JORDAN POND RESTORATION STUDY
PHASE 2 – STORMWATER MANAGEMENT PLAN
SHREWSBURY, MASSACHUSETTS
EXECUTIVE SUMMARY

In our Phase 1 of the Jordan Pond Restoration Study dated January 31, 2003, GZA
indicated that Jordan Pond is subject to significant loading of sediments, nutrients, and
bacteria. Past and continuing inputs of these constituents were found to be the primary
causes of the degradation of the pond – contributing to poor water quality, excessive
growth of aquatic plants, algae blooms, and loss of depth from the Pond. Testing and
modeling conducted as part of the Phase 1 study point to stormwater runoff as the
primary source of on-going loading into the Pond.

Based on the findings and alternatives presented in Phase 1 of the Restoration Study, the Town, in consultation with the Jordan Pond Watershed Association, instructed GZA to
pursue stormwater management as a means of reducing the loading of sediment and
contaminates into the Pond and thereby slowing the further degradation of the Pond. Inline stormwater treatment in the form of modified manhole structures was recommended by GZA as the preferred alternative. This Phase 2 study was then executed by GZA to provide planning and preliminary design guidance to the Town and Watershed Association for a future implementation program.

Hydrodynamic separators within modified manholes are currently among the most
advanced methods of stormwater best management practices (BMPs). These devices
may be retrofitted into the existing stormwater drainage pipe system. Sediment and
sorbed nutrients entering one of these devices are trapped within the deep sump.
Floatable debris, as well as oil and grease, are also segregated from the outflow and
retained in the structure. High flows into the unit are bypassed directly to the outlet to
prevent upstream flooding and limit re-suspension of sediment and contaminates.
Periodic cleaning of the devices with a vacuum truck removes the sediment and
contaminates from the system and prevents them from ultimately entering the Pond. A
number of manufacturers make proprietary systems, many of which perform essentially
the same function. Properly sized and maintained, the manufacturers of these devises
state that they can remove up to 80 percent or more of total suspended solids (TSS) from stormwater runoff.

Six critical sub-basins have been identified by GZA within the Jordan Pond watershed
where in-line stormwater treatment is believed to be both desirable and feasible. These
sub-basins are primarily areas with significant coverage of impervious surfaces such as
roadways, parking lots, or roof area. Sediments and contaminates tend to accumulate in
these areas and then wash directly into the storm sewer system and then quickly into the Pond. Also recommended is the treatment of runoff from residential areas nearest to the Pond. In areas outside of the six identified sub-basins, other management strategies have been suggested.

Stormwater management through the installation of in-line treatment devices is unlikely
to yield immediate, appreciable water quality improvements in the condition of Jordan
Pond, but it is an important first step in addressing identified sedimentation and water
quality problems in the Pond.