Chapter 4 Onsite Sewage Systems
Households and businesses that are not connected to the City's wastewater system must treat and dispose of their sewage, also known as wastewater, on site. There are approximately 4,225 septic systems, also known as onsite sewage systems (OSS), in Olympia and its urban growth area (UGA) - about 2,100 in the City and 2,125 in the UGA. Figure 4.1 shows an example map of the distribution of OSS in a select area of the City's Sewer Service Area. For complete mapping of lots served by OSS, see Chapter 5 and Appendix J.
OSS have historically been the most common method of sewage treatment in Thurston County. Many lots served by OSS were not connected to sewer service after sewer pipes were installed in the vicinity, sometimes directly in front of the property.
In the 1950s, reports of failing OSS and pollution of Capitol Lake and Budd Inlet made it clear that significant sewer infrastructure improvements were needed in the Olympia area. In the 1970s, concerns about public health risks associated with OSS led the Thurston County Board of Health to require inspection and certification of OSS. The focus of their monitoring program has been in the Henderson Inlet watershed due to pollution causing the closure of many beaches to shellfish harvesting. The increased oversight has led to many of the beaches being reopened for shellfish harvesting in recent years.
Currently, both Thurston County and the City of Olympia regulate the permitting and use of OSS within Olympia's Sewer Service Area (see Section 4.5 below for more details). Property owners are responsible for maintaining individual OSS.
This chapter reviews the types and functioning of OSS, the potential public health risks associated with the systems, proximity of OSS to Olympia's sewer system, potential costs of OSS conversion to public sewer and the current regulatory framework.
Challenges associated with OSS in the City and UGA are introduced and discussed in this chapter and summarized in Chapter 8. Goals and Strategies related to OSS are presented in Chapter 9.
View Figure 4.1 Example Map of Lots Served by Individual Onset Sewage Systems
4.1 Types of Onsite Sewage Systems (OSS)
There are two main types of onsite sewage systems, individual (OSS) and community (COSS). Normally, OSS only serve one dwelling, one duplex or one business. COSS treat sewage flows greater than 600 gallons per day (gpd) or flows discharged from three or more dwellings. Under state law, a public jurisdiction must own and operate COSS. In cities and their UGAs, COSS are considered an interim form of sewer service, to be used only until public sewer service become available. As part of the 1992 intergovernmental agreement with Thurston County (see Chapter 2), the City owns and maintains all COSS within the City's Sewer Service Area. Currently, there is only one COSS in Olympia's Sewer Service Area, built in 1994 and serving three single family residences.
Larger OSS, or LOSS, a type of COSS treating flows greater than 3,500 gpd, were regulated by Thurston County until 2011, and are now regulated by the Washington State Department of Health. There is no LOSS in the City or its UGA.
An OSS typically consists of a buried 500-1500 gallon, two-compartment septic tank and a drainfield. The tank collects sewage from the structure(s), which is then separated into (1) solids that settle and are broken down biologically by naturally occurring bacteria, (2) liquid that flows out of the tank and into the drainfield, and (3) fats, oils and grease (FOG) that float on top of the liquid in the tank and get partially broken down. In a properly functioning OSS, the liquid sewage either flows out of the tank by gravity, or is pumped to the drainfield, where it is evenly distributed in the drainfield.
As the sewage percolates through the drainfield and underlying soil, further filtration of the sewage occurs, as well as additional biological treatment before it reaches groundwater. The solids and FOG need to be pumped out of the tank on a regular basis, typically once every three to ten years, based on use.
Figure 4.2 is a conceptual diagram of an individual OSS, and Figure 4.3 shows a community onsite system (COSS).
Proper functioning of OSS depends on the soil's ability to process and filter the effluent. With the large silt fraction of soils in the South Puget Sound region, less than one percent of Thurston County soils are ideal for onsite sewage treatment, and 87% of the land by area is inappropriate for OSS (LOTT, 1998). See the Geology and Soils section in Chapter 2.
View Figure 4.2 Individual Onsite Sewage System
View Figure 4.3 Community Onsite Sewage System
4.2 Public Health Risks of OSS in Urban Areas
OSS can be an effective and safe method of treating and disposing of treated sewage when properly designed and installed, maintained regularly, and kept at moderate to low site densities. OSS are appropriate in rural areas but were not intended for use in increasingly dense developed cities. OSS require a treatment and disposal area large enough to adequately break down and dilute effluent-borne contaminants.
The presence of over 4,000 OSS in Olympia and its UGA creates the potential risk to environmental and public health from groundwater, surface water and soil contamination. Figure 4.4 illustrates these risks.
View Figure 4.4 Potential Risk to Groundwater and Surface Water from OSS
Risk of OSS Failure
Industry research has indicated that the design life of OSS is generally 20-30 years. The potential for failure increases with time, even if the system is properly sited and consistently maintained. However, records show some systems last much longer than the average.
OSS that are not properly sited and maintained may threaten water quality and public health by releasing bacteria, viruses, nitrogen, phosphorous, heavy metals and chemicals from household products into the environment. “Failure” means the system threatens public health because it is not adequately treating sewage or is creating a potential for people to come in contact with sewage. Examples of failure include:
• Sewage on the surface of the ground.
• Sewage discharged directly to surface water.
• Sewage backing up into a structure because of slow infiltration of effluent through the soil.
• Sewage leaking from a tank, pump chamber, holding tank or collection system.
• Inadequately treated effluent contaminating ground water or surface water (determined by dye tracing and/or fecal coliform count).
• Surface or ground water intrusion into a tank, pump chamber, holding tank, or collection system.
• Cesspools.
• Seepage pits where there is evidence of ground or surface water quality degradation.
Evidence of Contamination from OSS
OSS, especially when used at urban densities, create threats to both groundwater and surface water. Nitrates are a common groundwater contaminant associated with OSS, while bacteria linked to OSS are often found in surface water.
Nitrate is increasingly observed in groundwater, including the City's drinking water supply wells in Southeast Olympia. In some cases, the concentration of nitrate threatens the viability of both private and public drinking water supplies. OSS have been identified as a significant contributor to the problem through detailed studies conducted in the 1990s and 2000s. The City's wellhead protection areas are taken into account when the Utility evaluates sites for new and replacement OSS.
In addition, bacterial contamination from failing OSS is one of the principal causes of shellfish restrictions imposed on Puget Sound since 1980 (Grover 1996). Ongoing water quality monitoring confirms that streams and marine waters within Olympia have elevated levels of bacterial contamination.
Guidance on Siting of OSS
Research demonstrates that properly functioning OSS can pollute ground and surface water if they are concentrated in too small a land area (DeFeo, 1991; Yates, 1985). In Olympia and its UGA, an estimated 43 percent of OSS are sited on lots less than the minimum recommended lot size of 12,500 square feet (WAC 246-272-20501; Article IV, Section 21). Similarly, ground and surface water quality impacts have been observed where the average density of OSS is more than four systems per acre, even in well-drained soils (Brown and Bicki 1987, 1991). The maximum density of OSS in Olympia's Sewer Service Area is approximately 4 systems per acre, in areas of the southeast UGA. More typical densities in areas with OSS are less than 2 systems per acre. As a comparison, all of Olympia and its UGA is zoned or planned for densities with residential lot sizes of approximately 5,000 square feet or about 8.7 lots per acre.
Additional guidance recommends that OSS should be adequately separated from drinking water wells. Analysis on virus mortality and migration suggests that OSS should be at least 400 feet apart to reduce virus concentrations below safe drinking water standards in the groundwater (Brown & Bicki 1997, 1991; LOTT 1998). Under current County regulations, if a lot is served by a private well, the minimum lot size for an OSS is one acre (Article IV, Section 21). In addition, new OSS must be located at least 100 feet from a water supply source or other surface water and 200 feet from a public drinking water supply (WAC 246-272-09501; Article IV, Section 10).
Under State regulations, OSS cannot be installed within 100 feet of fresh or marine surface water (WAC 272-0950). With waivers, Thurston County maintains authority to reduce the buffer distance to 50 feet. In addition, the City's Shoreline Master Program prohibits OSS for new development within the shoreline jurisdiction. Under Olympia's Critical Areas Ordinance, OSS are not allowed in designated critical areas (e.g., wetlands and floodplains), or their buffers.
|
Onsite Sewage System Characteristic |
Approximate Number |
% of Total1 |
|---|---|---|
|
Lots less than 12,500 sq. ft. |
1,800 |
43% |
|
Lots with drinking water wells (100 ft from well required by WAC, 400 ft. between OSS recommended) |
1,200 |
28% |
|
Lots within 100 ft of surface water |
470 |
11% |
|
Lots within Olympia drinking water wellhead protection areas |
870 |
21% |
|
Lots within Olympia portion of Henderson Watershed Protection Area |
835 |
20% |
1Total adds up to more than 100% because some OSS meet more than one of the characteristics.
Assessment of Current Risks in Olympia
In response to increasing concern over the prevalence of OSS in the Lacey-Olympia-Tumwater area, Thurston County Environmental Health completed a planning-level analysis of existing OSS use and their environmental risks. The analysis used mapping technology to link the various densities of OSS in neighborhoods to screening criteria defining potential risks to both surface and ground water. This information provides a productive planning-level tool for considering jurisdictional needs for OSS policies and regulations, and the potential need to convert systems to sewer service.
The analysis documented the occurrence of individual OSS in the north Thurston County area. Areas with OSS were subsequently grouped into neighborhoods based on subdivision plats or lots that share similar characteristics. Commercial and multifamily OSS were converted to a single family residential equivalency unit. OSS densities in the neighborhoods were calculated and grouped as follows: ≤ 1 OSS unit/ acre, 1-2 units/acre, 2 to 4 units/acre, and ≥ 4 units/acre. For this analysis, the density of OSS was a key risk factor.
Given OSS densities, several natural resource parameters were used to refine the potential threat to both surface water and groundwater. The risk of surface water contamination from OSS increases with neighborhoods that are close to water bodies and that have soils that generate runoff rather than infiltrate. When combined with neighborhoods with relatively high densities of OSS, these geographic traits create a higher potential for contamination.
Similarly, neighborhoods located within drinking water protection areas and with soils that readily infiltrate generate relatively high risks to groundwater.
The analysis indicates that from a regional planning perspective the implications of OSS in Olympia may be modest, with many areas at lower risk to both groundwater and surface water. Maps depicting the outcomes of the analysis are provided in Appendix J. Chapters 8 and 9 further address OSS challenges and recommendations as well.
4.3 Proximity of OSS to Olympia Wastewater System
OSS are distributed throughout Olympia and its UGA. As surrounding homes and neighborhoods developed on public sewer, isolated or small pockets of systems have remained. Other areas such as portions of Northeast and Southeast Olympia include entire subdivisions served by OSS. Additionally, many undeveloped infill lots remain in Olympia. At some point, most of these isolated lots will develop and need sewer service.
In general, current City policies require a developing lot or a failing existing OSS to connect to the public system if located within 200 feet of the sewer pipe. Of the 4,225 OSS in Olympia and its UGA, over 1,100 are within 200 feet of public sewer. As shown in Table 4.2, an estimated 1,260 systems in the City and 1,840 in the UGA are further than 200 feet from sewer and could be connected only if sewer pipes were extended. The table also shows the distribution of OSS in relationship to existing sewer pipes.
|
|
Adjacent to Sewer Main |
Within 200 feet |
Over 200 feet |
Total |
|---|---|---|---|---|
|
Within City limits |
570 |
270 |
1,260 |
2,100 |
|
Within UGA |
230 |
55 |
1,840 |
2,125 |
|
Total |
800 |
325 |
3,100 |
4,225 |
Many undeveloped lots are within a feasible connection distance to the public wastewater system. For those undeveloped lots that are further than 200' from sewer, the lot size determines whether an OSS may be a viable option. Lots over one acre are more likely to be eligible for an OSS permit than lots under one acre. Prior to the 2013 Plan, only lots larger than an acre were eligible for new septic systems inside the city limits. As a result of the Plan and with input from Thurston County, the Utility changed the regulations in 2017 to allow new septic systems on lots smaller than an acre, but only if additional criteria are met. Table 4.3 shows characteristics of undeveloped lots in relationship to lot size and distance to existing sewer pipes.
|
|
Within 200 feet |
Over 200 feet and < 12,500 SF |
Over 200 feet and between 12,500 SF and 1 acre |
Over 200 feet and > 1 acre |
Total |
|---|---|---|---|---|---|
|
Within City limits |
1,650 |
140 |
110 |
100 |
2,000 |
|
Within UGA |
240 |
60 |
80 |
70 |
450 |
|
Total |
1,890 |
200 |
190 |
170 |
2,500 |
1Not all undeveloped lots are developable.
4.4 Potential Costs of Converting OSS to Public Sewer
For owners of OSS, the cost of connecting to City sewer can be substantial. Table 4.4 summarizes the potential costs of OSS conversion and highlights the high degree of variability of construction costs.
|
Item |
Range of Costs1 |
|
|---|---|---|
|
Construction Costs |
||
|
1. |
Construct Sewer Pipe in Street |
$0 (if sewer is available) $4,000 - $15,000+ |
|
2. |
Side Sewer Construction to House (high end is for grinder pump or STEP connection) |
$4,000 - $14,000+ |
|
3. |
OSS Abandonment |
$1,000 - $1,500 |
|
|
Construction Subtotal = |
$5,000 - $30,000+ |
|
2019 Applicable Fees and Permits |
||
|
4. |
LOTT Clean Water Alliance Capacity Development Charge (LOTT CDC) |
$1,5122 - $6,049 |
|
5. |
City Wastewater General Facility Charge (GFC) |
$03 - $3,442 |
|
6. |
Permits for Sewer Connection |
$500 - $2,000 |
|
7. |
OSS Abandonment Permit (Thurston County) |
$275 |
|
|
Connection Fees Subtotal = |
$2,300 - $12,000 |
|
|
Range of Total Costs to Convert = |
$7,300 - $42,000+ |
1In 2019 dollars, rounded figures.
2A limited number of 50% - 75% instant rebates are available to help pay for the LOTT CDC.
3The City Wastewater GFC is waived per Olympia Municipal Code 13.08.205(C) for properties with an existing OSS that connect to sewer within two years of notice of sewer availability or within two years of new ownership or with an approved LOTT CDC rebate.
Through its Septic to Sewer Program, the City assists homeowners with an OSS to convert to public sewer. The program was created in response to the environmental considerations discussed above. The program includes the following components:
• Public education and outreach
• General Facility Charge (GFC) Waivers
• Neighborhood Sewer Extension Program
The program was revised in 2017 to further assist property owners. The changes increased the number of properties eligible for GFC waivers. It also reduced the amount property owners reimburse the City for neighborhood sewer extensions.
The number of OSS conversions to public sewer increased from an average of 5 conversions per year between 1997 and 2008 to an average of 14 conversions per year between 2009 and 2018. The increased rate of conversion corresponds to implementation of the City’s Septic to Sewer conversion program. GFC waivers and neighborhood sewer extensions account for the increase in conversions. There has also been an increase in the number of conversions since the start of the LOTT Septic Conversion Incentive Program in 2017, featuring 50% to 75% rebates on the LOTT CDC. More information on both programs is available on the City webpage.
4.5 Current Regulations
Privately owned individual OSS and community OSS are regulated by the Thurston County Board of Health. The County Environmental Health Division is responsible for reviewing permit applications for new OSS and repair or expansion of existing systems. Its staff maintain OSS records, and oversee the inspection of OSS before property ownership is transferred.
This section summarizes the regulatory framework for individual and community OSS, special regulations for the Henderson Watershed Protection Area and pending regulations on underground greywater irrigation systems.
Individual Onsite Sewage Systems (OSS)
The City has no responsibility for owning, maintaining or managing private individual OSS. However, the City does have the authority within its Sewer Service Area, including in the UGA, to determine if a new OSS or repairs to an existing OSS are allowable, or whether the proposed or existing building(s) is required to connect to sewer service. Therefore, all OSS repair or new construction applications for sites located in the City or its UGA are routed to the City for review and recommendation for approval or denial. Applications in the UGA are reviewed only for sewer availability. See Appendix P for a flowchart that guides City and County staff in determining whether or not a proposed OSS can be permitted within the City or its UGA.
City regulations for permitting new OSS are more restrictive than State and County regulations. Under current State and County regulations (WAC 246-272A-C and Article IV of the Thurston County Sanitary Code, respectively), new OSS are allowed under certain conditions, most importantly when the following conditions can be met: it can function properly, it is located in suitable soils at a safe distance from a water well, and no public gravity line is accessible. Under State and County standards, OSS served by a public water system must be located on lots of at least 12,500 sq. ft. (with a density of 3.5 lots per acre or less); the County code allows OSS on smaller lots of record (i.e. lots created before 1995) if they meet other criteria (WAC 246-272A-0210 and WAC 246-272A-0320). City permitting regulations restrict new OSS inside the City limits to lots that are more than 200 feet from an available sewer pipe and for existing lots greater than one acre in size, except under certain circumstances outlined in Olympia Municipal Code section 13.08.090. Replacing existing OSS located more than 200 feet from municipal sewer can be permitted.
All new OSS in the City and UGA must be designed as interim and agree to connect within one year of being notified to do so.
The County Health Code requires owners of larger or more complex systems to have them certified and inspected every one to three years. High-risk OSS located in the Henderson Inlet Shellfish Protection Area have more stringent requirements (see below). A City-County Resolution also encouraged owners of OSS to register with the Thurston County Operational Certificate Program. Olympia Water Resources cooperates with Thurston County in periodic educational activities to encourage proper maintenance by OSS owners.
Community Onsite Sewage Systems (COSS)
Community onsite sewage systems (COSS) are considered by the Department of Ecology to be public sewerage treatment facilities, requiring the City to assume ownership and maintenance responsibility. Under an October 1992 intergovernmental agreement with Thurston County, the cities of Olympia, Lacey and Tumwater own and operate COSS within their UGAs. Public ownership is meant to encourage development within the UGA in the interim before sewer infrastructure is extended, and to ensure consistent Wastewater Utility services to all customers as mandated by the Growth Management Act.
Current Wastewater Utility practice allows approval of a COSS only if topography or other constraints preclude connection to the public sewer, and if the cost of extending the sewer exceeds COSS installation and lifecycle costs by 50 percent. Before the City takes over ownership and maintenance of a COSS, the developer must pay all up-front connection fees to the Wastewater Utility, including the CDC and GFC. Customers connected to a COSS must agree to pay the regular monthly sewer utility rate and connect to sewer service within one year after sewer becomes available, including paying any connection fees not previously paid to the City at the time of connection to the COSS.
COSS are considered interim systems and must be designed for efficient conversion to sanitary sewer. COSS permits in the UGA require that property owners sign an agreement to support an annexation petition, to take effect when the area becomes contiguous to the City.
Currently, Olympia maintains one COSS, located on Devoe Road in the UGA.
Henderson Watershed Protection Area
In May 2004, a Thurston County citizen advisory committee recommended a program to enforce OSS maintenance in the Henderson Inlet watershed (see Figure 4.4), where fecal coliform bacteria from human waste are contributing to the pollution in streams and marine waters (Thurston County, 2002). Woodland and Woodard Creeks, which capture runoff from northeast Olympia, Lacey and Thurston County, are on Washington State's 303(d) list of water quality impaired water bodies, a list maintained as a requirement of the federal Clean Water Act. The Olympia portion of these basins includes lots with 835 OSS, 530 within the City limits and 305 in Olympia's UGA.
Based on the committee's recommendations, Thurston County approved its first mandatory OSS operation and maintenance program to help restore water quality. The program requires that all high-risk OSS within the existing shellfish district be inspected on a regular basis and that owners maintain a current County Operational Certificate. See Article IV of the Sanitary Code for Thurston County for more information regarding this program.
The program has been successful in achieving the goal of reducing pollution contributed by failing OSS through a routine inspection and maintenance program. Measurable improvements in the marine water of Henderson Inlet have occurred, and the shellfish harvest status was upgraded for 340 acres of tideland. OSS owners have taken responsibility for the operation and maintenance of their systems - as evidenced by the 2,100+ homeowners that are certified to inspect their OSS and an ongoing compliance rate of about 87 percent. Additional information can be found on the web site for Thurston County Environmental Health.
View Figure 4.5 Henderson Inlet Watershed Protection Area (hatched area)