Environmental Products
AAI's QSC water quality and Material Identifier applications can be effectively used to search for failing sewer and septic systems that are impacting waterways. The following approach is used:
- The waterways are first searched for anomalous plumes of colored dissolved organic matter (CDOM) in the water from failing sewer or septic systems. CDOM is one of the few reliable, sensitive, and robust optical indicators of water exposed to raw sewage. Winter images are preferably used to suppress contributions from organic sources other than failing sewer and septic systems (e.g., decay of algae and aquatic vegetation).
- The spatial patterns of detected suspect plumes of CDOM are then used to locate where the contaminated water is entering the waterway.
- In addition to locating the entry points, the spatial patterns of the CDOM plumes can be used to select new or assess the suitability of existing field sampling site locations for obtaining representative additional needed analytical detail (e.g., phosphate and nitrate concentrations, fecal coliform and e. coli bacterial counts, etc.) to verify that the waterway is contaminated by sewage.
- Detected land cover features using AAI's Material Identifier can often be used to more exactly locate the entry points along the riverbank or shoreline, and trace the paths (such as aquifers, springs, or streams) involved in transport from the source.
- Land cover features from Material Identifier, such as anomalous patches of wet soil or enhanced vegetation cover, can also be sought. These features can arise from seepage of leaking nutrient-enriched sewage, and they can sometimes indicate candidate locations of the sources of contamination.
- Finally, these image-derived results can then be correlated with maps or records of septic system infrastructure to deduce the most likely candidate system failure point(s).
- Once sites are identified, quantitative relationships between the field-measured and image-derived information can be used to establish monitoring protocols for forensic analysis and long term remote monitoring of progress against impairment reduction targets.
Illustration 1: Regional Wastewater Treatment System Along the Potomac River
Example search for failing septic systems: QuickBird image (above) of the Lower Potomac River south of the Blue Plains Wastewater Treatment Plant, measured on 21 February 2006. The image-retrieved concentration "map" of CDOM is shown below. CDOM concentrations are generally less than 0.5µgC/l in this winter image. Four distinct plumes of CDOM appear as lighter blue at the indicated locations (red circles). Concentrations reach 4.0µgC/l in those areas.
Site 1 - Dogue Creek
Enlargement (above) of Site 1 (Dogue Creek, Ft. Belvoir). CDOM concentrations reveal a potential point of entry (red arrow) of the organic source material (likely raw sewage) into Dogue Creek. Concentrations may be elevated up-stream of the indicated entry point, but may be partially obscured by tree canopy in the processed image results.
Land cover characteristics (above) of Site 1, automatically retrieved from the image using AAI's Material Identifier application, further help to identify potential sources of CDOM away from the riverbank. This automatic subpixel land cover identification revealedan area of wet soil (yellow circle) that indicates a small incoming stream in close proximity to the indicated starting location of enhanced CDOM concentrations in Dogue Creek. Two areas of enhanced forest floor vegetation (red circle and ellipse) may indicate potential additional entry points of the CDOM source material. Close-up views of the three potential entry points are shown below.
An aerial photograph of the "wet soil" candidate CDOM entry point feature (above, yellow circle) confirms the presence of multiple streams entering from the south of Dogue Creek. One or more of these could be carrying CDOM from an area to the south. The area showing enhanced forest floor vegetation (red circle, below) in the land cover map appears no different than a nearby forested area (red arrow) in this aerial photograph. This indicates that the enhancements inside the circle at this possible upstream CDOM source location take the form of subtle and diffuse grasses and other ground cover, consistent with nutrient enhancement.
A close-up view of a second area containing an anomalous forest floor enhanced vegetation feature (red ellipse) is shown above. Note the small streams entering the river along the shoreline on the eastern part of the ellipse. A map of the Fairfax Co., VA sewer system (below) reveals that the CDOM entry point features (yellow circle, and red circle and ellipse) are within 100ft of the pressurized Dogue Creek Sewer Force Main (dashed red line, passing through the yellow circle and the red circle and ellipse). The area within the red circle is in close proximity to the Dogue Creek Waste Water Pumping Station.
A check of the Virginia DEP records reveals that Site 1 (Dogue Creek Watershed) is a verified impaired (fecal coliform exceedance) water body (Category 5, requiring a TMDL). The inferred source location(s) from the imagery are consistent with the independently assessed (VA DEQ) problems with the Dogue Creek Wastewater Pumping Station and Force Main. Dogue Creek was first listed as a 303(d) site in 2006. Sufficient exceedances of the instantaneous fecal coliform bacteria criterion were recorded at Virginia DEQ's ambient water quality monitoring station 1ADOU000.60 (5 of 24 samples - 20.1%) to assess the stream segment as not supportive of its recreational use goal. The monitoring station is situated at the head the image plume toward the confluence with the Potomac River. Although the source of the failure is officially listed as "unknown," Fairfax County, VA has requested that the Dogue Creek Force Main be replaced ($13M stimulus funding requested), and the Dogue Creek Wastewater Pumping Station (located near red circle) be rehabilitated ($8.5M stimulus funding requested) to comply with the TMDL schedule (2018).
Site 2 - Broad Creek, Ft. Washington, MD
Close-up view (above) of the Site 2 anomaly at Broad Creek, Ft. Washington, MD. The CDOM plume is emanating from two apparent entry points at the eastern end of Broad Creek (above, red circles). Concentrations are highest at these points, and the spatial pattern of the plume is consistent with tidally moderated flow toward the Potomac. Higher concentrations along the delta and northern shoreline may be tidally influenced accumulations of CDOM, although it is possible that there could be one or more additional sources along the northern shoreline. The sewer infrastructure map below reveals that the two inferred CDOM entry points (red circles) are close to the Broad Creek Waste Water Pumping Station (WWPS) and Force Main.
Close-up views of the inferred CDOM entry points reveal the proximity of these two locations to the Broad Creek WWPS (above) and sewer Force Main (below). The Washington Suburban Sanitary Commission (WSSC) has identified the susceptibility of the Broad Creek WWPS to frequent sanitary sewer overflows during wet weather and snowmelt events, at which times it releases raw sewage and fecal coliform bacteria through the overflow outfall (see above) into the Broad Creek Basin and Potomac. The sewage is pumped into the Force Main (see below) to the Piscataway Creek Waste Water Treatment Plant (see Site 4 below).
AAI's Material Identifier reveals several streams entering the main stream at the indicated CDOM entry point in the figure below (inside the red circle). The stream entering from the south could carry the contaminated water from a point further south, where it is close to the Force Main. The brown (wet soil) features along the eastern bank of the main stream inside the red circle represent small streams or springs, one or more of which may have carried contaminated water leaking from the Force Main to the east.
Broad Creek is known to be impaired (fecal coliform exceedance), and the inferred source location from the imagery (Broad Creek Waste Water Pumping Station) is consistent with the independently acknowledged source location by the Washington Suburban Sanitary Commission (WSSC). WSSC entered a Consent Decree (7 December, 2005) with EPA, US Dept of Justice, MD Dept of Environment, and various environmental groups to eliminate Sanitary System Overflows (SSOs) at the Broad Creek WWPS and into the Potomac. SSOs release untreated or partially treated raw sewage with fecal coliforms into Broad Creek and the Potomac. Broad Creek WWPS is susceptible to SSOs primarily during rainfall and snowmelt events, such as occurred just nine days earlier. Twelve major SSO events occurred between 2003 and 2006, and numerous additional smaller scale releases occurred due to rainfall dependent inflow and infiltration (RDII) of storm water and groundwater. Excessive RDII were attributed to elevated groundwater levels, broken manholes near streams, blockages, line breaks, sewer defects, lapses in pump operation and maintenance, as well as inadequate sewer.
Site 3 - Swan Creek, Ft. Washington, MD
An enlarged view of the Site 3 anomaly at Swan Creek, Ft. Washington, MD is shown below. Patterns in the CDOM concentrations suggest four apparent CDOM entry points.
AAI's Material Identifier revealed a small feeder stream (above, red arrow) at the inferred CDOM entry point on the eastern end of Swan Creek. This feeder stream is close to the Swan Creek Waste Water Pumping Station and Force Main (below). The Swan Creek WWPS pumps sewage into the Force Main to the Piscataway Creek Waste Water Treatment Plant (see Site 4 below).
The outfall stream entering at the CDOM entry point handles sanitary sewer overflows from the Swan Creek Waste Water Pumping Station (WWPS). As for the Broad Creek WWPS, the Washington Suburban Sanitary Commission (WSSC) has identified the susceptibility of the Swan Creek WWPS to sanitary sewer overflows during wet weather and snowmelt events, such as the one following the major 9" snowfall nine days earlier. During these events the WWPS releases raw sewage and fecal coliform bacteria via the overflow outfall channel (see above) into Swan Creek and the Potomac.
A wet soil feature (brown) indicates a spring or stream at the second apparent CDOM entry point (above). A close-up view confirms the likely presence of a spring or stream at the second apparent CDOM entry point (below), which could carry contaminated water leaking from a nearby sewer line.
The lack of "wet soil" features at the third apparent CDOM entry point (above) suggests a possible groundwater source at this location. The close-up view (below) reveals features consistent with drainage from groundwater sources along the shoreline. The groundwater may have carried sewage from excessive RDII following the large snowmelt event nine days earlier.
Wet soil land cover features (red arrows, above) indicate two incoming streams at the fourth apparent CDOM entry point. One or both of these two streams could carry contaminated water leaking from one or more nearby sewer lines due to the excessive rainfall dependent inflow and infiltration and system overload.
Site 3 (Swan Creek, Ft. Washington, MD) has a history of contamination. The inferred source location from the imagery for the eastern CDOM entry point coincides with the overflow outfall from the Swan Creek Waste Water Pumping Station. Swan Creek has been episodically contaminated by SSOs from the Swan Creek WWPS (e.g., 64,430 gal of untreated sewage on 12 May 2008 due to a lapse in pump operation during a power outage). The other three inferred CDOM entry point locations are in close proximity to sewer lines servicing the nearby residential areas of Ft. Washington. These may represent locations of smaller scale releases due to rainfall dependent inflow and infiltration (RDII) of storm water and groundwater. Excessive RDII could potentially have resulted from the same lapse in pump operation that produced a release from the WWPS. Other causes of the excessive RDII could have been elevated groundwater levels following the major snowmelt event, broken manholes near streams, blockages, line breaks, or other sewer defects.
Site 4 - Piscataway Creek, Accokeek, MD
The Site 4 plume of CDOM (above) has an apparent origin (highest CDOM concentrations) near the Piscataway Waste Water Treatment Plant (WWTP). A close-up view (below) of the apparent CDOM entry points is shown below.
The relationship between the deduced CDOM entry points and overflow outfall channels from the Piscataway WWTP is shown above. "Wet soil" land cover features (below) reveal apparent flow paths of the contaminated water.
The inferred source location (from the imagery) of the CDOM entry points coincide with the overflow outfall channels from the Piscataway Waste Water Treatment Plant. Piscataway WWTP overflow events have frequently contaminated Piscataway Creek and the Potomac with unpermitted and illegal raw sewage discharges. The major snowmelt event nine days earlier was likely responsible for the overload and SSO discharge. The Washington Suburban Sanitary Commission entered a Consent Decree on 7 December, 2005 with EPA, US Dept of Justice, MD Dept of Environment, and various environmental groups to eliminate Sanitary System Overflows (SSOs) at the Piscataway WWTP.
Blue Plains Waste Water Treatment Plant
Notable for the absence of CDOM plumes are the waters adjacent to the Blue Plains Waste Water Treatment Plant in the northern part of the image. There is no evidence for overflow of sewage from Blue Plains WWTP into the Potomac at the time of this image, in spite of the large snowmelt event nine days earlier.
Illustration 2: Failed Septic Systems Along the Patuxent River
The same basic approach used to search for failed sewer systems can also be used to search for evidence of failed septic systems along waterways. In the figure below is shown a zoomed-in view of an area along the lower Patuxent River in St. Mary's County, MD from a winter (16 February 2007) QuickBird image. The image-retrieved water quality results revealed a subtle plume of CDOM apparently emerging from a shoreline area along the Lower Patuxent, indicated by the red ellipse. The close-up view in the next figure reveals a cluster of homes within the ellipse, located in Queen Tree Landing, Mechanicsville, MD along Gibson Drive at the end of Queens Landing Road. The plume is consistent with one or more failed septic systems in this area. A field visit with dye tests would be needed to verify this and trace the specific source(s).
Summary
AAI has developed a unique suite of remote sensing technologies and products that can help to efficiently and thoroughly locate failing sewer and septic systems affecting water quality in watersheds. Images of the watershed measured by commercial satellite sensors can be processed to remotely search broad areas for key environmental water quality and land cover features that cue areas for field investigation. The search is thorough, quantitatively sensitive, and precise, enabling the entire watershed to be efficiently and thoroughly searched. Field-verified sites can be remotely monitored over time for both forensic analysis (past imagery), and direct measurement and meaningful documentation of progress against impairment reduction targets (future imagery). This service could be of significant benefit to agencies and other interested parties for identifying, documenting, and mitigating pollution discharge events in violation of the Clean Water Act and the terms and conditions of National Pollutant Discharge Elimination System permits.
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