Impacts of sewers around lakes on lake water quality

A recent discussion on the NPS Information Exchange Listserve provided some valuable information to those pondering what might be the impacts of constructing sewers around lakes on lake water quality. The complete transcript follows, beginning with the initial inquiry by Lyn Crighton:

—– Original Message —–
Lyn Crighton, Tippecanoe Watershed Foundation []
Sent: Thursday, February 05, 2009 11:34 AM
To: NPS Information Exchange
Subject: [npsinfo] Impacts of sewers around lakes on lake water quality

We have a bit of a sewer battle brewing. Some opponents are claiming that construction and installation of the sewers will do more harm to the lake (from erosion, I guess) than the benefits that will be provided from replacement of septic systems with a centralized sewer system.
Can anyone please point me (and our county commissioners) to some studies showing the benefits that sewers bring to lakes? And it would be especially helpful if any of these looked at the impacts from construction of the sewer.
Thank you!
Lyn Crighton, Executive Director
Tippecanoe Watershed Foundation
PO Box 55, 301 N Main St
North Webster, IN 46555
Phone: 574/834-3242
“promoting the understanding and management of our lakes and watershed, fostering their restoration and preservation for today and for the future.”

—– Original Message —–
“Perkins, John M”
Sent: Thu, February 5, 2009 12:08
Subject: RE: [npsinfo] Impacts of sewers around lakes on lake water quality

I am curious, are the septic systems that you are proposing to replace failing? If so, is there adequate repair area for another drain field or space to utilize some other onsite technology? And if they aren’t failing, why is it being proposed to replace them with the “Big Pipe”? Have all decentralized options been explored? One thing opponents may fear besides erosion is the sprawl that typically takes place when a centralized system goes through what was once a rural area.

John M. Perkins Supervisor
General Permits & Support Team
601 57th Street SE
Charleston, WV 25304
Ph: 304-926-0499 X-1031
Fax: 304-926-0495

—– Original Message —–
“William Frost”
Sent: Thu, February 5, 2009 12:16
Subject: RE: [npsinfo] Impacts of sewers around lakes on lake water quality

The main benefit is the reduction of nitrate loadings, which occur from both working and failed systems. I don’t have a document readily at hand to offer. We have done a few watershed pollutant loading models and found that in unsewered areas, the nitrate loads from septic systems were the primary source and were higher than those from urban runoff.

Bill Frost, PE
KCI Technologies, Inc.

—– Original Message —–
Doug Martin []
Sent: Thursday, February 05, 2009 5:11 PM
To: NPS Information Exchange
Subject: RE: re[2]: [npsinfo] Impacts of sewers around lakes on lake water quality

From the land of Lake Tahoe, 2 more cents.

Starting in the 1960s, there were plans to address conversion from septic tanks to wastewater treatment and our ultimate solution of exportation of effluent out of the basin.

To this topic, a piece of interesting data comes from USGS. Here’s presentation done in 2002 of their findings and a link. While not scientifically validated in this report, the finding that nitrates are decreasing more so than increasing in the Lake Tahoe Basin where septic tanks were removed decades ago and increasing more that decreasing the carson valley where septic tanks are increasing is an argument for replacing septic tanks.

Good Luck with your project.

Doug Martin
2002 Denver Annual Meeting (October 27-30, 2002)
Session No. 69
Application of Biological and Hydrochemical Tracers in Groundwater Quality Investigations
Colorado Convention Center: Ballroom 4
8:00 AM-12:00 PM, Monday, October 28, 2002

Presentation Time: 10:20 AM-10:35 AM

ROSEN, Michael R., Water Resources Division, United States Geol Survey, 333 West Nye Lane, Carson City, NV 89706,
Douglas County, located in western Nevada on the Nevada/California border, contains 3 general areas where ground water is used as a drinking water supply; these areas are the Carson River Basin (CRB), Lake Tahoe Basin (LTB) and Topaz Lake Basin (TLB). The population of the county has increased greatly over the past 30 years. This has placed increasing pressure on ground-water quality and quantity in the county. The county began monitoring water levels and quality in 1985 to measure the effects of population growth on ground-water resources in the county. Elevated nitrate concentrations have been the primary water-quality issue and there are a number of anthropogenic sources of nitrate in the county. These include nitrate from agriculture, irrigation using wastewater, septic tanks, and domestic fertilizer application. However, only contributions from septic tanks and home gardens and lawns are significant in the LTB and TLB. Distinguishing between the different sources of nitrate in the CRB is the main focus of this study.
Analysis of 37 monitoring wells in all three basins, which have long-term records (>5 years of data from 1980 to the present) of nitrate concentrations, indicates that 43% of these wells show increasing trends over time, 22% of wells show decreasing trends and 35% haven’t changed during the sampling period. All but three of the wells that show increasing trends are located in the CRB, while half of the wells that show decreasing trends are located in the LTB. Only 4 wells in the TLB have long-term records. Two of these wells show increasing trends and one shows a decreasing trend.
The number of septic tanks has increased in Douglas County over the last 30 years. In 1970, there were 610 registered septic tanks in the county. This figure has grown to 5157 in 2002, an increase of approximately 1500 septic tanks every 10 years. Most of this increase has been in the CRB; some of this has been at the expense of agricultural land.
Nitrate concentrations in the ground water do not show depth related trends in wells from the CRB and TLB (R2=0.01) or the LTB (R2=0.06). For example, ground-water samples taken from a well with a static water level 75 m below land surface has a nitrate concentration of >4 mg/L, which is double the mean nitrate concentration for the 37 wells sampled. Analysis presently is ongoing to better define the observed trends.
Doug Martin District Manager
Nevada Tahoe Conservation District
(775) 586-1610

—– Original Message —–
“Amy Macrellis”
Sent: Thu, February 5, 2009 12:26
Subject: RE: [npsinfo] Impacts of sewers around lakes on lake water quality

Hello Lynn,

Without knowing the specifics of your situation, I can say that there are both benefits and drawbacks to replacing septic systems around a lake with centralized sewers.
If there are many older structures, served by older and substandard septic systems, and the systems are often close to the lake and lots are small enough that replacement is not feasible, then sewering may well benefit the water quality in the lake.
However, sewers (particularly those with gravity collection systems) can also result in negative impacts on lakes. The collection system for a centralized sewer, though the excavations needed to install the collection system and through I&I into a gravity collection system, could have a long-term result of lowering groundwater levels in the area, potentially affecting the quantity of water in the lake you are trying to protect…not to mention the potential for exfiltration from a gravity collection system if the lines are above the water table, possibly resulting in raw sewage reaching the groundwater. And then, if the WWTP is discharging to the lake, there is a big responsibility and challenge to keep the plant functioning well–and to collect adequate user fees to keep the system operating properly–so that it does not become a negative impact on the resource.
Personally, I am an advocate for the ‘right’ wastewater treatment solution. Sometimes it is the sewer, and sometimes it’s not. Many communities in the US are upgrading and managing septic systems, or building smaller facilities with soil-based discharge, rather than constructing centralized sewers. I would be happy to discuss any of this further with you off-line.
Amy Macrellis
Water Quality Specialist
Direct / 802.229.1884 Cell / 802.272.8772
E-Mail /
Stone Environmental, Inc.
535 Stone Cutters Way, Montpelier, Vermont 05602
Tel / 802.229.4541 Fax / 802.229.5417
Web Site /

—– Original Message —–
“Richard A. Haimann”
Sent: Thu, February 5, 2009 13:39
Subject: re[2]: [npsinfo] Impacts of sewers around lakes on lake water quality
High BOD, fecal coliform, and ear infections in swimmers have been public opinion drivers toward conversion of septic to sewer in many communities. Resistance to that change has typically come from rate payers (septic owners usually pay nothing) and people with lakeside rural dwellings may want to keep them that way and not allow subdivision and buildup. There are a number of studies that can be employed to evaluate if the current septic are actually impairing the water body or not – sampling, dye tracers, modeling, etc.
So, I would recommend:

  1. Do the studies to determine if an impairment is occurring. Get the proponents of the upgrades to pay for the studies.
  2. Evaluate alternatives to mitigate the impairment – change septic standards (inclusive of required development setbacks, sewer the properties, do nothing… Evaluate the alteranatives against the general plan. Involve the electeds and stakeholders in the alternative evaluation and selection process. Include a financing study to determine what the community can afford.
  3. Pick the alteranative that mitigates the impairment and has stakeholder and elected buy in and get it approved by the council or board of supervisors in full public hearing.
  4. Finance, design, and build.
  5. Monitor to make sure it mitigates the impairment (assuming there is one).
Good luck.

—– Original Message —–
“Ken Ferry”
Sent: Thu, February 5, 2009 15:46
Subject: RE: re[2]: [npsinfo] Impacts of sewers around lakes on lake water quality
Some thoughts-at-large to add to the discussion:

  1. One possible way to detect possible connections between lakeside septic systems and the lake would be the use of an infrared scope or camera during the cold season.
  2. A possible way to ease local residents into the idea of paying a sewer charge would be to formalize septic system maintenance, including cleaning each septic tank and inspecting each system annually, with the costs covered by a “septic system fee.” Being a Hoosier born & bred, I would wager that most, if not all, of the systems would require extensive repairs and upgrades the first year. Maybe then the sewer system option would start to look better.
  3. Don’t overlook the non-gravity sewer options as a means of controlling costs and disruptions. I am preferential to low-pressure sewer collection technology (e.g. in areas difficult to serve with the traditional gravity system.
Ken Ferry, P.E.
Henderson Water Utility
Henderson, KY

—– Original Message —–
Trent, Martin []
Sent: Friday, February 06, 2009 8:53 AM
To: NPS Information Exchange
Subject: RE: re[2]: [npsinfo] Impacts of sewers around lakes on lake water quality
Data from Suffolk County, Long Island also shows lower groundwater nitrogen concentrations in sewered versus unsewered areas. Nitrogen in groundwater in sewered areas ranges from 2-5 mg/L while in unsewered areas the range is 5-12 mg/L N depending on housing density, i.e., the number of dwelling units per acre.
Martin Trent
Chief, Office of Ecology
Suffolk County Department of Health Services
360 Yaphank Avenue, Suite 2B
Yaphank, NY 11980
ph. 631 852-5750 fax 631 852 5812

—– Original Message —–
“Eileen Pannetier”
Sent: Fri, February 6, 2009 10:15
Subject: RE: [npsinfo] Impacts of sewers around lakes on lake water quality

I think you need to know a couple of things to decide whether sewers are good or not. First, what type of soils are common in the watershed? If they have a lot of clay, or if they are gravelly, or if high groundwater is a problem, then sewers are likely to help in that the septic systems may not be working as well as they could. If soils are decent, septic systems can usually do a good job.
If the local zoning would allow a greater density of houses if the area were sewered, or if current septic requirements restrict development, then you might want to get that under control before sewering as more houses equals more impact, with or without sewers.
Eileen Pannetier President/CEO
Comprehensive Environmental Inc.
225 Cedar Hill Street
Marlborough, MA 01752
Phone (508) 281-5160 X301
Fax (508) 281-5136

—– Original Message —–
“Bill Lucas”
Sent: Fri, February 6, 2009 10:17
Subject: RE: re[2]: [npsinfo] Impacts of sewers around lakes on lake water quality
As previous posters note, N loads from septic systems are substantial, particularly at higher densities. This has been found in so many places (DE, MD, RI, NY to name a few) that there is no doubt that septic systems will increase groundwater N, often over 10 mg/l. However, in freshwater lakes, P is most often the limiting nutrient. While P loads are typically much less due to immobilization in the profile, P export can be substantial in sandy soils. P loading from septic systems has been documented in the DE Inland Bays.
So as others note, you have to define the problem first, before you can pull the trigger on what should be done. I am in favor of ejector or effluent pump type systems, since the required collection methods are so much less intrusive (and costly).
Bill Lucas

—– Original Message —–
“Pio Lombardo”
Sent: Fri, February 6, 2009 11:06
Subject: RE: [npsinfo] Impacts of sewers around lakes on lake water quality

Sewer wars are a fairly common event, usually due to cost and secondary growth impacts.

The sewer plan should have identified the problem that sewering is proposed to solve. For inland freshwater lakes, they typically are excess phosphorous which is causing excess algal growth and the associated deteriorating water quality. FYI, nitrogen contamination is typically an issue only in coastal waters or freshwaters in unique areas that have more than sufficient phosphorous for maximum algal growth, such as the freshwaters in Florida. Nitrogen is an issue in drinking water supplies. Bacterial contamination is the other potential major factor for sewering. Very small lots and inadequate separation to drinking water wells may be an issue.
So the first question is whether the proposed sewer is the best way to correct the problem, as there are advanced on-site solutions to phosphorus, nitrogen and bacterial contamination issues with septics. Space may be an issue. Conventional septic systems many times do a poor job of phosphorous removal – especially for systems near the lake due to limited, and reversible, capacity of soils to remove phosphorous. Also, there are inexpensive, effective groundwater treatment techniques for nitrogen and phosphorous removal – to substitute for septic system upgrades or a sewer.
There are numerous sewer options – septic tank effluent gravity (STEG) or pressure, as required by site conditions, are usually the least costly option. STEG systems are very effective, low cost and do not have the problems associates with conventional gravity sewers. The additional technical issue to address is the proposed treatment and dispersal technique. One needs to confirm that the treatment technique will address the root cause of the problem – again if it is phosphorous then there needs to be a phosphorous removal system. Conventional phosphorous removal systems can be expensive with an O&M/Management headache. The dispersal technique needs to be well engineered.
One of the major issues with erosion is the phosphorus content of the soils that would get into the lake. Erosion control and treatment techniques exist to effectively address this issue. Innovative sewer installation techniques can eliminate erosion issues.
Costs usually are a major factor in sewer wars and should be a focus. Alternative technologies are generally more cost effective than conventional approaches
In terms of growth stimulation, there are soft (i.e. legal) and hard (design/sitting, etc.) techniques that can be used to manage growth. There are significant legal issues that need to be addressed
I will forward you by separate email the Wastewater Systems Planning Manual we prepared that addresses these issues and a case study on a project we engineered, which received an engineering excellence award, on how these issues were successfully addressed. We have engineered over $200 million of innovative wastewater projects that have incorporated all of the above issues, as well as having performed lake studies. I will be pleased to provide specifics on issues that are relevant to your situation

Pio Lombardo, P.E., DEE
Lombardo Associates, Inc.
Environmental Engineers/Consultants
49 Edge Hill Road
Newton, MA 02467
Tel: 617-964-2924
Fax: 617-332-5477
Cell: 617-529-4191

Web Site


  1. Here is a link to PDF Report < HREF="" REL="nofollow">Between the Rock and a Wet Place – Lake Hopatcong, New Jersey<>, replaced septic tanks with a pressure sewer system. Presented at WEFTEC 2008 and posted at the < HREF="" REL="nofollow">Environment/One Sewer Systems Technical Reprints Page<>


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