Pond and Lake Sealing: Technical Reference

A durable pond or lake leak repair begins with an explanation of where the water is going and why. Soil permeability, construction quality, the condition of the dam and outlet, and the amount of water entering the basin all influence the solution. The appropriate repair might involve compacting suitable soil, adding sodium bentonite, treating seepage through the water, installing a liner, or reconstructing a damaged part of the embankment.

Choosing among those approaches requires more than surface acreage or a photograph of a low pond. A pond that never held water presents a different investigation from one that operated successfully for decades before developing a leak. A small pond receiving runoff from a large watershed presents different operating and dam safety demands from a larger basin supplied primarily by a well.

Natural Waterscapes’ approach draws on more than 30 years of hydrology and pond and lake work. Natural Waterscapes begins by understanding the soil characteristics, establishing the water balance, and developing a design that can be constructed and verified. That approach serves owners prepared to invest in a dependable water body and reservoir operators evaluating avoidable losses.

Start with the Natural Waterscapes pond soil and leak evaluation or register for MyPond to begin organizing the site information. Mapped soil data supports an initial assessment; field observations and testing establish the conditions that a final repair must address.

Start with what the owner wants from the water body

A recommendation begins with the owner's interest in changing the situation. Natural Waterscapes advises on the consequences and available approaches; the owner decides how much to invest in the property. One owner may want a dependable swimming depth, another may want to reduce well operation, and another may accept a seasonal decline if the fishery and other uses remain satisfactory.

The lowest possible seepage rate is not the sole measure of a useful pond. A basin with relatively permeable soils may work well when a reliable, high-quality spring provides more water than the basin loses. The same basin can become expensive or difficult to manage if replacement water is scarce, costly, nutrient-rich, or sediment-laden. Soil performance and water supply have to be interpreted together.

That is why Natural Waterscapes does not prescribe a repair from pond acreage alone. The decision includes retention, inflow quality, reliability during dry periods, the owner's intended use, and the practical cost of achieving that outcome. A full pond is not proof of a tight bottom, and a falling pond is not proof that its soil suddenly changed.

Establish whether the water loss exceeds the expected water balance

Water level alone does not identify a leak. A pond can fall because evaporation and withdrawals exceed rainfall and inflow. It can also maintain its level while leaking if inflow continually replaces the escaping water. The useful question is how the observed change compares with the expected balance over the same period.

The governing relationship is straightforward:

Water entering - water leaving = change in stored water.

For a pond or reservoir, inputs can include rainfall directly on the water, watershed runoff, stream inflow, groundwater inflow, and pumped additions. Outputs can include evaporation, withdrawals, controlled releases, spillway discharge, and seepage. Storage is the volume held in the basin. USGS water budget studies account for these flows and storage changes when investigating water availability. [1]

Start with rainfall and evaporation

Natural Waterscapes begins many pond consultations by comparing precipitation and evaporation for the location and relevant time period. This establishes whether the weather alone suggests a net gain or loss from the water surface. The owner's observations then provide context: when the decline began, whether the pond previously held water, how quickly it falls, and whether a wet area has appeared below the dam.

Many owners who contact Natural Waterscapes describe substantial losses rather than a small difference that is difficult to distinguish from normal fluctuations. That makes the initial screen useful. A rainfall surplus accompanied by a falling pond deserves investigation, although withdrawals, outlet flows, changing groundwater conditions, and measurement uncertainty still have to be considered.

Precipitation minus evaporation is one part of the full balance. It does not include all the water entering from the surrounding land, nor does it establish the exact amount leaking. A regional weather estimate also has limits when applied to a particular pond.

Use the weather record without dismissing the owner's experience

Owners are often closely attuned to how their ponds behave. A new pattern deserves attention. Natural Waterscapes compares that history with the climatic record rather than treating the owner's observation as something to disprove. Where needed, historical weather helps distinguish a recent structural change from an unusually dry interval or a supply change that has exposed an older seepage problem.

Natural Waterscapes’ water-balance tool provides precipitation and evaporation comparisons for the preceding 7, 14, and 30 days in the United States. Those periods are useful screening windows, not a required waiting period. Natural Waterscapes has used the comparison to help owners recognize circumstances in which weather and limited inflow could explain the decline, avoiding unnecessary effort on a sealing project.

For a pond with little contributing watershed, the surface precipitation and evaporation comparison can be especially informative, provided other flows are considered. For a pond with substantial contributing land, stopping there can miss an important part of the supply. Use the same dates for the weather, water-level, pumping, and runoff records. Seasonal operating decisions can require a longer record than the most recent month.

Include the watershed when the decision requires a refined balance

MyPond can support watershed delineation and runoff analysis, bringing the contributing land area and its soils into the assessment. A pond surrounded by highly infiltrative soils may receive less runoff from a rainfall event than an equally sized pond below a watershed that generates more runoff.

Natural Waterscapes uses MyPond to bring watershed area and soil information into runoff assessment. For water-balance work, the required result is a runoff volume over the period being evaluated. The NRCS curve number method estimates direct runoff depth from storm rainfall; multiplying depth by contributing area gives a volume. It is distinct from the Rational Method, whose basic equation estimates peak discharge using a runoff coefficient and rainfall intensity. A peak flow should not be substituted for a measured or modeled event volume. Use the method and assumptions documented for the analysis being reviewed. [2, 16]

Monthly precipitation helps explain seasonal water availability, but rainfall timing matters too. Several small storms and one intense storm can produce different runoff from the same total rainfall. Groundwater contributions require their own evidence; a humid climate does not guarantee dependable groundwater inflow.

Understand what the contributing land adds

Consider a one-acre pond receiving drainage from about 15 acres. Watershed soils in hydrologic groups C or D can generate more runoff than more infiltrative soils under otherwise comparable conditions. Cover, land use, antecedent wetness, storm characteristics, and routing still matter. Fifteen acres on a map is not a guarantee that a particular volume reaches the pond.

Mapped information can help characterize those influences, but the calculation remains an estimate. It should not be described as an exact measurement of the soil everywhere in the watershed or an exact measurement of inflow. Groundwater can add another contribution, and Natural Waterscapes does not treat an unmeasured groundwater inflow as established simply because the site appears favorable.

Measure changes over a consistent period

A useful record connects water level readings with rainfall, pumping, withdrawals, overflow, and operating changes. For a reservoir, relate level to a stage-storage curve so the analysis compares volumes rather than assuming a constant surface area.

As a geometry example, a one-inch change over a constant one-acre surface represents approximately 27,154 US gallons. That is a storage change, not automatically a leakage measurement. Sloping banks change surface area as the level moves, and the water balance determines how much of the observed change remains unexplained.

There is no single inches-per-day threshold that establishes a leak for every pond. The significance of a loss depends on local weather, water supply, basin geometry, intended use, and the reliability of the measurements.

Use the pond history to direct the investigation

A pond that never held water properly

When a pond has never filled or retained water as expected, Natural Waterscapes examines the original soils and construction methods closely. Important questions include whether the basin intersected a permeable layer, whether suitable material was available, and whether the contractor placed and compacted it correctly.

The water supply also needs review. A basin with a limited contributing watershed may not receive enough water to meet its intended use even after seepage is reduced. A successful plan addresses both retention and supply.

A pond that held water for years before developing a leak

A new leak after years of satisfactory performance directs attention toward a change in the structure or a newly connected flow path. Natural Waterscapes commonly investigates animal burrows, decaying roots, damaged outlet pipes, and failed standpipe connections, particularly in embankment ponds.

Natural Waterscapes’ inspection starts along the downstream toe, or base, of the dam. Wet spots, flowing seepage, or unusually lush vegetation can identify areas requiring closer investigation. Natural Waterscapes then inspect the crest for settlement, slumps, animal activity, and other visible changes, while evaluating whether the observations could connect to the downstream wet area.

Outlet structures deserve separate attention. Water can escape through a damaged pipe or joint, or travel along the outside of a conduit where soil contact and seepage control are deficient. An old steel pipe may have corrosion; a PVC assembly may have a broken or improperly made connection.

One outlet failure Natural Waterscapes investigated involved a PVC pipe cut at an angle and inserted into a gasketed fitting. The connection appeared seated, but the gasket did not form a complete seal. Details like that explain why an apparently intact outlet still needs investigation.

Check whether the supply changed before assigning a new defect

An owner may accurately recall that the pond stayed full for decades even when some seepage was always present. A reduction in spring flow, runoff, or supplemental pumping can expose that loss. Natural Waterscapes compares the history with the weather and operating record while investigating structural changes; neither explanation should be assumed from the phrase it used to hold water alone.

Recognize signs that require an urgent dam response

Natural Waterscapes treats active flow carrying sediment from an embankment defect as especially concerning. Internal erosion, often called piping, can remove soil from within a dam or its foundation. ASDSO identifies muddy seepage, soil boils, and developing sinkholes as serious warning signs. New deformation or a rapid change in seepage also warrants prompt professional assessment. Clear water alone does not establish that a dam is safe. [3]

When failure may be developing, the operator should follow the emergency action plan and contact the responsible dam safety professionals and authorities. Active erosion, unstable ground, and potential downstream consequences take priority over a routine product application.

Temporary measures Natural Waterscapes may consider target a known opening where pond water enters a defect on the upstream side. They are professional stabilization measures selected for the particular situation. Blocking a downstream seepage exit or a designed drain can interfere with pressure relief and is not a substitute for repairing the source of the problem. [3]

Read the soil profile before selecting a treatment

The soil beneath the water body and the soil supplying its watershed perform different jobs. Basin and embankment materials control retention and structural behavior. Watershed soils influence how much rainfall becomes runoff. A useful site evaluation examines both.

Natural Waterscapes uses USDA NRCS soil information through MyPond and the pond leak evaluation tool to examine texture, soil horizons, hydraulic conductivity, and relevant suitability interpretations. These records help identify where further investigation is most valuable. [4]

Saturated hydraulic conductivity and its units

Saturated hydraulic conductivity, or Ksat, describes how readily water moves through saturated soil under a hydraulic gradient. It is expressed as a length per time, commonly micrometers per second, written μm/s, in the soil data discussed here. One μm/s equals 0.000001 meter per second. [5]

Natural Waterscapes places particular emphasis on Ksat when screening a pond that never held water despite a reasonable contributing watershed and precipitation supply. In that context, Natural Waterscapes uses the following ranges, expressed in micrometers per second, to guide the initial investigation:

These ranges guide Natural Waterscapes’ initial field assessment; they are not universal liner acceptance criteria. A value below either range does not certify that a pond or dam will perform adequately. The material, sampling location, soil condition, and source of the reported value must be understood.

Ksat is also not a direct prediction of how many inches the pond will fall each day. Seepage depends on the pressure difference driving flow, the length and area of the flow path, the arrangement of soil layers, and defects such as cracks or burrows. In the simplified Darcy relationship, flux equals hydraulic conductivity multiplied by hydraulic gradient. Translating that relationship into a site estimate requires a defensible representation of the actual flow system. [5]

Texture helps explain behavior but does not replace testing

Percent clay, silt, and sand helps characterize a soil and assess possible amendments. Texture must be read with the soil structure, condition, and profile. A single average clay percentage cannot show whether a connected sand layer, a root channel, or an inadequately compacted interface crosses the water-retaining zone.

Depth matters because excavation changes which horizons form the finished basin. A favorable surface soil may overlie a permeable layer. Materials moved during construction may be mixed, and soil placed in an embankment may behave differently from its undisturbed source.

Hydrologic soil groups and curve numbers describe runoff behavior relevant to water supply. An NRCS embankment suitability interpretation addresses a different question. These outputs should be used for their intended purposes rather than treated as interchangeable scores.

Verify mapped soil against the material on site

Natural Waterscapes compares observed soil characteristics with the NRCS descriptions. In Natural Waterscapes’ experience, many smaller pond embankments use material excavated on the property, sometimes from several parts of the basin. Imported fill is another possibility and should be established through construction records, observation, and testing where needed.

The map cannot establish what a contractor actually placed in a dam. Imported material should not be assumed superior merely because it came from elsewhere, and an acreage threshold cannot establish its origin. NRCS describes soil surveys as planning resources and notes that some engineering applications require onsite investigation. [6]

Where uncertainty affects the repair, representative test pits, borings, or other professional investigations can establish the profile and provide material for laboratory work. Natural Waterscapes favors particle-size analysis and saturated hydraulic conductivity testing, including the testing capability available within Natural Waterscapes. For an amended or reconstructed liner, the relevant question is how the proposed material performs in its intended compacted condition.

Scale testing to the consequences and uncertainty

Surface acreage is only one consideration. Suspected piping, the severity of damage, downstream exposure, and the contributing watershed can justify detailed investigation on a small pond.

Consider a one-acre pond receiving runoff from roughly 300 acres upstream. That configuration raises questions about the embankment, outlet, emergency spillway, and the inflow the system must manage. A 50-acre, well-supplied basin with only five acres of contributing watershed presents a different inflow problem. Its stored volume and downstream consequences still require attention.

Testing is valuable when it changes the design, establishes that an amendment can work, or prevents a major investment based on the wrong material assumption.

Treat karst indicators as a reason to investigate further

A sinkhole or evidence of soluble bedrock is a red flag for additional investigation, not an automatic rejection of the property. Natural Waterscapes’ approach is to examine the soil profile, depth and condition of bedrock, and potential water pathways with appropriate professional investigation. The same surface appearance can conceal very different conditions below.

In such settings, the design should limit leakage into susceptible underlying material and address stability as well as retention. A tight pond bottom may be an important part of that design, but it is not a substitute for understanding the foundation or a guarantee against karst processes. Test pits are useful where suitable; other investigation methods may be needed for conditions they cannot safely or adequately characterize.

Connect seepage reduction with water quality

Water quantity and water quality are connected decisions. A limestone spring supplying abundant, high-quality water can sustain a pond even where the bottom has appreciable conductivity. In that situation, the owner may reasonably accept the seepage. If the replacement water carries an undesirable nutrient or sediment load, retaining more of the existing water can reduce the amount of that replacement supply needed.

The practical objective may therefore be twofold: tighten the pond bottom and reduce the inflow that creates a water-quality burden, while retaining enough supply for the intended operating level. Natural Waterscapes does not recommend diverting water merely because it is runoff. Natural Waterscapes compares the actual sources, the pond's needs, and the consequences of changing them.

Persistent algae blooms can prompt investigation of phosphorus inputs, but the bloom itself does not identify the source. Watershed land use helps direct that investigation. Water testing is needed to characterize the incoming water, and conditions within the pond can also sustain nutrient availability. A useful assessment connects the source, its concentration, the volume entering, and the timing of delivery.

Sediment has a separate cost. An unstable watershed can repeatedly deliver material that settles in the pond, reduces depth, and creates future maintenance work. Controlling seepage does not eliminate that sediment source. Watershed stability and inlet management belong in the plan when they affect the pond's long-term usefulness.

Test well water rather than assuming it is the clean alternative

For ponds supplied by both watershed runoff and a well, Natural Waterscapes often tests storm-condition surface inflow and the well discharge separately. Natural Waterscapes has encountered wells with substantial phosphorus concentrations, despite the owner's reasonable expectation that groundwater would provide clean replacement water. Elevated mineral content can also affect suitability; the relevant constituents and intended water use determine what needs evaluation.

In some projects, the surface source had elevated phosphorus but the well contained more. Natural Waterscapes has installed pump intakes in an adjacent stream to use the more suitable available source and then treated the remaining phosphorus burden. That field example illustrates source selection based on evidence; it is not a general instruction to divert a stream or assume every stream is preferable to a well.

If the well is the better source, it may carry more of the supply requirement. If the surface inflow is high quality and reliable, Natural Waterscapes may favor that source and reduce well operation. Source concentration alone is not the whole comparison: the volume delivered, seasonal reliability, pumping cost, and any treatment requirements also matter.

Control replacement water according to need

Many pond wells run on timers. A timer determines how long water is pumped, but it does not establish whether the pond needs that water at the time. Where appropriate, a float or water-level sensor can limit pumping to periods when the pond falls below a selected level. The operating range should reflect the pond's intended use and the source's ability to keep up.

Where source-water treatment is justified, a metered dosing or filtration system may be considered. The choice depends on the contaminant, source testing, flow, water use, and operation. Dosing at an inlet does not by itself establish that phosphorus has been removed from the system; the design must address the treatment mechanism and the handling of any resulting solids or residuals.

Reducing seepage can therefore affect more than the number on a water-level gauge. It may reduce pumping hours, the mass of nutrients introduced with replacement water, and the quantity of treatment required. Those benefits should be evaluated from actual operation rather than promised as a fixed outcome.

Design inflow controls around useful water

Persistent outflow is a useful starting observation when evaluating whether all incoming water is needed. It can indicate an opportunity to manage the supply, but surplus during a wet period does not establish surplus during a dry period. Natural Waterscapes returns to the water balance and examine representative water-stressed periods, including sustained dry intervals, before deciding how much inflow to retain.

Where water approaches through a defined channel, the site may offer a practical point of control. A designed inlet basin with staged openings or a suitable weir arrangement can admit useful low flows while diverting part of the stormflow. The arrangement depends on channel levels, flow range, bypass capacity, sediment, and the receiving pond. Descriptions such as an inverted or reverse V-notch weir require an actual hydraulic detail before they become construction instructions.

The design does not create water. If base flow dries up, the pond still needs sufficient stored water, another suitable source, or an accepted decline in level. Use the dry-period balance to test that condition, and separately design safe passage for stormwater. Water-supply planning and flood conveyance answer different questions.

Automated controls, potentially including solar-powered gate actuation, are a future direction worth evaluating. They should not be presented as an existing feature of every installation. Source-water quality, sensor reliability, power, failure position, and maintenance would all influence whether automation improves a particular site.

Keep maintenance visible

Inlet controls can be out of sight and out of mind because forebays and intake structures are often away from the pond's high-use areas. Sediment buildup, gate failure, and clogged orifices or weir openings can change the supply before the owner notices. A design that performs only when clean needs an accessible and realistic inspection and cleanout plan.

Identify who will inspect the inlet, what normal operation looks like, and how to record a change. Maintenance should be considered when selecting the structure and locating access, not added after construction. A drop in admitted flow may reflect a blockage rather than a change in watershed hydrology.

Make compaction part of the construction specification

Inadequate compaction is one of the most common construction problems Natural Waterscapes encounters on private ponds. Some contractors propose driving a bulldozer or excavator over the soil instead of bringing a compactor to the site. Others have the appropriate equipment available but lack a clear plan for moisture, lift placement, and verification.

Tracked equipment spreads its weight over a large contact area to travel over the ground. Machine weight by itself does not establish that the soil received adequate compactive effort through the intended depth. Natural Waterscapes uses a comparison with a person's footprint to explain that principle, but the actual ground pressure depends on the equipment configuration and contact area.

Compaction reduces and rearranges pore space in suitable soil. Its effectiveness depends on the material and the conditions under which it is worked. Merely compressing a coarse, highly permeable soil does not make it an adequate pond liner. Extension guidance on renovating leaky ponds likewise treats compaction as a material-dependent repair method. [7]

Control the material moisture and lift placement

A construction specification should establish the soil or amended mixture to be used, the thickness of each placed layer, the acceptable moisture condition, and the compaction and testing requirements. The contractor then needs equipment capable of achieving that specification.

Padfoot equipment is central to Natural Waterscapes’ approach for suitable embankment and basin soils. Its action helps work successive soil layers together. The construction sequence must maintain contact between lifts so the embankment does not contain poorly bonded interfaces.

In the reservoir basin, Natural Waterscapes’ construction approach may follow padfoot compaction with a smooth-drum vibratory finishing pass to close the final surface. Natural Waterscapes’ embankment approach remains padfoot compaction, with attention to bonding successive lifts. Basin finishing must not be substituted for the specified embankment compaction procedure. The suitable equipment, moisture condition, and sequence depend on the soil and design; the roller's name alone is not a performance specification.

The owner's contract should make it possible to answer practical questions: what material was placed, at what moisture condition and lift thickness, how compaction was checked, and how inadequate areas were corrected. A smooth appearance or visible track marks cannot answer those questions.

Plan around workable soil conditions

Frozen or persistently wet soils frequently restrict compaction work during the colder part of the year in the northern United States. Late fall into early spring can be particularly challenging, with substantial regional and site differences.

The construction decision should follow actual frost, moisture, access, and forecast conditions. A calendar date alone does not establish readiness. Stabilizing an urgent defect and completing a durable earthwork repair may require separate phases.

Specify the lift rather than relying on a remembered thickness

A lift is a placed layer of fill. Its loose thickness before compaction and its thickness afterward are different measurements. The specification must say which is being controlled. Neither a six-inch figure nor a twelve-inch figure should be carried from one material, piece of equipment, or construction detail into another without checking its basis.

For the clean-water bentonite-treatment route described in the May 2016 national NRCS Standard 520, where the tabulated rates are used in the absence of applicable testing or similar-soil field evidence, the standard specifies a maximum six-inch lift. That provision should not be replaced with a general twelve-inch earthfill statement. Use the applicable state criteria and project specification for the actual installation. [9]

The purpose of limiting a lift is to make the entire layer workable and verifiable. A firm surface can conceal a poorly compacted lower portion. Confirm the selected material, moisture, mixing depth where relevant, equipment, and test results across the work; do not assume that additional passes correct every combination of excessive thickness and unsuitable moisture.

Understand what compaction tests actually demonstrate

A Proctor-based compaction requirement compares field dry density with a laboratory maximum dry density determined for the relevant material and specified test procedure. The required percentage and moisture range belong in the project design. A result without the correct material reference or moisture information can be misleading. Density acceptance also does not automatically establish the hydraulic conductivity of every liner mixture. [17]

A penetrometer measures penetration resistance. Texture, moisture, instrument type, and test procedure affect the reading. It may help investigate variation, but it is not a direct substitute for a field-density and moisture acceptance test. Natural Waterscapes’ observations of soft ground underfoot or the equipment used can identify questions for inspection; they do not certify the completed work. [18]

For perspective, Caterpillar publishes about five psi nominal ground pressure for a wide-track D6 LGP configuration. A hypothetical 200-pound person supported over 40 square inches also applies five psi. This compares average contact pressure, not equivalent compaction performance or a verified average human footprint. The machine's configuration and how it works the soil remain relevant. [19]

Respond to moisture conditions during construction

Construction planning should make use of workable weather windows. If material becomes too wet, the appropriate response may include pausing, drying or reworking it, or replacing unsuitable material, depending on the site and specification. Continuing simply to keep equipment moving can bury a problem in the finished structure.

In limited field situations involving soil that is only slightly too wet, Natural Waterscapes may evaluate bentonite amendment as part of a designed mixture. This is not a general instruction to dry wet earth with bentonite. Adding it changes the material, so mixing, moisture-density behavior, permeability, and construction suitability need to be evaluated together. It does not make saturated or frozen material automatically acceptable.

Connect the core trench to the entire retaining system

For new construction, Natural Waterscapes uses the term core trench for the low-permeability zone beneath the embankment. NRCS also uses foundation cutoff for this feature, so the terms overlap in engineering guidance. In Natural Waterscapes’ discussion of existing defects, a repair cutoff trench is a separate operation with its own excavation and stability considerations.

The soil investigation should establish the expected profile along the core-trench area before excavation. Remove organic material and unsuitable upper horizons so decaying roots and other weak or permeable materials do not remain within the intended barrier. Confirm the conditions encountered against the investigation rather than treating the planned depth as sufficient in itself.

NRCS Pond Standard 378 calls for the foundation cutoff to connect with relatively impervious material and for added seepage control where needed. Its national foundation-cutoff section does not prescribe one universal trench depth. The engineering handbook calls for detailed investigation where a suitable layer beneath a highly permeable foundation is beyond economical excavation reach. [14, 15]

Adding bentonite to the trench backfill can improve a designed soil mixture, but it does not automatically close a permeable pathway beneath or around the trench. The basin seal, trench, embankment, abutments, and penetrations must work together. A well-compacted segment cannot compensate for an unaddressed bypass elsewhere.

Where basin soils are marginal, an appropriate amended bottom can reduce contact between stored water and the underlying permeable material. Where embankment materials are also poor, Natural Waterscapes may consider amendment through the embankment lifts as part of the design. That more extensive approach requires attention to structural properties as well as water retention; it is not permission to add an unspecified amount throughout any dam.

Match the sealing method to the diagnosed problem

The choice between bentonite, a through-water treatment, imported soil, and a manufactured liner depends on the failure mechanism and the practical conditions of the project. Installed cost includes access, earthwork, material transport, dewatering where required, protection, testing, and restoration.

Sodium bentonite and PondLock

Sodium bentonite swells when hydrated and can reduce permeability when incorporated into an appropriate soil sealing system. Natural Waterscapes frequently favors a high-swell sodium bentonite amendment where the site can be prepared, mixed, and compacted correctly. Natural Waterscapes uses PondLock for that approach. [8]

Product selection should consider the material's documented swell characteristics and its performance in the proposed soil mixture. A swell test helps characterize the bentonite; it does not by itself establish the finished liner's leakage rate or the correct application quantity for every soil.

NRCS Conservation Practice Standard 520 addresses compacted soil liners with or without amendments. The May 2016 national document specifies sodium bentonite with at least 22 milliliters free swell under ASTM D5890 unless other types are supported by laboratory testing for the design. The applicable state guidance and project requirements should be checked before specifying work. Compliance involves the liner design and installation, not just one product property. [9]

Application quantities need a stated basis. Pounds per square foot of treated area, percentage of dry soil mass, and quantities for a specified lift thickness describe different things. They cannot be substituted without accounting for the mixture and dimensions. Procurement should follow the actual treatment area and design, including side slopes where relevant.

Bentonite also needs to be placed where it can form the intended barrier. Adding material to a full pond and hoping it reaches a leak is a different operation from constructing a continuous, compacted amended-soil liner. Those approaches should not be sold as equivalent work.

Soilfloc and treatment while water remains in place

Soilfloc is a two-part polymer treatment offered by Natural Waterscapes for soil seepage and application through the water column. It provides an option to evaluate when draining a pond or reservoir would be difficult, expensive, or disruptive. The product information describes swelling within soil pores and interaction with fine particles as part of its sealing action. [10]

The appropriate application still depends on the leak mechanism and site conditions. A candidate assessment needs to address whether the problem is soil seepage, where treatment must reach, and what operating conditions could affect placement. A broken outlet joint or a dam undergoing internal erosion requires a repair decision that addresses the defect itself.

Owners should obtain current application instructions for the specified product and review water use, aquatic life, application conditions, and site access with the supplier and project professional. The expectation should be a defined treatment objective and monitoring plan, with a contingency if the required improvement is not achieved.

Imported clay and compacted soil liners

Importing suitable soil can be appropriate where local materials cannot meet the retention requirement. In Natural Waterscapes’ experience, hauling, placing, and compacting imported clay may be more expensive than some manufactured liner alternatives. The comparison changes with haul distance, material availability, basin dimensions, and the complete liner design.

The description "clay" is not a sufficient acceptance specification. Representative material needs to be evaluated in relation to the intended construction, including its compatibility with the underlying soil. The repair must provide continuity across the area to be sealed and around connections that could bypass it.

Geomembranes and geosynthetic clay liners

A manufactured liner can be a strong candidate when the proposed soil treatment cannot meet the objective or when the owner prefers a liner system. It must be evaluated as an installed assembly, including its subgrade, seams, anchors, penetrations, protective layers, and any required drainage or venting. NRCS Standard 521 addresses these systems and the need to follow the selected material's installation requirements. [11]

Natural Waterscapes’ approach can include nonwoven geotextile below a geomembrane, the liner itself, protective fabric above, and a sand cover where the desired fishery and habitat call for it. That is a project approach rather than a universal requirement for every liner. The protective layers and cover must suit the material, slopes, loading, and use.

Large installations may require field seams. The appropriate response is a defined seaming and quality-control plan, together with careful treatment of penetrations and protection against damage. Seams do not make failure inevitable, but their workmanship is part of the system's performance.

A geosynthetic clay liner is another distinct option: a manufactured bentonite-containing barrier. It should not be confused with a loose bentonite application or an ordinary geotextile cushion. Material compatibility and the required cover or confinement belong in its design. [11]

Other amendments require their own technical basis

Chemical dispersants and proprietary liquid sealing systems are additional product categories. They have different soil requirements and application methods. NRCS recognizes dispersant treatment for appropriate soils, but a dispersant is not interchangeable with bentonite or a polymer sealant. [9]

An owner evaluating an alternative should ask for the specific mechanism, suitable and unsuitable soil conditions, required preparation, compatibility with the intended water use, and the evidence supporting the proposed result. A comparison based only on product price leaves out much of the work that determines success.

Design localized embankment repairs around the full defect

A root channel or animal burrow may create a concentrated pathway through otherwise suitable soil. Natural Waterscapes may excavate and rebuild an affected zone with compacted soil amended with sodium bentonite where site conditions support that repair.

The extent must be established from the soil, damage, flow path, and material encountered during excavation. A visible opening may reveal only part of the affected area. The repair needs to connect with suitable material around and below the defect while maintaining safe excavation conditions and embankment stability.

The visible opening does not determine the excavation limits. In a field example, a six-inch burrow illustrated a repair that could extend roughly 12 feet to either side and four feet below the defect where feasible. That is an example of the possible scale of a repair, not an NRCS sizing criterion, a universal ratio, or a homeowner excavation instruction. Soil conditions, the full flow path, structural stability, and the repair design establish the actual limits.

Temporary stabilization is a separate decision. Natural Waterscapes may consider sandbags and a chipped bentonite product called Hole Plug as possible measures for a known upstream entry. Their use does not establish that internal erosion has stopped or that the structure has regained its original strength. Permanent work requires investigation and a repair design.

An incoming storm or substantial stream inflow can change the urgency and available options. Pumping or a stabilized siphon are measures professionals may consider in an emergency plan. Capacity, expected inflow, safe discharge, and the dam's response to lowering all matter; "lower it as fast as possible" is not a general operating instruction.

Jim selected a contractor who would compact the embankment

One prospective pond owner, whom Natural Waterscapes will call Jim, had marginal soils and a limited watershed. A lower-cost contractor proposed building the pond without the dedicated compaction Natural Waterscapes considered necessary and offered photos of other ponds as reassurance.

Natural Waterscapes presented Jim with the soil information and the reasons compaction mattered at his site. Jim ultimately selected a contractor who would use a padfoot roller to compact the embankment. The pond was successful after he followed that advice.

Jim's experience illustrates a decision made before construction. It is not a measured before-and-after repair trial. The competing proposal was not built, so its outcome cannot be observed. Natural Waterscapes’ concern was that the marginal materials, if inadequately compacted, could allow piping and basin seepage.

Photos of another full pond do not establish that the same approach will work on a different site. That pond may have different soils, a larger watershed, a supplemental water supply, or a shorter operating history than the owner realizes.

The three investments Natural Waterscapes consistently emphasizes are soil analysis, sound design, and adequate compaction. If the available budget cannot support the work a site requires, postponing construction can be the responsible decision. A lower initial price does not make the resulting water body less demanding to repair.

Evaluate reservoir seepage as an operating issue

Reservoir seepage can carry a recurring cost even when it is not visible from the shoreline. The practical objective is to determine whether avoidable losses can be reduced in a way that improves operation and makes good use of a valuable water supply.

That investigation can begin before there is a precise estimate of recoverable water. Quantification becomes more useful as the evidence develops and the operator compares repair alternatives. A defensible opportunity can include improved operating reliability, reduced replacement pumping, or less pressure on a limited supply.

Reservoir owners already undertake substantial seepage investigation and remediation. For example, the US Army Corps of Engineers reported completion of the Wolf Creek Dam barrier wall in 2013. That project demonstrates the established role of seepage control; it is not evidence that a particular treatment is appropriate at another reservoir. [12]

Build on the operating data already available

Many reservoirs Natural Waterscapes evaluates have inflow instrumentation and withdrawal records, sometimes with observations at 15-minute or hourly intervals. The available information varies, and Natural Waterscapes does not set a universal data cutoff for starting a conversation.

The analysis should reconcile inflows, withdrawals, releases, spillway discharge, rainfall, evaporation, and storage change over matching periods. Where dam drains collect seepage, their records can help identify and track that component. Rating curves, meter accuracy, gaps, and changes in operating practice affect what the record can support.

Reporting volumes in acre-feet or millions of gallons does not establish measurement precision. The important question is whether the unexplained loss is distinguishable from uncertainty in the balance, and whether the observations are adequate for the next decision.

Separate a water balance residual from a confirmed leak location

Natural Waterscapes uses the combination of a water deficit and the absence of corresponding observed dam seepage to direct attention toward the reservoir basin. That is a useful investigation hypothesis, particularly where monitored drainage helps account for known embankment flows.

A balance alone does not locate the escape path. Foundation and abutment seepage may not appear as an obvious wet area on the dam. Groundwater exchange, temporary bank storage, unmeasured flows, and instrument error can also affect the residual. These possibilities need to be evaluated before assigning all unexplained water to the reservoir bottom. USGS describes the interaction of reservoirs, surface water, and groundwater as a connected system. [13]

Designed drainage also serves a safety function. A reduction in measured drain flow should be interpreted with reservoir level, instrumentation, and the condition of the drainage system, rather than automatically celebrated as a successful seal.

Include the cost of maintaining the water supply

The cost of lost water may include purchased replacement water, well pumping, conveyance energy, equipment wear, and staff time. Depending on the reservoir's use, lower operating levels can also affect irrigation delivery, intake access, recreation, or production.

Those costs should be established for the operator's actual system. A gallon retained does not always translate into a gallon that can be sold or an immediate cash saving. The benefit depends on whether the retained water is usable, when it is available, and what expense or constraint it avoids.

A useful comparison is:

Annual net operating benefit = avoidable replacement-water cost + other demonstrated operating savings - added annual maintenance and monitoring cost.

Avoid double-counting energy or labor already included in the replacement-water cost. Compare that benefit with the complete repair cost and expected service life. Where the retention improvement is uncertain, show a range of scenarios and identify the assumptions instead of presenting one promised outcome.

Design around continued operation

Some reservoirs cannot be emptied without interrupting service. Others have seasonal windows for drawdown or work on an exposed area. That constraint can materially change the appropriate treatment and its installed cost.

The evaluation should establish the operating level that must be maintained, access to the suspected seepage area, inflow during the work, and the implications for intakes, downstream releases, and water use. Any proposed product must be suitable for that reservoir's use and applicable requirements. Suitability for a private pond does not establish suitability for a drinking-water supply.

Where uncertainty remains, an appropriately designed pilot or staged treatment may provide useful evidence. The operator and project team should decide in advance what observations would justify expansion, modification, or a different repair approach.

Verify performance after the repair

Define success before work begins. For one pond, success may be maintaining the intended operating range without frequent well additions. For another, it may be a measurable reduction in unexplained loss at comparable water levels. A reservoir may require both an operating improvement and continued confirmation of dam safety.

Retain the original observations and construction records. Document the area treated, material and quantity used, installation conditions, relevant soil or compaction tests, and any changes to outlets or operating practices. Repeat water level and flow observations after treatment.

A slower decline after repair can be encouraging, but rainfall, cooler weather, reduced withdrawals, and a lower water level can also change the result. Compare periods with the water balance in view and continue observation long enough to test the intended operating conditions.

Keep retention performance and structural performance distinct. Less water loss does not prove that an internally eroded embankment has been restored. Conversely, a properly functioning drain may continue to discharge while controlling seepage safely. [3]

Return to the same balance after the work

Natural Waterscapes’ post-treatment review returns to the weather and supply analysis used at the start. The most recent 30-day precipitation and evaporation comparison can help explain the operating period. Where the watershed contribution is significant, bring in the runoff estimate using the soils, land cover, rainfall, and assumptions documented in that analysis.

Compare equivalent periods and identify changes in pumping or outflow. If the pond rises into a wider part of the basin, the same depth change represents a different storage volume. If it falls, the reduced hydraulic head can change seepage. These effects matter when claiming a measured reduction rather than simply reporting that the owner is pleased with the level.

A useful result can be less frequent pumping, a more reliable operating range, or a demonstrable reduction in losses. State the observed outcome and the limits of the evidence. Do not convert a successful field example into a promised performance percentage for a different pond.

Begin with the soils and water balance of your water body

Water has value even when its loss never appears as a separate line on a bill. Repeated pumping, an unreliable operating level, and the time spent compensating for seepage can accumulate for years. Understanding those losses makes it possible to evaluate a repair on its actual usefulness.

Use the pond soil and leak evaluation to examine the mapped soils beneath your pond and organize the initial leak assessment. Use MyPond to bring the pond, watershed, and water balance into a continuing management record. Both provide a starting point for the site-specific investigation.

For an existing pond, assemble its construction history, recent water level observations, inflow and withdrawal information, and photographs of suspect areas. For a new pond, investigate the soils and water supply before committing to the excavation plan. Reservoir operators can begin with the operating record and known seepage monitoring locations.

That information supports a recommendation grounded in the actual water body: what can be retained, which repair fits the problem, how the work should be executed, and how its performance will be judged.

Soil characteristics matter.

Start with an estimate and choose how much help you want

You do not need to finish a monitoring project before speaking with the Natural Waterscapes team. If you already have a good sense of the loss, start with an approximate drop in inches and the period over which it occurs. If you are unsure, say so. That opens the conversation; it does not claim to measure seepage precisely.

Tell the team whether you add water to maintain the level, where it comes from, and approximately how often or how long the pump runs. Clarify whether the reported drop occurs while pumping or when the pump is off. A nearly steady water level can conceal substantial replacement-water use.

Soil information is optional at this stage. Enter a soil description if you know it, or use the leak evaluation tool and provide the link to the completed report. You do not need to select the highest or lowest conductivity from multiple horizons. Interpreting those layers belongs in the assessment, not in a compulsory homeowner calculation.

Staff assistance and self-service remain available in parallel. You can explore the information yourself, speak with Natural Waterscapes’ team, or do both. Neither a completed checklist nor a particular level of uncertainty is required to ask for help.

Use an optional repeatable water level record

For a fixed dock that does not move with the water, mark one safely accessible reference point and measure vertically down to the water surface. Use the same point and units each time. A larger distance below that mark means the water level is lower. A floating dock cannot provide that fixed reference.

A securely installed staff gauge is another option. Record the scale reading at the water surface, along with the date and time. Weekly observations are a practical starting point for a homeowner, or select another interval that fits the situation. Record rainfall, pumping changes, or other observations when known; unknown entries are acceptable.

This optional record improves the context for a recommendation and can continue after treatment. It is not a mandatory waiting period. Reservoirs and projects requiring quantified performance may need a more detailed observation plan than a homeowner's weekly log.

Companion guide and ways to get help

Download the companion Pond and Lake Sealing Quick Reference. It supplements the explanation in this article and can be used without completing every field. You can use self-service resources or contact Natural Waterscapes’ team at any stage.

Explore the pond soil and leak evaluation

Talk with Natural Waterscapes’ team about your pond

Use MyPond

Sources and technical references

Field examples and recommendations attributed to Natural Waterscapes’ experience come from the Natural Waterscapes technical interview. Product pages are supplier information, not independent comparative trials. NRCS documents are identified by edition; consult applicable state and project requirements. Historical source prices are not used.

1. USGS Water Budget Science in Oklahoma and Texas

2. TxDOT NRCS Curve Number Loss Model

3. ASDSO Seepage Through Earthen Dams

4. Natural Waterscapes soil analysis and MyPond

5. NRCS Soil Survey Manual Chapter 3

6. NRCS Web Soil Survey

7. SRAC Renovating Leaky Ponds January 1999

8. PondLock supplier information

9. NRCS Standard 520 May 2016 national edition

10. Soilfloc supplier information and application guidance

11. NRCS Standard 521 August 2023R

12. US Army Corps of Engineers Wolf Creek Dam barrier wall completion April 2013

13. USGS Surface water and groundwater interactions

14. NRCS Pond Standard 378 July 2022 national edition

15. NRCS Engineering Field Handbook Chapter 11 Ponds and Reservoirs

16. TxDOT Procedure for using the Rational Method

17. NRCS Construction Inspection Earthfill and Rockfill March 2025

18. USDA ARS Penetrometer moisture dependence

19. Caterpillar D6 configurations and nominal ground pressure

For contractors and the provider program: Download the provider assessment worksheet.