State Summary: Delaware

Ranked 1st in Beachwater Quality (out of 30 states)
<1% of samples exceeded national standards for designated beach areas in 2012

Protecting swimmers from bacteria, viruses, and other contaminants in beachwater requires leadership. Federal officials must help clean up polluted stormwater runoff—the most commonly identified cause of beach closings and swimming advisories—by developing national rules that require pollution sources to prevent stormwater where it starts by retaining it on-site.

The Environmental Protection Agency must also set beachwater quality standards protective of human health and provide states with the support they need to monitor beach pollution and notify the public when pollution levels are high.

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Delaware 2012 Beachwater Quality Summary

Reported Sources of Beachwater Contamination
(number of closing/advisory days)

  • 1 (100%) unknown contamination sources

Delaware has 50 miles of Delaware Bay coastline, 25 miles of Atlantic Ocean coastline, and 115 miles of inland shoreline along Rehoboth Bay, Indian River Bay, and Little Assawoman Bay. The state's marine beachwater monitoring program is administered by the Delaware Department of Natural Resources and Environmental Control (DNREC).

What Are the Water Quality Challenges and Improvements in Delaware?

Leadership in Water Quality Monitoring

Delaware has a long-standing commitment to informing beachgoers about water quality and has sampled beaches since1979. DNREC's comprehensive program currently includes sampling for enterococcus bacteria, monitoring for rainfall and other factors known to impact water quality, and surveying the shoreline weekly. Additionally, the state's Floatables and Debris Program has a vessel in the water year-round in all weather conditions to monitor floating debris as well as oil spills, harmful algae blooms, sewage treatment discharges, nutrient runoff, and industrial discharges.

Addressing Pollution Sources

In conjunction with the University of Delaware Sea Grant, DNREC is conducting a source tracking study at designated recreational beaches. In 2012, studies began for certain marine beaches and will continue through 2013.One source tracking study was recently completed at a non-beach site in the Delaware Inland Bays to identify the source of high bacteria levels. It was determined that the bacteria originated from shorebirds that use the site to feed and nest nearby. Officials plan to complete the current source tracking study before the 2014 beach season.

Green Infrastructure

Delaware's coastal beaches historically have very clean water, due to efforts over 30 years to prevent point and non-point pollution. In 2012, the state continued its efforts to ensure clean water by adopting the Inland Bays Pollution Control Strategy and accompanying regulations for the Indian River, Indian River Bay, Rehoboth Bay, and Little Assawoman Bay watersheds. Contaminants in these bays come from many sources in the watershed, including failing septic systems, residential and agricultural runoff, and wildlife. Additionally, the sewage treatment plants in Lewes and Rehoboth discharge treated effluent into the Lewes and Rehoboth Canal, which feeds into the bays. Poor flushing of the shallow waters in these bays allows pollutants to linger; it can take more than two months for water to move through. The new plan aims to improve water quality through upgrading or replacing residential septic systems and reducing stormwater runoff and pollution from other non-point sources.

What Does Beachwater Monitoring Show?1

In 2012, Delaware reported 24 coastal beaches, of which 5 (21%) were monitored more than once a week and 19 (79%) were monitored once a week. In 2012, less than 1% of all reported beach monitoring samples exceeded the state's daily maximum bacterial standard of 104 colonies/100 ml. The only beach with an exceedance of the daily maximum standard in 2012 was Rehoboth-Rehoboth Ave. Beach (3%) in Sussex County. NRDC considers all reported samples individually (without averaging) when calculating the percent exceedance rates in this analysis. This includes duplicate samples and samples taken outside the official beach season, if any.

Delaware Percent of Samples Exceeding the State's Daily Maximum Bacterial Standard for 17 Beaches Reported 2008-2012*

    * Please note that only samples from a common set of beaches monitored each year from 2008-2012 are included in the bar chart.

    What Are Delaware's Sampling Practices?

    In 2012, the monitoring season extended from May 7 to September 24. The DNREC determines sampling practices, locations, standards, and notification protocols and procedures throughout the state. Samples are taken in knee-deep water.Monitoring frequency and locations are determined on the basis of how many months of the year the beaches are used recreationally, what kind of use and how much use they get, their proximity to potential sources of contamination, and whether the beaches could be impacted by stormwater runoff. All of Delaware's public ocean beaches are monitored, as are beaches along the southern half of the Delaware Bay coast from Slaughter Beach to Cape Henlopen.

    Once an advisory or closing is issued, resampling to confirm an exceedance is conducted immediately and the beach is monitored more frequently until the advisory can be lifted. States that monitor more frequently after an exceedance is found will tend to have higher percent exceedance rates and lower total closing/advisory days than they would if their sampling frequency did not increase after an exceedance was found.

    The DNREC also samples water and/or shellfish for toxins and for algal blooms of the harmful species Kareniabrevis and K.papilionacea. As appropriate, the DNREC issues harmful algal bloom swimming advisories at freshwater beaches.

    How Many Beach Closings and Advisories Were Issued in 2012?2

    Total closing/advisory days for 1 event lasting six consecutive weeks or less decreased 83% to 1 day in 2012 from 6 days in 2011. For prior years, there were 86 days in 2010, 94 days in 2009, and 11 days in 2008. In addition, there were no extended or permanent events in 2012. Extended events are those in effect more than six weeks but not more than 13 consecutive weeks; permanent events are in effect for more than 13 consecutive weeks. The 1 event lasting six consecutive weeks or less was due to monitoring that revealed elevated bacteria levels. This event occurred at Rehoboth Beach and was caused by stormwater outfall pipes; all pipes are being retrofitted for the 2013 swimming season.

    Due to water quality concerns, there is a permanent caution regarding swimming in Rehoboth Bay, Indian River Bay, and Little Assawoman Bay. This permanent caution includes Tower Road Bayside in Rehoboth Bay and Holts Landing Beach in Indian River Bay. Signs are posted at popular access points around the three bays to warn potential swimmers of the risks associated with swimming in these bodies of water, particularly after a heavy rain. NRDC does not include this permanent caution in its analysis of closing and advisory days.

    How Does Delaware Determine When to Warn Visitors About Swimming?

    Delaware's standards for marine beachwater quality are an enterococcus single-sample maximum of 104 cfu/100 ml and a geometric mean standard of 35 cfu/100 ml for the most recent five samples within 30 days. When a water quality exceedance shows there is a potential threat to public health, a swimming advisory or closure is issued immediately. Rare circumstances, such as leaking sampling containers, excessive sediment, or very rough surf, can justify a resample prior to issuance of an advisory.The DNREC informs the public of the advisory or closure through signs posted at the beach as well as via the DNREC website, instant messaging, and a toll-free hotline. Lifeguards also keep swimmers out of the water when conditions are unsafe.

    DNA analyses to track the source of bacteria at Slaughter Beach and Prime Hook Beach have shown that nonhuman sources contribute to indicator bacteria counts at these beaches. Monitoring results at these beaches are adjusted downward to account for nonhuman sources at these beaches before the water quality standard is applied. (Monitoring data are reported before this adjustment is made, and NRDC uses the unadjusted values in its analysis of exceedances.) For Slaughter Beach, the correction factor is 0.49 (which is multiplied by the raw count). This was calculated on the basis of a microbial source tracking study at this beach that found that 77% of fecal bacteria came from wildlife sources, with a 26% margin of error. At Prime Hook, microbial source tracking found that 70% of fecal bacteria came from wildlife, with a 24% margin of error, resulting in a correction factor of 0.54 for this beach.

    State policy is to issue advisories when fecal bacteria counts exceed either the single-sample or geometric mean standard. There are limited overriding factors, such as leaking sampling containers or excessive sediment in samples, that officials can take into account before issuing an advisory when a sample exceeds standards, but these are rare exceptions. Circumstances that would trigger an imminent health threat result in a closing rather than an advisory.

    Delaware has a standard for issuing preemptive rainfall advisories. For marine waters, the DNREC has determined that 3.5 inches of rainfall within 24 hours or 3 inches within 12 hours may trigger a closing. Preemptive closings are issued in the case of a known sewage spill.

    Delaware 2012 Monitoring Results and Closing/Advisory Days

    Assigned Monitoring Frequency
    Total Samples
    % of samples exceeding
    state standards
    Closing or Advisory days
      NOTE: Data and state-specific information for this summary were collected from U.S. EPA, direct conversations with beach managers in the state, state grant reports to U.S. EPA for BEACH Act funding, and the state water quality website. The information in this state summary reflects current data as of June 7, 2013.
    1. If the 2012 percent exceedance values in this summary don't match, why not? The value at the top of the page reflects the proportion of samples exceeding the national single-sample maximum standard for designated beach areas. The values in the "What Does Beach Monitoring Show?" section reflect the proportion of samples exceeding the state standard, which in some states is more or less stringent than the national designated beach standard. Additionally, only samples from a common set of beaches monitored each year from 2008-2012 are included in the bar chart. Because some beaches were not monitored in each of those years, the percent exceedance for this subset of beaches may not have the same value as the percent exceedance for all of the beaches monitored in 2012.
    2. Year-to-year changes in closing/advisory days should not necessarily be interpreted as an indication of the level of bacterial contamination. In some states and localities, the number of beaches and/or beach monitoring frequency may not be consistent from one year to the next, and beaches may be closed or under a swimming advisory for reasons other than known or suspected bacterial contamination. Other reasons include, but are not limited to, chemical/oil spills, medical waste washing up on shore, dangerous currents, lack of lifeguards, etc. In addition, because NRDC's totals of closing/advisory events focus on those events lasting six consecutive weeks or less, those tallies do not account for longer-duration closings or advisories. For trends in water quality, please refer to NRDC's year-to-year comparison of percent exceedance rates of state water quality standards.


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