True storm water management involves a change in design philosophy and methods
Meeting the current national, local, city and watershed rules and regulations poses the greatest challenge in storm water management practices. Civil and water resources engineers must address widely varied problems, including rate control, water quality, water conservation and flood protection. However, in spite of the extremely different issues, current best management practices (BMPs) typically focus on one narrow, specific problem; these BMPs lack the versatility to address diverse storm water challenges.
At the same time, present-day BMPs face obstacles raised by the centuries-old philosophy and historical model for storm water management that treats storm water as a waste product. This waste product model has resulted in the physical establishment of “slope” and runoff and the simultaneous construction of curb and gutter, catch basins, manholes, pipes and conveyance systems that exist solely for moving storm water quickly and efficiently to its final dumping ground. Therefore, a storm water movement, rather than management, system exists.
Unfortunately, this movement paradigm has created its own problems. For example, water in motion increases its kinetic energy, translating into a growing erosive force that not only moves sediments, pollutants and trash material from initial surfaces, but also creates destructive downhill power.
Figure 1 illustrates the curb-and-gutter standard: The sloped surfaces of the house, driveway, road and landscaping all lead to the manhole/catch basin structures in the road. Crystal-clear water that fell as a light rain event quickly turns brown in color as road rinseate and landscape erosion pick up particulates in motion (see Figure 2).
Particulates and debris moving toward the catch basin initially enter the below-ground pipe, then start restricting the catch basin openings, momentarily reducing the open area. Diversionary devices merely stage the pollutants for entry during subsequent higher-flow events or, through bi-pass, move the water mass with increasing energy to a lower collection device. However, plugged piping or volume miscalculations ultimately lead to system collapse and failure (see Figure 3).
The answer to storm water management does not include creating bigger and more expensive storm water management systems. Rather, it means changing our philosophy and methods to implement true water management systems that actually prevent and treat storm water pollutants.
Before pollution issues arose as significant, the curb-and-gutter systems served as convenient conduits to clean the immediate environment. Routinely hosing down driveways and walkways, flushing street traffic accident spills and debris to the nearest catch basins, spraying streets with street washing equipment and allowing rain to clear away waste seemed inconsequential. However, the process of cleaning the immediate environment simply transferred pollutants to larger bodies of water; it also assumed that environmental responsibility was irrelevant.
As population densities increased, so did impermeable surfaces. While engineering reconstruction kept up with water movement strategies, water pollutant dumping overwhelmed natural cleaning cycles, and pollution issues rose to the forefront.
Current BMPs have evolved toward crafting devises that filter and capture floating debris or gross visible pollutants. These devices include catch basin inserts, traps, filters, vortex cyclone flow devices, in-line diversion screens, manhole baffles, and capture screens and floating barriers at final discharge points. Even though gross pollutants account for the largest volume of contaminants from storm events, this pollutant category actually has the least amount of biological impact on the final receiving bodies of water. In general, the devices work as efficient debris removers in light storm water flows, but larger flows overwhelm them and they have to rely on the built-in bi-pass features.
These BMPs provide add-on improvements to existing curb-and-gutter systems, but they clearly fail to attempt to address, much less change, the foundational philosophy of such systems. Another problem involves the necessity of a higher maintenance cleaning and servicing schedule for these sorts of devices. Finally, though the eventual collection and disposal of these wastes improve aesthetics, these devices do little to prevent the inflow of phosphates or nitrates to ponds, streams, wetlands and lakes.
Storm water detention and retention structures in the form of National Urban Runoff Program (NURP) basins became a BMP standard to address the collection of sediment pollutants, the primary source of soil phosphates. In theory, slowing down incoming water to manmade ponds would allow some of the particulate matter to settle at the pond bottom, letting only slower and less contaminated surface flows continue to the major receiving waters. Surface debris could be skimmed off while the soil sediments settle (see figures 4 and 5).
While this BMP has become, mostly by regulation, a current state-of-the-art requirement for storm water mitigation, by nature the model creates a long list of spinoff problems; indeed, it is questionable that this BMP actually adds to the environmental equation of improving the terminal receiving bodies of water. Numerous problems with basins have been documented, but some in particular are worth noting: The basins are expensive to build and to maintain; they hog real estate; they stir up material during construction; they pose liability hazards; they are aesthetically unappealing; they create a mosquito-breeding habitat; they attract nuisance geese; they provide minimal recharge to groundwater; and they promote the re-suspension of pollutants.
If the ecological goal in storm water management is the reduction of pollutants that initiate algae blooms and consequential oxygen deprivation in the primary recipient bodies of water, then the focus in storm water management must be the reduction of nitrates and phosphate sources. Unfortunately, BMPs that tend to augment conventional curb-and-gutter water movement systems cannot mitigate the reduction of these contaminants and, in some cases, actually contribute to the increase of these contaminants.
Before we can advance true storm water management and treatment BMP systems, we must understand the nature of these two main storm water contaminants.
Nitrates. Nitrates (NO3¯) are the negative anions of a broad spectrum of basic chemical compounds commonly identified as sodium nitrate, ammonium nitrate, potassium nitrate, calcium nitrate, nitric acid, etc. Most nitrate compounds are soluble in water and therefore will travel anywhere that water goes. Holding a negative charge, they can travel great distances in soil, which by nature also carries a net negative charge. So, they can relocate to groundwater formations or larger bodies of water great distances away from the original point. Once formed, no non-biological chemical reaction in soil can precipitate or neutralize the compound. Nitrate movement and biological absorption become part of the planet’s nitrogen cycle.
Nitrate production is ubiquitous in storm water runoff because of excessive fertilizer application leaching, formation in rain from thunderstorm events and washings of surfaces exposed to automobile exhaust. Because nitrates are so highly soluble and negatively charged, an effort to control nitrate pollution by conventional curb-and-gutter systems cannot happen; water movement itself must actually be controlled.
Phosphates. The primary source of this group of nutrients is a natural rock mineral called phosphorite. It consists largely of calcium phosphate and is used as a raw material for the subsequent manufacture of phosphate fertilizers, phosphoric acid, phosphorus and animal feeds. While commercial grade deposits can be found in Florida; North Carolina; Tennessee; California; Wyoming; Montana; Utah; Idaho; Northern Africa; and Russia, some level of phosphate is universally present in all soils of agricultural quality (soils with the ability to grow plants whether they are weeds, turf or commercial crops).
The planet’s soils can be categorized as a percentage and combination of three particle size primary components: sand, silt and clay. All three particle components are derived from weathered rock and reflect the chemical characteristics of the many rock composition minerals, including the phosphorus-bearing molecules. Phosphorus molecules, unlike the negatively charged nitrate molecules, have a net positive charge and as such bind themselves quickly to the negatively charged soil particles. While nitrates readily move with water as compounds in solution, phosphates generally only move as “riders” on soil particles.
Sands (0.05 to 2 mm) by nature are larger particles and are primarily composed of quartz crystals. Therefore, there is less surface area or physical affinity for phosphates to attach as compared with the larger surface area and negative charges available on silt (0.002 to 0.05 mm) and clay (< 0.002 mm) particles. Effective BMPs for phosphate pollution control must integrate three source areas as phosphate control equates to the control of erosion and relocation of soil particles:
- Prevention of soil erosion;
- Sedimentation and removal of settleable solids formed as sands and silts; and
- Prevention of movement of suspended solids in the form of clay particulates, generally known as “muddy” or “turbid” water.
Some current BMPs can effectively settle sands and silts but cannot handle brown muddy water where the majority of phosphates reside. Specialized high-volume, pump-activated mechanical filters can make an attempt on “muddy water” in limited volumes, but high operating expense, frequent breakdown and service needs make these systems not a viable solution to storm water pollution problems.
Silver bullet BMP?
True storm water management involves a change in design philosophy and methods. Who wants to cause a paradigm shift within the storm water industry? Is there a silver bullet BMP that can apply to all or most site designs?
Imagine a BMP that:
- Effectively prevents passage of sediments and thus phosphates from moving downstream;
- Allows for effective biological absorption, de-nitrification and use of nitrates;
- Allows for effective storm water volume reduction by allowing infiltration to recharge the groundwater;
- Prevents infiltration in areas where it is undesirable due to soil contamination;
- Changes the way storm water is treated, used and reused;
- Filters, treats, stores and uses storm water as a valuable resource rather than a byproduct necessary to deal with as quickly as possible;
- Uses a simple design, therefore eliminating complicated maintenance;
- Allows the uptake of dissolved nutrients and other organic chemicals;
- Harvests storm water for irrigating landscaping and lawns, thus requiring 50 to 85% less water for irrigation;
- Becomes modular in form and works as a lineal BMP along county roads and highways;
- Cools and reduces the temperature of storm water runoff;
- Provides water quality treatment to the first flush and larger storm events with the possibility of having no out flow; and
- Accommodates a retrofit conversion of a wet to a dry detention pond with under drain system.
Until now, these benefits have appeared as only a lofty goal for one BMP. One versatile BMP, however, the EPIC System, has taken this new approach to storm water management (see Figure 6).
The system is based on a combination of the oldest of technology, a sand filtration system, and a patented and proprietary device that controls subsurface water flow. The system is an underground irrigation, drainage, storm water harvesting and storage management system. It captures and stores storm water as soon as it flows over the the system. The system can turn green space, shoulders, side slopes and ditch slopes into a storm water management system. It captures and quadruple filters sheet flow and storm water runoff and slowly releases the excess downstream in a controlled manner (see figures 8 and 9).
System & philosophy
In 1985, Jonas Sipaila, now of Rehbein Environmental Solutions, Inc., crafted the basic idea of the system. While visiting a construction site one day after a rain storm, Sipaila noticed a large pile of sand wicking up water from an adjacent puddle. This led to a 14-year study and refinement of Jonas’ innovative idea: to utilize a proven, reliable medium—sand—therefore taking advantage of first-century physics to solve 21st-century problems associated with irrigation and drainage. By combining the concepts of subsurface irrigation, subsurface drainage and the capillary movement of water through sand from nearby water sources, Sipaila invented and received a patent in 1999 for the first pipe designed specifically for contact with sand. Other subsurface systems have always had problems with clogging, thus hampering their effectiveness, but Jonas’ invention has eradicated those problems.
Essentially, the system is a passive subsurface irrigation and drainage system that uses capillary physics and gravity to deliver water and nutrients to plants and to move water through an interconnected series of chambers and pans. The low pressure and greatly reduced water volume means less energy is needed to move the water.
A simple explanation of how the system works: Rather than allowing water to run off any type of surface—parking lots, roofs, driveways, football fields—the gravity-based system (essentially a network of underground reservoirs) captures and filters storm water runoff at its source and stores the water for irrigation.
By using a layer of porous sand beneath the surface of the turf, the system draws and filters water to an underground storage area created through the combination of chambers, pans and PVC pipes. From this, water can then be wicked up through the same sand to the plant roots, thus taking care of all irrigation needs.
Therefore, while relying on zero moving parts and on an efficiency of 100%, this single product provides superior drainage, irrigation and storm water management benefits to a water resources industry hungry for real solutions.