-By John Martin, Baltimore City

INTRODUCTION AND PURPOSEThis paper describes the water quality conditions in BackRiver, a shallow tidal tributary of the upper ChesapeakeBay. Back River is located north of Baltimore Harbor onthe western shore of the Bay in Baltimore County.

The purpose of this study was to track changes inwater quality in Back River over time and correlatethem to upgrades in treatment processes at the BackRiver plant. We chose to develop this in-house monitor-ing program rather than rely on data collected by otheragencies such as the Maryland's Department of Natu-ral Resources because we could select stations tofocus on the portion of Back River surrounding theplant's outfall and could select a station that wouldfunction as a control.

Secondly, it would give us a body of data overwhich we maintain control and that we could share withother interested parties.

BACKGROUNDIn the early 1900s, Back River was selected to receiveeffluent from the Back River Wastewater TreatmentPlant because it was a sparsely populated area and itwould function as a polishing system for the plant'seffluent from its then state-of-the-art trickling filterprocess. By introducing sewage effluent into BackRiver, the Bay's oyster bars would be protected as wasrequired by law. The Back River plant was veryadvanced for the time utilizing secondary treatment,sludge elutriation and other innovative processes notwidely used in the U.S. at the time.

As the years went by and the Baltimore metropoli-tan region grew, flows increased and Back River waterquality suffered. After World War II, growth in the area

24

exploded, silt accumulated in the upper tidal portion ofthe river and, despite law suits and other environmentalactions, water quality remained poor with odors, algalblooms, and floating solids from the plant.

Fast forward to the passage of the Clean Water Actin 1972 and public outrage at the condition of thenation's waterways. Back River was not even close tofishable and swimable. Clearly something had to bedone and it was not going to be fast or cheap. Enter theconstruction grants program, an integral part of theClean Water Act. Now federal and state grant fundswere available to build new facilities. Around the coun-try, over the next decade or more, hundreds of waste-water treatment plants were upgraded and expandedand Baltimore's plants were among them.

Large new activated sludge facilities were built andplaced in service in 1988 allowing the trickling filtersfinally to be taken out of service. These had been oper-ating since the plant first went into service in 1912 andalthough inexpensive to operate and excellent at work-ing under varying hydraulic loads, they were not veryefficient; removing only approximately 75 to 80% ofinfluent organic waste.

In addition to these new activated sludge facilities,sand filters, new chlorine contact tanks, and a new out-fall structure were built. With all these facilities in serv-ice, reductions in biochemical oxygen demand (BOD)and total suspended solids (TSS) were now on theorder of 98 to 99 % while approximately 95% of phos-phorus and 70% of nitrogen were removed. Theseremoval rates continue today at the Back River plant.

On the solids processing side, air flotation thicken-ers were added to supplement the gravity sludge thick-eners, large egg-shaped anaerobic digesters greatlyimproved volatile solids reduction and more recently,gravity belt thickeners were added to improve the per-formance of sludge thickening.

Spring2010. Ecoletter

A byproduct of anaerobic digestion is methane gas,a valuable energy resource. This gas is used to heatthe digestion process and to provide comfort heat forthe plant's buildings. Those uses, however, do not con-sume all the gas produced so the surplus was flared.Recently, to address the energy wasted by flaring sur-plus digester gas, three large internal combustionengines, each turning a generator capable of produc-ing one megawatt of power have been installed to putthis surplus gas to good use.

In the early 1990s, the Wastewater Facilities Divi-sion (part of the Bureau of Waste and Wastewaterwhich is in turn part of Baltimore's Department of Pub-lic Works) initiated a water quality monitoring programto track pollutant concentrations, in situ parameters(dissolved oxygen, temperature, salinity, and pH), Sec-chi disk transparency, and most importantly, chlorophyllconcentration in the river.

Sampling started in 1993 and has continued fromMarch through October or November each year eversince. During this span of years, the Back River plant wasupgraded to biological nutrient removal (BNR). This tookplace in the late 1990s and lowered the effluent totalnitrogen concentration by approximately 40% to 50%.

Figure 1, -

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This paper will present the methods used and sum-maries of the water quality data spanning 1993 through2009.

METHODS

Monthly sampling trips were made from March throughOctober or November (depending on weather) eachyear to collect both water samples and field water qual-ity data at several stations in Back River with a controlstation located in neighboring Middle River. Sampleswere collected at the surface and from just above thebottom sediment using a small electric pump mountedon a pole. Separate samples were collected for analysisof BOD, TSS, and nutrients including total Kjeldahl nitro-gen (TKN), ammonia, nitrate, nitrite, orthophosphorus(OP), and total phosphorus (TP). The abbreviation NOxis used to refer to the sum of nitrate and nitrite.

Five sampling stations were visited each monthstarting: four in Back River and a control station in Mid-dle River (Figure 1).In Back River, stations were located0.75 miles upstream of the plant outfall, directly off theoutfall, 0.75 miles downstream of the outfall and then anadditional 1.5 miles downstream. A control sample wasContinued on page 26

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collected in the upper tidal portion ofMiddle River; the next river to thenorth and uninfluenced by a waste-water discharge. The location of theMiddle River station is approximatelythe same distance from the main

stem of the Bay as the upper BackRiver stations and thus is under

nearly the same environmental condi-tions. Note that the first three stationsbracket the outfall and are averagedin the presentation of the data to illus-trate typical conditions found in theupper tidal portion of Back River.Thefourth station is located in the lowerpart of the Back River estuary whilethe control station is in Middle River; adifferent tributary. In situ parameterswere also measured at an open Baystation located off the mouth of Middle River.

In addition to collecting samples for analysis of theparameters noted above, separate samples were col-lected for analysis of E. coli bacteria, Microtox andchlorophyll a. Separate samples were collected forthese latter analyses as they were analyzed by differ-ent laboratories.

In situ parameters were measured using a HydorlabSurveyor 4 and minisonde. Parameters include dis-solved oxygen using a luminescence probe (LOO), tem-perature, pH, salinity and probe depth. The unit wascalibrated immediately prior to each

sampling trip. Readings were taken at I Figure 6the surface and a few inches abovethe bottom at each station. As no sta-tion is deeper than approximately tenfeet, no mid-depth readings weretaken. Finally, at each station a stan-dard Secchi disk was used to meas-

ure light penetration into the water.

Back RiverContinued from page 25

RESULTS ANDDISCUSSIONAlthough there are numerous chartsplotting each parameter spatiallydown the river, the graphics pre-sented in this paper are those thatcompare concentrations of TKN, TP,NOx, and chlorophyll over the dura-tion of the study. In addition, rainfallat BWI Marshall Airport has beenplotted illustrating the extraordinary

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Figure2 Back River Water Quality SurveyTotal KjeJdahl Nitrogen Concentrations -1993 Through 2009

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IBNR Phased in 1995 tlru 1998 I. .

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Middle River

amount of precipitation that occurred in this area during1995 and 1996.

The trends during this period appear either to befluctuating randomly from year to year but not estab-lishing a trend in any particular direction (TKN and TP)or clearly declining in response to environmental con-ditions (NOx and chlorophyll).

The concentrations of TKN in Back River suggest avery slight downward trend over time while at the con-trol station in Middle River, the trend was upward from1993 through 2008 and then dropped back in 2009 to

Rainfall at BWI Marshall Airport1993 through 2009

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140

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a1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

8Annual Total []Normal Total

treatment plant effluent are below0.2 ppm per the plant's NPDES dis-charge permit while TP concentra-tions in the river frequentlyexceeded this level. Only one year(2009) was the average concentra-tion TP in Back River less than theplant's effluent concentration.

Oxides of nitrogen (NOx), prima-rily nitrate and nitrite, have declinednoticeably in Back River (Figure 4).Concentrations between 2 ppm and3 ppm were routinely observed dur-ing the period 1993 through 1996with 1995 being the exception. From1997 through 2001, the NOx con-centrations declined from 1.5 ppm to0.5 ppm and although they haverisen again some, they haveremained at 1.5 ppm or less through2009. Looking at the Middle Rivercontrol station, NOx concentrationshave remained consistently below

0.5 ppm throughout the entire 16-year study. Since theBack River WWTP was upgraded to include biologicalnutrient removal during the period 1995 through 1998,the decline in NOx concentration is most likely relatedto these improvements.

Chlorophyll concentrations in 1994 and 1995 aver-aged in excess of 150 1l9/L (Figure 5) with occasionalindividual samples exceeding 300 Ilg/L. Then, ratherdrastically, the concentrations declined to below 1001l9/L and in a few cases less that 50 Ilg/L. ChlorophyllContinued on page 28

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Figure 3 Back River Water Quality SurveyTotal Phosphorus Concentrations - 1993 Through 2009

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levels seen during the first few years of the study (Fig-ure 2). The reasons for these fluctuations are probablymore related to rainfall (Figure 6) and more importantly,exactly when the rainfall occurred. If a very wet periodfollows immediately after farm fields have been fertil-ized, then higher TKNs would result as one of the mainingredients in fertilizer is ammonia; a form of nitrogenthat is included in the TKN result.

The concentrations of TP at the Back River stations

also fluctuated considerably (Figure 3) with a high con-centration in 1995 echoing the high TKN value seen thatsame year. Similar also is the patternat the Middle River station where the

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d f. I I Figure 4concen ra Ions remalne air y con-

stant from 1993 through 2003, thenrose steadily through 2008 and thendeclined in 2009 back to levels seen in

the first few years of the study. Onecan only speculate at the cause ofthese fluctuations but rainfall remains

a prime suspect (Figure 6).Two factors influence the con-

centration of TP in Back River.Theseare the phosphorus discharged bythe treatment plant and the legacyphosphorus in the river sediment.Experiments have confirmed thatwhen pH rises, sediment phospho-rous solubilizes and contributes toTP in the water column above. This islikely the explanation for the TP con-centrations observed in Back Riversince the concentrations of TP in the

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Middle River

Back River Water Quality SurveyOxides of Nitrogen Concentrations - 1993 Through 2009

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IBNR Phased in 1995 thru 1998 I,

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27

Back River Water QualityContinued from page 27

Figure 5 Back River Water Quality SurveyChlorophyll a Concentrations -1994 Through 2009

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ISNR Phased In 1995 thru 1998 I. .200

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BNRPhased In 1995 thN 1998

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50

o+Average of Three Upper Back River Stations

concentrations at the Middle River control station,except for 1995, were all less than 50 1l9/Land mostlywere less than 25 Ilg/L.Recall that the concentration ofNOx also declined during the same period of timealthough not as dramatically as chlorophyll. The reasonor reasons for the decline in chlorophyll are likely thesame as the cause of the decline in NOx concentration;the Back River WWTP phased in BNR operations low-ering the concentration of NOx in the effluent. Notealso that in the charts illustrating both TP and TKN,concentrations were significantly lower in 2009 thanthey had been during the previous several years. Thispattern was not observed in either NOx or chlorophyll.

The effect of rainfall is evident in the very high TKN,TP and chlorophyll concentrations observed in 1995.Note that in 1995, rainfall in the area was approxi-mately three times the normal annual precipitationcausing much erosion all across the watershed andelevated nutrient concentrations in the upper Chesa-peake Bay.

CONCLUSIONSCompared to the period prior to the late 1980s, BackRiver today is in far better condition than it was previ-ously. Before the BNR upgrade was completed in 1998,algal blooms would sometimes turn the river a strikingshade of iridescent green. During these blooms, as thewind swept across the river, algal cells and colonies

28

would accumulate along the shoreline causing thewater to look as though someone had poured greenpaint on the surface. These were the days when thechlorophyll concentration would exceed 200 Ilg/L and

occasionally 300 Ilg/L. Today, algalblooms still occur but they are notnearly as severe as they were withchlorophyll concentrations nowaveraging 50 to 75 1l9/L rather thanthe 200 to 300 1l9/L previouslyseen. Although this seems like goodprogress, chlorophyll concentrationshould be more in the range of 25 to35 Ilg/L.

Water quality in Back Riverremains impaired for nutrients fortwo major reasons. The dischargefrom the Back River WWTP still

contributes significant tonnages ofNOx to the river and legacy phos-phorus pollution solubilizes from thesediment as the pH rises duringtimes of peak biological activity.These two sources provide suffi-cient nutrients to support the algalgrowth still observed in Back Riverthroughout the growing season.

These problems are being addressed as part of theoverall Bay restoration strategy and also as part of thenecessary steps to improve local water quality condi-tions in Back River. Currently under design are facilitiesto take the Back River Plant to enhanced nutrientremoval (ENR) levels. When these facilities are com-peted and operating efficiently, effluent total nitrogenconcentrations will be on the order of 3 to 4 mg/L ratherthan the 7 to 8 mg/L currently discharged. This willreduce by approximately half the concentration andtherefore loadings to Back River. Several years are stillneeded before these facilities will be constructed and in

service but when complete, reductions in nutrients,particularly nitrogen (TKN and NOx), should occuralong with concomitant reductions in chlorophyll con-centration and increases in Secchi disk transparency.

These improvements in water quality will likely notmake the river run clear again, however, as much of theobserved turbidity is due to the sediment load in thewater and not to the crop of phytoplankton and associ-ated organisms in the biological community. Until sedi-ment and erosion controls are fully in place, waterquality in Back River will continue to suffer with the riverturning brown after a hard rain.

Middle River

This is an on-going study and updates will be pub-lished from time to time as ENR facilities are com-

pleted and placed in service.

Spring2010. Ecoletter