The septic and stormwater surveys: What did we learn?

NOTE: The following article summarizes a report on the 2011 septic and stormwater surveys prepared by the consulting firm Forrest Bell Environmental for the Steering Committee of the Lake Wentworth/Crescent Lake Watershed Management Plan. A full copy of the consultants’ report, complete with photos, is available on this web site at:

As the summer of 2011 neared its end, a score of dedicated Lake Wentworth Association shore representatives fanned out along the camp roads distributing notices of an upcoming survey that would invite property owners around Lake Wentworth and Crescent Lake to share information about their homes – all this in the interest of supporting the development of a management plan for the watershed that surrounds both lakes.

In the weeks that followed the notification, those same shore reps revisited their neighbors, this time accompanied by environmental consultants gathering data about the location and age of residential septic systems. With the owner’s permission, the consultants also evaluated each property for signs of erosion and other damaging effects from runoff into the nearby lake or stream.

Threats to the water quality of the two lakes had been previously identified in a diagnostic study undertaken by NH Department of Environmental Services (DES) in 1999, and the study had recommended that a sanitary survey be conducted in order to better understand the role that septic systems may have in determining the water quality of the lakes.

That understanding is important because a failing septic system can be detrimental to human health, aquatic life, and water resources. Septic system effluent typically stores a thousand times the concentration of phosphorus typically found in lake waters, which means that even a small amount of effluent can have a major impact on nearby waters.

In addition, an outdated or improperly maintained septic system can result in the delivery of disease-causing bacteria and nutrients to nearby water bodies, causing gastro-intestinal illness in swimmers or severe ecosystem dysfunction for fish and wildlife. Untreated septic waste can also contain chemicals and hormones used in pharmaceutical and personal care products, which can have severe impacts on aquatic life.

Now, a dozen years after the diagnostic study, the Lake Wentworth Foundation has partnered with the Town of Wolfeboro, DES, and the University of New Hampshire to develop a management plan for the entire Lake Wentworth/Crescent Lake watershed. When completed sometime in the fall of this year, the plan will have identified current and potential threats to the surface waters that feed and make up the two lakes. The hope is that, in subsequent years, funding will be found to begin chipping away at the sources of the nutrients that are slowly undermining the health of the lakes and their tributaries.

Last year’s septic and stormwater runoff surveys were designed to collect baseline information about the state of septic systems within 250 feet of  the lakes and their tributaries. Those survey results can then be used to estimate phosphorus input to the lakes from developed areas in the watershed.

It is estimated that a total of about 2050 pounds of phosphorus enters Wentworth each year from all sources, including erosion, fertilizer use, and atmospheric deposition. About 1091 pounds enters Crescent Lake from all sources.

Approximately 174 pounds of phosphorus leaches into Lake Wentworth each year from the septic systems of shoreline properties. In Crescent Lake, the figure is about 28.6 pounds.

That means that fully 8% of the phosphorous entering Lake Wentworth leaches from septic systems.

Likewise, at least 3% of the phosphorous entering Crescent Lake is from surrounding septic systems. (The lower load at Crescent is a result of the public sewer system along some shores and the overall smaller number of homes around the lake. However, Lake Wentworth contributes another 6% of the phosphorus in Crescent, so that 9% of Crescent’s phosphorus comes from septic systems.)

For the two lakes taken together, 6% of load is from septic systems.

Significantly, estimates from lake modeling indicate that upgrades and regular maintenance of all septic systems in the watershed would reduce the phosphorus load from septic systems by 29% in Crescent Lake and 32% in Lake Wentworth. Those reduction estimates are equivalent to an overall reduction of 3% of the direct input to Crescent Lake (1% of the overall input if input from Lake Wentworth is taken into account) and a 3% phosphorus reduction to Lake Wentworth.

These values represent a small but potentially significant portion of the reductions needed to bring phosphorus levels in Lake Wentworth down by a targeted amount of 10%, which would in turn reduce phosphorus levels in  Crescent Lake enough to bring it back into “High Quality Water” status, according to the DES water quality standards.

General septic survey data

In the course of conducting the septic system survey, representatives from the watershed plan’s consulting firm, Forrest Bell Environmental, identified 625 properties located within 250 feet of the lakes or their tributaries. Of  that number, 552 properties were found to be eligible for surveying. In the 73 other cases, properties were vacant, there was no building on the property, or the landowner refused to participate.

Of the eligible 552 properties, 221 septic surveys were completed in-person. As a follow-up, 39 septic surveys were sent by mail and 12 surveys were sent by volunteers via e-mail. For those surveys that were either left at the door, mailed, or sent by e-mail to the landowner, 63 responded by mail and 18 responded online. A total of 296 septic surveys (54%) were completed for this project.

Most lake residents (75.2%) perceived the water quality of Lake Wentworth to be high. Only a small population of residents (2.7%) viewed the quality of lake water to be relatively poor. Eighty-three percent of residents surveyed used septic as their primary wastewater system; 8% were on town sewer and 6% used outhouses, primarily on the islands.

The age of septic systems in the shorezone was spread across the different age classes of the survey, with as many new systems (21%, 1-10 years old) as old (21%, greater than 25 years old). More than half of the surveyed houses were built prior to 1986 (greater than 25 years old), and 11% of properties were new developments within the last 10 years. In many instances, the home had been recently rebuilt or modified to upgrade an existing dwelling, at which time a new septic system was installed.

The annual usage of these lake properties is fairly equal between seasonal (30%), more than one season (37%), and year round (32%). Average occupancy was primarily couples and individuals (38%), small families (2-4 people, 39%), or seasonal multi-families or public facilities (4-6 and more than 6 people, 23%).

Most septic systems are located more than 50 feet away from a tributary or shoreline (83%), but 6% are within 20-50 feet. These properties tend to be older homes that have been grandfathered in regards to compliance with new septic system rules.

Approximately 35% of homeowners reported that they have their septic systems pumped out every 3 to 5 years; 38% said they have their systems pumped every 1-2 years; 2% indicated that they have their systems pumped out every 10 years or more; and 1% reported never having had their systems pumped.

A majority of homeowners use washing machines and dishwashers, while a smaller percentage use garbage disposals or water softeners. An encouraging 53% of surveyed residents claimed that they always check for no-phosphate labels on detergent products.

Survey findings for the islands

Since many volunteers participating in or assisting with the survey expressed concern about the condition of island sites, septic survey data was extracted specifically for the islands and is presented in  the table below.

Survey Question Finding
Perception of lake water quality Ranged 7 to 10 (medium to high rating)
Type of wastewater system (20) outhouses, (2) cesspools
Age of house (19) greater than 25 years, (1) 10-15 yrs
Annual usage (12) seasonal, (8) more than one season
Annual occupancy (6) 1-2 people, (11) 2-4 people, (1) 4-6 people, (2) more than 6 people
Distance to waterbody (4) 20-50 ft, (4) 50-75 ft, (6) greater than 75 ft, (6) no response
Washing devices Only one property with washing machine and dishwasher
Use of non-phosphate products (18) always, (1) sometimes, (1) never
Grassed lawn area None
Willingness to improve property Ranged 6 to 10
Total properties surveyed 20


Perception of lake water quality and willingness to improve properties rated very high in comparison with the entire watershed. Since all the surveyed island properties had outhouses and/or cesspools, no data was collected for age of system, pump-out frequency, and year of last pump-out. Most of the homes were older (greater than 25 years) and used only seasonally with less than 4 people annually. Due to the small size of the islands, outhouses were located more closely to shore. Awareness of the importance of using non-phosphate products was very high.


With the survey data in hand, the watershed consultants offered a number of recommendations for minimizing the effects of septic system leaching on water quality in the lakes and their tributaries.

For the Lake Wentworth Foundation:

ñ  Prioritize outreach activities to target homes using older systems (39%), landowners within 50 feet of the shorefront (6%), and landowners who rarely, if ever, pump their systems (3%)

ñ  Apply for federal/state grants and other funding sources to help fix potential septic system problems identified in the survey

For individual homeowners:

ñ  Pump septic tanks regularly (every 2 to 3 years for year round residences, 4-5 years for seasonal) and upgrade marginal systems

ñ  Reduce garbage disposal use, which can contribute excess nutrients to water treatment plants, by maintaining a backyard compost heap or an indoor vermicompost for kitchen food scraps

Stormwater survey methodology

Stormwater runoff is water that does not soak into the soil during a rain event but instead flows over the surface of the ground. Stormwater runoff picks up road salts, oil and grease, toxic chemicals, pesticides, bacteria from pet waste, and heavy metals from vehicles before discharging to the nearest waterbody. Additionally, runoff from warm, paved surfaces is a major source of thermal pollution that inhibits cold water organisms and degrades habitat.

The 1999 Lake Wentworth diagnostic study identified areas in the watershed where stormwater runoff, logging, sand pit activities, and beach erosion were a concern for water quality. Many of these sites are still a concern today, and there are many more sites that have not yet been documented.

The 2011 stormwater survey was conducted in conjunction with the septic survey to document sources of pollution on residential sites within the 250 foot shorezone. The survey documented sources of pollution including: roadside runoff into tributaries, direct runoff to the lakes, runoff from development, conversion of seasonal to year-round residences, use of fertilizers, erosion from poorly buffered properties and artificially created beaches, and runoff from parking lots adjacent to tributaries and shorelines. If no stormwater problems were identified on a property, no stormwater field survey sheet was not filled out for the site.

If a stormwater related problem was identified, the survey documented the type of land use activity, a description of the stormwater problem(s), size of exposed or eroded area, recommendations, impact of property to lake/stream water quality, and cost of materials for possible recommendation implementation. Sites with major erosion problems were combined into a common spreadsheet and forwarded to a second watershed plan consultant, Comprehensive Engineering Inc (CEI), for a follow-up visit as part of the larger watershed assessment.

The consultants note in their report that the purpose of the stormwater survey was not to point fingers at landowners with problem spots, nor was it to seek enforcement action against landowners not in compliance with ordinances. Instead, they expressed the hope that the Lake Wentworth Foundation and the Town of Wolfeboro can work with landowners to make improvements to help protect the water quality of Lake Wentworth and Crescent Lake.

Stormwater survey results

The survey team completed stormwater surveys for 481 parcels within the shorezone of the Lake Wentworth/Crescent Lake watershed. The survey team identified 106 sites in the watershed that are currently affecting or have the potential to negatively affect water quality. Only 71 properties were not surveyed for stormwater because the landowner refused or surveyors were unable to locate or access the property All parcels within the shorezone were assessed for stormwater impact, but generally parcels without septic systems did not have noticeable human-generated impacts.

Of the 106 surveys that were filled out because a problem was identified, 49 were completed with the landowner present. The total size of eroded area surveyed was approximately 77,315 sq ft. There were 13 artificially created beaches documented with stormwater issues. This is only a fraction of the total number of artificial beaches that the survey staff identified over the course of the survey, indicating that artificial beach enhancement is a lake-wide issue that requires more attention and education to reduce these areas and mitigate related stormwater issues.

Eighty-eight percent of properties were assessed for pollution resulting from stormwater runoff. The most problematic stormwater problem areas were from residential (37 surveys), beach access (42 surveys), and driveway (13 surveys) land use types.

Properties were fairly evenly split between having (44%) and not having (56%) a grassed lawn area within 100 feet of the water. Of those properties with a lawn, 80% claimed to use no fertilizer, and 19% claimed to use a low or no-phosphate fertilizer on some portion of their lawn within 100 feet of the water. (In a few instances when a landowner reported not using fertilizer, however, visitors subsequently saw the product on the property. The consultants reported that these cases illustrate that elimination of fertilizer use or the use of non-phosphate fertilizers on lawns near the water is an ongoing educational process.)

As illustrated in the table below, each site was rated for its potential impact to the lakes (or streams). Impact was based on slope, soil type, amount of soil eroding, proximity to water or buffer, and buffer size. “Low” impact sites are those with limited soil transport off-site. At “medium” impact sites, sediment is transported off-site, but the erosion doesn’t reach a high magnitude. “High” impact sites are large sites with significant erosion  that flows directly into a stream or the lake.


Category Low Impact Medium Impact High Impact Total
Beach Access




















Boat Access





Driveway & Beach Access





Beach Access & Trail





Residential & Trail





Private Road





State Road





Town Road











This sampling draws a fairly accurate picture of land use types in the watershed that are affecting the water quality of Lake Wentworth and Crescent Lake.

A majority of sites (75%) were determined to have a low impact rating. This is good news for landowners because the efforts needed to improve these problems will be minimal. However, the total number of low impact sites signals a concern for “death by a thousand cuts,” which is a common problem on developed lake shores. Every single property is having a small impact which adds up to a large impact.

Approximately 72% of surveyed landowners indicated that they were very willing to make improvements to their property. Individuals expressing a moderate willingness (14%) were concerned with the cost of making improvements.

The cost of labor and materials to fix each site was rated as follows:

ñ  “Low” cost sites were estimated to cost less than $500

ñ  An estimate of $500 to $2,500 was rated “medium”

ñ  If the estimated cost to fix a site exceeded $2,500, a “high” rating was assigned.

According to the consultants’ report, the majority of documented sites can be fixed easily with low-cost rating materials, including native vegetation, mulch or stone. Only two sites (2%) fell within the high cost category, which means that they,  along with a few of the medium cost sites, will likely need engineering to undertake mitigation.

In all, 15 high/medium sites were identified for follow-up assistance by engineers.

The most commonly observed problems were related to surface erosion, bare soil, and lack of shoreline vegetation. Surface erosion, which is exacerbated by bare soil and lack of shoreline vegetation, can originate from a number of places, including unpaved roads and road shoulders, ATV trails and unstable lake or stream banks. Lack of shoreline vegetation (that is, strips of vegetated land left in a “natural” state) can destabilize soil and increase pollutant loading to a lake or stream. Since phosphorous is often attached to soil particles, erosion serves as a fertilizer for lakes and can cause algal blooms.

The remainder of observed polluted runoff problems included artificially created beaches, roof runoff, ditch erosion, unstable access sites, and undersized culverts.

Of the 37 sites associated with residential areas, 34 were low impact, 2 were medium impact, and 1 was high impact. Residential areas were associated with 35% of the identified sources of polluted runoff. Most of these sites can be corrected with easy, low cost fixes.

Of the 42 sites associated with beach access sites, 28 were low impact, 11 were medium impact, and 3 were high impact. Beach access sites were associated with 39% of the identified sources of polluted runoff. Most of these sites can be corrected with easy, low cost fixes.

Of the remaining 27 sites, 13 were driveways, 6 were commercial sites, 5 were boat access sites, and 3 were roads. Commercial sites and roads accounted for 7 of the 8 high impact sites.

Roads are one of the biggest sources of pollution to New Hampshire lakes. Regular maintenance by road associations and town and state road departments is critical.

Stormwater mitigation recommendations

The watershed consultants offered a number of recommendations to landowners for minimizing the effects of stormwater runoff on water quality in the lakes and their tributaries. These include:

ñ  Avoid raking natural mulch (pine needles/leaves) from the shoreline, steep slopes, or paths and let lawn revert back to native plants. Roots help hold the soil in place and prevent erosion.

ñ  Avoid exposing bare soil. Seed and mulch bare areas.

ñ  Re-establish shoreline buffers of native vegetation.

ñ  Know the rules before starting any cutting, beach enhancement or soil disturbance projects.

The town was also encouraged to promote road crews, boards, commissions, and other decision-makers.

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