The Use of Retention Ponds in Residential Settings

Karen J. Jordan, Department of Earth Sciences, University of South Alabama, Mobile, AL 36688. E-mail: mayfly28@lycos.com .

Residential areas are often overlooked when considering stormwater runoff. Many impermeable surfaces such as streets, driveways, sidewalks, walkways, and roofs are in residential subdivisions. Retention ponds capture diverted stormwater runoff from these surfaces. The ponds provide two primary services. First, they retain the runoff before releasing it into streams. They release the water at flow rates and frequencies similar to those that existed under natural conditions. The flood volume held in a retaining pond reduces the impact on downstream stormwater systems. The second benefit of the retaining ponds is that they provide pollutant removal through settling and biological uptake. Turbidity, pH, and total hardness are tested at the retention ponds at Charleston Pointe and Darby Creek, located within the Dog River Watershed. Water samples are collected at the inflow area and outflow area of each pond. A LaMotte 2020 Turbidimeter tests water samples to determine turbidity. A LaMotte Company water quality test kit customized for Alabama Water Watch is used to chemically test pH and total hardness. Research results show a substantial decrease in turbidity between the inflow water and outflow water of the retention ponds. Retention ponds are ideal partners for residential areas within the Dog River Watershed, since the pollutant most commonly and successfully removed from stormwater is sediments.

Keyword: retention pond, residential area, turbidity, Dog River Watershed

Introduction:

When considering stormwater runoff from impermeable surfaces, most people often overlook residential areas. Subdivisions include impermeable surfaces such as streets, driveways, sidewalks, walkways, and roofs. Residential areas are prone to flooding and must deal with stormwater runoff as do large commercial sites such as grocery stores, restaurants, and retail stores. The stormwater systems in subdivisions are just as important as commercial areas. The stormwater systems flush rainwater quickly from streets and gutters and into the nearest waterway (EPA Victoria 2001). Unfortunately, stormwater is not treated and often contains many pollutants including car fuel, oil, and sediments. The use of ponds as BMP’s with stormwater systems in urban areas is becoming more widespread. It is already common to see retention ponds in commercial areas.

Retention ponds capture the diverted stormwater runoff from streets and gutters. These ponds provide two primary services. First, they retain the runoff before releasing it into streams. They release the water at flow rates and frequencies similar to those that existed under natural conditions. The flood volume held in a retaining pond reduces the impact on downstream stormwater systems (England 2001). The second benefit of the retaining ponds is that they provide pollutant removal through settling and biological uptake (Idaho DEQ 2001). Ponds remove 30-80% of certain pollutants from water before it enters nearby streams. Common pollutants reduced are sediments, bacteria, greases, oils, metals, total suspended solids, phosphorous, nitrogen, and trash (England 2001). Ponds are one of the most effective tools at providing channel protection and pollutant removal in urban streams (www.stormwatercenter.net 2001). Essentially, retention ponds provide water quality and quantity control (EPA 2001).

Two common classifications of retaining ponds are either “wet” or “dry.” Wet ponds, known as retention ponds, continually have a pool of water in them called dead storage. Dry ponds, detention ponds, do not have dead storage and dry out between storms (EPA 2001). Retention ponds are more effective than dry ponds. The permanent pool of water found in the wet ponds is more efficient at removing particle pollutants. It does this by absorbing energy from inflow of the stormwater as it enters the pond, preventing scour material from settling to the bottom, and exchanging new incoming stormwater with previously captured water. This provides extra time between storms for pollution to settle (Idaho DEQ 2001). Aquatic vegetation is often associated with wet ponds. Vegetation such as grasses and plants are able to establish themselves in the permanent pool of wet ponds thus providing extra pollutant removal. The aquatic plants and grasses serve as an extra filter in the pond. They assimilate dissolved pollutants and, by biological uptake, transform pollutants into less toxic materials. Microorganisms often establish themselves in wet ponds and aid in the breakdown of pollutants (EPA 2001).

There are ongoing activities within a residential setting. Common activities are things such as clearing lots, building houses and additions, landscaping, and the installation of swimming pools. Figure 1 shows (A) how red dirt used for a house foundation has run into the street and stormdrain after a rain and (B) fill dirt left exposed on a cleared lot. These activities may appear minimal when compared to commercial building, but the same idea of impact should be considered. These activities increase the possibility of sediments and other pollutants entering nearby streams. Residential areas also pose an added threat to the stormwater system and nearby stream with common activities such as fertilizing and watering lawns, washing cars, and painting houses. The ongoing activities within a residential area provide diverse challenges for a retention pond.

The area surrounding Second Creek is growing quickly, both commercially and residentially. There are a growing number of new residential subdivisions along Sollie Road south of Cottage Hill Road (Fig.2) . These subdivisions are especially close to Second Creek and can easily affect the creek. These new subdivisions bring an increase of impermeable surfaces, which in turn increase the possibility of stormwater runoff pollution.

Surprisingly two residential subdivisions on Sollie Road have their own retention ponds. Darby Creek and Charleston Pointe are two subdivisions found side by side on Sollie Road (See Figure 2). These subdivisions are unique in the fact that they include retention ponds in their design. The subdivisions both have ponds but are different from each other. Darby Creek has three lots designated as detention areas. The three lots in Darby Creek are almost unnoticeable. The lots look natural, but with closer inspection, the low-lying area contains aquatic vegetation such as prominent cattails and other plants and grasses hidden behind trees and underbrush (Fig. 3) . Charleston Pointe is next to Darby Creek and has a much more visible retention pond. The pond is new and includes a fence around the facility (Fig. 4) . The pipes from the stormwater drains are obvious within the embankment of the pond.

Research Question:

Is there a measurable difference in turbidity, pH, and total hardness found in the inflow water versus the outflow water of the retention ponds at Darby Creek and Charleston Pointe?

Methods:

Turbidity, pH, and total hardness were monitored at the retention pond at Charleston Pointe and at the pond at Darby Creek. Water testing of the retention ponds took place every Saturday. Additional testing was performed immediately following a rainfall event and again 72 hours later.

The weekly monitoring of the ponds established a short-term trend for the project. Measurements taken after rainfall establish the influence of stormwater on turbidity, pH, and total hardness. The next measurement 72 hours later shows how much the ponds stabilized following rainfall.

A water sample was collected at the inflow area and the outflow area of each pond. Each sample was collected in a 45ml test tube and taken back to the USA campus for testing. A LaMotte 2020 Turbidimeter was used to test water samples to determine turbidity. The turbidimeter measures turbidity in NTU’s (nephelometric turbidity units). The turbidimeter passes a beam of light through a sample of water, and turbidity is measured by the dispersion of light by suspended solids in the water sample (Melbourne Parks and Waterways 1995). A LaMotte Company water quality test kit customized for Alabama Water Watch was used to chemically test pH and total hardness. All of the test results were keyed into Excel and graphed.

Results:

Of the three parameters monitored during the project, turbidity showed substantial changes during the testing of the ponds. The fact that turbidity was influenced by rainfall was apparent. Turbidity is also affected by ongoing activities within the subdivisions .

Charleston Pointe currently has no houses built in the subdivision. No activity was recorded in the subdivision until the week of March 2, 2002. During this week, a lot near the entrance was cleared. The inflow turbidity averaged five NTU’s and the outflow turbidity averaged less than two NTU’s (Fig. 5) . On March 2, 2002 both the turbidity recorded at the inflow and outflow areas of the pond were higher than average. This may be due to the clearing of the lot in the subdivision. The highest recorded turbidity in Charleston Pointe during the study period was on March 26, 2002 . The inflow turbidity measured 45 NTU’s while the outflow turbidity measured 30 NTU’s. The high turbidity is due to a combination of heavy rain and exposed soil from the cleared lot. The decrease in turbidity between the inflow and outflow water on this date was greater than 30 percent. During the project, the turbidity measurements between inflow and outflow water decreased an average of 70 percent.

The inflow turbidity in Darby Creek averaged 15 NTU’s while the outflow averaged less than 11 NTU’s (Fig. 6) . After rainfall events, the inflow turbidity increased to greater than 25 NTU’s and the outflow turbidity increased to greater than 20 NTU’s. The largest turbidity reading was recorded on February 23, 2002. The inflow turbidity measured 150 NTU’s while the outflow measured 50 NTU’s. These extremely high measurements are attributed to some type of mortar mix being poured into the yard after brickwork on a house (Fig. 7a and Fig. 7b) . Turbidity was decreased by an average of 50 percent between inflow and outflow water over the course of the project.

Darby Creek recorded much higher turbidity readings than Charleston Pointe. There may be several reasons for this difference. One important factor in the higher turbidity readings is that Darby Creek is more developed than Charleston Pointe. During the project, there were five lots being cleared, two houses being built, one lot with ongoing foundation work, and one house in the final stages of brickwork. A second factor to consider is that the pond at Darby Creek is small and not as well engineered as the one found at Charleston Pointe. These differences between the ponds may also attribute to the difference in the quantity of turbidity reduced between inflow and outflow water.

The second parameter measured was pH. This is a measure of how acidic or basic water is. Seven is considered neutral whereas values less than 7.0 are considered acidic and values greater than 7.0 are basic. A pH range between 6.5 and 8.5 is considered most favorable for sustaining aquatic life (Alabama Water Watch 2000). It was found that pH did not fluctuate much during the project. The average pH measured at the inflow and outflow of both ponds was between 7.0 and 8.0.

The outflow pH recorded in Charleston Pointe was usually higher than the inflow pH (Fig. 8) . The higher pH recorded at the outflow area of Charleston Pointe may be due to the large amounts of aquatic plants and grasses found at the outflow area. Darby Creek 's outflow pH averaged the same or less than the pH recorded at the inflow (Fig. 9) . Darby Creek on the other hand has a relatively less amount of plants and grasses found at the outflow area. Most of the plants in the Darby Creek pond are found near the middle to front portion of the pond. Darby Creek recorded pH levels that are considered lethal to fish and organisms on February 23, 2002 . The inflow pH measured 10.5 and the outflow measured 8.5. This high measurement corresponds to the dumping of mortar mix into a nearby yard. The pH of water may change seasonally or even daily. Things such as soils, plants, rocks found in a pond may affect pH and this makes it hard to determine exactly what has affected the pH levels in water.

Total hardness was the third parameter measured in the project. Water hardness is a measure of the amount of dissolved calcium and magnesium. These minerals are important to plants and animals. Calcium is important to aquatic organisms as a component of shells, bones, and cell walls. Magnesium is a component of chlorophyll and is important for photosynthesis in plants (Alabama Water Watch 2000).

A relative difference in hardness was recorded between the inflow and outflow water at Charleston Pointe. The inflow water measured anywhere between 40 and 60 mg/L (Fig. 10) . The corresponding outflow water measured between 50 and 80 mg/L. Water that measures between 20 and 60 mg/L is considered moderately soft (Alabama Water Watch 2000). The higher measurements at the outflow area of Charleston Pointe may be attributed to the limestone rocks found in the area.

The hardness levels in Darby Creek had little to no change between inflow and outflow. Both inflow and outflow averaged between 40 and 60 mg/L (Fig. 11) . These measurements fall into the range of moderately soft. An extremely high hardness was recorded on February 23, 2002. The inflow and outflow water both measured greater than 90 mg/L. This is considered moderately hard. The high measurements are also attributed to mortar mix poured into a nearby yard.

Conclusion:

Retention ponds are beneficial for providing stormwater abatement and the removal of pollutants from stormwater. Many states such as California , Nevada, Idaho, North Carolina , and Florida realize the potential benefits of retention ponds. For example, the state of Florida began requiring stormwater treatment in new developments in the 1980's. New developments are required to reduce pollution associated with stormwater runoff. Thousands of ponds have been designed and built to help meet this need (England 2001).

Retention ponds are ideal partners for residential areas within the Dog River Watershed, since the pollutant most commonly and successfully removed from the stormwater is sediment. The retention ponds showed a measurable reduction in turbidity between inflow and outflow water (See Figures 5 and 6). This is ideal since one of the primary concerns with the Second Creek tributary is sediment pollution.

As the areas surrounding streams and creeks in the Dog River Watershed continue to develop, the addition of ponds to subdivisions will help control concerns of sedimentation and pollution. Retention ponds may be included in new subdivision designs and added to already existing subdivisions. These ponds are one of the least expensive BMP's to build when compared to others such as infiltration trenches, basins, and sand filters (EPA 1999). Though these ponds may be small, as a whole these ponds built in subdivisions in this area will help provide better water quality downstream in our watershed. The use of retention ponds in residential areas should become as common as their use in commercial areas.

References Cited:

Alabama Water Watch. 2000. Basic Certification Workbook Water Quality Monitoring. Alabama Water Watch Program, Auburn, Alabama

England , Gordon. 2001. The Use of Ponds for BMPs. Http://www.forester.net/sw_0107_use.html . Accessed on January 31, 2002.

EPA. 1999. Urban Storm Water Best Management Practices Study. Http://www.epa.gov.ost/stormwater/usw_d.pdf . Accessed on February 7, 2002.

EPA Victoria. 2001. Stormwater Issues. Http://158.45.12.229/programs/stormwater/issues_ copy( 1).asp . Accessed on January 31, 2002.

Idaho DEQ. 2001. Catalog of Stormwater Best Management Practices. Http://www2.state.id.us/deq/water/stormwater_catalog/chapter5_5.asp . Accessed on February 7, 2002.

Melbourne Parks and Waterways. 1995. Physical and Chemical Tests. Http://redtail.eou.edu/streamwatch/swm19.html . Accessed on March 1, 2002.

Unknown Author. 2001. The Environmental Impact of Stormwater Ponds. Http://www.stormwatercenter.net . Accessed on February 14, 2002.