Septic Installation Best Practices for Coastal North Carolina (Onslow, Pender, New Hanover, Carteret)

By Justin Wilder, Owner of Wild Water Plumbing | Septic Systems

BLUF (Bottom Line Up Front):
Coastal North Carolina’s septic systems fail early mainly because of high water tables, saturated soils, saltwater intrusion, and improper system selection. The best way to ensure long-lasting, low-maintenance systems in Onslow, Pender, New Hanover, and Carteret Counties is to perform thorough soil evaluations, use elevated or low-pressure systems when needed, install durable components, and educate homeowners on proper maintenance.

Understanding Local Challenges

Coastal North Carolina’s low-lying regions face unique challenges with septic systems.

 

High water tables are a constant issue – in many coastal neighborhoods, groundwater sits just a few feet below the surface year-round. This means soil beneath drain fields is often already saturated, leaving little dry soil to absorb wastewater. When the water table is high, the effluent has nowhere to go and can rise back toward the surface rather than percolate downward. Frequent heavy rainfall and hurricanes further saturate the ground, and storm surges can push saltwater inland.These floods can inundate drain fields, causing immediate overloads and long drying times.

Soil extremes add to the difficulty: some areas have fast-draining sandy soils, while others (like parts of Pender County) have dense clays. Sandy soils let wastewater pass too quickly for proper treatment, risking groundwater contamination, whereas clay soils hold water and prevent drainage, leading to constant backups. Coastal salt air and saltwater intrusion are additional threats – salt can kill the beneficial bacteria in septic tanks and corrode metal or concrete components, shortening system life.

Finally, high usage patterns (e.g. vacation rentals or multi-family homes common in beach communities) put extra strain on systems not designed for such volume. In short, an installer in these counties must account for wet conditions, variable soils, flooding, and salt exposure on every residential job.

Common Causes of Septic Failure in the Coastal Plain

Understanding why systems fail in this region will guide what to do (and not do) during installations. The most common failure causes include:

• Drain Field Saturation: By far the leading issue is saturated soil due to high groundwater and rainfall. When the drain field is in constantly wet ground, wastewater cannot filter and instead backs up or surfaces. Even normal household water use can overwhelm a waterlogged drain field. Low-elevation and marsh-adjacent lots see this problem fastest, as groundwater rises quickly after tides or storms.
• Saltwater Intrusion and Corrosion: Coastal storms and king tides can force brackish water into the soil and even into tanks. Salt kills essential bacteria that break down waste and accelerates drain field clogging with unprocessed solids. It also corrodes older concrete tanks, metal pipes, and fittings, causing structural failures. Over time, salt air alone rusts metal components; coastal systems tend to “rust out” faster than inland ones.
• Poor Soil Drainage or Improper Soil Type: In some inland portions of these counties, heavy clay soil drastically slows percolation. Effluent lingers and accumulates, leading to standing water and early drain field failure. Conversely, extremely sandy soil (typical on barrier islands) may drain so quickly that effluent isn’t adequately treated before reaching groundwater. Both situations spell trouble if not addressed by design.
• Lack of Maintenance (Solids Buildup): Homeowners who fail to pump the septic tank on schedule risk sending solids into the drain field. In coastal areas, tanks often fill faster due to groundwater infiltration or slow draining fields, so pumping is critical. When solids or grease clog drain lines, the field trenches become blocked and the system backs up.
• Root Intrusion and Physical Damage: The region’s lush vegetation means tree roots are a frequent culprit in cracked tanks and infiltrated drain lines. Likewise, parking vehicles or heavy equipment on the drain field can compact soil or crush pipes, especially in softer wet ground. Any broken or collapsed component will cause a system failure by preventing proper distribution of effluent.
• Undersized or Outdated Systems: Many older homes (or converted vacation rentals) have septic systems that are too small for today’s usage. An undersized tank or drain field will overload quickly under modern water use patterns. Older systems may also have deteriorated baffles, cracked distribution boxes, or other age-related issues that lead to leaks and failures if not upgraded.

By recognizing these common failure points, an installer can take proactive steps in design and construction to avoid the same pitfalls.

Essential Do’s and Don’ts for Installation

Proper practices during installation can make the difference between a long-lasting system and one headed for premature failure. Below are key do’s and don’ts tailored to coastal North Carolina conditions:

Do:

• Conduct Thorough Soil and Site Evaluations: Always perform a detailed soil profile and determine the seasonal high water table before finalizing the design. Identify any clay layers, depth to groundwater, and drainage patterns on the lot. This ensures you choose the right system type and elevation.
• Follow (or Exceed) Separation Requirements: Design the trench depth or mound height to maintain adequate clearance above the water table (per NC code, usually at least 24″ of unsaturated soil). In very wet areas, plan for extra separation by raising the drain field elevation.
• Use the Right System for the Soil: Match the system to site conditions. For sandy or variably wet soils, gravelless chamber or EZflow® drain fields are recommended – they handle moisture better, resist compaction, and last longer in these soils. In clay or high-water-table sites, opt for an elevated sand mound or at least a partially raised drain field, as these perform far better under such limitations. Use low-pressure dosing or time-dosed distribution if needed to prevent overloading of slow-draining soils.
• Oversize Where Possible: When in doubt, go bigger on critical components. A slightly larger septic tank provides more buffering and can prevent frequent fill-ups in slow-draining areas. Extra drain field length or additional trenches can improve longevity, especially in marginal soils. Building in a reserve expansion area is wise for future capacity.
• Include Effluent Filters and Riser Access: Install an effluent filter on the tank outlet to catch solids and protect the drain field. Also, use risers with secure, watertight lids on the tank and distribution box. These make maintenance easier and help prevent groundwater infiltration or rainwater entering the system.
• Use Durable, Corrosion-Resistant Materials: Coastal installs should use high-quality, non-corroding components. Prefer concrete or plastic tanks over thin steel; use PVC or HDPE piping and synthetic inlet/outlet tees. All fasteners and hardware should be stainless or brass to withstand salt air. Applying bituminous or epoxy coatings to any concrete exposed to soil moisture can add protection in salt-prone environments.
• Promote Good Drainage on the Property: Work with the homeowner on yard grading and drainage. Divert roof gutters, driveways, and surface runoff away from the drain field area. If the lot is flat or tends to collect water, install swales or French drains to channel stormwater out of the septic field’s vicinity. Keeping the leach field as dry as possible greatly extends its life in this region.
• Obtain Proper Permits and Inspections: Always follow North Carolina onsite wastewater regulations and county health department guidelines. The coastal counties often have strict rules due to environmental sensitivity – for example, extra setbacks from marshes or mandatory advanced treatment in certain high-risk zones. Ensure a certified inspector checks the installation (especially any specialized system) to catch issues before burial. Building it right the first time is key to avoiding failures.

Don’t:

• Don’t Install in Poorly Chosen Locations: Avoid placing drain fields in low spots that obviously flood or near tidal marsh boundaries without sufficient elevation. Also do not install trenches too deep into the water table – a trench bottom that sits in groundwater will fail virtually immediately. Choose the highest practical elevation on the lot for the field, and maintain required distances from wells, dunes, and surface waters.
• Don’t Ignore Soil Clues: If test pits show gray mottling, standing water, or clay that stays wet for days, do not proceed with a standard design. Those are red flags indicating high seasonal water or impermeable soil. In such cases, don’t force a conventional system – propose an alternative (mound, LPP, ATU, etc.) that can function in that soil. Skipping this will almost guarantee premature failure in coastal areas.
• Don’t Undersize or Shortcut the Drain Field: It may be tempting to use the minimum allowed trench length or omit a second field line to save cost, but this is a false economy in these counties. Overloading a small drain field on wet soil will lead to surfacing effluent and callbacks. Do not undersize the septic tank either – a tank that’s too small can’t buffer peak flows or settle solids properly, leading to solids carryover. Follow state guidelines for tank sizing (typically based on bedroom count) or even go one size up for longevity.
• Don’t Use Inappropriate Fill or Materials: If the design calls for imported sand (as in mound systems), don’t substitute random fill dirt or lower-quality material. Use the specified sand media and clean aggregate to ensure proper drainage. Similarly, avoid using any construction debris or limestone-based gravel in trenches – it can alter soil pH or clog with fines. Stick to approved gravelless chambers or washed stone and geofabric as the design dictates.
• Don’t Leave the System Unprotected During Construction: During installation, take care not to compact the absorption area. Do not allow heavy machinery to drive repeatedly over the future drain field footprint (plan excavation and backfilling routes accordingly). In wet weather, avoid smearing clay sides of trenches – don’t dig or install when soil is saturated if you can help it, as smeared clay walls severely limit percolation. Also, prevent open trenches from flooding during rain (cover or berm as needed) so the soil structure isn’t destroyed.
• Don’t Plant Trees or Allow Deep Roots Near the Field: Advise the client that large trees should not be near the septic drain field, and don’t plant new landscaping directly on it aside from grass or shallow-rooted plants. Roots seeking water and nutrients will invade leach lines and clog them. If the lot has existing trees very close to the proposed field area, consider removing them or relocating the field. It’s easier to address upfront than after roots have broken into pipes.
• Don’t Connect Stormwater or Extras to Septic: Never allow things like yard drains, sump pumps, or gutter downspouts to tie into the septic system. This is illegal and will overwhelm the system quickly. Likewise, don’t direct any surface drainage toward the tank or field (reiterating the importance of diversion). The septic system is designed for wastewater only – any extra clean water load is a recipe for failure.
• Don’t Forget Access and Serviceability: A common mistake is burying components without easy access. Don’t install a tank without a riser to grade (you’ll regret it at pumping time). Don’t bury junction boxes or valves without access points. Every septic system will need maintenance; do not “hide” components under concrete or decks, and avoid placing the field in areas that may later be built over by sheds, pools, etc. Plan ahead so that the system can be serviced over its decades-long life.

By rigorously following these do’s and don’ts, Wild Water Plumbing can ensure each installation is built to withstand the coastal conditions that often spell trouble for septic systems. It’s all about proactive design, quality construction, and avoiding known vulnerabilities.

Recommended Septic System Types for Longevity

Choosing the right type of septic system is crucial in these coastal counties. The goal is a system that lasts a long time with minimal maintenance, despite tough soil and climate conditions. Here are the best options to consider:

• Conventional Gravity System (with Enhancements): If a property has well-drained loamy sand and a deep water table (which is less common but possible in some upland spots), a standard tank-and-trench system can work. However, even for conventional systems in this region, it’s wise to include enhancements: a larger capacity tank, an effluent filter, and use of gravelless trenches or chambers instead of traditional gravel. Chamber or EZflow-style drain fields are “well suited to areas with high groundwater tables” and provide better distribution in variable soils. These systems are also easier to deliver and construct on sites with limited access or soft ground. By using modern gravelless technology, you improve the longevity and clog-resistance of a conventional system without adding moving parts.
• Elevated Sand Mound Systems: Mound systems are a top choice when soil depth or water table is a limiting factor. In Onslow, Pender, New Hanover, and Carteret Counties, many sites have only a thin layer of permeable soil above either clay or seasonally high groundwater. A sand mound places the drain field in an engineered sand fill above the natural grade, providing the needed treatment depth and separation from groundwater. While mounds require more space and careful construction, they allow otherwise unbuildable lots to have a functioning septic. A properly built mound (with a pump to dose the distribution bed) can last for decades and is relatively low-maintenance – the key is protecting it from erosion and overloading. Our experience shows that raised drain fields “perform far better in high-water-table areas,” making mounds or at least partially raised beds almost mandatory in flood-prone coastal neighborhoods.
• Low-Pressure Pipe (LPP) Systems: North Carolina pioneered the Low-Pressure Pipe system for sites that need shallow, evenly distributed effluent dispersal. LPP systems use a pump to deliver effluent into small diameter pipes with emitters in the drain field, usually in a shallow trench network. This is ideal for slowly permeable soils (like the Pender County clays) because it doses the field in controlled amounts and allows recovery between doses. It’s also useful on uneven terrain or odd-shaped lots where gravity trenches won’t work. An LPP is slightly more complex than gravity, but the pump is the only mechanical part. As long as the pump and controls are maintained, the system can run for many years. LPP fields are often designed smaller than gravity ones because of the improved efficiency, which can be a benefit on tight lots. For an installer, mastering LPP installation is valuable in these counties since many sites have just 18–24″ of suitable soil – a perfect scenario for low-pressure distribution.
• Aerobic Treatment Units (ATUs) and Advanced Treatment: In especially challenging environments – for instance, a home right on the sound with high water table and poor soil, or where lot size is very limited – an ATU or other advanced pretreatment system might be recommended by regulators. ATUs inject air to promote aerobic digestion, producing much cleaner effluent. Other media filters (like sand or peat filters, or proprietary biofilters) also greatly reduce pathogens and BOD before the effluent enters the soil. The advantage in coastal areas is that treated effluent can often be placed at a shallower depth or in a smaller drain field, mitigating the risks of groundwater contamination. For example, pretreating in an ATU and then using drip irrigation tubing in the topsoil is one strategy for high water table sites. However, ATUs and high-tech systems come with a caveat: they require regular maintenance by a certified operator and electrical energy. They are not “set and forget” systems. If the goal is longevity with minimal homeowner hassle, an advanced system is only as good as its maintenance program. They can function very well here – protecting sensitive coastal groundwater – but the homeowner must be on board with ongoing service contracts.
• Hybrid and Supplemental Systems: Each site is unique, so don’t shy away from creative combinations. A system might involve a septic tank followed by a pump chamber that doses into a mound (combining two approaches). Some properties near the sound may benefit from installing distribution boxes with flow diverters, so they can rest part of the drain field alternately (prolonging life). In areas with salt intrusion risk, using distributed (serial) drain fields or employing alternating beds could help the soil recover between tidal inundations. Also consider lining the distribution trench bottoms with an impermeable layer in salt-prone zones to prevent saltwater backflow – this is a specialized tactic, but thinking outside the box can add years of function. The bottom line: choose a system type (or combination) that specifically addresses the site’s weak points, whether that’s high water, poor percolation, or potential flooding. Designs that prioritize passive resilience (gravity flow, larger capacity, and so on) will generally have fewer maintenance issues over time.

By selecting appropriate system types and tailoring them to local soil and water conditions, you set the stage for a septic installation that can handle coastal Carolina’s challenges and protect both the homeowner’s investment and the environment.

Red Flags to Watch Out For During Installation

Even with a solid plan, installers should stay alert on site for warning signs that could spell trouble if unaddressed. Here are key red flags and pitfalls to avoid:

• Water at Shallow Depths: If you dig an excavation or percolation test hole and encounter water or soaked soil only a short distance down, take note. A perennially high water table is present – a standard in-ground trench is a risk here. This red flag means you should pivot to an elevated design or additional fill before proceeding. Don’t assume it’s “just rainwater” if the pit fills with water; in these counties it often indicates true groundwater level. Many failures occur because systems were installed in soil that was too wet, causing the drain field to stay flooded.
• Soil Mottling or Sulfur Odors: Mottled gray-red patterns in the soil profile or a sulfur (“rotten egg”) smell in the dirt indicate periodic saturation and anaerobic conditions. If you see extensive mottling near the depth of your proposed trench bottom, that’s a red flag for seasonal saturation. It means during part of the year the water table or perched water rises to that level. Adjust the design higher or use a different system. Ignoring this sign can lead to sewage surfacing during wet seasons. Similarly, a strong sulfur odor in deeper soil layers suggests long-term waterlogging – not ideal for a leach field.
• Dense Clay or Hardpan Layers: When the auger or backhoe brings up sticky clay or you hit a hardpan, pay attention. Impermeable layers will prevent percolation even if above them looks like sand. If clay is encountered where the drain field is planned, it’s a red flag that effluent could back up (clay soil in Maple Hill, for example, has caused many premature failures). The solution might be a modified system like an LPP or mound that sits largely above the clay lens. Don’t proceed with a conventional trench into heavy clay expecting it to work – it won’t for long.
• Site Subject to Tidal Flooding or Storm Surge: Take note if the property lies in a flood zone, near an estuary, or shows wrack lines/debris from past floods. A septic system there is at high risk of saltwater inundation and structural damage during storms. This is a red flag that special measures are needed: a sealed and anchored tank (to prevent it floating), elevating electrical components above flood height, and likely a mound or at-grade system to keep the field as high as possible. For barrier island sites like Topsail or Figure Eight Island, assume that storm tides will reach the system. Use corrosion-proof materials and consider an ATU with a drip dispersal that can be installed shallowly (which can recover faster if flooded). If these precautions seem too costly or impractical, the honest conversation might be recommending the homeowner connect to municipal sewer if available – some locations are just that challenging.
• Small or Crowded Lot Layout: If the lot has limited usable area due to a large house footprint, outbuildings, trees, or setbacks, be wary. Insufficient drain field area or no room for repair area is a red flag. You may need to get creative with compact technologies (ATUs, drip systems) or schedule 100% reserve area elsewhere on the property for future use. Never cram a drain field into a space that barely meets minimum sizing – any failure or clog will have nowhere to be fixed. Also, watch slopes: if a lot is steeply sloped, distribution must be designed carefully to avoid effluent surfacing downhill. Tight lots also raise concerns about neighbors’ wells or water bodies being too close; double-check all separation distances in the field before finalizing the install.
• Homeowner Red Flags: An installer should also gauge homeowner usage patterns and awareness. If the owner mentions things like “we have lots of visitors using the plumbing” or you notice a garbage disposal in heavy use, that’s a red flag to educate them (and possibly adjust design). High occupancy and disposals can load a system with solids and water far beyond normal residential levels. In such cases, upsizing the tank or adding a filter is prudent. Another subtle red flag: if there’s evidence the old system failed (lush green strips in the yard, odor, recent pumping records of emergency pump-outs), find out why. It could reveal an underlying issue (like illegal greywater connections or water infiltration) that you must address in the new installation.

Staying vigilant for these red flags during planning and installation allows you to adapt and prevent foreseeable problems. It’s much easier to fix a design or site issue before the system is in the ground than to troubleshoot a failure afterward. In coastal North Carolina, a little extra caution goes a long way toward successful septic installs.

Septic Maintenance Advice to Share with Homeowners

A septic system is not “install and forget” – especially not in our coastal environment. A crucial part of an installer’s job is educating the homeowner on proper use and upkeep. Here are key maintenance tips Wild Water Plumbing should convey to customers to ensure longevity and minimal problems:

• Regular Pumping and Inspection: Emphasize the importance of pumping the septic tank on a routine schedule – generally every 3 to 5 years, or even more frequently if the soil drains slowly. Coastal systems often need pumping on the shorter end of that range because groundwater and slow percolation cause tanks to fill faster. Encourage homeowners to also have an inspection at least annually (for example, each spring before the heavy summer rain/hurricane season). Regular check-ups can catch rising sludge levels, cracked lids, or saturated fields early, before they become catastrophic.
• Water Conservation and Staggered Usage: Homeowners should be mindful of how much water they send into the system, especially during wet periods. Advise them to spread out high-water-use activities – for instance, do laundry loads over several days rather than back-to-back, and consider upgrading to low-flow fixtures. In vacation areas, if a home will see a surge of guests, the owner should know the septic will be under stress. The system is designed for a certain daily flow; exceeding that routinely (like 10 people using a system sized for a family of 4) will shorten its life. The solution is either to increase capacity or practice strict water use rules. Simply put: use water wisely and avoid sudden large volumes entering the septic in one day.
• Be Careful What Goes Down the Drain: Educate customers that a septic system is not a trash can. No grease, fats, or oil should be poured down the kitchen drain, as these can congeal and clog pipes or the biomat. No flushable wipes, hygiene products, diapers, or similar items – even “septic safe” wipes don’t break down and will accumulate, often causing clogs or pump failures. Harsh chemicals (bleach, solvents, excessive drain cleaners) should be minimized, as they can kill the beneficial bacteria in the tank and drain field. If the home uses a water softener, ideally its backwash should not go into the septic (the salt can harm soil structure and microbes). The golden rule: if it’s not regular human waste or toilet paper, it shouldn’t go into a septic system. When in doubt, throw it in the trash instead of the drain.
• Protect the Drain Field Area: The homeowner must know where their drain field is and take care of that portion of the yard. Advise not to drive or park vehicles on the field, and avoid placing sheds, concrete patios, or any impermeable cover on it. The soil needs to breathe and water needs to evaporate through it; heavy weight can compact soil and crush pipes. Also, keep deep-rooted trees and shrubs away from the drain lines. If the yard is landscaped, plant only grass or very shallow-rooted plants over the drain field. It’s also wise to redirect any surface water – for example, if a neighbor’s runoff or gutter flows onto the field, mitigation (like a swale or berm) should be done to keep it as dry as possible. During extended wet weather, homeowners can even proactively limit water usage to ease the load until the ground dries out.
• Watch for Warning Signs: Encourage homeowners to stay alert to early signs of septic trouble. Gurgling sounds in plumbing, slow draining fixtures, or sewage odors in the yard are red flags that something is wrong. Unusually lush, green grass over the field (especially during dry weather) can indicate excessive nutrients from a leaking system. Any pooling water or spongy spots above the drain field are cause for concern. The moment a homeowner notices any of these, they should call for a professional evaluation – catching issues early can prevent full failure. We tell clients: “If you smell or see something, say something – don’t ignore it.” Regular users of the home will know what “normal” is for their system and should not dismiss changes like needing to pump more often as just coincidence.
• Prepare for Storms: Given the hurricane and tropical storm threat in our area, a few storm preparations and aftercare steps are wise. Advise homeowners to seal/cover the tank lid and ports if an extreme storm or flood is predicted – this can prevent debris infiltration. They should avoid using the system during peak flooding (when the drain field is saturated or underwater) to the extent possible. After a flood, a septic professional should inspect the system: saltwater inundation might require pumping out the tank to remove brine and silt, and a fresh bacterial starter may help the system recover. Remind them that saturating rains can cause temporary performance issues; short-term they should reduce water use and let the drain field dry out. Having an accessible service riser helps in these situations so the system can be checked and serviced quickly post-storm.
• Maintenance Contracts for Advanced Systems: If the installation includes an ATU, pump station, or filter, make sure the homeowner understands the required upkeep. Pumps and aerators can fail if neglected. For ATUs, North Carolina often mandates a maintenance contract. It’s in the owner’s interest to keep that active – the technician will perform routine cleaning, alarm testing, and part replacements before bigger problems arise. The homeowner’s role is usually just to keep electricity to the unit and respond to any alarm promptly. Emphasize that advanced units must not be ignored; otherwise they can turn into a nuisance rather than an asset.

By sharing these practical maintenance do’s and don’ts with customers, Wild Water Plumbing can empower homeowners to take good care of their new septic systems. A well-informed customer who practices sensible use can significantly extend the life of a system – which also reflects well on us as the installer. In summary, proper installation combined with owner education is the formula for septic systems that deliver long, trouble-free service in Onslow, Pender, New Hanover, and Carteret Counties.

By following this guide – respecting local environmental challenges, using appropriate system designs, adhering to best installation practices, and emphasizing maintenance – Wild Water Plumbing can build a strong reputation as a reliable septic installer in coastal North Carolina. Septic systems in this region truly operate on the edge of what the soil can handle, but with the right approach, we can avoid the common failures and keep our clients’ wastewater safely underground where it belongs. Here’s to long-lasting septic installations and happy, problem-free homeowners!

Stay safe and prepared, Jacksonville.
– Justin Wilder, Owner

📞 Call or text me directly at (910) 750-2312 to schedule your storm check today.
Wild Water Plumbing + Septic —Local, Veteran-Owned, and Always Ready.

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Sources:

• Carteret County Health Department. (n.d.). Homeowner’s guide to septic systems. Carteret County Government.
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• Environmental Protection Agency. (n.d.). Types of septic systems. U.S. Environmental Protection Agency.
• North Carolina Cooperative Extension. (n.d.). Understanding and maintaining your septic system. North Carolina State University.
• North Carolina Department of Health & Human Services. (2017). 15A NCAC 18A .1900: On-site wastewater rules. Raleigh, NC: Author.
• Onslow County Environmental Health. (n.d.). Septic system permitting and soil evaluation guidelines. Onslow County Government.
• Pender County Environmental Health. (n.d.). On-site wastewater system requirements and guidance. Pender County Government.
• Septic Blue Raleigh. (n.d.). Expected lifespan of septic tanks. Retrieved from https://www.septicblue.com
• UNC Institute for the Environment. (2024). Septic system vulnerability and failure rates in coastal North Carolina. University of North Carolina at Chapel Hill.
• WECT Staff. (2016). Pender County homeowners battle failing septic systems on newly built homes. WECT News. https://www.wect.com
• Wild Water Plumbing. (2024). Coastal North Carolina septic failures: High water table, stormwater saturation, and soil impacts. Wild Water Plumbing Educational Series.