Summary
Sawmill Brook is a tributary to the Charles River
which flows in a southwesterly direction through Brookline, Boston and
Newton and meets up with the main stem of the Charles near Millennium
Park in West Roxbury. Much of this stream is culverted as it flows
through Brookline and Newton. CRWA conducted water quality monitoring
on Sawmill Brook on July 27, 2007, a dry weather occasion. Samples were
collected at six sites along the 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 dissolved oxygen, specific conductivity and water
temperature.
Click here for monitoring results .
E. coli levels at four of six sites sampled
exceeded the Massachusetts Water Quality Bacterial Standard for swimming
(126 cfu/100mL) and two sites also exceed the State Boating Standard
(630 cfu/100mL). Potential sources of bacterial contamination to the
brook include illicit connections to the storm sewer system, pet and
wildlife waste and poorly maintained septic systems.
Additionally, total
phosphorus levels at all sites well exceeded US EPA's recommended total
phosphorus criteria in Level III, Ecoregion XIV. In fact, phosphorus
levels at some sites were as much as five times greater than the EPA
criteria. Excessive nutrients are a significant problem throughout the
Charles River, which requires the development and implementation of
nutrient TMDLs . 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.
CRWA also observed problems with total suspended
solids and dissolved oxygen in Sawmill Brook. The sediment
concentration at Site SAWM5 well exceeded CRWA's Action Limit for TSS.
This Action Limit is based on Water Quality Criteria proposed by U.S.
EPA and represents a threshold value, over which, TSS may cause
significant degradation to the water quality of the brook. Finally,
very low dissolved oxygen levels were observed at Sites SAWM5, SAWM B
and SAWM C. These sites were below the State Surface Water Quality
Standards of 5 mg/L and 60% saturation. At Site SAWM C nearly anoxic
conditions were observed as dissolved oxygen measured only 0.81 mg/L and
9.3%. When dissolved oxygen reaches dangerously low levels, such as
those observed here, aquatic life can no longer survive in this
environment. Such low dissolved oxygen levels are likely resultant of
high phosphorus levels feeding excessive algae growth in the springtime
leading to a massive summer die-off of algae which consumes dissolved
oxygen as it decomposes.
For
more information on Sawmill Brook see
sampling map ,
sampling site descriptions ,
Sawmill Brook photos , and
water quality monitoring results .
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