most reliable OSUR value with a 82% local agency response rate and 63 % of total new housing permits included in OSUR calculation. The national OSUR in 2015 is calculated to be 30%. The decrease in local agency response (45%) and new total housing (45%) for 2016 – 2018 fluctuates the adjusted national OSUR steadily around 29 – 32%. Therefore, at the most conservative level of estimation, the national OSUR for new housing is around a quarter. The most reliable dataset suggests approximately a third of annual new housing use onsite wastewater treatment systems.