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Beaver Brook, Waltham, MA
"Find It and Fix It" Water Quality Monitoring 


Beaver Brook winds from Hardy Pond through Lexington and Waltham to meet up with the Charles River near the Newton Street Bridge in Waltham.  The Brook is culverted between Route 20 and its discharge point.  CRWA conducted water quality monitoring on Beaver Brook on three occasions: 1) December 21, 2006 – a dry weather monitoring event, 2) January 12, 2007 – a dry weather monitoring event, 3) November 6, 2007 – a wet weather monitoring event.

Samples were collected at eighteen sites along Beaver Brook.  Click here for a site map.  Samples were analyzed for several pollutants of most concern in the watershed: E. coli bacteria, total suspended solids (TSS), and total phosphorus.  CRWA also measured several in situ parameters including pH, dissolved oxygen, specific conductivity and water temperature. 

E. coli levels at fifteen sites exceeded the Massachusetts Surface Water Quality Standard for swimming, 126cfu/100mL, during at least one of the sampling events.  Fourteen sites also exceeded State Boating Standards, 630cfu/100mL, during at least one sampling event. Certain sites, such as BEA_OUT1, BEA6, BEA8, BEA_OUT7, BEA9, BEA10 and BEA11 exhibited high bacterial counts during both dry and wet weather.  BEA6 stands out particularly as E. coli levels there exceeded 10,000 cfu/100mL during both wet and dry weather.  Such high E. coli levels observed during dry weather are usually indicative of illicit connections to the stormwater drainage system, causing raw, untreated sewage to flow directly into Beaver Brook and eventually the Charles River.  CRWA observed further evidence that illicit connections are likely flowing into Beaver Brook during our November 6, 2007 wet weather sampling event when soap suds were observed flowing out of the outfall pipe at Site BEA_OUT1 and a sewage smell was present at Site BEA_OUT4. 

The City of Waltham has begun efforts to identify and remove such connections. However, identifying and removing all illicit connections will take the continued effort of the City of Waltham and the support of its residents.  Pet and wildlife waste may also be increasing bacteria levels in the brook.

Also of water quality concern were the high total phosphorus concentrations observed during all three monitoring events.  During dry weather, Sites BEA_OUT1, BEA2, BEA5, BEA6, BEA8, BEA_OUT6, BEA10 and BEA11 all exceeded 0.0238 mg/L, US EPA’s recommended total phosphorus criteria in Level III, Ecoregion XIV.  During wet weather, all sites sampled well exceeded the EPA’s recommended total phosphorus criteria.  Total phosphorus concentrations ranged from 0.09 mg/L at Site BEA_OUT6 to 0.24 mg/L at Site BEA_OUT3, which exceeded the recommended criteria by an entire order of magnitude.  Excessive nutrients are a significant problem throughout the Charles River, which requires the development and implementation of nutrient TMDLs.  Runoff from large impervious surfaces is particularly problematic for urban and suburban waterways like Beaver Brook. Fertilizers from lawns, playing fields and golf courses, as well as pet and wildlife waste, organic matter from lawn clippings and leaf litter, detergents and automobile emissions, are some of the likely sources of nutrients to this brook.  

Elevated concentrations of TSS were observed during our wet weather monitoring event on November 6, 2007.  Three sites exceeded CRWA’s action limit for TSS, 30 mg/L, which is based upon EPA recommended water quality criteria.  Significant bank erosion has been observed near Site BEA6, and very severe erosion was observed surrounding an outfall pipe on the south side of the stream bank near Site BEA9.  High concentrations of TSS can also result from large areas of impervious surfaces, poorly managed constructions sites, road sanding, and stream banks with inadequate vegetation. In addition to the degraded instream water quality, large amounts of trash were observed both along the banks and in the brook during all three monitoring events. 

Last Updated December 2009